REVIEW

Myocardial Fibrosis in Heart Failure: Anti-FibroticTherapies and the Role of Cardiovascular MagneticResonance in Drug Trials

Matthew Webber . Stephen P. Jackson . James C. Moon .

Gabriella Captur

Received: July 14, 2020 / Published online: August 30, 2020� The Author(s) 2020

ABSTRACT

All heart muscle diseases that cause chronicheart failure finally converge into one dreadedpathological process that is myocardial fibrosis.Myocardial fibrosis predicts major adverse car-diovascular events and death, yet we are stillmissing the targeted therapies capable of halt-ing and/or reversing its progression. Funda-mentally it is a problem of disproportionateextracellular collagen accumulation that is partof normal myocardial ageing and accentuated

in certain disease states. In this article we dis-cuss the role of cardiovascular magnetic reso-nance (CMR) imaging biomarkers to trackfibrosis and collate results from the mostpromising animal and human trials of anti-fi-brotic therapies to date. We underscore theever-growing role of CMR in determining theefficacy of such drugs and encourage futuretrialists to turn to CMR when designing theirsurrogate study endpoints.

Keywords: Anti-fibrotic therapies; Cardiacmagnetic resonance imaging; Extracellularvolume; Myocardial fibrosis; T1 mapping

Digital Features This article is published with digitalfeatures to facilitate understanding of the article. Youcan access the digital features on the article’s associatedFigshare page. To view digital features for this article goto https://doi.org/10.6084/m9.figshare.12791828.

M. Webber � G. Captur (&)UCL MRC Unit for Lifelong Health and Ageing,University College London, Fitzrovia, LondonWC1E 7HB, UKe-mail: gabriella.captur@ucl.ac.uk

M. Webber � G. CapturCardiology Department, Centre for Inherited HeartMuscle Conditions, The Royal Free Hospital, PondStreet, Hampstead, London NW3 2QG, UK

M. Webber � J. C. Moon � G. CapturUCL Institute of Cardiovascular Science, UniversityCollege London, Gower Street, London WC1E 6BT,UK

S. P. JacksonDepartment of Biochemistry, The Wellcome Trust/Cancer Research UK Gurdon Institute, University ofCambridge, Cambridge CB2 1QN, UK

J. C. MoonCardiovascular Magnetic Resonance Unit, BartsHeart Centre, West Smithfield, London, UK

Cardiol Ther (2020) 9:363–376

https://doi.org/10.1007/s40119-020-00199-y

Key Summary Points

Myocardial fibrosis is the shared finalcommon pathological pathway in thedevelopment of chronic heart failure andit predicts poor prognosis.

Myocardial fibrosis results from theaccumulation of collagen in theextracellular matrix, mediated by thecomplex interplay between pro-fibroticcells, growth factors and inflammatorycytokines.

Various proposed anti-fibrotic drugs havebeen tested but their direct beneficialeffects on human myocardial fibrosis areyet to be proven.

CMR techniques like native T1 mappingand extracellular volume have become thegold standard non-invasive imagingbiomarkers of myocardial fibrosis.

Newer technologies in CMR are paving theway for large-scale, multicentre,randomised trials to determine theefficacy of newer anti-fibrotic therapies.

INTRODUCTION

Disruption of the interstitial extracellularmatrix (ECM) has an important role in theadverse myocardial remodelling that leads tosystolic and/or diastolic dysfunction and theeventual development of chronic heart failure[1, 2]. Myocardial fibrosis is characterised by thedisproportionate accumulation of collagen inthe ECM and it can be focal (following an acuteischaemic event) or diffuse (in non-ischaemiccardiomyopathy) [3]. Its presence is an impor-tant prognostic marker in the development ofadverse cardiovascular events such as acuteheart failure, malignant arrhythmia and death.

There are three types of myocardial fibrosis:(1) replacement fibrosis induced by cardiomy-ocyte injury and death, as seen post myocardial

infarction; (2) reactive fibrosis which is thegradual and reversible diffuse distribution ofexcess collagen in the ECM like that observed innon-ischaemic cardiomyopathy (Fig. 1a),valvular heart disease and normal ageing [4]; (3)infiltrative fibrosis that is secondary to theaccumulation (in ECM or in myocytes) of non-collagenous materials such as amyloid (in car-diac amyloidosis), iron (in haemochromatosis)or glycosphingolipids (in Fabry disease, Fig. 1b)[5].

A number of mediators have emerged aspotential targets for anti-fibrotic therapies butmost studies to determine their benefit arebased on animal models with mixed resultsfrom human studies.

Our understanding of the mechanisms ofcardiac fibrosis has improved greatly in recentyears allowing us to refine non-invasive imag-ing techniques to better track its developmentand CMR is at the forefront of these innovations[6].

This review explains how myocardial fibrosisdevelops and how it can be non-invasivelydetected and measured using CMR imaging. Wesummarise findings from selected animal andhuman trials of some of the more promisingtargeted anti-fibrotic therapies and re-examinethe potential future role of CMR in such trials.This review is based on previously conductedstudies and does not contain any studies withhuman participants or animals performed byany of the authors.

PATHOPHYSIOLOGYOF MYOCARDIAL FIBROSIS

The pathophysiological mechanisms ofmyocardial fibrosis have been discussed else-where [1]. Broadly speaking, the fibroticresponse involves a complex interplay betweencirculating pro-fibrotic cell types, growth fac-tors, hormones and pro-inflammatory cytoki-nes, which is summarised in Fig. 2.Cardiomyocyte call death (apoptosis) can resultfrom either a primary cardiac insult (e.g.ischaemia) or in the context of systemic disease(e.g. hypertension or chronic kidney disease)[2]. Apoptosis can result in fibroblast

364 Cardiol Ther (2020) 9:363–376

proliferation through direct or indirect activa-tion. Direct activation is facilitated by cell sig-nalling proteins e.g. microRNAs (miRNAs) [7]and matrix metalloproteinases (MMPs) [8].Indirect activation is via circulating pro-fibroticmediators such as endothelial, epithelial andinflammatory cells. Cardiac fibroblasts are thecellular precursors of myofibroblasts which areformed through a process of differentiation thatis driven by multiple growth factors and pro-inflammatory cytokines, such as connective

tissue growth factor (CTGF) [9], tissue growthfactor-b (TGFb) and tumour necrosis factor-a(TNFa) [1]. Renin–angiotensin–aldosterone sys-tem (RAAS) activation is also thought to play animportant role [10] as well as newer mediatorssuch as galectin-3 (Gal-3) [11], endothelin [12]and interleukin-11 (IL-11) [13]. The final com-mon pathway of cardiac fibrosis is the deposi-tion of collagen (from myofibroblasts) in theECM and histologically it can be quantified asthe collagen volume fraction (CVF), which is

Fig. 1 The value of CMR tissue characterisation indistinguishing the underlying cause for LVH phenotypes.Panel a shows a patient with familial HCM caused by apathogenicMYBPC3 mutation. There is asymmetric septalhypertrophy and extensive diffuse and patchy LGE in thehypertrophied segments with corresponding high nativemyocardial T1 in these areas of fibrosis. Panel b shows amale patient with LVH secondary to myocardial glycosph-ingolipid accumulation in Fabry disease as a result of which

myocardial T1 times are low and there is the classic patchof subepicardial fibrosis in the inferolateral wall. b/m/aSAX basal/mid/apical short axis, 4/2C 4/2-chamber,HCM hypertrophic cardiomyopathy, LGE late gadoliniumenhancement, LVH left ventricular hypertrophy, MOCOmotion-corrected, MOLLI modified Look-Locker inver-sion recovery, MYBPC3 myosin-binding protein C3, PSIRphase-sensitive inversion recovery, ShMOLLI shortenedMOLLI, SSFP steady-state free precession

Cardiol Ther (2020) 9:363–376 365

the proportion of collagen in the myocardiumcompared to the volume of the myocardialinterstitium [14]. Our understanding of thesemechanisms has allowed us to develop poten-tial therapeutic options which target the variouscomponents of the pathway, from basic scienceto animal and translational human trials.

CMR BIOMARKERSOF MYOCARDIAL FIBROSIS

Native T1

T1 mapping in CMR [15] measures the T1

relaxation time of the myocardium. The nativeT1 time, before the administration of

gadolinium-based contrast agents (GBCA),lengthens because of the expansion of theinterstitial space arising from infarction,oedema, fibrosis or infiltration and shortenswith accumulation of fat or iron [15]. The lategadolinium enhancement (LGE) and extracel-lular volume (ECV) techniques also measurerelated readouts of the myocardial T1 but afterthe administration of GBCA.

Native T1 mapping can be used to detectareas of diffuse or focal myocardial fibrosiswithout the need for any GBCA administration,which can be particularly useful in patients inwhom the use of gadolinium is contraindicated.The native myocardial T1 time predicts chronicheart failure, arrhythmia and death [16] andlengthens in the presence of frank myocardial

Fig. 2 Schema representing the development of myocar-dial fibrosis and sites of action of potential therapeutictargets. RAAS renin–angiotensin–aldosterone system,TGFb tissue growth factor-b, TNFa tumour necrosis

factor-a, CTGF connective tissue growth factor, IL-11interleukin-11, miRNA microRNA, MMP matrix metal-loproteinases, Gal-3 galectin-3

366 Cardiol Ther (2020) 9:363–376

scarring (areas of LGE [10]). However, it can alsolengthen in the absence of (resolvable) LGE, forexample in dilated cardiomyopathy [17],hypertrophic cardiomyopathy (HCM) [18] orsevere aortic stenosis [19] indicating more dif-fuse myocardial fibrosis. The ability to detectthis so-called preclinical fibrosis (i.e. before vis-ible LGE appears) is attractive because it meansthat T1 can serve as a surrogate endpoint intrials of novel anti-fibrotic therapies includingthe effects on early phenotypes to preventchronic, irreversible heart failure.

Research into T1 mapping is ongoing withthe aim of improving accuracy and overcomingchallenges in acquisition and processing times[15]. For example, motion artefacts are beingaddressed with free-breathing and single breath-hold sequences, and with whole heart T1 map-ping techniques [20, 21]. Similar innovationsare also being used in patients with arrhythmia,particularly atrial fibrillation [22]. Dark-bloodT1 mapping has been developed to clean themyocardial signal from the partial volumeeffects of the blood pool at the blood–myocar-dial interface which enables parametric map-ping of thin-walled structures and improvesdata quality towards the apex [23, 24]. Post-processing innovations and computer recon-structions continue to improve the accuracy ofT1 measurements [25]. Dedicated T1 mappingphantoms have been developed by our group toaid in quality assurance (QA) and bring into linethe CMR data across multiple sites each oper-ating different software and mapping sequences[26]. Such QA infrastructure opens up the pos-sibility for collaborative multicentre trials inrare heart muscle diseases that are urgentlyneeded to upscale the currently limited studiesof anti-fibrotic therapies.

Late Gadolinium Enhancement

LGE corresponds to an area of focal scar (focalfibrosis) in the myocardium and its presence isassociated with poor long-term cardiovascularoutcomes, including sudden cardiac death [27].In previous studies myocardial biopsy of LGEareas in patients with dilated cardiomyopathy[28], myocarditis [29] and hypertrophic

cardiomyopathy [27] revealed both inflamma-tion and fibrosis. One caveat of relying on thesole LGE biomarker as a drug-trial surrogateendpoint is its inability to detect diffuse fibrosis,meaning that subtle improvements with ther-apy will be missed. Another caveat is that theevolution of new LGE foci, even in advanceddisease states, is an indolent process whichrequires a certain threshold of conglomeratedmyocardial cell death to be detectable usingmodern-day CMR technologies. It means thatstudy follow-up to detect significant serialchange in LGE mass would have to be exceed-ingly long (and costly).

Extracellular Volume

The redistribution of water and collagen intothe extracellular space that occurs withmyocardial fibrosis can be quantified by mea-suring the myocardial T1 time before and afterGBCA administration and adjusting for bloodhaematocrit, yielding the ECV [30]. ECV hasbeen shown to correlate with the amount ofcollagen deposition on myocardial biopsy inpatients with various forms of cardiomyopathy[31, 32]. ECV measurements are technicallylimited in that they are most accurate in themidwall and may therefore miss myocardialfibrosis in the subendocardial and subepicardiallayers [1]. ECV’s correlation with fibrosis isdependent on the absence of oedema or infil-tration [30] and can be overestimated in thepresence of capillary vasodilation [15]. Despitethese potential drawbacks, a high myocardialECV has been consistently demonstrated inpatients with heart muscle disease [19, 33] andshown to predict poor outcome [30], sometimesbetter than LGE [30]. Interestingly in HCM,myocardial ECV was also shown to be increasedin asymptomatic, mutation-positive relatives ofHCM probands [18] in whom there was nodetectable LGE. Similar to native T1 therefore,ECV is lucrative biomarker of ‘subclinical’fibrosis and another ideal therapeutic target foranti-fibrotic therapies.

Cardiol Ther (2020) 9:363–376 367

T2 Mapping

T2 mapping, though not directly measuringfibrosis, does provide insight into closely affili-ated biological processes, namely myocardialinflammation and oedema [34]. It does sowithout the disadvantages of conventional T2-weighted techniques [6]. Magnetic resonancefingerprinting is an emerging technique whichallows for simultaneous T1 and T2 pixelwisemaps to be acquired in the same breathhold[35]. This has the advantage of reducing scantime whilst improving the reproducibilitybecause it allows for precise spatial correlationof T1 and T2 mapping values per voxel, for amore complete understanding of the interac-tion between myocardial inflammation andfibrosis [36]. It could prove to be a powerful toolin future trials testing the usefulness of anti-fi-brotic therapies.

TARGETED ANTI-FIBROTICTHERAPIES

In this next part of the review we collate resultsfrom the most promising animal and humantrials of anti-fibrotic therapies to date andhighlight some of the opportunities but also thechallenges of future clinical roll-out to patientcare.

Connective Tissue Growth FactorAntagonists

CTGF is a matricellular protein which modu-lates the cell signalling pathways responsible formyofibroblast activation which underpins thepathogenesis of fibrosis [9]. CTGF antagonistsmay represent a novel strategy to limit andreverse cardiac fibrosis. In one study, mice withpressure overload-induced heart failure treatedwith CTGF monoclonal antibodies (FG-3019)showed a significant improvement in left ven-tricular function when compared to controls[37].

Galectin-3 Inhibitors

Gal-3 is a soluble beta-galactoside-binding lec-tin and has recently emerged as a promisingbiological target in heart failure as it mediatescardiac fibroblast proliferation resulting infibrosis [38]. Multiple studies have shown thatGal-3 is upregulated in hypertrophied hearts[39–41], interstitial pneumonitis [42] and in theplasma of patients with heart failure [11]. In onestudy it was found that left ventricular hyper-trophy was prevented in Gal-3 knockout miceand that left ventricular function was amelio-rated [43]. Gal-3 knockout in hypertensive miceexposed to aldosterone led to reduced vascularinflammation and hypertrophy compared tocontrols [40]. Thus Gal-3 may serve not only asan important clinical biomarker of heart failurebut also as a therapeutic target capable ofslowing the progression of cardiac fibrosis [11].

Anti-MicroRNAs

MiRNAs are members of a class of non-codingRNAs expressed by cardiac myocytes whichregulate signalling pathways in fibroblasts.Silencing miRNas in vivo has been shown toprevent interstitial fibrosis and inhibit cardiacfunction in pressure-overloaded mouse hearts[7]. In another animal model, silencing the longnoncoding RNA (IncRNA) maternally expressedgene 3 (Meg3) following aortic constrictionresulted in reduced myocyte fibrosis andimproved diastolic function [44]. Proteomicscomparison studies have also shown that ratcardiac fibroblasts transfected with anti-miRNA(pre-miR-29b) lost their ability to stick to myo-cytes. It is this modulatory effect on the ECMthat has made miRNAs a tractable target fortherapeutic intervention but further work isneeded to improve our understanding of theircomplex role in facilitating cardiac fibrosis [45].

Renin–Angiotensin–Aldosterone SystemInhibitors

RAAS inhibitors were amongst the first drugsused to target cardiac fibrosis and many studiesproved their benefit independent of their

368 Cardiol Ther (2020) 9:363–376

antihypertensive effects. In a study of 34patients with hypertension, endomyocardialbiopsies showed a reduction in left ventricularchamber stiffness and fibrosis in those patientstreated with losartan [46]. Another biopsy studyfound that lisinopril reduced CVF in car-diomyocytes when compared tohydrochlorothiazide [47]. Similar results wereobtained when comparing losartan withamlodipine in patients with end-stage renaldisease [10] and hypertension [48]. The anti-fi-brotic effect of RAAS inhibitors has been verifiedby CMR in a cohort of losartan-treated patientswith HCM where a significant reduction in LGEwas observed [49]. Mineralocorticoid receptorantagonists (MRAs) share a similar anti-fibroticeffect. Circulating levels of fibrosis biomarkersprocollagen type 1 carboxy-terminal propeptide(PICP) and procollagen-N-peptide (PINP) havebeen used to study the effects of MRAs on car-diac fibrosis in humans. Spironolactone reducedPICP and PINP levels in 80 patients with meta-bolic syndrome whilst improving left ventricu-lar diastolic function [50]. Similar data emergedfor eplerenone in patients with heart failurewith preserved ejection fraction [51] and dias-tolic dysfunction [52].

Nevertheless, in clinical practice patientswith heart failure on optimal medical therapythat includes RAAS inhibitors continue to havepoor outcomes attributable to cardiac fibrosis,suggesting that more work is needed to eluci-date their anti-fibrotic benefits independent ofany combined antihypertensive and haemody-namic effects.

Tissue Growth Factor-b Inhibitors

TGFb is a powerful profibrotic cytokine with anactive role in cardiac fibrosis. TGFb inhibitorshave been shown to reduce ECM protein syn-thesis and fibrosis in pressure-overloaded mousehearts but the downside was increased mortalityand inflammation [53] which has limited theirclinical translation.

Pirfenidone (PFD) is an anti-fibrotic drugwhich reduces the synthesis and release of TGFb[54], thus reducing collagen deposition in bothlungs and kidneys [55]. In one murine study it

was also found to slow the decline in left ven-tricular dysfunction, resulting in less ventriculararrhythmia [56]. Similar effects were reportedfor cardiac stiffness [57], left ventricular hyper-trophy [58] and cardiac fibrosis [59] in pressure-overloaded animal models. PFD can, however,cause gastrointestinal upset and liver dysfunc-tion which may hamper its widespread use as atargeted anti-fibrotic drug.

Tranilast (N-[3,4-dimethoxycinnamoyl]an-thranilic acid), previously used to treat keloidscars and dermopathies characterised by exces-sive fibrosis, has been shown to reduce collagendeposition and improve left ventricular systolicand diastolic function [60] in a diabetic ratmodel. Yet results from the Prevention ofRestenosis With Tranilast and Its Outcomes(PRESTO) trial were negative for tranilast as thedrug failed to improve quantitative measures ofrestenosis using intravascular ultrasound andangiography whilst causing a range of adverseeffects [61]. Other anti-TGFb drugs are on thehorizon and they include compound FT011which is showing promising results andimproved tolerability when compared to trani-last [62].

Endothelin Inhibitors

Endothelin is thought to play an important rolein the pathophysiology of fibrosis, so endothe-lin receptor blockade could potentially preventthe fibrosis of heart failure. Indeed in animalmodels, endothelin antagonists reduced cardiacfibrosis and left ventricular hypertrophy, andimproved survival [12, 63] whilst in 36 patientswith heart failure, bosentan improved left andright heart haemodynamics including vascularresistance when compared to placebo [64].However, a more recent trial using CMR tomeasure left ventricular end-diastolic volumesfound that administration of enrasentan resul-ted in adverse cardiac remodelling compared tocontrols [63]. Similar disappointing results werereported in a large double-blind, placebo-con-trolled trial of darusentan based on CMR end-points of remodelling in chronic heart failure[65]. Taken together these data suggest thatendothelin blockers may not be the ideal anti-

Cardiol Ther (2020) 9:363–376 369

fibrotic molecules but more work is needed todemonstrate this conclusively.

Matricellular Protein Antagonists

Non-structural MMPs are overexpressed follow-ing myocardial damage and contribute to thefunctioning of cardiac fibroblasts [66]. MMPknockout in animal models improved left ven-tricular end-diastolic pressure following aorticconstriction [8] and reduced collagen deposi-tion following myocardial infarction [67]. It hasalso been postulated that angiotensin convert-ing enzyme inhibitors (ACEi) exhibit directMMP antagonism [68, 69] which could be animportant indicator of the targeted effects ofACEi in fibrosis. Less promising results havebeen reported in humans where MMP inhibi-tion failed to resolve left ventricular remod-elling in an echocardiographic study [70].Similarly, MMP deletion in mice exacerbatedcardiac dysfunction following scar formation inmyocardial infarction which continues to raisethe question of the usefulness of MMP inhibi-tors in clinical practice [71].

Relaxin

Relaxin is a vasodilator hormone which reducesthe synthesis of collagen in the ECM through avariety of processes including the inhibition ofprofibrotic factors such as TGFb [72]. Innumerous animal studies it has been shown toreduce cardiac fibrosis in the setting of acutemyocardial infarction [73], diabetes [74] andhypertension [75]. It also reduced the incidenceof atrial fibrillation by reducing collagen depo-sition and reversing atrial fibrosis in rat hearts[76]. In another animal model, however,endogenous relaxin had no effect on cardiacfibrosis or hypertrophy following an 8-weekperiod of simulated pressure overload [77].Clinical trials have replicated these negativefindings with the Relaxin for the Treatment ofAcute Heart Failure (RELAX-AHF) internationaldouble-blind, placebo-controlled trial showingthat treatment with serelaxin did not affecthospital readmission rates in acute heart failure[78]. A phase II randomised trial using

recombinant human relaxin in patients withscleroderma also showed no improvement inpatient symptoms as reflected by skin thicknessscores [79]. This disparity of benefit betweenanimal and human trials highlights the need forfurther research into the use of relaxin in real-world cardiac settings, in particular chronicheart failure.

Loop Diuretics

The loop diuretic torsemide was superior tofurosemide in improving plasma brain natri-uretic peptide levels, left ventricular functionand mortality in heart failure [80]. A ran-domised study of patients with chronic heartfailure found reduced levels of PICP and colla-gen deposition in septal myocardial biopsies inthose receiving torsemide compared to fur-osemide [81]. These findings were echoed inanother study showing a reduction in markersof fibrosis and improved left ventricular stiff-ness [82, 83]. The large multicentre randomisedTorasemide Prolonged Release Versus Fur-osemide in Patients With Chronic Heart Failure(TORAFIC) trial, however, found no significantdifference between torsemide and furosemide interms of circulating PICP levels [84], althoughpatients recruited to this study had milder heartfailure compared to those from previous studies[80]. There have been no CMR trials to datedirectly testing the myocardial impacts of tor-semide in terms of fibrosis burden.

Anti-Inflammatory Drugs

Inflammation has a role to play in the devel-opment of myocardial fibrosis so drugs withdirect and indirect inflammatory modulatoryeffects have long been trialled for their use inthis setting. Rosuvastatin reduced myocardialfibrosis and had a positive effect on left ven-tricular remodelling in a hypertensive ratemodel [85] but the results of recent human trialshave been disappointing. The drug failed toimprove clinical outcomes in patients withheart failure in a large (n = 5011) placebo-con-trolled trial [86] and these findings were echoedin subsequent trials showing an overall neutral

370 Cardiol Ther (2020) 9:363–376

benefit [87, 88]. TNFa has also been studied as apotential fibrotic target in heart failure but trialshave been surprisingly negative. The targetedanticytokine drug etanercept failed to show anyclinical benefit in chronic heart failure in termsof mortality and hospital admissions [89]. Arandomised study using infliximab, a selectiveTNFa antagonist, failed to show any benefit andactually increased hospitalization in patientswith moderate to severe heart failure [90].Overall, inflammatory modulating drugs havenot yet been shown to have a promising effectas targeted anti-fibrotic medication in heartfailure. There have been some promising dataemerging from a study that used peroxisomeproliferator-activated receptor (PPAR) in hyper-tensive rats which showed a reduction infibrosis and diastolic dysfunction [91]. However,the widespread use of PPAR agonists in cardio-vascular disease continues to be limited by theirunfavourable safety profile [91].

Anti-Fibrotic Therapies on the Horizon

IL-11 is believed to play an important role in thepro-fibrotic pathway, downstream of TGFb. Ithas been shown to be positively correlated withcardiac fibroblast number and ECM depositionultimately leading to the development of car-diac dysfunction [92]. In mouse models, dele-tion of the IL-11 receptor was protective againstthe development of myocardial fibrosis andanti-IL-11 antibodies negated the effects ofTGFb stimulation on atrial myofibroblasts. Thispromising work is inspiring the development ofa new class of anti-fibrotic therapies without theside effects of TGFb inhibition discussed previ-ously [13].

ROLE OF CMR IN TRIALLING ANTI-FIBROTIC THERAPIES

The problem with determining the efficacy ofanti-fibrotic therapies lies in proving causalitybetween fibrosis regression and improved out-comes. The majority of the aforementionedtreatments effect multiple generic disease path-ways so conclusively proving their specific anti-

fibrotic benefits is difficult. ECV may be espe-cially helpful here: it has already been shown tobe strongly and independently associated withpoor outcomes in patients with systolic heartfailure and in those with heart failure and pre-served ejection fraction [93]; it is a well-estab-lished CMR technique available to most CMRunits globally; and it is non-invasive and quick,making serial assessment affordable for drugcompanies, and tolerable for most patients.Importantly myocardial fibrosis burden as asses-sed by ECV has also been shown to have adose–response relationship with hospitalisationand death in heart failure independent of LGE[94], suggesting it is tracking additional biology.ECV may go some way to help establish thecausal link that is needed to energise anti-fibroticdrug trials. This biomarker is already beingexploited in randomised control trials as a sur-rogate endpoint [95, 96]. We call for morephase 2 and phase 3 drug trials to rely on theever-growingarmamentariumofCMR sequencesfor fibrosis, in an effort to improve the reliabilityand cost-effectiveness of studies, and maximisetheir translational impact.

CONCLUSIONS

Myocardial fibrosis is the final point of conver-gence for all heart muscle diseases, ushering inthe development of heart failure and death.Effective anti-fibrotic therapies are urgentlyneeded but clinical trials are proving expensiveand results frankly disappointing. CMR imagingbiomarkers, in particular ECV and native T1, arefascinating periscopes into the myocardialresponse to drug therapy yet they are under-utilised by pharma. These CMR techniques areso sensitive that they can detect subclinicalfibrosis, opening that all-important window ofearly drug intervention, before the irreversibledevastation caused by fibrosis takes hold.

ACKNOWLEDGEMENTS

Funding. No Rapid Service Fee was receivedby the journal for the publication of this article.

Cardiol Ther (2020) 9:363–376 371

Authorship. All named authors meet theInternational Committee of Medical JournalEditors (ICMJE) criteria for authorship for thisarticle, take responsibility for the integrity ofthe work as a whole, and have given theirapproval for this version to be published.

Disclosures. Matthew Webber and GabriellaCaptur are both supported by British HeartFoundation Special Programme Grant MyoFit46(SP/20/2/34841). Gabriella Captur and JamesCharles Moon are funded by the Heartome1000Barts Charity grant #1107/2356/MRC0140.Gabriella Captur is supported by the JosephineLansdell British Medical Association researchgrant. James Charles Moon is directly andindirectly supported by the UCL Hospitals NIHRBRC and Biomedical Research Unit at BartsHospital respectively. Stephen P Jackson has nodisclosures for this article.

Compliance with Ethics Guidelines. Thisarticle is based on previously conducted studiesand does not contain any studies with humanparticipants or animals performed by any of theauthors.

Data Availability. Data sharing is notapplicable to this article as no datasets weregenerated or analyzed during the current study.

Open Access. This article is licensed under aCreative Commons Attribution-NonCommer-cial 4.0 International License, which permitsany non-commercial use, sharing, adaptation,distribution and reproduction in any mediumor format, as long as you give appropriate creditto the original author(s) and the source, providea link to the Creative Commons licence, andindicate if changes were made. The images orother third party material in this article areincluded in the article’s Creative Commonslicence, unless indicated otherwise in a creditline to the material. If material is not includedin the article’s Creative Commons licence andyour intended use is not permitted by statutoryregulation or exceeds the permitted use, youwill need to obtain permission directly from thecopyright holder. To view a copy of this licence,

visit http://creativecommons.org/licenses/by-nc/4.0/.

REFERENCES

1. Gonzalez A, Schelbert EB, Dıez J, Butler J. Myocar-dial interstitial fibrosis in heart failure: biologicaland translational perspectives. J Am Coll Cardiol.2018;71:1696–706.

2. Fang L, Murphy AJ, Dart AM. A clinical perspectiveof anti-fibrotic therapies for cardiovascular disease.Front Pharmacol. 2017;8:186.

3. Aherne E, Chow K, Carr J. Cardiac T1 mapping:techniques and applications. J Magn Reson Imag-ing. 2020;51:1336–56.

4. Karamitsos TD, Arvanitaki A, Karvounis H, Neu-bauer S, Ferreira VM. Myocardial tissue characteri-zation and fibrosis by imaging. JACC CardiovascImaging. 2020;13:1221–344.

5. Mewton N, Liu CY, Croisille P, Bluemke D, LimaJAC. Assessment of myocardial fibrosis with car-diovascular magnetic resonance. J Am Coll Cardiol.2011;57:891–903.

6. Messroghli DR, et al. Clinical recommendations forcardiovascular magnetic resonance mapping of T1,T2, T2 and extracellular volume: a consensusstatement by the Society for Cardiovascular Mag-netic Resonance (SCMR) endorsed by the EuropeanAssociation for Cardiovascular Imaging (EACVI).J Cardiovasc Magn Reson. 2017;19:75.

7. Thum T, et al. MicroRNA-21 contributes tomyocardial disease by stimulating MAP kinase sig-nalling in fibroblasts. Nature. 2008;456:980–4.

8. Matsusaka H, et al. Targeted deletion of matrixmetalloproteinase 2 ameliorates myocardialremodeling in mice with chronic pressure overload.Hypertension. 2006;47:711–7.

9. Lipson KE, Wong C, Teng Y, Spong S. CTGF is acentral mediator of tissue remodeling and fibrosisand its inhibition can reverse the process of fibrosis.Fibrogenesis Tissue Repair. 2012;5:S24.

10. Shibasaki Y, et al. Impact of the angiotensin IIreceptor antagonist, losartan, on myocardial fibro-sis in patients with end-stage renal disease: assess-ment by ultrasonic integrated backscatter andbiochemical markers. Hypertens Res. 2005;28:787–95.

372 Cardiol Ther (2020) 9:363–376

11. de Boer RA, Voors AA, Muntendam P, van GilstWH, van Veldhuisen DJ. Galectin-3: a novel medi-ator of heart failure development and progression.Eur J Heart Fail. 2009;11:811–7.

12. Clozel M, Salloukh H. Role of endothelin in fibrosisand anti-fibrotic potential of bosentan. Ann Med.2005;37:2–12.

13. Schafer S, et al. IL-11 is a crucial determinant ofcardiovascular fibrosis. Nature. 2017;552:110–5.

14. Hoyt RH, Ericksen E, Collins SM, Skorton DJ.Computer-assisted quantitation of myocardialfibrosis in histologic sections. Arch Pathol Lab Med.1984;108:280–3.

15. Radenkovic D, Weingartner S, Ricketts L, Moon JC,Captur G. T1 mapping in cardiac MRI. Heart FailRev. 2017;22:415–30.

16. Puntmann VO, et al. T1-mapping and outcome innonischemic cardiomyopathy all-cause mortalityand heart failure. JACC Cardiovasc Imaging.2016;9:40–50.

17. Dass S, et al. Myocardial tissue characterizationusing magnetic resonance noncontrast T1 mappingin hypertrophic and dilated cardiomyopathy. CircCardiovasc Imaging. 2012;5:726–33.

18. Ho CY, et al. T1 measurements identify extracellu-lar volume expansion in hypertrophic cardiomy-opathy sarcomere mutation carriers with andwithout left ventricular hypertrophy. Circ Cardio-vasc Imaging. 2013;6:415–22.

19. Mahmod M, et al. Adenosine stress native T1mapping in severe aortic stenosis: evidence for arole of the intravascular compartment on myocar-dial T1 values. J Cardiovasc Magn Reson. 2014;16:92.

20. Chow K, Yang Y, Shaw P, Kramer CM, Salerno M.Robust free-breathing SASHA T1 mapping withhigh-contrast image registration. J CardiovascMagn Reson. 2016;18:47.

21. Mehta BB, Chen X, Bilchick KC, Salerno M, EpsteinFH. Accelerated and navigator-gated look-lockerimaging for cardiac T1 estimation (ANGIE): devel-opment and application to T1 mapping of the rightventricle. Magn Reson Med. 2015;73:150–60.

22. Zhao L, et al. Systolic MOLLI T1 mapping withheart-rate-dependent pulse sequence samplingscheme is feasible in patients with atrial fibrillation.J Cardiovasc Magn Reson. 2016;18:13.

23. Weingartner S, Meßner NM, Zollner FG, AkcakayaM, Schad LR. Black-blood native T1 mapping: bloodsignal suppression for reduced partial voluming in

the myocardium. Magn Reson Med. 2017;78:484–93.

24. Ferreira VM, et al. Systolic ShMOLLI myocardial T1-mapping for improved robustness to partial-volumeeffects and applications in tachyarrhythmias. J Car-diovasc Magn Reson. 2015;17:77.

25. Kellman P, Hansen MS. T1-mapping in the heart:accuracy and precision. J Cardiovasc Magn Reson.2014;16:2.

26. Captur G, et al. A medical device-grade T1 and ECVphantom for global T1 mapping quality assurance -the T1 mapping and ECV standardization in car-diovascular magnetic resonance (T1MES) program.J Cardiovasc Magn Reson. 2016;18:1–20.

27. Weng Z, et al. Prognostic value of LGE-CMR inHCM: a meta-analysis. JACC Cardiovasc Imaging.2016;9:1392–402.

28. Assomull RG, et al. Cardiovascular magnetic reso-nance, fibrosis, and prognosis in dilated cardiomy-opathy. J Am Coll Cardiol. 2006;48:1977–85.

29. Mahrholdt H, et al. Cardiovascular magnetic reso-nance assessment of human myocarditis: a com-parison to histology and molecular pathology.Circulation. 2004;109:1250–8.

30. Schelbert EB, Sabbah HN, Butler J, Gheorghiade M.Employing extracellular volume cardiovascularmagnetic resonance measures of myocardial fibrosisto foster novel therapeutics. Circ Cardiovasc Imag-ing. 2017;10:e005619.

31. Ravenstein CDM, et al. Histological validation ofmeasurement of diffuse interstitial myocardialfibrosis by myocardial extravascular volume frac-tion from Modified Look-Locker imaging (MOLLI)T1 mapping at 3 T. J Cardiovasc Magn Reson.2015;17:48.

32. Kammerlander AA, et al. T1 mapping by CMRimaging from histological validation to clinicalimplication. JACC Cardiovasc Imaging. 2016;9:14–23.

33. Su MYM, et al. CMR-verified diffuse myocardialfibrosis is associated with diastolic dysfunction inHFpEF. JACC Cardiovasc Imaging. 2014;7:991–7.

34. Mavrogeni S, et al. T1 and T2 mapping in cardiol-ogy: ‘mapping the obscure object of desire’. Cardi-ology. 2017;138:207–17.

35. Liu Y, Hamilton J, Rajagopalan S, Seiberlich N.Cardiac magnetic resonance fingerprinting: tech-nical overview and initial results. JACC CardiovascImaging. 2018;11:1837–53.

Cardiol Ther (2020) 9:363–376 373

36. Kvernby S, et al. Simultaneous three-dimensionalmyocardial T1 and T2 mapping in one breath holdwith 3D-QALAS. J Cardiovasc Magn Reson.2014;16:102.

37. Szabo Z, et al. Connective tissue growth factorinhibition attenuates left ventricular remodelingand dysfunction in pressure overload-induced heartfailure. Hypertension. 2014;63:1235–40.

38. Li X, Tang X, Lu J, Yuan S. Therapeutic inhibition ofgalectin-3 improves cardiomyocyte apoptosis andsurvival during heart failure. Mol Med Rep.2018;17:4106–12.

39. Sharma UC, et al. Galectin-3 marks activated mac-rophages in failure-prone hypertrophied hearts andcontributes to cardiac dysfunction. Circulation.2004;110:3121–8.

40. Calvier L, et al. Galectin-3 mediates aldosterone-induced vascular fibrosis. Arterioscler Thromb VascBiol. 2013;33:67–75.

41. Suthahar N, et al. Galectin-3 activation and inhi-bition in heart failure and cardiovascular disease: anupdate. Theranostics. 2018;8:593–609.

42. MacKinnon AC, et al. Regulation of transforminggrowth factor-b1-driven lung fibrosis by galectin-3.Am J Respir Crit Care Med. 2012;185:537–46.

43. Yu L, et al. Genetic and pharmacological inhibitionof galectin-3 prevents cardiac remodeling by inter-fering with myocardial fibrogenesis. Circ Heart Fail.2013;6:107–17.

44. Piccoli MT, et al. Inhibition of the cardiac fibrob-last-enriched lncRNAMeg3 prevents cardiac fibrosisand diastolic dysfunction. Circ Res. 2017;121:575–83.

45. Abonnenc M, et al. Extracellular matrix secretionby cardiac fibroblasts: role of MicroRNA-29b andMicroRNA-30c. Circ Res. 2013;113:1138–47.

46. Dıez J, et al. Losartan-dependent regression ofmyocardial fibrosis is associated with reduction ofleft ventricular chamber stiffness in hypertensivepatients. Circulation. 2002;105:2512–7.

47. Brilla CG, Funck RC, Rupp H. Lisinopril-mediatedregression of myocardial fibrosis in patients withhypertensive heart disease. Circulation. 2000;102:1388–93.

48. Lopez B, et al. Usefulness of serum carboxy-termi-nal propeptide of procollagen type I in assessmentof the cardioreparative ability of antihypertensivetreatment in hypertensive patients. Circulation.2001;104:286–91.

49. Shimada YJ, et al. Effects of losartan on left ven-tricular hypertrophy and fibrosis in patients withnonobstructive hypertrophic cardiomyopathy.JACC Heart Fail. 2013;1:480–7.

50. Kosmala W, et al. A randomized study of the ben-eficial effects of aldosterone antagonism on lvfunction, structure, and fibrosis markers in meta-bolic syndrome. JACC Cardiovasc Imaging. 2011;4:1239–49.

51. Deswal A, Richardson P, Bozkurt B, Mann DL.Results of the randomized aldosterone antagonismin heart failure with preserved ejection fraction trial(RAAM-PEF). J Card Fail. 2011;17:634–42.

52. Mak GJ, et al. Natural history of markers of collagenturnover in patients with early diastolic dysfunc-tion and impact of eplerenone. J Am Coll Cardiol.2009;54:1674–82.

53. Engebretsen KVT, et al. Attenuated development ofcardiac fibrosis in left ventricular pressure overloadby SM16, an orally active inhibitor of ALK5. CurrTher Res Clin Exp. 2014;76:148–57.

54. Lopez-de la Mora DA, et al. Role and new insights ofpirfenidone in fibrotic diseases. Int J Med Sci.2015;12:840–7.

55. Edgley AJ, Krum H, Kelly DJ. Targeting fibrosis forthe treatment of heart failure: a role for trans-forming growth factor-b. Cardiovasc Ther. 2012;30:e30–e40.

56. Nguyen DT, Ding C, Wilson E, Marcus GM, OlginJE. Pirfenidone mitigates left ventricular fibrosisand dysfunction after myocardial infarction andreduces arrhythmias. Heart Rhythm. 2010;7:1438–45.

57. Mirkovic S, et al. Attenuation of cardiac fibrosis bypirfenidone and amiloride in DOCA-salt hyperten-sive rats. Br J Pharmacol. 2002;135:961–8.

58. Yamazaki T, et al. The antifibrotic agent pir-fenidone inhibits angiotensin II-induced cardiachypertrophy in mice. Hypertens Res. 2012;35:34–40.

59. Yamagami K, et al. Pirfenidone exhibits cardiopro-tective effects by regulating myocardial fibrosis andvascular permeability in pressure-overloaded hearts.Am J Physiol Heart Circ Physiol. 2015;309:H512–H522522.

60. Kelly DJ, et al. Tranilast attenuates diastolic dys-function and structural injury in experimentaldiabetic cardiomyopathy. Am J Physiol Heart CircPhysiol. 2007;293:H2860–H2869.

374 Cardiol Ther (2020) 9:363–376

61. Holmes DR, et al. Results of prevention ofREStenosis with tranilast and its outcomes (PRE-STO) trial. Circulation. 2002;106:1243–50.

62. Zammit SC, et al. Evaluation and optimization ofantifibrotic activity of cinnamoyl anthranilates.Bioorganic Med Chem Lett. 2009;19:7003–6.

63. Prasad SK, et al. Comparison of the dual receptorendothelin antagonist enrasentan with enalapril inasymptomatic left ventricular systolic dysfunction:a cardiovascular magnetic resonance study. Heart.2006;92:798–803.

64. Sutsch G, et al. Short-term oral endothelin-receptorantagonist therapy in conventionally treatedpatients with symptomatic severe chronic heartfailure. Circulation. 1998;98:2262–8.

65. Anand I, et al. Long-term effects of darusentan onleft-ventricular remodelling and clinical outcomesin the Endothelin A Receptor Antagonist Trial inHeart Failure (EARTH): randomised, double-blind,placebo-controlled trial. Lancet. 2004;364:347–54.

66. Heymans S, et al. Searching for new mechanisms ofmyocardial fibrosis with diagnostic and/or thera-peutic potential. Eur J Heart Fail. 2015;17:764–71.

67. Ducharme A, et al. Targeted deletion of matrixmetalloproteinase-9 attenuates left ventricularenlargement and collagen accumulation afterexperimental myocardial infarction. J Clin Investig.2000;106:55–62.

68. Yamamoto D, Takai S. Pharmacological implica-tions of MMP-9 inhibition by ACE inhibitors. CurrMed Chem. 2009;16:1349–54.

69. Yamamoto D, et al. Molecular mechanism of imi-dapril for cardiovascular protection via inhibitionof MMP-9. J Mol Cell Cardiol. 2007;43:670–6.

70. Hudson MP, et al. Effects of selective matrix met-alloproteinase inhibitor (PG-116800) to preventventricular remodeling after myocardial infarction.Results of the PREMIER (prevention of myocardialinfarction early remodeling) trial. J Am Coll Car-diol. 2006;48:15–20.

71. Ma Y, et al. Matrix metalloproteinase-28 deletionexacerbates cardiac dysfunction and rupture aftermyocardial infarction in mice by inhibiting M2macrophage activation. Circ Res. 2013;112:675–88.

72. Wang D, Zhu H, Yang Q, Sun Y. Effects of relaxin oncardiac fibrosis, apoptosis, and tachyarrhythmia inrats with myocardial infarction. Biomed Pharma-cother. 2016;84:348–55.

73. Samuel CS, et al. Relaxin remodels fibrotic healingfollowing myocardial infarction. Lab Investig.2011;91:675–90.

74. Samuel CS, Hewitson TD, Zhang Y, Kelly DJ.Relaxin ameliorates fibrosis in experimental dia-betic cardiomyopathy. Endocrinology. 2008;149:3286–93.

75. Lekgabe ED, et al. Relaxin reverses cardiac and renalfibrosis in spontaneously hypertensive rats. Hyper-tension. 2005;46:412–8.

76. Henry BL, et al. Relaxin suppresses atrial fibrillationin aged rats by reversing fibrosis and upregulatingNa? channels. Heart Rhythm. 2016;13:983–91.

77. Xu Q, et al. Endogenous relaxin does not affectchronic pressure overload-induced cardiac hyper-trophy and fibrosis. Endocrinology. 2008;149:476–82.

78. Teerlink JR, et al. Serelaxin, recombinant humanrelaxin-2, for treatment of acute heart failure(RELAX-AHF): a randomised placebo-controlledtrial. Lancet. 2013;381:29–39.

79. Khanna D, et al. Recombinant human relaxin in thetreatment of systemic sclerosis with diffuse cuta-neous involvement: a randomized, double-blind,placebo-controlled trial. Arthritis Rheum. 2009;60:1102–11.

80. Buggey J, et al. A reappraisal of loop diuretic choicein heart failure patients. Am Heart J. 2015;169:323–33.

81. Lopez B, et al. Effects of loop diuretics on myocar-dial fibrosis and collagen type I turnover in chronicheart failure. J Am Coll Cardiol. 2004;43:2028–35.

82. Lopez B, et al. Identification of a potential cardiacantifibrotic mechanism of torasemide in patientswith chronic heart failure. J Am Coll Cardiol.2007;50:859–67.

83. Lopez B, et al. Impact of treatment on myocardiallysyl oxidase expression and collagen cross-linkingin patients with heart failure. Hypertension.2009;53:236–42.

84. Dıez J, et al. TORAFIC study protocol: torasemideprolonged release versus furosemide in patientswith chronic heart failure. Expert Rev CardiovascTher. 2009;7:897–904.

85. Chang SA, et al. Effect of rosuvastatin on cardiacremodeling, function, and progression to heartfailure in hypertensive heart with established leftventricular hypertrophy. Hypertension. 2009;54:591–7.

Cardiol Ther (2020) 9:363–376 375

86. Kjekshus J, et al. Rosuvastatin in older patients withsystolic heart failure. N Engl J Med. 2007;357:2248–61.

87. GISSI-HF investigators. Effect of rosuvastatin inpatients with chronic heart failure (the GISSI-HFtrial): a randomised, double-blind, placebo-con-trolled trial. Lancet. 2008;372:1231–9.

88. Krum H, et al. Double-blind, randomized, placebo-controlled study of high-dose HMG CoA reductaseinhibitor therapy on ventricular remodeling, pro-inflammatory cytokines and neurohormonalparameters in patients with chronic systolic heartfailure. J Card Fail. 2007;13:1–7.

89. Mann DL, et al. Targeted anticytokine therapy inpatients with chronic heart failure: results of therandomized etanercept worldwide evaluation(RENEWAL). Circulation. 2004;109:1594–602.

90. Chung ES, Packer M, Lo KH, Fasanmade AA,Willerson JT. Randomized, double-blind, placebo-controlled, pilot trial of infliximab, a chimericmonoclonal antibody to tumor necrosis factor-a, inpatients with moderate-to-severe heart failure:results of the anti-TNF therapy against congestiveheart failure (ATTACH) trial. Circulation. 2003;107:3133–40.

91. Sarma S. Use of clinically available PPAR agonistsfor heart failure; do the risks outweigh the potentialbenefits? Curr Mol Pharmacol. 2012;5:255–63.

92. Corden B, Adami E, Sweeney M, Schafer S, Cook SA.IL-11 in cardiac and renal fibrosis: late to the partybut a central player. Br J Pharmacol. 2020;177:1695–708.

93. Schelbert EB, et al. Temporal relation betweenmyocardial fibrosis and heart failure with preservedejection fraction: association with baseline diseaseseverity and subsequent outcome. JAMA Cardiol.2017;2:995–1006.

94. Schelbert EB, et al. Myocardial fibrosis quantified byextracellular volume is associated with subsequenthospitalization for heart failure, death, or bothacross the spectrum of ejection fraction and heartfailure stage. J Am Heart Assoc. 2015;4:e002613.

95. Heydari B, et al. Effect of omega-3 acid ethyl esterson left ventricular remodeling after acute myocar-dial infarction. Circulation. 2016;134:378–91.

96. Lewis GA, et al. Pirfenidone in heart failure withpreserved ejection fraction—rationale and design ofthe PIROUETTE trial. Cardiovasc Drugs Ther.2019;33:461–70.

376 Cardiol Ther (2020) 9:363–376