Effects of SCA40 on human isolated bronchus and human polymorphonuclear leukocytes: comparison with rolipram, SKF94120 and levcromakalim

Scope of adjuvant therapy using roflumilast, a PDE-4 inhibitor against COVID-19

The recent pandemic of COVID-19 caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) presents an extraordinary challenge to identify effective drugs for prevention and treatment. The pathogenesis implicate acute respiratory disorder (ARD) which is attributed to significantly triggered "cytokine storm" and compromised immune system. This article summarizes the likely benefits of roflumilast, a Phosphodiesterase-4 (PDE-4) inhibitor as a comprehensive support COVID-19 pathogenesis. Roflumilast, a well-known anti-inflammatory and immunomodulatory drug, is protective against respiratory models of chemical and smoke induced lung damage. There is significant data which demonstrate the protective effect of PDE-4 inhibitor in respiratory viral models and is likely to be beneficial in combating COVID-19 pathogenesis. Roflumilast is effective in patients with severe COPD by reducing the rate of exacerbations with the improvement of the lung function, which might further be beneficial for better clinical outcomes in COVID-19 patients. However, further clinical trials are warranted to examine this conjecture.

Bafetinib inhibits functional responses of human eosinophils in vitro

Eosinophils play a prominent role in the process of allergic inflammation. Non-receptor associated Lyn tyrosine kinases generate key initial signals in eosinophils. Bafetinib, a specific Abl/Lyn tyrosine kinase inhibitor has shown a potent antiproliferative activity in leukemic cells, but its effects on eosinophils have not been reported. Therefore, we studied the effects of bafetinib on functional and mechanistic responses of isolated human eosinophils. Bafetinib was more potent than non-specific tyrosin kinase comparators genistein and tyrphostin inhibiting superoxide anion triggered by N-formyl-Met-Leu-Phe (fMLF; 100 nM) (-log IC50=7.25 ± 0.04 M; 6.1 ± 0.04 M; and 6.55 ± 0.03 M, respectively). Bafetinib, genistein and tyrphostin did not modify the [Ca(2+)]i responses to fMLF. Bafetinib inhibited the release of EPO induced by fMLF with higher potency than genistein and tyrphostin (-log IC50=7.24 ± 0.09 M; 5.36 ± 0.28 M; and 5.37 ± 0.19 M, respectively), and nearly suppressed LTC4, ECP and chemotaxis. Bafetinib, genistein and tyrphostin did not change constitutive apoptosis. However bafetinib inhibited the ability of granulocyte-monocyte colony-stimulating factor to prevent apoptosis. The activation of Lyn tyrosine kinase, p-ERK1/2 and p-38 induced by fMLF was suppressed by bafetinib and attenuated by genistein and tyrphostin. In conclusion, bafetinib inhibits oxidative burst and generation of inflammatory mediators, and reverses the eosinophil survival. Therefore, future anti-allergic therapies based on bafetinib, could help to suppress excessive inflammatory response of eosinophils at inflammatory sites.

Roflumilast N-oxide, a PDE4 inhibitor, improves cilia motility and ciliated human bronchial epithelial cells compromised by cigarette smoke in vitro

BACKGROUND AND PURPOSE

Mucociliary malfunction occurs in chronic obstructive pulmonary disease (COPD) and compromised functions of ciliated bronchial epithelial cells may contribute to this. Cigarette smoke, a major risk factor for COPD, impairs ciliary beat frequency (CBF). cAMP augments CBF. This in vitro study addressed, in differentiated, primary human bronchial epithelial cells, whether roflumilast N-oxide, a PDE4 inhibitor, (i) augments CBF; (ii) prevents the reduction in CBF induced by cigarette smoke extract (CSE); and (iii) protects against the loss of the ciliated phenotype following long-term CSE exposure.

EXPERIMENTAL APPROACH

Air-liquid interface cultured human bronchial epithelial cells were incubated with roflumilast N-oxide and exposed to CSE. CBF was assessed by digital high speed video microscopy (DHSV). Ciliated cells were characterized by β-tubulin IV staining and analyses of Foxj1 and Dnai2 mRNA and protein (real-time quantitative PCR, Western blotting).

KEY RESULTS

Roflumilast N-oxide concentration-dependently triggered a rapid and persistent increase in CBF and reversed the decrease in CBF following CSE. Long-term incubation of bronchial epithelial cells with CSE resulted in a loss in ciliated cells associated with reduced expression of the ciliated cell markers Foxj1 and Dnai2. The PDE4 inhibitor prevented this loss in the ciliated cell phenotype and the compromised Foxj1 and Dnai2 expression. The enhanced release of IL-13 following CSE, a cytokine that diminishes the proportion of ciliated cells and in parallel, reduces Foxj1 and Dnai2, was reversed by roflumilast N-oxide.

CONCLUSION AND IMPLICATIONS

Roflumilast N-oxide protected differentiated human bronchial epithelial cells from reduced CBF and loss of ciliated cells following CSE.

Neutrophil activation in severe, early-onset COPD patients versus healthy non-smoker subjects in vitro: effects of antioxidant therapy

BACKGROUND

Neutrophils and oxidative stress have been implicated in the pathogenesis of COPD. Severe, early-onset COPD is characterized by a rapid decline in the lung function at an early age; however, nothing is known about neutrophil activation in COPD patients.

OBJECTIVES

The aim of this study was to evaluate peripheral blood neutrophil activation in severe, early-onset COPD patients versus healthy non-smokers and the effect of N-acetyl-L-cysteine (NAC) on neutrophil activation in vitro.

METHODS

Neutrophils were isolated from 15 severe, early-onset COPD patients and 15 age-matched healthy subjects and stimulated with N-formyl-Met-Leu-Phe (fMLP) in the presence or absence of NAC (10 μM to 10 mM). Neutrophil chemotaxis, elastase release, reactive oxygen species (ROS), intracellular thiols and apoptosis were measured by Boyden chamber, spectrofluorometry, CMFDA and H2DCF-DA dyes and by annexin V-FITC, respectively.

RESULTS

Chemotaxis of peripheral blood neutrophils from COPD patients in response to fMLP was 30% more increased than that observed in healthy subjects. Elastase release in response to fMLP was 2-fold higher in neutrophils from COPD patients versus healthy subjects. Intracellular thiol levels were 30% lower in COPD and ROS was approximately 30% higher in COPD versus healthy neutrophils. Spontaneous apoptosis showed no differences in both groups of patients and fMLP-induced apoptosis was higher in COPD. Pre-treatment with the antioxidant NAC effectively attenuated neutrophil chemotaxis, elastase release and ROS as well as effectively increased thiol levels in COPD.

CONCLUSIONS

Neutrophils in severe, early-onset COPD patients are highly activated and this is alleviated by NAC in vitro.

Prostanoids and phosphodiesterase inhibitors in experimental pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease with a poor prognosis, characterized by intimal lesions, medial hypertrophy, and adventitial thickening of precapillary pulmonary arteries. Several approved therapies are currently available for the treatment of PAH, of which intravenous epoprostenol is the best explored over the past decade. Newly available oral endothelin receptor antagonists, although clinically efficacious, bear the risk of liver toxicity in a significant portion of patients. Substances that stimulate the formation of the second messengers cyclic adenosine monophosphate (cAMP) or guanosine monophosphate (cGMP) have proved useful in the treatment of various forms of pre-capillary pulmonary hypertension. These second messengers of the endogenous vasodilator mediators that include prostacyclin and nitric oxide (NO) are hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs), a class of enzymes from which 11 isoforms have been characterized. This chapter highlights developments in the treatment of experimental pulmonary hypertension with special attention to prostanoids and PDE inhibitors. We summarize findings for the acute vasodilatory as well as chronic effects of prostanoids, PDE inhibitors, or combinations of both, in animal models of pulmonary hypertension.

Inhibitory effects of N-acetylcysteine on the functional responses of human eosinophils in vitro

BACKGROUND

Oxidative stress appears to be relevant in the pathogenesis of inflammation in allergic diseases like bronchial asthma. Eosinophils are oxidant-sensitive cells considered as key effectors in allergic inflammation.

OBJECTIVE

The aim of this work was to study the effects of the clinically used antioxidant N-acetyl-L-cysteine (NAC) on the functional responses of human-isolated eosinophils.

METHODS

Human eosinophils were purified from the blood of healthy donors by a magnetic bead separation system. The effects of NAC were investigated on the generation of reactive oxygen species (chemiluminescence and flow cytometry), Ca(2+) signal (fluorimetry), intracellular glutathione (GSH; flow cytometry), p47(phox)-p67(phox) translocation (Western blot) and eosinophil cationic protein (ECP) release (radioimmunoassay).

RESULTS

NAC (0.1-1 mm) inhibited the extracellular generation of oxygen species induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) and eotaxin (in the presence of IL-5) with -logIC(50) values of 3.61+/-0.03 and 3.36+/-0.09, respectively. Also, the intracellular generation of hydrogen peroxide was virtually abolished by NAC (0.5-1 mm). NAC (1 mm) did not alter the fMLP-induced Ca(2+) signal but augmented the eosinophil content of reduced GSH and inhibited p47(phox)-p67(phox) translocation. NAC inhibited the release of ECP ( approximately 90% inhibition at 1 mm) from fMLP-activated eosinophils.

CONCLUSION

Inhibition by NAC of human eosinophil functions in vitro is potentially useful in the treatment of allergic inflammation.

Airways disease: phenotyping heterogeneity using measures of airway inflammation

: Despite asthma and chronic obstructive pulmonary disease being widely regarded as heterogeneous diseases, a consensus for an accurate system of classification has not been agreed. Recent studies have suggested that the recognition of subphenotypes of airway disease based on the pattern of airway inflammation may be particularly useful in increasing our understanding of the disease. The use of non-invasive markers of airway inflammation has suggested the presence of four distinct phenotypes: eosinophilic, neutrophilic, mixed inflammatory and paucigranulocytic asthma. Recent studies suggest that these subgroups may differ in their etiology, immunopathology and response to treatment. Importantly, novel treatment approaches targeted at specific patterns of airway inflammation are emerging, making an appreciation of subphenotypes particularly relevant. New developments in phenotyping inflammation and other facets of airway disease mean that we are entering an era where careful phenotyping will lead to targeted therapy.

Olive oil-based lipid emulsion's neutral effects on neutrophil functions and leukocyte-endothelial cell interactions

BACKGROUND

Infection remains a drawback of parenteral nutrition (PN), probably related, among other factors, to immunosuppressive effects of its lipid component. Newer preparations may have lesser immunosuppressive impact. This study examines the effects of an olive oil-based lipid emulsion (long-chain triacylglycerols-monounsaturated fatty acids [LCT-MUFA]; ClinOleic) on various functions of human neutrophils in vitro and on rat leukocyte-endothelial cell interactions in vivo compared with LCT (Intralipid) and 50% LCT-50% medium-chain triacylglycerols (MCT; Lipofundin) mixture.

METHODS

Neutrophils isolated from healthy donors were incubated with concentrations (0.03-3 mmol/L) of lipid emulsions encompassing clinically relevant levels. In vivo leukocyte recruitment was studied with intravital microscopy within rat mesenteric microcirculation.

RESULTS

LCT-MUFA (3 mmol/L) did not alter the N-formyl-Met-Leu-Phe (FMLP)-induced rise in [Ca2+]i, oxidative burst, chemotaxis, and elastase release, whereas LCT-MCT decreased [Ca2+]i and chemotaxis and increased oxidative burst. FMLP-induced LTB4 production was augmented by lipid emulsions. Serum-opsonized zymosan-induced phagocytosis was unaltered by lipid emulsions. Basal and FMLP-induced CD11b expression was unaffected by lipid emulsions. Lipopolysaccharide (LPS)-induced TNF-alpha, IL-1beta and IL-8 mRNA, and protein expression was unaltered by LCT-MUFA, whereas LCT and LCT-MCT decreased IL-1beta mRNA and protein. LCT-MUFA did not alter apoptosis, but LCT increased apoptosis in absence and presence of GM-CSF. LPS (1 microg/mL)-induced increase in leukocyte rolling flux, adhesion, and emigration was inhibited by LCT and LCT-MCT but unaffected in LCT-MUFA-treated rats. Immunohistochemistry showed LPS-induced increase in P-selectin expression attenuated by LCT and LCT-MCT but not LCT-MUFA.

CONCLUSIONS

LCT-MUFA showed lower in vitro and in vivo impact on neutrophil function compared with LCT and LCT-MCT.

Getting new bronchodilator compounds from molecular topology

Molecular topology has been used to select new lead bronchodilator compounds. The main advantage of this method, as compared to others frequently used, is that it does not require a previous explicit knowledge of the mechanism of action (MOA) of the compounds analyzed. A large database (12,000 chemicals) has been examined in this study to find less than 5% compounds with bronchodilator activity. After removing those compounds already described as bronchodilators, we present here the results for 20 among these compounds, some of them showing other pharmacological activities. Some of the compounds selected in this study showed higher relaxation and higher potency than theophylline, which is the reference drug used in the bronchodilator assay performed. For instance, tetrahydro-papaveroline showed significantly higher values than theophylline (93.9% versus 77.0% and pD2=7.30 versus pD2=4.69, respectively). Other compounds, although eliciting small or no relaxation at 0.1mM, produced larger relaxation at higher concentrations (1mM). In conclusion, the molecular topology based approach used in this work has demonstrated to be effective in the search of new bronchodilators.

PDE4 inhibitors as new anti-inflammatory drugs: effects on cell trafficking and cell adhesion molecules expression

Phosphodiesterase 4 (PDE4) is a major cyclic AMP-hydrolyzing enzyme in inflammatory and immunomodulatory cells. The wide range of inflammatory mechanisms under control by PDE4 points to this isoenzyme as an attractive target for new anti-inflammatory drugs. Selective inhibitors of PDE4 have demonstrated a broad spectrum of anti-inflammatory activities including the inhibition of cellular trafficking and microvascular leakage, cytokine and chemokine release from inflammatory cells, reactive oxygen species production, and cell adhesion molecule expression in a variety of in vitro and in vivo experimental models. The initially detected side effects, mainly nausea and emesis, appear at least partially overcome by the 'second generation' PDE4 inhibitors, some of which like roflumilast and cilomilast are in the later stages of clinical development for treatment of chronic obstructive pulmonary disease. These new drugs may also offer opportunities for treatment of other inflammatory diseases.

Imidazo[1,2-a]quinoxalines: synthesis and cyclic nucleotide phosphodiesterase inhibitory activity

A group of imidazo[1,2-a]quinoxalines have been synthesised from quinoxaline by condensation of an appropriate haloester or intramolecular cyclisation of a keto moiety on an intracyclic nitrogen atom. The reactivity of the heterocycle was explored through diverse reactions such as electrophilic substitution, lithiation and halogen-metal exchange to give access to a new series of derivatives. Confirmation of their structure was mainly performed by NMR, after careful assignment of the signals in comparison to previous attributions made on the parent imidazo[1,2-a]quinoxaline and discussion of available data in the literature. The cyclic nucleotide phosphodiesterase inhibitor activity of some of these derivatives has been assessed on isoenzymes type III and type lV. Compound 15, 4-(methylamino)imidazo[1,2-a]quinoxaline-2-carbonitrile, exhibited potent relaxant activity on smooth muscle, with a potency similar to the one measured with SCA 40, its structural analogue in the imidazo[1,2-a]pyrazine series.

Contraction of human airways by oxidative stress protection by N-acetylcysteine

We examined the in vitro effects of tert-butylhydroperoxide (tBu-OOH) in human bronchial muscle. tert-Butylhydroperoxide produced concentration-dependent contractions of bronchial rings (maximum effect was 56.5 +/- 9.6% of contraction by 1 mM acetylcholine; effective concentration 50% was approximately 100 microM). tert-Butylhydroperoxide (0.5 mM)-induced contraction was enhanced by epithelial removal but abolished by indomethacin (cyclooxygenase inhibitor) and zileuton (lipoxygenase inhibitor). tert-Butylhydroperoxide produced a transient rise in intracellular calcium in human cultured airway smooth muscle cells (HCASMC). The bronchial reactivity to acetylcholine and histamine was not altered by tBu-OOH. In HCASMC, tBu-OOH (0.5 mM, 30 min) increased malondialdehyde levels (MDA; from 7.80 +/- 0.83 to 26.82 +/- 1.49 nmol mg(-1) protein), accompanied by a decrease of reduced glutathione (GSH; from 16.7 +/- 2.6 to 6.9 +/- 1.9 nmol mg(-1) protein) and an increase of oxidized glutathione (from 0.09 +/- 0.03 to 0.18 +/- 0.03 nmol mg(-1) protein). N-acetylcysteine (0.3 mM) inhibited by approximately 60% the bronchial contraction resulting from tBu-OOH (0.5 mM) and protected cultured cells exposed to tBu-OOH (MDA was lowered to 19.51 +/- 1.19 nmol mg(-1) protein, and GSH content was replenished). In summary, tBu-OOH caused contraction of human bronchial muscle mediated by release of cyclo-oxygenase and lipoxygenase products without producing airways hyperreactivity. N-acetylcysteine decreases tBu-OOH-induced contraction and protects human cultured airway smooth muscle cells exposed to tBu-OOH.

Bronchodilator and anti-inflammatory activities of glaucine: In vitro studies in human airway smooth muscle and polymorphonuclear leukocytes

1. Selective phosphodiesterase 4 (PDE4) inhibitors are of potential interest in the treatment of asthma. We examined the effects of the alkaloid S-(+)-glaucine, a PDE4 inhibitor, on human isolated bronchus and granulocyte function. 2. Glaucine selectively inhibited PDE4 from human bronchus and polymorphonuclear leukocytes (PMN) in a non-competitive manner (Ki=3.4 microM). Glaucine displaced [3H]-rolipram from its high-affinity binding sites in rat brain cortex membranes (IC50 approximately 100 microM). 3. Glaucine inhibited the spontaneous and histamine-induced tone in human isolated bronchus (pD2 approximately 4.5). Glaucine (10 microM) did not potentiate the isoprenaline-induced relaxation but augmented cyclic AMP accumulation by isoprenaline. The glaucine-induced relaxation was resistant to H-89, a protein kinase A inhibitor. Glaucine depressed the contractile responses to Ca2+ (pD'2 approximately 3.62) and reduced the sustained rise of [Ca2+]i produced by histamine in cultured human airway smooth muscle cells (-log IC50 approximately 4.3). 4. Glaucine augmented cyclic AMP levels in human polymorphonuclear leukocytes challenged with N-formyl-Met-Leu-Phe (FMLP) or isoprenaline, and inhibited FMLP-induced superoxide generation, elastase release, leukotriene B4 production, [Ca2+]i signal and platelet aggregation as well as opsonized zymosan-, phorbol myristate acetate-, and A23187-induced superoxide release. The inhibitory effect of glaucine on superoxide generation by FMLP was reduced by H-89. 5. In conclusion, Ca2+ channel antagonism by glaucine appears mainly responsible for the relaxant effect of glaucine in human isolated bronchus while PDE4 inhibition contributes to the inhibitory effects of glaucine in human granulocytes. The very low PDE4/binding site ratio found for glaucine makes this compound attractive for further structure-activity studies.

New imidazo(1,2-a)pyrazine derivatives with bronchodilatory and cyclic nucleotide phosphodiesterase inhibitory activities

New imidazo[1,2-a]pyrazine derivatives have been synthesized either by direct cyclization from pyrazines or by electrophilic substitutions. The presence of electron donating groups on position 8 greatly enhances the reactivity of the heterocycle towards such reactions on position 3 of the heterocycle. The activities of these derivatives in trachealis muscle relaxation and in inhibiting cyclic nucleotide phosphodiesterase (PDE) isoenzyme types III and IV have been assessed. All compounds demonstrated significantly higher relaxant potency than theophylline. All the derivatives were moderately potent in inhibiting the type IV isoenzyme of PDE but only those with a cyano group on position 2 were potent in inhibiting the type III isoenzyme.

The effects of phosphodiesterase type 4 inhibitors on tumour necrosis factor-alpha and leukotriene B4 in a novel human whole blood assay

1. The aim of this study was to assess the inhibitory activities of phosphodiesterase type 4 (PDE4) inhibitors on tumour necrosis factor-alpha (TNF-alpha) and leukotriene B4 (LTB4) production in a novel human whole blood assay. 2. Lipopolysaccharide (LPS) stimulation of human whole blood caused a time dependent increase in TNF-alpha and prostaglandin E2 (PGE2) plasma levels. Inhibition of LPS-induced TNF-alpha by the selective PDE4 inhibitor RP73401 was proportionally enhanced with endogenous PGE2 (maximal after 24 h). In contrast, blocking endogenous PGE2 production with indomethacin in blood stimulated with LPS for 24 h decreased the potency of RP73401 to that observed with a 4 h LPS incubation. 3. Non-selective and selective PDE4 inhibitors showed greater inhibition of LPS-induced TNF-alpha after 24 h compared to 4 h. Stereoselectivity was only achieved in the 24 h method. 4. LPS-stimulation of whole blood for either 30 min or 24 h followed by N-formyl-Met-Leu-Phe (fMLP) activation resulted in low plasma LTB4 levels. Combination of both treatments resulted in a greater than 7 fold increase in plasma LTB4 levels. Inhibition of the double LPS and fMLP-activated LTB4 production was observed with non-selective and PDE4-selective inhibitors. Their LTB4 inhibitory potencies were similar to that observed in the 24 h LPS-induced TNF-alpha assay. Thus, stimulation of human whole blood with two LPS stimulations followed by fMLP gives rise to both TNF-alpha and LTB4 and their inhibition by various compounds can be assessed in the same blood sample. 5. Calcium ionophore (A23187) stimulation of whole blood resulted in plasma LTB4 levels similar to the double LPS and fMLP method. Inhibition of A23187-induced LTB4 biosynthesis was also achieved by PDE4-selective inhibitors as well as the direct 5-lipoxygenase (5-LO) inhibitor L-739,010. 6. These results confirm the anti-inflammatory properties of PDE4 inhibitors. Thus, this novel human whole blood can be used to assess the biochemical efficacy of PDE4 inhibitors in human subjects.

Phosphodiesterase III and V inhibitors on pulmonary artery from pulmonary hypertensive rats: differences between early and established pulmonary hypertension

Milrinone and 6-bromo-8(methylamino)imidazo[1,2a]pyrazine-2-carbonitrile [SCA40; phosphodiesterase (PDE) III inhibitors], zaprinast (PDE V inhibitor), and 3-isobutyl-1-methyl xanthine (IBMX; nonselective PDE inhibitor) were examined on main pulmonary arteries from control rats and rats exposed to hypoxia (10% O2; 1 or 4 weeks) to induce pulmonary hypertension. Each drug fully relaxed preparations precontracted submaximally with phenylephrine. In the absence of endothelium or the presence of the nitric oxide synthase inhibitor, L-NAME, responses to zaprinast, but not the other drugs, were reduced but not abolished. The potencies [negative log median effective concentration (EC50)] of the drugs in 4-week hypoxic rats (established pulmonary hypertension; zaprinast, 5.60; milrinone, 5.64; SCA40, 6.41; IBMX, 5.38) were not different from corresponding control values (6.05; 5.88; 6.65; 5.64) but in early pulmonary hypertension (1-week hypoxic rats), all except IBMX had reduced potency. The potency of the adenylate cyclase activator, forskolin, was reduced in arteries from both groups of rats. In early, but not established, pulmonary hypertension, arteries had inherent tone, spontaneous contractions, and diminished endothelial function. In established, but not early, pulmonary hypertension, arteries had increased overall contractile ability. It is concluded that (a) PDE V inhibitors require cyclic guanosine monophosphate (cGMP) produced by endothelial nitric oxide for optimal effect, (b) the potencies of PDE III and V inhibitors are not compromised in established pulmonary hypertension, and (c) data on pulmonary vascular function obtained in 1-week hypoxic rats do not necessarily reflect data in rats exposed to hypoxia for longer periods.

Vasorelaxant effects of SCA40 (a phosphodiesterase III inhibitor) in pulmonary vascular preparations in rats

1. The novel phosphodiesterase (PDE) inhibitor SCA40 (6-bromo-8(methylamino)imidazo[1,2-a]pyrazine-2-carbonitrile) was examined for its vasorelaxant activity on isolated pulmonary vascular preparations from rats. 2. SCA40 relaxed ring preparations of main and intralobar pulmonary artery precontracted submaximally with either phenylephrine or U46619 (thromboxane-mimetic). Based on negative log EC50 values, SCA40 was six-to 14-fold more potent than the PDE III inhibitor milrinone or the non-selective PDE inhibitor 3-isobutyl-1-methyl xanthine (IBMX). The potency of SCA40 corresponded to its reported potency as a PDE III inhibitor. 3. In isolated perfused lungs, SCA40 reversed the vasoconstriction induced by alveolar hypoxia. It was 49-fold more potent than IBMX. 4. In main pulmonary artery the vasorelaxation induced by SCA40 was not blocked by the large-conductance calcium-activated potassium channel (BKCa) inhibitors iberiotoxin (50 and 100 nmol/L) or charybdotoxin (100 and 300 nmol/L). This was in contrast to data on guinea-pig trachea, where responses to SCA40 were significantly inhibited by charybdotoxin (100 nmol/L). 5. It is concluded that opening of BKCa channels does not contribute to the pulmonary vasorelaxant effects of SCA40 in main pulmonary artery and it is likely that responses reflect the PDE III inhibitory properties of the drug. 6. It is postulated that SCA40 may be useful as a pulmonary vasodilator in disorders such as pulmonary hypertension.

Effects of fenspiride on human bronchial cyclic nucleotide phosphodiesterase isoenzymes: functional and biochemical study

We have investigated the role of human bronchial cyclic nucleotide phosphodiesterases in the effects of fenspiride, a drug endowed with bronchodilator and anti-inflammatory properties. Functional studies on human isolated bronchi showed that fenspiride (10(-6)-3 x 10(-3) M, 30 min) induced a shift to the left of the concentration-response curves for isoprenaline and sodium nitroprusside with -logEC50 values of 4.1+/-0.1 (n = 7) and 3.5+/-0.2 (n = 8), respectively. Biochemical studies were carried out on three human bronchi in which separation of cyclic nucleotide phosphodiesterase isoenzymes was performed by ion exchange chromatography followed by determination of phosphodiesterase activity with a radioisotopic method. Phosphodiesterase 4 (cyclic AMP-specific) and phosphodiesterase 5 (cyclic GMP-specific) were the major phosphodiesterase isoforms present in the human bronchial tissue. The presence of phosphodiesterase 1 (Ca2+/calmodulin-stimulated), phosphodiesterase 2 (cyclic GMP-stimulated) and, in two cases, phosphodiesterase 3 (cyclic GMP-inhibited) was also identified. Fenspiride inhibited phosphodiesterase 4 and phosphodiesterase 3 activities with -logIC50 values of 4.16+/-0.09 and 3.44+/-0.12, respectively. Phosphodiesterase 5 activity was also inhibited with a -logIC50 value of approximately 3.8. Fenspiride (< or = 10(-3) M) produced less than 25% inhibition of phosphodiesterase 1 and phosphodiesterase 2 activities. In conclusion, fenspiride is an effective inhibitor of both cyclic AMP and cyclic GMP hydrolytic activity in human bronchial tissues and this action may contribute to its airway effects.

Effects of erythromycin on chemoattractant-activated human polymorphonuclear leukocytes

1. Erythromycin (2-100 micrograms ml-1) produced a concentration-related inhibition of superoxide generation and elastase release induced by in vitro exposure of human polymorphonuclear leukocytes (PMNs) to the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (FMLP; 30 nM). 2. By contrast, erythromycin (100 micrograms ml-1) did not alter the leukotriene B4 production elicited by FMLP (30 nM; in the presence of thimerosal 20 microM) or the intracellular calcium changes promoted by FMLP (30 nM; in the absence or presence of thimerosal 20 microM). 3. These results indicate that by reducing chemoattractant-triggered release of oxidative and proteolytic mediators from human PMNs, erythromycin may have clinically useful antiinflammatory effects.

Effects of SCA40 on bovine trachealis muscle and on cyclic nucleotide phosphodiesterases

While UK-93,928 (1-[[3-(6,9-dihydro-6-oxo-9-propyl-1H-purin-2-yl)-4-ethoxyphenyl] sulfonyl]-4-methylpiperazine; 5 nM-5 microM) was devoid of relaxant activity, benzafentrine, isoprenaline, levcromakalim and SCA40 (6-bromo-8-methylaminoimidazo[1,2-a]pyrazine-2-carbonitrile) each relaxed histamine (460 microM)-precontracted bovine isolated trachealis. Each of these relaxants was antagonised by a K+-rich (80 mM) medium. Except in the case of levcromakalim, nifedipine (1 microM) offset this antagonism. Charybdotoxin (100 nM) antagonised isoprenaline in a nifedipine-sensitive manner but did not antagonise SCA40 or benzafentrine. Iberiotoxin (100 nM) did not antagonise SCA40. Acting on tissue precontracted with carbachol, SCA40 potentiated isoprenaline but did not potentiate sodium nitroprusside. While levcromakalim (1 and 10 microM) induced hyperpolarisation, SCA40 (1 and 10 microM) induced little change in the membrane potential of bovine trachealis. In trachealis preloaded with 86Rb+, levcromakalim (1 and 10 microM) promoted efflux of the radiotracer while SCA40 (1 and 10 microM) had no effect. Tested as an inhibitor of isoenzymes of cyclic nucleotide phosphodiesterase, SCA40 was most potent against the type III, less potent against the type IV and least potent against the type I isoenzyme. It is concluded that neither inhibition of phosphodiesterase type V nor the promotion of BKCa channel opening explains the tracheal smooth muscle relaxant activity of SCA40. This compound relaxes bovine tracheal smooth muscle mainly by inhibiting phosphodiesterase isoenzyme types III and IV.

Pharmacological activity of PF-904 in guinea pig in vivo, and on human bronchus and neutrophils in vitro

The effects of PF-904 (4-amino-1-ethyl-6-methylpyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide), a pyrazinothiadiazine derivative, were examined in guinea-pig airways in vivo, in human isolated bronchus and human polymorphonuclear leukocytes. PF-904 (12.5-200 mg/kg, intraduodenal) reduced bronchoconstriction in response to histamine, arachidonic acid, platelet-activating factor (PAF) and methacholine. PF-904 (50-200 mg/kg) prevented PAF-induced airways hyperreactivity and inhibited antigen-induced bronchoconstriction, airway microvascular leakage and eosinophil lung accumulation, but antigen-induced airways hyperresponsiveness was not reduced. PF-904 (1 microM-1 mM) produced complete inhibition of spontaneous (-logEC50 = 3.57+/-0.04; n = 10) and histamine-stimulated tone (-logEC50 = 3.66+/-0.07; n = 10) of human isolated bronchus. Glibenclamide (10 microM) or precontraction with KCl (80 mM) did not impede PF-904-induced bronchial relaxation. PF-904 inhibited cyclic AMP (-logIC50 = 2.83+/-0.25; n = 8) and cyclic GMP (-logIC50 = 2.90+/-0.21; n = 8) phosphodiesterase activity in human bronchus. The activity of type IV phosphodiesterase was inhibited by PF-904 (-logIC50 = 3.43+/-0.11; n= 3). PF-904 also inhibited superoxide release by N-formylmethionyl-leucyl-phenylalanine-stimulated human polymorphonuclear leukocytes, but the maximal effect was approx. 50% of that produced by rolipram (10 microM). This profile of activities of PF-904 suggests that this compound has potential therapeutic value as an anti-asthma drug.

The spasmogenic effects of vanadate in human isolated bronchus

1. Inhalation of vanadium compounds, particularly vanadate, is a cause of occupational bronchial asthma. We have now studied the action of vanadate on human isolated bronchus. Vanadate (0.1 microM-3 mM) produced concentration-dependent, well-sustained contraction. Its -logEC50 was 3.74 +/- 0.05 (mean +/- s.e.mean) and its maximal effect was equivalent to 97.5 +/- 4.2% of the response to acetylcholine (ACh, 1 mM). 2. Vanadate (200 microM)-induced contraction of human bronchus was epithelium-independent and was not inhibited by indomethacin (2.8 microM), zileuton (10 microM), a mixture of atropine, mepyramine and phentolamine (each at 1 microM), or by mast cell degranulation with compound 48/80. 3. Vanadate (200 microM)-induced contraction was unaltered by tissue exposure to verapamil or nifedipine (each 1 microM) or to a Ca2+-free, EGTA (0.1 mM)-containing physiological salt solution (PSS). However, tissue incubation with ryanodine (10 microM) in Ca2+-free, EGTA (0.1 mM)-containing PSS reduced vanadate-induced contraction. A series of vanadate challenges was made in tissues exposed to Ca2+-free EGTA (0.1 mM)-containing PSS with the object of depleting intracellular Ca2+ stores. In such tissues cyclopiazonic acid (CPA; 10 microM) prevented Ca2+-induced recovery of vanadate-induced contraction. 4. Tissue incubation in K+-rich (80 mM) PSS, K+-free PSS, or PSS containing ouabain (10 microM) did not alter vanadate (200 microM)-induced contraction. Ouabain (10 microM) abolished the K+-induced relaxation of human bronchus bathed in K+-free PSS. This action was not shared by vanadate (200 microM). The tissue content of Na+ was increased and the tissue content of K+ was decreased by ouabain (10 microM). In contrast, vanadate (200 microM) did not alter the tissue content of these ions. Tissue incubation in a Na+-deficient (25 mM) PSS or in PSS containing amiloride (0.1 mM) markedly inhibited the spasmogenic effect of vanadate (200 microM). 5. Vanadate (200 microM)-induced contractions were markedly reduced by tissue treatment with each of the protein kinase C (PKC) inhibitors H-7 (10 microM), staurosporine (1 microM) and calphostin C (1 microM). Genistein (100 microM), an inhibitor of protein tyrosine kinase, also reduced the response to vanadate. 6 Vanadate (0.1-3 mM) and ACh (1 microM- 3 mM) each increased inositol phosphate accumulation in bronchus. Such responses were unaffected by a Ca2+-free medium either alone or in combination with ryanodine (10 microM). 7. In human cultured tracheal smooth muscle cells, histamine (100 microM) and vanadate (200 microM) each produced a transient increase in intracellular Ca2+ concentration ([Ca2+]i). 8. Intracellular microelectrode recording showed that the contractile effect of vanadate (200 microM) in human bronchus was associated with cellular depolarization. 9. It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store. The Ca2+ release mechanism involves both the production of inositol phosphate second messengers and inhibition of Ca-ATPase. The activation of PKC plays an important role in mediating vanadate-induced contraction at values of [Ca2+]i that are close to basal.

Inhibitory effects of N-acetylcysteine on superoxide anion generation in human polymorphonuclear leukocytes

It has been suggested that reactive oxygen species released by activated polymorphonuclear leukocytes (PMN) in man is one mechanism of tissue injury. Therapeutic action aimed at increasing antioxidant defence mechanisms is still a clinical challenge. This study examines the activity of N-acetylcysteine, a known antioxidant, in the protection of PMN exposed in-vitro to the chemoattractant peptide fMet-Leu-Phe (FMLP), the protein kinase C activator phorbol myristate acetate or the lipid peroxidation promoter t-butyl hydroperoxide. FMLP (3-300 nM) and phorbol myristate acetate (160 pm-160 nM) induced concentration-related superoxide anion generation. Pre-treatment with N-acetylcysteine (33-333 microM) resulted in concentration-related inhibition of superoxide production induced by FMLP (30 nM) or phorbol myristate acetate (16 nM);-log IC50 values were 3.97 +/- 0.07 and 3.91 +/- 0.10, respectively. Changes in intracellular calcium ion concentration ([Ca2+]i) induced by FMLP (30 nM) were studied in fura-2-loaded human PMN. FMLP produced a transient calcium response, i.e. a peak followed by decay to a residual value above baseline. N-Acetylcysteine (333 microM) did not affect either basal [Ca2+]i values or changes in [Ca2+]i values after treatment with FMLP. Activation by phorbol myristate acetate caused a reduction in glutathione levels from 5.94 +/- 0.86 (control) to 1.84 +/- 0.51 nmol/3 x 10(6) cells (P < 0.05 compared with control). Pre-treatment with N-acetylcysteine (333 microM) fully reversed the reduction in glutathione levels induced by phorbol myristate acetate (4.83 +/- 0.68 nmol/3 x 10(6) cells; P > 0.05 compared with control). Exposure to t-butyl hydroperoxide (0.5 mM, 30 min) markedly increased malondialdehyde levels (from 0.03 +/- 0.02 to 0.73 +/- 0.07 nmol/10(6) cells), and index of lipid peroxidation. Malondialdehyde levels were significantly reduced in PMN treated with N-acetylcysteine (333 microM; 0.55 +/- 0.04 nmol/10(6) cells; P < 0.05 compared with untreated cells exposed to t-butyl hydroperoxide). In conclusion, N-acetylcysteine reduces superoxide generation in response to FMLP and phorbol myristate acetate and partially protects against lipid peroxidation in PMN from man. The protection afforded by N-acetylcysteine is not related to alteration of the intracellular calcium signal but might be effected by replenishment of the intracellular glutathione levels.

SCA 40: studies of the relaxant effects on cryopreserved human airway and vascular smooth muscle

1. 6-Bromo-8-methylaminoimidazol[1,2-a]pyrazine-2carbonitrile (SCA 40) has been claimed to induce relaxation in guinea-pig trachea by opening high conductance, calcium-activated potassium (BKCa) channels. The mechanism of action of SCA 40 has now been further investigated in ring preparations from cryopreserved human airway and vascular smooth muscle preparations in vitro. 2. Human bronchi with spontaneous tone relaxed in response to SCA 40 in a biphasic way. A high affinity component (pD2 8.61 +/- 0.21; mean +/- s.e.mean) accounted for 30% of the response and a low affinity component (pD2 6.53 +/- 0.14) for the remaining 70%. In contrast, in bronchi contracted with carbachol, 1 microM, the concentration-response curve to SCA 40 was monophasic and yielded a pD2 of 6.31 +/- 0.29. 3. SCA 40 relaxed pulmonary and mesenteric arteries and peripheral veins which had been precontracted by 10 nM U46619 nearly completely and in a monophasic way; the pD2 values were 6.37 +/- 0.08, 6.17 +/- 0.15 and 5.45 +/- 0.25, respectively. 4. Lemakalim, an opener of ATP-dependent potassium (KATP) channels, also relaxed human bronchi under spontaneous tone and the vascular tissues. NS 1619, a recognised opener of BKca channels, was inactive up to 10 microM on bronchial and vascular tissues. 5. The SCA 40-induced relaxation of human bronchi was reduced concentration-dependently in the presence of high potassium chloride (20 and 80 mM). However, in the presence of 80 mM KCl and nifedipine, 30 nM, SCA 40 fully relaxed the remaining contractile response with pD2 values of 8.08 +/- 0.13 and 5.27 +/- 0.13 for the high and low affinity component, respectively. 6. Relaxation responses to SCA 40 in human bronchi were resistant to blockade by glibenclamide at concentrations up to 10 microM (which blocked the relaxant response to lemakalim), quinine (30 microM), apamin (100 nM), tetraethylammonium (0.1-1 mM) and charybdotoxin (10-100 nM), thus excluding the involvement of a variety of K+ channels including KATP and KCa channels. 7. In bronchi contracted with carbachol, 1 microM, the nature of the interaction between SCA 40 and the beta 2-adrenoceptor agonist, salbutamol, was synergistic. 8. These experiments establish that SCA 40 is a potent relaxant of human bronchial smooth muscle manifesting spontaneous tone. A low affinity relaxant component has its counterpart in the relaxation seen in both human arterial and venous smooth muscle. The consensus of the evidence suggests that K+ channel opening is not the basis of the relaxant response to SCA 40. Furthermore, BKCa channels appear to be of minor importance in the regulation of human airway smooth muscle tone. Our data suggest that inhibition of an adenosine 3':5'-cyclic monophosphate phosphodiesterase may contribute, at least to the low affinity relaxant component of SCA 40. However, the exact mechanism mediating the SCA 40-induced relaxation of human airways remains to be defined.