Transport of valproate and its effects on GABA uptake in astroglial primary culture

Mood regulation in bipolar disorders viewed through the pendulum dynamics concept

Bipolar disorders have been characterized by powerful fluctuations of energy, mood, and thinking patterns. Mood episodes (manic or depressive) could be considered as deviations of a psycho-physiological index above or below a conventionally defined value called 'normothymia'. In the present study, we analyzed the feedback techniques used to suppress the oscillatory activity exhibited on an inverted pendulum device. Subsequently, we examine the degree that this multimodal feedback design could be considered on a hypothetical pendulum where the mood plays the role of the suspended mass, and the force balance compensation circuitry is substituted by drug-specific therapeutic interventions. The study does not concern a model of bipolar illness that could simulate numerically various phases of mood episodes but focuses on the functional similarities regarding the correction treatments applied on the two different oscillating systems giving a potential perspective of how techniques of feedback control may enhance the conceptualization of the treatment schemes followed in recent guidelines for biological treatment of bipolar disorders. Our theoretical consideration, along with observations on clinical level, gives support to the concept that the compensation of the mood oscillations should be adaptive with selective therapeutic interventions that compensate the excited system in different time scales.

Ultrastructure of astrocytes in the cortex of the hippocampal gyrus and in the neocortex of the temporal lobe in experimental valproate encephalopathy and after valproate withdrawal

The aim of the study was to analyse the astrocyte ultrastructure within the hippocampal gyre cortex and neocortex of the temporal lobe in valproate encephalopathy induced by chronic administration of an anti-epileptic drug - sodium valproate (VPA) to rats for 1, 3, 6, 9 and 12 months, once daily intragastrically, in a dose of 200 mg/kg b.w. and after its withdrawal for 1 and 3 months. Prolonged application of VPA caused damage to protoplasmic astrocytes of the cortex regions examined, mainly in the pyramidal layer, which intensified in the later stages of the experiment, especially after 9 and 12 months. Ultrastructural alterations in astroglia during this experiment did not differ significantly between the hippocampal cortex and neocortex. The most pronounced astroglial abnormalities, concerning about 2/3 of protoplasmic astrocytes after 9 and 12 months, were characterized by considerable swelling of cells, with the presence of empty vacuolar structures in the cytoplasm, a substantial decrease in the number of gliofilaments or even their complete loss, which indicated fibrillopoietic failure of the cell, and the appearance of astrocytes showing phagocytic activity. The astrocytic changes coexisted with distinct damage to neurones and structural elements of the blood-brain barrier. One month after termination of chronic exposure to the drug, the abnormalities did not subside, whereas after 3 months features of distinct normalization could be observed in a considerable number, more than a half, of astrocytes. In valproate encephalopathy, apart from any direct effect of VPA and/or its metabolites on astrocytes, the main cause of the protoplasmic astroglial damage in the cortex of the CNS structures examined could be associated with changes in microcirculation in the cortex (vasogenic factor), leading to its ischaemia.

Anti-tumor mechanisms of valproate: a novel role for an old drug

Valproic acid (VPA, 2-propylpentanoic acid) is an established drug in the long-term therapy of epilepsy. During the past years, it has become evident that VPA is also associated with anti-cancer activity. VPA not only suppresses tumor growth and metastasis, but also induces tumor differentiation in vitro and in vivo. Several modes of action might be relevant for the biological activity of VPA: (1) VPA increases the DNA binding of activating protein-1 (AP-1) transcription factor, and the expression of genes regulated by the extracellular-regulated kinase (ERK)-AP-1 pathway; (2) VPA downregulates protein kinase C (PKC) activity; (3) VPA inhibits glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of the Wnt signaling pathway; (4) VPA activates the peroxisome proliferator-activated receptors PPARgamma and delta; (5) VPA blocks HDAC (histone deacetylase), causing hyperacetylation. The findings elucidate an important role of VPA for cancer therapy. VPA might also be useful as low toxicity agent given over long time periods for chemoprevention and/or for control of residual minimal disease.

The mood stabilizer valproic acid activates mitogen-activated protein kinases and promotes neurite growth

The mood-stabilizing agents lithium and valproic acid (VPA) increase DNA binding activity and transactivation activity of AP-1 transcription factors, as well as the expression of genes regulated by AP-1, in cultured cells and brain regions involved in mood regulation. In the present study, we found that VPA activated extracellular signal-regulated kinase (ERK), a kinase known to regulate AP-1 function and utilized by neurotrophins to mediate their diverse effects, including neuronal differentiation, neuronal survival, long term neuroplasticity, and potentially learning and memory. VPA-induced activation of ERK was blocked by the mitogen-activated protein kinase/ERK kinase inhibitor PD098059 and dominant-negative Ras and Raf mutants but not by dominant-negative stress-activated protein kinase/ERK kinase and mitogen-activated protein kinase kinase 6 mutants. VPA also increased the expression of genes regulated by the ERK pathway, including growth cone-associated protein 43 and Bcl-2, promoted neurite growth and cell survival, and enhanced norepinephrine uptake and release. These data demonstrate that VPA is an ERK pathway activator and produces neurotrophic effects.

Probenecid-inhibitable efflux transport of valproic acid in the brain parenchymal cells of rabbits: a microdialysis study

Delivery of valproic acid (VPA) to the human brain is relatively inefficient as reflected by a low brain-to-unbound plasma concentration ratio (< or =0.5) at steady state. Previous pharmacokinetic studies suggested that the unfavorable brain-to-plasma gradient is maintained by coupled efflux transport processes at both the brain parenchymal cells and blood-brain barrier (BBB); one or both of the efflux transporters are inhibitable by probenecid. The present study in rabbits utilized microdialysis to measure drug concentration in the brain extracellular fluid (ECF) of the cerebral cortex during steady-state i.v. infusion with VPA alone or with VPA plus probenecid. Probenecid co-infusion elevated VPA concentration in the brain tissue surrounding the tip of the microdialysis probe to a greater extent than in the ECF (230% versus 47%). Brain intracellular compartment (ICC) concentration was estimated. In control rabbits, the ICC concentration was 2.8+/-0.28 times higher than the ECF concentration. Probenecid co-infusion elevated the ICC-to-ECF concentration ratio to 4.2+/-0.44, which confirms the existence of an efflux transport system in brain parenchymal cells. The ECF-to-unbound plasma concentration ratio was well below unity (0.029), indicating an uphill efflux transport of VPA across the BBB. Co-infusion of probenecid did not have a significant effect on VPA efflux at the BBB as evidenced by a minimal change in the ECF-to-unbound plasma concentration ratio. This study suggests the presence of distinctly different organic anion transporters for the efflux of VPA at the parenchymal cells and capillary endothelium in the brain.

Effect of valproate on the metabolism of the central nervous system

The effects of valproate on brain energy and lipid metabolism is reviewed. Increasing evidence suggests that valproate uses the monocarboxylic acid carrier in order to cross the blood brain barrier (BBB) and the neural cell plasma membranes. The uptake of valproate into the brain through this mechanism would compete with the uptake of energy precursors, such as the monocarboxylic acids 3-hydroxybutyrate, lactate or pyruvate and with some amino acids, but not with glucose. This could impair brain fuel utilization, specially during the neonatal period or childhood, when lactate or 3-hydroxybutyrate furnishes alternative substrates to glucose for the brain. It is concluded that valproate interference with energy metabolism may have implications for the therapeutic action of the drug, stressing the possibility that valproate-mediated alterations in brain lipid synthesis may contribute to the pharmacological action of the drug.

Interactions between valproate, glutamate, aspartate, and GABA with respect to uptake in astroglial primary cultures

Astrocytes have been proposed to regulate the extracellular space in the brain, even if rather little is known about their specific functions. One possibility for obtaining more knowledge on the functions of astroglial cells is to examine how they respond on exposure to pharmacological agents. Na(+)-valproate is an anticonvulsive drug which is used in the treatment of several types of epilepsy. The mechanisms of action of the drug are not fully understood, but the GABA-ergic system, both in neurons and astrocytes, has been shown to be affected. In the present study, the effects of valproate were investigated on astroglial cells in primary cultures from newborn rat cerebral cortex. The transport of the drug itself and its effects on the transport of the amino acid transmitters glutamate, aspartate and gamma-aminobutyric acid (GABA) into astrocytes were examined. The [3H]valproate transport into the astrocytes was increased after exposure to L-glutamate but not L-aspartate. On the other hand, after acute exposure for the drug, the transport of [3H]L-glutamate and [3H]L-aspartate decreased, as also did the affinity but not the transport capacity for the [3H]GABA uptake. However, after 5 days chronic valproate exposure, no effects could be seen on the uptake kinetics of L-glutamate or L-aspartate. For GABA, the affinity decreased, while the transport capacity remained unchanged compared with controls. The results showed that valproate, glutamate, aspartate and GABA were capable of interacting significantly with each others transport into the astrocytes.

Receptor-coupled uptake of valproate in rat astroglial primary cultures

Various receptor ligands were investigated for their effects on the uptake of the antiepileptic drug valproic acid (VPA) in primary astroglial cultures from cerebral cortex of neonatal rats. After stimulation with the alpha 1-adrenoceptor agonist phenylephrine, 5-hydroxytryptamine (5-HT) or the glutamate receptor agonists glutamate, quisqualate and kainate, the Vmax and Km values for the drug transport increased. On the contrary, after exposure to the alpha 2-adrenoceptor agonist clonidine, Vmax and Km decreased. The effects were reversed in comparison to the control level in the presence of selective receptor antagonists. The data indicate a specific coupling between receptors and the uptake system for VPA. Furthermore, the results may have significant implications, as they suggest that receptors on astrocytes can be involved in the local regulation of drug transport in brain.