Functionalization of nanodiamond with vitamin E TPGS to facilitate oral absorption of curcumin

The purpose of this work was to develop a d-α-tocopherol polyethylene glycol 1000 succinate (TPGS) decorated nanodiamond (ND) system loading water-insoluble curcumin (ND/CUR/TPGS) to improve the colloidal dispersity and oral bioavailability of the preparation. CUR was physically loaded into ND clusters, then TPGS was coated to the ND/CUR complex forming amorphous nanostructure on the interparticle nanocage of the ND substrate. The formulation of the nanocomplexes was optimized using response surface methodology, and the optimal ND/CUR/TPGS showed small particle size (196.32 nm), high drug loading efficiency (81.59%) and core-shell structure. In vitro release study demonstrated that the nanocomplexes provided a sustained release behavior. The absorptive concentration of ND/CUR/TPGS was dramatically improved in total intestinal tract compared with CUR suspension, and the absorption was controlled by multiple transcytosis mechanisms. Furthermore, the pharmacokinetic studies demonstrated that ND/CUR/TPGS had significantly higher Cmax (4.50-fold), larger AUC0-t (10.67-fold), and longer MRT0-t (3.07-fold) in contrast with that of CUR suspension. Therefore, ND/CUR/TPGS presented great potential for oral delivery of insoluble and poorly permeable drugs.