The Effect of 4 Weeks of L-Citrulline Supplementation on Macro- and Microvascular Function in Type 2 Diabetes

Study Overview
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Brief Summary
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The purpose of this study is to examine the effect of 4 weeks of Citrulline supplementation on macro- and microvascular function during acute hyperglycemia in middle-aged and older adults with type 2 diabetes.

Detailed Description
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Using a double-blind, randomized, placebo-controlled, and cross-over design, middle-aged and older adults with type 2 diabetes will be randomized to receive either CIT supplementation (6g/day) or placebo (Microcrystalline Cellulose, 6g/day) for 4 weeks. There will be a total of 5 laboratory visits. Visit 1 (screening visit) will take approximately 1 hour and 30 minutes, visit 2 will take approximately 2 hours and 30 minutes, and visits 3-5 will be approximately 3 hours each. Visit 1 will measure blood pressure, blood glucose and lipid levels, anthropometry, body composition, and muscle strengths. Visits 2-5 will assess vascular function and glucose control during fasted and acute hyperglycemia conditions induced by 75g of glucose ingestion.

Official Title
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The Effect of 4 Weeks of L-Citrulline Supplementation on Macro- and Microvascular Function in Type 2 Diabetes

Conditions
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Type 2 Diabetes

Intervention / Treatment
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* Dietary Supplement: L-citrulline
* Dietary Supplement: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Middle-aged and older women and men between 40-75 years old A physician diagnosed type 2 diabetes at least 3 months ago Treated with an oral hypoglycemic medication Body mass index < 40 kg/m2 Systolic blood pressure < 160 mmHg Sedentary (defined as < 120 min/week of exercise) Not currently participating in exercise or dietary interventions for at least 2 months prior the present study and willing to abstain from participating in those strategies during the duration of this study. Exclusion Criteria: < 40 years of age and > 65 years of age Use of medications and/or any supplements that may affect outcome variables (such as arginine- or citrulline-containing supplements, nitrates, and nitroglycerin) Body mass index ≥ 40 kg/m2 Systolic blood pressure ≥ 160 mmHg Recent changes in medications within 3 months Current smoking any tobacco use Type 1 diabetes, severe cardiovascular/renal/pulmonary diseases More than 7 alcoholic drinks/week of consumption Premenopausal women with an irregular menstrual cycle (oligomenorrhea) or pregnancy

Ages Eligible for Study
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Minimum Age: 40 Years
Maximum Age: 75 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: Double-blind (subject, investigator), randomized, cross-over, placebo-controlled
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: L-citrulline<br>6 grams/day | Dietary Supplement: L-citrulline<br>* 4 weeks of L-citrulline (6 g/day) in 8 capsules. Supplementation will be ingested daily, half of the doses in the morning and half at night.<br>|
| Placebo Comparator: Placebo<br>Microcrystalline cellulose | Dietary Supplement: Placebo<br>* 4 weeks of microcrystalline cellulose in 8 capsules. Supplementation will be ingested daily, half of the doses in the morning and half at night.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in macrovascular endothelial function in the fasted condition | Macrovascular endothelial function will be measured using brachial artery flow mediated dilation (ultrasonography) during reactive hyperemia at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in macrovascular endothelial function during acute hyperglycemia | Macrovascular endothelial function will be measured using brachial artery flow mediated dilation (ultrasonography) during reactive hyperemia at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in microvascular endothelial function in the fasted condition | Microvascular endothelial function will be assessed using peripheral arterial tonometry (EndoPAT device) during reactive hyperemia at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in microvascular endothelial function in the fasted condition | Microvascular endothelial function will be assessed using forearm muscle oxygenation (near-infrared spectroscopy) during reactive hyperemia at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in microvascular endothelial function during acute hyperglycemia | Microvascular endothelial function will be assessed using forearm muscle oxygenation (near-infrared spectroscopy) during reactive hyperemia at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in blood glucose levels in the fasted condition | Blood glucose levels will be measured by finger prick at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in blood glucose levels during acute hyperglycemia | Blood glucose levels will be measured by finger prick at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in central and peripheral arterial stiffness in the fasted condition | Arterial stiffness will be assessed using the central (carotid-femoral) and peripheral (femoral-ankle) pulse wave velocity at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in central and peripheral arterial stiffness during acute hyperglycemia | Arterial stiffness will be assessed using the central (carotid-femoral) and peripheral (femoral-ankle) pulse wave velocity at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in blood pressure in the fasted condition | Brachial and aortic blood pressure will be measured using an automated sphygmomanometry arm cuff (SphygmoCor XCEL). Beat-to-beat blood pressure will be measured using an automated photoplethysmography finger cuff (Finometer). Blood pressure will be measured at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in blood pressure during acute hyperglycemia | Brachial and aortic blood pressure will be measured using an automated sphygmomanometry arm cuff (SphygmoCor XCEL). Beat-to-beat blood pressure will be measured using an automated photoplethysmography finger cuff (Finometer). Blood pressure will be measured at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in stroke volume in the fasted condition | Stroke volume will be measured using impedance cardiography (PhysioFlow) at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in stroke volume during acute hyperglycemia | Stroke volume will be measured using impedance cardiography (PhysioFlow) at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in total peripheral resistance in the fasted condition | Total peripheral resistance will be measured using impedance cardiography (PhysioFlow) at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in total peripheral resistance during acute hyperglycemia | Total peripheral resistance will be measured using impedance cardiography (PhysioFlow) at 60 minutes after oral glucose ingestion at baseline and after 4 weeks of supplementation. | 4 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in body composition | Body composition (fat and lean mass) will be measured at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in muscle strength | Maximal handgrip strength will be measured using handgrip dynamometer. Leg extension and plantar flexion strength will be measured using the 10RM test at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in insulin levels | Serum insulin levels will be tested at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in serum arginine levels | Serum arginine levels will tested at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in serum arginase activity levels | Serum arginase activity levels will tested at baseline and after 4 weeks of supplementation. | 4 weeks | 
| Change in 24-hour ambulatory blood pressure monitoring | Ambulatory blood pressure will be obtained using a monitor during daytime and nighttime on two separate days at baseline and after 4 weeks of supplementation. | 4 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Endothelial function, Arterial stiffness, Hyperglycemia, Oral glucose tolerance test, Aortic blood pressure, Blood glucose, Lean mass