Immunomodulatory effects of clove (Syzygium aromaticum) constituents on macrophages: In vitro evaluations of aqueous and ethanolic components

Abstract

The present work sought to investigate potential suppressive effects on mouse macrophages by in vitro treatment with clove (Syzygium aromaticum) ethanolic extracted essential oil (containing eugenol) or its water-soluble extract. Using doses (ranging from 0.001-1000 μg/ml) of each material freshly prepared in the laboratory, cell survival and production of nitric oxide (NO), tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-12 by the treated cells (that in all cases also had received LPS stimulation) were measured. Results indicated that, except at doses ≥100μg/ml, viability was unaffected in all groups. NO release by LPS-stimulated macrophages was generally significantly suppressed by either material; in contrast, low (i.e. 0.001-1 μg/ml) doses of either extract class appeared to enhance NO release by non-LPS (unstimulated)-treated macrophages. Among LPS-stimulated cells, TNFα release was also significantly affected by each extract; the ethanolic extract was suppressive at all doses tested, while the aqueous material was so up to 1 μg/ml and then became stimulatory. In contrast, nearly every dose of either extract appeared to stimulate IL-6 release from the LPS-treated cells. Effects on IL-12 production were overall inconsistent; in general, the ethanolic extract tended to be stimulatory of production by the LPS-treated cells. The data for the aqueous material showed no discernable pattern of effect. The results suggest that clove extracts do not have a distinct cytotoxic activity, but do impart potential anti- and pro-oxidant effects in cells, depending on their concentrations and on the activation state of the macrophages themselves at the time of exposure to the extracts. The impact of the extracts on macrophage cytokine release also displays a pattern of dose-relatedness.