Effect of the double bond conjugation on the vascular physiology and nitric oxide production of isomers of eicosapentaenoic and docosahexaenoic acids prepared from shark oil

A collection of evidence suggests that conjugation of double bonds of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, omega-3 polyunsaturated fatty acids (n-3 PUFAs), increases their anticarcinogenic activity; however, the effect of such conjugation on vascular tone activity remains unknown. We propose that the mixture of conjugated PUFAs exerts higher vasorelaxation activity than the corresponding mixture of nonconjugated PUFAs. The vascular response to different concentrations of conjugated and nonconjugated isomers of EPA and DHA, among other fatty acids (FAs) naturally present in shark oil, and the role of nitric oxide (NO) as a vasorelaxant agent were investigated. Both conjugated EPA (CEPA) and conjugated DHA (CDHA) were prepared by alkaline isomerization of all PUFAs contained in shark oil. Different concentrations of conjugated and nonconjugated PUFAs were placed in contact with precontracted aortic rings of Wistar rats to assess their effect on vascular tone. All tested samples exerted a vasorelaxant effect. Compared to nonconjugated PUFAs, conjugated isomers exhibited an increase in the dilatation of the aortic rings (P<0.001) in a dose-dependent manner (P<0.001). In addition, nonconjugated PUFAs produced nitric oxide (NO) in a dose-dependent manner, while conjugated PUFAs did not, suggesting that their dilatation mechanism is not totally dependent on NO.

Rapid Quantitative Determination of Squalene in Shark Liver Oils by Raman and IR Spectroscopy

Squalene is sourced predominantly from shark liver oils and to a lesser extent from plants such as olives. It is used for the production of surfactants, dyes, sunscreen, and cosmetics. The economic value of shark liver oil is directly related to the squalene content, which in turn is highly variable and species-dependent. Presented here is a validated gas chromatography-mass spectrometry analysis method for the quantitation of squalene in shark liver oils, with an accuracy of 99.0 %, precision of 0.23 % (standard deviation), and linearity of >0.999. The method has been used to measure the squalene concentration of 16 commercial shark liver oils. These reference squalene concentrations were related to infrared (IR) and Raman spectra of the same oils using partial least squares regression. The resultant models were suitable for the rapid quantitation of squalene in shark liver oils, with cross-validation r (2) values of >0.98 and root mean square errors of validation of ≤4.3 % w/w. Independent test set validation of these models found mean absolute deviations of the 4.9 and 1.0 % w/w for the IR and Raman models, respectively. Both techniques were more accurate than results obtained by an industrial refractive index analysis method, which is used for rapid, cheap quantitation of squalene in shark liver oils. In particular, the Raman partial least squares regression was suited to quantitative squalene analysis. The intense and highly characteristic Raman bands of squalene made quantitative analysis possible irrespective of the lipid matrix.

Lipid, fatty acid and energy density profiles of white sharks: insights into the feeding ecology and ecophysiology of a complex top predator

Lipids are major sources of metabolic energy in sharks and are closely linked to environmental conditions and biological cycles, such as those related to diet, reproduction and migration. In this study, we report for the first time, the total lipid content, lipid class composition and fatty acid profiles of muscle and liver tissue of white sharks, Carcharodon carcharias, of various lengths (1.5-3.9 m), sampled at two geographically separate areas off southern and eastern Australia. Muscle tissue was low in total lipid content (<0.9% wet mass, wm) and was dominated by phospholipids (>90% of total lipid) and polyunsaturated fatty acids (34±12% of total fatty acids). In contrast, liver was high in total lipid which varied between 51-81% wm and was dominated by triacylglycerols (>93%) and monounsaturated fatty acids (36±12%). With knowledge of total lipid and dry tissue mass, we estimated the energy density of muscle (18.4±0.1 kJ g-1 dm) and liver (34.1±3.2 kJ g-1 dm), demonstrating that white sharks have very high energetic requirements. High among-individual variation in these biochemical parameters and related trophic markers were observed, but were not related to any one biological or environmental factor. Signature fatty acid profiles suggest that white sharks over the size range examined are generalist predators with fish, elasmobranchs and mammalian blubber all contributing to the diet. The ecological applications and physiological influences of lipids in white sharks are discussed along with recommendations for future research, including the use of non-lethal sampling to examine the nutritional condition, energetics and dietary relationships among and between individuals. Such knowledge is fundamental to better understand the implications of environmental perturbations on this iconic and threatened species.

Liver lipids of female Carcharias taurus (spotted raggedtooth) sharks: a comparison between seasons

Female raggedtooth sharks (Carcharias taurus) migrate from the waters off the eastern Cape past KwaZulu-Natal and up to southern Mozambique and then back on an annual basis. They mate off the KwaZulu-Natal coast, gestate the pups off Mozambique, then deliver same off the eastern Cape. Prior to mating, they hypertrophise their livers and store large amounts of lipid, then towards the end of gestation subsist on this stored lipid as well as using it to feed their pups in utero. Raggedtooth sharks are aplacental, and hepatic lipids provide nutrients to the pups via continued ovulation throughout pregnancy. The fact of the liver hypertrophy was well documented, but whether the nature of the stored lipid or the amount of lipid per Kg of liver changed with season was unknown. Samples from raggedtooth females caught throughout the year were analysed for their lipid and fatty acid contents and significant differences noted between lipid, but not fatty acid, concentration with certain seasons. Liver mass decreased from spring to winter (16.3-9.9 kg) as did lipid concentration (572-326 mg/g). Within the fatty acids, 22:6n3 was ±17%, 20:5n3 ±7%, total n3 ±30% and total n6 ±7%. Also, both total polyunsaturates (±36%) and total monounsaturates (±33%) were greater than the total saturates (±28%).

Ether lipids

The naturally occurring 1-O-alkyl-sn-glycerols and their methoxylated congeners, 1-O-(2'-methoxyalkyl)-sn-glycerols, are biologically active compounds, ubiquitously found in nature as diacyl glyceryl ether lipids and phosphoether lipids. The chief objective of this article is to provide a comprehensive and up to date review on such ether lipids. The occurrence and distribution of these compounds in nature are extensively reviewed, their chemical structure and molecular variety, their biosynthesis and chemical synthesis and, finally, their various biological effects are described and discussed. An unprecedented biosynthesis of the 2'-methoxylated alkylglycerols is proposed. The first synthesis of enantiopure (Z)-(2'R)-1-O-(2'-methoxyhexadec-4'-enyl)-sn-glycerol, the most prevalent 2'-methoxylated type alkylglycerol present in cartilaginous fish, is described. It was accomplished by a highly convergent five step process.

The unusual energy metabolism of elasmobranch fishes

The unusual energy metabolism of elasmobranchs is characterized by limited or absent fatty acid oxidation in cardiac and skeletal muscle and a great reliance on ketone bodies and amino acids as oxidative fuels in these tissues. Other extrahepatic tissues in elasmobranchs rely on ketone bodies and amino acids for aerobic energy production but, unlike muscle, also appear to possess a significant capacity to oxidize fatty acids. This organization of energy metabolism is reflected by relatively low plasma levels of non-esterified fatty acids (NEFA) and by plasma levels of the ketone body ss-hydroxybutyrate that are as high as those seen in fasted mammals. The preference for ketone body oxidation rather than fatty acid oxidation in muscle of elasmobranchs under routine conditions is opposite to the situation in teleosts and mammals. Carbohydrates appear to be utilized as a fuel source in elasmobranchs, similar to other vertebrates. Amino acid- and lipid-fueled ketogenesis in the liver, the lipid storage site in elasmobranchs, sustains the demand for ketone bodies as oxidative fuels. The liver also appears to export NEFA and serves a buoyancy role. The regulation of energy metabolism in elasmobranchs and the effects of environmental factors remain poorly understood. The metabolic organization of elasmobranchs was likely present in the common ancestor of the Chondrichthyes ca. 400million years ago and, speculatively, it may reflect the ancestral metabolism of jawed vertebrates. We assess hypotheses for the evolution of the unusual energy metabolism of elasmobranchs and propose that the need to synthesize urea has influenced the utilization of ketone bodies and amino acids as oxidative fuels.

Fatty Acids in Liver, Muscle and Gonad of three Tropical Rays including Non-Methylene-Interrupted Dienoic Fatty Acids

Scientific investigation of lipids in Elasmobranchs has been conducted mainly on shark species. Because rays seem to be neglected, this study was performed to examine the complete fatty acid (FA) composition with a particular interest for long-chain polyunsaturated FA (PUFA) content in different tissues of three ray species including parts usually discarded. The total FA and PUFA profiles of total lipids were determined in muscle, liver, and gonad of Rhinobatos cemiculus, Rhinoptera marginata, and Dasyatis marmorata, the most often caught ray species from the East Tropical Atlantic Ocean. Fifty FA were characterized as methyl esters and N-acyl pyrrolidides by gas chromatography/mass spectrometry, showing significant levels of 20:5n-3 (EPA) (up to 5.3%) and 22:5n-3 (DPA) (up to 7.3%), high levels of 20:4n-6 arachidonic (ARA) (4.8-8.6% of total FA) and 22:6n-3 (DHA) (up to 20.0%). The results show that muscle, liver and gonad of rays can provide high amounts of essential PUFA, specially DHA, for direct human nutrition or the food processing industry. High proportions of DHA were particularly found in all samples of R. cemiculus (11.6-20.0%), and in muscle and liver of D. marmorata (11.1-16.1%). Regarding the high amounts of (n-3) PUFA, this study shows that these rays deserve a better up-grading, including the normally discarded parts, and describes the occurrence of unusual NMID FA in all tissues studied. Five non-methylene-interrupted dienoic fatty acids (NMID FA) (0-3.4%) were reported, including previously known isomers, namely 20:2 Delta7,13, 20:2 Delta7,15, 22:2 Delta7,13, 22:2 Delta7,15, and new 22:2 Delta6,14. These acids are quite unusual in fish and unprecedented in rays. The 22:2 Delta6,14 acid occurred in gonads of male specimens of R. cemiculus at 2.9%.

Variation in lipid classes and fatty acid composition of salmon shark (Lamna ditropis) liver with season and gender

The influence of season and gender on lipid content, lipid classes, and fatty acid compositions was assessed in livers of salmon shark (Lamna ditropis), caught in the Pacific Ocean. No significant difference in the hepatosomatic index was noted with season, though the lipid content was significantly higher (P<0.05) in winter. Triacylglycerol (TAG) was identified as the predominant lipid class (78.5-82.0%), followed by sterol esters (5.7-9.1%) and hydrocarbons (3.4-5.4%). No significant differences were observed in TAG composition with respect to the season or gender. However, diacylglyceryl ether contents were significantly higher (P<0.05) in winter (3.8-5.3%) than those obtained in summer (1.3-1.1%). Polyunsaturated fatty acids constituted the major fatty acid class of salmon shark total liver lipid and docosahexaenoic acid (C22:6n-3) (22.7-28.4%) was the most abundant fatty acid which was significantly lower (P<0.05) in winter. These results suggested that lipid characteristics of salmon shark liver were influenced by season, but not by gender.