Electroretinogram in sucrose-fed diabetic rats treated with an aldose reductase inhibitor or an anticoagulant

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.

Neurodegeneration in diabetic retinopathy: Potential for novel therapies

The complex pathology of diabetic retinopathy (DR) affects both vascular and neural tissue. The characteristics of neurodegeneration are well-described in animal models but have more recently been confirmed in the clinical setting, mostly by using non-invasive imaging approaches such as spectral domain optical coherence tomography (SD-OCT). The most frequent observations report loss of tissue in the nerve fiber layer and inner plexiform layer, confirming earlier findings from animal models. In several cases the reduction in inner retinal layers is reported in patients with little evidence of vascular lesions or macular edema, suggesting that degenerative loss of neural tissue in the inner retina can occur after relatively short durations of diabetes. Animal studies also suggest that neurodegeneration leading to retinal thinning is not limited to cell death and tissue loss but also includes changes in neuronal morphology, reduced synaptic protein expression and alterations in neurotransmission, including changes in expression of neurotransmitter receptors as well as neurotransmitter release, reuptake and metabolism. The concept of neurodegeneration as an early component of DR introduces the possibility to explore alternative therapies to prevent the onset of vision loss, including neuroprotective therapies and drugs targeting individual neurotransmitter systems, as well as more general neuroprotective approaches to preserve the integrity of the neural retina. In this review we consider some of the evidence for progressive retinal neurodegeneration in diabetes, and explore potential neuroprotective therapies.

Effect of cilostazol on the p50 of the oxygen-hemoglobin dissociation curve

Cilostazol is a drug used for the treatment of intermittent claudication caused by narrowing of the blood vessels and reduced oxygen supply, characterized by intense pain in the leg when walking. This study was designed to investigate the effect of cilostazol on the P50 of the oxygen hemoglobin dissociation curve. A total of eight healthy adult subjects were studied. Blood samples (0.5 mL) from each subject were mixed with 5, 10, and 20 μL of the 0.5 mg/mL stock solution of cilostazol to give concentrations of 10, 20, and 40 µg/mL equivalent to adult doses of 50, 100, and 200 mg, respectively. The control sample had no drug added. The oxygen hemoglobin dissociation curve of each sample was plotted and the P50 determined with a Hemox-Analyzer (TCS, Medical Products Division, Southampton, PA). The mean P50 for the control samples was 28.27 ± 0.43 mm Hg. The values of the samples exposed to 10, 20, and 40 µg/mL cilostozol were 29.63 ± 0.66, 30.15 ± 0.77, and 31.66 ± 0.62 mm Hg, respectively. There was a statistically significant difference (p < 0.01) between the control and samples exposed to 40 µg/mL cilostazol. This study suggests that cilostazol caused an increase in the release of oxygen from hemoglobin as shown in the P50 values. This effect was significant at the highest concentration of 40 µg/mL.

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.

Effect of anti-oxidants, Ricetrienol and α-tocopherol, on adipocytokine abnormalities and fatty liver in Otsuka Long-Evans Tokushima Fatty diabetic rats

Introduction:  We investigated the effect of Ricetrienol, which is an anti‐oxidant extracted from rice bran, and α‐tocopherol on the adipocytokine abnormalities and fatty liver in Otsuka Long‐Evans Tokushima Fatty (OLETF) rats.

Materials and Methods:  A total of 18 OLETF rats were bred using a 30% sucrose solution (the diabetic group; DM), whereas another 18 OLETF rats were bred using ordinary water (the non‐diabetic obese group; OB) as drinking water, respectively. After the sucrose‐fed rats developed diabetes, all of the rats from the diabetic and obese groups were randomly divided into three groups. Then each group was fed either standard chow (DM‐S, OB‐S group), 0.05% Ricetrienol‐containing chow (DM‐R, OB‐R group) or 0.05%α‐tocopherol‐containing chow (DM‐A, OB‐A group), respectively. After 12 weeks of feeding, all the rats were killed. Plasma insulin, adiponectin, resistin and leptin were assayed by enzyme immunoassay. Histopathological findings of liver tissue were scored according to Brunt and Kleiner’s method, and triglyceride contents of the liver tissue were investigated.

Results:  Plasma adiponectin was significantly reduced in DM‐S compared with OB‐S, but it had significantly increased in DM‐R and DM‐A as opposed to DM‐S. Plasma resistin showed a significant increase in DM‐S compared with OB‐S, but it was significantly reduced in DM‐A than in DM‐S. Though the triglyceride contents of liver tissue significantly increased in DM‐S as opposed to OB‐S, they were significantly reduced in DM‐R compared with DM‐S. Histopathological scores were significantly higher in DM‐S than OB‐S.

Conclusions:  The present study shows that Ricetrienol might prevent adipocytokine abnormalities and fatty liver in OLETF diabetic rats. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00090.x, 2011)

Potencial terapêutico para a prevenção e tratamento da nefropatia e neuropatia diabéticas: evidências do uso do cilostazol

O cilostazol é um inibidor seletivo da fosfodiesterase tipo III com ação vasodilatadora, antiagregante plaquetária e antitrombótica. É considerada a droga de primeira escolha na claudicação intermitente devido à doença arterial obstrutiva periférica. Vários estudos demonstraram melhora significativa na distância percorrida na caminhada sem dor e na qualidade de vida, sem aumentar o risco de sangramento. Essas ações também foram verificadas em pacientes diabéticos, pois o cilostazol não afeta o metabolismo da glicose. Estudos, principalmente experimentais, têm mostrado resultados satisfatórios na melhora do fluxo sangüíneo neural, na atividade da bomba de sódio e potássio, na resistência à insulina e na microalbuminúria. Neste artigo, apresentamos uma revisão do uso do cilostazol na prevenção e no tratamento das complicações do diabetes mellitus, como nefropatia e neuropatia. Ressalta-se a necessidade do controle adequado dos níveis glicêmicos, da hipertensão arterial sistêmica e do tabagismo. Um maior número de estudos clínicos é necessário para melhor compreensão desses efeitos benéficos.