Effects of Intranasal Insulin Administration on Tissue Specific Insulin Sensitivity
Condition: Insulin Resistance
MeSH terms: Insulin Resistance
Study type: Interventional

Summary: 
      Recent research has suggested that intranasally administered insulin can reach the brain
      quickly without passing through circulation and evoke increased insulin sensitivity and
      tissue glucose consumption during insulin stimulation (low-dose hyperinsulinemic, euglycemic
      clamp). It is still not known what mechanism causes these changes or what tissues are
      involved in this.

      In this study, the changes in tissue-specific insulin sensitivity and glucose uptake will be
      investigated by using glucose-analogue radiotracer ([18F]-fluorodeoxyglucose) with positron
      emission tomography (PET) imaging during insulin stimulation. Ten healthy males are studied,
      each receiving nasal sprays containing insulin or placebo in a randomized order on two
      separate days. After spray administration, glucose uptake in skeletal muscle, liver,
      subcutaneous and visceral adipose tissue, myocardium, intestines, brown adipose tissue and
      brain assessed by PET imaging and glucose uptake in these tissues is analyzed. Endogenous
      glucose production is calculated facilitating the measurements glucose and radiotracer uptake
      in tissues and tracer loss into urine.

      As skeletal muscle consumes most of the glucose available, it is likely that administration
      of insulin sprays will result in an increased uptake in this tissue. Some increase in glucose
      uptake might also be seen in other tissue types after insulin spray versus placebo spray
      administration.
    

Detailed description: 
      The objective of this study is to investigate the effects of intranasally administered
      insulin versus placebo on tissue specific glucose uptake of the key metabolic organs as well
      as on endogenous glucose production.

      SAMPLE SIZE:

      A total of ten (n=10) healthy males are planned to be included, and the study is conducted
      with a cross-over design with each subject being investigated twice, once using intranasal
      insulin and once using intranasal placebo in single-blinded randomized order.

      SCREENING VISIT/ELIGIBILITY:

      Main inclusion and exclusion criteria will be evaluated at a screening visit. This visit will
      include a frequently-sampled 75 g oral glucose tolerance test as well as anthropometric
      measurements and clinical examination.

      PET STUDY VISITS:

      On the PET study days two cannulas will be inserted, one in a radial or an antecubital vein
      for tracer injection and infusion of glucose and insulin, another in the opposite radial or
      antecubital vein for blood sampling. The arm where the samples are taken will be kept warm to
      obtain arterialized venous blood. The subjects will rest in supine position on the PET/CT
      scanner bed during the study.

      HYPERINSULINEMIC EUGLYCEMIC CLAMP:

      Whole-body insulin sensitivity will be assessed by hyperinsulinemic euglycemic clamp with an
      primed insulin infusion rate of 0.25 mU/kg/min. To maintain the glucose level at 5.0 mmol/l
      intravenous glucose infusion is administered individually as needed to maintain euglycemia.

      NASAL SPRAY ADMINISTRATION:

      After 30 minutes of intravenous insulin infusion, the subjects will receive either 160 IU
      human insulin or placebo intranasally. The small amount of insulin known to be absorbed into
      circulation after the insulin nasal spray will be mimicked on placebo day. Therefore subjects
      will be administered 2.5 mU/kg of additional intravenous insulin over 15 minutes together
      with placebo spray administration.

      LABORATORY SAMPLES:

      To verify comparable insulin levels in circulation during the study, serum insulin and
      C-peptide levels will be determined in fasting state, and repeatedly throughout the
      experiment.

      BLINDING:

      The clinician and the study nurse are aware which spray is given, but subjects are blinded
      and additional insulin infusion on placebo day is done in a manner that the subjects remain
      blinded. The sprays are given on a randomized order. The randomization code was generated by
      a statistician using SAS, version 9.3 for Windows. The randomization block size was four and
      the method was permuted block randomization. The randomization was done for 16 subjects in
      case of discontinuations.

      HEART RATE VARIABILITY:

      Heart rate variability is recorded to evaluate changes in autonomous nervous system activity
      after spray administration on both visits. Polar RS800CX heart rate monitor (Polar Electro
      Ltd., Kempele, Finland) with two electrodes is used.

      FDG-PET-IMAGING:

      70 minutes after the start of clamp and 40 minutes after the application of nasal sprays the
      positron emission tomography (PET) scanning is started with the injection of glucose-analogue
      tracer labeled with positron-emitting fluorine-18 ([18F]-fluorodeoxyglucose, [18F]-FDG).
      PET/CT, GE DiscoveryTM ST System (General Electric Medical Systems, Milwaukee, WI, USA) with
      final resolution of 3.75 mm in PET images is used. All data will be corrected for dead-time,
      decay and measured photon attenuation. Dynamic PET-scans will be reconstructed with iterative
      reconstruction method. Radiotracer [18F]-FDG is produced in the PET Centre radiochemistry
      laboratory. Plasma radioactivity is measured with an automatic gamma counter by a medical
      technologist in the laboratory of the Turku PET Centre (Wizard 1480 3", Wallac, Turku,
      Finland).

      PET-IMAGE ANALYSIS:

      To determine tissue-specific glucose uptake during insulin stimulation from PET data,
      time-activity-curves of tissue activity and activity measured from plasma during the scanning
      are analysed graphically to define tracer's fractional uptake (Ki). To calculate glucose
      uptake rate (reported as µmol/kg/min), Ki is multiplied with plasma glucose level, divided
      with a constant that accounts for the differences in transport and dephosphorylation rates
      between D-glucose and FDG (lumped constant, LC) and divided with tissue specific gravity.
      Based on previous studies the LC is 1,2 for skeletal muscle; 1,0 for heart and liver; 1,14
      for adipose tissue; 1,1 for intestines and 0,8 for brain. After the PET/CT an urine sample
      will be collected to quantify endogenous glucose production (EGP). This will be determined by
      subtracting urine loss and glucose infusion rate from rate of glucose disappearance.
    

Intervention name(s): Actrapid; Placebo; [18F]-FDG PET-CT; Hyperinsulinemic euglycemic clamp
Intervention type(s): Drug; Drug; Radiation; Drug
Intervention description(s): Subjects administer 2 intranasal sprays into each nostril every minute for 4 minutes, a total of 16 sprays or 160 IU of fast-acting human insulin (Actrapid, Novo Nordisk A/S, Bagsvaerd, Denmark). The glass spray flasks are produced by AeroPump GmBH, Germany and give 0,1 ml of fluid per spray.; Subjects administer 2 intranasal sprays into each nostril every minute for 4 minutes, a total of 16 sprays. Sprays contain Insulin Diluting Medium for Novorapid and Levemir (Novo Nordisk A/S, Bagsvaerd, Denmark). The glass spray flasks are produced by AeroPump GmBH, Germany and give 0,1 ml of fluid per spray. To account for the small amount of insulin absorbed into circulation after the insulin nasal sprays, on the placebo day subjects will be administered 2.5 mU/kg of additional intravenous insulin (Actrapid, Novo Nordisk A/S, Bagsvaerd, Denmark) over 15 minutes.; All subjects will undergo two positron emission tomography (PET) studies. On both visits they are injected with 185 MBq [18F]-fluorodeoxyglucose and scanned with a combined PET and computed tomography scanner.; All subjects will undergo two hyperinsulinemic euglycemic clamp studies. The insulin infusion will be administered intravenously at a steady rate of 0.25 mU/kg/min for approximately 170 minutes. Glucose will be administered intravenously as a 200 mg/ml fluid to at varying rate to maintain euglycemia.
Other intervention name(s): ATC-code A10AB01; Insulin Diluting Medium for Novorapid and Levemir; Tissue specific insulin sensitivity measurement; Whole-body insulin sensitivity measurement
Intervention MeSH terms: Insulin; Insulin, Globin Zinc
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Insulin; Intranasal; Glucose/metabolism; Glucose homeostasis