Single-cell ICP-MS for the studies of biological systems

Abstract

Recent research in single-cell analysis has shown that individual cells in a population can behave heterogeneously under the same experimental conditions. Cell heterogeneity is an important parameter for the investigation of the effects of environmental stress on biological cells. Single-cell ICP-MS provides useful information on the distribution of elemental contents of a cell population, which is not available by conventional bulk analysis. Therefore, application of single-cell ICP- MS to track the changes in metal contents of biological cells in response to external stimulation can potentially yield significant insight on cell heterogeneity. The method also requires only a small number of cells 〖(10〗^4) to establish the distribution of cellular elemental contents and the cell number density of a cell population.

In this study, the distribution of ICP-MS spike intensity of major essential elements of the cells is shown to correlate with the distribution of cell size of the model algal cells, Chlorella vulgaris. Direct correlation between the distributions of Mg spike intensity and cell volume during cell growth and under stress of toxic quantity of Cr(VI) is first reported. Dose-response curves of relative reduction in cell number density versus Cr(VI) concentration were constructed and 〖IC 〗_50(concentration for 50% of growth inhibition) was estimated from the curves.

The feasibility and capability of single-cell ICP-MS for toxicological study of the effects of Cr(VI) on C. vulgaris are first demonstrated. Mg, which is rich in the algal cells (5×〖(10〗^8 atoms/cell), was used as an intrinsic biomarker. The toxic effects versus exposure time and Cr(VI) concentration were determined by comparison of the peak maximum (average intensity) and full-width-at-half-maximum (FWHM) of the Mg intensity distribution of the Cr(VI)-treated cells to the control. Changes in the skewness of the distribution due to heterogeneous growth responses to Cr(VI) stress are first observed. The capability of single-cell ICP-MS to track the uptake of Cr is demonstrated. Simultaneous increase in cellular Mg content and Cr uptake versus exposure time and Cr(VI) concentration is first reported. Detection of other major (P, K) and trace elements (Mn, Cu, and Zn) in the cells and correlation of the intensity distributions to Cr(VI) toxicity are also presented.

Single-cell ICP-MS was also implemented for the analysis of changes in cellular elemental contents of Staphylococcus aureus during the course of infection of J774 murine macrophages. The Mg intensity spikes, corresponding to individual S. aureus cells, were measured. The changes in cellular metal contents in S. aureus cells during infection of macrophage were found to be dependent on the strain of bacterial cells, infection ratio of bacterial cells to macrophage cells, and infection time. The technique is also applied to the analysis of silver-containing nanoparticles in maternal organs and fetuses of pregnant rats after oral uptake of polyvinylpyrrolidone-coated silver nanoparticles. Sample pre-treatment method of enzymatic digestion was used to release the nanoparticles from the biological samples. Single-cell ICP-MS reveals heterogeneous metal distribution in the samples.