In vitro Immunomodulatory Effect of Lawsone Methyl Ether on Innate Immune Response of Human Phagocytes

Objectives: Lawsone methyl ether (LME) is a naphtoquinone compound found in the leaf of Impatiens balasamina L. It has been semi synthesized by methylation of lawsone. This compound possessed several pharmacological properties including the use for the treatment of infectious diseases. This study was undertaken to determine of immunomodulatory effect of LME on immune response of human phagocytes. Methods: Trypan blue exclusion method was applied to determine cell viability. A modified 48- well Boyden chamber was used to assess chemotactic activity, luminolbased chemiluminescene assay was performed to evaluate the effect of compound on respiratory burst of human phagocytes, while Myeloperoxidase (MPO) activity was observed using colorimetric assay. Results: LME at 6.25 and 100 μg/mL were non-toxic against the phagocytes after 25 h incubation. This compound showed strong inhibitory effect on the migration of polymorphonuclear cells (PMNs) towards chemoattractant with IC50 value of 7.63 µg/mL and was comparable to ibuprofen as a positive control. This compound also inhibited MPO enzyme system on PMNs with IC50 of 24.6 µg/mL. Preliminary screening on whole blood, LME strongly inhibited respiratory burst with IC50 value of 8.51 µg/mL. Furthermore, this compound also demonstrated a high inhibition effect on reactive oxygen species (ROS) production of PMNs and monocytes with IC50 of 9.43 and 6.49 µg/mL, respectively. Conclusion: These results suggest that LME was able to suppress human phagocyte at the different steps including chemotaxis and production of oxidative stress. This finding might emphasize that LME has potency as an anti-inflammatory agent by modulating innate response of human phagocytes.