Current Pharmaceutical Design - Volume 19, Issue 28, 2013

Structural changes of chromatin, which consists of nucleosomes and nucleosome-associated factors, lead to functional changes that are important determinants of eukaryotic gene regulation. These structural changes are regulated by modifications of histones and DNA, both of which are components of nucleosomes, as well as by replacement of histone variants and the actions of noncoding RNAs. In studies of chromatin modifications, a great deal of attention has been paid to histone acetylation. Progress in understanding this subject has been extensive, including i) elucidation of the relationship of histone acetylation and gene activity; ii) the first isolation of a histonemodifying enzyme; iii) the first identification of a factor that recognizes a modified site; iv) elucidation of the mechanism by which histone modification leads to structural changes in nucleosomes; and v) elucidation of the mechanism of border formation between euchromatin and heterochromatin. Histone acetylation is considered to be fundamental in several fields, including studies of a) the role of chromatin and epigenetics in higher-order biochemical systems such as transcription, DNA replication, and repair; b) biological phenomena such as cell proliferation and differentiation; and c) cancer and aging, potentially leading to clinical applications. In this review, I will discuss the histone code hypothesis, at one time believed to represent a unified theory regarding the functions of histone modification. In addition, I will describe the “modification web theory, ” by which the problems in the histone code hypothesis can be overcome, as well as the “signal router theory, ” which explains the mechanisms of formation, development, and evolution of the modification web from a structural viewpoint. Lastly, I will illustrate how these novel theories partially explain the robustness of biological systems against various perturbations, and elucidate the strategy that a cell employs to avoid fatal fragility.

Post-translational modification of histones is a primary mechanism through which epigenetic regulation of DNA transcription does occur. Among these modifications, regulation of histone acetylation state is an important tool to influence gene expression. Epigenetic regulation of neurodevelopment contributes to the structural and functional shaping of the brain during neurogenesis and continues to impact on neural plasticity lifelong. Alterations of these mechanisms during neurodevelopment may result in later occurrence of neuropsychatric disorders. The present paper reviews and discusses available data on histone modifications, in particular histone acetylation, in neurogenesis considering results obtained in culture systems of neural progenitors as well as in in vivo studies. Possible teratogenic effects of altered histone acetylation state during development are also considered. The use during pregnancy of drugs such as valproic acid, which acts as a histone deacetylase inhibitor, may result during postnatal development in autistic-like symptoms. The effect of gestational administration of the drug has been, therefore, tested on adult hippocampal neurogenesis in animals showing behavioral impairment as a consequence of the drug administration at a specific stage of pregnancy. These experimental results show that adult neurogenesis in the hippocampal dentate gyrus is not quantitatively altered by gestational valproic acid administration. Future steps and goals of research on the role and mechanisms of histone acetylation in neurodevelopment are briefly discussed.

Neuropsychiatric pathologies, including neurodegenerative diseases and neurodevelopmental syndromes, are frequently associated with dysregulation of various essential cellular mechanisms, such as transcription, mitochondrial respiration and protein degradation. In these complex scenarios, it is difficult to pinpoint the specific molecular dysfunction that initiated the pathology or that led to the fatal cascade of events that ends with the death of the neuron. Among the possible original factors, epigenetic dysregulation has attracted special attention. This review focuses on two highly related epigenetic factors that are directly involved in a number of neurological disorders, the lysine acetyltransferases CREB-binding protein (CBP) and E1A-associated protein p300 (p300). We first comment on the role of chromatin acetylation and the enzymes that control it, particularly CBP and p300, in neuronal plasticity and cognition. Next, we describe the involvement of these proteins in intellectual disability and in different neurodegenerative diseases. Finally, we discuss the potential of ameliorative strategies targeting CBP/p300 for the treatment of these disorders.

Epigenetic mechanisms, i.e. the control gene of expression without changing DNA sequence, include DNA methylation, histone post-translational modifications (PTMs) and microRNAs (miRNAs). Aberrant epigenetic modifications are associated with several pathological conditions, including brain diseases, resulting from environmental causes, ageing or genetic factors. The role of histone PTMs, including acetylation, phosphorylation, methylation and ubiquitylation, has been demonstrated in learning and memory, both in physiological conditions and in neuropathologies. Abnormalities in these modifications or in the machinery that control them are associated with several neurodegenerative, neuro-developmental and psychiatric diseases. Therefore, these epigenetic marks are promising targets to address memory-related diseases and strong efforts are presently focused on pharmacological and genetic approaches to this field.

4-phenylbutyrate (PBA) is a histone deacetylase (HDAC) inhibitor whose efficacy in the Tg2576 mouse model of Alzheimer´s disease (AD) is correlated with decreased tau phosphorylation, clearance of intraneuronal Aβ and restoration of dendritic spine density in hippocampal CA1 pyramidal neurons. PBA is also a chemical chaperone that facilitates cell proteostasis. To determine the relative contributions of HDAC inhibition and chaperone-like activity in the anti-AD effects of PBA, we compared the effect of PBA with that of sodium butyrate (NaBu), an HDAC inhibitor with no chaperone activity. In neuronal cultures from Tg2576 mice, we observed a correlation between histone 3 acetylation and decreased p-tau levels. Moreover, we observed a decrease in the processing of the amyloid precursor protein (APP) in Tg2576 neurons treated with PBA, but not with NaBu. In Tg2576 mice administered PBA or NaBu for 3 weeks, only PBA normalized the pathological AD markers, implicating, at least in part, other mechanism as the chaperone-like activity in the reversal of the AD-like phenotype of Tg2576 mice. Furthermore, treatment with PBA but not NaBu prevented the neuronal loss in the hippocampus of hAPPWT-overexpressing mice, as was particularly evident in the CA1 layer. In addition to its activity as a HDAC inhibitor, the chaperone activity of PBA appears to at least partially, mediate its reversal of the AD phenotype in Tg2576 mice and its neuroprotective effect in a model of hippocampal neuronal loss.

Gene expression is controlled by several epigenetic mechanisms involving post-translational modification of histones (acetylation, phosphorylation and others). These mechanisms in the brain are not only important for normal function but also for the development of pathologies when their derangement does occur. The present review deals with post-translational modifications of histones in two neurodegenerative diseases characterized by different etiology and pathological progression, Huntington’s disease and Parkinson’s disease. A relatively large body of evidence supports an important role of these mechanisms in Huntington’s disease while knowledge of similar mechanisms in Parkinson’s disease is at a lower degree of understanding. Starting from available information on pathologies, the present state of possible therapeutic targets is considered and future developments are discussed.

Among hereditary diseases, the group of motor neuron diseases (MNDs) includes some of the most devastating and rapidly progressive lethal conditions. Although degeneration of motor neurons is common to all of them, the phenotypic spectrum of MNDs is relatively broad and ranges from perinatal conditions like spinal muscular atrophy (SMA) to adult-onset diseases such as amyotrophic lateral sclerosis (ALS). While the understanding of the pathology of the diseases is constantly growing, the development of therapeutic approaches lags behind. In fact, there is no approved therapy for MNDs available at the moment. Recent findings demonstrated the existence of some patterns that are shared by several MNDs such as transcriptional dysregulation. In addition, conditions like SMA or certain types of Charcot-Marie-Tooth disease provide some defined targets which may be amenable to therapeutic approaches. Consequently, counteracting this dysregulation may be a valuable therapeutic option and ameliorate disease progression in MND patients. The feasibility of such an approach has been proven during the past years by the epigenetic treatment of various neoplastic entities with histone deacetylase inhibitors (HDACi). On these grounds, also epigenetic therapy of MNDs has become a promising option. So far, several HDACi have been tested in vitro and in animal models and some proceeded further and were evaluated in clinical trials. This review will summarize the advances of HDACi in MNDs and will give a perspective where the road will lead us.

Ischemic stroke is a leading cause of death and disability worldwide, with few available treatment options. The pathophysiology of cerebral ischemia involves both early phase tissue damage, characterized by neuronal death, inflammation, and blood-brain barrier breakdown, followed by late phase neurovascular recovery. It is becoming clear that any promising treatment strategy must target multiple points in the evolution of ischemic injury to provide substantial therapeutic benefit. Histone deacetylase (HDAC) inhibitors are a class of drugs that increase the acetylation of histone and non-histone proteins to activate transcription, enhance gene expression, and modify the function of target proteins. Acetylation homeostasis is often disrupted in neurological conditions, and accumulating evidence suggests that HDAC inhibitors have robust protective properties in many preclinical models of these disorders, including ischemic stroke. Specifically, HDAC inhibitors such as trichostatin A, valproic acid, sodium butyrate, sodium 4-phenylbutyrate, and suberoylanilide hydroxamic acid have been shown to provide robust protection against excitotoxicity, oxidative stress, ER stress, apoptosis, inflammation, and bloodbrain barrier breakdown. Concurrently, these agents can also promote angiogenesis, neurogenesis and stem cell migration to dramatically reduce infarct volume and improve functional recovery after experimental cerebral ischemia. In the following review, we discuss the mechanisms by which HDAC inhibitors exert these protective effects and provide evidence for their strong potential to ultimately improve stroke outcome in patients.

Identification of factors affecting platelet reactivity (PR) and high PR (HPR) or high platelet inhibition (HPI) rates while on prasugrel maintenance dose (MD) might be helpful in avoiding ischemic or bleeding complications. We retrospectively analyzed all patients (n=233) treated in our institution between April 2010 and November 2012 who had platelet function assessment pre-prasugrel and following prasugrel 10 mg MD for at least 5 days, using the Verify Now P2Y12 platelet function assay. Multiple linear regression and logistic regression models were applied to identify independent factors affecting post-prasugrel PR level, HPR and HPI status. The amount of variance in PR under prasugrel MD that could be explained by the model was 25.9% (adjusted R2), p<0.001. Pre-prasugrel treatment PR, acute coronary syndrome (ACS), prasugrel loading and smoking uniquely accounted for 10.8%, 1.3%, 3.5% and 1.2% of the observed variance, respectively. HPR and HPI were observed in 7.7% and 13.7% of the cases, respectively. On multivariate analysis, pre-prasugrel PR in the upper quartile (>313 PRU) was the only independent factor associated with HPR under prasugrel MD. In contrast, pre-prasugrel PR in the lower quartile (<242 PRU) and prasugrel loading emerged as the only independent predictors of HPI. In patients under different clinical settings receiving prasugrel 10 mg MD a significant amount of the PR variability in response to prasugrel may be explained by pre- treatment PR level, ACS, prasugrel loading and smoking status. A high pre- treatment PR is associated with HPR, while a low pre-treatment PR and prasugrel loading predict HPI.

With a constant focus on the primary tumor, the current approaches in drug development in oncology yield dismal results. However over 90 percent of cancer deaths today are due to metastasis formation and yet there is no anti-metastatic drug on the market. Tumor cell migration is the essential prerequisite for invasion and metastasis formation. It is regulated by signal substances in terms of the grade of activity and in terms of direction (chemotaxis). The latter is important for the organotropism, the localization of metastasis in certain organs. Ligands to G protein-coupled receptors, mainly chemokines and neurotransmitters, as well as ligands to receptor kinases, mainly cytokines and growth factors, form the most important group of such regulators. We provide an overview of currently available agonists and antagonists to these receptors, which have a potential as anti-metastatic targets. Moreover we provide with the example of beta-blockers, how established drugs in other indications are possibly effective and can be co-opted as such anti-metastatics. The increasing knowledge of such regulators opens new opportunities to target cancer spreading and may put forth the development of antimetastatic drugs for oncological therapy.

Much attention has been focused on cell-free DNA (cf-DNA) and its levels in the plasma, serum and body fluids of pregnant women and patients with cancer or autoimmune disease, and those with severe trauma; however, knowledge of its biology and relationship with myocardial infarction (MI) is still at an early stage. This paper introduces general aspects of the nomenclature, structure, function, release mechanisms and methodology of cf-DNA and summarizes the current literature on concentration variation and regulatory mechanisms in MI.

Since the recent emergence of swine and avian flu, there has been a sense of urgency to discover new anti-influenza drugs. In this study, a stable cell line with M2 ion channel/ enhanced Green fluorescent protein (EGFP) co-expression was established in order to develop an EGFP-based high-throughput assay for screening M2 ion channel inhibitors. This assay directly monitors the proton conductivity of the M2 ion channel by measuring the fluorescence intensity of EGFP, which is dependent on and sensitive to pH. The ability of amantadine to inhibit the M2 ion channel was detected by this novel EGFP-based assay and then confirmed by a patch clamp recording assay. With this assay, (1S,2S,3S,5R)-(+)-3-Isopinocampheylamine and (1R,2R,3R,5S)-(-)-3-Isopinocampheylamine were identified to inhibit M2 ion channel with an antiviral profile similar to that of amantadine. This new technique will facilitate the discovery of pharmaceutical candidates and will aid in the development of new, potent, and safe anti-influenza agents.

G-protein coupled receptors (GPCRs) are the most important class of current pharmacological targets. However, it is now widely acknowledged that their regulation is more complex than previously thought: the evidence that GPCRs can couple to several effector pathways, and the existence of biased agonists able to activate them differentially, has introduced a new level of complexity in GPCR drug research. Considering bias represents a challenge for the research of new GPCR modulators, because it demands a detailed characterization of compound properties for several effector pathways. Still, biased ligands could provide an opportunity to modulate GPCR function in a finer way and to separate therapeutic from side effects. Nowadays, a variety of agonists for GPCRs have been described, which differ in their ability to promote receptor coupling to different Gprotein families or even subunits, recruit signal transducers such as arrestins, activate a variety of downstream molecular pathways and induce certain phosphorylation signatures or gene expression patterns. In this review, we will cover some of the experimental techniques currently used to understand and characterize biased agonism and discuss their strengths and limitations. Additionally, we will comment on the computational efforts that are being devoted to study ligand-induced bias and on the potential they hold for rationalizing its structural determinants. Finally, we will discuss which of these strategies could be used for the rational design of biased ligands and give some examples of the potential therapeutic value of this class of compounds.