Damage to cultured lens epithelial cells of squirrels and rabbits by UV-A (99.9%) plus UV-B (0.1%) radiation and alpha tocopherol protection

Photobiomodulation of the Visual System and Human Health

Humans express an expansive and detailed response to wavelength differences within the electromagnetic (EM) spectrum. This is most clearly manifest, and most studied, with respect to a relatively small range of electromagnetic radiation that includes the visible wavelengths with abutting ultraviolet and infrared, and mostly with respect to the visual system. Many aspects of our biology, however, respond to wavelength differences over a wide range of the EM spectrum. Further, humans are now exposed to a variety of modern lighting situations that has, effectively, increased our exposure to wavelengths that were once likely minimal (e.g., “blue” light from devices at night). This paper reviews some of those biological effects with a focus on visual function and to a lesser extent, other body systems.

Corneal UV Protective Effects of a Topical Antioxidant Formulation: A Pilot Study on In Vivo Rabbits

This study aimed to evaluate the protective effect of a topical antioxidant and ultraviolet (UV) shielding action formulation containing riboflavin and D-α-tocopherol polyethylene glycol succinate (TPGS) vitamin E against corneal UV-induced damage in vivo rabbit eyes. In vivo experiments were performed using male albino rabbits, which were divided into four groups. The control group (CG) did not receive any UV irradiation; the first group (IG) was irradiated with a UV-B−UV-A lamp for 30 min; the second (G30) and third (G60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with one drop of the antioxidant and shielding formulation every 15 min, starting one hour before irradiation, until the end of UV exposure. The cornea of the IG group showed irregular thickening, detachment of residual fragments of the Descemet membrane, stromal fluid swelling with consequent collagen fiber disorganization and disruption, and inflammation. The cornea of the G30 group showed edema, a mild thickening of the Descemet membrane without fibrillar collagen disruption and focal discoloration, or inflammation. In the G60 group, the cornea showed a more severe thickening, a more abundant fluid accumulation underneath the Descemet membrane with focal detachment, and no signs of severe tissue alterations, as were recorded in the IG group. Our results demonstrate that topical application of eye drops containing riboflavin and TPGS vitamin E counteracts UV corneal injury in exposed rabbits.

Effects of an antioxidant protective topical formulation on eye exposed to ultraviolet-irradiation: a study in rabbit animal model

Ultraviolet-radiation exerts a well-known role in the development of various ocular diseases and may contribute to the progress of age-related macular degeneration. Therefore, the use of compounds able to protect the eyes from UV-induced cellular damage is challenging. The aim of this study has been to test the protective effects of an antioxidant topical formulation against UV-induced damage in rabbit eyes. Twelve male rabbits were used. Animals were divided into 4 groups of 3 animals each. Control group (CG) did not receive any irradiation and/or eye drop. The other three experimental groups were treated as follows: the first group received only UVR irradiation for 30 min, without eye drop supplementation (Irradiation group, IG), the second (G30) and the third (G60) groups received UV irradiation for 30' and 60', respectively, and eye drop supplementation (riboflavin, d-alpha-tocopheryl polyethylene glycol, proline, glycine, lysine and leucine solution) every 15 min for three hours. In the IG group a significant increase of oxidized glutathione (GSSG) and hydrogen peroxide (H(2)O(2)) was recorded in the aqueous humor, whereas ascorbic acid levels were significantly lower when compared to control eyes. In the groups exposed to UVR rays for 30 min, and treated with the topical antioxidant formulation, the GSSG, H(2)O(2) and ascorbic acid levels were similar to those recorded in controls, whereas in the G60 group the three markers significantly differ from control group. In the lens, a significant decrease of alpha tocopherol and total antioxidant capacity (TAC) was recorded in IG-animals as compared to control group, whereas malondialdehyde (MDA) levels were significantly higher in UV-induced eye than in control eyes. In the G30 groups the alpha tocopherol, MDA and TAC levels do not significantly differ from those recorded in controls, whereas in the G60 group these three markers significantly differ from control group. Present findings demonstrate that topical treatment with the antioxidant formulation used herein protects ocular structures from oxidative stress induced by UV exposure in in vivo animal model.

EVALUATION OF POTENTIAL RISK FACTORS ASSOCIATED WITH CATARACT IN CAPTIVE MACARONI (EUDYPTES CHRYSOLOPHUS) AND ROCKHOPPER PENGUINS (EUDYPTES CHRYSOCOME)

Complete ophthalmic examinations were performed on 160 Macaroni penguins ( Eudyptes chrysolophus ) and 90 Rockhopper penguins ( Eudyptes chrysocome ) at eight North American zoological institutions. Cataract prevalence in the Macaroni population was 46.5% (n = 74) of penguins and 42.3% (135/319) of eyes. Cataract prevalence in the Rockhopper population was 45.5% (n = 40) of penguins and 40.6% (73/180) of eyes. The mean age of Macaroni penguins without ocular disease was 7.4 ± 5.8 yr, while that of Rockhoppers was 9.8 ± 6.4 yr. Risk factors for cataract were examined through husbandry surveys completed by each institution and by evaluation of light intensity and ultraviolet (UV) light measurements acquired in each penguin exhibit. Risk factors associated with cataract in Macaroni penguins included age, dietary smelt, hand-feeding, and fluorescent exhibit lighting. Risk factors associated with cataract in Rockhopper penguins included age, dietary capelin, increasing population density, and increasing length of minimum photoperiod. Factors associated with decreased odds of cataract in Macaroni penguins included saltwater pool, monitoring of water quality for salinity, pH, and alkalinity; use of water additives; presence of pool filtration and sterilization systems; use of metal halide lightbulbs; increasing light intensity; and UV spectrum lighting. Factors associated with decreased odds of cataract in Rockhoppers included dietary herring and krill, increasing exhibit land area, pool temperature monitoring, increasing maximum photoperiod, and increasing minimum UV light.

Thioredoxin reductase activity may be more important than GSH level in protecting human lens epithelial cells against UVA light

This study compares the abilities of the glutathione (GSH) and thioredoxin (Trx) antioxidant systems in defending cultured human lens epithelial cells (LECs) against UVA light. Levels of GSH were depleted with either L-buthionine-(S,R)-sulfoximine (BSO) or 1-chloro-2,4-dinitrobenzene (CDNB). CDNB treatment also inhibited the activity of thioredoxin reductase (TrxR). Two levels of O2 , 3% and 20%, were employed during a 1 h exposure of the cells to 25 J cm(-2) of UVA radiation (338-400 nm wavelength, peak at 365 nm). Inhibition of TrxR activity by CDNB, combined with exposure to UVA light, produced a substantial loss of LECs and cell damage, with the effects being considerably more severe at 20% O2 compared to 3%. In contrast, depletion of GSH by BSO, combined with exposure to UVA light, produced only a slight cell loss, with no apparent morphological effects. Catalase was highly sensitive to UVA-induced inactivation, but was not essential for protection. Although UVA light presented a challenge for the lens epithelium, it was well tolerated under normal conditions. The results demonstrate an important role for TrxR activity in defending the lens epithelium against UVA light, possibly related to the ability of the Trx system to assist DNA synthesis following UVA-induced cell damage.

The use of some nanoemulsions based on aqueous propolis and lycopene extract in the skin's protective mechanisms against UVA radiation

BACKGROUND

The use of natural products based on aqueous extract of propolis and lycopene in the skin's protective mechanisms against UVA radiation was evaluated by means of experimental acute inflammation on rat paw edema. The aim of the present study was to evaluate the harmlessness of propolis - lycopene system through evaluation of skin level changes and anti-inflammatory action. The regenerative and protective effect of the aqueous propolis and lycopene extract is based on its richness in biologically active substances such as: tocopherols, flavonoids, amino acids, polyunsaturated fatty acids, the chlorophyll pigment, all substances with strong antioxidant activity, that modify the oxidative stress, mainly by reducing the prooxidant processes and enhancing the antioxidant ones. These substances participate in the synthesis of prostaglandins and phospholipids components of cell membrane thus enhancing skin protection mechanisms.

RESULTS

The experimental systems offered a sustained release of the drug, in vitro, for aim eight hours. The prepared formulations aim did not reveal a deteriorating effect on tissues. They proved a better therapeutic efficiency Compared to standard suspension, they provided a better therapeutic efficiency coupled with extended time interval of tested parameters (24 hours). Preliminary examination of tissues showed that the experimental formulations did not irritate. Local application of propolis and lycopene aqueous extract nanoemulsion has a high potential both regarding its efficiency (the analgesic effect) and therapeutic safety.

CONCLUSIONS

This study demonstrates that propolis and lycopene extract nanoemulsions, preparations contains active substances, can confer better therapeutic effects than those of the conventional formulations, based on local control-release of dozed form, for a longer period of time, which probably improve its efficiency and skin acceptance, meaning a better compliance. The information obtained in the present study suggests that administration of propolis and lycopene aqueous extract nanoemulsion is safe. The preparation can be useful for further preclinical studies lycopene embedded in aqueous propolis extract to be used in pharmaceuticals (targeted medical therapy).

Risk factors associated with cataracts and lens luxations in captive pinnipeds in the United States and the Bahamas

OBJECTIVE

To determine risk factors for lens luxation and cataracts in captive pinnipeds in the United States and the Bahamas.

DESIGN

Cross-sectional study.

ANIMALS

111 pinnipeds (99 California sea lions [Zalophus californianus], 10 harbor seals [Phoca vitulina], and 2 walruses [Odobenus rosmarus]) from 9 facilities.

PROCEDURES

Eyes of each pinniped were examined by a veterinary ophthalmologist for the presence of cataracts or lens luxations and photographed. Information detailing husbandry practices, history, and facilities was collected with a questionnaire, and descriptive statistical analyses were performed for continuous and categorical variables. Odds ratios and associated 95% confidence intervals were estimated from the final model.

RESULTS

Risk factors for lens luxation, cataracts, or both included age >or= 15 years, history of fighting, history of ocular disease, and insufficient access to shade.

CONCLUSIONS AND CLINICAL RELEVANCE

Diseases of the lens commonly affect captive pinnipeds. Access to UV-protective shade, early identification and medical management of ocular diseases, and prevention of fighting can limit the frequency or severity of lens-related disease in this population. An extended life span may result from captivity, but this also allows development of pathological changes associated with aging, including cataracts.

Alpha-tocopherol in plasma, red blood cells and lenses with and without cataract

PURPOSE

To compare levels of alpha-tocopherol in human lenses with cataract to clear human lenses and to determine associations between levels of alpha-tocopherol in plasma, red blood cells, and human lenses with cataract.

DESIGN

Cross-sectional study.

METHODS

Concentrations of alpha-tocopherol were measured by high-performance liquid chromatography in blood and in human lenses with and without cataract. Lenses were obtained during cataract surgery and from a regional eye bank. Peripheral alpha-tocopherol status in patients was assessed as plasma alpha-tocopherol (total and corrected for low-density lipoproteins) and as red blood cell bound alpha-tocopherol. Data (mean +/- standard error of the mean) are expressed as microM alpha-tocopherol/g lens protein, microM alpha-tocopherol/l plasma, microM alpha-tocopherol/g low-density lipoproteins, and microM alpha-tocopherol/T red blood cells.

RESULTS

Concentrations of alpha-tocopherol were measured in 27 lenses of cataract patients, 8 cadaver lenses with cataract and in 14 clear cadaver lenses. The concentration of alpha-tocopherol was significantly higher in cataract than in control cadaver lenses (0.49 +/- 0.04 vs 0.35 +/- 0.03, P < .05). The difference between alpha-tocopherol in lenses of cataract patients and control cadaver lenses was even higher (0.7 +/- 0.1 vs 0.35 +/- 0.03, P < .01). No significant correlation was observed between plasma alpha-tocopherol or red blood cell bound alpha-tocopherol and lens alpha-tocopherol in patients.

CONCLUSIONS

Serum and red blood cell levels of alpha-tocopherol may not reflect the alpha-tocopherol status of the lens itself and therefore may not be clinically relevant markers for cataract risk. Mechanisms leading to increased levels of alpha-tocopherol in cataract lenses need to be explored in future research.

Arsenite pre-conditioning reduces UVB-induced apoptosis in corneal epithelial cells through the anti-apoptotic activity of 27 kDa heat shock protein (HSP27)

Exposure to ultraviolet (UV) light poses a health risk for eye disease, and solar ultraviolet in the B range (UVB, 280-320 nm) is known to be related to various corneal disorders. In this study, we investigated whether pre-conditioning of cells with arsenite (AsO2(-1)) can reduce UVB-induced apoptosis in human corneal epithelial cells, and whether the anti-apoptotic activity of 27 kDa heat shock protein (HSP27), a small heat shock protein, plays a role in this protection. UVB at levels comparable to physiologic solar exposure induces apoptosis of corneal epithelial cells in culture, demonstrated by activation of caspase 9 and caspase 3, and DNA fragmentation. When cells were pre-conditioned with arsenite prior to UVB exposure, the UVB-induced cell death was reduced, and UVB-induced activation of caspases and DNA fragmentation was inhibited. When cells were pre-treated with SB 203580, which inhibits HSP27 phosphorylation through inhibition of p38 MAP kinase activation, the arsenite-induced reduction of UVB-induced apoptosis was partially reversed. Arsenite pre-conditioning inhibited UVB-induced apoptosis in a two-phase pattern, which was temporally correlated with arsenite-induced HSP27 expression and phosphorylation. Neutralization of intracellular HSP27 with its antibody reduced arsenite's inhibition of UVB-induced caspase3 activation. Our results suggest that forms of stress that upregulate HSP27 and its phosphorylation may be useful as novel approaches to prevent adverse ocular effects arising from UV exposure in humans.

Long-term lens organ culture system to determine age-related effects of UV irradiation on the eye lens

Aging of the eye lens represents the life-long accumulation of damage. Factors responsible for age-related cataract are unknown because medical evaluations of aged populations demonstrate a wide range of systemic diseases and medical disorders. There are some main suspected factors, which may contribute to accumulated age-related damage in the eye lens. (1) Diseases, such as diabetes, substantially increase the probability of cataract formation in the age group from 40 to 49, and double or triple this probability for ages 50 to 69. (2) Drugs, including systemic medications such as steroids. (3) Environmental factors, such as UV radiation, heat and electromagnetic radiation. Our study represents an effort to determine the effects of suspected cataractogenic factors on the eye lens. The experiments are performed using a unique long-term lens organ culture system of bovine lenses. In our system it is possible to give controlled amounts of insult and monitor changes in lens optical quality throughout the culture period of 8-15 days. The optical properties, monitored in association with biochemical analysis of lens epithelium, cortex and nuclear samples, help in determining the mechanisms of cataract formation. The present study investigates mechanisms by which UV-A radiation at 365 nm causes damage to the lens. It is believed that solar radiation is one of the major environmental factors involved in lens cataractogenesis. Bovine lenses were placed in our special culture cells for pre-incubation of 24 hr followed by irradiation of 29 or 33 J cm(-2). The lenses were maintained in the cells during irradiation. After irradiation, lens optical quality was monitored throughout the culture period and lens epithelium was taken for enzyme analysis. Using the culture system we learned that: (a) young lenses (less than one-year-old) are less sensitive to UV radiation than 3-year-old lenses; (b) the lenses have the ability to recover in organ culture conditions; (c) applying the insult in one step results in less damage than dividing the same insult in 4 steps with 24 hr interval between each one; and (d) the damage from UV is greater if the intervals between each irradiation stage are insufficient to permit full recovery.

The effects of sub-solar levels of UV-A and UV-B on rabbit corneal and lens epithelial cells

The purpose of this work was to establish whether exposing cultured rabbit corneal and lens epithelial cells to ultraviolet radiation equivalent to several hours under the sun would damage the cells. Confluent rabbit corneal epithelial cells were irradiated with broadband UV-A or UV-B, and confluent lens epithelial cells were irradiated with broadband UV-A. The maximum dose of UV-A was 6.3 J cm(-2) and that of UV-B was 0.60 J cm(-2). Damage to corneal epithelial cell was studied using the terminal deoxynucleotidyl transferase mediated dUTP-X nick end labeling (TUNEL) assay and damage to lens epithelial cell was studied using the single cell gel electrophoresis (comet) assay and trypan blue exclusion assay. Lipid peroxidation was assayed using the thiobarbituric acid reaction. Both UV-B and UV-A induced cell death in corneal epithelial cells with different latent periods. UV-A damage included cell death, decreased viability and increased lipid peroxidation of lens epithelial cell. In addition, UV irradiation of the corneal and lens epithelial cells decreased the activity of catalase to thirty to fifty percent of its original value, while the activities of glutathione peroxidase and superoxide dismutase did not decrease within experimental error. Thus, even sub-solar UV radiation can cause irreversible damage to corneal and lens epithelial cells.

Effects of UV-A irradiation on lens morphology and optics

Epidemiological studies have indicated that ultraviolet radiation (UVR) is one of the main factors leading to senile cataract formation. We investigated morphological changes in the eye lens caused by UVR-A. Twenty three pairs of lenses obtained from 23 one-year-old calves were used for this study. For each pair, one lens was exposed to 44 J/m(2) UVR in the 365 nm wavelength region while the contralateral lens was not exposed and served as a control. The lenses were placed in specially designed organ culture containers for pre-incubation. Lenses were exposed to UVR after one day in culture. After irradiation, lens optical quality was monitored throughout additional 15 days of the culture period and lenses were taken for morphological analysis by scanning electron microscopy. Damage to lens optical quality was evident as early as day 8 after the irradiation and increased with time in culture. We found irregularity of fiber morphology in lenses exposed to UV-A irradiation (but not in control lenses), similar to that reported previously for aged lenses. At the end of the culture period (day 16), lens fiber membranes also showed holes in fiber membranes. We conclude that UVR-A caused damage to cell membranes of the lens and alterations in lens optics, which may subsequently lead to senile cataract formation.

Ultraviolet radiation modulates nuclear factor kappa B activation in human lens epithelial cells

Exposure to ultraviolet radiation (UVR) is a known risk factor for cataract, but the molecular mechanisms involved have not been elucidated. We hypothesized that exposure to UVR would modulate the activation of nuclear factor kappa-B (NF-kappa B) within the human lens epithelium, since NF-kappa B is a key regulator of cellular responses to UVR stress in other cell types. Human lens epithelial (HLE) cells were exposed to acute physiological doses of ultraviolet A (UVAR), B (UVBR), C (UVCR) radiation, or interleukin-1 beta (IL-1 beta) and NF-kappa B activation was measured by electrophoretic shift assay (EMSA). Phosphorylation of I kappa B in response to UVAR was measured by Western blotting. Irradiation of HLE cells with UVAR (0-1100 J/m(2)) did not reduce cell survival, while UVBR (400-1600 J/m(2)) and UVCR (300-900 J/m(2)) significantly reduced HLE cell survival. EMSA analysis of HLE nuclear proteins indicated activation of NF-kappa B, but not activator protein-1 (AP-1), by UVAR. The effects of UVBR and UVCR were less pronounced. Exposure of HLE cells to UVAR (0-900 J/m(2)) followed by a 30-min incubation resulted in a dose-dependent activation of NF-kappa B. UVAR-induced NF-kappa B activation in HLE cells was evident 10 min postirradiation, maximal at 60 min and returned to control levels by 120 min. Western blot analysis of phosphorylation of the NF-kappa B inhibitory protein, I kappa B, revealed that UVAR activates NF-kappa B via a mechanism involving the phosphorylation of I kappa B-alpha; this effect was dose-dependent. Supershift analysis demonstrated that UVAR and IL-1 beta activate the transcriptionally active p65/p50 NF-kappa B dimer. These studies demonstrate that UVAR activates NF-kappa B in HLE cells in a time- and dose-dependent manner via signaling through I kappa B-alpha. The activation of NF-kappa B in HLE cells by UVAR may have implications for the development and progression of cataract and other related ocular disorders.

Sequential effects of ultraviolet radiation on the histomorphology, cell density and antioxidative status of the lens epithelium--an in vivo study

In vivo progressive effects of UV irradiation on the lens epithelium were studied using various histomorphological and biochemical parameters. Fifteen day old rat pups were exposed to 600 mW/m2 of radiation, including UV-A and UV-B, 12 h daily for 90, 120, 150 and 180 days. Biochemical parameters such as protein-bound and non-protein-bound sulfhydryl groups in both soluble and insoluble fractions and enzymes, which play an important role in combating the oxidative stress, were studied. Decreased cell density of lens epithelial cells (LEC) was observed in all three zones along with the decrease in the levels of soluble sulfhydryls (S-SH), glutathione reductase (GR), superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT). On the other hand, an increase in insoluble sulfhydryls was observed. Because of the decrease in S-SH and GR activities, the LEC became vulnerable to oxidative stress. Decreased activities of SOD, GPx and CAT suggest elevated oxidative stress. This effect of UV radiation may lead to cell death that may be responsible for the observed decrease in the cell density in all three zones of the lens epithelium.

Propyl gallate is a superoxide dismutase mimic and protects cultured lens epithelial cells from H2O2 insult

n-Propyl gallate (nPG) is a food preservative that is generally regarded as safe by the US FDA. It suppresses oxidation in biological systems. The mechanism by which nPG acts in biological systems is uncertain. We investigated whether nPG protected cultured lens epithelial cells from H(2)O(2)-induced damage. Cells were treated with H(2)O(2) or with nPG and then H(2)O(2). H(2)O(2) inhibited growth, caused membrane blebbing, decreased lactate production, increased the level of GSSG, decreased the levels of GSH, ATP and NAD(+), and G3PDH activity, stimulated the hexose monophosphate shunt and induced single-strand breaks in DNA. nPG prevented the H(2)O(2)-induced growth inhibition, membrane blebbing, drop in NAD(+) and single-strand breaks in DNA. The mechanism by which nPG acts at the chemical level was investigated using electron paramagnetic resonance (EPR), direct spectrophotometric kinetic measurements, and cyclic voltammetry. When nPG at low concentrations (nM to microM) was mixed with a large excess of O(2)(-)*, the superoxide signal was destroyed as indicated by UV visible spectroscopy and EPR. Kinetic analysis indicated that nPG dismutated O(2)(-)* in repetitive additions of superoxide with little loss of activity. The rate constant for the overall reaction of nPG with O(2)(-)* was ca. 10(6)M(-1)s(-1). nPG had a very low specific binding constant for Fe(2+) as determined by cyclic voltammetry. The evidence indicates that nPG dismutates the superoxide ion in a catalytic manner.

Induction of multinucleated cells caused by UVA exposure in different stages of the cell cycle

Fibroblasts of the line 3T3 from swiss albino mice were exposed to ultraviolet A (UVA) irradiation. The cells were synchronized by treatment with nocodazole and mitotic shake-off, and then exposed to UVA irradiation in different stages of the cell cycle. Their photosensitivity varied through the cell cycle, being greatest in the G2 phase. UVA irradiation was found to induce the formation of multinucleated cells. Cells in the G1 phase were found to be most prone to multinucleation 15 min after UVA irradiation, while cells exposed to UVA irradiation in S and G2 phases contained the largest fractions of multinucleated cells 24 h after treatment. The present results indicate that multinucleated cells are formed by fusion of two or more cells shortly after UVA irradiation of early G1 cells, while impairment of cytokinesis is a possible explanation for the delayed formation of multinucleated cells after irradiation in S and G2.

Influence of sex, smoking and age on human hprt mutation frequencies and spectra

Examination of the literature for hprt mutant frequencies from peripheral T cells yielded data from 1194 human subjects. Relationships between mutant frequency, age, sex, and smoking were examined, and the kinetics were described. Mutant frequency increases rapidly with age until about age 15. Afterward, the rate of increase falls such that after age 53, the hprt mutant frequency is largely stabilized. Sex had no effect on mutant frequency. Cigarette smoking increased mean mutant frequency compared to nonsmokers, but did not alter age vs. mutant frequency relationships. An hprt in vivo mutant database containing 795 human hprt mutants from 342 individuals was prepared. No difference in mutational spectra was observed comparing smokers to nonsmokers, confirming previous reports. Sex affected the frequency of deletions (>1 bp) that are recovered more than twice as frequently in females (P = 0. 008) compared to males. There is no indication of a significant shift in mutational spectra with age for individuals older than 19 yr, with the exception of A:T --> C:G transversions. These events are recovered more frequently in older individuals.

The molecular chaperone alphaA-crystallin enhances lens epithelial cell growth and resistance to UVA stress

alphaA-Crystallin (alphaA) is a member of the small heat shock protein (sHSP) family and has the ability to prevent denatured proteins from aggregating in vitro. Lens epithelial cells express relatively low levels of alphaA, but in differentiated fiber cells, alphaA is the most abundant soluble protein. The lenses of alphaA-knock-out mice develop opacities at an early age, implying a critical role for alphaA in the maintenance of fiber cell transparency. However, the function of alpha-crystallin in the lens epithelium is unknown. To investigate the physiological function of alphaA in lens epithelial cells, we used the following two systems: alphaA knock-out (alphaA(-/-)) mouse lens epithelial cells and human lens epithelial cells that overexpress alphaA. The growth rate of alphaA(-/-) mouse lens epithelial cells was reduced by 50% compared with wild type cells. Cell cycle kinetics, measured by fluorescence-activated cell sorter analysis of propidium iodide-stained cells, indicated a relative deficiency of alphaA(-/-) cells in the G2/M phases. Exposure of mouse lens epithelial cells to physiological levels of UVA resulted in an increase in the number of apoptotic cells in the cultures. Four hours after irradiation the fraction of apoptotic cells in the alphaA(-/-) cultures was increased 40-fold over wild type. In cells lacking alphaA, UVA exposure modified F-actin, but actin was protected in cells expressing alphaA. Stably transfected cell lines overexpressing human alphaA were generated by transfecting extended life span human lens epithelial cells with the mammalian expression vector construct pCI-neoalphaA. Cells overexpressing alphaA were resistant to UVA stress, as determined by clonogenic survival. alphaA remained cytoplasmic after exposure to either UVA or thermal stress indicating that, unlike other sHSPs, the protective effect of alphaA was not associated with its relocalization to the nucleus. These results indicate that alphaA has important cellular functions in the lens over and above its well characterized role in refraction.

Measurement of oxygen production by in vitro human and animal lenses with an oxygen electrode

PURPOSE

This paper describes an advantageous method of measuring the activity of the enzyme catalase, which has an important antioxidative role in the lens. This method allows the measurement of catalase in whole lenses.

METHODS

Exposure to UVA (99% UV-A) radiation was used to stress animal and human (Eye Bank) lenses in vitro. The ability of lens catalase to convert H2O2 into O2 was measured directly, using an oxygen electrode and meter. This method is very specific, as catalase is the only enzyme that converts H2O2 to O2.

RESULTS

Catalase in the lenses of humans, rabbits, and squirrels catalyzed the production of O2 from H2O2 very efficiently. The anterior equatorial regions of these lenses were the most active O2 producing areas. More than 95% of lens catalase activity was found in the capsule-epithelium layer. Exposure to UVA radiation, up to approximately 100 J/cm2 in 18 h, strongly inhibited O2 production from 0.77 mM H2O2 by the lenses. Catalase activity decreased with increasing age. Mixed cataractous human lenses produced O2 from H2O2 at only 60% of the rate of normal lenses of similar ages. Nuclear cataracts produced O2 at only 75% of the rate of normal lenses. Alpha-tocopherol (10(-5) M) protected lens catalase activity strongly. Alpha-tocopherol is known to accumulate in and protect against cell membrane peroxidation, and against singlet oxygen formation. These oxidative mechanisms appear to contribute to catalase photoinactivation.

CONCLUSIONS

The method described indicated that catalase is a crucial antioxidative enzyme in the normal lens. Its inactivation could upset the oxidation-reduction balance in the lens and stimulate lens opacification.

Ultraviolet action spectra for photobiological effects in cultured human lens epithelial cells

The action spectrum for cell killing by UV radiation in human lens epithelial (HLE) cells is not known. Here we report the action spectrum in the 297-365 nm region in cultured HLE cells with an extended lifespan (HLE B-3 cells) and define their usefulness as a model system for photobiological studies. Cells were irradiated with monochromatic radiation at 297, 302, 313, 325, 334 and 365 nm. Cell survival was determined using a clonogenic assay. Analysis of survival curves showed that radiation at 297 nm was six times more effective in cell killing than 302 nm radiation; 297 nm radiation was more than 260, 590, 1400 and 3000 times as effective in cell killing as 313, 325, 334 and 365 nm radiation, respectively. The action spectrum was similar in shape to that for other human epithelial cell lines and rabbit lens epithelial cells. The effect of UV radiation on crystallin synthesis was also determined at different wavelengths. To determine whether exposure to UV radiation affects the synthesis of beta-crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [35S]methionine and the newly synthesized beta-crystallin was analyzed by immunoprecipitation and western blotting using an antibody to beta-crystallin. The results show a decrease in crystallin synthesis in HLE cells irradiated at 302 and 313 nm at fluences causing low cytotoxicity. The effect of radiation on membrane perturbation was determined by measuring enhancement of synthesis of prostaglandin E2 (PGE2). Synthesis of PGE2 occurs at all UV wavelengths tested in the 297-365 nm region.(ABSTRACT TRUNCATED AT 250 WORDS)