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1 Gifford Laboratories for Diabetes Research, and Departments of 2 Internal Medicine, 3 Biochemistry, and 4 Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75235
Human obesity and high fat feeding in rats are associated
with the development of insulin resistance and perturbed carbohydrate and lipid metabolism. It has been proposed that these metabolic abnormalities may be reversible by interventions that increase plasma
leptin. Up to now, studies in nongenetic animal models of obesity and
in human obesity have concentrated on multiple injection therapy with
mixed results. Our study sought to determine whether a sustained,
moderate increase in plasma leptin, achieved by administration of a
recombinant adenovirus containing the leptin cDNA (AdCMV-leptin) would
be effective in reversing the metabolic abnormalities of the obese
phenotype. Wistar rats fed a high-fat diet (HF) were heavier (P < 0.05), had increased fat mass and intramuscular triglycerides
(mTG), and had elevated plasma glucose, insulin, triglyceride, and free
fatty acids compared with standard chow-fed (SC) control animals (all
P < 0.01). HF rats also had impaired glucose tolerance and
were markedly insulin resistant, as demonstrated by a 40% reduction in
insulin-stimulated muscle glucose uptake (P < 0.001).
Increasing plasma leptin levels to 29.0 ± 1.5 ng/ml (from 7.0 ± 1.4 ng/ml, P < 0.001) for a period of 6 days decreased adipose
mass by 40% and normalized plasma glucose and insulin levels. In
addition, insulin-stimulated skeletal muscle glucose uptake was
normalized in hyperleptinemic rats, an effect that correlated closely
with a 60% (P < 0.001) decrease in mTG. Importantly, HF rats
that received a control adenovirus containing the
-galactosidase
cDNA and were calorically matched to AdCMV-leptin-treated animals
remained hyperglycemic, hyperinsulinemic, insulin resistant, and
maintained elevated mTG. We conclude that a gene-therapeutic
intervention that elevates plasma leptin moderately for a sustained
period reverses diet-induced hyperglycemia, hyperinsulinemia, and
skeletal muscle insulin resistance, and that these improvements are
tightly linked to leptin-induced reductions in mTG.
obesity; tissue triglycerides; leptin action; insulin action
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