Intraocular penetration of pyruvate following its topical administration in mice

Previous studies from our laboratory have demonstrated that pyruvate, an endogenous alpha-keto acid metabolite, has a protective effect against oxidative stress induced damage to the ocular tissues including the lens, in which in addition to exerting its protective effect against tissue damage caused by oxyradicals generated under organ culture, it is also found effective in preventing actual cataract formation in vivo in animal models undergoing direct oxidative stress as well as in diabetes. In the latter studies, pyruvate was administered mixed with diet and drinking water. However, with the view of the desirability of treating eye diseases by topical administration of the pharmacological agents, the present studies were conducted to determine the penetrability of pyruvate through the cornea to the aqueous humor and the lens following its topical administration as its ester, ethyl pyruvate (EP). These experiments were done in CD-1 mice. After instillation of the drops in the conjunctival cul-de-sac, aqueous humor samples were aspirated at the desired times and analyzed for pyruvate. In a separate group of animals, analyses were done also in the lens. Analyses were done spectrophotometrically by monitoring the decrease in absorption of NADH due to the reduction of pyruvate to lactate by lactate dehydrogenase. The levels of pyruvate were found to be significantly elevated in both the aqueous humor as well as the lens, the peak concentrations being 4.7 and 3.6 mM, respectively. Such levels have been previously shown to be effective in exerting its antioxidant effects. The results are therefore considered pharmacological significant from the point of view of its potential use for topical treatment of cataracts induced by oxidative stress and diabetes.