Inflammation and Risk for Prematurity

Amy P. Murtha, MDDuke University Medical Center

Outline

• Preterm delivery• Inflammation in preterm delivery• Polymorphisms in inflammatory cytokines• Obstetrics and cytokine polymorphisms

Preterm Delivery

• 6-8% of all pregnancies deliver preterm• No improvement in preterm delivery rates

with current management strategies• Causes include

– Preterm premature rupture of membranes– Preterm labor– Maternal or fetal complications

• Rates of LBW continue to rise

Risk Factors for Preterm Delivery

• Previous obstetric history • Race/ethnicity• Vaginal bleeding• Multiple gestation• Incompetent cervix• Infection

Risk Factors for Preterm Delivery

• Marital Status• Substance use• Pre-Pregnancy Weight• Stress• Maternal Age• Congenital Anomalies

Racial Disparity for Preterm Birth and Infant Mortality

• LBW in singletons-– 11.4% in blacks – 5% in whites

• #1 contributor to disparity in infant mortality

Infant Mortality Rates by Maternal Race andEthnicity, 1997 U.S. Death Cohort

1368.5

868.5

604.6 595.4497.7

0

200

400

600

800

1000

1200

1400

1600

Black Am/Ind White Hispanic Asian/Pas

Race and Ethnicity of Mother

Deaths per 100,000 live

births

Preterm Birth and Family History

• Data from linked database of birth certificates of two generational cohorts

• Risk of PTD for preterm mothers was higher than those that had been born at term (OR 1.18)

• If preterm mother delivered <30 weeks OR increased to 2.38

Preterm Birth and Inflammatory Response

• Increased TNF production in whole blood stimulated by LPS in patients with history of PTB (Amory et al, Am J Obstet Gynecol, 2001)

Infection as a Noxious Stimuli

• BV is 2 times more prevalent among African Americans

• Higher prevalence not explained by known behaviors or risk factors

• High BV rates in African American women may account for up to 30% excess risk of PTD

The Effects of Stress

• Endocrine system (CRH production)• Immune system response• Maternal behaviors

– smoking – nutritional status– substance abuse

The Pathogeneses of Preterm Birth

• Decidual-chorioamniotic or systemic inflammation (40%)

• Activation of the maternal or fetal HPA (30%)

• Decidual hemorrhage (20%)• Pathologic overdistention (10%)

Lockwood and Kuczynski, Pediatric and Perinatal Epidemiology, 2001

Inflammatory Mediators and Preterm Birth

• Produced by choriodecidual tissues in response to infectious stimuli

• Elevated in maternal serum, amniotic fluid, cord blood, cervical/vaginal secretions in PTL and PPROM

• FIRS- elevated IL-6 by cordocentesisassociated with serious neonatal complication (Gomez, 1998)

Inflammatory Mediators and Intra-amniotic Infection

• Not always possible to document intra-amniotic infection

• Similar outcome in preterm patients with intra-amniotic inflammation and proven infection

Interleukin-6

• Elevated in maternal serum in chorioamnionitis (Greig, 1996)

• Elevated in fetal cord blood with funisitis (Swamy, 2002)

• Elevated in PPROM with FIRS• In amniotic fluid of PPROM, PTL

especially in presence of infection

Polymorphisms

• Common sequence variations that occur at a frequency greater than 1% – (Mutations occur <1%)

• Single nucleotide Polymorphism– occur every 500-1000 bases throughout the

genome– IL-6 gene polymorphism

Polymorphisms

• VNTR- common polymorphism that result form slippage during DNA replication– several copies of a repeated unit

• GAGAGAGAGA

• Depending on location may result in alterations in protein production– exon may alter the protein– promoter region alter amount produced

Cytokine Polymorphisms and Systemic Disease

• TNF: septic shock, RA, AIDs, MS, diabetes, lupus, graft versus host disease, cardiac and renal transplant rejection

• IL-6: JCA, cardiac disease, graft versus host disease and lupus

• IL-10: lupus, RA, asthma, cardiac and renal transplant rejection, graft versus host disease

Polymorphism and Transplantation

• Bronciolitis Obliterans in lung transplant patients with IL-6 -174G/C and IFN-gamma(+874) (Lu, Transplantation, 2002)

• Carriers of IL-6 -174C allele had inferior graft survival with RR of 3.7 for graft loss (Muller-Steinhardt, Kidney Int, 2002)

Cytokine Polymorphism and GVHD

• Acute GVHD independently associated with IL-10 gene polymorphisms– from the recipient (RR 7.9) and the donor (RR

3.5)

• Chronic GVHD independently associated with IL-6 gene polymorphism from recipient (RR 4.2, P=0.02)

(Socie, Transplantation, 2001)

Interleukin-6 Polymorphisms• -174G/C, -597G/A, -572G/C

– named for location in the gene in relation to start codon

• -174 located in the promoter region of IL-6 gene– Guanine replaced by cytosine

Interleukin-6 -174 G/C Polymorphism

• -174CC has been associated with elevated plasma levels in CABG patients (Brull, Arterioscler Thromb Vasc Biol, 2002)

• -174CC genotype is more responsive to statins (Basso, Arterioscler Thromb Vasc Biol, 2002)

• -174C allele associated with higher CRP, fibrinogen and IL-6 levels in CVD (Jenny, Arterioscler Throm Vasc Biol, 2002)

Interleukin-6 and CRP

• Vickers (Cardiovascular Research, 2002)

– 98 Caucasian families in the UK (4-7 members)– Log CRP was strongly associated with the C

allele (as a dominant gene)– CRP levels are highly heritable phenotype

associated with IL-6 -174G/C polymorphism

IL-6 -174G/C and Race

Race GG GC CCC Allele

FrequencyWhite 169 (40%) 188 (44%) 67 (16%) 38%

AfricanAmerican

182 (85%) 33 (15%) 0 (0%) 8%

(Jenny, Arterioscler Thromb Vasc Biol, 2002)

IL-6 -174G/C and Race

Race GG GC CCC AlleleFrequency

White 46 (41%) 40 (39%) 16 (16%) 55%

AfricanAmerican

35 (81%) 8 (19%) 0 (0%) 19%

(Cox, Transplantation, 2000)

Problems with Polymorphisms

• Many different polymorphisms– effect of polymorphism may be different

depending on the exposures• So many different candidate genes

Obstetrics and Cytokine Polymorphisms

• Little available data• Will need to consider both environmental

exposures as well as genetic predisposition

Tumor Necrosis Factor

• Case control study- 55 cases with 110 controls

• Cases included PTL and PPROM• TNF-308 more common in PPROM

compared to controls (OR 3.18, 95% CI 1.33-7.83)

(Roberts, Am J Obstet Gynecol, 1999)

Interleukin-1

• IL-1 +3953, IL-1RN • 52 pregnancies that resulted in PTD<34

weeks 197 controls– IL-1 +3953 was associated with PTD in African

American– IL-1RN associated with PTD in Hispanics

Genc, Am J Obstet Gynecol, 2002)

Interleukin-1 Receptor Antagonist

• Cohort study• 207 women in first trimester• 62% of the homozygote for allele 2

cultured positive for Ureaplasma– 47% of heterozygotes– 34% of homozygotes for the normal allele

• Vaginal concentrations of IL-1RA correlated with zygosity

(Barton, Infect Immun, 2003)

Obstetric evidence for link

• Ongoing study examining 500 preterm birth trios and 500 controls (Wang et al, Paediatr PerinatEpidemiol, 2001)

– candidate genes- IL-1, IL-6, TNF, CRH, MTHFR, and susceptibility to environmental toxins

• Polymorphism in metabolic genes altered association between smoking and birthwieght

Summary

Now What?

• Preterm delivery is a highly heterogeneous complex syndrome determined by both genetic and environmental factors