Effect of polyols on membrane structures of liposomes: A study using small-angle X-ray scattering data and generalized indirect Fourier transformation.

This study aimed to evaluate the membrane structure of distearoylphosphatidylcholine (DSPC) liposomes dispersed in water containing various types of polyols with low molecular weight such as glycerin (Gly), 1,3-butandiol (BG), and propylene glycol (PG). To clarify the detailed membrane structure, generalized indirect Fourier transformation (GIFT) analysis, which provides information about the bilayer spacing, bilayer thickness, number of lamellar layers, and membrane flexibility, was applied to small-angle X-ray scattering (SAXS) data of the present system. The GIFT results showed that the bilayer thickness of the DSPC liposomes followed the order Gly>>BG>PG. In addition, the membrane flexibility estimated by the Caille parameter was in the order Gly>>BG>PG; this result was supported by the gel-liquid crystal phase transition temperature (Tc) obtained by differential scanning calorimetry (DSC). These results, together with the Raman spectra, suggest that BG and PG incorporated into the bilayers of DSPC liposomes result in the formation of an interdigitated lamellar structure.

Varenicline promotes endothelial cell migration by lowering vascular endothelial-cadherin levels via the activated α7 nicotinic acetylcholine receptor-mitogen activated protein kinase axis.

Varenicline is a widely used and effective drug for smoking cessation. Despite its efficacy, varenicline increases the risk of cardiovascular disease. We previously demonstrated that varenicline aggravates atherosclerotic plaque formation in apolipoprotein E knockout mice. However, little is known about its effects in vascular endothelial cells. Therefore, we examined whether varenicline promotes migration of human umbilical vein endothelial cells (HUVECs) using the Boyden chamber assay. Varenicline (100µM) markedly promoted migration of HUVECs and decreased expression of vascular endothelial (VE)-cadherin, an endothelial adhesion molecule. Extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) signaling were markedly activated by varenicline. Methyllycaconitine (MLA; 100nM), an α7 nicotinic acetylcholine receptor (nAChR) antagonist, but not dihydro-ß-erythroidine hydrobromide (DHßE; 20µM) blocked varenicline-stimulated migration and varenicline-activated ERK, p38 and JNK signaling in HUVECs. MLA (100nM), PD98059 (an ERK inhibitor; 20µM), SB203580 (a p38 inhibitor; 20µM) and SP600125 (a JNK inhibitor; 20µM) also blocked cell migration and varenicline-induced downregulation of VE-cadherin expression in HUVECs. These findings suggest that varenicline promotes HUVEC migration by lowering VE-cadherin expression due to activated ERK/p38/JNK signaling through α7 nAChR. These processes probably contribute to varenicline-aggravated atherosclerotic plaque. Hence, an increased risk of cardiovascular events upon varenicline treatment might occur and must be considered in patients with cardiovascular diseases.

Varenicline enhances oxidized LDL uptake by increasing expression of LOX-1 and CD36 scavenger receptors through α7 nAChR in macrophages.

Varenicline is a widely used and effective drug for smoking cessation. It is a partial agonist of the α4ß2 nicotinic acetylcholine receptor (nAChR) and full agonist of α7 nAChR. We have reported that varenicline aggravates formation of atherosclerotic plaques through α7 nAChR in apolipoprotein E knockout mice. However, little is known about its effects on macrophages in atherosclerotic plaques. Here, we ascertained whether varenicline promotes oxidized low-density lipoprotein (oxLDL) uptake in mouse peritoneal macrophages in vitro and clarified its mechanism. We investigated the effects of varenicline (1-10µM) on expression of scavenger receptors (lectin-like oxidized LDL receptor-1 (LOX-1), cluster of differentiation (CD) 36 and scavenger receptor class A (SR-A)) in RAW264.7 cells. Expression of protein and mRNA was determined by western blotting and real-time quantitative reverse transcription-polymerase chain reaction, respectively. Effects of varenicline (10µM) on oxLDL uptake were examined by counting the number of macrophages stained with oil red O and hematoxylin. Varenicline significantly increased expression of the protein and mRNA of LOX-1 and CD36, but not SR-A, in RAW264.7 cells, and increased oxLDL uptake in macrophages. These effects of varenicline were blocked significantly by an α7 nAChR antagonist, methyllycaconitine (MLA) (50nM), but not by an α4ß2 nAChR antagonist, dihydro-ß-erythroidine hydrobromide (DHßE) (1µM). These data suggest that varenicline promotes oxLDL uptake by upregulating expression of LOX-1 and CD36 through α7 nAChR in macrophages. We found that varenicline significantly activated extracellular signal-regulated kinase 1/2 (ERK1/2) and nuclear factor-kappa B (NF-κB) signaling pathways in RAW264.7 cells. This activation was blocked by MLA but not DHßE. Therefore, ERK1/2-NF-κB signaling pathway is highly likely to be responsible for varenicline-induced upregulation of LOX-1 and CD36 expression through α7 nAChR in macrophages. These processes probably contribute to varenicline-aggravated atherosclerotic plaque formation. Hence, an increased risk of cardiovascular events upon varenicline treatment could occur, and must be considered in patients (especially those suffering from cardiovascular diseases).

Varenicline aggravates plaque formation through α7 nicotinic acetylcholine receptors in ApoE KO mice.

Varenicline is one of the most widely used drugs for smoking cessation. However, whether an adverse effect of varenicline is associated with the risk of serious cardiovascular events remains controversial. In this study, we determined if varenicline increases the risk of cardiovascular events using apolipoprotein E knockout (ApoE KO) mice. ApoE KO mice (8 weeks old) were injected with varenicline 0.5 mg kg(-1)day(-1) for 3 weeks. Varenicline aggravated atherosclerotic plaque formation in whole aorta from ApoE KO mice compared with vehicle. Methyllycaconitine, an α7 nicotinic acetylcholine receptor (nAChR) antagonist, inhibited varenicline-induced aggravated plaque formation. Our findings show that varenicline progresses atherosclerotic plaque formation through α7 nAChR, and thereby increases the risk of cardiovascular events.