Impaired graft healing due to hypercholesterolemia is prevented by dietary supplementation with alpha-tocopherol

p85α regulatory subunit isoform controls PI3-kinase and TRPC6 membrane translocation

Activation of phosphatidylinositol 3-kinase (PI3K) by lipid oxidation products, including lysophosphatidylcholine (lysoPC), increases the externalization of canonical transient receptor potential 6 (TRPC6) channels leading to a subsequent increase in intracellular calcium that contributes to cytoskeletal changes which inhibit endothelial cell (EC) migration in vitro and impair EC healing of arterial injuries in vivo. The PI3K p110α and p110δ catalytic subunit isoforms regulate lysoPC-induced TRPC6 externalization in vitro, but have many other functions. The goal of the current study is to identify the PI3K regulatory subunit isoform involved in TRPC6 externalization to potentially identify a more specific treatment regimen to improve EC migration and arterial healing, while minimizing off-target effects. Decreasing the p85α regulatory subunit isoform protein levels, but not the p85β and p55γ regulatory subunit isoforms, with small interfering RNA inhibits lysoPC-induced translocation of the PI3K catalytic subunit to the plasma membrane, dramatically decreased phosphatidylinositol (3,4,5)-trisphosphate (PIP3) production and TRPC6 externalization, and significantly improves EC migration in the presence of lysoPC. These results identify the important and specific role of p85α in controlling translocation of PI3K from the cytosol to the plasma membrane and PI3K-mediated TRPC externalization by oxidized lipids. Current PI3K inhibitors block the catalytic subunit, but our data suggest that the regulatory subunit is a novel therapeutic target to promote EC migration and healing after arterial injuries that occur with angioplasty.

P110α and P110δ catalytic subunits of PI3 kinase regulate lysophosphatidylcholine-induced TRPC6 externalization

Lipid oxidation products, including lysophosphatidylcholine (lysoPC) inhibit endothelial cell (EC) migration in vitro and impair EC healing of arterial injuries in vivo, in part by activating phosphatidylinositol 3-kinase (PI3K), which increases the externalization of canonical transient receptor potential 6 (TRPC6) channels and the subsequent increase in intracellular calcium. Inhibition of PI3K is a potential method to decrease TRPC6 activation and restore migration, but PI3K is involved in multiple intracellular signaling pathways and has multiple downstream effectors. The goal of this study is to identify the specific p110 catalytic subunit isoforms responsible for lysoPC-induced TRPC6 externalization to identify a target for intervention while minimizing impact on alternative signaling pathways. Down-regulation of the p110α and p110δ isoforms, but not the p110β or p110γ isoforms, with small interfering RNA significantly decreased phosphatidylinositol (3,4,5)-trisphosphate production and TRPC6 externalization, and significantly improved EC migration in the presence of lysoPC. These results identify an additional role of p110α in EC and reveal for the first time a specific role of p110δ in EC, providing a foundation for subsequent in vivo studies to investigate the impact of p110 isoform inhibition on arterial healing after injury.

Ginkgolide A-gold nanoparticles inhibit vascular smooth muscle proliferation and migration in vitro and reduce neointimal hyperplasia in a mouse model

BACKGROUND

Neointimal formation is mediated by phenotypic changes in vascular smooth muscle cells (SMC) and is an important mediator of restenosis following arterial reconstruction. We conjugated antioxidant ginkgolide A (GA) to gold nanoparticles (GNP) to determine the effect of GA delivery on neointimal formation.

MATERIALS AND METHODS

GA was conjugated to 80 nm GNP in an overnight incubation. Mouse P53LMAC01 vascular SMC were treated with various doses of GA-GNP, GA alone, GNP alone, and no treatment control. Cell proliferation and migration were analyzed, and superoxide anion levels and the phosphorylation status of ERK1/2 were determined. Mice underwent ligation of the common carotid artery along with local treatment with GNP (control) or GA-GNP. The carotid artery was harvested and subjected to immunohistochemical analysis.

RESULTS

GA-GNP treatment significantly inhibited SMC proliferation and migration in vitro in comparison to GNP treatment alone, and the effect persisted for up to 72 h after treatment. Treatment with GA-GNP also reduced superoxide anion levels in vitro. PDGF-BB substantially induced ERK1/2 phosphorylation in GNP control cells; this PDGE-BB induced ERK1/2 phosphorylation was significantly inhibited in GA-GNP-treated cells compared with GNP only. GA-GNP significantly reduced neointimal hyperplasia after injury in mice, and proliferating cell nuclear antigen (PCNA) staining was reduced substantially in the arteries of mice treated with GA-GNP.

CONCLUSIONS

GA-GNP reduce vascular SMC proliferation and migration in vitro through reduced activation of ERK1/2. Local treatment with GA-GNP in areas of arterial injury reduced neointimal hyperplasia and subsequent stenosis.

Antioxidant therapy reverses impaired graft healing in hypercholesterolemic rabbits

OBJECTIVE

Limited endothelial cell (EC) coverage and anastomotic intimal hyperplasia contribute to thrombosis and failure of prosthetic grafts. Lipid accumulation and lipid oxidation are associated with decreased EC migration and intimal hyperplasia. The goal of this study was to assess the ability of antioxidants to improve graft healing in hypercholesterolemic animals.

METHODS

Rabbits were placed in one of four groups: chow plus N-acetylcysteine (NAC), chow plus probucol, chow with 1% cholesterol plus NAC, or chow with 1% cholesterol plus probucol. After 2 weeks, expanded polytetrafluoroethylene grafts (12 cm long x 4-mm internal diameter) were implanted in the abdominal aorta. Grafts were removed after 6 weeks and analyzed for cholesterol content, EC coverage, anastomotic intimal thickness, and the cellular composition of the neointima. Plasma samples were obtained to assess systemic oxidative stress. The data were compared with previously reported data from animals fed diets of chow and chow with 1% cholesterol.

RESULTS

Prosthetic grafts from rabbits fed chow with 1% cholesterol had significantly greater anastomotic intimal thickening and lower EC coverage than grafts from rabbits fed a regular chow diet. In hypercholesterolemic rabbits, antioxidant therapy decreased global oxidative stress as evidenced by a 40% decrease in plasma thiobarbituric acid reactive substances. In rabbits fed the chow with 1% cholesterol diet, NAC decreased intimal hyperplasia at the proximal anastomosis by 29% and significantly increased graft EC coverage from 46% to 71% (P = .03). Following a similar pattern, probucol decreased intimal hyperplasia by 43% and increased graft EC coverage to 53% in hypercholesterolemic rabbits.

CONCLUSIONS

Global oxidative stress and anastomotic intimal hyperplasia are increased, and endothelialization of prosthetic grafts is significantly reduced in rabbits fed a high-cholesterol diet. Antioxidant treatment improves EC coverage and decreases intimal hyperplasia. Reducing oxidative stress may promote healing of prosthetic grafts.