Antioxidant and antiproliferative potential of exopolysaccharides from marine diatom Cylindrotheca closterium (Bacillariophyceae)

Microalgae have emerged as a valuable source of novel bioactive compounds with promising applications in biomedicine, as well as in the food and cosmetics industries. This study focused on the marine diatom Cylindrotheca closterium, evaluating the antioxidant and antiproliferative potential of its exopolysaccharides (EPS). The EPS isolated from C. closterium cultures in the stationary phase yielded 50.6 mg l–1 and contained 39.0% carbohydrates and 8.1% proteins, while elemental analysis revealed 25.3% carbon, 7.2% hydrogen and 1.8% nitrogen. The antioxidant activity, determined by ABTS (2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)) and H₂O₂ scavenging assays and the total antioxidant capacity (TAC) assay, showed a dose-dependent behaviour. ABTS scavenging activity reached 38.8% at an EPS concentration of 4 mg ml–1, while H₂O₂ scavenging activity and TAC were lower compared with ascorbic acid (6% and 20%, respectively). EPS showed strong antiproliferative potential in vitro against human pharynx carcinoma cells (Detroit 562) and human colon cancer cells (SW480, SW620, HCT116) by completely eradicating Detroit 562 cells at 750 μg ml–1 and reducing the survival of SW480, SW620 and HCT116 cells to 27%, 37% and 27%, respectively. These results suggest that C. closterium EPS possesses antioxidant and particularly antiproliferative properties, supporting its potential as a natural bioactive substance. Cylindrotheca closterium EPS shows mild antioxidant and strong antiproliferative activity.EPS inhibited the growth of human pharynx and colon carcinoma cells in vitro.EPS completely eradicated human pharynx carcinoma cells (Detroit, 562). Cylindrotheca closterium EPS shows mild antioxidant and strong antiproliferative activity. EPS inhibited the growth of human pharynx and colon carcinoma cells in vitro. EPS completely eradicated human pharynx carcinoma cells (Detroit, 562).