Gunnera perpensa L. - mediated gold nanoparticles with enhanced anti-gonococcal activity

Gonorrhoea is the second most prevalent sexually transmitted disease (STD) worldwide, with its treatment increasingly compromised by antibiotic resistance to available treatments. This has led to the investigation of bioactive plants as sources for novel drug development, with plant-based nanoparticles showing promise in treating STDs. This study aimed to evaluate the anti-gonococcal activity and cytotoxicity of the ethanolic root extract of Gunnera perpensa L. (GP) and to determine whether synthesis of gold nanoparticles (AuNPs) from GP showed enhanced biological activity. Characterization of the nanoparticles was performed using ultraviolet–visible spectrometry (UV–Vis), transmission electron microscopy (TEM), dynamic light scattering (DLS), Zeta potential, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Lastly, the anti-gonococcal activity and cytotoxicity of GP and GP-AuNPs were evaluated. The AuNPs exhibited a surface plasmon resonance at 536 nm, confirming the successful synthesis of nanoparticles, with a hydrodynamic size of 127.20 nm and a core size of 39.51 nm. The GP-AuNPs showed enhanced anti-gonococcal activity compared to GP with a minimum inhibitory concentration (MIC) of 10.40 and 46.70 μg/mL, respectively. Cytotoxicity was evaluated on human keratinocytes (HaCaT), human monocytes (THP-1), and STD-related human cervical adenocarcinoma (HeLa), with GP-AuNPs exhibiting fifty percent inhibitory concentrations (IC₅₀) of 22.12 ± 0.52, 27.53 ± 6.02, and >38.96 μg/mL, respectively. In contrast, GP showed IC₅₀ values > 400 μg/mL against all tested cell lines. These findings indicate that GP-AuNPs exhibit significant anti-gonococcal activity with greater selectivity for Neisseria gonorrhoeae over non-cancerous (HaCaT and THP-1) cells, as evidenced by selectivity indices (SIs) > 2. These findings suggest that both GP and GP-AuNP possess potential as lead candidates for the treatment of gonorrhoea. Their limited antiproliferative activity against HeLa cells (SI < 0.7) indicates they are unsuitable for treating STD-associated cervical cancers. To the best of our knowledge, no published studies have investigated the effect of plant-synthesized nanoparticles on their activity against N. gonorrhoeae ; therefore, this is the first use of GP-AuNPs against N. gonorrhoeae , advancing plant-based nanomedicine for STDs.