An investigation on percutaneous permeation of flurbiprofen enantiomers: The role of molecular interaction between drug and skin components

The molecular mechanisms underlying optical isomer arbutin permeating the skin: The molecular interaction between arbutin and skin components

Arbutin, a typical optical isomer, has garnered widespread acclaim in the whitening cosmetics for its favorable efficacy and safety. However, the molecular mechanisms underlying α-arbutin and β-arbutin permeating across the skin have not elucidated clearly yet. Herein we aimed to unveil how α-arbutin and β-arbutin interacted with keratin or SC lipids, further demonstrating the relationship with their drug permeability. We found that α-arbutin displayed significantly higher drug accumulation into the porcine skin than β-arbutin within 24 h through in vitro permeation test. Moreover, α-arbutin predominantly induced the alternations of secondary structure of amide II during the drug permeation, which was favorable for α-arbutin permeation. On the contrary, β-arbutin exhibited an observable effect on the stretching vibration of SC lipids, possessing a significantly stronger mixing energy, binding energy and compatibility with ceramide (Cer) than that of α-arbutin, which ultimately restricted its permeation. Interestingly, free fatty acids and ceramides of the SC lipids specifically utilized its oxygen atom of carboxyl group to dock the arbutin molecules, enhancing their affinity with β-arbutin, as confirmed by molecular simulation and 13Carbon Nuclear Magnetic Resonance. Nevertheless, a favorable compatibility between α-arbutin and keratin was observed. It was emphasized that the distinct spatial configuration and opposite optical rotation of arbutin was the leading factor affecting the intermolecular force between arbutin and the SC, thereby resulting in a diverse drug permeation. In cellular and in vivo skin pharmacokinetic studies, α-arbutin also possessed a higher cellular uptake and topical bioavailability than β-arbutin. This study revealed the transdermal permeation mechanisms of optical isomer arbutin at the molecular levels, providing methodological reference for the investigations of permeation behaviors of other isomers with similar spatial configuration.

Microemulsions strongly promoted the activity of α-bisabolol against different Leishmania species and its skin permeation

This study aimed to develop microemulsions (MEs) containing α-bisabolol for the topical treatment of cutaneous leishmaniasis (CL). Initially, pseudoternary phase diagrams were developed using α-bisabolol as the oil phase, Eumulgin® CO 40 as the surfactant, Polymol® HE as the co-surfactant, and distilled water as the aqueous phase. Two transparent liquid systems (TLS) containing 5% of α-bisabolol were selected and characterized (F5E25 and F5EP25). Next, skin permeation and retention assays were performed using Franz cells. The interaction of the formulation with the stratum corneum (SC) was evaluated using the FTIR technique. The cytotoxicity was evaluated in murine peritoneal macrophages. Finally, the antileishmanial activity of microemulsions was determined in promastigotes and amastigotes of L. amazonensis (strain MHOM/BR/77/LTB 0016). As a result, the selected formulations showed isotropy, nanometric size (below 25 nm), Newtonian behavior and pH ranging from 6.5 to 6.9. The MEs achieved a 2.5-fold increase in the flux and skin-permeated amount of α-bisabolol. ATR-FTIR results showed that microemulsions promoted fluidization and extraction of lipids and proteins of the stratum corneum, increasing the diffusion coefficient and partition coefficient of the drug in the skin. Additionally, F5E25 and F5EP25 showed higher activity against promastigotes (IC50 13.27 and 18.29, respectively) compared to unencapsulated α-bisabolol (IC50 53.8). Furthermore, F5E25 and F5EP25 also showed antileishmanial activity against intracellular amastigotes of L. amazonensis, with IC50 50 times lower than free α-bisabolol and high selectivity index (up to 15). Therefore, the systems obtained are favorable to topical administration, with significant antileishmanial activity against L. amazonensis promastigotes and amastigotes, being a promising system for future in vivo trials.

Design, optimization, and evaluation for a long-time-released transdermal microneedle delivery system containing estradiol

Transdermal drug delivery systems (TDDS) have drawbacks such as poor absorption, low blood concentration, and delayed effects. Dissolving microneedle has sharp tips and short length, which overcome patients' pain and improve transdermal efficiency but has low mechanical strength and drug loading capacity. This study thereby proposes a microemulsion-encapsulated and long-time-released transdermal microneedle (MN) delivery system with estradiol (Es) as the model drug. The microemulsion (ME) was optimized by utilizing the pseudo-ternary phase diagram and D-optimal mixture design. The estradiol microemulsion-encapsulated microneedle (Es-ME-MN) was optimized by Box-Behnken design and prepared by freeze-thaw method. The Es-ME-MN obtained was characterized and evaluated through a large variety of studies. Es-ME-MN had sufficient mechanical strength to pierce skin and was safe enough, the length of which was 600 μm, and the Es content was 177.12 ± 0.72 μg/patch without drug-excipient chemical interaction. In vitro permeation study showed that Es-ME-MN has a higher transdermal efficiency and lower retention capacity than commercial estradiol patch and conventional MN. Es plasma concentration began to increase at 3 h and remained at 12.98-23.52 ng/mL until 72 h by pharmacokinetic experiments in the Es-ME-MN group. Es-ME-MN rapidly achieves effective blood concentrations through needle puncture and microemulsion delivery and maintains blood concentrations through the baseplate long-time release. Microemulsion-encapsulated, organic solvent-free, and long-time-released transdermal microneedle will make progress and provide a new idea for transdermal delivery of lipophilic drugs.

Chiral Supramolecular Hydrogel Enhanced Transdermal Delivery of Sodium Aescinate to Modulate M1 Macrophage Polarization Against Lymphedema

Sodium aescinate (SA) shows great potential for treating lymphedema since it can regulate the expression of cytokines in M1 macrophages, however, it is commonly administered intravenously in clinical practice and often accompanied by severe toxic side effects and short metabolic cycles. Herein, SA-loaded chiral supramolecular hydrogels are prepared to prove the curative effects of SA on lymphedema and enhance its safety and transdermal transmission efficiency. In vitro studies demonstrate that SA- loaded chiral supramolecular hydrogels can modulate local immune responses by inhibiting M1 macrophage polarization. Typically, these chiral hydrogels can significantly increase the permeability of SA with good biocompatibility due to the high enantioselectivity between chiral gelators and stratum corneum and L-type hydrogels are found to have preferable drug penetration over D-type hydrogels. In vivo studies show that topical delivery of SA via chiral hydrogels results in dramatic therapeutic effects on lymphedema. Specifically, it can downregulate the level of inflammatory cytokines, reduce the development of fibrosis, and promote the regeneration of lymphatic vessels. This study initiates the use of SA for lymphedema treatment and for the creation of an effective chiral biological platform for improved topical administration.

Ternary Deep Eutectic Solvents System of Colchicine, 4-Hydroxyacetophenone, and Protocatechuic Acid and Characterization of Transdermal Enhancement Mechanism

This study aimed to prepare colchicine (CO), 4-hydroxyacetophenone (HA), and protocatechuic acid (CA) contained in transdermal rubber plasters into a more releasable and acrylate pressure-sensitive adhesive (PSA) to optimize traditional Touguling rubber plasters (TOU) with enhanced transdermal permeability by using deep eutectic solvents (DES) technology. We compared the difference in the release behavior of CO between rubber plaster and PSA, determined the composition of the patch through pharmacodynamic experiments, explored the transdermal behavior of the three components, optimized the patch formula factors, and improved the penetration of CO through the skin. We also focused on elucidating the interactions among the three components of DES and the intricate relationship between DES and the skin. The melting point of DES was determined using DSC, while FTIR, 13C NMR, and ATR-FTIR were used to explore the intricate molecular mechanisms underlying the formation of DES, as well as its enhancement of skin permeability. The results of this investigation confirmed the successful formation of DES, marked by a discernible melting point at 27.33°C. The optimized patch, formulated with a molar ratio of 1:1:1 for CO, HA, and CA, significantly enhanced skin permeability, with the measured skin permeation quantities being 32.26 ± 2.98 µg/cm2, 117.67 ± 7.73 µg/cm2, and 56.79 ± 1.30 µg/cm2 respectively. Remarkably, the optimized patch also demonstrated similar analgesic and anti-inflammatory effects compared to commercial diclofenac diethylamide patches in different pharmacodynamics studies. The formation of DES altered drug compatibility with skin lipids and increased retention, driven by the interaction among the three component molecules through hydrogen bonding, effectively shielding the skin-binding sites and enhancing component permeation. In summary, the study demonstrated that optimized DES patches can concurrently enhance the penetration of CO, HA, and CA, thereby providing a promising approach for the development of DES in transdermal drug delivery systems. The findings also shed light on the molecular mechanisms underlying the transdermal behavior of DES and offer insights for developing more effective traditional Chinese medicine transdermal drug delivery systems.

Development and Assessment of Acyclovir Gel Plaster Containing Sponge Spicules

Acyclovir is an acyclic purine nucleoside analog that is highly effective in inhibiting the herpes simplex virus. However, topical acyclovir has poor efficacy because of its low skin permeability. This study aimed to develop an acyclovir gel plaster containing sponge spicules (AGP-SS) to achieve synergistic improvements in skin absorption and deposition of acyclovir. The process of preparing the gel plaster was optimized by orthogonal experiments, while the composition of the formulation was optimized using the Plackett-Burman and Box-Behnken experimental designs. The selected formula was tested for physical properties, in vitro release, stability, ex vivo permeation, skin irritation, and pharmacokinetics. The optimized formulation exhibited good physical characteristics. In vitro release and ex vivo permeation studies showed that acyclovir release from AGP-SS was dominated by diffusion with significantly higher skin permeation (20.00 ± 1.07 μg/cm2) than that of the controls (p < 0.05). Dermatopharmacokinetic analyses revealed that the maximum concentration (78.74 ± 11.12 μg/g), area under the curve (1091.81 ± 29.05 μg/g/h) and relative bioavailability (197.12) of AGP-SS were higher than those of the controls. Therefore, gel plaster containing sponge spicules show potential for development as transdermal delivery systems to achieve higher skin absorption and deposition of acyclovir, especially in deep skin layers.

D, Jia W, Sun P, Li H, Yu G, Quan P, Liu M, Fang L. The enantioselective enhancing effect and mechanistic insights of chiral enhancers in transdermal drug delivery

Overlook of chiral consideration in transdermal drug delivery increases administrated dose and risk of side effects, decreasing therapeutical effects. To improve the transdermal delivery efficiency of eutomer, this work focused on investigating the law and mechanism of enantioselective enhancing effects of chiral permeation enhancers on drug enantiomers. Chiral nonsteroidal anti-inflammatory drugs and terpene permeation enhancers were selected as model drug and enhancers. The results indicated that the L-isomer of permeation enhancers increased the skin absorption of S-enantiomer of drug and D-isomer improve the permeation of R-enantiomer, in which the enhancement effect (ER) of L-menthol on S-enantiomer (ER = 3.23) was higher than that on R-enantiomer (ER = 1.49). According to the pharmacokinetics results, L-menthol tended to enhance the permeation of S-enantiomer better than R-enantiomer (2.56 fold), and showed excellent in vitro/in vivo correlations. The mechanism study showed that L-isomer of permeation enhancers improved the permeation of S-enantiomer by increasing the retention, but the D-isomer by improving partition for better permeation. Enantioselective mechanism indicated that the weaker chiral H-bond interaction between drug-chiral enhancers was caused by the enantiomeric conformation. Additionally, stronger chiral enhancers-skin interaction between L-isomer and S-conformation of ceramide produced better enhancing effects. In conclusion, enantioselective interaction of chiral drug-chiral enhancers and chiral enhancers-chiral skin played a critical role in transdermal drug delivery, rational utilization of which contributed to improving the uptake of eutomer and inhibiting distomers to decrease a half of dose and side effects, increasing transdermal therapeutical efficiency.

Formulation Development and Molecular Mechanism Characterization of Long-Acting Patches of Asenapine for Efficient Delivery by Combining API-ILs Strategy and Controlled-Release Polymers

The objective of our study, which combined API-ILs strategy and controlled-release polymers, was to prepare a 72 h long-acting drug-in-adhesive patch for optimum delivery of asenapine (ASE). Special attention was paid to the permeation promotion mechanism and the controlled release behavior of ASE-ILs in pressure sensitive adhesives (PSA). Formulation factors were investigated by ex vivo transdermal experiments. The optimized patch was evaluated by pharmacokinetics study and skin irritation test. The obtained formulation was as follows, 15% w/w ASE-MA (about 1136 μg/cm2 ASE, 413 μg/cm2 MA), AACONH2 (Amide adhesive) as the matrix, 80 μm thickness, backing film of CoTran™ 9733. The optimized patch displayed satisfactory ex vivo and in vivo performance with Q 72 h of 620 ± 44 µg/cm2 and Fabs of 62.4%, which utilization rate (54.6%) was significantly higher than the control group (38.3%). By using the classical shake flask method, 13C NMR, DSC, and FTIR, the physicochemical properties and structure of ILs were characterized. log Do/w, ATR-FTIR, Raman, and molecular dynamics simulation results confirmed that ASE-MA (MA: 3-Methoxypropionic acid) had appropriate lipophilicity, and affected lipid fluidity as well as the conformation of keratin to improve the skin permeation. The FTIR, MDSC, rheology, and molecular docking results revealed that hydrogen bond (H-bond), were formed between ASE-MA and PSA, and the drug increased the molecular mobility of polymer chains. In summary, the 72 h long-acting patch of ASE was successfully prepared and it supplied a reference for the design of long-acting patches with ASE.

Rapidly separable microneedle patch for the controlled and sustained release of 5-fluorouracil

5-Fluorouracil (5-FU) is frequently used in the treatment of tumors and swollen tissues. However, traditional administration methods can result in poor patient compliance and require to administrate frequently due to the short T_1/2 of 5-FU. Herein, the 5-FU@ZIF-8 loaded nanocapsules were prepared using multiple emulsion solvent evaporation methods to enable the controlled and sustained release of 5-FU. To decrease the drug release rate and enhance patient compliance, the obtained pure nanocapsules were added to the matrix to fabricate rapidly separable microneedles (SMNs). The entrapment efficiency (EE%) of 5-FU@ZIF-8 loaded nanocapsules was in the range of 41.55-46.29 %, and the particle size of ZIF-8, 5-FU@ZIF-8, and 5-FU@ZIF-8 loaded nanocapsules were 60 nm, 110 nm, and 250 nm respectively. According to the release study in vivo and in vitro, we concluded that 5-FU@ZIF-8 nanocapsules could achieve the sustained release of 5-FU and that the burst release of nanocapsules could be elegantly handled by incorporating nanocapsules into the SMNs. What's more, the use of SMNs could improve patient compliance due to the rapid separation of needles and backing of SMNs. The pharmacodynamics study also revealed that the formulation would be a better choice for the treatment of scars due to the advantages of painlessness, separation ability, and high delivery efficiency. In conclusion, the SMNs containing 5-FU@ZIF-8 loaded nanocapsules could serve as a potential strategy for some skin diseases therapy with controlled and sustained drug release behavior.

4'-OH as the Action Site of Lipids and MRP1 for Enhanced Transdermal Delivery of Flavonoids

To date, the transdermal delivery study mainly focused on the drug delivery systems' design and efficacy evaluation. Few studies reported the structure-affinity relationship of the drug with the skin, further revealing the action sites of the drugs for enhanced permeation. Flavonoids attained a considerable interest in transdermal administration. The aim is to develop a systematic approach to evaluate the substructures that were favorable for flavonoid delivery into the skin and understand how these action sites interacted with lipids and bound to multidrug resistance protein 1 (MRP1) for enhanced transdermal delivery. First, we investigated the permeation properties of various flavonoids on the porcine skin or rat skin. We found that 4'-OH (hydroxyl group on the carbon 4' position) rather than 7-OH on the flavonoids was the key group for flavonoid permeation and retention, while 4'-OCH₃ and -CH₂═CH₂-CH-(CH₃)₂ were unfavorable for drug delivery. 4'-OH could decrease flavonoids' lipophilicity to an appropriate log P and polarizability for better transdermal drug delivery. In the stratum corneum, flavonoids used 4'-OH as a hand to specifically grab the C═O group of the ceramide NS (Cer), which increased the miscibility of flavonoids and Cer and then disturbed the lipid arrangement of Cer, thereby facilitating their penetration. Subsequently, we constructed overexpressed MRP1 HaCaT/MRP1 cells by permanent transfection of human MRP1 cDNA in wild HaCaT cells. In the dermis, we observed that 4'-OH, 7-OH, and 6-OCH₃ substructures were involved in H-bond formation within MRP1, which increased the flavonoid affinity with MRP1 and flavonoid efflux transport. Moreover, the expression of MRP1 was significantly enhanced after the treatment of flavonoids on the rat skin. Collectively, 4'-OH served as the action site for increased lipid disruption and enhanced affinity for MRP1, which facilitate the transdermal delivery of flavonoids, providing valuable guidelines for molecular modification and drug design of flavonoids.

Science of, and insights into, thermodynamic principles for dermal formulations

Studies have demonstrated the significant role of the thermodynamic activity of drugs in skin drug delivery. This thermodynamic activity works as a driving force for increasing/improving the absorption of drugs by the skin. It can be changed according to the physicochemical parameters (e.g., solubility, partition coefficient, and water activity) of the drug in the vehicle. Thermodynamic principles have been used for the development of novel topical and transdermal delivery systems, demonstrating the importance of thermodynamic activity in enhancing drug permeation through the skin. In this review, we provide insights into thermodynamic principles and their roles in optimizing topical and transdermal drug delivery systems.

Hyaluronidase-powered microneedles for significantly enhanced transdermal delivery efficiency

Microneedles (MNs) with enhanced delivery efficiency have revolutionized the transdermal drug delivery system for treating systemic illness. However, the bioavailability of MNs was still far from the clinical requirements by only overcoming the stratum corneum barrier. Herein, hyaluronidase (HAase)-powered MNs were developed as a top-down permeation-enhancement strategy to hijack the sequential transdermal barriers for improved bioavailability. HAase MNs with robust mechanical strength showed excellent skin penetration ability and significantly enhanced the transdermal delivery efficacy of macromolecular drugs as compared to that of HAase-absent MNs, resulting in considerable effect to subcutaneous injection in terms of biodistribution, bioavailability, and therapeutical efficacy. As evidenced from the distribution of trypan blue and fluorescence underlying skin, the positive effects exerted by HAase MNs could be ascribed to the depolymerization of HA that would loosen the subcutaneous space and destruct the extracellular matrix barrier to promote drug diffusion and permeation in larger area and greater depth. Notably, the transient interconversion of keratin from α-helix to β-sheet that might assist the drug residues on the skin surface permeate across the stratum corneum during administration might be another reason not to be ignored. As a labor-saving strategy, HAase-powered MNs offers a promising and painless administration route for macromolecules.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

The Molecular Mechanism of Propylene Glycol Monocaprylate on Skin Retention: Probing the Dual Roles on the Molecular Mobility and Collagen Connection in Roflumilast Cream

The present work was to construct a roflumilast (ROF) cream for the treatment of psoriasis and clarify the dual roles of propylene glycol monocaprylate (PGM) in both molecular mobility of the cream, and drug-skin miscibility via drug-PGM-ceramide and drug-PGM-collagen intermolecular interaction. The cream formulation was screened through the stability study and in vitro skin administration study, optimized by Plackett-Burman and Box-Behnken design, and finally verified by the in vivo tissue distribution study. PGM demonstrated a significant drug skin retention enhancement effect (R_{max in vivo} = 19.5 μg/g). It increased the molecular mobility of the oil phase of the cream by decreasing the molecular interaction of oil molecules proven by the rheology study (E_c = 3.73 × 10^-4 mJ·m^-3). More importantly, because of the good stratum corneum (SC) compatibility (∆H =  - 403.88 J/g), PGM promoted an orderly flow of SC lipids (X-ray scattering, ΔLPP = 1.18 nm) and entered the viable epidermis/dermis (VE/DE) in large quantities (R_PGM = 1186 μg/g), acting as a bridge to connect the drug to collagen through two H-bonds (Length_H-bond = 2.846 Å and 3.313 Å), thus increasing the miscibility of drug and VE/DE significantly (∆H =  - 310.10 J/g, E_mix = 21.66 kcal/mol). In this study, a ROF cream was developed successfully and the effect of PGM on the skin retention was clarified at molecular level.

Comparison of percutaneous permeation profiles of flurbiprofen enantiomers

Flurbiprofen is clinically effective for the treatment of acute or long-term rheumatoid arthritis and osteoarthritis. Studies showed that S-flurbiprofen had better anti-inflammatory effect than R-flurbiprofen. As flurbiprofen racemates are usually used in the form of transdermal preparations, such as Flurbiprofen Cataplasms (Zepolas), it is of great significance to investigate the percutaneous permeation profiles of flurbiprofen enantiomers for considering whether it is necessary to develop the transdermal preparation with single optical enantiomer. Taking the economy into consideration, the flurbiprofen enantiomers as the mode drug and the CHIRALPAKAAGP column we had as instrument were used to perform the following experiments. On the basis of experiences provided by predecessors, we made some improvements to the analytical conditions, and method validation was developed to verify the feasibility of the method. The results showed that the established method could be used to analyze the percutaneous permeation profiles of flurbiprofen enantiomers in the flurbiprofen cataplasms accurately and effectively, and the percutaneous permeation profiles of flurbiprofen enantiomers had no significantly difference no matter under what conditions (P > 0.05).

Design of a Long-Acting Rivastigmine Transdermal Delivery System: Based on Computational Simulation

The purpose of our study was using a computational simulation to develop a long-acting patch of rivastigmine (RVS). A range of patch formulations were screened including pressure sensitive adhesive (PSA), pharmaceutical excipients, and controlled release membranes using transfer simulation based on a mathematical model. Diffusion dynamics parameters for simulated operations were acquired through in vitro release tests (IVRT) and in vitro skin permeation tests (IVPT). The mechanism of controlled release was studied by FTIR (Fourier transform infrared), DSC (differential scanning calorimeter) and molecular docking. Results of a rat in vitro permeation profile showed excellent correlation with the in vivo deconvolution profile (R²=0.998). Experiments testified to transfer of RVS at a relatively uniform speed with high skin permeation (2531.2±142.46 μg/cm²) in 72 h. Pharmacokinetic data obtained in vivo also confirmed stable plasma concentrations over 72 h for the optimized patch, and significant prolongation of both T_max (11.20±1.79 h) and MRT_0-t (33.91±5.33 h). C_max was controlled with AUC_0-t (267.34±24.46 h ng/ml), which was closely comparable to parameters of a commercial Exelon® Patch. The successful development of a long-acting patch of RVS thus underscores the potential of computer aided design in a context of promnesic transdermal delivery. Graphical abstract.