Eustigmatophyte strains with potential interest in cancer prevention and treatment: partial chemical characterization and evaluation of cytotoxic and antioxidant activity.

The interest in bioactive compounds from microalgae is increasing since they have medicinal and nutritional areas. The present work aims to evaluate the potential pharmaceutical interest of extracts from three eustigmatophyte strains from the Coimbra Collection of Algae (ACOI): Chlorobotrys gloeothece, Chlorobotrys regularis and Characiopsis aquilonaris. Antioxidant and antiproliferative activities were determined as well as chlorophyll a, carotenoid and phenolic total contents. In addition, major pigments and sterols were identified and quantified. The three strains were grown until the stationary phase and then the biomass was extracted. Antioxidant activity was measured by TEAC, DPPH and FRAP assays and antiproliferative effect was assessed by the MTT method on MCF-7, PC-3 and NHDF cells. The pigment and phenolic total contents were determined by spectrophotometry. Of these strains, C. aquilonaris showed the highest antioxidant activity measured by TEAC and FRAP assays (23.98 ± 0.01 µmol TE eq g-1 DW and 42.57 ± 0.04 µmol TE eq g-1 DW, respectively), a selective effect in reduting MCF-7 cells proliferation and a larger amount of chlorophyll a, carotenoids and phenolic content (18.40 ± 0.00 µg chlorophyll a mg-1 DW, 2.27 ± 0.00 mg carotenoids g-1 DW and 6.23 ± 0.01 mg GAE g-1 DW, respectively). A positive correlation between chlorophyll a and TEAC assay was observed, as well as between carotenoids and TEAC and FRAP assays, suggesting these compounds as important contributors to significant antioxidant activity. Violaxanthin, cholesterol and stigmasterol were present in larger amount in C. aquilonaris while C. regularis showed a higher amount of ß-carotene. These results suggest that these three ACOI eustigmatophytes are promising for applications in the improvement of human health, particularly in cancer prevention and treatment.

Overcoming recalcitrance in Porphyridium aerugineum Geitler employing encapsulation-dehydration cryopreservation methods.

Cultures of the recalcitrant microalga Porphyridium aerugineum were cryopreserved. A two-step, uncontrolled rapid freezing protocol, using methanol as cryoprotectant resulted in 23.8 percent viable cells. Cultures in the exponential growth phase, grown under low light intensity to prevent vacuole formation in cells, cryopreserved using a passive freezer, showed 22.4 percent viability. This value was enhanced to 31.5 percent when a controlled-rate freezer was employed. Optimized cultures in the exponential growth phase, cultivated in medium supplemented or not with vitamin B12, were then tested for freezing using the encapsulation-dehydration protocol. High cell loss was observed early during the sorbitol dehydration steps, but 63.6 percent of the remaining encapsulated cells were viable after thawing. This study confirmed the potential of encapsulation-dehydration as a method allowing to improve the low viability obtained with two-step freezing protocols. It also showed the importance of monitoring the response of algal cells to bead osmotic and evaporative dehydration pretreatments before freezing.