Lionel Ulmann

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.

Age-related changes in Δ6 and Δ5 desaturase activities in rat liver microsomes

Age-related changes in Δ6 desaturation of [1-14C]α-linolenic acid and [1-14C]linoleic acid and in Δ5 desaturation of [2-14C]dihomo-γ-linolenic acid were studied in liver microsomes from Wistar male rats at various ages ranging from 1.5 to 24 mon. Desaturase activities were expressed both as specific activity of liver microsomes and as the capacity of whole liver to desaturate by taking into account the total amount of liver microsomal protein. Δ6 Desaturation of α-linolenic acid increased from 1.5 to 3 mon and then decreased linearly up to 24 mon to reach the same desaturation capacity of liver measured at 1.5 mon. The capacity of liver to desaturate linoleic acid increased up to 6 mon and then remained constant, whereas microsomal specific activity was equal at 1.5 and 24 mon of age. The capacity of liver to convert dihomo-γ-linolenic acid to arachidonic acid by Δ5 desaturation decreased markedly from 1.5 to 3 mon. It then increased to reach, at 24 mon, the same level as that observed at 1.5 mon. Age-related changes in the fatty acid composition of liver microsomal phospholipids at the seven time points studied and of erythrocyte lipids at 1.5 and 24 mon were consistent with the variations in desaturation capacity of liver. In particular, arachidonic acid content in old rats was slightly higher than in young rats whereas contents in linoleic and docosahexaenoic acids varied little throughout the life span. The results suggest that, in liver, the activity of desaturases may be regulated in the course of aging to maintain a constant level of polyunsaturated fatty acids in cellular membranes.

Effects of age and dietary essential fatty acids on desaturase activities and on fatty acid composition of liver microsomal phospholipids of adult rats.

The combined effects of age and dietary n−6 and n−3 fatty acids were studied in 3-, 6- and 9-month-old rats. At each age, two groups were fed diets containing 5% (w/w) of vegetable oils rich in either 18∶3n−6 (borage group) or 18∶3n−6 plus 18∶4n−3 (black currant group), for a period increasing with age. A control group was fed the essential fatty acids 18∶2n−6 and 18∶3n−3 only. For each group, Δ6, Δ5 and δ9 desaturase activities were measured in liver microsomes, and fatty acid composition was determined in microsomal phospholipids. Desaturase activity varied as a function of age and dietary lipids. Δ6 Desaturation of 18∶3n−3 was more sensitive to these factors while Δ6 desaturation of 18∶2n−6 and Δ9 desaturation were more dependent on season than the other two. Desaturase activity was influenced more by the black currant than by the borage diet, especially at 6 and 9 months of age. A large proportion of arachidonic acid was maintained in the microsomes independent of the diet. Changes in the fatty acid composition did not strictly reflect the differences in desaturase activities. The effects of the two factors (age and diet) on the activities of the desaturases are complex, suggesting that the enzymes are susceptible to other factors as well.

Age-related changes in antioxidant defence mechanisms and peroxidation in isolated hepatocytes from spontaneously hypertensive and normotensive rats

The effects of age and hypertension on the antioxidant defence systems and the lipid peroxidation in rat isolated hepatocytes were studied. Four different age groups (1,3,6 and 12 months) were considered in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Age-associated changes were observed on vitamin E status, glutathione (GSH) level, MDA formation and glutathione peroxidase (GSH-Px) activity in both strains. Maximal levels or activities of these parameters were found at 3 and 6 months, except for MDA which was low at 3 months. Then, a fall was observed at 12-month-old compared to 6-month values. In addition, GSH-Px activity was significantly lower in SHR than in WKY rats, except at the age of one month. The decrease of this enzyme activity could induce an increased cellular generation of radical species and lipid peroxidation, which might be link to hypertension.

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...

Relationship between rat liver microsomal Δ6 and Δ5 desaturase activities and fatty acid composition: comparative effects of coconut and salmon oils during protein restriction

Abstract The aim of this work was to compare the effects of coconut and salmon oils on rat liver microsomal Δ6 and Δ5 desaturations, during protein restriction. A higher Δ6 desaturase activity was noted in rats fed the low-protein coconut oil diet, in comparison with that occurring in rats fed either a low-protein or normal-protein salmon oil diet. No variation was observed in Δ5 desaturase activity or in 20:4n-6/ 18:2n-6 ratio. The fatty acid composition of liver microsomal phospholipids provided evidence of higher levels of 20:5n-3 and 22:6n-3 in the normal-protein salmon oil group, when compared with the low-protein salmon oil group. No influence of experimental diets on the total n-3 and total n-6 fatty acids could be demonstrated. Aside from investigating the effects of protein restriction on the liver microsomal desaturases, this work shows that there is no correlation between microsomal desaturation rates and microsomal phospholipid profiles even when diets are rich in polyunsaturated fatty acids (salmon oil).

Elongation and desaturation of arachidonic and eicosapentaenoic acids in rat liver. Effect of clofibrate feeding

The fatty acid elongation-desaturation ability of 5,8,11,14-eicosatetraenoic (20:4(n-6)) and 5,8,11,14,17-eicosapentaenoic (20:5(n-3)) acids was determined in both liver microsomal and light mitochondrial (rich in peroxisomes) fractions of untreated and clofibrate treated rats. The elongation and the subsequent desaturation steps were performed in the corresponding favorable media. 20:5(n-3) elongation was about 2-times more extensive than that of 20:4(n-6). Clofibrate feeding for 10 days resulted in a marked decrease in the elongation rate with the two substrates, while the delta 4 desaturation rate was increased. There were small differences in the elongation rate between the microsomal and light mitochondrial fractions, however, the relative delta 4 desaturation rate was higher in the light mitochondrial fraction than microsomes.

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.