Metabolic Phenotyping in Humans (MetPhe)

• Euglycemic-hyperinsulinemic clamp for measurement of insulin sensitivity and metabolic flexibility [ Time Frame: 10 hours ] [ Designated as safety issue: Yes ]
  After taking fasting blood samples, a primed constant infusion of glucose is initiated. Plasma glucose levels are clamped at ~5 mmol/L by variable co-infusion of 20% glucose. Every 5 minutes, blood is sampled for immediate determination of plasma glucose concentration. Glucose infusion rate is adjusted to obtain plasma glucose levels of ~5 mmol/L (euglycemia). A bolus of insulin is then infused. Before and during steady state, substrate oxidation is measured using an indirect calorimeter, which determines metabolic flexibility.
  
  

• Evaluating mitochondrial function through measurement of phosphocreatine (PCr) recovery by phosphorus magnetic resonance spectroscopy (31P-MRS) within the skeletal muscle [ Time Frame: 1.5 hours ] [ Designated as safety issue: Yes ]
  The quantification of energy metabolites (Pi, PCr and ATP) in skeletal muscle will be performed in the v. lateralis at rest, during submaximal knee-extension exercise and during recovery. The rate at which PCr concentration is restored after exercise is an excellent in vivo measure of skeletal muscle mitochondrial oxidative capacity.
  
  

The aim of the present research proposal is to metabolically phenotype endurance trained athletes, lean and obese sedentary and type 2 diabetic individuals with the following objectives:

1. assess metabolic flexibility as measured by a euglycemic-hyperinsulinemic clamp
2. measure in vivo mitochondrial function by MRS of phosphocreatine (PCr) recovery
3. establish primary myoblast cell lines to correlate with the above in vivo measurements, as well as further explore dietary, pharmacological and genetic manipulations in vitro
4. quantify intramyocellular lipid (IMCL) and acetylcarnitine in vivo by MRS

Study population:

A total of 132 male participants (18-70 years) will participate in this study. The first group of 33 participants will be lean endurance-trained athletes, the second group will be lean sedentary control participants, the third group will be sedentary type 2 diabetic participants, and the last group of 33 participants will be obese, non-diabetic sedentary control participants. It is preferred to use male participants in order to minimize variation in the measurements by avoiding confounding factors such as hormones.

Main study parameters/endpoints: The main study parameters are differences in metabolic flexibility as measured by euglycemic-hyperinsulinemic clamp, PCr recovery, IMCL and acetylcarnitines as measured by MRS and establishment of primary myoblast cell lines for future use.