Evolution and multiple functions of sulfonation and cytosolic sulfotransferases across species

Organisms have conversion systems for sulfate ion to take advantage of the chemical features. The use of biologically converted sulfonucleotides varies in an evolutionary manner, with the universal use being that of sulfonate donors. Sulfotransferases have the ability to transfer the sulfonate group of 3'-phosphoadenosine 5'-phosphosulfate to a variety of molecules. Cytosolic sulfotransferases (SULTs) play a role in the metabolism of low-molecular-weight compounds in response to the host organism's living environment. This review will address the diverse functions of the SULT in evolution, including recent findings. In addition to the diversity of vertebrate sulfotransferases, the molecular aspects and recent studies on bacterial and plant sulfotransferases are also addressed.

Eight pharmacokinetic genetic variants are not associated with the risk of bleeding from direct oral anticoagulants in non-valvular atrial fibrillation patients

Background: Atrial fibrillation (AF) is the leading cause of ischemic stroke and treatment has focused on reducing this risk through anticoagulation. Direct Oral Anticoagulants (DOACs) are the first-line guideline-recommended therapy since they are as effective and overall safer than warfarin in preventing AF-related stroke. Although patients bleed less from DOACs compared to warfarin, bleeding remains the primary safety concern with this therapy. Hypothesis: Genetic variants known to modify the function of metabolic enzymes or transporters involved in the pharmacokinetics (PK) of DOACs could increase the risk of bleeding. Aim: To assess the association of eight, functional PK-related single nucleotide variants (SNVs) in five genes (ABCB1, ABCG2, CYP2J2, CYP3A4, CYP3A5) with the risk of bleeding from DOACs in non-valvular AF patients. Methods: A retrospective cohort study was carried out with 2,364 self-identified white non-valvular AF patients treated with either rivaroxaban or apixaban. Genotyping was performed with Illumina Infinium CoreExome v12.1 bead arrays by the Michigan Genomics Initiative biobank. The primary endpoint was a composite of major and clinically relevant non-major bleeding. Cox proportional hazards regression with time-varying analysis assessed the association of the eight PK-related SNVs with the risk of bleeding from DOACs in unadjusted and covariate-adjusted models. The pre-specified primary analysis was the covariate-adjusted, additive genetic models. Six tests were performed in the primary analysis as three SNVs are in the same haplotype, and thus p-values below the Bonferroni-corrected level of 8.33e-3 were considered statistically significant. Results: In the primary analysis, none of the SNVs met the Bonferroni-corrected level of statistical significance (all p > 0.1). In exploratory analyses with other genetic models, the ABCB1 (rs4148732) GG genotype tended to be associated with the risk of bleeding from rivaroxaban [HR: 1.391 (95%CI: 1.019-1.900); p = 0.038] but not from apixaban (p = 0.487). Conclusion: Eight functional PK-related genetic variants were not significantly associated with bleeding from either rivaroxaban or apixaban in more than 2,000 AF self-identified white outpatients.

Esomeprazole and apixaban pharmacokinetic interactions in healthy rats

Esomeprazole is used in various clinical settings where a decrease in gastric acid production is desired since it is a proton pump inhibitor. Apixaban, an anticoagulant, is used to reduce the risk of stroke in patients with certain cardiovascular diseases. This research aims to examine the effects of giving esomeprazole and apixaban to rats simultaneously, as well as to measure their pharmacokinetics and look for statistical differences or interactions. A method for the simultaneous determination of esomeprazole and apixaban in rat plasma was developed using HPLC/MS and validated by ICH guidelines. Five groups of Wistar rats were created, and the drugs were administered as follows: esomeprazole (5 mg/kg) intravenously, apixaban (125 mcg/Kg) intravenously, esomeprazole (5 mg/kg) orally, apixaban (250 mcg/kg) orally, and esomeprazole (5 mg/kg) and apixaban (250 mcg/kg) both orally. Both drugs' concentrations were measured in plasma samples collected on a predetermined schedule. The pharmacokinetics of both drugs were calculated and statistically analyzed using a 90% confidence interval and non-compartmental analysis. When the two drugs were combined, apixaban's C_max and AUC increased while esomeprazole's C_max and AUC decreased. On the other hand, Apixaban's T_max decreased with an increase in esomeprazole's T_max, indicating a possible interaction between the two drugs. When both drugs were taken together, their bioavailability was reduced, implying that less esomeprazole was absorbed over time.

Genetic determinants of apixaban plasma levels and their relationship to bleeding and thromboembolic events

Apixaban is a direct oral anticoagulant, a factor Xa inhibitor, used for the prevention of ischemic stroke in patients with atrial fibrillation. Despite using recommended dosing a few patients might still experience bleeding or lack of efficacy that might be related to inappropriate drug exposure. We conducted a genome-wide association study using data from 1,325 participants in the pivotal phase three trial of apixaban with the aim to identify genetic factors affecting the pharmacokinetics of apixaban. A candidate gene analysis was also performed for pre-specified variants in ABCB1, ABCG2, CYP3A4, CYP3A5, and SULT1A1, with a subsequent analysis of all available polymorphisms within the candidate genes. Significant findings were further evaluated to assess a potential association with clinical outcome such as bleeding or thromboembolic events. No variant was consistently associated with an altered apixaban exposure on a genome-wide level. The candidate gene analyses showed a statistically significant association with a well-known variant in the drug transporter gene ABCG2 (c.421G > T, rs2231142). Patients carrying this variant had a higher exposure to apixaban [area under the curve (AUC), beta = 151 (95% CI 59–243), p = 0.001]. On average, heterozygotes displayed a 5% increase of AUC and homozygotes a 17% increase of AUC, compared with homozygotes for the wild-type allele. Bleeding or thromboembolic events were not significantly associated with ABCG2 rs2231142. This large genome-wide study demonstrates that genetic variation in the drug transporter gene ABCG2 is associated with the pharmacokinetics of apixaban. However, the influence of this finding on drug exposure was small, and further studies are needed to better understand whether it is of relevance for ischemic and bleeding events.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Apixaban Pharmacokinetics and Pharmacodynamics in Subjects with Mild or Moderate Hepatic Impairment

Background

Hepatic impairment can impact apixaban pharmacokinetics and pharmacodynamics by decreasing cytochrome P450-mediated metabolism and factor X production.

Objective

This study evaluated the effect of mild or moderate (Child–Pugh A and B) hepatic impairment on apixaban pharmacokinetics, pharmacodynamics, and safety.

Methods

This open-label, parallel-group, single-dose study included eight mildly and eight moderately hepatically impaired subjects, and 16 healthy subjects. Subjects received a single oral apixaban 5-mg dose (day 1). Pharmacokinetic, pharmacodynamic, and safety assessments were completed at prespecified time points. Apixaban maximum plasma concentration and area under the concentration–time curve to infinity were compared between subjects with hepatic impairment and healthy subjects.

Results

Apixaban area under the concentration–time curve to infinity point estimates and 90% confidence intervals were 1.03 (0.80–1.32) and 1.09 (0.85–1.41) for subjects with mild and moderate hepatic impairment vs healthy subjects. Maximum plasma concentration results were similar. Mean (standard deviation) apixaban unbound fraction was 6.8% (1.4), 7.9% (1.8), and 7.1% (1.3) in subjects with mild or moderate hepatic impairment and in healthy subjects. Mean change from baseline in international normalized ratio (3 h post-dose) was 14.7%, 12.7%, and 10.7% for subjects with mild or moderate hepatic impairment and healthy subjects, respectively. A direct relationship was observed between apixaban anti-factor Xa activity and plasma concentration across groups. No serious adverse events or discontinuations due to adverse events occurred.

Conclusions

Mild or moderate hepatic impairment had no clinically relevant impact on apixaban pharmacokinetic or pharmacodynamic measures, suggesting that dose adjustment may not be required.

Apixaban Single-Dose Pharmacokinetics, Bioavailability, Renal Clearance, and Pharmacodynamics Following Intravenous and Oral Administration

This randomized, double-blind, placebo-controlled, ascending single intravenous (IV) bolus-dose study evaluated safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of apixaban, a direct factor Xa (FXa) inhibitor approved for multiple indications. Eight healthy subjects were randomized 3:1 (apixaban:placebo) within each IV dose cohort (0.5, 1.25, 2.5, 3.75, and 5 mg). The 2.5-mg IV panel also received 5 mg of oral apixaban or placebo. Blood samples were collected for PK and PD, including international normalized ratio, modified prothrombin time (mPT), and anti-FXa activity. Apixaban had 66.2% oral bioavailability, dose-proportional exposure, 17 to 26 L steady-state volume of distribution, and 3.2 to 3.5 L/h total plasma clearance. Renal clearance was ≈27%. Anti-FXa activity and mPT changes followed the apixaban plasma concentration-time profile; both were highly correlated with concentration (R² = 0.99 and R² = 0.93 for anti-FXa activity and mPT, respectively). International normalized ratio remained within reference range (0.9-1.3). There were no serious or bleeding-related adverse events. Overall, an apixaban single IV bolus was safe and well tolerated over a 10-fold dose range by these subjects. Apixaban had good oral bioavailability, dose-proportional exposure, and constant plasma clearance over a broad dose range, with modest renal clearance. Apixaban PD were consistent with reversible FXa inhibition.

Using Pharmacogenetics of Direct Oral Anticoagulants to Predict Changes in Their Pharmacokinetics and the Risk of Adverse Drug Reactions

Dabigatran, rivaroxaban, apixaban, and edoxaban are direct oral anticoagulants (DOACs) that are increasingly used worldwide. Taking into account their widespread use for the prevention of thromboembolism in cardiology, neurology, orthopedics, and coronavirus disease 2019 (COVID 19) as well as their different pharmacokinetics and pharmacogenetics dependence, it is critical to explore new opportunities for DOACs administration and predict their dosage when used as monotherapy or in combination with other drugs. In this review, we describe the details of the relative pharmacogenetics on the pharmacokinetics of DOACs as well as new data concerning the clinical characteristics that predetermine the needed dosage and the risk of adverse drug reactions (ADRs). The usefulness of genetic information before and shortly after the initiation of DOACs is also discussed. The reasons for particular attention to these issues are not only new genetic knowledge and genotyping possibilities, but also the risk of serious ADRs (primarily, gastrointestinal bleeding). Taking into account the effect of the carriership of single nucleotide variants (SNVs) of genes encoding biotransformation enzymes and DOACs metabolism, the use of these measures is important to predict changes in pharmacokinetics and the risk of ADRs in patients with a high risk of thromboembolism who receive anticoagulant therapy.

Pharmacokinetics and Pharmacogenetics of Apixaban

Apixaban is oral anticoagulant, it is widely used in prevention of stroke in non-valvular atrial fibrillation and treatment of deep vein thrombosis and pulmonary embolism. Its main mechanism of action is through reversible inhibition of factor Xa. It specifically binds and inhibits both free and bound factor Xa which ultimately results in reduction in the levels of thrombin formation. Apixaban is mainly metabolized by CYP3A4 with minor contributions from CYP1A2, CYP2C8, CYP2C9, CYP2C19 and CYP2J2 isoenzymes. Some of the major metabolic pathways of apixaban include o-demethylation, hydroxylation, and sulfation, with o-demethylapixabansulphate being the major metabolite. The aim of this review is analysis of associated researches of single nucleotide variants (SNV) of CYP3A5 and SULT1A1 genes and search for new candidate genes reflecting effectiveness and safety of apixaban. The search for full-text publications in Russian and English languages containing key words “apixaban”, “pharmacokinetics”, “effectiveness”, “safety” was carried out amongst literature of the past twenty years with the use of eLibrary, PubMed, Web of Science, OMIM data bases. Pharmacokinetics and pharmacogenetics of apixaban are considered in this review. The hypothesis about CYP и SULT1A enzymes influence on apixaban metabolism was examined. To date, numerous SNVs of the CYP3A5 and SULT1A1 genes have been identified, but their potential influence on pharmacokinetics apixaban in clinical practice needs to be further studies. The role of SNVs of other genes encoding beta-oxidation enzymes of apixaban (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2J2) and transporter proteins (ABCB1, ABCG2) in its efficacy and safety are not well understood, and ABCB1 and ABCG2 genes may be potential candidate genes for studies of the drug safety.

Drug-Drug Interactions with Direct Oral Anticoagulants

A large body of evidence suggests that not only direct anticoagulant effects but also major bleeding events and stroke prevention depend on plasma concentrations of direct oral anticoagulants (DOACs). Concomitant drugs that cause drug–drug interactions (DDIs) alter DOAC exposure by increasing or decreasing DOAC bioavailability and/or clearance; hence, they might affect the efficacy and safety of DOAC therapy. Patients with renal impairment already receive smaller DOAC maintenance doses because avoidance of elevated DOAC exposure might prevent serious bleeding events. For other causes of increased exposure such as DDIs, management is often less well-defined. Considering that DOAC patients are often older and have multiple co-morbidities, polypharmacy is highly prevalent. However, the effect of multiple drugs on DOAC exposure, and especially the impact of DDIs when concurring with drug–disease interactions as observed in renal impairment, has not been thoroughly elucidated. In order to provide effective and safe anticoagulation with DOACs, understanding the mechanisms and magnitude of DDIs appears relevant. Instead of avoiding drug combinations with DOACs, more DDI trials should be conducted and new strategies such as dose adjustments based on therapeutic drug monitoring should be investigated. However, dose adjustments based on concentration measurements cannot currently be recommended because evidence-based data are missing.

Pharmacogenomics of Novel Direct Oral Anticoagulants: Newly Identified Genes and Genetic Variants

Direct oral anticoagulants (DOAC) have shown an upward prescribing trend in recent years due to favorable pharmacokinetics and pharmacodynamics without requirement for routine coagulation monitoring. However, recent studies have documented inter-individual variability in plasma drug levels of DOACs. Pharmacogenomics of DOACs is a relatively new area of research. There is a need to understand the role of pharmacogenomics in the interpatient variability of the four most commonly prescribed DOACs, namely dabigatran, rivaroxaban, apixaban, and edoxaban. We performed an extensive search of recently published research articles including clinical trials and in-vitro studies in PubMed, particularly those focusing on genetic loci, single nucleotide polymorphisms (SNPs), and DNA polymorphisms, and their effect on inter-individual variation of DOACs. Additionally, we also focused on commonly associated drug-drug interactions of DOACs. CES1 and ABCB1 SNPs are the most common documented genetic variants that contribute to alteration in peak and trough levels of dabigatran with demonstrated clinical impact. ABCB1 SNPs are implicated in alteration of plasma drug levels of rivaroxaban and apixaban. Studies conducted with factor Xa, ABCB1, SLCOB1, CYP2C9, and VKORC1 genetic variants did not reveal any significant association with plasma drug levels of edoxaban. Pharmacokinetic drug-drug interactions of dabigatran are mainly mediated by p-glycoprotein. Strong inhibitors and inducers of CYP3A4 and p-glycoprotein should be avoided in patients treated with rivaroxaban, apixaban, and edoxaban. We conclude that some of the inter-individual variability of DOACs can be attributed to alteration of genetic variants of gene loci and drug-drug interactions. Future research should be focused on exploring new genetic variants, their effect, and molecular mechanisms that contribute to alteration of plasma levels of DOACs.

Xenobiotica-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

Studies on the metabolic fate of medical drugs, skin care products, cosmetics and other chemicals intentionally or accidently applied to the human skin have become increasingly important in order to ascertain pharmacological effectiveness and to avoid toxicities. The use of freshly excised human skin for experimental investigations meets with ethical and practical limitations. Hence information on xenobiotic-metabolizing enzymes (XME) in the experimental systems available for pertinent studies compared with native human skin has become crucial. This review collects available information of which—taken with great caution because of the still very limited data—the most salient points are: in the skin of all animal species and skin-derived in vitro systems considered in this review cytochrome P450 (CYP)-dependent monooxygenase activities (largely responsible for initiating xenobiotica metabolism in the organ which provides most of the xenobiotica metabolism of the mammalian organism, the liver) are very low to undetectable. Quite likely other oxidative enzymes [e.g. flavin monooxygenase, COX (cooxidation by prostaglandin synthase)] will turn out to be much more important for the oxidative xenobiotic metabolism in the skin. Moreover, conjugating enzyme activities such as glutathione transferases and glucuronosyltransferases are much higher than the oxidative CYP activities. Since these conjugating enzymes are predominantly detoxifying, the skin appears to be predominantly protected against CYP-generated reactive metabolites. The following recommendations for the use of experimental animal species or human skin in vitro models may tentatively be derived from the information available to date: for dermal absorption and for skin irritation esterase activity is of special importance which in pig skin, some human cell lines and reconstructed skin models appears reasonably close to native human skin. With respect to genotoxicity and sensitization reactive-metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the Conclusions section in the end of this review.

The genetic basis of antiplatelet and anticoagulant therapy: A pharmacogenetic review of newer antiplatelets (clopidogrel, prasugrel and ticagrelor) and anticoagulants (dabigatran, rivaroxaban, apixaban and edoxaban)

INTRODUCTION

The study of pharmacogenomics presents the possibility of individualised optimisation of drug therapy tailored to each patients' unique physiological traits. Both antiplatelet and anticoagulant drugs play a key role in the management of cardiovascular disease. Despite their importance, there is a substantial volume of literature to suggest marked person-to-person variability in their effect. Areas covered: This article reviews the data available for the genetic cause for this inter-patient variability of antiplatelet and anticoagulant drugs. The genetic basis for traditional antiplatelets (i.e. aspirin) is compared with the newly available antiplatelet medicines (clopidogrel, prasugrel and ticagrelor). Similarly, the pharmacogenetics of warfarin is compared with the newer direct oral anticoagulants (DOACs) in detail. Expert Opinion: We identify strengths and weaknesses in the research thus far; including shortcomings in trial design and a review of newer analytical techniques. The direction of this research and its real-world implications are discussed.

Effect of Rifampin on the Pharmacokinetics of Apixaban, an Oral Direct Inhibitor of Factor Xa

OBJECTIVE

Apixaban is a substrate of cytochrome P450 3A4 (CYP3A4) and P-glycoprotein. The effects of rifampin, a strong inducer of CYP3A4 and P-glycoprotein, on the pharmacokinetics of oral and intravenous apixaban were evaluated in an open-label, randomized, sequential crossover study.

METHODS

Twenty healthy participants received single doses of apixaban 5 mg intravenously on day 1 and 10 mg orally on day 3, followed by rifampin 600 mg once daily on days 5-15. Finally, participants received single doses of apixaban 5 mg intravenously and 10 mg orally separately on days 12 and 14 in one of two randomized sequences.

RESULTS

Apixaban, given intravenously and orally, was safe and well tolerated when administered in the presence and absence of rifampin. Apixaban absolute oral bioavailability was 49 % when administered alone and 39 % following induction by rifampin. Rifampin reduced apixaban area under the plasma concentration-time curve from time zero to infinity (AUC∞) by 39 % after intravenous administration and by 54 % after oral administration. Rifampin induction increased mean clearance by 1.6-fold for intravenous apixaban and mean apparent clearance by 2.1-fold for oral apixaban, indicating rifampin affected both pre-systemic and systemic apixaban elimination pathways.

CONCLUSION

Co-administration of apixaban with rifampin reduced apixaban exposure via both decreased bioavailability and increased systemic clearance.

Effect of ketoconazole and diltiazem on the pharmacokinetics of apixaban, an oral direct factor Xa inhibitor

AIM

Apixaban is an orally active inhibitor of coagulation factor Xa and is eliminated by multiple pathways, including renal and non-renal elimination. Non-renal elimination pathways consist of metabolism by cytochrome P450 (CYP) enzymes, primarily CYP3A4, as well as direct intestinal excretion. Two single sequence studies evaluated the effect of ketoconazole (a strong dual inhibitor of CYP3A4 and P-glycoprotein [P-gp]) and diltiazem (a moderate CYP3A4 inhibitor and a P-gp inhibitor) on apixaban pharmacokinetics in healthy subjects.

METHOD

In the ketoconazole study, 18 subjects received apixaban 10 mg on days 1 and 7, and ketoconazole 400 mg once daily on days 4-9. In the diltiazem study, 18 subjects received apixaban 10 mg on days 1 and 11 and diltiazem 360 mg once daily on days 4-13.

RESULTS

Apixaban maximum plasma concentration and area under the plasma concentration-time curve extrapolated to infinity increased by 62% (90% confidence interval [CI], 47, 78%) and 99% (90% CI, 81, 118%), respectively, with co-administration of ketoconazole, and by 31% (90% CI, 16, 49%) and 40% (90% CI, 23, 59%), respectively, with diltiazem.

CONCLUSION

A 2-fold and 1.4-fold increase in apixaban exposure was observed with co-administration of ketoconazole and diltiazem, respectively.

Methylation, Glucuronidation, and Sulfonation of Daphnetin in Human Hepatic Preparations In Vitro: Metabolic Profiling, Pathway Comparison, and Bioactivity Analysis

Our previous study demonstrated that daphnetin is subject to glucuronidation in vitro. However, daphnetin metabolism is still poorly documented. This study aimed to investigate daphnetin metabolism and its consequent effect on the bioactivity. Metabolic profiles obtained by human liver S9 fractions and human hepatocytes showed that daphnetin was metabolized by glucuronidation, sulfonation, and methylation to form 6 conjugates which were synthesized and identified as 7-O-glucuronide, 8-O-glucuronide, 7-O-sulfate and 8-O-sulfate, 8-O-methylate, and 7-O-suflo-8-O-methylate. Regioselective 8-O-methylation of daphnetin was investigated using in silico docking calculations, and the results suggested that a close proximity (2.03 Å) of 8-OH to the critical residue Lysine 144 might be the responsible mechanism. Compared with glucuronidation and sulfonation pathways, the methylation of daphnetin had a high clearance rate (470 μL/min/mg) in human liver S9 fractions and contributed to a large amount (37.3%) of the methyl-derived metabolites in human hepatocyte. Reaction phenotyping studies showed the major role of SULT1A1, -1A2, and -1A3 in daphnetin sulfonation, and soluble COMT in daphnetin 8-O-methylation. Of the metabolites, only 8-O-methyldaphnetin exhibited an inhibitory activity on lymphocyte proliferation comparable to that of daphnetin. In conclusion, methylation is a crucial pathway for daphnetin clearance and might be involved in pharmacologic actions of daphnetin in humans.

Characterization of regio- and stereo-selective sulfation of bufadienolides: exploring the mechanism and providing insight into the structure–sulfation relationship by experimentation and molecular docking analysis

Bufadienolides are a major class of bioactive compounds derived from amphibian skin secretion.

Evaluation of the effect of naproxen on the pharmacokinetics and pharmacodynamics of apixaban

AIM

To assess pharmacokinetic and pharmacodynamic interactions between naproxen (a non-steroidal anti-inflammatory drug) and apixaban (an oral, selective, direct factor-Xa inhibitor).

METHOD

In this randomized, three period, two sequence study, 21 healthy subjects received a single oral dose of apixaban 10 mg, naproxen 500 mg or co-administration of both. Blood samples were collected for determination of apixaban and naproxen pharmacokinetics and pharmacodynamics (anti-Xa activity, international normalized ratio [INR] and arachidonic acid-induced platelet aggregation [AAI-PA]). Adverse events, bleeding time and routine safety assessments were also evaluated.

RESULTS

Apixaban had no effect on naproxen pharmacokinetics. However, following co-administration, apixaban AUC(0,∞), AUC(0,t) and Cmax were 54% (geometric mean ratio 1.537; 90% confidence interval (CI) 1.394, 1.694), 55% (1.549; 90% CI 1.400, 1.713) and 61% (1.611; 90% CI 1.417, 1.831) higher, respectively. Mean (standard deviation [SD]) anti-Xa activity at 3 h post-dose was approximately 60% higher following co-administration compared with apixaban alone, 4.4 [1.0] vs. 2.7 [0.7] IU ml(-1) , consistent with the apixaban concentration increase following co-administration. INR was within the normal reference range after all treatments. AAI-PA was reduced by approximately 80% with naproxen. Co-administration had no impact beyond that of naproxen. Mean [SD] bleeding time was higher following co-administration (9.1 [4.1] min) compared with either agent alone (5.8 [2.3] and 6.9 [2.6] min for apixaban and naproxen, respectively).

CONCLUSION

Co-administration of naproxen with apixaban results in higher apixaban exposure and appears to occur through increased apixaban bioavailability. The effects on anti-Xa activity, INR and inhibition of AAI-PA observed in this study were consistent with the individual pharmacologic effects of apixaban and naproxen.

Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

The exposure of the skin to medical drugs, skin care products, cosmetics, and other chemicals renders information on xenobiotic-metabolizing enzymes (XME) in the skin highly interesting. Since the use of freshly excised human skin for experimental investigations meets with ethical and practical limitations, information on XME in models comes in the focus including non-human mammalian species and in vitro skin models. This review attempts to summarize the information available in the open scientific literature on XME in the skin of human, rat, mouse, guinea pig, and pig as well as human primary skin cells, human cell lines, and reconstructed human skin models. The most salient outcome is that much more research on cutaneous XME is needed for solid metabolism-dependent efficacy and safety predictions, and the cutaneous metabolism comparisons have to be viewed with caution. Keeping this fully in mind at least with respect to some cutaneous XME, some models may tentatively be considered to approximate reasonable closeness to human skin. For dermal absorption and for skin irritation among many contributing XME, esterase activity is of special importance, which in pig skin, some human cell lines, and reconstructed skin models appears reasonably close to human skin. With respect to genotoxicity and sensitization, activating XME are not yet judgeable, but reactive metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the “Overview and Conclusions” section in the end of this review.

Comparison of the effects of apixaban and rivaroxaban on prothrombin and activated partial thromboplastin times using various reagents

BACKGROUND

Clinical situations occur where expedient assessment of the anticoagulant activity of the direct factor Xa (FXa) inhibitors is required. Although quantitative anti-FXa (FXa) assays can be used to measure plasma levels of apixaban or rivaroxaban, turnaround is often slow and many laboratories do not perform these assays.

OBJECTIVE

We compared the in vitro effects of apixaban and rivaroxaban on two readily available laboratory tests, the prothrombin time (PT) and activated partial thromboplastin time (APTT), performed with different reagents. We aimed to identify the most sensitive reagents.

METHODS

Rivaroxaban or apixaban was added to human plasma at a range of concentrations covering expected peak and trough levels, and concentrations were confirmed using calibrated anti-FXa assays. Samples were assayed with six PT and seven APTT reagents using different coagulometers.

RESULTS AND CONCLUSIONS

TriniCLOT PT Excel S was the only reagent to demonstrate sensitivity to apixaban. All of the PT reagents were sensitive to rivaroxaban with TriniCLOT PT Excel S and HemosIL HS PLUS being the most sensitive. Sensitivity to rivaroxaban varied among APTT reagents; four reagents exhibited the greatest responsiveness, and of these, Actin FSL was the most responsive. Commonly used coagulation tests may be useful for assessing the anticoagulant effect of rivaroxaban but not of apixaban. The reason for the different effects of apixaban and rivaroxaban on the PT and APTT is unknown.

Genotype-guided use of oral antithrombotic therapy: a pharmacoeconomic perspective

Pharmacogenomics focuses on tailoring therapy to the individual as opposed to the historical model of fitting the individual to the therapy, and it offers the potential to maximize medication efficacy while reducing adverse events. By its very nature, personalized medicine is conducive to a patient-centered care model. Oral antithrombotics as a class could benefit immensely from this type of approach because an imbalance of safety and efficacy in either direction can yield deadly consequences. Since the current healthcare climate in the USA requires thoughtful allocation of resources, pharmacoeconomic analysis has become critical for all stakeholders, and the adoption of new technologies hinges upon economic impact. This article summarizes the current state of genetics in oral antithrombotic therapy, including clinical relevance as well as cost-effectiveness from a US healthcare system perspective, and provides insight into the future of pharmacogenomics in treating and preventing thromboembolic disorders.

The role of drug metabolizing enzymes in clearance

INTRODUCTION

Metabolism is one of the most important clearance pathways representing the major clearance route of 75% drugs. The four most common drug metabolizing enzymes (DME) that contribute significantly to elimination pathways of new chemical entities are cytochrome P450s, UDP-glucuronosyltransferases, aldehyde oxidase and sulfotransferases. Accurate prediction of human in vivo clearance by these enzymes, using both in vitro and in vivo tools, is critical for the success of drug candidates in human translation.

AREAS COVERED

Important recent advances of key DME are reviewed and highlighted in the following areas: major isoforms, tissue distribution, generic polymorphism, substrate specificity, species differences, mechanism of catalysis, in vitro-in vivo extrapolation and the importance of using optimal assay conditions and relevant animal models.

EXPERT OPINION

Understanding the clearance mechanism of a compound is the first step toward successful prediction of human clearance. It is critical to apply appropriate in vitro and in vivo methodologies and physiologically based models in human translation. While high-confidence prediction for P450-mediated clearance has been achieved, the accuracy of human clearance prediction is significantly lower for other enzyme classes. More accurate predictive methods and models are being developed to address these challenges.

Action of Halowax 1051 on Enzymes of Phase I (CYP1A1) and Phase II (SULT1A and COMT) Metabolism in the Pig Ovary

Polychlorinated naphthalenes (PCNs) are a group of organochlorinated compounds exhibiting dioxin-like properties. Previously published data showed the direct action of PCN-rich Halowax 1051 on ovarian follicular steroidogenesis. Taking into consideration that the observed biological effects of PCNs may be frequently side effects of metabolites generated by their detoxification, the aim of this study was to determine the activity and expression of enzymes involved in phase I (cytochrome P450, family 1 (CYP1A1)) and phase II (sulfotransferase (SULT1A) and catechol-O-methyltransferase (COMT)) detoxification metabolism. Cocultures of granulosa and theca interna cells collected from sexually mature pigs were exposed to 1 pg/mL to 10 ng/mL of Halowax 1051 for 1 to 48 hours, after which levels and activities of CYP1A1, SULT1A, and COMT were measured. Dose-dependent increases of CYP1A1 activity and expression were observed. High doses of Halowax 1051 were inhibitory to COMT and SULT1A activity and reduced their protein levels. In conclusion, fast activation of phase I enzymes with simultaneous inhibition of phase II enzymes indicates that the previously observed effect of Halowax 1051 on follicular steroidogenesis may partially result from metabolite action occurring locally in ovarian follicles.

Apixaban: a review of its use in the prevention of venous thromboembolism after knee or hip replacement surgery

Apixaban (Eliquis™) is an orally active and selective direct inhibitor of factor Xa indicated for twice-daily use in the EU for the prevention of venous thromboembolism (VTE) in adults who have had knee or hip replacement surgery. In this article, the pharmacological, clinical efficacy and tolerability data relevant to the use of apixaban in this indication are reviewed. Oral apixaban is a generally effective and well tolerated thromboprophylactic agent for use after major orthopaedic surgery. In the large, randomized, double-blind, phase III, noninferiority trials known as ADVANCE-2 and -3, apixaban 2.5 mg twice daily initiated after surgery was generally more effective in preventing VTE in patients undergoing knee or hip replacement surgery than subcutaneous enoxaparin sodium initiated before surgery at the EU recommended dosage of 40 mg once daily, with apixaban conferring this benefit without significantly increasing the risk of bleeding. However, when the same apixaban regimen was compared with the US recommended dosage regimen of subcutaneous enoxaparin sodium (30 mg twice daily, initiated after surgery) in patients undergoing knee replacement surgery in the similarly designed ADVANCE-1 trial, the thromboprophylactic efficacy of apixaban did not meet primary endpoint noninferiority criteria, although apixaban was associated with fewer major or clinically relevant nonmajor bleeds (composite endpoint) than this enoxaparin sodium regimen. Additional comparative efficacy and tolerability data are required to definitively position apixaban with respect to other anticoagulants, including rivaroxaban and dabigatran etexilate. In the meantime, currently available clinical data indicate that apixaban is an emerging option for the prevention of VTE in patients undergoing knee or hip replacement surgery.

Sulfation of selected mono-hydroxyflavones by sulfotransferases in vitro: a species and gender comparison

OBJECTIVES

Sulfation via sulfotransferases is an important metabolic pathway contributing to the low bioavailability of flavonoids. This study aims to characterize the sulfation of mono-hydroxyflavones (MHFs) to obtain useful information on structure-metabolizing relationships in animal species and gender differences.

METHODS

Three representative MHFs, namely, 7-, 6- and 4'-MHF, were studied by incubating each MHF at different concentrations with various liver S9 fractions (mouse, rat, dog and human).

KEY FINDINGS

One mono-sulfate was identified for each MHF. 7-MHF and 4'-MHF usually have greater sulfations than 6-MHF. Regardless of whether the S9 fraction came from a male or female, there was a difference in sulfation in the species observed for all MHFs; the highest activity of sulfotransferases was in dog S9. Furthermore, gender differences affect sulfation of MHFs significantly. In rats, all sulfations for the three MHFs were higher in males than that in females while the opposite was observed in mice.

CONCLUSIONS

Regiospecific, species and gender dependence exist in the sulfonation of all selected MHFs.

Preclinical discovery of apixaban, a direct and orally bioavailable factor Xa inhibitor

Apixaban (BMS-562247; 1-(4-methoxyphenyl)-7-oxo-6-(4-(2-oxopiperidin-1-yl)phenyl)-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-c]pyridine-3-carboxamide), a direct inhibitor of activated factor X (FXa), is in development for the prevention and treatment of various thromboembolic diseases. With an inhibitory constant of 0.08 nM for human FXa, apixaban has greater than 30,000-fold selectivity for FXa over other human coagulation proteases. It produces a rapid onset of inhibition of FXa with association rate constant of 20 μM⁻¹/s approximately and inhibits free as well as prothrombinase- and clot-bound FXa activity in vitro. Apixaban also inhibits FXa from rabbits, rats and dogs, an activity which parallels its antithrombotic potency in these species. Although apixaban has no direct effects on platelet aggregation, it indirectly inhibits this process by reducing thrombin generation. Pre-clinical studies of apixaban in animal models have demonstrated dose-dependent antithrombotic efficacy at doses that preserved hemostasis. Apixaban improves pre-clinical antithrombotic activity, without excessive increases in bleeding times, when added on top of aspirin or aspirin plus clopidogrel at their clinically relevant doses. Apixaban has good bioavailability, low clearance and a small volume of distribution in animals and humans, and a low potential for drug-drug interactions. Elimination pathways for apixaban include renal excretion, metabolism and biliary/intestinal excretion. Although a sulfate conjugate of Ο-demethyl apixaban (O-demethyl apixaban sulfate) has been identified as the major circulating metabolite of apixaban in humans, it is inactive against human FXa. Together, these non-clinical findings have established the favorable pharmacological profile of apixaban, and support the potential use of apixaban in the clinic for the prevention and treatment of various thromboembolic diseases.

Novel oral anticoagulants for prophylaxis and treatment of venous thromboembolism: part I (Factor Xa inhibitors)

The quest for an ideal anticoagulant is ongoing. Oral agents that do not require blood level monitoring are presently undergoing taut scrutiny for efficacies and potential side effects, and would potentially soon revolutionize coagulation medicine. The first part of this article reviews oral Factor Xa inhibitors, such as rivaroxaban, apixaban, eribaxaban, edoxaban and YM150--exploring the outcomes of major clinical trials for prophylaxis and treatment of venous thromboembolism--and also briefly outlining their pharmacological properties. The second part of the article (in a separate issue) will cover oral Factor IIa (thrombin), such as dabigatran and AZD0837 and oral Factor IX inhibitors, such as TTP889.

Comparative metabolism of 14C-labeled apixaban in mice, rats, rabbits, dogs, and humans

The metabolism and disposition of [(14)C]apixaban, a potent, reversible, and direct inhibitor of coagulation factor Xa, were investigated in mice, rats, rabbits, dogs, and humans after a single oral administration and in incubations with hepatocytes. In plasma, the parent compound was the major circulating component in mice, rats, dogs, and humans. O-Demethyl apixaban sulfate (M1) represented approximately 25% of the parent area under the time curve in human plasma. This sulfate metabolite was present, but in lower amounts relative to the parent, in plasma from mice, rats, and dogs. Rabbits showed a plasma metabolite profile distinct from that of other species with apixaban as a minor component and M2 (O-demethyl apixaban) and M14 (O-demethyl apixaban glucuronide) as prominent components. The fecal route was a major elimination pathway, accounting for >54% of the dose in animals and >46% in humans. The urinary route accounted for <15% of the dose in animals and 25 to 28% in humans. Apixaban was the major component in feces of every species and in urine of all species except rabbit. M1 and M2 were common prominent metabolites in urine and feces of all species as well as in bile of rats and humans. In vivo metabolite profiles showed quantitative differences between species and from in vitro metabolite profiles, but all human metabolites were found in animal species. After intravenous administration of [(14)C]apixaban to bile duct-cannulated rats, the significant portion (approximately 22%) of the dose was recovered as parent drug in the feces, suggesting direct excretion of the drug from gastrointestinal tracts of rats. Overall, apixaban was effectively eliminated via multiple elimination pathways in animals and humans, including oxidative metabolism, and direct renal and intestinal excretion.