RESUMO
The anti-PAF and the antibacterial activities of lipid extracts obtained from cultured sea bass (Dicentrarchus labrax) and cultured gilthead sea bream (Sparus aurata) were evaluated. Total lipids of sea bass and gilthead sea bream exerted PAF-like activity while, in higher amounts they inhibited this PAF activity. Neutral lipids of both sea bass and gilthead sea bream contained only PAF antagonists while the polar lipid fractions contained both PAF antagonists and agonists. Total lipids of sea bass exhibited stronger PAF-like activity than did those of gilthead sea bream; however, neutral lipids of sea bass contained stronger PAF antagonists than did gilthead sea bream. Total lipids of both sea bass and gilthead sea bream exhibited antibacterial activity only towards Staphylococcus aureus (S. aureus) with those of sea bass being more potent. Subsequently, neutral lipids of both sea bass and gilthead sea bream also showed antibacterial activity against S. aureus and less so towards Escherichia coli (E. coli), while only neutral lipids of sea bass showed antibacterial activity against Enterococcusfaecalis (E. faecalis). Sea bass neutral lipids were more active against S. aureus than were those of gilthead sea bream, while their activity towards E. coli was similar. Polar lipids of both sea bass and gilthead sea bream showed antibacterial activity against all bacteria strains. Sea bass polar lipids were more active towards S. aureus than were those of gilthead sea bream, while their activities against E. faecalis and E. coli were the same. The detected antibacterial activities of the lipid extracts isolated from sea bass and gilthead sea bream were observed in amounts equal to those that exerted either PAF inhibition or PAF-like activity, suggesting that PAF antagonists and agonists of fish lipids may be responsible for the antibacterial activity.
RESUMO
Cyanobacteria serve as a rich source of novel bioactive metabolites. Few studies on glycolipids reported them as having specific biological activities. In this study, total lipids of Scytonema julianum, a filamentous cyanobacterium isolated from a Greek cave, were separated into neutral and phospho- and glycolipids, and the latter were further fractionated by high-performance liquid chromatography (HPLC). Each glycolipid fraction was tested in vitro for its ability to inhibit platelet-activating factor (PAF)- and thrombin-induced washed rabbit platelet aggregation and/or to cause platelet aggregation. The structures of the most active fractions were elucidated by biological assays, by chemical determinations and identified by electrospray mass spectrometry. One fraction was a potent inhibitor of PAF-induced platelet aggregation. Structural studies of this fraction indicated the existence of a phosphoglyco-analog of acyl-sphingosine. Two fractions causing platelet aggregation were detected and identified as phosphoglycolipids. The first one was identified as a phosphoglyco-analog of acyl-acetylated sphingosine and the second one as a glyco-analog of phosphatidylglycerol. The presence of the above bioactive compounds demonstrates new types of lipids in cyanobacteria in regard to the structure and biological activity. In addition, the identified bioactive lipids may contribute to the allergic character of cyanobacteria.
