Pyridoxine, P2 Receptor Antagonism, and ATP-mediated Vasodilation in Young Adults

Previous research has identified adenosine triphosphate (ATP) as an important vasodilator that is released from red blood cells during exercise and exposure to hypoxic environments in adult humans. Further, older adults appear to have lower blood flow during both of these stressors and also have lower amounts of ATP released from their red blood cells. However, the contribution of ATP to vasodilation in response to exercise and hypoxia is currently unknown due to the lack of an effective ATP receptor antagonist. We aim to determine whether Vitamin B6 or its metabolite, Pyridoxal-5-Phosphate (PLP) is an effective ATP receptor antagonist.

Study Overview

• Status: Completed
• Conditions: Receptor Blockade
• Intervention / Treatment: Drug: Adenosine Triphosphate; Drug: Acetylcholine; Drug: Sodium Nitroprusside; Drug: Vitamin B 6; Drug: Pyridoxal 5'-Phosphate; Drug: Adenosine Diphosphate; Drug: Adenosine Monophosphate; Drug: Uridine Triphosphate; Drug: Adenosine

Detailed Description

Adenosine triphosphate (ATP) is an established vasodilator that is released from red blood cells during a variety of stimuli including exercise and exposure to hypoxic environments. Many studies have shown that infusion of ATP can lead to vasodilation similar to that which is achieved during exercise, and that plasma ATP concentrations increase in a graded fashion during graded exercise. Further, older adults have lower levels of blood flow during exercise and hypoxia compared to their younger counterparts, and the reduced blood flow is coupled with impaired release of ATP from red blood cells during these stimuli. Thus, ATP is believed to be an important vasodilator. However, the role of ATP in the regulation of blood flow is not fully understood due to the lack of an effective ATP receptor (P2Y2) antagonist. Development of an effective P2Y2 antagonist will allow researchers to determine the role of ATP in vasodilation to stimuli such as exercise by comparing blood flow during exercise with and without the blocker. Preliminary data from our laboratory suggests that Vitamin B6 (pyridoxine hydrochloride) or its metabolite Pyridoxal-5-Phosphate (PLP) may be an effective blocker of ATP-mediated vasodilation. As a result, the purpose of this study is to determine whether Vitamin B6 or PLP can inhibit vasodilation in response to intra-arterial infusions of ATP. This study also aims to determine the specificity of Vitamin B6 or PLP by measuring its effect on vasodilation in response to infusion of several other vasodilators.

Participants will be asked to complete one screening visit and one study visit. Once study eligibility has been determined, participants will report to the Human Performance Clinical Research Laboratory at Colorado State University following an overnight fast. A physician will then place a catheter in the brachial artery of the non-dominant arm, and participants will be randomized into one of three study arms to determine which drugs will be infused into the artery. Each arm includes ATP and two other vasodilators. The study will begin by measuring vasodilation in response to four standard doses of each vasodilator. Vasodilation in response to the vasodilators will then be assessed again following infusion of Vitamin B6 or PLP. Reduced vasodilation to any of the drugs during the second trial will suggest that Vitamin B6 or PLP is an antagonist to the channel through which the drug signals. Each study visit will last approximately 4-5 hours.

• Study Type: Interventional
• Enrollment (Actual): 9
• Phase: Early Phase 1

Contacts and Locations

Study Locations

• United States
  • Colorado
    • Fort Collins, Colorado, United States, 80523
      • Human Performance and Clinical Research Laboratory

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 14 years to 26 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Sedentary-moderately active
• Free of chronic disease

Exclusion Criteria:

• Current smoker
• BMI > 29.9 kg/m2
• Blood pressure equal to or greater than 140/90 mmHg
• Use of any medications including vitamin B6 supplements or antioxidants

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: ATP, Ach, SNP; All drugs will be administered via intra-arterial (brachial artery) infusion, and the dosages below will be administered two times: once before administration of Vitamin B6 (pyridoxine) and once following administration of the Vitamin B6 (pyridoxine) loading dose. Adenosine Triphosphate: 1.25, 2.5, 5, and 10 μg/dl forearm volume/min for 3 minutes each. Acetylcholine: 1, 4, 8, and 16 μg/dl forearm volume/min for 3 minutes each. Sodium Nitroprusside: 0.25, 0.5, 1, and 2 μg/dl forearm volume/min for 3 minutes each. Vitamin B6 (pyridoxine): up to 200 mg of pyridoxine will be infused over 20 minutes. A maintenance dose of 2.5 mg/min may be used throughout the remainder of the protocol. Pyridoxal-5-Phosphate (PLP) may be used as an alternative blocker instead of pyridoxine. It will be infused at doses up to 200 µg/dl forearm volume/min.	Drug: Adenosine Triphosphate; See arm/group descriptions; Other Names: ATP; Drug: Acetylcholine; See arm/group descriptions; Other Names: Ach; Drug: Sodium Nitroprusside; See arm/group descriptions; Other Names: SNP; Drug: Vitamin B 6; See arm/group descriptions; Other Names: Pyridoxine; Pyridoxine Hydrochloride; Drug: Pyridoxal 5'-Phosphate; See arm/group descriptions; Other Names: PLP; P5P; pyridoxal phosphate monohydrate; MC-1
Experimental: ATP, ADP, AMP; All drugs will be administered via intra-arterial (brachial artery) infusion, and the dosages below will be administered two times: once before administration of Vitamin B6 (pyridoxine) and once following administration of the Vitamin B6 (pyridoxine) loading dose. Adenosine Triphosphate: 1.25, 2.5, 5, and 10 μg/dl forearm volume/min for 3 minutes each. Adenosine Diphosphate: 20, 40, 80, and 160 μg/dl forearm volume/min for 3 minutes each. Adenosine Monophosphate: 25, 50, 100, and 200 μg/dl forearm volume/min for 3 minutes each. Vitamin B6 (pyridoxine): up to 200 mg of pyridoxine will be infused over 20 minutes. A maintenance dose of 2.5 mg/min may be used throughout the remainder of the protocol. Pyridoxal-5-Phosphate (PLP) may be used as an alternative blocker instead of pyridoxine. It will be infused at doses up to 200 µg/dl forearm volume/min.	Drug: Adenosine Triphosphate; See arm/group descriptions; Other Names: ATP; Drug: Vitamin B 6; See arm/group descriptions; Other Names: Pyridoxine; Pyridoxine Hydrochloride; Drug: Pyridoxal 5'-Phosphate; See arm/group descriptions; Other Names: PLP; P5P; pyridoxal phosphate monohydrate; MC-1; Drug: Adenosine Diphosphate; See arm/group descriptions; Other Names: ADP; Drug: Adenosine Monophosphate; See arm/group descriptions; Other Names: AMP
Experimental: ATP, UTP, Adenosine; All drugs will be administered via intra-arterial (brachial artery) infusion, and the dosages below will be administered two times: once before administration of Vitamin B6 (pyridoxine) and once following administration of the Vitamin B6 (pyridoxine) loading dose. Adenosine Triphosphate: 1.25, 2.5, 5, and 10 μg/dl forearm volume/min for 3 minutes each. Uridine Triphosphate: 1.25, 2.5, 5, and 10 μg/dl forearm volume/min for 3 minutes each. Adenosine: 3.125, 6.25, 12.5, and 25 μg/dl forearm volume/min for 3 minutes each. Vitamin B6 (pyridoxine): up to 200 mg of pyridoxine will be infused over 20 minutes. A maintenance dose of 2.5 mg/min may be used throughout the remainder of the protocol. Pyridoxal-5-Phosphate (PLP) may be used as an alternative blocker instead of pyridoxine. It will be infused at doses up to 200 µg/dl forearm volume/min.	Drug: Adenosine Triphosphate; See arm/group descriptions; Other Names: ATP; Drug: Vitamin B 6; See arm/group descriptions; Other Names: Pyridoxine; Pyridoxine Hydrochloride; Drug: Pyridoxal 5'-Phosphate; See arm/group descriptions; Other Names: PLP; P5P; pyridoxal phosphate monohydrate; MC-1; Drug: Uridine Triphosphate; See arm/group descriptions; Other Names: UTP; Drug: Adenosine; See arm/group descriptions; Other Names: Adenocard

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Vascular Conductance	Vascular conductance is an index of vascular tone through which vasodilation can be determined. Vascular conductance is calculated by measuring blood flow in response to infusion of a vasodilator and accounting for blood pressure. Thus, the change in blood flow is due to a change in vascular conductance.	Continuous measurement of vascular conductance during the 12 minute dose response for each drug. Measures are repeated following administration of Vitamin B6 or PLP.

Collaborators and Investigators

• Sponsor: Colorado State University

Publications and helpful links

Helpful Links

• Lab website

Study record dates

Study Major Dates

• Study Start (Actual): February 7, 2019
• Primary Completion (Actual): June 1, 2021
• Study Completion (Actual): June 1, 2021

Study Registration Dates

• First Submitted: November 8, 2018
• First Submitted That Met QC Criteria: November 8, 2018
• First Posted (Actual): November 13, 2018

Study Record Updates

• Last Update Posted (Actual): July 27, 2021
• Last Update Submitted That Met QC Criteria: July 26, 2021
• Last Verified: July 1, 2021

More Information

Terms related to this study

• Keywords: Cardiovascular; Adenosine Triphosphate; Pyridoxine; PLP; P5P
• Additional Relevant MeSH Terms: Physiological Effects of Drugs; Neurotransmitter Agents; Molecular Mechanisms of Pharmacological Action; Anti-Arrhythmia Agents; Antihypertensive Agents; Vasodilator Agents; Peripheral Nervous System Agents; Cholinergic Agents; Analgesics; Sensory System Agents; Purinergic Agents; Micronutrients; Cholinergic Agonists; Vitamins; Vitamin B Complex; Purinergic P1 Receptor Agonists; Purinergic Agonists; Nitric Oxide Donors; Adenosine; Vitamin B 6; Pyridoxal; Pyridoxine; Nitroprusside; Acetylcholine; Pyridoxal Phosphate
• Other Study ID Numbers: 17-7430H

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: No

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No