Sulfite exposure-induced hepatocyte death is not associated with alterations in p53 protein expression

• Na2SO3 is toxic to hepatocytes and decreases cell viability.
• Na2SO3 does not induce p53 and p-p53 (Ser15) expression, nor does it inhibit Mdm2 and Bcl-2 expression.
• Na2SO3 does not increase caspase-3 and PCNA expression.
• Na2SO3 increases the activity of ALT and AST in the supernatants of hepatocytes. These increases in activity are accompanied by increases in RIP1 expression.

Although sulfite (SO32−) is commonly used as an antimicrobial agent and preservative in foods, medicines and wine, it has also been listed as an important risk factor for the initiation and progression of liver diseases due to oxidative damage. In general, apoptosis that is induced by oxidative stress is triggered by increases in p53 and alterations in Mdm2 and Bcl-2. However, the level of involvement of the p53 signaling pathway, which has been shown to be upregulated in some animal studies, in hepatocyte death remains unclear. To examine the response of the p53 signaling pathway to stimulation with different concentrations of sulfite, a time course study of p53, Mdm2, and Bcl-2 expression was conducted in an immortalized hepatic cell line, HL-7702. When the HL-7702 cells were cultured in the presence of Na2SO3, the cell viability was significantly decreased after 24 h compared to that of the control group (0 mmol/L) (p < 0.05). Meanwhile, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in the supernatants of HL-7702 cells were significantly increased following Na2SO3 administration. Interestingly, the expression of p53 and p-p53 (Ser15) remained unchanged. In addition, no obvious alterations in Mdm2 and Bcl-2 expression were observed in HL-7702 cells that had been stimulated with various concentrations of sulfite. To further investigate the detailed mechanism underlying sulfite toxicity, caspase-3, PCNA and RIP1 expression in HL-7702 cells was studied. The expression levels of caspase-3 and PCNA were unchanged, but RIP1 expression was increased significantly after 24 h of exposure. In light of this evidence, we propose that sulfite is cytotoxic to hepatocytes, but this cytotoxicity is not achieved by direct interruption of the p53 signaling pathway. In addition, we propose that an alternative necrotic process underlies hepatocellular death following sulfite exposure.

Sulfite (SO32−) can cause oxidative damage to hepatocytes by ROS production and ATP depletion. Oxidative stress usually triggers increases in p53 and decreases in Mdm2 and Bcl-2. When HL-7702 cells were cultured with Na2SO3, cell viability was significantly decreased. Decreases in viability were accompanied by increases in AST and ALT activity in the culture medium. Treatment with sulfite did not alter the expression of p53, p-p53 (Ser15), Mdm2, or Bcl-2. Sulfite exposure did not alter the expression of caspase-3 or PCNA. However, sulfite exposure increased RIP1 expression after 24 h of exposure. Sulfite exposure can lead to necrosis and the release of ALT and AST in hepatocytes.Figure optionsDownload as PowerPoint slide