Protective mechanisms of inosine in platelet activation and cerebral ischemic damage.

OBJECTIVE: Inosine is a naturally occurring nucleoside degraded from adenosine. Recent studies have demonstrated that inosine has potent immunomodulatory and neuroprotective effects. In the present study, we further investigated the inhibitory effects of inosine on platelet activation in vitro and in vivo, as well as in attenuating middle cerebral artery occlusion (MCAO)-induced focal cerebral ischemia in rats. METHODS AND RESULTS: Inosine concentration-dependently (0.5 to 6.0 mmol/L) inhibited platelet aggregation stimulated by agonists. Inosine (1.5 and 3.0 mmol/L) inhibited phosphoinositide breakdown, [Ca+2]i, and TxA2 formation in human platelets stimulated by collagen (1 microg/mL). In addition, inosine (1.5 and 3.0 mmol/L) markedly increased levels of cyclic guanylate monophosphate (GMP) and cyclic GMP-induced vasodilator-stimulated phosphoprotein Ser157 phosphorylation. Rapid phosphorylation of a platelet protein of molecular weight 47,000 (P47), a marker of protein kinase C activation, was triggered by collagen (1 microg/mL). This phosphorylation was markedly inhibited by inosine (3.0 mmol/L). Inosine (1.5 and 3.0 mmol/L) markedly reduced hydroxyl radical in collagen (1 microg/mL)-activated platelets. In in vivo studies, inosine (400 mg/kg) significantly prolonged the latency period of inducing platelet plug formation in mesenteric venules of mice, and administration of 2 doses (100 mg/kg) or a single dose (150 mg/kg) of inosine significantly attenuated MCAO-induced focal cerebral ischemia in rats. CONCLUSIONS: Platelet aggregation contributes significantly to MCAO-induced focal cerebral ischemia. The most important findings of this study suggest that inosine markedly inhibited platelet activation in vitro and in vivo, as well as cerebral ischemia. Thus, inosine treatment may represent a novel approach to lowering the risk of or improving function in thromboembolic-related disorders and ischemia-reperfusion brain injury.

A potent antioxidant, lycopene, affords neuroprotection against microglia activation and focal cerebral ischemia in rats.

We investigated the effects of a potent antioxidant, lycopene, on the free radical-scavenging activity as evaluated by the DPPH test and lipid peroxidation in rat brain homogenates as well as nitric oxide (NO) formation in cultured microglia stimulated by lipopolysaccharide. In addition, we also investigated the therapeutic effect of lycopene in attenuating ischemia/reperfusion brain injury induced by middle cerebral artery (MCA) occlusion in rats. Lycopene (1, 2 and 5 microM) exerted increased DPPH decolorization in the DPPH test, and increased inhibition of iron-catalyzed lipid peroxidation (TBARS formation) in rat brain homogenates in concentration-dependent manners. Furthermore, lycopene (5 and 10 microM) significantly inhibited nitrite production by about 31% and 61% in microglia stimulated by LPS, respectively. Rats which received lycopene at a dosage of 4 mg/kg, but not at 2 mg/kg, showed significant infarct size reductions compared with those which received the solvent control (20% Tween 80). In conclusion, we demonstrate a protective effect of lycopene on ischemic brain injury in vivo. Lycopene, through its antioxidative property, mediates at least a portion of free radical-scavenging activity and inhibits microglia activation, resulting in a reduction in infarct volume in ischemia/reperfusion brain injury.