Metabolism of drugs and other xenobiotics in the gut lumen and wall

Application of artificial intelligence approaches to predict the metabolism of xenobiotic molecules by human gut microbiome

A highly complex, diverse, and dense community of more than 1,000 different gut bacterial species constitutes the human gut microbiome that harbours vast metabolic capabilities encoded by more than 300,000 bacterial enzymes to metabolise complex polysaccharides, orally administered drugs/xenobiotics, nutraceuticals, or prebiotics. One of the implications of gut microbiome mediated biotransformation is the metabolism of xenobiotics such as medicinal drugs, which lead to alteration in their pharmacological properties, loss of drug efficacy, bioavailability, may generate toxic byproducts and sometimes also help in conversion of a prodrug into its active metabolite. Given the diversity of gut microbiome and the complex interplay of the metabolic enzymes and their diverse substrates, the traditional experimental methods have limited ability to identify the gut bacterial species involved in such biotransformation, and to study the bacterial species-metabolite interactions in gut. In this scenario, computational approaches such as machine learning-based tools presents unprecedented opportunities and ability to predict the gut bacteria and enzymes that can potentially metabolise a candidate drug. Here, we have reviewed the need to identify the gut microbiome-based metabolism of xenobiotics and have provided comprehensive information on the available methods, tools, and databases to address it along with their scope and limitations.

Dissecting the human gut microbiome to better decipher drug liability: A once-forgotten organ takes center stage

BACKGROUND

The gut microbiome is a diverse system within the gastrointestinal tract composed of trillions of microorganisms (gut microbiota), along with their genomes. Accumulated evidence has revealed the significance of the gut microbiome in human health and disease. Due to its ability to alter drug/xenobiotic pharmacokinetics and therapeutic outcomes, this once-forgotten "metabolic organ" is receiving increasing attention. In parallel with the growing microbiome-driven studies, traditional analytical techniques and technologies have also evolved, allowing researchers to gain a deeper understanding of the functional and mechanistic effects of gut microbiome.

AIM OF REVIEW

From a drug development perspective, microbial drug metabolism is becoming increasingly critical as new modalities (e.g., degradation peptides) with potential microbial metabolism implications emerge. The pharmaceutical industry thus has a pressing need to stay up-to-date with, and continue pursuing, research efforts investigating clinical impact of the gut microbiome on drug actions whilst integrating advances in analytical technology and gut microbiome models. Our review aims to practically address this need by comprehensively introducing the latest innovations in microbial drug metabolism research- including strengths and limitations, to aid in mechanistically dissecting the impact of the gut microbiome on drug metabolism and therapeutic impact, and to develop informed strategies to address microbiome-related drug liability and minimize clinical risk.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We present comprehensive mechanisms and co-contributing factors by which the gut microbiome influences drug therapeutic outcomes. We highlight in vitro, in vivo, and in silico models for elucidating the mechanistic role and clinical impact of the gut microbiome on drugs in combination with high-throughput, functionally oriented, and physiologically relevant techniques. Integrating pharmaceutical knowledge and insight, we provide practical suggestions to pharmaceutical scientists for when, why, how, and what is next in microbial studies for improved drug efficacy and safety, and ultimately, support precision medicine formulation for personalized and efficacious therapies.

Multimodal interactions of drugs, natural compounds and pollutants with the gut microbiota

The gut microbiota contributes to diverse aspects of host physiology, ranging from immunomodulation to drug metabolism. Changes in the gut microbiota composition are associated with various diseases as well as with the response to medications. It is therefore important to understand how different lifestyle and environmental factors shape gut microbiota composition. Beyond the commonly considered factor of diet, small-molecule drugs have recently been identified as major effectors of the microbiota composition. Other xenobiotics, such as environmental or chemical pollutants, can also impact gut bacterial communities. Here, we review the mechanisms of interactions between gut bacteria and antibiotics, host-targeted drugs, natural food compounds, food additives and environmental pollutants. While xenobiotics can impact bacterial growth and metabolism, bacteria in turn can bioaccumulate or chemically modify these compounds. These reciprocal interactions can manifest in complex xenobiotic-microbiota-host relationships. Our Review highlights the need to study mechanisms underlying interactions with pollutants and food additives towards deciphering the dynamics and evolution of the gut microbiota.

Population pharmacokinetics of mycophenolic acid in paediatric patients

Mycophenolic acid (MPA) is widely used in paediatric kidney transplant patients and sometimes prescribed for additional indications. Population pharmacokinetic or pharmacodynamic modelling has been frequently used to characterize the fixed, random and covariate effects of MPA in adult patients. However, MPA population pharmacokinetic data in the paediatric population have not been systematically summarized. The objective of this narrative review was to provide an up-to-date critique of currently available paediatric MPA population pharmacokinetic models, with emphases on modelling techniques, pharmacological findings and clinical relevance. PubMed and EMBASE were searched from inception of database to May 2020, where a total of 11 studies have been identified representing kidney transplant (n = 4), liver transplant (n = 1), haematopoietic stem cell transplant (n = 1), idiopathic nephrotic syndrome (n = 2), systemic lupus erythematosus (n = 2), and a combined population consisted of kidney, liver and haematopoietic stem cell transplant patients (n = 1). Critical analyses were provided in the context of MPA absorption, distribution, metabolism, excretion and bioavailability in this paediatric database. Comparisons to adult patients were also provided. With respect to clinical utility, Bayesian estimation models (n = 6) with acceptable accuracy and precision for MPA exposure determination have also been identified and systematically evaluated. Overall, our analyses have identified unique features of MPA clinical pharmacology in the paediatric population, while recognizing several gaps that still warrant further investigations. This review can be used by pharmacologists and clinicians for improving MPA pharmacokinetic-pharmacodynamic modelling and patient care.

Personalized Mapping of Drug Metabolism by the Human Gut Microbiome

The human gut microbiome harbors hundreds of bacterial species with diverse biochemical capabilities. Dozens of drugs have been shown to be metabolized by single isolates from the gut microbiome, but the extent of this phenomenon is rarely explored in the context of microbial communities. Here, we develop a quantitative experimental framework for mapping the ability of the human gut microbiome to metabolize small molecule drugs: Microbiome-Derived Metabolism (MDM)-Screen. Included are a batch culturing system for sustained growth of subject-specific gut microbial communities, an ex vivo drug metabolism screen, and targeted and untargeted functional metagenomic screens to identify microbiome-encoded genes responsible for specific metabolic events. Our framework identifies novel drug-microbiome interactions that vary between individuals and demonstrates how the gut microbiome might be used in drug development and personalized medicine.

Insights from pharmacokinetic models of host-microbiome drug metabolism

Increasing evidence suggests a role of the gut microbiota in patients' response to medicinal drugs. In our recent study, we combined genomics of human gut commensals and gnotobiotic animal experiments to quantify microbiota and host contributions to drug metabolism. Informed by experimental data, we built a physiology-based pharmacokinetic model of drug metabolism that includes intestinal compartments with microbiome drug-metabolizing activity. This model successfully predicted serum levels of metabolites of three different drugs, quantified microbial contribution to systemic drug metabolite exposure, and simulated the effect of different parameters on host and microbiota drug metabolism. In this addendum, we expand these simulations to assess the effect of microbiota on the systemic drug and metabolite levels under conditions of altered host physiology, microbiota drug-metabolizing activity or physico-chemical properties of drugs. This work illustrates how and under which circumstances the gut microbiome may influence drug pharmacokinetics, and discusses broader implications of expanded pharmacokinetic models.

Where to Look into the Puzzle of Polyphenols and Health? The Postbiotics and Gut Microbiota Associated with Human Metabotypes

The full consensus on the role of dietary polyphenols as human-health-promoting compounds remains elusive. The two-way interaction between polyphenols and gut microbiota (GM) (i.e., modulation of GM by polyphenols and their catabolism by the GM) is determinant in polyphenols' effects. The identification of human metabotypes associated with a differential gut microbial metabolism of polyphenols has opened new research scenarios to explain the inter-individual variability upon polyphenols consumption. The metabotypes unequivocally identified so far are those involved in the metabolism of isoflavones (equol and(or) O-desmethylangolesin producers versus non-producers) and ellagic acid (urolithin metabotypes, including producers of only urolithin-A (UM-A), producers of urolithin-A, isourolithin-A, and urolithin-B (UM-B), and non-producers (UM-0)). In addition, the microbial metabolites (phenolic-derived postbiotics) such as equol, urolithins, valerolactones, enterolactone, and enterodiol, and 8-prenylnaringenin, among others, can exert differential health effects. The knowledge is updated and position is taken here on i) the two-way interaction between GM and polyphenols, ii) the evidence between phenolic-derived postbiotics and health, iii) the role of metabotypes as biomarkers of GM and the clustering of individuals depending on their metabotypes (metabotyping) to explain polyphenols' effects, and iv) the gut microbial metabolism of catecholamines to illustrate the intersection between personalized nutrition and precision medicine.

Whole Food–Based Approaches to Modulating Gut Microbiota and Associated Diseases

Intake of whole foods, such as fruits and vegetables, may confer health benefits to the host. The beneficial effects of fruits and vegetables were mainly attributed to their richness in polyphenols and microbiota-accessible carbohydrates (MACs). Components in fruits and vegetables modulate composition and associated functions of the gut microbiota, whereas gut microbiota can transform components in fruits and vegetables to produce metabolites that are bioactive and important for health. The progression of multiple diseases, such as obesity and inflammatory bowel disease, is associated with diet and gut microbiota. Although the exact causality between these diseases and specific members of gut microbiota has not been well characterized, accumulating evidence supported the role of fruits and vegetables in modulating gut microbiota and decreasing the risks of microbiota-associated diseases. This review summarizes the latest findings on the effects of whole fruits and vegetables on gut microbiota and associated diseases.

Sanguinarine metabolism and pharmacokinetics study in vitro and in vivo

Sanguinarine (SA) is a benzo[c] phenanthridine alkaloid which has a variety of pharmacological properties. However, very little was known about the pharmacokinetics of SA and its metabolite dihydrosanguinarine (DHSA) in pigs. The purpose of this work was to study the intestinal metabolism of SA in vitro and in vivo. Reductive metabolite DHSA was detected during incubation of SA with intestinal mucosa microsomes, cytosol, and gut flora. After oral (p.o.) administration of SA, the result showed SA might be reduced to DHSA in pig intestine. After i.m. administration, SA and DHSA rapidly increased to reach their peak concentrations (C_max , 30.16 ± 5.85, 5.61 ± 0.73 ng/ml, respectively) at 0.25 hr. Both compounds were completely eliminated from the plasma after 24 hr. After single oral administration, SA and DHSA rapidly increased to reach their C_max (3.41 ± 0.36, 2.41 ± 0.24 ng/ml, respectively) at 2.75 ± 0.27 hr. The half-life (T_1/2 ) values were 2.33 ± 0.11 hr and 2.20 ± 0.12 hr for SA and DHSA, respectively. After multiple oral administration, the average steady-state concentrations (C_ss ) of SA and DHSA were 3.03 ± 0.39 and 1.42 ± 0.20 ng/ml. The accumulation indexes for SA and DHSA were 1.21 and 1.11. The work reported here provides important information on the metabolism sites and pharmacokinetic character of SA. It explains the reasons for low toxicity of SA, which is useful for the evaluation of its performance.

Investigating the bioavailabilities of olerciamide A via the rat's hepatic, gastric and intestinal first-pass effect models

Olerciamide A (OA) is a new alkaloid isolated from Portulaca oleracea L. that has been proved to possess a low bioavailability (F) after oral administration in rats in our previous study. Hence, to clarify the reasons for its low bioavailability, hepatic, gastric and intestinal first-pass effect models were established, and a rapid, sensitive UHPLC method was validated and applied for the determination after dosing via the femoral, portal, gastric and intestinal routes. As inhibitors of CYP3A and P-gp, verapamil, midazolam and borneol in low and high dose groups were selected to improve the low bioavailability of olerciamide A. Moreover, a rectal administration method was also carried out to improve the bioavailability of olerciamide A. The results showed that the bioavailability of olerciamide A using hepatic, gastric and intestinal routes were 92.16%, 84.88% and 5.76%, respectively. The areas under the plasma concentration-time curve from zero to infinity (AUC_{0 → ∞} ) were increased a little after being dosed with 10 and 30 mg/kg verapamil (p > 0.05), but markedly increased after being dosed with 0.4 and 1.2 mg/kg midazolam as well as 8 and 24 mg/kg borneol (p < 0.05). Besides, the AUC_0 → ∞ values after the lower and upper rectal administrations were separately similar to the intravenous and intraportal administrations. Our study showed that the intestinal first-pass effect mainly contributed to the low bioavailability of olerciamide A in rats due to it being a substrate of CYP3A and P-gp as well as to its poor intestinal absorption.

Biogenic Amines: Signals Between Commensal Microbiota and Gut Physiology

There is increasing interest in the interactions among the gut microbiota, gut, and brain, which is often referred to as the "microbiota-gut-brain" axis. Biogenic amines including dopamine, norepinephrine, serotonin, and histamines are all generated by commensal gut microorganisms and are suggested to play roles as signaling molecules mediating the function of the "microbiota-gut-brain" axis. In addition, such amines generated in the gut have attracted attention in terms of possible clues into the etiologies of depression, anxiety, and even psychosis. This review covers the latest research related to the potential role of microbe-derived amines such as catecholamine, serotonin, histamine, as well as other trace amines, in modulating not only gut physiology but also brain function of the host. Further attention in this field can offer not only insight into expanding the fundamental roles and impacts of the human microbiome, but also further offer new therapeutic strategies for psychological disorders based on regulating the balance of resident bacteria.

Preclinical models for colonic absorption, application to controlled release formulation development

Oral controlled release (CR) formulations have many benefits and have become a valuable resource for the local and systemic administration of drugs. The most important characteristic of these pharmaceutical products is that drug absorption occurs mainly in the colon. Therefore, this review analyses the physiological and physicochemical features that may affect an orally administered CR product, as well as the different strategies to develop a CR dosage form and the methods used to evaluate the formulation efficacy. The models available to study the intestinal permeability and their applicability to colonic permeability determinations are also discussed.

Individual susceptibility to arsenic-induced diseases: the role of host genetics, nutritional status, and the gut microbiome

Arsenic (As) contamination in water or food is a global issue affecting hundreds of millions of people. Although As is classified as a group 1 carcinogen and is associated with multiple diseases, the individual susceptibility to As-related diseases is highly variable, such that a proportion of people exposed to As have higher risks of developing related disorders. Many factors have been found to be associated with As susceptibility. One of the main sources of the variability found in As susceptibility is the variation in the host genome, namely, polymorphisms of many genes involved in As transportation, biotransformation, oxidative stress response, and DNA repair affect the susceptibility of an individual to As toxicity and then influence the disease outcomes. In addition, lifestyles and many nutritional factors, such as folate, vitamin C, and fruit, have been found to be associated with individual susceptibility to As-related diseases. Recently, the interactions between As exposure and the gut microbiome have been of particular concern. As exposure has been shown to perturb gut microbiome composition, and the gut microbiota has been shown to also influence As metabolism, which raises the question of whether the highly diverse gut microbiota contributes to As susceptibility. Here, we review the literature and summarize the factors, such as host genetics and nutritional status, that influence As susceptibility, and we also present potential mechanisms of how the gut microbiome may influence As metabolism and its toxic effects on the host to induce variations in As susceptibility. Challenges and future directions are also discussed to emphasize the importance of characterizing the specific role of these factors in interindividual susceptibility to As-related diseases.

Impact of gut microbiota on drug metabolism: an update for safe and effective use of drugs

The intestinal mucosa and liver have long been considered as the main sites of drug metabolism, and the contribution of gut microbiota to drug metabolism has been under-estimated. However, it is now generally accepted that the gut microbiota plays an important role in drug metabolism prior to drug absorption or during enterohepatic circulation via various microbial enzymatic reactions in the intestine. Moreover, some drugs are metabolized by gut microbiota to specific metabolite(s) that cannot be formed in the liver. More importantly, the metabolism of drugs by gut microbiota prior to absorption can alter the systemic bioavailability of certain drugs. Therefore, understanding drug metabolism by gut microbiota is critical for explaining changes in the pharmacokinetics of drugs, which may cause significant alterations in drug-induced pharmacodynamics and toxicities. In this review, we describe recent progress with regard to the role of metabolism by gut microbiota in some drug-induced alterations of either pharmacological or toxicological effects to emphasize the clinical importance of gut microbiota for safe and effective use of drugs.

Regulation of gut luminal serotonin by commensal microbiota in mice

Gut lumen serotonin (5-hydroxytryptamine: 5-HT) contributes to several gastrointestinal functions such as peristaltic reflexes. 5-HT is released from enterochromaffin (EC) cells in response to a number of stimuli, including signals from the gut microbiota. However, the specific mechanism by which the gut microbiota regulates 5-HT levels in the gut lumen has not yet been clarified. Our previous work with gnotobiotic mice showed that free catecholamines can be produced by the deconjugation of conjugated catecholamines; hence, we speculated that deconjugation by bacterial enzymes may be one of the mechanisms whereby gut microbes can produce free 5-HT in the gut lumen. In this study, we tested this hypothesis using germ-free (GF) mice and gnotobiotic mice recolonized with specific pathogen-free (SPF) fecal flora (EX-GF). The 5-HT levels in the lumens of the cecum and colon were significantly lower in the GF mice than in the EX-GF mice. Moreover, these levels were rapidly increased, within only 3 days after exposure to SPF microbiota. The majority of 5-HT was in an unconjugated, free form in the EX-GF mice, whereas approximately 50% of the 5-HT was found in the conjugated form in the GF mice. These results further support the current view that the gut microbiota plays a crucial role in promoting the production of biologically active, free 5-HT. The deconjugation of glucuronide-conjugated 5-HT by bacterial enzymes is likely one of the mechanisms contributing to free 5-HT production in the gut lumen.

In Vitro Intestinal and Liver Models for Toxicity Testing

The human body is exposed to hundreds of chemicals every day. Many of these toxicants have unknown effects on the body that can be deleterious. Furthermore, chemicals can have a synergistic effect, resulting in toxic responses of cocktails at relatively low individual exposure levels. The gastrointestinal (GI) tract and the liver are the first organs to be exposed to ingested pharmaceuticals and environmental chemicals. As a result, these organs often experience extensive damage from xenobiotics and their metabolites. In vitro models offer a promising method for testing toxic effects. Many advanced in vitro models have been developed for GI and liver toxicity. These models strive to recapitulate the in vivo organ architecture to more accurately model chemical toxicity. In this review, we discuss many of these advances, in addition to recent efforts to integrate the GI and the liver in vitro for a more holistic toxicity model.

Evaluation of the synergistic effect of Allium sativum, Eugenia jambolana, Momordica charantia, Ocimum sanctum, and Psidium guajava on hepatic and intestinal drug metabolizing enzymes in rats

Aims/Background:

This study was to investigated the synergistic effect of polyherbal formulations (PHF) of Allium sativum L., Eugenia jambolana Lam., Momordica charantia L., Ocimum sanctum Linn., and Psidium guajava L. in the inhibition/induction of hepatic and intestinal cytochrome P450 (CYPs) and Phase-II conjugated drug metabolizing enzymes (DMEs). Consumption of these herbal remedy has been extensively documented for diabetes treatment in Ayurveda.

Methodology:

PHF of these five herbs was prepared, and different doses were orally administered to Sprague–Dawley rats of different groups except control group. Expression of mRNA and activity of DMEs were examined by real-time polymerase chain reaction and high performance liquid chromatography in isolated liver and intestine microsomes in PHF pretreated rats.

Results:

The activities of hepatic and intestinal Phase-II enzyme levels increased along with mRNA levels except CYP3A mRNA level. PHF administration increases the activity of hepatic and intestinal UDP-glucuronyltransferase and glutathione S-transferase in response to dose and time; however, the activity of hepatic sulfotransferase increased at higher doses.

Conclusions:

CYPs and Phase-II conjugated enzymes levels can be modulated in dose and time dependent manner. Observations suggest that polyherbal formulation might be a possible cause of herb-drug interaction, due to changes in pharmacokinetic of crucial CYPs and Phase-II substrate drug.

Predicting Drug Extraction in the Human Gut Wall: Assessing Contributions from Drug Metabolizing Enzymes and Transporter Proteins using Preclinical Models

Intestinal metabolism can limit oral bioavailability of drugs and increase the risk of drug interactions. It is therefore important to be able to predict and quantify it in drug discovery and early development. In recent years, a plethora of models-in vivo, in situ and in vitro-have been discussed in the literature. The primary objective of this review is to summarize the current knowledge in the quantitative prediction of gut-wall metabolism. As well as discussing the successes of current models for intestinal metabolism, the challenges in the establishment of good preclinical models are highlighted, including species differences in the isoforms; regional abundances and activities of drug metabolizing enzymes; the interplay of enzyme-transporter proteins; and lack of knowledge on enzyme abundances and availability of empirical scaling factors. Due to its broad specificity and high abundance in the intestine, CYP3A is the enzyme that is frequently implicated in human gut metabolism and is therefore the major focus of this review. A strategy to assess the impact of gut wall metabolism on oral bioavailability during drug discovery and early development phases is presented. Current gaps in the mechanistic understanding and the prediction of gut metabolism are highlighted, with suggestions on how they can be overcome in the future.

Effect of Kidney Function on Drug Kinetics and Dosing in Neonates, Infants, and Children

Neonates, infants, and children differ from adults in many aspects, not just in age, weight, and body composition. Growth, maturation and environmental factors affect drug kinetics, response and dosing in pediatric patients. Almost 80% of drugs have not been studied in children, and dosing of these drugs is derived from adult doses by adjusting for body weight/size. As developmental and maturational changes are complex processes, such simplified methods may result in subtherapeutic effects or adverse events. Kidney function is impaired during the first 2 years of life as a result of normal growth and development. Reduced kidney function during childhood has an impact not only on renal clearance but also on absorption, distribution, metabolism and nonrenal clearance of drugs. 'Omics'-based technologies, such as proteomics and metabolomics, can be leveraged to uncover novel markers for kidney function during normal development, acute kidney injury, and chronic diseases. Pharmacometric modeling and simulation can be applied to simplify the design of pediatric investigations, characterize the effects of kidney function on drug exposure and response, and fine-tune dosing in pediatric patients, especially in those with impaired kidney function. One case study of amikacin dosing in neonates with reduced kidney function is presented. Collaborative efforts between clinicians and scientists in academia, industry, and regulatory agencies are required to evaluate new renal biomarkers, collect and share prospective pharmacokinetic, genetic and clinical data, build integrated pharmacometric models for key drugs, optimize and standardize dosing strategies, develop bedside decision tools, and enhance labels of drugs utilized in neonates, infants, and children.

Population Pharmacokinetic Modeling of the Enterohepatic Recirculation of Fimasartan in Rats, Dogs, and Humans

Enterohepatic recirculation (EHC) can greatly enhance plasma drug exposures and therapeutic effects. This study aimed to develop a population pharmacokinetic model that can simultaneously characterize the extent and time-course of EHC in three species using fimasartan, a novel angiotensin II receptor blocker, as a model drug. All fimasartan plasma concentration profiles in 32 rats (intravenous doses, 0.3-3 mg/kg; oral doses, 1-10 mg/kg), 34 dogs (intravenous doses, 0.3-1 mg/kg; oral doses, 1-10 mg/kg), and 42 healthy volunteers (single or multiple oral doses, 20-480 mg) were determined via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and simultaneously modeled in S-ADAPT. The proposed model quantitatively characterized EHC in three species after oral and intravenous dosing. The median (range) fraction of drug undergoing recirculation was 76.3% (64.9-88.7%) in rats, 33.3% (24.0-45.9%) in dogs, and 65.6% (56.5-72.0%) in humans. In the presence compared with the absence of EHC, the area under the curve in plasma was predicted to be 4.22-fold (2.85-8.85) as high in rats, 1.50-fold (1.32-1.85) in dogs, and 2.91-fold (2.30-3.57) in humans. The modeled oral bioavailability in rats (median (range), 38.7% (20.0-59.8%)) and dogs (median, 7.13% to 15.4%, depending on the formulation) matched the non-compartmental estimates well. In humans, the predicted oral bioavailability was 25.1% (15.1-43.9%) under fasting and 18.2% (12.2-31.0%) under fed conditions. The allometrically scaled area under the curve predicted from rats was 420 ng·h/mL for 60 mg fimasartan compared with 424 ± 63 ng·h/mL observed in humans. The developed population pharmacokinetic model can be utilized to characterize the impact of EHC on plasma drug exposure in animals and humans.

Microbiome, HPA axis and production of endocrine hormones in the gut

Recent accumulating evidence indicates that the gut microbiome can affect the development and regulation of the hypothalamic-pituitary-adrenal axis and behavior, with central integrative systems being crucial in the successful physiological adaptation of the organism to external stressor. In contrast, host-derived hormones increase the bacterial proliferative capacity and pathogenicity. In the gut lumen, this type of cross-talk between microorganisms and the host is presumed to be performed continually through various kinds of luminal molecules, as numerous types of bacteria and host cells are in close proximity in the gastrointestinal tract of mammals.We herein focus on bidirectional signaling between the gut microbiome and the host in terms of commensal microbiota affecting the hypothalamic-pituitary-adrenal HPA axis response and behaviors and further discuss the role of gut luminal catecholamines and γ-aminobutyric acid, both of which are presumed to be involved in this signaling.

Paediatric oral biopharmaceutics: key considerations and current challenges

The complex process of oral drug absorption is influenced by a host of drug and formulation properties as well as their interaction with the gastrointestinal environment in terms of drug solubility, dissolution, permeability and pre-systemic metabolism. For adult dosage forms the use of biopharmaceutical tools to aid in the design and development of medicinal products is well documented. This review considers current literature evidence to guide development of bespoke paediatric biopharmaceutics tools and reviews current understanding surrounding extrapolation of adult methodology into a paediatric population. Clinical testing and the use of in silico models were also reviewed. The results demonstrate that further work is required to adequately characterise the paediatric gastrointestinal tract to ensure that biopharmaceutics tools are appropriate to predict performance within this population. The most vulnerable group was found to be neonates and infants up to 6 months where differences from adults were greatest.

Understanding and modulating mammalian-microbial communication for improved human health

The fact that the bacteria in the human gastrointestinal (GI) tract play a symbiotic role was noted as early as 1885, well before we began to manage microbial infections using antibiotics. However, even with the first antimicrobial compounds used in humans, the sulfa drugs, microbes were recognized to be critically involved in the biotransformation of these therapeutics. Thus, the roles played by the microbiota in physiology and in the management of human health have long been appreciated. Detailed examinations of GI symbiotic bacteria that started in the early 2000s and the first phases of the Human Microbiome Project that were completed in 2012 have ushered in an exciting period of granularity with respect to the ecology, genetics, and chemistry of the mammalian-microbial axes of communication. Here we review aspects of the biochemical pathways at play between commensal GI bacteria and several mammalian systems, including both local-epithelia and nonlocal responses impacting inflammation, immunology, metabolism, and neurobiology. Finally, we discuss how the microbial biotransformation of therapeutic compounds, such as anticancer or nonsteroidal anti-inflammatory drugs, can be modulated to reduce toxicity and potentially improve therapeutic efficacy.

Understanding and modulating mammalian-microbial communication for improved human health

The molecular basis for the regulation of the intestinal barrier is a very fertile research area. A growing body of knowledge supports the targeting of various components of intestinal barrier function as means to treat a variety of diseases, including the inflammatory bowel diseases. Herein, we will summarize the current state of knowledge of key xenobiotic receptor regulators of barrier function, highlighting recent advances, such that the field and its future are succinctly reviewed. We posit that these receptors confer an additional dimension of host-microbe interaction in the gut, by sensing and responding to metabolites released from the symbiotic microbiota, in innate immunity and also in host drug metabolism. The scientific evidence for involvement of the receptors and its molecular basis for the control of barrier function and innate immunity regulation would serve as a rationale towards development of non-toxic probes and ligands as drugs.

Gut microbiota limits heavy metals burden caused by chronic oral exposure

Environmental exposure to pollutants such as heavy metal(s) is responsible for various altered physiological functions which are detrimental for health. The gut microbiota is critical for intestinal homeostasis but its role on xenobiotic handling is not fully understood, especially when continuous sub-chronic exposure is addressed. We first confirmed the essential role of the intestinal microbiome to limit heavy metal body burden by using germ-free mice following 6-weeks oral exposure. Significant increases of cadmium and lead absorption and dissemination in blood and target organs were measured in germ-free mice when compared with conventional specific pathogen free (SPF) mice. Besides the "barrier" function of the luminal microbiota, this may involve specific host-genes such as metallothioneins, which are differentially expressed in the gastrointestinal tract of each group of mice. Considering genes relevant for divalent metal transporters and oxidative pathways, significant differences in basal gene expression were measured between control and germ-free mice. Moreover, the magnitude of induction of these genes upon stimulation by heavy metals varied greatly depending on the dose and type of metal as well as the microbial status of the animal. Collectively, these data illustrate the complex host-microbes interplay occurring with environmental pollutants inside the gut.

Pharmacokinetics and Pharmacodynamics of Once-Daily Controlled-Release Oxybutynin and Immediate-Release Oxybutynin

Oxybutynin is used to treat patients with urinary urgency, frequency, and urge incontinence. In this 2-way, multiple-dose, crossover study, the pharmacokinetics and pharmacodynamics of once-daily controlled-release oxybutynin were compared with immediate-release oxybutynin. Eighteen healthy male volunteers received one 15-mg controlled-release oxybutynin tablet once daily for 5 days or one 5-mg immediate-release oxybutynin tablet every 8 hours for 5 days. The washout period between treatments was > or =7 days. The mean steady-state AUC for oxybutynin following controlled-release oxybutynin treatment was higher (73.0 ng.h/mL) than following immediate-release oxybutynin treatment (53.6 ng.h/mL) (P = .0001). The mean C(max) was lower for controlled-release oxybutynin (5.7 ng/mL) than for immediate-release oxybutynin (7.5 ng/mL) (P = .0051), with a smaller fluctuation in oxybutynin plasma concentration for controlled-release oxybutynin (135.6%) than for immediate-release oxybutynin (319.3%) (P = .0001). Mean stimulated saliva output was greater for controlled-release oxybutynin, and mean dry mouth severity was less than immediate-release oxybutynin.

Critical role of gut microbiota in the production of biologically active, free catecholamines in the gut lumen of mice

There is increasing interest in the bidirectional communication between the mammalian host and prokaryotic cells. Catecholamines (CA), candidate molecules for such communication, are presumed to play an important role in the gut lumen; however, available evidence is limited because of the lack of actual data about luminal CA. This study evaluated luminal CA levels in the gastrointestinal tract and elucidated the involvement of gut microbiota in the generation of luminal CA by comparing the findings among specific pathogen-free mice (SPF-M), germ-free mice (GF-M), and gnotobiotic mice. Substantial levels of free dopamine and norepinephrine were identified in the gut lumen of SPF-M. The free CA levels in the gut lumen were lower in GF-M than in SPF-M. The majority of CA was a biologically active, free form in SPF-M, whereas it was a biologically inactive, conjugated form in GF-M. The association of GF-M with either Clostridium species or SPF fecal flora, both of which have abundant β-glucuronidase activity, resulted in the drastic elevation of free CA. The inoculation of E. coli strain into GF-M induced a substantial amount of free CA, but the inoculation of its mutant strain deficient in the β-glucuronidase gene did not. The intraluminal administration of DA increased colonic water absorption in an in vivo ligated loop model of SPF-M, thus suggesting that luminal DA plays a role as a proabsorptive modulator of water transport in the colon. These results indicate that gut microbiota play a critical role in the generation of free CA in the gut lumen.

Loss of orally administered drugs in GI tract

The aim of this review is to provide a broad perspective on intestinal absorption and the impact of intestinal first-pass metabolism on both clearance and drug-drug interaction prediction along with its historical perspectives. The review also considers abilities to bridge the gap between the increasing amount of intestinal in vitro data and the importance of intestinal first-pass metabolism in vivo. The significance of efflux transporters on the intestinal absorption is also discussed.

Neonatal pharmacology: extensive interindividual variability despite limited size

Providing safe and effective drug therapy to neonates requires knowledge of the impact of development on the pharmacokinetics and pharmacodynamics of drugs. Although maturational changes are observed throughout childhood, they are most prominent during the first year of life. Several of these processes overlap, making development an extremely dynamic system in the newborn compared with that in infants, children, or adults. Changes in body composition and porportions, liver mass, metabolic activity, and renal function collectively affect the pharmacokinetic behavior of medications. Instead of simply adapting doses by scaling adult or pediatric doses on the basis of a patient's weight and/or body surface area, integrated knowledge of clinical maturation and developmental pharmacology is critical to the safe and effective use of medications in neonates. Unfortunately, the effects of human ontogeny on both pharmacokinetics and pharmacodynamics have not been well established in these early stages of life, and information regarding the influence of developmental changes on the pharmacodynamics of medications is even more limited. Theoretically, age-dependent variations in receptor number and affinity for drugs have significant potential to influence an individual's response to drug therapy. In this review, some of the relevant covariates of pharmacokinetics and pharmacodynamics in neonates are reviewed and illustrated based on the published literature.

Effects of bacterial and presystemic nitroreductase metabolism of 2-chloro-5-nitro-N-phenylbenzamide on its mutagenicity and bioavailability

2-Chloro-5-nitro-N-phenylbenzamide (GW9662), a potent irreversible PPAR-γ antagonist, has shown promise as a cancer chemopreventive agent and is undergoing preclinical evaluations. Studies were initiated to assess its bacterial mutagenicity and pharmacokinetic profile in two animal species prior to subchronic oral toxicity evaluations and the results are reported here. GW9662 was mutagenic in both TA98 and TA100 bacterial strains with and without metabolic activation but was negative in the nitroreductase-deficient strains (TA98NR and TA100NR) also with and without metabolic activation, indicating that GW9662 mutagenicity is dependent on nitroreduction. The mutagenic activity was predominantly via a base-substitution mechanism. Following oral dosing in rats and dogs, the parent compound, GW9662, was virtually absent from plasma samples, but there was chromatographic evidence for the presence of metabolites in the plasma as a result of oral dosing. Metabolite identification studies showed that an amine metabolite ACPB (5-amino-2-chloro-N-phenylbenzamide), a product of nitro reduction, was the predominant species exhibiting large and persistent plasma levels. Thus systemic circulation of GW9662 has been attained largely in the form of its reduced metabolite, probably a product of gut bacterial metabolism. GW9662 was detectable in plasma of rats and dogs after intravenous dose albeit at low concentrations. Pharmacokinetic analysis following intravenous dosing in rats showed a rapid clearance and an extensive tissue distribution which could have accounted for the very low plasma levels. Of note, the amine metabolite was absent following intravenous dosing in both rats and dogs, confirming it being a product of presystemic metabolism. The potential utility of GW9662 as a chemopreventive agent, especially as an Estrogen Receptor-α (ER-α) inducer in an otherwise ER-α negative breast tissue, is of great interest. However, the results shown here suggest that additional animal toxicological and bioavailability studies are required to establish a role of GW9662 as a chemopreventive agent.

The influence of probiotic treatment on sulfasalazine metabolism in rat

Probiotics are live microorganisms claimed to exert beneficial effects on the host. This study investigated their effect on the metabolism and pharmacokinetics of sulfasalazine (SSZ), a drug whose efficacy depends on metabolism by azoreductase (AR) in the gut microbiota to sulfapyridine (SP) and 5-acetylsalicylic acid (5-ASA). The probiotic strains Lactobacillus acidophilus L10, Bifidobacterium lactis B94 and Streptococcus salivarius K12 possessed AR activity and a corresponding ability to metabolize SSZ. Treatment of male Wistar rats (n = 5) with oral 2 g doses of a mixture of the three probiotics (total dose 1.8 × 10⁹ cfu) every 12 h for 3 days resulted in a significant increase (p < 0.05) in AR activity in ex vivo colon contents with a corresponding increase in SSZ metabolism. Similar probiotic treatment of male Wistar rats (n = 8) followed by an oral 100 mg/kg dose of SSZ produced high plasma levels of SP, but pharmacokinetic parameters of SSZ and SP were not significantly different from control rats given SSZ. These results indicate that probiotic strains possess AR activity and can metabolize SSZ. Treatment with probiotics increases AR activity in the gut microbiota but has no effect on plasma levels of SSZ and SP following a subsequent oral dose of SSZ.

Investigation of endogenous metabolic changes in the urine of pseudo germ-free rats using a metabolomic approach

Gut microflora are recognized as an active metabolic compartment in whole body systems. Understanding their impact on host physiology is an ongoing process, although many studies demonstrate that they play significant roles in host life. To assess the impact of gut microflora on host physiology in normal or close to normal conditions of the intestine, we prepared pseudo germ-free rats by antibiotic treatment, and we investigated urinary metabolite profiles of pseudo germ-free rats using UPLC-QTOF-MS based on metabolomics. The repeatability and stability of the analysis were evaluated using QC samples and testmixes in both positive and negative ionization modes. When data sets were analyzed with OPLS-DA, 25 metabolites related to the activities of gut microflora were identified. The changes of amino acid metabolism, especially aromatic or sulfur amino acids, and alternations of bioactive nutrients, such as isoflavonoid and riboflavin were observed in the pseudo germ-free rats. Among the sulfur amino acid metabolites, the metabolites reflecting oxidative stress increased in the urine of pseudo germ-free animals, which imply that the activities of intestinal microorganisms can affect the host redox homeostasis. Altered isoflavonoid metabolism due to lack of gut bacteria may impact on steroid hormone metabolism in the body, especially estrogen metabolism. These results indicate that the some essential metabolic pathways are sensitive to the activities of gut microorganism and directly or indirectly affected by the state of intestinal bacteria, thus gut microflora plays an important role in whole body physiology.

Metabolism of cyadox by the intestinal mucosa microsomes and gut flora of swine, and identification of metabolites by high-performance liquid chromatography combined with ion trap/time-of-flight mass spectrometry

Cyadox (CYX), 2-formylquinoxaline-1,4-dioxide cyanoacetylhydrazone, is an antimicrobial and growth-promoting feed additive for food-producing animals. To reveal biotransformation of CYX in swine intestine, CYX was incubated with swine intestinal microsomes and mucosa in the presence of an NADPH-generating system and swine ileal flora and colonic flora, respectively. The metabolites of CYX were identified using high-performance liquid chromatography combined with ion trap/time-of-flight mass spectrometry (LC/MS-ITTOF). Structural elucidation of the metabolites was precisely performed by comparing their changes in molecular mass, full scan MS/MS spectra and accurate mass measurements with those of the parent drug. Finally, seven metabolites were identified as follows: three reduced metabolites (cyadox 1-monoxide (Cy1), cyadox 4-monoxide (Cy2) and bisdesoxycyadox (Cy4)); hydroxylation metabolite (3-hydroxylcyadox 1-monoxide (Cy3)); hydrolysis metabolite of the amide bond (N-decyanoacetyl cyadox (Cy5)); a hydrogenation metabolite (11,12-dihydro-bisdesoxycyadox (Cy6)) and a side-chain cleavage metabolite (2-hydromethylquinoxaline (Cy7)). Only one metabolite (Cy1) was found in intestinal microsomes. Cy1, Cy2 and Cy4 were detected in intestinal mucosa, ileal and colonic flora. In addition, Cy3 and Cy5 were only obtained from ileal flora, and Cy6 and Cy7 alone were observed in colonic bacteria. The results indicated that N→O group reduction was the main metabolic pathway of CYX metabolism in swine ileal flora, intestinal microsomes and mucosa. New metabolic profiles of hydrogenation and cleavage on the side chain were found in colonic bacteria. Among the identified metabolites, two new metabolites (Cy6, Cy7) were detected for the first time. These studies will contribute to clarify comprehensively the metabolism of CYX in animals, and provide evidence to explain the pharmacology and toxicology effects of CYX in animals.

Nutrition modulation of gastrointestinal toxicity related to cancer chemotherapy: from preclinical findings to clinical strategy

Chemotherapy-induced gut toxicity is a major dose-limiting toxicity for many anticancer drugs. Gastrointestinal (GI) complications compromise the efficacy of chemotherapy, promote overall malnutrition, aggravate cancer cachexia, and may contribute to worsened prognosis. The GI tract is an attractive target for nutrition modulation, owing to its direct exposure to the diet, participation in uptake and metabolism of nutrients, high rate of cell turnover, and plasticity to nutrition stimuli. Glutamine, ω-3 polyunsaturated fatty acids, and probiotics/prebiotics are therapeutic factors that potentially modulate GI toxicity related to cancer treatments. Preclinical and clinical evidence are reviewed to critically define plausible benefits of these factors and their potential development into adjuncts to cancer chemotherapy. Mechanisms underlying the action of these nutrients are being unraveled in the laboratory. Optimal strategies to translate these findings into clinical care still remain to be elucidated. Key questions that remain to be answered include the following: which nutrient or combination of nutrients is selected for which patient and chemotherapy regimen? What mechanisms are responsible for modulation, and how are nutrient(s) administered in a clinically optimal manner? Research exploring interactions between different nutrients in GI protection is ongoing and demands further understanding. How nutrition preparations given to chemotherapy-treated patients are formulated in terms of component selection and dose optimization should be carefully studied and justified.

The evolution of population pharmacokinetic models to describe the enterohepatic recycling of mycophenolic acid in solid organ transplantation and autoimmune disease

With the increasing use of mycophenolic acid (MPA) as an immunosuppressant in solid organ transplantation and in treating autoimmune diseases such as systemic lupus erythematosus, the need for strategies to optimize therapy with this agent has become increasingly apparent. This need is largely based on MPA's significant between-subject and between-occasion (within-subject) pharmacokinetic variability. While there is a strong relationship between MPA exposure and effect, the relationship between drug dose, plasma concentration and exposure (area under the concentration-time curve [AUC]) is very complex and remains to be completely defined. Population pharmacokinetic models using various approaches have been proposed over the past 10 years to further evaluate the pharmacokinetic and pharmacodynamic behaviour of MPA. These models have evolved from simple one-compartment linear iterations to complex multi-compartment versions that try to include various factors, which may influence MPA's pharmacokinetic variability, such as enterohepatic recycling and pharmacogenetic polymorphisms. There have been major advances in the understanding of the roles transport mechanisms, metabolizing and other enzymes, drug-drug interactions and pharmacogenetic polymorphisms play in MPA's pharmacokinetic variability. Given these advances, the usefulness of empirical-based models and the limitations of nonlinear mixed-effects modelling in developing mechanism-based models need to be considered and discussed. If the goal is to individualize MPA dosing, it needs to be determined whether factors which may contribute significantly to variability can be utilized in the population pharmacokinetic models. Some pharmacokinetic models developed to date show promise in being able to describe the impact of physiological processes such as enterohepatic recycling. Most studies have historically been based on retrospective data or poorly designed studies which do not take these factors into consideration. Modelling typically has been undertaken using non-controlled therapeutic drug monitoring data, which do not have the information content to support the development of complex mechanistic models. Only a few recent modelling approaches have moved away from empiricism and have included mechanisms considered important, such as enterohepatic recycling. It is recognized that well thought-out sampling schedules allow for better evaluation of the pharmacokinetic data. It is not possible to undertake complex absorption modelling with very few samples being obtained during the absorption phase (which has often been the case). It is important to utilize robust AUC monitoring which is now being propagated in the latest consensus guideline on MPA therapeutic drug monitoring. This review aims to explore the biological factors that contribute to the clinical pharmacokinetics of MPA and how these have been introduced in the development of population pharmacokinetic models. An overview of the processes involved in the enterohepatic recycling of MPA will be provided. This will summarize the components that complicate absorption and recycling to influence MPA exposure such as biotransformation, transport, bile physiology and gut flora. Already published population pharmacokinetic models will be examined, and the evolution of these models away from empirical approaches to more mechanism-based models will be discussed.

Development of colon targeted multiparticulate pulsatile drug delivery system for treating nocturnal asthma

The aim of the present study was to develop theophylline fast release enteric-coated pellets as a pulsatile drug delivery to the colon. The novelty of this work is the combination of pH and time-dependant enteric polymers as a single coating for the development of multiparticulate formulation. Theophylline pellets were optimized by applying a 2-factors 3-levels full factorial design. Continuous dissolution studies were carried out in simulated gastric, intestinal, and colonic fluid with pH 1.2 (0.1 N HCl), pH 7.4 and pH 6.8 (phosphate buffer), respectively. The lag time prior to the drug release was highly affected by combination of two factors, i.e. the percentage of Eudragit RL100 in polymer mixture and coating level. The formulation containing Eudragit RL100 and Eudragit S100 with a ratio of 4:1 and coating level of 12%w/w was found to be optimum. The results of serum study in New Zealand rabbits showed that the developed formulation provided a significant lag phase of 5 h. The present study demonstrates that the theophylline enteric-coated pellets could be successfully colon targeted by the design of pH- and time-dependant modified chronopharmaceutical formulation. In conclusion, pulsatile drug release over a period of 3-12 h is consistent with the requirements for chronopharmaceutical drug delivery.

The intestinal microbiome: a separate organ inside the body with the metabolic potential to influence the bioactivity of botanicals

For many years, it was believed that the main function of the large intestine was the resorption of water and salt and the facilitated disposal of waste materials. However, this task definition was far from complete, as it did not consider the activity of the microbial content of the large intestine. Nowadays it is clear that the complex microbial ecosystem in our intestines should be considered as a separate organ within the body, with a metabolic capacity which exceeds the liver with a factor 100. The intestinal microbiome is therefore closely involved in the first-pass metabolism of dietary compounds. This is especially true for botanical supplements, which are now marketed for various health applications. Being of natural origin, their structural building blocks, such as polyphenols, are often highly recognized by the human and especially the intestinal microbial metabolism machinery. Intensive metabolism results in often low circulating levels of the original products, with the consequence that final health effects of botanicals are often related to specific active metabolites which are produced in the body rather than being related to the product's original composition. Understanding how such metabolic processes contribute to the in situ exposure is therefore crucial for the proper interpretation of biological responses. A multidisciplinary approach, characterizing the food and phytochemical intake as well as the metabolic potency of the gut microbiota, while measuring biomarkers of both exposure and response in target tissues, is therefore of critical importance. With polyphenol metabolism as example, this review describes how the incorporation of microbial metabolism as an important variable in the evaluation of the final bioactivity of botanicals strongly increases the relevance and predictive value of the outcome. Moreover, knowledge about intestinal processes may offer innovative strategies for targeted product development.

Activities of biotransformation enzymes and flubendazole metabolism in lambs (Ovis aries): effect of gender and flubendazole therapy

The effect of flubendazole (FLU) therapy on in vitro FLU biotransformation and the activities of selected biotransformation enzymes were investigated in male and female lambs. Four experimental groups were used: control (untreated) ewes and rams and FLU-treated ewes and rams (orally, 15 mg/kg per day, for three consecutive days). Subcellular fractions were prepared from liver and intestinal mucosa 24 h after the final dosage was administered. Activities of cytochromes P450 (CYP), flavine monooxygenases (FMO), carbonyl reducing enzymes, UDP-glucuronosyl transferase (UGT) and glutathione S-transferase were tested. Significant gender differences were observed for FMO-mediated activity (2-fold higher in ram lambs) and UGT activity (up to 30% higher in ewe lambs), but no gender differences were observed in FLU metabolism. FLU-treatment of lambs moderately changed the activities of some CYPs, FMO, and UGT in liver microsomes. In vitro FLU reduction was not altered in the liver, but was slightly higher in the small intestine of FLU pre-treated lambs. This correlated with the higher carbonyl reductase activities measured in the gut mucosa of these animals.

Inhibition of warfarin hydroxylation by major tanshinones of Danshen (Salvia miltiorrhiza) in the rat in vitro and in vivo

Danshen (Salvia miltiorrhiza) is commonly used in the treatment of cardiovascular and cerebrovascular diseases. In this study, the effects of a Danshen ethyl acetate extract containing the major tanshinones, an aqueous extract containing salvianolic acid B and danshensu, and individual tanshinones (tanshinone I, tanshinone IIA and cryptotanshinone) on warfarin hydroxylation was investigated. In rat liver microsomes study, the ethyl acetate extract of Danshen, tanshinone I, tanshinone IIA and cryptotanshinone decreased the formation of 4'-, 6- and 7-hydroxy-warfarin, mediated by CYP1A1, CYP2C6 and CYP2C11 activities, respectively. The aqueous extract of Danshen had no effect on warfarin hydroxylation. Both acute and 3-day Danshen treatment significantly decreased Cmax and prolonged Tmax of warfarin in the rats. The formation of 4'- and 7-hydroxywarfarin in vivo was decreased significantly after 3-day danshen treatment. In steady state study in vivo, the steady state plasma warfarin concentration was increased by 23% when Danshen was co-administered. The results suggest that tanshinones inhibited CYP1A1, CYP2C6 and CYP2C11-mediated warfarin metabolism both in vitro and in vivo in the rats. The timing of Danshen intake relative to warfarin contributed to different pharmacokinetics of the free warfarin concentration.

The effect of dose on 2,3,7,8-TCDD tissue distribution, metabolism and elimination in CYP1A2 (-/-) knockout and C57BL/6N parental strains of mice

Numerous metabolism studies have demonstrated that the toxic contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is poorly metabolized. A hallmark feature of TCDD exposure is induction of hepatic CYP1A2 and subsequent sequestration leading to high liver-to-fat concentration ratios. This study was initiated to determine whether TCDD was inherently poorly metabolized or unavailable for metabolism because of sequestration to CYP1A2. [(3)H]TCDD was administered as a single, oral dose (0.1 and 10 microg/kg) to 12 male C57BL/6N mice or 12 CYP1A2 (-/-) mice. At 96 h, less than 5% of the dose was eliminated in the urine of all groups, and TCDD detected in urine was bound to mouse major urinary protein (mMUP). Feces were the major elimination pathway (24-31% of dose), and fecal extracts and non-extractables were quantitated by HPLC for metabolites. No great differences in urinary or fecal elimination (% dose) were observed between the high and low dose treatments. TCDD concentrations were the highest in adipose tissue for CYP1A2 knockout mice but in liver for C57BL/6N mice supporting the role of hepatic CYP1A2 in the sequestration of TCDD. Overall metabolism between parental and knockout strains showed no statistical differences at either the high or low doses. The data suggested that metabolism of TCDD is inherently slow, due principally to CYP1A1, and that hepatic CYP1A2 is not an active participant in the metabolism of TCDD in male mice. Rather, CYP1A2 governs the pharmacokinetics of TCDD by making it unavailable for hepatic CYP1A1 through sequestration and attenuating extrahepatic tissue disposition.

Interaction between phenolics and gut microbiota: role in human health

Dietary phenolic compounds are often transformed before absorption. This transformation modulates their biological activity. Different studies have been carried out to understand gut microbiota transformations of particular polyphenol types and identify the responsible microorganisms. Although there are potentially thousands of different phenolic compounds in the diet, they are typically transformed to a much smaller number of metabolites. The aim of this review was to discuss the current information about the microbial degradation metabolites obtained from different phenolics and their formation pathways, identifying their differences and similarities. The modulation of gut microbial population by phenolics was also reviewed in order to understand the two-way phenolic-microbiota interaction. Clostridium and Eubacterium genera, which are phylogenetically associated, are other common elements involved in the metabolism of many phenolics. The health benefits from phenolic consumption should be attributed to their bioactive metabolites and also to the modulation of the intestinal bacterial population.