Effect of lipopolysaccharide and cytokines on oxidative metabolism in neonatal rat hepatocytes.

BACKGROUND/PURPOSE: Lipopolysaccharide (LPS) and cytokines produced during neonatal sepsis trigger free radical production, which eventually results in inhibition of liver metabolism. Studies in adults have indicated a hypermetabolic response to sepsis; however, evidence for a hypermetabolic response in neonates is equivocal. This study was carried out to determine whether LPS and cytokines can cause liver hypermetabolism in neonates.

METHODS

The initial bacterial insult and cytokine cascade were mimicked by the addition of lipopolysaccharide (Escherichia coli 055:B5), tumour necrosis factor (TNF-alpha), and interleukin-6 (IL6) during the isolation of hepatocytes by collagenase digestion from 11- to 13-day-old Wistar rats. Hepatocyte oxygen consumption was measured polarographically with cells respiring on palmitate (0.5 mmol/L). Myxothiazol, a specific inhibitor of mitochondrial respiration, was used to distinguish extra- and intramitochondrial oxygen consumption. Morphologic changes were assessed by electron microscopy.

RESULTS

The addition of LPS, TNF-alpha and IL6 during hepatocyte isolation resulted in a 10% decrease in cell yield (P <.05) compared with untreated controls; however, cell viability was unchanged (n = 31). Both total and extramitochondrial oxygen consumption were significantly greater in treated cells compared with untreated controls (P <.05, Student's t test). Electron microscopy indicated that LPS, TNF-alpha, and IL6 did not cause ultrastructural changes to hepatocytes.

CONCLUSIONS

The increase in oxygen consumption was predominantly extramitochondrial and likely to be caused by increased oxygen requirement for cytosolic detoxification and repair purposes. This study shows that liver hypermetabolism metabolism can occur in response to LPS and cytokines. However, during in vivo neonatal sepsis, additional free radical damage may blunt this hypermetabolic response.