Abstract
We previously reported that in healthy mouse cerebral arteries, endothelial nitric oxide synthase (eNOS) produces H&sub2;O&sub2;, leading to endothelium-dependent dilation. In contrast, thromboxane A&sub2; (TXA&sub2;), a potent pro-oxidant and pro-inflammatory endogenous vasoconstrictor, is associated with eNOS dysfunction. Our objectives were to elucidate whether (1) the cerebrovascular eNOS-H&sub2;O&sub2; pathway was sensitive to oxidative stress associated with aging and dyslipidemia and (2) TXA&sub2; contributed to cerebral eNOS dysfunction. Atherosclerotic (ATX = LDLR(-/-); hApoB(+/+)) and wild-type (WT) control mice were used at 3 and 12 months old (m/o). Three-m/o ATX mice were treated with the cardio-protective polyphenol catechin for 9 months. Dilations to ACh and the simultaneous eNOS-derived H&sub2;O&sub2; production were recorded in isolated pressurized cerebral arteries. The age-associated decrease in cerebral eNOS-H&sub2;O&sub2; pathway observed in WT was premature in ATX mice, decreasing at 3 m/o and abolished at 12 m/o. Thromboxane synthase inhibition by furegrelate increased dilations at 12 months in WT and at 3 and 12 months in ATX mice, suggesting an anti-dilatory role of TXA&sub2; with age hastened by dyslipidemia. In addition, the non-selective NADP(H) oxidase inhibitor apocynin improved the eNOS-H&sub2;O&sub2; pathway only in 12-m/o ATX mice. Catechin normalized the function of this pathway, which became sensitive to L-NNA and insensitive to furegrelate or apocynin; catechin also prevented the rise in TXA&sub2; synthase expression. In conclusion, the age-dependent cerebral endothelial dysfunction is precocious in dyslipidemia and involves TXA&sub2; production that limits eNOS activity. Preventive catechin treatment reduced the impact of endogenous TXA&sub2; on the control of cerebral tone and maintained eNOS function.