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Biomedical subjects

M W Dunn

Publications and source records attributed to M W Dunn.

At least 37 records · Page 2Linked to original sources
PubMed1990

Hormonal stimulation of 12(R)-HETE, a cytochrome P450 arachidonic acid metabolite in the rabbit cornea.

12(R)-HETE [12(R)-hydroxy-5, 8, 10, 14 eicosatetraenoic acid] is one of the major arachidonic acid metabolites produced by microsomal cytochrome P450 of the corneal epithelium. This metabolite is a potent inhibitor of Na(+)-K(+)-ATPase activity in several tissues. We investigated endogenous production of 12(R)-HETE in the rabbit corneal epithelium. Incubation of corneal epithelial sheets (prelabeled with 14C-arachidonic acid) with arginine vasopressin resulted in the production of radioactive 12(R)-HETE suggesting its formation from endogenously labeled-arachidonic acid. The maximal response was obtained with 1 microM arginine vasopressin and represents a 15-fold increase in 12(R)-HETE formation compared with that of control tissues. Stimulation of 14C-arachidonic acid release with a detergent, digitonin, also resulted in endogenous 12(R)-HETE formation. Analysis of the incubation media following digitonin treatment of prelabeled corneal epithelial sheets revealed that 12(R)-HETE production was maximal at 20 microM digitonin, a 17-fold increase over control values. This study is the first to describe hormonal and traumatic stimulation of 12(R)-HETE formation from endogenously labeled arachidonic acid in intact corneal tissues. This study demonstrates that the formation of this Na(+)-K(+)-ATPase inhibitor can be modulated by physiological and pathophysiological regulation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1989

Ocular effects of a novel cytochrome P-450-dependent arachidonic acid metabolite.

Compound D is a novel arachidonic acid metabolite formed by a cytochrome P-450-dependent mono-oxygenase in bovine corneal epithelium. The structure of compound D was recently identified as 12-hydroxy-5,8,14-eicosatrienoic acid. In the current study, we described the biological properties and the ocular effects of this compound. Compound D is a potent vasodilator, and caused a dose-dependent relaxation of the rat tail artery preconstricted with phenylephrine with an EC50 of 1.5 microM, 4-5-fold more potent than acetylcholine. Topical application of as little as 10 ng of compound D onto the rabbit cornea produced a vasodilation of the conjunctival blood vessels. Intracameral injection of compound D (1-10 ng) caused a dose-dependent increase of up to 30-fold of the aqueous humor protein, indicating a breakdown of the blood-aqueous barrier. Compound D was also found to be a potent angiogenic factor, ie, it induced the appearance of new vessels in the cornea. The effects of 12-(R)-hydroxyeicosatrienoic acid (compound D) on the rabbit eye mimics the response of the eye to an inflammatory stimulus. We hypothesize, therefore, that ocular inflammation that occurs following injury to the cornea is mediated, at least in part, by the production of compound D by the corneal epithelium.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1987

Cytochrome P450, drug metabolizing enzymes and arachidonic acid metabolism in bovine ocular tissues.

Little information is available on drug metabolizing enzymes in ocular tissues. We investigated the presence of various cytochrome P450 isozymes by measuring different drug metabolizing enzymes, i.e., aryl hydrocarbon hydroxylase, 7 ethoxycoumarin-o-deethylase and benzphetamine demethylase activities in ciliary body, corneal epithelium and endothelium, retina and retinal pigment epithelium. Our results demonstrate that the ciliary body and the retinal pigment epithelium possess the highest activities of cytochrome P450-dependent monooxygenases in the eye. The highest activity of drug metabolizing enzymes is accompanied by high activity of NADPH cytochrome P450 (C) reductase, an integral component of this enzyme system. Heme oxygenase, a key enzyme for the regulation of heme availability to hemoproteins such as cytochrome P450 also demonstrate high activity in these two ocular tissues. Although the corneal epithelium has a lower activity of drug metabolizing enzymes, it possesses the highest activity of cytochrome P450 species capable of metabolizing arachidonic acid to biologically active compounds, whereas the other ocular tissues possess cyclooxygenase as the main microsomal enzyme that metabolizes arachidonic acid. Whether the observed catalytic activities of drug metabolizing enzymes seen in ocular tissues are associated with major or minor forms of cytochrome P450 is not yet know. However, the specialized location of cytochrome P450 isozymes in ocular tissues suggests a physiological function related to activation of endogenous compounds such as arachidonic acid, in addition to detoxification of drugs.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1987

Presence of heme oxygenase and NADPH cytochrome P-450 (c) reductase in human corneal epithelium.

The presence of heme oxygenase and NADPH cytochrome P-450 (c) reductase, the latter an integral component of heme oxygenase and cytochrome P-450-dependent drug metabolizing enzymes, was demonstrated in human corneal epithelium. We reported for the first time that human corneal epithelium contains heme oxygenase activity as high as 20% of that reported for the human liver. Using immunological techniques, we demonstrated that heme oxygenase proteins from human cornea and liver are very similar; both have a molecular weight of 32,000 as demonstrated by Western blot analysis. We also studied the presence of NADPH cytochrome P-450 (c) reductase. The human corneal epithelium contains significant amount of NADPH cytochrome P-450 (c) reductase activity, and this corneal protein is similar to the known liver protein; both have a molecular weight of 71,000 and react with antibodies prepared against purified liver NADPH cytochrome P-450 (c) reductase. As the heme oxygenase system is the rate limiting step in heme degradation, this system plays a pivotal role in regulation of cellular heme in corneal epithelium, thus modulating the activity of hemoproteins such as catalase, tryptophan pyrrolase and thromboxane synthetase.

Animals↗
PubMed1986

Aniridia, congenital glaucoma, and hydrocephalus in a male infant with ring chromosome 6.

A premature infant with unilateral aniridia and congenital ectropion uveae, contralateral Rieger anomaly, bilateral congenital glaucoma, and hydrocephalus was found to have ring chromosome 6. The findings are consistent with multiple manifestations of a neural crest-derived maldevelopment of the anterior segment and central nervous system. Comparison with the 14 previously reported cases of ring chromosome 6 illustrates the phenotypic variability of this syndrome.

Abnormalities, Multiple↗
PubMed1986

Neodymium:YAG laser iridectomy and acute cataract formation in the rabbit.

The Q-switched Neodymium:YAG (Nd:YAG) laser in the single pulse mode was used to perform iridectomies in pigmented and albino rabbits. Seventy-one iridectomies were attempted. Seventy-six percent (54/71) of these were patent at the time of enucleation. Iridectomy closure was not noted during the 24-day study period. Lenticular damage was not detected in any case. Patency rates in pigmented (70%) and albino (78%) irides were similar. Energy levels of 6 mJ or greater resulted in a higher rate of patency. Settings below 6 mJ were associated with more significant bleeding and had a low rate of success. The histology of acute Q-switched Nd:YAG laser iridectomy is characterized by fragmentation of the stroma and wide dispersion of the pigment epithelium. Minimal healing occurs with retention of normal iris architecture without atrophy or fibrosis. Results indicate that this procedure can be performed with minimal operative complications and without a tendency for closure.

Animals↗
PubMed1985

Cytochrome P450 dependent metabolism of arachidonic acid in bovine corneal epithelium.

Microsomes prepared from bovine corneal epithelium metabolized 14C-arachidonic acid into two unidentified products, separated by thin-layer chromatography and called Peaks I and II. Each peak was further separated by high performance liquid chromatography into two metabolites. The formation of these metabolites was dependent on the addition of NADPH and inhibited by carbon monoxide and SKF-525A, suggesting a cytochrome P450-dependent mechanism. The presence of cytochrome P450 in the corneal epithelium was assessed directly by measurement of the carbon monoxide reduced spectrum and indirectly by measuring aryl hydrocarbon hydroxylase activity. The activity of aryl hydrocarbon hydroxylase was protein- and NADPH-dependent and was inhibited by SKF-525A.

Animals↗
PubMed1985

5 beta-Dihydrocortisol: possible mediator of the ocular hypertension in glaucoma.

5 beta-dihydrocortisol potentiates the action of topically applied dexamethasone in raising the intraocular pressure (IOP) in young rabbits. Dexamethasone (0.06%) plus 5 beta-dihydrocortisol (0.1 and 1.0%) elevated the IOP 7-10 mmHg within 18 days of treatment. By contrast, 0.06% dexamethasone alone raised the IOP 3 to 4 mmHg in a similar period of time. Since 5 beta-dihydrocortisol accumulates abnormally in cultured cells derived from the outflow region of the eye from patients with primary open angle glaucoma (POAG), a similar potentiation in man may account for the sensitivity of these patients to the IOP raising effect of glucocorticoids. Further, this metabolite may potentiate endogenous glucocorticoids resulting in the ocular hypertension characteristic of POAG.

Animals↗
PubMed1985

The effect of dexamethasone on the synthesis of collagen in normal human trabecular meshwork explants.

This study demonstrates that the trabecular meshwork cells of the human eye incorporate 3H-Proline into collagen during in vitro incubation. Addition of dexamethasone to the incubation mixture produced a marked decrease in this incorporation. Dexamethasone was active at 10(-8) M and higher concentrations. The specificity of the hormone effect was demonstrated by its inability to alter 3H-leucine incorporation in these cells. These results indicate that dexamethasone decreases the synthesis of collagen, a major component of the extracellular matrix, in the trabecular meshwork.

Collagen↗
PubMed1983

Altered cortisol metabolism in cells cultured from trabecular meshwork specimens obtained from patients with primary open-angle glaucoma.

Cells cultured from trabecular meshwork specimens obtained from patients with primary open angle glaucoma (TMPOAG cells) exhibited two major differences in cortisol-metabolizing enzymes when compared with similar cells from nonglaucomatous patients. One is a marked increase (greater than 100-fold) in delta 4-reductase activity and the other is a decrease (4-fold) in 3-oxidoreductase activity. Peripheral lymphocytes from one of these patients as well as from five additional patients with POAG, did not show these abnormalities, indicating that the defects are not found in all cortisol-metabolizing cells. The abnormal metabolism of cortisol by TMPOAG cells may be of significance in the pathogenesis of POAG.

Adult↗
PubMed1983

Glucocorticoid target cells in human outflow pathway: autopsy and surgical specimens.

Target cells for glucocorticoids were found in trabeculectomy specimens obtained surgically from humans with glaucoma (primary and secondary) and from nonglaucomatous autopsy eyes using an autoradiographic technique. Specific nuclear localization of 3H-dexamethasone was found in cells of the trabecular meshwork, scleral fibroblasts, and in the endothelial lining of both Schlemm's canal and the outflow vessels. Glucocorticoids may alter the outflow facility by a direct effect on the metabolism of these cells. The autoradiographic method is suitable for studying competitors of glucocorticoid binding in small surgical specimens of human tissue involved in the outflow of aqueous humor.

Aqueous Humor↗
PubMed1983

The effect of dexamethasone on the in vitro incorporation of precursors of extracellular matrix components in the outflow pathway region of the rabbit eye.

The present study demonstrates that the cells of the outflow pathway region incorporate precursors of the extracellular matrix components during in vitro incubation. Addition of dexamethasone (10(-7) M) to the incubation mixture led to changes in precursor incorporation that were precursor and cell specific. The steroid significantly decreased the incorporation of 3H-glucosamine and increased the incorporation of 3H-proline in the outflow pathway cells and in the fibroblasts of the adjacent sclera. The specificity of the hormone effect was demonstrated by its inability to alter 3H-leucine incorporation. By contrast, in iridial fibroblasts dexamethasone caused a decreased incorporation of 3H-glucosamine while not affecting the incorporation of 3H-proline. Our results suggest that dexamethasone causes an increase in collagen synthesis in the target cells most closely related to the outflow pathway. Further, the decreased incorporation of 3H-glucosamine with dexamethasone suggests decreased synthesis of glycosaminoglycans, glycoproteins or possibly glycolipids in these same cells.

Animals↗
PubMed1982

Estrogens induce lipoxygenase derivative formation in rabbit lens.

The effect of estrogens on arachidonic acid metabolism was studied in lenses from normal and sex hormone-treated female rabbits. Analysis of the metabolites derived from incubation of these lenses with (1-14C) arachidonic acid provides the first evidence that estradiol activates the lipoxygenase pathway, as indicated by 5-S-hydroxy-6,8,11,14-eicosatetraenoic acid--like product formation, an effect that can be prevented by progestin treatment. Prostaglandin synthesis was not demonstrated by the control or estrogen-treated rabbit lenses, suggesting that lipoxygenase is the major arachidonic acid pathway in the lens.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1982

Glucocorticoid receptor binding in bovine lens.

The present study demonstrates glucocorticoid receptor localization in the nuclei of cells of the anterior epithelium and bow region and its absence in all other regions of the lens. Both autoradiographic and biochemical studies show that triamcinolone acetonide is inactive whereas tetrahydrocortisol (previously considered to be an inactive metabolite of cortisol) is an active competitor of dexamethasone binding to the glucocorticoid receptor in the bovine lens. The consistency of these findings by both techniques supports the validity of this observation. In addition, it indicates that autoradiography can be used for studying glucocorticoid agonist/antagonist relationships in the human lens, where only small amounts of tissue are available.

Animals↗