Toxicological evaluation of (processed) red meat ingredients and importance of heme oxygenase 1 in the context of colorectal carcinogenesis

• Applicant: Dr. Tina Kostka
• Subject Area: Toxicology, Laboratory Medicine
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 530306713

Colorectal cancer (CRC) formation is associated with processed and red meat consumption. Upon meat intake, heme is released from protein in the gastrointestinal tract, which results in oxidative stress, DNA strand breaks and mutations in intestinal epithelial cells. If red meat is additionally cured using nitrite, heme will be nitrosylated resulting to the formation of pink-colored NO-heme. It is generally assumed that nitrite increase the toxicity of meat compounds and therefore coloring alternatives like ZnPP are currently tested. Unfortunately, the toxic potential of ZnPP in meat was not yet analyzed. Contrary to the expectation, we were able to show that nitrosylated heme possess an equal or even lower toxicity in in vitro assays than heme. Moreover, as higher the nitrite content in food, as lower was the heme-induced urinary content of lipid peroxidation products. The beneficial effects of nitrite may relate to heme oxygenase 1 (HO-1), an detoxification enzyme responsible for the degradation of heme. The interaction of NO-heme with HO-1 was never tested before, whereby we established the only reliable synthesis method for NO-heme. Even if it was hypothesized that factors like heme, nitrite and HO-1 are involved in processed and red meat-related tumor formation, most aspects are still unknown. Therefore the aim of the project is to analyze such underlying molecular mechanisms as well as possibly occurring synergistic effects due to the complex food matrix including several factors. The following main questions will be answered: 1) Does the addition of nitrite influence the toxic effects of heme from red meat? 2) What is the role of HO-1 in (processed) red meat-associated CRC formation? 3) Is the HO-1 inhibitor ZnPP suitable as non-toxic nitrite alternative in processed red meat? By using an in vitro digestion model, endogenous modifications like nitrosylation reactions will be revealed, while the toxicity of digested meat samples and selected factors like heme compounds, nitrite and ZnPP will be evaluated in a broad range of in vitro toxicity assays. One of the main aspects is the interaction of the different heme compounds and ZnPP with HO-1 using established colon cell lines as well as a cell-free model. The HO-1 activity seems also be involved in tumor progression. Therefore, the toxic effects of meat compounds in presence and absence of HO-1 will be analyzed regarding cell migration, epithelial-mesenchymal transition and anchorage-independent growth.

• DFG Programme: Independent Junior Research Groups
• International Connection: France, Switzerland, USA
• Cooperation Partners: Wayne Backes, Ph.D.; Dr. Francoise Gueraud; Professorin Dr. Shana J. Sturla