RP 58802B, a long-acting beta 2-adrenoceptor agonist: assessment of antiasthma activity in the guinea-pig in vivo

2-Phenethylamines in Medicinal Chemistry: A Review

A concise review covering updated presence and role of 2-phenethylamines in medicinal chemistry is presented. Open-chain, flexible alicyclic amine derivatives of this motif are enumerated in key therapeutic targets, listing medicinal chemistry hits and appealing screening compounds. Latest reports in discovering new bioactive 2-phenethylamines by research groups are covered too.

Flexible low-cost system for small animal aerosol inhalation exposure to drugs, proteins, inflammatory agents, and infectious agents

The design for a simple, low-cost aerosol generation system for rodent inhalation studies is described here. This system is appropriate for low biohazard–level agents. In this study, two biosafety level 2 agents, Pasturella pneumotropica and Pseudomonas aeruginosa, were tested successfully. This system was also used to immunize mice and guinea pigs in ovalbumin-based models of pulmonary inflammation. This design is appropriate for studies with limited budgets and lower-level biosafety containment.

Report of the 2006 RSPCA/UFAW Rodent Welfare Group meeting

The RSPCA/UFAW Rodent Welfare Group holds a one-day meeting every autumn to discuss current welfare research and to exchange views on rodent welfare issues. A key aim of the group is to encourage people to think about the lifetime experience of laboratory rodents, ensuring that every potential influence on their well-being has been reviewed and refined. Speakers at the 2006 meeting presented preliminary findings of ongoing studies and discussed regulatory updates. Topics included the housing and husbandry of mice and rats, refining the use of rodents in asthma research, good practice for the euthanasia of rodents using carbon dioxide and achieving reduction by sharing genetically modified mice.

Inhaled procaterol inhibits histamine-induced airflow obstruction and microvascular leakage in guinea-pig airways with allergic inflammation

BACKGROUND

Beta2-adrenoceptor agonists (beta2-agonists) are shown to inhibit airway microvascular leakage in experimental animals. This effect may change in animals with chronic airway inflammation.

OBJECTIVE

We examined whether inhaled beta2-agonists inhibit microvascular leakage in guinea-pig airways with chronic allergic inflammation.

METHODS

Three weeks after the sensitization with ovalbumin (OA; 6 mg/mL), each guinea pig was challenged with inhaled OA once a day for 1 or 3 weeks. Control animals without sensitization with OA also inhaled vehicle for OA (saline) for 3 weeks. One day after the last challenge, different doses of inhaled procaterol (1, 3 or 10 microg/mL) or vehicle was given to animals for 10 min after an anaesthesia. Fifteen minutes after the end of inhalation, the animals were given i.v. Evans blue dye (EB dye; 20 mg/kg), a marker of microvascular leakage, and then i.v. histamine (3 or 30 microg/kg) or vehicle. Lung resistance, a parameter of airflow obstruction, was measured for 6 min and the lungs were removed to calculate the amount of extravasated EB dye into the airways.

RESULTS

A significant increase in eosinophil infiltration into the airways was seen in sensitized and challenged animals compared with control animals without sensitization. Among animals receiving antigenic exposure for either 0 (control), 1 or 3 weeks, 10 microg/mL procaterol significantly inhibited 30 microg/kg histamine-induced increase in EB dye extravasation to a similar degree (ranged from 28.7 to 69.8% inhibition) as well as that in lung resistance (more than 90% inhibition in all groups). The minimal dose of procaterol to inhibit 3 microg/kg histamine-induced microvascular leakage was not different between nonsensitized control animals and those sensitized and challenged for 3 weeks at all airway levels.

CONCLUSION

Inhaled beta2-adrenoceptor agonists may be also potent in attenuating microvascular leakage even in the airways with chronic allergic inflammation.

Cardiac inotropes inhibit the oedema caused by nifedipine in rabbit skin

1. We have shown previously that exposing the rat or rabbit microcirculation to nifedipine increases the permeability of the post-capillary venule, the segment of microcirculation that is known to control inflammatory oedema. 2. In the present study modulation by the inotropes isoprenaline, dopexamine and dobutamine of nifedipine-induced oedema was examined in the rabbit skin microcirculation by measuring the localised leakage of 125I-radiolabelled albumin after the i.d. injection of agents. 3. Coinjection of isoprenaline (10(-11) moles per site), dopexamine (10(-10) moles per site) or dobutamine (10(-10) moles per site) suppressed significantly (P < 0.05) the oedema response to nifedipine (10(-7.2) moles per site) in the rabbit dorsal skin microcirculation. 4. To confirm the oedema suppresser effect of the inotropes, dopexamine or dobutamine were also coinjected with histamine 10(-8) + PGE2 10(-10) moles per site, or bradykinin 10(-10) + PGE2 10(-10) moles per site. Both inotropes at 10(-10) moles per site reduced significantly (P < 0.05) the leakage of albumin caused by bradykinin + PGE2 and histamine + PGE2. 5. When measured by laser Doppler, basal local skin blood flow increased at 30 min by 57 +/- 14% with nifedipine 10(-7.2) moles per site and 15 +/- 11% with isoprenaline 10(-11) moles per site. Isoprenaline did not suppress the blood flow response to nifedipine, the response to coinjection being 68 +/- 11%. 6. Oedema caused by nifedipine can be suppressed by low concentrations of beta-adrenergic agonists that do not suppress the blood flow response to nifedipine. This suggests that cardiac inotropes can influence non-inflammatory changes in microvascular permeability.

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.

Some pharmacodynamic aspects on long-acting beta-adrenoceptor agonists

1. Formoterol and salmeterol are the first members of a new generation of long-acting beta(2)-adrenoceptor agonists for inhalation. The discovery of the long effect duration of formoterol was made by chance, while the development of salmeterol appeared to follow a purposeful research strategy. 2. Preclinical evaluation predictive of the clinical duration of effect of long-acting bronchodilators is not straightforward. Experiments in vitro may give false positive results, while experiments in vivo may show false negative results. 3. Once the principle of a long duration of effect was established, a number of novel long-acting beta(2)-adrenoceptor agonists of various chemical structure have emerged. 4. There are two alternative models for the explanation of the long duration of effect: the exosite binding explaining the mode of action of salmeterol, and the more general diffusion microkinetic model applicable for both formoterol and salmeterol. 5. Long-acting beta-adrenoceptor agonists with a relatively low efficacy like salmeterol may, under certain circumstances, inhibit competitively the relaxing effect of agonists with higher efficacy like formoterol and salbutamol. 6. Like all other beta(2)-adrenoceptor agonists in current clinical use, formoterol and salmeterol comprise racemic mixtures. Only the RR- and R-enantiomers are pharmacologically active. The experimental compounds TA-2005 and picumeterol have been developed as pure RR- and R-enantiomers, respectively.

Effects of selective phosphodiesterase inhibitors on platelet-activating factor- and antigen-induced airway hyperreactivity, eosinophil accumulation, and microvascular leakage in guinea pigs

There is currently interest in the potential use of selective inhibitors of cyclic nucleotide phosphodiesterases (PDE) in the treatment of asthma. In this study we examined the effects of three selective PDE inhibitors, milrinone (PDE III), rolipram (PDE IV) and zaprinast (PDE V), on the broncoconstriction produced by antigen and histamine, the airway hyperreactivity and microvascular leakage after aerosol exposure to platelet-activating factor (PAF) and antigen, and the antigen-induced eosinophil infiltration in guinea-pig lung. Inhaled rolipram (0.01-10 mg ml-1) inhibited dose dependently the bronchospasm produced by aerosol antigen (5 mg ml-1) an anaesthetised, ventilated guinea-pigs. Rolipram (10 mg ml-1) produced maximal inhibition of antigen-induced bronchoconstriction but only partial inhibition of the response to aerosol histamine (1 mg ml-1). Milrinone and zaprinast (each 10 mg ml-1) showed weak, or no, inhibitory effects against bronchoconstriction produced by aerosol antigen or histamine. Pretreatment with rolipram (10 mg kg-1, i.p.) prevented airway hyperreactivity to histamine which develops 24 h after exposure of conscious guinea-pigs to aerosol PAF (500 micrograms ml-1) or antigen (5 mg ml-1). The pulmonary eosinophil infiltration obtained with 24 h of antigen-exposure was inhibited by rolipram. In contrast, milrinone and zaprinast (each 10 mg kg-1, i.p.) failed to reduce either the airway hyperreactivity of the eosinophil accumulation in these animals. Rolipram (1-10 mg ml-1) reduced the extravasation of Evans blue after aerosol PAF (500 micrograms ml-1) at all airway levels while a lower dose (0.1 mg ml-1) was only effective at intrapulmonary airways. Rolipram (0.01-1 mg ml-1) markedly reduced airway extravasation produced by inhaled antigen (5 mg ml-1). Zaprinast (1-10 mg ml-1) was also effective against airway microvascular leakage produced by aerosol PAF or antigen while milrinone (10 mg ml-1) had no antiexudative effect. These data support previous suggestions that pharmacological inhibition of PDE IV results in anti-spasmogenic and anti-inflammatory effects in the airways and may be useful in the treatment of asthma.

Ability of inhaled procaterol, a beta 2 adrenoceptor agonist, to attenuate eicosanoid-induced airflow obstruction and airway microvascular leakage

Beta-2 adrenoceptor agonists are widely used as bronchodilators in the treatment of asthma mainly via inhalation. In the present study, we evaluated the ability of inhaled procaterol, a beta 2 adrenoceptor agonist, to reduce eicosanoid-induced airway microvascular leakage, and compared the ability with its inhibitory effect against bronchoconstriction. Tracheostomized guinea-pigs were given aerosolized procaterol (10 or 100 micrograms/ml) for 10 min under spontaneous breathing. Immediately after the end of inhalation, the animals were mechanically ventilated. Fourteen minutes after the end of inhalation, Evans blue dye (20 mg/kg) was given i.v. One minute later, 2 nmol/kg leukotriene D4 (LTD4), 50 nmol/kg U-46619, a thromboxane A2 mimetic, or vehicle was administered i.v. LTD4- or U-46619-induced increase in lung resistance was measured for 6 min. After removing the lungs, the amount of extravasated Evans Blue due in the lower airways was examined as an index of microvascular leakage. Inhaled procaterol significantly attenuated increases in both lung resistance and Evans Blue dye extravasation caused by these eicosanoids. The degree of inhibition was almost complete for lung resistance (approximately 90%), but it was only partial (range 18.5-61.2%) for the dye extravasation. No significant changes in mean systemic blood pressure and in heart rate was observed after an inhalation of 10 micrograms/ml procaterol. These results suggest that inhaled beta 2 adrenoceptor agonists may reduce airway microvascular leakage caused by inflammatory mediators such as eicosanoids without affecting systemic circulation.

Effects of beta 2-adrenoceptor agonists on anti-IgE-induced contraction and smooth muscle reactivity in human airways

1. The beta 2-adrenoceptor agonists, salbutamol, salmeterol and RP 58802 relaxed basal tone of human isolated bronchial smooth muscle. Salmeterol- and RP 58802-induced relaxations persisted for more than 4 h when the medium was constantly renewed after treatment. 2. Salbutamol, salmeterol and RP 58802 reversed histamine-induced contractions in human airways (pD2 values: 6.15 +/- 0.21, 6.00 +/- 0.19 and 6.56 +/- 0.12, respectively). 3. Anti-IgE-induced contractions were significantly inhibited immediately after pretreatment of preparations with beta 2-adrenoceptor agonists (10 microM). However, when tissues were treated with beta 2-agonists and then washed for a period of 4 h, salmeterol was the only agonist which significantly inhibited the anti-IgE response. 4. Histamine response curves were shifted to the right immediately after pretreatment of tissues with the beta 2-adrenoceptor agonists (10 microM; 20 min), but maximal contractions were not affected. After a 4 h washing period, the histamine curves were not significantly different from controls. Concentration-effect curves to acetylcholine (ACh) or leukotriene C4 (LTC4) were not significantly modified after beta 2-agonist pretreatment. 5. These results suggest that beta 2-adrenoceptor agonists may prevent anti-IgE-induced contraction by inhibition of mediator release rather than alterations of those mechanisms involved in airway smooth muscle contraction.