Enhanced passive pulmonary targeting and retention of PEGylated rigid microparticles in rats

Abstract

The current study examines the passive pulmonary targeting efficacy and retention of 6μm polystyrene (PS) microparticles (MPs) covalently modified with different surface groups [amine (A-), carboxyl (C-) and sulfate (S-)] or single (PEG(1)-) and double (PEG(2)-) layers of α,ω-diamino poly(ethylene glycol) attached to C-MPs. The ζ-potential of A-MPs (-44.0mV), C-MPs (-54.3mV) and S-MPs (-49.6mV) in deionized water were similar; however PEGylation increased the ζ-potential for both PEG(1)-MPs (-18.3mV) and PEG(2)-MPs (11.5mV). The biodistribution and retention of intravenously administered MPs to male Sprague-Dawley rats was determined in homogenized tissue by fluorescence spectrophotometry. PEG(1)-MPs and PEG(2)-MPs demonstrated enhanced pulmonary retention in rats at 48h after injection when compared to unmodified A-MPs (59.6%, 35.9% and 17.0% of the administered dose, respectively). While unmodified MPs did not significantly differ in lung retention, PEGylation of MPs unexpectedly improved passive lung targeting and retention by modifying surface properties including charge and hydrophobicity but not size.

Fig. 1

Scanning electronic micrographs of MPs. A: C-MPs; B: PEG₁-MPs; and C: Magnification of PEG₁-MPs. The surfaces of PEG1-MPs appear slightly irregular when compared to unmodified MPs; however there is no noticeable change in size or shape.

Fig. 2

The effect of pH on ζ-potential of MPs in buffer (pH 2-7: 1 mM phosphate buffer, pH 7-9: 1 mM borate buffer) (n = 2, mean ± S.D.). The ζ-potential of the unmodified MPs (A-, C- and S-MPs) is dominated by the sulfate group found on the original MPs, whereas PEG masks the negative ζ-potential.

Fig. 3

The biodistribution of 6 μm MPs with different surface properties at various time points. Biodistribution of MPs (A): A-MPs; (B) C-MPs; (C): S-MPs; (D): PEG₁-MPs; and (E): PEG₂-MPs (n = 3, mean ± S.D.). The biodistribution of the unmodified MPs is similar and the resulting lung AUCs (Table 2) are statistically different than the lung AUCs of the PEGylated MPs by one-way ANOVA. (F) Compilation of lung MP retention from (A)-(E); * = P < 0.05 compared to A-, C- or S-MPs; # = P < 0.05 compared to A- or S-MPs; † = P < 0.05 compared to S-MPs by one-way ANOVA. Figure 3C is reprinted with permission from Kutscher et al. (Kutscher et al., 2010).

Scheme 1

Synthesis of PEGylated MPs (PEG₁- and PEG₂-MPs) from C-MPs. Reagents and conditions: A) TSTU, DMSO, RT, 15 min; B) DAPEG (3.4 kDa), DMSO, RT 24 h; C) EDTA, DMSO, RT, 8 h; D) TSTU, DMSO, RT, 15 min; and E) DAPEG (3.4 kDa), DMSO, RT 24 h.