Inflammatory diseases such as rheumatoid arthritis and psoriasis are characterized by increases in circulating cytokines, which
play an important role in modulation of the disease state. Several marketed bio-therapeutics target cytokines and act as effective treatment
strategies. Previous in-vitro and in-vivo studies have suggested that cytokines may have both direct and indirect effects on drug metabolizing
enzyme levels in the liver. Few studies have characterized models to evaluate the risk of potential drug interactions that might be
mediated by changes in cytokine levels. In the present studies the potential of three cytokines (IL-2, IL-6 and TNF-α) to modulate gene
expression and activity of the major human cytochrome P450 (CYP) enzymes (CYP1A2, 2B6, 2C9, 2C19, 2D6, and 3A4) in cryopreserved
human hepatocytes (CHH) was investigated. Significant decreases in the activity of all 6 CYP isoforms occurred in hepatocytes
incubated with TNF-α or IL-6 (17-85% and 22-76% of untreated control values, respectively). TNF-α down-regulated the gene expression
of CYP1A2, 2D6 and 3A4 only, whereas IL-6 down-regulated gene expression of all of the tested CYP isoforms except 2D6. IL-2
had only mild effects on CYP activity and mRNA levels of examined isoforms. In CHH exposed to TNF-α, changes in CYP activity
were not always paralleled by gene expression alterations for three of the examined CYP isoforms. These studies highlight several potential
pitfalls in using isolated human hepatocytes for determination of drug interactions by bio-therapeutics including lack of correlation of
mRNA and activity measurements for some CYP isoforms when using single time point determinations, and appropriateness of the
model for indirect acting cytokine and cytokine modulators.
Keywords: Bio-therapeutics, cryopreserved human hepatocytes, cytokines, drug interactions, interleukin-6, liver, tumor necrosis factor, Interactions, Drugs, Inflammatory diseases, modulator, RXR, Heterodimerization, X receptor, RT-PCR.
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