Influence of formulation of ZnO nanoblokes containing metallic ions dopants on their cytotoxicity and protective factors: An in vitro study on human skin cells exposed to UVA radiation

Abstract

Application of ZnO nanoparticles in sunscreens exposes human skin with their adverse effects, which correlates to dissolution/translocation of free Zn⁺² ions. The possibility of decreasing solubility and therefore, reducing toxicity, by structural modifications have been discussed as a solution. The present investigation has developed new metallic lattices of ZnO to reduce cytotoxicity of ZnO nanoparticles. Novel metal-promoted Zn-based nanocomposites ([Zn(O)/M], M = Mg, Al, Ca, Ti) were synthesized and their physicochemical properties and their cytotoxicity were evaluated. Solubility and release studies showed that modification of ZnO structure decreases release of Zn⁺² into culture medium. XRD and UV absorbance analyses showed that metallic-dopants percolate into crystalline lattice of ZnO. This phenomenon is basic reason for stability of Zn-based network. Cell culture studies and MTT assay on human skin cells (HFF-1) exposed to UVA radiation showed that the level of protection of [Zn(O)/M] compounds were more than of [ZnO]. Dichlorofluoroscein diacetate-ROS assay and Zn⁺² release experiments indicated that [Zn(O)/M] nanocomposites decreased the level of ROS generation and Zn⁺² release in compared to ZnO, indicating higher safety of nanocomposites. This study shows that the synthesized Zn-based nanocomposites have potential to be used as safer and more effective sunscreens than ZnO.

Keywords: Cytotoxicity and protective effects; Human skin cells; Metal-promoted Zn-based nanocomposite; Safe ZnO nanoparticles; UVA radiation.

Graphical abstract

Fig. 1

XRD patterns of the (a) F1T ([ZnO]), (b) F2T ([Zn(O)/Mg]), (c) F3T ([Zn(O)/Al]), (d) F4T ([Zn(O)/Ca]), and (e) F5T ([Zn(O)/Ti]). The circles in (c) and (d) show aluminum oxide and calcium oxide, respectively.

Fig. 2

SEM and TEM images of the (a) F2T ([Zn(O)/Mg]), (b) F3T ([Zn(O)/Al]), (c) F4T ([Zn(O)/Ca]), and (d) F5T ([Zn(O)/Ti]).

Fig. 3

Sample particle size distribution of the (a) F1T ([ZnO]), (b) F2T ([Zn(O)/Mg]), (c) F3T ([Zn(O)/Al]), (d) F4T ([Zn(O)/Ca]), (e) and F5T ([Zn(O)/Ti]) in culture medium.

Fig. 4

FT-IR spectra of the (a) F2T ([Zn(O)/Mg]), (b) F3T ([Zn(O)/Al]), (c) F4T ([Zn(O)/Ca]), and (d) F5T ([Zn(O)/Ti]).

Fig. 5

Absorption spectra of F1T, F2T, F3T, F4T, F5T, and commercial ZnO in culture medium.

Fig. 6

Transmittance spectra of F1T, F2T, F3T, F4T, F5T, and commercial ZnO in culture medium.

Fig. 7

(A) Sedimentation and (B) turbidimetric measurements of F1T, F2T, F3T, F4T, and F5T in culture medium and room temperature (mean ± SD, n = 3).

Fig. 8

Cumulative released Zn⁺² profiles of F1T, F2T, F3T, F4T, F5T, and commercial ZnO in culture medium and 37 °C for 48 h (mean ± SD, n = 3).

Fig. 9

Zn⁺² release from F1T, F2T, F3T, F4T, and F5T in the presence of HFF-1 cell over 24 h (a) pure amount and (b) percent (mean ± SD, n = 3).

Fig. 10

Nature-dependent measurements of intracellular ROS production (pure amount and percent) in HFF-1 cells (a) for cells exposed to Zn-based compounds (in compared to untreated control) and (b) for cells exposed to Zn-based compounds and UVA radiation (in compared to untreated control) (mean ± SD, n = 3).

Fig. 11

Nature-dependent cell viability of HFF-1 cells exposed to Zn-based compounds and UVA radiation (mean ± SD, n = 3).