Effects of zinc on SN56 cholinergic neuroblastoma cells

Effects of Marginal Zn Excess and Thiamine Deficiency on Microglial N9 Cell Metabolism and Their Interactions with Septal SN56 Cholinergic Cells

Mild thiamine deficiency aggravates Zn accumulation in cholinergic neurons. It leads to the augmentation of Zn toxicity by its interaction with the enzymes of energy metabolism. Within this study, we tested the effect of Zn on microglial cells cultivated in a thiamine-deficient medium, containing 0.003 mmol/L of thiamine vs. 0.009 mmol/L in a control medium. In such conditions, a subtoxic 0.10 mmol/L Zn concentration caused non-significant alterations in the survival and energy metabolism of N9 microglial cells. Both activities of the tricarboxylic acid cycle and the acetyl-CoA level were not decreased in these culture conditions. Amprolium augmented thiamine pyrophosphate deficits in N9 cells. This led to an increase in the intracellular accumulation of free Zn and partially aggravated its toxicity. There was differential sensitivity of neuronal and glial cells to thiamine-deficiency-Zn-evoked toxicity. The co-culture of neuronal SN56 with microglial N9 cells reduced the thiamine-deficiency-Zn-evoked inhibition of acetyl-CoA metabolism and restored the viability of the former. The differential sensitivity of SN56 and N9 cells to borderline thiamine deficiency combined with marginal Zn excess may result from the strong inhibition of pyruvate dehydrogenase in neuronal cells and no inhibition of this enzyme in the glial ones. Therefore, ThDP supplementation can make any brain cell more resistant to Zn excess.

Metabolic and Cellular Compartments of Acetyl-CoA in the Healthy and Diseased Brain

The human brain is characterised by the most diverse morphological, metabolic and functional structure among all body tissues. This is due to the existence of diverse neurons secreting various neurotransmitters and mutually modulating their own activity through thousands of pre- and postsynaptic interconnections in each neuron. Astroglial, microglial and oligodendroglial cells and neurons reciprocally regulate the metabolism of key energy substrates, thereby exerting several neuroprotective, neurotoxic and regulatory effects on neuronal viability and neurotransmitter functions. Maintenance of the pool of mitochondrial acetyl-CoA derived from glycolytic glucose metabolism is a key factor for neuronal survival. Thus, acetyl-CoA is regarded as a direct energy precursor through the TCA cycle and respiratory chain, thereby affecting brain cell viability. It is also used for hundreds of acetylation reactions, including N-acetyl aspartate synthesis in neuronal mitochondria, acetylcholine synthesis in cholinergic neurons, as well as divergent acetylations of several proteins, peptides, histones and low-molecular-weight species in all cellular compartments. Therefore, acetyl-CoA should be considered as the central point of metabolism maintaining equilibrium between anabolic and catabolic pathways in the brain. This review presents data supporting this thesis.

Structural effects of zinc on phosphatidylserine-containing lipid membranes: kinetic analysis of membrane reorganization

Zinc induces reorganization of phosphatidylserine-containing lipid membranes.

Protection of Cholinergic Neurons against Zinc Toxicity by Glial Cells in Thiamine-Deficient Media

Brain pathologies evoked by thiamine deficiency can be aggravated by mild zinc excess. Cholinergic neurons are the most susceptible to such cytotoxic signals. Sub-toxic zinc excess aggravates the injury of neuronal SN56 cholinergic cells under mild thiamine deficiency. The excessive cell loss is caused by Zn interference with acetyl-CoA metabolism. The aim of this work was to investigate whether and how astroglial C6 cells alleviated the neurotoxicity of Zn to cultured SN56 cells in thiamine-deficient media. Low Zn concentrations did not affect astroglial C6 and primary glial cell viability in thiamine-deficient conditions. Additionally, parameters of energy metabolism were not significantly changed. Amprolium (a competitive inhibitor of thiamine uptake) augmented thiamine pyrophosphate deficits in cells, while co-treatment with Zn enhanced the toxic effect on acetyl-CoA metabolism. SN56 cholinergic neuronal cells were more susceptible to these combined insults than C6 and primary glial cells, which affected pyruvate dehydrogenase activity and the acetyl-CoA level. A co-culture of SN56 neurons with astroglial cells in thiamine-deficient medium eliminated Zn-evoked neuronal loss. These data indicate that astroglial cells protect neurons against Zn and thiamine deficiency neurotoxicity by preserving the acetyl-CoA level.

The Multifaceted Roles of Zinc in Neuronal Mitochondrial Dysfunction

Zinc is a highly abundant cation in the brain, essential for cellular functions, including transcription, enzymatic activity, and cell signaling. However, zinc can also trigger injurious cascades in neurons, contributing to the pathology of neurodegenerative diseases. Mitochondria, critical for meeting the high energy demands of the central nervous system (CNS), are a principal target of the deleterious actions of zinc. An increasing body of work suggests that intracellular zinc can, under certain circumstances, contribute to neuronal damage by inhibiting mitochondrial energy processes, including dissipation of the mitochondrial membrane potential (MMP), leading to ATP depletion. Additional consequences of zinc-mediated mitochondrial damage include reactive oxygen species (ROS) generation, mitochondrial permeability transition, and excitotoxic calcium deregulation. Zinc can also induce mitochondrial fission, resulting in mitochondrial fragmentation, as well as inhibition of mitochondrial motility. Here, we review the known mechanisms responsible for the deleterious actions of zinc on the organelle, within the context of neuronal injury associated with neurodegenerative processes. Elucidating the critical contributions of zinc-induced mitochondrial defects to neurotoxicity and neurodegeneration may provide insight into novel therapeutic targets in the clinical setting.

The Impact of Acetyl-CoA and Aspartate Shortages on the N-Acetylaspartate Level in Different Models of Cholinergic Neurons

N-acetylaspartate is produced by neuronal aspartate N-acetyltransferase (NAT8L) from acetyl-CoA and aspartate. In cholinergic neurons, acetyl-CoA is also utilized in the mitochondrial tricarboxylic acid cycle and in acetylcholine production pathways. While aspartate has to be shared with the malate–aspartate shuttle, another mitochondrial machinery together with the tricarboxylic acid cycle supports the electron transport chain turnover. The main goal of this study was to establish the impact of toxic conditions on N-acetylaspartate production. SN56 cholinergic cells were exposed to either Zn²⁺ overload or Ca²⁺ homeostasis dysregulation and male adult Wistar rats’ brains were studied after 2 weeks of challenge with streptozotocin-induced hyperglycemia or daily theophylline treatment. Our results allow us to hypothesize that the cholinergic neurons from brain septum prioritized the acetylcholine over N-acetylaspartate production. This report provides the first direct evidence for Zn²⁺-dependent suppression of N-acetylaspartate synthesis leading to mitochondrial acetyl-CoA and aspartate shortages. Furthermore, Zn²⁺ is a direct concentration-dependent inhibitor of NAT8L activity, while Zn²⁺-triggered oxidative stress is unlikely to be significant in such suppression.

Aggravated effects of coexisting marginal thiamine deficits and zinc excess on SN56 neuronal cells

Objectives: Zinc excitotoxicity and thiamine pyrophosphate deficiency (TD) are known pathogenic signals contributing to mechanism of different encephalopathies through inhibition of enzymes responsible for energy metabolism such as pyruvate dehydrogenase, aconitase or ketoglutarate dehydrogenase. The aim of this work was to investigate whether subclinical Zn excess and TD, frequent in aging brain, may combine yielding overt neuronal impairment.Results: Clonal SN56 cholinergic neuronal cells of septal origin were used as the model of brain cholinergic neurons, which are particularly susceptible to neurodegeneration in the course of Alzheimer's disease, hypoxia and other dementia-linked brain pathologies. Neither subtoxic concentration of Zn (0.10 mM) nor mild 20-25% TD deficits alone caused significant negative changes in cultured cholinergic neurons viability and their acetyl-CoA/acetylcholine metabolism. However, cells with mild TD accumulated Zn in excess, which impaired their energy metabolism causing a loss of neurons viability and their function as neurotransmitters. These negative effects of Zn were aggravated by amprolium which is an inhibitor of thiamine intracellular transport.Conclusion: Our data indicate that TD may amplify otherwise non-harmful border-line Zn excitotoxic signals yielding progress of neurodegeneration.

Protective effects of voltage-gated calcium channel antagonists against zinc toxicity in SN56 neuroblastoma cholinergic cells

One of the pathological site effects in excitotoxic activation is Zn²⁺ overload to postsynaptic neurons. Such an effect is considered to be equivalent to the glutamate component of excitotoxicity. Excessive uptake of Zn²⁺ by active voltage-dependent transport systems in these neurons may lead to significant neurotoxicity. The aim of this study was to investigate whether and which antagonists of the voltage gated calcium channels (VGCC) might modify this Zn²⁺-induced neurotoxicity in neuronal cells. Our data demonstrates that depolarized SN56 neuronal cells may take up large amounts of Zn²⁺ and store these in cytoplasmic and mitochondrial sub-fractions. The mitochondrial Zn²⁺ excess suppressed pyruvate uptake and oxidation. Such suppression was caused by inhibition of pyruvate dehydrogenase complex, aconitase and NADP-isocitrate dehydrogenase activities, resulting in the yielding of acetyl-CoA and ATP shortages. Moreover, incoming Zn²⁺ increased both oxidized glutathione and malondialdehyde levels, known parameters of oxidative stress. In depolarized SN56 cells, nifedipine treatment (L-type VGCC antagonist) reduced Zn²⁺ uptake and oxidative stress. The treatment applied prevented the activities of PDHC, aconitase and NADP-IDH enzymes, and also yielded the maintenance of acetyl-CoA and ATP levels. Apart from suppression of oxidative stress, N- and P/Q-type VGCCs presented a similar, but weaker protective influence. In conclusion, our data shows that in the course of excitotoxity, impairment to calcium homeostasis is tightly linked with an excessive neuronal Zn²⁺ uptake. Hence, the VGCCs types L, N and P/Q share responsibility for neuronal Zn²⁺ overload followed by significant energy-dependent neurotoxicity. Moreover, Zn²⁺ affects the target tricarboxylic acid cycle enzymes, yields acetyl-CoA and energy deficits as well.

The Regulatory Effects of Acetyl-CoA Distribution in the Healthy and Diseased Brain

Brain neurons, to support their neurotransmitter functions, require a several times higher supply of glucose than non-excitable cells. Pyruvate, the end product of glycolysis, through pyruvate dehydrogenase complex reaction, is a principal source of acetyl-CoA, which is a direct energy substrate in all brain cells. Several neurodegenerative conditions result in the inhibition of pyruvate dehydrogenase and decrease of acetyl-CoA synthesis in mitochondria. This attenuates metabolic flux through TCA in the mitochondria, yielding energy deficits and inhibition of diverse synthetic acetylation reactions in all neuronal sub-compartments. The acetyl-CoA concentrations in neuronal mitochondrial and cytoplasmic compartments are in the range of 10 and 7 μmol/L, respectively. They appear to be from 2 to 20 times lower than acetyl-CoA Km values for carnitine acetyltransferase, acetyl-CoA carboxylase, aspartate acetyltransferase, choline acetyltransferase, sphingosine kinase 1 acetyltransferase, acetyl-CoA hydrolase, and acetyl-CoA acetyltransferase, respectively. Therefore, alterations in acetyl-CoA levels alone may significantly change the rates of metabolic fluxes through multiple acetylation reactions in brain cells in different physiologic and pathologic conditions. Such substrate-dependent alterations in cytoplasmic, endoplasmic reticulum or nuclear acetylations may directly affect ACh synthesis, protein acetylations, and gene expression. Thereby, acetyl-CoA may regulate the functional and adaptative properties of neuronal and non-neuronal brain cells. The excitotoxicity-evoked intracellular zinc excess hits several intracellular targets, yielding the collapse of energy balance and impairment of the functional and structural integrity of postsynaptic cholinergic neurons. Acute disruption of brain energy homeostasis activates slow accumulation of amyloid-β_1-42 (Aβ). Extra and intracellular oligomeric deposits of Aβ affect diverse transporting and signaling pathways in neuronal cells. It may combine with multiple neurotoxic signals, aggravating their detrimental effects on neuronal cells. This review presents evidences that changes of intraneuronal levels and compartmentation of acetyl-CoA may contribute significantly to neurotoxic pathomechanisms of different neurodegenerative brain disorders.

Phenotype-Dependent Interactions between N-acetyl-L-Aspartate and Acetyl-CoA in Septal SN56 Cholinergic Cells Exposed to an Excess of Zinc

Pyruvate dehydrogenase reaction utilizing glucose-derived pyruvate is an almost exclusive source of acetyl-CoA in different cell mitochondrial compartments of the brain. In neuronal mitochondria, the largest fraction of acetyl-CoA is utilized for energy production and the much smaller one for N-acetyl-L-aspartate (NAA) synthesis. Cholinergic neurons, unlike others, require additional amounts of acetyl-CoA for acetylcholine synthesis. Therefore, several neurotoxic signals, which inhibit pyruvate dehydrogenase, generate deeper shortages of acetyl-CoA and greater mortality of cholinergic neurons than noncholinergic ones. NAA is considered to be a marker of neuronal energy status in neuropathic brains. However, there is no data on putative differential fractional distribution of the acetyl-CoA pool between energy producing and NAA or acetylcholine synthesizing pathways in noncholinergic and cholinergic neurons, respectively. Therefore, the aim of this study was to investigate whether zinc-excess, a common excitotoxic signal, may evoke differential effects on the NAA metabolism in neuronal cells with low and high expression of the cholinergic phenotype. Differentiated SN56 neuronal cells, displaying a high activity of choline acetyltransferase and rates of acetylcholine synthesis, contained lower levels of acetyl-CoA and NAA, being more susceptible to ZnCl2 exposition that the nondifferentiated SN56 or differentiated dopaminergic SHSY5Y neuronal and astroglial C6 cells. Differentiated SN56 accumulated greater amounts of Zn2 + from extracellular space than the other ones, and displayed a stronger suppression of pyruvate dehydrogenase complex activity and acetyl-CoA, NAA, ATP, acetylcholine levels, and loss of viability. These data indicate that the acetyl-CoA synthesizing system in neurons constitutes functional unity with energy generating and NAA or acetylcholine pathways of its utilization, which are uniformly affected by neurotoxic conditions.

Early and Late Pathomechanisms in Alzheimer's Disease: From Zinc to Amyloid-β Neurotoxicity

There are several systemic and intracerebral pathologic conditions, which limit provision and utilization of energy precursor metabolites in neuronal cells. Energy deficits cause excessive depolarization of neuronal cells triggering glutamate-zinc evoked excitotoxic cascade. The intracellular zinc excess hits several intraneuronal targets yielding collapse of energy balance and impairment functional and structural impairments cholinergic neurons. Disturbances in metabolism of acetyl-CoA, which is a direct precursor for energy, acetylcholine, N-acetyl-L-aspartate and acetylated proteins synthesis, play an important role in these pathomechanisms. Disruption of brain homeostasis activates slow accumulation of amyloid-β 1-42 , which extra and intracellular oligomeric deposits disrupt diverse transporting and signaling processes in all membrane structures of the cell. Both neurotoxic signals may combine aggravating detrimental effects on neuronal cell. Different neuroglial and neuronal cell types may display differential susceptibility to similar pathogenic insults depending on specific features of their energy and functional parameters. This review, basing on findings gained from cellular and animal models of Alzheimer's disease, discusses putative energy/acetyl-CoA dependent mechanism in early and late stages of neurodegeneration.

Intracellular redistribution of acetyl-CoA, the pivotal point in differential susceptibility of cholinergic neurons and glial cells to neurodegenerative signals

Intramitochondrial decarboxylation of glucose-derived pyruvate by PDHC (pyruvate dehydrogenase complex) is a principal source of acetyl-CoA, for mitochondrial energy production and cytoplasmic synthetic pathways in all types of brain cells. The inhibition of PDHC, ACO (aconitase) and KDHC (ketoglutarate dehydrogenase complex) activities by neurodegenerative signals such as aluminium, zinc, amyloid β-peptide, excess nitric oxide (NO) or thiamine pyrophosphate deficits resulted in much deeper losses of viability, acetyl-CoA and ATP in differentiated cholinergic neuronal cells than in non-differentiated cholinergic, and cultured microglial or astroglial cell lines. In addition, in cholinergic cells, such conditions caused inhibition of ACh (acetylcholine) synthesis and its quantal release. Furthermore, cholinergic neuronal cells appeared to be resistant to high concentrations of LPS (lipopolysaccharide). In contrast, in microglial cells, low levels of LPS caused severalfold activation of NO, IL-6 (interleukin 6) and TNFα (tumour necrosis factor α) synthesis/release, accompanied by inhibition of PDHC, KDHC and ACO activities, and suppression of acetyl-CoA, but relatively small losses in their ATP contents and viability parameters. Compounds that protected these enzymes against inhibitory effects of neurotoxins alleviated acetyl-CoA and ATP deficits, thereby maintaining neuronal cell viability. These data indicate that preferential susceptibility of cholinergic neurons to neurodegenerative insults may result from competition for acetyl-CoA between mitochondrial energy-producing and cytoplasmic ACh-synthesizing pathways. Such a hypothesis is supported by the existence of highly significant correlations between mitochondrial/cytoplasmic acetyl-CoA levels and cell viability/transmitter functions respectively.

Retinoic acid as a therapeutic option in Alzheimer's disease: a focus on cholinergic restoration

Retinoic acid is a potent cell differentiating factor, which through its nuclear receptors affects a vast range of promoter sites in brain neuronal and glial cells in every step of embryonic and postnatal life. Its capacities, facilitating maturation of neurotransmitter phenotype in different groups of neurons, pave the way for its application as a potential therapeutic agent in neurodegenerative diseases including Alzheimer's disease. Retinoic acid was found to exert particularly strong enhancing effects on acetylcholine transmitter functions in brain cholinergic neurons, loss of which is tightly linked to the development of cognitive and memory deficits in course of different cholinergic encephalopathies. Here, we review cholinotrophic properties of retinoic acid and its derivatives, which may justify their application in the management of Alzheimer's disease and the related neurodegenerative conditions.

Acetyl-CoA the key factor for survival or death of cholinergic neurons in course of neurodegenerative diseases

Glucose-derived pyruvate is a principal source of acetyl-CoA in all brain cells, through pyruvate dehydogenase complex (PDHC) reaction. Cholinergic neurons like neurons of other transmitter systems and glial cells, utilize acetyl-CoA for energy production in mitochondria and diverse synthetic pathways in their extramitochondrial compartments. However, cholinergic neurons require additional amounts of acetyl-CoA for acetylcholine synthesis in their cytoplasmic compartment to maintain their transmitter functions. Characteristic feature of several neurodegenerating diseases including Alzheimer’s disease and thiamine diphosphate deficiency encephalopathy is the decrease of PDHC activity correlating with cholinergic deficits and losses of cognitive functions. Such conditions generate acetyl-CoA deficits that are deeper in cholinergic neurons than in noncholinergic neuronal and glial cells, due to its additional consumption in the transmitter synthesis. Therefore, any neuropathologic conditions are likely to be more harmful for the cholinergic neurons than for noncholinergic ones. For this reason attempts preserving proper supply of acetyl-CoA in the diseased brain, should attenuate high susceptibility of cholinergic neurons to diverse neurodegenerative conditions. This review describes how common neurodegenerative signals could induce deficts in cholinergic neurotransmission through suppression of acetyl-CoA metabolism in the cholinergic neurons.

Effects of sodium metavanadate on in vitro neuroblastoma and red blood cells

Toxicity of vanadium on cells is one of the less studied effects. This prompted us to study the structural effects induced on neuroblastoma and erythrocytes by vanadium (V) sodium metavanadate. This salt was incubated with mice cholinergic neuroblastoma cells and intact human erythrocytes. To learn whether metavanadate interacts with membrane lipid bilayers it was incubated with bilayers built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE). These are phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Exposure of neuroblastoma cells to metavanadate showed significant decreases in cell viability as well as in cell number correlating with inhibition of aconitase activity. In scanning electron microscopy (SEM) and defocusing microscopy (DM) it was observed that induced on erythrocytes the formation of echinocytes. However, no effects were obtained when metavanadate was made to interact with DMPC and DMPE multibilayers and liposomes, assays performed by X-ray diffraction and differential scanning calorimetry (DSC), respectively. These results imply that the effects of metavanadate on erythrocytes are through interactions with proteins located in the membrane outer moiety, and could still involve other minor lipid components as well. Also, partly unsaturated lipids could interact differently the fully saturated chains in the model systems.

Human erythrocytes and neuroblastoma cells are in vitro affected by sodium orthovanadate

Research on biological influence of vanadium has gained major importance because it exerts potent toxic, mutagenic, and genotoxic effects on a wide variety of biological systems. However, hematological toxicity is one of the less studied effects. The lack of information on this issue prompted us to study the structural effects induced on the human erythrocyte membrane by vanadium (V). Sodium orthovanadate was incubated with intact erythrocytes, isolated unsealed human erythrocyte membranes (IUM) and molecular models of the erythrocyte membrane. The latter consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. This report presents evidence in order that orthovanadate interacted with red cell membranes as follows: a) in scanning electron microscopy (SEM) studies it was observed that morphological changes on human erythrocytes were induced; b) fluorescence spectroscopy experiments in isolated unsealed human erythrocyte membranes (IUM) showed that an increase in the molecular dynamics and/or water content at the shallow depth of the lipids glycerol backbone at concentrations as low as 50μM was produced; c) X-ray diffraction studies showed that orthovanadate 0.25-1mM range induced increasing structural perturbation to DMPE; d) somewhat similar effects were observed by differential scanning calorimetry (DSC) with the exception of the fact that DMPC pretransition was shown to be affected; and e) fluorescence spectroscopy experiments performed in DMPC large unilamellar vesicles (LUV) showed that at very low concentrations induced changes in DPH fluorescence anisotropy at 18°C. Additional experiments were performed in mice cholinergic neuroblastoma SN56 cells; a statistically significant decrease of cell viability was observed on orthovanadate in low or moderate concentrations.

Zinc pyrithione induces ERK- and PKC-dependent necrosis distinct from TPEN-induced apoptosis in prostate cancer cells

Zinc dyshomeostasis can induce cell death. However, the mechanisms involved have not been fully elucidated in prostate cancer (PCa) cells, which differ dramatically from normal cells in their zinc handling ability. Here, we studied the effects of the ionophore Zn-pyrithione (ZP) and the chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). Both compounds induced cell death at micromolar concentrations when incubated with androgen-dependent (LNCaP), androgen-independent (PC3, DU145) and androgen-sensitive (C4-2) PCa cell-lines. Compared to PCa cells, RWPE1 prostate epithelial cells were less sensitive to ZP and more sensitive to TPEN, but total cellular zinc levels were changed similarly. ZnSO4 enhanced the toxicity of ZP, but inhibited the effects of TPEN as expected. The morphological/biochemical responses to ZP and TPEN differed. ZP decreased ATP levels and stimulated ERK, AKT and PKC phosphorylation. DNA laddering was observed only at low doses of ZP but all doses of TPEN. TPEN activated caspase 3/7 and induced PARP-cleavage, DNA-fragmentation, ROS-formation and apoptotic bodies. PKC and ERK-pathway inhibitors, and antioxidants protected against ZP-induced but not TPEN-induced death. Inhibitors of MPTP-opening protected both. Cell death in response to TPEN (but not ZP) was diminished by a calpain inhibitor and largely prevented by a caspase 3 inhibitor. Overall, the results indicated primarily a necrotic cell death for ZP and an apoptotic cell death for TPEN. The enhanced sensitivity of PCa cells to ZP and the apparent ability of ZP and TPEN to kill quiescent and rapidly dividing cells in a p53-independent manner suggest that ZP/TPEN might be used to develop adjunct treatments for PCa.

Acetyl-CoA metabolism in amprolium-evoked thiamine pyrophosphate deficits in cholinergic SN56 neuroblastoma cells

Inhibition of pyruvate (PDHC) and ketoglutarate (KDHC) dehydrogenase complexes induced by thiamine pyrophosphate deficits is known cause of disturbances of cholinergic transmission in the brain, yielding clinical symptoms of cognitive, vegetative and motor deficits. However, particular alterations in distribution of key acetylcholine precursor, acetyl-CoA, in the cholinergic neuron compartment of thiamine pyrophosphate-deficient brain remain unknown. Therefore, the aim of our work was to find out how amprolium-induced thiamine pyrophosphate deficits (TD) affect distribution of acetyl-CoA in the compartment of pure cholinergic neuroblastoma SN56 cells originating from murine septum. Amprolium caused similar concentration-dependent decreases in thiamine pyrophosphate levels in nondifferentiated (NC) and differentiated (DC) cells cultured in low thiamine medium. In such conditions DC displayed significantly greater loss of viability than the NC ones, despite of lesser suppressions of PDHC activities and tetrazolium salt reduction rates in the former. On the other hand, intramitochondrial acetyl-CoA levels in DC were 73% lower than in NC, which explains their greater susceptibility to TD. Choline acetyltransferase activity and acetylcholine content in DC were two times higher than in NC. TD caused 50% decrease of cytoplasmic acetyl-CoA levels that correlated with losses of acetylcholine pool in DC but not in NC. These data indicate that particular sensitivity of DC to TD may result from relative shortage of acetyl-CoA due to its higher utilization in acetylcholine synthesis.

Acetyl-CoA and acetylcholine metabolism in nerve terminal compartment of thiamine deficient rat brain

The decrease of pyruvate and ketoglutarate dehydrogenase complex activities is the main cause of energy and acetyl-CoA deficits in thiamine deficiency-evoked cholinergic encephalopathies. However, disturbances in pathways of acetyl-CoA metabolism leading to appearance of cholinergic deficits remain unknown. Therefore, the aim of this work was to investigate alterations in concentration and distribution of acetyl-CoA and in acetylcholine metabolism in brain nerve terminals, caused by thiamine deficits. They were induced by the pyrithiamine, a potent inhibitor of thiamine pyrophosphokinase. The thiamine deficit reduced metabolic fluxes through pyruvate and ketoglutarate dehydrogenase steps, yielding deficits of acetyl-CoA in mitochondrial and cytoplasmic compartments of K-depolarized nerve terminals. It also inhibited indirect transport of acetyl-CoA though ATP-citrate lyase pathway being without effect on its direct Ca-dependent transport to synaptoplasm. Resulting suppression of synaptoplasmic acetyl-CoA correlated with inhibition of quantal acetylcholine release (r = 0.91, p = 0.012). On the other hand, thiamine deficiency activated non-quantal acetylcholine release that was independent of shifts in intraterminal distribution of acetyl-CoA. Choline acetyltransferase activity was not changed by these conditions. These data indicate that divergent alterations in the release of non-quantal and quantal acetylcholine pools from thiamine deficient nerve terminals could be caused by the inhibition of acetyl-CoA and citrate synthesis in their mitochondria. They in turn, caused inhibition of acetyl-CoA transport to the synaptoplasmic compartment through ATP-citrate lyase pathway yielding deficits of cholinergic functions.

Short-term effects of zinc on acetylcholine metabolism and viability of SN56 cholinergic neuroblastoma cells

Excessive accumulation of zinc in the brain is one of putative factors involved in pathomechanism of cholinergic encephalopathies. The aim of this work was to investigate whether short-term increase of zinc concentration in the extracellular space may affect energy and acetylcholine metabolism in SN56 cholinergic cells of septal origin. Short 30 min exposition of SN56 cells to increasing zinc levels caused greater loss of viability of differentiated (DC, [EC(0.4)] 0.09 mM) than nondifferentiated cells (NC, [EC(0.4)] 0.14 mM). Concentration-dependent accumulation of zinc displayed exponential non-saturable kinetics. Zinc accumulation caused the decrease of calcium accumulation in mitochondria and its increase in cytoplasmic compartment of SN56 cells. Significant inverse and direct correlations were found between zinc accumulation and calcium levels in mitochondrial (r=-0.96, p=0.028) and cytoplasmic (r=0.97, p=0.028) compartments of DC, respectively. Zinc exerted similar inhibition of pyruvate dehydrogenase, aconitase and isocitrate dehydrogenase both in NC and DC homogenates, at Ki values equal to about 0.07, 0.08 and 0.005 mM, respectively. On the other hand, ketoglutarate dehydrogenase activity in DC was inhibited by zinc (Ki 0.0005 mM) 8 times stronger that in NC (Ki 0.004 mM). Also zinc-evoked decreases in acetylcholine content and its release were significantly greater in DC than in NC. Same conditions caused suppression of cytoplasmic and mitochondrial content of acetyl-CoA, that positively correlated with inhibition of transmitter functions (r=0.995, p=005) and loss of cell viability (r=0.990, p=0.0006), respectively. Significant correlations were also found in zinc-challenged cells between pyruvate dehydrogenase activity and both mitochondrial acetyl-CoA content and cell viability. These data indicate that pyruvate dehydrogenase-dependent acetyl-CoA synthesis in neuronal mitochondria may be a primary target for short-term neurotoxic effects of zinc. In consequence, shortages of acetyl-CoA in the mitochondrial compartment would cause fast loss of functional and structural integrity of cholinergic neurons.

Direct intra-tumoral injection of zinc-acetate halts tumor growth in a xenograft model of prostate cancer

Intracellular levels of zinc have shown a strong inverse correlation to growth and malignancy of prostate cancer. To date, studies of zinc supplementation in prostate cancer have been equivocal and have not accounted for bioavailability of zinc. Therefore, we hypothesized that direct intra-tumoral injection of zinc could impact prostate cancer growth. In this study, we evaluated the cytotoxic properties of the pH neutral salt zinc acetate on the prostate cancer cell lines PC3, DU145 and LNCaP. Zinc acetate killed prostate cancer cell lines in vitro, independent of androgen sensitivity, in a dose-dependent manner in a range between 200 and 600 microM. Cell death occurred rapidly with 50% cell death by six hours and maximal cell death by 18 hours. We next established a xenograft model of prostate cancer and tested an experimental treatment protocol of direct intra-tumoral injection of zinc acetate. We found that zinc treatments halted the growth of the prostate cancer tumors and substantially extended the survival of the animals, whilst causing no detectable cytoxicity to other tissues. Thus, our studies form a solid proof-of-concept that direct intra-tumoral injection of zinc acetate could be a safe and effective treatment strategy for prostate cancer.

Zinc intake during pregnancy increases the proliferation at ventricular zone of the newborn brain

Neurogenesis involves cell proliferation, cell cycle arrest, differentiation, migration and the natural developmental death of the neural precursors. These processes are highly co-ordinated and governed by cell-cycle genes and neural transcription factors. Zn plays a crucial role as a functional and structural component of enzymes and transcription factors and components of the intracellular signaling pathway associated with the regulation of cell proliferation. The influence of additional Zn intake during pregnancy on the neuronal proliferation at ventricular zone of the developing fetus has been studied. Pups delivered by the group of mice provided with drinking water with 4.0 mM Zn supplement throughout pregnancy contained an increased number of proliferating neurons in the ventricular zone at P0 compared to those delivered by the mice provided with drinking water without any Zn supplement. This finding provides direct evidence to support the notion that maternal Zn levels influence the development of the nervous system of the offspring.