The Association Between COC Users With The Polymorphisms Of ACE/AGT Genes And The Risk Of Stroke

Combined oral contraceptives (COC) have been popular for theireffectiveness, convenience and reversibility since 1960s. There hashowever been increasing awareness of the risk of cardiovasculardiseases (stroke, myocardial infarction and venous thromboembolism).Recent research has shown that there was an association between COCexposure and stroke in women. The pathogenesis of stroke is extremelycomplicated, and is determined by a polygene and affected by multiplefactors in the environment. With the development of molecular geneticsand molecular epidemiology, it is possible to explore the correlation ofCOC exposures, angiotensiongen converting enzyme (ACE)gene,susceptibility to hypertension and stroke. Some studies of molecularepidemiology in recent years have been devoted to exploring theassociation and potential mechanism between hypertension and bothACE and angiotensiongen (AGT) gene-variation. However, the resultsof published reports derived from different, mostly small, subpopulations and regions were not consistent with each other, andthere were few observations about the joint effect between genes of ACEor AGT and the environment and the association between the genes andsusceptibility to hypertension. No studies to date are available on thejoint effect between hormonal contraceptives and ACE/AGT genes andthe joint effect between hormonal contraceptives and hypertension onthe risk of stroke. This study of population susceptibility tocardiovascular and cerebrovascular diseases associated with the use ofCOC and related genetic polymorphism provides scientific evidence forbuilding risk minimization strategies.To clarify the association between use of widely distributed low-doseCOC in China and the risk of stroke, we conducted a prospective cohortstudy and case-control study to evaluate the joint effects of COC andACE/AGT gene on the risk of stroke, and initially study a possiblemolecule mechanism of the risk of stroke increased by the combineCOC exposure with genetic predisposition in order to decrease adversereactions to COC.The prospective surveillance cohort study was undertaken in 25 towns intwo counties in Jiangsu Province, China. 44, 408 women on hormonalcontraceptives (HC) and 75, 230 women with an intrauterine device(IUD) were followed up from July 2004 to June 2000 to study thedifference in the incidence of stroke. The case-control study based onthe population of 25 towns in surveillance regions from July 1, 2000 toJune 30, 2004, the stroke index cases (157) were living and marriedwomen who were born after June 1932 and had stroke for the first time.Married hospitalized women with other diseases or neighborhood butcardiovascular diseases were selected as controls (267) at the sameperiod as cases with age no more or less than 3 years compared with the cases.ResultsPart 1 Prospective Cohort Study of the association between use oflow-dose oral contraceptives and stroke in Chinese women1. The incidence of haemorrhagic stroke (age-and-county standardizedrate) was far higher than that of ischaemic stroke (34.74 vs 11.25 per100, 000 person years) among HC cohort.2. The relative risk (RR) of incidence of haemorrhagic stroke in the HCcohort (52 cases) was 2.72 times compared with that in the IUD cohort(23 cases).3. Compared with IUD users, the current users of HC had a higher RRof 4.20 (95％CI: 2.11-8.36) of haemorrhagic stroke, and still reached2.17 (95％CI: 1.16-4.06) among past users after they stopped takingCOC for more than 10 years.4. The RR of haemorrhagic stroke was 3.09 (95％CI: 1.26-7.57) amongwomen who had last used low-dose COC during the previous five years.5. In women aged less than 45 years, compared to IUD users, thehaemorrhagic stroke was strongly associated with current use oflow-dose combined norethisterone pills, with RR being 19.06 (95％CI:3.08-118.03).Part 2 Case-control Study of joint effects of the COC use andACE/AGT gene on stroke1. The mean systolic blood pressure (MSBP 162.48±26.21mmHg) ofstroke group was significantly higher than that of control subjects by 33mmHg (P＜0.01), and the mean diastolic blood pressure (MDBP95.28±15.05mmHg) of stroke group was significantly higher than that ofcontrol subjects by 16 mmHg (P＜0.01). 2. Stratified analysis showed that women who had the history ofhypertension or used oral contraceptives more than 15 years had anincreased risk of stroke by 9.56 or 4.23, respectively.3. Joint effect of hypertension history and COCs exposure indicated a22.58-times elevated risk for stroke after adjustment for age and region(27.66 for hemorrhagic stroke and 17.04 for ischemic stroke).4. The analysis of the frequency of DD genotype of ACE I/Dpolymorphism between cases and controls indicated its significantassociation with stroke (P＜0.01), and suggested that the D allele maybe the potential risk allele of stroke.5. Women with COC exposure and ACE I/D genotype had an increasedrisk Of 5.38 for stroke (OR=6.38, 95％CI=1.82-22.41), and anincreased risk of 8.36 for hemorrhagic stroke(OR=9.36, 95％CI=1.44-60.91) by stratified analysis of COC use and no use; The increasedrisk of hemorrhagic stroke of joint effects of COC exposure withgene-gene combination exceeded that of COC exposure and singlegenotype; but this was not observed for ischemic stroke.6. Multivariate analyses showed that hypertension and COC exposurewere similarly significant risk factors for hemorrhagic stroke andischaemic stroke. Hyperlipemia was significant risk factor for ischaemicstroke and the joint effects of COC exposure with various genotypes ofthe related genes had critical effects on the risk of hemorrhagic stroke.The joint effects of COC exposure with ACE I/D polymorphism and AAgenotype of AGT A-20C polymorphism increased the risk of all strokeby more than 8 times, and increased the risk of hemorrhagic strokemore than 15 times.Conclusions1. There is certain association between increased risk of hemorrhagic stroke and use of the low-dose COC containing Norethisterone,appears to persist long after discontinuation, but effect may bereversible in prospective cohort study.2. It is clear that hypertension, COC use and hyperlipemia weresignificant risk factors for stroke, and that the joint effects of COCexposure and both ACE gene and the genotype of AGT genesignificantly increased the risk of all stroke, especially for hemorrhagicstroke in case-control study.Suggestions1. Based on our study findings, it is suggested that a post-marketingsurveillance system for contraceptive drugs and devices should beestablished. Improvement of blood pressure screening and follow upmonitoring among population of hormonal contraceptives, use of COCrestricted to less than 15 years seems the next logical step.2. Safety information should be incorporated into the training materialsfor grass roots family planning providers, so that they can provide amore informed choice of contraceptives and reproductive health serviceto reduce the incidence of ADRs among women taking contraceptives.3. More studies exploring the molecular mechanism of COC inducinghypertension and stroke should be undertaken, including setting ananimal model.