L-arginine and Brown Adipose Tissue

Study Overview
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Brief Summary
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The South Asian population is facing an epidemic of type 2 diabetes, of which the underlying cause is still unknown. It is currently hypothesized that an ethnic susceptibility towards a disturbed energy metabolism may underlie this disadvantageous metabolic phenotype. In line with this, the investigators recently discovered that Dutch South Asian subjects have 32% lower resting energy expenditure (REE) and 34% lower energy-combusting brown adipose tissue (BAT) compared to matched white Caucasians. Nitric oxide (NO) was recently shown to be crucial for BAT development and, interestingly, South Asians have diminished NO bioavailability. Thus, the disadvantageous metabolic phenotype in South Asians may be caused by diminished NO bioavailability resulting in lower BAT volume. Therefore, the investigators hypothesize that increasing NO generation in the body by administration of L-arginine, the precursor of NO, will improve their metabolic phenotype by increasing BAT volume, thereby increasing REE and clearance of triglycerides and glucose by BAT. To investigate this, the investigators will perform a randomized placebo-controlled multicenter cross-over study in moderately obese Dutch South Asians and matched white Caucasians. Subjects will receive L-arginine (9 gram/day) or placebo for 6 weeks, followed by a wash-out period of 4 weeks and then again 6 weeks of one of either treatments. At the end of both treatment periods, a cold-induced PET-CT scan will be performed. Furthermore, muscle and fat biopsies will be obtained and thermoregulation will be assessed.

Detailed Description
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Rationale: The South Asian population originally descends from the Indian subcontinent and represents approximately 20% of the total world population. This population is facing an epidemic of type 2 diabetes, of which the underlying cause is still unknown. A high prevalence of a disadvantageous metabolic phenotype, consisting of obesity, insulin resistance and dyslipidemia, may at least in part contribute to this excess risk. It is currently hypothesized that an ethnic susceptibility towards a disturbed energy metabolism may underlie this disadvantageous metabolic phenotype. In line with this, the investigators recently discovered that Dutch South Asian subjects have 32% lower resting energy expenditure (REE) and 34% lower energy-combusting brown adipose tissue (BAT) compared to matched white Caucasians. Nitric oxide (NO) was recently shown to be crucial for BAT development and, interestingly, South Asians have diminished NO bioavailability. Thus, the disadvantageous metabolic phenotype in South Asians may be caused by diminished NO bioavailability resulting in lower BAT volume. Therefore, the investigators hypothesize that increasing NO generation in the body by administration of L-arginine, the precursor of NO, will improve their metabolic phenotype by increasing BAT volume, thereby increasing REE and clearance of triglycerides and glucose by BAT. Objectives: The primary objectives are: 1) to determine the effect of L-arginine on glucose uptake by brown adipose tissue and to assess whether the effect differs between South Asian and white Caucasian subjects; 2) to determine the effect of L-arginine on whole body energy expenditure and to assess whether the effect differs between South Asian and white Caucasian subjects; 3) to determine the effect of L-arginine on fat mass and to assess whether the effect differs between South Asian and white Caucasian subjects. Study design: A randomized placebo-controlled multicenter cross-over study will be performed in moderately obese Dutch South Asians and matched white Caucasians. Subjects will receive L-arginine (9 gram/day) or placebo for 6 weeks, followed by a wash-out period of 4 weeks and then again 6 weeks of one of either treatments. At the end of both treatment periods, a cold-induced PET-CT scan will be performed. Furthermore, muscle and fat biopsies will be obtained, thermoregulation will be assessed, an oral glucose tolerance will be performed and the investigators will assess NO-dependent and independent vasodilation by means of iontophoresis. Study population: Mildly obese (BMI 25-30 kg/m2) pre-diabetic male volunteers of South Asian and white Caucasian descent aged between 35-50 years. Intervention: The intervention will consist of administration of 9 grams of L-arginine per day in three gifts (3dd 3 gram).

Official Title
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The Effect of L-arginine on Brown Adipose Tissue Metabolism in South Asian and White Caucasian Subjects

Conditions
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Adipose Tissue, Brown, Glucose Intolerance, Nitric Oxide

Intervention / Treatment
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* Drug: L-arginine
* Drug: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Caucasian or South Asian ethnicity Age: 35-50 years Gender: male BMI: 25-30 kg/m2 Plasma glucose levels 2 h after OGTT between 7.8 and 11 mM (e.g. impaired glucose tolerance) or Fasting plasma glucose levels > 5.5 mM Good general health Exclusion Criteria: Type 2 diabetes (determined on basis of oral glucose tolerance test (OGTT)) BMI > 30 kg/m2 Plasma glucose levels 2 h after OGTT < 7.8 mM Plasma L-arginine levels < 41 or > 114 uM Use of beta-blockers (these inhibit BAT activity) < 1 month before start of study or during study Systolic blood pressure < 90 mmHg Haematocrit < 0.41 or > 0.51 l/l Haemoglobin < 8.5 or > 11.0 Creatinine (enzymatic method) < 45 or > 100 μmol/L ASAT > 45 U/L ALAT > 50 U/L Alkaline phosphatase > 125 U/L Gamma GT > 45 U/L Participation in an intensive weight-loss program or vigorous exercise program during the last year before the start of the study Abuse of drugs and/or alcohol Hyperthyroidism or hypothyroidism Participation in earlier research or medical examinations that included PET-CT scanning Psychologically unstable subjects (as judged by the treating medical specialist) Subjects with mental retardation (as judged by the treating medical specialist) Subjects with severe behaviour disorders (as judged by the treating medical specialist)

Ages Eligible for Study
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Minimum Age: 35 Months
Maximum Age: 50 Years

Sexes Eligible for Study
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Male

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: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: L-arginine<br>Subjects will receive 9 gram of L-arginine per day in three gifts (3dd 3 gram) during 6 weeks. | Drug: L-arginine<br>* 9 gram L-arginine / day for 6 weeks<br>* Other names: Argimax;|
| Placebo Comparator: Placebo<br>Subjects will receive 9 gram of placebo per day in three gifts (3 dd 3 gram) during 6 weeks. | Drug: Placebo<br>* 9 gram placebo / day for 6 weeks<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Standard uptake value of Brown adipose tissue | Glucose uptake by brown adiopse tissue will be assessed by cold-induced 18F-FDG PET-CT scan | 6 weeks | 
| Energy expenditure | Energy expenditure will be determined by means of indirect calorimetrie | 6 weeks | 
| Fat mass | Fat mass will be determined by DEXA scan | 6 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Body temperatures | Skin and core body temperatures as well as gradients will be assessed by means of iButtons and ingestion of a telemetric pill, respectively. | 6 weeks | 
| Skin perfusion and endothelial-dependent and independent vasodilation | This will be measured by means of Laser Doppler Flowmetry (LDF) and iontophoresis | 6 weeks | 
| Skeletal muscle mitochondrial respiration/uncoupling | This will be determined in muscle biopsies by using the Oroboros 2k Oxygraph instrument present in our laboratory . | 6 weeks | 
| Brown adipocyte recruitment and inflammation in WAT | This will be measured in subcutaneous WAT biopsies by assessing mRNA expression via real time polymerase-chain reaction (RT-PCR) and protein content by immunohistochemical stainings. | 6 weeks | 
| Blood parameters | Venous blood will be drawn by means of a catheter placed in the antecubital vein of the underarm. By using radioimmunoassay, high performance liquid chromotogaphy (HPLC) and enzyme-linked immunosorbent assay (ELISA), blood parameters (i.e. lipids, glucose, inflammatory markers and endothelial activation markers) will be analyzed. In addition, we will perform DNA analyses from blood. | 6 weeks |