Effect Of NF-κB On Pulmonary Oxygen Toxicity

Hyperbaric oxygen exposure involves in diving medicine work and clinical hyperbaric oxygen treatment. The application of high partial pressure oxygen can improve the inert gas takes off saturation efficiency when reducing pressure, shorten the time of reducing pressure, improve underwater operation ability, and there is clear treatment result to some hypoxia diseases. But inhaling high partial pressure oxygen for a long time brings the issue oxygen toxicity. After body breath O₂ the pressure of which is higher than 50kPa for some time, structure and function of some organ may emerge pathological change. And the disorder caused by this change is oxygen toxicity. Oxygen toxicity is classified as eye type, brain type, and pulmonary type. Pulmonary oxygen toxicity is mainly showed as coughing, pain after the breast bone, dyspnea. Pathology observations show that main change in forepart time is inflammation exudation, including the lung congestion in large area, hemorrhage and hydroncus, inflammation cell infiltration. The pathogenesy of oxygen toxicity is still not clear completely to this day.Nuclear factor-kappa B (NF- k B) is a multipurpose nuclear factor. It has extensive biologic activity. Genetic transcription of cytokine, adhesion molecule, chemotatic factor and so on may be promoted after activation of NF-kB. So it plays a important role in stress, inflammation and immuneresponse. And it becomes the investigative focus in this year. Recently it was found that high partial pressure could active NF-k B.Tumor necrosis factor-alpha (TNF-a ) is a kind of cytokine whose expression was regulated by NF-k B, and it may promote the inflammation. The high expression of TNF-a may result in lung injury.The objective of this experiment is to study the change rule of NF-k B and TNF-a in oxygen toxicity, confirm that activation of NF-k B has effect on pulmonary oxygen toxicity, discuss the possible mechanism of pulmonary oxygen toxicity and provide a new idea for prevent pulmonary oxygen toxicity.In this study, the healthy SD rats breathe hyperbaric oxygen in closed oxygen cabin to duplicate pulmonary oxygen toxicity model. The animals are divided into 6 groups which are named as normal control group, normal oxygen hyperbaric nitrogen control group, 2h of 0. 23MPa hyperbaric oxygen expose group, 6h of 0. 23MPa hyperbaric oxygen expose group, lOh of 0. 23MPa hyperbaric oxygen expose group and PDTC pretreatment group. The rats in the PDTC pre-treatment group were intraperitoneal injected with PDTC for 120 mg/kg before exposed in 0. 23MPa hyperbaric oxygen for lOh.The animals were anesthetized after they departed from the cabin and the lungs were taken out by dissecting. The alteration of lung histomorphology was judged by pathological section. The cell nuclear protein of lung was extracted by nuclear extraction reagents kit and the content of NF-kB/P65 in the neucleoprotein was detected by Western blot. The TNF-a genetictranscription of lung cell was detected by RT-PCR. The content of TNF-a in the supernate fluid of lung homogenate was detected by ELISA. The results of our study are as follows:1. The changes of lung pathology: the lungs in control group are normal. There are no changes of the lungs after lOh of normal oxygen hyperbaric nitrogen exposure or 2h of hyperbaric oxygen exposure. Slight inflammation of the lungs was shown after 6h of hyperbaric oxygen exposure. The inflammation of the lungs aggravate obviously after lOh of hyperbaric oxygen exposure. Pretreatment with PDTC may lessen the inflammation of the lungs as compared with rats exposed in hyperbaric oxygen for lOh.2. TNF-a protein level in the supernatant of lung tissue homogenate: the contents of TNF- a protein in the supernatant of rat lung tissue increased obviously after 6h or lOh of hyperbaric oxygen exposure as compared with control group, and the difference is significant (P<0. 01). Pretreatment with PDTC may degrade the contents of TNF-a protein obviously as compared with rats exposed in hyperbaric oxygen for lOh (P<0. 01);nevertheless, it is still higher than control group (P<0. 01).3. The TNF-a mRNA expression of the lung tissue: agarose gel electro-phoresis was carried out after RT-PCR, and TNF-a positive zones were found at the place of 495bp. Expression are feeble of the lungs in the control group. There is no obvious increase after 2h hyperbaric oxygen exposure, and obvious increase is shown after 6h or lOh hyperbaric oxygen exposure. And thedistinction is significant (P<0. 01). Pretreatment with PDTC may degrade the expression of TNF-a mRNA as compared with rat exposed in hyperbaric oxygen for lOh (P<0.01);nevertheless, it is still higher than control group4. The contents of NF-kB/P65 in the nucleus of the lung tissue cells: compared with control group, the contents of NF-k B/P65 in the cell nucleus of the lung tissue increase after 2h hyperbaric oxygen exposure, and reach the peak after 6h hyperbaric oxygen exposure, and descend after lOh hyperbaric oxygen exposure;nevertheless, it is still higher than control group. Pretreatment with PDTC may degrade the contents of NF-k B/P65 as compared with rat exposed in hyperbaric oxygen for lOh, nevertheless, it is still higher than control group.The above results showed that hyperbaric oxygen may induce the high expression of TNF-a by the activation of NF-kB. And the high expression may promote the inflammation of pulmonary oxygen toxicity. PDTC, as the specific inhibitor of NF- k B, may lessen the inflammation of pulmonary oxygen toxicity obviously. It offer new idea for the defend of pulmonary oxygen toxicity.