Biomimetic Artificial Membrane Permeability Assay over Franz Cell Apparatus Using BCS Model Drugs

Permeability Benchmarking: Guidelines for Comparing in Silico, in Vitro, and in Vivo Measurements

Permeability is a measure of the degree to which cells can transport molecules across biological barriers. Units of permeability are distance per unit time (typically cm/s), where accurate measurements are needed to define drug delivery in homeostasis and to model dysfunction occurring during disease. This perspective offers a set of community-led guidelines to benchmark permeability data across multidisciplinary approaches and different biological contexts. First, we lay out the analytical framework for three methodologies to calculate permeability: in silico assays using either transition-based counting or the inhomogeneous-solubility diffusion approaches, in vitro permeability assays using cells cultured in 2D or 3D geometries, and in vivo assays utilizing in situ brain perfusion or multiple time-point regression analysis. Then, we demonstrate a systematic benchmarking of in silico to both in vitro and in vivo, depicting the ways in which each benchmarking is sensitive to the choices of assay design. Finally, we outline seven recommendations for best practices in permeability benchmarking and underscore the significance of tailored permeability assays in driving advancements in drug delivery research and development. Our exploration encompasses a discussion of "generic" and tissue-specific biological barriers, including the blood-brain barrier (BBB), which is a major hurdle for the delivery of therapeutic agents into the brain. By addressing challenges in reconciling simulated data with experimental assays, we aim to provide insights essential for optimizing accuracy and reliability in permeability modeling.

A Review on Microengineering of Epithelial Barriers for Biomedical and Pharmaceutical Research

Epithelial tissue forms a barrier around the human body and visceral organs, providing protection, permeation, sensation, and secretion. It is vital for our sustenance as it protects the tissue from harm and injury by restricting the entry of foreign bodies inside. Furthermore, it is a strong barrier to drugs, nutrients, and other essential deliverables. This layer also houses a large consortium of microbes, which thrive in tandem with human tissue, providing several health benefits. Moreover, the complex interplay of the microbiome with the barrier tissue is poorly understood. Therefore, replicating these barrier tissues on microdevices to generate physiological and pathophysiological models has been a huge interest for researchers over the last few decades. The artificially engineered reconstruction of these epithelial cellular barriers on microdevices could help underpin the host-microbe interaction, generating a physiological understanding of the tissue, tissue remodeling, receptor-based selective diffusion, drug testing, and others. In addition, these devices could reduce the burden of animal sacrifices for similar research and minimize the failure rate in drug discovery due to the use of primary human cells and others. This review discusses the nature of the epithelial barrier at different tissue sites, the recent developments in creating engineered barrier models, and their applications in pathophysiology, host-microbe interactions, drug discovery, and cytotoxicity. The review aims to provide know-how and knowledge behind engineered epithelial barrier tissue to bioengineers, biotechnologists, and scientists in allied fields.

PEO-b-PCL/Tween 80/cyclodextrin systems: from bioinspired fabrication to possible nasal administration of ropinirole hydrochloride

In this study, we designed and developed systems composed of poly(ethylene-oxide)-b-poly(ε-caprolactone) block copolymers of different molecular weights and compositions, non-ionic surfactant, and cyclodextrins. The innovation of this study lies in the combination of these diverse biomaterials to create biomimetic and bioinspired drug delivery supramolecular structures. The systems were formed by the thin-film hydration method. Extensive physicochemical and morphological characterization was conducted using differential scanning calorimetry, light scattering techniques, microcalorimetry analysis, high-resolution ultrasound spectroscopy, surface tension measurements, fluorescence spectroscopy, cryogenic transmission electron microscopy images, and in vitro cytotoxicity evaluation. These innovative hybrid nanoparticles were found to be attractive candidates as drug delivery systems with unique properties by encompassing the physicochemical and thermotropic properties of both classes of materials. Subsequently, Ropinirole hydrochloride was used as a model drug for the purpose of this study. These systems showed a high RH content (%), and in vitro diffusion experiments revealed that more than 90% of the loading dose was released under pH and temperature conditions that simulate the conditions of the nasal cavity. Promising drug release performance was observed with all tested formulations, worth further investigation to explore both ex vivo permeation through the nasal mucosa and in vivo performance in an experimental animal model.

Designing an effective dissolution test for bilayer tablets tailored for optimal melatonin release in sleep disorder management

This project aims to investigate the release performance of bilayer tablet (BL-Tablet) designed with both fast and slow-release technology, targeting sleep disorders. The tablet incorporates Melatonin, extracts of Eschscholzia californica and Melissa officinalis. In order to validate the effectiveness of the extended-release profile, an advanced dissolution test was herein proposed. This new method utilizes biorelevant intestinal fluid media and incorporates a stomach-to-intestine fluid changing (SIFC) system. To demonstrate the advantages of employing this method for assessing the controlled release profile of active ingredients, the dissolution results were compared with those obtained using the conventional EU Pharmacopoeia approach. Furthermore, the comparative analysis was extended to include a monolayer tablet version (ML-Tablet) lacking the slow-release technology. Technological characterization and bioaccessibility studies, including intestinal permeability test, were conducted as well to assess the pharmacological performance and bioavailability of active ingredients. The dissolution data recovered revealed that the two dissolution methods did not exhibit any significant differences in the release of ML-Tablet's. However, the dissolution profile of the BL-Tablet exhibited notable differences between the two methods particularly when assessing the behavior of the slow-release layer. In this scenario, both methods initially exhibited a similar release pattern within the first approximately 0.5 h, driven by the fast-release layer of the tablet. Following this, distinct gradual and sustained releases were observed, spanning 2.5 h for the EU Pharmacopoeia method and 8 h for the new SIFC-biorelevant dissolution method, respectively. Overall, the novel method demonstrated a substantial improvement compared to conventional EU Pharmacopoeia test in evaluating the performance of a controlled slow-release technology. Remarkably, the prolonged release technology did not have an adverse impact on melatonin intestinal absorption, and, consequently, maintaining its potential bioavailability of around 78%. Concluding, this research provides valuable insights into how the innovative dissolution test can assist formulators in developing controlled release formulations.

Towards personalized drug delivery via semi-solid extrusion: Exploring poly(vinyl alcohol-co-vinyl acetate) copolymers for hydrochlorothiazide-loaded films

The increasing need for personalized drug delivery requires developing systems with tailorable properties. The copolymer poly(vinyl alcohol-co-vinyl acetate) (PVA/PVAc) allows for adjusting the monomer ratio. This study explored the effect of vinyl alcohol (VA) and vinyl acetate (VAc) monomer ratio on the properties of hydrochlorothiazide (HCT) films. Five copolymers with different VA/VAc ratios were selected and characterized. Semi-solid extrusion was employed as a method for the preparation of HCT-PVA/PVAc films to address the challenges of HCT´s low water solubility, high melting point, and low permeability. All copolymers were suitable for semi-solid extrusion, however, the mechanical properties of films with higher VA proportions were more suitable. The drug was found to be homogeneously distributed on a micrometer level throughout the prepared films. It was found that using different monomer ratios in the copolymer allows for drug release tuning - higher VA proportions showed an increased rate of drug release. Experiments through HT29-MTX cell monolayers revealed differences in HCT permeability between the different formulations. In addition, no cytotoxicity was observed for the tested formulations. The results highlight the effect of monomer ratio on film properties, providing valuable guidance for formulators in selecting PVA/PVAc copolymers for achieving desired high-quality films. In addition, varying the monomer ratio allows tuning of the film properties, and can be applied for personalization, with flexible-dose adjustment and design of appealing shapes of the pharmaceutics, not least attractive for pediatric drug delivery.

In Vitro Permeability Study of Homotaurine Using a High-Performance Liquid Chromatography with Fluorescence Detection Pre-Column Derivatization Method

Homotaurine (HOM) is considered a promising drug for the treatment of Alzheimer's and other neurodegenerative diseases. In the present work, a new high-performance liquid chromatography with fluorescence detection (HPLC-FLD) (λex. = 340 nm and λem. = 455 nm) method was developed and validated for the study of substance permeability in the central nervous system (CNS). Analysis was performed on a RP-C18 column with a binary gradient elution system consisting of methanol-potassium phosphate buffer solution (pH = 7.0, 0.02 M) as mobile phase. Samples of homotaurine and histidine (internal standard) were initially derivatized with ortho-phthalaldehyde (OPA) (0.01 M), N-acetylcysteine (0.01 M) and borate buffer (pH = 10.5; 0.05 M). To ensure the stability and efficiency of the reaction, the presence of different nucleophilic reagents, namely (a) 2-mercaptoethanol (2-ME), (b) N-acetylcysteine (NAC), (c) tiopronin (Thiola), (d) 3-mercaptopropionic acid (3-MPA) and (e) captopril, was investigated. The method was validated (R2 = 0.9999, intra-day repeatability %RSD < 3.22%, inter-day precision %RSD = 1.83%, limits of detection 5.75 ng/mL and limits of quantification 17.43 ng/mL, recovery of five different concentrations 99.75-101.58%) and successfully applied to investigate the in vitro permeability of homotaurine using Franz diffusion cells. The apparent permeability (Papp) of HOM was compared with that of memantine, which is considered a potential therapeutic drug for various CNSs. Our study demonstrates that homotaurine exhibits superior permeability through the simulated blood-brain barrier compared to memantine, offering promising insights for enhanced drug delivery strategies targeting neurological conditions.

Commercially Available Cell-Free Permeability Tests for Industrial Drug Development: Increased Sustainability through Reduction of In Vivo Studies

Replacing in vivo with in vitro studies can increase sustainability in the development of medicines. This principle has already been applied in the biowaiver approach based on the biopharmaceutical classification system, BCS. A biowaiver is a regulatory process in which a drug is approved based on evidence of in vitro equivalence, i.e., a dissolution test, rather than on in vivo bioequivalence. Currently biowaivers can only be granted for highly water-soluble drugs, i.e., BCS class I/III drugs. When evaluating poorly soluble drugs, i.e., BCS class II/IV drugs, in vitro dissolution testing has proved to be inadequate for predicting in vivo drug performance due to the lack of permeability interpretation. The aim of this review was to provide solid proofs that at least two commercially available cell-free in vitro assays, namely, the parallel artificial membrane permeability assay, PAMPA, and the PermeaPad^® assay, PermeaPad, in different formats and set-ups, have the potential to reduce and replace in vivo testing to some extent, thus increasing sustainability in drug development. Based on the literature review presented here, we suggest that these assays should be implemented as alternatives to (1) more energy-intense in vitro methods, e.g., refining/replacing cell-based permeability assays, and (2) in vivo studies, e.g., reducing the number of pharmacokinetic studies conducted on animals and humans. For this to happen, a new and modern legislative framework for drug approval is required.

Ibuprofen in a Lipid Bilayer: Nanoscale Spatial Arrangement

Ibuprofen is a non-steroidal anti-inflammatory drug (NSAID) with analgesic and antipyretic effects. Understanding the molecular mechanisms of drug interaction with cell membranes is important to improving drug delivery, uptake by cells, possible side effects, etc. Double electron-electron resonance spectroscopy (DEER, also known as PELDOR) provides information on the nanoscale spatial arrangement of spin-labeled molecules. Here, DEER was applied to study (mono-)spin-labeled ibuprofen (ibuprofen-SL) in a bilayer of palmitoyl-oleoyl-sn-glycerophosphocholine (POPC). The results obtained show that the ibuprofen-SL molecules are located within a plane in each bilayer leaflet. At their low molar concentration in the bilayer χ, the found surface concentration of ibuprofen-SL is two times higher than χ, which can be explained by alternative assembling in the two leaflets of the bilayer. When χ > 2 mol%, these assemblies merge. The findings shed new light on the nanoscale spatial arrangement of ibuprofen in biological membranes.

Development and In Vitro-Ex Vivo Evaluation of Novel Polymeric Nasal Donepezil Films for Potential Use in Alzheimer's Disease Using Experimental Design

The objective and novelty of the present study is the development and optimization of innovative nasal film of Donepezil hydrochloride (DH) for potential use in Alzheimer’s disease. Hydroxypropyl-methyl-cellulose E50 (factor A) nasal films, with Polyethylene glycol 400 as plasticizer (factor B), and Methyl-β-Cyclodextrin, as permeation enhancer (factor C), were prepared and characterized in vitro and ex vivo. An experimental design was used to determine the effects of the selected factors on permeation profile of DH through rabbit nasal mucosa (response 1), and on film flexibility/foldability (response 2). A face centered central composite design with three levels was applied and 17 experiments were performed in triplicate. The prepared films exhibited good uniformity of DH content (90.0 ± 1.6%−99.8 ± 4.9%) and thickness (19.6 ± 1.9−170.8 ± 11.5 μm), storage stability characteristics, and % residual humidity (<3%), as well as favourable swelling and mucoadhesive properties. Response surface methodology determined the optimum composition for flexible nasal film with maximized DH permeation. All selected factors interacted with each other and the effect of these interactions on responses is strongly related to the factor’s concentration ratios. Based on these encouraging results, in vivo serum and brain pharmacokinetic study of the optimized nasal film, in comparison to DH oral administration, is ongoing in an animal model.

Synthesis of Spin-Labeled Ibuprofen and Its Interaction with Lipid Membranes

Ibuprofen is a non-steroidal anti-inflammatory drug possessing analgesic and antipyretic activity. Electron paramagnetic resonance (EPR) spectroscopy could be applied to study its interaction with biological membranes and proteins if its spin-labeled analogs were synthesized. Here, a simple sequence of ibuprofen transformations—nitration, esterification, reduction, Sandmeyer reaction, Sonogashira cross-coupling, oxidation and saponification—was developed to attain this goal. The synthesis resulted in spin-labeled ibuprofen (ibuprofen-SL) in which the spin label TEMPOL is attached to the benzene ring. EPR spectra confirmed interaction of ibuprofen-SL with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers. Using ²H electron spin echo envelope modulation (ESEEM) spectroscopy, ibuprofen-SL was found to be embedded into the hydrophobic bilayer interior.

Cystic Fibrosis Mucus Model to Design More Efficient Drug Therapies

Mucus represents a strong barrier to tackle for oral or pulmonary administered drugs, especially in mucus-related disorders. This study uses a pathological cystic fibrosis (CF) mucus model to investigate how mucus impacts the passive diffusion of 45 ad hoc commercial drugs selected to maximize physicochemical variability. An in vitro mucosal surface was recreated by coupling the mucus model to a 96-well permeable support precoated with structured layers of phospholipids (parallel artificial membrane permeability assay, PAMPA). Results show that the mucus model was not a mere physical barrier but it behaves like an interactive filter. In nearly one-half of the investigated compounds, the diffusion was reduced by mucus, while other drugs were not sensitive to the mucus barriers. We also found that permeability can be enhanced when drug-calcium salts are formed. This was confirmed with cystic fibrosis sputum as a rough ex vivo model of CF mucus. Since the drug discovery process is characterized by a high rate of failure, the mucus platform is expected to provide an efficient support to early reduce the number of poor-performing drug candidates.

Skin-on-a-Chip Technology for Testing Transdermal Drug Delivery-Starting Points and Recent Developments

During the last decades, several technologies were developed for testing drug delivery through the dermal barrier. Investigation of drug penetration across the skin can be important in topical pharmaceutical formulations and also in cosmeto-science. The state-of- the-art in the field of skin diffusion measurements, different devices, and diffusion platforms used, are summarized in the introductory part of this review. Then the methodologies applied at Pázmány Péter Catholic University are shown in detail. The main testing platforms (Franz diffusion cells, skin-on-a-chip devices) and the major scientific projects (P-glycoprotein interaction in the skin; new skin equivalents for diffusion purposes) are also presented in one section. The main achievements of our research are briefly summarized: (1) new skin-on-a-chip microfluidic devices were validated as tools for drug penetration studies for the skin; (2) P-glycoprotein transport has an absorptive orientation in the skin; (3) skin samples cannot be used for transporter interaction studies after freezing and thawing; (4) penetration of hydrophilic model drugs is lower in aged than in young skin; (5) mechanical sensitization is needed for excised rodent and pig skins for drug absorption measurements. Our validated skin-on-a-chip platform is available for other research groups to use for testing and for utilizing it for different purposes.

Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation

The gastrointestinal tract (GIT) can be broadly divided into several regions: the stomach, the small intestine (which is subdivided to duodenum, jejunum, and ileum), and the colon. The conditions and environment in each of these segments, and even within the segment, are dependent on many factors, e.g., the surrounding pH, fluid composition, transporters expression, metabolic enzymes activity, tight junction resistance, different morphology along the GIT, variable intestinal mucosal cell differentiation, changes in drug concentration (in cases of carrier-mediated transport), thickness and types of mucus, and resident microflora. Each of these variables, alone or in combination with others, can fundamentally alter the solubility/dissolution, the intestinal permeability, and the overall absorption of various drugs. This is the underlying mechanistic basis of regional-dependent intestinal drug absorption, which has led to many attempts to deliver drugs to specific regions throughout the GIT, aiming to optimize drug absorption, bioavailability, pharmacokinetics, and/or pharmacodynamics. In this Editorial we provide an overview of the Special Issue "Regional Intestinal Drug Absorption: Biopharmaceutics and Drug Formulation". The objective of this Special Issue is to highlight the current progress and to provide an overview of the latest developments in the field of regional-dependent intestinal drug absorption and delivery, as well as pointing out the unmet needs of the field.