The immunomodulatory activity of levan in RAW264.7 macrophage varies with its molecular weights

Abstract

Levan is a fructose homopolymer obtained from both plants and microorganisms. Microbial levan is typically produced in a variety of molecular weights (MW). Previous studies have shown that different MW of levan exhibit different biological activities. Though levan was reported for its immunomodulatory effect by increasing nitric oxide (NO) production in RAW264.7 macrophage cells, whether its MW can affect this activity remains unknown. In this study, the effect of different levan MW from Bacillus subtilis on its immunoregulatory properties was investigated. B. subtilis was cultivated using various cultivation parameters to obtain levan of different MW. Three weight average MW of levan, >8 × 105 Da (M1), 1.5 × 104 Da (M2) and 3.7 × 103 Da (M3), were selected to test for their effect on modulating NO levels in RAW264.7 cells. Our results showed that M2 increased NO production in a dose-dependent manner, and more effectively than that of M1 and M3. Consistent with these findings, M2 significantly stimulated inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX2) protein expression, while less pronounced effects were observed in the cells treated with M1 and M3. Therefore, our results demonstrate that various MW of levan have varying effects on its immunoregulatory activities in RAW264.7 cells. Furthermore, our findings suggest that the size of levan should be taken into account when employing levan as one of the active ingredients in functional foods and immunomodulatory products.