The Segregated Intestinal Flow Model (SFM) for Drug Absorption and Drug Metabolism: Implications on Intestinal and Liver Metabolism and Drug-Drug Interactions

Elucidating Contributions of Drug Transporters/Enzyme to Nonlinear Pharmacokinetics of Grazoprevir by PBPK Modeling With a Cluster Gauss-Newton Method

Grazoprevir (GZR), a direct-acting agent for hepatitis C virus, is recognized as a substrate for organic anion transporting polypeptide 1B (OATP1B), cytochrome P450 3A (CYP3A), and P-glycoprotein (P-gp). The objective of the present study was to elucidate the contribution of these molecules to the nonlinear pharmacokinetics of GZR using a physiologically based pharmacokinetic (PBPK) model. Utilizing plasma concentration-time profiles of GZR derived from reported dose-escalation (50-800 mg) clinical studies and cumulative excretion data, around 10 parameters, including Michaelis constants (Km) for OATP1B, CYP3A, and P-gp, were estimated via a cluster Gauss-Newton method (CGNM). Parameter combinations that could reproduce the clinical data of GZR were obtained; however, discrepancies were noted between the in vivo estimated Km and the corresponding in vitro Km. Next, by incorporating the in vitro Km values into our PBPK-CGNM analyses utilizing a penalized parameter method, newly obtained parameter combinations appropriately reflected both the in vivo and in vitro observations. Particularly regarding OATP1B, while saturation of uptake was not clearly observed in the in vitro experiments without human serum albumin (HSA), Km values capable of explaining in vivo saturation were obtained under physiological HSA concentrations. By estimating the extent of saturation for each molecule in the liver and intestine and conducting sensitivity analyses of the Km values, it was inferred that OATP1B3 contributed the most to the nonlinearity of plasma GZR concentrations, followed by P-gp. In conclusion, the PBPK-CGNM, supplemented by penalized in vitro parameters, was shown to be effective for analyzing complex pharmacokinetics involving drug transporters and enzymes.

Evaluation of BCRP-Related DDIs Between Methotrexate and Cyclosporin A Using Physiologically Based Pharmacokinetic Modelling

BACKGROUND AND OBJECTIVE

This study provides a physiologically based pharmacokinetic (PBPK) model-based analysis of the potential drug-drug interaction (DDI) between cyclosporin A (CsA), a breast cancer resistance protein transporter (BCRP) inhibitor, and methotrexate (MTX), a putative BCRP substrate.

METHODS

PBPK models for CsA and MTX were built using open-source tools and published data for both model building and for model verification and validation. The MTX and CsA PBPK models were evaluated for their application in simulating BCRP-related DDIs. A qualification of an introduced empirical uniform in vitro scaling factor of Ki values for transporter inhibition by CsA was conducted by using a previously developed model of rosuvastatin (sensitive index BCRP substrate), and assessing if corresponding DDI ratios were well captured.

RESULTS

Within the simulated DDI scenarios for MTX in the presence of CsA, the developed models could capture the observed changes in PK parameters as changes in the area under the curve ratios (area under the curve during DDI/area under the curve control) of 1.30 versus 1.31 observed and the DDI peak plasma concentration ratios (peak plasma concentration during DDI/peak plasma concentration control) of 1.07 versus 1.28 observed. The originally reported in vitro Ki values of CsA were scaled with the uniform qualified scaling factor for their use in the in vivo DDI simulations to correct for the low intracellular unbound fraction of the CsA effector concentration. The resulting predicted versus observed ratios of peak plasma concentration and area under the curve DDI ratios with MTX were 0.82 and 0.99, respectively, indicating adequate model accuracy and choice of a scaling factor to capture the observed DDI.

CONCLUSIONS

All models have been comprehensively documented and made publicly available as tools to support the drug development and clinical research community and further community-driven model development.

Physiologically based pharmacokinetic modeling of small molecules: How much progress have we made?

Physiologically based pharmacokinetic (PBPK) models of small molecules have become mainstream in drug development and in academic research. The use of PBPK models is continuously expanding, with the majority of work now focusing on predictions of drug-drug interactions, drug-disease interactions, and changes in drug disposition across lifespan. Recently, publications that use PBPK modeling to predict drug disposition during pregnancy and in organ impairment have increased reflecting the advances in incorporating diverse physiologic changes into the models. Because of the expanding computational power and diversity of modeling platforms available, the complexity of PBPK models has also increased. Academic efforts have provided clear advances in better capturing human physiology in PBPK models and incorporating more complex mathematical concepts into PBPK models. Examples of such advances include the segregated gut model with a series of gut compartments allowing modeling of physiologic blood flow distribution within an organ and zonation of metabolic enzymes and series compartment liver models allowing simulations of hepatic clearance for high extraction drugs. Despite these advances in academic research, the progress in assessing model quality and defining model acceptance criteria based on the intended use of the models has not kept pace. This Minireview suggests that awareness of the need for predefined criteria for model acceptance has increased, but many manuscripts still lack description of scientific justification and/or rationale for chosen acceptance criteria. As artificial intelligence and machine learning approaches become more broadly accepted, these tools offer promise for development of comprehensive assessment for existing observed data and analysis of model performance. SIGNIFICANCE STATEMENT: Physiologically based pharmacokinetic (PBPK) modeling has become a mainstream application in academic literature and is broadly used for predictions, analysis, and evaluation of pharmacokinetic data. Significant progress has been made in developing advanced PBPK models that better capture human physiology, but oftentimes sufficient justification for the chosen model acceptance criterion and model structure is still missing. This Minireview provides a summary of the current landscape of PBPK applications used and highlights the need for advancing PBPK modeling science and training in academia.

Individualized tacrolimus therapy: Insights from CYP3A5 polymorphisms and intestinal metabolism

CYP3A4 and CYP3A5 are the most abundant and important enzymes of the CYP3A subfamily, distributed in the liver, intestinal mucosa and kidney, and involved in tacrolimus metabolism. Here, we report a case of tacrolimus dosage refractoriness due to a genetic polymorphism of CYP3A5.

Advances in Modeling Approaches for Oral Drug Delivery: Artificial Intelligence, Physiologically-Based Pharmacokinetics, and First-Principles Models

Oral drug absorption is the primary route for drug administration. However, this process hinges on multiple factors, including the drug's physicochemical properties, formulation characteristics, and gastrointestinal physiology. Given its intricacy and the exorbitant costs associated with experimentation, the trial-and-error method proves prohibitively expensive. Theoretical models have emerged as a cost-effective alternative by assimilating data from diverse experiments and theoretical considerations. These models fall into three categories: (i) data-driven models, encompassing classical pharmacokinetics, quantitative-structure models (QSAR), and machine/deep learning; (ii) mechanism-based models, which include quasi-equilibrium, steady-state, and physiologically-based pharmacokinetics models; and (iii) first principles models, including molecular dynamics and continuum models. This review provides an overview of recent modeling endeavors across these categories while evaluating their respective advantages and limitations. Additionally, a primer on partial differential equations and their numerical solutions is included in the appendix, recognizing their utility in modeling physiological systems despite their mathematical complexity limiting widespread application in this field.

Quantitative analysis of gastrointestinal fluid absorption and secretion to estimate luminal fluid dynamics in rats

The drug absorption profile is dependent on the luminal drug concentration, which in turn is influenced by the gastrointestinal (GI) fluid dynamics. In the present study, therefore, we aimed to examine the luminal fluid dynamics by kinetically analyzing fluid absorption and secretion along the GI tract in rats using the in situ closed-loop technique with non-absorbable fluorescein isothiocyanate-dextran 4000 (FD-4) and tritium water labeling ([3H]water) under different osmotic conditions. We found that the luminal fluid volume in the jejunum and ileum, but not the colon, gradually decreased and reached a steady state. In contrast, [3H]water almost completely disappeared in all intestinal regions. Kinetic analysis revealed the following rank order for the rate constant of fluid secretion: jejunum > ileum > colon, whereas a negligible regional difference was observed in the rate constant of fluid absorption. Fluid secretion under an isosmotic condition (300 mOsm/kg) was higher than that at 0 mOsm/kg in all intestinal regions, though no significant changes in fluid absorption were observed. Thus, the fluid secretion process appears to be the major determinant of the regional differences in GI fluid dynamics. Our findings indicate that the luminal fluid volume is altered as a result of water ingestion, absorption, and secretion, and finally reaches an apparent steady state, which is regulated mainly by the process of fluid secretion.

Identification of histological threshold concepts in health sciences curricula: Students' perception

Students' metacognitive skills and perceptions are considered important variables for high-quality learning. In this study, students' perceptions were used to identify histological threshold concepts (integrative, irreversible, transformative, and troublesome) in three health sciences curricula. A specific questionnaire was developed and validated to characterize students' perceptions of histological threshold concepts. A sample of 410 undergraduate students enrolled in the dentistry, medicine, and pharmacy degree programs participated in the study. Concepts assessed in the study were clustered to ten categories (factors) by exploratory and confirmatory factor analysis. Concepts linked to tissue organization and tissue functional states received the highest scores from students in all degree programs, suggesting that the process of learning histology requires the integration of both static concepts related to the constituent elements of tissues and dynamic concepts such as stem cells as a tissue renewal substrate, or the euplasic, proplasic and retroplasic states of tissues. The complexity of integrating static and dynamic concepts may pose a challenging barrier to the comprehension of histology. In addition, several differences were detected among the students in different degree programs. Dentistry students more often perceived morphostructural concepts as threshold concepts, whereas medical students highlighted concepts related to two-dimensional microscopic identification. Lastly, pharmacy students identified concepts related to tissue general activity as critical for the comprehension and learning of histology. The identification of threshold concepts through students' perceptions is potentially useful to improve the teaching and learning process in health sciences curricula.

Predicting transporter mediated drug-drug interactions via static and dynamic physiologically based pharmacokinetic modeling: A comprehensive insight on where we are now and the way forward

The greater utilization and acceptance of physiologically-based pharmacokinetic (PBPK) modeling to evaluate the potential metabolic drug-drug interactions is evident by the plethora of literature, guidance's, and regulatory dossiers available in the literature. In contrast, it is not widely used to predict transporter-mediated DDI (tDDI). This is attributed to the unavailability of accurate transporter tissue expression levels, the absence of accurate in vitro to in vivo extrapolations (IVIVE), enzyme-transporter interplay, and a lack of specific probe substrates. Additionally, poor understanding of the inhibition/induction mechanisms coupled with the inability to determine unbound concentrations at the interaction site made tDDI assessment challenging. Despite these challenges, continuous improvements in IVIVE approaches enabled accurate tDDI predictions. Furthermore, the necessity of extrapolating tDDI's to special (pediatrics, pregnant, geriatrics) and diseased (renal, hepatic impaired) populations is gaining impetus and is encouraged by regulatory authorities. This review aims to visit the current state-of-the-art and summarizes contemporary knowledge on tDDI predictions. The current understanding and ability of static and dynamic PBPK models to predict tDDI are portrayed in detail. Peer-reviewed transporter abundance data in special and diseased populations from recent publications were compiled, enabling direct input into modeling tools for accurate tDDI predictions. A compilation of regulatory guidance's for tDDI's assessment and success stories from regulatory submissions are presented. Future perspectives and challenges of predicting tDDI in terms of in vitro system considerations, endogenous biomarkers, the use of empirical scaling factors, enzyme-transporter interplay, and acceptance criteria for model validation to meet the regulatory expectations were discussed.

Study on the antithrombotic effect and physiological mechanism of okanin

The objectives of this study were to investigate the antithrombotic effect and physiological mechanism of okanin, a flavonoid monomer in Coreopsis tinctoria Nutt. The antithrombotic effects of okanin were determined by the anticoagulant activity test in vitro and in vivo, the venous thrombosis and arterial thrombosis test in rats. To study the antithrombotic physiological mechanisms of okanin, UV spectrophotometer and enzyme-linked immunosorbent assay (ELISA) were used to determine the effects of three concentrations of okanin on the contents of 6-keto-prostaglandin F1α (6-Keto-PGF1α), thromboxane B2 (TXB2), endothelin-1 (ET-1), antithrombin III (AT-Ⅲ), protein C (PC) and von willebrand factor (vWF) in the plasma of rats with arterial thrombosis; ELISA was used to detect the effects of okanin on the contents of plasminogen (PLG), tissue plasminogen activator (t-PA) and type-1 plasminogen activator inhibitor (PAI-1) in the plasma of mice and Chinese white rabbits. The results showed that okanin could prolong the coagulation time in vitro and in vivo of animals (P < 0.01 in the high dose group) and the activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT) of human venous blood (ATPP of medium dose group P < 0.01; PT, TT P < 0.05. P < 0.01 in the high dose group); inhibit the maximum platelet aggregation rate of rabbits (P < 0.05 in the low dose group; P < 0.01 in the medium and high dose groups), decrease the dry and wet weight of venous thrombosis and the wet weight of common carotid artery thrombosis in rats (low dose group, P < 0.05; medium and high dose groups, P < 0.01); increase the levels of 6-Keto-PGF1α, AT-Ⅲ, PLG and t-PA in animal plasma; decrease the levels of TXB2, ET-1, vWF and PAI-1 in animal plasma. It is concluded that okanin can significantly inhibit thrombosis, and its physiological mechanisms were related to affecting the activation of related coagulation factors in endogenous and exogenous coagulation pathways, affecting the physiological characteristics of platelets, repairing damaged vascular endothelial cells and enhancing the activity of the fibrinolytic system.

Tissue Drug Concentration

Blood flow enables the delivery of oxygen and nutrients to the different tissues of the human body. Drugs follow the same route as oxygen and nutrients; thus, drug concentrations in tissues are highly dependent on the blood flow fraction delivered to each of these tissues. Although the free drug concentration in blood is considered to correlate with pharmacodynamics, the pharmacodynamics of a drug is actually primarily commanded by the concentrations of drug in the aqueous spaces of bodily tissues. However, the concentrations of drug are not homogeneous throughout the tissues, and they rarely reflect the free drug concentration in the blood. This heterogeneity is due to differences in the blood flow fraction delivered to the tissues and also due to membrane transporters, efflux pumps, and metabolic enzymes. The rate of drug elimination from the body (systemic elimination) depends more on the driving force of drug elimination than on the free concentration of drug at the site from which the drug is being eliminated. In fact, the actual free drug concentration in the tissues results from the balance between the input and output rates. In the present paper, we develop a theoretical concept regarding solute partition between intravascular and extravascular spaces; discuss experimental research on aqueous/non-aqueous solute partitioning and clinical research on microdialysis; and present hypotheses to predict in-vivo elimination using parameters of in-vitro metabolism.

Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation

The gastrointestinal tract (GIT) can be broadly divided into several regions: the stomach, the small intestine (which is subdivided to duodenum, jejunum, and ileum), and the colon. The conditions and environment in each of these segments, and even within the segment, are dependent on many factors, e.g., the surrounding pH, fluid composition, transporters expression, metabolic enzymes activity, tight junction resistance, different morphology along the GIT, variable intestinal mucosal cell differentiation, changes in drug concentration (in cases of carrier-mediated transport), thickness and types of mucus, and resident microflora. Each of these variables, alone or in combination with others, can fundamentally alter the solubility/dissolution, the intestinal permeability, and the overall absorption of various drugs. This is the underlying mechanistic basis of regional-dependent intestinal drug absorption, which has led to many attempts to deliver drugs to specific regions throughout the GIT, aiming to optimize drug absorption, bioavailability, pharmacokinetics, and/or pharmacodynamics. In this Editorial we provide an overview of the Special Issue "Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation". The objective of this Special Issue is to highlight the current progress and to provide an overview of the latest developments in the field of regional-dependent intestinal drug absorption and delivery, as well as pointing out the unmet needs of the field.

Two Faces of Milk Proteins Peptides with Both Allergenic and Multidimensional Health Beneficial Impact- Integrated In Vitro/In Silico Approach

The main food-origin antigens that the infant's body is in contact with are cow's milk proteins (CMP). Still, CMP are one of the main sources of beneficial biologically active peptides that play a role in treatment of non-communicable diseases. Safe methods to quickly predict the sensitizing potential of food proteins among their range of health-promoting properties are essential. The aim of study was to adapt an integrated approach combining several in silico (IS) studies and in vitro (IV) assays to screen the multifunctionality of CMP-derived peptides. Major histocompatability complex type II MHC II-binders, interleukin-4 and -10 inducers, interferon γ -inducers and immunobioactivity tools were used to predict the peptide-power of inducing allergies or tolerance. A comparison of the peptide profiless revealed the presence of one identical and one overlapping sequence in IS and IV hydrolysate. By IS analysis, four of 24 peptides were found to have high affinity and stimulate IL-4 expression, and by IV, one of seven peptides had this potential (Bos d9 peptide DIPNPIGSENSEK (195-208)). Three IV peptides may induce IL-10 expression. The IV/IS assessment seems promising agents for peptides' potential determination dedicated only to preliminary screening of peptides. The IV verification is still crucial in further steps of studies.

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.