In vitro DNA binding studies of Aspartame, an artificial sweetener

Intercalation of anticancer drug Palbociclib with calf-thymus DNA: new insights from molecular spectroscopic, molecular dynamic simulations and cleavage studies

The interaction between the anti-cancer drug Palbociclib (PAL) and calf-thymus DNA (CT-DNA) was investigated using various biophysical techniques in a physiological buffer (pH 7.4). It was found that PAL intercalated into the base pairs of CT-DNA as evidenced from the results of UV-Vis, fluorescence, circular dichroism (CD), competitive binding assay with ethidium bromide (EB) and Hoechst 33258, KI quenching study, the effect of denaturing agent and viscosity measurements. The magnitude of binding constants (106 M-1) at different temperatures suggested strong binding between PAL and CT-DNA during complexation. The observed ΔHo > 0 and ΔSo > 0 indicated that the binding process is primarily driven by hydrophobic interactions. Molecular docking studies indicated partial intercalation of pyridopyrimidine ring between the base pairs of DNA. Free energy surface (FES) analysis derived from metadynamics simulation studies revealed the PAL-induced cleavage of DNA, which was confirmed by gel electrophoresis experiments.Communicated by Ramaswamy H. Sarma.

Interaction studies of water-soluble Zn(II) complex with calf thymus DNA using biophysical and molecular docking methods"

The binding between a fluorescent water-soluble Zn(II) complex of {2-[N-(2-hydroxyethylammonioethyl) imino methyl] phenol} and calf thymus DNA (ct-DNA) was investigated using spectroscopic techniques. The complex was prepared and identified by FT-IR, and 1H NMR spectroscopies. The significant changes in the absorption and the circular dichroism spectra of ct-DNA in the presence of the Zn(II) complex implied the interaction between the Zn(II) complex and ct-DNA. Upon addition of ct-DNA, the fluorescence emission intensity of the Zn(II) complex was increased and indicated the interaction between the Zn(II) complex and ct-DNA was occurred. The binding constant values (Kb) resulted from fluorescence spectra clearly showed the Zn(II) complex affinity to ct-DNA. The fluorescence studies also approved the static enhancement mechanism in the Zn(II) complex-DNA complexation process. The thermodynamic profile exhibited the exothermic and spontaneous formation of ct-DNA-Zn(II) complex system via hydrogen bonds and van der Waals forces. The competitive fluorescence investigation by methylene blue (MB), and Hoechst 33258 demonstrated that the Zn(II) complex could replace the DNA-bound Hoechst and bind to the minor groove binding site in ct-DNA. The viscosity changes were negligible, representing the Zn(II) complex binding to DNA via the groove binding mode. Molecular docking simulation affirmed that the Zn(II) complex is located in the minor groove of ct-DNA near the DG12, DA17, DA18, and DG16 nucleobases.

Aspartame Safety as a Food Sweetener and Related Health Hazards

Aspartame is the methyl-ester of the aspartate-phenylalanine dipeptide. Over time, it has become a very popular artificial sweetener. However, since its approval by the main food safety agencies, several concerns have been raised related to neuropsychiatric effects and neurotoxicity due to its ability to activate glutamate receptors, as well as carcinogenic risks due to the increased production of reactive oxygen species. Within this review, we critically evaluate reports concerning the safety of aspartame. Some studies evidenced subtle mood and behavioral changes upon daily high-dose intake below the admitted limit. Epidemiology studies also evidenced associations between daily aspartame intake and a higher predisposition for malignant diseases, like non-Hodgkin lymphomas and multiple myelomas, particularly in males, but an association by chance still could not be excluded. While the debate over the carcinogenic risk of aspartame is ongoing, it is clear that its use may pose some dangers in peculiar cases, such as patients with seizures or other neurological diseases; it should be totally forbidden for patients with phenylketonuria, and reduced doses or complete avoidance are advisable during pregnancy. It would be also highly desirable for every product containing aspartame to clearly indicate on the label the exact amount of the substance and some risk warnings.

Binding studies of sertraline hydrochloride with CT-DNA using experimental and computational techniques

Sertraline Hydrochloride (STH) is an antidepressant drug that belongs to the selective serotonin reuptake inhibitor family (SSRIs), which inhibits serotonin uptake in presynaptic nerve fibers. The use of these medications without a legitimate prescription might result in adverse effects, and in rare circumstances, death. The interaction mechanism and binding mode of STH with duplex DNA were extensively investigated using spectroscopic and modeling techniques at different temperatures. The hypochromic shift of the absorption spectra of STH on binding with CT-DNA indicated groove binding. Fluorescence spectroscopic studies showed that CT-DNA quenches the fluorescence intensity of STH through a static quenching mechanism. The thermodynamic parameters indicated that the complex formation was spontaneous, and enthalpy driven. The competitive displacement binding study revealed that STH displaced DAPI from the minor groove of DNA. Molecular docking and molecular dynamics simulations also revealed that the complex was stable over 150 ns and that STH preferred the minor groove of DNA. The binding energy of the stable conformations were evaluated through MM/PBSA methods. A comparison of the bound poses at different timescales showed minor changes in STH structure upon DNA binding. Furthermore, a structural analysis of CT-DNA indicated that STH induced changes in the sugar-phosphate backbone had an impact on the minor groove's width which are in agreement with the CD spectroscopic results. This study provides a better understanding of STH binding with duplex DNA.

Structural aspects of formetanate hydrochloride binding with human serum albumin using spectroscopic and molecular modeling techniques

Formetanate Hydrochloride (FMT), a highly potent chemical, acts as an insecticide, acaricide, and miticide to protect various fruits and vegetables. The widespread use elevates concern about its presence in the ecosystem, impact upon human health via interaction with biological receptors. Spectroscopic and molecular modeling techniques at different temperatures were used to investigate the binding of FMT with Human serum albumin (HSA) at the molecular level. The experimental and computational results have provided the binding affinity, binding mode, conformational flexibility, and thermodynamic profile of FMT-HSA complex. The FMT binding appears to be spontaneous, and entropy driven. Overall binding affinity of FMT falls within -7.29 to -4.67 Kcal M-1. FMT binds in domain I, subdomain IA of HSA and is stabilized by hydrophobic interactions. Molecular dynamics simulations of the FMT-HSA complex over 100 ns at 288 K, 298 K and 308 K indicated that FMT showed minor adjustments in conformation and placement within the binding site. While, MM/PBSA analysis of the complex provided individual contributions of energy terms. Quantum mechanical (QM) calculations were used to calculate absolute energy values of different poses of FMT which in turn showed minor variations in energy suggesting slight conformational variation in the bound form. The computational results are in agreement with experimental findings.

Toxicological and Nutraceutical Screening Assays of Some Artificial Sweeteners

Artificial sweeteners are food additives worldwide used instead of fructose or glucose in many diet beverages. Furthermore, diet beverages intake has been increasing every year. Thus, some food agencies should regulate it based on toxicological studies. Debates and controversial results are demonstrated, and authority can revise its decision on the basis of new data reporting toxicological effects since cyclamate has been forbidden in some countries. Therefore, the aim of this study was to report new data about the toxicity of acesulfame-k, aspartame, and cyclamate, which are useful for authority agencies, determining the toxic potential and nutraceutical capabilities of these compounds. The toxicity, antitoxicity, genotoxicity, antigenotoxicity, and life expectancy assays were carried out in Drosophila as an in vivo model. In addition, in vitro HL-60 line cell was used to evaluate the chemopreventive activity determining the cytotoxic effect and the capability of producing DNA damage due to internucleosomal fragmentation or DNA strand breaks. Furthermore, the methylated status of these cancer cells treated with the tested compounds was assayed as a cancer therapy. Our results demonstrated that all tested compounds were neither toxic nor genotoxic, whereas these compounds resulted in antigenotoxic and cytotoxic substances, except for cyclamate. Aspartame showed antitoxic effects in Drosophila. All tested compounds decreased the quality of life of this in vivo organism model. Acesulfame-k, aspartame, and cyclamate induced DNA damage in the HL-60 cell line in the comet assay, and acesulfame-k generally increased the methylation status. In conclusion, all tested artificial sweeteners were safe compounds at assayed concentrations since toxicity and genotoxicity were not significantly induced in flies. Moreover, Aspartame and Cyclamate showed protective activity against a genotoxin in Drosophila Regarding nutraceutical potential, acesulfame-k and aspartame could be demonstrated to be chemopreventive due to the cytotoxicity activity shown by these compounds. According to DNA fragmentation and comet assays, a necrotic way could be the main mechanism of death cells induced by acesulfame-k and aspartame. Finally, Acesulfame-K hypermethylated repetitive elements, which are hypomethylated in cancer cells resulting in a benefit to humans.

Multi-Spectroscopic, thermodynamic and molecular dynamic simulation studies for investigation of interaction of dapagliflozin with bovine serum albumin

Dapagliflozin (DAPA) is a selective sodium-glucose cotransporter-2 inhibitor that reduces renal glucose reabsorption. The drug has recently become a crucial milestone in the management of diabetes and heart failure. In this study, the interaction of DAPA with bovine serum albumin (BSA) was investigated for the first time using various fluorescence spectroscopic techniques, UV-absorption spectroscopy, molecular docking, and molecular dynamic (MD) simulation. The fluorescence spectroscopic titration study performed at different temperatures showed that DAPA quenched the fluorescence of BSA through a combination of dynamic and static mechanisms, which was confirmed by UV absorption, fluorescence-resonance energy transfer measurements, and MD simulation. The binding thermodynamic parameters demonstrated that the binding stoichiometry between BSA and DAPA was 1:1. Competitive binding experiments using site-specific markers as well as molecular docking studies showed that DAPA binds to site I on BSA. The positive values of enthalpy change (ΔH) and entropy change (ΔS) revealed that hydrophobic forces played a predominant role in the binding of DAPA to BSA, whereas the negative value of Gibbs free energy change (ΔG) indicated the spontaneity of the interaction. Moreover, the synchronous fluorescence spectroscopy has shown that DAPA binding to the protein molecule occurs in the vicinity of the tryptophan residue. These findings were confirmed by the molecular docking and MD simulation studies.

Interaction of Carrier Protein with Potential Metallic Drug Candidate N-Glycoside 'GATPT': Validation by Multi-Spectroscopic and Molecular Docking Approaches

Lysozyme is often used as a model protein to study interaction with drug molecules and to understand biological processes which help in illuminating the therapeutic effectiveness of the drug. In the present work, in vitro interaction studies of 1-{(2-hydroxyethyl)amino}-2-amino-1,2-dideoxy-d-glucose triphenyl tin (IV) (GATPT) complex with lysozyme were carried out by employing various biophysical methods such as absorption, fluorescence, and circular dichroism (CD) spectroscopies. The experimental results revealed efficient binding affinity of GATPT with lysozyme with intrinsic binding (Kb) and binding constant (K) values in the order of 105 M-1. The number of binding sites and thermodynamic parameters ΔG, ΔH, and ΔS at four different temperatures were also calculated and the interaction of GATPT with lysozyme was found to be enthalpy and entropy driven. The CD spectra revealed alterations in the population of α-helical content within the secondary structure of lysozyme in presence of GATPT complex. The morphological analysis of the complex with lysozyme and lysozyme-DNA condensates was carried out by employing confocal and SEM studies. Furthermore, the molecular docking studies confirmed the interaction of GATPT within the larger hydrophobic pocket of the lysozyme via several non-covalent interactions.

Inhibitory mechanism of two homoisoflavonoids from Ophiopogon japonicus on tyrosinase activity: insight from spectroscopic analysis and molecular docking

The inhibition mechanism of two homoisoflavonoids from Ophiopogon japonicus including methylophiopogonanone A (MO-A) and methylophiopogonanone B (MO-B) on tyrosinase (Tyr) was studied by multiple spectroscopic techniques and molecular docking. The results showed that the two homoisoflavonoids both inhibited Tyr activity via a reversible mixed-inhibition, with a half inhibitory concentration (IC50) of (10.87 ± 0.25) × 10-5 and (18.76 ± 0.14) × 10-5 mol L-1, respectively. The fluorescence quenching and secondary structure change of Tyr caused by MO-A and B are mainly driven by hydrophobic interaction and hydrogen bonding. Molecular docking analysis indicated that phenylmalandioxin in MO-A and methoxy in MO-B could coordinate with a Cu ion in the active center of Tyr, and interacted with amino acid Glu322 to form hydrogen bonding, occupying the catalytic center to block the entry of the substrate and consequently inhibit Tyr activity. This study may provide new perspectives on the inhibition mechanism of MO-A and MO-B on Tyr and serve a scientific basis for screening effective Tyr inhibitors.

Spectroscopic studies on the interaction of aspartame with human serum albumin

In this work the binding of artificial sweetener aspartame with human serum albumin (HSA) was studied at physiological pH. Binding studies of aspartame (APM) with HSA are useful to understand APM -HSA interaction, mechanism and providing guidance for the application and design of new and more efficient artificial sweeteners. The interaction was investigated by spectrophotometric, spectrofluorometric competition experiment and circular dichroism (CD) techniques. The results indicated that the binding of APM to HSA caused fluorescence quenching of HSA through static quenching mechanism with binding constant 1.42 × 10⁺⁴ M^-1 at 298 K and the number of binding sites is approximately one. Thermodynamic parameters, enthalpy changes (ΔH) and entropy changes (ΔS) were calculated to be -41.20 kJ mol^-1 and -58.19 J mol^-1 K^-1, respectively, according to van't Hoff equation, which indicated that reaction is enthalpically driven. Quenching of the fluorescence of HSA was found to be a static quenching process. The binding constants and number of binding sites were obtained at three different temperatures (298, 308 and 318 K). Combining above results and those of spectrofluorometric competition experiment and circular dichroism (CD), indicated that APM binds to HSA via Sudlow's site I. Furthermore, the study of molecular docking on HSA binding also indicated that APM can strongly bind to the site I (subdomain IIA) of HSA mainly by hydrophobic interaction and hydrogen bond interactions exist between APM and HSA.

Dietary 5,6,7-Trihydroxy-flavonoid Aglycones and 1-Deoxynojirimycin Synergistically Inhibit the Recombinant Maltase-Glucoamylase Subunit of α-Glucosidase and Lower Postprandial Blood Glucose

1-Deoxynojirimycin (1-DNJ) is the major effective component of mulberry leaves, exhibiting inhibitory activity against α-glucosidase. However, due to the low content of 1-DNJ in mulberry products, its level cannot meet the lowest dose to exhibit its activity. In this study, a combination of dietary 5,6,7-trihydroxy-flavonoid aglycones with 1-DNJ showed synergistic inhibitory activity against maltase of mice α-glucosidase and recombinant C- and N-termini of maltase-glucoamylase (MGAM) and baicalein with 1-DNJ exhibited the strongest synergistic effect. The synergistic effect of the combination was also confirmed by the maltose tolerance test in vivo. Enzyme kinetics, molecular docking, fluorescence spectrum, and circular dichroism spectrometry studies indicated that the major mechanism of the synergism is that baicalein was a positive allosteric inhibitor and bound to the noncompetitive site of MGAM, causing an increase of the binding affinity of 1-DNJ to MGAM. Our results might provide a theoretical basis for the design of dietary supplements containing mulberry products.

Exploring the binding mode of donepezil with calf thymus DNA using spectroscopic and molecular docking methods

Donepezil (DNP) is one of approved drugs to treat Alzheimer's disease (AD). However, the potential effect of DNP on DNA is still unclear. Therefore, the interaction of DNP with calf thymus DNA (DNA) was studied in vitro using spectroscopic and molecular docking methods. Steady-state and transient fluorescence experiments showed that there was a clear binding interaction between DNP and DNA, resulting from DNP fluorescence being quenched using DNA. DNP and DNA have one binding site between them, and the binding constant (K_b ) was 0.78 × 10⁴ L·mol^-1 at 298 K. In this binding process, hydrophobic force was the main interaction force, because enthalpy change (ΔH) and entropy change (ΔS) of DNP-DNA were 67.92 kJ·mol^-1 and 302.96 J·mol^-1 ·K^-1 , respectively. DNP bound to DNA in a groove-binding mode, which was verified using a competition displacement study and other typical spectroscopic methods. Fourier transform infrared (FTIR) spectrum results showed that DNP interacted with guanine (G) and cytosine (C) bases of DNA. The molecular docking results further supported the results of spectroscopic experiments, and suggested that both Pi-Sigma force and Pi-Alkyl force were the major hydrophobic force functioning between DNP and DNA.

Multi-spectroscopic and molecular docking studies on the interaction of neotame with calf thymus DNA

In this paper, we have studied the in vitro binding of neotame (NTM), an artificial sweetener, with native calf thymus DNA using different methods including spectrophotometric, spectrofluorometric, competition experiment, circular dichroism (CD), and viscosimetric techniques. From the spectrophotometric studies, the binding constant (K_b) of NTM-DNA was calculated to be 2 × 10³ M^-1. The quenching of the intrinsic fluorescence of NTM in the presence of DNA at different temperatures was also used to calculate binding constants (K_b) as well as corresponding number of binding sites (n). Moreover, the obtained results indicated that the quenching mechanism involves static quenching. By comparing the competitive fluorimetric studies with Hoechst 33258, as a known groove probe, and methylene blue, as a known intercalation probe, and iodide quenching experiments it was revealed that NTM strongly binds in the grooves of the DNA helix, which was further confirmed by CD and viscosimetric studies. In addition, a molecular docking method was employed to further investigate the binding interactions between NTM and DNA, and confirm the obtained results.

Interaction studies of sodium cyclamate with DNA revealed by spectroscopy methods

The interaction between sodium cyclamate (SC) and calf thymus DNA in simulated physiological buffer (pH 7.4) using ethidium bromide (EB) as fluorescence probe was investigated by UV-vis spectrometry (UV), fluorescence, resonance light scattering (RLS) and Fourier transform infrared (FT-IR) spectroscopy, along with DNA melting studies and cyclic voltammetric (CV) measurements. The results indicate that SC can not only bind into the minor groove of DNA, but also intercalate into the DNA Base pairs. Based on UV data, the binding constant K and binding sites n of the formed DNA/SC complex were estimated to be 2.83 × 10³ mol/L and 2.0, respectively. Fluorescence results demonstrate that the quenching of DNA/EB induced by SC can mainly be attributed to static procedure. The melting studies and CV analysis further confirm that the interaction mechanism between the SC and DNA is similar to that of DNA intercalator.The results of FT-IR spectra show that a specific interaction mainly exist between SC and adenine and guanine bases of DNA, which resulting in potential damage due to some change in the information structure. The DNA saturation binding value estimated to be 1.67 based on the RLS data also indicated that SC may cause damage of DNA.

Exploring the binding mechanism of saccharin and sodium saccharin to promoter of human p53 gene by theoretical and experimental methods

In the past few decades, extensive discussions have been on the impact of artificial sweeteners on the risk of cancer. The present study aimed to evaluate the interaction of saccharin (SA) and sodium saccharin (SSA) with the promoter of the human p53 gene. The binding ability was assessed using the spectroscopic technique, molecular docking and molecular dynamics (MD) simulation methods. Free energy of binding has been calculated using Molecular Mechanics/Poisson-Boltzmann Surface Area (MM/PBSA) method. Fluorescence spectra of mentioned gene with concentration profiles of SA and SSA were obtained in a physiological condition. A gradual increase without any significant spectral shift in the fluorescence intensity of around 350 nm was evident, indicating the presence of an interaction between both compounds and gene. The docking results showed that both compounds were susceptible to bind to 5'-DG56DG57-3' nucleotide sequence of gene. Furthermore, the MD simulation demonstrated that the binding positions for SA and SSA were 5'-A1T3T4-3' and 5'-G44T45-3' sequences of gene, respectively. The binding of these sweeteners to gene made significant conformational changes to the DNA structure. Hydrogen and hydrophobic interactions are the major forces in complexes stability. Through the groove binding mode, the non-interactive DNA-binding nature of SSA and SA has been demonstrated by the results of spectrofluorometric and molecular modeling. This study could provide valuable insight into the binding mechanism of SA and its salt with p53 gene promoter as macromolecule at the molecular level in atomistic details. This work can contribute to the possibility of the potential hazard of carcinogenicity of this sweetener and to design and apply new and safer artificial sweeteners. AbbreviationsSASaccharinSSASodium SaccharinPp53gpromoter of human p53 geneMDMolecular dynamicsRMSDRoot-mean-square deviationRMSFRoot-mean-square fluctuationRgRadius of GyrationSASASolvent-Accessible Surface AreaADIAcceptable daily intakeMM/PBSAMolecular Mechanics/Poisson-Boltzmann Surface AreaCommunicated by Ramaswamy H. Sarma.

Binding mechanism of five typical sweeteners with bovine serum albumin

In this work, the interactions between bovine serum albumin (BSA) and five sweeteners including aspartame (APM), acesulfame (AK), sucralose (TGS), sodium cyclamate (SC), and rebaudioside-A (REB-A) have been studied by multispectroscopic techniques, and molecular simulation in order to provide much useful information for the application of new and safer artificial sweeteners. Fluorescence quenching assays indicated that the formation of complexes between sweeteners and BSA mainly induced the fluorescence quenching of protein and the binding site number were about 1 indicting that there is one mainly binding site of APM, AK, TGS, SC, or REB-A in domain of BSA with relatively weak interactions. Molecular modeling results indicated that hydrogen bonding interactions were the mainly binding forces of sweeteners with BSA. Circular dichroism spectra indicated that APM and REB-A obviously induced the secondary structure changes of BSA. The presence of APM increased the fraction of α-Helix of BSA from 65.4% to 73.8%, while the presence of REB-A resulted in decreasing the fraction of α-helix of BSA from 65.4% to 51.2%. The melting temperature studies showed that these five sweeteners except REB-A act as stabilizers to increase the thermal stability of BSA during the thermal denaturation process. In addition, AK, TGS, and SC obviously increased the esterase-like activity of BSA, and such loss of activity of BSA induced by APM and REB-A.

Direct evidences for the groove binding of the Clomifene to double stranded DNA

It has been reported that the antiestrogen Tamoxifen induces liver tumors in rats and genotoxic effects in vitro through DNA interaction. So, it can be proposed that its structural analogue, Clomifene, also can bind to DNA. To test this hypothesis, the DNA binding properties of Clomifene have been studied by absorption spectroscopy, fluorescence spectroscopy, cellular uptake, cell viability, cell proliferation and molecular modeling techniques. Evidences are provided that Clomifene could interact with DNA via minor groove interaction mode. The negative ΔG value implied that the interaction occurred between DNA and Clomifene spontaneously. Also, the positive ΔH and positive ΔS values indicated that the binding of Clomifene with DNA is mainly entropy driven and the enthalpy is unfavorable parameter. This also suggests that the hydrophobic interaction plays a major role in the binding with overall binding constant of K=5.645×10⁷M^-1 at 298K. From the results of docking, it can be concluded that Hydrogen bonds is also one of the most important interactions. The increase in entropy of system after binding might be due to the destruction of the DNA structure.

Probing the Characterization of the Interaction of Aflatoxins B1 and G1 with Calf Thymus DNA In Vitro

The binding characterization of aflatoxins with calf thymus DNA (ctDNA) under physiological conditions was investigated. Multispectroscopic techniques, ctDNA melting, viscosity measurements, and molecular docking techniques were employed to elucidate the binding mechanism of the aflatoxins with DNA. The fluorescence results indicated that both aflatoxin B1 (AFB1) and aflatoxin G1 (AFG1) bound to the ctDNA, forming complexes through hydrogen bonding. The binding constants of AFB1 and AFG1 with ctDNA reached up to 10³ L·mol-1 and 10⁴ L·mol-1, respectively, and AFG1 exhibited a higher binding propensity than that of AFB1. Furthermore, both AFB1 and AFG1 bound to the ctDNA through groove binding, as evidenced by the results of the spectroscopic, iodide quenching effect, viscosity, and ctDNA melting measurements. Changes in the circular dichroism signal manifested that both AFB1 and AFG1 induced an increase in the right-handed helicity, but only minimally influenced the base stacking of the DNA. A molecular docking study of the aflatoxin's binding with the DNA revealed a groove binding mode, which was driven mainly by hydrogen bonding. This study of aflatoxin-ctDNA interaction may provide novel insights into the toxicological effect of the mycotoxins.

Inhibitory Mechanism of Apigenin on α-Glucosidase and Synergy Analysis of Flavonoids

Inhibition of α-glucosidase activity may suppress postprandial hyperglycemia. The inhibition kinetic analysis showed that apigenin reversibly inhibited α-glucosidase activity with an IC50 value of (10.5 ± 0.05) × 10(-6) mol L(-1), and the inhibition was in a noncompetitive manner through a monophasic kinetic process. The fluorescence quenching and conformational changes determined by fluorescence and circular dichroism were due to the formation of an α-glucosidase-apigenin complex, and the binding was mainly driven by hydrophobic interactions and hydrogen bonding. The molecular simulation showed that apigenin bound to a site close to the active site of α-glucosidase, which may induce the channel closure to prevent the access of substrate, eventually leading to the inhibition of α-glucosidase. Isobolographic analysis of the interaction between myricetin and apigenin or morin showed that both of them exhibited synergistic effects at low concentrations and tended to exhibit additive or antagonistic interaction at high concentrations.

Membrane Destruction and DNA Binding of Staphylococcus aureus Cells Induced by Carvacrol and Its Combined Effect with a Pulsed Electric Field

Carvacrol (5-isopropyl-2-methylphenol, CAR) is an antibacterial ingredient that occurs naturally in the leaves of the plant Origanum vulgare. The antimicrobial mechanism of CAR against Staphylococcus aureus ATCC 43300 was investigated in the study. Analysis of the membrane fatty acids by gas chromatography-mass spectrometry (GC-MS) showed that exposure to CAR at low concentrations induced a marked increase in the level of unbranched fatty acids (from 34.90 ± 1.77% to 62.37 ± 4.26%). Moreover, CAR at higher levels severely damaged the integrity and morphologies of the S. aureus cell membrane. The DNA-binding properties of CAR were also investigated using fluorescence, circular dichroism, molecular modeling, and atomic-force microscopy. The results showed that CAR bound to DNA via the minor-groove mode, mildly perturbed the DNA secondary structure, and induced DNA molecules to be aggregated. Furthermore, a combination of CAR with a pulsed-electric field was found to exhibit strong synergistic effects on S. aureus.

Impact of aspartame and saccharin on the rat liver: Biochemical, molecular, and histological approach

The current work was undertaken to settle the debate about the toxicity of artificial sweeteners (AS), particularly aspartame and saccharin. Twenty-five, 7-week-old male Wistar albino rats with an average body weight of 101 ± 4.8 g were divided into a control group and four experimental groups (n = 5 rats). The first and second experimental groups received daily doses equivalent to the acceptable daily intake (ADI) of aspartame (250 mg/Kg BW) and four-fold ADI of aspartame (1000 mg/Kg BW). The third and fourth experimental groups received daily doses equivalent to ADI of saccharin (25 mg/Kg BW) and four-fold ADI of saccharin (100 mg/Kg BW). The experimental groups received the corresponding sweetener dissolved in water by oral route for 8 weeks. The activities of enzymes relevant to liver functions and antioxidants were measured in the blood plasma. Histological studies were used for the evaluation of the changes in the hepatic tissues. The gene expression levels of the key oncogene (h-Ras) and the tumor suppressor gene (P27) were also evaluated. In addition to a significant reduction in the body weight, the AS-treated groups displayed elevated enzymes activities, lowered antioxidants values, and histological changes reflecting the hepatotoxic effect of aspartame and saccharin. Moreover, the overexpression of the key oncogene (h-Ras) and the downregulation of the tumor suppressor gene (P27) in all treated rat groups may indicate a potential risk of liver carcinogenesis, particularly on long-term exposure.

Characterization of the interaction between resmethrin and calf thymus DNA in vitro

Resmethrin preferentially binds to the G–C rich region of the ctDNA groove, and the UV-vis spectral matrix is decomposed by MCR-ALS.

Groove binding interaction between daphnetin and calf thymus DNA

The binding characteristics of daphnetin with calf thymus DNA (ctDNA) were investigated by multispectroscopic and chemometric approaches coupled with DNA viscosity measurements, melting studies and molecular docking technique. The expanded UV-vis spectral data matrix was processed by multivariate curve resolution-alternating least-squares method to obtain the concentration profiles of the components (daphnetin, ctDNA and daphnetin-ctDNA complex) to quantitatively monitor the daphnetin-ctDNA interaction. The groove mode of daphnetin binding to ctDNA was concluded by little change in melting temperature, viscosity of ctDNA and iodide quenching effect as well as increase in single-stranded DNA quenching effect. Moreover, the quantitative data for the competitive binding between daphnetin and Hoechst 33258 for ctDNA obtained by resolving the three-way synchronous fluorescence spectra data using parallel factor analysis modeling further supported the groove binding. The molecular docking visualized the results of the Fourier transform infrared analysis that the adenine and thymine bases in the minor groove of ctDNA were the main binding sites for daphnetin, and the circular dichroism spectra showed that the groove binding of daphnetin to ctDNA led to the conformational change in ctDNA from B-form to A-form. This study revealed the interaction mechanism of daphnetin with ctDNA.

Intercalation binding of food antioxidant butylated hydroxyanisole to calf thymus DNA

The binding properties of food antioxidant butylated hydroxyanisole (BHA) associated with calf thymus DNA (ctDNA) in physiological buffer (pH 7.4) were investigated. Experimental results based on fluorescence, UV-vis absorption, circular dichroism (CD), viscosity measurements and autodocking techniques confirmed the intercalation binding between BHA and ctDNA. The changes in Fourier transform infrared spectra of ctDNA induced by BHA suggested that BHA was more prone to bind to G-C rich region of ctDNA, which was further ascertained with the molecular docking studies. Analysis of the CD spectra indicated that this binding interaction led to a transformation from B-like DNA structure toward A-like conformation. The complexation of BHA with ctDNA was driven mainly by hydrogen bonds and hydrophobic forces. The binding constants of the BHA-ctDNA complex were calculated to be 2.03 × 10(4), 1.92 × 10(4) and 1.59 × 10(4)L mol(-1) at 298, 304 and 310 K, respectively. Gel electrophoresis results suggested that intercalated BHA molecules did not significantly affect plasmid DNA. Moreover, the concentration profiles and the spectra for the three reaction components (BHA, ctDNA, and BHA-ctDNA complex) of the system by resolving the augmented UV-vis spectral data matrix with the use of multivariate curve resolution-alternating least squares approach provided quantitative data to estimate the progress of BHA-ctDNA interaction. This study is expected to provide new insights into the mechanism of interaction between BHA and ctDNA.

A review of the genotoxic and carcinogenic effects of aspartame: does it safe or not?

The objective of this article is to review genotoxicologic and carcinogenic profile of the artificial sweetener aspartame. Aspartame is a synthetic dipeptide, nearly 180-200 times sweeter than sucrose. It is the most widely used artificial sweetener especially in carbonated and powdered soft drinks, beverages, drugs and hygiene products. There is a discussion ongoing for many years whether aspartame posses genotoxic and carcinogenic risk for humans. This question led to many studies to specify the adverse effects of aspartame. Therefore, we aimed to review the oldest to latest works published in major indices to gather information within this article. With respect to published data, genotoxicity and carcinogenicity of aspartame is still confusing. So, consumers should be aware of the potential side effects of aspartame before they consume it.

Binding characteristics of sodium saccharin with calf thymus DNA in vitro

The binding characteristics of sodium saccharin (SSA), an artificial sweetener, with calf thymus DNA (ctDNA) were investigated by multispectroscopic techniques, chemometrics, and molecular simulation. A combined fluorescence and UV-vis spectroscopic data matrix was resolved by the multivariate curve resolution-alternating least-squares (MCR-ALS) chemometrics algorithm. The MCR-ALS analysis extracted simultaneously the concentration profiles and spectra for the three components (SSA, ctDNA, and SSA-ctDNA complex) to quantitatively monitor the SSA-ctDNA interaction, which is difficult to perform by conventional spectroscopic approach. The binding mode of SSA to ctDNA was principally through groove binding as revealed by ctDNA melting temperature studies, viscosity measurements, and iodide and salt quenching effects. Analysis of the Fourier transform infrared and circular dichroism spectra as well as molecular docking indicated that SSA preferentially bound to the guanine base of ctDNA and led to a transformation from B-like DNA structure to A-like conformation. Moreover, gel electrophoresis results suggested that SSA did not induce any significant cleavage in plasmid DNA.

Interaction of a copper (II) complex containing an artificial sweetener (aspartame) with calf thymus DNA

A copper (II) complex containing aspartame (APM) as ligand, Cu(APM)2Cl2⋅2H2O, was synthesized and characterized. In vitro binding interaction of this complex with native calf thymus DNA (CT-DNA) was studied at physiological pH. The interaction was studied using different methods: spectrophotometric, spectrofluorometric, competition experiment, circular dichroism (CD) and viscosimetric techniques. Hyperchromicity was observed in UV absorption band of Cu(APM)2Cl2⋅2H2O. A strong fluorescence quenching reaction of DNA to Cu(APM)2Cl2⋅2H2O was observed and the binding constants (Kf) and corresponding numbers of binding sites (n) were calculated at different temperatures. Thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were calculated to be+89.3 kJ mol(-1) and+379.3 J mol(-1) K(-1) according to Van't Hoff equation which indicated that reaction is predominantly entropically driven. Experimental results from spectroscopic methods were comparable and further supported by viscosity measurements. We suggest that Cu(APM)2Cl2⋅2H2O interacts with calf thymus DNA via a groove interaction mode with an intrinsic binding constant of 8×10+4 M(-1). Binding of this copper complex to DNA was found to be stronger compared to aspartame which was studied recently.