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BackgroundAtherosclerosis and inflammation are more common in patients with diabetes than in patients without diabetes, and atherosclerosis progression contributes to inflammation. Therefore, anti-inflammatory therapy is important for the prognosis of patients with diabetes. Linagliptin is the only bile-excreted, anti-diabetic oral dipeptidyl peptidase-4 (DPP-4) inhibitor. Although the anti-inflammatory effects of DPP-4 inhibitors in vivo and in vitro have been reported, few in vitro studies have examined the effects of linagliptin using monocytes, which play a central role in arteriosclerosis-related inflammation. Herein, we assessed the anti-inflammatory effects of linagliptin in human U937 monocytes.MethodsU937 cells at densities of 1 × 106 cells/mL were cultured in Roswell Park Memorial Institute medium supplied with 10% fetal bovine serum and treated with 100 nM phorbol myristate acetate for 48 h for differentiation into macrophages. The media were replaced, and the cells were pretreated with 1, 5, 10, 50, and 100 nM linagliptin for 1 h or were left untreated. The media were then replaced again, and the cells were treated with 1 μg/mL lipopolysaccharide (LPS) or 10 nM interleukin (IL)-1β only, in combination with 1, 5, 10, 50, and 100 nM linagliptin or were left untreated. The extracted media were used to measure IL-6 and tumor necrosis factor (TNF)-α levels using enzyme-linked immunosorbent assay kits.ResultsLPS alone significantly increased IL-6 and TNF-α production compared with the control treatment. The treatment of cells with linagliptin at all concentrations significantly inhibited the LPS-stimulated IL-6 and TNF-α production. Meanwhile, IL-1β alone significantly increased IL-6 production compared with the control treatment. No significant difference in IL-6 production was noted between the cells treated with IL-1β and simultaneous treatment with IL-1β and linagliptin.ConclusionsLinagliptin inhibited LPS-induced inflammation in human monocytic U937 cells.

BACKGROUNDBecause of the potential anti-inflammatory effects, linagliptin, a therapeutic dipeptidyl peptidase-4 inhibitor, is used as an effective drug for diabetic patients for whom inflammation is a prognosis-related factor. We investigated the anti-inflammatory mechanism of linagliptin using seven markers.METHODSWe pretreated human umbilical vein endothelial cells (HUVECs), with linagliptin and lipopolysaccharide (LPS). The cytosolic fractions were evaluated for protein kinase A (PKA), protein kinase B (PKB), protein kinase C (PKC), ratio of reactive oxygen species (ROS) and Cu/Zn superoxide dismutase (SOD), activator protein 1 (AP-1), and adenosine 3′,5′-cyclic monophosphate (cAMP).RESULTSLinagliptin increased the PKA and PKC activities and the cAMP levels in LPS-treated cells. However, it inhibited LPS-induced PKB phosphorylation, ratio of ROS and Cu/Zn SOD, and LPS-stimulated AP-1 nuclear translocation.CONCLUSIONWe reaffirmed the anti-inflammatory and antioxidant effects of linagliptin. These effects might be related to the three protein kinases. Our findings suggest that linagliptin has a wide range of anti-inflammatory effects.

We studied effects of Ca2+ in the incubation medium on [3H]dopamine ([3H]DA) uptake by rat striatal synaptosomes. Both the duration of the preincubation period with Ca2+ (0–30 min) and Ca2+ concentration (0–10 mM) in Krebs‐Ringer medium affected [3H]DA uptake by the synaptosomes. The increase was maximal at a concentration of 1 mM Ca2+ after a 10‐min preincubation (2.4 times larger than the uptake measured without preincubation), which reflected an increase in Vmax of the [3H]DA uptake process. On the other hand, [3H]DA uptake decreased rapidly after addition of ionomycin in the presence of 1 mM Ca2+. The Ca2+‐dependent enhancement of the uptake was still maintained after washing synaptosomes with Ca2+‐free medium following preincubation with 1 mM Ca2+. Protein kinase C inhibitors did not affect apparently Ca2+‐dependent enhancement of the uptake, whereas 1‐[N,O‐bis(1,5‐isoquinolinesulfonyl)‐N‐methyl‐l‐tyrosyl]‐4‐phenylpiperazine (KN‐62; a Ca2+/calmodulin‐dependent kinase II inhibitor) and wortmannin (a myosin light chain kinase inhibitor) significantly reduced it. Inhibitory effects of KN‐62 and wortmannin appeared to be additive. N‐(6‐Aminohexyl)‐5‐chloro‐1‐naphthalenesulfonamide hydrochloride (W‐7; a calmodulin antagonist) also remarkably inhibited the enhancement. These results suggest that Ca2+‐dependent enhancement of [3H]DA uptake is mediated by activation of calmodulin‐dependent protein kinases.