Use of a Caco-2 cell culture model for the characterization of intestinal absorption of antibiotics

The Development of an Age-Appropriate Fixed Dose Combination for Tuberculosis Using Physiologically-Based Pharmacokinetic Modeling (PBBM) and Risk Assessment

Background/Objectives: The combination of isoniazid (INH) and rifampicin (RIF) is indicated for the treatment maintenance phase of tuberculosis (TB) in adults and children. In Brazil, there is no current reference listed drug for this indication in children. Farmanguinhos has undertaken the development of an age-appropriate dispersible tablet to be taken with water for all age groups from birth to adolescence. The primary objective of this work was to develop and validate a physiologically-based biopharmaceutics model (PBBM) in GastroPlusTM, to link the product's in vitro performance to the observed pharmacokinetic (PK) data in adults and children. Methods: The PBBM was developed based on measured or predicted physico-chemical and biopharmaceutical properties of INH and RIF. The metabolic clearance was specified mechanistically in the gut and liver for both parent drugs and acetyl-isoniazid. The model incorporated formulation related measurements such as dosage form disintegration and dissolution as inputs and was validated using extensive literature as well as in house clinical data. Results: The model was used to predict the exposure in children across the targeted dosing regimen for each age group using the new age-appropriate formulation. Probabilistic models of efficacy and safety versus exposure, combined with real world data on children, were utilized to assess drug efficacy and safety in the target populations. Conclusions: The model predictions (systemic exposure) along with clinical data from the literature linking systemic exposure to clinical outcomes confirmed that the proposed dispersible pediatric tablet and dosing regimen are anticipated to be as safe and as effective as adult formulations at similar doses.

Conversion of Olmesartan to Olmesartan Medoxomil, A Prodrug that Improves Intestinal Absorption, Confers Substrate Recognition by OATP2B1

PURPOSE

Olmesartan medoxomil (olmesartan-MX), an ester-type prodrug of the angiotensin II receptor blocker (ARB) olmesartan, is predominantly anionic at intestinal pH. Human organic anion transporting polypeptide 2B1 (OATP2B1) is expressed in the small intestine and is involved in the absorption of various acidic drugs. This study was designed to test the hypothesis that OATP2B1-mediated uptake contributes to the enhanced intestinal absorption of olmesartan-MX, even though olmesartan itself is not a substrate of OATP2B1.

METHODS

Tetracycline-inducible human OATP2B1- and rat Oatp2b1-overexpressing HEK 293 cell lines (hOATP2B1/T-REx-293 and rOatp2b1/T-REx-293, respectively) were established to characterize OATP2B1-mediated uptake. Rat jejunal permeability was measured using Ussing chambers. ARBs were quantified by liquid chromatography-tandem mass spectrometry.

RESULTS

Significant olmesartan-MX uptake was observed in hOATP2B1/T-REx-293 and rOatp2b1/T-REx-293 cells, whereas olmesartan uptake was undetectable or much lower than olmesartan-MX uptake, respectively. Furthermore, olmesartan-MX exhibited several-fold higher uptake in Caco-2 cells and greater permeability in rat jejunum compared to olmesartan. Olmesartan-MX uptake in hOATP2B1/T-REx-293 cells and in Caco-2 cells was significantly decreased by OATP2B1 substrates/inhibitors such as 1 mM estrone-3-sulfate, 100 µM rifamycin SV, and 100 µM fluvastatin. Rat Oatp2b1-mediated uptake and rat jejunal permeability of olmesartan-MX were significantly decreased by 50 µM naringin, an OATP2B1 inhibitor. Oral administration of olmesartan-MX with 50 µM naringin to rats significantly reduced the area under the plasma concentration-time curve of olmesartan to 76.9%.

CONCLUSION

Olmesartan-MX is a substrate for OATP2B1, and the naringin-sensitive transport system contributes to the improved intestinal absorption of olmesartan-MX compared with its parent drug, olmesartan.

Plasma non-transferrin-bound iron uptake by the small intestine leads to intestinal injury and intestinal flora dysbiosis in an iron overload mouse model and Caco-2 cells

Iron overload often occurs during blood transfusion and iron supplementation, resulting in the presence of non-transferrin-bound iron (NTBI) in host plasma and damage to multiple organs, but effects on the intestine have rarely been reported. In this study, an iron overload mouse model with plasma NTBI was established by intraperitoneal injection of iron dextran. We found that plasma NTBI damaged intestinal morphology, caused intestinal oxidative stress injury and reactive oxygen species (ROS) accumulation, and induced intestinal epithelial cell apoptosis. In addition, plasma NTBI increased the relative abundance of Ileibacterium and Desulfovibrio in the cecum, while the relative abundance of Faecalibaculum and Romboutsia was reduced. Ileibacterium may be a potential microbial biomarker of plasma NTBI. Based on the function prediction analysis, plasma NTBI led to the weakening of intestinal microbiota function, significantly reducing the function of the extracellular structure. Further investigation into the mechanism of injury showed that iron absorption in the small intestine significantly increased in the iron group. Caco-2 cell monolayers were used as a model of the intestinal epithelium to study the mechanism of iron transport. By adding ferric ammonium citrate (FAC, plasma NTBI in physiological form) to the basolateral side, the apparent permeability coefficient (Papp) values from the basolateral to the apical side were greater than 3×10-6 cm s-1. Intracellular ferritin level and apical iron concentration significantly increased, and SLC39A8 (ZIP8) and SLC39A14 (ZIP14) were highly expressed in the FAC group. Short hairpin RNA (shRNA) was used to knock down ZIP8 and ZIP14 in Caco-2 cells. Transfection with ZIP14-specific shRNA decreased intracellular ferritin level and inhibited iron uptake. These results revealed that plasma NTBI may cause intestinal injury and intestinal flora dysbiosis due to the uptake of plasma NTBI from the basolateral side into the small intestine, which is probably mediated by ZIP14.

Endothelial tissue remodeling induced by intraluminal pressure enhances paracellular solute transport

The endothelial layers of the microvasculature regulate the transport of solutes to the surrounding tissues. It remains unclear how this barrier function is affected by blood flow-induced intraluminal pressure. Using a 3D microvessel model, we compare the transport of macromolecules through endothelial tissues at mechanical rest or with intraluminal pressure, and correlate these data with electron microscopy of endothelial junctions. On application of an intraluminal pressure of 100 Pa, we demonstrate that the flow through the tissue increases by 2.35 times. This increase is associated with a 25% expansion of microvessel diameter, which leads to tissue remodeling and thinning of the paracellular junctions. We recapitulate these data with the deformable monopore model, in which the increase in paracellular transport is explained by the augmentation of the diffusion rate across thinned junctions under mechanical stress. We therefore suggest that the deformation of microvasculatures contributes to regulate their barrier function.

Exploring Structural Determinants of Bias among D4 Subtype-Selective Dopamine Receptor Agonists

The high affinity dopamine D₄ receptor ligand APH199 and derivatives thereof exhibit bias toward the G_i signaling pathway over β-arrestin recruitment compared to quinpirole. Based on APH199, two novel groups of D₄ subtype selective ligands were designed and evaluated, in which the original benzyl phenylsemicarbazide substructure was replaced by either a biphenylmethyl urea or a biphenyl urea moiety. Functional assays revealed a range of different bias profiles among the newly synthesized compounds, namely, with regard to efficacy, potency, and GRK2 dependency, in which bias factors range from 1 to over 300 and activation from 15% to over 98% compared to quinpirole. These observations demonstrate that within bias, an even more precise tuning toward a particular profile is possible, which─in a general sense─could become an important aspect in future drug development. Docking studies enabled further insight into the role of the ECL2 and the EPB in the emergence of bias, thereby taking advantage of the diversity of functionally selective D₄ agonists now available.

Multi-armed antibiotics for Gram-positive bacteria

Antibiotic resistance is a serious threat to public health. Here, we propose a multi-armed chemical scaffold (MACS) for antibiotic screening, which refers to multi-armed molecules (MAMs) consisting of a core unit and three or four arms, neither of which is active for pathogens. Based on a structure-activity relationship study of MAMs, we discover a class of multi-armed antibiotics (MAAs) with a core similar to ethylene (E), carbon atom (C), benzene (B), nitrogen atom (N), and triazine (T) and three or four 4-phenylbenzoic acid (PBA) arms, or a B core and three 4-vinylbenzoic acid (VBA) or 4-ethynylbenzoic acid (EBA) arms. They can selectively interact with Gram-positive bacteria and inhibit cell wall assembly by targeting the lipid carriers of cell wall biosynthesis. MAAs have excellent antibacterial activities against Gram-positive bacteria, including clinical multi-drug-resistant (MDR) isolates. Our study provides a chemical scaffold and identifies eight antibacterial lead compounds for the development of antibiotics.

Effect of antibiotic-administration period on hepatic bile acid profile and expression of pharmacokinetic-related proteins in mouse liver, kidney, and brain capillaries

Antibiotic administration affects pharmacokinetics through changes in the intestinal microbiota, and bile acids are involved in this regulation. The purpose of the present study was to clarify the effect of different periods of antibiotic administration on the hepatic bile acid profile and expression of pharmacokinetic-related proteins in mouse liver, kidney, and brain capillaries. Vancomycin and polymyxin B were orally administered to mice for either 5- or 25-days. The hepatic bile acid profile of the 25-day treatment group was distinct. In the liver, the protein expression of cytochrome P450 (Cyp)3a11 showed the greatest reduction to 11.4% after the 5-day treatment and further reduced to 7.01% after the 25-day treatment. Similar reductions were observed for sulfotransferase 1d1, Cyp2b10, carboxylesterase 2e, UDP-glucuronosyltransferase (Ugt)1a5, and Ugt1a9. In the kidney and brain capillaries, no drug-metabolizing enzymes or drug transporters were changed with >1.5-fold or <0.66-fold statistical significance in either period. These results suggest that bile acids and metabolizing enzymes in the liver are affected in a period-dependent manner by antibiotic treatment, while the blood-brain barrier and kidneys are less affected. Drug-drug interactions of antibiotics via the intestinal microbiota should be considered by changing drug metabolism in the liver.

Understanding the suitability of established antibiotics for oral inhalation from a pharmacokinetic perspective: an integrated model-based investigation based on rifampicin, ciprofloxacin and tigecycline in vivo data

BACKGROUND

Treating pulmonary infections by administering drugs via oral inhalation represents an attractive alternative to usual routes of administration. However, the local concentrations after inhalation are typically not known and the presumed benefits are derived from experiences with drugs specifically optimized for inhaled administration.

OBJECTIVES

A physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model was developed to elucidate the pulmonary PK for ciprofloxacin, rifampicin and tigecycline and link it to bacterial PK/PD models. An exemplary sensitivity analysis was performed to potentially guide drug optimization regarding local efficacy for inhaled antibiotics.

METHODS

Detailed pulmonary tissue, endothelial lining fluid and systemic in vivo drug concentration-time profiles were simultaneously measured for all drugs in rats after intravenous infusion. Using this data, a PBPK/PD model was developed, translated to humans and adapted for inhalation. Simulations were performed comparing potential benefits of oral inhalation for treating bronchial infections, covering intracellular pathogens and bacteria residing in the bronchial epithelial lining fluid.

RESULTS

The PBPK/PD model was able to describe pulmonary PK in rats. Often applied optimization parameters for orally inhaled drugs (e.g. high systemic clearance and low oral bioavailability) showed little influence on efficacy and instead mainly increased pulmonary selectivity. Instead, low permeability, a high epithelial efflux ratio and a pronounced post-antibiotic effect represented the most impactful parameters to suggest a benefit of inhalation over systemic administration for locally acting antibiotics.

CONCLUSIONS

The present work might help to develop antibiotics for oral inhalation providing high pulmonary concentrations and fast onset of exposure coupled with lower systemic drug concentrations.

The Caco-2 Model: Modifications and enhancements to improve efficiency and predictive performance

The Caco-2 cell model has been widely used to assess the permeability of drug candidates. It has provided a high throughput in vitro platform, functionally resembling the enterocytes. Since the oral route is the most preferred for drug administration, the Caco-2 cell model acts as a very important tool to elucidate the oral "druggability" of a molecule by providing a fairly reliable estimate of its permeability through the intestinal membrane. Despite its shortcomings (the lack of a mucus layer, long cultivation period, inter-lab variability, and differences in expression of enzymes, transporters, and tight junction complexes) it remains heavily used due to its reliability, predictive performance, and wide acceptance. Various modifications have been made: co-culturing with other intestinal cells, applying biosimilar mucus, reducing culturing time, combining Caco-2 monolayer with the dissolution apparatus, enhancing protein expression, and redesigning the sampling apparatus. These modifications are intended to overcome some of the shortcomings of the Caco-2 model in order to make its use easier, quicker, economical, and more representative of the intestine. The aim of this review is to discuss such modifications to enhance this model's utility, predictive performance, and reproducibility.

Investigation of the Uptake and Transport of Two Novel Camptothecin Derivatives in Caco-2 Cell Monolayers

Irinotecan and Topotecan are two Camptothecin derivatives (CPTs) whose resistance is associated with the high expression of breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp). To reverse this resistance, two novel CPTs, FL77-28 (7-(3-Fluoro-4-methylphenyl)-10,11-methylenedioxy-20(S)-CPT) and FL77-29 (7-(4-Fluoro-3-methylphenyl)-10,11-methylenedioxy-20(S)-CPT), were synthesized by our group. In this study, the anti-tumor activities of FL77-28, FL77-29, and their parent, FL118 (10,11-methylenedioxy-20(S)-CPT), were evaluated and the results showed that FL77-28 and FL77-29 had stronger anti-tumor activities than FL118. The transport and uptake of FL118, FL77-28, and FL77-29 were investigated in Caco-2 cells for the preliminary prediction of intestinal absorption. The apparent permeability coefficient from apical to basolateral (P_{app AP-BL}) values of FL77-28 and FL77-29 were (2.32 ± 0.04) × 10⁻⁶ cm/s and (2.48 ± 0.18) × 10⁻⁶ cm/s, respectively, suggesting that the compounds had moderate absorption. Since the transport property of FL77-28 was passive diffusion and the efflux ratio (ER) was less than 2, two chemical inhibitors were added to further confirm the involvement of efflux proteins. The results showed that FL77-28 was not a substrate of P-gp or BCRP, but FL77-29 was mediated by P-gp. In conclusion, FL77-28 might be a promising candidate to overcome drug resistance induced by multiple efflux proteins.

Cellular Uptake and Transport Characteristics of FL118 Derivatives in Caco-2 Cell Monolayers

In the evaluation of the druggability of candidate compounds, it was vital to predict the oral bioavailability of compounds from apparent permeability (Papp) across Caco-2 cell-culture model of intestinal epithelium cultured on commercial transwell plate inserts. The study was to investigate the transport characteristics and permeability of FL118 (10, 11-Methylenedioxy-20(S)-camptothecin) derivatives 7-Q6 (7-(4-Ethylphenyl)-10, 11-methylenedioxy-20(S)-camptothecin) and 7-Q20 (7-(4-Trifluoromethylphenyl)-10, 11-methylenedioxy-20(S)-camptothecin). Transport characteristics and permeability of the tested compounds to the small intestine were assessed at different concentrations (0.5, 1 µM) via Caco-2 cell monolayers model in vitro. Uptake studies based on Caco-2 cells, including temperatures, concentrations, and the influence of efflux transporters, were combined to confirm the transport characteristics of the tested compounds. Furthermore, cytotoxicity results showed that the concentrations used in the experiments were non-toxic and harmless to cells. In addition, The Papp of 7-Q6 was (3.69 ± 1.07) × 10^-6 cm/s with efflux ratio (ER) 0.98, while the Papp of 7-Q20 was (7.78 ± 0.89) × 10^-6 cm/s with ER 1.05 for apical-to-basolateral (AP→BL) at 0.5 µM, suggesting that 7-Q20 might possess higher oral bioavailability in vivo. Furthermore, P-glycoprotein (P-gp) was proved to slightly affect the accumulations of 7-Q20, while the absorption of 7-Q6 was irrelevant with P-gp and breast cancer resistant protein (BCRP) based on the cellular uptake assays. Accordingly, 7-Q6 was completely absorbed by passive diffusion, and 7-Q20 was mainly dependent on passive diffusion with being effluxed by P-gp slightly. Meanwhile, both 7-Q6 and 7-Q20 were potential antitumor drugs that might exhibit high oral bioavailability in the body.

Global Analysis of Models for Predicting Human Absorption: QSAR, In Vitro, and Preclinical Models

Models intended to predict intestinal absorption are an essential part of the drug development process. Although many models exist for capturing intestinal absorption, many questions still exist around the applicability of these models to drug types like "beyond rule of 5" (bRo5) and low absorption compounds. This presents a challenge as current models have not been rigorously tested to understand intestinal absorption. Here, we assembled a large, structurally diverse dataset of ∼1000 compounds with known in vitro, preclinical, and human permeability and/or absorption data. In silico (quantitative structure-activity relationship), in vitro (Caco-2), and in vivo (rat) models were statistically evaluated for predictive performance against this human intestinal absorption dataset. We expect this evaluation to serve as a resource for DMPK scientists and medicinal/computational chemists to increase their understanding of permeability and absorption model utility and applications for academia and industry.

Absorption and Tissue Distribution of Siphonaxanthin from Green Algae

Siphonaxanthin has been known to possess inhibitory effects against obesity, inflammation, and angiogenesis. However, little information on its in vivo bioavailability and biotransformation is available. To assess the bioavailability and metabolism of siphonaxanthin, its absorption and accumulation were evaluated using intestinal Caco-2 cells and Institute of Cancer Research (ICR) mice. Siphonaxanthin was absorbed and exhibited non-uniform accumulation and distribution patterns in tissues of ICR mice. Notably, in addition to siphonaxanthin, three main compounds were detected following dietary administration of siphonaxanthin. Because the compounds showed changes on mass spectra compared with that of siphonaxanthin, they were presumed to be metabolites of siphonaxanthin in ICR mice. Siphonaxanthin mainly accumulated in stomach and small intestine, while putative metabolites of siphonaxanthin mainly accumulated in liver and adipose tissues. Furthermore, siphonaxanthin and its putative metabolites selectively accumulated in white adipose tissue (WAT), especially mesenteric WAT. These results provide useful evidence regarding the in vivo bioactivity of siphonaxanthin. In particular, the results regarding the specific accumulation of siphonaxanthin and its metabolites in WAT have important implications for understanding their anti-obesity effects and regulatory roles in lipid metabolism.

Predicting Drug-Drug Interactions Between Rifampicin and Long-Acting Cabotegravir and Rilpivirine Using Physiologically Based Pharmacokinetic Modeling

BACKGROUND

Cabotegravir and rilpivirine are 2 long-acting (LA) antiretrovirals that can be administered intramuscularly; their interaction with rifampicin, a first-line antituberculosis agent, has not been investigated. The aim of this study was to simulate and predict drug-drug interactions (DDIs) between these LA antiretroviral agents and rifampicin using physiologically based pharmacokinetic (PBPK) modeling.

METHODS

The designed PBPK models were qualified (according to European Medicines Agency guidelines) against observed data for oral formulations of cabotegravir, rilpivirine, and rifampicin. Induction potential of rifampicin was also qualified by comparing the DDI between oral cabotegravir and oral rilpivirine with rifampicin. Qualified PBPK models were utilized for pharmacokinetic prediction of DDIs.

RESULTS

PBPK models predicted a reduction in both area under the curve (AUC0-28 days) and trough concentration (Ctrough, 28th day) of LA cabotegravir of 41%-46% for the first maintenance dose coadministered with 600 mg once-daily oral rifampicin. Rilpivirine concentrations were predicted to decrease by 82% for both AUC0-28 days and Ctrough, 28th day following the first maintenance dose when coadministered with rifampicin.

CONCLUSIONS

The developed PBPK models predicted the theoretical effect of rifampicin on cabotegravir and rilpivirine LA intramuscular formulations. According to these simulations, it is likely that coadministration of rifampicin with these LA formulations will result in subtherapeutic concentrations of both drugs.

C1-CBP-vancomycin: Impact of a Vancomycin C-Terminus Trimethylammonium Cation on Pharmacological Properties and Insights into Its Newly Introduced Mechanism of Action

C1-CBP-vancomycin (3) was examined alongside CBP-vancomycin for susceptibility to acquired resistance upon serial exposure against two vancomycin-resistant enterococci strains where its activity proved more durable and remarkably better than many current therapies. Combined with earlier studies, this observation confirmed an added mechanism of action was introduced by incorporation of the trimethylammonium cation and that C1-CBP-vancomycin exhibits activity against vancomycin-resistant organisms through two synergistic mechanisms of action, both independent of d-Ala-d-Ala/d-Lac binding. New insights into this added mechanism of action, induced cell membrane permeabilization, can be inferred from studies that show added exogenous lipoteichoic acid reduces antimicrobial activity, rescues bacteria cell growth inhibition, and blocks induced cell permeabilization properties of C1-CBP-vancomycin, suggesting a direct binding interaction with embedded teichoic acid is responsible for the added mechanism of action and enhanced antimicrobial activity. Further studies indicate that the trimethylammonium cation does not introduce new liabilities in common pharmacological properties of the analogue and established that 3 is well tolerated in mice, displays substantial PK improvements over both vancomycin and CBP-vancomycin, and exhibits in vivo efficacy against a challenging multidrug-resistant and vancomycin-resistant S. aureus strain that is representative of the resistant pathogens all fear will emerge in the general population.

Akkermansia muciniphila-derived extracellular vesicles influence gut permeability through the regulation of tight junctions

The gut microbiota has an important role in the gut barrier, inflammation and metabolic functions. Studies have identified a close association between the intestinal barrier and metabolic diseases, including obesity and type 2 diabetes (T2D). Recently, Akkermansia muciniphila has been reported as a beneficial bacterium that reduces gut barrier disruption and insulin resistance. Here we evaluated the role of A. muciniphila-derived extracellular vesicles (AmEVs) in the regulation of gut permeability. We found that there are more AmEVs in the fecal samples of healthy controls compared with those of patients with T2D. In addition, AmEV administration enhanced tight junction function, reduced body weight gain and improved glucose tolerance in high-fat diet (HFD)-induced diabetic mice. To test the direct effect of AmEVs on human epithelial cells, cultured Caco-2 cells were treated with these vesicles. AmEVs decreased the gut permeability of lipopolysaccharide-treated Caco-2 cells, whereas Escherichia coli-derived EVs had no significant effect. Interestingly, the expression of occludin was increased by AmEV treatment. Overall, these results imply that AmEVs may act as a functional moiety for controlling gut permeability and that the regulation of intestinal barrier integrity can improve metabolic functions in HFD-fed mice.

Self-Nanoemulsifying Drug Delivery Systems Containing Plantago lanceolata-An Assessment of Their Antioxidant and Antiinflammatory Effects

The most important components of Plantago lanceolata L. leaves are catalpol, aucubin, and acteoside (=verbascoside). These bioactive compounds possess different pharmacological effects: anti-inflammatory, antioxidant, antineoplastic, and hepatoprotective. The aim of this study was to protect Plantago lanceolata extract from hydrolysis and to improve its antioxidant effect using self-nano-emulsifying drug delivery systems (SNEDDS). Eight SNEDDS compositions were prepared, and their physical properties, in vitro cytotoxicity, and in vivo AST/ALT values were investigated. MTT cell viability assay was performed on Caco-2 cells. The well-diluted samples (200 to 1000-fold dilutions) proved to be non-cytotoxic. The acute administration of PL-SNEDDS compositions resulted in minor changes in hepatic markers (AST, ALT), except for compositions 4 and 8 due to their high Transcutol contents (80%). The non-toxic compositions showed a significant increase in free radical scavenger activity measured by the DPPH test compared to the blank SNEDDS. An indirect dissolution test was performed, based on the result of the DPPH antioxidant assay; the dissolution profiles of Plantago lancolata extract were statistically different from each SNEDDS. The anti-inflammatory effect of PL-SNEDDS compositions was confirmed by the ear inflammation test. For the complete examination period, all compositions decreased ear edema as compared to the positive (untreated) control. It can be concluded that PL-SNEDDS compositions could be used to deliver active natural compounds in a stable, efficient, and safe manner.

Rifampin Stability and Solution Concentration Enhancement Through Amorphous Solid Dispersion in Cellulose ω-Carboxyalkanoate Matrices

Tuberculosis (TB) is a deadly infectious disease; approximately 2 billion people are currently latently infected with the causative agent Mycobacterium tuberculosis. Approximately 8 million new active cases and 2 million deaths due to TB are recorded annually.¹ Rifampin (Rif) is a vital first-line TB treatment drug. Its effectiveness is hampered by the high dose required (600 mg 1×/day) and by its moderate, variable bioavailability. These issues can be explained by Rif instability at gastric pH, limited solubility at neutral pH, polymorphism, and stimulation of its own metabolism. To overcome these obstacles, we developed new cellulose-based oral drug delivery systems aiming to increase and make more consistent Rif solubility and bioavailability. Amorphous solid dispersions (ASDs) of Rif with cellulose ω-carboxyalkanoates (cellulose acetate suberate, cellulose acetate propionate adipate, and cellulose acetate butyrate sebacate) were prepared and compared with crystalline Rif (negative) and carboxymethyl cellulose acetate butyrate ASD (positive) controls. Cellulose ω-carboxyalkanoate ASDs prevented acid-catalyzed degradation in conditions mimicking the acidic stomach and provided complete release of intact Rif at intestinal pH. Rif incorporation into ASD in these novel cellulose derivative matrices creates the potential for convenient, robust, consistent, and high Rif oral bioavailability for treatment of TB.

Intestinal Epithelial Cell-Specific Deletion of PLD2 Alleviates DSS-Induced Colitis by Regulating Occludin

Ulcerative colitis is a multi-factorial disease involving a dysregulated immune response. Disruptions to the intestinal epithelial barrier and translocation of bacteria, resulting in inflammation, are common in colitis. The mechanisms underlying epithelial barrier dysfunction or regulation of tight junction proteins during disease progression of colitis have not been clearly elucidated. Increase in phospholipase D (PLD) activity is associated with disease severity in colitis animal models. However, the role of PLD2 in the maintenance of intestinal barrier integrity remains elusive. We have generated intestinal-specific Pld2 knockout mice (Pld2 IEC-KO) to investigate the mechanism of intestinal epithelial PLD2 in colitis. We show that the knockout of Pld2 confers protection against dextran sodium sulphate (DSS)-induced colitis in mice. Treatment with DSS induced the expression of PLD2 and downregulated occludin in colon epithelial cells. PLD2 was shown to mediate phosphorylation of occludin and induce its proteasomal degradation in a c-Src kinase-dependent pathway. Additionally, we have shown that treatment with an inhibitor of PLD2 can rescue mice from DSS-induced colitis. To our knowledge, this is the first report showing that PLD2 is pivotal in the regulation of the integrity of epithelial tight junctions and occludin turn over, thereby implicating it in the pathogenesis of colitis.

Single-cell level methods for studying the effect of antibiotics on bacteria during infection

Considerable evidence about phenotypic heterogeneity among bacteria during infection has accumulated during recent years. This heterogeneity has to be considered if the mechanisms of infection and antibiotic action are to be understood, so we need to implement existing and find novel methods to monitor the effects of antibiotics on bacteria at the single-cell level. This review provides an overview of methods by which this aim can be achieved. Fluorescence label-based methods and Raman scattering as a label-free approach are discussed in particular detail. Other label-free methods that can provide single-cell level information, such as impedance spectroscopy and surface plasmon resonance, are briefly summarized. The advantages and disadvantages of these different methods are discussed in light of a challenging in vivo environment.

Pharmacokinetic characterization of 2-(3-benzoyl)-4-hydroxy-1,1-dioxo-2H-1,2-benzothiazine-2-yl-1-phenylethanone, a novel 11β-hydroxysteroid dehydrogenase type 1 inhibitor in rats

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is associated with metabolic syndromes such as type 2 diabetes mellitus and obesity. A new 11β-HSD1 inhibitor known as 2-(3-benzoyl)-4-hydroxy-1, 1-dioxo-2H-1, 2-benzothiazine-2-yl-1-phenylethanone (KR-66344) is being developed as a therapeutic agent for these metabolic diseases. The purpose of this study was to characterize the pharmacokinetics of KR-66344 to support further preclinical development. KR-66344 showed high liver microsomal stability with T1/2 values >3 h and high permeability with apparent permeability coefficients of 15.2-24.2 × 10(-6) cm/s in Caco-2 cell monolayers. KR-66344 was also strongly bound to plasma proteins (>98%). After intravenous dosing, KR-66344 exhibited low systemic clearance (0.27-0.37 L/h/kg) and a low to moderate volume of distribution at steady state (0.79-0.8 L/kg). The bioavailability and terminal half-lives of KR-66344 following oral administration were 25% and 1.7-3.3 h, respectively. In addition, KR-66344 showed dose-independent pharmacokinetics at 0.5-10 mg/kg in intravenous and oral pharmacokinetic studies.

Evaluation of the Cytotoxicity of α-Cyclodextrin Derivatives on the Caco-2 Cell Line and Human Erythrocytes

Cyclodextrins, even the 6-membered α-cyclodextrin, are approved in the various pharmacopoeias as pharmaceutical excipients for solubilizing and stabilizing drugs as well as for controlling drug release. Recently α-cyclodextrin has also been marketed as health food with beneficial effects on blood lipid profiles. However, the concentration of α-cyclodextrin used may be very high in these cases, and its toxic attributes have to be seriously considered. The objective of this study was to investigate the cytotoxicity of various, differently substituted α-cyclodextrin derivatives and determine relationship between the structures and cytotoxicity. Three different methods were used, viability tests (MTT assay and Real Time Cell Electronic Sensing on Caco-2 cells) as well as hemolysis test on human red blood cells. The effect of α-cyclodextrin derivatives resulted in concentration-dependent cytotoxicity, so the IC50 values have been determined. Based on our evaluation, the Real Time Cell Electronic Sensing method is the most accurate for describing the time and concentration dependency of the observed toxic effects. Regarding the cytotoxicity on Caco-2 cells, phosphatidylcholine extraction may play a main role in the mechanism. Our results should provide help in selecting those α-cyclodextrin derivatives which have the potential of being used safely in medical formulations.

Treatment of textile wastewater by submerged membrane bioreactor: In vitro bioassays for the assessment of stress response elicited by raw and reclaimed wastewater

The performance of a pilot-scale membrane bioreactor (MBR) system for the treatment of textile wastewater was investigated. The MBR was continuously operated for 7 months. Very high treatment efficiencies were achieved (color, 100%; chemical oxygen demand (COD), 98%; biochemical oxygen demand (BOD5), 96%; suspended solids (SS), 100%). Furthermore, the MBR treatment efficiency was analyzed from a toxicological-risk assessment point of view, via different In vitro bioassays using Caco-2 cells, a widely used cell model in toxicological studies. Results showed that MBR treatment significantly reduced the raw textile wastewater (RTWW) cytotoxicity on Caco-2 cells by 53% for a hydraulic retention time (HRT) of 2 days. Additionally, the RTWW-induced disruption in the barrier function (BF) of the Caco-2 cell monolayer was also significantly reduced after MBR treatment under a HRT of 2 days (no disruption of BF was observed). Moreover, the effect of RTWW and treated wastewater on stress response was investigated using different stress genes: AHSA1, HSPD1, HSPA1A, HSPA5 and HSPA8. The cell exposure to RTWW significantly increased the expression of all used stress genes; interestingly, the treated wastewater (HRT 2 days) did not show any significant modulation of the stress genes.

The enhanced inhibitory effect of different antitumor agents in self-microemulsifying drug delivery systems on human cervical cancer HeLa cells

The aim of this study was to develop topical self-microemulsifying drug delivery systems (SMEDDS) containing antitumor agents (bleomycin, cisplatin and ifosfamide) and to investigate their inhibitory potential in SMEDDS on human cervical cancer HeLa cells. The physicochemical properties of cytostatic drug loaded SMEDDS were characterized. The cytotoxicity of main components of SMEDDS was also investigated. Their IC₅₀ values were determined. HeLa cells were treated by different concentrations of cisplatin, bleomycin and ifosfamide alone and in various SMEDDS. The inhibitory effect on cell growth was analyzed by MTT cell viability assay. Inflammation is a driving force that accelerates cancer development. The inhibitory effect of these antitumor agents has also been tested on HeLa cells in the presence of inflammatory mediators (IL-1-β, TNF-α) as an in vitro model of inflamed human cervix. Significant differences in the cytotoxicity of cytostatic drugs alone and in SMEDDS have been found in a concentration-dependent manner. The self-micro emulsifying system may potentiate the effectiveness of bleomycin, cisplatin and ifosfamide topically. The effect of SMEDDS containing antitumor agents was decreased significantly in the presence of inflammatory mediators. According to our experiments, the optimal SMEDDS formulation is 1:1:2:6:2 ratios of Isopropyl myristate, Capryol 90, Kolliphor RH 40, Cremophor RH40, Transcutol HP and Labrasol. It can be concluded that SMEDDS may increase the inhibitory effect of bleomycin, ifosfamide and cisplatin on human cervical cancer HeLa cells. Inflammation on HeLa cells hinders the effectiveness of SMEDDS containing antitumor agents. Our results might ensure useful data for development of optimal antitumor formulations.

Sevoflurane-Sulfobutylether-β-Cyclodextrin Complex: Preparation, Characterization, Cellular Toxicity, Molecular Modeling and Blood-Brain Barrier Transport Studies

The objective of the present investigation was to study the ability of sulfobutylether-β-cyclodextrin (SBEβCD) to form an inclusion complex with sevoflurane (SEV), a volatile anesthetic with poor water solubility. The inclusion complex was prepared, characterized and its cellular toxicity and blood-brain barrier (BBB) permeation potential of the formulated SEV have also been examined for the purpose of controlled drug delivery. The SEV-SBEβCD complex was nontoxic to the primary brain microvascular endothelial (pEND) cells at a clinically relevant concentration of sevoflurane. The inclusion complex exhibited significantly higher BBB permeation profiles as compared with the reference substance (propranolol) concerning calculated apparent permeability values (P_app). In addition, SEV binding affinity to SBEβCD was confirmed by a minimal Gibbs free energy of binding (ΔG_bind) value of −1.727 ± 0.042 kcal·mol⁻¹ and an average binding constant (K_b) of 53.66 ± 9.24 mM indicating rapid drug liberation from the cyclodextrin amphiphilic cavity.

P-glycoprotein induction in Caco-2 cells by newly synthetized thioxanthones prevents paraquat cytotoxicity

The induction of P-glycoprotein (P-gp), an ATP-dependent efflux pump, has been proposed as a strategy against the toxicity induced by P-gp substrates such as the herbicide paraquat (PQ). The aim of this study was to screen five newly synthetized thioxanthonic derivatives, a group known to interact with P-gp, as potential inducers of the pump's expression and/or activity and to evaluate whether they would afford protection against PQ-induced toxicity in Caco-2 cells. All five thioxanthones (20 µM) caused a significant increase in both P-gp expression and activity as evaluated by flow cytometry using the UIC2 antibody and rhodamine 123, respectively. Additionally, it was demonstrated that the tested compounds, when present only during the efflux of rhodamine 123, rapidly induced an activation of P-gp. The tested compounds also increased P-gp ATPase activity in MDR1-Sf9 membrane vesicles, indicating that all derivatives acted as P-gp substrates. PQ cytotoxicity was significantly reduced in the presence of four thioxanthone derivatives, and this protective effect was reversed upon incubation with a specific P-gp inhibitor. In silico studies showed that all the tested thioxanthones fitted onto a previously described three-feature P-gp induction pharmacophore. Moreover, in silico interactions between thioxanthones and P-gp in the presence of PQ suggested that a co-transport mechanism may be operating. Based on the in vitro activation results, a pharmacophore model for P-gp activation was built, which will be of further use in the screening for new P-gp activators. In conclusion, the study demonstrated the potential of the tested thioxanthonic compounds in protecting against toxic effects induced by P-gp substrates through P-gp induction and activation.

Colchicine effect on P-glycoprotein expression and activity: in silico and in vitro studies

Colchicine is a P-glycoprotein (P-gp) substrate that induces its expression, thus increasing the risk for unexpected pharmacokinetic interactions with this drug. Because increased P-gp expression does not always correlate with increased activity of this efflux pump, we evaluated the changes in both P-gp expression and activity induced by colchicine using an in vitro model. Caco-2 cells were incubated with 0.1-100 μM colchicine up to 96 h. Cytotoxicity was evaluated by the MTT and LDH leakage assays, P-gp expression and activity were evaluated by flow cytometry and P-gp ATPase activity was measured in MDR1-Sf9 membrane vesicles. Furthermore, colchicine fitting in P-gp induction and competitive inhibition pharmacophore hypothesis, and docking studies evaluating the interaction between colchicine and P-gp drug binding pocket were tested in silico. Significant cytotoxicity was noted after 48 h. At 24 h a significant increase in P-gp expression was observed, which was not accompanied by an increase in transport activity. Moreover, colchicine significantly increased P-gp ATPase activity, demonstrating to be actively transported by the pump. New pharmacophores were constructed to predict P-gp modulatory activity. Colchicine fitted both the P-gp induction and competitive inhibition models. In silico, colchicine was predicted to bind to the P-gp drug-binding pocket suggesting a competitive mechanism of transport. These results show that colchicine induced P-gp expression in Caco-2 cells but the activity of the protein remained unchanged, highlighting the need to simultaneously evaluate P-gp expression and activity. With the newly constructed pharmacophores, new drugs can be initially screened in silico to predict such potential pharmacokinetic interactions.

Transport of hop aroma compounds across Caco-2 monolayers

Hop aroma compounds and digestive transformation products thereof were investigated in view of their human intestinal absorption and biotransformation processes.

An in vitro investigation of species-dependent intestinal transport of selenium and the impact of this process on selenium bioavailability

A range of Se species has been shown to occur in a variety of different foodstuffs. Depending on its speciation, Se is more or less bioavailable to human subjects. In the present study, the role of speciation as a determinant of Se bioavailability was addressed with an investigation of species-specific mechanisms of transport at the intestinal level. The present work focused on four distinct Se compounds (selenate (Se(VI)), selenite (Se(IV)), selenomethionine (SeMet) and methylselenocysteine (MeSeCys)), whose intestinal transport was mimicked through an in vitro bicameral model of enterocyte-like differentiated Caco-2 cells. Efficiency of Se absorption was shown to be species dependent (SeMet>MeSeCys>Se(VI)>Se(IV)). In the case of SeMet, MeSeCys and Se(VI), the highly polarised passage from the apical to basolateral pole indicated that a substantial fraction of transport was transcellular, whilst results for Se(IV) indicated paracellular diffusion. Passage of the organic Se species (SeMet and MeSeCys) became saturated after 3 h, but no such effect was observed for the inorganic species. In addition, SeMet and MeSeCys transport was significantly inhibited by their respective S analogues methionine and methylcysteine, which suggests a common transport system for both kinds of compounds.

Development and characterization of a new oral dapsone nanoemulsion system: permeability and in silico bioavailability studies

BACKGROUND

Dapsone is described as being active against Mycobacterium leprae, hence its role in the treatment of leprosy and related pathologies. Despite its therapeutic potential, the low solubility of dapsone in water results in low bioavailability and high microbial resistance. Nanoemulsions are pharmaceutical delivery systems derived from micellar solutions with a good capacity for improving absorption. The aim of this work was to develop and compare the permeability of a series of dapsone nanoemulsions in Caco-2 cell culture against that of effective permeability in the human body simulated using Gastroplus™ software.

METHODS AND RESULTS

The release profiles of the dapsone nanoemulsions using different combinations of surfactants and cosolvent showed a higher dissolution rate in simulated gastric and enteric fluid than did the dispersed dapsone powder. The drug release kinetics were consistent with a Higuchi model.

CONCLUSION

This comparison of dapsone permeability in Caco-2 cells with effective permeability in the human body simulated by Gastroplus showed a good correlation and indicates potential improvement in the biodisponibility of dapsone using this new system.

Evaluation of cytotoxicity of surfactants used in self-micro emulsifying drug delivery systems and their effects on paracellular transport in Caco-2 cell monolayer

The objective of this study was to examine the cellular effects of the members of two non-ionic amphiphilic tenside groups and their mixtures on human Caco-2 cell monolayers as dependent upon their chemical structures and physicochemical properties. The first group of polyethylene glycol esters is represented by Polysorbates and Labrasol alone and in blends, while the members of the second group. Capryol 90, Capryol PGMC, Lauroglycol 90 and Lauroglycol FCC were used as propylene glycol esters. They are increasingly used in SMEDDS as recent tensides or co-tensides to increase hydrophobic bioavailability of a drug. Critical micelle concentration was measured by determination of surface tension. CMC refers to the ability of solubilization of surfactants. Cytotoxicity tests were performed on Caco-2 cell monolayers by MTT and LDH methods. Paracellular permeability as a marker of the integrity of cell monolayers, was examined with Lucifer yellow assays combined with TransEpithelial Electrical Resistance (TEER) measurements. The effect of these surfactants on tight junctions as evidence for paracellular pathway was also characterized. The results of cytotoxicity assays were in agreement, and showed significant differences among the cytotoxic properties of surfactants in a concentration-dependent manner. Polysorbates 20, 60, 80 are the most toxic compounds. In the case of Labrasol, the degree of esterification and lack of sorbit component decreased cytotoxicity. If the hydrophyl head was changed from polyethylene glycol to propylene glycol the main determined factor of cytotoxicity was the monoester content and the length of carbon chain. In our CMC experiments, we found that only Labrasol showed expressed cytotoxicity above the CMC. It refers to good ability of micelle solubilization of Labrasol. In our paracellular transport experiments each of polyethylene glycol surfactants (Polysorbates and Labrasol) altered TEER values, but propylene glycol esters did not modify the monolayer integrity. Polyethylene glycol esters alone and in blends (0.05% Labrasol--0.001% Polysorbates 20, 60, 80) were able to increase Lucifer yellow permeability significantly below the IC₅₀ concentration. On the other hand Labrasol and Polysorbates 20 have expressed effect on tight junctions of Caco-2 monolayer. It could be concluded that polyethylene glycol ester-type tensides were able to enhance the paracellular permeability by the redistribution of junctional proteins. Our results might ensure useful data for selection of suitable tensides, co-tensides and tenside mixtures for SMEDDS formulations.

The cytotoxic effect of palytoxin on Caco-2 cells hinders their use for in vitro absorption studies

Palytoxin (PLTX), found in Palythoa zoanthids and Ostreopsis dinoflagellates, has also been detected in crabs and fish, through which it can enter into the food chain. Indeed, PLTX is considered the causative agent of several cases of human seafood poisoning resulting in systemic symptoms. Available epidemiological data on PLTX human toxicity suggest that the intestinal tract may be one of its in vivo targets and its potential site of access into the bloodstream. Hence, the purpose of this study was to investigate the suitability of the human intestinal Caco-2 cell line for evaluating PLTX oral absorption. A detailed analysis of PLTX cytotoxicity revealed a high sensitivity of Caco-2 cells: 4h toxin exposure reduced mitochondrial activity (MTT assay, EC(50) of 8.9±3.7×10(-12)M), cell density (SRB assay, EC(50) of 2.0±0.6×10(-11)M) and membrane integrity (LDH release, EC(50) of 4.5±1.4×10(-9)M and PI uptake, EC(50) of 1.0±0.8×10(-8)M). After low PLTX concentration (1.0×10(-11)M) exposure for 1-8h, followed by 24h recovery time in toxin-free medium, cell density reduction was only partially reversible. These results indicate that, due to the high susceptibility to PLTX cytotoxic effects, Caco-2 cells do not represent an appropriate and reliable model for investigating intestinal barrier permeation by this toxin.

Particulate matter air pollution causes oxidant-mediated increase in gut permeability in mice

BACKGROUND

Exposure to particulate matter (PM) air pollution may be an important environmental factor leading to exacerbations of inflammatory illnesses in the GI tract. PM can gain access to the gastrointestinal (GI) tract via swallowing of air or secretions from the upper airways or mucociliary clearance of inhaled particles.

METHODS

We measured PM-induced cell death and mitochondrial ROS generation in Caco-2 cells stably expressing oxidant sensitive GFP localized to mitochondria in the absence or presence of an antioxidant. C57BL/6 mice were exposed to a very high dose of urban PM from Washington, DC (200 μg/mouse) or saline via gastric gavage and small bowel and colonic tissue were harvested for histologic evaluation, and RNA isolation up to 48 hours. Permeability to 4 kD dextran was measured at 48 hours.

RESULTS

PM induced mitochondrial ROS generation and cell death in Caco-2 cells. PM also caused oxidant-dependent NF-κB activation, disruption of tight junctions and increased permeability of Caco-2 monolayers. Mice exposed to PM had increased intestinal permeability compared with PBS treated mice. In the small bowel, colocalization of the tight junction protein, ZO-1 was lower in the PM treated animals. In the small bowel and colon, PM exposed mice had higher levels of IL-6 mRNA and reduced levels of ZO-1 mRNA. Increased apoptosis was observed in the colon of PM exposed mice.

CONCLUSIONS

Exposure to high doses of urban PM causes oxidant dependent GI epithelial cell death, disruption of tight junction proteins, inflammation and increased permeability in the gut in vitro and in vivo. These PM-induced changes may contribute to exacerbations of inflammatory disorders of the gut.

Technique for real-time measurements of endothelial permeability in a microfluidic membrane chip using laser-induced fluorescence detection

Characterizing permeability of the endothelium that lines blood vessels and heart valves provides fundamental physiological information and is required to evaluate uptake of drugs and other biomolecules. However, current techniques used to measure permeability, such as Transwell insert assays, do not account for the recognized effects of fluid flow-induced shear stress on endothelial permeability or are inherently low-throughput. Here we report a novel on-chip technique in a two-layer membrane-based microfluidic platform to measure real-time permeability of endothelial cell monolayers on porous membranes. Bovine serum albumin (a model protein) conjugated with fluorescein isothiocyanate was delivered to an upper microchannel by pressure-driven flow and was forced to permeate a poly(ethylene terephthalate) membrane into a lower microchannel, where it was detected by laser-induced fluorescence. The concentration of the permeate at the point of detection varied with channel flow rates in agreement to less than 1% with theoretical analyses using a pore flow model. On the basis of the model, a sequential flow rate stepping scheme was developed and applied to obtain the permeability of cell-free and cell-bound membrane layers. This technique is a highly sensitive, novel microfluidic approach for measuring endothelial permeability in vitro, and the use of micrometer-sized channels offers the potential for parallelization and increased throughput compared to conventional shear-based permeability measurement methods.

Biowaiver monographs for immediate release solid oral dosage forms: rifampicin

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing rifampicin as the only Active Pharmaceutical Ingredient (API) are reviewed. Rifampicin's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Solubility and absolute BA data indicate that rifampicin is a BCS Class II drug. Of special concern for biowaiving is that many reports of failure of IR solid oral dosage forms of rifampicin to meet BE have been published and the reasons for these failures are yet insufficiently understood. Moreover, no reports were identified in which in vitro dissolution was shown to be predictive of nonequivalence among products. Therefore, a biowaiver based approval of rifampicin containing IR solid oral dosage forms cannot be recommended for either new multisource drug products or for major scale-up and postapproval changes (variations) to existing drug products.

Variability in Caco-2 and MDCK Cell-Based Intestinal Permeability Assays

Models predictive of intestinal drug absorption are important in drug development to identify compounds with promising biopharmaceutical properties. Since permeability is a factor affecting absorption, cell culture models (e.g., Caco-2, MDCK) have been developed to predict drug transport from the intestinal lumen into the bloodstream. The differences as to how the assays are performed, along with heterogeneity of the cell lines, have lead to different permeability values for the same drug. Transport and metabolic properties of cultured cells can vary due to culture conditions, seeding density, passage number, confluency, filter support, monolayer age, and stage of differentiation. During the transport experiment, cell absorption properties can change due to the composition and pH of the transport buffer, solute concentration and solubility, temperature, additives and/or cosolvents, agitation, sampling schedule, sink conditions, and analytical methods. Such variability within a laboratory can be avoided by characterizing a cell culture method and setting acceptance criteria in terms of monolayer integrity, passive transport, and active transport. The repeated evaluation of reference compounds will then facilitate intra-laboratory comparisons.

Discovery of diaryl imidazolidin-2-one derivatives, a novel class of muscarinic M3 selective antagonists (Part 1)

Pharmacophore-based structural identification, synthesis, and structure-activity relationships of a new class of muscarinic M3 receptor antagonists, the diaryl imidazolidin-2-one derivatives, are described. The versatility of the discovered scaffold allowed for several structural modifications that resulted in the discovery of two distinct classes of compounds, specifically a class of tertiary amine derivatives (potentially useful for the treatment of overactive bladder by oral administration) and a class of quaternary ammonium salt derivatives (potentially useful for the treatment of respiratory diseases by the inhalation route of administration). In this paper, we describe the synthesis and biological activity of tertiary amine derivatives. For these compounds, selectivity for the M3 receptor toward the M2 receptor was crucial, because the M2 receptor subtype is mainly responsible for adverse systemic side effects of currently marketed muscarinic antagonists. Compound 50 showed the highest selectivity versus M2 receptor, with binding affinity for M3 receptor Ki = 4.8 nM and for M2 receptor Ki = 1141 nM. Functional in vitro studies on selected compounds confirmed the antagonist activity toward the M3 receptor and functional selectivity toward the M2 receptor.

Intestinal Absorption of Miltefosine: Contribution of Passive Paracellular Transport

PURPOSE

This study aimed to characterize the transepithelial transport of miltefosine (HePC), the first orally effective drug against visceral leishmaniasis, across the intestinal barrier to further understand its oral absorption mechanism.

MATERIALS AND METHODS

Caco-2 cell monolayers were used as an in vitro model of the human intestinal barrier. The roles of active and passive mechanisms in HePC intestinal transport were investigated and the relative contributions of the transcellular and paracellular routes were estimated.

RESULTS

HePC transport was observed to be pH-independent, partially temperature-dependent, linear as a function of time and non-saturable as a function of concentration. The magnitude of HePC transport was quite similar to that of the paracellular marker mannitol, and EDTA treatment led to an increase in HePC transport. Furthermore, HePC transport was found to be similar in the apical-to-basolateral and basolateral-to-apical directions, strongly suggesting that HePC exhibits non-polarized transport and that no MDR-mediated efflux was involved.

CONCLUSIONS

These results demonstrate that HePC crosses the intestinal epithelium by a non-specific passive pathway and provide evidence supporting a concentration-dependent paracellular transport mechanism, although some transcellular diffusion cannot be ruled out. Considering that HePC opens epithelial tight junctions, this study shows that HePC may promote its own permeation across the intestinal barrier.