Angiotensin converting enzyme inhibiting therapy is associated with lower vitreous vascular endothelial growth factor concentrations in patients with proliferative diabetic retinopathy

Effects of Angiotensin-Converting Enzyme Inhibition on the Recurrence and Internal Structure of Chronic Subdural Hematomas

Background/Objectives: Chronic subdural hematoma (cSDH) is a common disease of growing significance due to the increasing use of antithrombotic drugs and population aging. There exists conflicting observational evidence that previous treatment with angiotensin-converting enzyme (ACE) inhibitors reduces the rate of cSDH recurrence. This study assesses the hypothesis that ACE inhibitors may affect recurrence rates by altering hematoma membrane formation. Methods: All patients with chronic subdural hematoma who were operated upon in a single university hospital between 2015 and 2020 were considered for inclusion. Hematomas were classified according to their structural appearance in computed tomography (CT) imaging into one of eight subtypes. Patients' own medication, prior to hospitalization for cSDH treatment, was noted, and the use of ACI-inhibitors was identified. Results: Of the included 398 patients, 142 (35.9%) were treated with ACE inhibitors before admission for cSDH treatment. Of these, 115 patients (81.0%) received ramipril, 13 received patients lisinopril (11.3%), and 11 patients (9.6%) received enalapril. Reflecting cardiovascular comorbidity, patients on ACE inhibitors were more often simultaneously treated with antithrombotics (63.4% vs. 42.6%; p ≤ 0.001). Hematomas with homogenous hypodense (OR 11.739, 95%CI 2.570 to 53.612; p = 0.001), homogenous isodense (OR 12.204, 95%CI 2.669 to 55.798; p < 0.001), and homogenous hyperdense (OR 9.472, 95%CI 1.718 to 52.217; p < 0.001) architectures, as well as the prior use of ACE inhibitors (OR 2.026, 95%CI 1.214 to 3.384; p = 0.007), were independently associated with cSDH recurrence. Conclusions: Once corrected for hematoma architecture, type of surgery, and use of antithrombotic medication, preoperative use of ACE inhibitors was associated with a twofold increase in the likelihood of hematoma recurrence.

Aldosterone as a Possible Contributor to Eye Diseases

Aldosterone, an effector molecule of the renin-angiotensin-aldosterone system (RAAS), has been receiving more attention in the field of ophthalmology because of its possible role in the pathogenesis of various eye diseases or abnormalities; it may even become a target for their treatment. Primary aldosteronism, a typical model of a systemic aldosterone excess, may cause vision loss due to various ocular diseases, such as retinal vein occlusion, central serous chorioretinopathy, and, possibly glaucoma. RAAS components are present in various parts and types of cells present in the eye. Investigations of the local RAAS in various animal models of diabetic macular edema, retinal vein occlusion, retinopathy of prematurity, central serous chorioretinopathy, and glaucoma have found evidence that aldosterone or mineralocorticoid receptors may exacerbate the pathology of these disorders. Further studies are needed to elucidate whether the modulation of aldosterone or mineralocorticoid receptors is an effective treatment for preventing vision loss in patients with eye diseases.

Changes in aqueous and vitreous inflammatory cytokine levels in proliferative diabetic retinopathy: a systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy is a major complication of diabetes mellitus, where in its most advanced form ischemic changes lead to the development of retinal neovascularization, termed proliferative diabetic retinopathy (PDR). While the development of PDR is often associated with angiogenic and inflammatory cytokines, studies differ on which cytokines are implicated in disease pathogenesis and on the strength of these associations. We therefore conducted a systematic review and meta-analysis to quantitatively assess the existing body of data on intraocular cytokines as biomarkers in PDR.

METHODS

A comprehensive search of the literature without year limitation was conducted to January 18, 2021, which identified 341 studies assessing vitreous or aqueous cytokine levels in PDR, accounting for 10379 eyes with PDR and 6269 eyes from healthy controls. Effect sizes were calculated as standardized mean differences (SMD) of cytokine concentrations between PDR and control patients.

RESULTS

Concentrations (SMD, 95% confidence interval, and p-value) of aqueous IL-1β, IL-6, IL-8, MCP-1, TNF-α, and VEGF, and vitreous IL-2, IL-4, IL-6, IL-8, angiopoietin-2, eotaxin, erythropoietin, GM-CSF, GRO, HMGB-1, IFN-γ, IGF, IP-10, MCP-1, MIP-1, MMP-9, PDGF-AA, PlGF, sCD40L, SDF-1, sICAM-1, sVEGFR, TIMP, TNF-α, and VEGF were significantly higher in patients with PDR when compared to healthy nondiabetic controls. For all other cytokines no differences, failed sensitivity analyses or insufficient data were found.

CONCLUSIONS

This extensive list of cytokines speaks to the complexity of PDR pathogenesis, and informs future investigations into disease pathogenesis, prognosis, and management.

Kinins and Their Receptors as Potential Therapeutic Targets in Retinal Pathologies

The kallikrein-kinin system (KKS) contributes to retinal inflammation and neovascularization, notably in diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Bradykinin type 1 (B1R) and type 2 (B2R) receptors are G-protein-coupled receptors that sense and mediate the effects of kinins. While B2R is constitutively expressed and regulates a plethora of physiological processes, B1R is almost undetectable under physiological conditions and contributes to pathological inflammation. Several KKS components (kininogens, tissue and plasma kallikreins, and kinin receptors) are overexpressed in human and animal models of retinal diseases, and their inhibition, particularly B1R, reduces inflammation and pathological neovascularization. In this review, we provide an overview of the KKS with emphasis on kinin receptors in the healthy retina and their detrimental roles in DR and AMD. We highlight the crosstalk between the KKS and the renin-angiotensin system (RAS), which is known to be detrimental in ocular pathologies. Targeting the KKS, particularly the B1R, is a promising therapy in retinal diseases, and B1R may represent an effector of the detrimental effects of RAS (Ang II-AT1R).

Recent trends in drug-delivery systems for the treatment of diabetic retinopathy and associated fibrosis

Diabetic retinopathy is a frequent microvascular complication of diabetes and a major cause of visual impairment. In advanced stages, the abnormal neovascularization can lead to fibrosis and subsequent tractional retinal detachment and blindness. The low bioavailability of the drugs at the target site imposed by the anatomic and physiologic barriers within the eye, requires long term treatments with frequent injections that often compromise patient's compliance and increase the risk of developing more complications. In recent years, much effort has been put towards the development of new drug delivery platforms aiming to enhance their permeation, to prolong their retention time at the target site and to provide a sustained release with reduced toxicity and improved efficacy. This review provides an overview of the etiology and pathophysiology of diabetic retinopathy and current treatments. It addresses the specific challenges associated to the different ocular delivery routes and provides a critical review of the most recent developments made in the drug delivery field.

Dysfunction of retinal neurons and glia during diabetes

Diabetic retinopathy is the leading cause of blindness in those of working age. It is well known that the retinal vasculature is altered during diabetes. More recently, it has emerged that neuronal and glial dysfunction occurs in those with diabetes. Current research is directed at understanding these neuronal and glial changes because they may be an early manifestation of disease processes that ultimately lead to vascular abnormality. This review will highlight the recent advances in our understanding of the neuronal and glial changes that occur during diabetes.

Angiotensin II and Angiotensin Receptors 1 and 2-Multifunctional System in Cells Biology, What Do We Know?

For years, the renin-angiotensin system (RAS) has been perceived as a system whose role is to primarily modulate the functioning of the cardiovascular system. Years of research into the role of RAS have provided the necessary data to confirm that the role of RAS is very complex and not limited to the cardiovascular system. The presence of individual elements of the renin-angiotensin (RA) system allows to control many processes, ranging from the memorization to pro-cancer processes. Maintaining the proportions between the individual axes of the RA system allows for achieving a balance, often called homeostasis. Thus, any disturbance in the expression or activity of individual RAS elements leads to pathophysiological processes.

Posterior vitreous detachment in patients with diabetes mellitus

PURPOSE

To compare the progression of posterior vitreous detachment (PVD) during aging among eyes of diabetics with diabetic retinopathy (DR), eyes of diabetics without DR, and eyes of nondiabetics.

STUDY DESIGN

Prospective cross-sectional study.

METHODS

One-hundred thirty-three diabetic eyes with DR (DR group), 254 diabetic eyes without DR (non-DR group), and 577 nondiabetic eyes (nondiabetic group) were divided into four age categories: 1) 40-49 years, 2) 50-59 years, 3) 60-69 years, and 4) 70-79 years. The PVD state was examined using swept source-optical coherence tomography and classified into five stages: 0 (non PVD), 1 (paramacular PVD), 2 (perifoveal PVD), 3 (vitreofoveal separation), and 4 (complete PVD).

RESULTS

The PVD stage significantly progressed in the DR, non-DR, and nondiabetic groups (p <0.0001). At 40-49 and 50-59 years, the PVD stage did not differ significantly among the three groups. At 60-69 and 70-79 years, the PVD stage was significantly less progressed in the DR than the non-DR and nondiabetic groups (p ≤0.0027), and did not differ significantly between the non-DR and nondiabetic groups. At 70-79 years, complete PVD was detected in 40.6% of eyes in the DR group, 69.6% in the non-DR group, and 73.5% of eyes in the nondiabetic group.

CONCLUSION

PVD progresses later in diabetic eyes with DR than in diabetic eyes without DR and nondiabetics eyes at 60 and 70 years of age, suggesting a stronger vitreomacular adhesion in diabetics with DR.

Outcomes of 25-Gauge Vitrectomy for Tractional and Nontractional Diabetic Macular Edema with Proliferative Diabetic Retinopathy

The benefit of pars plana vitrectomy with internal limiting membrane peeling for tractional macular edema and diffuse nontractional macular edema in diabetic retinopathy has been reported. Although these studies had included various stages, use of conventional 20-gauge vitrectomy system, small number of cases, single-center study, and lack of retinal structure measurements were limitations. We compared one-year outcomes of 25-gauge vitrectomy for refractory diabetic macular edema with or without the tractional proliferative membrane in proliferative diabetic retinopathy (PDR) eyes and examined the prognostic factors for postoperative visual acuity. A total of consecutive 116 PDR eyes of 116 patients that underwent 25-gauge vitrectomy for tractional macular edema (TME group: 56 eyes) or nontractional macular edema (nTME group: 60 eyes) at six centers were retrospectively reviewed. Visual acuity (VA), central macular thickness (CMT), complications, and postoperative treatments before and 12 months after vitrectomy were compared. Mean VA improved significantly in each group (both P < 0.01), and mean CMT decreased significantly in each group (both P < 0.01). Thirteen eyes underwent additional vitrectomy, six eyes developed neovascular glaucoma, six eyes received intravitreal anti-VEGF injection, and thirteen eyes received subtenon triamcinolone acetonide injection. Multiple linear regression analysis showed that baseline VA and CMT in the TME group and kidney function in the nTME group were the predictable factors of the 12-month postoperative VA. Twenty-five-gauge vitrectomy effectively improved VA and macular structure both in TME and nTME groups. Baseline VA, CMT, and kidney function are important factors affecting postoperative VA.

Evaluation of vascular endothelial growth factor levels in tears and serum among diabetic patients

Objective

Detection of vascular endothelial growth factor (VEGF) levels in ocular tissue may perhaps provide insight into the role of VEGF in the pathogenesis and progression of diabetic retinopathy (DR). The aim of this study was to evaluate the levels of VEGF in tears and serum amongst type 2 diabetes mellitus (DM) patients.

Methods

A comparative cross-sectional study was conducted between August 2016 and May 2018 involving type 2 DM patients with no DR, non-proliferative DR (NPDR), and proliferative DR (PDR). Tear samples were collected using no.41 Whatman filter paper (Schirmer strips) and 5 mL blood samples were drawn by venous puncture. VEGF levels in tears and serum were measured by enzyme-linked immunosorbent assay.

Results

A total of 88 type 2 DM patients (no DR: 30 patients, NPDR: 28 patients, PDR: 30 patients) were included in the study. Mean tear VEGF levels were significantly higher in the NPDR and PDR groups (114.4 SD 52.5 pg/mL and 150.8 SD 49.7 pg/mL, respectively) compared to the no DR group (40.4 SD 26.5 pg/mL, p < 0.001). There was no significant difference in the mean serum VEGF levels between the three groups. There was a fair correlation between serum and tear VEGF levels (p = 0.015, r = 0.263).

Conclusion

VEGF levels in tears were significantly higher amongst diabetic patients with DR compared to those without DR and were significantly associated with the severity of DR. There was a fair correlation between serum and tear VEGF levels. Detection of VEGF in tears is a good non-invasive predictor test for the severity of DR. A large cohort study is needed for further evaluation.

Evaluation of the growth factors VEGF-a and VEGF-B in the vitreous and serum of patients with macular and retinal vascular diseases

VEGF-A and VEGF-B are proangiogenic and key regulating factors for blood vessel growth. This study aims to compare VEGF-A and VEGF-B levels in the serum and vitreous of patients with neovascular pathology versus non-neovascular pathology. Our findings showed vitreous VEGF-A and VEGF-B levels increased in patients with neovascular disease, with higher levels of VEGF-A compared to VEGF-B (p ≤ .05). In the diabetic retinopathy (DR) group, higher vitreous VEGF-A or VEGF-B were found in proliferative diabetic retinopathy (PDR) than in non-PDR. The strong correlation between VEGF-A and VEGF-B demonstrates a simultaneous pathological increase of cytokines (p < .001), suggesting besides VEGF-A, VEGF-B is another contributor to ocular pathologies involving angiogenesis. There was no correlation between vitreous and serum VEGF-A or VEGF-B; however, a correlation between vitreous (VEGF-A or VEGF-B) and macular volume (p < .05) in DR patients was found. Targeting VEGF-A and VEGF-B in macular and retinal vascular diseases, involving neovascularization, may improve treatment outcomes.

The relationship between ACE/AGT gene polymorphisms and the risk of diabetic retinopathy in Chinese patients with type 2 diabetes

Aims:

This study aims to investigate the association between renin-angiotensin system gene polymorphism and diabetic retinopathy (DR) in Chinese patients with type 2 diabetes.

Methods:

We consecutively included 1491 patients for the assessment of ACE I/D and AGT M/T gene polymorphisms in 345 DR cases and 1146 patients without retinopathy (DNR). Albuminuria was defined by urine albumin creatinine ratio and albumin excretion rate.

Results:

Compared with the NDR patients, the DR cases displayed a higher proportion of diabetic nephropathy (32.68% vs. 6.52%, χ² = 150.713, p < 0.001). The DR cases and DNR individuals did not differ in the frequency of genotypes and alleles of ACE I/D and AGT M/T (all p > 0.05). Intriguingly, DR patients with obesity showed higher frequency of DD (χ² = 4.181, p = 0.041), but no significant difference exists in the other stratified BMI and hypertension analyses (all p > 0.05). Binary logistic regression displays that the association of the ACE and AGT gene polymorphisms in DR patients is not significant after adjusting for confounding covariates in all the comparisons.

Conclusions:

The ACE and AGT gene polymorphisms are not associated with the progress of diabetes developing into retinopathy in Chinese patients with type 2 diabetes. However, more investigations are needed to further prove the association.

Interaction of renin-angiotensin system gene polymorphisms with hypertension in Chinese patients with type 1 diabetes and retinopathy

Background

The objective of this research was to investigate the interaction of RAS gene polymorphisms in Chinese patients with type 1 diabetes mellitus (T1DM) and diabetic retinopathy (DR).

Methods

Genomic DNA was extracted from peripheral blood leukocytes and genotyping for the angiotensin converting enzyme (ACE) gene I/D and angiotensinogen (AGT) gene M/T polymorphisms was performed using the polymerase chain reaction method. 311 T1DM patients were recruited for the assessment of ACE and AGT polymorphisms relating to DR.

Results

Compared with the diabetic non-retinopathy (DNR) patients, DR patients had lower proportion of diabetic nephropathy (p<0.001) and M allele (p=0.013). Intriguingly, the frequency D allele (p=0.035) was lower in DR patients with hypertension, as well as DD (p=0.003) and DI genotype (p=0.012) in DR patients with normal blood pressure after multiple tests with Bonferroni correction, but D allele (p=0.025) displayed higher in normotensive patients with T1DM. Logistic regression analyses indicated that no significant relationship existed about the genotype and allele polymorphisms with the progress of DR after adjusting for confounding factors.

Conclusions

Interaction of hypertension and the RAS gene polymorphisms might have a role in the DR development in Chinese T1DM patients.

Vascular endothelial growth factors and placenta growth factor in retinal vasculopathies: Current research and future perspectives

Vision loss due to disease or degeneration of the eye (retina, choroid, retinal veins, or macula) is a leading cause of blindness worldwide. In most cases, vision-threatening ocular diseases are accompanied by abnormal changes in the vasculature of the eye, especially the retina, and these conditions are collectively referred to as retinal vasculopathies. Impaired blood supply or hypoxia stimulates angiogenesis in the vascular and non-vascular sections of the eye, which results in neovascularization, leading to conditions such as diabetic retinopathy or age-related macular degeneration. Studies show that vascular endothelial growth factors: VEGF-A, VEGF-B, and placental growth factor (PlGF) are elevated in these diseases, and hence, these factors could be used as markers for disease prognosis and therapy. In this review, we discuss the function of these growth factors in normal development and disease, with focus on ocular disorders and emphasize the importance of accurately determining their levels in the vitreous and serum of patients for correct diagnosis and therapy.

Effect of angiotensin II type 1 receptor blocker and angiotensin converting enzyme inhibitor on the intraocular growth factors and their receptors in streptozotocin-induced diabetic rats

AIM

To investigate the effect of angiotensin II type 1 receptor blocker (ARB) and angiotensin converting enzyme inhibitor (ACEI) on intraocular growth factors and their receptors in streptozotocin-induced diabetic rats.

METHODS

Forty Sprague-Dawley rats were divided into 4 groups: control, diabetes mellitus (DM), candesartan-treated DM, and enalapril-treated DM (each group, n=10). After the induction of DM by streptozotocin, candesartan [ARB, 5 mg/(kg·d)] and enalapril [ACEI, 10 mg/(kg·d)] were administered to rats orally for 4wk. Vascular endothelial growth factor (VEGF) and angiotensin II (Ang II) concentrations in the vitreous were measured using enzyme-linked immunosorbent assays, and VEGF receptor 2 and angiotensin II type 1 receptor (AT1R) levels were assessed at week 4 by Western blotting.

RESULTS

Vitreous Ang II levels were significantly higher in the DM group and candesartan-treated DM group than in the control (P=0.04 and 0.005, respectively). Vitreous AT1R increased significantly in DM compared to the other three groups (P<0.007). Candesartan-treated DM rats showed higher vitreal AT1R concentration than the enalapril-treated DM group and control (P<0.001 and P=0.005, respectively). No difference in vitreous Ang II and AT1R concentration was found between the enalapril-treated DM group and control. VEGF and its receptor were below the minimum detection limit in all 4 groups.

CONCLUSION

Increased Ang II and AT1R in the hyperglycemic state indicate activated the intraocular renin-angiotensin system, which is inhibited more effectively by systemic ACEI than systemic ARB.

Therapeutic targets of renin-angiotensin system in ocular disorders

Purpose

To review current literature on the renin-angiotensin system (RAS)-mediated pathogenic mechanisms and therapeutic targets in ocular diseases.

Methods

A comprehensive literature survey was performed on PubMed, Scopus, and Google Scholar databases published from 1977 to 2016. The search terms were a RAS, angiotensin, angiotensin receptor, prorenin, pro (renin) receptor, angiotensin converting enzyme inhibitor, angiotensin receptor blocker associated with ocular disorders like cataract, glaucoma, diabetic retinopathy (DR), macular degeneration, and uveitis. Articles were reviewed on the basis of the association between ocular disorders and RAS and relevant articles were discussed.

Results

The literature revealed that the individual RAS components including renin, angiotensins, angiotensin converting enzymes, and RAS receptors have been expressed in the specific ocular tissues like retina, choroid, and ciliary body. The activation of both circulatory and local RAS potentiate the various inflammatory and angiogenic signaling molecules, including vascular endothelial growth factor (VEGF), extracellular signal-regulated kinase, and advanced glycation end products (AGE) in the ocular tissues and leads to several blinding disorders like DR, glaucoma, and macular degeneration. The classical and newer RAS inhibitors have illustrated protective effects on blinding disorders, including DR, glaucoma, macular degeneration, uveitis, and cataract.

Conclusions

The RAS components are present in the extrarenal tissues including ocular tissue and have an imperative role in the ocular pathophysiology. The clinical studies are needed to show the role of therapeutic modalities targeting RAS in the treatment of different ocular disorders.

[Association between visual improvement after photocoagulation and the use of angiotensin converting enzyme inhibitors in diabetic macular oedema]

BACKGROUND

Angiotensin converting enzyme inhibitors are effective in delaying the progression of diabetic retinopathy. It is unknown if their use is associated with a better visual outcome in patients with diabetic macular oedema.

MATERIAL AND METHODS

A non-experimental, comparative, longitudinal and retrospective study was performed on patients with diabetic macular oedema treated by focal photocoagulation, and with systemic arterial hypertension treated with angiotensin converting enzyme inhibitors (Group 1), and without hypertension (Group 2). The dependent variable was the proportion with visual improvement, operatively defined as the gain of one or more lines of vision three weeks after photocoagulation. The independent variable was the use of angiotensin converting enzyme inhibitors. The proportion of eyes with visual improvement after treatment was compared between groups using the Chi squared (χ(2)) test.

RESULTS

A total of 33 eyes (51.6%) were assigned to group 1, and 31 (48.2%), to group 2. The mean of visual acuity improved after three weeks, compared with baseline (p=0.002). The proportion of eyes with visual improvement did not differ between patients treated with angiotensin converting enzyme inhibitors (45.5%) and those that did not use them (51.6%, p=0.4).

CONCLUSIONS

There was no statistical difference in the proportion of eyes with visual improvement between patients treated with angiotensin converting enzyme inhibitors and in those where they were not used. There is no support for the inhibition of angiotensin II in addition to photocoagulation for improving the outcome in patients with diabetic macular oedema.

Vascular endothelial growth factor concentration in chronic subdural hematoma fluid is related to computed tomography appearance and exudation rate

Chronic subdural hematoma (CSH) is characterized by a net increase of volume over time. Major underlying mechanisms appear to be hemorrhagic episodes and a continuous exudation, which may be studied using labeled proteins to yield an exudation rate in a given patient. We tested the hypothesis that the concentration of vascular endothelial growth factor (VEGF) in hematoma fluid correlates with the rate of exudation. Concentration of VEGF was determined in 51 consecutive patients with CSH by the sandwich immune enzyme-linked immunosorbent assay technique. Mean values were correlated with exudation rates taken from the literature according to the appearance of CSH on computed tomography (CT) images. The CT appearance of each CSH was classified as hypodense, isodense, hyperdense, or mixed density. Mean VEGF concentration was highest in mixed-density hematomas (22,403±4173 pg/mL; mean±standard error of the mean; n=27), followed by isodense (9715±1287 pg/mL; n=9) and hypodense (5955±610 pg/mL; n=18) hematomas. Only 1 patient with hyperdense hematoma fulfilled the inclusion criteria, and the concentration of VEGF found in this patient was 24,200 pg/mL. There was a statistically significant correlation between VEGF concentrations and exudation rates in the four classes of CT appearance (r=0.98). The current report is the first to suggest a pathophysiological link between the VEGF concentration and the exudation rate underlying the steady increase of hematoma volume and CT appearance.With this finding, the current report adds another piece of evidence in favor of the pathophysiological role of VEGF in the development of CSH, including mechanisms contributing to hematoma growth and CT appearance.

Association of angiotensin-converting enzyme gene 2350 G/A polymorphism with diabetic retinopathy in Chinese Han population

The angiotensin-converting enzyme (ACE) gene is one of the most studied candidate genes related to diabetic retinopathy (DR). ACE 2350 G/A polymorphism (rs4343) is known among the polymorphisms of this gene to have the most significant effect on plasma ACE concentrations. The aim of the present study was to investigate the relationship between 2350 G/A polymorphism of ACE gene and the susceptibility of DR in Chinese Han population. A case-control study for 145 type 2 diabetes mellitus (DM) patients, including 63 type 2 DM without DR (NDR) and 82 type 2 DM with DR (DR), and 90 subjects of age, gender matched normal controls (NC group) was performed. ACE 2350 G/A genotypes were identified by polymerase chain reaction and restriction digestion in all study participants. The distribution of the ACE 2350 G/A genotypes (GG, GA, and AA) was 35.56, 45.55, and 18.89 % in the NC group, 28.57, 46.03, and 25.40 % in the NDR group, and 15.85, 46.34, and 37.81 % in the DR group, respectively. There were no significant differences in either genotype frequency distribution (P = 0.5266) or allele frequency distribution (P = 0.2425) between the NC group and NDR group. However, the distribution of genotype frequency (P = 0.0026) and allele frequency (P = 0.0003) in the DR group showed a significant difference when compared to that of NC group (P = 0.0075). Moreover, there was statistical difference in allele frequency distribution (P = 0.0328) between the DR group and the NDR group. No statistical differences were observed between ACE 2350 G/A polymorphism and the diabetes duration or types of DR. Results obtained in this study indicate that ACE 2350 G/A polymorphism is associated with DR in Han Chinese patients with type 2 DM.

Relationship between vitreous and serum vascular endothelial growth factor levels, control of diabetes and microalbuminuria in proliferative diabetic retinopathy

BACKGROUND

Diabetic retinopathy is a serious microvascular disorder of the retina. Vascular endothelial growth factor (VEGF) expression, induced by high glucose levels and hypoxia, is a main feature in retinopathy. The aim of this study was to evaluate the relationship between vitreous and serum VEGF levels and control of diabetes and microalbuminuria in patients with proliferative diabetic retinopathy.

METHODS

Sixty-five patients were enrolled in this case-control study, comprising 30 patients with proliferative diabetic retinopathy (cases) and 35 patients with nonproliferative diabetic retinopathy (controls). The vitreous VEGF level was compared with the serum VEGF level in both groups. Glycosylated hemoglobin (HbA(1c)), microalbuminuria, serum creatinine, and stage of nephropathy and retinopathy were also measured in patients with proliferative diabetic retinopathy, and the relationship between these parameters and serum and vitreous VEGF levels was investigated.

RESULTS

Mean vitreous and serum VEGF levels were significantly higher in cases compared with controls (P = 0.001, P = 0.011, respectively). There was also a significant correlation between vitreous and serum VEGF levels (P = 0.012, r = 0.453). VEGF levels in patients with well controlled blood glucose (P = 0.039), on drug treatment (P = 0.045) and at an early stage of nephropathy (P = 0.042) were significantly lower. There was a significant correlation between VEGF and albumin to creatinine ratio (P = 0.017, r = 0.432).

CONCLUSION

Serum and vitreous VEGF levels was significantly lower in patients on oral therapy, in those with well controlled glycemia, and in those with early-stage retinopathy. Administration of anti-VEGF had a good effect in reducing the progression of proliferative diabetic retinopathy.

The relationship between ACE gene insertion/deletion polymorphism and diabetic retinopathy in Iranian patients with type 2 diabetes

BACKGROUND

The role of genetic factors in diabetic retinopathy (DR) is unclear. We investigated the relationship between DR and an insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene in Iranian patients with type 2 diabetes without overt nephropathy.

METHODS

A total of 178 consecutive type 2 diabetic patients with DR (Group A) and 206 type 2 diabetic patients without DR (Group B) were studied. The following variables were determined: age, sex, body mass index, diabetes duration, medications used, history of coronary artery disease and its complications, blood pressure (systolic and diastolic), fasting plasma glucose, hemoglobin A1c, total cholesterol, low- and high-density lipoproteins, triglycerides, plasma creatinine, and 24-h urine albumin excretion.

RESULTS

The groups were statistically similar in all variables except diabetes duration (P = 0.037), ACE activity (P < 0.001), and ACE genotype (P = 0.008). The DD genotype was significantly more common in Group A (32.6% versus 19.2% in Group B; P = 0.009). In multivariate regression analysis, the ID genotype (compared to the II genotype) was an independent predictor of DR (OR = 1.831, 95% CI = 1.074-3.124; P = 0.026).

CONCLUSIONS

The D allele of the ACE gene is independently associated with DR in Iranian type 2 diabetic patients.

Plasma and aqueous humor angiotensin-converting enzyme levels in patients with diabetic retinopathy

PURPOSE

To assess angiotensin-converting enzyme (ACE) levels in aqueous humor and plasma of patients with nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) as another potent ischemia-induced angiogenic factor.

METHODS

The clinical comparative study included 40 patients with diabetic retinopathy and 16 healthy subjects. For all patients, aqueous humors were collected during the cataract surgery or intravitreal injection of triamcinolone acetonide. ACE levels were measured using a solid-phase chemiluminescence immunoassay.

RESULTS

We observed significantly elevated ACE level in aqueous humor of patients with PDR compared with the patients with NPDR and normal subjects (P = 0.023), but no significant difference was detected between nonproliferative diabetics and control group (P = 0.239). There was no significant difference in plasma ACE levels among diabetic and control groups (P = 0.816).

CONCLUSION

Elevated ACE level may induce retinal angiogenesis and proliferative retinopathy in patients with DM. We consider that high levels of ACE in aqueous humor can reflect the association between retinal angiogenesis and DM serve as predictor in the progression of diabetic retinopathy.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

Soluble receptor for advanced glycation end products: a new biomarker in diagnosis and prognosis of chronic inflammatory diseases

The formation of advanced glycation end products (AGEs) is a result of the non-enzymatic reaction between sugars and free amino groups of proteins. AGEs, through interacting with their specific receptor for AGEs (RAGE), result in activation of pro-inflammatory states and are involved in numerous pathologic situations. The soluble form of RAGE (sRAGE) is able to act as a decoy to avoid interaction of RAGE with its pro-inflammatory ligands (AGEs, HMGB1, S100 proteins). sRAGE levels have been found to be decreased in chronic inflammatory diseases including atherosclerosis, diabetes, renal failure and the aging process. The use of measuring circulating sRAGEs may prove to be a valuable vascular biomarker and in this review, we describe the implications of sRAGE in inflammation and propose that this molecule may represent a future therapeutic target in chronic inflammatory diseases.

Activities of angiotensin-converting enzymes ACE1 and ACE2 and inhibition by bioactive peptides in porcine ocular tissues

PURPOSE

An active local renin-angiotensin system (RAS) has recently been found in the human eye. The aim of the present study was to compare the activities of central RAS enzymes (ACE1 and 2) in porcine ocular tissues, morphologically and physiologically close to the human eye. In addition, the effects of three ACE-inhibitory tripeptides on these enzymes were evaluated.

METHODS

Enucleated fresh porcine eyes were used. Activities of ACE1 and ACE2 and their inhibition by bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro, Leu-Pro-Pro) as well as by a standard ACE-inhibitor captopril were assayed in the vitreous body, the retina and the ciliary body using fluorometric detection methods.

RESULTS

Activity of ACE1 as well as ACE2 was found in all tissues evaluated. ACE1 activity was markedly higher in the ciliary body (3.7 +/- 0.7 mU/mg protein) than in retina (0.2 +/- 0.02 mU/mg), whereas ACE2 activities in the ciliary body (0.2 +/- 0.02 mU/mg) and retina (0.2 +/- 0.01 mU/mg) were at the same level. In the vitreous body ACE1 activity (8.2 +/- 0.31 nmol/min/mL) was manifold compared to that of ACE2 (0.1 +/- 0.02 nmol/min/mL). The tripeptides inhibited ACE1 at one-thousandth of the concentration needed to inhibit ACE2. All peptides studied evinced about equal inhibitory activities.

CONCLUSION

To our knowledge the present findings constitute the first evidence of ACE2 activity in the ciliary and vitreous bodies, in addition to previously described activity in the retina. The known favorable effects of ACE2 products vs. those of ACE1 suggest a counterbalancing interaction of these two enzyme homologues in physiological regulation of ocular circulation and pressure and possible protective role in certain ophthalmic disorders such as glaucoma and 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.

Endothelial dysfunction and diabetes: roles of hyperglycemia, impaired insulin signaling and obesity

Endothelial dysfunction comprises a number of functional alterations in the vascular endothelium that are associated with diabetes and cardiovascular disease, including changes in vasoregulation, enhanced generation of reactive oxygen intermediates, inflammatory activation, and altered barrier function. Hyperglycemia is a characteristic feature of type 1 and type 2 diabetes and plays a pivotal role in diabetes-associated microvascular complications. Although hyperglycemia also contributes to the occurrence and progression of macrovascular disease (the major cause of death in type 2 diabetes), other factors such as dyslipidemia, hyperinsulinemia, and adipose-tissue-derived factors play a more dominant role. A mutual interaction between these factors and endothelial dysfunction occurs during the progression of the disease. We pay special attention to the possible involvement of endoplasmic reticulum stress (ER stress) and the role of obesity and adipose-derived adipokines as contributors to endothelial dysfunction in type 2 diabetes. The close interaction of adipocytes of perivascular adipose tissue with arteries and arterioles facilitates the exposure of their endothelial cells to adipokines, particularly if inflammation activates the adipose tissue and thus affects vasoregulation and capillary recruitment in skeletal muscle. Hence, an initial dysfunction of endothelial cells underlies metabolic and vascular alterations that contribute to the development of type 2 diabetes.

High vitreous concentration of vascular endothelial growth factor in diabetic patients with proliferative retinopathy using statins

BACKGROUND

Vascular endothelial growth factor (VEGF) plays an important role in the development of diabetic retinopathy. Previous studies have suggested that angiotensin-converting enzyme (ACE) inhibitor therapy may reduce vitreous VEGF concentration in diabetic retinopathy. Also HMG CoA reductase inhibitors (statins), known for their beneficial effects on vascular endothelium, might influence vitreous VEGF concentration in diabetic retinopathy.

AIM

Vitreous VEGF concentration of diabetic patients with proliferative retinopathy using statin therapy and/or ACE inhibitor therapy was studied.

METHODS

Fifty diabetic patients with proliferative diabetic retinopathy, 21 diabetic control patients without proliferative retinopathy, and 43 non-diabetic control subjects underwent vitrectomy. Vitreous samples were collected at the beginning of surgery, and VEGF concentration was assessed using a chemiluminescent VEGF immunoassay.

RESULTS

Vitreous VEGF concentration was significantly higher in diabetic patients with proliferative retinopathy using statins than in those not using statins. The diabetic patients with proliferative retinopathy were divided into subgroups according to use of ACE inhibitor and/or statin medication. These groups did not differ significantly in concentration of vitreous VEGF.

CONCLUSIONS

Statin therapy is associated with high vitreous VEGF concentration in diabetic patients with proliferative retinopathy. In contrast to previous reports, ACE inhibitor use did not significantly influence vitreous VEGF concentration in these patients.

Prospects for angiotensin receptor blockers in diabetic retinopathy

Retinopathy is the most common microvascular complication of diabetes mellitus, and is an important cause of blindness worldwide. Clinical trials have demonstrated that tight metabolic control inhibits the progression of retinopathy. Good blood pressure control has been shown to be protective in type 2 diabetes, and it may also reduce proliferative retinopathy in type 1 diabetes. However, such control is often difficult to achieve in clinical practice, and may be associated with problems such as hypoglycaemia. New therapies are therefore needed to reduce the risk of retinopathy. There is growing evidence that the renin-angiotensin system (RAS) plays an important role in the pathogenesis of diabetic retinopathy, and this has led to interest in RAS inhibitors as agents to prevent retinopathy. Several trials have suggested that ACE inhibitor therapy can inhibit progression of retinopathy. The Diabetic Retinopathy Candesartan Trials (DIRECT) Programme is currently investigating the effects of the angiotensin II receptor blocker candesartan on the incidence of retinopathy in type 1 diabetes and its progression in type 1 and type 2 diabetes. It is hoped that the results from such large-scale clinical trials will provide more specific information about the medical treatment of diabetic retinopathy.

Effects of angiotensin-converting enzyme inhibitors and beta-adrenergic blockers on retinal vascular endothelial growth factor expression in rat diabetic retinopathy

Vascular endothelial growth factor (VEGF) plays a pivotal role in diabetic retinopathy (DR) and hypertension has been identified as an independent risk factor for DR. The aim of the present study was to: (1) explore whether beta-adrenergic blockers influence retinal VEGF expression; (2) determine the effect of angiotensin-converting enzyme inhibitors (ACEI) on retinal VEGF expression independently of their anti-hypertensive actions; and (3) investigate the correlation between retinal VEGF expression and changes in retinal capillary basement membrane thickness (BMT). Streptozotocin-induced diabetic rats and control animals were assigned at random to receive the beta-adrenergic blocker propranolol, the ACEI fosenopril sodium, or vehicle for 24 weeks. Enzyme linked immunosorbent assay, immunohistochemistry, Western blot, and real-time reverse transcription-polymerase chain reaction were used to assess VEGF protein and mRNA expression. Computer-assisted morphometric measurements of transmission electron microscopy photographs were performed to evaluate BMT. Vitreous fluid and retinal VEGF protein and retinal VEGF mRNA expression were significantly higher in diabetic rats than in control rats, with a significant reduction in fosenopril sodium-treated diabetic rats (p<0.01). There was no significant difference in VEGF levels in diabetic rats and propranolol-treated diabetic rats (p>0.05), but there was a significant difference in VEGF protein and mRNA expression in propranolol-treated diabetic rats and fosenopril sodium-treated diabetic rats (p<0.01) without any significant difference in systolic blood pressure in the latter two groups (p>0.05). There was a significant correlation between the level of retinal VEGF expression and changes in retinal BMT (p<0.01). These findings suggest that the effect of ACEI on retinal VEGF expression is independent of their anti-hypertensive actions and that ACEI could offer particular benefits beyond blood pressure reduction in the treatment of DR with or without hypertension. beta-adrenergic blockers had no influence on retinal VEGF expression in normal or diabetic rats.

Vitreous fluid biomarkers

Interactions between cells and the network of secreted proteins are associated with the ocular disease. In most cases, clinical appearcance is sufficiently diagnostic. However, in cases of nonspecific or atypical clinical presentation, diagnostic sampling of vitreous fluid can aid diagnosis and treatment for ocular disease. Progresses in the basic sciences, particularly molecular biology, and advances in surgical instrumentation have greatly enhanced the diagnostic armamentarium. These developments also have led to a better understanding of the pathophysiological processes involved in ocular diseases and have prompted evolution of new therapeutic modalities. In this chapter, we review techniques for vitreous fluid sampling and biomarker quantitation thereof. The molecular biology of bioactive vitreous fluid factors is also discussed with respect to their clinical involvement in the development of ocular disease.

Correlation between angiotensin-converting enzyme, vascular endothelial growth factor, and matrix metalloproteinase-9 in the vitreous of eyes with diabetic retinopathy

PURPOSE

To investigate the involvement of angiotensin-converting enzyme (ACE) with angiogenic factors, vascular endothelial growth factor (VEGF), and matrix metalloproteinase (MMP)-9 in the vitreous of eyes with proliferative diabetic retinopathy (PDR).

DESIGN

Observational case series.

METHODS

Angiotensin-converting enzyme activity in the vitreous was measured by using a synthetic substrate for ACE. VEGF and MMP-9 concentrations were determined by enzyme-linked immunosorbent assay.

RESULTS

Vitreous ACE activity was significantly higher in eyes with PDR (1.4 +/- 1.3 mU/ml) than in eyes with macular holes (0.22 +/- 0.11 mU/ml). Vitreous VEGF concentration in the eyes with PDR (1067 +/- 1076 pg/ml) was significantly higher than in eyes with macular holes (34 +/- 5.5 pg/ml). Vitreous MMP-9 concentration was also significantly higher in eyes with PDR (7.5 +/- 3.8 ng/ml) than in eyes with macular holes (4.2 +/- 1.4 ng/ml). Significant correlations between ACE and VEGF (P < .01) and between ACE and MMP-9 (P < .01) were observed in the vitreous of eyes with PDR.

CONCLUSIONS

Angiotensin-converting enzyme was significantly correlated with angiogenic factors, VEGF and MMP-9, in the vitreous of eyes with PDR.

Vascular complications in diabetes mellitus: the role of endothelial dysfunction

The endothelium is a complex organ with a multitude of properties essential for control of vascular functions. Dysfunction of the vascular endothelium is regarded as an important factor in the pathogenesis of diabetic micro- and macro-angiopathy. Endothelial dysfunction in Type I and II diabetes complicated by micro- or macro-albuminuria is generalized in that it affects many aspects of endothelial function and occurs not only in the kidney. The close linkage between microalbuminuria and endothelial dysfunction in diabetes is an attractive explanation for the fact that microalbuminuria is a risk marker for atherothrombosis. In Type I diabetes, endothelial dysfunction precedes and may cause diabetic microangiopathy, but it is not clear whether endothelial dysfunction is a feature of the diabetic state itself. In Type II diabetes, endothelial function is impaired from the onset of the disease and is strongly related to adverse outcomes. It is not clear whether impaired endothelial function is caused by hyperglycaemia or by other factors. Impaired endothelial function is closely associated with and may contribute to insulin resistance regardless of the presence of diabetes. Endothelial dysfunction in diabetes originates from three main sources. Hyperglycaemia and its immediate biochemical sequelae directly alter endothelial function or influence endothelial cell functioning indirectly by the synthesis of growth factors, cytokines and vasoactive agents in other cells. Finally, the components of the metabolic syndrome can impair endothelial function.

Quantitative measurement of retinal thickness in patients with diabetic macular edema is useful for evaluation of therapeutic agents

The effect of lisinopril (an angiotensin-converting enzyme inhibitor) on diabetic macular edema (DME) was investigated by quantitative measurement of macular thickness. In a nonrandomized clinical trial, 19 normotensive type 2 diabetic patients with DME prospectively received oral lisinopril therapy for 2 months. Another 10 normotensive type 2 diabetic patients with similar DME were prospectively followed for two months without treatment. Central macular thickness was measured with a retinal thickness analyzer (RTA). In the lisinopril group, visual acuity improved by two lines or more in two out of 19 eyes (11%), was unchanged in 15 eyes (78%), and deteriorated by two lines or more in two eyes (11%). The mean central macular thickness was significantly reduced after 2 months of treatment (381.3 +/- 121.1 microm) compared with that before administration (475.2 +/- 171.0 microm, P = 0.0093). In the control group, central macular thickness was not significantly decreased after 2 months (458.5 +/- 113.7 microm, P = 0.2178) compared with the baseline value (464.7 +/- 152.2). Fluorescein angiography showed that macular leakage was decreased in 10 patients from the lisinopril group (53%) and was unchanged in nine patients (47%). There was a significant difference of central macular thickness between the patients with and without improvement of macular leakage (P = 0.0040). Lisinopril therapy may reduce macular thickness in patients with DME, as shown by this quantitative study. In addition, quantitative measurement of retinal thickness is useful when evaluating therapeutic agents for DME.

Effect of angiotensin-converting enzyme-inhibiting therapy on the expression of vascular endothelial growth factor in hyperstimulated rat ovary

OBJECTIVE

To determine the effect of angiotensin-converting enzyme-inhibiting therapy on the expression of vascular endothelial growth factor (VEGF) in the hyperstimulated rat ovary.

DESIGN

Experimental study.

SETTING

University animal research laboratory.

ANIMAL(S)

Thirty Wistar albino adult female rats were studied; 20 rats were stimulated with gonadotropins (groups 1 and 2), and 10 were controls (group 3). Ten of the stimulated rats received additional treatment with enalapril (group 2).

INTERVENTION(S)

At the end of the treatment period, rat ovaries were subjected to immunohistochemical staining with anti-VEGF antibodies.

MAIN OUTCOME MEASURE(S)

VEGF staining intensity was graded semiquantitatively, and the H-score was calculated by light microscopic examination of the groups.

RESULT(S)

VEGF expression was found to be significantly higher in the endothelium and stroma in groups 1 and 2 compared with group 3. Although VEGF immunoreactivity was lower in the stimulation regimen plus enalapril group compared with the stimulation regimen-only group, the difference was insignificant.

CONCLUSION(S)

Enalapril does not seem to have a significant effect on VEGF expression in the hyperstimulated rat ovary. Because angiotensin II exerts its multiple actions via specific receptors, there may be other factors, such as a receptor blockade, that contribute to the VEGF expression.

Current approaches and perspectives in the medical treatment of diabetic retinopathy

Diabetic retinopathy is a leading cause of visual loss in industrialized countries. Its classification includes preclinical, nonproliferative (mild, moderate, and severe or preproliferative diabetic retinopathy) and proliferative stages (low risk, high risk, and advanced). Diabetic maculopathy (exudative, edematous, or ischemic) may be associated with either nonproliferative or proliferative retinopathy. Prevention requires the tightest possible control of both blood glucose and blood pressure. Laser photocoagulation remains the only procedure recommended for severe nonproliferative or proliferative retinopathy and maculopathy. Since it reduces legal blindness by more than 90% in proliferative retinopathy and prevents severe sight loss in diabetic maculopathy, photocoagulation is probably one of the most effective forms of treatment known today. Less destructive approaches are desirable, however, and those currently under phase 3 trial include blockade of angiotensin receptors, the beta-isoform of protein kinase C, and growth hormone secretion by long-acting analogues of somatostatin. Evidence from past randomized controlled studies does not support a role for inhibitors of platelet aggregation, aldose reductase, and advanced glycosylation end products in the prevention/treatment of retinopathy. Future approaches might include the use of thiamine and its analogues in the primary and secondary prevention of early retinopathy and blockers of vascular endothelial growth factor/vascular permeability factor in more advanced stages.

Preventing diabetic retinopathy through control of systemic factors

PURPOSE OF REVIEW

Diabetic retinopathy (DR), the leading cause of vision loss in working-age adults, is associated with many systemic factors that contribute to the severity and progression of this disease. Intensive glycemic and blood pressure control has been shown to delay both the onset and progression of diabetic retinopathy.

RECENT FINDINGS

Studies involving angiotensin-converting enzyme inhibitors are currently underway to elucidate the efficacy of these drugs in further reducing the progression of diabetic retinopathy by means other than just hypertensive control. Dyslipidemia is associated with macular exudates and vision loss. Anticoagulation with aspirin is neither contraindicated in diabetics nor associated with prevention or progression of diabetic retinopathy. The effects of smoking on diabetic retinopathy are equivocal. Pregnancy may be associated with the progression of diabetic retinopathy in the absence of long-term effects if serum glucose levels are well monitored and controlled prior to and during pregnancy.

SUMMARY

Genetic research is providing more insight into the pathogenesis and mechanisms of diabetic retinopathy, allowing possible identification of those at higher risk for developing diabetic retinopathy.

Medical management of diabetic retinopathy

Although current treatment and prevention of diabetic retinopathy with laser photocoagulation, and tight metabolic and blood pressure control has reduced the risk of visual loss, there is still a need for additional therapies. A literature review on medical therapies for diabetic retinopathy has been performed, and the following classes of drugs are discussed: blockers of the renin-angiotensin system, protein kinase C-beta inhibitors, glitazones, somatostatin analogues, lipid-lowering drugs and anti-inflammatory drugs. There is experimental and clinical data suggesting beneficial effect from several classes of drugs on diabetic retinopathy, and results from large clinical trials are awaited within the next 3-4 years.

Connective tissue growth factor is up-regulated in the diabetic retina: amelioration by angiotensin-converting enzyme inhibition

Connective tissue growth factor (CTGF) has been postulated to have prosclerotic and angiogenic properties. The aim of this present study was to characterize retinal CTGF expression in the absence and presence of diabetes and in the context of treatment with the angiotensin-converting enzyme (ACE) inhibitor, perindopril. Retinas were obtained from control, diabetic, and diabetic plus perindopril-treated (3 mg/d) rats. CTGF gene expression was quantitated by RT-PCR and localized by in situ hybridization. CTGF protein expression was analyzed by Western blotting and localized by immunohistochemistry. Diabetes was associated with a greater than 2-fold increase in CTGF mRNA levels, which was attenuated by perindopril treatment. CTGF immunoreactivity was increased almost 2-fold in diabetes and was ameliorated by the ACE inhibitor perindopril. By in situ hybridization and immunohistochemistry, the major site of CTGF gene expression in the retina of diabetic rats was the ganglion cell layer. Based on the known in vivo effects of CTGF, it is postulated that this growth factor plays a pivotal role in mediating diabetes-associated retinal pathology. Furthermore, the protective effects of ACE inhibitors on retinal pathology may partly be mediated via effects on retinal CTGF expression.

Pharmacologic therapy for diabetic retinopathy

Diabetic retinopathy remains one of the major causes of acquired blindness in developed nations. This is true despite the development of laser treatment, which can prevent blindness in the majority of those who develop macular oedema (ME) or proliferative diabetic retinopathy (PDR). ME is manifest by retinal vascular leakage and thickening of the retina. The hallmark of PDR is neovascularisation (NV)--abnormal angiogenesis that may ultimately cause severe vitreous cavity bleeding and/or retinal detachment. Pharmacologic therapy aimed specifically at preventing vascular leakage and NV would be a welcome addition to the armamentarium. PDR and ME could be prevented by improved metabolic control or by pharmacologically blunting the biochemical consequences of hyperglycaemia (e.g., with aldose reductase inhibitors, inhibitors of non-enzymatic glycation or by protein kinase C [PKC] inhibition). The angiogenesis in PDR could be treated via growth factor (e.g., vascular endothelial growth factor [VEGF], insulin like growth factor-1 [IGF-1]) blockade, integrin (e.g., alpha-v beta-3) blockade, extracellular matrix alteration (e.g., with steroid compounds) or interference with intracellular signal transduction pathways (e.g., PKC and mitogen activated protein kinase [MAPK] pathway proteins). Some of these antiangiogenic agents may also prove useful for treating or preventing ME. Numerous potentially useful antiangiogenic compounds are in development; two drugs are presently in clinical trials for treatment of the preproliferative stage of PDR, while two are in clinical trials for treatment of ME.

Reversion of 'early worsening' of diabetic retinopathy by deliberate restoration of poor metabolic control

Acutely lowering long-standing severe hyperglycaemia can trigger progression ('early worsening') of diabetic retinopathy, most likely by up-regulation of the circulating insulin-like growth factor 1 (IGF-1). This condition, also called 'florid retinopathy', rarely responds to standard laser coagulation treatment. In this retrospective report, 2 young patients with type 2 diabetes are described, in whom deliberate restoration of poor diabetes control reduced the serum IGF-1 levels and improved 'early worsened' diabetic retinopathy.

Relation of diabetic macular edema to cytokines and posterior vitreous detachment

PURPOSE

To investigate whether angiotensin II (AII) or vascular endothelial growth factor (VEGF) is related to diabetic macular edema (DME) in patients with and without posterior vitreous detachment (PVD).

DESIGN

A case-control study.

METHODS

Vitreous fluid samples were obtained at vitreoretinal surgery from 28 eyes of 28 DME patients without PVD, 8 eyes of 8 DME patients with PVD, 14 eyes of 14 nondiabetic patients, and 8 eyes of diabetic patients without retinopathy. The VEGF levels in vitreous fluid and plasma were determined by enzyme-linked immunosorbent assay, while AII levels were measured by radioimmunoassay.

RESULTS

The vitreous levels of AII and VEGF were significantly higher in DME patients with or without PVD than in nondiabetic patients or diabetic patients without retinopathy (without PVD: P < .0061, P < .0001, P = .0261, and P < .0001; with PVD: P < .0012, P < .0001, P = .0473, and P < .0001, respectively). There was no significant difference in the vitreous levels of AII or VEGF between patients with or without PVD (P = .4948 and P = .6642, respectively). The vitreous level of AII significantly correlated with that of VEGF in DME patients without PVD (P = .576) or with PVD (P = .488). AII and VEGF levels in vitreous fluid were significantly higher than the respective plasma levels.

CONCLUSIONS

We found that the vitreous levels of AII and VEGF were elevated in DME patients irrespective of the status of PVD. Angiotensin II and VEGF may be induced in the eyes and be related to the pathogenesis of DME.

Current and Future Strategies for the Management of Diabetic Neuropathy

Diabetic neuropathy is common, related to increased morbidity and mortality, and has no effective treatment at present. Interventions based on putative pathways thought to contribute to damage and repair of nerve fibres have yielded little success to date. Pain is a potentially debilitating manifestation of diabetic neuropathy and has many potential sites of origin and, hence, modulation. Its cause is unclear and it does not respond well to traditional pain therapies, proposed to mediate their benefits via multiple peripheral and central mechanisms. A better understanding of the mechanisms leading to nerve fibre degeneration and regeneration as well as pain has recently resulted in the development of a more targeted approach to the treatment of diabetic neuropathy. Thus, specific NMDA receptor antagonists and more specific neuronal serotonin and norepinephrine (noradrenaline) uptake inhibitors offer promise in the treatment of painful diabetic neuropathy. A number of treatments which include the aldose reductase inhibitors and neurotrophins have failed to reach the clinical arena. However, the antioxidant alpha-lipoic acid, as well as compounds which correct vascular dysfunction and hence neuropathy, such as ACE inhibitors and protein kinase C-beta inhibitors, have demonstrated more success.

The renin-angiotensin-aldosterone system and the eye in diabetes

Diabetic retinopathy is the leading cause of blindness in the under 65s, and with the burden of disease case load expected to exceed 200 million worldwide within 10 years, much effort is being spent on prophylactic interventions. Early work focused on improving glycaemic control; however, with the publication of EURODIAB Controlled trial of Lisinopril in Insulin-dependent Diabetes (EUCLID) and United Kingdom Prospective Diabetes Study (UKPDS), the focus has recently moved to control of blood pressure and specifically the renin-angiotensin system (RAS). There is a large body of evidence for a local RAS within the eye that is activated in diabetes. This appears to be directly responsible, as well as indirectly through other mediators, for an increase in concentration of vascular endothelial growth factor (VEGF), a selective angiogenic and vasopermeability factor that is implicated in the pathogenesis of diabetic retinopathy. Inhibition of angiotensin-converting enzyme appears to reduce concentrations of VEGF, with a concurrent anti-proliferative effect independent of systemic VEGF levels or blood pressure. Angiotensin II (Ang II) Type 1 (AT(1)) receptor blockade has been shown to reduce neovascularisation independent of VEGF levels in animal models. This may be due to antagonism of activation of mitogen-activated protein kinase, which is a potent cellular proliferation stimulator, by Ang II, although this needs further evaluation.