Vascular Dysfunction in Black Individuals: Roles of Nitric Oxide and Endothelin-1

Early Phase 1

Terminated

Conditions: Vascular Function
Racial Disparity

Interventions: Drug: Sildenafil 100 mg
Dietary Supplement: Dietary Nitrates 400 mg
Dietary Supplement: L-citrulline 3 g
Drug: Bosentan 125 mg

Registration Number: NCT04770155

Lead Sponsor: University of Mississippi Medical Center

Brief Summary: The research aims of this proposal are:

* Specific Aim 1: To test whether an increase in nitric oxide signaling can increase vasodilator responses in young Black individuals.

* Specific Aim 2: To test whether a decrease in endothelin-1 signaling can increase vasodilator responses in young Black individuals.

Detailed Description: Studies will be conducted in the Clinical Research and Trials Unit at the University of Mississippi Medical Center. All study visits will follow the same procedures, except for the drug or supplement being administered.

For Aim 1, double-blind, randomized, placebo-controlled crossover designs will examine the effects of increasing nitric oxide and cyclic guanosine monophosphate bioavailability on vascular function of young Black and White individuals. Three sets of two visits will be performed:

* Aim 1a: At the beginning of each visit, participants will ingest either a nitrate-rich beetroot juice or a nitrate-depleted beetroot juice (serving as placebo) in their liquid commercial form, which has a distinct color and flavor. The nitrates will be absorbed and reduced in the plasma to nitrite and nitric oxide, increasing endothelium-independent nitric oxide bioavailability.

* Aim 1b: Participants will receive a 7-day supplement of L-citrulline or placebo before each study visit, with a washout period of 7 days between visits. The activity of the endothelial nitric oxide synthase converts L-arginine into nitric oxide and L-citrulline, which is normally recycled back into L-arginine. Unlike L-arginine, oral ingestion of L-citrulline is not catabolized in the gut, nor is it extracted from systemic circulation through hepatic first-pass metabolism. Thus, ingested L-citrulline becomes available in large quantities in the plasma for enzymatic conversion into L-arginine, increasing endothelium-dependent nitric oxide bioavailability.

* Aim 1c: At the beginning of each visit, participants will ingest a liquid mixture prepared by Investigational Drug Services at the University of Mississippi Medical Center containing Sildenafil or placebo. Sildenafil inhibits phosphodiesterase 5, an enzyme that degrades cyclic guanosine monophosphate in the vascular smooth muscle cells inactivating the nitric oxide-mediated signal; thus, Sildenafil will prolong the availability of cyclic guanosine monophosphate, enhancing the nitric oxide-mediated intracellular cascade.

For Aim 2, a double-blind, randomized, placebo-controlled crossover design will examine the role of endothelin-1 on the vascular function of young Black and White individuals. Two visits will be performed, with a minimum of 7 days between them.

• Aim 2: At the beginning of each visit, participants will ingest a liquid mixture prepared by Investigational Drug Services at the University of Mississippi Medical Center containing Bosentan or placebo. Bosentan blocks ETA and ETB receptors, leading to a reduction in vasoconstrictor tone and a greater magnitude of vasodilator responses.

Recruitment & Eligibility

Status: TERMINATED

Sex: All

Target Recruitment: 8

Inclusion Criteria

Self-identification of their race and the race of their biological parents as being only Black (i.e., African American) or only White (i.e., Caucasian American)
Born and raised in the United States

Exclusion Criteria

Mixed races
Any chronic or ongoing disease
Prescribed pharmacological treatment
Smoking or tobacco use
Obesity (body mass index > 30 kg / m2)

Study & Design

Study Type: INTERVENTIONAL

Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Placebo (Aim 1c)	Sildenafil 100 mg	Upon arriving at the laboratory, participants will ingest a liquid mixture containing a placebo.
Beetroot juice (Aim 1a)	Dietary Nitrates 400 mg	Upon arriving at the laboratory, participants will ingest 140 ml of beetroot juice containing a high (\~12.8 mmol) concentration of nitrates (James White Drinks, Suffolk, UK).
Placebo (Aim 1a)	Dietary Nitrates 400 mg	Upon arriving at the laboratory, participants will ingest 140 ml of beetroot juice containing a low concentration (\~0.0055 mmol) of nitrates (James White Drinks, Suffolk, UK).
L-citrulline (Aim 1b)	L-citrulline 3 g	Participants will receive pills containing 3 g of L-citrulline (Superior Labs, Park City, UT) to take twice daily for 7 days before the study visit.
Placebo (Aim 1b)	L-citrulline 3 g	Participants will receive pills containing a placebo to take twice daily for 7 days before the study visit.
Sildenafil (Aim 1c)	Sildenafil 100 mg	Upon arriving at the laboratory, participants will ingest a liquid mixture containing Sildenafil (100 mg), an inhibitor of phosphodiesterase 5.
Bosentan (Aim 2)	Bosentan 125 mg	Upon arriving at the laboratory, participants will ingest a liquid mixture containing Bosentan (125 mg), a non-selective blocker of endothelin-1 receptors ETA and ETB.
Placebo (Aim 2)	Bosentan 125 mg	Upon arriving at the laboratory, participants will ingest a liquid mixture containing a placebo.

Primary Outcome Measures

Name	Time	Method
Muscle Hyperemia (Rhythmic Handgrip Exercise)	Baseline measurements with no drug/supplement administration before or after.	Changes in brachial artery blood flow and conductance during single handgrip contractions at 3 intensities.
Flow-mediated Dilation	Within 4 hours of drug/supplement administration.	The percent change in arterial diameter normalized to arterial shear rate during reperfusion after 5 minutes of circulatory occlusion.
Reactive Hyperemia (Cuff Release)	Within 4 hours of drug/supplement administration.	Blood velocity area-under-the-curve from the beginning of reperfusion to return to resting values.
Muscle Hyperemia (Passive Leg Movement)	Within 4 hours of drug/supplement administration.	Peak and the area-under-the-curve of the change in femoral artery blood flow during 1 minute of passive leg movement.
Muscle Hyperemia (Rhythmic Knee Extension Exercise)	Within 4 hours of drug/supplement administration.	Changes in femoral artery blood flow and conductance during 3 minutes of rhythmic knee extension exercise.