Interactions between p75 and TrkA receptors in differentiation and vulnerability of SN56 cholinergic cells to beta-amyloid.

NGF modifies cholinergic neurons through its low-p75 and high affinity-TrkA receptors. Native p75(+)TrkA(-) and trkA-transfected p75(+)TrkA(+) SN56 hybrid cholinergic septal cells were used here to discriminate effects mediated by each receptor. In TrkA(-) cells, NGF (100 ng/ml) affected neither choline acetyltransferase nor morphology but depressed pyruvate dehydrogenase activity by about 30%. Aged 25-35 beta-amyloid (1 microM) caused no changes in choline acetyltransferase and pyruvate dehydrogenase activities in nondifferentiated and differentiated TrkA(-) cells. On the contrary, in nondiferentiated TrkA(+) NGF brought about a 2.5-fold increase of choline acetyltransferase. In differentiated TrkA(+) cells, beta-amyloid resulted in no change in PDH but 65% suppression of choline acetyltransferase activity and reduction of their extensions. Thus, activation of TrkA receptors may overcome p75 receptor-mediated inhibitory effects on pyruvate dehydrogenase expression in cholinergic cells. On the other hand, it would make expression of choline acetyltransferase and cell differentiation more susceptible to suppressory effects of beta-amyloid.

Acute and chronic effects of aluminum on acetyl-CoA and acetylcholine metabolism in differentiated and nondifferentiated SN56 cholinergic cells.

Mechanisms of preferential loss of cholinergic neurons in the course of neurodegenerative diseases are unknown. Therefore, we investigated whether differentiation-evoked changes in acetyl-CoA and acetylcholine metabolism contribute to the susceptibility of cholinergic neuroblastoma to cytotoxic effects of Al. In SN56 cells differentiated with retinoic acid and dibutyryl cAMP (DC), pyruvate utilization and acetyl-CoA content were lower and acetylcholine level higher than in nondifferentiated cells (NC), respectively. In DC Al and Ca accumulations were 50% and 100%, respectively higher than in NC. Acute Al addition caused inhibition, whereas its chronic application had no effect on pyruvate utilization both in NC and in DC. On the other hand, in both experiments, Al evoked a greater decrease of acetyl-CoA level in DC than in NC. Acute addition of Al depressed acetylcholine release from DC to two times lower values than in NC. On the other hand, chronic addition of Al increased ACh release from DC over twofold, being without effect on its release from NC. These findings indicate that higher accumulation of Ca, along with low levels of acetyl-CoA, could make DC more susceptible to neurotoxic inputs than NC. Excessive acetylcholine release, evoked by Al, is likely to increase acetyl-CoA utilization for resynthesis of the neurotransmitter pool and cause deficit of this metabolite in DC. On the other hand, NC, owing to lower Ca accumulation, slower ACh metabolism, and higher level of acetyl-CoA, would be less prone to these harmful conditions.

Acetyl-CoA metabolism in cholinergic neurons and their susceptibility to neurotoxic inputs.

Cholinergic neurons, unlike other brain cells utilize acetyl-CoA not only for energy production but also for acetylcholine (ACh) synthesis. Therefore, suppression of acetyl-CoA metabolism by different neurotoxic inputs may be particularly harmful for this group of cells. Differentiation of SN56 cholinergic hybrid cells increased their choline acetyltransferase (ChAT) activity and ACh content but depressed pyruvate dehydrogenase activity and acetyl-CoA content. Differentiated cells were more susceptible to acute and chronic influences of aluminum, NO and amyloid-beta. Al decreased acetyl-CoA content, ACh release and increased Ca accumulation in differentiated cells (DC) to much higher degree than in non-differentiated ones (NC). NO strongly depressed acetyl-CoA level and increased ACh release in DC but did not affect NC. Additive effects of Al and NO were seen in DC but not in NC. Also long term suppressory effects of amyloid-beta, Al and NO on cholinergic phenotype and morphologic maturation were more evident in DC than in NC. Thus, relative shortage of acetyl-CoA in highly differentiated cholinergic neurons could make them particularly susceptible to degenerative insults in the course of different cholinergic encephalopathies.

Antifungal biflavones from Cupressocyparis leylandii.

From the leaves of Cupressocyparis leylandii (Cupressaceae) cupressuflavone, 4-O-methylcupressuflavone, amentoflavone, 7-O-methylamentoflavone, 4-O-methylamentoflavone and hinokiflavone were isolated. 1H- and 13C-NMR data for 4-O-methylcupressuflavone are given for the first time. The biflavones from cultivar varieties of C. leylandii (Naylor's Blue, Castlewellan Gold) were chromatographicaly (HPLC) compared. The antifungal activity of cupressuflavone and 4-O-methylcupressuflavone against Alternaria alternata, Cladosporium oxysporum, Fusarium culmorum and F. avenaceum was assayed.

[Mechanisms of selective vulnerability of cholinergic neurons to neurotoxic stimuli]. / Mechanizmy selektywnej wrazliwosci neuronów cholinergicznych na bodzce neurotoksyczne.

Preferential loss of cholinergic neurons in course of several encephalopathies may result from the fact that they utilize acetyl-CoA not only for energy production, but also for acetylcholine synthesis. Changes in activities of acetyl-CoA metabolizing enzymes and shifts in acetyl-CoA compartmentalization, found in different animal models of brain pathologies and in human post mortem brain, are discussed in therms of their impact on cholinergic system integrity.

Effects of aluminum and calcium on acetyl-CoA metabolism in rat brain mitochondria.

Al complexes are known to accumulate in extra- and intracellular compartments of the brain in the course of different encephalopathies. In this study possible effects of Al accumulation in the cytoplasmic compartment on mitochondrial metabolism were investigated. Al, like Ca, inhibited pyruvate utilization as well as citrate and oxoglutarate accumulation by whole brain mitochondria. Potencies of Ca2+(total) effects were 10-20 times stronger than those of Al. Al decreased mitochondrial acetyl-CoA content in a concentration-dependent manner, along with an equivalent rise of free CoA level, whereas Ca caused loss of both intermediates from mitochondria. In the absence of Pi in the medium, Ca had no effect on mitochondrial metabolism, whereas Al lost its ability to suppress pyruvate utilization and acetyl-CoA content in Ca-free conditions. Verapamil potentiated, whereas ruthenium red reversed, Ca-evoked suppression of mitochondrial metabolism. On the other hand, in Ca-supplemented medium, Al partially overcame the inhibitory influence of verapamil. Accordingly, verapamil increased mitochondrial Ca levels much more strongly than Al. However, Al partially reversed the verapamil-evoked rise of Ca2+(total) level. These data indicate that Al accumulated in cytoplasm in the form of the Al(PO4)OH- complex may inhibit mitochondrial functions by an increase of intramitochondrial [Ca2+]total resulting from the Al-evoked rise of cytoplasmic [Ca2+]free, as well as from inhibitory interference with the verapamil binding site on the Na+/Ca2+ antiporter.