Verapamil reduces intimal hyperplasia in a sheep carotid artery patch graft model

Sheep models for evaluation of novel patch and prosthesis material in vascular surgery: tips and tricks to avoid possible pitfalls

Background

In vascular surgery, novel synthetic prosthesis materials for patch-angioplasties, interpositions, bypasses and shunts are continuously under development and optimization. The characteristics of an ideal vascular prosthesis would display long-term patency, biocompatibility, durability, low porosity, lack of stich hole bleeding, ease of handling, kink resistance, infection resistance and reasonable costs. The aim of this study was to establish and report a reliable sheep model including potential pitfalls where those parameters could be analyzed. Before surgery, sheep were acclimatized for 4–8 weeks, during which parasite infections were treated and blood and serum parameters monitored. Twenty-four sheep underwent surgery, and carotid patch-angioplasties (n = 12), graft interpositions (n = 6) or arteriovenous prosthetic shunts (n = 6) were implanted. Half of the animals in each group were sacrificed after 2 weeks and the other half after 8 weeks. The implants were analyzed for patency, endothelialization, thrombogenicity and biocompatibility by clinical observation, blood flow measurement and pathological and histopathological (H&E, EvG) as well as immunohistochemical (Ki67, CD31) evaluations.

Results

Health monitoring of the sheep revealed a parasitic burden with endoparasites in all animals. Some animals showed thereby infestations in the bile duct causing fibrotic cholangitis with calcifications in the liver. In addition, sarcosporidia were detected in histopathological specimen of the heart in all animals. Parasitic burden correlated with blood counts and serum bilirubin levels. Both were significantly reduced by albendazole treatment within the acclimatization time. Patches, interposition grafts, and straight shunts were successfully implanted bilaterally in all animals. The total average operation time was 136 ± 21 min. Most animals (23/24) showed good patency rates and general condition after implantation. Pathological and histopathological/immunohistochemical analyses were suitable to determine thrombogenicity, endothelialization, cellular/fibroblastic proliferation, biocompatibility, inflammatory cell infiltration, and thickness of neointima in the prosthesis material.

Conclusions

We have developed a suitable experimental protocol with standardized and successful anesthesia- and surgical-procedures for patch-angioplasty, graft interposition, and arteriovenous prosthetic shunts. This sheep model allows testing of new prosthetic materials for biocompatibility, thrombogenicity, and endothelialization.

Antiproliferative effects of low molecular weight heparin

AIM

To investigate the effect of low molecular weight heparins (LMWH) on the inhibition of intimal hyperplasia (IH) developing in prosthetic vascular patch graft implanted into sheep carotid artery.

METHODS

A gelatin sealed Dacron patch graft was implanted into the common carotid artery of sheep, which were then allocated to a control group (n = 10) or to one of four treatment groups (each group n = 10) receiving either a low dose (LD) or high dose (HD) of one of two LMWH (enoxaparin 1 or 2 mg/kg/day, dalteparin 100 or 200 units/kg/day) administered subcutaneously for 4 weeks. Anti-activated factor X and activated partial thromboplastin time were assayed from blood collected prior to and at 1 and 2 h after LMWH administration on days 3, 7, 14, 21 and 28. Animals were killed on day 28 after taking blood samples prior to, then at 0.5, 1, 2, 3, 4, 6, 8, 12 and 24 h following the last injection. Grafts were collected for analysis and measurements of intimal thickness obtained under light microscopy from eight transverse sections of each grafted artery aided by computer image analysis. An IH index was calculated by dividing the area of IH (mm2) by the width of the graft (mm).

RESULTS

Intimal hyperplasia index measurements (mean +/- SD) were: controls 0.574 +/- 0.077, LD enoxaparin 0.471 +/- 0.056, LD dalteparin 0.404 +/- 0.025, HD enoxaparin 0.398 +/- 0.068, HD dalteparin 0.332 +/- 0.048. The reductions in IH index compared to controls were significant (P < 0.05) for both LD and HD dalteparin and for HD enoxaparin.

CONCLUSION

Both LMWH dalteparin and enoxaparin reduced the amount of IH formation with dalteparin showing a greater effect in the present animal study. The possibility that different LMWH might exert differing antiproliferative effects requires further investigation.

Vascular smooth muscle cell migration: current research and clinical implications

Atherosclerosis and intimal hyperplasia are major causes of morbidity and mortality. These processes develop secondary to endothelial injury due to multiple stimuli, including smoking, diabetes mellitus, hypertension, and hyperlipidemia. Once this injury occurs, an essential element in the development of both these processes is vascular smooth muscle cell (VSMC) migration. Understanding the mechanisms involved in VSMC migration and ultimately the development of strategies by which this process can be inhibited, has been a major focus of research. The authors present a review of the extracellular proteins (growth factors, extracellular matrix components, and cell surface receptors) and intracellular signaling pathways involved in VSMC migration, as well as potential therapeutic approaches to inhibit this process.

Calcium channel antagonist verapamil inhibits neointimal formation and enhances apoptosis in a vascular graft model

BACKGROUND

The potential of the calcium channel antagonist verapamil to cause apoptosis (programmed cell death) is of considerable importance in arterial injury where the loss of smooth muscle cells may contribute to a reduction in intimal hyperplasia development. The aim of this study was to determine whether verapamil induces vascular cell apoptosis after carotid artery synthetic grafting.

METHODS

Thirty-two adult-female Merino sheep received gelatin sealed fusiform shape-Dacron grafts into the left common carotid artery at day 0. After operation animals were randomly allocated to either a control group or one of three treatment groups (groups 2, 3, and 4). Group 1 animals (n = 9) received no treatment. For the treatment groups, intravenous verapamil was given at a rate of 0.5 mg/kg per day in two divided doses. Group 2, 3, and 4 sheep were treated for 1, 2, and 4 weeks, respectively. Animals were sacrificed at 4 weeks. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-fluorescent labelling. Proliferating cells and their phenotype were determined by doublestaining with antiproliferation cellular nuclei antigen and anti-alpha-actin or anti-HAM-56.

RESULTS

There were significantly more apoptotic cells in the perigraft adventitia in the 4-week treatment group than in the control group (P <0.05). The average number of proliferating cells at 2 and 4 weeks in the intima were significantly less than in the control (P <0.05). The average numbers of macrophages inside graft matrix in the 2 and 4 weeks treatment groups were significantly less than for the control (P <0.05). The number of proliferating cells inside the graft was significantly lower at 4 weeks compared with control (P <0.05). There was negative correlation between intimal PCNA expression and perigraft apoptotic expression level (P <0.05).

CONCLUSION

The antihypertensive agent verapamil inhibits intimal hyperplasia through enhancing adventitial cell apoptosis and inhibiting intimal cell proliferation after vascular grafting.