[Regulatory effects of luteolin on airway inflammation in asthmatic rats].

Objective: To explore the regulatory effects of luteolin on airway inflammation in asthmatic rats.

Methods: A total of 48 male Sprague-Dawley (SD) rats were randomly divided into 3 groups of control, asthmatic and luteolin(n = 16 each). The rat model of bronchial asthma was established in asthmatic and luteolin groups. The model was induced by intraperitoneally injecting a mixture of ovalbumin and aluminum hydroxide at Day 1 and 8. After two weeks, aomization excitation of normal saline (containing 1% ovalbumin) was induced thrice weekly. The treatment lasted 8 weeks. In control group, the mixture of ovalbumin, aluminum hydroxide and normal saline containing 1% ovalbumin was replaced by normal saline. At 30 min after aomization excitation, normal saline was given to rats in control and asthmatic groups, while 1 mg/kg luteolin was given intraperitoneally to luteolin group. The inflammatory cell number and level of interleukin-4 (IL-4) were measured in bronchoalveolar lavage fluid (BALF). The histopathological changes were observed under light microscope. The activities of peroxisome proliferator-activated receptors (PPARγ) and p38 mitogen-activated protein kinases (p38MAPK) in pulmonary tissues were detected by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR).

Results: The bronchial wall thickness of asthma group, along with smooth muscle thickness ((93.3 ± 7.4), (34.9 ± 2.3) µm) was more than that of control ((61.9 ± 8.2), (19.3 ± 1.5) µm) and luteolin ((76.6 ± 6.7), (25.4 ± 4.6) µm) groups (all P < 0.05). The total cell count ((5.61 ± 0.63)×10(9)/L), neutrophil count ((1.83 ± 0.09)×10(9)/L), eosinophil count ((0.59 ± 0.09)×10(9)/L) and level of IL-4 ((78.23 ± 12.73) pg/ml) in BALF of asthmatic group were markedly higher than those of control ((1.53 ± 0.31)×10(9)/L, (0.45 ± 0.21)×10(9)/L, (0.07 ± 0.03) ×10(9)/L and (21.21 ± 2.53) pg/ml) and luteolin ((3.24 ± 0.25)×10(9)/L, (1.54 ± 0.10)×10(9)/L, (0.33 ± 0.05)×10(9)/L and (43.24 ± 8.65) pg/ml) groups (all P < 0.05). The results of semi-quantitative immunohistochemical analysis showed that the p38 protein level in control group (0.143 ± 0.017) and luteolin group (0.251 ± 0.021) was significantly less than that in asthmatic group (0.362 ± 0.008) (both P < 0.01). As compared with asthmatic group, the expression of PPARγ protein markedly increased (0.247 ± 0.034) in control (0.331 ± 0.056) and luteolin (0.442 ± 0.031) groups (all P < 0.05). The level of p38 mRNA in asthmatic group (0.718 ± 0.064) was significantly higher than that of control (0.312 ± 0.052) and luteolin (0.426 ± 0.067) groups (all P < 0.01). However, the PPARγ mRNA level in asthmatic group (0.266 ± 0.036) was much less than that in control (0.573 ± 0.042) and luteolin (0.687 ± 0.054) groups (all P < 0.01).

Conclusion: The anti-inflammatory effects of luteolin may be associated with the regulation of PPARγ expression and p38MAPK signaling pathway in asthmatic rats.