Recent studies by our group and others have disclosed the presence of ceramides in mitochondria, and the activities of ceramide synthase and reverse ceramidase in mitochondria have also been reported. Since a possible contamination with the ER (endoplasmic reticulum)-related compartment MAM (mitochondria-associated membrane) could not be ruled out in previous studies, we have re-investigated the presence of the enzymes of ceramide metabolism in mitochondria and MAM highly purified from rat liver. In the present paper, we show that purified mitochondria as well as MAM are indeed able to generate ceramide in vitro through both ceramide synthase or reverse ceramidase, whereas the latter enzyme activity is barely detectable in microsomes. Moreover, ceramide synthase activities were recovered in outer mitochondrial membranes as well as in inner mitochondrial membranes. Using radiolabelled sphingosine as a substrate, mitochondria could generate ceramide and phytoceramide. However, the in vitro sensitivity of ceramide synthase toward FB1 (fumonisin B1) in mitochondria as well as in MAM was found to depend upon the sphingoid base: whereas dihydrosphingosine N-acyltransferase was inhibited by FB1 in a concentration-dependent manner, FB1 actually activated the ceramide synthase when using sphingosine as a substrate. Acylation of sphingosine 1-phosphate and dihydrosphingosine 1-phosphate, generating ceramide 1-phosphate, was also shown with both subcellular fractions. Moreover, the same difference in sensitivity towards FB1 for the ceramide synthase activities was seen between the two phosphorylated sphingoid bases, raising the possibility that distinct base-specific enzymes may be involved as ceramide synthases. Collectively, these results demonstrate the involvement of mitochondria in the metabolism of ceramides through different pathways, thereby supporting the hypothesis that topology of ceramide formation could determine its function.

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AGuIX are sub-5 nm nanoparticles made of a polysiloxane matrix and gadolinium chelates. This nanoparticle has been recently accepted in clinical trials in association with radiotherapy. This review will summarize the principal preclinical results that have led to first in man administration. No evidence of toxicity has been observed during regulatory toxicity tests on two animal species (rodents and monkeys). Biodistributions on different animal models have shown passive uptake in tumours due to enhanced permeability and retention effect combined with renal elimination of the nanoparticles after intravenous administration. High radiosensitizing effect has been observed with different types of irradiations in vitro and in vivo on a large number of cancer types (brain, lung, melanoma, head and neck…). The review concludes with the second generation of AGuIX nanoparticles and the first preliminary results on human.