Comparison of acute thrombogenicity and albumin adsorption in three different durable polymer coronary drug-eluting stents

Abstract

Background: The relative thrombogenicity and albumin adsorption and retention of different durable polymers used in coronary stents has not been tested.

Aims: This study sought to compare the thromboresistance and albumin binding capacity of different durable polymer drug-eluting stents (DES) using dedicated preclinical and in vitro models.

Methods: In an ex vivo swine arteriovenous shunt model, a fluoropolymer everolimus-eluting stent (FP-EES) (n=14) was compared with two durable polymer DES, the BioLinx polymer-coated zotarolimus-eluting stent (BL-ZES) (n=9) and a CarboSil elastomer polymer-coated ridaforolimus-eluting stent (EP-RES) (n=6), and bare metal stents (BMS) (n=10). Stents underwent immunostaining using a cocktail of antiplatelet antibodies and a marker for inflammation and were then evaluated by confocal microscopy (CM). Albumin retention was assessed using a flow loop model with labelled human serum albumin (FP-EES [n=8], BL-ZES [n=4], EP-RES [n=4], and BMS [n=7]), and scanned by CM.

Results: The area of platelet adherence (normalised to total stent surface area) was lower in the order FP-EES (9.8%), BL-ZES (32.7%), EP-RES (87.6%) and BMS (202.0%), and inflammatory cell density was least for FP-EES <BL-ZES <EP-RES <BMS. Although nearly full coverage by albumin binding was shown for all durable polymer DES, FP-EES showed significantly greater intensity of albumin as compared to BL-ZES, EP-RES and BMS (FP-EES 79.0%; BL-ZES 13.2%; EP-RES 6.1%; BMS 1.5%).

Conclusions: These results suggest that thromboresistance and albumin retention vary by polymer type and that these differences might result in different suitability for short-term dual antiplatelet therapy.

Figure 1

Representative confocal microscopic images using immunofluorescent staining against dual platelet markers (CD61/CD42b) in an ex vivo shunt model. A) Low (upper) and high (lower) power confocal microscopic images showed minimal platelet aggregation in FP-EES, whereas obvious platelet aggregation was observed in BL-ZES, EP-RES and BMS. B) Graph shows fluorescent positive area per stent surface. Data are presented as mean±standard deviation for each. * p<0.05 vs FP-EES; ? p<0.05 vs BL-ZES; ?? p<0.05 vs EP-RES.

Figure 2

Representative confocal microscopic images using immunofluorescent staining against a neutrophil marker (PM-1) and a monocyte marker (CD14) in an ex vivo shunt model. A) The upper panels (A1 and A2) show confocal microscopic images with PM-1 staining and the lower panels show confocal microscopic images with CD-14 staining. FP-EES showed minimal neutrophil and monocyte attachment. However, BL-ZES, EP-RES and BMS showed many neutrophils and monocytes on the stent surfaces. B) Graphs show the number of PM-1 (B1) and CD-14 (B2) positive cells on the stent struts. The number of PM-1 and CD-14 was significantly the least in FP-EES relative to BL-ZES, EP-RES and BMS. Data are presented as mean±standard deviation for each group. * p<0.05 vs FP-EES.

Figure 3

Representative confocal microscopic images using fluorescent human serum albumin in the flow loop model. The low (upper) and high (lower) power images show the stent surface fully covered by an obvious strong signal of fluorescent albumin in FP-EES. On the other hand, although BL-ZES and EP-RES also showed near complete coverage by albumin, the albumin signals (green) on the surface in BL-ZES and EP-RES were less intense relative to FP-EES. Minimal albumin signal was observed in BMS.

Figure 4

Quantitated images of confocal microscopy with fluorescent human albumin. A) High signal of fluorescent albumin was coloured yellow, whereas low signal of albumin was coloured grey. FP-EES was fully covered by a yellow colour, whereas BL-ZES and EP-RES were covered mostly by grey. BMS showed minimal grey colour. B), C) & D) Graphs show high signal of albumin, low signal and total signal in each stent. Data are presented as mean±standard deviation for each group. * p<0.05 vs FP-EES; ? p<0.05 vs BL-ZES; ?? p<0.05 vs EP-RES.

Figure 5

Percent coverage and intensity of albumin in each group over 30 minutes during washing phases. A) These images show quantitated coverage and intensity of albumin at the end of washing phases. All durable polymer DES showed nearly full albumin coverage. However, albumin intensity was higher in the order FP-EES, BL-ZES and EP-RES. Coverage and intensity of albumin were minimal in BMS. B) & C) Graphs show estimated mean percent coverage and intensity over 30 minutes during washing phases. There were significant differences in FP-EES, BL-ZES, and EP-RES versus BMS, although significant differences were not observed between FP-EES, BL-ZES and EP-RES. FP-EES had the highest intensity, followed by BL-ZES and EP-RES, with the least being in BMS. Significant differences were seen in all comparisons. In percent coverage and intensity, minimal changes were observed over 30 minutes.