Role of taraxerone isolated from Leucas lavandulifolia, as an immunomodulator

The Indian tradition system of medicine enlists a large number of plants for basic health care. Leucas lavandulifolia is mentioned in the ayurvedic medicinal system and also used among the folklores. The plant is used for the treatment of fever, asthma, psoriasis, dermatitis and healing snake bites. The scientific validation of the plant for their traditional use in different immune related disorders are yet to be explored.

The study aims to isolate immunomodulatory active compound from Leucas lavandulifolia and evaluating its efficiency in immune related disorders.

The immunomodulatory activity of the phytocompound is evaluated through in vitro and in vivo studies. The compound purification and identification were done by chromatography and LC/Q-TOF respectively. Its immunomodulatory activity was evaluated in cells like PBMC, neutrophils and macrophages by MTT assay and cell cycle analysis. Animal studies were performed on Swiss albino mice. The levels of IL-4 and IL-6 cytokines were also evaluated in both in vitro and in vivo models.

Leucas lavandulifolia stem portion was found to have good modulatory property. An active immunomodulator was isolated from the methanol extract of the plant. LC/Q-TOF data revealed the isolated compound to be taraxerone. In PBMC, the compound was capable of suppressing the proliferation rate of the compound indicated by a decrease in cell numbers. The activated IL-4 and IL-6 production was also suppressed actively at 25 μg/ml of taraxerone. Similar inhibitory effects were seen in RAW 264.7 and THP-1 macrophage cell lines. An IC₅₀ value of 17.5 μg/ml was obtained for taraxerone in LPS stimulated RAW 264.7 macrophage cell lines. The NO level, IL-4, IL-6 and phagocytosis in the LPS stimulated macrophage was effectively lowered by 25 μg/ml of taraxerone. In PMA stimulated THP-1 Macrophage Cell Lines, taraxerone was capable of suppressing the cell number and IL-6. The compound didn't show any effect on IL-4 levels. The compound exhibited an immunosuppressive activity in PHA induced PMN cells by suppressing the respiratory burst and interleukins IL-4 and IL-6. TX could also suppress the proliferation of DNCB induced monocyte cells and IL-4. The haematological parameters exhibited a significant suppression for the high dose group of taraxerone. The antibody titre and phagocytic index was suppressed by the high dose group, whereas the low dose group did not have any effect. So taraxerone at 50 mg/kg body weight is capable of modulating the B-lymphocytes and macrophages. But the compound has exhibited insignificant effect on the DTH hypersensitivity response and organ index.

Taraxerone at high concentration was capable of suppressing stimulated PBMC, macrophage and PMN. The activated nitric oxide, IL-4, IL-6 production and phagocytosis was also suppressed. The haematological parameters, antibody titre and phagocytic index was also lowered in antigenically challenged mice. The terpenoid taraxerone exhibits a good modulatory effect on the immune system and proves to be a potent drug for the treatment of many allergic disorders.