Effect of DPP4 Inhibition on Growth Hormone Secretion

Study Overview
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Brief Summary
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This study tests the following hypotheses: Aim 1: Test the hypothesis that acute dipeptidyl peptidase 4 (DPP4) inhibition with the currently available anti-diabetic drug, sitagliptin, will increase stimulated growth hormone (GH) secretion in healthy lean adults by decreasing the degradation of growth hormone releasing hormone (GHRH). Aim 2: Test the hypothesis that decreased degradation of GHRH during acute DPP4 inhibition will result in an increase in endothelium-dependent vasodilation mediated by GH and independent from GLP1 (glucagon like peptide-1) in healthy lean adults. This study promises to provide novel data regarding how this increasingly used class of anti-diabetic drugs affects the pituitary GH axis and could affect blood vessel relaxation. Growth hormone levels are low in the setting of obesity and pre-diabetes. A further study may evaluate the effect of chronic DPP4 inhibitor therapy in a population of patients with obesity and pre-diabetes.

Detailed Description
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Growth hormone secretion is low in patients with obesity, insulin resistance, and hyperlipidemia. GH therapy in these populations and others has been limited by side effects which include hyperglycemia. Another strategy to increase GH secretion is to enhance pulsatile GH secretion by growth hormone releasing hormone. Growth hormone releasing hormone (GHRH) has a half life of 5 minutes due to its rapid inactivation by DPP4. An alternative strategy to increase endogenous GH secretion is by inhibiting degradation of GHRH by DPP4. DPP4 inhibitors are currently approved therapies for the treatment of hyperglycemia in patients with type 2 diabetes mellitus. They additionally cause blood vessel relaxation. We therefore propose to test the hypothesis that DPP4 inhibition simultaneously enhances GH secretion while improving blood glucoses and vascular function in patient populations with low GH and increased cardiovascular risk. These preliminary aims serve primarily as a novel proof of concept study to define the effect of acute pharmacologic DPPIV inhibition on stimulated GH secretion.

Official Title
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The Effect of Dipeptidyl Peptidase IV Inhibition on Growth Hormone-Mediated Vasodilation

Conditions
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Obesity

Intervention / Treatment
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* Drug: Sitagliptin
* Drug: Pegvisomant
* Drug: Placebo
* Drug: L-NMMA
* Drug: Exendin 9-39


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age 18 to 40 years inclusive BMI ≤ 25 kg/m2 For female subjects: Status-post surgical sterilization, or If of child-bearing potential, utilization of a barrier method of birth control following negative serum pregnancy test at screening visit and on every study day Exclusion Criteria: Smoking Type 1 or Type 2 Diabetes Mellitus, as defined by a fasting glucose of 126 mg/dL or greater at the time of screening visit or the use of anti-diabetic medication Hypertension, as defined by an untreated seated systolic blood pressure (SBP) greater than 140 mmHg and/or an untreated diastolic blood pressure (DBP) greater than 90 mmHg at the time of screening visit or the use of anti-hypertensive medication History of reported or recorded hypoglycemia (plasma glucose < 70 mg/dL) Pregnancy and/or Breast-Feeding Use of any medication other than multivitamin, including use of transdermal as well as oral hormone replacement therapy or use of oral contraceptive therapy Anemia defined as hematocrit <35% at screening visit Cardiovascular or cerebrovascular disease, including history of myocardial infarction, history of congestive heart failure, history of stroke Pulmonary Hypertension Abnormal thyroid hormone levels (TSH) at the time of screening visit Abnormal serum insulin like growth factor-1 (IGF-1) at the time of screening visit Impaired renal function, defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m^2 Impaired hepatic function (alanine or aspartate transaminase > 2 X upper limit of normal range) Treatment with an investigational drug in the 1 month preceding the study

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: Other
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Other: Group A (14 healthy subjects)<br>In Aim 1: Healthy Lean adults are randomized in a double-blinded cross over fashion to sitagliptin versus placebo. In Aim 2: Healthy Lean adults receive sitagliptin and are randomized in a double-blinded cross over fashion to pre-treatment with either LNMMA (L-N-Monomethyl-arginine) versus placebo. | Drug: Sitagliptin<br>* During Aim 1, given on one of two study days (other study day subjects receive placebo.) During Aim 2, given during both of two study days.<br>* Other names: Januvia;Drug: Placebo<br>* During Aim 1, given on one of two study days (other study day subjects receive sitagliptin.) During Aim 2, given on one of two study days (other study day subjects receive either L-NMMA, pegvisomant, or Exendin 9-39 pending their group assignment)<br>* Other names: sugar pill;Drug: L-NMMA<br>* During Aim 2, given during one of two study days (Group A subjects only)<br>* Other names: L-N-Monomethyl-arginine;|
| Other: Group B (14 healthy subjects)<br>In Aim 1: Healthy Lean adults are randomized in a double-blinded cross over fashion to sitagliptin versus placebo. In Aim 2: Healthy Lean adults receive sitagliptin and are randomized in a double-blinded cross over fashion to pre-treatment with either pegvisomant versus placebo. | Drug: Sitagliptin<br>* During Aim 1, given on one of two study days (other study day subjects receive placebo.) During Aim 2, given during both of two study days.<br>* Other names: Januvia;Drug: Pegvisomant<br>* During Aim 2, given 72 hours prior to one of two study days (Group B subjects only)<br>* Other names: Somavert;Drug: Placebo<br>* During Aim 1, given on one of two study days (other study day subjects receive sitagliptin.) During Aim 2, given on one of two study days (other study day subjects receive either L-NMMA, pegvisomant, or Exendin 9-39 pending their group assignment)<br>* Other names: sugar pill;|
| Other: Group C (14 healthy subjects)<br>In Aim 1: Healthy Lean adults are randomized in a double-blinded cross over fashion to sitagliptin versus placebo. In Aim 2: Healthy Lean adults receive sitagliptin and are randomized in a double-blinded cross over fashion to pre-treatment with either Exendin 9-39 versus placebo. | Drug: Sitagliptin<br>* During Aim 1, given on one of two study days (other study day subjects receive placebo.) During Aim 2, given during both of two study days.<br>* Other names: Januvia;Drug: Placebo<br>* During Aim 1, given on one of two study days (other study day subjects receive sitagliptin.) During Aim 2, given on one of two study days (other study day subjects receive either L-NMMA, pegvisomant, or Exendin 9-39 pending their group assignment)<br>* Other names: sugar pill;Drug: Exendin 9-39<br>* During Aim 2, given during one of two study days (Group C subjects only)<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Aim 1: Stimulated Peak Growth Hormone Level | Subjects underwent two study days separated by a washout period. On one study day they will receive sitagliptin and on another placebo, in a randomized double-blind fashion. Growth hormone secretion was stimulated using arginine (30 grams i.v. over 30 minutes) on each study day. Growth hormone levels were assessed during a 3 hour period following arginine stimulation. | Growth Hormone Level at 30 minutes (i.e. at completion of arginine infusion), 45 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes | 
| Aim 1: Percent Change From Baseline in Forearm Vascular Resistance | Forearm blood flow was determined by strain gauge plethysmography. Forearm vascular resistance was then calculated by dividing this into mean arterial pressure. The percent change from baseline was determined at each timepoint. | Percent change from baseline in forearm vascular resistance at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes | 
| Aim 1: Percent Change From Baseline in Forearm Blood Flow | Forearm blood flow was determined by strain gauge plethysmography. The percent change from baseline was determined at each timepoint. | Percent change from baseline in forearm blood flow at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes. | 
| Aim 2: Percent Change From Baseline in Forearm Blood Flow | Subjects undergo two study days separated by a washout period. On one study day they received sitagliptin plus another study drug and on another sitagliptin plus placebo, in a randomized double-blind fashion. Forearm blood flow was assessed at each visit. | Percent change from baseline in forearm blood flow at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes. | 
| Aim 2: Percent Change From Baseline in Forearm Vascular Resistance | Subjects undergo two study days separated by a washout period. On one study day they will receive sitagliptin plus another study drug and on another sitagliptin plus placebo, in a randomized double-blind fashion. Forearm blood flow was assessed at each visit every 30 minutes for 3 hours. This was divided into mean arterial pressure to determine forearm vascular resistance. | Percent change from baseline in forearm vascular resistance at 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Aim 1: Venous Blood Sampling for Tissue Plasminogen Activator (TPA) Activity Levels | In Aim 1 subjects underwent two study days separated by a washout period. On one study day they received study drug and on another placebo, in a randomized double-blind fashion. Venous blood samples were obtained at each visit. | baseline and every 30 minutes for 180 minutes | 
| Aim 2: Venous Blood Sampling for Tissue Plasminogen Activator (TPA) Activity Levels | Subjects undergo two study days separated by a washout period. On one study day they received sitagliptin plus pegvisomant and on another sitagliptin plus placebo, in a randomized double-blind fashion. Tissue plasminogen activator activity (tPA) was assessed at each visit. | baseline and every 30 minutes until 180 minutes | 
| Aim 2: Measurement of Growth Hormone (GH) Levels | Subjects undergo two study days separated by a washout period. On one study day they received sitagliptin plus pegvisomant and on another sitagliptin plus placebo, in a randomized double-blind fashion. Growth hormone secretion following arginine stimulation was assessed at each visit. Growth hormone levels were determined using an assay that is not subject to interference by pegvisomant. | baseline and every 30 minutes until 180 minutes | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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obesity, growth hormone