Current Medicinal Chemistry - Anti-Inflammatory & Anti-Allergy Agents - Volume 1, Issue 2, 2002

Proteoglycans (PG) consist of a core protein and an associated glycosaminoglycan (GAG) chain and reside on the cell surface and in the extracellular matrix. The different GAG chains of PG, heparan sulfate / heparin (HS), dermatan / chondroitin sulfate, keratan sulfate and of hyaluronic acid, which is not associated with a core protein, are synthesized as polymers of repeating disaccharide units. However, the structures of GAG chains are highly diverse. For example, the post-polymerisation modification of heparan chains (a polymer of glucuronic acid β1-4 N-acetyl glucosamine) by the sulfation of specific residues and the epimerisation of glucuronate to iduronate generates HS, which has a potential sequence complexity greater than that of the human proteome. Although only a fraction of this chemical complexity is used, it provides the framework for GAG chains to interact with a vast repertoire of proteins, with a specificity that is as high as required. As a consequence of their multiple interactions, PG are intimately involved in the different stages of inflammation, from the recruitment of inflammatory cells to the release of mediators of inflammation by infiltrating leukocytes and the turnover of extracellular matrix. The overarching theme of PG in inflammation is the regulation of the inflammatory microenvironment, which must change continuously and dynamically during the progression of the inflammatory response as observed in various pathologies such as arthritis and asthma. These changes include the modulation of the activity of GAG-binding cytokines, growth factors, proteases and protease inhibitors. The interactions of these regulatory proteins with GAG provides much of the focus for GAG-based therapeutic targets.

Endocannabinoids are amides, esters and ethers of long chain polyunsaturated fatty acids, which include anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) as the main endogenous agonists of cannabinoid (CB) receptors. The biological actions of these compounds at CB receptors depend on their life span in the extracellular space, which for AEA is regulated by intracellular uptake through a selective AEA membrane transporter (AMT), followed by intracellular degradation by an AEA-degrading enzyme (fatty acid amide hydrolase, FAAH). Together with AEA and 2-AG and their synthetic enzymes, CB receptors, AMT and FAAH form the “endocannabinoid system”. Here, we review recent literature on the properties of the constituents of this system, and on its role in inflammation. We also show how restraining the flexibility of the acyl chain of AEA affects the ability of this compound to bind to CB receptors and to interact with AMT and FAAH. Furthermore, we show how molecular dynamics simulations with free and restrained AEA and a number of its analogs, generated by lipoxygenase-mediated hydroperoxidation, help to understand the structural requirements essential for the interaction with the proteins of the endocannabinoid system. The hydroxy AEAs described herein might act in vivo as inhibitors of endocannabinoid metabolism, the only ones of natural origin as yet known. The relevance of these findings, which help to predict and facilitate the design of novel drugs with greater potency and / or selectivity at the different molecular targets of AEA, will be discussed in the light of their therapeutic potential.

5-Lipoxygenase (5-LOX) is a protein with catalytic activity that is essential for transforming arachidonic acid into leukotrienes and that has the ability to bind and possibly affect the function of a number of cellular proteins, including cytoskeletal proteins. A limited number of clinically-used drugs target the 5-LOX pathway, they are either 5-LOX inhibitors or antagonists of leukotriene receptors and are primarily used for the treatment of asthma. 5-LOX is also expressed and enzymatically active in various compartments of the mammalian brain, including central nervous system (CNS) neurons. However, insufficient information is available on the extent to which 5-LOX-related drugs cross the blood-brain barrier. Research into the CNS 5-LOX pathway indicates that 5-LOX may participate in a number of brain pathologies, including developmental neurometabolic diseases, stroke, seizures, Alzheimer's disease, aging-associated neurodegeneration, prion disease, multiple sclerosis, and brain tumors. Physiologically, 5-LOX appears to be involved in neurogenesis. The expression of 5-LOX is affected by hormones and appears to be subject to epigenetic regulation via alterations in DNA methylation in the region of the 5-LOX promoter. In this review, we propose that a novel 5-LOX drug therapy could be targeted not only to 5-LOX enzymatic activity and leukotrienes, but also toward modifying 5-LOX expression and the possibility of interfering with non-enzymatic actions of 5-LOX proteins. It is suggested that a new 5- LOX pharmacopoeia, which would be effective in the CNS would significantly advance research on the role of 5-LOX in the brain.

An essential feature of different inflammatory conditions, such as infective, autoimmune, allergic or vascular diseases, is the recruitment of infiltrating leukocytes. A large number of chemoattractant cytokines termed chemokines appear as critical factors in the development of inflammatory cell infiltration by interacting with specific receptors on leukocytes and regulating leukocyte movements. Chemokines may also play important roles in many other leukocyte functions such as differentiation of effector phenotypes or cell growth.A limitation to understand the participation of chemokines in chronic inflammatory diseases and to the development of chemokine based therapy is redundancy and overlapping receptor-ligand profiles of this system. However, emerging evidences point to specific roles for individual chemokines or chemokine receptors in many chronic inflammatory disorders such as glomerulonephritis, multiple sclerosis, rheumatoid arthritis, atherosclerosis and lung and airway inflammatory diseases. Genetic deletion of chemokines or their receptors have confirmed a relevant role for these factors in murine models of inflammation.A variety of common drugs used to treat human inflammatory disease, including those inhibiting NF-κB activation, have indirect effects on chemokines expression. More potent and specific strategies for inhibition of different chemokines or their receptors are being developed. Neutralizing antibodies or a variety of peptides or small molecules have demonstrated their potential to target leukocyte infiltration in different animal models and provide the basis for their use to treat human inflammatory diseases.

Macrolides, an old class of antibiotics, have attracted intense interest in recent years because of their diverse non-antibiotic properties. Among these properties, their immunomodulating effects were most extensively examined. In this review, their broad range of effects on the immune system as shown by various in-vitro, ex-vivo, and in-vivo experiments and clinical studies were discussed. It is now evident that various macrolides can modulate the innate immune system, with greater effects from 14- and 15-membered than the 16-membered derivatives. Although results from in-vitro studies appear to depend on the use of individual drugs and experimental conditions, they provide clues to the mechanisms of modulating different pathways of the immune system. On the other hand, animal and clinical studies, which summarize the effects of individual pathways, concluded that many macrolides are useful in a wide variety of clinical situations, from treatment of inflammatory lung diseases to application in transplantation. As for adaptive immunity, limited data were available but attenuation by macrolides was also reported in preliminary studies. Owing to their diverse effects on the immune system and inconclusive results from different in-vitro studies, the mechanism of their immunomodulation is not yet fully understood and correlation of effects with chemical structures is not conclusive at the moment. It may be more valuable for future studies to concentrate on the genetic basis for mechanisms on one hand, and additional areas of clinical applications on the other.

The inflammation associated with allergic disease is complex and still not completely understood. With the identification of the various cells and mediators involved in the inflammatory response, new therapies have been and are being developed for use.The central effector cell in allergic inflammation is termed the TH2 helper cell, a member of the subset CD4+ Tlymphocytes, which secrete specific cytokines such as IL-4, IL-5, IL-9 and IL-13. These cytokines promote mast cell differentiation and IgE production, and also promote eosinophil growth, maturation, migration and activation. In contrast, TH1 helper lymphocytes secrete IFN-γ (interferon- γ), and stimulate phagocyte-dependent cell-mediated immunity. TH1 cells can downregulate TH2 cells, primarily through the effects of IFN-γ. Controlling allergic disease focuses on blocking mediators and down-regulating pro-inflammatory cytokines and inflammatory cells stimulated by the allergic TH2 response. Antihistamines are receptor antagonists for the primary mediator histamine released during the early allergic response. Currently, glucocorticosteroids are the mainstay of antiinflammatory therapy because of their ability to inhibit the production of inflammatory cytokines. Much has been accomplished in creating newer forms of topical steroids with more potent anti-inflammatory effects and reduced side effects. The main focus of research is on developing therapeutic strategies which target different pathways to modify the allergic inflammatory response. For example, leukotriene modifiers are a relatively new class of anti-inflammatory medications that block the products of arachidonic acid metabolism. The use of recombinant humanized monoclonal antibody directed against IgE to neutralize and eliminate free circulating IgE is showing success in clinical trials. In development are monoclonal antibodies directed against various inflammatory cytokines such as IL-4 and IL-5, and a recombinant human receptor for IL-4. Another focus is to administer IL-12 in an attempt to inhibit the TH2 response and promote a TH1 immune response. There are strategies for modifying immunotherapy to improve immunogenicity and improve TH1 immune response. All of these novel concepts are examples of tremendous strides that have made in the development of anti-allergy therapy.