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.

RS-alpha-lipoic acid protects cholinergic cells against sodium nitroprusside and amyloid-beta neurotoxicity through restoration of acetyl-CoA level.

The work presented here verifies the hypothesis that RS-alpha-lipoic acid may exert its cholinoprotective and cholinotrophic activities through the maintenance of appropriate levels of acetyl-CoA in mitochondrial and cytoplasmic compartments of cholinergic neurons. Sodium nitroprusside (SNP) and amyloid-beta decreased pyruvate dehydrogenase, choline acetyltransferase activities, acetyl-CoA content in mitochondria and cytoplasm, as well as increased fraction of non-viable, trypan blue positive cells in cultured differentiated cholinergic SN56 neuroblastoma cells. Lipoic acid totally reversed toxin-evoked suppression of choline acetyltrasferase and pyruvate dehydrogenase activities, as well as mitochondrial and cytoplasmic acetyl-CoA levels, and partially attenuated increase of cell mortality. Significant negative correlations were found between enzyme activities, acetyl-CoA levels and cell mortality in different neurotoxic and neuroprotective conditions employed here. The level of cytoplamic acetyl-CoA correlated with mitochondrial acetyl-CoA, whereas choline acetyltransferase activity followed shifts in cytoplasmic acetyl-CoA. Thus, we conclude that, in cholinergic neurons, particular elements of the pyruvate-acetyl-CoA-acetylcholine pathway form a functional unit responding uniformly to nerotoxic and neuroprotectory conditions.