Darryl W. O'Brien

A mechanism of airway injury in an epithelial model of mucociliary clearance

We studied the action of sodium metabisulphite on mucociliary transport in a frog palate epithelial injury model, hypothesizing that it may be useful for the study of mechanisms of airway injury. Sodium metabisulphite (MB) releases SO2 on contact with water. SO2 is a pollutant in automobile fumes and may play a role in the exacerbation of airway disease symptoms. We first investigated its effect on mucociliary clearance. MB 10-1 M, increased mucociliary clearance time (MCT) by 254.5 ± 57.3% of control values, (p < 0.001, n = 7). MB 10-4 and 10-2 M did not interfere with mucus clearance time compared to control values. In MB-treated frog palates, MCT did not return to control values after one hour (control, 97.3 ± 6.3% vs. MB, 140.9 ± 46.3%, p < 0.001, n = 7). Scanning EM images of epithelial tissue were morphometrically analyzed and showed a 25 ± 12% loss of ciliated cells in MB palates compared to controls with an intact ciliary blanket. Intact cells or groups of ciliated cells were found in scanning EM micrographs of mucus from MB-treated palates. This was associated with increased matrix metalloproteinase (MMP-9) activity in epithelial tissue and mucus. We suggest that the loss of ciliated cells as a result of MMP-9 activation prevented full recovery of MCT after MB 10-1 M. The mechanism of action may be on epithelial cell-cell or cell-matrix attachments leading to cell loss and a disruption of MCT. Further studies are warranted to determine whether this is an inflammatory mediated response or the result of a direct action on epithelial cells and what role this mechanism may play in the progression to chronic airway diseases with impaired mucociliary clearance.

Adaptation of an amphibian mucociliary clearance model to evaluate early effects of tobacco smoke exposure.

RationaleInhaled side-stream tobacco smoke brings in all of its harmful components impairing mechanisms that protect the airways and lungs. Chronic respiratory health consequences are a complex multi-step silent process. By the time clinical manifestations require medical attention, several structural and functional changes have already occurred. The respiratory system has to undergo an iterative process of injury, healing and remodeling with every exposure.MethodsTo have a better understanding of the initial changes that take place when first exposed to environmental tobacco smoke, we have developed an exposure model, using the frog palate that closely represents the features of obstructive airways where ciliary dysfunction and mucus hypersecretion occur.ResultsMucus transport was significantly reduced, even after exposure to the smoke of one cigarette (p < 0.05) and even further with 4-cigarettes exposure (p < 0.001). Morphometric and ultrastructural studies by SEM show extensive areas of tissue disruption. Gelatinase zymography shows activation of MMP9 in mucus from palates exposed to tobacco smoke.ConclusionsThe clearance of mucus on the frog palate is significantly reduced after exposure to environmental tobacco smoke. Cilia and the extracellular matrix are anatomically disrupted. Tobacco smoke triggers an increased activity of matrix metalloproteinases associated with a substantial defoliation of ciliated epithelium. These studies enhance the knowledge of the changes in the mucociliary apparatus that occur initially after exposure to environmental tobacco smoke, with the goal of understanding how these changes relate to the genesis of chronic airway pathologies in humans.

Evaluation of a Mucoactive Herbal Drug, Radix Ophiopogonis, in a Pathogenic Quail Model

We investigated the effect of Radix Ophiopogonis on airway mucociliary clearance and mucus secretion in anesthetized quails. The oral administration of 10 g/kg of Radix Ophiopogonis significantly increased tracheal mucociliary transport velocity (MTV). Moreover, either 10 g/kg or 3 g/kg of Radix Ophiopogonis markedly attenuated the human neutrophil elastase (HNE)-induced decrease in MTV. Furthermore, we found that 10 g/kg of Radix Ophiopogonis significantly abolished the HNE-induced increases in fucose and protein contents of tracheal lavage, whereas Radix Ophiopogonis at the same dose only significantly decreased the protein content in the control group. These results suggest that Radix Ophiopogonis improves airway mucociliary clearance and that the improvement may, at least in part, be ascribed to the amelioration of airway mucus secretion.

Does a hypertonic saline load predict fluid retention in pacing induced heart failure

OBJECTIVE We examined the response to hypertonic saline challenge (SC) as a potential predictor of fluid retention during heart failure induced by rapid ventricular pacing. METHODS Twelve dogs (22 +/- 4 kg) were given an intra-arterial bolus of 30 ml of 20% saline after establishing baseline fluid intake and urine output (24 h). Dogs were classified according to whether they drank more (Group A) or less (Group B) than the amount required to dilute the s.c. to isotonicity. Fluid retention was then assessed during heart failure after rapid ventricular pacing according to a graded ordinal scale and correlated with the responses to s.c.. RESULTS No difference was noted in baseline fluid intake (1112 +/- 236 ml in Group A vs. 809 +/- 129 ml in Group B). Five hours after s.c. cumulative water intake was significantly greater in Group A than in Group B (1018 +/- 136 vs. 591 +/- 17 ml) (P < 0.01). Urine sodium concentration was 113 +/- 11 and 124 +/- 28 mmol/l at baseline in Group A and B, respectively; increased to 190 +/- 21 and 295 +/- 59 mmol/l at 5 h and remained elevated 24 h after s.c., 177 +/- 60 and 274 +/- 55 mmol/l (both P < 0.01 for within-group comparisons vs. baseline). Urine sodium concentration was less in Group A than in Group B at 5 and 24 h (P < 0.05). The fluid retention score was greater in Group A (3.6 +/- 0.5) than in Group B (0.8 +/- 0.4) (P < 0.01). Fluid retention in heart failure correlated with water intake after the pre-pacing s.c. (r = 0.68, P < 0.025) and inversely with urine concentrating ability (r = -0.58, P < 0.05). Furthermore, water intake and urine concentrating ability following the s.c. were inversely related (r = -0.67, P < 0.02). CONCLUSIONS We conclude that normal dogs may be classified according to their fluid intake after s.c.. Those dogs that drank excessively and produced a dilute urine were more likely to retain fluid during pacing-induced heart failure. Hence, fluid intake and the ability to excrete a concentrated urine after a saline challenge may be useful variables to predict fluid retention in pacing-induced heart failure.

Efficacy of Pretreatment With the Angiotensin II Type 1 Receptor Blocker UP269-6 and Losartan in the Dog: Effect on Hemodynamics and Ischemia-Reperfusion

Background: Whether pretreatment with the novel oral angiotensin II (AngII) type 1 receptor (AT,R) antagonist UP269-6 (UP) can produce more effective AT,R blockade than losartan (LN) for cardioprotection during ischemia-reperfusion (IR) in the dog has not been deter mined. Methods and Materials: We compared the effect of UP (n = 5) and LN (n = 5) on serial in vivo hemodynamics, AngII pressor responses, and left ventricular (LV) volumes and function (echocardiograms) during escalation to optimal oral dosage over 7 days (day 0 to day 6), and acute IR (15 minutes ischemia, 30 minutes reperfusion) and ex vivo AT,R protein (Western immunoblots) with additional sham (n = 5) and IR (n = 5) controls on day 6. Compared with LN, UP produced greater vasodepression and decrease in diastolic volume during dose escalation and greater inhibition of the AngII pressor response over the range of escalating concentrations (0.05, 0.10, 0.25, and 0.50 μg/kg) on day 6. Acute IR after UP pretreatment resulted in less increase in LV filling pressure and LV diastolic and systolic volumes and greater ejection fraction, although UP and LN had similar effects on AT,R protein. Conclusion: Pretreatment with UP269-6 over 7 days produces more effective pharmacologi cal AT,R blockade and cardioprotection after acute IR than LN in the dog.

Novel methodology for echocardiographic quantification of cardiac shape

BACKGROUND Left ventricular (LV) shape is a major determinant of cardiac physiology with important prognostic implications. Current techniques are limited in their ability to characterize shape. Regional curvature analysis is a recently developed method that is free of idealized shape assumptions and is applicable globally or regionally. OBJECTIVE To measure the change in regional curvature from diastole to systole to determine whether modifications of this methodology can be applied to study LV shape noninvasively, and to compare this method with other shape analysis methods. ANIMALS Seventeen normal dogs underwent transthoracic echocardiography. LV dimensions were measured at end-diastole and end-systole. LV endocardial outlines were traced from apical four-chamber views. LV short to long axis (D/L) ratios and eccentricity index (E) were calculated. Regional curvatures were determined using customized software. Reproducibility of regional curvature was also determined. MAIN RESULTS LV regional curvature values were consistent among animals at diastole and systole in all areas. Regional curvature showed divergence in different areas. D/L ratios showed a 7% decrease from diastole to systole, whereas E demonstrated a 10% increase. However, regional curvature exhibited a 39% change, suggesting that this methodology is more sensitive. Duplicate curvature values from same or different cardiac cycles were highly reproducible. CONCLUSIONS Quantitative regional curvature analysis can be applied with echocardiography to study LV shape. This methodology is more sensitive than current methods, is reproducible and may be applicable to the noninvasive study of shape changes in cardiac disease.