Acanthamoebae bind to glycolipids of rabbit corneal epithelium

By use of a thin-layer chromatogram (TLC) overlay procedure, 35S-labeled acanthamoebae were shown to bind to seven glycolipids of rabbit corneal epithelium. Corneal epithelial cells were grown in culture and were subjected to Folch extraction to isolate a chloroform-rich lower phase containing neutral glycosphingolipids (NGSL) and an aqueous upper phase containing gangliosides, i.e., sialic acid-containing glycolipids. Thin-layer chromatography of the upper phase revealed the presence of 10 ganglioside components. Acanthamoebae were shown to bind to four of these components, referred to as 2, 3, 6, and 7. On TLC plates, ganglioside components 2 and 3 migrated slightly ahead of the glycolipid standard GD1a, component 7 comigrated with standard GM3, and component 6 migrated a little more slowly than GM3. Likewise, of the 10 NGSL known to be present in the lower phase, acanthamoebae bound to components 1, 5, and 6. NGSL components 1, 5, and 6 migrated on TLC plates with relative mobilities similar to those of standards asialo GM1, asialo GM2, and ceramidetrihexoside, respectively. We propose that one or more of the Acanthamoeba-reactive glycolipids of corneal epithelium identified in this study may play a role in the pathogenesis of Acanthamoeba keratitis by mediating the adherence of the parasites to the cornea.

Nuclear magnetic resonance and circular dichroism studies of a triple-helical peptide with a glycine substitution

The triple-helical conformation has the stringent amino acid sequence constraint that every third residue must be a glycine, (X-Y-Gly)n. We use nuclear magnetic resonance and circular dichroism to quantify the consequences of a substitution in the glycine position of a triple-helical peptide, and to enhance our understanding of interactions in this basic structural motif. A 30-residue peptide with a Gly----Ala change forms a stable trimer at a folding rate somewhat less than that of the unsubstituted peptide, and the substitution results in a marked decrease in thermal stability and a conformational perturbation of about 30% of the triple-helical structure. Two models were generated for this peptide, one with the alanine residues packed inside the triple helix and one with a looping out of the chain at the substitution site. Studies on the Gly----Ala peptide are useful in understanding connective tissue diseases which result from the substitution of one glycine residue in the triple-helix of fibrillar collagens.

Decreased tear osmolarity and absence of the inferior marginal tear strip after sleep

To better understand some of the clinical syndromes that patients experience on eyelid opening in the morning, we examined four patients clinically and measured tear osmolarity immediately after sleep and later in the day. The inferior marginal tear strip was absent, and tear osmolarity was at its nadir on eyelid opening after sleep. We propose a mechanism whereby decreased osmolarity, together with a probable decrease in tear volume, may increase lid-corneal and soft contact lens-corneal adhesion during sleep, and help explain both the development of recurrent corneal erosions on awakening and the tendency of soft contact lenses to adhere to the cornea overnight.

NMR and CD studies of triple-helical peptides

Triple-helix formation of the peptide (Pro-Hyp-Gly)10 was monitored by nmr and CD spectroscopy. The two-dimensional nmr spectra indicated that the Gly C alpha H and Pro C delta H proton resonances shift upfield in going from the nonhelical to helical form, while hydroxy-proline resonances are unchanged. The integrated areas of the helical and nonhelical resonances could be monitored in the one-dimensional nmr spectrum, and indicate that in the (Pro-Hyp-Gly)10 about 90% of the residues are in a defined triple-helical conformation. The introduction of a glycine to alanine substitution or the deletion of a single hydroxyproline residue in the stable triple-helical peptide (Pro-Hyp-Gly)10 still allows trimers to be formed, but the trimers show a substantial loss of triple helix and decreased thermal stability compared with (Pro-Hyp-Gly)10. Two computer models were generated for the Gly----Ala peptide, one with the Ala side chains packed inside the helix and the other with the region containing the alanines forming a beta-bend that loops out from the helix. The nmr data is more consistent with the latter model.

Proton NMR assignments and secondary structure of the snake venom protein echistatin

The snake venom protein echistatin is a potent inhibitor of platelet aggregation. The inhibitory properties of echistatin have been attributed to the Arg-Gly-Asp sequence at residues 24-26. In this paper, sequence-specific nuclear magnetic resonance assignments are presented for the proton resonances of echistatin in water. The single-chain protein contains 49 amino acids and 4 cystine bridges. All of the backbone amide, C alpha H, and side-chain resonances, except for the eta-NH of the arginines, have been assigned. The secondary structure of the protein was characterized from the pattern of nuclear Overhauser enhancements, from the identification of slowly exchanging amide protons, from 3JC alpha H-NH coupling constants, and from circular dichroism studies. The data suggest that the secondary structure consists of a type I beta-turn, a short beta-hairpin, and a short, irregular, antiparallel beta-sheet and that the Arg-Gly-Asp sequence is in a flexible loop connecting two strands of the distorted antiparallel beta-sheet.

Neuraminidase activity in acanthamoeba species trophozoites and cysts

Acanthamoeba species, a widely distributed group of free-living amoeba, can infect humans and spread hematogenously after direct interaction with the mucosal surfaces. The mechanism underlying Acanthamoeba damage to the target cell is unknown. The authors report that trophozoites and cysts of Acanthamoeba species exhibit a neuraminidase activity that is membrane associated and released into the culture medium at the start of the logarithmic phase of growth. The enzyme activity is optimal at pH 5 and at 25-30 degrees C. Live parasites release sialic acid from human cells. Therefore, the neuraminidase of Acanthamoeba species could be relevant in the colonization and damage of the sialic acid-rich corneal epithelium and in the alterations of glycolipids associated with meningoencephalitis.

Auranofin therapy for juvenile rheumatoid arthritis: results of the five-year open label extension trial

Eighty-eight children with juvenile rheumatoid arthritis (JRA) who completed a double blind, randomized placebo controlled trial of oral gold were entered into an open label extension phase during which they received auranofin (AF) at a dosage of 0.15-0.2 mg/kg/day (9 mg/day maximum). Eleven (12.5%) patients completed 5 years of AF therapy; 77 (87.5%) did not. Fifteen (17%) of the 88 were in disease remission at the final visit. Mean duration of therapy for those who discontinued was 646 days. Parental/patient decision and insufficient therapeutic effect were the 2 most frequent reasons for early termination, followed by adverse effects. Though relatively well tolerated, AF provides adequate longterm management for only a small percentage of patients with JRA.

Clinical and histopathologic studies of two families with lattice corneal dystrophy and familial systemic amyloidosis (Meretoja syndrome)

Lattice corneal dystrophy associated with familial systemic amyloidosis (Meretoja syndrome) has rarely been described other than in patients of Finnish origin. The authors report two North American patients with this disease who manifest blepharochalasis, lattice corneal dystrophy, open-angle glaucoma, and cranial neuropathy. In one patient, a corneal intraepithelial and subepithelial pseudodendrite was managed by superficial keratectomy, and this same patient benefited from surgical brow suspension for facial muscular weakness. In the second patient, penetrating keratoplasty was complicated by a neurotrophic persistent epithelial defect. Corneal tissue from both superficial keratectomy and penetrating keratoplasty exhibited ultrastructurally characteristic amyloid filaments and associated elastoid material. Transmission electron microscopy of conjunctiva and skin biopsies similarly revealed amyloid deposits associated with most basement membranes, the perineurium and endoneurium of most peripheral nerves, and the intima and media of arteries. By immunoperoxidase staining, the corneal amyloid deposits were positive for the amyloid P-component protein but negative for the nonimmunoglobulin amyloid A protein and prealbumin. Serum prealbumin and amyloid A related protein were normal.

Differential binding of P. aeruginosa and S. aureus to corneal epithelium in culture

Adherence of bacteria to corneal epithelium is a prerequisite for corneal infection. We used two methods to study the binding of Pseudomonas aeruginosa and Staphylococcus aureus to rabbit corneal epithelial cells in culture. In the first method, rabbit corneal epithelial cells grown on glass slides were incubated with P. aeruginosa or S. aureus (10(7) CFU/ml) at room temperature for 90 min, and the bacterial binding to the epithelial cells was examined by light microscopy. Both P. aeruginosa and S. aureus bound to epithelial cells. P. aeruginosa was bound to the cell periphery whereas S. aureus was bound randomly to the cell surface. In the second method, suspension cultures of corneal epithelial cells were used. In contrast to the findings in cultures on slides, binding pattern with cells in suspension was similar for both species and resembled that for S. aureus in cultures on slides. A much greater number of P. aeruginosa (186 +/- 11 bacteria/epithelial cell) than S. aureus (30 +/- 1.5 bacteria/epithelial cell) bound to epithelial cells grown on glass slides. In contrast, a similar number of P. aeruginosa (25 +/- 5.1) and S. aureus (20 +/- 4.7) bound to epithelial cells grown in suspension cultures. Using either method, Escherichia coli and Streptococcus pyogenes did not bind significantly (less than 5/cell) to corneal epithelial cells. The above methods should prove useful for characterization of bacterial binding to corneal epithelial cells in culture.

Neutral glycolipids of migrating and nonmigrating rabbit corneal epithelium in organ and cell culture

It is generally believed that plasma membrane glycoconjugates influence corneal epithelial cell migration after wounding. Previous studies have focused on the role of glycoproteins in this event. The present study was designed to determine whether migration-specific glycolipids are synthesized by epithelium of healing rabbit corneas. Migrating and nonmigrating rabbit corneal epithelia were incubated with [3H]-galactose in an organ culture system for 48 hr. At the end of the labeling period, a neutral glycosphingolipid (NGSL) fraction was isolated from each radiolabeled epithelium and was analyzed by thin-layer chromatography. Three radiolabeled NGSL components, M1, M2 and M3 (M1-M3), were present in significantly higher amounts in the extracts of migrating as compared to nonmigrating epithelium. Chromatographic mobility of M3 was similar to that of a standard glucosylceramide; M1 and M2 migrated more slowly than M3. For characterization of the migration-related NGSL, a large amount of the starting material is required. Experiments, therefore, were conducted using cell cultures of rabbit corneal epithelium. Confluent (nonmigrating) cell cultures of rabbit corneal epithelium were found to synthesize either minimal or undetectable amounts of NGSL M1-M3. In contrast, we found that the NGSL M1-M3 are synthesized as major components by sparse (migrating) corneal epithelial cell cultures. Components M1-M3 were synthesized as major components by sparse cultures even in the absence of cell mitosis. This suggests that the increased synthesis of components M1-M3 by sparse cell cultures may be related to cell migration rather than cell mitosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial adherence to extended wear soft contact lenses

The authors studied the adherence of Pseudomonas aeruginosa and Staphylococcus aureus to extended wear soft contact lenses (EWSCLs) with and without focal deposits using both a radiolabeling technique and electron microscopy. P. aeruginosa showed significant adherence to contact lenses in vitro. In contrast, S. aureus failed to show significant adherence to contact lenses in vitro (i.e., the radioactive uptake was not significantly above background). The extent of adherence of Pseudomonas was proportional to the number of focal deposits on the lenses. Results of electron microscopic examination showed the bacteria to be adherent primarily to large focal deposits (greater than or equal to 150 microns). There was no pseudomonal adherence to the small focal deposits (less than or equal to 50 microns) and little adherence to the areas in between the focal deposits. The authors hypothesize that worn lenses, especially those with large focal deposits, serve as a vehicle for the transport of P. aeruginosa to the cornea. This hypothesis could be a partial explanation for the high incidence of keratitis caused by P. aeruginosa in EWSCL patients.

[Fresh gas flow and artificial respiration in anesthesia. Technical requirements for the adequate use of rebreathing systems]

The majority of modern anaesthetic machines is designed for the rebreathing method. But frequently high fresh gas flows are employed, thus minimising the rebreathing fraction of expiratory gases. However, only by reducing the fresh gas flow substantially, the advantages of the rebreathing technique can be obtained. To evaluate the practicability of flow reduction, minimal flow anaesthesia was carried out with four different anaesthetic machines: AV 1 (Drägerwerk AG, Lübeck), ELSA (Gambro Engström AB, Bromma, Sweden), SULLA 808 V (Drägerwerk AG, Lübeck) und VIVOLEC (Hoyer Medizintechnik, Bremen). Fresh gas flow was reduced to 0.5 l/min after an initial phase of 15-20 min, during which the fresh gas flow was kept at a high level of 4.4 l/min. The minute volumes before and after fresh gas flow reduction were compared. The minute volume decreased markedly and significantly in the SULLA 808 group, whereas it remained nearly unchanged in the AV 1, the ELSA, and the VIVOLEC groups. The differences result from different modes of fresh gas delivery into the breathing circuit. If anaesthetic apparatus that maintain their tidal volume with different fresh gas flow rates are employed, rebreathing systems may be used judiciously by changing the fresh gas flow according to the individual uptake or any particular clinical requirement.

Binding of Pseudomonas aeruginosa to neutral glycosphingolipids of rabbit corneal epithelium

35S-labeled Pseudomonas aeruginosa isolates were shown to bind to neutral glycosphingolipids (NGSLs) of rabbit corneal epithelia in culture by a thin-layer chromatogram overlay procedure. The lipids of the corneal epithelial cells grown in culture were extracted and partitioned into a chloroform-rich lower phase containing NGSLs and an aqueous upper phase containing gangliosides. By using a dot-blot assay, at least six times more radiolabeled P. aeruginosa isolates were shown to bind to the lipids in the lower phase compared with those in the upper phase. Thin-layer chromatography of the lower-phase lipids followed by staining with an orcinol spray revealed at least 10 NGSL components and several fast-migrating, nonglycosylated neutral lipid components (including cholesterol). 35S-labeled P. aeruginosa was shown to bind to NGSL components 1, 2, 5, 6, and 9. P. aeruginosa-reactive NGSL components 6 and 9 migrated with chromatographic mobilities similar to those of the standards ceramide trihexoside (CT) and ceramide monohexoside, respectively. Components 1 and 2 migrated slightly ahead of asialo GM1, and component 5 migrated faster than globoside but slower than CT. Among the various standards tested, P. aeruginosa bound to asialo GM1 and, to a lesser extent, to ceramide dihexoside and CT but not to GM1, GD1A, GM3, or ceramide monohexoside. It remains to be determined whether any of the five P. aeruginosa-reactive NGSL components of corneal epithelium identified in this study plays a role in the development of corneal infection. However, we have previously shown that component 9, one of the five P. aeruginosa-reactive NGSL components identified in this study, is present in significantly greater amounts in migrating epithelia than it is in nonmigrating epithelia (N. Panjwani, G. Michalopoulos, J. Song, G. Yogeeswaran, and J. Baum, Invest. Ophthalmol. Vis. Sci., in press). This may prove to be of biological significance because it is generally believed that traumatized (migrating) epithelia are more susceptible to infection than normal (nonmigrating) epithelia are.

Protein-related abnormalities in keratoconus

Two-dimensional electrophoretic maps of extracts from eleven normal and eleven keratoconus corneas were compared. Of the eleven corneas analyzed, eight were pooled and the remaining three were analyzed individually. Several differences were demonstrated between electrophoretic patterns of normal and keratoconus corneas. In keratoconus corneas, 1) two abnormal components (MW 54kD and 26kD) were observed; 2) three normal corneal components (MW 12kD, 14kD, and 39kD) were present in significantly higher amounts; and 3) three normal corneal proteins (MW 66kD, 55kD, and 13kD) were present in reduced amounts. The molecular weight and isoelectric point of one of the normal corneal proteins that we found to be reduced in keratoconus corneas were close to that of a subunit of prolyl-4-hydroxylase, an enzyme required for hydroxylation of proline residues of collagen. The possibility the abnormal proteins detected in the keratoconus corneas were derived from those normal corneal proteins which were absent or were present in reduced amounts in the keratoconus corneas remains to be established. This study may provide protein markers for elucidation of the biochemical abnormality in keratoconus.

Effect of lid closure on contact lens-associated Pseudomonas keratitis

New or used extended-wear soft contact lenses, preincubated in suspensions of Pseudomonas aeruginosa, were placed on the corneas of rabbits. The lids were then sutured shut for either 1 or 2 weeks. Bacterial keratitis occurred in 9 of 9 eyes fitted with the used contaminated lenses but in none of 12 eyes fitted with new contaminated or new noncontaminated lenses. Similar experiments were carried out with other lenses specifically designed to fit the cornea of rabbits. Some of these lenses were preworn by rabbits for 1 week (used), whereas others were new. A significantly greater incidence of bacterial keratitis was found in eyes that had undergone lid closure after the placement of used contaminated lenses (4 of 5) than in closed eyes with new contaminated lenses (1 of 8) and in open eyes with used contaminated lenses (0 of 13). These findings suggest that extended eyelid closure is a risk factor in the experimental model and may be a factor in clinical Pseudomonas keratitis associated with the wearing of extended-wear soft contact lenses.

Altered keratan sulfate epitopes in keratoconus

Extracts of normal and keratoconus human corneas were assayed for keratan sulfate (KS) and for the protein core of corneal keratan sulfate proteoglycan (KSPG), using a solid-phase immunoassay. Aliquots from guanidine-HCl extracts of four to six pooled corneas were adsorbed to nitrocellulose membrane and assayed for binding of a monoclonal antibody against KS or of an affinity-purified rabbit polyclonal antibody against the KSPG protein core using 125I-labeled secondary antibodies. The amount of antigen in the extracts was estimated from standard curves with purified bovine KSPG. Extracts from keratoconus corneas contained only an average of 48% as much (P less than 0.001) KS-antigen as normal corneal extracts when assayed with anti-KS monoclonal antibody. There was no significant difference in the amount of KSPG core protein antigens in keratoconus and normal corneal extracts. These results suggest that corneas with keratoconus contain a form of KSPG that contains fewer keratan sulfate chains or in which the keratan sulfate has a modified structure.