We then analyzed two additional cytokines induced by polyI:C, TNF-α and IL-1, which have been shown to modulate CYP expression when administered in patients or animals.31 However, both TNF-α-deficient mice (Tnfa−/−) and IL-1 receptor-deficient mice (IL-1R−/−) were protected by polyI:C against
APAP-induced hepatotoxicity (Supporting Fig. 4). TLR3 is the primary membrane-bound receptor for mediating the innate immune response to polyI:C.21 In the absence of TLR3, APAP-induced hepatotoxicity was suppressed when mice were pretreated with polyI:C (Fig. 6B). This finding was confirmed using mice deficient in TRIF, the adaptor protein required for TLR3 signaling18 (Fig. 6A). Moreover, mice lacking Cardif, the adaptor protein for cytoplasmic receptors JAK inhibitor selleck chemicals llc of polyI:C, were also protected against APAP-induced hepatic injury18 (Fig. 6C). However, polyI:C pretreatment in double knockout mice deficient in both Cardif and TLR3 failed to protect against APAP-induced hepatotoxicity (Fig. 6D). These findings suggest that membrane-bound and cytosolic receptors of polyI:C play complementary roles in this animal model. There are many documented examples of impaired drug metabolism in patients with viral infections.1, 2 These effects have been attributed to modulation of CYP enzymes in response to activation of the innate immune system.4 Although the activity and expression levels of CYPs have been shown to
be altered during viral infection or inflammatory states, the underlying molecular mechanisms are not well characterized. Our previous work identified a potential mechanism of how innate immune activation can MCE lead to enhanced ASA-induced hepatotoxicity through down-regulation of CYP3A11, the CYP enzyme required
for the clearance of the toxic intermediate of ASA.5 PolyI:C stimulation can lead to transcriptional down-regulation of RXRα and subsequently decreasing the presence of RXRα on the PXR/RXR ER6 binding region on the promoter of CYP3A4 (human homolog of Cyp3a11) in Huh7 cells.5 Here we studied the effects of such crosstalk between antiviral responses and nuclear hormone receptors on the transcriptional regulation of CYPs involved in the metabolism and toxicity of another commonly used analgesic, APAP. In this study we report that VSV infection as well as polyI:C pretreatment results in attenuated APAP-induced hepatotoxicity in mice. Early studies have also reported similar phenomena; however, the molecular mechanism by which such protection is mediated was never studied in detail.32 Our findings suggest that this protection against APAP-induced toxicity can potentially be due to inhibition of nuclear hormone receptor-regulated metabolism, as we have shown that polyI:C suppresses expression of PXR, RXRα, and their target genes, CYP3A11 and CYP1A2. The transcription of the other CYP involved in APAP metabolism, CYP2E1, however, was not altered, as this gene is not downstream of any known nuclear hormone receptors.