Isoprostanoid Profiling of Marine Microalgae

Abstract

Algae result from a complex evolutionary history that shapes their metabolic network. For example, these organisms can synthesize different polyunsaturated fatty acids, such as those found in land plants and oily fish. Due to the presence of numerous double-bonds, such molecules can be oxidized nonenzymatically, and this results in the biosynthesis of high-value bioactive metabolites named isoprostanoids. So far, there have been only a few studies reporting isoprostanoid productions in algae. To fill this gap, the current investigation aimed at profiling isoprostanoids by liquid chromatography -mass spectrometry/mass spectrometry (LC-MS/MS) in four marine microalgae. A good correlation was observed between the most abundant polyunsaturated fatty acids (PUFAs) produced by the investigated microalgal species and their isoprostanoid profiles. No significant variations in the content of oxidized derivatives were observed for Rhodomonas salina and Chaetoceros gracilis under copper stress, whereas increases in the production of C18-, C20- and C22-derived isoprostanoids were monitored in Tisochrysis lutea and Phaeodactylum tricornutum. In the presence of hydrogen peroxide, no significant changes were observed for C. gracilis and for T. lutea, while variations were monitored for the other two algae. This study paves the way to further studying the physiological roles of isoprostanoids in marine microalgae and exploring these organisms as bioresources for isoprostanoid production.

Keywords: PUFAs; isoprostanoids; micro-LC-MS/MS; microalgae; oxidative stress.

Figure 1

Structure of some isoprostanoids isomers derived from n-3 polyunsaturated fatty acids (PUFAs): ALA (α-linolenic acid), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid).

Figure 2

Structure of some isoprostanoids isomers derived from n-6 PUFAs: AA (arachidonic acid), DPA_n-6 (docosapentaenoic acid) and AdA (adrenic acid).

Figure 3

Changes in contents of selected isoprostanoids for the cryptophyte Rhodomonas salina between the control condition (CTL) and oxidative stress (Cu²⁺ and H₂O₂) conditions. Statistically relevant responses between the control and stress conditions (one-way ANOVA) are indicated by asterisks: * p < 5 × 10⁻² and ** p < 5 × 10⁻³; ns, not significant.

Figure 4

Changes in contents of selected isoprostanoids for the haptophyte Tisochrysis lutea between the control condition (CTL) and oxidative stress (Cu²⁺ and H₂O₂) conditions. Statistically relevant responses between the control and stress conditions (one-way ANOVA) are indicated by asterisks: * p < 5 × 10⁻², ** p < 5 × 10⁻³ and *** p < 5 × 10⁻⁴; ns, not significant.

Figure 5

Changes in content of selected isoprostanoids for the diatom Chaetoceros gracilis between the control condition (CTL) and oxidative stress (Cu²⁺ and H₂O₂) conditions. Statistically relevant responses between the control and stress conditions (one-way ANOVA) are indicated by asterisks: * p < 5 × 10⁻² and ** p < 5 × 10⁻³; ns, not significant.

Figure 6

Changes in contents of selected isoprostanoids for the diatom Phaeodactylum tricornutum between the control condition (CTL) and oxidative stress (Cu²⁺ and H₂O₂) conditions. Statistically relevant responses between the control and stress conditions (one-way ANOVA) are indicated by asterisks: * p < 5 × 10⁻², ** p < 5 × 10⁻³, *** p < 5 × 10⁻⁴ and **** p < 1 × 10⁻⁴; ns, not significant.