Immune suppressive effect of cinnamaldehyde due to inhibition of proliferation and induction of apoptosis in immune cells: implications in cancer.

BACKGROUND: Besides its anti-inflammatory effects, cinnamaldehyde has been reported to have anti-carcinogenic activity. Here, we investigated its impact on immune cells. METHODS: Activation of nuclear factor-κB by cinnamaldehyde (0-10 µg/ml) alone or in combination with lipopolysaccharide was assessed in THP1XBlue human monocytic cell line and in human peripheral blood mononuclear cells (PBMCs). Proliferation and secretion of cytokines (IL10 and TNFα) was determined in primary immune cells and the human cell lines (THP1, Jurkat E6-1 and Raji cell lines) stimulated with cinnamaldehyde alone or in conjunction with lipopolysaccharide. Nitric oxide was determined in mouse RAW264.7 cells. Moreover, different treated PBMCs were stained for CD3, CD20 and AnnexinV. RESULTS: Low concentrations (up to 1 µg/ml) of cinnamaldehyde resulted in a slight increase in nuclar factor-kB activation, whereas higher concentrations led to a dose-dependent decrease of nuclear factor-kB activation (up to 50%) in lipopolysachharide-stimulated THP1 cells and PBMCs. Accordingly, nitric oxide, interleukin 10 secretion as well as cell proliferation were reduced in lipopolysachharide-stimulated RAW264.7 cells, PBMCs and THP1, Raji and Jurkat-E6 immune cells in the presence of cinnamaldehyde in a concentration-dependent manner. Flow cytometric analysis of PBMCs revealed that CD3+ were more affected than CD20+ cells to apopotosis by cinnamaldehyde. CONCLUSION: We attribute the anti-inflammatory properties of cinnamaldehyde to its ability to block nuclear factor-κB activation in immune cells. Treatment with cinnamaldehyde led to inhibition of cell viability, proliferation and induced apoptosis in a dose-dependent manner in primary and immortalized immune cells. Therefore, despite its described anti-carcinogenic property, treatment with cinnamaldehyde in cancer patients might be contraindicated due to its ability to inhibit immune cell activation

Impact of cinnamaldehyde on cytokine and NO secretion.

<p>Human PBMCs were incubated with increasing concentration of CA in the presence (black circles) or absence (open triangle) of LPS for 24 h and supernatants were analysed for A. IL10 and B. TNF-α levels. Data presented as mean ± SD from PBMCs of three subjects. C. Secretion of nitric oxide was determined in RAW264.7, stimulated with increasing concentration of CA in the presence or absence of LPS after 24 h. Representative data from one of three independent experiments, performed in triplicates. Data presented as mean ± SD; * p<0.05, in relation to control samples in each group.</p

Cinnamaldehyde induced apoptosis in human primary immune cells.

<p>Human PBMCs were incubated with CA and stained for CD3, CD20 and AnnexinV and analysed by flow cytometry. Data of three independent experiments are presented as mean ± SD of AnnexinV positive A. CD3 + cells and B. CD20 + cells.</p

Cinnamaldehyde influences NF-κB activation in human immune cells.

<p>A. THP1-XBlue cells or B. PBMCs were treated with different concentrations of CA alone (white bars) or in combination with LPS stimulation (black bars) for 24 h. Bars represent data from A. three independent experiments normalized to LPS alone group and B. three human subjects. Data presented as mean ± SD, * p<0.05.</p

Cinnamaldehyde affects viability and proliferation of human immune cells.

<p>A. Human PBMCs, B. THP-1, C. Jurkat E6-1 and D. Raji cells were incubated with increasing concentration of CA in the presence (black bars) or absence (white bars) of LPS. Viable cells were detected using a tetrazolium-based assay. Bars represent data from one of three independent experiments performed in triplicates. Data presented as mean ± SD, * p<0.05, in relation to control samples.</p