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Effects of pro-inflammatory cytokines on human hepatocyte drug and ammonia metabolism

Roberto Gramignoli¹, Veysel Tahan¹, Kenneth Dorko¹, David Geller², George Mazariegos², Raman Venkataramanan³, Ira Fox², Ewa Ellis⁴, Stephen Strom¹

¹Pathology, University of Pittsburgh; ²Surgery, University of Pittsburgh Medical Center; ³Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, PA, United States; ⁴Clinical Science, Intervention and Technology, Karolinska Institute, Stockholm, Sweden

Hepatocyte transplantation (HTx) has shown benefit as a treatment for metabolic liver disease and acute liver failure. Patients with urea cycle defects are common HTx recipients. Because tracking the cells after transplantation is difficult, continued function of the donor cells is inferred from the ammonia levels in recipients. However, in cases of sepsis or viral infection, ammonia levels can significantly and abruptly increase in patients with urea cycle defects. If this occurs in a HTx recipient, one might suspect that the cell graft was being rejected. Pro-inflammatory cytokines associated with viral or bacterial infections are known to suppress many liver functions, including the drug metabolizing enzymes and hepatic transport activities. We examined the influence of mediators of the immune response such as tumor necrosis factor-alpha (TNFa), interleukin-1beta (IL-1b) and interleukin-6 (IL-6) on drug metabolizing activity and ammonia metabolism in primary cultures of human hepatocytes. Human hepatocytes were isolated from normal donors and patients with different metabolic diseases. Ten different measures of hepatocyte viability and function including, plating efficiency, ammonia metabolism, conjugation reactions and cytochrome (CYP) P450-mediated metabolism were examined. Ammonia metabolism and other CYP isoform activities were analyzed immediately after isolation and after three days of exposure to concentrations of 0.1 to 10 ng/ml of the three cytokines, alone and in combination.

Both CYP-mediated drug metabolism and ammonia metabolism were profoundly suppressed in hepatocytes exposed to IL-6 and/or IL-1 b. Metabolic activities were less affected by TNF-alpha exposure. These data indicate that like CYP-mediated drug metabolism, suppression of ammonia metabolism occurs in hepatocytes exposed to pro-inflammatory cytokines in the absence of cell death. These observations have significance for urea cycle patients following HTx procedures in that abrupt spikes in ammonia levels concurrent with bacterial or viral infections do not necessarily indicate a rejection response or loss of the cell graft.