Biomedical subjects

C A Paterson

Publications and source records attributed to C A Paterson.

At least 73 records · Page 4Linked to original sources

PubMed1990

Inhibition of Pseudomonas aeruginosa elastase and Pseudomonas keratitis using a thiol-based peptide.

Pseudomonas aeruginosa elastase is a zinc metalloproteinase which is released during P. aeruginosa infections. Pseudomonas keratitis, which occurs following contact lens-induced corneal trauma, can lead to rapid, liquefactive necrosis of the cornea. This destruction has been attributed to the release of both host-derived enzymes and the bacterial products P. aeruginosa elastase, alkaline protease, exotoxin A, and lipopolysaccharide endotoxin. A synthetic metalloproteinase inhibitor, HSCH2 (DL)CH[CH2CH(CH3)2]CO-Phe-Ala-NH2, which we previously showed to be a potent inhibitor of corneal collagenase and alkali-induced corneal ulceration, was tested as a potential inhibitor of P. aeruginosa elastase. Inhibition constants (Kis) for the resolved diastereomers were determined with the chromogenic substrate furylacryloyl-glycyl-L-leucyl-L-alanine. One isomer had a Ki of 0.3 microM, while the other had a Ki of 0.4 microM. The more potent diastereomer was evaluated in vivo in experimentally induced Pseudomonas keratitis in rabbits. Following inoculation of one cornea of each rabbit, topical treatment with a 1 mM solution of the inhibitor significantly delayed the onset of corneal melting and perforation, as compared with the results for the control and gentamicin-treated groups. This protective effect suggests that the inhibitor may have a therapeutic application by delaying the progression of corneal destruction in Pseudomonas keratitis.

Amino Acid Sequence↗

PubMed1990

Ocular blood flow and vascular permeability in endotoxin-induced inflammation.

Blood flow was measured in several tissues of the rabbit eye following intravitreal injection of a dose of endotoxin that induces an inflammatory response. In separate experiments, the vascular permeability of the inflamed eye was estimated by iris fluorescein angiography and by measuring protein influx into the aqueous humor. The effect of topical corticosteroid treatment upon blood flow and vascular permeability was also measured. Following intravitreal endotoxin injection, minor changes in blood flow occurred in retina and optic nerve head. Marked changes were observed in blood flow in iris, ciliary processes, and choroid. Steroid treatment had no effect upon the increased blood flow 24 h after the endotoxin injection, although from a clinical standpoint the steroid-treated eyes appeared less inflamed. Fluorescein angiography demonstrated a massive increase in iris vessel permeability 6 and 24 h following endotoxin injection. Topical steroid treatment reduced fluorescein entry into the anterior chamber at both time periods. On the other hand, the increase in protein influx into the aqueous humor in the endotoxin-inflamed eye was not inhibited by steroid pretreatment. It is suggested that corticosteroids have a selective effect upon the permeability of different components of the blood-aqueous barrier, namely the ciliary processes and the iris vasculature.

Animals↗

PubMed1990

Inhibition of alkali-induced corneal ulceration and perforation by a thiol peptide.

Corneal ulceration and perforation following a severe alkali burn occur as a consequence of collagen destruction by locally released enzymes. A thiol peptide, which recently was shown to be a potent inhibitor of corneal collagenase in vitro, was tested in alkali-burned rabbit corneas to determine its effectiveness in inhibiting corneal ulceration. Following a standard alkali burn to one eye of each rabbit, ten animals were treated topically six times daily and subconjunctivally one time daily with a 1 mM solution of the peptide for a period of 3 weeks. A control group of ten rabbits was administered vehicle only using the same regimen as the experimental group. Corneal ulceration occurred in ten out of ten of the control eyes and seven out of ten progressed to perforation. The experimental group demonstrated ulcerations in four out of nine animals, only one of which was deep (one of nine), and no perforations. There was no significant difference when comparing the onset of ulceration between the two groups, but the difference was significant when comparing the total number of ulcerations (0.02 less than P less than 0.05), deep ulcerations (0.01 less than P less than 0.02) and perforations (0.001 less than P less than 0.01) between the two groups. Histologic examination of the corneas after 3 weeks of treatment revealed that the experimental, thiol-treated corneas that did not ulcerate contained relatively few PMNs, whereas the control corneas demonstrated a marked inflammatory infiltrate in the form of PMNs, most notably at sites of corneal ulceration. These findings demonstrate that a synthetic thiol peptide inhibits alkali-induced corneal ulceration and perforation in vivo.

Analysis of Variance↗

PubMed1990

Time course of rabbit ocular inflammatory response and mediator release after intravitreal endotoxin.

An inflammatory response was elicited in the rabbit eye by intravitreal injection of endotoxin. The appearance in aqueous humor of selected metabolites of arachidonic acid metabolism at various times was correlated with the influx of protein and myeloperoxidase activity in the iris-ciliary body. After intravitreal injection of endotoxin, aqueous humor protein levels increased substantially within 2 hr. This aqueous humor protein increase occurred before a significant appearance of prostaglandin E2 (PGE2) in the aqueous humor. Myeloperoxidase activity in the iris-ciliary body, a measure of polymorphonuclear leukocyte (PMN) infiltration, showed little elevation until 6 hr after endotoxin injection and then increased rapidly through 24 hr. The appearance of the leukotriene B4 (LTB4) followed a similar time course: levels in the aqueous humor were partially elevated until 6 hr after endotoxin injection, when levels begin to rise rapidly. These findings are interpreted to demonstrate the dependence of PMN infiltration on the release and accumulation of LTB4; the initial breakdown of the blood-aqueous barrier and influx of protein appears to be independent of significant release of PGE2.

Animals↗

PubMed1990

Prostaglandin E2 binding sites in bovine iris-ciliary body.

In the eye, prostaglandins (PGs), in particular PGE2 and PGF2 alpha, may induce vasodilation, disruption of the blood-aqueous barrier, and biphasic effects on intraocular pressure, depending on the species. The initial event leading to many of these physiologic responses is the interaction between the PG and a receptor. We have explored the specificity and selectivity of PGE2 receptors in bovine iris-ciliary body (ICB) membrane preparations. Pigment-free bovine ICB membranes were prepared by high-speed sucrose density-gradient centrifugation. Membranes were incubated with 1 nM 3H-PGE2 in the presence or absence of varying concentrations of unlabeled PGE2 or F2 alpha. Binding of 3H-PGE2 to membranes at 37 degrees C increased linearly with protein concentration, and binding reached equilibrium in 30 min. Specific PGE2 binding represented 80% of total 3H-PGE2 binding. Studies with unlabeled PGE2 or F2 alpha, as competing ligands, showed a dose-dependent inhibition of 3H-PGE2 specific binding. The IC50 for unlabeled PGE2 and F2 alpha was 3 and 379 nM, respectively, which suggests a 100-fold greater selectivity of the binding sites for PGE2 over F2 alpha. Scatchard analysis of saturation data revealed a mean Kd value of 13.3 nM with a Bmax of 156 fmoles bound/mg protein. The general linearity of our Scatchard plots tends to suggests a single class of binding sites for PGE2, although more than a single binding site could be present. These results indicate that binding sites selective for PGE2 exist in the bovine ICB.

Animals↗

PubMed1989

Effects of ebselen on arachidonate metabolism by ocular and non-ocular tissues.

The formation of cyclooxygenase products in rabbit and rat ocular and non-ocular tissues in vitro, detected by radio-thin-layer chromatography, was inhibited in a concentration-dependent manner by ebselen (PZ 51), an anti-inflammatory seleno-organic compound which has glutathione peroxidase and anti-oxidant activities. The exception was prostaglandin F2 alpha (PGF2 alpha) formation in the rabbit irisciliary body which was stimulated by ebselen in the concentration range 2-10 microM. These observations were confirmed by gas chromatography-mass spectrometry. The concentration that inhibited 50% of prostaglandin biosynthesis (IC50) in the rabbit iris-ciliary body was 9.3 microM. Ebselen also inhibited the formation of 12-hydroxyeicosatetraenoic acid (12-HETE) in rabbit and rat ocular tissues and rabbit platelets. The IC50 in the rabbit cornea was 4 microM, whereas higher concentrations were generally required to achieve similar inhibition in other tissues. The formation of 12-HETE by rabbit spleen, however, was not decreased by ebselen at concentrations that were inhibitory in other tissues.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1989

Oxidant and anti-oxidant effects on arachidonate metabolism by rabbit ocular tissues.

Ocular tissues have the capacity to metabolize arachidonate to prostaglandins and related materials, such as hydroxy arachidonate derivatives (HETEs) which are potent mediators of the inflammatory response. Reactive oxygen species are also present during the inflammatory response, resulting in an altered oxidative environment within the eye. This study was designed to evaluate the possible impact of the oxidant hydrogen peroxide and anti-oxidants, ascorbic acid and glutathione, upon arachidonate metabolism. It was found that hydrogen peroxide was observed to potently inhibit arachidonate metabolism in the cornea, but not in the iris-ciliary body. This might be related to a more efficient detoxification of hydrogen peroxide by iris-ciliary body. Ascorbate appeared to have a general stimulatory influence upon arachidonate metabolism in the iris-ciliary body. In the cornea, ascorbate selectively reduced metabolism to HETE while enhancing the products generated by the cyclo-oxygenase pathway. In both cornea and iris-ciliary body reduced glutathione suppressed conversion of arachidonate to its active metabolites. These observations indicate that arachidonate metabolism in ocular tissues is sensitive to the oxidative environment.

Animals↗

PubMed1989

Ca2+-ATPase activity in the human lens.

A membrane-rich preparation of paired human lenses was prepared in such a manner as to preserve ATPase activity. The lipid:protein ratio of these preparations was increased 12-fold with an 85% recovery of total phospholipid. The pattern of stimulation of ATPase activity by a range of calcium concentrations was found to be similar in membrane preparations of epithelium and cortex. The concentration of calcium necessary for half-maximal simulations of ATPase activity was approximately 10(-6) M. Ca2+-ATPase activity is undetectable in the lens nuclear region. A shift in the sensitivity of lens epithelial Ca2+-ATPase activity was observed with increasing age concomitant with a general increase in Ca2+-ATPase activity suggesting age related modifications of the membrane.

Adolescent↗

PubMed1989

Studies on the distribution of cholesterol, phospholipid, and protein in the human and bovine lens.

The regional distribution of cholesterol, phospholipid and protein content was determined on pools of human lenses ranging from 13 to 68 years old. The study was undertaken to establish age matched controls for comparison with cataractous lenses. Future spectroscopic structure analysis of human lenses will be performed and the results related to chemical composition. The molar cholesterol to phospholipid ratio was 3.5 +/- 0.3 for human lens. This ratio is high for human tissue. The lens ratio increased from 2.2 +/- 0.3 in the equatorial region to 9.2 +/- 1.6 in the nuclear region. This trend was also observed in the bovine lens. The relative amount of protein increased concomitantly from 0.13 +/- 0.02 Kg protein per gram lipid in the equatorial region to 0.33 +/- 0.06 in the nucleus. The cholesterol to protein ratio remained constant throughout the lens at 0.073 +/- 0.003 Kg suggesting cholesterol could be associated with the crystallin proteins. In partially purified membrane preparations the cholesterol to phospholipid molar ratio was 2.6 +/- 0.2 and 3.2 +/- 0.2 for the cortex and nucleus respectively, three times lower than for the whole tissue. The high cholesterol content could account for the observed rigidity of membranes measured by infrared spectroscopic examination of the CH stretching band.

Adolescent↗

PubMed1989

Inhibition of purified collagenase from alkali-burned rabbit corneas.

The inhibitory potency of four classes of compounds that inhibit corneal ulceration (thiols, tetracyclines, sodium citrate and sodium ascorbate) was assessed with collagenase purified from culture medium of alkali-burned rabbit corneas. The most potent inhibitor, a beta-mercaptomethyl tripeptide HSCH2(DL)CH[CH2CH(CH3)2]CO-Phe-Ala-NH2, exhibited 50% inhibition (IC50) at approximately 10 nM using the synthetic metalloproteinase substrate Dnp-Pro-Leu-Gly-Leu-Trp-Ala-D-Arg-NH2. The inhibitor was somewhat less potent with type 1 collagen as substrate (IC50 between 1 and 3 microM), possibly because autooxidation of the essential - SH moiety of the inhibitor occurred during the longer time required for assay with the natural substrate. An N-carboxyalkyl tripeptide, CH3(CH2)2(DL)CH-(COOH)-Leu-Phe-Ala-NH2, was less potent (IC50 = 25 microM) than the thiol peptide. N-acetylcysteine, which is used to treat corneal ulceration, gave IC50 values of 2.7 mM and less than 10 mM with the synthetic and natural substrates, respectively. The IC50 values for the tetracyclines using the synthetic substrate were 15, 190 and 350 microM for doxycycline, minocycline and tetracycline, respectively. Inhibition by sodium citrate, but not the tetracyclines, could be reversed by excess Ca2+. Sodium ascorbate did not inhibit collagenase-mediated hydrolysis of either collagen or the synthetic substrate, thus indicating that the mechanism by which this agent inhibits corneal ulceration is not related to inhibition of collagen degradation by collagenase.

Animals↗

PubMed1989

Oxidative inhibition of Ca2+-ATPase in the rabbit lens.

Hydrogen peroxide inhibition of maximum Ca2+-ATPase and Na+,K+-ATPase activity was measured in a membrane-enriched preparation of rabbit lens cortical fibers and epithelium. At 5 X 10(-6) M hydrogen peroxide maximum Ca2+-ATPase activity was inhibited by 39%, while maximum Na+,K+-ATPase activity was stimulated. Ca2+-ATPase activity was almost completely inhibited at 5 X 10(-4) M hydrogen peroxide, in comparison to Na+,K+-ATPase activity, which was only inhibited by 28% at a concentration of hydrogen peroxide an order of magnitude larger. The addition of catalase to hydrogen peroxide-pretreated samples did not reverse the inhibition of Ca2+-ATPase by hydrogen peroxide.

Animals↗

PubMed1989

Prompt irrigation of chemical eye injuries may avert severe damage.

Chemical burns to the eye are among the most urgent of ocular emergencies. The clinical outcome of the injury is directly related to the expediency with which treatment is begun. Copious irrigation is the most important emergency treatment of the chemically-burned eye. This irrigation should begin immediately at the scene of the accident with any non-toxic liquid. Removal of any particulate matter must be done to prevent further ocular damage. The subsequent therapy is directed at the treatment of secondary sequelae and at preserving the globe to surgically rehabilitate the eye. Many of the treatments which are used in the intermediate and late phases of the injury are used to prevent corneal ulceration and perforation. These are the most difficult sequelae to threat in alkali injuries; thus, preventing the progression to this stage is of the utmost importance. Again the immediate and continuous irrigation of the eye may help accomplish this goal. The availability of emergency eye-wash equipment dispensing a safe, preserved, pH-balanced, physiologically correct solution in the industrial, agricultural and even the home setting is a necessity. The education of employees and family members in the proper technique of irrigating the eye following a chemical burn is also of extreme importance. Immediate irrigation of the eye, continued during rapid transport to a medical care facility, minimizes the damage to the eye and enhances the eventual clinical outcome.

Acids↗

PubMed1989

Distribution of phospholipid-malondialdehyde-adduct in the human lens.

The distribution of phospholipid-malondialdehyde adduct was measured in human lenses pooled by age over a range of 13 to 68 years. Lipid extracts from sections of the central core and from the equatorial region of the lens were probed for lipid adduct using laser induced fluorescence. For an excitation of 351.1/363.8 nm the fluorescence maximum occurred at 473 nm for all ages and regions of the lens. The adduct concentration was always highest in the anterior nuclear section of the central core and decreased toward the anterior and posterior surfaces. The adduct concentration was lowest in the equatorial section for all samples. The regional distribution observed suggests that the formation of lipid-malondialdehyde adduct in the lens could be influenced by the cumulative amount of UV radiation absorbed. No changes with age were observed in the concentration of the adduct in the whole lens nor in the cortical and nuclear regions suggesting the possibility of an equilibrium between the formation and degradation of the adduct.

Adolescent↗

PubMed1988

Lens membrane properties following hydrogen peroxide exposure.

Rabbit lenses exposed to 0.5 mM hydrogen peroxide for 1 h and then incubated for an additional 19 h demonstrated small yet significant changes in electrolyte balance. Active cation pumping by the lens, as determined by 86Rb uptake studies, was partially impaired following 1 h hydrogen peroxide exposure; the cation pump further deteriorated during the subsequent 19-hour incubation. Passive membrane permeability of the lens, measured by 86Rb efflux, was elevated following 1 h hydrogen peroxide but no further increase in leakiness was observed during the subsequent 19-hour incubation. These findings suggest that even relatively brief exposure to oxidative damage initiates a chain of events from which the lens is unable to recover.

Animals↗

PubMed1988

Alteration of lens electrolyte transport parameters following transient oxidative perturbation.

Rabbit lenses were incubated, in vitro, for 20 hr. During the first 60 min of the incubation period, the lenses were exposed to hydrogen peroxide at specified concentrations. Deranged electrolyte balance was observed in lenses exposed to hydrogen peroxide concentrations exceeding 0.1 mM. Lenticular sodium pump activity, as evidenced by lens 86Rb uptake, was reduced to 61% of control when examined immediately after exposure to 0.5 mM hydrogen peroxide for 1 hr. Upon further incubation in peroxide-free medium, the sodium pump activity of hydrogen peroxide treated lenses continued to deteriorate. The deterioration of sodium pump activity in lenses transiently challenged with hydrogen peroxide was not altered by supplementation of the incubation medium with antioxidants or by substitution of calcium in the medium. Lenticular potassium permeability, as evidenced by the rate of 86Rb efflux from the lens, was found to be elevated immediately after exposure to 0.5 mM hydrogen peroxide for 1 hr. However, no further change in the rate of 86Rb efflux was noted when the hydrogen peroxide treated lens was incubated for an additional 19 hr in peroxide-free medium. Na,K-ATPase and Ca-ATPase activities were measured in membrane preparations isolated from lenses that had been exposed to 0.5 mM hydrogen peroxide and then cultured in control medium for 19 hr. Neither of the transport enzyme activities was diminished in the hydrogen peroxide treated lenses indicating that the deterioration in sodium pump activity in lenses temporarily exposed to hydrogen peroxide is not due to a progressive loss of Na,K-ATPase enzyme.

Animals↗

PubMed1988

Ca-ATPase activity in the rabbit and bovine lens.

Membrane-rich vesicle preparations of rabbit and bovine lenses were prepared in such a manner as to preserve ATPase activity. The lipid:protein ratio of these preparations was increased 22- to 33-fold with a 94% recovery of total phospholipid. Using this preparation, calcium stimulated ATPase was routinely determined in both individual lenses and in pooled specimens. The pattern of stimulation of ATPase activity by a range of calcium concentrations was found to be similar in membrane preparations of epithelium and cortex, from rabbit and bovine lenses. The concentration of calcium necessary for half-maximal stimulation of ATPase activity was approximately 10(-6) M. Calcium concentrations in excess of 10(-4) M reduced the ATPase activity. Calcium-ATPase was undetectable in the lens nuclear region of both species. The regional distribution of sodium-potassium ATPase was also measured.

Animals↗

PubMed1987

Vitamin C levels in human tears.

Human tears, collected using the Schirmer strip method, were analyzed by high-performance liquid chromatography for vitamin C (ascorbic acid). In "basal" tears, the levels of ascorbic acid ranged from 3.9 to 23 mg/dL (220 to 1310 mumol/L); lower values correlated with higher tear flow rates. In reflex tears, induced by brief ammonia inhalation, the ascorbic acid level fell dramatically and appeared to reach a minimum level around 2 mg/dL (110 mumol/L). Even the low level in reflex tears, however, was consistently higher than plasma levels. Ascorbic acid in tears has a potential anti-inflammatory role.

Adult↗

PubMed1987

The influence of topical corticosteroid therapy upon polymorphonuclear leukocyte distribution, vascular integrity and ascorbate levels in endotoxin-induced inflammation of the rabbit eye.

An acute inflammatory response was initiated in the rabbit eye by an intravitreal injection of bacterial endotoxin. We examined the effect of topical corticosteroid therapy upon polymorphonuclear leukocyte (PMN) infiltration into the eye, protein leakage into aqueous humor and ascorbate level in aqueous humor. Corticosteroid therapy initiated prior to injection of endotoxin suppresses the clinical signs of inflammation, partially prevents the fall in aqueous-humor ascorbate level, has little effect upon protein leakage, but markedly reduces PMN infiltration. Corticosteroid therapy initiated after the injection of endotoxin also suppresses the clinical signs of inflammation, reduces the fall in ascorbate levels and does not influence protein leakage. However, in this case there is a marked persistence of PMN infiltration into ocular tissues. Thus the number of PMNs present in the ocular tissues is little different from that in non-steroid treated control eyes, although the clinical signs of inflammation are reduced. We suggest that in the clinical situation, the initial anti-inflammatory activity of the corticosteroids is related to an inhibitory effect upon the activity of PMNs already within the tissues, which then prevents the ensuing cascade of characteristic inflammatory events.

Administration, Topical↗