calpain-inhibitor-iii and Cataract

Two dipeptide aldehyde cell permeable calpain inhibitors, cBz-Val-Phe and calpeptin, have been assessed for their ability to prevent cytoskeletal proteolysis and loss of transparency in whole rat lenses. Calcium overload, induced by ionomycin in artificial aqueous humor with 1mM calcium, resulted in lens opacification and degradation of cytoskeletal proteins including spectrin, filensin, and vimentin. No such changes resulted from incubation in ionomycin in the absence of calcium. In calcium overload lenses both inhibitors gave some protection against cytoskeletal protein degradation and loss of transparency. These experiments indicate that calpain has a role in cortical opacification in high calcium lenses and that cell penetrating calpain inhibitors do indeed enter lens cells and reduce both proteolysis and opacification.

Topics: Animals; Calcium; Calpain; Cataract; Cattle; Cell-Free System; Cysteine Proteinase Inhibitors; Cytoskeletal Proteins; Dipeptides; Eye Proteins; Intermediate Filament Proteins; Ionophores; Lens, Crystalline; Light; Rats; Rats, Wistar; Scattering, Radiation; Spectrin; Vimentin

E64, an inhibitor of calpain (EC 3.4.22.17) and other cysteine proteases, slows the rate of formation of cataract in cultured rat lenses. The purpose of this study was to determine (1) why E64, a charged compound with little cell permeability, was effective in reducing cataract in cultured lens and (2) whether uncharged more permeable protease inhibitors are more effective than E64 in preventing cataract. Results showed that E64 entered the lens, but only after the lens was treated with the calcium ionophore, A23187, or sodium selenite, both of which cause cataracts. Therefore, the uptake and subsequent effectiveness of E64 may be related to a generalized increase in membrane permeability during induction of cataract in culture. Three protease inhibitors, reported to have improved cell permeability, were compared with E64 for their ability to prevent cataracts in cultured lenses. cBz-ValPheH, calpain inhibitors I and II, are uncharged-aldehyde inhibitors of calpain. Calpain inhibitors I and II even at high concentrations were not effective at reducing lens opacity caused by calcium ionophore and were toxic to the lens. cBz-ValPheH, which is slightly toxic to the lens, was able to significantly reduce lens opacity induced by calcium ionophore. The presented data suggest that while E64 decreases cataract formation in cultured lens, the more cell permeable inhibitor, cBz-ValPheH, may have greater efficacy as an anticataract drug in vivo.

Topics: Amino Acid Sequence; Animals; Calcimycin; Calpain; Cataract; Cell Membrane Permeability; Chromatography, High Pressure Liquid; Culture Techniques; Cysteine Proteinase Inhibitors; Dipeptides; Drug Interactions; Electrophoresis, Polyacrylamide Gel; Glycoproteins; Lens, Crystalline; Leucine; Leupeptins; Molecular Sequence Data; Rats; Rats, Sprague-Dawley