Multiplex LA-ICP-MS bio-imaging of brain tissue of a parkinsonian mouse model stained with metal-coded affinity-tagged antibodies and coated with indium-spiked commercial inks as internal standards

Background: Immunohistochemistry techniques represent a powerful tool to detect and quantify disease related proteins. Improvements were accomplished by tagged antibodies using laser ablation and inductively coupled plasma mass spectrometry (LA-ICP-MS). However, these approaches are effected by day-to-variations due to instrumental drift. New Method: Brain tissue from line 62, a Parkinson's disease model, and control mice were incubated with four antibodies relevant to the disease and standardized to three house-keeping proteins. In addition, a new standardization approach was developed and the results compared. This new approach consisted of coating specimens with gelatin and printing an indium-doped ink with a commercial ink jet printer. Furthermore, the method was evaluated for different ablation spot sizes with respect to resolution and signal-to-noise ratio. Results: Normalization using house-keeping proteins led to high background signals even at high resolution. Normalization using indium-doped ink improved the signal-to-noise ratio even when small laser spot sizes were used and further improved by overlaying tissue specimen with gelatin. Comparison with Existing Methods: Line 62 mice had more a-Synuclein and gliosis but decreased numbers of neurons, as found by conventional immunohistochemistry. These data are in line with the results obtained by LA-ICP-MS with indium standardization. However, differences between L62 and controls for tyrosine hydroxylase were only detected by LA-ICP-MS. Conclusions: Internal standardisation using indium-doped inks is an effective method to overcome day-to-day variations and instrumental drifts. The new approach results in an increased signal-to-noise ratio and only under these conditions small but significant changes were detected, as seen for tyrosine hydroxylase.