Insulin Sensitivity and Metabolomics During Oral Administration of Glucose and Graded Intravenous Infusion
Condition: Type 2 Diabetes Mellitus
MeSH terms: Diabetes Mellitus; Diabetes Mellitus, Type 2; Insulin Resistance
Study type: Interventional

Summary: 
      Bariatric surgery has been proven to be an effective treatment of type 2 diabetes and it has
      highlighted to role of the small intestine in glucose homeostasis. Improvement of glucose
      homeostasis occurs just a few days after the bariatric surgery, where parts of the small
      intestine is bypassed, has been performed. Furthermore, conditioned medium from the duodenum
      and the jejunum from both diabetic rodents and humans are able to induce insulin resistance
      in normal mice and in myocytes. Hence the hypothesis is that the small intestine secretes
      factors that are able to induce insulin resistance.

      This project aims to study how orally ingested glucose is able to induce insulin resistance
      and if this response differs in patients with normal glucose tolerance, impaired glucose
      tolerance and in patients with type 2 diabetes mellitus. To address this question glucose
      homeostasis will be studied by comparing whole body glucose uptake during a progressively
      increased oral glucose load with a graded glucose infusion where the blood glucose levels
      will be kept in the same range as during the oral glucose load in patients with normal
      glucose tolerance, impaired glucose tolerance and patients with type 2 diabetes mellitus.

      Previous studied have shown that different metabolites and bile acids could be involved the
      regulation of glucose homeostasis. Hence, it is possible that the gut regulates metabolites
      that could be involved in small intestine-induced insulin resistance described above. The aim
      of this research is to study metabolomics in plasma collected during the oral glucose
      tolerance test with increasing load of glucose and the graded glucose infusion where plasma
      glucose level will be held in the same levels as during the oral glucose tolerance test and
      study the differences in patients with normal glucose tolerance, impaired glucose tolerance
      and in patients with type 2 diabetes mellitus.

      The expected results in this study will demonstrate that the gut plays an important role in
      glucose homeostasis and that this system is dysregulated in type 2 diabetes. More
      importantly, novel factors derived or regulated from the gut that regulate insulin resistance
      and glucose tolerance will be identified which could be possible targets for future
      antidiabetic therapies.
    

Detailed description: 
      The incidence of obesity and obesity-associated metabolic disorders such as insulin
      resistance and type 2 diabetes is increasing worldwide. To date, bariatric surgery is the
      only obesity treatment that results in long-term weight reduction. In addition, bariatric
      surgery has been reported to promote remission of type 2 diabetes and to be a more effective
      treatment than standard medication for type 2 diabetes. Surprisingly, improvement in glucose
      homeostasis after some bariatric surgery procedures occurs before weight loss is achieved.
      The mechanisms behind this improvement are still unclear but a recent study indicates that
      the bypassing of jejunum could play an important role in glucose homeostasis. Moreover,
      jejunum-derived proteins present in serum in both human and mice induce insulin resistance in
      cell cultures of myocytes and in mice. This taken together indicates that the gut may play an
      important role in glucose homeostasis in type 2 diabetes mellitus.

      Metabolomics has recently been regarded to be one of the most suitable technologies for
      investigating complex diseases such as type 2 diabetes mellitus because it represent a
      real-time functional portrait of the organisms. Previous studies have shown that different
      metabolites and bile acids could be involved in the regulation of glucose homeostasis. Hence
      it is possible that the gut regulates metabolites that could be involved in the impaired
      glucose tolerance and type 2 diabetes mellitus.

      The specific aims of this research project are:

      Aim 1: To demonstrate that orally ingested glucose induces insulin resistance and to
      determine if this regulation of glucose homeostasis differs between subjects with normal
      glucose tolerance, impaired glucose tolerance and subjects with type 2 diabetes mellitus.

      Aim 2: To identify metabolites regulated by the gut that are associated with impaired glucose
      tolerance and type 2 diabetes mellitus.

      To address this aim, differences in glucose kinetics will be studied when glucose is orally
      administrated (in an oral glucose tolerance test, OGTT) compared to an graded intravenous
      glucose infusion, were plasma glucose levels are held in the same range as during the OGTT,
      in subjects with normal glucose tolerance (n = 8), impaired glucose tolerance (n = 8) and
      type 2 diabetes mellitus (n = 8).

      Basal glucose kinetics will first be assessed by double glucose tracer technique. In the
      basal part of the glucose tolerance tests glucose tracer nr 1 will be infused and then be
      followed by either a continued infusion and a gradually increasing oral glucose load (25 g,
      75 g and 125 g with a 2 h interval during the OGTT) with glucose tracer nr 2 or an graded
      intravenous glucose tracer infusion where plasma glucose levels are adjusted to those
      obtained during the OGTTs.

      Gas chromatography/mass spectrometry will be used to measure isotopic enrichment of glucose
      tracers. Insulin, glucagon, total glucagon-like peptide 1 (GLP-1) and C-peptide will be
      measured by radioimmunoassays repeatedly during the glucose tolerance tests. Glucose kinetics
      including endogenous glucose production, insulin sensitivity and insulin secretion will be
      calculated. Differences in glucose kinetics between the oral and intravenous administration
      of glucose will be calculated and compared in subjects with normal glucose tolerance,
      impaired glucose tolerance or type 2 diabetes mellitus.

      Analysis of metabolomics will be performed in plasma collected during the OGTT and the graded
      intravenous glucose infusion. Metabolites in plasma samples will be analyzed using two global
      profiling analytical platforms and a targeted profiling platform. Two-dimensional gas
      chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS) will be performed to
      measure small polar metabolites. Molecular lipids will be assessed by a global platform using
      ultra performance liquid chromatography coupled to quadrupole-TOFMS (UPLC-QTOFMS). A targeted
      platform based on UPLC coupled to triple-quadrupole MS (UPLC-QqQMS) will be performed to
      quantify both unconjugated and conjugated forms of bile acids.

      Differences in plasma metabolites during OGTT and graded intravenous glucose infusion will be
      studied to assess information on possible regulation by the gut and the results will be
      compared in subjects with normal glucose tolerance, impaired glucose tolerance and subjects
      with type 2 diabetes mellitus.

      Significance The expected results in this study will demonstrate that the gut plays an
      important role in glucose homeostasis and that this system is dysregulated in type 2
      diabetes. More importantly, novel factors derived or regulated from the gut that regulate
      insulin resistance and glucose tolerance will be identified which could be possible targets
      for future antidiabetic therapies.
    

Intervention name(s): Oral glucose tolerance test; Graded intravenous glucose infusion
Intervention type(s): Other; Other
Intervention description(s): Oral glucose tolerance tests were glucose is administrated orally with an increasing load (25g, 75g, 100 g); Graded intravenous glucose infusion where glucose is infused in order to receive an plasma glucose pattern comparable to those received during the oral glucose tolerance tests.
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Intervention model description: Patients with either normal glucose tolerance, impaired glucose tolerance or with diagnosed type 2 diabetes mellitus will undergo oral glucose tolerance tests with an increasing load of glucose and thereafter isoglycemic intravenous glucose infusion.
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Type 2 Diabetes Mellitus; Impaired glucose tolerance; Metabolomics