Natriuretic Effect of GLP-1in Healthy Non Obese Subjects
Condition: Sodium Excretion by Urination
Study type: Interventional
Phase: Early Phase 1

Summary: 
      Adipose and diabetic patients have glomerular hyperfiltration and enhanced reabsorption of
      sodium in the kidney leading to fluid retention and hypertension. It is already known that
      obese mice (db/db) have salt retention and elevated intrarenal angiotensin II , and that the
      mechanism of the salt retention is similar to the one described in human beings. In
      experimental study from 2009 done by Hirata K and al., published in Biochemical and
      Biophysical Research Communications to both obese type 2 diabetic db/db mice and non-diabetic
      db/m mice hypertension was artificially induced (acute sodium-loading and angiotensin
      II-infusion). Two groups of mice were treated with exendin-4 or vehicle for 12 weeks. Obese
      type 2 diabetic db/db mice show high salt-sensitivity. Exendin-4 demonstrated
      anti-hypertensive effect in db/db mice and angiotensin II-infused mice, related to
      attenuation of high salt-sensitivity. That observation confirmed that exendin-4, a GLP-1
      (Glucagon-like peptide-1) analogue, has extra-islet effect including the regulation of salt
      handling. More then ten years before mentioned observations the presence of GLP 1 receptors
      was confirmed all over the body, also in kidneys. In 2004 Gutzwiller published a study in
      Journal of Clinical Endocrinology and Metabolism that examined 15 healthy subjects and 16
      obese men (mean body mass index, 36 kg/m2) in a double-blind, placebo-controlled, crossover
      study. After overnight fasting hypertonic saline was infuse followed by 3-h infusion of
      GLP-1. Intravenous infusions of GLP-1 enhanced sodium excretion, reduced H+ secretion, and
      reduced glomerular hyperfiltration in obese men. These findings suggest an action at the
      proximal renal tubule and a potential renoprotective effect. Two years later same author with
      colleagues published a new study in Digestion. In a part of new study he observed 8
      volunteers. The protocol included intravenous salt load compared to the effect of an infusion
      of GLP-to isotonic saline (placebo). Extracellular volume expansion induced by an intravenous
      infusion of hypertonic saline was partially compensated by an increase in urinary sodium and
      water excretion with GLP-1. He explained that volume expansion was associated with increased
      renal perfusion, rise in glomerular filtration and the filtered sodium load. It was observed
      that GLP-1 is able to increase renal sodium excretion by 69% and urine volume by 86%.
      Considering all mentioned above it is obvious that GLP-1 have natriuretic effect, although
      its exact mechanism and clinical usefulness remain unclear. Both GLP1 analogues and
      inhibitors of DPP4 (dipeptidyl peptidase 4), elevate GLP1 level, and it would not be a
      surprise to observe similar natriuretic effects in the body. Since GLP 1 is a peptide given
      IV. or sc. there are on long-term studies that observe final possible effect no blood
      pressure, but GLP1 analogues and DPP4 inhibitors enhancing the incretin action demonstrate
      some antihypertensive properties. 2008 in a study done by Mistry GC and al., published in
      Journal of Clinical Pharmacology antihypertensive effect of sitagliptin was observed. In
      nineteen patients on stable treatment with antihypertensive agent(s) investigators found
      small but statistically significant reductions of 24-hour ambulatory blood pressure. There
      are no many definitive clues why the blood pressure should droop during any treatment that
      elevates serum GLP1. At the end of 2009 an analysis was published in American Journal of
      Hypertension, showing results from six trials including 2,171 subjects treated with exenatide
      for at least 6. Again, a significantly greater reduction in systolic blood pressure was
      confirmed, not giving an explanation why it happened so. Finally, Prof. Sjöholm from
      Karolinska institute Sweden published in Diabetes, obesity and metabolism a review concerning
      impact of GLP-1 on endothelial function. He mentioned again decreased blood pressure through
      improvements in diuresis and natriuresis, but he also added a new element, improved
      endothelial dysfunction through GLP-1 receptor-dependent pathway. Though there are many
      speculations, exact antihypertensive effects and water homeostasis of both GLP-1 itself, also
      of GLP1 analogues and DPP4 inhibitors is still unknown. Finally, recent review (Tanaka et
      all) from 2011 confirms mentioned speculations regarding natriuretic effect of GLP1, quote …"
      Incretin mimetics and DPP-IV inhibitors are a novel class of antihypertensive drugs with
      natriuretic properties. They can be used in the treatment of salt-sensitive hypertension,
      which is characterized by edema. The idea is to investigate the effect of GLP1 on
      diuresis/natriuresis compared with placebo in healthy non-obese people and to compare
      natriuresis with GLP-1, BNP (brain natriuretic peptide) and ADH (antidiuretic hormone) levels
      in serum.
    

Detailed description: 
      This is a cross-over study. Totally 15 participants will be randomized (or other number later
      determined by power test). The duration of the study is 9 days that will include 3 visits and
      screening visit before starting the study.

      Screening (day -1) Inclusion criteria are fulfilled before approaching Visit 1 on screening.
      Participants are instructed do come next day fasting and to collect 24h of urine sample.

      Visit 1 (day 1) Participant voluntarily agrees to participate by giving informed written
      consent. Baseline study assessment is going to be performed fasting: blood count and
      differential, blood chemistry (liver enzymes, sodium, potassium, calcium, phosphorus,
      magnesium, chloride, serum amorality, urea and creatinine, lipid panel including cholesterol,
      triglycerides, HDL and LDL cholesterol, coagulation, uric acid, glucose and insulin, renin
      activity, aldosterone, GLP1 level, T4 TSH-thyroid stimulating hormone, ADH, BNP) In the 24 h
      urine collection sodium, chloride and calcium excretion, osmolality, creatinine are going to
      be measured, glomerular filtration is going to be assessed by creatinine clearance, urin
      analysis with microscopy is going to be preformed, EKG, kidney ultrasound together with 24-h
      blood pressure monitor. HOMA2 (The Homeostasis Model Assessment ) index is calculated and a
      total body water percentage determinated via Bioelectrical Impedance Analysis. All samples of
      renin activity and aldosterone in a study are going to be taken while being in horizontal
      position at least for 3 hours. Participants are going to be randomized regarding the glucose
      tolerance test. First group it the one with fasting glucose 4,5 -5,7 mmol/L and at 2 hour
      OGTT (the amount of sodium in OGTT fluid used is 0,4 mg of sodium and 0,3 mg of chloride in
      0,2 L of water) glucose level below 7.8 mmol/l. The other group is the one with fasting
      glucose from 5,7 to 7 mmol/l and/or at 2 hour OGTT glucose level form 7.8 mmol/l to 11,1
      mmol/L (venous sample). Patients are instructed to come on the next day fasting again.

      Visit 2 (day 2) is a next study assessment: 24-h blood pressure monitor is removed, after the
      overnight fast oral saline load is going to be given in a form of a standardized meal (soup)
      in a amount of 12 g of NaCl (average daily intake of salt in Croatia). The soup is going to
      be consumed in 30 minutes. Volunteers are going to be instructed to drink afterwards 1/2 L of
      water during next 1 h. Placebo in a form iv infusion of hypertonic saline is going to be
      given at a rate of 0.06 ml/kg/in and infused during 3 hours from beginning of oral sodium
      load. During 6 hours (from oral sodium load) urine is gong to be collected. Finally, blood
      samples are going to be drawn for glucose, insulin, sodium, potassium, serum osmolality,
      serum creatinine, renin activity, and aldosterone, BNP, ADH and GLP1 level after 3 and 6
      hours. Sodium, chloride and calcium excretion, osmolality and creatinine are going to be
      measured in the urine after 3 hours. Patients are instructed to come again after 7 days
      fasting.

      Visit 3 (day 9) after the overnight fast again oral sodium load is going to be given in a
      form of a standardized meal (soup) in a same amount as previous day and again consumed in 30
      minutes, they are going to drink afterwards 1/2 L of water during next 1 h like pervious day.
      Synthetic GLP-1 (1.5 pmol/kg/min) dissolved in 500 ml 0.9% saline is going to be infused
      during 3 hours from beginning of oral sodium load. During 6 hours (from oral sodium load)
      urine is gong to be collected, blood samples are going to be drawn after 3 and 6 hours for
      the same analysis as in Visit 2, just like urine collection after 6 hours.
    

Intervention name(s): Synthetic GLP-1 (1.5 pmol/kg/min) dissolved in 500 ml 0.9% saline; 500 ml 0.9% saline
Intervention type(s): Drug; Other
Intervention description(s): infusion of synthetic GLP-1 (1.5 pmol/kg/min) saline; infusion of saline
Allocation: Non-Randomized
Intervention model: Crossover Assignment
Masking: Single (Participant)
Primary purpose: Basic Science