Soluble P-selectin promotes acute myocardial infarction onset but not severity.

P­selectin, an integral membrane glycoprotein of platelets and endothelial cells, and the soluble form of P­selectin are hypothesized to play a role in the initiation of atherosclerosis and acute myocardial infarction (AMI). However, limited data are available with which to evaluate the main role of soluble P­selectin (sP­selectin) in the onset or the severity of AMI. In the present study, we investigated 15 patients who suffered from angina, 10 patients who underwent percutaneous coronary intervention (PCI) therapy and 10 patients who underwent thrombolysis therapy, compared with 15 volunteers with no cardiovascular disease. We confirmed that the plasma sP­selectin levels were increased in patients with obesity (particularly pericardial obesity) and hyperlipidemia, positively correlated with plasma tumor necrosis factor (TNF)­α and strongly negatively correlated with adiponectin in all patients regardless of AMI status. Furthermore, sP­selectin levels were significantly higher in PCI and thrombolysis patients compared with angina patients and the control cohort. However, we observed that sP­selectin levels did not change following PCI and thrombolysis therapy. In addition, there was no correlation between sP­selectin levels and the severity of AMI in the cohort which received PCI or thrombolysis therapy. Therefore, we deduced that sP­selectin only induced the onset of AMI but did not promote its severity. To confirm this hypothesis, a P­selectin inhibitor was administered to an atherosclerosis formation model, plaque rapture model and neointimal hyperplasia model. We revealed that atherosclerotic plaque formation and rupture, neointimal formation and neointimal bleeding were suppressed by the sP­selectin inhibitor. We concluded that sP­selectin, induced by systemic inflammation in conditions including obesity and hyperlipidemia, promoted atherosclerotic plaque and neointimal formation, plaque rapture and neointimal bleeding, further leading to AMI. We also demonstrated that sP­selectin had no effect on the severity of AMI.

Mechanism of matrix metalloproteinase axis-induced neointimal growth.

Tumor necrosis factor-α, platelet-derived growth factor, matrix metalloproteinases 9 and 2 have very important roles in neointimal hyperplasia, which develops after endovascular injury. However, the relationships among the four factors in inducing neointimal hyperplasia are unclear. Here, we used a mouse model of femoral arterial transluminal wire injury, and examined neointimal hyperplasia within the 28 days that followed the injury. We confirmed that the neointima kept growing during the 28 days, and found that expression of TNF-α and PDGF mRNAs in femoral arteries peaked within 24h after injury. However, MMP9 mRNA expression peaked 7 days, and MMP2 mRNA expression peaked 28 days after injury. Then, we administered exogenous TNF-α or PDGF to the peri-femoral artery following an injury, and found that exogenous TNF-α led to significantly more neointimal hyperplasia during the first 2 weeks, and PDGF led to increased neointimal hyperplasia during the second 2 weeks after injury. We also used the model of femoral artery injury in MMP9- or MMP2-deficient (MMP9-/- or MMP2-/-) mice. We found that neointimal hyperplasia was reduced in MMP9-/- mice during the first 2 weeks after injury, and neointimal hyperplasia was reduced in MMP2-/- mice during the second 2 weeks after injury. When TNF-α or PDGF was administered to the peri-femoral artery immediately after injury, TNF-α did not promote neointimal hyperplasia in MMP9-/- mice during the first 2 weeks after injury but did in MMP2-/- mice, and PDGF did not promote neointimal hyperplasia in MMP2-/- mice during the second 2 weeks after injury but did in MMP9-/- mice. We used an in vitro system to treat vascular smooth muscle cells (VSMCs) with TNF-α or PDGF; TNF-α induced MMP9, but not MMP2, expression at a fast reaction speed, while PDGF induced MMP2, but not MMP9, expression at a slow reaction speed. Meanwhile, TNF-α induced VSMC migration in a MMP9-dependent manner, and PDGF induced VSMC proliferation in a MMP2-dependent manner. Taken together, our studies elucidated the axis of TNF-α-MMP9-VSMC migration and PDGF-MMP2-VSMC proliferation, both of which contributed to the mechanism of neointimal hyperplasia formation.

Propionyl-L-carnitine induces eNOS activation and nitric oxide synthesis in endothelial cells via PI3 and Akt kinases.

Propionyl-l-carnitine (PLC) is a natural short-chain derivative of l-carnitine (LC), a natural amino acid that plays an important role in fatty acid metabolism. Recent studies suggest that PLC has vascular protective effects. Because of the importance of endothelial nitric oxide synthase (eNOS) and its product, antiatherogenic molecule nitric oxide (NO), in vascular endothelial function, we sought to elucidate that if PLC would stimulate eNOS and its upstream activators Akt and phosphatidylinositol 3-kinase (PI3 Kinase) in cultured human aortic endothelial cells (HAEC). PLC caused eNOS phosphorylation at Ser-1177, and dominant negative Akt and a novel Akt-selective inhibitor MK-2206 inhibited both PLC-mediated phosphorylation and activation of the enzyme. PI3 kinase inhibition also blocked the phosphorylation and activation of eNOS by PLC. Studies with specific drug inhibitors PD173955 and PP2 showed that the non-receptor tyrosine kinase, src, is an upstream stimulator of the PI3 kinase-Akt pathway in this pathway. In addition, PLC significantly decreased intracellular ATP/ADP ratio and activate AMPK, subsequently leading to Src activation. Finally, we demonstrated that the effects of PLC to augment eNOS activity were associated with a net increase in NO release from endothelial cells. NO production following incubation with PLC was abolished in endothelial cells coincubated with L-NAME, PD173955, LY294002, MK-2206 and compound C. In conclusion, PLC, via AMPK/Src-mediated signaling that leads to activation of PI3 kinase and Akt, stimulates eNOS, leading to increased production of NO.