Toxicity of processed red meat: Endogenous synthesis of different heme species and their potential implication in colon cancer formation

流行病学研究表明，加工肉类的消费与结肠直肠癌的发病率之间存在相关性。虽然原因和机制尚未明确，但在腌制盐添加到肉类中时形成的亚硝基化血红素长期以来被认为是最重要的因素之一。然而，申请人的初步工作首次对这一假设提出了质疑。此外，这些结果将物质β-血红素作为一种可能的内源性致癌物纳入关注范围，在此之前，在食品（毒理学）相关背景下完全未知，尽管已描述了该化合物对巨噬细胞和肺细胞的不良影响。此外，科学文献表明，β-血红素可以在某些条件下在哺乳动物器官中形成。因此，人体暴露，例如，在食用加工过的肉类后，在加工肉类的促致癌作用的背景下，β-高铁血红素尚未被考虑。没有关于其作为人类饮食和消化成分的研究，也没有分析其对肠上皮细胞的毒性作用。因此，本项目的目的是填补这些研究空白，设想首次将β-血红素与人类营养及其作为不同血红素种类降解产物的内源形成联系起来，这将通过使用体外消化技术加以证明。因此，重点是检测结构变化，以及对人体消化系统（口腔，胃，小肠和结肠）的各个隔室特异性的新血红素基物质的形成。首先，在β-高铁血红素形成中的重要因素的相互作用（例如，脂质层、酸性pH和作为β-血红素前体的亚硝基化血红素的存在）将被单独和组合地检查。消化将使用两个单独的血红素物种，但也与加工红肉和肉类结合富含亚硝酸盐的蔬菜。在第二步中，考虑到生理相关浓度，将单独和组合分析内源性血红素物质的潜在毒性效应。已建立的人结肠肿瘤细胞系，以分化的上皮细胞的形式或与巨噬细胞共培养，将作为模型。目的是研究化合物特异性诱导氧化应激、DNA损伤、炎症反应、膜完整性损伤以及研究这些效应背后的信号转导途径。最终，只有当消化系统中实际存在的物质、它们的内源性激活、它们在肠道内的各自分布及其毒性作用已知时，才能制定有效的预防措施作为素食的替代品。

Epidemiological studies show a correlation between the consumption of processed meat and the incidence of colorectal cancer. Although the causes and mechanisms have not yet been clearly identified, nitrosylated heme, which is formed when curing salts are added to meat, was long considered to be one of the most important factors. However, this hypothesis has been put to question, for the first time, by the preliminary work of the applicant. In addition, these results brought the substance β-hematin as a possible endogenously formed carcinogen into focus, which was completely unknown in a food (toxicology)-related context until then, although adverse effects of this compound on macrophages and pneumocytes have been described. Moreover, scientific literature shows that β-hematin can be formed in mammalian organs under certain conditions. Therefore, a human exposure, e.g., after consumption of processed meat, would be possible. In the context of the pro-carcinogenic effects of processed meat, β-hematin has not yet been considered. There are no studies on its occurrence as a component of human diet and digestion, nor have the toxic effects on the intestinal epithelium been analyzed. It is therefore the aim of the present project to close these research gaps.It is envisaged to link, for the first time, β-hematin with human nutrition and its endogenous formation as a degradation product of different heme species, which will be demonstrated by using in vitro digestion techniques. The focus is thereby on the detection of structural changes, as well as the formation of new heme-based substances specific to the individual compartments of the human digestive system (oral cavity, stomach, small intestine and colon). Firstly, the interplay of putatively important factors in β-hematin formation (e.g., the presence of a lipid layer, an acidic pH, and nitrosylated heme as a precursor for β-hematin) will be examined individually and in combination. Digestion would be performed using both individual heme species, but also with processed red meat and meat in combination with nitrite-rich vegetables. In the second step, the potentially toxic effects of the endogenously occurring heme species would be analyzed individually and in combination, taking into account physiologically relevant concentrations. Established tumor cell lines of the human colon, either in the form of differentiated epithelial cells or as co-culture with macrophages, will serve as models. The aim is to investigate the compound-specific induction of oxidative stress, DNA damage, an inflammatory response, damage to membrane integrity as well as to investigate the signal transduction pathways underlying these effects. Ultimately, effective preventive measures can be developed as an alternative to a vegetarian diet only when substances actually present in the digestive system, their endogenous activation, their respective distribution within the intestines and their toxic effects are known.