Copper-catalyzed ascorbate oxidation results in glyoxal/AGE formation and cytotoxicity.
Previously we showed that 10 muM glyoxal compromised hepatocyte resistance to hydrogen peroxide (H(2)O(2)) by increasing glutathione (GSH) and NADPH oxidation and decreasing mitochondrial membrane potential (MMP) before cytotoxicity ensued. Since transition metal-catalyzed oxidation of ascorbate (Asc) has been shown to result in the generation of both glyoxal and H(2)O(2), we hypothesized that glyoxal formation during this process compromises hepatocyte resistance to H(2)O(2). We used isolated rat hepatocytes and incubated them with Asc/copper and measured cytotoxicity, glyoxal levels, H(2)O(2), GSH levels, and MMP. To investigate the role of Asc/copper on glyoxal-BSA adducts, we measured the appearance of advanced glycation end-products (AGE) in the presence and absence of catalase or aminoguanidine (AG). Asc/copper increased glyoxal and H(2)O(2) formation. Hepatocyte GSH levels were decreased and cytotoxicity ensued after a collapse of the hepatocyte MMP. Glyoxal traps protected hepatocytes against Asc/copper-induced cytotoxicity. In cell-free studies with BSA, incubation with Asc and copper resulted in glyoxal-hydroimidazolone formation, which was decreased by both AG and catalase. To the best of our knowledge, this is the first study that illustrates the importance of glyoxal production by transition metal-catalyzed Asc autoxidation. Understanding this mechanism of toxicity could lead to the development of novel copper chelating drug therapies to treat diabetic complications.
Shangari
Nandita
N
Department of Pharmaceutical Sciences, Faculty of Pharmacy, University of Toronto, Toronto, Canada.
Chan
Tom S
TS
Chan
Katie
K
Huai Wu
Shuo
S
O'Brien
Peter J
PJ
D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry* / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects*; D002474:Cell-Free System; D003300:Copper / Q000737:chemistry* / Q000494:pharmacology; D005978:Glutathione / Q000032:analysis; D017127:Glycation End Products, Advanced / Q000032:analysis* / Q000737:chemistry; D006037:Glyoxal / Q000032:analysis* / Q000737:chemistry / Q000494:pharmacology; D022781:Hepatocytes / Q000737:chemistry / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007093:Imidazoles / Q000737:chemistry; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects / Q000502:physiology; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000032:analysis; D012710:Serum Albumin, Bovine / Q000737:chemistry
D017127:Glycation End Products, Advanced; D007093:Imidazoles; D017382:Reactive Oxygen Species; C117197:imidazolone; D012710:Serum Albumin, Bovine; D006037:Glyoxal; D003300:Copper; D006861:Hydrogen Peroxide; D005978:Glutathione; D001205:Ascorbic Acid