What is the mechanism of fumonisin toxicity in relation to sphingolipid metabolism?

• A. Inhibition of cholesterol synthesis.
• B. Inhibition of the conversion of sphinganine to sphingosine in sphingolipid biosynthesis.
• C. Inhibition of purine synthesis.
• D. Activation of glycolysis.

Answer: (B)

Fumonisins disrupt sphingolipid metabolism by inhibiting ceramide synthase, the enzyme that attaches a fatty acid to sphinganine to form ceramide. Blocking this step prevents proper production of ceramide, causing accumulation of sphinganine (and often sphingosine) and depletion of complex sphingolipids. This imbalance disrupts membrane structure and key signaling pathways, leading to cellular toxicity.

The idea expressed here fits with the concept that fumonisin toxicity arises from interference with sphingolipid biosynthesis, rather than affecting cholesterol synthesis, purine synthesis, or glycolysis. While the exact enzymatic target is ceramide synthase (not the desaturation step from sphinganine to sphingosine), the result is a blockade within the sphingolipid pathway that underpins the toxin’s harmful effects.