Protective Effect of Cell-Permeable Ceramide Analogs against Modeccin, Ricin, Pseudomonas Toxin, and Diphtheria Toxin

Abstract

We investigated the effects of various ceramide (Cer) analogs and related sphingolipids on the cytotoxicities of modeccin, ricin, Pseudomonas toxin, and diphtheria toxin in various cell lines. The most pronounced protective effect by C6Cer, a short-chain cell-permeable Cer analog, was observed in modeccin cytotoxicity in Vero, BER-40, and MDCK cells, whereas the cytotoxicity of diphtheria toxin was not affected by any of the ceramide analogs tested. C6Cer did not affect the binding and internalization of ricin and modeccin in Vero and BER-40 cells. C2Cer and C8Cer also protected against modeccin cytotoxicity, albeit less effectively than C6Cer. However, related sphingolipids including sphingosine, sphingomyelin, lactosylceramide, C18Cer (the naturally occurring ceramide), and dihydro C6Cer had no effect. A correlation was found between the ability of ceramides to inhibit bulk protein secretion and the inhibition of modeccin cytotoxicity by ceramides. Among Cer analogs tested, C6Cer, the most potent inhibitor of modeccin cytotoxicity, strongly inhibited bulk protein secretion in Vero, BER-40, and MDCK cells. PtK1 cells, which were not protected by ceramides against toxins, were resistant to ceramide-induced inhibition of bulk protein secretion. These results confirm that Cer may modulate the intracellular transport of proteins through the Golgi complex. Such Cer-sensitive processes may be involved in the intoxication of cells by plant and bacterial toxins, especially modeccin.