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A Robichaud

Publications and source records attributed to A Robichaud.

At least 19 recordsLinked to original sources
PubMed2002

Assessing the emetic potential of PDE4 inhibitors in rats.

1. Type 4 phosphodiesterase (PDE4) inhibitors mimic the pharmacological actions of alpha(2)-adrenoceptor antagonists. This has been postulated as the mechanism by which PDE4 inhibitors induce emesis and was also demonstrated by their ability to reverse xylazine/ketamine-induced anaesthesia. We further characterized this latter effect since it appears to reflect the emetic potential of PDE4 inhibitors. 2. Selective inhibitors of PDE 1, 2, 3, 4 and 5 were studied in rats, on the duration of anaesthesia induced by the combination of xylazine (10 mg kg(-1), i.m.) and ketamine (10 mg kg(-1), i.m.). PMNPQ (i.e. 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline) - PDE4 inhibitor: 0.01 - 3 mg kg(-1)), like MK-912 (alpha(2)-adrenoceptor antagonist: 0.01 - 3 mg kg(-1)), dose-dependently reduced the duration of anaesthesia. In contrast, vinpocetine (PDE1 inhibitor), EHNA (PDE2 inhibitor), milrinone (PDE3 inhibitor) and zaprinast (PDE5 inhibitor) had no significant effect at the doses tested (1 - 10 mg kg(-1)). Analysis of plasma and cerebrospinal fluid (CSF) of treated animals confirmed the absorption and distribution to the brain of the inactive inhibitors. 3. Neither MK-912 (3 mg kg(-1)) nor PMNPQ (0.1 - 1 mg kg(-1)) altered the duration of anaesthesia induced via a non-alpha(2)-adrenoceptor pathway (sodium pentobarbitone 50 mg kg(-1), i.p.). 4. Central NK(1) receptors are involved in PDE4 inhibitor-induced emesis. Consistently, [sar(9), Met(O(2))(11)]-substance P (NK(1) receptor agonist, 6 microg i.c.v.) reduced the duration of anaesthesia induced by xylazine/ketamine. 5. In summary, this model is functionally coupled to PDE4, specific to alpha(2)-adrenoceptors and relevant to PDE4 inhibitor-induced emesis. It therefore provides a novel way of evaluating the emetic potential of PDE4 inhibitors in rats.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

Localization of phosphodiesterase-4 isoforms in the medulla and nodose ganglion of the squirrel monkey.

Pre-clinical and clinical studies are currently underway to evaluate the potential of phosphodiesterase-4 (PDE4) inhibitors for the treatment of chronic obstructive pulmonary disease and other inflammatory conditions of the airways. The most common side effect associated with this class of compounds is emesis. The squirrel monkey provides a model for evaluating the efficacy of PDE4 inhibitors and their emetic potential. The distribution of three PDE4 isoforms (A, C and D) has been investigated in the squirrel monkey medulla and nodose ganglion to determine which isoform(s) could be responsible for the emetic adverse effects. The distribution of PDE4 isoforms was delineated using immunohistochemistry with antibodies specific for PDE4A, PDE4C and PDE4D and by in situ hybridization with isoform-selective riboprobes. PDE4A was present in the medulla where expression was mostly restricted to glial cells and the vasculature. PDE4C was not detected in either the medulla or nodose ganglion. Finally, the PDE4D isoform was localized to neurons in the nodose ganglion and found through many structures of medulla including the area postrema, neurons of the nucleus tractus solitarius and locus coeruleus. These data are consistent with a role for PDE4D in the emetic response.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

PDE4 inhibitors induce emesis in ferrets via a noradrenergic pathway.

The objective of this work was to assess the role of alpha(2)-adrenoceptors in emesis induced by inhibitors of type 4 phosphodiesterase (PDE4) in ferrets. Pre-treatment with yohimbine, MK-912 or MK-467 (alpha(2)-adrenoceptor antagonists) caused sudden and unexpected vomiting. In contrast, clonidine (alpha(2)-adrenoceptor agonist) did not induce emesis at doses ranging from 62.5-250 microg/kg s.c. At the dose of 250 microg/kg, clonidine also provided protection against emesis induced by the PDE4 inhibitors, PMNPQ (i.e. 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline, CT-2450 and R-rolipram. It was postulated that PDE4 inhibitors trigger emesis by mimicking the pharmacological actions of alpha(2)-adrenoceptor antagonists. This hypothesis was strengthened by the demonstration that PDE4 inhibitors can reverse the hypnotic effect of an alpha(2)-adrenoceptor mediated anaesthetic regimen in rats and ferrets. Similar to alpha(2)-adrenoceptor antagonists, PMNPQ, R-rolipram and S-rolipram dose-dependently decreased the duration of anaesthesia in rats injected with the combination xylazine/ketamine. While subcutaneous injections of CT-2450 (3-30 mg/kg) were without effect, a central infusion (6 microg i.c.v.) decreased the duration of anaesthesia. These studies suggest that the ferret is an appropriate model to study emesis induced by PDE4 inhibitors and that these compounds trigger the emetic reflex via a noradrenergic pathway, mimicking the pharmacological actions of a pre-synaptic alpha(2)-adrenoceptor inhibition.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

The next generation of PDE4 inhibitors.

A number of highly potent PDE4 inhibitors are being developed for the treatment of asthma, chronic obstructive pulmonary disease, rheumatoid arthritis, multiple sclerosis and Crohn's disease. Cilomilast (Ariflo, SB 207499, SmithKline Beecham), the most advanced member of the class in Phase III clinical trials, was reported to have a limited therapeutic window. Other inhibitors with improved profiles in preclinical models are entering into (or are in) clinical trials. The recent developments in understanding PDE4 catalysis, inhibitor binding and their emetic response should facilitate the design of the next generation of PDE4 inhibitors.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2000

Selective potentiating effect of RS14203 on a serotoninergic pathway in anesthetized rats.

The usefulness of selective inhibitors of type 4 phosphodiesterase (PDE4) in the treatment of inflammation and pulmonary diseases is limited by their side effects: nausea and vomiting. We studied the effect of three structurally diverse PDE4 inhibitors on the vagal nerve afferent and efferent fibers in anesthetized rats. The effects of RS14203, (R)-rolipram, and CT-2450 were evaluated on the von Bezold-Jarisch reflex (vagal afferent fibers) and in a model of vagal electrical stimulation (vagal efferent fibers). All three PDE4 inhibitors were administered at 1, 10, or 100 microg/kg (iv) 15 min prior to the induction of bradycardia by an iv injection of 2-methyl-5-HT (von Bezold-Jarisch reflex) or by vagal electrical stimulation. At 100 microg/kg, RS14203 significantly potentiated the 2-methyl-5-HT response. No statistically significant effects were observed with (R)-rolipram or CT-2450 at the doses studied. RS14203, (R)-rolipram, or CT-2450 (1-100 microg/kg iv) did not affect the bradycardia induced by vagal electrical stimulation. Consequently, our results show that RS14203 selectively facilitates serotoninergic neurotransmission in vagal afferent fibers. The emetic action of RS14203 may be mediated by this mechanism.

Afferent Pathways↗
PubMed1999

Substituted furans as inhibitors of the PDE4 enzyme.

The synthesis and in vitro activity of a series of substituted furans as a novel structural class of PDE4 inhibitors is described. Comparison of emetic threshold with known PDE4 inhibitors is presented.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

Emesis induced by inhibitors of type IV cyclic nucleotide phosphodiesterase (PDE IV) in the ferret.

Emesis induced by inhibitors of type IV cyclic nucleotide phosphodiesterase (PDE IV) has been investigated in the ferret. The PDE IV inhibitors studied were: RS14203, R-rolipram and CT-2450 (i.e. (R)-N-[4-[1-(3-cyclopentyloxy-4-methoxyphenyl)-2-(4-pyridyl)ethyl]phenyl ]N'-ethylurea), in addition to the less active enantiomers S-rolipram and CT-3405. Following oral administrations, different emetic profiles were observed with time. Emesis induced by RS14203 exhibited a dose-response relationship but no such relationship was seen for R-rolipram or CT-2450. The incidence of emesis was positively influenced by the dose of PDE IV inhibitors administered, allowing a rank order of potency: RS14203 > R-rolipram > S-rolipram > CT-2450 > CT-3405. PDE IV inhibitor-induced emesis was abolished by the tachykinin NK1 receptor antagonist, CP-99,994. No peripheral release of substance P by PDE IV inhibitors seems to be involved in triggering the emetic reflex since L-743,310, which only has peripheral NK1 receptor antagonist activity, was without effect. The implication of 5-HT3 receptors in PDE IV inhibitor-induced emesis was variable. Our results suggest that the PDE IV inhibitors studied are mixed peripheral-central emetogens. PDE IV inhibition itself could be plausible mechanism of action of these agents. However, whether emesis is mediated via a specific isoform of PDE IV remains to be established.

Animals↗
PubMed1998

Phosphodiesterase expression in human epithelial cells.

Epithelial cells play a critical role in airway inflammation and have the capacity to produce many inflammatory mediators, including bioactive lipids and proinflammatory cytokines. Intracellular levels of cAMP and cGMP are important in the control of inflammatory cell function. These cyclic nucleotides are inactivated via a family of phosphodiesterase (PDE) enzymes, providing a possible site for drug intervention in chronic inflammatory conditions. We studied the expression of PDE activity in an epithelial cell line (A549) and in primary human airway epithelial cells (HAECs). We measured PDE function using specific inhibitors to identify the PDE families present and used RT-PCR to elucidate the expression of PDE isogenes. Both A549 cells and HAECs predominantly expressed PDE4 activity, with lesser PDE1, PDE3, and PDE5 activity. RT-PCR identified HSPDE4A5 and HSPDE4D3 together with HSPDE7. Inhibition of PDE4 and PDE3 reduced secretion by these cells. Epithelial PDE may be an important target for PDE4 inhibitors in the development of the control of asthmatic inflammation, particularly when delivered via the inhaled route.

1-Methyl-3-isobutylxanthine↗
PubMed1998

Inhaled corticosteroids increase interleukin-10 but reduce macrophage inflammatory protein-1alpha, granulocyte-macrophage colony-stimulating factor, and interferon-gamma release from alveolar macrophages in asthma.

We determined the effect of inhaled corticosteroid, budesonide, on the release of the anti-inflammatory cytokine, interleukin-10 (IL-10), and of pro-inflammatory cytokines, macrophage inflammatory protein-1alpha (MIP-1alpha), interferon-gamma (IFN-gamma), and granulocyte-macrophage colony-stimulating factor (GM-CSF), from blood monocytes and alveolar macrophages of mild asthmatic subjects in a double-blind, cross-over, placebo-controlled study. Budesonide reduced bronchial hyperresponsiveness and improved baseline FEV1. Alveolar macrophages were obtained by bronchoalveolar lavage performed at the end of each treatment phase. IL-10 from blood monocytes was not altered, but both IL-10 mRNA and protein expression from alveolar macrophages stimulated by lipopolysaccharide and IL-1beta were increased after corticosteroid therapy. By contrast, alveolar macrophages released significantly less MIP-1alpha, IFN-gamma, and GM-CSF after steroid treatment. In comparison to alveolar macrophages from normal nonasthmatic volunteers, those from asthmatic patients released more MIP-1alpha, IFN-gamma, and GM-CSF but lower amounts of IL-10 particularly at baseline and after IL-1beta stimulation. The ability of steroids to inhibit pro-inflammatory cytokines but to enhance the anti-inflammatory cytokine such as IL-10 may contribute to their beneficial actions in asthma. Asthma is characterized by alveolar macrophages exhibiting both an enhanced capacity to release pro-inflammatory cytokines and a reduced capacity to produce IL-10.

Administration, Inhalation↗
PubMed1998

Effect of inhibition of nitric oxide synthase on Pseudomonas aeruginosa infection of respiratory mucosa in vitro.

We studied the effect of the nitric oxide synthase (NOS) inhibitor asymmetric dimethyl arginine (ADMA) and the inactive enantiomer N G-methyl-D-arginine (D-NMMA) on Pseudomonas aeruginosa infection of the respiratory mucosa in nasal turbinate organ cultures. We also investigated the effect of P. aeruginosa culture filtrate on the expression of inducible NOS (iNOS) messenger RNA (mRNA) by an epithelial cell line (A549). Organ cultures were preincubated with ADMA (0.1 to 4 x 10(-4) M) or D-NMMA (2 x 10(-4) M) for 30 min prior to bacterial infection. Infected organ cultures (8 h) had significantly (P <= 0.05) greater epithelial damage and fewer ciliated and unciliated cells than did control cultures. There was an increased level of nitrite in the medium feeding infected organ cultures as compared with control cultures. ADMA significantly (P <= 0.05) reduced both bacterially induced epithelial damage and loss of ciliated cells in a concentration-dependent manner. D-NMMA did not influence the effect of P. aeruginosa infection of the mucosa. ADMA, but not D-NMMA, significantly (P <= 0.04) reduced total bacterial numbers adherent to the respiratory mucosa. P. aeruginosa culture filtrates (24 h and 36 h) significantly (P = 0.02) increased iNOS with respect to glyceraldehyde-3-phosphate dehydrogenase mRNA expression. These results show that P. aeruginosa stimulates iNOS expression by a cell line and NO production by an organ culture. ADMA reduces mucosal damage and loss of ciliated cells, which suggests that NO may be a mediator of epithelial damage caused by P. aeruginosa.

Arginine↗
PubMed1997

Human airway smooth muscle cells express and release RANTES in response to T helper 1 cytokines: regulation by T helper 2 cytokines and corticosteroids.

RANTES is a basic 8-kDa polypeptide of the C-C chemokine subfamily with strong chemotactic activity for eosinophils, lymphocytes, and monocytes. We determined the regulation of RANTES production by human airway smooth muscle cells in culture. While TNF-alpha, but not IFN-gamma, increased RANTES mRNA expression and protein release, the combination of TNF-alpha and IFN-gamma caused a greater degree of expression and release in a time- and dose-dependent manner. Sequential treatment of airway smooth muscle cells with TNF-alpha and IFN-gamma showed that IFN-gamma sensitized the cells to the stimulatory effect of TNF-alpha. Using a modified Boyden chamber technique, RANTES separated by reverse-phase liquid chromatography from cell culture supernatants of airway smooth muscle cells stimulated by TNF-alpha and IFN-gamma showed a strong chemoattractant effect on human eosinophils, an effect inhibited by an anti-RANTES Ab. RANTES production induced by TNF-alpha and IFN-gamma was inhibited partly by the Th2-derived cytokines, IL-4, IL-10, and IL-13, as well as by dexamethasone. Our studies indicate that, in addition to contractile responses and mitogenesis, airway smooth muscle cells have synthetic and secretory potential with the release of RANTES. They may participate in chronic airway inflammation by interacting with both Th1- and Th2-derived cytokines to modulate chemoattractant activity for eosinophils, activated T lymphocytes, and monocytes/macrophages.

Adrenal Cortex Hormones↗
PubMed1996

Expression of RANTES in human airway epithelial cells: effect of corticosteroids and interleukin-4, -10 and -13.

RANTES is a C-C chemokine with strong chemoattractant and activating properties for eosinophils, basophils and T lymphocytes. We investigated the expression of RANTES in human airway epithelial cells and its modulation. Epithelial cells obtained from tracheas of donor lungs were stimulated with interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) or with a mixture of the three cytokines ('cytomix'). Levels of mRNA and protein were assayed by Northern blot and radioimmunoassay, respectively. Each individual cytokine produced a small increase in RANTES protein: IL-1 beta 24 +/- 1 pM, TNF-alpha 13 +/- 7 pM and IFN-gamma 29 +/- 7 pM, but cytomix increased protein to 236 +/- 22 pM (P < 0.002) and mRNA expression by > 20-fold (P < 0.002). Both RANTES protein and mRNA expression were inhibited by dexamethasone (10(-6) M) (38 +/- 5%, P < 0.05 and 55 +/- 8%, P < 0.007, respectively), and by IL-4 (42 +/- 7%, P < 0.03 and 19 +/- 1%, not significant, respectively). No inhibitory effect was observed with IL-10 or IL-13. We also demonstrated in vivo expression of RANTES protein by epithelial cells in human airways using immunohistochemistry. Our data show that human airway epithelial cells can be stimulated to express and release RANTES, an effect that is inhibited by corticosteroids and IL-4, but not by IL-10 and IL-13.

Blotting, Northern↗
PubMed1996

Inhibition of inducible nitric oxide synthase expression by interleukin-4 and interleukin-13 in human lung epithelial cells.

Nitric oxide produced by the inducible enzyme, nitric oxide synthase (iNOS), is implicated in immunological and inflammatory processes. We determined the effects of T-helper (Th)2-derived cytokines on the induction of iNOS from an epithelial A549 cell line and human airway epithelial cells stimulated by a mixture of interleukin-1 beta (IL-1 beta), interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha). Interleukin-4 (IL-4) and interleukin-13 (IL-13) but not interleukin-10 (IL-10) inhibited both iNOS mRNA expression and nitrite release in A549 cells. On human airway epithelial cells, IL-4 and IL-13 reduced iNOS mRNA expression. Dexamethasone also inhibited both iNOS expression and nitrite release. Th2 cytokines, IL-4 and IL-13, inhibit iNOS upregulation by Th1 cytokines, indicating an important reciprocal role of Th1 and Th2 T-cell subsets on lung epithelial cells.

Blotting, Northern↗
PubMed1996

Microanatomy of secretory granule release from guinea pig tracheal goblet cells.

The microanatomy of mucin granule release from epithelial goblet cells has been investigated in guinea pig tracheae. Using a tannic acid arrest procedure, granule release under basal conditions and after high K+ or acetylcholine (ACh) application was arrested and a variety of granule fusion sites were identified in ultrathin sections and freeze-fracture replicas. Rather than there being subclasses of secretory cells containing either electron-lucent granules (indicative of mucin) or smaller electron-dense (serous) granules, the majority of secretory cells in both control and treated groups contained granules with an electrondense core surrounded by an electron-lucent region. Granule release sites were of three principal types: (1) simple exocytosis, where the membranes of single granules fused directly with the plasma membrane to give an "omega" profile; (2) compound exocytosis, where granule membranes, fused together intracellularly, were found in continuity with the plasma membrane; and (3) apocrine-like secretion, which involved the loss of the central apical mass of granules together with elements of the cell cytoplasm. In treated preparations, there was an increase in the number of cells exhibiting fusion sites; the percentage showing simple fusions fell from 82% to 59% (with ACh) and 57% (with KCl), whereas the percentage of cells exhibiting compound and apocrine-like secretion increased. Dense cores were frequently retained at the sites of fusion and, despite the expansive decondensation of mucin known to occur, there was also evidence of some retention of the electron-lucent material.

Acetylcholine↗
PubMed1995

Expression of inducible nitric oxide synthase mRNA in Brown Norway rats exposed to ozone: effect of dexamethasone.

We studied the effects of ozone exposure and dexamethasone on inducible nitric synthase (iNOS) gene expression in Brown Norway rats in vivo. Using a murine iNOS cDNA probe, we detected a 4.4 kb iNOS mRNA by Northern analysis in rat lung. The iNOS signal was weak in control lungs, but increased in lungs exposed to ozone (3 ppm, 6 h). Ozone-induced iNOS mRNA expression was time-dependent, with maximal expression at 2 h, declining by 8 h and increasing again at 24 h postexposure. Dexamethasone significantly reduced the iNOS mRNA expression in the lungs of both controls and ozone-exposed rats. These results demonstrate that ozone inhalation induces iNOS expression in vivo, thus providing evidence at the molecular level for the possible involvement of nitric oxide generation in ozone-induced pulmonary inflammation or lung damage.

Administration, Inhalation↗
PubMed1995

Plasma atrial natriuretic peptide during spontaneous bronchoconstriction in asthmatics.

The aim of this work was to establish the role of endogeneous ANP during a spontaneous asthma attack. Forced expiratory lung volume in 1 s (FEV1), cardiovascular parameters, and plasma ANP, cAMP, and cGMP were measured for 60 min before and 10 min after treatment with a bronchodilator in 10 asthmatics. The results show that in the presence of moderate bronchoconstriction, FEV1 was 54 +/- 3% (+/-SE); ANP levels initially were slightly elevated at 47 +/- 10 pg/ml and decreased to 26 +/- 3 pg/ml (p < 0.05) over 60 min, with no change in FEV1. Following salbutamol inhalation, FEV1 increased to 77 +/- 4% with no change in ANP. We conclude that endogenous ANP does not act as a bronchodilator in asthmatics with moderate bronchospasm.

Acute Disease↗
PubMed1994

Negative chronotropic effect of the atrial natriuretic peptide in an anesthetized dog model.

The effects of atrial natriuretic peptide (ANP) on heart rate and on the chronotropic response induced by angiotensin II were evaluated. The action of angiotensin II, injected into the sinus node artery, on heart rate was determined in anaesthetized and vagotomized dogs pretreated with beta-adrenoceptor antagonist (n = 9), before and after the infusion of physiological and pharmacological doses (10 and 50 ng/kg per min) of ANP. ANP plasma concentrations were determined by radioimmunoassay. Compared to the baseline concentration values (117 +/- 3 pg/ml), a slight increase was produced by the lower dose (293 +/- 45 pg/ml), whereas a significant augmentation was noted with the higher dose of ANP (1024 +/- 255 pg/ml). The basal heart rate and mean systemic arterial pressure were decreased (26.3 and 13.5%) during the intravenous infusion of the physiological dose of the peptide and were significantly reduced (32.5 and 29.2%, P < 0.05) by the administration of the pharmacological dose of ANP. Angiotensin II had a positive chronotropic effect (29 +/- 3 beats/min) that was significantly inhibited by the pharmacological dose of ANP. Our results suggest that ANP might have a role in the control of heart rate.

Adrenergic beta-Antagonists↗