Processing of alkylcobalamins in mammalian cells: A role for the MMACHC (cblC) gene product

The MMACHC gene product of the cblC complementation group, referred to as the cblC protein, catalyzes the in vitro and in vivo decyanation of cyanocobalamin (vitamin B(12)). We hypothesized that the cblC protein would also catalyze the dealkylation of newly internalized methylcobalamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl), the naturally occurring alkylcobalamins that are present in the diet. The hypothesis was tested in cultured endothelial cells using [(57)Co]-AdoCbl and MeCbl analogs consisting of [(57)Co]-labeled straight-chain alkylcobalamins ranging from C2 (ethylcobalamin) to C6 (hexylcobalamin). [(57)Co]-AdoCbl was converted to [(57)Co]-MeCbl by cultured bovine aortic endothelial cells, suggesting that a dealkylation process likely involving the cblC protein removed the 5'-deoxyadenosyl alkyl group. Surprisingly, all of the straight-chain alkylcobalamins served as substrates for the biosynthesis of both AdoCbl and MeCbl. Dealkylation was then assessed in normal skin fibroblasts and fibroblasts derived from three patients with mutations in the MMACHC gene. While normal skin fibroblasts readily converted [(57)Co]-propylcobalamin to [(57)Co]-AdoCbl and [(57)Co]-MeCbl, there was little or no conversion in cblC mutant fibroblasts. These studies suggest that the CblC protein is responsible for early processing of both CNCbl (decyanation) and alkylcobalamins (dealkylation) in mammalian cells.

Effects of low- or high-dose hormone therapy on fasting and post-methionine homocysteine levels in postmenopausal women

OBJECTIVE

To evaluate the effect of two different hormone therapy (HT) doses on fasting and post-methionine homocysteine levels, an independent risk factor for cardiovascular and thromboembolic diseases.

METHODS

Forty-eight women in natural postmenopause randomly received calcium 1 mg/day (control group; n = 12) or calcium plus low dose (1 mg estradiol plus 0.5 mg norethisterone; n = 18) or high dose (2 mg estradiol plus 1 mg norethisterone; n = 18) HT in a 6-month randomized, controlled, prospective study.

RESULTS

Folate levels did not vary in any group, while levels of vitamin B12 significantly decreased after low- (-12.2 +/- 6.6%; p < 0.04) or high-dose HT (-13.9 +/- 6.1%; p < 0.01). Fasting homocysteine was reduced by either HT dose in a way that was inversely related to pretreatment homocysteine levels (-0.675x; r = 0.644; p < 0.0001). Modification of post-load homocysteine increase was influenced by the HT dose and inversely related to the homocysteine response to methionine observed at baseline. The regression slope observed with the low-dose HT (-1.637x; r = 0.57; p < 0.02) was significantly steeper (p < 0.001) than that observed with the high-dose HT (-0.304x; r = 0.554; p < 0.03) dose.

CONCLUSIONS

Low- or high-dose HT similarly influences fasting homocysteine levels. Low-dose HT seems to be more effective than high-dose HT in reducing the post-methionine homocysteine increase.

Exogenous thioredoxin prevents ethanol-induced oxidative damage and apoptosis in mouse liver

Ethanol-induced liver injury is characterized by increased formation of reactive oxygen species (ROS) and inflammatory cytokines, resulting in the development of hepatic steatosis, injury, and cell death by necrosis and apoptosis. Thioredoxin (Trx), a potent antioxidant and antiinflammatory molecule with antiapoptotic properties, protects animals from a number of inflammatory diseases. However, the effects of ethanol on Trx or its role in ethanol-induced liver injury are not known. Female C57BL/6 mice were allowed ad libitum access to a Lieber-deCarli ethanol diet with 5.4% of calories as ethanol for 2 days to acclimate them to the diet, followed by 2 days with 32.4% of calories as ethanol or pair-fed control diet. Hepatic Trx-1 was decreased by ethanol feeding; daily supplementation with recombinant human Trx (rhTrx) prevented this ethanol-induced decrease. Therefore, we tested the hypothesis that administration of rhTrx during ethanol exposure would attenuate ethanol-induced oxidative stress, inflammatory cytokine production, and apoptosis. Mice were treated with a daily intraperitoneal injection of either 5 g/kg of rhTrx or phosphate-buffered saline (PBS).

CONCLUSION

Ethanol feeding increased accumulation of hepatic 4-hydroxynonenal protein adducts, expression of hepatic tumor necrosis factor alpha, and resulted in hepatic steatosis and increased plasma aspartate aminotransferase and alanine aminotransferase. In ethanol-fed mice, treatment with rhTrx reduced 4-hydroxynonenal adduct accumulation, inflammatory cytokine expression, decreased hepatic triglyceride, and improved liver enzyme profiles. Ethanol feeding also increased transferase-mediated dUTP-biotin nick-end labeling-positive cells, caspase-3 activity, and cytokeratin-18 staining in the liver. rhTrx treatment prevented these increases. In summary, rhTrx attenuated ethanol-induced increases in markers of oxidative stress, inflammatory cytokine expression, and apoptosis.

Accurate assessment and identification of naturally occurring cellular cobalamins

BACKGROUND

Accurate assessment of cobalamin profiles in human serum, cells, and tissues may have clinical diagnostic value. However, non-alkyl forms of cobalamin undergo beta-axial ligand exchange reactions during extraction, which leads to inaccurate profiles having little or no diagnostic value.

METHODS

Experiments were designed to: 1) assess beta-axial ligand exchange chemistry during the extraction and isolation of cobalamins from cultured bovine aortic endothelial cells, human foreskin fibroblasts, and human hepatoma HepG2 cells, and 2) to establish extraction conditions that would provide a more accurate assessment of endogenous forms containing both exchangeable and non-exchangeable beta-axial ligands.

RESULTS

The cobalamin profile of cells grown in the presence of [ 57Co]-cyanocobalamin as a source of vitamin B12 shows that the following derivatives are present: [ 57Co]-aquacobalamin, [ 57Co]-glutathionylcobalamin, [ 57Co]-sulfitocobalamin, [ 57Co]-cyanocobalamin, [ 57Co]-adenosylcobalamin, [ 57Co]-methylcobalamin, as well as other yet unidentified corrinoids. When the extraction is performed in the presence of excess cold aquacobalaminacting as a scavenger cobalamin (i.e. "cold trapping"), the recovery of both [ 57Co]-glutathionylcobalamin and [ 57Co]-sulfitocobalamin decreases to low but consistent levels. In contrasts, the [ 57Co]-nitrocobalamin observed in the extracts prepared without excess aquacobalamin is undetected in extracts prepared with cold trapping.

CONCLUSION

This demonstrates that beta-ligand exchange occur with non-covalently bound beta-ligands. The exception to this observation is cyanocobalamin with a non-exchangeable CN- group. It is now possible to obtain accurate profiles of cellular cobalamin.

Study on homocysteine levels and methylenetetrahydrofolate reductase gene variant (C677T) in a population of Buenos Aires City

The substitution of cytosine (C) by thymine (T) at nucleotide 677 of the methylenetetrahydrofolate reductase (MTHFR) gene, which converts an alanine to a valine residue, is a frequent polymorphism with reduced specific activity, associated with moderate increase in plasma homocysteine levels (tHcy) and risk of vascular diseases.

OBJECTIVES

This study was designed to investigate an association of this polymorphism with tHcy and vascular risk factors.

METHODS

We used a cross-sectional study on subjects affiliated to three health centers from Buenos Aires city. The diagnosis of hypertension was ascertained by patients' clinical history. Only subjects under long-term antihypertensive treatment were included.

RESULTS

Samples from 138 physically active individuals (44 men and 94 women) randomly selected were included. The mean tHcy was significantly higher amongst hypertensives (HT) than normotensives (NT). The risk of hypertension was compared in subjects with CC genotype and the combined number of subjects with at least one T allele (CT/TT). There was no significant difference regarding the risk of hypertension between NT and HT groups in the overall sample. However, as obesity is considered a risk factor for hypertension development, when only HT (n = 29) and NT (n = 66) subjects with body mass index below 30 kg/m(2) (BMI<30) were compared, subjects bearing CT/TT presented a significantly higher risk of hypertension than those bearing the CC genotype and significantly higher concentration of tHcy.

CONCLUSIONS

Our results indicate an association of hyper-tHcy and MTHFR C677T mutation with hypertension. MTHFR C677T mutation may contribute to hypertension or affect the development of hypertension through hyperhomocysteinemia.

Glutathione precursor, N-acetyl-cysteine, improves mismatch negativity in schizophrenia patients

In schizophrenia patients, glutathione dysregulation at the gene, protein and functional levels, leads to N-methyl-D-aspartate (NMDA) receptor hypofunction. These patients also exhibit deficits in auditory sensory processing that manifests as impaired mismatch negativity (MMN), which is an auditory evoked potential (AEP) component related to NMDA receptor function. N-acetyl-cysteine (NAC), a glutathione precursor, was administered to patients to determine whether increased levels of brain glutathione would improve MMN and by extension NMDA function. A randomized, double-blind, cross-over protocol was conducted, entailing the administration of NAC (2 g/day) for 60 days and then placebo for another 60 days (or vice versa). 128-channel AEPs were recorded during a frequency oddball discrimination task at protocol onset, at the point of cross-over, and at the end of the study. At the onset of the protocol, the MMN of patients was significantly impaired compared to sex- and age- matched healthy controls (p=0.003), without any evidence of concomitant P300 component deficits. Treatment with NAC significantly improved MMN generation compared with placebo (p=0.025) without any measurable effects on the P300 component. MMN improvement was observed in the absence of robust changes in assessments of clinical severity, though the latter was observed in a larger and more prolonged clinical study. This pattern suggests that MMN enhancement may precede changes to indices of clinical severity, highlighting the possible utility AEPs as a biomarker of treatment efficacy. The improvement of this functional marker may indicate an important pathway towards new therapeutic strategies that target glutathione dysregulation in schizophrenia.

Homocysteine in restless legs syndrome

BACKGROUND AND PURPOSE

Total plasma homocysteine (tHcy) may be a risk factor for vascular diseases and is associated with renal failure or deficiency of vitamin B12 or folate. Recently, elevated tHcy concentrations were observed in patients with Parkinson's disease (PD), particularly those under levodopa treatment. Our objective was to determine whether changes in tHcy are also found in patients with restless legs syndrome (RLS) in relation to levodopa treatment and whether folate and vitamins B6 and B12 play a role in RLS.

METHODS

In a total of 228 subjects, tHcy and B vitamin status (vitamins B6 and B12, folate) were studied: 97 patients with idiopathic RLS (40 under levodopa therapy), 39 with PD (25 under levodopa therapy), and 92 healthy controls adjusted for age and gender.

RESULTS

No significant differences were observed in tHcy levels between RLS patients and controls or between the RLS groups without treatment or with levodopa or dopamine agonist treatment. Mean tHcy was significantly higher in PD patients (13.8 micromol/l) than in either RLS patients (11.7 micromol/l) or controls (11.0 micromol/l; p<0.001). There was an inverse association between tHcy and vitamin B12 in each group.

CONCLUSIONS

RLS and, in particular, levodopa treatment in RLS are not associated with hyperhomocysteinemia. Elevated tHcy could, however, be confirmed in PD patients.

Elevated plasma homocysteine and low vitamin B-6 status in nonsupplementing older women with rheumatoid arthritis

OBJECTIVE

The purpose of this study was to determine if nonsupplementing older women (aged >or=55 years) with rheumatoid arthritis had higher plasma homocysteine and lower B-vitamin status compared to healthy controls. Elevated plasma homocysteine, a risk factor for cardiovascular disease, may help explain why individuals with rheumatoid arthritis have an increased risk of cardiovascular disease.

METHODS

Older, free-living women were classified as rheumatoid arthritis (n=18) or healthy control (n=33). Participants were not using B-vitamin supplements. Fasting blood samples were measured for pyridoxal 5'phosphate (PLP) (the metabolically active coenzyme form of vitamin B-6), folate, red blood cell folate, vitamin B-12, transcobalamin II, homocysteine, C-reactive protein, and lipid concentrations. Participants completed 7-day weighed food records, the Stanford Health Assessment Questionnaire (HAQ), and a visual analog pain scale.

RESULTS

PLP concentrations were lower in the rheumatoid arthritis vs healthy control participants (4.93+/-3.85 vs 11.35+/-7.11 ng/mL [20+/-16 vs 46+/-29 nmol/L]; P<0.01) whereas plasma homocysteine was higher in the rheumatoid arthritis group (1.63+/-0.74 vs 1.15+/-0.38 mg/L [12.1+/-5.5 vs 8.5+/-2.8 micromol/L]; P=0.02). Red blood cell folate concentrations were lower in the rheumatoid arthritis vs healthy control participants [414+/-141 vs 525+/-172 ng/mL [938+/-320 vs 1,190+/-390 nmol/L]; P=0.02). No significant differences were found for plasma folate, vitamin B-12, and transcobalamin II. An inverse correlation was found between PLP concentrations and the HAQ disability index (r=-0.37; P<0.01). A positive correlation was found between homocysteine concentrations and the HAQ disability index (r=0.36; P=0.01). Total cholesterol and low-density lipoprotein cholesterol levels were lower in the rheumatoid arthritis group (cholesterol 191+/-43 vs 218+/-33 mg/dL [4.95+/-1.11 vs 5.65+/-0.85 mmol/L]; P=0.02; low-density lipoprotein cholesterol 110+/-36 vs 137+/-29 mg/dL [2.85+/-0.93 vs 3.55+/-0.75 mmol/L]; P<0.01). No significant differences were seen between groups for protein (g/day), fat (g/day), cholesterol (mg/day), folate (microg/day), vitamin B-12 (microg/day), and vitamin B-6 (mg/day) dietary intakes.

CONCLUSIONS

Poor vitamin B-6 status and elevated plasma homocysteine concentrations were seen in older women with rheumatoid arthritis compared to healthy controls and may contribute to their increased risk of cardiovascular disease.

Homocysteine upregulates resistin production from adipocytes in vivo and in vitro

OBJECTIVE

Homocysteine (Hcy) is epidemiologically related to insulin resistance, which has been speculated to be a low-grade systemic inflammatory condition. Resistin acts as a critical mediator of insulin resistance associated with inflammatory conditions. We aimed to determine whether Hcy can induce insulin resistance by directly regulating the expression and secretion of resistin from adipose tissue.

RESEARCH DESIGN AND METHODS

The effect of Hcy on the expression and secretion of resistin and insulin resistance was investigated using primary rat adipocytes and mice with hyperhomocysteinemia (HHcy).

RESULTS

Hcy impaired glucose transport and, particularly, the insulin signaling pathway as shown by decreased insulin-stimulated tyrosine phosphorylation of insulin receptor and insulin receptor substrate (IRS)-1, increased serine phosphorylation of IRS-1, and inhibited Akt phosphorylation both in vitro and in vivo, and these impairments were accompanied by an increase in resistin expression. Compared with normal mice, HHcy mice with a clinically relevant level of plasma Hcy (19 micromol/l) showed significantly increased resistin production from adipose tissue (33.38 +/- 3.08 vs. 19.27 +/- 1.71 ng/ml, P < 0.01). Hcy (300-1000 micromol/l) also increased mRNA expression of resistin in primary rat adipocytes in a time- and concentration-dependent manner, with maximal induction at 24 h of approximately fourfold with 1,000 micromol/l. In addition, Hcy-induced resistin expression attenuated by treatment with reactive oxygen species (ROS) scavengers, protein kinase C (PKC), and nuclear factor (NF)-kappaB inhibitors implies a role in the process for ROS, PKC, and NF-kappaB.

CONCLUSIONS

HHcy may promote insulin resistance through the induction of resistin expression and secretion from adipocytes via the activation of the ROS-PKC-NF-kappaB pathway.

Hyperhomocysteinemia induced by methionine supplementation does not independently cause atherosclerosis in C57BL/6J mice

A causal relationship between diet-induced hyperhomocysteinemia (HHcy) and accelerated atherosclerosis has been established in apolipoprotein E-deficient (apoE(-/-)) mice. However, it is not known whether the proatherogenic effect of HHcy in apoE(-/-) mice is independent of hyperlipidemia and/or deficiency of apoE. In this study, a comprehensive dietary approach using C57BL/6J mice was used to investigate whether HHcy is an independent risk factor for accelerated atherosclerosis or dependent on additional dietary factors that increase plasma lipids and/or inflammation. C57BL/6J mice at 4 wk of age were divided into 6 dietary groups: chow diet (C), chow diet + methionine (C+M), western-type diet (W), western-type diet + methionine (W+M), atherogenic diet (A), or atherogenic diet + methionine (A+M). After 2, 10, 20, or 40 wk on the diets, mice were sacrificed, and the levels of total plasma homocysteine, cysteine, and glutathione, as well as total plasma cholesterol and triglycerides were analyzed. Aortic root sections were examined for atherosclerotic lesions. HHcy was induced in all groups supplemented with methionine, compared to diet-matched control groups. Plasma total cholesterol was significantly increased in mice fed the W or A diet. However, the W diet increased LDL/IDL and HDL levels, while the A diet significantly elevated plasma VLDL and LDL/IDL levels without increasing HDL. No differences in plasma total cholesterol levels or lipid profiles were observed between methionine-supplemented groups and the diet-matched control groups. Early atherosclerotic lesions containing macrophage foam cells were only observed in mice fed the A or A + M diet. Furthermore, lesion size was significantly larger in the A + M group compared to the A group at 10 and 20 wk; however, mature lesions were never observed even after 40 wk on these diets. The presence of lymphocytes, increased hyaluronan staining, and the expression of endoplasmic reticulum (ER) stress markers were also increased in atherosclerotic lesions from the A + M group. Taken together, these results suggest that HHcy does not independently cause atherosclerosis in C57BL/6J mice even in the presence of increased total plasma lipids induced by the W diet. However, HHcy can accelerate atherosclerotic lesion development under dietary conditions that increase plasma VLDL levels and/or inflammation.

Mesna for treatment of hyperhomocysteinemia in hemodialysis patients: a placebo-controlled, double-blind, randomized trial

BACKGROUND AND OBJECTIVES

Increased plasma total homocysteine is a graded, independent risk factor for the development of atherosclerosis and thrombosis. More than 90% of patients with end-stage renal disease have hyperhomocysteinemia despite vitamin supplementation. It was shown in previous studies that a single intravenous dose of mesna 5 mg/kg caused a drop in plasma total homocysteine that was significantly lower than predialysis levels 2 d after dosing. It was hypothesized 5 mg/kg intravenous mesna administered thrice weekly, before dialysis, for 8 wk would cause a significant decrease in plasma total homocysteine compared with placebo.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with end-stage renal disease were randomly assigned to receive either intravenous mesna 5 mg/kg or placebo thrice weekly before dialysis. Predialysis plasma total homocysteine concentrations at weeks 4 and 8 were compared between groups by paired t test.

RESULTS

Mean total homocysteine at 8 wk in the placebo group was 24.9 micromol/L compared with 24.3 micromol/L in the mesna group (n = 22 [11 pairs]; mean difference 0.63). Interim analysis at 4 wk also showed no significant difference between mesna and placebo (n = 32 [16 pairs]; placebo 26.3 micromol/L, mesna 24.5 micromol/L; mean difference 1.88). Multivariable adjustments for baseline characteristics did not alter the analysis. Plasma mesna seemed to reach steady-state concentrations by 4 wk.

CONCLUSIONS

It is concluded that 5 mg/kg mesna does not lower plasma total homocysteine in hemodialysis patients and that larger dosages may be required.

Physical activity is inversely associated with total homocysteine levels, independent of C677T MTHFR genotype and plasma B vitamins

The homocysteine level is considered to be a product of genetic and lifestyle interactions, mainly mutated methylenetetrahydrofolate reductase (MTHFR) and the intake of folate, vitamin B12 and pyridoxine, and their blood levels. Physical activity has been associated with lower homocysteine levels in some population studies, especially among elderly subjects. To further elucidate the observed association between homocysteine and physical activity, while accounting for the effect of the MTHFR C677T genotype, and of plasma levels of folate and B12 vitamins, a cross-sectional study of 620 males and females, aged 70.5 +/- 6.8 years, was carried out. Information on lifestyle habits was collected and laboratory examinations of 12-h fasting total plasma homocysteine, folate, and vitamin B12, as well as DNA analysis for MTHFR C677T variant, were performed. Median total homocysteine values were 11.4 micromol/l for males and 9.4 for females; p < 0.001. Smoking and ethnic origin were not found to be associated with homocysteine levels. Physically active subjects had significantly lower total homocysteine levels when adjusted for sex (p = 0.01). Significant inverse correlations were found between body mass index, plasma folate, B12 and homocysteine levels. Homocysteine levels of the CC, CT and TT genotypes were 9.7, 10.6 and 10.2 mumol/l, respectively (p = 0.002, controlling for sex). In a multiple linear regression model, a sedentary lifestyle increased homocysteine levels by 7% as compared to an active one (p = 0.03) controlling for sex, age, body mass index, folate, vitamin B12, and C677T genotype, all of which were also found to be significantly associated with homocysteine levels. Any level of physical activity was found to be independently associated with lower homocysteine levels in an elderly population, controlling for MTHFR genotype, plasma B-vitamins, age, sex, smoking and BMI. This study emphasizes the importance of maintaining a physically active lifestyle in the elderly.

Relationship between metabolic syndrome categorized by newly recommended by International Diabetes Federation criteria with plasma homocysteine concentration

Plasma total homocysteine (tHcy) is an independent risk factor for cardiovascular disease and increased tHcy levels have been reported to be a novel risk factor of atherosclerotic disease. The aim of this study was to assess the association of the metabolic syndrome components with plasma (tHcy) level. Total 722 participants (284 men, 438 women) from the medical checkup program were enrolled in this study. The clinical characteristics and biochemical parameters of the subjects were assessed and the tHcy levels were compared according to the components of metabolic syndrome diagnosed by Adult Treatment Panel (ATP) III guideline and International Diabetes Federation (IDF) criteria. Among the components, groups with larger waist circumference and higher fasting blood glucose levels showed significantly higher tHcy level than the counterparts. Although statistically insignificant, mean concentrations of tHcy was higher in subjects with metabolic syndrome defined by both criteria. In multiple regression analysis, age, sex and systolic blood pressure were the independent determinants of tHcy level. In conclusion, tHcy level was not associated with metabolic syndrome defined by either criteria in Korean subjects.

Homocysteine and glutathione peroxidase-1

Mildly elevated homocysteine levels (Hcy) increase the risk for atherothrombotic vascular disease in the coronary, cerebrovascular, and peripheral arterial circulations. The molecular mechanisms responsible for decreased bioavailability of endothelium-derived nitric oxide (NO) by Hcy involve an increase of vascular oxidant stress and inhibition of important antioxidant capacity. Glutathione peroxidase-1 (GPx-1), a selenocysteine-containing antioxidant enzyme, may be a key target of Hcy's deleterious actions, and several experimental and clinical studies have demonstrated a complex relationship between plasma total homocysteine (tHcy), GPx-1, and endothelial dysfunction. Hcy may promote endothelial dysfunction, in part by decreasing GPx-1 expression; however, there is evidence to suggest that overexpression of GPx-1 can compensate for these effects. This review summarizes the current knowledge of the metabolism of Hcy, the effects of hyperhomocysteinemia observed in in vitro and in vivo models that lead to endothelial dysfunction and the possible mechanisms for these actions, and the role of GPx-1 in the pathogenesis of Hcy-induced cardiovascular disease (CVD).

High-throughput and simultaneous measurement of homocysteine and cysteine in human plasma and urine by liquid chromatography-electrospray tandem mass spectrometry

Total homocysteine (tHcy) and cysteine (tCys) concentrations in biological fluids are routinely used in the clinical diagnosis of genetic and metabolic diseases, and this necessitates the development of rapid and sensitive methods for quantification. Liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) was used to measure tHcy and tCys in 23 plasma and 21 urine samples from healthy adults and 14 urine samples from healthy children. The results were compared with a standard high-performance liquid chromatography (HPLC) method. The coefficient of variation (CV) for the LC-MS/MS method ranged from 2.9% to 6.1% for the intraassay and 4.8% to 6.4% for the interassay. Mean recoveries were close to 100% for both plasma and urinary tHcy and tCys. The mean plasma tHcy and tCys concentrations in healthy adults were 8.62 and 261.40 micromol/L, respectively. The mean urinary tHcy and tCys in adults were 0.98 and 22.60 micromol/mmol creatinine, respectively. The mean urinary tHcy and tCys in children were 1.17 and 27.43 micromol/mmol creatinine, respectively. Bland-Altman difference plots of method comparison between LC-MS/MS and HPLC showed good agreement in plasma and urinary tHcy and tCys concentrations. Our method is suitable for rapid measurements, and the reported urinary values in children will help to develop a pediatric reference range for clinical use.

Mesna as a nonvitamin intervention to lower plasma total homocysteine concentration: implications for assessment of the homocysteine theory of atherosclerosis

Elevated plasma total homocysteine is independently associated with atherosclerosis. Recent randomized trials show that vitamins lower total homocysteine but do not prevent cardiovascular events, suggesting the need for nonvitamin therapies to evaluate whether a causative relationship exists. Mesna (sodium 2-mercaptoethanesulfonate) is a thiol-containing drug capable of liberating homocysteine bound by disulfide bonds to proteins, facilitating its excretion. The effect of oral mesna on total homocysteine has not been evaluated and was the objective of this study. Eleven healthy volunteers received vehicle or 10 mg/kg mesna in random order, after which serial blood and urine samples were collected over 4 hours. Plasma total homocysteine decreased by 24.2% (P < .0001) following mesna. Urinary homocysteine excretion was significantly greater with mesna (3.9 +/- 2.4 mumol) compared to vehicle (0.4 +/- 0.1 mumol), P < .01. Oral mesna decreases plasma total homocysteine and is a potential nonvitamin treatment for assessing the homocysteine theory of atherosclerosis.

Plasma homocysteine levels in cycling, pregnant, and spayed bitches

The aim of this study was to evaluate the physiological range of homocysteine (Hcy) exhibited by bitches during the follicular (pro-oestrus), luteal (dioestrus) and anoestrus phases of cycling animals, and in pregnant and spayed bitches. The lowest concentrations of Hcy were observed during dioestrus (3.2+/-1.27micromol/L) and in pregnant bitches (3.9+/-1.72micromol/L), and the highest concentrations during anoestrus (7.8+/-0.6micromol/L) and in spayed bitches (12.1+/-5.16micromol/L).

The protective effects of melatonin and Vitamin E on antioxidant enzyme activities and epididymal sperm characteristics of homocysteine treated male rats

The aims of this study were to investigate the effects of homocysteine (Hcy) on epididymal sperm characteristics, plasma testosterone level and biochemical changes related to oxidative stress and to examine the effects of melatonin (Mlt) or Vitamin E (VE) administration on these parameters in Hcy-treated male rats. In this study, 32 adult male albino rats of Wistar strain were used. The rats were randomly divided into four groups. The first group of rats received only Hcy (0.71 mg/kg/day) intraperitonially (ip) for 6 weeks. The second group of rats was given Hcy along with simultaneous administration of Mlt (1mg/kg/day) subcutaneously. The third group of rats received Hcy along with simultaneous administration of VE (125 mg/kg/day, ip). The fourth group of rats served as control during 6 weeks and was daily given 0.1 mL of physiological saline (NaCl, 0.9%) ip. While the plasma malondialdehyde level significantly (p<0.05) increased, the plasma superoxide dismutase, glutathione peroxidase and catalase activities significantly (p<0.05) decreased in Hcy-treated rats when compared to control rats. Furthermore, the epididymal sperm concentration, the percentage of progressive sperm motility and plasma testosterone level were significantly (p<0.05) lower in Hcy-treated rats than those of the control rats. The simultaneous administration of Mlt or VE to Hcy-treated animals impeded the decrease in the plasma antioxidant enzyme activities, testosterone level, the epididymal sperm concentration and motility. In conclusion, this study indicates that chronic administration of Hcy has the harmful effect on the epididymal sperm characteristics of male rats. The administration of Mlt or VE can prevent adverse effects of Hcy on the plasma antioxidant enzyme activities, testosterone level, epididymal sperm count and motility in male rats.

The Effect of Mesna on Plasma Total Homocysteine Concentration in Hemodialysis Patients

BACKGROUND

Plasma total homocysteine (tHcy) level is an independent risk factor for the development of atherosclerosis. The degree of risk in most of the population is decreased by using dietary vitamin supplementation; however, more than 90% of patients with end-stage renal disease have increased tHcy levels despite supplementation. Only a small fraction of tHcy is removed by hemodialysis because of extensive disulfide bonding to albumin. The objective of this study is to determine whether a single intravenous dose of mesna, a thiol-containing drug analogue of taurine, facilitates tHcy clearance during hemodialysis.

METHODS

Initial in vitro thiol exchange tests were performed with mesna in plasma from dialysis patients. Mesna, 300 micromol/L (49.2 mg/L), was incubated with plasma at 37 degrees C, and free homocysteine was measured at various times. In vivo, mesna activity was tested in 10 hemodialysis patients by administering 2.5 or 5.0 mg/kg of mesna intravenously at the beginning of a treatment cycle. Blood samples were drawn throughout dialysis, and plasma tHcy levels were compared with those obtained from a previous dialysis session in which mesna was not administered.

RESULTS

In vitro, mesna liberated 36.5% +/- 2.5% of protein-bound homocysteine in 30 minutes. In vivo, a single 2.5-mg/kg dose of mesna was ineffective; however, at 5.0 mg/kg, it caused a 55.2% +/- 3.9% decrease in plasma tHcy levels postdialysis compared with a 34.2% +/- 5.3% decrease with dialysis alone (P < 0.001).

CONCLUSION

Intravenous mesna causes a rapid decrease in plasma tHcy levels during hemodialysis.

Methylenetetrahydrofolate reductase gene polymorphism, homocysteine and risk of macroangiopathy in Type 2 diabetes mellitus

OBJECTIVE

A polymorphism in the gene for methylenetetrahydrofolate reductase (MTHFR) has been reported to be associated with hyperhomocysteinemia and risk for atherosclerotic vascular diseases. In this case-control study, we examined the distribution of the MTHFR genotypes in the Chinese population and clarified the relationship between the gene polymorphism for MTHFR and macroangiopathy in Chinese Type 2 diabetes mellitus.

METHODS

Two hundred and sixteen unrelated patients with Type 2 diabetes mellitus, 112 of whom had macroangiopathy, and 114 healthy control subjects, were recruited. The MTHFR C677T genotype was analyzed by polymerase chain reaction-restriction fragment length polymorphism. Plasma total homocysteine levels were measured using high-performance liquid chromatography (HPLC) with fluorescence detection.

RESULTS

In 114 healthy control subjects, the frequency of the mutant T allele was 31.1%. The genotype distribution did not differ between control subjects and Type 2 diabetic patients (chi2=3.03, p=0.220). Genotypic analysis revealed that the MTHFR genotype was different between diabetic patients with and without macroangiopathy (chi2=12.42, p=0.002). Type 2 diabetic patients with macroangiopathy displayed a greater prevalence of T allele than Type 2 diabetic patients without macroangiopathy (44.6 vs 29.3%; chi2=10.82, p=0.001). The odds ratio for macroangiopathy in Type 2 diabetic patients in presence of T allele was 1.94 [confidence interval (CI) 95%: 1.31-2.89]. Moreover, plasma homocysteine levels were markedly higher in individuals with TT genotype than those with CC or CT genotype.

CONCLUSIONS

The C677T mutation of MTHFR gene is common in the Chinese population. MTHFR C677T gene polymorphism associated with a predisposition to increased plasma homocysteine levels could constitute a useful predictive marker for macroangiopathy in Chinese Type 2 diabetic patients.

Thiol exchange: An in vitro assay that predicts the efficacy of novel homocysteine lowering therapies

Elevated plasma total homocysteine (tHcy) is a risk factor for atherosclerosis. Hcy is 70-80% bound to albumin as a disulfide. Recent trials have evaluated ability of thiol-containing drugs to exchange with protein bound Hcy and consequently increase its renal clearance. The objective of this study was to develop an in vitro assay to predict the efficacy of thiol-containing drugs to lower tHcy in the clinical setting. The assay was used to test the effects of N-acetylcysteine (NAC), mesna, captopril, dimercaptosuccinic acid (DMSA), and penicillamine. Hcy was added in vitro to plasma of healthy subjects (n = 6) and equilibrated. Concentrations of thiol exchange agent were added and incubated at 37 degrees C. Aliquots were removed at selected intervals and free Hcy determined. Mesna, captopril, and NAC caused a concentration-dependent increase in free Hcy. Three-hundred micromolar mesna and captopril had a greater effect than equimolar NAC, increasing free Hcy by 33.9 +/- 5.0% and 32.0 +/- 2.6%, respectively compared to 22.3 +/- 2.4% for NAC, p < 0.001. Our in vitro results indicate that mesna, captopril, and NAC effectively exchange with covalently bound Hcy. This assay can act as screening tool for novel tHcy lowering therapies and should spare the expense of negative trials.

Serum Homocysteine and Long-Term Risk of Myocardial Infarction and Sudden Death in Patients with Coronary Heart Disease

We have prospectively evaluated the risk of incident coronary events in association with serum total homocysteine in patients with preexisting chronic coronary heart disease. A nested case-control design was used. Total homocysteine concentration was measured in baseline fasting serum samples from patients with chronic coronary heart disease enrolled in the Bezafibrate Infarction Prevention Study (n = 3,090) who developed coronary events during 6.2 years of follow-up (n = 69). They were matched for age and gender with controls without subsequent cardiovascular events. Elevated homocysteine levels were associated with 2.5 times higher risk of subsequent coronary events and each 5 mumol/l increment was associated with a 25% higher risk.

Homocysteine- and cysteine-mediated growth defect is not associated with induction of oxidative stress response genes in yeast

Intracellular thiols like cysteine, homocysteine and glutathione play a critical role in the regulation of important cellular processes. Alteration of intracellular thiol concentration results in many diseased states; for instance, elevated levels of homocysteine are considered to be an independent risk factor for cardiovascular disease. Yeast has proved to be an excellent model system for studying many human diseases since it carries homologues of nearly 40% of human disease genes and many fundamental pathways are highly conserved between the two organisms. In the present study, we demonstrate that cysteine and homocysteine, but not glutathione, inhibit yeast growth in a concentration-dependent manner. Using deletion strains (str2Delta and str4Delta) we show that cysteine and homocysteine independently inhibit yeast growth. Transcriptional profiling of yeast treated with cysteine and homocysteine revealed that genes coding for antioxidant enzymes like glutathione peroxidase, catalase and superoxide dismutase were down-regulated. Furthermore, transcriptional response to homocysteine did not show any similarity to the response to H2O2. We also failed to detect induction of reactive oxygen species in homocysteine- and cysteine-treated cells, using fluorogenic probes. These results indicate that homocysteine- and cysteine-induced growth defect is not due to the oxidative stress. However, we found an increase in the expression of KAR2 (karyogamy 2) gene, a well-known marker of ER (endoplasmic reticulum) stress and also observed HAC1 cleavage in homocysteine- and cysteinetreated cells, which indicates that homocysteine- and cysteine-mediated growth defect may probably be attributed to ER stress. Transcriptional profiling also revealed that genes involved in one-carbon metabolism, glycolysis and serine biosynthesis were up-regulated on exogenous addition of cysteine and homocysteine, suggesting that cells try to reduce the intracellular concentration of thiols by up-regulating the genes involved in their metabolism.

Hyperhomocysteinaemia and aortic calcification are associated with fractures in patients on haemodialysis

BACKGROUND

Fractures and atherosclerosis are common in patients with renal failure; this may be due to hyperhomocysteinemia.

AIM

To examine the relationships between fractures, vascular calcification and homocysteine levels in haemodialysis patients.

DESIGN

Cross-sectional survey.

METHODS

We enrolled 37 men and 15 women who had been on haemodialysis for at least 1 year. We identified prevalent spine fractures by radiographs. Non-spine fractures were identified by self-report and confirmed by review of radiographs or radiology reports. We classified the presence and severity of lumbar aortic calcifications with lateral lumbar radiographs. We measured serum homocysteine in all subjects within 30 days of study entry.

RESULTS

After adjusting for age and weight, increased levels of homocysteine were associated with an increased risk fracture (OR per mmol/l increase in homocysteine 1.6, 95%CI 1.2-2.0), as was the presence of aortic calcification (OR 1.6, 95%CI 1.2-2.1). Homocysteine and lumbar aortic calcification were highly correlated (r = 0.86).

DISCUSSION

Hyperhomocysteinaemia may explain the relationship between fractures and atherosclerosis in patients with renal failure.

Hypersensitivity of HIV-1-Infected Cells to Reactive Sulfonamide Metabolites Correlated to Expression of the HIV-1 Viral Protein Tat

Impairment of human immunodeficiency virus (HIV)-infected cells to deal with reactive drug metabolites may be a mechanism for the increased rate of adverse drug reactions seen in AIDS. HIV Tat protein expression may be associated with increased oxidative stress within HIV-infected cells. To determine the relationship between expression of HIV Tat and sensitivity to reactive drug metabolites, we studied toxicity of sulfamethoxazole (SMX) and its reactive hydroxylamine intermediate (SMX-HA) in lymphocytes transfected with the HIV tat gene. Over a concentration range from 0 to 400 microM SMX-HA, there was a significant concentration-dependent increase in cell death in transfected cell lines expressing Tat compared with controls. Jurkat T cells transfected with a dose-dependent inducible tat gene showed increased toxicity in response to SMX-HA as more Tat expression was induced. Enhanced sensitivity to SMX-HA was accompanied by significantly lower concentrations of total intracellular glutathione compared with controls (P < 0.05). Sensitivity to reactive drug metabolites in HIV-infected cells seems to be mediated by the viral protein Tat.

Homocysteine Down-regulates Cellular Glutathione Peroxidase (GPx1) by Decreasing Translation

Hyperhomocysteinemia contributes to vascular dysfunction and an increase in the risk of cardiovascular disease. An elevated level of homocysteine in vivo and in cell culture systems results in a decrease in the activity of cellular glutathione peroxidase (GPx1), an intracellular antioxidant enzyme that reduces hydrogen peroxide and lipid peroxides. In this study, we show that homocysteine interferes with GPx1 protein expression without affecting transcript levels. Expression of the selenocysteine (SEC)-containing GPx1 protein requires special translational cofactors to "read-through" a UGA-stop codon that specifies SEC incorporation at the active site of the enzyme. These factors include a selenocysteine incorporation sequence (SECIS) in the 3'-untranslated region of the GPx1 mRNA and cofactors involved in the biosynthesis and translational insertion of SEC. To monitor SEC incorporation, we used a reporter gene system that has a UGA codon within the protein-coding region of the luciferase mRNA. Addition of either the GPx1 or GPx3 SECIS element in the 3'-untranslated region of the luciferase gene stimulated read-through by 6-11-fold in selenium-replete cells; absence of selenium prevented translation. To alter cellular homocysteine production, we used methionine in the presence of aminopterin, a folate antagonist, co-administered with hypoxanthine and thymidine (HAT/Met). This treatment increased homocysteine levels in the media by 30% (p < 0.01) and decreased GPx1 enzyme activity by 45% (p = 0.0028). HAT/Met treatment decreased selenium-mediated read-through significantly (p < 0.001) in luciferase constructs containing the GPx1 or GPx3 SECIS element; most importantly, the suppression of selenium-dependent read-through was similar whether an SV40 promoter or the GPx1 promoter was used to drive transcription of the SECIS-containing constructs. Furthermore, HAT/Met had no effect on steady-state GPx1 mRNA levels but decreased GPx1 protein levels, suggesting that this effect is not transcriptionally mediated. These data support the conclusion that homocysteine decreases GPx1 activity by altering the translational mechanism essential for the synthesis of this selenocysteine-containing protein.

Plasma homocysteine level and functional outcome of patients with ischemic stroke

OBJECTIVE

To investigate the possible relationships between total plasma homocysteine level (tHcy) and functional outcome of stroke patients as evaluated by the FIM instrument.

DESIGN

Retrospective chart analysis.

SETTING

Inpatient stroke rehabilitation ward of a university-affiliated referral hospital.

PARTICIPANTS

Consecutive patients (N=113) presenting with acute ischemic stroke. Patients were divided into 2 groups according to their tHcy levels (< or = 15 micromol/L, >15 micromol/L) and into 3 groups according to their FIM scores (low, < or =40; moderate, 41-80; high, >80).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

The tHcy level was determined shortly after stroke onset by a high performance liquid chromatography method with fluorescence detection. Functional outcome was measured by the FIM instrument at admission and discharge. The tHcy level and FIM scores were obtained for all patients. Data outcomes were analyzed by t tests, 1-way analysis of variance, Mann-Whitney U, and Fisher exact tests, as well as by the 2 ordered polytomous logistic regression model.

RESULTS

The 2 tHcy groups were similar in demographic, stroke, and comorbidity characteristics, differing only by higher frequency of hypertension in those with a tHcy greater than 15 micromol/L (51.7% vs 80.8%, respectively, P=.01). Compared with patients who had tHcy levels at 15 micromol/L or lower and were discharged from rehabilitation being in the highest FIM score group (>80), higher tHcy levels were not associated with a discharge FIM score of less than 40 (odds ratio [OR]=.77; 95% confidence interval [CI], 0.13-4.65; P=.77) or with a better functional outcome FIM score between 40 and 80 (OR=3.71; 95% CI, 0.73-18.99; P=.11).

CONCLUSIONS

Our findings suggest that determination of tHcy level does not correlate with functional outcome in patients presenting for rehabilitation after acute ischemic stroke.

Conditional risk factors for atherosclerosis

Although most patients who experience a coronary heart disease (CHD) event have one or more of the conventional risk factors for atherosclerosis, so do many people who have not yet experienced such an event. Therefore, predictive models based on conventional risk factors have a lower than desired accuracy, providing a stimulus to search for new tools to refine CHD risk prediction. In particular, there is intense interest in evaluating circulating biomarkers related to the atherosclerotic process that might add to our ability to better predict CHD risk. One such group of biomarkers was termed conditional risk factors in an American Heart Association/American College of Cardiology statement in 1999. The conditional risk factors include homocysteine, fibrinogen, lipoprotein(a), low-density lipoprotein particle size, and C-reactive protein. This review updates the conditional risk factors. The main focus is on the potential utility of these risk factors, which are currently available to clinicians, in the prediction of CHD risk in asymptomatic persons. The putative mechanisms of risk, available assays, evidence for association with CHD, and the clinical implications thereof are discussed for each of the risk factors.

Methylenetetrahydrofolate reductase polymorphism associated with susceptibility to coronary heart disease in Chinese type 2 diabetic patients

OBJECTIVE

Epidemiological studies have identified hyperhomocyst(e)inemia as an independent risk factor for atherosclerosis. The C677T variant of the methylenetetrahydrofolate reductase (MTHFR) gene, one of the key enzymes catalyzing remethylation of homocysteine, might play a role in the development of coronary heart disease (CHD). In this study, we examined the distribution of the MTHFR genotypes in the Chinese population and the association between the C677T variant and CHD in Chinese type 2 diabetic patients.

METHODS

Two hundred and twenty-eight unrelated patients with type 2 diabetes mellitus (126 with coronary heart disease) and 114 healthy control subjects were recruited. The MTHFR genotype was analyzed by PCR followed by HinfI digestion. Plasma total homocysteine levels were measured using high-performance liquid chromatography (HPLC) with fluorescence detection.

RESULTS

In 114 healthy control subjects, the frequency of the mutant T allele was 38.0%, comparable to that of a Hong Kong (Chinese) population. The genotype distribution did not differ between control subjects and type 2 diabetic patients (chi(2) = 3.67, P > 0.05). Genotypic analysis revealed that type 2 diabetic patients with CHD displayed a greater prevalence of T allele (45.2%) than type 2 diabetic patients without CHD (30.4%) (chi(2) = 8.72, P < 0.005). The odds ratio for CHD in type 2 diabetic patients in presence of T allele was 1.89 (CI 95%, 1.24-2.88). The MTHFR genotype were different between diabetic patients with and without CHD (chi(2) = 11.98, P < 0.005). Moreover, plasma homocysteine levels were markedly higher in individuals with TT genotype than those with CC or CT genotype or CC plus CT genotype.

CONCLUSIONS

The C677T mutation of MTHFR gene is common in the Chinese population. MTHFR C677T gene polymorphism associated with a predisposition to increased plasma homocysteine levels could constitute a useful predictive marker for CHD in Chinese type 2 diabetic patients.

Analysis of plasma amino acids by HPLC with photodiode array and fluorescence detection

BACKGROUND

Plasma amino acids are usually analyzed by ion-exchange chromatography (IEC), a reproducible but time consuming method. Here, we test whether plasma amino acids can be analyzed using reverse-phase high performance liquid chromatography (HPLC).

METHODS

Filtered plasma, with S-carboxymethyl-l-cysteine as the internal standard, was derivatized and analyzed by an Agilent 1100 HPLC system. Primary amino acids were derivatized with o-phthalaldehyde 3-mercaptopropionic acid (OPA) and detected by a diode array detector. Secondary amino acids were derivatized with 9-fluorenylmethyl chloroformate (FMOC) and detected fluorometrically. Chromatographic separation is achieved by two gradient elutions (two injections per sample), starting at different pHs, on a reverse phase Agilent Zorbax Eclipse C(18) column AAA (4.6 x 150 mm).

RESULTS

The HPLC method evaluated correlated well with IEC (0.89</=r</=1.00) with linearity up to 2500 mumol/l. The between- and within-run CVs were <6.0%. In addition, this method is able to separate argininosuccinic acid, homocystine and allo-isoleucine, rare but clinically significant amino acids.

CONCLUSION

This HPLC method was comparable to IEC and could represent an alternative for amino acid analysis.

Life-style habits and homocysteine levels in an elderly population

BACKGROUND AND AIMS

Increased plasma total homocysteine (Hcy) is a known cardiovascular disease (CVD) risk factor, related to several components of the established CVD risk profile. Observational studies support the role of modifying life-style related risk factors such as diet, physical activity and alcohol consumption in CVD prevention. Regular physical activity protects against coronary artery disease, possibly through its role in controlling risk factors such as hypertension, diabetes mellitus and obesity, but also independently. The aim of our study was to test the hypothesis that there is an association between physical activity, life-style habits and plasma Hcy levels in an elderly population.

METHODS

In this cross-sectional study, 423 males and females aged 69.0 +/- 6.7 years completed an interview and laboratory examinations. Our main outcome measure was plasma levels of Hcy.

RESULTS

Mean Hcy values were 10.5 +/- 5.5 micromol/L (11.4 +/- 6.1 for males and 9.3 +/- 4.5 for females; p < 0.001). Smoking and BMI were not found to be associated with Hcy levels. Physically active subjects, as well as B vitamin supplement users, had significantly lower Hcy levels (p = 0.002 and p = 0.004, respectively). In a multiple linear regression model, the Hcy level was 10% higher amongst participants with a sedentary life-style, 17% higher amongst males, 1% higher for each one-year increment in age, and 10% higher amongst participants who used no B vitamin supplements.

CONCLUSIONS

Any level of physical activity was found to be an independent life-style habit associated with a lower Hcy level in an elderly population. This study supports existing recommendations for elderly persons to maintain a physically active life-style.

Assessment of the coagulation profile in hemato-oncological patients receiving ATG-based conditioning treatment for allogeneic stem cell transplantation

Antithymocyte globulin (ATG) is increasingly used in pre-allogeneic stem cell transplantation (allo-SCT) conditioning regimens to prevent graft rejection and graft-versus-host disease. However, ATG was also found to be associated with increased incidence of thrombosis during organ transplantation. In the present study, we tested the coagulation status of 21 patients with hematologic malignancies undergoing allo-SCT who received ATG-based (11 patients) or non-ATG-based (10) conditioning treatment. We assessed several thrombophilia markers as well as circulating total and endothelial microparticles (TMP/EMP) and soluble CD40 ligand (CD40L). No significant difference in the mean values of prothrombin time, partial thromboplastin time, fibrinogen, antithrombin, protein C, protein S, thrombin-antithrombin III complex, homocysteine levels, prevalence of genetic thrombophilia markers and levels of EMP, TMP or CD40L was observed between the ATG-treated and ATG-untreated patients, as well as before and after conditioning in each group separately. Platelet counts decreased significantly in ATG-treated patients; however, this decrease was not associated with clinical or laboratory evidence of disseminated intravascular coagulation. No patient developed thromboembolic event or veno-occlusive liver disease. Our results suggest that allo-SCT is not associated with increased hypercoagulability and addition of ATG to conditioning regimen has no significant procoagulant effect.

Comparison of isotope dilution mass spectrometry methods for the determination of total homocysteine in plasma and serum

Two independent methods have been critically evaluated and applied to the measurement of total homocysteine in serum and plasma: solid-phase anion extraction (SPAE) gas chromatography/mass spectrometry (GC/MS) and protein precipitation liquid chromatography/tandem mass spectrometry (LC/MS/MS). In addition, analysis of samples prepared by SPAE was accomplished by liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS. These methods have been used to determine total homocysteine levels in several existing serum-based Standard Reference Materials (SRMs) from the National Institute of Standards and Technology and in patient plasma samples provided by the Centers for Disease Control and Prevention. The precision of the homocysteine measurements in serum and plasma was critically evaluated, and method comparisons were carried out using Bland-Altman plots and bias analysis. On the basis of the excellent precision and close agreement of the mass spectrometric (MS) methods, the MS-based methods will be used for certification of a serum-based SRM for homocysteine and folates.

N-acetyl-cysteine in the prevention of vascular restenosis after percutaneous balloon angioplasty

BACKGROUND

Vascular inflammation generating oxidized metabolites at the site of balloon angioplasty is believed to play a major role in the process of vessel restenosis. Glutathione, the most potent endogenous antioxidant, may have protective effects after angioplasty by suppressing local inflammatory response. The aim of the study was to test the hypothesis that oral administration of N-acetyl-cysteine (NAC, a precursor of glutathione) reduces restenosis in an animal model of vascular injury.

METHODS

In New Zealand white rabbits, an atherosclerotic lesion was introduced to both iliac arteries by air denudation of the endothelium while feeding the animals a high-cholesterol diet. After 4 weeks, all animals underwent balloon angioplasty of the endothelial injury site and half of the group was started on 150 mg/kg NAC per day. Quantitative angiography was performed prior to the angioplasty and at the final procedure 3 weeks later. Glutathione levels were determined in all animals at the beginning and the end of the study.

RESULTS

Although not statistically significant, plasma glutathione level increased in the NAC group from 32.4+/-4.4 to 39.7+/-11.6 micromol/l, while it decreased from 30.6+/-13.4 to 28.3+/-11.5 micromol/l in the control group. During the study period, 6 vessels occluded leaving 14 vessels for analysis. Quantitative angiographic analyses prior to angioplasty and at follow-up showed no significant difference with respect to stenosis progression between the groups. Measurement of neointima formation by histology showed also no significant difference between the groups (0.175+/-0.040 mm(2) vs. 0.123+/-0.075 mm(2)), neither did intimal macrophage count as a marker for local inflammatory response.

CONCLUSIONS

Despite an increase in plasma glutathione level in the NAC-treated group, there was no reduction in lesion progression after balloon angioplasty. Therefore, NAC does not seem to prevent restenosis after vascular intervention in this animal model.

Genetic polymorphism of methylenetetrahydrofolate reductase as a risk factor for diabetic nephropathy in Chinese type 2 diabetic patients

OBJECTIVE

Genetic predisposition has been implicated in diabetic nephropathy (DN). The C677T variant of the methylenetetrahydrofolate reductase (MTHFR) gene, one of the key enzymes catalyzing remethylation of homocysteine, may play a role in the development of not only vascular disease but also diabetic microangiopathies. In this study, we examined the distribution of the MTHFR genotypes in the Chinese population and the association between the C677T variant and diabetic nephropathy.

METHODS

220 unrelated patients with type 2 diabetes mellitus and 130 controls were recruited. The MTHFR genotype was analyzed by PCR followed by HinfI digestion. Plasma total homocysteine levels were measured using high-performance liquid chromatography (HPLC) with fluorescence detection.

RESULTS

In 130 healthy control subjects, the frequency of the mutant T allele was 30.0%, comparable to that of a Hong Kong (Chinese) population. The distribution of the three genotypes was as follows: TT genotype, 16.9%; CT genotype, 26.2%; and CC genotype, 56.9%. This genotype distribution did not differ between control subjects and type 2 diabetic patients in which 19.1% were TT, 34.5% were CT and 46.4% were CC (2=3.85, P>0.05). The frequency of the mutant T allele was 42.3% in diabetic patients with nephropathy (n=124) versus 28.6% in those without nephropathy (n=96). The genotype frequencies were TT, 21.0%; CT, 42.7%; CC, 36.3% in diabetic patients with nephropathy versus TT, 16.7%; CT, 23.9%; CC, 59.4% in those without nephropathy. The MTHFR genotype and allele frequencies were different between diabetic patients with and without nephropathy (chi2=12.27, P<0.005; chi2=8.77, P<0.005, respectively). Moreover, plasma homocysteine levels were markedly higher in individuals with TT genotype than those with CC or CT genotype.

CONCLUSIONS

The C677T mutation of MTHFR gene is common in the Chinese population. MTHFR C677T gene polymorphism associated with a predisposition to increased plasma homocysteine levels may represent a genetic risk factor for diabetic nephropathy in Chinese type 2 diabetic patients.

Homocysteine and folic acid are inversely related in black women with preeclampsia

Black women have an increased risk of preeclampsia compared with white women. Plasma homocysteine is increased in preeclampsia. Homocysteine concentrations are affected by nutritional deficiencies, particularly decreased folic acid and B12, leading to increased homocysteine. Previous studies have reported racial differences in nutritional intake including folic acid. Therefore, we investigated whether there were racial differences in plasma homocysteine, folic acid, and vitamin B12 among women with preeclampsia. We tested for an association between homocysteine and folic acid and B12, and we hypothesized an inverse relationship of homocysteine and folic acid in preeclampsia, more so in black women in whom preeclampsia developed. Black women with preeclampsia (n=26) had elevated homocysteine concentrations (8.7+/-1.4 micromol/L) compared with black women with normal pregnancy (n=52, 7.6+/-0.5 micromol/L), white women with preeclampsia (n=34, 7.5+/-0.6 micromol/L), and white women with normal pregnancy (n=48, 5.5+/-0.3 micromol/L). Folic acid concentrations were lower in black women (14.1+/-0.8 ng/mL) compared with white women (18.5+/-0.9 ng/mL, P<0.01). However, plasma homocysteine was inversely related to folic acid only among black women with preeclampsia (r=-0.23, P=0.01). These racial differences may have implications for the higher rates of preeclampsia in this group and may have long-term implications for future cardiovascular risk. Racial differences in diet, adherence to folic acid supplementation, or interactions of nutritional and maternal factors warrant further study by race and pregnancy status.

Effect of supraphysiologic doses of testosterone on fasting plasma total homocysteine concentrations in men with Klinefelter's syndrome

OBJECTIVE

To examine the effect of supraphysiologic doses of testosterone (T) on plasma total homocysteine (tHcy) concentrations in patients with Klinefelter's syndrome (KS).

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENT(S)

Thirty-two newly diagnosed male patients with KS, and 20 healthy, volunteer controls matched by age and body mass index.

INTERVENTION(S)

Testosterone was administered IM every 2 weeks for 6 months. Initially, pretreatment fasting blood samples were collected after overnight fasting. Posttreatment blood samples were drawn 7 days after the last injection.

MAIN OUTCOME MEASURE(S)

Plasma total homocysteine.

RESULT(S)

The KS patients had lower tHcy levels than the controls. However, plasma fasting tHcy concentrations increased in a statistically significant manner after 6 months of treatment. As compared with the levels among controls, pretreatment levels of the serum creatinine, hemoglobin, and hematocrit were significantly lower, and increased in a statistically significant way following treatment. Posttreatment levels of total cholesterol were statistically significantly higher than the baseline. The pretreatment folate and cobalamin levels also were statistically significantly higher in patients when compared with controls, and decreased significantly after treatment. The linear regression analysis showed that only creatinine, cobalamin, and folate were independently associated with plasma tHcy levels in patients before and after treatment.

CONCLUSION(S)

The patients with KS showed lower tHcy concentrations than healthy, age-matched male controls. Testosterone treatment increased plasma tHcy levels.

Modulation of cystathionine beta-synthase level regulates total serum homocysteine in mice

Elevated total plasma homocysteine is an independent risk factor in the development of vascular disease in humans. Cystathionine beta-synthase (CBS) is an enzyme that condenses homocysteine with serine to form cystathionine. In this article, we describe the effects of modulating CBS activity using a transgenic mouse that contains the human CBS cDNA under control of the zinc-inducible metallothionein promoter (Tg-CBS). In the presence of zinc, Tg-CBS mice have a 2- to 4-fold increase in liver and kidney CBS activity compared with nontransgenic littermates. Transgenic mice on standard mouse chow had a 45% decrease in their serum homocysteine (12.1 to 7.2 micromol/L; P<0.0001) when zinc was added to drinking water, although zinc had minimal effect on their nontransgenic siblings (13.2 micromol/L versus 13.0 micromol/L; P=NS). Tg-CBS mice maintained on a high-methionine, low-folate diet also had significantly lower serum homocysteine compared with control animals (179 micromol/L versus 242 micromol/L; P<0.02). CBS overexpression also significantly lowered serum cysteinylglycine (3.6 versus 2.8 micromol/L; P<0.003) levels and reduced the levels of many amino acids in the liver. We also found that expression of Tg-CBS rescued the severe hyperhomocysteinemia and neonatal lethality of Cbs deletion animals. Our results show that elevating CBS activity is an effective method to lower plasma homocysteine levels. In addition, the creation of an inducible mouse system to modulate plasma homocysteine will also be useful in the study of homocysteine-related vascular disease.

Total plasma homocysteine and primary open-angle glaucoma

PURPOSE

To evaluate total plasma homocysteine (tHcy) levels in patients diagnosed with primary open-angle glaucoma (POAG) and normal subjects.

DESIGN

Case-control study.

METHODS

This study involved 55 POAG patients, 16 patients with secondary open-angle glaucoma or angle-closure glaucoma (non-POAG group), and 39 control healthy subjects undergoing ocular surgery. All glaucoma patients had characteristic glaucomatous optic disk damage and visual field loss. Fasting tHcy concentrations of all study participants were determined using high-performance liquid chromatography. Analysis of variance was used to compare homocysteine levels among the three diagnostic groups, and multivariate analysis was conducted to assess the associations between tHcy and diagnostic group, age, gender, smoking status, systemic hypertension, hyperlipidemia, and cardiovascular or cerebrovascular disease.

RESULTS

Mean +/- standard deviation of tHcy levels in POAG individuals, non-POAG patients and control subjects was 14.90 +/- 6.45 micromol/l, 14.30 +/- 4.35 micromol/l, and 14.81 +/- 4.56 micromol/l, respectively (P =.93; ANOVA). No statistically significant difference was found in the proportion of patients with abnormal tHcy levels among the three diagnostic groups. In multivariate analysis, only age and positive smoking status were significantly correlated with total plasma homocysteine levels.

CONCLUSION

No significant difference was found in plasma homocysteine levels among POAG patients and normal control individuals.

Meta-analysis of plasma homocysteine, serum folate, serum vitamin B12, and thermolabile MTHFR genotype as risk factors for retinal vascular occlusive disease

PURPOSE

To assess the role of plasma total homocysteine (tHcy) levels, serum folate and vitamin B(12)levels, and homozygosity for the thermolabile methylenetetrahydrofolate reductase genotype (TT) as risk factors for retinal vascular occlusive disease.

DESIGN

Meta-analysis of literature.

METHODS

A MEDLINE search was performed to identify all published case-control studies of plasma tHcy levels, serum folate and vitamin B(12) levels, and TT genotype in persons with retinal vascular occlusive disease. Main outcome measures included calculation of plasma tHcy, serum folate, and serum vitamin B(12) standard differences and odds ratios (OR) of TT genotype between cases and controls.

RESULTS

In total, 614 patients with all types of retinal vein occlusion had higher plasma tHcy levels than 762 control subjects (standard difference, 0.867; 95% confidence interval [CI] = 0.735, 0.999; P <.001). Plasma tHcy levels were also higher in 154 patients with retinal artery occlusion compared with 358 control subjects (standard difference 1.174; 95% CI = 0.947, 1.402; P <.001). Serum folates, but not vitamin B(12) levels, were lower in 287 patients with retinal vascular occlusion than in the same number of control subjects (standard difference, 0.508; 95% CI = 0.340, 0.675; P <.001; and -0.060; 95% CI = -0.024, 0.104; P =.474, respectively). Similar proportions of 690 patients with retinal vein occlusion and 2754 control subjects demonstrated the TT genotype (OR = 1.332; 95% CI = 0.995, 1.783; P =.054) as did 152 patients with retinal artery occlusions and 435 control subjects (OR = 1.716; 95% CI = 0.977, 3.014; P =.060).

CONCLUSIONS

Retinal vascular occlusion is associated with elevated plasma tHcy levels and low serum folate levels, but not serum vitamin B(12) levels and TT genotype. Until a prospective multicenter trial is undertaken, plasma tHcy levels and serum folate levels should be determined in patients with retinal vascular occlusions, and dietary supplementation with low doses of folate and vitamin B(12) should be considered for affected persons.

In Vitro and in Vivo Interactions of Homocysteine with Human Plasma Transthyretin

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease and an emerging risk factor for cognitive dysfunction and Alzheimer's disease. Greater than 70% of the homocysteine in plasma is disulfide-bonded to protein cysteine residues. The identity and functional consequences of protein homocysteinylation are just now emerging. The amyloidogenic protein transthyretin (prealbumin), as we now report, undergoes homocysteinylation at its single cysteine residue (Cys10) both in vitro and in vivo. Thus, when human plasma or highly purified transthyretin was incubated with 35S-L-homocysteine followed by SDS-PAGE and PhosphorImaging, two bands corresponding to transthyretin dimer and tetramer were observed. Treatment of the labeled samples with beta-mercaptoethanol prior to SDS-PAGE removed the disulfide-bound homocysteine. Transthyretin-Cys10-S-S-homocysteine was then identified in vivo in plasma from normal donors, patients with end-stage renal disease, and homocystinurics by immunoprecipitation and high performance liquid chromatography/electrospray mass spectrometry. The ratios of transthyretin-Cys10-S-S-homocysteine and transthyretin-Cys10-S-S-sulfonate to that of unmodified transthyretin increased with increasing homocysteine plasma concentrations, whereas the ratio of transthyretin-Cys10-S-S-cysteine to that of unmodified transthyretin decreased. The hyperhomocysteinemic burden is thus reflected in the plasma levels of transthyretin-Cys10-S-S-homocysteine, which in turn may contribute to the pathological consequences of amyloid disease.

Hyperhomocysteinemia as a component of syndrome X

Syndrome X, a cluster of several metabolic disorders that includes hyperinsulinemia, hypertriglyceridemia, and hypertension, is associated with severe vascular morbidity. Hyperhomocysteinemia is another risk factor for cardiovascular and cerebrovascular diseases, often exhibited by insulin-resistant patients. In the current study, we investigated the relationship between syndrome X and hyperhomocysteinemia in a rat model. Two groups of rats were fed either fructose-enriched diet or standard rat chow for 5 weeks. Systolic blood pressure (SBP), as well as fasting plasma insulin, triglycerides, total cholesterol, and total homocysteine levels, were determined at the beginning and at the end of the study. A complete metabolic syndrome was induced by the fructose-enriched diet, including hyperinsulinemia, hypertriglyceridemia, and hypertension. Homocysteine concentration was 72% higher after 5 weeks on the fructose diet (8.49 +/- 1.6 v 4.92 +/- 0.9 micromol/l, P<.01). Insulin, triglycerides, SBP, and homocysteine levels were insignificantly changed during 5 weeks on standard rat chow. Homocysteine was positively and significantly correlated with any original component of syndrome X (r=0.565, P=.014 with insulin, r=0.662, P=.001 with triglycerides, and r=0.774, P<.001 with SBP). The results of the present study indicate that hyperhomocysteinemia is an integral component of this rat model of syndrome X. It is thus highly likely that hyperhomocysteinemia is an integral component of the human syndrome X as well, and thereby contributes to the overall high vascular risk associated with this condition.

Folic acid supplement decreases the homocysteine increasing effect of filtered coffee. A randomised placebo-controlled study

OBJECTIVE

Elevated levels of plasma total homocysteine (tHcy) are identified as independent risk factors for coronary heart disease and for fetal neural tube defects. tHcy levels are negatively associated with folic acid, pyridoxine and cobalamine, and positively associated with coffee consumption and smoking. A total of 600 ml of filtered coffee results in a tHcy increase that 200 mug of folic acid or 40 mg of pyridoxine supplementation might eliminate.

DESIGN

Randomised, blinded study with two consecutive trial periods.

SETTING

Free living population. Volunteers.

SUBJECTS

A total of 121 healthy, nonsmoking men and women (78%) aged 29-65 y.

INTERVENTIONS

(1) A coffee-free period of 3 weeks, (2) 600 ml coffee/day and a supplement of 200 mug folic acid/day or placebo for 4 weeks, (3) 3-week coffee-free period, (4) 600 ml coffee/day and 40 mg pyridoxine/day or placebo for 4 weeks.

MAIN OUTCOME MEASURES

The difference between the change in tHcy in the supplement group and the change in tHcy in the placebo group during the 4-week trial period.

RESULTS

Coffee abstention resulted in a tHcy decrease of 1.04 mumol/l for the whole group. In the subsequent coffee period, a further decrease of 0.17 mumol/l was observed in the folic acid group whereas an increase of 1.26 mumol/l was observed in the placebo group, the difference was 1.43 mumol/l (95% CI: 0.80, 2.07). Pyridoxine supplement had no impact on tHcy levels.

CONCLUSIONS

Supplementation of 200 mug folic acid/day eliminates the tHcy increasing effect of 600 ml filtered coffee in subjects not already on folic acid supplements. A supplement of 40 mg pyridoxine/day does not have the same effect.

Captopril Restores Endothelium-Dependent Relaxation of Rat Aortic Rings After Exposure to Homocysteine

This study was designed to investigate the effects of captopril, an angiotensin-converting enzyme inhibitor, on inhibition of endothelium-dependent relaxation induced by homocysteine in isolated rat aorta. Isometric tension recordings were used to assess inhibitory effects of homocysteine and protective effects of captopril on endothelium-dependent relaxation of aortic rings. Exposure of aortic rings to homocysteine (0.3 approximately 3 mmol/L) for 30 min induced a significant concentration-dependent inhibition of endothelium-dependent relaxation response to acetylcholine (ACh), but did not affect endothelium-independent relaxation response to sodium nitroprusside. Pre-incubation of aortic rings with captopril (3 approximately 30 micromol/L) for 15 min and co-incubation of aortic rings with homocysteine (1 mmol/L) for another 30 min attenuated the inhibition of homocysteine in a dose-dependent manner. Moreover, superoxide dismutase (SOD, 200 U/mL), a scavenger of superoxide anions, reduced homocysteine-induced inhibition. L-Arginine (3 mmol/L), a precursor of nitric oxide (NO), also attenuated the impairment of vasorelaxation induced by homocysteine. However, in the combined presence of SOD and L-arginine, the inhibitory effect of homocysteine was reversed, which was very similar to the effect of 30 micromol/L captopril. These results suggest that captopril can prevent the inhibition of endothelium-dependent relaxation induced by homocysteine in isolated rat aorta, which may be related to scavenging oxygen free radicals and enhancing NO production.