## 4 Discussion
turuturu_ (E1-E4), bioactive compounds such as sulfated polysaccharides, phenolic compounds and carotenoids may be present and responsible for the antimicrobial activity, since they are known to alter the microbial cell permeability and to interfere with the membrane, leading to the loss of cellular integrity [34]. The wide antimicrobial activity of these extracts shows the potential for the cosmetic industry, as functional ingredients, but also as natural preservatives of cosmetic formulations, increasing the shelf-life of the product by reducing the microbial contamination [2,34]. In this study, a dose-response evaluation of each extract was performed in a mouse fibroblast cell line, 3T3, since these cells are one of the main constituents of the skin, using a range of concentrations between 0.01 and 4 mg\(\cdot\)mL\({}^{-1}\), in order to evaluate the security of the extracts for skincare applications (Figure S1). E1 and E2 (extraction with 50% ethanol/50% water) were the extracts with cell toxicity associated with more concentrations, while for E3 to E6, only the highest concentrations were responsible for a reduction in cell viability, the lowest concentrations tested being responsible for an increase in the neutral red signal, suggesting a growth promotion. The presented results show that for all the extracts tested, several concentrations were not cytotoxic to fibroblast cells, being an excellent preliminary result about their security for potential applications in skincare products. Another important feature of red seaweeds for the cosmetic industry is the production of bioactive compounds with photoproduction activity, able to protect the skin from damages such as sunburn, photo-aging, photo-dermatoses and skin cancer, among others [2,11]. The production of such compounds by macroalgae consists of electrophysiological strategies developed to avoid the deleterious effects of the constant exposure to UV radiation, through the absorption of UV radiation [11,37]. In fact, bioactive compounds able to absorb UV radiation were found to protect human fibroblasts from cell death and to retard the signs of aging induced by UV radiation [2,38]. Red macroalgae are known to produce a variety of compounds with this ability, such as phenolic compounds, pigments and MAAs. Between them, MAAs are known to be the most relevant for this function [2,37]. These secondary metabolites present high antioxidant and UV absorbing capacities, acting as excellent UV filters and thus having a great potential for the cosmetic industry as antioxidants and photoprotectors [2,29]. Based on the results obtained for cytotoxicity in 3T3 cells, a photoprotection assay using the concentrations closer to 100% of cell viability found for each extract was performed (Figure 2). Cells were exposed to a UV radiation dose capable of reaching the IC\({}_{50}\) of cells in the presence and absence of extracts. The results show that none of the extracts tested presented photoprotection capacity. From the six extracts, E1, E3, and E6 did not show any differences compared with the control (cells without extracts and exposed to UV radiation), while E2 (\(p<0.05\)), E4 (\(p<0.0001\)), and E5 (\(p<0.001\)) revealed a phototoxic behavior, which was not an expected result for hydroethanolic extracts of the red seaweed _G. turuturu_. Comparing with the UV absorbance capacity of each extract, it is not possible to correlate the data, since E1 and E2, extracts with higher ethanol concentrations and consequently more phenolic compounds, were not the ones presenting less phototoxicity. However, several factors may contribute to explain these results. Specifically, a dose-response evaluation for the phototoxicity test could help to understand the effect of extract concentrations on this bioactivity.