Nimodipine-Loaded Pluronic® Block Copolymer Micelles: Preparation, Characterization, In-vitro and In-vivo Studies

Abstract

Nimodipine (NM), as a lipophilic calcium channel blocker indicated for the prevention and treatment of neurological disorders, suffers from an extensive first pass metabolism, resulting in low oral bioavailability. Polymeric micelles, self-assembled from amphiphilic polymers, have a core-shell structure which makes them unique nano-carriers with excellent performance as drug delivery. This investigation was aimed to develop NM-loaded polymeric micelles and evaluate their potential to cross the blood brain barrier (BBB). Micelles from Pluronics^®P85, F127 and F68 were fabricated for the delivery of NM, using thin film hydration and direct dissolution techniques. Critical micelle concentration of the drug-free micelles was determined by pyrene fluorescence spectroscopy. Dynamic light scattering showed that in most cases, micelles less than 100 nm and low polydispersity indices were successfully developed. Transmission electron microscopy demonstrated spherical shape of micelles. The NM-loaded micelles were also characterized for particle size, morphology, entrapment efficiency, drug loading , in vitro drug release in phosphate buffer and artificial cerebrospinal fluid (CSF). Stability was assessed from size analysis, clarity of dispersion on standing and EE(%), following 3 months storage at room temperature. The in-vitro release of NM from polymeric micelles presented the sustained-release profile. Animal studies revealed the existence of fluorescein 5-isothiocyanate-labeled micelles in rat CSF following intraperitoneal administration, proving that the micelles crossed the BBB. Anticonvulsant effect of NM was shown to be significantly greater than that of NM solution. Our results confirmed that Pluronic micelles might serve as a potential nanocarrier to improve the activity of NM in brain.

Keywords: Blood brain barrier; FITC; Nimodipine; Pluronics; Polymeric micelles.

Scheme 1

Synthesis of FITC-labeled Pluronic P85 (P85-FITC).

Figure 1

Plot of I339/I333 vs. log of P85 concentration in DI water. As depicted, the CMC value was related to the intensity ratio of the emission spectra profile

Figure 2

Size distribution of P85 blank micelles (10 % w/v).

Figure 3

Transmission electron photomicrographs of the blank P85 polymeric micelles (F4). The scale bar represents 50 nm

Figure 4

Transmission electron photomicrographs of the NM-loaded P85 polymeric micelles (F4). The scale bar represents 50 nm

Figure 5

Release profiles of NM from micelles fabricated with various concentrations of Pluronics in PBS (pH 7.4) at 37 °C (Mean ± SD; n = 3

Figure 6

Release profiles of NM from micelles fabricated with various Pluronics in CSF at 37 °C (Mean ± SD; n = 3