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To the Editor: Identifying human anagen hair follicles (HFs) ex vivo is readily accomplished by stereomicroscopic analysis. However, to reliably distinguish other hair cycle stages, namely late catagen and telogen, by stereomicroscopic analysis alone is difficult, and the gold standard remains histologic analysis, which obviously precludes their use for ex vivo culture.
helps to distinguish late catagen from telogen HFs intravitally for subsequent organ culture, thus expanding translational preclinical research into these poorly investigated, but clinically important, human hair cycle stages.
Using follicular unit hair transplantation methodology (by grouping follicular units on the basis of the number of HFs they contain),
we recorded the number of anagen, catagen, and telogen follicles found in 800 follicular units from 8 white male patients (100 follicular units/patient) undergoing a standardized follicular unit extraction hair transplant procedure, with informed patient consent. Because anagen VI follicles are easily identifiable,
such as the identification of a prominent epithelial strand (Fig 1, A), a key feature of late catagen HFs that is absent in telogen HFs. Correct hair cycle stage classification by this method was confirmed by Ki67 and TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) immunofluorescence microscopy (Fig 1, D).
Importantly, methylene blue staining enabled correct identification of the hair stage of 95.63% of cases, compared with 72.02% of nonmethylene blue–stained HFs. Thus, this simple, economical, and fast technique constitutes a significant methodologic advance in human hair research, since it facilitates ex vivo research on human catagen and telogen HFs without having to resort to histology.
Our analyses revealed a higher percentage of catagen than telogen HFs in all patients (89% anagen, 6.7% catagen, and 3.6% telogen). This data support the previous proposal that the percentage of scalp telogen HFs has been overestimated
and photo-trichograms, neither of which can definitively distinguish between late catagen and telogen HFs. Although, in our study, the HFs were from patients with androgenetic alopecia (AGA) and the ratio of anagen:catagen:telogen might differ in comparison with individuals without AGA, we believe that our data are unlikely to reflect sampling bias, as HFs were harvested from occipital scalp, generally unaffected by AGA. We propose that hair stage distribution in healthy human scalp needs a more systematic re-evaluation, including comparative studies with histologic sections. This is important when assessing candidate hair growth–modulating agents, considering minor shifts in the percentage of telogen or catagen HFs can result in major changes in the degree of visible effluvium.
van Beek N.
Methods in hair research: how to objectively distinguish between anagen and catagen in human hair follicle organ culture.
Drs Alam and Platt contributed to this work equally.
Funding sources: Supported in part by a basic translational research grant from Unilever, Colworth, United Kingdom (to Dr Paus), by Monasterium Laboratory, Münster, Germany, and by the National Institute of Health Research Manchester Biomedical Research Centre (Inflammatory Hair Diseases program).