Antioxidant and antidiabetic potential of Cystoseira myrica-mediated green metallic zinc nanoparticles using the algal extract: synthesis and characterization

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Abstract Cystoseira myrica marine macroalgae (CSR) were used to produce metallic zinc nanoparticle composites by utilizing the phytochemicals naturally found in the algae. This involves homogenizing the residuals of CSR (10 g), zinc nitrate solution (5 M; 100 ml), and methanol liquid extract (100 ml) at 30 °C for 24 h of sonication and stirring, followed by filtration and drying. This resulted in a hybrid bio-composite (Zn/CSR), which demonstrated strong antioxidant and antidiabetic properties when compared to zinc oxide (ZnO) and CSR used separately. The Zn/CSR hybrid showed excellent antioxidant activity against common radicals such as DPPH (91.5 ± 1.66%), nitric oxide (90.4 ± 1.2%), ABTS (92.2 ± 1.9%), and O2 ·− (27.8 ± 1.12%) (p < 0.05), performing better than the standard antioxidant, ascorbic acid. Regarding its antidiabetic properties, the Zn/CSR composite significantly inhibited key enzymes involved in diabetes, including both commercial enzyme forms (α-amylase (80.3 ± 1.65%), α-glucosidase (96.6 ± 1.11%), amyloglucosidase (95.8 ± 1.3%)) and their crude intestinal forms (α-amylase (72.3 ± 1.5%), α-glucosidase (94.2 ± 1.7%)) (p < 0.05). This improvement increases the impact of the green CSR extract in reducing the agglomeration behaviors of the loaded metal and the formation of a capping layer from the phytochemicals on its surface, in addition to the beneficial effects of the CSR as substrate, which enhances the biological functions of the loaded metal and its interaction interfaces. The Zn/CSR composite also outperformed commercial miglitol drugs and slightly surpassed acarbose in effectiveness. Given the high cost and potential side effects of current medications, the Zn/CSR composite could be a cost-effective alternative for antioxidant and antidiabetic treatments. These findings also emphasize the role of CSR-derived phytochemicals and algae residues in enhancing the biological activity of the metal nanoparticles.