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H J Blom

Publications and source records attributed to H J Blom.

At least 37 records · Page 2Linked to original sources
PubMed2002

Early molecular events in the development of the diabetic cardiomyopathy.

UNLABELLED: Oxidative damage to DNA has been well documented in cardiac cells isolated from diabetic patients and rats with streptozotocin-induced diabetes mellitus (DM). This study evaluates possible molecular mechanisms for early events in the development of DM-induced cardiomyopathy. METHODS: To analyze the mechanism of overexpression of p21(WAF1/CIP1) and inhibition of cyclin D(1) expression in cardiomyocytes of diabetic rats we examined the methylation status of these genes by MS-PCR and assessed the possibility of epigenetic control of their expression. RESULTS: We found that the steady-state expression of both genes is influenced by their methylation status, as an epigenetic event, of their 5'-flanking regions upon development of diabetes. CONCLUSIONS: Oxidative damage contributes to the development of cardiomyopathy via p53-dependent activation of cardiac cell death. This pathway includes de novomethylation of the P53-inducible p21(WAF1/CIP1)-gene encoding a protein which binds to and inhibits a broad range of cyclin-cyclin-dependent kinase complexes.

Animals↗
PubMed2002

Homocysteine and folate status in methotrexate-treated patients with rheumatoid arthritis.

OBJECTIVE: To study (i) the influence of methotrexate (MTX) therapy on homocysteine and folate metabolism in patients with rheumatoid arthritis (RA), (ii) the influence of the C677T mutation in the methylenetetrahydrofolate reductase gene (MTHFR) on the change in plasma homocysteine levels during MTX treatment, and (iii) the interference of folate and homocysteine metabolism with the efficacy and toxicity of treatment with MTX. METHODS: The 113 patients enrolled in this study were participating in a 48-week, multicentre, double-blind, placebo-controlled study comparing the efficacy and toxicity of MTX treatment with and without folic or folinic acid supplementation. The MTX dose was 7.5 mg/week initially and increased to a maximum of 25 mg/week if necessary. Concentrations of total folate, 5-methyl tetrahydrofolate (in serum and in erythrocytes) and of homocysteine, cysteine and cysteine-glycine and the MTHFR genotype were determined before the start of the study, after 6 weeks, and after 48 weeks or on withdrawal from the study. Blood was drawn from fasting patients at a standardized time in the morning, 16 h after intake of MTX. The laboratory results were related to parameters of efficacy and toxicity of MTX treatment. RESULTS: Baseline values were distributed equally in the three treatment groups. The mean plasma homocysteine level (normal range 6-15 micromol/l) before the start of MTX was relatively high in all groups: 15.4 micromol/l [95% confidence interval (CI) 13.5 to 17.2] in the MTX plus placebo group (n=39), 14.3 micromol/l (95% CI 12.2 to 16.4) in the MTX plus folic acid group (n=35) and 15.9 micromol/l (95% CI 13.7 to 18.1) in the MTX plus folinic acid group (n=39). After 48 weeks of MTX therapy, the mean homocysteine level showed an increase in the placebo group (+3.6 micromol/l, 95% CI 1.7 to 5.6). In contrast, a decrease was observed in the groups supplemented with folic or folinic acid (folic acid, -2.7 micromol/l, 95% CI -1.4 to -4.0; folinic acid, -1.6 micromol/l, 95% CI -0.1 to -3.0). The differences in the change in plasma homocysteine level between the placebo group and each of the two folate-supplemented groups were statistically significant (P<0.0001), contrary to the difference between the folic and folinic acid groups (P=0.26). Linear regression analysis showed that the change in plasma homocysteine level was statistically significantly associated with folic or folinic acid supplementation (P=0.0001) but not with the presence or absence of the C677T mutation in the MTHFR gene. Homozygous mutants had a higher plasma homocysteine concentration at baseline. No relationship was found between the change in disease activity and the change in homocysteine concentration or the mean homocysteine concentration after 48 weeks of MTX therapy. Toxicity-related discontinuation of MTX treatment was not associated with the change in homocysteine concentration. CONCLUSIONS: Low-dose MTX treatment in RA patients leads to an increased plasma homocysteine level. Concomitant folate supplementation with either folic or folinic acid decreases the plasma homocysteine level and consequently protects against potential cardiovascular risks. No relationship was found between the change in homocysteine concentration and the presence or absence of the C677T mutation in the MTHFR gene. Homocysteine metabolism was not associated with efficacy or toxicity of MTX treatment.

Adult↗
PubMed2002

Negligible urinary cysteamine loss in cystinosis patients with Fanconi syndrome.

Cystinosis is an inborn error of lysosomal cystine transporter, resulting in cystine accumulation in lysosomes of all cells. Renal Fanconi syndrome is an early sign of kidney involvement in cystinosis patients. Cysteamine, a small amino-thiol, depletes intralysosomal cystine content and reduces organ damage. However, it does not reverse renal Fanconi syndrome and only postpones the progression to renal failure. We examined whether cysteamine could be lost in the urine of cystinosis patients with Fanconi syndrome, which may explain the inefficiency of treatment. Urinary cysteamine loss was studied in 6 cystinosis patients with and without Fanconi syndrome and was less than I% of ingested dose in all patients.

Adolescent↗
PubMed2001

Lifestyle factors and plasma homocysteine concentrations in a general population sample.

The authors cross-sectionally investigated the extent to which coffee, tea, and alcohol consumption, physical activity, and smoking were associated with nonfasting total plasma homocysteine concentrations in a random sample of 3,025 Dutch adults aged 20--65 years from a population-based cohort examined in 1993--1996 (n = 19,066). The lifestyle factors most strongly associated with plasma total homocysteine level were smoking (positive), alcohol drinking (negative), and coffee consumption (positive). The smoking effect was most prominent in women, and the alcohol effect was most pronounced in men. Data indicated that independently of other lifestyle factors, age, and intake of folate and B vitamin supplements, a change in lifestyle could result in a 0.1- to 1.7-micromol/liter change in plasma total homocysteine level. The authors conclude that lifestyle changes could result in a public-health-relevant change in plasma total homocysteine concentrations.

Adult↗
PubMed2001

The C677T mutation in the methylenetetrahydrofolate reductase gene: a genetic risk factor for methotrexate-related elevation of liver enzymes in rheumatoid arthritis patients.

OBJECTIVE: To study the possible relationship between the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene and the toxicity and efficacy of treatment with methotrexate (MTX) in patients with rheumatoid arthritis (RA). METHODS: Genotype analysis of the MTHFR gene was done in 236 patients who started MTX treatment with (n = 157) or without (n = 79) folic or folinic acid supplementation. Outcomes were parameters of efficacy of MTX treatment, patient withdrawal due to adverse events, discontinuation of MTX treatment because of elevated liver enzyme levels, and the total occurrence of elevated liver enzyme levels during the study. Multivariate logistic regression analysis was used to study the relationship between the presence of the MTHFR C677T mutation and toxicity outcomes of MTX treatment. RESULTS: Forty-eight percent of the patients showed the homozygous (T/T) or heterozygous (T/C) mutation. The presence of the C677CT or C677TT genotypes was associated with an increased risk of discontinuing MTX treatment because of adverse events (relative risk 2.01; 95% confidence interval 1.09, 3.70), mainly due to an increased risk of elevated liver enzyme levels (relative risk 2.38; 95% confidence interval 1.06, 5.34). Efficacy parameters were not significantly different between the patients with and those without the mutation. CONCLUSION: The C677T mutation is the first identified genetic risk factor for elevated alanine aminotransferase values during MTX treatment in patients with RA. We postulate that the incidence of clinically important elevation of liver enzyme levels during MTX treatment is mediated by homocysteine metabolism. Supplementation with folic or folinic acid reduced the risk of toxicity-related discontinuation of MTX treatment both in patients with and in patients without the mutation.

Alanine Transaminase↗
PubMed2001

Is mutated serine hydroxymethyltransferase (SHMT) involved in the etiology of neural tube defects?

Neural tube defects (NTD) arise in the first weeks of pregnancy due to a combination of environmental and genetic factors. In mothers of children with NTD elevated homocysteine (Hcy) levels and decreased plasma folate levels were observed, which suggests a defect in the folate-dependent Hcy metabolism. Therefore, mutations in genes coding for enzymes of this metabolism could be involved in NTD. Serine hydroxymethyltransferase (SHMT) catalyzes the reversible reaction of serine and tetrahydrofolate (THF) to glycine and 5,10-methylene THF. Two different isoforms of SHMT are known, one is present in the cytosol (cSHMT) and the other in the mitochondrion (mSHMT). Theoretically, mutated SHMT could lead to elevated Hcy levels and to an altered distribution of the different folate derivatives and might therefore become a risk factor for NTD. This study concerns the molecular genetic analysis of genes coding for both isoforms of the SHMT enzyme by single-stranded conformation polymorphism analysis. Several mutations as well as polymorphisms were found in both genes. The relevance of two variations, the 1420 C>T mutation of the cytosolic isoform and the 4-bp deletion of the mitochondrial isoform (delTCTT 1721-1724), to NTD risk was tested in a study group, which consisted of 109 NTD patients, 120 mothers of children with NTD, and 420 controls. Neither of the two polymorphisms led to an increased risk of NTD. In mothers with the 1420 CC genotype, significant increased Hcy levels are present. Also, significantly decreased red blood cell folate and plasma folate levels were present in individuals with the 1420 CC genotype. Probably, the 1420 C>T polymorphism causes a shift in distribution of the different folate derivatives. The 4-bp deletion of the mSHMT gene did not lead to altered Hcy or folate levels. So far, the results of this study provide no direct evidence for a role of defective SHMT functioning in NTD. Still, the influence of the 1420 C>T polymorphism of the cSHMT gene on the folate-related risk of NTD needs further investigation.

Adolescent↗
PubMed2001

A second common variant in the methylenetetrahydrofolate reductase (MTHFR) gene and its relationship to MTHFR enzyme activity, homocysteine, and cardiovascular disease risk.

Molecular defects in genes encoding enzymes involved in homocysteine metabolism may account for mild hyperhomocysteinemia, an independent and graded risk factor for cardiovascular disease (CVD). We examined the relationship of two polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, the 677C-->T and 1298A-->C variants, to MTHFR activity, homocysteine concentrations, and risk of CVD in a population of 190 vascular disease patients and 601 apparently healthy controls. The mean specific and residual MTHFR activities were significantly lower in 677CT and 677TT individuals (both P<0.001). The 1298A-->C mutation alone showed no effect on MTHFR activities. However, when the 677C-->T genotype was taken into account, the 1298A-->C mutation also caused a significant decrease in MTHFR activities, which was observed in both the homozygous 1298CC (P<0.001) and the heterozygous 1298AC states (P=0.005). Both the 677TT as the 677CT genotypes were associated with significantly higher fasting and postload homocysteine levels than 677CC (P<0.001 and P=0.003, respectively). The 1298A-->C mutation had no effect on fasting or postload homocysteine levels. Since homocysteine itself is considered to be positively associated with the risk of CVD, these findings indicate that the 1298A-->C mutation cannot be considered a major risk factor for CVD.

Adult↗
PubMed2001

The homocysteine distribution: (mis)judging the burden.

The nonfasting plasma total homocysteine (P-tHcy) concentration was measured in a random sample of 3025 Dutch adults aged 20-65 years (main study). The positively skewed distribution had a geometric mean of 13.9 micromol/L in men and 12.6 micromol/L in women. Blood of the main study was not cooled or centrifuged immediately after drawing. A stability study (n = 26) indicated that this could have resulted in a small (0.4 micromol/L) overestimation of the means. A comparative study (n = 88), and a reproduction of these results in an entirely different population (n = 213), showed a systematic difference in P-tHcy concentration of -2.4 micromol/L between our laboratory (Nijmegen, the Netherlands) and that in Bergen, Norway. With the information of the additional studies we provided precise and valid data of the Dutch P-tHcy distribution, from which we conclude the status in the Netherlands is worse than in other European countries. Furthermore, we showed that comparison of P-tHcy data is complicated unless the interlaboratory differences are known. @ 2001 Elsevier Science Inc.

Adult↗
PubMed2001

A 31 bp VNTR in the cystathionine beta-synthase (CBS) gene is associated with reduced CBS activity and elevated post-load homocysteine levels.

Molecular defects in genes encoding enzymes involved in homocysteine metabolism may account for mild hyperhomocysteinaemia, an independent and graded risk factor for cardiovascular disease (CVD). Although heterozygosity for cystathionine beta-synthase (CBS) deficiency has been excluded as a major genetic cause of mild hyperhomocysteinaemia in vascular disease, mutations in (non-)coding DNA sequences may lead to a mildly decreased CBS expression and, consequently, to elevated plasma homocysteine levels. We assessed the association between a 31 bp VNTR, that spans the exon 13-intron 13 boundary of the CBS gene, and fasting, post-methionine load and increase upon methionine load plasma homocysteine levels in 190 patients with arterial occlusive disease, and in 381 controls. The 31 bp VNTR consists of 16, 17, 18, 19 or 21 repeat units and shows a significant increase in plasma homocysteine concentrations with an increasing number of repeat elements, in particular after methionine loading. In 26 vascular disease patients the relationship between this 31 bp VNTR and CBS enzyme activity in cultured fibroblasts was studied. The CBS enzyme activity decreased with increasing number of repeat units of the 31 bp VNTR. RT-PCR experiments showed evidence of alternative splicing at the exon 13-intron 13 splice junction site. The 31 bp VNTR in the CBS gene is associated with post-methionine load hyperhomocysteinaemia that may predispose individuals to an increased risk of cardiovascular diseases.

Alleles↗
PubMed2001

Determinants of changes in plasma homocysteine in hyperthyroidism and hypothyroidism.

OBJECTIVE: Hyperhomocysteinaemia is a risk factor for premature atherosclerotic vascular disease and venous thrombosis. The aim of the present study was to assess plasma total homocysteine (tHCys) concentrations in hypo- as well as hyperthyroid patients before and after treatment, and to evaluate the role of potential determinants of plasma tHCys levels in these patients. DESIGN: Prospective follow up study. PATIENTS: Fifty hypothyroid and 46 hyperthyroid patients were studied in the untreated state and again after restoration of euthyroidism. MEASUREMENTS: Fasting plasma levels of tHCys and its putative determinants (plasma levels of free thyroxine (fT4), folate, vitamin B(12), renal function, sex, age, smoking status and the C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene were measured before and after treatment. RESULTS: Restoration of the euthyroid state decreased both tHCys (17.6 +/- 10.2-13.0 +/- 4.7 micromol/l; P < 0.005) and creatinine (83.9 +/- 22.0-69.8 +/- 14.2 micromol/l; P < 0.005) in hypothyroid patients and increased both tHCys (10.7 +/- 2.5-13.4 +/- 3.3 micromol/l; P < 0.005) and creatinine (49.0 +/- 15.4-66.5 +/- 15.0 micromol/l; P < 0.005) in hyperthyroid patients (values as mean +/- SD). Folate levels were lower in the hypothyroid group compared to the hyperthyroid group (11.7 +/- 6.4 and 15.1 +/- 7.6 nmol/l; P < 0.05). Pretreatment tHCys levels correlated with log fT(4) (r = - 0.47), folate (r = - 0.21), plasma creatinine (r = 0.45) and age (r = 0.35) but not with C677T genotype. Multivariate analysis indicated that pretreatment log(fT(4)) levels and age accounted for 28% the variability of pre-treatment tHCys (tHCys = 14.2-5.50 log(fT(4)) + 0.14 age). After treatment the logarithm of the change (Delta) in fT(4) (expressed as the post-treatment fT(4)/pre-treatment fT(4) ratio) accounted for 45% of the variability in change of tHCys ( tHCys = - 0.07-4.94 log ( fT(4))); there was no independent contribution of changes in creatinine which was, however, strongly related to changes in tHCys (r = 0.61). CONCLUSIONS: Plasma tHCys concentrations increased in hypothyroidism and decreased in hyperthyroidism. Plasma fT(4) is an independent determinant of tHCys concentrations. Lower folate levels and a lower creatinine clearance in hypo-thyroidism, and a higher creatinine clearance in hyperthyroidism only partially explain the changes in tHCys.

Adult↗
PubMed2001

Association between B vitamin intake and plasma homocysteine concentration in the general Dutch population aged 20-65 y.

BACKGROUND: An elevated plasma total homocysteine (tHcy) concentration is associated with an increased risk of cardiovascular diseases. Folate, riboflavin, vitamin B-6, and vitamin B-12 are essential in homocysteine metabolism. OBJECTIVE: The objective was to describe the association between dietary intakes of folate, riboflavin, vitamin B-6, and vitamin B-12 and the nonfasting plasma tHcy concentration. DESIGN: A random sample of 2435 men and women aged 20-65 y from a population-based Dutch cohort examined in 1993-1996 was analyzed cross-sectionally. RESULTS: Univariately, intakes of all B vitamins were inversely related to the plasma tHcy concentration. In multivariate models, only folate intake remained inversely associated with the plasma tHcy concentration. Mean plasma tHcy concentrations (adjusted for intakes of riboflavin, vitamin B-6, vitamin B-12, and methionine and for age, smoking, and alcohol consumption) in men with low (first quintile: 161 microg/d) and high (fifth quintile: 254 microg/d) folate intakes were 15.4 and 13.2 micromol/L, respectively; in women, plasma tHcy concentrations were 13.7 and 12.4 micromol/L at folate intakes of 160 and 262 microg/d, respectively. In men, the difference in the mean plasma tHcy concentration between men with low and high folate intakes was greater in smokers than in nonsmokers (2.8 compared with 1.6 micromol/L) and greater in nondrinkers than in drinkers of >2 alcoholic drinks/d (3.5 compared with 1.4 micromol/L). In women, the association between folate intake and plasma tHcy was not modified by smoking or alcohol consumption. CONCLUSIONS: In this Dutch population, folate was the only B vitamin independently inversely associated with the plasma tHcy concentration. Changing dietary habits may substantially influence the plasma tHcy concentration in the general population.

Adult↗
PubMed2001

Cobalamin supplementation improves cognitive and cerebral function in older, cobalamin-deficient persons.

BACKGROUND: Mild cobalamin (Cbl) deficiency is frequently found in older persons and is associated with cognitive and cerebral abnormalities. The effects of Cbl supplementation on these abnormalities are largely unknown. METHODS: In a single-blind, placebo-controlled intervention study, 16 healthy community-dwelling elderly subjects with low plasma Cbl concentration and no cognitive impairments were studied. Subjects underwent 1 month of treatment with placebo, followed by 5 months of treatment with intramuscular injections of hydroxycobalamin. Before and after measurements of plasma cobalamin, total homocysteine (tHcy), methylmalonic acid (MMA), quantitative electroencephalograph (qEEG), and psychometric tests were taken. RESULTS: After Cbl supplementation, plasma Cbl concentrations increased, and plasma MMA and tHcy concentrations decreased. The performance on the Verbal Word Learning Test, Verbal Fluency and Similarities improved. qEEG showed more fast activity and less slow activity. Lower plasma tHcy concentrations were related to increased fast activity on qEEG on the one hand and improved performance on the Verbal Word Learning Test and Similarities on the other. Increased fast or decreased slow activity on qEEG was associated with improved performance on the Verbal Word Learning Test, Similarities and Verbal Fluency. CONCLUSIONS: Electrographic signs of improved cerebral function and improved cognitive function were found after Cbl supplementation in older subjects with low plasma Cbl concentrations who were free of significant cognitive impairment. These improvements were related to a reduction of plasma tHcy concentration.

Aged↗
PubMed2001

Reduced vitamin B12 binding by transcobalamin II increases the risk of neural tube defects.

Periconceptional folic acid supplementation reduces the risk of neural tube defects (NTD). Homocysteine levels are elevated in mothers of NTD children, which may be due to decreased cellular vitamin B12 levels, as vitamin B12 is a cofactor for the methylation of homocysteine. Transcobalamin II (TC II) transports vitamin B12 to the tissues. To examine whether altered plasma transcobalamin levels are a risk factor for NTD, we determined the apo and holo form of TC II and haptocorrin (TCI+TCIII), vitamin B12 and homocysteine concentrations in the plasma of 46 mothers with NTD children, and in 73 female controls. Holo-tc II levels and holo-tc II percentages (holo-tc II/total tc II) in the first quartile of the control distribution were related to a three-fold (OR 2.9, 95%CI 0.9-9.2) and five-fold (OR 5.0, 95%CI 1.3-19.3) risk, respectively, for having a child with NTD, when compared with the last quartile. Homocysteine levels were significantly higher among individuals with low holo-tc II, low total vitamin B12 concentrations and low holo-tc II percentages. These low holo-tc II percentages are probably caused by reduced affinity of TC II for vitamin B12, which may be explained by genetic variation in the TC II gene. Vitamin B12 supplementation might therefore be warranted, in addition to folate, in the prevention of NTD.

Adult↗