Aminoguanidine and the effects of modified LDL on cultured retinal capillary cells

PURPOSE. Compared with normal low density Lipoprotein (N-LDL), LDL minimall y modified in vitro by glycation, minimal oxidation, or glycoxidation (G-, MO-, GO-LDL) decreases survival of cultured retinal capillary endothelial c ells and pericytes. Similar modifications occurring in vivo in diabetes may contribute to retinopathy. The goal of this study was to determine whether low concentrations of aminoguanidine might prevent cytotoxic modification of LDL and/or protect retinal capillary cells from previously modified LDL. METHODS. Minimal in vitro modification of LDL (3 days, 37 degrees C) was ac hieved with glucose (0, 50 mM), under antioxidant conditions (for N-LDL, G- LDL). or under mild oxidant conditions (for MO-, GO-LDL) in the presence/ab sence of aminoguanidine (0, 1, 10, 100 mu M). Glucose and aminoguanidine we re then removed by dialysis. Confluent bovine retinal capillary endothelial cells (n = 13) and pericytes (n = 14) were exposed to LDL (100 mg/l) for 3 days, with and without aminoguanidine (100 mu M) in media. Cell counts wer e determined by hemocytometer. RESULTS. A decrease in cell counts after exposure to modified compared with N-LDL was confirmed (P < 0.001) but was significantly mitigated if LDL had been modified in the presence of aminoguanidine (P < 0.001). Aminoguanidin e was as effective at 1 mu M as at the higher concentrations. Aminoguanidin e (100 mu M) present in culture media conferred no additional protection, a nd showed slight evidence of toxicity. Aminoguanidine present during LDL mo dification had no effect on measured glycation or oxidation products, or on LDL oxidizability. CONCLUSIONS. Very low concentrations of aminoguanidine mitigate toxicity of LDL exposed to stresses that simulate the diabetic environment. This actio n may contribute to the beneficial effects of aminoguanidine observed in ex perimental diabetic retinopathy.