Oral 6R-BH4 for the Treatment of Isolated Systolic Hypertension and Endothelial Dysfunction

Inclusion Criteria: * No change in prescribed antihypertension medications within the previous 30 days * Study staff able to visualize and measure the brachial artery diameter by high resolution vascular ultrasound required for FMD measurements * ISH with the following mean seated BP: SBP \> 145 and \< 180 mmHg. Diastolic blood pressure \< 90mmHg Exclusion Criteria: * Has known hypersensitivity to 6RBH4 or its excipients * Pregnant or breastfeeding at screening * Use of any investigational product or investigational medical device within 30 days prior to screening * Current disease or condition that would interfere with study participation or safety such as the following: heart failure, atrial fibrillation, aortic valve disease, bleeding disorders, history of repeated syncope or vertigo, severe GERD, GI ulcer, symptomatic coronary or peripheral vascular disease, arrhythmia, serious neurologic disorders including seizures, organ transplant or organ failure * Hypertension secondary to other medical conditions * Any severe comorbid condition that would limit life expectancy to \<6 months * Current use of any nicotine containing substances * History of drug or alcohol abuse * MI, stroke or surgery within 90 days before Screening Visit * CABG within 6 months before the Screening Visit * Serum creatinine \>2.0mg/dl or AST, ALT, GGT levels \>2times upper limit of normal * Concomitant treatment with: any drug known to inhibit folate metabolism, any phosphodiesterase-5 or -3 inhibitor * Previous treatment with any formulation of BH4