Sensitive and simultaneous quantification of zinc pyrithione and climbazole deposition from anti-dandruff shampoos onto human scalp

Seborrheic dermatitis: topical therapeutics and formulation design

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

Targeted Delivery of Zinc Pyrithione to Skin Epithelia

Zinc pyrithione (ZnPT) is an anti-fungal drug delivered as a microparticle to skin epithelia. It is one of the most widely used ingredients worldwide in medicated shampoo for treating dandruff and seborrheic dermatitis (SD), a disorder with symptoms that include skin flaking, erythema and pruritus. SD is a multi-factorial disease driven by microbiol dysbiosis, primarily involving Malassezia yeast. Anti-fungal activity of ZnPT depends on the cutaneous availability of bioactive monomeric molecular species, occurring upon particle dissolution. The success of ZnPT as a topical therapeutic is underscored by the way it balances treatment efficacy with formulation safety. This review demonstrates how ZnPT achieves this balance, by integrating the current understanding of SD pathogenesis with an up-to-date analysis of ZnPT pharmacology, therapeutics and toxicology. ZnPT has anti-fungal activity with an average in vitro minimum inhibitory concentration of 10-15 ppm against the most abundant scalp skin Malassezia species (Malassezia globosa and Malassezia restrica). Efficacy is dependent on the targeted delivery of ZnPT to the skin sites where these yeasts reside, including the scalp surface and hair follicle infundibulum. Imaging and quantitative analysis tools have been fundamental for critically evaluating the therapeutic performance and safety of topical ZnPT formulations. Toxicologic investigations have focused on understanding the risk of local and systemic adverse effects following exposure from percutaneous penetration. Future research is expected to yield further advances in ZnPT formulations for SD and also include re-purposing towards a range of other dermatologic applications, which is likely to have significant clinical impact.

Effect of zinc pyrithione shampoo treatment on skin commensal Malassezia

Malassezia restricta and Malassezia globosa are lipid dependent commensal yeasts associated with dandruff. Antifungal actives such as zinc pyrithione are commonly used in antidandruff shampoos, although their efficacy is not clearly demonstrated. In this study, we assessed the efficacy of antifungal treatments on scalp Malassezia via a combination of culturomic and genomic detection methods. Zinc pyrithione inhibited Malassezia growth at low minimum inhibitory concentrations (MICs). In a longitudinal pilot study, quantitative polymerase chain reaction (qPCR) analysis showed a decrease in M. restricta on the scalp after zinc pyrithione treatment. These findings validate the antifungal efficacy of zinc pyrithione as a dandruff treatment.

LAY ABSTRACT

Malassezia yeasts are associated with dandruff and seborrheic dermatitis. Zinc pyrithione is effective against Malassezia growth in vitro and when tested on human skin as a shampoo. These findings will be useful for investigating the role of Malassezia in skin microbiome intervention studies.

A validated LC-MS/MS method for the quantification of climbazole metabolites in human urine

Climbazole is a preservative and an anti-dandruff ingredient with applications in various cosmetic products. The general population is therefore exposed to this chemical, and exposure monitoring is desirable. We have postulated a pathway for the human metabolism of climbazole, leading to two specific metabolites which can be excreted via urine. An analytical method for the determination of these metabolites in human urine was developed and validated. The sample preparation includes an enzymatic hydrolysis protocol. The measurement as such is based on online solid phase extraction (SPE), coupled to ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Intra- and inter-series coefficients of variation (CV) were determined in the concentration range from 1 µg/l to 100 µg/l with spiked pooled urine samples, and they were consistently below 15%, mostly below 10%. The corresponding accuracies (mean relative recovery rates) in spiked pooled urine varied from 97% to 103%. The robustness of the method was estimated by spiking individual urine samples. At 1 µg/l, the robustness was rather limited due to interfering matrix peaks in several samples, but excellent results were obtained at 10 µg/l and 100 µg/l, with CVs between 7% and 14% and accuracies from 101% to 110%. Matrix interferences often seemed to be associated with higher creatinine contents (≥2.0 g/l) of the samples. We subsequently applied the method to urine specimens from a human metabolism study involving documented climbazole exposures. We were able to identify and quantify the postulated metabolites in those real samples, thus validating our metabolism hypothesis. We also investigated the precision and accuracy of the enzymatic deconjugation with the real samples. The deconjugation step was found to be highly repeatable and largely quantitative. Both metabolites formed glucuronides, though varying fractions were also excreted in unconjugated (free) forms. Phase II conjugates other than glucuronides did not seem to be produced in significant amounts. With our method, both climbazole metabolites can be reliably quantified in the range between about 1.5 µg/l (depending on matrix interferences in individual samples) and at least 500 µg/l.

Topical delivery of climbazole to mammalian skin

Dandruff is a common condition, affecting up to half the global population of immunocompetent adults at some time during their lives and it has been highly correlated with the over-expression of the fungus Malassezia spp. Climbazole (CBZ) is used as an antifungal and preservative agent in many marketed formulations for the treatment of dandruff. While the efficacy of CBZ in vitro and in vivo has previously been reported, limited information has been published about the uptake and deposition of CBZ in the skin. Hence, our aim was to investigate the skin permeation of CBZ as well as the influence of various solvents on CBZ skin delivery. Four solvents were selected for the permeability studies of CBZ, namely propylene glycol (PG), octyl salicylate (OSal), Transcutol® P (TC) and polyethylene glycol 200 (PEG). The criteria for selection were based on their wide use as excipients in commercial formulations, their potential to act as skin penetration enhancers and their favourable safety profiles. 1% (w/v) solutions of CBZ were applied under infinite and finite dose conditions using Franz type diffusion cells to human and porcine skin. In line with the topical use of CBZ as an antidandruff agent, comparatively low amounts of CBZ penetrated across the skin barrier (<1% of the applied dose of CBZ). Finite dose studies resulted in a higher extraction of CBZ from human skin compared with infinite dose studies (p < 0.05). CBZ was also taken up to a higher extent in porcine skin (>7-fold) compared with human skin (p < 0.05). Nevertheless, no statistical differences were observed in the amounts that permeated across the different membranes. These preliminary results confirm the potential of simple formulations of CBZ to target the outer layers of the epidermis. The PG and OSal formulations appear to be promising vehicles for CBZ in terms of overall skin extraction and penetration. Future work will expand the range of vehicles studied and explore the reasons underlying the retention of CBZ in the outer layers of the skin.

Visualization of zinc pyrithione particles deposited on the scalp from a shampoo by tape-strip sampling and scanning electron microscopy/energy dispersive X-ray spectroscopy measurement

OBJECTIVE

Zinc pyrithione (ZnPT) is widely used as an anti-fungal active in commercial anti-dandruff (AD) shampoos. The AD efficacy of ZnPT is highly dependent on the deposition of ZnPT particles onto the scalp during the process of shampoo application and rinse-off. Since ZnPT materials with different particle sizes and morphologies have different deposition behaviours, the measurement of the actual ZnPT deposition is critical to understand the AD performance delivered by different ZnPT shampoos. The aim of this study is to develop a robust and reliable method for visualizing the particle size and morphology of ZnPT deposited on the scalp from AD shampoos.

METHODS

Hair was washed with a commercially available AD shampoo containing ZnPT and zinc carbonate (ZnCO₃ ). Tape strips were applied to collect the deposited particles from the scalp after AD shampoo application and rinse-off. The scalp tape strip samples were subjected to scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) measurement. The morphology of the ZnPT particles was visualized by SEM imaging and identification of ZnPT particles was confirmed by EDX analysis.

RESULTS

For the commercial shampoo studied it was observed that two zinc-containing particulates with different morphologies and composition remained on the scalp after shampoo application and rinse-off. As indicated by the EDX spectra, the ZnPT particles deposited onto the scalp surface had polygonal crystal structures. ZnCO₃ was also deposited onto the scalp surface. This material was mainly present as aggregated particulates.

CONCLUSION

An ex vivo method that combines tape strip sampling and SEM/EDX has been developed for measuring and visualizing the particle size, morphology and composition of ZnPT deposited on the scalp from AD shampoos. This ex vivo measurement method provides higher imaging resolution and more chemical specificity than reflectance confocal microscopy (RCM). To the best of our knowledge, this is the first time that ZnPT particles were distinguishable from other zinc particles on the scalp. Moreover, the new method allows the microstructures of both ZnPT and other zinc particles on the scalp to be imaged.

Zinc-containing compounds for personal care applications

It is well-known that zinc ions are widely used in cosmetic products. Their popularity is associated with the multifunctional profile of Zn²⁺ , which is classified as an essential chemical element in the human body. This review examines numerous beneficial biological properties of zinc-containing compounds and classifies the compounds used in cosmetic products according to their functionality profile: antioxidant, sunscreen, anti-inflammatory, anti-pigmentation, anti-ageing, anti-acne, antimicrobial, anti-odour, cleansing or stabilizing activity. It also underlines the significance of zinc in enzymatic processes, which depends on the enzyme type acts as inhibitor or enzymatic stimulator. Moreover, the article describes the chemical nature of the most interesting groups of Zn compounds.

Imaging microscopic distribution of antifungal agents in dandruff treatments with stimulated Raman scattering microscopy

Treatment of dandruff condition usually involves use of antidandruff shampoos containing antifungal agents. Different antifungal agents show variable clinical efficacy based on their cutaneous distribution and bioavailability. Using stimulated Raman scattering (SRS), we mapped the distribution of unlabeled low-molecular weight antifungal compounds zinc pyrithione (ZnPT) and climbazole (CBZ) on the surface of intact porcine skin with cellular precision. SRS has sufficient chemical selectivity and sensitivity to detect the agents on the skin surface based on their unique chemical motifs that do not occur naturally in biological tissues. Moreover, SRS is able to correlate the distribution of the agents with the morphological features of the skin using the CH 2 stretch mode, which is abundant in skin lipids. This is a significant strength of the technique since it allows the microscopic accumulation of the agents to be correlated with physiological features and their chemical environment without the use of counter stains. Our findings show that due to its lower solubility, ZnPT coats the surface of the skin with a sparse layer of crystals in the size range of 1 to 4 ?? ? m . This is consistent with the current understanding of the mode of action of ZnPT. In contrast, CBZ being more soluble and hydrophobic resulted in diffuse homogeneous distribution. It predominantly resided in microscopic lipid-rich crevasses and penetrated up to 60 ?? ? m into the infundibular spaces surrounding the hair shaft. The ability of the SRS to selectively map the distribution of agents on the skin’s surface has the potential to provide insight into the mechanisms underpinning the topical application of antifungal or skin-active agents that could lead to the rational engineering of enhanced formulations.