Our broad goal is to determine the mechanism(s) of cataracts caused by inhibitors of lens cholesterol biosynthesis. These inhibitors are the most prescribed drugs in the U.S. New classes of drugs in development may be highly cataractogenic.
The specific aims of the project are based on two new findings: simvastatin rapidly induces cataracts strain specifically in rats and apparently all members of the new class of drugs, the oxidosqualene cyclase (OSC) inhibitors, are cataractogenic. Thus, our specific aims are to determine mechanisms of cataracts induced by simvastatin and the OSC inhibitors and the basis of the selective genetic susceptibility to the simvastatin cataract. The susceptible rats are Chbb:THOM (CT), a European Wistar. We hypothesize that lenses of CT rats possess lower levels of HMG CoA reductase protein and mRNA which make them more sensitive to inhibition by simvastatin. Western blotting and quantitative RT-PCR will be used to measure drug induced changes in lens protein and mRNA, respectively. We hypothesize that the simvastatin rat cataract is mainly due to restricting isoprenes needed for activation of small GTP binding proteins (master regulators of cell function). This idea will be tested by measuring drug induced changes in specific GTP binding proteins, particularly the Rho class, by 2D immunoblots. The effects of simvastatin treatment on lens epithelial cell migration and differentiation will be assessed in vivo by following the distribution of pulse-labeled epithelial cells between capsule and lens body with time after injecting 3H-thymidine. Finally, we hypothesize that the cataracts are due to either accumulation of toxic by-products of sterol synthesis or to direct damage of membranes. Gas-chromatography will be used to measure lens oxysqualenes and oxysterols. Biophysical techniques (infrared spectroscopy, fluorescence anisotropy and X-ray diffraction) will be used to determine if the OSC inhibitors (cationic-tertiary amines) can intercalate into lens membranes and directly perturb them. Information on the mechanism of these cataracts may influence decisions to introduce new hypocholesterolemic drugs and permit discrimination by society between the available drugs for lowest ocular toxicity. These are obvious benefits to public health considering the intended life-long use of the drugs.
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