Antioxidant, Antibacterial, and Antiparasitary Activities of Green Nanoparticles Synthesized Using Water-Soluble Melanins of Fruits

Vitex Genus as a Source of Antimicrobial Agents

Vitex L. is the largest genus of the Lamiaceae family, and most of its species are used in the traditional medicinal systems of different countries. A systematic review was conducted, according to the PRISMA methodology, to determine the potential of Vitex plants as sources of antimicrobial agents, resulting in 2610 scientific publications from which 141 articles were selected. Data analysis confirmed that Vitex species are used in traditional medicine for symptoms of possible infectious diseases. Conducted studies showed that these medicinal plants exhibited in vitro antimicrobial activity against Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. Vitex agnus-castus L. and Vitex negundo L. have been the most studied species, not only against bacterial strains but also against fungi such as Aspergillus niger and Candida albicans, viruses such as HIV-1, and parasites such as Plasmodium falciparum. Natural products like agnucastoside, negundol, negundoside, and vitegnoside have been identified in Vitex extracts and their antimicrobial activity against a wide range of microbial strains has been determined. Negundoside showed significant antimicrobial activity against Staphylococcus aureus (MIC 12.5 µg/mL). Our results show that Vitex species are potential sources of new natural antimicrobial agents. However, further experimental studies need to be conducted.

Recent Applications of Melanin-like Nanoparticles as Antioxidant Agents

Nanosized antioxidants are highly advantageous in terms of versatility and pharmacokinetics, with respect to conventional molecular ones. Melanin-like materials, artificial species inspired by natural melanin, combine recognized antioxidant (AOX) activity with a unique versatility of preparation and modification. Due to this versatility and documented biocompatibility, artificial melanin has been incorporated into a variety of nanoparticles (NP) in order to give new platforms for nanomedicine with enhanced AOX activity. In this review article, we first discuss the chemical mechanisms behind the AOX activity of materials in the context of the inhibition of the radical chain reaction responsible for the peroxidation of biomolecules. We also focus briefly on the AOX properties of melanin-like NP, considering the effect of parameters such as size, preparation methods and surface functionalization on them. Then, we consider the most recent and relevant applications of AOX melanin-like NPs that are able to counteract ferroptosis and be involved in the treatment of important diseases that affect, e.g., the cardiovascular and nervous systems, as well as the kidneys, liver and articulations. A specific section will be dedicated to cancer treatment, since the role of melanin in this context is still very debated. Finally, we propose future strategies in AOX development for a better chemical understanding of melanin-like materials. In particular, the composition and structure of these materials are still debated, and they present a high level of variability. Thus, a better understanding of the mechanism behind the interaction of melanin-like nanostructures with different radicals and highly reactive species would be highly advantageous for the design of more effective and specific AOX nano-agents.

Eugenia uniflora L. Silver and Gold Nanoparticle Synthesis, Characterization, and Evaluation of the Photoreduction Process in Antimicrobial Activities

Eugenia uniflora linnaeus, known as Brazilian cherry, is widely distributed in Brazil, Argentina, Uruguay, and Paraguay. E. uniflora L. extracts contain phenolic compounds, such as flavonoids, tannins, triterpenes, and sesquiterpenes. The antimicrobial action of essential oils has been attributed to their compositions of bioactive compounds, such as sesquiterpenes. In this paper, the fruit extract of E. uniflora was used to synthesize silver and gold nanoparticles. The nanoparticles were characterized by UV–Vis, transmission electron microscopy, elemental analysis, FTIR, and Zeta potential measurement. The silver and gold nanoparticles prepared with fruit extracts presented sizes of ~32 nm and 11 nm (diameter), respectively, and Zeta potentials of −22 mV and −14 mV. The antimicrobial tests were performed with Gram-negative and Gram-positive bacteria and Candida albicans. The growth inhibition of EuAgNPs prepared with and without photoreduction showed the important functional groups in the antimicrobial activity.