Effect of L-dopa on plasma homocysteine in PD patients: relationship to B-vitamin status

BACKGROUND

The antiparkinsonian drug L-dopa causes increased cellular synthesis of homocysteine and consequent hyperhomocysteinemia in rats. This effect of L-dopa on plasma homocysteine is accentuated under conditions of impaired homocysteine metabolism such as folate deficiency.

OBJECTIVE

To investigate the effect of L-dopa administration and B-vitamin status on plasma homocysteine concentrations in humans with PD.

METHODS

Plasma homocysteine, folate, vitamin B(12), and pyridoxal-5'-phosphate (PLP) concentrations were determined in 40 individuals diagnosed with idiopathic PD who were being treated as outpatients at the Boston University Medical Center Neurology Clinic. Twenty of the patients were on L-dopa therapy (treatment group) and 20 were L-dopa-naive (control group).

RESULTS

The mean plasma homocysteine concentration was higher in the treatment group than in the controls (p = 0.018). Plasma homocysteine was correlated with plasma folate, vitamin B(12), and PLP concentrations in the treatment group (p <or= 0.007) but not in the controls.

CONCLUSION

L-Dopa can cause hyperhomocysteinemia in PD patients, the extent of which is influenced by B-vitamin status. The B-vitamin requirements necessary to maintain normal plasma homocysteine concentrations are higher in L-dopa-treated patients than in those not on L-dopa therapy. B-Vitamin supplements may be warranted for PD patients on L-dopa therapy.

Folic acid fortification increases red blood cell folate concentrations in the Framingham study

In 1996 the Food and Drug Administration (FDA) issued a regulation to take effect in January 1998 that all enriched cereal grain products include 140 microg of folic acid/100 g. The present cross-sectional study was undertaken to assess the effect of this fortification on RBC folate concentrations in the Framingham Offspring Cohort. Among those who did not take B-vitamin supplements, we compared RBC folate in 561 individuals who were examined before implementation of the FDA mandatory folic acid fortification (not exposed) vs. 354 individuals who were examined after implementation of fortification (exposed). We calculated the prevalence of deficient (<160 microg/L, 362.6 nmol/L) and acceptable (>200 microg/L, 453.2 nmol/L) RBC folate concentrations in both groups. Those exposed to folic acid fortification had a mean RBC folate of 450.0 microg/L (1019.7 nmol/L), a value 38% higher than the mean RBC folate of 325.3 microg/L (737.1 nmol/L) in those who were not exposed to fortification (P < 0.001). The prevalence of individuals with deficient RBC folate was 4.9% in the group not exposed to fortification compared with 1.9% in the group exposed to fortification (P < 0.02), and the prevalence of individuals with acceptable RBC folate was 87.0% in the group not exposed to fortification compared with 96.1% in the group exposed to fortification (P < 0.001). Similar results were seen in individuals who used supplements containing B-vitamins. The results of this study showed that in this cohort, the introduction of folic acid fortification significantly improved folate nutritional status measured as RBC folate.

Plasma homocysteine, B vitamins, and amino acid concentrations in cats with cardiomyopathy and arterial thromboembolism

Arterial thromboembolism (ATE) is a common complication of cats with cardiomyopathy (CM), but little is known about the pathophysiology of ATE. In people, high plasma concentrations of homocysteine and low B vitamin concentrations are risk factors for peripheral vascular disease. In addition, low plasma arginine concentrations have been linked to endothelial dysfunction. The purpose of this study was to compare concentrations of homocysteine, B vitamins, and amino acids in plasma of normal cats to those of cats with CM and ATE. Plasma concentrations of homocysteine, vitamin B6, vitamin B12, folate, and amino acids were measured in 29 healthy cats, 27 cats with CM alone, and 28 cats with both CM and ATE. No differences were found between groups in homocysteine or folate. Mean vitamin B12 concentration (mean +/- standard deviation) was lower in cats with ATE (866 +/- 367 pg/mL) and cats with CM (939 +/- 389 pg/mL) compared with healthy controls (1,650 +/- 700 pg/mL; P < .001). Mean vitamin B6 concentration was lower in cats with ATE (3,247 +/- 1.215 pmol/mL) and cats with CM (3,200 +/- 906 pmol/mL) compared with healthy control animals (4,380 +/- 1,302 pmol/mL; P = .005). Plasma arginine concentrations were lower in cats with ATE (75 +/- 33 nmol/mL) compared with cats with CM (106 +/- 25 nmol/mL) and healthy control animals (96 +/- 25 nmol/ mL; P < .001). Vitamin B12 concentration was significantly correlated with left atrial size. We interpret the results of this study to suggest that vitamin B12 and arginine may play a role in CM and ATE of cats.

Effect of dietary patterns on serum homocysteine: results of a randomized, controlled feeding study

BACKGROUND

Elevated blood levels of homocysteine are associated with an increased risk of atherosclerotic cardiovascular disease. Although numerous studies have assessed the impact of vitamin supplements on homocysteine, the effect of dietary patterns on homocysteine has not been well studied.

METHODS AND RESULTS

During a 3-week run-in, 118 participants were fed a control diet, low in fruits, vegetables, and dairy products, with a fat content typical of US consumption. During an 8-week intervention phase, participants were then fed 1 of 3 randomly assigned diets: the control diet, a diet rich in fruits and vegetables but otherwise similar to control, or a combination diet rich in fruits, vegetables, and low-fat dairy products and reduced in saturated and total fat. Between the end of run-in and intervention periods, mean change in homocysteine was +0.46 micromol/L in the control diet, +0.21 micromol/L in the fruits and vegetables diet (P=0.47 compared with control), and -0.34 micromol/L in the combination diet (P=0.03 compared with control, P=0.12 compared with the fruits and vegetables diet). In multivariable regression models, change in homocysteine was significantly and inversely associated with change in serum folate (P=0.03) but not with change in serum vitamin B(12) (P=0.64) or pyridoxal 5' phosphate, the coenzyme form of vitamin B(6) (P=0.83).

CONCLUSIONS

Modification of dietary patterns can have substantial effects on fasting levels of total serum homocysteine. These results provide additional insights into the mechanisms by which diet might influence the occurrence of atherosclerotic cardiovascular disease.

A prospective study on folate, B12, and pyridoxal 5'-phosphate (B6) and breast cancer

To investigate the incidence of breast cancer and prediagnostic serum levels of folate, B12, and pyridoxal 5'-phosphate (B6), we conducted a nested case-control study using resources from the Washington County (Maryland) serum bank. In 1974, 12,450 serum specimens were donated, and in 1989, 14,625 plasma specimens were donated by female residents of Washington County. One hundred ninety-five incident breast cancer cases and 195 controls were matched by age, race, menopausal status at donation, and cohort participation as well as by date of blood donation. In both cohorts and all menopausal subgroups, median B12 concentrations were lower among cases than controls. Differences reached statistical significance only among women who were postmenopausal at donation (1974 cohort, 413 versus 482 pg/ml, P = 0.03; 1989 cohort, 406 versus 452 pg/ml, P = 0.02). Among women postmenopausal at blood donation, observed associations of B12 suggested a threshold effect with increased risk of breast cancer in the lowest one-fifth compared to the higher four-fifths of the control distribution [lowest versus highest fifth: 1974 cohort, matched odds ratio = 4.00 (95% confidence interval = 1.05-15.20); 1989 cohort, matched odds ratio = 2.25 (95% confidence interval = 0.86-5.91)]. We found no evidence for an association between folate, B6, and homocysteine and breast cancer. Findings suggested a threshold effect for serum B12 with an increased risk of breast cancer among postmenopausal women in the lowest one-fifth compared to the higher four-fifths of the control distribution. These results should stimulate further investigations of potentially modifiable risk factors, such as these B-vitamins, for prevention of breast cancer.

Treatment of hyperhomocysteinemia in renal transplant recipients. A randomized, placebo-controlled trial

BACKGROUND

Stable renal transplant recipients have an excess prevalence of hyperhomocysteinemia, which is a risk factor for arteriosclerosis.

OBJECTIVE

To determine the effect of treatment with 1) vitamin B6 or 2) folic acid plus vitamin B12 on fasting and post-methionine-loading plasma total homocysteine levels in renal transplant recipients.

DESIGN

Block-randomized, placebo-controlled, 2 x 2 factorial study.

SETTING

University-affiliated transplantation program.

PATIENTS

29 clinically stable renal transplant recipients.

INTERVENTION

Patients were randomly assigned to one of four regimens: placebo (n = 8); vitamin B6, 50 mg/d (n = 7); folic acid, 5 mg/d, and vitamin B12, 0.4 mg/d (n = 7); or vitamin B6, 50 mg/d, folic acid, 5 mg/d, and vitamin B12, 0.4 mg/d (n = 7).

MEASUREMENTS

Fasting and 2-hour post-methionine-loading plasma total homocysteine levels.

RESULTS

Vitamin B6 treatment resulted in a 22.1% reduction in geometric-mean post-methionine-loading increases in plasma total homocysteine levels (P = 0.042), and folic acid plus vitamin B12 treatment caused a 26.2% reduction in geometric-mean fasting plasma total homocysteine levels (P = 0.027). These results occurred after adjustment for age; sex; and pretreatment levels of total homocysteine, B vitamins, and creatinine.

CONCLUSIONS

Vitamin B6 should be added to the combination of folic acid and vitamin B12 for effective reduction of both post-methionine-loading and fasting plasma total homocysteine levels in renal transplant recipients.

Elevated fasting total plasma homocysteine levels and cardiovascular disease outcomes in maintenance dialysis patients. A prospective study

There is an excess prevalence of hyperhomocysteinemia in dialysis-dependent end-stage renal disease (ESRD) patients. Cross-sectional studies of the relationship between elevated total homocysteine (tHcy) levels and prevalent cardiovascular disease (CVD) in this patient population suffer from severe methodologic limitations. No prospective investigations examining the association between tHcy levels and the subsequent development of arteriosclerotic CVD outcomes among maintenance dialysis patients have been reported. To assess whether elevated plasma tHcy is an independent risk factor for incident CVD in dialysis-dependent ESRD patients, we studied 73 maintenance peritoneal dialysis or hemodialysis patients who received a baseline examination between March and December 1994, with follow-up through April 1, 1996. We determined the incidence of nonfatal and fatal CVD events, which included all validated coronary heart disease, cerebrovascular disease, and abdominal aortic/lower-extremity arterial disease outcomes. After a median follow-up of 17.0 months, 16 individuals experienced at least one arteriosclerotic CVD event. Cox proportional-hazards regression analyses, unadjusted and individually adjusted for creatinine, albumin, and total cholesterol levels, total/HDL cholesterol ratio, dialysis adequacy/residual renal function, baseline CVD, and the established CVD risk factors (ie, age, sex, smoking, hypertension, diabetes/glucose intolerance, and dyslipidemia) revealed that tHcy levels in the upper quartile (> or = 27.0 mumol/L) versus the lower three quartiles (< 27.0 mumol/L) were associated with relative risk estimates (hazards ratios, with 95% confidence intervals for the occurrence of (pooled) nonfatal and fatal CVD ranging from 3.0 to 4.4; 95% confidence intervals (1.1-8.1) to (1.6-12.2). We conclude that the markedly elevated fasting tHcy levels found in dialysis-dependent ESRD patients may contribute independently to their excess incidence of fatal and nonfatal CVD outcomes.

Excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients

Hyperhomocysteinemia, either fasting or after methionine loading, may contribute to the increased incidence of cardiovascular disease events experienced by renal transplant recipients. Limited data are available on fasting homocysteine (Hcy) levels, and none on postmethionine-loading Hcy levels, in these patients. We assessed the prevalence and potential determinants of fasting and postmethionine-loading hyperhomocysteinemia in 29 stable renal transplant recipients and 58 age- and sex-matched, population-based controls free of renal disease with serum creatinine levels of 1.5 mg/dL or less. Total (t) plasma Hcy was determined fasting and 2 hours after methionine loading, along with fasting determinations of the B-vitamin cofactors/substrates for Hcy metabolism, ie, pyridoxal 5'-phosphate, B-12, and folate and serum creatinine. Geometric mean fasting (18.1 versus 9.8 microM, P < .001) and postmethionine-loading increase (22.0 versus 15.2, P = .001) in tHcy levels were significantly greater in the renal transplant recipients, as were the prevalence odds (with 95% confidence intervals) for fasting [14.8 (3.4-64.7)], postmethionine loading [6.9 (1.5-32.8)], combined fasting and postmethionine-loading [18.0 (2.3-142.1)] hyperhomocysteinemia, and inadequate circulating folate [4.2 (1.1-16.5)] or pyridoxal 5'-phosphate [3.2 (0.9-11.0) status. Correlation analyses suggested important potential relationships between creatinine and both fasting (+0.64, P < .001) and postmethionine-load increase (+0.38, P = .045) in tHcy, folate and fasting (-0.41, P = .025) tHcy, and pyridoxal 5'-phosphate and postmethionine-loading increase (-0.33, P = .091) in tHcy. We conclude that there is an excess prevalence of fasting and postmethionine-loading hyperhomocysteinemia in stable renal transplant recipients. Renal function is related to both fasting and postmethionine loading-hyperhomocysteinemia, inadequate folate status is associated with fasting hyperhomocysteinemia, and inadequate vitamin B-6 status may be related to postmethionine-loading hyperhomocysteinemia in this patient population.

Abnormal homocysteine metabolism in rheumatoid arthritis

OBJECTIVE

To assess total homocysteine (tHcy) metabolism in patients with rheumatoid arthritis (RA).

METHODS

Assessments were performed to determine the fasting levels of tHcy and the increase in tHcy in response to methionine (Met) challenge in blood samples from 28 patients with RA and 20 healthy age-matched control subjects.

RESULTS

Fasting levels of tHcy were 33% higher in the RA patients than in the control subjects (mean +/- SD 11.7 +/- 1.5 nmoles/ml versus 8.8 +/- 1.1 nmoles/ml; P < 0.01). Four hours after Met challenge, the increase in plasma tHcy levels (delta tHcy) was higher in the RA patients (20.9 +/- 10.4 nmoles/ml) than in the control subjects (15.5 +/- 1.6 nmoles/ml) (P < 0.02). In a subgroup analysis, the delta tHcy in patients taking methotrexate (12.9 +/- 2.2 nmoles/ml) did not differ from that in the control group, while the delta tHcy in patients not taking methotrexate (25.3 +/- 1.7 nmoles/ml) was significantly higher (P < 0.0001).

CONCLUSION

Elevated tHcy levels occur commonly in patients with RA, and may explain some of the increased cardiovascular mortality seen in such patients. Studies of the prevalence and mechanism of hyperhomocysteinemia in RA are warranted.

Effect of L-Dopa and the catechol-O-methyltransferase inhibitor Ro 41-0960 on sulfur amino acid metabolites in rats

L-Dopa is the most effective drug known for the treatment of Parkinson's disease. However, the large doses required to treat this neurodegenerative disorder can significantly affect tissue concentrations of sulfur amino acid metabolites due to peripheral and central O-methylation. These effects include decreases in tissue concentrations of the biochemical methyl donor S-adenosylmethionine (SAM), increases in tissue concentrations of the methylation inhibitor S-adenosylhomocysteine (SAH), and increases in plasma concentrations of homocysteine, recently identified as an independent risk factor for vascular disease. In the present study, the ability of the catechol-O-methyltransferase inhibitor Ro 41-0960 to prevent L-Dopa-induced changes in SAM, SAH, and homocysteine concentrations was determined in rats. Rats were injected intraperitoneally with Ro 41-0960 or vehicle 30 min prior to an intraperitoneal injection of L-Dopa or vehicle. One hour after the second injection, the rats were killed and their brains, livers, spleens, kidneys, and plasma collected. SAM and SAH concentrations were then determined in discrete brain regions and peripheral tissues, and total homocysteine concentrations were determined in plasma. In the rats treated with only L-Dopa, decreased SAM concentrations and increased SAH concentrations were found in all brain regions and peripheral tissues measured, and increased homocysteine concentrations were found in plasma, consistent with previous reports. In rats pretreated with Ro 41-0960, however, these L-Dopa-induced effects on sulfur amino acid metabolite concentrations were attenuated or prevented entirely. It remains to be determined if this sparing effect of Ro 41-0960 on sulfur amino acid metabolites has clinical significance.

Plasma homocysteine as a risk factor for atherothrombotic events in systemic lupus erythematosus

BACKGROUND

The aim of this study was to assess whether plasma homocysteine is a risk factor for stroke and other thrombotic events in patients with systemic lupus erythematosus (SLE)--a condition known to be associated with premature atherothrombotic complications.

METHODS

In this prospective study, we investigated the association between homocysteine and risk of stroke and thrombotic events in 337 SLE patients in the Hopkins Lupus Cohort Study, with follow-up of 1619 person-years (mean 4.8 [SD 1.7] years). Each patient had four follow-up assessments per year to obtain information about established risk factors for thrombosis and coronary artery disease. The prospectively defined endpoints were occurrence of stroke and arterial or venous thrombotic events between 1987 and 1995. Blood samples were taken at study entry from fasting patients. Plasma homocysteine, folate, vitamin B12, and pyridoxal 5'-phosphate (PLP) concentrations were measured. Raised homocysteine concentrations were defined as more than 14.1 mumol/L.

FINDINGS

93% of the study population were women, 54% African American, and 45% white. The mean age of participants was 34.9 (SD 11.7) years. During follow-up there were 29 cases of stroke and 31 arterial thrombotic events. Raised homocysteine concentrations were found in 51 (15%) SLE patients. The log-transformed total homocysteine concentrations correlated with serum folate (r = 0.31, p = 0.0001). In univariate analyses, raised homocysteine concentrations were significantly associated with stroke (odds ratio 2.24 [95% CI 1.22-4.13], p = 0.01) and arterial thrombotic events (3.74 [1.96-7.13], p = 0.0001). After adjustment for established risk factors, total plasma homocysteine concentrations remained an independent risk factor for stroke (2.44 [1.04-5.75], p = 0.04) and arterial thromboses (3.49 [0.97-12.54], p = 0.05).

INTERPRETATION

Homocysteine is a potentially modifiable, independent risk factor for stroke and thrombotic events in patients with SLE.

Hyperhomocysteinemia, hyperfibrinogenemia, and lipoprotein (a) excess in maintenance dialysis patients: a matched case-control study

Maintenance dialysis patients experience an exceedingly high incidence of arteriosclerotic cardiovascular disease (CVD) events that are poorly predicted by traditional CVD risk factor indices. We evaluated the prevalence of three non-traditional CVD risk factors, i.e. hyperhomocysteinemia, hyperfibrinogenemia, and lipoprotein (a) Lp(a)) excess, and combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, in maintenance dialysis patients. Fasting total plasma homocysteine (Hcy), fibrinogen, Lp(a), glucose, and total and HDL cholesterol levels, and traditional CVD risk factor (i.e. glucose tolerance, smoking, hypertension, dyslipidemia) prevalences were assessed in 71 dialysis patients and 71 age, sex, and race matched Framingham Study controls free of clinical renal disease, with normal serum creatinine (< or = 1.5 mg/dl). Mean plasma Hcy 23.7 vs. 9.9 microM, P = 0.0001), fibrinogen (457 vs. 309 mg/dl, P = 0.0001), and Lp(a) (30 vs. 17 mg/dl, P = 0.0070) levels were substantially increased in the dialysis patients. Matched odds ratios (with 95% confidence intervals), dialysis patients/controls, for hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess, alone or combined, were markedly greater in the dialysis patients, with no evidence of confounding by the traditional CVD risk factors: hyperhomocysteinemia, 105.0 (29.9-368.9); hyperfibrinogenemia, 16.6 (6.6-42.0); Lp(a) excess, 3.5 (1.5-8.4); all three combined 35.0 (5.7-199.8). Given in vitro evidence that Hcy, Lp(a), and fibrinogen interact to promote atherothrombosis, combined hyperhomocysteinemia, hyperfibrinogenemia, and Lp(a) excess may contribute to the high incidence of vascular disease sequelae experienced by dialysis patients, which is inadequately explained by traditional CVD risk factors. Controlled, prospective studies of well-characterized maintenance dialysis cohorts are urgently required to substantiate this hypothesis.

Folate status is the major determinant of fasting total plasma homocysteine levels in maintenance dialysis patients

Limited data are available on the determinants of homocysteinemia or the association between plasma homocysteine (Hcy) levels and prevalent cardiovascular disease (CVD) in maintenance dialysis patients. We assessed etiology of renal failure, residual renal function and dialysis adequacy-related variables, and vitamin status, as determinants of fasting total plasma homocysteine (Hcy) in 75 maintenance dialysis patients. We also assessed the potential interactive effect on plasma Hcy of folate status and a common mutation (ala to val; homozygous val-val frequency approximately 10%) in methylenetetrahydrofolate reductase (MTHFR), a folate-dependent enzyme crucial for the remethylation of homocysteine (Hcy) to methionine. Lastly, we evaluated whether the Hcy levels differed amongst these patients in the presence or absence of prevalent CVD, after adjustment for the traditional CVD risk factors. Fasting total plasma Hcy, folate, pyridoxal 5'-phosphate (PLP; active B6), B12, creatinine, glucose, total and HDL cholesterol levels, and presence of the ala to val MTHFR mutation were determined, and clinical CVD and CVD risk factor prevalence were ascertained. General linear modelling/analysis of covariance revealed: (1) folate status and serum creatinine were the only significant independent predictors of fasting Hcy; (2) there was a significant interaction between presence of the val mutation and folate status, i.e., among patients with plasma folate below the median (< 29.2 ng/ml), geometric mean Hcy levels were 33% greater (29.0 vs. 21.8 microM, P = 0.012) in the pooled homozygotes (val-val) and heterozygotes (ala-val) for the ala to val mutation, vs. normals (ala-ala); (3) there was no association between prevalent CVD and plasma Hcy. Given potentially intractable survivorship effects, prospective cohort studies will be required to clarify the relationship between plasma Hcy or any putative CVD risk factor, and incident CVD in dialysis patients. If a positive association between plasma Hcy and incident CVD can be established in maintenance dialysis patients, the current data provide a rationale for additional folic acid supplementation in this patient population.

Lack of effect of oral N-acetylcysteine on the acute dialysis-related lowering of total plasma homocysteine in hemodialysis patients

Hyperhomocysteinemia refractory to standard B-vitamin supplementation treatment persists in > or = 75% of maintenance dialysis patients, potentially increasing their risk for atherothrombotic sequelae. We examined whether predialysis administration of oral N-acetylcysteine (NAC), which acutely increases the non-protein bound, dialyzable fraction of plasma homocysteine, might augment the homocysteine-lowering effect of dialysis therapy. Predialysis and postdialysis total plasma homocysteine levels were determined on a control day, and on a day in which oral NAC (1200 mg) was administered predialysis in n = 11 maintenance hemodialysis patients. Although NAC treatment had no significant effect on hemodialysis removal of plasma homocysteine (P = 0.594), we observed a 16% reduction (P = 0.033) in non-fasting prehemodialysis total plasma homocysteine on the NAC treatment vs. non-treatment day. Longer term, placebo-controlled confirmation of this finding will be required to evaluate the possible chronic homocysteine-lowering efficacy of NAC treatment in hemodialysis patients.

Hyperhomocysteinemia in chronic alcoholism: correlation with folate, vitamin B-12, and vitamin B-6 status

Serum homocysteine concentrations have been shown to be a sensitive functional indicator of intracellular folate, vitamin B-12, and vitamin B-6 status. Chronic alcoholism is known to interfere with one-carbon metabolism, for which the above vitamins serve as coenzymes. In the present study, these vitamins were assessed in 32 chronic alcoholics and 31 healthy volunteers by measuring blood vitamin concentrations as well as serum homocysteine concentrations. In chronic alcoholics, serum pyridoxal 5'-phosphate and red blood cell folate concentrations were significantly lower than in the control subjects (P < 0.001 and P = 0.008, respectively). Mean serum homocysteine was twice as high in chronic alcoholics than in nondrinkers (P < 0.001). Beer consumers had significantly lower concentrations of homocysteine compared with drinkers of wine or spirits (P = 0.05). These results suggest that by interfering with folate or vitamin B-6 metabolism, chronic alcohol intake may impair the disposal of homocysteine through the transmethylation or transsulfuration pathways.

High dose-B-vitamin treatment of hyperhomocysteinemia in dialysis patients

Hyperhomocysteinemia, an arteriosclerotic risk factor, persists in 75% of dialysis patients despite routine low dose supplementation with the B-vitamin co-factors/substrates for homocysteine (Hcy) metabolism, and normal or supernormal plasma status of these vitamins (Atherosclerosis 114:93, 1995). We conducted a placebo-controlled eight-week trial of the effect on plasma homocysteine of adding supraphysiologic dose folic acid (15 mg/day), B-6 (100 mg/day), and B-12 (1 mg/day) to the usual daily dosing of 1 mg folic acid, 10 mg B-6, and 12 micrograms B-12, in 27 hyperhomocysteinemic dialysis patients. Total plasma homocysteine was measured at baseline, and after four and eight weeks. Blinded analyses revealed no evidence of toxicity in the group randomized to supraphysiologic dose B-vitamin supplementation. Plasma homocysteine was significantly reduced after both four weeks (-29.8% vs. -2.0%; P = 0.0024) and eight weeks (-25.8% vs. +0.6%; P = 0.0009) of active versus placebo treatment. Also, 5 of 15 treated versus 0 of 12 placebo group patients had their plasma Hcy reduced to within the normative range (< 15 mumol/liter). Supraphysiologic doses of B-vitamins may be required to correct hyperhomocysteinemia in dialysis patients.

Net uptake of plasma homocysteine by the rat kidney in vivo

Hyperhomocysteinemia is a common finding in dialysis-dependent end-stage renal disease (ESRD) patients, but its etiology and refractoriness to standard homocysteine-lowering B-vitamin therapy are poorly understood. In the absence of actual in vivo data, it has been hypothesized that loss of normal renal parenchymal uptake and metabolism of homocysteine is an important determinant of hyperhomocysteinemia in ESRD, given that urinary homocysteine excretion by healthy kidneys is trivial. We assessed net renal uptake and metabolism of homocysteine using an established rat model for measuring arteriovenous amino acid differences across the rat kidney, along with simultaneous determination of renal plasma flow, urine flow, and urinary homocysteine concentration. Substantial homocysteine uptake and metabolism by normal rat kidneys was demonstrated, and we also confirmed that urinary homocysteine excretion is minimal. These data suggest that loss of the sizable homocysteine metabolizing capacity of the intact kidneys may be an important determinant of the refractory, potentially atherothrombotic hyperhomocysteinemia frequently observed in ESRD.

Post-methionine load hyperhomocysteinemia in persons with normal fasting total plasma homocysteine: initial results from the NHLBI Family Heart Study

Hyperhomocysteimia, either fasting or after oral methionine loading, appears to be an independent risk factor for coronary heart disease (CHD). It remains unclear whether fasting total homocysteine determination alone adequately detects the full spectrum of hyperhomocysteinemic individuals. We measured fasting and 4-h post methionine loading (0.1 g L-methionine/kg body weight) total plasma homocysteine in 274 participants in The NHLBI Family Heart Study, a population-based investigation of genetic and non-genetic determinants of CHD. Of the total number (n = 47) of hyperhomocysteinemic persons, 43% (20/47) were identified only by methionine loading, while 32% (15/47) of the total number, and 75% of those with post-methionine loading hyperhomocysteinemia only (15/20), had fasting total homocysteine concentrations below the 75th percentile (10.7 mumol/l). We conclude that fasting total plasma homocysteine determination alone fails to identify a sizable percentage (> 40%) of persons who may have clinically relevant hyperhomocysteinemia post methionine loading.

Abnormal vitamin B6 status in rheumatoid cachexia. Association with spontaneous tumor necrosis factor alpha production and markers of inflammation

OBJECTIVE

To compare vitamin B6 levels in rheumatoid arthritis (RA) patients and healthy control subjects.

METHODS

We measured levels of vitamin B6 in 23 adults with well-controlled RA, and in 23 healthy control subjects matched for age, sex, race, and weight.

RESULTS

Although plasma folate and vitamin B12 concentrations and erythrocyte B6 activity coefficients were similar in the patients and controls, plasma levels of pyridoxal-5'-phosphate (PLP) were lower in the RA patient group (mean +/- SD 46.1 +/- 48.1 versus 69.3 +/- 58.4 nmoles/liter; P < 0.004). In multivariate analyses, PLP was inversely associated with tumor necrosis factor alpha (TNF alpha) production by peripheral blood mononuclear cells (PBMC) (P < 0.001), after adjustment for age, pain score, erythrocyte sedimentation rate, and use of nonsteroidal antiinflammatory drugs.

CONCLUSION

PLP levels are reduced in patients with RA. This reduction is associated with TNF alpha production by PBMC.

Vitamin B-6 deficiency vs folate deficiency: comparison of responses to methionine loading in rats

The plasma homocysteine response to methionine loading was assessed in vitamin B-6- and folate-deficient rats. Rats fed vitamin B-6- or folate-deficient diets for 4 wk were administered a gastric gavage of methionine (100 mg/kg body wt). Subsequent plasma analyses revealed a peak post-methionine load increase in plasma homocysteine concentration of > 300 mumol/L in the vitamin B-6-deficient rats. Folate-deficient rats exhibited no significant changes in plasma homocysteine after the load. These disparate responses can be explained by the observed increase in hepatic S-adenosylmethionine (SAM) concentration because of the load. In vitamin B-6 deficiency, increased SAM inhibits homocysteine remethylation, which, in conjunction with the impaired homocysteine catabolism due to the deficiency and the increased synthesis of homocysteine due to the methionine load, leads to a large elevation of homocysteine in the blood. In folate deficiency, increased SAM activates homocysteine catabolism, which compensates for the increased synthesis of homocysteine due to the load and thus no change in blood homocysteine is observed. These results have significant bearing on the interpretation of both positive and negative responses to methionine loading in humans.

Folate-deficiency-induced homocysteinaemia in rats: disruption of S-adenosylmethionine's co-ordinate regulation of homocysteine metabolism

In a recent hypothesis [Selhub and Miller (1992) Am. J. Clin. Nutr. 55, 131-138], we proposed that homocysteinaemia arises from an interruption in S-adenosylmethionine's (AdoMet) coordinate regulation of homocysteine metabolism. The present study was undertaken to test a prediction of this hypothesis, that homocysteinaemia due to folate deficiency results from impaired homocysteine remethylation due to the deficiency and impaired synthesis of AdoMet, with the consequent inability of this metabolite to function as an activator of homocysteine catabolism through cystathionine synthesis. Rats were made folate-deficient by feeding them with a folate-free amino-acid-defined diet supplemented with succinylsulphathiazole. After 4 weeks, the deficient rats exhibited a 9.8-fold higher mean plasma homocysteine concentration and a 3.2-fold lower mean hepatic AdoMet concentration compared with folate-replete controls. Subsequent supplementation for 3 weeks of the folate-deficient rats with increasing levels of folate in the diet resulted in graded decreases in plasma homocysteine levels, accompanied by graded increases in hepatic AdoMet levels. Thus plasma homocysteine and hepatic AdoMet concentrations were inversely correlated as folate status was modified. In a second experiment, the elevation of plasma homocysteine in the deficient rats was found to be reversible within 3 days by intraperitoneal injections of ethionine. This effect of ethionine is thought to be exerted through S-adenosylethionine, which is formed in the liver of these rats. Like AdoMet, S-adenosylethionine is an activator of cystathionine beta-synthase and will effectively promote the catabolism of homocysteine through cystathionine synthesis. In crude liver homogenates of the rats treated with ethionine, cystathionine beta-synthase activity was 3-fold higher than that measured in homogenates from vehicle-treated controls.

Metabolism of estradiol and estrone in organ cultures of dorsolateral and ventral prostate of untreated and sex hormone-implanted rats

Since dorsolateral but not ventral prostate undergoes estrogen-induced dysplasia in the androgen-supported Noble rat in 16 weeks, we studied estrogen metabolism by these tissues from untreated and sex hormone-implanted animals. We incubated 8.5 nM [6,7-3H]-labeled estradiol (E2) and estrone (E1) for 21 hours in serum-free, prostate-lobe cultures and 8.5 nM [2-3H]E2 with explants from untreated rats and animals treated with testosterone, 5 alpha-dihydrotestosterone, or E2 plus testosterone. Untreated rat ventral prostate metabolized 3.7 times as much E2 to E1 as dorsolateral prostate, whereas the latter tissue converted 2.5 times as much E1 to E2 as the former. After dorsolateral prostate culture with 8.5 nM [6,7-3H]-labeled E2 or E1, 0.6 M KCl-extracted, Sephadex G25-excluded nuclear protein bound preponderantly E2, whereas the counterpart nuclear protein fraction from ventral prostate explants incubated with E2 bound substrate and E1 almost equally. The combination sex hormone treatment decreased E2 metabolism and increased its uptake by the dysplastic dorsolateral prostate. Implantation of 5 alpha-dihydrotestosterone, but not of testosterone, also decreased E2 metabolism to E1 by dorsolateral prostate cultures. Treatments with E2 plus testosterone and with 5 alpha-dihydrotestosterone changed E2 uptake/E1 retention in dorsolateral prostate explants from 2.4 to 7.4 and 8.5, respectively. C-2 tritium release marking the 2,3-catechol estrogen pathway was greater for ventral than dorsolateral prostate, but was unaffected by the sex hormone treatments.(ABSTRACT TRUNCATED AT 250 WORDS)