The dietary peroxidized lipid, 13-HPODE, promotes intestinal inflammation by mediating granzyme B secretion from natural killer cells.

It is well known that consumption of a high-fat diet (HFD) promotes intestinal inflammation despite little being known about causative factors. Recent evidence implicates dietary peroxidized lipids (POLs), which are typically formed from the oxidation of polyunsaturated fatty acid double bonds, as potential contributors due to their enrichment in HFDs, ability to be formed during gastrointestinal transit, and immunogenic and cytotoxic properties. 13-HPODE, the most common dietary POL, demonstrates pro-inflammatory activity in a variety of immune cells, especially Natural Killer (NK) cells whose role in mediating intestinal inflammation remains unclear. Therefore, we set out to investigate how 13-HPODE and other POLs modulate NK-cell activity in the context of intestinal inflammation. We not only found that NK cells fully decompose exogenous 13-HPODE, but that direct treatment stimulates TNF-α and MCP1 expression as well as Granzyme B (GZMB) secretion in a dose-dependent manner. Similar results were observed upon incubation of NK cells with oxidized, but not-unoxidized, low-density lipoproteins. Secretory products from 13-HPODE-treated NK cells were able to induce Caco2 intestinal cell inflammation in the same way as exogenous GZMB with greater sensitivity in undifferentiated compared to differentiated cells. Results were recapitulated in 13-HPODE-fed mice, demonstrating both spatial and temporal patterns of elevated GZMB expression that favored acute treatments in the distal intestinal epithelium. Collectively, our results suggest that that HFD-derived POLs, like 13-HPODE, potentially contribute to intestinal inflammation by stimulating the secretion of pro-inflammatory granzymes by resident NK cells, ultimately revealing a more direct role for diet in modulating gut homeostasis and the immune environment.

Are Fried Foods Unhealthy? The Dietary Peroxidized Fatty Acid, 13-HPODE, Induces Intestinal Inflammation In Vitro and In Vivo.

Inflammatory Bowel Disease (IBD) is a chronic inflammatory disorder characterized by progressive inflammation and the erosion of the gut mucosa. Although the exact cause of IBD is unknown, multiple factors contribute to its complex pathogenesis. Diet is one such factor and a strong correlation exists between the western-style, high fat diets (HFDs) and IBD incidence rates. In this study, we propose that the peroxidized fatty acid components of HFDs could contribute to inflammation of the gut. The inflammatory nature of peroxidized linoleic acid (13-HPODE), was confirmed in vitro by analyzing pro-inflammatory gene expression in Caco-2 cells via RT-PCR and ELISA. Additionally, peroxide induced apoptosis was tested by Annexin-V fluorescent staining, while permeability was tested by FITC-dextran flux and TEER. The 13-HPODE-induced inflammation of intestinal epithelium was evaluated in vivo by analyzing pro-inflammatory cytokines under acute and chronic conditions after feeding 13-HPODE to C57BL/6J mice. Our data show that 13-HPODE significantly induced pro-inflammatory gene expression of TNF-α and MCP-1 in vitro, most notably in differentiated Caco-2 cells. Further, acute and chronic 13-HPODE treatments of mice similarly induced pro-inflammatory cytokine expression in the epithelium of both the proximal and distal small intestines, resident immune cells in Peyer's patches and peritoneal macrophages. The results of this study not only confirm the pro-inflammatory properties of peroxidized fats on the gut mucosa, but for the first time demonstrate their ability to differentially induce pro-inflammatory gene expression and influence permeability in the intestinal epithelium and mucosal cells. Collectively, our results suggest that the immunogenic properties of HFD's in the gut may be partly caused by peroxide derivatives, providing potential insight into how these diets contribute to exacerbations of IBD.