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，食用加工肉类与结直肠癌发病率之间存在相关性。虽然原因和机制尚未明确，但长期以来，当腌制盐添加到肉类中时形成的亚硝化血红素被认为是最重要的因素之一。然而，申请人的初步工作第一次对这一假设提出了质疑。此外，这些结果将β-hematin物质作为一种可能的内源性致癌物质引起了关注，在此之前，在与食物(毒理学)相关的背景下，这一点完全未知，尽管这种化合物对巨噬细胞和肺细胞的不利影响已被描述。此外，科学文献表明，在一定条件下，哺乳动物器官中可以形成β-hematin。因此，人类接触，例如在食用加工肉类之后，将是可能的。在加工肉类的致癌作用的背景下，β-hematin尚未被考虑。目前还没有关于它作为人类饮食和消化的组成部分的研究，也没有对其对肠道上皮的毒性影响进行分析。因此，本项目的目标是缩小这些研究差距。预计将首次将β-hematin与人类营养及其作为不同血红素种类的降解产物的内源形成联系起来，这将通过体外消化技术进行证明。因此，重点是检测结构变化，以及人类消化系统各部分(口腔、胃、小肠和结肠)特有的新的以血红素为基础的物质的形成。首先，将单独和联合研究在β-血红素形成中可能重要的因素(例如，脂层的存在、酸性pH和硝化血红素作为β-血红素的前体)的相互作用。消化将使用两种单独的血红素，也可以使用加工过的红肉和肉类与富含亚硝酸盐的蔬菜相结合。在第二步中，将考虑到生理上相关的浓度，单独和结合分析内源性血红素物种的潜在毒性影响。已建立的人类结肠肿瘤细胞系，无论是以分化的上皮细胞的形式，还是作为与巨噬细胞共培养的形式，都将作为模型。其目的是研究化合物对氧化应激、DNA损伤、炎症反应、膜完整性的损害以及这些影响背后的信号转导途径。归根结底，只有当消化系统中实际存在的物质、它们的内源性激活、它们在肠道中的分布以及它们的毒性影响都是已知的时，才能制定有效的预防措施作为素食饮食的替代方案。

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.