iridoids and pyrazolanthrone

Uncoupling protein 2 (UCP2) was reported to be involved in insulin-glucose homeostasis, based on well established event that inhibition of UCP2 stimulates insulin secretion in pancreatic beta-cells. However, the role of UCP2 on insulin-stimulated glucose uptake in adipose tissue, which is an indispensable process in insulin-glucose homeostasis, remains unknown. In this study, UCP2 was inhibited by genipin in 3T3-L1 adipocytes, which increased mitochondrial membrane potential, intracellular ATP level and production of reactive oxygen species (ROS). Importantly, insulin-stimulated glucose uptake in 3T3-L1 adipocytes was largely impaired in the presence of genipin, and recovered by CCCP, a mitochondrial uncoupler. Furthermore, genipin leaded to suppression of insulin signal transduction through hyperactivation of c-Jun N-terminal kinase (JNK) and subsequent serine phosphorylation of insulin receptor substrate-1 (IRS-1). These results suggest that mitochondrial uncoupling in adipocytes positively regulates insulin-stimulated glucose uptake in adipocytes, and UCP2 may play an important role in insulin resistance.

Topics: 3T3-L1 Cells; Adenosine Triphosphate; Adipocytes; Animals; Anthracenes; Biological Transport, Active; Glucose; Insulin; Insulin Resistance; Ion Channels; Iridoid Glycosides; Iridoids; JNK Mitogen-Activated Protein Kinases; Membrane Potential, Mitochondrial; Mice; Mitochondrial Proteins; Models, Biological; Protein Kinase Inhibitors; Reactive Oxygen Species; Signal Transduction; Uncoupling Protein 2

We have demonstrated the herbal derivative penta-acetyl geniposide ((Ac)(5)GP) induces C6 glioma cell apoptosis through the critical sphingomyelinase (SMase)/nerve growth factor (NGF)/p75 and its downstream signals. It has been reported mitogen-activated protein kinase (MAPK) mediates NGF synthesis induced by SMase activation. In this study, ERK, p38 and JNK are shown to mediate (Ac)(5)GP-induced glioma cell apoptosis and elevation of NGF and p75. Treatment of PD98059 (ERK-specific inhibitor), SB203580 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor) decreases the elevation of NGF and p75 mRNA induced by (Ac)(5)GP, indicating possible transcription regulation via MAPKs. The results of nuclear extract blotting and EMSA further confirm (Ac)(5)GP maximally increases AP-1 and NF-kappaB DNA binding at 6h. Inhibition of ERK, p38 and JNK block the activation of AP-1 and NF-kappaB, suggesting these MAPKs are involved in (Ac)(5)GP-induced transcription regulation. We thereby used RT-PCR to analyze cells treated with (Ac)(5)GP, with or without AP-1 or NF-kappaB inhibitors. AP-1 inhibitor NDGA decreases NGF/p75 and expression of FasL and caspase 3 induced by (Ac)(5)GP, suggesting the importance of AP-1 in mediating NGF/p75 and their downstream apoptotic signals. However, FasL and caspase 3 do not change with the NF-kappaB inhibitor PDTC; NF-kappaB might be linked to other cellular events. Overall, we demonstrate that MAPK mediates (Ac)(5)GP-induced activation of AP-1, promoting the transcription of NGF/p75 and downstream apoptotic signals. These results further highlight the potential therapeutic effects of (Ac)(5)GP in chemoprevention or as an anti-tumor agent.

Topics: Animals; Anthracenes; Anti-Inflammatory Agents, Non-Steroidal; Antioxidants; Apoptosis; Cell Line, Tumor; Electrophoretic Mobility Shift Assay; Flavonoids; Gardenia; Glioma; Glucosides; Imidazoles; Immunoblotting; Iridoid Glucosides; Iridoids; Keratolytic Agents; Masoprocol; Mitogen-Activated Protein Kinases; Molecular Structure; Nerve Growth Factor; NF-kappa B; Peptide Fragments; Pyridines; Rats; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transcription Factor AP-1; Transcriptional Activation