The present invention is directed to a novel methods and compositions for the therapeutic intervention of vascular complications associated with diabetes, hyperlipidemias, and various cardiovascular disorders including but not limited to recalcitrant hypertension, coronary artery disease, pulmonary arterial hypertension, congestive heart failure, and hemolytic anemias. More specifically, the specification describes methods and compositions for treating such vascular disorders using compositions comprising BH4 and derivative thereof. Combination therapies of BH4 and other therapeutic regimens are contemplated.