Involvement of angiotensin II-dependent vascular endothelial growth factor gene expression via NADPH oxidase in the retina in a type 2 diabetic rat model

Effects of Angiotensin Receptor Blockers on Streptozotocin-Induced Diabetic Cataracts

This study aimed to determine the role of oxidative stress produced by the renin-angiotensin system (RAS) in cataract formation in streptozotocin-induced diabetic rats (STZ) using angiotensin II receptor blockers (ARBs). Rats were treated with streptozotocin and orally administered candesartan (2.5 mg/kg/day) or a normal diet for 10 weeks until sacrifice. Cataract progression was assessed through a slit-lamp examination. Animals were euthanized at 18 weeks, and the degree of cataract progression was evaluated. Oxidative stress was also assessed. In STZ-treated rats, lens opacity occurred at 12 weeks. Cataract progression was inhibited in the ARB-treated group compared with the placebo group (p < 0.05). STZ-treated rats exhibited upregulated angiotensin-converting enzyme (ACE) gene expression than control rats. Oxidative stress-related factors were upregulated in the placebo-treated group but suppressed in the ARB-treated group. A correlation coefficient test revealed a positive correlation between ACE gene expression and oxidative stress-related factors and a negative correlation between ACE and superoxide dismutase. Immunostaining revealed oxidative stress-related factors and advanced glycation end products in the lens cortex of the placebo-treated group. The mechanism of diabetic cataracts may be related to RAS, and the increase in focal ACE and angiotensin II in the lens promotes oxidative stress-related factor production.

Brain Renin-Angiotensin System at the Intersect of Physical and Cognitive Frailty

The renin–angiotensin system (RAS) was initially considered to be part of the endocrine system regulating water and electrolyte balance, systemic vascular resistance, blood pressure, and cardiovascular homeostasis. It was later discovered that intracrine and local forms of RAS exist in the brain apart from the endocrine RAS. This brain-specific RAS plays essential roles in brain homeostasis by acting mainly through four angiotensin receptor subtypes; AT₁R, AT₂R, MasR, and AT₄R. These receptors have opposing effects; AT₁R promotes vasoconstriction, proliferation, inflammation, and oxidative stress while AT₂R and MasR counteract the effects of AT₁R. AT₄R is critical for dopamine and acetylcholine release and mediates learning and memory consolidation. Consequently, aging-associated dysregulation of the angiotensin receptor subtypes may lead to adverse clinical outcomes such as Alzheimer’s disease and frailty via excessive oxidative stress, neuroinflammation, endothelial dysfunction, microglial polarization, and alterations in neurotransmitter secretion. In this article, we review the brain RAS from this standpoint. After discussing the functions of individual brain RAS components and their intracellular and intracranial locations, we focus on the relationships among brain RAS, aging, frailty, and specific neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and vascular cognitive impairment, through oxidative stress, neuroinflammation, and vascular dysfunction. Finally, we discuss the effects of RAS-modulating drugs on the brain RAS and their use in novel treatment approaches.

NADPH Oxidase Inhibition: Preclinical and Clinical Studies in Diabetic Complications

Significance: Oxidative stress plays a critical role in the development and progression of serious micro- and macrovascular complications of diabetes. Nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) significantly contribute to oxidative stress-associated inflammatory pathways that lead to tissue damage of different organs, including the kidneys, retina, brain, nerves, and the cardiovascular system. Recent Advances: Preclinical studies, including genetic-modified mouse models or cell culture models, have revealed the role of specific NOX isoforms in different diabetic complications, and suggested them as a promising target for the treatment of these diseases. Critical Issues: In this review, we provide an overview of the role of ROS and oxidative stress in macrovascular complications, such as stroke, myocardial infarction, coronary artery disease, and peripheral vascular disease that are all mainly driven by atherosclerosis, as well as microvascular complications, such as diabetic retinopathy, nephropathy, and neuropathy. We summarize conducted genetic deletion studies of different Nox isoforms as well as pharmacological intervention studies using NOX inhibitors in the context of preclinical as well as clinical research on diabetic complications. Future Directions: We outline the isoforms that are most promising for future clinical trials in the context of micro- and macrovascular complications of diabetes.

Involvement of premacular mast cells in the pathogenesis of macular diseases

We previously reported on the elevated intravitreal activities of tryptase and chymase in association with idiopathic epiretinal membrane (ERM) and idiopathic macular hole (MH). In this present study, we investigated the potential intraocular production of these serine proteases, and measured and compared tryptase and chymase activities in the vitreous body and serum in ERM, MH, proliferative diabetic retinopathy (PDR), and rhegmatogenous retinal detachment (RRD) patients. In addition, nuclear staining with hematoxylin and eosin (H&E) and mast-cell staining with toluidine blue were performed on samples of the vitreous core and bursa premacularis (BPM) of MH. We also performed immunostaining on the above two regions of vitreous samples for MH with anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, anti-lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1) antibody, and anti-fibroblast antibody. Moreover, we performed immunostaining with anti-tryptase antibody and anti-chymase antibody on ERMs collected intraoperatively. Tryptase activity in the vitreous body was significantly higher in ERM and MH than in PDR. However, no significant differences were observed in the tryptase activity in the serum among these four diseases. Chymase activity in the vitreous body was significantly higher in MH than in the other three diseases, yet chymase activity in the serum was below detection limit in any of the diseases. Nuclear staining with H&E revealed an abundance of nuclei in the BPM region, but few in the surrounding area. Mast-cell staining with toluidine blue revealed that the BPM showed metachromatic staining. In immunostaining with anti-fibroblasts antibody, anti-tryptase antibody, anti-chymase antibody, anti-podoplanin antibody, and anti-LYVE-1 antibody, the BPM stained more strongly than the vitreous core. Tryptase and chymase-positive cells were also observed in ERM. These findings revealed that the presence of mast cells in the BPM potentially represent the source of these serine proteases. Moreover, the BPM, as a lymphatic tissue, may play an important role in the pathogenesis of macular disease.

Periocular injection of candesartan-PLGA microparticles inhibits laser-induced experimental choroidal neovascularization

Purpose

Microparticle technology enables local administration of medication. The purpose of this study was to examine the inhibitory effect of locally administered candesartan (CAN)-encapsulated microparticles on experimental choroidal neovascularization (CNV).

Methods

Laser photocoagulation was used to induce CNV in Brown Norway rats. The rats were pretreated with subconjunctival injections of CAN (5.0 mg/eye) or phosphate buffer saline for 3 days before photocoagulation. The volume of CNV was evaluated 7 days after laser injury using the lectin staining technique. The infiltration of macrophages within the CNV lesion was determined using immunofluorescent staining with an anti-CD68 antibody. mRNA levels of MCP-1, IL1-β and VEGF in the retinal pigment epithelium/choroid complex were determined using quantitative PCR (q-PCR).

Results

CNV volume was significantly suppressed by the treatment with CAN compared with that in vehicle-treated eyes (P<0.05, two-tailed Student’s t-test). Subconjunctival injections of CAN decreased the numbers of CD68⁺ cells in the CNV lesion. The increased mRNA levels of MCP-1, IL1-β, and VEGF induced by photocoagulation was significantly suppressed following the local administration of CAN (P<0.05, two-tailed Student’s t-test).

Conclusion

Local administration of CAN inhibited experimentally induced CNV possibly through anti-inflammatory effects.

Serum microRNA-221 as a biomarker for diabetic retinopathy in patients associated with type 2 diabetes

AIM

To investigate the candidate microRNA (miRNA), miR-221 as a novel biomarker for diabetic retinopathy (DR) in patients associated with type 2 diabetes (T2D).

METHODS

The subjects involved were divided into four groups: healthy control (HC), no diabetic retinopathy (NDR), non-proliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) group. Serum miR-221 was validated by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Also, serum angiotensin II (Ang II) and vascular endothelial growth factor (VEGF) were examined by enzyme-linked immunosorbent assay. In addition, receiver operating characteristic (ROC) curve was performed to explore the diagnostic accuracy of miR-221, Ang II and VEGF for DR in patients with T2D. Spearman's rank correlation coefficient was executed to estimate the correlations of serum miR-221 with metabolic parameters and serum markers in patients with T2D.

RESULTS

Primarily, serum miR-221, Ang II and VEGF were increased significantly in T2D patients compared to HC participant respectively, and progressive up-regulated in NDR, NPDR and PDR groups (P<0.001). Additionally, miR-221 in serum was remarkably positively correlated with metabolic parameters such as glycated hemoglobin (r=0.310, P=0.002) and homeostasis model assessment for insulin resistance (r=0.413, P<0.001), as well as serum markers for instance Ang II (r=0.667, P<0.001) and VEGF (r=0.499, P<0.001). Furthermore, serum miR-221 (AUC, 0.894; 95%CI, 0.833-0.955; P<0.001), Ang II (AUC, 0.888; 95%CI, 0.828-0.949; P<0.001) and VEGF (AUC, 0.785; 95%CI, 0.695-0.875; P<0.001) had evidently diagnostic efficiency in DR, and miR-221 is the most effective among them.

CONCLUSION

Serum miR-221 as a potential biomarker could be related to not only occurrence but also progression for DR in patients with T2D. However, a prospective clinical trial is warranted.

Oxidative stress and reactive oxygen species: a review of their role in ocular disease

For many years, oxidative stress arising from the ubiquitous production of reactive oxygen species (ROS) has been implicated in the pathogenesis of various eye diseases. While emerging research has provided some evidence of the important physiological role of ROS in normal cell function, disease may arise where the concentration of ROS exceeds and overwhelms the body’s natural defence against them. Additionally, ROS may induce genomic aberrations which affect cellular homoeostasis and may result in disease. This literature review examines the current evidence for the role of oxidative stress in important ocular diseases with a view to identifying potential therapeutic targets for future study. The need is particularly pressing in developing treatments for conditions which remain notoriously difficult to treat, including glaucoma, diabetic retinopathy and age-related macular degeneration.

Diabetic Retinopathy in the Spontaneously Diabetic Torii Rat: Pathogenetic Mechanisms and Preventive Efficacy of Inhibiting the Urokinase-Type Plasminogen Activator Receptor System

The spontaneously diabetic Torii (SDT) rat is of increasing preclinical interest because of its similarities to human type 2 diabetic retinopathy (DR). The system formed by urokinase-type plasminogen activator (uPA) and its receptor (uPAR) is a player in blood-retinal barrier (BRB) breakdown in DR. Here, we investigated whether in SDT rats, preventive administration of UPARANT, an inhibitor of the uPAR pathway, counteracts the retinal impairment in response to chronic hyperglycemia. Electroretinogram (ERG) monitoring was followed over time. Fluorescein-dextran microscopy, CD31 immunohistochemistry, quantitative PCR, ELISA, Evans blue perfusion, and Western blot were also used. UPARANT prevented ERG dysfunction, upregulation of vascular endothelial growth factor and fibroblast growth factor-2, BRB leakage, gliosis, and retinal cell death. The mechanisms underlying UPARANT benefits were studied comparing them with the acute streptozotocin (STZ) model in which UPARANT is known to inhibit DR signs. In SDT rats, but not in the STZ model, UPARANT downregulated the expression of uPAR and its membrane partners. In both models, UPARANT reduced the levels of transcription factors coupled to inflammation or inflammatory factors themselves. These findings may help to establish the uPAR system as putative target for the development of novel drugs that may prevent type 2 DR.

Downregulating p22phox ameliorates inflammatory response in Angiotensin II-induced oxidative stress by regulating MAPK and NF-κB pathways in ARPE-19 cells

Oxidative stress and inflammation are two interrelated biological events implicated in the pathogenesis of many diseases. Reactive oxygen species (ROS) produced under oxidative stress play a key role in pathological conditions. Inhibition of p22phox, an indispensable component of the NADPH oxidase (NOX) complex comprising the main source of ROS, plays a protective role in many ocular conditions by inhibiting the activation of NOXs and the generation of ROS. However, little is understood regarding the role of p22phox in oxidative stress-related inflammation in the eye. We used a p22phox small interfering RNA (siRNA) to transfect the retinal pigment epithelium (RPE)-derived cell line ARPE-19, and human primary RPE (hRPE) cells, then stimulated with Ang II. We observed a potent anti-inflammatory effect and studied the underlying mechanism. Downregulating p22phox resulted in decreased ROS generation, a reduction of NOXs (NOX1, 2, 4) and a decrease in inflammatory cytokine. In addition, p22phox downregulation reduced the activation of the MAPK and NF-κB signaling pathways. We conclude that inhibition of p22phox has an anti-inflammatory effect in Ang II-induced oxidative stress. Suppressing the MAPK and NF-κB pathways is involved in this protective effect. These results suggest that p22phox may provide a promising therapeutic target for oxidative stress-induced ocular inflammation

Angiotensin II-related hypertension and eye diseases

Systemic vascular disease, especially hypertension, has been suspected as a risk factor for some eye diseases including, diabetic retinopathy and age-related macular degeneration. Hypertension can contribute to chronic diseases by hemodynamic injury and/or cellular actions induced by hypertension-related hormones or growth factors. Among the most important is Angiotensin II (Ang II), which controls blood pressure and induces different cellular functions that may be dependent or independent of its effect on blood pressure. Importantly, as is true for heart, kidney and other organs, the renin-angiotensin system (RAS) is present in the eye. So, even in the absence of hypertension, local production of Ang II could be involved in eye diseases. The goal of this manuscript is to review the most relevant scientific evidence supporting the role of the RAS activation, in the development of age-related macular degeneration and diabetic retinopathy, and highlight the importance of Ang II in the etiology of these diseases.

Oxidative stress: implications for the development of diabetic retinopathy and antioxidant therapeutic perspectives

In recent decades, localized tissue oxidative stress has been implicated as a key component in the development of diabetic retinopathy (DR). Increasing evidence shows that oxidative stress caused by diabetes-induced metabolic abnormalities is the most common mechanism associated with the pathogenesis of DR for both type 1 and type 2 diabetes. Increase in intracellular reactive oxygen species (ROS) concentrations results in the activation of several mechanisms involved in the pathogenesis of DR. In particular, damage or dysfunction caused by oxidative stress still persists even after glycemia has been normalized. Despite considerable evidence showing the beneficial effects of antioxidants in preventing the development of retinopathy, results from large-scale clinical trials on classic antioxidants are somewhat ambiguous. Scavenging reactive radicals may not be the most ideal antioxidant strategy in DR. Advances in understanding the function of ROS in the development of DR can lead to the development of new therapeutic strategies based on the mechanisms of ROS generation and scavenging. Increasing amounts of data have demonstrated the promising prospect of antioxidant therapy and its beneficial effects in vision protection. Therefore, new strategies that utilize antioxidants as additive therapy should be implemented in the treatment of DR.

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.

Nox as a target for diabetic complications

Oxidative stress has been linked to the pathogenesis of the major complications of diabetes in the kidney, the heart, the eye or the vasculature. NADPH oxidases of the Nox family are a major source of ROS (reactive oxygen species) and are critical mediators of redox signalling in cells from different organs afflicted by the diabetic milieu. In the present review, we provide an overview of the current knowledge related to the understanding of the role of Nox in the processes that control cell injury induced by hyperglycaemia and other predominant factors enhanced in diabetes, including the renin–angiotensin system, TGF-β (transforming growth factor-β) and AGEs (advanced glycation end-products). These observations support a critical role for Nox homologues in diabetic complications and indicate that NADPH oxidases are an important therapeutic target. Therefore the design and development of small-molecule inhibitors that selectively block Nox oxidases appears to be a reasonable approach to prevent or retard the complications of diabetes in target organs. The bioefficacy of these agents in experimental animal models is also discussed in the present review.

Reactive oxygen species, Nox and angiotensin II in angiogenesis: implications for retinopathy

Pathological angiogenesis is a key feature of many diseases including retinopathies such as ROP (retinopathy of prematurity) and DR (diabetic retinopathy). There is considerable evidence that increased production of ROS (reactive oxygen species) in the retina participates in retinal angiogenesis, although the mechanisms by which this occurs are not fully understood. ROS is produced by a number of pathways, including the mitochondrial electron transport chain, cytochrome P450, xanthine oxidase and uncoupled nitric oxide synthase. The family of NADPH oxidase (Nox) enzymes are likely to be important given that their primary function is to produce ROS. Seven isoforms of Nox have been identified named Nox1-5, Duox (dual oxidase) 1 and Duox2. Nox1, Nox2 and Nox4 have been most extensively studied and are implicated in the development of conditions such as hypertension, cardiovascular disease and diabetic nephropathy. In recent years, evidence has accumulated to suggest that Nox1, Nox2 and Nox4 participate in pathological angiogenesis; however, there is no clear consensus about which Nox isoform is primarily responsible. In terms of retinopathy, there is growing evidence that Nox contribute to vascular injury. The RAAS (renin-angiotensin-aldosterone system), and particularly AngII (angiotensin II), is a key stimulator of Nox. It is known that a local RAAS exists in the retina and that blockade of AngII and aldosterone attenuate pathological angiogenesis in the retina. Whether the RAAS influences the production of ROS derived from Nox in retinopathy is yet to be fully determined. These topics will be reviewed with a particular emphasis on ROP and DR.

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.

The retinal renin-angiotensin system: roles of angiotensin II and aldosterone

In the present review we examine the experimental and clinical evidence for the presence of a local renin-angiotensin system within the retina. Interest in a pathogenic role for the renin-angiotensin system in retinal disease originally stemmed from observations that components of the pathway were elevated in retina during the development of certain retinal pathologies. Since then, our knowledge about the contribution of the RAS to retinal disease has greatly expanded. We discuss the known functions of the renin-angiotensin system in retinopathy of prematurity and diabetic retinopathy. This includes the promotion of retinal neovascularization, inflammation, oxidative stress and neuronal and glial dysfunction. The contribution of specific components of the renin-angiotensin system is evaluated with a particular focus on angiotensin II and aldosterone and their cognate receptors. The therapeutic utility of inhibiting key components of the renin-angiotensin system is complex, but may hold promise for the prevention and improvement of vision threatening diseases.

Preventing retinal apoptosis--is there a common therapeutic theme?

There is an urgent need for therapies for retinal diseases; retinitis pigmentosa sufferers have no treatment options available and those targeted at other retinopathies have shown limited effectiveness. The process of programmed cell death or apoptosis although complex, remains a possible target for the treatment of retinal diseases. Having identified apoptosis in the vertebrate retina in populations of immature neurons as an essential part of development it was proposed that re-activation of these developmental cell death pathways might provide insight into the death mechanisms operating in retinal diseases. However, the discovery that numerous factors initiate and mediate the apoptotic cascade in mature photoreceptors has resulted in a relatively untargeted approach to examining and arresting apoptosis in the retina. In the last 5 years, mouse models have been treated with a diverse range of drugs or factors including anti-oxidants, growth factors, steroid hormones, calcium/calpain inhibitors and tetracycline antibiotics. Therefore to draw a unifying theme from these broad research areas is challenging. However, this review focusses on two targets which are currently under investigation, reactive oxygen species and mammalian target of rapamycin, drawing together the common themes of these research areas.

Angiotensin receptor blockers and angiogenesis: clinical and experimental evidence

Angiotensin II type 1 receptor antagonists [ARBs (angiotensin receptor blockers)] are indicated for BP (blood pressure)-lowering, renal protection and cardioprotection in patients unable to tolerate ACEIs (angiotensin-converting enzyme inhibitors). A recent meta-analysis revealed an association between ARBs and tumour development, possibly due to enhancement of angiogenesis. However, published evidence is conflicting on the effects of ARBs on angiogenesis or the expansion of the existing vascular network. ARBs have been shown to exert primarily anti-angiogenic effects in basic science studies of cancer, retinopathy, peripheral artery disease and some models of cardiovascular disease. In animal and cellular models of myocardial infarction and stroke, however, ARB administration has been associated with robust increases in vascular density and improved recovery. The aim of the present review is to examine the angiogenic effects of ARBs in animal and cellular models of relevant disease states, including proposed molecular mechanisms of action of ARBs and the clinical consequences of ARB use.

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

Diabetic microvascular complications: possible targets for improved macrovascular outcomes

The results of recent outcome trials challenge hypotheses that tight control of both glycohemoglobin and blood pressure diminishes macrovascular events and survival among type 2 diabetic patients. Relevant questions exist regarding the adequacy of glycohemoglobin alone as a measure of diabetes control. Are we ignoring mechanisms of vasculotoxicity (profibrosis, altered angiogenesis, hypertrophy, hyperplasia, and endothelial injury) inherent in current antihyperglycemic medications? Is the polypharmacy for lowering cholesterol, triglyceride, glucose, and systolic blood pressure producing drug interactions that are too complex to be clinically identified? We review angiotensin-aldosterone mechanisms of tissue injury that magnify microvascular damage caused by hyperglycemia and hypertension. Many studies describe interruption of these mechanisms, without hemodynamic consequence, in the preservation of function in type 1 diabetes. Possible interactions between the renin-angiotensin-aldosterone system and physiologic glycemic control (through pulsatile insulin release) suggest opportunities for further clinical investigation.

New approaches to blockade of the renin-angiotensin-aldosterone system: chymase as an important target to prevent organ damage

Chymase plays a crucial role in angiotensin II formation in various tissues. Angiotensin II induces gene expression of transforming growth factor (TGF)-beta and matrix metalloproteinase (MMP)-9 precursors, and chymase can convert precursors of TGF-beta and MMP-9 to their active forms. In cultured fibroblasts, significant increases in cell growth and TGF-beta levels were observed after chymase injection; these increases were inhibited by a chymase inhibitor, but not by an angiotensin II-receptor blocker. In apolipoprotein E-deficient mice, abdominal aortic aneurysm (AAA) development depends on an increase in MMP-9 activities induced by angiotensin II infusion, but the inhibition of MMP-9 activation by a chymase inhibitor resulted in attenuation of the angiotensin II-induced AAA development. The upregulation of MMP-9 and TGF-beta levels is involved in damage to various organs, but these gene expressions are not completely induced by angiotensin II alone. Therefore, chymase inhibition may be useful for attenuating MMP-9 and TGF-beta levels, in addition to reducing angiotensin II formation, and this function may provide powerful organ protection. In this review, we propose the possible use of chymase inhibitors as agents to prevent organ damage.

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.

Protective effect of perindopril on diabetic retinopathy is associated with decreased vascular endothelial growth factor-to-pigment epithelium-derived factor ratio: involvement of a mitochondria-reactive oxygen species pathway

OBJECTIVE

This study aimed to verify whether the decreased vascular endothelial growth factor (VEGF)-to-pigment epithelium-derived factor (PEDF) ratio can serve as an indicator for the protective effect of angiotensin-converting enzyme inhibitors (ACEIs) on diabetic retinopathy (DR) and to investigate the role of mitochondrial reactive oxygen species (ROS) in the downregulated VEGF-to-PEDF ratio.

RESEARCH DESIGN AND METHODS

Diabetic rats and control animals were randomly assigned to receive perindopril or vehicle for 24 weeks, and bovine retinal capillary endothelial cells (BRECs) were incubated with normal or high glucose with or without perindopril. VEGF, PEDF, PPARgamma, and uncoupling protein-2 (UCP-2) in the rat retinas or BREC extracts were examined by Western blotting and real-time RT-PCR. The levels of VEGF and PEDF in cell culture media were examined by ELISA. Mitochondrial membrane potential (Deltapsim) and ROS production were assayed using JC-1 or CM-H2DCFDA.

RESULTS

The VEGF-to-PEDF ratio was increased in the retina of diabetic rats; perindopril lowered the increased VEGF-to-PEDF ratio in diabetic rats and ameliorated the retinal damage. In BRECs, perindopril lowered the hyperglycemia-induced elevation of VEGF-to-PEDF ratio by reducing mitochondrial ROS. We found the decreased ROS production was a result of perindopril-induced upregulation of PPARgamma and UCP-2 expression and the subsequent decrease of Deltapsim.

CONCLUSIONS

It is concluded that the protective effect of ACEI on DR is associated with a decreased VEGF-to-PEDF ratio, which involves the mitochondria-ROS pathway through PPARgamma-mediated changes of UCP-2. This study paves a way for future application of ACEI in treatment of DR.