Current Drug Metabolism - Volume 17, Issue 1, 2016

Bile acids, synthesized by hepatocytes from cholesterol, are specific and quantitatively important organic components of bile, where they are the main driving force of the osmotic process that generates bile flow toward the canaliculus. The bile acid pool comprises a variety of species of amphipathic acidic steroids. They are not mere detergent molecules that play a key role in fat digestion and the intestinal absorption of hydrophobic compounds present in the intestinal lumen after meals, including liposoluble vitamins. They are now known to be involved in the regulation of multiple functions in liver cells, mainly hepatocytes and cholangiocytes, and also in extrahepatic tissues. The identification of nuclear receptors, such as farnesoid X receptor (FXR or NR1H4), and plasma membrane receptors, such as the G protein-coupled bile acid receptor (TGR5, GPBAR1 or MBAR), which are able to trigger specific and complex responses upon activation (with dissimilar sensitivities) by different bile acid molecular species and synthetic agonists, has opened a new and promising field of research whose implications extend to physiology, pathology and pharmacology. In addition, pharmacological development has taken advantage of advances in the understanding of the chemistry and biology of bile acids and the biological systems that interact with them, which in addition to the receptors include several families of transporters and export pumps, to generate novel bile acid derivatives aimed at treating different liver diseases, such as cholestasis, biliary diseases, metabolic disorders and cancer. This review is an update of the role of bile acids in health and disease.

Carvedilol and metoprolol are two of the most commonly prescribed β-blockers in cardiovascular medicine and primarily used in the treatment of hypertension and heart failure. Cytochrome P450 2D6 (CYP2D6) is the predominant metabolizing enzyme of these two drugs. Since the first description of a CYP2D6 sparteinedebrisoquine polymorphism in the mid-seventies, substantial genetic heterogeneity has been reported in the human CYP2D6 gene, with ~100 different polymorphisms identified to date. Some of these polymorphisms render the enzyme completely inactive while others do not modify its activity. Based on all the identified variants, four metabolizer phenotypes are nowadays used to characterize drug metabolism via CYP2D6 in humans: ultra-rapid metabolizer (UM); extensive metabolizer (EM); intermediate metabolizer (IM); and poor metabolizer (PM) phenotypes. As a consequence of these CYP2D6 metabolizer phenotypes, pharmacokinetics and bioavailability of carvedilol and metoprolol can range from therapeutically ineffective levels (in the UM patients) to excessive (overdose) and potentially toxic concentrations (in PM patients). This, in turn, can result in elevated risks for either treatment failure (in terms of blood pressure reduction of hypertensive patients and of improving survival and cardiovascular function of heart failure patients) or for adverse effects (e.g. hypotension and bradycardia). The present review will discuss the impact of these CYP2D6 genetic polymorphisms on the therapeutic responses of cardiovascular patients treated with either of these two β-blockers. In addition, the potential advantages and disadvantages of implementing CYP2D6 genetic testing in the clinic to guide/personalize therapy with these two drugs will be discussed.

Combination therapy has become an important strategy for treating cancer in recent years. Ceramide, which is a powerful tumor suppressor, regulating the processes of cell proliferation, differentiation, senescence and apoptosis, has attracted tremendous attention in combination therapy for cancer treatment. It has been demonstrated that combination of chemotherapeutic drugs and ceramide led to a reversion of multidrug resistance (MDR), synergistic tumor inhibition while simultaneously reducing systemic toxicity in cancer treatment. In this review, we aim to reveal the interactions between some anticancer drugs and ceramide, and summarize the research progress in combination therapies based on ceramide. Synthesis, metabolism and anticancer mechanisms of ceramide were described. Furthermore, the advantages of combination of chemotherapeutic drugs and exogenous ceramide, ceramidegenerating agents or modulators of ceramide metabolism were highlighted. Future perspective and problems to solve before the extension of ceramide’s applications were also discussed. It is hoped that this review will provide new ideas for combination therapies in cancer treatment.

For healthcare professionals, the volume of literature available on herb-drug interactions often makes it difficult to separate experimental/potential interactions from those deemed clinically relevant. There is a need for concise and conclusive information to guide pharmacotherapy in HIV/AIDS. In this review, the bases for potential interaction of medicinal herbs with specific antiretroviral drugs are presented, and several botanicals are discussed for which clinically relevant interactions in humans are established. Such studies have provided, in most cases, sufficient ground to warrant the avoidance of concurrent administration of antiretroviral (ARVs) drugs with St John’s wort (Hypericum perforatum), black pepper (Piper species) and grapefruit juice. Other botanicals that require caution in the use with antiretrovirals include African potato (Hypoxis hemerocallidea), ginkgo (Ginkgo biloba), ginseng (Panax species), garlic (Allium sativum), goldenseal (Hydrastis canadensis) and kava kava (Piper methysticum). The knowledge of clinically significant herb-drug interaction will be important in order to avoid herb-induced risk of sub-therapeutic exposure to ARVs (which can lead to viral resistance) or the precipitation of toxicity (which may lead to poor compliance and/or discontinuation of antiretroviral therapy).

Cytochrome P450 enzymes are responsible for the hydroxylation of various endogenous estrogens of the Phase I metabolic pathway. Cytochrome P450s produce hormonally active estrogen metabolites that are typically reactive and mutagenic. Although these metabolites are known to have important roles in autoimmunity, the underlying mechanism of this remains unknown. Here we report that cytochrome P450-mediated estrogen metabolites produce high ROS concentrations that can result in DNA damage. Such DNA damage can alter its immunogenicity, resulting in the induction and elevation of autoantibody concentrations, thus generating various autoimmune conditions. Here we focus on the mechanisms through which cytochrome P450-catalyzed estrogen metabolites induce immune responses and subsequently produce the autoimmune phenomenon.

Cardioncology is a major topic of the day, since cardiotoxicity of chemotherapy agents can limit its real use and it can also become a clinical problem years after the end of anticancer therapy. These cardiac problems largely increase the mortality and morbidity of cancer-treated patients. Actually, as the number of cancer survivors is increasing each decade, late cardiotoxicity related to anticancer therapy is expected to grow exponentially in the fore coming years. The mechanisms of cardiotoxicity of anticancer drugs are still largely unknown. The metabolism of some drugs can lead to more active anticancer metabolites but those metabolites can likewise contribute to the observed cardiotoxicity. The alcohols and aglycone metabolites of anthracyclines are known to be cardiotoxic, while regarding 5-fluorouracil, fluoroacetate is considered one of the major metabolites responsible for its cardiotoxicity. Regarding mitoxantrone, the toxicity of the majority of the metabolites has not been assessed so far and concerning cyclophosphamide metabolites, both hydroxycyclophosphamide and acrolein are shown to be more cardiotoxic than the parent drug. Still, the contribution of drug metabolism to the cardiotoxicity of chemotherapy agents is largely unknown and poorly discussed. This review presents a new link between several cardiotoxic anticancer drugs and their drug metabolites, as they can play an important role in the widely reported heart damage inflicted by chemotherapy. Anthracyclines, cyclophosphamide, mitoxantrone, and 5- fluorouracil will be mainly focused, given the vast literature and clinical use. The current knowledge shows the possible involvement of drug metabolism in bioactivation mechanisms that can contribute to their cardiotoxicity.

Induced pluripotent stem cells (iPSC) can be produced from adult cells by transfecting them with a definite set of pluripotency-associated genes. Under adequate growth conditions and stimulation iPSC can differentiate to almost every somatic lineage in the body. Patients' derived iPSC are an innovative model to study mechanisms of adverse drug reactions in individual patients and in cell types that cannot be easily obtained from human subjects. Proof-of concept studies with known toxicants have been performed for liver, cardiovascular and central nervous system cells: neurons obtained from iPSC have been used to elucidate the mechanism of chemotherapyinduced peripheral neuropathy by evaluating the effects of neurotoxic drugs such as vincristine. However, no study has been performed yet on pancreatic tissue and drug induced pancreatitis. Thiopurines (azathioprine and mercaptopurine) are immunosuppressive antimetabolite drugs, commonly used to treat Crohn's disease. About 5% of Crohn's disease patients treated with thiopurines develop pancreatitis, a severe idiosyncratic adverse event; these patients have to stop thiopurine administration and may require medical treatment, with significant personal and social costs. Molecular mechanism of thiopurine induced pancreatitis (TIP) is currently unknown and no fully validated biomarker is available to assist clinicians in preventing this adverse event. Hence, in this review we have reflected upon the probable research applications of exocrine pancreatic cells generated from patient specific iPS cells. Such pancreatic cells can provide excellent insights into the molecular mechanism of TIP. In particular three hypotheses on the mechanism of TIP could be explored: drug biotransformation, innate immunity and adaptative immunity.