A pH-sensitive microsphere system for the colon delivery of tacrolimus containing nanoparticles

Nanoparticles (NP) are known to accumulate at the site of inflammation in inflammatory bowel disease. In order to avoid premature uptake or degradation of NP during their passage through the small intestine, it appeared necessary to devise a form of local delivery system for NP. Tacrolimus (FK506) loaded poly(lactic-co-glycolic acid) NP entrapped into pH-sensitive microspheres (NPMS) were designed to achieve greater selectivity to their site of action when administered orally. The therapeutic efficacy of this drug delivery system was tested in an experimental colitis in rats. The in vitro characterization showed a successful incorporation of FK506-NP and strongly pH-sensitive release kinetics of both NP and drug. During the in vivo studies, clinical activity, colon/body weight index, and myeloperoxidase activity were determined to assess the severity of inflammation. Systemic availability of a fluorescent dye entrapped in the microspheres was measured in order to determine possible adverse effects. The NPMS as well as the controls of NP and MS formulations exhibited significant mitigating effects in the clinical activity index after 3 days of treatment with similar levels for the various therapies. When observing colon/body weight index and myeloperoxidase activity, only the NPMS group reached statistically significant differences (P<0.05) compared to the colitis control group while other groups did not (colitis control: 21.94+/-4.97; FK506 solution: 15.81+/-3.42; FK506-NP: 17.03+/-5.52; FK506-MS: 15.17+/-7.81; and FK-NPMS: 10.26+/-7.76 U/mg tissue). Moreover, the NPMS system reduced the systemic absorption of the entrapped dye compared to the dye solution or simple NP formulation (relative biovailability-solution: 100+/-14.9%; NP: 46.8+/-8.6%; and NPMS: 29.4+/-3.3%). The results suggest that the NPMS system can provide selective delivery of NP in the colon and develop a significant mitigating effect, while the control group treatments appeared to be insufficient.