Time course of hemosiderin production by alveolar macrophages in a murine model

STUDY OBJECTIVES

The diagnosis of alveolar hemorrhage is assisted by the presence of hemosiderin-laden macrophages (HLMs) in the BAL fluid or lung tissue. Despite the importance of this diagnostic method in clinical settings, limited information is available on the formation and clearance of HLMs as a function of time. The objectives of this study are to determine the time course of HLMs within the BAL and lung tissue, and to evaluate the effect of a single blood aspiration on the recruitment of inflammatory cells within the BAL.

DESIGN

Under light anesthesia, Balb/c mice received a single intranasal instillation of species-specific blood (50 microL). Control animals received heparinized sterile saline solution in a similar manner. At several time points after blood aspiration, BAL was recovered for cell differentials and determination of HLMs. The time course for HLMs was also established in the lung tissue.

RESULTS

Hemosiderin staining within alveolar macrophages was first detected in the BAL and lung tissue at day 3, peaked at day 7, and persisted through 2 months. The analysis of the BAL revealed an increased number of total cells, with an acute inflammatory reaction that resolved within 2 weeks.

CONCLUSIONS

Our findings demonstrate the validity of this model for the study of HLM production after blood aspiration. Additional work using animal models of lung hemorrhage is needed to further characterize the cellular events leading to clearance of erythrocytes within the lung.

Mechanisms of cholinergic dysfunction in rabbits following recurrent aspiration of cow's milk

Recurrent aspiration of cow's milk has been shown to alter neural control of airways in young rabbits (Gelfand et al., 1997). The purpose of this study was to define the mechanisms responsible for in vitro cholinergic hyperresponsiveness in this model. Beginning at 1 week of age, rabbits received either 0.5 mL/kg whole cow's milk or sterile saline intranasally while under light anesthesia. This was repeated each weekday for 2 weeks. At 8 weeks of age, rabbits were sacrificed. Portions of lungs underwent lavage with sterile saline. Tracheal smooth muscle (TSM) segments were also removed. Segments were assessed for acetylcholine (ACh) release by high-performance liquid chromatography ( HPLC) with electrochemical detection or acetylcholinesterase (AChE) kinetic activity by spectrophotometry. Substance P (SP), a neuropeptide that can increase ACh release from nerves, was also assessed using an enzyme immunoassay to define the content in lavage and TSM segments. Immunohistochemistry for SP within airways was also assessed. We found that recurrent aspiration of milk led to statistically significant alterations in many parameters. Acetylcholine release was significantly greater in segments of airways from rabbits that had aspirated cow's milk (27.5 +/- 1.7 vs. 20.1 +/- 1.6 pmol/min/g tissue) than saline. At the same time, AChE activity was less in the group that aspirated milk (8.7 +/- 0.4 vs. 10.2 +/- 0.5 nmol/min/mg protein) compared to saline. The amount of SP within both lavage as well as tissue homogenates was greater in the group that had aspirated the foreign protein (159.1 +/- 28.9 vs. 41.9 +/- 5.2 pmol/mg protein in lavage; 158.7 +/- 31.9 vs. 80.5 +/- 7.8 pmol/mg protein in tissues) than saline controls. While total cholinergic nerve density as assessed by choline acetyltransferase was not significantly different between groups, SP-positive immunoreactive nerves were easily identified in the group that aspirated cow's milk. This study suggests that cholinergic hyperresponsiveness caused by repeated aspiration of milk is due to several abnormalities, including prejunctional (increase in ACh release) as well as junctional (decrease in AChE) mechanisms within the airways. In addition, an upregulation of SP within airways is part of this process.

Adenosine-dependent airway inflammation and hyperresponsiveness in partially adenosine deaminase-deficient mice

Adenosine is a signaling nucleoside that is elevated in the lungs of asthmatics. We have engineered a mouse model that has elevated levels of adenosine as a result of the partial expression of the enzyme that metabolizes adenosine, adenosine deaminase (ADA). Mice with lowered levels of ADA enzymatic activity were generated by the ectopic expression of an ADA minigene in the gastrointestinal tract of otherwise ADA-deficient mice. These mice developed progressive lung inflammation and damage and died at 4-5 mo of age from respiratory distress. Associated with this phenotype was a progressive increase in lung adenosine levels. Examination of airway physiology at 6 wk of age revealed alterations in airway hyperresponsiveness. This was reversed following the lowering of adenosine levels using ADA enzyme therapy and also through the use of the adenosine receptor antagonist theophylline, implicating both the nucleoside and its receptors in airway physiological alterations. All four adenosine receptors were expressed in the lungs of both control and partially ADA-deficient mice. However, transcript levels for the A(1), A(2B), and A(3) adenosine receptors were significantly elevated in partially ADA-deficient lungs. There was a significant increase in alveolar macrophages, and monocyte chemoattractant protein-3 was found to be elevated in the bronchial epithelium of these mice, which may have important implications in the regulation of pulmonary inflammation and airway hyperresponsiveness. Collectively, these findings suggest that elevations in adenosine can directly impact lung inflammation and physiology.

Induction and regulation of nitric oxide synthase in airway epithelial cells by respiratory syncytial virus

In this study, we evaluated the effects of respiratory syncytial virus (RSV) infection on nitric oxide (NO) production in human airway epithelial cells. In addition, we evaluated whether T-helper type 1 (Th1)- and Th2-type cytokines modulate the release of NO in response to RSV infection. To do this, we infected monolayers of A549 cells with RSV and determined nitrite levels in the supernatant fluids. We also measured nitrite levels in human small-airway epithelial cells (SAEC) in primary culture and in the bronchoalveolar lavage fluid (BALF) obtained from Balb/c mice after RSV infection. To further support our observations in these analyses, we performed immunocytochemistry and Western blot analysis for inducible nitric oxide synthase (iNOS) in A549 cells. To evaluate the regulation of NO production in response to RSV, we performed experiments in the absence and presence of the Th1 and Th2 type cytokines: interferon (IFN)-gamma, interleukin (IL)-4, and IL-13. In addition, we assessed the inhibitory effect of dexamethasone on iNOS in RSV infected A549 cells. Results were expressed in terms of nmol/mg protein and shown as percents of control values (mean +/- SE). RSV increased the release of nitrites in A549 cells, SAEC, and BALF. The increase in nitrite levels was supported by immunocytochemistry and Western blot analysis for iNOS protein in A549 cells, indicating activation of iNOS in response to RSV infection. IFN-gamma and IL-13 did not affect the RSV-induced increase in NO production. By contrast, IL-4 and dexamethasone suppressed the release of NO in response to RSV infection. These observations show that RSV infection leads to activation of iNOS within the airway epithelium and that IL-4 and dexamethasone inhibit the production of NO in response to RSV infection.

Recurrent milk aspiration produces changes in airway mechanics, lung eosinophilia, and goblet cell hyperplasia in a murine model

Recurrent aspiration of milk into the respiratory tract has been implicated in the pathogenesis of a variety of inflammatory lung disorders including asthma. However, the lack of animal models of aspiration-induced lung injury has limited our knowledge of the pathophysiological characteristics of this disorder. This study was designed to evaluate the effects of recurrent milk aspiration on airway mechanics and lung cells in a murine model. Under light anesthesia, BALB/c mice received daily intranasal instillations of whole cow's milk (n = 7) or sterile physiologic saline (n = 9) for 10 d. Respiratory system resistance (Rrs) and dynamic elastance (Edyn,rs) were measured in anesthetized, tracheotomized, paralyzed and mechanically ventilated mice 24 h after the last aspiration of milk. Rrs and Edyn,rs were derived from transrespiratory and plethysmographic pressure signals. In addition, airway responses to increasing concentrations of i.v. methacholine (Mch) were determined. Airway responses were measured in terms of PD(100) (dose of Mch causing 100% increase from baseline Rrs) and Rrs,max (% increase from baseline at the maximal plateau response) and expressed as % control (mean +/- SE). We found recurrent milk aspiration did not affect Edyn and baseline Rrs values. However, airway responses to Mch were increased after milk aspiration when compared with control mice. These changes in airway mechanics were associated with an increased percentage of lymphocytes and eosinophils in the bronchoalveolar lavage, mucus production, and lung inflammation. Our findings suggest that recurrent milk aspiration leads to alterations in airway function, lung eosinophilia, and goblet cell hyperplasia in a murine model.

A novel diagnostic method for pulmonary aspiration in a murine model. Immunocytochemical staining of milk proteins in alveolar macrophages

Aspiration of foreign material into the lungs has been implicated in the etiology of a variety of pulmonary disorders. Although aspiration is a common clinical problem, its diagnosis represents a major challenge due to the lack of sensitive and/or specific tests. In this study, we evaluated the sensitivity and specificity of a novel diagnostic method in a murine model of milk aspiration. Under light anesthesia, BALB/c mice received either single or repeated intranasal instillation of milk. Control animals received sterile physiologic saline or were infected with respiratory pathogens in a similar manner. After isolation and cannulation of the trachea, mouse lungs were lavaged with PBS at various time points after the last aspiration event. Cells were recovered for Oil Red O (ORO) staining as well as immunocytochemistry for milk proteins: alpha-lactalbumin and beta-lactoglobulin. After single aspiration of milk, a large number of alveolar macrophages displayed a strong immunoreactivity for alpha-lactalbumin for 2-96 h. After single and repeated aspiration, the percentage of positive cells for alpha-lactalbumin was significantly higher when compared with ORO staining at 24, 48, and 72 h (p < 0.05). No immunoreactivity for milk proteins was found in alveolar macrophages obtained from our control groups. These findings demonstrate that immunocytochemical staining of milk proteins within alveolar macrophages represents a novel, sensitive, and specific test for the diagnosis of aspiration in a murine model.

Isolation of Stachybotrys from the lung of a child with pulmonary hemosiderosis

Recently, Stachybotrys atra, a toxigenic fungus, has been implicated as a potential cause of pulmonary hemorrhage/hemosiderosis in infants living in water-damaged homes. Although epidemiologic evidence supports this association, neither the organism nor its toxic products has ever been recovered from humans. We report the first case in which Stachybotrys was isolated from the bronchoalveolar lavage fluid of a child with pulmonary hemorrhage. Stachybotrys was also recovered from his water-damaged home. The patient recovered completely after his immediate removal from the environment and subsequent cleaning of his home. This case provides further evidence that this fungus is capable of causing pulmonary hemorrhage in children.

Neural control mechanisms within airways: disruption by respiratory syncytial virus

Among the factors influencing airway function are neural control mechanisms, including adrenergic, cholinergic, nonadrenergic noncholinergic inhibitory, and nonadrenergic noncholinergic excitatory pathways. Respiratory infections affect these pathways in ways that are not entirely clear.

OBJECTIVE

To determine acute and chronic effects of respiratory syncytial virus infection on airway neural control mechanisms.

STUDY DESIGN

Acute effects were studied in cotton rats, which received human respiratory syncytial virus or uninfected cell culture medium intranasally at 5 weeks of age. Chronic effects were studied in ferrets, which received human respiratory syncytial virus or uninfected cell culture medium intranasally during the first 10 days of life. The responsiveness of tracheal smooth muscle segments was studied in vitro 4 days after infection of cotton rats and when ferrets were 4, 8, and 24 weeks of age.

RESULTS

Tracheal smooth muscle segments from cotton rats demonstrated significant increases in contractile responses to nerve stimulation (cholinergic responses). In the presence of neurokinin A, contractile responses increased (enhanced nonadrenergic noncholinergic excitatory response), and relaxation of airways by nerve stimulation (nonadrenergic noncholinergic inhibitory response) was severely impaired. Airway epithelium was also disrupted. These alterations favor airway obstruction and a hyper-responsive state. Contractile responses to nerve stimulation were increased in 4- and 8-week-old ferrets infected with human respiratory syncytial virus compared with ferrets in a control group, a difference that resolved by 24 weeks. Nonadrenergic noncholinergic inhibitory responses were absent in all 4-week-old ferrets and significantly decreased in 8-week-old ferrets infected with human respiratory syncytial virus. A significant difference persisted at 24 weeks of age.

CONCLUSION

Human respiratory syncytial virus causes acute and chronic changes in neural control of airways in animal models. When infection occurs early in life, the alterations persist for long periods.

Human respiratory syncytial virus produces prolonged alterations of neural control in airways of developing ferrets

A dysfunction of pathways that normally cause contraction or relaxation of airways has been proposed to explain heightened levels of responsiveness produced by various insults to the airway. For example, we previously reported (4) that infection of cotton rats with the human respiratory syncytial virus (HRSV) leads to a significant decrease in an airway's nonadrenergic noncholinergic inhibitory (NANCi) response shortly after the infection. In the present study we addressed the more chronic effects of HRSV infection on airway function in young ferrets during a period of rapid somatic growth. Animals 1 wk old received HRSV or uninfected cell culture medium intranasally. In vitro studies of airway function were performed on tracheal smooth muscle (TSM) segments at 4, 8, and 24 wk of age. To evaluate neurally mediated contractile responses, frequency-response curves to electrical field stimulation (EFS) were performed with results expressed in terms of the frequency causing 50% of the maximal contractile response (ES50). In addition, contractile responses of TSM to methacholine (MCh) were also assessed with results expressed as the concentration needed to produce 50% of the maximal contractile response (EC50). To gauge NANCi responses, TSM was contracted with neurokinin A in the presence of atropine, propranolol, and indomethacin. Relaxant responses to EFS were assessed at frequencies from 5 to 30 Hz, with results expressed as mean percent relaxation. We found increased contractile responses to EFS in infected animals compared with that in the control group in both 4- and 8-wk old animals (p = 0.001 and p = 0.008, respectively). This difference had resolved by 24 wk of age. There was no difference in TSM responses to MCh between the groups at any age. Although there were no NANCi responses in 4-wk-old ferrets from either group, NANCi responses were significantly decreased in 8-wk-old ferrets previously infected with HRSV in the first week of life (p = 0.0001). A significant difference persisted (p = 0.008), albeit to a lesser degree, at 24 wk of age. These findings demonstrate that HRSV produces prolonged alterations of TSM function in ferret airways in vitro.

Effect of aspiration of milk on mechanisms of neural control in the airways of developing rabbits

We studied the effects of recurrent aspiration of milk on neural control of airways in young developing rabbits. Beginning at 1 week of age, rabbits received 0.5 ml/kg of whole milk or sterile physiologic saline intranasally while under light methoxyflourane anesthesia 5 days a week for a period of 3 weeks. At 4 and 8 weeks of age, in vitro studies of contractile and relaxant responses of tracheal smooth muscle (TSM) segments were evaluated. To assess the neurally mediated contractile responses, frequency response curves to electrical field stimulation (EFS) were performed with results expressed in terms of frequency of EFS causing 50% of the maximal contractile response (ES50) values. In addition, the contractile responsiveness of TSM to methacholine (MCh) as reflected by the concentration causing 50% of the maximal contractile response (EC50) values was also determined to evaluate the underlying cholinergic reactivity of this segment of airway. To assess nonadrenergic noncholinergic inhibitory (NANCi) responses, experiments were performed on TSM contracted with neurokinin A in the presence of atropine, propranolol, and indomethacin. EFS was delivered to the contracted tissue at stimulation frequencies ranging from 5 to 30 Hz with results expressed as mean percent relaxation. Recurrent aspiration of milk but not saline increased EFS-induced contractile responses, as shown by significantly lower ES50 values compared with the control group: P = 0.02 and P = 0.001 at 4 and 8 weeks of age, respectively. TSM responsiveness to MCh was no different between the two groups, suggesting that alterations in prejunctional mechanisms of neural control were most likely responsible for the increased contractile response to EFS. The NANCi responses were significantly decreased by milk aspiration at both 4 and 8 weeks of age, with the abnormalities less pronounced at the later time point. These findings demonstrate that repeated aspiration of milk leads to abnormal mechanisms of neural control within airways of developing rabbits. While aspiration of milk altered both contractile and relaxant responses to EFS, the former abnormalities became more pronounced with time while the latter appeared to be resolving. These observations suggest that injury to an airway early in development does not necessarily resolve with time but may persist, with functional abnormalities becoming more pronounced even after the airway insult has ceased.

Human respiratory syncytial virus affects nonadrenergic noncholinergic inhibition in cotton rat airways

A dysfunction of the nonadrenergic noncholinergic inhibitory (NANCi) system has been invoked as a possible mechanism underlying or contributing to altered airway function. In the present study we assessed whether human respiratory syncytial virus (HRSV) infection affects the airways' neurally mediated contractile and relaxant (NANCi) responses in vitro. NANCi responses were studied on tracheal smooth muscle (TSM) segments obtained from young adult cotton rats, a well-established model for HRSV infection. To assess NANCi responses, TSM segments were removed and placed in tissue baths containing modified Krebs-Henseleit, atropine (1 x 10(-6) M) and propranolol (5 x 10(-6) M). After contraction with neurokinin A (1 x 10(-5) M), electrical field stimulation (EFS) was applied at stimulation frequencies ranging from 5 to 30 Hz. The NANCi responses were measured and expressed as the mean (+/- SE) percent relaxation. To evaluate neurally mediated contractile responses, full frequency response curves (0.5-30 Hz) to EFS were also performed. We found significantly decreased NANCi responses in TSM segments obtained from infected cotton rats (n = 12) compared with control animals (n = 9) (P < 0.002). Furthermore, the contractile responses to EFS were increased in infected animals compared with the control group (P = 0.0001). These findings demonstrate that HRSV infection leads to an enhanced contractile response to EFS and a significant decrease in NANCi response in cotton rat airways in vitro. This disruption of the neural control of airways may lead to the development of altered airway function.

Modulation of acetylcholine release in rabbit airways in vitro

We investigated the effects of substance P (SP) and vasoactive intestinal peptide (VIP) on acetylcholine (ACh) released from nerve endings by electrical field stimulation (EFS) in rabbit airways in vitro. ACh release was directly measured using high-performance liquid chromatography with electrochemical detection. Airway smooth muscle (ASM) segments, dissected from the midtrachea down to the left mainstem bronchus, were obtained from New Zealand White rabbits and mounted in organ baths containing modified Krebs-Henseleit solution, physostigmine, and choline. EFS at 20 Hz was delivered for 15 min to define baseline ACh release (pmol per gram of tissue per minute). There were no significant regional differences in ACh release during these baseline studies. A second stimulation was then performed in the absence (control) and presence of one or more of the following substances: SP (10(-7) M), a nonpeptide antagonist of the NK1 receptor (10(-7) M CP-96,345; Pfizer), and VIP (10(-7) M). Results for ACh release are expressed as a percentage of the first stimulation (means +/- SE). SP significantly increased ACh release in all ASM segments. This effect was abolished by CP-96,345. VIP alone did not affect ACh release. However, it significantly decreased SP-induced ACh release in all ASM segments. We conclude that SP significantly increases ACh release, thus facilitating cholinergic neurotransmission; its effect is abolished by CP-96,345. VIP decreases SP-induced ACh release, indicating a modulatory effect on cholinergic neurotransmission.

SP-induced contraction of airway smooth muscle in normal and allergen-sensitized rabbits: mechanism of action

We studied the mechanisms involved in the airway smooth muscle (ASM) contraction to substance P (SP) in normal (control) and allergen-sensitized (immune) rabbits as well as immune rabbits exposed to allergen via the airways (immune challenged). Cumulative concentration-response curves to SP (1 x 10(-9) to 1 x 10(-4) M) were performed in ASM segments in the absence and presence of atropine (10(-5) M) in vitro. The maximal contractile response (g tension/g tissue) at 10(-4) M SP and ASM contractions at various concentrations of SP were expressed as means +/- SE. We found no difference in the contractile response to SP between control and immune animals. ASM segments obtained from immune-challenged rabbits were more responsive to SP. Atropine shifted to the right the concentration-response curves and decreased the maximal ASM contraction at 10(-4) M SP in all three groups; this effect, however, was greater in immune-challenged tissues. These findings demonstrate an increased contractile response to SP in immune-challenged animals mediated by a more pronounced facilitation of cholinergic neurotransmission. We conclude that the final ASM response to SP is the result of a complex interaction between direct effects on ASM and indirect effects through modulation of cholinergic neurotransmission.

Maturation of nonadrenergic noncholinergic inhibitory system in normal and allergen-sensitized rabbits

We investigated the functional existence of the nonadrenergic noncholinergic inhibitory (NANCi) system in developing rabbit airways in vitro. Furthermore, we evaluated the effect of parenteral exposure to a specific allergen (ragweed) on the maturation of this neural pathway. NANCi responses were studied on tracheal smooth muscle (TSM) segments obtained from normal and ragweed-sensitized New Zealand White rabbits at 1, 2, 4, and 12 wk of age. The TSM segments were removed and placed in tissue baths containing modified Krebs-Henseleit solution, atropine (1 x 10(-5) M), and propranolol (5 x 10(-6) M). After contraction with neurokinin A (1 x 10(-5) M), electrical field stimulation was applied at stimulation frequencies ranging from 5 to 30 Hz to determine the frequency that produced maximal relaxation. The NANCi response to EFS was measured and expressed as the mean (+/- SE) percent relaxation at 20 Hz, because this stimulation frequency gave the maximal NANCi response at each age studied. TSM segments obtained from control rabbits at 1 wk of age did not demonstrate a NANCi response at the frequencies of stimulation used. By contrast, a reproducible NANC relaxation was demonstrated in TSM from 2-, 4-, and 12-wk-old rabbits. The magnitude of this response was 27 +/- 4.7 (n = 10), 29 +/- 4.8 (n = 9), and 37 +/- 4% (n = 18), respectively. The same experiments performed on TSM segments obtained from ragweed-sensitized animals gave significantly decreased values of NANCi response. In 2-, 4-, and 12-wk-old rabbits, the NANCi responses were 11.5 +/- 3.4 (n = 9), 11 +/- 2 (n = 13), and 16 +/- 4.2% (n = 14).(ABSTRACT TRUNCATED AT 250 WORDS)

Decrease in the airways' nonadrenergic noncholinergic inhibitory system in allergen sensitized rabbits

A decrease in the airways' nonadrenergic noncholinergic inhibitory (NANC-i) system is one of the mechanisms that may contribute to allergen-induced changes in neural control within airways. We measured the airways' neurally mediated contractile and relaxant (NANC-i) responses in tracheal segments and left mainstem bronchus (LMB) from normal (control), immune (ragweed sensitized), and immune challenged rabbits. Immune rabbits were sensitized to mixed ragweed extract through parenteral injections from birth, while the immune challenged group had an additional airway exposure to aerosolized ragweed 48 hours prior to the in vitro studies. Neurally mediated contractile responses to electrical field stimulation (EFS) were increased in the immune challenged group, with the increase most significant in tracheal smooth muscle at a stimulation frequency of 20 Hz. To assess NANC-i responses, airway smooth muscle (ASM) segments from these groups were placed in tissue baths containing atropine (10(-6) M) and propranolol (5 x 10(-6) M). After contraction of the tissue with neurokinin A (NKA, 10(-5) M), the NANC-i response to EFS at 20 Hz was measured and reported as the mean (+/- SEM) percent relaxation. No significant differences were seen in the contractile responses of ASM segments to NKA among the three groups. The tracheal segments showed a significantly different NANC-i relaxation response among all groups: in the control group, 29.1 +/- 3.7; in the immune group 15.8 +/- 2.3%; and in the immune challenged group, 2.1 +/- 4.2%.(ABSTRACT TRUNCATED AT 250 WORDS)

Day/night variations of airway reactivity after drug premedication

Seventeen asthmatic, non-atopic patients (aged 15-48 years) were studied at different hours of the day. On 3 different days, they were submitted to a fog-test at 03:00 p.m. and at 03:00 a.m. On 2 different days, they were given fenoterol (200 micrograms) or Duovent (fenoterol 200 micrograms plus ipratropium bromide 80 micrograms). We were able to demonstrate significant inter-hour differences of the basal values of all parameters, except FVC, in all patients at 03:00 p.m. and at 03:00 a.m. We did not observe any inter-hour difference after the fog-test. Both fenoterol and Duovent improved challenge-induced bronchoconstriction. After the fog-test, both drugs showed an inter-hour variability of ventilatory parameters, which was not significant without drugs because it was masked by the magnitude of the obstructive response to challenge.