dihydroceramide and Carcinoma--Hepatocellular

Hepatocellular carcinoma (HCC) shows a remarkable heterogeneity and is recognized as a chemoresistant tumor with dismal prognosis. In previous studies, we observed significant alterations in the serum sphingolipids of patients with HCC. This study aimed to investigate the in vitro effects of sorafenib, which is the most widely used systemic HCC medication, on the sphingolipid pathway as well as the effects of inhibiting the sphingolipid pathway in HCC. Huh7.5 and HepG2 cells were stimulated with sorafenib, and inhibitors of the sphingolipid pathway and cell proliferation, viability, and concentrations of bioactive metabolites were assessed. We observed a significant downregulation of cell proliferation and viability and a simultaneous upregulation of dihydroceramides upon sorafenib stimulation. Interestingly, fumonisin B1 (FB1) and the general sphingosine kinase inhibitor SKI II were able to inhibit cell proliferation more prominently in HepG2 and Huh7.5 cells, whereas there were no consistent effects on the formation of dihydroceramides, thus implying an involvement of distinct metabolic pathways. In conclusion, our study demonstrates a significant downregulation of HCC proliferation upon sorafenib, FB1, and SKI II treatment, whereas it seems they exert antiproliferative effects independently from sphingolipids. Certainly, further data would be required to elucidate the potential of FB1 and SKI II as putative novel therapeutic targets in HCC.

Topics: Apoptosis; Basic Helix-Loop-Helix Transcription Factors; Biomarkers, Tumor; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Proliferation; Cell Survival; Ceramides; Hep G2 Cells; Humans; Liver Neoplasms; Protein Kinase Inhibitors; Sorafenib; Sphingolipids

Maximal induction of the acute-phase proteins C-reactive protein (CRP) and serum amyloid A (SAA) in the human hepatoma cell line Hep3B requires the combination of interleukin (IL)-6 and IL-1. In contrast, IL-1 inhibits fibrinogen induction by IL-6. To explore the possible participation of the sphingomyelin-ceramide pathway in the transduction of cytokine effects, the role of this pathway in expression of CRP, SAA and alpha-fibrinogen was investigated. The cell-permeable ceramide analogues C2 and C6 each greatly potentiated induction of both CRP and SAA mRNA by IL-6+IL-1beta but did not affect the responses of alpha-fibrinogen to IL-6 or to IL-6+IL-1beta. The combination of IL-6+IL-1beta led to increased turnover of sphingomyelin in Hep3B cells. D609, an inhibitor of ceramide production by acidic but not neutral sphingomyelinases, substantially inhibited induction of CRP and SAA by IL-6+IL-1beta. The ability of C2 and C6 to potentiate the effects of cytokines suggests that the sphingomyelin-ceramide pathway participates in induction of CRP and SAA by IL-6+IL-1beta under these experimental conditions, most likely by transducing the effects of IL-1beta. C2 and C6 were unable to substitute for IL-1beta in enhancing IL-6 effects on CRP and SAA, consistent with other reports indicating that the sphingomyelin-ceramide pathway is only a single component of multiple necessary converging pathways for induction of many genes. In contrast, this pathway does not appear to participate in mediating the inhibitory effects of IL-1beta on fibrinogen induction by IL-6.

Topics: Apolipoproteins; Bridged-Ring Compounds; C-Reactive Protein; Carcinoma, Hepatocellular; Ceramides; Fibrinogen; Humans; Interleukin-1; Interleukin-6; Norbornanes; RNA, Messenger; Serum Amyloid A Protein; Signal Transduction; Sphingomyelin Phosphodiesterase; Sphingomyelins; Sphingosine; Thiocarbamates; Thiones; Tumor Cells, Cultured