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

Study Overview
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Brief Summary
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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
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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.

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

Conditions
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Vascular Function, Racial Disparity

Intervention / Treatment
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* Dietary Supplement: Dietary Nitrates 400 mg
* Dietary Supplement: L-citrulline 3 g
* Drug: Sildenafil 100 mg
* Drug: Bosentan 125 mg


Participation Criteria
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Eligibility Criteria
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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)

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 40 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Beetroot juice (Aim 1a)<br>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). | Dietary Supplement: Dietary Nitrates 400 mg<br>* The nitrates in the beetroot juice will be absorbed and reduced in the plasma to nitrite and nitric oxide, increasing endothelium-independent nitric oxide bioavailability.<br>* Other names: Beet It Sport Nitrate 400;|
| Placebo Comparator: Placebo (Aim 1a)<br>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). | Dietary Supplement: Dietary Nitrates 400 mg<br>* The nitrates in the beetroot juice will be absorbed and reduced in the plasma to nitrite and nitric oxide, increasing endothelium-independent nitric oxide bioavailability.<br>* Other names: Beet It Sport Nitrate 400;|
| Active Comparator: L-citrulline (Aim 1b)<br>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. | Dietary Supplement: L-citrulline 3 g<br>* Ingested L-citrulline becomes available in large quantities in the plasma for enzymatic conversion into L-arginine. The activity of the endothelial nitric oxide synthase converts L-arginine into nitric oxide, increasing endothelium-dependent nitric oxide bioavailability.<br>|
| Placebo Comparator: Placebo (Aim 1b)<br>Participants will receive pills containing a placebo to take twice daily for 7 days before the study visit. | Dietary Supplement: L-citrulline 3 g<br>* Ingested L-citrulline becomes available in large quantities in the plasma for enzymatic conversion into L-arginine. The activity of the endothelial nitric oxide synthase converts L-arginine into nitric oxide, increasing endothelium-dependent nitric oxide bioavailability.<br>|
| Active Comparator: Sildenafil (Aim 1c)<br>Upon arriving at the laboratory, participants will ingest a liquid mixture containing Sildenafil (100 mg), an inhibitor of phosphodiesterase 5. | Drug: Sildenafil 100 mg<br>* 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.<br>* Other names: Viagra, Revatio;|
| Placebo Comparator: Placebo (Aim 1c)<br>Upon arriving at the laboratory, participants will ingest a liquid mixture containing a placebo. | Drug: Sildenafil 100 mg<br>* 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.<br>* Other names: Viagra, Revatio;|
| Active Comparator: Bosentan (Aim 2)<br>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. | Drug: Bosentan 125 mg<br>* Bosentan blocks endothelin-1 receptors ETA and ETB, leading to a reduction in vasoconstrictor tone and a greater magnitude of vasodilator responses.<br>* Other names: Tracleer;|
| Placebo Comparator: Placebo (Aim 2)<br>Upon arriving at the laboratory, participants will ingest a liquid mixture containing a placebo. | Drug: Bosentan 125 mg<br>* Bosentan blocks endothelin-1 receptors ETA and ETB, leading to a reduction in vasoconstrictor tone and a greater magnitude of vasodilator responses.<br>* Other names: Tracleer;|

What is the study measuring?
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Primary Outcome Measures

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

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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White, Hyperemia, Black, African American, Caucasian American, Blood Flow, Conductance