Protein kinase C beta inhibitor prevents diabetic peripheral neuropathy, but not histopathological abnormalities of retina in Spontaneously Diabetic Torii rat

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.

Electron Donor-Acceptor Complex Induced Fused Indoles with Hypervalent Iodine(III) Reagents

An operationally simple and efficient method for the cyclization of tertiary amines and hypervalent iodine reagents enabled by an EDA complex has been developed. A series of [1,2-α]indoles derivatives were obtained in good yields, including some key intermediates for the synthesis of biologically active molecules. In addition, this established strategy features a broad substrate scope and good functional group tolerance.

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.

An insight on established retinal injury mechanisms and prevalent retinal stem cell activation pathways in vertebrate models

Implementing different tools and injury mechanisms in multiple animal models of retina regeneration, researchers have discovered the existence of retinal stem/progenitor cells. Although they appear to be distributed uniformly across the vertebrate lineage, the reparative potential of the retina is mainly restricted to lower vertebrates. Regenerative repair post-injury requires the creation of a proliferative niche, vital for proper stem cell activation, propagation, and lineage differentiation. This seems to be lacking in mammals. Hence, in this review, we first discuss the many forms of retinal injuries that have been generated using animal models. Next, we discuss how they are utilized to stimulate regeneration and mimic eye disease pathologies. The key to driving stem cell activation in mammals relies on the information we can gather from these models. Lastly, we present a brief update about the genes, growth factors, and signaling pathways that have been brought to light using these models.

Animal models of diabetic retinopathy

The retina is the posterior neuro-integrated layer of the eye that conducts impulses induced by light to the optic nerve for human vision. Diseases of the retina often leads to diminished vision and in some cases blindness. Diabetes mellitus (DM) is a worldwide public health issue and globally, there is an estimated 463 million people that are affected by DM and its consequences. Diabetic retinopathy (DR) is a blinding complication of chronic uncontrolled DM and is the most common cause of blindness in the United States between the ages 24-75. It is estimated that the global prevalence of DR will increase to 191.0 million by 2030, of those 56.3 million possessing vision-threatening diabetic retinopathy (VTDR). For the most part, current treatment modalities control the complications of DR without addressing the underlying pathophysiology of the disease. Therefore, there is an unmet need for new therapeutics that not only repair the damaged retinal tissue, but also reverse the course of DR. The key element in developing these treatments is expanding our basic knowledge by studying DR pathogenesis in animal models of proliferative and non-proliferative DR (PDR and NPDR). There are numerous models available for the research of both PDR and NPDR with substantial overlap. Animal models available include those with genetic backgrounds prone to hyperglycemic states, immunologic etiologies, or environmentally induced disease. In this review we aimed to comprehensively summarize the available animal models for DR while also providing insight to each model's ocular therapeutic potential for drug discovery.

Tandem Carbenoid C-H Functionalization/Conia-ene Cyclization of N-Propargyl Indoles Generates Pyrroloindoles under Cooperative Rh(II)/Zn(II) Catalysis

The decomposition of diazodicarbonyl compounds in the presence of various metal catalysts has become a reliable method for the functionalization of indoles via carbenoid intermediates. Exploiting the nucleophilic reactivity of the in situ generated malonic ester product formed, we herein report a tandem C-H functionalization/Conia-ene cyclization of N-alkyne tethered indoles. This double functionalization of diazodicarbonyls generates a range of pyrrolo[1,2-a]-, pyrido[1,2-a]-, and azepino[1,2-a]indole products with good synthetic efficiency.

Visible light photocatalytic asymmetric synthesis of pyrrolo[1,2-a]indoles via intermolecular [3+2] cycloaddition

The asymmetric synthesis of pyrrolo[1,2-a]indoles is developed through a [3+2] cycloaddition between silyl-indole derivatives and α,β-unsaturated N-acyl oxazolidinones by merging photocatalysis and Lewis acid catalysis.

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.

Relationship between Immunological Abnormalities in Rat Models of Diabetes Mellitus and the Amplification Circuits for Diabetes

A better understanding of pathogenic mechanisms is required in order to treat diseases. However, the mechanisms of diabetes mellitus and diabetic complications are extremely complex. Immune reactions are involved in the pathogenesis of diabetes and its complications, while diabetes influences immune reactions. Furthermore, both diabetes and immune reactions are influenced by genetic and environmental factors. To address these issues, animal models are useful tools. So far, various animal models of diabetes have been developed in rats, which have advantages over mice models in terms of the larger volume of tissue samples and the variety of type 2 diabetes models. In this review, we introduce rat models of diabetes and summarize the immune reactions in diabetic rat models. Finally, we speculate on the relationship between immune reactions and diabetic episodes. For example, diabetes-prone Biobreeding rats, type 1 diabetes model rats, exhibit increased autoreactive cellular and inflammatory immune reactions, while Goto-Kakizaki rats, type 2 diabetes model rats, exhibit increased Th2 reactions and attenuation of phagocytic activity. Investigation of immunological abnormalities in various diabetic rat models is useful for elucidating complicated mechanisms in the pathophysiology of diabetes. Studying immunological alterations, such as predominance of Th1/17 or Th2 cells, humoral immunity, and innate immune reactions, may improve understanding the structure of amplification circuits for diabetes in future studies.

Contribution of hyperglycemia on diabetic complications in obese type 2 diabetic SDT fatty rats: effects of SGLT inhibitor phlorizin

The spontaneously diabetic torii (SDT) fatty rat is a new model of type 2 diabetes showing overt obesity, hyperglycemia and hyperlipidemia. With early onset of diabetes mellitus, diabetic microvascular complications, including nephropathy, peripheral neuropathy and retinopathy, are observed at young ages. In the present study, blood glucose levels of female SDT fatty rats were controlled with phlorizin, a non-selective SGLT inhibitor, to examine whether and how these complications are caused by hyperglycemia. Phlorizin treatment adequately controlled plasma glucose levels during the experiment. At 29 weeks of age, urinary albumin excretion considerably increased in SDT fatty rats. Glomerulosclerosis and tubular pathological findings also indicate diabetic nephropathy. These renal parameters tended to decrease with phlorizin; however, effects were partial. Sciatic nerve conduction velocities were significantly delayed in SDT fatty rats compared with Sprague-Dawley (SD) rats. Intraepidermal nerve fiber density, an indicator of subclinical small nerve fiber neuropathy, significantly decreased in SDT fatty rats. Retinal dysfunction (prolongation of peak latency for oscillatory potential in electroretinograms) and histopathological eye abnormalities, including retinal folding and mature cataracts were also observed. Both nerve and eye disorders were prevented with phlorizin. These findings indicate that severe hyperglycemia mainly causes diabetic complications in SDT fatty rats. However, other factors, such as hyperlipidemia and hypertension, may affect diabetic nephropathy. These characteristics of diabetic complications will become helpful in evaluating new drugs for diabetic complications using SDT fatty rats.

Neuropeptides, trophic factors, and other substances providing morphofunctional and metabolic protection in experimental models of diabetic retinopathy

Vision is the most important sensory modality for many species, including humans. Damage to the retina results in vision loss or even blindness. One of the most serious complications of diabetes, a disease that has seen a worldwide increase in prevalence, is diabetic retinopathy. This condition stems from consequences of pathological metabolism and develops in 75% of patients with type 1 and 50% with type 2 diabetes. The development of novel protective drugs is essential. In this review we provide a description of the disease and conclude that type 1 diabetes and type 2 diabetes lead to the same retinopathy. We evaluate existing experimental models and recent developments in finding effective compounds against this disorder. In our opinion, the best models are the long-term streptozotocin-induced diabetes and Otsuka Long-Evans Tokushima Fatty and spontaneously diabetic Torii rats, while the most promising substances are topically administered somatostatin and pigment epithelium-derived factor analogs, antivasculogenic substances, and systemic antioxidants. Future drug development should focus on these.

[Immunological disorders of diabetes mellitus in experimental rat models]

A comprehensive understanding of the pathogenic mechanism is the prerequisite for proper disease management. However, the mechanisms of diabetes mellitus and diabetic complication remain extremely complicated and unresolved. While immune reactions are involved in the pathogenesis of diabetes and diabetic complication, the diabetic condition itself can influence immune responses. Furthermore, both diabetes and immune reactions are regulated by genetic and environmental factors. As a result, animal models have evolved to be powerful research tools to elucidate the complicated mechanisms for the pathogenesis of diabetes. Recently, various animal models of diabetes have been developed in rats, which provide advantages over mouse models in the scale of tissue samples and variation in type 2 diabetes models. In this review, we introduced rat models of diabetes and summarized the immune reactions in diabetic rats to propose the relationship between immune reactions and diabetes. Type 1 diabetes is induced by self-reactive cellular immune reactions. On the other hand, type 2 diabetes in rat models is associated with augmentation of innate immune reactions and increased humoral immunity. For example, helper T (Th) 1/Th17 cells are prevalent in non-obese type 1 diabetes rats (diabetes-prone BioBreeding rats), while non-obese type 2 diabetes rats (Goto-Kakizaki rat) show higher levels of natural IgM and T cell ratios with elevated Th2 cells compared with Wister rats. The investigation of immunological disorders in various diabetic rat models is useful to elucidate complicated mechanisms for the pathophysiology of diabetes. In future studies, immunological experimentations altering Th1/Th17 or Th2 cell levels and natural immune reactions may lend support to understanding the causes of diabetes and predicting the pathological conditions in diabetes.

Spontaneous type 2 diabetic rodent models

Diabetes mellitus, especially type 2 diabetes (T2DM), is one of the most common chronic diseases and continues to increase in numbers with large proportion of health care budget being used. Many animal models have been established in order to investigate the mechanisms and pathophysiologic progress of T2DM and find effective treatments for its complications. On the basis of their strains, features, advantages, and disadvantages, various types of animal models of T2DM can be divided into spontaneously diabetic models, artificially induced diabetic models, and transgenic/knockout diabetic models. Among these models, the spontaneous rodent models are used more frequently because many of them can closely describe the characteristic features of T2DM, especially obesity and insulin resistance. In this paper, we aim to investigate the current available spontaneous rodent models for T2DM with regard to their characteristic features, advantages, and disadvantages, and especially to describe appropriate selection and usefulness of different spontaneous rodent models in testing of various new antidiabetic drugs for the treatment of type 2 diabetes.

Metabolic Disorders and Diabetic Complications in Spontaneously Diabetic Torii Lepr (fa) Rat: A New Obese Type 2 Diabetic Model

Spontaneously Diabetic Torii Lepr (fa) (SDT fatty) rat, established by introducing the fa allele of the Zucker fatty rat into SDT rat genome, is a new model of obese type 2 diabetes. Both male and female SDT fatty rats show overt obesity, and hyperglycemia and hyperlipidemia are observed at a young age as compared with SDT rats. With early incidence of diabetes mellitus, diabetic complications, such as nephropathy, retinopathy, and neuropathy, in SDT fatty rats were seen at younger ages compared to those in the SDT rats. In this paper, we overview pathophysiological features in SDT fatty rats and also describe new insights regarding the hematology, blood pressure, renal complications, and sexual dysfunction. The SDT fatty rats showed an increase of leukocytes, especially the monocyte count, prominent hypertension associated with salt drinking, end-stage renal disease with aging, and hypogonadism. Unlike other diabetic models, the characteristic of SDT fatty rat is to present an incidence of diabetes in females, hypertension, and retinopathy. SDT fatty rat is a useful model for analysis of various metabolic disorders and the evaluation of drugs related to metabolic disease.

The spontaneously diabetic torii rat: an animal model of nonobese type 2 diabetes with severe diabetic complications

The Spontaneously Diabetic Torii (SDT) rat is an inbred strain of Sprague-Dawley rat and recently is established as a nonobese model of type 2 diabetes (T2D). Male SDT rats show high plasma glucose levels (over 700 mg/dL) by 20 weeks. Male SDT rats show pancreatic islet histopathology, including hemorrhage in pancreatic islets and inflammatory cell infiltration with fibroblasts. Prior to the onset of diabetes, glucose intolerance with hypoinsulinemia is also observed. As a result of chronic severe hyperglycemia, the SDT rats develop profound complications. In eyes, retinopathy, cataract, and neovascular glaucoma are observed. Proliferative retinopathy, especially, resulting from retinal neovascular vessels is a unique characteristic of this model. In kidney, mesangial proliferation and nodular lesion are observed. Both peripheral neuropathy such as decreased nerve conduction velocity and thermal hypoalgesia and autonomic neuropathy such as diabetic diarrhea and voiding dysfunction have been reported. Osteoporosis is another complication characterized in SDT rat. Decreased bone density and low-turnover bone lesions are observed. Taking advantage of these features, SDT rat has been used for evaluating antidiabetic drugs and drugs/gene therapy for diabetic complications. In conclusion, the SDT rat is potentially a useful T2D model for studies on pathogenesis and treatment of diabetic complications in humans.

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.

Diabetic peripheral neuropathy in Spontaneously Diabetic Torii-Lepr(fa) (SDT fatty) rats

Spontaneously Diabetic Torii (SDT) rat is a hereditary model of diabetes. Although the SDT rat shows severe diabetic complications, the onset of hyperglycemia is late. SDT fatty rat, established by introducing the fa allele of the Zucker fatty rat to SDT rat, develops diabetes much faster than SDT rat. In the present study, diabetic peripheral neuropathy (DPN) was evaluated to show the further usefulness of this animal model. Motor nerve conduction velocity (MNCV) was delayed, and the number of sural nerve fibers was decreased in SDT fatty rat. Treatment of pioglitazone lowered blood glucose level and prevented delay of MNCV in SDT fatty rats. SDT fatty rat is a useful animal model for studies of DPN in type 2 diabetes.

Pathophysiological characteristics of diabetic ocular complications in spontaneously diabetic torii rat

The Spontaneously Diabetic Torii (SDT) rat, a nonobese type 2 diabetes model, develops severe diabetic retinopathy as result of chronic severe hyperglycemia. Although existing diabetes animal models also develop ocular complications, severe retinal lesions frequently observed in human diabetes patients such as preretinal neovascularization or retinal detachment are not found. Distinctive features in SDT rat are hypermature cataract, tractional retinal detachment with fibrous proliferation, and massive hemorrhaging in the anterior chamber. These pathophysiological changes are caused by sustained hyperglycemic condition and subsequent increased expression of vascular endothelial growth factor (VEGF) in retina, iris, and ciliary body. Although some differences in diabetic retinopathy exist between SDT rats and humans (e.g., a low incidence of neovascular formation and poor development of nonperfused area are found in this animal), SDT rat will be a useful model in studies of the pathogenesis and treatment of diabetic retinopathy.