Concomitant proliferation and caspase-3 mediated apoptosis in response to low shear stress and balloon injury.

BACKGROUND: Arterial remodeling occurs as a response to hemodynamic change and direct vessel wall injury through the process of neointimal hyperplasia (NH). A concomitant response of vascular smooth muscle cell (VSMC) proliferation and apoptosis exists. The purpose of this study is to assess the cellular response of vessels following exposure to low shear stress (tau) and balloon injury in order to further elucidate the mechanisms underlying vascular injury. Our hypothesis is that the combination of low tau and balloon injury results in NH approximating that seen in clinical arterial restenosis, and that quantitative analysis of VSMC proliferation and apoptosis correlates with the associated increase in arterial remodeling. METHODS AND RESULTS: New Zealand White rabbits underwent surgery on the carotid artery creating low tau (n =11), balloon injury (n = 11), combined low tau and balloon injury (n =11), and sham (n = 13) groups. Experiments were terminated at 1, 3, and 28 d. Day 1 and 3 arteries were analyzed with immunohistochemistry for apoptotic markers, terminal transferase dUTP nick end labeling (TUNEL), and activated caspase-3, and a cellular proliferation marker, accumulated proliferating cell nuclear antigen (PCNA), as well as immunoblot analysis for activated caspase-3 and PCNA at day 3. There was significantly greater apoptosis in the combined group as compared with the other groups assessed by quantitative TUNEL and activated caspase-3 levels at both days 1 and 3. Similarly, an increase in cellular proliferation assessed by PCNA expression, was significantly greater in the combined group as compared with the other groups. At 28 d there was no difference in NH observed in the low tau (26 +/- 3 microm) and balloon injury (51 +/- 17 microm) groups. However, significantly more NH was observed in the combined group (151 +/- 35 microm) as compared with the other groups. CONCLUSIONS: An increase in VSMC apoptosis via a caspase-3 dependent pathway is up-regulated by 24 h in the face of combined low shear stress and balloon-induced vessel wall injury. Paradoxically, this increase in VSMC apoptosis is associated with a significant increase in neointimal thickening at 28 d. The concomitant increase of both apoptosis and proliferation are indicative of a robust arterial remodeling response.

Attenuated herpes simplex virus 1 blocks arterial apoptosis and intimal hyperplasia induced by balloon angioplasty and reduced blood flow.

Injury caused by distention of the arterial wall by balloon angioplasty can result in apoptosis and vascular smooth muscle cell proliferation. Here, we report that a brief exposure of the arterial lumen to a genetically engineered, attenuated herpes simplex virus 1 blocks activation of caspase 3-dependent apoptosis and MAPK-dependent cell proliferation induced by carotid artery balloon angioplasty and ligation to reduce blood flow. The procedure enables the restoration of the endothelial cell layer lining the lumen and prevents neointimal hyperplasia and restenosis. These findings have a broad application in prevention of balloon angioplasty-induced restenosis.

Slower onset of low shear stress leads to less neointimal thickening in experimental vein grafts.

Vein grafts respond to low flow and shear stress (tau(w)) by generating thicker walls and smaller lumens through the processes of neointimal hyperplasia and remodeling. Clinically, however, vein grafts with obviously low tau(w), such as those distal to high-grade proximal obstructions, are not infrequently found to be widely patent and pliable. One possible explanation for this phenomenon may be that vein grafts remodel more favorably in response to changes in shear that occur gradually over time compared to abruptly. This hypothesis was tested in an experimental animal model in this report. Two separate models of experimental vein graft failure were created, causing either immediate exposure to ultralow tau(w) (<1 dyne/cm2) or delayed exposure to ultralow tau(w). Under general anesthesia and using a sterile technique, the right external jugular (EJ) veins of 28 New Zealand white rabbits were surgically exposed and isolated. An end-to-side distal EJ/common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. For the immediate exposure group (n = 5), the EJ was suture-ligated just proximal to the thoracic inlet, distal to a small 10-50 microm venous tributary. This created a reversed vein segment immediately and abruptly exposed to high wall tension (2.0 +/- 0.3 x 10(4) dyne/cm) and ultralow tau(w) (0.15 +/- 0.08 dyne/cm2). For the delayed exposure group (n = 22), the EJ was ligated over a 0.035 guidewire, leaving a small aperture to sustain some measure of blood flow and tau(w). This predictably resulted in slightly less wall tension (1.4 +/- 0.2 x 10(4) dyne/cm) and higher tau(w) (0.68 +/- 0.21 dyne/cm2) than the immediate exposure group. During the first week, the small outflow aperture in the delayed exposure grafts thrombosed, eventually exposing them to the same low level of tau(w) as the immediate exposure grafts. Thus, the only difference in the two models was that delayed exposure grafts enjoyed a slower decline in tau(w) than immediate exposure grafts. Fourteen rabbits in the delayed exposure group were harvested over the first 7 days to define the patency curve of the restricted outflow channel. As expected, the small aperture had thrombosed in all animals by 7 days. The remaining 14 grafts were harvested after 4 weeks, and 13/14 remained patent. Examination of the hemodynamic parameters at the time of death confirmed that wall tension and tau(w) had equalized (wall tension 0.9 +/- 0.1 vs. 1.1 +/- 0.1 x 10(4) dyne/cm, tau(w) 0.45 +/- 0.12 vs. 0.30 +/- 0.08 dyne/cm2). Histological examination revealed less neointimal hyperplasia in the delayed exposure group compared to the immediate exposure group (wall thickness 266 +/- 16 vs. 180 +/- 24 microm, p = 0.025) as well as a slightly greater luminal diameter (0.30 +/- 0.02 vs. 0.40 +/- 0.02 cm, p = 0.038). The results of this experiment suggest that slow exposure to reduced tau(w) results in more favorable remodeling (less thickening) than abrupt exposure. This finding may explain the occasional clinical observation of a widely patent vein graft even in the face of proximal arterial obstruction and very low flow; the change in tau(w) presumably occurred slowly mitigating the remodeling response.

Modulation of vascular remodeling induced by a brief intraluminal exposure to the recombinant R7020 strain of Herpes simplex-1.

OBJECTIVE: Vascular remodeling in response to injury or low shear stress (or both) is characterized by neointimal hyperplasia and luminal contraction. When profound, the response leads to restenosis after percutaneous endovascular intervention as well as to de novo stenosis in vein grafts. It has recently been reported that exposure of vein patches to neurovirulence-attenuated Herpes simplex virus-1 (HSV-1) decreases neointimal hyperplasia and increases luminal area. This experiment tested the hypothesis that R7020, a more highly attenuated mutant of HSV-1, would modulate the vascular remodeling response of experimental vein grafts chronically exposed to low shear stress. METHODS: The external jugular veins of 31 New Zealand white rabbits were clamped and intraluminally exposed to vehicle (phospate-buffered saline solution, n = 11), R7020 2.5 x 10(8) plaque forming units [PFU]/mL (n = 8), or R7020 2.5 x 10(9) PFU/mL (n = 12) for 10 or 30 minutes at an average pressure of 80 mm Hg. After exposure, an end-to-side distal external jugular-to-common carotid artery anastomosis was created, resulting in a widely patent arteriovenous fistula. The external jugular was suture-ligated just proximal to the thoracic inlet, distal to a small 10- to 50-microm venous tributary, creating a reversed vein "graft" segment immediately and abruptly exposed to arterial pressure (48 +/- 3 mm Hg) and low shear stress (0.12 +/- .02 dyne/cm(2)). In the 29 animals (N = 31) that survived to harvest, 26 grafts were found to be patent and were analyzed further. Nine grafts were harvested within the first week after operation, snap frozen in liquid nitrogen, and assayed for the presence of the Herpes viral immediate-response protein ICP0 by Western blot analysis. The 17 remaining grafts were perfusion-fixed, excised, stained, and analyzed morphometrically by digital planimetry. RESULTS: In patent grafts, the hemodynamic environment of low shear stress was maintained (shear stress at harvest, 0.26 +/- .06 dyne/cm(2)). Western blot analysis revealed the presence of ICP0 in R7020-exposed vein grafts after 2, 3, 7, and 14 days; ICP0 was not detected in unexposed vein grafts or adjacent carotid arteries. After 4 weeks, vein grafts exposed to R7020 exhibited a statistically significantly increased ratio of luminal radius to wall thickness, indicating altered remodeling (vehicle, 6.7 +/- 1.3; R7020 2.5 x 10(8), 9.1 +/- 1.3; R7020 2.5 x 10(9) ratio, 11.3 +/- 1.4; P < .05 for high dose compared with vehicle). CONCLUSION: A brief exposure of the neurovirulence-attenuated HSV-1 strain R7020 results in an increased ratio of luminal radius to wall thickness in experimental vein grafts chronically exposed to low shear stress.