Study On The Apoptosis And Bcl-2/Bax, STAT-3 Expressions Of Human Hepatoma SMMC-7721 Cells After Exposure To Heavy-ion Irradiation

Malignant tumor is a kind of enormous dangerous disease to human health. Radiotherapy is one of the most important treatment modalities. Conventional radiotherapy includes the treatments ofγ-, X-ray and electron beam, characterized by an exponentially decreasing depth-dose distribution while penetrating the patient body. Therefore, serious damage to normal tissue would be caused after the conventional radiotherapy. Heavy ion beams is characterized by an energy deposition maximum (Bragg peak) at the end of its range and an increased relative biological effectiveness (RBE) within the peak, so it could protect the healthy tissues from damage induced by radiation. Because of these merits, heavy ion beam is an ideal method of radiotherapy. The present study used human hepatoma cells SMMC-7721 as experimental material to investigate cell proliferation, cell apoptosis, cell cycle distributions and the expression of apoptotic proteins such as bcl-2/bax, STAT-3 induced by heavy ion beam irradiation. The purpose is to investigate the elemental principles of heavy ion beam used in caner treatment. Several important experimental results were acquired as summarized as below:1. When the human hepatoma cells SMMC-7721 were radiated with heavy ion beam, the appearances of typical characters of apoptotic cells such as DNA double strand break, nucleus pycnosis, and apoptotic body and so on were increased with the increase of heavy ion radiation doses. Heavy ion beam could induce SMMC-7721 cells undergone apoptosis, and the extent of apoptosis was related to radiation dose.2. Standard colony-forming assay was used to determine the survival fraction of SMMC-7721 cells which were radiated by heavy ion beam. The results showed that SMMC-7721 cells were more sensitive to heavy ion beam radiation than X-rays (P<0.05), and this result was important to apply the heavy ion beam in cancer treatment.3. FCM was used to check the cell cycle distributions of SMMC-7721 cells after heavy ion beam and X-rays irradiations. The G₂/M cells were increased obviously. Heavy ion beam could depress the cancerous cell replication.4. MTT assay applied to determine the proliferate activity of radiated cells. The results showed that cells viability decreased obviously with increase of radiation dose. Heavy ion beam radiation could depress the proliferation of cancerous cells. The drepress effection presented a time-dose dependent manner. This would provid necessary data for chosing suitable radiation dose in cancer treatment.5. The expression of bax gene in SMMC-7721 cells was increased markedly after heavy ion beam radiation, meanwhile, the expression of bcl-2 gene was depressed. When SMMC-7721 cells were radiated with heavy ion beam, the expression of bax gene was up regulated and the expression of bcl-2 gene was depressed as well. And then the cell apoptosis was induced. This indicated that heavy ion beam has higher radiation efficiency than X-rays.6. STAT-3 expression was checked by RT-PCR and Western blot. Heavy ion beam radiation could induce STAT-3 gene expressed obviously. STAT-3 might be a reason why cancerous cells posssess radiosensitivity.The present study reveals that heavy ion beam could induce cell apoptosis more effectively than X-rays in cell morphological changes. Survival fraction and cell viability of radiated cells suggested that heavy ion beam could depress the proliferation of cancerous cells effectively. Heavy ion beam radiation could induce SMMC-7721 cells restrained at G₂/M phase and undergo apoptosis so as to improve the sensitivity of cancerous cells to heavy ion therapy. The determination of bcl-2/bax expression shows that heavy ion beam radiation can induce the changement of apoptosis-related proteins, and then promote cell apoptosis.