Predicting skin permeability

Artificial intelligence for skin permeability prediction: deep learning

BACKGROUND AND OBJECTIVE

Researchers have put in significant laboratory time and effort in measuring the permeability coefficient (Kp) of xenobiotics. To develop alternative approaches to this labour-intensive procedure, predictive models have been employed by scientists to describe the transport of xenobiotics across the skin. Most quantitative structure-permeability relationship (QSPR) models are derived statistically from experimental data. Recently, artificial intelligence-based computational drug delivery has attracted tremendous interest. Deep learning is an umbrella term for machine-learning algorithms consisting of deep neural networks (DNNs). Distinct network architectures, like convolutional neural networks (CNNs), feedforward neural networks (FNNs), and recurrent neural networks (RNNs), can be employed for prediction.

METHODS

In this project, we used a convolutional neural network, feedforward neural network, and recurrent neural network to predict skin permeability coefficients from a publicly available database reported by Cheruvu et al. The dataset contains 476 records of 145 chemicals, xenobiotics, and pharmaceuticals, administered on the human epidermis in vitro from aqueous solutions of constant concentration either saturated in infinite dose quantities or diluted. All the computations were conducted with Python under Anaconda and Jupyterlab environment after importing the required Python, Keras, and Tensorflow modules.

RESULTS

We used a convolutional neural network, feedforward neural network, and recurrent neural network to predict log kp.

CONCLUSION

This research work shows that deep learning networks can be successfully used to digitally screen and predict the skin permeability of xenobiotics.

Machine learning for skin permeability prediction: random forest and XG boost regression

Background: Machine learning algorithms that can quickly and easily estimate skin permeability (Kp) are increasingly being used in drug delivery research. The linear free energy relationship (LFER) developed by Abraham is a practical technique for predicting Kp. The permeability coefficients and Abraham solute descriptor values for 175 organic compounds have been documented in the scientific literature.Purpose: The purpose of this project was to use a publicly available dataset to make skin permeability predictions using the random forest and XBoost regression techniques.Methods: We employed Pandas-based methods in JupyterLab to predict permeability coefficient (Kp) from solute descriptors (excess molar refraction [E], combined dipolarity/polarizability [S], overall solute hydrogen bond acidity and basicity [A and B], and the McGowan's characteristic molecular volume [V]).Results: The random forest and XG Boost regression models established statistically significant association between the descriptors and the skin permeability coefficient.

Delivery of small hydrophilic molecules across the stratum corneum: Identification of model systems and parameters to study topical delivery of free amino acids

Free amino acids (FAAs) constitute the largest component (∼40 %) of the so-called natural moisturizing factors of the skin. Their level declines in dry skin conditions and one strategy to overcome this problem may involve the topical delivery of FAAs through appropriate strategy. The objective of the present study was therefore to identify alternative skin models and study the corneocyte-water partition coefficients (KCOR/W) and permeation coefficient (KP) of 18 FAAs. The KCOR/W was studied using standard protocols and the permeation studies were conducted using Franz diffusion cell. The results indicate that the FAAs have high partitioning behavior to the corneocytes. The KCOR/W values of the human COR and that of pig ear skin were better correlated with each other than that of keratin isolated from chicken feathers. The presence of lipid in the stratum corneum (SC), initial concentration of the FAAs, and permeation enhancers affect the KCOR/W. The FAAs have low permeation into the SC which suggests the need for permeation enhancers in designing dosage form containing these compounds. Even though the investigated mathematical models show good prediction of the Kp values, better prediction could be obtained by considering factors such as the possible entrapment of the FAAs by the CORs.

Polycyclic aromatic hydrocarbon skin permeation efficiency in vitro is lower through human than pigskin and decreases with lipophilicity

Polycyclic aromatic hydrocarbons (PAH) are persistent environmental pollutants, which occasionally appear as contaminants in consumer products. Upon dermal contact, transfer of PAH into the stratum corneum (s.c.) and migration through the skin may occur, resulting in this class of highly toxic compounds to become bioavailable. In this study, dermal penetration through human and porcine skin of 24 PAH, comprising broad molar mass (M: 152-302 g/mol) and octanol-water partition coefficient (logP: 3.9-7.3) ranges, was evaluated via Franz diffusion cell in vitro assays. More lipophilic and potentially more toxic PAH had decreased permeation rates through the rather lipophilic s.c. into the more hydrophilic viable (epi-)dermis. Furthermore, human skin was less permeable than pigskin, a commonly used surrogate in skin penetration studies. In particular, the s.c. of human skin retains a greater share of PAH, an effect that is more pronounced for smaller PAH. Additionally, we compared the skin permeation kinetics of different PAH in pigskin. While small PAH (M < 230 g/mol, logP < 6) permeate the skin quickly and are detected in the receptor fluid after 2 h, large PAH (M > 252 g/mol, logP ≥ 6) do not fully permeate the skin up to 48 h. This indicates that highly lipophilic PAH do not become bioavailable as readily as their smaller congeners when transferred to the skin surface. Our data suggest that pigskin could be used as a surrogate for worst case scenario estimates of dermal PAH permeation through human skin.

An in-silico receptor-pharmacophore based multistep molecular docking and simulation study to evaluate the inhibitory potentials against NS1 of DENV-2

DENV-2 strain is the most fatal and infectious of the five dengue virus serotypes. The non-structural protein NS1 encoded by its genome is the most significant protein required for viral pathogenesis and replication inside the host body. Thus, targeting the NS1 protein and designing an inhibitor to limit its stability and secretion is a propitious attempt in our fight against dengue. Four novel inhibitors are designed to target the conserved cysteine residues (C55, C313, C316, and C329) and glycosylation sites (N130 and N207) of the NS1 protein in an attempt to halt the spread of the dengue infection in the host body altogether. Numerous computer-aided drug designing techniques including molecular docking, molecular dynamics simulation, virtual screening, principal component analysis, and dynamic cross-correlation matrix were employed to determine the structural and functional activity of the NS1-inhibitor complexes. From our analysis, it was evident that the extent of structural and atomic level fluctuations of the ligand-bound protein exhibited a declining trend in contrast to unbound protein which was prominently noticeable through the RMSD, RMSF, Rg, and SASA graphs. The ADMET analysis of the four ligands revealed a promising pharmacokinetics and pharmacodynamic profile, along with good bioavailability and toxicity properties. The proposed drugs when bound to the targeted cavities resulted in stable conformations in comparison to their unbound state, implying they have good affinity promising effective drug action. Thus, they can be tested in vitro and used as potential anti-dengue drugs.Communicated by Ramaswamy H. Sarma.

Reduced estrogenic risks of a sunscreen additive: Theoretical design and evaluation of functionally improved salicylates

Salicylic esters (SEs), the widely used ultraviolet (UV) absorbers in sunscreen products, have been found to have health risks such as skin sensitization and estrogenic effects. This study aims to design SE substitutes that maintain high UV absorbance while reducing estrogenicity. Using molecular docking and Gaussian09 software for initial assessments and further application of a combination of two-dimensional and three-dimensional quantitative structure-activity relationships (2D-QSAR and 3D-QSAR, respectively) models, we designed 73 substitutes. The best-performing molecules, ethylhexyl salicylate (EHS)-5 and EHS-15, significantly reduced estrogenicity (44.54 % and 17.60 %, respectively) and enhanced UV absorbance (249.56 % and 46.94 %, respectively). Through screening for human health risks, we found that EHS-5 and EHS-15 were free from skin sensitivity and eye irritation and exhibited reduced skin permeability compared with EHS. Furthermore, the photolysis and synthetic pathways of EHS-5 and EHS-15 were deduced, demonstrating their good photodegradability and potential synthesizability. In addition, we analyzed the mechanisms underlying the changes in estrogenic effects and UV absorption properties. We identified covalent hydrogen bond basicity and acidity Propgen value for atomic molecular properties and the highest occupied molecular orbital eigenvalue as the main factors affecting the estrogenic effect and UV absorbance of SEs, respectively. This study focuses on the design and screening of SEs, exhibiting enhanced functionality, reduced health risks, and synthetic feasibility.

A database of chemical absorption in human skin with mechanistic modeling applications

Whether from environmental and occupational hazards or from topical pharmaceuticals, the human skin comes into contact with various chemicals every day. In vivo experiments not only require large investments of both time and money, but in vivo experiments can also be unethical due to the need to intentionally or incidentally expose humans or animals to toxic chemicals. Comparatively, in vitro experiments offer ethical and financial advantages when combined with the opportunity to selectively choose chemicals for experimentation. With in vivo experimentation being so infeasible, many scientists have chosen to make their in vitro data available publicly. Using these data, a detailed database containing 73 chemicals was created with a robust set of descriptors to be used in connection with mathematical modeling to predict diffusion, permeability, and partition coefficients. This resulting database is tailored to be easily used in various coding languages.

Repurposing the Open Global Health Library for the discovery of novel Mpro destabilizers with scope as broad-spectrum antivirals

The SARS coronavirus 2 (SARS-CoV-2) epidemic remains globally active. The emergence of new variants of interest and variants of concern (VoCs), which are potentially more vaccine-resistant and less sensitive to existing treatments, is evident due to their high prevalence. The prospective spread of such variants and other coronaviruses with epidemic potential demands preparedness that can be met by developing fast-track workflows to find new candidates that target viral proteins with a clear in vitro and in vivo phenotype. Mpro (or 3CLpro) is directly involved in the viral replication cycle and the production and function of viral polyproteins, which makes it an ideal target. The biological relevance of Mpro is highly conserved among betacoronaviruses like HCoV-OC43 and SARS-CoV-2, which makes the identification of new chemical scaffolds targeting them a good starting point for designing broad-spectrum antivirals. We report an optimized methodology based on orthogonal cell-free assays to identify small molecules that inhibit the binding pockets of both SARS-CoV-2-Mpro and HCoV-OC43-Mpro; this blockade correlates with antiviral activities in HCoV-OC43 cellular models. By using such a fast-tracking approach against the Open Global Health Library (Merck KGaA), we have found evidence of the antiviral activity of compound OGHL98. In silico studies dissecting intermolecular interactions between OGHL98 and both proteases and comprising docking and molecular dynamics simulations (MDSs) concluded that the binding mode was primarily governed by conserved H-bonds with their C-terminal amino acids and that the rational design of OGHL98 has potential against VoCs proteases resistant to current therapeutics.

Interaction mechanism of oseltamivir phosphate with bovine serum albumin: multispectroscopic and molecular docking study

Oseltamivir phosphate (OP) is an antiviral drug with potential risks to human health due to overuse, leading to serious consequences such as gastrointestinal disturbances, abnormal neuropsychiatric symptoms, and sudden death. Therefore, gaining an in-depth understanding of its interaction with proteins is crucial. We investigated the interaction between OP and bovine serum albumin (BSA) utilizing multispectral methods (i.e., fluorescence, ultraviolet absorption, circular dichroism) combined with molecular docking techniques. Fluorescence spectroscopy indicated that OP quenched BSA fluorescence by forming the OP-BSA complex. The Stern-Volmer constants (KSV) between OP and BSA were determined to be 3.06 × 103 L/mol, 2.36 × 103 L/mol, and 1.86 × 103 L/mol at 293 K, 298 K, and 303 K, respectively. OP occupies exclusively one binding site on BSA, and the fluorescent probe displacement measurements revealed that this is BSA site I. Thermodynamic data (∆H, ∆S, and ∆G) obtained by fitting the van't Hoff equation were - 77.49 kJ/mol, -176.54 J/(mol∙K), and - 24.88 kJ/mol, respectively, suggesting that hydrogen bonding and van der Waals forces mainly participate in OP-BSA complex stabilization. Moreover, the reaction occurs spontaneously at room temperature. Synchronous fluorescence spectra indicated that OP interacts with tryptophan residue of BSA. The results of ultraviolet (UV) and 3D fluorescence spectroscopy indicated that the OP-BSA complex formation altered the microenvironment around amino acid residues. Circular dichroism spectra revealed that the addition of OP decreased the α-helix content of BSA by 7.13%. Docking analysis confirmed that OP binds to BSA site I through hydrogen bonding with amino acids VAL342, SER453, and ASP450. Finally, ADMET studies were conducted to explore the pharmacokinetics of OP as an antiviral drug.

Syagrus coronata fixed oil prevents rotenone-induced movement disorders and oxidative stress in Drosophila melanogaster

One prominent aspect of Parkinson's disease (PD) is the presence of elevated levels of free radicals, including reactive oxygen species (ROS). Syagrus coronata (S. coronata), a palm tree, exhibits antioxidant activity attributed to its phytochemical composition, containing fatty acids, polyphenols, and flavonoids. The aim of this investigation was to examine the potential neuroprotective effects of S. coronata fixed oil against rotenone-induced toxicity using Drosophila melanogaster. Young Drosophila specimens (3-4 d old) were exposed to a diet supplemented with rotenone (50 µM) for 7 d with and without the inclusion of S. coronata fixed oil (0.2 mg/g diet). Data demonstrated that rotenone exposure resulted in significant locomotor impairment and increased mortality rates in flies. Further, rotenone administration reduced total thiol levels but elevated lipid peroxidation, iron (Fe) levels, and nitric oxide (NO) levels while decreasing the reduced capacity of mitochondria. Concomitant administration of S. coronata exhibited a protective effect against rotenone, as evidenced by a return to control levels of Fe, NO, and total thiols, lowered lipid peroxidation levels, reversed locomotor impairment, and enhanced % cell viability. Molecular docking of the oil lipidic components with antioxidant enzymes showed strong binding affinity to superoxide dismutase (SOD) and glutathione peroxidase (GPX1) enzymes. Overall, treatment with S. coronata fixed oil was found to prevent rotenone-induced movement disorders and oxidative stress in Drosophila melanogaster.

Investigating the Free Volumes as Nanospaces in Human Stratum Corneum Lipid Bilayers Using Positron Annihilation Lifetime Spectroscopy (PALS)

This work is the first one that provides not only evidence for the existence of free volumes in the human stratum corneum but also focuses on comparing these experimental data, obtained through the unique positron annihilation lifetime spectroscopy (PALS) method, with theoretical values published in earlier works. The mean free volume of 0.269 nm was slightly lower than the theoretical value of 0.4 nm. The lifetime τ3 (1.83 ns with a coefficient of variation CV of 3.21%) is dependent on the size of open sites in the skin. This information was used to calculate the free volume radius R (0.269 nm with CV 2.14%), free volume size Vf (0.081 nm3 with CV 4.69%), and the intensity I3 (9.01% with CV 10.94%) to estimate the relative fractional free volume fv (1.32 a.u. with CV 13.68%) in human skin ex vivo. The relation between the lifetime of o-Ps (τ3) and the radius of free volume (R) was formulated using the Tao-Eldrup model, which assumes spherical voids and applies to sites with radii smaller than 1 nm. The results indicate that PALS is a powerful tool for confirming the existence of free volumes and determining their size. The studies also focused on describing the probable locations of these nanospaces in SC lipid bilayers. According to the theory, these play an essential role in dynamic processes in biological systems, including the diffusion of low-molecular-weight hydrophobic and moderately hydrophilic molecules. The mechanism of their formation has been determined by the molecular dynamics of the lipid chains.

Penetration pathways, influencing factors and predictive models for dermal absorption of exobiotic molecules: A critical review

This review provides a comprehensive summary of the skin penetration pathways of xenobiotics, including metals, organic pollutants, and nanoparticles (NPs), with a particular focus on the methodologies employed to elucidate these penetration routes. The impacts of the physicochemical properties of exogenous substances and the properties of solvent carriers on the penetration efficiencies were discussed. Furthermore, the review outlines the steady-state and transient models for predicting the skin permeability of xenobiotics, emphasizing the models which enable realistic visualization of pharmaco-kinetic phenomena via detailed geometric representations of the skin microstructure, such as stratum corneum (SC) (bricks and mortar) and skin appendages (hair follicles and sebaceous gland units). Limitations of published research, gaps in current knowledge, and recommendations for future research are highlighted, providing insight for a better understanding of the skin penetration behavior of xenobiotics and associated health risks in practical application contexts.

Imidazole-Derived Alkyl and Aryl Ethers: Synthesis, Characterization, In Vitro Anticancer and Antioxidant Activities, Carbonic Anhydrase I-II Inhibition Properties, and In Silico Studies

Imidazole derivatives display extensive applications in pharmaceutical chemistry and have been investigated as bioactive compounds for medicinal chemistry. In this study, besides the starting materials (3a-c and 4a-c), synthesis, characterization, and biological activity studies were conducted on a total of 18 compounds, nine of which are known and the other nine are original. The compounds investigated in the study are a series of alkyl (7-15) and aryl (16-24) ether derivatives bearing substituted phenyl and imidazole rings, which were characterized using various methods including 1H NMR, 13C NMR, FT-IR analysis, elemental analysis, and mass spectroscopy. Computer-aided drug design studies have been carried out to predict the biological activities of compounds. Besides DFT calculations, the binding affinities of the compounds to EGFR, VEGFR2, FGFR1, HSP90, hCA I, and hCA II were investigated. Additionally, drug-likeness and ADME analyses were performed on the compounds. Anticancer, antioxidant, and enzyme inhibition activity tests were performed in biological activity studies on the synthesized compounds. Among the synthesized compounds, compounds 17 and 19-24 generally exhibited inhibition profiles against the widespread cytosolic hCA I isozyme with IC50 values ranging from 4.13 to 15.67 nM and cytosolic hCA II isozyme with IC50 values ranging from 5.65 to 14.84 nM. L929 (mouse fibroblast cell line) was used as the control healthy cell line, and MCF7 (breast cancer), C6 (rat glioblastoma), and HT-29 (colon cancer) cells were used in cell culture studies as cancer cell lines. Before the study on cancer cells, all compounds were examined on healthy cells, and their cytotoxicity was determined. As a result of these data, studies continued with six compounds determined to be nontoxic. On cancerous cells, it was determined that compounds 3a, 3b, 4a, 4b, 4c, and 7 had cytotoxic effects on both colon cancer and brain tumors. It was found that compound 3b had a more toxic effect than cisplatin on the glioma cell line with an IC50 value of 10.721 ± 0.38 μM, and compound 3a had a more toxic effect on the colon cancer cell line with an IC50 value of 20.88 ± 1.02 μM. However, it was determined that the same compounds did not have a statistically significant effect on breast cancer. Flow cytometry studies also showed that when the IC50 dose of compound 3b was applied to the C6 cell line, the cells tended to early and late apoptosis. Additionally, it has been shown by flow cytometry that the cell cycle stops in the G0/G1 phase. A similar effect was observed in the colon cancer cell line with compound 3a. Compound 3b caused early and late apoptosis of the colon cancer cell line with the applied IC50 dose and stopped the cell cycle in the G0/G1 phase. Finally, the FRAP method studied all synthesized compounds' antioxidant effects. According to the measured antioxidant power results, it was determined that no compound had a more effective reducing power than vitamin E.

New Approach Methodologies (NAMs) for ad hoc human health risk assessment of food and non-food products - Proceedings of a workshop

RIVM convened a workshop on the use of New Approach Methodologies (NAMs) for the ad hoc human health risk assessment of food and non-food products. Central to the workshop were two case studies of marketed products with a potential health concern: the botanical Tabernanthe iboga which is used to facilitate mental or spiritual insight or to (illegally) treat drug addiction and is associated with cardiotoxicity, and dermal creams containing female sex hormones, intended for use by perimenopausal women to reduce menopause symptoms without medical supervision. The workshop participants recognized that data from NAM approaches added valuable information for the ad hoc risk assessment of these products, although the available approaches were inadequate to derive health-based guidance values. Recommendations were provided on how to further enhance and implement NAM approaches in regulatory risk assessment, specifying both scientific and technical aspects as well as stakeholder engagement aspects.

Ability of biomimetic chromatography and physicochemical systems to predict the skin permeation of neutral compounds. A comparison study

Five in vitro physicochemical systems have been evaluated in terms of its ability to emulate the skin permeation of neutral compounds: the permeation in two different PAMPA membranes, the classical octanol-water partition coefficient, and two biomimetic chromatography systems, one based in cerasome electrokinetic chromatography and another based in reversed-phase liquid chromatography measurements. The coefficients of the solvation parameter model equation of the mentioned systems have been compared to the ones of the skin permeation process through different comparison parameters. Moreover, a method to predict whether a physicochemical system is able to emulate satisfactorily a biological one, just by the analysis of the equation coefficients has been developed. Results reveal that the two PAMPA systems are a good choice to emulate directly the skin permeation of neutral compounds. Instead, the other three systems need a volume correction term to provide a satisfactory emulation. However, after the correction, all the evaluated systems show a similar ability to emulate well skin permeation, as predicted.

Computational Applications: Beauvericin from a Mycotoxin into a Humanized Drug

Drug discovery was initially attributed to coincidence or experimental research. Historically, the traditional approaches were complex, lengthy, and expensive, entailing costly random screening of synthesized compounds or natural products coupled with in vivo validation largely depending on the availability of appropriate animal models. Currently, in silico modeling has become a vital tool for drug discovery and repurposing. Molecular docking and dynamic simulations are being used to find the best match between a ligand and a molecule, an approach that could help predict the biomolecular interactions between the drug and the target host. Beauvericin (BEA) is an emerging mycotoxin produced by the entomopathogenic fungus Beauveria bassiana, being originally studied for its potential use as a pesticide. BEA is now considered a molecule of interest for its possible use in diverse biotechnological applications in the pharmaceutical industry and medicine. In this manuscript, we provide an overview of the repurposing of BEA as a potential therapeutic agent for multiple diseases. Furthermore, considerable emphasis is given to the fundamental role of in silico techniques to (i) further investigate the activity spectrum of BEA, a secondary metabolite, and (ii) elucidate its mode of action.

Structural insight and in silico prediction of the pharmacokinetic parameters and toxicity of alkaline earth metal compounds strontium and barium with the non-steroidal anti-inflammatory drug nimesulide

In the crystals of alkaline earth metal compounds strontium and barium with the non-steroidal anti-inflammatory drug nimesulide, the strontium cation is nine-coordinated with a distorted tricapped trigonal prismatic geometry TCTPR-9, whereas the ten-coordinated barium ion exhibits a distorted tetracapped trigonal prismatic geometry TCTPR-10.

In Vitro Human Dermal Absorption Studies on Pesticides in Complex Mixtures: Investigation of Guidance Criteria and Possible Impact Parameters

Pesticides must not pose unacceptable risks to human health, so risk assessments are conducted before products are authorised. Dermal exposure is often the main route of intake, so estimating realistic and trustworthy dermal absorption values is crucial for risk assessment. Although there are agreed test guidelines for in vitro dermal absorption studies, not every product is tested due to cost reasons. The present dataset consists of 945 individual in vitro experiments on the dermal absorption of human skin with 179 active substances of pesticides in 353 different mixtures, including concentrates and dilutions. The dataset was evaluated to identify the possible impacts of experimental conditions and physico-chemical properties on dermal absorption. The dataset was also analysed to assess the appropriateness of the pro rata correction for untested dilutions, and the set concentration cut-off to decide on the dilution status for choosing a default value on dermal absorption. The study found that the implementation of specific guidelines improved the harmonisation of study conduct, with support for approaches such as pro rata correction and default values. Further analysis of the specific co-formulants may identify influencing factors that may be more important than the experimental variables.

Exploring Cassia mimosoïdes as a promising natural source of steroids with potent anti-cancer, urease inhibition, and antimicrobial properties

The genus Cassia is a rich source of physiologically active secondary metabolites, including a novel compound named 21-methylene-24-ethylidene lophenol, alongside 15 known compounds. These compounds were characterized using different spectroscopic techniques. They exhibited promising antimicrobial activity, particularly against bacteria causing gastrointestinal infections. Compound 1 showed strong anti-bacterial activity against H. pylori and S. aur with MIC values of 0.28 and 0.12 μg mL-1 respectively. The study investigated their impact on H. pylori, a contributor to ulcer development, by inhibiting the urease enzyme. Inhibiting urease can reduce H. pylori's pathogenic potential, evident from the fact that the compounds evaluated toward urease enzyme showed higher inhibitory activity (1.024 ± 0.43 6.678±0.11 μM) compared to standard thiourea (IC50 = 18.61 ± 0.11 μM). Molecular docking studies confirmed their inhibitory action, with compound 7 notably outperforming thiourea in inhibiting urease (-6.95 kcal mol-1vs. -3.13 kcal mol-1). Additionally, these compounds showed positive effects on liver functioning, which H. pylori can impair. Compound 9 shows the best response against human HepG2 liver cancer cell lines i.e., % viability is 14.47% ± 0.69 and IC50 is 7.8 μM ± 0.21. These compounds hold potential as lead compounds for addressing gastrointestinal and liver disorders caused by H. pylori.

Effect of ion pair strategy on transdermal delivery of guanfacine: Which factor dominates drug permeation?

Ion pair is an effective chemical approach to promoting drug transdermal permeation, and the traditional interpretation for its enhanced permeation effect is mainly attributed to counterions altering the physicochemical properties of the drug (lipophilicity, melting point, etc.). In this work, guanfacine (GFC), a non-stimulant for anti-attention deficit and hyperactivity disorder (ADHD), was used as a model drug, and several organic or inorganic acids were designed thereby successfully constructing ion pairs. The transdermal permeation ability of ion pairs through isolated porcine skin was observed and ranked as follows: guanfacine caprylate (GFC-CA) > GFC > guanfacine laurate (GFC-LA) > guanfacine fumarate (GFC-FA) > guanfacine hydrochloride (GFC-HA) > guanfacine palmitate (GFC-PA). The effect of key physicochemical properties (octanol-water partition coefficient, molecular volume, melting point) on the transdermal permeation rate of the model drug was analyzed in detail. In addition, GFC-CA was observed to alter the lipid structure of the skin, suggesting the traditional explanation of the action of ion pair may be inadequate and underrated, and ion pair may also enhance permeation by disrupting skin structure. The intriguing phenomenon is expected to provide a novel approach to achieving precise transdermal drug delivery.

In Vitro and In Vivo Antileishmanial Activity of Thioridazine

INTRODUCTION

Leishmaniasis is a neglected disease with high prevalence and incidence in tropical and subtropical areas. Existing drugs are limited due to cost, toxicity, declining efficacy and unavailability in endemic places. Drug repurposing has established as an efficient way for the discovery of drugs for a variety of diseases.

PURPOSE

The objective of the present work was testing the antileishmanial activity of thioridazine, an antipsychotic agent with demonstrated effect against other intracellular pathogens.

METHODS

The cytotoxicity for mouse peritoneal macrophages as well as the activity against Leishmania amazonensis, Leishmania mexicana and Leishmania major promastigotes and intracellular amastigotes, as well as in a mouse model of cutaneous leishmaniasis, were assessed.

RESULTS

Thioridazine inhibited the in vitro proliferation of promastigotes (50% inhibitory concentration-IC50-values in the range of 0.73 µM to 3.8 µM against L. amazonensis, L. mexicana and L. major) and intracellular amastigotes (IC50 values of 1.27 µM to 4.4 µM for the same species). In contrast, in mouse peritoneal macrophages, the 50% cytotoxic concentration was 24.0 ± 1.89 µM. Thioridazine inhibited the growth of cutaneous lesions and reduced the number of parasites in the infected tissue of mice. The dose of thioridazine that inhibited lesion development by 50% compared to controls was 23.3 ± 3.1 mg/kg and in terms of parasite load, it was 11.1 ± 0.97 mg/kg.

CONCLUSIONS

Thioridazine was effective against the promastigote and intracellular amastigote stages of three Leishmania species and in a mouse model of cutaneous leishmaniasis, supporting the potential repurposing of this drug as an antileishmanial agent.

Enhanced in vitro and ex vivo transdermal permeation of microemulsion gel of tapentadol hydrochloride

Aim of the current study is to develop a microemulsion gel for transdermal delivery of tapentadol hydrochloride. Microemulsion was developed using phase diagram and subjected to assay, globule size, PDI, zeta potential, TEM and in vitro drug release studies. The optimized microemulsion was converted into gel using carbopol 934 NF and evaluated for viscosity, spreadability, in vitro, ex vivo, FTIR, DSC, stability and skin irritation studies. The mean globule size, PDI, zeta potential and in vitro drug release of microemulsion were found 247.3 nm, 0.298, -17.6 mV and 98.42% respectively. In vitro and ex vivo drug release of gel was found 92.2% and 88.6% in 24 h. Viscosity and spreadability results indicated ease of application and no incompatibility was observed from FTIR studies. The skin irritation studies showed absence of erythema. Key findings from the current research concluded that microemulsion gel was suitable for effective transdermal delivery.

Pyrimidine Schiff Bases: Synthesis, Structural Characterization and Recent Studies on Biological Activities

Recently, 5-[(4-ethoxyphenyl)imino]methyl-N-(4-fluorophenyl)-6-methyl-2-phenylpyrimidin-4-amine has been synthesized, characterized, and evaluated for its antibacterial activity against Enterococcus faecalis in combination with antineoplastic activity against gastric adenocarcinoma. In this study, new 5-iminomethylpyrimidine compounds were synthesized which differ in the substituent(s) of the aromatic ring attached to the imine group. The structures of newly obtained pyrimidine Schiff bases were established by spectroscopy techniques (ESI-MS, FTIR and 1H NMR). To extend the current knowledge about the features responsible for the biological activity of the new 5-iminomethylpyrimidine derivatives, low-temperature single-crystal X-ray analyses were carried out. For all studied crystals, intramolecular N-H∙∙∙N hydrogen bonds and intermolecular C-H∙∙∙F interactions were observed and seemed to play an essential role in the formation of the structures. Simultaneously, their biological properties based on their cytotoxic features were compared with the activities of the Schiff base (III) published previously. Moreover, computational investigations, such as ADME prediction analysis and molecular docking, were also performed on the most active new Schiff base (compound 4b). These results were compared with the highest active compound III.

Synthesis, spectral characterisation, biocidal investigation, in-silico and molecular docking studies of 4-[(2-chloro-4-methylphenyl)carbamoyl]butanoic acid derived triorganotin(IV) compounds

Three triorganotin(IV) compounds, R3Sn(L), with R = CH3 (1), n-C4H9 (2) and C6H5 (3), and LH = 4-[(2-chloro-4-methylphenyl)carbamoyl]butanoic acid, were prepared and confirmed by various techniques. A five-coordinate, distorted trigonal-bipyramidal geometry was elucidated for tin(IV) centres both in solution and solid states. An intercalation mode was confirmed for the compound SS-DNA interaction by UV-visible, viscometric techniques and molecular docking. MD simulation revealed stable binding of LH with SS-DNA. Anti-bacterial investigation revealed 2 to be generally the most potent, especially against Sa and Ab, i.e. having the lowest MIC values (≤0.25 μg/mL) compared to the standard anti-biotics vancomycin-HCl (MIC = 1 μg/mL) and colistin-sulphate (MIC = 0.25 μg/mL). Similarly, the anti-fungal profile shows 2 exhibits 100% inhibition against Ca and Cn fungal strains and has MIC values (≤0.25 μg/mL) comparatively lower than standard drug fluconazole (0.125 and 8 μg/mL for Ca and Cn, respectively). Compound 2 has the greatest activity with CC50 ≤ 25 μg/mL and HC50 > 32 μg/mL performed against HEC239 and RBC cell lines. The anti-cancer potential was assessed against the MG-U87 cell line, using cisplatin as the standard (133 µM), indicates 2 displays the greatest activity (IC50: 5.521 µM) at a 5 µM dose. The greatest anti-leishmanial potential was observed for 2 (87.75 at 1000 μg/mL) in comparison to amphotericin B (90.67). The biological assay correlates with the observed maximum of 89% scavenging activity exhibited by 2. The Swiss-ADME data publicised the screened compounds generally follow the rule of 5 of drug-likeness and have good bioavailability potential.

Chemical Characterization, DNA-Damage Protection, Antiproliferative Activity and in Silico Studies of the Essential Oils from Perralderia coronopifolia Coss

In this study, for the first time, we analyzed the chemical composition of essential oils (EOs) steam-distilled from the flowers and leaves of Perralderia coronopifolia by GC-FID/MS. The objective was to explore new anticancer and antioxidant bioactive substances and understand their mechanisms of action through the use of plant-derived natural products. The major chemical components characterizing the EOs were cis-chrysanthenyl acetate 1, 6-oxocyclonerolidol 2, cis-8-acetoxychrysanthenyl acetate 3, and 6α-hydroxycyclonerolidol 4, respectively. Furthermore, the EOs inhibited cell proliferation in HeLa (human cervix carcinoma) and PC3 (human prostate cancer) cells and protected plasmid DNA from oxidative damage caused by UV-photolyzed H2 O2 . Employing a molecular docking study, we elucidated the main compounds' inhibition mechanisms. Consequently, the antitumor activity could be related to the inhibitory property of compound 3 against CDC25B phosphatase. The evaluation of ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties and the density functional theory (DFT) calculations of the major compounds, especially compound 3, offer potential insights for designing and developing new cancer drug candidates. In conclusion, our study provides a framework for future research and development in the field by establishing a scientific foundation for the use of Perralderia coronopifolia essential oils as a prospective source of antioxidant and anticancer agents.

Model-Informed Drug Development: In Silico Assessment of Drug Bioperformance following Oral and Percutaneous Administration

The pharmaceutical industry has faced significant changes in recent years, primarily influenced by regulatory standards, market competition, and the need to accelerate drug development. Model-informed drug development (MIDD) leverages quantitative computational models to facilitate decision-making processes. This approach sheds light on the complex interplay between the influence of a drug's performance and the resulting clinical outcomes. This comprehensive review aims to explain the mechanisms that control the dissolution and/or release of drugs and their subsequent permeation through biological membranes. Furthermore, the importance of simulating these processes through a variety of in silico models is emphasized. Advanced compartmental absorption models provide an analytical framework to understand the kinetics of transit, dissolution, and absorption associated with orally administered drugs. In contrast, for topical and transdermal drug delivery systems, the prediction of drug permeation is predominantly based on quantitative structure-permeation relationships and molecular dynamics simulations. This review describes a variety of modeling strategies, ranging from mechanistic to empirical equations, and highlights the growing importance of state-of-the-art tools such as artificial intelligence, as well as advanced imaging and spectroscopic techniques.

Induction of antimicrobial, antioxidant metabolites production by co-cultivation of two red-sea-sponge-associated Aspergillus sp. CO2 and Bacillus sp. COBZ21

The growing spread of infectious diseases has become a potential global health threat to human beings. According to WHO reports, in this study, we investigated the impact of co-cultivating the isolated endophytic fungus Aspergillus sp. CO2 and Bacillus sp. COBZ21 as a method to stimulate the production of natural bioactive substances. (GC/MS)-based metabolomics profiling of two sponge-associated microbes, Aspergillus sp. CO2 and Bacillus sp. COBZ21, revealed that the co-culture of these two isolates induced the accumulation of metabolites that were not traced in their axenic cultures. By detection of different activities of extracts of Bacillus sp. COBZ21 and Aspergillus sp. CO2 and coculture between Bacillus sp. COBZ21 and Aspergillus sp. CO2. It was noted that the coculture strategy was the reason for a notable increase in some different activities, such as the antimicrobial activity, which showed potent activity against Escherichia coli ATCC 25,922, Staphylococcus aureus NRRLB-767, and Candida albicans ATCC 10,231. The antibiofilm activity showed significant biofilm inhibitory activity toward Bacillus subtilis ATCC 6633, Pseudomonas aeruginosa ATCC 10,145, and Staph aureus NRRLB-767, with activity up to 53.66, 71.17, and 47.89%, while it showed low activity against E. coli ATCC 25,922, while the antioxidant activity based on the DPPH assay showed maximum activity (75.25%). GC-MS investigations revealed the presence of variable chemical constituents belonging to different chemical categories, which reflected their chemical diversity. The main components are (+-) cis-Deethylburnamine (2.66%), Bis(3,6,9,12-tetraoxapentaethylene) crowno-N,N,N',N'-tetra methylpphanediamine (2.48%), and 11-phenyl-2,4,6,8-tetra(2-thienyl)-11-aza-5,13-dithiaeteracyclo[7.3.0.1(2,8)0.0(3,7)] trideca-3,6-diene-10,12,13-trione (3.13%), respectively, for Bacillus sp. axenic culture, Aspergillus sp. CO2, Aspergillus sp. CO2, and Bacillus sp. COBZ21 coculture. By studying the ADME-related physicochemical properties of coculture extract, the compound showed log Po/w values above 5 (8.82). The solubility of the substance was moderate. In order to provide a comprehensive definition of medicinal chemistry and leadlikness, it is important to note that the latter did not meet the criteria outlined in the rule of three (RO3). The toxicity prediction of the coculture extract was performed using the ProTox II web server, which showed that the selected compound has no pronounced toxicity.

Dose-dependent effect on skin permeation of polar and non-polar compounds

The study of the relationship between the amount of drug applied to the skin and fraction of drug absorbed can improve our understanding of finite-dose percutaneous absorption in the development of topical products and risk assessment of hazardous chemical exposure. It has been previously shown that an increase in the dose applied to the skin leads to a decrease in the fraction of drug permeated the skin (dose-dependent effect). The objective of this research was to examine the dose-dependent effect using permeants of varying physiochemical properties. The dose-dependent effect was studied using human epidermal membrane under finite dose conditions in Franz diffusion cell with model permeants at doses ranging from 0.1 to 200 μg. The dose-dependent effect was evident with model permeants caffeine, corticosterone, dexamethasone, and estradiol, consistent with the relationship of decreasing fraction of dose permeated the skin at increasing the applied dose. However, no significant dose-dependent effect was observed for the polar model permeants urea, mannitol, tetraethyl ammonium, and ethylene glycol, suggesting different transport mechanisms for these permeants. It was also found that, at relatively high doses, estradiol, dexamethasone, and corticosterone could increase the permeation of polar and lipophilic permeants, which could counter the dose-dependent effect under the conditions studied.

Aquatic toxicity, ecological effects, human exposure pathways and health risk assessment of liquid crystal monomers

Liquid crystal monomers (LCMs), one of the key materials for liquid crystal displays, have been considered as emerging pollutants in recent years. However, the environmental behaviors of LCMs have not yet been well investigated. The toxicity data of 1173 LCMs were calculated by integrated computational simulation methods in this study. It showed that 64.6% LCMs exhibited PBT (persistent, bioaccumulative, and toxic) properties. Based on the results, 1173 LCMs were identified as molecules possessing the highest level of acute toxicity to aquatic organisms. Among which, and a human health risk priority control list about LCMs was generated in this study, among which 435 were classified as requiring priority control LCMs. It was confirmed that LCMs could eventually accumulate in the human body along the aquatic food chain or penetrate the bloodstream through the dermis, thereby causing harm to health by identifying the exposure pathways of LCMs in humans. Additionally, the electronegativity of the side chain group of LCMs is the main factor causing toxicity differences; therefore, the LCMs containing halogens presented significant acute and chronic toxic effects. This study provided a more comprehensive understanding of LCMs for the public and scientific strategies for controlling LCMs.

Repurposing immune boosting and anti-viral efficacy of Parkia bioactive entities as multi-target directed therapeutic approach for SARS-CoV-2: exploration of lead drugs by drug likeness, molecular docking and molecular dynamics simulation methods

The COVID-19 pandemic has caused adverse health (severe respiratory, enteric and systemic infections) and environmental impacts that have threatened public health and the economy worldwide. Drug repurposing and small molecule multi-target directed herbal medicine therapeutic approaches are the most appropriate exploration strategies for SARS-CoV-2 drug discovery. This study identified potential multi-target-directed Parkia bioactive entities against SARS-CoV-2 receptors (S-protein, ACE2, TMPRSS2, RBD/ACE2, RdRp, MPro, and PLPro) using ADMET, drug-likeness, molecular docking (AutoDock, FireDock and HDOCK), molecular dynamics simulation and MM-PBSA tools. One thousand Parkia bioactive entities were screened out by virtual screening and forty-five bioactive phytomolecules were selected based on favorable binding affinity and acceptable pharmacokinetic and pharmacodynamics properties. The binding affinity values of Parkia phyto-ligands (AutoDock: -6.00--10.40 kcal/mol; FireDock: -31.00--62.02 kcal/mol; and HDOCK: -150.0--294.93 kcal/mol) were observed to be higher than the reference antiviral drugs (AutoDock: -5.90--9.10 kcal/mol; FireDock: -35.64--59.35 kcal/mol; and HDOCK: -132.82--211.87 kcal/mol), suggesting a potent modulatory action of Parkia bioactive entities against the SARS-CoV-2. Didymin, rutin, epigallocatechin gallate, epicatechin-3-0-gallate, hyperin, ursolic acid, lupeol, stigmasta-5,24(28)-diene-3-ol, ellagic acid, apigenin, stigmasterol, and campesterol strongly bound with the multiple targets of the SARS-CoV-2 receptors, inhibiting viral entry, attachment, binding, replication, transcription, maturation, packaging and spread. Furthermore, ACE2, TMPRSS2, and MPro receptors possess significant molecular dynamic properties, including stability, compactness, flexibility and total binding energy. Residues GLU-589, and LEU-95 of ACE2, GLN-350, HIS-186, and ASP-257 of TMPRSS2, and GLU-14, MET-49, and GLN-189 of MPro receptors contributed to the formation of hydrogen bonds and binding interactions, playing vital roles in inhibiting the activity of the receptors. Promising results were achieved by developing multi-targeted antiviral Parkia bioactive entities as lead and prospective candidates under a small molecule strategy against SARS-CoV-2 pathogenesis. The antiviral activity of Parkia bioactive entities needs to be further validated by pre-clinical and clinical trials.

High-throughput virtual screening, pharmacophore modelling and antagonist effects of small molecule inhibitors against cytotoxin-induced cytotoxicity

Cobra venom cytotoxins (CTX) cause dermonecrosis in envenomed patients who suffered from limb amputations due to the limitation of serotherapy-based antivenoms. This study aimed to identify small molecule inhibitors against CTX. A structure-based high-throughput virtual screening (HTVS) was conducted based on a conserved CTX, using the Natural Product Activity and Species Source (NPASS) screening library. The hits were valerenic acid, 1-oxo-2H-isoquinoline-4-carboxylic acid, acenaphthene, and 5-bromopyrrole-2-carboxamide, which interacted with contemporary antivenom binding site A and functional loops I-III of CTX, respectively, in molecular docking studies. Furthermore, molecular dynamic simulations were performed along with analysis of ligand fitness through their pharmacophore and pharmacokinetics properties. The antagonist effects of these hits on CTX-induced cytotoxicity were examined in human keratinocytes (HaCaT). Despite having a low binding affinity (KD = 14.45 × 10-4 M), acenaphthene demonstrated a significant increase of cell viability at 6 h and 24 h in experimental envenomed HaCaT. It also demonstrated the highest neutralization potency against CTX with a median effective concentration (EC50) of 0.05 mL/mg. Acenaphthene interacted with the functional loop II, which is the crucial cytotoxic site of CTX. It has an aromatic ring as its primary pharmacophoric feature, commonly used for rational drug design. In conclusion, acenaphthene could be a promising lead compound as a small molecule inhibitor.Communicated by Ramaswamy H. Sarma.

Promising 8-Aminoquinoline-Based Metal Complexes in the Modulation of SIRT1/3-FOXO3a Axis against Oxidative Damage-Induced Preclinical Neurons

The discovery of novel bioactive molecules as potential multifunctional neuroprotective agents has clinically drawn continual interest due to devastating oxidative damage in the pathogenesis and progression of neurodegenerative diseases. Synthetic 8-aminoquinoline antimalarial drug is an attractive pharmacophore in drug development and chemical modification owing to its wide range of biological activities, yet the underlying molecular mechanisms are not fully elucidated in preclinical models for oxidative damage. Herein, the neuroprotective effects of two 8-aminoquinoline-uracil copper complexes were investigated on the hydrogen peroxide-induced human neuroblastoma SH-SY5Y cells. Both metal complexes markedly restored cell survival, alleviated apoptotic cascades, maintained antioxidant defense, and prevented mitochondrial function by upregulating the sirtuin 1 (SIRT1)/3-FOXO3a signaling pathway. Intriguingly, in silico molecular docking and pharmacokinetic prediction suggested that these synthetic compounds acted as SIRT1 activators with potential drug-like properties, wherein the uracil ligands (5-iodoracil and 5-nitrouracil) were essential for effective binding interactions with the target protein SIRT1. Taken together, the synthetic 8-aminoquinoline-based metal complexes are promising brain-targeting drugs for attenuating neurodegenerative diseases.

A Synthetic Model of the Mucosa for Oral Penetration Studies

The main objective of this study is the evaluation of the use of a synthetic membrane, Nuclepore, as a model for permeation studies through sublingual mucosa. The permeability of two types of membranes, porcine sublingual oral mucosa and a synthetic Nuclepore membrane, to water was compared. Moreover, the water permeability of membranes modified with waterproofing formulations was measured to study their ability to protect against the penetration of viruses, toxins, etc. A relatively high correlation (R2 0.88) was obtained between the transmucosal water loss (TMWL) values of the artificial membrane and the mucosa. These results support the possible use of this synthetic membrane in the screening of the water permeability of formulations. In addition, studies of the permeation of different actives, drugs, and biocides through the two membranes were carried out, and these results were compared with their skin permeation data. The synthetic membrane does not seem to discern between compounds in terms of permeability. However, the permeation of caffeine through intact or modified membranes incorporating waterproofing formulations presents similar permeation profiles through the synthetic membrane and mucosa. The results from these assays should lend support to the use of this synthetic membrane when screening formulations to be applied in oral penetration studies.

An examination of published datasets of skin permeability and partition coefficients

Permeability and partition coefficients of the skin barrier are important for assessing dermal absorption, bioavailability, and safety of cosmetics and medicine. We use the Potts and Guy equation to analyse the dependence of skin permeability on the hydrophobicity of permeants and highlight the significant differences in published datasets. Correlations of solute partition to skin are examined to understand the likely causes of the differences in the skin permeability datasets. Recently published permeability datasets show weak correlation and low dependence on hydrophobicity. As expected, early datasets show good correlation with hydrophobicity due to the related derivation. The weaker correlation of later datasets cannot be explained by the partition to skin lipids. All the datasets of solute partition to skin lipid showed a similar correlation to hydrophobicity where the log-linear correlation coefficient of partition is almost the same of the log-linear coefficient of Potts and Guy equation. Weak correlation and dependence of the late permeability datasets with SC lipid/water partition and that they are significantly under predicted by the Potts and Guy equation suggests either additional non-lipid pathway at play or a weaker skin barrier property.

New approaches build upon historical studies in dermal toxicology

These are my personal reflections on the history of approaches to understanding dermal toxicology brought together for the Paton Prize Award. This is not a comprehensive account of all publications from in vivo studies in humans to development of in vitro and in silico approaches but highlghts important progress. I will consider what is needed now to influence approaches to understanding dermal exposure with the current development and use of NAMs (new approach methodologies).

Visualisation of drug distribution in skin using correlative optical spectroscopy and mass spectrometry imaging

A correlative methodology for label-free chemical imaging of soft tissue has been developed, combining non-linear optical spectroscopies and mass spectrometry to achieve sub-micron spatial resolution and critically improved drug detection sensitivity. The approach was applied to visualise the kinetics of drug reservoir formation within human skin following in vitro topical treatment with a commercial diclofenac gel. Non-destructive optical spectroscopic techniques, namely stimulated Raman scattering, second harmonic generation and two photon fluorescence microscopies, were used to provide chemical and structural contrast. The same tissue sections were subsequently analysed by secondary ion mass spectrometry, which offered higher sensitivity for diclofenac detection throughout the epidermis and dermis. A method was developed to combine the optical and mass spectrometric datasets using image registration techniques. The label-free, high-resolution visualisation of tissue structure coupled with sensitive chemical detection offers a powerful method for drug biodistribution studies in the skin that impact directly on topical pharmaceutical product development.

Synthesis, Characterization, DFT, and In Silico Investigation of Two Newly Synthesized β-Diketone Derivatives as Potent COX-2 Inhibitors

Despite extensive genetic and biochemical characterization, the molecular genetic basis underlying the biosynthesis of β-diketones remains largely unexplored. β-Diketones and their complexes find broad applications as biologically active compounds. In this study, in silico molecular docking results revealed that two β-diketone derivatives, namely 2-(2-(4-fluorophenyl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione and 5,5-dimethyl-2-(2-(2-(trifluoromethyl)phenyl)hydrazono)cyclohexane-1,3-dione, exhibit anti-COX-2 activities. However, recent docking results indicated that the relative anti-COX-2 activity of these two studied β-diketones was influenced by the employed docking programs. For improved design of COX-2 inhibitors from β-diketones, we conducted molecular dynamics simulations, density functional theory (DFT) calculations, Hirshfeld surface analysis, energy framework, and ADMET studies. The goal was to understand the interaction mechanisms and evaluate the inhibitory characteristics. The results indicate that 5,5-dimethyl-2-(2-(2-(trifluoromethyl)phenyl)hydrazono)cyclohexane-1,3-dione shows greater anti-COX-2 activity compared to 2-(2-(4-fluorophenyl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione.

Enhancement of Skin Permeability Prediction through PBPK Modeling, Bayesian Inference, and Experiment Design

Physiologically based pharmacokinetic (PBPK) models of skin absorption are a powerful resource for estimating drug delivery and chemical risk of dermatological products. This paper presents a PBPK workflow for the quantification of the mechanistic determinants of skin permeability and the use of these quantities in the prediction of skin absorption in novel contexts. A state-of-the-art mechanistic model of dermal absorption was programmed into an open-source modeling framework. A sensitivity analysis was performed to identify the uncertain compound-specific, individual-specific, and site-specific model parameters that impact permeability. A Bayesian Markov Chain Monte Carlo algorithm was employed to derive distributions of these parameters given in vitro experimental permeability measurements. Extrapolations to novel contexts were generated by simulating the model following its update with samples drawn from the learned distributions as well as parameters that represent the intended scenario. This algorithm was applied multiple times, each using a unique set of permeability measurements sourced under experimental contexts that differ in terms of the compound, vehicle pH, skin sample anatomical site, and the number of compounds under which each subject's skin samples were tested. Among the data sets used in this study, the highest accuracy and precision in the extrapolated permeability was achieved in those that include measurements conducted under multiple vehicle pH levels and in which individual subjects' skin samples are tested under multiple compounds. This work thus identifies factors for consideration in the design of experiments for the purpose of training dermal models to robustly estimate drug delivery and chemical risk.

Fragment contribution models for predicting skin permeability using HuskinDB

Mathematical models to predict skin permeation tend to be based on animal derived experimental data as well as knowing physicochemical properties of the compound under investigation, such as molecular volume, polarity and lipophilicity. This paper presents a strikingly contrasting model to predict permeability, formed entirely from simple chemical fragment (functional group) data and a recently released, freely accessible human (i.e. non-animal) skin permeation database, known as the 'Human Skin Database - HuskinDB'. Data from within the database allowed development of several fragment-based models, each including a calculable effect for all of the most commonly encountered functional groups present in compounds within the database. The developed models can be applied to predict human skin permeability (logKp) for any compound containing one or more of the functional groups analysed from the dataset with no need to know any other physicochemical properties, solely the type and number of each functional group within the chemical structure itself. This approach simplifies mathematical prediction of permeability for compounds with similar properties to those used in this study.

Molecular Organization of the Skin Barrier

Cryo-electron microscopy of vitreous sections allows for investigation directly in situ of the molecular architecture of skin. Recently, this technique has contributed to the elucidation of the molecular organization of the skin's permeability barrier and its stepwise formation process. The aim of this review is to provide an overview of the procedure for cryo-electron microscopy of vitreous sections, its analysis using atomic detail molecular dynamics modelling and electron microscopy simulation, and its application in the investigation of the barrier structure and formation process of the skin.

Designing and Exploration of the Biological Potentials of Novel Centrosymmetric Heteroleptic Copper(II) Carboxylates

Copper(II) complexes with a general formula [Cu2(3,4-F2C6H3CH2COO)4(L)2], where L = 2-methylpyridine (1) and 3-methylpyridine (2), are reported here. The FTIR spectra of the complexes confirmed the bridging bidentate coordination mode of the carboxylate ligand. The low (475 and 449 cm-1) and strong (727 & 725 cm-1) intensity bands in the FTIR spectra, due to Cu-N stretches and pyridyl ring vibrations, confirmed coordination of the 2-/3-methyl pyridine co-ligands in complexes 1 and 2, respectively. A binuclear paddlewheel structural arrangement with a square pyramidal geometry was confirmed for copper atoms in the complexes via single-crystal X-ray analysis. The DPPH, •OH radical, and α-amylase enzyme inhibition assays showed higher activities for the complexes than for the free ligand acid. The binding constant (Kb = 1.32 × 105 for 1 and 5.33 × 105 for 2) calculated via UV-VIS absorption measurements and docking scores (-6.59 for 1 and -7.43 for 2) calculated via molecular docking showed higher SS-DNA binding potential for 2 compared to 1. Viscosity measurement also reflected higher DNA binding ability for 2 than 1. Both complexes 1 and 2 (docking scores of -7.43 and -6.95, respectively) were found to be more active inhibitors than the free ligand acid (docking score of -5.5159) against the target α-amylase protein. This in silico study has shown that the herein reported compounds follow the rules of drug-likeness and exhibit good potential for bioavailability.

Design of β-Keto Esters with Antibacterial Activity: Synthesis, In Vitro Evaluation, and Theoretical Assessment of Their Reactivity and Quorum-Sensing Inhibition Capacity

This work proposes the design of β-keto esters as antibacterial compounds. The design was based on the structure of the autoinducer of bacterial quorum sensing, N-(3-oxo-hexanoyl)-l-homoserine lactone (3-oxo-C6-HSL). Eight β-keto ester analogues were synthesised with good yields and were spectroscopically characterised, showing that the compounds were only present in their β-keto ester tautomer form. We carried out a computational analysis of the reactivity and ADME (absorption, distribution, metabolism, and excretion) properties of the compounds as well as molecular docking and molecular dynamics calculations with the LasR and LuxS quorum-sensing (QS) proteins, which are involved in bacterial resistance to antibiotics. The results show that all the compounds exhibit reliable ADME properties and that only compound 7 can present electrophile toxicity. The theoretical reactivity study shows that compounds 6 and 8 present a differential local reactivity regarding the rest of the series. Compound 8 presents the most promising potential in terms of its ability to interact with the LasR and LuxS QS proteins efficiently according to its molecular docking and molecular dynamics calculations. An initial in vitro antimicrobial screening was performed against the human pathogenic bacteria Pseudomonas aeruginosa and Staphylococcus aureus as well as the phytopathogenic bacteria Pseudomonas syringae and Agrobacterium tumefaciens. Compounds 6 and 8 exhibit the most promising results in the in vitro antimicrobial screening against the panel of bacteria studied.

Making the Case for Quantum Mechanics in Predictive Toxicology─Nearly 100 Years Too Late?

The use of quantum mechanics (QM) has long been the norm to study covalent-binding phenomena in chemistry and biochemistry. The pharmaceutical industry leverages QM models explicitly in covalent drug discovery and implicitly to characterize short-range interactions in noncovalent binding. Predictive toxicology has resisted widespread adoption of QM, including in the pharmaceutical industry, despite its obvious relevance to the metabolic processes in the upstream of adverse outcome pathways and advances in both QM methods and computational resources, which support fit-for-purpose applications in reasonable timeframes. Here, we make the case for embracing QM as an indispensable part of a toxicologist's toolkit. We argue that QM provides the necessary orthogonality to alert-based expert systems and traditional QSARs, consistent with calls for animal-free integrated testing strategies for safety assessments of commercial chemicals. We outline existing roadblocks to this transition, including the need to train model developers in QM and the shift toward service-based toxicity models that utilize high-performance computing clusters. Lastly, we describe recent examples of successful implementations of QM in hazard assessments and propose how in silico toxicology can be further advanced by integrating QM with artificial intelligence.

The depsidones from marine sponge-derived fungus Aspergillus unguis IB151 as an anti-MRSA agent: Molecular docking, pharmacokinetics analysis, and molecular dynamic simulation studies

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging nosocomial pathogen among hospitalized patients, with high morbidity and mortality rates. The discovery of a novel antibacterial is urgently needed to address this resistance problem. The present study aims to explore the antibacterial potential of three depsidone compounds: 2-clorounguinol (1), unguinol (2), and nidulin (3), isolated from the marine sponge-derived fungus Aspergillus unguis IB1, both in vitro and in silico. The antibacterial activity of all compounds was evaluated by calculating the Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) against MRSA using agar diffusion and total plate count methods, respectively. Bacterial cell morphology changes were  studied for the first time using scanning electron microscopy (SEM). Molecular docking, pharmacokinetics analysis, and molecular dynamics simulation were performed to determine possible protein-ligand interactions and the stability of the targeting penicillin-binding protein 2a (PBP2a) against 2-clorounguinol (1). The research findings indicated that compounds 1 to 3 exhibited MIC and MBC values of 2 µg/mL and 16 µg/mL against MRSA, respectively. MRSA cells displayed a distinct shape after the addition of the depsidone compound, as observed in SEM. According to the in silico study, 2-chlorounguinol exhibited the highest binding-free energy (BFE) with PBP2a (-6.7 kcal/mol). For comparison, (E)-3-(2-(4-cyanostyryl)-4-oxoquinazolin-3(4H)-yl) benzoic acid inhibits PBP2a with a BFE less than -6.6 kcal/mol. Based on the Lipinski's rule of 5, depsidone compounds constitute a class of compounds with good pharmacokinetic properties, being easily absorbed and permeable. These findings suggest that 2-chlorounguinol possesses potential antibacterial activity and could be developed as an antibiotic adjuvant to reduce antimicrobial resistance.

Flux-Type versus Concentration-Type Sensors in Transdermal Measurements

New transdermal biosensors measure analytes that diffuse from the bloodstream through the skin, making it important to reduce the system response time and understand measurement output. While highly customized models have been created for specific sensors, a generalized model for transdermal sensor systems is lacking. Here, a simple one-dimensional diffusion model was used to characterize the measurement system and classify biosensors as either flux types or concentration types. Results showed that flux-type sensors have significantly faster response times than concentration sensors. Furthermore, flux sensors do not measure concentration, but rather have an output measurement that is proportional to skin permeability. These findings should lead to an improved understanding of transdermal measurements and their relation to blood analyte concentration. In the realm of alcohol research, where the majority of commercially available sensors are flux types, our work advocates toward moving away from transdermal alcohol concentration as a metric, and instead suggests embracing transdermal alcohol flux as a more suitable alternative.

Understanding Drug Skin Permeation Enhancers Using Molecular Dynamics Simulations

Our skin constitutes an effective permeability barrier that protects the body from exogenous substances but concomitantly severely limits the number of pharmaceutical drugs that can be delivered transdermally. In topical formulation design, chemical permeation enhancers (PEs) are used to increase drug skin permeability. In vitro skin permeability experiments can measure net effects of PEs on transdermal drug transport, but they cannot explain the molecular mechanisms of interactions between drugs, permeation enhancers, and skin structure, which limits the possibility to rationally design better new drug formulations. Here we investigate the effect of the PEs water, lauric acid, geraniol, stearic acid, thymol, ethanol, oleic acid, and eucalyptol on the transdermal transport of metronidazole, caffeine, and naproxen. We use atomistic molecular dynamics (MD) simulations in combination with developed molecular models to calculate the free energy difference between 11 PE-containing formulations and the skin's barrier structure. We then utilize the results to calculate the final concentration of PEs in skin. We obtain an RMSE of 0.58 log units for calculated partition coefficients from water into the barrier structure. We then use the modified PE-containing barrier structure to calculate the PEs' permeability enhancement ratios (ERs) on transdermal metronidazole, caffeine, and naproxen transport and compare with the results obtained from in vitro experiments. We show that MD simulations are able to reproduce rankings based on ERs. However, strict quantitative correlation with experimental data needs further refinement, which is complicated by significant deviations between different measurements. Finally, we propose a model for how to use calculations of the potential of mean force of drugs across the skin's barrier structure in a topical formulation design.

Designing a Novel Coamorphous Salt Formulation of Telmisartan with Amlodipine to Enhance Permeability and Oral Absorption

Coamorphous formulation is a useful approach for enhancing the solubility of poorly water-soluble drugs via intermolecular interactions. In this study, a hydrogen-bonding-based coamorphous system was developed to improve drug solubility, but it barely changed the apparent permeability (Papp) of the drug. This study aimed to design a novel coamorphous salt using ionic interactions to improve drug permeability and absorption. Telmisartan (TMS), with an acidic group, was used to form a coamorphous salt with basic amlodipine (AML). Evaluation of the physicochemical properties confirmed the formation of a coamorphous salt via ionic interactions between the amine group of AML and the carboxyl group of TMS at a molar ratio of 1:1. The coamorphous salt of TMS/AML enhanced the partitioning of both drugs into octanol, indicating increased lipophilicity owing to the interaction between TMS and AML. The coamorphous salt dramatically enhanced TMS solubility (99.8 times that of untreated TMS) and decreased AML solubility owing to the interaction between TMS and AML. Although the coamorphous salt showed a decreased Papp in the permeation study in the presence of a thicker unstirred water layer (UWL) without stirring, Papp increased in the presence of a thinner UWL with stirring. The oral absorption of TMS from the coamorphous salt increased by up to 4.1 times compared to that of untreated TMS, whereas that of AML remained unchanged. Although the coamorphous salt with increased lipophilicity has a disadvantage in terms of diffusion through the UWL, the UWL is thin in human/animal bodies owing to the peristaltic action of the digestive tract. Dissociation of the coamorphous salt on the membrane surface could contribute to the partitioning of the neutral form of drugs to the membrane cells compared with untreated drugs. As a result, coamorphous salt formation has the advantage of improving the membrane permeation and oral absorption of TMS, owing to the enhanced solubility and supply of membrane-permeable free TMS on the surface of the membrane.

Nanostructured Lipid Carriers Enriched Hydrogels for Skin Topical Administration of Quercetin and Omega-3 Fatty Acid

Chronic skin exposure to external hostile agents (e.g., UV radiation, microorganisms, and oxidizing chemicals) may increase oxidative stress, causing skin damage and aging. Because of their well-known skincare and protective benefits, quercetin (Q) and omega-3 fatty acids (ω3) have attracted the attention of the dermocosmetic and pharmaceutical sectors. However, both bioactives have inherent properties that limit their efficient skin delivery. Therefore, nanostructured lipid carriers (NLCs) and enriched PFC® hydrogels (HGs) have been developed as a dual-approach vehicle for Q and/or ω3 skin topical administration to improve bioactives' stability and skin permeation. Two NLC formulations were prepared with the same lipid composition but differing in surfactant composition (NLC1-soy lecithin and poloxamer 407; NLC2-Tween® 80 and dioctyl sodium sulfosuccinate (DOSS)), which have an impact on physicochemical properties and pharmaceutical and therapeutic performance. Despite both NLCs presenting high Q loading capacity, NLC2's physicochemical properties make them more suitable for topical skin administration and ensure longer colloidal stability. Additionally, NLC2 demonstrated a more sustained Q release, indicating higher bioactive storage while improving permeability. The occlusive effect of NLCs-enriched HGs also has a positive impact on skin permeability. Q-loaded NLC2, with or without ω3, -enriched HGs demonstrated efficacy as antioxidant and photoprotective formulations as well as effective reduction in S. aureus growth, indicating that they constitute a promising approach for topical skin administration to prevent skin aging and other damaging cutaneous processes.

Rational Design of Topical Semi-Solid Dosage Forms-How Far Are We?

Specific aspects of semi-solid dosage forms for topical application include the nature of the barrier to be overcome, aspects of susceptibility to physical and chemical instability, and a greater influence of sensory perception. Advances in understanding the driving forces of skin penetration as well as the design principles and inner structure of formulations, provide a good basis for the more rational design of such dosage forms, which still often follow more traditional design approaches. This review analyses the opportunities and constraints of rational formulation design approaches in the industrial development of new topical drugs. As the selection of drug candidates with favorable physicochemical properties increases the speed and probability of success, models for drug selection based on theoretical and experimental approaches are discussed. This paper reviews how progress in the scientific understanding of mechanisms and vehicle-influence of skin penetration can be used for rational formulation design. The characterization of semi-solid formulations is discussed with a special focus on modern rheological approaches and analytical methods for investigating and optimizing the chemical stability of active ingredients in consideration of applicable guidelines. In conclusion, the combination of a good understanding of scientific principles combined with early consideration of regulatory requirements for product quality are enablers for the successful development of innovative and robust semi-solid formulations for topical application.

Thymus satureioides Coss.: Mineral Composition, Nutritional Value, Phytochemical Profiling, and Dermatological Properties

Zaitra, Thymus satureioides, is an aromatic plant with a long history of use in traditional medicine. In this study, we assessed the mineral composition, nutritional value, phytocontents, and dermatological properties of the aerial parts of T. satureioides. The plant contained high contents of calcium and iron, moderate levels of magnesium, manganese, and zinc, and low contents of total nitrogen, total phosphorus, total potassium, and copper. It is rich in several amino acids, including asparagine, 4-hydroxyproline, isoleucine, and leucine, and the essential amino acids account for 60.8%. The extract contains considerable amounts of polyphenols and flavonoids (TPC = 118.17 mg GAE/g extract and TFC = 32.32 mg quercetin/g extract). It also comprises 46 secondary metabolites, identified through LC-MS/MS analysis, belonging to phenolic acids, chalcones, and flavonoids. The extract elicited pronounced antioxidant activities, inhibited the growth of P. aeruginosa (MIC = 50 mg/mL), and reduced biofilm formation by up to 35.13% using the ¼ sub-MIC of 12.5 mg/mL. Moreover, bacterial extracellular proteins and exopolysaccharides were diminished by 46.15% and 69.04%, respectively. Likewise, the swimming of the bacterium was impaired (56.94% decrease) in the presence of the extract. In silico, skin permeability and sensitization effects revealed that out of the 46 identified compounds, 33 were predicted to be exempt from any skin sensitivity risk (Human Sensitizer Score ≤ 0.5), while extensive skin permeabilities were observed (Log K_p = -3.35--11.98 cm/s). This study provides scientific evidence about the pronounced activities of T. satureioides, supports its traditional uses, and promotes its utilization in the development of new drugs, food supplements, and dermatological agents.