Study On The Enhancement Of Oral Bioavailability Of Raloxifene Using Mesoporous Carbon Nanospheres

ObjectivesRaloxifene(RXF), an amphiphobic drug for the treatment of postmenopausal osteoporosis, shows low oral bioavailability(< 2%) in humans due to its poor water solubility and extensive metabolism. This work aimed to prepare mesoporous carbon nanospheres(MCNs) for oral delivery of RXF and to evaluate their performance in bioavailability enhancement. Methods 1. Glucose-based MCNs were prepared by hydrothermal reaction followed by high-temperature activation. The optimized MCNs were characterized by dynamic light scattering, SEM, and BET nitrogen adsorption. 2. RXF-loaded MCNs(RXF-MCNs) were prepared by solvent-diffusion /high-pressure homogenization and stabilized by phospholipid. RXF-MCNs were fully characterized by particle size, morphology, DSC and in vitro drug release. 3. The SD rats were administered with RXF-MCNs and RXF suspensions(the control group) by gavage, and RXF solution by jugular vein injection. Blood samples were collected at predetermined time points. The plasma drug concentration was quantified by UPLC-QTOF/MS. Non-compartmental model was used to estimate the relative bioavailability of RXF-MCNs versus RXF suspension. 4. RXF-MCNs and RXF solution were incubated with UGT1A1-overexpressing MDCK cells respectively. The effect of MCNs loading on intestinal glucuronidation metabolism of RXF was evaluated by detecting the contents of intracellular and extracellular metabolites. 5. The mesenteric lymph of rats were intubated to evaluate the lymphatic transport of RXF. Black staining test and the histological analysis of black lymph nodes were performed to determine the lymphatic accumulation of MCNs. Fluorescence-labeled carbon nanospheres(FCNs) were prepared by one-pot synthesis of glucose with sodium fluorescein. The cellular internalization of FCNs was determined using MDCK cells. The transepithelial transport of RXF-MCNs was examined by fluorescent imaging. To inspect the bioadhesion of carbon nanoparticles, RXF-MCNs were orally given to rats and the intestinal adhesion was evaluated by black staining of intestinal mucosa. Results 1. The optimized MCNs were 150 nm in particle size with spherical shape and porous surface. The specific surface area of MCNs was 2138 m2/g. The relative adsorption quantity of RXF was up to 450 mg/g(to a maximum of 480 mg/g). 2. The prepared RXF-MCNs were 230 nm around in particle size with PDI value of less than 0.3 and ζ potential of 41.7 mV. RXF-MCNs showed high entrapment efficiency(95.35%) and satisfactory physical stability. In addition, drug in RXF-MCNs was in an amorphous state and exhibited a unique release pattern characterized by initial burst release and later slow release. 3. The maximum plasma concentration(Cmax) and bioavailability of RXF-MCNs were increased by 1.93 times and 2.07 times, respectively. 4. It was shown that the intestinal glucuronidation metabolism of RXF can be reduced due to drug entrapment into MCNs. 5. The accumulative amount of lymphatic transport of RXF-MCNs is 8.14 times of the control group. The lymph drug concentrations at each time point were significantly higher than the control group. The maximum lymphatic drug concentration reached 1.66 μg/mg. MCNs can accumulate in the lymph nodes, suggestive of its high lymphatic tropism. The efficient internalization of FCNs provided evidence that FCNs can facilitate the transmembrane transport of RXF. Further, the intestinal epithelial fluorescence analysis revealed a good epithelial membrane permeability of FCNs. In addition, RXF-MCNs possessed excellent intestinal adhesion which will enhance the drug residence in the gastrointestinal tract. ConclusionThe results suggest that MCNs are suitable nanocarriers for oral delivery of poorly bioavailable RXF.