Detection of retinal lipid hydroperoxides in experimental uveitis

Dynamics of Cyclooxygenase-1 Positive Microglia/Macrophage in the Retina of Pathological Model Mice as a Biomarker of the Retinal Inflammatory Diseases

In an intraocular inflammatory state, microglia residing in the retina become active and migrate inside the retina. In this study, we investigated whether cyclooxygenase-1 (COX-1) expressed by retinal microglia/macrophage can be a biomarker for the diagnosis of retinal diseases. COX-1 was immunopositive in microglia/macrophage and neutrophils, while COX-2 was immunopositive in astrocytes and neurons in the inner layer of normal retina. The number of COX-1 positive cells per section of the retinal tissue was 14 ± 2.8 (mean ± standard deviation) in normal mice, which showed significant increase in the lipopolysaccharide (LPS)-administrated model (62 ± 5.0, p = 8.7 × 10⁻⁹). In addition to microglia, we found neutrophils that were positive for COX-1. In the early stage of inflammation in the experimental autoimmune uveoretinitis (EAU), COX-1 positive cells, infiltrating from the ciliary body into the retinal outer nuclear layer, were observed. The number of infiltrating COX-1 positive cells correlated with the severity of EAU. Taken together, the increased number of COX-1 positive microglia/macrophage with morphological changes were observed in the retinas of retinal inflammatory disease models. This suggests that COX-1 can be a marker of disease-related activities of microglia/macrophage, which should be useful for the diagnosis of retinal diseases.

12-Lipoxygenase is a Critical Mediator of Type II Pneumocyte Senescence, Macrophage Polarization and Pulmonary Fibrosis after Irradiation

Radiation-induced pulmonary fibrosis (RIPF) is a chronic, progressive complication of therapeutic irradiation of the thorax. It has been suggested that senescence of type II pneumocytes (AECIIs), an alveolar stem cell, plays a role in the development of RIPF through loss of replicative reserve and via senescent AECII-driven release of proinflammatory and profibrotic cytokines. Within this context, we hypothesized that arachidonate 12-lipoxygenase (12-LOX) is a critical mediator of AECII senescence and RIPF. Treatment of wild-type AECIIs with 12S-hydroxyeicosateraenoic acid (12S-HETE), a downstream product of 12-LOX, was sufficient to induce senescence in a NADPH oxidase 4 (NOX4)-dependent manner. Mice deficient in 12-LOX exhibited reduced AECII senescence, pulmonary collagen accumulation and accumulation of alternatively activated (M2) macrophages after thoracic irradiation (5 × 6 Gy) compared to wild-type mice. Conditioned media from irradiated or 12S-HETE-treated primary pneumocytes contained elevated levels of IL-4 and IL-13 compared to untreated pneumocytes. Primary macrophages treated with conditioned media from irradiated AECII demonstrated preferential M2 type polarization when AECIIs were derived from wild-type mice compared to 12-LOX-deficient mice. Together, these data identified 12-LOX as a critical component of RIPF and a therapeutic target for radiation-induced lung injury.

Macrophages and Uveitis in Experimental Animal Models

Resident and infiltrated macrophages play relevant roles in uveitis as effectors of innate immunity and inductors of acquired immunity. They are major effectors of tissue damage in uveitis and are also considered to be potent antigen-presenting cells. In the last few years, experimental animal models of uveitis have enabled us to enhance our understanding of the leading role of macrophages in eye inflammation processes, including macrophage polarization in experimental autoimmune uveoretinitis and the major role of Toll-like receptor 4 in endotoxin-induced uveitis. This improved knowledge should guide advantageous iterative research to establish mechanisms and possible therapeutic targets for human uveitis resolution.

Oxidative photoreceptor cell damage in autoimmune uveitis

Uveitis comprises an extensive array of intraocular inflammatory diseases and often results in irreversible visual loss. Experimental autoimmune uveitis (EAU) is an animal model used to study human uveitis. Both innate and adaptive immune responses are known to mediate retinal damage in EAU. The innate immune response occurs first with activation of toll-like receptors which upregulate inflammatory cytokines, leading to oxidative stress; subsequently, the adaptive immune response results in inflammatory cytokine upregulation and mitochondrial oxidative stress. In early EAU, mitochondrial DNA is damaged before inflammatory cellular infiltration and alters mitochondrial protein levels and the functions of mitochondria in AU. Our recent study confirms the importance of TLR4 in the generation of inflammatory cytokines, initiation of oxidative DNA damage, and induction of mitochondrial oxidative stress. Like EAU, sympathetic ophthalmia also results in photoreceptor mitochondrial oxidative damage. Agents that prevent mitochondrial oxidative stress and photoreceptor apoptosis may help prevent retinal damage and preserve vision in uveitis.

Protective effects of bilberry ( Vaccinium myrtillus L.) extract against endotoxin-induced uveitis in mice

Endotoxin-induced uveitis (EIU), a useful animal model of ocular inflammation, is induced by injection of lipopolysacharide (LPS). These experiments showed that the nitric oxide (NO) level significantly increased in the whole eye homogenate of BALB/C mice 24 h after footpad injection of LPS at a dosage of 100 mg/mouse. However, the elevated NO level was significantly reduced by oral administration of bilberry extract (containing 42.04% anthocyanins) at dosages of 50, 100, and 200 mg/kg/day for 5 days before the LPS injection. In addition, bilberry extract decreased malondialdehyde (MDA) level and increased oxygen radical absorbance capacity (ORAC) level, glutathione (GSH) level, vitamin C level, and total superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities. Moreover, bilberry extract increased expression of copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and GPx mRNA. Taken together, bilberry extract showed protective effects against EIU, whereas the effects of bilberry extract (100 and 200 mg/kg/day, 5 days) were dose-dependent. In conclusion, these results provide new evidence to elucidate the beneficial effects of bilberry extract on eye health.

Alpha-tocopherol protects against oxidative damage to lipids of the rod outer segments of the equine retina

Oxidative stress is a possible risk factor for eye diseases. Lipid peroxidation is one of the major events induced by oxidative stress and is particularly active in polyunsaturated fatty acid (PUFA)-rich biomembranes. This work evaluated endogenous lipid antioxidants, in vitro non-enzymatic lipid peroxidation of rod outer segment membranes (ROS), the fatty acid composition during oxidative damage of total lipids from equine retina and ROS, and the protective action of alpha-tocopherol (alpha-Toc). The major lipid soluble antioxidant was alpha-Toc followed by retinoids and carotenoids. The retina contained a high percentage of PUFAs, mainly docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6). Lipid peroxidation of the equine ROS, induced by Fe(2+)-ascorbate, was monitored using chemiluminescence (CL) with or without pre-treatment with alpha-Toc. With alpha-Toc pre-treatment, CL values were significantly decreased. The most abundant fatty acid was 22:6n-3. After 3h incubation, 95% of total PUFAs were destroyed by peroxidation, whereas in alpha-Toc pre-treated ROS the percentage was significantly decreased. The results show that the retina has an endogenous lipid soluble antioxidant system. ROS were highly sensitive to oxidative damage, since their fatty acid composition was markedly modified during the lipid peroxidation process. The protective role of alpha-Toc as an antioxidant was evident and it could be used in the treatment of equine ocular diseases in which free radicals are involved.

The in vitro protective effect of alpha-tocopherol on oxidative injury in the dog retina

Oxidative stress is a risk factor for eye diseases. Free radicals elicited during the inflammatory process often lead to oxidative damage of lipids (lipid peroxidation). The retina is highly vulnerable because of its high content of polyunsaturated fatty acids (PUFAs). The aim of this study was to investigate in vitro the effect of alpha-tocopherol on the Fe(2+)-ascorbate induced lipid peroxidation in the canine retina. Lipid peroxidation of retinal homogenates was carried out with and without the addition of alpha-tocopherol and monitored both by chemiluminescence and production of thiobarbituric acid reactive substances (TBARS). Total chemiluminescence counts per minute was lower in those homogenates pre-incubated with alpha-tocopherol. Thus, with 1 micromol alpha-tocopherol/mg of protein, 100% inhibition of chemiluminescence and a decrease of TBARS content from 20.46+/-0.85 to 2.62+/-2.77 nmol/mg protein were observed. Simultaneously, changes produced by oxidative stress were noted in the fatty acid composition of retinal lipids. Docosahexaenoic acid was decreased from 14.33+/-2.32% to 1.84+/-0.14% after peroxidation, but this fatty acid remained unaltered in the presence of 1 micromol alpha-tocopherol. These results show that under these experimental conditions, alpha-tocopherol may act as anti-oxidant protecting retinal membranes from deleterious effects. Further studies are required to assess its use in free radical generating conditions affecting the canine retina.

The effects of Ginkgo biloba extract on lipopolysaccharide-induced inflammation in vitro and in vivo

PURPOSE

Ginkgo biloba extract (GBE) contains many different flavone glycosides and terpenoides. Several previous studies have demonstrated that GBE exhibits a wide variety of biological activities, including an antioxidant action, on which we focused our attention. The aim of the present study was to investigate the efficacy of GBE on endotoxin induced uveitis in rats. The anti-inflammatory potency of GBE in vivo was compared with that of prednisolone. In addition, we also investigated nitric oxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha) and the expression of iNOS in a mouse macrophage cell line (RAW 264.7) treated with GBE in vitro to clarify the anti-inflammatory effect.

METHODS

EIU was induced in male Lewis rats by a footpad injection of lipopolysaccharide (LPS). Immediately after the LPS inoculation, either 1, 10 or 100 microg of GBE were injected intravenously. 24hr later, the aqueous humor was collected from both eyes, and the number of infiltrating cells, protein concentration and NO level in the aqueous humor was determined. The RAW 264.7 cells were pretreated with various concentrations of GBE for 24hr and subsequently incubated with LPS for 24hr. Levels of NO, PGE2 and TNF-alpha were determined by enzyme-linked immunosorbent assay. The expression of iNOS protein was analyzed by Western blotting method.

RESULTS

GBE treatment in vivo decreased the concentrations of protein and NO in the aqueous humor of EIU rats. The anti-inflammatory effect of 1 mg GBE was as strong as that of same dose prednisolone. It also significantly reduced the concentration of PGE2, TNF-alpha and NO production in the medium of RAW 264.7 cells compared to that of the LPS group in vitro. The expression of iNOS protein in the 1000 microg ml(-1) of GBE treated cells decreased significantly.

CONCLUSION

The present results indicate GBE suppresses the inflammation of EIU by blocking the iNOS protein expression and its anti-inflammatory effect on eye is comparable with the effect of prednisolone used in similar doses.

Role of oxygen and nitrogen species in experimental uveitis: anti-inflammatory activity of the synthetic antioxidant ebselen

This study was aimed at examining the role of oxygen and nitrogen reactive species in a model of experimental uveitis upon intravitreal injection of bacterial endotoxin to albino New Zealand rabbits. The inflammatory response was evaluated in terms of: (i) the integrity of the blood aqueous barrier (protein and cell content in samples of aqueous humor), (ii) histopathological changes of the eyes, (iii) clinical evaluation (with a score index based on clinical symptoms), and (iv) the concentration of malondialdehyde (MDA), in aqueous humor, as a marker of oxidative stress. Betamethasone was used as reference treatment, superoxide dismutase as quencher of superoxide anion, L-N(G)-nitro-L-arginine-methyl-esther (L-NAME) and chlorpromazine as nitric oxide synthase inhibitors, and ebselen, a glutathione peroxidase mimic, as peroxynitrite reductant. All the substances were injected subconjunctivally to the rabbits immediately after the intravitreal endotoxin injection. Ebselen was the only treatment able to decrease MDA concentration to control values, exerting an effect similar to that elicited by L-NAME on the rest of the parameters tested. The data presented render ebselen a notable choice for the treatment of uveitis, with implications for clinical trials.

Correlation of blood-glucose control with oxidative metabolites in plasma and vitreous body of diabetic patients

PURPOSE

In diabetes hyperglycemia and other mechanisms lead to the production of oxidative metabolites that can enhance the production of growth factors, leading to increased proliferative activity. Strict blood-glucose control reduces the progression of retinopathy better than standard control. This study investigated patients with diabetic retinopathy for evidence of oxidative metabolites in plasma and the vitreous body, correlating these values with blood-glucose control.

METHODS

The study comprised 136 patients suffering from proliferative diabetic retinopathy. They were grouped according to their mean glycosylated hemoglobin value for the last 9-12 months. Patients with values < or = 10% (mean 8.7%; n=64) were considered strict glucose control patients, those with values > 10% (mean 12.8%; n=72) were considered standard glucose control patients. Lipid peroxides were determined in blood plasma and the vitreous body by two methods (thiobarbituric acid reactive substances and malondialdehyde-like substances). If present, retinal traction with fibrovascular proliferations (>2 disk areas) was quantified and served as an indicator of proliferative activity.

RESULTS

Patients with strict blood-glucose control had significantly (p < 0.01) lower lipid peroxide values in plasma and the vitreous body than standard glucose control patients. These latter had significantly (p<0.01) higher rate of fibrovascular proliferation (50%) than strict glucose control patients (9. 7%).

DISCUSSION

Strict blood-glucose control leads to reduced oxidative tissue damage both systemically and locally in the eye, and reduced proliferative activity. Oxidative metabolites can stimulate proliferation by increasing the amounts of different growth factors an cytokines such as vascular endothelial growth factor. Thus, it can be speculated that in hyperglycemia the relative increase of oxidative metabolites contributes both to damage of retinal vessels and to more pronounced proliferative activity in diabetic retinopathy.

Studies on receptor binding and signal transduction pathways of unoprostone isopropyl

We examined the binding characteristics of unoprostone isopropyl and its metabolite, M1 (M1), in bovine corpus luteum membranes, mobilization of intracellular calcium in human ciliary muscle cells and cyclic AMP generation in rabbit iris-ciliary body. The ligand binding assay of 3H-unoprostone isopropyl and M1 did not demonstrate any specific binding of these compounds in the bovine corpus luteum membranes. However, there was a high specific binding of prostaglandin F2alpha. Competitive ligand binding studies showed that neither the docosanoid, unoprostone isopropyl, nor M1 binds to prostaglandin receptor sites. In human ciliary muscle cells that express EP1, EP2 and FP receptors, unoprostone isopropyl did not increase the mobilization of intracellular calcium nor was it able to generate cyclic AMP at low concentrations in rabbit iris-ciliary body. Similar observations were made with M1 on the above signal transduction pathways. From these results, it is concluded that unoprostone isopropyl and M1 do not bind to prostaglandin (PG) receptor sites in the bovine corpus luteum membranes and do not have affinity for PG receptors linked to intracellular calcium and cyclic AMP second messenger systems.

Colocalization of aldehyde dehydrogenases and Fe/NADPH-induced lipid peroxidation in tissue sections of rat retina

Epidemiological and experimental studies suggest the involvement of lipid peroxidation (LPO) in retinal diseases. Clinicians usually prescribe antioxidants to help in the treatment of proliferative diabetic vitreoretinopathy and age-related macular degeneration. In spite of this, these processes inexorably induce visual impairment and may progress towards blindness. In addition to other pathogenic mechanisms not fully understood, it may be that peroxidic aldehydes from LPO occurring in the eyes, acting as cytotoxic chemicals, mediate in these chronic disorders. To test the mechanisms of removing peroxidic aldehydes from retinal cells and in an attempt to understand long-lasting changes induced by LPO, the distribution and activity of aldehyde dehydrogenases (ALDH) in the rat retina were studied and compared with the LPO sites induced by iron/nicotine adenine dinucleotide phosphate. Histochemical and immunocytochemical assays revealed the colocalization of LPO and ALDH, mainly in the photoreceptors and inner retinal layers. This suggests the involvement of ALDH in detoxifying peroxidic aldehydes from the retina. Any change in ALDH retinal expression and distribution might be of crucial importance in assessing the paths of LPO-mediated vitreoretinopathies. Further research is needed to evaluate these findings and their application to new ophthalmic therapy.

Free radical mediated photoreceptor damage in uveitis

Uveitis is a major cause of blindness, with the visual loss that occurs being due primarily to retinal tissue damage. The tissue damage is mediated mainly by phagocytic inflammatory cells, such as macrophages, by the release of various proteolytic enzymes, arachidonic acid metabolites, cytokines and free radicals. The latter are found to be potent cytotoxic agents that readily cause tissue damage by peroxidation of lipid cell membranes. Recent studies of experimental uveitis indicate that other potent oxidants are generated in uveitis by macrophages. One of these is ONOO-, which is formed from *NO and O(-)2. The macrophages generate *NO preferentially in the outer retina following iNOS expression. In these phagocytes, outer retinal proteins, especially arrestin, are found to be potent iNOS inducers. Current studies of RPE show that these cells protect the retina from ONOO- mediated damage in uveitis by releasing a novel protein called retinal pigment epithelial protective protein. This protein is found to suppress O(-)2 and *NO generation by the phagocytes, in both in vitro and in vivo uveitis models. The protective protein expression is restricted to RPE, its suppressive effect is a result of the inhibition of the phosphorylation of cytosolic proteins, p47-phox, required for the assembly of NADPH and activation of NFkappaB, which are required for generation of 0(-)2 and expression of iNOS respectively. Either pharmacologically or chemically, up-regulation of RPP generation could help in preventing retinal degeneration in uveitis or other degenerative dis

PRK and LASIK--their potential risk of cataractogenesis: lipid peroxidation changes in the aqueous humor and crystalline lens of rabbits

PURPOSE

There are insufficient data on the possible cataractogenic side effects of excimer laser corneal surgery. Higher malondialdehyde (MDA) levels could indicate oxidative events related to the cataractogenic process. We therefore examined MDA levels after refractive laser surgery.

METHODS

Six white Russian rabbits received laser in situ keratomileusis (LASIK) (Schwind keratome) in the right eye and a 250-microm-deep microkeratome cut (Schwind microkeratome) in the left eye. Six others underwent photorefractive keratectomy (PRK) in the right eye; the left eye remained untreated. The 180 mJ/cm2 fluence applied at a rate of 10 Hz with an optical zone diameter of 5 mm in all rabbits (438 pulses) resulted in an estimated central photoablation depth of 116 microm. Two weeks later, lenses and aqueous were taken immediately after death. MDA was detected in aqueous and homogenate of lenses after reacting with thiobarbituric acid (TBA). MDA bound to TBA (MDA-TBA) was specifically analyzed by high-performance liquid chromatography (HPLC) (excitation, 525 nm; emission, 551 nm) using phosphate-buffered methanol as eluent.

RESULTS

No significant laser-induced MDA alteration was found in either the aqueous or the lens. The microkeratome group, however, had two to three times higher MDA levels in the lenses than the control group (p = 0.12) or the PRK (p = 0.03) group.

CONCLUSION

Elevation of MDA in the lens of the microkeratome group indicates that LASIK, but not PRK, may be a risk factor in cataractogenesis. The increased MDA levels in the LASIK group are probably caused by the microkeratome incision rather than the secondary radiation of the excimer laser. Postoperative inflammation may explain the surprising results.

Oral vitamins C and E as additional treatment in patients with acute anterior uveitis: a randomised double masked study in 145 patients

AIM

To investigate the effect of additional oral vitamins C and E on acute anterior uveitis.

METHODS

A placebo controlled double masked study on the effect of vitamin C 500 mg in combination with vitamin E 100 mg twice daily in 145 patients with acute anterior uveitis. As a primary end point variable, laser cell/flare measurements were performed. Best corrected and stenopeic visual acuity (VA) testing and clinical variable scores were measured.

RESULTS

Laser flare measurements (ph/s) before treatment were 207.1 (SD 258) in the vitamin group and 143.6 (156) in the placebo group. After 3 days corresponding values were 80.2 (129) and 54.7 (82), after 7 days 89.2 (187) (12.5) and 85.8 (208), after 14 days 47.1 (109.5) and 40.5 (116) after 28 days 23.1 (53.6) and 23.1 (48), and after 56 days 15.6 (26) and 15.3 (17). There was no significant difference in time trend between the two treatment groups (RMANOVA; p = 0.53). Baseline VA (logMAR) was 0.106 (0.241) in the vitamin group and 0.128 (0.456) in the placebo group. VA after 3 days was 0. 236 (0.293) and 0.344 ( 0.489), after 7 days 0.204 (0.292) and 0.292 (0.479), after 14 days 0.162 (0.274) and 0.193 (0.454), after 28 days 0.096 (0.232) and 0.158 (0.436), and 0.026 (0.213) and 0.106 (0. 437) after 56 days. Although no significant difference in time trend was detected, evaluation of the VA data of the last time point (56 days) by means of the Mann-Whitney test showed a significantly better VA in the vitamin group (p = 0.01).

CONCLUSIONS

There was no significant effect of vitamins C and E on laser flare measurements. The significant effect of the oral vitamins on visual acuity at 8 weeks after start of the oral vitamins C and E may indicate a protective effect in patients with acute anterior uveitis.

Efficacy of the antioxidant ebselen in experimental uveitis

Inflammation results in the production of free radicals. In a model of experimental uveitis upon subcutaneous injection of endotoxin to Lewis rats, i.e., endotoxin-induced experimental uveitis (EIU), we have evaluated the status of the antioxidant capacity of ocular tissues. EIU results in a decrease of glutathione (GSH) content and glutathione peroxidase (GPx) activity in whole eye homogenates 24-h after endotoxin administration. Furthermore, an increase in malondialdehyde (MDA) content was observed in these same samples, thus confirming the involvement of oxidative stress in the pathophysiology of the process. In view of the ability of the antioxidant ebselen as GPx enzyme mimic, we tested the effect of the oral treatment with two doses of 100 mg/kg body weight of ebselen (first dose administered at the same time of endotoxin, and the second after 12 h). Ebselen administration normalized the GSH and MDA contents and protected the GPx activity of the EIU rat eyes. The GPx activity in the eye homogenate of the treated rats could be completely acounted for by the ebselen-dependent GPx-like activity, i.e., GPx activity measured in the acidic supernatant of the homogenate after neutralization. Unmodified ebselen was detected in whole eye homogenates, thus it shows for the first time the penetration of ebselen through the blood-aqueous and blood-retina barrier. The results herein may allow the proposal of ebselen as a suitable antiinflammatory agent in ocular tissues.

Effects of allopurinol and steroids on inflammation and oxidative tissue damage in experimental lens induced uveitis: a biochemical and morphological study

AIMS

To evaluate the effects of allopurinol in lens induced uveitis (LIU) by morphological methods and to compare these effects with those of steroids and a combination of both drugs biochemically and morphologically.

METHODS

Lipid peroxides (LPO) of the retinal tissue were determined by two different methods (thiobarbituric acid assay (TBA) and high performance liquid chromatography expressed as malondialdehyde-like substances). Myeloperoxidase (MPO) activity in the iris/ciliary body complex was analysed spectrophotometrically. Histological changes on three morphological levels of LIU eyes were evaluated.

RESULTS

Both allopurinol and the combination of allopurinol/prednisolone led to a significant reduction in the increaed retinal LPO values. Prednisolone only revealed significant effects on retinal LPO when being measured with the TBA method. MPO activity in iris and ciliary body was significantly reduced in all therapy groups. The morphological evaluation of the sections by two masked investigators revealed a significant reduction (p < 0.05) in the inflammation score in all therapy groups. Morphometric studies using the QUANTIMED system (Leica, Cambridge) showed significantly reduced values (p < 0.05) in the allopurinol group and in the group receiving prednisolone and allopurinol. Prednisolone alone did not lead to a significant reduction in the values.

CONCLUSIONS

The findings show that both allopurinol and steroids exert positive effects on the variables determined in LIU. The effects of steroids are believed to be mostly due to their direct action on inflammatory cells. The recently reported scavenging effects of methylprednisolone should play a minor role in this disease model. Allopurinol and oxypurinol act as direct scavengers of free radicals and hypochlorous acid, which is produced via MPO catalysis, thus leading to a reduction in tissue inflammation and tissue damage.

Lipid peroxidation products in human subretinal fluid

The concentrations of thiobarbituric acid reacting substances (TBARS) and proteins in the subretinal fluid (SF) of patients undergoing retinal detachment surgery have been determined. We have tried to establish the correlations between these biochemical and other clinical features of these patients: evolution time of the retinal detachment, age, degree of myopia, and macular affection. Caucasian patients, 19 men and 19 women (57.42 +/- 12.85 average age, interval 20-80) were randomly selected for this study. SF samples were obtained by puncture after scleral indentation. TBARS and protein concentrations were determined by the corresponding colorimetric assays. A linear correlation exists between TBARS and protein contents in these samples. No correlation could be established between evolution time of the retinal detachment and TBARS content in SF. TBARS in SF increases with increasing age in nonmyopic patients. In the samples of myopic patients the correlation was established between TBARS content and degree of myopia. The group of patients with more than 10 dioptres show a significant higher TBARS concentration in SF than any of the other groups studied. It can be concluded that lipid peroxidation products in SF originate, at least partially, from rod outer segments, and that lipid peroxidation is a process that might play a role in the pathogenesis of retinal detachment, specially in myopic patients.

Membrane damage in UV-irradiated lenses

The purpose of this study was to investigate three possible causes of membrane damage following UV irradiation: photooxidation of membrane thiol (SH) groups, peroxidation of membrane lipids and inhibited synthesis of membrane proteins. Thiol loss was not observed. Thin-layer chromatography showed a four-fold increase in several primary lipid peroxidation products such as hydroperoxyl lipids in the epithelial membrane preparations isolated from irradiated lenses. The formation of new hydroxyl lipid bands not seen in control preparations was also observed in isolated membranes from irradiated lenses. Irradiation in the presence or absence of oxygen produced lipid peroxidation products. Aerobic irradiation produced small, but statistically significant increases in lipid hydroxyls and hydroperoxyls relative to controls. Repair of initial damage might be compromised by the observed 60% reduction in rate of protein synthesis measured in lens membranes following irradiation. Synthesis was affected by means other than depleted potassium or elevated calcium levels.

Lipid peroxidation. Biopathological significance

Peroxidation of unsaturated lipids, initially studied in the chemistry of oil and fat rancidity, has become a problem of increasing interest in the biological field, because of its proposed role in a variety of pathological conditions. The general mechanism of the process, the formation of toxic aldehydes capable to react with protein and non protein thiols, and the overall effects in cellular membranes are reviewed. The possible implications of lipid peroxidation as one of the main mechanisms of cellular damage in both toxic injury and other pathological conditions are discussed.