Fasting tHcy Research Articles

Determinants of plasma total homocysteine levels in Korean chronic renal transplant recipients

Objective: Study the determinants of plasma total homocysteine (tHcy) levels, such as fasting levels of serum creatinine (SCr), albumin, plasma tHcy, folate, B 12, and pyridoxal-5′-phosphate (PLP) in chronic Korean renal transplant recipients (RTR). Design: Cross-sectional study. Setting: Nephrology & Transplant Service in Catholic University Kangnam St. Mary's Hospital, Seoul, Korea. Participants: Ninety-one chronic Korean RTR with stable renal function who were ≥6 months post-transplant. Measures: Used medical record review and anthropometric measurements, and overnight (10 to 14 hours) fasting blood samples were measured for plasma tHcy, PLP, folate, B 12, SCr, and albumin. Results: The prevalence of hyperhomocysteinemia (tHcy > 12 μmol/L) was 56%, and 47% had low plasma folate levels (<3 ng/mL). Linear modeling with analysis of covariance adjusted for age, sex, albumin, SCr, and plasma B-vitamin status revealed that only SCr (standard regression coefficient R = +0.663, P < .001), plasma folate (R = −0.276, P = .001), and B 12 (R = −0.149, marginal, P = .08) were independent determinants of fasting tHcy levels in this patient population. Conclusion: Renal function is the major independent determinant of the fasting tHcy levels among chronic, stable Korean RTR, and that B-vitamin status plays a secondary role among such patients.

The effect of different treatment regimens in reducing fasting and postmethionine-load homocysteine concentrations.

To determine the homocysteine-lowering effect of different treatment regimens on both fasting and postmethionine-load plasma total homocysteine (tHcy) concentrations. Descriptive study of consecutive hyperhomocysteinaemic subjects per treatment regimen. Homocysteine was measured in the fasting state and 6 h after methionine loading, both before and after 8 weeks of vitamin therapy. Hyperhomocysteinaemia was defined as a fasting tHcy and/or increase in tHcy (postmethionine-load minus fasting tHcy concentration) exceeding the 95th percentile of local controls. Outpatient clinic of internal medicine of a large non-academic teaching hospital. One hundred and seventeen hyperhomocysteinaemic subjects (vascular patients and first-degree relatives). There were four regimens: pyridoxine, 200 mg; folic acid, 5 mg; combination of folic acid 0.5 mg and pyridoxine 100 mg; and folic acid, 0.5 mg daily. All regimens, except pyridoxine 200 mg, significantly reduced fasting tHcy without differences in the percentage reduction (32-38%). All regimens produced a significant reduction in the increase in tHcy and postmethionine-load tHcy. The reduction in postmethionine-load tHcy was smaller for pyridoxine 200 mg than for combination therapy. No differences were found in the percentage reduction (for both increase in tHcy and postmethionine-load tHcy) between folic acid 5 mg and folic acid 0.5 mg. Monotherapy folic acid (0.5 mg daily) is the lowest effective therapy for reducing both fasting and postmethionine-load tHcy concentrations, with the same results as high-dose folic acid (5 mg daily). Pyridoxine has no additional value.

Impaired glucose tolerance (IGT) is not associated with disturbed homocysteine metabolism.

Elevated plasma total homocysteine (tHcy) has been suggested to be an additional risk factor for cardiovascular disease in subjects with impaired glucose tolerance (IGT) and Type 2 diabetes (T2D). In order to investigate whether an insulin resistant/chronic hyperinsulinemic situation in male diabetic and prediabetic subjects directly influences the tHcy metabolism, fasting tHcy and post-methionine load tHcy plasma levels (PML-tHcy) were determined in 15 men with IGT, 13 men with newly diagnosed T2D, and 16 normoglycemic controls (NGT). Fasting tHcy (IGT, 13.1 +/- 4.6; T2D, 12.8 +/- 4.0; NGT, 10.7 +/- 4.4 micromol/L) and PML-tHcy (IGT, 46.5 +/-17.39; T2D, 41.1 +/- 6.8; NGT, 38.0 +/- 9.7 micromol/L) showed no differences between the groups. Fasting tHcy and PML-tHcy correlated with fasting proinsulin (r = 0.395, p < 0.05; r = 0.386, p< 0.05) and creatinine (r = 0.489, p < 0.01; r = 0.339, p < 0.05), resp. Multiple regression analysis showed only a relationship between fasting tHcy and creatinine. No relationships have been found between fasting tHcy and PML-tHcy, resp., and indicators of an insulin resistant state, e.g., insulin and proinsulin, as well as serum cobalamin and folate concentrations. In conclusion, our data suggest that the degree of glucose intolerance has no direct impact on the metabolism of homocysteine. However, tHcy levels tend to be elevated with the development of nephropathy, indicating an association between tHcy and renal function in these subjects.

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.

Contribution of the Cystathionine β-Synthase Gene (844ins68) Polymorphism to the Risk of Early-onset Venous and Arterial Occlusive Disease and of Fasting Hyperhomocysteinemia

The frequency of the heterozygous 844ins68 mutation of the cystathionine beta-synthase (CBS) gene and of its association with the homozygous C677T transition of the methylenetetrahydrofolate reductase (MTHFR) gene, plasma fasting tHcy, folate and vitamin B12 levels were evaluated in 309 consecutive patients with objectively diagnosed early-onset venous (n = 200) or arterial thromboembolic disease (n = 109) recruited over 25 months in Milan (North Italy) and Naples (South Italy). The above gene polymorphisms were also evaluated in a population of 787 unmatched controls, 204 of whom--similar to patients for age- and sex-distribution--had fasting tHcy, vitamins and activated protein C resistance measured in their plasma. Moderate fasting hyperhomocysteinemia was detected in 15.5% of patients and in 5.9% of 204 controls (Mantel-Haenszel OR after stratification for type of occlusive disease and gender: 2.88; 1.48-5.32). The frequencies of the 677TT mutation of the MTHFR gene and of the heterozygous 844ins68 insertion of the CBS gene were not significantly different in the patient (19.4% and 6.9%) and the control population (16.5% and 7.8%), but the association of the two gene polymorphisms found in 3.9% of patients and in 1.1% of controls - was significantly associated with an increased risk of venous or arterial occlusive diseases (RR = 3.63; 1.48-8.91). The MTHFR 677TT mutation (RR: 6.92; 3.86-12.4) and its association with the 844ins68 insertion (RR: 21.9; 8.35-57.4), but not the isolated insertion (RR: 0.71), were more frequent in patients and controls with fasting hyperhomocysteinemia than in normohomocysteinemic subjects, irrespective of the type of occlusive disease (venous or arterial). When adjusted for determinants of hyperhomocysteinemia in the patient and the control populations (generalized linear model), fasting tHcy levels were significantly higher in subjects with association of the two gene abnormalities (24.2+/-3.8 micromol/L) than in subjects with the MTHFR 677TT mutation only (14.0+/-5.8 micromol/L, p = 0.004). Activated protein C resistance was significantly more prevalent in venous patients (9.9%) than in controls (3.9%, OR = 2.69; 1.08-6.88). Six of 21 venous patients with APC-resistance also had hyperhomocysteinemia (RR = 5.04; 0.68-37.6), but isolated fasting hyperhomocysteinemia retained statistical significance for the association with venous occlusive disease (RR = 2.84; 1.34-6.01). Heterozygosity for the 844ins68 mutation of the CBS gene is not per se a risk factor for premature arterial and/or venous occlusive diseases. However, when detected in combination with thermolabile MTHFR, it increases by almost 4-fold the risk of occlusive diseases (arterial and/or venous), by increasing the risk and the degree of fasting hyperhomocysteinemia.

Serum Total Homocysteine and Cardiovascular Disease Occurrence in Chronic, Stable Renal Transplant Recipients

Renal transplant recipients have disproportionately high rates of arteriosclerotic outcomes, and recent studies provided controlled evidence that clinically stable renal transplant recipients have an excess prevalence of hyperhomocysteinemia. Few studies suggest that hyperhomocysteinemia may be a cardiovascular risk factor in renal transplant recipients. In the study presented here, the association between atherosclerotic events and homocysteine concentrations was examined in 207 stable renal transplant recipients. The role of hyperhomocysteinemia was analyzed with respect to other known cardiovascular risk factors. The mean follow-up was 21.2 +/- 1.9 mo (range, 14 to 26). Mean total homocysteine (tHcy) was 21.1 +/-9.5 micromol/L and median concentration was 19 micromol/L. Seventy percent of patients (n = 153) were hyperhomocysteinemic (values >15 micromol/L). tHcy correlated negatively with folate concentration (r = -0.3; P < 0.01). tHcy was closely related to creatinine concentration (r = 0.54; P < 0.001). Cardiovascular disease events (CVE) including death were observed in 30 patients (14.5 %; 7.34 events per 1000 person-months of follow-up). Fasting tHcy values were higher in patients who experienced CVE (31.5 +/- 10.3 versus 17.8 +/- 7.5; P < 0.001). Cox regression analysis showed that tHcy was a risk factor for cardiovascular complications (relative risk [RR] 1.06; 95% confidence interval (95% CI), 1.04 to 1.09; P < 0.0001). This corresponds to an increase in RR for CVE of 6% per micromol/L increase in tHcy concentration. Age (RR 1.55; 95% CI, 1.09 to 2.19; P < 0.01) and creatinine concentration (RR 1.34; 95% CI, 1.08 to 1.66; P < 0.01) were also independent predictors for CVE. This study demonstrates that elevated fasting tHcy is an independent risk factor for the development of CVE in chronic stable renal transplant recipients. Randomized, placebo-controlled homocysteine studies of the effect of tHcy lowering on CVE rates are urgently required in this patient population.

Reducción de concentraciones elevadas de homocisteína con ácido fólico y vitaminas B en pacientes con tromboembolia venosa: relación entre respuesta y genotipo C677T de la metilén tetrahidrofólico reductasa (MTHFR)

High levels of plasma total homocysteine (tHcy) are involved in arterial or venous occlusive diseases. It essentially depends on the nutritional status of folic acid (FA) and vitamins B12 or B6, but also on the methylenetetrahydrofolate reductase (MTHFR) enzymatic activity. We aim to evaluate the response of the hyperhomocysteinemia (HHcy) to a standard schedule of vitamin supplementation, according with the MTHFR genotype. 227 patients, diagnosed with venous thromboembolism (VTE) were analysed for tHcy (in fasting conditions), and for the MTHFR-C677T gene polymorphism. When the tHcy exceeded the cut-off point (men = 16, women = 15 mumol/l), the patients were supplemented with a dose equivalent to 1 mg FA, 0.2 mg B12 and 100 mg of B6, daily by 6 weeks. Afterwards they were reanalysed and the reduction was stratified by MTHFR genotype, looking for any difference in the response. The mean fasting tHcy was 12.3 mumol/l (SD = 8). The 51 hyperhomocysteinemic patients (22%) were older (65.1 y) than the normal ones (55.0 y) (p = 0.0001). The treatment was carried out properly in 46 patients (90%). The pre-treatment mean Hcy was 23.2 (SD = 10.5) mumol/l, and it was reduced to 13.0 (SD = 5.9) (p = 0.0001) (mean reduction = 42.1%). By genotype, the C/C reduced from 21.0 to 13.2 mumol/l (37%) (n = 18), the C/T from 25.0 to 12.6 mumol/l (46%) (n = 24), and the abnormal homozygotes T/T from 22.7 to 14.5 mumol/l (39%) (n = 4), although no statistical significant differences were found. In 80% of cases (37/46), tHcy values normalised. A negative correlation (r = -0.471) (p = 0.005) was observed between age and response. The FA/B6/B12 based therapy reduces in a simple, quick and effective way (> 40% in 6 weeks) the pathologic tHcy levels on a VTE population and this is not influenced by the MTHFR genotype. As HHcy seems related with recurrences of venous thrombosis, we could speculate if it would be useful to analyse routinely the tHcy, attempting reduction in selected cases.

Homocysteine, vitamin status and risk of vascular disease; effects of gender and menopausal status. European COMAC Group.

Elevated plasma total homocysteine (tHcy) is a known risk factor for vascular disease. Gender, age, and circulating levels of folate, vitamins B(6)and B(12)affect tHcy levels. Objectives To study associations of gender and age with levels of plasma tHcy, and to examine the relationships of tHcy and circulating levels of folate, vitamins B(6)and B(12)with risk of vascular disease in men and women (pre- and post-menopausal). In a multicentre case-control study in Europe, 750 patients (544 men, 206 women) with documented vascular disease of the coronary, cerebral, or peripheral vessels and 800 control subjects (570 men, 230 women) were enrolled. Plasma tHcy levels (fasting and after methionine loading) and circulating levels of the vitamins were measured. Adjustment for age and centre was carried out for all statistical analyses, with additional adjustment for serum creatinine and vitamins for the tHcy comparisons between the sexes and between cases and controls. Risk analyses included adjustment for creatinine and traditional risk factors. Relationships between age, gender and tHcy were studied among control subjects only. Fasting tHcy levels were lower in women than in men. Levels of tHcy showed a positive association with age, for both sexes. In the post-menopausal age category, female post-methionine load tHcy levels surpassed levels of men. Elevation of tHcy (defined as >80th percentile of controls) appeared to be at least as strong a risk factor for vascular disease in women as in men, even before the menopause. For post-methionine load tHcy, there was a 40% stronger association with vascular disease in women than in men. In both sexes, but especially in pre-menopausal women, low circulating levels of vitamin B(6)conferred a two- to threefold increased risk of vascular disease, independent of tHcy. In men, but not in women, low (defined as <20th percentile of controls) circulating folate levels were associated with a 50% increased risk of vascular disease. Elevation of tHcy appears to be at least as strong a risk for vascular disease in women as men, even before the menopause. Our data indicate that associations of the various tHcy measurements (and the vitamins that determine them), with risks of vascular disease may differ between the sexes. The tHcy-independent relationship of vitamin B(6)with vascular disease indicates that it will be advisable to test the effects of vitamin B(6)in clinical trials.

Short-term reproducibility of total homocysteine determinations in stable renal transplant recipients

BETWEEN 1972 and 1996, at least 17 independent investigative groups documented the presence of significantly increased plasma or serum levels of the putatively arteriosclerotic sulfur amino acid homocysteine in endstage renal disease (ESRD) patients. Despite the chronic, modest reduction in fasting total homocysteine (tHcy) levels afforded by successful renal transplantation relative to ongoing maintenance dialysis in ESRD patients, we recently demonstrated that an excess prevalence of both fasting and postmethionine loading hyperhomocysteinemia persists in stable renal transplant recipients versus matched, population-based controls free of renal disease. Hyperhomocysteinemia may contribute to the disproportionately high rate of arteriosclerotic outcomes experienced by renal transplant recipients, which remains unexplained by the traditional vascular disease risk factors. The reproducibility of any putative risk factor measurement (eg, tHcy), determines, to an important extent, the ability to ascertain its potential association with a disease (eg, arteriosclerotic vascular disease) in a given population. Although data are available on the reliability of fasting or postmethionine loading tHcy determinations in general populations, no comparable analyses have been performed in clinically stable renal transplant recipients. The purpose of our study was to evaluate the short-term reproducibility of fasting and postmethionine loading tHcy level measurements in this specific patient population. For comparison, we simultaneously evaluated the short-term reproducibility of fasting total cholesterol, an established arteriosclerotic risk factor in general populations, and a likely arteriosclerotic risk factor in renal transplant recipients.

Determinants of fasting plasma total homocysteine levels among chronic stable renal transplant recipients.

Although several studies have demonstrated an unadjusted association between folate status and fasting plasma total homocysteine (tHcy) levels among renal transplant recipients, no data confirming the strength or independence of this association have been reported. We determined fasting plasma folate, B12, and pyridoxal 5'-phosphate (active vitamin B6) levels, along with other potential determinants of plasma tHcy levels (i.e., age, sex, creatinine levels, and Cockcroft-Gault estimated creatinine clearance, current immunosuppressive regimen, and history of clinical cardiovascular disease), among 86 renal transplant recipients. The recipients were > or =6 months after transplantation, lived in the Providence, Rhode Island metropolitan area, and were examined between February and June 1998. Stepwise general linear modeling with analysis of covariance revealed that only creatinine level, age, and vitamin status were independent regressors (i.e., P<0.100) of tHcy levels. Moreover, creatinine level alone determined most of the variability in tHcy levels (i.e., R2) accounted for by these independent variables (R2=0.416 for creatinine level alone; total R2=0.575). In contrast, the R2 for folate alone was only 0.046, and even for all three B vitamins combined, the R2 was just 0.088. We conclude that renal function is the overriding independent determinant of fasting tHcy levels among stable renal transplant recipients. In comparison to renal function, vitamin status has a relatively marginal influence on tHcy levels and cyclosporine use has essentially none at all.

Prevalence of mild fasting hyperhomocysteinemia in renal transplant versus coronary artery disease patients after fortification of cereal grain flour with folic acid

Cereal grain flour products fortified with 140 μg folic acid per 100 g flour became widely available in southeast New England by July 1997. We hypothesized that improved folate status secondary to this fortification policy would have a much more limited impact on the prevalence of mild fasting hyperhomocysteinemia in renal transplant versus coronary artery disease patients. Between October 1997 and October 1998, fasting plasma total homocysteine (tHcy), folate and vitamin B12 levels were determined in a total of 86 renal transplant patients with stable allograft function, and 175 coronary artery disease patients whose serum creatinine was (1.4 mg/dl). All subjects lived in the Providence, RI, metropolitan area, and were either non-users of any supplements containing folic acid, vitamins B6 or B12, or had refrained from using such supplements for ≥6 weeks. Geometric mean fasting tHcy levels were 88.0% higher (15.6 vs. 8.3 μmol/l; P<0.001), and the prevalence of fasting tHcy levels ≥12 μM (69.8% vs. 10.9%, P<0.001) was markedly increased in the renal transplant patients, despite a much younger mean age and a relative preponderance of women. In the era of folic acid fortified flour, hyperhomocysteinemia is much more common in stable renal transplant versus coronary artery disease patients. As a result, renal transplant patients are a preferable high risk target population for controlled trials evaluating the tenable hypothesis that lowering total homocysteine levels will reduce cardiovascular disease outcomes.

Hyperhomocysteinemia but not the C677T mutation of methylenetetrahydrofolate reductase is an independent risk determinant of carotid wall thickening. The Perth Carotid Ultrasound Disease Assessment Study (CUDAS)

Hyperhomocysteinemia has been identified as a potential risk factor for atherosclerosis. This study examined whether a modest elevation of plasma total homocysteine (tHcy) was an independent risk factor for increased carotid artery intimal-medial wall thickness (IMT) and focal plaque formation in a large, randomly selected community population. We also examined whether vitamin cofactors and the C677T genetic mutation of the methylenetetrahydrofolate reductase (MTHFR) enzyme were major contributors to elevated plasma tHcy and carotid vascular disease. In 1111 subjects (558 men, 553 women) 52+/-13 years old (mean+/-SD; range, 27 to 77 years) recruited from a random electoral roll survey, we measured fasting tHcy and performed bilateral carotid B-mode ultrasound. For the total population, mean tHcy was 12.1+/-4.0 micromol/L. Plasma tHcy levels were correlated with IMT (Spearman rank rs=0.31, P=0.0001). After adjustment for age, sex, and other conventional risk factors, subjects in the highest versus the lowest quartile of tHcy had an odds ratio of 2.60 (95% CI, 1.51 to 4.45) for increased IMT and 1.76 (95% CI, 1.10 to 2.82) for plaque. Serum and dietary folate levels and the C677T mutation in MTHFR were independent determinants of tHcy (all P=0.0001). The mutant homozygotes (10% of the population) had higher mean tHcy than heterozygotes or those without the mutation (14.2 versus 12.3 versus 11.6 micromol/L, respectively, P=0.0001). The inverse association of folate levels with tHcy was steeper in the mutant homozygotes. Despite this, the C677T MTHFR mutation was not independently predictive of increased carotid IMT or plaque formation. Mild hyperhomocysteinemia is an independent risk factor for increased carotid artery wall thickness and plaque formation in a general population. Lower levels of dietary folate intake and the C677T mutation in MTHFR are important causes of mild hyperhomocysteinemia and may therefore contribute to vascular disease in the community.

Hyperhomocysteinemia and hypofibrinolysis in young adults with ischemic stroke.

Data from epidemiological and case-control studies suggest that increased total homocysteine (tHcy) levels are associated with increased risk for thromboembolic disease. The mechanisms by which hyperhomocysteinemia contributes to thrombogenesis are incompletely understood. The main objectives of this study of young ischemic stroke patients were (1) to examine fasting and post-methionine load levels of tHcy, (2) to ascertain the genotype frequency of the C677CT mutation in the methylenetetrahydrofolate reductase gene (TT genotype), and (3) to study the possible interaction between plasma tHcy levels and fibrinolytic factors. This case-control study was based on 80 consecutive patients aged 18 to 44 years admitted between January 1992 and May 1996 as a result of a first-ever ischemic stroke. Forty-one healthy control subjects were recruited. Measurement of fasting tHcy and post-methionine load levels and evaluation of the fibrinolytic system were undertaken at least 3 months (mean, 5.1+/-1. 9 months) after admission. Genotyping of the methylenetetrahydrofolate reductase gene was performed. Although the increase after methionine loading (ie, postload tHcy minus fasting-level tHcy) was significantly higher among patients, there was no difference in fasting and postload tHcy levels. After adjustment for conventional risk factors, elevated postload increase tHcy levels were associated with a 4.8-fold increased risk of ischemic stroke. There was no difference between patients and control subjects in either TT genotype frequency or T allele frequency. Abnormal response to methionine loading was associated with higher tissue plasminogen activator (tPA) mass concentration, higher plasminogen activator inhibitor-1 levels, and lower tPA activity. After adjustment for age, sex, body mass index, serum cholesterol, and triglycerides, an abnormal increase in postload tHcy levels remained significantly associated with tPA mass concentration levels (P=0.03). A moderately elevated increase in tHcy levels after methionine loading was associated with an increased risk for ischemic stroke in young adults. In contrast, fasting tHcy levels did not differ between patients and controls. A moderately elevated increase in tHcy after methionine loading may provide a additional thrombogenic risk mediated in part by interactions with the fibrinolytic system. In young stroke patients, a methionine loading test to detect hyperhomocysteinemia should always be considered in the convalescent phase of the disease.

Determinants of fasting and post-methionine homocysteine levels in families predisposed to hyperhomocysteinemia and premature vascular disease.

Elevated plasma total homocysteine (tHcy) levels, either measured in the fasting state or after oral methionine loading, are associated with an increased risk of atherothrombotic disease. Fasting and post-methionine hyperhomocysteinemia (HHC) overlap to a limited extent; both can occur as familial traits. We investigated determinants of fasting, postmethionine and delta (ie, post-methionine minus fasting levels) tHcy levels in 510 subjects of 192 HHC-prone families including 161 patients with clinical vascular disease and 349 without vascular disease. We focused on tHcy levels in relation to levels of vitamin B12, B6 and folate and the methylenetetrahydrofolate reductase (MTHFR) C677T mutation. Multivariate linear analyses adjusted for the presence of vascular disease showed that fasting tHcy was significantly related to folate and vitamin B12, and the presence of the MTHFR TT genotype and the T allele, and to age, smoking habits, and serum levels of creatinine. Both post-methionine and delta tHcy levels were related to serum folate levels, and the presence of the MTHFR TT genotype and the T allele, and to postmenopausal status, and body mass index. An interaction was found between MTHFR TT genotype and serum folate levels for both fasting and post-methionine tHcy, ie, for a given decrease in serum folate, homocysteine levels increased more in subjects with the TT genotype than in those with the CC genotype. Fasting, post-methionine and delta tHcy were higher in patients with vascular disease than in their healthy siblings, but these levels were less dependent on serum folate levels (P<0.05), whereas the effect of MTHFR genotype was stronger (P=0.01). This study found evidence that post-methionine and delta tHcy levels are not only influenced by factors affecting homocysteine transsulfuration but also by factors that affect remethylation. The explained variances of fasting, post-methionine and delta tHcy were 49%, 62%, and 78%, respectively. We also found evidence, in patients with premature vascular disease but not in their healthy siblings, for a factor that increases tHcy levels but weakens the normal inverse relation between folate and tHcy and amplifies the effect of the MTHFR genotype.

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.

Effect of immunosuppressive therapy, serum creatinine, and time after transplant on plasma total homocysteine in patients following heart transplantation

Objectives: To determine the prevalence of hyperhomocysteinemia in heart transplant recipients, and to assess the effect of renal function and immunosuppressive medication on total plasma homocysteine (tHcy) levels. Background Elevated plasma tHcy levels have been associated with increased risk of mortality in patients with established coronary artery disease. Graft coronary disease is the major cause of morbidity and mortality in long-term survivors of heart transplantation. The tHcy has been found to be elevated in heart and kidney transplant patients, however, the etiologic factors have not been clearly delineated. Methods The study group consisted of 70 heart transplant recipients (56 males, 14 females, mean age 53 ± 13 years [range 17 to 69 years]). The parameters evaluated were fasting tHcy level, cumulative cyclosporine (CyA) dose, cumulative prednisone dose, serum creatinine, and time from transplantation. Results The mean fasting tHcy level was 20.5 ± 10.2 μmol/L (range 5.2 to 59.0 μmol/L). Sixty-one (87%) had fasting tHcy levels greater than the seventy-fifth percentile of the general population (> 12.2 μmol/L in males, and > 10.1 μmol/L in females). There was no difference in mean post-transplant tHcy level between patients with and without coronary artery disease before transplantation (21.0 ± 11.4 vs 19.3 ± 6.7 μmol/L, p = NS). There were significant relationships between the tHcy level and the serum creatinine ( r = 0.76, p < 0.001), and cumulative exposure to CyA ( r = 0.31, p < 0.01). There were no significant relationships between tHcy levels and cumulative prednisone dose, or time from transplantation. Conclusions Fasting tHcy levels are markedly elevated in the majority of patients following heart transplantation, and are correlated to serum creatinine. Further studies are needed to determine other etiologic factors of elevated tHcy following heart transplantation, and to examine the impact of elevated tHcy on clinical outcomes.

Relationship Between Cyclosporine, Creatinine, And Homocysteine In Cardiac Transplant Patients.

405 Background: We have previously demonstrated that cyclosporine 2 hour peak level (C2) correlates better with the area under the curve than trough levels (C0) in heart transplant patients receiving Neoral. We sought to determine the relationship between total plasma homocysteine (tHcy) and C2 as the latter method of Neoral monitoring is used in our institution. Methods: 38 consecutive cardiac transplant patients (31 men and 7 women) seen between April-May 1998 were studied. Mean age was 58.2±9.3 years. Length of time from transplantation ranged from 6 months to 9 years. All patients were clinically stable on therapy with prednisone, Neoral, and azathioprine. There was no acute rejection during the time of the study. Fasting tHcy, serum creatinine (Cr), C0 and C2 were measured on entry into the study and at 12 weeks. Results: Mean initial and final values for the following were: tHcy 14.5±5.8 (n=38) and 12.6 ±4.9 (n=37) μmol/L; serum Cr 123±35 (n=38) and 120±38 (n=35) μmol/L; C0 167±59 ng/mL (n=28) and 123±17 (n=4), and C2 689± 233 (n=33) and 672± 269 (n=26) ng/mL. The following correlations were observed: (Table)TableConclusions: As noted by others, tHcy shows a strong positive correlation with Cr. In contrast, we demonstrate a negative correlation of tHcy to cyclosporine when using C2 levels. This is consistent with the negative correlation between Cr and C2 that was also observed. This relationship between Cr and C2 may reflect the dosing regime and/or the pharmacokinetics of cyclosporine in renal dysfunction.

HOMOCYSTEINE LEVELS IN RENAL TRANSPLANTATION: DETERMINANTS IN THE ERA OF FOLIC ACID FORTIFIED FLOUR

638 There are no data available on the independent relationship between total homocysteine (tHcy) levels and folate status among renal transplant recipients (RTRs) after adjustment for established determinants of tHcy levels, in particular, renal function. We determined fasting tHcy, folate, vitamin B12, pyridoxal 5′-phosphate (PLP, "active" vitamin B6), creatinine, & albumin levels among n=86 RTRs who were ≥ 6-months post-transplantation, & had stable graft function. All subjects were examined at least 6-months after cereal grain flour products fortified with folic acid at 100 μg/100 g flour became widely available. Results from stepwise linear modeling with tHcy as the dependent variable, & age, sex, use of cyclosporine A (CsA), plasma vitamin status, presence of vascular disease, albumin, & creatinine, as the potential explanatory variables, are displayed in the table. Only creatinine, age, & vitamin status were independent regressors (i.e., P < 0.100) of tHcy levels (final, "Full Model", below):TableConclusion: Renal function is the overriding independent determinant of fasting tHcy levels among stable RTRs in the era of folic acid fortified cereal grain flour. Vitamin status has a relatively marginal influence on tHcy levels, & CsA use, essentially none at all.

Combination of low-dose folic acid and pyridoxine for treatment of hyperhomocysteinaemia in patients with premature arterial disease and their relatives

Hyperhomocysteinaemia is an independent risk factor for atherosclerotic disease and venous thrombosis. The optimal homocysteine-lowering vitamin dose and target total homocysteine (tHcy) concentration are currently unknown. We prospectively studied the homocysteine-lowering effect after 8 weeks low-dose combination of folic acid (0.5 mg) and pyridoxine (100 mg) in 49 hyperhomocysteinaemic persons (33 patients with documented premature arterial disease and 16 of their first-degree relatives). Hyperhomocysteinaemia was in both sexes defined as fasting tHcy concentration > 12 micromol/l and/or post-methionine load tHcy concentration > 38 micromol/l. Low-dose vitamin therapy significantly reduced fasting tHcy concentration (median 13.9 to 9.3 micromol/l, reduction 32% (95% CI: 27-37%)) and post-load tHcy concentration (median 55.2 to 36.5 micromol/l, reduction 30% (95% CI: 25-35%)). Fasting tHcy reduction was similar in women and men, as well as in patients and relatives. Post-load tHcy reduction was significantly less in men compared to women (P = 0.04) and in relatives compared to patients (P = 0.03). Although low-dose combination of folic acid and pyridoxine results in a substantial reduction of tHcy concentrations (30-32%) in subjects with hyperhomocysteinaemia, the normalisation percentage to predefined criteria was less impressive (49%).

The Frequency Distribution of Methylenetetrahydrofolate Reductase (MTHFR) Polymorphism and Association between the Genotypes and Total Homocysteine Level in Patients with Coronary Artery Disease

Background:Increased homocysteine levels are an independent risk factor for coronary artery disease (CAD). A common genetic mutation (nucleotide 677 C-to-T) in methylenetetrahydrofolate reductase (MTHFR), an enzyme required for efficient homocysteine metabolism, creates a thermolabile enzyme with reduced activity. Homozygotes of MTHFR mutation represent 5% to 12% of general population in Canada, America, and Japan. In this study, we examined the distribution of the MTHFR genotypes in CAD patients and healthy volunteers and the association between the genotypes and the total homocysteine level (tHcy). Methods:We screened 60 Korean patients with CAD (CAD group) and 97 healthy volunteers (control group) for the MTHFR 677 C-to-T mutation. Fasting and post-methionineload tHcy level, folic acid, and vitamine B12 level were determined with other clinical variables in CAD group. Results:The frequency of the MTHFR V/V homozygous genotype was 20% in CAD group (with 40% heterozygous and 40% wild type) and 14% in control group (with 48% heterozygous and 38% wild type). In CAD group, homozygotes of MTHFR mutation had significant higher fasting tHcy level than wild type (homozygote, 18.83±6.37 μmol/L;wild type, 12.36±3.21 μmol/L;p< 0.01). The tHcy level correlated with the age (r=0.425, p<0.01), the folate level (r=-0.534, p<0.01), and the presence of the mutant MTHFR gene (r=0.565, p<0.01) after adjustment of other clinical variables. Conclusion:We find that homozygotes of MTHFR mutation have higher homocysteine level independent of 논문접수일:1999년 1월 25일 심사완료일:1999년 7월 7일 교신저자:문건웅, 150-010 서울 영등포구 여의도동 62 가톨릭대학교 의과대학 내과학교실 전화:(02) 3779-1325·전송:(02) 3779-1374 E-mail:echo1@cmc.cuk.ac.kr