It is well documented that obesity and metabolic syndrome have a deep association with the intestinal immune system of the host animal. Recent studies indicate that some selected probiotics can modulate the immune responses of the host animal, thereby altering its lipid metabolism. However, the underlying mechanisms are still not fully understood. This study was conducted to investigate the possibility of probiotics to activate macrophages in the hosts, thus alter the differentiation of pre-adipocytes. In this study, Streptococcus thermophilus MN-ZLW-002 (MN-ZLW-002) was co-cultured with RAW264.7 macrophages, with Lactobacillus rhamnosus GG (LGG) as a control. The conditioned medium (CM) of the co-culture was collected and then added to 3T3-L1 pre-adipocytes. Viable and heat-killed (80 °C, 30 min) MN-ZLW-002 stimulated RAW264.7 cells to produce significant amounts of interleukin (IL)-6 and tumor necrosis factor (TNF)-α and induced intense phosphorylation of P38, p44/42 mitogen-activated protein kinase (MAPK) (extracellular signal-regulated kinase (ERK)) and nuclear factor κB (NF-κB). Cytokine production reduced dramatically when heat-killed MN-ZLW-002 was treated with Ribonuclease. Viable and heat-killed LGG induced less cytokine production and little signaling protein activation. Viable and heat-killed MN-ZLW-002-stimulated RAW264.7-CM notably suppressed pre-adipocytes differentiation. However, viable LGG-stimulated RAW264.7-CM had a weaker effect and heat-killed LGG-stimulated RAW264.7-CM had no effect. These findings suggest that viable and heat-killed (80 °C, 30 min) MN-ZLW-002 may alter its lipid metabolism by regulating its immune response, possibly via the release of cytokine, particularly TNF-α. The RNA of heat-killed MN-ZLW-002 may be a key component in its immune activation effect.
Keywords: Streptococcus thermophilus; macrophage; obesity; pre-adipocyte; tumor necrosis factor α.