Intestinal exposure to metals: impact on cell differentiation and intestinal cell funtions.

加拿大排在前五大生产国之列的镉(Cd)具有多种工业用途。在人类中，两种主要的吸收途径是吸入(职业接触和吸烟者)和通过受污染的食物摄取(普通人群)。几十年来，我们研究了肠道对Cd的摄取作为金属形态(即化学金属物种)的函数，重点是必需金属的抑制作用。在过去的五年里，我们开始研究肠上皮作为金属摄取后的靶组织。这种上皮细胞经历了快速和持续的更新，细胞的增殖和成熟是时间和功能上联系在一起的现象，一些细胞蛋白在其中起着至关重要的作用。我们最近发现，镉可能会改变这些细胞内蛋白的活性，从而调节肠道细胞的成熟。我们还观察到，肠道细胞可能会对Cd产生一些抵抗力，但获得这种抵抗力的能力随着细胞成熟状态的不同而有很大差异。最后，我们已经证明，在肠道细胞中存在镉的排泄途径，预计这些途径也会随着细胞成熟状态的不同而变化。因此，我们计划继续研究镉对细胞成熟过程和肠道功能的影响，并确定获得性对镉的耐药性是否可逆。此外，由于肠上皮在有毒化合物和药物的代谢中起着关键作用，我们的目的是更好地了解Cd可以在多大程度上通过直接或间接作用改变这一功能。预期的结果将增加我们对以下方面的认识：(1)细胞水平上的金属毒性机制；(2)长期暴露于低水平的金属如何影响肠道代谢活动，这是毒理学和药理学非常感兴趣的问题。

Cadmium (Cd), for which Canada ranks in the top five producers, has various industrial uses. In humans, the two main routes of absorption are inhalation (occupational exposure and smokers) and ingestion through contaminated food products (general population). During decades we have studied the intestinal uptake of Cd as a function of metal speciation (i.e. chemical metal species) focusing on inhibition by essential metals. During the past five years we began to study the intestinal epithelium as a target tissue following metal ingestion. This epithelium is subjected to rapid and constant renewal for which cellular proliferation and maturation are temporally- and functionally-linked phenomena for which some cellular protein play crucial role. We have recently shown that Cd may modify the activity of some of these intracellular proteins which regulate the intestinal cell maturation. We have also observed that the intestinal cell may develop some resistance to Cd but the capacity to acquire this resistance vary considerably with the cell maturation status. Finally, we have shown that there are excretory pathways for Cd in intestinal cells that are also expected to vary with the cell maturation status. We thus plan to pursue our investigation on how Cd may impact on the cell maturation processes and the intestinal functions, and determine whether the acquired resistance to Cd is reversible. Moreover, because the intestinal epithelium play a critical role in the metabolism of toxic compounds as well as pharmaceutical drugs, we aim better understanding to which extent Cd may modify, by direct or indirect action, this function. The expected results will increase our knowledge on: (1) mechanisms of metal toxicity at the cellular level and; (2) how 'chronic' exposure to low levels of metals affect intestinal metabolism activities which is of great interest for toxicology and pharmacology.