LIPID PEROXIDE AND REACTIVE OXYGEN SPECIES GENERATING SYSTEMS OF THE CRYSTALLINE LENS

Lipid peroxidation (LPO) could be one of the mechanisms of cataractoge nesis, initiated by enhanced production of oxygen free radicals in the eye fluids and tissues and impaired enzymatic and non-enzymatic defen ces of the lens. The increased concentrations of primary molecular LPO products (diene conjugates, lipid hydroperoxides) and end fluorescent LPO products were detected in the lipid moiety of the aqueous humor s amples obtained from patients with cataract as compared to normal dono rs. Isolated human transparent and cataractous lenses and normal mouse and rabbit lenses were incubated with liposomes in organ culture in t he presence and absence of LPO inhibitors, free radical scavengers and enzymes (catalase, superoxide dismutase (SOD)) in order to examine th e potential of the lenses to induce LPO in the surrounding medium. LPO assayed spectrophotometrically were diene and triene conjugates, and malonaldehydes (MDA) were determined as thiobarbituric acid-reactive m aterial. A chemiluminescence detection catalysed by peroxidase was use d to measure H2O2 and O-2(-). was assayed spectrophotometrically using cytochrome C reduction. The level of lipid peroxides in liposomes was significantly (2.5-4.5-fold) higher after 3 h of incubation of the tr ansparent lenses (or the lenses at the initial stage of cataract) than after the proper time of incubation of human mature cataractous lense s and virtually no oxidation of liposomes was detected in the absence of the lens. LPO in this system was decreased in the presence of free radical scavengers and enzymes that degrade H2O2 (EDTA, SOD, L-carnosi ne, chelated iron and catalase). The most effective agent was EDTA whi ch chelates the free metal cations required to generate O-2(-). radica ls that initiate the free radical process culminating in LPO. Lenses g enerated more H2O2 into the medium in the presence of exogenous ascorb ate. Release of the oxidants, (O-2(-)., H2O2, OH. and lipid hydroperox ides) by the intact lenses in the absence of respiratory inhibitors in dicates that these metabolites are normal physiological products inver sely related to the lens life-span potential (maturity of cataract) ge nerated, probably, through the metal-ion catalysed redox-coupled pro-o xidant activation of the lens reductants (ascorbic acid, glutathione).