Current Medicinal Chemistry - Volume 20, Issue 26, 2013

Diabetic retinopathy affects one-third of people with diabetes and is the most frequent cause of blindness in working aged adults. Although diabetic retinopathy blindness appears to have fallen in the developed world, the rapidly increasing number of persons with diabetes worldwide has resulted in a continuous increase in the global burden of this disease. The major risk factors for diabetic retinopathy include duration of diabetes, hyperglycemia, and hypertension, but this is accountable for only a small amount of the variation in the risk of diabetic retinopathy. Research into new markers for retinopathy including genetics, blood biomarkers and retinal imaging will further improve our understanding of the risk factors and pathogenesis of diabetic retinopathy.

Although it has become acceptable that neuroretinal cells are also affected in diabetes, vascular lesions continue to be considered as the hallmarks of diabetic retinopathy. Animal models are essential for the understanding and treatment of human diabetic retinopathy, and the mouse is intensively used as a model because of its similarity to human and the possibility to be genetically modified. However, until today not all retinal vascular lesions developed in diabetic patients have been reproduced in diabetic mice, and the reasons for this are not completely understood. In this review, we will summarize retinal vascular lesions found in diabetic and diabetic-like mouse models and its comparison to human lesions. The goal is to provide insights to better understand human and mice differences and thus, to facilitate the development of new mouse models that mimic better human diabetic retinopathy.

The onset of diabetic retinopathy is characterized by morphologic alterations of the microvessels, with thickening of the basement membrane, loss of inter-endothelial tight junctions and early and selective loss of pericytes, together with increased vascular permeability, capillary occlusions, microaneurysms and, later, loss of endothelial cells (EC). A key role in the evolution of the disease is played by pericytes, specialized contractile mesenchymal cells of mesodermal origin, that, in capillaries, exert a function similar to smooth muscle cells in larger vessels, regulating vascular tone and perfusion pressure. Thickening of the basement membrane, together with systemic and local hypertension, hyperglycaemia, advanced glycation end-product formation and hypoxia, may disrupt the tight link between pericytes and EC causing pericyte apoptosis, while endothelium, deprived of proliferation control, can give rise to new vessels. Pericyte dropout has great consequences on capillary remodelling and may cause the first abnormalities of the diabetic eye which can be observed clinically. Hyperglycaemia and local hypertension are known to be a direct cause of pericyte apoptosis and dropout, and intracellular biochemical pathways of the glucose metabolites have been explored. However, the exact mechanisms are not yet fully understood and need further clarification in order to develop new effective drugs for the prevention of retinopathy.

Diabetic retinopathy is the leading cause of blindness in young adults, and with the incidence of diabetes increasing at a frightening rate, retinopathy is estimated to threaten vision for almost 51 million patients worldwide. In diabetes, mitochondria structure, function and DNA (mtDNA) are damaged in the retina and its vasculature, and the mtDNA repair machinery and biogenesis are compromised. Proteins encoded by mtDNA become subnormal contributing to dysfunctional electron transport system, and the transport of proteins that are important in mtDNA biogenesis and function, but are encoded by nuclear DNA, is impaired. These diabetes-induced abnormalities in mitochondria continue even when hyperglycemic insult is terminated, and are implicated in the metabolic memory phenomenon associated with the continued progression of diabetic retinopathy. Diabetes also facilitates epigenetic modifications-the changes in histones and DNA methylation in response to cells changing environmental stimuli, which the cell can memorize and pass to the next generation. Epigenetic modifications contribute to the mitochondria damage, and are postulated in the development of diabetic retinopathy, and also to the metabolic memory phenomenon. Thus, strategies targeting mitochondria homeostasis and/or enzymes important for histone and DNA methylation could serve as potential therapies to halt the development and progression of diabetic retinopathy.

Diabetic retinopathy (DR) has a complex pathogenesis which is impacted by a raft of systemic abnormalities and tissue-specific alterations occurring in response to the diabetes milieu. Many pathogenic processes play key roles in retinal damage in diabetic patients. One such pathway is the formation and accumulation of advanced glycation endproducts (AGEs) and advanced lipoxidation end products (ALEs) which are relevant modifications with roles in the initiation and progression of pathology. In this review, AGE/ALE formation in the diabetic retina is discussed alongside their impact on retinal cell function. In addition, various inhibitors of the AGE-RAGE system and their therapeutic utility for DR will also be evaluated.

Diabetic retinopathy (DR), commonly classified as a microvascular complication of diabetes, is now recognized as a neurovascular complication or sensory neuropathy resulting from disruption of the neurovascular unit. Current therapies for DR target the vascular complication of the disease process, including neovascularization and diabetic macular edema. Since neurodegeneration is an early event in the pathogenesis of DR, it will be important to unravel the mechanisms that contribute to neuroretinal cell death in order to develop novel treatments for the early stages of DR. In this review we comment on how inflammation, the metabolic derangements associated with diabetes, loss of neuroprotective factors, and dysregulated glutamate metabolism may contribute to retinal neurodegeneration during diabetes. Promising potential therapies based on these specific aspects of DR pathophysiology are also discussed. Finally, we stress the importance of developing and validating new markers of visual function that can be used to shorten the duration of clinical trials and accelerate the delivery of novel treatments for DR to the public.

Diabetic retinopathy (DR) has been classically considered to be a microcirculatory disease of the retina. However, there is growing evidence to suggest that retinal neurodegeneration is an early event in the pathogenesis of DR which participates in the microcirculatory abnormalities that occur in DR. Among the neuroprotective factors synthesized by the retina, somatostatin (SST) is one of the most relevant. In DR there is a downregulation of retinal expression of SST that is associated with retinal neurodegeneration. There is growing evidence suggesting that SST could play a key role in the main pathogenic mechanisms involved in the development of DR (neurodegeneration, neovascularization and vascular leackage). Recently, first evidence that the topical administration of SST prevents retinal neurodegeneration in streptozotozin- induced diabetic rats has been reported. Indeed, SST eye drops prevented b-wave abnormalities in the ERG which are considered sensitive indicators of DR. In addition, SST eye drops prevented, glial activation, apoptosis and the misbalance between proapoptotic and survival signalling caused by diabetes. Furthermore, SST eye drops reduce glutamate- induced excitotoxicity. Therefore, topical administration of SST could be contemplated as an appropriate therapeutic approach for DR. However, clinical trials will be needed to establish its exact position in the treatment of this devastating complication of diabetes. Diabetic retinopathy (DR) has been classically considered to be a microcirculatory disease of the retina. However, there is growing evidence to suggest that retinal neurodegeneration is an early event in the pathogenesis of DR which participates in the microcirculatory abnormalities that occur in DR [1]. The retina synthesizes neuroprotective factors which counteract the deleterious effects of neurotoxic factors involved in neurodegeneration. The loss of these neuroprotective factors or the reduction of their effectiveness is essential for the development of retinal neurodegeneration. Among the neuroprotective and neurotrophic factors somatostatin (SST) is one of the most relevant. The main aim of the present review is to provide experimental evidence supporting the promising therapeutical use of SST to prevent or arrest DR.

Despite improving standards of care, people with diabetes remain at risk of development and progression of diabetic retinopathy (DR) and visual impairment. Identifying novel therapeutic approaches, preferably targeting more than one pathogenic pathway in DR, and at an earlier stage of disease, is attractive. There is now consistent evidence from two major trials, the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study and the Action to Control Cardiovascular Risk in Diabetes Eye (ACCORD-Eye) study, totalling 11,388 people with type 2 diabetes (5,701 treated with fenofibrate) that fenofibrate reduces the risk of development and progression of DR. Therefore, fenofibrate may be considered a preventive strategy for patients without DR or early intervention strategy for those with mild DR. A number of putative therapeutic mechanisms for fenofibrate, both dependent and independent of lipids, have been proposed. A deeper understanding of the mode of action of fenofibrate will further help to define how best to use fenofibrate clinically as an adjunct to current management of DR.

Purpose: To review the most important metabolic effects and clinical safety data of subthreshold micropulse diode laser (D-MPL) in diabetic macular edema (DME). Methods: Review of the literature about the mechanisms of action and role of D-MPL in DME. Results: The MPL treatment does not damage the retina and is selectively absorbed by the retinal pigment epithelium (RPE). MPL stimulates secretion of different protective cytokines by the RPE. No visible laser spots on the retina were noted on any fundus image modality in different studies, and there were no changes of the outer retina integrity. Mean central retinal sensitivity (RS) increased in subthreshold micropulse diode laser group compared to standard ETDRS photocoagulation group. Conclusions: MPL is a new, promising treatment option in DME, with both infrared and yellow wavelengths using the less aggressive duty cycle (5%) and fixed power parameters. It appears to be safe from morphologic and functional point of view in mild center involving DME.

To study novel treatments for high grade gliomas (WHO grade III and IV) we need animal models of those disorders. Orthotopic tumors in mouse or rats seem at present the most reliable in vivo glioma model in order to develop specific therapies. The orthotopic tumor characteristics should yet closely mimic the human glioma features (in particular infiltrating growth and neovascularization). In this regard, glioma cell lines with stem properties (glioma stem cells – GSC) may fulfill at best those needs. Orthotopic gliomas developed from some widely used, established non-stem cell lines showing poor infiltrating capacity are not suitable. Therapeutic and diagnostic procedures recently developed using orthotopic rodent glioma tumors along their potentialities and pitfalls are analyzed.

Migraine is one of the most frequent neurological disorder with high impact on the quality of life. Primary headaches such as migraine are pathophysiologically complex disorders. The concept of the trigeminovascular system dysfunction in migraine has led to a number of drug discoveries dramatically changing the treatment options. Acute and prophylactic therapy targeting either the trigeminovascular system or central structures involve several groups of drugs with peculiar medicinal chemistry. In the proposed review up to date concept of treatment strategy, medicinal chemistry data of the drugs used will be summarized. The present review gives detailed information on drugs effective in aborting migraine attacks (by inhibiting prostanoid synthesis, are agonists of serotonin 5-HT1B/D receptors, on the recently introduced CGRP-receptor antagonists) and the drugs recommended for prophylactic treatment (selected beta-adrenergic receptor antagonists, Ca-channel inhibitors, antiepileptics, antidepressants). The pharmacokinetics, fate in the body (absorption, distribution, metabolism, excretion) and significant pharmacological effects as well as the recent bioanalytical methods for their determination are presented.