Lipid status of the two high latitude fish species, Leptoclinus maculatus and Lumpenus fabricii

Partitioning into phosphatidylcholine-cholesterol membranes: liposome measurements, coarse-grained simulations, and implications for bioaccumulation

Membrane-water partitioning is an important physical property for the assessment of bioaccumulation and environmental impact. Here, we advance simulation methodology for predicting the partitioning of small molecules into lipid membranes and compare the computational predictions to experimental measurements in liposomes. As a step towards high-throughput screening, we present an automated mapping and parametrization procedure to produce coarse-grained models compatible with the Martini 3 force field. The methodology is general and can also be used for other applications where coarse-grained simulations are appropriate. This article addresses the effect on membrane-water partitioning of adding cholesterol to POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) membranes. Nine contrasting neutral, zwitterionic and charged solutes are tested. Agreement between experiment and simulation is generally good, with the most challenging cases being permanently charged solutes. For all solutes, partitioning is found to be insensitive to membrane cholesterol concentration up to 25% mole fraction. Hence, for assessment of bioaccumulation into a range of membranes (such as those found in fish), partitioning data measured in pure lipid membranes are still informative.

Lipid profiling suggests species specificity and minimal seasonal variation in Pacific Green and Hawksbill Turtle plasma

In this study, we applied multiple reaction monitoring (MRM)-profiling to explore the relative ion intensity of lipid classes in plasma samples from sea turtles in order to profile lipids relevant to sea turtle physiology and investigate how dynamic ocean environments affect these profiles. We collected plasma samples from foraging green (Chelonia mydas, n = 28) and hawksbill (Eretmochelys imbricata, n = 16) turtles live captured in North Pacific Costa Rica in 2017. From these samples, we identified 623 MRMs belonging to 10 lipid classes (sphingomyelin, phosphatidylcholine, free fatty acid, cholesteryl ester, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, phosphatidylethanolamine, ceramide, and triacylglyceride) and one metabolite group (acyl-carnitine) present in sea turtle plasma. The relative ion intensities of most lipids (80%) were consistent between species, across seasons, and were not correlated to body size or estimated sex. Of the differences we observed, the most pronounced was the differences in relative ion intensity between species. We identified 123 lipids that had species-specific relative ion intensities. While some of this variability is likely due to green and hawksbill turtles consuming different food items, we found indications of a phylogenetic component as well. Of these, we identified 47 lipids that varied by season, most belonging to the structural phospholipid classes. Overall, more lipids (n = 39) had higher relative ion intensity in the upwelling (colder) season compared to the non-upwelling season (n = 8). Further, we found more variability in hawksbill turtles than green turtles. Here, we provide the framework in which to apply future lipid profiling in the assessment of health, physiology, and behavior in endangered sea turtles.

The lipid metabolism in carp during invasion by the tapeworn Bothriocephalus acheilognathi

The changes in total lipids, their fatty acid composition and the ratio of individual classes were established in tissues of the intestine, hepatopancreas and skeletal muscles of carp (Cyprinus carpio Linnaeus, 1758), with body weight 14.5–20.5 g, at different rates of invasion by Bothriocephalus acheilognathi (Yamaguti, 1934) helminth, which belongs to the family Bothriocephalidae, of the Pseudophyllidae order, of the Cestoda class. The examined carp was divided into three groups: first group of fish was free from intestinal helminths of B. acheilognathi (control); second group of fish was weakly infected with helminths (intensity of invasion is 1–3 helminths per fish); the third group of fish was highly infected (the invasion intensity is 4 worms and more per fish). Our results showed that fish infected with helminth B. acheilognathi compared to uninfected fish had reduced total lipid level in the gut due to phospholipids, triacylglycerols, and also lipids were characterized by lower content of linoleic, linolenic, arachidonic, penta- and hexanoic fatty acids; decrease in the level of unsaturated and increase in the content of saturated fatty acids, which leads to an increase of the saturation factor. During the infection of carp with B. acheilognathi in the hepatopancreas, the content of total lipids, structural lipids – phospholipids and reserve energy sources – triacylglycerols is probably reduced, and lipids are characterized by a high content of saturated fatty acids (С14:0, С16:0, С18:0) and lower content of unsaturated: arachidonic (С20:4), linolenic (С18:3) and linoleic acid (С18:2), which is associated with a decrease in the source for the synthesis of a number of polyunsaturated fatty acids, especially docosahexaenoic (С22:6). The total content of lipids, triacylglycerols, free fatty acids and phospholipids in skeletal muscle of carp during the Bothriocephalus invasion decreased and the content of free cholesterol, mono- and triacylglycerols increased. Helminth B. acheilognathi has the effect of reducing the total lipids of the skeletal muscle content of С18-, С20-, С22-polyunsaturated fatty acids and increasing the content of saturated (С14:0, С16:0, С18:0) and monounsaturated (С16:1, С18:1) fatty acids. The obtained results prove that the parasite B. acheilognathi in the intestine of the carp significantly affects the nutrition processes of the host depending on the intensity of the damage by helminths, which is accompanied by impaired lipid metabolism.

Tiny but Fatty: Lipids and Fatty Acids in the Daubed Shanny (Leptoclinus Maculatus), a Small Fish in Svalbard Waters

The seasonal dynamic of lipids and their fatty acid constituents in the lipid sac and muscles of pelagic postlarval Leptoclinus maculatus, an ecologically important fish species in the Arctic food nets, in Kongsfjord, Svalbard waters was studied. The determination of the qualitative and quantitative content of the total lipids (TLs), total phospholipids (PLs), triacylglycerols (TAGs), cholesterol (Chol), cholesterol esters (Chol esters) and wax esters was analyzed by TLC, the phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), lysophosphatidylcholine (LPC) and sphingomyelin (SM) were determined by HPLC, and fatty acids of total lipids using GC. The lipid sac is a system of cavities filled with lipids, and it is not directly connected to organs of the digestive system. The wall’s inner layer is a multinuclear symplast that has a trophic function. The results provide additional knowledge on the role of lipids in the biochemical and physiological adaptation of fish to specific environments and clarify the relationship between fatty acids and the food specialization of postlarvae. Analysis of the fatty acid (FA) profile of TLs in the muscles and lipid sac of daubed shanny pelagic postlarvae showed it to be tissue- and organ-specific, and tightly associated with seasonal variations of environmental factors (temperature conditions and trophic resources).

Partial characterization of the lipidome of the cold-water scallop, Chlamys islandica

Fingerprinting of the main lipid components of the digestive gland of the Icelandic scallop-Chlamys islandica-has been performed by ultra-high-performance liquid chromatography coupled with time of flight high-resolution mass spectrometry, UHPLC-HRMS/ToF. This method allowed the identification of 224 lipids, including phosphatidylcholines (PC), plasmanyl (PC-O)/plasmenyl (PC-P) phosphatidylcholines, lyso-phosphatidylcholines (LPC), and their plasmanyl/plasmenyl forms (LPC-O/LPC-P). Diacylglycerols (DG), triacylglycerols (TG), and cholesteryl esters (CE) were the neutral lipids (NL) analyzed. While all of the lipids showed a strong seasonal dependence in terms of quantity, only NLs presented significant qualitative changes. Principal component analysis (PCA) of TG and DG profiles evidenced a prevalence of low unsaturated TGs and DGs in spring, which were replaced by species with a higher degree of unsaturations in summer. In autumn, long and highly unsaturated TGs constitute the lipid fraction of the digestive gland of the scallop, while DG species offer a mixed profile. This study contributes to the characterization and the elucidation of the lipidome of Chlamys islandica and provides baseline data for further study of the effects of pollutants on the lipidome of the Icelandic scallop, often used as a sentinel species in biomonitoring programs.

Dynamics of Estradiol Level during Metamorphosis in the Daubed Shanny (Leptoclinus maculatus, Fries, 1838) from Spitsbergen Island

The estradiol content of muscles during metamorphosis in the daubed shanny (Leptoclinus maculatus) from different fjords of Spitsbergen Island, Svalbard, have been studied using mass spectrometry. The level of estradiol at the L4 larval stage of development is significantly lower than at the L2 stage. Values of this parameter in adults are significantly higher than in post-larvae (stage L5). Variations in the estradiol level during metamorphosis can be associated with the growth stimulation and regulation of the process.

Effect of elevated temperature on membrane lipid saturation in Antarctic notothenioid fish

Homeoviscous adaptation (HVA) is a key cellular response by which fish protect their membranes against thermal stress. We investigated evolutionary HVA (long time scale) in Antarctic and non-Antarctic fish. Membrane lipid composition was determined for four Perciformes fish: two closely related Antarctic notothenioid species (Trematomus bernacchii and Pagothenia borchgrevinki); a diversified related notothenioid Antarctic icefish (Chionodraco hamatus); and a New Zealand species (Notolabrus celidotus). The membrane lipid compositions were consistent across the three Antarctic species and these were significantly different from that of the New Zealand species. Furthermore, acclimatory HVA (short time periods with seasonal changes) was investigated to determine whether stenothermal Antarctic fish, which evolved in the cold, stable environment of the Southern Ocean, have lost the acclimatory capacity to modulate their membrane saturation states, making them vulnerable to anthropogenic global warming. We compared liver membrane lipid composition in two closely related Antarctic fish species acclimated at 0 °C (control temperature), 4 °C for a period of 14 days in T. bernacchii and 28 days for P. borchgrevinki, and 6 °C for 7 days in both species. Thermal acclimation at 4 °C did not result in changed membrane saturation states in either Antarctic species. Despite this, membrane functions were not compromised, as indicated by declining serum osmolality, implying positive compensation by enhanced hypo-osmoregulation. Increasing the temperature to 6 °C did not change the membrane lipids of P. borchgrevinki. However, in T. bernacchii, thermal acclimation at 6 °C resulted in an increase of membrane saturated fatty acids and a decline in unsaturated fatty acids. This is the first study to show a homeoviscous response to higher temperatures in an Antarctic fish, although for only one of the two species examined.