AL-4114

Aldose reductase is part of the sorbitol pathway, which has been linked to many diabetic complications such as retinopathy and cataracts. This study has determined whether two aldose reductase inhibitors, AL-1576 and AL-4114, may be inducersof hepaticbiotransformation in New Zealandwhiterabbits or Sprague-Dawley rats. The drugs were administered either by intraperitoneal injection (ip) once a day for 4 days (10 mg/kg or 50 mg/kg) to rats and rabbits or by topical-ocular dosing three times a day for 14 days to rabbits (0.5% or 5.0%). Rats dosed ip had increased hepatic cytochrome P450 monooxygenase activity toward methoxy count ar in and benzphetamine, glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene, and uridine diphosphate (UDP)-glucurono-syltr an sferase activity toward 4-hydroxybiphenyl and 1-naphthol. In rabbits, ip dosing increased only glucuronosyltransferase activity toward 4-hydroxybiphenyl after AL-4114, and no hepatic biotr an sformation enzyme activities were increased after topical-ocular dosing with either AL-4114 or AL-1576. Activities of other enzymes, including P-450 monooxygenase toward benzo(a)pyrene, N-acetyltr an sferase toward 2-aminofluorene and β-naphthylamine, UDP-glucuronosyltransferase toward 4-methylumbelliferone, styreneoxidehydrolase, and 2-naphthol suIfotransferase, were not increased by either topical-ocular or ip dosing with AL-1576 or AL-4114 in either rats or rabbits, although ip dosing with AL-1576 decreased monooxygenase activity toward ethoxyresorufin in rabbit liver. These results indicate that AL-1576 and AL-4114, though inducers of hepatic biotr an sformation in rats, do not induce hepatic biotran sformation in rabbits when administered by either ip or topical-ocular dosing.

Aldehyde reductase (EC 1.1.1.2) has been regarded so far as an exclusively cytosolic enzyme. The present investigation shows that mitochondria of rat liver, kidney cortex and, tentatively, heart also contain an enzyme catalyzing oxidation of NADPH by aldehydes, p-nitrobenzaldehyde, methylglyoxal and glyceraldehyde. Activity of the mitochondrial enzyme can only be measured after the organelles are disrupted by sonication or solubilized with nonionic detergents. Mitochondrial aldehyde reductase activity contributed to about 4.6% and 2.5% of the total cellular activity in liver and kidney cortex, respectively. However, the specific activity in liver mitochondria was about one third and in kidney cortex mitochondria one tenth of that in the cytosol of the corresponding organ. The mitochondrial enzyme resembled the cytosolic one by its absolute specificity towards NADPH as the electron donor, a similar profile of aldehydic electron acceptors and identical Km values. Mitochondrial aldehyde reductase differed from the cytosolic enzyme by low sensitivity to known inhibitors of cytosolic aldehyde reductase, AL-1576, AL-4114 and ONO-2235. In liver, about 60% of the mitochondrial activity was tightly bound to the membranes whereas about 40% was present in the mitochondrial matrix. The membrane-bound activity was inactivated by digestion of mitoplasts with trypsin, alpha-chymotrypsin or papain, thus pointing to exposition of the substrate-binding site at the external surface of the inner membrane. On the other hand, latency of the enzyme in intact mitochondria indicates that the NADPH-binding site is located at the inner surface. These data provide the first direct evidence for the existence of aldehyde reductase in mitochondria of some rat tissues.