PXR-Mediated Xenobiotic Response in the Pathogenesis Hemorrhagic Shock

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Title: PXR-Mediated Xenobiotic Response in the Pathogenesis Hemorrhagic Shock Project Summary/Abstract: The goal of this proposal is to understand the role of xenobiotic receptor pregnane X receptor (PXR) in the pathogenesis and clinical outcome of hemorrhagic shock (HS). HS is a life-threatening condition often associated with traumatic injuries. Severe HS can lead to injury to multiple tissues, including the liver. In addition to the liver injury, HS and the resulting tissue hypofusion also induce a cascade of inflammatory and oxidative stress, leading to an overall suppression of drug metabolism in the liver. The HS-responsive suppression of hepatic drug metabolism has potential clinical implications, because seriously injured trauma patients are uniformly prescribed with multiple medications. PXR is a master regulator of xenobiotic response through its transcriptional regulation of the phase I and phase II drug-metabolizing enzymes (DMEs) and transporters, especially in the liver. In addition to inducing cytochrome P450 (CYP) enzymes, another potential outcome of PXR activation is the increased production of reactive oxygen species (ROS) as a result of increased CYP-mediated oxidations. Many of the drugs often prescribed to the HS patients before or after the occurrence of trauma, such as RIF and DEX, are known PXR activators and DME inducers in the liver. It has also been reported that the expression and activity of PXR decreased in experimental HS. However, it is unclear whether PXR plays a role in the regulation of hepatic drug metabolism in the setting of HS and if so, whether activation of PXR is beneficial or detrimental to the HS-responsive liver injury. Our preliminary results showed that: 1) Mice subjected to HS exhibit a dynamic regulation of PXR and hepatic P450 enzymes, such as the Cyp3a11; 2) HS suppresses the metabolism of midazolam and Oxycodone, two drugs commonly used in trauma care; 3) Genetic activation of PXR in transgenic mice sensitizes mice to HS- responsive liver injury, but had little effect on HS-responsive lung injury; 4) The HS-responsive liver injury, but not lung injury, was attenuated in Pxr-/- mice; 5) The sensitizing effect of the PXR transgene on HS-induced liver injury is Cyp3a dependent; 6) The sensitizing effect of the PXR transgene on HS-responsive liver injury is associated with increased hepatic oxidative stress; 7) The hPXR-hCYP3A4 humanized mice have been created; and 8) Activation of constitutive androstane receptor (CAR) does not affect HS-responsive liver injury. Based on these observations, we propose a reciprocal interaction between hemorrhagic shock (HS) and hepatic drug metabolism or the regulation of hepatic drug metabolism. Specifically, we hypothesize that 1) HS causes liver damage and has a dynamic effect on the expression of PXR, CYP3A and other DMEs; and 2) Activation of PXR sensitizes HS-responsive liver injury by inducing the expression of CYP3A and increasing oxidative stress. We propose three specific aims to test our hypotheses: 1) To determine whether pharmacological activation of PXR in humanized mice sensitizes them to HS-induced liver injury; 2) To determine whether the expression and regulation of CYP3A4 in humanized mice are required for the sensitizing effect of PXR on HS-induced liver injury; and 3) To determine whether the induction of oxidative stress is responsible for the sensitizing effect of PXR on HS-induced liver injury in humanized mice. Taken together, our results suggest that the HS-responsive suppression of PXR may represent a protective response and/or secondary response to HS-induced liver injury. The unavoidable use of PXR-activating drugs prior to HS or during the clinical management of trauma may restore drug metabolism, but has the potential to exacerbate HS-induced liver injury in trauma patients, which can be mitigated by the co-administration of anti- oxidative agents or PXR antagonists.