Responses of animal cells to cadmium stress: defense mechanisms and cellular functional state.

By Sandy Thijssen  

Cadmium is a toxic metal. It occurs in trace concentrations in soil, water and air. Natural increases are mainly found in ore cropping and serpentine soils. Concentration in the different compartments may enhance mainly due to industrial activities (ore mining, metal smelting, etc) and agricultural practices (application of phosphate fertilizers and sewage sludge).Cadmium has a long biological half-life and may cause loss of function in living cells or cause sub lethal stress and weaken the cell’s response to an additional aggression, leading eventually to the cell’s death and loss of tissue function. Cadmium is stored in the liver and the kidney. In kidney cells, it is excreted only very slowly and its storage and gradual accumulation in the cells cause tubular dysfunction and cell damage (elevated urinary cadmium levels, glucosuria, calciuria, proteinuria etc.)

The goal of the present study is to investigate cadmium stress and toxicity in animals at the cellular level. We intend to apply doses that provoke a cadmium burden comparable to that occurring in tissues of humans and that are environmentally realistic. These findings will be compared with the results in plants, and differences and similarities will be determined in responses in plant versus animal cells.First of all, adequate doses of cadmium need to be determined. Therefore groups of experimental and control animals (mice) will be fed with a diet containing a cadmium salt in the experimental groups. Collection and separation of urine and faeces will be possible during the experiment and afterwards, the liver and kidney will be analyzed for their cadmium and metallothionein content and differences in biochemical processes.

The second objective is to measure the intracellular cadmium concentration in tubule segments of the control group of animals (negative control), of the group that has been exposed to cadmium and of the same control group, in which the cells will be acutely exposed to a high dose of cadmium, inducing uptake into the cytosol (positive control). Therefore we want to try and develop a cadmium sensitive double-barreled microelectrode and monitor the cytosolic cadmium activity.

The third objective of this project is to investigate the effect of exposure to cadmium on the mitochondrial function inside the intact, isolated cell. It will be of primary interest to try and find a correlation between intracellular free cadmium concentration and the state of the mitochondria in the intact cell in different conditions.For this experiment, the proximal tubular culture needs to be established and characterized. Microfluorescence and imaging techniques will be used to determine the functional state. Whenever possible fluorescence imaging microscopy will be used.

So, in combining different techniques and approaching the problem from different angles, we aim to obtain a more complete picture of the events taking place in cells when exposed to cadmium and to determine differences and similarities in responses in plant versus animal cells.