Microsomal P450 Enzymes Research Articles

Modulatory potentials of nitric oxide in obesity-induced endothelial dysfunction

Obesity is caused by a significant increase in adipose tissue due to excessive caloric intake that exceeds energy expenditure. Obesity has emerged as a significant public health issue in both poor resource and economic developed nations, owing to its increased incidence and links to chronic diseases, such osteoarthritis, hypertension, non-alcoholic fatty liver disease (NAFLD), and cardiovascular diseases (CVDs). It is believed that uncoupled eNOS, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidase, lipoxygenase, cyclooxygenase, microsomal P-450 enzymes, and pro-oxidant heme molecules are responsible for the drastic decrease in NO production and the relative increase in reactive oxygen species (ROS) secretion, which are considered as the molecular mechanisms associated with obesity-induced endothelial dysfunction. Vascular endothelium defines a monolayer of cells, which lies between the vascular smooth muscle cells (VSMCs) and the vessel lumen. It performs a number of protective actions facilitated by the release of nitric oxide (NO), a soluble gas that is generated in endothelial cells by the amino acid L-arginine through the action of endothelial nitric oxide synthase (eNOS). The maintenance of vascular homeostasis is facilitated by various biological actions of NO, such as modulation of vascular dilator tone, control of local cell growth, and protection of the endothelium from the harmful effects of cellular components in blood circulation, while maintaining normal endothelial functions. Decreased peripheral arterial endothelium-dependent dilation (EDD) in response to mechanical (intravascular shear) or chemical (acetylcholine) stimuli suggests that decreased NO bioavailability has been recognised as major molecular mechanisms associated with the progress and development of obesity-induced endothelial dysfunction. In this review, the modulatory effects of NO in obesity-induced endothelial dysfunction will be discussed.

Probe substrates assay estimates the effect of polyphyllin H on the activity of cytochrome P450 enzymes in human liver microsomes.

Cytochrome P450 enzymes (CYPs) play a crucial role in phase I metabolic reactions. The activity of CYPs would affect therapeutic efficacy and may even induce toxicity. Given the complex components of traditional Chinese medicine, it is important to understand the effect of active ingredients on CYPs activity to guide their prescription. This study aimed to evaluate the effect of polyphyllin H on the activity of CYPs major isoforms providing a reference for the clinical prescription of polyphyllin H and its source herbs. The effects of polyphyllin H were evaluated in pooled human liver microsomes using probe substrates of CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 to determine their activities. The Lineweaver-Burk was used to model the inhibition, and a time-dependent inhibition experiment was performed to understand the characteristics of the inhibition. Polyphyllin H significantly suppressed the activity of CYP1A2, 2D6, and 3A4 with IC50 values of 6.44, 13.88, and 4.52 μM, respectively. The inhibition of CYP1A2 and 2D6 was best fitted with a competitive model, yielding the inhibition constant (Ki) values of 3.18 and 6.77 μM, respectively. The inhibition of CYP3A4 was fitted with the non-competitive model with the Ki value of 2.38 μM. Moreover, the inhibition of CYP3A4 was revealed to be time-dependent with the inhibition parameters inhibition constant (KI) and inactivation rate constant (Kinact) values of 2.26 μM-1 and 0.045 min-1. Polyphyllin H acted as a competitive inhibitor of CYP1A2 and 2D6 and a non-competitive and time-dependent inhibitor of CYP3A4.

Inhibition of soluble epoxide hydrolase by natural isothiocyanates

GoalThe long-term goal of our research is to develop safe and effective soluble epoxide hydrolase (sEH) inhibitors. The objective of this study is to evaluate the potency and selectivity of six natural isothiocyanates (ITCs) as sEH inhibitors. MethodsMolecular docking was used to model likely interactions between the ligands and receptors. The sEH inhibitory activity was tested using a validated fluorescence-based assay and PHOME as a substrate. To evaluate their selectivity as sEH inhibitors, the inhibitory potential of the ITCs was determined on microsomal epoxide hydrolase (mEH) and cytochrome P450 (CYP) enzymes in human liver microsomes. Probe substrates such as styrene oxide (mEH substrate) and established substrates for CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 were used in this study. The metabolites of these substrates were analyzed using validated LC-MS/MS and HPLC-UV assays. ResultsMolecular Docking revealed significant differences in binding site preference among the ITCs in silico and pointed to important interactions between the ligands and the catalytic residues of the sEH enzyme. In vitro, the ITCs showed varying degrees of sEH inhibition, but sulforaphane (SFN) and phenyl isothiocyanate (PITC) were the most potent inhibitors with IC50 values of 3.65 and 7.5 μM, respectively. mEH was not significantly inhibited by any of the ITCs. Erucin and iberin were the only ITCs that did not inhibit the activity of any of the tested CYP enzymes. ConclusionOur results demonstrate that natural ITCs have the potential to offer safe, selective, and potent sEH inhibition.

Effect of tubeimoside I on the activity of cytochrome P450 enzymes in human liver microsomes

This study assessed the effect of tubeimoside I on CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 to reveal the potential of tubeimoside I to induce drug-drug interaction. The evaluation of cytochromes P450 enzyme (CYP) activity was performed in pooled human liver microsomes with probing substrates of CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4. Typical inhibitors were employed as positive controls and the effect of 0, 2.5, 5, 10, 25, 50, and 100 μM tubeimoside I was investigated. The activity of CYP2D6, 2E1, and 3A4 was significantly inhibited by tubeimoside I with the IC50 values of 10.34, 11.58, and 9.74 μM, respectively. The inhibition of CYP2D6 and 2E1 was competitive with the Ki value of 5.66 and 5.29 μM, respectively. While the inhibition of CYP3A4 was non-competitive with the Ki value of 4.87 μM. Moreover, the inhibition of CYP3A4 was time-dependent with the KI and K inact values of 0.635 μM−1 and 0.0373 min−1, respectively. Tubeimoside I served as a competitive inhibitor of CYP2D6 and 2E1 exerting weak inhibition and a non-competitive inhibitor of CYP3A4 exerting moderate inhibition.

Effects of chronic cirrhosis induced by intraperitoneal thioacetamide injection on the protein content and Michaelis-Menten kinetics of cytochrome P450 enzymes in the rat liver microsomes.

Chronic intraperitoneal injection of thioacetamide (TAA) in rats has been used as an animal model of human cirrhosis to study the effects of the disease on drug metabolism. However, TAA inhibits P450 enzymes directly and independently of cirrhosis. We investigated the effects of chronic cirrhosis in rats, induced by 10 weeks of intraperitoneal TAA, on the P450 enzymes after a 10-day washout period to eliminate TAA. Liver histology and serum biomarkers of hepatic function confirmed cirrhosis in all animals. Microsomal total P450 content, P450 reductase activity and ethoxycoumarin O-deethylase activity, a general marker of P450 activity, were significantly reduced by 30%-50% in cirrhotic animals. Additionally, the protein content and Michaelis-Menten kinetics of the activities of CYP2D, CYP2E1 and CYP3A were investigated. Whereas cirrhosis reduced the microsomal protein contents of CYP2D and CYP3A by 70% and 30%, respectively, the protein contents of CYP2E1 were not affected. However, the activities of all the tested isoenzymes were substantially lower in the cirrhotic livers. It is concluded that the TAA model of cirrhosis that incorporates a 10-day washout period after intraperitoneal injection of the chemical to rats produces isoenzyme-selective reductions in the P450 proteins or activities, which are independent of the direct inhibitory effects of TAA.

In vitro study on the effect of leonurine hydrochloride on the enzyme activity of cytochrome P450 enzymes in human liver microsomes

Leonurine hydrochloride (LH) is derived from an ingredient of Leonurus japonicus Houtt which is widely used for diseases in women. The influence of LH on the activity of cytochrome P450 (CYPs) enzymes was investigated in this study. The effect of LH on CYPs enzyme activities were studied using the enzyme-selective substrates phenacetin (1A2), coumarin (2A6), diclofenac (2C9), S-mephenytoin (2C19), paclitaxel (2C8), dextromethorphan (2D6), chlorzoxazone (2E1) and testosterone (3A4). The IC50 value was calculated to express the strength of inhibition. The inhibition of CYPs was fitted with competitive or non-competitive inhibition models and corresponding parameters were also obtained. LH exerted inhibitory effects on the activity of CYP1A2, 2D6, and 3A4 with the IC50 values of 18.05, 15.13, and 20.09 μM, respectively. The obtained results showed that LH inhibited the activity of CYP1A2 and CYP2D6 via competitive manners (Ki = 8.667 μM and Ki = 7.805 μM, respectively), while LH attenuated the CYP3A4 activity via a non-competitive manner (Ki = 9.507 μM). Moreover, LH showed time-dependent inhibition on CYP3A4 with the KI/Kinact value of 4.31/0.044 min−1·μM−1. The inhibition of CYP1A2, CYP2D6, and CYP3A4 by LH, demonstrated in vitro, indicated the potential herb–drug interaction. Therefore, pharmacokinetic interactions involving LH and CYP1A2 or CYP2D6 or CYP1A2 substrates are likely to occur.

Disorders of Sex Development.

Disorders of Sex Development.

Comparable Intestinal and Hepatic First-Pass Effect of YL-IPA08 on the Bioavailability and Effective Brain Exposure, a Rapid Anti-PTSD and Anti-Depression Compound.

YL-IPA08, exerting rapid antidepressant-like and anxiolytic-like effects on behaviors by translocator protein (TSPO) mediation, is a novel compound that has been discovered and developed at our institute. Fit-for-purpose pharmacokinetic properties is urgently needed to be discovered as early as possible for a new compound. YL-IPA08 exhibited low bioavailability (∼6%) during the preliminary pharmacokinetics study in rats after oral administration. Our aim was to determine how metabolic disposition by microsomal P450 enzymes in liver and intestine limited YL-IPA08’s bioavailability and further affected brain penetration to the target. Studies of in vitro metabolic stability and permeability combined with in vivo oral bioavailability, panel CYP inhibitor co-administration via different routes, and double cannulation rats were conducted to elucidate the intestinal and hepatic first-pass effect of YL-IPA08 on bioavailability. Unbound brain-to-plasma ratio (K p,uu) in rats was determined at steady state. Results indicated that P450-mediated elimination appeared to be important for its extensive first-pass effect with comparative contribution of gut (35%) and liver (17%), and no significant species difference was observed. The unbound concentration of YL-IPA08 in rat brain (6.5 pg/ml) was estimated based on K p,uu (0.18) and was slightly higher than in vitro TSPO-binding activity (4.9 pg/ml). Based on the onset efficacy of YL-IPA08 toward TPSO in brain and K p,uu, therapeutic human plasma concentration was predicted to be ∼27.2 ng/ml would easily be reached even with unfavorable bioavailability.

Lung injury induced by pyrrolizidine alkaloids depends on metabolism by hepatic cytochrome P450s and blood transport of reactive metabolites.

Pyrrolizidine alkaloids (PAs) are common phytotoxins with both hepatotoxicity and pneumotoxicity. Hepatic cytochrome P450 enzymes are known to bioactivate PAs into reactive metabolites, which can interact with proteins to form pyrrole-protein adducts and cause intrahepatic cytotoxicity. However, the metabolic and initiation biochemical mechanisms underlying PA-induced pneumotoxicity remain unclear. To investigate the in vivo metabolism basis for PA-induced lung injury, this study used mice with conditional deletion of the cytochrome P450 reductase (Cpr) gene and resultant tissue-selective ablation of microsomal P450 enzyme activities. After oral exposure to monocrotaline (MCT), a pneumotoxic PA widely used to establish animal lung injury models, liver-specific Cpr-null (LCN) mice, but not extrahepatic Cpr-low (xh-CL) mice, had significantly lower level of pyrrole-protein adducts in the serum, liver and lungs compared with wild-type (WT) mice. While MCT-exposed LCN mice had significantly higher blood concentration of intact MCT, compared to MCT-exposed WT or xh-CL mice. Consistent with the MCT in vivo bioactivation data, MCT-induced lung injury, represented by vasculature damage, in WT and xh-CL mice but not LCN mice. Furthermore, reactive metabolites of MCT were confirmed to exist in the blood efflux from the hepatic veins of MCT-exposed rats. Our results provide the first mode-of-action evidence that hepatic P450s are essential for the bioactivation of MCT, and blood circulating reactive metabolites of MCT to the lung causes pneumotoxicity. Collectively, this study presents the scientific basis for the application of MCT in animal lung injury models, and more importantly, warrants public awareness and further investigations of lung diseases associated with exposure to not only MCT but also different PAs.

Kinetics of metabolism of deltamethrin and cis- and trans-permethrin in vitro. Studies using rat and human liver microsomes, isolated rat hepatocytes and rat liver cytosol

The kinetics of metabolism of deltamethrin (DLM) and cis- and trans-permethrin (CPM and TPM) was studied in male Sprague-Dawley rat and human liver microsomes. DLM metabolism kinetics was also studied in isolated rat hepatocytes, liver microsomes and cytosol. Apparent intrinsic clearance (CLint) values for the metabolism of DLM, CPM and TPM by cytochrome P450 (CYP) and carboxylesterase (CES) enzymes in rat and human liver microsomes decreased with increasing microsomal protein concentration. However, when apparent CLint values were corrected for nonspecific binding to allow calculation of unbound (i.e., corrected) CLint values, the unbound values did not vary greatly with microsomal protein concentration. Unbound CLint values for metabolism of 0.05-1 μM DLM in rat liver microsomes (CYP and CES enzymes) and cytosol (CES enzymes) were not significantly different from rates of DLM metabolism in isolated rat hepatocytes. This study demonstrates that the nonspecific binding of these highly lipophilic compounds needs to be taken into account in order to obtain accurate estimates of rates of in vitro metabolism of these pyrethroids. While DLM is rapidly metabolised in vitro, the hepatocyte membrane does not appear to represent a barrier to the absorption and hence subsequent hepatic metabolism of this pyrethroid.

Metabolic pathway of dibenzoylmethane, a β-diketone analogue of curcumin, by NADPH-dependent cytochrome P450 enzymes in mouse liver microsomes

Dibenzoylmethane (DBM), a curcumin-related β-diketone analogue, has been reported to exhibit a remarkable inhibitory effect on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis in Sencar mice. Investigation of the underlying mechanisms of DBM in the prevention of mammary tumorigenesis implied its role as an effector of Phase I enzymatic system. In this report, the metabolic fate of DBM by NADPH-dependent cytochrome P450 enzymes in mouse liver microsomes was demonstrated. Isolation of the major reductive metabolites of DBM (DBMH2), together with several minor metabolites identified by NMR, GC and LC-MS, explained the potential role of DBM as a modulator of the cytochrome P450 reductase that is required for the function of oxidase to metabolize DMBA. These might also contribute to the result of the inhibitory effect of DBM on DMBA-induced mouse mammary tumorigenesis.

Clinical, endocrinological, and molecular features of four Korean cases of cytochrome P450 oxidoreductase deficiency

PurposeCytochrome P450 oxidoreductase (POR) deficiency is a rare autosomal recessive disorder caused by mutations in the POR gene encoding an electron donor for all microsomal P450 enzymes. It is characterized by adrenal insufficiency, ambiguous genitalia, maternal virilization during pregnancy, and skeletal dysplasia. In this study, we investigated the clinical, hormonal, and molecular characteristics of patients with POR deficiency in Korea.MethodsThis study included four patients with POR deficiency confirmed by biochemical and molecular analysis of POR. Clinical and biochemical findings were reviewed retrospectively. Mutation analysis of POR was performed by Sanger sequencing after polymerase chain reaction amplification of all coding exons and the exon-intron boundaries.ResultsAll patients presented with adrenal insufficiency and ambiguous genitalia regardless of their genetic sex. Two patients harbored homozygous p.R457H mutations in POR and presented with adrenal insufficiency and genital ambiguity without skeletal phenotypes. The other two patients with compound heterozygous mutations of c.[1329_1330insC];[1370G>A] (p.[I444Hfs*6];[R457H]) manifested skeletal abnormalities, such as craniosynostosis and radiohumeral synostosis, suggesting Antley-Bixler syndrome. They also had multiple congenital anomalies involving heart, kidney, and hearing ability. All patients were treated with physiologic doses of oral hydrocortisone.ConclusionsWe report the cases of 4 patients with POR deficiency identified by mutation analysis of POR. Although the study involved a small number of patients, the POR p.R457H mutation was the most common, suggesting founder effect in Korea. POR deficiency is rare and can be misdiagnosed as 21-hydroxylase or 17α-hydroxylase/17,20-lyase deficiency. Therefore, molecular analysis is critical for confirmatory diagnosis.

The atypical neuroleptics iloperidone and lurasidone inhibit human cytochrome P450 enzymes in vitro. Evaluation of potential metabolic interactions

BackgroundThe present study aimed at examining the inhibitory effect of two atypical neuroleptics iloperidone and lurasidone on the main human cytochrome P450 (CYP) enzymes in pooled human liver microsomes and cDNA-expressed CYP enzymes (supersomes).MethodsThe activity of these enzymes was determined by the following CYP-specific reactions: caffeine 3-N-demethylation/CYP1A2, diclofenac 4′-hydroxylation/CYP2C9, perazine N-demethylation/CYP2C19, bufuralol 1′-hydroxylation/CYP2D6 and testosterone 6β-hydroxylation/CYP3A4, respectively, using HPLC.ResultsIloperidone inhibited the activity of CYP3A4 via a noncompetitive mechanism (Ki = 0.38 and 0.3 µM in liver microsomes and supersomes, respectively) and CYP2D6 via a competitive mechanism (Ki = 2.9 and 10 µM in microsomes and supersomes). Moreover, iloperidone attenuated the activity of CYP1A2 (Ki = 45 and 31 µM in microsomes and supersomes) and CYP2C19 via a mixed mechanism (Ki = 6.5 and 32 µM in microsomes and supersomes) but did not affect CYP2C9. Lurasidone moderately inhibited CYP1A2 (Ki = 12.6 and 15.5 µM in microsomes and supersomes), CYP2C9 (Ki = 18 and 3.5 µM in microsomes and supersomes) and CYP2C19 via a mixed mechanism (Ki = 18 and 18.4 µM in microsomes and supersomes), and CYP3A4 via a competitive mechanism (Ki = 29.4 and 9.1 µM in microsomes and supersomes). Moreover, lurasidone competitively, though weakly diminished the CYP2D6 activity (Ki = 37.5 and 85 µM in microsomes and supersomes).ConclusionThe examined neuroleptics showed inhibitory effects on different CYP enzymes. The obtained results indicate that metabolic/pharmacokinetic interactions with iloperidone (involving mainly CYP3A4 and CYP2D6) and possibly with lurasidone (involving CYP1A2, CYP2C9 or CYP2C19) may occur during combined therapy.

Effects of Thioacetamide—Induced Cirrhosis, after a Drug Washout Period, on the Michaelis–Menten Kinetics of Major Cytochrome P450 Enzymes in the Rat Liver Microsomes

PurposeThioacetamide (TAA) is used to induce liver cirrhosis in rodents. However, the drug itself directly inhibits cytochrome P450 (CYP450) enzymes. The purpose of this study was to determine the effects of TAA‐induced liver cirrhosis, after a washout period to eliminate TAA, on the Michaelis‐Menten (MM) kinetics and protein contents of the major CYP450 enzymes CYP2D, CYP2E1, and CYP3A in rat liver microsomes.MethodsAdult, male Sprague‐Dawley rats were treated for 10 weeks with either TAA (200 mg/kg ip, 3 days per week) or vehicle (n = 7/each group). After a 10‐day washout period, animals were euthanized, and the liver was collected after cardiac perfusion with cold saline. Liver microsomes (MC) were prepared by differential centrifugation. The activities of the liver microsomal CYP2D (dextromethorphan O‐demethylation), CYP2E1 (chlorzoxazone 6‐hydroxylation) and CYP3A (midazolam 1′‐hydroxylation) were estimated by measurement of the metabolites by LC‐MS/MS. The microsomal CYP450 reductase (CPR) activity was analyzed spectrophotometry. Furthermore, the protein expressions of the isoenzymes were determined using Western blot analysis. The MM kinetic parameters maximum velocity (Vmax) and MM constant (Km) were determined using nonlinear regression analysis. Unpaired t‐test was used for statistical analysis of data, with a p value of < 0.05 as significant.ResultsWhereas the MM kinetics of dextromethorphan demethylation (CYP2D) were best fit by a two‐enzyme equation, those of chlorzoxazone hydroxylation (CYP2E1) and midazolam 1′‐hydroxylation (CYP3A) were best fit by a single‐enzyme equation. Cirrhosis resulted in significant reductions in the Vmax values for all the tested microsomal activities. The microsomal high‐ and low‐capacity Vmax values for CYP2D demethylase activity were significantly reduced by 74% (p value < 0.0001) and 51% (p < 0.05), respectively, in the TAA group. This was associated with a significant (p < 0.001) reduction (71%) in the protein contents of CYP2D in the TAA group. However, Km values were not affected by cirrhosis. For CYP2E1, cirrhosis caused a significant reduction (52%) in the Vmax value (p < 0.0001) for the chlorzoxazone hydroxylation activity. However, the Km values and protein contents of CYP2E1 remained unchanged. The Vmax and Km values of microsomal CYP3A hydroxylase activity, resulting in 1′‐hydroxylation of midazolam, were significantly reduced by 71% (p < 0.001) and 46% (p < 0.05), respectively, which was associated with a 30% reduction (p < 0.05) in the protein contents of CYP3A. Cirrhotic animals also showed a 31% decline (p < 0.05) in the microsomal CPR activity.ConclusionsTAA‐induced cirrhosis in rats resulted in a decreased liver microsomal activity of CPR and major CYP450 enzymes (CYP2D, CYP2E1, and CYP3A). Except for CYP2E1, the decreased isoenzyme activities were also associated with decreases in the protein concentrations of the isoenzymes. However, the cirrhosis‐induced decrease in the CYP2E1 activity, which was in the absence of a change in its protein levels, is possibly due to a decrease in the microsomal CPR activity.Support or Funding InformationFunding: Chapman University School of Pharmacy

Contributions of Hepatic and Intestinal Metabolism to the Disposition of Niclosamide, a Repurposed Drug with Poor Bioavailability.

Niclosamide, an antiparasitic, has been repositioned as a potential therapeutic drug for systemic diseases based on its antiviral, anticancer, and anti-infection properties. However, low bioavailability limits its in vivo efficacy. Our aim was to determine whether metabolic disposition by microsomal P450 enzymes in liver and intestine influences niclosamide's bioavailability in vivo, by comparing niclosamide metabolism in wild-type, liver-Cpr-null (LCN), and intestinal epithelium-Cpr-null (IECN) mice. In vitro stability of niclosamide in microsomal incubations was greater in the intestine than in liver in the presence of NADPH, but it was much greater in liver than in intestine in the presence of UDPGA. NADPH-dependent niclosamide metabolism and hydroxy-niclosamide formation were inhibited in hepatic microsomes of LCN mice, but not IECN mice, compared with wild-type mice. In intestinal microsomal reactions, hydroxy-niclosamide formation was not detected, but rates of niclosamide-glucuronide formation were ∼10-fold greater than in liver, in wild-type, LCN, and IECN mice. Apparent Km and V max values for microsomal niclosamide-glucuronide formation showed large differences between the two tissues, with the intestine having higher Km (0.47 μM) and higher V max (15.8) than the liver (0.09 μM and 0.75, respectively). In vivo studies in LCN mice confirmed the essential role of hepatic P450 in hydroxy-niclosamide formation; however, pharmacokinetic profiles of oral niclosamide were only minimally changed in LCN mice, compared with wild-type mice, and the changes seem to reflect the compensatory increase in hepatic UDP-glucuronosyltransferase activity. SIGNIFICANCE STATEMENT: These results suggest that efforts to increase the bioavailability of niclosamide by blocking its metabolism by P450 enzymes will unlikely be fruitful. In contrast, inhibition of niclosamide glucuronidation in both liver and intestine may prove effective for increasing niclosamide's bioavailability, thereby making it practical to repurpose this drug for treating systemic diseases.

Hypersensitivity to Cisplatin and Gentamycin Induced Nephrotoxicity in Mice with Decreased Expression of NADPH‐Cytochrome P450 Reductase

Cytochrome P450 reductase (CPR or POR) is an obligatory redox partner for all microsomal P450 enzymes. A large, global decrease in POR expression, in a Cpr‐low mouse model, was previously found to lead to altered sex steroid hormone homeostasis, female infertility, and decreased capacity for xenobiotic metabolism. The aim of this study was to further characterize the Cpr‐low mouse model, in order to identify additional phenotypes that may reveal vulnerability in people with low POR expression. Here, we report differences between wild‐type and Cpr‐low mice in their sensitivities to drug‐induced toxicity in the renal proximal tubules. We studied two drugs, the anticancer drug cisplatin and the antibiotic drug gentamycin, which are known as renal toxicants, but are not P450 substrates. Toxicity was assessed by blood urea nitrogen (BUN) levels and histopathology of the kidney. At drug doses that do not cause renal toxicity in wild‐type mice, cisplatin caused significant increases in BUN levels over vehicle control group in both male and female Cpr‐low mice, whereas gentamycin caused significant increases in BUN levels over vehicle control group in male but not female Cpr‐low mice. Corresponding histopathological changes, including appearance of extensive proximal tubule vacuolization, were found in the kidneys of drug‐treated Cpr‐low mice. These findings suggest that POR expression level could be a risk factor for drug‐induced nephrotoxicity in patients.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Managing a side effect: Cyclophosphamide-induced hemorrhagic cystitis

Cyclophosphamide is a nonphase-specific cytotoxic agent that can kill cells at any phase of the cell cycle. The drug is metabolized by hepatic cytochrome P450 microsomal enzymes, which results in the formation of the active metabolites phosphoramide mustard and acrolein. It is the acrolein which is responsible for hemorrhagic cystitis as a complication of cyclophosphamide therapy. An early diagnosis and prompt management holds the key in its management.

Ethnopharmacology†

Background: Ethnopharmacology relates to the study of substances used medicinally by different ethnic or cultural groups or handling of, drugs-based ethnicity or pharmacogenetics.Aims: To review the key aspects of ethnopharmacology.Method: This lecture gives an overview of the relationship between geography, culture, pharmacogenomics and prescribing. Results: Although the majority of antipsychotics, antidepressants and mood-stabilisers are widely and cheaply available in generic forms, prescription rates can vary. Clozapine is one such example with prescribing-rates ranging from less than 10 patients per 100,000 people to nearly 180 patients/100,000 people. Pharmacogenetic studies of antipsychotics and antidepressants concern gene polymorphisms that may affect both, pharmacodynamic or pharmacokinetic properties. Considerable genetic and ethnic variability has been seen for the P450 microsomal enzymes CYP 2D6 and 1A2.Conclusions: With accelerated global mobility and increased understanding of medicinal substances at molecular level, understanding of ethnopharmacology will become increasingly important in routine clinical practice.

Sulfenylation of Human Liver and Kidney Microsomal Cytochromes P450 and Other Drug-Metabolizing Enzymes as a Response to Redox Alteration

The lumen of the endoplasmic reticulum (ER) provides an oxidizing environment to aid in the formation of disulfide bonds, which is tightly regulated by both antioxidant proteins and small molecules. On the cytoplasmic side of the ER, cytochrome P450 (P450) proteins have been identified as a superfamily of enzymes that are important in the formation of endogenous chemicals as well as in the detoxication of xenobiotics. Our previous report described oxidative inhibition of P450 Family 4 enzymes via oxidation of the heme-thiolate cysteine to a sulfenic acid (-SOH) (Albertolle, M. E. et al. (2017) J. Biol. Chem. 292, 11230-11242). Further proteomic analyses of murine kidney and liver microsomes led to the finding that a number of other drug-metabolizing enzymes located in the ER are also redox-regulated in this manner. We expanded our analysis of sulfenylated enzymes to human liver and kidney microsomes. Evaluation of the sulfenylation, catalytic activity, and spectral properties of P450s 1A2, 2C8, 2D6, and 3A4 led to the identification of two classes of redox sensitivity in P450 enzymes: heme-thiolate-sensitive and thiol-insensitive. These findings provide evidence for a mammalian P450 regulatory mechanism, which may also be relevant to other drug-metabolizing enzymes. (Data are available via ProteomeXchange with identifier PXD007913.).

Tacrolimus interaction with oral oestrogen in kidney transplant recipients: A case-control study.

Oestrogens could inhibit the metabolism of drugs, such as calcineurin inhibitors, that are substrates for cytochrome P-450 microsomal enzymes. This study assessed the potential tacrolimus interaction with oral conjugated oestrogen in kidney transplant recipients who received conjugated oestrogen as prophylaxis against bleeding, before kidney biopsy. In this case-control study, 13 kidney transplant recipients who received oral conjugated oestrogen as prophylaxis against uraemic bleeding before allograft biopsy were considered as cases. Thirteen matched kidney transplant recipients with similar immunosuppressive regimen served as controls. In this study, comparisons were made between the groups regarding daily dose, blood trough concentrations and calculated concentration corrected for dose of tacrolimus at three time points of the study. All patients in the case group received conjugated oestrogen at a dose of 3.75mg/day for 4.78±0.83days. Without any change in tacrolimus dose, the blood concentration of tacrolimus increased during concomitant administration of conjugated oestrogen (from 8.10±2.85 to 12.35±4.62ng/mL; P=.11) and decreased after cessation of conjugated oestrogen (6.07±2.18ng/mL; P=.015). The calculated concentration corrected for dose of tacrolimus increased from 127.04±79.23 to 211.40±146.38 ngmLmgkg/d after conjugated oestrogen administration (P=.036). Thereafter, it decreased to 108.55±78.61 ngmLmgkg/d after cessation of oestrogen (P=.003). Only one patient experienced nausea while taking oestrogen without any change in her liver enzymes. Concomitant administration of oral oestrogen increased tacrolimus blood concentration. Hence, it is necessary to monitor tacrolimus blood levels during concomitant oestrogen therapy and for several days after oestrogen withdrawal.