Selective, quantitative measurement of releasable synaptic zinc in human autopsy hippocampal brain tissue from Alzheimer's disease patients

Abstract

Aberrant central nervous system zinc homeostasis has been reported in Alzheimer’s disease (AD). However, there are conflicting reports describing zinc concentration either increased or decreased in the brain of AD patients. Such discrepancies may be due to differences in the brain area examined, zinc detection method, and/or tissue composition. Furthermore, detection and measurement of the releasable zinc pool in autopsy tissue is difficult and usually unreliable. Obtaining an adequate assessment of this releasable zinc pool is of particular significance in AD research in that zinc can coordinate with and stabilize toxic amyloid beta oligomers, which are believed to play a key role in AD neuropathology. In addition, zinc released into the synaptic cleft can interact with the postsynaptic neurons causing altered signaling and synaptic dysfunction, which is a well established event in AD. The method presented here combines two approaches, biochemical fractionation and atomic absorption spectrophotometry, to allow, in addition to extracellular zinc concentration, the reliable and quantitative measurement of zinc specifically localized in synaptic vesicles, which contain the majority of the neuronal releasable zinc. Using this methodology, we found that synaptic vesicle zinc concentrations were increased in AD hippocampi compared to age-matched controls and that this increase in releasable zinc matched increased concentration of zinc in the extracellular space.

Zinc in the central nervous system: From molecules to behavior

“…Consistent with these observations, Bjorklund et al [45] detected increased levels of both synaptically releasable and extracellular zinc in hippocampal tissue from AD patients compared to age-matched control tissue. Kozin et al [46] recently identified the primary Aβ zinc recognition site responsible for binding zinc ions and inducing dimerization and subsequent oligomerization and aggregation of Ab.…”

Postsynaptic Proteome of Non-Demented Individuals with Alzheimer’s Disease Neuropathology

“…For proteomic studies, synaptic fractionation was performed as described previously [36–38]. Briefly, hippocampal tissue was homogenized in 0.32 M sucrose solution containing 1x Protease Inhibitor Cocktail (Sigma-Aldrich) and Halt Phosphatase Inhibitor Cocktail (Life Technologies, Inc) using a Dounce glass homogenizer.…”

Zinc: The Metal of Life

“…These salts do not interfere with transmissible gastroenteritis virus cell binding (Wei and others ). Bacterial cellulose when dissolved in zinc chloride aqueous solution (ZnCl2·3H2O) showed typical shear‐thinning behavior (Lu and Shen ). Intratesticular injection of zinc gluconate acts as a contraceptive for dogs. When metamizole sodium was concurrently administered it did not interfere with chemical sterilization (Oliveira and others ). In neurodegenerative conditions such as AD, releasable synaptic zinc plays a key role in toxic amyloid beta oligomer formation and their dysfunctional targeting to postsynaptic elements (Bjorklund and others ). Under severe oxidative stress, cell lethality caused by ZnCl 2 was significantly greater than that caused by polaprezinc (Seo and others ). Zn induces oxidative stress via the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and depletion of glutathione (GSH) which, in turn, activate the apoptotic machinery leading to dopaminergic neurodegeneration similar to paraquat (Kumar and others ). Zinc pyrithione (ZPT) directly protects cardiomyocytes from reperfusion injury by a mechanism that attenuates NADPH oxidase‐mediated intracellular oxidative stress (Kasi and others ). An inverse correlation between serum zinc concentrations and immune activation marker neopterin was observed which correlated with increased inflammatory processes in patients referred for coronary angiography with low zinc levels (Murr and others ). A positive relationship between red meat intake and maternal hair zinc levels was observed in infants and their mothers (Ozden and others ). Photocatalytic therapy of human squamous cell carcinoma (HNSCC) with zinc oxide nanoparticles (ZnO‐NPs) enhances the cytotoxic action of chemotherapeutic agents synergistically, indicating a promising potential for ZnO‐NPs in antitumor applications (Hackenberg and others ). Zinc oxide nanoparticles can be clastogenic/genotoxic and cytotoxic agents on the root cells of Allium cepa (Kumari and others ). Pediatric reference values for serum zinc concentration in Iranian subjects were determined by flame atomic absorption spectrometry. Overall 95% reference values for serum zinc concentrations were 9.7 to 31.5, 9.2 to 30.9, and 9.3 to 31.1 μmol/L in boys, girls, and total population of Iran, respectively (Ghasemi and others ). Most of the zinc complexes so far tested for their antidiabetic potential exert significant toxicity, but Zn‐flavonol has significant antihyperglycemic activity in STZ‐induced diabetic rats and is nontoxic when orally administered at a concentration of 5 mg/kg b.w./rat/d for 30 d (Vijayaraghavan and others ). The zinc lozenge effect on common cold duration is heterogeneous.…”