Chemical properties of epidermal lipids, especially sphingolipids, of the Antarctic minke whale

It is well known that sphingolipids specifically exist in the terrestrial mammal epidermis and correlate with skin barrier functions. However, the lipid properties of the marine mammal epidermis have not been examined in detail. We thus investigated the chemical composition of lipid components, especially sphingolipids, in the black epidermis (outer skin) of Antarctic minke whales (six mature and six immature specimens). Complex lipid fractions mainly contained cerebroside (CE), cholesteryl sulfate and sphingomyelin (SM), as well as two glycerophospholipids. Moreover, in the superficial layer of the black epidermis, CE was richly abundant but phospholipids were scarce. As component fatty acids, the nonhydroxy monounsaturated very long chain fatty acids (VLFA) within 34 carbons were generally present in CE and SM in the black epidermis. CE also consisted of alpha-hydroxy fatty acids with monounsaturation within C34 (17%) and a slight proportion of omega-hydroxy ones (32:1 and 34:1), the latter being probably derived from acyl-CE. Component sphingoid bases of both sphingolipids were predominantly 4-sphingenine (64%), followed by a C16 analogue (21%). When comparing these by different maturities, mature whales showed sphingolipid profiles with higher levels of unsaturated fatty acids and with shorter sphingoid base chains than those of immature ones. Component analysis revealed that CE sugars were 67% glucose and 33% galactose, and alpha-hydroxy fatty acids only bound to galactose.