## 2 Bioactive Compounds Present in _Cystoseira_ Extracts for Neurodegenerative Disease Management
### F#  
Fucoidans form a group of sulfated polysaccharides present in brown algae and are generally linear, composed mainly of repeated units of sulfated fucoses in C-2 and/or C-4 with \(\alpha\)-(1-3) and/or \(\alpha\)-(1-4) bonds [81]. The chemical composition varies according to the species of algae and can vary within the same species [33]. The anti-inflammatory and antioxidant activities of fucoidan extracts from three Mediterranean species of the genus \(C\)\(\bullet\)\  
most common ones consist in carbon nanotubes, gold, silver and magnetic NPs, among others. Micelles, liposomes, solid lipid NPs and dendrimers t the organic type of carriers. NPs are very versatile and have numerous applications in the eld of biomedicine, which are listed in Table 2 and Figure 4.  
NPs can be directed to the desired local of the treatment either by passive or active targeting. Passive targeting is often associated with the treatment of various types of tumors. This is due to the irregularities that the vascularity around tumors present, having various leakages such as leaky vasculature and defective lymphatic drainage due to the rapid and uncontrolled growth needed to supplement cancer cells, for the growth of the tumor. One can use NPs with a small size that can accumulate speci call in these leakage sites around the tumor and reach their desired therapeutic site [90]. Although this method can be simple and ef cient, active targeting is normally preferred since there is no ef cient passive method to deliver molecules to other diseases in other parts of the human body. Active targeting consists in the functionalization of the surface of nanoparticles with molecules that are  
Figure 4: Main nanoparticle types and strategies to achieve accumulation in target tissues, by passive or active (including ligand-mediated) targeting. specifically recognized by cells in the local of the treatment. Moreover, this functionalization can improve the nanoparticles pharmacokinetic and pharmacodynamic properties [91]. These can include various types of antibodies, folic acid, proteins, and hyaluronic acid, among others (Figure 4). Interestingly, algae extracts are often utilized not only as compounds that are encapsulated in NPs for the treatment of various diseases, but also as stabilizers and catalyzers for metallic NPs production [92; 93]. In addition, some studies combine the use of chitosan-based NPs with commercially acquired bioactive compounds, such as fucoidan, developing thus chitosan/fucoidan NPs for the delivery of chemicals in breast cancer treatment and nerve regeneration [94; 95]. Regarding the last three years, we can find some studies based on fucoidan-based nanoparticles, which allow the enhancement of fucoidan biological activity. In addition, it has already been demonstrated that the synthesis of NPs is promoted by the molecular weight, as well as the structure of fucoidan [96]. Furthermore, the combination of this natural compound with others, or even drugs, may result in the enhancement of the desired effect. As example, [PERSON] and colleagues have developed fucoidan-coated mesoporous silica NPs to deliver curcumin to the colon tumor site microenvironment [97], which is a polyphenol compound that has also been shown to have neuroprotective effects [98]. The green synthesis of NPs is also a very current topic, which makes it possible to take full advantage of the therapeutic properties, avoiding the use of highly toxic materials and proving to be an ecologically correct and low-cost technique [99; 100]. A much smaller number of studies that deliver compounds using NPs are found. [PERSON] and colleagues have developed mesoporous silica NPs to deliver fucoidan to A549 cells [101], and, in line with the main application that we review in this article, PLGA-PEG NPs were developed by [PERSON] and colleagues to facilitate anti-Alzheimer's effects of fucoxanthin [102]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Nanosystem** & **Size (nm)** & **Characteristics** & **Applications** & **Refs.