Biomedical subjects

Scheffer C G Tseng

Publications and source records attributed to Scheffer C G Tseng.

62 records · Page 4Linked to original sources

PubMed2002

Management of primary and recurrent pterygium using amniotic membrane transplantation.

This review discusses the relative merits of the various techniques used in pterygium surgery with particular reference to the growing interest in the use of amniotic membrane transplantation (AMT) because it is safe, effective, and may be employed in conjunction with other techniques, such as limbal transplantation. The efficacy of AMT is comparable to the established method of conjunctival autograft transplantation (CG) and it is especially indicated when there exists a very large conjunctival defect to cover as in primary double-headed pterygium, or in the context of preserving superior bulbar conjunctiva for future glaucoma surgeries. The authors explain how current management principles (eg, use of anti-inflammatory agents, adequate removal of fibrovascular tissue) are based on known differences in pathogenesis and clinical behavior between primary and recurrent pterygium.

Amnion↗

PubMed2002

Connexin 43 expression and proliferation of human limbal epithelium on intact and denuded amniotic membrane.

PURPOSE: Stem cell (SC)-containing limbal basal epithelium and transient amplifying cell (TAC)-containing corneal basal epithelium lie on different mesenchymal matrices. The gap junction protein connexin 43 (Cx43) is absent in the limbal basal epithelium but is present in the corneal basal epithelium, suggesting that the expression of Cx43 denotes SC differentiation into TACs. Amniotic membrane (AM) can expand limbal epithelial progenitor cells in vivo and in culture for subsequent corneal surface reconstruction. In this study, the modulation of Cx43 expression, gap junction intercellular communication (GJIC), and proliferative activity of ex vivo expanded human limbal epithelial (HLE) cells on intact and epithelially denuded AM was investigated. METHODS: HLE cells were expanded on intact (i.e., remaining devitalized amniotic epithelium) or epithelially denuded AM (EDTA-treated). Cx43 expression and 24-hour 5-bromo-2'-deoxyuridine-5'monophosphate (BrdU) labeling index (percentage) were determined by double immunostaining. GJIC was investigated by a scrape-loading dye transfer assay. In a subset of cultures Cx43 and K3 keratin as well as BrdU-retaining nuclei were analyzed in the stratified epithelium obtained 5 days after subcutaneous transplantation in NIH bg-nu-xidBR mice of AM cultures continuously labeled with BrdU for 7 days. RESULTS: The outgrowth rate, overall, was significantly higher on EDTA-treated AM than on intact AM (P < 0.05). Cx43 was expressed in 12.4% +/- 14.5% (n = 5) on intact and 57.5% +/- 18.2% (n = 5) on EDTA-treated AM (P < 0.05). The BrdU labeling index was 2.4% +/- 0.9% (n = 5) for the intact AM group, which was significantly less than 22.5% +/- 8.2% (n = 5) for EDTA-treated AM (P < 0.05). BrdU-labeled cells did not express Cx43. The dye transfer assay revealed reduced GJIC on both AM-cultured groups compared with the control culture on plastic (P < 0.002). GJIC on intact AM (17%) was reduced compared with that on EDTA-treated AM (27%; P = 0.42). After xenotransplantation, the basal layer of the stratified epithelium was Cx43 and K3 keratin negative and retained BrdU on intact AM, resembling characteristics of the limbal basal epithelium in vivo. In contrast, that of EDTA-treated AM was Cx43 and K3 keratin positive without BrdU retention, resembling characteristics of the corneal epithelium in vivo. CONCLUSION: These data indicate that denudation of the devitalized amniotic epithelium to expose its basement membrane might be a microenvironmental cue to promote TAC differentiation. The model system described herein is ideal for future exploration of the exact mechanistic operation in the microenvironmental niche that maintains the "stemness" of limbal SCs as well as in the signal that promotes corneal TAC differentiation.

Amnion↗

PubMed2002

The role of NGF signaling in human limbal epithelium expanded by amniotic membrane culture.

PURPOSE: Amniotic membrane (AM) transplantation facilitates rapid epithelialization in severe neurotrophic corneal ulcers. To elucidate its action mechanism, we investigated the expression of ligands and receptors of the neurotrophin family by human limbal epithelial (HLE) cells expanded on AM cultures. METHODS: Expression of nerve growth factor (NGF); neurotrophins (NT)3 and NT4; brain-derived neurotrophic factor (BDNF); tyrosine kinase-transducing receptors TrkA, TrkB, and TrkC; and a pan-NT low-affinity receptor (p75(NTR)) was examined by immunostaining in the normal human corneolimbus, HLE grown on intact epithelially denuded AM, and stratified HLE, after subcutaneous implantation in NIH-bg-nu-xid BR mice. NGF protein level was assayed by an ELISA in extracts of intact and epithelially denuded AM. K252a, a specific inhibitor of TrkA autophosphorylation, was added to test whether it would inhibit HLE expansion on AM culture. RESULTS: Strong positive TrkA staining was confined to the basal epithelial cell layer of normal corneal and limbal epithelia, with the highest intensity noted in the limbus. TrkA staining was also strongly positive in the basal layer of HLE cells cultured on intact and epithelially denuded AM and in basal and some suprabasal layers of stratified HLE transplanted in nude mice. Positive staining of p75(NTR) was noted in the full-thickness of the corneal epithelium but was limited to the superficial layers of the limbus and in HLE cells cultured on intact and epithelially denuded AM, but was weak in HLE transplanted to nude mice. Weak staining of NT3 and TrkC was noted in the suprabasal layers of corneal and limbal epithelia but was negative in the stratified HLE in nude mice. Negative staining of NGF, NT4, BDNF, and TrkB was noted in all specimens tested. The NGF protein level was readily measured as 35.6 +/- 9.1 and 41 +/- 12.5 pg/mg protein in the homogenate of the intact and epithelially denuded AM, respectively (P = 0.0256). K252a significantly inhibited the HLE outgrowth on intact AM culture (P = 0.024). CONCLUSIONS: The strong expression of TrkA but not p75(NTR) in the limbal basal epithelial cells in vivo suggests that NGF signaling favors limbal epithelial stem cell survival. Such a phenotype is preserved in HLE cells on AM. Blocking NGF signaling significantly retarded HLE expansion on AM, supporting the notion that NGF is important in expansion of limbal epithelial progenitor cells. Furthermore, a high and therapeutic level of NGF was present in AM. Collectively, these findings indicate that denervated neurotrophic ulcers are associated with poor epithelial stem cell function at the limbus. Future studies are needed to determine whether AM transplantation to heal such ulcers may include the promotion of nerve regeneration and survival of epithelial progenitor cells.

Amnion↗

PubMed2002

Factors affecting outcome following transplantation of ex vivo expanded limbal epithelium on amniotic membrane for total limbal deficiency in rabbits.

PURPOSE: To determine factors affecting the outcome of corneal surface reconstruction in rabbits with total limbal stem cell deficiency (LSCD), by using autologous limbal epithelial stem cells (LSC) ex vivo, expanded on rabbit amniotic membrane (AM). METHODS: Left eyes of 52 rabbits were rendered totally limbal stem cell deficient by n-heptanol debridement of the entire corneal epithelium followed by surgical removal of 360 degrees of limbal rim. After cytologic verification of LSCD, the fibrovascular pannus of each cornea was removed. Group I (n = 10) received a rabbit AM transplant, whereas groups II, III, and IV (n = 42) underwent transplantation of LSCs cultured on rabbit AM (LSC-AM graft) derived from a small limbal biopsy specimen from the right eye. Clinical outcome was graded as a success if a smooth, avascular corneal surface was restored, a partial success if more than two quadrants of corneal surface were smooth, or a failure if the corneal surface was revascularized and irregular. RESULTS: A long-term follow-up of more than 1 year was achieved. Compared with the 100% failure rate in group I, inclusion of expanded LSCs resulted in variable success rates in groups II, III, and IV (all P < 0.001). Kaplan-Meier survival analysis showed that different suturing techniques, subconjunctival injection of long-acting steroid, and tarsorrhaphy used in groups II (n = 17) and III (n = 13) did not significantly alter the outcome (P = 0.89). However, the use of a larger graft and human AM as a temporary patch with the explant retained for 1 week in group IV (n = 12) significantly improved the success rate to 83% (P = 0.002). Among eyes showing clinical failure, there was a significant correlation between the logarithm of the first day when an epithelial defect was noted and the time of graft failure (r(2) = 0.60, P < 0.001). Furthermore, the presence of severe lid deformity was borderline significant when correlated with failure cases in all four groups (P = 0.069). CONCLUSIONS: Ex vivo expansion of LSCs can be achieved by using rabbit AM culture. Such expanded LSCs can successfully reconstruct corneal surfaces affected by total LSCD. This animal model is useful to investigate culturing variables affecting epithelial stemness so that surgical reconstruction of corneas with total LSCD can be successfully performed. Furthermore, this model can be used to test the feasibility of gene therapies targeting LSCD in the future.

Amnion↗

PubMedDate not supplied

Ex vivo expansion of limbal epithelial stem cells: amniotic membrane serving as a stem cell niche.

Identification, maintenance, and expansion of stem cells for subsequent transplantation has become a new strategy for treating many diseases in most medical subspecialties. The stem cells of the corneal epithelium are located in the limbal basal layer and are the ultimate source for constant corneal epithelial renewal. Like those in other tissues, limbal stem cells are supported by a unique stromal microenvironment called the stem cell niche, which consists of certain extracellular matrix components, cell membrane-associated molecules, and cytokine dialogues. Destructive loss of limbal stem cells or dysfunction of their stromal environment renders many corneas with a clinical entity called limbal stem cell deficiency, which is characterized by variable extents of conjunctival ingrowth depending on the severity of limbal damage. A new strategy of treating limbal stem cell deficiency is to transplant a bio-engineered graft by expanding limbal epithelial stem cells ex vivo on amniotic membrane. This review summarizes the published literature data collectively explaining how amniotic membrane is an ideal biological substrate that can help maintain and support the expansion of limbal epithelial stem cells.

Amnion↗

PubMedDate not supplied

Successful management of conjunctival intraepithelial neoplasia by interferon alpha-2b.

BACKGROUND: Interferon alpha-2b (IFN alpha 2b) was recently shown to be effective as an alternative therapy for conjunctival intraepithelial neoplasia (CIN). Herein, we report our successful management of CIN by the use of IFN alpha 2b. CASE: A 73-year-old woman presented with a complaint of irritation due to a tumorous lesion in her left eye. Slit-lamp microscope examination revealed a tumorous lesion involving the bulbar and palpebral conjunctiva as well as the limbus, from the 3-o'clock position to the 8-o'clock position. She had already undergone cryotherapy in the same eye in another hospital, twice for a lesion on the lower tarsal conjunctiva and once for a lesion on the upper tarsal conjunctiva. The histological diagnosis had been CIN. OBSERVATIONS: In treating this patient, IFN alpha 2b was injected subconjunctivally twice and also applied as eye drops for 12 weeks. Two weeks after the initial treatment, the tumorous lesion disappeared. During a 1-year follow-up period, no recurrence was noted. CONCLUSION: Topical and subconjunctival IFN alpha 2b is a valuable treatment option for CIN.

Administration, Topical↗

PubMedDate not supplied

Ocular surface changes in laser in situ keratomileusis-induced neurotrophic epitheliopathy.

PURPOSE: To evaluate the ocular surface changes in patients with laser in situ keratomileusis (LASIK)-induced neurotrophic epitheliopathy. METHODS: Seven consecutive patients with LASIK-induced neurotrophic epitheliopathy were studied prospectively and compared to a control group (seven consecutive patients who had LASIK- but without neurotrophic epitheliopathy). Bilateral sequential LASIK was performed at a 1-week interval; the first operated eye of each patient was considered for statistical analysis. Blinking, corneal sensitivity, tear break-up time, tear secretion and clearance were measured preoperatively (T0) and postoperatively at 1 week after surgery on the first eye (T1), and 1 week (T2), 1 month (T3), and 3 months (T4) after surgery was performed on the second eye. RESULTS: Laser in situ keratomileusis-induced neurotrophic epitheliopathy occurred bilaterally in all patients. During follow-up, patients with LASIK-induced neurotrophic epitheliopathy showed a significant decrease in blinking (P = .0002), which was not observed in cases without LASIK-induced neurotrophic epitheliopathy [corrected] Compared to eyes without LASIK-induced neurotrophic epitheliopathy, those with LASIK-induced neurotrophic epitheliopathy revealed lower values of sensitivity in the central cornea preoperatively and early postoperatively (T0, P = .004; T1, P = .003; T2, P = .003). A trend towards reduced sensitivity was also detected in the central cornea in late follow-up and in the superior, temporal, and nasal sectors of the flap at all examinations. No significant differences were observed in break-up time, tear secretion, or clearance within or between the two groups. CONCLUSION: Decreased blinking seems to be involved in the pathogenesis of LASIK-induced neurotrophic epitheliopathy. The reduction probably depends on the lower levels of corneal sensitivity and induces the epitheliopathy by increasing the ocular surface exposure.

Adult↗

PubMedDate not supplied

Temporary use of a customized, glued-on hard contact lens before penetrating keratoplasty for descemetocele or corneal perforation.

Descemetocele or corneal perforation makes it difficult to perform penetrating keratoplasty (PKP). To circumvent this difficulty, a polymethylmethacrylate hard contact lens with a diameter of 4.0 mm was customized and applied to the cornea with tissue adhesive prior to PKP in three patients, one with corneal perforation and two with descemetoceles. The results showed that this modified method facilitated trephination during PKP without complications in all three patients, suggesting that it may be applicable to other similar clinical situations.

Aged↗