Lipoxygenase Products in Marine Diatoms: A Concise Analytical Method to Explore the Functional Potential of Oxylipins1

Abstract

Oxylipins are oxygenated derivatives of polyunsaturated fatty acids (PUFAs) that act as chemical mediators in many ecological and physiological processes in marine and freshwater diatoms. The occurrence and distribution of these molecules are relatively widespread within the lineage with considerable species-specific differences due to the variability of both the fatty acids recognized as substrates and the enzymatic transformations. The present review provides a general introduction to recent studies on diatom oxylipins and describes an analytical method for the detection and assessment of these elusive molecules in laboratory and field samples. This methodology is based on selective enrichment of the oxylipin fraction by solvent extraction, followed by parallel acquisition of full-scan UV and tandem mass spectra on reverse phase liquid chromatography (LC) peaks. The analytical procedure enables identification of potential genetic differences, enzymatic regulation, and ecophysiological conditions that result in different oxylipin signatures, thus providing an effective tool for probing the functional relevance of this class of lipids in plankton communities. Examples of oxylipin measurements in field samples are also provided as a demonstration of the analytical potential of the methodology.

Non-volatile oxylipins can render some diatom blooms more toxic for copepod reproduction

“…One of these compounds, 15S-HEPE, acts similarly to PUAs in that it induces malformations in newlyhatched nauplii and arrests embryogenesis at elevated concentrations (Ianora et al, 2011b). Interestingly, many diatom species seem to produce only these NVOs and not PUAs (Barreiro et al, 2011;Cutignano and Lamari, 2011;d'Ippolito et al, 2009;Fontana et al, 2007;Nanjappa et al, 2014). Similar compounds are also produced by benthic diatoms, where these compounds have been suggested to play a role as foraging kairomones, indicating the presence of abundant food (Jü ttner et al, 2010).…”

“…2E-Decenal was used as internal standard. Other non-volatile oxylipins (NVOs) were analyzed with reverse-phase liquid chromatography-mass spectrometry (LC-MS) (microMass Q-tof with a Waters Alliance HPLC (Milford, MA, USA) equipped with a C18-Synergy column) after methylation of the extracts with ethereal diazomethane (Cutignano and Lamari, 2011). Values are expressed in mg PUAs, NVOs per mg protein content, measured according to the Bradford assay with bovine serum albumin (BSA, 1 g L À1 ) as a standard.…”

Specificity of Lipoxygenase Pathways Supports Species Delineation in the Marine Diatom Genus Pseudo-nitzschia

“…In algae, LOX products have been reported in brown and red algae ([15], [16] [17]) and seem to be intermediates for innate immunity [18], [12]. Oxylipins have been reported also in diatoms [19], [20], [21]. These compounds are suggested to impair the reproductive biology of copepods, the principal plankton grazers, and to mediate intracellular communication (e.g.…”

“…Recently we described a novel protocol for rapid characterization of oxylipins in lipid extracts of diatoms by reverse phase liquid chromatography and tandem quadrupole-ToF mass spectrometry (qToF LC-MS/MS) [21]. In addition to traditional metabolite profiling, the method permits to deduce the positional specificity of lipoxygenation by MS/MS fragmentation of hydroxy-epoxy PUFA derivatives, generically named epoxy-alcohols, which are among the major classes of oxylipins so far reported in diatoms.…”

Exploring Valuable Lipids in Diatoms

“…Around 30% of marine diatoms produce an array of oxylipin metabolites (Wichard et al, 2005;Sieg et al, 2011). Biosynthesis of oxylipins (Figure 1) is condition-dependent and immediately activated upon predation (D'ippolito et al, 2005;Cutignano et al, 2011;Nanjappa et al, 2014). Particularly, oxylipin production starts by the oxidation action of iron non-heme enzymes lipoxygenases (LOXs) on the precursor PUFAs and membrane phospholipids upon loss of cell integrity (Orefice et al, 2015).…”