Red meat-derived, endogenously formed nitroso compounds: potential to malignantly transform human colon cell cells and underlying modes of action

在工业化国家，食用红肉与结直肠癌发病率相关。已有研究表明，红肉而不是白肉可剂量依赖性地诱导人体肠道内亚硝基化合物的形成，如亚硝酰血红素和亚硝硫醇。由于红肉比白肉含有更多的血红素，亚硝基化合物的内源形成与血红素的摄入量有直接关系。在此背景下，人们推测，内源性亚硝基化合物可能导致烷基化试剂重氮乙酸酯的形成，重氮乙酸酯进而产生O6-羧甲基鸟嘌呤加合物，导致特定的基因突变，最终导致结直肠癌。该项目的目的是：1)确定一方面由人粪便与硝酸盐/亚硝酸盐和血红素反应形成的亚硝基化合物，以及另一方面由NO与血红素反应在培养液中形成的亚硝基血红素是否能够恶性转化人结肠上皮细胞；2)确定人结肠上皮细胞与内源性亚硝基化合物和亚硝基血红素孵育是否导致处理细胞中形成O6-羧甲基鸟嘌呤加合物；3)确定恶性转化的人结肠上皮细胞中是否存在Ki-ras、APC和/或p53基因突变；4)确定同时给予亚硝酸盐和血红素是否伴随着O6-羧甲基鸟嘌呤加合物的形成，诱导Ki-ras、APC和/或p53基因突变，以及促进实验动物结肠和/或直肠癌前病变和肿瘤病变的形成。计划中的实验将首次揭示上述途径(硝酸盐/亚硝酸盐+血红素、内源性亚硝基化合物、O6-羧甲基鸟嘌呤加合物、Ki-ras、APC和/或p53基因突变)是否导致人结肠上皮细胞恶性转化。动物实验将证明上述一连串事件是否真的在体内发生。

In industrialized nations consumption of red meat correlates with colorectal cancer incidence. It has been shown that red but not white meat dose-dependently induces the endogenous formation of nitroso compounds such as nitrosyl heme and nitrosothiols in the human gut. Since red meat contains much more heme than white meat, a direct relationship between heme intake and the endogenous formation of nitroso compounds has been suggested. In this context, it has been postulated that endogenously formed nitroso compounds may lead to the formation of the alkylating agent diazoacetate, which in turn gives rise to O6-carboxymethylguanine adducts, results in specific gene mutations and in the end induces colorectal cancer. The aims of the project are: 1) to determine if on the one hand nitroso compounds formed by incubating human faeces with nitrate/nitrite and heme and on the other hand nitrosyl heme formed in the culture medium by the reaction of NO with heme are able to malignantly transform human colon epithelial cells; 2) to determine whether the incubation of human colon epithelial cells with endogenously formed nitroso compounds and nitrosyl heme results in the formation of O6-carboxymethylguanine adducts in the treated cells; 3) to determine whether Ki-ras, APC and/or p53 gene mutations are present in the malignantly transformed human colon epithelial cells; 4) to determine whether the simultaneous administration of nitrite and heme to rats is accompanied by the formation of O6-carboxymethylguanine adducts, the induction of Ki-ras, APC and/or p53 gene mutations and an enhanced formation of preneoplastic and neoplastic lesions in the colon and/or rectum of the experimental animals. The planned experiments will show for the first time whether the above-mentioned pathway (nitrate/nitrite + heme, endogenously formed nitroso compounds, O6-carboxymethylguanine adducts, Ki-ras, APC and/or p53 gene mutations) leads to the malignant transformation of human colon epithelial cells. The animal experiment will show whether the above-mentioned chain of events does in fact occur in vivo.