Background: Inflammatory mediators, including cytokines and reactive oxygen species, are associated with the pathology of chronic liver disease. Hepatocytes are generally considered as targets but not producers of these important mediators.
Objectives: To investigate whether cells of hepatocellular lineage are a potential source of various cytokines we estimated the expression and secretion of tumor necrosis factor alpha, transforming growth factor beta 1, and interleukins 1 beta, 6 and 8 in the culture of well-differentiated human HepG2 cells treated for 24 hours with ethanol, acetaldehyde and lipopolysaccharide. Lipid peroxidation damage, glutathione content and glutathione peroxidase, catalase and superoxide dismutase activity were also determined.
Methods: HepG2 cells were treated for 24 hours with ethanol (50 mM), acetaldehyde (175 microM) and LPS (1 microgram/ml). TNF-alpha, TGF-beta, IL-1 beta, IL-6 and IL-8 mRNA were determined by reverse transcriptase polymerase chain reaction and secretion by enzyme-linked immunoassay. Lipid peroxidation damage, glutathione content and antioxidant enzyme activities were determined spectrophotometrically.
Results: Exposure to ethanol for 24 hours induced the expression of TNF-alpha and TGF-beta 1, secretion of IL-1 beta and TGF-beta 1 and decreased catalase activity. Acetaldehyde markedly increased TNF-alpha and IL-8 expression, stimulated IL-1 beta and IL-8 secretion, increased lipid peroxidation damage and decreased catalase activity, while LPS exposure induced the expression of TNF-alpha, TGF-beta 1, IL-6 and IL-8, the secretion of TGF-beta 1, IL-1 beta, IL-6 and IL-8, and a decrease in catalase activity. No change in GSH, GSHPx or SOD was found in any experimental condition.
Conclusions: The present studies confirm and extend the notion that hepatocytes respond to ethanol, acetaldehyde and LPS-producing cytokines. Oxidative stress produced by the toxic injury plays an important role in this response through up-regulation of inflammatory cytokines.