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Biomedical subjects

C Heller

Publications and source records attributed to C Heller.

At least 19 recordsLinked to original sources
PubMed1999

A fully automated multicapillary electrophoresis device for DNA analysis.

We describe the construction and performance of a fully automated multicapillary electrophoresis system for the analysis of fluorescently labeled biomolecules. A special detection system allows the simultaneous spectral analysis of all 96 capillaries. The main features are true parallel detection without any moving parts, high robustness, and full compatibility to existing protocols. The device can process up to 40 microtiter plates (96 and 384 well) without human interference, which means up to 15,000 samples before it has to be reloaded.

Automation↗
PubMed1999

Separation of double-stranded and single-stranded DNA in polymer solutions: I. Mobility and separation mechanism.

We have studied the separation of single-stranded and double-stranded DNA in a matrix of entangled, linear poly-N,N-dimethylacrylamide. Our results give better insight into the mechanisms involved during separations in polymer solutions. The dependence of different parameters on DNA size, electric field, pore size and the polymer chain length are evaluated and compared to theoretical predictions. Striking differences between experimental data and predicted scaling laws are found. Our data should help to optimize DNA separation in capillary electrophoresis and to improve existing models for DNA separation in porous matrices.

Acrylamides↗
PubMed1999

Separation of double-stranded and single-stranded DNA in polymer solutions: II. Separation, peak width and resolution.

The electrophoretic separation of single-stranded and double-stranded DNA has been examined, using a matrix of linear poly-N,N-dimethylacrylamide (pDMA). The dependence of peak spacing, peak width and resolution on important parameters such as polymer concentration, polymer chain length and electric field strength, has been studied. This work complements our systematic study on electrophoretic mobility under different conditions (C. Heller, Electrophoresis 1999, 20, 1962-1977), and will help to further optimize and improve high performance DNA separation in capillary electrophoresis with entangled polymer solutions.

Acrylamides↗
PubMed1998

Finding a universal low-viscosity polymer for DNA separation.

We have investigated the viscosity of different commercially available polymers in solution and found that dextran has a low viscosity compared to other polymers of comparable molecular weight and resolving power. This makes it a potentially useful matrix for DNA separation in capillary electrophoresis, where either short time or low pressure are preferred for matrix replacement. We showed that dextran performs well for the separation of oligonucleotides and double-stranded DNA fragments. Together with the well-known application for protein separation, this makes dextran a universal polymer for the separation of biological macromolecules.

DNA↗
PubMed1998

Finding a universal low viscosity polymer for DNA separation (II).

When investigating the use of different polymers for capillary electrophoresis we found that poly-N,N-dimethylacrylamide (pDMA) has a very low viscosity compared to other polymers of comparable molecular mass and resolving power. This makes it a potentially useful matrix for DNA separation in multi-capillary electrophoresis, where short cycle times or low pressure for matrix replacement are preferred. We have characterized this matrix by systematic studies on concentration, chain length and field strength dependence. It is shown that pDMA performs well for the separation of oligonucleotides and double-stranded DNA fragments. Together with the application of DNA sequencing, pDMA is a universal polymer for the separation of biological macromolecules.

Acrylamides↗
PubMed1997

Micropreparative capillary electrophoresis of DNA by direct transfer onto a membrane.

We have developed a new technique for the collection of DNA fragments separated by capillary electrophoresis, by direct transfer from the capillary outlet to a positively charged membrane. Transfer and post-run detection of two different nonradioactively labeled DNA standards, ranging in size from 150 bp to 2 kbp and 120 bp to 23 kbp are presented, and discussed. Capillary electrophoresis with direct blotting presents several advantages over the blotting from gels: the separation is faster and requires less manual steps, the resolution is higher, and each DNA fragment is collected into a very concentrated spot on the membrane due to the small surface of the capillary outlet and to a design of the collection device inducing a refocusing of field lines across the hybridization membrane. Therefore, very small amounts of DNA (in the pg range) can be detected. This fraction collection makes further analysis of the sample possible, e.g. by hybridization, thus suppressing one of the major present limitations of the capillary electrophoresis technique for DNA analysis.

DNA↗
PubMed1996

DNA: an extensible molecule.

The force-displacement response of a single duplex DNA molecule was measured. The force saturates at a plateau around 70 piconewtons, which ends when the DNA has been stretched about 1.7 times its contour length. This behavior reveals a highly cooperative transition to a state here termed S-DNA. Addition of an intercalator suppresses this transition. Molecular modeling of the process also yields a force plateau and suggests a structure for the extended form. These results may shed light on biological processes involving DNA extension and open the route for mechanical studies on individual molecules in a previously unexplored range.

Chemical Phenomena↗
PubMed1996

Lipid interference in the determination of the concentration of haemoglobin in plasma using the ACA SX analyzer.

In comparison to a triple wavelength procedure, the dual wavelength method for the determination of plasma haemoglobin concentration using the ACA analyzer showed considerable interference with hypertriglyceridaemic (triacylglycerols > 2.3 mmol/l) plasma. By addition of isolated human lipoprotein fractions to normotriglyceridaemic plasma, chylomicrons were identified as a major source of interference with the ACA plasma haemoglobin method, whereas VLDL was without effect up to a triacylglycerol concentration of 5.7 mmol/l. Airfuge ultracentrifugation proved to be a reliable means for removal of interfering lipid. We conclude that the extent of lipid interference with the ACA plasma haemoglobin method is highly dependent on the type of lipoprotein present. An accurate measurement of plasma haemoglobin concentrations in non-fasting plasma can only be ensured after lipid removal through airfuge ultracentrifugation.

Chylomicrons↗
PubMed1996

Leveraging information technology for quality improvement.

The information technology that is absolutely essential to gather, analyze, manipulate, and report on treatment approaches, practice patterns, and clinical outcomes remains in the background, but it is absolutely key to success in virtually every effort at health care quality improvement.

Cardiovascular Diseases↗
PubMed1995

Idebenone protects hepatic microsomes against oxygen radical-mediated damage in organ preservation solutions.

The ability of the benzoquinone coenzyme Q-10 or its derivative QSA-10 (idebenone) to protect against lipid peroxidation and protein damage mediated by the pro-oxidative system NADPH/ADP/Fe3+ was tested in a rat liver microsomal model incubated in University of Wisconsin (UW) or histidine-tryptophan-ketoglutarate (HTK) solutions. Lipid peroxidation, as followed by direct determination of lipid hydroperoxides and by monitoring of malondialdehyde equivalents, was 1.8-fold enhanced in HTK and 3-fold attenuated in UW compared with HEPES buffer. Function and integrity of microsomal enzymes were investigated using glutathione S-transferase and cytochrome P-450 IIIA activity as assessed by lidocaine N-deethylation to monoethylglycinexylidide as well as by Western blot analysis of the cytochrome P-450 IIIA protein. Glutathione S-transferase activity was reduced by about 70% in HEPES compared with 50% in HTK and 36% in UW. Cytochrome P-450 IIIA was inactivated by about 75% in HEPES and HTK, compared with 55% in UW. The enzyme inactivation was paralleled by a loss of immunoreactive cytochrome P-450 IIIA protein. Supplementation of HTK with 0.1 mumol/L QSA-10 offered complete protection against lipid peroxidation, compared with 100 mumol/L with Q-10. QSA-10 (20 mumol/L) prevented protein damage in both preservation solutions, whereas Q-10 (20 mumol/L) offered only partial protection in UW and had no effect in HTK. The use of QSA-10 during liver transplantation may therefore have the potential of increasing the efficacy of organ preservation, maintaining donor organ quality, and preventing reperfusion injury. It is suitable for human use and has energy-conserving properties in addition to its antioxidant nature.

Adenosine↗
PubMed1995

Systematic study of field and concentration effects in capillary electrophoresis of DNA in polymer solutions.

A systematic study of the separation of double-stranded DNA in hydroxypropylcellulose (HPC) with a molecular mass of 10(6) was undertaken, using a variety of concentrations (from 0.1 to 1%) and different electric fields (from 6 to 540 V/cm). The data show that at high polymer concentrations ( > or = 0.4%) and low fields, the separation mechanism is similar to that occurring in gels. The results are in good agreement with theoretical models, and in particular with a recently proposed theory for gels with a pore size smaller than the persistence length of DNA. For more dilute solutions and high fields, however, the separation pattern cannot be explained by existing theories. The existence of an original mechanism was confirmed by the direct observation of the conformation of double-stranded DNA molecules in the polymer solution by fluorescence videomicroscopy. Practical conclusions for the capillary electrophoretic separation of duplex DNA are drawn.

Benzoxazoles↗
PubMed1995

Segregation in DNA solutions induced by electric fields.

DNA solutions subjected to an electric field exhibit an instability that leads to DNA segregation in aggregates tilted with regard to the field. With the use of epifluorescence videomicroscopy, the evolution of DNA patterns in capillaries as a function of DNA concentration, DNA size, field strength, and field frequency was studied. The field threshold for segregation was decreased when the frequency was lowered or when the DNA molecular weight or concentration was increased. Aggregation is attributed to an electrohydrodynamic instability triggered by the dipole-dipole interaction. This phenomenon explains the failure of earlier attempts to separate large DNA in capillaries.

DNA↗
PubMed1995

DNA separation with field inversion capillary electrophoresis.

We have built an automated pulsed field capillary electrophoresis system on the basis of a commercially available device. Using entangled polymer solutions as separating matrix, we demonstrate a considerable improvement of separation of double-stranded DNA in the range of 1-50 kbp under pulsed field conditions. The influence of the main parameters, i.e. pulse frequency and electric field, is studied and the results are compared to existing electrophoresis theories.

Autoanalysis↗
PubMed1995

Individualized developmental care for very-low-birth-weight premature infants.

Forty very-low-birth-weight neonatal intensive care unit (NICU) infants with birth weights < or = 1,250 g were randomly assigned to treatment or control groups. Behavior of the treatment infants was systematically evaluated, and individualized developmentally oriented care plans were implemented to enhance stability. Treatment babies required fewer days of intermittent mandatory ventilation and continuous positive airway pressure and achieved full enteral feedings sooner. Length of hospital stay and hospital charges were less for treatment than control infants. There were favorable effects on treatment infants' behavioral performance at 42 weeks' postconceptional age. These results support the hypothesis that behaviorally sensitive, developmentally oriented care improves medical and neurodevelopmental outcome in the NICU.

Hospital Charges↗