Effects of zinc on SN56 cholinergic neuroblastoma cells

Abstract

Zinc is a trace element necessary for proper development and function of brain cells. However, excessive accumulation of zinc exerts several cytotoxic effects in the brain. The aim of this work was to see whether cytotoxic effects of zinc are quantitatively correlated with changes in acetyl-CoA metabolism. The zinc levels up to 0.20 mmol/L caused concentrationdependent inhibition of pyruvate dehydrogenase (PDH) activity that correlated with the increase in trypan blue-positive fraction and the decrease in cultured cell number (r = 0.96, p = 0.0001). Chronic exposure of cells to 0.15 mmol/L zinc decreased choline acetyltransferase and aconitase activities, cytoplasmic acetyl-CoA and whole cell ATP level by 38%, 57%, 35%, and 62%, respectively but caused no change in mitochondrial acetyl-CoA level and activities of other enzymes of glycolytic and tricarboxylic acid cycle. DL-a-lipoamide when added simultaneously with zinc to cultured cells or their homogenates attenuated its chronic or acute suppressive effects. In homogenates of chronically Zn-treated cells, lipoamide overcame PDH but not aconitase inhibition. Presented data indicate that acute-transient elevation of zinc caused reversible inhibition of PDH, aconitase activities and acetylCoA metabolism, which when prolonged could lead to irreversible enzyme inactivation yielding decrease in cell viability and secondary suppression of their cholinergic phenotype.

Structural effects of Zn2+ on cell membranes and molecular models

“…Such mechanism would impair metabolic flux through tricarboxylic acid cycle and generate energy deficits. Depletion of acetyl-CoA in mitochondria could also inhibit its transport to cytoplasmic compartment yielding secondary inhibition of acetylcholine synthesis by choline acetyltransferase due to the substrate deficit [11]. The decrease of acetylcholine content in Zn-treated cells showed here remains in accord with this mechanism (Fig.…”

“…6). However, one has to assume that Zn-evoked inhibition of tricarboxylic acid cycle itself could also contribute to alterations in cell morphology [11]. One has to stress that [IC 0.5 ] value for Zn-dependent inhibition of acetylcholine release was over 10 times lower than [IC 0.5 ] for Zn-evoked suppression in acetylcholine content (Fig 7).…”

“…Chronic toxic effects of 0.15 mM Zn observed after 24 h exposure of neuroblastoma cells may be a result of a remote outcome of acute inhibition by this metal to several enzymes of oxidative metabolism such as pyruvate dehydrogenase (PDH) and aconitase [11]. Prolonging inhibition of PDH in cholinergic cells during culture impaired synthesis of acetyl-CoA in their mitochondrial compartment, whereas inhibition of aconitase hampered its utilization in tricarboxylic acid cycle.…”

“…Zinc uptake into cholinergic neuroblastoma cells mediated by M1 muscarinic receptors was found to alter a transcriptional regulation of their zinc finger genes [10]. However, in pathological conditions, excessive accumulation of zinc or its release from the binding sites may become detrimental for neurons [11]. These effects of Zn 2+ ions have prompted us to study the structural effects that this ion induces to cell membranes.…”

Bioinorganic Chemistry of Alzheimer’s Disease

“…860 However, underlying causes of the acetylcholine neurotransmitter shortage, which leads to cognitive decline, 62 must be described in a unified view of AD. The most obvious explanation for acetylcholine deficiency in AD according to the MT/Zn dysfunction hypothesis is that free Zn 2+ inhibits choline acetyltransferase 985 or pyruvate dehydrogenase, which produces acetylcoenzyme A. 986 …”