Diatom milking: a review and new approaches.

The rise of human populations and the growth of cities contribute to the depletion of natural resources, increase their cost, and create potential climatic changes. To overcome difficulties in supplying populations and reducing the resource cost, a search for alternative pharmaceutical, nanotechnology, and energy sources has begun. Among the alternative sources, microalgae are the most promising because they use carbon dioxide (CO2) to produce biomass and/or valuable compounds. Once produced, the biomass is ordinarily harvested and processed (downstream program). Drying, grinding, and extraction steps are destructive to the microalgal biomass that then needs to be renewed. The extraction and purification processes generate organic wastes and require substantial energy inputs. Altogether, it is urgent to develop alternative downstream processes. Among the possibilities, milking invokes the concept that the extraction should not kill the algal cells. Therefore, it does not require growing the algae anew. In this review, we discuss research on milking of diatoms. The main themes are (a) development of alternative methods to extract and harvest high added value compounds; (b) design of photobioreactors;

Lysophosphatidylcholine-DHA Specifically Induces Cytotoxic Effects of the MDA-MB-231 Human Breast Cancer Cell Line In Vitro-Comparative Effects with Other Lipids Containing DHA.

Docosahexaenoic acid (DHA, C22:6 ω-3) is a dietary polyunsaturated fatty acid that has an important role in human health. Epidemiological studies linked a high intake of DHA to a reduced risk of certain cancers. Recently, attention focused on how the lipid carrier in which DHA is delivered, i.e., esterified on acylglycerols, phospholipids, or free, affects its biological effects. However, studies comparing the effects of these different forms for DHA supply to cancer cells in vitro are limited. In this study, the effect of free DHA and five lipids carrying one to three DHA chains (LPC-DHA, PC-DHA, MAG-DHA, DAG-DHA and TAG-DHA) on the viability of the MDA-MB-231 breast cancer cell line was compared. Our results revealed a strong structure-function relationship of DHA-carrying lipids on the viability of MDA-MB-231 cells. Glycerophosphocholine-based lipids are the most effective DHA carriers in reducing the viability of MDA-MB-231 cells, with LPC-DHA being more effective (IC50 = 23.7 µM) than PC-DHA (IC50 = 67 µM). The other tested lipids are less toxic (MAG-DHA, free DHA) or even not toxic (DAG-DHA, TAG-DHA) under our conditions. Investigating the mechanism of cell death induced by LPC-DHA revealed increased oxidative stress and membrane cell damage.

Acyl migration during deacylation of phospholipids rich in docosahexaenoic acid (DHA): an enzymatic approach for evidence and study.

Non-enzymatic acyl migration could be counter-productive for the preparation of structured phospholipids with docosahexaenoic acid (DHA) at a designated position. Therefore enzymatic approaches have been developed to investigate acyl migration. First, acyl migration from sn-2 to sn-1 position has been set into relief by a three step enzymatic method using a typo-selective lipase, a phospholipase A2 and a non-selective lipase. The effect of reaction temperature on acyl migration from sn-2 to sn-1 was monitored: lowering the reaction temperature from 40 to 30 degrees C allowed a reduction of DHA migration rate of 40%. Secondly, acyl migration from sn-1 to sn-2 position was negligible. This last result was obtained through the study of structured phosphatidylcholine selective deacylation using a phospholipase A2.

Lipase-catalyzed Synthesis of Oleoyl-lysophosphatidylcholine by Direct Esterification in Solvent-free Medium without Water Removal.

In this work, the synthesis of oleoyl-lysophosphatidylcholine by lipase-catalyzed esterification of glycerophosphocholine (GPC) and free oleic acid in a reaction medium without solvent is presented. The complete solubilisation of GPC, which is a crucial issue in non-polar liquids such as melted free fatty acids, was reached by heating the GPC/oleic acid mixture at high temperature during a short time. The immobilized lipase from Rhizomucor miehei (Lipozyme RM-IM) was shown to catalyze the reaction more efficiently than the immobilized lipases from Thermomyces lanuginosus (Lipozyme TL-IM) and Candida antarctica (Novozym 435). The condition reactions leading to the highest yield were as follows: substrate ratio: 1/20 (GPC/oleic acid); amount of catalyst: 10% (w/w of substrates); temperature: 50°C. Under these conditions, a yield of 75% of oleoyl-lysophosphatidylcholine was achieved in 24 h under stirring and almost no dioleoyl-lysophosphatidylcholine was produced. Unlike other studies dealing with the esterification of GPC with free fatty acids, the removal of the water produced while the reaction proceeds was not necessary to reach high yields.

An ultraviolet spectrophotometric assay for measuring lipase activity using long-chain triacyglycerols from Aleurites fordii seeds.

In this study, we designed a specific, continuous, and sensitive UV spectrophotometric lipase assay using natural triacylglycerols (TAGs) from the Aleurites fordii seed oil (tung oil). alpha-Eleostearic acid (9,11,13-cis, trans,trans-octadecatrienoic acid) is the main fatty acid component (it accounts for up to 70%) of the TAGs from tung oil. The conjugated triene present in alpha-eleostearic acid constitutes an intrinsic chromophore, which confers strong UV absorption properties on both the free fatty acid and the TAGs from tung oil. The lipase assay is based on the difference between the apparent molar extinction coefficients of the two types of alpha-eleostearic acid present, that which is esterified into TAGs and that which is released into the reaction medium. This difference is responsible for the variations in the UV absorption spectrum of the reaction medium occurring upon enzymatic TAGs hydrolysis. Using the purified lipase from Thermomyces lanuginosa (TLL) and the detergent sodium taurodeoxycholate (NaTDC, 4 mM), it was established that the most suitable method of measuring lipolysis consisted of monitoring the decrease in the OD at 292 nm, which was linear with time and proportional to the amount of lipase added. In order to be able to estimate the specific activity of TLL, we determined an apparent molar extinction coefficient of alpha-eleostearic acid (epsilon = 13,900 M(-1) cm(-1)) under the assay conditions. Amounts of pure TLL as small as 1 ng can be easily detected in the presence of 4 mM NaTDC. Interestingly, the NaTDC concentration can be decreased as far as 0.05 mM. In comparison with other well-known methods of lipase assay, the detection limit of this new method is 100-fold lower than with the pH-stat method and similar to that of a fluorescent assay recently developed at our laboratory.