In the present study, the concentration of sodium metabisulfite (SMB) in dried plums and its toxicity effects on the cell lines of K-562 (human leukemia cell line) and L-929 (normal fibroblast cell line) were measured. Samples of dried plums were randomly collected from the shops located in Neyshabur and Mashhad (Iran). SMB residue was measured using iodometric titration and high- performance liquid chromatography. To analyze the cytotoxicity, the cells were treated with various concentrations of SMB, and cell viability was determined by the MTT and LDH methods. The average concentration of SMB in the samples of dried plums was selected to evaluate the apoptosis/necrosis by flow cytome- ter. The expression analysis of apoptosis marker genes (BAX, Bcl-2, and P53) was also assessed. Results indicated that the average concentration of SMB residue in 12 samples of dried plum was 516 ± 285.39 mg/kg. When K-562 cells were treated with 500 mg/L of SMB, apoptosis increased significantly (p < 0.01). The IC50 of SMB for K-562 and L-929 cells after a 48-h exposure was 200.31 and 257.82 mg/L, respectively. SMB-treated cells showed that cell viability in both cell lines decreased in a dose-dependent manner after 72 h (p < 0.01). The percent- age of apoptotic but not necrotic cells was 69.49% for K-562 and 77.32% for L-929 cells, whereas apoptosis of untreated control cells was 0.17%. Our findings also showed an opposite mRNA expression of Bcl-2 (anti-apoptotic marker) and Bax2 (pro-apoptotic marker) when k-562 cells were treated with SMB. The results indi- cated that the concentration of sulfite residue in some dried plums poses a cell toxicity risk for normal cells. KEYWORDS cell apoptosis, cytotoxicity, dried plum, sodium metabisulfite

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