Ultraviolet radiation is the major environmental insult to the skin and stimulates the synthesis of
melanin in melanocytes, which then distribute it to the neighboring keratinocytes where it confers photo-protection. Skin color results from the paracrine interaction between these two cell types. Recent studies suggest that
endocannabinoids are potential mediators in the skin. Here, we investigated whether
cannabinoid drugs play a role in melanogenesis and if ultraviolet radiation modifies the cutaneous
endocannabinoid system. We used human melanotic
melanoma cell line (SK-mel-1) in monoculture or co-culture with human keratinocytes (HaCat).
Endocannabinoid levels,
cannabinoid receptors expression, and
melanin content were evaluated under basal conditions and after ultraviolet-B irradiation (311 nm). We provide evidence that human
melanoma cells (SK-mel-1) express CB(1) receptors, and when in co-culture with keratinocytes (HaCat), the selective CB(1) receptor agonist
arachidonyl-2-chloroethylamide (ACEA 1 and 10 μM) inhibited (by 33.4 and 37.3%, respectively) basal melanogenesis. In addition, ultraviolet-B-induced melanogenesis in co-cultures was abolished by ACEA 10 μM. Both ACEA inhibitory effects were reversed by
AM251 (1 μM), a selective CB(1) antagonist. Furthermore, ultraviolet-B radiation increased
endocannabinoids levels only in keratinocytes, whereas CB(1)
cannabinoid receptor expression was up-regulated only in
melanoma cells. Our results collectively suggest that ultraviolet radiation activates paracrine CB(1)-mediated
endocannabinoid signaling to negatively regulate
melanin synthesis. The
endocannabinoid system in the skin may be a possible target for future
therapies in pigmentary disorders.