Content and activity of human liver microsomal protein and prediction of individual hepatic clearance in vivo

Investigating the Correlation between Genotypes and Hepatic Protein Expression of CYP2C9, CYP2C19, CYP2D6, and CYP3A5 Using Postmortem Tissue from a Danish Population

The cytochrome P450 (CYP) family of enzymes plays a central role in the metabolism of many drugs. CYP genes are highly polymorphic, which is known to affect protein levels, but for some low frequent CYP genotypes the correlation between genotype and CYP protein expression is less established. In this study, we determined the CYP2C9, CYP2C19, CYP2D6, and CYP3A5 genotypes of 250 Danish individuals included in a postmortem study. For 116 of the individuals, the hepatic CYP protein levels were investigated by a proteomics approach. Overall, we found the postmortem genetic and proteomic data to be in agreement with those of other studies performed on fresh hepatic tissue, showing the usability of postmortem hepatic tissue for this type of investigation. For less investigated genotypes, we could corroborate previously found results: 1) statistically significantly lower levels of hepatic CYP2C9 protein in individuals carrying the CYP2C9*3 variant compared with individuals with two wild type (wt) alleles; 2) comparable levels of CYP2C19 in CYP2C19*2/*17 and CYP2C19*1/*2 individuals; 3) reduced CYP2D6 protein levels in heterozygous individuals with the CYP2D6*3, CYP2D6*4, and CYP2D6*5 gene deletion variants; and 4) significantly lower levels of CYP3A5 protein in CYP3A5*3 homozygous individuals compared with individuals who were heterozygous for the CYP3A5*3 allele or homozygous individuals for the wt alleles. In conclusion, the use of postmortem tissue significantly increases the access to human specimens for research purposes, and postmortem proteomics can be used to investigate the link between CYP genotypes and hepatic protein expression. SIGNIFICANCE STATEMENT: In tissue samples from a large postmortem cohort (n = 250) we determined the CYP2C9, CYP2C19, CYP2D6, and CYP3A5 genotypes. Hepatic CYP protein levels were investigated in 116 individuals using a proteomics approach. For common genotypes, we found results similar to previous knowledge, pointing toward the usability of postmortem tissue. For the less investigated genotypes, we were able to corroborate genotype/protein expression correlations. It is a novel approach to use a large postmortem cohort to investigate genetic/protein expression correlations.

Discovery of a novel homocysteine thiolactone hydrolase and the catalytic activity of its natural variants

Homocysteine thiolactone (HTL), a toxic metabolite of homocysteine (Hcy) in hyperhomocysteinemia (HHcy), is known to modify protein structure and function, leading to protein damage through formation of N-Hcy-protein. HTL has been highly linked to HHcy-associated cardiovascular and neurodegenerative diseases. The protective role of HTL hydrolases against HTL-associated vascular toxicity and neurotoxicity have been reported. Although several endogeneous enzymes capable of hydrolyzing HTL have been identified, the primary enzyme responsible for its metabolism remains unclear. In this study, three human carboxylesterases were screened to explore new HTL hydrolase and human carboxylesterase 1 (hCES1) demonstrates the highest catalytic activity against HTL. Given the abundance of hCES1 in the liver and the clinical significance of its single-nucleotide polymorphisms (SNPs), six common hCES1 nonsynonymous coding SNP (nsSNPs) variants were examined and characterized for their kinetic parameters. Variants E220G and G143E displayed 7.3-fold and 13.2-fold lower catalytic activities than its wild-type counterpart. In addition, the detailed catalytic mechanism of hCES1 for HTL hydrolysis was computational investigated and elucidated by Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) method. The function of residues E220 and G143 in sustaining its hydrolytic activity of hCES1 was analyzed, and the calculated energy difference aligns well with experimental-derived results, supporting the validity of our computational insights. These findings provide insights into the potential protective role of hCES1 against HTL-associated toxicity, and warrant future studies on the possible association between specific genetic variants of hCES1 with impaired catalytic function and clinical susceptibility of HTL-associated cardiovascular and neurodegenerative diseases.

In silico modeling and simulation of organ-on-a-chip systems to support data analysis and a priori experimental design

Organ-on-a-chip (OoC) systems are a promising new class of in vitro devices that can combine various tissues, cultured in different compartments, linked by media flow. The properties of these novel in vitro systems linked to increased physiological relevance of culture conditions may lead to more in vivo-relevant cell phenotypes, enabling better in vitro pharmacology and toxicology assessment. Improved cell activities combined with longer lasting cultures offer opportunities to improve the characterization of absorption, distribution, metabolism, and excretion (ADME) processes, potentially leading to more accurate prediction of human pharmacokinetics (PKs). The inclusion of barrier tissue elements and metabolically competent tissue types results in complex concentration-time profiles (in vitro PK) for test drugs and their metabolites that require appropriate mathematical modeling of in vitro data for parameter estimation. In particular, modeling is critical to estimate in vitro ADME parameters when multiple different tissues are combined in a single device. Therefore, sophisticated in silico data analysis and a priori experimental design are highly recommended for OoC experiments in a manner not needed with standard ADME screening. The design of the experiment should be optimized based on an investigation of the structural characteristics of the in vitro system, the ADME features of the test compound and any available knowledge of cell phenotypes. This tutorial aims to provide such a modeling framework to inform experimental design and refine parameter estimation in a Gut-Liver OoC (the most studied multi-organ systems to predict the oral drug PKs) to improve translatability of data generated in such complex cellular systems.

Novel Psilocin Prodrugs with Altered Pharmacological Properties as Candidate Therapies for Treatment-Resistant Anxiety Disorders

The psychedelic prodrug psilocybin has shown therapeutic benefits for the treatment of numerous psychiatric conditions. Despite positive clinical end points targeting depression and anxiety, concerns regarding the duration of the psychedelic experience produced by psilocybin, associated with enduring systemic exposure to the active metabolite psilocin, pose a barrier to its therapeutic application. Our objective was to create a novel prodrug of psilocin with similar therapeutic benefits but a reduced duration of psychedelic effects compared with psilocybin. Here, we report the synthesis and functional screening of 28 new chemical entities. Our strategy was to introduce a diversity of cleavable groups at the 4-hydroxy position of the core indole moiety to modulate metabolic processing. We identified several novel prodrugs of psilocin with altered pharmacokinetic profiles and reduced pharmacological exposure compared with psilocybin. These candidate prodrugs have the potential to maintain the long-term benefits of psilocybin therapy while attenuating the duration of psychedelic effects.

Sex- and Lifestyle-Related Factors are Associated with Altered Hepatic CYP Protein Levels in People Diagnosed with Mental Disorders

In this study, we used human postmortem tissue to investigate hepatic protein expression levels of cytochrome P450 (CYP) 1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4 by LC-MS/MS in a population of people suffering from mental disorders (n = 171). We report hepatic protein levels of these six CYP isoforms in 171 individuals in total, and define a focused population dataset of 116 individuals after excluding 55 samples due to low microsomal protein per gram of liver (MPPGL) yield. Postmortem decay was most likely the reason for the low MPPGL yield in the 55 samples. In the focused population, we found women to have significantly higher protein levels of CYP3A4 than men in addition to decreased CYP3A4 protein levels among obese individuals. Furthermore, MPPGL was negatively correlated with body mass index (BMI). An increase in CYP1A2 protein levels was observed among smokers, and increased CYP2E1 protein levels were observed among individuals with a history of alcohol abuse. Finally, individuals who received phenobarbital (CYP3A4 inducer) had significantly higher CYP3A4 levels. In conclusion, lifestyle-related factors prevalent among people suffering from mental disorders are associated with altered CYP protein levels, which may alter drug metabolism and affect the efficacy of commonly prescribed drugs. Furthermore, this investigation demonstrates that postmortem hepatic tissue can be used to study how lifestyle and effectors affect hepatic CYP-levels in a large cohort of patients. SIGNIFICANCE STATEMENT: Using a large number of postmortem hepatic tissue specimens (n=116) originating from the autopsy of individuals diagnosed with mental disorders, we were able to show that hepatic CYP-levels were affected by alcohol, smoking, BMI, and sex and that MPPGL was affected by BMI. These lifestyle-related changes may alter drug metabolism and affect the efficacy of commonly prescribed drugs. It is a novel approach to use a large postmortem cohort to investigate how lifestyle and effectors affect hepatic CYP-levels.

Stepwise Targeted Matching Strategy for Comprehensive Profiling of Xanthohumol Metabolites In Vivo and In Vitro Using UHPLC-Q-Exactive Orbitrap Mass Spectrometer

Xanthohumol (XN), a natural prenylated flavonoid extracted and isolated from the hop plant (Humulus lupulus), possesses diverse pharmacological activities. Although the metabolites of XN have been investigated in the previous study, a comprehensive metabolic profile has been insufficient in vivo or in vitro until now. The current study was aimed at systematically elucidating the metabolic pathways of XN after oral administration to rats. Herein, a UHPLC-Q-Exactive Orbitrap MS was adopted for the potential metabolites detection. A stepwise targeted matching strategy for the overall identification of XN metabolites was proposed. A metabolic net (53 metabolites included) on XN in vivo and in vitro, as well as the metabolic profile investigation, were designed, preferably characterizing XN metabolites in rat plasma, urine, liver, liver microsomes, and feces. On the basis of a stepwise targeted matching strategy, the net showed that major in vivo metabolic pathways of XN in rats include glucuronidation, sulfation, methylation, demethylation, hydrogenation, dehydrogenation, hydroxylation, and so on. The proposed metabolic pathways in this research will provide essential data for further pharmaceutical studies of prenylated flavonoids and lay the foundation for further toxicity and safety studies.

Targeted Metabolomics of Organophosphate Pesticides and Chemical Warfare Nerve Agent Simulants Using High- and Low-Dose Exposure in Human Liver Microsomes

Our current understanding of organophosphorus agent (pesticides and chemical warfare nerve agents) metabolism in humans is limited to the general transformation by cytochrome P450 enzymes and, to some extent, by esterases and paraoxonases. The role of compound concentrations on the rate of clearance is not well established and is further explored in the current study. We discuss the metabolism of 56 diverse organophosphorus compounds (both pesticides and chemical warfare nerve agent simulants), many of which were explored at two variable dose regimens (high and low), determining their clearance rates (Clint) in human liver microsomes. For compounds that were soluble at high concentrations, 1D-NMR, 31P, and MRM LC-MS/MS were used to calculate the Clint and the identity of certain metabolites. The determined Clint rates ranged from 0.001 to 2245.52 µL/min/mg of protein in the lower dose regimen and from 0.002 to 98.57 µL/min/mg of protein in the high dose regimen. Though direct equivalency between the two regimens was absent, we observed (1) both mono- and bi-phasic metabolism of the OPs and simulants in the microsomes. Compounds such as aspon and formothion exhibited biphasic decay at both high and low doses, suggesting either the involvement of multiple enzymes with different KM or substrate/metabolite effects on the metabolism. (2) A second observation was that while some compounds, such as dibrom and merphos, demonstrated a biphasic decay curve at the lower concentrations, they exhibited only monophasic metabolism at the higher concentration, likely indicative of saturation of some metabolic enzymes. (3) Isomeric differences in metabolism (between Z- and E- isomers) were also observed. (4) Lastly, structural comparisons using examples of the oxon group over the original phosphorothioate OP are also discussed, along with the identification of some metabolites. This study provides initial data for the development of in silico metabolism models for OPs with broad applications.

Simplifying the Extended Clearance Concept Classification System (EC3S) to Guide Clearance Prediction in Drug Discovery

PURPOSE

The Extended Clearance Concept Classification System was established as a development-stage tool to provide a framework for identifying fundamental mechanism(s) governing drug disposition in humans. In the present study, the applicability of the EC3S in drug discovery has been investigated. In its current format, the EC3S relies on low-throughput hepatocyte uptake data, which are not frequently generated in a discovery setting.

METHODS

A relationship between hepatocyte uptake clearance and MDCK permeability was first established along with intrinsic clearance from human liver microsomes. The performance of this approach was examined by categorizing 64 drugs into EC3S classes and comparing the predicted major elimination pathway(s) to that observed in humans. As an extension of the work, the ability of the simplified EC3S to predict human systemic clearance based on intrinsic clearance generated using in-vitro metabolic systems was evaluated.

RESULTS

The assessment enabled the use of MDCK permeability and unscaled unbound intrinsic clearance to generate cut-off criteria to categorize compounds into four EC3S classes: Class 12ab, 2cd, 34ab, and 34cd, with major elimination mechanism(s) assigned to each class. The predictivity analysis suggested that systemic clearance could generally be predicted within threefold for EC3S class 12ab and 34ab compounds. For classes 2cd and 34cd, systemic clearance was poorly predicted using in-vitro systems explored in this study.

CONCLUSION

Collectively, our simplified classification approach is expected to facilitate the identification of mechanism(s) involved in drug elimination, faster resolution of in-vitro to in-vivo disconnects, and better design of mechanistic pharmacokinetic studies in drug discovery.

Establishing allometric relationships between microsomal protein and cytochrome P450 content with body weight in vertebrate species

Data from in vitro studies are routinely used to estimate in vivo hepatic clearance of chemicals and this information is needed to parameterise physiologically based kinetic models. Such clearance data can be obtained from laboratory experiments using liver microsomes, hepatocytes, precision-cut liver slices or recombinant enzymes. Irrespective of the selected test system, scaling factors are required to convert the in vitro measured intrinsic clearance to a whole liver intrinsic clearance. Scaling factors such as the hepatic microsomal protein per gram of liver and/or the amount of cytochrome P450 per hepatocyte provide a means to calculate the whole liver intrinsic clearance. Here, a database from the peer-reviewed literature has been developed and provides quantitative metrics on microsomal protein (MP) and cytochrome P450 contents in vertebrate orders namely amphibians, mammals, birds, fish and reptiles. This database allows to address allometric relationships between body weight and MP content, and body weight and cytochrome P450 content. A total of 85 and 74 vertebrate species were included to assess the relationships between log10 body weight versus log10 MP, and between log10 body weight and log10 cytochrome P450 content, respectively. The resulting slopes range from 0.76 to 1.45 in a range of vertebrate species. Such data-driven allometric relationships can be used to estimate the MP content necessary for in vitro to in vivo extrapolation of in vitro clearance data. Future work includes applications of these relationships for different vertebrate taxa using quantitative in vitro to in vivo extrapolation models coupled to physiologically based kinetic models using chemicals of relevance as case studies including pesticides, contaminants and feed additives.

Simple In Vitro 18O Labeling for Improved Mass Spectrometry-Based Drug Metabolites Identification: Deep Drug Metabolism Study

The identification of drug metabolites formed with different in vitro systems by HPLC-MS is a standard step in preclinical research. In vitro systems allow modeling of real metabolic pathways of a drug candidate. Despite the emergence of various software and databases, identification of compounds is still a complex task. Measurement of the accurate mass, correlation of chromatographic retention times and fragmentation spectra are often insufficient for identification of compounds especially in the absence of reference materials. Metabolites can "slip under the nose", since it is often not possible to reliably confirm that a signal belongs to a metabolite and not to other compounds in complex systems. Isotope labeling has proved to be a tool that aids in small molecule identification. The introduction of heavy isotopes is done with isotope exchange reactions or with complicated synthetic schemes. Here, we present an approach based on the biocatalytic insertion of oxygen-18 isotope under the action of liver microsomes enzymes in the presence of ¹⁸O₂. Using the local anesthetic bupivacaine as an example, more than 20 previously unknown metabolites were reliably discovered and annotated in the absence of the reference materials. In combination with high-resolution mass spectrometry and modern methods of mass spectrometric metabolism data processing, we demonstrated the ability of the proposed approach to increase the degree of confidence in interpretating metabolism data.

The Analytical Strategy of “Ion Induction and Deduction Based on Net-Hubs” for the Comprehensive Characterization of Naringenin Metabolites In Vivo and In Vitro Using a UHPLC-Q-Exactive Orbitrap Mass Spectrometer

Naringenin (5,7,4′-trihydroxyflavanone), belonging to the flavanone subclass, is associated with beneficial effects such as anti-oxidation, anticancer, anti-inflammatory, and anti-diabetic effects. Drug metabolism plays an essential role in drug discovery and clinical safety. However, due to the interference of numerous endogenous substances in metabolic samples, the identification and efficient characterization of drug metabolites are difficult. Here, ultra-high-performance liquid chromatography (UHPLC) coupled with high-resolution mass spectrometry was used to obtain mass spectral information of plasma (processed by three methods), urine, feces, liver tissue, and liver microsome samples. Moreover, a novel analytical strategy named “ion induction and deduction” was proposed to systematically screen and identify naringenin metabolites in vivo and in vitro. The analysis strategy was accomplished by the establishment of multiple “net-hubs” and the induction and deduction of fragmentation behavior. Finally, 78 naringenin metabolites were detected and identified from samples of rat plasma, urine, feces, liver tissue, and liver microsomes, of which 67 were detected in vivo and 13 were detected in vitro. Naringenin primarily underwent glucuronidation, sulfation, oxidation, methylation, ring fission, and conversion into phenolic acid and their composite reactions. The current study provides significant help in extracting target information from complex samples and sets the foundation for other pharmacology and toxicology research.

Ru(II) photocages enable precise control over enzyme activity with red light

The cytochrome P450 family of enzymes (CYPs) are important targets for medicinal chemistry. Recently, CYP1B1 has emerged as a key player in chemotherapy resistance in the treatment of cancer. This enzyme is overexpressed in a variety of tumors, and is correlated with poor treatment outcomes; thus, it is desirable to develop CYP1B1 inhibitors to restore chemotherapy efficacy. However, possible off-target effects, such as inhibition of liver CYPs responsible for first pass metabolism, make selective inhibition a high priority to avoid possible drug-drug interactions and toxicity. Here we describe the creation of light-triggered CYP1B1 inhibitors as "prodrugs", and achieve >6000-fold improvement in potency upon activation with low energy (660 nm) light. These systems provide a selectivity index of 4,000-100,000 over other off-target CYPs. One key to the design was the development of coordinating CYP1B1 inhibitors, which suppress enzyme activity at pM concentrations in live cells. The metal binding group enforces inhibitor orientation in the active site by anchoring to the iron. The second essential component was the biologically compatible Ru(II) scaffold that cages the inhibitors before photochemical release. These Ru(II) photocages are anticipated to provide similar selectivity and control for any coordinating CYP inhibitors.

Next Generation Risk Assessment of the Anti-Androgen Flutamide Including the Contribution of Its Active Metabolite Hydroxyflutamide

In next generation risk assessment (NGRA), non-animal approaches are used to quantify the chemical concentrations required to trigger bioactivity responses, in order to assure safe levels of human exposure. A limitation of many in vitro bioactivity assays, which are used in an NGRA context as new approach methodologies (NAMs), is that toxicokinetics, including biotransformation, are not adequately captured. The present study aimed to include, as a proof of principle, the bioactivity of the metabolite hydroxyflutamide (HF) in an NGRA approach to evaluate the safety of the anti-androgen flutamide (FLU), using the AR-CALUX assay to derive the NAM point of departure (PoD). The NGRA approach applied also included PBK modelling-facilitated quantitative in vitro to in vivo extrapolation (QIVIVE). The PBK model describing FLU and HF kinetics in humans was developed using GastroPlus™ and validated against human pharmacokinetic data. PBK model-facilitated QIVIVE was performed to translate the in vitro AR-CALUX derived concentration-response data to a corresponding in vivo dose-response curve for the anti-androgenicity of FLU, excluding and including the activity of HF (-HF and +HF, respectively). The in vivo benchmark dose 5% lower confidence limits (BMDL05) derived from the predicted in vivo dose-response curves for FLU, revealed a 440-fold lower BMDL05 when taking the bioactivity of HF into account. Subsequent comparison of the predicted BMDL05 values to the human therapeutic doses and historical animal derived PoDs, revealed that PBK modelling-facilitated QIVIVE that includes the bioactivity of the active metabolite is protective and provides a more appropriate PoD to assure human safety via NGRA, whereas excluding this would potentially result in an underestimation of the risk of FLU exposure in humans.

In vitro-in silico-based prediction of inter-individual and inter-ethnic variations in the dose-dependent cardiotoxicity of R- and S-methadone in humans

New approach methodologies predicting human cardiotoxicity are of interest to support or even replace in vivo-based drug safety testing. The present study presents an in vitro–in silico approach to predict the effect of inter-individual and inter-ethnic kinetic variations in the cardiotoxicity of R- and S-methadone in the Caucasian and the Chinese population. In vitro cardiotoxicity data, and metabolic data obtained from two approaches, using either individual human liver microsomes or recombinant cytochrome P450 enzymes (rCYPs), were integrated with physiologically based kinetic (PBK) models and Monte Carlo simulations to predict inter-individual and inter-ethnic variations in methadone-induced cardiotoxicity. Chemical specific adjustment factors were defined and used to derive dose–response curves for the sensitive individuals. Our simulations indicated that Chinese are more sensitive towards methadone-induced cardiotoxicity with Margin of Safety values being generally two-fold lower than those for Caucasians for both methadone enantiomers. Individual PBK models using microsomes and PBK models using rCYPs combined with Monte Carlo simulations predicted similar inter-individual and inter-ethnic variations in methadone-induced cardiotoxicity. The present study illustrates how inter-individual and inter-ethnic variations in cardiotoxicity can be predicted by combining in vitro toxicity and metabolic data, PBK modelling and Monte Carlo simulations. The novel methodology can be used to enhance cardiac safety evaluations and risk assessment of chemicals.

IVIVE: Facilitating the Use of In Vitro Toxicity Data in Risk Assessment and Decision Making

During the past few decades, the science of toxicology has been undergoing a transformation from observational to predictive science. New approach methodologies (NAMs), including in vitro assays, in silico models, read-across, and in vitro to in vivo extrapolation (IVIVE), are being developed to reduce, refine, or replace whole animal testing, encouraging the judicious use of time and resources. Some of these methods have advanced past the exploratory research stage and are beginning to gain acceptance for the risk assessment of chemicals. A review of the recent literature reveals a burst of IVIVE publications over the past decade. In this review, we propose operational definitions for IVIVE, present literature examples for several common toxicity endpoints, and highlight their implications in decision-making processes across various federal agencies, as well as international organizations, including those in the European Union (EU). The current challenges and future needs are also summarized for IVIVE. In addition to refining and reducing the number of animals in traditional toxicity testing protocols and being used for prioritizing chemical testing, the goal to use IVIVE to facilitate the replacement of animal models can be achieved through their continued evolution and development, including a strategic plan to qualify IVIVE methods for regulatory acceptance.

Pharmacokinetic Herb-Drug Interactions of Xiang-Sha-Liu-Jun-Zi-Tang and Paclitaxel in Male Sprague Dawley Rats and Its Influence on Enzyme Kinetics in Human Liver Microsomes

Paclitaxel is a prescribed anticancer drug used to treat various cancers. It is a substrate of cytochrome P-450 (CYP-450) enzymes. Despite its efficacy, paclitaxel has severe side effects. Herbal medicines are commonly used to treat the side effects of chemotherapy. They can be administered before, during, and after chemotherapy. Xiang-Sha-Liu-Jun-Zi Tang (XSLJZT) is a herbal formula commonly used in breast cancer patients. The main purpose of this study was to assess the pharmacokinetic (PK) influence of XSLJZT on paclitaxel PK parameters, determine its effect on CYP-450 enzyme expression, and evaluate its effect on enzyme activity. Sprague Dawley rats were classified into pretreatment and co-treatment groups, where XSLJZT was pre-administered for 3, 5, and 7 days and co-administered 2 h before paclitaxel administration. The rat liver tissues and Hep-G2 cells were used to determine the effects of XSLJZT on CYP3A1/2 and CYP3A4 enzymes respectively. Western blot analysis was used to detect changes in the CYP3A1/2 and CYP3A4 enzymes expression. The influence of XSLJZT on enzyme activity was evaluated using human liver microsomes, and a liquid chromatography-tandem mass spectrometric system was developed to monitor paclitaxel levels in rat plasma. Results demonstrated that XSLJZT increased the area under the concentration versus time curve (AUC) for paclitaxel in pretreatment groups by 2-, 3-, and 4-fold after 3, 5, and 7 days, respectively. In contrast, no significant change in the AUC was observed in the co-treatment group. However, the half-life was prolonged in all groups from 17.11 min to a maximum of 37.56 min. XSLJZT inhibited CYP3A1/2 expression in the rat liver tissues and CYP3A4 enzymes in Hep-G2 cells in a time-dependent manner, with the highest inhibition observed after 7 days of pretreatment in rat liver tissues. In the enzyme kinetics study, XSLJZT inhibited enzyme activity in a competitive dose-dependent manner. In conclusion, there is a potential interaction between XSLJZT and paclitaxel at different co-treatment and pretreatment time points.

Towards the Elucidation of the Pharmacokinetics of Voriconazole: A Quantitative Characterization of Its Metabolism

The small-molecule drug voriconazole (VRC) shows a complex and not yet fully understood metabolism. Consequently, its in vivo pharmacokinetics are challenging to predict, leading to therapy failures or adverse events. Thus, a quantitative in vitro characterization of the metabolism and inhibition properties of VRC for human CYP enzymes was aimed for. The Michaelis-Menten kinetics of voriconazole N-oxide (NO) formation, the major circulating metabolite, by CYP2C19, CYP2C9 and CYP3A4, was determined in incubations of human recombinant CYP enzymes and liver and intestine microsomes. The contribution of the individual enzymes to NO formation was 63.1% CYP2C19, 13.4% CYP2C9 and 29.5% CYP3A4 as determined by specific CYP inhibition in microsomes and intersystem extrapolation factors. The type of inhibition and inhibitory potential of VRC, NO and hydroxyvoriconazole (OH-VRC), emerging to be formed independently of CYP enzymes, were evaluated by their effects on CYP marker reactions. Time-independent inhibition by VRC, NO and OH-VRC was observed on all three enzymes with NO being the weakest and VRC and OH-VRC being comparably strong inhibitors of CYP2C9 and CYP3A4. CYP2C19 was significantly inhibited by VRC only. Overall, the quantitative in vitro evaluations of the metabolism contributed to the elucidation of the pharmacokinetics of VRC and provided a basis for physiologically-based pharmacokinetic modeling and thus VRC treatment optimization.

Multitarget Hybrid Fasudil Derivatives as a New Approach to the Potential Treatment of Amyotrophic Lateral Sclerosis

Hybrid compounds containing structural fragments of the Rho kinase inhibitor fasudil and the NRF2 inducers caffeic and ferulic acids were designed with the aid of docking and molecular mechanics studies. Following the synthesis of the compounds using a peptide-coupling methodology, they were characterized for their ROCK2 inhibition, radical scavenging, effects on cell viability (MTT assay), and NRF2 induction (luciferase assay). One of the compounds (1d) was selected in view of its good multitarget profile and good tolerability. It was able to induce the NRF2 signature, promoting the expression of the antioxidant response enzymes HO-1 and NQO1, via a KEAP1-dependent mechanism. Analysis of mRNA and protein levels of the NRF2 pathway showed that 1d induced the NRF2 signature in control and SOD1-ALS lymphoblasts but not in sALS, where it was already increased in the basal state. These results show the therapeutic potential of this compound, especially for ALS patients with a SOD1 mutation.

The proteomic characterization of the peritumor microenvironment in human hepatocellular carcinoma

The tumor microenvironment (TME) was usually studied in tumor tissue and in relation to only tumor progression, with little involved in occurrence, recurrence and metastasis of tumor. Thus, a new concept "peritumor microenvironment (PME)" was proposed in the proteomic characterization of peritumor liver tissues in human hepatocellular carcinoma (HCC). The PME for occurrence (PME-O) and progression (PME-P) were almost totally different at proteome composition and function. Proteins for occurrence and progression rarely overlapped and crossed. Immunity played a central role in PME-O, whereas inflammation, angiogenesis and metabolism were critical in PME-P. Proteome profiling identified three PME subtypes with different features of HCC. Thymidine phosphorylase (TYMP) was validated as an antiangiogenic target in an orthotopic HCC mouse model. Overall, the proteomic characterization of the PME revealed that the entire processes of HCC occurrence and progression differ substantially. These findings could enable advances in cancer biology, diagnostics and therapeutics.

Ontogeny of Scaling Factors for Pediatric Physiology-Based Pharmacokinetic Modeling and Simulation: Microsomal Protein Per Gram of Liver

Microsomal protein per gram of liver (MPPGL) is an important scaling factor for bottom-up physiology-based pharmacokinetic modeling and simulation, but data in pediatrics are limited. Therefore, MPPGL was determined in 160 liver samples from pediatric (n = 129) and adult (n = 31) donors obtained from four sources: the University of Maryland Brain and Tissue Bank (UMBTB), tissue retrieval services at the University of Minnesota and University of Pittsburgh, and Sekisui-Xenotech. Tissues were homogenized and subjected to differential centrifugation to prepare microsomes, and cytochrome c reductase activities in tissue homogenates and microsomes were used to estimate cytochrome P450 reductase (POR) activity as a marker of microsomal recovery; microsomal POR content was also assessed by quantitative proteomics. MPPGL values varied 5- to 10-fold within various age groups/developmental stages, and tissue source was identified as a contributing factor. Using a "trimmed" dataset comprised of samples ranging from 3 to 18 years of age common to the four sources, POR protein abundance and activity in microsomes and POR activity in homogenates was lower in UMBTB samples (autopsy) compared with other sources (perfused/flash-frozen). Regression analyses revealed that the UMBTB samples were driving an apparent age effect as no effect of age on log-transformed MPPGL values was observed when the UMBTB samples were excluded. We conclude that a mean±SD MPPGL value of 30.4±1.7 mg/g is representative between one month postnatal age and early adulthood. Potential source effects should be considered for studies involving tissue samples from multiple sources with different procurement and processing procedures. SIGNIFICANCE STATEMENT: Microsomal protein per gram of liver (MPPGL) is an important scaling factor for bottom up PBPK modeling and simulation, but data in pediatrics are limited. Although MPPGL varies 5- to 10-fold at a given developmental stage, a value of 30.4 ± 1.7 mg/g (mean ± SD) is representative between one month postnatal age and early adulthood. However, when tissue samples are obtained from multiple sources, different procurement and processing procedures may influence the results and should be taken into consideration.

Assembling the P450 puzzle: on the sources of nonadditivity in drug metabolism

There is an increasing number of indications of an oversimplification in the premise that the cumulative properties of the human drug-metabolizing ensemble represent a simple aggregate of the properties of the constituting enzymes. Recent studies of the functional effects of hetero-association of multiple cytochrome P450 species and their interactions with metabolically related enzymes revealed a tight integration in the drug-metabolizing ensemble. In our opinion, the sources of interindividual variability in drug metabolism can be elucidated only when considering this ensemble as a multienzyme system, the functional parameters of which are determined by interactions between its constituents. In this article, we present a conceptual model providing a mechanistic explanation for the functional effects of the interactions between multiple P450 species and propose a clue to understanding the nonadditive behavior of the drug-metabolizing ensemble.

PharmVar GeneFocus: CYP2C9

The Pharmacogene Variation Consortium (PharmVar) catalogues star (*) allele nomenclature for the polymorphic human CYP2C9 gene. Genetic variation within the CYP2C9 gene locus impacts the metabolism or bioactivation of many clinically important drugs, including nonsteroidal anti-inflammatory drugs, phenytoin, antidiabetic agents, and angiotensin receptor blockers. Variable CYP2C9 activity is of particular importance regarding efficacy and safety of warfarin and siponimod as indicated in their package inserts. This GeneFocus provides a comprehensive overview and summary of CYP2C9 and describes how haplotype information catalogued by PharmVar is utilized by the Pharmacogenomics Knowledgebase and the Clinical Pharmacogenetics Implementation Consortium.

Hepatic Scaling Factors for In Vitro-In Vivo Extrapolation of Metabolic Drug Clearance in Patients with Colorectal Cancer with Liver Metastasis

In vitro-in vivo extrapolation (IVIVE) linked with physiologically based pharmacokinetics (PBPK) modeling is used to predict the fates of drugs in patients. Ideally, the IVIVE-PBPK models should incorporate systems information accounting for characteristics of the specific target population. There is a paucity of such scaling factors in cancer, particularly microsomal protein per gram of liver (MPPGL) and cytosolic protein per gram of liver (CPPGL). In this study, cancerous and histologically normal liver tissue from 16 patients with colorectal liver metastasis were fractionated to microsomes and cytosol. Protein content was measured in homogenates, microsomes, and cytosol. The loss of microsomal protein during fractionation was accounted for using corrections based on NADPH cytochrome P450 reductase activity in different matrices. MPPGL was significantly lower in cancerous tissue (24.8 ± 9.8 mg/g) than histologically normal tissue (39.0 ± 13.8 mg/g). CPPGL in cancerous tissue was 42.1 ± 12.9 mg/g compared with 56.2 ± 16.9 mg/g in normal tissue. No correlations between demographics (sex, age, and body mass index) and MPPGL or CPPGL were apparent in the data. The generated scaling factors together with assumptions regarding the relative volumes of cancerous versus noncancerous tissue were used to simulate plasma exposure of drugs with different extraction ratios. The PBPK simulations revealed a substantial difference in drug exposure (area under the curve), up to 3.3-fold, when using typical scaling factors (healthy population) instead of disease-related parameters in cancer population. These indicate the importance of using population-specific scalars in IVIVE-PBPK for different disease states. SIGNIFICANCE STATEMENT: Accuracy in predicting the fate of drugs from in vitro data using IVIVE-PBPK depends on using correct scaling factors. The values for two of such scalars, namely microsomal and cytosolic protein per gram of liver, is not known in patients with cancer. This study presents, for the first time, scaling factors from cancerous and matched histologically normal livers. PBPK simulations of various metabolically cleared drugs demonstrate the necessity of population-specific scaling for model-informed precision dosing in oncology.

Influence of Proteome Profiles and Intracellular Drug Exposure on Differences in CYP Activity in Donor-Matched Human Liver Microsomes and Hepatocytes

Human liver microsomes (HLM) and human hepatocytes (HH) are important in vitro systems for studies of intrinsic drug clearance (CLint) in the liver. However, the CLint values are often in disagreement for these two systems. Here, we investigated these differences in a side-by-side comparison of drug metabolism in HLM and HH prepared from 15 matched donors. Protein expression and intracellular unbound drug concentration (Kpuu) effects on the CLint were investigated for five prototypical probe substrates (bupropion-CYP2B6, diclofenac-CYP2C9, omeprazole-CYP2C19, bufuralol-CYP2D6, and midazolam-CYP3A4). The samples were donor-matched to compensate for inter-individual variability but still showed systematic differences in CLint. Global proteomics analysis outlined differences in HLM from HH and homogenates of human liver (HL), indicating variable enrichment of ER-localized cytochrome P450 (CYP) enzymes in the HLM preparation. This suggests that the HLM may not equally and accurately capture metabolic capacity for all CYPs. Scaling CLint with CYP amounts and Kpuu could only partly explain the discordance in absolute values of CLint for the five substrates. Nevertheless, scaling with CYP amounts improved the agreement in rank order for the majority of the substrates. Other factors, such as contribution of additional enzymes and variability in the proportions of active and inactive CYP enzymes in HLM and HH, may have to be considered to avoid the use of empirical scaling factors for prediction of drug metabolism.

Whole-Body Pharmacokinetics and Physiologically Based Pharmacokinetic Model for Monomethyl Auristatin E (MMAE)

Monomethyl auristatin E (MMAE) is one of the most commonly used payloads for developing antibody–drug conjugates (ADC). However, limited studies have comprehensively evaluated the whole-body disposition of MMAE. Consequently, here, we have investigated the whole-body pharmacokinetics (PK) of MMAE in tumor-bearing mice. We show that while MMAE is rapidly eliminated from the plasma, it shows prolonged and extensive distribution in tissues, blood cells, and tumor. Highly perfused tissues (e.g., lung, kidney, heart, liver, and spleen) demonstrated tissue-to-plasma area under the concentration curve (AUC) ratios > 20, and poorly perfused tissues (e.g., fat, pancreas, skin, bone, and muscle) had ratios from 1.3 to 2.4. MMAE distribution was limited in the brain, and tumor had 8-fold higher exposure than plasma. A physiological-based pharmacokinetic (PBPK) model was developed to characterize the whole-body PK of MMAE, which accounted for perfusion/permeability-limited transfer of drug in the tissue, blood cell distribution of the drug, tissue/tumor retention of the drug, and plasma protein binding. The model was able to characterize the PK of MMAE in plasma, tissues, and tumor simultaneously, and model parameters were estimated with good precision. The MMAE PBPK model presented here can facilitate the development of a platform PBPK model for MMAE containing ADCs and help with their preclinical-to-clinical translation and clinical dose optimization.

Prediction of Drug Clearance from Enzyme and Transporter Kinetics

Accurate estimation of in vivo clearance in human is pivotal to determine the dose and dosing regimen for drug development. In vitro-in vivo extrapolation (IVIVE) has been performed to predict drug clearance using empirical and physiological scalars. Multiple in vitro systems and mathematical modeling techniques have been employed to estimate in vivo clearance. The models for predicting clearance have significantly improved and have evolved to become more complex by integrating multiple processes such as drug metabolism and transport as well as passive diffusion. This chapter covers the use of conventional as well as recently developed methods to predict metabolic and transporter-mediated clearance along with the advantages and disadvantages of using these methods and the associated experimental considerations. The general approaches to improve IVIVE by use of appropriate scalars, incorporation of extrahepatic metabolism and transport and application of physiologically based pharmacokinetic (PBPK) models with proteomics data are also discussed. The chapter also provides an overview of the advantages of using such dynamic mechanistic models over static models for clearance predictions to improve IVIVE.

Variation in the expression of cytochrome P450-related miRNAs and transcriptional factors in human livers: Correlation with cytochrome P450 gene phenotypes

Cytochrome P450 (CYP) gene expression exhibits large interindividual variation attributable to diverse regulatory factors including microRNAs (miRNAs) and hepatic transcription factors (TFs). We used real-time qPCR with 106 human liver samples to measure the expression and interindividual variation of seven miRNAs and four TFs that have been reported to regulate the expression of CYPs; we also identified factors that influence their expression. The results show that expression of the seven miRNAs and the four TFs exhibits a non-normal distribution and the expression variability is high (89- to 618-fold for miRNA and 12- to 85-fold for TFs). Age contributed to the interindividual variation for miR-148a, miR-27b and miR-34a, whereas cigarette smoking and alcohol consumption significantly reduced HNF4α mRNA levels. Association analysis showed significant correlations among the seven miRNAs as well as the four TFs. Furthermore, we systematically evaluated the impact of the seven miRNAs and four TFs on protein content, mRNA levels, translation efficiency and activity of 10 CYPs. The results show that numerous associations (positive and negative) are present between the seven miRNAs or the four TFs and the 10 CYP phenotypes (as indicated by mRNA, protein and activity); specifically, miR-27b, miR-34a and all four TFs played key roles in the interindividual variation of CYPs. Our results extend previous findings and suggest that miR-27b and miR-34a may be potential direct or indirect master regulators of CYP expression and thereby contribute to the interindividual variations in CYP-mediated drug metabolism.

Parameterization of Microsomal and Cytosolic Scaling Factors: Methodological and Biological Considerations for Scalar Derivation and Validation

Mathematical models that can predict the kinetics of compounds have been increasingly adopted for drug development and risk assessment. Data for these models may be generated from in vitro experimental systems containing enzymes contributing to metabolic clearance, such as subcellular tissue fractions including microsomes and cytosol. Extrapolation from these systems is facilitated by common scaling factors, known as microsomal protein per gram (MPPG) and cytosolic protein per gram (CPPG). Historically, parameterization of MPPG and CPPG has employed the use of recovery factors, commonly benchmarked to cytochromes P450 which work well in some contexts, but could be problematic for other enzymes. Here, we propose absolute quantification of protein content and supplementary assays to evaluate microsomal/cytosolic purity that should be employed. Examples include calculation of microsomal latency by mannose-6-phosphatase activity and immunoblotting of subcellular fractions with fraction-specific markers. Further considerations include tissue source, as disease states can affect enzyme expression and activity, and the methodology used for scalar parameterization. Regional- and organ-specific expression of enzymes, in addition to differences in organ physiology, is another important consideration. Because most efforts have focused on the liver that is, for the most part, homogeneous, derived scalars may not capture the heterogeneity of other major tissues contributing to xenobiotic metabolism including the kidneys and small intestine. Better understanding of these scalars, and how to appropriately derive them from extrahepatic tissues can provide support to the inferences made with physiologically based pharmacokinetic modeling, increase its accuracy in characterizing in vivo drug pharmacokinetics, and improve confidence in go-no-go decisions for clinical trials.

Digital Microfluidics-Enabled Analysis of Individual Variation in Liver Cytochrome P450 Activity

The superfamily of hepatic cytochrome P450 (CYP) enzymes is responsible for the intrinsic clearance of the majority of therapeutic drugs in humans. However, the kinetics of drug clearance via CYPs varies significantly among individuals due to both genetic and external factors, and the enzyme amount and function are also largely impacted by many liver diseases. In this study, we developed a new methodology, based on digital microfluidics (DMF), for rapid determination of individual alterations in CYP activity from human-derived liver samples in biopsy-scale. The assay employs human liver microsomes (HLMs), immobilized on magnetic beads to facilitate determination of the activity of microsomal CYP enzymes in a parallelized system at physiological temperature. The thermal control is achieved with the help of a custom-designed, inkjet-printed microheater array modularly integrated with the DMF platform. The CYP activities are determined with the help of prefluorescent, enzyme-selective model compounds by quantifying the respective fluorescent metabolites based on optical readout in situ. The selectivity and sensitivity of the assay was established for four different CYP model reactions, and the diagnostic concept was validated by determining the interindividual variation in one of the four model reaction activities, that is, ethoxyresorufin O-deethylation (CYP1A1/2), between five donors. Overall, the developed protocol consumes only about 15 μg microsomal protein per assay. It is thus technically adaptable to screening of individual differences in CYP enzyme function from biopsy-scale liver samples in an automated fashion, so as to support tailoring of medical therapies, for example, in the context of liver disease diagnosis.

Physiologically based kinetic (PBK) modelling and human biomonitoring data for mixture risk assessment

Human biomonitoring (HBM) data can provide insight into co-exposure patterns resulting from exposure to multiple chemicals from various sources and over time. Therefore, such data are particularly valuable for assessing potential risks from combined exposure to multiple chemicals. One way to interpret HBM data is establishing safe levels in blood or urine, called Biomonitoring Equivalents (BE) or HBM health based guidance values (HBM-HBGV). These can be derived by converting established external reference values, such as tolerable daily intake (TDI) values. HBM-HBGV or BE values are so far agreed only for a very limited number of chemicals. These values can be established using physiologically based kinetic (PBK) modelling, usually requiring substance specific models and the collection of many input parameters which are often not available or difficult to find in the literature. The aim of this study was to investigate the suitability and limitations of generic PBK models in deriving BE values for several compounds with a view to facilitating the use of HBM data in the assessment of chemical mixtures at a screening level. The focus was on testing the methodology with two generic models, the IndusChemFate tool and High-Throughput Toxicokinetics package, for two different classes of compounds, phenols and phthalates. HBM data on Danish children and on Norwegian mothers and children were used to evaluate the quality of the predictions and to illustrate, by means of a case study, the overall approach of applying PBK models to chemical classes with HBM data in the context of chemical mixture risk assessment. Application of PBK models provides a better understanding and interpretation of HBM data. However, the study shows that establishing safety threshold levels in urine is a difficult and complex task. The approach might be more straightforward for more persistent chemicals that are analysed as parent compounds in blood but high uncertainties have to be considered around simulated metabolite concentrations in urine. Refining the models may reduce these uncertainties and improve predictions. Based on the experience gained with this study, the performance of the models for other chemicals could be investigated, to improve the accuracy of the simulations.

Ontogeny of Phase I Metabolism of Drugs

Capturing ontogeny of enzymes involved in phase I metabolism is crucial to improve prediction of dose-concentration and concentration-effect relationships throughout infancy and childhood. Once captured, these patterns can be integrated in semiphysiologically or physiology-based pharmacokinetic models to support predictions in specific pediatric settings or to support pediatric drug development. Although these translational efforts are crucial, isoenzyme-specific ontogeny-based models should also incorporate data on variability of maturational and nonmaturational covariates (eg, disease, treatment modalities, pharmacogenetics). Therefore, this review provides a summary of the ontogeny of phase I drug-metabolizing enzymes, indicating current knowledge gaps and recent progresses. Furthermore, we tried to illustrate that straightforward translation of isoenzyme-specific ontogeny to predictions does not allow full exploration of scenarios of potential variability related to maturational (non-age-related variability, other isoenzymes or transporters) or nonmaturational (disease, pharmacogenetics) covariates, and necessitates integration in a "systems" concept.

Involvement of NF-κB in the reversal of CYP3A down-regulation induced by sea buckthorn in BCG-induced rats

Previous studies reported that sea buckthorn (Hippophae rhamnoides L., Elaeagnaceae, HRP) exhibits hepatoprotective effects via its anti-inflammatory and antioxidant properties as well as its inhibitory effects on collagen synthesis. However, it is unclear whether this hepatoprotective effect is also achieved by regulating liver drug metabolism enzyme pathways. Herein, we examined the regulatory effect of HRP on cytochrome P450 3A (CYP3A) in rats with immune liver injury, and explored the molecular mechanism of its hepatoprotective effect. Rat models of immunological liver injury were induced by intravenous injections of Bacillus Calmette-Guerin (BCG; 125 mg kg-1; 2 wks). Specific protein levels were detected by ELISA or western blot, and CYP3A mRNA expression was detected by RT-PCR. High-performance liquid chromatography (HPLC) detected relative changes in CYP3A metabolic activity based on the rates of 1-hydroxylation of the probe drug midazolam (MDZ). BCG pretreatment (125 mg kg-1) significantly down-regulated liver CYP3A protein expression compared with the control, metabolic activity, and transcription levels while up-regulating liver NF-κB, IL-1β, TNF-α and iNOS. HRP intervention (ED50: 78 mg kg-1) moderately reversed NF-κB, inflammatory cytokines, and iNOS activation in a dose-dependent manner (P < 0.05), and suppressed CYP3A down-regulation (P < 0.05); thereby partially alleviating liver injury. During immune liver injury, HRP may reverse CYP3A down-regulation by inhibiting NF-κB signal transduction, and protect liver function, which involves regulation of enzymes transcriptionally, translationally and post-translationally. The discovery that NF-κB is a molecular target of HRP may initiate the development and optimization of a clinical therapeutic approach to mitigate hepatitis B and other immunity-related liver diseases.

Impact of Ethnicity-Specific Hepatic Microsomal Scaling Factor, Liver Weight, and Cytochrome P450 (CYP) 1A2 Content on Physiologically Based Prediction of CYP1A2-Mediated Pharmacokinetics in Young and Elderly Chinese Adults

BACKGROUND

The vast majority of physiological and biological data required for physiologically based predictions are primarily available in Caucasians rather than other ethnic populations, which leads to a lack of confidence in the application of physiologically based pharmacokinetic (PBPK) modeling for ethnicity-specific prediction of pharmacokinetics in the Chinese population.

OBJECTIVES

In this study we recalibrate the system parameters of Chinese-specific PBPK modeling and explore for the first time the relative importance of ethnicity-specific microsomal protein per gram of liver (MPPGL), liver weight, and cytochrome P450 (CYP) 1A2 abundance to the projection of drug disposition mediated by CYP1A2 in young and elderly Chinese adults.

METHODS

Chinese MPPGL levels and associated variability were parameterized and incorporated for the first time into ethnicity-specific PBPK models for the Chinese adults. Parameterization of Chinese liver weights was also recalibrated on the basis of autopsy data from Chinese individuals (n = 4081) across the entire adult age range. Uncertainty surrounding the Chinese-specific CYP1A2 content has also been explored and clarified by conducting ethnicity-related PBPK simulations under different scenarios. Various ethnicity-related or 'what-if' scenarios for PBPK modeling were implemented to assess the predictive performance and explore the relative importance of ethnicity-specific MPPGL and liver weight to the projection of drug disposition mediated by CYP1A2 in terms of two typical CYP1A2 substrates, caffeine and theophylline, in young and elderly Chinese adults by comparing the predicted concentration-time data and associated pharmacokinetic parameter estimates with observations.

RESULTS

Compared with 0.85, the liver scalar of 0.9 generally produced more accurate liver weight levels in virtual Chinese peers. Additionally, simulated MPPGL levels on the basis of Caucasian data were not able to reflect the age-independent pattern observed in Chinese adults, dissimilar to that on the basis of Chinese-specific adult MPPGL data. The modeling Scenarios A and B provided similar predictions for theophylline pharmacokinetics in young Chinese adults across different age groups, while Scenario B provided the most accurate prediction for theophylline pharmacokinetics in elderly Chinese adults. However, the use of a stratified value of CYP1A2 content derived from a Han Chinese cohort with a small sample size instead of the pooled value of all Chinese cohorts involved regardless of Chinese sub-ethnicity resulted in inadequate prediction of CYP1A2-mediated pharmacokinetics in terms of caffeine and theophylline in either young or elderly Chinese subjects. Additionally, the impact of ethnic-specific MPPGL on predictive accuracy of theophylline pharmacokinetics in elderly Chinese subjects is more evident than that of liver weight.

CONCLUSION

We provided quantitative information pertaining to Chinese-specific levels of liver weight and MPPGL, and recalibrated these system parameters for PBPK modeling for young and elderly Chinese subjects. Uncertainty surrounding the Chinese-specific CYP1A2 content has also been clarified. PBPK modeling based on the recalibrated system parameters can accurately simulate CYP1A2-mediated pharmacokinetics in both young and elderly Chinese adults, particularly in elderly individuals.

Predicting the Acute Liver Toxicity of Aflatoxin B1 in Rats and Humans by an In Vitro-In Silico Testing Strategy

SCOPE

High-level exposure to aflatoxin B1 (AFB1) is known to cause acute liver damage and fatality in animals and humans. The intakes actually causing this acute toxicity have so far been estimated based on AFB1 levels in contaminated foods or biomarkers in serum. The aim of the present study is to predict the doses causing acute liver toxicity of AFB1 in rats and humans by an in vitro-in silico testing strategy.

METHODS AND RESULTS

Physiologically based kinetic (PBK) models for AFB1 in rats and humans are developed. The models are used to translate in vitro concentration-response curves for cytotoxicity in primary rat and human hepatocytes to in vivo dose-response curves using reverse dosimetry. From these data, the dose levels at which toxicity would be expected are obtained and compared to toxic dose levels from available rat and human case studies on AFB1 toxicity. The results show that the in vitro-in silico testing strategy can predict dose levels causing acute toxicity of AFB1 in rats and human.

CONCLUSIONS

Quantitative in vitro in vivo extrapolation (QIVIVE) using PBK modeling-based reverse dosimetry can predict AFB1 doses that cause acute liver toxicity in rats and human.

Evaluating Lean Liver Volume as a Potential Scaler for In Vitro-In Vivo Extrapolation of Drug Clearance in Obesity Using the Model Drug Antipyrine

BACKGROUND

In vitro-in vivo extrapolation (IVIVE) of hepatic drug clearance (CL) involves the scaling of hepatic intrinsic clearance (CL_int,uH) by functional liver size, which is approximated by total liver volume (LV) as per the convention. However, in most overweight and obese patients, LV includes abnormal liver fat, which is not thought to contribute to drug elimination, thus overestimating drug CL. Therefore, lean liver volume (LLV) might be a more appropriate scaler of CL_int,uH.

OBJECTIVE

The objective of this work was to assess the application of LLV in CL extrapolation in overweight and obese patients (BMI >25 kg/m2) using a model drug antipyrine.

METHODS

Recently, a model to predict LLV from patient sex, weight, and height was developed and evaluated. In order to assess the LLV model's use in IVIVE, a correlation-based analysis was conducted using antipyrine as an example drug.

RESULTS

In the overweight group (BMI >25 kg/m2), LLV could describe 36% of the variation in antipyrine CL (R² = 0.36), which was >2-fold higher than that was explained by LV (R² = 0.17). In the normal-weight group (BMI ≤25 kg/m2), the coefficients of determination were 58% (R² = 0.58) and 43% (R²= 0.43) for LLV and LV, respectively.

CONCLUSION

The analysis indicates that LLV is potentially a more appropriate descriptor of functional liver size than LV, particularly in overweight individuals. Therefore, LLV has a potential application in IVIVE of CL in obesity.

In vitro-in vivo extrapolation of metabolic clearance using human liver microsomes: factors showing variability and their normalization

In vitro-in vivo extrapolation (IVIVE) using human liver microsomes has been widely used to predict metabolic clearance, but some of the factors used in the process of prediction show variability for the same compound: notably, microsomal intrinsic clearance values corrected by the unbound fraction (CL_{int, u}), physiological parameters used for scale-up, and the source of in vivo clearance data.The purpose of this study was to assess the correlation between in vitro and in vivo CL_int with a focus on factors showing variability using four cytochrome P450 (CYP)3A substrates.We surveyed in vivo clearance values in literature and also determined the microsomal CL_{int, u} values. A scaling factor (SF_direct) was defined as in vivo CL_int divided by the microsomal CL_{int, u}, which ranged from 1190 to 2310 (mg protein per kg body weight). The application of a mean SF_direct of 1600 (mg protein per kg body weight) and further normalization by the microsomal CL_{int, u} values of midazolam, the most commonly used substrate, resulted in improved prediction accuracy for CL_{int, u} values from various microsomal batches.The results suggest the normalization of variability might be useful for predicting the in vivo CL_int.

A novel mass spectrometry method for the absolute quantification of several cytochrome P450 and uridine 5'-diphospho-glucuronosyltransferase enzymes in the human liver

Cytochrome P450 (CYP450) and 5'-diphosphate glucuronosyltransferases (UGT) are the two major families of drug-metabolizing enzymes in the human liver microsome (HLM). As a result of their frequent abundance fluctuation among populations, the accurate quantification of these enzymes in different individuals is important for designing patient-specific dosage regimens in the framework of precision medicine. The preparation and quantification of internal standards is an essential step for the quantitative analysis of enzymes. However, the commonly employed stable isotope labeling-based strategy (QconCAT) suffers from requiring very expensive isotopic reagents, tedious experimental procedures, and long labeling times. Furthermore, arginine-to-proline conversion during metabolic isotopic labeling compromises the quantification accuracy. Therefore, we present a new strategy that replaces stable isotope-labeled amino acids with lanthanide labeling for the preparation and quantification of QconCAT internal standard peptides, which leads to a threefold reduction in the reagent costs and a fivefold reduction in the time consumed. The absolute amount of trypsin-digested QconCAT peptides can be obtained by lanthanide labeling and inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis with a high quantification accuracy (%RE < 20%). By taking advantage of the highly selective and facile ICP-OES procedure and multiplexed large-scale absolute target protein quantification using biological mass spectrometry, this strategy was successfully used for the absolute quantification of drug-metabolizing enzymes. We obtained good linearity (correlation coefficient > 0.95) over concentrations spanning 2.5 orders of magnitude with improved sensitivity (limit of quantification = 2 fmol) in nine HLM samples, indicating the potential of this method for large-scale absolute target protein quantification in clinical samples. Graphical abstract.

Metabolic stability and its role in the discovery of new chemical entities

Determination of metabolic profiles of new chemical entities is a key step in the process of drug discovery, since it influences pharmacokinetic characteristics of therapeutic compounds. One of the main challenges of medicinal chemistry is not only to design compounds demonstrating beneficial activity, but also molecules exhibiting favourable pharmacokinetic parameters. Chemical compounds can be divided into those which are metabolized relatively fast and those which undergo slow biotransformation. Rapid biotransformation reduces exposure to the maternal compound and may lead to the generation of active, non-active or toxic metabolites. In contrast, high metabolic stability may promote interactions between drugs and lead to parent compound toxicity. In the present paper, issues of compound metabolic stability will be discussed, with special emphasis on its significance, in vitro metabolic stability testing, dilemmas regarding in vitro-in vivo extrapolation of the results and some aspects relating to different preclinical species used in in vitro metabolic stability assessment of compounds.

Use of high-throughput enzyme-based assay with xenobiotic metabolic capability to evaluate the inhibition of acetylcholinesterase activity by organophosphorous pesticides

The inhibition of acetylcholinesterase (AChE) has pharmaceutical applications as well as potential neurotoxic effects. The in vivo metabolites of some chemicals including organophosphorus pesticides can become more potent AChE inhibitors compared to their parental compounds. To account for the effects of biotransformation, we have developed and characterized a high-throughput screening method for identifying AChE inhibitors that become active or more potent following xenobiotic metabolism. In this study, an enzyme-based assay was developed in 1536-well plates using recombinant human AChE combined with human or rat liver microsomes. The AChE activity was measured by two methods with different readouts: colorimetric and fluorescent. The assay exhibited exceptional performance characteristics including large assay signal window, low well-to-well variability and high reproducibility. The performance of the assays with microsomes was characterized by testing a group of known AChE inhibitors including parent compounds and their metabolites. Large potency differences between the parent compounds and the metabolites were observed in the assay with microsome addition. Both assay readouts were required for maximal sensitivity. These results demonstrate that this platform is a promising method to profile large numbers of chemicals that require metabolic activation for inhibiting AChE activity.

Intraindividual Variation and Correlation of Cytochrome P450 Activities in Human Liver Microsomes

We systematically studied and explored intraindividual variation and correlation in the activities of cytochrome P450 (CYP) using 105 normal liver samples. The intraindividual percentage coefficients of variation of relative K_m, V_max, and CL_int were 45.9% (18.3-140%), 44.0% (16.8-127%), and 52.0% (24.2-134%). Overall values of relative K_m, V_max, and CL_int for 10 CYPs were sorted. The order, from highest to lowest, was CYP2D6, 3A4/5, 2C19, 2C9, 2B6, 1A2, 2A6, 2C8, and 2E1 for K_m; CYP3A4/5, 2C19, 2D6, 2C8, 2E1, 2B6, 1A2, 2A6, and 2C9 for V_max; and CYP2D6, 2B6, 3A4/5, 2C19, 2C9, 1A2, 2E1, 2C8, and 2A6 for CL_int. CYP2A6*4, 2B6 785A>G, and 2D6 100C>T contributed to intraindividual variation of CYP activities. The correlations and similarities among 10 CYP activities were analyzed, and it was found that the highest correlation and similarity for V_max, K_m, and CL_int occurred between CYP2C9 and 2C8, CYP2C9 and 1A2, and CYP2C9 and 2C8, respectively. In conclusion, CYP activities exhibit considerable intraindividual variation, with some notable correlations, which might be helpful to comprehensively understand the internal connection among CYP activities and to guide the rational use of drugs.

A Standardized Collagen-Based Scaffold Improves Human Hepatocyte Shipment and Allows Metabolic Studies over 10 Days

Due to pronounced species differences, hepatotoxicity of new drugs often cannot be detected in animal studies. Alternatively, human hepatocytes could be used, but there are some limitations. The cells are not always available on demand or in sufficient amounts, so far there has been only limited success to allow the transport of freshly isolated hepatocytes without massive loss of function or their cultivation for a long time. Since it is well accepted that the cultivation of hepatocytes in 3D is related to an improved function, we here tested the Optimaix-3D Scaffold from Matricel for the transport and cultivation of hepatocytes. After characterization of the scaffold, we shipped cells on the scaffold and/or cultivated them over 10 days. With the evaluation of hepatocyte functions such as urea production, albumin synthesis, and CYP activity, we showed that the metabolic activity of the cells on the scaffold remained nearly constant over the culture time whereas a significant decrease in metabolic activity occurred in 2D cultures. In addition, we demonstrated that significantly fewer cells were lost during transport. In summary, the collagen-based scaffold allows the transport and cultivation of hepatocytes without loss of function over 10 days.

Systems, variation, individuality and plant hormones

Inter-individual variation in plants and particularly in hormone content, figures strongly in evolution and behaviour. Homo sapiens and Arabidopsis exhibit similar and substantial phenotypic and molecular variation. Whereas there is a very substantial degree of hormone variation in mankind, reports of inter-individual variation in plant hormone content are virtually absent but are likely to be as large if not larger than that in mankind. Reasons for this absence are discussed. Using an example of inter-individual variation in ethylene content in ripening, the article shows how biological time is compressed by hormones. It further resolves an old issue of very wide hormone dose response that result directly from negative regulation in hormone (and light) transduction. Negative regulation is used because of inter-individual variability in hormone synthesis, receptors and ancillary proteins, a consequence of substantial genomic and environmental variation. Somatic mosaics have been reported for several plant tissues and these too contribute to tissue variation and wide variation in hormone response. The article concludes by examining what variation exists in gravitropic responses. There are multiple sensing systems of gravity vectors and multiple routes towards curvature. These are an aspect of the need for reliability in both inter-individual variation and unpredictable environments. Plant hormone inter-individuality is a new area for research and is likely to change appreciation of the mechanisms that underpin individual behaviour.

The use of PBPK modeling across the pediatric age range using propofol as a case

The project SAFEPEDRUG aims to provide guidelines for drug research in children, based on bottom-up and top-down approaches. Propofol, one of the studied model compounds, was selected because it is extensively metabolized in liver and kidney, with an important role for the glucuronidation pathway. Besides, being a lipophilic molecule, it is distributed into fat tissues, from where it redistributes into the systemic circulation. In the past, both bottom-up (Physiologically based pharmacokinetic, PBPK) and top-down approaches (population pharmacokinetic, popPK) were applied to describe its pharmacokinetics (PK). In this work, a combination of the two was used to check their performance to describe PK in children and neonates (both term and preterm) using propofol as a case compound. First, in vitro data was generated in human liver microsomes and recombinant enzymes and used to develop an adult PBPK model in Simcyp^®. Activity adjustment factors (AAFs) were calculated to account for differences between in vitro and in vivo enzyme activity. Clinical data were analyzed using a 3-compartment model in NONMEM. These data were used to construct a retrograde PBPK model and for qualification of the PBPK models. Once an accurate in vivo clearance was obtained accounting for the contribution of the different metabolic pathways, the resulting PBPK models were challenged with new data for qualification. After that, the constructed adult PPBK model for propofol was extrapolated to the pediatric population. Both the default built-in and in vivo derived ontogeny functions were used to do so. The models were qualified by comparing their predicted PK parameters to published values, and by comparison of predicted concentration-time profiles to available clinical data. Clearance values were predicted well, especially when compared with values obtained from trials where long-term sampling was applied, whereas volume of distribution was lower compared to the most common popPK model predictions. Concentration-time profiles were predicted well up until and including the preterm neonatal population. In this work, it was thus shown that PBPK can be used to predict the PK up to and including the preterm neonatal population without the use of pediatric in vivo data. This work adds weight to the need for further development of PBPK models, especially regarding distribution modeling and the use of in vivo derived ontogeny functions.