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Biomedical subjects

I Molnar

Publications and source records attributed to I Molnar.

At least 19 recordsLinked to original sources
PubMed2002

Two-dimensional optimization using different pairs of variables for the reversed-phase high-performance liquid chromatographic separation of a mixture of acidic compounds.

Computer-facilitated method development has been extended for the simultaneous optimization of any two variables in separations by HPLC and other chromatographic procedures (gas chromatography, supercritical fluid chromatography, capillary electrophoresis, etc.). The application of this approach to HPLC method development is illustrated by the reversed-phase separation of a nine-component mixture of organic acids. Two of four variables (temperature, solvent strength (%B), pH and buffer concentration) were separately optimized in terms of selectivity, and the results are compared in terms of which variables and other conditions are most effective in providing maximum resolution for samples that contain ionizable compounds.

Acids↗
PubMed2002

Advanced high-performance liquid chromatography method development. Discovering unexpected choices in chromatography.

The influence of some important experimental parameters on the resolution of compounds as well as the validity of widely used rules of thumb and of common expectations about how to improve resolution is discussed. It will be shown, on the basis of selected examples, that the general expectations about how the experimental parameters have to be adjusted for better resolution does not cover all chances for resolution improvement. The tool for understanding the method and to discover all chances for increasing selectivity is the resolution map of a method.

Algorithms↗
PubMed2002

Arthritis associated with recurrent erythema multiforme responding to oral acyclovir.

Erythema multiforme is a skin condition frequently associated with herpes simplex virus and has a tendency to recur. Oral acyclovir has been successful in suppression of the disease. Here we report a patient who had recurrent erythema multiforme associated with recurrent polyarthritis that responded to oral acyclovir suppression therapy.

Acyclovir↗
PubMed2001

Cadmium inhibits epoxidation of diatoxanthin to diadinoxanthin in the xanthophyll cycle of the marine diatom Phaeodactylum tricornutum.

Cd has pleiotropic effects on plant physiology and in particular on photosynthesis. It has not been established yet if Cd alters the functioning of the xanthophyll cycle. To answer this question, an exponentially growing culture of the marine diatom Phaeodactylum tricornutum was incubated with Cd (20 mg/l) for 24 h and irradiated with a light activating the xanthophyll cycle, which in diatoms, consists of the reversible deepoxidation of diadinoxanthin to diatoxanthin. The measurements show that the deepoxidation step is not influenced by Cd. In contrast, the Cd concentration used sharply inhibits the epoxidation of diatoxanthin to diadinoxanthin.

Cadmium↗
PubMed2000

Prevalence of iodine deficiency and goitre during pregnancy in east Hungary.

OBJECTIVE: To assess the iodine nutritional status and the prevalence of goitre during pregnancy in a region of Hungary that appeared to be iodine sufficient in previous studies. DESIGN: A cross-sectional voluntary screening study was organized in which 313 pregnant women participated. METHODS: Urine iodine concentration and the volume of the thyroid gland were measured in every woman. In the presence of low urinary iodine concentrations, goitre, or both, thyroid function tests were performed. RESULTS: Iodine deficiency was found in 57.1% of the pregnant women, and was severe in 15.6%. The volume of the thyroid gland was enlarged in 19.2% of individuals. Nodular goitre was found in 17 women (5.4%). The frequency of goitre and the mean thyroid volume were increased in the group of iodine-deficient women. In the 89 cases of iodine deficiency or goitre, thyrotrophin concentrations were in the normal range; however, the free triiodothyronine:free throxine ratio was increased in 97% of them, indicating that the thyroid gland was in a stimulated state in these individuals. CONCLUSIONS: Iodine deficiency with high prevalence of goitre was recognized among pregnant women in an area that previously appeared to be iodine sufficient. An unexpected mild iodine deficiency was also noted in the non-pregnant control group. Reassessment and continuous monitoring of iodine nutritional status is warranted even in populations that are apparently considered to be 'at no risk' of iodine deficiency, especially in pregnant women. Regular administration of iodine, starting at preconception or in early pregnancy and continuing during the period of nursing, is recommended in these regions.

Adult↗
PubMed1997

The pipecolate-incorporating enzyme for the biosynthesis of the immunosuppressant rapamycin--nucleotide sequence analysis, disruption and heterologous expression of rapP from Streptomyces hygroscopicus.

An open reading frame (rapP) encoding the putative pipecolate-incorporating enzyme (PIE) has been identified in the gene cluster for the biosynthesis of rapamycin in Streptomyces hygroscopicus. Conserved amino acid sequence motifs for ATP binding, ATP hydrolysis, adenylate formation, and 4'-phosphopantetheine attachment were identified by sequence comparison with authentic peptide synthetases. Disruption of rapP by phage insertion abolished rapamycin production in S. hygroscopicus, and the production of the antibiotic was specifically restored upon loss of the inserted phage by a second recombination event. rapP was expressed in both Escherichia coli and Streptomyces coelicolor, and recombinant PIE was purified to homogeneity from both hosts. Although low-level incorporation of [14C]beta-alanine into recombinant PIE isolated from E. coli was detected, formation of the covalent acylenzyme intermediate could only be shown with the PIE from S. coelicolor, suggesting that while the recombinant PIE from S. coelicolor was phosphopantetheinylated, only a minor proportion of the recombinant enzyme from E. coli was post-translationally modified.

Amino Acid Sequence↗
PubMed1997

Computerized optimization of the high-performance liquid chromatographic enantioseparation of a mixture of 4-dinitrophenyl amino acids on a quinine carbamate-type chiral stationary phase using DRYLAB.

A method is proposed for the sensitive chiral analysis of amino acid enantiomers by high-performance liquid chromatography (HPLC). Thus the enantiomers of a mixture of seven racemic amino acids were resolved as their DNP derivatives from each other and from the peak of the hydrolyzed reagent, employing a quinine carbamate-based chiral anion exchange-type chiral stationary phase (CSP) and aqueous buffered mobile phases. However, the initial isocratic chromatogram yielded many peak overlaps although the corresponding enantiomers were well resolved. Therefore, the separation of the complex mixture had to be optimized; we utilized the commercial computer method development software DRYLAB. First, the influence of the manifold mobile phase parameters and chromatographic conditions (pH, type and content of organic modifier, buffer concentration, temperature, type of co-ion, etc.) on retention and resolution was studied by isocratic elution. Furthermore, with such optimized conditions linear and multi-segmented organic modifier and buffer salt gradients, respectively, were simulated with the computer program and experimentally verified. Average errors of prediction of retention times lay between 2 and 8%. Finally, a highly improved HPLC gradient method resulted in almost all components being baseline separated and equally spaced and accelerated by a factor of more than 3 compared to the initial run.

Amino Acids↗
PubMed1997

Beneficial effect of pentoxifylline on thyroid associated ophthalmopathy (TAO)*: a pilot study.

We have previously found that pentoxifylline (Ptx) inhibited cytokine induced HLA-DR expression and glycosaminoglycan (GAG) synthesis by retroorbital fibroblasts. We have now tested the clinical efficacy of Ptx in treating TAO. Ten patients with moderately severe ophthalmopathy were selected for study. All patients were euthyroid before and during the 12 weeks of the Ptx therapy. Serum GAG, TNF-alpha, anti-TSH-receptor, anti-eye muscle, anti-thyroglobulin and anti-thyroid peroxidase antibodies were determined sequentially. At the end of 12 weeks eight of the ten patients showed improvement in soft tissue but not in proptosis or extraocular muscle involvement. At baseline the levels of GAG (5.2+/-0.92 mg/dl v.s. 0.7+/-0.14 mg/dl, p<0.001) and TNF-alpha (33.6+/-6.6 pg/ml v.s. 5.4+/-1.3 pg/ml, p<0.001) were increased in patients compared to controls. They gradually decreased in the eight patients who responded to Ptx: after 4, 8 and 12 weeks of therapy serum GAG was 3.4+/-0.42 mg/dl, 2.5+/-0.77 mg/dl (p<0.01) and 1.1+/-0.2 mg/dl (p<0.001), respectively and serum TNF-alpha was 20.9+/-4.8 pg/ml, 14.9+/-2.2 pg/ml (p<0.05) and 9.7+/-1.8 pg/ml (p<0.01), respectively. Serum GAG and TNF alpha did not fall in the two patients who did not respond. The titre of anti-eye muscle antibodies but not anti-thyroid antibodies were lower at 12 weeks. Ptx has a beneficial effect on inflammatory symptoms of TAO and associated laboratory parameters in the majority of patients.

Adult↗
PubMed1992

Computer simulation for the prediction of separation as a function of pH for reversed-phase high-performance liquid chromatography. I. Accuracy of a theory-based model.

Computer simulation software (DryLab I/mp) is described for predicting high-performance liquid chromatographic separation as a function of changes in mobile phase pH. Three experimental runs with pH (only) varied are used to derive values of pKa plus capacity factors (k') for the ionized and non-ionized form of each ionizable solute. Various tests of the experimental data then allow classification of each solute as acidic, basic, neutral (including strong or weak acids or bases) and amphoteric. Experimental data are reported for the separation of several substituted anilines as a function of pH and solvent composition (%B). Experimental requirements for the accurate prediction of separation (ca. +/- 2-4% in alpha) as a function of pH are discussed. The reliability of the software is demonstrated for three different samples: mixtures of (a) substituted benzoic acids, (b) substituted anilines and (c) catecholamine-related compounds.

Aniline Compounds↗
PubMed1992

Computer simulation for the prediction of separation as a function of pH for reversed-phase high-performance liquid chromatography. II. Resolution as a function of simultaneous change in pH and solvent strength.

The optimization of reversed-phase high-performance liquid chromatographic separation by the simultaneous variation of pH and solvent strength (%B) was studied for acidic (substituted benzoic acids) and basic samples (substituted anilines). The combination of these two variables was expected to be more useful than either variable alone. This proved to be the case for the benzoic acid sample, but not for the aniline sample. Column plate numbers were also studied for each sample and as a function of pH. With the exception of one compound (3,5-dimethylaniline) in one particular pH range (3.0-4.5), plate numbers of 12,000-20,000 were observed for each sample.

Aniline Compounds↗
PubMed1992

Biostatistical manual (BIOSTAT) for potency control and for evaluation of effectiveness of the WHO-EPI vaccines: software for personal computers.

In accordance with WHO requirements, a specialized software has been developed for personal computers to analyse the potency data of the EPI vaccines and to evaluate the effectiveness of the vaccination. The software has three parts and allows users to create files from control data (BIOSTAT), to check the function of the software and statistical formulae (BIOSDEMO), and to understand the logic and structure of the data processing system and the statistical models (BIOSDOC).

Evaluation Studies as Topic↗
PubMed1992

Intrapulmonary thrombin generation and its relation to monomethylmethacrylate plasma levels during hip arthroplasty.

Frequent peroperative sampling of arterial and mixed venous blood was undertaken in eight consecutive patients during cemented hip arthroplasty to obtain a sequential picture of thrombin-antithrombin (TAT) and methylmethacrylate monomer (MMA) concentrations. TAT, detected neo-antigenically, reached its maximum levels after bone preparation, prior to introduction of cement and prosthesis. Furthermore, TAT values were higher in arterial than in mixed venous blood, indicating generation and inactivation of thrombin when blood is passing the lung. MMA concentration, measured by high pressure liquid chromatography, increased very rapidly and declined within 1 min following socket as well as shaft implantation, reaching the highest mean value of 3599 ng/ml only 30 s after femoral impaction of cement. MMA concentration was higher in mixed venous than in arterial blood, indicating elimination of the monomer during lung passage. This study confirms our previous observation that coagulation is activated prior to the implantation of bone cement and prosthesis into the femoral shaft; in addition, it provides further evidence of the thrombin-generating potential of the pulmonary capillary bed. Very frequent sampling was necessary to reveal the sharp rise in MMA levels following impaction of cement. Further investigations are needed to establish whether interaction between activated coagulation and MMA may predispose to cardiovascular complications.

Aged↗
PubMed1990

Isolation and characterization of the cytosolic and chloroplastic 3-phosphoglycerate kinase from spinach leaves.

The cytosol and chloroplast 3-phosphoglycerate kinases (3-PGK) from spinach (Spinacia oleracea L.) were purifled to apparent homogeneity. The procedure included a conventional anion-exchange chromatography on DEAE-cellulose and mainly a series of HPLC columns. The charge differences of the two isoenzymes were so small that separation was only successful by anion-exchange chromatography on a HPLC SynChropak AX 300 column. The portion of the two isoenzmyes in leaf tissue was estimated as 5% and 95%. The major 3-PGK was associated with isolated chloroplasts while the other 3-PGK was only found in the soluble cell fraction. The specific activity of the purified enzymes were in the order of 800 units (per milligram of protein). The molecular weight for the two 3-PGKs under nondenaturing (size exclusion chromatography) and denaturing (SDS-PAGE) conditions were in the order of 40 kilodaltons, with the cytosolic 3-PGK being slightly smaller than the chloroplastic 3-PGK. An antiserum against the chloroplastic 3-PGK showed only 4.6% cross-reaction of the chloroplastic 3-PGK with the cytosolic 3-PGK. The kinetics for glycerate-3-phosphate and MgATP(2-) were biphasic. The presence of Na(2)SO(4) changed the MgATP(2-) dependence to linearity but not the glycerate-3-phosphate dependence.

Journal Article↗
PubMed1989

Tooth wear in Australian aboriginal populations from the River Murray Valley.

The study of tooth wear among prehistoric and recent populations has frequently been concerned with the rate and pattern of wear over the dental arches. In this report we considered the question of tooth wear variation among collections of Australian Aboriginal crania recovered from several sites along the Murray River in Southeastern Australia. These crania represent the remains of relatively recent populations from about 2,000 years ago until the early 19th century. The degree of tooth wear for each dental arch was recorded by an established method of determining the ratio of exposed dentin. The pattern or distribution of wear over each arch was summarized by principal component analysis. The mean wear degree and pattern were compared among four geographical grouping of crania separated by up to 700 miles of river frontage. Our results showed, as expected, a significant difference between the well-defined population at the Lower Murray site (Swanport) and the three upriver groups. However, there were significant differences among these three collections as well. Sexual dimorphism was noted but was only significant in the Lower Murray group; the mean wear was greater and also more variable among the males. At the second of the Middle Murray sites the pattern of wear was different and the degree of wear was significantly less than in the other groups. A possible explanation for this diversity may be environmental and subsistence base differences. The evidence from the Lower Murray supports this possibility, but the differences among the other three groups are not as clearly established. However, our results do suggest that the Murray Black collection, from which these crania were obtained, may not be as homogeneous a group as previously believed.

Australia↗