Abstract
To assess whether vertebrates can acquire, from their diet, ultraviolet radiation-absorbing mycosporine-like amino acids (MAAs), medaka fish and hairless mice were maintained for 150 and 130 days, respectively, on diets either including Mastocarpus stellatus (rich in MAAs) or the same diets without this red alga. In medaka, the MAAs palythine and asterina-330, present in trace quantities in the diet with added M. stellatus, were present in significantly greater quantities in the eyes of fish fed this diet than in the eyes of control fish. Only traces of MAAs were present in the skin of medaka fed the diet containing MAAs. Shinorine, the principal MAA in M. stellatus, was not found in any tissues of medaka, which raises questions about the specificity of transport of MAAs. In hairless mice, no dietary MAAs were found in the tissues of the eyes, skin, or liver after maintenance on the experimental diet. Low concentrations of shinorine were present only in the tissues of the small and large intestines. These results indicate that MAAs are acquired from their diet and translocated to superficial tissues by teleost fish, but that mammals may be incapable of such. Thus, dietary supplementation with MAAs may be useful in aquacultured species of fish, but MAAs as `dietary sunscreens' may not be an option for mammals, including humans. Nevertheless, our demonstration of the uptake of shinorine by human skin cancer cells in culture raises evolutionary questions regarding the organ specificity of the capacity for the cellular transport of MAAs.
