Cytotoxicity evaluation of enzyme inhibitors and absorption enhancers in Caco-2 cells for oral delivery of salmon calcitonin

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Development of a multiparametric (bio)sensing platform for continuous monitoring of stress metabolites

There is a growing need for real-time monitoring of metabolic products that could reflect cell damages over extended periods. In this paper, we report the design and development of an original multiparametric (bio)sensing platform that is tailored for the real-time monitoring of cell metabolites derived from cell cultures. Most attractive features of our developed electrochemical (bio)sensing platform are its easy manufacturing process, that enables seamless scale-up, modular and versatile approach, and low cost. In addition, the developed platform allows a multiparametric analysis instead of single-analyte analysis. Here we provide an overview of the sensors-based analysis of four main factors that can indicate a possible cell deterioration problem during cell-culture: pH, hydrogen peroxide, nitric oxide/nitrite and lactate. Herein, we are proposing a sensors platform based on thick-film coupled to microfluidic technology that can be integrated into any microfluidic system using Luer-lock connectors. This platform allows obtaining an accurate analysis of the secreting stress metabolites during cell/tissues culture.

Food contact materials and gut health: Implications for toxicity assessment and relevance of high molecular weight migrants

Gut health is determined by an intact epithelial barrier and balanced gut microbiota, both involved in the regulation of immune responses in the gut. Disruption of this system contributes to the etiology of various non-communicable diseases, including intestinal, metabolic, and autoimmune disorders. Studies suggest that some direct food additives, but also some food contaminants, such as pesticide residues and substances migrating from food contact materials (FCMs), may adversely affect the gut barrier or gut microbiota. Here, we focus on gut-related effects of FCM-relevant substances (e.g. surfactants, N-ring containing substances, nanoparticles, and antimicrobials) and show that gut health is an underappreciated target in the toxicity assessment of FCMs. Understanding FCMs' impact on gut health requires more attention to ensure safety and prevent gut-related chronic diseases. Our review further points to the existence of large population subgroups with an increased intestinal permeability; this may lead to higher uptake of compounds of not only low (<1000 Da) but also high (>1000 Da) molecular weight. We discuss the potential toxicological relevance of high molecular weight compounds in the gut and suggest that the scientific justification for the application of a molecular weight-based cut-off in risk assessment of FCMs should be reevaluated.

Caco-2 cells cytotoxicity of nifuroxazide derivatives with potential activity against Methicillin-resistant Staphylococcus aureus (MRSA)

It is important to determine the toxicity of compounds and co-solvents that are used in cell monolayer permeability studies to increase confidence in the results obtained from these in vitro experiments. This study was designed to evaluate the cytotoxicity of new nifuroxazide derivatives with potential activity against Methicillin-resistant Staphylococcus aureus (MRSA) in Caco-2 cells to select analogues for further in vitro permeability analyses. In this study, nitrofurantoin and nifuroxazide, in addition to 6 furanic and 6 thiophenic nifuroxazide derivatives were tested at 2, 4, 6, 8 and 10 μg/mL. In vitro cytotoxicity assays were performed according to the MTT (methyl tetrazolium) assay protocol described in ISO 10993-5. The viability of treated Caco-2 cells was greater than 83% for all tested nitrofurantoin concentrations, while those treated with nifuroxazide at 2, 4 and 6 μg/mL had viabilities greater than 70%. Treatment with the nifuroxazide analogues resulted in viability values greater than 70% at 2 and 4 μg/mL with the exception of the thiophenic methyl-substituted derivative, which resulted in cell viabilities below 70% at all tested concentrations. Caco-2 cells demonstrated reasonable viability for all nifuroxazide derivatives, except the thiophenic methyl-substituted compound. The former were selected for further permeability studies using Caco-2 cells.

Evaluation of protein stability and in vitro permeation of lyophilized polysaccharides-based microparticles for intranasal protein delivery

Biocompatible microparticles prepared by lyophilization were developed for intranasal protein delivery. To test for the feasibility of this formulation, stability of the incorporated protein and enhancement of in vitro permeation across the nasal epithelium were evaluated. Lyophilization was processed with hydroxypropylmethylcellulose (HPMC) or water soluble chitosan (WCS) as biocompatible polymers, hydroxypropyl-β-cyclodextrin (HP-β-CD) and d-alpha-tocopheryl poly(ethylene glycol 1000) succinate (TPGS 1000) as permeation enhancers, sugars as cryoprotectants and lysozyme as the model protein. As a result, microparticles ranging from 6 to 12μm were developed where the maintenance of the protein conformation was verified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism and fluorescence intensity detection. Moreover, in vitro bioassay showed that the lysozyme activity was preserved during the preparation process while exhibiting less cytotoxicity in primary human nasal epithelial (HNE) cells. Results of the in vitro release study revealed slower release rate in these microparticles compared to that of the lysozyme itself. On the other hand, the in vitro permeation study exhibited a 9-fold increase in absorption of lysozyme when prepared in lyophilized microparticles with HPMC, HP-β-CD and TPGS 1000 (F4-2). These microparticles could serve as efficient intranasal delivery systems for therapeutic proteins.

Liposomes containing glycocholate as potential oral insulin delivery systems: preparation, in vitro characterization, and improved protection against enzymatic degradation

Background:

Oral delivery of insulin is challenging and must overcome the barriers of gastric and enzymatic degradation as well as low permeation across the intestinal epithelium. The present study aimed to develop a liposomal delivery system containing glycocholate as an enzyme inhibitor and permeation enhancer for oral insulin delivery.

Methods:

Liposomes containing sodium glycocholate were prepared by a reversed-phase evaporation method followed by homogenization. The particle size and entrapment efficiency of recombinant human insulin (rhINS)-loaded sodium glycocholate liposomes can be easily adjusted by tuning the homogenization parameters, phospholipid:sodium glycocholate ratio, insulin:phospholipid ratio, water:ether volume ratio, interior water phase pH, and the hydration buffer pH.

Results:

The optimal formulation showed an insulin entrapment efficiency of 30% ± 2% and a particle size of 154 ± 18 nm. A conformational study by circular dichroism spectroscopy and a bioactivity study confirmed the preserved integrity of rhINS against preparative stress. Transmission electron micrographs revealed a nearly spherical and deformed structure with discernable lamella for sodium glycocholate liposomes. Sodium glycocholate liposomes showed better protection of insulin against enzymatic degradation by pepsin, trypsin, and α-chymotrypsin than liposomes containing the bile salt counterparts of sodium taurocholate and sodium deoxycholate.

Conclusion:

Sodium glycocholate liposomes showed promising in vitro characteristics and have the potential to be able to deliver insulin orally.

Novel dry powder inhaler formulation of glucagon with addition of citric acid for enhanced pulmonary delivery

Glucagon, a gut hormone, is one of the key regulatory elements in glucose homeostasis, and is clinically used for treatment of hypoglycemia and premedication in peroral endoscopy. Dry powder inhaler (DPI) form of glucagon is believed to be a promising new dosage form, and the present study aimed to develop a novel glucagon-DPI using absorption enhancer for improved pharmacological effects. The cytotoxicity of citric and capric acids, the potential absorption enhancers, at 1 and 10 mM was assessed by monitoring extracellular LDH levels in rat alveolar L2 cells, and a concentration- and time-dependent release of LDH was observed in capric acid, but not in citric acid-treated cells. DPI form of glucagon containing citric acid was prepared with a jet mill, and laser diffraction and cascade impactor analyses of the newly developed glucagon-DPI suggested high dispersion and deposition in the respiratory organs with an emitted dose and fine particle fraction of 99.5 and 25%, respectively. Addition of citric acid in glucagon-DPI improved the dissolution behavior, and did not impair the solid-state stability of glucagon-DPI. Intratracheal administration of glucagon-DPI (50 microg-glucagon/kg body weight of rat) containing citric acid led to 2.9-fold more potent hyperglycemic effect in rats, as compared to inhaled glucagon-DPI without citric acid. Based on these physicochemical and pharmacological characterization, the dry powder inhaler of glucagon with addition of citric acid would be of use as an alternative to injection form.

A modified fast (4 day) 96-well plate Caco-2 permeability assay

INTRODUCTION

The Caco-2 permeability assay is widely used for lead optimization in drug discovery. A 3 to 5-day system using a 24-well plate and a 10 to 21-day system using a 96-well plate have been established. Here, we modified the assay system to provide a ready-to-use Caco-2 cell monolayer using a 96-well plate in just 4 days.

METHODS AND RESULTS

In our system, collagen-coated inserts and the prolongation of the culture period after seeding leads to greater Caco-2 cell proliferation and sufficient contact-inhibition. The differentiation of Caco-2 cells was enhanced, when the contact-inhibited Caco-2 cells were exposed to the differentiation-inducing agent butyric acid. The permeability to nine well-known compounds showed a statistical correlation between our 4-day system using a 96-well plate and the conventional 21-day system using a 24-well plate.

DISCUSSION

We conclude that our system is more useful for evaluating many compounds for lead optimization in drug discovery.

Protective effect of Carbopol on enzymatic degradation of a peptide-like substrate. I: Effect of various concentrations and grades of Carbopol and other reaction variables on trypsin activity

The purpose of this study was to determine and compare the effect of various concentrations and grades of Carbopol on trypsin-induced degradation of a prototype substrate, N(alpha)-benzoyl-L-arginine ethyl ester hydrochloride (BAEE). Effect of other reaction variables, such as viscosity and ionic strength of the medium on the trypsin activity, was also analyzed simultaneously. Four concentrations and three commercially available grades of Carbopol were used. The effect of Carbopol was expressed in terms of change in the velocity of degradation reaction. A modified trypsin assay was developed and used for analysis. Up to a concentration of 0.35% w/v, Carbopol 934P showed a concentration-dependent increase in its ability to reduce the rate of enzymatic hydrolysis of BAEE. Similar inhibitory effect was observed with all three grades of Carbopol. The activity of trypsin was unaffected by other reaction variables, suggesting that interaction between the protein and the polymer could be the mechanism responsible for reduced trypsin activity. This study suggests that Carbopol can be a useful excipient for oral delivery of bioactive proteins and peptides, due to its ability to reduce the enzyme-induced degradation of these agents.

Chemical modification and formulation approaches to elevated drug transport across cell membranes

Drug delivery across cellular barriers, such as intestinal, nasal, buccal, alveolar, vaginal, ocular and blood-brain, is a challenging task. Multiple physiological mechanisms, such as cellular organisation, efflux, and chemical and enzymatic degradation, as well as physicochemical properties of the drug molecule itself, determine the penetration of xenobiotics across epithelial cell layers. Limited intestinal absorption of many novel and highly potent lead compounds has stimulated an intense search for strategies that can effectively enhance permeation across these biological barriers. This review discusses some of the approaches that have been, and are currently being, investigated for transepithelial drug delivery. Transdermal drug delivery requires a separate discussion on its own and is thus outside the scope of this review article.

An androgen-independent androgen receptor function protects from inositol hexakisphosphate toxicity in the PC3/PC3(AR) prostate cancer cell lines

BACKGROUND

Inositol hexakisphosphate (IP6) is a phytochemical exhibiting anticancer activity. Because few prostate cancer (PCa) cell lines have been used to study IP6, we assessed its efficacy in a panel of PCa cell lines.

METHODS AND RESULTS

Using WST-1 assays we observed that, although androgens did not modulate its efficacy, IP6 was more active in androgen receptor (AR) negative cells than in AR-positive cells. Stable expression of the AR in PC3 cells (PC3(AR)) decreased the response to IP6, which was reversed by an AR-targeting siRNA. Furthermore, AR expression in PC3 cells resulted in significantly reduced caspase-3 activation (P < 0.001) and DNA fragmentation (P < 0.05) in response to IP6. Similarly, although treatment with IP6 caused the upregulation of NF-kappaB-responsive (IkappaB-alpha, IRF-2) and p53/E2F-responsive genes (Puma, Noxa) in PC3 cells, this increase was reduced in PC3AR cells (P < 0.01).

CONCLUSION

We conclude that resistance to IP6 can be linked to a ligand-independent AR function.

Trypsin is associated with the rotavirus capsid and is activated by solubilization of outer capsid proteins

The rotavirus capsid is made up of three concentric protein layers. The outer layer, consisting of VP7 and VP4, is lost during virus entry into the host cell. Rotavirus field isolates can be adapted to high-titre growth in tissue culture by treatment with trypsin and by supplementing the culture medium with trypsin, which cleaves VP4 into two fragments, VP8* and VP5*. It is known that protease inhibitors reduce the replication of rotavirus in vitro and in vivo and also diminish disease symptoms in a mouse model. To clarify the molecular basis of these observations, a series of assays were conducted on purified rotavirus particles grown in the presence of trypsin. Results of HPLC and mass spectrometry followed by N-terminal sequencing showed that viral particles contain molecules of trypsin. When associated with triple-layer particles (TLPs), trypsin is inactive and not accessible to protease inhibitors, such as aprotinin. When the outer layer is solubilized by calcium-chelating agents, VP5*, VP8* and VP7 are released and the associated trypsin is activated, allowing cleavage of the viral capsid proteins, as well as other exogenous proteins. It is shown that addition of trypsin inhibitors significantly reduces synthesis of viral mRNA and viral proteins in cells and has a major inhibitory effect if present when virus enters the cell. These data indicate that incorporation of trypsin into rotavirus particles may enhance its infectivity.

Correlation of in vitro cytotoxicity with paracellular permeability in Caco-2 cells

This in vitro study aims to develop a cell culture model that compares paracellular permeability (PP) with acute cytotoxicity (AC). Caco-2 cells were seeded in 96-well plates and on polycarbonate filter inserts. Confluent monolayers were exposed to increasing concentrations of 20 reference chemicals for 24-h and 72-h. Cytotoxicity was determined using MTT and NRU cell viability assays in 96-well plates. PP was measured using transepithelial electrical resistance (TEER) measurements, as well as passage of lucifer yellow (LY), [3H]-mannitol (both low mw indicators), and FITC-dextran (higher mw indicator) in culture inserts. Inhibitory concentrations 50% (IC50s) suggest that there were good correlations between 24-h and 72-h exposures. NRU IC50 values correlated better with TEER, which is consistent with the Registry of Cytotoxicity (RC; ICCVAM) database report. Both cell viability assays indicate that cytotoxicity occurs before TEER is compromised. In addition, 24-h and 72-h NRU assays, and 72-h TEER measurements, displayed the highest correlations with established rodent LD50s. PP experiments showed that passive paracellular transport of the tight junction markers, especially [3H]-mannitol, correlates with the IC50s determined with the viability assays and TEER measurements. Our AC/TEER/PP model thus allows for the differentiation between the concentrations necessary for AC and those needed to interfere with PP. We propose that the in vitro AC, TEER and PP results be used to compute a formula which can "normalize" and improve the predictive ability of in vitro acute cytotoxicity assays for in vivo lethality.

Future alternative therapies in a quest to halt aberrations in diabetes mellitus

Under normal physiological conditions, euglycaemia is maintained principally by the homeostatic balance of insulin and glucagon which are secreted from the pancreas. In both type 1 and type 2 diabetes mellitus there is a substantial and chronic increase in the circulating glucose concentration. This elevation in glucose levels is accompanied by a plethora of other biochemical disturbances, including disruption of carbohydrate, fat and protein metabolism. Clinical manifestations of diabetes, which arise from the metabolic disturbances vary between individuals but are often a serious threat to quality and length of life. Pancreas transplantation (Tx) and islet modifications are methods used to restore endogenous insulin secretion in insulin-dependent diabetic patients. In order for this to be achieved successfully, however, some of the problems such as hyperglycemia states (> 150 mg/dl), which may harm pancreatic graft beta cells, immunorejection, the effects of immunosuppression, for example, must be overcome. Considering these problems, therefore, it seems logical that the replacement of the islet tissue itself, either by transplanting a vascularised pancreatic allograft or by transplanting modified pancreatic islet cells, provides a better alternative therapeutic approach than simply replacing insulin that has been lost. This review will show the recent development in the use of pancreatic islets and their modification in a quest to halt the aberrations seen in diabetes mellitus.

Development of Cultured Rabbit Corneal Epithelium for Drug Permeation Studies: A Comparison with Excised Rabbit Cornea

The aim of this study was to prepare and test an artificial corneal epithelium (reconstituted rabbit corneal epithelium, RRCE) exhibiting barrier characteristics and paracellular permeability similar to those of native rabbit cornea. The RRCE was obtained from a rabbit corneal epithelium (RCE) cell line grown for 8 days in submerged culture, then for 7 days in air-interface conditions on Snapwell polyester membranes. Permeation studies on the RRCE were carried out in comparison with rabbit excised corneas in vitro, using timolol maleate (TM) as the test drug, alone and in association with the following ocular permeation enhancers: benzalkonium chloride, ethylene-diaminetetraacetic acid sodium salt, polyethoxylated castor oil, polyoxyethylene stearyl ether, sodium deoxycholate, and escin. The integrity of the RRCE was assessed by measuring the transepithelial electrical resistance (TEER) during culture time and after every permeation experiment. When TM was tested alone, the permeation parameters (apparent permeability coefficient, lag time) obtained with the RRCE were similar to those of excised rabbit corneas. The artificial epithelium, however, was less sensitive than native cornea to the effect of permeation enhancers.