Gaining Insights into Cell Ionomics Using icpTOF Technology

This single cell ICP-MS article reveals the power of icpTOF technology for examining the cell ionome on an individual cell basis, without any foreknowledge of the cell elemental composition.

Olga Borovinskaya^1, Simran Aulakh², Markus Ralser²
1. TOFWERK, Thun, Switzerland  2. The Francis Crick Institute, England

Metals and non-metals such as S, P, Na, K, Ca, Mg, Mn, Fe, Cu, Zn, Se are necessary constituents of a living cell. Indeed, they regulate vital cell functions, either integrated into the structure of proteins or as free ions. For example:

• Sodium, chlorine, potassium and calcium enable nerve cells to transmit electrical signals.
• Sulfur supports the connections between different proteins
• Phosphorous is present as phosphate in ATP, GTP, DNA, and RNA
• Additional trace metals are needed by proteins and enzymes to execute chemical reactions.

Conventional Cell Ionomics

The distribution of elements in cells – usually known as the cell ionome¹ – can be utilized to establish the states of development and growth rates among cells. Transformations in elemental composition can be used to examine the response to drugs or toxic compounds, e.g., Pt-based compounds utilized in cancer therapy.

Typically, cell ionomic research uses ICP-MS after acid digestion of a cell pellet. This technique ordinarily necessitates a relatively high quantity of cells, increasing analysis costs, and providing only the average results for a stated cell population. The heterogeneity within the cell population is not examined and research is deprived of data on cell-to-cell variability.

Figure 1. Example of a recorded signal for a single Wickerhamomyces anomalus yeast cell. Data were acquired with an integration time of 120 µs.

Multi-Parametric Ionomics

However, each cell is characteristically distinctive. Consequently, the analysis of singular cells provides fresh insight into cell-environment interactivity and intracellular biochemistry. Due to the interconnectivity of a number of processes in a biological system, access to every element in the cell augments the efficiency and power of the experiment, resulting in improved models and predictions.

The TOFWERK icpTOF mass spectrometer allows the researcher to simultaneously detect every element in a single cell², rendering it an exemplary and distinctive tool for multi-parametric ionomics.

Figure 2. Left: Fractional mean counts of different elements in single cells (defined as counts of element X/Sum of counts of all elements). Right: Mean counts of different elements in single cells from different cell species. The difference in mean and fractional counts indicate the difference in element concentrations between different cell species.

Figure 3. PCA plot for different species. The analysis shows no clear separation of cell populations from different species. There was just a minor difference between S. cerevisiae and S. pombe and S. pombe and W. anomalus detected.

Single Cell ICP-MS Analysis Results

This study administered an analysis of the cell ionome of divergent yeast cell species cultivated in Synthetic Complete Glucose Broth media spiked with Co, Ni and Cd. An icpTOF R was supplied with a traditional sample introduction system and operated at an acquisition rate of 8250 spectra/s in triggered mode (120 µs integration time) or 550 spectra/s in continuous mode (1.8 ms integration time).

Utilizing the Particle Processing Module in TOFWERK’s TofPilot software, signals of single cells were isolated from the ionic background.

P, Mg and Zn were observed in all cells, while K, Fe, Mn and Cd were observed in a proportion of these (likely the larger cells). Only the data of P, Mg and Zn were examined, yielding a detectable variability in average and relative concentrations of different elements in different species (Figure 2). However, supported by the outcome of Principal Component Analysis (PCA), it was accepted that the complete separation of cells from different species was not possible.

There was only a slight difference between S. cerevisiae and S. pombe and S. pombe and W. anomalus. This example reveals the power of the icpTOF technology for researching the cell ionome on an individual cell basis without any foreknowledge of the cell elemental composition.

References

1. Malinouski, M.; Hasan, N. M.; Zhang, Y.; Seravalli, J.; Lin, J.; Avanesov, A.; Lutsenko, S.; Gladyshev, V. N., Genome-wide RNAi ionomics screen reveals new genes and regulation of human trace element metabolism. Nature Communications 2014, 5, 3301.
2. Hendriks, L.; Gundlach-Graham, A.; Hattendorf, B.; Günther, D., Characterization of a new ICP-TOFMS instrument with continuous and discrete introduction of solutions. J. Anal. At. Spectrom. 2017, 32 (3), 548-561.

This information has been sourced, reviewed and adapted from materials provided by TOFWERK.

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