Protective effects of retinyl palmitate on streptozotocin- and alloxan-induced beta cell toxicity and diabetes in the rat.

The cellular effects of retinoids may be relevant to protection against chemical-induced diabetes mellitus. To determine whether retinyl palmitate protects the beta cell from streptozotocin- and alloxan-induced diabetes, we injected streptozotocin, 60 mg/kg, or alloxan, 100 mg/kg, with or without varying doses of retinyl palmitate intraperitoneally or by tail vein. Plasma glucose was measured for over 4 weeks. To determine if the protective effects of retinyl palmitate were mediated through effects on superoxide dismutase, a scavenger of tissue free radicals, we determined whether retinyl palmitate affected islet superoxide dismutase activity. Retinyl palmitate, given intraperitoneally or by tail vein, protected against both streptozotocin- and alloxan-induced diabetes. The effect was dependent on the route of administration. When given intraperitoneally, the protective effect was greater than when given intravenously. When given by tail vein, the protective effect was dose dependent. Retinyl palmitate in vitro did not affect insulin secretion or islet superoxide dismutase. We conclude that retinyl palmitate treatment protects against streptozotocin- and alloxan-induced diabetes. Further studies are needed to determine whether retinyl palmitate protects against the development of diabetes in other animal models and whether this effect is relevant to diabetes in man.