Effect of Acetazolamide and Furosemide on Obesity-induced Glomerular Hyperfiltration
Condition: Obesity-induced Hyperfiltration
MeSH terms: Obesity
Study type: Interventional

Summary: 
      Background:

      Obesity is associated with a high prevalence of chronic kidney disease.The glomerular
      hyperfiltration associated with obesity may play a role in the pathogenesis of obesity
      associated chronic kidney disease. Attenuation of hyperfiltration by pharmacological means
      may slow down the development and progression of chronic renal failure. The investigators
      have previously shown that acetazolamide, a proximally acting diuretic that activates
      tubuloglomerular feedback(TGF) by increasing solute delivery to the Macula DENSA, abates
      glomerular hyperfiltration. The present study was designed to test the hypothesis that this
      decrease in hyperfiltration is specific to acetazolamide and not due to a non specific
      diuretic effect. The aim of the present study is to compare the effects of furosemide and
      acetazolamide on glomerular hemodynamics in subjects with severe obesity.

      Methods:

      A randomized double-blind crossover controlled design will be used. Fifteen obese subjects
      and ten subjects with normal body weight will participate in the study. Obese subjects will
      undergo measurement of glomerular filtration rate (GFR)(inulin clearance), renal plasma flow
      (RPF) (p-aminohippuric acid clearance), filtration fraction, fractional excretion of lithium
      (FE LI) and blood pressure, before and after intravenous administration of furosemide 2 mg.
      and acetazolamide 5 mg/kg BW. Ten subjects with normal body weight will undergo measurement
      of renal function without administration of diuretics.
    

Detailed description: 
      BACKGROUND Almost half of the causes of death in the industrial world are due to
      cardio-vascular (CV) disease. Two of the main risk factors for CV disease have become much
      more prevalent during the last decades, reaching epidemic dimensions in the 21st century:
      hypertension and obesity. In 2003-2004, 66% of the adult USA population had a body mass
      index(BMI)over 25, while 32% had a BMI over 30 .Hypertension is more prevalent in obese than
      in lean subjects .The cause and effect relationship between these two conditions is supported
      by the fact that weight loss is associated with a decrease in blood pressure .

      Salt retention by the kidney is one of the important mechanisms involved in the pathogenesis
      of hypertension in obesity. Studies in animal models and in humans showed that increased salt
      reabsorption occurs in the tubules in obesity. Another renal functional abnormality occurring
      in obesity is glomerular hyperfiltration, characterized by increased renal plasma flow (RPF)
      and increased glomerular filtration rate(GFR) up to twice the normal level . The structural
      basis to these functional abnormalities is renal hypertrophy and glomerular enlargement.

      These functional and structural abnormalities have deleterious consequences:

        1. Increased urinary albumin excretion. Microalbuminuria, an important risk factor for CV
           disease, has a high prevalence in obese subjects .

        2. Increased risk for the development of focal segmental glomerulosclerosis, the so-called
           obesity related glomerulopathy. The incidence of this disease has multiplied 10 times
           within 15 yrs in the USA .

        3. Increased rate of progression of chronic renal insufficiency in kidney disease not
           primarily caused by obesity. Following initial glomerular damage from any cause, the
           number of remnant functioning glomeruli decreases. The consequent compensatory increase
           in single nephron filtration rate of these remnant glomeruli leads to further glomerular
           damage in kidney disease not related to obesity . In the obese with chronic renal
           damage, the obesity related hyperfiltration amplifies the compensatory augmentation in
           single nephron GFR of remnant nephrons, thus worsening glomerular damage, irrespective
           of the cause of the primary insult.

      The clinical relevance of these abnormalities is reflected in the sharp increase in the risk
      of developing end stage renal disease in the obese. This relative risk, independently of
      confounders as diabetes mellitus, hypertension and dyslipidemia, is 3 to 5 depending on the
      severity of obesity .

      Considering the role of hyperfiltration in the pathogenesis of chronic kidney disease (CKD)
      in the obese, attenuation of hyperfiltration by pharmacological means may slow down the
      development and progression of chronic renal failure. One of the tools available is
      activating tubuloglomerular feedback (TGF). Tubuloglomerular feedback (TGF) refers to the
      alterations in GFR that can be induced by changes in tubular flow rate. An increase in the
      delivery of chloride to the Macula DENSA results in a reduction in GFR, resulting in a
      decrease in the tubular flow rate delivered to the Macula DENSA. An increase in chloride
      delivery to the Macula DENSA can be obtained by administrating acetazolamide, a diuretic
      acting on the proximal tubule. We have previously shown that administration of acetazolamide
      to obese subjects results in attenuation of glomerular hyperfiltration.

      The aim of the present study is to show that the effect of acetazolamide on GFR is specific
      and not due to its diuretic effect. We will study the effects of furosemide, a diuretic which
      does not activate TGF ,on GFR and RPF in obese subjects in comparison with acetazolamide.

      Methods:

      A 24-hour urine collection will be performed during the week prior to the renal function test
      studies for assessment of sodium intake.

      Obese subjects: A randomized double-blind crossover controlled design will be used. Two renal
      function studies will be performed: one before and after intravenous furosemide and the
      second before and after intravenous acetazolamide. Subjects will receive 300 mg of lithium
      carbonate at 22.00 the day before the renal function tests. They will be instructed to drink
      250 ml of water at bedtime. Renal function tests will start at 08.00 a.m. after a 10-hour
      fast, excepting a drink of 250 ml of water at 07.00 a.m. Intravenous catheters will be placed
      in each upper limb for infusion of clearance markers and blood sampling. After blood sampling
      for urea, creatinine, proteins, glucose, electrolytes, blood gases, insulin, renin,
      aldosterone, Hba1c, CBC. A priming dose of inulin (50 mg/kg) and p-aminohippuric acid (8
      mg/kg) will be administered and a 200-300 ml p.o water load will be given. Thereafter, inulin
      and p-aminohippuric acid will be infused continuously. After the first 60 minutes, 8
      accurately timed urine collections of 30 to 40 minutes will be obtained by spontaneous
      voiding. Peripheral venous blood will be drawn to bracket each urine collection. Arterial
      pressure will be measured by a trained observer, after 30 minutes of rest in the supine
      position, using an electronic oscillometric blood pressure measuring device. The cuff will be
      appropriately sized to the diameter of the arm and the arm positioned at the heart level. At
      least 8 measurements will be performed during the study, each measurement being the mean of 3
      readings. After the first 4 timed urine collections, participants will receive intravenous
      furosemide 2 mg/5min or intravenous acetazolamide 5 mg/kg/5 min. Four other times urine
      collections will be performed thereafter. Subjects will be randomized to receive during the
      first study either furosemide or acetazolamide. The second study will be performed one to two
      weeks after the first study, using the drug that had not administrated during the first
      study.

      Subjects with normal body weight: will undergo measurement of renal function without
      administration of diuretics (one renal function study, same protocol like obese subjects,
      with 4 urine collections only).

      Laboratory procedures: Plasma and urinary concentrations of inulin and p-aminohippuric acid
      will be analyzed by colorimetric methods .Lithium in serum and urine will be measured . Urine
      microalbumin will be determined by competitive chemiluminescent enzyme immunoassay .

      Calculations: GFR will be determined from the average value for the timed inulin clearances,
      and renal plasma flow (RPF) - from the average value for the timed p-aminohippurate
      clearances. The fractional excretion of lithium (FE Li) will be calculated as lithium
      clearance / GFR, using two timed urine collections. FE Li will be determined as the average
      value for these two measurements Statistical Analysis: The significance of differences
      between groups will be evaluated by paired and unpaired two-tailed Student's t-test. The
      Student's t-test will be applied to non-normally distributed data (albumin excretion rate and
      fractional lithium excretion) after log transformation. P<0.05 will be considered as
      significant. The response to treatment with furosemide will be compared to the response to
      treatment with acetazolamide using ANOVA.
    

Intervention name(s): Furosemide first, then Acetazolamide; Acetazolamide first, then Furosemide
Intervention type(s): Drug; Drug
Intervention description(s): Two renal function studies will be performed: one before and after intravenous furosemide and the second before and after intravenous acetazolamide. Subjects will receive 300 mg of lithium carbonate at 22.00 the day before the renal function tests. A priming dose of inulin (50 mg/kg) and p-aminohippuric acid (8 mg/kg) will be administered and a 200-300 ml p.o water load will be given. Thereafter, inulin and p-aminohippuric acid will be infused continuously. After the first 60 minutes, 8 accurately timed urine collections of 30 to 40 minutes will be obtained by spontaneous voiding. After the first 4 timed urine collections, participants will receive intravenous furosemide 2 mg/5min or intravenous acetazolamide 5 mg/kg/5 min.Four other times urine collections will be performed thereafter.; Two renal function studies will be performed: one before and after intravenous acetazolamide and the second before and after intravenous furosemide. Subjects will receive 300 mg of lithium carbonate at 22.00 the day before the renal function tests.A priming dose of inulin (50 mg/kg) and p-aminohippuric acid (8 mg/kg) will be administered and a 200-300 ml p.o water load will be given. Thereafter, inulin and p-aminohippuric acid will be infused continuously. After the first 60 minutes, 8 accurately timed urine collections of 30 to 40 minutes will be obtained by spontaneous voiding. After the first 4 timed urine collections, participants will receive intravenous furosemide 2 mg/5min or intravenous acetazolamide 5 mg/kg/5 min.Four other times urine collections will be performed thereafter.
Intervention MeSH terms: Furosemide; Acetazolamide
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: obesity; acetazolamide; furosemide