Investigating the Antioxidant, Pro-Inflammatory Enzyme Inhibitory, Neuroprotective, and Antineuroinflammatory Bioactives of <i>Osbeckia octandra</i> Using <i>In Vitro</i> and <i>In Silico</i> Approaches: A Pilot Study

<i>Osbeckia octandra</i> (Melastomataceae) is an endemic Sri Lankan edible plant traditionally used for liver health. Oxidative stress, pro-inflammatory enzyme-mediated hepatic inflammation, and neuroinflammation are interconnected conditions that exacerbate liver diseases. The study investigates the antioxidant, pro-inflammatory enzyme inhibitory, neuroprotective, and antineuroinflammatory potential of the bioactives from <i>O. octandra</i>. The leaves were sequentially extracted with petroleum ether, ethyl acetate, and ethanol using a cold extraction technique. Antioxidant activity was evaluated using DPPH free radical scavenging and oxygen radical absorbance capacity (ORAC) assays. Pro-inflammatory enzyme inhibition was assessed using lipoxygenase (LOX), xanthine oxidase, hyaluronidase, and nitric oxide production inhibition assays. Bioassay-guided fractionation was conducted using chromatography techniques, and the compounds were characterized using spectroscopic techniques. <i>In silico</i> investigations computationally validated the promising experimental findings. The ethyl acetate extract showed the highest LOX inhibition (IC₅₀: 36.21 ± 1.09 μg/mL), the highest DPPH free radical scavenging activity (IC₅₀: 42.29 ± 1.29 μg/mL), and the highest ORAC (470.33 ± 3.16 mg TE/g). The LOX inhibition-guided fractionation of the ethyl acetate and petroleum ether extracts led to the isolation of the compounds casuarinin (<b>1</b>) and lupeol (<b>2</b>), respectively. Casuarinin (<b>1</b>) showed strong, dose-dependent anti-LOX (IC₅₀: 33.94 ± 0.59 μg/mL) and antioxidant activities. <i>In silico</i> investigation predicted that casuarinin (<b>1</b>) forms multiple hydrogen bonds at the LOX active site despite kinetically limited active site access. Casuarinin (<b>1</b>) exhibited dose-dependent (13.3-213.3 μM) antineuroinflammatory properties (>50%) in mouse microglia cells. It also demonstrated significant neuroprotective effects on H₂O₂-induced apoptotic SH-SY5Y neuroblastoma cells, with a notable increase in cell viability at 10.7 μM (73.74 ± 2.04%) and 106.7 μM (99.07 ± 1.43%). The bioactives from <i>O. octandra</i> exhibited significant antioxidant, LOX enzyme inhibitory, antineuroinflammatory, and neuroprotective properties, substantiating its therapeutic potential, positioning it as a promising candidate for phytotherapeutic applications.