Enhanced Skin Permeation of Salicylate by Ion-Pair Formation in Non-aqueous Vehicle and Further Enhancement by Ethanol and l-Menthol

Multifunctional Deep Eutectic Solvent-Based Microemulsion for Transdermal Delivery of Artemisinin

As a serious public health issue, malaria threatens the health of millions of people. Artemisinin, a gift from traditional Chinese medicine, has been used in the treatment of malaria and has shown good therapeutic efficiency. However, due to its low solubility, poor bioavailability, and short half-life time, some smart delivery strategies are still required. Herein, a multifunctional DES prepared from ibuprofen and menthol was prepared. This DES was shown to efficiently promote the solubility of artemisinin up to 400-fold. Then, it was further applied as the oil phase to construct an O/W microemulsion with the help of Tween-80 + Span-20 mixed surfactants. The prepared microemulsion displayed high efficiency in improving the permeability of artemisinin, which can be ascribed to the presence of the permeation enhancer menthol in DES and the microstructure of the O/W microemulsion. Moreover, the simultaneous permeation of artemisinin and ibuprofen further indicated the potential benefits of the presented formulation in the treatment of malaria. To sum up, the microemulsion based on multifunctional DES presented herein provided an effective method for transdermal delivery of artemisinin.

Anti-acne activity of carnitine salicylate and magnolol through the regulation of exfoliation, lipogenesis, bacterial growth and inflammation

BACKGROUND

Salicylic acid has been used as an anti-acne agent with its comedolytic property and antimicrobial activity. However, there is a limit to use for leave-on cosmetics because of the transient skin irritation and low efficacy at neutral pH condition. We prepared a salicylic acid-based ionic pair with L -carnitine (we named, IP-BHA) overcoming the limitation of salicylic acid. We examined the effect of IP-BHA as well as the combination effect with magnolol, a bioactive organic lignan, in order to clarify their efficacy as anti-acne agents.

METHODS

After verifying the structure of IP-BHA, we confirmed anti-acne activities including the regulation of exfoliation, lipogenesis, bacterial growth, and inflammation with IP-BHA and/or magnolol.

RESULTS

The antibacterial activity of IP-BHA and magnolol was evaluated by determining the minimum antibacterial inhibitory concentration. Magnolol showed strong activity against Cutibacterium acnes, which was better than a medical antibiotic acne drug, clindamycin. The combined application with IP-BHA was more effective in antibacterial activity by 2.5 times. It was confirmed that testosterone-induced lipogenesis was significantly inhibited by treatment with IP-BHA and magnolol, while single treatment had no significant inhibitory effect. Interestingly, MMP-1 and VEGF were induced by C. acnes lysate in human keratinocytes. We found that these inflammatory molecules were completely inhibited by combined application of IP-BHA and magnolol. Through ex vivo test, the dose-dependent exfoliation effect of IP-BHA was confirmed at pH 5.5, and the synergic exfoliation effect was shown in the combined application of IP-BHA and magnolol. When topically applied, the emulsion containing IP-BHA and magnolol relieved the sodium dodecyl sulfate-induced erythema and improved inflamed acne with papule and pustule.

CONCLUSION

Our data demonstrate that the ionic paired salicylic acid with L -carnitine can overcome the limitations of salicylic acid at low concentration and natural skin pH. Based on the dual administration effects, we suggest that IP-BHA and magnolol may be the potential agent for acne by improving inflammatory skin condition.

New Lidocaine-Based Pharmaceutical Cocrystals: Preparation, Characterization, and Influence of the Racemic vs. Enantiopure Coformer on the Physico-Chemical Properties

This study describes the preparation, characterization, and influence of the enantiopure vs. racemic coformer on the physico-chemical properties of a pharmaceutical cocrystal. For that purpose, two new 1:1 cocrystals, namely lidocaine:dl-menthol and lidocaine:d-menthol, were prepared. The menthol racemate-based cocrystal was evaluated by means of X-ray diffraction, infrared spectroscopy, Raman, thermal analysis, and solubility experiments. The results were exhaustively compared with the first menthol-based pharmaceutical cocrystal, i.e., lidocaine:l-menthol, discovered in our group 12 years ago. Furthermore, the stable lidocaine/dl-menthol phase diagram has been screened, thoroughly evaluated, and compared to the enantiopure phase diagram. Thus, it has been proven that the racemic vs. enantiopure coformer leads to increased solubility and improved dissolution of lidocaine due to the low stable form induced by menthol molecular disorder in the lidocaine:dl-menthol cocrystal. To date, the 1:1 lidocaine:dl-menthol cocrystal is the third menthol-based pharmaceutical cocrystal, after the 1:1 lidocaine:l-menthol and the 1:2 lopinavir:l-menthol cocrystals reported in 2010 and 2022, respectively. Overall, this study shows promising potential for designing new materials with both improved characteristics and functional properties in the fields of pharmaceutical sciences and crystal engineering.

Microneedle-Assisted Percutaneous Transport of Magnesium Sulfate

OBJECTIVE

In vitro diffusion experiments were performed to assess the permeation of magnesium sulfate across pig skin.

METHODS

The mean thickness of the dermatomed porcine skin was 648 ± 12 µm. Magnesium concentration was measured using inductively coupled plasma-optical emission spectroscopy. Transdermal flux of magnesium sulfate across MN-treated and untreated porcine skin was obtained from the slope of the steady-state linear portion of cumulative amount versus time curve.

RESULTS

Statistical analysis of the results was done with Student's t-test. The transdermal flux of magnesium sulfate across microneedle-treated porcine skin was 134.19 ± 2.4 µg/cm2/h and transdermal flux across untreated porcine skin was 4.64 ± 0.05 µg/cm2/h. Confocal microscopy was used to visualize the microchannels created by a solid microneedle roller (500 µm).

CONCLUSION

From our confocal microscopy studies, it was evident that the 500 μm long microneedles disrupted the stratum corneum and created microchannels measuring 191 ± 37 µm. The increase in transdermal flux across the microneedle-treated skin was statistically significant compared to that of controls, i.e., without the application of microneedles. With the application of microneedles, the transdermal flux of magnesium permeated over 12 h was approximately 33-fold higher in comparison to passive diffusion across an intact stratum corneum.

A Multiscale Study on the Penetration Enhancement Mechanism of Menthol to Osthole

Menthol is a widely used penetration enhancer in clinical medicine due to its high efficiency and relative safety. However, details of the penetration enhancement mechanism of menthol on the molecular level is rarely involved in the discussion. In this work, the penetration enhancement (PE) mechanism of menthol is explored by a multiscale method containing molecular dynamics simulations, in vitro penetration experiments, and transmission electron microscopy. Osthole is chosen to be the tested drug due to its common use in external preparations and because it often accompanies menthol as a PE in the preparations. The results show that menthol in each testing concentration can impair the lipid packing of stratum corneum (SC) and promote osthole permeating into SC, and the penetration promoting effect has an optimal concentration. At a low concentration, menthol causes the bilayer to relax with a reduction in thickness and increment in the lipid headgroup area. At a high concentration, menthol destroys the bilayer structure of SC and causes lipids to form a reversed micelle structure. The penetration enhancement mechanism of menthol is characterized mainly by the disruption of the highly ordered SC lipid in low concentrations and an improvement in the partitioning of drugs into the SC in high concentrations. The results can provide some assistance for additional studies and applications of menthol as a penetration enhancer.

Lidocaine self-sacrificially improves the skin permeation of the acidic and poorly water-soluble drug etodolac via its transformation into an ionic liquid

Poor transdermal penetration of active pharmaceutical ingredients (APIs) impairs both bioavailability and therapeutic benefits and is a major challenge in the development of transdermal drug delivery systems. Here, we transformed a poorly water-soluble drug, etodolac, into an ionic liquid in order to improve its hydrophobicity, hydrophilicity and skin permeability. The ionic liquid was prepared by mixing etodolac with lidocaine (1:1, mol/mol). Both the free drug and the transformed ionic liquid were characterized by differential scanning colorimetry (DSC), infrared spectroscopy (IR), and saturation concentration measurements. In addition, in vitro skin-permeation testing was carried out via an ionic liquid-containing patch (Etoreat patch). The lidocaine and etodolac in ionic liquid form led to a relatively lower melting point than either lidocaine or etodolac alone, and this improved the lipophilicity/hydrophilicity of etodolac. In vitro skin-permeation testing demonstrated that the Etoreat patch significantly increased the skin permeation of etodolac (9.3-fold) compared with an etodolac alone patch, although an Etoreat patch did not increase the skin permeation of lidocaine, which was consistent with the results when using a lidocaine alone patch. Lidocaine appeared to self-sacrificially improve the skin permeation of etodolac via its transformation into an ionic liquid. The data suggest that ionic liquids composed of approved drugs may substantially expand the formulation preparation method to meet the challenges of drugs which are characterized by poor rates of transdermal absorption.

Interaction of menthol with mixed-lipid bilayer of stratum corneum: A coarse-grained simulation study

Menthol is a widely used penetration enhancer in clinical medicine due to its high efficiency and relative safety. Although there are many studies focused on the penetration-enhancing activity of menthol, the details of molecular mechanism are rarely involved in the discussion. In this study, we present a series of coarse-grained molecular dynamics simulations to investigate the interaction of menthol with a mixed-lipid bilayer model consisting of ceramides, cholesterol and free fatty acids in a 2:2:1 molar ratio. Taking both the concentration of menthol and temperature into consideration, it was found that a rise in temperature and concentration within a specific range (1-20%) could improve the penetration-enhancing property of menthol and the floppiness of the bilayer. However, at high concentrations (30% and more), menthol completely mixed with the lipids and the membrane can no longer maintain a bilayer structure. Our results elucidates some of the molecular basis for menthol's penetration enhancing effects and may provide some assistance for the development and applications of menthol as a penetration enhancer. Furthermore, we establish a method to investigate the penetration enhancement mechanism of traditional Chinese medicine using the mixed-lipid bilayer model of stratum corneum by molecular dynamics simulations.

Effect of O-acylmenthol and salt formation on the skin permeation of diclofenac acid

PURPOSE

To enhance the transdermal delivery of diclofenac acid (DA) by using O-acylmenthol as a penetration enhancer and complexing with amines, or by a combination of the two methods.

METHODS

The skin permeability of diclofenac was tested in vitro across rat skin with each of the evaluated permeants in a saturated isopropyl myristate (IPM) donor solution.

RESULTS

A 4.5-fold increase in the flux of diclofenac was observed by ion-pair formation with diethylamine; however, the cations with hydroxyl groups had negative effects on the transdermal delivery of diclofenac. 2-isopropyl-5-methylcyclohexyl 2-hydroxypanoate and 2-isopropyl-5-methylcyclohexyl heptanoate produced significant increase in the permeation of diclofenac potassium (D-K); however, both of them were ineffective for the other diclofenac salts, including diclofenac diethylamine (D-DETA), diclofenac ethanolamine (D-EA), diclofenac diethanolamine (D-DEA), diclofenac triethanolamine, and diclofenac N-(hydroxylethyl) piperidine. 2-isopropyl-5-methylcyclohexyl tetradecanoate was effective on the penetration of D-K, D-DETA, D-EA, and D-DEA. Also, it is exciting to note that the combined use of diethylamine with 2-isopropyl-5-methylcyclohexyl tetradecanoate produced a 9.74-fold increase in accumulation amount of diclofenac compared with DA in IPM.

CONCLUSIONS

The use of ion pair in combination with O-acylmenthol is necessary to further increase the diclofenac flux to provide better compliance for the patients undergoing clinical therapy.

The enhancing effect of ion-pairing on the skin permeation of glipizide

The purpose of the present study was to investigate the permeation of glipizide (GP) and observe the effect of an interaction with amines as counter ions, including diethylamine, triethylamine, ethanolamine, diethanolamine, triethanolamine, N-(2-hydroxylethyl) piperidine. Permeation experiments were performed in vitro, using rat abdominal skin as a barrier. The lipophilic donor system consisting of isopropyl myristate (IPM) and ethanol (EtOH; EI system, 8:2) produced a marked enhancement of GP flux through rat skin. All the amines investigated in this study had performed an enhancing effect on GP flux, and triethylamine had the most potent enhancing effect on GP in the vehicle IPM:EtOH = 8:2(w/w). In the presence of counter ions, the solubility of GP in the donor solution (IPM:EtOH = 8:2) was increased and the log K (o/w) of GP was decreased, which may due to higher solubility of the GP in the IPM:EtOH = 8:2(w/w). (13)C NMR spectroscopy was used to identify the ion-pairing formation between GP and the respective counter ion. It was surprising that all the four enhancers examined, such as isopropyl myristate, propylene glycol, N-methyl-2-pyrrolidone, azone, and oleic acid, had no enhancing effect on the percutaneous permeation of GP. This study showed that the formation of ion-pairs between GP and counter ions is a useful method to promote the skin permeation of GP.

Lipid Core Peptide System for Gene, Drug, and Vaccine Delivery

A vast number of biologically active compounds await efficient delivery to become therapeutic agents. Lipidation has been demonstrated to be a convenient and useful approach to improve the stability and transport across biological membranes of potential drug molecules. The lipid core peptide (LCP) system has emerged as a promising lipidation tool because of its versatile features. This review discusses the progress in the development of the LCP system to improve cell permeability of nucleotides, physicochemical properties of potential drugs, and vaccine immunogenicity. Emphasis was put on the application of the LCP system to deliver antigens for the prevention of group A streptococcus infection, novel techniques of conjugation of target molecules to the LCP, and new alterations of the LCP system itself.

Formulation optimization of an indomethacin-containing photocrosslinked polyacrylic acid hydrogel as an anti-inflammatory patch

Photocrosslinked polyacrylic acid hydrogel, made from polyacrylic acid (PAA) modified with 2-hydroxyethyl methacrylate (HEMA), is a promising candidate adhesive for dermatological patches. In this study, we investigated the further availability of hydrogel as an adhesive for dermatological patches using a hydrogel containing indomethacin (IDM) as a model anti-inflammatory patch. From an orthogonal experimental study, we clarified the relationships between formulation factors and characteristics of model formulation. Formulations with a lower degree of swelling were prepared by increasing the degree of HEMA modification and the addition of Tween 80. Apparent permeation rate was increased by addition of L-menthol and Tween 80. A tendency for higher HEMA modification to be accompanied by the prolongation of the lag time of IDM was observed. To obtain an applicable anti-inflammatory patch, we conducted a formulation optimization study using a novel optimization method, a response-surface method incorporating multivariate spline interpolation (RSM-S). Consequently, a highly functional anti-inflammatory patch in terms of its adhesive properties and bioavailability was successfully obtained. Since a wide range of functions can be fully controlled by manipulating the formulation factors, photocrosslinked polyacrylic acid hydrogel is an attractive candidate adhesive for dermatological patches.

Evidence for dopamine involvement in ambulation promoted by menthone in mice

The present study examines the mechanism that underlies the ability of menthone (MTN), a constituent of peppermint oil, to promote mouse ambulation. Since bupropion (BUP), a dopamine (DA) uptake inhibitor, promotes mouse ambulation, the effect of MTN combined with BUP on ambulation was investigated. The results showed that BUP with MTN produced an additive interaction on mouse ambulation. The effects of DA antagonists chlorpromazine, fluphenazine, haloperidol, SCH12679 and spiperone on the ability of MTN to promote ambulation were then examined. All of these antagonists attenuated the effects of MTN. Prior exposure to the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine, which inhibits catecholamines synthesis, decreased subsequent sensitivity to the effect of MTN. These results suggest that DA is involved in the ability of MTN to promote ambulation in mice.

Enhanced Skin Permeation of Diclofenac by Ion-Pair Formation and Further Enhancement by Microemulsion

Enhancement of skin permeability of anionic diclofenac from non-aqueous vehicle isopropyl myristate (IPM) by ion-pair formation with either alkylamines or benzylamine as model cationic ions was examined in guinea pig dorsal skin. Diclofenac ion flux increased in the presence of these amines due to an increase in solubility. Maximum flux was observed in the presence of n-hexylamine, which induced 7.3-fold increase accompanied by a 45-fold increase in solubility. Permeability coefficients of the ionic form of diclofenac in the presence of benzylamine, n-hexylamine and iso-octylamine as counter ions in IPM were larger than those of the non-ionic form of diclofenac. Since the solubility of diclofenac was still limited, to obtain further enhancement of skin permeation, the effects of microemulsions as a vehicle consisting of phosphate buffered saline (PBS), isopropyl myristate (IPM), polyoxyethylene sorbitan monooleate (Tween 80) and ethanol were examined for transport of diclofenac-benzylamine ion-pairs. All microemulsion formulations tested increased diclofenac flux 4.9-fold to 10.7-fold over the value without a microemulsion accompanied by a 217-fold to 302-fold improvement in the solubility of diclofenac-benzylamine ion-pairs, but permeability coefficients were decreased 28-44 fold. Maximum enhancement was observed for a microemulsion with a ratio of PBS, IPM, ethanol and Tween 80 of 25 : 8 : 47 : 20 (w/w). The present findings suggest the usefulness of combined use of ion-pairs with microemulsions for enhancement of skin permeation of ionic drugs.