Therapeutic efficacy of Eugenol in ameliorating ovalbumin-induced allergic airway inflammation via HDAC inhibition and NF-κB downregulation in Asthma: In vivo and in silico analysis.

BACKGROUND: Asthma is a chronic inflammatory airway disorder characterized by persistent airway inflammation, oxidative stress, and airway remodeling. Eugenol, a major bioactive constituent of Syzygium aromaticum L. (clove), exhibits potent anti-inflammatory and antioxidant properties and has been traditionally utilized in Ayurveda for respiratory ailments. Nevertheless, the comprehensive and precise mechanisms underlying its anti-inflammatory effects and antioxidant capabilities against asthma not yet have been completely understood.

HYPOTHESIS/PURPOSE: The aim of the study was to investigate the therapeutic efficacy of Eugenol on OVA-induced asthma and to explore its underlying mechanisms.

STUDY DESIGN AND METHODS: Swiss albino female mice were sensitized and exposed to OVA, following administration of Eugenol by oral gavage. Samples of bronchoalveolar lavage fluid (BALF), serum and pulmonary tissues were obtained at 48 h after the final challenge. Quantification of differential inflammatory cells in the BALF and measurement of inflammatory cytokine levels were performed using ELISA. Oxidative stress was assessed by measuring serum NO levels and lung tissue levels of MDA, GSH, SOD, and CAT. Additionally, serum creatinine was evaluated to monitor the systemic safety profile of Eugenol administration. The activation of HDAC1 and NF-κB p65 signaling was investigated by semi-quantitative analysis using immunohistochemistry. In addition, the lung tissues were stained using hematoxylin and eosin as well as Masson's trichrome stain for histopathological examination. The anti-inflammatory effect of eugenol was also examined via inhibiting HDAC1 and assessed their effectiveness in silico. The study incorporated molecular docking and MDS analyses to comprehensively evaluate the binding affinity, molecular interactions, and structural stability of eugenol with its target proteins.

RESULTS: The administration of Eugenol treatment significantly reduced the expression of HDAC1 and NF-κB p65 in lung tissues. It showed antiasthmatic properties by lowering oxidative stress, decreasing MDA, and enhancing levels of GSH, CAT, and SOD. Moreover, it reduced the levels of inflammatory cytokines and nitrite in the serum of mice with acute OVA-induced asthma and ameliorated histopathological alterations. Molecular dynamics simulations conducted over 100 ns demonstrated the stability of the ligand-protein complexes, suggesting a robust connection. It also exhibited favorable docking scores of -5.70 kcal/mol with NF-κB p65 and -5.40 kcal/mol with HDAC1. The compound consistently formed complexes with the protein target in molecular dynamics simulations performed over 100 ns timeframe. The inhibitory potential of eugenol was confirmed by MM-GBSA estimates of free energy. Moreover, in silico investigations on the proposed strategy expand the therapeutic potential of eugenol in alleviating asthma symptoms.

CONCLUSION: The study demonstrates that eugenol present in clove exerts anti-asthmatic benefits by inhibiting the HDAC1 and NF-κB p65 signaling pathway.