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Objectives: Cystathionine-gamma-lyase (CSE) in the transsulfuration pathway generates hydrogen sulfide (H2S), suggested regulating cardiovascular function. The G1208T polymorphism in the CTH gene, rs1021737, has, in addition to MTHFR, been found to increase homocysteine, related to myocardial infarction (MI) risk. This study aimed, for the first time, to investigate the associations of the polymorphisms CTH G1208T, MTHFR C677T, and A1298C with the prospective risk of developing a fatal or non-fatal first MI.

Methods: This case-referent study included 545 cases later developing a first-ever MI and 1,054 referents from the Northern Sweden Health and Disease Study. Fatal MI was defined as death within 28 days after MI symptoms.

Results: Women, but not men, had a positive association between fatal MI and the CTH G1208T, odds ratio [95% confidence interval] 3.14 [1.16-8.54] for heterozygotes, and the dominant model 3.22 [1.22-8.51], and for the MTHFR A1298C heterozygotes 3.24 [1.26-8.34] and the dominant model 2.63 [1.06-6.50]. The MTHFR C677T polymorphism was not related to MI.

Conclusions: This study indicates that the minor alleles of CTH G1208T and MTHFR A1298C polymorphisms are associated with a higher risk for a fatal MI among women but not for non-fatal MI. No association was found in men.

Background: Globally, cardiovascular diseases (CVD), including myocardial infarction (MI) and stroke, are the leading cause of illness and death and constitute a significant part of the disease burden in Sweden and Western Europe. Age, hypertension, smoking, obesity, dyslipoproteinemia, diabetes, and impaired renal function are considered established risk factors for CVD. However, these factors do not explain all MI cases, and much is still unknown. Homocysteine is a sulfur-containing amino acid used in clinical practice as a biomarker of functional vitamin B12 and folate status. Earlier observational studies have shown associations with higher plasma homocysteine concentrations (tHcy) and CVD. The causal relationship between tHcy and MI has been debated as homocysteine-lowering prevention studies have not shown a protective effect on MI, although there may be a protective effect on ischemic stroke. Still, tHcy is a prognostic biomarker or risk determinant of MI. There is a need for more knowledge on the pathophysiologic mechanisms of how homocysteine interacts with its determinants, and other risk factors, on the risk of MI.

Aims: The overall aim of the thesis was to expand knowledge about how homocysteine, as a risk determinant, can have an impact on cardiovascular disease. Specifically, the purposes were to explore the associations between tHcy, determinants of homocysteine and risk factors of CVD, and the associated risk of prospectively developing a first-ever MI.

Material and methods: In papers I, III, and IV, a prospective incident nested case-referent study design was used with 545 cases of MI and 1054 matched referents. In paper II the design was cross-sectional, comparing strictly defined smokers and snus users. All study subjects emanated from the Northern Sweden Health and Disease Study (NSHDS). Blood samples stored frozen at -80ºC were later thawed, and analyses of biomarkers for renal function, lipids, B-vitamins, tHcy, cotinine, and genetic polymorphisms related to homocysteine metabolism were performed. 

Results: In a prospective setting, folate, but not tHcy, was positively associated with apolipoprotein A1 (Apo A1). The association was seen among referents and not among those later developing an MI. 

Among strictly defined smokers and snus users, cotinine was positively associated with tHcy among smokers but not among snus users, despite higher cotinine concentrations in snus users. No association was observed between tHcy and the number of cigarettes/day.

The CTH G1208T and MTHFR A1298C polymorphisms were, among women, associated with a higher risk of developing a first-ever MI with a fatal outcome. No such associations were seen among men or all MI patients. Further, no associations were seen between the MTHFR C677T polymorphism and the risk of having an MI, fatal or non-fatal. 

Mild impairment of renal glomerular function defined by eGFRcystatin C /eGFRcreatinine ratio and the associated risk of MI is previously not studied prospectively. In the present study, a lower eGFRcystatin C/eGFRcreatinine ratio was associated with a higher risk of later developing a first-ever MI among women, both when analyzed as a continuous variable and across the quartiles of the ratio. These associations did not appear among men.

Conclusions: The independent association of folate but not tHcy with Apo A1 emphasizes the need to adjust for possible confounding effects in studies on homocysteine and endpoints or biomarkers. The results suggest a possible link between one-carbon metabolism and lipid metabolism. 

The independent association between cotinine and tHcy in smokers and not among snus users indicate that nicotine per se may not mediate higher tHcy concentrations. Cotinine concentrations in plasma appeared as a better predictor of tHcy than self-reported smoking data. Thus, whenever possible, self-reported smoking should be supplemented by biomarkers, such as cotinine, in epidemiological studies. 

After outcome stratification, fatal or non-fatal MI, the associated higher risk among women of a fatal MI and CTH G1208T and MTHFR A1298C polymorphisms, respectively, may indicate that women with the minor alleles risk having a more serious MI leading to death than women with the wild-type alleles. 

In a prospective setting, the eGFRcystatin C/eGFR creatinine ratio was associated with an increased risk of later developing a first-ever MI among women. The eGFRcystatin C/eGFRcreatinine ratio may be a tool, easily implemented at clinical laboratories, for evaluating the risk of having a future first-ever MI.

Impaired renal function is associated both with the development of cardiovascular disease and its prognosis. A new syndrome called ' Shrunken Pore Syndrome ' has been suggested, as the estimated glomerular filtration rate for cystatin C (eGFR(cystatin C)) is affected earlier due to differences in molecular size compared to eGFR(creatinine). The aim was to investigate if a lower eGFR(cystatin C)/eGFR(creatinine) ratio in a prospective setting increases the risk of later developing a first-ever myocardial infarction (MI) independently of other cardiovascular risk factors. We used a nested case-referent study design within the Northern Sweden Health and Disease Study, and 545 subjects (29.0% women) were identified who prospectively developed a first-ever MI, and their 1054 matched referents. For women, but not for men, one standard deviation (SD) increase of ln z-scores of eGFR(cystatin C)/eGFR(creatinine) ratio was associated with a lower risk of a future MI: odds ratio [95% confidence interval] 0.58 [0.34-0.99], adjusted for apolipoprotein B/A1 ratio, CRP, homocysteine, systolic blood pressure, body mass index, and diabetes. Furthermore, a high eGFR(creatinine) associated independently with an increased risk of future MI in men only: OR 1.25 [1.05-1.48]. Thus, for women, a lower eGFR(cystatin C)/eGFR(creatinine) ratio is associated with a higher risk of having a future first-ever MI, and it may be a valuable, easily implemented biomarker for risk of cardiovascular disease.

Plasma total homocysteine (tHcy) is a risk marker, and smoking is an established risk factor for cardiovascular disease. It is unclear if the effect of smoked tobacco on homocysteine is mediated by nicotine or other combustion products in smoked tobacco. Snus (moist smokeless tobacco) is high nicotine-containing tobacco, and little is known about the effect of snus on plasma homocysteine. Therefore, we studied, in a cross-section of subjects (n = 1375) from the Northern Sweden Health and Disease Study, with strictly defined current smokers (n = 194) and snus users (n = 47), the impact of tobacco exposure on tHcy, assessed by self-reported tobacco habits and plasma cotinine concentrations. The snus users had higher cotinine concentrations than the smokers. Cotinine, creatinine, methylmalonic acid, and the methylenetetrahydrofolate reductase genotype (MTHFR) T allele were positively associated with tHcy among the smokers, but not among the snus users. No association was observed between tHcy and the number of cigarettes/day. There was a positive association between cotinine and tHcy in the smokers, but not among the snus users. This indicates that substances other than nicotine in tobacco smoke could be responsible for the differential effects on homocysteine status. Self-reported smoking should be complemented by a cotinine assay whenever possible.

Tobacco consumption is a renal risk factor, but the effects on the estimated glomerular filtration rate (eGFR) remain unclear. We aimed to evaluate the possible impact of using tobacco products (smoking and snus) on eGFR based on creatinine or cystatin C. We used a first cohort with 949 participants and a second cohort with 995 participants; none had pre-existing renal disease. All subjects donated a blood sample and completed a questionnaire, including questions about tobacco use. To assess the effect on eGFR, hierarchical multiple linear regression models were used. Active smoking associated independently with a higher eGFRcreatinine in all subjects (p < 0.001; β = 0.11). Further analyses stratified for sex, showed similar findings for men (p < 0.001; β = 0.14) and for women (p = 0.026; β = 0.10). eGFRcystatin C was significantly associated with active smoking in all subjects (p = 0.040; β = −0.05), but no association was seen after stratification for sex. Snus did not associate with eGFR. In conclusion, smoking associated significantly with a higher eGFRcreatinine. The mechanism may be renal hyperfiltration of smaller molecules such as creatinine. This is probably caused by substances from smoked tobacco other than nicotine, as no effect was seen for snus.

Background: Elevated total plasma homocysteine (tHcy) in humans is associated with cardiovascular disease but prevention trials have failed to confirm causality. Reported reasons for this association have been that homocysteine and its major genetic determinant methylenetetrahydrofolate reductase (MTHFR) may have an effect on HDL and Apolipoprotein (Apo) A1 levels. We wanted to study if tHcy and its major determinants were correlated with Apo A1 levels in a large population without folate fortification.

Methods: This study was a prospective incident nested case-referent study within the Northern Sweden Health and Disease Study Cohort (NSHDSC), including 545 cases with first myocardial infarction and 1054 matched referents, median age at inclusion was 59 years. Univariate and multiple regression analyzes was used to study the associations between apolipoproteins Apo A1 and B, tHcy, folate and vitamin B12 in plasma as well as MTHFR polymorphisms 677C>T and 1298A>C.

Results: Apo A1 and Apo B were strongly associated with the risk of a first myocardial infarction. tHcy was not associated with Apo A1 levels. Instead, folate had an independent positive association with Apo A1 levels in univariate and multiple regression models. The associations were seen in all men and women, among referents but not among cases. MTHFR polymorphisms had no clear effect on Apo A1 levels.

Conclusions: Analyzing over 1500 subjects we found an independent positive association between plasma folate (major dietary determinant of tHcy) and Apo A1 levels among those who later did not develop a first myocardial infarction. No association was seen between tHcy and Apo A1.