Abstract
Recently, we reported that repeated injection of PEGylated liposomes (PEG-L) at certain intervals to the same rat lead to the disappearance of their long-circulating properties, referred to as "accelerated blood clearance (ABC)" phenomenon. Evidence from our recent studies suggest cytochrome P450s (CYPs) partly contribute to the induction of the ABC phenomenon, which had previously been ignored. However, little is known about the details of the mechanism for the induction of CYPs. This study was undertaken to investigate the roles of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) in the ABC phenomenon, which are the major upstream transcriptional regulators of the CYP genes including CYP3A1, CYP2C6 and CYP1A2. The results demonstrated that the expression of rat PXR and CAR were significantly increased in such phenomenon, accompanied by elevated CYP3A1, CYP2C6 and CYP1A2 levels. Further findings revealed that PXR but not CAR protein was substantially upregulated in the hepatocyte nucleus, together with marked nuclear co-localization of PXR-retinoid X receptor alpha (RXRα) transcriptionally active heterodimer, indicating that nuclear translocation of PXR was induced in the ABC phenomenon, whereas nuclear translocation of CAR was not observed. Notably, pretreatment with the specific PXR inducer-dexamethasone significantly induced accelerated systemic clearance of the subsequent injection of PEG-L, associating with increased nuclear co-localization of PXR-RXRα. These results revealed that the induction of CYPs in the ABC phenomenon may be largely attributable to the activation of PXR induced by sequential injections of PEG-L, thus confirming the crucial involvement of PXR-CYPs axis in promoting ABC phenomenon.
SIGNIFICANCE STATEMENT The results of this study revealed that the induction of CYPs in the ABC phenomenon may be largely attributable to the activation of PXR induced by sequential injections of PEG-L, thus confirming the crucial involvement of PXR-CYPs axis in promoting ABC phenomenon. The data may help to extend our insights into 1) the role of CYPs, which are regulated by the liver-enriched nuclear receptor PXR, in the ABC phenomenon, and 2) the therapeutic potential of targeting the PXR-CYP axis for reducing the magnitude of the ABC phenomenon in clinical practice.
- cytochrome P450
- distribution
- enzyme induction
- HPLC
- liposomes
- mass spectrometry/MS
- nuclear receptors
- pharmacokinetics
- pregnane X receptor/PXR/SXR
- signalling pathways
- The American Society for Pharmacology and Experimental Therapeutics