Virginie Mimouni

The Potential of Microalgae for the Production of Bioactive Molecules of Pharmaceutical Interest

Through the photosynthetic activity, microalgae process more than 25% of annual inorganic carbon dissolved in oceans into carbohydrates that ultimately, serve to feed the other levels of the trophic networks. Besides, microalgae synthesize bioactive molecules such as pigments and lipids that exhibit health properties. In addition, abiotic stresses, such as high irradiance, nutrient starvation, UV irradiation, trigger metabolic reorientations ending with the production of other bioactive compounds such as ω-3 fatty acids or carotenoids. Traditionally, these compounds are acquired through the dietary alimentation. The increasing, and often unsatisfied, demand for compounds from natural sources, combined with the decrease of the halieutic resources, forces the search for alternative resources for these bioactive components. Microalgae possess this strong potential. For instance, the diatom Odontella aurita is already commercialized as dietary complement and compete with fish oil for human nutrition. In this contribution, the microalga world is briefly presented. Then, the different types of biologically active molecules identified in microalgae are presented together with their potential use. Due to space limitation, only the biological activities of lipids and pigments are described in details. The contribution ends with a description of the possibilities to play with the environmental constrains to increase the productivity of biologically active molecules by microalgae and by a description of the progresses made in the field of alga culturing.

Plastids of marine phytoplankton produce bioactive pigments and lipids.

Phytoplankton is acknowledged to be a very diverse source of bioactive molecules. These compounds play physiological roles that allow cells to deal with changes of the environmental constrains. For example, the diversity of light harvesting pigments allows efficient photosynthesis at different depths in the seawater column. Identically, lipid composition of cell membranes can vary according to environmental factors. This, together with the heterogenous evolutionary origin of taxa, makes the chemical diversity of phytoplankton compounds much larger than in terrestrial plants. This contribution is dedicated to pigments and lipids synthesized within or from plastids/photosynthetic membranes. It starts with a short review of cyanobacteria and microalgae phylogeny. Then the bioactivity of pigments and lipids (anti-oxidant, anti-inflammatory, anti-mutagenic, anti-cancer, anti-obesity, anti-allergic activities, and cardio- neuro-, hepato- and photoprotective effects), alone or in combination, is detailed. To increase the cellular production of bioactive compounds, specific culture conditions may be applied (e.g., high light intensity, nitrogen starvation). Regardless of the progress made in blue biotechnologies, the production of bioactive compounds is still limited. However, some examples of large scale production are given, and perspectives are suggested in the final section.

The role of Odontella aurita , a marine diatom rich in EPA, as a dietary supplement in dyslipidemia, platelet function and oxidative stress in high-fat fed rats

BackgroundDietary changes are a major factor in determining cardiovascular risk. n-3 polyunsaturated fatty acids modulate the risk factors for metabolic syndrome via multiple mechanisms, including the regulation of the lipid metabolism. We therefore investigated the effect of Odontella aurita, a microalga rich in EPA, which is already used as a food supplement, on the risk factors for high-fat diet induced metabolic syndrome in rats.MethodsMale Wistar rats were divided into 4 groups and were fed with a standard diet (control); with the standard diet supplemented with 3% freeze-dried O. aurita (COA); with a high-fat diet (HF); or with the high-fat diet supplemented with 3% of freeze-dried O. aurita (HFOA) for 7 weeks. In this study we evaluated the impact of these different diets on the risk factors for metabolic syndrome, such as hyperlipidemia, platelet aggregation, thromboxane B2 production, and oxidative stress.ResultsAfter 7 weeks of treatment, high fat feeding had increased final body weight, glycemia, triacylglycerol, and total cholesterol levels in plasma and liver compared to the control diet. Collagen-induced platelet aggregation and basal platelet thromboxane B2 were also higher in the high-fat fed rats than in those in the control group. In the liver, oxidative stress was greater in the HF group than in the control group. O. aurita intake in HFOA-fed rats resulted in lower glycemia and lipid levels in the plasma and liver relative than in the HF group. Thus, in the HFOA group, n-3 polyunsaturated fatty acid levels in the tissues studied (plasma, liver, and platelets) were higher than in the HF group. Platelet hyper-aggregability tended to decrease in HFOA-fed rats as basal platelet thromboxane B2 production decreased. Finally, O. aurita reduced oxidative stress in the liver, with lower malondialdehyde levels and increased glutathione peroxidase activity.ConclusionsO. aurita is a marine diatom rich in EPA as well as in other bioactive molecules, such as pigments. The synergistic effect of these microalgal compounds, displayed a beneficial effect in reducing the risk factors for high-fat induced metabolic syndrome: hyperlipidemia, platelet aggregation, and oxidative stress.

ENVIRONMENTAL FACTORS AFFECTING GROWTH AND OMEGA 3 FATTY ACID COMPOSITION INSKELETONEMA COSTATUM.THE INFLUENCES OF IRRADIANCE AND CARBON SOURCE: Communication presented at the 25èmeCongrès Annuel de l'Association des Diatomistes de Langue Francaise (ADLaF), Caen, 25-28 September 2006

The effects of carbon sources and three different irradiance levels on the growth and polyunsaturated fatty acid composition of the diatom Skeletonema costatum have been studied. Diatoms were grown in artificial seawater (ASW), which contained sodium bicarbonate (photoautotrophic growth) or sodium acetate (photoheterotrophic growth) at the same concentration (2.07 mM). The optimum growth conditions were between 100–340 μmol photons m−2 s−1 in presence of sodium bicarbonate, both of which enhance photosynthesis. However, under limiting irradiance, results suggested that sodium acetate was more efficiently used than sodium bicarbonate during batch growth. As a consequence, in natural conditions and under low irradiance, availability of sodium acetate could be a limiting factor for cell metabolism. This diatom also seems to be able to support efficiently mixotrophic growth under low irradiance (20 μmol photons m−2 s−1). The highest eicosapentaenoic acid (EPA) amounts were observed when cells were cultured under saturating irradiance (340 μmol photons m−2 s−1) during the late experimental and stationary phases. On the contrary, an increase in the EPA level was observed during the decline phase under limiting irradiance. Indeed, at low irradiance, an accumulation of omega 3 fatty acids in the thylakoid membranes could facilitate the photosynthetic reactions suggesting a peculiar photoadaptation of Skeletonema costatum. Finally, during the exponential phase, a decreased of omega 3 fatty acid amount and specifically EPA with acetate as a carbon source has been observed under limiting and saturating irradiance. This could be explained by the decreased acetate availability that could be considered as responsible for the fall in EPA level.The effects of carbon sources and three different irradiance levels on the growth and polyunsaturated fatty acid composition of the diatom Skeletonema costatum have been studied. Diatoms were grown in artificial seawater (ASW), which contained sodium bicarbonate (photoautotrophic growth) or sodium acetate (photoheterotrophic growth) at the same concentration (2.07 mM). The optimum growth conditions were between 100–340 μmol photons m−2 s−1 in presence of sodium bicarbonate, both of which enhance photosynthesis. However, under limiting irradiance, results suggested that sodium acetate was more efficiently used than sodium bicarbonate during batch growth. As a consequence, in natural conditions and under low irradiance, availability of sodium acetate could be a limiting factor for cell metabolism. This diatom also seems to be able to support efficiently mixotrophic growth under low irradiance (20 μmol photons m−2 s−1). The highest eicosapentaenoic acid (EPA) amounts were observed when cells were cultured un...

Light-dependent utilization of two radiolabelled carbon sources, sodium bicarbonate and sodium acetate, and relationships with long chain polyunsaturated fatty acid synthesis in the microalga Pavlova lutheri (Haptophyta)

Pavlova lutheri is a common member of the Pavlovophyceae (Haptophyta), often used as a food source for aquatic filter-feeders and cultured in laboratories to produce high levels of polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively), which are known to have benefits for human health. Consequently, we investigated the pathways involved in the biosynthesis of long chain polyunsaturated fatty acids (LC-PUFAs) in this alga during photosynthesis in relation to light intensity. Using two radiolabelled carbon sources, [14C] sodium bicarbonate and [1-14C] sodium acetate, we obtained data suggesting that P. lutheri is able to synthesize LC-PUFAs by successive elongation and desaturation steps. It converts palmitic acid into palmitoleic acid by Δ7-desaturation. Moreover, significant incorporation of [1-14C] acetate (organic carbon) and its subsequent use in lipid metabolism suggest that P. lutheri may have a mixotrophic capacity for carbon assimilation. Synthesis of lipids, including galactolipids and phospholipids, increased with light intensity when the cells were incubated with [14C] bicarbonate (inorganic carbon), but was less sensitive to differences in light intensity when incubated with [1-14C] acetate, a heterotrophic carbon source that stimulates the synthesis of monounsaturated fatty acids, such as oleic acid. In the case of n-3 fatty acids, EPA and DHA synthesis was lower at high light (340 µmol photons m−2 s−1) with the [14C] bicarbonate, but did not vary with [1-14C] acetate. Finally, P. lutheri seems to have two distinct enzyme pools involved in LC-PUFA synthesis, one is intra-chloroplastidic and dependent on light intensity, and the other is extra-chloroplastidic and independent of light.

Maternal supplementation with n-3 long chain polyunsaturated fatty acids during perinatal period alleviates the metabolic syndrome disturbances in adult hamster pups fed a high-fat diet after weaning ☆

Perinatal nutrition is thought to affect the long-term risk of the adult to develop metabolic syndrome. We hypothesized that maternal supplementation with eicosapentaenoic acid and docosahexaenoic acid during pregnancy and lactation would protect offspring fed a high-fat diet from developing metabolic disturbances. Thus, two groups of female hamsters were fed a low-fat control diet, either alone (LC) or enriched with n-3 long chain polyunsaturated fatty acids (LC-PUFA) (LO), through the gestational and lactation periods. After weaning, male pups were randomized to separate groups that received either a control low-fat diet (LC) or a high-fat diet (HC) for 16 weeks. Four groups of pups were defined (LC-LC, LC-HC, LO-LC and LO-HC), based on the combinations of maternal and weaned diets. Maternal n-3 LC-PUFA supplementation was associated with reduced levels of basal plasma glucose, hepatic triglycerides secretion and postprandial lipemia in the LO-HC group compared to the LC-HC group. Respiratory parameters were not affected by maternal supplementation. In contrast, n-3 LC-PUFA supplementation significantly enhanced the activities of citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase compared to the offspring of unsupplemented mothers. Sterol regulatory element binding protein-1c, diacylglycerol O-acyltransferase 2, fatty acid synthase, stearoyl CoA desaturase 1 and tumor necrosis factor α expression levels were not affected by n-3 LC-PUFA supplementation. These results provide evidence for a beneficial effect of n-3 LC-PUFA maternal supplementation in hamsters on the subsequent risk of metabolic syndrome. Underlying mechanisms may include improved lipid metabolism and activation of the mitochondrial oxidative pathway.

Light Intensity Regulates LC-PUFA Incorporation into Lipids of Pavlova lutheri and the Final Desaturase and Elongase Activities Involved in Their Biosynthesis.

The microalga Pavlova lutheri is a candidate for the production of omega-3 long-chain polyunsaturated fatty acid (LC-PUFA), due to its ability to accumulate both eicosapentaenoic (EPA) and docosahexaenoic acids. Outstanding questions need to be solved to understand the complexity of n-3 LC-PUFA synthesis and partitioning into lipids, especially its metabolic regulation, and which enzymes and/or abiotic factors control their biosynthesis. In this study, the radioactivity of 14C-labeled arachidonic acid incorporated into the total lipids of P. lutheri grown under different light intensities and its conversion into labeled LC-PUFA were monitored. The results highlighted for the first time the light-dependent incorporation of LC-PUFA into lipids and the light-dependent activity of the final desaturation and elongation steps required to synthesize and accumulate n-3 C20/C22 LC-PUFA. The incorporation of arachidonic acid into lipids under low light and the related Δ17-desaturation activity measured explain the variations in fatty acid profile of P. lutheri, especially the accumulation of n-3 LC-PUFA such as EPA under low light conditions.

Modulation of lipid biosynthesis by stress in diatoms

Diatoms are responsible for up to 40% of the carbon fixation in our oceans. The fixed carbon is moved through carbon metabolism towards the synthesis of organic molecules that are consumed through interlocking foodwebs, and this process is strongly impacted by the abiotic environment. However, it has become evident that diatoms can be used as ‘platform’ organisms for the production of high valuable bio-products such as lipids, pigments and carbohydrates where stress conditions can be used to direct carbon metabolism towards the commercial production of these compounds. In the first section of this review, some aspects of carbon metabolism in diatoms and how it is impacted by environmental factors are briefly described. The second section is focused on the biosynthesis of lipids and in particular omega-3 long-chain polyunsaturated fatty acids and how low temperature stress impacts on the production of these compounds. In a third section, we review the recent advances in bioengineering for lipid production. Finally, we discuss new perspectives for designing strains for the sustainable production of high-value lipids. This article is part of the themed issue ‘The peculiar carbon metabolism in diatoms’.

A comparative study on the effect of argan oil versus fish oil on risk factors for cardio-vascular disease in high-fat-fed rats

OBJECTIVES The aim of this study was to investigate the effects of two different sources of polyunsaturated fatty acid-fish oil (FO) and argan oil (AO)-on some risk factors for cardiovascular disease, such as platelet aggregation, dyslipidemia, and oxidative stress. METHODS To explore this, four groups of six male rats were fed with different diets: The first group received a standard diet (control); the second group received a high-fat diet; the third was fed with a high-fat diet supplemented with 5% FO, and the last group received a high-fat diet supplemented with 5% AO. RESULTS After 8 wk of the diet, AO showed a decrease in plasma lipids similar to that of FO. However, unlike FO, AO had no significant effect on hepatic lipid levels. On the other hand, supplementation with AO and FO similarly reduced platelet hyperactivity induced by high-fat diet. Concerning the results of oxidative stress, AO showed an antioxidant effect in the tissues and platelets greater than that observed in the high-fat FO group. CONCLUSIONS For rats, the consumption of FO prevented the development of adiposity, restored insulin sensitivity, decreased plasma and liver lipid levels, and also prevented the prothrombotic effect. Intake of AO as a food supplement did not affect adiposity or liver lipid levels but decreased plasma lipid levels and improved oxidative status and platelet activity. FO and, to a lesser degree, AO thus represent promising nutritional tools in the prevention of cardiovascular disease.

Lipids From Microalgae

Abstract In this chapter, we propose to describe the major cellular lipids and their fatty acids in microalgae. This development will concern both prokaryotes (cyanophytes) and eukaryotes (diatoms, chlorophytes, cryptophytes, rhodophytes, …). The different types of lipids (particularly fatty acids) will be listed, but also the sterols, glycolipids, and phospholipids knowing that the accumulation of lipids depends on the microalgal species, growth, and environmental conditions. The neutral lipids or nonpolar lipids other than triacylglycerides, such as sterols and free fatty acids, are present at lower levels but these lipids are of great interest for the valorization of microalgae in aquaculture, nutrition, or biofuel production. Polar lipids, such as glycolipids or betaine lipids (BL) will be studied more specifically. Moreover, BL and some unusual lipids may be characteristic of a particular genus or species. BL represent a widespread class of functional and structural lipids that have been slowly studied and recognized. During stress conditions such as phosphorus deprivation, these lipids can completely replace the phospholipids in their metabolic role. Then, we will focus on the specific role played by the subcellular fractions of lipids involved in the constitution of diatoms and especially the role played by the plastids and the endoplasmic reticulum compartments in which polyunsaturated fatty acids and polar lipids are specifically synthesized.