Lo MC, Chen MH, Lee WS, Lu CI, Chang CR, Kao SH, Lee HM. N ε -(carboxymethyl) lysine-induced mitochondrial fission and mitophagy cause decreased insulin secretion from ␤-cells. Am J Physiol Endocrinol Metab 309: E829 -E839, 2015. First published September 22, 2015; doi:10.1152/ajpendo.00151.2015 ε -(carboxymethyl) lysine-conjugated bovine serum albumin (CML-BSA) is a major component of advanced glycation end products (AGEs). We hypothesised that AGEs reduce insulin secretion from pancreatic ␤-cells by damaging mitochondrial functions and inducing mitophagy. Mitochondrial morphology and the occurrence of autophagy were examined in pancreatic islets of diabetic db/db mice and in the cultured CML-BSA-treated insulinoma cell line RIN-m5F. In addition, the effects of ␣-lipoic acid (ALA) on mitochondria in AGEdamaged tissues were evaluated. The diabetic db/db mouse exhibited an increase in the number of autophagosomes in damaged mitochondria and receptor for AGEs (RAGE). Treatment of db/db mice with ALA for 12 wk increased the number of mitochondria with wellorganized cristae and fewer autophagosomes. Treatment of RIN-m5F cells with CML-BSA increased the level of RAGE protein and autophagosome formation, caused mitochondrial dysfunction, and decreased insulin secretion. CML-BSA also reduced mitochondrial membrane potential and ATP production, increased ROS and lipid peroxide production, and caused mitochondrial DNA deletions. Elevated fission protein dynamin-related protein 1 (Drp1) level and mitochondrial fragmentation demonstrated the unbalance of mitochondrial fusion and fission in CML-BSA-treated cells. Additionally, increased levels of Parkin and PTEN-induced putative kinase 1 protein suggest that fragmented mitochondria were associated with increased mitophagic activity, and ALA attenuated the CML-BSAinduced mitophage formation. Our study demonstrated that CML-BSA induced mitochondrial dysfunction and mitophagy in pancreatic ␤-cells. The findings from this study suggest that increased concentration of AGEs may damage ␤-cells and reduce insulin secretion. advanced glycated end products; mitochondrial dynamics; mitophagy; diabetes DIABETES MELLITUS IS CHARACTERIZED BY HYPERGLYCEMIA and long-term irreversible change of vascular and connective tissue. Advanced glycated end products (AGEs) have been directly implicated in the development of chronic complications of diabetes such as nephropathy, arteriosclerosis, retinopathy, neuropathy, and cataracts (30). AGEs can be formed via either the nonenzymatic "Maillard reaction" or increased polyol pathway flux (14). In particular, the reactive carbonyl group of methylglyoxal reacts with the amino group of lysine to produce protein conjugates with 3-deoxyglucosone-imidazolone, pyrraline, pentosidine, and N ε -(carboxymethyl) lysine (14). AGEs may impair insulin secretion and lead to the development of diabetes (7). A previous report showed that serum levels of N ε -(carboxymethyl) lysine-conjugated AGEs, a major constituent of AGEs, were elevated up to 42-44 U/ml in 7-mo-ol...

Diabetes mellitus (DM), a state of chronic hyperglycemia, is associated with a variety of serious complications. Hyperglycemia-induced advanced glycation end products (AGEs) play an important role in the development of diabetic complications. In vivo, we demonstrated that disrupted mitochondria and autophagy was elevated in type II DM db/db mice. Mitophagy was evidenced by increased autophagosome formation in the beta-islet cells. The adducts of N(epsilon)-(carboxymethyl) lysine (CML), a major AGE, and bovine serum albumin (CML-BSA) stimulated the conversion of microtubule-associated protein 1 light chain 3-I (LC3-I) to LC3-II in rat insulinoma cells (RIN-m5F). CML-BSA increased ROS generation as demonstrated in a time-dependent manner. Experiments with mitochondrial targeted enhanced yellow fluorescent protein transfected RIN-m5F cells, massive fragmented mitochondria were visualized in the CML-BSA treated cells. Taken together, these data suggested that AGEs may cause mitochondrial dysfunction and mitophagosome formation, and AGEs-induced glycoxidative stress may trigger mitophagic process to modulate mitochondrial fates leading to either cell survival or cell death.