Luminescent Nanocomposite SiO2/EuTTA/ZIF‑8 Loaded with Uvaol: Synthesis, Characterization, Anti-Inflammatory Effects, and Molecular Docking Analysis

Abstract

Asthma is a chronic inflammatory respiratory condition that requires innovative approaches for effective drug delivery. Uvaol, a natural triterpene with potent anti-inflammatory effects, holds promise for asthma treatment. However, its low bioavailability limits its therapeutic applications. To overcome this challenge, we synthesized a europium-based nanocomposite (SiO₂/EuTTA/ZIF-8) to enhance uvaol delivery. The nanomaterials were characterized using UV-visible absorption spectroscopy, fluorescence analysis, and molecular docking simulations. Drug loading and release studies were conducted in PBS to evaluate encapsulation efficiency and controlled release properties. Cytotoxicity assays were performed to assess biocompatibility, and molecular docking was used to analyze interactions between uvaol and ZIF-8. The synthesized nanocomposite demonstrated efficient uvaol encapsulation and controlled release in PBS. Cytotoxicity assays revealed biocompatibility at low concentrations (≤10 μg/mL) and toxicity at higher concentrations (≥50 μg/mL). In addition, SiO₂/EuTTA/ZIF-8-uvaol revealed the inhibition of the lipopolysaccharide (LPS)-induced secretion of IL-6 and TNF-α in J774 cells. Molecular docking studies highlighted hydrophobic interactions and π-π stacking between uvaol and ZIF-8, supporting stable drug-nanocarrier binding. These findings suggest that SiO₂/EuTTA/ZIF-8-uvaol is a promising platform for improving uvaol bioavailability and enabling controlled drug delivery in asthma therapy. Additionally, europium luminescence offers the advantage of real-time monitoring, further enhancing the potential of this nanocomposite for therapeutic applications.

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X-ray diffraction patterns of synthesized materials. Powder X-ray diffraction patterns are shown for ZIF-8, SiO₂, SiO₂/EuTTA/ZIF-8, and the simulated patterns of ZIF-8 and SiO₂ obtained from crystallographic data (CCDC 947064 and ICSD 29122, respectively).

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Morphological analysis of synthesized nanoparticles via SEM. SEM micrographs are shown for (A) SiO₂, (B) ZIF-8, (C) SiO₂/EuTTA, and (D) SiO₂/EuTTA/ZIF-8.

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Chemical analysis of the synthesized materials was performed using FT-IR spectroscopy. FT-IR spectra are shown for EuTTA (red line), SiO₂ (blue line), ZIF-8 (black line), SiO₂/EuTTA (yellow line), and SiO₂/EuTTA/ZIF-8 (green line).

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Thermal stability analysis by TGA. Thermograms are shown for compounds ZIF-8 (black line) and SiO₂/EuTTA/ZIF-8 (blue line).

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Analysis of photoluminescent properties in the nanocomposite. Emission spectra (λ_Ex = 397 nm) are shown for EuTTA compound (black line), SiO₂/EuTTA (blue line), and SiO₂/EuTTA/ZIF-8 (red line)

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Uvaol loading efficiency on SiO₂/EuTTA/ZIF-8. Percentage of uvaol loading on the SiO₂/EuTTA/ZIF-8 nanocomposite is shown as a function of the added amount of uvaol, evaluated at adsorption times of 24 and 72 h. The bars represent the mean ± standard error of the mean (S.E.M.) of three experiments performed in triplicate.

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Drug release profile of SiO₂/EuTTA/ZIF-8-uvaol. Drug release profile of the SiO₂/EuTTA/ZIF-8-uvaol nanocomposite in PBS (pH = 7.4) is shown over a 48-h period. Each data point (■) represents the mean ± standard error of the mean (S.E.M.) of three experiments performed in triplicate.

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Molecular docking analysis of uvaol interactions with ZIF-8. Data is shown as a bar graph depicting grouping of different conformations simulated in the interaction of uvaol in ZIF-8.

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Predicted binding modes from molecular docking. Overlay of the 84 conformations clustered in the docking calculations, showing the most probable binding modes.

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Interaction distances in docking simulations. Interaction distances between the low-energy conformation of uvaol and ZIF-8 is shown, derived from the docking simulation of the 84% conformational cluster.

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Interaction distances in docking simulations. Interaction distances between the low-energy conformation of uvaol and ZIF-8 are shown, obtained from the docking simulation of the 16% conformational grouping.

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Effect of uvaol, SiO₂/EuTTA/ZIF-8, and SiO₂/EuTTA/ZIF-8-uvaol on cell viability. Macrophages and epithelial cells were plated and treated with uvaol (0.1–100 μg/mL) for 24 h. Cell viability was measured by MTT assay. The bars represent the mean ± standard error of the mean (S.E.M.) of three experiments performed in triplicate.

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Impact of Uvaol, SiO₂/EuTTA/ZIF-8, and SiO₂/EuTTA/ZIF-8-uvaol on lipopolysaccharide (LPS)-induced cytokine secretion. J774 cells were pretreated for 1 h with uvaol and its nanostructures, and stimulated with LPS (20 μg/mL) for 24 h. Then, production of (A) TNF-α and (B) IL-6 were analyzed using enzyme-linked immunosorbent assay (ELISA). Bars represent means ± standard error of the mean (S.E.M.) of three independent experiments. +++P < 0.001 compared to unstimulated cells; # P < 0.05, ## P < 0.01 and ###P < 0.01 compared to LPS-stimulated cells.

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Inhibition of TGF-β1-Induced EMT in A549 Cells. The effect of uvaol, SiO₂/EuTTA/ZIF-8, and SiO₂/EuTTA/ZIF-8-uvaol on TGF-β1-induced morphological changes in A549 cells was assessed. Morphologic changes consistent with EMT were observed in TGF-β1-treated cells for 24 h, compared with vehicle-treated cells. Control cells (not exposed to TGF-β1 at 5 ng/mL and cultured in DMEM medium) retained the cobblestone morphology characteristic of epithelial cells (as shown by the arrows in the control panel). Phenotypic changes toward a fibroblast-like phenotype were evident in TGF-β1-treated cells as evaluated by light microscopy and crystal violet staining (panel A). Violin plots display the distribution of circularity (panel B) and roundness (panel C) in A549 cells treated with either vehicle (DMSO) alone or TGF-β1 for 24 h. Morphometric analyses were conducted using ImageJ FiJi software, and statistically significant differences between groups were identified by One-way ANOVA followed by the Kruskal–Wallis test. Data are represented as means ± standard error of the mean (S.E.M.). Statistical significance is indicated as follows: +++ P < 0.001 compared to unstimulated cells; * P < 0.05, ** P < 0.01, and *** P < 0.01 compared to TGF-β1-stimulated cells.

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Reduction of TGF-β1-induced cell migration. Cells were treated with (0.1 μg/mL) uvaol, SiO₂/EuTTA/ZIF-8, and SiO₂/EuTTA/ZIF-8-uvaol, and images were captured to calculate the scratch closure. Representative photomicrography images showing the scratched area of cells treated with vehicle (control) or uvaol, and cell migration toward the cell-free area after 24 h (Magnification 10×; panel A). Percentage of scratch covered was measured by quantifying the total distance that cells moved from the edge of the scratch toward the center of the scratch, using ImageJ software, followed by conversion to a percentage of the wound that was covered (panel B). Bars represent means ± standard error of the mean (S.E.M.) of three independent experiments. Statistical significance among groups was determined by one-way ANOVA followed by Tukey’s post-test. +++P < 0.001 compared to respective vehicle-treated cells; ** P < 0.01 and *** P < 0.001.