Protective effects of ketamine on allergen-induced airway inflammatory injure and high airway reactivity in asthma: experiment with rats

Abstract

To observe the effects of ketamine on bronchial hyperresponsiveness and airway inflammation in equal asthma. 56 Brown-Norway rats were randomly assigned to seven groups: negative control group (Group A), asthma model group (Group B) and inhalation groups with nebulized ketamine at different concentrations (Group C, D, E) and intraperitoneal injection groups with ketamine at different doses (Group F, G). The rats were sensitized by injection of ovalbumin (OVA) together with aluminum hydroxide and Bordetella pertussis as adjuvants, then challenged by repeated intermittent (thrice weekly) exposure to aerosolized OVA for two weeks. Before challenge, the sensitized rats were exposed to an aerosol of phosphate buffered saline (PBS) or ketamine at the concentrations of 12.5 mg/ml, 25 mg/ml and 50 mg/ml respectively in Groups B, C, D and E. The sensitized rats were intraperitoneally injected with ketamine at the doses of 50 microg/kg or 100 microg/kg respectively in Group F and G. The sensitized rats in Group A received phosphate buffered solution (PBS) by inhalation. The airway reactivity to acetylcholine (ACH) was assessed in vivo 24 hr after the last OVA challenge, then the lungs were removed for measurement of the mRNA and protein expression of iNOS and production of NO and lung sections for histopathologic examination. (1) In the OVA-sensitized and challenged rats, the dose-response curve of the expiratory resistance (Re) shifted to the upper-left +/- ward compared with that of PBS control rats. In addition, the provocation doses required to increase the Re by 100%, 200% and 400% for OVA-sensitized and challenged rats in Group B were significantly lower than those of the PBS control rats (14.65 +/- 1.19 vs 32.28 +/- 1.43, 15.17 +/- 1.19 vs 38.91 +/- 1.39, and 16.28 +/- 1.18 vs 56.53 +/- 1.38, all P < 0.01). The OVA-sensitized rats treated with ketamine before OVA challenge demonstrated a significant decrease in AHR by a rightward shift of the dose-response curves to ACH and significant higher provocation doses compared with that of the OVA control rats (P < 0.05). (2) Marked inflammatory changes in the airways of Group B were present, while obviously lessen inflammatory cell infiltration in peribronchial and perialveolar tissues and improved lung edema were observed in the groups treated with ketamine. (3) Quantitation by densitometry showed that the relative density of iNOS mRNA bands normalized to beta-actin was significantly higher in the OVA control than the PBS control (1.0 +/- 0.07 vs 0.48 +/- 0.07, P < 0.01). Treatment with ketamine significantly decreased the expression of iNOS mRNA in Group C (0.65 +/- 0.07), Group D (0.58 +/- 0.09), Group E (0.56 +/- 1.00), and Group F (0.66 +/- 0.06) when compared with Group B (all P < 0.05). (4) The relative iNOS protein levels (ratios of iNOS/beta-actin) determined by densitometry analysis showed a 4-fold increase in Group A compared with those in the negative group (0.54 +/- 0.08 vs 0.13 +/- 0.08, P < 0.05). When compared with those of the OVA control, the levels of relative iNOS protein expression showed a significant decrease in the lungs from the rats treated with ketamine inhalation at the doses of 12.5 mg/ml (0.20 +/- 0.03) and 25 mg/ml (0.18 +/- 0.03) and with ketamine and intraperitoneally the at dose of 50 microg/kg (0.21 +/- 0.04) (P < 0.05). (5) NO production in pulmonary tissues was significantly higher in the OVA-treated rats compared to the PBS controls (0.39 +/- 0.04 micromol/g protein vs 0.13 +/- 0.01 micromol/g protein, P < 0.01), but this OVA-triggered NO production was significantly decreased by treatment with 12.5 and 25 mg/ml inhaled ketamine (0.19 +/- 0.03 micromol/g and 0.17 +/- 0.03 micromol/g, both P < 0.05) and 50 microg/kg i.p.-injected ketamine (0.16 +/- 0.04 micromol/g, P < 0.05) when compared with the OVA-treated rats. Both inhalation and systemic administration of ketamine attenuate inflammatory the lung injury and airway hyperreactivity of the OVA-induced asthma model. The protective effects of ketamine is achieved by inhibiting OVA-provoked over-expression of mRNA and protein of iNOS and reducing the production of NO in pulmonary tissues.