pH measurement as quality control on human post mortem brain tissue: a study of the BrainNet Europe consortium

Abstract

Aims: Most brain diseases are complex entities. Although animal models or cell culture experiments mimic some disease aspects, human post mortem brain tissue remains essential to advance our understanding of brain diseases using biochemical and molecular techniques. Post mortem artefacts must be properly understood, standardized, and either eliminated or factored into such experiments. Here we examine the influence of several premortem and post mortem factors on pH, and discuss the role of pH as a biochemical marker for brain tissue quality.

Methods: We assessed brain tissue pH in 339 samples from 116 brains provided by 8 different European and 2 Australian brain bank centres. We correlated brain pH with tissue source, post mortem delay, age, gender, freezing method, storage duration, agonal state and brain ischaemia.

Results: Our results revealed that only prolonged agonal state and ischaemic brain damage influenced brain tissue pH next to repeated freeze/thaw cycles.

Conclusions: pH measurement in brain tissue is a good indicator of premortem events in brain tissue and it signals limitations for post mortem investigations.

Figure 1

Boxplot of pH values from control cases by tissue source: (1) Barcelona (n = 33, pH 6.17 ± SD 0.30); (2) Würzburg Neuropathology (n = 63, pH 6.14 ± SD 0.31); (3) Münster (n = 15, pH 6.23 ± SD 0.39); (4) Kuopio (n = 32, pH 6.14 ± SD 0.30); (5) London (n = 468, pH 6.15 ± SD 0.23); (6) Tübingen (n = 3, pH 6.22 ± SD 0.09); (7) Sydney (n = 52, pH 6.28 ± SD 0.25); (8) Victoria (n = 19, pH 6.24 ± SD 0.23); (9) Würzburg Psychiatry (n = 6, pH 5.94 ± SD 0.24); (10) Göttingen (n = 20, pH 5.81 ± SD 0.32). Samples from Würzburg Psychiatry (9) and Göttingen (10) had significantly lower pH values compared with the remaining centres (*P < 0.001). Those samples were repeatedly frozen and thawed. Overall mean (n = 265, pH 6.18 ± SD 0.28). anova, *P < 0.05.

Figure 2

Boxplot diagram of pH from controls (n = 265, pH 6.18 ± SD 0.28), infarct (n = 18, pH 6.51 ± SD 0.41; P < 0.001) and global ischaemia samples (n = 48, pH 5.94 ± SD 0.28; P < 0.001). There were significant differences (*P < 0.001) between the infarct and control groups, and also between the global ischaemia and control groups. anova, *P < 0.05.

Figure 3

pH values for single-infarct samples. The range among the samples from 5.78 to 7.26 illustrates that this is a heterogeneous group. Overall mean (n = 19, pH 6.5 ± SD 0.43).

Figure 4

Boxplot diagram of pH values from control samples by brain region: frontal cortex (n = 73, mean = 6.19 ± SD 0.29), cerebellum (n = 62, mean = 6.14 ± SD 0.27), striatum (n = 63, mean = 6.17 ± SD 0.29) and gyrus cinguli (n = 63, mean = 6.20 ± SD 0.29). There is no significant difference in pH among brain regions.

Figure 5

Scatter plot diagram with linear regression line of pH distribution for PMD [post mortem delay, (a)], age (b) and storage time (c) reveals no significant relationship. A significant relationship was found for gender (d) (*P < 0.001): men had higher pH values (pH 6.27 ± SD 0.27) than women (pH 6.09 ± SD 0.28) shown in boxplot in (d). anova, *P < 0.05.

Figure 6

Boxplot diagram of pH in relation to agonal state duration: prolonged (n = 63, pH 6.07 ± SD 0.29), intermediate (n = 58, pH 6.22 ± SD 0.28) and rapid (n = 108, pH 6.23 ± SD 0.25). Prolonged agonal state samples had significant lower pH values (*P < 0.001) than rapid death samples; anova, *P < 0.05.