Exploring thyroxine binding globulin structural changes and its release from human hepatoblastoma cells upon interaction with silica particles: A prelude to unrevealing the mechanism of thyroid hormone dysregulation

Endocrine dysregulation in the presence of environmental chemical risk factors is a global adverse health concern. The aim of this investigation was to explore the structural changes and binding affinity of thyroxine (T4) binding protein (TBG) upon interaction with SiO2 particles as the second largest mineral in the Earth's crust and one of the most important constituents of rock, soil, and dust. Therefore, the interaction of TBG with SiO2 particles was assessed by fluorescence quenching, molecular docking, ANS and synchronous fluorescence, and far-UV CD analyses. Also, the release of TBG from human hepatoblastoma cell line, Hep G2, was assessed by ELISA assay. The results displayed that the value of stoichiometry of binding site (n) of TBG for T4 was approximately equal to one, which was reduced to 0.36 in the presence of SiO2 particles. Also, the binding affinity (Kb) values revealed that the binding affinity between T4 and TBG was strong (97.90 × 105 L/mol), while the presence of SiO2 particles resulted in the calculation of a Kb around 0.00159 × 105 L/mol, which was significantly lower than that of the absence of SiO2 particles. This data was also verified by molecular docking analyses which indicated that SiO2 particles interacted with the T4 binding pocket of TBG. Moreover, further studies exhibited that although the equimolar concentration of T4 to TBG resulted in the superior stability of TBG-T4 complex relative to free TBG, the presence of SiO2 particles with the same concentration led to denaturation of the secondary structure of TBG. Furthermore, it was seen that the amount of released TBG in the cell culture medium of Hep G2 was about 2.21 ng/mL protein, whereas this amount in SiO2 particles-treated cell group was significantly reduced to 1.71 ng/mL protein (*P < 0.05). In conclusion, this study implies that SiO2 particles show the potential to result in inhibition of TBG release, TBG denaturation, and interfere with TBG binding affinity which may lead to dysregulation of the thyroid hormone transport and associated signaling pathways.

Spectroscopic and molecular docking studies of the in vitro interaction between puerarin and cytochrome P450

Puerarin, an isoflavone glycoside extracted from Pueraria plants, has various medical functions. Cytochrome P450s (CYPs) are crucial phase I metabolizing enzymes, which have been spotlighted for their effects on drug metabolism. The interaction between puerarin and CYPs (CYP1A2 and CYP2D6) was investigated by fluorescence, UV-Vis and circular dichroism spectroscopies, as well as molecular docking, to explore the underlying mechanism under simulated physiological conditions. The molecular docking results indicated that puerarin interacted with CYPs mainly by hydrophobic force and hydrogen bonding. The fluorescences of CYPs were quenched statically. Binding constants (K_a) and number of binding sites (n) at different temperatures were calculated, with the results being consistent with those of molecular docking. At the same temperature, puerarin bound to CYP1A2 more weakly than it did to CYP2D6. UV-Vis and circular dichroism spectroscopies confirmed the micro-environmental and conformational changes of CYP1A2 and CYP2D6. The findings provide reliable evidence for clarifying the structures and functions of CYPs.

Development and Validation of a RP-HPLC Method for Estimation of Prulifloxacin in Tablet Dosage Form

A simple, precise, rapid, accurate and economic reverse phase high performance liquid chromatographic method has been developed for the estimation of prulifloxacin in tablet dosage form. The separation was achieved by using octadecylsilane column (C₁₈) and KH₂PO₄ buffer: acetonitrile adjusted to pH 7.3 with triethyl amine in proportion of 10:90 v/v as mobile phase, at a flow rate of 1.0 ml/min. The detection was carried out at 278 nm. The retention time of prulifloxacin was found to be 2.4 min. The limit of detection and limit of quantitation were found to be 0.14 μg/ml and 0.42 μg/ml respectively. The accuracy and reliability of the proposed method was ascertained by evaluating various validation parameters like linearity, precision, accuracy and specificity according to ICH guidelines. The proposed method provides an accurate and precise quality control tool for routine analysis of prulifloxacin in tablet dosage form.