Unveiling the tyrosinase inhibitory potential of phenolics from Centaurium spicatum: Bridging in silico and in vitro perspectives.

Phenolics, abundant in plants, constitute a significant portion of phytoconstituents consumed in the human diet. The phytochemical screening of the aerial parts of Centaurium spicatum led to the isolation of five phenolics. The anti-tyrosinase activities of the isolated compounds were assessed through a combination of in vitro experiments and multiple in silico approaches. Docking and molecular dynamics (MD) simulation techniques were utilized to figure out the binding interactions of the isolated phytochemicals with tyrosinase. The findings from molecular docking analysis revealed that the isolated phenolics were able to bind effectively to tyrosinase and potentially inhibit substrate binding, consequently diminishing the catalytic activity of tyrosinase. Among isolated compounds, cichoric acid displayed the lowest binding energy and the highest extent of polar interactions with the target enzyme. Analysis of MD simulation trajectories indicated that equilibrium was reached within 30 ns for all complexes of tyrosinase with the isolated phenolics. Among the five ligands studied, cichoric acid exhibited the lowest interaction energies, rendering its complex with tyrosinase the most stable. Considering these collective findings, cichoric acid emerges as a promising candidate for the design and development of a potential tyrosinase inhibitor. Furthermore, the in vitro anti-tyrosinase activity assay unveiled significant variations among the isolated compounds. Notably, cichoric acid exhibited the most potent inhibitory effect, as evidenced by the lowest IC50 value (7.92 ± 1.32 µg/ml), followed by isorhamnetin and gentiopicrin. In contrast, sinapic acid demonstrated the least inhibitory activity against tyrosinase, with the highest IC50 value. Moreover, cichoric acid exhibited a mixed inhibition mode against the hydrolysis of l-DOPA catalyzed by tyrosinase, with Ki value of 1.64. Remarkably, these experimental findings align well with the outcomes of docking and MD simulations, underscoring the consistency and reliability of our computational predictions with the actual inhibitory potential observed in vitro.

Mechanistic aspects of reactive metabolite formation in clomethiazole catalyzed biotransformation by cytochrome P450 enzymes.

Clomethiazole (CLM), a sedative and anticonvulsant drug, is commonly employed for the treatment of alcohol withdrawal syndrome because it suppresses cytochrome P450 (P450) activity associated with the generation of free radicals and liver damage. The catalyzed biotransformation of thiazole-containing drugs by P450 is known to afford reactive metabolites. These metabolites can alter the biological functions of macromolecules and result in toxicity and adverse drug interactions. Multitargeted molecular modeling and quantum chemical DFT calculations were performed to explore the binding modes and molecular mechanisms underlying the mechanism-based inactivation (MBI) of P450 by CLM. The mechanistic details associated with reactive metabolite formation from further metabolic processes were extensively assessed. Seven possible routes were proposed for CLM-P450 biotransformation including CLM hydroxylation, sulfoxidation, N-oxidation, CN epoxidation (oxaziridine formation), and CC epoxidation. The results revealed a degree of preference for the C-N epoxidation pathway because of the low energy requirements of its rate-determining step (8.74 and 10.07 kcal mol-1 for LS and HS states, respectively). A kinetic competition for the CLM-methyl hydroxylation pathway was detected because the H-abstraction energy barrier was relatively comparable to the thermodynamically prevailing oxaziridine formation rate-determining step (12.58 and 14.52 kcal mol-1 for quartet and doublet states, respectively). Our studies assessed the mechanisms of covalent nucleophilic epoxide adduct formation through nucleophilic addition, hydrolysis of epoxidation products, and nonenzymatic degradation. CLM was shown to display P450-inhibitory activity by forming covalent adducts rather than further metabolization to reactive metabolites. The outcomes of molecular docking allowed assessing the binding profile of CLM with three human P450 isozymes, namely, CYP2E1, CYP3A4, and CYP2D6.

Molecular modeling and DFT studies on the antioxidant activity of Centaurea scoparia flavonoids and molecular dynamics simulation of their interaction with ß-lactoglobulin.

Plants of the genus Centaurea have been widely used as natural therapeutics in different countries. This study investigated the antioxidant-structure activity relationship of eight flavonoids isolated from Centaurea scoparia using DFT studies and in vitro radical scavenging and xanthine oxidase (XO) inhibition assays, and to correlate the theoretical values with the experimental findings. Docking analysis was carried out to explore the binding modes of the isolated phytochemicals with XO and bovine ß-lactoglobulin (BLG). Interactions of the isolated compounds with BLG were studied using molecular dynamics (MD) simulations which revealed the involvement of hydrogen bonding. The root-mean-square deviation (RMSD) of BLG and BLG-flavonoid complexes reached equilibrium and fluctuated during the 10 ns MD simulations. The radius of gyration (Rg) and solvent accessible surface area (SASA) revealed that various systems were stabilized at approximately 2500 ps. In addition, the RMS fluctuations profile indicated that the ligand's active site exerted rigidity behavior during the simulation. The hydrogen atom transfer (HAT) and the energies of hydrogen abstractions were estimated by calculating the bond dissociation enthalpy (BDE) of O-H in gas phase and water. The isolated compounds showed radical scavenging and XO inhibitory activities along with binding affinity with XO as revealed in silico. The BDE was linked to the radical scavenging processes occurring in polar solvents. These processes are single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Our calculations indicated the agreement between the calculated results and the experimentally measured antioxidant activity of the flavonoids isolated from C. scoparia.

Xanthine Oxidase Inhibitory Activity of Euphorbia peplus L. Phenolics.

BACKGROUND: Various phenolics show inhibitory activity towards xanthine oxidase (XO), an enzyme that generates reactive oxygen species which cause oxidative damage. OBJECTIVE: This study investigated the XO inhibitory activity of Euphorbia peplus phenolics. METHODS: The dried powdered aerial parts of E. peplus were extracted, fractioned and phenolics were isolated and identified. The XO inhibitory activity of E. peplus extract (EPE) and the isolated phenolics was investigated in vitro and in vivo. RESULTS: Three phenolics were isolated from the ethyl acetate fraction of E. peplus. All isolated compounds and the EPE showed inhibitory activity towards XO in vitro. In hyperuricemic rats, EPE and the isolated phenolics decreased uric acid and XO activity. Molecular docking showed the binding modes of isolated phenolics with XO, depicting significant interactions with the active site amino acid residues. Molecular dynamics simulation trajectories confirmed the interaction of isolated phenolics with XO by forming hydrogen bonds with the active site residues. Also, the root mean square (RMS) deviations of XO and phenolics-XO complexes achieved equilibrium and fluctuated during the 10 ns MD simulations. The radius of gyration and solvent accessible surface area investigations showed that different systems were stabilized at ≈ 2500 ps. The RMS fluctuations profile depicted that the drug binding site exhibited a rigidity behavior during the simulation. CONCLUSION: In vitro, in vivo and computational investigations showed the XO inhibitory activity of E. peplus phenolics. These phenolics might represent promising candidates for the development of XO inhibitors.

Combination and tricombination therapy to destabilize the structural integrity of COVID-19 by some bioactive compounds with antiviral drugs: insights from molecular docking study.

Recently, the SARS-CoV-2 (COVID-19) pandemic virus has been spreading throughout the world. Until now, no certified drugs have been discovered to efficiently inhibit the virus. The scientists are struggling to find new safe bioactive inhibitors of this deadly virus. In this study, we aim to find antagonists that may inhibit the activity of the three major viral targets: SARS-CoV-2 3-chymotrypsin-like protease (6LU7), SARS-CoV-2 spike protein (6VYB), and a host target human angiotensin-converting enzyme 2 (ACE2) receptor (1R42), which is the entry point for the viral encounter, were studied with the prospects of identifying significant drug candidate(s) against COVID-19 infection. Then, the protein stability produced score of less than 0.6 for all residues of all studied receptors. This confirmed that these receptors are extremely stable proteins, so it is very difficult to unstable the stability of these proteins through utilizing individual drugs. Hence, we studied the combination and tricombination therapy between bioactive compounds which have the best binding affinity and some antiviral drugs like chloroquine, hydroxychloroquine, azithromycin, simeprevir, baloxavir, lopinavir, and favipiravir to show the effect of combination and tricombination therapy to disrupt the stability of the three major viral targets that are mentioned previously. Also, ADMET study suggested that most of all studied bioactive compounds are safe and nontoxic compounds. All results confirmed that caulerpin can be utilized as a combination and tricombination therapy along with the studied antiviral drugs for disrupting the stability of the three major viral receptors (6LU7, 6VYB, and 1R42). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11224-020-01723-5.

Rumex dentatus L. phenolics ameliorate hyperglycemia by modulating hepatic key enzymes of carbohydrate metabolism, oxidative stress and PPARγ in diabetic rats.

Rumex dentatus L. is a flowering plant with promising therapeutic effects. This study investigated the antioxidant efficacy of phenolic compounds isolated from R. dentatus L. in vitro and by conducting density function theory (DFT) studies to explore the mechanisms of action. The antioxidant, anti-inflammatory and antidiabetic effects of polyphenols-rich R. dentatus extract (RDE) were investigated in type 2 diabetic rats. Phytochemical investigation of the aerial parts of R. dentatus resulted in the isolation of one new and seven known compounds isolated for the first time from this species. All isolated phenolics showed in vitro radical scavenging activity. The antioxidant activity of the compounds could be oriented by the hydrogen atom transfer and sequential proton loss electron transfer mechanisms in gas and water phases, respectively. In diabetic rats, RDE attenuated hyperglycemia, insulin resistance and liver injury and improved carbohydrate metabolism. RDE suppressed oxidative stress and inflammation and upregulated PPARγ. In silico molecular docking analysis revealed the binding affinity of the isolated compounds toward PPARγ. In conclusion, the computational calculations were correlated with the in vitro antioxidant activity of R. dentatus derived phenolics. R. dentatus attenuated hyperglycemia, liver injury, inflammation and oxidative stress, improved carbohydrate metabolism and upregulated PPARγ in diabetic rats.