Cardin Guillaume B, Mantha Marc, Jumarie Catherine
Département des sciences biologiques, Centre TOXEN, Université du Québec à Montréal, Succursale Centre-ville, Montreal, QC, Canada.
Biometals. 2009 Oct;22(5):753-69. doi: 10.1007/s10534-009-9223-6. Epub 2009 Mar 18.
Cadmium (Cd) is a highly toxic metal that enters the food chain. Following oral ingestion, the intestinal epithelium is the first biological barrier crossed by Cd and is also an important target tissue. In the present study, the human intestinal Caco-2 cell line was used to evaluate the impact of a low level of exposure on both undifferentiated and differentiated intestinal cells. As revealed by the LC(50) values estimated with the 3-[4,5-dimethyl-2-thiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, mature Caco-2 cells were more resistant to Cd. However, following a 24-h exposure to non-cytotoxic levels of Cd (10 microM) or zinc (Zn, 100 microM), threefold increases were obtained in the LC(50) values of 7-day-old cells, whereas increased resistance in 21-day-old cells was observed exclusively with Zn. Induction of MT-IIa and HSP70 mRNAs was higher in undifferentiated cells and an increase in cellular glutathione (GSH) content was observed exclusively in these cell cultures. However, the results obtained with cycloheximide used for inhibiting protein synthesis and with L-buthionine sulfoximine (BSO), which inhibits GSH synthesis, revealed that protein synthesis is not a prerequisite to the development of resistance. The presence of 100 mM 3-amino-1,2,4-triazole (3AT), a catalase inhibitor, prevented Cd-induced but not Zn-induced resistance, as well as sensitized cells to Cd toxicity. These results show for the first time differences in constitutive and acquired resistance to Cd as a function of enterocytic differentiation status and suggest the involvement of different mechanisms for Cd- and Zn-induced adaptation in the intestinal cells. Redox signals may trigger Cd-induced adaptation mechanisms but pro-oxidant conditions would eliminate proliferative intestinal cells capability to develop resistance. This would be critical for Cd- but not Zn-induced mechanisms of resistance since Cd but not Zn may cause oxidative stress.
镉（Cd）是一种进入食物链的剧毒金属。经口摄入后，肠上皮是Cd穿过的第一道生物屏障，也是重要的靶组织。在本研究中，使用人肠道Caco-2细胞系评估低水平暴露对未分化和分化肠道细胞的影响。用3-[4,5-二甲基-2-噻唑-2-基]-2,5-二苯基四氮唑溴盐（MTT）法估算的半数致死浓度（LC50）值表明，成熟的Caco-2细胞对Cd更具抗性。然而，在非细胞毒性水平的Cd（10微摩尔）或锌（Zn，100微摩尔）暴露24小时后，7日龄细胞的LC50值增加了三倍，而仅在Zn处理的21日龄细胞中观察到抗性增加。未分化细胞中金属硫蛋白-IIa（MT-IIa）和热休克蛋白70（HSP70）mRNA的诱导更高，并且仅在这些细胞培养物中观察到细胞内谷胱甘肽（GSH）含量增加。然而，用用于抑制蛋白质合成的放线菌酮和抑制GSH合成的L-丁硫氨酸亚砜胺（BSO）得到的结果表明，蛋白质合成不是抗性发展的先决条件。过氧化氢酶抑制剂100毫摩尔3-氨基-1,2,4-三唑（3AT）的存在可阻止Cd诱导的抗性，但不能阻止Zn诱导的抗性，并且使细胞对Cd毒性敏感。这些结果首次表明，对Cd的组成型和获得性抗性因肠细胞分化状态而异，并提示肠道细胞中Cd和Zn诱导的适应性涉及不同机制。氧化还原信号可能触发Cd诱导的适应机制，但促氧化条件会消除增殖性肠道细胞产生抗性的能力。这对于Cd诱导的抗性机制而非Zn诱导的抗性机制至关重要，因为Cd而非Zn可能导致氧化应激。
