The effect of superoxide anion on autoregulation of cerebral blood flow.

BACKGROUND AND PURPOSE: Recent studies have suggested that autoregulation of cerebral blood flow (CBF) is impaired after traumatic and ischemic brain injury. Given that the levels of superoxide anion (O2*-) are increased in these conditions, we postulate that O2*- contributes to the impairment of CBF autoregulation. METHODS: CBF was monitored with laser Doppler flowmetry during increases in blood pressure. RESULTS: During the control period, CBF was well autoregulated after the increase in mean arterial pressure (MAP) from 98+/-3 to 140+/-6 mm Hg. The autoregulation index (AI; DeltaCBF/DeltaMAP) averaged 0.25+/-0.02 (n=6). O2*- in the brain was then increased by subdural perfusion of xanthine/xanthine oxidase (different concentrations) and catalase. Low concentrations of O2*- decreased basal CBF by 10+/-1.6% but had no effect on autoregulation (AI, 0.19+/-0.02; n=6). Higher concentrations of O2*- (0.2 mmol/L xanthine and either 3 or 20 mU xanthine oxidase) increased basal CBF by 30+/-2% and 42+/-4%, respectively, and impaired autoregulation of CBF (AI, 0.55+/-0.03 and 0.76+/-0.02; n=6). Inclusion of superoxide dismutase in the O2*(-)-generating system restored autoregulation (AI, 0.28+/-0.05; n=6). Neither inhibition of NO synthase nor the addition of deferioxamine had any effect on the ability of higher concentrations of O2*- to impair autoregulation of CBF (AI, 0.65+/-0.07 and 0.72+/-0.05 respectively; n=6). O2*- also increased the activity of KCa channels in cerebral vascular smooth muscle cells (VSMCs; n=8). CONCLUSIONS: These results suggest that O2*- increases basal CBF and impairs autoregulation of CBF, likely through the activation of KCa channels in cerebral VSMCs.

Antiangiogenic effect of inhibitors of cytochrome P450 on rats with glioblastoma multiforme.

Cytochrome P450 epoxygenase catalyzes 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) from arachidonic acid (AA). In 1996, our group identified the expression of the cytochrome P450 2C11 epoxygenase (CYP epoxygenase) gene in astrocytes. Because of our finding an array of physiological functions have been attributed to EETs in the brain, one of the actions of EETs involves a predominant role in brain angiogenesis. Blockade of EETs formation with different epoxygenase inhibitors decreases endothelial tube formation in cocultures of astrocytes and capillary endothelial cells. The intent of this investigation was to determine if pharmacologic inhibition of formation of EETs is effective in reducing capillary formation in glioblastoma multiforme with a concomitant reduction in tumor volume and increase in animal survival time. Two mechanistically different inhibitors of CYP epoxygenase, 17-octadecynoic acid (17-ODYA) and miconazole, significantly reduced capillary formation and tumor size in glial tumors formed by injection of rat glioma 2 (RG2) cells, also resulting in an increased animal survival time. However, we observed that 17-ODYA and miconazole did not inhibit the formation of EETs in tumor tissue. This implies that 17-ODYA and miconazole appear to exert their antitumorogenic function by a different mechanism that needs to be explored.

20-HETE contributes to the acute fall in cerebral blood flow after subarachnoid hemorrhage in the rat.

This study examined the effects of blocking the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) on the acute fall in cerebral blood flow after subarachnoid hemorrhage (SAH) in the rat. In vehicle-treated rats, regional cerebral blood flow (rCBF) measured with laser-Doppler flowmetry fell by 30% 10 min after the injection of 0.3 ml of arterial blood into the cisterna magna, and it remained at this level for 2 h. Pretreatment with inhibitors of the formation of 20-HETE, 17-octadecynoic acid (17-ODYA; 1.5 nmol intrathecally) and N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine (HET0016; 10 mg/kg iv), reduced the initial fall in rCBF by 40%, and rCBF fully recovered 1 h after induction of SAH. The concentration of 20-HETE in the cerebrospinal fluid rose from 12 +/- 2 to 199 +/- 17 ng/ml after SAH in vehicle-treated rats. 20-HETE levels averaged only 15 +/- 11 and 39 +/- 13 ng/ml in rats pretreated with 17-ODYA or HET0016, respectively. HET0016 selectively inhibited the formation of 20-HETE in rat renal microsomes with an IC(50) of <15 nM and human recombinant CYP4A11, CYP4F2, and CYP4F3 enzymes with an IC(50) of 42, 125, and 100 nM, respectively. These results indicate that 20-HETE contributes to the acute fall in rCBF after SAH in rats.