Basement membrane and human epidermal differentiation in vitro

An in vitro comparison of human corneal epithelial cell activity and inflammatory response on differently designed ocular amniotic membranes and a clinical case study

Amniotic membrane (AM) is a naturally derived biomaterial with biological and mechanical properties important to Ophthalmology. The epithelial side of the AM promotes epithelialization, while the stromal side regulates inflammation. However, not all AMs are equal. AMs undergo different processing with resultant changes in cellular content and structure. This study evaluates the effects of sidedness and processing on human corneal epithelial cell (HCEC) activity, the effect of processing on HCEC inflammatory response, and then a case study is presented. Three differently processed, commercially available ocular AMs were selected: (1) Biovance®3L Ocular, a decellularized, dehydrated human AM (DDHAM), (2) AMBIO2®, a dehydrated human AM (DHAM), and (3) AmnioGraft®, a cryopreserved human AM (CHAM). HCECs were seeded onto the AMs and incubated for 1, 4 and 7 days. Cell adhesion and viability were evaluated using alamarBlue assay. HCEC migration was evaluated using a scratch wound assay. An inflammatory response was induced by TNF-α treatment. The effect of AM on the expression of pro-inflammatory genes in HCECs was compared using quantitative polymerase chain reaction (qPCR). Staining confirmed complete decellularization and the absence of nuclei in DDHAM. HCEC activity was best supported on the stromal side of DDHAM. Under inflammatory stimulation, DDHAM promoted a higher initial inflammatory response with a declining trend across time. Clinically, DDHAM was used to successfully treat anterior basement membrane dystrophy. Compared with DHAM and CHAM, DDHAM had significant positive effects on the cellular activities of HCECs in vitro, which may suggest greater ocular cell compatibility in vivo.

Amnion and Chorion Membranes: Potential Stem Cell Reservoir with Wide Applications in Periodontics

The periodontal therapy usually aims at elimination of disease causing bacteria and resolution of inflammation. It involves either resective or regenerative surgery to resolve the inflammation associated defects. Over the years, several methods have been used for achievement of periodontal regeneration. One of the oldest biomaterials used for scaffolds is the fetal membrane. The amniotic membranes of developing embryo, that is, amnion (innermost lining) and chorion (a layer next to it), have the properties with significant potential uses in dentistry. This paper reviews the properties, mechanism of action, and various applications of these placental membranes in general and specifically in Periodontics.

Amniotic membranes in ophthalmology: long term data on transplantation outcomes

The use of amniotic membrane (AM) is a widespread clinical practice for eye surgeries and the treatment of an increasing number of ocular surface pathologies. Here we describe the AM collection methods and donor selection criteria adopted by our tissue bank to distribute 5349 amniotic membrane patches over the last 12 years for the treatment of several ocular pathologies. Specific quality control measures are described and the long term results attained using the reported procedure are presented. A case of AM utilized to treat severe ocular ulceration is also described as an example of AM transplantation. Collective data for the total amniotic membrane patches deployed to treat various ocular diseases are discussed and success rates for AM transplantations are reported. An extensive follow-up is illustrated. The results suggest that the procedures and protocols used by the Treviso Tissue Bank Foundation and Veneto Eye Bank Foundation for collection, preservation, distribution and follow-up are of an optimal standard. Accordingly, the authors conclude that the safety and efficiency of the proposed procedure for the therapeutic use of AM to treat various ocular pathologies are reproducible, with additional evidence favoring the use of AM as an alternative to conventional medical treatment for certain ocular conditions.

Repair of oral mucosal defects with cryopreserved human amniotic membrane grafts: prospective clinical study

The aim of this study was to evaluate the clinical outcome of the surgical repair of oral mucosal defects using cryopreserved human amniotic membrane (HAM) as a graft material. Thirty-four patients with precancerous lesions such as leukoplakia, erythroplakia, and verrucous hyperplasia were included. Fresh amniotic membrane was obtained from women undergoing elective caesarean section; the membrane was cleaned, prepared in antibiotic solutions, and preserved at -80°C. Results suggested that HAM promotes healing and epithelialization without specific complications. Thus we conclude that the use of HAM gives promising results in the repair of post-surgical oral mucosal defects.

Human amniotic membrane transplantation: Different modalities of its use in ophthalmology

The amniotic membrane (AM) is the inner layer of the fetal membranes and consist of 3 different layers: the epithelium, basement membrane and stroma which further consists of three contiguous but distinct layers: the inner compact layer, middle fibroblast layer and the outermost spongy layer. The AM has been shown to have anti-inflammatory, anti-fibrotic, anti-angiogenic as well as anti-microbial properties. Also because of its transparent structure, lack of immunogenicity and the ability to provide an excellent substrate for growth, migration and adhesion of epithelial corneal and conjunctival cells, it is being used increasingly for ocular surface reconstruction in a variety of ocular pathologies including corneal disorders associated with limbal stem cell deficiency, surgeries for conjunctival reconstruction, as a carrier for ex vivo expansion of limbal epithelial cells, glaucoma surgeries and sceral melts and perforations. However indiscriminate use of human AM needs to be discouraged as complications though infrequent can occur. These include risk of transmission of bacterial, viral or fungal infections to the recipient if the donors are not adequately screened for communicable diseases, if the membrane is not processed under sterile conditions or if storage is improper. Optimal outcomes can be achieved only with meticulous case selection. This review explores the ever expanding ophthalmological indications for the use of human AM.

Plant-derived human collagen scaffolds for skin tissue engineering

Tissue engineering scaffolds are commonly formed using proteins extracted from animal tissues, such as bovine hide. Risks associated with the use of these materials include hypersensitivity and pathogenic contamination. Human-derived proteins lower the risk of hypersensitivity, but possess the risk of disease transmission. Methods engineering recombinant human proteins using plant material provide an alternate source of these materials without the risk of disease transmission or concerns regarding variability. To investigate the utility of plant-derived human collagen (PDHC) in the development of engineered skin (ES), PDHC and bovine hide collagen were formed into tissue engineering scaffolds using electrospinning or freeze-drying. Both raw materials were easily formed into two common scaffold types, electrospun nonwoven scaffolds and lyophilized sponges, with similar architectures. The processing time, however, was significantly lower with PDHC. PDHC scaffolds supported primary human cell attachment and proliferation at an equivalent or higher level than the bovine material. Interleukin-1 beta production was significantly lower when activated THP-1 macrophages where exposed to PDHC electrospun scaffolds compared to bovine collagen. Both materials promoted proper maturation and differentiation of ES. These data suggest that PDHC may provide a novel source of raw material for tissue engineering with low risk of allergic response or disease transmission.

Amniotic membrane in oral and maxillofacial surgery

PURPOSE

Following its renaissance in ophthalmology during the 1990s, preserved human amniotic membrane (HAM) has become an attractive biomaterial for all surgical disciplines. This article reviews the current and potential use of HAM in oral and maxillofacial surgery, its postulated properties and common preservation techniques.

METHODS

Literature was identified by an electronic search of PubMed in July 2012; this was supplemented from the reference lists of the consulted papers.

RESULTS

HAM has been used in the field of oral and maxillofacial surgery from 1969 onwards because of its immunological preference and its pain-reducing, antimicrobial, mechanical and side-dependent adhesive or anti-adhesive properties. The effects of HAM on dermal and mucosal re-epithelialisation have been highlighted. Typically, HAM is applied after being banked in a glycerol-preserved, DMSO-preserved or freeze-dried and irradiated state. Whereas the use of HAM in flap surgery and in intra-oral and extra-oral lining is reported frequently, novel HAM applications in post-traumatic orbital surgery and temporomandibular joint surgery have been added since 2010. Tissue engineering with HAM is a fast-expanding field with a high variety of future options.

CONCLUSIONS

Preserved HAM is considered to be a safe and sufficient biomaterial in all fields of oral and maxillofacial wound healing. Recently published novel indications for HAM application lack a high level of evidence and need to be studied further.

Amniotic membrane: from structure and functions to clinical applications

Amniotic membrane (AM) or amnion is a thin membrane on the inner side of the fetal placenta; it completely surrounds the embryo and delimits the amniotic cavity, which is filled by amniotic liquid. In recent years, the structure and function of the amnion have been investigated, particularly the pluripotent properties of AM cells, which are an attractive source for tissue transplantation. AM has anti-inflammatory, anti-bacterial, anti-viral and immunological characteristics, as well as anti-angiogenic and pro-apoptotic features. AM is a promoter of epithelialization and is a non-tumorigenic tissue and its use has no ethical problems. Because of its attractive properties, AM has been applied in several surgical procedures related to ocular surface reconstruction and the genito-urinary tract, skin, head and neck, among others. So far, the best known and most auspicious applications of AM are ocular surface reconstruction, skin applications and tissue engineering. However, AM can also be applied in oncology. In this area, AM can prevent the delivery of nutrients and oxygen to cancer cells and consequently interfere with tumour angiogenesis, growth and metastasis.

Amnion graft following hysteroscopic lysis of intrauterine adhesions

AIM

To evaluate the safety and efficacy of amnion grafting after hysteroscopic lysis of intrauterine adhesions.

METHODS

In a pilot study involving 25 patients with moderate or severe intrauterine adhesions, hysteroscopic adhesiolysis was followed by intrauterine application of a fresh amnion graft over an inflated balloon of a Foley's catheter for 2 weeks. Follow-up hysteroscopy was performed after 4 months. Outcome measures included recurrence of adhesions, achievement of normal menstrual flow, and improvement in the uterine length.

RESULTS

Moderate (group A) and severe (group B) adhesions were found in 12 and 13 subjects, respectively. Uterine perforation occurred in two patients in group B, one treated conservatively and the other via laparoscopy. No clinical evidence of infection was observed, and spontaneous expulsion of the balloon occurred within days in three patients, with easy removal after 2 weeks in the rest of the subjects. Significant improvement in uterine length was found in both groups. Despite improvement, failure to achieve normal menstrual flow was found in 16.7% in group A versus 23.1% in group B. Follow-up hysteroscopy revealed adhesion reformation in 48%, all belonging to group B, all with minimal adhesions. Moderate adhesions were found in only two subjects with previous tuberculous endometritis.

CONCLUSION

Hysteroscopic lysis of intrauterine adhesions with amnion grafting seems to be a promising procedure for decreasing recurrence of adhesions and encouraging endometrial regeneration. Randomized comparative studies are needed to validate its benefits, including reproductive outcome.

Type II Collagen Accumulation in Overlying Dermo-Epidermal Junction of Pilomatricoma Is Mediated by Bone Morphogenetic Protein 2 and 4

Pilomatricoma consists of the cells differentiating towards hair matrix cells. Immunohistochemical study revealed the deposition of type II collagen in the overlying dermo-epidermal junction (DEJ) of this benign tumor. Proalpha(1)(II) mRNA was detected by RT-PCR in the overlying epidermal layer but not in the dermal layer prepared from the lesional skin of pilomatricoma. The neutral salt-soluble proteins extracted from the tumor of pilomatricoma induced proalpha(1)(II) mRNA in the cultured human keratinocytes but not in the cultured dermal fibroblasts. Bone morphogenetic protein 2 or 4 (BMP2 or 4) was immunohistochemically detected in some shadow cells of pilomatricoma. Recombinant BMP2 and BMP4 were found to induce proalpha(1)(II) mRNA concentration dependently in the cultured human keratinocytes but not in the cultured fibroblasts. Proalpha(1)(II) mRNA induced by BMP2 and in cultured keratinocytes contained exon 2, indicating that the mRNA species is non-chondrogenic type IIA form. The results strongly suggest that BMP2 or 4 expressed in pilomatricoma is responsible for the induction of proalpha(1)(II) collagen mRNA in the overlying epidermal cells resulting in the deposition of type II collagen in the DEJ. When human keratinocytes were cultured on type II collagen substratum in vitro, the cell proliferation was accelerated at the early period of culture but was inhibited at the late period of culture, whereas the cell proliferation was persistently accelerated by type I or IV collagen substratum. Type II collagen deposition in the DEJ may potentially exert profound effects on keratinocyte proliferation and differentiation.

The amniotic membrane in ophthalmology

The amniotic membrane is the innermost of the three layers forming the fetal membranes. It was first used in 1910 in skin transplantation. Thereafter it has been used in surgical procedures related to the genito-urinary tract, skin, brain, and head and neck, among others. The first documented ophthalmological application was in the 1940s when it was used in the treatment of ocular burns. Following initial reports, its use in ocular surgery abated until recently when it was re-discovered in the Soviet Union and South America. Its introduction to North America in the early 1990s heralded a massive surge in the ophthalmic applications of this membrane. The reintroduction of amniotic membrane in ophthalmic surgery holds great promise; however, although it has been shown to be a useful and viable alternative for some conditions, it is currently being used far in excess of its true useful potential. In many clinical situations it offers an alternative to existing management options without any distinct advantage over the others. Further studies will undoubtedly reveal the true potential of the membrane, its mechanism(s) of action, and the effective use of this tissue in ophthalmology.

Synthesis of Tissues and Organs

Symbolism that describes the synthetic processes for chemical compounds has been used to describe, in qualitative terms, the synthesis of tissues and organs at the correct anatomical site. The synthetic process is summarized in the reaction diagram, a shorthand representation of the reactants, reactor, and products. Analysis of a large number of independent protocols has led to identification of the simplest synthetic pathways for two organs that have been studied extensively: skin and peripheral nerves. These apparently irreducible reaction diagrams for the two organs are not only simple but surprisingly similar, a fact suggesting the existence of general rules for the synthesis of other organs as well. The only two reactants that are required are an active scaffold (a macromolecular network synthesized as a highly porous analogue of the extracellular matrix) and a seeding of epithelial cells of the organ being synthesized. Scaffolds possessed biological (regenerative) activity provided that they were capable of blocking the contraction process that leads to closure of the injured site. Such activity requires that the density of ligands for binding of contractile cells on the scaffold maintains a sufficiently high level over the period of synthesis.

Thygeson lecture. Amniotic membrane transplantation: why is it effective?

PURPOSE

To review the uses and previously proposed mechanisms of action of amniotic membrane transplantation (AMT) and to suggest a new mechanism of action for the effectiveness of AMT in resolving a persistent epithelial defect (PED).

METHODS

Significant clinical and experimental publications are reviewed.

RESULTS

Evidence from the scientific literature suggests a new hypothesis for the effectiveness of AMT in the reepithelialization of a PED and the reduction of corneal stromal inflammation and continued fibrosis.

CONCLUSION

It is suggested that reepithelialization of a PED, and hence the reduction of stromal inflammation and continued fibrosis following reepithelialization, is aided by the combination of oxygenation, moisture and protection of the fragile epithelium by the amniotic membrane.

Symptomatic management of postoperative bullous keratopathy with nonpreserved human amniotic membrane

PURPOSE

To report the results of the management of painfully symptomatic postoperative bullous keratopathy (PBK) by performing a nonpreserved human amniotic membrane (NP-AMT) transplantation in nine eyes with poor visual potential.

METHODS

A prospective, comparative, nonrandomized management of symptomatic PBK was done by performing a complete corneal de-epithelialization followed by a NP-AMT transplantation (NP-AMT group) or no NP-AMT transplantation (control group). We evaluated time for re-epithelialization, patient's symptoms, and appearance of new bullae.

RESULTS

In the NP-AMT group, mean follow-up time was 40 weeks. Mean re-epithelialization time was 11.2 days. Symptoms of PBK resolved completely in eight patients (88%), who were asymptomatic and showing very quiet eyes from postoperative day 1, and resolved partially in one patient in whom we observed barely symptomatic bullae at the peripheral NP-AMT border (sixth postoperative week) and an asymptomatic one at the corneal center under the NP-AMT (seventh postoperative week). In the control group, mean follow-up time was 18 weeks; there were recurrences of symptomatic bullae in four of five patients at a mean time of 6.3 days.

CONCLUSIONS

NP-AMT is a good alternative for the management of painful PBK in eyes with poor visual potential; NP-AMT is widely available, the technique is easy to perform, and it has good results from both the symptomatic and esthetic standpoint.

Amniotic membrane surgery

Human amniotic membrane (AM) is composed of three layers: a single epithelial layer, a thick basement membrane, and an avascular stroma. Amniotic membrane has anti-adhesive properties and is felt to promote epithelialization and decrease inflammation, neovascularization, and fibrosis. Amniotic membrane transplantation (AMT) is currently being used for a continuously widening spectrum of ophthalmic indications. Amniotic membrane transplantation has been shown to be effective in the reconstruction of the corneal surface in the setting of persistent epithelial defects, sterile corneal ulcerations, and partial limbal stem cell (LSC) deficiency states, including those secondary to chemical or thermal burns. Amniotic membrane transplantation also has been used in conjunction with limbal stem cell transplantation (LSCT) both in a concurrent fashion as well as in preparation for LSCT. Amniotic membrane transplantation also has been used in place of conjunctival autografting after pterygium excision and to reconstruct the conjunctival surface after removal of conjunctival lesions. Most recently, ex vivo cultivation and expansion of limbal epithelial cells has been performed utilizing AM as a matrix. However, the superiority of AMT over other treatment modalities in many of these settings needs to be substantiated by controlled clinical trials.

Amniotic membrane transplantation in the management of shield ulcers of vernal keratoconjunctivitis

PURPOSE

To report our experience with amniotic membrane transplantation in the management of severe shield ulcers.

DESIGN

Retrospective, interventional, noncomparative case series.

PARTICIPANTS

Four patients (seven eyes) with grade 2 (ulcer with opaque base) and grade 3 (plaquelike lesions) shield ulcers not responding to steroid therapy with or without surgical debridement.

INTERVENTION

Amniotic membrane transplantation with stromal side down was performed after meticulous debridement of the ulcer.

MAIN OUTCOME MEASURES

Healing of the ulcer with no epithelial defect.

RESULTS

The ulcers healed with disintegration or retraction of the membrane in all patients within 2 weeks.

CONCLUSIONS

Amniotic membrane transplantation in combination with debridement is an effective surgical modality in the management of severe shield ulcers. Further studies are warranted to confirm the efficacy of amniotic membrane transplantation in the management of shield ulcer and its correct position in the treatment algorithm.

Amniotic membrane transplantation after extensive removal of primary and recurrent pterygia

OBJECTIVE

To evaluate the postoperative outcome and the recurrence rate after extensive removal of primary and recurrent pterygia combined with amniotic membrane transplantation.

DESIGN

A noncomparative interventional case series.

PARTICIPANTS

Fifty-four eyes in 54 subjects with either primary (n = 33) or recurrent (n = 21) pterygia operated on by one surgeon (SCGT).

INTERVENTION

All subjects were operated on for pterygia with an extensive excision of the lesion followed by amniotic membrane transplantation and intraoperative injection of a depot corticosteroid.

MAIN OUTCOME MEASURES

Cumulative rates of conjunctival (grade 3) and corneal (grade 4) recurrence and incidence of complications.

RESULTS

The mean follow-up was 12.8 +/- 4.3 months for primary and 14.3 +/- 4.9 months for recurrent pterygia. The true recurrence rate (grade 4) was 3.0%, 9.5%, and 5.6% for primary, recurrent, and all pterygia, respectively. The cumulative proportion of recurrence-free eyes at 12 months was 0.90 +/- 0.06 for primary and 0.69 +/- 0.11 for recurrent pterygia (P = 0.047, log-rank test). Removal of the semilunar fold was associated with longer survival times (P = 0.063) and decreased failure rate (P = 0.046). A similar success rate was achieved in double-head pterygia (1 recurrence in 11 eyes).

CONCLUSIONS

Amniotic membrane transplantation is an effective and safe procedure for pterygium surgery, with a relatively low recurrence rate for both primary and recurrent pterygia. It can be a useful alternative to conjunctival autograft when a large conjunctival defect has to be covered, such as in primary double-head pterygia and in large recurrent pterygia.

Amniotic membrane transplantation for symptomatic conjunctivochalasis refractory to medical treatments

PURPOSE. To determine whether preserved human amniotic membrane can restore the large conjunctival defect created during surgical removal of conjunctivochalasis.

METHODS

Amniotic membrane transplantation was performed at two facilities in 40 consecutive patients (47 eyes) with symptomatic conjunctivochalasis refractory to conventional treatments.

RESULTS

The majority of patients were elderly (73.1 +/- 9.7 years) and women (75%). Over a follow-up period of 6.9 +/- 4.3 months, 46 (97.8%) eyes recovered smooth, quiet, and stable conjunctival surfaces. Epithelial defects healed in 16.5 +/- 7.3 days. Episodic epiphora was resolved in 24 of 30 (83.3%) eyes and improved in five other eyes. Notable relief was also noted for such symptoms as fullness or heaviness (19/19, 100%), sharp pain (6/6, 100%), redness (14/17, 88.2%), tiredness (17/20, 80.9%), itching (11/13, 78.6%), blurry or decreased vision (6/8, 75%), burning (8/13, 61.5%), foreign body sensation (8/13, 61.5%), and crust formation (1/2, 50%). Complications included focal inflammation of the host conjunctiva adjacent to the graft (six eyes), scar formation (five eyes), and suture-induced granuloma (one eye).

CONCLUSION

Amniotic membrane transplantation can be considered as an effective means for conjunctival surface reconstruction during removal of conjunctivochalasis.

Current status of limbal conjunctival autograft

The past decade has witnessed several major advances in the field of ocular surface reconstruction. It is now established that the limbal and corneal epithelia belong to the same clonogenic lineage and that conjunctival transdifferentiation does not occur. These facts have engendered the increasing use of limbal transplantation in several ocular conditions involving limbal compromise. Many reports on this procedure have been published in the past year. They add to the growing body of evidence that limbal transplantation is efficacious in replenishing the stem cell pool, promoting improved vision and enhancing ocular comfort. Recent clinical studies on limbal autograft transplantation also underscore the importance of preoperative impression cytology in donor eyes, highlight the fact that transplantation in inflamed eyes is to be avoided, and indicate that the procedure is likely to provide better outcomes if performed several months after ocular surface burns. The appreciation of the utility of amniotic membrane transplantation in ocular surface reconstruction has provided a surgical tool to use in tandem with limbal transplantation. Questions such as why limbal autografts fail, the long-term results of LAT, and whether limbal inclusion is mandatory during conjunctival transplantation after pterygium excision have not been answered fully. Studies on long-term outcomes with limbal allograft transplantation and those reporting on experience with newer techniques such as epithelial transplantation using tissue culture-cultivated epithelium are likely to provide better perspectives on the best way to reconstruct the ocular surface in stem cell-deficient eyes.

Use of nonpreserved human amniotic membrane for the reconstruction of the ocular surface

PURPOSE

To describe the use of nonpreserved human amniotic membrane (NP-AMT) as an alternative to preserved human amniotic membrane (AMT) for the reconstruction of the ocular surface in several diseases.

METHODS

NP-AMT was used in the treatment of five patients with the following diseases: noninvasive conjunctival squamous cell carcinoma, corneal persistent epithelial defect, severe alkali burn, near total limbal deficiency secondary to multiple surgeries, and ocular cicatricial pemphigoid. In some cases, a limbal autograft or allograft was employed simultaneously, sutured on top of the NP-AMT. All sutures were made with 10-0 Nylon and were removed at two weeks.

RESULTS

Ocular surface was satisfactorily reconstructed, eyes were quiet, and patients were comfortable despite prolonged deepithelialization in some cases. There was a case of a limbal autograft ischemia--in the burned patient--that caused partial corneal conjunctivalization. Initially, the NP-AMT looks thickened but thins around the fifth day and looks similar to AMT.

CONCLUSION

Results using NP-AMT are similar to those of AMT. It is a good alternative and it is easily obtained in places were AMT is not available or is too expensive to procure.

Characterization of a composite tissue model that supports clonal growth of human melanocytes in vitro and in vivo

To aid in the investigation of factors that control the proliferation and function of melanocytes, we have characterized a skin equivalent model that supports melanocyte growth and function in vitro and in vivo. Passenger melanocytes survive and proliferate at low numbers when keratinocytes of the epidermis are cultured in serum-containing medium using a fibroblast feeder layer. When the surface of de-epidermalized acellular dermis was seeded with these cultured cells, the keratinocytes formed a stratified epithelium in vitro containing rete ridges, and the melanocytes were preferentially located in the bottom of these rete ridges. Melanocyte cell number was much less than in normal skin, but in some areas the melanocytes were in clusters, consistent with clonal growth of the cells. When transplanted to athymic mice, the grafts formed foci of pigmentation at 3 wk that expanded and repigmented the entire graft by 8 wk. Histologic examination of these foci revealed that they corresponded to clusters of melanocytes that proliferated and migrated to eventually repopulate the entire graft. In grafts of mixed cells from light and dark skin donors, distinct foci of pigmentation were obvious at 3 wk and, instead of progressing to complete repigmentation, these foci remained stable for over 6 wk. Histologic examination confirmed that these grafts of mixed cells were entirely repopulated with melanocytes and that the grafts contained distinct zones of melanocytes that were of exclusively dark or light skin origin. This model should be valuable for studying the clonal growth of melanocytes in the context of the epidermis.

Amniotic membrane transplantation for conjunctival surface reconstruction

PURPOSE

To determine whether preserved human amniotic membrane can be used to reconstruct the conjunctival defect created during surgical removal of a large lesion or during symblepharon lysis.

METHODS

Amniotic membrane transplantation was performed in six consecutive patients (seven eyes) during removal of large conjunctival lesions and in nine patients (nine eyes) during removal of conjunctival scars or symblepharon.

RESULTS

During a mean follow-up period +/- SD of 10.9 +/- 9.1 months (range, 2.2 to 34.0 months), 10 patients (11 eyes) showed successful surface reconstruction without recurrence, five patients (five eyes) showed improved visual acuity, and one patient (one eye) showed epithelialization within 3 weeks and resolution of motility restriction. Two patients (two eyes) showed partial success, with surrounding conjunctival inflammation. Three cases (three eyes) failed and exhibited recurrent scarring: one patient had received mitomycin treatment and beta radiation, whereas the transplanted amniotic membrane of the second patient was partially, and of the third patient was completely, dissolved or replaced by the inflamed pseudopterygial tissue. Two patients (two eyes) had epithelial cyst formation.

CONCLUSION

Amniotic membrane transplantation can be considered an alternative substrate for conjunctival surface reconstruction during removal for large tumors, disfiguring scars, or symblepharon, especially for those whose surrounding conjunctival tissue remains relatively normal.

Comparison of conjunctival autografts, amniotic membrane grafts, and primary closure for pterygium excision

OBJECTIVE

The purpose of the study is to determine whether amniotic membrane can be used as an alternative to conjunctival autograft after pterygium excision.

DESIGN

A prospective study of amniotic membrane grafts (group A) and primary closure (group B) was compared retrospectively with conjunctival autografts (group C) in patients with pterygia.

PARTICIPANTS

Group A included 46 eyes with primary pterygia and 8 eyes with recurrent pterygia, group B had 20 eyes with primary pterygia, and group C consisted of 78 eyes with primary and 44 eyes with recurrent pterygia.

INTERVENTION

For the above three different surgeries, the amount of tissue removed was estimated from histopathologic analysis, and the result was evaluated by clinical examination.

MAIN OUTCOME MEASURES

Recurrence, survival analysis, and final appearance were compared.

RESULTS

In group A, the recurrence rate was 10.9%, 37.5%, and 14.8% for primary, recurrent, and all pterygia, respectively (mean follow-up, 11 months). These three rates were significantly higher than 2.6%, 9.1%, and 4.9% noted in group C (mean follow-up, 23 months) (P < 0.001, 0.018, and 0.01, respectively). However, the latter recurrence rate was significantly lower than 45% (mean follow-up, 5.2 months) in group B for primary pterygia (P < 0.001). The onset of recurrence was delayed significantly in group C as compared with that of groups A and B.

CONCLUSIONS

The relatively low recurrence rate for primary pterygia allows one to use amniotic membrane transplantation as an alternative first choice, especially for advanced cases with bilateral heads or those who might need glaucoma surgery later.

Amniotic membrane transplantation for persistent epithelial defects with ulceration

PURPOSE

To determine whether preserved human amniotic membrane can be used as an alternative substrate for treating persistent corneal epithelial defects with sterile ulceration.

METHODS

Amniotic membrane transplantation was performed in 11 eyes of 11 consecutive patients with corneal ulcers of different causes that had persisted for a mean +/- SD of 17.5 +/- 13.9 weeks.

RESULTS

Ten patients healed in 3.9 +/- 2.3 weeks (P < .01) without recurrence for 9.0 +/- 5.9 months. One patient failed to heal because of preexisting corneal perforation pursuant to severe rheumatoid arthritis.

CONCLUSION

Amniotic membrane transplantation may be considered an alternative method for treating persistent epithelial defects and sterile ulceration that are refractory to conventional treatment and before considering treatment by conjunctival flaps or tarsorrhaphy.

Evaluation of human skin reconstituted from composite grafts of cultured keratinocytes and human acellular dermis transplanted to athymic mice

This study evaluates the use of composite grafts of cultured human keratinocytes and de-epidermalized, acellular human dermis to close full-thickness wounds in athymic mice. Grafts were transplanted onto athymic mice and studied up to 8 wk. Graft take was excellent, with no instances of infection or graft loss. By 1 wk, the human keratinocytes had formed a stratified epidermis that was fused with mouse epithelium, and by 8 wk the grafts resembled human skin and could be freely moved over the mouse dorsum. Immunostaining for keratins 10 and 16 and for involucrin revealed an initial pattern of epithelial immaturity, which by 8 wk had normalized to that of mature unwounded epithelium. Mouse fibroblasts began to infiltrate the acellular dermis as early as 1 wk. By 8 wk fibroblasts had completely repopulated the dermis, and blood vessels were evident in the most superficial papillary projections. Dermal elements, such as rete ridges and elastin fibers, which were present in the starting dermis, persisted for the duration of the experiment. Grafts using keratinocytes from dark-skinned donors as opposed to light-skin donors had foci of pigmentation as early as 1 wk that progressed to homogenous pigmentation of the graft by 6 wk. These results indicate that melanocytes that persist in vitro are able to resume normal function in vivo. Our study demonstrates that composite grafts of cultured keratinocytes combined with acellular dermis are a useful approach for the closure of full-thickness wounds.

Characterization of hair follicle bulge in human fetal skin: the human fetal bulge is a pool of undifferentiated keratinocytes

It has been suggested that the bulge of the hair follicle contains a pool of follicular stem cells that may serve as a target site of graft-versus-host disease and as a source of cells with carcinogenic potential. The bulge is prominent in the developing follicle although it is a subtle swelling in the adult follicle. In this paper, we studied the bulge in human fetal skin specimens. Ultrastructurally, the bulge cells, especially the interior cells, have abundant free ribosomes and glycogen particles, but almost no cytoplasmic organelles indicative of differentiation. Immunostaining with several specific anti-keratin antibodies demonstrated that the bulge cells express keratins of both stratified and simple epithelia. Melanocytes and Merkel cells, defined by immunohistochemical and ultrastructural criteria, are seen among bulge cells. Laser confocal microscopy revealed that primitive smooth muscle cells attached directly to the bulge initially at the mid-bulbous hair peg, the stage when the bulge is most prominent. K-laminin and type VII collagen are strongly expressed in the dermoepidermal junction of the bulge and between the matrix area of the bulb and the dermal papilla. Thus, the bulge of human hair follicle is not only an attachment site for arrector pili muscle, but also a pool of keratinocytes that are relatively undifferentiated.

Expression of basement membrane components in skin equivalents--influence of dermal fibroblasts

We have made a skin equivalent constructed of fibroblasts embedded in a type I collagen, with an overlying stratified keratinocyte epithelium to examine formation of the basement membrane. We assessed the influence of the existence and species of fibroblasts in the collagen gel. Cultured human keratinocytes were well attached to the dermal equivalent. Plating efficiency was not clearly different among several types of gel. On the control and mouse fibroblast gel, sheet formation was delayed and epithelial stratification on the human fibroblast gel was more remarkable than on the control gel. On the human fibroblast gel, we observed the expression of basement membrane components (bulbous phemphigoid antigen, laminin, type IV collagen and fibronectin) between the sheet of cultured keratinocytes and the human fibroblast gel earlier than those on the control gel and mouse fibroblast gel. Type VIII collagen was not observed in any of the models at 4 weeks.

The role of the basement membrane in differential expression of keratin proteins in epithelial cells

Extracellular matrix is considered to play an important role in determining the phenotype of cells with which it interacts. Here we have investigated the possibility that extracellular matrix is involved in specifying the pattern of keratin expression in epithelial cells. For these studies, we have developed an explant system in which epithelial cells from one type of stratified epithelial tissue, namely conjunctiva, are maintained on an extracellular matrix substrate derived from a different tissue, namely cornea. These ocular tissues are ideal for such analyses since they express distinct sets of keratins. For example, bovine conjunctival epithelium processed for immunofluorescence is not recognized by antibody preparations against keratin K3 or K12. In contrast, K3 and K12 antibodies generate intense staining in bovine corneal epithelium. At the immunochemical level, conjunctival cells in situ appear to possess no K12 and only trace amounts of K3, whereas corneal epithelial cells in situ possess both K3 and K12. When conjunctival cells are maintained on a corneal substrate with an intact basement membrane for 10 days in vitro they begin to express keratin K12 as determined by immunofluorescence. On the other hand, conjunctival cells that are maintained on a corneal substrate lacking a basement membrane fail to show staining with K12 antibodies. Conjunctival cells begin to show intense staining using K3 antibodies within about 10 days of being placed in culture regardless of their substrate. These results indicate that basement membrane can play a positive role in determining cell-specific expression of certain keratins such as K12. However, other keratins such as K3 may be "unmasked" and/or their expression may be upregulated simply by placing conjunctival epithelial cells in culture. We speculate that in conjunctiva K3 expression is influenced by certain negative exogenous factors. We discuss the possible means of regulation of keratin expression in our model system.

In vitro reconstitution of skin: fibroblasts facilitate keratinocyte growth and differentiation on acellular reticular dermis

Extensive full-thickness burns require replacement of both epidermis and dermis. We have described a method in which allogeneic dermis from engrafted cryopreserved cadaver skin was combined with cultured autologous keratinocytes. In the present study we combined human keratinocytes and fibroblasts, and acellular human dermis in vitro and transplanted this "reconstituted skin" into athymic mice. Both human papillary dermis in which the basement membrane zone has been retained and human reticular dermis that has been repopulated with human dermal fibroblasts are good substrates for keratinocyte attachment, stratification, growth, and differentiation. Both of these dermal preparations can be lyophilized and stored at room temperature without losing their ability to support keratinocyte growth. In contrast, human papillary dermis that has been treated with trypsin lacks laminin and collagen type IV in the BMZ and supports keratinocyte attachment and differentiation less well.

Localization of the 230-kilodalton bullous pemphigoid antigen in cultured keratinocytes: formation of a prehemidesmosome

The hemidesmosome is the major attachment structure of the epidermal basal cell visible ultrastructurally in skin. The importance of its components to cultured cell attachment to substratum is not understood, however. A component of the hemidesmosome, the 230-kDa bullous pemphigoid antigen (p230), has been shown to be present in an insoluble or particulate fraction of cultured cells. In order to more fully characterize its potential importance for cell-matrix adhesion in cultured keratinocytes, specific antibodies were raised to the C-terminal region of p230 expressed as a bacterial fusion protein. Such antibodies recognize the hemidesmosome of epidermis, binding on the cytoplasmic region of its plaque. In addition, keratinocytes cultured in a 0.15 mM Ca(2+)-defined medium contain a detergent-resistant pool of p230 which appears to lie in the same focal plane as the culture substrate and has a patchy or irregular distribution by indirect immunofluorescence. Treatment of cultured cells at 4 degrees C with trypsin or pronase sufficient to release keratinocytes from the culture dish does not affect the electrophoretic migration of p230 on SDS-gels, suggesting that p230 is not exposed to the extracellular space. In cells cultured in 0.15 mM Ca2+, 230-kDa BP antigen is localized to discrete clusters resting near the basal plasma membrane of the cell by immunogold staining following brief detergent treatment and fixation. These clusters are approximately 0.1 micron in diameter, which is similar in size to the in vivo hemidesmosome. Fully formed electron dense hemidesmosomal plaques are not observed under the same culture conditions, however. It appears that these clusters are early precursors of the hemidesmosome.

Epithelial-mesenchymal interactions enhance expression of collagen VII in vitro

Expression of collagen VII, the major structural protein of the anchoring fibrils, was assessed in vitro using indirect immunofluorescence staining and immunoblotting of collagen VII isolated from cultures. A very low level of expression was observed in monocultures of normal human fibroblasts or keratinocytes, but the expression was greatly stimulated when fibroblasts and keratinocytes were co-cultured. Primary skin explants under culture conditions supporting growth of both cell types, or mixed co-cultures of purified fibroblasts and keratinocytes, exhibited clearly enhanced synthesis of collagen VII, and the intact tissue form of this collagen could be extracted from small co-cultures. Three-dimensional skin equivalents were constructed with fibroblasts embedded in a contracted gel of collagen I and III, with an overlying stratified keratinocyte epithelium. In these equivalents, expression of collagen VII was observed primarily in the lowest epithelial cells, indicating that these cells are the main manufacturers of collagen VII. Laminin and collagen IV were deposited in a linear fashion onto the epithelial-mesenchymal interface. The results suggest that epithelial-mesenchymal interactions, either through physical interactions and/or through soluble mediators, are necessary for efficient synthesis of collagen VII and biogenesis of the anchoring fibrils.

Restoration of the epidermal phenotype by follicular outer root sheath cells in recombinant culture with dermal fibroblasts

In order to better understand how outer root sheath (ORS) cells are able to reepithelialize superficial skin wounds, the level of epidermal differentiation achieved by isolated ORS cells in vitro was determined. Using postmitotic human dermal fibroblasts (HDF) as efficient feeder cells, large numbers of ORS cells from individual follicles were generated. Passaged ORS cells were grown exposed to air on HDF-populated collagen gels in the CRD device (Noser and Limat, In vitro 23, 541-545, 1987) which allows histiotypic tissue organization. In such recombinant organotypic cultures, ORS cells developed distinct epidermal strata comparable to interfollicular keratinocytes (NEK). Ultrastructurally, desmosomes and intermediate filaments increased in number toward the epithelial surface and small keratohyalin (KH) granules (but no large irregular KH granules as in NEK) were abundant, adjacent to an electrondense stratum corneum. Also, synthesis of epidermal suprabasal keratins (K1 and 10;2D gels) was lower in ORS cultures, but clearly visible suprabasally by immunofluorescence along with other epidermal markers (involucrin, filaggrin, surface glycoprotein gp80, pemphigus vulgaris antigen). Basement membrane components (laminin, type IV collagen, bullous pemphigoid antigen) were detectable in both ORS and NEK in these assays. Thus, phenotypic expression was largely comparable, but, whereas terminal differentiation (keratinization) was progressing in NEK cultures limiting their lifespan, this seemed to be better controlled in ORS cultures and viable cell layers persisted resulting in longer survival time.

Barrier function of human keratinocyte cultures grown at the air-liquid interface

Stratum corneum (SC), the outermost and least permeable layer of skin, is the major barrier to passive transepidermal water loss. In the research described in this paper, we have used human keratinocyte cultures, grown at the air-liquid (A/L) interface, to examine the relationship between epidermal differentiation (including SC formation) and barrier function. Histologically, the A/L culture showed several markers of complete differentiation, including the presence of well-organized and defined epidermal cell layers, keratohyalin granules, and a multilayered SC. The permeability of tritiated water through epidermal cultures, which had grown for 3 weeks at the A/L interface, was measured with a microdiffusion apparatus. The results of these experiments demonstrated that: a) the human keratinocyte cultures developed a substantial barrier (i.e., a multilayered SC) to water diffusion across the entire surface. If the relative humidity of the culturing environment was lowered from 100% to around 75%, the barrier was significantly improved; b) the differentiation promoter, 1.25-dihydroxy-vitamin-D3, increased the number of SC layers and reduced water permeation through the culture; c) the nature of the keratinocyte support matrix could be altered to improve the morphology as well as the barrier function of the epidermal cultures. Overall, the observations are consistent with the relationship that is believed to exist between SC intercellular lipid content and percutaneous penetration. Confirmation of this hypothesis will further the considerable potential of human keratinocyte A/L cultures as a valuable and relevant model in which to study drug absorption and metabolism.