Fluoxetine promotes human hair follicle pigmentation ex vivo: serotonin reuptake inhibition as a new antigreying strategy?
DEAR EDITOR, The commonly prescribed antidepressant, fluoxetine, has been reported to (rarely) induce epidermal hyperpigmentation after systemic application.1 This selective serotonin reuptake inhibitor (SSRI) can also stimulate melanin production in murine hair follicles (HFs) in vivo under conditions of perceived stress and in cultured human epidermal melanocytes in vitro.2,3 Given the distinct neuroendocrine controls that human HF melanocytes underlie compared with epidermal melanocytes,4and that any pigmentary effects of fluoxetine observed in vivo may have been indirectly mediated, it remains entirely unclear whether fluoxetine impacts directly on human HF pigmentation, specifically in the absence of systemic and neural inputs. In the current pilot study we explored this question after determining the presence of the serotonin transporter and serotonin receptors 1A and 2A at the mRNA and protein levels (data not shown).
Specifically, we asked whether fluoxetine (chosen among other SSRIs for its long half‐life and known pigmentary effect in mice)2,3 can alter the pigmentation of microdissected, organ‐cultured human scalp HFs, using our previously reported HF pigmentation readouts and established protocols.5,6Pigmented, full‐length scalp HFs in anagen VI (obtained from facelift surgery of female donors after written patient consent and ethics approval) were treated for 48 h with 100 nmol L−1 and 1 μmol L−1fluoxetine in serum‐free supplemented Williams’ E medium.5,6 Given the very limited availability of human HFs, the fluoxetine test concentrations were selected based on previously published results.2
Quantitative Masson–Fontana histomorphometry showed that fluoxetine further and significantly increased melanin production in the HF pigmentary unit of already maximally pigmented anagen VI HFs ex vivo (Fig. 1a). This provides the first evidence that fluoxetine can directly stimulate human HF pigmentation in the absence of systemic or neural inputs.
As white HFs occasionally retain a few functionally active melanocytes in their pigmentary unit,7 we next asked whether fluoxetine can stimulate some degree of repigmentation in a very small number of white HFs isolated from five female donors with > 50% canities over a period of ≥ 6 years. These HFs were obtained from 6‐mm punches collected by a contract research organization after receiving written patient consent and ethics approval. Strikingly, fluoxetine induced significant restimulation of intrafollicular melanin production after 6 days of HF organ culture, as measured by quantitative Masson–Fontana histomorphometry (Fig. 1c). This was accompanied by a tendency for upregulation of gp100 immunoreactivity (data not shown), indicating increased premelanosome production and melanocyte activity.5,6 This preliminary evidence in a low number of HFs suggests that at least some canities‐affected HFs can, in principle, be reactivated by fluoxetine to produce melanin
Given that α‐melanocyte‐stimulating hormone (MSH) is a key neuroendocrine stimulator of human HF pigmentation and is synthesized within human anagen scalp HFs,4 and that fluoxetine can modulate the expression and production of α‐MSH in rats and humans,8 we next investigated the effect of fluoxetine on this melanotropic neurohormone. Immunofluorescence microscopy for α‐MSH was performed on anagen HFs and assessed by quantitative immunohistomorphometry in a defined reference area (proximal outer root sheath). This showed that 1 μmol L−1 fluoxetine slightly, but not significantly, stimulated α‐MSH protein expression. While overall this did not reach statistical significance, individual HFs showed a marked increase of α‐MSH immunoreactivity (Fig. 1b). Essentially the same effect was seen in white HFs (Fig. 1d).
Given the low number of HFs we could analyse, the current pilot data are obviously preliminary and require rigorous reproduction in additional HFs from more individuals. However, our preliminary observations strongly suggest that fluoxetine directly promotes human HF pigmentation and may even reverse the depigmentation of at least some ‘white’ female human scalp HFs. Furthermore, the observation that fluoxetine can also upregulate the intrafollicular production of a melanotropic neurohormone (α‐MSH) in some white HFs of women with long‐standing canities suggests that this SSRI may exert longer‐lasting, neuroendocrine changes within white HFs. This would facilitate HF repigmentation by enhancing the capacity of ‘white’ HFs to restore their pigmentation production capacity before the point of no return in HF greying, i.e. when HF melanocyte stem cells have been lost.
The obvious clinical key challenge now is to study whether the observed ex vivo effects of fluoxetine translate to the in vivo situation (ideally after topical application) and to dissect whether or not topical application of this SSRI also stimulates epidermal hyperpigmentation, which would be undesired in the scalp skin of most individuals undergoing hair greying. In any case, our pilot study strongly encourages systematic exploration of fluoxetine as a candidate hair antigreying agent.
