Is there a glucocorticoid receptor in the bovine lens?

The safety of intraocular usage of aspirin

PURPOSE

To determine the effects of intravitreally injected aspirin on normal ocular tissues.

METHODS

Six eyes of 3 rabbits as a control group, 18 eyes of 9 albino rabbits which were injected aspirin intravitreally were studied. In the control group, the same volume of balanced salt solution (BSS) as in drug groups were injected. Clinical examination methods including biomicroscopy, indirect ophthalmoscopy, and Schiotz tonometry, electrophysiological test including ERG, and histopathological examination including light microscopy were used to evaluate the ocular effects after drug injections. All the study tests were performed before the injections and 1 week, 1 month, and 3 months after the injections as well.

RESULTS

No significant toxicity was determined after injection in terms of the clinical examination methods in all eyes. Cataracts were observed in 27.7% (5/18) of the eyes in the study group. All cataracts in 5 eyes disappeared at the end of three months. In tonometry, no value out of the normal range of rabbits (17.5 ± 3.1 mmHg) was observed. No toxicity sign was observed at electrophysiological and histopathological evaluations.

CONCLUSION

After intravitreal injection of aspirin, no significant toxicity sign was observed other than a reversible cataract. Thus, intravitreal aspirin injections may be an additional or alternative treatment option for several anterior or posterior segment ocular diseases in addition to their topical utilization.

Cell adhesion molecule expression in human lens epithelial cells after corticosteroid exposure

Aim:

The aim of the study was to investigate changes in cell adhesion molecule expression in human lens epithelial cells (HLEC) subjected to glucocorticoids.

Methods:

Human lens epithelial cells were exposed to different concentrations of dexamethasone for 24 hours. Cell adhesion molecule expression was studied by western blot and immunohistochemistry of vimentin, N-cadherin, E-cadherin, α-catenin, β-catenin and γ-catenin. Expression of the glucocorticoid receptor (GR) was also studied. Cell morphology was examined by transmission electron microscopy (TEM).

Result:

Expression of N-cadherin, α-catenin, β-catenin and GR was significantly decreased in dexamethasone exposed cells as compared to unexposed cells. No significant change in γ-catenin was present. Visualization of adhesion molecules, N-cadherin and α-catenin, by immunohistochemistry showed decreased antigen reactivity in dexamethasone exposed as compared to the unexposed cells. However, no change was seen for β-catenin and γ-catenin. E-cadherin was not detectable using western blot or immunohistochemistry.

TEM showed multilayering of cells, vacuole formation and appearance of electron-dense multivesicular bodies in HLEC exposed to 0, 0.1, 1, 10 and 100 αM dexamethasone.

Conclusion:

Glucocorticoids affect several adhesion molecules in lens epithelial cells, something that may contribute to the pathogenesis of posterior subcapsular opacification.

Inhibition of glucocorticoid-induced changes of Na(+), K(+)-ATPase in rat lens by a glucocorticoid receptor antagonist RU486

Cataract formation can be induced by prolonged use of glucocorticoids. The underlying mechanism is not fully understood yet. The presence of the functional glucocorticoid receptor (GR) in human and rat lens epithelial cells suggests that glucocorticoids target lens epithelial cells directly and specifically. Na(+), K(+)-ATPase has long been recognized for its role in regulating electrolyte concentration in the lens, contributing to lens transparency. We previously reported that the inactivation of Na(+), K(+)-ATPase induced by a glucocorticoid in rat lens. Therefore, the question is whether the changes of Na(+), K(+)-ATPase can be induced through the specific GR activation in glucocorticoid-induced cataract formation. Clear rat lenses were cultured in vitro and were treated with or without dexamethasone (Dex) or RU486 (a GR antagonist). The lenses were cultured for 7 days and photographed daily to record the development of opacity. The activity of Na(+), K(+)-ATPase was determined by using spectrophotometric analysis. The mRNA and protein level expressions of Na(+), K(+)-ATPase α1 were examined by reverse transcription polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry analysis, respectively. Our findings are presented in this study and show that mist-like opacity of the lens was observed as early as 5 days after incubation with dexamethasone. The opacity was more obvious at day 7 in the Dex group. The lenses of the untreated group and the RU486+Dex group remained transparent throughout the incubation. The activity of Na(+), K(+)-ATPase in the Dex-treated group decreased in a time-dependent manner. There was no significant loss of enzyme activity in either the control or the RU486+Dex group throughout the incubation period. Both the protein and mRNA expression levels of Na(+), K(+)-ATPase α1 in the capsule-epithelium of lenses decreased in the Dex-treated group. The GR antagonist RU486 inhibited the decrease of the expression of Na(+), K(+)-ATPase α1 induced by Dex. All of the above results suggested that the GR-mediated reduction of Na(+), K(+)-ATPase may contribute to the formation of steroid-induced cataract. Intervention in this pathway maybe helpful to avoid glucocorticoids-cataract formation.

Search for a functional glucocorticoid receptor in the mammalian lens

Prolonged glucocorticoid treatment of medical conditions such as rheumatoid arthritis or asthma can lead to the formation of a posterior subcapsular cataract as a negative side effect. Currently, the only treatment for this cataract is surgery because very little is known about the mechanism of glucocorticoid action in the mammalian lens. Understanding of a lens glucocorticoid response is essential for the treatment and prevention of a steroid induced cataract. It has been suggested that glucocorticoids exert their effects on the lens indirectly, non-specifically, or through non-classical mechanisms. While these modes of action may contribute to the formation of glucocorticoid induced posterior subcapsular cataract, the finding of a classical, specific, functional lens glucocorticoid receptor suggests that glucocorticoids target lens epithelial cells directly, specifically, and similar to what has been observed in other cells types. This review explores the discovery of the glucocorticoid receptor in humans lens epithelial cells and the lens specific glucocorticoid response. The distinct changes in lens epithelial cell signaling pathways (MAPK and PI3K-AKT) suggest that glucocorticoids modulate several cellular functions and may explain why a lens glucocorticoid response has been difficult to elucidate.

The Etiology of Steroid Cataract

Steroid-induced posterior subcapsular cataracts (PSCs) exhibit three main distinctive characteristics: (i) association only with steroids possessing glucocorticoid activity, (ii) involvement of aberrant migrating lens epithelial cells, and (iii) a central posterior location. The first characteristic suggests a key role for glucocorticoid receptor activation and subsequent changes to the transcription of specific genes. Glucocorticoid receptor activation is associated in many cell types with proliferation, suppressed differentiation, a reduced susceptibility to apoptosis, altered transmembrane transport, and enhancement of reactive oxygen species activity. Glucocorticoids may be capable of inducing changes to the transcription of genes in lens epithelial cells that are related to many of these cellular processes. This review examines the various mechanisms that have been proposed to account for the development of PSC in the context of recent DNA array studies. Additionally, given that the glucocorticoid receptor can also engender wide-ranging indirect activities, glucocorticoids could also indirectly affect the lens through the responses of other cells within the ocular compartment and/or through effects on cells at more remote locations. These indirect mechanisms, which, for example, could be mediated through alterations to the intraocular levels of growth factors that normally orchestrate lens development and maintain lens homeostasis, are also discussed. Although the mechanism of steroid cataract induction remains unknown, glucocorticoid-induced gene transcription events in lens epithelial cells, and also other intraocular or systemic cells, likely interact to generate steroid cataracts. Finally, although evidence for glucocorticoid-protein adduct formation in the lens is inconclusive, the generation of such adducts cannot yet be discounted as a contributing factor and must necessarily be retained in discussions of the etiology of steroid cataract.

Specific activation of the glucocorticoid receptor and modulation of signal transduction pathways in human lens epithelial cells

PURPOSE

Prolonged use of glucocorticoids (GCs) can lead to cataract formation. Lens GC responses have been difficult to elucidate. A previous study showed the presence of the glucocorticoid receptor (GR) in immortalized and primary human lens epithelial cells (hLECs) and GC-induced changes in gene expression. This study demonstrates specific GR activation and identifies the biological effect of GC-induced changes in gene expression in hLECs.

METHODS

HLE B-3 (B-3) and primary cultures of hLECs were transfected with pGRE.Luc and treated with or without dexamethasone (Dex), RU-486, spironolactone, or vehicle. mRNA and protein expression were examined by real-time PCR and Western blot analysis, respectively. Cell proliferation and apoptosis were examined by WST-1 and flow cytometry, respectively.

RESULTS

Dex treatment of B-3 and primary cultures demonstrated specific GR, but not mineralocorticoid receptor (MR), activation and phosphorylation. Pathway analysis revealed GC-induced changes in expression of MAPK regulators. Increased expression of GILZ mRNA and MKP-1 mRNA and protein was observed in immortalized and donor hLECs. This corresponded with a decrease in the phosphorylated forms of RAF, ERK, p38, and AKT, but not in JNK. No net change in LEC proliferation or apoptosis was observed with Dex treatment.

CONCLUSIONS

GC treatment of hLECs activates the GR to modulate the expression of MAPK and PI3K/AKT regulators. This is the first demonstration of GC signaling in hLECs. GCs, MAPK, and PI3K/AKT are involved in cell processes implicated in steroid-induced cataractogenesis. The absence of a net change in cell activity with acute steroid treatment is consistent with the possibility that chronic treatment leads to prolonged modulation of these pathways and steroid-induced cataract.

Involvement of hepatic glucocorticoid receptor-mediated functions in steroid-induced cataract formation

Determination of whether the steroid-induced cataract formation is caused through glucocorticoid (GC) receptor-mediated process was conducted by using GC antagonist (RU486) and anti-GC receptor antibody, and by sucrose density gradient ultracentrifugation analysis. (1) When 15 day-old chick embryos were treated with dexamethasone (DEX, 0.025 micromol per egg), their lenses started to form an opaque ring around the peri-nuclear region (stage II-III) after 12 hr and developed into nuclear-like cataract (stage IV-V) after 44 hr. The cataract formation examined at the 44 hr could be effectively prevented by administration of RU486 (0.2 micromol per egg) ranging from 2 hr before to 12 hr after the DEX administration. (2) GC receptor was present in liver, but could not be determined in lens by western blot analysis using monoclonal anti-GC receptor antibody. (3) Sucrose gradient ultracentrifugation analysis indicated that the receptor (9S) in the liver could be transformed to the 4S form after 0.4M NaCl treatment. Combined with our previous data, this suggests that changes in hepatic functions mediated by the GC receptor after the GC administration may be involved in the process of the cataract formation.

Inhaled corticosteroids: past lessons and future issues

Inhaled corticosteroids play a pivotal role in the treatment of asthma. Inhalation permits effective delivery of the corticosteroid in high concentration to target sites within the lung while minimizing systemic exposure. Consequently, the safety profile of inhaled corticosteroids is markedly better than that of oral corticosteroid therapy. However, although it was first thought that direct delivery might eliminate systemic adverse effects, this has not been confirmed by clinical trials and experience. Inhaled corticosteroids are absorbed from the lungs into the systemic circulation, in which they can acutely decrease growth velocity in children, an effect that fortunately appears to be temporary and might have no effect on final adult height. In sufficient dosages, they also produce bone mineral loss leading to osteoporosis and might increase the risk of cataracts, glaucoma, skin atrophy, and vascular changes that increase the risk of ecchymoses. Effective evaluation of the severity and significance of these complications is challenging because highly sensitive tests do not reliably predict clinically significant events, and short-term observations do not predict long-term consequences. Also, compliance wanes with long-term treatment, and susceptibility to a particular adverse event can vary over time, even in the same individual, because of developmental or hormonal changes. This journal supplement will review what has been learned about the safety of inhaled cortico-steroids during the past decade, discussing some of the questions that remain and considering the characteristics of an "ideal" inhaled corticosteroid: one with high local activity in the lung and minimal or no adverse systemic effects.

The molecular chaperone, alpha-crystallin, protects against loss of antigenicity and activity of esterase caused by sugars, sugar phosphate and a steroid

Previously we showed that glycation-induced inactivation and loss of antigenicity of enzymes occur simultaneously. Alpha-crystallin, a major structural protein of the mammalian lens, prevents the aggregation of other proteins and protects enzyme function against post-translational modification in vitro. However, it is not known whether alpha-crystallin can also protect against loss of antigenicity of enzymes. Esterase activity in the lens is decreased in senile cataract and diabetes. We investigated the loss of antigenicity of esterase caused by different insults and the ability of alpha-crystallin to protect. Inactivation of carboxylesterase by sugars, fructose 6-phosphate (F6P) and a steroid, prednisolone-21-hemisuccinate (P-21-H), was measured spectrophotometrically in the presence and absence of alpha-crystallin, while loss of antigenicity was monitored simultaneously using an immunoprecipitation method. The esterase was progressively inactivated by fructose, F6P, ribose, and P-21-H. Bovine alpha-crystallin fully protected against inactivation of esterase by all four compounds, and also protected against loss of antigenicity of the esterase by fructose, ribose and P-21-H at a molar ratio of 1:1. The results indicated that alpha-crystallin, under our experimental conditions, clearly exhibited the ability to prevent loss of antigenicity and inactivation of esterase. The protective effect of alpha-crystallin against loss of antigenicity indicates a novel aspect of its chaperoning function.

Receptor-mediated adrenocorticoid hormone signaling in ocular tissues

Sodium-water balance is causally linked to the functional expression of a number of important ocular tissues, viz. corneal deturgescence, aqueous humor secretion by the iris, hydration of the lens, retinal photoreception, and choriocapillary angiogenesis. The regulation of sodium absorption in the eye is generally believed to be under the control of Na(+),K(+)-activated adenosine triphosphatase, although evidence for this view is at best circumstantial. Contemporary work has shown widespread distribution of the mineralocorticoid hormone receptor and its colocalization with the amiloride-sensitive sodium channel in cells of diverse embryological origins. All available evidence favors the idea that the transcriptional regulation of the apical sodium channel by adrenocorticoids, and not the basolateral sodium pump, is critically important to sodium-water homeostasis in various ocular tissues, in a manner previously believed to be limited exclusively to the epithelial cell in various peripheral organs. Based upon these parameters, models are presented to help in understanding the direction of sodium absorption in a number of ocular tissues. Thus, the regulation of the sodium channel by steroid hormones seems to be a universal feature of the living cell that may have important implications in the understanding and management of normal ocular functions and their modification in human pathology.

Immunomagnetic capture of lens membrane fractions containing steroid binding protein

This study describes the use of magnetic Dynabeads to purify microsomes from a crude microsomal fraction. A 28 kDa membrane-associated protein is proposed to mediate the binding of progesterone and other steroid hormones to ocular lens membranes and the rapid-nongenomic actions of these steroids. The subcellular location of this membrane steroid binding protein (MSBP) was probed by capture of organelles containing MSBP by magnetic beads displaying an antibody to a cytoplasmic domain of the protein. The beads were exposed to a crude microsomal fraction from lens epithelia. Western blotting was used to identify captured organelles and confirm the presence of MSBP. Microsomes and trace fiber cell plasma membrane were captured. Microsomes contained the 28 kDa MSBP. Lens fiber cell membrane contained a 55 kDa immunoreactive protein. The role of this serendipitously recognized protein in binding of steroids is unknown.

What causes steroid cataracts? A review of steroid-induced posterior subcapsular cataracts

Prolonged use of glucocorticoids is a significant risk factor for the development of posterior subcapsular cataract. This places restrictions on the use of glucocorticoids in the treatment of systemic and/or ocular inflammatory conditions as well as in organ transplantation. The mechanisms responsible for the opacification are unknown and no effective treatment, other than surgical removal of the lens, is available. Difficulties in establishing suitable in vivo or in vitro models have limited research in this area. Nevertheless, several mechanisms, based on observations with other types of cataracts, have been proposed. In this review, these mechanisms are evaluated in light of the evidence available. A novel mechanism is also proposed, in which steroids do not directly act on the lens but rather affect the balance of ocular cytokines and growth factors.