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In this work, we have measured, by means of optical tweezers, forces acting on depletion-induced DNA condensates due to the presence of the DNA-like charged protein bovine serum albumin (BSA). The stretching and unfolding measurements performed on the semi-flexible DNA chain reveal (1) the softening of the uncondensed DNA contour length and (2) a mechanical behavior strikingly different from those previously observed: the force-extension curves of BSA-induced DNA condensates lack the "saw-tooth" pattern and applied external forces as high as ≈80 pN are unable to fully unfold the condensed DNA contour length. This last mechanical experimental finding is in agreement with force-induced "unpacking" detailed Langevin dynamics simulations recently performed by Cortini et al. on model rod-like shaped condensates. Furthermore, a simple thermodynamics analysis of the unfolding process has enabled us to estimate the free energy involved in the DNA condensation: the estimated depletion-induced interactions vary linearly with both the condensed DNA contour length and the BSA concentration, in agreement with the analytical and numerical analysis performed on model DNA condensates. We hope that future additional experiments can decide whether the rod-like morphology is the actual one we are dealing with (e.g. pulling experiments coupled with super-resolution fluorescence microscopy). [ABSTRACT FROM AUTHOR]

We use optical tweezers to perform stretching experiments on DNA molecules when interacting with the drugs daunomycin and ethidium bromide, which intercalate the DNA molecule. Our results show that the persistence length of the DNA-drug complexes increases strongly as the drug concentration increases up to some critical value. Above this critical value, the persistence length decreases abruptly and remains approximately constant for larger drug concentrations, at least in the concentration range used in our experiments. Measured intercalators critical concentrations for the persistence length transition coincide with the reported values for the helix-coil transition of DNA-drug complexes obtained from sedimentation experiments. The contour length of the molecules increases monotonically and saturates as the drug concentration increases. The neighbor exclusion model fits to our results for the total drug concentration as a function of the relative increase of the contour length. [ABSTRACT FROM AUTHOR]

By attaching one end of a single λ-DNA molecule to a microscope coverslip and the other end to a polystyrene microsphere trapped by an optical tweezers, we can study the entropic elasticity of the λ-DNA by measuring force versus extension as we stretch the molecule. This powerful method permits single molecule studies. We are particulary interested in the effects of the photosensitive drug psoralen on the elasticity of the DNA molecule. We have illuminated the sample with different light sources, studying how the different wavelengths affect the psoralen-DNA linkage. To do this, we measure the persistence length of individual DNA-psoralen complexes. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Inthis work we have characterized the effects of the intercalatorethidium bromide (EtBr) on the DNA condensation process by using forcespectroscopy and gel electrophoresis. We have tested two condensingagents: spermine (spm4+), a tetravalent cationic aminewhich promotes cation-induced DNA condensation, and poly(ethyleneglycol) (PEG), a neutral polymer which promotes DNA ψ-condensation.Two different types of experiments were performed. In the first type,bare DNA molecules disperse in solution are first treated with EtBrfor intercalation, and then the condensing agent is added to the samplewith the purpose of verifying the effects of the intercalator in hinderingDNA condensation. In the second experiment type, the bare DNA moleculesare first condensed, and then the intercalator is added to the samplein order to verify its influence on the previously condensed DNA.The results obtained with the two different experimental techniquesused agree very well, indicating that previously intercalated EtBrcan hinder both cation-induced and ψ-condensation, being moreefficient in the first case. On the other hand, EtBr has little effecton the previously formed cation-induced condensates, but is efficientin unfolding the ψ-condensates. [ABSTRACT FROM AUTHOR]

Esophageal motor abnormalities are frequently found in patients with gastroesophageal reflux disease. The role of bile in reflux-induced dysmotility is still elusive. Furthermore, it is questionable weather mucosal or muscular stimulation leads to motor dysfunction. The aims of this study were to analyze (i) the effect of bile in the amplitude of esophageal contractions; and (ii) the effect of mucosal versus muscular stimulation. Eighteen guinea pig esophagi were isolated, and its contractility assessed with force transducers. Three groups were studied. In group A ( n= 6), the entire esophagus was incubated in 100 µmL ursodeoxycholic acid for 1 hour; in group B ( n= 6) the mucosal layer was removed and the muscular layer incubated in 100 µmL ursodeoxycholic acid for 1 hour; and in group C ( n= 6) (control group) the entire esophagus was incubated in saline solution. In all groups, five sequential contractions induced by 40 mm KCl spaced by 5 minutes were measured before and after incubation. Contractions amplitudes before incubation were 1.319 g, 0.306 g, and 1.795 g, for groups A, B, and C, respectively. There were no differences between groups A and C ( P= 0.633), but there were differences between groups A and B ( P= 0.039), and B and C ( P= 0.048). After incubation amplitude of contraction were 0.709 g, 0.278 g, and 1.353 g for groups A, B, and C, respectively. Only group A showed difference when pre and post-stimulation amplitudes were compared ( P= 0.030). Our results show that (i) bile exposure decreases esophageal contraction amplitude; and (ii) the esophageal mucosa seems to play an important role in esophageal motility. [ABSTRACT FROM AUTHOR]

A theoretical treatment of optical tweezers is presented at a level suitable for undergraduates. We explore the Rayleigh and the geometrical optics regimes with an emphasis on the latter. We discuss a model for the geometrical optics regime, including spherical aberration effects, and show that the model can easily be implemented numerically. A comparison of the model with experimental data yields excellent agreement between theory and experiment. We also briefly discuss a theory of optical tweezers valid for microspheres of any size. [ABSTRACT FROM AUTHOR]

We discuss measurements of the laser power at the focus of high numerical aperture objectives used in optical microscopy and optical tweezers. For a given power, the focused incident laser beam heats a small mercury bead that jumps when it reaches the boiling temperature of water, the medium used in the experiments. From the size of the mercury beads, the heat conductivities of water and glass-slide, and the absorption coefficient of mercury for the laser wavelength used, the incident power can be obtained using the solution of the associated heat problem. This problem is mapped onto the problem of a charged conducting sphere embedded in a semi-infinite medium of dielectric constant ϵ1, separated from another semi-infinite medium of dielectric constant ϵ2. [ABSTRACT FROM AUTHOR]

The authors measure the persistence and contour lengths of DNA-psoralen complexes, as a function of psoralen concentration, for intercalated and crosslinked complexes. In both cases, the persistence length monotonically increases until a certain critical concentration is reached, above which it abruptly decreases and remains approximately constant. The contour length of the complexes exhibits no such discontinuous behavior. By fitting the relative increase of the contour length to the neighbor exclusion model, we obtain the exclusion number and the intrinsic intercalating constant of the interaction. Ab initio calculations are employed in order to provide an atomistic picture of these experimental findings. [ABSTRACT FROM AUTHOR]

Plants not only respond to herbivorous damage but adjust their defense system after egg deposition by pest insects. Thereby, parasitoids use oviposition-induced plant volatiles to locate their hosts. We investigated the olfactory behavioral responses of Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) to volatile blends emitted by maize (Zea mays L.) with singular and stacked events after oviposition by Spodoptera frugiperda Smith, 1797 (Hymenoptera: Trichogrammatidae) moths. Additionally, we examined possible variations in gene expression and on oviposition-induced volatiles. We used a Y-tube olfactometer to test for the wasp responses to volatiles released by maize plants oviposited by S. frugiperda and not-oviposited plants. Using the real-time PCR technique (qRT-PCR), we analyzed the expression of lipoxygenase and three terpene synthases genes, which are enzymes involved in the synthesis of volatile compounds that attract parasitoids of S. frugiperda. Olfactometer tests showed that T. pretiosum is strongly attracted by volatiles from transgenic maize emitted by S. frugiperda oviposition (VTPRO 3, more than 75% individuals were attracted). The relative expression of genes TPS10, LOX e STC was higher in transgenic hybrids than in the conventional (isogenic line) hybrids. The GC-MS analysis revealed that some volatile compounds are released exclusively by transgenic maize. This study provides evidence that transgenic hybrids enhanced chemical cues under oviposition-induction and helped to increase T. pretiosum efficiency in S. frugiperda control. This finding shows that among the evaluated hybrids, genetically modified hybrids can improve the biological control programs, since they potentialize the egg parasitoid foraging, integrating pest management. [ABSTRACT FROM AUTHOR]

In the present work we have gone a step forward in the understanding of the DNA-cisplatin interaction, investigating the role of the ionic strength on the complexes formation. To achieve this task, we use optical tweezers to perform force spectroscopy on the DNA-cisplatin complexes, determining their mechanical parameters as a function of the drug concentration in the sample for three different buffers. From such measurements, we determine the binding parameters and study their behavior as a function of the ionic strength. The equilibrium binding constant decreases with the counterion concentration ([Na]) and can be used to estimate the effective net charge of cisplatin in solution. The cooperativity degree of the binding reaction, on the other hand, increases with the ionic strength, as a result of the different conformational changes induced by the drug on the double-helix when binding under different buffer conditions. Such results can be used to modulate the drug binding to DNA, by appropriately setting the ionic strength of the surrounding buffer. The conclusions drawn provide significant new insights on the complex cooperative interactions between the DNA molecule and the class of platinum-based compounds, much used in chemotherapies. [ABSTRACT FROM AUTHOR]

We have studied the interaction ofthe DNA molecule with the ligand3,3′-diaminobenzidine (DAB) by performing single molecule stretchingexperiments with optical tweezers and dynamic light scattering (DLS)on the DNA–DAB complexes. In the stretching experiments, thepersistence and contour lengths of the complexes were measured asa function of DAB concentration, allowing one to infer the main bindingmechanism and also to determine the physicochemical parameters ofthe interaction. In the DLS experiments, the effective size of thecomplexes, measured as the hydrodynamic radius, was monitored as afunction of DAB concentration. We found a qualitative agreement betweenthe results obtained from the two techniques by comparing the behaviorsof the hydrodynamics radius and the radius of gyration, since thislast one can be expressed as a function of the persistence and contourlengths. [ABSTRACT FROM AUTHOR]

Byperforming single molecule stretching experiments with opticaltweezers, we have studied the DNA interaction with the ligand Hoechst33258. The mechanical properties of the complexes formed as a functionof ligand concentration were directly determined from these measurementsby fitting the force × extension curve to the WormLike Chainmodel of semiflexible polymers. In addition, the physicochemical parametersof the interaction were extracted from the persistencelength data by using a previously developed two-sites quenched disorderstatistical model, allowing the determination of the binding isotherm.Such approach has allowed us to decouple the two different bindingmodes present in this system. In particular, it was found that thebinding isotherm consists of two Hill-type processes, one noncooperativeand the other strongly cooperative. Finally, DNA condensation dueto the interaction with the ligand was also verified and characterizedhere by analyzing the apparent contour length of the complexes. [ABSTRACT FROM AUTHOR]

By performing single-molecule force spectroscopy with optical tweezers, we have characterized the interaction between the platinum-based compound transplatin and the DNA molecule, establishing a critical comparison with its isomer cisplatin. While transplatin is ineffective against tumor cells, its isomer is one of the most used drugs in current chemotherapies, and a molecular study on this difference performed at the single-molecule level was lacking until the present work. Our experiments show that transplatin binds DNA under low chloride concentrations (a situation usually found inside many cells) with an equilibrium association binding constant about four orders of magnitude lower than cisplatin. In addition, we have found that, at saturation, transplatin binds preferentially forming interstrand cross links and monoadducts, a situation very different from cisplatin, which forms preferentially intrastrand cross links. Such differences explain the ineffectiveness of transplatin in killing tumor cells. From a physical point of view, the present study advances in using the mechanical properties of the DNA molecule as sensors to evaluate the therapeutic efficiency of drugs. [ABSTRACT FROM AUTHOR]

Abstract: This study aimed to assess anthropogenic impact of surrounding population in the Private Reserve of Natural Heritage at Pantanal, the world's largest freshwater wetland ecosystem located in the centre of South America. Viral aetiological agents of acute gastroenteritis as rotavirus A (RVA), noroviruses, human adenoviruses, klassevirus and of hepatitis, as hepatitis A virus, were investigated in different aquatic matrices. Annual collection campaigns were carried out from 2009 to 2012, alternating dry and rainy seasons. Viral particles present in the samples were concentrated by the adsorption–elution method, with negatively charged membranes, and detected by qualitative and quantitative PCR. From a total of 43 samples at least one virus was detected in 65% (28) of them. Viruses were detected in all matrices with concentrations ranging from 2 × 102 to 8·3 × 104 genome copies per litre. A significant higher RVA frequency was observed in the dry season. Our data revealing dissemination of human enteric viruses in water matrices both inside and outside the reserve could be useful to trace faecal contamination in the environment and to minimize the risk of infection by exposure of susceptible individuals. Significance and Impact of the Study: This study is part of a collaborative project designed to investigate the environmental and health conditions of the Private Reserve of Natural Heritage at Pantanal, the largest seasonally flooded wetland in the world. The project aimed to promote health and quality of human and wildlife extending technical‐scientific knowledge about pathogens present in the region. By assessing the occurrence of human enteric viruses in different water matrices we demonstrated the anthropogenic impact of surrounding population and pointed out the potential risk of infection by exposure of susceptible individuals. [ABSTRACT FROM AUTHOR]

Maturity‐Onset Diabetes of the Young (MODY) type 4 or PDX1 ‐MODY is a rare form of monogenic diabetes caused by heterozygous variants in PDX1 . Pancreatic developmental anomalies related to PDX1 are reported only in neonatal diabetes cases. Here, we describe dorsal pancreatic agenesis in 2 patients with PDX1 ‐MODY. The proband presented with diabetes since 14 years of age and maintained regular glycemic control with low doses of basal insulin and detectable C‐peptide levels after 38 years with diabetes. A diagnosis of MODY was suspected. Targeted next‐generation sequencing identified a heterozygous variant in PDX1 : c.188delC/p.Pro63Argfs*60. Computed tomography revealed caudal pancreatic agenesis. Low fecal elastase indicated exocrine insufficiency. His son had impaired glucose tolerance, presented similar pancreatic agenesis, and harbored the same allelic variant. The unusual presentation in this Brazilian family enabled expansion upon a rare disease phenotype, demonstrating the possibility of detecting pancreatic malformation even in cases of PDX1 ‐related diabetes diagnosed after the first year of life. This finding can improve the management of MODY4 patients, leading to precocious investigation of pancreatic dysgenesis and exocrine dysfunction. [ABSTRACT FROM AUTHOR]

Objectives The aim of this study was to evaluate by central composite design the influence of colouring agents in lipstick colour, expressed by L*, a*, b* parameters (CIELab system) where L* indicates lightness, and a* and b* are the chromaticity coordinates. The a* indicates colour direction from red to green and b* from yellow to blue. Methods Lipsticks were formulated as described by (Recent Adv. Prosp. Potent Med. Plants, 2009 and 39). The combined effect of three variables (dye, pigment and opacifier) was evaluated by different formulations in a central composite design. Colour parameters ( L*, a*, b*) were analysed by reflectance spectrophotometry. Lipsticks were characterized by visual analyses and melting point. Results All formulations were integrate and homogeneous. The pigments and dye do not influence in colour transfer neither in melting point of lipsticks. On the other hand, results indicated that variables studied show influence only in parameter b*, whereas for L* and a* values there was no significant difference ( P < 0.05). Conclusion It was possible to verify that only the colour parameter b* was influenced by the variation in colouring agent's concentrations in lipstick formulation, leading to the production of the colour ranging between violet and light red. Such results are useful for developing new lipstick formulations to obtain the desired colour in the final product. [ABSTRACT FROM AUTHOR]

Binding of ligands to DNA can be studied by measuring the change of the persistence length of the complex formed, in single-molecule assays. We propose a methodology for persistence length data analysis based on a quenched disorder statistical model and describing the binding isotherm by a Hill-type equation. We obtain an expression for the effective persistence length as a function of the total ligand concentration, which we apply to our data of the DNA-cationic β-cyclodextrin and to the DNA-HU protein data available in the literature, determining the values of the local persistence lengths, the dissociation constant, and the degree of cooperativity for each set of data. In both cases the persistence length behaves nonmonotonically as a function of ligand concentration and based on the results obtained we discuss some physical aspects of the interplay between DNA elasticity and cooperative binding of ligands. [ABSTRACT FROM AUTHOR]

The study of trace element levels is of great importance due to their relevance in agingand several neurodegenerative diseases. This work compares the elemental concentrations in different postnatal ages and between the temporal cortex, entorhinal cortex and hippocampus from Wistar rats, using X-ray total reflection fluorescence with synchrotron radiation. Ten elements were determined in brain samples: Ti, Cr, Mn, Fe, Cu, Zn, (at trace level) and P, S, Cl and K (at major levels). The elements that increased with aging in cortical areas were: S, K, Fe, Cu and Zn. Ca and Zn levels decreased with advancing age in the hippocampus. In addition to this, Ti, Mn and Fe levels were more conspicuous in the entorhinal cortex. [ABSTRACT FROM AUTHOR]

We propose a method to determine the DNA-cisplatin binding mechanism peculiarities by monitoring the mechanical properties of these complexes. To accomplish this task, we have performed single molecule stretching experiments by using optical tweezers, from which the persistence and contour lengths of the complexes can be promptly measured. The persistence length of the complexes as a function of the drug total concentration in the sample was used to deduce the binding data, from which we show that cisplatin binds cooperatively to the DNA molecule, a point which so far has not been stressed in binding equilibrium studies of this ligand. [ABSTRACT FROM AUTHOR]

As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB (“geometrical optics”) approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and “jump” effects are also confirmed. [ABSTRACT FROM AUTHOR]

In this work we use single molecule force spectroscopy performed with optical tweezers in order to characterize the complexes formed between the anticancer drug Pixantrone (PIX) and the DNA molecule, at two very different ionic strengths. Firstly, the changes of the mechanical properties of the DNA-PIX complexes were studied as a function of the drug concentration in the sample. Then, a quenched-disorder statistical model of ligand binding was used in order to determine the physicochemical (binding) parameters of the DNA-PIX interaction. In particular, we have found that the PIX molecular mechanism of action involves intercalation into the double helix, followed by a significant compaction of the DNA molecule due to partial neutralization of the phosphate backbone. Finally, this scenario of interaction was quantitatively compared to that found for the related drug Mitoxantrone (MTX), which binds to DNA with a considerably higher equilibrium binding constant and promotes a much stronger DNA compaction. The comparison performed between the two drugs can bring clues to the development of new (and more efficient) related compounds. [ABSTRACT FROM AUTHOR]

Cyclodextrins and cyclodextrins-modified molecules have interesting and appealing properties due to their capacity to host components that are normally insoluble or poorly soluble in water. In this work, we investigate the interaction of a β-cyclodextrin polymer (poly-β-CD) with λ-DNA. The polymers are obtained by the reaction of β-CD with epichlorohydrin in alkaline conditions. We have used optical tweezers to characterize the changes of the mechanical properties of DNA molecules by increasing the concentration of poly-β-CD in the sample. The physical chemistry of the interaction is then deduced from these measurements by using a recently developed quenched-disorder statistical model. It is shown that the contour length of the DNA does not change in the whole range of poly-β-CD concentration (<300μM). On the other hand, significant alterations were observed in the persistence length that identifies two binding modes corresponding to the clustering of ~2.6 and ~14 polymer molecules along the DNA double helix, depending on the polymer concentration. Comparing these results with the ones obtained for monomeric β-CD, it was observed that the concentration of CD that alters the DNA persistence length is considerably smaller when in the polymeric form. Also, the binding constant of the polymer-DNA interaction is three orders of magnitude higher than the one found for native (monomeric) β-CD. These results show that the polymerization of the β-CD strongly increases its binding affinity to the DNA molecule. This property can be wisely used to modulate the binding of cyclodextrins to the DNA double helix. [ABSTRACT FROM AUTHOR]