Role of hydrogen peroxide and the impact of glutathione peroxidase-1 in regulation of cerebral vascular tone

Abstract

Although arachidonic acid (AA) has diverse vascular effects, the mechanisms that mediate these effects are incompletely defined. The goal of our study was to use genetic approaches to examine the role of hydrogen peroxide (H2O2), glutathione peroxidase (Gpx1, which degrades H2O2), and CuZn-superoxide dismutase (SOD1, which produces H2O2 from superoxide) in mediating and in determining vascular responses to AA. In basilar arteries in vitro, AA produced dilation in nontransgenic mice, and this response was reduced markedly in transgenic mice overexpressing Gpx1 (Gpx1 Tg) or in those genetically deficient in SOD1. For example, AA (1 nmol/L to 1 mumol/L) dilated the basilar artery and this response was reduced by approximately 90% in Gpx1 Tg mice (P<0.01), although responses to acetylcholine were not altered. Dilation of cerebral arterioles in vivo in response to AA was inhibited by approximately 50% by treatment with catalase (300 U/mL) (P<0.05) and reduced by as much as 90% in Gpx1 Tg mice compared with that in controls (P<0.05). These results provide the first evidence that Gpx1 has functional effects in the cerebral circulation, and that AA-induced vascular effects are mediated by H2O2 produced by SOD1. In contrast, cerebral vascular responses to the endothelium-dependent agonist acetylcholine are not mediated by H2O2.

Figure 1

Changes in diameter of cerebral arterioles in response to arachidonic acid (left panel) and papaverine (right panel) in C57Bl/6 mice in the absence (Control) and presence of catalase (300 U/ml). Values are means±SE. * = P<0.05 versus control.

Figure 2

Changes in diameter of the basilar artery in response to arachidonic acid in the absence and presence of indomethacin (10 µM, n=4). Baseline diameter of the basilar artery was 128±10 µm under control conditions and 91±7 µm after preconstriction with U46619. Values are means±SE. * = P<0.001 versus control.

Figure 3

Changes in diameter of the basilar artery in response to arachidonic acid (upper left panel) and acetylcholine (lower left panel) in non-Tg and Gpx1 Tg mice. Effects of hydrogen peroxide on vessel diameter in non-Tg mice (upper middle panel) and in non-Tg and Gpx1 Tg mice (upper right panel). Vascular responses to papaverine and KCl are also shown (lower middle panel and lower right panel, respectively). In non-Tg and Gpx1 Tg mice respectively, vessel diameter was 131±4 and 130±5 µm under baseline conditions and 92±4 and 91±4 µm after preconstriction with U46619. Values are means±SE. * = P<0.05 versus non-Tg mice unless otherwise noted.

Figure 4

Changes in diameter of cerebral arterioles in response to arachidonic acid (left panel) and papaverine (right panel) in non-transgenic controls (non-Tg) and Gpx1 Tg mice. Values are means±SE. * = P<0.05 versus non-Tg mice.

Figure 5

Changes in diameter of the basilar artery in response to arachidonic acid (upper left) and acetylcholine (upper right) in wild-type and and SOD1 deficient mice. Effect of DDC on changes in diameter of cerebral arterioles in responses to acetylcholine in C57Bl/6 mice are also shown (upper middle panel). Vascular responses to papaverine and KCl are also shown (lower left and lower middle, respectively). Effects of arachidonic acid on basilar artery diameter in control a R⁺A⁺ mice are shown in the lower right panel. In wild-type and SOD1 deficient mice respectively, vessel diameter was 136±6 and 136±6 µm under baseline conditions and 97±5 and 102±5 µm after preconstriction with U46619. In control and R⁺A⁺ mice respectively, vessel diameter was 141±4 and 140±3 µm under baseline conditions and 99±3 and 95±1 µm after preconstriction with U46619. Values are means±SE. * = P<0.05 versus control or wild-type mice unless otherwise noted.