Central Nervous System Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Central Nervous System Agents) - Volume 9, Issue 2, 2009

In the past 20 years, a number of new antiepileptic drugs (AEDs) have been introduced and other molecules are in development, some of which are advantageous in terms of pharmacokinetics, tolerability and potential for drug interactions. These drugs are regarded as second generation compared to older agents such as barbiturates, phenytoin, carbamazepine, ethosuximide and valproic acid. Although some of these second generation compounds may be advantageous in terms of kinetics, tolerability and potential for drug interactions, all of them still target voltage-gated channels or GABA-mediated inhibition, predominantly, without any real improvement in epilepsy therapy. Studies on mechanisms of seizure generation and propagation have identified new potential targets for AEDs. The growing understanding of the pathophysiology of epilepsy and the structural and functional characterization of the molecular targets provide many opportunities to create improved epilepsy therapies. In this review the molecular targets for new AEDs are discussed, providing further suggestions on how future research can be improved.

The disease activity of multiple sclerosis (MS) is known to be ameliorated during pregnancy, and pregnancy is also found to be protective in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Estrogen levels increase during pregnancy and basic researches have shown that estrogens have immunomodulatory effects on immune cells. The importance of estrogen in pathogenic autoimmune diseases has also been demonstrated in EAE by altering hormone levels. Mice treated with estrogen experienced significantly decreased EAE severity and delayed onset of disease as a result of neuroprotective and anti-inflammatory effects. Brain atrophy has been detected at the early stages of MS by using MRI; thus, as a neuoprotective agent, estrogen might be effective against brain atrophy. Estrogen's effects are primarily mediated by the nuclear estrogen receptor (ER), and recent studies have shown the presence of nuclear ERs on the cells involved in the immune response. There have been some reports on genetic polymorphisms of ERs in MS. In this review paper, we discuss increasing evidence that points to a link between estrogen and MS. We also analyze the therapeutic potential of estrogens in MS and review current genetic studies on ER.

The insulin-like growth factor-1 (IGF-1) is a pleiotropic factor. Many studies have revealed its importance in the development and maintenance of the central nervous system (CNS). This review will discuss the IGF-1 axis, from the factor itself to the signalling pathways it activates, and its tight regulation. Particular focus will be brought on potential therapeutic targets of the IGF-1 axis in CNS disorders, including brain tumours and neurodegenerative diseases affecting neurons and oligodendrocytes.

Tissue-specific stem cells replenish organs by replacing cells lost due to tears and wears or injury throughout life. Long considered as an exception to this rule, the adult mammalian brain has consistently been found to possess stem cells that ensure neurogenesis. Neural stem cells persist within the subventricular zone bordering the lateral ventricles of the brain. Constitutively, neural stem cells proliferate and produce a continuous supply of new neurons that migrate towards the olfactory bulb where they ensure turnover of interneurons. Owing to their potential clinical use for the treatment of neurodegenerative diseases, the factors that control proliferation, self-renewal and differentiation of neural stem cells have received increasing interest. These studies have unraveled that the cellular dynamic within the subventricular zone is tightly controlled by astrocytes and endothelial cells that neighbor neural stem cells. These neighboring cells produce substrate- bound and soluble factors that make up a specialized microenvironment named the neurogenic niche. The equilibrium between neural stem cells activity and quiescence is adjusted by neurons located in remote brain areas that adapt neuron production to physiological and pathological constraints. Brain injury or neurodegenerative diseases affect neural stem cells proliferation, differentiation and migration suggesting that neural stem cells are involved in brain self-repair. Understanding the endogenous mechanisms that regulate neural stem cells will help to replenish cellular constituents lost by injury and thereby allow an effective development of neural stem cells based therapies of brain diseases.

Prosaposin, a 66 kDa glycoprotein, was identified initially as the precursor of the sphingolipid activator proteins, saposins A-D, which are required for the enzymatic hydrolysis of certain sphingolipids by lysosomal hydrolases. While mature saposins are distributed to lysosomes, prosaposin exists in secretory body fluids and plasma membranes. In addition to its role as the precursor, prosaposin shows a variety of neurotrophic and myelinotrophic activities through a receptor- mediated mechanism. In studies in vivo, prosaposin was demonstrated to exert a variety of neuro-efficacies capable of preventing neuro-degeneration following neuro-injury and promoting the amelioration of allodynia and hyperalgesia in pain models. Collective findings indicate that prosaposin is not a simple house-keeping precursor protein; instead, it is a protein essentially required for the development and maintenance of the central and peripheral nervous systems. Accumulating evidence over the last decade has attracted interests in exploring and developing new therapeutic approaches using prosaposin for human disorders associated with neuro-degeneration. In this review we detail the structure characteristics, cell biological feature, in vivo efficacy, and neuro-therapeutic potential of prosaposin, thereby providing future prospective in clinical application of this multifunctional protein.

Schizophrenia (SZ) that is resistant to treatment with dopamine (DA) D2 antagonists may involve changes other than those in the dopaminergic system. Recently, histamine (HA), which regulates arousal and cognitive functions, has been suggested to act as a neurotransmitter in the central nervous system. Four HA receptors-H1, H2, H3, and H4- have been identified. Our recent basic and clinical studies revealed that brain HA improved the symptoms of SZ. The H3 receptor is primarily localized in the central nervous system, and it acts not only as a presynaptic autoreceptor that modulates the HA release but also as a presynaptic heteroreceptor that regulates the release of other neurotransmitters such as monoamines and amino acids. H3-receptor inverse agonists have been considered to improve cognitive functions. Many atypical antipsychotics are H3-receptor antagonists. Imidazole-containing H3-receptor inverse agonists inhibit not only cytochrome P450 but also hERG potassium channels (encoded by the human ether-a-go-go-related gene). Several imidazole H3-receptor inverse agonists also have high affinity for H4 receptors, which are expressed at high levels in mast cells and leukocytes. Clozapine is an H4-receptor agonist; this agonist activity may be related to the serious side effect of agranulocytosis caused by clozapine. Therefore, selective non-imidazole H3-receptor inverse agonists can be considered as novel antipsychotics that may improve refractory SZ.

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is chronic progressive myelopathy characterized by bilateral pyramidal tracts involvement with sphincteric disturbances. HTLV-I infects approximately 10-20 million people worldwide. There are large endemic areas in southern Japan, the Caribbean, Central and South America, the Middle East, Melanesia, and equatorial regions of Africa. Since the primary neuropathological feature of HAM/TSP is chronic inflammation caused by HTLV-I infection in the spinal cord, various treatments focusing on immunomodulatory or anti-viral effects were performed for HAM/TSP patients until now. However, there are still many of problems, such as insufficient effects, side effects and expensive costs in long-term treatments, etc., in these treatments. Therefore, an ideal therapeutic strategy against HAM/TSP is still not established yet. Although only a small proportion of HTLV-I-infected individuals develops HAM/TSP, neurological symptoms are certainly progressive once myelopathy develops, leading to deterioration of the quality of life. Therefore, we now need the therapeutic regimens to protect the development, or be able to commence the treatments as soon as possible after the development safely and inexpensively even in long-term course or lifelong course of treatment. As HTLV-I-infected CD4+ T cells are the first responders in the immunopathogenesis of HAM/TSP, the ideal treatment is the elimination of HTLV-Iinfected cells from the peripheral blood. In this article, we will review the therapeutic strategies against HAM/TSP up to now and will introduce our new therapeutic approach focusing on the targeting of HTLV-I-infected cells in HAM/TSP patients.

Aim of this paper is to give a concise overview of what is known about the trigeminal nociceptive system in birds. Several types of nociceptors have been discovered, thermal nociceptors and polymodal, i.e. mechanothermal and mechanochemical receptors. Information from these receptors reaches the Laminae I and II of the caudal subnucleus of the descending trigeminal system and of the dorsal horn of the rostral spinal cord. The organization of the afferents to the avian brainstem and of the primary nociceptive centers is largely the same as that in mammals. This is also true for a number of histochemical characteristics of these primary centers. The comparability of the ascending nociceptive system in birds and mammals is more problematic. This is due to the differences in organization of the forebrain in mammals and birds. The paper concludes with a short discussion on the sense of pain and the connection with nociception.