Current Drug Targets (v.14, #1)

Stroke Prevention: From Available Antiplatelet Drugs to Novel Molecular Targets by Matteo Nicola Dario Di Minno, Stefania Momi, Alessandro Di Minno, Anna Russolillo (3-12).
Stroke is the third most common cause of death in the industrialized countries and adequate primary and secondary prevention strategies are mandatory. In addition to lifestyle-changes and correction of cardiovascular risk factors, the mainstay of the atherothrombotic stroke prevention is represented by antiplatelet treatment. Although aspirin and thienopyridines have proved their efficacy in the prevention of arterial thrombotic events, limited efficacy, increased risk of bleeding, significant inter-individual variability in the response and extended duration of action that cannot be reversed if the need for haemostasis or emergency surgery arises represent major limitations of these drugs. Moreover, despite recommendations and guidelines about stroke prevention, registries data clearly suggest an underuse of antiplatelet drugs, mainly because of bleeding episodes fear. At variance with newer anticoagulant drugs, which showed a series of advantages as compared with the traditional warfarin treatment, newer antiplatelet drugs have only partially overcome these limitations. Although ad hoc studies on their efficacy in the stroke prevention are currently lacking, newer antiplatelet agents (mainly ticagrelor and prasugrel) do not provide a significant better protection over and above aspirin and/or clopidogrel in the prevention of atherothrombotic stroke. In addition, a significantly increased bleeding risk has been reported in subjects receiving these new thienopyridines. According to these data, the identification of further molecular targets is needed, in order to design future antiplatelet drugs. In this review, after summarizing major literature data about traditional and newer antiplatelet drugs, we will specifically focus on novel potential target candidates for antiplatelet therapy.

Oxidation Inhibits Iron-Induced Blood Coagulation by Etheresia Pretorius, Janette Bester, Natasha Vermeulen, Boguslaw Lipinski (13-19).
Blood coagulation under physiological conditions is activated by thrombin, which converts soluble plasma fibrinogen (FBG) into an insoluble clot. The structure of the enzymatically-generated clot is very characteristic being composed of thick fibrin fibers susceptible to the fibrinolytic degradation. However, in chronic degenerative diseases, such as atherosclerosis, diabetes mellitus, cancer, and neurological disorders, fibrin clots are very different forming dense matted deposits (DMD) that are not effectively removed and thus create a condition known as thrombosis. We have recently shown that trivalent iron (ferric ions) generates hydroxyl radicals, which subsequently convert FBG into abnormal fibrin clots in the form of DMDs. A characteristic feature of DMDs is their remarkable and permanent resistance to the enzymatic degradation. Therefore, in order to prevent thrombotic incidences in the degenerative diseases it is essential to inhibit the iron-induced generation of hydroxyl radicals. This can be achieved by the pretreatment with a direct free radical scavenger (e.g. salicylate), and as shown in this paper by the treatment with oxidizing agents such as hydrogen peroxide, methylene blue, and sodium selenite. Although the actual mechanism of this phenomenon is not yet known, it is possible that hydroxyl radicals are neutralized by their conversion to the molecular oxygen and water, thus inhibiting the formation of dense matted fibrin deposits in human blood.

Global Cerebral Ischemia: Synaptic and Cognitive Dysfunction by Jake T. Neumann, Charles H. Cohan, Kunjan R. Dave, Clinton B. Wright, Miguel A. Perez-Pinzon (20-35).
Cardiopulmonary arrest is one of the leading causes of death and disability, primarily occurring in the aged population. Numerous global cerebral ischemia animal models induce neuronal damage similar to cardiac arrest. These global cerebral ischemia models range from vessel occlusion to total cessation of cardiac function, both of which have allowed for the investigation of this multifaceted disease and detection of numerous agents that are neuroprotective. Synapses endure a variety of alterations after global cerebral ischemia from the resulting excitotoxicity and have been a major target for neuroprotection; however, neuroprotective agents have proven unsuccessful in clinical trials, as neurological outcomes have not displayed significant improvements in patients. A majority of these neuroprotective agents have specific neuronal targets, where the success of future neuroprotective agents may depend on non-specific targets and numerous cognitive improvements. This review focuses on the different models of global cerebral ischemia, neuronal synaptic alterations, synaptic neuroprotection and behavioral tests that can be used to determine deficits in cognitive function after global cerebral ischemia.

A Key Role for Connexin Hemichannels in Spreading Ischemic Brain Injury by Joanne O. Davidson, Colin R. Green, Laura Bennet, Louise F.B. Nicholson, Helen Danesh-Meyer, Simon J. O'Carroll, Alistair J. Gunn (36-46).
Brain damage resulting from cerebral ischemia remains a significant problem at all stages of life. In adults, ischemic stroke is the third leading cause of death and the leading cause of disability in the developed world. In term newborns, moderate to severe brain damage after hypoxia-ischemia (HI) occurs in 1-3 per 1000 live births. One of the most striking features of HI injury is that after initial recovery of cellular oxidative metabolism, there is a delayed, ‘secondary’ mitochondrial failure that spreads over time from the most severely damaged areas outwards, into previously undamaged regions. This secondary failure is accompanied by transient seizure activity and cytotoxic edema. The specific mechanisms of this spread are poorly understood, but it is at least partly associated with spreading waves of depression that can trigger cell death in neighboring uninjured tissues. The waves are propagated through cell-cell communication via gap junction channels (the so called “bystander effect”). It has recently been proposed that unopposed connexin hemichannels (connexons) also play a significant role by mediating release of paracrine molecules that in turn propagate cell death messages by releasing intracellular mediators such as ATP, NAD(+), or glutamate or by abnormally prolonged opening to allow cell edema. There is increasing evidence that connexin hemichannels contribute to injury after many neural insults and that it is possible to significantly reduce the spread of damage after injury by suppressing the induction or activity of the connexin proteins that form hemichannels.

Minocycline Mediated Mitochondrial Cytoprotection: Premises for Therapy of Cerebrovascular and Neurodegenerative Diseases by Andonis Karachitos, Julian Solis Garcia del Pozo, Piet W.J. de Groot, Hanna Kmita, Joaquin Jordan (47-55).
In the last decades, emerging molecular targets for ischemic neuroprotection and regeneration have been postulated. This fact allowed that classical drugs with well established therapeutic applications might be used in cerebrovascular diseases as well as neurodegenerative diseases. Minocycline is a commonly used antibiotic of the tetracycline family (7-dimethylamino-6-dimethyl-6-deoxytetracycline) which reveals cytoprotective capability and potential use in treatment of different diseases. Here, we discuss the literature concerning minocycline. The available data indicate that the antibiotic has multi-faceted effects on cell functions and, consequently, a number of clinical properties that are useful and/or could be useful for treatment of different diseases including bacterial infections, cancer, autoimmune disorders, ischemia as well as neurodegenerative and psychiatric diseases. Thus, application of minocycline as a therapeutic agent is the subject of clinical trials for various diseases. It is also evident that minocycline-mediated cytoprotection, including neuroprotection, is an important aspect of its clinical application. Here, we have reviewed the basis of the minocycline activity as well as different studies indicating that minocycline can be used as potential therapeutic agent in both cerebrovascular and neurodegenerative diseases in human.

Inhalation Gases or Gaseous Mediators As Neuroprotectants for Cerebral Ischaemia by Brad A. Sutherland, Joanne C. Harrison, Shiva M. Nair, Ivan A. Sammut (56-73).
Ischaemic stroke is one of the leading causes of morbidity and mortality worldwide. While recombinant tissue plasminogen activator can be administered to produce thrombolysis and restore blood flow to the ischaemic brain, therapeutic benefit is only achieved in a fraction of the subset of patients eligible for fibrinolytic intervention. Neuroprotective therapies attempting to restrict the extent of brain injury following cerebral ischaemia have not been successfully translated into the clinic despite overwhelming pre-clinical evidence of neuroprotection. Therefore, an adequate treatment for the majority of acute ischaemic stroke patients remains elusive. In the stroke literature, the use of therapeutic gases has received relatively little attention. Gases such as hyperbaric and normobaric oxygen, xenon, hydrogen, helium and argon all possess biological effects that have shown to be neuroprotective in pre-clinical models of ischaemic stroke. There are significant advantages to using gases including their relative abundance, low cost and feasibility for administration, all of which make them ideal candidates for a translational therapy for stroke. In addition, modulating cellular gaseous mediators including nitric oxide, carbon monoxide, and hydrogen sulphide may be an attractive option for ischaemic stroke therapy. Inhalation of these gaseous mediators can also produce neuroprotection, but this strategy remains to be confirmed as a viable therapy for ischaemic stroke. This review highlights the neuroprotective potential of therapeutic gas therapy and modulation of gaseous mediators for ischaemic stroke. The therapeutic advantages of gaseous therapy offer new promising directions in breaking the translational barrier for ischaemic stroke.

Effective efforts to screen for agents that protect against the devastating effects of stroke have not produced viable results thus far. As a result this article reviews the possible role of ethanol as a neuroprotective agent in stroke and traumatic brain injury (TBI). Previous studies have associated ethanol consumption with a decreased risk of ischemic stroke, suggesting a neuroprotective mechanism. The translation of this clinical knowledge into basic science research with the goal of new therapy for acute stroke patients remains in its initial stages. In a recent study involving rats, we have shown that ethanol administration, in the correct dose after stroke onset, protects against ischemia-induced brain injury. The purpose of this paper is to discuss ethanol's neuroprotective properties in stroke when consumed as a preconditioning agent, in TBI with a positive blood alcohol content, and finally in stroke treatment, with the goal of using post-ischemia ethanol (PIE) therapy to ameliorate brain damage in the future.

Ischemic stroke is one of the leading causes of death and disability worldwide. There is no effective treatment for ischemic stroke apart from thrombolytic therapy, which has a narrow therapeutic time window. Gene therapy has proven to be effective in experimental stroke, but it suffers from disadvantages that limit its clinical application, such as difficulty in intracranial delivering of therapeutic genes, low efficacy in transfecting host cells and long-term expression of exogenous genes. Delivering therapeutic genes to the ischemic brain via stem cells is an alternative strategy of combined gene and stem cell therapy. There are advantages for stem cell-mediated gene delivery as opposed to direct gene transfer. In recent years, studies used stem cells that over-express different neurotrophic factors, such as BDNF, GDNT, or NT3, and found that the delivery of these genetically-modified stem cells to animal models of ischemic stroke is safe and effective, thus suggesting that stem cell-based gene therapy may be a promising treatment for stroke. This review summarizes the advantages and recent progress of stem cell-based gene therapy for ischemic stroke. We also discuss the relevant strategy for optimizing stem cell-based gene therapy and discuss the potential strategies for its future application.

microRNAs: Innovative Targets for Cerebral Ischemia and Stroke by Yi-Bing Ouyang, Creed M. Stary, Guo-Yuan Yang, Rona Giffard (90-101).
Stroke is one of the leading causes of death and disability worldwide. Because stroke is a multifactorial disease with a short therapeutic window many clinical stroke trials have failed and the only currently approved therapy is thrombolysis. MicroRNAs (miRNA) are endogenously expressed noncoding short single-stranded RNAs that play a role in the regulation of gene expression at the post-transcriptional level, via degradation or translational inhibition of their target mRNAs. The study of miRNAs is rapidly growing and recent studies have revealed a significant role of miRNAs in ischemic disease. miRNAs are especially important candidates for stroke therapeutics because of their ability to simultaneously regulate many target genes and since to date targeting single genes for therapeutic intervention has not yet succeeded in the clinic. Although there are already quite a few review articles about miRNA in ischemic heart disease, much less is currently known about miRNAs in cerebral ischemia. This review summarizes current knowledge about miRNAs and cerebral ischemia, focusing on the role of miRNAs in ischemia, both changes in expression and identification of potential targets, as well as the potential of miRNAs as biomarkers and therapeutic targets in cerebral ischemia.

Human Ether-a-Go-Go-Related Gene Channel Blockers and its Structural Analysis for Drug Design by N. S. Hari Narayana Moorthy, Maria J. Ramos, Pedro A. Fernandes (102-113).
The human ether-a-go-go-related gene (hERG) is a K+ channel protein mainly expressed in the heart and the nervous systems and its blockade by non-cardiovascular acting drugs resulted in tachycardia and sudden death. In this present review, we have focused the physicochemical properties responsible for the hERG blocking activity of structurally different compounds. The reported research works showed that the hydrophobicity on the van der Waals (vdW) surface of the molecules (aroused from the aromatic ring) necessary for the hERG blocking activity along with topological and electronic properties. The quinolizidine alkaloids (natural products) such as oxymatrine, sophoridine, sophocarpine and matrine carry the common molecular structure of O=C=N-C-C-C-N that possessed positive ionotropic effect and hERG blocking activity. Acehytisine hydrochloride (previously named Guangfu base A) was isolated from the root of Aconitum coreanum (Levl.), is an anti-arrhythmic drug in phase IV clinical trial. The isoquinoline alkaloid, neferine (Nef) induces a concentration-dependent decrease in current amplitude (IC50 of 7.419 MM). Most of these natural product compounds contain non-flexible aromatic structures but have significant activity due to the presence of optimum hydrophobicity. Recent research works revealed that Eag and hERG channels are expressed by a variety of cancer cell lines and tissues. The Eag channel showed an oncogenic potential while hERG channels are associated with more aggressive tumors and have a role in mediating invasion. This review concluded that the consideration of physicochemical properties necessary for the hERG blocking activity will guide to develop novel drugs with less cardiotoxicity.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by progressive loss of memory and cognitive impairment. Aggregation of amyloid-β (Aβ) peptides is the crucial factor in the onset of AD. The toxic Aβ peptides Aβ40 and Aβ42 are produced from the Aβ precursor protein (APP), a transmembrane protein which is folded and modified in endoplasmic reticulum (ER). ER is the main organelle for the synthesis and processing of nearly all proteins as well as the main cellular source of Ca2+. Under stress conditions, three main ER pathways including inositol- requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor 6 become activated causing the accumulation of unfolded or misfolded proteins within ER lumen. These pathways manage the stress by regulating the expression of chaperones and enzymes involved in protein folding. Several studies have reported the dysfunction of these stress-sensing pathways in pathological conditions, including neurodegenerative diseases. Recent studies have proposed that neuronal death in AD arises from dysfunction of the ER. Here, we will review recent research findings on the interaction between ER and mitochondria, and its effect on apoptotic pathways. We further provide insights into studies which suggest the role of ER in animal and/or cellular models of AD. Therapeutic strategies that modulate ER could represent a promising approach for prevention or treatment of AD.

Colloidal Drug Delivery Systems in Vaccine Delivery by Sarwar Beg, Abdus Samad, Iram Nazish, Ruksar Sultana, Mahfoozur Rahman, Md Zaki Ahmad, Md Akbar (123-137).
Vaccines play a vital role in the field of community medicine to combat against several diseases of human existence. Vaccines primarily trigger the acquired immune system to develop long-lasting immunity against pathogens. Conventional approaches for vaccine delivery lacks potential to target a particular antigen to develop acquired immunity by specific antibodies. Recent advancements in vaccine delivery showed that inclusion of adjuvants in vaccine formulations or delivery of them in a carrier helps in achieving desired targeting ability, reducing the immunogenicity and significant augmentation in the immune response. Colloidal carriers (liposomes, niosomes, microspheres, proteosomes, virosomes and virus like particles (VLPs), antigen cochleates, dendrimers and carbon nanotubes) have been widely explored for vaccine delivery. Further, surface engineering of these carriers with ligands, functional moieties and monoclonal antibodies tend to enhance the immune recognition potential of vaccines by differentiation of antigen specific memory T-cells. The current review, therefore, provides an updated account on the recent advancements in various colloidal delivery systems in vaccine delivery, outlining the mechanism of immune response initiated by them along with potential applications and marketed instances in an explicit manner.