Is C677T polymorphism in methylenetetrahydrofolate reductase gene a risk factor for diabetic nephropathy or diabetes mellitus in a Chinese population?

BACKGROUND AND AIMS: To date, case-control studies on the association between C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR) gene and diabetes mellitus (DM) or diabetic nephropathy (DN) in different populations have provided inconclusive results. To clarify the effect of the C677T polymorphism on the risk of both DM and DN in a Chinese population, a meta-analysis was performed. METHODS: A comprehensive literature search was conducted to collect data from all case-control observational studies that investigated association of C677T polymorphism in MTHFR gene with DM or DN in a Chinese population. RESULTS: Overall, 12 studies in a Chinese population published up to 2011 were combined, and the heterogeneity among them varied from none to moderate. The 677T allele showed significant association with DN (OR = 1.97, 95% CI [1.71, 2.28], p <0.00001), but no relationship with DM (OR = 1.03, 95% CI [0.89, 1.18], p = 0.70) compared with the 677C allele in a Chinese population. Similarly, evidence of significant association with DN was detected in the additive model, the recessive model and the dominant model for allele T (additive model: OR = 3.26, 95% CI [2.46, 4.31], p <0.00001; recessive model: OR = 2.32, 95% CI [1.81, 2.97], p <0.00001; dominant model: OR = 2.35, 95% CI [1.89, 2.91], p <0.00001); however, no relationship with DM was found (additive model: OR = 1.01, 95% CI [0.76, 1.35], p = 0.94; recessive model: OR = 0.98, 95% CI [0.76, 1.26], p = 0.87; dominant model: OR = 1.23, 95% CI [0.91, 1.65], p = 0.18). There were no sources of bias in the selected studies, and the sensitivity analysis (exclusion of studies not in Hardy-Weinberg equilibrium) suggested stability of this meta-analysis. CONCLUSIONS: C677T polymorphism in MTHFR gene may be a risk factor for DN, but not for DM, in a Chinese population.

Angiotensin II type 1 receptor expression is increased via 12-lipoxygenase in high glucose-stimulated glomerular cells and type 2 diabetic glomeruli.

BACKGROUND: Angiotensin II type 1 receptor (AT1) plays an important role in the development of diabetic nephropathy (DN). However, the roles played by 12-lipoxygenase (12-LO) in the AT1 expression in glomerular cells exposed to high glucose (HG) and diabetic glomeruli remain unclear. Our objective in the present study was to investigate the role of 12-LO in the AT1 expression in glomerular cells and glomeruli under diabetic conditions. METHODS: Mesangial cells (MCs), podocytes and glomeruli isolated from rats were used in this study. The rats fed a high fat diet received low-dose streptozotocin to make type 2 diabetes. The 12-LO product 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] was infused to rats by osmotic mini-pump. Morphometric measurement for glomerular volume, competitive reverse transcription polymerase chain reaction for mRNA expression, western blot and immunohistochemistry for protein expression were performed, respectively. RESULTS: Both the 12(S)-HETE and HG increased AT1 protein expression in MCs and podocytes. Furthermore, the levels of the AT1 were significantly higher in glomeruli derived from 12(S)-HETE-treated rats compared with control rats. In addition, HG-induced AT1 expression was significantly reduced by the 12-LO inhibitor cinnamyl-3,4-dihydroxy-alpha-cynanocinnamate (CDC). Compared with the non-diabetic controls, DN rats showed significant glomerular hypertrophy and albuminuria. This was associated with significant increases in AT1 protein expression. These abnormalities were prevented by treatment of the CDC. CONCLUSIONS: These results indicate that AT1 expression is enhanced, at least in part, by 12-LO in the type 2 diabetic glomeruli, and 12-LO inhibition can ameliorate DN progression through downregulation of AT1 expression.