Cytomegalovirus antivirals and development of improved animal models

INTRODUCTION: Cytomegalovirus (CMV) is a ubiquitous pathogen that establishes a lifelong asymptomatic infection in healthy individuals. Infection of immunesuppressed individuals causes serious illness. Transplant and AIDS patients are highly susceptible to CMV leading to life-threatening end-organ disease. Another vulnerable population is the developing fetus in utero, where congenital infection can result in surviving newborns with long-term developmental problems. There is no vaccine licensed for CMV and current antivirals suffer from complications associated with prolonged treatment. These include drug toxicity and emergence of resistant strains. There is an obvious need for new antivirals. Candidate intervention strategies are tested in controlled preclinical animal models but species specificity of human CMV precludes the direct study of the virus in an animal model. AREAS COVERED: This review explores the current status of CMV antivirals and development of new drugs. This includes the use of animal models and the development of new improved models such as humanized animal CMV and bioluminescent imaging of virus in animals in real time. EXPERT OPINION: Various new CMV antivirals are in development, some with greater spectrum of activity against other viruses. Although the greatest need is in the setting of transplant patients, there remains an unmet need for a safe antiviral strategy against congenital CMV. This is especially important as an effective CMV vaccine remains an elusive goal. In this regard, greater emphasis should be placed on suitable preclinical animal models and greater collaboration between industry and academia.     

Smoking during pregnancy: lessons learned from epidemiological studies and experimental studies using animal models

Numerous epidemiological studies in the human population clearly indicate that smoking while pregnant has deleterious effects on fetal development as well as long-term adverse consequences on postnatal development and maturation of several organ systems. Low birth weight, sudden infant death syndrome (SIDS), behavioral disorders including attention deficit hyperactivity disorder (ADHD), externalizing and internalizing behavioral problems and conduct disorders in children have all been linked to prenatal exposure to tobacco smoke. The major pharmacologically active chemical found in tobacco smoke is nicotine, and prenatal exposure to nicotine has been shown to have significant effect on the development of multiple organ systems, including the nervous, respiratory, and cardiovascular systems. In this review, we define mainstream and sidestream smoke, summarize the major classes of compounds found in cigarette smoke, and describe how use of laboratory animal models can be used to assess mechanisms of toxicity and risk in the human population in general. We then discuss the association with smoking during pregnancy and the occurrence of reduced lung function, low birth weight, the incidence of congenital structural malformations, SIDS, ADHD, cognitive impairment, and mood disorders in children, and review pertinent experimental studies using a variety of animal models of developmental nicotine exposure, including, rats, mice, monkeys, lambs, and pigs that have increased our understanding of the pathophysiology of these disorders.     

Smoking during pregnancy: lessons learned from epidemiological studies and experimental studies using animal models

Numerous epidemiological studies in the human population clearly indicate that smoking while pregnant has deleterious effects on fetal development as well as long-term adverse consequences on postnatal development and maturation of several organ systems. Low birth weight, sudden infant death syndrome (SIDS), behavioral disorders including attention deficit hyperactivity disorder (ADHD), externalizing and internalizing behavioral problems and conduct disorders in children have all been linked to prenatal exposure to tobacco smoke. The major pharmacologically active chemical found in tobacco smoke is nicotine, and prenatal exposure to nicotine has been shown to have significant effect on the development of multiple organ systems, including the nervous, respiratory, and cardiovascular systems. In this review, we define mainstream and sidestream smoke, summarize the major classes of compounds found in cigarette smoke, and describe how use of laboratory animal models can be used to assess mechanisms of toxicity and risk in the human population in general. We then discuss the association with smoking during pregnancy and the occurrence of reduced lung function, low birth weight, the incidence of congenital structural malformations, SIDS, ADHD, cognitive impairment, and mood disorders in children, and review pertinent experimental studies using a variety of animal models of developmental nicotine exposure, including, rats, mice, monkeys, lambs, and pigs that have increased our understanding of the pathophysiology of these disorders.     

Tracing the development of psychosis and its prevention: what can be learned from animal models

Schizophrenia (SCZ) is a neurodevelopmental disorder manifested symptomatically after puberty whose pharmacotherapy remains unsatisfactory. In recent years, longitudinal structural neuroimaging studies have revealed that neuroanatomical aberrations occur in this disorder and in fact precede symptom onset, raising the exciting possibility that SCZ can be prevented. There is some evidence that treatment with atypical antipsychotic drugs (APDs) prior to the development of the full clinical phenotype reduces the risk of transition to psychosis, but results remain controversial. It remains unknown whether progressive structural brain aberrations can be halted. Given the diagnostic, ethical, clinical and methodological problems of pharmacological and imaging studies in patients, getting such information remains a major challenge. Animal neurodevelopmental models of SCZ are invaluable for investigating such questions because they capture the notion that the effects of early brain damage are progressive. In recent years, data derived from such models have converged on key neuropathological and behavioral deficits documented in SCZ attesting to their strong validity, and making them ideal tools for evaluating progression of pathology following in-utero insults as well as its prevention. We review here our recent studies that use longitudinal in vivo structural imaging to achieve this aim in the prenatal immune stimulation model that is based on the association of prenatal infection and increased risk for SCZ. Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Male and female offspring were imaged and tested behaviorally on postnatal days (PNDs) 35, 46, 56, 70 and 90. In other experiments, offspring of poly I:C- and saline-treated dams received the atypical antipsychotic drugs (APDs) clozapine or risperidone in two developmental windows: PND 34-47 and PND 48-61, and underwent behavioral testing and imaging at adulthood. Prenatal poly I:C-induced interference with fetal brain development led to aberrant postnatal brain development as manifested in structural abnormalities in the hippocampus, the striatum, the prefrontal cortex and lateral ventricles (LV), as seen in SCZ. The specific trajectories were region-, age- and sex-specific, with females having delayed onset of pathology compared to males. Brain pathology was accompanied by development of behavioral abnormalities phenotypic of SCZ, attentional deficit and hypersensitivity to amphetamine, with same sex difference. Hippocampal volume loss and LV volume expansion as well as behavioral abnormalities were prevented in the offspring of poly I:C mothers who received clozapine or risperidone during the asymptomatic period of adolescence (PND 34-47). Administration at a later window, PNDs 48-61, exerted sex-, region- and drug- specific effects. Our data show that prenatal insult leads to progressive postnatal brain pathology, which gradually gives rise to "symptoms"; that treatment with atypical APDs can prevent both brain and behavioral pathology; and that the earlier the intervention, the more pathological outcomes can be prevented.     

Old and new synthetic cannabinoids: lessons from animal models

Abstract

Synthetic cannabinoids have long been studied for their therapeutic potentials. However, during the last decade, new generations of synthetic cannabinoid agonists appeared on the drug market. These new psychoactive substances are currently sold as ‘marijuana-like’ products as they claim to mimic the effects of the psychoactive component of cannabis, delta-9-tetrahydrocannabinol (THC). Yet, their effects are more intense and potent than THC, typically last longer and are often associated to serious psychiatric consequences. Animal models of drug addiction are frequently used in preclinical research to assess the abuse potential of new compounds, evaluate drug positive reinforcing effects and analyze drug-induced behaviors. Some of these protocols have been used recently to study the newly synthesized cannabinoid agonists and have started elucidating their pharmacology and actions in the brain. The aim of this review is to summarize the major findings reported by animal studies that tested synthetic cannabinoids of first, second, and third generation by using self-administration and reinstatement models, drug discrimination and conditioned place preference procedures. Altogether, behavioral studies clearly indicate that synthetic cannabinoids possess abuse liability, are likely to activate the brain reward circuit and induce positive subjective and reinforcing effects.     

Type 1 diabetes vaccine development: animal models vs. humans

The loss of tolerance towards self-antigens on pancreatic β-cells is the hallmark of type 1 diabetes that ultimately causes destruction of the islets of Langerhans, loss of blood glucose control and severe long-term complications. One major aspect that contributes to the emergence of autoreactivity may be the interplay of several microbial agents with the immune system that, depending on its nature, may promote autoreactivity or confer protection. Since there is no curative treatment available that can be safely administered to the increasing number of patients suffering from this disease, the development of a vaccine that prevents autoreactivity or re-introduces immune regulation once autoreactivity occurs is of great interest, particularly because other treatment options almost entirely depend on general immunosuppression. Here, we will discuss recent developments in vaccine discovery and, since a majority of the available information is derived from animal models, will focus on the question, how these observations may be translated to a therapy for human type 1 diabetes.     

Cardiovascular complications in diabetes: lessons from animal models

Micro- and macro-vascular complications are the leading causes of morbidity and mortality in type 1 and type 2 diabetic patients. Despite the vast clinical experience linking diabetic metabolic abnormalities to cardiovascular lesions, the molecular basis of individual susceptibility to diabetic cardiovascular injury is still largely unknown. Significant advances in this area may come from studies on suitable animal models. Although no animal model can accurately reproduce the human disease, experimental studies in animals have the great advantage to eliminate factors such as ethnicity, economic and geographic variables, drug interactions, diet, gender and age differences that importantly limit clinical studies. Indeed, appropriate animal models have provided important information on genetic and environmental risks of diabetes, and helped to dissect molecular mechanisms underlying the development, progression and therapeutic control of this disease. Unfortunately, none of the diabetic models presently available fully mimics the human syndrome. Therefore, the current knowledge on the pathogenesis of cardiovascular complications relies on the evaluation of distinct phenotypes from various diabetic models. In addition to strains prone to diabetes, this disease can be induced by surgical, pharmacological or genetic manipulation in several animal species. Rodents are the most used, although some studies are still performed in larger animals as rabbits, cats, pigs or monkeys. Far from being exhaustive, this work should serve as a general overview of the most relevant clues provided by major species and models for the overall comprehension of cardiovascular complications in type 1 and type 2 diabetes.     

Botulinum neurotoxin for pain management: insights from animal models

The action of botulinum neurotoxins (BoNTs) at the neuromuscular junction has been extensively investigated and knowledge gained in this field laid the foundation for the use of BoNTs in human pathologies characterized by excessive muscle contractions. Although much more is known about the action of BoNTs on the peripheral system, growing evidence has demonstrated several effects also at the central level. Pain conditions, with special regard to neuropathic and intractable pain, are some of the pathological states that have been recently treated with BoNTs with beneficial effects. The knowledge of the action and potentiality of BoNTs utilization against pain, with emphasis for its possible use in modulation and alleviation of chronic pain, still represents an outstanding challenge for experimental research. This review highlights recent findings on the effects of BoNTs in animal pain models.     

Immunologic factors in transplant arteriopathy: insight from animal models

Transplant arteriopathy is the leading cause of long-term morbidity and mortality following heart transplantation. The pathologic hallmark of this disease is intimal proliferation. Animal models have demonstrated that immunologic factors, including cytokines, cellular adhesion molecules and inflammatory cells, play a significant role in the development of this arteriopathy. One goal of future studies will be to translate findings in animal models into effective treatments in humans.     

Measuring maladaptive avoidance: from animal models to clinical anxiety

Avoiding stimuli that predict danger is required for survival. However, avoidance can become maladaptive in individuals who overestimate threat and thus avoid safe situations as well as dangerous ones. Excessive avoidance is a core feature of anxiety disorders, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD). This avoidance prevents patients from confronting maladaptive threat beliefs, thereby maintaining disordered anxiety. Avoidance is associated with high levels of psychosocial impairment yet is poorly understood at a mechanistic level. Many objective laboratory assessments of avoidance measure adaptive avoidance, in which an individual learns to successfully avoid a truly noxious stimulus. However, anxiety disorders are characterized by maladaptive avoidance, for which there are fewer objective laboratory measures. We posit that maladaptive avoidance behavior depends on a combination of three altered neurobehavioral processes: (1) threat appraisal, (2) habitual avoidance, and (3) trait avoidance tendency. This heterogeneity in underlying processes presents challenges to the objective measurement of maladaptive avoidance behavior. Here we first review existing paradigms for measuring avoidance behavior and its underlying neural mechanisms in both human and animal models, and identify how existing paradigms relate to these neurobehavioral processes. We then propose a new framework to improve the translational understanding of maladaptive avoidance behavior by adapting paradigms to better differentiate underlying processes and mechanisms and applying these paradigms in clinical populations across diagnoses with the goal of developing novel interventions to engage specific identified neurobehavioral targets.Subject terms: Emotion, Anxiety     

Antiepileptics and the treatment of neuropathic pain: evidence from animal models

Neuropathic pain is characterised by both positive (hyperalgesia and allodynia) and negative (sensory deficits) symptoms and remains intractable to many commonly used analgesics. Antiepileptics are increasingly utilised in the treatment of neuropathic pain. This class of drugs works via three major mechanisms of action in order to dampen neuronal hyperexcitability within the central nervous system: potentiation of GABA transmission, reduction of glutamate-mediated excitatory transmission, and block of voltage-activated ion channels. The latter mechanism of action in particular, is exemplified by the success of the newer generation of antiepileptics such as lamotrigine and gabapentin in the clinical treatment of neuropathic pain symptoms. In the current review article, we will examine in detail, the antinociceptive effects of a diverse range of antiepileptics as tested in animal models of nerve injury. Where appropriate, we will compare these findings with their analgesic efficacy in the clinical treatment of neuropathic pain.     

Cognitive disorders related to immune dysfunction: Novel animal models for drug development

With the recent emphasis on drug development for mental disorders of late life, a need has arisen for animal models useful in preclinical evaluation of potential treatment strategies. Although the animal models now available exhibit behavioral and neurological commonalities with their target clinical syndromes, few models incorporate etiologic similarities. A review of the literature is presented relating immune factors to aging-associated cognitive disorders, and parallels are drawn to immune factors and related behavioral impairments in autoimmune New Zealand black and nonautoimmune C57BL/6 mice. These mouse strains are proposed as potentially useful immunologic models for both theoretical investigation and drug development.     

Peptide immunotherapies in Type 1 diabetes: lessons from animal models

Insulin dependent diabetes mellitus (Type 1 diabetes, T1D) is a chronic autoimmune disorder characterized by the destruction of insulin-producing pancreatic beta cells by proinflammatory autoreactive T cells. In the past, several therapeutic approaches have been exploited by immunologists aiming to regulate the autoimmune response; this can occur by deleting lymphocyte subsets and/or re-establishing immune tolerance via activation of regulatory T cells. The use of broad immunosuppressive drugs was the first approach to be explored. Subsequently, antibody-based immunotherapies failed to discriminate between autoreactive versus non-autoimmune effectors. Antigen-based immunotherapy is a third approach developed to manipulate beta cell autoimmunity. This approach allows the selective targeting of disease-relevant T cells, while leaving the remainder of the immune system intact. Animal models have been successfully employed to prevent or treat T1D by injection of either the self proteins or peptides derived from them. Peptide immunotherapies have been mainly experimented in the NOD mouse spontaneous model of disease. In this review we therefore report the main approaches that rely on the use of peptides obtained from relevant autoantigens such as glutamic acid decarboxylase, isoform 65 (GAD65), insulin, proinsulin and islet-specific glucose 6 phosphatase catalytic subunit-related protein (IGRP). Protective peptides have proven to be effective in treating or delaying the diabetic process. We also highlight the main difficulties encountered in extrapolating data to guide clinical translational investigations in humans.     

Current concepts and animal models of sudden cardiac death for drug development

Sudden cardiac death (SCD) or sudden coronary death, occurring in patients with unstable angina (angina at rest), myocardial ischemia with or without myocardial infarction (MI), and congestive heart failure (CHF), emerges as one of the most important challenges in cardiovascular medicine at present. Of the 1.5 million cases of myocardial infarction that occur each year in the U.S., about 540,000 patients will die and more than 300,000 of these will die before they reach a hospital, mostly due to ventricular fibrillation (VF) and/or SCD. About 4.8 million people alive in the U.S. have a history of myocardial infarction, angina pectoris, or both and are prime candidates for SCD. About 3 million people in the U.S. have congestive heart failure (CHF) and about 400,000 new cases are reported each year. One year mortality due to CHF is 33–58% and about 45% of the deaths are sudden. These patients were not those who had deleterious hemodynamic parameters whose demise could be predicted; they were those that died suddenly and unexpectedly of VF. Current pharmacological intervention in patients with a documented myocardial infarction with marketed antiarrhythmic agents has not reduced the overall mortality of SCD significantly. This suggests that an efficacious antiarrhythmic/antifibrillatory agent for the prevention of SCD does not exist at present and that there is an urgent need for such an agent.     

Modeling heart failure in animal models for novel drug discovery and development

Introduction: When investigating drugs that treat heart diseases, it is critical when choosing an animal model for the said model to produce data that is translatable to the human patient population, while keeping in mind the principles of reduction, refinement, and replacement of the animal model in the research.

Areas covered: In this review, the authors focus on mammalian models developed to study the impact of drug treatments on human heart failure. Furthermore, the authors address human patient variability and animal model invariability as well as the considerations that need to be made regarding choice of species. Finally, the authors discuss some of the most common models for the two most prominent human heart failure etiologies; increased load on the heart and myocardial ischemia.

Expert opinion: In the authors’ opinion, the data generated by drug studies is often heavily impacted by the choice of species and the physiologically relevant conditions under which the data are collected. Approaches that use multiple models and are not restricted to small rodents but involve some verification on larger mammals or on human myocardium, are needed to advance drug discovery for the very large patient population that suffers from heart failure.     

Transgenic animal models of neurodegenerative diseases and their application to treatment development

Neurodegenerative disorders of the aging population affect over 5 million people in the US and Europe alone. The common feature is the progressive accumulation of misfolded proteins with the formation of toxic oligomers. Previous studies show that while in Alzheimer's disease (AD) misfolded amyloid-beta protein accumulates both in the intracellular and extracellular space, in Lewy body disease (LBD), Parkinson's disease (PD), Multiple System Atrophy (MSA), Fronto-Temporal dementia (FTD), prion diseases, amyotrophic lateral sclerosis (ALS) and trinucleotide repeat disorders (TNRD), the aggregated proteins accumulate in the plasma membrane and intracellularly. Protein misfolding and accumulation is the result of an altered balance between protein synthesis, aggregation rate and clearance. Based on these studies, considerable advances have been made in the past years in developing novel experimental models of neurodegenerative disorders. This has been in part driven by the identification of genetic mutations associated with familial forms of these conditions and gene polymorphisms associated with the more common sporadic variants of these diseases. Transgenic and knock out rodents and Drosophila as well as viral vector driven models of Alzheimer's disease (AD), PD, Huntington's disease (HD) and others have been developed, however the focus for this review will be on rodent models of AD, FTD, PD/LBD, and MSA. Promising therapeutic results have been obtained utilizing amyloid precursor protein (APP) transgenic (tg) models of AD to develop therapies including use of inhibitors of the APP-processing enzymes beta- and gamma-secretase as well as vaccine therapies.