Effect of Sorbic Acid on the Induction of Static Growth Inhibition in Mouse Mastocytoma P-815 Cells

Sorbic acid and its salts are commonly used as preservatives because of their ability to inhibit the growth of molds, yeasts, and fungi without causing bacterial death. Despite several investigations on sorbic acid-induced static growth inhibition of microorganisms, its implications in mammals remain unexplored. This study investigated the effect of sorbic acid on the growth of mouse mastocytoma P-815 cells (P-815 cells) in culture medium. Our findings indicated that sorbic acid induced static growth inhibition, with optimal results achieved when P-815 cells were exposed to 2.5 mM sorbic acid for at least 48 h, starting approximately 20 h after administration. Notably, the same static growth inhibition by sorbic acid was observed in human promyelocytic leukemia cells but not in mouse bone marrow mast cells. Sorbic acid-induced static growth inhibition increased the number of cells in the G1 and G2 phases and decreased the number of cells in the S phase, demonstrating that sorbic acid affects the cell cycle's G1/S and G2/M transitions. When P-815 cells synchronized at the G1 phase of the cell cycle were treated with sorbic acid, the onset of the cell population was noticeably delayed, whereas S-phase cells revealed almost no delay. The cellular amount of sorbic acid 10 h post-administration was higher in the acidic medium (pH 7.0) than in the medium (pH 7.4), which can be attributed to the inhibition of extracellular release of sorbic acid. Verapamil, a modulator of P-glycoprotein, and sodium azide, an inhibitor of ATP synthesis, inhibited intracellular accumulation of sorbic acid. This suggests that P-glycoprotein plays a role in regulating the intracellular levels of sorbic acid. Administration of sorbic acid led to an increase in intracellular calcium concentration ([Ca²⁺]i), which was suppressed by co-administration with verapamil. Sorbic acid administration decreased the [Ca²⁺]i levels, which were elevated by thapsigargin, an inhibitor of Ca²⁺-ATPase in the ER. This inhibitory effect was observed regardless of whether thapsigargin was administered before or after treatment. This is the first study to report that sorbic acid has a static growth inhibitory effect, causing stagnation in the G1 phase in animal cancer cells such as P-815 cells. The primary mechanism involves suppression of thapsigargin-induced intracellular Ca²⁺ release from Ca²⁺ stores in the ER.