Lactobacillus plantarum-Derived Inorganic Polyphosphate Regulates Immune Function via Inhibiting M1 Polarization and Resisting Oxidative Stress in Macrophages

Inorganic polyphosphate (PolyP) is a high-molecular-weight polymer that plays multiple roles in regulating immune responses. However, the specific anti-inflammatory mechanisms of bacteria-derived PolyP are unclear. In the present study, PolyP was extracted from <i>Lactobacillus plantarum</i> (<i>L. plantarum</i>), and the chain length was estimated to be approximately 250 Pi residues. The immune regulatory functions of PolyP were investigated using a lipopolysaccharide (LPS)-induced RAW264.7 cell oxidative stress model, and dexamethasone was used as a positive control. The result revealed that both dexamethasone and PolyP were protective against oxidative stress by inhibiting macrophage M1 polarization and the production of several markers, such as nitric oxide (NO), reactive oxygen species (ROS), inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX)-2. In addition, PolyP suppressed inflammation progression by regulating the production of several cytokines, such as interleukin (IL)-1β, interferon (INF)-γ, tumor necrosis factor (TNF)-α, and IL-6, and inhibited the expressions of <i>inhibitory κB kinase</i> (<i>IKK</i>) <i>α</i>, <i>IKKβ</i>, and extracellular regulated protein kinases 2 (<i>ERK2</i>). Conclusively, PolyP derived from <i>L. plantarum</i> has the ability to protect cells from oxidative stress damage by inhibiting M1 polarization in macrophages. These findings provide insights into the function of PolyP and offer support for the potential application of PolyP in immune-related diseases.