Angiotensin converting enzyme inhibitors potentiate the bronchoconstriction induced by substance P in the guinea-pig

The role of TRPA1 and TRPV4 channels in bronchoconstriction and plasma extravasation in airways of rats treated with captopril

Angiotensin-converting enzyme inhibitors (ACEis) may cause adverse airway events, such as cough and angioedema, due to a reduction in bradykinin breakdown and consequent activation of bradykinin type 2 receptor (B₂ receptor). Recent studies have shown that bradykinin can also sensitize pro-inflammatory receptors such as the transient receptor potential ankyrin 1 (TRPA1) and vanilloid 4 (TRPV4), which are implicated in several inflammatory airway diseases. Based on these considerations, the aim of this study was to understand the role of TRPA1 and TRPV4 channels in the bronchoconstrictive response and plasma extravasation in the trachea of rats pretreated with captopril. Using methods to detect alterations in airway resistance and plasma extravasation, we found that intravenous (i.v.) administration of bradykinin (0.03-0.3 μmol/kg, B₂ receptor agonist), allyl isothiocyanate (100-1000 μmol/kg, TRPA1 agonist) or GSK1016790A (0.01-0.1 μmol/kg, TRPV4 agonist), but not des-arg⁹-bradykinin (DABK; 100-300 μmol/kg, B₁ receptor agonist), induced bronchoconstriction in anaesthetized rats. In doses that did not cause significant bronchoconstriction, bradykinin (0.03 μmol/kg) or allyl isothiocyanate (100 μmol/kg), but not GSK1016790A (0.01 μmol/kg) or DABK (300 μmol/kg) induced an increased bronchoconstrictive response in rats pretreated with captopril (2.5 mg/kg, i.v.). On the other hand, in rats pretreated with captopril (5 mg/kg, i.v.), an increased bronchoconstrictive response to GSK1016790A (0.01 μmol/kg) was observed. The bronchoconstrictive response induced by bradykinin in captopril-pretreated rats was inhibited by intratracheal treatment (i.t.) with HC030031 (300 μg/50 μl; 36 ± 9%) or HC067047 (300 μg/50 μl; 35.1 ± 16%), for TRPA1 and TRPV4 antagonists, respectively. However, the co-administration of both antagonists did not increase this inhibition. The bronchoconstriction induced by allyl isothiocyanate in captopril-pretreated rats (2.5 mg/kg) was inhibited (58.3 ± 8%) by the B₂ receptor antagonist HOE140 (10 nmol/50 μl, i.t.). Similarly, the bronchoconstriction induced by GSK1016790A in captopril-pretreated rats (5 mg/kg) was also inhibited (84.2 ± 4%) by HOE140 (10 nmol/50 μl, i.t.). Furthermore, the plasma extravasation induced by captopril on the trachea of rats was inhibited by pretreatment with HC030031 (47.2 ± 8%) or HC067047 (38.9 ± 8%). Collectively, these findings support the hypothesis that TRPA1 and TRPV4, via a B₂ receptor activation-dependent pathway, are involved in the plasma extravasation and bronchoconstriction induced by captopril, making them possible pharmacological targets to prevent or remediate ACEi-induced adverse respiratory reactions.

Peptidyl dipeptidases (Ance and Acer) of Drosophila melanogaster: major differences in the substrate specificity of two homologs of human angiotensin I-converting enzyme

Drosophila melanogaster angiotensin converting enzyme (Ance) and angiotensin converting enzyme related (Acer) are single domain homologs of mammalian peptidyl dipeptidase A (angiotensin I-converting enzyme) whose physiological substrates have not as yet been identified. We have investigated the in vitro substrate specificities of the two peptidases towards a variety of insect and mammalian peptides. Ance was generally much better than Acer at hydrolyzing peptides of 5-13 amino acids in length. Only two of the peptides, [Leu(5)]enkephalinamide and leucokinin-I were cleaved faster by Acer. Increasing NaCl concentration had opposite affects on the cleavage of [Leu(5)]enkephalin and [Leu(5)]enkephalinamide by Acer, decreasing the activity towards [Leu(5)]enkephalin but increasing the activity towards [Leu(5)]enkephalinamide. Of the insect peptides tested, the tachykinin-related peptide, Lom TK-1, proved to be the best substrate for Ance with a k(cat)/K(m) ratio of 0.122s(-1) microM(-1). However, in comparison, the D. melanogaster tachykinins, DTK-1, DTK-2, DTK-3 and DTK-4 were poor Ance substrates. DTK-5 was the best substrate of this family, but the apparent high K(m) for hydrolysis by Ance suggested that this peptide would not be a natural Ance substrate. This low affinity for DTK-5 is the likely reason why the peptide was not rapidly degraded in D. melanogaster hemolymph, where Ance was shown to be a major peptide-degrading activity.

Angiotensin converting enzyme in human synovium: increased stromal [(125)I]351A binding in rheumatoid arthritis

OBJECTIVE

To determine whether tissue angiotensin converting enzyme (ACE) is increased in synovia from patients with rheumatoid arthritis, osteoarthritis or chondromalacia patellae.

METHODS

Sections of synovia from patients with rheumatoid arthritis (n = 7), osteoarthritis (n = 7) or chondromalacia patellae (n = 6) were tested for immunoreactivity for ACE, and for binding of the ACE inhibitor [(125)I]351A. The amount of ACE was measured with computer assisted image analysis as the proportion of synovial section area occupied by ACE-immunoreactive cells, and the density of [(125)I]351A binding.

RESULTS

[(125)I]351A binding sites had characteristics of ACE and colocalised with ACE-like immunoreactivity to microvascular endothelium and fibroblast-like stromal cells in inflamed and non-inflamed human synovium. Stromal [(125)I]351A binding densities (B(eq)) and the fraction of synovial section area occupied by ACE-immunoreactivity (fractional area) were higher in synovia from patients with rheumatoid arthritis (B(eq) 28 amol/mm(2), fractional area 0.21) than from those with osteoarthritis (B(eq) 9 amol/mm(2), fractional area 0.10) or chondromalacia patellae (B(eq) 9 amol/mm(2), fractional area 0.09)(p < 0.05). Density of [(125)I]351A binding to stroma was similar to that to blood vessels in rheumatoid arthritis, but less dense than vascular binding in chondromalacia patellae and osteoarthritis. Increases in [(125)I]351A binding densities were attributable to increases in the numbers of binding sites, and were consistent with an increase in the density of ACE bearing stromal cells.

CONCLUSION

ACE is upregulated in synovial stroma in rheumatoid arthritis. Increased tissue ACE may result in increased local generation of the vasoconstrictor and mitogenic peptide angiotensin II and thereby potentiate synovial hypoxia and proliferation in rheumatoid arthritis.

Pulmonary C-fiber activation before and after peptidase inhibition in rats

Inhibition of peptidases within the lungs not only potentiates the effects of neuropeptides released from C-fibers but also the effects of bradykinin and capsaicin both of which stimulate C-fibers. To determine if peptidase inhibition potentiates C-fiber activation, we challenged pulmonary C-fibers in rats with capsaicin or bradykinin before and after inhibition of neutral endopeptidase (NEP) or angiotensin converting enzyme (ACE). Inhibition of NEP by phosphoramidon (10 mg/kg, i.v.) potentiated the effect of capsaicin (0.5-1 micrograms, i.v.) on C-fiber activity but did not change the response to bradykinin (1-2 micrograms, i.v.). Inhibition of ACE by captopril (5 mg/kg, i.v.) potentiated C-fiber activation by either bradykinin or capsaicin. Aerosol administration of either phosphoramidon (1 x 10(-5) M, 2 min) or captopril (4.6 x 10(-3) M, 2 min) potentiated C-fiber activation by capsaicin aerosol (1.6 x 10(-4) M, 1 min) but not by bradykinin aerosol (9.4 x 10(-5) M, 1 min). Therefore, inhibition of NEP or ACE may potentiate airway obstructive mechanisms initiated by C-fiber stimulation.

Use of baclofen to suppress cough induced by angiotensin-converting enzyme inhibitors

OBJECTIVE

To determine whether baclofen can suppress the cough induced by angiotensin-converting enzyme (ACE) inhibitors.

DESIGN

Prospective, open-label, clinical trial of a 4-week course of low-dose oral baclofen (5 mg tid days 1-7, 10 mg tid days 8-28).

SUBJECTS

Seven patients with severe, persistent ACE inhibitor-induced cough.

SETTING

University-affiliated teaching hospital.

MAIN OUTCOME MEASURES

Study participants kept daily diaries monitoring the frequency of cough during and after completion of baclofen therapy.

RESULTS

All subjects demonstrated diminution of cough after initiation of baclofen. Initial improvement was noted by a mean of 4.0 days (range 3-6), and maximal improvement during treatment was achieved by a mean of 10.7 days (range 5-15). In addition, all subjects demonstrated persistent suppression of cough (range 25-74 d) after discontinuation of the study drug.

CONCLUSIONS

Low-dose oral baclofen therapy caused a prolonged antitussive effect in all subjects without inducing any adverse reactions. Baclofen may offer an alternative to the discontinuation of ACE inhibitor therapy in patients for whom these drugs are required.

Antitussive effect of moguisteine on the enhanced coughing associated with enalapril in guinea-pig

The effect of moguisteine, a novel peripherally acting non-narcotic antitussive drug, on coughs associated with enalapril was examined in guinea-pigs. Chronic treatment with enalapril markedly enhanced the number of capsaicin-induced coughs. Moguisteine dose-dependently suppressed the number of coughs at doses between 3-30 mg/kg p.o., in both vehicle-treated and enalapril-treated animals. There was no significant difference in the antitussive ED50 (95% confidence limit) value of moguisteine between vehicle-treated (16.4 (13.7-19.7) mg/kg) and enalapril-treated (13.7 (3.9-47.6) mg/kg) animals. On the other hand, dihydrocodeine also dose-dependently suppressed the number of coughs in the same dose range as moguisteine in both vehicle-treated and enalapril-treated animals. There was no significant difference in the antitussive ED50 (95% confidence limit) of dihydrocodeine between vehicle-treated (11.7 (4.9-28.3) mg/kg) and enalapril-treated (11.2 (9.4-13.3) mg/kg) animals. Furthermore, the antitussive effect of moguisteine was identical to that of dihydrocodeine in both vehicle-treated and enalapril-treated animals. On the other hand, while chronic co-treatment with moguisteine significantly reduced the number of enhanced coughs associated with enalapril, chronic co-treatment with dihydrocodeine had no significant effect on the number of enhanced coughs associated with enalapril treatment. These results suggest that moguisteine may have a therapeutical benefit in reducing the coughing associated with treatment with inhibitors of angiotensin-converting enzyme.

Effect of angiotensin-converting enzyme inhibition on bronchial responsiveness

The effect of angiotensin-converting enzyme (ACE) inhibition on bronchial responsiveness has not been clearly established. Because ACE degrades bradykinin and substance P, inhibition of the enzyme may lead to accumulation of these potent bronchoconstrictors in the lung, potentially leading to enhanced bronchial reactivity or bronchospasm. Previous studies of the effect of ACE inhibition on airway responsiveness have yielded conflicting results. A randomized, double-blind, placebo-controlled study was therefore conducted to evaluate the effect of a 14-day course of oral lisinopril (10 mg for days 1-3, 20 mg for days 4-14) on bronchial responsiveness to inhaled methacholine in a group of healthy volunteers. No significant change in methacholine responsiveness occurred in any of the participants receiving lisinopril. The mean ( +/- SD) concentration of methacholine producing a decrease in FEV1 of 20% from baseline (PC20; mg/mL) was 23.3 +/- 5.0 before the study and 23.5 +/- 4.5 at the end of the study for the lisinopril group, and 23.0 +/- 4.6 before the study and 21.8 +/- 6.9 after the study for the placebo group. The 14-day course of ACE inhibitor therapy did not enhance nonspecific bronchial responsiveness in healthy volunteers.

Tachykinin receptors and non-cholinergic bronchoconstriction in the anaesthetized guinea-pig

1. Bronchoconstriction can be evoked by electrical stimulation of the vagus nerves in the presence of atropine. We have used novel, highly selective tachykinin receptor antagonists, together with a procedure for on-line, breath-by-breath analysis of total lung resistance (R(L), subtractor method) and dynamic lung compliance (C(dyn)), to investigate the role of tachykinins in this response in anaesthetized, paralysed guinea-pigs. 2. In the presence of 1 mg/kg phosphoramidon (a neutral endopeptidase inhibitor), CP 96345 (the non-peptide NK1 selective antagonist) at 200 nmol/kg had no effect on the increase in R(L) caused by vagal stimulation, but significantly inhibited the associated decrease in C(dyn). 3. The NK2 selective antagonist, MDL 29913 (1 mu mol/kg), significantly antagonized the changes in both R(L) and C(dyn). In the absence of phosphoramidon, MDL 29913 again significantly inhibited the changes in R(L) and C(dyn) although CP 96345 no longer had any effect. 4. The non-peptide NK2 selective antagonist, SR 48968 (100 nmol/kg), also effectively inhibited the responses to vagal stimulation and was more potent than MDL 29913. 5. These results emphasize the importance of the NK2 receptor system in mediating non-cholinergic bronchoconstriction evoked by vagal stimulation in the guinea-pig.

The pharmacological characterization of FK 739, a new angiotensin II-receptor antagonist

The pharmacological properties of FK 739, a new angiotensin II-receptor antagonist, were examined. FK 739 inhibited the specific binding of [125I]-angiotensin II to rat aortic smooth muscle cell membrane with an IC50 value of 8.6 nM, but did not displace the specific binding of [125I]-angiotensin II to bovine cerebellum membrane. In isolated helical strips of rabbit aorta, FK 739 shifted the concentration-response curve of angiotensin II-induced contraction in parallel to the right, and the values of the slope and pA2 were 1.06 and 8.45, respectively. In in vivo studies, oral administration of FK 739 at 10 mg/kg significantly inhibited the angiotensin I-induced pressor response in normotensive rats and dogs, and it caused a fall of mean blood pressure in renal hypertensive rats and dogs. In spontaneously hypertensive rats, FK 739 at 32 and 100 mg/kg significantly decreased the mean blood pressure in a dose-dependent manner. Additionally, we studied whether FK 739 would cause side effects such as dry cough, like other ACE inhibitors did. Oral administration of FK 739 (10 and 32 mg/kg) did not affect the capsaicin-induced bronchial edema. On the other hand, captopril (10 mg/kg) significantly enhanced capsaicin-induced bronchial edema. These results indicate that FK 739 is a potent and competitive antagonist for AT1-type receptors, and suggest that FK 739 might be a safe and useful agent for the treatment of hypertension in clinical trials.

Cough induced activity of spirapril in rats

1. We examined the effect of spirapril, a potent angiotensin converting enzyme (ACE) inhibitor, on the number of capsaicin-induced coughs in rats and compared with that of enalapril. 2. Chronic treatment with enalapril, at doses of 1 and 3 mg/kg, p.o., significantly and dose-dependently enhanced the number of capsaicin-induced coughs. 3. Chronic treatment with higher dose of spirapril (3 mg/kg, p.o.) also significantly enhanced the number of capsaicin-induced coughs. However, lower dose (1 mg/kg, p.o.) of spirapril had no significant effect on the number of capsaicin-induced coughs. 4. These results suggest that cough induced activity, one of the most serious side effects associated with chronic treatment with ACE inhibitors, of spirapril is relatively lower than that of enalapril.

The in vivo effect of tachykinins on airway mast cells of the rat

The tachykinins substance P (SP) and neurokinin A (NKA) have been demonstrated in sensory airway nerves of animals and man and are thought to be neurotransmitters of local axon reflexes, generated by stimuli such as cigarette smoke, dust, histamine, and bradykinin. We previously showed that intravenous SP and NKA caused bronchoconstriction in anesthetized, mechanically ventilated rats. Pharmacologic studies suggested that this occurred by an indirect mechanism, probably mediated by acetylcholine and serotonin. In this study, we demonstrate that the bronchoconstriction caused by SP and NKA in Fisher 344 rats is accompanied by a dose-dependent release of histamine and serotonin in bronchoalveolar lavage (BAL) fluid. In rats depleted of mast cell mediators by pretreatment with compound 48/80, the effects of SP and NKA on lung resistance and serotonin in BAL fluid were abolished. Local instillation of NKA in the airways caused a significant dose-dependent increase in BAL histamine. After pretreatment with thiorphan, an inhibitor of neutral endopeptidase (NEP), the bronchoconstriction and the histamine and serotonin release in BAL fluid caused by SP and NKA were enhanced. After pretreatment with a combination of thiorphan and the angiotensin-converting enzyme inhibitor captopril, NKA and SP were almost equipotent in causing bronchoconstriction and serotonin release in the airways. This study indicates that mast cells are largely involved in the bronchoconstrictor effect of intravenously administered neurokinins in rats. As in the guinea pig, NEP is involved in the termination of the bronchoconstrictor effect of tachykinins. Moreover, NEP also affects the airway histamine and serotonin release caused by these tachykinins in the Fisher 344 rat.

A facilitatory effect of anti-angiotensin drugs on vagal bradycardia in the pithed rat and guinea-pig

1. In pithed rats, preganglionic vagal nerve stimulation (at 5 Hz) elicited a bradycardia. This bradycardia was potentiated by the angiotensin converting enzyme inhibitor, captopril (1 mg kg-1, i.v.) by about 40%. Subsequent angiotensin II infusion (0.03 micrograms kg-1 min-1) reversed this effect. A similar facilitatory effect was also seen with the angiotensin receptor antagonist, losartan (10 mg kg-1, i.v.). These results suggest a tonic inhibitory effect of endogenous angiotensin II on vagal transmission. 2. The effect of captopril in potentiating vagal bradycardia appears to be at the level of vagal neurones, since the bradycardia elicited by the muscarinic agonist, methacholine was unaffected. 3. After the pithed rats were nephrectomized, captopril had no effect on vagally-induced bradycardia, suggesting that the formation of the endogenous angiotensin II responsible for the effect was dependent on renin release from the kidney. 4. When the sympathetic nerves of the pithed rat were electrically stimulated there was a tachycardia, and this was unaffected by captopril. However, when the sympathetic and vagus nerves were activated concurrently, the resulting tachycardia was inhibited by captopril. 5. In pithed guinea-pigs, captopril also potentiated the bradycardia caused by vagal nerve stimulation. This appears to be a tissue-selective effect since the bronchoconstriction due to the vagal stimulation was not affected by captopril. 6. These results suggest that endogenous angiotensin II can have a tonic inhibitory effect on cardiac vagal transmission. Disruption of this mechanism by anti-angiotensin drugs may attenuate the reflex tachycardia associated with the fall in blood pressure in anti-hypertensive therapy.

The effect of hydrochlorothiazide on the enhanced coughing associated with treatment with enalapril

The effect of hydrochlorothiazide, a diuretic which is used in the treatment not only of edema but also of hypertension, on coughs associated with treatment with enalapril was studied in guinea pigs. Chronic treatment with enalapril markedly and dose dependently enhanced the number of capsaicin-induced coughs. However, chronic treatment with hydrochlorothiazide significantly reduced the number of coughs associated with enalapril treatment, also in a dose-dependent manner. These results suggest that diuretics might be used to reduce the coughing associated with treatment with inhibitors of angiotensin-converting enzyme in patients with hypertension.