Rapamycin and Paclitaxel Affect Human Aortic Smooth Muscle Cells-Derived Foam Cells Viability and Proliferation

Drug-eluting stents (DES) coated with rapamycin or paclitaxel as antiproliferative substances significantly reduced the incidence of clinical restenosis and had fewer side effects after percutaneous coronary intervention. However, DES coated with rapamycin or paclitaxel still cause restenosis due to abnormal tissue growth which remained a therapeutic problem, particularly in certain subgroups, possibly due to drug concentrations. This study examined the impact of different concentrations of rapamycin and paclitaxel on cytokine, cell viability and proliferation in human aortic smooth muscle cells (HASMC)-derived foam cells.

The foam cell model was established in vitro by incubating HASMC with 20 µg/mL oxidized low-density lipoprotein (ox-LDL) for 48 hours. Subsequently, foam cells were treated with different concentrations (0.01 µg/mL, 0.1 µg/mL, 0.5 µg/mL, 1 µg/mL, 5 µg/mL and 10 µg/mL) of rapamycin or paclitaxel for 48 hours, to measure cytokine, cell viability and proliferation by ELISA and MTT, respectively. Finally, viability and proliferation were measured by MTT after the foam cells were treated with 1 µg/mL rapamycin or paclitaxel combined with cytokine antibody for 48 hours.

After incubation of HASMC with ox-LDL, the ratios of cholesterol ester and total cholesterol increased significantly (55.29%) (P<0.01). Lipid staining with Oil Red O showed many lipid vacuoles and red dye particles in the cells. Meanwhile, cell viability and proliferation significantly increased compared with the control. This indicated that HASMC had been transformed into foam cells (P<0.01) while rapamycin or paclitaxel concentrations ≥0.1 µg/mL can significantly decrease the foam cell proliferation (P<0.05 or P<0.01), and 1 µg/mL of rapamycin or paclitaxel appeared the most effective concentration. As for cytokines, rapamycin or paclitaxel concentrations ≥1 ug/mL could significantly increase the level of inflammatory cytokines IL-6 (P<0.05 or P<0.01), which was enhanced with the increase of drug concentration. However, rapamycin or paclitaxel concentrations ≥1 µg/mL could significantly reduce the levels of anti-inflammatory cytokines IL-35 and transforming growth factor beta (TGF-β) (P<0.05 or P<0.01), which decreased with the increase of drug concentration. In addition, rapamycin or paclitaxel combined with anti-IL-1β, anti-IL-6, anti- TNF-α or anti-IL-35 had no significant effect on foam cell proliferation compared to the drug alone. However, rapamycin or paclitaxel combined with anti-IL-10 or anti-TGF-β can significantly enhance foam cell proliferation (P<0.01). In addition, there was no difference in the effects of the same concentrations of rapamycin and paclitaxel on foam cells.

Although rapamycin or paclitaxel can reduce foam cell proliferation, too high or too low concentrations could decrease effectiveness. In particular, a high dose can induce foam cells to increase inflammatory cytokines secretion, reduce anti-inflammatory cytokines secretion, and thus affect the inhibiting proliferation. For rapamycin- and paclitaxel-eluting stents, this conclusion may explain the clinical observation of in-stent restenosis after percutaneous coronary intervention. DES coated with an appropriate concentration of rapamycin or paclitaxel may, at least to some extent, contribute significantly to reducing incidence of late in-stent restenosis.