Overexpression of CYP3A aggravates endotoxin-induced liver injury in hypophysectomized female rats

Organotin compound DBDCT induces CYP3A suppression through NF-κB-mediated repression of PXR activity

Organotin anticancer agent di-n-butyl-di-(4-chlorobenzohydroxamato)tin(iv) (DBDCT) exerted an inhibitory effect on its major metabolic enzyme cytochrome CYP3A. But whether hepatic drug-metabolizing enzymes and their regulatory nuclear receptors including pregnane PXR and constitutive androstane CAR binding with retinoid receptor RXR as a heterodimer are involved in the DBDCT-mediated regulation of CYP3A remains unclear. This study was undertaken to determine the mechanisms responsible for the effects of DBDCT on CYP3A suppression, focusing on the PXR-mediated and NF-κB pathways. The results indicated DBDCT suppressed CYP3A expression by inhibiting CAR expression. But what's interesting is, both protein and mRNA of PXR increased with increasing DBDCT. A further exploration, dual luciferase reporter gene analysis, clarified that DBDCT induced CYP3A expression elevation via the PXR-mediated pathway and this induction was countered by activation of NF-κB, which played a pivotal role in suppression of CYP3A through disrupting the association of the PXR-RXRα complex with DNA sequences by EMSA. PXR-mediated CYP3A expression was similarly demonstrated by RNAi. As expected, expression of CYP3A and its mRNA levels were reduced by DBDCT only in NF-κB(+/+) but not in NF-κB(-/-) cells. The inductive effect of DBDCT on CYP3A4 mRNA was enhanced in PXR shRNA-transfected cells but weakened in the ip65 group, which showed both PXR up-regulated CYP3A expression and NF-κB p65 activation directly contributed to CYP3A inhibition. In conclusion, activated NF-κB by DBDCT interacts directly with the DNA-binding domain of PXR, and disrupts the binding between the PXR-RXR dimer, thereby affecting the regulatory process for CYP3A transcription and, therefore, leading to a decrease of the expression of the PXR-regulated CYP3A.

Inhibition of cytochrome P450 3A in rat liver by the Diorganotin (IV) compound di-n-Butyl-di-(4-chlorobenzo-hydroxamato)tin (IV) and Its Probable Mechanism

The specific aims of this study were to evaluate the inhibition effect on CYP3A of di-n-butyl-di-(4-chlorobenzohydroxamato)tin (IV) (DBDCT), a tin-based complex with high antitumor activity, and the probable mechanism(s) of this action. Adult male SD rats were treated separately with natural saline (NS), lipopolysaccharide (LPS, 5 mg/kg), DBDCT (1.25, 2.5 and 5.0 mg/kg) intraperitoneally for 2 days after induction of CYP3A with dexamethasone (DEX, 100 mg/kg) for 4 days. Western blot analysis and fluorescent quantitation PCR (FQ-PCR) were conducted to determine the changes in expression of CYP3A, PXR, CAR and RXR. The biological accumulation of DBDCT and total Sn were determined by high-performance liquid chromatography (HPLC) and atomic fluorescence spectrometry (AFS). CYP450 content and CYP3A activities were significantly inhibited (p < 0.05) in DBDCT-treated rats compared with the control group, as was the expression of CYP3A (p < 0.05) at both protein and mRNA levels. In DBDCT-treated groups, the expression of PXR protein and mRNA increased, while the expression of CAR decreased. The biological accumulation of DBDCT and Sn in rat livers treated with DBDCT was high. The accumulation of DBDCT and Sn due to the inhibition of CYP3A may be involved in the mechanism of toxicity of DBDCT in rat liver.

The expression and ovarian steroid regulation of endometrial micro-RNAs

MicroRNAs (miRNAs) which regulate gene expression stability displayed an aberrant expression profile in ectopic endometrium (ECE) as compared to eutopic (EUE) and normal endometrium (NE). We assessed the expression of miR-17-5p, miR-23a, miR-23b and miR-542-3p, their predicted target genes, steroidogenic acute regulatory protein, aromatase and cyclooxygenase-2, and influence of ovarian steroids on their expression in endometrial stromal (ESC) and glandular epithelial cells (GEC). The results indicated a lower expression of miR-23b and miR-542-3p and higher level of miR-17-5p in paired ECE and EUE as compared with NE. These levels were elevated and inversely correlated with the level of expression of their respective target genes in ECE. The expression of these miRNAs and genes was differentially regulated by 17beta- estradiol, medroxyprogesterone acetate, ICI-182780 and RU-486, or their respective combinations in ESC and GEC. We concluded that altered expression of specific miRNAs in ECE, affecting the stability of their target genes expression, has direct implications in pathogenesis of endometriosis.

A novel endotoxin-induced pathway: upregulation of heme oxygenase 1, accumulation of free iron, and free iron-mediated mitochondrial dysfunction

Mitochondria are involved in the development of organ failure in critical care diseases. However, the mechanisms underlying mitochondrial dysfunction are not clear yet. Inducible hemoxygenase (HO-1), a member of the heat shock protein family, is upregulated in critical care diseases and considered to confer cytoprotection against oxidative stress. However, one of the products of HO-1 is Fe2+ which multiplies the damaging potential of reactive oxygen species catalyzing Fenton reaction. The aim of this study was to clarify the relevance of free iron metabolism to the oxidative damage of the liver in endotoxic shock and its impact on mitochondrial function. Endotoxic shock in rats was induced by injection of lipopolysaccharide (LPS) at a dose of 8 mg/kg (i.v.). We observed that the pro-inflammatory cytokine TNF-alpha and the liver necrosis marker aspartate aminotransferase were increased in blood, confirming inflammatory response to LPS and damage to liver tissue, respectively. The levels of free iron in the liver were significantly increased at 4 and 8 h after onset of endotoxic shock, which did not coincide with the decrease of transferrin iron levels in the blood, but rather with expression of the inducible form of heme oxygenase (HO-1). The proteins important for sequestering free iron (ferritin) and the export of iron out of the cells (ferroportin) were downregulated facilitating the accumulation of free iron in cells. The temporarily increased concentration of free iron in the liver correlated with the temporary impairment of both mitochondrial function and tissue ATP levels. Addition of exogenous iron ions to mitochondria isolated from control animals resulted in an impairment of mitochondrial respiration similar to that observed in endotoxic shock in vivo. Our data suggest that free iron released by HO-1 causes mitochondrial dysfunction in pathological situations accompanied by endotoxic shock.