Metabolic Characterization of Type 2 Diabetic, Obese, Lean Sedentary and Endurance Trained Individuals in vivo, ex vivo and in vitro

Type 2 diabetes (T2D) is a global burden disease affecting almost 200 million
people and is expected to nearly double by 2030. It is imperative that this
disease is kept under control, and that we begin to reverse the direction of
its incidence. We propose to start by identifying the physiological and
molecular aspects of the problem in all spectrums of the disease (ie from
insulin sensitive athletes to sedentary lean and obese individuals and further
to overt type 2 diabetics), and focus our efforts on examining the differences
and identifying the stages of progression for possible targets of future
intervention. The proposed study *Metabolic Phenotyping* is novel in its target
populations and innovative in its use of state-of-the-art techniques. We
hypothesize that the in vivo differences in metabolic flexibility and
mitochondrial function between endurance athletes and type 2 diabetics and
their lean and obese controls are retained in vitro and will offer a new model
in which to study the underlying mechanisms of the progression of T2D.

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) To assess metabolic flexibility as measured by a
euglycemic-hyperinsulinemic clamp
(2) To measure in vivo mitochondrial function by magnetic resonance
spectroscopy (MRS) of phosphocreatine (PCr) recovery
(3) To 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) To quantify intramyocellular lipid (IMCL) and acetylcarnitine in vivo by
magnetic resonance spectroscopy (MRS).
(5) To measure the differences in BAT activity and brown adipocyte recruitment
in white adipose tissue ("browning") between endurance atheletes and untrained
sedentary lean subjects.

132 male participants will be recruited to Maastricht University (See Study
Population). Eligible participants will undergo a euglycemic-hyperinsulinemic
clamp, MRS for PCr recovery and muscle fat content, body composition
measurements and a skeletal muscle biopsy to complete the three study
objectives.

After participants send back the informed consent, they will be invited to the
University for a screening. During the screening visit participants will be
screened to assess eligibility, which will include fasting blood samples,
resting blood pressure, body weight and height, a medical history
questionnaire, an oral glucose tolerance test (OGTT, only for the type 2
diabetic group), a resting 12-lead electrocardiogram (ECG), a pretest to
determine maximal knee extension capacity and a cycling test (VO2max). The
total duration of the screening visit will be 1.5 hours. Following
determination of eligibility, the participants will return to the University
for 2 separate testing days (consecutive if possible) that total 13 hours in
duration. Test Day 1 consists of a muscle biopsy and a
euglycemic-hyperinsulinemic clamp (10 hours in total). Test Day 2 consists of
an MRS scan for intramyocellular lipid and acetylcarnitine content and PCr
recovery and a DEXA scan for body composition (3 hours in total).

A burden is the time that the participants spend undergoing the study
procedures (3 visits, total time 13h). In an effort to limit this burden, all
study procedures are only performed once. Blood draws are done through
cannulas that are inserted for the euglycemic-hyperinsulinemic clamp. There is
risk of pain, swelling of the vein, bleeding, or bruising at the site of the
cannula insertion on the arm. Sterile technique and trained personnel minimize
these risks. During MRS, kan er ongemak ervaren worden tijdens het uitoefenen
van druk met het been tegen de weerstand; dit is echter van korte duur (~5
minuten). Er is een kleine kans op een onverwachte medische bevinding bij de
analyse van de MR opnames. In dat geval zal de deelnemer worden geïnformeerd en
ook zijn behandelend arts zal op de hoogte gesteld worden. Tijdens de MRS scan
kan het lawaai als onplezierig ervaren worden, maar deelnemers krijgen
oordoppen en/of een hoofdtelefoon. Er is een minimale hoeveelheid radiatie
geassocieerd met de DEXA scan voor lichaamssamenstelling. It is roughly equal
to 12 hours of background sun radiation. There is some pain associated with
the muscle biopsy; however, this is associated with the injection of xylocaine
to desensitize the skin and muscle for the procedure and is thus short in
duration (~1 minute). Sterile technique and trained personnel minimize these
risks. The primary benefits of participation is knowledge of one*s own ability
to switch between oxidation of glucose and fat, as well the ability to
resynthesize phosphocreatine after a bout of exercise. Another benefit of
participation is monetary compensation (¤150).
For the endurance trained athletes and the lean sedentary group a white biopsy
will be taken. There will be a risk for a haemotoma during this procedure.
Furthermore, there is a small chance on finding an unexpected medical issue on
the PET-CT image. In that case the participant will be informed including his
general physician. The total absorbed radiation dose from one FDG-PET/CT-scans
after administration of one time 74 MBq of 18F-FDG is 3.2 mSv, which is
considered as a low risk.