| Summary: | Lipidology, or the scientific investigation of cellular lipids in biological systems, as well as their pathways and networks, is becoming an increasingly integral component in the investigation of metabolic disease and, outside the healthcare fields, in the elucidation of adaptations to specific environmental stressors. Sphingolipid and whole phospholipid profiles were examined in several species of marine mammals (and in two tissue types in one marine mammal species), as well as in the skeletal muscle of obese, pre-diabetic mice. The fatty acid composition of the cells (the sum total of intracellular lipid and the fatty acids of membrane phospholipids) was also examined in obese, pre-diabetic skeletal muscle of the mouse. Marine mammal species were compared based on diving ability. Shallower divers (harbor seals, Phoca vitulina) demonstrated significantly higher C16 ceramide, 16:0 sphingomyelin, and dipalmitoylphosphatidylcholine (DPPC) levels compared to deeper divers (Weddell seals, Leptonychotes weddellii). Additionally, in comparing ringed seal (Pusa hispida) skeletal muscle to liver tissue, liver tissue showed significantly higher levels of C16:0 sphingomyelin, dipalmitoylphosphatidlycholine, and C16 ceramide. Pre-diabetic mice were found to have no significant changes in sphingolipids or whole phospholipids after high-fat diet (HFD) feeding compared to controls, but had statistically significant elevations of PUFAs (particularly omega-6s), and statistically significant declines in MUFAs. These results suggest that harbor seals are under greater stress than Weddell seals, based on upregulated levels of C16 ceramide and 16:0 sphingomyelin, and this increased stress likely results from an increased time at depth. Likewise, the liver of ringed seals shows significant signs of physiological stress, but here, the difference may be one of varying blood flow between the liver and skeletal muscle during diving. DPPC levels were higher in ringed seal liver, as well as harbor seal skeletal muscle, suggesting these ...
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