Effects of MKS-492 on antigen-induced bronchoconstriction and allergic reaction in guinea pigs and rats

Aminophylline, administered at usual doses for rodents in pharmacological studies, induces hippocampal neuronal cell injury under low tidal volume hypoxic conditions in guinea-pigs

OBJECTIVES

To establish whether aminophylline, administered at usual doses for rodents in pharmacological studies, induces brain injury in systemic hypoxaemia in guinea-pigs.

METHODS

 A hypoxaemia (partial oxygen tension of arterial blood (PaO₂) = 40-60 mmHg) model was developed by low tidal volume mechanical ventilation in guinea-pigs.

KEY FINDINGS

Under hypoxic conditions, aminophylline significantly increased the concentration of brain-specific creatine kinase in the serum in a dose- and time-dependent manner. A reduced number of hippocampal neuronal cells in the CA1 region, an increase in the concentration of neuron-specific enolase (NSE) in cerebrospinal fluid (CSF), an increase in lipid hydroperoxides and a decrease in the ratio of glutathione to glutathione disulfide in the brain tissues were also observed. These effects were not observed when aminophylline at the same doses was administered under normoxic conditions (PaO₂ = 80-100 mmHg). There was no difference in either serum or CSF concentrations of theophylline between normoxic and hypoxic conditions. Another methylxanthine, caffeine, did not increase the concentration of NSE in CSF.

CONCLUSIONS

Aminophylline potentially induces brain damage under hypoxic conditions. We suggest that aminophylline treatment has adverse effects in patients with hypoxaemia subsequent to respiratory disorders such as asthma.

A possible involvement of oxidative lung injury in endotoxin-induced bronchial hyperresponsiveness to substance P in guinea pigs

Reactive oxygen-derived free radical species have been implicated in the pathogenesis and pathophysiology of inflammatory lung diseases. In a guinea pig model of aerosolized endotoxin-induced bronchial hyperresponsiveness to substance P, a possible involvement of oxidative lung injury was assessed by measuring the changes in membrane-bound neutral endopeptidase activity in the airway tissues and the level of lipid peroxides in the plasma. Vehicle-treated animals developed a neutrophilic airway inflammation, bronchial hyperresponsiveness to substance P associated with neutral endopeptidase hypoactivity, and elevation of lipid peroxides at 18 to 24 h after an exposure to endotoxin (75 microgram/ml, 40 min). A nonselective phosphodiesterase inhibitor, aminophylline, and selective phosphodiesterase isoenzyme inhibitors, SDZ-ISQ-844 (type III/IV) and SDZ-MKS-492 (type III), attenuated the neutrophilic airway inflammation induced by endotoxin. Aminophylline, SDZ-MKS-492, and a superoxide anion-generating NADPH-oxidase inhibitor apocynin inhibited bronchial hyperresponsiveness to substance P with attenuation of neutral endopeptidase inactivation induced by endotoxin. SDZ-ISQ-844, SDZ-MKS-492, and apocynin attenuated the elevation of lipid peroxides. The generation of hypochlorite (OCl-) from whole blood leukocytes was attenuated by aminophylline, SDZ-ISQ-844, SDZ-MKS-492, and apocynin at 1 to 2 h after exposure. These results suggest that reactive oxygen-derived free radical species-mediated oxidative lung injury may play an important role in endotoxin-induced bronchial hyperresponsiveness to substance P, and that phosphodiesterase isoenzyme inhibitors may be potentially useful as anti-inflammatory drugs.

Effects of isoenzyme selective phosphodiesterase inhibitors on bacterial lipopolysaccharide-induced bronchial hyperreactivity in guinea pigs

1. Effects of cilostazol and vesnarinone (selective PDE III inhibitors), rolipram (selective PDE IV inhibitor) and theophylline (nonselective PDE inhibitor) on LPS-induced bronchial hyperreactivity were investigated in guinea pigs. 2. Cilostazol (50 mg/kg PO), vesnarinone (100 mg/kg PO), rolipram (20 mg/kg PO), and theophylline (50 mg/kg PO), significantly inhibited bronchial hyperreactivity to acetylcholine (Ach) and TNF release into bronchoalveolar lavage fluid following LPS exposure. None of these compounds influenced neutrophil influx into bronchoalveolar lavage fluid. 3. Rolipram and theophylline antagonized Ach-induced bronchoconstriction in normal guinea pigs.