Bioactive properties and applications of UV-screening compounds from some cyanobacteria and green algae

Abstract

The depletion of the ozone layer by anthropogenic emission has further exposed Earth’s surface to solar ultraviolet radiation. Cellular structures of various organisms, including microalgae and cyanobacteria naturally protect against UV-induced damage via UV-screening compounds, such as those in cinnamon and mycosporine-like amino acids. These compounds, therefore, are potential sources for UV protection and photo-oxidative stress reduction. In this research, UV-screening compounds from 74 isolates of cyanobacteria and 142 isolates of green algae were investigated by measuring the absorbance within the range of 200-400 nm by using a UV-Vis spectrophotometer. It was found that 27 isolates of green algae, 30 isolates of cyanobacteria, and 2 samples of freshwater macroalgae were extracted with methanol (MeOH). These extracts absorb light at a wavelength range of 310-365 nm. In addition, nine isolates of green microalgae, 18 isolates of cyanobacteria, and two samples of freshwater macroalgae extracted with ethyl acetate: methanol (EtOAc:MeOH), absorb light at a wavelength range of 250-400 nm. To stimulate their biomass and UV-screening compound production, two algae, namely Euastrum sp. AARL G001 and Nostoc sp. AARL C008, were cultured and the formula components of the Jaworski's medium and BG-11 medium were optimized by using the Plackett-Burman and Central Composite Design for biomass production. It was found that the optimization of both media was not significant to produce biomass. Moreover, two algae were cultured to increase the production of UV-screening compounds by varying light intensity, salinity, light and dark cycle, and UV-B exposure. The UV-screening compounds produced by Euastrum sp. AARL G001 has the highest absorbance of UV radiation under salinity of 7-56 ppt, light intensity 25 µmol photons/m2 /s, light:dark cycle of 12:12 hrs and UV-B exposure time of 1-3 hrs. Nostoc sp. AARL C008 cultured under salinity of 90.0 ppt, light intensity of 25-75 µmol photons/m2 /s, light:dark cycle of 12:12 hr, and UVB exposure time of 12-72 hr, showed the highest absorbance of UV radiation. Dried Euastrum sp. AARL G001 extracted using EtOAc:MeOH (1:1, v/v) and MeOH with 1:200 (w/v, g/mL) of algae per solvent ratio gave high absorbance of UV-screening compounds. Nostoc sp. AARL C008 used fresh algae with acetone:MeOH (1:1, v/v) and MeOH with1:200 (w/v, g/mL) of algae per solvent ratio gave high absorbance of UV-screening compounds. Furthermore, the bioactive properties from MeOH and EtOAc:MeOH crude extracts of Euastrum sp. AARL G001 and Nostoc sp. AARL C008 were examined for antioxidative activities, including ABTS, DPPH and reducing power, while a total phenolic compound was determined by the Folin-Ciocalteu reagent method. In addition, MTT assay was employed for cytotoxicity evaluation with Vero cells and melanoma cells. The crude methanolic extracts of Nostoc sp. AARL C008 showed strong antioxidative activity and high content of phenolic compounds. Also, the toxicity to cancer cells is higher than those from the Euastrum sp. ARRL G001. Moreover, the LCMS data of the methanolic extracts of the two microalgae exhibited functional relationships between metabolites and bioactive activities, as well as cinnamic acid and its derivatives. These metabolites belong to phenolic compounds, which supported the amount of total phenolic contents of Nostoc sp. C008 and the high antioxidant activity of Nostoc sp. C008. Therefore, the crude methanolic extract of Nostoc sp. AARL C008 was mixed with a base sunscreen cream by adding 5% and 20% extract. The mixture was tested for stability by heating-cooling cycles. Then, the color, odor, viscosity, separation, and pH were observed. The SPF of the cream was also measured. The results showed that the color and odor of the cream containing 5% extract was better than the cream containing 20% extract. Meanwhile, the viscosity, separation, and pH of the cream were k unchanged after 6 cycles of heating-cooling. Further, the SPF of the cream containing 5% extract was higher than the base cream by 13 times. Thus, the methanolic extracts of Nostoc sp. AARL C008 is an interesting alternative and suitable ingredient in cosmeceutical and skin products for UV protection.