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Circulating apolipoprotein J (ApoJ) is closely associated with insulin resistance; however, the effect of exercise on circulating ApoJ levels and the association of ApoJ with metabolic indices remain unknown. Here, we investigated whether a combined exercise can alter the circulating ApoJ level, and whether these changes are associated with metabolic indices in patients with type 2 diabetes mellitus.
Postmenopausal women with type 2 diabetes mellitus were randomly assigned into either an exercise (EXE,
In the EXE group, ApoJ levels decreased 26.3% and 19.4%, relative to baseline, at 8 and 12 weeks, respectively. Between-group differences were significant at 8 and 12 weeks (
Exercise training resulted in a significant decrease in the circulating ApoJ level, with changes in ApoJ associated with an improvement in some insulin resistance indices. These data suggest that circulating ApoJ may be a useful metabolic marker for assessing the effects of exercise on insulin resistance.
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Chronic exposure to elevated levels of free fatty acids contributes to pancreatic β-cell dysfunction. Although it is well known that metformin induces cellular energy depletion and a concomitant activation of AMP-activated protein kinase (AMPK) through inhibition of the respiratory chain, previous studies have shown inconsistent results with regard to the action of metformin on pancreatic β-cells. We therefore examined the effects of metformin on pancreatic β-cells under lipotoxic stress.
NIT-1 cells and mouse islets were exposed to palmitate and treated with 0.05 and 0.5 mM metformin. Cell viability, glucose-stimulated insulin secretion, cellular adenosine triphosphate, reactive oxygen species (ROS) levels and Rho kinase (ROCK) activities were measured. The phosphorylation of AMPK was evaluated by Western blot analysis and mRNA levels of endoplasmic reticulum (ER) stress markers and NADPH oxidase (NOX) were measured by real-time quantitative polymerase chain reaction analysis.
We found that metformin has protective effects on palmitate-induced β-cell dysfunction. Metformin at a concentration of 0.05 mM inhibits NOX and suppresses the palmitate-induced elevation of ER stress markers and ROS levels in a AMPK-independent manner, whereas 0.5 mM metformin inhibits ROCK activity and activates AMPK.
This study suggests that the action of metformin on β-cell lipotoxicity was implemented by different molecular pathways depending on its concentration. Metformin at a usual therapeutic dose is supposed to alleviate lipotoxic β-cell dysfunction through inhibition of oxidative stress and ER stress.
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