Superoxide Dismutase Restores Impaired Histamine‐Induced Increase in Venular Macromolecular Efflux During Diabetes Mellitus

Counter regulatory effects of PKCbetaII and PKCdelta on coronary endothelial permeability

OBJECTIVE

The aim of this study was to examine the endothelial distribution and activity of selected PKC isoforms in coronary vessels with respect to their functional impact on endothelial permeability under the experimental conditions relevant to diabetes.

METHODS AND RESULTS

En face immunohistochemistry demonstrated a significant increase of PKC(betaII) and decrease of PKCdelta expression in coronary arterial endothelium of Zucker diabetic rats. To test whether changes in PKC expression alter endothelial barrier properties, we measured the transcellular electric resistance in human coronary microvascular endothelial monolayers and found that either PKC(betaII) overexpression or PKCdelta inhibition disrupted the cell-cell adhesive barrier. Three-dimensional fluorescence microscopy revealed that hyperpermeability was caused by altered PKC activity in association with distinct translocation of PKC(betaII) to the cell-cell junction and PKCdelta localization to the cytosol. Further analyses in fractionated endothelial lysates confirmed the differential redistribution of these isozymes. Additionally, FRET analysis of PKC subcellular dynamics demonstrated a high PKC(betaII) activity at the cell surface and junction, whereas PKCdelta activity is concentrated in intracellular membrane organelles.

CONCLUSIONS

Taken together, these data suggest that PKC(betaII) and PKCdelta counter-regulate coronary endothelial barrier properties by targeting distinctive subcellular sites. Imbalanced PKC(betaII)/PKCdelta expression and activity may contribute to endothelial hyperpermeability and coronary dysfunction in diabetes.

Hog barn dust extract increases macromolecular efflux from the hamster cheek pouch

The purpose of this study was to determine whether short-term exposure to an aqueous extract of hog barn dust increases macromolecular efflux from the intact hamster cheek pouch and, if so, to begin to determine the mechanism(s) underlying this response. By using intravital microscopy, we found that suffusion of hog barn dust extract onto the intact hamster cheek pouch for 60 min elicited a significant, concentration-dependent leaky site formation and increase in clearance of FITC-labeled dextran (molecular mass, 70 kDa). This response was significantly attenuated by suffusion of catalase (60 U/ml), but not by heat-inactivated catalase, and by pretreatment with dexamethasone (10 mg/kg iv) (P < 0.05). Catalase had no significant effects on adenosine-induced increase in macromolecular efflux from the cheek pouch. Suffusion of hog barn dust extract had no significant effects on arteriolar diameter in the cheek pouch. Taken together, these data indicate that hog barn dust extract increases macromolecular efflux from the in situ hamster cheek pouch, in part, through local elaboration of reactive oxygen species that are inactivated by catalase. This response is specific and attenuated by corticosteroids. We suggest that plasma exudation plays an important role in the genesis of upper airway dysfunction evoked by short-term exposure to hog barn dust.

Generation of superoxide anion impairs histamine-induced increases in macromolecular efflux

The first goal of this study was to determine the effect of generation of superoxide anion using pyrogallol on histamine-induced increases in macromolecular efflux. We used intravital microscopy and fluorescein isothiocyanate-dextran (FITC-dextran; MW 70K) to examine macromolecular extravazation from postcapillary venules in the hamster cheek pouch in response to histamine before and following topical application of vehicle or pyrogallol. Extravazation of macromolecules was quantitated by counting venular leaky sites. Histamine elicited reproducible increases in venular leaky sites before and during infusion of vehicle. In contrast, topical application of pyrogallol (0.5 mM) abolished histamine-induced increases in formation of venular leaky sites. Our second goal was to examine whether pyrogallol-induced inhibition of venular leaky site formation could be reversed by superoxide dismutase. Application of superoxide dismutase (300 U/ml) to the cheek pouch in the presence of pyrogallol restored histamine-induced increases in venular leaky sites. Thus, the generation of superoxide anion alters histamine-induced increases in macromolecular efflux. These results support the concept that disease states that produce oxidative stress may impair agonist-induced increases in microvascular permeability via inactivation of nitric oxide.

Aminoguanidine suppresses basal macromolecular extravasation during diabetes mellitus

The goal of this study was to determine the effect of aminoguanidine on basal macromolecular efflux from the microcirculation of the hamster cheek pouch during diabetes mellitus. We used intravital fluorescent microscopy and fluorescein isothiocyanate dextrans (FITC-dextran; mw = 70 and 20K) to examine basal macromolecular extravasation in nondiabetic hamsters, nondiabetic hamsters treated with a topical application of aminoguanidine (0.5 mM), diabetic hamsters (6-10 weeks after injection of streptozotocin), and diabetic hamsters treated with a topical application of aminoguanidine (0.5 mM). Increases in macromolecular efflux were quantitated by calculating the clearance (ml/s x 10(-6)) of FITC-dextran-70K and -20K. In nondiabetic hamsters, the clearance of FITC-dextran-70K and -20K remained relatively constant during the experimental period, although the clearance of FITC-dextran-70K was less than that for FITC-dextran-20K. Topical application of aminoguanidine did not alter basal permeability characteristics in nondiabetic hamsters. In diabetic hamsters, clearance of FITC-dextran-70K and -20K also remained relatively constant during the experimental period. However, the magnitude of clearance of FITC-dextran-70K and and -20K was significantly greater in diabetic compared to nondiabetic hamsters (P < 0.05). Topical application of aminoguanidine restored basal permeability characteristics of diabetic hamsters to that observed in nondiabetic hamsters. These findings suggest that acute treatment of the microcirculation in vivo with aminoguanidine ameliorates basal increases in extravasation of macromolecules during diabetes mellitus. We suggest that aminoguanidine suppresses basal macromolecular efflux in diabetic hamsters via inhibition of nitric oxide synthase. Thus, it appears that the use of aminoguanidine may be an important therapeutic approach for the treatment of diabetes-related vascular dysfunction.