Develop A Lung Cancer Model In Rats Induced By 3,4-benzopyrene Pulmonary Injection And Study Of Lung Cancer Prevention By Green Tea And Its Mechanism

Objective The incidence of Lung cancer continues to be high inindustrialized countries and is still increasing in many developingcountries of the world. The 5-year survival following treatment has notimproved significantly over the past decades.So the strategy ofchemopreventive intervention has been emphasized to prevent lungcancer. One of the most promising strategies for cancer chemopreventionis prevention by daily used food and beverages. Tea is the second only towater as the most consumed beverage in the world.Green tea,which ismore effective than black tea in cancer prevention,may be the mostpromising chemopreventive agent against lung cancer.But controversiesare still emerged in some studys of tea and tea extracts against lungcancer, and the mechanism of integrated green tea other than green teaextracts in lung cancer prevention remains to be unknown.In addition,asatisfactory animal model plays a important role in evaluation ofprevention and treatment of lung cancer.But various of animal models incurrent lung cancer study are imperfect. The purpose of the current studyis to explore a simple and convenient and reliable method for lungneoplasm model establishing induced by 3,4-benzopyrene-com oilsolution pulmonary injection in rats and to evaluation the effect oftreament with 1%green tea on 3,4-benzopyrene pulmonary injection induced lung tumorigenesis in Sprague Dawley (SD) rats and modulationof p53,Bcl-2 expression in lung neoplasm tissues,and to furtherinvestigation the effect of green tea on p53 and Bcl-2 expression in lungtissues injuring by 3,4-benzopyrene. methods The study was carriedout in three parts. In the first part, The prepared female SD rats,with therange from 180 to 220g of body weight,were divided into three grop atrandom.In the model group of lung neoplasm,the rats were given 2 mg of3,4-benzopyrene soluting in 0.2 mL corn oil fortnightly pulmonaryinjection for 4 times through right middle-chest percutaneous punctureunder control of anaesthesia by pentobarbital sodium i.p. The negativecontrols were given 0.2 mL corn oil pulmonary injection only. Thepositive controls were given 2 mg of 3,4-benzopyrene soluting in 0.2 mLcorn oil injection under skin of scapular area fortnightly for 2 times.Therats were sacrificed after suffering from dyspnea,and the survived rat 1year after the first 3,4-benzopyrene toxicosis were sacrificed at narcotism.Lung,brain,liver, oesophagus and stomach of all cases were anatomizedin search of tumor. In the second part,the animal model of lung neoplasmwas established as previous description. The rats in the green teaadministration group were given 1% green tea drinking only beginningfrom 2 weeks before 3,4-benzopyrene treatment to the end of one-year'sobservation, the controls were given water drinking only.The incidence oflung neoplasm in rats per group were counted. Each case of lung neoplasm was examined for expression of p53 and Bcl-2 withinsituhybridization analysis and immunohistochemistry staining. In thethird part,animals were treatment with 1% green tea drinking beginningfrom 2 weeks before the first 3,4-benzopyrene-com oil solutionpulmonary injection to the end of the 16-week's observation. The ratswere sacrificed at the begining and 1,4,8,16 weeks after 3,4-benzopyreneinjection respectively. Insituhybridization and immunohistochemistrywere performed to analyse p53 and Bcl-2 expression in lung tissues ingreen tea administration groups and in controls. Results No lungneoplasm was found in the negative controls within 1 year's observation.Malignant neoplasm was found in every rat under skin in the positivecontrol within 17 weeks,and the cancerogenic rate with 3,4-benzopyreneinjection under skin was 100%. The average time of tumor removing inthis positive control was 15.83 week with a median of 16 weeks.It wasfound that approximately 70% of rats emerged carcinoma at the local ofright lung during 1 year. No tumour was found in brain,liver, oesophagusand stomach in rats. The average time of tumor removing in this groupwas 31.54 week with a median of 30 weeks.It is more difficult thatmalignant neoplasm induced by 3,4-benzopyrene in the lung in rats thanunder skin. Green tea administration reduced lung carcinoma to 30%.Expression of p53 gene was slight upregulation by green teaadministration in lung carcinoma tissues,however expression of Bcl-2 gene was significantly downregulation in lung carcinoma tissues in ratswith green tea administration (P＜0.05).Further study showed thatoverexprssion of p53 and Bcl-2 were appeared in bronchial epithelialcells,cells under mucosa, vascular endothelial cells, lymphocytes andinterstitial cells in 1,4,8,16 weeks after 3,4-benzopyrene pulmonaryinjection. Green tea significantly enhanced p53 gene expression andsignificantly inhibited Bcl-2 gene expression in lung tissues during thewhole term beginning the 1th week to the 16th week after3,4-benzopyrene treatment (P＜0.05). Conclusion Carcinogen3,4-benzopyrene pulmonary injection by percutaneous puncture is anefficiency method for lung neoplasm model establishing in rats. Green teainhibit lung carcinogenesis and can upregulate expression of p53,downregulate expression of Bcl-2 in lung cancer induced by benzopyreneand in lung tessues injuring by benzopyrene attack, and this may berelated to the mechanism of lung cancer prevention. In addition,there mayhave a strong "defend cell" prevention mechanism in lung tissue toresisting canceration,and this may be play an important role in lungcarcinogenesis inhibiting. Green tea probably improve the function of"defend cell" during the process of lung cancer chemoprevention.