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Abnormalities in homocysteine metabolism have been suggested as risk factors for stroke and myocardial infarction. In retrospective studies, elevated levels of total plasma homocysteine (tHcy) and/or methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism have indicated an increase in risk. However, the fewer prospective studies have not been as conclusive. To further explore this, tHcy was studied in four prospective settings.

The first was a prospective nested case-referent cohort within the Västerbotten Intervention Program (VIP) and WHO MONICA project on 312 ischemic and 60 haemorrhagic first-ever strokes. The aim was to study tHcy and its main genetic determinant MTHFR. Risk for haemorrhagic stroke increased exponentially through tHcy quartiles, independent of hypertension and BMI, and increased for MTHFR 677 CT and TT. MTHFR 1298A>C appeared to be protective. In multivariate models, after adjustment for tHcy, BMI and hypertension, both tHcy and MTHFR remained as independent predictors for hemorrhagic stroke. Neither tHcy, nor the two MTHFR polymorphisms were significant predictors for ischemic strokes.

The second was a prospective long-term follow-up study within the VIP and MONICA cohorts to determine whether a first-ever myocardial infarction (AMI) causes increased levels of tHcy. Fifty cases developing AMI after the first screening participated in a second screening (mean follow-up 8.5 years) with 56 matched referents. Increase in tHcy did not differ between cases and referents. tHcy was related to AMI at follow-up, but not at baseline and no longer significant after adjusting for creatinine and albumin.

The third was a method study to determine if cystatin C, creatinine, albumin and other lipoprotein risk markers of cardiovascular disease could be analysed in Stabilyte™ plasma stored at -80°C. It was found to be suitable for all analyses tested and using this tube would simplify sampling for epidemiological studies.

The fourth study was a prospective longitudinal long-term study of 735 subjects (340 men and 395 women, age 25-64 at first screening), participating in two MONICA screenings nine years apart, who donated blood in Stabilyte™ tubes to study change over time in tHcy and its determinants. We confirmed the age dependency in a cross sectional setting. In contrast, if followed longitudinally over time, no change in tHcy or in the prevalence of hyperhomocysteinemia was found. Cystatin C and creatinine increased, and albumin decreased. In multivariate models baseline levels of albumin, creatinine, cystatin C, and to some extent hs-CRP, were predictors of tHcy at follow-up but gender differences were seen. Age was not a major determinant of change in tHcy over nine years.

In conclusion, tHcy and MTHFR are risk factors for first-ever haemorrhagic, but not ischemic stroke in a prospective setting. A first myocardial infarction does not cause an increase in tHcy. No long-term changes were seen in tHcy over a nine-year period in neither men, nor in women.

The development of a first myocardial infarction is associated with a large number of contributing factors. Age, male sex, hypertension, smoking, diabetes, body mass index and hypercholesterolemia are considered as established risk factors.

The primary aim of the present dissertation was to evaluate whether specific biomarkers could improve the prediction of subjects at risk for a first myocardial infarction when considered in addition to established cardiovascular risk factors. The biomarkers investigated include: tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1), thrombomodulin (TM), von Willebrand factor (VWF), dehydroepiandrosterone sulfate (DHEAS), lipoprotein (a) (Lp(a)), leptin, apolipoproptein A1 (ApoA1), proinsulin, homocysteine and homozygosity for the 5,10- methylenetetrahydrofolate reductase (MTHFR) C>T genotype. A secondary objective was to determine whether a first myocardial infarction leads to increased plasma homocysteine concentrations and whether the association between homocysteine and myocardial infarction was greater at follow-up compared to baseline.

The study population consisted of 36 405 subjects screened and included in the Västerbotten Intervention Program and the Northern Sweden MONICA cohorts between January 1, 1985 and September 30, 1994. A nested incident case-referent study design was used. Seventy eight cases with a first myocardial infarction were identified, and from the same cohort twice as many sex and age matched referents were randomly selected. Moreover, a follow-up health survey (average 8.5 years between surveys) was conducted with 50 cases and 56 matched referents.

High plasma levels of tPA and PAI-1 mass concentration, VWF, proinsulin, leptin and Lp(a) and low plasma levels of ApoA1 were associated with subsequent development of a first myocardial infarction in univariate conditional logistic regression analysis. For PAI-1 and tPA, this relation was found in both men and women. For tPA, but not for PAI-1 and VWF, this association was independent of established risk factors. In women, high plasma concentrations of TM were associated with significant increases in risk of a first myocardial infarction. No predictive values of DHEAS, homocysteine or for the point mutation C677>T in the gene for MTHFR was found regarding the risk of a first myocardial infarction. The summarised importance of haemostatic and metabolic variables (proinsulin, lipids including Lp(a) and leptin) in predicting first myocardial infarction in men, as well as possible interactions among these variables, were studied. High tPA and Lp(a) and low ApoA1 remained significant risk markers in multivariate analysis independent of established risk factors. There were non-significant synergic interactions between high Lp(a) and leptin and tPA respectively, and between high Lp(a) and low ApoA1.

In the follow-up study plasma homocysteine and plasma creatinine increased significantly, and plasma albumin decreased significantly over time. Conditional univariate logistic regression indicated that high homocysteine at follow-up but not at baseline was associated with first myocardial infarction but the relation disappeared in multivariate analyses including plasma creatinine and plasma albumin. High plasma creatinine remained associated with first myocardial infarction at both baseline and follow-up.

In conclusion, the present results support the hypothesis that biomarkers, in addition to the traditional cardiovascular risk factors, carry predictive information on the risk of developing a first myocardial infarction.