The central role of the neutrophil in ischaemic/reperfusion injury

Inadequate blood flow to an organ, ischaemia, may lead to both local and remote tissue injury characterized by oedema, increased microvascular permeability to protein and degradation of connective tissue components. This damage is probably caused by the accumulation and inappropriate activation of neutrophils which occurs when the tissue is reperfused. To test this hypothesis a number of in vitro models of the sequential stages of ischaemia/reperfusion injury were examined. Methods were initially developed to examine the adhesion of neutrophils to monolayers of a cultured endothelial cell line (ECV304) after periods of hypoxia and reoxygenation. Neutrophil migration in response to factors secreted by the treated endothelial cells was then assessed. The genesis of an inappropriate oxidative burst by the neutrophil upon exposure to endothelial chemoattractants and adhesion molecules was also measured. Finally to appraise how tissue function might be affected by endothelial cell hypoxia the contractility of vascular smooth muscle was examined. Neutrophil adhesion to ECV304 cells, which had been hypoxic for 4 hours and then reoxygenated for 30 minutes, was significantly increased. This response was probably initiated by reactive oxygen species (ROS) generated by the endothelial cells. Blockage of their production by allopurinol reduced the heightened adhesion. Similarly removal of ROS by superoxide dismutase or catalase also attenuated adhesion. ROS generation in turn caused the release of a soluble factor (s) which induced a conformational change on the neutrophil surface allowing it to bind to the intercellular adhesion molecule 1 (ICAM-1) on the endothelial cell. Soluble factor (s) from hypoxia/reoxygenated endothelial cells also had a powerful neutrophil chemoattractant ability. When neutrophils were exposed to both hypoxic/reoxygenated endothelial cells and the soluble factor (s) released by them a large oxidative burst was elicited. This response was greatest immediately after reoxygenation and one hour later was diminishing suggesting at least one of the components involved was labile. Analysis of the supernatant from hypoxic/reoxygenated endothelial cell cultures and studies using inhibitors of secretion suggested platelet activating factor (PAF) may be a major component in this overall sequence of events. Lesser roles for IL-8, TNF and LTB4 were also suggested. The secretory products from hypoxia/reoxygenated endothelial cells also affected smooth muscle contractility having an anti-vasoconstrictor or relaxation property, similar to that exerted by PAF.

Free radical reaction products and antioxidant capacity in beating heart coronary artery surgery compared to conventional bypass

Oxygen-derived free radicals are important agents of tissue injury during ischemia and reperfusion. The aim of this study was to investigate changes in protein and lipid oxidation and antioxidant status in beating heart coronary artery surgery and conventional bypass and to compare oxidative stress parameters between the two bypass methods. Serum lipid hydroperoxide, nitric oxide, protein carbonyl, nitrotyrosine, vitamin E, and β-carotene levels and total antioxidant capacity were measured in blood of 30 patients undergoing beating heart coronary artery surgery (OPCAB, off-pump coronary artery bypass grafting) and 12 patients undergoing conventional bypass (CABG, on-pump coronary artery bypass grafting). In the OPCAB group, nitric oxide and nitrotyrosine levels decreased after reperfusion. Similarly, β-carotene level and total antioxidant capacity also decreased after anesthesia and reperfusion. In the CABG group, nitric oxide and nitrotyrosine levels decreased after ischemia and reperfusion. However, protein carbonyl levels elevated after ischemia and reperfusion. Vitamin E, β-carotene, and total antioxidant capacity decreased after ischemia and reperfusion. Significantly decreased nitration and impaired antioxidant status were seen after reperfusion in both groups. Moreover, elevated protein carbonyls were found in the CABG group. The off-pump procedure is associated with lower degree of oxidative stress than on-pump coronary surgery. © 2011 Pleiades Publishing, Ltd.

Parental information needs in chronic renal failure and diabetes mellitus

The information needs of parents of children with end stage renal failure (ESRF) or with insulin dependent diabetes mellitus (IDDM) were assessed by questionnaires over a 2-year period. Questionnaires were posted on seven occasions at 4-monthly intervals and were sent to both mothers and fathers. Most information needs were reported to be for detailed test results, for new information about the condition and about the child's future social development. Questions responsible for the three highest scores were concerned with the future: the child's fertility; their social, career and marriage prospects; and the hope for a new improved treatment. For the IDDM mothers, scores were significantly different depending on age of the child (P = 0.02). Change in treatment mode had no significant effect on the information needs of parents of children with ESRF (P = 0.81). Occupation was significantly associated with the mean general information needs scores for parents, with occupations of a lower socioeconomic status associated with higher information needs scores. There were no significant differences between the reported mean general information needs scores of parents of children with ESRF and of parents of children with IDDM (P = 0.69) or between mothers and fathers mean general information needs scores (P = 0.58). CONCLUSION: Multidisciplinary team members need to tailor information to the needs of the individual families and be sensitive to socioeconomic factors and communication issues.

Renal dopamine and salt-retaining states

Although generally regarded as a neurotransmitter, dopamine is also known to be secreted by the kidney whereby it promotes sodium excretion in its role as a natriuretic honnone. Peripheral dopamine may be formed by two alternative pathways; the decarboxylation of circulating L-Dopa by L-aromatic amino acid decarboxylase (LAAAD), and the desulphation of dopamine sulphate by arylsulphatase A (ASA), the latter being poorly represented in the literature. In many conditions and diseases with which sodium retention is associated, a reduced urinary excretion of dopamine has been noted implicating the involvement of dopamine in the maintenance of sodium homeostasis.This study investigates renal dopamine production via the desulphation of dopamine sulphate in a sample cohort during normal unregulated dietary sodium intake and following a low sodium regimen. After dietary salt restriction urinary dopamine sulphate levels were significantly increased, indicating that dopamine sulphate is indeed a physiological reservoir of active free dopamine, the necessity for which is reduced during self depletion. This confirmed the dopamine/dopamine sulphate pathway as one which may be relevant to the maintenance of sodium homeostasis. The activity of urinary ASA was investigated in diabetes mellitus as an example of a sodium-retaining state, and compared with that in a matched normal control group. A decreased ASA activity was anticipated, given the blunted dopamine excretion observed in many sodium-retaining states, however an unexpected increase in activity in the diabetic group was observed. Enzyme kinetic analysis of ASA showed that this was not due to the existence of an isoform having an altered affinity for dopamine sulphate. This rather paradoxical situation, that urinary-dopamine is decreased while ASA activity is increased, may be explained by the sequestering of free dopamine by autoxidation to 6-hydroxydopamine as has been hypothesised recently to occur in diabetes mellitus. To confirm the homogeneity of ASA in the normal and diabetic groups, four amplicons spanning the 3637bp intronic and exonic regions of the gene were generated by PCR. These were sequence utilising a fluorescent-dye terminator reaction using the forward PCR primer as sequencing primer. Although single nucleotide polymorphisms were observed between the two groups these occurred either in intronic regions or, when exonic, generated silent mutations, supporting the enzyme kinetic data. The expression of ASA was investigated to determine the basis of the increased activity observed in diabetes mellitus. Although a validated comparative RT-PCR assay was developed for amplification of arsa transcripts from fresh blood samples, expression analysis from archived paraffin-embedded renal tissue was complicated by the low yield and degradation of unprotected mRNA. Suggestions for the development of this work using renal cell-culture are discussed.

Glutathione adducts induced by ischemia and deletion of glutaredoxin-1 stabilize HIF-1α and improve limb revascularization

Reactive oxygen species (ROS) are increased in ischemic tissues and necessary for revascularization; however, the mechanism remains unclear. Exposure of cysteine residues to ROS in the presence of glutathione (GSH) generates GSH-protein adducts that are specifically reversed by the cytosolic thioltransferase, glutaredoxin-1 (Glrx). Here, we show that a key angiogenic transcriptional factor hypoxia-inducible factor (HIF)-1α is stabilized by GSH adducts, and the genetic deletion of Glrx improves ischemic revascularization. In mouse muscle C2C12 cells, HIF-1α protein levels are increased by increasing GSH adducts with cell-permeable oxidized GSH (GSSG-ethyl ester) or 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanyl thiocarbonylamino) phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), an inhibitor of glutathione reductase. A biotin switch assay shows that GSSG-ester-induced HIF-1α contains reversibly modified thiols, and MS confirms GSH adducts on Cys520 (mouse Cys533). In addition, an HIF-1α Cys520 serine mutant is resistant to 2-AAPA–induced HIF-1α stabilization. Furthermore, Glrx overexpression prevents HIF-1α stabilization, whereas Glrx ablation by siRNA increases HIF-1α protein and expression of downstream angiogenic genes. Blood flow recovery after femoral artery ligation is significantly improved in Glrx KO mice, associated with increased levels of GSH-protein adducts, capillary density, vascular endothelial growth factor (VEGF)-A, and HIF-1α in the ischemic muscles. Therefore, Glrx ablation stabilizes HIF-1α by increasing GSH adducts on Cys520 promoting in vivo HIF-1α stabilization, VEGF-A production, and revascularization in the ischemic muscles

The relationship of systemic markers of renal function and vascular function with retinal blood vessel responses

Purpose: To test the hypothesis of a significant relationship between systemic markers of renal and vascular function (processes linked to cardiovascular disease and its development) and retinal microvascular function in diabetes and/or cardiovascular disease.Methods: Ocular microcirculatory function was measured in 116 patients with diabetes and/or cardiovascular disease using static and continuous retinal vessel responses to three cycles of flickering light. Endothelial function was evaluated by von Willebrand factor (vWf), endothelial microparticles and soluble E selectin, renal function by serum creatinine, creatinine clearance and estimated glomerular filtration rate (eGFR). HbA1c was used as a control index.Results: Central retinal vein equivalence and venous maximum dilation to flicker were linked to HbA1c (both p<0.05). Arterial reaction time was linked to serum creatinine (p=0.036) and eGFR (p=0.039), venous reaction time was linked to creatinine clearance (p=0.018). Creatinine clearance and eGFR were linked to arterial maximum dilatation (p<0.001 and p=0.003 respectively) and the dilatation amplitude (p=0.038 and p=0.048 respectively) responses in the third flicker cycle. Of venous responses to the first flicker cycle, HbA1c was linked to the maximum dilation response (p=0.004) and dilatation amplitude (p=0.017), vWf was linked to the maximum constriction response (p=0.016), and creatinine clearance to the baseline diameter fluctuation (p=0.029). In the second flicker cycle, dilatation amplitude was linked to serum creatinine (p=0.022). Conclusions: Several retinal blood vessel responses to flickering light are linked to glycaemia and renal function, but only one index is linked to endothelial function. Renal function must be considered when interpreting retinal vessel responses.

Reactive oxygen and nitrogen species production in cardiomyoblasts during hypoxia and reoxygenation

Hypoxia is a stress condition in which tissues are deprived of an adequate O2 supply; this may trigger cell death with pathological consequences in cardiovascular or neurodegenerative disease. Reperfusion is the restoration of an oxygenated blood supply to hypoxic tissue and can cause more cell injury. The kinetics and consequences of reactive oxygen and nitrogen species (ROS/RNS) production in cardiomyoblasts are poorly understood. The present study describes the systematic characterization of the kinetics of ROS/RNS production and their roles in cell survival and associated protection during hypoxia and hypoxia/reperfusion. H9C2 cells showed a significant loss of viability under 2% O2 for 30min hypoxia and cell death; associated with an increase in protein oxidation. After 4h, apoptosis induction under 2% O2 and 10% O2 was dependent on the production of mitochondrial superoxide (O2-•) and nitric oxide (•NO), partly from nitric oxide synthase (NOS). Both apoptotic and necrotic cell death during 2% O2 for 4h could be rescued by the mitochondrial complex I inhibitor; rotenone and NOS inhibitor; L-NAME. Both L-NAME and the NOX (NADPH oxidase) inhibitor; apocynin reduced apoptosis under 10% O2 for 4h hypoxia. The mitochondrial uncoupler; FCCP significantly reduced cell death via a O2-• dependent mechanism during 2% O2, 30min hypoxia. During hypoxia (2% O2, 4h)/ reperfusion (21% O2, 2h), metabolic activity was significantly reduced with increased production of O2-• and •NO, during hypoxia but, partially restored during reperfusion. O2-• generation during hypoxia/reperfusion was mitochondrial and NOX- dependent, whereas •NO generation depended on both NOS and non-enzymatic sources. Inhibition of NOS worsened metabolic activity during reperfusion, but did not effect this during sustained hypoxia. Nrf2 activation during 2% O2, a sustained hypoxia and reperfusion was O2-•/•NO dependent. Inhibition of NF-?B activation aggravated metabolic activity during 2% O2, 4h hypoxia. In conclusion, mitochondrial O2-•, but, not ATP depletion is the major cause of apoptotic and necrotic cell death in cardiomyoblasts under 2% O2, 4h hypoxia, whereas apoptotic cell death under 10% O2, 4h, is due to NOS-dependent •NO. The management of ROS/RNS rather than ATP is required for improved survival during hypoxia. O2-• production from mitochondria and NOS is cardiotoxic during hypoxia/reperfusion. NF-?B activation during hypoxia and NOS activation during reperfusion is cardiomyoblast protective.

The development, evaluation and use of freshly isolated renal proxinal tubule systems in the fischer rat

The investigation of renal pathophysiology and toxicology has traditionally been advanced by the development of increasingly defined and refined in vitro preparations. This study has sought to develop and evaluate various methods of producing pure samples of renal proximal tubules (PTs) from the Fischer rat. The introduction summarised the most common in vitro preparations together with the parameters used to monitor viability - particularly with regard to toxic events. The most prevalent isolation methods have involved the use of collagenase to produce dissociation of the cortex. However, the present study has shown that even the mildest collagenase treatment caused significant structural damage which resulted in a longevity of only 3hr in suspension. An alternative mechanical isolation technique has been developed in this study that consists of perfusion loading the renal glomeruli with Fe304 followed by disruption of the cortex by homogenisation and sequential sieving. The glomeruli are removed magnetically and the PTs then harvested by a 64μM sieve. PTs isolated in this way showed a vastly superior structural preservation over their collagenase isolated counterparts; also oxygen consumption and enzyme leakage measurements showed a longevity in excess of 6hr when incubated in a very basic medium. Attempts were then made to measure the cytosolic calcium levels in both mechanical and collagenase isolated PTs using the fluorescent calcium indicator Fura. However results were inconclusive due to significant binding of the Fura to the external PT surfaces. In conclusion, PTs prepared by the present mechanical isolation technique exhibit superior preservation and longevity compared with even the mildest collagenase isolation technique and hence appear to offer potential advantages over collagenase isolation as an in vitro renal system.

Tissue transglutaminase and the progression of human renal scarring

ABSTRACT. Experimental renal scarring indicates that tissue transglutaminase (tTg) may be associated with the accumulation of extracellular matrix (ECM), both indirectly via TGF-β1 activation and directly by the formation of ε(γ-glutamyl) lysine dipeptide bonds within the ECM. The latter potentially accelerates deposition and confers the ECM with resistance to proteolytic digestion. Studied were 136 human renal biopsy samples from a range of chronic renal diseases (CRD) to determine changes in tTg and ε(γ-glutamyl) lysine crosslinking. Immunofluorescence for insoluble tTg showed a 14-fold increase in the kidneys of CRD patients (5.3 ± 0.5 versus 76 ± 54 mV/cm2), which was shown to be active by a similar 11-fold increase in the ε(γ-glutamyl) lysine crosslink (1.8 ± 0.2 versus 19.3 ± 14.2 mV/cm2). Correlations were obtained with renal function for tTg and crosslink. In situ hybridization for tTg mRNA showed that tubular epithelial cells were the major source of tTg; however, both mesangial and interstitial cells also contributed to elevated levels in CRD. This mRNA pattern was consistent with immunohistochemistry for soluble tTg. Changes in renal tTg and its product, the ε(γ-glutamyl) lysine crosslink, occur in progressive renal scarring in humans independently of the original etiology and in a similar manner to experimental models. tTg may therefore play a role in the pathogenesis of renal scarring and fibrosis in patients with CRD and can therefore be considered a potential therapeutic target. E-mail: T.Johnson@sheffield.ac.uk

Ankyrin is the major oxidised protein in erythrocyte membranes from end-stage renal disease patients on chronic haemodialysis and oxidation is decreased by dialysis and vitamin C supplementation

Chronically haemodialysed end-stage renal disease patients are at high risk of morbidity arising from complications of dialysis, the underlying pathology that has led to renal disease and the complex pathology of chronic kidney disease. Anaemia is commonplace and its origins are multifactorial, involving reduced renal erythropoietin production, accumulation of uremic toxins and an increase in erythrocyte fragility. Oxidative damage is a common risk factor in renal disease and its co-morbidities and is known to cause erythrocyte fragility. Therefore, we have investigated the hypothesis that specific erythrocyte membrane proteins are more oxidised in end-stage renal disease patients and that vitamin C supplementation can ameliorate membrane protein oxidation. Eleven patients and 15 control subjects were recruited to the study. Patients were supplemented with 2 × 500 mg vitamin C per day for 4 weeks. Erythrocyte membrane proteins were prepared pre- and post-vitamin C supplementation for determination of protein oxidation. Total protein carbonyls were reduced by vitamin C supplementation but not by dialysis when investigated by enzyme linked immunosorbent assay. Using a western blot to detect oxidised proteins, one protein band, later identified as containing ankyrin, was found to be oxidised in patients but not controls and was reduced significantly by 60% in all patients after dialysis and by 20% after vitamin C treatment pre-dialysis. Ankyrin oxidation analysis may be useful in a stratified medicines approach as a possible marker to identify requirements for intervention in dialysis patients.

Investigation of liquid sodium alginates as mucoadhesive bandages coating the oesophageal mucosa and protecting it from gastric reflux

Gastro-oesophageal Reflux Disease (GORD), is generally caused by excess gastric reflux back to the oesophagus where damage to the mucosa results in injury. GORD is a very common disease in western countries, more than a quarter of western people are suffering from this disease and there is a trend that the percentage population in eastern countries who are diagnosed as GORD is increasing. GORD and its complications damage the quality of life and can lead to serious oesophageal diseases including Barrett’s disease and oesophageal carcinoma. Sodium alginate dissolved in water forms a viscous liquid and can coat on oesophageal mucosa for a period of time. In this study the ability of the liquid alginate to adhere to the oesophageal mucosa was investigated and the factors that affect this retention were examined. The potential of this liquid alginate as a drug delivery vehicle to extend the duration of contact with the oesophageal mucosa was confirmed by this study. The capacity of an alginate coating to retard acid and pepsin diffusion, the two main aggressive factors in gastric reflux, was investigated. A significant reduction in acid and pepsin diffusion by alginate gel layer was demonstrated in this project, indicating that alginate has great potential to protect against damage caused by acidic reflux. A novel method was introduced using an independent score system to assess the protection of oesophageal tissue by a coating of liquid alginate using microscopy as a technique. This technique demonstrated that alginate can protect the oesophageal epithelial tissue from the damage caused by gastric acid and pepsin. Many techniques were used in this study. The experimental results suggested that liquid sodium alginate is a very promising candidate in treating local oesophageal diseases through forming a coating on the oesophageal mucosal surface, retarding the diffusion of components of gastric refluxate and thus reducing the contact of these noxious factors with the epithelium and minimising injury.

High-performance liquid chromatography and pharmacokinetics of some antibiotics

The principles of High Performance Liquid Chromatography (HPLC) and pharmacokinetics were applied to the use of several clinically-important drugs at the East Birmingham Hospital. Amongst these was gentamicin, which was investigated over a two-year period by a multi-disciplinary team. It was found that there was considerable intra- and inter-patient variation that had not previously been reported and the causes and consequences of such variation were considered. A detailed evaluation of available pharmacokinetic techniques was undertaken and 1- and 2-compartment models were optimised with regard to sampling procedures, analytical error and model-error. The implications for control of therapy are discussed and an improved sampling regime is proposed for routine usage. Similar techniques were applied to trimethoprim, assayed by HPLC, in patients with normal renal function and investigations were also commenced into the penetration of drug into peritoneal dialysate. Novel assay techniques were also developed for a range of drugs including 4-aminopyridine, chloramphenicol, metronidazole and a series of penicillins and cephalosporins. Stability studies on cysteamine, reaction-rate studies on creatinine-picrate and structure-activity relationships in HPLC of aminopyridines are also reported.

Placenta growth factor-1 exerts time-dependent stabilization of adherens junctions following VEGF-induced vascular permeability

Increased vascular permeability is an early event characteristic of tissue ischemia and angiogenesis. Although VEGF family members are potent promoters of endothelial permeability the role of placental growth factor (PlGF) is hotly debated. Here we investigated PlGF isoforms 1 and 2 and present in vitro and in vivo evidence that PlGF-1, but not PlGF-2, can inhibit VEGF-induced permeability but only during a critical window post-VEGF exposure. PlGF-1 promotes VE-cadherin expression via the trans-activating Sp1 and Sp3 interaction with the VE-cadherin promoter and subsequently stabilizes transendothelial junctions, but only after activation of endothelial cells by VEGF. PlGF-1 regulates vascular permeability associated with the rapid localization of VE-cadherin to the plasma membrane and dephosphorylation of tyrosine residues that precedes changes observed in claudin 5 tyrosine phosphorylation and membrane localization. The critical window during which PlGF-1 exerts its effect on VEGF-induced permeability highlights the importance of the translational significance of this work in that PLGF-1 likely serves as an endogenous anti-permeability factor whose effectiveness is limited to a precise time point following vascular injury. Clinical approaches that would pattern nature's approach would thus limit treatments to precise intervals following injury and bring attention to use of agents only during therapeutic windows.

Diabetes therapies in renal impairment

Depending on age, duration of diabetes and glycaemic control, 20-40% of patients with type 2 diabetes will incur a moderate or severe deterioration of renal function. This will impact the choice of blood glucose-lowering therapy and require more frequent monitoring of both renal function and glycaemic control. Moderate renal impairment (glomerular filtration rate 30-<60 ml/min) requires consideration of dose reduction or treatment cessation for metformin, glucagon-like peptide-1 receptor agonists, some sulphonylureas and some dipeptidyl peptidase-4 inhibitors. At lower rates of glomerular filtration down to about 15 ml/min it may be appropriate to use a meglitinide, pioglitazone or certain sulphonylureas with careful consideration of dose and co-morbidities. Dipeptidyl peptidase-4 inhibitors can be used at reduced dose in patients with very low rates of glomerular filtration, and linagliptin can be used without dose reduction, and has been used in patients on dialysis. Insulin can be used at any stage of renal impairment, but the regimen and the dose must be suitably adjusted and accompanied by adequate monitoring. © The Author(s), 2012.

Obstructive sleep apnoea is associated with sight threatening retinopathy and predicts the developement of preproliferative and proliferative retinopathy in patients with type 2 diabetes:a longitudinal analysis

troduct I on . An observational longitudinal study. P ur P ose . Assess the relationship between obstructive sleep apnoea (OSA) and DR cross-sectionally and longitudinally. M ethods . Adults with Type 2 diabetes mellitus (T2DM), who were re - cruited from a hospital-based diabetes clinic in the UK. Patients with pre-existing OSA, end-stage renal disease and non-diabetic retinopa - thy were excluded. OSA (apnoea hypopnea index ≥ 5 events/hour) was assessed by a single overnight home-based cardio-respiratory study (Alice PDX, Philips Respironics, USA). DR was assessed us - ing retinal images between 2007 and 2012. Sight threatening diabetic retinopathy (STDR) was defined as presence of pre-proliferative or proliferative DR, maculopathy or photocoagulation. Advanced DR was defined as pre-proliferative or proliferative DR. r esults . 199 patients were included (57.3% (n=114) men, 47.7% (n=95) White Europeans). STDR and OSA prevalence were 38.7% (n=77) and 62.8% respectively. A t b A sel I ne . STR prevalence was higher in patients with OSA (OSA+) compared to those without OSA (OSA-) [48.8% n=61 vs. 21.6% n=16, p<0.001]. After adjustment for confounders, OSA remained independently associated with STR (OR 3.7, 95% CI 1.6-8.9, p=0.006), maculopathy (OR 4.5, 95% CI 1.8-11.4, p=0.002) and advanced DR (OR 3.9, 95% CI 1.02-15.3, p=0.047). Mild and moderate to severe OSA were independently associated with STR and maculopathy and only moderate to severe OSA was associated with advanced DR following adjustment for con - founders. l ong I tud I n A lly . Over the follow-up period of (4.4±1 years), more OSA+ patients progressed from no or background DR to advanced DR (15.3% (n=17) vs. 3% (n=2), p=0.01). OSA was an independent pre - dictor of advanced DR development after adjustment for confounders (OR 6.6, 95% CI 1.2-35.1, p=0.03). OSA did not predict the develop - ment of maculopathy. c onclus I ons . OSA is independently associated with STR and predicts the development of preproliferative and proliferative DR. Intervention - al studies are needed to assess the impact of OSA treatment on DR.