Biomedical subjects

R A Alexander

Publications and source records attributed to R A Alexander.

At least 37 records · Page 2Linked to original sources

PubMed1997

Effect of varying the mitomycin-C treatment area in glaucoma filtration surgery in the rabbit.

PURPOSE: To investigate the effect of varying the treatment area of subconjunctival mitomycin-C (MMC) using an adapted rabbit model of filtration surgery. METHODS: Twenty-four New Zealand White rabbits underwent filtration surgery, with random allocation to one of three treatments: 5-minute subconjunctival applications of MMC (0.4 mg/ml) with either a large (8 x 10 mm) or small (4 x 2 mm) sponge or no treatment (control). Drainage was achieved by placing an intravenous cannula through a scleral tunnel into the anterior chamber. Rabbits were examined at set intervals for up to 30 days after surgery. Measurements of appearance, size, height, and vascularity of blebs and of intraocular pressure and anterior chamber depth were made by a masked observer. Histologic analysis of eyes was performed at 3, 14, and 30 days. RESULTS: Statistical analysis showed a significant difference in bleb survival among all groups (log rank P = 0.0054, with 100% survival with large areas of MMC treatment). Comparison between large and small treatment area groups revealed significant differences in bleb survival (log rank P = 0.0388); bleb area (between-subject analysis, P = 0.009), and bleb height (between-subject analysis, P = 0.005). These differences were seen clinically, with large areas of MMC treatment producing diffuse and elevated blebs, small areas of treatment producing thin-walled and localized blebs with scarring at 21 days, and no treatment resulting in comparatively vascularized and scarred blebs before 14 days. Histologic analysis revealed clear differences among groups, with an increase in subconjunctival cellularity and scar tissue in eyes with failed blebs. CONCLUSIONS: The size of the area of subconjunctival MMC treatment significantly affects surgical outcome. Histologic features mirror differences observed clinically. Alteration of the size of the MMC treatment area may provide an alternative and more controllable approach to modulating the wound-healing response after drainage surgery and, more important in the clinical context, to modifying bleb morphology.

Animals↗

PubMed1997

Single exposures to antiproliferatives: long-term effects on ocular fibroblast wound-healing behavior.

PURPOSE: To determine the long-term effects of single, 5-minute exposures to 5-fluorouracil (5FU) and mitomycin-C (MMC) on Tenon's capsule fibroblast migration, growth factor production, growth factor receptor expression, and extracellular matrix (ECM) production. METHODS: Monolayer cultures and the overlying growth medium of Tenon's capsule fibroblasts exposed to 5FU (0.25 to 25 mg/ml) or MMC (0.001 to 0.1 mg/ml) were harvested up to 48 days after treatment. The expression of growth factors and growth factor receptors, including transforming growth factor beta (TGFbeta), basic fibroblast growth factor (bFGF), and epidermal growth factor (EGF), and ECM molecules (collagen type I, collagen type III, and fibronectin) were quantitated at the mRNA and protein levels. The ability of fibroblasts exposed to 5FU and MMC to migrate to fetal calf serum was also investigated up to 48 days after treatment. RESULTS: Control cultures were found to produce the growth factors TGFbeta and bFGF but not EGF. Exposure to 5FU or MMC resulted in an initial significant increase (P < 0.05) in the production of TGFbeta and bFGF, with levels then decreasing toward those of controls. Cells exposed to 5FU or MMC exhibited an initial significant decrease (P < 0.05) in the number of TGFbeta, bFGF, and EGF growth factor receptors, with subsequent recovery toward control levels by day 48 after treatment. Both 5FU and MMC caused a significant reduction (P < 0.05) in collagen type I and fibronectin production compared to controls throughout the 48-day culture period. The production of collagen type III was initially elevated (P < 0.05) compared to controls after exposure to 5FU or MMC, production then decreasing toward control levels over the remainder of the 48-day culture period. The migration of cells exposed to 5FU or MMC was significantly reduced (P < 0.05) compared to controls up to 48 days after treatment; these cells exhibited a partial recovery of migratory ability throughout this period. CONCLUSIONS: Fibroblasts whose growth was arrested using single, short exposures to 5FU or MMC appear to be capable of performing several crucial aspects of wound healing, including the expression of growth factors and receptors and ECM molecules and the ability to migrate. These findings may help explain why in some patients treated with antiproliferatives, glaucoma filtration surgery fails because of scarring.

Antimetabolites↗

PubMed1996

Microvessel count predicts survival in uveal melanoma.

Microvessel density has become established as an important prognostic indicator for many tumor types. This study investigates the microvessel density as a prognostic factor for survival in patients with uveal melanoma, which is the commonest intraocular tumor and has a clear tendency for metastatic spread to the liver. Factor VIII-related antigen was identified immunohistochemically in bleached sections from 123 tumors. Maximum blood vessel density in an area of 0.25 mm2 was recorded, along with other accepted prognostic information. Microvessel density was the single most important prognostic factor on univariate testing, and in a Cox proportional hazard model, tumor size was the only other variable to be entered. No other accepted prognostic factor entered the model. We conclude that microvessel density is an important prognostic factor for survival in patients with uveal melanoma and allows the identification of high-risk patients for whom adjuvant therapy should be considered.

Biomarkers, Tumor↗

PubMed1996

The immunoalkaline phosphatase technique in immunohistochemistry: the effect of permanganate-oxalate melanin bleaching upon four final reaction products.

Melanin bleaching prior to the application of primary antibody can alter the immunoreactivity of a number of antigens. The effect of melanin bleaching subsequent to antigen visualisation by four different chromogens used with an immunoalkaline phosphatase technique was investigated. Vector black was the only final reaction product that withstood exposure to the permanganate-oxalate sequence for a time sufficient to bleach melanin.

Choroid Neoplasms↗

PubMed1995

Descemet's membrane in the iridocorneal-endothelial syndrome: morphology and composition.

The iridocorneal-endothelial syndrome is a disease of the ocular anterior segment characterized by corneal failure, glaucoma and iris destruction. Specular photomicroscopical and histological studies suggest the disorder is caused by a population of abnormal corneal endothelial cells. In other corneal endotheliopathies Descemet's membrane, the basement membrane underlying the endothelial cells, is disfigured by the presence of an abnormal region of extracellular matrix termed a posterior collagenous layer, which is laid down by the diseased endothelial cells. In this study we sought to establish the typical morphology and composition of Descemet's membrane in the iridocorneal-endothelial syndrome. Ultrastructural examination of Descemet's membrane in 27 keratoplasty specimens identified three morphologic patterns. In the majority there was a posterior collagenous layer which in all cases consisted of an anterior layer of wide-spaced collagen and a posterior layer of microfibrils embedded in an amorphous matrix. In four specimens which did not possess a posterior collagenous layer the anterior banded zone of Descemet's membrane was absent. In five corneas Descemet's membrane was normal. The composition of the posterior collagenous layer was examined by immunoelectron microscopy (five corneas) and histochemistry (six corneas). Collagen Types I, III, V, VI and VIII, fibronectin, tenascin and oxytalan were microfibrillar components, collagen Type VIII formed wide-spaced collagen whilst laminin was present in the amorphous matrix. The stereotyped derangements of structure and composition identified in the endothelial basement membrane may significantly influence the pathobiology of this disorder.

Adult↗

PubMed1995

Estrogen and progesterone receptor analysis in ocular melanomas.

BACKGROUND: It has been suggested that pregnancy may promote metastases in melanoma and that the contraceptive pill may be an etiologic factor. The purpose of this study is to determine if uveal or conjunctival melanomas express estrogen or progesterone receptors. METHODS: Twenty-seven choroidal and five conjunctival melanomas were investigated. Immunohistochemistry was performed using the antibodies ER-D5, which recognizes heat-shock protein 27 (formerly called the estrogen receptor-associated cytoplasmic antigen); ER-1D5, which recognizes the estrogen receptor; and PgR, which recognizes the progesterone receptor. RESULTS: Most of the conjunctival and uveal melanomas stained strongly for heat-shock protein 27 but none of the tumors showed positive nuclear staining for either the estrogen or the progesterone receptor. CONCLUSIONS: No evidence was found for either estrogen receptor or progesterone receptor expression in choroidal or conjunctival melanomas. Based on the literature, there is little evidence for these hormones having a role in the development or progression of these tumors.

Adult↗

PubMed1995

Effects of chronic elevated levels of CO2 on the concentration of blood cellular elements and plasma corticosterone in the male rat.

The mean CO2 concentration on the Space Shuttle is 0.3% and has reached 0.7%, for extended periods of time. Following space flight, it has been shown that both humans and animals have significant changes in red blood cell counts (RBC) and white blood cell counts (WBC). In other studies, where no difference occurred in total WBC, a significant change did occur in the distribution of WBC. WBC are affected by circulating levels of glucocorticoids, which often increase when animals or humans are exposed to adverse and/or novel stimuli (e.g. elevated CO2 levels or weightlessness). The purpose of this study was to determine if elevations in CO2 concentration produce changes in total WBC and/or their distribution.

Animals↗

PubMed1995

Connective tissue fibre production in keratoconus.

In a histochemical and electron microscopic study of 45 cases of keratoconus, oxytalan fibres, a member of the elastic fibre family, were found in the extracellular tissues of the cornea. Oxytalan fibres were identified beneath the epithelium over the thinned central region of the conical cornea as well as in areas of stromal scarring. In a number of instances the apparently thickened Descemet's membrane was shown to include an oxytalan-containing retro-corneal layer. Oxytalan fibres were found to be immunostained by antibodies raised against collagen type VI.

Contractile Proteins↗

PubMed1995

Immunohistochemical techniques: the effect of melanin bleaching.

This study addresses two questions: i) which antigens can withstand bleaching by 2.5 g/L of potassium permanganate followed by 10 g/L of oxalate, before immunohistochemical staining; and ii) are any other steps in the immunohistochemical staining technique resistant to bleaching? A panel of 10 antigens was stained immunohistochemically and the results compared with staining performed with a bleaching step interpolated at different steps in the procedures. Four antigens (HMB-45, S-100, factor VIII-related antigen and collagen type IV) were unaffected by bleaching; two antigens (CD-20 and CD-45) had their staining enhanced by bleaching; one had the staining reduced (hsp27); and in three it was abolished (CD-45Ro, CD-31 and Ulex/anti-ulex antibody) by bleaching. Two antibodies (UCHL-1 and L-26) showed evidence for altered specificity following bleaching. None of the steps after application of the primary antibody was resistant to bleaching. Three chromagens used for peroxidase demonstration-amino ethyl-carbazole, diaminobenzidine and chloro-naphthol-were also found to be sensitive to bleaching. While some antigens were resistant to the effects of bleaching, some were not, and no other step in the immunohistochemical procedure could withstand bleaching.

Antigens, Neoplasm↗

PubMed1994

Are most intraocular "leiomyomas" really melanocytic lesions?

BACKGROUND: Intraocular smooth muscle tumors have long been a subject of controversy. The advent of immunohistochemistry with antibodies against HMB-45, S-100, smooth muscle actin, desmin, and vimentin has helped greatly in the distinction between smooth muscle tumors and melanocytic lesions. METHODS: Twenty-seven archival tissue blocks from patients who had had intraocular leiomyomas or leiomyosarcomas diagnosed were located and fresh sections cut and stained for the above markers. The cases constituted 24 iris lesions and 3 ciliary body lesions. RESULTS: All 24 iris tumors were reclassified as iris melanocytic lesions. Two of the three ciliary body leiomyomas retained their classification, and the third was reclassified as a spindle B-cell melanoma. CONCLUSION: The authors suggest that intraocular leiomyomas are much rarer than previously suggested and that many of the cases previously reported in the literature are open to question.

Actins↗

PubMed1994

Effects of single exposures to antiproliferative agents on ocular fibroblast-mediated collagen contraction.

PURPOSE: To determine the effects of short-duration treatments with 5-fluorouracil (5FU) and mitomycin-c (MMC) on "activated" and "nonactivated" ocular fibroblasts in collagen lattices. METHODS: Activated and nonactivated ocular fibroblasts seeded in collagen lattices were exposed to single 5-minute treatments with 5FU (0.01 to 25 mg/ml) and MMC (0.01 to 1 mg/ml). The effects of these treatments on lattice contraction, cellularity, cellular viability, cellular structure, and actin distribution were investigated. RESULTS: Treatment with 5FU (0.01 to 25 mg/ml) or MMC (0.1 to 1 mg/ml) significantly inhibited (P < 0.001 and P < 0.0001, respectively) lattice contraction compared to water controls. The degree of inhibition was greater in lattices containing nonactivated cells than in those containing activated cells. Activated cell viability and cellularity, unlike their nonactivated counterparts, were not significantly affected (P > 0.0083) by treatment with 5FU at high concentrations (25 mg/ml). MMC treatment had significant effects on cell viability and cellularity (P < 0.0001). Treatment with 5FU and MMC also affected cellular structure and actin distribution compared to water controls. CONCLUSIONS: Single, short exposures to 5FU or MMC inhibit ocular fibroblast-mediated collagen contraction. MMC causes cell death and a decrease in cellularity at high concentrations. The results also indicate that collagen lattices seeded with activated and nonactivated fibroblasts are differentially affected by short-term exposures to 5FU or MMC. These findings may have important clinical implications regarding the concentrations of these agents used in the treatment of different patient groups.

Actins↗

PubMed1993

Immunologic cross-reactivity in the pathogenesis of ocular onchocerciasis.

PURPOSE: Onchocerca volvulus, a filarial worm, is a major cause of infectious blindness and inflammatory eye disease. An autoimmune cause for ocular onchocerciasis has been suggested since the identification of a recombinant antigen of O. volvulus that shows immunologic cross-reactivity with a host ocular component of 44,000 M(r). The aim of this study was to establish the distribution of the cross-reactive antigens in both host tissues and the parasite, and to determine if significant autoantibody responses to the host antigen could be detected in infected persons. METHODS: The tissue and organ distribution of the 44,000 M(r) antigen was determined by immunocytochemistry and Western blot analysis. Human autoantibody responses to the ocular antigen were demonstrated by Western blot analysis using sera collected from persons with onchocerciasis, with and without posterior segment pathology, Bancroftian filariasis, and Europeans with no filarial infection. RESULTS: The tissue distribution of the 44,000 M(r) antigen correlates with the sites of pathology in onchocerciasis and antibody reactivity against this antigen could be detected in all persons with onchocerciasis and posterior segment pathology. The antigen is also recognized by sera from persons with Bancroftian filariasis, but not from normal persons. CONCLUSIONS: A role is proposed for immunologic cross-reactivity in the pathogenesis of onchocerciasis and it is suggested that intraocular presentation of the cross-reactive parasite antigen by microfilariae is essential for the development of disease.

Adult↗

PubMed1992

Oxytalan fibres in proliferative vitreoretinopathy.

The distribution of elastic and related fibres was studied in 29 fibrocellular membranes associated with proliferative vitreoretinopathy using histochemical, immunohistochemical and ultrastructural techniques. Ten subretinal and ten epiretinal membranes were subjected to light microscopical investigation, whilst the remaining nine membranes were examined by transmission electron microscopy. Oxytalan fibres, an elastic fibre precursor that is found in a variety of normal and pathological connective-tissue matrices, were identified in all of the specimens. Mature elastic fibres were not observed in any of the 29 membranes. The demonstration that oxytalan connective-tissue fibres contribute to the infrastructure of PVR membranes adds further evidence to the suggestion that this proliferative tissue might be the result of a repair mechanism.

Adolescent↗

PubMed1991

Oestrogen receptors in conjunctival malignant melanoma: immunocytochemical study using formalin fixed paraffin wax sections.

In a group of 15 women with conjunctival malignant melanoma six cases (40%) were shown to have oestrogen receptor positivity using a monoclonal antibody to oestrogen receptor related antigen (ER-D5, Amersham RPN.710) on formalin fixed, paraffin wax sections. Receptors were also present in the epithelium of these six cases but not in controls and cases without ER-D5 positivity in their tumours. A subset of these aggressive, intractable unilateral tumours may therefore be amenable to hormone treatment.

Adolescent↗

PubMed1989

The effect of argon laser trabeculoplasty upon the normal human trabecular meshwork.

The effect of argon laser trabeculoplasty (ALT) upon the normal human trabecular meshwork, as determined by scanning and transmission electron microscopy is reported. The lower nasal and temporal quadrants of an eye received ALT 5 and 1 day, respectively, prior to enucleation. Laser impact sites were identified as focal disruptions of trabeculae, together with connective tissue and cellular debris. Surviving trabecular endothelial cells near the laser lesions exhibited signs of phagocytic and migratory activity. Exogenous macrophages also contributed to the clearance of debris. Activated trabecular cells were observed leaving the meshwork by migrating over the corneal endothelium. By 5 days post-ALT increased amounts of trabeculae lacked an endothelial covering. More activated trabecular cells but fewer macrophages were noted. A laser lesion sited close to Schwalbe's line induced, within 5 days, a local corneal endothelial wave front to advance towards it, thus reflecting many late failed ALT specimens that we have seen.

Humans↗

PubMed1989

Sorsby's fundus dystrophy. A light and electron microscopic study.

The light and electron microscopic changes in both eyes of a patient with Sorsby's fundus dystrophy are reported. The most striking finding was a 30-microns thick deposit present within Bruch's membrane that stained positive for lipids. The deposit has several unique features when compared with those found in other retinal dystrophies and in aged eyes. In addition, there was gross loss of the outer retina, the retinal pigment epithelium was discontinuous, and there was atrophy of the choriocapillaris. These findings are discussed in relation to the published clinical observations of other members of this pedigree.

Choroid↗

PubMed1989

Morphological effects of argon laser trabeculoplasty upon the glaucomatous human meshwork.

Thirty four trabeculectomy specimens from open angle glaucoma patients who had under argon laser trabeculoplasty as part of their treatment, were studied by scanning electron microscopy. Three of these were also examined by transmission electron microscopy. The intervals between laser therapy and surgery ranged from one month to five years. A sub-group consisted of six patients who had received laser treatment on more than one occasion prior to surgery. Electron microscopy revealed distortion of trabecular beams, loss of trabecular endothelial cells and the development of a cellular sheet extending from the region of Schwalbe's line and covering the anterior surfaces of the anterior portion of the uveal meshwork. The sheet occluded the trabecular spaces of the region; thus, when extensive, contributing to laser trabeculoplasty failure. It is concluded that argon laser trabeculoplasty induces a repair process, in the form of repopulating a cellular deficient meshwork, but which can become detrimental as a consequence of its success.

Adult↗

PubMed1988

The retinal pigment epithelium and other tissues immunocytochemical studies using hybridoma supernatants.

We describe the production of hybridomas producing antibody reactive with retinal pigment epithelium. The patterns of reactivity obtained when supernatants from these hybrids were used to immuno-stain ocular and non-ocular tissues are described. From the patterns of reactivity obtained we suggest that the RPE shares common features with simple and glandular epithelia as well as myoepithelial cells. These findings may lend support to the hypotheses of RPE cell migration and contraction in the formation of epiretinal membranes and retinal detachment.

Animals↗