Depilatory chemical thioglycolate affects hair cuticle and cortex, degrades epidermal cornified envelopes and induces proliferation and differentiation responses in keratinocytes

• Published in: Experimental dermatology 2019-01, Vol.28 (1), p.76-79
• Main Authors: Duit, Rebecca, Hawkins, Tim J., Määttä, Arto
• Format: Article
• Language: English
• Subjects: Cell Differentiation - drug effects; Cell Line; Cell Proliferation - drug effects; Dermatologic Agents - pharmacology; Drug delivery; Electron microscopy; Envelopes; Enzyme inhibitors; Epidermis; Female; fluorescence lifetime imaging; Fluorophores; hair; Hair - diagnostic imaging; Hair - drug effects; Hair - ultrastructure; Hair Removal; Heat shock proteins; HSP27 Heat-Shock Proteins - metabolism; Hsp27 protein; HSP70 Heat-Shock Proteins - metabolism; Hsp70 protein; Humans; JNK Mitogen-Activated Protein Kinases - antagonists & inhibitors; JNK protein; keratinocyte differentiation; Keratinocytes; Keratinocytes - physiology; label‐free imaging; Microscopy, Confocal; Microscopy, Electron; Microscopy, Fluorescence; Neuroimaging; Protein Kinase Inhibitors - pharmacology; Protein Precursors - antagonists & inhibitors; Protein Precursors - metabolism; Protein structure; Stratum corneum; stress signalling; Thioglycolates - pharmacology
• ISSN: 0906-6705; 1600-0625
• DOI: 10.1111/exd.13838

Thioglycolate is a potent depilatory agent. In addition, it has been proposed to be useful as a penetration enhancer for transepidermal drug delivery. However, the effects on hair structure and stress responses it elicits in epidermal keratinocytes have not been fully characterised. We have used label‐free confocal and fluorescence lifetime imaging supported by electron microscopy to demonstrate how thioglycolate damages hair cuticle cells by generating breakages along the endocuticle and leading to swelling of cortex cells. Maleimide staining of free SH‐groups and a decrease in the average fluorescence lifetime of endogenous fluorophores demonstrate a specific change in protein structure in both hair cuticle and cortex. We found that the thioglycolate damages cornified envelopes isolated from the stratum corneum of the epidermis. However, thioglycolate‐treated epidermal equivalent cultures recover within 48 hours, which highlights the reversibility of the damage. HaCaT keratinocytes respond to thioglycolate by increased proliferation, onset of differentiation and expression of the chaperone protein Hsp 70, but not Hsp 27. Up‐regulation of involucrin can be blocked by an application of c‐Jun N–terminal kinase (JNK) inhibitor, but the up‐regulation of Hsp 70 takes place regardless of the presence of the JNK inhibitor.