Diabetic retinopathy and choroidal angiopathy in diabetic rats (WBN/Kob)

Diabetic retinopathy: a comprehensive update on in vivo, in vitro and ex vivo experimental models

Diabetic retinopathy (DR), one of the leading causes of visual impairment and blindness worldwide, is one of the major microvascular complications in diabetes mellitus (DM). Globally, DR prevalence among DM patients is 25%, and 6% have vision-threatening problems among them. With the higher incidence of DM globally, more DR cases are expected to be seen in the future. In order to comprehend the pathophysiological mechanism of DR in humans and discover potential novel substances for the treatment of DR, investigations are typically conducted using various experimental models. Among the experimental models, in vivo models have contributed significantly to understanding DR pathogenesis. There are several types of in vivo models for DR research, which include chemical-induced, surgical-induced, diet-induced, and genetic models. Similarly, for the in vitro models, there are several cell types that are utilised in DR research, such as retinal endothelial cells, Müller cells, and glial cells. With the advancement of DR research, it is essential to have a comprehensive update on the various experimental models utilised to mimic DR environment. This review provides the update on the in vitro, in vivo, and ex vivo models used in DR research, focusing on their features, advantages, and limitations.

Recent Advances and Perspectives in Relation to the Metabolomics-Based Study of Diabetic Retinopathy

Diabetic retinopathy (DR), a prevalent microvascular complication of diabetes, is a major cause of acquired blindness in adults. Currently, a clinical diagnosis of DR primarily relies on fundus fluorescein angiography, with a limited availability of effective biomarkers. Metabolomics, a discipline dedicated to scrutinizing the response of various metabolites within living organisms, has shown noteworthy advancements in uncovering metabolic disorders and identifying key metabolites associated with DR in recent years. Consequently, this review aims to present the latest advancements in metabolomics techniques and comprehensively discuss the principal metabolic outcomes derived from analyzing blood, vitreous humor, aqueous humor, urine, and fecal samples.

Rodent Models of Diabetic Retinopathy as a Useful Research Tool to Study Neurovascular Cross-Talk

Diabetes is a group of metabolic diseases leading to dysfunction of various organs, including ocular complications such as diabetic retinopathy (DR). Nowadays, DR treatments involve invasive options and are applied at the sight-threatening stages of DR. It is important to investigate noninvasive or pharmacological methods enabling the disease to be controlled at the early stage or to prevent ocular complications. Animal models are useful in DR laboratory practice, and this review is dedicated to them. The first part describes the characteristics of the most commonly used genetic rodent models in DR research. The second part focuses on the main chemically induced models. The authors pay particular attention to the streptozotocin model. Moreover, this section is enriched with practical aspects and contains the current protocols used in research in the last three years. Both parts include suggestions on which aspect of DR can be tested using a given model and the disadvantages of each model. Although animal models show huge variability, they are still an important and irreplaceable research tool. Note that the choice of a research model should be thoroughly considered and dependent on the aspect of the disease to be analyzed.

Animal models of diabetic microvascular complications: Relevance to clinical features

Diabetes has become more common in recent years worldwide, and this growth is projected to continue in the future. The primary concern with diabetes is developing various complications, which significantly contribute to the disease's mortality and morbidity. Over time, the condition progresses from the pre-diabetic to the diabetic stage and then to the development of complications. Years and enormous resources are required to evaluate pharmacological interventions to prevent or delay the progression of disease or complications in humans. Appropriate screening models are required to gain a better understanding of both pathogenesis and potential therapeutic agents. Different species of animals are used to evaluate the pharmacological potentials and study the pathogenesis of the disease. Animal models are essential for research because they represent most of the structural, functional, and biochemical characteristics of human diseases. An ideal screening model should mimic the pathogenesis of the disease with identifiable characteristics. A thorough understanding of animal models is required for the experimental design to select an appropriate model. Each animal model has certain advantages and limitations. The present manuscript describes the animal models and their diagnostic characteristics to evaluate microvascular diabetic complications.

Alterations in choroidal vascular parameters following panretinal photocoagulation using enhanced-depth imaging optical coherence tomography in diabetic retinopathy

PURPOSE

To investigate the alteration of choroid in patients with very severe non-proliferative diabetic retinopathy (NPDR) or early proliferative diabetic retinopathy (PDR) following panretinal photocoagulation (PRP).

METHODS

Thirty-nine eyes of 21 patients with very severe non-proliferative diabetic retinopathy (NPDR) (19 eyes) and early proliferative diabetic retinopathy (PDR) (20 eyes) were recruited. Enhanced-depth imaging optical coherence tomography at baseline, 1, and 6 months after PRP was employed to measure choroidal parameters including total choroidal area (TCA) and choroidal vascular index (CVI).

RESULTS

In eyes with very severe NPDR, subfoveal TCA decreased non-significantly at month 1, which increased significantly at month 6 (539 ± 131µm², 502 ± 134µm², and 598 ± 168µm² at baseline and months 1 and 6, respectively; P = 0.003). Subfoveal CVI increased at month 1 and then decreased at month 6 (68.25 ± 3.05, 69.74 ± 3.62, and 67.84 ± 1.77 at baseline and months 1 and 6, respectively; P < 0.001). A reverse pattern occurred in eyes with early PDR, a non-significant increase in TCA at month 1 followed by a decrease at month 6 (497 ± 95µm², 514 ± 133µm², and 425 ± 95µm² at baseline and months 1 and 6, respectively; P = 0.011). CVI decreased at month 1 and remained relatively stable at month 6 (69.34 ± 3.11, 68.33 ± 3.41, and 68.50 ± 5.04 at baseline, and months 1 and 6, respectively; P = 0.023). Alteration of choroidal thickness was not statistically significant in both groups.

CONCLUSION

Eyes with very severe NPDR and early PDR exhibit a reverse pattern regarding choroidal indices after PRP.

Raman spectroscopy reveals collagen and phospholipids as major components of hyalinosis in the arteriolosclerotic ulcer of Martorell

BACKGROUND

Arteriolosclerotic ulcers of Martorell are histologically characterized by hyaline arteriolosclerosis resulting in concentric occlusion of the arteriolar lumina. Although several authors have previously reported on hyaline changes in hypertensive arteriolopathies, so far, little information is available on the molecular composition of hyaline wall depositions.

OBJECTIVES

This study aimed at the molecular characterization of hyaline arteriolar deposits in patients with hypertensive arteriolopathy using confocal Raman spectroscopy.

METHODS

Samples of patients diagnosed with arteriolosclerotic ulcers of Martorell were analysed using confocal Raman spectroscopy. The findings were correlated with histological analyses. Skin samples from healthy, non-hypertensive patients served as controls.

RESULTS

Confocal Raman spectroscopy analysis revealed that subendothelial hyaline deposits in arteriolosclerotic ulcers are mainly composed of collagen and phospholipids, in particular phosphatidylcholine. The presence of collagen within hyaline deposits was confirmed by Masson's Trichrome and Picrosirius Red staining. Additionally, the presence of collagen could also be shown for hypertensive nephrosclerosis. Actin was markedly decreased in hyalinized compared to control vessels, corresponding to the loss of smooth muscle cells in the process of hyalinization. This was confirmed by immunofluorescence staining for α-smooth muscle actin and desmin.

CONCLUSION

The present findings suggest that arteriolar hyaline deposits in hypertensive arteriolopathy are mainly composed of collagen and phospholipids, in particular phosphatidylcholine. Together with the concurrent absence of actin, these findings suggest that potentially critical disease mechanisms involve pressure-induced vascular smooth muscle cell apoptosis with subsequent deposition of collagen.

Animal Models of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is one of the most common complications associated with chronic hyperglycemia seen in patients with diabetes mellitus. While many facets of DR are still not fully understood, animal studies have contributed significantly to understanding the etiology and progression of human DR. This review provides a comprehensive discussion of the induced and genetic DR models in different species and the advantages and disadvantages of each model.

RECENT FINDINGS

Rodents are the most commonly used models, though dogs develop the most similar morphological retinal lesions as those seen in humans, and pigs and zebrafish have similar vasculature and retinal structures to humans. Nonhuman primates can also develop diabetes mellitus spontaneously or have focal lesions induced to simulate retinal neovascular disease observed in individuals with DR. DR results in vascular changes and dysfunction of the neural, glial, and pancreatic β cells. Currently, no model completely recapitulates the full pathophysiology of neuronal and vascular changes that occur at each stage of diabetic retinopathy; however, each model recapitulates many of the disease phenotypes.

Proliferative retinopathy and neovascularization of the anterior segment in female type 2 diabetic rats

BACKGROUND

To examine the presence of diabetic retinopathy in a female rat model of type 2 diabetes fed on a high-fat diet (HFD).

METHODS

Wistar rats were injected with streptozotocin (STZ) at the age of two days and fed on an HFD from eight weeks onwards. Five diabetic animals were euthanized at 110 weeks of disease, together with a control group of age-matched, non-diabetic animals. A group of diabetic animals at 57 weeks of disease was included for comparison. Cross sections of the rats' corneas, iris and retinas were histologically examined and analysed by immunohistochemistry and immunofluorescence, using glial-fibrillary-acidic-protein (GFAP), the vascular endothelial growth factor (VEGF) and the Von Willebrand factor (vWF). The trypsine digestive technique was used for the pericytes count.

RESULTS

Neovascularization was only found in the retinas, irises and corneas of the diabetic animals of 110 weeks of disease. There was also a significantly lower number of pericytes in these animals than in the controls.

CONCLUSION

The female rat model of type 2 diabetes fed on an HFD may prove useful in evaluating the mechanisms involved in diabetic retinopathy, together with strategies to reduce its severity.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Update on animal models of diabetic retinopathy: from molecular approaches to mice and higher mammals

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the major causes of blindness worldwide. The pathogenesis of DR has been investigated using several animal models of diabetes. These models have been generated by pharmacological induction, feeding a galactose diet, and spontaneously by selective inbreeding or genetic modification. Among the available animal models, rodents have been studied most extensively owing to their short generation time and the inherited hyperglycemia and/or obesity that affect certain strains. In particular, mice have proven useful for studying DR and evaluating novel therapies because of their amenability to genetic manipulation. Mouse models suitable for replicating the early, non-proliferative stages of the retinopathy have been characterized, but no animal model has yet been found to demonstrate all of the vascular and neural complications that are associated with the advanced, proliferative stages of DR that occur in humans. In this review, we summarize commonly used animal models of DR, and briefly outline the in vivo imaging techniques used for characterization of DR in these models. Through highlighting the ocular pathological findings, clinical implications, advantages and disadvantages of these models, we provide essential information for planning experimental studies of DR that will lead to new strategies for its prevention and treatment.

Animal models of diabetic retinopathy: summary and comparison

Diabetic retinopathy (DR) is a microvascular complication associated with chronic exposure to hyperglycemia and is a major cause of blindness worldwide. Although clinical assessment and retinal autopsy of diabetic patients provide information on the features and progression of DR, its underlying pathophysiological mechanism cannot be deduced. In order to have a better understanding of the development of DR at the molecular and cellular levels, a variety of animal models have been developed. They include pharmacological induction of hyperglycemia and spontaneous diabetic rodents as well as models of angiogenesis without diabetes (to compensate for the absence of proliferative DR symptoms). In this review, we summarize the existing protocols to induce diabetes using STZ. We also describe and compare the pathological presentations, in both morphological and functional aspects, of the currently available DR animal models. The advantages and disadvantages of using different animals, ranging from zebrafish, rodents to other higher-order mammals, are also discussed. Until now, there is no single model that displays all the clinical features of DR as seen in human. Yet, with the understanding of the pathological findings in these animal models, researchers can select the most suitable models for mechanistic studies or drug screening.