Hepatocyte apoptosis, expression of death receptors, and activation of NF-kappaB in the liver of nonalcoholic and alcoholic steatohepatitis patients

Abstract

Objectives: The increasing incidence of nonalcoholic (NASH) and alcoholic steatohepatitis (ASH), associated with lack of effective treatment, has prompted intensive studies on disease pathogenesis. Apoptosis is recognized as common in liver injury and may also contribute to tissue inflammation, fibrogenesis, and development of cirrhosis. In this study, we identified mechanisms of apoptosis induction in human steatohepatitis, and evaluated potential associations between apoptosis, liver pathology, and clinical presentation in NASH and ASH.

Methods: Hepatocyte apoptosis was evaluated by the TUNEL assay in 20 patients with NASH (all ambulatory), 40 with ASH (20 ambulatory, 20 hospitalized), and 20 controls. Liver biopsies were also graded for inflammation and fibrosis. Immunohistochemistry was performed for death receptors (Fas and TNF-R1), activated caspase-3, NF-kappaB p65, antiapoptotic Bcl-2 protein, and uncoupling protein 2 (UCP-2).

Results: TUNEL-positive hepatocytes were markedly increased in NASH (p < 0.05) and ASH (p < 0.01). Similar results were obtained for activated caspase-3, confirming the occurrence of apoptosis. The Fas receptor was upregulated in ASH, especially in hospitalized patients (p < 0.01), whereas TNF-R1 was expressed both in NASH and ASH (p < 0.01). In addition, patients with ASH showed a remarkable expression of active NF-kappaB, as compared to NASH and controls (p < 0.01). Degrees of inflammation and fibrosis correlated with NF-kappaB p65 expression, which in turn coincided with apoptosis albeit Bcl-2 and UCP-2 expression.

Conclusions: Liver injury in NASH and ASH is associated with increased hepatocyte apoptosis mediated by death receptors. Further, apoptosis correlates with active NF-kappaB expression, and disease severity. This potential mechanistic link might provide multiple interesting targets for therapeutic intervention.