Loss of TRPV2-mediated blood flow autoregulation recapitulates diabetic retinopathy in rats.

Loss of retinal blood flow autoregulation is an early feature of diabetes that precedes the development of clinically recognizable diabetic retinopathy (DR). Retinal blood flow autoregulation is mediated by the myogenic response of the retinal arterial vessels, a process that is initiated by the stretch­dependent activation of TRPV2 channels on the retinal vascular smooth muscle cells (VSMCs). Here, we show that the impaired myogenic reaction of retinal arterioles from diabetic animals is associated with a complete loss of stretch­dependent TRPV2 current activity on the retinal VSMCs. This effect could be attributed, in part, to TRPV2 channel downregulation, a phenomenon that was also evident in human retinal VSMCs from diabetic donors. We also demonstrate that TRPV2 heterozygous rats, a nondiabetic model of impaired myogenic reactivity and blood flow autoregulation in the retina, develop a range of microvascular, glial, and neuronal lesions resembling those observed in DR, including neovascular complexes. No overt kidney pathology was observed in these animals. Our data suggest that TRPV2 dysfunction underlies the loss of retinal blood flow autoregulation in diabetes and provide strong support for the hypothesis that autoregulatory deficits are involved in the pathogenesis of DR.

Influential factors in patient uptake of influenza vaccination during pregnancy; a survey-based audit in a tertiary hospital setting.

AIM: The aim of this study was to determine the key influential factors for pregnant or recently pregnant women in deciding on influenza vaccination. METHOD: This study was conducted in a single tertiary hospital in New Zealand using an anonymous and voluntary patient survey. Ethnicity, age and stage of pregnancy along with self-reported data on factors that influenced the decision to vaccinate against influenza during pregnancy were recorded. RESULTS: We included 101 participants over the one-week study period, 76% of whom had received the influenza vaccination. The most commonly reported reason for vaccination was the desire for neonatal protection, the common reasons for not being vaccinated were not receiving information on vaccination or safety concerns. CONCLUSION: There are a variety of factors influencing women when deciding on antenatal influenza vaccination. Further studies are needed to expand on the findings of this small local study in order to be able to improve vaccination uptake through empathetic delivery of evidence-based recommendations.

The Placental Growth Factor Pathway and Its Potential Role in Macular Degenerative Disease.

There is growing evidence that placental growth factor (PlGF) is an important player in multiple pathologies, including tumorigenesis, inflammatory disorders and degenerative retinopathies. PlGF is a member of the vascular endothelial growth factor (VEGF) family and in the retina, binding of this growth factor to specific receptors is associated with pathological angiogenesis, vascular leakage, neurodegeneration and inflammation. Although they share some receptor signalling pathways, many of the actions of PlGF are distinct from VEGF and this has revealed the enticing prospect that it could be a useful therapeutic target for treating early and late stages of diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Recent research suggests that modulation of PlGF could also be important in the geographic atrophy (GA) form of late AMD by protecting the outer retina and the retinal pigment epithelium (RPE). This review discusses PlGF and its signalling pathways and highlights the potential of blocking the bioactivity of this growth factor to treat irreversible visual loss due to the two main forms of AMD.

The vasoreparative potential of endothelial colony-forming cells in the ischemic retina is enhanced by cibinetide, a non-hematopoietic erythropoietin mimetic.

PURPOSE: Retinal ischemia remains a common sight threatening end-point in blinding diseases such as diabetic retinopathy and retinopathy of prematurity. Endothelial colony forming cells (ECFCs) represent a subpopulation of endothelial progenitors with therapeutic utility for promoting reparative angiogenesis in the ischaemic retina. The current study has investigated the potential of enhancing this cell therapy approach by the dampening of the pro-inflammatory milieu typical of ischemic retina. Based on recent findings that ARA290 (cibinetide), a peptide based on the Helix-B domain of erythropoietin (EPO), is anti-inflammatory and tissue-protective, the effect of this peptide on ECFC-mediated vascular regeneration was studied in the ischemic retina. METHODS: The effects of ARA290 on pro-survival signaling and function were assessed in ECFC cultures in vitro. Efficacy of ECFC transplantation therapy to promote retinal vascular repair in the presence and absence of ARA290 was studied in the oxygen induced retinopathy (OIR) model of retinal ischemia. The inflammatory cytokine profile and microglial activation were studied as readouts of inflammation. RESULTS: ARA290 activated pro-survival signaling and enhanced cell viability in response to H2O2-mediated oxidative stress in ECFCs in vitro. Preconditioning of ECFCs with EPO or ARA290 prior to delivery to the ischemic retina did not enhance vasoreparative function. ARA290 delivered systemically to OIR mice reduced pro-inflammatory expression of IL-1ß and TNF-α in the mouse retina. Following intravitreal transplantation, ECFCs incorporated into the damaged retinal vasculature and significantly reduced avascular area. The vasoreparative function of ECFCs was enhanced in the presence of ARA290 but not EPO. DISCUSSION: Regulation of the pro-inflammatory milieu of the ischemic retina can be enhanced by ARA290 and may be a useful adjunct to ECFC-based cell therapy for ischemic retinopathies.

CAMKII as a therapeutic target for growth factor-induced retinal and choroidal neovascularization.

While anti-VEGF drugs are commonly used to inhibit pathological retinal and choroidal neovascularization, not all patients respond in an optimal manner. Mechanisms underpinning resistance to anti­VEGF therapy include the upregulation of other proangiogenic factors. Therefore, therapeutic strategies that simultaneously target multiple growth factor signaling pathways would have significant value. Here, we show that Ca2+/calmodulin-dependent kinase II (CAMKII) mediates the angiogenic actions of a range of growth factors in human retinal endothelial cells and that this kinase acts as a key nodal point for the activation of several signal transduction cascades that are known to play a critical role in growth factor-induced angiogenesis. We also demonstrate that endothelial CAMKIIγ and -δ isoforms differentially regulate the angiogenic effects of different growth factors and that genetic deletion of these isoforms suppresses pathological retinal and choroidal neovascularization in vivo. Our studies suggest that CAMKII could provide a novel and efficacious target to inhibit multiple angiogenic signaling pathways for the treatment of vasoproliferative diseases of the eye. CAMKIIγ represents a particularly promising target, as deletion of this isoform inhibited pathological neovascularization, while enhancing reparative angiogenesis in the ischemic retina.

Glucocorticoids exert differential effects on the endothelium in an in vitro model of the blood-retinal barrier.

PURPOSE: Glucocorticoids (GCs) are used as treatment in diabetic macular oedema, a condition caused by blood-retinal barrier (BRB) disruption. The proposed mechanisms by which GCs reduce macular oedema are indirect anti-inflammatory effects and inhibition of VEGF production, but direct effects on the BRB endothelium may be equally important. Here, we investigated direct effects of GCs on the endothelium to understand the specific pathways of GC action, to enable development of novel therapeutics lacking the adverse side-effects of the presently used GCs. METHODS: Primary bovine retinal endothelial cells (BRECs) were grown on Transwell inserts and treated with hydrocortisone (HC), dexamethasone (Dex) or triamcinolone acetonide (TA). Molecular barrier integrity of the BRB was determined by mRNA and protein expression, and barrier function was assessed using permeability assays. In addition, we investigated whether TA was able to prevent barrier disruption after stimulation with VEGF or cytokines. RESULTS: Treatment of BRECs with GCs resulted in upregulation of tight junction mRNA (claudin-5, occludin, ZO-1) and protein (claudin-5 and ZO-1). In functional assays, only TA strengthened the barrier function by reducing endothelial permeability. Moreover, TA was able to prevent cytokine-induced permeability in human retinal endothelial cells and VEGF-induced expression of plasmalemma vesicle-associated protein (PLVAP), a key player in VEGF-induced retinal vascular leakage. CONCLUSION: Glucocorticoids have differential effects in an experimental in vitro BRB model. TA is the most potent in improving barrier function, both at the molecular and functional levels, and TA prevents VEGF-induced expression of PLVAP.

Lipoprotein-associated phospholipase A2 (Lp-PLA2) as a therapeutic target to prevent retinal vasopermeability during diabetes.

Lipoprotein-associated phospholipase A2 (Lp-PLA2) hydrolyses oxidized low-density lipoproteins into proinflammatory products, which can have detrimental effects on vascular function. As a specific inhibitor of Lp-PLA2, darapladib has been shown to be protective against atherogenesis and vascular leakage in diabetic and hypercholesterolemic animal models. This study has investigated whether Lp-PLA2 and its major enzymatic product, lysophosphatidylcholine (LPC), are involved in blood-retinal barrier (BRB) damage during diabetic retinopathy. We assessed BRB protection in diabetic rats through use of species-specific analogs of darapladib. Systemic Lp-PLA2 inhibition using SB-435495 at 10 mg/kg (i.p.) effectively suppressed BRB breakdown in streptozotocin-diabetic Brown Norway rats. This inhibitory effect was comparable to intravitreal VEGF neutralization, and the protection against BRB dysfunction was additive when both targets were inhibited simultaneously. Mechanistic studies in primary brain and retinal microvascular endothelial cells, as well as occluded rat pial microvessels, showed that luminal but not abluminal LPC potently induced permeability, and that this required signaling by the VEGF receptor 2 (VEGFR2). Taken together, this study demonstrates that Lp-PLA2 inhibition can effectively prevent diabetes-mediated BRB dysfunction and that LPC impacts on the retinal vascular endothelium to induce vasopermeability via VEGFR2. Thus, Lp-PLA2 may be a useful therapeutic target for patients with diabetic macular edema (DME), perhaps in combination with currently administered anti-VEGF agents.

Abnormal Glycogen Storage by Retinal Neurons in Diabetes.

PURPOSE: It is widely held that neurons of the central nervous system do not store glycogen and that accumulation of the polysaccharide may cause neurodegeneration. Since primary neural injury occurs in diabetic retinopathy, we examined neuronal glycogen status in the retina of streptozotocin-induced diabetic and control rats. METHODS: Glycogen was localized in eyes of streptozotocin-induced diabetic and control rats using light microscopic histochemistry and electron microscopy, and correlated with immunohistochemical staining for glycogen phosphorylase and phosphorylated glycogen synthase (pGS). RESULTS: Electron microscopy of 2-month-old diabetic rats (n = 6) showed massive accumulations of glycogen in the perinuclear cytoplasm of many amacrine neurons. In 4-month-old diabetic rats (n = 11), quantification of glycogen-engorged amacrine cells showed a mean of 26 cells/mm of central retina (SD ± 5), compared to 0.5 (SD ± 0.2) in controls (n = 8). Immunohistochemical staining for glycogen phosphorylase revealed strong expression in amacrine and ganglion cells of control retina, and increased staining in cell processes of the inner plexiform layer in diabetic retina. In control retina, the inactive pGS was consistently sequestered within the cell nuclei of all retinal neurons and the retinal pigment epithelium (RPE), but in diabetics nuclear pGS was reduced or lost in all classes of retinal cell except the ganglion cells and cone photoreceptors. CONCLUSIONS: The present study identifies a large population of retinal neurons that normally utilize glycogen metabolism but show pathologic storage of the polysaccharide during uncontrolled diabetes.

Relative respiratory syncytial virus cytopathogenesis in upper and lower respiratory tract epithelium.

RATIONALE: Respiratory syncytial virus (RSV) is a major pathogen that primarily infects airway epithelium. Most infants suffer mild upper respiratory tract (URT) symptoms, whereas approximately one-third progress to lower respiratory tract (LRT) involvement. Despite the ubiquity of URT infection, little is known about the relative cytopathogenesis of RSV infection in infant URT and LRT. OBJECTIVES: This study aimed to compare RSV cytopathogenesis in nasal- and bronchial-derived epithelium from the same individuals using novel models derived from well-differentiated primary pediatric nasal (WD-PNECs) and bronchial epithelial cells (WD-PBECs). METHODS: WD-PNECs and WD-PBECs were generated from nasal and bronchial brushes, respectively, and mock-infected or infected with RSV BT2a. RSV tropism, infectivity, cytopathology, growth kinetics, cell sloughing, apoptosis, and cytokine and chemokine responses were determined. MEASUREMENTS AND MAIN RESULTS: RSV infection in both cultures was restricted to apical ciliated cells and occasional nonciliated cells but not goblet cells. It did not cause gross cytopathology. Infection resulted in apical release of progeny virus, increased apical cell sloughing, apoptosis, and occasional syncytia. RSV growth kinetics and peak titers were higher in WD-PBECs, coincident with higher ciliated cell contents, cell sloughing, and slightly compromised tight junctions. However, proinflammatory chemokine responses were similar for both cultures. Also, lambda IFNs, especially IL-29, were induced by RSV infection. CONCLUSIONS: RSV induced remarkably similar, albeit quantitatively lower, cytopathogenesis and proinflammatory responses in WD-PNECs compared with WD-PBECs that reproduce many hallmarks of RSV pathogenesis in infants. WD-PNECs may provide an authentic surrogate model with which to study RSV cytopathogenesis in infant airway epithelium.

Toll-like receptor 4 is not targeted to the lysosome in cystic fibrosis airway epithelial cells.

The innate immune response to bacterial infection is mediated through Toll-like receptors (TLRs), which trigger tightly regulated signaling cascades through transcription factors including NF-κB. LPS activation of TLR4 triggers internalization of the receptor-ligand complex which is directed toward lysosomal degradation or endocytic recycling. Cystic fibrosis (CF) patients display a robust and uncontrolled inflammatory response to bacterial infection, suggesting a defect in regulation. This study examined the intracellular trafficking of TLR4 in CF and non-CF airway epithelial cells following stimulation with LPS. We employed cells lines [16hBE14o-, CFBE41o- (CF), and CFTR-complemented CFBE41o-] and confirmed selected experiments in primary nasal epithelial cells from non-CF controls and CF patients (F508del homozygous). In control cells, TLR4 expression (surface and cytoplasmic) was reduced after LPS stimulation but remained unchanged in CF cells and was accompanied by a heightened inflammatory response 24 h after stimulation. All cells expressed markers of the early (EEA1) and late (Rab7b) endosomes at basal levels. However, only CF cells displayed persistent expression of Rab7b following LPS stimulation. Rab7 variants may directly internalize bacteria to the Golgi for recycling or to the lysosome for degradation. TLR4 colocalized with the lysosomal marker LAMP1 in 16 hBE14o- cells, suggesting that TLR4 is targeted for lysosomal degradation in these cells. However, this colocalization was not observed in CFBE41o- cells, where persistent expression of Rab7 and release of proinflammatory cytokines was detected. Consistent with the apparent inability of CF cells to target TLR4 toward the lysosome for degradation, we observed persistent surface and cytoplasmic expression of this pathogen recognition receptor. This defect may account for the prolonged cycle of chronic inflammation associated with CF.

Effects of an endothelin receptor antagonist on a model of hypertensive retinopathy.

Hypertensive retinopathy manifests itself as progressive retinal microvascular pathology in response to aberrant blood flow. The current study sought to evaluate whether dysfunction of the vasoactive endothelin-1 (ET-1) system is involved in the pathogenesis of hypertension-induced retinopathy in an animal model of systemic hypertension. The endothelin receptor antagonist, bosentan, was administered to spontaneously hypertensive rats (SHRs) and comparisons were made with untreated SHRs and normotensive Wistar Kyoto (WKY) rats. The retinal mRNA expression of ET-1, ET-converting enzyme-1, ET(A) and ET(B) receptors and the basement membrane proteins, laminin beta1, collagen IV and fibronectin was quantified using real-time RT-PCR. In addition, retinal arteriole and/or capillary bed damage was assessed by qualitative and quantitative microscopy. mRNA for the ET(A) receptor was increased in SHRs, when compared to WKY control animals (p < 0.001). Treatment with bosentan in SHRs significantly reduced the expression of ET-1 (p < 0.05), and both the ET(A) (p < 0.0001) and ET(B) (p < 0.05) receptor subtypes. The laminin beta1, collagen IV and fibronectin mRNA expression was significantly higher in SHRs when compared to WKY control animals (p < 0.001). Treatment with bosentan abolished these responses and also the appearance of various microvascular lesions. ET-mediated vasoregulation abnormalities in the retinal microvasculature could play an associative role in lesion formation during hypertensive retinopathy.

Inhibition of advanced glycation and absence of galectin-3 prevent blood-retinal barrier dysfunction during short-term diabetes.

Breakdown of the inner blood-retinal barrier (iBRB) occurs early in diabetes and is central to the development of sight-threatening diabetic macular edema (DME) as retinopathy progresses. In the current study, we examined how advanced glycation end products (AGEs) forming early in diabetes could modulate vasopermeability factor expression in the diabetic retina and alter inter-endothelial cell tight junction (TJ) integrity leading to iBRB dysfunction. We also investigated the potential for an AGE inhibitor to prevent this acute pathology and examined a role of the AGE-binding protein galectin-3 (Gal-3) in AGE-mediated cell retinal pathophysiology. Diabetes was induced in C57/BL6 wild-type (WT) mice and in Gal-3(-/-) transgenic mice. Blood glucose was monitored and AGE levels were quantified by ELISA and immunohistochemistry. The diabetic groups were subdivided, and one group was treated with the AGE-inhibitor pyridoxamine (PM) while separate groups of WT and Gal-3(-/-) mice were maintained as nondiabetic controls. iBRB integrity was assessed by Evans blue assay alongside visualisation of TJ protein complexes via occludin-1 immunolocalization in retinal flat mounts. Retinal expression levels of the vasopermeability factor VEGF were quantified using real-time RT-PCR and ELISA. WT diabetic mice showed significant AGE -immunoreactivity in the retinal microvasculature and also showed significant iBRB breakdown (P < .005). These diabetics had higher VEGF mRNA and protein expression in comparison to controls (P < .01). PM-treated diabetics had normal iBRB function and significantly reduced diabetes-mediated VEGF expression. Diabetic retinal vessels showed disrupted TJ integrity when compared to controls, while PM-treated diabetics demonstrated near-normal configuration. Gal-3(-/-) mice showed significantly less diabetes-mediated iBRB dysfunction, junctional disruption, and VEGF expression changes than their WT counterparts. The data suggests an AGE-mediated disruption of iBRB via upregulation of VEGF in the diabetic retina, possibly modulating disruption of TJ integrity, even after acute diabetes. Prevention of AGE formation or genetic deletion of Gal-3 can effectively prevent these acute diabetic retinopathy changes.

Bioadhesive, non-drug-loaded nanoparticles as modulators of candidal adherence to buccal epithelial cells: a potentially novel prophylaxis for candidosis.

Adherence of microorganisms, such as Candida albicans, represents the initial step in the establishment of infection and, accordingly, modification of this step represents a method by which the incidence of infection may be reduced. Therefore, this study uniquely examined the effects of polymeric nanoparticles on the adherence of blastospores of C. albicans to human buccal epithelial cells (BEC) in vitro. Poly(propylcyanoacrylate) nanoparticles were produced by emulsion polymerisation using a range of anionic, cationic and non-ionic surfactants, their particle size and zeta potential characterised and incubated with stationary phase blastospores of C. albicans for a defined period. Following this, the surface properties and size of blastospores with adsorbed nanoparticles were characterised. phosphate buffered saline-treated and nanoparticle-treated blastospores were incubated with human BEC for 2 h, following which the number of adherent blastospores was enumerated by light microscopy. The size and zeta potential of the nanoparticles were dependent on the surfactant employed in the manufacture process. Following nanoparticle adsorption, alteration of the zeta potential and an increase in the diameter of blastospores were observed. However, as this increase in diameter was indirectly related to the size of the nanoparticles, this may indicate a preference for the adsorption of smaller particles. In addition, following nanoparticle adsorption, the cell surface hydrophobicity (CSH) of C. albicans blastospores was increased and, importantly, the subsequent adherence to BEC in vitro was reduced. Most notably, the adherence of blastospores that had been treated with nanoparticles (stabilised with docusate sodium) was circa 73% lower than that of untreated blastospores. A moderate correlation between increased CSH and reduced adherence and a low correlation between blastospore zeta potential and adherence were observed, inferring that other mechanisms, most likely stearic hindrance, are responsible for the antiadherent properties of adsorbed nanoparticles. In light of their ability to reduce candidal adherence to BEC, it is suggested that polymeric nanoparticles may be useful in the prophylaxis of candidosis of the oral cavity.

The AGE inhibitor pyridoxamine inhibits development of retinopathy in experimental diabetes.

We examined the ability of pyridoxamine (PM), an inhibitor of formation of advanced glycation end products (AGEs) and lipoxidation end products (ALEs), to protect against diabetes-induced retinal vascular lesions. The effects of PM were compared with the antioxidants vitamin E (VE) and R-alpha-lipoic acid (LA) in streptozotocin-induced diabetic rats. Animals were given either PM (1 g/l drinking water), VE (2,000 IU/kg diet), or LA (0.05%/kg diet). After 29 weeks of diabetes, retinas were examined for pathogenic changes, alterations in extracellular matrix (ECM) gene expression, and accumulation of the immunoreactive AGE/ALE N( epsilon )-(carboxymethyl)lysine (CML). Acellular capillaries were increased more than threefold, accompanied by significant upregulation of laminin immunoreactivity in the retinal microvasculature. Diabetes also increased mRNA expression for fibronectin (2-fold), collagen IV (1.6-fold), and laminin beta chain (2.6-fold) in untreated diabetic rats compared with nondiabetic rats. PM treatment protected against capillary drop-out and limited laminin protein upregulation and ECM mRNA expression and the increase in CML in the retinal vasculature. VE and LA failed to protect against retinal capillary closure and had inconsistent effects on diabetes-related upregulation of ECM mRNAs. These results indicate that the AGE/ALE inhibitor PM protected against a range of pathological changes in the diabetic retina and may be useful for treating diabetic retinopathy.