Current Medicinal Chemistry - Volume 14, Issue 24, 2007

The first consistent observations that viruses could be associated with some types of cancer where made almost a century ago. Since then researchers have spent a great deal of effort to address the infectious origins of human cancer. As a result of these studies, a strong link between some viral agents and several human cancers has been established. Some viruses as the Epstein-Barr virus (EBV), hepatitis B virus (HBV), hepatitis C virus (HCV), human T-cell lymphotropic virus type I (HTLV-I), immunodeficiency virus type I (HIV-I) and several human papillomavirus types (including types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 66) have been classified as group 1 carcinogens by the International Agency for Research in Cancer (IARC). Infection by these viruses constitutes a heavy burden for human populations as it accounts for almost 15% of all human malignancies. Furthermore, many other viral agents have been classified as possibly carcinogenic to humans and others have been occasionally found in human tumors suggesting that this figure may be an underestimation of virus involvement in the etiology of human cancer. Therefore, viral infection appears as one of the main preventable cancer risk factors. We summarize the current state of knowledge concerning virus-induced/associated cancers and discuss its significance in the context of human carcinogenesis. Prevention and control of infection by these agents could dramatically reduce the incidence of some prevalent cancers and, consequently, have a great impact on public health.

The chromatin structure of a gene plays an important role in regulating its expression. This structure is established through the action of various protein complexes that remodel nucleosomes, catalyse post-translational modifications, deposit histone variants and methylate DNA. Together these complexes establish epigenetic marks that influence expression of the gene. Some of these epigenetic marks are transient while others, such as those involved in silencing genes are more stable and can require several cell divisions to be fully implemented or reversed. Deregulated gene expression programs are a feature of cancer biology and it is now apparent that epigenetic changes, as well as genetic changes, are important in establishing these aberrant expression patterns. However, unlike genetic alterations, epigenetic changes are reversible. The complexes that catalyse these modifications therefore represent valuable targets for therapeutic intervention. Here we will review the most recent literature describing the protein complexes that catalyse epigenetic modifications and the inhibitors of these complexes that are being pursued as cancer drugs. In addition we will highlight those epigenetic modifiers that provide promise as therapeutic targets but for which inhibitors are not currently available.

Because epigenetic alterations are believed to be involved in the repression of tumor suppressor genes and promotion of tumorigenesis in endometrial cancers and ovarian cancers, novel compounds endowed with a histone deacetylase (HDAC) inhibitory activity are an attractive therapeutic approach. Clonogenic assay in soft agar and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays showed that many endometrial and ovarian cancer cell lines were sensitive to the growth inhibitory effect of HDAC inhibitors (HDACIs), although normal endometrial epithelial cells were viable after the treatment with the same doses of HDACIs that induced growth inhibition of endometrial and ovarian cancer cells. Cell cycle analysis indicated that their exposure to HDACIs decreased the proportion of cells in the S-phase and increased the proportion in the G0/G1 phases and/or G2/M phases of the cell cycle. Induction of apoptosis was confirmed by TUNEL assay, annexin V staining of externalized phosphatidylserine, and loss of the transmembrane potential of mitochondria. This induction occurred in concert with altered expression of genes related to cell growth, malignant phenotype, and apoptosis. In nude mice experiments, valproic acid significantly inhibited human endometrial and ovarian tumor growth without toxic sideeffects. Although there are few clinical trials on these cancers, some clinical trials showed that HDACIs in well tolerated doses have significant antitumoral activities in another cancers. These results raise the possibility that HDACIs may prove particularly effective in the treatment of endometrial cancers and ovarian cancers.

The vagal nerve conveys primary afferent information from the intestinal mucosa to the brain stem. Activation of vagal afferent fibers results in inhibition of food intake, gastric emptying, and stimulation of pancreatic secretion. Afferents nerves terminating near to the mucosa are in a position to monitor the composition of the luminal contents. As afferents do not project directly into the lumen, their activation depends on an intermediary step, i.e. neuronal activation by a secondary substance released from within the mucosal epithelium. This review addresses the role for both cholecytokinin (CCK) and serotonin (5-HT) released from enteroendocrine cells and acting as paracrine agents on the terminals of vagal afferents in responses to a number of luminal signals. CCK acted on both high- and lowaffinity CCK-A receptors present on distinct vagal primary afferent neurons. Neurons of the nodose ganglia respond to intraduodenal perfusions of maltose, glucose, and hypertonic saline. These neurons were also sensitive to exogenous luminally applied 5-HT at concentrations that mimic physiologic levels. Intravenous administration of a 5-HT3 antagonist blocked these responses suggesting that nodose neuronal responses to luminal osmolarity and to the digestion products of carbohydrates are dependent on the release of endogenous 5- HT from the mucosal enterochromaffin (EC) cells, which acts on the 5-HT3 receptors on vagal afferent fibers to stimulate vagal afferent neurons. Double-labeling studies revealed that nodose neurons responded to 5-HT-dependent luminal stimuli contain mainly glutamate and substance P. Over the past year or so it has become clear that there are multiple possible excitatory inputs to a common vagal afferent route with synergistic interactions being common. The nodose ganglion contains neurons that may possess only high- or low-affinity CCK-A receptors or 5-HT3 receptors. Some neurons that express high-affinity CCK-A receptors also express 5-HT3 receptors and (or) secretin receptors. Pre-exposure to luminal 5-HT may augment the subsequent response to a subthreshold dose of CCK. Synergistic interaction between CCK and secretin also occurs at the nodose ganglia; this is mediated by high affinity CCK-A receptor. This may explain the robust postprandial secretion of enzyme, bicarbonate, and fluid despite the modest increase in CCK after a meal. Some neurons that possess low-affinity CCK-A receptor colocalize with leptin receptors (OB-Rs). These neurons also respond to mechanical distention. Interaction between CCK-A receptor and OB-Rs in these neurons likely facilitates leptin mediation of short-term satiety.

Exercise is a well-recognized facet of modern living; however, the threat of sedentary lifestyle is ever increasing with the arrival of the technological period. Although the beneficial effects of exercise to the health and function of the brain have been accepted by the scientific and medical community, much remains to be achieved to understand its mechanisms of action. With the advent of modern investigative tools, several more key molecular and cellular players have been implicated in the above process. Such include the family of neurotrophins (e.g. NGF and BDNF) and their receptors, some pro-inflammatory cytokines (L-1β, IL-6, TNF-α, IFN-γ), microglia and astrocytes, and the cholinergic neuronal cells in the forebrain. While experiments based on the voluntary exercise paradigm has been the preferred approach to studying the brain, less is known about the forced paradigm. We will discuss in this review how molecular players may feature differently in the context of exercise and more importantly how their actions converged to impact the structure, and function (learning and memory) of the CNS.

Coeliac disease is a multifactorial disease characterized by a dysregulated immune response to ingested wheat gluten and related cereal proteins. With an incidence of about 1% of the general population, it is considered the most common food intolerance disorder. The mainstay of coeliac disease treatment is strict lifelong adherence to a gluten-free diet. Elimination of gluten and related proteins from the diet leads to clinical and histological improvement. However, some patients do not respond to dietary therapy and others have poor dietary compliance. This has prompted the search for a therapy alternative to a gluten-free diet. Tissue transglutaminase is a crucial factor in coeliac disease because it promotes the gluten-specific T-cell response and is also the target of the autoimmune response. Tissue transglutaminase induces changes in gluten, which in turn, cause the generation of a series of gluten peptides that bind to HLA-DQ2 or DQ8 molecules with high affinity. The resulting HLA-DQ2 (DQ8)-gluten peptide interaction triggers the proinflammatory T cell response. Tissue transglutaminase is also involved in other non-T-cell-mediated biological activities of gliadin peptides. For these reasons, tissue transglutaminase is a potential target for therapeutic intervention. In this paper we review the state-of-the-art of tissue transglutaminase inhibition, and examine known and new-generation inhibitors and their activity in in vitro and in vivo models. We also examine their potential as therapeutic tools for coeliac disease.

Genistein, a natural bioactive compound derived from legumes, has drawn wide attention during the last decade because of its potentially beneficial effects on some human degenerative diseases. It has a weak estrogenic effect and is a well-known non-specific tyrosine kinase inhibitor at pharmacological doses. Epidemiological studies show that genistein intake is inversely associated with the risk of cardiovascular diseases. Data from animal and in vitro studies suggest a protective role of genistein in cardiovascular events. However, the mechanisms of the genistein action on vascular protective effects are unclear. Past extensive studies exploring its hypolipidemic effect resulted in contradictory data. Genistein also is a relatively poor antioxidant. However, genistein protects against pro-inflammatory factor-induced vascular endothelial barrier dysfunction and inhibits leukocyte-endothelium interaction, thereby modulating vascular inflammation, a major event in the pathogenesis of atherosclerosis. Recent studies found that genistein exerts a novel non-genomic action by targeting on important signaling molecules in vascular endothelial cells (ECs). Genistein rapidly activates endothelial nitric oxide synthase and production of nitric oxide in ECs. This genistein effect is novel since it is independent of its known effects, but mediated by the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) cascade. Further studies demonstrated that genistein directly stimulates the plasma membrane-associated adenylate cyclases, leading to activation of the cAMP signaling pathway. In addition, genistein activates peroxisome proliferator-activated receptors, ligand-activated nuclear receptors important to normal vascular function. Furthermore, genistein reduces reactive oxygen species (ROS) by attenuating the expression of ROS-producing enzymes. These new findings reveal the novel roles for genistein in the regulation of vascular function and provide a basis for further investigating its therapeutic potential for inflammatory-related vascular disease.

Over 95% of the oxygen we metabolize undergoes a four-electron reduction to produce two molecules of water. Whenever electrons escape from the mitochondrial electron-transport chain and pass directly onto oxygen, oxidants that can cause cytotoxicity are generated. The lung being constantly exposed to atmospheric oxygen is more susceptible to oxidant-induced cellular damage. For instance, increased generation of oxidants is implicated in many pulmonary pathological conditions including emphysema, adult respiratory distress syndrome, idiopathic pulmonary fibrosis and asthma. Sulfur is an essential major inorganic element with a recently described protective cellular role. One of its many biologically important functions is the formation of disulfide bridges between two cysteine molecules thus stabilizing protein conformation. Also, it provides the site for attachment and transfer of 1-C methyl groups via formation of S-adenosylmethionine, and most importantly it is an essential constituent of the antioxidant tripeptide, glutathione, and vitamins like thiamin and biotin. However, its protective role emanates from its antioxidant properties in the context of sulfur-containing compounds (S-adenosylmethionine, cysteine, taurine, glutathione etc) that are known to act in protecting against oxidant-induced lung disease. The efficacy of these sulfur-containing compounds in scavenging oxidants directly or indirectly and consequently protecting against lung diseases is discussed herein.

Tropone or tropolone and its derivatives (here together called troponoids) belong to a family of natural products with a sevenmembered aromatic ring and various side groups. They are mainly synthesized by plants and fungi, and most troponoids play roles of antibacterial defenses in these organisms. With an increasingly severe situation of antibiotic resistant bacteria, as well as a requirement for antifungal medicines, troponoids have attracted extensive studies since they have powerful antibacterial and antifungal activity, particularly against antibiotic-resistant bacteria. In addition, many other biological activities such as antiviral, antitumor, antioxidant, antiinflammatory, insecticidal, or enzyme inhibitor activities are associated with troponoids. After extensive studies in the 1960s-70s, interests in natural troponoids dedclined. However, chemical and biomedical studies on troponoids bloom again from the 1990s. To date great progress has been made with troponoid study in terms of identification of new natural troponoids, chemical synthesis and properties, biological activity, biosynthesis and metabolism. Particularly, bioassay-guided screening strategy and structure-activity relation-directed structure modification and drug design has resulted in the synthesis and discovery of many new derivatives. Many of them have great promise to be developed into new medicines for their potent and specific activities. This review presents the recent advances in troponoid studies and highlights multiple faceted biological activities of troponoids, as well as their relationships with chemical structures. Chemistry, biosynthesis, and production via biotechnology of troponoids are also briefly reviewed. Applications of troponoids in daily life, agriculture, medicine, and industry, and the related patents have been considered to further extend our understanding of the increasing impact of troponoids on humans.

Considerable epidemiological data confirmed the existence of favorable associations between fish consumption and mortality from cardiovascular disease.Accumulating evidence suggests that n-3 polyunsaturated fatty acids supplementation is an effective additive treatment for the primary and secondary prevention of cardiovascular disease. Another indication for the use of n-3 PUFA is the treatment of hypertriglyceridemia as monotherapy or in combination with other lipid lowering agents (e.g. statins or fibrates). However, high doses of n-3 PUFA are required for this effect (e.g. 3-4 g/day). Fish oils may be acting via several mechanisms that include antiarrhythmic, antithrombotic and anti-inflammatory effects as well as plaque stabilization. Despite the current evidence supporting a beneficial effect of fish oils on vascular disease, more definitive studies than the ones already performed are required. Some ongoing trials may provide further insight into the indications for fish oil supplementation. This review considers the mechanisms accounting for the cardioprotective properties of n-3 polyunsaturated fatty acids. We also discuss the epidemiological and interventional studies evaluating the relationship between n-3 polyunsaturated fatty acids consumption and cardiovascular disease.