Multispectroscopic Investigation of the Interaction Between two Ruthenium(II) Arene Complexes of Curcumin Analogs and Human Serum Albumin

Formation mechanism, prevention of malignant ascites effusion and reduction of intestinal mucosal irritation of natural microemulsion from Euphorbia lathyris Pulveratum

Malignant ascites effusion (MAE) is a common complication of advanced malignant tumors with limited treatments. Euphorbia lathyris (EL) has a long history of application in patients with edema and ascites. Herein, we reported for the first time a mode in which EL and EL Pulveratum (PEL) spontaneously formed natural microemulsions (ELM and PELM) without the addition of any carriers and excipients, and found that the protein and phospholipid contained in them encapsulated fatty oil and diterpenoid esters through non-covalent interactions. The denaturation and degradation of protein in PELM resulted in stronger binding of diterpenoid esters to the hydrophobic region of protein, which facilitated the sustained and slow release of diterpenoid esters and improved their bioavailability in vivo, thereby retaining the efficacy of preventing MAE while alleviating the irritation of intestinal mucosa. The mechanism by which PELM retained efficacy might be related to increased feces moisture and urine volume, and decreased expression of AVPR2, cAMP, PKA and AQP3 in MAE mice. And its mechanism of reducing intestinal mucosal irritation was related to decreased cell apoptosis, amelioration of oxidative stress, elevation of mitochondrial membrane potential, and up-regulation of Occludin and Claudin-1 expression in IEC-6 cells. This nano-adjuvant-free natural microemulsions may be a promising therapeutic strategy in the field of phytochemistry for promoting the application of natural and efficient nano-aggregates spontaneously formed by medicinal plants in MAE, and provide a new perspective for advancing the development of the fusion of Chinese herbal medicine and nanomedicine and its clinical translation.

Investigations of the Interaction Mechanism Between Orphenadrine Hydrochloride and Bovine Serum Albumin by Spectroscopic and Voltammetric Techniques

The interaction of orphenadrine hydrochloride (ORD) with the model protein, bovine serum albumin (BSA), was investigated using a variety of spectroscopic techniques such as steady-state fluorescence, ultraviolet-visible, Fourier transform infrared, 3-D spectroscopy, and electrochemical methods under physiological conditions. Stern-Volmer plots were used to calculate fluorescence quenching at various temperatures. The findings point to a static quenching mechanism between ORD and BSA. At various reaction times, the binding sites (n) and binding constants (K) of ORD to BSA were recorded. Thermodynamic parameters ∆H0, ∆S0 and ∆G0 between ORD and BSA were calculated and reported. The average binding distance (r) between the donor (BSA) and acceptor (ORD) molecules was predicted using Förster's theory. Three-dimensional fluorescence spectra, Fourier transform infrared spectra, and synchronous fluorescence studies all supported the alternations in protein structure following the interaction with ORD. A displacement study using site probes such as warfarin, ibuprofen, and digitoxin confirmed ORD binding at Sudlow's site I of BSA. The effect of common metal ions such as Cu2+, Ni2+, Ca2+, Co2+, and Zn2+ on binding constant values was investigated and reported.

Comparison of the Effects on Bovine Serum Albumin Induced by Different Forms of Vanadium

Various forms of vanadium coexist in vivo, and the behavior mechanism is different. An investigation of the separate and simultaneous binding of three vanadium forms with bovine serum albumin (BSA) was performed. VO(acac)₂/NaVO₃/VOSO₄ bound to site I of BSA, and their binding constants were 4.26 × 10⁵, 9.18 × 10³, and 4.31 × 10² L mol^-1 at 298 K, respectively. VO(acac)₂ had the strongest binding ability to BSA and had the most influence on the secondary structure of BSA and the microenvironment of around amino acid residues. The effect of NaVO₃ and VOSO₄ coexistence on the binding of VO(acac)₂ to BSA was therefore further investigated. Both NaVO₃ and VOSO₄ had an effect on the binding of VO(acac)₂ and BSA, with NaVO₃ having the most noticeable effect. NaVO₃ interfered with the binding process of VO(acac)₂ and BSA, increased the binding constant, and changed the binding forces between them. Competition and allosteric effect may be responsible for the change of binding process between VO(acac)₂ and BSA in the presence of NaVO₃/VOSO₄.

New Insights into the Inhibition of Hesperetin on Polyphenol Oxidase: Inhibitory Kinetics, Binding Characteristics, Conformational Change and Computational Simulation

The inhibitory activity of hesperetin on polyphenol oxidase (PPO) and their interaction characteristics were investigated using multiple spectroscopic methods and computational simulation. Hesperetin, a mixed inhibitor, reversibly inhibited PPO activity, and its half-maximum inhibitory concentration (IC₅₀) values on monophenolase and diphenolase were 80.8 ± 1.4 μM and 776.0 ± 15.5 μM, respectively. Multivariate curve resolution-alternate least squares (MCR-ALS) analysis suggested PPO interacted with hesperetin and formed PPO-hesperetin complex. Hesperetin statically quenched PPO's endogenous fluorescence, and hydrophobic interactions mainly drove their binding. Hesperetin affected the polarity of the microenvironment around the Trp residues in PPO, but had no effect on that around Tyr residues. Circular dichroism (CD) results showed that hesperetin increased α-helix content and decreased β-fold and random coil contents, thus tightening PPO's structure. Molecular docking showed that hesperetin entered the hydrophobic cavity of PPO, bound near the dinuclear copper active center, interacted with Val283, Phe264, His85, Asn260, Val248, and His263 via hydrophobic interactions, formed hydrogen bonds with Met280, His89, and His259 residues and also interacted with Phe292, His61, Phe90, Glu256, His244, Asn260, Phe264, and Gly281 via van der Waals forces. The molecular dynamics simulation results also demonstrated that the addition of hesperetin reduced the stability and hydrophobicity of PPO and increased PPO's structural denseness. Thus, the inhibition of hesperetin on PPO may be because hesperetin bound near the active center of PPO, interacted with the surrounding residues, occupied the binding site for substrate, and induced the changes in PPO's secondary structure, thus inhibiting the catalytic activity of PPO. This study may provide novel views for the inhibition of hesperetin on PPO and theoretical guidance for developing flavonoids as new and efficient PPO inhibitors.

Investigations on the binding properties of hydroxylated polybrominated diphenyl ethers with lysozyme using the multispectral techniques and molecular modeling

As a kind of phenolic chemical with endocrine disrupting potency, hydroxylated polybrominated diphenyl ethers (OH-PBDEs) cause a latent threat to human health from their residue in the environment. Their binding efficiency with lysozyme (LYSO) was studied by molecular simulation combined with fluorescence, UV-vis absorption and circular dichroism (CD), so as to assess their toxicity at the molecular level. Molecular docking data indicate that van der Waals force is the principal interaction force between OH-PBDEs and LYSO. The binding site for 5'-OH-BDE-25 in LYSO is ascertained as the active site, which interaction with the TRP63 and TRP108 residues of LYSO to take shape a strong face-to-face stacked rank (F-shaped). Both 4'-OH-BDE-99 and 3'-OH-BDE-154 display a certain degree of deviation from the active site. Nevertheless, their F-shaped interaction with TRP63 conduce to bind LYSO and stabilize the docking conformation. Combined with dynamics simulation and spectral analysis, the secondary structure of LYSO can be induced by the three kinds of OH-PBDEs. CD spectrum shows that the combination of LYSO and OH-PBDEs will make α- Helix content increased. The combination of OH-PBDEs and LYSO touch upon a static quenching mechanism as a result of steady state fluorescence. The energy decomposition analysis exhibited that LYSO-OH-PBDEs binding site was stable by van der Waals and hydrophobic interaction. As enzyme activity experiments demonstrate that OH-PBDEs can inhibit the activity of LYSO, which is helpful to clarify the molecular toxicity mechanism of OH-PBDEs.

Study on the stereoselective binding of cytosine nucleoside enantiomers to human serum albumin

Nucleoside drugs are known for their remarkable anticancer and antiviral properties. The development of nucleoside drugs has attracted much attention and generated a great deal of research interest. β-L-cytidine and β-D-cytidine are a pair of cytosine nucleoside enantiomers. In this work, the interactions between cytosine nucleoside enantiomers and human serum albumin were studied by ultraviolet-visible spectra, fluorescence spectrum and circular dichroism spectrum under simulated human physiological environment. The data of fluorescence spectra were corrected for the inner-filter effect to improve accuracy. Stern-Volmer quenching constants and binding constants in addition to thermodynamic parameters have been analyzed, which established that complexes formation have taken place via static quenching mechanism, and that hydrophobic force involved in these interactions. CD spectrum revealed that on addition of cytosine nucleoside enantiomers, the α-helix% of HSA increased slightly. What's more, molecular modeling method indicated that cytosine nucleoside enantiomers prefer binding at the IIIA site of HSA.

Binding mechanisms of half-sandwich Rh(III) and Ru(II) arene complexes on human serum albumin: a comparative study

Abstract

Various half-sandwich ruthenium(II) arene complexes and rhodium(III) arene complexes have been intensively investigated due to their prominent anticancer activity. The interaction of the organometallic complexes of Ru(η⁶-p-cymene) and Rh(η⁵-C₅Me₅) with human serum albumin (HSA) was studied in detail by a combination of various methods such as ultrafiltration, capillary electrophoresis, ¹H NMR spectroscopy, fluorometry and UV–visible spectrophotometry in the presence of 100 mM chloride ions. Binding characteristics of the organometallic ions and their complexes with deferiprone, 2-picolinic acid, maltol, 6-methyl-2-picolinic acid and 2-quinaldic acid were evaluated. Kinetic aspects and reversibility of the albumin binding are also discussed. The effect of low-molecular-mass blood components on the protein binding was studied in addition to the interaction of organorhodium complexes with cell culture medium components. The organometallic ions were found to bind to HSA to a high extent via a coordination bond. Release of the bound metal ions was kinetically hindered and could not be induced by the denaturation of the protein. Binding of the Ru(η⁶-p-cymene) triaqua cation was much slower (ca. 24 h) compared to the rhodium congener (few min), while their complexes interacted with the protein relatively fast (1–2 h). The studied complexes were bound to HSA coordinatively. The highly stable and kinetically inert 2-picolinate Ru(η⁶-p-cymene) complex bound in an associative manner preserving its original entity, while lower stability complexes decomposed partly or completely upon binding to HSA. Fast, non-specific and high-affinity binding of the complexes on HSA highlights their coordinative interaction with various types of proteins possibly decreasing effective drug concentration.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s00775-019-01683-0) contains supplementary material, which is available to authorized users.

The progresses in curcuminoids-based metal complexes: especially in cancer therapy

Curcuminoids (CURs), a series of derivatives in turmeric (Curcuma longa), are commonly discovered to control the deterioration of cancers. However, the physiochemical properties and the original side effects of many CURs complexes put barriers in their medical applications. To address them, the investigation of metal-based complexes with CURs is in progress. The complexes were summarized according to articles in recent years. The results showed that the complexes improved the physicochemical properties or therapeutic performances compared with pure CURs. Further, it is possible for the novel complexes to be applied in chemical detecting, paramagnetic-luminescent and bio-imaging fields. Therefore, the formation of the metal-based CURs complexes (MBCCs) is beneficial for the development of CURs especially in medical fields.

Similarities and differences in d6 low-spin ruthenium, rhodium and iridium half-sandwich complexes: synthesis, structure, cytotoxicity and interaction with biological targets

In this paper, we discussed the similarities and differences in d⁶ low-spin half-sandwich ruthenium, rhodium and iridium complexes containing 2,2′-biimidazole (H₂biim). Three new complexes, {[RuCl(H₂biim)(η⁶-p-cymene)]PF₆}₂·H₂O (1), [(η⁵-Cp)RhCl(H₂biim)]PF₆ (2), and [(η⁵-Cp)IrCl(H₂biim)]PF₆ (3), were fully characterized by CHN, X-ray diffraction analysis, UV–Vis, FTIR, and ¹H, ¹³C and ¹⁵N NMR spectroscopies. The complexes exhibit a typical pseudooctahedral piano-stool geometry, in which the aromatic arene ring (p-cymene or Cp) forms the seat, while the bidentate 2,2′-biimidazole and chloride ion form the three legs of the piano stool. Moreover, the cytotoxic activities of the compounds were examined in the LoVo, HL-60, MV-4-11, MCF-7 human cancer cell lines and BALB/3T3 normal mouse fibroblasts. Notably, the investigated complexes showed no cytotoxic effects towards the normal BALB/3T3 cell line compared to cisplatin, which has an IC₅₀ value of 2.20 µg. Importantly, 1 displayed the highest activity against HL-60 (IC₅₀ 4.35 µg). To predict a binding mode, we explored the potential interactions of the metal complexes with CT-DNA and protein using UV absorption and circular dichroism. The obtained data suggest that the complexes could interact with CT-DNA via an outside binding mode. Moreover, binding of the complexes with the GSH via UV–Vis and ESI mass spectra was determined. Comparative studies have shown that the rhodium complex (2) is the most GSH reactive, which is probably responsible for its deactivation towards LoVo and MCF-7 tumour cells. The influence of the metal ion on the biological activity of isostructural Rh(III) and Ir(III) complexes was an important goal of the presented investigation.

Anti-Proliferative and Anti-Migration Activity of Arene–Ruthenium(II) Complexes with Azole Therapeutic Agents

The efficacy of organoruthenium complexes containing ergosterol biosynthesis inhibitors (CTZ: clotrimazole, KTZ: ketoconazole and FCZ: fluconazole) against tumor cells, and their interaction with important macro-biomolecules such as human serum albumin and DNA have been investigated here. Our experimental results indicated that these ruthenium(II) complexes present spontaneous electrostatic interactions with albumin, and act as minor groove binders with the DNA. The ability of these Ru(II)–azole complexes to inhibit the proliferation of selected human tumor and non-tumor cell lines was determined by MTT assay. Complexes [RuCl(CTZ)(η6-p-cymene)(PPh3)]PF6 (3) and [RuCl(KTZ)(η6-p-cymene)(PPh3)]PF6 (4) were shown to be between 3- and 40-fold more cytotoxic than the free ligands and the positive control cisplatin. Complex 3 was selected to continue studies on the triple negative breast tumor cell line MDA-MB-231, inducing morphological changes, loss of adhesion, inhibition of colony formation, and migration through Boyden chambers, cell cycle arrest in the sub-G1 phase, and a mechanism of cell death by apoptosis. All these interesting results show the potential of this class of organometallic Ru(II) complexes as an antiproliferative agent.

Human serum albumin binding and synergistic effects of gefitinib in combination with regorafenib on colorectal cancer cell lines

This study aimed to evaluate the combination effect of gefitinib (GEF) and regorafenib (REG) against HCT116, CT26 and SW948 colorectal cancer cell lines. Results showed synergistic effects on HCT116 and CT26 cells, while the additive effect was observed on SW948 cells. Combination of GEF and REG induced sub-G1 peak as the apoptotic population on HCT116 cells, through flow cytometry histogram. Downregulation of AKT1 and TGFB2 and upregulation of CASP3 were observed in the combination of GEF and REG in HCT116 cells, using quantitative real-time PCR analysis. HSA binding properties exhibit that the first drug increased binding affinity between the second drug and HSA; as a result, HSA could transport both drugs. Thus, we hope this study creates a promising strategy to treat colorectal cancer.

In vitro interaction investigation between three Ru(ii) arene complexes and human serum albumin: structural influences

In vitro interactions between three Ru(ii) arene complexes and human serum albumin were systematically investigated by multi-spectroscopic techniques.