H2O2-dependent NADH oxidation activity in senile cataractous human lens: its relation to glutathione redox cycle

The present study has demonstrated that H2O2-dependent NADH oxidation activity in aged transparent and senile cataractous human lenses is due to a glutathione redox cycle which consists of reduced glutathione, oxidized glutathione, glutathione peroxidase and glutathione reductase. Especially, the NADH oxidation activity was proportional to the content of free glutathione (reduced plus oxidized forms) under our assay conditions. Employing this simple assay method, the present report has also shown that in the aged and cataractous lenses with pale yellow, yellow or dark yellow nucleus, the free glutathione contents tend to decrease with the increase of insoluble protein contents. However, lens protein was remarkably insolubilized in the lenses with cataracta brunescens, regardless of their exhibiting low or high glutathione contents. The relationship among protein aggregation, coloration and glutathione concentration in the cataractous lenses has been discussed from these findings.