A Phase 2, Pharmacokinetic (PK) Study of 6R-BH4 Alone or 6R-BH4 With Vitamin C in Subjects With Endothelial Dysfunction

Inclusion Criteria: * Willing and able to provide written, signed informed consent after the nature of the study has been explained, and prior to any research-related procedures. * Age is ≥ 18 years and ≤ 75 years. * Willing and able to comply with all study procedures. * If currently receiving treatment with or taking any of the following supplements, be willing and able to discontinue taking them throughout the treatment period: * Vit C supplements * Multivitamins containing vit C * Any other dietary supplements, nutraceuticals, or other over- the-counter products containing vit C * Vitamin E-containing supplements * History of cardiovascular disease or cardiovascular risk factors, eg, stable and well-controlled Type 2 diabetes, peripheral arterial disease, obesity, smoking, hypercholesterolemia * Endothelial dysfunction, documented at screening by an abnormal peripheral arterial tonometry (PAT) of ≤ 1.70. * Sexually active subjects must be willing to use an acceptable method of contraception while participating in the study. * Females of childbearing potential must have a negative pregnancy test at Screening and be willing to have additional pregnancy tests during the study. Females considered not of childbearing potential include those who have been in menopause at least 2 years, or had tubal ligation at least 1 year prior to screening, or who have had total hysterectomy. Exclusion Criteria: * Hypertension secondary to other medical conditions (e.g., renal fai…