Laser AblationCoupled with LC-ICP-MS for Local Speciationof Trace Elements in Tissues

The body mitigates the toxic effects of metals through diverse detoxification mechanisms that are activated depending on the chemical species and the burden of metals in each tissue. In this regard, analytical methods that can obtain information on the chemical form and the abundance of metals are required to elucidate the full range of detoxification mechanisms. Laser ablation (LA) is used to trim a specific microregion from tissue sections and visualize elements in it. Speciation analysis by liquid chromatography (LC) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) has been optimized for microvolume samples from small tissue sections. In this study, we developed a combined method of LA and LC-ICP-MS (LA/LC-ICP-MS) and applied it to rat brain and kidney tissues. Differences in copper (Cu) and zinc (Zn) abundance in each brain tissue region are reflected in the peak intensities of metallothioneins (MTs) detected by LC-ICP-MS analysis. In addition to revealing differences in the distribution and the concentration of mercury (Hg) in the kidneys of rats exposed to inorganic mercury (iHg) or methylmercury (MeHg) by LA-ICP-MS, we also revealed differences in the type of proteins that bind these Hg species by LC-ICP-MS. We found that in the iHg-exposed group, MT induction occurred mainly in the renal cortex and the outer medulla with elevated Cu and Zn, whereas in the MeHg-exposed group, Hg was mainly bound to hemoglobin (Hb). LA/LC-ICP-MS can simultaneously provide qualitative and quantitative information on metals in a small tissue region.