Impact of lactate on exosomes and its role in acute pancreatitis-associated inflammation

Abstract

Acute pancreatitis (AP) is an inflammatory condition often associated with systemic complications, and macrophages are key regulators of the inflammatory response, while exosomes, a subtype of small extracellular vesicles (sEVs), are important mediators of intercellular crosstalk and can influence immune cell behavior, and lactated Ringer's solution (LR), commonly used in AP treatment, contains lactate, which has demonstrated anti-inflammatory effects, so this study explores whether exosome exposure to lactate modifies their effect on macrophage inflammatory response. Exosomes were isolated from human pancreatic BxPC3 cells and incubated with either different concentrations of lactate or with a fixed concentration equivalent to that present in LR, for different durations, and exosomes were characterized by nanoparticle tracking analysis and Western blot, then THP-1-derived macrophages were treated with these exosomes, and macrophage pro- and anti-inflammatory gene expression was analyzed by RT-qPCR, while exosome uptake was assessed by fluorescence microscopy and STAT3 localization was evaluated by immunofluorescence. Optimizing the exosome isolation protocol improved sEV yield and purity, and macrophages treated with lactate-exposed exosomes exhibited reduced expression of M1-associated markers (TNF-a, IL-1b) and increased expression of M2 markers (IL-10, MRC-1, ARG-1), suggesting a shift towards an anti-inflammatory phenotype, and these effects were observed across all lactate concentrations and exposure times, with just 10 minutes of incubation being sufficient to induce changes, while STAT3 is not involved in the observed polarization and exosome uptake was comparable between lactate-treated exosomes and control groups. Lactate modifies exosome properties, promoting macrophage polarization shift towards the M2 phenotype, and this effect is independent of STAT3 activation or exosome internalization, supporting an anti-inflammatory role of lactate mediated by exosomes and highlighting a potential mechanism by which LR mitigates inflammation in AP.