Botulinum neurotoxin type DC (BoNT/DC) cleavage of VAMP3 reduces melanin production in melanocytes

Melanin in skin and hair protects cells from UV damage; however, uneven skin color or hyperpigmentation is a common aesthetic concern. Melanin is synthesized in melanosomes, organelles within melanocytes, where tyrosinase converts tyrosine to melanin. Trafficking of tyrosinase or other cargo (eg, premelanosome protein [PMEL]) may depend on vesicle-associated membrane proteins (VAMPs); interfering with VAMPs has been reported to impact melanogenesis. Botulinum neurotoxin type DC (BoNT/DC) is a naturally occurring mosaic serotype that cleaves the SNARE proteins VAMP1-3. This study evaluated BoNT/DC as a potential treatment for hyperpigmentation by testing if it affects melanogenesis. In melanocytes, BoNT/DC cleaved VAMP2 and VAMP3, and knockdown of VAMP3, but not VAMP2, reduced melanin content, which suggests that BoNT/DC may affect melanogenesis via VAMP3 cleavage. Indeed, BoNT/DC (5 nM) produced a ∼50 % reduction in melanin content in melanocytes, and in 2 human melanocyte models, BoNT/DC, but not BoNT/A, significantly reduced melanin content (∼40-50 %) without cytotoxicity. Electron microscopy showed that BoNT/DC-treated melanocytes contained more early-stage (II) and fewer late-stage (IV) melanosomes than vehicle- or BoNT/A-treated melanocytes. Overall, BoNT/DC reduced melanin content in multiple melanocyte models, and its lightening effects are likely due to VAMP3 cleavage interfering with trafficking of cargo (eg, tyrosinase, PMEL) required for melanogenesis.