The pleiotropic effects of simvastatin on retinal microvascular endothelium has important implications for ischaemic retinopathies

Artificial intelligence in therapeutic management of hyperlipidemic ocular pathology

Hyperlipidemia has many ocular manifestations, the most prevalent being retinal vascular occlusion. Hyperlipidemic lesions and occlusions to the vessels supplying the retina result in permanent blindness, necessitating prompt detection and treatment. Retinal vascular occlusion is diagnosed using different imaging modalities, including optical coherence tomography angiography. These diagnostic techniques obtain images representing the blood flow through the retinal vessels, providing an opportunity for AI to utilize image recognition to detect blockages and abnormalities before patients present with symptoms. AI is already being used as a non-invasive method to detect retinal vascular occlusions and other vascular pathology, as well as predict treatment outcomes. As providers see an increase in patients presenting with new retinal vascular occlusions, the use of AI to detect and treat these conditions has the potential to improve patient outcomes and reduce the financial burden on the healthcare system. This article comprehends the implications of AI in the current management strategies of retinal vascular occlusion (RVO) in hyperlipidemia and the recent developments of AI technology in the management of ocular diseases.

Enhancing the human health and lifespan: a targeted strategy emphasizing statins

There has been substantial research interest in finding activities/agents that slow the onset and reduce the severity of numerous age-related diseases/conditions. This assessment indicates that the most studied agent intended to promote health in human population investigations for a broad spectrum of diseases are the statins, with large-scale epidemiological studies addressing numerous health endpoints. The key findings are that statin treatment consistently reduces the occurrence and attenuates the course of numerous non-communicable and contagious pathologies and numerous types of cancer with high mortality rates by about 20-50%. That one agent could affect such a broad based and consistently positive trends in epidemiological studies is unexpected and impressive, along with consistent cell and animal model research. Underlying mechanisms have been proposed that significantly contribute to the spectrum of salutary effects of statins, especially the capacity to activate Nrf2 showing hormetic dose responses in multiple organs and cell types, due to its bioavailability and broad tissue distribution. The widespread use of statins, which has the capacity to enhance human health span, should be considered for experimental exploration as a novel public health strategy that includes practical approaches for reduction of the most common adverse effects of this class of drugs including myalgia/myopathy and transaminitis.

The Effect of Systemic Parameters and Baseline Characteristics in Short-Term Response Analysis with Intravitreal Ranibizumab in Treatment-Naive Patients with Neovascular Age-Related Macular Degeneration

Anti-vascular endothelial growth factor drugs keep being the main therapy for neovascular age-related macular degeneration (AMD). Possible predictive parameters (demographic, biochemical and/or inflammatory) could anticipate short-term treatment response with ranibizumab. 46 treatment-naive patients were included in a prospective observational study. They underwent three monthly injections of intravitreal ranibizumab for neovascular AMD and the clinical examination was made at baseline and one month after the third injection. Demographic characteristics, co-morbidities and concomitant treatments were recorded at the baseline visit. Biochemical parameters, complete blood count and inflammation biomarkers were also measured at these times. Uric Acid was found to be statistically significant with a one-point difference between good and poor responders in both basal and treated patients, but only in basal parameters was statistical significance reached (p = 0.007 vs. p = 0.071 in treated patients). Cholesterol and inflammatory parameters such as white blood cell count and neutrophils were significantly reduced over time when treated with intravitreal ranibizumab. On the other hand, women seemed to have a worse prognosis for short-term response to intravitreal ranibizumab treatment. Uric acid may help identify possible non-responders before initial treatment with ranibizumab, and cholesterol and white blood cells could be good candidates to monitor short-term response to ranibizumab treatment.

Mechanistic insights into the alterations and regulation of the AKT signaling pathway in diabetic retinopathy

In the early stages of diabetic retinopathy (DR), diabetes-related hyperglycemia directly inhibits the AKT signaling pathway by increasing oxidative stress or inhibiting growth factor expression, which leads to retinal cell apoptosis, nerve proliferation and fundus microvascular disease. However, due to compensatory vascular hyperplasia in the late stage of DR, the vascular endothelial growth factor (VEGF)/phosphatidylinositol 3 kinase (PI3K)/AKT cascade is activated, resulting in opposite levels of AKT regulation compared with the early stage. Studies have shown that many factors, including insulin, insulin-like growth factor-1 (IGF-1), VEGF and others, can regulate the AKT pathway. Disruption of the insulin pathway decreases AKT activation. IGF-1 downregulation decreases the activation of AKT in DR, which abrogates the neuroprotective effect, upregulates VEGF expression and thus induces neovascularization. Although inhibiting VEGF is the main treatment for neovascularization in DR, excessive inhibition may lead to apoptosis in inner retinal neurons. AKT pathway substrates, including mammalian target of rapamycin (mTOR), forkhead box O (FOXO), glycogen synthase kinase-3 (GSK-3)/nuclear factor erythroid 2-related factor 2 (Nrf2), and nuclear factor kappa-B (NF-κB), are a research focus. mTOR inhibitors can delay or prevent retinal microangiopathy, whereas low mTOR activity can decrease retinal protein synthesis. Inactivated AKT fails to inhibit FOXO and thus causes apoptosis. The GSK-3/Nrf2 cascade regulates oxidation and inflammation in DR. NF-κB is activated in diabetic retinas and is involved in inflammation and apoptosis. Many pathways or vital activities, such as the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and mitogen-activated protein kinase (MAPK) signaling pathways, interact with the AKT pathway to influence DR development. Numerous regulatory methods can simultaneously impact the AKT pathway and other pathways, and it is essential to consider both the connections and interactions between these pathways. In this review, we summarize changes in the AKT signaling pathway in DR and targeted drugs based on these potential sites.

Vascular therapy for Duchenne muscular dystrophy (DMD)

Duchenne muscular dystrophy (DMD) is a progressive disease characterized by the wasting of the muscles that eventually lead to difficulty moving and, ultimately, premature death from heart and respiratory complications. DMD deficiency is caused by mutations in the gene encoding dystrophin, which prevents skeletal muscle, cardiac muscle, and other cells from producing the functional protein. Located on the cytoplasmic face of the plasma membrane of muscle fibers, dystrophin serves as a component of the dystrophin glycoprotein complex (DGC), mechanically reinforces the sarcolemma, and stabilizes the DGC, preventing it from contraction-mediated muscle degradation. In DMD muscle, dystrophin deficiency leads to progressive fibrosis, myofiber damage, chronic inflammation, and dysfunction of the mitochondria and muscle stem cells. Currently, DMD is incurable, and treatment involves the administration of glucocorticoids in order to delay disease progression. In the presence of developmental delay, proximal weakness, and elevated serum creatine kinase levels, a definitive diagnosis can usually be made after an extensive review of the patient's history and physical examination, as well as confirmation through muscle biopsy or genetic testing. Current standards of care include the use of corticosteroids to prolong ambulation and delay the onset of secondary complications, including respiratory muscle and cardiac functions. However, different studies have been carried out to show the relationship between vascular density and impaired angiogenesis in the pathogenesis of DMD. Several recent studies on DMD management are vascular targeted and focused on ischemia as a culprit for the pathogenesis of DMD. This review critically discusses approaches-such as modulation of nitric oxide (NO) or vascular endothelial growth factor (VEGF)-related pathways-to attenuate the dystrophic phenotype and enhance angiogenesis.

Association of Use of Statins with Progression of Diabetic Retinopathy at a Tertiary Care Hospital in Southern India

Purpose:

To study the role of statin therapy on diabetic retinopathy (DR) progression.

Methods:

This retrospective study was carried out at a tertiary care hospital in southern India. Data were collected from the medical records of patients admitted from January 2013 to December 2018. Out of 1673 patients of DR enrolled in the study, 171 met the inclusion criteria. Patients' demographic data, drug history, clinical characteristics, and laboratory investigations were recorded as per the pro forma. The patients were divided into statin users and nonusers. The results were analyzed to compare the DR progression between the two groups.

Results:

DR progressed in 67% of nonstatin users and 37% of statin users (P < 0.001). The use of statins decreased the risk of DR progression (P < 0.001). Center-involving macular edema was seen in 8 of 79 statin users (10%) and 16 of 92 statin nonusers (16%) based on optical coherence tomography findings during the follow-up period (P = 0.17).

Conclusion:

In patients with type 2 diabetes, lipid-lowering therapy with statins has the potential to retard DR progression.

Association between Statins and Retinal Vascular Occlusion: A Population-Based Cohort Study

Retinal vascular occlusion (RVO), including retinal arterial occlusion and retinal vein occlusion, is a common retinal vascular disease that causes visual disturbance. The exact pathogenesis of RVO remains unclear. In all types of RVO patients, hyperlipidemia is more than twofold more common than in controls. Statins have been used to control blood cholesterol levels and have been found to reduce the risk of cardiovascular morbidity and mortality. Moreover, the immunomodulatory functions of statins may play a role in treating inflammatory diseases. This study aimed to evaluate whether patients taking statins have a lower risk of developing RVO compared to patients not taking statins. Adult patients with statins usage on the index date identified from the Taiwan National Health Insurance Research Database (NHIRD) between 2000 and 2013 were included. A threefold matched group was selected using age, sex, and year of index date for comparison. During the mean follow-up period of 12.87 ± 1.88 years, the cumulative incidence of RVO was significantly lower in the statin-user group (29.96 per 105 person-years [PYs]) than in the non-statin-user group (39.35 per 105 PYs). The results showed a lower cumulative incidence rate of RVO in patients prescribed statins than in those not prescribed statins (log-rank test, p = 0.020). The adjusting hazard ratio (HR) was significantly greater for RVO in the statin-user group (adjusted HR, 0.704; 95% CI, 0.591-0.873). Statin users had a decreased risk for all types of RVO development, including central retinal artery occlusion, arterial branch occlusion, central retinal vein occlusion, and branch retinal vein occlusion. In conclusion, patients undergoing statin treatment have a lower risk of developing RVO compared to patients not taking statins.

Effect of oral statin use on mitomycin-C augmented trabeculectomy outcomes

Purpose

The effect of statins on wound healing is controversial, and their effect on trabeculectomy outcomes remains unclear. This study aimed to examine the relationship between oral statin use and trabeculectomy outcomes.

Methods

Medical records of patients who underwent primary mitomycin-C augmented trabeculectomy with 2 years of follow-up were reviewed. Pre- and postoperative intraocular pressures (IOP) and numbers of medications, subconjunctival 5-fluorouracil (5-FU) injections, and bleb-needling procedures were compared between statin users and nonusers. Failure was defined as an eye that failed to achieve a 20% lowering of IOP from baseline or had an IOP > 21 mm Hg, as well as an eye that required further surgical intervention, developed hypotony, or had no light perception visual acuity.

Results

In total, 158 subjects were enrolled, with 47 eyes from statin users and 111 eyes from statin nonusers. The 24-month cumulative probability of failure was 78.7% for statin users and 60.4% for nonusers (P = .013). Cox proportional-hazards modeling showed a significantly higher hazard risk in statin users (adjusted hazard ratio 1.61, P = .026). There were no significant between-group differences in mean IOPs or number of medications (both P > .05) at 24 months. Multivariable Poisson regression analysis that statin use was associated with increased numbers of 5-FU injections (P = .014) and bleb-needling procedures (P = .031).

Conclusions

This study demonstrated that oral statin use was associated with higher rates of trabeculectomy failure and increased numbers of 5-FU injections and bleb-needling procedures.

Emerging Roles of Dyslipidemia and Hyperglycemia in Diabetic Retinopathy: Molecular Mechanisms and Clinical Perspectives

Diabetic retinopathy (DR) is a significant cause of vision loss and a research subject that is constantly being explored for new mechanisms of damage and potential therapeutic options. There are many mechanisms and pathways that provide numerous options for therapeutic interventions to halt disease progression. The purpose of the present literature review is to explore both basic science research and clinical research for proposed mechanisms of damage in diabetic retinopathy to understand the role of triglyceride and cholesterol dysmetabolism in DR progression. This review delineates mechanisms of damage secondary to triglyceride and cholesterol dysmetabolism vs. mechanisms secondary to diabetes to add clarity to the pathogenesis behind each proposed mechanism. We then analyze mechanisms utilized by both triglyceride and cholesterol dysmetabolism and diabetes to elucidate the synergistic, additive, and common mechanisms of damage in diabetic retinopathy. Gathering this research adds clarity to the role dyslipidemia has in DR and an evaluation of the current peer-reviewed basic science and clinical evidence provides a basis to discern new potential therapeutic targets.

Inhibiting NF-κB Signaling Activation Reduces Retinal Neovascularization by Promoting a Polarization Shift in Macrophages

Purpose

Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling is involved in regulating tumor angiogenesis and metastasis; however, the exact mechanism of action in retinal neovascularization (RNV) remains unclear. The purpose of this study was to determine the role and underlying mechanism of NF-κB in regulating RNV in retinal neovascularization mice.

Methods

Expression levels of NF-κB signaling were detected by immunofluorescence staining and western blotting in retinas of oxygen-induced retinopathy (OIR) mice. OIR mice were treated with either pyrrolidinedithiocarbamate (PDTC), a NF-κB signaling inhibitor, or PBS, and retinal flat-mounts were performed to quantify the area of RNV and the recruitment of retinal macrophages by immunofluorescence staining. Macrophage polarization detected by flow cytometric analysis and the expression of macrophage polarization-associated genes were evaluated by immunofluorescence staining, quantitative RT-PCR, and western blotting.

Results

Expression levels of phosphorylated IκBα (p-IκBα) and p-p65 increased in OIR mice. Inhibiting NF-κB signaling activation by PDTC significantly reduced RNV. After treatment with PDTC, a reduction in the quantity of macrophages was observed: M1 polarized macrophages decreased, and M2 polarized macrophages increased; the expression of M1 macrophage-associated cytokines decreased and M2 macrophage-associated cytokines increased in the retinas of OIR mice.

Conclusions

Blocking activation of NF-κB signaling reduces RNV by promoting polarization of M1 macrophages to M2 macrophages in OIR mice.

Ovarian cancer cell-secreted exosomal miR-205 promotes metastasis by inducing angiogenesis

Background: By providing oxygen, nutrients and metastatic conduits, tumour angiogenesis is essential for cancer metastasis. Cancer cell-secreted microRNAs can be packaged into exosomes and are implicated in different aspects of tumour angiogenesis. However, the underlying mechanisms are incompletely understood. Methods: The GEPIA database and in situ hybridization assay were used to analyse expression of miR-205 in ovarian tissues. Immunohistochemistry was performed to examine the relationship between miR-205 and microvessel density. Expression of circulating miR-205 was evaluated by RT-PCR and GEO database analysis. Co-culture and exosome labelling experiments were performed to assess exosomal miR-205 transfer from ovarian cancer (OC) cells to endothelial cells ECs. Exosome uptake assays were employed to define the cellular pathways associated with the endocytic uptake of exosomal miR-205. The role of exosomal miR-205 in angiogenesis was further investigated in vivo and in vitro. Western blotting and rescue experiments were applied to detect regulation of the PTEN-AKT pathway by exosomal miR-205 in ECs. Results: miR-205 was up-regulated in OC tissues, and high expression of miR-205 was associated with metastatic progression in OC patients. Moreover, miR-205 was highly enriched in cancer-adjacent ECs, and up-regulation of miR-205 correlated positively with high microvessel density in OC patients. Importantly, miR-205 was markedly enriched in the serum of OC patients, and a high level of miR-205 in circulating exosomes was associated with OC metastasis. In addition, OC-derived miR-205 was secreted into the extracellular space and efficiently transferred to adjacent ECs in an exosome-dependent manner, and the lipid raft-associated pathway plays an important role in regulating uptake of exosomal miR-205. Exosomal miR-205 from OC cells significantly promoted in vitro angiogenesis and accelerated angiogenesis and tumour growth in a mouse model. Furthermore, we found that exosomal miR-205 induces angiogenesis via the PTEN-AKT pathway. Conclusion: These findings demonstrate an exosome-dependent mechanism by which miR-205 derived from cancer cells regulates tumour angiogenesis and implicate exosomal miR-205 as a potential therapeutic target for OC.

Intravitreal Delivery of VEGF-A165-loaded PLGA Microparticles Reduces Retinal Vaso-Obliteration in an In Vivo Mouse Model of Retinopathy of Prematurity

PURPOSE

Retinopathy of prematurity (ROP) is a condition of abnormal retinal vascularization with reduced levels of vascular endothelial growth factor (VEGF) causing vaso-obliteration (Phase I), followed by abnormal neovascularization from increased VEGF (Phase II). We hypothesized that intravitreal pro-angiogenic VEGF-A in microparticle form would promote earlier retinal revascularization in an oxygen-induced ischemic retinopathy (OIR) mouse model.

MATERIALS AND METHODS

Wildtype mice (39) were exposed to 77% oxygen from postnatal day 7 (P7) to P12. VEGF-A₁₆₅-loaded poly(lactic-co-glycolic acid) (PLGA) (n = 15) or empty PLGA (n = 14) microparticles were fabricated using a water-in-oil-in-water double emulsion method, and injected intravitreally at P13 into mice right eyes (RE). Left eyes (LE) were untreated. At P20, after retinal fluorescein angiography, vascular parameters were quantified. Retinal VEGF levels at P13 and flatmounts at P20 were performed separately.

RESULTS

VEGF-A₁₆₅-loaded microparticles had a mean diameter of 4.2 μm. with a loading level of 8.6 weight.%. Retinal avascular area was reduced in VEGF-treated RE (39.5 ± 9.0%) compared to untreated LE (52.6 ± 6.1%, p < 0.0001) or empty microparticle-treated RE (p < 0.001) and untreated LEs (p = 0.001). Retinal arteries in VEGF-treated RE were less tortuous than untreated LE (1.08 ± 0.05 vs. 1.18 ± 0.08, p < 0.001) or empty-microparticles-treated RE (p = 0.02). Retinal arterial tortuosity was similar in the LE of VEGF and empty microparticle-treated mice (P > 0.05). Retinal vein width was similar in VEGF-treated and empty microparticle-treated RE (P > 0.9), which were each less dilated than their contralateral LE (p < 0.01). VEGF levels were higher in P13 OIR mice than RA mice (p < 0.0001). Retinal flatmounts showed vaso-obliteration and neovascularization.

CONCLUSIONS

Endogenous retinal VEGF is suppressed in OIR mice. Exogenous intravitreal VEGF-A₁₆₅-loaded microparticles in OIR mice reduced retinal vaso-obliteration and accelerated recovery from vein dilation and arterial tortuosity. This may be beneficial in preventing Phase II ROP without systemic effects.

'Statins in retinal disease'

Statins are known for their blood cholesterol-lowering effect and are widely used in patients with cardiovascular and metabolic diseases. Research over the past three decades shows that statins have diverse effects on different pathophysiological pathways involved in angiogenesis, inflammation, apoptosis, and anti-oxidation, leading to new therapeutic options. Recently, statins have attracted considerable attention for their immunomodulatory effect. Since immune reactivity has been implicated in a number of retinal diseases, such as uveitis, age-related macular degeneration (AMD) and diabetic retinopathy, there is now a growing body of evidence supporting the beneficial effects of statins in these retinopathies. This review evaluates the relationship between statins and the pathophysiological basis of these diseases, focusing on their potential role in treatment. A PubMed database search and literature review was conducted. Among AMD patients, there is inconsistent evidence regarding protection against development of early AMD or delaying disease progression; though they have been found to reduce the risk of developing choroidal neovascular membranes (CNV). In patients with retinal vein occlusion, there was no evidence to support a therapeutic benefit or a protective role with statins. In patients with diabetic retinopathy, statins demonstrate a reduction in disease progression and improved resolution of diabetic macular oedema (DMO). Among patients with uveitis, statins have a protective effect by reducing the likelihood of uveitis development.

PLGA Microparticles Entrapping Chitosan-Based Nanoparticles for the Ocular Delivery of Ranibizumab

Age-related macular degeneration (AMD) is the leading cause of certified vision loss worldwide. The standard treatment for neovascular AMD involves repeated intravitreal injections of therapeutic proteins directed against vascular endothelial growth factor, such as ranibizumab. Biodegradable polymers, such as poly(lactic-co-glycolic acid) (PLGA), form delivery vehicles which can be used to treat posterior segment eye diseases, but suffer from poor protein loading and release. This work describes a "system-within-system", PLGA microparticles incorporating chitosan-based nanoparticles, for improved loading and sustained intravitreal delivery of ranibizumab. Chitosan-N-acetyl-l-cysteine (CNAC) was synthesized and its synthesis confirmed using FT-IR and (1)H NMR. Chitosan-based nanoparticles composed of CNAC, CNAC/tripolyphosphate (CNAC/TPP), chitosan, chitosan/TPP (chit/TPP), or chit/TPP-hyaluronic acid (chit/TPP-HA) were incorporated in PLGA microparticles using a modified w/o/w double emulsion method. Nanoparticles and final nanoparticles-within-microparticles were characterized for their protein-nanoparticle interaction, size, zeta potential, morphology, protein loading, stability, in vitro release, in vivo antiangiogenic activity, and effects on cell viability. The prepared nanoparticles were 17-350 nm in size and had zeta potentials of -1.4 to +12 mV. Microscopic imaging revealed spherical nanoparticles on the surface of PLGA microparticles for preparations containing chit/TPP, CNAC, and CNAC/TPP. Ranibizumab entrapment efficiency in the preparations varied between 13 and 69% and was highest for the PLGA microparticles containing CNAC nanoparticles. This preparation also showed the slowest release with no initial burst release compared to all other preparations. Incorporation of TPP to this formulation increased the rate of protein release and reduced entrapment efficiency. PLGA microparticles containing chit/TPP-HA showed the fastest and near-complete release of ranibizumab. All of the prepared empty particles showed no effect on cell viability up to a concentration of 12.5 mg/mL. Ranibizumab released from all preparations maintained its structural integrity and in vitro activity. The chit/TPP-HA preparation enhanced antiangiogenic activity and may provide a potential biocompatible platform for enhanced antiangiogenic activity in combination with ranibizumab. In conclusion, the PLGA microparticles containing CNAC nanoparticles showed significantly improved ranibizumab loading and release profile. This novel drug delivery system may have potential for improved intravitreal delivery of therapeutic proteins, thereby reducing the frequency, risk, and cost of burdensome intravitreal injections.

Statin-conferred enhanced cellular resistance against bacterial pore-forming toxins in airway epithelial cells

Statins are widely used to prevent cardiovascular disease. In addition to their inhibitory effects on cholesterol synthesis, statins have beneficial effects in patients with sepsis and pneumonia, although molecular mechanisms have mostly remained unclear. Using human airway epithelial cells as a proper in vitro model, we show that prior exposure to physiological nanomolar serum concentrations of simvastatin (ranging from 10-1,000 nM) confers significant cellular resistance to the cytotoxicity of pneumolysin, a pore-forming toxin and the main virulence factor of Streptococcus pneumoniae. This protection could be demonstrated with a different statin, pravastatin, or on a different toxin, α-hemolysin. Furthermore, through the use of gene silencing, pharmacological inhibitors, immunofluorescence microscopy, and biochemical and metabolic rescue approaches, we demonstrate that the mechanism of protection conferred by simvastatin at physiological nanomolar concentrations could be different from the canonical mevalonate pathways seen in most other mechanistic studies conducted with statins at micromolar levels. All of these data are integrated into a protein synthesis-dependent, calcium-dependent model showing the interconnected pathways used by statins in airway epithelial cells to elicit an increased resistance to pore-forming toxins. This research fills large gaps in our understanding of how statins may confer host cellular protection against bacterial infections in the context of airway epithelial cells without the confounding effect from the presence of immune cells. In addition, our discovery could be potentially developed into a host-centric strategy for the adjuvant treatment of pore-forming toxin associated bacterial infections.

Lipids and Diabetic Retinopathy

The relationship between lipids and the development and/or severity of diabetic retinopathy (DR) is complex. Large epidemiologic studies suggest an inconsistent and overall modest association between serum triglycerides or major cholesterol species and the severity of DR; however, certain specific lipoprotein species may have stronger associations with DR severity, suggesting a pathophysiological role for lipoproteins analogous to that seen in atherosclerosis. In this lipoprotein-mediated DR pathogenesis model, damage to the blood-retinal barrier allows extravasation of lipoprotein species, which are modified in the intraretinal environment, creating substantial local damage. Additionally, hypolipidemic therapy with statins and fibrates--particularly the latter--have been shown to modulate DR in large-scale studies. Since serum lipid profile changes do not necessarily correlate with DR modulation, the efficacy of these agents may be due to their tissue-specific changes in lipoproteins and/or their anti-inflammatory, antioxidative, antiangiogenic, and antiapoptotic functions.

Intravitreal AAV2.COMP-Ang1 Prevents Neurovascular Degeneration in a Murine Model of Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness in the working-age population in the U.S. The vision-threatening processes of neuroglial and vascular dysfunction in DR occur in concert, driven by hyperglycemia and propelled by a pathway of inflammation, ischemia, vasodegeneration, and breakdown of the blood retinal barrier. Currently, no therapies exist for normalizing the vasculature in DR. Here, we show that a single intravitreal dose of adeno-associated virus serotype 2 encoding a more stable, soluble, and potent form of angiopoietin 1 (AAV2.COMP-Ang1) can ameliorate the structural and functional hallmarks of DR in Ins2Akita mice, with sustained effects observed through six months. In early DR, AAV2.COMP-Ang1 restored leukocyte-endothelial interaction, retinal oxygenation, vascular density, vascular marker expression, vessel permeability, retinal thickness, inner retinal cellularity, and retinal neurophysiological response to levels comparable with nondiabetic controls. In late DR, AAV2.COMP-Ang1 enhanced the therapeutic benefit of intravitreally delivered endothelial colony-forming cells by promoting their integration into the vasculature and thereby stemming further visual decline. AAV2.COMP-Ang1 single-dose gene therapy can prevent neurovascular pathology, support vascular regeneration, and stabilize vision in DR.

Prevalence and risk factors of retinal vein occlusion: the Gutenberg Health Study

OBJECTIVE

To determine the age- and sex-specific prevalence and determinants of retinal vein occlusions (RVOs) in a large population-based German cohort.

METHODS

The investigation included 15,010 participants (aged 35-74 years) from the Gutenberg Health Study. We determined the prevalence of RVO (central retinal vein occlusion [CRVO] and branch retinal vein occlusion [BRVO]) for the local population by assessing fundus photographs of 12 954 (86.3%; 49.8% women and 50.2% men) participants. Further, we analyzed the associations of RVO with cardiovascular, anthropometric, and ophthalmic parameters.

RESULTS

The weighted prevalences of RVO, CRVO, and BRVO were 0.40%, 0.08%, and 0.32%, respectively. Men were 1.7 times more frequently affected by RVO than were women. Prevalence of RVO was 0.2% in participants aged 35-44 and 45-54 years, respectively, 0.48% in those aged 55-64 years, and 0.92% in those aged 65-74 years. Of persons with RVO, 91.5% had one or more cardiovascular risk factor or disease vs. 75.9% of persons without RVO. BRVO was associated with arterial hypertension (odds ratio 2.69, 95% confidence interval 1.27-5.70) and atrial fibrillation (3.37, 1.24-9.12) and CRVO with higher age (7.02, 1.63-30.19) and a family history of stroke (4.64, 1.18-18.25). Median visual acuity (base 10 logarithm of minimum angle of resolution) was 0.2 in persons with RVO vs. 0.05 in those without.

CONCLUSION

The prevalence of RVO in this German population was 0.4%, and men were 1.7 times more frequently affected than women. CRVO was associated with higher age and a family history of stroke, and BRVO was associated with arterial hypertension and atrial fibrillation.

Low intravitreal angiopoietin-2 and VEGF levels in vitrectomized diabetic patients with simvastatin treatment

PURPOSE

To investigate the intravitreal levels of potent vasoactive, angiogenic and extracellular matrix remodelling factors in the diabetic patients with simvastatin treatment.

METHODS

This is an institutional, prospective, observational case-control study. Type-1 and type-2 diabetic patients on lipophilic simvastatin (N = 14) compared with patients without statin medication (N = 50). Vitreous samples were subjected to protein measurements of angiopoietin (Ang)-1 and Ang-2, erythropoietin (EPO), transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF) by ELISA and matrix metalloproteinase (MMP)-2 and MMP-9 by gelatin zymography.

RESULTS

Intravitreal levels of Ang-2 (p = 0.029), VEGF (p = 0.001) and proMMP-9 (p = 0.015) were lower in simvastatin-treated than in non-statin-treated controls. In diabetics with macular oedema (DME), intravitreal Ang-2 (p = 0.006) and VEGF (p = 0.002) levels were lower in simvastatin-treated patients compared with non-statin-treated controls. In those patients with proliferative diabetic retinopathy (PDR), intravitreal Ang-2 (p = 0.002), TGF-β1 (p = 0.037), VEGF (p = 0.001) and pro- and totalMMP-9 (p = 0.004 and p = 0.007) levels were lower when receiving simvastatin medication.

CONCLUSIONS

In diabetic patients with DME or PDR, the intravitreal levels of permeability and proangiogenic factors Ang-2 and VEGF were lower in simvastatin-treated than in those without statin medication. Moreover, the levels of MMP-9 and TGF-β1, factors involved in the breakdown of basement membrane and fibroproliferation, were lower in patients with PDR having simvastatin medication. When acetylsalicylic acid was combined with simvastatin treatment, the intraocular levels of Ang-2 and VEGF were significantly lower than in diabetics treated with simvastatin alone. These data provide a novel insight into the potential protective mechanisms underlying simvastatin medication in patients with diabetic retinopathy complications.

Stem cell therapies in the management of diabetic retinopathy

Diabetic retinopathy is the leading cause of blindness in the working population. We now understand that the pathogenesis of the disease contains both a neurodegenerative and vasodegenerative component. Yet despite this, current treatment is still limited to combating the proliferative end stage component of the disease rather than addressing its underlying causes. In recent years, much basic research has focused on demonstrating the potential that several classes of stem cells have in conferring both neuro- and vasoprotection on the diabetic retina. Further, progress has been made in using stem cells to stimulate both neuro and vascular regeneration. This review will discuss the current understanding as to what mechanisms underlie diabetic retinopathy while highlighting the types of stem cells which offer hope as potential novel therapies for diabetic retinopathy, including those that are now in clinical trial.

High pre-transplant serum nitrate levels predict risk of acute steroid-refractory graft-versus-host disease in the absence of statin therapy

Steroid-refractory graft-versus-host disease is a life-threatening complication after allogeneic stem cell transplantation. Evidence is accumulating that steroid-refractory graft-versus-host disease is associated with endothelial distress. Endothelial cell homeostasis is regulated by nitric oxide, and serum nitrates are derived from nitric oxide synthase activity or dietary sources. In this retrospective study based on 417 patients allografted at our institution we investigated whether quantification of serum nitrates could predict steroid-refractory graft-versus-host disease. Elevated pre-transplant levels of serum nitrates (>26.5 μM) predicted steroid-refractory graft-versus-host disease (P=0.026) and non-relapse mortality (P=0.028), particularly in combination with high pre-transplant angiopoietin-2 levels (P=0.0007 and P=0.021, respectively). Multivariate analyses confirmed serum nitrates as independent predictors of steroid-refractory graft-versus-host disease and non-relapse mortality. Differences in serum nitrate levels did not correlate with serum levels of tumor necrosis factor or C-reactive protein or expression of inducible nitric oxide synthase in blood cells. Patients with high pre-transplant nitrate levels had significantly reduced rates of refractory graft-versus-host disease (P=0.031) when pravastatin was taken. In summary, patients at high risk of developing steroid-refractory graft-versus-host disease could be identified prior to transplantation by serum markers linked to endothelial cell function. Retrospectively, statin medication was associated with a reduced incidence of refractory graft-versus-host disease in this endothelial high-risk cohort.

Simvastatin induces caspase-dependent apoptosis and activates P53 in OCM-1 cells

Simvastatin is a cholesterol-lowering drug which exhibits numerous pleiotropic effects including anti-cancer activity. Yet, the anti-cancer effects in choroidal melanoma remain poorly characterized. Therefore, in this study, we investigated the effects of simvastatin on OCM-1 cells growth, apoptosis and cycle. Simvastatin showed an inhibitory effects on OCM-1 cells viability in dose-dependent (2-10 μM) and time-dependent (24-72 h) manner. Further study suggested that simvastatin-induced inhibition OCM-1 cells proliferation was associated with G1 phase arrest, decreased protein and mRNA expression of proliferation marker cyclin D1, cyclin E, cyclin dependent kinase (CDK)2 and increased expression of CDK inhibitory protein P21. In addition, simvastatin resulted in an increase in levels of reactive oxygen species (ROS) in OCM-1 cells and simvastatin significantly triggered apoptosis in OCM-1 cells, which was characterized by increased chromatin condensation, activation of caspase-9 and cleaved-caspase-3, increased expression mitochondrion-related apoptosis protein of P53, Bax and decreased expression of Bcl2 and iASPP. Collectively, our study demonstrated that simvastatin can efficiently inhibit proliferation and induce apoptosis in OCM-1 cells.

Exosome uptake depends on ERK1/2-heat shock protein 27 signaling and lipid Raft-mediated endocytosis negatively regulated by caveolin-1

The role of exosomes in cancer can be inferred from the observation that they transfer tumor cell derived genetic material and signaling proteins, resulting in e.g. increased tumor angiogenesis and metastasis. However, the membrane transport mechanisms and the signaling events involved in the uptake of these virus-like particles remain ill-defined. We now report that internalization of exosomes derived from glioblastoma (GBM) cells involves nonclassical, lipid raft-dependent endocytosis. Importantly, we show that the lipid raft-associated protein caveolin-1 (CAV1), in analogy with its previously described role in virus uptake, negatively regulates the uptake of exosomes. We find that exosomes induce the phosphorylation of several downstream targets known to associate with lipid rafts as signaling and sorting platforms, such as extracellular signal-regulated kinase-1/2 (ERK1/2) and heat shock protein 27 (HSP27). Interestingly, exosome uptake appears dependent on unperturbed ERK1/2-HSP27 signaling, and ERK1/2 phosphorylation is under negative influence by CAV1 during internalization of exosomes. These findings significantly advance our general understanding of exosome-mediated uptake and offer potential strategies for how this pathway may be targeted through modulation of CAV1 expression and ERK1/2 signaling.

Simvastatin reduces venous stenosis formation in a murine hemodialysis vascular access model

Venous neointimal hyperplasia (VNH) is responsible for hemodialysis vascular access malfunction. Here we tested whether VNH formation occurs, in part, due to vascular endothelial growth factor-A (VEGF-A) and matrix metalloproteinase (MMP)-9 gene expression causing adventitial fibroblast transdifferentiation to myofibroblasts (α-SMA-positive cells). These cells have increased proliferative and migratory capacity leading to VNH formation. Simvastatin was used to decrease VEGF-A and MMP-9 gene expression in our murine arteriovenous fistula model created by connecting the right carotid artery to the ipsilateral jugular vein. Compared to fistulae of vehicle-treated mice, the fistulae of simvastatin-treated mice had the expected decrease in VEGF-A and MMP-9 but also showed a significant reduction in MMP-2 expression with a significant decrease in VNH and a significant increase in the mean lumen vessel area. There was an increase in terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, and decreases in α-SMA density, cell proliferation, and HIF-1α and hypoxyprobe staining. This latter result prompted us to determine the effect of simvastatin on fibroblasts subjected to hypoxia in vitro. Simvastatin-treated fibroblasts had a significant decrease in myofibroblast production along with decreased cellular proliferation, migration, and MMP-9 activity but increased caspase 3 activity suggesting increased apoptosis. Thus, simvastatin results in a significant reduction in VNH, with increase in mean lumen vessel area by decreasing VEGF-A/MMP-9 pathway activity.

Advances in our understanding of diabetic retinopathy

Diabetic retinopathy remains the most common complication of diabetes mellitus and is a leading cause of visual loss in industrialized nations. The clinicopathology of the diabetic retina has been extensively studied, although the precise pathogenesis and cellular and molecular defects that lead to retinal vascular, neural and glial cell dysfunction remain somewhat elusive. This lack of understanding has seriously limited the therapeutic options available for the ophthalmologist and there is a need to identify the definitive pathways that initiate retinal cell damage and drive progression to overt retinopathy. The present review begins by outlining the natural history of diabetic retinopathy, the clinical features and risk factors. Reviewing the histopathological data from clinical specimens and animal models, the recent paradigm that neuroretinal dysfunction may play an important role in the early development of the disease is discussed. The review then focuses on the molecular pathogenesis of diabetic retinopathy with perspective provided on new advances that have furthered our understanding of the key mechanisms underlying early changes in the diabetic retina. Studies have also emerged in the past year suggesting that defective repair of injured retinal vessels by endothelial progenitor cells may contribute to the pathogenesis of diabetic retinopathy. We assess these findings and discuss how they could eventually lead to new therapeutic options for diabetic retinopathy.

Restoration of alveolar type II cell function contributes to simvastatin-induced attenuation of lung ischemia-reperfusion injury

Alveolar type (AT) II cells transdifferentiate into ATI cells and as such represent a promising source for regenerating lung epithelium following lung injury. ATII cells are characterized by the presence of lamellar bodies (LBs), which store and secrete the surfactant protein-C (SP-C). Lung ischemia-reperfusion injury (LIRI) causes a distinct impairment of the ATII cell function, subsequently hindering lung repair by loss of ATI transdifferentiation. In this study, we provide new evidence that the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin may restore the function of impaired ATII cells in vitro and in vivo. ATII cell lines, A549 (human) and MLE-12 (mouse), were subjected to hypoxia-reoxygenation (H/R) injury. Simvastatin pretreatment at low (5-20 µM), but not high (50-100 µM) doses markedly reduced apoptosis and increased proliferation and SP-C expression. In a rat lung ischemia-reperfusion (I/R) model, simvastatin treatment also increased ATII cell proliferation in vivo, as demonstrated by proliferating cell nuclear antigen/SP-C double staining. Transmission electron microscopy revealed that the number and volume density of LBs were significantly increased in the simvastatin-treated rat lungs. The protective effects of simvastatin were reversed in vitro by PI3-kinase (PI3K) inhibitors wortmannin and L-mevalonate, indicating that the PI3K/Akt and mevalonate pathways may be involved in simvastatin-induced ATII cell function restoration. These data demonstrate that an appropriate dose of simvastatin has a protective effect on LIRI in vitro and in vivo, due at least partially to restored ATII cell function via the HMG-CoA reductase pathway-dependent activation of PI3K/Akt signaling in a mevalonate pathway-dependent manner.

Statins induce the accumulation of regulatory T cells in atherosclerotic plaque

CD4⁺CD25⁺ regulatory T cells (Tregs) mediate immune suppression and prevent autoimmune disorders. Recently, Tregs were found to present in atherosclerotic lesions and play an important role in the progression of atherosclerosis. Statins have immunomodulatory properties, and the effect of statins on atherosclerosis depends in part on their immunomodulatory mechanisms. We sought to determine whether statins exhibit an effect on Tregs in atherosclerotic plaques and in peripheral circulation of patients with acute coronary syndrome (ACS). In an in vivo experiment, we induced atherosclerotic plaques in apolipoprotein E-deficient (ApoE⁻/⁻) mice. The mice were randomly divided into two groups for 6-wk treatment: simvastatin (50 mg/kg/d) or vehicle (control). Simvastatin significantly increased the number of Tregs and the expression of Treg marker Foxp3 (Forkhead/winged helix transcription factor), transforming growth factor (TGF)-β and interleukin (IL)-10 in atherosclerotic plaques. Moreover, simvastatin played an important role in modulating the balance between antiinflammatory (Tregs and Th2 cells) and proinflammatory (Th17 and Th1 cells) subsets of T cells. In an in vitro experiment, peripheral blood mononuclear cells (PBMCs) were isolated from patients with ACS and incubated with simvastatin. After an incubation for 96 h, simvastatin significantly enhanced the frequency and functional suppressive properties of Tregs. Therefore, statin treatment may influence Tregs in atherosclerotic lesions. Furthermore, statins improved the quantity and suppressive function of Tregs in ACS patients.

Fenofibrate plus simvastatin (fixed-dose combination) for the treatment of dyslipidaemia

INTRODUCTION

Statin use results in a significant reduction of cardiovascular disease (CVD) risk. However, patients still have residual CVD risk, even if they are receiving optimal statin treatment.

AREAS COVERED

This review, based on a Pubmed/Scopus search, discusses the available evidence regarding the use of a fixed-dose fenofibrate plus simvastatin combination. This combination is useful for patients with mixed dyslipidaemia because it improves the overall lipoprotein profile. Although in clinical trials the rate of adverse events was not significantly greater than monotherapy, patients who receive combination treatment should be monitored carefully. Furthermore, in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) Study, this combination did not result in a significant reduction of CVD events compared with simvastatin monotherapy. However, a possible benefit in this trial was observed in the subgroup of patients with high triglyceride and low high-density lipoprotein cholesterol levels.

EXPERT OPINION

The fixed-dose fenofibrate plus simvastatin combination treatment produces additive results and is safe when patients are properly monitored. Existing evidence appears to support the addition of fenofibrate to simvastatin treatment for the reduction of residual CVD risk in patients with atherogenic dyslipidaemia. However, this combination did not lead to better clinical outcomes in the absence of dyslipidaemia.

Myeloid angiogenic cells act as alternative M2 macrophages and modulate angiogenesis through interleukin-8

Endothelial progenitor cells (EPCs) promote angiogenesis, and clinical trials have shown such cell therapy to be feasible for treating ischemic disease. However, clinical outcomes have been contradictory owing to the diverse range of EPC types used. We recently characterized two EPC subtypes, and identified outgrowth endothelial cells as the only EPC type with true progenitor and endothelial characteristics. By contrast, myeloid angiogenic cells (MACs) were shown to be monocytic cells without endothelial characteristics despite being widely described as "EPCs." In the current study we demonstrated that although MACs do not become endothelial cells or directly incorporate into a microvascular network, they can significantly induce endothelial tube formation in vitro and vascular repair in vivo. MAC-derived interleukin-8 (IL-8) was identified as a key paracrine factor, and blockade of IL-8 but not vascular endothelial growth factor (VEGF) prevented MAC-induced angiogenesis. Extracellular IL-8 transactivates VEGFR2 and induces phosphorylation of extracellular signal-regulated kinases. Further transcriptomic and immunophenotypic analysis indicates that MACs represent alternative activated M2 macrophages. Our findings demonstrate an unequivocal role for MACs in angiogenesis, which is linked to paracrine release of cytokines such as IL-8. We also show, for the first time, the true identity of these cells as alternative M2 macrophages with proangiogenic, antiinflammatory and pro-tissue-repair properties.

Trans-Chalcone prevents VEGF expression and retinal neovascularization in the ischemic retina

Retinal neovascularization (RNV) is a critical pathological event and a major cause of blindness. Vascular inflammation and oxidative stress have been shown to play a key role in the induction and progression of RNV. Trans-Chalcone-derived flavonoids have been previously shown to be negative modulators of oxidative stress and inflammatory responses as well as tumor angiogenesis. In this study, we characterized the effects of the flavonoid trans-Chalcone in preventing RNV in a model of ischemic retinopathy. Ischemic retinopathy was induced in neonatal mice subjected to oxygen-induced retinopathy. Trans-Chalcone was administered intra-peritoneum at the dose of 25 mg/kg/day. Vascular density was assessed by morphometric analysis of flat mounted retinas stained with Texas red-Isolectin B4. Western blotting analysis was conducted to determine protein levels of vascular endothelial growth factor (VEGF), inter-cellular adhesion molecule 1 (ICAM-1) and the transcriptional activators' signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa beta (NF-κB). Treatment with trans-Chalcone significantly inhibited RNV in the ischemic retina, as shown by decreased number of neovascular tufts. Trans-Chalcone also blocked ischemia-induced VEGF and ICAM-1 expression and this effect correlated with inhibition of activated STAT3 and NF-κB. Our results show that trans-Chalcone effectively prevents RNV in the murine retina thus suggesting that Chalcone-derived flavonoids may be beneficial in preventing pathological neovascularization in the ischemic retina.

Vascular stem cells and ischaemic retinopathies

Retinal ischaemic disorders such as diabetic retinopathy and retinal vein occlusion are common. The hypoxia-related stimuli from oxygen-deprived neural and glial networks can drive expression of growth factors and cytokines which induce leakage from the surviving vasculature and/or pre-retinal and papillary neovascularisation. If left untreated, retinal vascular stasis, hypoxia or ischaemia can lead to macular oedema or fibro-vascular scar formation which are associated with severe visual impairment, and even blindness. Current therapies for ischaemic retinopathies include laser photocoagulation, injection of corticosteroids or VEGF-antibodies and vitreoretinal surgery, however they carry significant side effects. As an alternative approach, we propose that if reparative intra-retinal angiogenesis can be harnessed at the appropriate stage, ischaemia could be contained or reversed. This review provides evidence that reperfusion of ischaemic retina and suppression of sight-threatening sequelae is possible in both experimental and clinical settings. In particular, there is emphasis on the clinical potential for endothelial progenitor cells (EPCs) to promote vascular repair and reversal of ischaemic injury in various tissues including retina. Gathering evidence from an extensive published literature, we outline the molecular and phenotypic nature of EPCs, how they are altered in disease and provide a rationale for harnessing the vascular reparative properties of various cell sub-types. When some of the remaining questions surrounding the clinical use of EPCs are addressed, they may provide an exciting new therapeutic option for treating ischaemic retinopathies.

Inhibition of reactive oxygen species by Lovastatin downregulates vascular endothelial growth factor expression and ameliorates blood-retinal barrier breakdown in db/db mice: role of NADPH oxidase 4

OBJECTIVE

Oxidative stress is a key pathogenic factor in diabetic retinopathy. We previously showed that lovastatin mitigates blood-retinal barrier (BRB) breakdown in db/db mice. The purpose of this study is to determine the mechanisms underlying the salutary effects of lovastatin in diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Expression of NADPH oxidase (Nox) 4, vascular endothelial growth factor (VEGF), and hypoxia-inducible factor (HIF)-1alpha; production of reactive oxygen species (ROS); and retinal vascular permeability were measured in cultured retinal capillary endothelial cells (RCECs) and in db/db mice treated with lovastatin.

RESULTS

Expressions of Nox4 and VEGF were significantly increased in retinas of db/db mice and reduced by lovastatin treatment. In cultured RCECs, hypoxia and high glucose upregulated mRNA and protein expression of Nox4, ROS generation, and VEGF level. These changes were abrogated by pretreatment with lovastatin or NADPH oxidase inhibitor diphenyleneiodonium chloride. Overexpression of Nox4 increased basal level of ROS generation, HIF-1alpha, and VEGF expression in RCECs. In contrast, blockade of Nox4 activity using adenovirus-expressing dominant-negative Nox4 abolished hypoxia- and high-glucose-induced ROS production and VEGF expression. Moreover, inhibition of Nox4 attenuated hypoxia-induced upregulation of HIF-1alpha and high-glucose-elicited phosphorylation of STAT3. Finally, depletion of Nox4 by adenovirus-delivered Nox4 small interfering RNA significantly decreased retinal NADPH oxidase activity and VEGF expression and reduced retinal vascular premeability in db/db mice.

CONCLUSIONS

Activation of Nox4 plays an important role in high-glucose- and hypoxia-mediated VEGF expression and diabetes-induced BRB breakdown. Inhibition of Nox4, at least in part, contributes to the protective effects of lovastatin in diabetic retinopathy.

Diverse effects of statins on angiogenesis: new therapeutic avenues

Angiogenesis is an important process for a variety of physiologic and pathologic conditions. Different angiogenic modulating targets are under extensive investigation both experimentally and clinically. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are the first-line agents used in hypercholesterolemia. They are also characterized by having other benefits apart from their lipid-lowering effects. Among these pleiotropic effects are the pro- and antiangiogenic properties of statins. The pleiotropic effects of statins and how they modulate new blood vessel formation are discussed in this review. The currently available data from both animal and human studies regarding the effects of statins on angiogenesis in ischemic heart disease, stroke, ocular diseases, and cancer are also reviewed. Statins are safe, orally available agents that may acquire novel therapeutic indications through their angiogenic modulating effects.

Reviewing statin therapy in diabetes--towards the best practise

Statin therapy is considered critical both in primary and secondary prevention of cardiovascular disease in diabetes. Cholesterol Treatment Trialists' Collaborators meta-analysis of 14 randomised trials of statins in 18686 people with diabetes provides the latest and largest evidence showing a significant 21% reduction in major vascular events per mmol/l reduction in LDL cholesterol. Importantly, the risk reduction was similar in both types of diabetes. Growing evidence supports the view that statin therapy reduces microvascular complications as well. This review updates the current knowledge of statin therapy in preventing micro- and macrovascular complications in both type 1 and type 2 diabetes.

Antiangiogenic mechanisms of simvastatin in retinal endothelial cells

BACKGROUND

While statins have an anti-angiogenic property, their underlying mechanisms are not fully understood. We investigated intracellular mechanisms of simvastatin-mediated reduction in VEGF-induced signalings.

METHODS

The effects of simvastatin on cell proliferation and viability were evaluated by [(3)H]-thymidine incorporation in retinal endothelial cells (RECs) and cell counting. The impact of simvastatin on VEGF-induced phosphorylation of p44/42 mitogen-activated protein (MAP) kinase, myosin light chain (MLC), and VEGF-receptor (VEGFR) 2 were examined by Western blotting. Involvement of the mevalonate pathway in VEGF-induced signaling was also examined.

RESULTS

Simvastatin (1 and 10 microM) suppressed VEGF-induced RECs proliferation in a concentration-dependent manner, without affecting cell viability. Simvastatin significantly inhibited VEGF-induced phosphorylation of VEGFR2 and its downstream mediators, p44/42 MAP kinase and MLC. Mevalonate completely reversed VEGF-induced VEGFR2 phosphorylation, but only partially reversed the phosphorylation of p44/42 MAP kinase and MLC.

CONCLUSION

These data indicate that simvastatin exerts its anti-angiogenic effects through the reduction of VEGFR2 phosphorylation in RECs at least in part. However, there seems to be both mevalonate-dependent and independent pathway in simvastatin's anti-angiogenic property.

Pleiotropic effects of rosuvastatin on microvascular function in type 2 diabetes

Rosuvastatin is known to reduce low-density lipoprotein (LDL)-cholesterol and improve endothelial function. In addition to lipid-lowering, statins may exert pleiotropic (nonlipid lowering) effects on microvascular function. We compared the neurophysiological and vascular responses of dietary control and treatment with 10 mg of rosuvastatin in 16 subjects with neuropathy and established type 2 diabetes. Skin blood flow (SkBF) measurements were measured at baseline, after 18 weeks of diet, and after 18 weeks of diet and treatment with rosuvastatin in response to local warming and ischemia reperfusion. The study results show that total cholesterol (196.50 ± 8.02 to 134.88 ± 10.86 mg/dL) and LDL-cholesterol (114 ± 10.4 to 63.4 ± 8.48 mg/dL) decreased significantly after 18 weeks of rosuvastatin, but not after 18 weeks of diet. Neuropathy scores decreased from 8.34 ± 1.26 at baseline to 6.00 ± 0.90 after rosuvastatin treatment. Basal SkBF was significantly different from baseline, 6.81 ± 0.42 to 9.92 ± 0.78 after rosuvastatin treatment (P ≤ 0.001). These results indicate that rosuvastatin therapy positively changed basal SkBF and measures of neurovascular function. Although there was a profound lipid lowering, it is not clear that this mediated the increases in SkBF and decreases in neuropathy scores.

Pleiotropic effects of YC-1 selectively inhibit pathological retinal neovascularization and promote physiological revascularization in a mouse model of oxygen-induced retinopathy

Vascular endothelial growth factor (VEGF) and inducible nitric-oxide synthase (iNOS) have been implicated in ischemia-induced retinal neovascularization. Retinal ischemia has been shown to induce VEGF and iNOS expression. It has been postulated that one of the crucial consequences of iNOS expression in the ischemic retina is the inhibition of angiogenesis. Furthermore, iNOS was shown to be overexpressed in Müller cells from patients with diabetic retinopathy. YC-1, a small molecule inhibitor of hypoxia-inducible factor (HIF)-1 alpha, has been shown to inhibit iNOS expression in various tissue models. Our aim was to assess the pleiotropic effects of YC-1 in an oxygen-induced retinopathy (OIR) mouse model and evaluate its therapeutic potential in HIF-1- and iNOS-mediated retinal pathologies. Dual-injections of YC-1 into the neovascular retinas decreased the total retinopathy score, inhibited vaso-obliteration and pathologic tuft formation, and concomitantly promoted physiological retinal revascularization, compared with dimethyl sulfoxide (DMSO)-treated group. Furthermore, YC-1-treated retinas exhibited a marked increase in immunoreactivities for CD31 and von Willebrand factor and displayed significant inhibition in HIF-1alpha protein expression. Furthermore, YC-1 down-regulated VEGF, erythropoietin, endothelin-1, matrix metalloproteinase-9, and iNOS message and protein levels. When hypoxic Müller and neuoroglial cells were treated with YC-1, iNOS mRNA and protein levels were reduced in a dose-dependent fashion. We demonstrate that YC-1 inhibits pathological retinal neovascularization by exhibiting antineovascular activities, which impaired ischemia-induced expression of HIF-1 and its downstream angiogenic molecules. Furthermore, YC-1 enhanced physiological revascularization of the retinal vascular plexuses via the inhibition of iNOS mRNA and protein expressions. The pleiotropic effects of YC-1 allude to its possible use as a promising therapeutic iNOS inhibitor candidate for the treatment of retinal neovascularization.

Early intervention of tyrosine nitration prevents vaso-obliteration and neovascularization in ischemic retinopathy

Diabetic retinopathy and retinopathy of prematurity are blinding disorders that follow a pathological pattern of ischemic retinopathy and affect premature infants and working-age adults. Yet, the treatment options are limited to laser photocoagulation. The goal of this study is to elucidate the molecular mechanism and examine the therapeutic effects of inhibiting tyrosine nitration on protecting early retinal vascular cell death and late neovascularization in the ischemic retinopathy model. Ischemic retinopathy was developed by exposing neonatal mice to 75% oxygen [postnatal day (p) 7-p12] followed by normoxia (21% oxygen) (p12-p17). Peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTPPS) (1 mg/kg), the nitration inhibitor epicatechin (10 mg/kg) or the thiol donor N-acetylcysteine (NAC, 150 mg/kg) were administered (p7-p12) or (p7-p17). Vascular endothelial cells were incubated at hyperoxia (40% oxygen) or normoxia (21% oxygen) for 48 h. Vascular density was determined in retinal flat mounts labeled with isolectin B4. Expression of vascular endothelial growth factor, caspase-3, and poly(ADP ribose) polymerase (PARP), activation of Akt and p38 mitogen-activated protein kinase (MAPK), and tyrosine nitration of the phosphatidylinositol (PI) 3-kinase p85 subunit were analyzed by Western blot. Hyperoxia-induced peroxynitrite caused endothelial cell apoptosis as indicated by expression of cleaved caspase-3 and PARP leading to vaso-obliteration. These effects were associated with significant tyrosine nitration of the p85 subunit of PI 3-kinase, decreased Akt activation, and enhanced p38 MAPK activation. Blocking tyrosine nitration of PI 3-kinase with epicatechin or NAC restored Akt phosphorylation, and inhibited vaso-obliteration at p12 and neovascularization at p17 comparable with FeTPPS. Early inhibition of tyrosine nitration with use of epicatechin or NAC can represent safe and effective vascular-protective agents in ischemic retinopathy.

Translocation of H-Ras and its implications in the development of diabetic retinopathy

H-Ras, a small molecular weight G-protein, undergoes post-translational modifications enabling its translocation from cytosol to the membrane. Hyperglycemia increases apoptosis of retinal capillary cells via activation of H-Ras, which can be ameliorated by farnesylation inhibitors. Our aim is to investigate the mechanism of retinal H-Ras activation in diabetes. H-Ras and Raf-1 were quantified in the retinal membrane and cytosol fractions obtained from streptozotocin-induced diabetes rats, and the role of post-translation modification was determined by investigating the effect of simvastatin on diabetes-induced alterations. The effect of H-Ras-siRNA on membrane translocation and apoptosis was also determined in bovine retinal endothelial cells (BRECs). Diabetes increased expressions of H-Ras and Raf-1 in the retinal membranes, and simvastatin prevented such translocation. Glucose-exposure of BRECs increased membrane H-Ras expression and H-Ras-siRNA prevented this translocation, and also decreased their apoptosis. Thus, membrane translocation of H-Ras is a plausible mechanism responsible for accelerated apoptosis of retinal capillary cells in diabetes.

Systemic administration of HMG-CoA reductase inhibitor protects the blood-retinal barrier and ameliorates retinal inflammation in type 2 diabetes

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) are frequently used lipid-lowering drugs in type 2 diabetes. Recent emerging evidence suggests that statins protect cardiovascular function via lipid-independent mechanisms. However, the potential role of statins in diabetic retinopathy in type 2 diabetes is largely unclear. In the present study we have investigated the effect of lovastatin on blood-retinal barrier and inflammatory status in the retina of db/db mice and in cultured retinal cells. Male C57BL/KsJ db/db mice were randomly chosen to receive gastric gavage of lovastatin (10mg/kg/day) or vehicle control for 6 weeks. Retinal vascular permeability, the tight junction and inflammation were determined. The results showed that db/db mice at the age of 19 weeks exhibited significantly increased retinal vascular leakage and decreased tight junction protein level in the retina. Moreover, the expression of pro-inflammatory factors, e.g. ICAM-1 and TNF-alpha, was drastically up-regulated in diabetic retina. Lovastatin treatment normalized all of these changes. In cultured bovine retinal capillary endothelial cells (RCECs) and human ARPE-19 cells, lovastatin attenuated the decrease of tight junction protein (occludin) and adherens junction protein (VE-cadherin) expression-induced by TNF-alpha, a major pro-inflammatory cytokine in diabetic retinopathy. Lovastatin also attenuated TNF-alpha expression in RCEC. Towards the mechanism, we showed that lovastatin ameliorated ICAM-1 expression-induced by hypoxia and TNF-alpha in both RCECs and ARPE-19 cells, in part through inhibition of NF-kappaB activation. Taken together, these findings indicate that lovastatin protects blood-retinal barrier in diabetic retinopathy, which is likely via its anti-inflammatory effects.