Methyl- and acetyltransferases are stable epigenetic markers postmortem.

Postmortem brain tissue has been reported to be suitable to delineate regional pattern of possible disturbances underlying epigenetic functionality. However, from many parameters that have been detected in postmortem brain regions it is noteworthy that an effect of postmortem interval (PMI), storage time and premortem parameters should not be underestimated. Our previous investigation revealed that tryptophan (TRP) levels in postmortem brain tissue is affected by PMI and storage time. Since, alteration in TRP levels are assumed to be due to protein degradation, we further investigated whether TRP correlates to variables such as RNA, proteins and DNA modulators. In addition, we aimed to elucidate whether established postmortem variables may influence epigenetic parameters. These were investigated in well characterized postmortem human brain tissue originating from the European Brain Bank consortium II (BNEII). We could confirm previous findings, in which some protein levels alter because of prolonged PMI. Similarly, we demonstrated an influence of increased storage period on TRP levels, which might indicate degradation of proteins. Still not all proteins degrade in a similar manner, therefore a specific analysis for the protein of interest would be recommended. We found that methyltransferase- and acetyltransferase-activities were relatively preserved with PMI and storage duration. In conclusion, preservation of acetyltransferase- and methyltransferase-activities provides possible evidence of stability for epigenetic studies using postmortem tissue.

Tryptophan is a marker of human postmortem brain tissue quality.

Postmortem human brain tissue is widely used in neuroscience research, but use of tissue originating from different brain bank centers is considered inaccurate because of possible heterogeneity in sample quality. There is thus a need for well-characterized markers to assess the quality of postmortem brain tissue. Toward this aim, we determined tryptophan (TRP) concentrations, phosphofructokinase-1 and glutamate decarboxylase activities in 119 brain tissue samples. These neurochemical parameters were tested in samples from autopsied individuals, including control and pathological cases provided by 10 different brain bank centers. Parameters were assessed for correlation with agonal state, postmortem interval, age and gender, brain region, preservation and freezing methods, storage conditions and storage time, RNA integrity, and tissue pH value. TRP concentrations were elevated significantly (p = 0.045) with increased postmortem interval; which might indicate increased protein degradation. Therefore, TRP concentration might be one useful and convenient marker for estimating the quality of human postmortem brain tissue.

Brain tryptophan rather than pH-value is altered as consequence of artificial postmortem interval and storage conditions.

Brain bank centers around the world attempt to standardize postmortem brain collection and quality control. Antemortem as well postmortem factors may influence tissue quality. Previously, we could demonstrate that increased tryptophan (TRP) levels significantly correlate to prolonged postmortem interval (PMI) and storage duration, whereas pH-value altered merely as consequence of prolonged agonal state and ischemic brain damage additionally to repeated freeze and thaw cycles. Therefore, we aimed to investigate in artificial PMI conditions, with three brain tissue storage temperatures (4°C, room temperature and 37°C) as well as oxidizing conditions (open/close tube), whether TRP levels and pH-value alter. We could confirm that prolonged PMI at higher storage temperatures and oxidizing conditions significantly correlate to increased TRP levels, while pH-value did not correlate at all. In conclusion, from these results PMI intervals until autopsy should be kept as short as possible and storage until autopsy should be at 4°C in order to preserve brain tissue quality as much as possible.