Effect of Methylimidazole-Induced Hypothyroidism in a Model of Low Retinal Neovascular Incidence

PURPOSE. To determine the effect of methylimidazole (MMI)-induced hypothyroidism in a newborn rat model of low retinal neovascular (NV) incidence. METHODS. Control and MMI-exposed newborn rats were raised either in room air or variable oxygen (40/15) until P14. All groups were then exposed to room air between postnatal day (P)14 and P20. Dams drank either tap water or water containing MMI. Eyes of animals in all groups were enucleated, and retinas were removed and stained with adenosine diphosphatase and analyzed for peripheral avascularity, vascular density, and NV incidence and severity. RESULTS. In the control group, MMI treatment did not promote the development of retinal NV although a linear relationship (r ϭ 0.99, P Ͻ 0.01) was found between increased MMI dose and lower peripheral retinal vascular densities. In all the 40/15 groups, peripheral retinal vascular densities were lower (P Ͻ 0.05) than normal and were not a function of MMI dose. Increased MMI dose produced increased retinal incidence of NV (r ϭ 0.99, P Ͻ 0.05). CONCLUSIONS. These data are consistent with the notions that thyroid function contributes to normal retinal vascular density and that hypothyroidism can play a permissive role in the development of retinal NV. (Invest Ophthalmol Vis Sci. 2004; 45:919 -921) DOI:10.1167/iovs.03-0914 V ery-low-birth-weight infants are at substantially higher risk for blinding complications, such as the development of retinal neovascularization (NV) associated with retinopathy of prematurity (ROP). To minimize the impact of retinal NV on vision, photocoagulation is currently used, but it is a destructive approach that is not always effective. A better understanding is needed of the pathogenic factors involved in the formation of retinal NV in ROP so that new methods of prevention and treatment can be developed. To date, studies have demonstrated an important link between insulin-like growth factor (IGF)-1 and normal and abnormal retinal vascular development. 1-3 IGF-1 is, among other functions, a downstream modulator of thyroid activity. Infants born very prematurely (Ͻ27 weeks) are more likely to have low thyroxine (T 4 ) levels, indicating an abnormal hypothalamus-pituitary-thyroid axis function. In this study, we used a clinically relevant model of ROP involving newborn rats exposed to a variable oxygen environment from postnatal day (P)0 to P14 and then to room air between P15 and P20. 6 -8 In animals exposed to an oxygen environment that alternates between 40% and 15% every other day (the 40/15 model), only a small percentage (Ͻ10%) of the rat pups exhibit 1 clock hour of NV in the peripheral retina. -14 METHODS The animals were treated in accordance with the NIH Guide for the Care and Use of Laboratory Animals and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. MMI Between P0 and P20, rat pups were raised in room air and received MMI (0.05%, 0.1%, 0.13%, or 0.15% wt/vol; Sigma-Aldrich, St. Louis, MO), added to the drinking water of the dam. Control dams and their pups drank untreated water. In the control and 0.13% and 0.15% MMI-treated 40/15 groups, measurements of T 4 , thyroid stimulating hormone (TSH), and IGF-1 were performed (Anilytics Inc., Gaithersburg, MD) on pooled blood samples. Pooled blood samples were used because of the limited amount of blood available from individual newborn rats (Ͻ30 g). However, retinal histopathology was not investigated, because 0.13% and 0.15% MMI doses usually resulted in substantial (Ͼ90%) pup attrition (data not shown). Animal Model 7 Briefly, Sprague-Dawley dams and litters (12-15 pups per litter) were housed in modified pediatric incubators where the oxygen levels were varied between 40% and 15% (40/15) every 24 hours for the first 14 days after birth. Rats were then allowed to recover in room air (21%) during the next 6 days until P20. The drinking water in one of two cages per incubator was supplemented with MMI between P0 and P20. Holes in the sides of the pediatric incubators were purposely not sealed so that the incubators would be somewhat leaky and minimize the unwanted buildup of carbon dioxide. Although we did not directly assess whether airflow at the holes reversed during the variable oxygen exposure, it is unlikely that this happened, because the computercontrolled (Oxycycler; Biospherix, Ltd., Redfield, NY) variable oxygen procedure constantly maintain positive pressure inside the incubator by injecting the appropriate mixture of 100% oxygen or nitrogen to maintain either a 40% or 15% oxygen environment. In addition, each incubator housed one untreated and one MMI-treated 40/15 cage and so these groups experienced similar variable oxygen exposures. From th

Refractive Development in the “ROP Rat”

Although retinopathy of prematurity (ROP) is clinically characterized by abnormal retinal vessels at the posterior pole of the eye, it is also commonly characterized by vascular abnormalities in the anterior segment, visual dysfunction which is based in retinal dysfunction, and, most commonly of all, arrested eye growth and high refractive error, particularly (and paradoxically) myopia. The oxygen-induced retinopathy rat model of ROP presents neurovascular outcomes similar to the human disease, although it is not yet known if the “ROP rat” also models the small-eyed myopia characteristic of ROP. In this study, magnetic resonance images (MRIs) of albino (Sprague-Dawley) and pigmented (Long-Evans) ROP rat eyes, and age- and strain-matched room-air-reared (RAR) controls, were examined. The positions and curvatures of the various optical media were measured and the refractive state (℞) of each eye estimated based on a previously published model. Even in adulthood (postnatal day 50), Sprague-Dawley and Long-Evans ROP rats were significantly myopic compared to strain-matched controls. The myopia in the Long-Evans ROP rats was more severe than in the Sprague-Dawley ROP rats, which also had significantly shorter axial lengths. These data reveal the ROP rat to be a novel and potentially informative approach to investigating physiological mechanisms in myopia in general and the myopia peculiar to ROP in particular

Systemic Retinaldehyde Treatment Corrects Retinal Oxidative Stress, Rod Dysfunction, and Impaired Visual Performance in Diabetic MiceSystemic Retinaldehyde Treatment in Diabetic Mice

PurposeDiabetes appears to induce a visual cycle defect because rod dysfunction is correctable with systemic treatment of the visual cycle chromophore 11-cis-retinaldehyde. However, later studies have found no evidence for visual cycle impairment. Here, we further examined whether photoreceptor dysfunction is corrected with 11-cis-retinaldehyde. Because antioxidants correct photoreceptor dysfunction in diabetes, the hypothesis that exogenous visual chromophores have antioxidant activity in the retina of diabetic mice in vivo was tested.MethodsRod function in 2-month-old diabetic mice was evaluated using transretinal electrophysiology in excised retinas and apparent diffusion coefficient (ADC) MRI to measure light-evoked expansion of subretinal space (SRS) in vivo. Optokinetic tracking was used to evaluate cone-based visual performance. Retinal production of superoxide free radicals, generated mostly in rod cells, was biochemically measured with lucigenin. Diabetic mice were systemically treated with a single injection of either 11-cis-retinaldehyde, 9-cis-retinaldehyde (a chromophore surrogate), or all-trans-retinaldehyde (the photoisomerization product of 11-cis-retinaldehyde).ResultsConsistent with previous reports, diabetes significantly reduced (1) dark-adapted rod photo responses (transretinal recording) by ∼18%, (2) rod-dominated light-stimulated SRS expansion (ADC MRI) by ∼21%, and (3) cone-dominated contrast sensitivity (using optokinetic tracking [OKT]) by ∼30%. Both 11-cis-retinaldehyde and 9-cis-retinaldehyde largely corrected these metrics of photoreceptor dysfunction. Higher-than-normal retinal superoxide production in diabetes by ∼55% was also significantly corrected following treatment with 11-cis-retinaldehyde, 9-cis-retinaldehyde, or all-trans-retinaldehyde.ConclusionsCollectively, data suggest that retinaldehydes improve photoreceptor dysfunction in diabetic mice, independent of the visual cycle, via an antioxidant mechanism

Oral rivaroxaban versus standard therapy for the treatment of symptomatic venous thromboembolism : a pooled analysis of the EINSTEIN-DVT and PE randomized studies

Background: Standard treatment for venous thromboembolism (VTE) consists of a heparin combined with vitamin K antagonists. Direct oral anticoagulants have been investigated for acute and extended treatment of symptomatic VTE; their use could avoid parenteral treatment and/or laboratory monitoring of anticoagulant effects. Methods: A prespecified pooled analysis of the EINSTEIN-DVT and EINSTEIN-PE studies compared the efficacy and safety of rivaroxaban (15 mg twice-daily for 21 days, followed by 20 mg once-daily) with standard-therapy (enoxaparin 1.0 mg/kg twice-daily and warfarin or acenocoumarol). Patients were treated for 3, 6, or 12 months and followed for suspected recurrent VTE and bleeding. The prespecified noninferiority margin was 1.75. Results: 8282 patients were enrolled. 4151 received rivaroxaban and 4131 received standard-therapy. The primary efficacy outcome occurred in 86 rivaroxaban-treated patients (2.1%) compared with 95 (2.3%) standard-therapy-treated patients (hazard ratio, 0.89; 95% confidence interval [CI], 0.66-1.19; pnoninferiority<0.001). Major bleeding was observed in 40 (1.0%) and 72 (1.7%) patients in the rivaroxaban and standard-therapy groups, respectively (hazard ratio, 0.54; 95% CI, 0.37-0.79; p=0.002). In key subgroups, including fragile patients, cancer patients, patients presenting with large clots and those with a history of recurrent VTE, the efficacy and safety of rivaroxaban was similar compared with standard-therapy. Conclusion: The single-drug approach with rivaroxaban resulted in similar efficacy to standard-therapy and was associated with a significantly lower rate of major bleeding. Efficacy and safety results were consistent among key patient subgroups

Daily Light Onset and Plasma Membrane Tethers Regulate Mitochondria Redistribution within the Retinal Pigment Epithelium

Funding Information: This work was funded by the MRC (MR/X020827/1) awarded to T.B., Wellcome Trust (212216/Z/18/Z) awarded to C.E.F., National Institutes of Health (RO1\u2019s AG058171, AG081981, EY034309) awarded to B.A.B and Diabetes UK fellowship (23/0006514) and Moorfields Eye Charity fellowship (GR001526) award to G.D.R. Publisher Copyright: © 2024 by the authors.The retinal pigment epithelium (RPE) is an essential component of the retina that plays multiple roles required to support visual function. These include light onset- and circadian rhythm-dependent tasks, such as daily phagocytosis of photoreceptor outer segments. Mitochondria provide energy to the highly specialized and energy-dependent RPE. In this study, we examined the positioning of mitochondria and how this is influenced by the onset of light. We identified a population of mitochondria that are tethered to the basal plasma membrane pre- and post-light onset. Following light onset, mitochondria redistributed apically and interacted with melanosomes and phagosomes. In a choroideremia mouse model that has regions of the RPE with disrupted or lost infolding of the plasma membrane, the positionings of only the non-tethered mitochondria were affected. This provides evidence that the tethering of mitochondria to the plasma membrane plays an important role that is maintained under these disease conditions. Our work shows that there are subpopulations of RPE mitochondria based on their positioning after light onset. It is likely they play distinct roles in the RPE that are needed to fulfil the changing cellular demands throughout the day.publishersversionpublishe

Functional Changes Within the Rod Inner Segment Ellipsoid in Wildtype Mice: An Optical Coherence Tomography and Electron Microscopy Study

Purpose: To test the hypothesis that changing energy needs alter mitochondria distribution within the rod inner segment ellipsoid. Methods: In mice with relatively smaller (C57BL/6J [B6J]) or greater (129S6/ev [S6]) retina mitochondria maximum reserve capacity, the profile shape of the rod inner segment ellipsoid zone (ISez) was measured with optical coherence tomography (OCT) under higher (dark) or lower (light) energy demand conditions. ISez profile shape was characterized using an unbiased ellipse descriptor (minor/major aspect ratio). Other bioenergy indexes evaluated include the external limiting membrane–retinal pigment epithelium (ELM-RPE) thickness and the magnitude of the signal intensity of a hyporeflective band located between the photoreceptor tips and apical RPE. The spatial distribution of rod ellipsoid mitochondria were also examined with electron microscopy. Results: In B6J mice, darkness produced a greater ISez aspect ratio, thinner ELM-RPE, and a smaller hyporeflective band intensity than in light. In S6 mice, dark and light ISez aspect ratio values were not different and were greater than in light-adapted B6J mice; dark-adapted S6 mice showed smaller ELM-RPE thinning versus light, and negligible hyporeflective band intensity in the light. In B6J mice, mitochondria number in light increased in the distal inner segment ellipsoid and decreased proximally. In S6 mice, mitochondria number in the inner segment ellipsoid were not different between light and dark, and were greater than in B6J mice. Conclusions: These data raise the possibility that rod mitochondria activity in mice can be noninvasively evaluated based on the ISez profile shape, a new OCT index that complements OCT energy biomarkers measured outside of the ISez region