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，红肉的消费与结肠直肠癌的发病率有关。已经表明，红色而非白色肉剂量依赖性地诱导亚硝基化合物如亚硝酰血红素和亚硝基硫醇在人肠道中的内源性形成。由于红肉比白色肉含有更多的血红素，血红素摄入量和亚硝基化合物的内源性形成之间有直接关系。在这种情况下，它已被假定，内源性形成的亚硝基化合物可能会导致形成的烷化剂重氮乙酸，这反过来又会产生O 6-羧甲基鸟嘌呤加合物，导致特定的基因突变，并最终诱导结直肠癌。该项目的目的是：1）确定一方面通过将人粪便与硝酸盐/亚硝酸盐和血红素温育形成的亚硝基化合物以及另一方面通过NO与血红素反应在培养基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形成的亚硝基化合物和亚硝基血红素的孵育是否导致O 6- 3）确定Ki-ras、APC和/或p53基因突变是否存在于恶性转化的人结肠上皮细胞中; 4）确定同时给予大鼠亚硝酸盐和血红素是否伴随O 6-羧甲基鸟嘌呤加合物的形成，Ki-ras的诱导，APC和/或p53基因突变以及实验动物结肠和/或直肠中肿瘤前病变和肿瘤病变的形成增强。计划中的实验将首次显示上述途径（硝酸盐/亚硝酸盐+血红素、内源性形成的亚硝基化合物、O 6-羧甲基鸟嘌呤加合物、Ki-ras、APC和/或p53基因突变）是否导致人类结肠上皮细胞的恶性转化。动物实验将表明上述一连串的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.