Induction of a hypermetabolic state in cultured hepatocytes by glucagon and H₂O₂

Stress hormones and pro-inflammatory cytokines are putative signals triggering increased energy expenditure or "hypermetabolism" commonly observed in inflammatory states. Cytokines also cause the release of reactive oxidants by immune cells resident in tissues in vivo. Therefore, we hypothesized that oxidative stress plays a role in the induction of hypermetabolism. We examined the effect of glucagon (1.0nM), a catabolic stress hormone, and the oxidant H₂O₂ (1.0 mM) on the metabolism of stable hepatocyte cultures for 4 days. Combined H₂O₂ and glucagon treatment, but not H₂O₂ or glucagon used alone, increased the hepatocyte oxygen uptake rate 25% above control untreated cells after a lag-time of 72 h. The same treatment also increased the expression of mitochondrial uncoupling protein-2 (UCP2). These effects were significantly inhibited by the antioxidant N-acetylcysteine (5 mM) and the pentose phosphate pathway (PPP) inhibitor dehydroepianderosterone (200 μM). Glucagon alone induced urea synthesis and H₂O₂ alone induced the PPP. These findings show, for the first time, that oxidative stress, in combination with glucagon, increases metabolic energy expenditure in cultured cells, and that this effect may be mediated by UCP-2. Furthermore, the results implicate the PPP in the induction of the hypermetabolic response.