Nutrient excess is known to lead to mitochondrial dysfunction with
consequential effects on lipid and glucose metabolism. Mitochondrial
dysfunction in adipose tissue has been reported in patients with obesity
and/or type 2 diabetes [57,58]. Mitochondrial DNA copy number, and
mitochondrial mass and activity are decreased in the WAT of mouse
models of obesity [59,60]. In humans, there is a correlation between
downregulation of the expression and activity of the components of
oxidative phosphorylation in WAT and obesity [61,62]. Dysfunctional
mitochondria may lead to oxidative stress through excessive production
of reactive oxygen species (ROS). Indeed, oxidative stress is associated
with adiposity and lipid peroxide levels, and hydrogen peroxide generation
is elevated in adipose tissue, but not in skeletal muscle or the aorta
[63]. Considering that mitochondria are the most important source of
intracellular ROS, it is possible that the adipose tissue in obese individuals
represents a major source of ROS. In human studies, the extent of
fat accumulation has been correlated with various markers of systemic
oxidative stress