The Research On Cell Damage Induced By Heavy Metals

With the development of economy, food safety problems and environmental issues are constantly emerging. The excess contact with heavy metals affect people’s health physically, which are drawing more and more attention. Heavy metals usually come from contaminated water, soil and atmosphere. Once the heavy metals are taken into body, they will react with certain proteins or enzymes in cells resulting in the loss of the activity of proteins, and also will induce DNA damages in cell replication and cause DNA mutations. The damages of protein and DNA induced by heavy metals will accumulate in certain organs in the body and result in serious problem to health by chronic poisoning.In this study, the damages of cells induced by heavy metals were investigated. Firstly, sample pretreatment was optimized to determine the best acid system and acid ratio followed by optimization of the graphite furnace temperature program to give the best ashing and atomization temperatures. Then the absorption of four heavy metals including cadmium(Cd), lead(Pb), nickel(Ni) and copper(Cu) were determined using high-resolution continuum source graphite furnace atomic absorption spectrometry(HR-CS GFAAS). The viability of the cells treated with the heavy metals was also determined using CCK-8 method. The results showed that the cell survival rates of Cd, Pb, Ni and Cu were 81.8-100%, c 66.4-100%, 89.5-100% and 47.2-100%, respectively. The variances of the cell survival rates in the cells treated by Pb and Cu are more significant than those by Cd and Ni. The cell survival rates decrease with the increasing of the concentrations of heavy metals, in which dramatic decrease was observed in the cells treated with Pb and Cu compared to the slight decrease in the cells treated with Cd and Ni. This result indicates that the cells tolerance to Cd and Ni is stronger than thant to Pb and Cu, which may be associated with the expression of cellular proteins, such as glutathione, binding to Cd and Ni much easier than to Pb and Cu. The bingding of glutathione with heavy metals protects the cells from DNA damage, cell proliferation inhibition and cell apoptosis.The absorption rates of Cd, Pb, Ni and Cu were 20.0-76.0%, 1.0-20.7%, 65.0-87.6% and 2.9-11.5%, respectively. Higher absorption rates of heavy metals in cells were found for Ni and Cd, but lower rates were observed for Pb and Cu. This result shows that cells can selectively absorb heavy metals. The absorption rates of Cd was observed to gradully increase and this trend becomes significant after the Cd concentration exceeds 10 μg/L. The maximum of the absorption rates of Cd is 76.0% when the concentration Cd reaches 25 μg/L followed by a plateau of the absorption rates. this might be affected by the change of structure of calcium ion channel protein that inhibits Cd from entering the cell. Cells absorption rates of Pb gradually increases followed by desrease. The absorption rate reaches a maximum of 20.7% when the concentration of Pb is 300 μg/L, then gradually decreases to 2.9%, which may be related to the change of binding sites of enzyme protein or metal binding protein of divalent metal ion. Cellular uptake rate of Ni gradually increases and reaches highest amount of 87.6% at 500 μg/L followed by a slight decrease without being influenced by the increased concentrations of heavy metal. This may be due to the Ca2+ cooperative transport and divalent cation carrier transportation. Cellular uptake rate of Cu is gradually increased and reaches a summit of 11.5% at 3000 μg/L followed by a slow decrease to 8.8%, which may be related to the self protection of Cu target mitochondria that blocks the further absorption of Cu. Compared with the high absorption rates of Cd and Ni, the cell tolerances toward Cd and Ni are stronger than those of Pb and Cu, which results in a weaker apoptotic effect of Cd and Ni than Pb and Cu. This may be attribute to the formation of metal ion protein complexes after Cd and Ni entering the cell through ion pump or protein binding, which contributes to a decrease of toxicity.In this study, experimental data were provided for the clarification of cell damage caused by heavy metal. Wet digestion was employed as a pre-treatment method for the mixtures of cells and culture medium. High resolution continuum source graphite furnace atomic absorption spectrometry was used to establish a reliable method for the determination of heavy metals in cells. The influence of heavy metals to cells was explored by determing the cellular absorption rates of the heavy metals. This study will contribute to the investigations on the hazard of heavy metals to human health.