Low-dose inorganic arsenic exposure reprograms macrophages differentiation and function toward tumor-promoting phenotypes.

Inorganic arsenic (iAs) is a known carcinogen and immunotoxicant that contaminates groundwater used for drinking, food production, and irrigation, exposing an estimated 200 million people worldwide to levels above the World Health Organization safe drinking water limit of 10 μg/L. Classified as a known carcinogen classified by the International Agency for Research on Cancer (IARC), iAs alsond causes increasesd susceptibility to infectious diseases, highlighting its role as an immunotoxicant. This study elucidates the effects of arsenic on macrophages using in vitro exposure models. Bone marrow-derived macrophages (BMDMs) were cultured from adult male and female C57BL/6 mice. Naïve macrophages ("M0" BMDMs) were exposed to a non-cytotoxic dose of iAs during the 7-day differentiation period and stimulated for 24 h with LPS and IFNγ, or IL-4 and IL-13, to induce "M1" or "M2" activation, respectively. In parallel, RAW 264.7 (RAW) macrophages were chronically exposed to iAs for 70 days, and activated in the last 24 h s. Culture supernatant analysis indicated reduced nitric oxide production in "M1" RAW macrophages, but not BMDMs upon iAs exposure; whereas BMDMs displayed predominantly suppressed cytokine/chemokine profiles, albeit with notable sex-dependent differences across activation states. Flow cytometry confirmed these sex- and stimulation-dependent changes in macrophage polarization, with "M2" markers being upregulated upon iAs exposure, whereas the functional markers iNOS and MHCII were reduced in male BMDMs only. Increased lipid droplet formation and altered lipidomic and metabolomic profiles further suggested iAs exposure induces a pro-tumorigenic microenvironment. Accordingly, iAs-exposed macrophages displayed increased migration toward cancer cell-conditioned media and promoted cancer cell proliferation. Collectively, these results provide phenotypic and mechanistic insights that iAs not only suppresses immune function but also skews macrophage polarization and immunometabolism towards tumor promoting phenotypes.