Polyvinyl alcohol-grafted-multiwalled carbon nanotubes as a delivery system for curcumin in H2O2-induced damaged neuroblastoma SH-SY5Y cells

Abstract

Treating neurodegenerative disease using Curcumin, a pigment from turmeric is found difficult due to its low bioavailability. To overcome this problem, polyvinyl alcohol multi-walled carbon nanotubes (PVA-MWCNT) was developed to improve its delivery and uptake by the brain cells. It was first prepared by oxidizing pristine MWCNT (p-MWCNT) in 3:1 sulfuric and nitric acid mixture. Three methods were employed to optimize production of oxidized MWCNT (ox-MWCNT); which is stirring and sonication for 2 and 6 hours. The selected ox-MWCNT with minimal structural damage was then functionalized with PVA via carbodiimide esterification, and confirmed by field-emission scanning electron microscopy (FESEM), Fourier transform infra-red (FTIR) spectroscopy, dispersion test and thermal gravimetric analysis (TGA). Next, Curcumin was loaded onto PVA-MWCNT, p-MWCNT and ox-MWCNT, and evaluated their adsorption capacity and behaviour using adsorption kinetics, isotherm and thermodynamic studies. Percentage of Curcumin desorbed from the MWCNT was analyzed in physiological buffers of pHs 7.4 and 5.5. Lastly, potential of Curcumin loaded on PVA-MWCNT (Cur-PVA-MWCNT) to protect neurons was screened in neuroblastoma SH-SY5Y cells, including other Cur-loaded MWCNT samples. The cells were pre-incubated with hydrogen peroxide (H2O2) at half the maximal inhibitory concentration (IC50) for 1 hour, before concurrent treatment of the samples. Cell survival was compared to controls treated with Curcumin-unloaded MWCNT, i.e. PVA-MWCNT, ox-MWCNT and p-MWCNT. From the results, MWCNT was oxidized with minimal structural damage using stirring method. The evidence of PVA grafting was confirmed through the presence of matrix polymer embedded on ox-MWCNT in FESEM, high stability in water, identification C=O stretching of ester group at 1736 cm-1 in FTIR and its stable structure compared to ox-MWCNT and p-MWCNT in TGA. PVA-MWCNT adsorbed Curcumin at only 5.1 mg/g, which follows the Freundlich isotherm model (physisorption), while the highest amount was loaded on ox-MWCNT at 714 mg/g that follows the Langmuir model (chemisorption). Although Curcumin adsorption on PVA-MWCNT was only at minimal amount, it showed the most efficient desorption occurred at pH 5.5 (25%) rather than pH 7.4 (3%) with sustained release over a 3-day incubation. This suggests Curcumin weak binding through physisorption to the PVAMWCNT facilitated its release at lower pH. Cur-PVA-MWCNT also protected SHSY5Y cells from H2O2-induced oxidative stress most significantly at 100 ng/ml, 1 μg/ml and 10 μg/ml compared to PVA-MWCNT. Cur-ox-MWCNT and Cur-p- MWCNT indicated no obvious difference as compared to their controls. The change in the cell environment after damage perhaps encouraged the pH to become acidic which may facilitate Curcumin release from PVA-MWCNT. Overall, PVA-MWCNT was considered promising for loading and the release of Curcumin. The efficacy of the system in in vitro cell lines was also enhanced, demonstrating it as a prospective carrier for Curcumin in the treatment of neurodegenerative disease.