PX-18 Protects Human Saphenous Vein Endothelial Cells under Arterial Blood Pressure.

BACKGROUND: Arterial blood pressure-induced shear stress causes endothelial cell apoptosis and inflammation in vein grafts after coronary artery bypass grafting. As the inflammatory protein type IIA secretory phospholipase A2 (sPLA2-IIA) has been shown to progress atherosclerosis, we hypothesized a role for sPLA2-IIA herein. METHODS: The effects of PX-18, an inhibitor of both sPLA2-IIA and apoptosis, on residual endothelium and the presence of sPLA2-IIA were studied in human saphenous vein segments (n = 6) perfused at arterial blood pressure with autologous blood for 6 hrs. RESULTS: The presence of PX-18 in the perfusion blood induced a significant 20% reduction in endothelial cell loss compared to veins perfused without PX18, coinciding with significantly reduced sPLA2-IIA levels in the media of the vein graft wall. In addition, PX-18 significantly attenuated caspase-3 activation in human umbilical vein endothelial cells subjected to shear stress via mechanical stretch independent of sPLA2-IIA. CONCLUSIONS: In conclusion, PX-18 protects saphenous vein endothelial cells from arterial blood pressure-induced death, possibly also independent of sPLA2-IIA inhibition.

Arterial Blood Pressure Induces Transient C4b-Binding Protein in Human Saphenous Vein Grafts.

BACKGROUND: Complement is an important mediator in arterial blood pressure-induced vein graft failure. Previously, we noted activation of cell protective mechanisms in human saphenous veins too. Here we have analyzed whether C4b-binding protein (C4bp), an endogenous complement inhibitor, is present in the vein wall. METHODS: Human saphenous vein segments obtained from patients undergoing coronary artery bypass grafting (n = 55) were perfused in vitro at arterial blood pressure with either autologous blood for 1, 2, 4, or 6 hr or with autologous blood supplemented with reactive oxygen species scavenger N-acetylcysteine. The segments were subsequently analyzed quantitatively for presence of C4bp and complement activation product C3d using immunohistochemistry. RESULTS: Perfusion induced deposition of C3d and C4bp within the media of the vessel wall, which increased reproducibly and significantly over a period of 4 hr up to 3.8% for C3d and 81% for C4bp of the total vessel area. Remarkably after 6 hr of perfusion, the C3d-positive area decreased significantly to 1.3% and the C4bp-positive area to 19% of the total area of the vein. The areas positive for both C4bp and C3d were increased in the presence of N-acetylcysteine. CONCLUSIONS: Exposure to arterial blood pressure leads to a transient presence of C4bp in the vein wall. This may be part of a cell-protective mechanism to counteract arterial blood pressure-induced cellular stress and inflammation in grafted veins.

C1-esterase inhibitor protects against early vein graft remodeling under arterial blood pressure.

OBJECTIVES: Arterial pressure induced vein graft injury can result in endothelial loss, accelerated atherosclerosis and vein graft failure. Inflammation, including complement activation, is assumed to play a pivotal role herein. Here, we analyzed the effects of C1-esterase inhibitor (C1inh) on early vein graft remodeling. METHODS: Human saphenous vein graft segments (n=8) were perfused in vitro with autologous blood either supplemented or not with purified human C1inh at arterial pressure for 6h. The vein segments and perfusion blood were analyzed for cell damage and complement activation. In addition, the effect of purified C1inh on vein graft remodeling was analyzed in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. RESULTS: Application of C1inh in the in vitro perfusion model resulted in significantly higher blood levels and significantly more depositions of C1inh in the vein wall. This coincided with a significant reduction in endothelial loss and deposition of C3d and C4d in the vein wall, especially in the circular layer, compared to vein segments perfused without supplemented C1inh. Administration of purified C1inh significantly inhibited vein graft intimal thickening in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. CONCLUSION: C1inh significantly protects against early vein graft remodeling, including loss of endothelium and intimal thickening. These data suggest that it may be worth considering its use in patients undergoing coronary artery bypass grafting.

Diastolic stiffness of the failing diabetic heart: importance of fibrosis, advanced glycation end products, and myocyte resting tension.

BACKGROUND: Excessive diastolic left ventricular stiffness is an important contributor to heart failure in patients with diabetes mellitus. Diabetes is presumed to increase stiffness through myocardial deposition of collagen and advanced glycation end products (AGEs). Cardiomyocyte resting tension also elevates stiffness, especially in heart failure with normal left ventricular ejection fraction (LVEF). The contribution to diastolic stiffness of fibrosis, AGEs, and cardiomyocyte resting tension was assessed in diabetic heart failure patients with normal or reduced LVEF. METHODS AND RESULTS: Left ventricular endomyocardial biopsy samples were procured in 28 patients with normal LVEF and 36 patients with reduced LVEF, all without coronary artery disease. Sixteen patients with normal LVEF and 10 with reduced LVEF had diabetes mellitus. Biopsy samples were used for quantification of collagen and AGEs and for isolation of cardiomyocytes to measure resting tension. Diabetic heart failure patients had higher diastolic left ventricular stiffness irrespective of LVEF. Diabetes mellitus increased the myocardial collagen volume fraction only in patients with reduced LVEF (from 14.6+/-1.0% to 22.4+/-2.2%, P<0.001) and increased cardiomyocyte resting tension only in patients with normal LVEF (from 5.1+/-0.7 to 8.5+/-0.9 kN/m2, P=0.006). Diabetes increased myocardial AGE deposition in patients with reduced LVEF (from 8.8+/-2.5 to 24.1+/-3.8 score/mm2; P=0.005) and less so in patients with normal LVEF (from 8.2+/-2.5 to 15.7+/-2.7 score/mm2, P=NS). CONCLUSIONS: Mechanisms responsible for the increased diastolic stiffness of the diabetic heart differ in heart failure with reduced and normal LVEF: Fibrosis and AGEs are more important when LVEF is reduced, whereas cardiomyocyte resting tension is more important when LVEF is normal.