Failure of antiplatelet therapy with ibuprofen (Motrin) to prevent neointimal fibrous hyperplasia

Intimal hyperplasia is reduced by ornithine decarboxylase inhibition

Polyamines are intracellular cations that are thought to play a role in the regulation of cell growth and differentiation. This study was undertaken to determine if inhibition of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine synthesis, suppresses formation of intimal hyperplasia (IH) after arterial injury. Twenty New Zealand white rabbits underwent balloon catheter deendothelialization of a common carotid artery. Treated animals (n = 10) were given alpha-difluoromethylornithine (DFMO), an inhibitor of ODC, ad lib in drinking water as a 2% solution. DFMO was begun 3 days prior to surgery and continued until vessel harvest. Vessels were perfusion-fixed at harvest, 2 (n = 10) and 4 (n = 10) weeks postoperatively. All arteries remained patent. There were no histologic differences in the IH between treated and untreated animals. The intima and media surface areas on serial arterial cross sections were determined using computer-assisted planimetry. There was a significant difference in the IH surface area of injured arteries between untreated and DFMO-treated animals at both 2 (17.6 +/- 2.0 vs 3.0 +/- 1.6 microns 2; P less than or equal to 0.001) and 4 weeks 27.4 +/- 5.6 vs 7.1 +/- 1.8 microns 2; P less than or equal to 0.008). No differences were seen in medial thickness. We conclude that ODC inhibition reduces early development of IH after arterial deendothelialization. These data support the hypothesis that polyamines may be cellular messengers involved in the regulation of IH formation.

Prostacyclin production in the area of arterial endothelial denudation

The goal of this study was to quantify arterial prostacyclin (PGI2) synthesis and platelet aggregation in the immediate area of vessel injury. Twelve mongrel dogs whose platelets aggregated maximally to added arachidonic acid (AA) were equally divided into three groups. Controls received no drug while other dogs were treated with the platelet inhibitors aspirin (ASA) 3 mg/kg/day or BM 13.505 (BM), a thromboxane receptor antagonist, 25 mg/kg/day. After 3 days of treatment, the dogs underwent balloon catheter endothelial denudation of both carotid and femoral arteries. Blood was sampled from the first carotid artery just distal to the injury at 0, 1, 5, and 10 min after restoration of flow. Venous blood samples were also obtained at 1 and 2 weeks postoperatively. Dogs were sacrificed at 2 weeks and arterial rings from a proximal normal and a denuded region were excised and tested for PGI2 production in response to added AA. While control dogs showed no statistical change in AA-induced platelet aggregation postoperatively, there appeared to be a trend for enhanced responsiveness at 1 week. Aspirin and BM inhibited AA-induced aggregation completely in all samples at all timepoints. Levels of the stable metabolite of PGI2, 6-keto-PGF1 alpha, were determined by radioimmunoassay. In control dogs, baseline PGI2 levels were 72 +/- 17 pg/ml which increased to 479 +/- 20 pg/ml immediately after restoration of flow (P less than 0.001, Student t test) and returned to basal values in 10 min (85 +/- 5 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Myointimal hyperplasia: pathogenesis and implications. 2. Animal injury models and mechanical factors

Arterial wall injury either by balloon catheter, drying, or scraping results in a denudation of endothelial cells (EC) and a subsequent proliferation of smooth-muscle cells (SMC). The degree of SMC proliferation appears to be dependent on the degree of initial injury and not to the loss of the overlying endothelium. Successful reendothelialization of denuded areas depends on the size of the denuded segment as well as SMC-EC interactions. Prolonged exposure of SMC to serum substances results in inhibition of EC regrowth, the production of prostacyclin by SMC, and the development of a thromboresistant surface. Heparin appears to inhibit SMC proliferation in vivo (as well as in vitro), an effect that is independent of platelet SMC interaction. EC-derived heparin in vivo may also result in inhibition of SMC proliferation. Platelets may play an important role in the early response to arterial injury and development of myointimal hyperplasia (MIH), but their long-term role appears to be minor. Antiplatelet agents have widely varying species-dependent effects on platelets and platelet-vessel wall interactions, but in specific circumstances they may inhibit MIH. The precise role of steroid drugs and immunosuppression on MIH in arterial injury models awaits further study. The role of lipoproteins in MIH is unclear; however, the inhibition of MIH by omega-3 fatty acids in vivo as well as their inhibition of platelet-derived growth factor production by EC in vitro implies a regulatory role. Acute hypertension results in a marked proliferation of EC and SMC in vivo and enhances the proliferative response to injury as well. Low wall shear stress, turbulence, and boundary layer separation all increase EC turnover, a likely influence on EC growth factor production. The compliance mismatch resulting from graft-artery anastomoses, injury, and endarterectomy results in locally increased cyclical stretch, which may predispose to SMC proliferation.

Stenosis following laser thermal angioplasty--a blinded controlled randomized study between aspirin against Probucol

Long-term patency of vascular angioplasties is limited by stenosis from neointimal hyperplasia or progressive arteriosclerosis. This study evaluated the hypothesis that ASA (an antiprostaglandin) or Probucol (an antioxidant) may be useful in preventing stenosis following laser thermal angioplasty. Aortoiliac arteriosclerosis was induced in 17 female New Zealand white rabbits with a combination of endothelial denudation (4 Fr. Fogarty balloon catheters) and 2% cholesterol-supplemented diet for 6 weeks. All rabbits then underwent arteriography and were immediately randomized to one of three groups: Group I (n = 6), control, laser but no adjunctive therapy; Group II (n = 5), laser and ASA 10 mg/kg/day; Group III (n = 6), laser and 1% Probucol diet. Retrograde laser thermal angioplasty was performed with a 1-mm coronary Laserprobe. Six watts of argon laser energy was delivered for a single 5-sec pulse using a continuous motion from the right common iliac artery to the aorta. Pre- and postlaser arteriography was performed in all groups. Rabbits were sacrificed 1 month following laser angioplasty, and aortoiliac sections were taken after in situ perfusion fixation with paraformaldehyde and 0.05% glutaraldehyde. Serial 5-mm segments, proximal to the aortic bifurcation and distally from the same, were taken, stained, and evaluated by quantitative morphometry. From each segment, lesion area and lesion area/internal elastic laminae area were evaluated and compared. Serum cholesterol increased from 60.8 +/- 19.5 to 1494.7 +/- 12.7 mg% following institution of the cholesterol diet (P less than 0.05). Arteriosclerotic lesions were observed in all rabbits and maximally located around the common iliac artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Patency and intimal hyperplasia: the effect of aspirin on small arterial anastomosis

This experiment evaluated the effect of aspirin (ASA) on the patency and development of intimal hyperplasia in autologous, small caliber, arterial end-to-side anastomosis. Twenty-eight adult female rabbits had their distal left external iliac artery transposed and anastomosed to the right proximal external iliac artery. Fourteen rabbits received ASA 40 mg by gavage twice in the 24 hours preceding the operation and 5 times a week postoperatively (experimental) and 14 rabbits received no ASA therapy (control). Plasma salicylate levels range from 25 to 36 micrograms per milliliter in experimental animals. Patency of the reconstruction was assessed by Doppler examination each month, confirmed by autopsy and calculated by life table analysis. Five cross sections of each patent anastomosis harvested at six and nine months were examined by light microscopy. A total of seven thromboses occurred in the control group versus two occlusions in the experimental group. Four of the thromboses in the control group occurred less than seven days after the reconstruction, whereas no such events occurred in the experimental group. Patency by actuarial methods at nine months was 45.5% versus 81.8% (p less than .05) in control and experimental groups, respectively. This improvement occurred in spite of similar values for intimal thickness and lumen-to-basement membrane ratios in both control and experimental groups. We conclude that aspirin significantly improves the nine month patency rate of small autologous end-to-side anastomosis, and its effect is most noticeable in the early postoperative period.(ABSTRACT TRUNCATED AT 250 WORDS)