Experimental models for predicting drug absorption and metabolism

Ex vivo gut-hepato-biliary organ perfusion model to characterize oral absorption, gut-wall metabolism, pre-systemic hepatic metabolism and biliary excretion; application to midazolam

To date, characterization of the first-pass effect of orally administered drugs consisting of local intestinal absorption and metabolism, portal vein transport and hepatobiliary processes remains challenging. Aim of this study was to explore the applicability of a porcine ex-vivo perfusion model to study oral absorption, gut-hepatobiliary metabolism and biliary excretion of midazolam. Slaughterhouse procured porcine en bloc organs (n = 4), were perfused via the aorta and portal vein. After 120 min of perfusion, midazolam, atenolol, antipyrine and FD4 were dosed via the duodenum and samples were taken from the systemic- and portal vein perfusate, intestinal faecal effluent and bile to determine drug and metabolite concentrations. Stable arterial and portal vein flow was obtained and viability of the perfused organs was confirmed. After intraduodenal administration, midazolam was rapidly detected in the portal vein together with 1-OH midazolam (EG-pv of 0.16±0.1) resulting from gut wall metabolism through oxidation. In the intestinal faecal effluent, 1-OH midazolam and 1-OH midazolam glucuronide (EG-intestine 0.051±0.03) was observed resulting from local gut glucuronidation. Biliary elimination of midazolam (0.04±0.01 %) and its glucuronide (0.01±0.01 %) only minimally contributed to the enterohepatic circulation. More extensive hepatic metabolism (FH 0.35±0.07) over intestinal metabolism (FG 0.78±0.11) was shown, resulting in oral bioavailability of 0.27±0.05. Ex vivo perfusion demonstrated to be a novel approach to characterize pre-systemic extraction of midazolam by measuring intestinal as well as hepatic extraction. The model can generate valuable insights into the absorption and metabolism of new drugs.

Utility of human induced pluripotent stem cell-derived small intestinal epithelial cells for pharmacokinetic, toxicological, and immunological studies

The small intestine, which plays a crucial role in the absorption and metabolism of drugs and foods, serves as a target organ for drug-induced toxicity and immune interactions with functional foods and intestinal bacteria. Current alternative models of the human small intestine, such as Caco-2 cells and experimental animals, have limitations due to variations in the expression levels of metabolic enzymes, transporters, and receptors. This study presents investigations into the utility of human induced pluripotent stem cell-derived small intestinal epithelial cells (hiSIECs) for pharmacokinetic, toxicological, and immunological studies, respectively. While hiSIECs displayed small intestinal epithelial cell characteristics and barrier function, they demonstrated pharmacokinetic properties such as cytochrome P450 3A4/5 activity equivalent to human primary enterocytes and stable P-glycoprotein activity. These cells also demonstrated potential for assessing two forms of intestinal toxicity caused by anticancer drugs and gamma-secretase inhibitors, displaying immune responses mediated by toll-like and fatty acid receptors while serving as an inflammatory gut model through the addition of tumor necrosis factor alpha and interferon gamma. Overall, hiSIECs hold promise as an in vitro model for assessing pharmacokinetics, toxicity, and effects on the intestinal immunity of pharmaceuticals, functional foods, supplements, and intestinal bacteria.

Experimental and computational models to investigate intestinal drug permeability and metabolism

Oral administration is the preferred route for drug administration that leads to better therapy compliance. The intestine plays a key role in the absorption and metabolism of oral drugs, therefore, new intestinal models are being continuously proposed, which contribute to the study of intestinal physiology, drug screening, drug side effects, and drug-drug interactions.Advances in pharmaceutical processes have produced more drug formulations, causing challenges for intestinal models. To adapt to the rapid evolution of pharmaceuticals, more intestinal models have been created. However, because of the complexity of the intestine, few models can take all aspects of the intestine into account, and some functions must be sacrificed to investigate other areas. Therefore, investigators need to choose appropriate models according to the experimental stage and other requirements to obtain the desired results.To help researchers achieve this goal, this review summarised the advantages and disadvantages of current commonly used intestinal models and discusses possible future directions, providing a better understanding of intestinal models.

Development of 3D-Bioprinted Colitis-Mimicking Model to Assess Epithelial Barrier Function Using Albumin Nano-Encapsulated Anti-Inflammatory Drugs

Physiological barrier function is very difficult to replicate in vitro. This situation leads to poor prediction of candidate drugs in the drug development process due to the lack of preclinical modelling for intestinal function. By using 3D bioprinting, we generated a colitis-like condition model that can evaluate the barrier function of albumin nanoencapsulated anti-inflammatory drugs. Histological characterization demonstrated the manifestation of the disease in 3D-bioprinted Caco-2 and HT-29 constructs. A comparison of proliferation rates in 2D monolayer and 3D-bioprinted models was also carried out. This model is compatible with currently available preclinical assays and can be implemented as an effective tool for efficacy and toxicity prediction in drug development.

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

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

Do Thickening Agents Used in Dysphagia Diet Affect Drug Bioavailability?

Swallowing oral solid dosage forms is challenging in patients with dysphagia who are at risk of aspiration or choking. The most common method to facilitate drug administration in dysphagia patients is to mix the powdered drug with a small amount of thickened water, however little is known about the effects of this method on in vivo bioavailability of drugs. This study aimed to evaluate the impact of thickened liquids on dissolution rate and bioavailability of levetiracetam as a model drug. Powdered commercial tablets of levetiracetam, carbamazepine, atenolol and cefixime were mixed with water thickened with two commercial thickeners, modified maize starch (MS) and xanthan gam (XG), at three thickness levels: nectar, honey and pudding in test groups, and mixed with only water in the control group. At the first stage, the effects of thickened water on in vitro drug release of 4 drugs (levetiracetam, carbamazepine, atenolol and cefixime) were tested by using dialysis membrane method. Addition of both thickeners significantly reduced the release of three drugs compared to the control group, except carbamazepine. Levetiracetam which had the highest solubility was chosen as the model drug for in vivo experiments. In the second stage, New Zealand albino female rabbits (n=24) were divided into two groups as: control group (water+drug, n=6) and test group (thickened water+drug, n=18). Powdered levetiracetam tablets were mixed with water thickened with XG (n=9, 1.2 %, 2.4 %, 3.6 %) and MS (n=9, 4 %, 6%, 8 %) at three thickness levels and administered to the rabbits by intragastric gavage. Blood samples were collected at 9 time points following administration. After two-weeks of wash-out, test groups were crossed over and sample collection was repeated. Blood samples were analysed using liquid chromatography with tandem mass spectrometry (LC-MS/MS). An in vitro-in vivo correlation (IVIVC) model was developed using in vitro drug dissolution (%) and in vivo plasma concentrations of levetiracetam for control group and test groups. The peak plasma concentration (C_max) was lower and time to reach C_max (t_max) was relatively higher in test groups compared to control group. The lowest C_max was detected at the highest thickness level, however, the differences between groups were not statistically significant (p=0.117 and p=0.495 for C_max and t_max, respectively). No significant difference in total amount of levetiracetam absorbed (AUC) was found between groups (p=0.215 and p=0.183 for AUC_infinity and AUC_last, respectively). The comparisons according to the type of thickener also revealed that pharmacokinetic parameters did not significantly differ between groups, except for a significantly lower C_max when drug was mixed with MS-thickened water at nectar consistency (1.2 %) compared to drug mixed with XG (4 %) at the same thickness level (p=0.038). A good correlation was observed between in vitro and in vivo data, which was characterized by higher r² values as the concentration of the thickening agents was increased, but not for all thickness levels studied, indicating an inability of this in vitro model to fully predict the in vivo response. These results suggest that regardless of the thickness level, the administration of levetiracetam with two commercial thickening agents commonly used in dysphagia for safe swallowing, do not affect the pharmacokinetic efficiency and thus, the bioavailability of the drug.

Intestinal explant barrier chip: long-term intestinal absorption screening in a novel microphysiological system using tissue explants

The majority of intestinal in vitro screening models use cell lines that do not reflect the complexity of the human intestinal tract and hence often fail to accurately predict intestinal drug absorption. Tissue explants have intact intestinal architecture and cell type diversity, but show short viability in static conditions. Here, we present a medium throughput microphysiological system, Intestinal Explant Barrier Chip (IEBC), that creates a dynamic microfluidic microenvironment and prolongs tissue viability. Using a snap fit mechanism, we successfully incorporated human and porcine colon tissue explants and studied tissue functionality, integrity and viability for 24 hours. With a proper distinction of transcellular over paracellular transport (ratio >2), tissue functionality was good at early and late timepoints. Low leakage of FITC-dextran and preserved intracellular lactate dehydrogenase levels indicate maintained tissue integrity and viability, respectively. From a selection of low to high permeability drugs, 6 out of 7 properly ranked according to their fraction absorbed. In conclusion, the IEBC is a novel screening platform benefitting from the complexity of tissue explants and the flow in microfluidic chips.

Baicalin Enhanced Oral Bioavailability of Sorafenib in Rats by Inducing Intestine Absorption

Background: Sorafenib (SOR) is an oral, potent, selective, irreversible epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) used as the first-line therapy for advanced hepatocellular carcinoma (HCC). Baicalin (BG) is used as adjuvant therapy for hepatitis, which accounts for the leading cause of the development of HCC, and is commonly coadministered with SOR in clinic. The purpose of the current study was to characterize the pharmacokinetic changes of SOR and the potential mechanism when SOR is administered concomitantly with BG in rats for single and multiple doses.

Methods: Parallel randomized pharmacokinetic studies were performed in rats which received SOR (50 mg/kg, i.g.) alone or coadministered with BG (160 mg/kg, i.g.) for single and multiple doses (7 days). Plasma SOR levels were quantified by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). Rat liver microsomes (RLMs) which isolated from their livers were analyzed for CYP3A and SOR metabolism activities. The inhibitory effect of BG on the metabolism of SOR was also assessed in pooled human liver microsomes (HLMs). The effects of BG on the intestine absorption behaviors of SOR were assessed in the in situ single-pass rat intestinal perfusion model.

Results: Coadministration with BG (160 mg/kg, i.g.) for single or multiple doses significantly increased the C_max, AUC_0–t, and AUC_0–∞ of orally administered SOR by 1.68-, 1.73-, 1.70-fold and 2.02-, 1.65-, 1.66- fold in male rats and by 1.85-, 1.68-, 1.68-fold and 1.57-, 1.25-, 1.24- fold in female rats, respectively (p < 0.01 or p < 0.05). In vitro incubation assays demonstrated that there were no significant differences of K_m, V_max, and CL_int of 1-OH MDZ and SOR N-oxide in RLMs between control and multiple doses of BG-treated groups. BG has no obvious inhibitory effects on the metabolism of SOR in HLMs. In comparison with SOR alone, combining with BG significantly increased the permeability coefficient (P_eff) and absorption rate constant (K_a) of the SOR in situ single-pass rat intestinal perfusion model.

Conclusion: Notably enhanced oral bioavailability of SOR by combination with BG in rats may mainly account for BG-induced SOR absorption. A greater understanding of potential DDIs between BG and SOR in rats makes major contributions to clinical rational multidrug therapy in HCC patients. Clinical trials in humans and HCC patients need to be further confirmed in the subsequent study.

Does Chemotherapy-Induced Gastrointestinal Mucositis Affect the Bioavailability and Efficacy of Anti-Infective Drugs?

Antimicrobial prophylaxis is increasingly being used in patients with hematological malignancies receiving high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT). However, few studies have focused on the potential impact of gastrointestinal mucositis (GI-M), a frequently observed side effect of chemotherapy in patients with cancer that affects the gastrointestinal microenvironment, on drug absorption. In this review, we discuss how chemotherapy leads to an overall loss of mucosal surface area and consequently to uncontrolled transport across the barrier. The barrier function is depending on intestinal luminal pH, intestinal motility, and diet. Another factor contributing to drug absorption is the gut microbiota, as it modulates the bioavailability of orally administrated drugs by altering the gastrointestinal properties. To better understand the complex interplay of factors in GI-M and drug absorption we suggest: (i) the longitudinal characterization of the impact of GI-M severity on drug exposure in patients, (ii) the development of tools to predict drug absorption, and (iii) strategies that allow the support of the gut microbiota. These studies will provide relevant data to better design strategies to reduce the severity and impact of GI-M in patients with cancer.

Prediction of hepatic drug clearance with a human microfluidic four-cell liver acinus microphysiology system

Predicting human hepatic clearance remains a fundamental challenge in both pharmaceutical drug development and toxicological assessments of environmental chemicals, with concerns about both accuracy and precision of in vitro-derived estimates. Suggested sources of these issues have included differences in experimental protocols, differences in cell sourcing, and use of a single cell type, liver parenchymal cells (hepatocytes). Here we investigate the ability of human microfluidic four-cell liver acinus microphysiology system (LAMPS) to make predictions as to hepatic clearance for seven representative compounds: Caffeine, Pioglitazone, Rosiglitazone, Terfenadine, Tolcapone, Troglitazone, and Trovafloxacin. The model, whose reproducibility was recently confirmed in an inter-lab comparison, was constructed using primary human hepatocytes or human induced pluripotent stem cell (iPSC)-derived hepatocytes and 3 human cell lines for the endothelial, Kupffer and stellate cells. We calculated hepatic clearance estimates derived from experiments using LAMPS or traditional 2D cultures and compared the outcomes with both in vivo human clinical study-derived and in vitro human hepatocyte suspension culture-derived values reported in the literature. We found that, compared to in vivo clinically-derived values, the LAMPS model with iPSC-derived hepatocytes had higher precision as compared to primary cells in suspension or 2D culture, but, consistent with previous studies in other microphysiological systems, tended to underestimate in vivo clearance. Overall, these results suggest that use of LAMPS and iPSC-derived hepatocytes together with an empirical scaling factor warrants additional study with a larger set of compounds, as it has the potential to provide more accurate and precise estimates of hepatic clearance.

Generation of tetracycline-controllable CYP3A4-expressing Caco-2 cells by the piggyBac transposon system

Caco-2 cells are widely used as an in vitro intestinal epithelial cell model because they can form a monolayer and predict drug absorption with high accuracy. However, Caco-2 cells hardly express cytochrome P450 (CYP), a drug-metabolizing enzyme. It is known that CYP3A4 is the dominant drug-metabolizing enzyme in human small intestine. In this study, we generated CYP3A4-expressing Caco-2 (CYP3A4-Caco-2) cells and attempted to establish a model that can simultaneously evaluate drug absorption and metabolism. CYP3A4-Caco-2 cells were generated by piggyBac transposon vectors. A tetracycline-controllable CYP3A4 expression cassette (tet-on system) was stably transduced into Caco-2 cells, thus regulating the levels of CYP3A4 expression depending on the doxycycline concentration. The CYP3A4 expression levels in CYP3A4-Caco-2 cells cultured in the presence of doxycycline were similar to or higher than those of adult small intestine. The CYP3A4-Caco-2 cells had enough ability to metabolize midazolam, a substrate of CYP3A4. CYP3A4 overexpression had no negative effects on cell proliferation, barrier function, and P-glycoprotein activity in Caco-2 cells. Thus, we succeeded in establishing Caco-2 cells with CYP3A4 metabolizing activity comparable to in vivo human intestinal tissue. This cell line would be useful in pharmaceutical studies as a model that can simultaneously evaluate drug absorption and metabolism.

Physicochemical Stability of Enriched Phenolic Fractions of Cyclopia genistoides and ex vivo Bi-directional Permeability of Major Xanthones and Benzophenones

Fractions of an ultrafiltered Cyclopia genistoides extract, respectively enriched in xanthones and benzophenones, were previously shown to inhibit mammalian α-glucosidase in vitro. The present study investigated ex vivo intestinal transport of these fractions, using excised porcine jejunal tissue, to determine whether the gut could be a predominant in vivo site of action. The major bioactive compounds, the xanthones (mangiferin, isomangiferin) and benzophenones (3-β-D-glucopyranosyliriflophenone, 3-β-D-glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone) exhibited poor permeation in the absorptive direction with a relatively high efflux ratio (efflux ratio > 1). The efflux ratio of 3-β-D-glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone (3.05) was similar to rhodamine 123 (2.99), a known substrate of intestinal P-glycoprotein 1 efflux transporters. Low epithelial membrane transport rates, coupled with efflux mechanisms, would effectively concentrate these bioactive compounds at the target site (gut lumen). Storage stability testing and moisture sorption assays of the xanthone-enriched fraction, benzophenone-enriched fraction, and ultrafiltered Cyclopia genistoides extract were performed to determine their susceptibility to physical and chemical degradation during storage. Hygroscopicity of the powders, indicated by moisture uptake, decreased in the order: benzophenone-enriched fraction (22.7%) > ultrafiltered Cyclopia genistoides extract (14.0%) > xanthone-enriched fraction (10.7%). 3-β-D-Glucopyranosylmaclurin, a minor benzophenone, was the least stable of the compounds, degrading faster in the benzophenone-enriched fraction than in ultrafiltered Cyclopia genistoides extract, suggesting that the ultrafiltered extract matrix may provide a degree of protection against chemical degradation. Compound degradation during 12 wk of storage at 40 °C in moisture-impermeable containers was best explained by first order reaction kinetics.

Cell culture as a toolbox to generate phase I metabolites for antidoping screening

The knowledge of the biotransformation of compounds prohibited by the World Anti Doping Agency is of high concern as doping analyses are mostly based on the detection of metabolites instead of the parent compounds abused by athletes. While the self-administration of doping-relevant compounds is from an ethical point of view a rather problematic method to investigate metabolism, the usage of cell culture systems allows for studies on biotransformation in vitro. Five cell culture models with different tissue origin (liver, ovary, skin, kidney, and testis) were comparatively incubated with testosterone and epitestosterone as well as with the synthetic testosterone derivatives 17α-methyltestosterone and 4-chlorotestosterone to investigate the impact of synthetic modifications on phase I metabolic pathways. Cell culture supernatants were analyzed by high-performance liquid chromatography-tandem mass spectrometry. All cell lines possessed the default steroid phase I biotransformation reactions. The highest conversion rate was observed in ovarian (BG-1) and liver cells (HepG2). For BG-1 and skin cells (HaCaT), the 5α-reductase products 5α-dihydrotestosterone (for both) and 5α-androstane-3α/β,17β-diol (for BG-1 solely) were found to be prevailing after testosterone incubation. In kidney (COS-1) and HepG2 cells, the 17β-hydroxysteroid dehydrogenase activity was predominant as supported by the observation that the 17α-OH (epitestosterone) and the methyl group (17α-methyltestosterone) impeded the conversion rate in these cell lines. In conclusion, future work should extend the characterization of the BG-1 and HepG2 cells on phase II metabolic pathways to examine whether they are suitable models for the generation of metabolite reference collections comparable to those obtained by human excretion studies.

A bespoke microfluidic pharmacokinetic compartment model for drug absorption using artificial cell membranes

Early prediction of the rate and extent of intestinal absorption is vital for the efficient development of orally administered drugs. Here we show a new type of pharmacokinetic compartment model that shows a threefold improvement in the prediction of molecular absorption in the jejunum than the current state-of-the-art in vitro technique, parallel artificial membrane permeability assays (PAMPA). Our three-stage pharmacokinetic compartment model uses microfluidic droplets and bespoke, biomimetic artificial cells to model the path of a drug proxy from the intestinal space into the blood via an enterocyte. Each droplet models the buffer and salt composition of each pharmacokinetic compartment. The artificial cell membranes are made from the major components of human intestinal cell membranes (l-α-phosphatidylcholine, PC and l-α-phosphatidylethanolamine, PE) and sizes are comparable to human cells (∼0.5 nL). We demonstrate the use of the microfluidic platform to quantify common pharmacokinetic parameters such as half-life, flux and the apparent permeability coefficient (P_app). Our determined P_app more closely resembles that of actual intestinal tissue than PAMPA, which overestimates it by a factor of 20.

Proteomic analysis of intracellular protein corona of nanoparticles elucidates nano-trafficking network and nano-bio interactions

The merits of nanomedicines are significantly impacted by the surrounding biological environment. Similar to the protein corona generated on the surface of nanoparticles in the circulation system, the intracellular protein corona (IPC) might be formed on nanoparticles when transported inside the cells. However, little is known currently about the formation of IPC and its possible biological influence.

Methods: Caco-2 cells, a classical epithelial cell line, were cultured in Transwell plates to form a monolayer. Gold nanoparticles (AuNPs) were prepared as the model nanomedicine due to their excellent stability. Here we focused on identifying IPC formed on the surface of AuNPs during cell transport. The nanoparticles in the basolateral side of the Caco-2 monolayer were collected and analyzed by multiple techniques to verify IPC formation. High-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomics was utilized to analyze the composition of IPC proteins. In particular, we established a dual-filtration strategy to exclude various interference in IPC identification. Based on the subcellular localization of specific IPC proteins, we elicited the nano-trafficking network of AuNPs. The transport pathways of AuNPs identified by proteomic analysis were also verified by various conventional technologies. Finally, we explored the influence of IPC on the uptake and stress response of endothelium.

Results: The existence of IPC was demonstrated on the surface of AuNPs, in which 227 proteins were identified. Among them, 40 proteins were finally ascertained as the specific IPC proteins. The subcellular location analysis indicated that these “specific” IPC proteins could back-track the transport pathways of nanoparticles in the epithelial cell monolayer. According to the subcellular distribution of IPC proteins and co-localization, we discovered a new pathway of nanoparticles from endosomes to secretory vesicles which was dominant during the transcytosis. After employing conventional imageology and pharmacology strategies to verify the result of proteomic analysis, we mapped a comprehensive intracellular transport network. Our study also revealed the merits of IPC analysis, which could readily elucidate the molecular mechanisms of transcytosis. Besides, the IPC proteins increased the uptake and stress response of endothelium, which was likely mediated by extracellular matrix and mitochondrion-related IPC proteins.

Conclusion: The comprehensive proteomic analysis of IPC enabled tracing of transport pathways in epithelial cells as well as revealing the biological impact of nanoparticles on endothelium.

Clinical Trials for Disease-Modifying Therapies in Alzheimer's Disease: A Primer, Lessons Learned, and a Blueprint for the Future

Alzheimer’s disease (AD) has no currently approved disease-modifying therapies (DMTs), and treatments to prevent, delay the onset, or slow the progression are urgently needed. A delay of 5 years if available by 2025 would decrease the total number of patients with AD by 50% in 2050. To meet the definition of DMT, an agent must produce an enduring change in the course of AD; clinical trials of DMTs have the goal of demonstrating this effect. AD drug discovery entails target identification followed by high throughput screening and lead optimization of drug-like compounds. Once an optimized agent is available and has been assessed for efficacy and toxicity in animals, it progresses through Phase I testing with healthy volunteers, Phase II learning trials to establish proof-of-mechanism and dose, and Phase III confirmatory trials to demonstrate efficacy and safety in larger populations. Phase III is followed by Food and Drug Administration review and, if appropriate, market access. Trial populations include cognitively normal at-risk participants in prevention trials, mildly impaired participants with biomarker evidence of AD in prodromal AD trials, and subjects with cognitive and functional impairment in AD dementia trials. Biomarkers are critical in trials of DMTs, assisting in participant characterization and diagnosis, target engagement and proof-of-pharmacology, demonstration of disease-modification, and monitoring side effects. Clinical trial designs include randomized, parallel group; delayed start; staggered withdrawal; and adaptive. Lessons learned from completed trials inform future trials and increase the likelihood of success.

Intestinal Drug Absorption Enhancement by Aloe vera Gel and Whole Leaf Extract: In Vitro Investigations into the Mechanisms of Action

The co-administration of absorption enhancing agents with macromolecular drugs (e.g., protein and peptide drugs) has been identified as a means to improve the oral bioavailability of these drugs. Absorption-enhancing agents of natural origins have received a great deal of attention due to their sustainable production, in support of green chemistry. In previous studies, certain parts of the Aloe vera leaf (e.g., gel and whole leaf extract) have shown a potential to enhance drug permeation across the intestinal epithelial barrier. The mechanism of the drug-absorption-enhancement action and the capacity for absorption-enhancement of the A. vera gel and whole leaf, were investigated in this study. A clear decrease in transepithelial electrical resistance (TEER) of Caco-2 cell monolayers exposed to A. vera gel and wholeleaf extract, in various concentrations, indicated the opening of tight junctions between the epithelial cells. The transport of Fluorescein isothiocyanate (FITC)-dextran, with a molecular weight of 4 kDa (FD-4), could be enhanced across the Caco-2 cell monolayers, by the A. vera gel and whole-leaf extract, but not the FITC-dextran with larger molecular weights (i.e., 10, 20, and 40 kDa), which indicated a limited drug absorption enhancement capacity, in terms of the molecular size. Accumulation of FD-4 between the Caco-2 cells (and not within the cells), after treatment with the A. vera gel and whole-leaf extract was shown with a confocal laser scanning microscopy (CLSM) imaging, indicating that the paracellular transport of FD-4 occurred after the interaction of the A. vera gel and whole-leaf extract, with the epithelial cell monolayers. Furthermore, changes in the F-actin distribution in the cytoskeleton of the Caco-2 cell monolayers was observed by means of a fluorescence staining, which confirmed tight junction modulation as the mechanism of action for the absorption enhancement effect of the A. vera gel and whole-leaf extract.

Higher-energy collision-induced dissociation for the quantification by liquid chromatography/tandem ion trap mass spectrometry of nitric oxide metabolites coming from S-nitroso-glutathione in an in vitro model of the intestinal barrier

RATIONALE

The potency of S-nitrosoglutathione (GSNO) as a nitric oxide (NO) donor to treat cardiovascular diseases (CVDs) has been highlighted in numerous studies. In order to study its bioavailability after oral administration, which represents the most convenient route for the chronic treatment of CVDs, it is essential to develop an analytical method permitting (i) the simultaneous measurement of GSNO metabolites, i.e. nitrite, S-nitrosothiols (RSNOs) and nitrate and (ii) to distinguish them from other sources (endogenous synthesis and diet).

METHODS

Exogenous GSNO was labeled with ¹⁵ N, and the GS¹⁵ NO metabolites after conversion into the nitrite ion were derivatized with 2,3-diaminonaphthalene. The resulting 2,3-naphthotriazole was quantified by liquid chromatography/tandem ion trap mass spectrometry (LC/ITMS/MS) in multiple reaction monitoring mode after Higher-energy Collision-induced Dissociation (HCD). Finally, the validated method was applied to an in vitro model of the intestinal barrier (monolayer of Caco-2 cells) to study GS¹⁵ NO intestinal permeability.

RESULTS

A LC/ITMS/MS method based on an original transition (m/z 171 to 156) for sodium ¹⁵ N-nitrite, GS¹⁵ NO and sodium ¹⁵ N-nitrate measurements was validated, with recoveries of 100.8 ± 3.8, 98.0 ± 2.7 and 104.1 ± 3.3%, respectively. Intra- and inter-day variabilities were below 13.4 and 12.6%, and the limit of quantification reached 5 nM (signal over blank = 4). The permeability of labeled GS¹⁵ NO (10-100 μM) was evaluated by calculating its apparent permeability coefficient (P_app ).

CONCLUSIONS

A quantitative LC/ITMS/MS method using HCD was developed for the first time to selectively monitor GS¹⁵ NO metabolites. The assay allowed evaluation of GS¹⁵ NO intestinal permeability and situated this drug candidate within the middle permeability class according to FDA guidelines. In addition, the present method has opened the perspective of a more fundamental work aiming at studying the fragmentation mechanism leading to the ion at m/z 156 in HCD tandem mass spectrometry in the presence of acetonitrile.

In Vitro and In Vivo Inhibition of Intestinal Glucose Transport by Guava (Psidium Guajava) Extracts

SCOPE

Known pharmacological activities of guava (Psidium guajava) include modulation of blood glucose levels. However, mechanistic details remain unclear in many cases.

METHODS AND RESULTS

This study investigated the effects of different guava leaf and fruit extracts on intestinal glucose transport in vitro and on postprandial glucose levels in vivo. Substantial dose- and time-dependent glucose transport inhibition (up to 80%) was observed for both guava fruit and leaf extracts, at conceivable physiological concentrations in Caco-2 cells. Using sodium-containing (both glucose transporters, sodium-dependent glucose transporter 1 [SGLT1] and glucose transporter 2 [GLUT2], are active) and sodium-free (only GLUT2 is active) conditions, we show that inhibition of GLUT2 was greater than that of SGLT1. Inhibitory properties of guava extracts also remained stable after digestive juice treatment, indicating a good chemical stability of the active substances. Furthermore, we could unequivocally show that guava extracts significantly reduced blood glucose levels (≈fourfold reduction) in a time-dependent manner in vivo (C57BL/6N mice). Extracts were characterized with respect to their main putative bioactive compounds (polyphenols) using HPLC and LC-MS.

CONCLUSION

The data demonstrated that guava leaf and fruit extracts can potentially contribute to the regulation of blood glucose levels.

Bioprinted 3D Primary Human Intestinal Tissues Model Aspects of Native Physiology and ADME/Tox Functions

The human intestinal mucosa is a critical site for absorption, distribution, metabolism, and excretion (ADME)/Tox studies in drug development and is difficult to recapitulate in vitro. Using bioprinting, we generated three-dimensional (3D) intestinal tissue composed of human primary intestinal epithelial cells and myofibroblasts with architecture and function to model the native intestine. The 3D intestinal tissue demonstrates a polarized epithelium with tight junctions and specialized epithelial cell types and expresses functional and inducible CYP450 enzymes. The 3D intestinal tissues develop physiological barrier function, distinguish between high- and low-permeability compounds, and have functional P-gp and BCRP transporters. Biochemical and histological characterization demonstrate that 3D intestinal tissues can generate an injury response to compound-induced toxicity and inflammation. This model is compatible with existing preclinical assays and may be implemented as an additional bridge to clinical trials by enhancing safety and efficacy prediction in drug development.

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Bioprinted 3D human intestinal tissues enable complex modeling of ADME/Tox in vitro

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3D intestinal tissues develop barrier function and polarized transporter expression

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Key cytochrome P450 enzymes are expressed, metabolically active, and inducible

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GI toxicants can trigger barrier disruption and cytotoxicity in 3D intestinal tissues

3D gut-liver chip with a PK model for prediction of first-pass metabolism

Accurate prediction of first-pass metabolism is essential for improving the time and cost efficiency of drug development process. Here, we have developed a microfluidic gut-liver co-culture chip that aims to reproduce the first-pass metabolism of oral drugs. This chip consists of two separate layers for gut (Caco-2) and liver (HepG2) cell lines, where cells can be co-cultured in both 2D and 3D forms. Both cell lines were maintained well in the chip, verified by confocal microscopy and measurement of hepatic enzyme activity. We investigated the PK profile of paracetamol in the chip, and corresponding PK model was constructed, which was used to predict PK profiles for different chip design parameters. Simulation results implied that a larger absorption surface area and a higher metabolic capacity are required to reproduce the in vivo PK profile of paracetamol more accurately. Our study suggests the possibility of reproducing the human PK profile on a chip, contributing to accurate prediction of pharmacological effect of drugs.

In Vitro Assessment of the Effect of Antiepileptic Drugs on Expression and Function of ABC Transporters and Their Interactions with ABCC2

ABC transporters have a significant role in drug disposition and response and various studies have implicated their involvement in epilepsy pharmacoresistance. Since genetic studies till now are inconclusive, we thought of investigating the role of xenobiotics as transcriptional modulators of ABC transporters. Here, we investigated the effect of six antiepileptic drugs (AEDs) viz. phenytoin, carbamazepine, valproate, lamotrigine, topiramate and levetiracetam, on the expression and function of ABCB1, ABCC1, ABCC2 and ABCG2 in Caco2 and HepG2 cell lines through real time PCR, western blot and functional activity assays. Further, the interaction of AEDs with maximally induced ABCC2 was studied. Carbamazepine caused a significant induction in expression of ABCB1 and ABCC2 in HepG2 and Caco2 cells, both at the transcript and protein level, together with increased functional activity. Valproate caused a significant increase in the expression and functional activity of ABCB1 in HepG2 only. No significant effect of phenytoin, lamotrigine, topiramate and levetiracetam on the transporters under study was observed in either of the cell lines. We demonstrated the interaction of carbamazepine and valproate with ABCC2 with ATPase and 5,6-carboxyfluorescein inhibition assays. Thus, altered functionality of ABCB1 and ABCC2 can affect the disposition and bioavailability of administered drugs, interfering with AED therapy.

Alternative Methods to Animal Testing for the Safety Evaluation of Cosmetic Ingredients: An Overview

The safety of cosmetics sold in Europe is based on the safety evaluation of each individual ingredient conducted by those responsible for putting the product on the market. However, those substances for which some concern exists with respect to human health (e.g., colorants, preservatives, UV-filters, nanomaterials) are evaluated at the European Commission level by a scientific committee, currently called the Scientific Committee on Consumer Safety (SCCS). According to the Cosmetics Regulation (European Commission, 2009), it is prohibited in the European Union (EU) to market cosmetic products and ingredients that have been tested on animals. However, the results of studies performed before the ban continue to be accepted. In the current study, we evaluated the use of in vitro methods in the dossiers submitted to the SCCS in the period between 2013 and 2016 based on the published reports issued by the scientific committee, which provides a scientific opinion on these dossiers. The results of this evaluation were compared with those of an evaluation conducted four years previously. We found that, despite a slight increase in the number of studies performed in vitro, the majority of studies submitted to the SCCS is still done principally in vivo and correspond to studies performed before the ban.

Cell cultures in drug discovery and development: The need of reliable in vitro-in vivo extrapolation for pharmacodynamics and pharmacokinetics assessment

For ethical and cost-related reasons, use of animals for the assessment of mode of action, metabolism and/or toxicity of new drug candidates has been increasingly scrutinized in research and industrial applications. Implementation of the 3 "Rs"¹; rule (Reduction, Replacement, Refinement) through development of in silico or in vitro assays has become an essential element of risk assessment. Physiologically based pharmacokinetic (PBPK²) modeling is the most potent in silico tool used for extrapolation of pharmacokinetic parameters to animal or human models from results obtained in vitro. Although, many types of in vitro assays are conducted during drug development, use of cell cultures is the most reliable one. Two-dimensional (2D) cell cultures have been a part of drug development for many years. Nowadays, their role is decreasing in favor of three-dimensional (3D) cell cultures and co-cultures. 3D cultures exhibit protein expression patterns and intercellular junctions that are closer to in vivo states in comparison to classical monolayer cultures. Co-cultures allow for examinations of the mutual influence of different cell lines. However, the complexity and high costs of co-cultures and 3D equipment exclude such methods from high-throughput screening (HTS).³In vitro absorption, distribution, metabolism, and excretion assessment, as well as drug-drug interaction (DDI), are usually performed with the use of various cell culture based assays. Progress in in silico and in vitro methods can lead to better in vitro-in vivo extrapolation (IVIVE⁴) outcomes and have a potential to contribute towards a significant reduction in the number of laboratory animals needed for drug research. As such, concentrated efforts need to be spent towards the development of an HTS in vitro platform with satisfactory IVIVE features.

Intestine-on-a-Chip Microfluidic Model for Efficient in Vitro Screening of Oral Chemotherapeutic Uptake

Many highly effective chemotherapeutic agents can only be administered intravenously as their oral delivery is compromised by low gastro-intestinal solubility and permeability. SN-38 (7-ethyl-10-hydroxycamptothecin) is one such drug; however, recently synthesized lipophilic prodrugs offer a potential solution to the low oral bioavailability issue. Here we introduce a microfluidic-based intestine-on-a-chip (IOAC) model, which has the potential to provide new insight into the structure-permeability relationship for lipophilic prodrugs. More specifically, the IOAC model utilizes external mechanical cues that induce specific differentiation of an epithelial cell monolayer to provide a barrier function that exhibits an undulating morphology with microvilli expression on the cell surface; this is more biologically relevant than conventional Caco-2 Transwell models. IOAC permeability data for SN38 modified with fatty acid esters of different chain lengths and at different molecular positions correlate excellently with water-lipid partitioning data and have the potential to significantly advance their preclinical development. In addition to advancing mechanistic insight into the permeability of many challenging drug candidates, we envisage the IOAC model to also be applicable to nanoparticle and biological entities.

Oral drug absorption in pediatrics: the intestinal wall, its developmental changes and current tools for predictions

The dissolution, intestinal absorption and presystemic metabolism of a drug depend on its physicochemical characteristics but also on numerous physiological (e.g. gastrointestinal pH, volume, transit time, morphology) and biochemical factors (e.g. luminal enzymes and flora, intestinal wall enzymes and transporters). Over the past decade, evidence has accumulated indicating that these factors may differ in children and adults resulting in age-related changes in drug exposure and drug response. Thus, drug dosage may require adjustment for the pediatric population to ensure the desired therapeutic outcome and to avoid side-effects. Although tremendous progress has been made in understanding the effects of age on intestinal physiology and function, significant knowledge gaps remain. Studying and predicting pharmacokinetics in pediatric patients remains challenging due to ethical concerns associated with clinical trials in this vulnerable population, and because of the paucity of predictive in vitro and in vivo animal assays. This review details the current knowledge related to developmental changes determining intestinal drug absorption and pre-systemic metabolism. Supporting experimental approaches as well as physiologically based pharmacokinetic modeling are also discussed together with their limitations and challenges. Copyright © 2016 John Wiley & Sons, Ltd.

Permeation characteristics of hypericin across Caco-2 monolayers in the presence of single flavonoids, defined flavonoid mixtures or Hypericum extract matrix

OBJECTIVES

The major aim of this study was to get a detailed understanding of the exposure and fate of hypericin in the Caco-2 cell system when combined with various flavonoids, mixtures of flavonoids or Hypericum perforatum extract matrix (STW3-VI).

METHODS

The permeation characteristics of hypericin in the absence or presence of quercetin, quercitrin, isoquercitrin, hyperoside and rutin were tested. Hypericin (5 μm) was mixed with single flavonoids (20 μm) or with different flavonoid combinations (each flavonoid 4 or 10 μm, total flavonoid concentration: 20 μm). Further, the uptake of hypericin (5 μm) in the presence of H. perforatum extract matrix (7.25, 29 and 58 μg/ml) was studied.

KEY FINDINGS

Following application of hypericin to the apical side of the monolayer, only negligible amounts of the compound were found in the basolateral compartment. From all tested flavonoids, only quercitrin increased the basolateral amount of hypericin. Dual flavonoid combinations were not superior compared to the single combinations. The amount of hypericin in the basolateral compartment increased concentration-dependently in the presence of extract matrix (from 0 to 7.5%).

CONCLUSION

Comparing the effects of various flavonoid mixtures vs the extract matrix, it can be concluded that, besides flavonoids, the extract seems to contain further compounds (e.g. phenolic acids or proanthocyanidins) which substantially improve the permeation characteristics of hypericin.

Models for drug absorption from the small intestine: where are we and where are we going?

The small intestine is a complex organ with movements, flora, mucus and flows. Despite this, the most widely used absorption models consider the organ a cylindrical monoepithelial tube. This review presents the recent evolution of models to take into consideration the complex nature of gut physiology. The most commonly encountered issues are ethical (in vivo models) and differences in drug transport as a result of a modified expression of drug transporters or metabolic enzymes compared with human (in vitro and in vivo models). Finally, this review discusses the way forward to reach an ideal equilibrium between reproducibility, predictability and efficiency for predicting permeability. The features of an ideal model are listed as a guideline for future development.

Application of multi-target phytotherapeutic concept in malaria drug discovery: a systems biology approach in biomarker identification

There is an urgent need for new anti-malaria drugs with broad therapeutic potential and novel mode of action, for effective treatment and to overcome emerging drug resistance. Plant-derived anti-malarials remain a significant source of bioactive molecules in this regard. The multicomponent formulation forms the basis of phytotherapy. Mechanistic reasons for the poly-pharmacological effects of plants constitute increased bioavailability, interference with cellular transport processes, activation of pro-drugs/deactivation of active compounds to inactive metabolites and action of synergistic partners at different points of the same signaling cascade. These effects are known as the multi-target concept. However, due to the intrinsic complexity of natural products-based drug discovery, there is need to rethink the approaches toward understanding their therapeutic effect. This review discusses the multi-target phytotherapeutic concept and its application in biomarker identification using the modified reverse pharmacology - systems biology approach. Considerations include the generation of a product library, high throughput screening (HTS) techniques for efficacy and interaction assessment, High Performance Liquid Chromatography (HPLC)-based anti-malarial profiling and animal pharmacology. This approach is an integrated interdisciplinary implementation of tailored technology platforms coupled to miniaturized biological assays, to track and characterize the multi-target bioactive components of botanicals as well as identify potential biomarkers. While preserving biodiversity, this will serve as a primary step towards the development of standardized phytomedicines, as well as facilitate lead discovery for chemical prioritization and downstream clinical development.

Mechanisms of transport of polymeric and lipidic nanoparticles across the intestinal barrier

Unraveling the mechanisms of nanoparticle transport across the intestinal barrier is essential for designing more efficient nanoparticles for oral administration. The physicochemical parameters of the nanoparticles (e.g., size, surface charge, chemical composition) dictate nanoparticle fate across the intestinal barrier. This review aims to address the most important findings regarding polymeric and lipidic nanoparticle transport across the intestinal barrier, including the evaluation of critical physicochemical parameters of nanoparticles that affect nanocarrier interactions with the intestinal barrier.

Characterizing drug-metabolizing enzymes and transporters that are bona fide CAR-target genes in mouse intestine

Intestine is responsible for the biotransformation of many orally-exposed chemicals. The constitutive androstane receptor (CAR/Nr1i3) is known to up-regulate many genes encoding drug-metabolizing enzymes and transporters (drug-processing genes/DPGs) in liver, but less is known regarding its effect in intestine. Sixty-day-old wild-type and Car^−/− mice were administered the CAR-ligand TCPOBOP or vehicle once daily for 4 days. In wild-type mice, Car mRNA was down-regulated by TCPOBOP in liver and duodenum. Car^−/− mice had altered basal intestinal expression of many DPGs in a section-specific manner. Consistent with the liver data (Aleksunes and Klaassen, 2012), TCPOBOP up-regulated many DPGs (Cyp2b10, Cyp3a11, Aldh1a1, Aldh1a7, Gsta1, Gsta4, Gstm1-m4, Gstt1, Ugt1a1, Ugt2b34, Ugt2b36, and Mrp2–4) in specific sections of small intestine in a CAR-dependent manner. However, the mRNAs of Nqo1 and Papss2 were previously known to be up-regulated by TCPOBOP in liver but were not altered in intestine. Interestingly, many known CAR-target genes were highest expressed in colon where CAR is minimally expressed, suggesting that additional regulators are involved in regulating their expression. In conclusion, CAR regulates the basal expression of many DPGs in intestine, and although many hepatic CAR-targeted DPGs were bona fide CAR-targets in intestine, pharmacological activation of CAR in liver and intestine are not identical.

Discovery and resupply of pharmacologically active plant-derived natural products: A review

Medicinal plants have historically proven their value as a source of molecules with therapeutic potential, and nowadays still represent an important pool for the identification of novel drug leads. In the past decades, pharmaceutical industry focused mainly on libraries of synthetic compounds as drug discovery source. They are comparably easy to produce and resupply, and demonstrate good compatibility with established high throughput screening (HTS) platforms. However, at the same time there has been a declining trend in the number of new drugs reaching the market, raising renewed scientific interest in drug discovery from natural sources, despite of its known challenges. In this survey, a brief outline of historical development is provided together with a comprehensive overview of used approaches and recent developments relevant to plant-derived natural product drug discovery. Associated challenges and major strengths of natural product-based drug discovery are critically discussed. A snapshot of the advanced plant-derived natural products that are currently in actively recruiting clinical trials is also presented. Importantly, the transition of a natural compound from a "screening hit" through a "drug lead" to a "marketed drug" is associated with increasingly challenging demands for compound amount, which often cannot be met by re-isolation from the respective plant sources. In this regard, existing alternatives for resupply are also discussed, including different biotechnology approaches and total organic synthesis. While the intrinsic complexity of natural product-based drug discovery necessitates highly integrated interdisciplinary approaches, the reviewed scientific developments, recent technological advances, and research trends clearly indicate that natural products will be among the most important sources of new drugs also in the future.

Using the BacMam Baculovirus System to Study Expression and Function of Recombinant Efflux Drug Transporters in Polarized Epithelial Cell Monolayers

The ATP-binding cassette (ABC) transporter superfamily includes several membrane-bound proteins that are critical to drug pharmacokinetics and disposition. Pharmacologic evaluation of these proteins in vitro remains a challenge. In this study, human ABC transporters were expressed in polarized epithelial cell monolayers transduced using the BacMam baculovirus gene transfer system. The purpose of the study was to evaluate the efficacy of BacMam baculovirus to transduce cells grown in monolayers. In a porcine kidney cell line, LLC-PK1 cells, baculoviral transduction is successful only via the apical side of a polarized monolayer. We observed that recombinant ABC transporters were expressed on the cell surface with post-translational modification. Furthermore, sodium butyrate played a critical role in recombinant protein expression, and preincubation in the presence of tunicamycin or thapsigargin enhanced protein expression. Cells overexpressing human P-glycoprotein (P-gp) showed vectorial basolateral-to-apical transport of [(3)H]-paclitaxel, which could be reversed by the inhibitor tariquidar. Similarly, coexpression of human P-gp and ABCG2 in LLC-PK1 cells resulted in higher transport of mitoxantrone, which is a substrate for both transporters, than in either P-gp- or ABCG2-expressing cells alone. Taken together, our results indicate that a high level of expression of efflux transporters in a polarized cell monolayer is technically feasible with the BacMam baculovirus system.

Orlistat limits cholesterol intestinal absorption by Niemann-pick C1-like 1 (NPC1L1) inhibition

The known mechanism by which orlistat decreases the absorption of dietary cholesterol is by inhibition of intestinal lipases. The aim of this study was to investigate the ability of orlistat to limit cholesterol absorption by inhibition of the cholesterol transport protein Niemann-Pick C1-like 1 (NPC1L1) as another mechanism of action. In situ rat intestinal perfusion studies were conducted to study the effect of orlistat on jejunal cholesterol absorption. Inhibition kinetic parameters were calculated from in vitro inhibition studies using Caco2 and NPC1L1 transfected cell lines. The in situ studies demonstrated that intestinal perfusion of orlistat (100µM) was able to reduce cholesterol absorption by three-fold when compared to control (i.e. in the absence of orlistat, P<0.01). In vitro studies using Caco2 cells demonstrated orlistat to reduce the cellular uptake of cholesterol by 30%. Additionally, orlistat reduced the cellular uptake of cholesterol in dose dependent manner in NPC1L1 transfected cell line with an IC50=1.2µM. Lineweaver-Burk plot indicated a noncompetitive inhibition of NPC1L1 by orlistat. Beside the already established mechanism by which orlistat reduces the absorption of cholesterol, we demonstrated for the first time that orlistat limits cholesterol absorption by the inhibition of NPC1L1 transport protein.