Strain differences in change in airway responsiveness after repeated antigenic challenge in three strains of rats

Hyperresponsiveness to adenosine in sensitized Wistar rats over-expressing A1 receptor

Airway hyperreactivity is characterized by increased responsiveness to bronchoconstrictor stimuli and it is hallmark of asthma. Adenosine is an ubiquitous signaling nucleoside resulting from ATP catabolism, whose extracellular levels increase following cellular damage or stress. Adenosine plays a role in asthma; asthmatics, but not normal subjects, present bronchoconstriction following inhalation of adenosine or of its precursor, adenosine-5'-monophosphate, most likely via adenosine A(2B) receptor on mast cells. However, the mechanism underling the increased airway smooth muscle sensitivity to adenosine in asthmatics remains to be elucidated. Early experimental studies suggested the involvement of A(1) receptor; this hypothesis has been confirmed by more recent studies on guinea pigs and is corroborated by the finding of an increased adenosine A(1) expression on asthmatic bronchial tissues. Brown Norway rats, the strain usually used to assess asthma models, develop hyperresponsiveness to adenosine 3h following allergen challenge, but not 24h thereafter, without involvement of A(1) receptor. Here, we investigated the role of adenosine A(1) receptor in sensitized Wistar rats showing airway hyperresponsiveness 24h following allergen challenge. We found that on bronchi of sensitized Wistar rats challenged with allergen there is an increased adenosine A(1) receptor expression on smooth muscle that is responsible for hyperresponsiveness to adenosine and ovalbumin.

Augmented PDBu-mediated contraction of bronchial smooth muscle of mice with antigen-induced airway hyperresponsiveness

To explore the role of protein kinase C (PKC) in the augmented bronchial smooth muscle (BSM) contraction observed in the antigen-induced airway hyperresponsive (AHR) mice, the effects of a PKC activator, phorbol 12,13-dibutylate (PDBu), on BSM contraction were compared between the AHR and control mice. Actively sensitized mice were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge the isometrical contractions of the BSMs were measured. The BSM contraction induced by acetylcholine, but not high K(+) depolarization, was significantly augmented in the AHR mice. In BSMs of control mice, PDBu caused a significant increase in tension when the tissues were precontracted with high K(+), although PDBu itself had no effect on basal tone. The PDBu-mediated contraction was markedly augmented in BSMs of the AHR mice. These findings suggest that an increase in the PKC-mediated signaling is involved in the augmented contraction of BSMs in the antigen-induced AHR mice.

Antigen challenge influences various transcription factors of rat bronchus: protein/DNA array study

Although the transcription factors are required for expression of the proinflammatory cytokines and immune proteins which are involved in airway hyperresponsiveness and inflammation of bronchial asthma, the antigen-induced alterations of the transcription factors in bronchi have not yet been revealed. Therefore, in order to profile the alteration pattern of the transcription factors after antigen challenge in bronchi, we used protein/DNA arrays. Rats were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen. Half, 1, 2 and 4 h after the last antigen challenge, protein/DNA array was performed with nuclear extract of bronchial tissue. Twenty-one the transcription factors exhibited an activation after the last antigen challenge in rat bronchial tissue. Among them, upstream transcription factor-1 (USF-1) and CAAT box general (CBF) were markedly activated after the last antigen challenge. Conversely, 4 transcription factors were inactivated after the last challenge. In development of bronchial asthma, some of the transcription factors may have an ability to modulate the transcription of inflammatory proteins such as cytokines, inflammatory enzymes, etc. Furthermore, the transcription factors, such as USF-1 and CBF, which have not been taken notice so far are also presumed to play an important role in the development of bronchial asthma.

Increased expression of G alpha q protein in bronchial smooth muscle of mice with allergic bronchial asthma

In the present study, the change in Gq protein level in bronchial smooth muscle of mice with antigen-induced airway hyperresponsiveness (AHR) was determined. BALB/c mice were actively sensitized and repeatedly challenged with ovalbumin antigen to induce bronchial smooth muscle hyperresponsiveness. The contraction induced by 10 microM AlF4(-) (generated by 10 microM AlCl3 plus 10 mM NaF) of bronchial smooth muscles isolated from the antigen-challenged mice was significantly augmented as compared with that from the control animals. The G alpha q protein level determined by immunoblotting was also significantly increased in bronchial smooth muscles of the antigen-challenged group. Thus, an upregulation of G alpha q protein may be involved in the pathogenesis of bronchial smooth muscle hyperresponsiveness, one of the causes of AHR in asthmatics.

Glucocorticoids inhibited airway hyperresponsiveness through downregulation of CPI-17 in bronchial smooth muscle

Glucocorticoids are the most effective anti-inflammatory treatment for asthma, and inhaled corticosteroids are the most effective long-term control therapy for persistent asthma. In the present study, to determine the mechanism of the inhibitory effect of glucocorticoids on airway hyperresponsiveness, the effects of glucocorticoids on the expression and activation of PKC-potentiated protein phosphatase 1 inhibitory protein of 17 kDa (CPI-17) were examined in bronchial smooth muscles of antigen-induced airway hyperresponsive rats. Repeated antigen inhalation to animals sensitized with DNP-Ascaris antigen caused a marked bronchial smooth muscle hyperresponsiveness to acetylcholine, accompanied by upregulation and acetylcholine-induced activation of CPI-17 to result in an increase in myosin light chain (MLC) phosphorylation. Treatment with glucocorticoids (prednisolone or beclomethasone, 10 mg/kg, i.p., respectively) significantly inhibited the airway hyperresponsiveness, and markedly reduced both the protein and mRNA levels of CPI-17 in bronchial smooth muscle. The acetylcholine-induced activation of CPI-17, i.e., phosphorylation of CPI-17, was also significantly inhibited by glucocorticoids. Glucocorticoids also prevented the augmented acetylcholine-induced MLC phosphorylation observed in the airway hyperresponsive rats. Therefore, glucocorticoids might inhibit the airway hyperresponsiveness through the inhibition of overexpression and activation of CPI-17.

Glucocorticoids ameliorate antigen-induced bronchial smooth muscle hyperresponsiveness by inhibiting upregulation of RhoA in rats

To determine the mechanism(s) of the inhibitory effect of glucocorticoids on airway hyperresponsiveness in allergic bronchial asthma, the effects of systemic treatment with glucocorticoids on bronchial smooth muscle hyperresponsiveness and RhoA upregulation were investigated in rats with allergic bronchial asthma. Rats were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen. Animals were also treated with prednisolone or beclomethasone (each 10 mg/kg, i.p.) once a day during the antigen inhalation period. Repeated antigen inhalation caused a marked bronchial smooth muscle hyperresponsiveness to acetylcholine with an upregulation of RhoA. Augmented acetylcholine-induced activation of RhoA and phosphorylation of myosin light chain were observed in bronchial smooth muscles of the antigen-exposed animals. Systemic treatment with either glucocorticoid used inhibited the bronchial smooth muscle hypercontraction until the level of the sensitized control rats that received saline inhalation instead of antigen challenge. Interestingly, both glucocorticoids also inhibited the upregulation of RhoA and augmented acetylcholine-induced activation of RhoA and phosphorylation of myosin light chain. In conclusion, glucocorticoids ameliorated the augmented bronchial smooth muscle contraction by inhibiting upregulation of RhoA. These effects of glucocorticoids may account for, in part, their beneficial effects in the treatment of asthma.

Lovastatin inhibits bronchial hyperresponsiveness by reducing RhoA signaling in rat allergic asthma

Recent studies revealed an importance of a monomeric GTP-binding protein, RhoA, in contraction of bronchial smooth muscle (BSM). RhoA and its downstream have been proposed as a new target for the treatment of airway hyperresponsiveness in asthma. Statins are known to inhibit the functional activation of RhoA via the depletion of geranylgeranylpyrophosphate. To determine the beneficial effects of statins on the airway hyperresponsiveness in allergic bronchial asthma, we investigated the effects of systemic treatment with lovastatin on the augmented BSM contraction and activation of RhoA in rats with allergic bronchial asthma. Rats were sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen. Animals were also treated with lovastatin (4 mg kg(-1) day(-1) ip) once a day before and during the antigen inhalation period. Repeated antigen inhalation caused a marked BSM hyperresponsiveness to ACh with the increased expression and translocation of RhoA. Lovastatin treatments significantly attenuated both the augmented contraction and RhoA translocation to the plasma membrane. Lovastatin also reduced the increased cell number in bronchoalveolar lavage fluids and histological changes induced by antigen exposure, whereas the levels of immunoglobulin E in sera and interleukins-4, -6, and -13 in bronchoalveolar lavage fluids were not significantly changed. These findings suggest that lovastatin ameliorates antigen-induced BSM hyperresponsiveness, an important factor of airway hyperresponsiveness in allergic asthmatics, probably by reducing the RhoA-mediated signaling.

Augmentation of endothelin-1-induced phosphorylation of CPI-17 and myosin light chain in bronchial smooth muscle from airway hyperresponsive rats

Airway hyperresponsiveness (AHR) associated with heightened airway resistance and inflammation is a characteristic feature of bronchial asthma. It has been demonstrated that contraclile responsiveness to endothelin-1 (ET-1) in repeated antigen challenge-induced airway hyperresponsive bronchial preparation was significantly increased. ET-1 is a potent contracting substance for various smooth muscles including airways. In addition to the classical Ca(2+)-mediated contraction, ET-1 also induced Ca(2+) sensitization of contraction. However, it is not clear whether ET-1 stimulation also activates the CPI-17 (PKC-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) pathway in airway smooth muscles. Therefore, the changes in ET-1-induced activation/phosphorylation of CPI-17 and myosin light chain (MLC) in bronchial smooth muscle of repeatedly antigen-challenged rats were examined. The levels of ET-1-induced phosphorylation of CPI-17 and MLC were increased much more markedly in the AHR group than in the sensitized control animals. It might be suggested that the augmented activation of CPI-17 observed in the hyperresponsive bronchial smooth muscle is responsible for the enhanced agonists-induced contraction of bronchial smooth muscle in AHR rats.

Possible involvement of CPI-17 in augmented bronchial smooth muscle contraction in antigen-induced airway hyper-responsive rats

Airway hyper-responsiveness (AHR) associated with heightened airway resistance and inflammation is a characteristic feature of asthma. It has been demonstrated that contractile responsiveness and Ca(2+) sensitization to acetylcholine (ACh) in repeated antigen challenge-induced airway hyper-responsive bronchial preparation were significantly increased. The CPI-17 (PKC-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) is activated by protein kinase C and acts on a myosin light-chain phosphatase-specific target. The aim of the present study was to explore the role of CPI-17 in hyper-responsiveness of bronchial smooth muscle in antigen-induced AHR rats. In immunoblotting, the levels of expression of CPI-17 mRNA and protein were significantly increased in bronchus from rats that were repeatedly challenged with antigen. ACh-induced CPI-17 phosphorylation and translocation to membrane fraction were also significantly increased in bronchus from antigen-challenged rats. In conclusion, we suggest that augmented expression and activation of CPI-17 observed in the hyper-responsive bronchial smooth muscle might be responsible for the enhanced ACh-induced Ca(2+) sensitization of bronchial smooth muscle contraction associated with AHR.

Involvement of M3 Muscarinic Receptors in ACh-Induced Increase in Membrane-Associated RhoA of Rat Bronchial Smooth Muscle

It is known that RhoA is translocated from cytoplasm to cell membrane in bronchial smooth muscle when activated by acetylcholine (ACh) stimulation. In the present study, the effects of selective muscarinic receptor antagonist methoctramine, AF-DX116 (for M(2)) and 4-diphenylacetoxy N-methylpiperidine (4-DAMP; for M(3)) on the ACh-induced rat bronchial smooth muscle contraction and increase in membrane-associated RhoA were investigated to elucidate the muscarinic receptor subtype participating in these responses. To evaluate ACh-induced contraction of bronchial smooth muscle, bronchial ring of rat was prepared, suspended in an organ bath and the tension was measured isometrically. To quantify the ACh-induced increase in membrane-associated RhoA protein, western blot analysis was performed by using homogenates of membrane and cytosolic fractions of the rat bronchi. The muscarinic M(2) and M(3) receptors were detected by using RT-PCR in rat bronchial smooth muscle. Both the ACh-induced smooth muscle contraction and increase in membrane-associated RhoA were markedly inhibited by 4-DAMP, but not by methoctramine or AF-DX116. In conclusion, these results indicated contraction for the first time that the activation of RhoA occurs via M(3) receptor in rat bronchial smooth muscle.

TNF-alpha augments the expression of RhoA in the rat bronchus

While nonspecific airway hyperresponsiveness (AHR) is a central feature of allergic bronchial asthma, the mechanism underlying the development of AHR is not clearly understood. We have previously demonstrated in vitro hyperresponsiveness of bronchial smooth muscle to acetylcholine (ACh) in rats that were actively sensitized and repeatedly challenged with aerosolized antigen. It has also been demonstrated that the ACh-induced, RhoA-mediated Ca(2+) sensitization is markedly augmented concomitantly with an increased expression and activation of RhoA protein in the bronchial smooth muscle of the antigen-treated rats. In the present study, we have investigated whether TNF-alpha, a proinflammatory cytokine which is involved in bronchial asthma, causes upregulation of RhoA mRNA and protein in the rat bronchus. Treatment of rat bronchial smooth muscle preparations with TNF-alpha (300 ng/ml for 24 hr) significantly shifted the concentration-response curve to ACh upwards, but did not alter the response to high K(+), when compared to that of control tissues. Levels of RhoA mRNA and protein in the TNF-alpha-treated bronchus were significantly greater than those in the control group. In conclusion, it is suggested that the augmentation of the ACh-induced contractile response evoked by TNF-alpha might be mediated by an upregulation of RhoA in rat bronchial smooth muscle.

Involvement of p42/44 MAPK and RhoA protein in augmentation of ACh-induced bronchial smooth muscle contraction by TNF-alpha in rats

Bronchial asthma is characterized by chronic inflammation of airway tissues and nonspecific airway hyperresponsiveness (AHR), but the underlying mechanisms of AHR have yet to be elucidated. Recently, tumor necrosis factor-alpha (TNF-alpha) has been identified as a proinflammatory cytokine that might be important in the hyperresponsiveness of airway tissue. We have investigated the effects of SB-203580 (a p38 MAPK inhibitor), U-0126 (an inhibitor of p42/44 MAPK activation), and cycloheximide (an inhibitor of protein synthesis) on TNF-alpha-augmented ACh-induced bronchial smooth muscle contraction. We have also investigated the phosphorylation of p42/44 MAPK and upregulation of RhoA protein by TNF-alpha. Treatment of rat bronchial smooth muscles with TNF-alpha (300 and 1,000 ng/ml for 24 h) resulted in a significant upward shift in the concentration-response curve to ACh, but not to high K(+), compared with control tissues. The effect of TNF-alpha was completely blocked by pretreatment with U-0126 or cycloheximide, but not with SB-203580. Immunoblotting demonstrated that p42/44 MAPK was phosphorylated and RhoA protein was increased in bronchial tissue by TNF-alpha. Furthermore, the TNF-alpha-induced upregulation of RhoA protein was abolished by U-0126 pretreatment. In conclusion, we suggest that TNF-alpha might be one of the important mediators involved in the pathogenesis of augmented bronchial smooth muscle contractility in AHR. For the first time, we have demonstrated that augmentation of ACh-induced contractile response evoked by TNF-alpha was mediated by synthesis of protein, such as RhoA, through activation of p42/44, but not p38 MAPK, in rat bronchial smooth muscle.

Gq protein level increases concurrently with antigen-induced airway hyperresponsiveness in rats

In the present study, bronchial Gq protein level of the airway hyperresponsive rats was determined by using immunoblot analysis. In the airway hyperresponsive rats that were sensitized and repeatedly antigen challenged, the in vitro bronchial responsiveness to acetylcholine was significantly enhanced as compared with that in the sensitized control group. Moreover, the bronchial contraction induced by 10 microM AlF(4)(-) (generated by 10 microM AlCl(3) plus 10 mM NaF) was significantly elevated after repeated antigen challenge (0.44+/-0.13 and 1.09+/-0.09 g tension in the control and airway hyperresponsive groups, respectively; P<0.01). In both groups, immunoblotting with the antibody against G alpha q gave a single 42 kD band. The G alpha q protein levels in the airway hyperresponsive group (0.58+/-0.12) estimated by G alpha q/beta-actin ratio was significantly greater than those in the control group (0.30+/-0.10; P<0.05). These findings suggest that the increase in G alpha q protein level may be involved in the pathogenesis of antigen-induced airway hyperresponsiveness in rats.

Abnormal modulation of cholinergic neurotransmission by opioid in hyperresponsive bronchus of rats

1. The electrical field stimulation (EFS)-induced bronchoconstriction in vitro in rats challenged by DNP-Ascaris antigen was significantly greater than that in normal rats. 2. Morphine inhibited the EFS-induced bronchoconstriction in normal rats. Whereas the inhibition of EFS-induced bronchoconstriction by the opioid was little, if any, in the DNP-Ascaris-challenged rats. 3. These findings suggest that dysfunction of presynaptic inhibitory modulation through the opioid receptor may take place in the airways of DNP-Ascaris-challenged rats.

Characteristics of muscarinic cholinoceptors in airways of antigen-induced airway hyperresponsive rats

The antagonist and agonist binding sites of muscarinic receptors were investigated by using membrane preparations of airways from nonsensitized normal control, sensitized control and repeatedly antigen challenged rats. The in vitro bronchial responsiveness to ACh was markedly increased in repeatedly antigen challenged group but not in sensitized control group. No significant difference was observed in receptor density and antagonist affinity among these three groups. The affinity of ACh for high-affinity agonist binding sites of repeatedly antigen challenged group was much greater than those in the other groups; the affinity significantly reduced in the presence of GTP gamma S. We concluded that enhanced G protein level might be involved in inducing airway hyperresponsiveness in rats.

Alteration in Ca2+ availability involved in antigen-induced airway hyperresponsiveness in rats

The origin of Ca2+ contributing to the enhancement of acetylcholine-induced bronchial smooth muscle constriction in airway hyperresponsiveness induced by antigen challenge was investigated. Under Ca(2+)-free (concomitant with 10(-6) M nicardipine) conditions, the contractile responses of bronchial rings to 1 mM acetylcholine were significantly greater in rings from rats with hyperresponsive airways (0.15 +/- 0.04 g) than those of rings from normal rats (0.02 +/- 0.004 g; P < 0.05). The cumulatively administered Ca2+ induced a markedly greater bronchoconstriction in rings from rats with hyperresponsive airways in Ca(2+)-free solution when muscles were pretreated with 1 mM acetylcholine (in the presence of 10(-6) M nicardipine) than in rings from normal rats, whereas no significant difference in Ca(2+)-induced bronchoconstriction was observed between the two groups when muscles were pretreated with 60 mM K+ (in the presence of 10(-6) M atropine). These findings suggest that enhancement of the availability of Ca2+ released from intracellular stores and/or influxed through receptor-operated Ca2+ channels in airway smooth muscles might be involved in the airway hyperresponsiveness to acetylcholine in rats.

Antigen-induced airway hyperresponsiveness is associated with airway tissue NEP hypoactivity in rats

In the present study, the role of sensory neuropeptides in the airway hyperresponsiveness (AHR) was investigated. First, the effect of the depletion of sensory neuropeptides by systemic capsaicin treatment on the AHR to acetylcholine (ACh) induced by repeated antigenic challenge to sensitized rats was studied. We secondly investigated whether the neutral endopeptidase (NEP) activity was altered at the antigen-induced AHR. Male Wistar rats were sensitized and repeatedly challenged with DNP-Ascaris antigen. Twenty-four hours after the last antigenic challenge, a marked AHR to inhaled ACh (0.001-0.03%) was observed. This AHR was significantly attenuated by systemic capsaicin pretreatment prior to sensitization. On the other hand, in normal rats, the airway responsiveness to inhaled ACh was significantly increased by pretreatment with NEP inhibitor, phosphoramidon (3 mg/kg, i.v.), but the NEP inhibitor-induced effect was no more observed in the antigen-induced AHR rats. Furthermore, it was found that the airway NEP activity was significantly decreased at the antigen-induced AHR. These findings suggest that NEP hypoactivity and resultant increased sensory neuropeptides have an important role in the pathogenesis of antigen-induced AHR in rats.