Tocochromanol Profiles in Chlorella sorokiniana, Nannochloropsis limnetica and Tetraselmis suecica Confirm the Presence of 11'-α-Tocomonoenol in Cultured Microalgae Independently of Species and Origin

Metabolism of 11'-α- and 11'-γ-Tocomonoenols in HepG2 Cells Favors the γ-Congener and Results Predominantly in Carboxymethylbutyl-Hydroxychromans

SCOPE

Tocomonoenols (T1) are little-known vitamin E derivatives naturally occurring in foods. Limited knowledge exists regarding the cellular uptake and metabolism of α-tocomonoenol (αT1) and none about that of γ-tocomonoenol (γT1).

METHODS AND RESULTS

The study investigates the cytotoxicity, uptake, and metabolism of αT1 and γT1 in HepG2 cells compared to the α- and γ-tocopherols (T) and -tocotrienols (T3). None of the studied tocochromanols are cytotoxic up to 100 µmol L-1. The uptake of the γ-congeners is significantly higher than that of the corresponding α-forms, whereas no significant differences are observed based on the degree of saturation of the sidechain. Carboxymethylbutyl-hydroxychromans (CMBHC) are the predominant short-chain metabolites of all tocochromanols and conversion is higher for γT1 than αT1 as well as for the γ-congeners of T and T3. The rate of metabolism increases with the number of double bonds in the sidechain. The rate of metabolic conversion of the T1 is more similar to tocopherols than to that of the tocotrienols.

CONCLUSION

This is the first evidence that both αT1 and γT1 follow the same sidechain degradation pathway and exert similar rates of metabolism than tocopherols. Therefore, investigation into the biological activities of tocomonoenols is warranted.

Monodopsis subterranea is a source of α-tocomonoenol, and its concentration, in contrast to α-tocopherol, is not affected by nitrogen depletion

α-Tomonoenols (αT1) are tocochromanols structurally related to tocopherols (T) and tocotrienols (T3), the bioactive members of the vitamin E family. However, limited evidence exists regarding the sources and biosynthesis of tocomonoenols. Nitrogen depletion increases the content of α-tocopherol (αT), the main vitamin E congener, in microalgae, but little is known regarding its effect on other tocochromanols, such as tocomonoenols and tocotrienols. We therefore quantified the concentrations of T, T1, and T3, in freeze-dried biomass from nitrogen-sufficient, and nitrogen-depleted Monodopsis subterranea (Eustigmatophyceae). The identities of isomers of αT1 were confirmed by LC-MS and GC-MS. αT was the predominant tocochromanol (82% of total tocochromanols). αT1 was present in higher quantities than the sum of all T3 (6% vs. 1% of total tocochromanols). 11'-αT1 was the main αT1 isomer. Nitrogen depletion increased αT, but not αT1 or T3 in M. subterranea. In conclusion, nitrogen depletion increased the content of αT, the biologically most active form of vitamin E, in M. subterranea without affecting αT1 and T3 and could potentially be used as a strategy to enhance its nutritional value but not to increase αT1 content, indicating that αT1 accumulation is independent of that of αT in microalgae.

LC-Orbitrap-HRMS Determination of Two Novel Plastochromanol Homologues

SCOPE

The antioxidant plastochromanol-8 (PC-8) is a tocochromanol which differs from γ-tocotrienol in having an unsaturated side chain of eight instead of three isoprene units. The recent isolation of PC-8 from flaxseed oil indicates the additional presence of lower shares of two previously unknown homologues, plastochromanol-7 (PC-7) and plastochromanol-9 (PC-9), which feature seven and nine isoprenoid units respectively on the γ-chromanol backbone. Here, a fast LC-Orbitrap-HRMS method is applied for the determination of PC-7 and PC-9 in seven plant oils and a plant extract.

METHODS AND RESULTS

The presence of PC-7, PC-8, and PC-9 is confirmed in all eight investigated samples by LC-Orbitrap-HRMS analysis after saponification. PC-8 amounts of ≈315-350 mg kg-1 in two flaxseed oils, ≈75 mg kg-1 in rapeseed oil, ≈38 mg kg-1 in camelina oil, ≈80-120 mg kg-1 in two mustard oils, ≈90 mg kg-1 in candle nut oil, and ≈900 mg kg-1 dry weight in Cecropia leaves are determined by quantification. Semi-quantification of PC-7 and PC-9 indicated the presence of ≈0.1-1% of PC-7 and PC-9 in varied relative ratios.

CONCLUSION

The novel plastochromanol homologues are of particular interest to researchers with focus on vitamin E and other tocochromanols because of their unexplored bioactivity.

Diet effects on longevity, heat tolerance, lipid peroxidation and mitochondrial membrane potential in Daphnia

The dietary supply of polyunsaturated fatty acids (PUFA) crucially affects animals' performance at different temperatures. However, the underlying physiological mechanisms are still insufficiently understood. Here, we analyzed lifespan and heat tolerance of four genotypes of Daphnia magna reared on either the green alga Scenedesmus obliquus that lacks long-chain (> C18) PUFA, or the heterokont alga Nannochloropsis limnetica that contains C20 PUFA, both either at saturating and near-starvation levels. A significant genotype-by-diet interaction in lifespan was observed at saturating diets. The C20 PUFA-rich diet eliminated differences in lifespan among genotypes on the PUFA-deficient diet. Corrected for body length, acute heat tolerance was higher at low than at high food concentration, at least in the older of the two age groups analyzed. Genotypes differed significantly in heat tolerance, but there were no genotype-by-diet interactions. As predicted, the C20 PUFA-rich diet resulted in higher lipid peroxidation (LPO) and a lower mitochondrial membrane potential (ΔΨ_m). LPO levels averaged across clones and rearing conditions were inversely related to acute heat tolerance. Yet, heat tolerance was higher on the PUFA-rich diet than on the PUFA-deficient diet, particularly in older Daphnia, indicating that the C20 PUFA-rich diet allowed Daphnia to compensate for higher LPO. In contrast, Daphnia with intermediate levels of ΔΨ_m showed the lowest heat tolerance. Neither LPO nor ΔΨ_m explained the diet effects on lifespan. We hypothesize that antioxidants present in the PUFA-rich diet may have enabled higher heat tolerance of Daphnia despite higher LPO, which may also explain the lifespan expansion of otherwise short-lived genotypes.

Sustainable Microalgae and Cyanobacteria Biotechnology

Marine organisms are a valuable source of new compounds, many of which have remarkable biotechnological properties, such as microalgae and cyanobacteria, which have attracted special attention to develop new industrial production routes. These organisms are a source of many biologically active molecules in nature, including antioxidants, immunostimulants, antivirals, antibiotics, hemagglutinates, polyunsaturated fatty acids, peptides, proteins, biofuels, and pigments. The use of several technologies to improve biomass production, in the first step, industrial processes schemes have been addressed with different accomplishments. It is critical to consider all steps involved in producing a bioactive valuable compound, such as species and strain selection, nutrient supply required to support productivity, type of photobioreactor, downstream processes, namely extraction, recovery, and purification. In general, two product production schemes can be mentioned; one for large amounts of product, such as biodiesel or any other biofuel and the biomass for feeding purposes; the other for when the product will be used in the human health domain, such as antivirals, antibiotics, antioxidants, etc. Several applications for microalgae have been documented. In general, the usefulness of an application for each species of microalgae is determined by growth and product production. Furthermore, the use of OMICS technologies enabled the development of a new design for human therapeutic recombinant proteins, including strain selection based on previous proteomic profiles, gene cloning, and the development of expression networks. Microalgal expression systems have an advantage over traditional microbial, plant, and mammalian expression systems for new and sustainable microalga applications, for responsible production and consumption.