Methylenetetrahydrofolate reductase gene polymorphism, hyperhomocysteinemia and occlusive retinal vascular disease in type 2 diabetic and non-diabetic subjects.

BACKGROUND: Methylenetetrahydrofolate reductase (MTHFR) gene polymorphism may cause hyperhomocysteinemia, which affects the vascular endothelium and may induce occlusive vascular disease (OVD). Hypertension thickens small-sized arterial walls and attenuates intramural blood flow. Such OVD can be studied in retinal angiograms as a decrease in the arterio-venous ratio (AVR). Diabetes, by altering microvascular structure and function, in many ways modifies this AVR. OBJECTIVE: To assess whether MTHFR gene polymorphism (C677T) by causing hyperhomocysteinemia affects the retinal AVR in type 2 diabetic and non-diabetic subjects. METHODS: Eighty-four recently diagnosed (< 1 year) type 2 diabetic and 115 non-diabetic subjects were included in the study. Retinal fluoresceine angiograms were recorded and the mean AVR was calculated by measuring transverse vessel diameters at 6 locations. The mean AVR was used as a marker of OVD. The MTHFR VV, VA and AA genotypes were determined by PCR and plasma homocysteine by high-pressure liquid chromatography. RESULTS: In the diabetic subjects with the VV, VA and AA genotypes, the plasma homocysteine levels were 16.5 +/- 7, 12.5 +/- 4.6 and 11.3 +/- 4.9 microM, respectively (p = 0.008, ANCOVA). The corresponding values in controls were 14.6 +/- 3.8, 13.7 +/- 5.7 and 11.6 +/- 4.4 (p = 0.08). Correspondingly, in the diabetic subjects, the AVR values were 0.71 +/- 0.07, 0.75 +/- 0.07 and 0.73 +/- 0.1 (p = NS, ANOVA) and in the control subjects they were 0.8 +/- 0.14, 0.81 +/- 0.12 and 0.76 +/- 0.09 (p = NS, ANOVA). Multiple linear regression analysis (best model chi2 = 18.2, R2 = 0.10, p < 0.001) showed that AVR was related to diastolic blood pressure (t = -3.7, p < 0.001) and GFR (t = -2.2, p = 0.03). There was no relation between the AVR and plasma homocysteine levels. CONCLUSION: In the present study of recently diagnosed type 2 diabetic and non-diabetic subjects, MTHFR gene polymorphism (C677T mutation) slightly affected the plasma homocysteine level but did not alter the arterio-venous ratio.

Methylenetetrahydrofolate reductase gene C677T mutation is related to the defects in the internal elastic lamina of the artery wall.

BACKGROUND: The C677T mutation of the methylenetetrahydrofolate reductase (MTHFR) gene leads to C/C, C/T and T/T genotypes, which affect the plasma homocysteine concentration in humans. In mini-pigs, high serum homocysteine levels are associated with defects in the internal elastic lamina (IEL) of the artery wall, which are apparently related to the migration of smooth muscle cells into the intima during atherogenesis. We studied the association between the MTHFR genotypes and the number of gaps in the IEL in the wall of the five major abdominal arteries. MATERIALS AND METHODS: The autopsy study included 123 subjects (90 males and 33 females) aged 18-93. For the light microscopy, a 0.5 cm circular segment of the coeliac, the superior mesenteric, the inferior mesenteric and the renal arteries were cut and embedded in paraffin blocks. The circumference of the IEL, the thickness of the intima and the number of the gaps per millimetre in the IEL were measured by MOP 3 image analysis. RESULTS: The T-allele carriers (C/T and T/T) of the MTHFR gene had significantly less gaps in the IEL than the subjects with the C/C genotype in the superior mesenteric and in the left renal arteries (2.02 +/- 2.25 vs. 2.53 +/- 1.89, P < 0.04 and 0.56 +/- 1.09 vs. 1.82 +/- 2.66, P < 0.02, respectively). The trend was similar for the coeliac and the right renal arteries. CONCLUSIONS: Our result suggests that MTHFR polymorphism may be involved in the fragmentation of the IEL.

Novel candidate genes for atherosclerosis are identified by representational difference analysis-based transcript profiling of cholesterol-loaded macrophages.

OBJECTIVES: To analyze the early gene expression in macrophages accompanying the phenotypic changes into foam cells upon exposure to oxidized low-density lipoprotein. To identify candidate genes and markers for further studies into the pathogenesis of atherosclerosis. METHODS: Cells of the monocytic cell line THP-1 were activated by PMA and exposed to oxidized low-density lipoprotein. Gene expression profiles were investigated after 24 h, using a solid phase cDNA representational difference analysis (RDA) method and shotgun sequencing. Results were verified by microarray hybridization, and analyzed in the virtual chip display of a novel software tool for transcript profile exploration. RESULTS: By comparing transcript profiles of exposed/unexposed cells, 1,984 transcript sequences, representing a total of 921 genes with altered expression levels in response to oxidized low-density lipoprotein exposure, were identified. Genes that are central to cell cycle control and proliferation, inflammatory response, and of pathways not previously implicated in atherosclerosis were identified. The data obtained is also made available on-line at http:// biobase.biotech.kth.se/thp1a for further exploration. CONCLUSION: The identification of new candidate genes for atherosclerotic disease through RDA-based transcript profiling facilitates further functional genomic studies in coronary artery disease. Candidate genetic polymorphism markers of potential clinical relevance can be identified by filtering information in genome variation databases through the virtual chip analysis of the transcript profiles and subsequently tested in association studies.

Mutation C677T of methylenetetrahydrofolate reductase gene is not associated with coronary artery disease, but possibly with albuminuria, in type 2 diabetic patients.

The missense mutation in the 677th nucleotide (C677T) of methylenetetrahydrofolate reductase gene causes substitution of valine (V) for alanine (A) resulting in three genotypes VV, VA and AA. The VV genotype causes hyperhomocysteinemia and may be a risk factor for coronary artery disease. We determined genotypes by polymerase chain reaction and subsequent restriction fragment length analysis and compared them in 84 patients with type 2 diabetes and in 115 non-diabetic subjects with and without coronary disease. Fractional urinary excretion rate of albumin was assessed by nephelometry. The VV, VA, and AA frequencies in the diabetic and in the control groups were 0.095, 0.357, 0.548 and 0.061, 0.417, 0.522, respectively (p = NS, diabetic vs. controls, chi2 test). Genotype frequencies did not differ in either diabetic or control subjects between those with or those without coronary disease (chi2 test). The fractional urinary excretion rate of albumin (mean +/-SD) in diabetic patients with the VV genotype i.e. 1.59 +/-0.71 was lower (Kruskall-Wallis test p = 0.002) than in the other genotypes i.e. VA 5.98 +/-9.75 and AA 3.75 +/-4.77, respectively (post-hoc Mann-Whitney test VV vs. VA p = 0.005 and VV vs. AA p = 0.054, respectively). We found that in patients with type 2 diabetes the methylenetetrahydrofolate reductase VV genotype was associated with a low urinary albumin excretion but not with coronary artery disease or diabetes per se.