6R-BH4 Pulmonary Arterial Hypertension Study

The primary objective of the study is to evaluate the safety of oral 6R-BH4, administered in escalating doses in addition to standard care, in subjects with pulmonary arterial hypertension (PAH). The secondary objective of the study is to evaluate change in biochemical markers of endothelial dysfunction and nitric oxide synthetase activity (coupled and uncoupled) in subjects with PAH receiving escalating doses of oral 6R-BH4 in addition to standard care. The third objective of the study is to evaluate change in biomarkers of disease progression, 6-minute walk (6MW) distance, Borg dyspnea scores, and quality of life (QOL) measures in subjects with PAH receiving escalating doses of oral 6R-BH4 in addition to standard care.