TNF-α modulation by natural bioactive molecules in mouse RAW 264.7 macrophage cells

The present study was designed to examine the anti-inflammatory effects of plant-derived products marketed for human health benefits.

The tumor necrotic factor-α (TNF-α) was used as a proinflammatory biomarker generated by mouse macrophage RAW 264.6 cells. The in vitro tested plant products include Saskatoon berry (SKB), quercetin, purified oat beta-glucan (OBG), curcumin, and turmeric. Quantification of TNF-α in cell culture supernatants was carried out using mouse TNF-α assay kit and the cell proliferation was determined by MTT (3-(4, 5-dimethylthiazolyl-2)-2,5- diphenyltetrazolium bromide) assay. The cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% heat-inactivated fetal bovine serum and 100 U/mL penicillin and 100 µg/mL streptomycin. Bacterial lipopolysaccharide (LPS) at a concentration of 500 ng/mL was employed to stimulate the TNF-α production in mouse macrophage cells.

Results showed that curcumin at 10 µM (3.7 µg/mL) level effectively attenuated the LPS-induced inflammatory response, and at 100 µM completely inhibited macrophage RAW cell growth (p<0.05). The aqueous turmeric extract caused inhibitory effect on TNF-α at 25, 50, 100, and 500 µg/mL. SKB inhibited TNF-α production at 50, 100, 500, and 1,000 µg/mL. On the other hand, at 10, 25, 500, and 1,000 µg/mL SKB promoted significant cell growth/proliferation. Quercetin at 10, 25, 50 and 100 µg/mL inhibited TNF-α, but at 500 and 1,000 µg/mL stimulated cell growth. OBG at 10, 25, and 50 µg/mL inhibited TNF-α, but in some cases OBG stimulated TNF-α At 1,000 and 10,000 µg/mL OBG proved to be extremely toxic or lethal to the macrophage cells.

Overall, the plant products showed anti-inflammatory effects as well as cell proliferation or inhibition in the in vitro system used in this investigation. The underlying mechanisms of dualistic actions caused by plant-derived ingredients, viz., macrophage cellular growth stimulation or retardation, remain to be elucidated.