Tuning Dunaliella tertiolecta for Enhanced Antioxidant Production by Modification of Culture Conditions

Toxic effects of nSiO2 and mPS on diatoms Nitzschia closterium f. minutissima

To investigate the toxic mechanism of SiO2 nanoparticles (nSiO2) and polystyrene microplastics (mPS) on microalgae Nitzschia closterium f. minutissima, growth inhibition tests were carried out. The growth and biological responses of the algae exposed to nSiO2 (0.5, 1, 2, 5, 10, 30 mg L-1) and mPS (1, 5, 10, 30 and 75 mg L-1) were explored in f/2 media for 96 h. Both micro-/nano-particles (MNPs) inhibited the growth of N. closterium f. minutissima in a concentration- and time-dependent manner. The toxic effect of mPS on N. closterium f. minutissima is higher than that of nSiO2, because silicon is essential for diatoms to maintain cell wall integrity, and the addition of appropriate amounts of nSiO2 can be absorbed and used as a nutrient to promote diatom growth and protect the integrity of the siliceous shell to some extent. Both MNPs induce the production of excess oxidation and activate the cellular antioxidant defense system, leading to increased SOD and CAT activity as a means to resist oxidative damage to the cell, and eliminating excess ROS and maintaining normal cell morphology and metabolism. SEM is consistent with the results of MDA, showing that mPS with high concentrations attach to the surface of algal cells to produce heterogeneous aggregates and disrupt the cell wall and cell membrane, causing the cells to expand and rupture. This study contributes to the understanding of the size effect of MNPs on the growth of marine diatom.

Extraction and Characterization of Bioactive Compounds from Diverse Marine Microalgae and Their Potential Antioxidant Activities

This study compared free and bound phenolic compounds in various marine microalgae species. It assessed total phenolic content (TPC), total flavonoid content (TFC) and total condensed tannin content (TCT) and their antioxidant capacities using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⋅+ ) radical cation-based assay and ferric ion reducing antioxidant power assay. Liquid chromatography-mass spectrometry (LC-MS) was also employed to characterize the phenolic profiling. Results showed that free phenolic compounds ranged from 1.83-6.45 mg GAE/g d. w., while bound phenolic compounds ranged from 4.03-26.03 mg GAE/g d. w., indicating significant differences. These variations were consistent across assays, highlining unique profiles in different species. A total 10 phenolics were found in these seven microalgae, including 1 phenolic acid, 6 flavonoids, 1 other polyphenol and 2 lignans. 4'-O-methyl-(-)-epigallocatechin 7-O-glucuronide and chrysoeriol 7-O-glucoside in microalgae were firstly reported in microalgal samples. These findings have implications for future applications in industries.

Developmental and behavioral toxicity assessment of opicapone in zebrafish embryos

The use of clinical psychoactive drugs often poses unpredictable threats to fetal development. Catechol-O-methyltransferase (COMT) is a key enzyme that regulates dopamine metabolism and a promising target for modulation of cognitive functions. Opicapone, a newly effective third-generation peripheral COMT inhibitor, is used for the treatment of Parkinson's disease (PD) and possibly to improve other dopamine-related disorders such as alcohol use disorder (AUD) and obsessive-compulsive disorder (OCD). The widespread use of opicapone will inevitably lead to biological exposure and damage to the human body, such as affecting fetal development. However, the effect of opicapone on embryonic development remains unknown. Here, zebrafish larvae were used as an animal model and demonstrated that a high concentration (30 μM) of opicapone exposure was teratogenic and lethal, while a low concentration also caused developmental delay such as a shortened body size, a smaller head, and reduced locomotor behaviors in zebrafish larvae. Meanwhile, opicapone treatment specifically increased the level of dopamine (DA) in zebrafish larvae. The depletion response of the total glutathione level (including oxidized and reduced forms of glutathione) and changed antioxidant enzymes activities in zebrafish larvae suggest oxidative damage caused by opicapone. In addition, enhanced glutathione metabolism and cytokine-cytokine receptor interaction were found in zebrafish larvae treated with opicapone, indicating that opicapone treatment caused an oxidation process and immune responses. Our results provide a new insight into the significant developmental toxicity of opicapone in zebrafish larvae.

Study on high-CO2 tolerant Dunaliella salina and its mechanism via transcriptomic analysis

Microalgae has been regarded as a promising method for reducing CO2 emission. High CO2 concentration generally inhibits algal growth, and previous studies have mostly focused on breeding freshwater algae with high CO2 tolerance. In this study, one marine algal strain Dunaliella salina (D. salina) was grown under 0.03%-30 % CO2 and 3% NaCl conditions, and was evaluated to determine its potential for CO2 assimilation. The results showed that D. salina could tolerate 30% CO2 , and its maximum biomass concentration could reach 1.13 g·L-1 after 8 days incubation, which was 1.85 times higher than that of incubation in air (0.03%). The phenomenon of high-CO2 tolerance in D. salina culture was discussed basing on transcriptome analysis. The results showed that D. salina was subjected to oxidative stress under 30% CO2 conditions, and the majority genes involving in antioxidant system, such as SOD, CAT, and APX genes were up-regulated to scavenge ROS. In addition, most of the key enzyme genes related to photosynthesis, carbon fixation and metabolism were up-regulated, which are consistent with the higher physiological and biochemical values for D. salina incubation under 30% CO2 .

Extraction and characterization of microalgae-derived phenolics for pharmaceutical applications: A systematic review

Microalgae are regarded as a rich trove of diverse secondary metabolites that exert remarkable biological activities. In particular, microalgae-derived bioactive phenolic compounds (MBPCs) are a boon to biopharmaceutical and nutraceutical industries due to their diverse bioactivities, including antimicrobial, anticancer, antiviral, and immunomodulatory activities. The state-of-the-art green technologies for extraction and purification of MBPCs, along with the modern progress in the identification and characterization of MBPCs, have accelerated the discovery of novel active pharmaceutical compounds. However, several factors regulate the production of these bioactive phenolic compounds in microalgae. Furthermore, some microalgae species produce toxic phenolic compounds that negatively impact the aquatic ecosystem, animal, and human life. Therefore, the focus of this review paper is to bring into light the current innovations in bioprospection, extraction, purification, and characterization of MBPCs. This review is also aimed at a better understanding of the physicochemical factors regulating the production of MBPCs at an industrial scale. Finally, the present review covers the recent advances in toxicological evaluation, diverse applications, and future prospects of MBPCs in biopharmaceutical industries.