Development of Solid Lipid Nanoparticles by Cold Dilution of Microemulsions: Curcumin Loading, Preliminary In Vitro Studies, and Biodistribution

Abstract

Background: Solid lipid nanoparticles (SLNs) are attractive drug delivery systems for lipophilic molecules like curcumin (CURC) with low chemical stability. Methods: A simple, innovative, and cold-operating method, named "cold dilution of microemulsion" is developed by the authors to produce SLNs. An oil-in-water microemulsion (µE), whose disperse phase consisted of a solution of trilaurin in a partially water-miscible solvent, was prepared after mutually saturating solvent and water. Trilaurin SLNs precipitated following solvent removal upon water dilution of the µE. After SLN characterization (mean size, Zeta potential, CURC entrapment efficiency, and over time stability), they were tested for in vitro cytotoxicity studies on pancreatic adenocarcinoma cell lines and for in vivo preliminary biodistribution studies in Wistar healthy rats. Results: CURC loaded SLNs (SLN-CURC) had mean diameters around 200 nm, were negatively charged, stable over time, and able to entrap CURC up to almost 90%, consequently improving its stability. SLN-CURC inhibited in vitro pancreatic carcinoma cell growth in concentration-dependent manner. Their in vivo intravenous administration suggested a possible long circulation. Conclusions: These results, according to a concomitant study on chitosan-coated SLNs, confirm the possibility to apply the developed SLN-based delivery systems as a means to entrap CURC, to improve both its water dispersibility and chemical stability, facilitating its application in therapy.

Keywords: cancer chemoprevention; cell line; drug delivery system; microemulsions; nanoparticles; poorly water-soluble drug.

Figure 1

Phase diagram at room temperature (25 °C) of the systems containing lipophilic phase/aqueous phase/surfactant:co-surfactant (trilaurin (TL) solution in EA_s/W_s-BenzOH/lecithin-PEG-6 hydrogenated castor oil-sodium taurocholate (Na TC). M: µE domain; LC: liquid crystal domain.

Figure 2

Mean diameter (nm) of empty solid lipid nanoparticles (SLNs) dispersed in Pluronic^® F68 aqueous solution at different polymer percentages.

Figure 3

Scanning electronic microscopy (SEM) picture of SLN-CURC (Detector SE1, EHT 15.00 KV, Mag 10.00 KX, 500 nm).

Figure 4

Stability of SLN-CURC in term of mean diameter (nm) and CURC concentration (µg/mL) over time after storage at 4 °C. Zeta potential (mV) was 1 day = −10.02 mV ± 2.32; 6 days = −13.57 mV ± 2.71; 15 days = −18.86 mV ± 2.98; 30 days = −19.53 mV ± 2.77.

Figure 5

CURC release from SLN-CURC compared to reference solution (up to 6 h).

Figure 6

Inhibition of proliferation following empty SLN, SLN-CURC, and free CURC administration. PANC-1 and CFPAC-1 cells (800 cells/well) were treated with increasing concentrations of SLN-CURC and CURC for 72 h; the result was expressed as the percentage of viable cells versus the control expressed as mean ± S.E.M (n = 5). Asterisks mean statistically significant differences of SLN-CURC vs. CURC-treated cells at the same concentrations (* p < 0.05 and ** p < 0.01).

Figure 7

Biodistribution profile over time for each organ of CURC in SLN-CURC (A) and free CURC (B).