Suppressive effect of ghrelin on nicotine-induced clock gene expression in the mouse pancreas.

Those who smoke nicotine-based cigarettes have elevated plasma levels of ghrelin, a hormone secreted from the stomach. Ghrelin has various physiological functions and has recently been shown to be involved in regulating biological rhythms. Therefore, in this study, in order to clarify the significance of the plasma ghrelin increase in smokers, we sought to clarify how nicotine and ghrelin affect the expression dynamics of clock genes using a mouse model. A single dose of nicotine administered intraperitoneally increased plasma ghrelin concentrations transiently, whereas continuous administration of nicotine with an osmotic minipump did not induce any change in the plasma ghrelin concentration. Single administration of nicotine resulted in a transient increase in ghrelin gene expression in the pancreas but not in the stomach, which is the major producer of ghrelin. In addition, in the pancreas, the expression of clock genes was also increased temporarily. Therefore, in order to clarify the interaction between nicotine-induced ghrelin gene expression and clock gene expression in the pancreas, nicotine was administered to ghrelin gene-deficient mice. Administration of nicotine to ghrelin-gene deficient mice increased clock gene expression in the pancreas. However, upon nicotine administration to mice pretreated with octanoate to upregulate ghrelin activity, expression levels of nicotine-inducible clock genes in the pancreas were virtually the same as those in mice not administered nicotine. Thus, our findings indicate that pancreatic ghrelin may suppress nicotine-induced clock gene expression in the pancreas.

Tea polyphenols direct Bmal1-driven ameliorating of the redox imbalance and mitochondrial dysfunction in hepatocytes.

Circadian rhythms are intimately linked to cellular redox status homeostasis via the regulation of mitochondrial function. Tea polyphenols (TP) are nutraceuticals that possess powerful antioxidant properties, especially ameliorating oxidative stress. The objective of this study was to investigate whether circadian clock is involved in the protection effect of TP on oxidative stress cell models. TP ameliorate H2O2-triggered relatively shallow daily oscillations and phase shift of circadian clock genes transcription and protein expression. Meanwhile, TP attenuate H2O2-stimulated excessive secretions of reactive oxygen species (ROS) and restore the depletions of mitochondrial function in a Bmal1-dependent manner. Furthermore, TP treatment accelerates nuclear translocation of Nrf2 and modulates the downstream expressions of antioxidant enzymes. Intriguingly, knockdown of Bmal1 notably blocked Nrf2/ARE/HO-1 redox-sensitive transcription pathway. Our study revealed that TP, as a Bmal1-enhancing natural compound, alleviated redox imbalance via strengthening Keap1/Nrf2 antioxidant defense pathway and ameliorating mitochondrial dysfunction in a Bmal1-dependent manner.