Levan promotes antiproliferative and pro-apoptotic effects in MCF-7 breast cancer cells mediated by oxidative stress.

Exopolysaccharides are high-valued bio-products produced by various microbial species and have been described to possess biological response modifying activities. These bio-products have been effective as therapeutic agents in various human disease conditions. The objective of this study was to examine the effects of levan (a (2→6)-ß-d-fructan) produced on sucrose by the halophilic bacterium, Halomonas smyrnensis AAD6T, in human breast cancer MCF-7 cells. MCF-7 cells were exposed to levan for 24 and 48h. The antiproliferative activity was analyzed by the MTT assay. Oxidative stress was measured by the CM-H2DCFDA assay, and cell apoptosis was analyzed by the caspase-3/7 assay. Cell cycle was analyzed by flow cytometry and gene expression was determined by RT-PCR. Levan showed a time- and concentration-dependent antiproliferative activity, and this effect was associated with an increase in cell apoptosis and oxidative stress. In addition, levan increased the gene expression of p53 and p27. Here we demonstrated that levan exhibited an antiproliferative effect that was mediated by an increase in apoptosis and oxidative stress.

Effective stimulating factors for microbial levan production by Halomonas smyrnensis AAD6T.

Levan is a bioactive fructan polymer that is mainly associated with high-value applications where exceptionally high purity requirements call for well-defined cultivation conditions. In this study, microbial levan production by the halophilic extremophile Halomonas smyrnensis AAD6(T) was investigated systematically. For this, different feeding strategies in fed-batch cultures were employed and fermentation profiles of both shaking and bioreactor cultures were analyzed. Initial carbon and nitrogen source concentrations, production pH, NaCl and nitrogen pulses, nitrogen and phosphorous limitations, trace elements and thiamine contents of the basal production medium were found to affect the levan yields at different extends. Boric acid was found to be the most effective stimulator of levan production by increasing the sucrose utilization three-fold and levan production up to five-fold. This significant improvement implied the important role of quorum sensing phenomenon and its regulatory impact on levan production mechanism. Levan produced by bioreactor cultures under conditions optimized within this study was found to retain its chemical structure. Moreover, its biocompatibility was assessed for a broad concentration range. Hence H. smyrnensis AAD6(T) has been firmly established as an industrially important resource microorganism for high-quality levan production.