Genipin ((+)-Genipin), an active aglycone derived from an iridoid glycoside called geniposide, is found in the fruit of Gardenia jasminoides Ellis.

Genipin stimulats glucose uptake in a time- and dose-dependent manner. The maximal effect is achieved at 2?h with a concentration of 10?μM. In myotubes, genipin promotes glucose transporter 4 (GLUT4) translocation to the cell surface, which increases the phosphorylation of insulin receptor substrate-1 (IRS-1), AKT, and GSK3β. Meanwhile, genipin increases ATP levels, closed KATP channels, and then increases the concentration of calcium in the cytoplasm in C2C12 myotubes. Genipin-stimulated glucose uptake could be blocked by both the PI3-K inhibitor wortmannin and calcium chelator EGTA. Moreover, genipin increases the level of reactive oxygen species and ATP in C2C12 myotubes[1]. Genipin increases mitochondrial membrane potential, which then increases ATP levels and closes KATP channels, thereby stimulating insulin secretion in pancreatic β-cells. Genipin activates glucose-excited POMC neurons[2]. Cytochrome c content increases significantly in the cytosol of genipin-treated FaO cells. Activation of caspase-3 and caspase-7 is ultimately responsible for genipin-induced apoptotic process in hepatoma cells. ROS level notably increases in Hep3B cells treated with 200 μM genipin[3].

Briefly, the peptide substrate N-acetyl-Asp-Glu-Val-Asp-ρ-nitroanilide (Ac-DEVD-ρNA) is added to the cell lysates in assay buffer (50 mM HEPES, pH 7.4, 100 mM NaCl, 0.1% CHAPS, 10 mM dithiothreitol, 1 mM EDTA, 10% glycerol) and incubated at 37°C. The cleavage of the substrate is monitored at 405 nm.