Does fumonisin B1 disrupt sphingolipid metabolism and cell signaling?

Fumonisin B1 (FB1) is a potent environmental mycotoxin that profoundly disrupts cellular homeostasis by targeting the core machinery of sphingolipid synthesis.

Molecular mechanism of disruption

• Enzyme inhibition: FB1 acts as a structural analog to sphingoid bases, competitively blocking the sphingoid base binding site of ceramide synthase (CerS), while its tricarballylic acid side chains obstruct the fatty acyl-CoA binding site.
• Covalent trapping: CerS acylates FB1 to form N-acyl-FB1, which remains tightly bound to the catalytic site, inactivating the enzyme with submicromolar to low-micromolar potency.
• Metabolic imbalance: This blockade halts both de novo and salvage ceramide synthesis, resulting in a dramatic accumulation of free sphinganine (Sa) relative to sphingosine (So) and severely elevating the intracellular Sa/So ratio.

Impact on membrane architecture and signaling

• Structural alteration: Depleting complex sphingolipids (such as sphingomyelin) alters localized bilayer thickness, increases membrane fluidity, and destabilizes lipid raft microdomains.
• Signaling suppression: These physical changes in the membrane disrupt the lateral clustering of receptor tyrosine kinases (RTKs), suppressing downstream MAPK/ERK phosphorylation.
• Receptor and channel displacement: Loss of raft-associated ceramides prevents the assembly of death receptor (Fas/CD95) and TLR4 signaling platforms—blunting p38 MAPK and pro-inflammatory pathways—while displacing TRPC5 ion channels to suppress calcium flux.

Bottom line

• Fumonisin B1 is a highly potent inhibitor of ceramide synthase that directly impairs cell-membrane structural integrity and downstream signaling cascades (such as the MAPK/ERK pathway) by blocking ceramide synthesis, accumulating toxic free sphingoid bases, and destabilizing lipid raft architecture.