Differentiation of absorption and first-pass gut and hepatic metabolism in humans: studies with cyclosporine

Therapeutic potential and limitation of condensed and hydrolyzed tannins in Parkinson's disease

Parkinson's disease is a complex neurodegenerative disorder characterized by neuroinflammation, mitochondrial dysfunction, and the accumulation of misfolded proteins such as α-synuclein. This review explores the therapeutic potential of tannins, particularly proanthocyanidins and hydrolyzable tannins from grape seeds, in alleviating Parkinson's disease pathology. Condensed tannins exhibit significant antioxidant properties, can cross the blood-brain barrier, reduce oxidative stress, upregulate antioxidant proteins, and prevent neuronal apoptosis. Hydrolyzable tannins, through their unique chemical structure, further help reduce neuroinflammation and improve mitochondrial function. Both types of tannins can modulate inflammatory responses and enhance mitochondrial integrity, addressing key aspects of Parkinson's disease pathogenesis. Tannins possess excellent neuroprotective effects, representing a promising therapeutic approach. However, due to their chemical nature and structural characteristics, the bioavailability of tannins in the human body remains low. Current methods to enhance their bioavailability are limited. Further exploration is needed to improve their bioavailability and strengthen their potential clinical applications. Based on this, new Parkinson's disease treatment strategies can be developed, warranting in-depth research and clinical validation.

Enhancing Drug Solubility, Bioavailability, and Targeted Therapeutic Applications through Magnetic Nanoparticles

Biological variability poses significant challenges in the development of effective therapeutics, particularly when it comes to drug solubility and bioavailability. Poor solubility across varying physiological conditions often leads to reduced absorption and inconsistent therapeutic outcomes. This review examines how nanotechnology, especially through the use of nanomaterials and magnetic nanoparticles, offers innovative solutions to enhance drug solubility and bioavailability. This comprehensive review focuses on recent advancements and approaches in nanotechnology. We highlight both the successes and remaining challenges in this field, emphasizing the role of continued innovation. Future research should prioritize developing universal therapeutic solutions, conducting interdisciplinary research, and leveraging personalized nanomedicine to address biological variability.

An Enhanced Dissolving Cyclosporin-A Inhalable Powder Efficiently Reduces SARS-CoV-2 Infection In Vitro

This work illustrates the development of a dry inhalation powder of cyclosporine-A for the prevention of rejection after lung transplantation and for the treatment of COVID-19. The influence of excipients on the spray-dried powder's critical quality attributes was explored. The best-performing powder in terms of dissolution time and respirability was obtained starting from a concentration of ethanol of 45% (v/v) in the feedstock solution and 20% (w/w) of mannitol. This powder showed a faster dissolution profile (Weibull dissolution time of 59.5 min) than the poorly soluble raw material (169.0 min). The powder exhibited a fine particle fraction of 66.5% and an MMAD of 2.97 µm. The inhalable powder, when tested on A549 and THP-1, did not show cytotoxic effects up to a concentration of 10 µg/mL. Furthermore, the CsA inhalation powder showed efficiency in reducing IL-6 when tested on A549/THP-1 co-culture. A reduction in the replication of SARS-CoV-2 on Vero E6 cells was observed when the CsA powder was tested adopting the post-infection or simultaneous treatment. This formulation could represent a therapeutic strategy for the prevention of lung rejection, but is also a viable approach for the inhibition of SARS-CoV-2 replication and the COVID-19 pulmonary inflammatory process.

Optimized self-microemulsifying drug delivery system improves the oral bioavailability and brain delivery of coenzyme Q10

Our study aimed to develop a self-microemulsifying drug delivery system for the poorly aqueous-soluble drug Coenzyme Q₁₀, to improve the dissolution and the oral bioavailability. Excipients were selected based on their Coenzyme Q₁₀ solubility, and their concentrations were set for the optimization of the microemulsion by using a D-optimal mixture design to achieve a minimum droplet size and a maximum solubility of Coenzyme Q₁₀ within 15 min. The optimized formulation was composed of an oil (omega-3; 38.55%), a co-surfactant (Lauroglycol® 90; 31.42%), and a surfactant (Gelucire^® 44/14; 30%) and exhibited a mean droplet size of 237.6 ± 5.8 nm and a drug solubilization (at 15 min) of 16 ± 2.48%. The drug dissolution of the optimized formulation conducted over 8 h in phosphate buffer medium (pH 6.8) was significantly higher when compared to that of the Coenzyme Q₁₀ suspension. A pharmacokinetic study in rats revealed a 4.5-fold and a 4.1-fold increase in the area under curve and the peak plasma concentration values generated by the optimized formulation respectively, as compared to the Coenzyme Q₁₀ suspension. A Coenzyme Q₁₀ brain distribution study revealed a higher Coenzyme Q₁₀ distribution in the brains of rats treated with the optimized formulation than the Coenzyme Q₁₀ suspension. Coenzyme Q₁₀-loaded self microemulsifying drug delivery system was successfully formulated and optimized by a response surface methodology based on a D-optimal mixture design and could be used as a delivery vehicle for the enhancement of the oral bioavailability and brain distribution of poorly soluble drugs such as Coenzyme Q₁₀.

Importance of Gastric Secretion and the Rapid Gastric Emptying of Ingested Water along the Lesser Curvature ("Magenstraße") in Predicting the In Vivo Performance of Liquid Oral Dosage Forms in the Fed State Using a Modeling and Simulation

The objective of the present study was to develop an in silico model of the stomach for predicting oral drug absorption in fed humans. We focused on a model capable of simulating dynamic fluid volume changes and included a simulated Magenstraße "stomach road," a route along the lesser curvature that often carries fluids rapidly to assess the gastric emptying of drugs. Two types of model liquid drug formulations, liquid-filled soft gelatin capsules (enzalutamide, cyclosporine, and nifedipine) and oral solutions (levofloxacin and fenfluramine), were used. An in silico model was assembled, and simulations were performed using Stella Professional software. The secretion rate of the gastric juice induced by food ingestion was assessed along with the gastric emptying of the ingested water via the Magenstraße in the fed state. The model for the fed state successfully described the in vivo performance of the model drug formulations. These results clearly indicate the importance of including gastric secretion and the kinetics of Magenstraße when predicting the in vivo performance of dosage forms using an in silico modeling and simulation of fed humans. This simulation model should be further optimized to allow for the different physiological mechanisms following the ingestion of different types of meals, as well as modifications for interindividual and intraindividual variabilities in gastrointestinal physiology in the fed state in the future.

Best practices in current models mimicking drug permeability in the gastrointestinal tract - an UNGAP review

The absorption of orally administered drug products is a complex, dynamic process, dependent on a range of biopharmaceutical properties; notably the aqueous solubility of a molecule, stability within the gastrointestinal tract (GIT) and permeability. From a regulatory perspective, the concept of high intestinal permeability is intrinsically linked to the fraction of the oral dose absorbed. The relationship between permeability and the extent of absorption means that experimental models of permeability have regularly been used as a surrogate measure to estimate the fraction absorbed. Accurate assessment of a molecule's intestinal permeability is of critical importance during the pharmaceutical development process of oral drug products, and the current review provides a critique of in vivo, in vitro and ex vivo approaches. The usefulness of in silico models to predict drug permeability is also discussed and an overview of solvent systems used in permeability assessments is provided. Studies of drug absorption in humans are an indirect indicator of intestinal permeability, but in vitro and ex vivo tools provide initial screening approaches are important tools for direct assessment of permeability in drug development. Continued refinement of the accuracy of in silico approaches and their validation with human in vivo data will facilitate more efficient characterisation of permeability earlier in the drug development process and will provide useful inputs for integrated, end-to-end absorption modelling.

Comparing Predictions of a PBPK Model for Cyclosporine With Drug Levels From Therapeutic Drug Monitoring

This study compared simulations of a physiologically based pharmacokinetic (PBPK) model implemented for cyclosporine with drug levels from therapeutic drug monitoring to evaluate the predictive performance of a PBPK model in a clinical population. Based on a literature search model parameters were determined. After calibrating the model using the pharmacokinetic profiles of healthy volunteers, 356 cyclosporine trough levels of 32 renal transplant outpatients were predicted based on their biometric parameters. Model performance was assessed by calculating absolute and relative deviations of predicted and observed trough levels. The median absolute deviation was 6 ng/ml (interquartile range: 30 to 31 ng/ml, minimum = -379 ng/ml, maximum = 139 ng/ml). 86% of predicted cyclosporine trough levels deviated less than twofold from observed values. The high intra-individual variability of observed cyclosporine levels was not fully covered by the PBPK model. Perspectively, consideration of clinical and additional patient-related factors may improve the model's performance. In summary, the current study has shown that PBPK modeling may offer valuable contributions for pharmacokinetic research in clinical drug therapy.

Current challenges and future perspectives in oral absorption research: An opinion of the UNGAP network

Although oral drug delivery is the preferred administration route and has been used for centuries, modern drug discovery and development pipelines challenge conventional formulation approaches and highlight the insufficient mechanistic understanding of processes critical to oral drug absorption. This review presents the opinion of UNGAP scientists on four key themes across the oral absorption landscape: (1) specific patient populations, (2) regional differences in the gastrointestinal tract, (3) advanced formulations and (4) food-drug interactions. The differences of oral absorption in pediatric and geriatric populations, the specific issues in colonic absorption, the formulation approaches for poorly water-soluble (small molecules) and poorly permeable (peptides, RNA etc.) drugs, as well as the vast realm of food effects, are some of the topics discussed in detail. The identified controversies and gaps in the current understanding of gastrointestinal absorption-related processes are used to create a roadmap for the future of oral drug absorption research.

Drug-Metabolizing Cytochrome P450 Enzymes Have Multifarious Influences on Treatment Outcomes

Drug metabolism is a critical process for the removal of unwanted substances from the body. In humans, approximately 80% of oxidative metabolism and almost 50% of the overall elimination of commonly used drugs can be attributed to one or more of various cytochrome P450 (CYP) enzymes from CYP families 1-3. In addition to the basic metabolic effects for elimination, CYP enzymes in vivo are capable of affecting the treatment outcomes in many cases. Drug-metabolizing CYP enzymes are mainly expressed in the liver and intestine, the two principal drug oxidation and elimination organs, where they can significantly influence the drug action, safety, and bioavailability by mediating phase I metabolism and first-pass metabolism. Furthermore, CYP-mediated local drug metabolism in the sites of action may also have the potential to impact drug response, according to the literature in recent years. This article underlines the ability of CYP enzymes to influence treatment outcomes by discussing CYP-mediated diversified drug metabolism in primary metabolic sites (liver and intestine) and typical action sites (brain and tumors) according to their expression levels and metabolic activity. Moreover, intrinsic and extrinsic factors of personal differential CYP phenotypes that contribute to interindividual variation of treatment outcomes are also reviewed to introduce the multifarious pivotal role of CYP-mediated metabolism and clearance in drug therapy.

Intestinal absorption of BCS class II drugs administered as nanoparticles: A review based on in vivo data from intestinal perfusion models

An established pharmaceutical strategy to increase oral drug absorption of low solubility–high permeability drugs is to create nanoparticles of them. Reducing the size of the solid-state particles increases their dissolution and transport rate across the mucus barrier and the aqueous boundary layer. Suspensions of nanoparticles also sometimes behave differently than those of larger particles in the fed state. This review compares the absorption mechanisms of nano- and larger particles in the lumen at different prandial states, with an emphasis on data derived from in vivo models. Four BSC class II drugs—aprepitant, cyclosporine, danazol and fenofibrate—are discussed in detail based on information from preclinical intestinal perfusion models.

The Critical Role of Passive Permeability in Designing Successful Drugs

Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients.

Lipid Drug Carriers for Cancer Therapeutics: An Insight into Lymphatic Targeting, P-gp, CYP3A4 Modulation and Bioavailability Enhancement

In the treatment of cancer, chemotherapy plays an important role though the efficacy of anti-cancer drug administered orally is limited, due to their poor solubility in physiological medium, inability to cross biological membrane, high Para-glycoprotein (P-gp) mediated drug efflux, and pre-systemic metabolism. These all factors cumulatively reduce drug exposure at the target site leading to multidrug resistance (MDR). Lipid based carriers systems has been explored to overcome solubility and permeability related issues of anti-cancer drugs. The lipid based formulations have also been reported to circumvent the effect of P-gp and CYP3A4. Further long chain triglycerides (LCT) has shown their ability to access Lymphatic route over Medium Chain Triglycerides, as the former has been extensively used for targeting anti-cancer drugs at proliferating cells through lymphatic route. Therefore this review tries to reflect the usefulness of lipid based drug carriers systems (viz. liposome, solid lipid nanoparticle, nano-lipid carriers, self-emulsifying, lipidic pro-drugs) in targeting lymphatic system and overcoming issues related to solubility and permeability of anti-cancer drugs. Moreover, we have also tried to reflect how critically lipid based carriers are important in maximizing therapeutic safety and efficacy of anti-cancer drugs.

Model-Informed Drug Discovery and Development Strategy for the Rapid Development of Anti-Tuberculosis Drug Combinations

The increasing emergence of drug-resistant tuberculosis requires new effective and safe drug regimens. However, drug discovery and development are challenging, lengthy and costly. The framework of model-informed drug discovery and development (MID3) is proposed to be applied throughout the preclinical to clinical phases to provide an informative prediction of drug exposure and efficacy in humans in order to select novel anti-tuberculosis drug combinations. The MID3 includes pharmacokinetic-pharmacodynamic and quantitative systems pharmacology models, machine learning and artificial intelligence, which integrates all the available knowledge related to disease and the compounds. A translational in vitro-in vivo link throughout modeling and simulation is crucial to optimize the selection of regimens with the highest probability of receiving approval from regulatory authorities. In vitro-in vivo correlation (IVIVC) and physiologically-based pharmacokinetic modeling provide powerful tools to predict pharmacokinetic drug-drug interactions based on preclinical information. Mechanistic or semi-mechanistic pharmacokinetic-pharmacodynamic models have been successfully applied to predict the clinical exposure-response profile for anti-tuberculosis drugs using preclinical data. Potential pharmacodynamic drug-drug interactions can be predicted from in vitro data through IVIVC and pharmacokinetic-pharmacodynamic modeling accounting for translational factors. It is essential for academic and industrial drug developers to collaborate across disciplines to realize the huge potential of MID3.

Oral Delivery of Anticancer Agents Using Nanoparticulate Drug Delivery System

Background:

Conventionally, anti-cancer agents were administered through the intravenous route. The major drawbacks associated with the intravenous route of administration are: severe side effects, need of hospitalization, nursing care, and palliative treatment. In order to overcome the drawbacks associated with the intravenous route of administration, oral delivery of anti-cancer agents has gained tremendous interest among the scientific fraternity. Oral delivery of anti-cancer agents principally leads to a reduction in the overall cost of treatment, and aids in improving the quality of life of patients. Bioavailability of drugs and inter-subject variability are the major concerns with oral administration of anti-cancer agents. Factors viz. physicochemical and biological barriers (pre-systemic metabolism and transmembrane efflux of the drug) are accountable for hampering oral bioavailability of anti-cancer agents can be efficiently overcome by employing nanocarrier based drug delivery systems. Oral delivery of anticancer agents by employing these drug delivery systems will not only improve the quality of life of patients but will also provide pharmacoeconomic advantage and lead to a reduction in the overall cost of treatment of life-threatening disease like cancer.

Objective:

This article aims to familiarize the readers with some of the recent advancements in the field of nanobased drug delivery systems for oral delivery of anticancer agents.

Conclusion:

Advancement in the field of nanotechnology-based drug delivery systems has opened up gateways for the delivery of drugs that are difficult to administer orally. Oral delivery of anti-cancer agents by these drug delivery systems will not only improve the quality of life of patients but will also provide pharmacoeconomic advantage and lead to a reduction in the overall cost of treatment of life-threatening disease like cancer.

Microphysiological systems for ADME-related applications: current status and recommendations for system development and characterization

Over the last decade, progress has been made on the development of microphysiological systems (MPS) for absorption, distribution, metabolism, and excretion (ADME) applications. Central to this progress has been proof of concept data generated by academic and industrial institutions followed by broader characterization studies, which provide evidence for scalability and applicability to drug discovery and development. In this review, we describe some of the advances made for specific tissue MPS and outline the desired functionality for such systems, which are likely to make them applicable for practical use in the pharmaceutical industry. Single organ MPS platforms will be valuable for modelling tissue-specific functions. However, dynamic organ crosstalk, especially in the context of disease or toxicity, can only be obtained with the use of inter-linked MPS models which will enable scientists to address questions at the intersection of pharmacokinetics (PK) and efficacy, or PK and toxicity. In the future, successful application of MPS platforms that closely mimic human physiology may ultimately reduce the need for animal models to predict ADME outcomes and decrease the overall risk and cost associated with drug development.

Investigations on hepatic and intestinal drug-metabolizing cytochrome P450 enzymes in wild boar compared to domestic swine

Drug-metabolizing cytochrome P450 (CYP) enzymes are especially important in wild animals as they are directly exposed to environmental pollutants and bioactive molecules of plants. Our main goal was to monitor the activity of certain CYP enzymes in wild boar compared to domestic swine, and to assess various modulatory factors of xenobiotic biotransformation in wild boar. Liver and intestinal mucosa (duodenum, jejunum, ileum, caecum) samples were collected from 49 hunted free-range wild boars and 15 wild boar fetuses; domestic pig samples (n = 40) were gained from a slaughter house. Specific activity of CYP1A2, CYP2C9, and CYP3A4 enzymes was assessed by luminometric assays. The activity of hepatic CYP1A2 and CYP3A4 enzymes was significantly higher in wild boars than in domestic pigs, while CYP2C9-mediated hepatic metabolism was significantly less intense in wild boars than in pigs. Certain modulatory factors (sex, sexual maturation, and season) were also confirmed in wild boars. The activity of all investigated intestinal CYP enzymes remained under detection level in each gut section in both species. Hepatic CYP2C9 and CYP3A4 enzymes were measurable in wild boar fetuses, but their activity was remarkably lower than in adults. The described interspecies differences might be explained with the altered exposure of wild and domesticated animals to specific CYP modulators. As CYP enzymes in wild boars can be highly influenced by environmental pollutants, following further studies, they may serve as ecotoxicological markers of agricultural or industrial toxicants. Investigating CYP-related drug metabolism in wildlife species can clarify some toxicokinetic interactions, thus having huge importance in the production of safe game meat.

The mechanisms of pharmacokinetic food-drug interactions - A perspective from the UNGAP group

The simultaneous intake of food and drugs can have a strong impact on drug release, absorption, distribution, metabolism and/or elimination and consequently, on the efficacy and safety of pharmacotherapy. As such, food-drug interactions are one of the main challenges in oral drug administration. Whereas pharmacokinetic (PK) food-drug interactions can have a variety of causes, pharmacodynamic (PD) food-drug interactions occur due to specific pharmacological interactions between a drug and particular drinks or food. In recent years, extensive efforts were made to elucidate the mechanisms that drive pharmacokinetic food-drug interactions. Their occurrence depends mainly on the properties of the drug substance, the formulation and a multitude of physiological factors. Every intake of food or drink changes the physiological conditions in the human gastrointestinal tract. Therefore, a precise understanding of how different foods and drinks affect the processes of drug absorption, distribution, metabolism and/or elimination as well as formulation performance is important in order to be able to predict and avoid such interactions. Furthermore, it must be considered that beverages such as milk, grapefruit juice and alcohol can also lead to specific food-drug interactions. In this regard, the growing use of food supplements and functional food requires urgent attention in oral pharmacotherapy. Recently, a new consortium in Understanding Gastrointestinal Absorption-related Processes (UNGAP) was established through COST, a funding organisation of the European Union supporting translational research across Europe. In this review of the UNGAP Working group "Food-Drug Interface", the different mechanisms that can lead to pharmacokinetic food-drug interactions are discussed and summarised from different expert perspectives.

Baicalin reduces ciclosporin bioavailability by inducing intestinal p-glycoprotein in rats

Objectives

To investigate the effects of multiple doses of baicalin (BG) on the pharmacokinetics of ciclosporin (CsA) in rats and the potential mechanisms.

Methods

Pharmacokinetic parameters of CsA were determined in male rats after administration of CsA (3 mg/kg, i.g. or i.v.) to rats in the presence and absence of BG (80 mg/kg, i.g. or i.v.) for 7 days. The livers and intestines of rats were isolated and the CYP3A and p-glycoprotein (P-gp) expression were analysed. The effect of BG on the intestinal absorptive behaviour of CsA was also investigated using in-vitro everted rat gut sac model.

Key findings

Baicalin (80 mg/kg, i.v., 7 days) had no effect on the intravenously administered CsA. However, BG (80 mg/kg, i.g., 7 days) significantly decreased the Cmax, AUC0–t and AUC0–∞ of orally administered CsA by 38, 26 and 25%, respectively (P < 0.01 or P < 0.05). Further study revealed that the expression of P-gp in intestine increased in oral multiple doses of BG-treated rats. The in-vitro everted rat gut sac model demonstrated BG (10 μm) significantly decreased the absorption of CsA (10 μm) in intestine (P < 0.05).

Conclusions

Multiple doses of BG decreased the oral bioavailability of CsA in rats significantly, which may be mainly attributable to inhibition of absorption of CsA in intestine and induction of P-gp. The interaction between BG and CsA may occur when BG and CsA were co-administered for long-term use. The dosage adjustment and blood concentration monitoring of CsA may be required in clinic.

Gut Microbiota-Mediated Bile Acid Transformations Alter the Cellular Response to Multidrug Resistant Transporter Substrates in Vitro: Focus on P-glycoprotein

Pharmacokinetic research at the host-microbe interface has been primarily directed toward effects on drug metabolism, with fewer investigations considering the absorption process. We previously demonstrated that the transcriptional expression of genes encoding intestinal transporters involved in lipid translocation are altered in germ-free and conventionalized mice possessing distinct bile acid signatures. It was consequently hypothesized that microbial bile acid metabolism, which is the deconjugation and dehydroxylation of the bile acid steroid nucleus by gut bacteria, may impact upon drug transporter expression and/or activity and potentially alter drug disposition. Using a panel of three human intestinal cell lines (Caco-2, T84, and HT-29) that differ in basal transporter expression level, bile acid conjugation-, and hydroxylation-status was shown to influence the transcription of genes encoding several major influx and efflux transporter proteins. We further investigated if these effects on transporter mRNA would translate to altered drug disposition and activity. The results demonstrated that the conjugation and hydroxylation status of the bile acid steroid nucleus can influence the cellular response to multidrug resistance (MDR) substrates, a finding that did not directly correlate with directionality of gene or protein expression. In particular, we noted that the cytotoxicity of cyclosporine A was significantly augmented in the presence of the unconjugated bile acids deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) in P-gp positive cell lines, as compared to their taurine/glycine-conjugated counterparts, implicating P-gp in the molecular response. Overall this work identifies a novel mechanism by which gut microbial metabolites may influence drug accumulation and suggests a potential role for the microbial bile acid-deconjugating enzyme bile salt hydrolase (BSH) in ameliorating multidrug resistance through the generation of bile acid species with the capacity to access and inhibit P-gp ATPase. The physicochemical property of nonionization is suggested to underpin the preferential ability of unconjugated bile acids to attenuate the efflux of P-gp substrates and to sensitize tumorigenic cells to cytotoxic therapeutics in vitro. This work provides new impetus to investigate whether perturbation of the gut microbiota, and thereby the bile acid component of the intestinal metabolome, could alter drug pharmacokinetics in vivo. These findings may additionally contribute to the development of less toxic P-gp modulators, which could overcome MDR.

Expression of clinically relevant drug-metabolizing enzymes along the human intestine and their correlation to drug transporters and nuclear receptors: An intra-subject analysis

The oral bioavailability of many drugs is highly influenced not only by hepatic but also by intestinal biotransformation. To estimate the impact of intestinal phase I and II metabolism on oral drug absorption, knowledge on the expression levels of the respective enzymes is an essential prerequisite. In addition, the potential interplay of metabolism and transport contributes to drug disposition. Both mechanisms may be subjected to coordinative regulation by nuclear receptors, leading to unwanted drug-drug interactions due to induction of intestinal metabolism and transport. Thus, it was the aim of this study to comprehensively analyse the regional expression of clinically relevant phase I and II enzymes along the entire human intestine and to correlate these data to expression data of drug transporters and nuclear receptors of pharmacokinetic relevance. Gene expression of 11 drug-metabolizing enzymes (CYP2B6, 2C8, 2C9, 2C19, 2D6, 3A4, 3A5, SULT1A, UGT1A, UGT2B7, UGT2B15) was studied in duodenum, jejunum, ileum and colon from six organ donors by real-time RT-PCR. Enzyme expression was correlated with expression data of the nuclear receptors PXR, CAR and FXR as well as drug transporters observed in the same cohort. Intestinal expression of all studied metabolizing enzymes was significantly higher in the small intestine compared to colonic tissue. CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4/5, SULT1A, UGT1A and UGT2B7 expression increased from the duodenum to jejunum but was markedly lower in the ileum. In the small intestine, that is, the predominant site of drug absorption, the highest expression has been observed for CYP3A4, CYP2C9, SULT1A and UGT1A. In addition, significant correlations were found between several enzymes and PXR as well as ABC transporters in the small intestine. In conclusion, the observed substantial site-dependent intestinal expression of several enzymes may explain regional differences in intestinal drug absorption. The detected correlations between intestinal enzymes, transporters and nuclear receptors provide indirect evidence for their coordinative expression, regulation and function in the human small intestine.

Effects of tomato juice on the pharmacokinetics of CYP3A4-substrate drugs

We previously demonstrated that tomato juice (TJ) contains potent mechanism-based inhibitor(s) of CYP3A4. In this study, we investigated the effects of TJ and grapefruit juice (GFJ) on the pharmacokinetics of the CYP3A4-substrate drugs, nifedipine (NFP) and midazolam (MDZ), in male Wistar rats. Oral administration of GFJ 90 min before the intraduodenal administration of NFP or MDZ increased the area under the concentration–time curves (AUCs) of NFP and MDZ by 32.4% and 89.4%, respectively. TJ increased MDZ blood concentrations and AUC after intraduodenal MDZ administration; however, it had no effect on NFP. When MDZ and NFP were intravenously administered, GFJ significantly increased the AUC of MDZ, but only slightly increased that of NFP. In contrast, TJ only slightly increased the AUC of MDZ. These results suggest that, similar to GFJ, TJ influences the pharmacokinetics of CYP3A4-substrate drugs; however, it may be a drug-dependent partial effect.

BDDCS, the Rule of 5 and drugability

The Rule of 5 methodology appears to be as useful today in defining drugability as when it was proposed, but recognizing that the database that we used includes only drugs that successfully reached the market. We do not view additional criteria necessary nor did we find significant deficiencies in the four Rule of 5 criteria originally proposed by Lipinski and coworkers. BDDCS builds upon the Rule of 5 and can quite successfully predict drug disposition characteristics for drugs both meeting and not meeting Rule of 5 criteria. More recent expansions of classification systems have been proposed and do provide useful qualitative and quantitative predictions for clearance relationships. However, the broad range of applicability of BDDCS beyond just clearance predictions gives a great deal of further usefulness for the combined Rule of 5/BDDCS system.

Oral nanomedicine approaches for the treatment of psychiatric illnesses

Psychiatric illnesses are a leading cause of disability and morbidity globally. However, the preferred orally dosed pharmacological treatment options available for depression, anxiety and schizophrenia are often limited by factors such as low drug aqueous solubility, food effects, high hepatic first-pass metabolism effects and short half-lives. Furthermore, the discovery and development of more effective psychotropic agents has stalled in recent times, with the majority of new drugs reaching the market offering similar efficacy, but suffering from the same oral delivery concerns. As such, the application of nanomedicine formulation approaches to currently available drugs is a viable option for optimizing oral drug delivery and maximizing treatment efficacy. This review focuses on the various delivery challenges encountered by psychotropic drugs, and the ability of nanomedicine formulation strategies to overcome these. Specifically, we critically review proof of concept in vitro and in vivo studies of nanoemulsions/microemulsions, solid lipid nanoparticles, dendrimers, polymeric micelles, nanoparticles of biodegradable polymers and nanosuspensions, and provide new insight into the various mechanisms for improved drug performance. The advantages and limitations of current oral nanomedicine approaches for psychotropic drugs are discussed, which will provide guidance for future research directions and assist in fostering the translation of such delivery systems to the clinical setting. Accordingly, emphasis has been placed on correlating the in vitro/in vivo performance of these nanomedicine approaches with their potential clinical outcomes and benefits for patients.

[Molecular Biological Analysis of Factors Influencing Pharmacokinetics to Achieve Personalized Pharmacotherapy]

Large individual variations in drug efficacy and safety could be explained in part by pharmacokinetics regulated by drug transporters and drug-metabolizing enzymes. However, expression and/or function of these proteins often fluctuate in pathological conditions, causing individual pharmacokinetic variability. To achieve a personalized pharmacotherapy after liver transplantation, our group has been investigating the pharmacokinetics of drugs and factors causing its variation based on molecular biological analysis using rats with liver ischemia-reperfusion (I/R) injury as a model for injuries immediately after liver transplantation. The first finding is that the oral bioavailability of cyclosporine A (CsA), which is an immunosuppressant, was decreased by increased first-pass metabolism due to elevated CYP3A and P-glycoprotein (P-gp) specifically in the upper small intestine after liver I/R. Expression of CYP3A in the small intestine was also elevated through transcriptional regulation by endogenous bile acids, whereas expression and function of intestinal P-gp were increased by post-transcriptional regulation via microRNA-145. Next, the pharmacokinetics of a cationic drug, cimetidine, which is eliminated from the kidney, and the expressional variation of drug transporters in the kidney after liver I/R were examined. Liver I/R decreased tubular secretion of cimetidine, mainly because of decreased expression of rat organic cation transporter 2 in the kidney. These findings provide useful information on the etiology of liver I/R injury and appropriate use of immunosuppressants and drugs eliminated from the kidney after liver transplantation.

Interactions of pharmacokinetic profile of different parts from Ginkgo biloba extract in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts from Ginkgo biloba L. leaves confer their therapeutic effects through the synergistic actions of flavonoid and terpenoid components, but some non-flavonoid and non-terpenoid components also exist in this extract. In the study of this paper, an investigation was carried out to compare the pharmacokinetic parameters of fourteen compounds to clarify the influences of non-flavonoid and non-terpenoid fraction (WEF) on the pharmacokinetics profile of the flavonoid fraction (FF) and the terpene lactone fraction (TLF) from Ginkgo biloba extracts.

MATERIALS AND METHODS

A selective and sensitive UPLC-MS/MS method was established to determine the plasma concentrations of the fourteen compounds to compare the pharmacokinetic parameters after orally administration of FF, TLF, FF-WEF, FF-TLF, TLF-WEF and FF-TLF-WEF with approximately the same dose. At different time points, the concentration of rutin (1), isoquercitrin (2), quercetin 3-O-[4-O-(-β-D-glucosyl)-α-L-rhamnoside] (3), ginkgolide C (4), bilobalide (5), quercitrin (6), ginkgolide B (7), ginkgolide A (8), luteolin (9), quercetin (10), apigenin (11), kaempferol (12), isorhamnetin (13), genkwanin (14) in rat plasma were determined and main pharmacokinetic parameters including T1/2, Tmax, Cmax and AUC were calculated using the DAS 3.2 software package. The statistical analysis was performed using the Student׳s t-test with P<0.05 as the level of significance.

RESULTS

FF and WEF had no effect on the pharmacokinetic behaviors and parameters of the four terpene lactones, but the pharmacokinetic profiles and parameters of flavonoids changed while co-administered with non-flavonoid components. It was found that Cmax and AUC of six flavonoid aglycones in group FF-WEF, FF-TLF and FF-TLF-WEF had varying degrees of reduction in comparison with group FF, especially in group FF-TLF-WEF. On the contrary, the values of Cmax, Tmax and AUC of four flavonoid glycosides in group FF-TLF-WEF were significantly increased compared with those in group FF.

CONCLUSIONS

These results indicate that non-flavonoid components in Ginkgo biloba extracts could increase the absorption and improve the bioavailability of flavonoid glycosides but decrease the absorption and reduce the bioavailability of flavonoid aglycones.

Sex- and smoke-related differences in gastrointestinal transit of cyclosporin A microemulsion capsules

The aim of this work was to study the effect of the sex and the smoking status on the pharmacokinetics and the bioequivalence assessment of a branded and a generic cyclosporine A microemulsion formulation in soft-gelatin capsule. Sixteen healthy volunteers (eight women and eight men) participated in a CyA bioequivalence study, with nine of the volunteers being smokers. Sandimmun Neoral® (brand formulation; Reference) and Sigmasporin Microral® (generic formulation; Test) were administered under fasting conditions. Pharmacokinetic parameters were calculated through non compartmental analysis. Bioequivalence was declared based on the 90% confidence intervals (90% CI) for the T/R ratio of the geometric means for each parameter. In vitro determination of the capsules opening time was performed in simulated gastric fluid without enzyme with USP Apparatus 2. The extent of absorption was similar between both products for all subjects or each sex-group. The absorption rate was similar for both products when considering all subjects, whereas a significant difference in the TMAX between the two products was observed for the male subjects only, which relates to its slower capsule opening time observed in vitro (12.4 versus 6.0 min). No differences were observed in women that could relate to their slower gastric emptying. Differences in drug exposure were observed between smokers and non-smokers. Sex- and smoke-related differences in the gastrointestinal transit should be considered when the on-set time would be determinant for the treatment success of a drug.

Understanding and preventing drug-drug and drug-gene interactions

Concomitant administration of multiple drugs can lead to unanticipated drug interactions and resultant adverse drug events with their associated costs. A more thorough understanding of the different cytochrome P450 isoenzymes and drug transporters has led to new methods to try to predict and prevent clinically relevant drug interactions. There is also an increased recognition of the need to identify the impact of pharmacogenetic polymorphisms on drug interactions. More stringent regulatory requirements have evolved for industry to classify cytochrome inhibitors and inducers, test the effect of drug interactions in the presence of polymorphic enzymes, and evaluate multiple potentially interacting drugs simultaneously. In clinical practice, drug alert software programs have been developed. This review discusses drug interaction mechanisms and strategies for screening and minimizing exposure to drug interactions. We also provide future perspectives for reducing the risk of clinically significant drug interactions.

Ciclosporin 10 years on: indications and efficacy

Ciclosporin is a lipophilic cyclic polypeptide with powerful immunosuppressive and immunomodulatory properties that has been used in veterinary medicine for two decades. It is a calcineurin inhibitor whose principal mode of action is to inhibit T cell activation. The drug is principally absorbed from the small intestine and is metabolised in the intestine and liver by the cytochrome P450 enzyme system. Ciclosporin is known to interact with a wide range of pharmacological agents. Numerous studies have demonstrated good efficacy for the management of canine atopic dermatitis and this has been a licensed indication since 2003. In addition to the treatment of atopic dermatitis, it has been used as an aid in the management of numerous other dermatological conditions in animals including perianal fistulation, sebaceous adenitis, pododermatitis, chronic otitis externa and pemphigus foliaceus. This article reviews the mode of action, pharmacokinetics, indications for use and efficacy of ciclosporin in veterinary dermatology.

Regional intestinal drug permeation: biopharmaceutics and drug development

Over the last 25 years, profound changes have been seen in both the development and regulation of pharmaceutical dosage forms, due primarily to the extensive use of the biopharmaceutical classification system (BCS) in both academia and industry. The BCS and the FDA scale-up and post-approval change guidelines were both developed during the 1990s and both are currently widely used to claim biowaivers. The development of the BCS and its wide acceptance were important steps in pharmaceutical science that contributed to the more rational development of oral dosage forms. The effective permeation (Peff) of drugs through the intestine often depends on the combined outcomes of passive diffusion and multiple parallel transport processes. Site-specific jejunal Peff cannot reflect the permeability of the whole intestinal tract, since this varies along the length of the intestine, but is a useful approximation of the fraction of the oral dose that is absorbed. It appears that drugs with a jejunal Peff>1.5×10(-4)cm/s will be completely absorbed no matter which transport mechanisms are utilized. In this paper, historical clinical data originating from earlier open, single-pass perfusion studies have been used to calculate the Peff of different substances from sites in the jejunum and ileum. More exploratory in vivo studies are required in order to obtain reliable data on regional intestinal drug absorption. The development of experimental and theoretical methods of assessing drug absorption from both small intestine and various sites in the colon is encouraged. Some of the existing human in vivo data are discussed in relation to commonly used cell culture models. It is crucial to accurately determine the input parameters, such as the regional intestinal Peff, as these will form the basis for the expected increase in modeling and simulation of all the processes involved in GI drug absorption, thus facilitating successful pharmaceutical development in the future. It is suggested that it would be feasible to use open, single-pass perfusion studies for the in vivo estimation of regional intestinal Peff, but that care should be taken in the study design to optimize the absorption conditions.

Quantitation of small intestinal permeability during normal human drug absorption

BACKGROUND

Understanding the quantitative relationship between a drug's physical chemical properties and its rate of intestinal absorption (QSAR) is critical for selecting candidate drugs. Because of limited experimental human small intestinal permeability data, approximate surrogates such as the fraction absorbed or Caco-2 permeability are used, both of which have limitations.

METHODS

Given the blood concentration following an oral and intravenous dose, the time course of intestinal absorption in humans was determined by deconvolution and related to the intestinal permeability by the use of a new 3 parameter model function ("Averaged Model" (AM)). The theoretical validity of this AM model was evaluated by comparing it to the standard diffusion-convection model (DC). This analysis was applied to 90 drugs using previously published data. Only drugs that were administered in oral solution form to fasting subjects were considered so that the rate of gastric emptying was approximately known. All the calculations are carried out using the freely available routine PKQuest Java (http://www.pkquest.com) which has an easy to use, simple interface.

RESULTS

Theoretically, the AM permeability provides an accurate estimate of the intestinal DC permeability for solutes whose absorption ranges from 1% to 99%. The experimental human AM permeabilities determined by deconvolution are similar to those determined by direct human jejunal perfusion. The small intestinal pH varies with position and the results are interpreted in terms of the pH dependent octanol partition. The permeability versus partition relations are presented separately for the uncharged, basic, acidic and charged solutes. The small uncharged solutes caffeine, acetaminophen and antipyrine have very high permeabilities (about 20 x 10-4 cm/sec) corresponding to an unstirred layer of only 45 μm. The weak acid aspirin also has a large AM permeability despite its low octanol partition at pH 7.4, suggesting that it is nearly completely absorbed in the first part of the intestine where the pH is about 5.4.

CONCLUSIONS

The AM deconvolution method provides an accurate estimate of the human intestinal permeability. The results for these 90 drugs should provide a useful benchmark for evaluating QSAR models.

Population pharmacokinetics of cyclosporine in transplant recipients

A number of classical pharmacokinetic studies have been conducted in transplant patients. However, they suffer from some limitations, for example, (1) the study design was limited to intense blood sampling in small groups of patients during a certain posttransplant period, (2) patient factors were evaluated one at a time to identify their association with the pharmacokinetic parameters, and (3) mean pharmacokinetic parameters often cannot be precisely estimated due to large intraindividual variability. Population pharmacokinetics provides a potential means of addressing these limitations and is a powerful tool to evaluate the magnitude and consistency of drug exposure. Population pharmacokinetic studies of cyclosporine focused solely on developing limited sampling strategies and Bayesian estimators to estimate drug exposure, have been summarized before, and are, therefore, not a subject of this review. The major focus of this review is to describe factors (demographic factors, hepatic and gastrointestinal functions, drug-drug interactions, genetic polymorphisms of drug metabolizing enzymes and transporters) that have been identified to contribute to the large portion of observed variability in the pharmacokinetics of cyclosporine in transplant patients. This review summarizes and interprets the conclusions as well as the nonlinear mixed-effects modeling methodologies used in such studies. A highly diversified collection of structural models, variability models, and covariate submodels have been evaluated and validated using internal or external validation methods. This review also highlights areas where additional research is warranted to improve the models since a portion of model variability still remains unexplained.