Angiotensin converting enzyme (ACE) inhibition has been recently suggested to have retinoprotective actions in diabetic patients but the mechanism of this effect is not known. In vitro, angiotensin ...II stimulates expression of vascular endothelial growth factor (VEGF), a permeability-inducing and endothelial cell specific angiogenic factor which has been implicated in the pathogenesis of diabetic retinopathy in humans and in experimental animals. We sought to determine the effects of ACE inhibition on retinal VEGF expression and permeability in experimental diabetic retinopathy.
Streptozotocin-induced diabetic rats and control animals were assigned at random to receive ACE inhibitor treatment or vehicle. At 24 weeks the retinal VEGF protein gene expression was assessed by northern blot analysis and in situ hybridisation. Retinal permeability to albumin was measured using a double isotope technique.
Experimental diabetes was associated with cell specific two to fourfold increase in retinal VEGF protein gene expression (p < 0.01) and a 2-fold increase in retinal vascular permeability to albumin (p < 0.01). The localization of VEGF expression in the retina was not altered in animals with experimental diabetes. Angiotensin converting enzyme inhibitor treatment of diabetic rats reduced diabetes-associated changes in VEGF gene expression and vascular permeability.
These findings implicate the renin-angiotensin system in the VEGF overexpression and hyperpermeability which accompany diabetic retinopathy and provide a potential mechanism for the beneficial effects of ACE inhibition in diabetic retinal disease.
In addition to hyperglycemia, hypertension and the renin-angiotensin system have been consistently implicated in the pathogenesis of diabetic nephropathy. Each of these pathogenetic factors may ...induce changes in cellular function by a common intracellular signaling pathway, the activation of protein kinase C (PKC) beta. The present study thus sought to determine the in vivo effect of PKC beta inhibition in experimental diabetic nephropathy in the setting of continued hyperglycemia, hypertension, and activation of the RAS. Studies were conducted in the (mRen-2)27 rat, a rodent that is transgenic for the entire mouse renin gene (Ren-2) and develops many of the structural, functional, and molecular characteristics of human diabetic nephropathy when experimental diabetes is induced with streptozotocin (STZ). Six-week-old female Ren-2 rats received an injection of STZ or vehicle and were maintained for 6 months. Within 24 h, diabetic rats were further randomized to receive treatment with the specific PKC beta inhibitor, LY333531, admixed in diet (10 mg x kg(-1) x d(-1)) or no treatment (n = 8/group). Diabetic rats developed albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis with a concomitant increase in transforming growth factor-beta (TGF-beta). Western blot analysis demonstrated increased PKC beta in diabetic animals, localized by immunofluorescence to the glomerular mesangium. In vivo inhibition of PKC beta with LY333531 led to a reduction in albuminuria, structural injury, and TGF-beta expression, despite continued hypertension and hyperglycemia.
Rapid arterial O(2) desaturation during apnea in the preterm infant has obvious clinical implications but to date no adequate explanation for why it exists. Understanding the factors influencing the ...rate of arterial O(2) desaturation during apnea (Sa(O)₂) is complicated by the non-linear O(2) dissociation curve, falling pulmonary O(2) uptake, and by the fact that O(2) desaturation is biphasic, exhibiting a rapid phase (stage 1) followed by a slower phase when severe desaturation develops (stage 2). Using a mathematical model incorporating pulmonary uptake dynamics, we found that elevated metabolic O(2) consumption accelerates Sa(O)₂throughout the entire desaturation process. By contrast, the remaining factors have a restricted temporal influence: low pre-apneic alveolar P(O)₂causes an early onset of desaturation, but thereafter has little impact; reduced lung volume, hemoglobin content or cardiac output, accelerates Sa(O)₂during stage 1, and finally, total blood O(2) capacity (blood volume and hemoglobin content) alone determines Sa(O)₂during stage 2. Preterm infants with elevated metabolic rate, respiratory depression, low lung volume, impaired cardiac reserve, anemia, or hypovolemia, are at risk for rapid and profound apneic hypoxemia. Our insights provide a basic physiological framework that may guide clinical interpretation and design of interventions for preventing sudden apneic hypoxemia.
On 17th February 2003, a congestion charging scheme (CCS), operating Monday–Friday, 07:00–18:00, was introduced in central London along with a programme of traffic management measures. We ...investigated the potential impact of the introduction of the CCS on measured pollutant concentrations (oxides of nitrogen (NO
X, NO and NO
2), particles with a median diameter less than 10 microns (PM
10), carbon monoxide (CO) and ozone (O
3)) measured at roadside and background monitoring sites across Greater London. Temporal changes in pollution concentrations within the congestion charging zone were compared to changes, over the same time period, at monitors unlikely to be affected by the CCS (the control zone) and in the boundary zone between the two. Similar analyses were done for CCS hours during weekends (when the CCS was not operating).
Based on the single roadside monitor with the CCS Zone, it was not possible to identify any relative changes in pollution concentrations associated with the introduction of the scheme. However, using background monitors, there was good evidence for a decrease in NO and increases in NO
2 and O
3 relative to the control zone. There was little change in background concentrations of NO
X. There was also evidence of relative reductions in PM
10 and CO. Similar changes were observed during the same hours in weekends when the scheme was not operating.
The causal attribution of these changes to the CCS per se is not appropriate since the scheme was introduced concurrently with other traffic and emissions interventions which might have had a more concentrated effect in central London. This study provides important pointers for study design and data requirements for the evaluation of similar schemes in terms of air quality. It also shows that results may be unexpected and that the overall effect on toxicity may not be entirely favourable.
Choosing Wisely Canada and most major anesthesia and preoperative guidelines recommend against obtaining preoperative tests before low-risk procedures. However, these recommendations alone have not ...reduced low-value test ordering. In this study, the theoretical domains framework (TDF) was used to understand the drivers of preoperative electrocardiogram (ECG) and chest X-ray (CXR) ordering for patients undergoing low-risk surgery ('low-value preoperative testing') among anesthesiologists, internal medicine specialists, nurses, and surgeons.
Using snowball sampling, preoperative clinicians working in a single health system in Canada were recruited for semi-structured interviews about low-value preoperative testing. The interview guide was developed using the TDF to identify the factors that influence preoperative ECG and CXR ordering. Interview content was deductively coded using TDF domains and specific beliefs were identified by grouping similar utterances. Domain relevance was established based on belief statement frequency, presence of conflicting beliefs, and perceived influence over preoperative test ordering practices.
Sixteen clinicians (7 anesthesiologists, 4 internists, 1 nurse, and 4 surgeons) participated. Eight of the 12 TDF domains were identified as the drivers of preoperative test ordering. While most participants agreed that the guidelines were helpful, they also expressed distrust in the evidence behind them (knowledge). Both a lack of clarity about the responsibilities of the specialties involved in the preoperative process and the ease by which any clinician could order, but not cancel tests, were drivers of low-value preoperative test ordering (social/professional role and identity, social influences, belief about capabilities). Additionally, low-value tests could also be ordered by nurses or the surgeon and may be completed before the anesthesia or internal medicine preoperative assessment appointment (environmental context and resources, beliefs about capabilities). Finally, while participants agreed that they did not intend to routinely order low-value tests and understood that these would not benefit patient outcomes, they also reported ordering tests to prevent surgery cancellations and problems during surgery (motivation and goals, beliefs about consequences, social influences).
We identified key factors that anesthesiologists, internists, nurses, and surgeons believe influence preoperative test ordering for patients undergoing low-risk surgeries. These beliefs highlight the need to shift away from knowledge-based interventions and focus instead on understanding local drivers of behaviour and target change at the individual, team, and institutional levels.
We investigated whether inhibition of platelet-derived growth factor (PDGF) receptor tyrosine kinase activity would affect pericyte viability, vascular endothelial growth factor (VEGF)/vascular ...endothelial growth factor receptor-2 (VEGFR-2) expression and angiogenesis in a model of retinopathy of prematurity (ROP). ROP was induced in Sprague Dawley rats by exposure to 80% oxygen from postnatal (P) days 0 to 11 (with 3 hours/day in room air), and then room air from P12–18 (angiogenesis period). Shams were neonatal rats in room air from P0–18. STI571, a potent inhibitor of PDGF receptor tyrosine kinase, was administered from P12–18 at 50 or 100 mg/kg/day intraperitoneal (i.p.). Electron microscopy revealed that pericytes in the inner retina of both sham and ROP rats appeared normal; however STI571 induced a selective pericyte and vascular smooth muscle degeneration. Immunolabeling for caspase-3 and α-smooth muscle cell actin in consecutive paraffin sections of retinas confirmed that these degenerating cells were apoptotic pericytes. In all groups, VEGF and VEGFR-2 gene expression was located in ganglion cells, the inner nuclear layer, and retinal pigment epithelium. ROP was associated with an increase in both VEGF and VEGFR-2 gene expression and blood vessel profiles in the inner retina compared to sham rats. STI571 at both doses increased VEGF and VEGFR-2 mRNA and exacerbated angiogenesis in ROP rats, and in sham rats at 100 mg/kg/day. In conclusion, PDGF is required for pericyte viability and the subsequent prevention of VEGF/VEGFR-2 overexpression and angiogenesis in ROP.
Extracytoplasmic solute receptors (ESRs) are important components of solute uptake systems in bacteria, having been studied extensively as parts of ATP binding cassette transporters. Herein we report ...the first crystal structure of an ESR protein from a functionally characterized electrochemical ion gradient dependent secondary transporter. This protein, SiaP, forms part of a tripartite ATP-independent periplasmic transporter specific for sialic acid in Haemophilus influenzae. Surprisingly, the structure reveals an overall topology similar to ATP binding cassette ESR proteins, which is not apparent from the sequence, demonstrating that primary and secondary transporters can share a common structural component. The structure of SiaP in the presence of the sialic acid analogue 2,3-didehydro-2-deoxy-N-acetylneuraminic acid reveals the ligand bound in a deep cavity with its carboxylate group forming a salt bridge with a highly conserved Arg residue. Sialic acid binding, which obeys simple bimolecular association kinetics as determined by stopped-flow fluorescence spectroscopy, is accompanied by domain closure about a hinge region and the kinking of an α-helix hinge component. The structure provides insight into the evolution, mechanism, and substrate specificity of ESR-dependent secondary transporters that are widespread in prokaryotes.
The relationship between the renin–angiotensin system (RAS) and the progression of diabetic renal disease has been a major focus of investigation over the past 20 years. More recently, experimental ...and clinical studies have also suggested that the RAS may have a pathogenetic role at other sites of micro‐ and macrovascular injury in diabetes. Complementing major advances into the understanding of the local, as distinct from the systemic RAS, a number of large clinical trials have examined whether blockade of the RAS might provide protection from the long‐term complications of diabetes, beyond that due to blood pressure reduction alone. While some controversy remains, these studies have, in general, suggested that angiotensin converting enzyme (ACE) inhibition and more recently, angiotensin receptor blockade reduce the development and progression of diabetic nephropathy, cardiovascular disease and possibly retinopathy. This review will focus on recent developments in our understanding of the tissue‐based RAS and its role in end‐organ injury in diabetes, the results of recent clinical trials and newer strategies for the pharmacological manipulation of the RAS.
Effects of endothelin or angiotensin II receptor blockade on diabetes in the transgenic (mRen-2)27 rat.
Endothelin (ET) and angiotensin II (Ang II) are vasoactive/trophic peptides that may contribute ...to the progression of diabetic nephropathy. The transgenic (mRen-2)27 rat exhibits overexpression of Ang II at sites of normal physiological expression. Unlike other rat strains, the streptozotocin-induced diabetic Ren-2 rat develops progressive renal pathology associated with a declining glomerular filtration rate (GFR) and provides a convenient model to evaluate the role of these vasoactive peptides in the nephropathic process.
Oral administration of either the endothelin A (ETA) and ETB receptor antagonist bosentan or the angiotensin type 1 (AT1) receptor antagonist valsartan for 12 weeks reduced systolic blood pressure (SBP) of nondiabetic and diabetic Ren-2 rats to normotensive levels. Diabetic renal pathology was associated with intense renin mRNA and protein in the proximal tubules and juxtaglomerular cells along with overexpression of transforming growth factor-β1 (TGF-β1) and collagen IV mRNA in glomeruli and tubules. With valsartan but not bosentan, renin mRNA and protein in the proximal tubules were not detected. Valsartan but not bosentan reduced TGF-β1 and collagen IV mRNA and the severity of diabetic renal pathology. A declining GFR with diabetes was attenuated by both treatments. Albuminuria in diabetic rats rose further with bosentan but was reduced with valsartan.
Despite producing normotension, severe diabetic renal pathology was not prevented by bosentan, suggesting dissociation of ET, albuminuria, and hypertension from the structural injury in this diabetic model. The beneficial effects afforded by valsartan therapy strengthen the importance of the local renin-angiotensin system in mediating progressive diabetic renal injury.
The prostaglandin-cyclooxygenase (COX) pathway influences new blood vessel growth in a variety of tissues. This study was conducted to determine the cellular location of COX-2 in the retina and ...whether the inhibition of COX-2 would reduce retinal angiogenesis in a rodent model of retinopathy of prematurity (ROP).
ROP was induced in C57BL/6 mice by exposing 7-day-old mice to 75% oxygen (hyperoxia) for 5 days followed by 5 days in room air (relative hypoxia and retinal angiogenesis). Normal mice were those with a normally developing retinal vasculature exposed to room air from birth until postnatal day (P)17. The COX-2 inhibitor, rofecoxib (15 mg/kg body weight intraperitoneally) was administered to normal and ROP mice from P12 to P17. Immunohistochemistry for COX-2 was performed on retinas from all groups by the avidin-biotin method. Histologic methods were used to count blood vessel profiles (BVPs) in the inner retina (inner limiting membrane, ganglion cell layer, and inner plexiform layer) with a masked approach.
Intense COX-2 immunolabeling was specifically localized to ganglion cells and blood vessels of all mice retinas. In ROP mice, COX-2 immunolabeling was detected on blood vessels extending into the vitreous cavity. Quantitation of BVPs in the inner retina revealed an increase in untreated ROP mice compared with untreated normal mice (P < 0.001). Rofecoxib decreased BVPs by approximately 45% in normal mice and 37% in ROP mice.
COX-2 is localized to sites associated with retinal blood vessels. The finding that the selective COX-2 inhibitor, rofecoxib, attenuated the retinal angiogenesis that accompanies ROP, and normal retinal development indicates that COX-2 plays an important role in blood vessel formation in the retina.
PDF
