Mangiferin, a natural C-glucoside xanthone, has anti-inflammatory, anti-oxidative, neuroprotective actions. Our previous study showed that mangiferin could attenuate diabetes-associated cognitive impairment of rats by enhancing the function of glyoxalase 1 (Glo-1) in brain. The aim of this study was to investigate whether Glo-1 upregulation by mangiferin in central neurons exposed to chronic high glucose may be related to activation of Nrf2/ARE pathway. Compared with normal glucose (25 mmol/L) culture, Glo-1 protein, mRNA, and activity levels were markedly decreased in primary hippocampal and cerebral cortical neurons cultured with high glucose (50 mmol/L) for 72 h, accompanied by the declined Nrf2 nuclear translocation and protein expression of Nrf2 in cell nucleus, as well as protein expression and mRNA level of γ-glutamylcysteine synthetase (γ-GCS) and superoxide dismutase activity, target genes of Nrf2/ARE signaling. Nonetheless, high glucose cotreating with mangiferin or sulforaphane, a typical inducer of Nrf2 activation, attenuated the above changes in both central neurons. In addition, mangiferin and sulforaphane significantly prevented the formation of advanced glycation end-products (AGEs) reflecting Glo-1 activity, while elevated the level of glutathione, a cofactor of Glo-1 activity and production of γ-GCS, in high glucose cultured central neurons. These findings demonstrated that Glo-1 was greatly downregulated in central neurons exposed to chronic high glucose, which is expected to lead the formation of AGEs and oxidative stress damages. We also proved that mangiferin enhanced the function of Glo-1 under high glucose condition by inducing activation of Nrf2/ARE signaling pathway.
Glyoxalase 1 (Glo-1) is an ubiquitous cellular enzyme that participates in the detoxification of methylglyoxal (MG), a cytotoxic byproduct of glycolysis that induces protein modification (advanced glycation end products [AGEs]), oxidative stress, and inflammation. The concentration of MG is elevated under high-glucose conditions, such as diabetes. Therefore, Glo-1 and MG have been implicated in the pathogenesis of diabetic encephalopathy. We investigated the effect of quercetin on brain damage that was caused by diabetes in rats and the mechanisms associated with Glo-1. Streptozotocin-induced diabetic rats were treated orally with quercetin (30, 60, and 90 mg/kg) or distilled water for 14 weeks. The temporal cortex and hippocampus were harvested and analyzed for different indices assays. Quercetin, especially at a high dose, increased the levels of reduced glutathione and the activity of superoxide dismutase and decreased the levels of AGEs, the receptor for AGEs (RAGE), and malondialdehyde in the diabetic brain. Quercetin also significantly decreased the levels of inflammatory markers (cyclooxygenase-2, interleukin-1β, and tumor necrosis factor α) in diabetic brains. Most importantly, Glo-1 activity and protein expression were increased in quercetin-treated diabetic rat brains compared with untreated diabetic brains. These results indicate that quercetin exerts beneficial effects by decreasing protein glycation, oxidative stress, and inflammation through the upregulation of Glo-1, which may ameliorate diabetic encephalopathy.
This study was designed to investigate the effects of mangiferin on renal fibrosis, osteopontin production, and inflammation in the kidney of diabetic rats. Diabetes was induced through the single administration of streptozotocin (55 mg/kg, i.p.). Diabetic rats were treated with mangiferin (15, 30, and 60 mg/kg/day, i.g.) for 9 weeks. The kidney was fixed in 10% formalin for glomerulus fibrosis examination using Masson trichrome staining. Kidney and blood were obtained for assays of the associated biochemical parameters. Chronic mangiferin treatment prevented renal glomerulus fibrosis evidenced by decreases in Mason-stained positive area of glomeruli, protein expression of type IV collagen, and α-smooth muscle actin in the kidney of diabetic rats, in comparison with decreases in mRNA and protein expression of osteopontin as well as protein expression of cyclooxygenase 2 and NF-кB p65 subunit in the renal cortex of diabetic rats. Moreover, mangiferin reduced the levels of interleukin 1β in both the serum and the kidney of diabetic rats. Our findings demonstrate that mangiferin prevents the renal glomerulus fibrosis of diabetic rats, which is realized through the suppression of osteopontin overproduction and inflammation likely via inactivation of NF-кB.
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