Phytochemical characterization and immunomodulatory effects of aqueous and ethanolic extracts and essential oil of Moroccan Laurus nobilis L. (Lauraceae) on human neutrophils

Introduction: The leaves of Moroccan bay laurel (Laurus nobilis L.) have been used in several forms of extracts to cure rheumatic pain due to their anti-inflammatory properties. Our work aimed to evaluate the effects of aqueous and ethanolic extracts, as well as the essential oil (EO) from laurel, on the microbicidal activity of human neutrophils when compared to the effect of eucalyptol. Methods: The extracts (ethanolic and aqueous) were subject to phytochemical profiling and high-performance liquid chromatography (HPLC) analyses. The EO obtained by hydrodistillation from laurel was analyzed by gas chromatography-mass spectrometry (GC-MS). The immunomodulatory effects on neutrophil microbicidal activity of the extracts, EO, and eugenol were carried out by 3-(4,5-diméthylthiazol-2-yl)-2,5-diphényltétrazolium (MTT) assay. Results: The phytochemical analysis of the extracts revealed the presence of flavonoids, coumarins, phenols, flavone aglycones, and tannins. HPLC analysis showed the presence of numerous phenolic molecules such as syringic acid, ferulic acid, gallic acid, caffeine, and quercetin. The chemical composition of EO revealed that the major components were eucalyptol (44.14%), α-terpinyl acetate (11.11%), and β-phellandrene (6.74%). Aqueous and ethanolic extracts and EO revealed a significant and dose-dependent ability to inhibit neutrophils microbicidal activity with maximal inhibition at 200 µg/mL concentration with 30.42%, 24.7%, and 38.13%, respectively (P<0.001). Conclusion: The obtained results revealed the immunomodulatory properties of laurel as a potential natural anti-inflammatory agent that would also allow the development of new anti-inflammatory drugs.