Vitreous levels of oxidative stress biomarkers and the radical-scavenger α1-microglobulin/A1M in human rhegmatogenous retinal detachment

Structure, Functions, and Implications of Selected Lipocalins in Human Disease

The lipocalin proteins are a large family of small extracellular proteins that demonstrate significant heterogeneity in sequence similarity and have highly conserved crystal structures. They have a variety of functions, including acting as carrier proteins, transporting retinol, participating in olfaction, and synthesizing prostaglandins. Importantly, they also play a critical role in human diseases, including cancer. Additionally, they are involved in regulating cellular homeostasis and immune response and dispensing various compounds. This comprehensive review provides information on the lipocalin family, including their structure, functions, and implications in various diseases. It focuses on selective important human lipocalin proteins, such as lipocalin 2 (LCN2), retinol binding protein 4 (RBP4), prostaglandin D2 synthase (PTGDS), and α1-microglobulin (A1M).

Role of Oxidative Stress in Ocular Diseases: A Balancing Act

Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

Vitreous Humor Proteome: Targeting Oxidative Stress, Inflammation, and Neurodegeneration in Vitreoretinal Diseases

Oxidative stress is defined as an unbalance between pro-oxidants and antioxidants, as evidenced by an increase in reactive oxygen and reactive nitrogen species production over time. It is important in the pathophysiology of retinal disorders such as diabetic retinopathy, age-related macular degeneration, retinal detachment, and proliferative vitreoretinopathy, which are the focus of this article. Although the human organism’s defense mechanisms correct autoxidation caused by endogenous or exogenous factors, this may be insufficient, causing an imbalance in favor of excessive ROS production or a weakening of the endogenous antioxidant system, resulting in molecular and cellular damage. Furthermore, modern lifestyles and environmental factors contribute to increased chemical exposure and stress induction, resulting in oxidative stress. In this review, we discuss the current information about oxidative stress and the vitreous proteome with a special focus on vitreoretinal diseases. Additionally, we explore therapies using antioxidants in an attempt to rescue the body from oxidation, restore balance, and maximize healthy body function, as well as new investigational therapies that have shown significant therapeutic potential in preclinical studies and clinical trial outcomes, along with their goals and strategic approaches to combat oxidative stress.

Antioxidant Status in the Vitreous of Eyes with Rhegmatogenous Retinal Detachment with and without Proliferative Vitreoretinopathy, Macular Hole and Epiretinal Membrane

(1) Background: The aim of the study was to test the hypothesis that the antioxidant status in the vitreous body of eyes, which had been vitrectomized due to rhegmatogenous retinal detachment (RRD) with or without proliferative vitreoretinopathy (PVR), is higher than in eyes vitrectomized due to other retinal diseases. (2) Methods: four patient groups were analyzed: 22 eyes of patients with RRD without PVR, 27 eyes with RRD and PVR, 22 eyes with macular hole (MH) and 10 eyes with epiretinal membrane (ERM). Spectrophotometric methods were used to determine the total antioxidant status (TAS) values as well as superoxide dismutase (SOD) and glutathione reductase (GR) activities in the vitreous fluid samples. (3) Results: no significant differences in TAS values and antioxidant enzyme activities were observed among patient with RRD with and without PVR and with MH and ERM. The longer the duration of RRD leading to PVR and better postoperative visual acuity, the higher the TAS level. No significant differences were found between "macula on" and "macula off" subgroups within the RRD group and the RRD combined with PVR group. (4) Conclusions: The preliminary results do not support the thesis that the antioxidant status of vitrectomized eyes is different in patients with RRD with or without PVR in comparison to patients with MH and ERM. In patients with RRD, PVR presence and detached macula do not affect the values of TAS, SOD and GR in the vitreous fluid. The duration of the disease influences TAS in the vitreous in eyes with RRD complicated with PVR.

Lipid Peroxidation in Subretinal Fluid: Some Light on the Prognosis Factors

The aim of this study was to identify a relation between the clinical characteristics and differences in lipid peroxidation in the subretinal fluid (SRF) of rhegmatogenous retinal detached patients by malondialdehyde (MDA) quantification. We collected 65 SRF samples from consecutive patients during scleral buckling surgery in rhegmatogenous retinal detachment (RRD) eyes. In addition to a complete ophthalmic evaluation, we studied the refractive status, evolution time, and the number of detached retinal quadrants to establish the extension of RRD. We studied the clinical aspects and oxidative stress and compared the characteristics among groups. We found that neither the evolution time of RRD nor the patients’ age correlated with the MDA concentration in the SRF. The MDA and the protein content of the SRF increased in the patients with high myopia and with more extended RRD. Our results suggest that oxidative imbalance was important in more extended retinal detachment (RD) and in myopic eyes and should be taken into account in the managing of these cases.

Structure, Functions, and Physiological Roles of the Lipocalin α1-Microglobulin (A1M)

α₁-microglobulin (A1M) is found in all vertebrates including humans. A1M was, together with retinol-binding protein and β-lactoglobulin, one of the three original lipocalins when the family first was proposed in 1985. A1M is described as an antioxidant and tissue cleaning protein with reductase, heme- and radical-binding activities. These biochemical properties are driven by a strongly electronegative surface-exposed thiol group, C34, on loop 1 of the open end of the lipocalin barrel. A1M has been shown to have protective effects in vitro and in vivo in cell-, organ-, and animal models of oxidative stress-related medical conditions. The gene coding for A1M is unique among lipocalins since it is flanked downstream by four exons coding for another non-lipocalin protein, bikunin, and is consequently named α₁-microglobulin-bikunin precursor gene (AMBP). The precursor is cleaved in the Golgi, and A1M and bikunin are secreted from the cell separately. Recent publications have suggested novel physiological roles of A1M in regulation of endoplasmic reticulum activities and erythrocyte homeostasis. This review summarizes the present knowledge of the structure and functions of the lipocalin A1M and presents a current model of its biological role(s).

Experimental models and examination methods of retinal detachment

Retinal detachment refers to the separation of the retinal neuroepithelium and pigment epithelium, usually involving the death of photoreceptor cells. Severe detachment may lead to permanent visual impairment if not treated properly and promptly. According to the underlying causes, retinal detachment falls into one of three categories: exudative retinal detachment, traction detachment, and rhegmatogenous retinal detachment. Like many other diseases, it is difficult to study the pathophysiology of retinal detachment directly in humans, because the human retinal tissues are precious, scarce and non-regenerative; thus, establishing experimental models that better mimic the disease is necessary. In this review, we summarize the existing models of the three categories of retinal detachment both in vivo and in vitro, along with an overview of their examination methods and the major strengths and weaknesses of each model.

xCT regulates redox homeostasis and promotes photoreceptor survival after retinal detachment

BACKGROUNDS

Photoreceptor degeneration underlies various retinal disorders that lead to vision impairment. Currently, no effective medication is available to rescue photoreceptors under disease conditions. Elucidation of the molecular pathways involved in photoreceptor degeneration is a prerequisite for the rational design of therapeutic interventions. Photoreceptors are among the most energy-demanding tissues that require highly active oxidative phosphorylation. Therefore, disruption of metabolic support to photoreceptors results in a redox imbalance and subsequent cell death. We hypothesize that the redox regulatory pathway could be a potential therapeutic target to rescue photoreceptors under disease conditions.

METHODS

Experimental retinal detachment was induced in mice. A murine photoreceptor-derived 661w cell line treated with H₂O₂ was employed as an in vitro model to study the cellular response to oxidative stress. The expression and functional role of xCT, an upstream regulator of redox homeostasis, was assessed in vivo and in vitro. An xCT expression vector was constructed for an in vivo study to evaluate the therapeutic potential of this molecule.

RESULTS

xCT expression was upregulated in detached retina and H₂O₂-stimulated 661w cells compared to the control cells. Pharmacological inhibition of xCT by sulfasalazine (SAS) promoted photoreceptor degeneration after retinal detachment and 661w cell death upon H₂O₂ treatment. Additionally, SAS treatment induced reactive oxidative species (ROS) accumulation, glutathione (GSH) depletion, and glutamate release in 661w cells. In contrast, xCT overexpression via viral infection protected photoreceptors from degeneration after retinal detachment.

CONCLUSION

We conclude that xCT expression is upregulated in photoreceptors after retinal detachment and plays a neuroprotective role in preserving photoreceptors. Mechanistically, xCT promotes cellular homeostasis by regulating intracellular ROS and GSH levels, which are critical to photoreceptor survival after retinal detachment. Collectively, our findings identify xCT as a potential therapeutic target for protection of photoreceptors under disease conditions.

The Role of α1-Microglobulin (A1M) in Erythropoiesis and Erythrocyte Homeostasis-Therapeutic Opportunities in Hemolytic Conditions

α₁-microglobulin (A1M) is a small protein present in vertebrates including humans. It has several physiologically relevant properties, including binding of heme and radicals as well as enzymatic reduction, that are used in the protection of cells and tissue. Research has revealed that A1M can ameliorate heme and ROS-induced injuries in cell cultures, organs, explants and animal models. Recently, it was shown that A1M could reduce hemolysis in vitro, observed with several different types of insults and sources of RBCs. In addition, in a recently published study, it was observed that mice lacking A1M (A1M-KO) developed a macrocytic anemia phenotype. Altogether, this suggests that A1M may have a role in RBC development, stability and turnover. This opens up the possibility of utilizing A1M for therapeutic purposes in pathological conditions involving erythropoietic and hemolytic abnormalities. Here, we provide an overview of A1M and its potential therapeutic effect in the context of the following erythropoietic and hemolytic conditions: Diamond-Blackfan anemia (DBA), 5q-minus myelodysplastic syndrome (5q-MDS), blood transfusions (including storage), intraventricular hemorrhage (IVH), preeclampsia (PE) and atherosclerosis.

Electrolyte, Nitric Oxide and Oxidative Stress Levels of Aqueous Humor in Patients with Retinal Detachment and Silicone Oil Tamponade

Purpose: To enlighten the pathogenesis of silicone oil (SiO)-related complications via measuring aqueous humor levels of electrolytes, nitric oxide (NO), and oxidative stress in SiO, retinal detachment (RD), and control groups. Materials and Methods: In this prospective study, 56 patients were grouped as SiO (n = 29), RD (n = 12), and control (n = 15). The results of pre- and post-operative ophthalmological examinations, aqueous humor electrolyte and NO levels, total antioxidant and oxidant status (TAS, TOS) and oxidative stress index (OSI) were analyzed. Results: SiO group had a higher mean Na⁺ level compared to controls (144.77 ± 11.48 vs 137.56 ± 6.57 mmol/kg, p = .02). Also, the mean Na⁺ and Cl^- levels of RD group were higher than controls (149.04 ± 12.05 vs. 137.56 ± 6.57 mmol/kg, p = .02, 115.2 ± 7.79 vs 106.23 ± 8.99 mmol/kg, p = .031 for Na⁺ and Cl^-, respectively). The mean NO level of RD group was higher than that of SiO group (51.07 ± 19.56 vs. 34.07 ± 13.84 μM, p = .009). The mean TAS and TOS were lower in SiO group compared to controls (1.92 ± 0.64 vs. 2.49 ± 0.56 μmolTroloxEqv./L, p = .021, 34.98 ± 26.55 vs. 61.46 ± 22.69 μmolH₂O₂Eqv./L, p = .004 for TAS and TOS, respectively). Intraocular retention time of SiO demonstrated positive correlation with post-operative visual acuity (logMAR) and negative correlation with TOS. Conclusions: Elevated aqueous humor Na⁺ and Cl^- in RD patients might reflect abolished function of ion channels on detached retina. Increased Na⁺ and lack of NO response to elevated intraocular pressure in SiO-filled eyes might contribute to secondary cataract and glaucoma formation. SiO is associated with low levels of oxidative stress in aqueous humor; however, increased intraocular retention time of SiO is related to a poor visual outcome.

α1-Microglobulin Binds Illuminated Flavins and Has a Protective Effect Against Sublethal Riboflavin-Induced Damage in Retinal Epithelial Cells

Riboflavin (vitamin B2) is an important constituent of the prosthetic groups flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are utilized as electron-carriers in energy metabolism. Excitation by UV-light leads to the generation of riboflavin radicals and reactive oxygen species (ROS), which can oxidize a wide range of biomolecules. The human protein α₁-microglobulin (A1M) is a reductase and a radical scavenger, which can protect cells and matrix against oxidative damage. Here, we provide evidence of a molecular interaction between illuminated riboflavin and A1M, similar to the radical scavenging reactions previously seen between A1M and other organic radicals. Binding between riboflavin and A1M was demonstrated by gel migration shift, UV-absorbance and fluorescence spectrum analysis. The reaction between A1M and UV-light illuminated riboflavin involved covalent modification of A1M and proteolytic release of an N-terminal part of the protein. Furthermore, A1M also inhibited the ROS-induced photoreduction reaction of riboflavin, in a reaction involving the free thiol group in position C34. Finally, the results show a protective effect of A1M, analyzed by gene expression rates of stress genes, against sublethal damage in retinal epithelial cells in culture. Together, our results suggest a new role of A1M as a scavenger of riboflavin radicals and ROS produced during illumination of riboflavin.

Mice With a Combined Deficiency of Superoxide Dismutase 1 (Sod1), DJ-1 (Park7), and Parkin (Prkn) Develop Spontaneous Retinal Degeneration With Aging

Purpose

Chronic oxidative stress is an important mechanism of disease in aging disorders. We do not have a good model to recapitulate AMD and other retinal disorders in which chronic oxidative stress plays an important role. We hypothesized that mice with a combined deficiency in superoxide dismutase 1 (Sod1), DJ-1 (Park-7), and Parkin (Prkn) (triple knock out, TKO) would have an increased level of chronic oxidative stress in the retina, with anatomic and functional consequences just with aging.

Methods

Eyes of TKO and B6J control mice were (1) monitored with optical coherence tomography (OCT) and electroretinography (ERG) over time, and (2) collected for oxidative marker protein analysis by ELISA or immunohistochemistry and for transmission electron microscopy studies.

Results

TKO mice developed qualitative disruptions in outer retinal layers in OCT by 3 months, increased accumulation of fundus spots and subretinal microglia by 6 months of age, significant retinal thinning by 9 months, and decreased ERG signal by 12 months. Furthermore, we found increased accumulation of the oxidative marker malondialdehyde (MDA) in the retina and increased basal laminal deposits (BLD) and mitochondria number and size in the retinal pigment epithelium of aging TKO mice.

Conclusions

TKO mice can serve as a platform to study retinal diseases that involve chronic oxidative stress, including macular degeneration, retinal detachment, and ischemic retinopathies. In order to model each of these diseases, additional disease-specific catalysts or triggers could be superimposed onto the TKO mice. Such studies could provide better insight into disease mechanisms and perhaps lead to new therapeutic approaches.

Is there a relationship between dopamine and rhegmatogenous retinal detachment?

Dopamine and its receptors have been widely studied in the neurological conditions and in the retina. In this study, we evaluated the possible role of dopamine in rhegmatogenous retinal detachment (RRD) by comparing the amount of 3,4-dihydroxyphenylacetic acid (DOPAC), a surrogate index of retinal dopamine levels, in the vitreous sample of patients affected by RRD with those affected by macular pucker and vitreous hemorrhage. Our results showed that significantly higher levels of DOPAC were found in the vitreous sample of patients affected by RRD compared with those affected by vitreous hemorrhage and macular pucker (P = 0.002). Specifically, no trace of the substance was found in vitreous hemorrhage and macular pucker samples. A slightly significant positive correlation was found among DOPAC and post-operative best corrected visual acuity (r = 0.470, P = 0.049). No correlation was found between DOPAC and the days elapsed between diagnosis and surgery (P = 0.317). For the first time our findings suggest that DOPAC is released in RRD, but not in other retinal diseases such as vitreous hemorrhage and macular pucker. Moreover, we showed a correlation between visual acuity outcome and the amount of DOPAC in the vitreous. This might have a potential, although still unknown, implication in the pathogenesis of the disease and/or in the associated photoreceptors loss. This study was approved by the Ethics Committee of Rome Tor Vergata University Hospital (R.S.92.10) on September 24, 2010.

Gender differences in albumin and ascorbic acid in the vitreous antioxidant system

Ascorbic acid is present at high concentrations in the vitreous and plays a central role in vitreous redox chemistry. Albumin is the main protein in the vitreous with antioxidant properties and occurs in different oxidation states, which can be used as redox indicators, but have not been studied in the vitreous. This study, therefore, addressed the vitreous redox state of cysteine-34 of albumin in relation to the ascorbic acid content, which has been suggested to exert a main function in detoxifying reactive oxygen in the vitreous. A total of 58 vitreous samples obtained from patients undergoing vitrectomy were analyzed for (i) human mercaptalbumin (HMA), the reduced thiol form; (ii) human non-mercaptalbumin1 (HNA1), a reversible oxidative modification with a disulfide at cysteine-34; and (iii) human non-mercaptalbumin2 (HNA2), a non-reversibly (highly) oxidized form of albumin; as well as (iv) ascorbic acid concentrations, to study possible relations. In addition, blood samples were taken to compare albumin redox state between plasma and the vitreous. Vitreous albumin showed greater variability in the redox state of cysteine-34 and a shift to the oxidized fractions compared to plasma albumin (P < 0.001). A strong positive relation was observed between the vitreous ascorbic acid concentrations and the reversibly oxidized form, HNA1 (P < 0.001), and a negative relation with the reduced form, HMA. Positive relations between ascorbic acid and HNA1 in the vitreous were stronger in men than in women. In contrast to HMA and HNA1, there was a distinct gender difference noted for the irreversibly oxidized form, HNA2. While males showed a positive relation between the vitreous ascorbic acid concentrations and HNA2, there was no correlation found with HNA2 in females. Our results support the view that ascorbic acid, by decreasing either directly or indirectly the concentrations of molecular oxygen, generates hydrogen peroxide, and that thiols, including HMA, are acting as antioxidants. This study for the first time provides evidence that vitreous albumin can be used as a marker molecule for the appearance of reactive oxygen species in the vitreous of patients undergoing vitrectomy. Moreover, it can be shown that there are gender differences in vitreous ascorbic acid and albumin concentrations as well as in oxidation state of vitreous albumin.

Update on the human and mouse lipocalin (LCN) gene family, including evidence the mouse Mup cluster is result of an "evolutionary bloom"

Lipocalins (LCNs) are members of a family of evolutionarily conserved genes present in all kingdoms of life. There are 19 LCN-like genes in the human genome, and 45 Lcn-like genes in the mouse genome, which include 22 major urinary protein (Mup) genes. The Mup genes, plus 29 of 30 Mup-ps pseudogenes, are all located together on chromosome (Chr) 4; evidence points to an “evolutionary bloom” that resulted in this Mup cluster in mouse, syntenic to the human Chr 9q32 locus at which a single MUPP pseudogene is located. LCNs play important roles in physiological processes by binding and transporting small hydrophobic molecules —such as steroid hormones, odorants, retinoids, and lipids—in plasma and other body fluids. LCNs are extensively used in clinical practice as biochemical markers. LCN-like proteins (18–40 kDa) have the characteristic eight β-strands creating a barrel structure that houses the binding-site; LCNs are synthesized in the liver as well as various secretory tissues. In rodents, MUPs are involved in communication of information in urine-derived scent marks, serving as signatures of individual identity, or as kairomones (to elicit fear behavior). MUPs also participate in regulation of glucose and lipid metabolism via a mechanism not well understood. Although much has been learned about LCNs and MUPs in recent years, more research is necessary to allow better understanding of their physiological functions, as well as their involvement in clinical disorders.

Iron is neurotoxic in retinal detachment and transferrin confers neuroprotection

In retinal detachment (RD), photoreceptor death and permanent vision loss are caused by neurosensory retina separating from the retinal pigment epithelium because of subretinal fluid (SRF), and successful surgical reattachment is not predictive of total visual recovery. As retinal iron overload exacerbates cell death in retinal diseases, we assessed iron as a predictive marker and therapeutic target for RD. In the vitreous and SRF from patients with RD, we measured increased iron and transferrin (TF) saturation that is correlated with poor visual recovery. In ex vivo and in vivo RD models, iron induces immediate necrosis and delayed apoptosis. We demonstrate that TF decreases both apoptosis and necroptosis induced by RD, and using RNA sequencing, pathways mediating the neuroprotective effects of TF are identified. Since toxic iron accumulates in RD, we propose TF supplementation as an adjunctive therapy to surgery for improving the visual outcomes of patients with RD.

α1-Microglobulin Protects Against Bleeding-Induced Oxidative Damage in Knee Arthropathies

Knee injury increases the risk of developing knee osteoarthritis (OA). Recent evidence suggests involvement of oxidative stress induced by inflammation and bleeding in the joint. This study investigates the role in this process of α₁-microglobulin (A1M), a plasma and tissue antioxidant protein with reducing function, and heme- and radical-binding properties. We studied matched knee synovial fluid (sf) and serum (s) samples from 122 subjects (mean age 40 years, 31% females): 10 were knee healthy references, 13 had acute inflammatory arthritis (AIA), 79 knee injury 0–10 years prior to sampling, and 20 knee OA. Using immunoassays, we measured sf-A1M and s-A1M, sf-hemoglobin (sf-Hb), sf-total free heme (sf-Heme), and sf-carbonyl groups (sf-Carbonyl). We explored associations by partial correlation, or linear regression models with adjustments for age, sex and diagnosis, and evaluated diagnostic capacity by area under the receiver operator characteristics curve (AUC). The AIA group had 1.2- to 1.7-fold higher sf-A1M and s-A1M concentrations compared to the other diagnostic groups; other biomarkers showed no between-group differences. sf-A1M and s-A1M were with AUC of 0.76 and 0.78, respectively, diagnostic for AIA. In the injury group, the amount of bleeding in the joint was inversely correlated to time after injury when measured as sf-Heme (r = -0.41, p < 0.001), but not when measured as sf-Hb (r = -0.19, p = 0.098). A similar inverse association with time after injury was noted for sf-A1M (r = -0.30, p = 0.007), but not for s-A1M and sf-Carbonyl. Linear regression models showed that sf-Heme was more strongly associated with sf-A1M and sf-Carbonyl than sf-Hb. Independent of diagnosis, sf-Heme explained 5.7% of the variability in sf-A1M and 3.0% in the variability in sf-Carbonyl, but appeared unrelated to s-A1M. High sf-A1M and low sf-Heme or sf-Hb were independently associated with low sf-Carbonyl. In conclusion, our results demonstrate that independent of disease, Hb and heme within a knee joint correlates with an increased sf-A1M concentration that appears to be protective of oxidative damage, i.e., a reduction in carbonyl groups. High concentrations of A1M in synovial fluid and serum was further diagnostic for AIA.

Overexpression of the X-Linked Inhibitor of Apoptosis Protects Against Retinal Degeneration in a Feline Model of Retinal Detachment

Retinal detachment is an acute disorder in humans that is caused by trauma or disease, and it can often lead to permanent visual deficits that result from the death of photoreceptors in the retina. The final pathway for photoreceptor cell death is apoptosis and necroptosis. The X-linked inhibitor of apoptosis (XIAP) has been shown to block both of these cell death pathways. This study tested the effects of XIAP on photoreceptor survival in a feline model of retinal detachment. The study was performed in 12 cats, divided into two experimental groups. Six animals received a subretinal injection of adeno-associated virus (AAV) carrying XIAP, and six animals received AAV carrying green fluorescent protein (GFP) as a control. Three weeks after viral delivery, retinas were detached by injecting C3F8 gas into the subretinal space. Optical coherence tomography revealed that the retinal detachments resolved within 3-6 weeks as the gas was slowly resorbed. Analysis of histological sections through the plane of the detachment showed significant preservation of the photoreceptor layer in AAV-XIAP-treated animals compared to AAV-GFP-treated animals at 9 weeks after the detachment. XIAP-treated detached retinas were similar to intact controls. These studies support the potential for XIAP therapy in the treatment of human retinal detachment.

The Role of Mitochondria, Oxidative Stress, and the Radical-binding Protein A1M in Cultured Porcine Retina

PURPOSE

The purpose of this study was to explore the relationship between oxidative stress, antioxidant defense, mitochondrial structure, and biomechanical tissue support in the isolated porcine retina.

METHODS

Full-thickness retinal sheets were isolated from adult porcine eyes. Retinas were cultured for 2 or 48 h using (1) a previously established low-support explant protocol with photoreceptors positioned against the culture membrane (porous polycarbonate) or (2) a high-support procedure developed by our group, apposing the Müller cell endfeet and inner limiting membrane against the membrane. The grafts were analyzed by quantitative polymerase chain reaction (PCR), immunohistochemistry, and transmission electron microscopy (TEM), and culture medium was assayed for the cell damage and oxidative stress markers lactate dehydrogenase and protein carbonyls.

RESULTS

In explants cultured with physical support to the inner border, cone photoreceptors were preserved and lactate dehydrogenase levels were reduced, although an initial (2 h), transient, increased oxidative stress was observed. Elevated expression of the antioxidants α₁-microglobulin and heme oxygenase-1 was seen in the mitochondria-rich inner segments after 48 h compared to low-support counterparts. Housekeeping gene expression suggested a higher degree of structural integrity of mitochondria in high-support explants, and TEM of inner segments confirmed preservation of a normal mitochondrial morphology.

CONCLUSION

Providing retinal explants with inner retinal support leads to mobilization of antioxidant proteins, preservation of mitochondrial function, and increased cell viability. Consequently, the failure of low-support retinal cultures to mobilize an adequate response to the oxidative environment may play a key role in their rapid demise. These findings shed new light on pathological reactions in biomechanically related conditions in vivo.

The Development of a Cat Model of Retinal Detachment and Re-attachment

We present an optimized surgical technique for feline retinal detachment which allows for natural re-attachment, reduces retinal scarring and vitreal bands, and allows central placement of the detachment in close proximity to the optic nerve. This enables imaging via Optical Coherence Tomography (OCT) and multifocal electroretinography (mfERG) analysis. Ideal detachment conditions involve a lensectomy followed by a three-port pars plana vitrectomy. A 16-20 % retinal detachment is induced by injecting 8 % C3F8 gas into the subretinal space in the central retina with a 42G cannula. The retinal detachment resolves approximately 6 weeks post-surgery. Imaging is enhanced by using a 7.5 and 20 diopter lens for OCT and mfERG fundus imaging, respectively, to compensate for the removed lens.

Proteomic Analysis of the Vitreous following Experimental Retinal Detachment in Rabbits

Purpose. The pathogenesis of rhegmatogenous retinal detachment (RRD) remains incompletely understood, with no clinically effective treatment for potentially severe complications such as photoreceptor cell death and proliferative vitreoretinopathy. Here we investigate the protein profile of the vitreous following experimental retinal detachment using a comparative proteomic based approach. Materials and Methods. Retinal detachment was created in the right eyes of six New Zealand red pigmented rabbits. Sham surgery was undertaken in five other rabbits that were used as controls. After seven days the eyes were enucleated and the vitreous was removed. The vitreous samples were evaluated with two-dimensional polyacrylamide gel electrophoresis and the differentially expressed proteins were identified with tandem mass spectrometry. Results. Ten protein spots were found to be at least twofold differentially expressed when comparing the vitreous samples of the sham and retinal detachment surgery groups. Protein spots that were upregulated in the vitreous following retinal detachment were identified as albumin fragments, and those downregulated were found to be peroxiredoxin 2, collagen-Iα1 fragment, and α-1-antiproteinase F. Conclusions. Proteomic investigation of the rabbit vitreous has identified a set of proteins that help further our understanding of the pathogenesis of rhegmatogenous retinal detachment and its complications.

A1M, an extravascular tissue cleaning and housekeeping protein

Alpha-1-microglobulin (A1M) is a small protein found intra- and extracellularly in all tissues of vertebrates. The protein was discovered 40 years ago and its physiological role remained unknown for a long time. A series of recent publications have demonstrated that A1M is a vital part of tissue housekeeping. A strongly electronegative free thiol group forms the structural basis of heme-binding, reductase, and radical-trapping properties. A rapid flow of liver-produced A1M through blood and extravascular compartments ensures clearing of biological fluids from heme and free radicals and repair of oxidative lesions. After binding, both the radicals and the A1M are electroneutral and therefore do not present any further oxidative stress to tissues. The biological cleaning cycle is completed by glomerular filtration, renal degradation, and urinary excretion of A1M heavily modified by covalently linked radicals and heme groups. Based on its role as a tissue housekeeping cleaning factor, A1M constitutes a potential therapeutic drug candidate in treatment or prophylaxis of diseases or conditions that are associated with pathological oxidative stress elements.

Short-time prone posturing is well-tolerated and reduces the rate of unintentional retinal displacement in elderly patients operated on for retinal detachment

Purpose

To evaluate the feasibility, efficacy and safety of strict prone posturing taken for 2 hours after operation in preventing the occurrence of unintentional retinal displacement in elderly patients operated on for retinal detachment (RD).

Methods

Twenty patients aged 60 or more with diagnosis of macula-off RD were asked to keep a strict face-down posturing for 2 hours after vitrectomy and 20% sulfur hexafluoride tamponade. IOP was measured immediately before and after surgery and after the 2-hour posturing. A questionnaire was administered to each patient to evaluate the rate of discomfort experienced because of the face-down posturing. Unintentional displacement of the retina was assessed by evaluating the presence of retinal vessel printings on fundus autofluorescence images taken 4 weeks after operation.

Results

The 2-hour posturing was generally well-tolerated. A mild neck pain was the most common reported symptom. Only a few patients experienced moderate breath shortness while posturing and none had to break the posturing because of respiratory problems. Intraocular pressure (IOP) measured before operation (11.7 ± 2.6 mmHg) was significantly different from IOP recorded at the end of surgery (18.9 ± 4.9 mmHg) and from IOP measured 2 hours after surgery (16.8 ± 4.7 mmHg, P<0.05, Friedman test). IOPs measured immediately and 2 hours after surgery did not differ significantly. Fundus autofluorescence imaging showed RVPs in 7 eyes.

Conclusions

This study shows that a 2-hour face-down posturing is effective in reducing the rate of retinal displacement in patients operated on for rhegmatogenous retinal detachment using vitrectomy and SF6 20%. A 2-hour face-down posturing is feasible for elderly patients and does not appear to cause unwanted, post-operative IOP raises.