Search

Marine and freshwater microalgae were evaluated for their antioxidant properties and lipid composition. Both lipophilic (L) and hydrophilic (H) oxygen radical absorbance capacity (ORAC) values were measured. Among the tested microalgae, the marine microalga Nannochloropsis granulata showed the highest total ORAC value at 6948 μmol TE (100 g)−1, followed by the freshwater species Neochloris oleoabundans at 4508 μmol TE (100 g)−1 and Scenedesmus obliquus at 4406 μmol TE (100 g)−1 of algal biomass. Freeze-dried algal biomass was also examined for lipid content by the Folch method. Lipid content ranged from 30.9 to 49.3% and linear regression analysis revealed a statistically significant correlation between the lipid content and the ORAC values. Tested microalgae showed moderate and dose-dependent DPPH radical scavenging activity. The total phenol assay shows that marine microalga Tetraselmis chui had the highest phenolic content at 57.5 μmol GAE g−1 and N. oleoabundans had the lowest at 26.6 μmol GAE g−1 of MeOH extract. A statistically significant correlation was detected between DPPH radical scavenging activity and the phenolic content. Fatty acid analysis revealed that polyunsaturated fatty acids constituted > 45% of the total fatty acid content in N. oleoabundans, Phaeodactylum tricornutum, Porphyridium aerugineum, S. obliquus, and Scenedesmus sp. Total carotenoid concentration ranged from 1.1 to 29.5 mg g−1 of dry algal biomass. Lutein, zeaxanthin, and β-carotene are common carotenoids found in most of the algae tested. P. tricornutum contains significant amount of fucoxanthin at 24.3 mg g−1 algal biomass. These carotenoids also contributed to the overall antioxidative activity of microalgae.

The EtOAc soluble fraction of a MeOH/CHCl3 extract of Palmaria palmata showed strong nitric oxide (NO) inhibitory activity against lipopolysaccharide (LPS)-induced NO production in murine RAW264.7 cells. NO inhibition-guided isolation led to identification of three new polar lipids including a sulfoquinovosyl diacylglycerol (SQDG) (2S)-1-O-eicosapentaenoyl-2-O- myristoyl-3-O-(6-sulfo-α-d-quinovopyranosyl)-glycerol (1) and two phosphatidylglycerols, 1-O-eicosapentaenoyl-2-O-trans-3-hexadecenoyl-3-phospho- (1′-glycerol)-glycerol (3) and 1-O-eicosapentaenoyl-2-O-palmitoyl-3- phospho-(1′-glycerol)-glycerol (4) from the EtOAc fraction. Seven known lipids were also isolated including a SQDG (2), a phospholipid (5) and five galactolipids (6-10). Structures of the isolated lipids were elucidated by spectral analyses. The isolated SQDGs, phosphatidylglycerols and phospholipid possessed strong and dose-dependent NO inhibitory activity compared to N G-methyl-l-arginine acetate salt (l-NMMA), a well-known NO inhibitor used as a positive control. Further study suggested that these polar lipids suppressed NO production through down-regulation of inducible nitric oxide synthase (iNOS).

A MeOH extract of cultivated Chondrus crispus showed dose-dependent nitric oxide (NO) inhibition of lipopolysaccharide-induced NO production in macrophage RAW264.7 cells. NO inhibition-guided fractionation of the extract led to identification of eicosapentaenoic acid (EPA, 1), arachidonic acid (AA, 2), lutein (3), and eight galactolipids as active components. Based on spectral analysis, the isolated galactolipids were identified as (2S)-1,2-bis-O-eicosapentaenoyl-3-O-β-d-galactopyranosylglycerol (4), (2S)-1-O-eicosapentaenoyl-2-O-arachidonoyl-3-O-β-d-galactopyranosylglycerol (5), (2S)-1-O-(6Z,9Z,12Z,15Z-octadecatetranoyl)-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (6), (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (7), (2S)-1,2-bis-O-arachidonoyl-3-O-β-d-galactopyranosylglycerol (8), (2S)-1-O-arachidonoyl-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (9), (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (10), and (2S)-1-O-arachidonoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (11). All the isolated compounds showed significant NO inhibitory activity. This is the first report of the isolation and identification of individual galactolipids from C. crispus. Moreover, (2S)-1,2-bis-O-arachidonoyl −3-O-β-d-galactopyranosylglycerol (8) is a novel compound.

Chemical investigation of polar lipids from the marine eustigmatophyte microalga Nannochloropsis granulata led to the isolation of six betaine lipid diacylglyceryltrimethylhomoserine (DGTS), namely, (2S)-1,2-bis-O-eicosapentaenoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (1), (2S)-1-O-eicosapentaenoyl-2-O-arachidonoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (2), (2S)-1-O-eicosapentaenoyl-2-O-myristoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (3), (2S)-1-O-eicosapentaenoyl-2-O-palmitoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (4), (2S)-1-O-eicosapentaenoyl-2-O-palmitoleoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (5), and (2S)-1-O-eicosapentaenoyl-2-O-linoleoylglyceryl-3-O-4′-(N,N,N-trimethyl)-homoserine (6). Structures of the isolated DGTSs were elucidated based on both spectroscopic technique and degradation methods. This is the first report of isolation of 1 in pure state, and 2–6 are all new compounds. The isolated betaine lipids showed dose-dependent nitric oxide (NO) inhibitory activity against lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophage cells. Further study suggested that these betaine lipids (1–6) inhibit NO production in RAW264.7 macrophage cells through downregulation of inducible nitric oxide synthase expression, indicating the possible use as an anti-inflammatory agent. This is the first report of DGTS with anti-inflammatory activity.

Chemical investigation of the freshwater rhodophyte microalga Porphyridium aerugineum led to the isolation of five new galactolipids, namely, (2S)-1-O-eicosapentaenoyl-2-O-arachidonoyl-3-O-β-d-galactopyranosylglycerol (1), (2S)-1-O-eicosapentaenoyl-2-O-linoleoyl-3-O-β-d-galactopyranosylglycerol (2), (2S)-1-O-arachidoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (6), (2S)-1-O-eicosapentaenoyl-2-O-arachidoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (7), and (2S)-1-O-eicosapentaenoyl-2-O-linoleoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (8) together with five known galactolipids. The stereo-structures of all new galactolipids were elucidated by spectroscopic analyses and both enzymatic and chemical degradation methods. This is the first report of galactolipids from P. aerugineum. The newly isolated galactolipids showed strong and dose-dependent nitric oxide (NO) inhibitory activity against lipopolysaccharide-induced NO production in RAW264.7 macrophage cells. Both galactolipids 1 and 2 possessed stronger NO inhibitory activity than N G-methyl-l-arginine acetate salt, a well-known NO inhibitor used as a positive control. Further study suggested that these galactolipids inhibit NO production through downregulation of inducible nitric oxide synthase expression.