Kinetics of adventitial repair in the rat carotid model

Adventitial contributions of the extracellular signal-regulated kinase and Akt pathways to neointimal hyperplasia

BACKGROUND

We recently reported that the efficacy of nitric oxide (NO) appears to be based on both sex and hormone status. The mechanism responsible for this differential efficacy is unknown. The aim of this study was to characterize the effect of sex, hormones, and NO on the extracellular signal-regulated kinase (ERK) and Akt signaling pathways after arterial injury.

METHODS

Male and female Sprague-Dawley rats underwent castration or sham surgery. Two weeks later, they underwent carotid artery balloon injury. Treatment groups included the following: control, injury, and injury + 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO) (n = 5 per group). Arteries were harvested 2 weeks after injury and assessed for phospho-ERK (pERK) and phospho-Akt (pAkt) expression.

RESULTS

After injury, more pERK and pAkt activity was seen in the adventitia than media in both sexes, regardless of hormone status (P < .05). In hormonally intact males, NO further increased pERK (44%) and pAkt (120%) after injury (P < .001). Castration attenuated the effects of NO. In hormonally intact females, NO caused the opposite pattern with pERK activity but did not affect pAkt activity.

CONCLUSIONS

After arterial injury, ERK and Akt activity is significantly greater in the adventitia than the media, and depends on sex, hormone status, and NO. Understanding adventitial regulation of proliferative signaling pathways will allow the development of targeted therapies for neointimal hyperplasia.

Increased vascular injury reduces the degree of intimal hyperplasia following angioplasty in rabbits

BACKGROUND/AIMS

Formation of intimal hyperplasia following angioplastic procedures can lead to complications, including restenosis and accelerated atherosclerosis. The vessel wall media is a main source of neointimal cells. However, evidence suggests that there are additional cell sources, such as the adventitia. Here we investigate whether an extensive loss of vascular smooth muscle cells (VSMCs) in the media results in less intimal hyperplasia or if there is compensatory cell recruitment from the adventitia.

METHODS

A balloon catheter was pulled through the rabbit carotid artery 4 times (major injury) or 2 times (minor injury). Adventitial cells were labeled with 5-bromo-2-deoxyuridine or PKH26.

RESULTS

The major injury, but not the minor injury, resulted in a complete loss of VSMCs in large parts of the media and significant leukocyte infiltration. The major injury resulted in less neointima compared with the minor injury. The thinnest neointima was seen at the most injured parts of the media in the major injury group. Cell-tracking experiments showed that the media, but not the adventitia, served as a source of neointimal cells.

CONCLUSION

An augmented angioplastic injury with extensive VSMC loss in rabbits reduced the degree of intimal hyperplasia. No compensatory recruitment of neointimal cells from the adventitia occurred.

CaMKII-delta isoform regulation of neointima formation after vascular injury

OBJECTIVE

The purpose of this study was to test the function of the calcium/calmodulin-dependent protein kinase II delta2 isoform (CaMKIIdelta2) in regulating vascular smooth muscle (VSM) cell proliferation and migration in response to vascular injury.

METHODS AND RESULTS

CaMKII isoform content was assessed in rat carotid arteries after balloon angioplasty-induced injury by Western blotting with isoform specific antibodies. Within 3 days after injury, a significant increase in CaMKIIdelta2 and decrease in CaMKIIgamma isoform content was observed in both medial smooth muscle and adventitial fibroblasts. Neointimal VSM cells expressed primarily the delta2 isoform. Incubation of the injured vessel with adenovirus encoding siRNA targeting CaMKIIdelta isoforms prevented upregulation of the delta2 isoform in the media and adventitia; inhibited cell proliferation assessed by PCNA expression in both layers and markedly inhibited neointima formation and adventitial thickening.

CONCLUSIONS

CaMKIIdelta2 is specifically induced in VSM and adventitial fibroblasts during the response of an artery to injury and is a positive regulator of proliferation and migration in the vessel wall contributing to neointima formation and vascular remodeling. This provides a potential mechanism for Ca2+-dependent regulation of VSM and myofibroblast proliferation and migration in response to vascular injury or disease.

Inhibition of in-stent restenosis by oral copper chelation in porcine coronary arteries

Stress-induced release of IL-1alpha and fibroblast growth factor-1 is dependent on intracellular copper and is a major driver of neointimal hyperplasia. Therefore, we assessed the effect of tetrathiomolybdate (TTM), a clinically proven copper chelator, on in-stent restenosis. Nine pigs were treated with TTM (5 mg/kg po) twice daily for 2 wk before stent implantation and for 4 wk thereafter, and nine pigs served as controls. In-stent restenosis was assessed by quantitative coronary angiography (QCA), intravascular ultrasound (IVUS), and histomorphometry. Serum ceruloplasmin activity was used as a surrogate marker of copper bioavailability. In TTM-treated animals, ceruloplasmin dropped 70 +/- 10% below baseline levels. Baseline characteristics were comparable in TTM-treated and control animals. At 4-wk follow-up, all parameters relevant to in-stent restenosis were significantly reduced in TTM-treated animals: minimal lumen diameter by QCA was 2.03 +/- 0.57 and 1.47 +/- 0.45 mm in TTM-treated and control animals, respectively (P < 0.05), percent stenosis diameter was 39% less in TTM-treated animals (27.1 +/- 16.6% vs. 44.5 +/- 16.1%, P < 0.05), minimal lumen area by IVUS was 60% larger in TTM-treated animals (4.27 +/- 1.56 vs. 2.67 +/- 1.19 mm(2), P < 0.05), and neointimal volume by histomorphometry was 37% less in TTM-treated animals (34.9 +/- 11.5 vs. 55.2 +/- 19.6 mm(3), P < 0.05). We conclude that systemic copper chelation with a clinically approved chelator significantly inhibits in-stent restenosis.

Effects of delayed (24 h postintervention) β-irradiation therapy after coronary angioplasty and stenting in de novo native coronary artery lesions

BACKGROUND

The effects of brachytherapy performed 24 h postintervention in de novo native coronary artery lesions.

METHODS AND RESULTS

Thirty-nine patients with 39 de novo coronary artery lesions were randomised to prompt (immediately after intervention, n=21) or delayed (24 h later, n=18) beta brachytherapy ((90)Sr/(90)Y) after been successfully revascularized with stenting. Clinical follow-up data up to 21 months (median time) were compared. After irradiation and at 6-month follow-up, paired volumetric analysis of the stented segment and the 5-mm proximal and distal reference segments was performed; this included measurements of the external elastic membrane, lumen, plaque, and media (external elastic membrane minus lumen), stent and intima hyperplasia (stent minus lumen). Baseline clinical and angiographic characteristics were similar in the two groups. Postintervention measurements of stent, lumen, and intima hyperplasia volumes as well as postintervention minimum lumen cross-sectional areas were not different. In the stented segments and in the segments 5 mm proximal and distal to the stent, similar changes of all IVUS measurements were measured in the two patient groups, but in the lumen volume at the proximal stent edge of patients irradiated 24 h postinjury. At 21 months median follow-up time, target lesion revascularization (TLR) was performed in 8 patients (38%) in the prompt irradiation group compared with 3 (17%) in the delayed (P=.17).

CONCLUSION

Beta irradiation is similarly effective whether performed immediately after percutaneous coronary intervention or 24 h later.