Dexamethasone-induced decrease in HMG-CoA reductase and protein-farnesyl transferase activities does not impair ras processing in AR 4-2J cells

Prednisone and Its Active Metabolite Prednisolone Attenuate Lipid Accumulation in Macrophages

BACKGROUND

Synthetic forms of glucocorticoids (GCs; eg, prednisone, prednisolone) are anti-inflammatory drugs that are widely used in clinical practice. The role of GCs in cardiovascular diseases, including atherosclerosis, is highly controversial, and their impact on macrophage foam cell formation is still unknown. We investigated the effects of prednisone and prednisolone on macrophage oxidative stress and lipid metabolism.

METHODS AND RESULTS

C57BL/6 mice were intraperitoneally injected with prednisone or prednisolone (5 mg/kg) for 4 weeks, followed by lipid metabolism analyses in the aorta and peritoneal macrophages. We also analyzed the effect of serum samples obtained from 9 healthy human volunteers before and after oral administration of prednisone (20 mg for 5 days) on J774A.1 macrophage atherogenicity. Finally, J774A.1 macrophages, human monocyte-derived macrophages, and fibroblasts were incubated with increasing concentrations (0-200 ng/mL) of prednisone or prednisolone, followed by determination of cellular oxidative status, and triglyceride and cholesterol metabolism. Prednisone and prednisolone treatment resulted in a significant reduction in triglyceride and cholesterol accumulation in macrophages, as observed in vivo, ex vivo, and in vitro. These effects were associated with GCs' inhibitory effect on triglyceride- and cholesterol-biosynthesis rates, through downregulation of diacylglycerol acyltransferase 1 and HMG-CoA reductase expression. Glucocorticoid-induced reduction of cellular lipid accumulation was mediated by the GC receptors on the macrophages, because the GC-receptor antagonist (RU486) abolished these effects. In fibroblasts, unlike macrophages, GCs showed no effects.

CONCLUSION

Prednisone and prednisolone exhibit antiatherogenic activity by protecting macrophages from lipid accumulation and foam cell formation.

Screening a library of approved drugs reveals that prednisolone synergizes with pitavastatin to induce ovarian cancer cell death

The survival rate for patients with ovarian cancer has changed little in the past three decades since the introduction of platinum-based chemotherapy and new drugs are needed. Statins are drugs used for the treatment and prevention of cardiovascular diseases. Recent work from our laboratory has shown that pitavastatin has potential as a treatment for ovarian cancer if dietary geranylgeraniol is controlled. However, relatively high doses of statins are required to induce apoptosis in cancer cells, increasing the risk of myopathy, the most common adverse effect associated with statins. This makes it desirable to identify drugs which reduce the dose of pitavastatin necessary to treat cancer. A drug-repositioning strategy was employed to identify suitable candidates. Screening a custom library of 100 off-patent drugs for synergistic activity with pitavastatin identified prednisolone as the most prominent hit. Prednisolone potentiated the activity of pitavastatin in several assays measuring the growth, survival or apoptosis in several ovarian cancer cells lines. Prednisolone, alone or in some cases in combination with pitavastatin, reduced the expression of genes encoding enzymes in the mevalonate pathway, providing a mechanistic explanation for the synergy.

Co-administration of simvastatin and cytotoxic drugs is advantageous in myeloma cell lines

We have evaluated the potential application of simvastatin (Sim) combined with conventional cytotoxic drugs for the treatment of multiple myeloma. RPMI 8226 and U266 myeloma cells seeded in culture plates were treated with Sim (5 and 10 microM, respectively) combined with melphalan (Mel; 25 and 20 microM, respectively) or dexamethasone (Dex; 1 microM). We assessed cell cycle (propidium iodide staining and flow cytometric analysis), cell morphology, viability (WST1), total cell count and cell death (Trypan blue exclusion). Sim significantly enhanced the anti-myeloma activity of cytotoxic agents in vitro (p<0.05). Incubation of U266 and RPMI 8226 with Sim prior to Mel increased the cytotoxicity in an additive manner, whereas the exposure of U266 to combined Sim and Dex resulted in a synergistic amplification of the individual effects. Combined application of Dex and Sim to RPMI 8226 cells resulted in antagonistic activity. The possible roles of Ras and phosphoinositol 3-kinase are discussed.

Oncoviral bovine leukemia virus G4 and human T-cell leukemia virus type 1 p13(II) accessory proteins interact with farnesyl pyrophosphate synthetase

G4 and p13(II) are accessory proteins encoded by the X region of bovine leukemia virus and human T-cell leukemia virus type 1 (HTLV-1), respectively. Disruption of the G4 and p13(II) open reading frames interferes with viral spread in animal model systems, indicating that the corresponding proteins play a key role in viral replication. In addition, G4 is oncogenic in primary cell cultures and is absolutely required for efficient onset of leukemogenesis in sheep. To gain insight into the function of these proteins, we utilized the yeast two-hybrid system to identify protein partners of G4. Results revealed that G4 interacts with farnesyl pyrophosphate synthetase (FPPS), a protein involved in the mevalonate/squalene pathway and in synthesis of FPP, a substrate required for prenylation of Ras. The specificity of the interaction was verified by glutathione S-transferase (GST) pull-down assays and by coimmunoprecipitation experiments. Furthermore, confocal microscopy showed that the subcellular localization of G4 was profoundly affected by FPPS. The G4 protein itself was not prenylated, at least in rabbit reticulocyte lysate-based assays. The domain of G4 required for binding to FPPS was restricted to an amphipathic alpha-helix rich in arginine residues. Subtle mutation of this alpha-helix abrogated G4 oncogenic potential in vitro, providing a biological relevance for FPPS-G4 complex formation in cells. Finally, HTLV-1 p13(II) was also found to specifically interact with FPPS (in yeast as well as in GST pull-down assays) and to colocalize with G4 in mitochondria, suggesting a functional analogy between these oncoviral accessory proteins. Identification of FPPS as a molecular partner for p13(II) and G4 accessory proteins opens new prospects for treatment of retrovirus-induced leukemia.