Central Nervous System Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Central Nervous System Agents) - Volume 9, Issue 1, 2009

Central nervous system (CNS)-related pathologies have been one of the most ongoing challenges for scientists. Nowadays, these pathologies affect worldwide and in a majority of cases they lack of adequate therapies. Therefore, neurodegenerative diseases, pain and neurotoxicity are examples of disorders which still need important efforts and better solutions for their management. In this context, this issue reviews the state-of-art of diagnostic techniques, surrogates and biomarkers and new pharmacological approaches for the treatment of these old and new diseases. This issue contains eight reviews contributed by leading experts in the field. Drs. I. Dupiereux, W. Zorzi, I. Quadrio A. Perret-Liaudet, G.G. Kovacs, E. Heinen and B. Elmoualij review the methods of early detection and diagnosis together with the need of specific surrogates and biomarkers for some of the neuropathological conditions associated to protein misfolding including Alzheimer's, Parkinson's and prion diseases such as Creutzfeld-Jakob disease. More focused in Alzheimer's disease, Drs. S. Hashioka, P.L. McGeer, A. Monji and S. Kanba, summarize the mechanism by which antidepressants have antiinflammatory properties and therefore can represent a preventive treatment for Alzheimer or other pathologies with a neuroinflammatory component. In relation with this class of disorders, multiple sclerosis remains as one of the most challenging considering its prevalence among young adults and the lack of adequate drugs for its treatment. In this context, Drs. D. Huang and A. Rae-Grant offer a current perspective about the approved therapies as well as the current status of some of the pharmacological agents in clinical phases. With respect to CNS disorders derived from motor neuron degeneration, Drs. Y. Chen, V. Meininger and G.J. Guillemin review some of the recent advances in the treatment of amyothrophic lateral sclerosis with a special focus on the importance of kynurenine pathway inhibitors. This issue is further extended by Drs. T. Chu and W. Wu to the spinal root avulsion injury, which also causes motoneuron death. In their review, they discuss the potential of different trophic factors as motoneuron neuroprotective agents.

Depositions of proteins in form of amyloid and non-amyloid plaques are common pathogenic signs of more than 20 degenerative diseases affecting the central nervous system or a variety of peripheral tissues. Among the neuropathological conditions, Alzheimer's, Parkinson's and the prion diseases, such as Creutzfeldt-Jakob disease (CJD), present ambiguities as regarding their differential diagnosis. At present, their diagnosis must be confirmed by post-mortem examination of the brain. Currently the ante-mortem diagnosis is still based on the integration of multiple data (clinical, paraclinical and biological analyses) because no unique marker exists for such diseases. The detection of specific biomarkers would be useful to develop a differential diagnostic, distinguishing not only different neurodegenerative diseases but also the disease from the non-pathological effects of aging. Several neurodegenerative biomarkers are present at very low levels during the early stages of the disease development and their ultra-low detection is needed for early diagnosis, which should permit more effective therapeutic interventions, before the disease concerned can progress to a stage where considerable damage to the brain has already occurred. In the case of prion diseases, there are concerns regarding not only patient care, but the wider community too, with regard to the risk of transmission of prions, especially during blood transfusion, for which, four cases of variant CJD infection associated with transfusion of non-leukocyte-depleted blood components have been confirmed. Therefore the development of techniques with high sensitivity and specificity represent the major challenge in the field of the protein misfolding diseases. In this paper we review the current analytical and/or biochemical diagnostic technologies used mainly in prion, but also in Alzheimer and Parkinson diseases and emphasizing work on the protein detection as a surrogates and specific biomarker in the body fluid of patients (urine, CSF and blood). This review highlights the urgency of the development of early and sensitive diagnostics in terms of therapeutic challenge.

Increasing evidence of pro-inflammatory mediator expression in major depressions indicate that inflammatory changes may play a role. If this is true, the efficacy of antidepressants may be partially attributable to suppression of inflammation. Various types of antidepressants can suppress serum and plasma levels of pro-inflammatory mediators in patients with major depression. Therefore they can inhibit the production of pro-inflammatory mediators by immune cells. These include glial cells, which are the main sources and targets of cytokines in the brain. This review summarizes the evidence showing that antidepressants have an anti-inflammatory potential. The putative mechanisms are also discussed. Because of the anti-inflammatory effects of antidepressants, they might also act as preventives for neurodegenerative dementias including Alzheimer's disease, where the pathogenesis involves chronic inflammation associated with activated microglia.

Multiple sclerosis (MS) is a disorder of the central nervous system (CNS). It is characterized by episodic and progressive neurological dysfunction resulting from inflammatory and autoimmune reactions, myelin loss, conduction block, oligodendrocyte pathology, gliosis, and axonal loss in CNS. Recent years have witnessed advances in better understanding the immune pathogenesis of MS, prompted by animal models, human pathological observations and MRI studies. There have been significant changes in the therapeutic regimens in MS, with an emphasis on preventative treatment of an ongoing disease process. Agents in use and in the research pipeline have mechanisms that act on various antiinflammatory and immunomodulatory properties, including blocking leukocyte migration into CNS and targeting chemoattraction. In addition, recent studies on the neurodegenerative components of MS have directed therapeutic trials to neuroprotection and neurorestoration. In this paper, we summarize the current understanding of the mechanisms of approved pharmacological agents and review the putative mechanisms and status of some important agents in clinical phase two or three trials in MS.

Amyotrophic lateral sclerosis (ALS) is an adult onset, progressive and fatal motor neuron degenerative disease [1]. The aetiology of ALS is currently unknown, though strongly suggested to be multifactorial. Recently, the kynurenine pathway (KP) has emerged as a potential contributing factor [2]. The KP is a major route for the metabolism of tryptophan, generating neuroactive intermediates in the process. These catabolites include the excitotoxic N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid (QUIN) [3] and the neuroprotective NMDA receptor antagonist, kynurenic acid (KYNA) [4,5]. These catabolites appear to play a key role in the communication between the nervous and immune systems, and also in modulating cell proliferation and tissue function [6]. As the cause of ALS is still unknown, there is presently no efficient treatment for it. Currently, Riluzole is the drug of choice but its effect is relatively modest [7]. Targeting the KP, hence, could offer a new therapeutic option to improve ALS treatment [8]. Several drugs that block the KP are already under investigation by our laboratory and others, some of which are in or about to enter clinical trials for other diseases. For example, the KP inhibitors, Teriflunomide (Sanofi- Aventis) and Laquinimod (Teva Neuroscience). Recently, a KP inhibitor has also reached the Japan market as an immunomodulative drug [9]: Tranilast/Rizaben® (Angiogen Ltd.) is an anthranilic acid derivative [8]. Finally, the 8- hydroxyquinolinine metal attenuating compounds, Clioquinol and PBT2®, interestingly have close structural similarity with KYNA and QUIN. Such drugs would open a new and important therapeutic door for ALS.

Spinal root avulsion injury causes motoneuron death and immediate loss of sensory and motor functions. Surgical intervention such as reimplantation of avulsed root is proven useful to restore neural circuitry of spinal cord and targeted muscles. Yet, additional strategies are required for faster and better functional recovery which is overall unsatisfactory. Accumulating evidences in animal studies, particularly in peripheral nerve injuries, demonstrated the effectiveness of neurotrophic factors in rescuing injured motoneurons and promoting axon regeneration. It is, however, important to recognize the differences between peripheral nerve and avulsion injury. In this review, we will briefly describe the changes in motoneurons after avulsion and provides a comprehensive list of neurotrophic factors which are known to exert neuroprotective effects on motoneurons. We will include recent studies on trophic factors for motoneuron survival and regeneration in peripheral nerve and avulsion injuries. We will also discuss the potential use of trophic factors in the context of avulsion injuries.

Several viruses may cause central nervous system diseases with a broad range of clinical manifestations. The time course of the viral encephalitis can be acute, subacute, or chronic. Pathologically there are encephalitis with direct viral entry into the CNS in which brain parenchyma exhibits neuronal damaging and viral antigens and there are postinfectious autoimmune encephalitis associated with systemic viral infections with brain tissue presenting perivascular aggregation of immune cells and myelin damaging. Some virus affect previously healthy individuals while others produce encephalitis among imunocompromised ones. Factors such evolving lifestyles and ecological changes have had a considerable impact on the epidemiology of some viral encephalitis [e.g. West-Nile virus, and Japanese B virus]. Citomegalovirus and JC virus are examples of infections of the brain that have been seen more frequently because they occur in immunocompromised patients. In the other hand many scientific achievements in neuroimaging, molecular diagnosis, antiviral therapy, immunomodulatory treatments, and neurointensive care have allowed more precise and earlier diagnoses and more efficient treatments, resulting in improved outcomes. In this article, we will present the current drug options in the management of the main acute and chronic viral infection of the central nervous system of immunocompetent and immunocompromised adults, focusing on drugs mechanisms of action, efficacy, and side effects. The early diagnosis and correct management of such diseases can reduce mortality and neurological sequelae; however, even with recent treatment advances, potentially devastating outcomes are still possible.

Many dopamine antagonists are proven acute migraine treatments. Genetic studies also imply that polymorphisms in dopamine genes (DRD2 receptors) in persons with migraine may create dopamine hypersensitivity. However, treatment is limited by the adverse event profiles of conventional neuroleptics including extrapyramidal symtoms, anticholinergic and antihistaminergic effects, hyperprolactinemia, and prolonged cardiac QT interval. Atypical neuroleptics cause less extrapyramial symptoms and some atypical neuroleptics, including olanzapine and quetiapine, may be beneficial as both acute and preventive migraine treatment. The combination of prochlorperazine, indomethacin, and caffeine is effective in the treatment of the acute migraine attack. The mechanism of action by which neuroleptics relieve headache is probably related to dopamine D2 receptor antagonist. Other actions via serotonin (5HT) receptor antagonists may also be important, particularly for migraine prevention. Additional studies to clarify the mechanism of action of neuroleptics in migraine could lead to new drugs and better management of migraine.

Neuropathic pain (pain associated with lesions or dysfunction of nervous system) is relatively common, occurring in about 1% of the population. Studies in animal models describe a number of peripheral and central pathophysiological processes after nerve injury that would be the basis of underlying neuropathic pain mechanism. A change in function, chemistry, and structures of neurons (neural plasticity) underlie the production of the altered sensitivity characteristics of neuropathic pain. Peripheral sensitization acts on the nociceptors, and central sensitization takes place at various levels ranging from the dorsal horn to the brain. In addition, abnormal interactions between the sympathetic and sensory pathways contribute to mechanisms mediating neuropathic pain. Despite recent advances in identification of peripheral and central sensitization mechanisms related to nervous system injury, the effective treatment of patients suffering from neuropathic pain remains a clinical challenge. Although numerous treatment options are available for relieving neuropathic pain, there is no consensus on the most appropriate treatment. However, recommendations can be proposed for first-line, second-line, and third-line pharmacological treatments based on the level of evidence for the different treatment strategies. Beside opioids, the available therapies shown to be effective in managing neuropathic pain include anticonvulsants, antidepressants, topical treatments (lidocaine patch, capsaicin), and ketamine. Tricyclic antidepressants are often the first drugs selected to alleviate neuropathic pain (first-line pharmacological treatment). Although they are very effective in reducing pain in several neuropathic pain disorders, treatment may be compromised (and outweighed) by their side effects. In patients with a history of cardiovascular disorders, glaucoma, and urine retention, pregabalin and gabapentine are emerging as first-line treatment for neuropathic pain. In addition these anti-epileptic drugs have a favourable safety profile with minimal concerns regarding drug interactions and showing no interference with hepatic enzymes. Despite the numerous treatment options available for relieving neuropathic pain, the most appropriate treatment strategy is only able to reduce pain in 70% of these patients. In the remaining patients, combination therapies using two or more analgesics with different mechanisms of action may also offer adequate pain relief. Although combination treatment is clinical practice and may result in greater pain relief, trials regarding different combinations of analgesics are lacking (which combination to use, occurrence of additive or supra-additive effects, sequential or concurrent treatment, adverse-event profiles of these analgesics, alone and in combination) are lacking. Additionally, 10% of patients still experience intractable pain and are refractory to all forms of pharmacotherapy. If medical treatments fail, invasive therapies such as intrathecal drug administration and neurosurgical interventions may be considered.