title: Ammonium chloride and L-tyrosine enhance melanogenesis in vitro but not in vivo even in combination with ultraviolet radiation.
abstract: OBJECTIVE
  Melanogenesis can be induced in vitro in melanoma cells and melanocytes by adding substances able to neutralize intracellular acidic organelles like melanosomes. Further addition of l-tyrosine enhances the melanogenesis by increasing the tyrosinase activity. As such, the property of tyrosine as a pigmentation enhancer is used in promoting creams containing tyrosine. The objective of this study was to investigate whether such an effect could actually be seen in a short term in vivo mouse study.
  
  
  METHODS
  Lightly pigmented C3.Cg/TifBomTac hairless mice capable of pigmenting had ammonium chloride (NH4Cl) and/or l-tyrosine applied topically (1/day for 3 weeks). Pigmentation of the mice was determined using the Kodak Gray Scale at days 0, 7, 14, and 21.
  
  
  RESULTS
  Both NH4Cl and l-tyrosine yielded no significant effect, either alone or in combination, when applied using either hydrogel or moisturizing cream. Exposing mice to simulated solar radiation (4 standard erythema doses, 3/week) yielded increased pigmentation. However, no statistically significant difference was found between treatment with simulated solar radiation alone or in combination with NH4Cl and l-tyrosine.
  
  
  CONCLUSIONS
  In spite of the commercial value of adding l-tyrosine to 'pigmentation-enhancing' creams, topically applied l-tyrosine showed no pigmentation-enhancing effect, neither alone nor in combination with ultraviolet (UV) radiation, providing a basis to contest such promotional measures.
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, Copenhagen, Denmark. bm14@bbh.regionh.dk
authors.forename: Brian
authors.initials: B
authors.lastname: Kongshoj
authors.forename: Nikolaj Dam
authors.initials: ND
authors.lastname: Mikkelsen
authors.forename: Takasi
authors.initials: T
authors.lastname: Kobayasi
authors.forename: Catharina Margrethe
authors.initials: CM
authors.lastname: Lerche
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D008543:Melanins / Q000096:biosynthesis*; D051379:Mice; D008812:Mice, Hairless; D008854:Microscopy, Electron; D014443:Tyrosine / Q000494:pharmacology*; D014466:Ultraviolet Rays