Non-Invasive Visualization of Melanin and Melanocytes by Reflectance-Mode Confocal Microscopy

Abstract

In vivo visualization of epidermal melanin was performed by reflectance-mode confocal microscopy (RCM). Firstly, we examined the distribution of epidermal melanin in pigmented animals and compared with that of the human skin. Melanocytes in the skin of pigmented animals were found to accumulate a large amount of melanin that can be easily visualized because of its brightness. Their RCM images correlated well with the Fontana-Masson-stained sections for melanin. In contrast, in the human skin, typical dendritic melanocytes were hardly observed even in pigmented lesions, although supranuclear melanin caps were easily visible. These results suggested that human melanocytes rapidly transfer the produced melanin to keratinocytes and do not accumulate it. Secondly, to elucidate the production of melanin by human melanocytes, we evaluated the changes of melanin after a single ultraviolet (UV) exposure. The melanin-accumulating melanocytes were clearly visualized during the skin pigmentation process. The RCM images showed the brightness because of melanin gradually increased from day 4, then dendrite-elongated melanocytes appearing from day 8, and finally melanin caps formed from day 29. In conclusion, RCM successfully evidenced the difference in melanin distribution between the pigmented animals and humans, and the UV-induced pigmentation process in vivo as well.

Ethnic skin types: are there differences in skin structure and function?1

“…It has been reported that in type III (French) skin nuclear melanin caps were absent from basal keratinocytes in subjects tanned during their vacation period [23]. This has recently also been demonstrated in Japanese subjects [24]. This would indicate that the initial stages of the tanning process come from a redistribution of already preformed melanin and/or transfer of already synthesized melanosomes to suprabasal keratinocytes.…”

Complete Regression of a Melanocytic Nevus under Intense Pulsed Light Therapy for Axillary Hair Removal in a Cosmetic Center

“…These melanosome accumulations (melanosome clusters or packaged melanosomes) form cap-like structures over the nuclei of keratinocytes to protect the nuclei from the damaging effects of ultraviolet radiation. The highest density of melanin is present in the epidermal basal layer as supranuclear melanin caps [3]. …”

In vivo reflectance confocal microscopy imaging of melanocytic skin lesions: Consensus terminology glossary and illustrative images

“…The appearance of normal skin on RCM has been described to a limited extent. 1,15,16 Part of this work has been done using direct correlation with histology using horizontal tissue sectioning. 1 Without doubt, the intraindividual variation in RCM attributes of normal skin for different body sites (eg, trunk vs extremity), as well as the interindividual , compatible with pigmented basal keratinocytes, are aggregated almost back-to-back, in a cobblestone pattern.…”