Dr. Jan  Kucera   image

Dr. Jan Kucera

150 S Huntington Ave Neurology 127
Boston MA 02130
857 644-4750
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #: 55071
NPI: 1174638407
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Elemental characterization of single-wall carbon nanotube certified reference material by neutron and prompt γ activation analysis. - Analytical chemistry
Instrumental neutron activation analysis with both relative and k0 standardization was used in four experienced laboratories to determine element mass fractions in single-wall carbon nanotube certified reference material (CRM) SWCNT-1. Results obtained were evaluated using the National Institute of Standards and Technology (NIST) "Type B On Bias" approach and yielded consensus values in agreement with National Research Council Canada (NRCC) certified values for Fe, Co, Ni, and Mo and provided mass fraction values for 13 additional elements, namely, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Br, La, W, and Au. In addition, prompt γ neutron activation analysis was employed to determine mass fractions of H, B, Co, Ni, and Mo. Results of this work provide a basis for the establishment of reference values of element mass fractions in CRM SWCNT-1, thus expanding its usability for more accurate characterization and benchmarking of similar nanotechnology materials.
Cancer-associated fibroblasts are not formed from cancer cells by epithelial-to-mesenchymal transition in nu/nu mice. - Histochemistry and cell biology
Cancer-associated fibroblasts are bioactive elements influencing the biological properties of malignant tumors. Their origin from different cell types has been established, and the possibility of their formation by epithelial-to-mesenchymal transition from cancer cells is under debate. This study shows that human cancer cells grafted to nu/nu mice induced formation of tumor stroma with the presence of typical smooth muscle actin-containing cancer-associated fibroblasts. These cells seem to be of the host origin because they are not recognized by an antibody specific for human vimentin, as was also verified in vitro. These results suggest that cancer-associated stromal fibroblasts are not formed by epithelial-to-mesenchymal transition from cancer cells.
Gain-of-function mutation of the SCN5A gene causes exercise-induced polymorphic ventricular arrhythmias. - Circulation. Cardiovascular genetics
Over the past 15 years, a myriad of mutations in genes encoding cardiac ion channels and ion channel interacting proteins have been linked to a long list of inherited atrial and ventricular arrhythmias. The purpose of this study was to identify the genetic and functional determinants underlying exercise-induced polymorphic ventricular arrhythmia present in a large multigenerational family.A large 4-generation family presenting with exercise-induced polymorphic ventricular arrhythmia, which was followed for 10 years, was clinically characterized. A novel SCN5A mutation was identified via whole exome sequencing and further functionally evaluated by patch-clamp studies using human embryonic kidney 293 cells. Of 37 living family members, a total of 13 individuals demonstrated ≥50 multiformic premature ventricular complexes or ventricular tachycardia upon exercise stress tests when sinus rate exceeded 99±17 beats per minute. Sudden cardiac arrest occurred in 1 individual during follow-up. Exome sequencing identified a novel missense mutation (p.I141V) in a highly conserved region of the SCN5A gene, encoding the Nav1.5 sodium channel protein that cosegregated with the arrhythmia phenotype. The mutation p.I141V shifted the activation curve toward more negative potentials and increased the window current, whereas action potential simulations suggested that it lowered the excitability threshold of cardiac cells.Gain-of-function of Nav1.5 may cause familial forms of exercise-induced polymorphic ventricular arrhythmias.© 2014 American Heart Association, Inc.
Synthetic routes contaminate graphene materials with a whole spectrum of unanticipated metallic elements. - Proceedings of the National Academy of Sciences of the United States of America
The synthesis of graphene materials is typically carried out by oxidizing graphite to graphite oxide followed by a reduction process. Numerous methods exist for both the oxidation and reduction steps, which causes unpredictable contamination from metallic impurities into the final material. These impurities are known to have considerable impact on the properties of graphene materials. We synthesized several reduced graphene oxides from extremely pure graphite using several popular oxidation and reduction methods and tracked the concentrations of metallic impurities at each stage of synthesis. We show that different combinations of oxidation and reduction introduce varying types as well as amounts of metallic elements into the graphene materials, and their origin can be traced to impurities within the chemical reagents used during synthesis. These metallic impurities are able to alter the graphene materials' electrochemical properties significantly and have wide-reaching implications on the potential applications of graphene materials.
Nonlinear behaviour of conduction and block in cardiac tissue with heterogeneous expression of connexin 43. - Journal of molecular and cellular cardiology
Altered gap junctional coupling potentiates slow conduction and arrhythmias. To better understand how heterogeneous connexin expression affects conduction at the cellular scale, we investigated conduction in tissue consisting of two cardiomyocyte populations expressing different connexin levels. Conduction was mapped using microelectrode arrays in cultured strands of foetal murine ventricular myocytes with predefined contents of connexin 43 knockout (Cx43KO) cells. Corresponding computer simulations were run in randomly generated two-dimensional tissues mimicking the cellular architecture of the strands. In the cultures, the relationship between conduction velocity (CV) and Cx43KO cell content was nonlinear. CV first decreased significantly when Cx43KO content was increased from 0 to 50%. When the Cx43KO content was ≥60%, CV became comparable to that in 100% Cx43KO strands. Co-culturing Cx43KO and wild-type cells also resulted in significantly more heterogeneous conduction patterns and in frequent conduction blocks. The simulations replicated this behaviour of conduction. For Cx43KO contents of 10-50%, conduction was slowed due to wavefront meandering between Cx43KO cells. For Cx43KO contents ≥60%, clusters of remaining wild-type cells acted as electrical loads that impaired conduction. For Cx43KO contents of 40-60%, conduction exhibited fractal characteristics, was prone to block, and was more sensitive to changes in ion currents compared to homogeneous tissue. In conclusion, conduction velocity and stability behave in a nonlinear manner when cardiomyocytes expressing different connexin amounts are combined. This behaviour results from heterogeneous current-to-load relationships at the cellular level. Such behaviour is likely to be arrhythmogenic in various clinical contexts in which gap junctional coupling is heterogeneous.Copyright © 2014 Elsevier Ltd. All rights reserved.
Synthetic polyamine BPA-C8 inhibits TGF-β1-mediated conversion of human dermal fibroblast to myofibroblasts and establishment of galectin-1-rich extracellular matrix in vitro. - Chembiochem : a European journal of chemical biology
Cancer-associated fibroblasts (CAFs) play a role in the progression of malignant tumors. They are formed by conversion of fibroblasts to smooth muscle α-actin-positive (SMA-positive) myofibroblasts. Polyamines are known to change the arrangement of the actin cytoskeleton by binding to the anionic actin. We tested the effect of the synthetic polyamine BPA-C8 on the transition of human dermal fibroblasts to myofibroblasts induced either by TGF-β1 alone or by TGF-β1 together with adhesion/growth-regulatory galectin-1. Pre-existing CAFs, myofibroblasts from pancreatitis, and rat smooth muscle cells were also exposed to BPA-C8. BPA-C8 impaired myofibroblast formation from activated fibroblasts, but it had no effect on cells already expressing SMA. BPA-C8 also reduced the occurrence of an extracellular matrix around the activated fibroblasts. The reported data thus extend current insights into polyamine activity, adding interference with tumor progression to the tumor-promoting processes warranting study.© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Computational tools to investigate genetic cardiac channelopathies. - Frontiers in physiology
The aim of this perspective article is to share with the community of ion channel scientists our thoughts and expectations regarding the increasing role that computational tools will play in the future of our field. The opinions and comments detailed here are the result of a 3-day long international exploratory workshop that took place in October 2013 and that was supported by the Swiss National Science Foundation.
Chondrogenic differentiation of mesenchymal stem cells in a hydrogel system based on an enzymatically crosslinked tyramine derivative of hyaluronan. - Journal of biomedical materials research. Part A
Hyaluronan-based tissue substitutes are promising materials in cartilage reconstruction surgery. Herein, the chondrogenesis of human mesenchymal stem cells (MSC) in a hydrogel based on a tyramine derivative of hyaluronan crosslinked by hydrogen peroxidase (HA-TA) was evaluated. Human MSC seeded in the scaffold were incubated in standard chondrogenic medium and medium enriched with bone morphogenetic protein-6 (BMP6). Cell viability, the gene expression of selected markers (collagen type II, aggrecan, SOX9, collagen type X, and osteopontin), and the histological characteristics were examined during three weeks of in vitro cultivation. The tissue reaction of both unseeded and MSC seeded HA-TA scaffolds were tested in vivo after subcutaneous application in rats for 12 weeks. The data showed that cells resisted the process of crosslinking and remained viable for the whole time while exhibiting changes in cell organization. Human MSC cultivated in HA-TA hydrogel expressed genes of both chondrogenic and osteogenic differentiation and the addition of BMP6 revealed a tendency to potentiate both processes. Histological analysis of HA-TA in vivo implants did not reveal a chronic inflammatory reaction. In both cases, in vivo HA-TA implants were continuously degraded and MSC-seeded hydrogels tended to form clusters similar to in vitro samples. In conclusion, MSC chondrogenic differentiation may proceed in a HA-TA scaffold that is biocompatible. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3523-3530, 2014.© 2013 Wiley Periodicals, Inc.
Characterization of 2 genetic variants of Na(v) 1.5-arginine 689 found in patients with cardiac arrhythmias. - Journal of cardiovascular electrophysiology
Hundreds of genetic variants in SCN5A, the gene coding for the pore-forming subunit of the cardiac sodium channel, Na(v) 1.5, have been described in patients with cardiac channelopathies as well as in individuals from control cohorts. The aim of this study was to characterize the biophysical properties of 2 naturally occurring Na(v) 1.5 variants, p.R689H and p.R689C, found in patients with cardiac arrhythmias and in control individuals. In addition, this study was motivated by the finding of the variant p.R689H in a family with sudden cardiac death (SCD) in children. When expressed in HEK293 cells, most of the sodium current (I(Na)) biophysical properties of both variants were indistinguishable from the wild-type (WT) channels. In both cases, however, an ∼2-fold increase of the tetrodotoxin-sensitive late I(Na) was observed. Action potential simulations and reconstruction of pseudo-ECGs demonstrated that such a subtle increase in the late I(Na) may prolong the QT interval in a nonlinear fashion. In conclusion, despite the fact that the causality link between p.R689H and the phenotype of the studied family cannot be demonstrated, this study supports the notion that subtle alterations of Na(v) 1.5 variants may increase the risk for cardiac arrhythmias.© 2013 Wiley Periodicals, Inc.
Uncovering the dynamics of cardiac systems using stochastic pacing and frequency domain analyses. - PLoS computational biology
Alternans of cardiac action potential duration (APD) is a well-known arrhythmogenic mechanism which results from dynamical instabilities. The propensity to alternans is classically investigated by examining APD restitution and by deriving APD restitution slopes as predictive markers. However, experiments have shown that such markers are not always accurate for the prediction of alternans. Using a mathematical ventricular cell model known to exhibit unstable dynamics of both membrane potential and Ca²⁺ cycling, we demonstrate that an accurate marker can be obtained by pacing at cycle lengths (CLs) varying randomly around a basic CL (BCL) and by evaluating the transfer function between the time series of CLs and APDs using an autoregressive-moving-average (ARMA) model. The first pole of this transfer function corresponds to the eigenvalue (λ(alt)) of the dominant eigenmode of the cardiac system, which predicts that alternans occurs when λ(alt) ≤ -1. For different BCLs, control values of λ(alt) were obtained using eigenmode analysis and compared to the first pole of the transfer function estimated using ARMA model fitting in simulations of random pacing protocols. In all versions of the cell model, this pole provided an accurate estimation of λ(alt). Furthermore, during slow ramp decreases of BCL or simulated drug application, this approach predicted the onset of alternans by extrapolating the time course of the estimated λ(alt). In conclusion, stochastic pacing and ARMA model identification represents a novel approach to predict alternans without making any assumptions about its ionic mechanisms. It should therefore be applicable experimentally for any type of myocardial cell.

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