Minimal amount of tissue-based pH measurement to improve quality control in neuropsychiatric post-mortem brain studies

Aim: Tissue pH and RNA integrity are crucial quality-control indicators of human post-mortem brain tissues in the identification of the pathogeneses of neuropsychiatric disorders, but pH has not been measured as often due to limitations in the amount of tissue available. This study was designed to develop and validate a protocol for tissue pH evaluation using a minimal amount of human post-mortem tissues. Methods: A procedure that included a proper ratio of brain tissue weight to water for homogenization and the duration of homogenization was designed based on preliminary experiments using mouse brain tissues. The minimal (10 mg) and typical (100 mg) amounts of post-mortem brain tissue from 52 subjects were homogenized in 5 volumes (50 μL/10 mg tissue) and 10 volumes (1000 μL/100 mg tissue) of nuclease-free water and subjected to pH measurements using an InLab Ultra micro pH electrode. Results: The pH values based on the new protocol using a minimal amount of tissue significantly correlated with measurements of the standard protocol (r² = 0.86). The correlation coefficients of the pH values between gray and white matter of the same brain region, and the values between different brain regions were 0.73 and 0.54, respectively. Conclusion: The proposed protocol used one-tenth of the tissue amount of current standard protocol and enabled us to evaluate the exact quality of post-mortem brain tissue subjected to subsequent analyses. The application of this protocol may improve the detection of biological phenomena of interest in post-mortem brain studies by diminishing confounding factors.