Molecular mechanism of adipose tissue inflammation induced by acute exposure to cooking oil fumes

Background Cooking oil fumes are closely related to immune response, and adipose tissue also plays an important role in immune regulation. At present, the biological effect and mechanism of inflammation of adipose tissue induced by oil fume exposure are not clear yet.

Objective To investigate the inflammatory effect of different exposure duration of cooking fumes on adipose tissue in mice and explore the role of Nod-like receptor pyrin domain 3 (NLRP3)/cysteinyl aspartate specific proteinase 1 (Caspase 1)/interleukin (IL)-1β signaling pathway.

Methods Forty 8-week-old female C57BL/6J mice were randomly divided into 3-day control group (CON₃ group), 7-day control group (CON₇ group), 3-day oil fume exposure group (COF₃ group), and 7-day oil fume exposure group (COF₇ group), with 10 mice in each group. The mice were exposed to oil fumes in a cooking oil fume formation and exposure equipment (COFFEE) for 20 min, followed by a 10-min pause, 1 h a day for consecutive 3 d or 7 d. General condition of mice was observed and body weight was measured every day. After exposure, blood was sampled from the eyeball. Serum levels of IL-6, IL-27, and IL-1β were detected by enzyme-linked immunosorbent assay (ELISA). The adipose tissue of mice was collected and observed after hematoxylin-eosin (HE) staining. The percentages of CD4⁺ and CD8⁺T cells in adipose tissue were detected by flow cytometry. Real-time quantitative PCR (RT-qPCR) was used to detect the expression levels of nuclear factor-κB (NF-κB), NLRP3, Caspase 1, and IL-1β in adipose tissue. Western blot was used to detect the expression levels of NLRP3, Caspase 1, and IL-1β in adipose.

Results Compared with the corresponding control group, serum IL-6, IL-27, and IL-1β contents in the COF₃ group and the COF₇ group were significantly increased (P<0.05) except IL-6 in the COF₃ group, and the levels in the COF₇ group were significantly higher than those in the COF₃ group (P<0.05). Vacuolar lipid droplets in adipocytes decreased, cytoplasm shrank, and inflammatory cells infiltrated in the COF₇ group after HE staining. The flow cytometry results showed that the proportions of CD4⁺ and CD8⁺T cells in adipocytes of the COF₃ group and the COF₇ group were increased compared to the corresponding control group, with a significant increase in the COF₇ group (P<0.05), and the CD4⁺/CD8⁺T ratio also significantly increased progressively in the two groups (P<0.05). The results of RT-qPCR showed that compared with the corresponding control group, the mRNA expression levels of NF-κB, NLRP3, Caspase 1, and IL-1β in adipose tissue of mice in the COF₃ group and the COF₇ group were significantly increased (P<0.05, P<0.01). The mRNA expression levels of mice in each exposure group gradually increased over time. The Western blot results showed that compared with the corresponding control group, the protein expressions of NLRP3 and Caspase 1 in the COF₃ group were significantly increased (P<0.01), and the expression of IL-1β protein also increased but without statistical significance. The protein expressions of NLRP3, Caspase 1, and IL-1β in the COF₇ group were significantly higher than those in the CON₇ group (P<0.05, P<0.01).

Conclusion Acute exposure to cooking oil fumes can induce significant inflammatory response in adipose tissue, and the effect gradually increases with the extension of exposure time. The mechanism of action may be related to the activation of NLRP3 inflammasome signaling pathway.