Nonlinear Pharmacokinetics of Topical Flurbiprofen Gel in a Phase I Study Among Chinese Healthy Adults

INTRODUCTION

PDX-02 (Flurbiprofen sodium) is a topical nonsteroidal anti-inflammatory drug in gel formulation for local analgesia and anti-inflammation. A Phase I clinical trial was conducted to assess the safety, tolerability, and pharmacokinetics of single and multiple doses of PDX-02 gel in Chinese healthy adults.

METHODS

The trial comprised three parts: (1) a single-dose ascending study with three dose levels (0.5%, 1% to 2% PDX-02 gel) applied on a 136 cm2 skin area; (2) a multiple-dose study with either 1% or 2% PDX-02 gel applied on a 136 cm2 skin area for 7 consecutive days; and (3) a high dose group with 2% PDX-02 gel on an 816 cm2 skin area and a frequent multiple dose group with 2% PDX-02 gel on a 272 cm2 skin area four times a day for 7 consecutive days. The safety, tolerability and pharmacokinetics of the PDX-02 gel were evaluated in each part.

RESULTS

A total of sixty participants completed the trial, with all adverse events recovered and all positive skin reaction being transient and recovered. The overall absorption of topical PDX-02 gel was slow with a mean peak time exceeding 9 h. The elimination rate remained consistent between dose groups. A less-than-dose-proportional nonlinear pharmacokinetics relationship was observed within the studied dose range, and this is likely due to the autoinduction of skin first-pass metabolism.

CONCLUSION

The topical PDX-02 gel showed favorable safety and tolerability in both single and multiple dosing studies, with a less-than-dose-proportional nonlinear pharmacokinetics observed.

Human Skin Drug Metabolism: Relationships between Methyl Salicylate Metabolism and Esterase Activities in IVPT Skin Membranes

The presence of esterase enzymes in human skin and their role in drug metabolism has been reported, but their distribution in the various skin layers and the relative contributions of those layers to metabolism is poorly defined. To gain further insight into esterase distribution, we performed in vitro skin permeation of a commercial 28.3% methyl salicylate (MeSA) cream (Metsal™) in Franz diffusion cells, using a range of human skin membranes, all from the same donor. The membranes were viable epidermis separated by a dispase II enzymatic method, heat separated epidermis, dermatomed skin, and dermis separated by a dispase II enzymatic method. Methyl salicylate and its metabolite, salicylic acid (SA), were measured by high-performance liquid chromatography. Alpha naphthyl acetate and Hematoxylin and Eosin staining provided qualitative estimations of esterase distribution in these membranes. The permeation of methyl salicylate after 24 h was similar across all membranes. Salicylic acid formation and permeation were found to be similar in dermatomed skin and dermis, suggesting dermal esterase activity. These results were supported by the staining studies, which showed strong esterase activity in the dermal-epidermal junction region of the dermis. In contrast with high staining of esterase activity in the stratum corneum and viable epidermis, minimal stained and functional esterase activity was found in heat-separated and dispase II-prepared epidermal membranes. The results are consistent with dispase II digesting hemidesmosomes, penetrating the epidermis, and affecting epidermal esterases but not those in the dermis. Accordingly, whilst the resulting dispase II-generated dermal membranes may be used for in vitro permeation tests (IVPT) involving esterase-based metabolic studies, the dispase II-generated epidermal membranes are not suitable for this purpose.

Skin Metabolomics

Skin retains numerous low-molecular-weight compounds (metabolites). Some of these compounds fulfill specific physiological roles, while others are by-products of metabolism. The skin surface can be sampled to detect and quantify skin metabolites related to diseases. Miniature probes have been developed to detect selected high-abundance metabolites secreted with sweat. To characterize a broad spectrum of skin metabolites, specimens are collected with one of several available methods, and the processed specimens are analyzed by chromatography, mass spectrometry (MS), or other techniques. Diseases for which skin-related biomarkers have been found include cystic fibrosis (CF), psoriasis, Parkinson's disease (PD), and lung cancer. To increase the clinical significance of skin metabolomics, it is desirable to verify correlations between metabolite levels in skin and other biological tissues/matrices.

Comparison of the metabolism of 10 chemicals in human and pig skin explants

Skin metabolism is important to consider when assessing local toxicity and/or penetration of chemicals and their metabolites. If human skin supply is limited, pig skin can be used as an alternative. To identify any species differences, we have investigated the metabolism of 10 chemicals in a pig and human skin explant model. Phase I metabolic pathways in skin from both species included those known to occur via cytochrome P450s, esterases, alcohol dehydrogenases and aldehyde dehydrogenases. Common Phase II pathways were glucuronidation and sulfation but other conjugation pathways were also identified. Chemicals not metabolized by pig skin (caffeine, IQ and 4‐chloroaniline) were also not metabolized by human skin. Six chemicals metabolized by pig skin were metabolized to a similar extent (percentage parent remaining) by human skin. Human skin metabolites were also detected in pig skin incubations, except for one unidentified minor vanillin metabolite. Three cinnamyl alcohol metabolites were unique to pig skin but represented minor metabolites. There were notable species differences in the relative amounts of common metabolites. The difference in the abundance of the sulfate conjugates of resorcinol and 4‐amino‐3‐nitrophenol was in accordance with the known lack of aryl sulfotransferase activity in pigs. In conclusion, while qualitative comparisons of metabolic profiles were consistent between pig and human skin, there were some quantitative differences in the percentage of metabolites formed. This preliminary assessment suggests that pig skin is metabolically competent and could be a useful tool for evaluating potential first‐pass metabolism before testing in human‐derived tissues.

We have investigated the metabolism of 10 chemicals in viable pig and human skin. Phase I and II metabolic pathways were present in skin from both species. Chemicals not metabolized by pig skin were also not metabolized by human skin. Six chemicals metabolized by pig skin were also metabolized to a similar extent by human skin. Pig and human skin produced common metabolites, although some species differences were observed and as their relative amounts differed.

Antioxidant Nanoplatforms for Dermal Delivery: Melatonin

BACKGROUND

Melatonin is emerging as a promising therapeutic agent, mainly due to its role as antioxidant. Substantial evidences show that melatonin is potentially effective in a variety of diseases as cancer, inflammation and neurodegenerative diseases. The excellent antioxidant capacity with pharmacokinetics characteristics and the emerging search for new pharmaceutical nanotechnology based systems, make it particularly attractive to elaborate nanoplatforms based on melatonin for biomedical or cosmetic dermal applications. Different nanosystems for dermal delivery have been investigated.

OBJECTIVE

This review focuses on nanocarrier production strategies, dermal melatonin application and delivery advances in vivo and in vitro. Equally, future perspectives of this assisted melatonin delivery have also been discussed.

METHOD

In the current review, we have revised relevant articles of the available literature using the major scientific databases.

RESULTS

One hundred and thirteen papers were included in the review, the majority of which represent latest researches in nanosized platforms for the dermal delivery of melatonin including liposomes, ethosomes, niosomes, polymeric nanoparticles, solid lipid nanoparticles and cyclodextrins. Furthermore, relevant papers reporting in vitro and in vivo application studies of these nano-based melatonin platforms were also discussed.

CONCLUSION

The use of nanoplatforms for the dermal melatonin delivery as antioxidant agent could improve the efficacy of conventional melatonin administration due to the preservation of the drug from premature oxidation and the enhancement of drug permeation through the skin providing greater exposure times.

Effect of Repeated Daily Dosing with 2,4-Dinitrochlorobenzene on Glutathione Biosynthesis and Nrf2 Activation in Reconstructed Human Epidermis

Glutathione (GSH) plays a major role in skin detoxification processes due to its ability to conjugate electrophilic exogenous compounds with, and sometimes without, catalysis by glutathione-s-transferase (GST). GST activity has been demonstrated both in skin and in most in vitro skin equivalents but so far studies have focussed on chemical clearance (conjugate identification and rate of conjugation) and did not consider the GSH lifecycle (conjugation, recycling, synthesis). We used the model skin sensitizer 2,4-dinitrochlorobenzene (DNCB) to investigate the effects of chemical exposure on GSH lifecycle in reconstructed human epidermis (RHE). We demonstrated that the RHE model is suitable to carry out repeated cycles of 2-h exposure to DNCB over a 3-day period. After each exposure to DNCB, the level of GSH is diminished in a dose dependent manner. After a 22-h recovery period, GSH is replenished back to initial levels. Accumulation of the nuclear factor E2-related factor 2 (Nrf2) in the cytosol also occurs within the 2 h of exposure to DNCB but returns to baseline during each recovery period, demonstrating that activation of the Nrf2 signaling pathway offers a rapid response to chemical stress. The amount of dinitrophenyl-glutathione (DNP-SG) formed with DNCB (1) increased between the first and second exposure and (2) reached a plateau between the second and third exposure. Collectively, these data suggest that the metabolic capacity of skin may not be fixed in time but defence mechanisms might be activated in response to exposure to exogenous compounds, resulting in their accelerated clearance.