Tryptophan is a marker of human postmortem brain tissue quality

Medical Assistance in Death as a Unique Opportunity to Advance Human Immunodeficiency Virus Cure Research

The inability to sample deep-tissue reservoirs in individuals living with human immunodeficiency virus (HIV) has greatly hindered accurate estimates of viral reservoir size and distribution. Animal models and collection of tissues during autopsies of HIV-positive individuals are 2 proposed solutions to this problem. Each, however, has its limitations. In this Viewpoint, we argue that tissue donation following medical assistance in death (MAiD) will form an invaluable resource for the characterization of the viral reservoir in the context of current HIV cure research. In support, we discuss a recent instance in which an individual living with HIV chose to donate their body/tissues to HIV research prior to undergoing MAiD at our institution. Going forward, we hope this will help provide support to individuals in their decisions around tissue donation following MAiD, while highlighting how healthcare providers, by complying with such wishes, can affect patient satisfaction in the last days of life.

Neurochemical markers as potential indicators of postmortem tissue quality

Premortem, postmortem, and storage conditions are parameters that can influence the quality and interpretation of data from studies of postmortem tissue. While many neurochemicals in the brain are relatively stable for several hours after death if stored at 4°C, the postmortem delay nevertheless becomes an important variable when examining the disease state because neurochemical levels may change with extended postmortem delay. Moreover, in the postmortem brain, neurochemical levels may also play a key role in determining the diagnosis. This is particularly true for some neurodegenerative disorders where many of the clinical features of the disease are not exclusive to one illness. It is therefore imperative to employ brain tissue of the highest quality from both nondiseased (control) and diseased brain tissue to ascertain the specific molecular and genetic mechanisms particular to the disease pathogenesis. Consequently, it would be very useful if specific markers could be employed to demonstrate and determine the quality of postmortem brain tissue that is suitable for such studies. In this chapter, the following neurochemical markers are critically reviewed as potential candidates to assess the quality of postmortem brain tissue: tryptophan levels, glutathione levels (and glutathione metabolic enzymes), enzymatic activities (glutamate decarboxylase, phosphofructokinase-1), epigenetic enzymes (acetyltransferase, methyltransferase), and tissue pH. In conclusion, the neurochemical tryptophan appears to be the most suitable candidate for assessing the integrity and quality of postmortem brain tissue. However, to optimize the quality of the samples, neuropathologic diagnostic characterization must also be employed in the interpretation and understanding of the data generated. It would also be judicious to consider as many premortem and postmortem conditions as possible as they can also affect the genetic and molecular integrity of the brain tissue.

Stroke, Vascular Dementia, and Alzheimer's Disease: Molecular Links

Stroke is a brain disease that occurs when blood flow stops, resulting in reduced oxygen supply to neurons. Stroke occurs at any time and at any age, but increases after the age of 55. It is the second leading cause of death and the third leading cause of disability-adjusted, life-years. The pathophysiology of ischemic stroke is complex and recent molecular, cellular, and animal models and postmortem brain studies have revealed that multiple cellular changes have been implicated, including oxidative stress/mitochondrial dysfunction, inflammatory responses, micro RNA alterations, and marked changes in brain proteins. These cellular changes provide new information for developing therapeutic strategies for ischemic stroke treatment. Research also revealed that stroke increases with a number of modifiable factors and most strokes can be prevented and/or controlled through pharmacological or surgical interventions and lifestyle changes. Ischemic stroke is the major risk factor for vascular dementia and Alzheimer's disease. This review summarizes the latest research findings on stroke, including causal factors and molecular links between stroke and vascular disease/Alzheimer's disease.

Translational Research in Pediatrics IV: Solid Tissue Collection and Processing

Solid tissues are critical for child-health research. Specimens are commonly obtained at the time of biopsy/surgery or postmortem. Research tissues can also be obtained at the time of organ retrieval for donation or from tissue that would otherwise have been discarded. Navigating the ethics of solid tissue collection from children is challenging, and optimal handling practices are imperative to maximize tissue quality. Fresh biopsy/surgical specimens can be affected by a variety of factors, including age, gender, BMI, relative humidity, freeze/thaw steps, and tissue fixation solutions. Postmortem tissues are also vulnerable to agonal factors, body storage temperature, and postmortem intervals. Nonoptimal tissue handling practices result in nucleotide degradation, decreased protein stability, artificial posttranslational protein modifications, and altered lipid concentrations. Tissue pH and tryptophan levels are 2 methods to judge the quality of solid tissue collected for research purposes; however, the RNA integrity number, together with analyses of housekeeping genes, is the new standard. A comprehensive clinical data set accompanying all tissue samples is imperative. In this review, we examined: the ethical standards relating to solid tissue procurement from children; potential sources of solid tissues; optimal practices for solid tissue processing, handling, and storage; and reliable markers of solid tissue quality.

Mitochondrial function in human brains is affected by pre- and post mortem factors

AIM

Mitochondrial function and the ensuing ATP synthesis are central to the functioning of the brain and contribute to neuronal physiology. Most studies on neurodegenerative diseases have highlighted that mitochondrial dysfunction is an important event contributing to pathology. However, studies on the human brain mitochondria in various neurodegenerative disorders heavily rely on post mortem samples. As post mortem tissues are influenced by pre- and post mortem factors, we investigated the effect of these variables on mitochondrial function.

METHODS

We examined whether the mitochondrial function (represented by mitochondrial enzymes and antioxidant activities) in post mortem human brains (n=45) was affected by increased storage time (11.8-104.1 months), age of the donor (2 days to 80 years), post mortem interval (2.5-26 h), gender difference and agonal state [based on Glasgow Coma Scale: range=3-15] in the frontal cortex, as a prototype.

RESULTS

We observed that the activities of citrate synthase, succinate dehydrogenase and mitochondrial reductase (MTT) were significantly affected only by gender difference (citrate synthase: P=0.005; succinate dehydrogenase: P=0.01; mitochondrial reductase: P=0.006), being higher in females, but not by any other factor. Mitochondrial complex I activity was significantly inhibited by increasing age (r=-0.40; P=0.05). On the other hand, the mitochondrial antioxidant enzyme glutathione reductase decreased with severe agonal state (P=0.003), while the activity of glutathione-S-transferase declined with increased storage time (P=0.005) and severe agonal state (P=0.02).

CONCLUSION

Our data highlight the influence of pre- and post mortem factors on preservation of mitochondrial function with implications for studies on brain pathology employing stored human samples.

Alteration of the pro-oxidant xanthine oxidase (XO) in the thalamus and occipital cortex of patients with schizophrenia

OBJECTIVES

Mounting evidence shows that oxidative stress (OS) and the purine/adenosine system play a key role in the pathophysiology of schizophrenia. Lately, our group pointed out that not only antioxidants, but also the prooxidant system plays an important role in neuro-psychiatric disorders. Xanthine oxidase (XO) is an enzyme of special interest in this context, since it acts as a prooxidant, but its main product is a vastly important antioxidant, uric acid (UA). Furthermore, XO plays major part in the purine/adenosine metabolism, which has been hypothesised to play a role in schizophrenia as well.

METHODS

We examined the activity of XO in the striato-cortico-limbic system of schizophrenic patients (SP) and controls using a commercially available activity assay.

RESULTS

We found decreased activity of XO in the occipital cortex and thalamus of patients with psychosis. Furthermore, XO shows a significant positive correlation with chlorpromazine equivalents in the putamen and the temporal cortex.

CONCLUSIONS

Nevertheless, our results might suggest a downregulation of cellular defence mechanisms in schizophrenia in several brain regions, which could account for neuronal alterations which have been described before. This demonstrates that more research is needed to fully understand the role of the complex enzyme XO in the pathophysiology of schizophrenia.

Gene-environment interaction research and transgenic mouse models of Alzheimer's disease

The etiology of the sporadic form of Alzheimer's disease (AD) remains largely unknown. Recent evidence has suggested that gene-environment interactions (GxE) may play a crucial role in its development and progression. Whereas various susceptibility loci have been identified, like the apolipoprotein E4 allele, these cannot fully explain the increasing prevalence of AD observed with aging. In addition to such genetic risk factors, various environmental factors have been proposed to alter the risk of developing AD as well as to affect the rate of cognitive decline in AD patients. Nevertheless, aside from the independent effects of genetic and environmental risk factors, their synergistic participation in increasing the risk of developing AD has been sparsely investigated, even though evidence points towards such a direction. Advances in the genetic manipulation of mice, modeling various aspects of the AD pathology, have provided an excellent tool to dissect the effects of genes, environment, and their interactions. In this paper we present several environmental factors implicated in the etiology of AD that have been tested in transgenic animal models of the disease. The focus lies on the concept of GxE and its importance in a multifactorial disease like AD. Additionally, possible mediating mechanisms and future challenges are discussed.

Postmortem interval effect on RNA and gene expression in human brain tissue

Banked tissue is essential to the study of neurological disease but using postmortem tissue introduces a number of possible confounds. Foremost amongst these are factors relating to variation in postmortem interval (PMI). Currently there are conflicting reports on how PMI affects overall RNA integrity, and very few reports of how gene expression is affected by PMI. We analyzed total RNA extracted from frozen cerebellar cortex from 79 deceased human subjects enrolled in the Banner Sun Health Research Institute Brain and Body Donation Program. The PMI, which ranged from 1.5 to 45 h, correlated with overall RNA quality measures including RNA Integrity Number (RIN) (r = -0.34, P = 0.002) and RNA quantitative yield (r = -0.25, P = 0.02). Additionally, we determined the expression of 89 genes using a PCR-based gene expression array (RT(2) Profiler™ PCR Array: Human Alzheimer's Disease; SABiosciences™, Frederick, MD). A greater proportion of genes had decreased rather than increased expression with increasing PMI (65/89 vs. 20/89; P < 0.0001). Of these, transcripts from the genes ADAM9, LPL, PRKCG, and SERPINA3 had significantly decreased expression with increasing PMI (P < 0.01). No individual gene transcripts had significantly increased expression with increasing PMI. In conclusion, it is apparent that RNA degrades progressively with increasing PMI and that measurement of gene expression in brain tissue with longer PMI may give artificially low values. For tissue derived from autopsy, a short PMI optimizes its utility for molecular research.