The Interface between Cell Signaling Pathways and Pregnane X Receptor

Highly expressed in the enterohepatic system, pregnane X receptor (PXR, NR1I2) is a well-characterized nuclear receptor (NR) that regulates the expression of genes in the liver and intestines that encode key drug metabolizing enzymes and drug transporter proteins in mammals. The net effect of PXR activation is to increase metabolism and clear drugs and xenobiotics from the body, producing a protective effect and mediating clinically significant drug interaction in patients on combination therapy. The complete understanding of PXR biology is thus important for the development of safe and effective therapeutic strategies. Furthermore, PXR activation is now known to specifically transrepress the inflammatory- and nutrient-signaling pathways of gene expression, thereby providing a mechanism for linking these signaling pathways together with enzymatic drug biotransformation pathways in the liver and intestines. Recent research efforts highlight numerous post-translational modifications (PTMs) which significantly influence the biological function of PXR. However, this thrust of research is still in its infancy. In the context of gene-environment interactions, we present a review of the recent literature that implicates PXR PTMs in regulating its clinically relevant biology. We also provide a discussion of how these PTMs likely interface with each other to respond to extracellular cues to appropriately modify PXR activity.

Interindividual Variability of Cytochromes P450 2B Mediated Oxidation in Human Liver

The cytochromes P450 (CYPs) are a group of enzymes that are primarily responsible for oxidative drug biotransformation in people. CYP2B6, which metabolizes numerous drugs including bupropion, propofol and other drug shows great variability in rates of drug oxidation between individuals. In this chapter we discuss the contribution of selected genetic and environmental factors to this variability. Several studies identified and quantified the most common CYP2B6 mRNA splice such as deletion of exons 4 to 6 and of exon 4 which were significantly and negatively correlated with CYP2B6 protein and enzyme activity. CYP2B6 gene expression is highly inducible by phenobarbital. Alcohol ingestion has been associated with increased CYP2B6 levels this involves the constitutive androstane receptor (CAR) and/or the pregnane X receptor (PXR). CYP2B7 is considered a pseudogene because of the presence of a single premature stop codon (TGA) in exon 7. In 10 out of 24 African-Americans (but none out of 48 European-Americans) there is a single nucleotide polymorphism that results in an arginine codon instead of a stop codon (X378R). The results of these studies identify certain CYP2B6 genetic polymorphisms, mRNA splicing variants, and alcohol ingestion as significant factors that determine interindividual variability of CYP2B-mediated oxidation of drugs in people.

Unveiling the Role of Cytochrome P450 (2E1) in Human Brain Specifically in Parkinson’s Disease - Literature Review

Background: In recent years, the significance of cytochrome P450 enzymes (CYPs) has expanded beyond their role in liver. Factors such as genetics, environmental toxins, drug biotransformation and underlying diseases mediate the expression of these enzymes. Among the CYP enzymes, CYP2E1, a well-recognized monooxygenase enzyme involved in the metabolism of various endogenous and exogenous substances, plays a crucial role in the brain concerning the development of Parkinson’s disease. The expression of CYP2E1 varies in different brain regions making certain regions more vulnerable than others. CYP2E1 expression is inducible which generates tissue-damaging radicals leading to oxidative stress, mitochondrial dysfunction and ultimately neurodegeneration. Objective: Less is understood about the role of CYP2E1 in the central nervous system, therefore the purpose of the study was to investigate the relationship between the expression and activity of CYP2E1 enzyme relevant to Parkinson’s disease and to identify whether an increase in the expression of CYP2E1 is associated with neurodegeneration. Methods: The objectives of the study were achieved by implicating an unsystematic integrative literature review approach in which the literature was qualitatively analysed, critically evaluated and a new theory with an overall view of the mechanism was presented. Results : The contribution of CYP2E1 in the development of Parkinson’s disease was found to be significant as the negative effects of CYP2E1 overshadowed its protective detoxifying role. Conclusion: Overexpression of CYP2E1 seems detrimental to dopaminergic neurons, therefore, to overcome this, a synthetic biochemical is required which paves the way for further research and development of valuable biomolecules.

Risk management strategy for preventing the reduced treatment effectiveness from the position of drug interactions and polypharmacy in patients with coronary heart disease

Introduction: In modern clinical practice, various drug combinations are widely used, especially in cardiological patients. The existing clinical recommendations necessitate using organ protective agents, especially with a patient having a comorbid pathology and with an ineffective monotherapy. In some cases, drug interaction decreases the effectiveness of pharmacotherapy and increases the risk of developing adverse events (AE). The purpose of the study was to analyze the modern pharmacotherapy of patients with coronary heart disease (CHD), identify polypharmacy of treatment, evaluate its significance for the treatment process, and determine ways to solve the problem of using a multi-component system of pharmacotherapy risk management. Materials and methods: The study involved 156 patients with CHD, among whom 39 received more than 8 drugs at a time. Results and discussion: In these patients, the evaluation of drug interactions revealed 580 variants (48 were dangerous, 428 – significant, 104 – insignificant). The administration of a therapy to comorbid patients, taking into account possible changes in the activity of cytochrome P450 isoenzymes, is one of the promising ways to improve the safety of a combined pharmacotherapy. Conclusion: It was revealed that with a mutated cytochrome P450 most of processes of drug biotransformation occurs. And there is a greater risk of developing AE against the background of polypragmasia in polymorbid patients, which makes it possible to individually adjust the dose of beta-blockers, thus affecting the frequency of their development. The choice of management measures should be determined considering all the areas of personalized medicine, including pharmacogenetic predictors, pharmacoepidemiological data, pharmacoeconomic effectiveness, the development of adverse reactions, polypragmasia, and medical and social risk factors.

The Pharmacogenetics of Cytochrome P-450 and its Effect on Drug Metabolism

Cytochrome P-450 (CYP-450) enzyme plays an essential role in the oxidation of most drugs, and thus it can affect the toxicity and efficacy of many medications. Factors that influence the function and presence of cytochrome have a key impact on the outcomes of therapy. More specifically, characteristics of cytochrome pharmacogenetics and procedures of cytochrome enzymes induction and inhibition can greatly influence the rate of drug biotransformation and the rate of elimination. So, an understanding of genetic variants which are associated with drug responses and illnesses could improve and enhance the outcome of treatment. Clinical data in genetic tests may be useful in order to develop methods for assessing genetic risks. Positively, genetic tests for monogenic sicknesses have already proven to be a useful test and any changes may trigger a new field of personalized drug. This review will look at the influence of pharmacogenetics in drug metabolism and the importance of using personal genetic data in achieving optimal therapy and in preventing any possible adverse effects. Keywords: Pharmacogenetics, Biotransformation, CYP-450

Polymorphisms of methotrexate metabolism genes—as predictors of its hepatotoxicity in rheumatoid arthritis

Objective: to identify among the allelic polymorphisms of the folate cycle genes: RFC-1 80G> A, MTHFR C677T and A1298C, TS2R/3R and 6bp del/ins, GGH-401C>T, MDR1 C3435T, hepatotoxicity predictors of methotrexate in patients with rheumatoid arthritis.Materials and methods: the frequency of liver dysfunction in 85 patients with rheumatoid arthritis was analyzed retrospectively with methotrexate therapy, followed by an assessment of the correlation with allelic polymorphisms of the folate cycle genes that regulate the diff erent stages of drug biotransformation.Results: an analysis of the distribution of alleles and genotypes of the folate cycle genes mentioned above allowed the identifi cation of protective genetic markers for methotrexate-induced hepatotoxicity in the form of allelic polymorphisms MTHFR1298AC and TS6bp del/ins, as well as suggesting the role of TS6bp ins/ins polymorphism in the development of hyperfermentemia.Conclusion: the ambiguity of the literature data on the search for prognostic markers of hepatotoxicity of methotrexate, as well as our data, which do not have comparable results in both domestic and foreign publications, dictate the need to continue research on the safety of methotrexate in rheumatoid arthritis.

Rifampicin: biotransformation study using the fungus Cunninghamella elegans and monitoring through UHPLC-MS

Drug biotransformation studies appear as an alternative to pharmacological investigations of metabolites, development of new drug candidates with reduced investment and most efficient production. The objective of this study was to evaluate the capacity of biotransformation of Rifampicin (RIF) by the filamentous fungus Cunninghamella elegans as a microbial model of mammalian metabolism. In 120 h, C. elegans transformed the drug into the following two metabolites: rifampicin quinone and novel metabolite. The products of rifampicin formed in vitro were monitored by HPLC-PDA, being identified through UHPLC–QTOF/MS. Metabolites were characterized according to their chromatographic profile, mass fragments and UV spectral data. The major metabolic pathways of rifampicin transformed by the fungus were oxidation, demethylation and mono-oxidation. The microbial transformation of RIF showed the potential of Cunninghamella species to produce RIF metabolites. This process can be used for a cost effective method for both known and unknown metabolite production.

Targeting Pharmacokinetic Drug Resistance in Acute Myeloid Leukemia Cells with CDK4/6 Inhibitors

Pharmacotherapy of acute myeloid leukemia (AML) remains challenging, and the disease has one of the lowest curability rates among hematological malignancies. The therapy outcomes are often compromised by the existence of a resistant AML phenotype associated with overexpression of ABCB1 and ABCG2 transporters. Because AML induction therapy frequently consists of anthracycline-like drugs, their efficiency may also be diminished by drug biotransformation via carbonyl reducing enzymes (CRE). In this study, we investigated the modulatory potential of the CDK4/6 inhibitors abemaciclib, palbociclib, and ribociclib on AML resistance using peripheral blood mononuclear cells (PBMC) isolated from patients with de novo diagnosed AML. We first confirmed inhibitory effect of the tested drugs on ABCB1 and ABCG2 in ABC transporter-expressing resistant HL-60 cells while also showing the ability to sensitize the cells to cytotoxic drugs even as no effect on AML-relevant CRE isoforms was observed. All tested CDK4/6 inhibitors elevated mitoxantrone accumulations in CD34+ PBMC and enhanced accumulation of mitoxantrone was found with abemaciclib and ribociclib in PBMC of FLT3-ITD- patients. Importantly, the accumulation rate in the presence of CDK4/6 inhibitors positively correlated with ABCB1 expression in CD34+ patients and led to enhanced apoptosis of PBMC in contrast to CD34− samples. In summary, combination therapy involving CDK4/6 inhibitors could favorably target multidrug resistance, especially when personalized based on CD34− and ABCB1-related markers.

In-Silico Modeling in Drug Metabolism and Interaction: Current Strategies of Lead Discovery

Background: Drug metabolism is a complex mechanism of human body systems to detoxify foreign particles, chemicals, and drugs through bio alterations. It involves many biochemical reactions carried out by invivo enzyme systems present in the liver, kidney, intestine, lungs, and plasma. After drug administration, it crosses several biological membranes to reach into the target site for binding and produces the therapeutic response. After that, it may undergo detoxification and excretion to get rid of the biological systems. Most of the drugs and its metabolites are excreted through kidney via urination. Some drugs and their metabolites enter into intestinal mucosa and excrete through feces. Few of the drugs enter into hepatic circulation where they go into the intestinal tract. The drug leaves the liver via the bile duct and is excreted through feces. Therefore, the study of total methodology of drug biotransformation and interactions with various targets is costly. Methods: To minimize time and cost, in-silico algorithms have been utilized for lead-like drug discovery. Insilico modeling is the process where a computer model with a suitable algorithm is developed to perform a controlled experiment. It involves the combination of both in-vivo and in-vitro experimentation with virtual trials, eliminating the non-significant variables from a large number of variable parameters. Whereas, the major challenge for the experimenter is the selection and validation of the preferred model, as well as precise simulation in real physiological status. Results: The present review discussed the application of in-silico models to predict absorption, distribution, metabolism, and excretion (ADME) properties of drug molecules and also access the net rate of metabolism of a compound. Conclusion: : It helps with the identification of enzyme isoforms; which are likely to metabolize a compound, as well as the concentration dependence of metabolism and the identification of expected metabolites. In terms of drug-drug interactions (DDIs), models have been described for the inhibition of metabolism of one compound by another, and for the compound–dependent induction of drug-metabolizing enzymes.