Abstract 5201: Low-dose Tetrahydrobiopterin Supplementation Reduces Atherosclerosis Progression in Apolipoprotein E-Knockout Mice via Effects on Vascular T cell Infiltration
Tetrahydrobiopterin (BH4) supplementation improves endothelial function in models of vascular disease by maintaining endothelial nitric oxide synthase coupling and nitric oxide bioavailability. Recent studies using pharmacological and transgenic endothelial-specific BH4 supplementation highlighted the therapeutic potential of BH4 in native atherosclerosis and vascular injury and suggested a potential role for BH4 as regulator of inflammation and vascular remodeling. However, the cellular mechanisms through which this leads to reduced atherosclerosis remain unclear. We have used a pharmaceutical BH4 formulation to address the hypothesis that improved endothelial function resulting from exogenous BH4 supplementation leads to reduced atherosclerosis through effects on vascular inflammation. Single oral dose pharmacokinetic studies revealed rapid BH4 uptake from the gastrointestinal tract into plasma and organs. While in most organs BH4 levels returned to baseline by 8 hours after dosing, BH4 levels in aorta remained markedly increased at 24 hours, suggesting an active mechanism for BH4 retention. Daily oral BH4 supplementation in 8 week old chow-fed ApoE-KO mice for 8 or 12 weeks had no effect on plasma lipids or hemodynamic parameters, but resulted in a significant 45% relative reduction in aortic root atherosclerosis only at 10 mg/kg BH4, compared with placebo controls (0.049 vs. 0.088 mm2, P<0.05 after 8 weeks; 0.142 vs. 0.259 mm2, P<0.05 after 12 weeks). BH4 treatment led to a striking reduction in T cell infiltration, both within plaques (0.001886 vs. 0.006653 mm2; P<0.05) and in the surrounding adventitia (0.007741 vs. 0.020133 mm2; P<0.05). Importantly, BH4 treatment had no effect on circulating leukocyte numbers, and furthermore no evidence for BH4 uptake by peripheral blood mononuclear cells from plasma after single oral supplementation was found. Experiments using endothelium-targeted GTP-cyclohydrolase 1 transgenic mice, with a specific increase in endothelial BH4 levels, revealed a similar reduction in vascular T cell infiltration, suggesting that BH4 supplementation reduces atherosclerosis through a reduction in vascular T cell infiltration mediated by salutary effects on endothelial nitric oxide bioavailability.