## 7 MAA Bioactivities  
Considering the ability of MAAs to absorb light between 310 and 360 nm, which comprises the UV-B and UV-A spectrum, numerous studies have focused on their potential for the development of natural sunscreens. UV radiation also induces high production of reactive oxygen species (ROS) that can promote other effects, such as premature skin aging or immunosuppression. Thus, photoproduction also involves other bioactivities such as antioxidant, immuno-modulatory, or anti-aging properties [41; 140; 141] (Figure 5). Several authors analyzed the potential antioxidant activity of MAAs in vitro. Wada et al. [41] reviewed the molecular diversity of MAAs and their antioxidant activities. De la Coba et al. [127] evaluated, using different methods, the antioxidant potential of different MAAs (mycyclicine, asterine-330, shinorine, and porphyra-334). The authors found that the antioxidant activity of all MAAs depended on the dose and pH, with greater activity in alkaline pH. Mycosporine-glycine showed the highest activity in all pH tested. This MAA had previously shown concentration-dependent antioxidant potential [142]. More recently, Torres et al. [143] observed high antioxidant activity in some limino-MAAs (polyhrine, asterina-330, shinorine, or porphyra-334) under alkaline pH. However, they also found pro-oxidant effects in some of these MAAs. Most of the studies concluded that MAAs can eliminate ROS in vitro, although the role of these molecules in vivo is not yet fully understood. In addition, the antioxidant activity of MAAs can also increase due to changes in the molecules such as glycosylations or hybridizations with the chromophores [41]. A high production of ROS can also cause elastic fiber dystrophy and secretion of elastases, which activate matrix metalloproteinases (MMPs). MMPs and elastases degrade collagen and elastin fibers, respectively. The reduction of collagen and elastin leads to the formation of wrinkles and accelerated aging [144]. For this reason, MAAs that prevent ROS production and activation of MMPs have high potential to prevent photoaging. Ryu et al. [123] studied the anti-photoaging role of the MAA porphyra-334. This MAA reduces the reactive oxygen species (ROS) production and the levels of matrix metalloproteinases (MMPs) in human fibroblasts exposed to UV-A. Hartmann et al. [145] also demonstrated the inhibition of metalloproteinases by porphyra-334, shinorine, and paly  
Figure 5: Scheme of the different bioactivities described in MAAs, indicating the relevance of some MAAs [33; 41; 142; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155]. thine. Orfanoudaki et al. [146] investigated the collagenase inhibition activity of different isolated MAAs. The authors proved the collagenase inhibition activity for all MAAs, and the inhibition of glycation end products in most of MAAs, which is a property that prevents a decrease in skin elasticity. They also evidenced the ability of shinorine, porphyra-334, mycosporine-glycine-alanine, and bostrychine B to stimulate human keratinocyte migration in vitro, indicating a wound-healing property. Oxidative stress can also activate various biochemical pathways related to immunotherapy-modulatory activities. In UV-induced inflammation, cyclooxygenase-2 (COX-2) mRNA is overexpressed. Some MAAs have the potential to suppress this gene, such as mycosporine-glycine [147]. According to Lawrence et al. [33], the expression of COX-2 appears to be linked to shorter UV wavelengths. Thus, MAAs that absorb shorter wavelengths, such as mycosporine-glycine and shinorine, would be more effective in inhibiting COX-2. Exposure to UV radiation can also activate the nuclear transcription factor-kB (NF-kB), which regulates the expression of pro-inflammatory molecules. Tryptophan metabolism is also involved in immunoregulation, and its breakdown and availability depend on an IDO-1 enzyme. NF-kB and IDO-1 appear to be affected by antioxidant molecules. Becker et al.