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Modulation of Lipid Biosynthesis by Stress in Diatoms
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
Bing Huang, Virginie Mimouni, Annick Morant-Manceau, Justine Marchand, Lionel Ulmann, Benoit Schoefs
It is well documented that TAG accumulation is a consequence of re-allocation of carbon from intermediates of the TCA cycle but also from the degradation of chrysolaminarin (Zhu et al., 2016). Diatoms can produce both lipids and chrysolaminarin as energy reserves, with lipid-to-chrysolaminarin ratios that depend on growth conditions. In the most common situation, chrysolaminarin is the primary energy compound, but how its production switches to FAs or TAG under specific conditions is not completely understood. Daboussi et al. (2014) were the first to report that a block of the chrysolaminarin pathway by disruption of the UDP-glucose pyrophosphorylase gene (UGPase) using nucleases (meganucleases and TALEN) in P. tricornutum resulted in a 45-fold increase in TAG accumulation. Zhu et al. (Zhu et al., 2016), by knocking down the same gene in P. tricornutum (69% of the UGPase activity was inactivated), highlighted a significant decrease in chrysolaminarin content and an increase in lipid synthesis. In T. pseudonana, Hildebrand, Manandhar-Shrestha and Abbriano (2017) demonstrated that knockdown transformants were accumulating less chrysolaminarin and increased their TAG level, suggesting that UGPase plays an important role in carbon allocation. Their data also suggest that the effect of chrysolaminarin levels on TAG accumulation is triggered by growth cessation and is transient. Silencing nitrate assimilation can also be a strategy to direct the carbon flux toward lipids since they require little nitrogen (Levitan et al., 2015b). In diatoms, the rate‐limiting reaction in the assimilation of nitrate is the reduction of the molecule to nitrite, a reaction catalyzed by the nitrate reductase. The silencing of the nitrate reductase in P. tricornutum revealed an accumulation of over 40% more fatty acids with a 50% lower expression and activity of the enzyme in the transformants compared to the wild type. In contrast to nitrogen‐stressed WT cells, which grow at about 20% of the rate of nitrogen‐replete cells, growth of the transformants was only reduced by about 30% (Levitan et al., 2015b).
Evaluation of cytotoxicity, analysis of metals and cumulative risk assessment in microalgae
Published in Toxicology Mechanisms and Methods, 2023
Mercedes Taroncher, Yelko Rodríguez-Carrasco, Francisco J. Barba, María José Ruiz
The T. chuii has a strong scavenging activity against 2,2-difenyl-1-picrylhydrazyl (DPPH) and peroxyl radicals and it stimulates a response to cell damage and activates a repairing mechanism in human epidermal cells (Jo et al. 2012). These microalgae are gained increasing interest due to various valuable constituents. Gille et al. made lipophilic fractions of P. tricornutum and detected carotenoids, α-tocopherol, fatty acids and lipophilic peroxides (Gille et al. 2020). And, Hernández-López et al. made ethanolic extracts of Tetraselmis sp. and analyzed polyphenols, carotenoids and chlorophylls (Hernández-López et al. 2021). In this study, we assess the effect of the P. triconutum and T. chuii extracts on mitochondrial metabolic activity, as an indicator of cell viability. We evaluated the potential cytotoxic of ethanolic extracts at increasing concentrations after 24 h of exposure in HepG2 cells by MTT assay. We observed a decreased cell viability after P. triconutum 0% DR exposure at 50 and 100 µg/mL, respect to control. Similarly, Koo and coworkers evaluated the cytotoxic effect of fucoxanthin (a marine carotenoid found in P. triconutum) and P. triconutum extract in 3T3-L1 cells (Koo et al. 2019). They observed that fucoxanthin was cytotoxic to cells at concentrations above 80 µM, and P. triconutum extract at 1000 µg/mL. Moreover, Neumann and coworkers observed a decrease in metabolic activity of RAW 264.7 cells exposed to 50 µg/mL fucoxanthin (Neumann et al. 2019). Also, fucoxanthin was also able to reduce the metabolic activity of HepG2, HeLa and Caco-2 cells in a dose-dependent manner. An inhibitory effect of up to 58% at 50 µg/mL was observed in HepG2 cells, whereas in HeLa and Caco-2 cells, the cytotoxic effect was stronger (Neumann et al. 2019). Furthermore, the cytotoxic effect of the ethanolic and hexane P. tricornutum extracts on peripheral blood mononuclear (PBMCs) cells was evaluated using the MTT assay. The PBMCs cells were exposed to different concentrations of the P. tricornutum extracts (0.01, 0.1, and 1%) for 24 h. Only 1% ethanolic extract decreased the cell viability by 76% (Neumann et al. 2018). In the same way, the cytotoxicity of a chrysolaminarin-enriched extract (0.01, 0.1, 1% w/v) obtained from P. tricornutum was evaluated and the results demonstrated that all concentrations impair cell viability of primary dermal cell (NHDF) in a concentration-dependent manner (Carballo et al. 2018). According to Samarakoon and coworkers, inhibitory viability effect of hexane, chloroform, ethyl acetate and aqueous P. tricornutum extracts (in a range of concentration from 6.25 to 50 µg/mL) was reported in RAW 264.7 macrophages (Samarakoon et al. 2013). Also, 25 and 50 µg/mL of P. tricornutum extracts decreased viability of endothelial HMEC-1 cells (le Goff et al. 2019).