Abstract: Phytoglycogen (PG) is a plant-based, high-density carbohydrate nanoparticle that has been demonstrated as a promising encapsulation and delivery system for curcumin (CCM) with enhanced solubility in our previous study. In this study, the effects of PG loading on the stability, biological activity and release of CCM were further investigated and the possible underlying mechanism was explored. CCM was encapsulated into PG nanoparticles at different concentrations, yielding 1% PG-CCM, 3% PG-CCM and 5% PG-CCM, respectively. The particle size and surface potential of the bare and loaded nanoparticles were measured by a laser particle size analyzer. The loading characteristics of CCM were evaluated, and the stability of PG-CCM was tested by determining the retention rate of CCM under UV irradiation and different pH conditions. The antioxidant properties of curcumin before and after encapsulation were evaluated using ferric reducing antioxidant power (FRAP) assay and 2,2’-azino-bis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical cation scavenging activity assay. The in vitro inhibitory efficacies of PG-CCM against A549 and MCF-7 cells were investigated using invasion-3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The release of CCM from PG-CCM complex was investigated using simulated gastric fluid (SGF) and intestinal fluid (SIF). The results showed the mean particle size and zeta potential of PG-CCM complex were found to be about 70–75 nm with a narrow size distribution and 0 mV at pH 7.0, respectively. PG-CCM protected the encapsulated CCM from UV irradiation. The CCM encapsulated in PG nanoparticles had higher antioxidant and antitumor activity than pristine CCM, likely due to the improved dispersibility. The CCM complexes with 1% and 5% PG shared the common characteristic: the initial burst release of the encapsulated CCM, and the release rate of CCM was higher in SGF than in SIF. In addition, the PG concentration used for CCM encapsulation had a great impact on loading characteristics of CCM into PG nanoparticles, as well as CCM stability, release behavior and biological activity. Up to 37.5% of CCM was loaded on the surface of nanoparticles for 1% PG-CCM and 17.3% for 5% PG-CCM. Compared with 1% PG-CCM, 5% PG-CCM showed higher CCM stability but lower release rate and cancer cell growth inhibitory activity. The stability, in vitro release characteristics and biological activity seemed to be dependent on the loading characteristics of CCM. PG showed considerable potential to improve the stability of the encapsulated CCM, increase its antioxidant activity and enable its anticancer efficacy, thereby improving its bioavailability. The simple approach used in this work is promising for the development of curcumin-based therapeutic and dietary supplement formulations with enhanced bioavailability.

Key words: phytoglycogen, curcumin, stability, antioxidant activity, cancer cell inhibition capacity