New sesquiterpene from Vietnamese agarwood and its induction effect on brain-derived neurotrophic factor mRNA expression in vitro.

Agarwood, one of the valuable non-timber products in tropical forest, is a fragrant wood, whose ethereal fragrance has been prized in Asia for incense in ceremony, as well as sedatives in traditional medicine. We separated the 70% EtOH extract of Vietnamese agarwood, which showed significant induction effect on brain-derived neurotrophic factor (BDNF) mRNA expression in rat cultured neuronal cells, to isolate a new compound and a 2-(2-phenylethyl)chromone derivative. The new compound was determined to be a spirovetivane-type sesquiterpene, (4R,5R,7R)-1(10)-spirovetiven-11-ol-2-one, by spectroscopic data and showed induction effect of BDNF mRNA.

Deltamethrin, a pyrethroid insecticide, is a potent inducer for the activity-dependent gene expression of brain-derived neurotrophic factor in neurons.

The mRNA expression of brain-derived neurotrophic factor (BDNF) is controlled in an activity-dependent manner through Ca(2+) influx into neurons. Pyrethroids are widely used insecticides of low acute toxicity in mammals, but their effects on sodium channels are known to lead to hyperexcitation in neuronal cells of insects. In this study, we found that deltamethrin, a type II pyrethroid insecticide, was highly effective in inducing BDNF expression in culture and in the rat brain. Addition of deltamethrin to rat cortical cells in culture markedly increased the expression of BDNF exon III-V mRNA and protein, dependent upon the neuronal activity accompanying the influx of Ca(2+) into neurons and the Ca(2+) influx-dependent phosphorylation of extracellular signal-regulated kinases 1/2. The elevated expression was maintained for at least 48 h, even after deltamethrin was withdrawn from the culture medium. Comparison of the effects of selected pyrethroids on the expression revealed that type II but not type I pyrethroids effectively induced BDNF mRNA expression. In addition, administration of deltamethrin to rats increased the level of BDNF protein in the cerebral cortex and hippocampus. These results indicate that deltamethrin is a potent inducer of BDNF expression in neurons and that it may induce neuronal hyperexcitation if it reaches the brain.

Additional repression of activity-dependent c-fos and BDNF mRNA expression by lipophilic compounds accompanying a decrease in Ca2+ influx into neurons.

Recently, it has been proposed that a variety of environmental disruptors (EDs) disturb the neonatal development of the brain in mammals because of their lipophilic characteristics. Therefore, the synergism of these lipophilic compounds is important when evaluating the risk from EDs. In mouse cerebellar granule cells (CGCs), the activity-dependent expression of the brain-derived neurotrophic factor (BDNF) gene is activated through an influx of calcium ions (Ca2+) into CGCs caused by membrane depolarization, which is involved in the activity-dependent development of not only the cerebellum but also other regions of the brain after birth. In our previous study, we reported that permethrin and some other pyrethroid insecticides, which are suspected of being EDs, repressed the induction of c-fos and BDNF mRNA expression, accompanying a reduction of Ca2+ influx at doses non-toxic to CGCs. In the present study, we investigated whether other lipophilic compounds influenced the Ca2+ signal-induced expression of both genes as permethrin did and, if so, whether these effects were synergistic or additional. Pretreatment with p,p'-DDT, diethylstilbestrol (DES) or bisphenol A dose-dependently repressed the induction of both genes as well as the increase in the uptake of Ca2+ by CGCs. Simultaneous exposure of CGCs with permethrin, p,p'-DDT and DES, in addition, revealed an additional repression on the induction of the genes and the Ca2+ uptake. These results suggest that toxic effects of EDs might, at least additionally, occur in the brain even if the concentration of each compound is lower than the effective dose for humans.

Brain-derived neurotrophic factor protects cultured rat hippocampal neurons from aluminum maltolate neurotoxicity.

Aluminum is environmentally abundant but not an essential trace element. Although there is increasing evidence suggesting the implication of aluminum in the pathogenesis of Alzheimer's disease, it is still controversial. We found and report here that aluminum maltolate, a stable and hydrophilic aluminum complex, causes death of primary cultured rat hippocampal neurons in a time- and dose-dependent manner. Degenerated neurons were TUNEL-positive. Immunohistochemical detection of synapsin I and microtubule associated protein 2 revealed the synapse loss between neurons intoxicated by aluminum maltolate. To explore the mechanism underlying its neurotoxicity, we administered various pharmacological compounds prior to the application of aluminum maltolate, and found that brain-derived neurotrophic factor (BDNF) markedly attenuated the neurotoxicity. Furthermore, aluminum maltolate inhibited the elevation of intracellular calcium levels caused by BDNF. Our results suggest the involvement of BDNF in the molecular mechanism underlying neurotoxicity induced by aluminum maltolate.

Neonatal exposure of newborn mice to pyrethroid (permethrin) represses activity-dependent c-fos mRNA expression in cerebellum.

In a previous report, we demonstrated that the exposure of cultured mouse cerebellar granule cells to permethrin, a type I pyrethroid insecticide, repressed the induction of activity-dependent c- fos and brain-derived neurotrophic factor (BDNF) gene expression, accompanying a decrease in Ca(2+) influx into neurons. In addition, it has been suggested that some pyrethroids, including permethrin, are endocrine-modulating chemicals and accumulate in human breast milk. In this study, therefore, we investigated whether lactational exposure of newborn mice to permethrin influenced c- fos, BDNF and beta-actin gene expression in the developing neonatal cerebellum. In the cerebella of control neonates, c- fos mRNA expression was characterized by a significant increase in postnatal weeks 2 and 3, followed by a marked decrease. In the cerebella of permethrin-treated neonates, the expression of c- fos mRNA was dose-dependently repressed by cis-permethrin more effectively than by trans-permethrin at postnatal week 3, without alterations in the body or cerebellum weights of neonates. In the fourth and fifth week, however, c- fos mRNA expression had decreased to the same level as that in the control and permethrin-treated neonates. A decrease in BDNF mRNA expression tended to be observed in the cerebella of newborn mice on exposure to permethrin. Thus, our results indicate that the activity-dependent gene expressions in cerebellar neuronal cells can be repressed by permethrin both in vitro and in vivo, and suggest that lactational exposure to pyrethroids might affect the postnatal development of the mammalian brain.