Quantification of 4-Beta-Hydroxycholesterol in Human Plasma Using Automated Sample Preparation and LC-ESI-MS/MS Analysis

Gene Polymorphisms of NLRP3 Associated With Plasma Levels of 4β-Hydroxycholesterol, an Endogenous Marker of CYP3A Activity, in Patients With Asthma

Inflammation decreases the activity of cytochrome P450 3A (CYP3A). Nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) is responsible for regulating the inflammatory response, and its genetic polymorphisms have been linked to inflammatory diseases such as asthma. However, there have been few studies on the effect of NLRP3 on CYP3A activity. We aimed to investigate the association between polymorphisms in the NLRP3 gene and plasma 4β-hydroxycholesterol (4βOHC), an endogenous marker of CYP3A activity, in patients with asthma. In this observational study including 152 adult asthma patients, we analyzed 10 NLRP3 gene single-nucleotide polymorphisms (SNPs). Plasma 4βOHC levels were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results showed that five SNPs were associated with significantly lower plasma 4βOHC concentrations. Among these SNPs, rs3806265, rs4612666, rs1539019, and rs10733112 contributed to a significant increase in plasma IL-6 concentrations. Moreover, a multivariate regression model showed that the rs3806265 TT, rs4612666 CC, rs1539019 AA, and rs10733112 TT genotypes were significant factors for decreased plasma 4βOHC, even after including patient background factors and CYP3A5*3 (rs776746) gene polymorphisms as covariates. These results were also observed when plasma 4βOHC concentrations were corrected for cholesterol levels. We conclude that NLRP3 gene polymorphisms are involved in increasing plasma IL-6 concentrations and decreasing plasma 4βOHC concentrations in patients with asthma. Therefore, NLRP3 gene polymorphisms may be a predictive marker of CYP3A activity in inflammatory diseases such as asthma.

Novel Approaches to Characterize Individual Drug Metabolism and Advance Precision Medicine

Interindividual variability in drug metabolism can significantly affect drug concentrations in the body and subsequent drug response. Understanding an individual's drug metabolism capacity is important for predicting drug exposure and developing precision medicine strategies. The goal of precision medicine is to individualize drug treatment for patients to maximize efficacy and minimize drug toxicity. While advances in pharmacogenomics have improved our understanding of how genetic variations in drug-metabolizing enzymes (DMEs) affect drug response, nongenetic factors are also known to influence drug metabolism phenotypes. This minireview discusses approaches beyond pharmacogenetic testing to phenotype DMEs-particularly the cytochrome P450 enzymes-in clinical settings. Several phenotyping approaches have been proposed: traditional approaches include phenotyping with exogenous probe substrates and the use of endogenous biomarkers; newer approaches include evaluating circulating noncoding RNAs and liquid biopsy-derived markers relevant to DME expression and function. The goals of this minireview are to 1) provide a high-level overview of traditional and novel approaches to phenotype individual drug metabolism capacity, 2) describe how these approaches are being applied or can be applied to pharmacokinetic studies, and 3) discuss perspectives on future opportunities to advance precision medicine in diverse populations. SIGNIFICANCE STATEMENT: This minireview provides an overview of recent advances in approaches to characterize individual drug metabolism phenotypes in clinical settings. It highlights the integration of existing pharmacokinetic biomarkers with novel approaches; also discussed are current challenges and existing knowledge gaps. The article concludes with perspectives on the future deployment of a liquid biopsy-informed physiologically based pharmacokinetic strategy for patient characterization and precision dosing.

Clinical Evaluation Based on a New Approach to Improve the Accuracy of 4β-Hydroxycholesterol Measurement as a Biomarker of CYP3A4 Activity

This study examines 4β-Hydroxycholesterol (4β-HC), which is considered to be a potential marker for the CYP3A4 induction of new chemical entities (NCEs) in drug development. To ensure the use of 4β-HC as a practical biomarker, it is necessary to accurately measure 4β-HC and demonstrate that CYP3A4 induction can be appropriately assessed, even for weak inducers. In clinical trials of NCEs, plasma is often collected with various anticoagulants, in some cases, the plasma is acidified, then stored for an extended period. In this study, we examined the effects of these manipulations on the measurement of 4β-HC, and based on the results, we optimized the plasma collection and storage protocols. We also found that a cholesterol oxidation product is formed when plasma is stored, and by monitoring the compound, we were able to identify when plasma was stored inappropriately. After evaluating the above, clinical drug-drug interaction (DDI) studies were conducted using two NCEs (novel retinoid-related orphan receptor γ antagonists). The weak CYP3A4 induction by the NCEs (which were determined based on a slight decline in the systemic exposure of a probe substrate (midazolam)), was detected by the significant increase in 4β-HC levels (more specifically, 4β-HC/total cholesterol ratios). Our new approach, based on monitoring a cholesterol oxidation product to identify plasma that is stored inappropriately, allowed for the accurate measurement of 4β-HC, and thus, it enabled the evaluation of weak CYP3A4 inducers in clinical studies without using a probe substrate.

Formation of CYP3A-specific metabolites of ibrutinib in vitro is correlated with hepatic CYP3A activity and 4β-hydroxycholesterol/cholesterol ratio

Ibrutinib is an orally administered Bruton's tyrosine kinase inhibitor approved for the treatment of B-cell malignancies, including chronic lymphocytic leukemia. Ibrutinib is metabolized primarily via oxidation by cytochrome P450 (CYP) 3A4/5 to M37 (the primary active metabolite), M34, and M25. The objectives of this study were to assess the relationship between formation of the major CYP3A-specific ibrutinib metabolites in vitro and hepatic CYP3A activity and protein abundance, and to evaluate the utility of the endogenous CYP3A biomarker, plasma 4β-hydroxycholesterol (4β-HC) to cholesterol ratio, to predict ibrutinib metabolite formation in individual cadaveric donors with matching hepatocytes. Ibrutinib (5 μM) was incubated with single-donor human liver microsomes (n = 20) and primary human hepatocytes (n = 15), and metabolites (M37, M34, and M25) were measured by liquid chromatography-tandem mass spectrometry analysis. CYP3A4/5 protein concentrations were measured by quantitative targeted absolute proteomics, and CYP3A activity was measured by midazolam 1'-hydroxylation. Ibrutinib metabolite formation positively correlated with midazolam 1'-hydroxylation in human liver microsomes and hepatocytes. Plasma 4β-HC and cholesterol concentrations were measured in plasma samples obtained at the time of liver harvest from the same 15 donors with matching hepatocytes. Midazolam 1'-hydroxylation in hepatocytes correlated with plasma 4β-HC/cholesterol ratio. When an infant donor (1 year old) was excluded based on previous ontogeny studies, M37 and M25 formation correlated with plasma 4β-HC/cholesterol ratio in the remaining 14 donors (Spearman correlation coefficients [r] 0.62 and 0.67, respectively). Collectively, these data indicate a positive association among formation of CYP3A-specific ibrutinib metabolites in human hepatocytes, hepatic CYP3A activity, and plasma 4β-HC/cholesterol ratio in the same non-infant donors.

Sensitive UHPLC-MS/MS quantification method for 4β- and 4α-hydroxycholesterol in human plasma for accurate CYP3A phenotyping

4β-Hydroxycholesterol (4β-OHC) is formed by CYP3A4 and CYP3A5 and has drawn attention as an endogenous phenotyping probe for CYP3A activity. However, 4β-OHC is also increased by cholesterol autooxidation occurring in vitro due to dysregulated storage and in vivo by oxidative stress or inflammation, independent of CYP3A activity. 4α-hydroxycholesterol (4α-OHC), a stereoisomer of 4β-OHC, is also formed via autooxidation of cholesterol, not by CYP3A, and thus may have clinical potential in reflecting the state of cholesterol autooxidation. In this study, we establish a sensitive method for simultaneous quantification of 4β-OHC and 4α-OHC in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Plasma samples were prepared by saponification, two-step liquid-liquid extraction, and derivatization using picolinic acid. Intense [M+H]+ signals for 4β-OHC and 4α-OHC di-picolinyl esters were monitored using electrospray ionization. The assay fulfilled the requirements of the US Food and Drug Administration guidance for bioanalytical method validation, with a lower limit of quantification of 0.5 ng/mL for both 4β-OHC and 4α-OHC. Apparent recovery rates from human plasma ranged from 88.2% to 101.5% for 4β-OHC, and 91.8% to 114.9% for 4α-OHC. Additionally, matrix effects varied between 86.2% and 117.6% for 4β-OHC, and between 89.5% and 116.9% for 4α-OHC. Plasma 4β-OHC and 4α-OHC concentrations in healthy volunteers, stage 3-5 chronic kidney disease (CKD) patients, and stage 5D CKD patients as measured by the validated assay were within the calibration ranges in all samples. We propose this novel quantification method may contribute to accurate evaluation of in vivo CYP3A activity.

Absence of OATP1B (Organic Anion-Transporting Polypeptide) Induction by Rifampin in Cynomolgus Monkeys: Determination Using the Endogenous OATP1B Marker Coproporphyrin and Tissue Gene Expression

Organic anion-transporting polypeptide (OATP) 1B induction is an evolving mechanism of drug disposition and interaction. However, there are contradictory reports describing OATP1B expression in hepatocytes and liver biopsies after administration of an inducer. This study investigated the in vivo effects of the common inducer rifampin (RIF) on the activity and expression of cynomolgus monkey OATP1B1 and OATP1B3 transporters, which are structurally and functionally similar their human OATP1B counterparts. Multiple doses of oral RIF (15 mg/kg) resulted in a steady 3.9-fold increase of CYP3A biomarker, 4β-hydroxycholesterol (4βHC), in the plasma samples collected before each RIF dose during the treatment period (i.e., predose). In contrast, the predose plasma levels of OATP1B biomarkers coproporphyrin (CP) I and CPIII did not change when compared with RIF treatment. The trough concentration, area under plasma concentration-time curve (AUC), and half-life of RIF decreased markedly during RIF treatment, suggesting that RIF induced its own clearance. Consequently, RIF treatment increased CPI and CPIII AUCs substantially after a single administration and, to a lesser extent, after multiple administrations compared with preadministration AUCs. In addition, OATP1B1 and OATP1B3 mRNA expressions were not modulated by RIF treatment (0.85-1.3-fold), whereas CYP3A8 expression was increased 3.7-5.0-fold, which correlated well with the predose levels of CP and 4βHC. Rifampin treatment showed 2.0-3.3-fold increases in P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) expression in the small intestine. Collectively, these findings indicate that monkey OATP1B and OATP1B3 are not induced by RIF, and further investigation of OATP1B induction by RIF and other nuclear receptor activators in humans is warranted. SIGNIFICANCE STATEMENT: In this study, combined endogenous biomarker and gene expression data suggested that RIF did not induce OATP1B in cynomolgus monkeys. For the first time, the study determines transporter gene expression in the nonhuman primate liver, gut, and kidney tissues after administration of RIF for 7 days, leading to a better understanding of the induction of OATP1B and other major drug transporters. Finally, it provides evidence to strengthen the claim that coproporphyrin is a suitable endogenous probe of OATP1B activity.

Modeling and simulation of the endogenous CYP3A induction marker 4β-hydroxycholesterol during enasidenib treatment

Background

Enasidenib (IDHIFA^®, AG-221) is a first-in-class, targeted inhibitor of mutant IDH2 proteins for treatment of relapsed or refractory acute myeloid leukemia. This was a Phase I/II study evaluating safety, efficacy, and pharmacokinetics/pharmacodynamics (PK/PD) of orally administered enasidenib in subjects with advanced hematologic malignancies with an IDH2 mutation.

Methods

Blood samples for PK and PD assessment were collected. A semi-mechanistic nonlinear mixed effect PK/PD model was successfully developed to characterize enasidenib plasma PK and to assess enasidenib-induced CYP3A activity.

Results

The PK model showed that enasidenib plasma concentrations were adequately described by a one-compartment model with first-order absorption and elimination; the PD model showed a high capacity to induce CYP3A (E_max=7.36) and a high enasidenib plasma concentration to produce half of maximum CYP3A induction (EC₅₀ =31,400 ng/mL). Monte Carlo simulations based on the final PK/PD model showed that at 100 mg once daily dose there was significant drug accumulation and a maximum of three-fold CYP3A induction after multiple doses. Although the EC₅₀ value for CYP3A induction by enasidenib is high, CYP3A induction was observed due to significant drug accumulation.

Conclusion

CYP3A induction following enasidenib dosing should be considered when prescribing concomitant medication metabolized via this pathway.

4β-Hydroxycholesterol as an Endogenous Biomarker for CYP3A Activity: Literature Review and Critical Evaluation

A number of cytochrome P450 (CYP)3A phenotyping probes have been used to characterize the drug interaction potential of new molecular entities; of these, midazolam has emerged as the gold standard. Recently, plasma 4β-hydroxycholesterol (4β-OHC), the metabolite of CYP3A-mediated cholesterol metabolism, has been championed as an endogenous biomarker for CYP3A, particularly during chronic conditions where CYP3A activity is altered by disease and in long-term treatment studies where midazolam administration is not optimal. Multiple studies in humans have shown that 4β-OHC can qualitatively differentiate among weak, moderate, and potent CYP3A induction when an inducer, typically rifampin, is administered for up to 2 weeks. Conversely, longer durations of CYP3A inhibitor administration (≥1 month) appear to be necessary to differentiate among weak, moderate, and potent CYP3A inhibitors. A number of studies have reported statistically significant linear relationships between 4β-OHC plasma concentrations (and 4β-OHC:cholesterol ratios) and midazolam clearance. However, sufficiently powered studies assessing the ability of 4β-OHC or 4β-OHC:cholesterol ratios to measure CYP3A activity (ie, predictive performance) have not been conducted to date. Additional limitations associated with 4β-OHC phenotyping include inability to detect acute changes in CYP3A activity, uncertainty with regard to its intestinal formation, ambiguity surrounding the role of CYP3A5 in its metabolism, and lack of clarity regarding the role of transporters in its disposition. As such, the data do not support the use of 4β-OHC or 4β-OHC:cholesterol ratios as an endogenous biomarker for CYP3A activity.

Accurate quantification of PGE2 in the polyposis in rat colon (Pirc) model by surrogate analyte-based UPLC-MS/MS

An accurate and reliable UPLC-MS/MS method is reported for the quantification of endogenous Prostaglandin E2 (PGE₂) in rat colonic mucosa and polyps. This method adopted the "surrogate analyte plus authentic bio-matrix" approach, using two different stable isotopic labeled analogs - PGE₂-d9 as the surrogate analyte and PGE₂-d4 as the internal standard. A quantitative standard curve was constructed with the surrogate analyte in colonic mucosa homogenate, and the method was successfully validated with the authentic bio-matrix. Concentrations of endogenous PGE₂ in both normal and inflammatory tissue homogenates were back-calculated based on the regression equation. Because of no endogenous interference on the surrogate analyte determination, the specificity was particularly good. By using authentic bio-matrix for validation, the matrix effect and exaction recovery are identically same for the quantitative standard curve and actual samples - this notably increased the assay accuracy. The method is easy, fast, robust and reliable for colon PGE₂ determination. This "surrogate analyte" approach was applied to measure the Pirc (an Apc-mutant rat kindred that models human FAP) mucosa and polyps PGE₂, one of the strong biomarkers of colorectal cancer. A similar concept could be applied to endogenous biomarkers in other tissues.

Impact of genetic and nongenetic factors on interindividual variability in 4β-hydroxycholesterol concentration

PURPOSE

Individual variability in the endogenous CYP3A metabolite 4β-hydroxycholesterol (4βOHC) is substantial, but to which extent this is determined by genetic and nongenetic factors remains unclear. The aim of the study was to evaluate the explanatory power of candidate genetic variants and key nongenetic factors on individual variability in 4βOHC levels in a large naturalistic patient population.

METHODS

We measured 4βOHC concentration in serum samples from 655 patients and used multiple linear regression analysis to estimate the quantitative effects of CYP3A4*22, CYP3A5*3, and POR*28 variant alleles, comedication with CYP3A inducers, inhibitors and substrates, sex, and age on individual 4βOHC levels.

RESULTS

4βOHC concentration ranged >100-fold in the population, and the multiple linear regression model explained about one fourth of the variability (R ² = 0.23). Only comedication with inducers or inhibitors, sex, and POR genotype were significantly associated with individual variability in 4βOHC level. The estimated quantitative effects on 4βOHC levels were greatest for inducer comedication (+>313%, P < 0.001), inhibitor comedication (-34%, P = 0.021), and female sex (+30%, P < 0.001), while only a modestly elevated 4βOHC level was observed in carriers vs. noncarriers of POR*28 (+11%, P = 0.023).

CONCLUSIONS

These findings suggest that the CYP3A4*22, CYP3A5*3, and POR*28 variant alleles are of limited importance for overall individual variability in 4βOHC levels compared to nongenetic factors.

UHPLC-MS/MS bioanalysis of urinary DHEA, cortisone and their hydroxylated metabolites as potential biomarkers for CYP3A-mediated drug-drug interactions

AIM

A UHPLC-MS/MS assay was developed to quantify urinary dehydroepiandrosterone (DHEA), 7β-hydroxy-DHEA, cortisone and 6β-hydroxycortisone as potential biomarkers to predict CYP3A activity.

RESULTS

A sensitive assay at LLOQ of 0.500 ng/ml with good accuracy and precision was developed for the four analytes in human urine. This UHPLC-MS/MS assay was optimized by eliminating nonspecific loss of the analytes in urine, ensuring complete hydrolysis of the conjugates to unconjugated forms and use of the product ions of [M+H-H₂O]⁺ for multiple reaction monitoring detection of DHEA and 7β-hydroxy-DHEA.

CONCLUSION

This assay was successfully applied to a pilot clinical study. It is also suitable for future drug-drug interaction studies to continue evaluating the potential of these steroids as biomarkers for CYP3A inhibition and induction.

Managing the Risk of CYP3A Induction in Drug Development: A Strategic Approach

Induction of cytochrome P450 (P450) can impact the efficacy and safety of drug molecules upon multiple dosing with coadministered drugs. This strategy is focused on CYP3A since the majority of clinically relevant cases of P450 induction are related to these enzymes. However, the in vitro evaluation of induction is applicable to other P450 enzymes; however, the in vivo relevance cannot be assessed because the scarcity of relevant clinical data. In the preclinical phase, compounds are screened using pregnane X receptor reporter gene assay, and if necessary structure-activity relationships (SAR) are developed. When projects progress toward the clinical phase, induction studies in a hepatocyte-derived model using HepaRG cells will generate enough robust data to assess the compound's induction liability in vivo. The sensitive CYP3A biomarker 4β-hydroxycholesterol is built into the early clinical phase I studies for all candidates since rare cases of in vivo induction have been found without any induction alerts from the currently used in vitro methods. Using this model, the AstraZeneca induction strategy integrates in vitro assays and in vivo studies to make a comprehensive assessment of the induction potential of new chemical entities. Convincing data that support the validity of both the in vitro models and the use of the biomarker can be found in the scientific literature. However, regulatory authorities recommend the use of primary human hepatocytes and do not advise the use of sensitive biomarkers. Therefore, primary human hepatocytes and midazolam studies will be conducted during the clinical program as required for regulatory submission.

Perspective: 4β-hydroxycholesterol as an emerging endogenous biomarker of hepatic CYP3A

A key goal in the clinical development of a new molecular entity is to quickly identify whether it has the potential for drug-drug interactions. In particular, confirmation of in vitro data in the early stage of clinical development would facilitate the decision making and inform future clinical pharmacology study designs. Plasma 4β-hydroxycholesterol (4β-HC) is considered as an emerging endogenous biomarker for cytochrome P450 3A (CYP3A), one of the major drug metabolizing enzymes. Although there are increasing reports of the use of 4β-HC in academic- and industry-sponsored clinical studies, a thorough review, summary and consideration of the advantages and challenges of using 4β-HC to evaluate changes in CYP3A activity has not been attempted. Herein, we review the biology of 4β-HC, its response to treatment with CYP3A inducers, inhibitors and mixed inducer/inhibitors in healthy volunteers and patients, the association of 4β-HC with other probes of CYP3A activity (e.g. midazolam, urinary cortisol ratios), and present predictive pharmacokinetic models. We provide recommendations for studying hepatic CYP3A activity in clinical pharmacology studies utilizing 4β-HC at different stages of drug development.

Chemical derivatization for enhancing sensitivity during LC/ESI-MS/MS quantification of steroids in biological samples: a review

Sensitive and specific methods for the detection, characterization and quantification of endogenous steroids in body fluids or tissues are necessary for the diagnosis, pathological analysis and treatment of many diseases. Recently, liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) has been widely used for these purposes due to its specificity and versatility. However, the ESI efficiency and fragmentation behavior of some steroids are poor, which lead to a low sensitivity. Chemical derivatization is one of the most effective methods to improve the detection characteristics of steroids in ESI-MS/MS. Based on this background, this article reviews the recent advances in chemical derivatization for the trace quantification of steroids in biological samples by LC/ESI-MS/MS. The derivatization in ESI-MS/MS is based on tagging a proton-affinitive or permanently charged moiety on the target steroid. Introduction/formation of a fragmentable moiety suitable for the selected reaction monitoring by the derivatization also enhances the sensitivity. The stable isotope-coded derivatization procedures for the steroid analysis are also described.

Rapid LC-MS/MS method for the determination of 4-hydroxycholesterol/cholesterol ratio in serum as endogenous biomarker for CYP3A activity in human and foals

Cytochrome P450 3A (CYP) enzymes are involved in the elimination of many drugs and are known to be regulated by several environmental factors. Thus, it was the aim of this study to develop and validate an analytical method allowing estimation of the hepatic CYP3A enzyme activity using the 4-hydroxycholesterol to cholesterol ratio as an endogenous biomarker in serum. Both compounds were isolated from the biological matrix by liquid-liquid extraction using n-hexane after saponification with ethanolic sodium methoxide solution (2M) to cleave the steroids from their esterified forms without any kind of further derivatization. Chromatographic separation was achieved on a reversed-phase column (SupelcoAcsentis(®), C8) within 7min using an isocratic elution with ammonium acetate 5mM (pH=3.8, 10%) and acetonitrile (90%) at a flow rate of 300μl/min. d6-cholesterol and d7-4β-hydroxycholesterol were used as internal standards. Detection was done on a triple quadrupole mass spectrometer using the following mass transitions: 369.3/161.5, 369.3/147.1 and 369.3/95.2 for cholesterol; 385.2/367.4, 385.2/109.1 for 4-hydroxycholesterol; 374.4/152.7 and 392.2/108.9 for d6-cholesterol and d7-4-hydroxycholesterol, respectively as the internal standards. The method was validated according to current bioanalytical guidelines considering selectivity, linearity, accuracy, precision, recovery, stability. The analytical range was 5-250 and 50-1000ng/ml, for 4-hydroxycholesterol and cholesterol, respectively. The method was shown to be selective for both compounds with good linearity over the selected range (r>0.99) as well as good within- and between day accuracy (error: -1.2-3.7% for 4-hydroxycholesterol and -7.7-9.5% for cholesterol) and within- and between day precision (2.1-14.6% for 4-hydroxycholesterol and 1.1-14.9% for cholesterol). Recovery was found to be over 80% for both analytes while significant stability issues could not be observed. Finally, the validated assay was applied to measure 4-hydroxycholesterol and cholesterol in serum samples of clinical studies in humans and foals that could verify induction of hepatic CYP3A4 (human) and CYP3A89 (foals) after premedication with the known enzyme inducer rifampicin.

Determination of 7α-OH cholesterol by LC-MS/MS: Application in assessing the activity of CYP7A1 in cholestatic minipigs

An LC-MS/MS method was developed and validated to determine 7α-OH cholesterol in liver microsome. This method was convenient and fast with high specificity and sensitivity. Briefly, a gradient elution was performed on a Synergi polar-C18 column (50×4.6mm i.d., 3μm). The mobile phase (consisting of 0.1% HCOOH solution and acetonitrile) eluted in gradient at a flow rate of 1ml/min. MS detection was operated on APCI (+) mode; the MRM transitions for 7α-OH cholesterol and D7-cholesterol (I.S.) were 385.1≥159.1 and 376.4≥266.3, respectively. The linear response range of 7α-OH cholesterol was covered from 1.563 to 100.0ng/ml. All of the validation items meet the requirement of FDA guidance for bioanalytical method validation. This method was applied to enzymatic studies for determination of cholesterol 7alpha-hydroxylation activity catalyzed by CYP7A1 in the cholestatic minipigs liver microsomes.

The γ-Secretase Modulator, BMS-932481, Modulates Aβ Peptides in the Plasma and Cerebrospinal Fluid of Healthy Volunteers

The pharmacokinetics, pharmacodynamics, safety, and tolerability of BMS-932481, a γ-secretase modulator (GSM), were tested in healthy young and elderly volunteers after single and multiple doses. BMS-932481 was orally absorbed, showed dose proportionality after a single dose administration, and had approximately 3-fold accumulation after multiple dosing. High-fat/caloric meals doubled the C_max and area under the curve and prolonged T_max by 1.5 hours. Consistent with the preclinical pharmacology of GSMs, BMS-932481 decreased cerebrospinal fluid (CSF) Aβ39, Aβ40, and Aβ42 while increasing Aβ37 and Aβ38, thereby providing evidence of γ-secretase enzyme modulation rather than inhibition. In plasma, reductions in Aβ40 and Aβ42 were observed with no change in total Aβ; in CSF, modest decreases in total Aβ were observed at higher dose levels. Increases in liver enzymes were observed at exposures associated with greater than 70% CSF Aβ42 lowering after multiple dosing. Although further development was halted due to an insufficient safety margin to test the hypothesis for efficacy of Aβ lowering in Alzheimer’s disease, this study demonstrates that γ-secretase modulation is achievable in healthy human volunteers and supports further efforts to discover well tolerated GSMs for testing in Alzheimer’s disease and other indications.

Interindividual Variability in Cytochrome P450-Mediated Drug Metabolism

The cytochrome P450 (P450) enzymes are the predominant enzyme system involved in human drug metabolism. Alterations in the expression and/or activity of these enzymes result in changes in pharmacokinetics (and consequently the pharmacodynamics) of drugs that are metabolized by this set of enzymes. Apart from changes in activity as a result of drug-drug interactions (by P450 induction or inhibition), the P450 enzymes can exhibit substantial interindividual variation in basal expression and/or activity, leading to differences in the rates of drug elimination and response. This interindividual variation can result from a myriad of factors, including genetic variation in the promoter or coding regions, variation in transcriptional regulators, alterations in microRNA that affect P450 expression, and ontogenic changes due to exposure to xenobiotics during the developmental and early postnatal periods. Other than administering a probe drug or cocktail of drugs to obtain the phenotype or conducting a genetic analysis to determine genotype, methods to determine interindividual variation are limited. Phenotyping via a probe drug requires exposure to a xenobiotic, and genotyping is not always well correlated with phenotype, making both methodologies less than ideal. This article describes recent work evaluating the effect of some of these factors on interindividual variation in human P450-mediated metabolism and the potential utility of endogenous probe compounds to assess rates of drug metabolism among individuals.

Use of 4β-hydroxycholesterol in animal and human plasma samples as a biomarker for CYP3A induction

Background: 4β-hydroxycholesterol (4βHC) has recently been proposed as a potential endogenous biomarker for CYP3A activity. Developing bioanalytical assays for 4βHC is challenging for several reasons, including endogenous background levels in plasma; the presence of free and ester forms; the inherent lack of MS sensitivity; and the presence of multiple positional isomers. Results: Bioanalytical assays in mouse, rat, dog and human plasma were adapted and modified from a previous published human plasma assay for 4βHC by using alkaline de-esterification, picolinic derivatization, a surrogate analyte (d7-4βHC) in authentic matrices and chromatographic conditions that showed good separation from isobaric, positional isomers. Conclusion: These assays were applied to multiple studies and demonstrated potential applications of 4βHC as a CYP3A biomarker across preclinical and clinical settings.

4β-hydroxycholesterol correlates with dose but not steady-state concentration of carbamazepine: indication of intestinal CYP3A in biomarker formation?

AIM

4β-hydroxycholesterol (4βOHC) is an endogenous CYP3A(4) biomarker, which is elevated by use of the CYP3A4 inducer carbamazepine. Our aim was to compare to what extent serum concentration of 4βOHC correlates with dose (presystemic exposure) and steady-state concentration (systemic exposure) of carbamazepine.

METHODS

The study was based on a therapeutic drug monitoring material, including information about daily doses and steady-state concentrations (Css ) of carbamazepine. 4βOHC concentrations were determined in residual serum samples of 55 randomly selected carbamazepine-treated patients and 54 levetiracetam-treated patients (negative controls) by UPLC-APCI-MS/MS after liquid-liquid extraction. Correlation analyses between 4βOHC concentration and daily dose and Css of carbamazepine, respectively, were performed by Spearman's tests. In addition, 4βOHC concentrations in females vs. males were compared in induced and non-induced patients.

RESULTS

Median 4βOHC concentration was ~10-fold higher in carbamazepine- vs. levetiracetam-treated patients (650 vs. 54 nmol l(-1) , P < 0.0001). There was a significant, positive correlation between carbamazepine dose and 4βOHC concentration (Spearman r = 0.53, 95% confidence interval [CI] 0.27, 0.72, P < 0.001). No significant correlation between carbamazepine Css and 4βOHC concentration was found (Spearman r = 0.14; 95% CI -0.14, 0.40, P = 0.3). Enzyme-induced females had significantly higher 4βOHC concentrations than males (P < 0.001), while no significant gender difference was found in non-induced patients (P = 0.52).

CONCLUSION

Serum concentrations of 4βOHC correlate with presystemic, but not systemic exposure of the CYP3A4 inducer carbamazepine. This suggests a stronger inductive effect of carbamazepine on presystemic than systemic CYP3A4 phenotype and might indicate a role of the intestine in 4βOHC formation. Moreover, CYP3A4 inducibility seems to be higher in females than males.

Validation of 4β-hydroxycholesterol and evaluation of other endogenous biomarkers for the assessment of CYP3A activity in healthy subjects

AIMS

This study aimed to assess changes in the plasma concentrationss of 4β-hydroxycholesterol (4βHC) against intravenous (i.v.) and oral midazolam (MDZ) pharmacokinetics (PK) after administration of a potent CYP3A inhibitor [ketoconazole (KETO)] and inducer [rifampicin (RIF)].

METHODS

Thirty-two healthy subjects (HS) were allocated into three groups of 12 each in KETO and RIF and 10 in a placebo group (PLB). All HS were randomized to receive oral and i.v. MDZ on day 1 or 2 and on day 15 or 16 after receiving RIF (600 mg once daily), KETO (400 mg once daily) or PLB for 2 weeks. Subjects were followed until day 30. The effect of treatments on 4βHC was assessed by analyzing % change from baseline using a linear spline mixed effects model.

RESULTS

Compared with PLB, KETO decreased 4βHC mean values up to 13% (P = 0.003) and RIF increased 4βHC mean values up to 220% (P < 0.001). Within 14 days of stopping KETO and RIF, 4βHC had either returned to baseline (KETO) or was still returning to baseline (RIF). Compared with baseline, mean oral MDZ AUC increased by 11-fold (90% CI ranging from 9-fold to 13-fold increase) and decreased by 92% (90% CI ranging from 90% to 95% decrease) after KETO and RIF, respectively. Similar trends were observed for 6β-hydroxycortisol : cortisol (6βHCL : CL) urinary ratios.

CONCLUSIONS

Changes in plasma 4βHC can be utilized as a surrogate for MDZ PK after multiple doses of potent CYP3A inducers. There is a more limited dynamic range for 4βHC for assessment of potential CYP3A inhibitors. 4βHC is a valuable tool for the assessment of potential CYP3A inducers in early drug development.

Evaluation of 4β-Hydroxycholesterol as a Clinical Biomarker of CYP3A4 Drug Interactions Using a Bayesian Mechanism-Based Pharmacometric Model

A Bayesian mechanism–based pharmacokinetic/pharmacodynamic model of cytochrome P450 3A4 (CYP3A4) activity was developed based on a clinical study of the effects of ketoconazole and rifampin on midazolam exposure and plasma 4β-hydroxycholesterol (4βHC) concentrations. Simulations from the model demonstrated that the dynamic range of 4βHC as a biomarker of CYP3A4 induction or inhibition was narrower than that of midazolam; an inhibitor that increases midazolam area under the curve by 20-fold may only result in a 20% decrease in 4βHC after 14 days of dosing. Likewise, an inducer that elevates CYP3A4 activity by 1.2-fold would reduce the area under the curve of midazolam by 50% but would only increase 4βHC levels by 20% after 14 days of dosing. Elevation in 4βHC could be reliably detected with a twofold induction in CYP3A4 activity with study sample sizes (N ~ 6–20) typically used in early clinical development. Only a strong CYP3A4 inhibitor (e.g., ketoconazole) could be detected with similar sample sizes.

Cytochrome P450-mediated metabolic alterations in preeclampsia evaluated by quantitative steroid signatures

Although preeclampsia has been suggested potential risk factors including placental and systemic inflammation, oxidative stress, and abnormal steroid metabolism during pregnancy, the pathogenesis of preeclampsia has not fully been elucidated, particularly in steroid metabolism. The association between various cytochrome P450 (CYP)-mediated steroid metabolic markers and preeclampsia risk was therefore investigated. The serum levels of 54 CYP-mediated regioselective hydroxysteroids and their substrates were quantitatively evaluated from both pregnant women with preeclampsia (n=30; age, 30.8±4.5 years) and normotensive controls (n=30; age, 31.0±3.5 years), who were similar with respect to maternal age, gestational age, and body mass index. The levels of 6ß-, 7a-, and 11ß-hydroxymetabolites of androgens and corticoids were significantly increased in women with preeclampsia. In addition, the levels of oxysterols, including 7a-, 7ß-, 4ß-, 20a-, 24S-, and 27-hydroxycholesterol, were markedly higher, while the levels of 16a-OH-DHEA, 16a-OH-androstenedione, and cholesterol were significantly decreased in patients. The 6ß-hydroxylation of androgens and corticoids by CYP3A4 (P<0.01), the activation of 20,22-desmolase (a cholesterol side-chain cleavage enzyme) by CYP11A1 (P<0.00001), and the multi-hydroxylation of cholesterol at C-4ß, C-7a, C-7ß, C-24S, C-27, and C-20a (P<0.0001) by catalytic or enzymatic reaction (e.g. CYP3A4, CYP7A1, CYP27A1, and CYP46A1) were differed between preeclamptic women and control subjects. In particular, an increased oxysterols (induction>2.0-fold) were positively correlated with the conditions of preeclampsia. Our metabolic profiling suggests the CYP-mediated alterations in steroid metabolism and hydroxylation in pregnancy-induced hypertension. These multiple markers could serve as background information for improved clinical diagnosis and management during pregnancy. This article is part of a Special Issue entitled "Pregnancy and Steroids".

Significant increase in plasma 4β-hydroxycholesterol concentration in patients after kidney transplantation

Several previous studies have shown that renal failure decreases not only renal elimination but also metabolic clearance of drugs, particularly those metabolized by CYP3A. However, whether recovery of renal function results in recovery of hepatic CYP3A activity remains unknown. In this study, we evaluated the effect of renal function on CYP3A activity after kidney transplantation in patients with end-stage renal disease (ESRD) by measuring the change in CYP3A activity using plasma concentration of 4β-hydroxycholesterol as a biomarker. The study enrolled 13 patients with ESRD who underwent the first kidney allograft transplantation. Morning blood samples were collected before and 3, 7, 10, 14, 21, 30, 60, 90, 120, 150 and 180 days after kidney transplantation. Plasma concentration of 4β-hydroxycholesterol was measured using GC-MS. Compared with before kidney transplantation, creatinine clearance increased significantly from day 3 after kidney transplantation and stabilized thereafter. Plasma concentration of 4β-hydroxycholesterol was elevated significantly on days 90 and 180 after kidney transplantation. In conclusion, this study suggests the recovery of CYP3A activity with improvement in renal function after kidney transplantation in patients with ESRD.

Comparison of the quantification of a therapeutic protein using nominal and accurate mass MS/MS

Background: The quantification of proteins and peptides in in vivo samples is a critical part of supporting the drug development process for biotherapeutics. LC–MS/MS using tandem quadrupole mass spectrometers is well established as the technology of choice for the quantification of small-molecule drugs and their metabolites in biological fluid. The application of accurate mass MS for quantification in a DMPK environment has attracted considerable interest in recent years. Materials & Methods: In this article we describe and compare the application of LC–high-resolution MS and LC–selected reaction monitoring (SRM) for the quantification of a therapeutics proteins. Results: The accurate mass instrumentation showed acceptable linearity and sensitivity to quantify the protein therapeutic to the level of 10 ng/ml. The accurate mass instrument was operated in accurate mass SRM using high resolution (SRM-HR), the assay was demonstrated to be linear over three orders of magnitude. By narrowing the mass window from 100 mDa to 40 mDa and then to 20 mDa the assay specificity was significantly improved, hence increasing the S/N and improving the assay sensitivity. Conclusion: The high-resolution instrument was demonstrated to be reproducible over the course of the assay. The accurate mass method sensitivity was determined to be within one order of magnitude of that obtained with a tandem quadrupole MS/MS assay.