impactjournals | Morbidly obese patients who accomplish substantial weight loss often
display a long-term decline in their resting metabolism, causing even
relatively restrained caloric intake to trigger a relapse to the obese
state. Paradoxically, we observed that morbidly obese mice receiving
chemotherapy for cancer experienced spontaneous weight reduction despite
unabated ingestion of their high fat diet (HFD). This response to
chemotherapy could also be achieved in morbidly obese mice without
cancer. Optimally dosed methotrexate (MTX) or cyclophosphamide (CY)
enabled the mice to completely and safely normalize their body weight
despite continued consumption of obesogenic quantities of HFD. Weight
reduction was not attributable to decreased HFD intake, enhanced energy
expenditure or malabsorption. MTX or CY dosing significantly depleted
both adipose tissue and preadipocyte progenitors. Remarkably, however,
despite continued high fat feeding, a compensatory increase in
hepatocyte lipid storage was not observed, but rather the opposite. Gene
microarray liver analyses demonstrated that HFD mice receiving MTX or
CY experienced significantly inhibited lipogenesis and lipid storage,
whereas Enho (energy homeostasis) gene expression was
significantly upregulated. Further metabolic studies employing a human
hepatocellular line revealed that MTX treatment preserved robust
oxidative phosphorylation, but also promoted mitochondrial uncoupling
with a surge in proton leak. This is the first report that certain
optimally dosed chemotherapeutic agents can induce weight loss in
morbidly obese mice without reduced dietary intake, apparently by
depleting stores of adipocytes and their progenitors, curtailment of
lipogenesis, and inconspicuous disposal of incoming dietary lipid via a
steady state partial uncoupling of mitochondrial oxidative
phosphorylation.
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