Skeletal muscle mitochondrial (dys)function in humans:
Relating macroscopic in vivo observations to mechanistic understanding at molecular scale

Mitochondrial dysfunction in skeletal muscle has been associated with
metabolic diseases and aging. We want to investigate the molecular mechanisms
underlying mitochondrial dysfunction in several patients / subject groups: i.e.
mitochondrial myotpathy, type 2 diabetes and elderly with a sedentary or active
lifestyle. At the moment, it is possible to measure mitochondrial function in
vivo by 31P MRS. Differences in the molecular make-up of muscle cells can be
detected by analysis of muscle biopsy samples. What has been lacking is
methodology for relating the changes in molecular make-up of the muscle to the
observed dysfunction in vivo in a quantitative and mechanistic manner. To
overcome this limitation a mathematical model of skeletal muscle energy
metabolism is being developed at Eindhoven University of Technology
(BioModeling and Bioinformatics, BioMedical NMR group). In the present study we
want to apply the mathematical model to relate mitochondrial dysfunction as
observed in vivo to mechanisms at molecular scale. By combining the
mathematical model and an extensive newly obtained dataset it is expected we
will gain novel insight in the origin of mitochondrial dysfunction in type 2
diabetes and aging. This knowledge may eventually be useful for the
identification of biomarkers, molecular intervention targets and personalized
medicine.

The main objective of the study is to quantify mitochondrial dysfunction in
vivo and obtain information of molecular scale adaptations of the muscle cells
that potentially underlie the observed dysfunction. The mathematical model will
be applied to relate in vivo measurements to the results of the muscle biopsy
analysis. Model simulations will provide the link between the macroscopic in
vivo measurements and the results from the muscle biopsy analysis.
Secondary objective is to test if supplementation of 500mL/day of beetroot
juice to normal diet improves exercise performance in patients with
mitochondrial myopathy.

case - control study

Subjects will visit Máxima Medical Center, Erasmus Medical Center or Eindhoven
University of Technology 3 or 4 times in a period of 3 or 4 weeks. During these
visits the subjects will undergo a VO2max test on a bicycle ergometer, the
collection of a blood sample in fastened state, assessment of mitochondrial
function by means of 31P magnetic resonance spectroscopy and the collection of
a muscle biopsy sample. In addition, all subjects are asked to fill in a
questionnaire quantifying their daily activity.
The VO2max test and blood sample collection are routinely performed in the
clinic and the associated risks are considered to be very low. 31P MRS
spectroscopy is less frequently applied, however the risks associated with this
technology are also considered to be very low [34]. The muscle biopsy can, in
some cases, be painful. Infections and bleeding afterwards are possible, but
rare.
Yet, the data acquired from these experiments will contribute to an improved
understanding of the molecular mechanisms underlying mitochondrial dysfunction
in humans. . This knowledge is expected to be useful for the identification of
biomarkers, molecular intervention targets and personalized medicine.

The subjects diagnosed with mitochondrial myopathy and the healthy controls
will receive 8 days of dietary inorganic nitrate supplementation to their
normal diet and will visit the clinic on 3 more days to undergo additional
exercise test on a hometrainer (50%Wmax), 31P magnetic resonance spectroscopy
scan and muscle biopsy collection.
The oral ingestion of 8.5 mg/kg body wt/day dietary inorganic nitrate is
reported to be without additional risks. The expected benefit of inorganic
nitrate intake will be a reduction in the O2 cost of exercise thereby improving
the exercise tolerance and quality of life of these patients.