Advanced glycation end products (AGEs) are substances composed of amino groups of proteins and reducing sugars. The initial and propagation phases of the glycation process are accompanied by the production of a large amount of free radicals, carbonyl species, and reactive dicarbonyl species, of which, methylglyoxal (MG) is the most reactive and can cause dicarbonyl stress, influencing normal physiological functions. In the advanced phase, the production of AGEs and the interaction between AGEs and their receptor, RAGE, are also considered to be among the causes of chronic diseases, oxidative stress, and inflammatory reaction. Till date, multiple physiological activities of polyphenols have been confirmed. Recently, there have been many studies discussing the ability of polyphenols to suppress the MG and AGEs formation, which was also confirmed in some in vivo studies. This review article collects recent literatures concerning the effects of polyphenols on the generation of MG and AGEs through different pathways and discusses the feasibility of the inhibition of glycative stress and dicarbonyl stress by polyphenols.

No abstract

The objective of the present study was to investigate the effects of b-conglycinin and soya isoflavones on diabetic nephropathy (DN). DN was induced by an intravenous injection of streptozotocin (25 mg/kg) in spontaneously hypertensive rats. DN rats were divided into a non-diabetic group (C, control group) and three DN groups (D, DN with control diet; B, DN þ control diet with one-eighth of casein replaced by b-conglycinin as the protein source; and I, DN þ control diet with 0·01 % soya isoflavones). After a 4-week experimental period, we found that fasting blood sugar and plasma and kidney advanced glycation end product levels and 24 h urinary protein excretion of the B group were significantly lower than those of the D group and insulin sensitivity and nephrin expression of the B group were significantly higher than those of the D group. In addition, systolic blood pressure, angiotensin-converting enzyme activity, angiotensin II level and plasma TAG level of the B group were significantly lower than those of the D group, whereas only the levels of plasma TAG and thiobarbituric acid-reactive substances of the I group were lower than those of the D group. In conclusion, b-conglycinin may be beneficial for retarding DN progression and this effect cannot be completely explained by its isoflavone content.

The objective of this study was to evaluate the effects of the hot-water extract of defatted Camellia oleifera seeds (CSE) on body and liver fat accumulation in rats. Forty rats were divided into five groups and each group was fed either an isocaloric control diet (C) or a high-fat liquid diet with 0% (H), 0.12% (H1), 0.24% (H2), or 0.48% CSE (H3) for 8 weeks. Ingestion of the high-fat liquid diet increased abdominal and liver fat accumulation, although no difference was found in body weights compared to rats fed the control diet. We found that rats fed the H2 and H3 diets had lower plasma alanine aminotransferase activities than the H group in the 4th and 8th weeks. At the end of the study, the H2 and H3 groups also had lower epididymal and retroperitoneal fat masses, and all CSE groups had lower circulatory leptin levels than the H group. CSE consumption decreased hepatic fat accumulation in terms of liver triglycerides and a histopathology analysis, and ameliorated high-fat diet-induced elevation of hepatic tumor necrosis factor-α levels. We also found that CSE groups had lower malondialdehyde and hydroxyproline levels in the liver. Our results suggested that CSE may exert beneficial effects through decreasing body fat accumulation and hepatic steatosis and regulating adipokine levels in diet-induced non-alcoholic fatty liver disease.