pH-Responsive Nanoparticles for Delivery of Paclitaxel to the Injury Site for Inhibiting Vascular Restenosis

Abstract

A high incidence of restenosis has been reported at the site of inflammation following angioplasty and stent implantation. The anti-proliferative drug paclitaxel (PTX) could help to reduce inflammation and restenosis; however, it has poor water solubility and serious adverse side effects at high doses. Given the presence of metabolic acidosis at the site of inflammation, we hypothesized that nanoparticles that are responsive to low pH could precisely release the loaded drug at the target site. We successfully constructed pH-responsive poly(D, L-lactic-co-glycolic acid) (PLGA) nanoparticles loaded with PTX and NaHCO₃ as a pH-sensitive therapeutic agent (PTX-NaHCO₃-PLGA NPs). The NPs exhibited remarkable pH sensitivity and a good safety profile both in vitro in rat vascular smooth muscle cells and in vivo in Sprague Dawley rats after tail vein injection. In the rat model, the PTX-NaHCO₃-PLGA NPs treatment group showed suppressed intimal proliferation following balloon-induced carotid artery injury compared with that of the saline-treated control. Overall, these results demonstrate that our newly developed pH-responsive nanodrug delivery platform has the potential to effectively inhibit restenosis.

Keywords: drug delivery; pH-responsive nanoparticles; paclitaxel; sodium bicarbonate; vascular restenosis.

Scheme 1

Design of pH-responsive nanoparticles for the treatment of vascular restenosis.

Figure 1

Characterization of PTX-NaHCO₃-PLGA NPs. (A) SEM image and (B) TEM image of PTX-NaHCO₃-PLGA NPs. (C) The size distribution and (D) pH value of PTX-NaHCO₃-PLGA NPs in neutral PBS with prolonged time duration (n = 3). (E) Release profiles of PTX from PTX-NaHCO₃-PLGA NPs at pH 7.4, 6.0, and 5.0, respectively. (F) FTIR of PTX, NaHCO₃-PLGA NPs, and PTX-NaHCO₃-PLGA NPs.

Figure 2

Biosafety evaluation of PTX-NaHCO₃-PLGA NPs. (A) Cell viability of VSMCs with various concentrations of NPs. (B) Hemolysis test of PTX-NaHCO₃-PLGA NPs. (C–H) Blood biochemical index results (ALT, AST, TP, CREA, BUN, and LDH). (I) H&E-stained sections of major organs in the PBS and PTX-NaHCO₃-PLGA NPs groups. Scale bar: 100 μm. TP, total protein; AST, aspartate aminotransferase; ALT, alanine aminotransferase; CREA, creatinine; BUN, blood urea nitrogen; LDH, L-lactate dehydrogenase. Data are presented as mean ± SD (n = 3).

Figure 3

Fluorescence images and fluorescence analysis of vascular sections stained with the pH-sensitive fluorescent probe BCECF AM. (A–E) Fluorescence images at different time points after injury. (F) Quantitative analysis of fluorescence intensity of vascular sections. Data in (F) are presented as mean ± SD. * p < 0.05, *** p < 0.001, **** p < 0.0001.

Figure 4

Evaluation of the efficacy of PTX-NaHCO₃-PLGA NPs in the treatment of vascular restenosis. (A) H&E staining of blood vessel sections. Scale bar: 100 μm. (B–D) Quantitative analysis of the intimal area (B), medial area (C), and intimal hyperplasia index (D) of carotid arteries between four groups. Data in (B–D) are presented as mean ± SD (n = 5). * p < 0.05, ** p < 0.01.

Figure 5

Immunohistochemical analysis of cross-sections of carotid arteries between two groups. (A) Microscopic images showing sections stained with antibodies to α-SMA. Scale bar: 100 μm. (B) Quantitative analysis of the percent of α-SMA staining area. (C) Microscopic images showing sections stained with antibodies to PCNA. Scale bar: 100 μm. (D) Quantitative analysis of the percent of PCNA staining area. Data in (B,D) are presented as mean ± SD (n = 5). ** p < 0.01, *** p < 0.001.