Defect-Rich La₂O₃ Nanoparticles with Antioxidant Activity for Human Keratinocytes

Abstract

A deficiency in the human antioxidant system to scavenge free radicals results in mounting oxidative stress, causing various pathological conditions including immune system constraints. To support an underperforming antioxidant system and regulate homeostatic function, efficient and biocompatible reactive oxygen species (ROS) scavengers may be employed. At present, metal oxide-based antioxidants nanoparticles are of fundamental interest because of their smart surface property tailoring. A spray precipitation method was employed in this work to develop a strained and defect rich lanthanum oxide (La 2 O 3 ) nanostructure. A contraction in d-spacing and distortion in planes and vacancies were observed in the nanostructure, causing microstrain as verified by the William-Hall uniform deformation model (UDM). Photocatalytic activity was evaluated against commercial La 2 O 3 and Evonik Aeroxide TiO 2 P25 via dye degradation experiments. A 30% degradation reduction confirmed the ability of the nanostructure to scavenge free radicals generated by P25 upon ultraviolet (UV) irradiation. Compared to the commercial La 2 O 3 , the nanostructured La 2 O 3 showed an increase in UV absorption (200−400) nm due to a decrease in the optical band gap. A positive surface charge of the nanoparticles was observed from zeta potential measurements, suggesting sufficient colloidal stability. In vitro toxicity studies toward the nonmalignant human keratinocyte cell line (HaCaT) over a 24 h treatment period with the La 2 O 3 nanoparticles exhibited no toxicity in comparison with the control and ZnO nanoparticles. The antioxidant properties of the nanoparticles were investigated by a dichlorofluorescein (DCF)-based assay which revealed a decrease in intracellular ROS in comparison with Nacetylcysteine (NAC) and H 2 O 2 . In addition, confocal microscopy imaging showed the internalization of the nanoparticles and subsequent DCF intensity change between the treated and untreated cells, as supported by flow cytometry analysis. Our findings suggest that defect-rich La 2 O 3 nanoparticles could be used effectively as active inorganic UV filter and fluorescent contrast agent owing to their biocompatible antioxidant properties.

Microenvironmental Behaviour of Nanotheranostic Systems for Controlled Oxidative Stress and Cancer Treatment

“…The La2O3 nanostructure synthesised by the spray precipitation method for biological applications was reported by Rehman et al [182]. Mostly, an irregular or thick plate-like morphology was observed in the SEM imaging (Figure 16a).…”

“…A lower dye degradation (~44%) was recorded in the presence of La 2 O 3 NPs compared to the P25-only assay (~96%) shown in Figure 16c. A confocal microscopy study showed the cellular (HaCaT cell line) internalisation of NPs (Figure 16d) [182]. The cytotoxicity data revealed the biocompatible nature of the nanostructure, even at a higher concentration (500 mg L −1 ) with reference to ZnO (Figure 16e).…”

“…A higher ROS scavenging was observed in La2O3 NP-treated cells than NAC-treated cells compared to the positive control. ROS scavenging in non-malignant HaCaT cells lowered ROS-induced oxidative stress [182]. The most dominating mechanism of ROS scavenging is the interconversion of La2O3−x, La(OH)3 and La2O3 is shown in Figure 17.…”

“…The filling of the 4f shell increases with the increase in the atomic number, whereas 5d 1 configuration appears in La, Ce, Gd and Lu [184][185][186]. The availability of 4f and 5d electrons for reaction imparts unique magnetic, fluorescent, electrical and catalytic properties in rare-earth oxides [182].…”

“…Lanthanum (La) is a rare-earth (RE) element and is finding many technological and industrial applications in the form of lanthanum oxide (La 2 O 3 ), such as chemical catalysts, laser material, precision optical glasses, electrode material, light-emitting material (blue powder) and hydrogen storage material [178,179]. It is also employed in many biomedical applications, such as targeted drug delivery within the body, suppression of bacteria and viruses [180][181][182], binding agent for several proteins, calcium channel suppression, fluorescence dyes and ROS scavenging activity [181,183]. In the electronic configuration of La, 6S electrons are drawn inward due to the poor shielding of the nuclear charge by 4f electrons and results in the contraction of the atomic radius.…”