Red Blood Cell ATP Release and Vascular Function in Humans

Study Overview
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Brief Summary
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Previous work demonstrates that the red blood cells of older adults do not release a potent vasodilator (ATP) as well as the red blood cells of younger adults. The investigators are targeting a pathway within the red blood cell using fasudil hydrochloride to determine if both the release of ATP from red blood cells and blood flow responses to low oxygen (hypoxia) and exercise in older adults can be improved.

Detailed Description
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Participants will initiate contact with the investigators by responding to flyers placed in the community either by phone or email. The first correspondence (phone or email) will provide a brief description of the research and ask a series of screening questions to determine age, height, weight, and any medications participants may be taking as well as the current health status (diagnoses, basic health history, and physical activity level) of participants. If they qualify, a two hour screening visit is scheduled during a time when the participant will be examined by the physician. All participants will undergo informed consent in a face to face private meeting with the research coordinator. Following informed consent, participants will be evaluated by a physician and undergo a treadmill stress test to rule out cardiovascular disease. During the study, heart rate will be monitored with a 3-lead ECG and blood pressure will be monitored noninvasively with a blood pressure cuff on the finger (finometry). Venous blood will be collected at multiple time points via a catheter inserted into a forearm vein draining skeletal muscle circulation for measurement of blood gases (0.5 mL/sample) and plasma [ATP] (2 mL/sample), with less than 100 mL of blood being drawn in total ( 60mL total). Blood flow at rest and in response to hypoxia and exercise will be measured non-invasively using Doppler ultrasound of the brachial artery. Hypoxia trials will be performed by having participants breathe a low oxygen gas mixture via a mouthpiece that is hooked up to gas tanks and an anesthesia monitor to decrease their oxygen saturation to  80% (similar to hiking a 14er) for 10 minutes. Exercise trials will last for approximately 15 minutes and will involve participants performing graded-intensity rhythmic handgrip exercise by lifting weights (corresponding to a low, moderate, and high workload) using a pulley system. The drug treatment used in this study (fasudil) is being given because it may improve red blood cell ATP release in older adults. This is a double-blinded placebo controlled study, thus participation will occur on two randomized experimental days.

Official Title
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Red Blood Cell ATP Release and Vascular Function in Humans

Conditions
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Cardiovascular Diseases

Intervention / Treatment
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* Drug: Fasudil Hydrochloride
* Other: Saline


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy Sedentary to moderately active 18 to 30 years old for young subjects 60 to 80 years old for older subjects Exclusion Criteria: Obesity (BMI ≥ 30 kg/m^2) Cardiovascular disease Metabolic disease Use of medications that can influence cardiovascular function Blood pressure greater than or equal to 140/90 Smoker Use of hormone replacement therapy

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 80 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
Interventional Model Description: This is a randomized, double-blind, placebo-controlled, crossover study. Approximately 20 young and 20 older adults will be recruited for participation and randomly assigned to either a placebo (saline) infusion or a fasudil hydrochloride infusion. The dose of fasudil hydrochloride is 60 mg/ 60 min.
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Fasudil hydrochloride<br>Participants will receive a 100 mL intravenous infusion (in 60 minutes) of 60 mg of fasudil hydrochloride + saline prior to measurements of vascular function and ATP release. | Drug: Fasudil Hydrochloride<br>* 10 mg/mL vial of fasudil hydrochloride. 6 mL (60 mg) of fasudil hydrochloride are added to a 100 mL saline bag for delivery to subjects.<br>|
| Placebo Comparator: Saline<br>Participants will receive a 100 mL intravenous infusion (in 60 minutes) of saline (placebo) prior to measurements of vascular function and ATP release. | Other: Saline<br>* 100 mL saline bag.<br>* Other names: Placebo;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Forearm Blood Flow Responses to Hypoxia After Administration of Intervention | Forearm blood flow measured using Doppler ultrasound before and after 5 minutes of exposure to hypoxia (breathing a mix of low-oxygen gas and room air to achieve oxygen saturations of  80%). | Within 4 hours after administration of intervention | 
| Forearm Blood Flow Responses to Exercise After Administration of Intervention | Forearm blood flow measured using Doppler ultrasound before and during continuous rhythmic handgrip exercise at a low, moderate, and high intensity workload (4 minutes at each workload for 12 minutes in total). | Within 4 hours after administration of intervention | 
| Change in ATP Release to Hypoxia After Administration of Intervention | Venous plasma concentrations of ATP measured using a luminometer before and after 5 minutes of exposure to hypoxia (breathing a mix of low-oxygen gas and room air to achieve oxygen saturations of  80%). | Within 4 hours after administration of intervention | 
| Change in ATP Release to Exercise After Administration of Intervention | Venous plasma concentrations of ATP measured using a luminometer before and during continuous rhythmic handgrip exercise at a low, moderate, and high intensity workload (4 minutes at each workload for 12 minutes in total). | Within 4 hours after administration of intervention | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Arterial Stiffness After Administration of Intervention | Arterial stiffness measured non-invasively using a SphygmoCor system after administration of saline (placebo) and fasudil. This is a randomized crossover design study, so participants will receive 1 treatment (saline or fasudil) on their first visit and the other treatment on their second visit. | Immediately following administration of intervention |