American Journal of Gastroenterology ISSN 0002-9270C! 2007 by Am. Coll. of Gastroenterology doi: 10.1111/j.1572-0241.2006.00943.xPublished by Blackwell Publishing

CLINICAL REVIEWS

Inflammation and Coagulation in Inflammatory BowelDisease: The Clot Thickens

CME

Silvio Danese, M.D.,1 Alfredo Papa, M.D.,2 Simone Saibeni, M.D.,3 Alessandro Repici, M.D.,1

Alberto Malesci, M.D.,1 and Maurizio Vecchi, M.D.3,4

1Division of Gastroenterology, IRCCS Istituto Clinico Humanitas, Rozzano, Milan, Italy; 2Departmentof Internal Medicine, Gemelli Hospital, Rome, Italy; 3Policlinico Hospital, University of Milan, Milan, Italy; and4Gastroenterology Unit, IRCCS Policlinico San Donato, Milan, Italy

Inflammation and coagulation play crucial roles in the pathogenesis of multiple chronic inflammatory disorders.Growing evidence highlights a tight mutual network in which inflammation, coagulation, and fibrinolysis playclosely related roles. Crohn’s disease (CD) and ulcerative colitis (UC), the two major forms of inflammatory boweldisease (IBD), are chronic inflammatory conditions, characterized by a hypercoagulable state and prothromboticconditions, and accompanied by abnormalities in coagulation. From a pathophysiological point of view, cells andmolecules classically implicated in the physiological process of coagulation have now been shown to behaveabnormally in IBD and possibly to also play an active role in disease pathogenesis and/or disease progression. Thispaper reviews studies performed on the coagulation profile and risk factors for thrombosis in IBD. In particular, anoverview is provided of the epidemiology, clinical features, and etiology of thromboembolic complications in IBD.Furthermore, we review hemostatic abnormalities in IBD, as well as the cell types involved in such processes.Finally, we highlight the coagulation system as a dynamic participant in the multifaceted process of chronicintestinal inflammation. Overall, an overview is provided that the coagulation system represents an important,though previously underestimated, component of IBD pathogenesis, and may be a possible target for therapeuticintervention.

(Am J Gastroenterol 2007;102:174–186)

INTRODUCTION

Inflammation and coagulation play crucial roles in the patho-genesis of multiple chronic inflammatory disorders. Grow-ing evidence highlights a tight mutual network in which in-flammation, coagulation, and fibrinolysis play closely relatedroles. Indeed, activation of coagulation acts as a constituent ofthe inflammatory response by directly mediating cytokine re-sponses (1–3), and some proinflammatory cytokines, such asinterleukin-6 (IL-6), activate coagulation (4, 5). In addition,it appears that hypofibrinolysis, a prothrombotic condition,is a typical feature of inflammation (6).

Crohn’s disease (CD) and ulcerative colitis (UC), thetwo major forms of inflammatory bowel disease (IBD), arechronic inflammatory conditions, characterized by local andsystemic inflammation. Although it is well established thatgenetic predisposition and immune dysregulation play keyroles in IBD pathogenesis, clinical experience and bench re-search have clearly demonstrated that, in both forms of IBD,a hypercoagulable state and a prothrombotic condition exist,while coagulation abnormalities are an intimate part of theIBD clinical picture. In addition, it has recently been demon-strated that cells and molecules classically implicated in thephysiological process of coagulation behave abnormally in

To access a continuing medical education exam for this article, please visitwww.acg.gi.org/journalcme.

IBD and possibly also play an active role in disease patho-genesis and/or progression.

In the following sections, we review the studies performedon the coagulation profile and the risk factors for thrombosisin IBD. Moreover, we identify the coagulation system as adynamic participant in the multifaceted process of chronicintestinal inflammation. It represents an important and previ-ously underestimated component of IBD pathogenesis, andmay be a possible target for therapeutic intervention.

METHODS

Referenced papers were identified by an electronic search ofEMBASE and BioMedNet Medline. The search terms “co-agulation,” “inflammation,” “coagulation factors,” “throm-bosis,” “platelets,” “thrombomodulin,” and “tissue factor”were combined separately with the key words “inflammatorybowel disease,” “Crohn’s disease,” and “ulcerative colitis” toidentify publications for this review article. Additional rel-evant publications were selected from the reference lists ofthe retrieved papers. Only papers published in English wereincluded.

Epidemiology and Clinical Features of ThromboembolicComplications in IBDPatients with IBD frequently suffer from thromboembolicevents, which represent an important cause of morbidity and

174

Inflammation and Coagulation in IBD 175

mortality (7, 8). The incidence of systemic thromboembolism(TE) in IBD ranges between 1 and 7.7% in clinical studies(7, 9), rising to 39–41% in postmortem studies (10). Fur-thermore, a recently performed population-based study hasshown that IBD patients have a threefold greater risk fordeveloping deep venous thrombosis (DVT) and pulmonaryembolism (PE) than the general population (11). This findingwas confirmed in another study, which demonstrated that TEis a specific feature of IBD, as neither rheumatoid arthritis,another chronic inflammatory disease, nor celiac disease, an-other chronic bowel disease, displays a greater risk for TEcompared with control subjects (12). TE was also shown tooccur at a younger age in IBD patients (13).

It appears that both the arterial and venous systems maybe involved. TE occurs more often in the deep vein of theleg and pulmonary circulation, but it has been described tooccur less frequently in other sites, such as the cerebrovascu-lar system, portal vein, mesenteric veins, and retinal vein(14–19). Arterial TE complications occur less frequentlythan venous TE in patients with IBD, and the majority oc-cur after surgery. The complications include thrombosis ofretinal, cerebral, and renal arteries, but the arteries of theupper and lower limbs can also be involved (16, 20–23).In addition, there have been reports of cases of coronaryartery thrombosis in young patients (24, 25) and aortic muralthrombi (26, 27). In accordance with these observations, arecent study demonstrated that IBD patients have a greaterintima-media thickness of the carotid arteries, a markerof early atherosclerosis, than healthy control individuals(28).

In the largest series that has been investigated thus far,it appeared that thromboembolic events were more frequentwhen IBD was in an active phase (7, 12, 29, 30) and werefurther correlated with the extent of disease (particularly pan-colonic involvement in UC patients or colonic involvementin CD patients) (22, 31, 32). These findings have been cor-roborated by a recent revisiting of a series of IBD patientswith DVT or PE evaluated at Mayo Clinic, Rochester, overthe course of a decade (1990–2000). Approximately 80% ofthe patients had active disease at the time of the DVT/PE,and of the patients in which these occurred, approximatelythree-fourths with UC had entire colonic involvement andthree-fourths with CD had colonic involvement (33). How-ever, it is worth noting that, in a larger study, one-thirdof thromboembolic complications occurred during diseasequiescence, supporting the hypothesis of a greater proco-agulant tendency in IBD, independent of disease activity(7, 34).

Finally, indirect evidence that vascular thrombosis couldbe involved in the pathogenesis of IBD was provided by anepidemiological study performed on a large cohort of subjectswith hemophilia or von Willebrand’s disease (35). In thispopulation, IBD occurred less frequently than expected, andit has been suggested that inherited disorders of coagulationmight be protective against IBD, even if this study has thelimitation of being a retrospective study.

Table 1. Acquired Prothrombotic Factors in IBD

InflammationProlonged immobilizationSurgeryFluid depletionSteroid therapyCentral venous cathetersHyperhomocysteinemia/vitamin deficienciesSmokingOral contraceptives

The Etiology of Thrombosis in IBD Is MultifactorialThrombosis is a pathologic process that leads to the formationof a (semi)-solid mass within the vascular system. The patho-logic extension of the normal hemostatic process, thrombosis,is a complex event in which several mechanisms and causalfactors, inherited and acquired, are implicated, complicatingthe identification of its causes.

In IBD, acquired prothrombotic risk factors are frequentlyobserved, such as inflammation, fluid depletion, immobil-ity, surgery, steroid therapy, and the use of central venouscatheters (Table 1) (36). In addition, vitamin deficienciesare a common feature, and these are well known to lead tohyperhomocysteinemia, a prothrombotic condition (37, 38).Furthermore, CD has been associated with known risk fac-tors for TE, such as smoking and oral contraceptive use (39)(Table 1).

Despite reports of several qualitative and quantitative ab-normalities in hemostatic parameters in IBD patients (40–45)(Table 2), the reasons for the greater occurrence of TE in IBDare nonetheless not completely understood. It appears to bemultifactorial, because no consistent unifying etiology hasbeen identified. It has been suggested that, in the majorityof thrombotic IBD patients, at least one prothrombotic riskfactor can be detected (32, 33), but other authors (8) have in-dicated that approximately half of IBD patients develop TEwithout any identifiable reason, reinforcing the hypothesisthat IBD represents a per se risk factor for thrombosis.

Hemostasis Under Physiological ConditionsUnder physiological conditions, both coagulation and fib-rinolysis are precisely regulated by the participation of sub-strates, activators, inhibitors, cofactors, and receptors (Fig. 1).These coordinated events ensure blood fluidity while prevent-ing blood loss, in particular in response to vascular injury.Briefly, adhesion, activation, and aggregation of platelets arethe first steps of hemostasis, which are followed by activationof coagulation (clot formation) and finally by the fibrinolyticprocess (clot dissolution). In the classical cascade model, co-agulation is initiated via an extrinsic pathway and an intrin-sic pathway that are strictly linked and interdependent, andthen maintained by the cascade activation of several factors(Fig. 1). The activation of coagulation, triggered by tissuedamage, is crucially dependent on upregulation of tissuefactor (TF) and ultimately generates thrombin, which results

176 Danese et al.

Table 2. Abnormalities of Hemostasis Parameters Observed in Pa-tients Affected by Inflammatory Bowel Diseases

Abnormalities of coagulation" Fibrinogen" Factors V, VIII, IX" Fragment 1 + 2, fibrinopeptide A and B,

TAT (thrombin antithrombin complex)# Factor XIII/subunit A factor XIII# Protein C, protein S, antithrombin III# TFPI (tissue factor pathway inhibitor)

Abnormalities of platelets" Number, activation, aggregation

Abnormalities of fibrinolysis# tPA (tissue-type plasminogen activator)" PAI (plasminogen activator inhibitor),

TAFI (thrombin-activatable fibrinolyis inhibitor)" D-dimer, FDP (fibrin degradation products),

FgDP (fibrinogen degradation products)Endothelial abnormalities

" Circulating thrombomodulin, ECPR,and von Willebrand factor

# Tissue thrombomodulin and EPCRNutritional abnormalities

" Homocysteinemia, lipoprotein A# Vitamin B6

Immunological abnormalitiesAntibodies: antiphospholipid, antiprotein S,

antiendothelial cells, anti-tPA

in clot formation by conversion of fibrinogen to fibrin andby platelet activation. Recent observations suggest that mi-croparticles and leukocyte adhesion molecules play a role inthrombus development (1). However, clot formation is coun-terbalanced by various anticoagulant mechanisms to main-tain homeostasis. In particular, tissue factor pathway inhibitor(TFPI), protein C (PC), protein S (PS), antithrombin (AT),endothelial protein C receptor (EPCR) and thrombomodulin(TM) act as physiological anticoagulants (46) (Fig. 2).

An essential component of the fibrinolytic system is the zy-mogen plasminogen, which is converted to plasmin by tissueplasminogen activator (tPA) as well as by urokinase (uPA); itis inhibited by plasminogen activator inhibitor 1 and 2 (PAI-1, PAI-2) and !2-antiplasmin (Fig. 3). Once formed, plasmincleaves fibrin, generating soluble degradation products. Re-cently, thrombin-activatable fibrinolysis inhibitor (TAFI) hasbeen characterized and its active form (TAFIa) is a potentattenuator of fibrinolysis by inhibiting plasmin generation,stabilizing fibrin thrombi, and establishing a regulatory con-nection between coagulation and fibrinolysis (47). Becausegreater inflammation can increase coagulation, which in turncan enhance inflammation, the failure of natural anticoagu-lant mechanisms to control the clotting process would natu-rally increase the inflammatory process. The twin observa-tions that inflammation downregulates natural anticoagulantmechanisms and that these mechanisms have antiinflamma-tory activity above and beyond their antithrombotic functionsfurther exacerbate the situation (48). Table 3 describes how

inflammation impairs the hemostatic balance and how acti-vation of coagulation modulates the inflammatory response.

Coagulation Abnormalities in IBDIn general, interpretation of studies of hemostatic variablesis difficult because of the intra- and interassay variability ofthe different tests, pretest circumstances (i.e., modalities ofsampling), and laboratory handling that may influence the re-sults. In IBD, comparisons of the different studies are furthercomplicated by additional factors, such as differences in theclinical and demographic features of the patients studied andin disease activity evaluation.

Despite these limitations, both a prothrombotic conditionand a hypercoagulable state are established features of IBD.

PROTHROMBOTIC CONDITION. A prothrombotic con-dition is defined as an increase in risk factors for thrombo-sis and/or a decrease in natural anticoagulant factors (49).In IBD, greater plasmatic levels of several recognized riskfactors for thrombosis, some of which are also consideredacute-phase reactants, have been consistently described, suchas greater levels of factor V, VII, and VIII (50), lipoprotein(a) (29), and fibrinogen (50). In addition, a decrease in nat-ural anticoagulant factors, such as antithrombin III (AT III),protein C (PC)-protein S (PS), and TFPI, has also been de-scribed in IBD. Lower AT III plasma levels are possibly aresult of consumption, while PC plasma levels appear un-changed (51). Also PS and TFPI plasma levels have beenreported to be lower (44, 52, 53).

A prothrombotic condition may also result from reducedfibrinolytic activity. The fibrinolytic system has been widelyinvestigated in IBD and both hypofibrinolysis and hyperfibri-nolysis have been described, although it seems that hypofib-rinolysis prevails. Indeed, a reduction in activators (such astPA) and an increase in inhibitors (such as PAI and TAFI) ofthe fibrinolytic system have been described in IBD (41, 45,54, 55).

Homocysteine has also been implicated in the coagulanttendency observed in IBD. Indeed, homocysteinemia is sig-nificantly more common in IBD patients than in the generalpopulation (31, 56–58). Greater homocysteine plasma lev-els mainly result from the low levels of folate, vitamin B6,and vitamin B12 that are frequently observed in patients af-fected by IBD, likely a result of several mechanisms, suchas reduced dietary intake, malabsorption, hypercatabolism,or drug interference. It has been demonstrated that vitaminsupplementation is able to normalize homocysteine plasmalevels (56). Furthermore, lower plasma levels of vitamin B6,which is an independent risk factor for thrombosis, have alsobeen described in IBD patients, especially in those with activedisease (59).

Finally, other mechanisms could be implicated in deter-mining the prothrombotic condition of IBD. The role of cellcomponents called “microparticles” in the field of vasculardiseases has been recently defined. These are vesicles ofcell membrane released when cells are activated or during

Inflammation and Coagulation in IBD 177

Negative surface Vascular injury

Kallikrein, HMWK FVIIa, FIXa, FXa FXII FXIIa TF TF FVIIa calcium FVII Thrombin

FXI FXIa

calcium FVIIa FIX FIXa FIX FIXa

FVIII FVIIIa FXa FX FXa FX FV FVa Thrombin prothrombin

calcium, phospholipids

fibrin stabilization fibrin fibrinogen FXIIIa thrombin

FXIII HMWK = high molecular weight kininogenTF = tissue factor “a” indicates the activated coagulation factors

Extrinsic way

Intrinsic way

Figure 1. Schematic representation of coagulation cascade.

apoptosis, in a large part derived from platelets. They haveprocoagulant properties (mainly as a result of the expressionof TF on their surface) and are implicated in inflammatoryprocesses and in the modulation of endothelial functions (60).These have been reported to circulate in a greater number dur-ing the active phases of IBD, suggesting a potential role inthe procoagulant tendency (61).

HYPERCOAGULABILITY STATE. Hypercoagulabilityidentifies an imbalance in the coagulation cascade towardprocoagulant forces because of an excessive activation ofcoagulation enzymes without clinical signs of thrombosis.Several studies have been published describing the mostsensitive markers of activation of coagulation, such asprothrombin fragment 1 + 2 (F1 + 2), the thrombin-antithrombin III complex (TAT), fibrinopeptide A (FPA),and fibrinopeptide B (FPB), showing findings compatiblewith subclinical activation of coagulation in IBD (44,62–64). It is debated whether this evidence of activation ofcoagulation is secondary to inflammation or is a feature ofIBD, independent of clinical activity and features (43, 65).

Evidence of the activation of blood coagulation is alsoprovided by a decrease in factor XIII (FXIII) plasma con-centrations; indeed, reduced levels of FXIII have been fre-quently described during active IBD, while they appear tobe unchanged during quiescent phases of the disease (64,66–69). One of the potential causes of reduced factor XIIIaplasma levels in IBD may be consumption in foci of thrombo-sis (67) or enhanced turnover during active inflammation (69).

Further evidence of activation of the coagulation system inIBD is the greater fibrinolytic activity, demonstrated by highplasma levels of fibrin degradation products, such as D-dimerand fibrinogen degradation products (FgDP).

ENDOTHELIAL INVOLVEMENT. Markers of endothelialdamage, such as von Willebrand factor (vWF), endothelialprotein C receptor (EPCR), and thrombomodulin (TM), areincreased in the serum of IBD patients, and this has beenfound to correlate with disease activity and/or acute phasereactants (70–72). It has been debated whether the intestinalvascular involvement observed in IBD is the primum movensof these diseases (73) or a consequence, with amplificationof local and/or systemic inflammation (74).

IMMUNE ALTERATIONS. IBD is characterized by theproduction of a wide range of antibodies, some of whichare potentially involved in the greater thrombotic risk. Forexample, antiphospholipid antibodies (75) could impair en-dothelial and platelet functions, antiprotein S antibodies (53)could reduce natural anticoagulant potential, and anti-tPA an-tibodies could impair fibrinolytic activity (76).

Genetic Factors for TE in General and in IBDFactor V Leiden (FVL), the most frequent cause of inher-ited thrombophilia, makes the activated form of factor Vrelatively resistant to degradation by activated protein C(APC), resulting in greater thrombin generation. The preva-lence of FVL ranges from 20% to 30% in unselected patientswith venous thrombosis. Published data have mostly found

178 Danese et al.

TF TFPI/FXa FIX FVIIa inhibition

AT FIXa APC/PS/FV inhibition FVIIIa

FX

FX

FXa AT FVa inhibition APC/PS

Prothrombin

Thrombin AT inhibition

Fibrin FXIIIa FVa, FVIIIa FXIa Activated platelets

AT = antithrombin APC = activated protein C PS = protein S TFPI = tissue factor pathway inhibitor TF = tissue factor “a” indicates the activated coagulation factors

Figure 2. The natural anticoagulant systems.

no difference in the prevalence of FVL between IBD pa-tients and healthy controls (77–80). In addition, the preva-lence of FVL in IBD patients with previous TE appearsnot to differ from that found in non-IBD patients withTE (81).

The G20210A mutation is a genetic variation of the pro-thrombin (PT) gene. Heterozygous carriers of this mutationhave approximately 30% higher PT levels than healthy con-trols, and this is presumed to be the mechanism underlyingits thrombotic effects. Its prevalence is about 2% in healthycontrols and 6.2% in patients with DVT (81). Several studieshave been performed in IBD patients, indicating a lack of as-sociation between IBD and the PT gene G20210A mutation(77–82). Furthermore, studies comparing the prevalence ofthe PT variant in IBD and in non-IBD thrombotic individualsfound no significant difference (81).

Methylenetetrahydrofolate reductase (MTHFR) is a crit-ical enzyme involved in the remethylation pathway of ho-mocysteine metabolism. A common mutation (C677T) hasbeen identified in the MTHFR gene, and homozygosity forthis polymorphism is a cause of moderate hyperhomocys-teinemia. Studies of the prevalence of C677T homozygos-ity in IBD have found discordant results (81), probably be-cause of regional and ethnic variations in the prevalence ofpolymorphism in the general population. However, it is notpossible to speculate a role for the C677T mutation in TEcomplications in IBD, because the only available study com-paring the prevalence of C677T homozygosity between IBDthrombotic patients and non-IBD thrombotic subjects showedno significant difference (81).

A recent study comparing the prevalence of FVL andG20210A PT in thrombotic IBD patients and in thrombotic

Inflammation and Coagulation in IBD 179

Table 3. Mutual Interactions Between Inflammation and Coagula-tion

During inflammation" Fibrinogen, factor VIII" Tissue factor expression on cell surfaces of leukocytes" Platelet production, procoagulant activity, and reactivity" Number of microparticles and concentration of tissue factor

on the particle surface" Monocyte-endothelial cell interactions" PAI-1, TAFI" Complement activation, apoptosis, or necrosis (providing the

key membrane surfaces for initiation and amplification ofcoagulation)

# Protein C pathway, mainly by TM and EPCR downregulation# Antithrombin

During coagulation activation-Proinflammatory

" CD40L by activated platelets" PARs (protease activated receptors) activation and MHC

class II expression on macrophages" Endothelial PAF formation

-Antiinflammatory# Tissue factor and IL-6 expression in monocytes and

endothelial cells# Leukocyte adhesion and migration# NF-"B signaling in monocytes# Endothelial cell apoptosis# TNF! release

non-IBD subjects showed a lower prevalence of inherited riskfactors in thrombotic IBD patients. This suggests that ac-quired risk factors play the most relevant role in determiningthromboembolic events observed in IBD patients (30).

Finally, the inherited Val34Leu factor XIII polymorphism,which is protective against thrombosis, has been evaluated inIBD patients (83). The mutant factor XIII seems to affect thestructure of cross-linked fibrin clots, that is, the fibrin clotsprepared in vitro from FXIIILeu-containing plasma show re-duced fiber mass/length (“thinner” fibers) and porosity. Avail-able data report no significant difference in the prevalence ofthis polymorphism in IBD with respect to the general popu-lation (42, 84, 85).

Thus, there are currently no clearly identifiable increasesto the risk for thrombosis related to the interaction betweeninherited causes of thrombophilia and IBD.

Coagulation Abnormalities and Implications for MucosalInflammationIn addition to the demonstration that coagulation abnormal-ities and thromboembolic complications are clinically rele-vant events in IBD, they have been shown to exert effectsat the mucosal level, where a coagulative imbalance exists.In fact, one of the earliest abnormalities in CD mucosa isthe presence of platelet thrombi cross-linked with fibrin inthe mucosal microvasculature (86). This feature, however,is not specific to CD and can be found in other idiopathicIBD (87). In reality, the intimate adherence of platelets tothe endothelium is a general phenomenon characteristic of

the early manifestations of regional immune reactivity (88)and persists throughout the course of several inflammatoryconditions, including IBD (86, 89). At the mucosal level,crucial changes to the mucosal microvasculature comprisingvascular injury, focal arteritis, fibrin deposition, microinfarc-tion, and neoangiogenesis have been observed in CD (73).Moreover, intracapillary clots have been observed in rectalbiopsies of UC patients (89). In addition, endothelial injuryand disruption could lead to exposure of the subendothelialmatrix, to which platelets are exquisitely attracted, thus fur-ther promoting microthrombi formation.

An imbalance in the coagulant potential of the inflamedmucosal microvasculature occurs in active IBD. Indeed, thereis greater expression of the procoagulant molecule TF, whichclosely correlates with the degree of thrombosis in the mu-cosal microvasculature of CD patients (87). In contrast, adramatic downregulation in the expression of the anticoag-ulant thrombomodulin (TM) and endothelial protein C re-ceptor (EPCR) has been reported in IBD microvessels (90).These changes in TM and EPCR expression would be ex-pected to affect the conversion of protein C in its activatedform, which, in addition to its anticoagulant properties, alsohas potent antiinflammatory activity (91). It is worth notingthat TNF-! is able to trigger a procoagulant profile on en-dothelial cells, increasing TF expression and downregulatingTM and EPCR. This further supports the notion that coag-ulation and inflammation pathways are crucially linked inthe mucosa of patients with IBD, and that these two systemscrosstalk and influence each other (91).

Very recently, homocysteine was also shown to partici-pate in microvascular inflammation in IBD. Treatment of gut-derived endothelial cells with homocysteine, or with a com-bination of TNF-! and homocysteine (which were found tosynergize), triggered endothelial inflammation, resulting inVCAM-1 upregulation, MCP-1 production, and p38 phos-phorylation. These events led to a greater capacity of the en-dothelium to adhere T cells and monocytes and was blockedby treatment with folic acid. This supports a proinflammatoryrole of homocysteine in IBD (58).

Platelet Abnormalities in IBDIt is now well established that platelets behave aberrantlyin both CD and UC (92). An increase in platelet number(“reactive thrombocytosis,” defined as a platelet count >450$ 109/L) frequently occurs during the active phase of IBD(93). The high platelet number correlates well with diseaseseverity and serum orosomucoid concentration, a marker ofsystemic inflammation and, interestingly, may persist evenafter bowel resection (94, 95). Therefore, platelet count hasbeen proposed as a simple method to distinguish IBD frominfectious diarrhea (96). The reason for the greater numberof platelets in the circulation of IBD patients is not wellunderstood, but it is usually considered to be a nonspecificresponse to inflammation, similar to what occurs in otherchronic inflammatory conditions such as rheumatoid arthri-tis or systemic lupus erythematosus. It has also been proposed

180 Danese et al.

tPA uPA

PAI-1 PAI-2

PLASMINOGEN PLASMIN

!2-ANTIPLASMIN TAFI

FIBRIN FDP, FgDP

tPA = tissue-type plasminogen activator uPA = urokinase plasminogen activator PAI = plasminogen activator inhibitor TAFI = thrombin activatable fibrinolysis inhibitor FDP = fibrin degradation products FgDP = fibrinogen degradation products

Figure 3. The fibrinolytic process (boxed molecules are inhibitors).

that the thrombocytosis of CD and UC could reflect a distur-bance in thrombopoiesis, as suggested by the greater plasmalevels of thrombopoietin and interleukin (IL)-6, two criticalfactors involved in megakaryocytic maturation (97). Besidestheir increase in number, platelets in patients with IBD havea small mean corpuscular volume (98) that has also been pro-posed as a potential marker of clinical disease activity, beinginversely proportional to the levels of classical inflamma-tory markers such as C-reactive protein and the erythrocytesedimentation rate (99). Despite a reduced platelet volume,platelets in IBD have an augmented granular content, as in-dicated by studies performed with a computerized analysisof platelet density distribution (98).

In vitro studies have demonstrated that platelets sponta-neously aggregate in more than 30% of IBD patients com-pared with none of the control individuals, and that this isindependent of disease severity (9). An intriguing aspect ofthis complication is that it may not simply represent a conse-quence of chronic inflammation, but may instead be a char-acteristic of IBD, because platelet aggregates are found invivo circulating in IBD patients but not in patients with othertypes of chronic inflammation (100). Finally, compared withplatelets in healthy control individuals, platelets in patients

with IBD are more sensitive to activation induced by a varietyof proaggregating substances, including adenosine diphos-phate, collagen, ristocetin, and arachidonic acid (9, 101).

Collins et al. showed that, in patients with IBD, plateletscirculate in an activated state, demonstrated by the expressionof surface activation markers such as P-selectin and GP53and serum measurement of the platelet activation marker#-thromboglobulin (#-TG) (100). As for other common pa-rameters, the increased platelet activation state was indepen-dent of clinical activity, perhaps suggesting that chronicityof the disease process could lead to enhanced platelet acti-vation even if the disease is clinically silent. A complemen-tary observation, likely to be relevant to disease pathogene-sis, is that in CD the enhanced expression of P-selectin onplatelets is found in capillary compared with peripheral ve-nous blood, probably indicating that platelet activation occursin the intestinal microcirculation, a concept also supportedby the demonstration of a higher platelet aggregation in themesenteric circulation in IBD (102, 103).

The most recent confirmation of a heightened platelet ac-tivation state in IBD is the detection of surface CD40 ligand(CD40L), an activation marker that allows platelets to interactwith a broad variety of immune and nonimmune cells (104).

Inflammation and Coagulation in IBD 181

Compared with healthy controls, circulating platelets in bothCD and UC patients have significantly greater expression ofthis potent immunoregulatory and proinflammatory moleculethan normal platelets, and this difference persists even after invitro thrombin stimulation (105). In addition, these CD40L-positive platelets are essentially the only source of the greaterplasma levels of the soluble form of CD40L (sCD40L) in IBD(106).

Platelet Contribution to IBD PathogenesisOne of the first suggestions that platelets could be in-volved in chronic intestinal inflammation was inferred fromhistopathological studies that revealed the presence of mu-cosal capillary thrombi in rectal biopsies of patients with IBD(89). Intravascular microthrombi are frequently observed inthe mucosa of patients with CD and UC, even though theirpresence is unrelated to the severity of inflammation, andthey are consistently absent in the mucosa of normal sub-jects (89). Platelet activation occurs in IBD mucosa, as orig-inally suggested by the finding of greater platelet aggregatesin the mesenteric blood of CD patients (103) and as recentlyreproduced in vitro using platelets cocultured with humanintestinal microvascular endothelial cells (HIMEC). HIMECpretreated with IL-1# to mimic IBD endothelium can activateplatelets through simple physical contact, as evidenced by asustained upregulation of P-selectin and CD40L expressionon the platelet surface (106). In the last few years, it has be-come accepted that activated platelets are inflammatory cells(107). Therefore, because in IBD platelets circulate in an ac-tivate state, it appears logical that these cells are acting asinflammatory cells in this situation (92, 108).

The best evidence that platelets promote mucosal inflam-mation is the recent demonstration that platelets from patientswith IBD express high levels of surface CD40L, creating a bi-ological bridge that allows interaction with and activation ofmucosal endothelium. This series of events actually occurs,as CD40L-positive platelets in IBD have been detected in vivoadhering to mucosal microvascular endothelium where theytrigger or amplify a proinflammatory response (105). Indeed,ligation of CD40L-positive platelets to CD40-positive mi-crovasculature triggers inflammation by the upregulation ofVCAM-1 and ICAM-1, and secretion of IL-8, the major neu-trophil chemoattractant. In addition to IL-8, IBD platelets re-lease biologically active RANTES (109), a chemokine criticalfor recruitment of monocytes and memory T cells. Becauseplatelets also express CD40, they can be activated by bothsCD40L and activated CD40L-positive T cells, and secretegranular RANTES (110). HIMEC retain this platelet-derivedRANTES on their surface, which can thus mediate adhesionof T cells to mucosal endothelium. This cycle functionallylinks two key phenomena, platelet activation and T-cell re-cruitment, and implicates platelets in cell-mediated immunephenomena that occur during gut inflammation (105). An-other functional link between platelets and leukocytes hasbeen recently postulated. T cells adhering to an inflamed mi-crovascular bed may create an effective platform onto which

platelets bind and further interact with the endothelium itself(111). Specifically, Vowinkel and colleagues, using an ex-perimental colitis model, have recently shown that platelet-leukocyte interactions are mediated by CD40L, as revealedby the significant reduction in circulating platelet-leukocyteaggregates if CD40L-deficient animals are used (112). Fur-thermore, platelet and leukocyte aggregates (PLA) are morefrequent in IBD patients than in healthy controls, and suchaggregates are more likely to adhere to mucosal endotheliumthan leukocytes that circulate alone and to induce upregula-tion of TF by monocytes (40).

Therapeutic ConsiderationsAs described above, acquired risk factors appear to play themost relevant role in thrombosis, complicating the course ofIBD; moreover, many of the hemostatic alterations appearto be related to disease activity. Indeed, as already demon-strated, inflammation may increase the risk for thrombosisvia several mechanisms, for example, increasing the countand activity of platelets, activating the coagulation cascade,impairing anticoagulant and fibrinolytic activities, and lead-ing to hyperhomocysteinemia as a result of hypercatabolismand/or malabsorption.

As a consequence, major efforts to prevent thromboticcomplications should focus on prevention or correction ofacquired risk factors. Physicians who care for IBD patientsshould always keep in mind that a greater risk for throm-bosis exists and every effort should be made to avoid thiscomplication, which affects young people and is an impor-tant cause of morbidity and mortality. Moreover, prophylac-tic antithrombotic treatment should be started in all clinicalconditions that are associated with a greater risk for throm-bosis, such as prolonged inactivity or surgical interventions.Finally, considering the crosstalk between coagulation andinflammation, it seems reasonable to hypothesize that an-tiinflammatory therapies can affect coagulation per se andvice versa.

TREATMENT OF IBD IN ORDER TO PREVENTTHROMBOSIS. A good and continuous control of diseaseactivity as well as vitamin supplementation is recommendedin IBD patients. Indeed, this attitude should reduce the riskfactors for thrombosis linked to systemic inflammation andvitamin deficiencies. Furthermore, many of the drugs withantiinflammatory activity also modify coagulation, and it hasbeen suggested that the efficacy of therapies in inducing re-mission in patients with IBD also depends on a reduction inprothrombotic tendency.

For example, 5-aminosalicylic acid (5-ASA), a mainstayof IBD therapy, induces a wide array of modulatory activ-ities, including the inhibition of platelet activation. In fact,platelets isolated from the circulation of IBD patients receiv-ing mesalazine or olsalazine display reduced spontaneousand thrombin-induced platelet activation in vitro, as well aslow expression of P-selectin in vivo (113). A plausible ex-planation is that reduced activation results in less interaction

182 Danese et al.

with endothelial and inflammatory cells and, subsequently,diminished release of proinflammatory mediators, leading todownregulation of gut inflammation.

Azathioprine and its active metabolite 6-mercaptopurine(6MP) are the two most widely used immunosuppres-sant agents in IBD. Besides their well-known effects onthe immune system, these agents also inhibit adenosinediphosphate-induced platelet aggregation in vitro (114), andit is has been reported that this blockade inhibits formation ofplatelet-leukocyte aggregates (PLA), which plays a role in thepathogenesis of IBD and thrombosis (112, 115). Finally, in-fliximab, the chimeric monoclonal antibody directed againstTNF-!, is also able to normalize hemostatic parameters (116)and to reduce the amount of circulating microparticles in CD(117) and the prothrombotic sCD40L (118).

TREATMENT OF IBD WITH DRUGS THAT AFFECTTHE CLOTTING SYSTEM. Because it is clear that theclotting system is potentially involved in IBD pathogenesisand/or in perpetuating and amplifying the inflammatory pro-cess, the use of anticoagulant or coagulation-related drugscan be considered for the treatment of IBD. Because reducedplasma levels of activated factor XIII (factor XIIIa) have beenfrequently observed in IBD, it has been suggested that re-duced factor XIIIa plasma levels might contribute to mucosaldamage and perpetuate the bleeding tendency during activeIBD (68). Therefore, factor XIIIa supplementation has beentested as IBD treatment. Although uncontrolled reports haveshown some efficacy of factor XIII substitution in the treat-ment of steroid-resistant active UC (119) and perianal fistulasin CD (120), these data were not confirmed in a double-blind,prospective trial performed in patients with UC (121).

The potential therapeutic value of both unfractionated hep-arin and low molecular weight heparin (LMWH) has beenaddressed in IBD, mainly in UC. Heparin is known for itsanticoagulant indication, but it is also characterized by anti-inflammatory properties (122). Initial reports showed a po-tential benefit of systemic heparin treatment in patients withIBD; however, data derived from controlled studies overallsuggest a lack of efficacy of these molecules (122). Drugs thattarget the inflammatory potential of platelets have also beenproposed as a possible treatment of IBD. However, the useof ridogrel (a combined thromboxane synthase inhibitor andthromboxane/prostaglandin endoperoxide antagonist), pico-tamide (a thromboxane synthesis inhibitor receptor antago-nist), and SR27417A (a platelet-activating factor antagonist)did not show convincing efficacy (123–125). However, be-cause these drugs have been used at a low dose and not at thefull dose, it would be possible that randomized, double-blindtrials using the appropriate dose would show some efficacyfor this class of molecules.

A very important issue that should be considered in the caseof anticoagulant or antiplatelet therapy during active IBD isthe potential risk for intestinal bleeding as an adverse event.This adverse effect was reported as a complication occurringduring a trial evaluating the efficacy of heparin, although

such worsening of rectal bleeding is infrequent in treated UCpatients (126). To avoid the systemic effects of heparins, arecent open-label study evaluated the safety and efficacy oforal, colonic-release, low molecular weight heparin-MMxTM

for the treatment of mild to moderate left-sided UC. Thisappears to be a safe and effective treatment option in mild tomoderate UC, and controlled studies are warranted to confirmits therapeutic effects (127).

TREATMENT OF THROMBOSIS IN PATIENTS WITHIBD. The treatment of thromboembolic events that com-plicate the course of IBD is similar to that of thromboem-bolic events occurring in the general population (36). Be-cause of the possibility of recurrence of thrombosis, it isdebated whether or not maintenance therapy with anticoagu-lants is useful. A panel of coagulation laboratory parametersand genetic tests is advisable to exactly define the prothrom-botic risk of individuals after the occurrence of their firstthrombotic event. This is particularly recommended in IBDpatients, in whom macrovascular thrombosis is a relativelyfrequent complication and often a life-threatening condition,considering that acquired and inherited risk factors of throm-bosis can coexist, strengthening each. However, multicenterstudies, with a larger number of IBD patients with thrombo-sis, are needed to clarify the relationship between IBD andacquired and inherited thrombophilia. This would identifya subgroup of patients in whom anticoagulant prophylactictherapy would be advisable.

CONCLUSIONS

IBD pathophysiology is a very intriguing and complicatedpuzzle, and in the last few years we have made tremendousprogress in adding new pieces in the knowledge of mecha-nisms of disease.

During the last couple of decades, it has been realized thatthe complexity of CD and UC is not limited to the clini-cal manifestations, but extends to the underlying pathogenicmechanisms. The worldwide occurrence of IBD, the recog-nition of the determining role of genetics, a deeper under-standing of cellular and molecular mechanisms of inflam-mation, tissue injury and repair, and the reaffirmation of theenteric flora as the target of immune reactivity have con-solidated the hypothesis that IBD is the result of a com-plex interplay of environmental, genetic, immune and non-immune, and microbial factors. IBD pathogenesis has beendominated by the investigation of mucosal immunity events,and only more recently, proper emphasis has been given to ge-netics, intestinal microbial ecology, and the tissue response.In reality, until the exact cause and mechanisms of IBD arefully understood, each pathogenic component should be pur-sued in detail. Moreover, IBD is typically chronic in nature,and special attention must be devoted to the factors respon-sible for the maintenance of gut inflammation. Therefore,considering that the coagulation system is a dynamic par-ticipant in the multifaceted process of chronic intestinal

Inflammation and Coagulation in IBD 183

inflammation and represents an important, though previouslyunderestimated, component of IBD pathogenesis, it appearslogical that a safe blockade may lead to novel therapeutic ap-proaches, keeping in mind the basic principles of medicine“primum non nocere.”

ACKNOWLEDGMENT

This work was supported by a grant from the Broad MedicalResearch Program to S.D.

Reprint requests and correspondence: Silvio Danese, M.D., Di-vision of Gastroenterology, Istituto Clinico Humanitas-IRCCS inGastroenterology, Viale Manzoni, Rozzano, Milan, Italy.

Received May 2, 2006; accepted July 24, 2006.

REFERENCES

1. Gabay C, Kushner I. Acute-phase proteins and othersystemic responses to inflammation. N Engl J Med1999;340:448–54.

2. McEver RP. Adhesive interactions of leukocytes, platelets,and the vessel wall during hemostasis and inflammation.Thromb Haemost 2001;86:746–56.

3. Johnson K, Aarden L, Choi Y, et al. The proinflammatorycytokine response to coagulation and endotoxin in wholeblood. Blood 1996;87:5051–60.

4. Stouthard JM, Levi M, Hack CE, et al. Interleukin-6 stim-ulates coagulation, not fibrinolysis, in humans. ThrombHaemost 1996;76:738–42.

5. Levi M, van der Poll T, ten Cate H, et al. The cytokine-mediated imbalance between coagulant and anticoagulantmechanisms in sepsis and endotoxaemia. Eur J Clin Invest1997;27:3–9.

6. Devaraj S, Xu DY, Jialal I. C-reactive protein increasesplasminogen activator inhibitor-1 expression and activ-ity in human aortic endothelial cells: Implications forthe metabolic syndrome and atherothrombosis. Circulation2003;107:398–404.

7. Talbot RW, Heppell J, Dozois RR, et al. Vascular com-plications of inflammatory bowel disease. Mayo Clin Proc1986;61:140–5.

8. Jackson LM, O’Gorman PJ, O’Connell J, et al. Thrombosisin inflammatory bowel disease: Clinical setting, procoagu-lant profile and factor V Leiden. Q J Med 1997;90:183–8.

9. Webberley MJ, Hart MT, Melikian V. Thromboembolismin inflammatory bowel disease: Role of platelets. Gut1993;34:247–51.

10. Sloan WP Jr, Bargen JA, Gage RB. Life histories of patientswith chronic ulcerative colitis: A review of 2,000 cases.Gastroenterology 1968;54:(suppl):819–22.

11. Bernstein CN, Blanchard JF, Houston DS, et al. The in-cidence of deep venous thrombosis and pulmonary em-bolism among patients with inflammatory bowel dis-ease: A population-based cohort study. Thromb Haemost2001;85:430–4.

12. Miehsler W, Reinisch W, Valic E, et al. Is inflammatorybowel disease an independent and disease specific risk fac-tor for thromboembolism? Gut 2004;53:542–8.

13. Grip O, Svensson PJ, Lindgren S. Inflammatory bowel dis-ease promotes venous thrombosis earlier in life. Scand JGastroenterol 2000;35:619–23.

14. Johns DR. Cerebrovascular complications of inflammatorybowel disease. Am J Gastroenterol 1991;86:367–70.

15. Maccini DM, Berg JC, Bell GA. Budd-Chiari syndromeand Crohn’s disease. An unreported association. Dig DisSci 1989;34:1933–6.

16. Schneiderman JH, Sharpe JA, Sutton DM. Cerebral andretinal vascular complications of inflammatory bowel dis-ease. Ann Neurol 1979;5:331–7.

17. Keyser BJ, Hass AN. Retinal vascular disease in ulcerativecolitis. Am J Ophthalmol 1994;118:395–6.

18. Hatoum OA, Spinelli KS, Abu-Hajir M, et al. Mesentericvenous thrombosis in inflammatory bowel disease. J ClinGastroenterol 2005;39:27–31.

19. Umit H, Asil T, Celik Y, et al. Cerebral sinus thrombosis inpatients with inflammatory bowel disease: A case report.World J Gastroenterol 2005;11:5404–7.

20. Younes-Mhenni S, Derex L, Berruyer M, et al. Large-arterystroke in a young patient with Crohn’s disease. Role ofvitamin B6 deficiency-induced hyperhomocysteinemia. JNeurol Sci 2004;221:113–5.

21. Levy PJ, Tabares AH, Olin JW. Lower extremity arterialocclusions in young patients with Crohn’s colitis and pre-mature atherosclerosis: Report of six cases. Am J Gas-troenterol 1997;92:494–7.

22. Novotny DA, Rubin RJ, Slezak FA, et al. Arterial throm-boembolic complications of inflammatory bowel disease.Report of three cases. Dis Colon Rectum 1992;35:193–6.

23. Ashkan K, Nasim A, Sayers RD, et al. Arterial thrombo-sis: A complication of loop ileostomy. Eur J GastroenterolHepatol 1998;10:795–6.

24. Efremidis M, Prappa E, Kardaras F. Acute myocardial in-farction in a young patient during an exacerbation of ul-cerative colitis. Int J Cardiol 1999;70:211–2.

25. Mutlu B, Ermeydan CM, Enc F, et al. Acute myocardialinfarction in a young woman with severe ulcerative colitis.Int J Cardiol 2002;83:183–5.

26. Szychta P, Reix T, Sevestre MA, et al. Aortic thrombosisand ulcerative colitis. Ann Vasc Surg 2001;15:402–4.

27. Novacek G, Haumer M, Schima W, et al. Aortic muralthrombi in patients with inflammatory bowel disease: re-port of two cases and review of the literature. InflammBowel Dis 2004;10:430–5.

28. Papa A, Santoliquido A, Danese S, et al. Increased carotidintima-media thickness in patients with inflammatorybowel disease. Aliment Pharmacol Ther 2005;22:839–46.

29. Hudson M, Chitolie A, Hutton RA, et al. Thromboticvascular risk factors in inflammatory bowel disease. Gut1996;38:733–7.

30. Spina L, Saibeni S, Battaglioli T, et al. Thrombosis ininflammatory bowel diseases: Role of inherited throm-bophilia. Am J Gastroenterol 2005;100:2036–41.

31. Oldenburg B, Fijnheer R, van der Griend R, et al. Ho-mocysteine in inflammatory bowel disease: A risk factorfor thromboembolic complications? Am J Gastroenterol2000;95:2825–30.

32. Oldenburg B, Van Tuyl BA, van der Griend R, et al. Riskfactors for thromboembolic complications in inflammatorybowel disease: The role of hyperhomocysteinaemia. DigDis Sci 2005;50:235–40.

33. Solem CA, Loftus EV, Tremaine WJ, et al. Venous throm-boembolism in inflammatory bowel disease. Am J Gas-troenterol 2004;99:97–101.

34. Wong T, Nightingale J, Winter M, et al. Spontaneous ve-nous thrombosis in inflammatory bowel disease: relevanceof factor V Leiden and the prothrombin gene mutation. JThromb Haemost 2003;1:1326–8.

184 Danese et al.

35. Thompson NP, Wakefield AJ, Pounder RE. Inherited disor-ders of coagulation appear to protect against inflammatorybowel disease. Gastroenterology 1995;108:1011–5.

36. Koutroubakis IE. Therapy insight: Vascular complicationsin patients with inflammatory bowel disease. Nat Clin PractGastroenterol Hepatol 2005;2:266–72.

37. Welch GN, Loscalzo J. Homocysteine and atherothrombo-sis. N Engl J Med 1998;338:1042–50.

38. Cattaneo M, Martinelli I, Mannucci PM. Hyperhomocys-teinemia as a risk factor for deep-vein thrombosis. N EnglJ Med 1996;335:974–5; author reply 975–6.

39. Danese S, Sans M, Fiocchi C. Inflammatory bowel dis-ease: The role of environmental factors. Autoimmun Rev2004;3:394–400.

40. Irving PM, Pasi KJ, Rampton DS. Thrombosis and in-flammatory bowel disease. Clin Gastroenterol Hepatol2005;3:617–28.

41. van Bodegraven AA. Haemostasis in inflammatorybowel diseases: Clinical relevance. Scand J Gastroenterol2003;239(suppl):51–62.

42. Hayat M, Ariens RA, Moayyedi P, et al. Coagulation factorXIII and markers of thrombin generation and fibrinolysisin patients with inflammatory bowel disease. Eur J Gas-troenterol Hepatol 2002;14:249–56.

43. Chiarantini E, Valanzano R, Liotta AA, et al. Hemostaticabnormalities in inflammatory bowel disease. Thromb Res1996;82:137–46.

44. Souto JC, Martinez E, Roca M, et al. Prothrombotic stateand signs of endothelial lesion in plasma of patients withinflammatory bowel disease. Dig Dis Sci 1995;40:1883–9.

45. Saibeni S, Bottasso B, Spina L, et al. Assessment ofthrombin-activatable fibrinolysis inhibitor (TAFI) plasmalevels in inflammatory bowel diseases. Am J Gastroenterol2004;99:1966–70.

46. Esmon CT. The protein C pathway. Chest 2003;124(suppl 3):26S–32S.

47. Cesarman-Maus G, Hajjar KA. Molecular mechanisms offibrinolysis. Br J Haematol 2005;129:307–21.

48. Esmon CT. Crosstalk between inflammation and thrombo-sis. Maturitas 2004;47:305–14.

49. Barger AP, Hurley R. Evaluation of the hypercoagulablestate. Whom to screen, how to test and treat. Postgrad Med2000;108:59–66.

50. Lee LC, Spittell JA Jr, Sauer WG, et al. Hypercoagulabilityassociated with chronic ulcerative colitis: Changes in bloodcoagulation factors. Gastroenterology 1968;54:76–85.

51. Heneghan MA, Cleary B, Murray M, et al. Activated pro-tein C resistance, thrombophilia, and inflammatory boweldisease. Dig Dis Sci 1998;43:1356–61.

52. Aadland E, Odegaard OR, Roseth A, et al. Free proteinS deficiency in patients with chronic inflammatory boweldisease. Scand J Gastroenterol 1992;27:957–60.

53. Saibeni S, Vecchi M, Valsecchi C, et al. Reduced free pro-tein S levels in patients with inflammatory bowel disease:Prevalence, clinical relevance, and role of anti-protein Santibodies. Dig Dis Sci 2001;46:637–43.

54. de Jong E, Porte RJ, Knot EA, et al. Disturbed fibri-nolysis in patients with inflammatory bowel disease. Astudy in blood plasma, colon mucosa, and faeces. Gut1989;30:188–94.

55. Gris JC, Schved JF, Raffanel C, et al. Impaired fibri-nolytic capacity in patients with inflammatory bowel dis-ease. Thromb Haemost 1990;63:472–5.

56. Cattaneo M, Vecchi M, Zighetti ML, et al. High prevalenceof hyperchomocysteinemia in patients with inflammatorybowel disease: A pathogenic link with thromboemboliccomplications? Thromb Haemost 1998;80:542–5.

57. Romagnuolo J, Fedorak RN, Dias VC, et al. Hyperhomo-cysteinemia and inflammatory bowel disease: Prevalenceand predictors in a cross-sectional study. Am J Gastroen-terol 2001;96:2143–9.

58. Danese S, Sgambato A, Papa A, et al. Homocysteine trig-gers mucosal microvascular activation in inflammatorybowel disease. Am J Gastroenterol 2005;100:886–95.

59. Saibeni S, Cattaneo M, Vecchi M, et al. Low vitamin B(6)plasma levels, a risk factor for thrombosis, in inflammatorybowel disease: Role of inflammation and correlation withacute phase reactants. Am J Gastroenterol 2003;98:112–7.

60. Diamant M, Tushuizen ME, Sturk A, et al. Cellular mi-croparticles: New players in the field of vascular disease?Eur J Clin Invest 2004;34:392–401.

61. Andoh A, Tsujikawa T, Hata K, et al. Elevated cir-culating platelet-derived microparticles in patients withactive inflammatory bowel disease. Am J Gastroenterol2005;100:2042–8.

62. Vecchi M, Cattaneo M, de Franchis R, et al. Risk of throm-boembolic complications in patients with inflammatorybowel disease. Study of hemostasis measurements. Int JClin Lab Res 1991;21:165–70.

63. Hudson M, Hutton RA, Wakefield AJ, et al. Evidence foractivation of coagulation in Crohn’s disease. Blood CoagulFibrinolysis 1992;3:773–8.

64. Chamouard P, Grunebaum L, Wiesel ML, et al. Prothrom-bin fragment 1 + 2 and thrombin-antithrombin III com-plex as markers of activation of blood coagulation in in-flammatory bowel diseases. Eur J Gastroenterol Hepatol1995;7:1183–8.

65. van Bodegraven AA, Schoorl M, Linskens RK, et al. Per-sistent activation of coagulation and fibrinolysis after treat-ment of active ulcerative colitis. Eur J Gastroenterol Hep-atol 2002;14:413–8.

66. Stadnicki A, Kloczko J, Nowak A, et al. Factor XIII sub-units in relation to some other hemostatic parameters inulcerative colitis. Am J Gastroenterol 1991;86:690–3.

67. Hudson M, Wakefield AJ, Hutton RA, et al. Factor XIIIAsubunit and Crohn’s disease. Gut 1993;34:75–9.

68. Lorenz R, Olbert P, Born P. Factor XIII in chronicinflammatory bowel diseases. Semin Thromb Hemost1996;22:451–5.

69. Van Bodegraven AA, Tuynman HA, Schoorl M, et al. Fib-rinolytic split products, fibrinolysis, and factor XIII activ-ity in inflammatory bowel disease. Scand J Gastroenterol1995;30:580–5.

70. Stevens TR, James JP, Simmonds NJ, et al. Circulatingvon Willebrand factor in inflammatory bowel disease. Gut1992;33:502–6.

71. Boehme MW, Autschbach F, Zuna I, et al. Elevated serumlevels and reduced immunohistochemical expression ofthrombomodulin in active ulcerative colitis. Gastroenterol-ogy 1997;113:107–17.

72. Meucci G, Pareti F, Vecchi M, et al. Serum von Willebrandfactor levels in patients with inflammatory bowel diseaseare related to systemic inflammation. Scand J Gastroenterol1999;34:287–90.

73. Wakefield AJ, Sawyerr AM, Dhillon AP, et al. Pathogen-esis of Crohn’s disease: Multifocal gastrointestinal infarc-tion. Lancet 1989;2:1057–62.

74. Binion DG, West GA, Volk EE, et al. Acquired increase inleucocyte binding by intestinal microvascular endotheliumin inflammatory bowel disease. Lancet 1998;352:1742–6.

75. Aichbichler BW, Petritsch W, Reicht GA, et al. Anti-cardiolipin antibodies in patients with inflammatory boweldisease. Dig Dis Sci 1999;44:852–6.

Inflammation and Coagulation in IBD 185

76. Saibeni S, Ciscato C, Vecchi M, et al. Antibodies to tissue-type plasminogen activator (tPA) in patients with inflam-matory bowel disease: High prevalence, interactions withfunctional domains of tPA and possible implications inthrombosis. J Thromb Haemost 2006;4:1510–6.

77. Turri D, Rosselli M, Simioni P, et al. Factor V Leiden andprothrombin gene mutation in inflammatory bowel diseasein a Mediterranean area. Dig Liver Dis 2001;33:559–62.

78. Papa A, De Stefano V, Gasbarrini A, et al. Prevalence offactor V Leiden and the G20210A prothrombin-gene mu-tation in inflammatory bowel disease. Blood Coagul Fibri-nolysis 2000;11:499–503.

79. Haslam N, Standen GR, Probert CS. An investigation ofthe association of the factor V Leiden mutation and in-flammatory bowel disease. Eur J Gastroenterol Hepatol1999;11:1289–91.

80. Vecchi M, Sacchi E, Saibeni S, et al. Inflammatorybowel diseases are not associated with major heredi-tary conditions predisposing to thrombosis. Dig Dis Sci2000;45:1465–9.

81. Papa A, Danese S, Grillo A, et al. Review article: Inher-ited thrombophilia in inflammatory bowel disease. Am JGastroenterol 2003;98:1247–51.

82. Mahmood A, Needham J, Prosser J, et al. Prevalence of hy-perhomocysteinaemia, activated protein C resistance andprothrombin gene mutation in inflammatory bowel disease.Eur J Gastroenterol Hepatol 2005;17:739–44.

83. Franco RF, Reitsma PH, Lourenco D, et al. Factor XIIIVal34Leu is a genetic factor involved in the etiology ofvenous thrombosis. Thromb Haemost 1999;81:676–9.

84. Helio T, Wartiovaara U, Halme L, et al. Arg506Gln factorV mutation and Val34Leu factor XIII polymorphism inFinnish patients with inflammatory bowel disease. Scand JGastroenterol 1999;34:170–4.

85. Saibeni S, Vecchi M, Faioni EM, et al. Val34Leu factorXIII polymorphism in Italian patients with inflammatorybowel disease. Dig Liver Dis 2003;35:32–6.

86. Sankey EA, Dhillon AP, Anthony A, et al. Early mucosalchanges in Crohn’s disease. Gut 1993;34:375–81.

87. More L, Sim R, Hudson M, et al. Immunohistochemi-cal study of tissue factor expression in normal intestineand idiopathic inflammatory bowel disease. J Clin Pathol1993;46:703–8.

88. Saadi S, Wrenshall LE, Platt JL. Regional manifestationsand control of the immune system. FASEB J 2002;16:849–56.

89. Dhillon AP, Anthony A, Sim R, et al. Mucosal capillarythrombi in rectal biopsies. Histopathology 1992;21:127–33.

90. Faioni EM, Ferrero S, Fontana G, et al. Expression of en-dothelial protein C receptor and thrombomodulin in theintestinal tissue of patients with inflammatory bowel dis-ease. Crit Care Med 2004;32(suppl 5):S266–70.

91. Van de Wouwer M, Collen D, Conway EM.Thrombomodulin-protein C-EPCR system: integratedto regulate coagulation and inflammation. ArteriosclerThromb Vasc Biol 2004;24:1374–83.

92. Danese S, De La Motte C, Fiocchi C, et al. Platelets in In-flammatory bowel disease: clinical, pathological and ther-apeutical implications. Am J Gastroenterol 2004;99:938–45.

93. Talstad I, Rootwelt K, Gjone E. Thrombocytosis in ulcer-ative colitis and Crohn’s disease. Scand J Gastroenterol1973;8:135–8.

94. Harries AD, Fitzsimons E, Fifield R, et al. Platelet count: Asimple measure of activity in Crohn’s disease. BMJ (ClinRes Ed) 1983;286:1476.

95. Chiarantini E, Valanzano R, Liotta AA, et al. Persistenceof hemostatic alterations in patients affected by Crohn’sdisease after bowel surgery. Thromb Res 1997;87:539–46.

96. Harries AD, Beeching NJ, Rogerson SJ, et al. Theplatelet count as a simple measure to distinguish inflam-matory bowel disease from infective diarrhoea. J Infect1991;22:247–50.

97. Heits F, Stahl M, Ludwig D, et al. Elevated serum throm-bopoietin and interleukin-6 concentrations in thrombocy-tosis associated with inflammatory bowel disease. J Inter-feron Cytokine Res 1999;19:757–60.

98. Jaremo P, Sandberg-Gertzen H. Platelet density andsize in inflammatory bowel disease. Thromb Haemost1996;75:560–1.

99. Kapsoritakis AN, Koukourakis MI, Sfiridaki A, et al. Meanplatelet volume: A useful marker of inflammatory boweldisease activity. Am J Gastroenterol 2001;96:776–81.

100. Collins CE, Cahill MR, Newland AC, et al. Platelets cir-culate in an activated state in inflammatory bowel disease.Gastroenterology 1994;106:840–5.

101. van Wersch JWJ, Houben P, RiJken J. Platelet count,platelet function, coagulation activity and fibrinolysis in theacute phase of inflammatory bowel disease. J Clin ChemClin Biochem 1990;28:513–7.

102. Tschope D, Schwippert B, Schumacher B, et al. IncreasedP-selectin (CD62) expression on platelets from capillarywhole blood of patients with Crohn’s disease. Gastroen-terology 1993;104:A793.

103. Collins CE, Rampton DS, Rogers J, et al. Platelet aggrega-tion and neutrophil sequestration in the mesenteric circu-lation in inflammatory bowel disease. Eur J GastroenterolHepatol 1997;9:1213–7.

104. Danese S, Fiocchi C. Platelet activation and theCD40/CD40L pathway: mechanisms and implications forhuman disease. Crit Rev Immunol 2005:25:103–22.

105. Danese S, de La Motte C, Sturm A, et al. Platelets trigger aCD40-dependent inflammatory response in the microvas-culature of inflammatory bowel disease patients. Gastroen-terology 2003;124:1249–64.

106. Danese S, Katz J, Saibeni S, et al. Activated platelets arethe source of elevated levels of soluble CD40 ligand in thecirculation of inflammatory bowel disease patients. Gut2003; 52:1435–41.

107. Klinger MH. Platelets and inflammation. Anat Embryol(Berl) 1997;196:1–11.

108. Collins CE, Rampton DS. Review article: Platelets ininflammatory bowel disease—pathogenetic role andtherapeutic implications. Aliment Pharmacol Ther1997;11:237–47.

109. Power CA, Clemetson JM, Clemetson KJ, et al. Chemokineand chemokine receptor mRNA expression in humanplatelets. Cytokine 1995;7:479–82.

110. Danese S, de la Motte C, Reyes BM, et al. Cutting edge: Tcells trigger CD40-dependent platelet activation and gran-ular RANTES release: A novel pathway for immune re-sponse amplification. J Immunol 2004;172:2011–5.

111. Russell J, Cooper D, Tailor A, et al. Low venular shearrates promote leukocyte-dependent recruitment of adher-ent platelets. Am J Physiol Gastrointest Liver Physiol2003;284:G123–9.

112. Vowinkel T, Mori M, Overell K, et al. Platelet–leukocyte(WBC) interactions in experimental colitis are mediatedby CD40L and ICAM-1. Gastroenterology 2004;126(suppl2):A-21.

113. Carty E, MacEy M, Rampton DS. Inhibition of plateletactivation by 5-aminosalicylic acid in inflammatory boweldisease. Aliment Pharmacol Ther 2000;14:1169–79.

186 Danese et al.

114. Thomas G, Skrinska VA, Lucas FV. The influence of glu-tathione and other thiols on human platelet aggregation.Thromb Res 1986;44:859–66.

115. Inwald DP, McDowall A, Peters MJ, et al. CD40 is consti-tutively expressed on platelets and provides a novel mech-anism for platelet activation. Cir Res 2003;92:1041–8.

116. Hommes DW, van Dullemen HM, Levi M, et al. Beneficialeffect of treatment with a monoclonal anti-tumor necrosisfactor-alpha antibody on markers of coagulation and fibri-nolysis in patients with active Crohn’s disease. Haemostasis1997;27:269–77.

117. Chamouard P, Desprez D, Hugel B, et al. Circulating cell-derived microparticles in Crohn’s disease. Dig Dis Sci2005;50:574–80.

118. Danese S, Sans M, Scaldaferri F, et al. TNF-alphablockade downregulates the CD40/CD40L pathway inthe mucosal microcirculation: A novel anti-inflammatorymechanism of infliximab in Crohn’s disease. J Immunol2006;176:2617–24.

119. Lorenz R, Born P, Olbert P, et al. Factor XIII substitutionin ulcerative colitis. Lancet 1995;345:449–50.

120. Oshitani N, Nakamura S, Matsumoto T, et al. Treatmentof Crohn’s disease fistulas with coagulation factor XIII.Lancet 1996;347:119–20.

121. Bregenzer N, Caesar I, Andus T, et al. Lack of clinicalefficacy of additional factor XIII treatment in patients withsteroid refractory colitis. The Factor XIII Study Group. ZGastroenterol 1999;37:999–1004.

122. Papa A, Danese S, Gasbarrini A, et al. Review article: Po-tential therapeutic applications and mechanisms of actionof heparin in inflammatory bowel disease. Aliment Phar-macol Ther 2000;14:1403–9.

123. Carty E, Rampton DS, Schneider H, et al. Lack of efficacyof ridogrel, a thromboxane synthase inhibitor, in a placebo-controlled, double-blind, multi-centre clinical trial in activeCrohn’s disease. Aliment Pharmacol Ther 2001;15:1323–9.

124. Tytgat GN, Van Nueten L, Van De Velde I, et al. Efficacyand safety of oral ridogrel in the treatment of ulcerativecolitis: two multicentre, randomized, double-blind studies.Aliment Pharmacol Ther 2002;16:87–99.

125. Patscheke H. Thromboxane A2/prostaglandin H2 re-ceptor antagonists. A new therapeutic principle. Stroke1990;21(suppl 12):139–42.

126. Panes J, Esteve M, Cabre E, et al. Comparison of heparinand steroids in the treatment of moderate and severe ulcer-ative colitis. Gastroenterology 2000;119:903–8.

127. Saibeni S, Spina L, Signorelli C, et al. Safety and efficacyof oral, colonic-release, low molecular weight heparin-MMxTM for the treatment of mild to moderate left-sidedulcerative colitis: Preliminary report of a pilot study. Gas-troenterology 2006;130:A1339.

CONFLICT OF INTEREST

Guarantor of the article: Silvio DaneseSpecific author contributions: Silvio Danese: conceptual-ization and writing; all other authors: writing.Financial support: This work was supported by a grant fromthe Broad Medical Research Program to S.D.Potential competing interests: None