Investigation of Orlistat effects on PXR activation and CYP3A4 expression in primary human hepatocytes and human intestinal LS174T cells

Molecular mechanism of down-regulating adipogenic transcription factors in 3T3-L1 adipocyte cells by bioactive anti-adipogenic compounds

Obesity is growing at an alarming rate, which is characterized by increased adipose tissue. It increases the probability of many health complications, such as diabetes, arthritis, cardiac disease, and cancer. In modern society, with a growing population of obese patients, several individuals have increased insulin resistance. Herbal medicines are known as the oldest method of health care treatment for obesity-related secondary health issues. Several traditional medicinal plants and their effective phytoconstituents have shown anti-diabetic and anti-adipogenic activity. Adipose tissue is a major site for lipid accumulation as well as the whole-body insulin sensitivity region. 3T3-L1 cell line model can achieve adipogenesis. Adipocyte characteristics features such as expression of adipocyte markers and aggregation of lipids are chemically induced in the 3T3-L1 fibroblast cell line. Differentiation of 3T3-L1 is an efficient and convenient way to obtain adipocyte like cells in experimental studies. Peroxisome proliferation activated receptor γ (PPARγ) and Cytosine-Cytosine-Adenosine-Adenosine-Thymidine/Enhancer-binding protein α (CCAAT/Enhancer-binding protein α or C/EBPα) are considered to be regulating adipogenesis at the early stage, while adiponectin and fatty acid synthase (FAS) is responsible for the mature adipocyte formation. Excess accumulation of these adipose tissues and lipids leads to obesity. Thus, investigating adipose tissue development and the underlying molecular mechanism is important in the therapeutical approach. This review describes the cellular mechanism of 3T3-L1 fibroblast cells on potential anti-adipogenic herbal bioactive compounds.

Example of the drug interaction between ciclosporin and orlistat, resulting in relapse of Evan's syndrome

A man aged 35 years with a history of Evan's syndrome presented to the clinic with jaundice and shortness of breath, with further testing indicating a relapse of his previously well-controlled condition, for which he was taking ciclosporin. This followed shortly after he had started taking orlistat to prevent weight gain from a course of steroids, and once the orlistat was stopped, his platelets began to rise. The patient required 4 months of steroid treatment before his platelet levels finally stabilised and he could be put back on his regular medicine regime.

PXR antagonists and implication in drug metabolism

Adopted orphan nuclear receptor (NR), pregnane X receptor (PXR), plays a central role in the regulation of xeno- and endobiotic metabolism. Since the discovery of the functional role of PXR in 1998, there is evolving evidence for the role of PXR agonists in abrogating metabolic pathophysiology (e.g., cholestasis, hypercholesterolemia, and inflammation). However, more recently, it is clear that PXR is also an important mediator of adverse xeno- (e.g., enhances acetaminophen toxicity) and endobiotic (e.g., hepatic steatosis) metabolic phenotypes. Moreover, in cancer therapeutics, PXR activation can induce drug resistance, and there is growing evidence for tissue-specific enhancement of the malignant phenotype. Thus, in these instances, there may be a role for PXR antagonists. However, as opposed to the discovery efforts for PXR agonists, there are only a few antagonists described. The mode of action of these antagonists (e.g., sulforaphane) remains less clear. Our laboratory efforts have focused on this question. Since the original discovery of azoles analogs as PXR antagonists, we have preliminarily defined an important PXR antagonist pharmacophore and developed less-toxic PXR antagonists. In this review, we describe our published and unpublished findings on recent structure-function studies involving the azole chemical scaffold. Further work in the future is needed to fully define potent, more-selective PXR antagonists that may be useful in clinical application.

Pregnane X receptor and yin yang 1 contribute to the differential tissue expression and induction of CYP3A5 and CYP3A4

The hepato-intestinal induction of the detoxifying enzymes CYP3A4 and CYP3A5 by the xenosensing pregnane X receptor (PXR) constitutes a key adaptive response to oral drugs and dietary xenobiotics. In contrast to CYP3A4, CYP3A5 is additionally expressed in several, mostly steroidogenic organs, which creates potential for induction-driven disturbances of the steroid homeostasis. Using cell lines and mice transgenic for a CYP3A5 promoter we demonstrate that the CYP3A5 expression in these organs is non-inducible and independent from PXR. Instead, it is enabled by the loss of a suppressing yin yang 1 (YY1)-binding site from the CYP3A5 promoter which occurred in haplorrhine primates. This YY1 site is conserved in CYP3A4, but its inhibitory effect can be offset by PXR acting on response elements such as XREM. Taken together, the loss of YY1 binding site from promoters of the CYP3A5 gene lineage during primate evolution may have enabled the utilization of CYP3A5 both in the adaptive hepato-intestinal response to xenobiotics and as a constitutively expressed gene in other organs. Our results thus constitute a first description of uncoupling induction from constitutive expression for a major detoxifying enzyme. They also suggest an explanation for the considerable tissue expression differences between CYP3A5 and CYP3A4.