Jacob Selhub

Homocysteine and Arteriosclerosis Subclinical and Clinical Disease Associations

In 1969, the clinical observations of McCully1 first linked marked hyperhomocysteinemia (ie, equivalent to total homocysteine [tHcy] levels of 100 to 450 μmol/L by current assays) to precocious arteriosclerotic disease in autopsied children who died from distinct metabolic forms of homocystinuria. Intermittent reports of severe thrombotic outcomes specifically involving the extracranial carotid arteries in homocystinuric patients have been reported dating back at least 20 years.2 3 4 Excepting 2 small but notable studies,5 6 overall a rather consistent body of published data has emerged linking plasma tHcy levels to extracranial carotid artery wall thickening in young adults homozygous7 or heterozygous8 for cystathionine synthase deficiency, among young heterozygotes for familial hypercholesterolemia,9 and in general population samples of middle-aged, asymptomatic individuals free of clinical cardiovascular disease (CVD).10 11 12 13 In addition, tHcy levels have also been associated with more advanced extracranial carotid artery arteriosclerosis (ie, percentage of luminal stenosis) in elderly subjects14 15 16 17 and those with prevalent cerebrovascular disease.18 Thirty years after McCully’s initial report,1 a burgeoning amount of clinical evidence has accumulated that indicates that mild to moderate fasting, nonfasting, or post–methionine loading (PML) hyperhomocysteinemia (ie, tHcy levels ≥12 to ≤100 μmol/L fasting or nonfasting or ≥50 to ≤140 μmol/L 6 hours PML) is an independent risk factor for hard, arteriosclerotic outcomes. A recent series of pooled observational studies examining the relationship …

Renal Insufficiency, Vitamin B12 Status, and Population Attributable Risk for Mild Hyperhomocysteinemia Among Coronary Artery Disease Patients in the Era of Folic Acid–Fortified Cereal Grain Flour

Abstract—Fortification of enriched cereal grain flour products with folic acid has drastically reduced the prevalence of deficient plasma folate status, a major determinant of plasma total homocysteine (tHcy) levels. We hypothesized that even more liberally defined “suboptimal” plasma folate status might no longer contribute importantly to the population attributable risk (PAR) for mild hyperhomocysteinemia, a putative atherothrombotic risk factor. We determined fasting plasma tHcy, folate, vitamin B12, and pyridoxal 5′-phosphate levels, along with serum creatinine and albumin levels, in 267 consecutive patients (aged 61±9 [mean±SD] years, 76.4% men and 26.6% women) with stable coronary artery disease (CAD) who were nonusers of vitamin supplements or had abstained from supplement use for at least 6 weeks before examination. Subjects were evaluated a minimum of 3 months after the implementation of flour fortification was largely completed. Relative risk estimates for the calculation of PAR were derived from a multivariable-adjusted logistic regression model with ≥12 &mgr;mol/L tHcy as the dependent variable and with age, sex, pyridoxal 5′-phosphate (continuous), albumin (continuous), <5 ng/mL folate, <250 pg/mL vitamin B12, and ≥1.3 mg/dL creatinine as the independent variables. The prevalence of ≥12 &mgr;mol/L plasma tHcy was 11.2% (30 of 267 patients). PAR estimates (percentage) for ≥12 &mgr;mol/L tHcy were as follows: <5 ng/mL folate (<1%), <250 pg/mL vitamin B12 (24.5%), and ≥1.3 mg/dL creatinine (37.5%). In the era of folic acid–fortified cereal grain flour, renal insufficiency and suboptimal vitamin B12 status (but not folate status) contribute importantly to the PAR for mild hyperhomocysteinemia among patients with stable CAD.

Plasma Homocysteine and Parental Myocardial Infarction in Young Adults in Jerusalem

Background—A causal role for mildly elevated plasma homocysteine (tHcy) in cardiovascular disease remains undetermined. To address the unresolved issue of the antecedent-consequent directionality of the relationship, we assessed the familial association of tHcy with parental myocardial infarction (MI) in young Israeli men and women. We also compared tHcy concentrations in Jerusalem, where rates of coronary heart disease (CHD) are high, with the United States Third National Health and Examination Survey (NHANES III). Methods and Results—A total of 8646 17-year-olds and 6952 parents were examined from 1976 to 1979 in Jerusalem. At ages 28 to 32 years, offspring of parents who experienced a documented MI during a 10-year follow-up (n=133 men, 62 women; 72% response) and offspring of CHD-free parents (n=389 men, 208 women; 71% response) were reexamined. tHcy levels were determined by the same laboratory for the NHANES non-Hispanic white population aged 25 to 34 years (n=379) and the Jerusalem population sample (n=858). Men from Jerusalem, but not women, had clearly higher tHcy levels than the sample from the United States (90th percentile, 23 versus 14 &mgr;mol/L). This difference was largely attributable to lower plasma vitamin B12 levels in the Israeli population. Male case offspring had higher adjusted tHcy than did controls (1.9 &mgr;mol/L, P =0.002). Logistic modeling revealed a graded increase in risk of parental MI across quintiles of offspring tHcy, with an adjusted odds ratio of 2.7 in the 5th quintile (P =0.0026 for trend). Conclusions—The higher tHcy in young male offspring of parents with CHD suggests that elevated tHcy precedes manifestation of CHD. The elevated population tHcy in men may contribute to the high incidence of CHD in Israel.

Milk folate binding protein (FBP): A secretory protein for folate?

Abstract Analyses of human milk samples reveal that although folate binding protein (FBP) concentration varies considerably among individuals, a positive correlation with milk folate concentrations exists. The equation expressing this relationship is Y=29.2+0.78 X, where Y and X represent FBP and folate concentrations, respectively. Since folylpolglutamates comprise at least half of total milk folate and are known not to cross biological membranes, these data suggest that folate is likely to be secreted from the lactating cell as a complex with FBP. This complex could exit from the lactating cell by a route which is common to other milk proteins.

Affinity chromatography of naturally occurring folate derivatives

In a previous report (1980, in Methods in Enzymology, Vol. 66, p. 686, Academic Press, New York) we described the preparation and use of purified milk folate-binding protein covalently linked to a Sepharose matrix. The present study was undertaken to test the capacity of this preparation to purify quantitatively folates from tissue extracts. In experiments that employed tissue extracts containing biologically synthesized [3H]folates, recovery of radioactivity from columns of the immobilized folate-binding protein (affinity columns) was consistently 90-95%. Folates eluted from the affinity column were practically pure. Anion-exchange chromatography of the purified fraction from rat liver extract yielded a number of uv-absorbing peaks which corresponded to the elution profile based on 3H counts, with respect to both the position and the area of the peaks. Treatment of the original extracts with folylpolyglutamate hydrolases resulted in the shift of these peaks to lower retention times, which corresponded to mono- or diglutamyl folate derivatives. Similar results were obtained with extracts from Lactobacillus casei. The purification of tissue folates by affinity chromatography allows determination of folate activity by direct physiochemical methods, which is particularly useful for analysis of folate composition in tissues.

Cross-sectional relations of multiple biomarkers representing distinct biological pathways to plasma markers of collagen metabolism in the community.

Objective Hyperhomocysteinemia, neurohormonal activation, inflammation and altered fibrinolysis have been linked to atherothrombosis as well as to myocardial fibrosis and heart failure. Hence, we related a panel of biomarkers representing these pathways to plasma markers of collagen metabolism in a large community-based sample. Methods We related nine biomarkers representing select biologic pathways (independent variables: C-reactive protein, B-type natriuretic peptide, N-terminal proatrial natriuretic peptide, aldosterone, renin, fibrinogen, D-dimer, plasminogen activator inhibitor-1 and homocysteine) to three plasma markers of collagen turnover [dependent variables, separate models for each: aminoterminal propeptide of type III collagen, tissue inhibitor of metalloproteinases-1 and matrix metalloproteinase-9 (present versus absent)] in 921 Framingham Heart study participants (mean age 57 years; 58% women). Participants were separated a priori into those with left ventricular end-diastolic dimensions and wall thickness below sex-specific median values (referent group) and either measure at least 90th sex-specific percentile (‘remodeled’ group). We used stepwise multivariable regression analysis adjusting for cardiovascular risk factors to relate the panel of systemic biomarkers to the three biomarkers of collagen metabolism. Results Plasma homocysteine was positively related to all three markers of collagen metabolism in the remodeled group and to aminoterminal propeptide of type III collagen and tissue inhibitor of metalloproteinases-1 in the referent group. Plasminogen activator inhibitor-1 was positively related to aminoterminal propeptide of type III collagen and tissue inhibitor of metalloproteinases-1 in both groups, whereas the natriuretic peptides were associated positively with these collagen markers in the referent group. Conclusion In our large community-based sample, plasma homocysteine and plasminogen activator inhibitor-1 were positively related to circulating collagen biomarkers, consistent with experimental studies implicating these pathways in cardiovascular collagen turnover.

Blood Homocysteine Levels in the National Health and Nutrition Examination Survey (Nhanes III) in the United States: Preliminary Findings by Age and Sex

Evidence from scores of observational studies from many parts of the world have demonstrated an association between elevated blood total homocysteine levels and the risk of cardiovascular disease, peripheral vascular disease, and stroke [1,2]. These conditions are more prevalent in males than in females in virtually all populations studied, and their prevalence increases with advancing age. A much smaller body of data exists that describes an increasing tendency to higher homocysteine levels with increasing age.