Line Optical Tweezers Instrument for Measuring Nanoscale Interactions and Kinetics

We describe an optical tweezers instrument for measuring short-ranged colloidal interactions, based on a combination of a continuous wave line optical tweezers, high speed video microscopy, and laser illumination. Our implementation can measure the separation of two nearly contacting microspheres to better than 4 nm at rates in excess of 10 kHz. A simple image analysis algorithm allows us to sensibly remove effects from diffraction blurring and microsphere image overlap for separations ranging from contact to at least 100 nm. The result is a versatile instrument for measuring steric, chemical and single-molecular interactions and dynamics, with a force resolution significantly better than achievable with current atomic force microscopy. We demonstrate the effectiveness of the instrument with measurements of the pair interactions and dynamics of microspheres in the presence of transient molecular bridges of DNA or surfactant micelles

Colloidal Interactions and Self-Assembly Using DNA Hybridization

The specific binding of complementary DNA strands has been suggested as an ideal method for directing the controlled self-assembly of microscopic objects. We report the first direct measurements of such DNA-induced interactions between colloidal microspheres, as well as the first colloidal crystals assembled using them. The interactions measured with our optical tweezer method can be modeled in detail by well-known statistical physics and chemistry, boding well for their application to directed selfassembly. The microspheres’ binding dynamics, however, have a surprising power-law scaling that can significantly slow annealing and crystallization

Atrial fibrillation in healthy adolescents after highly caffeinated beverage consumption: two case reports

<p>Abstract</p> <p>Introduction</p> <p>Energy drinks and highly caffeinated drinks comprise some of the fastest growing products of the beverage industry, often targeting teenagers and young adults. Cardiac arrhythmias in children related to high caffeine consumption have not been well described in the literature. This case series describes the possible association between the consumption of highly caffeinated drinks and the subsequent development of atrial fibrillation in the adolescent population.</p> <p>Case presentations</p> <p>We report the cases of two Caucasian adolescent boys of 14 and 16 years of age at the time of presentation, each without a significant cardiac history, who presented with palpitations or vague chest discomfort or both after a recent history of excessive caffeine consumption. Both were found to have atrial fibrillation on electrocardiogram; one patient required digoxin to restore a normal sinus rhythm, and the other self-converted after intravenous fluid administration.</p> <p>Conclusion</p> <p>With the increasing popularity of energy drinks in the pediatric and adolescent population, physicians should be aware of the arrhythmogenic potential associated with highly caffeinated beverage consumption. It is important for pediatricians to understand the lack of regulation in the caffeine content and other ingredients of these high-energy beverages and their complications so that parents and children can be educated about the risk of cardiac arrhythmias with excessive energy drink consumption.</p

Thymic Stromal-Cell Abnormalities and Dysregulated T-Cell Development in IL-2-Deficient Mice

The role that interleukin-2 (IL-2) plays in T-cell development is not known. To address this issue, we have investigated the nature of the abnormal thymic development and autoimmune disorders that occurs in IL-2-deficient (IL-2(–/–)) mice. After 4 to 5 weeks of birth, IL-2(–/–) mice progressively develop a thymic disorder resulting in the disruption of thymocyte maturation. This disorder is characterized by a dramatic reduction in cellularity, the selective loss of immature CD4(-)8(-) (double negative; DN) and CD4(+)8(+) (double positive; DP) thymocytes and defects in the thymic stromal-cell compartment. Immunohistochemical staining of sections of thymuses from specific pathogen-free and germ-free IL-2(–/–) mice of various ages showed a progressive ,loss of cortical epithelial cells, MHC class II-expressing cells, monocytes, and macrophages. Reduced numbers of macrophages were apparent as early as week after birth. Since IL-2(–/–) thymocyte progenitor populations could mature normally on transfer into a normal thymus, the thymic defect in IL-2(–/–) mice appears to be due to abnormalities among thymic stromal cells. These results underscore the role of IL-2 in maintaining functional microenvironments that are necessary to support thymocyte growth, development, and selection

Force-clamp analysis techniques reveal stretched exponential unfolding kinetics in ubiquitin

Force-clamp spectroscopy reveals the unfolding and disulfide bond rupture times of single protein molecules as a function of the stretching force, point mutations and solvent conditions. The statistics of these times reveal whether the protein domains are independent of one another, the mechanical hierarchy in the polyprotein chain, and the functional form of the probability distribution from which they originate. It is therefore important to use robust statistical tests to decipher the correct theoretical model underlying the process. Here we develop multiple techniques to compare the well-established experimental data set on ubiquitin with existing theoretical models as a case study. We show that robustness against filtering, agreement with a maximum likelihood function that takes into account experimental artifacts, the Kuiper statistic test and alignment with synthetic data all identify the Weibull or stretched exponential distribution as the best fitting model. Our results are inconsistent with recently proposed models of Gaussian disorder in the energy landscape or noise in the applied force as explanations for the observed non-exponential kinetics. Since the physical model in the fit affects the characteristic unfolding time, these results have important implications on our understanding of the biological function of proteins

Controlling the temperature sensitivity of DNA-mediated colloidal interactions through competing linkages

We propose a new strategy to improve the self-assembly properties of DNA-functionalised colloids. The problem that we address is that DNA-functionalised colloids typically crystallize in a narrow temperature window, if at all. The underlying reason is the extreme sensitivity of DNA-mediated interactions to temperature or other physical control parameters. We propose to widen the window for colloidal crystallization by exploiting the competition between DNA linkages with different nucleotide sequences, which results in a temperature-dependent switching of the dominant bond type. Following such a strategy, we can decrease the temperature dependence of DNA-mediated self assembly to make systems that can crystallize in a wider temperature window than is possible with existing systems of DNA functionalised colloids. We report Monte Carlo simulations that show that the proposed strategy can indeed work in practice for real systems and specific, designable DNA sequences. Depending on the length ratio of the different DNA constructs, we find that the bond switching is either energetically driven (equal length or `symmetric' DNA) or controlled by a combinatorial entropy gain (`asymmetric' DNA), which results from the large number of possible binding partners for each DNA strand. We provide specific suggestions for the DNA sequences with which these effects can be achieved experimentally

Cholangiocarcinoma progression depends on the uptake and metabolization of extracellular lipids

[Background and Aims] Cholangiocarcinoma (CCA) includes a heterogeneous group of biliary cancers with a dismal prognosis. We investigated if lipid metabolism is disrupted in CCA and its role in tumor proliferation.[Approach and Results] The in vitro and in vivo tumorigenic capacity of five human CCA cell lines was analyzed. Proteome, lipid content, and metabolic fluxes were evaluated in CCA cells and compared with normal human cholangiocytes (NHC). The Akt1/NOTCH1 intracellular cytoplasmic domain (Nicd1)-driven CCA mouse model was also evaluated. The proteome of CCA cells was enriched in pathways involved in lipid and lipoprotein metabolism. The EGI1 CCA cell line presented the highest tumorigenic capacity. Metabolic studies in high (EGI1) versus low (HUCCT1) proliferative CCA cells in vitro showed that both EGI1 and HUCCT1 incorporated more fatty acids (FA) than NHC, leading to increased triglyceride storage, also observed in Akt1/Nicd1-driven CCA mouse model. The highly proliferative EGI1 CCA cells showed greater uptake of very-low-density and HDLs than NHC and HUCCT1 CCA cells and increased cholesteryl ester content. The FA oxidation (FAO) and related proteome enrichment were specifically up-regulated in EGI1, and consequently, pharmacological blockade of FAO induced more pronounced inhibition of their tumorigenic capacity compared with HUCCT1. The expression of acyl-CoA dehydrogenase ACADM, the first enzyme involved in FAO, was increased in human CCA tissues and correlated with the proliferation marker PCNA.[Conclusions] Highly proliferative human CCA cells rely on lipid and lipoprotein uptake to fuel FA catabolism, suggesting that inhibition of FAO and/or lipid uptake could represent a therapeutic strategy for this CCA subclass.This work was supported by “Ayudas para apoyar grupos de investigación del sistema Universitario Vasco” (IT971‐16 to PA), MCIU/AEI/FEDER, UE (2018‐095134‐B‐100 to PA and by the University of Basque Country COLAB20/01 to PA; Spanish Carlos III Health Institute (ISCIII) (FIS PI15/01132, PI18/01075, PI21/00922, and Miguel Servet Program CON14/00129 and CPII19/00008 to JMB; FIS PI14/00399, PI17/00022 and PI20/00186 to MJP; Sara Borrell [CD19/00254 to PMR]) cofinanced by “Fondo Europeo de Desarrollo Regional” (FEDER); CIBERehd (ISCIII) to JMB, MJP, PMR, PA and LB); “Diputación Foral Gipuzkoa” (DFG15/010, DFG16/004 to JMB and 2020‐CIEN‐000067‐01 to PMR), Department of Health of the Basque Country (2019111024 to MJP, 2017111010 to JMB, and 2020111077 to JMB and PA), “Euskadi RIS3” (2016222001, 2017222014, 2018222029, 2019222054, 2020333010 to JMB), BIOEF (Basque Foundation for Innovation and Health Research: EiTB Maratoia BIO15/CA/016/BD to JMB) and Department of Industry of the Basque Country (Elkartek: KK‐2020/00008 to JMB); La Caixa Scientific Foundation (HR17‐00601 to JMB). “Fundación Científica de la Asociación Española Contra el Cáncer” (AECC Scientific Foundation, to JMB). AMMF‐The Cholangiocarcinoma Charity (EU/2019/AMMFt/001, to JMB and PMR). MRDG was funded by “Fundación Científica de la Asociación Española Contra el Cáncer” (AECC de Bizkaia), MJP was funded by the Spanish Ministry of Economy and Competitiveness (MINECO: “Ramón y Cajal” Program RYC‐2015‐17755), IL, AL and FG‐R by the Basque Government (PRE_2016_1_0152, PRE_2018_2_0195 and PRE 2020 2 02500, respectively), AN‐Z and BG‐S by the UPV/EHU, AB‐V by “Programa de especialización de Personal Investigador Doctor” at the UPV/EHU (2019‐2020) and MA by the MCIU/AEI/FEDER

Phono-spectrographic analysis of heart murmur in children

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