Interaction of Poly lactic-co-glycolic acid (PLGA) with Curcumin: PLGA Based Nanocapsules for Curcumin Delivery and Biomedical Application

Abstract

Nanotechnology is a promising developing field presenting a potential tools for the loading of curcumin in order to enhance its various applications. Several types of nanoparticles have arisen one of them is polymeric nanocapsules. In the present work curcumin (Cur) loaded Poly lactic-co-glycolic acid (PLGA) nanocapsules were synthesized using solid-in-oil-in water (s/o/w) emulsion technique. The prepared nanocapsules were coated by poly (diallyldimethylammonium) chloride (PDDA) polymer in order to increase the entrapement of curcumin into the core of PLGA polymer.

PLGA-Cur-PDDA nanocapsules were characterized using spectroscopic and microscopic techniques such as fluorescence spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis (TGA), X-Ray diffraction technqiue (XRD), scanning electron microscopy (SEM), and Zeta potential analysis. The formed PLGA-CUR-PDDA NCs were established as nanoprobe for the detection of dopamine molecule. The selectivity and specificity of nanocapsules toward dopamine was achieved by measuring the fluorescence emission spectra of the NCs in the presence of other interference molecules such as tryptophan, melamine, adenine, etc. It was noticed that increasing the concentration of the different molecules had no significant change in the fluorescence signal of the nanocapsules. These results confirm the strong quenching between dopamine and curcumin in the nanocapsules. Hence, fluorescence emission technique was found to be selective, easy and fast with low cost for the determination of dopamine in a concentration range up to 5 mM with a detection limit equal to 23 μM. Additionally, the antiviral activity of these nanocapsules was investigated against the influenza A virus. Cytotoxicity assessment of the nanocapsules was performed. MTT results revealed that up to a concentration of 20 µM of the curcumin nanocapsules is well tolerated by A549 cells with cell death< 20 %. Then, using plaque reduction assay, antiviral activity against influenza A virus propagated in the A549 cell culture was evaluated. Results showed that a reduction in the plaque size was obtained upon treating infected PR8 cells with 10 µM of nanocapsules. Also, the EC50 was estimated to be 20 μM.

Besides, multilayered polymeric nanocapsules were prepared in three different compositions, using PLGA, PDDA polymer and silica nanoparticles. These nanocapsules were characterized using different techniques. The effect of additive layer was established; where it was found that silica nanoparticles and PDDA polymer increase the stability of the encapsulated curcumin. Drug release profile was examined for PLGA-Cur-PDDA nanocapsules at three different pHs (4, 6 and 7). Highest release of curcumin was obtained at pH 4. Thus to control curcumin release at this pH, effect of multilayers addition was studied. Results showed a lower release of curcumin with the addition of multilayers where high encapsulation efficiency equal to 98.21% was obtained.

Moreover, the interaction between PLGA, PDDA and Curcumin was investigated by fluorescence spectroscopy. The modified Stern-Volmer equation was used to estimate the value of the binding constant Ka and the van't Hoff equation was used to estimate the corresponding thermodynamic parameters (ΔHo, ΔSo, and ΔGo). The obtained results showed that the binding constant between PLGA and Curcumin is due to the formation of hydrogen bonds and van der Waals forces. However, PDDA interacts with curcumin through hydrophobic interactions. Moreover, zeta potential measurements were obtained for these polymers and the surface charge was compared in presence and absence of the negatively charged curcumin molecules. It was found that the results obtained by zeta potential measurements are in agreement with those obtained by fluorescence spectroscopy. It is also found that binding of curcumin with PDDA is further encouraged in the presence of PLGA.

Furthermore, the physical properties of Poly(lactic-co-glycolic acid) (PLGA polymer) are studied for the first time in solution using emission fluorescence technique and curcumin as a molecular probe. On the first hand, curcumin at a concentration of 2 μM was added to different concentrations of PLGA. In this case, the fluorescence of curcumin has been tracked. It was found that the critical micellar concentration (CMC) was equal to 0.31 g/L and the critical micellar temperature (CMT) was obtained at 25°C respectively. Furthermore, an insight on the effect of NaCl salt on the CMC value of PLGA is assessed through curcumin probing. Therefore, a decrease in the CMC has been observed with the increase in the concentration of NaCl. Moreover, in order to understand the aggregation behavior of PLGA in different solutions, CMC experiments were investigated using chloroform as a solvent. Results showed that the solvent does not affect the CMC value of the polymer; however, it only affects the shape of the obtained micelle. Finally, fluorescence quenching of curcumin with hydrophobic cetyl-pyridinium bromide CPB and hydrophilic KI quenchers was established, where it was proved that curcumin is located near the hydrophobic pocket of Stern-layer of PLGA micelle.