Induction of apoptosis in cultured human proximal tubule cells by fumonisins and fumonisin metabolites

Abstract

It is well-known that fumonisin B₁ (FB₁) stimulates apoptosis in a variety of cell types and tissues but the apoptotic potential of other fumonisins and fumonisin metabolites has not been investigated. In our studies we exposed human proximal tubule-derived cells (IHKE cells) to FB₁, fumonisin B₂ (FB₂), hydrolyzed fumonisin B₁ (HFB₁) and N-palmitoyl-hydrolyzed fumonisin B₁ (N-Pal-HFB₁) and investigated caspase 3 activation and DNA fragmentation. Only exposure to 10 μmol/L FB₁ for 24h led to a significantly increased activity of caspase 3 and to DNA fragmentation. All other compounds tested did not show any significant activation of caspase 3 activity. Further we examined wether a sphinganine accumulation is correlated with the induction of apoptosis in IHKE cells. Therefore we developed a liquid chromato-graphy/electrospray ionization-tandem-mass spectrometry(HPLC-MS/MS)-method using phytosphingosine as an internal standard to determine sphinganine- and sphingosine concentrations in incubated IHKE cells. Whereas a significant increase of sphinganine was observed with all substrates, sphingosine levels remained unchanged. This shows that FB₁ exposure leads to apoptosis in a sphinganine-independent mechanism.