Biomedical subjects

K R Kenyon

Publications and source records attributed to K R Kenyon.

At least 73 records · Page 4Linked to original sources

PubMed1989

Lens redox fluorometry: pyridine nucleotide fluorescence and analysis of diabetic lens.

We performed both ex vivo and in vivo fluorometric analyses of pyridine nucleotides (PN) in rabbit and rat lenses. Rabbit lens PN fluorescence (99% NADH) was found to have an excitation maximum at 366 nm and an emission maximum at 462 nm (366:462). The only other fluorescent chromophore in that region of the spectrum has excitation and emission peaks at 328 and 460 nm, respectively. Anaerobic glycolysis in the lens was stimulated by KCN, a known inhibitor of mitochondrial respiration, after which a time-study of fluorescence intensities was performed. Over the course of a 3.5 hr period following treatment with KCN, the PN signal showed a statistically significant increase relative to that in the control lenses (those treated with KCl). while the 328:460 signal (which may be due to some protein involved in energy transfer with the PN) had a significantly greater decrease. We also found that fluorescence intensity of NADH in solution is linearly proportional to physiologic-range concentration. Moreover, there was a close correlation between fluorescence intensity of rat lens PN as measured on a specular microscope-coupled redox fluorometer capable of in vivo use, and the lens PN levels as determined by the analytical cycling assay technique. This fluorometer was then employed to assess the redox state in rats with streptozotocin-induced diabetes. The normalized ratio of PN to flavoproteins (Fp) in the lens epithelium increased from 0.96 +/- 0.12 in the normal state to 1.48 +/- 0.30 2 weeks after diabetes induction. In contrast, the ratio in the diabetic lens treated with an aldose reductase inhibitor, sorbinil, did not increase. The increase in the PN:Fp ratio therefore reflects activation of the polyol pathway and its associated metabolic activities, which results in an increase in the NADH:NAD ratio in the diabetic rat lenses. Our results indicate that the non-invasive, real-time method of redox fluorometry may be useful in the early detection and evaluation of cataracts and other disorders in lens metabolism, long before opacities occur. It can be used to monitor the disease process and evaluate the efficacy of such drugs as aldose reductase inhibitors on a biochemical level.

Animals↗

PubMed1989

Hard contact lens-induced metabolic changes in rabbit corneas.

The biochemistry of contact lens-cornea interaction is not well understood, although previous studies have suggested that corneal metabolic changes may be the underlying factor in morphological alterations. Using a rabbit model, this interaction has been examined with 31P nuclear magnetic resonance (NMR) spectroscopy, which detects signals principally from the epithelium. The examination was supplemented with electron microscopy and histochemistry. Polymethylmethacrylate lenses caused reversible changes, including activation of anaerobic glycolysis and disturbance of membrane metabolite levels. These changes were far more severe than those occurring during prolonged eye closure. There appears to be an association between cellular deterioration and loss of membrane metabolites. On the other hand, oxygen-permeable silicone lenses allowed maintenance of nearly normal metabolic patterns. These results show multifaceted corneal response to hard contact lens wear.

Animals↗

PubMed1989

Limbal autograft transplantation for ocular surface disorders.

Limbal autograft transplantation is presented in 26 consecutive cases comprising both acute and chronic chemical injury (20 cases), thermal burns (2 cases), contact lens-induced keratopathy (3 cases), and ocular surface failure after multiple surgical procedures (1 case), with follow-up ranging from 2 to 45 months (mean, 18 months). The operative technique usually involved transfer of two free grafts of limbal tissue from the uninjured or less injured donor eye to the severely injured recipient eye, the latter having been prepared by limited conjunctival research and superficial dissection of fibrovascular pannus without keratectomy. Clinical results in 21 patients with follow-up of 6 months or more have consistently shown improved visual acuity (17 cases), rapid surface healing (19 cases), stable epithelial adhesion without recurrent erosion or persistent epithelial defect (20 cases), arrest or regression of corneal neovascularization (15 cases), and probable increased success for lamellar or penetrating keratoplasty (8 cases). No intraoperative complications were encountered, and no adverse reactions developed in donor eyes. Impression cytology in selected cases showed restoration of the corneal epithelial phenotype and regression of goblet cells from the recipient cornea. Therefore, limbal autograft transplantation is recommended for treatment of widespread ocular surface damage with loss of limbal epithelial stem cells and, specifically, for chemical or thermal burns, contact lens-induced keratopathy, and selected persistent corneal epithelial defects.

Adolescent↗

PubMed1989

Distribution of collagenase and cell types in sterile ulceration of human corneal grafts.

Extensive clinical and experimental evidence has suggested a role for corneal epithelium, keratocytes, and acute inflammatory cells in sterile corneal ulceration, although the precise role of these cell types in stromal matrix degradation has not been elucidated. We studied two corneal buttons and two whole corneas from 4 patients with corneal grafts and sterile stromal ulceration. Each cornea was divided into several sections and examined morphologically, while adjacent sections were placed in tissue culture and assayed for collagenase activity against type I collagen. In each case, collagenase activity was present in tissue from ulcerating and nonulcerating areas and, in most regions assayed, exceeded collagenase activity in normal control peripheral donor corneas. Collagenase levels were not always greatest in areas of most advanced ulceration. Although polymorphonuclear leukocytes were extensively present histologically in two cases, one case had a mixed inflammatory cell population at the site of ulceration, and another had only keratocytes (fibroblasts) present in the entire cornea. We conclude that regional differences in collagen degradation are due not only to the presence of collagenase, but also to cellular and humoral activators and inhibitors that determine collagenolytic activity.

Adult↗

PubMed1989

Keratopathy of the rabbit cornea following complete eyelid closure.

The corneal response to a complete tarsorrhaphy was studied in 46 rabbits for time periods up to 21 days. During the first 7 days of complete eyelid closure corneal thickness increased up to 18.4%, glycogen decreased 32.2%, and lactate rose 27.2%. A steep increase in corneal thickness to 89.8% appeared after 14 days, followed by decreasing values at 21 days, which was concomitant with the formation of extensive vascularized pannus. These results confirm previous findings that the partial pressure of O2 under closed eye conditions is substantially below physiologic requirements, affects endothelial pump capability, and results in major corneal swelling. When silicone contact lenses were fitted immediately before eyelid closure, corneal swelling 2 days after lid closure did not differ from that in eyes without lenses.

Animals↗

PubMed1989

Time course of human conjunctival mast cell degranulation in response to compound 48/80.

Compound 48/80, a non-immunogenic mast cell degranulatory agent, is known to produce the signs and symptoms of ocular allergy. Maximal mast cell degranulation of human conjunctiva occurred within the first hour after stimulation by a single topical dose of compound 48/80 (20 microliters, 7.5 mg/ml). The average percentage of fully degranulated mast cells in treated specimens (n = 9) was 31% (range 5-60%) versus 6% (range 0-20%) in control specimens (n = 5). Exact correlates of representative granulated, partially degranulated, and fully degranulated mast cells were determined by light and transmission electron microscopy.

Conjunctiva↗

PubMed1989

Limbal autograft transplantation for chemical and thermal burns.

The technique of limbal autograft transplantation is presented which has been used in 25 cases of uniocular chemical and thermal burns. With up to 4 years follow-up, these cases have consistently demonstrated: (1) improved visual acuity; (2) rapid surface healing; (3) stable epithelial adhesion without recurrent erosion or persistent epithelial defect; (4) consistent regression of corneal neovascularization; (5) restoration of a smooth and optically improved ocular surface; and (6) probably increased success for subsequent keratoplasty.

Burns↗

PubMed1989

Standard models of corneal injury using alkali-immersed filter discs.

Central corneal alkali burn injuries were induced in rabbits by applying five NaOH concentrations on uniformly soaked 7 mm filter paper discs. Clinical parameters were evaluated daily by microscopic examination and photography, and corneal myeloperoxidase levels were measured periodically. Satisfactory alkali burn models of corneal inflammation, vascularization and ulceration were developed by manipulating the alkali concentration.

Alkalies↗

PubMed1989

Adherence of viable and nonviable bacteria to soft contact lenses.

Bacterial viability in bacterial adherence to new soft contact lenses (SCLs) was studied by exposing polymacon and lidofilcon A lenses to Pseudomonas aeruginosa: L, live, untreated bacteria; H, bacteria heated for 1 h at 100 degrees C; and P, bacteria treated with 3% hydrogen peroxide for 1 h. Cultures of groups L, H, and P showed heavy, no, and minimal bacterial growth, respectively. Scanning electron microscopy (SEM) showed significantly less bacteria on new SCLs in groups H and P. Transmission electron microscopy (TEM) showed that bacterial shape was mostly preserved in all groups, with marked intracellular and cell membrane changes and breaks (groups H and P), margination of intracellular electron-dense material (group H), and central and peripheral vacuolation (group P). Adherence to new SCLs appears to be an active process, as killed or altered bacteria adhere less.

Bacterial Adhesion↗

PubMed1989

Elevated intraocular pressure following penetrating keratoplasty.

IOP was retrospectively studied in 229 consecutive cases of PK, with a mean follow-up period of 84 weeks. Twenty-seven percent of the cases had preoperative glaucoma, three-fourths of which were medically controlled prior to keratoplasty. Following PK, 34% of the total sample developed sustained elevated IOP but only five (2%) patients required surgical treatment for glaucoma. The mean time from PK to first IOP rise was 24 weeks. Variables which were significantly associated with IOP rise included preoperative glaucoma (P less than .001), aphakia (P less than .01), and IOL removal (P less than .01). When eyes with preoperative diagnoses of glaucoma were excluded from the analysis, aphakia was no longer associated with postoperative IOP rise. Keratoconus patients were at significantly less risk than patients with other corneal diagnoses. Factors not associated with IOP rise included previous PKs, pseudophakia, intraoperative vitrectomy, PAS lysis, iridoplasty, secondary IOL placement, and concomitant cataract extraction with IOL (triple procedure).

Aphakia↗

PubMed1989

Paracellular permeability of corneal and conjunctival epithelia.

The paracellular permeability of normal rabbit cornea and conjunctiva was studied in vivo and in vitro. After intravenous administration, horseradish peroxidase was found to percolate to the intercellular space of conjunctival epithelia and was restricted by the tight junctions of the superficial epithelium. Only minimal tracer was present in the limbus and cornea. The difference between corneal and conjunctival paracellular pathways was further compared in vitro by tissue perfusion studies using various tracers from subepithelial space to apical surface. The intact full-thickness cornea was permeable to mannitol (MW 182) but not to inulin or dextran. The conjunctiva was permeable to mannitol, inulin and FITC-dextran (MW 20,000). The quantitative permeability to 3H-mannitol (X10(-8) cm/sec) of adult rabbit cornea was 0.12 +/- 0.02, which is about 55-fold and 50-fold lower than that of conjunctiva (6.78 +/- 0.21) and peritoneum (6.12 +/- 0.63), respectively. Removal of the corneal epithelium increased the permeability 40-fold; however, removal of the endothelium had little effect on the solute permeation. When both corneal epithelium and endothelium were debrided, the bare stroma became edematous and the permeability increased 70-fold. The permeability of 1-week-old rabbit cornea was 1.32 +/- 0.18, which decreased to 0.46 +/- 0.06 in 2-week-old rabbits, and became similar to the adult level at 4 weeks of age. When Tenon's capsule was included in the perfusion, the conjunctival permeability decreased 2.5-fold. With the apposition of bare corneal stroma to the conjunctiva and Tenon's capsule, the permeability decreased further (4-fold).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Metabolic changes in the cornea of vitamin A-deficient rats.

We have investigated alterations of the metabolic state in vitamin A-deficient (A-) corneas using phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy. Comparing to the control, A- corneas showed a prominent rise of phosphocreatine (PCr) as well as a total loss of glycerophosphorylcholine (GPC). Further, ATP levels were lower, and sugar phosphates (SP) and inorganic phosphate (Pi) were higher than those of the control. The accumulation of PCr and Pi, and decrease of ATP indicate that the activity of creatine kinase may be altered in vitamin A deficiency. These results suggest that vitamin A may have a role in creatine kinase activation and/or induction and that its deficiency causes a decline of energy metabolism in corneal epithelium. Moreover, disappearance of GPC implies an impaired cellular membrane metabolism. When retinyl acetate was supplied to A-rats for 5 weeks, the 31P profiles of vitamin A-repleted rat corneas recovered to normal.

Adenosine Triphosphate↗

PubMed1989

Factors influencing predilection and outcome in bacterial keratitis.

Complete records from 175 patients with 176 episodes of culture-proven bacterial keratitis treated over a 4-year period at the Massachusetts Eye and Ear Infirmary in Boston were analyzed. Sixty-three percent of the infections involved gram-positive organisms, and 40% involved gram-negative organisms; 15% were polymicrobial. There was a high incidence of infection with Staphylococcus aureus (28%), coagulase-negative staphylococci (14%), diphtheroids (14%), Pseudomonas aeruginosa (14%), and Streptococcus pneumoniae (12%). Gram stain correlation was achieved in 55%. Potential predisposing factors, usually multiple, were identified in 97% of the patients. Fifty percent of the ulcers were associated with such iatrogenic factors as prior topical corticosteroid therapy, penetrating keratoplasty, and contact lens use. Trauma occurred in only 16%. Several statistically significant associations of epidemiologic factors and outcome variables were revealed. Ninety-five percent of the ulcers resolved with therapy, but only 44% of the patients had visual acuity better than the level at admission, and 13% developed major complications.

Adolescent↗

PubMed1989

Dynamics of corneal epithelial healing after an alkali burn. A statistical analysis.

A precise definition of epithelial healing kinetics following chemical injury is necessary to aid the investigation of control mechanisms, potential therapeutic intervention and ophthalmic drug toxicity. Wound healing was studied photographically at frequent intervals in rabbits following 1N or 4N alkali burns. Planar wound areas were determined by computerized planimetry and transformed mathematically to curved surface data. The decrease in equivalent wound radius with time was computer-modelled using two linear and three nonlinear regressions. A periodic function was also investigated. Serial photographs showed that intermittent attrition of small areas of the migrating wound edge was a common confounding variable. Although excellent coefficients of determination were found for all models, the addition of nonlinear factors gave a small advantage. A mean lag phase of 3.96 and 6.52 hr occurred after 1N and 4N alkali burns, respectively; wound edge attrition was notably prevalent in early healing. Epithelial healing in the rabbit had a fundamental linear component, with mean epithelial migration rates of 76 and 80 microns/hr after 1N and 4N alkali burns, respectively, and which continued to closure. A quadratic nonlinear component was also suggested. No significant circadian component was detected.

Alkalies↗

PubMed1989

Gentamicin-resistant pseudomonal infection. Rationale for a redefinition of ophthalmic antimicrobial sensitivities.

Eight pseudomonal species were involved in 106 invasive infections of the eye; all were community acquired. Eighteen percent of the total and 9% of the Pseudomonas aeruginosa strains were gentamicin resistant, as defined using conventional criteria. All 10 cases of "resistant" pseudomonal (nine P. aeruginosa) keratitis responded satisfactorily to treatment with gentamicin. The resistance breakpoint (defined by safe serum levels in parenteral therapy) for most P. aeruginosa is much lower than ocular gentamicin levels achievable by optimal local application. We argue for a specific ophthalmologic definition of antibiotic resistance in infections of the cornea and external eye. MIC quantitative determinations of ocular isolates would provide more useful information to ophthalmologists than conventional qualitative disc sensitivity testing.

Adult↗

PubMed1989

Microbiology of contact lens-related keratitis.

We reviewed 397 cases of microbial keratitis examined at the Massachusetts Eye and Ear Infirmary, Boston, MA, U.S.A., from January 1982 through December 1985. Of these, 136 cases (34%) were related to contact lens use. Extended-wear contact lenses were used by 107 (79%) of these patients. Cosmetic contact lenses accounted for 59 (44%) of lens-related cases, aphakic contact lenses 44 (32%), and therapeutic (bandage) contact lenses 33 (24%). Fifty-three microbial keratitis cases associated with contact lens wear were culture-positive: 28 (52%) were gram-positive, and 19 (36%) were gram-negative. Mixed cultures, fungi, and Acanthamoeba accounted for two cases (4%) each. Pseudomonas aeruginosa was specifically associated with cosmetic soft contact lens use.

Adult↗

PubMed1989

Expression of transforming growth factor-beta in wound healing of vitamin A-deficient rat corneas.

Transforming growth factor-beta (TGF-beta) is a multifunctional peptide that modulates cell proliferation and differentiation in many cell types and accelerates tissue repair response. In this study, expression of TGF-beta was investigated immunohistochemically in the healing of central 3 mm epithelial wounds of vitamin A-deficient (A-) rat and pair-fed controls. In control rat corneas, a positive reaction to TGF-beta was not evident during wound healing. In A- rat corneas at 4 hr post-abrasion, acute inflammatory cells showing high positivity to TGF-beta appeared in the peripheral stroma and gradually spread to the central cornea. By 24 hr, these cells accumulated and formed a pseudomembrane in the epithelial defect, which also showed an intense positivity to TGF-beta, suggesting that the peptide participates even in the acute inflammatory response. From about 16 hr post-injury, many fibroblasts revealing intense positivity to TGF-beta infiltrated the entire stroma and were part of the healing process. Reepithelialization occurred over the pseudomembrane and was completed by 48 hr. The central cornea showed remodeling of collagen structure and neovascularization. Fibroblasts containing TGF-beta were seen in the stroma, indicating that TGF-beta plays an important role in corneal wound healing. Indeed, in the absence of vitamin A, a common modulator of cell differentiation, TGF-beta may play a more important role in wound healing than in the normal state.

Animals↗

PubMed1989

Effects of hypertonic solutions on conjunctival epithelium and mucinlike glycoprotein discharge.

A simple, semiquantitative, histochemical method using periodic acid-Schiff (PAS) staining was developed to measure the mucinlike glycoprotein content of bathing solutions exposed to rabbit conjunctiva. Rabbit eyes were bathed in vivo in solutions of various tonicity (160, 260, 300, 330, and 363 mOsm/L). Eyes bathed in hypotonic or isotonic solutions (160, 260, and 300 mOsm/L) exhibited a steady-state glycoprotein secretion (50-100 micrograms/h). In hypertonic solutions (330 and 363 mOsm/L), glycoprotein discharge increased to 150-360 micrograms/h when the solutions were exchanged hourly for 6 h, but glycoprotein discharge increased to a much lower rate (100-167 micrograms/h) after prolonged bathing for 6 h without solution exchange. Periodic acid-Schiff--positive glycoprotein aggregates were noted more frequently on the filters of hypertonic solutions than on those of other tonicity. After eyes were bathed in hypertonic solutions, increased disruption of the surface epithelium, increased abnormal discharge of mucin granules, and decreased goblet cell density were noted in the biopsied conjunctiva. These data suggest that mucinlike glycoprotein secretion from the conjunctival goblet cells can be enhanced by the tonicity of the bathing solution, and that nonphysiological hypertonic solutions can also affect the conjunctival epithelium.

Animals↗