Oral L-citrulline administration improves memory deficits following transient brain ischemia through cerebrovascular protection.

L-citrulline (L-Cit) is known to increase nitric oxide (NO) production via the increase of L-arginine (L-Arg) concentration in the blood and improve endothelial dysfunction in cardiovascular diseases. However, little is known about the effects of L-Cit on cerebrovascular dysfunction. Here we showed that oral L-Cit administration prevents cerebrovascular injury following cerebral ischemia using a 20-min bilateral common carotid artery occlusion (BCCAO) mouse model. After BCCAO ischemia, mice were treated with L-Cit (50, 75, or 100 mg/kg p.o.) for 10 days once a day. L-Cit administration not only prevented neuronal cell death but also prevented capillary loss in the hippocampal region following brain ischemia. The cerebrovascular protective effect of L-Cit was associated with the restoration of endothelial nitric oxide synthase (eNOS) expression in the hippocampus. In addition, we devised a novel protocol to analyze NOx(-) (NO(2-) and NO(3-)) productions following L-Arg infusion using in vivo microdialysis and revealed that decreased L-Arg-induced NOx(-) levels were improved in the hippocampus of BCCAO mice following repeated L-Cit administration. Finally, memory deficits following brain ischemia were improved by oral administration of L-Cit. In summary, L-Cit is a potential therapeutic agent that protects cerebrovascular injury and in turn prevents neuronal cell death. Thereby, oral L-Cit administration improves cognitive deficits following brain ischemia.