Acetyl- L -carnitine decreases glycation of lens proteins: in vitro studies

Although the role of carnitine system in the ocular tissues is not clearly understood, earlier studies showed that lenticular levels of L -carnitine were the highest among ocular tissues and there was a dramatic depletion of lenticular L -carnitine and acetyl- L -carnitine in streptozotocin-diabetic rats. As protein glycation has been implicated in the development of several diabetic complications including cataracts, this study was initiated to show the possible effects of L -carnitine and acetyl- L -carnitine on the glycation and advanced glycation (AGEs) of lens proteins. Calf lens soluble fraction (crystallins) was incubated with 50 m m glucose (containing14C glucose) with or without 5-50 m ml -carnitine, 5-50 m m acetyl- L -carnitine and 5-50 m m acetyl salicylic acid, for 15 days. The results show that while L -carnitine did not have any effect on in vitro glycation of lens crystallins, acetyl- L -carnitine and acetyl salicylic acid decreased crystallin glycation by 42% and 63%, respectively-this decrease was concentration dependent. Glycated crystallins were separated on HPLC which showed that the rate of glycation is in the following order: alpha>beta>gamma. Interestingly, acetyl- L -carnitine inhibited glycation of alpha crystallin more than other crystallins. In vitro incubations with [3H-acetyl] acetyl- L -carnitine showed that acetyl- L -carnitine acetylates lens crystallins (non-enzymatically) and alpha crystallin is the major acetylated protein. Furthermore, there was a 70% reduction in anti-AGE antibody reactivity when 50 m m acetyl- L -carnitine was included in the incubation of lens crystallins and 10 m m erythrose, suggesting that inhibition of glycation by acetyl- L -carnitine also affected the generation of AGEs. This in vitro study shows, for the first time, that acetyl- L -carnitine could acetylate potential glycation sites of lens crystallins, and protect them from glycation-mediated protein damage.