Lenses from Brown‐Norway pigmented rats are more tolerant to in vitro ultraviolet irradiation than lenses from Fischer‐344 albino rats

Purpose: To investigate if the previously shown difference in in vivo‐induced ultraviolet B radiation (UVR‐B) cataractogenesis between pigmented and albino rats can be seen also with in vitro irradiation. The shielding effect of the iris and UVR absorption in the anterior segment is nullified, and inherent differences in lenticular UVR‐B sensitivity between the strains may be revealed. Methods: Lenses from albino (Fischer‐344) and pigmented (Brown‐Norway) rats were irradiated in vitro with 1.8 kJ/m² UVR‐B. The lenses were cultured in standard environment in a culture incubator. Cataract was quantified daily by measuring the amount of lens forward light scattering over a period of 1 week. All lenses were photographed during the week. Results: Two days after exposure, both strains developed significant cataract compared to control lenses, and the light scattering increased exponentially to the last day. From day 4, exposed Fischer lenses scattered more light than Brown‐Norway lenses. This difference increased towards the end of the week. The type of cataract (anterior subcapsular, equatorial, and posterior cortical cataract) was similar in both strains. No anterior polar or nuclear cataract was observed. Conclusions: Lenses from albino Fischer rats are more sensitive to in vitro UVR‐B than lenses from pigmented Brown‐Norway rats. Ultraviolet B radiation cataract type induced in vitro differs from in vivo cataract in pigmented rats, but not from albino rats. In vitro UVR‐B exposure induces more cataract than corresponding lenticular UVR‐B in vivo exposures, for both albino and pigmented rat.     

High lenticular tolerance to ultraviolet radiation‐B by pigmented guinea‐pig; application of a safety limit strategy for UVR‐induced cataract

Purpose: The purpose of this study was to determine a threshold measure, maximum tolerable dose (MTD), for avoidance of UVR‐B‐induced cataract in the pigmented guinea‐pig. Methods: Thirty pupil‐dilated anesthetized young female guinea‐pigs, divided into five equal groups, received between 0 and 84.9 kJ/m² unilateral UVR‐B. Lens extraction and in vitro lens photography occurred 24 hr after exposure. Measurement of intensity of lens light scattering served as quantifying tool for the degree of cataract. Data analysis included regression, using a second order polynomial model. The applied MTD concept was based on the UVR‐B dose–response curve obtained for the pigmented guinea‐pig. A smaller number of pigmented guinea‐pigs, pigmented rats and albino rats underwent morphometric analysis of the anterior segment geometry. Results: All eyes exposed to UVR‐B developed cataract in the anterior subcapsular region. MTD for avoidance of UVR‐B‐induced cataract was 69.0 kJ/m² in the pigmented guinea‐pig. Iris was considerably thicker in the guinea‐pig than in the rats. Lens blockage by the dilated iris was lowest in the guinea‐pig. Conclusions: Maximum tolerable dose for avoidance of UVR‐B‐induced cataract in the pigmented guinea‐pig was 69.0 kJ/m², over 10‐fold higher than the threshold 5 kJ/m² obtained by Pitts et al. in the pigmented rabbit. Maximum tolerable dose is an appropriate method for estimation of toxicity for UVR‐B‐induced cataract in the guinea‐pig. The pigmented guinea‐pig is significantly less sensitive to UVR‐B exposure than the pigmented rabbit and pigmented rat.     

Drinking water supplementation with ascorbate is not protective against UVR‐B‐induced cataract in the guinea pig

Purpose: To study if ascorbate supplementation decreases ultraviolet radiation (UVR)‐induced cataract development in the guinea pig. Methods: Sixty 6–9‐week‐old pigmented guinea pigs received drinking water supplemented with or without 5.5 mm l ‐ascorbate for 4 weeks. After supplementation, 40 animals were exposed unilaterally in vivo under anaesthesia to 80 kJ/m² UVR‐B. One day later, the animals were killed and lenses were extracted. Degree of cataract was quantified by measurement of intensity of forward lens light scattering. Lens ascorbate concentration was determined with high‐performance liquid chromatography (HPLC) with UVR detection at 254 nm. Twenty animals were used as non‐exposed control. Results: Supplementation increased lens ascorbate concentration significantly. In UVR‐exposed animals, mean 95% confidence intervals (CIs) for animal‐averaged lens ascorbate concentration (μmol/g wet weight lens) were 0.54 ± 0.07 (no ascorbate) and 0.83 ± 0.05 (5.5 mm ascorbate). In non‐exposed control animals, mean 95% CIs for animal‐averaged lens ascorbate concentration (μmol/g wet weight lens) were 0.72 ± 0.12 (0 mm ascorbate) and 0.90 ± 0.15 (5.5 mm ascorbate). All non‐exposed lenses were devoid of cataract. Superficial anterior cataract developed in all UVR‐exposed lenses. The lens light scattering was 39.2 ± 14.1 milli transformed equivalent diazepam concentration (m(tEDC)) without and 35.9 ± 14.0 m(tEDC) with ascorbate supplementation. Conclusion: Superficial anterior cataract develops in lenses exposed to UVR‐B. Ascorbate supplementation is non‐toxic to both UVR‐B‐exposed lenses and non‐exposed control lenses. Ascorbate supplementation does not reduce in vivo lens forward light scattering secondary to UVR‐B exposure in the guinea pig.     

Bilateral cataract induced by unilateral UVR‐B exposure – evidence for an inflammatory response

Purpose: To investigate whether unilateral in vivo UVR‐B exposure of one eye affects the fellow eye in a co‐cataractogenic, sympathetic reaction and to determine whether an inflammatory response could be involved in the pathogenesis. Methods: C57BL/6 mice were unilaterally exposed in vivo to UVR‐B for 15 min. In the group of 24 animals each received 0×/2×/3×/or 4× cataract threshold equivalent dose. Following 48‐hr UVR‐B exposure, cataract morphology was documented in dark‐field illumination photography, and light scattering was quantified, in both lenses in vitro. Serum levels of pro‐inflammatory cytokines IL‐1ß, IL‐6 and TNF‐α were analysed with ELISA. Immunohistochemistry was performed for inflammatory infiltration in exposed and contralateral eyes. Results: UVR‐B exposure induced cataract in all exposed lenses. There was additionally a significant UVR dose–dependent increase in light scattering in the lenses of the non‐exposed fellow eye. Inflammatory infiltration was detected immunohistochemically in the anterior segment of both eyes. IL‐1β serum concentration increased with increasing UVR‐B exposure dose. There was a similar trend for serum IL‐6 but not for TNF‐α. Conclusion: Unilateral UVR‐B exposure to one eye is associated with intraocular inflammation and an increase in lens light scattering also in the unexposed, fellow eye. A resulting systemic inflammatory response might be mediated by IL‐1β and possibly IL‐6. The finding that an inflammatory response may play a role in UVR‐B‐induced cataract development might initiate new strategies in the prevention of the disease.     

Evolution of light scattering and redox balance in the rat lens after in vivo exposure to close‐to‐threshold dose ultraviolet radiation

Acta Ophthalmol. 2010: 88: 779–785

Abstract.

Purpose: To investigate the evolution of cataract development and glutathione redox balance in the rat lens after in vivo close‐to‐threshold dose exposure to ultraviolet radiation (UVR) around 300 nm. Methods: Three groups of 10 Sprague–Dawley rats were unilaterally exposed to 8 kJ/m² UVR‐300 nm for 15 min, and a fourth group of 10 rats was kept without UVR exposure as nonexposed control animals. The exposed animals were killed at 1, 3 and 7 days after exposure. Both lenses from all animals were extracted and photographed and the intensity of forward light scattering was measured quantitatively. Thereafter, the lenses were homogenized. The concentration of reduced glutathione (GSH) and oxidized glutathione (GSSG), and the activity of glutathione reductase (GR) and glutathione peroxidase (GPx), respectively, were determined spectrophotometrically. The mean paired differences between exposed and nonexposed lenses were used as primary data in the statistical analyses. Results: All exposed lenses developed cataract. Lens light scattering increased throughout the 7 days after UVR exposure. GSH concentration and GPx rate transiently increased at 1 day after exposure and then decreased throughout follow‐up, with GSH concentration having a negative balance at the end. GSSG concentration and GR activity did not change after UVR exposure. Conclusion: In vivo close‐to‐threshold UVR exposure induces a gradual increase in rat lens opacification/cataract development and time dependently alters the redox balance in the lens.     

Interaction of anaesthetic drugs and UV-B irradiation in the anterior segment of the rat eye

PURPOSE: To determine the impact of anaesthesia on acute transient cataractogenesis and ultraviolet radiation (UVR)-induced cataractogenesis. METHODS: Sprague-Dawley rats were anaesthetized with pentobarbital, which caused almost full eyelid closure, or xylazine/ketamine, which caused eyelid retraction and proptosis. The eyelids of one eye were kept open with either a suture or adhesive tape, or both. The other eye was kept closed with either a suture or tape. Cataract was graded clinically and quantified in vitro as intensity of forward light scattering. In two UVR experiments, anaesthetized rats were irradiated unilaterally with 5 kJ/m2 UVR-B 300 nm for 15 mins. The difference between the two UVR experiments was the degree of proptosis in the pentobarbital group. Corneal drying was judged clinically with a grading scale. RESULTS: Within 60 mins of anaesthesia induction in the first experiment, almost all lenses in open eyes developed cataract, whereas all lenses in closed eyes remained clear. In the first UVR experiment the lens light scattering was significantly higher in the xylazine/ketamine group. In the second UVR experiment the pentobarbital group was treated to achieve proptosis similar to that in the xylazine/ketamine group, which led to a smaller difference in lens light scattering between the two anaesthesia groups. Lens light scattering in the pentobarbital groups was significantly higher with forced proptosis than without prominent proptosis. CONCLUSIONS: Xylazine/ketamine anaesthesia facilitates the development of UVR-induced cataract, whereas pentobarbital anaesthesia does not. Xylazine/ketamine anaesthesia induces more proptosis and therefore leads to increased exposure of the cornea and, secondarily, the lens.     

Lens opacities after repeated exposure to ultraviolet radiation

PURPOSE: To investigate the effect of the interval between two, near-threshold exposures to ultraviolet radiation (UVR) on cataract development. METHODS: One eye of Sprague-Dawley rats was exposed twice to 4 kJ/m2 narrow band UVR (lambdaMAX=300 nm) for 15 min each. The interval between exposures was 0, 6, 24 or 48 h. One week after the first exposure both lenses were removed for photography and measurement of the intensity of forward light scattering to quantify lens opacities. RESULTS: All exposed lenses developed cataract. Forward light scattering was the same after double exposure with no interval or a 6 h interval. Forward light scattering after a 24 or 48 h interval was nearly twofold greater than that following no interval or a 6 h interval. The exposed lenses in all groups had mild anterior surface opacities and intense equatorial opacities as judged with a stereomicroscope. CONCLUSION: Two, near-threshold UVR exposures at 0 or a 6 h interval produce the same degree of lens opacification. When the second exposure follows 24 or 48 h after the first, lenticular damage increases. Repair processes between 24 and 48 h after exposure appear to be sensitive to UVR, and an additional exposure during this time may aggravate cataract development.     

Dose-response function for lens forward light scattering after in vivo exposure to ultraviolet radiation

· Background: It is known that different types of radiation, as well as aging and metabolic disorders, can cause cataract. Several epidemiological investigations show a correlation between cataract development and the dose of ultraviolet radiation (UVR) received. It is well established experimentally that exposure of animal eyes to UVR induces cataract. The purpose of the present study was to determine the dose-response function for UVR-induced opacities in the rat lens after in vivo exposure. · Methods: Sprague-Dawley rats received 0.1, 0.4, 1.3, 3, 5, 8 or 14 kJ/m² UVR (λ_MAX=300 nm, λ_0.5=10 nm) unilaterally for 15 min. At 1 week after exposure both lenses were removed, photographs were taken and the intensity of forward-scattered light was measured. · Results: One week after UVR exposure, opacities occurred on the lens surface, as observed with a microscope. With increased UVR dose the opacities became more intense and occurred also in the equatorial area of the lens, but not in the nucleus. The intensity of forward light scattering increased with increased UVR dose between 3 and 14 kJ/m². No significant change in intensity of forward light scattering was observed for lower UVR doses. · Conclusion: The intensity of forward light scattering in the rat lens increases exponentially with increased UVR dose between 0.1 and 14 kJ/m². Received: 7 April 1997 Revised version received: 8 September 1997 Accepted: 11 November 1997     

Reversal of reciprocity failure for UVR-induced cataract with vitamin E

PURPOSE: The authors have previously described that the photochemical reciprocity law does not apply for ultraviolet radiation (UVR)-induced cataract. The aim of this study was to elucidate if failure of the reciprocity reverses with vitamin E (alpha-tocopherol) administration. METHODS: Altogether, 80 rats were divided into one group fed alpha-tocopherol and one control group. For each group, half of rats were exposed to UVR for 5 min and the remaining rats for 15 min. RESULTS: Lenses exposed to UVR for 5 min showed no difference in light scattering between alpha-tocopherol-treated and untreated groups. Lenses exposed to UVR for 15 min showed significant difference in light scattering between alpha-tocopherol-treated and untreated groups. CONCLUSIONS: Failure in exposure time-intensity reciprocity for UVR-induced cataract with exposures shorter than 30 min may be due to consumption of antioxidants in the lens.     

Time dependency of metabolic changes in rat lens after in vivo UVB irradiation analysed by HR-MAS 1H NMR spectroscopy

The lens ability to protect against, and repair ultraviolet radiation (UVR) induced damages, is of crucial importance to avoid cataract development. The influence of UVR-induced damage and repair processes on the lens metabolites are not fully understood. Observation of short- and long-term changes in light scattering and the metabolic profile of pigmented rat lenses after threshold UVR exposure might serve to better understand the protective mechanisms in the lens. By using high resolution magic angle spinning (HR-MAS) 1H NMR spectroscopy it was possible to investigate the metabolites of intact rat lenses. Brown-Norway rats were exposed to 15 kJm(-2) UVB irradiation. One eye was exposed and the contralateral served as control. The rats were sacrificed 5, 25, 125, and 625 hr post-exposure and the lenses were removed. The degree of cataract was quantified by measurement of lens forward light scattering. Thereafter, proton NMR spectra from intact lenses were obtained and relative changes in metabolite concentrations were determined. The light scattering in the lens peaked at 25 hr post-exposure and decreased thereafter. The lowest level of light scattering was measured 625 hr after exposure. No significant changes in concentration were observed for the metabolites 5 and 25 hr post-exposure except the total amount of adenosine tri- and diphosphate (ATP/ADP) that showed a significant decrease already 5 hr after exposure. At 125 hr the lens concentrations of lactate, succinate, phospho-choline, taurine, betaine, myo-inositol, and ATP/ADP showed a significant decrease (p<0.05). Phenylalanine was the only metabolite that revealed a significant increase 125 hr post-exposure. At 625 hr most of the metabolic changes seemed to normalise back to control levels. However, the concentration of betaine and phospho-choline were still showing a significant decrease 625 hr after UVB irradiation. The impact of UVB irradiation on the metabolic profile did not follow the same time dependency as the development of cataract. While the light scattering peaked at 25 hr post-exposure, significant changes in the endogenous metabolites were observed after 125 hr. Both the metabolic changes and the light scattering seemed to average back to normal within a month after exposure. Significant decrease in osmolytes like taurine, myo-inositol and betaine indicated osmotic stress and loss of homeostasis. This study also demonstrated that HR-MAS 1H NMR spectroscopy provides high quality spectra of intact lenses. These spectra contain a variety of information that might contribute to a better understanding of the metabolic response to drugs or endogenous stimuli like UVB irradiation.     

Dose dependent cataractogenesis and Maximum Tolerable Dose (MTD(2.3:16)) for UVR 300 nm-induced cataract in C57BL/6J mice

The purpose of the present study was to investigate the in vivo dose response function for UVR 300 nm-induced cataract in the C57BL/6J mouse lens and to establish a cataract threshold estimate expressed as Maximum Tolerable Dose (MTD(2.3:16)) for UVR 300 nm-induced cataract in the C57BL/6J mouse lens. Knowledge of the MTD(2.3:16) in the C57BL/6J mouse will permit quantitative in vivo comparison of UVR-B threshold sensitivity of knockout mice, e.g. animals deficient in key antioxidative enzymes or mice suffering from genetically predetermined eye disease, to wild type animals. Eighty C57BL/6J mice were divided into four dose groups. The animals were exposed unilaterally to 0, 2, 4, or 8 kJ/m(2) UVR 300 nm for 15 min (n=20). The radiation output of the UVR-source had lambda(max) at 302.6 nm with 5 nm full width at half maximum. Two days after exposure cataract was quantified as forward lens light scattering intensity in the exposed and the contralateral non-exposed lens. Morphological lens changes were documented using grid and dark field illumination photography. MTD(2.3:16) was estimated from the forward light scattering measurements. Two days after exposure mainly anterior subcapsular but also cortical and nuclear cataract developed in lenses that had received 2, 4, and 8 kJ/m(2) UVR 300 nm. Forward light scattering intensity increased with increasing UVR 300 nm dose. MTD(2.3:16) for the mouse lens was estimated to 2.9 kJ/m(2) UVR 300 nm. Lens light scattering intensity in the C57BL/6J mouse lens increases with UVR 300 nm in vivo dose in the range 0-8 kJ/m(2). The MTD(2.3:16) of 2.9 kJ/m(2) in the C57BL/6J mouse lens determined here, is essential to quantify and compare in vivo the impact of genetic modulation on lens susceptibility to oxidative stress and plan dose-ranges in future investigations of UVR 300 nm-induced cataract pathogenesis.     

Dose-response relationship for α-tocopherol prevention of ultraviolet radiation induced cataract in rat

The purpose of this study is to establish the dose response relationship for α-tocopherol protection of ultraviolet radiation (UVR) induced cataract in the rat. Four groups of 20 six-week-old albino Sprague Dawley rats received 5, 25, 50, and 100 IU/day α-tocopherol, whilst another group of 20 rats without any α-tocopherol feeding was the control group. After 4 weeks of feeding, each rat was unilaterally exposed to 8 kJ/m² UVR-300 nm for 15 min. At 1 week after exposure, the rats were sacrificed and lens light scattering was measured quantitatively. Lens total reduced (GSH) and oxidized (GSSG) glutathione; glutathione reductase (GR) and peroxidase (GPx) were determined spectrophotometrically. The UVR-exposed lenses in the α-tocopherol fed groups developed superficial cataract, whereas lenses in the control group developed cortical and equatorial opacities. Light scattering in lenses from the α-tocopherol-supplemented rats was lower than in lenses from the control group. The difference of light scattering between the exposed and contralateral non-exposed lens decreased with increasing doses of α-tocopherol to an asymptote level. UVR-exposure caused a significant depletion of lens GSH in rats without or at low α-tocopherol supplementation. The depletion of GSH became less with higher α-tocopherol supplementation. There was no detectable difference in lens GSSG, GR or GPx at any level of α-tocopherol supplementation. Orally administered α-tocopherol dose dependently protects against UVR-induced cataract. The protection is associated with an α-tocopherol dose-dependent GSH depletion secondary to UVR exposure. UVR-induced light scattering only occurs if the GSH depletion exceeds a threshold.     

Evolution of damage in the lens after in vivo close to threshold exposure to UV-B radiation: Cytomorphological study of apoptosis

The purpose of the present study was to investigate cataractogenesis and recovery of lens damage after in vivo close to threshold ultraviolet (UV)-B radiation around 300 nm. Eighty six-week-old albino Sprague-Dawley rats were familiarized to a rat restrainer five days prior to exposure. Groups of non-anesthetized rats were exposed unilaterally to 8 kJ/m² UVR-300 nm. The animals were sacrificed at 1, 7, 48 and 336 h following exposure. The lenses were extracted for imaging of dark-field lens macro anatomy and measurement of intensity of forward lens light scattering to quantify lens opacities. Three exposed lenses and one non-exposed lens from each time interval were examined with light and transmission electron microscopy (TEM). Macro anatomy and lens light scattering revealed that all contralateral non-exposed lenses were clear. The degree of lens opacity (difference in lens light scattering between exposed and non-exposed lenses) increased during the 336 h, reaching a plateau towards the end of the observation period. Light microscopy and TEM demonstrated that apoptotic features appeared in the epithelium already 1 h after UVR exposure, and small vacuoles were seen in the outer cortex. Epithelial damage occurs during the first 48 h after exposure and is followed by regenerative repair at 336 h post-exposure. Apoptotic epithelial cells were phagocytized by adjacent epithelial cells. Cortical fiber cells exhibited increasing damage throughout the observation period without any clear repair after 336 h. In conclusion, acute UVR-induced cataract is partly a reversible. Lens epithelium is a primary target for UVR exposure. Damage to cortical fiber cells remained irreversible.     

Maximum acceptable dose of ultraviolet radiation: a safety limit for cataract

PURPOSE: To develop a method for experimental estimation of toxicity for continuous dose-response relationships. To apply this method to cataract induced by ultraviolet radiation (UVR) in young rats. METHODS: After establishing experimentally the frequency distribution of light scattering of normal physiologically clear lenses, the lower limit of pathological light scattering is defined such that a certain fraction, for example 97.5%, of normal lenses scatter less light. RESULTS: The dose-response function for UVR and cataract is determined experimentally. With this function, the dose corresponding to the lower limit of pathological light scattering may be determined as the maximum acceptable dose (MAD). The MAD0.975 for UVR 300 nm was determined to be 2.2 kJ/m2. CONCLUSIONS: The method can serve as a basis for establishing safety standards for UVR-induced cataract and probably other continuous dose-response functions.     

Ultraviolet radiation-B-induced cataract in albino rats: maximum tolerable dose and ascorbate consumption

PURPOSE: To investigate the maximum tolerable dose (MTD) for cataract induced by ultraviolet radiation-B (UVB) in 7-week-old albino rats and to study the effect of UVB eye exposure on lens ascorbate content. METHODS: Fifty 7-week-old albino Sprague Dawley rats were unilaterally exposed in vivo to 300-nm UVB under anaesthesia, receiving 0, 0.25, 3.5, 4.3 and 4.9 kJ/m(2). The MTD was estimated based on lens forward light scattering measurements. Lens ascorbate content was determined in the processed lens using high performance liquid chromatography with UVR detection. RESULTS: Animals exposed to UVB doses >or=3.5 kJ/m(2) developed cortical cataracts. The MTD for avoidance of UVB-induced cataract was estimated to 3.01 kJ/m(2). UVB exposure decreased lens ascorbate concentration in the exposed lens in line with UVB dose, H(e), according to the models: C = C(NonCo) + C(Co)e(-kH(e) ) for exposed lenses; C = C(NonCo) + C(Co) for non-exposed lenses, and C(d) = C(Co)(e(-kH(e) ) - 1). Parameters for consumable and non-consumable ascorbate were estimated to C(NonCo) = 0.04 and C(Co) = 0.11 micromol/g wet weight of lens. For lens ascorbate difference, tau = 1/k = 0.86 kJ/m(2). A total of 63% of UVB consumable ascorbate has been consumed after only tau = 0.86 kJ/m(2), while MTD(2.3 : 16) = 3.01 kJ/m(2), indicating that ascorbate decrease is in the order of 3.5 times more sensitive to detecting UVR damage in the lens than forward light scattering. CONCLUSIONS: The MTD for avoidance of UVB-induced cataract in the 7-week-old albino Sprague Dawley rat was estimated to be 3.01 kJ/m(2). In vivo UVB exposure of the rat eye decreases lens ascorbate content following an exponential decline, and suprathreshold doses cause greater effect than subthreshold doses.     

Impact of age and sex in ultraviolet radiation cataract in the rat

PURPOSE: The purpose of this study was to determine the influence of age and sex on the development of ultraviolet radiation (UVR) cataract in rats. Current safety limits for lens damage due to UVR do not consider age or sex. METHODS: Four age groups of Sprague-Dawley rats (3, 6, 17, and 52 weeks) were exposed to 300-nm UVR at either 5 or 8 kJ/m(2), delivered during 15 minutes. The interval between irradiation and cataract assessment was 1 or 8 weeks. Moreover, two groups of 6-week-old male and female rats were exposed to 5 kJ/m(2) UVR, with cataract assessment after 1 week. The severity of cataract was quantified by measurement of forward light-scattering in isolated lenses. RESULTS: The youngest age group showed development of anterior subcapsular, equatorial, and nuclear cataract, whereas the three older groups exhibited the first two types. The two younger age groups had significantly more cataract than the other groups. The degree of cataract increased from 1 to 8 weeks after irradiation. There was no difference in cataract severity between sexes. CONCLUSIONS: Young rats are more sensitive to UVR than old rats. Nuclear UVR cataract develops in young rats but not in adult rats. With the chosen waveband and dose, the time for maximum cataract development to occur is longer than 1 week. There is no difference in UVR sensitivity between the sexes.     

Influence of exposure time for UV radiation-induced cataract

PURPOSE: It is believed that for a certain ultraviolet radiation (UVR) exposure, the biologic effect depends on the product of irradiance and exposure time (the reciprocity Bunsen-Roscoe law). The purpose of this study was to investigate the validity of the reciprocity law for UVR-induced cataract. METHODS: Two experiments were conducted. In the first one, 100 Sprague-Dawley rats were exposed to UVR divided into five groups according to exposure time: 7.5, 15, 30, 60, and 120 minutes. In the second experiment, 80 Sprague-Dawley rats were exposed to UVR divided into four groups according to exposure time: 5, 7.5, 11, and 15 minutes. All the animals were unilaterally exposed to the same dose of UVR (8 kJ/m(2)) in the 300-nm wavelength region. One week after exposure both lenses were removed to measure the intensity of forward light scattering and for microphotography. Groups were compared by evaluating the difference between exposed and nonexposed eyes. RESULTS: The group exposed to UVR for 5 minutes had the lowest intensity of forward light scattering. The highest intensity of forward light scattering was found in the group that was exposed for 15 minutes. With longer exposure intervals, the intensity of forward light scattering decreased as the exposure time increased. No difference in intensity of forward light scattering was found between the groups exposed for 60 and 120 minutes. CONCLUSIONS; Exposure time strongly influenced cataract formation after low-dose UVR. In this model of UVR-induced cataract, the photochemical reciprocity law was modulated by a biologic response.     

RPE65 is highly uveitogenic in rats

PURPOSE: To examine the hypothesis that RPE65, a protein specific to the retinal pigment epithelium, is uveitogenic in rats. METHODS: Rats of four inbred strains (Lewis, Brown Norway, Fischer, and SHR) were immunized with native or recombinant bovine RPE65, or with S-antigen (S-Ag), emulsified with complete Freund adjuvant, and treated simultaneously with killed Bordetella pertussis bacteria, as indicated. Development of ocular changes was examined and scored both clinically and histologically. RESULTS: Lewis rats immunized with RPE65 showed development of acute and severe inflammatory eye disease that affected most ocular tissues. The minimum uveitogenic dose of RPE65 was similar to that of S-Ag (1 microg per rat), but the changes induced by RPE65 at higher dose ranges were less severe than those induced by S-Ag. Concurrent treatment of the RPE65-immunized rats with B. pertussis bacteria was not critical for disease induction, but enhanced dramatically the pathogenic reaction. Unlike the results with several other retinal proteins, no pinealitis was detected in rats immunized with RPE65. Fischer (F344) rats resembled Lewis rats in being similarly affected by RPE65 or S-Ag. In contrast, Brown Norway (BN) rats developed severe disease when immunized with RPE65, but showed minimal changes in response to S-Ag. SHR rats responded poorly to disease induced by RPE65, and S-Ag-induced disease failed to develop. CONCLUSIONS: RPE65 is highly uveitogenic in rats, thus suggesting that this molecule could be involved in pathogenic autoimmunity in the human eye.     

Repair in the rat lens after threshold ultraviolet radiation injury

PURPOSE: To investigate the development and recovery of lens damage after in vivo close-to-threshold exposure to ultraviolet B radiation. METHODS: One eye of young, female Sprague-Dawley rats was exposed to 5 kJ/m2 narrowband ultraviolet radiation (UVR) (lambda(max) = 302 nm) for 15 minutes. Groups of rats were killed 1, 7, and 56 days after exposure. The structure of the exposed and nonexposed lenses was examined with light microscopy, scanning electron microscopy, transmission electron microscopy, freeze-fracture, fluorescent membrane staining, and Fourier transform analysis. RESULTS: One day after UVR exposure the lens surface had flakelike opacities. Seven days after exposure, the lens surface appeared opaque and corrugated, and the equatorial cortex had small opacities. At 56 days postexposure, the surface and equator appeared clear, but the cortex had a subtle shell-shaped opacity. At 1 day postexposure, apoptotic cell death occurred in the lens epithelium, but the cortical fibers were normal. At 7 days postexposure, the epithelium and the fibers between the 10th and 40th growth shell below the capsule contained extracellular spaces of different sizes. After 56 days, the epithelial layer appeared normal, and the extracellular spaces had disappeared; but abnormal fibers were found between the 60th and 100th growth shell below the capsule. Fibers above and below the damaged growth shells appeared fully normal. CONCLUSIONS: A close-to-threshold dose of UVR causes cataract, which is largely reversible. The UVR exposure leads to apoptosis in the lens epithelium, and after a latency period of several days, lens fibers are abnormal. Extracellular spaces develop in the epithelium and fibers. Within several weeks after exposure, the epithelium fully recovers and new fibers develop normally. The originally affected fibers are repaired. However, this repair is incomplete, leaving a small zone of enhanced light scattering in the equatorial cortex.     

An alternative method of steroid-induced lens opacification in brown norway rat eyes applying systemic pulse administration

PURPOSE: To confirm whether long-term administration of prednisolone sodium succinate (prednisolone) alone is able to induce cataract in rat eyes. MATERIALS AND METHODS: A 1% solution of prednisolone was administered topically as eye drops to Brown Norway rat eyes, and a systemic pulse administration of 10 mg/kg/day was given via the tail vein. Both administration methods were applied in different combinations. Eighty-three 6-week-old male rats were divided into 8 groups: group 1 = control; group 2 = topical instillation every day; group 3 = single pulse; group 4 = single pulse + eye drops; group 5 = 3 times pulse; group 6 = 3 times pulse + eye drops; group 7 = 3 times pulse per 2 months; group 8 = 3 times pulse per 2 months + eye drops. Observations for changes of lens transparency were made by slitlamp microscopy and documented by an anterior eye segment analysis system (Nidek EAS-1000) from the onset of drug administration to a maximum period of 16 months. RESULTS: Lens opacity in the shallow anterior and posterior lens layers developed from the tenth month following commencement of prednisolone administration. The incidence of anterior and/or posterior cortical cataract at the sixteenth month was 15% in group 2, 12.5% in group 5, 25% in group 6, 17.9% in group 7 and 35.3% in group 8. The lenses of groups 1, 3 and 4 maintained their transparency throughout the observation period. Light scattering intensity in groups 8 and 7 was the highest, followed by groups 6 and 5, then groups 2, 4, 3 and 1. CONCLUSION: Cortical cataract was successfully induced in Brown Norway rat eyes by sustained administration of prednisolone succinate alone applied as systemic pulse.