An Optimal Condition of Bronchial Cell Proliferation Stimulated by Insulin-Like Growth Factor-I

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Background: It is known that growth hormones such as insulin-like growth factor-I (IGF-I) and several kinds of cytokines are involved in the regeneration process of injured epithelial cells in chronic respiratory inflammatory diseases such as bronchial asthma. Repetitive degeneration/regeneration processes of the airway epithelial layer is supposed to be responsible for the remodeling and irreversible organic changes of the airway in bronchial asthma. The purpose of this study is to establish a simple and reliable in vitro method for studying airway epithelial cell growth and proliferation using IGF-I. Method: By altering the number of cultured epithelial cells (strain NCI-H₂₉₂), culture duration before stimulation with IGF-I, concentration of IGF-I, and duration of IGF-I stimulation, the optimum conditions for epithelial cell growth was determined. The epithelial cell growth was evaluated using [methyl-³H]thymidine uptake. Result: Among various culture conditions, the epithelial cells cultured at 1 × 10³ cells/well for 24 h followed by 24 h of stimulation by 10^–8 M of IGF-I showed the highest growth. Conclusion: The method for the evaluation of epithelial cell growth established in this study requires a small number of cells and has no complicated procedure. This simple model enables us to investigate the effect of various substances on bronchial epithelial cell growth in the presence of IGF-I.