Antioxidant Sulfated Polysaccharide from Edible Red Seaweed Gracilaria birdiae is an Inhibitor of Calcium Oxalate Crystal Formation.

The genus Gracilaria synthesizes sulfated polysaccharides (SPs). Many of these SPs, including those synthesized by the edible seaweed Gracilaria birdiae, have not yet been adequately investigated for their use as potential pharmaceutical compounds. Previous studies have demonstrated the immunomodulatory effects of sulfated galactans from G. birdiae. In this study, a galactan (GB) was extracted from G. birdiae and evaluated by cell proliferation and antioxidant tests. GB showed no radical hydroxyl (OH) and superoxide (O2-) scavenging ability. However, GB was able to donate electrons in two further different assays and presented iron- and copper-chelating activity. Urolithiasis affects approximately 10% of the world's population and is strongly associated with calcium oxalate (CaOx) crystals. No efficient compound is currently available for the treatment of this disease. GB appeared to interact with and stabilize calcium oxalate dihydrate crystals, leading to the modification of their morphology, size, and surface charge. These crystals then acquired the same characteristics as those found in healthy individuals. In addition, GB showed no cytotoxic effect against human kidney cells (HEK-293). Taken together, our current findings highlight the potential application of GB as an antiurolithic agent.

Anti-Thrombin, Anti-Adhesive, Anti-Migratory, and Anti-Proliferative Activities of Sulfated Galactans from the Tropical Green Seaweed, Udotea flabellum.

In this study, sulfated polysaccharide-rich extracts were isolated from 22 tropical seaweeds (4 red, 11 brown, and 7 green) found in northeastern Brazil, and evaluated for the role of anticoagulant agents. Fifteen of the extracts showed anticoagulant activity, including all the extracts from green seaweeds. Udotea flabellum (a green seaweed) extract was the most potent, requiring an amount of only 3 µg to double the plasma coagulation time in the activated partial thromboplastin time test. A similar result was obtained with 1 µg of heparin. Two sulfated homogalactans with anticoagulant activity, F-I (130 kDa) and F-II (75 kDa), were isolated from this extract using several bio-guided purification steps. Their anticoagulant activity, as well as properties related to antitumor activity (anti-proliferative, anti-adhesive, and anti-migratory), were accessed. Their anticoagulant activities were close to that of heparin. We found that F-I and F-II (0.5⁻10 µg/mL) were not able to directly inhibit thrombin. In the presence of anti-thrombin, F-I (0.5 µg/mL) was more effective than heparin (0.5 µg/mL) in inhibiting thrombin, while F-II showed similar effects as heparin. F-I and F-II also inhibited B16-F10 (murine melanoma cells) adhesion, migration, and proliferation on a fibronectin-coated surface, but not on laminin- or collagen I-coated surfaces. Except for the antiproliferative activity, the other effects of F-I and F-II were eliminated upon their desulfation (~50%), indicating that the degree of sulfation is not as important for F-I and F-II anti-proliferative activity as the sulfation position. Taken together, the results provide strong evidence for the potential utility of sulfated galactans from U. flabellum, making these compounds an interesting option for future investigations that aim to design new anticoagulant/antitumor agents.

Antibacterial, Antiproliferative, and Immunomodulatory Activity of Silver Nanoparticles Synthesized with Fucans from the Alga Dictyota mertensii.

In this study, we aimed to synthesize silver nanoparticles containing fucans from Dictyota mertensii (Martius) Kützing using an environmentally friendly method and to characterize their structure as well as antiproliferative, immunomodulatory, and antibacterial effects. Fucan-coated silver nanoparticles (FN) were characterized by Fourier-transform infrared analysis, dynamic light scattering, zeta potential, atomic force microscopy, energy dispersive X-ray spectroscopy, and inductively coupled plasma emission spectrometry. They were evaluated for their effect on cell viability, minimum inhibitory bactericidal concentration, and release of nitric oxide and cytokines. The FN were successfully synthesized using an environmentally friendly method. They were size-stable for 16 months, of a spherical shape, negative charge (-19.1 mV), and an average size of 103.3 ± 43 nm. They were able to inhibit the proliferation of the melanoma tumor cell line B16F10 (60%). In addition, they had immunomodulatory properties: they caused an up to 7000-fold increase in the release of nitric oxide and cytokines (IL-10; IL-6 and TNF-α) up to 7000 times. In addition, the FN showed inhibitory effect on Gram-positive and -negative bacteria, with MIC values of 50 µg/mL. Overall, the data showed that FN are nanoparticles with the potential to be used as antitumor, immunomodulatory, and antibacterial agents.