We have demonstrated the loading of curcumin onto starch maleate (SM) under mild conditions by mixing dissolved curcumin and SM nanoparticles separately in absolute ethanol and ethanol/aqueous (40 : 60 v/v), respectively. Curcumin-loaded starch-maleate (CurSM) nanoparticles were subsequently precipitated from a homogeneous mixture of these solutions in absolute ethanol based on the solvent exchange method. TEM analysis indicated that the diameters of CurSM nanoparticles were ranged between 30 nm and 110 nm with a mean diameter of 50 nm. The curcumin loading capacity of SM as a function of loading duration was investigated using the UV-visible spectrophotometer. The loading of curcumin onto SM increased rapidly initially with loading duration, and the curcumin loading capacity of 15 mg/g was reached within 12 hours. CurSM nanoparticles exhibited substantially higher water solubility of 6.0 × 10−2 mg/mL which is about 300 times higher than that of pure curcumin. With enhanced water solubility and bioaccessibility of curcumin, the potential utility of CurSM nanoparticles in various biomedical applications is therefore envisaged.
Curcumin, a non-toxic bioactive component of turmeric even at high dosage [
Any drawback due to poor water solubility of hydrophobic bioactive agents such as curcumin could be circumvented via the development of nanoparticle-based drug delivery systems that are dispersible in aqueous media. Intense research efforts have therefore been focused on developing curcumin-loaded polymeric nanoparticles for enhancing the water solubility of curcumin. Anand and co-researchers [
Various attempts have been made to synthesize polysaccharide-loaded curcumin nanoparticles. Being a type of polyphenolic molecule, curcumin could interact strongly with glucan molecule through hydrogen bonding. Such noncovalent interactions of curcumin might play a decisive role in its mechanism of actions during various pharmacological activities. Cyclodextrin, a type of polysaccharide, is known to form inclusion complexes with curcumin [
In this paper, we have reported a facile synthesis approach for the preparation of water soluble curcumin-loaded starch-maleate (CurSM) nanoparticles by loading curcumin onto highly water-soluble starch-maleate monoester. The chemical structure, morphology, and mean size of CurSM nanoparticles were characterized by both FTIR and TEM. The curcumin loading capacity of SM nanoparticles and the resulting water solubility of CurSM nanoparticles were determined by the UV-visible spectrophotometer.
Native sago starch powder was obtained from local grocery store. Sodium hydroxide (CAS No. 1310-73-2) was supplied by Mallinckrodt. Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) (CAS No. 458-37-7) and maleic anhydride (CAS No. 108-31-6) were purchased from Merck. Absolute ethanol (CAS No. 64-17-5) was purchased from Hamburg. All chemicals were used without further purification. Ultrapure water (18.2 MΩ) was used in all syntheses.
The preparation of starch-maleate monoester (SM) was described elsewhere with some modifications [
The total loading of curcumin onto SM was determined by dissolving CurSM nanoparticles in ultrapure water. 0.020 g of CurSM nanoparticles was dissolved in ultrapure water to form 5 mL of CurSM solution at ambient temperature. The amount of curcumin adsorbed was then determined using a UV-vis spectrophotometer (Perkin Elmer/Lambda 25) at the wavelength of 350 nm.
A small drop of the CurSM dispersion in absolute ethanol was mounted on a slide and visualized using a confocal laser scanning microscope (CLSM) (LSM 410, Carl Zeiss, USA).
Dispersed CurSM samples in absolute ethanol were dropped onto formvar-coated copper grids and characterized using a transmission electron microscope (TEM) (JEOL Model JEM 1010). The mean size of CurSM nanoparticles was determined by measuring randomly 50 nanoparticles as observed in the TEM micrographs.
Fourier transformed infrared spectrometry (FTIR) spectra of CurSM, SM as well as curcumin samples pelleted with potassium bromide (KBr) were generated using a fourier transformed infrared spectrometer (SHIMADZU Model FTIR-8201PC) within the wave number range of 4000 and 400 cm−1.
Curcumin was successfully loaded onto starch-maleate monoester (SM) and subsequently formed discrete CurSM nanoparticles of irregular distorted spherical shape via the nanoprecipitation process in absolute ethanol. Figure
Particle size distribution of CurSM nanoparticles prepared with a loading duration of 14 hours at 50–60°C. Inset shows the TEM micrograph of CurSM nanoparticles precipitated in absolute ethanol.
Figure
UV-visible spectra of (a) SM (aqueous), CurSM (aqueous), and curcumin (ethanolic) solutions, and (b) 0.4% (w/v) aqueous solutions of CurSM samples prepared with different loading durations (3–16 hours).
The UV-visible spectra of CurSM aqueous solutions with samples prepared at different curcumin loading durations within the wavelength range of 200 and 400 nm were shown in Figure
Figure
The loading profile of curcumin onto starch maleate as a function of loading duration (0.4% of CurSM solution).
Since curcumin produced natural fluorescent in the visible green spectrum, no further labeling of curcumin was necessary when it was being examined using a confocal laser scanning microscope (CLSM). Prior to CLSM analysis, the CurSM sample was rinsed three times with absolute ethanol in order to remove any free curcumin adhered onto the sample surface. As shown in Figure
Aconfocal laser scanning micrograph of curcumin loaded starch maleate (CurSM) dispersed in absolute ethanol.
Figure
FTIR spectra of (a) curcumin, (b) starch maleate (SM), and (c) curcum loaded starch-maleate (CurSM).
Curcumin is extremely insoluble in water, and this feature has restricted its clinical applications. However, concerted research efforts had been focused on synthesizing water soluble curcumin derivatives due to their superior antioxidant activity against
Absorbance of alkaline curcumin aqueous solution at the wavelength of 350 nm within the concentration range of 0–0.08 Mm.
As shown in Figure
Photographs of CurSM samples in (a) absolute ethanol and (b) water.
Schematic representation of interactions between curcumin molecules and starch-maleate molecules via hydrogen bonding.
The enhanced solubility of CurSM nanoparticles in aqueous medium could also be attributed to their nano-sized dimensions and associated large specific surface area, as well as the highly hydrophilic nature of starch-maleate molecules. Besides, traces of NaOH could be entrapped within CurSM samples despite our efforts to remove them by reprecipitating these CurSM samples in absolute ethanol for several times. Such traces of entrapped NaOH could have also contributed towards the observed higher aqueous solubility of CurSM samples.
The present study has demonstrated a facile approach for loading of curcumin onto starch-maleate monoester. Besides, water soluble curcumin-loaded starch-maleate (CurSM) nanoparticles of spherical shape were synthesized in aqueous-based system through controlled nanoprecipitation of CurSM solution in absolute ethanol. The total loading of curcumin onto SM nanoparticles could be modulated by varying the duration of loading. Due to their biocompatibility, nontoxic nature, and enhanced water solubility, the potential utility of CurSM nanoparticles in biomedical applications is therefore envisaged.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors wish to thank Ting Woei for her skillful assistance in carrying out the TEM works. Financial support from UNIMAS (Research Grant DI/09/2008(17)) and scholarship award from the Ministry of Education, Malaysia are gratefully acknowledged.