Elevation of sphingoid base 1-phosphate as a potential contributor to hepatotoxicity in fumonisin B₁-exposed mice

Fumonisins are causative agents of diseases in mice and rats, including liver and renal toxicities, as well as cancer, and are specific inhibitors of ceramide synthase in the metabolism of sphingolipid. The purpose of this study was to determine whether an elevated level of sphingoid base 1-phosphate was related to the expressions of metabolism enzymes in the liver of fumonisin B₁ (FB₁-treated mice and acted as a contributing factor to hepatotoxicity. In our previous study, FB₁ was confirmed to be toxic to both liver and kidneys, coupled with simultaneous elevation of sphinganine 1-phosphate (Kim et al., 2006). ICR mice were treated intraperitoneally with 10 mg/kg/day FB₁ for 5 days, with the concentrations of sphingolipid metabolites in the serum and liver measured using HPLC following Bligh-Dyer extraction. The levels of sphingoid bases and their 1-phosphates in the serum and liver were markedly elevated in response to treatment with FB₁. In the liver, FB₁ increased the expression of sphingosine kinase and inhibited the expression of sphingosine 1-phosphate lyase. The cleaved form of caspase-3 was detected in the liver of FB₁-treated mice, indicating the occurrence of apoptosis in the liver following exposure to FB₁. The expressions of proapoptotic signaling molecules, such as phosphorylated forms of c-Jun N-terminus kinase (JNK), p38 MAPK and extracellular signal-regulated kinase (ERK), were increased in the liver of FB ₁-treated mice. In conclusion, these results suggest the elevation of sphingoid base 1-phosphate, as a result of the activation of sphingosine kinase and the inhibition of sphingosine 1-phosphate lyase, may be a major target for FB₁-induced hepatotoxicity via the activation of an apoptotic signaling pathway.