The Effects of Muscle Mass on Homocyst(e)ine Levels in Plasma and Urine.

The present study was designed to examine the relationship between homocyst(e)ine (H[e]) levels and muscle mass. Two experimental groups each of 24 Caucasian males, one consisting of higher-muscle mass subjects (HMM) and the other of lower-muscle mass subjects (LMM) participated in this study. Muscle mass was estimated from 24-hour urine collections of creatinine (Crt). Muscle mass was 40.3 ± 15.9 kg in HMM and 37.2 ± 11.4 kg in LMM (P= 0.002). Mean plasma H(e) levels in HMM were 10.29 ± 2.9 nmol/mL, and in LMM were 10.02 ± 2.4 nmol/L (Not significant, [NS]). Urinary H(e) levels (UH[e]) were 9.95 ± 4.3 nmol/mL and 9.22 ± 2.9 nmol/mL for HMM and LMM, respectively (NS). Plasma H(e) levels correlated well with UH(e) (HMM: r= 0.58, P= 0.009; LMM: r= 0.66, P= 0.004). Muscle mass and was not correlated to either plasma H(e) or UH(e). However, in HMM trends were identified for body mass to be correlated with UH(e) (r= 0.39, P= 0.10) and UCrt (r= 0.41, P= 0.08). Surprisingly, in HMM plasma and UCrt were only weakly correlated (r= 0.44, P= 0.06). Our results do not support a causal relationship between the amount of muscle mass and H(e) levels in plasma or urine.

Elevated soluble vascular cell adhesion molecule-1, elevated Homocyst(e)inemia, and hypertriglyceridemia in relation to preeclampsia risk.

BACKGROUND: We examined the relationship of maternal plasma concentrations of soluble vascular cell adhesion molecule-1 (sVCAM-1), a specific marker of endothelial dysfunction, and risk of preeclampsia. We also evaluated the relationship in the presence and absence of maternal hypertriglyceridemia and hyperhomocystein(e)mia. METHODS: A total of 170 women with preeclampsia and 184 control subjects were included in this case-control study analysis. Maternal postdiagnosis plasma sVCAM-1 concentrations were determined using immunoassays. Total plasma homocysteine (tHcy) was measured using high-performance liquid chromatography with electrochemical detection procedures; and triglyceride concentrations were determined using standard enzymatic procedures. Logistic regression procedures were used to estimate odds ratios (OR) and 95% confidence intervals (CI) adjusted for confounders. RESULTS: The relative risk of preeclampsia (as estimated by the OR) was increased 3.6-fold for women with sVCAM-1 concentrations >/=842 ng/mL compared with women who had lower concentrations (OR = 3.6; 95% CI 1.8 to 7.4). Of the three biological markers investigated, elevated sVCAM-1 concentrations was most strongly related to preeclampsia risk (OR = 4.6, 95% CI 1.6 to 13.5), followed by hyperhomocysten(e)mia (OR = 2.4, 95% CI 0.8 to 7.4) and hypertriglyceridemia (OR = 2.1, 95% CI 0.9 to 5.0). Compared with women who did not have any of the three risk factors, those with all three risk factors had an extremely high risk of preeclampsia (OR = 26.4; 95% CI 8.5 to 81.9). CONCLUSIONS: These findings suggest that elevated sVCAM-1 concentrations are associated with an increased risk of preeclampsia. Our findings extend the literature by documenting progressively increased risk with increasing numbers of biological markers of dyslipidemia and endothelial dysfunction.

Hyperhomocyst(e)inemia impairs angiogenesis in a murine model of limb ischemia.

Hyperhomocyst(e)inemia (HH) is an established independent risk factor for coronary, cerebral and peripheral vascular diseases. Recent studies have indicated that certain cardiovascular risk factors, including diabetes and hypercholesterolemia, impair expression of vascular endothelial growth factor (VEGF) and endogenous angiogenesis. In this study, we investigate the impact of moderate HH on angiogenesis and VEGF pathway in a mouse model of hindlimb ischemia. Upon induction of unilateral hindlimb ischemia, endogenous angiogenesis, expression of VEGF, and phosphorylation of the VEGF receptor Flk-1 were evaluated in mice heterozygous for a deletion of the cystathionine beta-synthase gene (CBS) and compared with those observed in CBS+/+ mice. CBS+/- mice exhibit moderate HH, as demonstrated by measuring plasma total homocyst(e)ine (tHcy) levels, which were significantly higher in these animals compared with CBS+/+ mice (4.77 +/- 0.82 vs 2.10 +/- 0.28, p < 0.01). Twenty-eight days after induction of ischemia, hindlimb blood flow was significantly reduced in CBS+/- mice compared with CBS+/+ animals (0.49 +/- 0.03, n = 12 vs 0.71 +/- 0.09, n = 10; p < 0.05). In addition, there was a significant negative correlation between plasma homocyst(e)ine levels and the laser Doppler perfusion ratio in CBS+/- mice (p = 0.0087, r = -0.7171). While VEGF expression and Flk-1 phosphorylation were not impaired in the ischemic muscles of CBS+/- mice, phosphorylation of the endothelial cell survival factor Akt was significantly inhibited by homocyst(e)ine in a dose-dependent manner in human umbilical vein endothelial cell (HUVECs) in vitro. In conclusion, our findings demonstrate that endogenous angiogenesis is inversely related to plasma levels of homocyst(e)ine in genetically engineered, heterozygous mice with moderate HH. This impairment, however, is not dependent on reduced expression of VEGF or impaired phosphorylation of its receptor Flk-1. In contrast, our data suggest that impaired Akt phosphorylation mediates the impairment of angiogenesis associated with HH.

Hyperhomocyst(e)inemia and elevated soluble vascular cell adhesion molecule-1 concentrations are associated with an increased risk of preeclampsia.

Hyperhomocyst(e)inemia (HHcy) is a risk factor of endothelial dysfunction and preeclampsia. Soluble vascular cell adhesion molecule-1 (sVCAM-1), a specific marker of endothelial dysfunction, is elevated in preeclampsia. Few have assessed the joint contribution of these biomarkers in predicting preeclampsia. We assessed the extent to which HHcy and elevated sVCAM-1 are independently and jointly associated with preeclampsia. We conducted a case-control analysis of 100 preeclampsia cases and 100 controls to test our study hypothesis. Maternal plasma was collected before labor onset. Total plasma homocysteine (tHcy) was measured using high-performance liquid chromatography with electrochemical detection procedures. Plasma sVCAM-1 was determined using ELISA. Using the distribution of each analyte among controls, elevated tHcy was defined as plasma tHcy >6.6 micromol/l and elevated sVCAM-1 was defined as plasma concentrations >845 ng/ml (i.e., values above the median). Odds ratios (OR) and 95% confidence intervals (CIs) were calculated. Compared with women without elevated tHcy and without elevated sVCAM-1 (the referent group), those with elevated sVCAM-1 alone had a 4.1-fold increased risk of preeclampsia (95% CI 1.2-13.8). The OR for women with elevated tHcy alone was 2.2 (95% CI 0.6-7.9). The OR for women with elevated tHcy and sVCAM-1 was 13.2 (95% CI 4.1-42.2). Elevated tHcy and sVCAM-1 together were strongly associated with an increased risk of preeclampsia. Larger, prospective studies are needed to confirm these findings and to determine the extent to which elevated tHcy and sVCAM-1 together in early pregnancy are predictive of preeclampsia risk.

Lowering homocysteine in patients with ischemic stroke to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for Stroke Prevention (VISP) randomized controlled trial.

CONTEXT: In observational studies, elevated plasma total homocysteine levels have been positively associated with ischemic stroke risk. However the utility of homocysteine-lowering therapy to reduce that risk has not been confirmed by randomized trials. OBJECTIVE: To determine whether high doses of folic acid, pyridoxine (vitamin B6), and cobalamin (vitamin B12), given to lower total homocysteine levels, reduce the risk of recurrent stroke over a 2-year period compared with low doses of these vitamins. DESIGN: Double-blind randomized controlled trial (September 1996-May 2003). SETTING AND PARTICIPANTS: 3680 adults with nondisabling cerebral infarction at 56 university-affiliated hospitals, community hospitals, private neurology practices, and Veterans Affairs medical centers across the United States, Canada, and Scotland. INTERVENTIONS: All participants received best medical and surgical care plus a daily multivitamin containing the US Food and Drug Administration's reference daily intakes of other vitamins; patients were randomly assigned to receive once-daily doses of the high-dose formulation (n = 1827), containing 25 mg of pyridoxine, 0.4 mg of cobalamin, and 2.5 mg of folic acid; or the low-dose formulation (n = 1853), containing 200 microg of pyridoxine, 6 microg of cobalamin and 20 microg of folic acid. MAIN OUTCOME MEASURES: Recurrent cerebral infarction (primary outcome); coronary heart disease (CHD) events and death (secondary outcomes). RESULTS: Mean reduction of total homocysteine was 2 micromol/L greater in the high-dose group than in the low-dose group, but there was no treatment effect on any end point. The unadjusted risk ratio for any stroke, CHD event, or death was 1.0 (95% confidence interval [CI], 0.8-1.1), with chances of an event within 2 years of 18.0% in the high-dose group and 18.6% in the low-dose group. The risk of ischemic stroke within 2 years was 9.2% for the high-dose and 8.8% for the low-dose groups (risk ratio, 1.0; 95% CI, 0.8-1.3) (P =.80 by log-rank test of the primary hypothesis of difference in ischemic stroke between treatment groups). There was a persistent and graded association between baseline total homocysteine level and outcomes. A 3- micromol/L lower total homocysteine level was associated with a 10% lower risk of stroke (P =.05), a 26% lower risk of CHD events (P<.001), and a 16% lower risk of death (P =.001) in the low-dose group and a nonsignificantly lower risk in the high-dose group by 2% for stroke, 7% for CHD events, and 7% for death. CONCLUSIONS: In this trial, moderate reduction of total homocysteine after nondisabling cerebral infarction had no effect on vascular outcomes during the 2 years of follow-up. However, the consistent findings of an association of total homocysteine with vascular risk suggests that further exploration of the hypothesis is warranted and longer trials in different populations with elevated total homocysteine may be necessary.

Plasma total homocysteine levels and cranial magnetic resonance imaging findings in elderly persons: the Cardiovascular Health Study.

BACKGROUND: An elevated plasma total homocysteine (tHcy) level is associated with an increased risk of vascular disease. Some studies have shown associations between tHcy level and small-vessel disease of the brain on magnetic resonance imaging (MRI). DESIGN: In the Cardiovascular Health Study, 622 elderly participants without a history of transient ischemic attack or stroke had results for tHcy level and cranial MRI. We sought associations between tHcy level and MRI findings of ventricular grade, sulcal grade, white matter grade, and infarcts. We controlled for other factors, including levels of creatinine, folate, and vitamins B(6) and B(12) and methylenetetrahydrofolate reductase genotype. RESULTS: After controlling for age and sex, tHcy level was not associated with the individual MRI findings. Further adjustments for other factors and other blood tests had little effect on these findings. The only significant finding was a linear trend across quintiles of tHcy level and a pattern of MRI findings combining infarcts and high white matter grade. The linear trend remained significant after controlling for other risk factors and atherosclerotic markers (top quintile vs bottom quintile odds ratio, 3.3; 95% confidence interval, 0.96-11.20; P =.04 for linear trend) but was slightly diminished after further controlling for creatinine, folate, and vitamins B(6) and B(12) (odds ratio, 3.2; 95% confidence interval, 0.81-13.10; P =.07 for linear trend). CONCLUSION: We were unable to confirm the results of previous studies with respect to tHcy level and individual MRI findings, although an association was seen for an MRI pattern combining infarcts and high white matter grade.

Endothelial dysfunction induced by hyperhomocyst(e)inemia: role of asymmetric dimethylarginine.

BACKGROUND: Endothelial function is impaired by hyperhomocyst(e)inemia. We have previously shown that homocyst(e)ine (Hcy) inhibits NO production by cultured endothelial cells by causing the accumulation of asymmetric dimethylarginine (ADMA). The present study was designed to determine if the same mechanism is operative in humans. METHODS AND RESULTS: We studied 9 patients with documented peripheral arterial disease (6 men; 3 women; age, 64+/-3 years), 9 age-matched individuals at risk for atherosclerosis (older adults; 9 men; age, 65+/-1 years), and 5 young control subjects (younger adults; 5 men; age, 31+/-1 years) without evidence of or risk factors for atherosclerosis. Endothelial function was measured by flow-mediated vasodilatation of the brachial artery before and 4 hours after a methionine-loading test (100 mg/kg body weight, administered orally). In addition, blood was drawn at both time points for measurements of Hcy and ADMA concentrations. Plasma Hcy increased after the methionine-loading test in each group (all, P<0.001). Plasma ADMA levels rose in all subjects, from 0.9+/-0.2 to 1.6+/-0.2 micromol/L in younger adults, from 1.5+/-0.2 to 3.0+/-0.4 micromol/L in older adults, and from 1.8+/-0.1 to 3.9+/-0.3 micromol/L in peripheral arterial disease patients (all, P<0.001). Flow-mediated vasodilatation was reduced from 13+/-2% to 10+/-1% in younger adults, from 6+/-1% to 5+/-1% in older adults, and from 7+/-1% to 3+/-1% in peripheral arterial disease patients (all, P<0.001). Furthermore, we found positive correlations between plasma Hcy and ADMA concentrations (P=0.03, r=0.450), as well as ADMA and flow-mediated vasodilatation (P=0.002, r=0.623). CONCLUSIONS: Our results suggest that experimental hyperhomocyst(e)inemia leads to accumulation of the endogenous NO synthase inhibitor ADMA, accompanied by varying degrees of endothelial dysfunction according to the preexisting state of cardiovascular health.

Effect of hyperhomocysteinemia on protein C activation and activity.

Hyperhomocysteinemia has been proposed to inhibit the protein C anticoagulant system through 2 mechanisms: decreased generation of activated protein C (APC) by thrombin, and resistance to APC caused by decreased inactivation of factor Va (FVa). We tested the hypotheses that generation of APC by thrombin is impaired in hyperhomocysteinemia in monkeys and that hyperhomocysteinemia produces resistance to APC in monkeys, mice, and humans. In a randomized crossover study, cynomolgus monkeys were fed either a control diet or a hyperhomocysteinemic diet for 4 weeks. Plasma total homocysteine (tHcy) was approximately 2-fold higher when monkeys were on the hyperhomocysteinemic diet than when they were on the control diet (9.8 +/- 2.0 microM versus 5.6 +/- 1.0 microM; P <.05). After infusion of human thrombin (25 microg/kg of body weight), the peak level of plasma APC was 136 +/- 16 U/mL in monkeys fed the control diet and 127 +/- 13 U/mL in monkeys fed the hyperhomocysteinemic diet (P >.05). The activated partial thromboplastin time was prolonged to a similar extent by infusion of thrombin in monkeys fed the control diet and in those fed the hyperhomocysteinemic diet. The sensitivity of plasma FV to human APC was identical in monkeys on control diet and those on hyperhomocysteinemic diet. We also did not detect resistance of plasma FV to APC in hyperhomocysteinemic mice deficient in cystathionine beta-synthase (plasma tHcy, 93 +/- 16 microM) or in human volunteers with acute hyperhomocysteinemia (plasma tHcy, 45 +/- 6 microM). Our findings indicate that activation of protein C by thrombin and inactivation of plasma FVa by APC are not impaired during moderate hyperhomocysteinemia in vivo.

Hyperhomocyst(e)inemia induces accelerated transplant vascular sclerosis in syngeneic and allogeneic rat cardiac transplants.

Chronic rejection (CR) and transplant vascular sclerosis (TVS) cause the majority of graft failures in cardiac transplantation. Hyperhomocyst(e)inemia [hH(e)] is associated with human TVS without a proven causal relationship. This study investigated the effect of hH(e) on graft survival and TVS in allogeneic and syngeneic rat cardiac transplants. Lewis recipients of heterotopic F344 heart allografts, received normal or hH(e)-inducing (folate, methionine) diets [controls: syngeneic transplanted [+/- hH(e), + CsA] and nontransplanted rats [+/- hH(e), +/- CsA]]. Serial plasma homocyst(e)ine [H(e)] levels were measured. TVS was assessed in clinically rejected grafts and a subset of pre-rejection normal diet allografts (day 64) (neointimal index, NI). The hH(e) diet elevated plasma H(e) levels. When compared with normal diet controls (n = 9), hH(e) diet allografts (n = 9) had decreased time to onset of CR (40 +/- 9 vs. 72 +/- 10d, p = 0.02), and graft failure (64 +/- 10 vs. 107 +/- 12d, p = 0.009). hH(e) diet allografts at rejection (n = 9, 64d) had more severe TVS (NI = 68 +/- 2) than both time-matched normal diet allografts (NI = 49 +/- 6, n = 8, 64d, p <0.001) and normal diet allografts at rejection (NI = 58 +/- 5, n = 9, 107d, p = 0.007). hH(e) induced TVS in syngeneic grafts (NI=50 +/- 3, n = 10 vs. NI = 5 +/- 3, n = 10, 130d, p <0.001). hH(e) accelerated rejection and increased the severity of TVS in allogeneic cardiac transplants, and induced TVS in syngeneic cardiac transplants.

Hyperhomocyst(e)inemia and hemostatic factors: the atherosclerosis risk in communities study.

PURPOSE: To determine whether homocyst(e)ine (H(e)) is related to hemostatic factors in a population-based sample without evidence of cardiovascular disease. METHODS: A subsample of 660 participants--67 African-American women, 53 African-American men, 201 white women, and 339 white men--was selected from the Atherosclerosis Risk in Communities Study baseline cohort. This was based on carotid intimal-medial wall thickness above the 90th percentile or below the 75th percentile of the population distribution, assessed by B-mode ultrasonography. Unadjusted and multivariable-adjusted associations between fasting plasma H(e) and the hemostatic factors fibrinogen, factor VII:c, factor VIII:c, protein C antigen, hematocrit, platelet count, beta-thromboglobulin (beta-TG), tissue plasminogen activator (tPA), PAI-1, D-dimer, and lipoprotein[a] were examined. RESULTS: Mean age-adjusted H(e) was positively, albeit weakly, correlated with beta-TG, tPA, hematocrit, D-dimer and PAI-1; inversely correlated with protein C; and was higher in smokers, men and African-Americans. In multivariable regression, beta-TG, tPA, and factor VII:c were positively associated with H(e), as well as age, black race, male sex, and current cigarette smoking. CONCLUSIONS: These cross-sectional data for a biracial group of middle-aged individuals suggest that H(e) levels falling below values consistent with homocyst(e)inemia are associated with several prothrombotic factors after adjustment for sociodemographic factors. If H(e) change is antecedent to altered hemostasis, FDA-mandated fortification of grain products with folic acid for prevention of fetal neural tube defects may lead to both reduced plasma H(e) levels and improved hemostatic profiles.

Changes in plasma homocyst(e)ine in the acute phase after stroke.

BACKGROUND AND PURPOSE: Elevated plasma homocyst(e)ine [H(e)] concentration has been associated with an increased risk of stroke. Although the literature suggests that H(e) increases from the acute to the convalescent phase after a stroke, it is not known whether H(e) changes within the acute period. METHODS: A prospective, multicenter study was conducted to examine changes in H(e) during the 2 weeks after an incident stroke. Blood samples were collected at days 1, 3, 5, 7, and between 10 and 14 days after the stroke. RESULTS: Seventy-six participants (51 men) were enrolled from 9 sites from February 1997 through June 1998. Mean age was 65.6 years, and subjects had at least two H(e) measurements. The estimated mean H(e) level at baseline was 11.3+/-0.5 micromol/L, which increased consistently to a mean of 12.0+/-0.05, 12.4+/-0.5, 13.3+/-0.5, and 13.7+/-0.7 micromol/L at days 3, 5, 7, and 10 to 14, respectively. The magnitude of the change in H(e) was not affected by age, sex, smoking status, alcohol use, history of hypertension or diabetes, or Rankin Scale Score. CONCLUSIONS: ; These data suggest that the clinical interpretation of H(e) after stroke and the eligibility for clinical trials assessing treatment for elevated H(e) levels require an adjustment in time since stroke to properly interpret the observed H(e) levels.

Neointimal hyperplasia in balloon-injured rat carotid arteries: the influence of hyperhomocysteinemia.

PURPOSE: Hyperhomocyst(e)inemia (hH[e]) is a risk factor for atherosclerosis. Neointimal hyperplasia (NH) after vessel injury can contribute to atherosclerosis. In this study, we investigated the effects of hH(e) on NH formation after arterial balloon injury in rats. METHODS: Lewis rats that were given a hH(e)-inducing (high methionine, low folate) or normal diet for 150 days underwent common carotid artery (CCA) balloon injury. Two and 4 weeks after injury, CCAs were formalin perfusion-fixed, sectioned, and stained for elastin. Neointimal index (NI, percent lumen occlusion) and neointima (N) and media (M) area were measured by using computer-interfaced microscopy. RESULTS: Plasma homocyst(e)ine (H[e]) levels were elevated in rats given the study diet compared with rats given the normal diet at days 40 and 90 (69 +/- 8 and 73 +/- 9 micromol/L vs 4 +/- 0.4 and 4 +/- 0.6 micromol/L, P <.001). After balloon injury, the CCA NI and N/M ratio, but not the M area, were increased by hH(e) compared with normal plasma H(e) (2 weeks [n = 6,7]: NI = 7.3 +/- 1.7 vs 2.9 +/- 0.7, P =.002, and N/M = 0.31 +/- 0.08 vs 0.08 +/- 0.02, P <.001; 4 weeks [n = 4,7]: NI = 13.1 +/- 2.2 vs 6.3 +/- 1.3, P =.002, and N/M = 0.36 +/- 0.08 vs 0.17 +/- 0.03, P <.001). CONCLUSION: hH(e) accelerates NH in a rat CCA balloon-injury model. The effect of hH(e) on NH may contribute to increased atherosclerosis in humans with hH(e).