Four subunits (αβγδ) of the epithelial sodium channel (ENaC) are expressed in the human eye in various locations

PURPOSE

The epithelial sodium channel (ENaC) is typically expressed in sodium-absorbing epithelia. Several reports suggest that ENaC is also expressed in ocular tissues and may play a role in aqueous humor secretion and glaucoma. However, the precise localization of ENaC in the human eye is still unclear. Here, the authors studied ENaC expression in 12 normal human donor eyes and in six eyes of patients with glaucoma.

METHODS

Quantitative real-time PCR was used to investigate the expression of α-, β-, γ-, and δ-ENaC transcripts in ocular tissues. In addition, the authors performed immunohistochemical studies using recently generated antibodies against human β- and γ-ENaC.

RESULTS

At the mRNA level, all four ENaC subunits were found to be expressed in a wide range of ocular tissues from normal and glaucomatous human eyes, with the cornea, ciliary body, iris, and retina showing the highest expression levels. At the protein level, β- and γ-ENaC subunits showed distinct distribution patterns and could be immunolocalized primarily to the cell membranes of epithelial cells of the cornea and to the conjunctiva, iris, ciliary body, lens, and retinal pigment epithelium but also to vascular endothelial cells, smooth muscle cells, stromal cells, and retinal neurons. The authors found no altered mRNA level of any subunit in glaucomatous eyes.

CONCLUSIONS

All four ENaC subunits (αβγδ) are expressed in the normal human eye, with distinct localization of subunits possibly reflecting different functional states of the channel. The (patho-)physiological roles of ENaC in the various localizations in the eye remain to be determined.

Corneal higher-order aberrations after Descemet's membrane endothelial keratoplasty

PURPOSE

We compared corneal higher-order aberrations (HOAs) in eyes after Descemet's membrane endothelial keratoplasty (DMEK), Descemet's stripping automated endothelial keratoplasty (DSAEK), and penetrating keratoplasty (PK), and in a control group that had not undergone surgery.

DESIGN

Retrospective analysis of clinical data.

PARTICIPANTS

Thirty eyes of 30 patients who had undergone standard DMEK, 20 eyes of 20 patients after DSAEK, 20 eyes of 20 patients after PK, and 20 eyes of 20 controls were analyzed.

METHODS

In addition to standard postoperative examinations, each participant was analyzed with the Pentacam high-resolution rotating Scheimpflug imaging system (Pentacam HR, Oculus, Wetzlar, Germany). Data were compared between groups.

MAIN OUTCOME MEASURES

Visual acuity and HOAs.

RESULTS

The mean follow-up was 6.5 ± 1.2 months after DMEK, 22.6 ± 11.8 months after DSAEK, and 103.1 ± 74.2 months after PK. There were no statistically significant differences for the anterior 4.0-mm zones between the DMEK group and the controls or between the DMEK and DSAEK groups. The DMEK procedure compared with PK showed statistically significant differences in all terms for the 4.0-mm zones. All combined Zernike terms for mean posterior aberrations of the central 4.0-mm zones showed statistically significant higher aberrations for DMEK compared with controls. The DMEK procedure compared with DSAEK showed statistically significant lower mean values for all combined Zernike terms, except for coma and coma-like terms in the central 4.0-mm zones of the posterior corneal surface. Compared with PK, DMEK showed statistically significant lower mean values for all combined Zernike terms for the central 4.0-mm zones of the posterior corneal surface, except for spherical aberration (SA) and SA-like terms. Best spectacle-corrected visual acuity (BSCVA) after DMEK was statistically significantly better than after DSAEK (P=0.001) and PK (P=0.005). There was no statistically significant difference when BSCVA was compared with controls (P=0.998).

CONCLUSIONS

Both DSAEK and PK exhibit increased posterior corneal HOAs even years after surgery. Patients receiving DMEK display only slight changes in posterior corneal HOAs.

Regulation of lysyl oxidase-like 1 (LOXL1) and elastin-related genes by pathogenic factors associated with pseudoexfoliation syndrome

PURPOSE

Pseudoexfoliation (PEX) syndrome/glaucoma is a complex, late-onset disorder of the elastic fiber system. Strong genetic risk is conferred by the lysyl oxidase-like 1 (LOXL1) gene, but additional comodulating factors are necessary for the manifestation of the disease. The aim of this study was to analyze the effect of various PEX-associated pathogenic factors on the genotype-correlated expression of LOXL1 and elastin-related genes.

METHODS

Cultured human Tenon's capsule fibroblasts with high- and low-risk LOXL1 haplotypes were exposed to transforming growth factor (TGF)-β1, interleukin (IL)-6, homocysteine, oxidative stress, hypoxia, or ultraviolet (UV) radiation. Changes in the expression of LOXL1 and elastic constituents of PEX material and TGF-β1 were assessed by quantitative real-time PCR, Western blotting, immunohistochemistry, and electron microscopy.

RESULTS

Treatment of fibroblasts with TGF-β1, oxidative stress, UV light, and hypoxia induced a significant increase in expression levels of LOXL1 and elastic proteins, whereas the effect of IL-6 was limited to induction of elastic constituents. Immunohistochemistry and electron microscopy confirmed an upregulation of LOXL1 and elastic fiber proteins and their assembly into extracellular microfibrillar networks with focal aggregation of microfibrils into PEX-like fibrils on stimulation with TGF-β1 and oxidative stress. Basal and stimulated expression of LOXL1 mRNA and protein was slightly decreased in cells carrying the high-risk compared with the low-risk haplotype of LOXL1, but the differences between groups were statistically not significant.

CONCLUSIONS

The findings support the notion that both genetic and nongenetic fibrogenic factors, particularly TGF-β1 and oxidative stress, may cooperate in the stable accumulation of PEX aggregates.

Split cornea transplantation for 2 recipients - review of the first 100 consecutive patients

PURPOSE

To evaluate the feasibility of split cornea transplantation for 2 recipients by combining deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK).

DESIGN

Interventional case series.

METHODS

Fifty consecutive eyes with anterior stromal disease suitable for DALK and 50 eyes with endothelial disease suitable for DMEK were scheduled for split cornea transplantation combining both procedures within 72 hours. Main outcome measures included success of using a single donor cornea for 2 recipients, best spectacle-corrected visual acuity (BSCVA), and complication rates within 6 months' follow-up.

RESULTS

A single donor cornea could be used for 2 recipients in 47 cases (94%). In 3 eyes (6%), the DALK procedure had to be converted to penetrating keratoplasty (PK) requiring a full-thickness corneal graft. Thereby, 47 donor corneas (47%) could be saved. Six months after surgery, mean BSCVA was 20/36 in the 47 eyes that underwent successful DALK, 20/50 in the 3 eyes that underwent conversion from DALK to PK, and 20/29 in the 50 eyes that underwent DMEK. Postoperative complications after DALK included Descemet folds in 5 eyes (11%) and epitheliopathy in 3 eyes (6%). After DMEK, partial graft detachment occurred in 26 eyes (52%) and was managed successfully with intracameral air reinjection. All corneas remained clear up to 6 months after surgery. No intraocular infections occurred.

CONCLUSION

Split use of donor corneal tissue for combined DALK and DMEK procedures in 2 recipients within 3 subsequent days is a feasible approach to reduce donor shortage in corneal transplantation in the future.

Evidence of endothelial cell migration after descemet membrane endothelial keratoplasty

PURPOSE

To investigate the hypothesis that adult corneal endothelial cells can migrate after Descemet membrane endothelial keratoplasty (DMEK).

DESIGN

Prospective observational study.

METHODS

Five patients with Fuchs endothelial dystrophy were examined 1 year after uneventful DMEK. These patients had been selected on the basis of slightly decentered grafts and/or large descemetorrhexis showing areas of denuded corneal stroma, which were covered by neither the patients' Descemet membrane (DM) nor the graft. These areas were investigated by in vivo confocal laser scanning microscopy using a specially designed Heidelberg Retina Tomograph II and Rostock cornea module equipped with custom-made software. Source data (frame rate 30 Hz, 384 × 384 pixels, 400 × 400 μm) were used to create large-scale maps of the scanned area in automatic real-time composite mode. In each case an on-line mapping with maximum size up to 3.2 × 3.2 mm (3072 × 3072 pixels) was performed.

RESULTS

Corneal stroma overlying areas devoid of DM was transparent. In vivo confocal laser scanning microscopy of stroma devoid of DM revealed a monolayer of endothelial cells in all patients observed. The morphologic pattern of these cells was similar to that of endothelial cells on DM grafts but different from the morphology of the patients' own endothelium, suggesting migration of donor endothelial cells from DMEK grafts.

CONCLUSIONS

The results strongly support the hypothesis that adult corneal endothelial cells are able to migrate in the human eye. Furthermore, we provide evidence to support the hypothesis that grafted endothelium migrates onto the host tissue, repopulating the corneal stroma with a regular endothelial phenotype.

Pathogenesis of involutional ectropion and entropion: the involvement of matrix metalloproteinases in elastic fiber degradation

PURPOSE

To determine the elastic fiber content and ultrastructure as well as the expression of elastin-degrading enzymes in biopsy specimens from patients with involutional ectropion and entropion.

MATERIALS AND METHODS

Twenty consecutive patients with involutional ectropion (group 1) and twenty consecutive patients with entropion (group 2) were matched with twenty control patients (basal cell carcinoma) regarding age and gender. Full-thickness eyelid resections performed in study and control patients were examined by light and transmission electron microscopy, computer-assisted measurements, and immunohistochemistry using antibodies against matrix metalloproteinase (MMP)-2, MMP- 7, and MMP-9. The Kruskal-Wallis test and the Pearson chi-square test were performed.

RESULTS

Histopathologic analysis of the surgical specimens from patients with involutional ectropion and entropion showed a significant loss of elastic fibers in the eyelid skin, the pretarsal orbicularis oculi muscle, the perimeibomian tarsal stroma, and the intermeibomian tarsal stroma (P < 0.001). Residual elastic fibers revealed an abnormal ultrastructure. Immunohistochemistry demonstrated a significant overexpression of MMP- 2, MMP-7, and MMP-9 in the eyelid skin, the pretarsal orbicularis oculi muscle, the perimeibomian tarsal stroma, the intermeibomian tarsal stroma, and the conjunctiva in groups 1 and 2 compared to controls (P < 0.001).

CONCLUSIONS

The present findings indicate that upregulation of elastolytic enzymes contributes to elastic fibre degradation in patients with involutional ectropion and entropion.

[Selective lacrimal sac biopsy for external dacryocystorhinostomy: a clinical pathological study]

BACKGROUND

Tumors of the lacrimal drainage system are rare but potentially life-threatening. The purpose of this study was to investigate the applicability of selective lacrimal sac biopsy in 500 cases of external dacryocystorhinostomy for acquired dacryostenosis.

PATIENTS AND METHODS

Lacrimal sac biopsy was obtained selectively for atypical clinical and/or intraoperative findings. The frequency and spectrum of biopsies were recorded and correlated with the follow-up results.

RESULTS

Lacrimal sac biopsy was performed in 19 external dacryocystorhinostomies (3.8%) including non-Hodgkin B-cell lymphoma (3), squamous carcinoma (2), mucoepidermoid carcinoma (1), malignant melanoma (1), oncocytoma (1), pyogenic granuloma (4), Wegener's granulomatosis (4) and sarcoidosis (3). Within 5 years none of the patients without biopsy developed systemic inflammatory diseases or lacrimal neoplasms. The 5-year survival was 87% in patients with significant lacrimal sac pathology and 96% in patients without significant pathology.

CONCLUSION

External dacryocystorhinostomy with selective biopsy for atypical clinical and intraoperative findings allows safe diagnosis and management of potentially life-threatening lacrimal lesions.

Myofibroblast metaplasia after descemet membrane endothelial keratoplasty

PURPOSE

To describe myofibroblastic metaplasia of corneal endothelial cells in 2 cases with impaired visual function despite complete graft adherence after Descemet membrane endothelial keratoplasty (DMEK).

DESIGN

Interventional case series.

METHODS

In 2 of 90 consecutive DMEK surgeries, the cornea failed to clear up to 6 months postoperatively despite complete graft attachment. After secondary penetrating keratoplasty, both corneal buttons were examined using histopathologic analysis and transmission electron microscopy.

RESULTS

Light microscopy revealed distinct corneal endothelial cell attenuation with the presence of an abnormal posterior collagenous layer in both cases. Most of the remaining endothelial cells had an elongated fibroblast-like appearance with immunopositivity for α-smooth muscle actin indicative of myofibroblast metaplasia. Transmission electron microscopy showed a slightly thickened Descemet membrane with an abnormal posterior fibrillar collagenous layer and a myofibroblast-like transformation of the remaining endothelial cells. Descemet membrane grafts closely adjoined the collagen lamellae of the host corneal stroma similar to the Descemet membrane-stroma interface of a normal cornea.

CONCLUSION

Myofibroblastic metaplasia of attenuated corneal endothelial cells with formation of an abnormal posterior collagenous layer may contribute to an impaired visual function despite complete graft adherence after Descemet membrane endothelial keratoplasty (DMEK).

Donor tissue culture conditions and outcome after descemet membrane endothelial keratoplasty

PURPOSE

To investigate the effect of culture conditions of donor tissue on functional outcome after Descemet membrane endothelial keratoplasty.

DESIGN

Retrospective, single-center, consecutive case series.

METHODS

Descemet membrane endothelial keratoplasty was performed routinely in 82 eyes of 82 consecutive patients using corneal donor tissue prestored in either short-term culture (Optisol-GS; Bausch & Lomb) at 4 C (group A; n = 37) or organ culture (Dulbecco Modified Eagle Medium [Biochrom]; CorneaMax Medium [Eurobio]) at 34 C (group B; n = 45) in a randomized fashion. Main outcome measures included the number of air injections necessary for graft attachment as well as best-corrected visual acuity (in logarithm of the minimal angle of resolution [logMAR] units), central corneal thickness, and endothelial cell density at 1, 3, and 6 months after surgery.

RESULTS

Best-corrected visual acuity increased from 0.69 ± 0.53 logMAR and 0.67 ± 0.31 logMAR before surgery to 0.33 ± 0.21 logMAR and 0.28 ± 0.18 logMAR after 1 month (P < .05), to 0.24 ± 0.16 logMAR and 0.18 ± 0.16 logMAR after 3 months (P < .05), and to 0.18 ± 0.12 logMAR and 0.15 ± 0.10 logMAR after 6 months (n.s.) in groups A and B, respectively. Endothelial cell density decreased from 2647 ± 236 cells/mm(2) and 2515 ± 249 cells/mm(2) before surgery to 1499 ± 277 cells/mm(2) and 1526 ± 205 cells/mm(2) after 1 month (P < .05), to 1441 ± 213 cells/mm(2) and 1443 ± 316 cells/mm(2) after 3 months (n.s.), and to 1587 ± 366 cells/mm(2) and 1457 ± 285 cells/mm(2) after 6 months (n.s.) in groups A and B, respectively. Central corneal thickness declined from 664 ± 89 and 662 ± 107 μm before surgery to 529 ± 92 μm and 517 ± 62 μm after 1 month (P < .05), to 511 ± 46 μm and 510 ± 46 μm after 3 months (P < .05), and to 529 ± 68 μm and 507 ± 50 μm after 6 months (n.s.) in groups A and B, respectively. Best-corrected visual acuity, endothelial cell density, and central corneal thickness values showed no significant differences between both groups at any time point after surgery. However, a significantly higher total number of air injections was necessary in group A (n = 34) compared with group B (n = 26) to obtain graft attachment (P < .05).

CONCLUSIONS

These findings suggest that donor tissue culture conditions have no significant effect on functional outcome, but may influence graft adhesion and rebubbling rate after Descemet membrane endothelial keratoplasty surgery.

From hair to cornea: toward the therapeutic use of hair follicle-derived stem cells in the treatment of limbal stem cell deficiency

Limbal stem cell deficiency (LSCD) leads to severe ocular surface abnormalities that can result in the loss of vision. The most successful therapy currently being used is transplantation of limbal epithelial cell sheets cultivated from a limbal biopsy obtained from the patient's healthy, contralateral eye or cadaveric tissue. In this study, we investigated the therapeutic potential of murine vibrissae hair follicle bulge-derived stem cells (HFSCs) as an autologous stem cell (SC) source for ocular surface reconstruction in patients bilaterally affected by LSCD. This study is an expansion of our previously published work showing transdifferentiation of HFSCs into cells of a corneal epithelial phenotype in an in vitro system. In this study, we used a transgenic mouse model, K12(rtTA/rtTA) /tetO-cre/ROSA(mTmG) , which allows for HFSCs to change color, from red to green, once differentiation to corneal epithelial cells occurs and Krt12, the corneal epithelial-specific differentiation marker, is expressed. HFSCs were isolated from transgenic mice, amplified by clonal expansion on a 3T3 feeder layer, and transplanted on a fibrin carrier to the eye of LSCD wild-type mice (n = 31). The HFSC transplant was able to reconstruct the ocular surface in 80% of the transplanted animals; differentiating into cells with a corneal epithelial phenotype, expressing Krt12, and repopulating the corneal SC pool while suppressing vascularization and conjunctival ingrowth. These data highlight the therapeutic properties of using HFSC to treat LSCD in a mouse model while demonstrating a strong translational potential and points to the niche as a key factor for determining stem cell differentiation.

SPARC is expressed in scars of the Tenon's capsule and mediates scarring properties of human Tenon's fibroblasts in vitro

PURPOSE

To investigate the expression of the matricellular protein SPARC (secreted acidic cysteine-rich glycoprotein) in scarred human Tenon's capsule and in cultured human Tenon's fibroblasts (HTF), and to analyze the influence of SPARC on cell proliferation and collagen matrix contraction in vitro.

METHODS

Human Tenon's capsule scars obtained from surgical revisions after filtration surgery were analyzed for SPARC expression by immunohistochemistry. In cultured HTF cells, SPARC expression was assessed by northern and western blot analyses after incubation with transforming growth factor (TGF)-β1 and TGF-β2. Cell proliferation was determined by bromodeoxyuridine (BrdU)-labeling and HTF cells-mediated collagen matrix contraction by morphometric measurements of three-dimensional collagen lattices after treatment with SPARC and/or TGF-β1.

RESULTS

In scarred human Tenon's capsule specimens, an increased expression of SPARC was mainly localized to the extracellular matrix and to blood vessel walls as compared to healthy control Tenon's capsule. In cultured HTF cells, treatment with TGF-β1 more than TGF-β2 induced the expression of SPARC both on the mRNA and protein level. Incubation of HTF cells with SPARC resulted in an increase in collagen matrix contraction and cell proliferation. Moreover, a combined incubation of SPARC and TGF-β1 stimulated HTF cell proliferation significantly over the levels that were observed after single treatment.

CONCLUSIONS

Our data provide evidence that SPARC contributes to excessive wound healing and scar formation in human Tenon's capsules after filtration surgery and may thus represent a novel target for anti-fibrotic strategies.

Tumors of the lacrimal drainage system

Tumors of the lacrimal drainage system are rare, but potentially life-threatening. They comprise a large and variable spectrum of entities grouped into three major categories of primary epithelial, primary nonepithelial and inflammatory lesions. The most common primary epithelial tumors include papilloma, squamous cell carcinoma and transitional cell carcinoma, the most frequent primary nonepithelial tumors fibrous histiocytoma, malignant lymphoma and malignant melanoma, and the most common inflammatory lesions sarcoidosis, Wegener granulomatosis and pyogenic granuloma. This review outlines the incidence, types, management and prognosis of tumors affecting the lacrimal drainage system.

Genome-wide association study with DNA pooling identifies variants at CNTNAP2 associated with pseudoexfoliation syndrome

Genetic and nongenetic factors contribute to development of pseudoexfoliation (PEX) syndrome, a complex, age-related, generalized matrix process frequently associated with glaucoma. To identify specific genetic variants underlying its etiology, we performed a genome-wide association study (GWAS) using a DNA-pooling approach. Therefore, equimolar amounts of DNA samples of 80 subjects with PEX syndrome, 80 with PEX glaucoma (PEXG) and 80 controls were combined into separate pools and hybridized to 500K SNP arrays (Affymetrix). Array probe intensity data were analyzed and visualized with expressly developed software tools GPFrontend and GPGraphics in combination with GenePool software. For replication, independent German cohorts of 610 unrelated patients with PEX/PEXG and 364 controls as well as Italian cohorts of 249 patients and 190 controls were used. Of 19, 17 SNPs showing significant allele frequency difference in DNA pools were confirmed by individual genotyping. Further single genotyping at CNTNAP2 locus revealed association between PEX/PEXG for two SNPs, which was confirmed in an independent German but not the Italian cohort. Both SNPs remained significant in the combined German cohorts even after Bonferroni correction (rs2107856: P(c)=0.0108, rs2141388: P(c)=0.0072). CNTNAP2 was found to be ubiquitously expressed in all human ocular tissues, particularly in retina, and localized to cell membranes of epithelial, endothelial, smooth muscle, glial and neuronal cells. Confirming efficiency of GWAS with DNA-pooling approach by detection of the known LOXL1 locus, our study data show evidence for association of CNTNAP2 with PEX syndrome and PEXG in German patients.

Split cornea transplantation for 2 recipients: a new strategy to reduce corneal tissue cost and shortage

PURPOSE

To evaluate the feasibility of using a single donor cornea for 2 recipients by combining deep anterior lamellar keratoplasty (DALK) and Descemet's membrane endothelial keratoplasty (DMEK) surgeries on the same day.

DESIGN

Single-center, nonrandomized, prospective, interventional case series.

PARTICIPANTS

Twelve consecutive donor corneas were scheduled for split cornea transplantation combining DALK for a keratoconus patient and DMEK for a Fuchs' endothelial dystrophy patient on the same surgery day.

METHODS

First, a big-bubble DALK procedure was performed for the keratoconus eye. When bare Descemet's membrane was prepared successfully requiring no conversion to penetrating keratoplasty (PK), then during surgery the donor, endothelium-Descemet's membrane layer was removed and stored for subsequent DMEK in a second patient, and the remaining anterior lamella of the donor cornea was used to complete the DALK surgery. Afterward, a DMEK procedure was performed on the second patient with Fuchs' endothelial dystrophy, grafting the stored endothelium-Descemet's membrane layer of the original donor button.

MAIN OUTCOME MEASURES

Success of using a single donor cornea for 2 recipient eyes, best spectacle-corrected visual acuity (BSCVA), and complication rates within 6 months follow-up.

RESULTS

A single donor cornea could be used for 2 recipients in 10 of 12 donor buttons (83%). In 2 cases (17%), the DALK procedure had to be converted to PK requiring a full-thickness corneal graft. Therefore, 10 donor corneas (45%) could be saved. Six months after surgery, mean BSCVA was 20/35 (range, 20/50-20/25) in 10 eyes that underwent successful DALK, 20/50 (range, 20/63-20/40) in 2 eyes that underwent conversion from DALK to PK, and 20/31 (range, 20/50-20/16) in 10 eyes that underwent DMEK. Postoperative complications after DALK included Descemet's folds in 3 eyes (30%) and epitheliopathy in 2 eyes (20%). After DMEK, partial graft detachment occurred in 5 eyes (50%) and was managed successfully with intracameral air reinjection. All corneas remained clear up to 6 months after surgery.

CONCLUSIONS

Split use of donor corneal tissue for combined DALK and DMEK procedures in 2 recipients on the same surgery day is a promising strategy to reduce donor shortage and cost in corneal transplantation surgery in the future.

Proinflammatory cytokines are involved in the initiation of the abnormal matrix process in pseudoexfoliation syndrome/glaucoma

Pseudoexfoliation (PEX) syndrome, which is an age-related, generalized elastotic matrix process, currently represents the most common identifiable risk factor for open-angle glaucoma. Dysregulated expression of proinflammatory cytokines has been implicated in the initiation of various fibrotic disorders and in the pathophysiology of glaucoma. Here we investigated the presence, expression, regulation, and functional significance of proinflammatory cytokines in eyes with early and late stages of PEX syndrome/glaucoma in comparison with normal and glaucomatous control eyes using multiplex bead analysis, immunoassays, real-time PCR, Western blotting, immunohistochemistry, and cell culture models. Early stages of PEX syndrome were characterized by approximately threefold (P < 0.005) elevated interleukin (IL)-6 and IL-8 levels in the aqueous humor and a concomitant approximately twofold (P < 0.001) increase in mRNA expression levels in anterior segment tissues as compared with controls. In contrast, late stages of PEX syndrome/glaucoma did not differ significantly from controls. IL-6, IL-6 receptor, and phospho-signal transducer and activator of transcription 3 could be mainly localized to walls of iris vessels and to the nonpigmented epithelium of ciliary processes. IL-6 and IL-8 were significantly up-regulated by ciliary epithelial cells in response to hypoxia or oxidative stress in vitro, whereas IL-6, but not IL-8, induced the expression of transforming growth factor-beta1 and elastic fiber proteins. These findings support a role for a stress-induced, spatially, and temporally restricted subclinical inflammation in the onset of the fibrotic matrix process characteristic of PEX syndrome/glaucoma.

The prostaglandin transporter OATP2A1 is expressed in human ocular tissues and transports the antiglaucoma prostanoid latanoprost

PURPOSE

Latanoprost, a prostaglandin F(2alpha) analogue, has become one of the most widely used medications for the treatment of glaucoma. The authors hypothesized that organic anion transporting polypeptides (OATPs) are responsible for the uptake of latanoprost into ocular tissues and, hence, that they contribute to the interindividual differences in drug concentrations and effects.

METHODS

Expression of prostaglandin (PG) transporters (OATP2A1, OATP2B1) in human ocular tissues was determined using real-time RT-PCR and immunofluorescence. The inhibitory interactions between latanoprost and its active metabolite (the free acid) and the uptake of prototypical substrates (PGE(2) and bromosulfophthalein) were tested in stably transfected human embryonic kidney cells overexpressing either OATP2A1 or OATP2B1. These cells were also used to investigate whether latanoprost and latanoprost acid are substrates of OATP2A1 or OATP2B1.

RESULTS

OATP2A1 and OATP2B1 mRNA expression was highest in the choroid/retinal pigment epithelium (RPE) complex and ciliary body. OATP2A1 protein expression was most prominent in the RPE and in epithelial and endothelial cell layers of anterior segment tissues, such as cornea, conjunctiva, iris, and ciliary body, whereas OATP2B1 protein was additionally expressed in trabecular meshwork, Schlemm canal, and choroidal vasculature. Latanoprost and latanoprost acid significantly inhibited both OATP2A1 and OATP2B1. Uptake experiments demonstrated that latanoprost acid is effectively transported by OATP2A1 (affinity constant [K(m)], 5.4 microM; maximum uptake rate [V(max)], 21.5 pmol/mg protein/min) and less effectively by OATP2B1.

CONCLUSIONS

The results presented herein suggest that at least OATP2A1 plays a role in the intraocular disposition of the therapeutically used prostanoid latanoprost.