Anandamide Concentration-Dependently Modulates Toll-Like Receptor 3 Agonism or UVB-Induced Inflammatory Response of Human Corneal Epithelial Cells

Photodamage-induced and viral keratitis could benefit from treatment with novel nonsteroid anti-inflammatory agents. Therefore, we determined whether human corneal epithelial cells (HCECs) express members of the endocannabinoid system (ECS), and examined how the endocannabinoid anandamide (AEA, N-arachidonoyl ethanolamine) influences the Toll-like receptor 3 (TLR3) agonism- or UVB irradiation-induced inflammatory response of these cells. Other than confirming the presence of cannabinoid receptors, we show that endocannabinoid synthesizing and catabolizing enzymes are also expressed in HCECs in vitro, as well as in the epithelial layer of the human cornea in situ, proving that they are one possible source of endocannabinoids. p(I:C) and UVB irradiation was effective in promoting the transcription and secretion of inflammatory cytokines. Surprisingly, when applied alone in 100 nM and 10 μM, AEA also resulted in increased pro-inflammatory cytokine production. Importantly, AEA further increased levels of these cytokines in the UVB model, whereas its lower concentration partially prevented the transcriptional effect of p(I:C), while not decreasing the p(I:C)-induced cytokine release. HCECs express the enzymatic machinery required to produce endocannabinoids both in vitro and in situ. Moreover, our data show that, despite earlier reports about the anti-inflammatory potential of AEA in murine cornea, its effects on the immune phenotype of human corneal epithelium may be more complex and context dependent.

Transepithelial versus epithelium-off corneal crosslinking for progressive keratoconus

BACKGROUND

Keratoconus is the most common corneal dystrophy. It can cause loss of uncorrected and best-corrected visual acuity through ectasia (thinning) of the central or paracentral cornea, irregular corneal scarring, or corneal perforation. Disease onset usually occurs in the second to fourth decade of life, periods of peak educational attainment or career development. The condition is lifelong and sight-threatening. Corneal collagen crosslinking (CXL) using ultraviolet A (UVA) light applied to the cornea is the only treatment that has been shown to slow progression of disease. The original, more widely known technique involves application of UVA light to de-epithelialized cornea, to which a photosensitizer (riboflavin) is added topically throughout the irradiation process. Transepithelial CXL is a recently advocated alternative to the standard CXL procedure, in that the epithelium is kept intact during CXL. Retention of the epithelium offers the putative advantages of faster healing, less patient discomfort, faster visual rehabilitation, and less risk of corneal haze.

OBJECTIVES

To assess the short- and long-term effectiveness and safety of transepithelial CXL compared with epithelium-off CXL for progressive keratoconus.

SEARCH METHODS

To identify potentially eligible studies, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2020, Issue 1); Ovid MEDLINE; Embase.com; PubMed; Latin American and Caribbean Health Sciences Literature database (LILACS); ClinicalTrials.gov; and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not impose any date or language restrictions. We last searched the electronic databases on 15 January 2020.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which transepithelial CXL had been compared with epithelium-off CXL in participants with progressive keratoconus.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We included 13 studies with 723 eyes of 578 participants enrolled; 13 to 119 participants were enrolled per study. Seven studies were conducted in Europe, three in the Middle East, and one each in India, Russia, and Turkey. Seven studies were parallel-group RCTs, one study was an RCT with a paired-eyes design, and five studies were RCTs in which both eyes of some or all participants were assigned to the same intervention. Eleven studies compared transepithelial CXL with epithelium-off CXL in participants with progressive keratoconus. There was no evidence of an important difference between intervention groups in maximum keratometry (denoted 'maximum K' or 'Kmax'; also known as steepest keratometry measurement) at 12 months or later (mean difference (MD) 0.99 diopters (D), 95% CI -0.11 to 2.09; 5 studies; 177 eyes; I² = 41%; very low certainty evidence). Few studies described other outcomes of interest. The evidence is very uncertain that epithelium-off CXL may have a small (data from two studies were not pooled due to considerable heterogeneity (I² = 92%)) or no effect on stabilization of progressive keratoconus compared with transepithelial CXL; comparison of the estimated proportions of eyes with decreases or increases of 2 or more diopters in maximum K at 12 months from one study with 61 eyes was RR 0.32 (95% CI 0.09 to 1.12) and RR (non-event) 0.86 (95% CI 0.74 to 1.00), respectively (very low certainty). We did not estimate an overall effect on corrected-distance visual acuity (CDVA) because substantial heterogeneity was detected (I² = 70%). No study evaluated CDVA gain or loss of 10 or more letters on a logarithm of the minimum angle of resolution (logMAR) chart. Transepithelial CXL may result in little to no difference in CDVA at 12 months or beyond. Four studies reported that either no adverse events or no serious adverse events had been observed. Another study noted no change in endothelial cell count after either procedure. Moderate certainty evidence from 4 studies (221 eyes) found that epithelium-off CXL resulted in a slight increase in corneal haze or scarring when compared to transepithelial CXL (RR (non-event) 1.07, 95% CI 1.01 to 1.14). Three studies, one of which had three arms, compared outcomes among participants assigned to transepithelial CXL using iontophoresis versus those assigned to epithelium-off CXL. No conclusive evidence was found for either keratometry or visual acuity outcomes at 12 months or later after surgery. Low certainty evidence suggests that transepithelial CXL using iontophoresis results in no difference in logMAR CDVA (MD 0.00 letter, 95% CI -0.04 to 0.04; 2 studies; 51 eyes). Only one study examined gain or loss of 10 or more logMAR letters. In terms of adverse events, one case of subepithelial infiltrate was reported after transepithelial CXL with iontophoresis, whereas two cases of faint corneal scars and four cases of permanent haze were observed after epithelium-off CXL. Vogt's striae were found in one eye after each intervention. The certainty of the evidence was low or very low for the outcomes in this comparison due to imprecision of estimates for all outcomes and risk of bias in the studies from which data have been reported.

AUTHORS' CONCLUSIONS

Because of lack of precision, frequent indeterminate risk of bias due to inadequate reporting, and inconsistency in outcomes measured and reported among studies in this systematic review, it remains unknown whether transepithelial CXL, or any other approach, may confer an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to further progression of keratoconus, visual acuity outcomes, and patient-reported outcomes (PROs). Arrest of the progression of keratoconus should be the primary outcome of interest in future trials of CXL, particularly when comparing the effectiveness of different approaches to CXL. Furthermore, methods of assessing and defining progressive keratoconus should be standardized. Trials with longer follow-up are required in order to assure that outcomes are measured after corneal wound-healing and stabilization of keratoconus. In addition, perioperative, intraoperative, and postoperative care should be standardized to permit meaningful comparisons of CXL methods. Methods to increase penetration of riboflavin through intact epithelium as well as delivery of increased dose of UVA may be needed to improve outcomes. PROs should be measured and reported. The visual significance of adverse outcomes, such as corneal haze, should be assessed and correlated with other outcomes, including PROs.

Blue Light Induces Impaired Autophagy through Nucleotide-Binding Oligomerization Domain 2 Activation on the Mouse Ocular Surface

In this study, we investigated the effects of blue light exposure on nucleotide-binding oligomerization domain 2 (NOD2) expression on the mouse ocular surface and evaluated the role of NOD2 activation in light-induced cell death. Mice were divided into wild-type (WT), NOD2-knock out (KO), WT + blue light (WT + BL), and NOD2-KO + blue light (NOD2-KO + BL) groups, and the mice in the WT+BL and NOD2-KO + BL groups were exposed to blue light for 10 days. After 10 days of blue light exposure, increased reactive oxygen species and malondialdehyde were observed in the WT + BL and NOD2-KO + BL groups, and the WT + BL group showed a higher expression of NOD2 and autophagy related 16 like 1. Although both WT+BL and NOD2-KO + BL groups showed an increase in the expression of light chain 3-II, NOD2-KO + BL mice had a significantly lower p62 expression than WT + BL mice. In addition, NOD2-KO+BL mice had significantly lower corneal epithelial damage and apoptosis than WT + BL mice. In conclusion, blue light exposure can induce impaired autophagy by activation of NOD2 on the ocular surface. In addition, the reactive oxygen species (ROS)-NOD2-autophagy related 16 like 1 (ATG16L) signaling pathway may be involved in the blue-light-induced autophagy responses, resulting in corneal epithelial apoptosis.

UV damage of the anterior ocular surface - microstructural evidence by in vivo confocal microscopy

PURPOSE

To evaluate and describe the microstructural changes at the ocular surface in response to habitual ocular sun exposure, correlate them with the UV protection habits and follow their dynamics using in vivo confocal microscopy(ICM).

METHODS

For a period of minimum 4 months 200 subjects (400 eyes), aged 28 ± 7.3 years, were recruited with the agreement that they will spend their summer exclusively in the region of the Black Sea coast at 43 °N latitude and will be examined before and after the summer. All subjects filled in a questionnaire about habitual UV protection and were examined clinically and by ICM.

RESULTS

Questionnaire results demonstrated that 83.5% (167 participants) of the subjects considered the sun dangerous for their eyes, but 78% (156 subjects) believed that there is danger exclusively during the summer period. Although no clinical changes were detected, microstructural analysis of the cornea demonstrated statistically significant (p = 0.021) decrease of the basal epithelial density - from 6167 ± 151 cells/mm² before to 5829 ± 168 cells/mm² after the summer period. Microstructural assessment of the conjunctiva demonstrated characteristic cystic lesions with dark centres and bright borders encountered in only 25 eyes(6%) before, and affecting 118 eyes(29.5%) after the summer. The total area of the cysts after the summer increased fivefold. Spearman analysis proved negative correlation between sun protection habits and number of cysts.

CONCLUSION

Summer sun exposure for one season leads to clinically undetectable, microstructural changes affecting the cornea, bulbar and palpebral conjunctiva with transient, but possibly cumulative nature.

A novel role for CRIM1 in the corneal response to UV and pterygium development

Pterygium is a pathological proliferative condition of the ocular surface, characterised by formation of a highly vascularised, fibrous tissue arising from the limbus that invades the central cornea leading to visual disturbance and, if untreated, blindness. Whilst chronic ultraviolet (UV) light exposure plays a major role in its pathogenesis, higher susceptibility to pterygium is observed in some families, suggesting a genetic component. In this study, a Northern Irish family affected by pterygium but reporting little direct exposure to UV was identified carrying a missense variant in CRIM1 NM_016441.2: c.1235 A > C (H412P) through whole-exome sequencing and subsequent analysis. CRIM1 is expressed in the developing eye, adult cornea and conjunctiva, having a role in cell differentiation and migration but also in angiogenesis, all processes involved in pterygium formation. We demonstrate elevated CRIM1 expression in pterygium tissue from additional individual Northern Irish patients compared to unaffected conjunctival controls. UV irradiation of HCE-S cells resulted in an increase in ERK phosphorylation and CRIM1 expression, the latter further elevated by the addition of the MEK1/2 inhibitor, U0126. Conversely, siRNA knockdown of CRIM1 led to decreased UV-induced ERK phosphorylation and increased BCL2 expression. Transient expression of the mutant H412P CRIM1 in corneal epithelial HCE-S cells showed that, unlike wild-type CRIM1, it was unable to reduce the cell proliferation, increased ERK phosphorylation and apoptosis induced through a decrease of BCL2 expression levels. We propose here a series of intracellular events where CRIM1 regulation of the ERK pathway prevents UV-induced cell proliferation and may play an important role in the in the pathogenesis of pterygium.

TNF-R1 and FADD mediate UVB-Induced activation of K+ channels in corneal epithelial cells

The goal of this study was to elucidate the role of Fas, TNF-R1, FADD and cytochrome c in UVB-induced K+ channel activation, an early step in UVB-induced apoptosis, in human corneal limbal epithelial (HCLE) cells. HCLE cells were treated with Fas, TNF-R1 or FADD siRNA and exposed to 80 or 150 mJ/cm2 UVB. K+ channel activation and loss of intracellular K+ were measured using whole-cell patch-clamp recording and ion chromatography, respectively. Cytochrome c was measured with an ELISA kit. Cells in which Fas was knocked down exhibited identical UVB-induced K+ channel activation and loss of intracellular K+ to control cells. Cells in which TNF-R1 or FADD were knocked down demonstrated reduced K+ channel activation and decreased loss of intracellular K+ following UVB, relative to control cells. Application of TNF-α, the natural ligand of TNF-R1, to HCLE cells induced K+ channel activation and loss of intracellular K+. Cytochrome c was translocated to the cytosol by 2 h after exposure to 150 mJ/cm2 UVB. However, there was no release by 10 min post-UVB. The data suggest that UVB activates TNF-R1, which in turn may activate K+ channels via FADD. This conclusion is supported by the observation that TNF-α also causes loss of intracellular K+. This signaling pathway appears to be integral to UVB-induced K+ efflux, since knockdown of TNF-R1 or FADD inhibits the UVB-induced K+ efflux. The lack of rapid cytochrome c translocation indicates cytochrome c does not play a role in UVB-induced K+ channel activation.

Experimental and Numerical Determination of the Local Temperature Distribution during Phacoemulsification and Comparison of Different Surgery Situations within Enucleated Porcine Eyes

Phacoemulsification, a common treatment for cataract, is accompanied by cell damage at the corneal endothelium. Thermal exposure during treatment has been considered a reason for this damage, but a thorough experimental and theoretical assessment of the local temperature distribution inside the eye had not yet been conducted. Measurements in porcine eyes and a finite-element simulation enabled such an assessment and localized the highest temperature rise very close to the probe. The results described in this study indicate that a distance of 1 mm between the probe and the endothelium should be maintained during treatment as a safety margin, especially when fluid flow is blocked. The highest measured temperature rise with surgically reasonable system settings and unblocked fluid flow was 1.11°C. The finite-element simulation described here is able to calculate the temperature rise at the endothelium and could serve as a tool for comparing arbitrary surgical situations with respect to thermal exposure of the endothelium.

[CYSTEAMINE-INDUCED MODIFICATION OF CYTOGENETIC DAMAGES TO THE CORNEAL EPITHELIUM OF MICE EXPOSED TO CORPUSCULAR RADIATION WITH VARYING LINEAR TRANSFER ENERGIES]

Cytogenetic damages to cells of the corneal epithelium were studied in mice exposed to protons (10, 25, 50 and 645 MeV), ions of boron, carbon and neon, and X-rays (180 keV) within the dose range from 25 to 750 cGy and injected with a radioprotector. Animals were subjected to a single exposure. The protective effect of β-mercaptoethylamine was tested in the experiment. The radioprotector (0.2 ml) was introduced intraperitoneally 30 minutes before exposure in 350 mI/kg dose. Control animals received the same amount of sodium chloride solution. The animals were sacrificed by cervical dislocation in 24 and 72 hrs. after exposure. It was shown that cysteamine effectively protects in vivo corneal epithelium cells of mice exposed to electromagnetic radiation or protons in a broad energy spectrum (10 to 645 MeV), and to a broad range of radiation doses (25 to 750 cGy), as judged from levels of aberrant mitosis and mitotic activity. The radioprotector exhibited the highest effectiveness in animals exposed to the doses of 50 to 300 cGy. These findings prove that cysteamine may potentially be used for pharmacological protection from protons. The radioprotector failed to prevent chromosomal aberrations after exposure to heavy charged particles of boron, carbon and neon, which implies the need to design radioprotectors against this type of corpuscular radiation specifically.

[Cytogenetic damage to the corneal epithelium of mice due to the in vivo exposure to ionizing radiation with different levels of linear energy transfer]

Damages to corneal epithelium cells were studied in mice irradiated by protons with the energies of 10, 25, 50 and 645 MeV, 60Co γ-quanta and accelerated ions of boron, carbon and neon with the energies of 7.5; 2.5 and 6.0 MeV/nucleon, respectively. X-rays (180 keV) were used as a standard radiation. Animals were exposed to a single dose in the range from 25 to 760 cGy. The mitotic index and aberrant mitoses were counted in corneal preparations in 24 hrs after irradiation. No matter the type of radiation, the mitotic index had an inverse dose dependence, i.e. the higher the dose, the lower the mitotic index. Exposure to all types of radiation resulted in a sharp increase in the number of chromosomal aberrations in the corneal epithelium; frequency of aberrations was a function of dose and type of radiation. The number of chromosomal aberrations displayed a peculiar direct dose dependence irrespective of type of radiation; however, heavy ions of carbon and boron are the most damaging to the cytogenetic apparatus of epithelial cells. Protons at the Bragg peak and ensuing fall, and of 50 MeV also contribute to the production of chromosomal aberrations as compared with sparsely ionizing gamma- and X-rays and high-energy protons with low linear energy transfer. Coefficients of relative biological effectiveness were calculated based on the mitotic index and evidence of aberrant mitosis.

Brm inhibits the proliferative response of keratinocytes and corneal epithelial cells to ultraviolet radiation-induced damage

Ultraviolet radiation (UV) from sunlight is the primary cause of skin and ocular neoplasia. Brahma (BRM) is part of the SWI/SNF chromatin remodeling complex. It provides energy for rearrangement of chromatin structure. Previously we have found that human skin tumours have a hotspot mutation in BRM and that protein levels are substantially reduced. Brm−/− mice have enhanced susceptibility to photocarcinogenesis. In these experiments, Brm−/− mice, with both or a single Trp53 allele were exposed to UV for 2 or 25 weeks. In wild type mice the central cornea and stroma became atrophic with increasing time of exposure while the peripheral regions became hyperplastic, presumably as a reparative process. Brm−/−, Trp53+/−, and particularly the Brm−/− Trp53+/− mice had an exaggerated hyperplastic regeneration response in the corneal epithelium and stroma so that the central epithelial atrophy or stromal loss was reduced. UV induced hyperplasia of the epidermis and corneal epithelium, with an increase in the number of dividing cells as determined by Ki-67 expression. This response was considerably greater in both the Brm−/− Trp53+/+ and Brm−/− Trp53+/− mice indicating that Brm protects from UV-induced enhancement of cell division, even with loss of one Trp53 allele. Cell division was disorganized in Brm−/− mice. Rather than being restricted to the basement membrane region, dividing cells were also present in the suprabasal regions of both tissues. Brm appears to be a tumour suppressor gene that protects from skin and ocular photocarcinogenesis. These studies indicate that Brm protects from UV-induced hyperplastic growth in both cutaneous and corneal keratinocytes, which may contribute to the ability of Brm to protect from photocarcinogenesis.

Hyaluronic acid-dependent protection against UVB-damaged human corneal cells

Within ultraviolet radiation, ultraviolet B (UVB) is the most energetic and damaging to humans. At the protein level, UVB irradiation downregulates the expression of antioxidant enzymes leading to the accumulation of reactive oxygen species (ROS). Due to lacking of a global analysis of UVB-modulated corneal proteome, we investigate in vitro the mechanism of UVB-induced corneal damage to determine whether hyaluronic acid (HA) is able to reduce UVB irradiation-induced injury in human corneal epithelial cells. Accordingly, human corneal epithelial cell lines (HCE-2) were irradiated with UVB, followed by incubation with low molecular weight HA (LMW-HA, 100 kDa) or high molecular weight HA (HMW-HA, 1,000 kDa) to investigate the physiologic protection of HMW-HA in UVB-induced corneal injury, and to perform a global proteomic analysis. The data demonstrated that HA treatment protects corneal epithelial cells in the UVB-induced wound model, and that the molecular weight of HA is a crucial factor. Only HMW-HA significantly reduces the UVB-induced cytotoxic effects in corneal cells and increases cell migration and wound-healing ability. In addition, proteomic analysis showed that HMW-HA might modulate cytoskeleton regulation, signal transduction, biosynthesis, redox regulation, and protein folding to stimulate wound healing and to prevent these UVB-damaged cells from cell death. Further studies evidenced membrane-associated progesterone receptor component 1 (mPR) and malate dehydrogenase (MDH2) play essential roles in protecting corneal cells from UVB irradiation. This study reports on UVB-modulated cellular proteins that might play an important role in UVB-induced corneal cell injury and show HMW-HA to be a potential substance for protecting corneal cells from UVB-induced injury.

The effect of ultraviolet radiation on the cornea - experimental study

Ultraviolet (UV) radiation in high doses may have harmful effects on the eye. The sources of UV radiation are the sun, as well as some artificial sources such as UV lamps or voltaic arcs. Chronic exposure to UV can cause damage to the anterior pole of the eye, ranging from minor (pterygium) to serious photokeratitis. In our study, we applied a UV dose of 6.5 J/cm(2) in the wavelength range of 290-400 nm, for five consecutive days per rat anterior pole of the eye. Seven days after the last dose of radiation, the animals were sacrificed, harvesting both the irradiated and the non-irradiated eye. Histological and immunohistochemical examination of the lesions revealed that the greatest damage to the epithelium was recorded prior to and 2/3 of the remaining corneal stroma. The epithelial lesions we found varied from pseudokeratosis and detachment of the Bowman epithelium membrane to deep epithelial necrosis. Within the corneal stroma, we observed the formation of interstitial edema with disruption of the collagen structure. We also noticed the presence of an inflammatory infiltrate composed mainly of lymphocytes and CD68+ and CD163+ macrophages, as well as the occurrence of vascular devices. These consisted of angiogenesis capillaries with structured wall composed mainly of endothelial CD34+ precursor cells and a basal membrane rich in collagen IV fibers.

[Effects of damage and post-radiation reparation of cornea epithelium cells chromosomal apparatus in mice following irradiation by protons with the energy of 25 MeV]

Damage and post-radiation reparation processes were studied in cornea epithelium cells of mice irradiated by protons with the energy of 25 MeV and 60Co gamma-rays singly and in 2 fractions. Protons linear energy transfer (LET) was equal to 2.1 keV/microm, dose rate - 0.5 cGy/s. Animals were irradiated singly by 25 and 750 cGy and doubly (25 + 25; 50 + 50; 125 + 125; 250 + 250 cGy) with a 24-hr interval. Investigations were performed in 24, 72 and 120 hrs. after single and in 24 hrs. after double irradiation. Preparations were analyzed with the anaphase technique. 25 MeV protons were shown to cause more severe damages to the chromosomal apparatus in mammal cells including dramatic suppression of cell division and profuse formation of cells with aberrant mitoses as compared with gamma-induced damages. Exchange-type aberrations were more frequent. There was a reliable decrease of the aberrant mitosis rate in consequence of fractionated irradiation by 25 MeV protons and gamma-rays. On passing 24, 72 and 120 hours, coefficients of relative biological effectiveness (RBE) of 25 MeV protons were equal to 1.4 +/- 0.2; 1.3 +/- 0.1; 1.2 +/- 0.1 for the mitotic index and 1.5 +/- 0.1; 1.3 +/- 0.2; 1.1 +/- 0.1 for aberrant mitosis, respectively.

Activation of oxidative stress-regulated Bcl-3 suppresses CTCF in corneal epithelial cells

Epigenetic factor CTCF (CCCTC binding factor) plays important roles in genetic controls of the cell fate. Previous studies found in corneal epithelial cells that CTCF is regulated by epidermal growth factor (EGF) through activation of NF-κB p65/p50. It also found that CTCF is suppressed in ultraviolet (UV) stress-induced corneal epithelial cells. However, it is still unknown how UV stress down-regulates CTCF affecting the cell fate. In the present study, we report that regulation of CTCF by extracellular stress signals is dependent upon activations of an oxidative stress-regulated protein Bcl-3. We found that activated Bcl-3 was able to bind to the κB sites identified in the CTCF promoter region. Bcl-3 was activated by UV irradiation to interact with NF-κB p50 by forming a Bcl-3/p50 heterodimer complex. The Bcl-3/p50 complex suppressed CTCF promoter activity to down-regulate CTCF transcription. Unlike the effect of EGF, UV stress-induced Bcl-3 activation suppressed CTCF activity without involving the IκBα and p65 pathway. Thus, results of the study reveal a novel mechanism for regulatory control of CTCF in UV stress-induced human corneal epithelial cells, which requires activation and formation of Bcl-3/p50 complex through a noncanonical NF-κB pathway.

[The state of epithelial cells and tissues exposed to an electromagnetic field]

Based on the analysis of 56 references available in the Russian and foreign literature, the authors provide information on the mechanism of exposure of tissues and cells to electromagnetic fields. The electromagnetic filed can regulate the orientation of epithelial cell division and cause their directional movement. There are different explanations for such movement. This property may be used in ophthalmology to control corneal epithelial regeneration. This problem has been inadequately investigated.

UV dose-dependent caspase activation in a corneal epithelial cell line

PURPOSE

To characterize the UVB radiation-dependent patterns of caspase activation and cell death in SV 40 immortalized corneal epithelial cells.

METHODS

Cell death in immortalized human corneal epithelial cells (T-HCEC) was induced by exposure to low (50 mJ/cm2) and high (450 mJ/cm2) doses of UVB. Cell death morphology was examined by fluorescence microscopy using the cell death marker propidium iodide (PI). Apoptosis of T-HCEC was analyzed by DNA fragmentation assays, and enzyme activity was measured for caspase 3 and 9 by fluorophotometry. Changes in mitochondrial inner membrane potential were measured by flow cytometry using the fluorescent marker, rhodamine 123. Redistribution of cytochrome c, the upstream trigger of caspase 9, was measured in the cytosol fraction of T-HCEC following irradiation.

RESULTS

PI staining revealed a fragmented staining pattern of the nucleus consistent with apoptosis in detached cells irradiated with low-dose UVB, while cells receiving high dose UVB demonstrated round, well bordered staining of the nucleus. Flow cytometry revealed irreversible mitochondrial damage in the high dose group shown by decreased levels of rhodamine 123 fluorescence. Cells in the low-dose group had intact mitochondrial inner membrane potential, increased cytosolic cytochrome c, and showed a significantly higher rate of DNA fragmentation and caspase activation than the high dose group.

CONCLUSION

Low dose UVB caused cytochrome c redistribution, caspase activation and apoptosis of corneal epithelial cells, which was not observed at high irradiation levels of UVB.

[Infrared cold laser radiation as an antimutagen]

Effects of infrared cold laser radiation (IRCLR) on mutagenesis and proliferation of the corneal epithelium were studied with laboratory white mice subjected to instigated circulatory hypoxia of the brain. The experiment was to reveal whether IRCLR influences the frequency of chromosomal rearrangements and to allow calculation of the corneal cells mitotic index for circulatory brain hypoxia. Laser radiation was shown to reconstitute the normal frequency of chromosomal aberrations as well as the mitotic cycle in epithelial cells of the mice cornea. Data of the experiment are promising from the standpoint of antihypoxic use of IRCLR in ophthalmology.

[Investigation of the processes of post-radiation reparation of the corneal epithelium cells of mice irradiated by helium ions with various LET values]

Biological effectiveness and post-radiation recovery of corneal epithelium cells of mice were studied. Mice were exposed to a broad range of doses from accelerated helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon once and twice with a 24-hr. interval. LET values for these energies were 120 and 0.88 keV/microm, respectively. Gamma-source 137Cs (LET = 0.3 keV/microm) was used as a radiation standard. Animals irradiated by 25-400 sGy were sacrificed in 24 and 72 hrs. by way of cervical dislocation. Total corneal preparations made from enucleated eyeballs were analyzed for the mitotic index and aberrant mitoses using the anaphase method. High damaging properties of accelerated helium ions with the energy of 4 MeV/nucleon were manifested by a considerable reduction of the mitotic index and a more marked rise in the number of aberrant mitoses following the single and repeated exposure. Fractional irradiation by helium ions with the energy of 4 MeV/nucleon resulted in inhibition and even arrest of reparation suggesting additivity of separate radiation fractions. From the dose values that produced the double reduction of the mitotic index, coefficients of the relative biological effectiveness (RBE) for helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon were estimated to be 5.3-8.6 and 1.3-1.8, respectively. In the context of the number of aberrant mitoses, RBE coefficients were significantly lower ranging 2.3-3.5 and 1.1-1.3 for these energies, respectively.

Light Absorption Properties of the Rabbit Cornea Repeatedly Irradiated with UVB Rays

Under normal conditions, the cornea absorbs the majority of UVB (ultraviolet B, 280-320 nm) rays, which is very important for the protection of the inner eye against their damaging effect. Our previous studies have shown that repeated irradiation of the rabbit cornea with UVB rays for 5 days (daily dose of 1.01 J cm(- 2)) caused photokeratitis accompanied by swelling (hydration) of the corneal stroma, thinning of the corneal epithelium and decrease in antioxidants. The purpose of this study was to examine the light absorption properties of such damaged rabbit cornea. Results of both spectrophotometry of the whole corneal buttons and corneal tissue dissolved in sodium hydroxide show that because of above mentioned disturbances, UVB-irradiated cornea absorbs more light throughout the whole measurable UV-VIS spectral range than the normal cornea. Increased corneal thickness (result of hydration), changes of corneal transparency (the cornea becomes grayish) and some increase in protein content all contribute to the increased light absorption of UVB irradiated corneas. We suggest that the UVB-irradiated cornea, although damaged and nearly without antioxidants, might actually through its higher UV absorbance protect the inner eye against further damage from UVB rays.

Pathway-specific effect of caffeine on protection against UV irradiation-induced apoptosis in corneal epithelial cells

PURPOSE

To define the role of molecular interaction between the UV-induced JNK (c-Jun N-terminal kinase) cascade and corneal epithelial cell apoptosis and protection against apoptosis by caffeine.

METHODS

Rabbit and human corneal epithelial cells were cultured in DMEM/F12 medium containing 10% FBS and 5 microg/mL insulin at 37 degrees C in 5% CO(2). DNA fragmentation and ethidium bromide/acridine orange (EB/AO) nuclear staining were performed to detect cell death. Western blot, immunoprecipitation, and kinase assays were used to measure UV-induced mitogen-activated protein (MAP) kinase activity.

RESULTS

UV irradiation-induced apoptosis through apoptosis signal-regulating kinase 1 (ASK1) and MAKK4 (SEK1) upstream from JNK was caffeine sensitive. Caffeine (1,3,7-trimethylxanthine), an agent that is one of the most popular additions to food consumed in the world and a potential enhancer of chemotherapy, effectively protected corneal epithelial cells against apoptosis by its specific effect on the JNK cascade. Theophylline (1,3-dimethylxanthine) exhibited an effect similar to that of caffeine on prevention of UV irradiation-induced apoptosis. However, alterations of either intracellular cAMP or Ca(2+) levels did not alter the effect of caffeine on the JNK signaling pathway. In addition, the blockade of PI3K-like kinases by wortmannin had no impact on the protective effect of caffeine against UV irradiation-induced apoptosis, suggesting that the protective effect of caffeine acts through a specific mechanism involving UV irradiation-induced activation of ASK1 and SEK1. In contrast, caffeine had no effects on melphalan-, hyperosmotic stress-, or IL-1beta-induced activation of the JNK signaling pathway in these cells.

CONCLUSIONS

UV irradiation stress-induced activation of the ASK1-SEK1-JNK signaling pathway leading to apoptosis is a caffeine-sensitive process, and caffeine, as a multifunctional agent in cells, can specifically interact with the pathway to protect against apoptosis.

Carboxymethyl β-glucan Binds to Corneal Epithelial Cells and Increases Cell Adhesion to Laminin and Resistance to Oxidative Stress

PURPOSE

Polysaccharides are frequently used as viscoelastic agents to improve pharmacokinetics of ophthalmic preparations. Recently, polysaccharides from yeast cell walls such as beta-glucans have emerged as bioactive molecules endowed with immunomodulatory and cytoprotective properties. In this study, we investigated the effects of carboxymethyl beta-glucan (CMG), a water-soluble derivative of yeast beta-glucan, on cultured rabbit corneal epithelial cells.

METHODS

We developed a fluorescein-labeled CMG to visualize its binding to corneal cells by means of digital microscopy and image deconvolution. The effects of CMG on adhesion and survival of corneal epithelial cells exposed to noxious stimuli were also studied.

RESULTS

CMG binds defined regions scattered throughout the body of corneal cells, suggesting binding specificity. Tridimensional reconstruction of fluorescence shows that binding is localized mainly at the plasma and nuclear membranes. Interestingly, CMG binding is highly represented at the level of focal adhesion of cells spreading onto laminin. Accordingly, CMG promotes adhesion of corneal epithelial cells to laminin without affecting their proliferation rate. CMG also protects cells from oxidative stress-dependent cell death, being ineffective in preventing ultraviolet B cytotoxicity.

CONCLUSIONS

Data show that CMG dynamically binds to corneal epithelial cells, promoting cell adhesion and resistance to oxidative stress.

UV absorption in human oral mucosal epithelial sheets for ocular surface reconstruction

BACKGROUND

Ocular surface reconstruction with autologous oral mucosal epithelium has attracted attention as a novel treatment strategy that avoids allograft rejection.

OBJECTIVES

To evaluate the absorption of ultraviolet (UV) A or B irradiation by human oral mucosal epithelium cultured on human amniotic membrane.

METHODS

Human oral mucosal and limbal epithelial cells were co-cultured on amniotic membrane with inactivated 3T3 fibroblasts. The cell sheets were also subjected to UV-A (365 nm) or UV-B (302 nm) irradiation at energy levels ranging from 50 to 800 microW/cm2, and the UV absorption rate was measured with a UV irradiation meter.

RESULTS

Cultured oral mucosal epithelium had a structure with 3-5 layers of cells, consistent with the histological features of cultured corneal limbal epithelium after 4 weeks. The decrease in UV-A absorption of cultivated oral mucosal epithelium ranged from 25 to 36% of that for cultured corneal epithelium. The increase in UV-B absorption by cultured oral mucosal epithelium between 200 and 800 microW/cm2 was approximately 145% of that for cultured corneal limbal epithelium.

CONCLUSION

Our data demonstrated that cultured oral mucosal epithelium has low UV-A and high UV-B absorption capacity as compared with those of cultured corneal epithelium, suggesting that oral mucosal epithelium can compensate for UV absorption of corneal epithelium.

Phototoxic effects of commercial photographic flash lamp on rat eyes

BACKGROUND

To determine whether exposure of the cornea and retina of rats to flashes from a commercial photographic flash lamp is phototoxic.

METHODS

Sprague-Dawley rats were exposed to 10, 100, or 1,000 flashes of the OPTICAM 16M photographic flash lamp (Fujikoeki, Japan) placed 0.1, 1, or 3 m from the eyes. Corneal damage was assessed by a fluorescein staining score, and the retinal damage by eletroretinography (ERG) and histology before and 24 h after exposure.

RESULTS

Exposure of the eyes to 1,000 flashes at 0.1 m increased the fluorescein staining score significantly (P = 0.009, the Mann-Whitney test). Scanning electron microscopy (SEM) of the cornea showed a detachment of the epithelial cells from the surface after this exposure. The amplitude of the a-wave was decreased significantly by 23.0% (P = 0.026) of the amplitude before the exposure, and the b-wave by 19.7% (P = 0.0478) following 1,000 flashes at 0.1 m but not by the other exposures. TUNEL-positive cells were present in the outer nuclear layer only after the extreme exposure, but no significant decrease in retinal thickness was seen under any condition. The fluorescein staining score and ERGs recovered to control levels within 1 week.

CONCLUSIONS

Light exposure to a photographic flash lamp does not induce damage to the cornea and retina except when they are exposed to 1,000 flashes at 0.1 m.

Transglutaminase Participates in UVB-Induced Cell Death Pathways in Human Corneal Epithelial Cells

PURPOSE

Ultraviolet light (UVB) is known to cause apoptosis in human corneal epithelial cells. This study evaluates the role of transglutaminase in regulating tumor necrosis factor (TNF) receptor clustering as well as caspase activation in UVB-induced apoptosis in human corneal epithelial cells.

METHODS

A human corneal epithelial cell line was used. A single dose of UVB (20 mJ/cm2) was used as a stimulus. Cell viability and cell death were investigated by MTT, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL), and caspase-3 assays. Immunofluorescent staining was used to investigate TNF receptor-I clustering at various time intervals after UVB. Short interfering RNA was used to knock down transglutaminase-2 expression. Fluorescein-cadaverine uptake was used to assess transglutaminase activity. A noncovalent peptide delivery system was used to transfect guinea pig liver transglutaminase into corneal epithelial cells.

RESULTS

UVB increased transglutaminase activity, reduced cell viability, and increased TUNEL staining. UVB or TNF-alpha promoted TNF-receptor-I clustering, a process inhibited by the transglutaminase inhibitor, mono-dansyl cadaverine. UVB also increased activated caspase-3, in a manner suppressible by mono-dansyl cadaverine. Intracellular delivery of exogenous transglutaminase markedly increase caspase-3 activation compared with the vehicle control.

CONCLUSIONS

Transglutaminase enzymatic activity is involved in corneal epithelial cell death after UVB and appears to participate in two steps regulating this process, clustering of TNF receptor-I and caspase-3 activation.

Stress-induced corneal epithelial apoptosis mediated by K+ channel activation

One of the functional roles of the corneal epithelial layer is to protect the cornea, lens and other underlying ocular structures from damages caused by environmental insults. It is important for corneal epithelial cells to maintain this function by undergoing continuous renewal through a dynamic process of wound healing. Previous studies in corneal epithelial cells have provided substantial evidence showing that environmental insults, such as ultraviolet (UV) irradiation and other biohazards, can induce stress-related cellular responses resulting in apoptosis and thus interrupt the dynamic process of wound healing. We found that UV irradiation-induced apoptotic effects in corneal epithelial cells are started by the hyperactivation of K+ channels in the cell membrane resulting in a fast loss of intracellular K+ ions. Recent studies provide further evidence indicating that these complex responses in corneal epithelial cells are resulted from the activation of stress-related signaling pathways mediated by K+ channel activity. The effect of UV irradiation on corneal epithelial cell fate shares common signaling mechanisms involving the activation of intracellular responses that are often activated by the stimulation of various cytokines. One piece of evidence for making this distinction is that at early times UV irradiation activates a Kv3.4 channel in corneal epithelial cells to elicit activation of c-Jun N-terminal kinase cascades and p53 activation leading to cell cycle arrest and apoptosis. The hypothetic model is that UV-induced potassium channel hyperactivity as an early event initiates fast cell shrinkages due to the loss of intracellular potassium, resulting in the activation of scaffolding protein kinases and cytoskeleton reorganizations. This review article presents important control mechanisms that determine Kv channel activity-mediated cellular responses in corneal epithelial cells, involving activation of stress-induced signaling pathways, arrests of cell cycle progression and/or induction of apoptosis.

UVB Irradiation-Induced Changes in the 27-kd Heat Shock Protein (HSP27) in Human Corneal Epithelial Cells

PURPOSE

This study investigated the presence of the 27-kd heat shock protein (HSP27) and its responses to ultraviolet B (UVB) irradiation in human corneal epithelium and in cultured corneal epithelial cells.

METHODS

Human corneal epithelial cells including presumed corneal epithelial stem cells were cultured in vitro. HSP27 expression and intracellular localization in normal corneas or cultured corneal cells were examined using immunofluorescence staining. The expression of HSP27 in cultured corneal cells was also detected using western blotting, and the phosphorylated isoforms of HSP27 were identified using isoelectric focusing.

RESULTS

In normal corneal tissue, HSP27 was present in limbal basal and suprabasilar epithelial cells. In cultured epithelial corneal cells, HSP27 expression was heterogeneous: Some cells expressed virtually no HSP27 and others showed relatively strong expression. HSP27 was localized to the cytoplasm in nonstressed cells and translocated to the perinuclear and nuclear areas after UVB irradiation. UVB irradiation also induced the phosphorylation of HSP27, resulting in the increase in monophosphorylated isoform and formation of biphosphorylated isoform. UV induced the phosphorylation of HSP27 apparently through activation of p38 mitogen-activated protein kinase.

CONCLUSION

HSP27 is present mainly as a nonphosphorylated isoform in corneal epithelium and cultured corneal epithelial cells under nonstressed conditions. The constitutional expression of HSP27 suggests that it plays a physiologic role in the cornea. After UVB irradiation, HSP27 undergoes rapid phosphorylation and translocation. This stress response may be related to a protective role of HSP27 for survival of UVB-exposed corneal cells.

Effect of CTCF-binding motif on regulation of PAX6 transcription

PURPOSE

Previous studies indicate that the CCCTC binding transcription factor (CTCF) regulates homeobox PAX6 gene transcription in corneal epithelial cells. In the present study, the effect was investigated of CTCF activity on PAX6 transcription through interaction with five essential motifs located in an 80-bp region upstream from the PAX6 P0 promoter.

METHODS

An electrophoretic mobility shift assay (EMSA) was used to determine the interaction between CTCF and DNA binding motifs. DNA mutagenesis was applied in identification of DNA motif functions. Immunohistochemistry and Western blot analyses were performed to detect the stress-induced effect on CTCF activity.

RESULTS

The five identified CTCF-binding motifs were mutated one by one or in different combinations. Interactions of CTCF with these mutated motifs were determined by EMSA and DNA-binding competitions. All five CCCTC motifs were functional for the CTCF binding and DNA-binding activity of CTCF was proportionally decreased after increases in mutations of motif numbers. In addition, ultraviolet (UV) irradiation and epidermal growth factor (EGF) induced suppression and activation of CTCF expression, respectively. Effects of UV and EGF induction were due to alterations in CTCF expression and activity resulting in changes in CTCF DNA binding activity to the PAX6 promoter region detected by EMSA.

CONCLUSIONS

These findings indicate that CTCF regulates PAX6 expression in response to stress-induced conditions and that the molecular base of CTCF controlling PAX6 expression is through five functional and specific motifs in the region upstream from the PAX6 P0 promoter in corneal epithelial cells.

Expression and regulation of cornified envelope proteins in human corneal epithelium

PURPOSE

Stratified squamous epithelial cells assemble a specialized protective barrier structure on their periphery, termed the cornified envelope. The purpose of this study was to evaluate the presence and distribution of cornified envelope precursors in human corneal epithelium, their expression in human corneal epithelial cell cultures, and the effect of ultraviolet radiation (UVB) and transglutaminase (TG) inhibition on their expression.

METHODS

Tissue distribution of small proline-rich proteins (SPRRs) and filaggrin and involucrin was studied in human cornea sections by immunofluorescence staining. Primary human corneal epithelial cells (HCECs) from limbal explants were used in cell culture experiments. A single dose of UVB at 20 mJ/cm2 was used to stimulate these cells, in the presence or absence of mono-dansyl cadaverine (MDC), a TG inhibitor. SPRR2 and involucrin protein levels were studied by immunofluorescence staining and Western blot analysis. Gene expression of 12 proteins was investigated by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

In human cornea tissue, SPRR1, SPRR2, filaggrin, and involucrin protein expression were detected in the central and peripheral corneal and limbal epithelium. In HCECs, SPRR2 and involucrin proteins were detected in the cytosolic fraction, and involucrin levels increased after UVB. Both SPRR2 and involucrin levels accumulated in the presence of MDC. Nine genes including involucrin, SPRR (types 1A, 1B, 2A, 2B, and 3), late envelope protein (LEP) 1 and 16, and filaggrin were expressed by HCECs. SPRR 4, loricrin, and LEP 6 transcripts were not detected. UVB downregulated SPRR (2A, 2B) and LEP 1 transcripts.

CONCLUSIONS

Various envelope precursors are expressed in human corneal epithelium and in HCECs, acute UVB stress differentially alters their expression in HCECs. The expression of envelope precursors and their rapid modulation by UVB supports the role of these proteins in the regulation of ocular surface stress. TG function may be relevant in the regulation of soluble precursors in UVB-stimulated corneal epithelium.

Analysis of gene regulation in rabbit corneal epithelial cells induced by ultraviolet radiation

Ultraviolet (UV)-induced cataracts are becoming a major environmental health concern because of the possible decrease in the stratospheric ozone layer. Experiments were designed to isolate gene(s) affected by UV irradiation in rabbit cornea tissues using fluorescent differential display-reverse transcription-polymerase chain reaction (FDDRT-PCR). The epithelial cells were grown in standard medium for 2 or 4 hours post treatment. Cornea epithelial cells were irradiated with UVB for 20 minutes. RNA was extracted and amplified by reverse transcriptase-polymerase chain reaction using poly A+ specific anchoring primers and random arbitrary primers. Polyacrylamide gel electrophoresis revealed several differentially expressed genes in untreated versus UV irradiated cells. Complimentary DNA (cDNA) fragments resulting from fluorescent differentially expressed mRNAs were eluted from the gel and re-amplified. The re-amplified PCR products were cloned directly into the PCR-TRAP cloning system. These data showed that FDDRT-PCR is a useful technique to elucidate UV-regulated gene expressions. Future experiments will involve sequence analysis of cloned inserts. The identification of these genes through sequence analysis could lead to a better understanding of cataract formation via DNA damage and mechanisms of prevention.

Atomic force microscopy analysis of normal and photoablated porcine corneas

We showed the capabilities and accuracy of atomic force microscopy (AFM) techniques for imaging and analyzing the corneal epithelium and the photoablated corneal stroma. Eight normal porcine corneas, half of which were ablated using a scanning-spot excimer laser, were examined. All the corneas were imaged in balanced salt solution after fixation in glutaraldehyde. In the normal untreated corneas we observed the epithelial surface showing the typical polygonal cells and presenting numerous microprojections. The superficial epithelial cells were classified in three types as a result of the anterior-surface roughness measurements. AFM images of the photoablated corneal specimens showed undulations and granule-like features on the ablated stromal surface, specific to 193-nm ArF laser irradiation. Nevertheless, the quantitative analysis confirmed the precision of excimer laser surgery in removing sub-micrometric amounts of tissue. AFM showed to be a high-resolved imaging tool for the scanning of both native as well as photoablated corneal specimens. Also, this technique permits precise topographic analysis of the corneal plane, in the nanometric scale, of which smoothness is an important physical characteristic and necessary to achieve an optimal optical quality of the eye.

UV-mediated DNA strand breaks in corneal epithelial cells assessed using the comet assay procedure

Ultraviolet (UV)-mediated DNA damage in various tissues has been well documented. However, research on the damaging effect of UV irradiation on the DNA of corneal epithelium is scarce, even though this is of interest because the cornea is directly exposed to damaging solar (UV) radiation. In this study, we developed a corneal epithelium Comet assay model to assess the background DNA damage (as strand breaks) in cells retrieved from different layers of the porcine corneal epithelium, and to investigate the effect of UV irradiation on DNA damage in corneal epithelial cells. Results show that the background DNA strand breaks decreased significantly (P < 0.001) toward deeper layers of the epithelium. Exposure to the same intensity (0.216 J/cm2) of UVA, UVB and UVC caused a significant (P < 0.001) increase in DNA strand breaks of deeper-layer cells: mean +/- SD %DNA scores (10 gels per treatment, with 100 irradiated cells scored per gel) were 10.2% +/- 1.4% for UVA, 27.4% +/- 4.6% for UVB, and 14.7% +/- 1.8% for UVC compared with 4.2% +/- 0.5% for controls (ambient room light). This study has shown for the first time that the Comet assay for DNA strand breaks can be used successfully with corneal epithelial cells. This report will support future studies investigating environmental influences on corneal health and the assessment of possible protective strategies, and in applying DNA lesion-specific versions of the Comet assay in this corneal epithelial cell model.

Corneal keratocytes: phenotypic and species differences in abundant protein expression and in vitro light-scattering

PURPOSE

Previous studies suggest that corneal haze after injury involves changes in the light-scattering properties of keratocytes that are possibly linked to the abundant expression of water-soluble proteins. The purpose of this study was to determine the protein expression pattern of keratocytes from different species and different cultured rabbit keratocyte phenotypes and to assess differences in light-scattering in vitro.

METHODS

Water-soluble proteins were isolated from corneal epithelial cells and keratocytes of several species, including human (Hu), mouse (Mo), rabbit (Ra), chicken (Ch), and pig (P) and different cultured rabbit keratocyte phenotypes. Proteins were then characterized by SDS-PAGE, tryptic peptide sequence analysis, and Western blot analysis. Light-scattering and actin organization from cultured cells were determined with confocal reflectance and fluorescence microscopy, respectively.

RESULTS

Protein expression patterns varied substantially between species and cell types, with five new abundantly expressed proteins identified including, LDH (Ra, Ch), G3PDH (Hu, Ch), pyruvate kinase (Ch), Annexin II (Ch), and protein disulfide isomerase (Ch). Different rabbit keratocyte phenotypes also showed different levels of expression of ALDH1A1 and TKT, with myofibroblasts showing the greatest reduction. Myofibroblasts showed significantly greater (P < 0.05) light-scattering but also showed the greatest organization of actin filaments.

CONCLUSIONS

Abundant protein expression is a characteristic feature of corneal keratocytes that is lost when cells are phenotypically modulated in culture. Greater light-scattering by myofibroblasts also provides support for a link between cellular transparency and haze after injury that is possibly related to loss of protein expression or development of prominent actin filament bundles.

Translocation of Nuclear Factor-κB on Corneal Epithelial Cells Induced by Ultraviolet B Irradiation

PURPOSE

This study was performed to elucidate the role of nuclear factor-kappaB (NF-kappaB) in the death of corneal epithelial cells after ultraviolet (UV) irradiation.

METHODS

Simian virus 40-transfected human corneal epithelial cells (T-HCECs) were used in this study. Cell cultures were irradiated with a UVB (312 nm) source located 10 cm from the bottom of the slides for 10, 20, 30, or 40 s. Cytotoxicity was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. Translocation of NF-kappaB was examined by immunocytochemistry using anti-NF-kappaB p65 antibody and electrophoretic mobility shift assay (EMSA). Sulfasalazine and SN-50, specific NF-kappaB inhibitors, were used to confirm the role of NF-kappaB by pretreating samples for 30 min before UV irradiation, after which cytotoxicity and NF-kappaB translocation were evaluated.

RESULTS

When T-HCECs were irradiated with UVB, translocation of NF-kappaB was observed with immunocytochemistry. These translocations peaked 2 h after UV irradiation during EMSA. When pretreated with sulfasalazine or SN-50, the translocation of NF-kappaB was blocked. Cellular death after UV irradiation was also markedly blocked by sulfasalazine.

CONCLUSION

These findings suggest that NF-kappaB plays an important role in cellular death after UV irradiation.

Ultraviolet irradiation-induced K(+) channel activity involving p53 activation in corneal epithelial cells

Recent studies from our lab found that ultraviolet (UV) irradiation induces a voltage-gated potassium (Kv) channel activation and subsequently activates JNK signaling pathway resulting in apoptosis. The present study in rabbit corneal epithelial (RCE) cells is to investigate mechanisms of UV irradiation-induced Kv channel activity involving p53 activation in parallel to DNA damage-induced signaling pathway. UV irradiation-induced signaling events were characterized by measurements of JNK activation and further downstream p53 phosphorylation. UV irradiation elicited an early response in the cell membrane through activation of Kv channels to activate the JNK signaling pathway and p53 phosphorylation. Exposure of RCE cells to UV irradiation within a few min resulted in JNK and p53 activations that were markedly inhibited by suppression of Kv channel activity. However, suppression of Kv channel activity failed to prevent p53 activation induced by extended DNA damages through prolonging UV exposure time (more than 15 min). In addition, caffeine inhibited UV-induced activation of SEK, an upstream MAPK kinase of JNK, resulting in suppression of both Kv channel-involved and DNA damage-induced p53 activation. Our results indicate in these cells that UV irradiation induces earlier and later intracellular events that link to activation of JNK and p53. The early event in response to UV irradiation is initiated by activating Kv channels in the cell membrane, and the later event is predominated by UV irradiation-caused DNA damage.

Carteolol hydrochloride protects human corneal epithelial cells from UVB-induced damage in vitro

PURPOSE

To investigate whether carteolol hydrochloride has protective effects against ultraviolet B (UVB)-induced damage in human corneal epithelial cells (HCECs).

METHODS

Cultured HCECs were exposed to a single dose of UVB 300 mJ/cm, and the cell viability was measured 12 hours after the UVB irradiation using a cell-counting kit. Test samples at 0.01-1.0 mmol/L (carteolol hydrochloride, timolol maleate, betaxolol hydrochloride, levobunolol hydrochloride, or nipradilol) were added to the HCECs before, during, or after UVB irradiation. UV absorption spectra for each drug sample were determined using a spectrophotometer. Hydrogen peroxide (H2O2) and carteolol hydrochloride were simultaneously added to the HCECs for 10 minutes, and the cell viability was measured 12 hours later. The ability of carteolol hydrochloride to scavenge superoxide anion (O2) and singlet oxygen (O2) was investigated using the MCLA chemiluminescence method.

RESULTS

UVB irradiation decreased the number of viable HCECs in a dose-dependent manner. Carteolol hydrochloride at 1 mmol/L attenuated the UVB-induced cell damage when added before, during, or after UVB irradiation (P<0.01). Levobunolol hydrochloride at 1 mmol/L (P<0.01) added during or after irradiation and timolol maleate at 0.1 mmol/L or higher (P<0.05) added during irradiation attenuated the UVB-induced cell damage. Betaxolol hydrochloride and nipradilol had no effect. The UV absorption spectra of timolol maleate and levobunolol hydrochloride overlapped with the UVB wavelength spectrum, while carteolol hydrochloride, betaxolol hydrochloride, and nipradilol showed a partial overlap. Carteolol hydrochloride at 1 mmol/L (P<0.05) significantly inhibited H2O2-induced cell damage and was able to scavenge O2 (EC50 value: 48 mmol/L).

CONCLUSIONS

These data strongly suggest that carteolol hydrochloride has a protective action against UVB-induced HCEC damage, and its radical scavenging ability may be an important basis for this effect.

Protective role of corneal epithelium against ultraviolet radiation damage

PURPOSE

It is known that the corneal epithelium strongly absorbs ultraviolet radiation (UVR). The aim of the present study was to examine the protective role of corneal epithelium against UVR damage by comparing the biological effect of UVR exposure on whole corneas with that on de-epithelialized corneas.

METHODS

Six New Zealand albino rabbit corneas were exposed to UVR centred around 280 nm at a dose that causes biomicroscopically significant keratitis (012 J/cm(2)). Three corneas underwent manual de-epithelialization prior to UVR exposure. A control group of three rabbits underwent only manual de-epithelialization. The animals were killed 76 hours after treatment. The corneas were stained with haematoxylin and evaluated by light microscopy.

RESULTS

Corneas that underwent only the exposure to UVR showed a loss of epithelial cells in the treated area. No damage to keratocytes or the stroma was detected. Corneas that underwent manual de-epithelialization showed a loss of epithelial cells, and also keratocytes in the anterior quarter of the corneal stroma. However, corneas that were exposed to UVR after manual de-epithelialization showed very deep stromal damage. The keratocytes disappeared through the entire thickness of the stroma in the UVR-exposed area.

CONCLUSION

Exposure to UVR at 280 nm alone does not result in any deep damage to the corneal stroma and keratocytes. Manual de-epithelialization causes the disappearance of anterior keratocytes. However, the stromal damage caused by UVR in the de-epithelialized corneas was very deep. The corneal epithelium serves to protect the deeper corneal structures against UVR damage, probably by absorbing a substantial amount of the UVR energy applied to the eye.

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.

Identification of genes responsive to UV-A radiation in human lens epithelial cells using complementary DNA microarrays

UV-A radiation produces cataract in animals, enhances photoaging of the lens and skin and increases the phototoxicity of drugs. However, the nature of genes that are activated or repressed after cellular exposure to UV-A radiation remains enigmatic. Because lens epithelial cells exposed to UV-A radiation undergo apoptosis 4 h after exposure to the stress, we sought to establish the change in gene expression in cells by UV-A radiation using gene expression profiling using complementary DNA microarrays containing about 12 000 genes. We identified 78 genes abnormally expressed in UV-A-irradiated cells (showing >2.5-fold change at P < 0.05). These genes are implicated in various biological processes, including signal transduction and nucleic acid binding, and genes encoding enzymes. A majority of the genes were downregulated. Our analysis revealed that the expression of genes for the transcription factors ATF-3 and Pilot increased four-fold, whereas the gene for the apoptosis regulator NAPOR-1 decreased five-fold. These changes were confirmed by real-time quantitative reverse transcriptase-polymerase chain reaction. The calpain large polypeptide 3 (CANP3) gene also increased nine-fold after UV-A radiation. In addition, peroxisomal biogenesis factor 7, glucocorticoid receptor-alpha and tumor-associated calcium signal transducer genes decreased three- to eight-fold. Western blot analysis further confirmed the increase in protein expression of ATF-3 and CANP3 and decreased expression of glucocorticoid receptor-alpha in the irradiated cells. Surprisingly, most of these genes had not been previously shown to be modulated by UV-A radiation. Our results show that human lens epithelial cells respond to a single dose of UV-A radiation by enhancing or suppressing functionally similar sets of genes, some of which have opposing functions, around the time at which apoptosis occurs. These studies support the intriguing concept that activation of competing pathways favoring either cell survival or death is a means to coordinate the response of cells to UV-A stress.

corneal epithelial injury thresholds for exposures to 1.54 microm radiation-dependence on beam diameter

Corneal epithelial injury thresholds have been determined for exposures to 1.54 mum infrared radiation from an Erbium fiber laser. Thresholds were determined for beam diameters from 0.05 to 0.7 cm for exposures having durations from approximately 1 to 100 s and for a fixed beam diameter of 0.1 cm for exposures with durations between 0.036 and 0.26 s. Near-threshold damage appeared within 30 min post-exposure. There was no evidence of latent damage from lesser exposures appearing up to 24-48 h post-exposure. The dependence of the threshold radiant exposures on laser beam diameter for exposures >1 s provides strong evidence supporting a critical temperature damage model. However, the shorter exposures are not in accord with a critical temperature damage model. Thresholds for exposures longer than 1 s are greater than 10 times the maximum permissible exposure (MPE) in ANSI Z-136.5-2000; however, the safety factor decreases to less than 10 for exposures less than 0.1 s with a 0.1-cm-diameter beam.

Nuclear ferritin in corneal epithelial cells: tissue-specific nuclear transport and protection from UV-damage

We have identified the heavy chain of ferritin as a developmentally regulated nuclear protein of embryonic chicken corneal epithelial cells. The nuclear ferritin is assembled into a supramolecular form that is indistinguishable from the cytoplasmic form of ferritin found in other cell types. Thus it most likely has iron-sequestering capabilities. Free iron, via the Fenton reaction, is known to exacerbate UV-induced and other oxidative damage to cellular components, including DNA. Since corneal epithelial cells are constantly exposed to UV light, we hypothesized that the nuclear ferritin might protect the DNA of these cells from free radical damage. To test this possibility, primary cultures of cells from corneal epithelium and other tissues were UV irradiated, and damage to DNA was detected by an in situ 3'-end labeling assay. Consistent with the hypothesis, corneal epithelial cells with nuclear ferritin had significantly less DNA breakage than the other cells types examined. However, when the expression of nuclear ferritin was inhibited the cells now became much more susceptible to UV-induced DNA damage. Since ferritin is normally cytoplasmic, corneal epithelial cells must have a mechanism that effects its nuclear localization. We have determined that this involves a nuclear transport molecule which binds to ferritin and carries it into the nucleus. This transporter, which we have termed ferritoid for its similarity to ferritin, has at least two domains. One domain is ferritin-like and is responsible for binding the ferritin; the other domain contains a nuclear localization signal that is responsible for effecting the nuclear transport. Therefore, it seems that corneal epithelial cells have evolved a novel, nuclear ferritin-based mechanism for protecting their DNA against UV damage. In addition, since ferritoid is structurally similar to ferritin, it may represent an example of a nuclear transporter that evolved from the molecule it transports (i.e., ferritin).

Long-Term Changes in Rabbit Cornea After Ionizing Radiation

PURPOSE

To investigate long-term changes in the cornea after ionizing irradiation in rabbits.

METHODS

Mature albino rabbits (n = 4) were unilaterally irradiated with 20 Gy of x-rays. The contralateral eye served as a control. The rabbits were examined with slit-lamp biomicroscopy for 5 years. The eyes were then enucleated for histopathologic examinations with light microscopy and transmission electron microscopy.

RESULTS

On biomicroscopy, there was no corneal abnormality during the 5-year follow-up period. On histopathology, no abnormality was observed in the corneal epithelium. In the endothelium, a vacuole-like structure was recognized by light microscopy, and transmission electron microscopy revealed marked enlargement of intercellular space and anamorphosis of the nuclei.

CONCLUSION

Moderate x-ray irradiation to rabbit eye did not induce any long-term damage to the corneal epithelium, but the endothelium demonstrated persistent and irreversible damage, which was observed even 5 years after irradiation.

Measurement of small-signal absorption coefficient and absorption cross section of collagen for 193-nm excimer laser light and the role of collagen in tissue ablation

A 193-nm ArF excimer laser transmission was measured at subablative fluence through varying strength solutions of dissolved collagen, yielding an absorption cross section of 1.14 x 10(-17) cm2 for the peptide bond, which accounts for 96% of the total collagen attenuation that is based on additional transmission measurements through solutions of isolated constituent amino acids. The measured absorption cross sections, in combination with typical corneal tissue composition, yield a predicted corneal tissue absorption coefficient of 16,000 cm(-1). In addition, dry collagen films were prepared and ablation-rate data were recorded as a function of laser fluence. Ablation rates were modeled by use of a Beer-Lambert blow-off model, incorporating a measured ablation threshold and an absorption coefficient that are based on the measured collagen absorption cross section and the film bond density. The measured ablation rates and those predicted by the model were in very good agreement. The experiments suggest that collagen-based absorption coefficients are consistent with predicted corneal tissue ablation rates and previously observed dynamic changes in tissue properties under ablative conditions.

[Effects of low-dose accelerated charged particles of varying LET on cytogenetic changes in comeal epithelium cells in mice]

Effects of low-dose heavy charged particles (HCP) of varying LET on quantitative and qualitative changes in chromosomes of the comeal epithelium cells were studied in mice. Cytogenetic damages in the comeal epithelium cells were analyzed after irradiation by ions of helium and carbon with an energy of 300 MeV/nucleon (LET = 1.36 and 12.6 keV/microm), and 137Cs gamma-rays with the doses from 5 to 200 Gy. Accelerated nuclei were shown to be more effective. On the basis of aberrant mitosis rate, RBE values for helium and carbon ions in 24, 72 and 120 hrs. after irradiation were 6.0; 3.6 and 2.2 for helium ions and 7.0; 3.8 and 2.4 for carbon ions, respectively. The dose region of 20-30 Gy turned to be dose-independent. It was established that the period of chromosomal aberration sustenance in cells is also LET-dependent.

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.

[Cell loss in the posterior corneal epithelium after cataract extraction by Nd:YAG laser with wave length 1.44 mcm]

The purpose of the case study, as described in the paper, was to evaluate the cell loss in the corneal posterior epithelium (CPE) after laser cataract extraction (LCE) by means of a new laser unit designed on the basis of ND:YAG laser with a wave length of 1.44 microns. The conditions of 59 eyes with high (degrees 3-4) and extra high (degree 5) lens density were analyzed preoperatively and 3 months after LCE. Group 1 comprised 51 surgical cases, which were ideal in the technical respect; Group 2 comprised 8 surgical cases involving an intraoperative short-time lifting of the fragmentized lens mass into the eye anterior chamber during aspiration. The method of contactless endothelial biomicroscopy ("SP-1000" unit, "Topcon Co.", Japan) was made use of. According to the obtained results, it can be stated: the CPE cell loss made 1-9% (4.69 +/- 0.7%) and 1-18% (9.4 +/- 8.4%) in Groups 1 and 2, respectively. The total energy exposition level to laser radiation is the most significant factor affecting the CPE cell loss. The pulse energy radiation level did not affect the CPE cell loss. The corneal posterior surface was subject to a highly adverse impact in the fragmentation of brown cataracts. Finally, the results are indicative of an insignificant surgical trauma in LCE.

Specular microscopic study of X-ray-irradiated rabbit cornea

PURPOSE

To investigate the influence of ionizing radiation on the corneal epithelium and endothelium of rabbit eyes.

METHODS

Five healthy mature albino rabbits were unilaterally irradiated with 20 Gy of X-rays (250 kV, 12 mA). Slit-lamp biomicroscopic observation and specular microscopic examination of the corneal epithelium and endothelium were carried out before and 1, 4, 8, 12, 16, 20, 24, and 36 weeks after irradiation. We evaluated mean area of the superficial corneal epithelial cells, mean area and the percentage of hexagonal cells of the corneal endothelial cells, and corneal thickness. The statistical difference between the irradiated and control eyes was assessed using paired t-test.

RESULTS

All animals developed cataract within 24 weeks. Slit-lamp biomicroscopy showed no apparent corneal abnormalities over the 36-week follow-up period. Specular microscopy revealed a significant enlargement of the superficial corneal epithelial cells from 4 to 12 weeks after irradiation (P<0.01), which disappeared at 16 weeks post-irradiation. Specular microscopy of the corneal endothelium showed enlargement and morphological alterations of the cells beginning 8 weeks after irradiation (P<0.05). These changes persisted throughout the study period. There were no statistically significant changes in corneal thickness.

CONCLUSION

After X-ray radiation of 20 Gy, transient damage occurred in the corneal epithelium, while delayed and irreversible changes were seen in the endothelium.

UV-B induced production of MMP-2 and MMP-9 in human corneal cells

The purpose of this study was to determine the production of metalloproteinases (MMP) 2 and 9 following UV-B irradiation in human corneal epithelial cells and fibroblasts. Epithelial cells and fibroblasts were separated from human donor corneas and exposed to UV-B lamp irradiation for 20, 40, 80 and 120 s. Media samples were collected at 8, 24, 48 and 72 h and gelatinase A and B production was assayed by the ELISA test. Statistical significance of production was assessed by the paired t-test. Increased production of MMP-2 was found in human corneal fibroblasts in response to UV-B irradiation. A statistically significant production of MMP-2 was not observed in human corneal epithelial cells following UV-B exposure. We did not detect any increase in MMP-9 after irradiation in either epithelial cells or fibroblasts. MMP-2 is produced by the corneal fibroblasts in the acute phase after UV-B irradiation. MMP-9 is not released in vitro following UV-B irradiation damage and therefore does not directly participate in the pathophysiology of acute photokeratitis.

Impact of the environment on the mammalian corneal epithelium

PURPOSE

To evaluate whether the content of ascorbic acid in the corneal epithelium and aqueous humor reflects seasonal fluctuations in parallel with environmental changes.

METHODS

Reindeer, cattle, rabbits, and humans were examined, to cover a broad spectrum of overlapping habitats. Ascorbic acid was determined by high-performance liquid chromatography. The thickness of the corneal epithelium was measured, and the number of cells was counted in the tissue sections.

RESULTS

Three groups of reindeer eyes were used, two of them collected during summer, the third group during winter. Ascorbate content did not show seasonal variation in either the corneal epithelium or the aqueous humor, whereas epithelial thickness and number of cells decreased significantly from summer to winter. In cattle, ascorbate content, thickness of the epithelium, and number of cells were lower in animals tended indoors compared with those tended outdoors, whereas ascorbate level in the aqueous humor remained similar in both cases. The rabbit showed significantly reduced ascorbate content in the corneal epithelium but not in the aqueous humor in tarsorrhaphy-treated eyes. This procedure did not change epithelial thickness, but the number of cells was slightly increased. The mean epithelial thickness in human corneas successively decreased with increasing latitude and decreasing radiation exposure from the summer season in Oslo to the midnight sun, polar night, conditions in Tromsø, 10 degrees far north, although the differences did not reach statistical significance.

CONCLUSIONS

Ambient radiation is needed to sustain high ascorbic acid concentration in the corneal epithelium. Corneal epithelial thickness and number of cells are prone to seasonal fluctuations regulated by ambient radiation. In contrast, ascorbate content of the aqueous humor is uninfluenced by environmental change. It is suggested that seasonal adaptation of mammalian corneal epithelium in response to variation in ambient radiation may be nature's strategy for countering radiation damage to the eye.

The radiobiological effects of heavy ions on mammalian cells and bacteria

The radiobiological effects of heavy ions have been studied in experiments with mouse corneal epithelium, liver cells of rats irradiated in vivo, and the bacterium Escherichia coli B. From exposure of E. coli B to radiations with different LET, the effectiveness of the modifying influence of anoxia and some other radioprotectors has been determined.

Investigation of radiation sensitivity in mammals under long duration weightlessness

Preliminary results of the radiobiological experiments carried out on the biosatellite Cosmos 690 with a radiation exposure unit on board are presented. The duration of the satellite flight was 20.5 days. On the tenth day of the flight 35 rats were exposed on board the satellite to 220 or 800 rads of gamma radiation. Comparison of data obtained in test and control groups of animals has shown that under the influence of space flight factors a somewhat more severe radiation injury develops than in on-ground conditions.