Abstract: Trichoplusia ni Hübner cells were used to study the toxicity mechanism of azadirachtin A (Aza A) at the cellular level. Growth inhibition effect of Aza A on Hi-5 cells was tested. No obvious growth inhibition effect of Aza A on Hi-5 cells was found in the first two days post treatment. However, the inhibition effect went higher in the following days. By using the Giemsa dying method, we observed the change in shape of Hi-5 cells treated with 1.25 μg/mL Aza A. Most cells could not attach to the bottom wall of tissue culture flasks. The cells changed into rotundity. Apoptotic bodies appeared in the treated cells. The fluorescence microscope was used to observe the cell nucleus after stained with Ho33342. The results showed that some of Hi-5 cell chromosomes were abnormally condensed after treatment for 1 d. The ratios of condensed nuclei increased later, and the nuclear membrane was damaged obviously. To study the effect of Aza A on protein content, the FITC staining was performed. The DI value was 1.070±0.018 on the 1st day post treatment with 1.25 μg/mL Aza A, and increased to 1.912±0.019

Key words: Azadirachtin A (Aza A), Trichoplusia ni Hübner Hi-5 cell line, cell toxicity, cell morphology, total protein content, GSH content