Suppression of pro-inflammatory signalling pathways by sulforaphane
Low-grade inflammation has been associated with the risk of chronic pathologies including cancer, atherosclerosis and type 2 diabetes. Epidemiological studies demonstrate an inverse correlation between diets rich in cruciferous vegetables and risk of cancer, cardiovascular disease mortality and circulating levels of pro-inflammatory cytokines. Sulforaphane (SF), an isothiocyanate obtained from broccoli, has many biological functions. The aim of this thesis was to test whether SF was able to suppress pro-inflammatory signalling using in vitro models of chronic inflammation. In human monocytes (PBMCs and THP-1 cells), physiologically relevant concentrations of SF significantly suppressed the production of LPS-induced cytokines IL-6, IL-1β and TNFα. The suppression was also observed with all genes induced by 1ng/ml LPS as measured by whole genome arrays. In addition, it was demonstrated that SF could directly interact with thiol groups of cysteine residues 609 and 246 within the LPS receptor, TLR4 under non-reducing conditions, to reduce the levels of inflammatory mediators that are produced in response to LPS. The anti-inflammatory effect of SF was not restricted to the TLR4 pathway, and significant reductions were observed in NF-κB activity induced in response to TLR2 and NOD2 ligands. These findings were translated into a more complex in vitro model, investigating the effect of SF on lipid accumulation within adipocytes and adipose tissue inflammation in response to macrophage-conditioned medium (MaCM) using human SGBS adipocytes. SF at 10μM significantly reduced levels of lipid accumulation within adipocytes and increased the expression of carnitine palmitoyltransferase-1A (CPT1A), suggesting a role in energy metabolism, a process often disrupted in obesity. In addition, a significant suppression in SGBS adipocyte IL-1β and IL-6 expression was observed when adipocytes were exposed to MaCM from SF-treated macrophages, when SF was used at a concentration as low as 2μM. This work demonstrates that concentrations of SF that could be achieved via reasonable broccoli consumption can suppress pro-inflammatory cytokine production, induced in response to a number of signalling pathways in addition to suppression of lipid accumulation and adipose tissue inflammation. The relevance of this data supports the concept that consumption of broccoli could lead to a reduction in the chronic inflammatory status in vivo as well as a suppression of lipid accumulation within adipocytes, to reduce the risk of developing chronic disease.
Networked Digital Library of Theses and Dissertations