n-caproylsphingosine and sphingosine-1-phosphate

Sparse scan partial thermal ablation (TA) with focused ultrasound (FUS) may be deployed to treat solid tumors and increase delivery of systemically administered therapeutics. Furthermore, C6-ceramide-loaded nanoliposomes (CNLs), which rely upon the enhanced-permeation and retention (EPR) effect for delivery, have shown promise for treating solid tumors and are being tested in clinical trials. Here, our objective was to determine whether CNLs synergize with TA in the control of 4T1 breast tumors. CNL monotherapy of 4T1 tumors yielded significant intratumoral bioactive C6 accumulation by the EPR effect, but tumor growth was not controlled. TA increased bioactive C6 accumulation by ~ 12.5-fold over the EPR effect. In addition, TA + CNL caused shifts in long-chain to very-long-chain ceramide ratios (i.e., C16/24 and C18/C24) that could potentially contribute to tumor control. Nonetheless, these changes in intratumoral ceramide levels were still insufficient to confer tumor growth control beyond that achieved when combining with TA with control "ghost" nanoliposomes (GNL). While this lack of synergy could be due to increased "pro-tumor" sphingosine-1-phosphate (S1P) levels, this is unlikely because S1P levels exhibited only a moderate and statistically insignificant increase with TA + CNL. In vitro studies showed that 4T1 cells are highly resistant to C6, offering the most likely explanation for the inability of TA to synergize with CNL. Thus, while our results show that sparse scan TA is a powerful approach for markedly enhancing CNL delivery and generating "anti-tumor" shifts in long-chain to very-long-chain ceramide ratios, resistance of the tumor to C6 can still be a rate-limiting factor for some solid tumor types.

Topics: Ceramides; Humans; Neoplasms; Sphingosine

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid capable of regulating critical physiological and pathological functions. Here, we report for the first time that S1P stimulates aldosterone secretion in cells of the zona glomerulosa of the adrenal gland. Regulation of aldosterone secretion is important because this hormone controls electrolyte and fluid balance and is implicated in cardiovascular homeostasis. S1P-stimulated aldosterone secretion was dependent upon the protein kinase C (PKC) isoforms alpha and delta and extracellular Ca2+, and it was inhibited by pertussis toxin (PTX). S1P activated phospholipase D (PLD) through a PTX-sensitive mechanism, also involving PKC alpha and delta and extracellular Ca2+. Primary alcohols, which attenuate the formation of phosphatidic acid (the product of PLD), and cell-permeable ceramides, which inhibit PLD activity, blocked S1P-stimulated aldosterone secretion. Furthermore, propranolol, chlorpromazine, and sphingosine, which are potent inhibitors of phosphatidate phosphohydrolase (PAP) (the enzyme that produces diacylglycerol from phosphatidate), also blocked aldosterone secretion. These data suggest that the PLD/PAP pathway plays a crucial role in the regulation of aldosterone secretion by S1P and that Gi protein-coupled receptors, extracellular Ca2+, and the PKC isoforms alpha and delta are all important components in the cascade of events controlling this process.

Topics: Aldosterone; Angiotensin II; Animals; Calcium; Cattle; Cells, Cultured; Ceramides; Chlorpromazine; Enzyme Inhibitors; Isoenzymes; Lysophospholipids; Pertussis Toxin; Phosphatidate Phosphatase; Phospholipase D; Propranolol; Protein Kinase C-alpha; Protein Kinase C-delta; Sphingosine; Zona Glomerulosa

Ceramide is a lipid second messenger that was recently identified as mediator of pulmonary edema in vivo. Here, we investigated the effect of ceramide on the permeability of confluent endothelial cell monolayers. In monolayers of bovine pulmonary artery and human microvascular pulmonary endothelial cells, incubation with C6-ceramide for 3 h elevated permeability in a concentration-dependent manner, whereas dihydroceramide was without effect. After 3 h of incubation with ceramide, we found no signs of necrosis (release of lactate dehydrogenase, loss of thiazylyl blue reduction) or apoptosis (ssDNA, caspase-8 activity). The increased endothelial permeability in response to ceramide was attenuated by the Ser/Thr protein kinase inhibitors K252a, K252b and H-7, as well as by the phosphatidylinositol-specific phospholipase C inhibitor L108. Since in some systems sphingosine-1-phosphate (S1P) acts antagonistic to ceramide, the effect of S1P was studied. S1P transiently increased endothelial cell resistance, whether it was given together with ceramide or 90 min thereafter. These data provide a novel example of the antagonism between S1P and ceramide. Our findings further suggest that ceramide alters vascular permeability by activation of pathways dependent on unidentified phospholipase C and Ser/Thr kinase isoenzymes.

Topics: Animals; Apoptosis; Cattle; Cell Membrane Permeability; Cells, Cultured; Ceramides; Dose-Response Relationship, Drug; Endothelial Cells; Endothelium, Vascular; Enzyme Inhibitors; Lysophospholipids; Necrosis; Sphingosine