Presystemic Drug Metabolism Research Articles

A Critical Overview of the Biological Effects of Excipients (Part I): Impact on Gastrointestinal Absorption.

Traditionally, excipients have been considered in drug development from the perspective of their influence on drug solubility, manufacturability, and ability to control in vitro and in vivo drug release. These effects have been largely evaluated through studies involving in vitro dissolution methods. However, there is a growing awareness that what had previously been considered biologically inert excipients can exert numerous in vivo effects. This includes the potential to change gastrointestinal (GI) transit time, enterocyte passive transcellular or paracellular permeability, active transport activity, or presystemic drug metabolism. In this critical overview of the biological effects of excipients (Part I), we provide a summary of select published studies that explore these various in vivo factors. We also include a table that points readers to published reviews that list a range of excipients known to have biological activity. A subsequent discussion on in vitro, in vivo, and in silico methods that can be used to explore these excipient effects is provided in a separate (Part 2) continuation of this critical overview.

Экспериментальная фармакокинетика новых нейротропных пептидных лекарственных средств

Представлены результаты исследований сравнительной экспериментальной фармакокинетики и метаболизма 3 новых нейротропных пептидных лекарственных препаратов: аналогов природных нейропептидов — ноотропного препарата ноопепт, антипсихотического средства — дилепт и селективного анксиолитика — соединения ГБ-115 у 2 видов животных (крыс и кроликов). Установлено, что эфирные производные нейропептидов ноопепт и дилепт, в отличие от анксиолитика ГБ-115, являющегося амидом, подвергаются интенсивной биотрансформации у крыс с образованием активного метаболита ноопепта — циклопролил-L-глицина (ЦПГ) и активного метаболита дилепта — капроил-L-пролил-L-тирозина (М-1). Фармакокинетические параметры, характеризующие распределение анксиолитика ГБ-115 у крыс, свидетельствуют о его возможном накоплении во внутренних органах и тканях, что следует учитывать при его повторном введении. Установлено, что изучаемые соединения в организме кроликов в меньшей степени подвергаются энзиматическому воздействию и более продолжительное время определяются в плазме крови в неизмененном виде, что связано не только со структурными особенностями изучаемых дипептидов, но и с различиями активности энзиматических систем ЖКТ, принимающих участие в их пресистемном метаболизме, а также с различиями в скорости печеночного и почечного кровотока у крыс и кроликов.

Expression Profiles of Metabolic Enzymes and Drug Transporters in the Liver and along the Intestine of Beagle Dogs

Beagle dogs are widely used in preclinical pharmacokinetic, safety, and formulation studies. However, little is known about intestinal and hepatic distribution of major enzymes and transporters involved in oral absorption and presystemic drug metabolism. We characterized mRNA levels of CYP3A12, CYP3A26, CYP2D15, UGT1A6, ABCB1 (MDR1), ABCC1 (MRP1), ABCG2 (BCRP), SLC15A1 (PEPT1), and SLC22A1 (OCT1) in dog liver and along the intestine by real-time quantitative reverse transcription-polymerase chain reaction. Tissue protein levels of CYP2D15, MDR1, and PEPT1 were obtained by Western blot. Gene distribution and expression variability was statistically described by a generalized additive mixed model smoothing function and correspondence analysis. Results were compared with the expression pattern known for the human orthologs. Hepatic mRNA levels for metabolic enzymes were generally higher than those for membrane transporters, whereas in the intestine the opposite was observed. Hepatic mRNA levels followed the order CYP2D15 > UGT1A6 ≈ CYP3A26 > ABCB1 ≈ SLC15A1 ≈ SLC22A1 > ABCG2 > ABCC1 ≈ CYP3A12. Along the gut, the genes were differentially distributed with greatest expression in duodenum/upper jejunum (ABCG2), middle jejunum (ABCB1 and SLC15A1), or in cecum/colon (ABCC1 and CYP2D15). CYP3A12, CYP3A26, SLC22A1, and UGT1A6 had a rather uniform expression. Intestinal mRNA profiles of CYP2D15, ABCB1, and SLC15A1 correlated with the respective protein levels. Canine CYP3A12/26, CYP2D15, and ABCB1 colonic distributions differed from those of human orthologs, whereas UGT1A6, ABCC1, ABCG2, SLC15A1, and SLC22A1 were comparable to those of humans in both small and large intestine. We aim to apply these data to better interpret pharmacokinetic studies in dogs with respect to their human relevance.

Intestinal enzymatic metabolism of drugs

The intestinal stability of perorally administered drugs has so far been determined using simulated intestinal fluid containing porcine pancreatin (SIF/P), as human gastrointestinal fluids are in most cases not available. In this study the metabolism of six low molecular mass drugs in SIF/P was compared with that in freshly collected porcine intestinal juice and on excised porcine intestinal mucosa. The drugs used were oseltamivir, atazanavir, diloxanide, diltiazem, cephalothin and cefoxitin. Metabolism studies were carried out by incubating each drug in the in-vitro models and by analysing the percentage of unmodified remaining drug at fixed time points. Three drugs showed higher degradation on porcine mucosa compared with that in SIF/P and for five compounds a significantly higher metabolism in collected porcine intestinal juice versus SIF/P was observed. Metabolism of diloxanide furoate in collected intestinal juice, for example, was 40-fold higher compared with SIF/P. Moreover, the involvement of different metabolic pathways in porcine mucosa and intestinal juice was observed for cephalothin, being metabolized to desacetylcephalothin and thienyl-acetylglycine, whereas these metabolites were not found in SIF/P. In addition, diltiazem solution (0.25% m/v) was found to be significantly degraded in intestinal juice whereas its metabolism in SIF/P was negligible. These findings demonstrated that the use of SIF/P for evaluation of presystemic drug metabolism could be highly misleading. Incubation of drugs in freshly collected porcine intestinal juice will likely lead to the improvement of the mimicry of body conditions to evaluate presystemic drug metabolism.

The Gut Microbiome and Pre-systemic Metabolism: Current State and Evolving Research

The evolution of the complex metabolic interaction between intestinal microbiota in the human gut with its host is multidimensional. Our understanding of this complex interaction has evolved in the past years either with the use of more sophisticated analytical techniques or by reported adverse drug effects that have been associated with intestinal drug metabolism such as with sorivudine. The composition of the intestinal microbiome is initially determined by environmental and genetic factors although external influences as well as host immune reactions provide for adjustment of the delicate balance in both health and disease conditions. The metabolism of drugs by both intestinal bacteria and further by enterocytes leading to their systemic absorption deserves further attention and may provide valuable insights into pre-systemic drug metabolism, delivery, and toxicity. A better understanding of the metabolic pathways may aid in the drug development and toxicity evaluation process.

Advances and potential applications of chitosan derivatives as mucoadhesive biomaterials in modern drug delivery

Pharmaceutical technologists have been working extensively on various mucoadhesive polymeric systems to create an intimate and prolonged contact at the site of administration. Chitosan is one of the most promising polymers because of its non-toxic, polycationic biocompatible, biodegradable nature, and particularly due to its mucoadhesive and permeation enhancing properties. Due to its potential importance in controlled drug delivery applications, pharmaceutical scientists have exploited this mucoadhesive polymer. However, chitosan suffers from limited solubility at physiological pH and causes presystemic metabolism of drugs in intestinal and gastric fluids in the presence of proteolytic enzymes. These inherent drawbacks of chitosan have been overcome by forming derivatives such as carboxylated, various conjugates, thiolated, and acylated chitosan, thus providing a platform for sustained release formulations at a controlled rate, prolonged residence time, improved patient compliance by reducing dosing frequency, enhanced bioavailability and a significant improvement in therapeutic efficacy. We have explored the potential benefits of these improved chitosan derivatives in modern drug delivery.

Grapefruit‐Drug Interactions: The Effect of Furanocoumarins and Polymethoxylated Flavones on P‐glycoprotein Activity in Vitro

Grapefruit juice (GFJ) carries the American Heart Associations's healthy “heart check” food mark and contains compounds that may both reduce atherosclerotic plaque formation and inhibit cancer cell proliferation. However, grapefruit juice has been demonstrated to interact with a variety of prescription medications, raising the potential for concern regarding the concomitant consumption with drugs. The major mechanism for GFJ-drug interaction involves the inhibition of the drug-metabolizing enzyme cytochrome P-450 3A4 (CYP450 3A4) in the small intestine, resulting in a significant reduction of the presystemic metabolism of drugs. An additional mechanism is the interaction with P-glycoprotein (P-gp), an energy-dependent membrane efflux-transporter carrying a wide range of substrates from the enterocyte back to the intestinal lumen. In this study, several grapefruit compounds which are discussed to be involved in GFJ-drug interactions were tested in Caco-2 coloncarcinoma cells in their influence on P-glycoprein. None of the compounds tested changed the apical to basolateral permeability of the β-blocker talinolol (100 μMol/L). The basolateral to apical transport was significantly decreased by naringin, naringenin, epoxybergamottin; 6′,7′-dihydroxybergamottin, nobiletin, tangeretin, sinensetin, and heptamethoxyflanone at IC50 ranging from 2-1252 μMol/L. Results from this study contribute to the risk assessment of concomitant use of P-gp substrates with GFJ and ultimately may result in dosing recommendations for affected drugs, ensuring a better and safer therapeutic outcome of drug therapy.

A mechanistic approach to understanding the factors affecting drug absorption: a review of fundamentals.

This article provides an overview of the patient-specific and drug-specific variables that can affect drug absorption following oral product administration. The oral absorption of any chemical entity reflects a complex spectrum of events. Factors influencing product bioavailability include drug solubility, permeability, and the rate of in vivo dissolution. In this regard, the Biopharmaceutics Classification System has proven to be an important tool for predicting compounds likely to be associated with bioavailability problems. It also helps in identifying those factors that may alter the rate and extent of drug absorption. Product bioavailability can also be markedly influenced by patient attributes such as the integrity of the gastrointestinal tract, physiological status, site of drug absorption, membrane transporters, presystemic drug metabolism (intrinsic variables), and extrinsic variables such as the effect of food or concomitant medication. Through an awareness of a drug's physicochemical properties and the physiological processes affecting drug absorption, the skilled pharmaceutical scientist can develop formulations that will maximize product availability. By appreciating the potential impact of patient physiological status, phenotype, age, gender, and lifestyle, dosing regimens can be tailored to better meet the needs of the individual patient.

Formulation and Physiological and Biopharmaceutical Issues in the Development of Oral Lipid-Based Drug Delivery Systems

The rapidly increasing availability of drug receptor structural characteristics has permitted the receptor-guided synthesis of potential new drug molecules. This synthesis strategy frequently results in the creation of polycyclic and highly hydrophobic compounds, with attendant poor oral bioavailability resulting from low solubility and slow dissolution rate in the primarily aqueous contents of the gastrointestinal (GI) tract. In an attempt to improve the solubility-limited bioavailability associated with these compounds, formulators have turned to the use of lipid excipients in which the compounds can be solubilized prior to oral administration. This new class of excipients presents the pharmaceutical scientist with a number of new challenges at all stages of the formulation development process, beginning with the excipient selection and stability assessment of the prototype formulation, up to and including scale-up and mass production of the final market-image product. The interaction of lipid-based formulations with the gastrointestinal system and associated digestive processes presents additional challenges and opportunities that will be understood more fully as we begin to unravel the intricacies of the GI processing of lipid excipients. For example, an increasing body of evidence has shown that certain lipids are capable of inhibiting both presystemic drug metabolism and drug efflux by the gut wall mediated by p-glycoprotein (PGP). And, it is well known that lipids are capable of enhancing lymphatic transport of hydrophobic drugs, thereby reducing drug clearance resulting from hepatic first-pass metabolism. This review addresses the current state of knowledge regarding oral lipid-based formulation development and scale-up issues and the physiological and biopharmaceutical aspects pertinent to the development of an orally bioavailable and efficacious dosage form.

The human intestinal epithelial cell line Caco-2; pharmacological and pharmacokinetic applications

The gastrointestinal tract remains the most popular and acceptable route of administration for drugs. It offers the great advantage of convenience and many compounds are well absorbed and thereby provide acceptable plasma concentration-time profiles. Currently there is considerable interest from the pharmaceutical industry in development of cell culture systems that would mimic the intestinal mucosa in order to evaluate strategies for investigating and/or enhancing drug absorption. The intestinal epithelial cells of primary interest, from the standpoint of drug absorption and metabolism, are the villus cells, which are fully differentiated cells. An in vitro cell culture system consisting of a monolayer of viable, polarized and fully differentiated villus cells, similar to that found in the small intestine, would be a valuable tool in the study of drug and nutrient transport and metabolism. The Caco-2 cell line, which exhibits a well-differentiated brush border on the apical surface and tight junctions, and expresses typical small-intestinal microvillus hydrolases and nutrient transporters, has proven to be the most popular in vitro model (a) to rapidly assess the cellular permeability of potential drug candidates, (b) to elucidate pathways of drug transport (e.g., passive versus carrier mediated), (c) to assess formulation strategies designed to enhance membrane permeability, (d) to determine the optimal physicochemical characteristics for passive diffusion of drugs, and (e) to assess potential toxic effects of drug candidates or formulation components on this biological barrier. Since differentiated Caco-2 cells express various cytochrome P450 isoforms and phase II enzymes such as UDP-glucuronosyltransferases, sulfotransferases and glutathione-S-transferases, this model could also allow the study of presystemic drug metabolism.

Influence of food on the presystemic metabolism of drugs

Influence of food on the presystemic metabolism of drugs

The influence of nutrition on the systemic availability of drugs. Part II: Drug metabolism and renal excretion.

Plasma concentrations of an active compound vary between individuals and within a subject, even if the same drug dosage is used. These differences are related to variations of drug absorption from the gastrointestinal tract, of presystemic drug metabolism in the intestine or the liver, and of drug elimination from the systemic circulation, for instance by hepatic metabolism or renal excretion. All of these processes can be modified by nutrition. However it is necessary to emphasize the significance of the pharmaceutical formulation for variations of both drug absorption and elimination. The role of nutrition should receive adequate attention during therapeutic use of drugs as well as in drug disposition studies. Recent guidelines for the assessment of the systemic availability of drugs therefore do recommend nutrition to be controlled.

An alternative prodrug approach for reducing presystemic metabolism of drugs

An alternative prodrug approach for reducing presystemic metabolism of drugs