Curcumin Nanodiscs Improve Solubility and Serve as Radiological Protectants against Ionizing Radiation Exposures in a Cell-Cycle Dependent Manner

Abstract

Curcumin, a natural polyphenol derived from the spice turmeric (Curcuma longa), contains antioxidant, anti-inflammatory, and anti-cancer properties. However, curcumin bioavailability is inherently low due to poor water solubility and rapid metabolism. Here, we further refined for use curcumin incorporated into "biomimetic" nanolipoprotein particles (cNLPs) consisting of a phospholipid bilayer surrounded by apolipoprotein A1 and amphipathic polymer scaffolding moieties. Our cNLP formulation improves the water solubility of curcumin over 30-fold and produces nanoparticles with ~350 µg/mL total loading capacity for downstream in vitro and in vivo applications. We found that cNLPs were well tolerated in AG05965/MRC-5 human primary lung fibroblasts compared to cultures treated with curcumin solubilized in DMSO (curDMSO). Pre-treatment with cNLPs of quiescent G0/G1-phase MRC-5 cultures improved cell survival following ¹³⁷Cs gamma ray irradiations, although this finding was reversed in asynchronously cycling log-phase cell cultures. These findings may be useful for establishing cNLPs as a method to improve curcumin bioavailability for administration as a radioprotective and/or radiomitigative agent against ionizing radiation (IR) exposures in non-cycling cells or as a radiosensitizing agent for actively dividing cell populations, such as tumors.

Keywords: curcumin; ionizing radiation; nanodisc; radioprotector; radiosensitizer.

Figure 1

Forming curcumin nanoparticles. Curcumin-DMSO, DMPC, and an amphipathic telodendrimer (green) polymer are mixed to form curcumin-telodendrimer nanodiscs (cur-telodiscs). After cur-telodisc formation, Δ49ApoA1 protein (blue) is added to form curcumin-apolipoprotein nanodiscs. Removal of DMSO is achieved by dialysis overnight in 1× PBS. The next morning, additional DMPC lipid is added, and the resulting mixture contains solubilized small and large nanodiscs, collectively termed cNLPs.

Figure 2

Characterization of curcumin-NLPs (cNLPs). (A) Size exclusion chromatogram demonstrates that curcumin associates within larger (leftmost peak) as well as smaller (rightmost peak) ApoA1-NLPs via co-localized 280 nm protein absorbance (black) and 430 nm curcumin absorbance (orange). (B) Dynamic Light Scattering of cNLPs demonstrates that these particles average about 43 nm in diameter. (C) Comparison of curcumin fluorescence when solubilized in water, DMSO, or curcumin-telodendrimer nanodiscs at 0.015–0.5 mg/mL concentrations.

Figure 3

MRC-5 cells tolerate cNLP better than DMSO solubilized curcumin. AG05965/MRC-5 fibroblasts were pre-treated for 18 h with various concentrations of empty NLP (no curcumin) or with curcumin solubilized in nanodiscs (cNLP) or DMSO (curDMSO). MTS reagent was applied to measure cell proliferative capacity. Shown is the mean normalized absorbance ± SD. All wells were normalized to cells treated with media alone. p-values are labeled as <0.05 (*), <0.01 (**), <0.001 (***), and <0.0001 (****).

Figure 4

Curcumin pre-treatment alters foci persistence following ¹³⁷Csexposures. AG05965/MRC-5 fibroblasts were pre-treated for 18 h with cNLP, curDMSO, or 0.1% DMSO alone prior to 50 cGy ¹³⁷Cs gamma rays. Cells were fixed at 15 min, 2 h, 6 h, and 24 h post-irradiation. Data are mean induced foci per cell with 95% confidence intervals (CI, (A)) or SD (B) at each time point. p-values are labeled as <0.05 (*), <0.01 (**), <0.001 (***), and <0.0001 (****).

Figure 5

Curcumin NLP pre-treatment alters cell survival following ¹³⁷Csexposures. Quiescent (A,B) and log-phase (C,D) AG05965/MRC-5 fibroblasts were pre-treated for 18 h with cNLP, curDMSO, empty NLP, or 0.1% DMSO alone prior to ¹³⁷Cs gamma ray irradiation. Data are mean relative surviving fraction ± SD per treatment.