We recently provided evidence suggesting a role for
cytokine-mediated inhibition of Akt/Forkhead box O 1 (FOXO1) signalling in the induction of
muscle atrophy and impairment of muscle
carbohydrate oxidation during
lipopolysaccharide (LPS)-induced endotoxaemia in rats. We hypothesized that a low-dose
dexamethasone (Dex;
anti-inflammatory agent) infusion during endotoxaemia would prevent the LPS-induced impairment of Akt/FOXO1 signalling, and therefore prevent the
muscle atrophy and impairment of
carbohydrate oxidation. Chronically instrumented Sprague-Dawley rats received a continuous
intravenous infusion of LPS (15 microg kg(-1) h(-1)), Dex (12.5 microg kg(-1) h(-1)), Dex+LPS or saline for 24 h at 0.4 ml h(-1). LPS infusion caused haemodynamic changes consistent with a hyperdynamic circulation and induced increases in muscle tumour
necrosis factor-alpha (
TNF-alpha; 10-fold, P < 0.001),
interleukin-6 (IL-6; 14-fold, P < 0.001) and metallothionein-1A (MT-1A; 187-fold, P < 0.001)
mRNA expression. Dex co-administration abolished most of the haemodynamic effects of LPS and reduced the increase in muscle
TNF-alpha,
IL-6 and MT-1A by 51% (P < 0.01), 85% (P < 0.001) and 58% (P < 0.01), respectively. Dex infusion during endotoxaemia also prevented the LPS-induced 40% reduction in the
muscle protein:
DNA ratio and decrease in Akt phosphorylation, and partially prevented the reduction in FOXO1 phosphorylation. However, Dex did not prevent the LPS-mediated increase in
muscle atrophy F-box (MAFbx) and muscle RING finger 1 (MuRF1)
mRNA expression, but did significantly reduce the LPS-mediated increase in
cathepsin-L mRNA expression and
enzyme activity by 43% (P < 0.001) and 53% (P < 0.05), respectively. Furthermore, Dex suppressed LPS-induced
pyruvate dehydrogenase kinase 4 (PDK4)
mRNA upregulation by approximately 50% (P < 0.01), and prevented LPS-mediated muscle
glycogen breakdown and
lactate accumulation. Thus, low-dose Dex infusion during endotoxaemia prevented
muscle atrophy and the impairment of
carbohydrate oxidation, potentially through suppression of
cytokine-mediated Akt/FOXO inhibition, and blunting of
cathepsin-L-mediated lysosomal
protein breakdown.