One of the key factors in the pathogenesis of diabetes and its complications is oxidative stress. To inhibit this process, antioxidants may be helpful. Herein, we focused on the protective properties of taxifolin spheroidal form (TS) in the streptozotocin rat model of diabetes mellitus. After 4 weeks of treatment with TS, the fasting blood glucose level of the diabetic animals decreased by 12% compared with the level right after the injection of streptozotocin. While the feed intake in the untreated diabetic rats increased by 5.3% compared with the healthy group, the TS-treated group showed a pronounced 15.3% decrease. Therapeutic administration of TS has a protective effect on the pancreas and the liver against the cytotoxic action of streptozotocin. The plasma antioxidant capacity of all diabetic groups appeared to be approximately 15% lower than in healthy rats with no significant difference between the TS-treated and untreated diabetic animals. Apparently, this can be attributed to taxifolin and plasma proteins binding. These data demonstrate the potential of TS in antidiabetic therapy.

The concomitant utilization of flavonoids and α-tocopherol has the potential to establish a comprehensive antioxidant system that operates in both hydrophilic and lipophilic environments. The objective of this study was to examine the antioxidant interactions between dihydroquercetin, a flavonoid that has shown promise in various studies, as well as structurally related flavonoids, and α-tocopherol in various ratios. The antioxidant capacity was assessed using two ABTS^•+ radical-cation inhibition assays: a decolorization assay and a lag-time assay. The results of this study indicated that formulations of dihydroquercetin, quercetin, rutin, or morin with α-tocopherol exhibited additive or mildly subadditive interactions, independent of their ratios. A two-phase pattern was exhibited by the lag-time data, which, in comparison with individual components, allowed us to suggest that α-tocopherol appeared to dominate the initial phase of radical scavenging, while flavonoids became active in the later phase. This finding indicates that α-tocopherol may play a role in protecting flavonoids from premature oxidation in alcoholic media. The findings could prove valuable for the rational design of antioxidant formulations in the nutraceutical, cosmeceutical, and pharmaceutical industries. Additionally, the two-stage antioxidant behavior offers prospects for the formulation of straightforward, cost-effective analytical approaches to measure components in binary antioxidant formulations.

Introduction. Flavonoids are a family of biologically active substances, representatives of which are often found in the human diet, in particular quercetin, rutin, and morin. When ingested with food, these compounds exhibit their antioxidant properties within the biomolecular system, where α-tocopherol is an important component. Systems formed by antioxidants are characterized by a certain total antioxidant effect, which often differs from the simple sum of their antioxidant capacities to a greater extent in the case of synergy or to a lesser extent in the case of subadditive interaction. From this point of view, the nature of the studied flavonoid's interaction with the endogenous antioxidant α-tocopherol is interesting. The identified inter-action effects can serve as a basis for improved antioxidant formulations, as well as the subsequent study of the cooperation mechanisms in vivo. Aim. The study aims to determine the interaction effects of the α-tocopherol compositions with quercetin, rutin, and morin at their different ratios. Material and methods. Solutions of individual substances and flavonoid–α-tocopherol compositions in ratios from 1:1 to 1:20 were assessed. The antioxidant capacity was evaluated by the ABTS/PP method, implemented in the form of decolorization and kinetic approaches. Results. The values of the TEAC index of the studied flavonoids obtained by the decolorization and kinetic method are close and lie in the range of 0.85–3.73 (decolorization) and 0.94–3.22 (kinetic method). Antioxidant capacity increased in the next order: α-tocopherol, rutin, morin, and quercetin. In the first 10 minutes of incubation, flavonoids captured 50–80% of the total number of ABTS•+ radical cations, while α-tocopherol showed the maximum of its antioxidant capacity already in the 1st minute. The composition effects were additive and slightly subadditive for the studied compositions of ru-tin, morin, and quercetin with α-tocopherol demonstrating maximum values up to –13% in the composition of morin–α-tocopherol 1:10 and quercetin–α-tocopherol 1:20. No dependence of the component’s ratios on the composition effect was found. Conclusions. The studied compositions of bioflavonoids and α-tocopherol exhibit additive and minor subadditive effects.

INTRODUCTION: Dihydroquercetin, as a natural polyphenol with a wide spectrum of pharmacological activity, can inhibit free radical formation process which plays a significant role in the pathogenesis of diabetes mellitus. However, currently, flavonoid antioxidants, in particular, dihydroquercetin are not included in the recommendations for the treatment of diabetes mellitus, which may be due to its low biological availability and some other factors. Earlier, a spheroidal form of dihydroquercetin (DHQsph) was obtained from the pharmaceutical substance dihydroquercetin by spray drying, characterized by better solubility, prolonged liberation and a higher safety profile. AIM: Identification of the effect of (DHQsph) on the antioxidant capacity of blood plasma of rats with streptozotocin-induced diabetes mellitus. MATERIALS AND METHODS: The study used plasma of adult male Wistar rats divided into three groups. The antioxidant capacity of intact plasma samples and of a model mixture of DHQsph solution with blood plasma from healthy rats was evaluated using modified ABTS/PP-method. RESULTS: The antioxidant capacity of blood plasma of rats with streptozotocin-induced diabetes mellitus decreased by 15% relative to the healthy group, however, no differences were found between groups with streptozotocin-induced diabetes treated and not treated with DHQsph. The model mixture of plasma with added DHQsph was shown to have 32% lower antioxidant capacity than the theoretically calculated additive sum. CONCLUSION: Antioxidant capacity of plasma of rats with diabetes was significantly lower in comparison with that of the healthy group. The effect of masking of antioxidant capacity of dihydroquercetin with blood plasma of rats was demonstrated on the model mixture of plasma with the added spheroidal form of dihydroquercetin.

Introduction. Flavanonol dihydroquercetin (DHQ) is known for its pronounced antioxidant properties, which are associated with a wide range of biological activity of this compound. Due to the presence of two chiral centers at positions 2 and 3 of the benzopyranone ring, this flavonoid is characterized by the phenomenon of cis-trans isomerism. However, a comparative analysis of the antioxidant properties of DHQ diastereomers has not been performed before. Aim. To evaluate the effect of diastereomeric composition on the reducing and radical scavenging properties of DHQ samples. Materials and methods. The diastereomeric composition of the DHQ samples was controlled under reverse phase chromatography with UV detection. The antioxidant capacity was studied using a model of inhibition of radical cations of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS ^+• ). The reducing ability of the DHQ samples was evaluated using a 5-(2,4-disulfophenyl)-3-(2-methoxy-4-nitrophenyl)-2-(4-nitrophenyl)-2 H -tetrazolium monosodium salt (WST-8) model. Both tests were performed under the control of UV spectrophotometry. Results and discussion. The chromatograms of the samples obtained at 288 nm are characterized by two peaks with retention times of 18.79 ± 0.08 and 19.87 ± 0.08 min, which correspond to trans - and cis -diastereomers of DHQ. After 6 minutes of DHQ samples containing 0.8, 3.7, and 9.5 % of the cis-isomer adding to the ABTS ^•+ solution, the optical density at 730 nm decreased by 0.588 ± 0.008, 0.581 ± 0.017, and 0.602 ± 0.012, respectively (α 0.05, p 0.2196, r 0.7857), while in WST-8 solutions at 450 nm for similar samples, an increase in optical density was observed by 0.178 ± 0.030, 0.222 ± 0.026, and 0.188 ± 0.036, respectively (α 0.05, p 0.5157, r 0.0284). Conclusion. These results indicate that there is no significant effect of the diastereomeric composition on the antioxidant properties of the DHQ samples. Thus, the observed differences in the pharmacology of cis - and trans -DHQ should be explained by the selectivity of interaction with biological targets, rather than the free radicals scavenging activity.

Introduction. Polyphenols are widely distributed in plant world and recognized for their high antioxidant activity. Traditional methods of polyphenolic compounds quantification, such as Folin – Ciocalteu and aluminum chloride assays, measure total phenolic or flavonoid content but fail to identify individual compounds in complex mixtures. Combining the kinetic profiling of antioxidant activity manifestation for a combination of antioxidants has certain potential for the development of inexpensive and simple quantitate analysis approaches. Aim. To develop an approach for the quantitative determination of individual polyphenols in binary combinations through the measurement of ABTS ^•+ radical cations accumulation kinetics based on a lag-time experimental strategy. Materials and methods. We have studied formulations of flavonoid dihydroquercetin (DHQ) and lignan secoisolariciresinol (SECO) and a combination of DHQ with essential antioxidant alpha-tocopherol (α-TOH). The antioxidants induced the inhibition of ABTS ^•+ radical cations accumulation initiated by potassium persulfate, which resulted in a lag-time formation and was monitored spectrophotometrically at 730–750 nm. Results and discussion. Both combinations demonstrated two lag-time periods pattern typical for additive type interactions between its components. Lag-time period duration depends on concentration of the component. We matched every lag-time period with specific polyphenol which allowed us to determine the content of every component of studied combinations. Developed technique measured the content of polyphenols with value of relative standard deviation (RSD) being not higher than 2 % and value of relative measurement error (δ) not exceeding 3,7 %. Conclusion. Our study confirmed that an antioxidant capacity measurement approach could be successfully applied for content determination of individual polyphenols in complex mixtures. Developed methodology demonstrated high reproducibility and acceptable accuracy levels for binary combinations constituents’ quantification.