In Vitro and In Vivo Studies on Hexane Fraction of Nitzschia palea , a Freshwater Diatom for Oxidative Damage Protective and Anti-inflammatory Response

Diatoms are eukaryotic, photosynthetic microalgae, primary producer of organic matters in aquatic environments, known for high content of carotenoids and ω-3 fatty acids. In this study, bioactive volatile compounds of hexane extract of freshwater diatom, Nitzschia palea (Kutzing) W. Smith 1856, Bacillariophyceae, were identified using gas chromatography mass spectrometry. The extract was tested for eight different in vitro anti-oxidant and free radical scavenging activities. Macromolecular damage prevention properties were investigated by electrophoretic methods, and anti-hemolytic properties were studied by lactate dehydrogenase assay, atomic force microscope, and scanning electron microscope image analysis. Further, the extract was evaluated for in vitro and in vivo anti-inflammatory properties using murine macrophage (RAW 264.7) cells and mouse model. The extract showed significant results in all eight anti-oxidant assays, DNA and protein damage prevention, and anti-hemolytic properties which are comparable with standard synthetic anti-oxidants. In vitro anti-inflammatory properties of the extract showed cell viability of IC50 93.5 μg/ml was evidenced with inhibition of inflammatory cytokines such as nitric oxide, TNF-α, IL-6, and PGE2 in all tested doses. Similarly, results of in vivo studies showed paw edema inhibition at 4 h in extract-fed mouse group, in addition to this selective inhibition of cyclooxygenase-2 and myeloperoxidase activity dose dependently. The observed activity was correlated with identified important metabolites such as 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, tetracosane, hexacosane, 1,2-benzenedicarboxylicacid butyl 2-methylpropyl ester, squalene, methyl palmitate, ethyl palmitate, heptadecane, and hentriacontane. The study concludes that the N. palea has potential pharmacologically active compounds for commercial applications in nutraceuticals and oxidative stress–related inflammatory diseases.