Optimization of skin permeation and distribution of ibuprofen by using nanostructures (coagels) based on alkyl vitamin C derivatives

The role of biophysical properties in defining the functional applications of alkyl esters of L-ascorbic acid

Lipophilic derivatives of vitamin C, known as ascorbyl-6-O-alkanoates (ASCn), have been mainly developed for use in cosmetics, pharmaceuticals, and the food industry as antioxidant additives. These derivatives are of biotechnological interest due to their antioxidant properties, amphiphilic behavior, capacity to self-organize into nano- and micro-structures, anionic nature, and low cost of synthesis. In this review, we will focus on the commercial amphiphile, 6-O-palmitoyl L-ascorbic acid (ASC16), and the shorter acyl chains derivatives, such as 6-O-myristoyl (ASC14) and 6-O-lauroyl L-ascorbic acid (ASC12). The biophysical characteristics of the ASCn family members make them promising candidates for applications such as antioxidant additives, drug carriers in topical pharmaceutical formulations, skin permeation enhancers, and vaccine adjuvants. Furthermore, they exhibit antimicrobial and antibiofilm activities, drawing attention from new biotechnology frontiers. By exploring the biophysical properties of ASCn derivatives, this review highlights their potential applications and the fundamental mechanisms driving their functionality.

Lyotropic liquid crystal mesophases as transdermal delivery systems for lipophilic drugs: A comparative study

The present work aimed to evaluate different Liquid Crystal Mesophases (LCM) as transdermal drug delivery systems (TDDS) for nifedipine (NFD), a lipophilic drug model. The formulations composed of water, Citrus sinensis essential oil (CSEO), PPG-5-CETETH-20, and Olive oil ester PEG-7 were obtained and characterized by polarized light microscopy (PLM), rheology, small-angle x-ray scattering (SAXS), Fourier transform infrared coupled with an attenuated total reflection accessory (FTIR-ATR) and in vitro assays: bioadhesion, drug release, skin permeation, and retention tests. As a result, changes in component proportions led to several transparent viscous systems with an anisotropic profile. PLM and SAXS proved the presence of lamellar (S1), hexagonal (S3), and lamellar + hexagonal (S2) LCM, and rheology showed a high viscoelasticity profile. LCMs were able to adhere to the skin, and S2 achieved higher adhesion strength. NFD (5 mg/mL) has not modified the organization of LCMs. Results also showed that S3 promoted higher permeation and retention and higher disorganization of stratum corneum lipids, which is the main permeation-enhancing mechanism. Thus, the formulations obtained can carry and improve drug delivery through the skin and are promising TDDS for lipophilic drug administration, such as NFD.

Safety Assessment of Ethers and Esters of Ascorbic Acid as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) reviewed the safety of 7 ethers and esters of ascorbic acid, which collectively function as antioxidants, skin-conditioning agents, skin protectants, fragrance ingredients, and skin bleaching agents in cosmetic products. The Panel reviewed relevant data relating to the safety of these ingredients, and concluded that the ethers and esters of ascorbic acid are safe in the present practices of use and concentration, as described in this safety assessment.

Microemulsions and Nanoemulsions in Skin Drug Delivery

Microemulsions and nanoemulsions are lipid-based pharmaceutical systems with a high potential to increase the permeation of drugs through the skin. Although being isotropic dispersions of two nonmiscible liquids (oil and water), significant differences are encountered between microemulsions and nanoemulsions. Microemulsions are thermodynamically stable o/w emulsions of mean droplet size approximately 100–400 nm, whereas nanoemulsions are thermodynamically unstable o/w emulsions of mean droplet size approximately 1 to 100 nm. Their inner oil phase allows the solubilization of lipophilic drugs, achieving high encapsulation rates, which are instrumental for drug delivery. In this review, the importance of these systems, the key differences regarding their composition and production processes are discussed. While most of the micro/nanoemulsions on the market are held by the cosmetic industry to enhance the activity of drugs used in skincare products, the development of novel pharmaceutical formulations designed for the topical, dermal and transdermal administration of therapeutic drugs is being considered. The delivery of poorly water-soluble molecules through the skin has shown some advantages over the oral route, since drugs escape from first-pass metabolism; particularly for the treatment of cutaneous diseases, topical delivery should be the preferential route in order to reduce the number of drugs used and potential side-effects, while directing the drugs to the site of action. Thus, nanoemulsions and microemulsions represent versatile options for the delivery of drugs through lipophilic barriers, and many synthetic and natural compounds have been formulated using these delivery systems, aiming to improve stability, delivery and bioactivity. Detailed information is provided concerning the most relevant recent scientific publications reporting the potential of these delivery systems to increase the skin permeability of drugs with anti-inflammatory, sun-protection, anticarcinogenic and/or wound-healing activities. The main marketed skincare products using emulsion-based systems are also presented and discussed.

Permeability of Ibuprofen in the Form of Free Acid and Salts of L-Valine Alkyl Esters from a Hydrogel Formulation through Strat-M™ Membrane and Human Skin

This paper aimed to evaluate the effect of vehicle and chemical modifications of the structure of active compounds on the skin permeation and accumulation of ibuprofen [IBU]. In vitro permeation experiments were performed using human abdominal skin and Strat-M™ membrane. The HPLC method was used for quantitative determinations. The formulations tested were hydrogels containing IBU and its derivatives and commercial gel with ibuprofen. The results obtained indicate that Celugel® had an enhancing effect on the skin penetration of IBU. The average cumulative mass of [IBU] after 24 h permeation test from Celugel® formulation through human skin was over 3 times higher than for the commercial product. Three ibuprofen derivatives containing [ValOiPr][IBU], [ValOPr][IBU], and [ValOBu][IBU] cation were evaluated as chemical penetration enhancers. The cumulative mass after 24 h of penetration was 790.526 ± 41.426, 682.201 ± 29.910, and 684.538 ± 5.599 μg IBU cm-2, respectively, compared to the formulation containing unmodified IBU-429.672 ± 60.151 μg IBU cm-2. This study demonstrates the perspective of the transdermal hydrogel vehicle in conjunction with the modification of the drug as a potential faster drug delivery system.

Design, Preparation, and Characterization of Effective Dermal and Transdermal Lipid Nanoparticles: A Review

Limited permeability through the stratum corneum (SC) is a major obstacle for numerous skin care products. One promising approach is to use lipid nanoparticles as they not only facilitate penetration across skin but also avoid the drawbacks of conventional skin formulations. This review focuses on solid lipid nanoparticles (SLNs), nanostructured lipid nanocarriers (NLCs), and nanoemulsions (NEs) developed for topical and transdermal delivery of active compounds. A special emphasis in this review is placed on composition, preparation, modifications, structure and characterization, mechanism of penetration, and recent application of these nanoparticles. The presented data demonstrate the potential of these nanoparticles for dermal and transdermal delivery.

Hydrogel-assisted delivery of lipophilic molecules into aqueous medium for transdermal medication based on environment-specific, regioselective adsorption of graphene oxides

Graphene oxide (GO)-laden agarose composite hydrogels (GOACHs) were utilized to deliver lipophilic molecules from organic to aqueous media without alteration of the lipophilic nature of the molecules and the hydrophilic nature of the GOACHs. After the agarose host networks of the GOACHs were impregnated with the non-polar organic solution of lipophilic molecules via stepwise solvent exchange, their GO guests wielded the edge polar groups to effectively adsorb the lipophilic molecules via hydrogen bonding. After being transferred to aqueous media, the GOACHs were able to not only release the loaded lipophilic molecules but also to adsorb the released lipophilic molecules on the GO non-polar carbon lattice planes via hydrophobic interactions, thus resulting in deliberately balanced release of lipophilic molecules in aqueous media. Based on this environment-specific, regioselective adsorption of their GO guests, the GOACHs were harnessed as carriers for sustained delivery of ibuprofen across rat skin, underpinning their applicability in transdermal medication.

Self-assembled nanostructures of L-ascorbic acid alkyl esters support monomeric amphotericin B

Hypothesis

Amphotericin B (AmB) is a highly effective antimicrobial, with broad antimycotic and antiparasitic effect. However, AmB poor water-solubilisation and aggregation tendency limits its use for topical applications. We studied the capacity of nanostructures formed by alkyl esters of L-ascorbic acid (ASCn) to solubilise AmB and tested the relationship between the prevalence of the monomeric form of AmB and its effectiveness as antimicrobial agent.

Experiments

We developed self-assembled nanostructures formed by the commercial compound, palmitoyl ascorbic acid, as well as the shorter chained myristoyl and lauroyl ascorbic acid. AmB loaded ASCn nanostructures were studied by a combination of spectroscopic techniques, together with particle analysis, differential scanning calorimetry, microbiological tests, and Langmuir monolayer visualisation.

Findings

We found no direct relation between the antimicrobial capacity and the prevalence of the monomeric form of the drug. However, the later was related to chemical stability and colloidal robustness. Nanostructures formed by ASC16 in its anionic state provide an appropriate environment for AmB in its monomeric form, maintaining its antimicrobial capacity. Langmuir film visualisation supports spectrophotometric evidence, indicating that ASC16 allows the in-plane solubilisation of AmB. Coagels formed by ASC16 appear as promising for carrying AmB for dermal delivery.

Evaluation of Formulation Parameters on Permeation of Ibuprofen from Topical Formulations Using Strat-M® Membrane

Topical drug delivery is an attractive alternative to conventional methods because of advantages such as non-invasive delivery, by-pass of first pass metabolism, and improved patient compliance. However, several factors such as skin, physicochemical properties of the drug, and vehicle characteristics influence the permeation. Within a formulation, critical factors such as concentration of drug, physical state of drug in the formulation, and organoleptic properties affect the flux across the skin. The aim of the study was to develop and investigate topical semisolid preparations (creams and gels) with ibuprofen as the model drug and investigate the effect of various formulation parameters on the in-vitro performance across the Strat-M® membrane using flow-through cells. In addition, the physical stability of the developed formulations was investigated by studying viscosity, pH, and appearance. All the formulations developed in the study had appealing appearance with smooth texture and no signs of separation. Viscosity and pH of the formulations were acceptable. Cumulative amount of drug permeated at the end of 24 h was highest for clear gel (3% w/w ibuprofen; F6: 739.6 ± 36.1 µg/cm2) followed by cream with high concentration of ibuprofen in suspended form (5% w/w; F3: 320.8 ± 17.53 µg/cm2), emulgel (3% w/w ibuprofen; F5: 178.5 ± 34.5 µg/cm2), and cream with solubilized ibuprofen (3% w/w; F2A: 163.2 ± 9.36 µg/cm2). Results from this study showed that permeation of ibuprofen was significantly influenced by formulation parameters such as concentration of ibuprofen (3% vs. 5% w/w), physical state of ibuprofen (solubilized vs. suspended), formulation type (cream vs. gel), mucoadhesive agents, and viscosity (high vs. low). Thus, findings from this study indicate that pharmaceutical formulation scientists should explore these critical factors during the early development of any new topical drug product in order to meet pre-determined quality target product profile.

l-Ascorbic acid alkyl esters action on stratum corneum model membranes: An insight into the mechanism for enhanced skin permeation

L-ascorbic acid alkyl esters (ASCn) are lipophilic forms of vitamin C, which act as skin permeation enhancers. We investigated the physical changes induced by incorporating ASCn into stratum corneum (SC) lipid membranes and correlated this with the mechanism proposed in the literature for skin permeation enhancement phenomena. We used lipid monolayers to explore the 2D structure and elasticity of the lipid-enhancer systems. As a comparison, the classic permeation enhancer, oleic acid (OA) and the non-enhancer analogue stearic acid (SA) were analysed. The incorporation of ASCn or OA into SC membranes resulted in more liquid-like films, with a dose-dependent lowering of the compressibility modulus. Brewster angle microscopy (BAM) evidenced partial miscibility of the enhancer with SC lipid components, stabilising the liquid-expanded phase. At the nanoscale, AFM showed that SC lipids form heterogeneous membranes, which underwent structural alterations after incorporating ASCn and fatty acids, such as SA and OA. The lower, cholesterol-enriched phase appears to concentrate the enhancers, whilst the higher ceramide-enriched phase concentrated the non-enhancer SA. Our results and previously reported pieces of evidence indicate a strong pattern in which the rheological properties of SC lipid films are determinant for skin permeation phenomena.

Formulation and delivery strategies of ibuprofen: challenges and opportunities

Ibuprofen, a non-steroidal anti-inflammatory drug (NSAID), is mostly administered orally and topically to relieve acute pain and fever. Due to its mode of action this drug may be useful in the treatment regimens of other, more chronic conditions, like cystic fibrosis. This drug is poorly soluble in aqueous media and thus the rate of dissolution from the currently available solid dosage forms is limited. This leads to poor bioavailability at high doses after oral administration, thereby increasing the risk of unwanted adverse effects. The poor solubility is a problem for developing injectable solution dosage forms. Because of its poor skin permeability, it is difficult to obtain an effective therapeutic concentration from topical preparations. This review aims to give a brief insight into the status of ibuprofen dosage forms and their limitations, particle/crystallization technologies for improving formulation strategies as well as suggesting its incorporation into the pulmonary drug delivery systems for achieving better therapeutic action at low dose.

The Rheological Properties of Lipid Monolayers Modulate the Incorporation of l-Ascorbic Acid Alkyl Esters

In this work, we tested the hypothesis that the incorporation of amphiphilic drugs into lipid membranes may be regulated by their rheological properties. For this purpose, two members of the l-ascorbic acid alkyl esters family (ASCn) were selected, ASC16 and ASC14, which have different rheological properties when organized at the air/water interface. They are lipophilic forms of vitamin C used in topical pharmacological preparations. The effect of the phase state of the host lipid membranes on ASCn incorporation was explored using Langmuir monolayers. Films of pure lipids with known phase states have been selected, showing liquid-expanded, liquid-condensed, and solid phases as well as pure cholesterol films in liquid-ordered state. We also tested ternary and quaternary mixed films that mimic the properties of cholesterol containing membranes and of the stratum corneum. The compressibility and shear properties of those monolayers were assessed in order to define its phase character. We found that the length of the acyl chain of the ASCn compounds induces differential changes in the rheological properties of the host membrane and subtly regulates the kinetics and extent of the penetration process. The capacity for ASCn uptake was found to depend on the phase state of the host film. The increase in surface pressure resultant after amphiphile incorporation appears to be a function of the capacity of the host membrane to incorporate such amphiphile as well as the rheological response of the film. Hence, monolayers that show a solid phase state responded with a larger surface pressure increase to the incorporation of a comparable amount of amphiphile than liquid-expanded ones. The cholesterol-containing films, including the mixture that mimics stratum corneum, allowed a very scarce ASCn uptake independently of the membrane diffusional properties. This suggests an important contribution of Cho on the maintenance of the barrier function of stratum corneum.

Transcutaneous delivery of leflunomide nanoemulgel: Mechanistic investigation into physicomechanical characteristics, in vitro anti-psoriatic and anti-melanoma activity

The present study is a mechanistic validation of 'proof of concept' of effective topical delivery of leflunomide (LFD) nanoemulgel for localized efficient treatment of psoriatic lesions as well as melanoma affected skin regions. Hyperproliferation of keratinocytes in psoriasis and symbiotic relationship between keratinocytes and melanocytes, justifies the need of dual acting treatment. LFD is recently introduced significantly effective disease modifying anti-rheumatic drug and has been considered valuable for the treatment of psoriatic arthritis as well as melanoma. Current available treatments for psoriasis and melanoma are inefficient due to systemic side effects, poor transcutaneous permeation and thus present a challenge for development of novel colloidal carriers. We newly reformulated LFD as a nanoemulgel based on self nanoemulsifying technique using Capryol 90, Cremophor EL, Transcutol HP as nanoemulsifying components and Pluronic F127 as a gelling agent. This thermodynamically stable nanoemuslsifying preconcentrate after gelation showed mean globule size, 123.7 nm and viscosity 9620 ± 93 cp. Complete mechanical characterization was carried out using Texture Analyzer and hardness, adhesiveness and springiness index were found to be 523 gms, 431 gms and 1.02, respectively. Ex vivo permeation through rat abdominal skin revealed significant improvement in flux, apparent permeability coefficient, steady state diffusion coefficient and drug deposition in skin due to nanoemulsification of LFD. The in vitro cytoxicity of LFD nanoemulgel in human HaCaT, melanoma A375 and SK-MEL-2 cell lines showed significantly enhanced therapeutic response. In gist, LFD nanoemulgel for trancutaneous delivery will reduce the overall dose and drug consumption, by effectively localizing at the applied target site and will ultimately minimize systemic side effects.

In vitro, ex vivo, and in vivo evaluation of the effect of saturated fat acid chain length on the transdermal behavior of ibuprofen-loaded microemulsions

In this study, the effect of the saturated fatty acid (FA) chain length in the oil phase on the behavior of Ibuprofen (IBU)-loaded transdermal microemulsion (ME) was evaluated in vitro, ex vivo, and in vivo. Three oils classified as long (LFA), medium (MFA), and short (SFA) chain length oils, Cremophor RH40 (surfactant) and Transcutol P (cosurfactant) were selected after experimental optimization. The physicochemical properties of ME were characterized, including IBU solubility in excipients, pseudo-ternary phase diagram construction, particle size, zeta potential, viscosity, and stability. Permeation flux and residual amount of IBU ex vivo using Franz cell system occurred in the following order: MFA-based ME > LFA-based ME > SFA-based ME, which correlated well with the results of confocal scanning laser microscopy study and the in vivo retention study. The results of in vitro cytotoxicity study and skin irritation tests measured by differential scanning calorimetry were ranked in the following order: LFA-based ME > MFA-based ME > SFA-based ME. Moreover, MFA-based ME has the highest analgesic activity among all the treatment groups. MFA was found to be an optimal oil phase with appropriate FA chain length for IBU-loaded transdermal ME, which exhibited excellent physicochemical properties, low toxicity, and good permeability profile.

Adjuvant activity of CpG-ODN formulated as a liquid crystal

The adjuvants approved in human vaccine with recombinant/purified antigens induce weak cellular immune response and so the development of new adjuvant strategies is critical. CpG-ODN has successfully been used as an adjuvant (phase I-III clinical trials) but its bioavailability needs to be improved. We investigated the adjuvant ability of CpG-ODN formulated with a liquid crystal nanostructure of 6-O-ascorbyl palmitate (Coa-ASC16). Mice immunized with OVA/CpG-ODN/Coa-ASC16 elicited a potent specific IgG1, IgG2a, Th1 and Th17 cellular response without systemic adverse effects. These responses were superior to those induced by OVA/CpG-ODN (solution of OVA with CpG-ODN) and to those induced by the formulation OVA/CpG-ODN/Al(OH)3. Immunization with OVA/CpG-ODN/Coa-ASC16 resulted in a long-lasting cell-mediated immune response (at least 6.5 months). Furthermore, Coa-ASC16 alone allows a controlled release of CpG-ODN in vitro and induces local inflammatory response, independent of TLR4 signaling, characterized by an influx of neutrophils and Ly6C(high) monocytes and pro-inflammatory cytokines. Remarkably, the adjuvant capacity of CpG-ODN co-injected with Coa-ASC16 (OVA/CpG-ODN plus Coa-ASC16) was similar to the adjuvant activity of OVA/CpG-ODN, supporting the requirement for whole formulation to help CpG-ODN adjuvanticity. These results show the potential of this formulation, opening a new avenue for the development of better vaccines.

Use of photoacoustic spectroscopy in the characterization of inclusion complexes of benzophenone-3-hydroxypropyl-β-cyclodextrin and ex vivo evaluation of the percutaneous penetration of sunscreen

This work is aimed to evaluate the application of photoacoustic spectroscopy (PAS) in the characterization of inclusion complexes of benzophenone-3 (BZ-3) and hydroxypropyl-β-cyclodextrin (HPCD) and to analyze the ex vivo percutaneous penetration of sunscreens and their reaction with the skin. The formation of inclusion complexes of BZ-3 and HPCD was performed by co-precipitation in stoichiometric ratios of 1:1 and 1:2. Thermal analysis and PAS characterized these inclusion complexes, and they indicated that the stoichiometric ratio of 1:2 was best. Sunscreen formulations were prepared and applied on the ears of rabbits. PAS suggested that the formulation with the complex resulted in lower penetration of BZ-3. Histological analysis demonstrated that the use of the formulation with BZ-3 was associated with an increase in the comedogenic effect and the presence of acanthosis, while no such effect was found in the formulation with the complex. The formulation with the BZ-3-HPCD complex is a promising strategy for improving the photoprotective effect of BZ-3. PAS can be used in the study of inclusion complexes with cyclodextrins and the evaluation of the percutaneous penetration of sunscreen formulations. Further tests are being conducted using PAS to monitor in vivo changes in the optical absorption spectra of formulations and to investigate their photostability.