Matrix metalloproteinase 2: involvement in keratoconus

PURPOSE: The activation of matrix metalloproteinase-2 (MMP-2) is postulated to be a crucial pathogenic factor behind progressive and chronic diseases in which basement membranes are disrupted. An ocular example is keratoconus. The purpose of the present enquiry was therefore to investigate and compare the activities of the MMP-2 secreted by keratocytes of normal and keratoconic corneas. METHODS: The spectrum of MMP-2 activities secreted by cultures of keratocytes derived from normal and keratoconic corneas was analysed by zymography. Subsequently, selected preparations were assayed for peptidase activity, using Type I, Type III, Type IV and Type V collagen as substrate, under native conditions and after treatment with a variety of putative activating reagents. RESULTS: Although MMP-2 of Mr 65,000 on SDS gelatin polyacrylamide gels is the major protease secreted by keratocytes of normal corneas, the keratocytes of early-phase keratoconic corneas secrete an additional zymographic activity of Mr 61,000. From their N-terminal amino acid sequences, both these proteins were shown to be conformers of proMMP-2. Treatment with SDS followed by protein fractionation was required to achieve in vitro activation of the MMP-2 secreted by normal corneal keratocytes. Treatment with SDS alone partially activated the enzyme produced by early-phase keratoconic corneal keratocytes. This procedure and autocatalysis, yielded an enzyme of Mr 43,000 that selectively hydrolysed Type IV and denatured Type 1 collagen. CONCLUSIONS: The zymographic gelatinase activities of apparent Mr 65,000 and 61,000 are conformers of corneal proMMP-2. Activated enzyme, of Mr 43,000, is more readily generated from protein preparations of the culture media of early phase keratoconic corneal keratocytes than from protein preparations of the culture media of normal corneal keratocytes.     

The control of matrix metalloproteinase-2 expression in normal and keratoconic corneal keratocyte cultures

PURPOSE: Early phase keratoconic corneas and their cultured keratocytes abnormally produce the Mr 62,000 form of the matrix metalloproteinase-2 (MMP-2). It is known that platelet derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) are involved in the regulation of MMP activity and tissue inhibitor of metalloproteinase (TIMP) production in non-ocular tissues. The purpose of this enquiry was to determine whether these growth factors also play a role in the activity and/or production of corneal MMP-2 and TIMP, and whether their activity could account for the existence of the Mr 62,000 form of MMP-2 in keratoconic corneas. METHODS: Confluent cultures of normal and early-phase keratoconic corneal keratocytes were established and incubated in serum-free media in the presence or absence of PDGF and TGF-beta. The proteins secreted by these cells over periods of 7 days were harvested for analysis. The total protein produced was determined spectrophotometrically. MMP-2 was visualised by SDS-gelatin polyacrylamide gel electrophoresis and assayed using radiolabelled type IV collagen as substrate. The enzyme inhibitors, TIMP-1 and TIMP-2, were quantified by dot blot immunoassay. RESULTS: The addition of PDGF or TGF-beta to the culture medium of keratoconic corneal keratocytes had no significant effect on overall protein production, MMP-2 activity or on the amounts of TIMP- 1 and TIMP-2 secreted. These observations also applied to normal corneal keratocytes, with the exception that PDGF induced expression of the Mr 62,000 species of MMP-2. CONCLUSIONS: PDGF may be involved in the production of the Mr 62,000 species of MMP-2 that is abnormally produced by early-phase keratoconic corneal keratocytes.     

Matrilysin cleavage of corneal collagen type XVIII NC1 domain and generation of a 28-kDa fragment

PURPOSE: To localize endostatin and collagen type XVIII in human corneas and to characterize the enzymatic action of matrix metalloproteinases (MMPs) in the cleavage of collagen type XVIII and generation of endostatin in the cornea. METHODS: Anti-endostatin and anti-hinge antibodies were generated using peptide fragments corresponding to the endostatin region and the adjacent nonendostatin hinge region of collagen XVIII noncollagenous (NC)1 domain, respectively. Confocal immunostaining was performed to localize collagen XVIII in human corneas. SV40-immortalized corneal epithelial cells were immunoprecipitated and incubated with active MMP-1, -2, -3, -7, or -9, and Western blot analysis was performed to study collagen XVIII cleavage. Incubation with MMP-7 was performed at various concentrations (0, 2, 4, and 6 microg/ml) and time intervals (0, 1, 5, and 12 hours). Purified recombinant NC1 fragment of collagen XVIII was also digested with MMP-7, and the cleavage product was sequenced. RESULTS: Collagen XVIII was immunolocalized to the human corneal epithelium, epithelial basement membrane, and Descemet membrane. Western blot analysis demonstrated a 180- to 200-kDa band corresponding to collagen XVIII. MMP-7 (but not MMP-1, -2, -3, and -9) cleaved corneal epithelium-derived collagen XVIII to generate a 28-kDa endostatin-spanning fragment in a time- and concentration-dependent fashion. MMP-7 cleaved purified recombinant 34-kDa NC1 fragment of collagen XVIII in the hinge region to generate a 28-kDa fragment. CONCLUSIONS: Collagen XVIII is present in human cornea. MMP-7 cleaves the collagen XVIII NC1 domain to generate a 28-kDa fragment in the cornea.     

Organ-cultured corneal grafts from septic donors: a retrospective study

PURPOSE: To evaluate the quality of corneal grafts from donors, who have died from septic multi-organ failure and who are called septic donors in the following. METHODS: One hundred and eighty-two corneal grafts from septic donors were stored in organ culture for 10-14 days. Graft evaluation was performed according to the criteria of the European Eye Bank Association. Only donor corneas with cell density values above 2000 cells/mm(2) were transplanted. Ninety-one patients who received these transplanted corneas were examined retrospectively with special emphasis on endophthalmitis, graft failure and incidence of immune reactions. RESULTS: Ninety-one of 182 donor corneas (50%) from septic donors were discarded mainly due to endothelial damage (61; 67%). Only seven (8%) were discarded due to medium contamination. In contrast, 452 of 1261 donor corneas (36%) from non-septic donors during the same period were discarded, again mainly due to endothelial damage (264; 58%). In this group, 48 donor corneas (11%) were discarded due to medium contamination. No patient who had received a graft from a septic donor has experienced endophthalmitis. The rate of immune reactions and graft failure was in the same range when compared to a larger group who received grafts from non-septic donors. CONCLUSION: Our data reveal no contraindication against the use of corneal grafts derived from septic donors, critical graft assessment in organ culture provided.     

Role of ocular matrix metalloproteinases in peripheral ulcerative keratitis

AIM: Peripheral ulcerative keratitis (PUK) is an ocular manifestation of rheumatoid arthritis and other similar systemic diseases. The purpose of this inquiry was to investigate the involvement of matrix metalloproteinases (MMPs) in the induction and/or maintenance of PUK. METHODS: Substrate gel electrophoresis was used to characterise the MMP activities secreted by primary cultures of keratocytes derived from normal and perforated pathological corneal specimens, and those present in tears of normal subjects and patients with PUK. Substrate specificity and the in vivo activity status of the secreted MMPs was assessed by SDS-polyacrylamide gel electrophoresis of standard collagens incubated in the presence or absence of the various enzyme preparations. RESULTS: In addition to MMP-2 of M(r) 66,000, cultured keratocytes derived from perforated corneas of patients with PUK abnormally produce the MMP-2 of apparent M(r) 62,000. Other MMPs and in particular MMP-9 of M(r) 92,000, also occur in the tears of these patients. Their visualisation on substrate polyacrylamide gels correlated with clinical manifestations of disease activity; during periods of disease quiescence they were barely detectable. The steroid prednisolone, frequently used in systemic therapy, had no effect on the in vitro activity of MMP-2, or on its production by cultured corneal keratocytes. Although the in vitro activity of MMP-2 was inhibited by both Cu(2+) and Zn(2+), Cu(2+) apparently induced the keratocytes to produce activated enzyme and Zn(2+) irreversibly inhibited their production of MMP-2. CONCLUSION: Overexpression of corneal MMP-2 and tear film MMP-9 are characteristic features of patients with PUK and their activation may be a crucial facet of disease initiation or progression. Although effective in systemic therapy for PUK, prednisolone had no direct control over corneal MMP-2 production or activity. Zn(2+) on the other hand inhibited both MMP-2 production and MMP-2 activity and may, therefore, be of therapeutic value if suitably formulated and used in conjunction with systemic steroid treatment.     

热烧伤后的人角膜组织中基质金属蛋白酶-2、-9表达的研究

目的:研究热烧伤后人角膜组织中的基质金属蛋白酶-2、-9(MMP-2、MMP-9)的表达与分布,探讨其含量的变化与角膜病变的相关性。方法:收集铁水烫伤后行角膜移植患者病变角膜19例,正常角膜组织10例。应用免疫组化染色方法检测MMP-2、MMP-9在角膜各层次中的分布与表达,应用图像分析系统进行半定量分析。结果:MMP-2、MMP-9在正常角膜组织中均未见阳性表达,平均灰度值分别为117.8188±3.7967,119.1902±0.9679。热烧伤后角膜组织中,MMP-2的阳性表达主要分布于角膜基质层,平均灰度值为94.4197±5.8327;MMP-9的阳性表达主要分布于角膜上皮层和基底膜附近,平均灰度值为115.0188±0.7149。将正常角膜组织中和病变角膜组织中两种酶的平均灰度值分别进行统计学分析,P值均<0.05。随着病程的发展,在病变角膜组织中MMP-2的阳性表达先呈现逐渐增高趋势14d后逐渐下降,角膜基质层溶解达高峰时阳性表达的量最高;MMP-9在患病初期角膜基底膜病变明显时表达较高,后期逐渐下降。结论:MMP-2、MMP-9对热烧伤后的人角膜组织病变的发展起重要的作用。MMP-2主要参与角膜基质层的损害,MMP-9主要参与角膜上皮层和基底膜的损害。     

正常角膜与圆锥角膜中的Ⅰ型、Ⅵ型胶原与金属蛋白酶-2

目的对比正常角膜与圆锥角膜中的Ⅰ型,Ⅵ型胶原及金属蛋白酶-2的定位与含量。方法应用酶免疫组化及间接免疫荧光技术检测正常与圆锥角膜中Ⅰ型、Ⅵ型胶原及金属蛋白酶-2（MMP-2)的定位。阳性结果应用图像分析系统进行定量分析。结果免疫组化结果显示所有角膜中Ⅰ型胶原存在于前弹力层和基质中;Ⅵ型胶原存在于上皮基底膜、前弹力层、基质、后弹力层;MMP-2存在于上皮、基质、内皮中。同正常角膜比,圆锥角膜中Ⅰ型、Ⅵ型胶原的含量无差别而MMP-2的含量明显增多,差异有显著性。结论圆锥角膜的MMP-2含量增多,其所导致的胶原降解异常可能是圆锥角膜发病的关键。     

Graft failure in human donor corneas due to transmission of herpes simplex virus

AIM: To report the clinical consequences of contamination of human donor corneas by herpes simplex virus (HSV) in organ culture. METHODS: Two patients without previous history of ocular HSV infection underwent penetrating keratoplasty (PK), one for keratoconus and the other for Fuchs' endothelial dystrophy. One patient suffered primary graft failure while the other developed a persistent epithelial defect, ultimately resulting in graft failure. Viral culture of swabs taken from both corneas during the early postoperative period was undertaken. The failed donor corneas were examined histopathologically by immunohistochemistry (IHC) for HSV-1 antigens, transmission electron microscopy (TEM), and by polymerase chain reaction (PCR) for HSV DNA. Both failed corneas were replaced within 6 weeks of the initial surgery. The records of the fellow donor corneas were also examined for evidence of infection. RESULTS: HSV was cultured from both corneas during the early postoperative period. Histology of both donor corneas demonstrated a thickened corneal stroma with widespread necrosis of keratocytes and loss of endothelial cells. IHC showed keratocytes positive with antibodies to HSV-1 antigens. TEM demonstrated HSV-like viral particles within degenerating keratocytes. PCR performed on the failed corneal grafts was positive for HSV-1 DNA, whereas PCR performed on the excised host corneal buttons was negative in both patients. Records of the fellow donor corneas showed that one cornea was successfully transplanted into another recipient after 18 days in organ culture, whilst the other was discarded because of extensive endothelial cell necrosis noted after 15 days in organ culture. CONCLUSION: HSV within a donor cornea may cause endothelial destruction in organ culture and both primary graft failure and ulcerative keratitis after transplantation. Endothelial necrosis of a donor cornea in culture also raises the possibility of HSV infection within the fellow cornea.     

Culture-proven herpetic keratitis after penetrating keratoplasty in patients with no previous history of herpes disease

OBJECTIVE: To report three cases of herpetic infection in recipients of organ-cultured donor corneas among 586 consecutive corneal transplantation procedures. METHODS: Three patients with no history of symptomatic herpes infection underwent corneal transplantation for keratoconus (2 patients) and Fuchs dystrophy (1 patient). Two patients developed keratouveitis and primary graft failure. The third patient developed dendritic keratitis in the graft. Culture of corneal scrapings and the patient's bandage contact lens were positive for herpes simplex virus type 1 (HSV-1). Donor and recipient sera were tested for HSV serology by EIA. Recipient corneal buttons were studied by means of transmission electron microscopy and immunohistochemistry. The three HSV-1 strains were genotyped by sequencing part of a variable antigenic domain of glycoprotein B (gB). RESULTS: None of the donor corneas showed endothelial cell necrosis after organ culture. All keratoplasties performed with the three mate donor corneas had an uncomplicated course. All three donor sera were positive for HSV. Preoperative recipient sera were positive for HSV. Analysis of the recipient corneal buttons showed no evidence of herpetic infection. Sequence analysis revealed three different gB genotypes. CONCLUSION: Ascertaining that a postoperative herpetic infection in a corneal transplant originates from the donor tissue is still difficult. Although some features of the reported cases suggest donor-to-host transmission of herpes simplex virus, the recipients could have been the source of the virus.     

Extracellular matrix and matrix metalloproteinase changes in human corneas after complicated laser-assisted in situ keratomileusis (LASIK).

PURPOSE: To characterize extracellular matrix (ECM) and nine matrix metalloproteinase (MMP) changes in two corneas that underwent a complicated laser-assisted in situ keratomileusis (LASIK) procedure. METHODS: The first patient underwent bilateral LASIK. The flap on the left eye was transected in several locations and placed back. This cornea later developed edema, and the removed flap was analyzed after lamellar keratoplasty. The second patient had a LASIK flap lifted, replaced twice, and then completely removed. The epithelium grew over the stroma, but haze and severe ectasia occurred. After penetrating keratoplasty, the recipient cornea was analyzed. An autopsy cornea from a person who underwent uneventful LASIK and ten normal autopsy corneas served as controls. Corneas were analyzed by immunohistochemistry. RESULTS: Both flap regions in the treated corneas had marked alterations of ECM components and MMPs. Stromal deposits of various ECM proteins, including those normally absent in the central cornea (tenascin-C, fibrillin-1, type XIV collagen), were found. Rare myofibroblasts and inflammatory cells were present. The epithelial basement membrane (BM) was altered in both cases. The most dramatic change was poor or no staining for alpha3-alpha6 type IV collagen chains and thrombospondin. The limbal alpha1-alpha2 type IV collagen and laminin-2 (alpha2beta1gamma1) appeared in the central epithelial BM. Other components were altered to a lesser extent. The anterior stroma was positive for MMP-1 and MMP-2, and some MMP-7 was seen in the epithelium. These ECM and MMP patterns were not seen in uneventful LASIK or normal corneas. CONCLUSIONS: In the flaps of LASIK-treated corneas, fibrosed areas of anterior stroma had increased levels of MMP-1 and MMP-2 that may have caused loss of specific type IV collagen isoforms in the epithelial BM. These changes may reflect an ongoing wound healing process and contribute to the development of ectasia.     

Transplant of corneal epithelium to rabbit corneal wounds in vivo

Sheets of corneal epithelium removed from 9-mm buttons of adult rabbit corneas using Dispase II were placed on abraded (basement membrane intact) or keratectomized corneas of anesthetized rabbits. Both types of wounds extended from limbus to limbus. The host animals were maintained under deep anesthesia for 3 hr, during which time culture medium was dripped onto the surface of the transplant. A soft contact lens then was placed over the cornea and the eye bandaged shut. Short-term experiments indicated that after 24 hr the transplanted epithelium was adherent to both abraded and keratectomized corneas (n = 4). Hemidesmosomes had formed between basal cells of donor epithelium and denuded host basement membrane, and cytoplasmic blebs had extended from donor epithelium into host keratectomized stroma. Seven transplants to abraded corneas and 17 transplants to keratectomized corneas were followed for longer time periods. Six of the seven transplants to abraded corneas were maintained until termination of the experiment (four at 4 weeks, one at 2 weeks, one at 1 week). Three of the 17 transplants to keratectomized corneas were maintained until termination (one at 4 weeks, one at 2 weeks, and one at 6 days). The remaining 14 sloughed between days 2 and 6. These data indicate that it is feasible to transplant corneal epithelial sheets and that they can be maintained most successfully if the host basement membrane is present.     

Detection of herpes simplex virus DNA in donor cornea culture medium by polymerase chain reaction.

AIMS/BACKGROUND: Herpes simplex virus (HSV) may establish latent infection in the cornea and therefore be transmissible by corneal transplantation. Monitoring of donor cornea culture medium was evaluated for HSV infection. METHODS: HSV was sought using virus isolation in cell culture, and its DNA was amplified to detectable levels using the polymerase chain reaction (PCR). RESULTS: Virus isolation in cell culture was negative on neat, cell pellet, and cell free supernatant prepared from the spent culture media of 80 corneas. Three cell pellets (3.8%) were positive for HSV DNA. The PCR positive culture negative results might have reflected latent rather than active HSV infection of the cornea. Post transplant follow up of the three recipients of corneas with HSV PCR positive organ culture media revealed no evidence of HSV induced eye disease or primary graft failure. CONCLUSION: Screening of corneal culture medium for HSV by virus culture or for HSV DNA by PCR could not be recommended.     

Human grafts preserved at +37 degrees C. Initial clinical results

This study reports the clinical use of donor corneas stored at +37 degrees C in organ culture medium. Twenty-five penetrating keratoplasties were performed. The mean storage time of organ-cultured donor corneas was 12.3 days (3-21). The follow up of the patients was 12 months. The criteria for the survival of corneal grafts was mean central corneal thickness, clarity of the cornea and mean endothelial cell density. The graft survival was 92% at 12 months. The mean central corneal thicken was 0.54 mm. The mean endothelial cell density was 1625 cells/mm2. The mean decrease in endothelial cell density at 12 months was 40.6%.     

Immunohistochemical evaluation of two corneal buttons with post-LASIK keratectasia

PURPOSE: To examine immunohistochemically 2 human corneal buttons after corneal transplantation for post-laser in situ keratomileusis (LASIK) keratectasia. METHODS: Two ectatic corneas after penetrating keratoplasty and 2 postmortem control corneas from a patient after uncomplicated LASIK were used. Cryostat sections were stained by immunofluorescence for >30 extracellular matrix (ECM) components and proteinases. RESULTS: The ratios of distance between LASIK flap interface and the upper epithelial layer to total corneal thickness were 0.27-0.34 in all cases. The whole flap interface was positive only for total and cellular fibronectin. Stromal types VI and XIV collagen, fibrillin-1, tenascin-C, and vitronectin were unchanged with no evidence of fibrosis. In ectasia cases, keratocytes adjacent to the flap did not express nidogens. Staining for type IV collagen alpha5 chain, nidogen-2, chains of laminin-8, and laminin-10 was weak and discontinuous in the epithelial basement membrane (EBM). Type IV collagen alpha1/alpha2 chains were found in the EBM of ectasia cases only. Matrix metalloproteinase (MMP)-10 showed increase in the epithelium, and MMP-3, in some keratocytes near the flap interface of ectatic corneas. Also, cathepsin F was seen at the flap margin only. Staining for limbal basal epithelial marker, alpha-enolase, was mostly absent in the ectatic cases, suggesting largely normal epithelial differentiation. CONCLUSIONS: Abnormal EBM structure similar to that previously observed in keratoconus and bullous keratopathy and an increase in certain proteinases suggest ongoing EBM lysis and remodeling. Immunohistochemical staining for fibronectin may be used to reveal the position of flap interface.     

Expression of type XII collagen and hemidesmosome-associated proteins in keratoconus corneas

PURPOSE: Keratoconus is a disease characterized by thinning of the central and paracentral cornea and scarring in advanced cases. This study was performed to examine the expression of type XII collagen, proteins associated with hemidesmosomes, and beta1 integrin in keratoconus corneas. METHODS: Corneal buttons were collected from normal subjects and patients with keratoconus and other corneal diseases. Immunofluorescence staining was performed on frozen sections for type XII collagen, bullous pemphigoid antigen (BP180), and integrin subunits alpha6, beta4, and beta1. RESULTS: To varying degrees, all proteins examined were expressed in normal human corneas. The staining intensity of type XII collagen was diminished in keratoconus corneas in the epithelial basement membrane zone and the stromal matrix. No significant variation was found in either the staining patterns or intensities for BP180, or integrins alpha6, beta4, and beta1. CONCLUSIONS: The level of type XII collagen was reduced in the epithelial basement membrane zone and stromal matrices in keratoconus corneas. These alterations may affect critical interactions of the corneal epithelium with the under-lying basement membrane, and cell-matrix interactions and matrix organization in the stroma.     

Frequency of positive donor rim cultures after penetrating keratoplasty using hypothermic and organ-cultured donor corneas

PURPOSE: To compare the frequency of positive rim cultures after penetrating keratoplasty using corneas preserved by hypothermic and organ culture storage. To evaluate the influence of standard procurement techniques on the frequency of microbial donor rim contamination. METHODS: Six hundred four donor corneas stored at 31 degrees C and 214 at 4 degrees C were studied. Microbiology studies were carried out during organ culture storage, and corneas with positive medium cultures were discarded. Frequency of postoperative positive rim cultures was related to the type of corneal storage and procurement technique used. RESULTS: Thirty-nine (6.4%) corneas with positive medium cultures were discarded during organ culture. Microbiology reports of 628 donor rims cultures from 671 (94%) consecutive transplants were reviewed. Positive rim cultures resulted in 24 (3.8%) cases. None of the patients developed endophthalmitis. The frequency of postoperative positive rim cultures was greater after hypothermic than organ culture storage, being 9.8% and 1.3%, respectively (chi(2) = 24.9; P < 0.001). With organ culture storage, the frequency of positive rim cultures was 1.3% and 1.4% after enucleation and in situ corneal excision, respectively (chi(2) = 0.03; P = 0.638). After hypothermic storage, positive rim cultures were found in 8% of the corneas procured using enucleation and 12% of the corneas excised in situ (chi(2) = 0.829; P = 0.254). CONCLUSIONS: Organ culture storage allows one to recognize and discard corneas with microbial contamination during storage. This method significantly reduces the frequency of postoperative positive rim cultures compared with hypothermic storage. Procurement methods do not influence the percentage of positive rim cultures.     

Abnormal deposition of laminin and type IV collagen at corneal epithelial basement membrane during wound healing in diabetic rats

PURPOSE: To understand the pathophysiology of the corneal basement membrane in diabetes, we compared the localization of laminin and type IV collagen in the epithelial basement membrane during corneal epithelial wound healing in diabetic and nondiabetic rats. METHODS: Streptozotocin was used to induce diabetes in half the rats. Two weeks later, the whole corneal epithelium was debrided. Diabetic and healthy rats (3-5 per group) were sacrificed before debridement and 1, 3, and 7 days and 1 month afterwards. The localization of laminin and type IV collagen was observed in cryosections by epifluorescence microscopy. RESULTS: In unwounded corneas of both diabetic and normal rats, laminin and type IV collagen were localized in the corneal epithelial basement. The intensity of fluorescence, however, was clearly stronger in the diabetic rats. In normal rats, wounding initially removed laminin and type IV collagen, but during healing these two proteins reappeared beneath the resurfacing corneal epithelium. Although similar results were observed in diabetic rats, the expression of laminin and type IV collagen was delayed, and their deposition was fragmented and irregular. CONCLUSIONS: These results suggest that delayed corneal epithelial wound healing in diabetes might involve delayed reappearance and abnormal reformation of epithelial basement membrane proteins.     

Characterization of human corneal collagenase

Collagenolytic activities have been detected in the culture media from an eye bank cornea and in media from corneal tissues biopsied at the time of surgery. The eye bank cornea was not pathological but was not used for corneal grafting because of the donor age (77). The corneal biopsies were from keratoplasty patients with no history of corneal ulceration. Enzymes from both sources cleave tropocollagen at the same site as do tadpole-tail collagenase and rabbit corneal collagenases, and, because of the restricted cleavage, belong to the class of enzymes known as “tissue collagenases”. The human corneal collagenase activities also degrade reconstituted collagen fibrils. The collagenase activity(ies) from human keratoplasty tissues is inhibited by Calcium-EDTA and N-acetyl-l-cysteine, both of which have been found previously to prevent ulceration in the alkali-burned rabbit cornea and to inhibit collagenases produced by the ulcerating rabbit cornea. The serum antiprotease, α₂-Macroglobulin, has also been found to inhibit the collagenase(s) from keratoplasty tissues, an observation which supports the ophthalmologist's sometime contention that serum inhibits corneal ulceration. It is hoped that the human corneal collagenase(s) produced by the culture of keratoplasty tissues and of eye bank corneas judged unfit for corneal grafting will facilitate the discovery of effective inhibitors of corneal ulceration.     

Distribution of specific collagen types and fibronectin in normal and keratoconus corneas

The distribution of five types of collagen and fibronectin in 6 normal and 9 keratoconus corneas was examined, using immunofluorescent staining and the enzyme-labeled antibody method. Types I, III and V collagens were detected in the corneal stroma. There was essentially no difference between normal and keratoconus corneas in their distribution. Type IV collagen and fibronectin were detected in the basement membrane of the normal corneal epithelium, while in the keratoconus corneas the disruption of the basement membrane as well as the excrescence of basement membrane materials was observed. The abnormal distribution of the type IV collagen and fibronectin was also observed in the anterior stromal area of keratoconus corneas.