The Effects of Heparin Administration in an Animal Model of Chronic Peritoneal Dialysate Exposure

Diverse modes of heparin administration have been used in animal models of chronic peritoneal dialysate exposure to maintain catheter patency and prevent fibrinous adhesions. Heparin has biological actions independent of its well-known anticoagulant activity, including the ability to modulate extracellular matrix synthesis, cellular proliferation, angiogenesis, and inflammation. These actions may interfere with peritoneal membrane homeostasis. The present study evaluated the influence of the mode of heparin administration on technique survival and infection rate in a rat model of chronic dialysate exposure. Further, the incorporation of heparin in the peritoneal membrane was examined.

A 3.86% glucose dialysate was injected twice daily into Wistar rats with a heparin-coated catheter (group A1), or with a standard catheter with heparin injections during the entire exposure time (group A2) or only during 1 week (group A3). Sham manipulations were performed in a fourth group and a fifth group was left untreated. Technique survival was 80% in group A1, 60% in group A2, and 40% in group A3. The rate of infection was highest in group A1 and lowest in group A2. Intraperitoneally administered heparin accumulated in the peritoneal membrane, whereas dextran, with a molecular weight similar to that of heparin, was not incorporated in the peritoneum.

In conclusion, intraperitoneal heparin reduced the incidence of infection in an animal model of chronic dialysate exposure. The best technique survival was, however, obtained using a heparin-coated catheter. Heparin is incorporated in the peritoneal membrane, where it may exert diverse biological actions and thus bias study results. The use of a heparin-coated catheter in combination with antibiotics may be the optimal approach to obtaining peritoneal access in animal models of chronic dialysate exposure.

Comparison of acute inflammatory and chronic structural asthma-like responses between C57BL/6 and BALB/c mice

BACKGROUND

The interactions between airway responsiveness, structural remodelling and inflammation in allergic asthma remain poorly understood. Prolonged challenge with inhaled allergen is necessary to replicate many of the features of airway wall remodelling in mice. In both mice and humans, genetic differences can have a profound influence on allergy, inflammation, airway responsiveness and structural changes.

METHODS

The aim of this study was to provide a comparative analysis of allergen-induced airway changes in sensitized BALB/c and C57BL/6 mice that were exposed to inhaled allergen for 2 ('acute'), 6 or 9 weeks ('chronic'). Inflammation, remodelling and responsiveness were analyzed.

RESULTS

Both strains developed a Th-2-driven airway inflammation with allergen-specific IgE, airway eosinophilia and goblet cell hyperplasia upon 2 weeks of allergen inhalation. This was accompanied by a significant increase in airway smooth muscle mass and hyperresponsiveness in BALB/c but not in C57BL/6 mice. However, airway eosinophilia was more pronounced in the C57BL/6 strain. Chronic allergen exposure (6 or 9 weeks) resulted in an increase in airway smooth muscle mass as well as subepithelial collagen and fibronectin deposition in both strains. The emergence of these structural changes paralleled the disappearance of inflammation in both C57BL/6 and BALB/c mice and loss of hyperresponsiveness in the BALB/c strain. TGF-beta(1 )was accordingly elevated in both strains.

CONCLUSION

Airway inflammation, remodelling and hyperresponsiveness are closely intertwined processes. Genetic background influences several aspects of the acute allergic phenotype. Chronic allergen exposure induces a marked airway remodelling that parallels a decreased inflammation, which was largely comparable between the two strains.

Effect of combining salmeterol and fluticasone on the progression of airway remodeling

In subjects insufficiently controlled with low to moderate doses of inhaled corticosteroids, adding beta-agonists is clinically more beneficial than increasing the dose of inhaled corticosteroids. In the present study, we investigated the effect of adding salmeterol to fluticasone on allergen-induced airway inflammation and remodeling. Sensitized rats, in which characteristics of remodeling had been induced by ovalbumin exposure every 2 days from Days 14 to 28, were further exposed to ovalbumin or PBS from Days 29 to 42. During the last 2 weeks, before allergen exposure, rats were treated with aerosolized fluticasone propionate (10 mg), salmeterol (1 mg), salmeterol (1 mg) plus fluticasone propionate (10 mg), or placebo. After 4 weeks of ovalbumin exposure, the airways showed inflammatory changes, goblet cell hyperplasia, and enhanced fibronectin and collagen deposition. Salmeterol in monotherapy decreased bronchoalveolar lavage fluid eosinophil number but had no influence on structural changes. Combining salmeterol with fluticasone propionate counteracted goblet cell hyperplasia, but increased the amount of fibronectin and collagen in the airway wall. These effects of salmeterol did not influence airway responsiveness. We conclude that the combination of salmeterol and fluticasone propionate enhances aspects of allergen-induced airway remodeling. This is not accompanied by changes in airway responsiveness.

Dose-related effect of inhaled fluticasone on allergen-induced airway changes in rats

To examine whether fluticasone propionate (FP) dose-dependently inhibits inflammatory as well as structural changes, Brown Norway rats were sensitised to ovalbumin (OA) on day 0 and 7. From day 14-28, rats were exposed to aerosolised OA (1%) or phosphate buffered saline every 2 days. Thirty minutes before each allergen exposure, animals were pre-treated with aerosolised placebo or FP (0.1, 1 or 10 mg) or prednisolone 3 mg x kg(-1) i.p. At day 29, 0.1 mg FP had no measurable effect, either on inflammatory or structural changes, such as goblet cell hyperplasia and airway wall thickening. The allergen-induced increase in eosinophilic inflammation in bronchoalveolar lavage fluid and in the airway mucosa, as well as increased fibronectin deposition, were inhibited by treatment with FP from a dose of 1 mg onwards. Inhibition of goblet cell hyperplasia and thickening of the airway wall required 10 mg inhaled FP. At this dose, systemic effects were observed. However, for a comparable degree of systemic activity, prednisolone was far less effective at preventing airway changes. The dose of inhaled fluticasone propionate required to inhibit allergen-induced structural alterations was higher than to prevent eosinophil influx, and caused systemic side-effects. However, for a similar systemic activity, prednisolone was ineffective in preventing airway remodelling.

The effects of heparin administration in an animal model of chronic peritoneal dialysate exposure

Diverse modes of heparin administration have been used in animal models of chronic peritoneal dialysate exposure to maintain catheter patency and prevent fibrinous adhesions. Heparin has biological actions independent of its well-known anticoagulant activity, including the ability to modulate extracellular matrix synthesis, cellular proliferation, angiogenesis, and inflammation. These actions may interfere with peritoneal membrane homeostasis. The present study evaluated the influence of the mode of heparin administration on technique survival and infection rate in a rat model of chronic dialysate exposure. Further, the incorporation of heparin in the peritoneal membrane was examined. A 3.86% glucose dialysate was injected twice daily into Wistar rats with a heparin-coated catheter (group A1), or with a standard catheter with heparin injections during the entire exposure time (group A2) or only during 1 week (group A3). Sham manipulations were performed in a fourth group and a fifth group was left untreated. Technique survival was 80% in group A1, 60% in group A2, and 40% in group A3. The rate of infection was highest in group A1 and lowest in group A2. Intraperitoneally administered heparin accumulated in the peritoneal membrane, whereas dextran, with a molecular weight similar to that of heparin, was not incorporated in the peritoneum. In conclusion, intraperitoneal heparin reduced the incidence of infection in an animal model of chronic dialysate exposure. The best technique survival was, however, obtained using a heparin-coated catheter. Heparin is incorporated in the peritoneal membrane, where it may exert diverse biological actions and thus bias study results. The use of a heparin-coated catheter in combination with antibiotics may be the optimal approach to obtaining peritoneal access in animal models of chronic dialysate exposure.

Repeated allergen exposure changes collagen composition in airways of sensitised Brown Norway rats

Increased or altered collagen deposition in the airway wall is one of the characteristics of airway remodelling in asthma. The mechanisms underlying this increase, and its functional consequences remain to be established further. Representative in vivo animal models might be useful in this respect. In the present study, collagen deposition after prolonged allergen exposure was characterised in the airway wall of Brown Norway rats. Sensitised rats were repeatedly exposed to ovalbumin (OA) or phosphate-buffered saline during 2 and 12 weeks. The deposition of collagen type I, III, IV, V and VI was not altered in animals exposed to OA for 2 weeks. After 12 weeks of OA exposure, more collagen type I was deposited in the inner and outer airway wall and more type V and VI collagen was observed in the outer airway wall. At 12 weeks the number of vessels, identified via type IV collagen staining was not increased, but the total vessel area was. In conclusion, prolonged allergen exposure in sensitised rats is associated with enhanced deposition of type I, V and VI collagens and increased vascularity. This suggests that some aspects of airway remodelling in asthma could be driven by long-term allergen exposure.

Fluticasone inhibits the progression of allergen-induced structural airway changes

BACKGROUND

Inhaled corticosteroids are widely used as first-line therapy in patients with asthma. The concept of early introduction is more and more accepted.

OBJECTIVE

In our rat model of airway remodelling, we investigated whether treatment with inhaled fluticasone propionate can inhibit further progression of established structural airway changes.

METHODS

Sensitized Brown Norway rats were exposed to aerosolized ovalbumin (1%) from day 14 to 42. From day 28 to 42, animals were treated with inhaled fluticasone or placebo 30 min before each allergen challenge. One control group was exposed to PBS from day 28 to 42, a second control group throughout the whole experiment.

RESULTS

Exposure to ovalbumin during 2 weeks induced structural airway changes, including epithelial cell proliferation, increase in airway wall area and fibronectin deposition. Goblet cell number was increased, although not significantly compared with PBS. Continuing allergen exposure for 2 weeks further enhanced each of these features. In addition, the amount of collagen in the airway wall was enhanced by 4 weeks allergen exposure compared with PBS-exposed animals. These additional increases were inhibited by treatment with fluticasone during the last 2 weeks.

CONCLUSION

The progression of established allergen-induced structural airway changes in sensitized rats can be inhibited by treatment with fluticasone.

Effect of age on allergen-induced structural airway changes in brown Norway rats

It remains to be fully established whether allergen-induced airway inflammation and remodeling are influenced by age. The aim of the present study was to compare allergen-induced airway changes in young and adult rats. Brown Norway rats were sensitized at 4 weeks of age (young) or 13 weeks of age (adult) and exposed to aerosolized ovalbumin (OA) or phosphate-buffered saline for 2 weeks. In both age groups OA exposure induced an increase in OA-specific Immunoglobulin E and in the number of peribronchial eosinophils. OA-challenged animals also developed an increase in total airway wall area, enhanced fibronectin deposition, and goblet cell hyperplasia. Both inflammatory and structural alterations were more pronounced in the airways of young compared with adult OA-exposed rats. The number of peribronchial eosinophils was increased in young animals (685.4 +/- 75.0 versus 389.9 +/- 37.8/mm2 in adult rats; p < 0.001). A higher degree of goblet cell hyperplasia was observed in young rats (65.37 +/- 4.68 versus 34.74 +/- 3.68/mm basement membrane in adult rats; p < 0.001) and area of fibronectin deposition in the airway wall was higher in young compared with adult animals (5.08 +/- 0.46 versus 3.62 +/- 0.29 microm2/microm basement membrane; p < 0.005). In conclusion, in young rats airways are more susceptible to allergen-induced inflammatory and structural airway changes.

Fluticasone inhibits but does not reverse allergen-induced structural airway changes

Ethical and technical reasons limit the possibility of evaluating the effects of inhaled corticosteroids on structural changes in airways of humans with asthma. We therefore evaluated whether fluticasone propionate (FP) modifies airway remodeling, induced by repeated allergen exposure in rats. Sensitized BN rats were exposed to aerosolized ovalbumin (OA) for 2 wk. To assess the effect of FP on the development of or on established airway remodeling, animals were treated with aerosolized FP or placebo during allergen exposure or for 2 wk afterward. Compared with animals exposed to phosphate-buffered saline (PBS), OA-challenged animals developed an increase in total airway wall area, enhanced fibronectin deposition, epithelial cell proliferation, goblet cell hyperplasia, and airway hyperresponsiveness. Concomitant treatment with FP decreased all allergen-induced structural changes without being able to reverse them to normal. Initiating FP treatment after the allergen exposure had no effect on any of the OA-induced structural airway changes. The increase in total airway wall area, enhanced fibronectin deposition, and epithelial cell proliferation persisted. The goblet cell hyperplasia disappeared spontaneously. In conclusion, concomitant treatment with FP partly inhibits structural airway changes as well as hyperresponsiveness induced by OA exposure. Post hoc treatment fails to reverse established airway remodeling.

Prolonged allergen exposure induces structural airway changes in sensitized rats

The pathogenesis and functional consequences of airway remodeling in asthma remain to be fully established. In the present study we evaluated the effect of prolonged allergen exposure on airway function and structure in rats. Sensitized Brown Norway rats were repeatedly exposed for periods of 2, 4, or 12 wk to aerosolized ovalbumin (OA) or phosphate-buffered saline (PBS). OA exposure induced a persistent increase in OA-specific serum IgE and in the number of peribronchial eosinophils. After 2 wk of OA exposure, airway histology revealed goblet-cell hyperplasia, an increase in bromodeoxyuridine-positive cells in airway epithelium, increased fibronectin deposition, and a thickening of the airway inner wall area. This coincided with airway hyperresponsiveness (AHR) to aerosolized carbachol. After OA exposure for 12 wk, increased fibronectin (p < 0.05 versus PBS) and collagen deposition (p < 0.05 versus PBS) were observed in the submucosa. After 12 wk of exposure, neither total nor inner wall area or airway responsiveness to carbachol were any longer significantly different from those of PBS-exposed animals. In conclusion, prolonged OA exposure in rats induces structural airway changes that bear similarities to airway remodeling in asthma. The study data further indicate that depending on the extent and distribution of remodeling, changes in the extracellular matrix can enhance or protect against AHR.