Phospholipase D (PLD)-mediated transphosphatidylation of squid skin lecithin with L-serine was examined to prepare docosahexaenoic acid-containing phosphatidylserine (DHA-PS). When a biphasic system with organic solvent and 0.2 M acetate buffer (pH 5.5) was used, PS synthesis was significantly affected by the amount of 3.4 M L-serine-containing acetate buffer. L-Serine concentration in the acetate buffer and choice of organic solvent were also crucial. In a typical reaction with 0.8 unit of PLD (Streptomyces sp.), 2.5 mL of ethyl acetate substrate solution containing 30 mg of squid skin lecithin in combination with 3 mL of 3.4 M L-serine-containing 0.2 M acetate buffer (pH 5.5), PS content in the recovered phospholipid fraction increased to 43.1% after 24 h. DHA composed 37.6% of fatty acids in the converted PS. This was the same DHA level as in the substrate. Phosphatidylcholine (squid skin PC, DHA 44.2%) in the squid skin lecithin was more effectively converted to PS than phosphatidylethanolamine.

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It has been demonstrated that the amount and type of dietary fat are factors involved in the risk of arteriosclerosis and coronary or cerebral artery disease through lipid metabolism. In this study, we investigated the effects of phospholipids (PLs) containing n-3PUFAs on lipid metabolism in rats. PLs containing n-3PUFAs were prepared from squid (Todarodes pacificus) mantle muscle. Groups of male Wistar rats were fed AIN93G diet containing soybean oil (SO, 7%), fish oil (1.2%) þ SO (5.8%), soybean PLs (1.8%) þ SO (5.2%), or PLs containing n-3PUFAs (1.8%) þ SO (5.2%). The following indicators were assayed as indexes of lipid metabolism: TAG and cholesterol in serum and liver, fecal cholesterol, bile-acid excretion, and liver mRNA expression levels of genes encoding proteins involved in cholesterol homeostasis. Serum and liver TAG contents decreased significantly in the group fed PLs containing n-3PUFAs as compared to other groups, accompanied by a significant decline in the expression level of sterol regulatory element binding protein-1c. The decrease in cholesterol content in the group fed PLs containing n-3PUFAs was due to the increase in fecal cholesterol excretion and the increase of mRNA expression levels of ATPbinding cassette (ABC) G5 and ABCG8 in liver.Practical applications: PLs containing n-3PUFAs decreased serum and liver TAG contents compared with that induced by soybean PLs. Further, PLs containing n-3PUFAs can induce a reduction in serum and liver cholesterol concentrations as well as the triglyceride-reducing effect of conventional n-3PUFAs containing TAG. In other words, dietary n-3PUFAs contained in PLs can prevent life-style diseases such as hyperlipidemia, arteriosclerosis and coronary, or cerebral artery disease more effectively than TAG containing n-3PUFAs. Therefore, it is expected that the risk of lifestyle diseases would be decreased if PL containing n-3PUFAs can be supplied routinely. In this study, PLs containing n-3PUFAs were prepared from squid mantle muscle. On an industrial scale, such PLs can be produced from various unused resources and waste materials of fisheries. We conclude that highly functional foods could be developed based on the findings of this study, and would be available for health promotion worldwide. Abbreviations: ABC, ATP-binding cassette; ACAT-1, acylcoenzyme:cholesterol acyltransferase-1; AIN-93G, American Institute of Nutrition; CYP7A1, cholesterol 7a-hydroxylase; FO, fish oil; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; HMGR, 3-hydroxy-3-methylglutaryl coenzyme A reductase; LDL-C, LDL-cholesterol; LDLR, LDL receptor; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PI, phosphatidylinositol; PLs, phospholipids; SO, soybean oil; SPL, soybean PLs; SREBP-1c, sterol regulatory element binding protein-1c; SREBP-2, sterol regulatory element binding protein-2; WAT, white adipose tissues.

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