Reduction of Radiation-Induced Vascular Nitrosative Stress by the Vitamin E Analog γ-Tocotrienol: Evidence of a Role for Tetrahydrobiopterin

BH4 bioavailability is reduced in the early postradiation phase. Exogenous administration of BH4 reduces postirradiation vascular oxidative stress. GT3 potently reduces the expression of GFRP, one of the key regulatory proteins in the BH4 pathway, and may thus exert some of its beneficial effects on postradiation free radical production partly by counteracting the decrease in BH4.