Molecular mechanism and thermodynamic study of Rosuvastatin interaction with human serum albumin using a surface plasmon resonance method combined with a multi-spectroscopic, and molecular modeling approach

Generating globin-like reactivities in [human serum albumin-FeII(heme)] complex through N-donor ligand addition

Human serum albumin (HSA) has a strong binding affinity for heme b, forming a complex in a 1:1 ratio with the co-factor ([HSA-FeIIIheme]). This system displays spectroscopic and functional properties comparable to globins when chemical derivatives mimicking them are incorporated into the protein matrix. The aim of this study is to generate globin-like systems using [HSA-FeIIIheme] as a protein template and binding N-donor ligands (imidazole, Im; and 1-methylimidazole, 1-MeIm) to construct artificial [HSA-Fe(heme)-(N-donor)] complexes. Their electronic structure and binding thermodynamics are investigated using UV-vis and (synchronous) fluorescence spectroscopies, while ligand-protein interactions are visualized using docking simulations. The imidazole derivatives have a strong affinity for [HSA-FeIIIheme] (K ∼ 104-106), where the spontaneous binding of Im and 1-MeIm are dominated by entropic and enthalpic effects, respectively. The reduced form of the [HSA-Fe(heme)-(N-donor)] complexes demonstrate nitrite reductase (NiR) activity similar to that observed in globins, but with significant differences in their rates. [HSA-FeIIheme-(1-MeIm)] reduces nitrite ∼4× faster than the Im analogue, and ∼ 30× faster than myoglobin (Mb). The enhanced NiR activity of [HSA-FeIIheme-(1-MeIm)] is a cumulative effect of several factors including a slightly expanded and more optimal heme binding pocket, nearby residues as possible proton sources, and a H-bonding interaction between 1-MeIm and residues Arg160 and Lys181 that may have a long-distance influence on the heme π electron density.

Ligand binding to proteins - When flawed fluorescence quenching methodology and interpretation become the new norm

Intrinsic protein fluorescence quenching measurements have become a widespread methodology to determine ligand-binding properties of in particular serum albumin. Particularly common is the use of double log equations to extract parameters like binding constant and stoichiometry and/or number of binding sites. In this article we discuss that the methodology has several significant and often unrecognized pitfalls, and the double log equations are improperly derived for their purported use. Using simulations, it is shown that the binding stoichiometry and binding constants obtained using these equations may differ substantially from their true values. In addition, it is illustrated how this methodology, via the use of site markers, is unsuited to determine the binding site of ligands on serum albumin. We thus call for a reassessment of the literature in which this methodology plays a central role in characterizing ligand binding to proteins.

Interaction studies of cannabidiol with human serum albumin by surface plasmon resonance, spectroscopy, and molecular docking

The binding interaction of cannabidiol (CBD) and human serum albumin (HSA) under physiological blood pH conditions (pH 7.4) was conducted by surface plasmon resonance (SPR), fluorescence spectroscopy, UV-Visible spectrophotometry, and molecular docking. The responses from SPR measurement increased with the increase in CBD concentration until equilibrium was reached at the equilibrium dissociation constant (KD) of 9.8 × 10-4 M. The results from fluorescence and UV-Visible spectroscopy showed that CBD bound to HSA at one site in a spontaneous manner to form protein-CBD complexes. The quenching process involved both static and dynamic mechanisms while the static mechanism contributed predominantly to the binding between CBD and albumin. The binding constants estimated from the fluorescence studies were from 0.16 × 103 to 8.10 × 103 M-1, which were calculated at different temperature conditions using Stern-Volmer plots. The thermodynamic parameters demonstrated that the binding interaction was a spontaneous reaction as Gibbs free energy had negative values (ΔG = -12.57 to -23.20 kJ.mol-1). Positive ΔH and ΔS values (ΔH = 2.46 × 105 J.mol-1 and ΔS = 869.81 J.mol-1K-1) indicated that the hydrophobic force was the major binding interaction. Finally, confirmation of the type and extent of interaction was provided using UV-spectroscopy and molecular docking studies. The outcomes of this study are expected to serve as a platform to conduct future studies on binding interactions and toxicological research of CBD.Communicated by Ramaswamy H. Sarma.

Drug Release and Stability Study of Innovated Losartan Potassium and Rosuvastatin Calcium Fixed-dose Combination Tablet

BACKGROUND

Patient adherence to therapy and compliance is always a challenge for care providers in the management of chronic disorders with multiple medications.

OBJECTIVE

Our study focused on formulating concurrently prescribed ARB (Angiotensin Receptor Blocker), i.e., losartan potassium, and a cholesterol-lowering statin derivative, i.e., rosuvastatin calcium, in a fixed-dose combination tablet.

METHODS

The drugs were selected based on the presence of synergism and variation in solubility characteristics. Trial batches with fixed concentrations of both active pharmaceutical ingredients (APIs) and varying quantities of different excipients were prepared by dry granulation technique and subjected to different quality control tests for tablets. Batch F5 was selected on the basis of in-process quality control data for the development of a drug release protocol. Experimental conditions were optimized. Based on the sink condition, phosphate buffer (pH 6.8) was selected as the dissolution medium. Simultaneous determination of both APIs in samples collected at predetermined time intervals was carried out using the RP-HPLC technique with acetonitrile, methanol, and water (20:25:55 v/v/v) as mobile phase.

RESULTS

Complete dissolution of both APIs in the FDC tablet was achieved in 45 min in 900 mL of the selected medium. The in vitro drug release protocol was validated for accuracy and precision without interference with sample analysis.

CONCLUSION

In this study, a validated, accurate, and robust dissolution testing method was developed for the newly formulated FDC tablet.

Molecular Recognition Study toward the Mitochondrial Electron Transport Chain Inhibitor Mubritinib and Human Serum Albumin

The ability to bind plasma proteins helps in comprehending relevant aspects related to the pharmacological properties of many drugs. Despite the vital role of the drug mubritinib (MUB) in the prophylaxis of various diseases, its interaction with carrier proteins still needs to be clarified. The present work focuses on the interaction between MUB and Human serum albumin (HSA), investigated by employing multispectroscopic, biochemical, and molecular docking approaches. The results reveal that MUB has quenched HSA intrinsic fluorescence (following a static mechanism) by attaching very close (r = 6.76 Å) and with moderate affinity (Kb ≈ 104 M-1) to the protein site I (mainly by H-bonds, hydrophobic and Van der Waals forces). On one side, the HSA-MUB interaction has been accompanied by a slight disturbance in the HSA chemical environment (around the Trp residue) and protein secondary structure modifications. On another side, MUB competitively inhibits HSA esterase-like activity, which is very similar to other Tyrosine kinase inhibitors, and evidence that protein functional alterations have been triggered by MUB interaction. In summary, all of the presented observations can shed light on diverse pharmacological factors associated with drug administration.

Two green spectrofluorimetric methods for the assay of atomoxetine hydrochloride in pure form and commercial capsules with application to content uniformity testing

Atomoxetine hydrochloride (ATX) is a potent and non-stimulant drug which was approved for the treatment of attention-deficit hyperactivity disorder. Owing to its importance, two green, simple and validated spectrofluorimetric methods were developed for its sensitive assay in pure and capsule forms. The first method (Method I) relied on measuring the enhanced fluorescence of ATX by the use of sodium dodecyl sulfate in alkaline medium at λ _ex 227 nm/λ _em 298 nm. The second method (Method II) involved complex formation of ATX with Erythrosine B (EB) in aqueous acidic solution resulting in quantitative quenching of the EB naive fluorescence. This complex was formed in the presence of Britton-Robinson buffer (pH 4.0). The difference in fluorescence intensity was measured at λ _ex 527/λ _em550 nm. The calibration curves were linear through the ranges of 0.2-2.0 µg ml^-1 for Method I, 0.2-4.0 µg ml^-1 for Method II with good correlation coefficient (r = 0.9998) for both methods. The suggested methods were perfectly applied for determination of ATX in its commercial capsules and content uniformity test. The greenness of the proposed methods was confirmed by three different assessment tools and it was found that both methods were green, eco-friendly and environmentally safe.

Utility of a xanthene-based dye for determination of nilotinib using two spectroscopic approaches. Applications to bulk powder, capsules, and spiked human plasma

Novel, selective, facile, and precise spectroscopic approaches were validated to determine nilotinib hydrochloride, a tyrosine kinase inhibitor used to treat patients with chronic myeloid leukemia. These approaches depend on the reaction of the tertiary amine group of nilotinib with erythrosine B in the Britton-Robinson buffer at pH 4. Method I, depends on measuring the absorbance of the formed complex at 551 nm. The absorbance concentration plot showed linearity over the concentration range of 1.0 to 9.0 μg/ml. Method II, involved the measurement of the quenching of the native fluorescence of erythrosine B by adding nilotinib in an acidic medium. The fluorescence quenching of erythrosine B was measured at 549 nm after excitation at 528 nm. This approach showed excellent linearity in the concentration range of 0.04 to 0.7 μg/ml. The limit of detection values for Method I and Method II were 0.225 and 0.008 μg/ml, respectively, while the limit of quantitation values for Method I and Method II were 0.68 and 0.026 μg/ml, respectively. To get the optimal conditions, factors that may affect the formation of the ion-pairing complex were thoroughly examined. The two approaches were carefully validated following the International Conference of Harmonization (ICH Q2R1) guidelines. Statistical assessment of the results achieved using the suggested and previously published comparison approaches showed no significant difference. The approaches were successful in determining nilotinib in a pharmaceutical dosage form as well as spiked human plasma samples. The eco-friendly properties of the methods were evaluated by three different tools.

Utility of a novel turn-off fluorescence probe for the determination of tranilast, an adjunctive drug for patients with severe COVID-19

Tranilast (TR) could be investigated as a suitable anti-inflammatory and NLRP3 inflammasome inhibitor medication for the treatment of COVID-19 acute patients. Owing to its importance, our study was constructed for the determination of TR using a new, fast, sensitive, and reliable green spectrofluorimetric method. TR was quantified in this study by forming a complex with the acriflavine (AC) reagent. The reaction between TR and AC quenched the fluorescence of AC through the formation of an ion-association complex and the response was measured at 493 nm after excitation at 263 nm. It was observed that the quenching of the fluorescence of AC was linear (r = 0.9998) with the concentration of TR in the range of 1.0–15.0 μg mL⁻¹. The limit of detection was 0.224 μg mL⁻¹, and the limit of quantification was 0.679 μg mL⁻¹. The fluorescence quenching mechanism was carefully studied and was confirmed to be able to analyze TR in its pure form and its prepared pharmaceutical dosage form. To validate the method, the international conference of harmonization (ICH) Q₂R₁ guidelines were followed. The statistical assessment of the proposed and comparison methods revealed no significant differences between them. Moreover, the green criteria of the method were evaluated and confirmed.

Tranilast (TR) could be investigated as an anti-inflammatory and NLRP3 inflammasome inhibitor medication using acriflavine.

Structural Analysis of Human Serum Albumin in Complex with the Fibrate Drug Gemfibrozil

Gemfibrozil (GEM) is an orally administered lipid-regulating fibrate derivative drug sold under the brand name Lopid^®, among others. Since its approval in the early 80s, GEM has been largely applied to treat hypertriglyceridemia and other disorders of lipid metabolism. Though generally well tolerated, GEM can alter the distribution and the free, active concentration of some co-administered drugs, leading to adverse effects. Most of them appear to be related to the ability of GEM to bind with high affinity human serum albumin (HSA), the major drug-carrier protein in blood plasma. Here, we report the crystal structure of HSA in complex with GEM. Two binding sites have been identified, namely Sudlow’s binding sites I (FA7) and II (FA3–FA4). A comparison of the crystal structure of HSA in complex with GEM with those of other previously described HSA–drug complexes enabled us to appreciate the analogies and differences in their respective binding modes. The elucidation of the molecular interaction between GEM and HSA might offer the basis for the development of novel GEM derivatives that can be safely and synergistically co-administered with other drugs, enabling augmented therapeutic efficacies.