Serine palmitoyltransferase inhibition reverses anti-proliferative effects of ceramide synthase inhibition in cultured renal cells and suppresses free sphingoid base accumulation in kidney of BALBc mice

The purpose of this study was to determine the ability of the fungal serine palmitoyltransferase (SPT) inhibitor, myriocin, to prevent the anti-proliferative and cytotoxic effects of fumonisin B 1 in cultured pig kidney epithelial cells, LLC-PK 1. In an earlier study with LLC-PK 1 cells, β-chloroalanine (a nonspecific SPT inhibitor) was found to inhibit the fumonisin-induced accumulation of free sphinganine by >90% but only partially reversed (50–60%) fumonisin’s antiproliferative and cytotoxic effects. β-Chloroalanine is not the ideal SPT inhibitor for this type of study because it also inhibits other pyridoxal 5′-phosphate-dependent enzymes. A potent and selective fungal SPT inhibitor (myriocin) was partially purified from liquid cultures of Isaria (= Cordyceps) sinclairii by a combination of organic extraction and column chromatography. The various fractions were bioassayed for their ability to inhibit fumonisin-induced sphinganine accumulation in LLC-PK 1 cells. The activity in partially purified material was compared to the activity of highly purified myriocin and the results expressed as myriocin equivalents. The estimated IC 50 and IC 95 for inhibition of fumonisin-induced sphinganine accumulation were approximately 1.8 and 22 nM, respectively. The IC 95 concentration of the fungal SPT inhibitor reversed the antiproliferative effects and prevented fumonisin-induced apoptosis after 48 h exposure to 50 μM fumonisin B 1. The SPT inhibitor was also effective at reducing free sphinganine in vivo. Free sphinganine concentration was reduced 60% in kidney of mice injected i.p. with SPT inhibitor plus fumonisin B 1 when compared to fumonisin B 1 alone. The ability of SPT inhibition to reduce fumonisin B 1-induced sphinganine accumulation in vivo may be useful in the development of therapeutic agents for treatment of animals suspected to have been exposed to toxic levels of fumonisin in feeds.