L-Cystine-Containing Hair-Growth Formulation Supports Protection, Viability, and Proliferation of Keratinocytes.

Purpose: Clinical studies have confirmed that the hair-growth-promoting effect of approved oral drug combinations is beneficial for the treatment of diffuse telogen effluvium, which is characterized by the excessive loss of telogen club hairs. Since data elucidating the mode of action of such combinations are limited, our study focused on the identification of cellular processes potentially supporting the treatment of hair loss. Materials and Methods: A minimal growth culture system (MGM) was used to mimic in vitro the reduced activity of human hair follicular keratinocytes (HHFKs). The effect of four core compounds (L-cystine, thiamine, calcium D-pantothenate, and folic acid) of a marketed oral combination (Panto[vi]gar (R)), which are approved for the treatment of diffuse hair loss, was examined by comparing HHFKs cultured either with or without the com-pounds. After determining their impact on metabolic activity and proliferation, we conducted a comparative whole-genome gene expression study with subsequent functional grouping of differentially expressed genes to identify cellular processes influenced by the tested compounds. Results: The four core compounds of an oral hair-growth formulation enhanced proliferation and metabolic activity of HHFKs compared to HHFKs cultivated in MGM only. Functional grouping of differentially expressed genes confirmed the regulation of cell cycle-/proliferation-associated genes (cdk1, HJURP) and revealed regulation of cell death- and oxidative stress-associated gene groups. A supportive effect of the compounds on cell viability was demonstrated by lower sensitivity to solar-simulated UV-radiation and increased protection against oxidative stress. We established a central role for L-cystine, as changes in the expression of the anti-oxidative gene hmox1 were L-cystine-dependent. However, to reach a maximal stimulating effect on proliferation, the combination of all four compounds was necessary. Conclusion: The tested compound combination had positive effects on metabolic activity, cell viability, and proliferation of keratinocytes. Furthermore, this study suggested that L-cystine primarily contributes to the observed protection against endogenous oxidative stress.