Esteraseaktivität eines organotypischen humanen Kornea-Konstrukts (HCC) als In-vitro-Modell für Permeationsuntersuchungen

Organotypic cornea equivalents are used as in vitro models for permeation studies. Many ophthalmic drugs are applied as ester prodrugs to achieve a higher bioavailability. The esterase activity of three corneal human cell lines (epithelial, stromal, endothelial cells) as well as of excised porcine cornea, human donor cornea and human cornea construct (HCC) was investigated and compared. Esterase activity was determined using p-nitrophenyl acetate and hydrocortisone acetate (HCA) as esterase substrates. Hydrocortisone acetate permeation across porcine cornea, human donor cornea and HCC was studied in vitro using Franz-diffusion cells. Corneal epithelial cells showed the highest esterase activity and only small differences to keratocytes and endothelial cells were detectable. The permeation barrier properties of the different corneal tissues were very similar in the case of HCA permeation whereas HCA metabolism rates were in the ranking order of porcine cornea > HCC > human donor cornea. Permeation and metabolism studies indicate that the in vitro permeation model HCC is able to adequately convert hydrocortisone acetate to hydrocortisone.

Matrix metalloproteinase distribution during early corneal wound healing

AIM

To compare matrix metalloproteinase (MMP) localisation in anterior keratectomy (AK) and lamellar keratectomy (LK) wounds.

METHODS

Wounds were produced in one eye of 24 rabbits. The AK wounds were made to approximately 120 microm in depth and then allowed to re-epithelialise. The LK wounds were of similar depth, but the anterior stroma and epithelium were replaced after a second deeper keratectomy had been performed. Immunohistochemistry was used to localise the MMP-1, -2, -3, and -9 at intervals from 4 h to 14 days following surgery. The contralateral eyes acted as controls.

RESULTS

After an AK wound MMP-1 was present at the leading edge of migrating epithelium after 18 h, while MMP-2 and -9 were localised behind the advancing epithelial edge. The presence of these enzymes rapidly fell to low levels after epithelial closure. There was only faint MMP-3 localisation between days 3 and 7. After an LK wound, MMP-1, -3, and -9 were not detected in the stromal interface, but MMP-2 was present at all time points.

CONCLUSIONS

This study suggests that after an AK wound, MMP-1 is a key mediator of epithelial migration, while MMP-2 and -9, and to a lesser extent MMP-3, may participate in the remodelling of corneal stroma and the reformation of epithelial basement membrane. In contrast, an LK wound results in a much lower stimulus for MMP activation. The action of MMP-2 in stromal repair is thus partly independent of epithelial injury.

[Experimental research of the expression of telomerase in corneal limbal epithelial cells]

OBJECTIVE

To explore the possibility of using telomerase as a marker of corneal limbal stem cells.

METHODS

Corneal limbal tissues and central corneal epithelial tissues from 8 rabbits were examined for telomerase activity qualitatively by telomere repeat amplification protocol (TRAP) and quantitatively by detecting the light value with bioluminescent technique. 5-Fu (20 mg) was injected subconjunctivally in 4 rabbits and the other 4 rabbits were not injected.

RESULTS

Telomerase activity was positive in all corneal limbal tissues and negative in all central corneal tissues. Telomerase activity of corneal limbal cells (light value 165,575) was significantly higher than that of central corneal epithelial cells (light value 34,912) by bioluminescent technique (P = 0.001). 5-Fu injection group showed higher telomerase activity than that of the group without injection (light value 145,754) (P = 0.02).

CONCLUSIONS

Positive telomerase activity is detected in the corneal limbal tissues. It suggests that there are cells with high proliferative ability in the corneal limbus. Telomerase activity may be used as a marker of corneal limbal stem cells.

Attenuation of extracellular acidic pH-induced cyclooxygenase-2 expression by nitric oxide

Corneal endothelial cells play an important role in maintaining the transparency and ionic balance of the cornea. Inflammation causes many changes in the intracellular and extracellular environment of the cornea, including acidosis. We examined the relationship between changes in extracellular pH and expression of cyclooxygenase-2 in cultured bovine corneal endothelial cells. When extracellular pH ([pH]o) was reduced to pH 6.4, COX-2 mRNA increased, with a peak at 2 h. This was blocked by pretreatment with actinomycin D and incubation with spermine NONOate (SPER/NO, a nitric oxide donor). Exposure to the H+ ionophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP), also raised COX-2 mRNA levels. CCCP-induced COX-2 mRNA expression was also reduced by SPER/NO. These results were confirmed immuno-cytochemically. These data demonstrate that COX-2 expression is stimulated by the lowering of extracellular pH that could result from bacterial infection, and that this is countered by over-production of nitric oxide, which could also result from bacterial infection.

Doxycycline inhibits TGF-beta1-induced MMP-9 via Smad and MAPK pathways in human corneal epithelial cells

PURPOSE

To evaluate the effects of TGF-beta1 and doxycycline on production of gelatinase MMP-9 and activation of Smad, c-Jun N-terminal kinase (JNK), extracellular-regulated kinase (ERK), and p38 mitogen-activated protein kinase (MAPK) signaling pathways in human corneal epithelial cells.

METHODS

Primary human corneal epithelial cells were cultured to confluence. The cells were treated with different concentrations of TGF-beta1 (0.1, 1, or 10 ng/mL), with or without TGF-beta1-neutralizing mAb (5 microg/mL), SP600125 (30 microM), PD98059 (40 microM), SB202190 (20 microM), or doxycycline (5-40 microg/mL) for different lengths of time. Conditioned media were collected from cultures treated for 24 to 48 hours to evaluate the MMP-9 production by zymography and activity assay. Total RNA was isolated from cells treated for 6 to 24 hours to evaluate MMP-9 expression by semiquantitative RT-PCR and Northern hybridization. Cells treated for 5 to 60 minutes were lysed in RIPA buffer for Western blot with phospho-specific antibodies against Smad2, JNK1/2, ERK1/2, or p38.

RESULTS

TGF-beta1 increased expression, production, and activity of MMP-9 by human corneal epithelial cells in a concentration-dependent fashion. TGF-beta1 also induced activation of Smad2, JNK1/2, ERK1/2, and p38 within 5 to 15 minutes, with peak activation at 15 to 60 minutes. Doxycycline markedly inhibited the TGF-beta1-induced production of MMP-9 and activation of the Smad, JNK1/2, ERK1/2, and p38 signaling pathways. Its inhibitory effects were of a magnitude similar to SP600125, PD98059, and SB202190, specific inhibitors of the JNK1/2, ERK1/2, and p38 pathways, respectively.

CONCLUSIONS

These findings demonstrated that doxycycline inhibits TGF-beta1-induced MMP-9 production and activity, perhaps through the Smad and MAPK signaling pathways. These inhibitory effects may explain the reported efficacy of doxycycline in treating MMP-9-mediated ocular surface diseases.

Expression and immunolocalization of plasma membrane calcium ATPase isoforms in human corneal epithelium

PURPOSE

Plasma membrane Ca2+-ATPases (PMCAs) are integral membrane proteins essential to the control of intracellular Ca2+ ([Ca2+]i) concentration. Four genes encode PMCA proteins termed PMCA1-PMCA4. Little is known about the expression of these isoforms in corneal epithelium (CE). The purpose of this investigation is to characterize the expression and distribution of PMCAs in human CE (hCE).

METHODS

PMCA mRNA expression was examined by RT-PCR analysis of total RNA from native hCE using PMCA gene specific primers. PMCA isoform expression at the protein level in native hCE was examined by immunoblotting using isoform specific antibodies (Abs) and a panPMCA Ab that recognizes all PMCAs. Distribution of PMCAs in postmortem and surgical sections of hCE was determined by immunohistochemistry with the same Abs.

RESULTS

Immunoblot analysis with the panPMCA Ab yielded an intense band of approximately 135 kDa and several faintly staining bands above and below this major band. The isoform specific Abs labeled one or more bands that corresponded to bands detected with the panPMCA Ab. RT-PCR analysis of total RNA from hCE yielded PCR DNAs that were identified by sequencing as products of PMCA1, PMCA2, PMCA3, and PMCA4, thus confirming the immunoblot data. Immunohistochemistry demonstrated localization of PMCAs in all layers of hCE. PMCA4 was the predominant isoform, and was expressed along the plasma membrane of cells in all layers of CE, except with a notable absence along the basal cell membranes adjacent to the stroma. PMCA1 and PMCA2 were found mainly on basal and wing cells. In contrast to PMCA4, PMCA1 immunoreactivity (IR) was located on portions of basal cell plasma membranes adjacent to the stroma. PMCA2 IR was detected cytoplasmically within basal and wing cells in both central cornea and limbus. PMCA3 IR was located in basal cell nuclei in central cornea, but in a perinuclear location in the limbal, basal, and wing cells.

CONCLUSIONS

Human CE expresses multiple PMCA isoforms that are differentially expressed and localized among the layers and cells that comprise the CE. We propose that the differential expression of multiple PMCA isoforms affords CE the requisite flexibility to respond to the demands for Ca2+ regulation required during renewal and regeneration of its multiple cell types.

Detection and Subcellular Localization of Two 15S-Lipoxygenases in Human Cornea

PURPOSE

There are two human 15-lipoxygenases (LOX), 15-LOX-1 and -2, which convert arachidonic acid to 15S-hydroxyeicosatetraenoic acid (15S-HETE). The presence of both 15-LOXs in the human cornea prompted this study to delineate their roles in the human corneal epithelium.

METHODS

Human corneal epithelia from donor corneas and a human corneal epithelial (HCE) cell line were used in [1-(14)C]arachidonic acid incubations, Western blot analysis, and quantitative real-time RT-PCR. Cell cultures of HCE were treated with 15S-HETE to measure its effect on cell growth. HCE cells were transfected with plasmids to express green fluorescent (GFP) fusion proteins of 15-LOX-1 and -2, and in vivo laser confocal microscopy was performed to determine the subcellular localization of the 15-LOX fusion proteins.

RESULTS

[1-(14)C]Arachidonic acid incubations yielded 15S-HETE as the only LOX product. Treatment with 15S-HETE (5-10 microM) reduced growth rate and induced apoptosis in cultured HCE cells in a dose-dependent manner. 15-LOX-2 but not 15-LOX-1 was detected by Western blot analysis, although we were able to detect similar levels of both 15-LOX mRNAs by real-time quantitative RT-PCR. 15-LOX-1 and -2 proteins showed different subcellular expression patterns. 15-LOX-2 GFP was expressed in the cytoplasm and nucleus (actively taken up into the nucleus). 15-LOX-1 GFP fusion protein expression was restricted to the cytoplasm.

CONCLUSIONS

These findings indicate that 15-LOX-2 is the predominant 15-LOX protein in human cornea, and its product, 15S-HETE, plays a role in cellular proliferation. Because the two 15-LOXs have different subcellular compartmentalization, the authors hypothesize that their products are also compartmentalized and therefore exert different molecular effects in the human corneal epithelium.

Role of Matrix Metalloproteinase-9 in Ex Vivo Expansion of Human Limbal Epithelial Cells Cultured on Human Amniotic Membrane

PURPOSE

To investigate the expression and pivotal role of matrix metalloproteinase (MMP)-9 in the ex vivo expansion of human limbal explants with or without amniotic membrane (AM).

METHODS

Corneoscleral buttons were cultured on intact, denuded AM or plastic dishes for 3 weeks. To determine the role of MMP-9 in cell migration, either the MMP inhibitor GM6001 or an MMP-9 antibody was used. Expression of MMP-9 was determined by gelatin zymography, reverse transcription-polymerase chain reaction, and immunohistochemical staining.

RESULTS

The expression of MMP-9 in all culture conditions increased in a time-dependent manner. However, the active form of MMP-9 emerged only in cultures on both intact and denuded AM from the second week. The averaged corrected ratio of MMP-9 expression in cultures on intact AM versus those on denuded AM or plastic dishes was 2.76 +/- 0.69- or 4.25 +/- 0.30-fold, respectively, when total RNA was used as an internal control. MMP-9 transcripts were upregulated in cultures on intact AM compared with the other two culture conditions. Immunohistochemical staining demonstrated that the MMP-9 protein was located on the limbal epithelial cells. Upregulation of MMP-9 associated with cell migration was significantly attenuated by both GM6001 and MMP-9 antibody, consistent with the inhibition of MMP-9 activity, as determined by gelatin zymography. In contrast, the sizes of limbal outgrowth were not different between the control and MMP-9 antibody-treated plastic dishes.

CONCLUSIONS

These results demonstrated that MMP-9 not only was upregulated, it was also involved in the outgrowth of limbal epithelial cells. These results suggest that cell-cell matrix interaction is involved in the expansion of limbal epithelial cells on intact AM, and MMP-9 may be a key element.

Age-related changes in superoxide dismutase, glutathione peroxidase, catalase and xanthine oxidoreductase/xanthine oxidase activities in the rabbit cornea

The activities of superoxide dismutase, glutathione peroxidase (GPX) and catalase--the enzymatic scavengers of reactive oxygen species and the activities of xanthine oxidoreductase and xanthine oxidase, an enzyme known to generate reactive oxygen species, were studied in the corneas of normal rabbit eyes of various ages (1 month--young eyes; 4-9.5 months--young adult eyes; 2.0-2.75 years--middle aged eyes; 3.0-5.0 years--aged eyes). The activities of GPX, superoxide dismutase, xanthine oxidoreductase and xanthine oxidase were investigated biochemically in the scraped corneal epithelium. Catalase activity was detected histochemically in the corneal epithelium and endothelium. The results show that young corneas revealed lower activities of all the antioxidant enzymes investigated than did young adult corneas, in which enzymatic activities reached their maximum. In middle-aged corneas, GPX and catalase activities remained approximately at the same levels as seen in young adult corneas, whereas superoxide dismutase activity was decreased. In aged corneas, the activities of all antioxidant enzymes were dramatically decreased or even lost (catalase activity in the corneal endothelium). In contrast, xanthine oxidoreductase activity only slightly decreased with age and the xanthine oxidase proportion of total xanthine oxidoreductase remained unchanged. GPX, superoxide dismutase and catalase are important antioxidant enzymes protecting the cornea against the oxidative damage. Because the activities of these enzymes are lower in young animals and greatly reduced in aged animals, it is suggested that young and particularly aged corneas might be more susceptible to oxidative stress than are young adult corneas. This presumption is supported by the fact that the activities of prooxidant enzymes (xanthine oxidoreductase/xanthine oxidase) are only slightly decreased in aged corneas as compared to young adult corneas so that some imbalance between antioxidant and prooxidant enzymes exists already in the normal aged corneas.

Expression of phospholipases A2 and C in human corneal epithelial cells

PURPOSE

To achieve a better understanding of the involvement of phospholipases in the inflammation and wound-healing processes in human corneal epithelial cells (HCECs), expression of phospholipase A2s (PLA2s) and phospholipase Cs (PLCs) was examined in the human corneal epithelium.

METHODS

Specific primers were designed for RT-PCR amplification of the known secreted (s)PLA2, cytosolic (c)PLA2, and PLC mRNAs. Corresponding PCR products were cloned and the DNA sequenced. Immunofluorescence of flatmounted corneal sections and Western blot analyses were used to detect the PLA2s and PLCs expressed by HCECs.

RESULTS

The mRNAs for the following phospholipases were detected by RT-PCR in the HCECs: sPLA2GIII, -GX, and -GXIIA; cPLA2alpha and -gamma; PLCbeta1, -beta2, -beta3, -beta4, -gamma1, -gamma2, -delta1, -delta3, -delta4, and -epsilon. Immunofluorescence analyses conducted on corneal epithelium cryosections and Western blot on freshly isolated HCECs demonstrated the presence of sPLA2GIII, -GX, and -GXIIA; cPLA2alpha and -gamma; and PLCbeta2, -beta3, -gamma1, -gamma2, and -delta3.

CONCLUSIONS

Many phospholipase isoforms are expressed by HCECs and may play a major role in signal transduction (PLCs) as well as in the release of precursors of potent mediators of inflammation, such as leukotrienes and prostaglandins (PLA2s). Moreover, the sPLA2s expressed by the corneal epithelium could be involved in the normal antibacterial activity in the tears and in wound healing.

[Expression of matrix metalloproteinase in human pterygia]

PURPOSE

To determine the cellular distribution and activation of MMP-2 and MMP-9 in human pterygium.

METHODS

The expression and activation of MMP-2 and MMP-9 were determined by immunohistochemistry and quantitative gelatinase zymography from 27 pterygia (26 cases, 18 eyes in stationary pterygia and 9 eyes in progressive pterygia) and 6 normal conjunctival specimens.

RESULTS

MMP-2 was expressed in all pterygium examined, specifically localized to the epithelium. MMP-9 was the most abundant in pterygium vascular endothelium and inflammatory cell. MMP-2 levels were no difference between the stationary pterygia [(235+/-18.17) scanning units] and the progressive pterygia [(221+/-22.53) scanning units]. MMP-9 levels in the progressive pterygia [(159+/-19.28) scanning units] were significantly higher than that in the stationary pterygia [(46+/-32.21) scanning units] (P < 0.05).

CONCLUSION

This investigation located the expression of MMP-2 and MMP-9 in pterygium of the human eyes. These enzymes may be responsible for the progression of pterygia.

Stimulation of matrix metalloproteinases by hyperosmolarity via a JNK pathway in human corneal epithelial cells

PURPOSE

To investigate whether exposure of human corneal epithelial cells to hyperosmotic stress activates the c-Jun NH(2)-terminal kinase (JNK) stress-activated protein kinase (SAPK) pathway, and stimulates production of the matrix metalloproteinases (MMPs): gelatinase (MMP-9), collagenases (MMP-1 and -13), and stromelysin (MMP-3).

METHODS

Primary human corneal epithelial cells cultured in normal osmolar medium (312 mOsM) were exposed to media with higher osmolarity (350-500 mOsM) achieved by adding NaCl, with or without SB202190, an inhibitor of the JNK pathway; dexamethasone; or doxycycline for different lengths of time. The conditioned media were collected after 24 hours of exposure for zymography and ELISA. Total RNA was extracted from cultures treated for 6 hours and subjected to semiquantitative RT-PCR. Cells treated for 5 to 60 minutes were lysed in RIPA buffer and subjected to Western blot with phospho (p)-specific antibodies against p-JNK and p-c-Jun. JNK1 activation was also detected with an immunoassay system.

RESULTS

The concentrations of MMP-9, -1, and -3 proteins in 24-hour conditioned media of corneal epithelial cells progressively increased as the media's osmolarity was increased from 312 to 500 mOsM by the addition of NaCl. The concentration of MMP-13 progressively increased to a peak at 450 mOsM. Active p-JNK-1, p-JNK-2, and p-c-Jun were detected by Western blot as early as 5 minutes and peaked at 60 minutes in cells exposed to hyperosmolar media. The levels of p-JNK-1, p-JNK-2, and p-c-Jun correlated positively with the osmolarity of the culture media. The p-JNK inhibitor SB202190 and doxycycline markedly inhibited the stimulation of p-JNK-1, p-JNK-2, and p-c-Jun, as well as MMP-9, -1, -13, and -3 at both the mRNA and protein levels in the cells exposed to hyperosmolar media.

CONCLUSIONS

Expression and production of MMP-9, -1, -13, and -3 by human corneal epithelial cells correlated positively with increasing media osmolarity. This increase was mediated at least in part through activation of the JNK SAPK pathway. Doxycycline, an agent used to treat MMP-mediated ocular surface disease, inhibited the hyperosmolarity-induced MMP production and JNK activation. The relevance of these findings to stimulated production of MMPs by the elevated tear osmolarity in dry eye remains to be determined.

Histologic and Histochemical Changes in Rabbit Cornea Produced by an Orthokeratology Lens

PURPOSE

To report the histologic and histochemical properties of rabbit cornea after insertion of an orthokeratology lens.

METHODS

An orthokeratology lens was placed on the left corneas of rabbits for 8 hours daily, and their eyes were enucleated after 7, 14, 21, and 28 days and examined histologically and histochemically. The right eyes were used as controls.

RESULTS

After 7-14 days, hematoxylin and eosin staining of the cornea revealed that the epithelial layer was slightly thinner in the central area and thicker in the intermediate area, but its thickness gradually became normal toward the limbus. Periodic acid-Schiff staining showed no abnormal distribution of glycogen granules or glycogen producing cells. 5-bromo-2-deoxyuridine staining revealed more mitoses in the central area than in the intermediate area. Histochemical staining showed lactic dehydrogenase activity in the central area of the lens, whereas alkaline phosphatase activity and beta-glucuronidase activity were slightly increased in the intermediate area. There were no other clearly abnormal findings.

CONCLUSIONS

The thickness of the corneal epithelium showed topographical variation consistent with the effect of orthokeratology. The result of histochemical studies suggested that there were no marked alterations in epithelial function.

TGF-beta1 stimulates production of gelatinase (MMP-9), collagenases (MMP-1, -13) and stromelysins (MMP-3, -10, -11) by human corneal epithelial cells

Matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of ocular surface diseases. This study investigated the regulated expression of gelatinases (MMP-2 and -9), collagenases (MMP-1 and -13) and stromelysins (MMP-3, -10, and -11) by TGF-beta1 in cultured human corneal epithelial cells. Primary human corneal epithelial cell cultures were grown to confluence and treated with different concentrations (0.1, 1.0, 10 ng ml(-1)) of TGF-beta1 in serum-free medium for 6-24 hr. Total RNA was isolated from cultured cells with or without TGF-beta1 treatment for 6 hr and subjected to semi-quantitative RT-PCR and Northern hybridization. Conditioned media were collected from cultures with or without TGF-beta1 treatment for 24 hr to evaluate the MMP production by ELISA and activity assays. Semi-quantitative RT-PCR revealed that the expressions of MMP-9, -1, -13, -3, -10 and -11 mRNA were up-regulated by TGF-beta1 in a concentration-dependent fashion, while MMP-2 and MMP-14 production did not change. Northern hybridization confirmed these findings. Gelatin zymography, MMP ELISA and activity assays showed concentration-dependent stimulated production and activity of MMP-9, -1, -13, -3 and -10 protein in the conditioned media of cultures treated for 24 hr with TGF-beta1. In conclusion, our results demonstrate that TGF-beta1 stimulates the expression and production of gelatinase (MMP-9), collagenases (MMP-1, -13) and stromelysins (MMP-3, -10, -11) in human corneal epithelial cells. These findings suggest that TGF-beta1 may play a role in the pathogenesis of MMP mediated ocular surface diseases, such as sterile corneal ulceration.

Cdk5 regulates activation and localization of Src during corneal epithelial wound closure

Recent studies have shown that Cdk5, a member of the cyclin-dependent-kinase family, regulates adhesion and migration in a mouse corneal epithelial cell line. Here, we extend these findings to corneal wound healing in vivo and examine the mechanism linking Cdk5 to cytoskeletal reorganization and migration. Cdk5 was overexpressed in the corneal epithelium of transgenic mice under control of the ALDH3 promoter. Elevated Cdk5 expression retarded corneal debridement wound closure in these animals and suppressed remodeling of the actin cytoskeleton. Conversely, the Cdk5 inhibitor, olomoucine, accelerated debridement wound healing in organ cultured eyes of normal mice, caused migrating cells to separate from the epithelial cell sheet, and increased the level of activated Src(pY416) along the wound edge. To explore the relationship between Cdk5 and Src in greater detail, we examined scratch-wounded cultures of corneal epithelial cells. Src was activated in cells along the wound edge and blocking this activation with the Src kinase inhibitor, PP1, inhibited wound closure by 85%. Inhibiting Cdk5 activity with olomoucine or a dominant negative construct, Cdk5T33, increased the concentration of Src(pY416), shifted its subcellular localization to the cell periphery and enhanced wound closure. Cdk5(pY15), an activated form of Cdk5, also appeared along the wound edge. Inhibiting Src activity with PP1 blocked the appearance of Cdk5(pY15), suggesting that Cdk5 phosphorylation is Src dependent. Cdk5 and Src co-immunoprecipitated from scratch-wounded cultures, demonstrating that both kinases are part of an intracellular protein complex. These findings indicate that Cdk5 exerts its effects on cell migration during corneal epithelial wound healing by regulating the activation and localization of Src.

COX-2 lack of function in hypoxia-induced ocular surface inflammation

Injury to the ocular surface increases corneal epithelial production of cyclooxygenase (COX)-derived eicosanoids but this increase correlates poorly to the inflammatory sequelae. Moreover, corticosteroids are effective in treatment of this inflammation but NSAIDs are not. The discovery of COX-2 that is differentially affected by common NSAIDs reopened the question of the role of prostaglandins in ocular surface inflammation. We examined the presence and inducibility of COX-2 in the corneal epithelium following hypoxia-induced injury in vivo and in vitro. COX-2, but not COX-1, protein levels markedly increased following hypoxia. Use of the selective COX-2 inhibitor, NS-398, indicated that COX activity in hypoxic corneas or cells is essentially that of COX-2; in control cells, both COX-1 and COX-2 contributed equally to the production of PGE2. COX-2 protein overexpression induced by hypoxia was not associated with a parallel increase in PGE2 accumulation but the enzyme regained full catalytic activity when cells were re-exposed to normoxia in the presence of heme and arachidonic acid. Decreases in the levels of oxygen and heme, essential substrates/cofactors for COX catalytic activity, contributed to a diminished prostanoid production during hypoxia. These results suggest that in hypoxic injury, molecules other than COX-derived prostanoids play a major pro-inflammatory role. Furthermore, this study provides an explanation for the ineffectiveness of classical NSAIDs in the treatment of hypoxia-related ocular surface inflammation.

Doxycycline-a role in ocular surface repair

BACKGROUND/AIMS

Doxycycline is a broad spectrum antibiotic that chelates metal ions and is frequently used as part of the treatment of ocular surface diseases. Its therapeutic value has been ascribed to an ability to inhibit matrix metalloproteinase (MMP) activity and both MMP and IL-1 synthesis. The aim of this study was to evaluate the role of doxycycline as an inhibitor of corneal MMPs and assess its contribution to ocular surface repair mechanisms.

METHODS

Corneal epithelial cell and keratocyte cultures were grown to confluence and incubated with IL-1alpha, LPS, doxycycline, or doxycycline and LPS in serum free medium for 4 days. The cells were either harvested and assayed for caspase-3 activity or stained with either AE5 or antivimentin antibodies. Media samples were concentrated and assayed for MMP activity by zymography or using a fluorigenic substrate. ELISA was used to quantify IL-1alpha, MMPs -1,-2,-3,-9, and TIMPs -1 and -2.

RESULTS

IL-1alpha and LPS had no effect on MMP/TIMP production by cultured corneal epithelial cells and keratocytes. Corneal MMP-2 inhibition by doxycycline was partially [Ca(2+)] dependent but irreversible. At the minimum inhibitory concentration, 100 micro m, doxycycline had no apparent effect on MMP and TIMP production, but ultimately caused the death of keratocytes and some of the epithelial cells that detached from their basement membrane. Caspase-3 activity was not detected in dead or dying keratocytes. The mechanism of cell death in cultured corneal epithelial cells was not caspase-3 related apoptosis as the activity of this enzyme, normally detectable, was lost. The epithelial cells that survived doxycycline treatment did not bind antivimentin antibody and compared with controls, reacted less with the AE5 antibody. They were probably transient amplifying cells.

CONCLUSIONS

Doxycycline irreversibly inhibits corneal MMP-2 activity by chelating the metal ions that are catalytically and structurally essential. Corneal MMP/TIMP production in vitro is not modulated by IL-1alpha, LPS, or doxycycline. The therapeutic value of doxycycline may depend upon its effective concentration at the ocular surface and probably relates to its chelating properties.

Interactions of olopatadine and selected antihistamines with model and natural membranes

OBJECTIVE

Olopatadine, an effective topical ocular human conjunctival mast cell stabilizer/antihistaminic antiallergic drug, was evaluated and compared to selected classical antihistamines for their interaction with model and natural membranes to ascertain potential functional consequences of such interactions.

METHODS

The model membranes examined consisted of the argon-buffer interface and monomolecular films of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) at the argon-buffer interface. Interactions with the model membranes were detected as changes in surface tension, i.e., surface pressure. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage, hemoglobin release, lactate dehydrogenase release, and histamine release from appropriate cell types.

RESULTS

Measurements at the argon-buffer interface revealed intrinsic surface activity for all agents that ranged from highly surface-active to weakly surface-active in the order of: desloratadine > clemastine > azelastine congruent with ketotifen > diphenhydramine> pyrilamine > emedastine > epinastine > or = olopatadine. This order of amphipathic behavior was confirmed for most of the compounds by estimates of their dissociation constants (K(d,L)) determined from interactions with SOPC monolayers adjusted to a surface pressure approximating that of natural membranes. Epinastine was the only antihistamine that showed a disproportionately greater increase in surface activity toward SOPC in monolayer when compared to other antihistamines. Dissociation constants could not be established for olopatadine because of its low affinity for both the argon-buffer interface and the SOPC monolayer. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage (erythrocyte ghosts), hemoglobin release (erythrocytes), lactate dehydrogenase release (conjunctival mast cells, corneal epithelial cells), and histamine release (conjunctival mast cells). Aside from olopatadine and emedastine, all antihistamines promoted a concentration-dependent leakage of hemoglobin from intact erythrocytes. The concentration of drug required to cause half-maximal hemoglobin release (H(50)) from erythrocytes correlated linearly (r = 0.98) with the SOPC dissociation constants (K( d,L)) estimated for the different antihistaminic agents interacting with SOPC monolayers. A similarly high correlation (r = 0.85) emerged from a plot with a slope approaching unity that related drug concentrations required for half-maximal hemoglobin leakage from erythrocytes to threshold doses of drug that caused histamine release from human conjunctival mast cells. Olopatadine was the only agent that did not promote membrane perturbation as monitored by either hemoglobin release from intact erythrocytes, LDH release from human conjunctival mast cells, or 6-carboxyfluorescein release from erythrocyte ghosts. Assessment of the lytic potential of marketed concentrations of ketotifen (0.025%), azelastine (0.05%), and epinastine (0.05%) revealed significant membrane perturbation of human conjunctival mast cells and, importantly, human corneal epithelial cells as indexed by LDH release. This was in contrast to marketed concentrations of olopatadine (0.1%) which maintained normal mast cell and corneal epithelial cell membrane function.

CONCLUSIONS

Combined, these results support the notion that the disruption of natural cell membranes by surface-active antihistamines occurs not through a receptor-mediated process, but is the consequence of a direct interaction of these agents with the cell membrane. This is corroborated by surface pressure-concentration isotherms for adsorption of five different antihistaminic agents to SOPC monolayers where 50% lysis occurred at a surface pressure of 42.9 +/- 1.1 mN/m. Olopatadine appears to be unique among the agents tested by demonstrating low intrinsic surface activity, thus limiting its interaction with natural membranes. At concentrations of about half-maximal compound solubility (, 5.0 mM or a 0.19% drug solution), olopatadine generated SOPC monolayer surface pressures (i.e., 39.82 +/- 0.10 mN/m) that were below those that promoted membrane perturbation and onset of hemoglobin leakage. Olopatadine's restricted interaction with membrane phospholipids limits the degree of membrane perturbation and release of intracellular constituents, including histamine, LDH, and hemoglobin, which is believed to contribute to olopatadine's topical ocular comfort and patient acceptance.

Retinoic Acid Induces Corneal Epithelial CYP4B1 Gene Expression and Stimulates the Synthesis of Inflammatory 12-Hydroxyeicosanoids

Injury to the ocular surface provokes an inflammatory response that is mediated, at least in part, by corneal epithelial derived 12-hydroxyeicosanoids (HETEs) including 12-HETE and 12-HETrE; both metabolites exhibit potent inflammatory and angiogenic properties and are formed by a cytochrome P450 (CYP) 4B1. Retinoids are known to mediate wound-healing processes in many tissues and, as such, are integral components of the inflammatory response. We studied the effect of various retinoids on corneal synthesis of 12-hydroxyeicosanoids and on activation of CYP4B1 gene expression. Corneal organ cultures were used to assess the effect of retinoic acid on epithelial metabolism of arachidonic acid to 12-hydroxyeicosanoids. Luciferase reporter vectors containing different lengths of the CYP4B1 3.4 kb-5'-untranslated region were used to examine the effect of vitamin D and retinoids (9-cis-retinoic acid and all-trans retinoic acid) on transcriptional activation of CYP4B1 in transient transfection experiments with HepG2 cells. Vitamin D had no effect on CYP4B1 promoter activity, but 9-cis and all-trans retinoic acids increased promoter activity by up to 70% over control. Addition of both 9-cis and all-trans retinoic acids resulted in an additive effect increasing promoter activity by 2-fold. The increased promoter activity correlated with the presence of RAR/RXR binding motifs. Incubation of corneal organ culture for 24 hours in the presence of 9-cis and all-trans retinoic acids increased the synthesis of 12-HETE and 12-HETrE by 2-fold. The finding that retinoic acid increases the expression of the CYP4B1 gene and enhances production of the inflammatory 12-hydroxyeicosanoids in the corneal epithelium may provide a linkage between wound healing and inflammation in the ocular surface.

Comparative histochemical and immunohistochemical study on xanthine oxidoreductase/xanthine oxidase in mammalian corneal epithelium

We have previously found that xanthine oxidase (one form of xanthine oxidoreductase that generates reactive oxygen species, such as superoxide radicals and hydrogen peroxide) is present in corneal epithelium of normal rabbit eye. It was suggested that the reactive oxygen species contribute to additional eye damage related to prolonged continuous contact lens wear and irradiation of the eye with UV-B light. To further explore the potential danger of xanthine oxidase as a source of reactive oxygen species, we have examined in the present paper whether xanthine oxidoreductase and xanthine oxidase are present in corneal epithelium of other mammalian species, employing immunohistochemical and enzyme histochemical methods. In corneal epithelium of normal eyes of ox, pig, guinea-pig, and rat xanthine oxidoreductase activity was detected by the tetrazolium salt reduction method and xanthine oxidase activity was localized by a method based on cerium ions capturing hydrogen peroxide. For the immunohistochemical demonstration of the enzymes, rabbit anti-bovine xanthine oxidase antibody, rabbit anti-human xanthine oxidase antibody and monoclonal mouse anti-human xanthine oxidase/xanthine dehydrogenase/aldehyde oxidase antibody were used. The immunohistochemical and enzyme histochemical results show that xanthine oxidoreductase and xanthine oxidase are present both as proteins and as active enzymes in the corneal epithelium of all animals studied. It is hypothesized that under various pathological states, xanthine oxidase-generated reactive oxygen species might contribute to eye damage.

Role of p38 MAP Kinase in Regulation of Cell Migration and Proliferation in Healing Corneal Epithelium

PURPOSE

The purpose of the present study was to examine the roles of signaling pathways potentially activated by TGFbeta (i.e., Smad and p38 mitogen-activated kinase [MAPK]) in regulation of cell migration and proliferation of healing mouse corneal epithelium.

METHODS

Activation of Smads or p38MAPK was evaluated by immunohistochemistry in healing mouse corneal epithelium after debridement. The role of endogenous TGFbeta or p38MAPK in epithelial healing was determined in organ-cultured mouse corneas with an epithelial defect, in the presence or absence of a TGFbeta-neutralizing antibody or p38MAPK inhibitors, respectively. Cell proliferation was evaluated by incorporation of bromodeoxyuridine.

RESULTS

Migrating mouse corneal epithelium had minimal cell proliferation. Smad3 and -4 were found in nuclei of normal corneal epithelium, whereas they were absent in nuclei of migrating cells in association with Smad7 upregulation on epithelial debridement. Administration of TGFbeta-neutralizing antibody reduced the protein expression of Smad7 in vivo after a corneal injury. In contrast, phosphorylation and nuclear translocation of p38MAPK were markedly evident in migrating epithelium during healing, but not in uninjured epithelium. In organ culture, addition of p38MAPK inhibitors blocked cell migration more markedly than neutralizing TGFbeta-antibody and enhanced cell proliferation in the injured corneal epithelium, in association with phosphorylation of Erk.

CONCLUSIONS

Endogenous TGFbeta enhances migration of corneal epithelium during wound healing in mice. The p38MAPK, but not the Smad, cascade plays a major role in promoting cell migration and in suppressing cell proliferation in migrating epithelium.

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

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

Up-regulation of urokinase-type plasminogen activator in corneal epithelial cells induced by wounding

PURPOSE

To investigate the possible role of urokinase-type plasminogen activator (uPA) in corneal epithelial wound healing by examining its expression both in the rabbit corneal epithelium in situ and in rabbit corneal epithelial (RCE) cells in vitro.

METHODS

The rabbit cornea was subjected to mechanical wounding, and frozen sections of the tissue were subsequently prepared and subjected both to immunostaining with antibodies to uPA and to in situ zymography for the detection of PA activity. RCE cell monolayers were also subjected to scrape wounding, after which they were immunostained for uPA. The amounts of uPA protein in the culture medium and of uPA mRNA in cell lysates were also determined by enzyme-linked immunosorbent assay and by reverse transcription and real-time quantitative polymerase chain reaction analysis, respectively.

RESULTS

Immunostaining and in situ zymography of the wounded cornea revealed that uPA was restricted to the leading edge of the migrating corneal epithelium. In contrast, tissue-type PA was expressed throughout the corneal epithelium. Scraping of RCE cell monolayers induced the expression of uPA in the migrating cells at the wound edge. The amount of uPA in the culture medium of RCE cells increased with the number of scrape wounds applied. Wounding also induced a time-dependent increase in the abundance of uPA mRNA in the cell monolayers. The migration of RCE cells was inhibited by antibodies to uPA.

CONCLUSIONS

Mechanical wounding induces up-regulation of uPA at both the protein and mRNA levels in corneal epithelial cells. uPA may thus contribute to epithelial cell migration during corneal epithelial wound healing.

Regulated expression of collagenases MMP-1, -8, and -13 and stromelysins MMP-3, -10, and -11 by human corneal epithelial cells

PURPOSE

This study investigated the regulated expression of collagenases (MMP-1, -8, and -13) and stromelysins (MMP-3, -10, and -11) by human corneal epithelial cells treated with IL-1 beta, TNF-alpha, and doxycycline, a medication used to treat ocular surface diseases.

METHODS

Primary human corneal epithelial cell cultures were treated with IL-1 beta or TNF-alpha, with or without their corresponding inhibitors. Total RNA extracted from cells treated for 4 to 24 hours was subjected to semiquantitative RT-PCR and Northern hybridization. Conditioned media from 24-hour-treated cultures were evaluated for MMP production by ELISA and activity assays.

RESULTS

Semiquantitative RT-PCR and Northern hybridization revealed that the mRNAs of MMP-1, -13, -3, -10, and -11 were dose dependently upregulated by IL-1 beta and TNF-alpha, whereas MMP-8 and -14 and tissue inhibitor of metalloproteinase (TIMP)-1 were not altered, in corneal epithelial cells. MMP ELISA and activity assays confirmed this dose-dependent increase in MMP-1, -13, -3, and -10 protein production in conditioned media by IL-1 beta and TNF-alpha. This stimulated production was inhibited by their neutralizing antibodies and by IL-1 receptor antagonist. Doxycycline suppressed stimulated MMP-1, -10, and -13 production at both the mRNA and protein levels.

CONCLUSIONS

This study demonstrated that IL-1 beta and TNF-alpha upregulate collagenases (MMP-1, -13) and stromelysins (MMP-3, -10, and -11) in human corneal epithelial cells. Doxycycline suppresses stimulated MMP-1, -13, and -10 at the mRNA and protein levels, which suggests that collagenases and stromelysins may play a role in the pathogenesis of sterile corneal ulceration and other ocular surface diseases.

Effects of topical nonsteroidal antiinflammatory drugs on the expression of matrix metalloproteinases in the cornea

PURPOSE

To assess the effects of nonsteroidal antiinflammatory drug (NSAID) eyedrops on the expression of matrix metalloproteinases in corneal tissue.

SETTING

Ocular Microbiology and Immunology Laboratory, Refractive Surgery Research Laboratory, The Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, USA.

METHODS

Seventy rats were divided into 2 groups: intact and debrided epithelium. Uniform central corneal epithelial defects were created in the right eye of the debrided corneal group. Each group was divided into 4 subgroups, each receiving 1 of the following eyedrops or artificial tears: The 3 NSAIDs were diclofenac sodium 0.1% (Falcon or Voltaren) and preservative-free ketorolac 0.5% (Acular PF). The artificial tears were carboxymethylcellulose sodium 0.5% (Refresh Plus PF). The eyedrops were administered 4 times a day for 1 week. The rats were killed on days 2 and 7. The corneas were excised and processed for immunohistochemical staining, Western blot assay, and zymography studies to determine the localization of the production of the following matrix metalloproteinases (MMPs): MMP-1, MMP-2, MMP-8, and MMP-9.

RESULTS

Matrix metalloproteinase-1, MMP-8, and MMP-2 were detected in rat corneas at 48 hours in the debrided and intact epithelium groups treated with NSAID eyedrops. The MMP-1 and MMP-8 expression levels were higher in intact corneas in the diclofenac sodium groups than in the ketorolac and artificial tears groups. The expression was localized mostly in the epithelial cells and occasionally in keratocytes.

CONCLUSION

This study provides preliminary evidence that topical application of some NSAIDs can induce the early expression of MMP-1, MMP-2, and MMP-8 in the cornea, suggesting that MMPs play a role in the corneal cytotoxicity of certain NSAIDs.