An In Vitro and In Silico Study of Luteolin-Loaded Zinc Oxide Nanoparticles: Enhancing Bioactivity and Efficacy for Advanced Therapeutic Applications Against Cariogenic Microorganisms.

Introduction Recent studies have explored alternative methods to enhance caries prevention and treatment. Luteolin compound has been noted for its antimicrobial properties, while zinc nanoparticles (Zn NPs) are recognized for their potent antibacterial effects. This study investigates the synthesis, characterization, and antimicrobial efficacy of luteolin-loaded Zn oxide NPs (Luteo-ZnONPs) against cariogenic bacteria. By combining the biofilm-targeting capabilities of luteolin with the antimicrobial properties of Zn NPs, we aim to explore a novel approach for dental caries management. Methods Luteo-ZnONPs were synthesized and characterized using ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy, confirming their successful formation and stability. Antimicrobial efficacy was assessed through minimum inhibitory concentration (MIC), demonstrating effectiveness against cariogenic bacteria such as , and in different concentrations. The agar well plate method was employed to analyze the growth inhibitory effect of Luteo-ZnONPs (50 and 100 µg/ml, respectively). Streptomycin (100 µg/ml) was used as a positive control. The results (zone of inhibition (ZOI) in millimeter, mm) were represented as mean ± standard deviation. One-way analysis of variance (ANOVA) was employed to detect the significance (p < 0.05) between the groups. Cytotoxicity was analyzed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against MG63 cells, and doxorubicin was used as a positive control. Wilcoxon rank test was used for the statistical method. Gyrase B was downloaded from Protein Data Bank (PDB id: 6F86) and docked against luteolin using Autodock software (version 4.2). The binding score was presented as kcal/mol in table format. Results Characterization results showed that UV-vis spectroscopy revealed characteristic peaks, indicating the successful synthesis and stability of Luteo-ZnONPs. FTIR spectroscopy confirmed the presence of functional groups from luteolin compound interacting with the Zn NPs. It showed effective inhibition against  on 50 µg/ml as 12.45 mm as ZOI and increased with concentration (100 µg/ml as 17.13 mm). It showed minimal ZOI on  (8.12, 12.21 on 50 and 100µg/ml, respectively). The cytotoxicity of Luteo-ZnONPs was lesser than doxorubicin on MG63 cells with statistical high significance (p < 0.0014). These results showed that Luteo-ZnONPs had effective antimicrobial nature against family. Thus, gyrase B from was selected for the molecular docking analysis. The catalytic tunnel in gyrase B , PDB: 6F86), influenced by Luteo-ZnONPs, indicated potential for novel, broad-spectrum antimicrobials via selective inhibition at conserved active sites.  Conclusion The agar well plate and MIC confirmed that Luteo-ZnONPs exhibited potent antibacterial activity, especially at higher concentrations compared to streptomycin. One- way ANOVA demonstrated significant differences in antibacterial efficacy between treatments, validating its superior performance. Its strong interaction on in silicolevel showed the targeted mechanism of action. Luteo-ZnONPs showed lesser toxicity than doxorubicin on MG63 cells. These findings underscore the potential of its broad spectrum antimicrobial nature paving the way for its development into innovative, nontoxic therapeutic solutions.