Costimulation with high-fat diet and acidic bile salts may promote Warburg effect in gastric carcinogenesis around the squamocolumnar junction in Gan mice

Epidemiological studies demonstrated relationships between gastric cardia adenocarcinoma (GCA) and metabolic syndrome (MetS). We aimed to clarify the mechanism underlying their relationship. To investigate whether systemic inflammation against high-fat diet (HFD)-related dysbiosis promotes the Warburg effect in tumors at the squamocolumnar junction (SCJ), we applied K19-Wnt1/C2mE (Gan) mice, fed either HFD or control diet ± acidic bile salts (ABS) with/without clodronate liposomes (CLs), and in vitro studies using MKN7 cells with/without THP1-derived macrophages. Then, we assessed the involvement of oxidative stress (OS) in the Warburg effect by comparing nuclear factor-erythroid 2-related factor 2 (Nrf2) knockout Gan mice with Gan mice. Tumors with macrophage infiltration in the HFD þ ABS group were larger than in the control group. Gene Set Enrichment Analysis revealed enhancement of the OS signaling in tumor of the HFD þ ABS group. The HFD þ ABS group mice demonstrated induction of OS, Nqo1, tumor necrosis factor alpha (TNFa), and the Warburg effect in tumors and mucosal barrier dysfunction of dysbiotic gut. All of them were abolished with diminishing macrophage infiltration by additional CL treatment. Stimulation with TNFa, but not ABS nor lipopolysaccharide, on MKN7 cells activated the Warburg effect. In MKN7 cells cocultured with the macrophages whose TNFa expression was induced by the lipopolysaccharide pretreatment, the Warburg effect was enhanced in TNFa concentration-dependent manners. In Nrf2 knockout Gan mice, tumors shrank with reducing OS, TNFa, and Warburg effect, along with decreasing macrophage infiltration. Accordingly, MetS may develop GCA through the Nrf2-related Warburg effect under the TNFa stimulation from the macrophages activated by both local ABS exposure and systemic lipopolysaccharide exposure from leaky gut with HFD-related dysbiosis.