Release and pharmacokinetics of near-infrared labeled albumin from monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) microspheres after subcapsular renal injection.

Subcapsular renal injection is a novel administration method for local delivery of therapeutics for the treatment of kidney related diseases. The aim of this study was to investigate the feasibility of polymeric microspheres for sustained release of protein therapeutics in the kidney and study the subsequent redistribution of the released protein. For this purpose, monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) (PLHMGA) microspheres (40 μm in diameter) loaded with near-infrared dye-labeled bovine serum albumin (NIR-BSA) were prepared by a membrane emulsification method. Rats were injected with either free NIR-BSA or with NIR-BSA loaded microspheres (NIR-BSA-ms) and the pharmacokinetics of the released NIR-BSA was studied for 3 weeks by ex vivo imaging of organs and blood. Quantitative release data were obtained from kidney homogenates and possible metabolism of the protein was investigated by SDS-PAGE analysis of the samples. The ex vivo images showed a rapid decrease of the NIR signal within 24h in kidneys injected with free NIR-BSA, while, importantly, the signal of the labeled protein was still visible at day 21 in kidneys injected with NIR-BSA-ms. SDS-PAGE analysis of the kidney homogenates showed that intact NIR-BSA was released from the microspheres. The locally released NIR-BSA drained to the systemic circulation and subsequently accumulated in the liver, where it was degraded and excreted renally. The in vivo release of NIR-BSA was calculated after extracting the protein from the remaining microspheres in kidney homogenates. The in vivo release rate was faster (89 ± 4% of the loading in 2 weeks) compared to the in vitro release of NIR-BSA (38 ± 1% in 2 weeks). In conclusion, PLHMGA microspheres injected under the kidney capsule provide a local depot from which a formulated protein is released over a prolonged time-period.