Cellular Events Preceding Acetaminophen Cataractogenesis Studied by Confocal Fluorescence Microscopy

Abstract

Acetaminophen (APAP) is biotransformed by hepatic cytochrome P450 (CYP) enzymes to the cataractogenic metabolite N-acetyl-p-benzoquinone imine (NAPQI). In the previous studies in which NAPQI was injected into the anterior chamber of mouse eye, we observed mitochondrial dysfunction and disturbances in Ca²⁺ homeostasis in the lens epithelium, and activation of the nonlysosomal neutral protease calpain. In this work we investigated whether intraperitoneal injection of APAP elicits similar cellular responses in the lens epithelium prior to the onset of lens opacity development. Following APAP injection, reactive oxygen species generation, intracellular free Ca²⁺ increase and calpain activation in the lens epithelium were determined in situ by fluorescence confocal microscopy. It was found that cellular events in the lens prior to the onset of opacification were essentially identical to those elicited by NAPQI. In addition, lens calpain activities were characterized based on their Ca²⁺ requirement and several calpain inhibitors were shown to prevent cataract development.