Review of natural products actions on cytokines in inflammatory bowel disease

The purpose of this review is to provide an overview of the effects that natural products have on inflammatory bowel disease (IBD) and to provide insight into the relationship between these natural products and cytokines modulation. More than 100 studies from the past 10 years were reviewed herein on the therapeutic approaches for treating IBD. The natural products having anti-IBD actions included phytochemicals, antioxidants, microorganisms, dietary fibers, and lipids. The literature revealed that many of these natural products exert anti-IBD activity by altering cytokine production. Specifically, phytochemicals such as polyphenols or flavonoids are the most abundant, naturally occurring anti-IBD substances. The anti-IBD effects of lipids were primarily related to the n-3 polyunsaturated fatty acids. The anti-IBD effects of phytochemicals were associated with modulating the levels of tumor necrosis factor α (TNF-α), interleukin (IL)-1, IL-6, inducible nitric oxide synthase, and myeloperoxide. The anti-IBD effects of dietary fiber were mainly mediated via peroxisome proliferator-activated receptor-γ, TNF-α, nitric oxide, and IL-2, whereas the anti-IBD effects of lactic acid bacteria were reported to influence interferon-γ, IL-6, IL-12, TNF-α, and nuclear factor-κ light-chain enhancer of activated B cells. These results suggest that the anti-IBD effects exhibited by natural products are mainly caused by their ability to modulate cytokine production. However, the exact mechanism of action of natural products for IBD therapy is still unclear. Thus, future research is needed to examine the effect of these natural products on IBD and to determine which factors are most strongly correlated with reducing IBD or controlling the symptoms of IBD.