Plasma tHcy Concentrations Research Articles

Determinants of plasma total homocysteine concentration in the Framingham Offspring cohort

Established determinants of fasting total homocysteine (tHcy) concentration include folate and vitamin B-12 status, serum creatinine concentration, and renal function. Our objective was to examine the relation between known and suspected determinants of fasting plasma tHcy in a population-based cohort. We examined the relations between fasting plasma tHcy concentrations and nutritional and other health factors in 1960 men and women, aged 28-82 y, from the fifth examination cycle of the Framingham Offspring Study between 1991 and 1994, before the implementation of folic acid fortification. Geometric mean tHcy was 11% higher in men than in women and 23% higher in persons aged > or = 65 y than in persons aged < 45 y (P < 0.001). tHcy was associated with plasma folate, vitamin B-12, and pyridoxal phosphate (P for trend < 0.001). Dietary folate, vitamin B-6, and riboflavin were associated with tHcy among non-supplement users (P for trend < 0.01). The tHcy concentrations of persons who used vitamin B supplements were 18% lower than those of persons who did not (P < 0.001). tHcy was positively associated with alcohol intake (P for trend = 0.004), caffeine intake (P for trend < 0.001), serum creatinine (P for trend < 0.001), number of cigarettes smoked (P for trend < 0.001), and antihypertensive medication use (P < 0.001). Our study confirmed, in a population-based setting, the importance of the known determinants of fasting tHcy and suggested that other dietary and lifestyle factors, including vitamin B-6, riboflavin, alcohol, and caffeine intakes as well as smoking and hypertension, influence circulating tHcy concentrations.

Effect ofMTHFR genotypes and hyperhomocysteinemia on patient and graft survival in kidney transplant recipients

The total homocysteine (tHcy) plasma level, which is partly determined by the MTHFR 677C-->T genotype, may be associated with vascular disease. We prospectively examined the influence of MTHFR genotypes (677C-->T, 1298A-->C) and tHcy plasma concentration on all cause mortality and graft outcomes of renal transplant recipients. Baseline tHcy plasma levels of 189 patients (three groups with either the MTHFR 677CC, CT or TT genotype, including 63 patients in each group, were matched for age, gender, body mass index and creatinine clearance at baseline), were obtained between September 1996 and May 1997. Follow-up data (time until return to dialysis therapy, time and cause of death) were collected from April to June 1999. Kaplan-Meier survival estimations were calculated and plotted, the groups (three MTHFR 677C-->T genotype groups, or three MTHFR 1298A-->C genotype groups, or two groups with tHcy plasma levels above/below 15 micromol/L) were compared by log-rank test. Age, gender, body mass index (BMI), time since transplantation, serum creatinine, creatinine clearance, combined MTHFR 677C-->T/1298A-->C genotypes, tHcy, folate and vitamin B12 plasma levels were evaluated with regard to graft and patient survival in a multivariate Cox-proportional hazard regression model. During the follow-up period of 2.26 +/- 0.66 years, 9 patients died (5 in the TT, 2 in the CT and 2 in the CC genotype group; P = 0.34) and 22 returned to dialysis treatment (7 in the TT, 9 in the CT and 6 in the CC genotype group; P = 0.65). There was also no influence of MTHFR 1298A-->C genotypes (AA genotype, 114 patients; AC genotype, 64 patients; CC genotype, 11 patients) on patient or graft survival (P = 0.7087 and P = 0.1633, respectively). Two of 93 patients with a tHcy plasma level < or = 15 micromol/L died, in contrast to 7 of 96 patients in the tHcy > 15 micromol/L group, P = 0.0778. Two patients in the low tHcy group had to return to dialysis, in contrast to 20 patients in the high tHcy group (P = 0.0001). In the multivariate model there was no significant predictor of patient survival, and the serum creatinine was the only predictor of graft survival (P < 0.0001). In summary, our study shows that neither MTHFR 677C-->T/1298A-->C genotypes nor hyperhomocysteinemia are independently associated with patient or graft survival following kidney transplantation.

5,10-methylenetetrahydrofolate reductase common mutations, folate status and plasma homocysteine in healthy French adults of the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI.MAX) cohort

The 677cytosine mutation identified in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene has been frequently associated with an elevated plasma homocysteine concentration. The aim of the present study was to determine the impact of this MTHFR common mutation on plasma and erythrocyte folate (RCF) and plasma total homocysteine (tHcy) concentrations in healthy French adults. A cohort of 291 subjects living in the Paris area and participating in the Supplementation en Vitamines et Mineraux Antioxydants (SU.VI.MAX) study were analysed to assess the impact of MTHFR polymorphism 677C-->T on folate status and plasma tHcy concentration. The frequency of the mutant homozygote for 677C-->T polymorphism (677TT genotype) in the present cohort was 16.8%. There were significant differences in plasma tHcy between 677CC, 677CT and 677TT genotype groups. The RCF concentrations were significantly different between each genotype, the lowest levels being associated with the 677TT genotype. When segregated by gender, no differences in tHcy between homozygous 677TT, heterozygous 677CT and wild-type 677CC genotype groups in women were observed. The fasting tHcy in women was unrelated to the 677C-->T mutation. However, tHcy was significantly increased in men with the homozygous 677TT genotype. We also analysed the possible implication of a second new MTHFR polymorphism (1298A-->C) in subjects with mild hyperhomocysteinaemia (4th quartile of homocysteinaemia; tHcy >11.1 micromol/l). The polymorphism 1298A-->C did not have a notable effect on tHcy or on the RCF levels. Our observations confirm a relatively high frequency of the 677TT genotype in the French population. Women with this genotype did not show the same increase in tHcy observed in men. In the present study dietary folate intake was not measured. Thus, the interaction of dietary folate with the MTHFR genotype in the French population needs further study.

Methylenetetrahydrofolate reductase mutation (677C → T) negatively influences plasma homocysteine response to marginal folate intake in elderly women

Individuals who are homozygous for the methylenetetrahydrofolate reductase (MTHFR) 677C → T mutation have depressed serum folate (SF) and elevated plasma total homocysteine (tHcy) concentrations, which may affect folate requirements and increase the risk for coronary artery disease. A controlled metabolic study (14 weeks) using a depletion/repletion protocol was performed in women (aged 60 to 85 years, N = 33) to provide age-specific data on the effects of the MTHFR mutation on SF and tHcy status. Subjects consumed a moderately folate-deplete diet (118 μg/d) for 7 weeks, followed by 7 weeks of folate repletion with 200 or 415 μg/d provided as two different treatments. Following folate depletion, the mean SF concentration was lower for homozygous (P = .017) versus heterozygous subjects. Homozygotes for the 677C → T mutation showed a higher (P = .015) percent increase in plasma tHcy (44%) than heterozygous (20%) or normal (15%) subjects. At week 7, the mean plasma tHcy concentration was higher in homozygous subjects (12.5 ± 5.3 μmol/L, mean ± SD) versus the heterozygous (10.8 ± 3.8 μmol/L, P = .008) or normal (11.3 ± 2.7 μmol/L, P = .001) genotype groups. Following folate repletion, plasma tHcy concentrations were not different between genotype groups, despite a higher (P < .016) SF concentration in subjects with the homozygous genotype. These data suggest that older women who are homozygous for the MTHFR 677C → T mutation may be at risk for greater elevations in plasma tHcy in response to moderately low folate intake as compared with individuals with the normal or heterozygous genotypes. Copyright © 2000 by W.B. Saunders Company

Evaluation of the AxSYM Homocysteine Assay and Comparison with the IMx Homocysteine Assay

Increased plasma total homocysteine (tHcy), a sulfur amino acid, is an important risk factor for vascular disease (1) and for arterial and venous thromboembolism (2). Several techniques have been developed to measure plasma or serum tHcy concentrations (3). Given the extension of this determination to routine clinical chemistry laboratories, an immunoassay has been developed for use with the AxSYM analyzer (4). The AxSYM is a completely automated system, which allows immediate and continuous access. We evaluated the analytical performance of the automated AxSYM assay and compared it with the IMx Hcy assay (5), a method widely used for tHcy determination in laboratories. Both methods use reduction of protein-bound Hcy by dithiothreitol, conversion of Hcy to S -adenosylhomocysteine in the presence of adenosine catalyzed by hydrolase …

Plasma total homocysteine concentration and the risk of acute coronary events: the Kuopio Ischaemic Heart Disease Risk Factor Studytpdel

Results from prospective studies concerning the association between plasma total homocysteine (tHcy) concentration and coronary heart disease (CHD) are conflicting. The purpose of this study was to test the hypothesis that plasma tHcy is associated with an increased risk of acute coronary events in middle-aged men. We investigated this association in a prospective nested case-control study among Eastern Finnish men aged 42-60 years. Plasma tHcy measurements were carried out for 163 men who had an acute coronary event during an average 8 years and 11 months follow-up of the whole cohort and for 163 control subjects. Both the cases and the controls were from a cohort of 2005 men who had no clinical CHD at the Kuopio Ischaemic Heart Disease (KIHD) baseline. Men in the highest plasma tHcy concentration quarter had no increase in the risk of coronary events compared with men with lower tHcy concentrations (odds ratio = 0.88, 95% confidence interval 0.44-1.76). Average follow-up time before the first coronary event was 4.9 years (SD 3.2) in men in the highest plasma tHcy quarter and 5.5 years (SD 3.1) in men in the three lowest quarters (P = 0.368). We conclude that plasma tHcy is not associated with an increased risk of coronary events in the middle-aged male population in eastern Finland.

Plasma total homocysteine levels in postmenopausal women with unstable coronary artery disease

An elevated plasma total homocysteine (tHcy) level is considered a risk factor for coronary artery disease (CAD), but the relationship between plasma tHcy and well-defined CAD in women is still unclear. Plasma tHcy concentrations and the covariates serum folate, vitamin B12, and creatinine were analysed in 157 angiographically examined postmenopausal women with unstable CAD and in 101 healthy controls. At coronary angiography, 16% had normal vessels and 84% had coronary atherosclerosis. Mean plasma tHcy concentration (μmol/l, 95% confidence interval) did not differ in patients compared to controls (13.1 (12.3–13.8) vs. 12.5 (11.6–13.5)) or in patients with or without coronary atherosclerosis (13.3 (12.4–14.1) vs. 12.0 (10.8–13.2)). A trend to an increasing plasma tHcy with increasing degree of coronary atherosclerosis was attenuated after adjustment for age and the previous mentioned covariates. Odds ratio for the risk of coronary artery disease and coronary atherosclerosis in hyperhomocysteinemic patients (≥90th percentile in controls) was approximately 3. However, the confidence interval included unity in half of the groups and the significance was therefore difficult to judge. Receiver operating characteristics showed age to be the only variable with a significant discriminatory ability regarding the presence of coronary atherosclerosis (area 0.77). Mild hyperhomocysteinemia seems not to be related to the risk of unstable CAD in postmenopausal women. The trend towards higher plasma tHcy with increasing degree of coronary atherosclerosis may be a marker of the disease. In future studies adjustment for age and the other three covariates should be considered.

Folate Status of Elderly Women following Moderate Folate Depletion Responds Only to a Higher Folate Intake

Dietary Reference Intakes (DRI) for folate for elderly women have been based primarily on data extrapolated from studies in younger women. This study was conducted to provide the first age-specific data in elderly women (60-85 y) from a controlled metabolic study on which to base folate intake recommendations. Subjects (n = 33) consumed a moderately folate-deplete (118 microg/d) diet for 7 wk, followed by repletion diets providing either 200 or 415 microg folate/d as diet plus folic acid (FA) or a combination of FA and orange juice (OJ) for 7 wk (n = 30). Comparisons among and within groups were made for serum folate (SF), RBC folate and plasma total homocysteine (tHcy) concentrations. SF concentrations decreased significantly (P < 0.001) during depletion (65 +/- 15%). Postrepletion, the adjusted SF concentration for subjects consuming 415 microg folate/d was significantly greater (P = 0.003) than for subjects consuming 200 microg folate/d. RBC folate concentrations decreased (P < 0.001) during depletion (21 +/- 10%) and further (P < 0.001) during repletion (5 +/- 14%). During depletion, plasma tHcy concentrations increased significantly (P < 0.001) and an inverse relationship between SF and plasma tHcy concentrations was observed in 94% of subjects (P < 0.001). Reversal of this inverse relationship was significant only for subjects consuming 415 microg folate/d (P < 0.001). Postrepletion, subjects consuming 200 microg folate/d had a significantly higher (P = 0.009) adjusted plasma tHcy concentration than subjects consuming 415 microg folate/d. These data in elderly women indicate that 415 microg/d folate, provided as a combination of diet, FA and OJ, or diet and FA, normalizes folate status more effectively than does 200 microg/d, thus providing age-specific data for future folate intake recommendations.

Cigarette smoking and plasma total homocysteine levels in young adults with type 1 diabetes.

The purposes of this study were to compare plasma total homocysteine (tHcy) levels, a recognized cardiovascular risk factor, in nondiabetic subjects and type 1 diabetic patients, and to evaluate whether chronic cigarette smoking had a deleterious effect on plasma tHcy levels in type 1 diabetic patients. Plasma tHcy concentrations were measured in 60 young type 1 diabetic patients without clinical evidence of macroangiopathy and in 30 healthy control subjects who were matched for age, sex, BMI, and smoking habit. Plasma tHcy levels were significantly higher in type 1 diabetic patients than in control subjects (12.5 +/- 4.8 vs. 10.3 +/- 2.2 micromol/l, P = 0.01). After stratification by smoking status, diabetic smokers had values for age, sex, BMI, lipids, creatinine, blood pressure, glycometabolic control, diabetes duration, and microvascular complications that were superimposable on their nonsmoking counterparts. Nevertheless, plasma tHcy levels were markedly elevated in diabetic smokers versus nonsmokers (15.5 +/- 5.7 vs. 10.6 +/- 3 pmol/l, P < 0.0001) in a dose-dependent fashion (P < 0.0001, by analysis of variance when subjects were categorized for the number of cigarettes smoked daily). Chronic cigarette smoking seems to adversely affect plasma tHcy levels in young adults with type 1 diabetes.

Homocysteine concentrations and methionine loading in patients on antiepileptic drugs.

A few reports have shown elevated fasting total plasma homocysteine (tHcy) in patients taking antiepileptic drugs (AEDs). In this study we determined the influence of AEDs on plasma tHcy levels prior to and following methionine loading. Thirty-four patients on different AEDs and 34 matched controls were recruited. Blood samples were drawn prior to and 6 h post-methionine loading (6h-PML). The patients on AEDs inducing the cytochrome P450 (carbamazepine, phenytoin, phenobarbital, primidone), had higher fasting and 6h-PML plasma tHcy concentrations than the controls (P = 0.01 and P<0.001). Patients on AED inhibiting the cytochrome P450 (valproate [VPA]), had lower 6h-PML p-tHcy concentrations than controls (P = 0.01). Our data indicate that not only fasting but also 6h-PML tHcy levels should be determined in order to identify hyperhomocysteinemia among patients on AEDs. Inducer AEDs seem to have an opposite effect than the inhibitor VPA on plasma tHcy, erythrocyte folate and serum folate levels.

Polygenic influence on plasma homocysteine: association of two prevalent mutations, the 844ins68 of cystathionine β-synthase and A 2756G of methionine synthase, with lowered plasma homocysteine levels

A moderately elevated plasma total homocysteine (tHcy), whether measured during fasting or post-methionine load (PML), is increasingly being recognized as a risk factor for coronary artery diseases (CAD). However, etiologies for moderately elevated plasma tHcy, particularly with regard to the role of genetic influence on plasma tHcy levels, are still not well understood. In the current investigation, we studied 1025 individuals with respect to the effect of the 68-bp insertion (844ins68 variant) of the cystathionine β-synthase (CBS) gene, the A 2756G transition of the B 12-dependent methionine synthase (MS) gene and the C 677T transition of the methylenetetrahydrofolate reductase (MTHFR) gene on fasting and 4 h PML tHcy. Of these individuals, 153 (14.9%) were heterozygous for the 68-bp insertion, 329 (32.1%) were heterozygous for the G 2756 allele and 122 (11.9%) were homozygous for the C 677T transition. Individuals heterozygous for the insertion had significantly lower PML increase in tHcy concentrations, while individuals homozygous for the A 2756G transition had significantly lower fasting tHcy levels. A 2-way ANOVA showed that there was no interaction between the 844ins68 and the A 2756G transition for either fasting tHcy or PML increase in tHcy, confirming the fact that the effect of these two genotypes on plasma tHcy levels are additive. The effects are opposite but additive with the C 677T genotype of the MTHFR gene. In conclusion, we document evidence of polygenic regulation of plasma tHcy. Overall, >50% of all individuals in this study carried polymorphic traits, which predisposed them to either higher or lower plasma tHcy concentrations, thus providing new evidence of the importance of genetic influences as determinants of tHcy levels.

Assay methods for the measurement of total homocyst(e)ine in plasma.

Analytical methods to measure plasma total homocyst(e)ine (tHcy) concentrations are reviewed. High-pressure liquid chromatography (HPLC) with fluorometric detection is the most widely used method to determine plasma tHcy concentrations. Both monobromobimane and ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate (SBD-F) are popular thiol-specific fluorogenic agents suitable for tHcy analysis. Monobromobimane has the advantage that it is highly reactive towards thiols, but its hydrolysis products are also fluorogenic, thus necessitating complex chromatography to obtain satisfactory separation between the compounds of interest and interferents. SBD-F does not show fluorescence, thus allowing isocratic separation of SBD-F derivatized thiols. SBD-thiol adducts are light sensitive and require protection against light to ensure reliable results. HPLC with electrochemical detection is also often used and has the advantage that no derivatization of thiols is required prior to detection. A recently reported liquid chromatography electrospray tandem mass spectrometric assay has the potential to become the reference method for plasma tHcy analysis. Other methods to measure plasma tHcy concentrations include gas-liquid chromatography, capillary electrophoresis, and immunoassays. Fluorescence polarization immunoassay compares well with gas chromatography-mass spectrometry and may become the method of choice in routine diagnostic clinical chemistry laboratories. Instability of tHcy in whole blood as well as postprandial and orthostatic variation are preanalytical factors that should be accounted for in plasma tHcy analysis. Between-method and between-laboratory variations in serum tHcy analysis are not yet satisfactory; certified reference material and standardization of the plasma tHcy assay will be essential to reduce between-laboratory bias.

Homocysteine and risk of cardiovascular disease.

This pictorial introduction to homocysteine illustrates at a glance the nature of homocysteine and its role in cardiovascular disease by means of eight simple figures and an essential bibliography. Homocysteine is a sulfur-containing metabolite of methionine. Conversion back to methionine or transsulfuration to cysteine are the two major metabolic pathways that reduce total homocysteine (tHcy) concentrations in cells and blood. B vitamins are essential cofactors in homocysteine metabolism. Median fasting total homocysteine levels in adult males are approximately 10 micromol/L. Increased plasma tHcy concentrations are found with methionine-rich diets, low vitamin B intake, male gender, age, impaired renal function, and genetically determined defects of the enzymes involved in homocysteine metabolism. An inverse relation exists between plasma tHcy and circulating folate or vitamin B(6) concentrations, and folic acid supplements of 0.5 mg/d can reduce tHcy levels by approximately 25%. Homocystinuric patients, who have severe hyperhomocysteinemia, die prematurely of atherothrombotic disease. Many (but not all) cross-sectional and prospective studies indicate, on average, that plasma tHcy levels <.10 micromol/L are associated with, or predict the development of, coronary, cerebral, and peripheral vascular disease. The risk conferred by hyperhomocysteinemia is graded and is independent of traditional risk factors, with an estimated odds ratio for ischemic heart disease of 1.4 for every 5 micromol/L increase in plasma tHcy. In vitro and in vivo, tHcy has been found to impair endothelial function. It is now well established that tHcy represents a marker of current or subsequent ischemic vascular disease. However, irrefutable proof that hyperhomocysteinemia actually causes atherothrombosis will come only if interventions to lower plasma tHcy will produce concomitant reductions in cardiovascular events.

Changes of plasma total homocysteine levels during the menstrual cycle.

It is known that plasma total homocysteine (tHcy) levels are lower in premenopausal and pregnant women compared with postmenopausal women. To confirm the suggestion that sex steroid hormones are nongenetic factors affecting homocysteine metabolism, we investigated the effect of natural steroid hormone levels on the fasting plasma tHcy in healthy women during the menstrual cycle. Fifteen premenopausal women were enrolled in this study. Plasma tHcy, estradiol, progesterone and cortisol concentrations were measured in the luteal and follicular phase. The plasma tHcy concentration was determined by high performance liquid chromatography with fluorescence detection, and the steroid hormones by RIA methods. Mean homocysteine values increased from 7.8 micromol L-1 in the luteal phase to 8.9 micromol L-1 in the follicular phase (P < 0.000005, Student's paired t-test). We also found slight negative but insignificant correlations of homocysteine levels with estradiol in both phases of the menstrual cycle. In the case of cortisol and progesterone, no significant correlations with plasma homocysteine were found. The study provides the first evidence of significant differences in plasma homocysteine concentration during the menstrual cycle. From our observed findings it is necessary to account for the phase of the menstrual cycle when determining homocysteine in premenopausal women.

Effective correction of hyperhomocysteinemia in hemodialysis patients by intravenous folinic acid and pyridoxine therapy

Effective correction of hyperhomocysteinemia in hemodialysis patients by intravenous folinic acid and pyridoxine therapy. Folic acid supplementation is only partially efficacious in correcting moderate elevation of plasma total homocysteine (tHcy) concentrations observed in hemodialysis (HD) patients. Experimental and clinical data have suggested that this partial efficacy may be due to impairment of folic acid metabolism to 5-methyltetrahydrofolate (MTHF) and of MTHF transmembrane transport as well. To bypass these difficulties, we assessed the efficacy of intravenous (i.v.) folinic acid, a ready precursor of MTHF, on reducing plasma tHcy concentrations in HD patients. In a cohort of 37 patients on intermittent HD treatment, plasma tHcy concentrations were determined before and during i.v. supplementation of folinic acid (50 mg once per week), together with i.v. pyridoxine (250 mg 3 times per week), to prevent vitamin deficiency, particularly in those treated by recombinant erythropoietin. Folinic acid and pyridoxine i.v. supplementation was given for 11.2 +/- 2.45 months (range 7.5 to 17 months). The mean plasma tHcy levels decreased significantly from 37. 3 +/- 5.8 microM at baseline to 12.3 +/- 5.4 microM on folinic acid treatment (P < 0.001). Moreover, 29 of the 37 patients (78%) had normal plasma tHcy levels at the end of follow-up (that is, <14.1 microM, mean 9.8 microM, range 6.2 to 13 microM). No adverse effects attributable to folinic acid treatment were observed during this time. Intravenous folinic acid therapy (50 mg) once per week associated with pyridoxine supplementation appears to be an effective and safe strategy to normalize plasma tHcy levels in the majority of chronic HD patients.

The Plasma Levels of Homocysteine Are Elevated in Moderate Renal Insufficiency but Do Not Predict the Rate of Progression

Background: Chronic renal failure is characterized by specific alterations of the lipoprotein metabolism. It is also characterized by elevated plasma levels of total homocysteine (tHcy). Hyperhomocysteinemia has been shown to be a risk factor for atherosclerosis in both the general population and in patients with end-stage renal disease. Aim: To analyze whether elevated tHcy levels also may contribute to a higher rate of progression of renal insufficiency in patients with moderately advanced renal failure. Methods: To investigate whether tHcy concentrations are associated with an accelerated rate of progression of renal insufficiency, we have correlated baseline plasma concentrations of tHcy with the progressive decline of renal function in an observational study of human chronic renal disease. Results: Sixty-three nondiabetic patients (49 men, 14 women) were studied as part of an observational study of patients with moderately advanced renal insufficiency. The average follow-up time of the patient population was 3.0 years, and the mean rate of decline in glomerular filtration rate (⁵¹Cr- EDTA clearance) was –3.2 ± (SD) 3.9 ml/min × 1.73 m² body surface area. The mean plasma concentration of tHcy at the beginning of the study was 28.3 ± 12.0 µmol/l. Plasma tHcy concentrations correlated significantly with the glomerular filtration rate (r = –0.32, p < 0.01). However, there was no association between the initial plasma level of tHcy and the rate of progression as assessed by linear regression analysis (r = 0.02; NS). In contrast, increased levels of apolipoprotein B, low-density lipoprotein cholesterol, and proteinuria were all significantly associated with a more rapid decline in renal function. Conclusions: Patients with moderately advanced chronic renal insufficiency have elevated plasma levels of homocysteine. The tHcy plasma levels increase in parallel with the degree of reduction in renal function. However, the hyperhomocysteinemia is not prospectively associated with a higher rate of progression of the renal functional impairment. Hence, there is no indication that elevated homocysteine levels play a contributing role for an accelerated glomerulosclerotic process.

Comparison of Three Different Plasma Homocysteine Assays with Gas Chromatography–Mass Spectrometry

Various methods are available to measure plasma total homocyst(e)ine (tHcy) concentrations, but whether plasma tHcy assays may be used interchangeably is not known. Results from three different methods [HPLC with fluorescence detection, enzyme immunoassay (EIA), and fluorescence polarization immunoassay (FPIA)] to determine fasting (n = 163) and post-methionine load (n = 80) plasma tHcy concentrations were compared with those obtained by gas chromatography-mass spectrometry (GC-MS). Difference plots on non-transformed and log-transformed data were used to assess the agreement between HPLC and GC-MS, EIA and GC-MS, and FPIA and GC-MS. The closest agreement between methods was observed between GC-MS and FPIA for fasting tHcy concentrations, with 95% of the FPIA values between 19% above and 24% below the corresponding GC-MS results. Post-methionine load tHcy concentrations measured by EIA showed the least agreement with GC-MS, with 95% of values measured by EIA ranging between 52% above and 16% below the GC-MS values. With respect to GC-MS, the above-mentioned methods showed a negative bias for fasting tHcy concentrations, but a positive bias for both immunoassays for post-methionine load tHcy concentrations. The agreement among methods is insufficient to allow them to be used interchangeably. The intermethod differences emphasize the need for standardization of plasma tHcy assays.

Plasma total homocysteine and cysteine in relation to glomerular filtration rate in diabetes mellitus

The plasma concentrations of total homocysteine (tHcy) and total cysteine (tCys) are determined by intracellular metabolism and by renal plasma clearance, and we hypothesized that glomerular filtration is a major determinant of plasma tHcy and tCys. We studied the relationships between the glomerular filtration rate (GFR) and plasma tHcy and tCys in populations of diabetic patients with particularly wide ranges of GFR. We measured GFR, urine albumin excretion rate (UAER), plasma tHcy, tCys, methionine, vitamin B12, folate, C-peptide, and routine parameters in 50 insulin-dependent diabetes mellitus (IDDM) and 30 non-insulin-dependent diabetes mellitus (NIDDM) patients. All patients underwent intensive insulin treatment and had a serum creatinine concentration below 115 micromol/liter. Mean plasma tHcy in diabetic patients (0.1 micromol/liter) was lower than in normal persons (11.1 micromol/liter, P = 0.0014). Mean plasma tCys in diabetic patients (266.1 micromol/liter) was also lower than in normal persons (281.9 micromol/liter, P = 0.0005). Seventy-three percent of the diabetic patients had relative hyperfiltration. Plasma tHcy and tCys were closely and independently associated with GFR, serum folate, and serum B12. However, plasma tHcy was not independently associated with any of the 22 other variables tested, including age, serum creatinine concentration, UAER, total daily insulin dose, and glycemic control. Glomerular filtration rate is an independent determinant of plasma tHcy and tCys concentrations, and GFR is rate limiting for renal clearance of both homocysteine and cysteine in diabetic patients without overt nephropathy. Declining GFR explains the age-related increase in plasma tHcy, and hyperfiltration explains the lower than normal mean plasma tHcy and tCys concentrations in populations of diabetic patients.

Maternal plasma homocysteine, placenta status and docosahexaenoic acid concentration in erythrocyte phospholipids of the newborn

The enhanced transport of long-chain polyunsaturated fatty acids, in particular docosahexaenoic acid (22:6 omega-3) (DHA), to the fetus is a placental function important for adequate membrane phospholipid formation and herewith decisive for the quality of fetal CNS myelination. A compromised placental function is correlated with signs of vascular pathology. As elevated plasma total homocysteine (tHcy) concentrations are considered an independent risk for premature occlusive vascular disease, the influence of maternal plasma tHcy concentrations on placental function was indirectly studied, determining the DHA content in erythrocyte membrane phospholipids of the newborn. A total of 60 unselected pregnant women (age range: 21 to 39 years) were investigated at delivery. Gestational age ranged from 26 to 41 weeks. Prior to delivery a placental ultrasound scan was performed. Complete sets of data could be obtained from 43 mothers and their offspring. tHcy concentrations were determined in the plasma of cord and maternal blood. The fatty acid pattern of erythrocyte membrane phospholipids was determined in the mothers and their newborns. Z-scores of the birth weights ranged from -3.4 to 2.1 and of the placental weights from -3.8 to 4.7. The mean maternal plasma tHcy concentration was 6.29 +/- 3.34 micromol/l ranging from below our limit of detection up to 15 micromol/l. These maternal concentrations were correlated with those of their infants (r = 0.71; P < 0.0001). The tHcy concentrations were significantly higher in mothers with pregnancies complicated by gestosis or placental calcifications. The Z-scores of birth weights as well as placental weights showed a significant negative correlation with maternal plasma tHcy concentrations. The mean DHA percentage of total fatty acids in erythrocyte phospholipids was 3.2 +/- 2.2% in the mothers and 3.4 +/- 2.3% in their newborns. Most importantly the maternal plasma tHcy levels and the erythrocyte phospholipid DHA concentrations of their offspring were significantly correlated (r = -0.51; P < 0.0003). In this study, total homocysteine concentrations were elevated in the plasma of pregnant women with signs of placental vasculopathy. Maternal plasma total homocysteine concentrations were positively correlated with erythrocyte phospholipid docosahexaenoic acid of their offspring and may be an indicator for the integrity of placental vascular function. The nutritional status as well as predisposing genetic factors of pregnant mothers need to be investigated more thoroughly.

Influence of Aromatase Inhibitors on Plasma Total Homocysteine in Postmenopausal Breast Cancer Patients

In this study, we evaluated the effect of estrogen suppression with three aromatase inhibitors, aminoglutethimide (n = 30), formestane (n = 12), and exemestane (n = 10), and the progestin megestrol acetate (n = 21) on plasma total homocysteine (tHcy) in patients suffering from advanced breast cancer. Treatment with 1 g/day aminoglutethimide for 2 and 3-5 months increased plasma tHcy by a mean value of 24.5% [95% confidence interval, 10.5-40.4%] at 2 months and 35.8% (95% confidence interval, 18.2-55.9%) at 3-5 months, corresponding to increases in the mean plasma tHcy of 1.90 and 3.67 micromol/L, respectively. In contrast, none of the other treatment options influenced plasma tHcy concentrations. The finding that aminoglutethimide, but none of the other aromatase inhibitors or megestrol acetate, influenced plasma tHcy suggests that this effect is achieved by mechanisms not related to suppression of plasma estrogens or to the glucocorticoids administered in concert.