Evaluation of advanced glycation end products and carbonyl compounds in patients with different conditions of oxidative stress

Advanced glycation end products (AGE) and dicarbonyl compounds accumulate in serum and tissues of patients with diabetes and chronic renal failure. Pentosidine, free pentosidine, glyoxal and methylglyoxal have been evaluated in plasma of diabetic patients with poor metabolic control at baseline and after the improvement of glycemic levels, and in plasma and peritoneal dialysate of patients with renal failure before and after 12 h of peritoneal dialysis. In diabetic patients, acceptable metabolic control was unable to normalize levels of pentosidine (after 2 and 10 months), glyoxal and methylglyoxal (after 2 months). In patients with end-stage renal disease, mean values of pentosidine, free pentosidine, glyoxal and methylglyoxal decreased in plasma after dialysis. No pentosidine or free pentosidine were present in the peritoneal dialysate at time 0, but were found after 12 h of peritoneal dialysis; glyoxal and methylglyoxal decreased after 12 h of dialysis. So, glyoxal and methylglyoxal, already present in the dialysis fluid, can react with the peritoneal matrix protein, giving a reason for the gradual loss of peritoneal membrane function often observed in patients undergoing long-term peritoneal dialysis.     

Epigallocatechin gallate (EGCG) binds to low-density lipoproteins (LDL) and protects them from oxidation and glycation under high-glucose conditions mimicking diabetes

The aim of this study was to determine whether low-density lipoprotein (LDL)-bound epigallocatechin gallate (EGCG) attenuates LDL oxidation and glycation under high-glucose (HG) conditions mimicking diabetes. Pooled plasma was preincubated with EGCG for three hours, followed by sequential ultracentrifugation and extensive dialysis to isolate LDL. The kinetics of α-tocopherol and EGCG consumption in LDL were measured by a solid-phase extraction system with HPLC-diode array detection (HPLC-DAD) upon oxidation. EGCG enrichment effectively increased the resistance of LDL to oxidation caused by HG/Cu²⁺. A dose-dependent inhibition of HG-mediated long-term glycation of LDL was also observed by LDL-bound EGCG. Data from HPLC-DAD demonstrated that EGCG was able to bind lipoproteins and to facilitate the antioxidant and antiglycation properties of LDL. This study suggests that loading plasma with EGCG is an efficient way to increase the content of this phytochemical in LDL, which may imply favourable in vivo activity of EGCG in diabetes.     

体内美拉德反应及其产物的病理作用研究进展

体内美拉德反应(Maillard reaction)是普遍存在于生物体中的还原糖与蛋白质之间的化学反应,其反应过程及产物十分复杂,反应终产物被称为晚期糖基化终产物(Advanced Glycation Endproductions,AGEs)。越来越多的研究表明,体内美拉德反应在疾病发生发展过程中起着重要作用。本文就体内美拉德反应的机制(包括反应过程、重要的反应中间产物和终产物)、在疾病发生发展过程的作用及其美拉德反应抑制剂的研究进行综述。     

糖基化反应条件对鲢鱼鱼肉木瓜蛋白酶酶解产物清除DPPH自由基影响

为提高鲢鱼鱼肉蛋白酶酶解产物抗氧化活性,将葡萄糖和低聚异麦芽糖通过糖基化反应分别引入到鲢鱼鱼肉木瓜蛋白酶酶解产物中,利用分光光度计测定其清除DPPH自由基能力。研究结果表明,木瓜蛋白酶酶解物与葡萄糖以1:4的比例、在60℃下进行糖基化反应,可以得到清除DPPH自由基能力较强的产物,其清除能力可达78.12%。     

Glycolaldehyde‐modified β‐lactoglobulin AGEs are unable to stimulate inflammatory signaling pathways in RAGE‐expressing human cell lines

Scope: Advanced glycation endproducts (AGEs) are suspected to stimulate inflammatory signaling pathways in target tissues via activation of the receptor for AGEs. Endotoxins are generally recognized as potential contamination of AGE preparations and stimulate biological actions that are very similar as or identical to those induced by AGEs. Methods and results: In our study, we used glycolaldehyde‐modified β‐lactoglobulin preparations as model AGEs and employed two methods to remove endotoxin using either affinity columns or extraction with Triton X‐114 (TX‐114). Affinity column‐purified AGEs retained their ability to stimulate inflammatory signaling as measured by mRNA expression of inflammatory cytokines in the human lung epithelial cell line Beas2b. However, glycolaldehyde‐modified AGEs purified by extraction with TX‐114 did not show any stimulation of mRNA expression of inflammatory cytokines. The presence of a cell stimulating endotoxin‐like activity was demonstrated in the detergent phase after extraction with TX‐114, thus indicating that not AGEs but a lipophilic contamination was responsible for the stimulation of inflammatory signaling. Conclusion: Our results demonstrate that glycolaldehyde‐modified AGEs are unable to induce inflammatory signaling in receptor for AGE‐expressing cells. The observed cell‐activating activity can be ascribed to an endotoxin‐like lipophilic contamination present in AGE preparations and affinity column purification was insufficient to remove this contamination.     

Transformation of Free and Dipeptide‐Bound Glycated Amino Acids by Two Strains of Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae transforms branched‐chain and aromatic amino acids into higher alcohols in the Ehrlich pathway. During microbiological culturing and industrial fermentations, this yeast is confronted with amino acids modified by reducing sugars in the Maillard reaction (glycation). In order to gain some preliminary insight into the physiological “handling” of glycated amino acids by yeasts, individual Maillard reaction products (MRPs: fructosyllysine, carboxymethyllysine, pyrraline, formyline, maltosine, methylglyoxal‐derived hydroimidazolone) were administered to two strains of S. cerevisiae in a rich medium. Only formyline was converted into the corresponding α‐hydroxy acid, to a small extent (10 %). Dipeptide‐bound pyrraline and maltosine were removed from the medium with concomitant emergence of several metabolites. Pyrraline was mainly converted into the corresponding Ehrlich alcohol (20–60 %) and maltosine into the corresponding α‐hydroxy acid (40–60 %). Five specific metabolites of glycated amino acids were synthesized and characterized. We show for the first time that S. cerevisiae can use glycated amino acids as a nitrogen source and transform them into new metabolites, provided that the substances can be transported across the cell membrane.     

色氨酸抑制体外模型中晚期糖基化终末产物形成机理

食源性晚期糖基化终末产物(advanced glycation end products,AGEs)与多种慢性疾病密切相关,尤其是糖尿病和肾脏疾病.为减少AGEs对机体的健康风险,降低食品中AGEs含量,本研究从13种氨基酸中筛选出具有良好AGEs抑制效果的色氨酸(tryptophan,Trp),利用牛血清白蛋白(bo...