Study of Vitamin D and Uric Acid Lowering on Kidney and Blood Vessel Function

Phase 3

Completed

Conditions: Renal Function
Overweight
Obesity
Endothelial Function
Blood Pressure

Interventions: Drug: Vitamin D ergocalciferol
Drug: Allopurinol
Drug: Placebo
Drug: Probenecid

Registration Number: NCT01320722

Lead Sponsor: Brigham and Women's Hospital

Brief Summary: The investigators hypothesize that, among non-hypertensive overweight and obese individuals, treatment of vitamin D deficiency and lowering uric acid concentrations (by either xanthine oxidase inhibition or increased renal excretion) will attenuate renin angiotensin system (RAS) activation, improve endothelial function, and lower blood pressure.

Detailed Description: We have demonstrated that lower levels of 25-hydroxyvitamin D (25\[OH\]D) and higher concentrations of uric acid are both potentially modifiable factors that are independently associated with an increased risk of developing hypertension (high blood pressure) in humans. Other investigators have shown that vitamin D supplementation, or lowering uric acid with allopurinol, may reduce blood pressure. Animal experiments suggest that activation of both the systemic and local kidney-specific renin angiotensin systems (RAS) may be the principal mechanism linking 25(OH)D and uric acid with hypertension. In human parallels to these animal studies, we have shown in cross-sectional analyses that non-hypertensive individuals with lower 25(OH)D and higher uric acid levels have increased activation of their systemic and kidney-specific RAS, independent of other factors. However, whether vitamin D supplementation or uric acid lowering attenuates RAS activation has never been demonstrated in humans. Both lower 25(OH)D and higher uric acid concentrations are also associated with endothelial dysfunction in humans, and endothelial function may modulate the RAS and provide an alternate mechanism for the development of hypertension. It remains unclear, however, whether an intervention to increase 25(OH)D or decrease uric acid levels among non-hypertensive adults improves endothelial function; furthermore, it is unknown whether treatment of these individuals would lower blood pressure. Determining whether treatment of 25(OH)D and uric acid concentrations, per se, can attenuate RAS activation, improve endothelial function, and lower blood pressure among nonhypertensive individuals is critically important, with implications stretching beyond hypertension prevention, since RAS activation, endothelial dysfunction, and blood pressure are also implicated in the pathology of cardiovascular and chronic kidney disease. Individuals who are overweight and obese (two-thirds of US adults) represent an important population who are known to have lower 25(OH)D levels, higher uric acid concentrations, activation of the RAS, endothelial dysfunction, and an increased risk of hypertension, cardiovascular disease, and chronic kidney disease. Interestingly, our preliminary data demonstrate that among overweight and obese individuals with normal 25(OH)D or low uric acid levels, adiposity is no longer associated with activation of the RAS, suggesting that low 25(OH)D and high uric acid concentrations might be mediators of the adverse consequences of overweight and obesity.

Recruitment & Eligibility

Status: COMPLETED

Sex: All

Target Recruitment: 242

Inclusion Criteria

25(OH)D < 20 ng/mL OR Uric acid ≥ 5 mg/dL
Age ≥ 18, ≤ 75 years
Body Mass Index (BMI) ≥ 25 kg/m^2

Exclusion Criteria

Hypertension, or on BP-lowering medicine
Diabetes
Coronary Heart Disease
estimated glomerular filtration rate (EGFR) <60 mL/min
Kidney stones
Active cancer (except non-melanoma skin cancer)
Pregnant
Taking vitamin D supplements and unwilling to stop
Osteoporosis
Hypo- or hypercalcemia
Hypo- or hyperphosphatemia
Known allergy to angiotensin-converting enzyme (ACE)-inhibitors
Taking medication for hyperuricemia
Gout, anemia, cirrhosis, active/chronic hepatitis, abnormal aspartate aminotransferase (AST), alanine aminotransferase (ALT) or total bilirubin levels, or anemia
Known allergy to either allopurinol or probenecid
Current use of didanosine, azothioprine, methotrexate, ketoprofen, ketorolac, mycophenolate, or ACE-inhibitors

Study & Design

Study Type: INTERVENTIONAL

Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
Vitamin D	Vitamin D ergocalciferol	Vitamin D ergocalciferol 50,000 unit soft gel capsule once per week for 8 weeks.
Allopurinol	Allopurinol	Allopurinol 300 mg tablet once per day for 4 weeks then either 300 mg once per day or 600 mg once per day for 4 weeks (8 weeks total).
Placebo- Vitamin D	Placebo	Placebo soft gel once per week for 8 weeks.
Placebo- Uric Acid	Placebo	Placebo tablet once per day for 4 weeks then twice per day for 4 weeks (eight weeks total).
Probenecid	Probenecid	Probenecid 500 mg tablet once per day for 4 weeks, then either 500 mg tablet once per day for 4 weeks or 1000 mg once per day for 4 weeks (8 weeks total).

Primary Outcome Measures

Name	Time	Method
Change in Renal Plasma Flow (RPF) in Response to Captopril in High Sodium Balance [Vitamin D]	Week 8 (pre and post captopril)	Change in RPF in response to captopril is a measure of the vasodilator effect from inhibiting angiotensin II (AngII)- mediated vascular tone and therefore the degree of kidney specific Renin Angiotensin System (RAS) activity. Participants consumed a high sodium diet 3 days prior to the test. Following an 8 hour fast, participants remained in a supine (lying down) position and had an intravenous (IV) catheter inserted in each arm, one for infusion and one for blood collection. An 8 milligrams (mg)/kilogram(kg) loading dose of para-aminohippuric acid (PAH) was given, immediately followed by a continuous PAH infusion at 12 mg/minute. After 60 minutes a single dose of 25 mg of captopril was administered. Three pre-captopril measurements and three post-captopril measurements of RPF were made. RPF was normalized to body surface area of 1.73 meters squared (m\^2). The change in RPF was calculated as post-captopril RPF- pre-captopril RPF.
Plasma Renin Activity (PRA) [Vitamin D]	Week 8	PRA is a measure of systemic renin angiotensin system (RAS) activation. Blood was collected and plasma PRA was analyzed using a competitive binding radioimmunoassay (RIA) laboratory test.
Angiotensin II (ATII) Concentration [Vitamin D]	Week 8	ATII concentration is a measure of systemic renin angiotensin system (RAS) activation. Blood was collected and plasma ATII was analyzed using a double-antibody radioimmunoassay (RIA) laboratory test.
Change in Renal Plasma Flow (RPF) Response to Captopril in High Sodium Balance [Uric Acid]	Week 8 (pre and post captopril)	RPF in response to captopril iis a measure of the vasodilator effect from inhibiting angiotensin II (AngII)- mediated vascular tone and therefore the degree of kidney specific Renin Angiotensin System (RAS) activity. Participants consumed a high sodium diet 3 days prior to the test. Following an 8 hour fast, participants remained in a supine (lying down) position and had an intravenous (IV) catheter inserted in each arm, one for infusion and one for blood collection. An 8 milligrams (mg)/kilogram(kg) loading dose of para-aminohippuric acid (PAH) was given, immediately followed by a continuous PAH infusion at 12 mg/minute. After 60 minutes a single dose of 25 mg of captopril was administered. Three pre-captopril measurements and three post-captopril measurements of RPF were made. RPF was normalized to body surface area of 1.73 meters squared (m\^2). The change in RPF was calculated as post-captopril RPF- pre-captopril RPF.
Plasma Renin Activity (PRA) [Uric Acid]	Week 8	PRA is a measure of systemic renin angiotensin system (RAS) activation. Blood was collected and plasma PRA was analyzed using a competitive binding radioimmunoassay (RIA) laboratory test.
Angiotensin II (ATII) Concentration [Uric Acid]	Week 8	ATII concentration is a measure of systemic renin angiotensin system (RAS) activation. Blood was collected and plasma ATII was analyzed using a double-antibody radioimmunoassay (RIA) laboratory test.

Secondary Outcome Measures

Name	Time	Method
Change in Endothelium-Dependent Vasodilation (EDV)	Baseline and Week 8 (pre and post ischaemic stimulus)	Endothelial function was assessed by EDV using brachial artery ultrasonography. Measurements of brachial artery diameter were made under basal conditions and reactive hyperemia following ischaemic stimulus. A blood pressure cuff on the forearm was pumped up for 5 minutes then released. Images were taken at baseline and after reactive hyperemia (increased blood flow). The maximum diameter was determined by the investigator. Change in EDV was expressed as a percent of brachial luminal diameter calculated as post-ischaemic brachial artery diameter - pre-ischaemic brachial artery diameter/pre-ischaemic brachial artery diameter \* 100.
Mean 24-Hour Ambulatory Blood Pressure (ABP)	Baseline and Week 8	A 24-hour mean ambulatory blood pressure was monitored using a 24 hour ABP device. The ABP device is a small box that is worn on the belt or pant/skirt line with a line that connect under the clothing to the cuff on the upper arm. Blood Pressure was recorded every 30 minutes during the day and every 60 minutes during the night for 24 hours.
Mean 24-Hour Ambulatory Blood Pressure (ABP) Nocturnal Dipping	Baseline and Week 8	A 24-hour mean ambulatory blood pressure was monitored using a 24 hour ABP device. The ABP device is a small box that is worn on the belt or pant/skirt line with a line that connect under the clothing to the cuff on the upper arm. Blood Pressure was recorded every 30 minutes during the day and every 60 minutes during the night for 24 hours. Nocturnal dipping is the percent change lower between the daytime and nighttime values.