Downregulation of Hepatic Cytochrome P-450 Isoforms and PPAR-γ: Their Role in Hepatic Injury and Proinflammatory Responses in a Double-Hit Model of Hemorrhage and Sepsis

Background: The "double-hit" model of hemorrhage and sepsis mimics the critically ill patient admitted to the surgical intensive care unit. Although the protein expression of a cytochrome (CYP) P-450 isoform CYP1A2 is reduced in the late stage of sepsis, the effect of hemorrhage on CYP isoforms and the anti-inflammatory nuclear receptor peroxisome proliferator-activated receptor-γ (PPAR-γ) has not been investigated. We hypothesized that hemorrhage down-regulates CYP isoforms and PPAR-γ in the liver, which plays an important role in producing tissue injury and proinflammatory responses after the subsequent sepsis (i.e., double-hit). Materials and methods: Male Sprague Dawley rats were divided into four groups. Animals in the double-hit group underwent hemorrhage (40 ± 2 mmHg for 90 min) followed by fluid resuscitation. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) 20 h after hemorrhage, and the animals were sacrificed 4 h after CLP. Rats in the hemorrhage-alone group were sacrificed 20 h after the insult. Rats in the CLP-alone group were sacrificed 4 h after the onset of sepsis. Animals in the sham-operated group underwent neither hemorrhage nor CLP. The gene expression of P-450 isoforms (i.e., CYP1A2 and 2C11) and PPAR-γ in the liver was determined using RT-PCR. Serum concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate, and proinflammatory cytokines (i.e., IL-6, TNF-α) were also assessed. Results: In the hemorrhage-alone group, hepatic mRNA expression of CYP1A2, CYP2C11, and PPAR-γ was significantly down-regulated 20 h after the initial stress compared with sham-operated rats. Double-hit did not appear to further decrease CYP and PPAR-γ gene expression. In contrast, serum levels of AST, ALT, lactate, IL-6, and TNF-α did not change significantly in either hemorrhaged or septic animals. Those organ injury indicators and cytokines, however, were significantly elevated after the double-hit of hemorrhage and sepsis. Conclusions: Hepatic CYP1A2, CYP2C11, and PPAR-γ were down-regulated after the initial stress (hemorrhage). These down-regulated CYPs and PPAR-γ seem to work as important factors contributing to the progression of organ injury and proinflammatory responses after the second stress (CLP).