Danijela Krstić

Prooxidative properties of hafnium(IV)-substituted Wells-Dawson polyoxometalate, K16[Hf(α2-P2W17O61)2]·19H2O (Hf-WD 1:2), a promising contrast agent for micro-computed tomography (microCT) and biological transmission electron microscopy (TEM) imaging, were evaluated in vitro. The effect of Hf-WD 1:2 on carbonylated protein level, as a biomarker of severe oxidative stress, was determined in human plasma after 4-hour exposure to 1-100 µM Hf-WD 1:2 at 37 °C. The studied contrast agent candidate did not result in increased oxidative protein modification compared to control sample, that indicates its favourable toxicity profile and safe biomedical application. Additionally, 100 µM Hf-WD 1:2 induced a remarkable decrease of carbonylated protein concentration. This result forms a basis for further research on the antioxidant potential of Hf-WD 1:2.

Transmission electron microscopy (TEM) is a key tool for ultrastructural analysis, yet its performance critically depends on contrast agents, many of which are constrained by toxicity and regulatory concerns. In this study, Wells–Dawson (WD)-type polyoxometalates (POMs), including Parent WD-POM, Lacunary WD-POM, Zr-WD 1:2 POM, and Hf-WD 1:2 POM, were investigated as alternative contrast agents for TEM imaging of rat kidney tissue. Among the tested compounds, Hf-WD 1:2 POM provided the most consistent contrast enhancement, enabling clear visualization of subcellular structures with minimal background interference and no detectable aggregation. Its contrast performance depended on both concentration and incubation time, with higher concentration (0.01 mol/L) and prolonged incubation (24 h) yielding increased signal-to-noise ratio (SNR), although SNR alone did not fully reflect image quality. In comparison with conventional staining agents (uranyl acetate and Uranyless), Hf-WD 1:2 POM achieved significantly improved contrast effectiveness without inducing detectable tissue damage. These findings identify Hf-WD 1:2 POM as a promising non-radioactive alternative for TEM imaging and support the potential of POMs as versatile platforms for the development of advanced contrast agents.

The aim of this study was to elucidate the potential mechanism of the antihyperglycemic action of the donut-shaped Preyssler-Pope-Jeannin polyanion salt (NH₄)₁₄[NaP₅W₃₀O₁₁₀] 31H₂O (NaP₅W₃₀) and its effect on metabolic disorders associated with diabetes. For this purpose, relevant parameters of blood glucose regulation, lipid profile, and electrolyte status were monitored in streptozotocin (STZ)-induced diabetic rats that were orally treated with 20 mg/kg/day NaP₅W₃₀ for three weeks. The serum insulin concentration was increased in diabetic animals treated with NaP₅W₃₀ (20 mg/kg/day, per os, three weeks), which could be one of the possible mechanisms of the confirmed antihyperglycemic effect. In addition, the administration of NaP₅W₃₀ significantly reduced hyperglycemia and glycated haemoglobin A_1c (HbA_1c) in STZ-induced diabetic rats, although normoglycemic values were not achieved. Furthermore, a statistically significant 1.3-fold reduction in serum total cholesterol and a 1.7-fold reduction in high-density lipoprotein (HDL) cholesterol were observed in the NaP₅W₃₀ treatment group compared to the diabetic control group. In contrast, NaP₅W₃₀ had no effect on homeostasis model assessment of insulin resistance (HOMA-IR) index values, electrolyte concentrations, or serum concentrations of low-density lipoprotein (LDL) cholesterol, apolipoprotein A1 (Apo A1), apolipoprotein B (Apo B), or total triglycerides. In summary, NaP₅W₃₀ effectively improved glycoregulation in diabetic rats via the considerable stimulation of insulin as a putative mechanism. Moreover, NaP₅W₃₀ did not affect rat weight or disrupt lipid and electrolyte status, common diabetes-followed side effects and risk factors for various life-threatening complications. Thus, NaP₅W₃₀ could be considered a promising antidiabetic drug-candidate that deserves further investigation. Graphical abstract

The aim of this study was to investigate the antioxidant capacity of fruit wines and their protective effects against hydrogen peroxide-induced oxidative stress in rat synaptosomes in vitro. The wines were produced from strawberries and drupe fruits (i.e., plum, sweet cherry, peach, and apricot) through microvinification with a pure S. cerevisiae yeast culture. Fruit wines were produced with and without added sugar before the start of fermentation, whereas subvariants with and without pits were only applied to drupe fruit wines. First, synaptosomes were treated with the wines, while oxidative stress was induced with H₂O₂. Subsequently, the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)) and the content of malondialdehyde (MDA), an indicator of membrane injury, were determined. In addition, the Briggs–Rauscher reaction (BR) was used to evaluate the inhibition capacity against free radicals. All investigated fruit wines increased the activity of the studied antioxidant enzymes and decreased MDA content compared to the corresponding controls (synaptosomes treated with H₂O₂). After synaptosomal treatment with plum wine, the highest activities were observed for SOD (5.57 U/mg protein) and GPx (0.015 U/mg protein). Strawberry wine induced the highest CAT activity (0.047 U/mg protein) and showed the best ability to reduce lipid peroxidation, yielding the lowest MDA level (2.68 nmol/mg). Strawberry, plum, and sweet cherry wines were identified as samples with higher antioxidant activity in both principal component analysis (PCA) and hierarchical cluster analysis (HCA). Finally, plum wine exhibited the highest inhibitory activity in the BR reaction (397 s). The results suggest that fruit wines could be considered potential functional food due to their protective effects against oxidative stress.

Polyoxotungstate nanoclusters have recently emerged as promising contrast agents for computed tomography (CT). In order to evaluate their clinical potential, in this study, we evaluated the in vitro CT imaging properties, potential toxic effects in vivo, and tissue distribution of monolacunary Wells–Dawson polyoxometalate, α₂-K₁₀P₂W₁₇O₆₁^.20H₂O (mono-WD POM). Mono-WD POM showed superior X-ray attenuation compared to other tungsten-containing nanoclusters (its parent WD-POM and Keggin POM) and the standard iodine-based contrast agent (iohexol). The calculated X-ray attenuation linear slope for mono-WD POM was significantly higher compared to parent WD-POM, Keggin POM, and iohexol (5.97 ± 0.14 vs. 4.84 ± 0.05, 4.55 ± 0.16, and 4.30 ± 0.09, respectively). Acute oral (maximum-administered dose (MAD) = 960 mg/kg) and intravenous administration (1/10, 1/5, and 1/3 MAD) of mono-WD POM did not induce unexpected changes in rats’ general habits or mortality. Results of blood gas analysis, CO-oximetry status, and the levels of electrolytes, glucose, lactate, creatinine, and BUN demonstrated a dose-dependent tendency 14 days after intravenous administration of mono-WD POM. The most significant differences compared to the control were observed for 1/3 MAD, being approximately seventy times higher than the typically used dose (0.015 mmol W/kg) of tungsten-based contrast agents. The highest tungsten deposition was found in the kidney (1/3 MAD—0.67 ± 0.12; 1/5 MAD—0.59 ± 0.07; 1/10 MAD—0.54 ± 0.05), which corresponded to detected morphological irregularities, electrolyte imbalance, and increased BUN levels.

The objective of this study was to investigate the simultaneous effect of a monolacunary Wells- Dawson polyoxometalate (mono-WD), α2-K10P2W17O61.20H2O, which exhibited remarkable cytotoxicity against HeLa cells, and L(+)-ascorbic acid sodium salt (ascorbate), as a strong antioxidant, against HeLa cells as a commonly used model system for research purposes. HeLa cells were treated in vitro (single exposure) with different concentrations of mono-WD (0.001 – 1 mM) and ascorbate (0.040 – 40 mM) for 24 and 48 hours. In addition, the tumor cells were simultaneously exposed to mixtures containing the same concentrations of mono-WD and ascorbate (ratio 1:40). Mono-WD and ascorbate induced concentration-dependent cytotoxic effects against HeLa cells, with EC50 values of 0.042 and 0.017 mM (for 24 and 48 hours, respectively) for mono- WD and 0.88 and 0.36 mM (for 24 and 48 hours, respectively) for ascorbate. The results of mono- WD/ascorbate mixtures (concentration ratio 1:40) indicated an additive/synergistic cytotoxic effect of the studied compounds against HeLa cell viability. Conclusively, ascorbate improves the antitumour properties of mono-WD as a potential chemotherapeutic candidate.

The influence of L(+)-ascorbic acid sodium salt (ascorbate), as a widely used antioxidant, on the anti-human melanoma A375 activity of a monolacunary Wells-Dawson polyoxometalate (mono- WD), α2-K10P2W17O61.20H2O was assessed in this study. A375 cells were in vitro exposed to the selected concentrations of mono-WD (the concentration range of 0.001 – 1 mM), ascorbate (0.040 – 40 mM), and the mixtures of mono-WD and ascorbate in the ratio of 1:40, for 24 and 48 hours. Both mono-WD and ascorbate induced concentration- dependent cytotoxic effects on A375 tumour cells, for both exposure times. The cell viability inhibiting potential of ascorbate was higher after 24-hour exposure, whereas similar cytotoxic effects of the studied compounds were obtained for 48- hour treatment. In summary, the results of the simultaneous exposure of A375 cells to mono-WD and ascorbate (mixed in the ratio of 1:40) showed that the presence of ascorbate does not affect remarkably the observed antitumour potency of the studied polyoxotungstate as a potential metallo- therapeutic.

This study aimed to investigate the simultaneous effect of Fe(III)-substituted monolacunary Wells-Dawson polyoxometalate (Fe-WD), K7[FeIII(α2-P2W17O61)(H2O)] and L(+)-ascorbic acid sodium salt (ascorbate) on cell viability of human melanoma A375 cells. A375 cells were exposed in vitro to Fe-WD (0.001 – 1 mM), ascorbate (0.040 – 40 mM), and Fe-WD/ascorbate mixtures (concentration ratio 1:40) for 24, 48, and 72 h. Fe-WD and ascorbate inhibited cell viability in a concentration-dependent manner for three treatment durations. Obtained EC50 values were 1, 0.58, and 0.52 mM (for 24-, 48-, and 72-hour exposure, respectively) for Fe-WD and 1.32, 1.12, and 0.80 mM (for 24, 48, and 72 hours, respectively) for ascorbate. The simultaneous exposure to Fe-WD/ascorbate mixtures resulted in cytotoxic effects weaker than the mathematical sum of effects induced by single Fe-WD and ascorbate treatments, indicating an antagonistic inhibitory effect of the studied compounds on A375 cell viability. Conclusively, Fe-WD seems to reduce the cytotoxic effect of sodium ascorbate due to the possible autoxidation of ascorbate by oxygen in the presence of ferric (Fe(III)) ions.

The Institute of Medical Chemistry one of the oldest institutes of the Faculty of Medicine University of Belgrade, was founded in 1923. Recognizing the role of chemistry in understanding medical sciences, the founders of the Faculty of Medicine engaged leading authorities of the time in the field of chemistry: Sima Lozanić, Milivoje Lozanić, and Petar Matavulj, establishing a solid foundation for the quality education of future doctors. Over more than a century, the teachers and associates of the Institute have successfully addressed specific challenges in medical education, adapting to contemporary trends in science and education.

Reactive oxygen species cause cell damage when its generation is higher than activity of antioxidants. It can be solve by usage of antioxidants from natural sources. Study investigated protective effect of black chokeberry wines against oxidative stress induced by H2O2 in rat synaptosomes. Wines were produced from black chokeberry, according to an innovative microvinification procedure. Phenolic profile highlighted phenolic acids and flavonoids. Total phenolic content was determined by Folin-Ciocalteu method. Antiradical activity investigated by application of DPPH radical, while for antioxidant activity was applied Ferric Reducing Ability of Plasma method. Parameters of oxidative stress, malondialdehyde, superoxide dismutase, glutathione peroxidase, and catalase were monitored. Protection of synaptosomes against induced oxidative stress was observed for all wines. Black chokeberry wine activity is result of synergistic effect of all natural antioxidant compounds present in the wine.