Abstract W P230: Tetrahydrobiopterin Attenuates Cerebrovascular Oxidative Stress in Tg2576 Mouse Model of Alzheimer’s Disease

Abstract

Background: The present study was designed to test the hypothesis that supplementation of tetrahydrobiopterin (BH4) to transgenic mice expressing the Swedish double mutation of human amyloid precursor protein (Tg2576 mice) results in restoration of BH4 levels required for activation of endothelial nitric oxide synthase (eNOS), and in turn, prevents oxidative stress in cerebral microvasculature. Methods: Cerebral microvessels were obtained from 4-5 months old female wild-type and Tg2576 mice. Biopterin levels, enzymatic activity of GTP cyclohydrolase I (GTPCH-I) and superoxide production were measured by HPLC. The effects of supplementation of BH4 on oxidative stress were studied by injecting wild-type and Tg2576 mice subcutaneously with 100 mol/kg (b.w.) of BH 4 ([ 6R ]-5,6,7,8-tetrahydro-L-biopterin dihydrochloride; [ 6R ]-BH4). Results: Enzymatic activity of GTPCH-I, rate limiting enzyme in BH4 biosynthesis, was not different between cerebral microvessels of wild-type and Tg2576 mice. However, bioavailability of BH4, was significantly reduced in cerebral microvessels of Tg2576 mice (P<0.05, n=8). Production of superoxide anions was significantly elevated in cerebral microvessels of Tg2576 mice (P<0.01, n=6), indicative of oxidative stress. This increased superoxide anion production was abolished by L-NAME, a NOS inhibitor, suggestive of eNOS uncoupling (P<0.05, n=6). Supplementation of [ 6R ]-BH4 to wild-type and Tg2576 mice resulted in significant increase in BH4 bioavailability (P<0.05, n=6). Notably, supplementation of [ 6R ]-BH4 abrogated the increase in superoxide anion production in cerebral microvessels of Tg2576 mice (P<0.05, n=5), while superoxide anion production remained unchanged in cerebral microvessels of WT mice. Furthermore, the inhibitory effects of L-NAME on superoxide anion production in cerebral microvessels of Tg2576 mice were abolished following [ 6R ]-BH4 supplementation (P<0.05, n=4). Conclusion: Supplementation of [ 6R ]-BH4 restored bioavailability of BH4, thereby abrogating superoxide anion production derived from eNOS. Our results suggest that uncoupling of eNOS contributes to oxidative stress in cerebral microvessels of Tg2576 mice.