Drug Delivery Strategies for Avobenzone: A Case Study of Photostabilization

Several developments and research methods are ongoing in drug technology and chemistry research to elicit effectiveness regarding the therapeutic activity of drugs along with photoprotection for their molecular integrity. The detrimental effect of UV light induces damaged cells and DNA, which leads to skin cancer and other phototoxic effects. The application of sunscreen shields to the skin is important, along with recommended UV filters. Avobenzone is widely used as a UVA filter for skin photoprotection in sunscreen formulations. However, keto-enol tautomerism propagates photodegradation into it, which further channelizes the phototoxic and photoirradiation effects, further limiting its use. Several approaches have been used to counter these issues, including encapsulation, antioxidants, photostabilizers, and quenchers. To seek the gold standard approach for photoprotection in photosensitive drugs, combinations of strategies have been implemented to identify effective and safe sunscreen agents. The stringent regulatory guidelines for sunscreen formulations, along with the availability of limited FDA-approved UV filters, have led many researchers to develop perfect photostabilization strategies for available photostable UV filters, such as avobenzone. From this perspective, the objective of the current review is to summarize the recent literature on drug delivery strategies implemented for the photostabilization of avobenzone that could be useful to frame industrially oriented potential strategies on a large scale to circumvent all possible photounstable issues of avobenzone.

Systemic availability of lipophilic organic UV filters through dermal sunscreen exposure

BACKGROUND

Chemical UV filters are common components in sunscreens and cosmetic products and used to protect the skin against harmful effects of sunlight like sunburn. However, the effectiveness of sunscreens in the prevention of skin cancer is in some parts still controversial. Meanwhile, questions about negative effects of the chemical UV filters on human health arise and request an effective risk assessment. Real-life exposure data in humans after application of these products are still rare. Thus, we explored whether and to what extent UV filters are absorbed through the skin into the human body.

MATERIAL AND METHODS

Plasma and urine samples from 20 healthy volunteers were collected before, during and after a real-life exposure scenario (1st application: 2 mg/cm²; 2nd and 3rd (after 2 and 4 h): 1 mg/cm² each) using a commercial sunscreen formulation for one day. These samples were analyzed for their content of the currently prominent UV filters octocrylene and avobenzone as well as 2-cyano-3,3-diphenylacrylic acid (CDAA) as the main octocrylene metabolite by using different liquid chromatography electrospray-ionization tandem mass spectrometric procedures.

RESULTS

Following dermal sunscreen exposure, avobenzone, octocrylene and CDAA reached concentrations up to 11 μg/L, 25 μg/L and 1352 μg/L in plasma. In urine detection rates of avobenzone and octocrylene were low while CDAA showed a high detection rate and reached up to 5207 μg/g creatinine. Kinetic models could be fitted for octocrylene and CDAA in plasma and CDAA in urine. Concentration peaks were reached between 10 and 16 h after first application and half-life periods were in the range of 1.5 to 2 days. The lipophilic UV filter octocrylene and its metabolite CDAA showed a much slower elimination than other more hydrophilic UV filters. Concordantly, the metabolite CDAA in particular showed a markedly increased renal excretion over the whole sampling period and indicated high internal exposure to OC.

DISCUSSION

Real-life sunscreen usage leads to considerable bioavailability of organic UV filters and their metabolites which is rarely seen for other environmental exposures. A combined monitoring of the parent compound and its metabolites is important to fully address internal exposure to the UV filter in humans. Considering the kinetic profiles a prolonged systemic release due to depot formation in skin and a potential accumulation through multi-day exposure is presumed. High in-vivo loads call for a critical toxicological assessment of the UV filters and their metabolites.

Self-assembled organogelators as artificial stratum corneum models: Key-role parameters for skin permeation prediction

Self-assembled organogelators were explored as artificial stratum corneum (SC) models for the in vitro skin permeation assessment. Four SC models consisting of binary (organogels) or ternary (microemulsion-based organogels) mixtures were developed using stearic acid, tristearin, or sorbitan tristearate, at two different concentrations, gelled in squalene. The permeation of lipophilic butyl-methoxydibenzoylmethane and hydrophilic methylene blue as the permeant compounds across the SC models was compared with ex vivo experiments using excised porcine ear skin. A multi-analytical approach was adopted to provide detailed understanding about organogelator organization within the SC models and find possible parameters playing key-roles in SC permeation prediction. The SC models were investigated for gelling properties and microstructure. Parameters such as gel occurrence, organogelator concentration, and rheological properties appeared as negligible conditions for skin permeation prediction. Conversely, arrangement packing, interactions, and crystallinity extent of the self-assembled organogelator were found to play a fundamental role in the simulation of SC barrier function according to the permeant feature.

Skin absorption and human exposure estimation of three widely discussed UV filters in sunscreens--In vitro study mimicking real-life consumer habits

Due to health concerns about safety, three UV-filters (Benzophenone-3, BP3, 10%; Ethylhexyl Methoxycinnamate, EHMC, 10%; Butyl Methoxydibenzoylmethane, BMDBM; 5%) were examined in vitro for absorption on full-thickness pig-ear skin, mimicking human in-use conditions. Kinetic profiles confirmed the rapid permeation of BP3; after the first hour of skin (frozen-stored) exposure to 2 mg/cm(2) (W/O sunscreen; recommended but unrealistic amount), about 0.5% of the applied dose passed into the receptor fluid. The absorption rate of filters was higher from W/O than from O/W emulsions. The fresh/frozen-stored skin permeability coefficient (0.83-0.54) for each UV filter was taken into account. Systemic Exposure Dosage of BP3, EHMC, BMDBM for humans as a consequence of (i) whole-body and (ii) face treatment with 0.5 mg/cm(2) of W/O sunscreen for 6-h skin exposure followed by washing and subsequent 18-h permeation (a realistic scenario) were estimated to be (i) 4744, 1032 and 1036 μg/kg-bw/day, and (ii) 153, 33 and 34 μg/kg-bw/day, respectively. From Margin of Safety for BP3, EHMC and BMDBM (i) 42, 485 and 192 as well as (ii) 1307; 15,151 and 5882, respectively, only the value of 42 (<100) for BP3 indicated a possible health risk. Escalation of a phobia towards all organic UV filters is undesirable.

Microencapsulation of a cyclodextrin complex of the UV filter, butyl methoxydibenzoylmethane: in vivo skin penetration studies

Lipid microparticles loaded with the complex between hydroxypropyl-β-cyclodextrin (HP-β-CD) and the sunscreen agent, butyl methoxydibenzoylmethane (BMDBM) were evaluated for their effect on the UV filter percutaneous penetration. The microparticles were prepared by the melt emulsification technique using tristearin as lipidic material and hydrogenate phosphatidylcholine as the surfactant. Human skin penetration was investigated in vivo by the tape stripping technique, a minimal invasive procedure based on the progressive removal of the upper cutaneous layers (stratum corneum) with adhesive tape strips. The amount of sunscreen fixed to each strip was determined by HPLC after solvent extraction. The recovery of the UV filter from spiked adhesive tapes was >94.4% and the precision of the method was better than 7.6% relative standard deviation. Non-encapsulated BMDBM, its complex with HP-β-CD, the lipid microparticles loaded with the sunscreen alone or the BMDBM/HP-β-CD complex were introduced into oil-in-water emulsions and applied to human volunteers. Compared to the cream with the non-encapsulated sunscreen agent (percentage of the applied dose penetrated, 9.7%±2.5), the amount of BMDBM diffusing into the stratum corneum was increased by the formulations containing the BMDBM/HP-β-CD complex (17.1%±3.2 of the applied dose) or the microparticles loaded with BMDBM only (15.1%±2.7 of the applied dose). On the contrary, a significant decrease in the level of UV filter penetrated into the stratum corneum was achieved by the cream containing the microencapsulated BMDBM/HP-β-CD complex (percentage of the applied dose penetrated, 6.0%±1.5). The reduced BMDBM percutaneous penetration attained by the latter system should enhance the UV filter efficacy and limit potential toxicological risks.

Formulation and in vitro evaluation of a PEGylated microscopic lipospheres delivery system for ceftriaxone sodium

The aim of this study was to formulate and evaluate in vitro, ceftriaxone sodium lipospheres dispersions for oral administration. Ceftriaxone sodium lipospheres were prepared by melt-emulsification using 30%w/w Phospholipon 90H in Softisan 154 as the lipid matrix containing increasing quantities of PEG 4000 (10, 20, 30, and 40%w/w). Characterization based on particle size, particle morphology, encapsulation efficiency, loading capacity and pH were carried out on the lipospheres. Microbiological studies of the ceftriaxone sodium-loaded lipospheres were performed using Escherichia coli as the model organism. In vitro permeation of ceftriaxone sodium from the lipospheres through artificial membrane (0.22 microm pore size) was carried out using Franz cell and simulated intestinal fluid (SIF) without pancreatin as acceptor medium. Photomicrographs revealed spherical particles within a micrometer range with minimal growth after 1 month (Maximum size = 64.76 +/- 3.81 microm). Microbiological studies indicated that lipospheres formulated with 20%w/w of PEG 4000 containing 2%w/w or 3%w/w of ceftriaxone sodium gave significantly (p < 0.05) higher inhibition zone diameter than those with 30%w/w or 40%w/w of PEG 4000. The result also indicated that lipospheres with 10%w/w PEG 4000 resulted in significantly higher encapsulation efficiency (p < 0.05) while those with 30%w/w gave the least, while the loading capacity values ranged from 3.22 mg of ceftriaxone sodium/100 mg of lipid to 6.36 mg of ceftriaxone sodium/100 mg of lipid. Permeation coefficient values varied and ranged from 8.55 x 10(-7) cm/s to 2.08 x 10(-6) cm/s depending on the concentration of PEG 4000. The result of this study gave insight that the issue of ceftriaxone stability in oral formulation could be adequately addressed by tactical engineering of lipid drug delivery systems such as lipospheres.

Carriers in the topical treatment of skin disease

Topical drug application is less prone to severe systemic side-effects than systemic application. Starting with the liposomes, various types of nanosized and microsized drug carriers have been developed to increase the notoriously low penetration of active agents into the skin, which limits not only the topical therapy of skin disease but also transdermal therapy. Today, liposome- and microsponge-based preparations are approved for dermatomycosis, acne and actinic keratosis. Under investigation are drug carriers such as lipid nanoparticles, polymeric particles, dendrimers, and dendritic-core multi-shell nanotransporters. According to the rapidly increasing research in this field, both in academia and industry, a breakthrough appears likely, once stability problems (nanoparticles) and safety concerns (dendrimers) are overcome. Technical approaches and results of in vitro, ex vivo and in vivo testing are described, taking into account pharmacokinetic, efficacy and safety aspects.