Immunostimulatory and antioxidant activities of a lignin isolated from Conocarpus erectus leaves.

In this work, we investigated the antioxidant and immunomodulatory activities of a lignin isolated from Conocarpus erectus leaves. The lignin was characterized by FTIR, 1H NMR, 13C NMR and gel permeation chromatography analysis as well as ultraviolet/visible absorption spectra. The lignin was evaluated for total antioxidant activity (TAA), DPPH and ABTS+ scavenging abilities, and by a lipid peroxidation inhibition assay. Immunomodulatory activity of the lignin (10 μg/mL) on human peripheral blood mononuclear cells (PBMCs) was determined. The C. erectus lignin was found to be of the guaiacyl-syringyl-p-hydroxyphenyl (G-S-H) type, with an average molecular weight of 2709 Da (polydispersity index: 2.1). It showed low TAA (17.92%) and moderate antioxidant activity against DPPH and ABTS+ (IC50: 231.16 and 356.03 μg/mL, respectively). It also inhibited lipid peroxidation by 42.14%. The lignin promoted an increase in mitochondrial ROS levels as well as cytosolic Ca2+ in PBMCs. In addition, it promoted the differentiation and activation of CD8+ T lymphocytes, differentiation of CD14+ monocytes, and stimulated the release of nitric oxide and cytokines, mainly those linked to a Th1 response. The results showed that the C. erectus lignin may be used in future studies in which the modulation of the immune response is a key factor.