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Biomedical subjects

M Karlsson

Publications and source records attributed to M Karlsson.

At least 19 recordsLinked to original sources
PubMed1992

Escherichia coli ribonucleotide reductase. Radical susceptibility to hydroxyurea is dependent on the regulatory state of the enzyme.

Ribonucleotide reductase catalyzes the reduction of ribonucleotides to their corresponding deoxyribonucleotides via a radical-mediated mechanism. The enzyme from Escherichia coli consists of the two non-identical proteins, R1 and R2, the latter of which contains the necessary free radical located to a tyrosine residue. The radical scavenger hydroxyurea was found to reduce the tyrosyl radical of R2 in a second-order reaction. The rate constant (0.50 M-1 s-1 at 25 degrees C) for this process was several orders of magnitude lower than the hydroxyurea-dependent reduction of free tyrosyl radicals in solution. This difference probably reflects the fact that the R2 tyrosyl radical is buried in the interior of the protein. Formation of the R1R2 complex changed the susceptibility of the radical to hydroxyurea in a manner that reflects the regulatory state of the holoenzyme. Furthermore, binding of substrate or product to the holoenzyme complex made the R2 radical at least 10 times more susceptible to inactivation by hydroxyurea than it was in the isolated R2 protein. One active site mutation in the R1 protein was shown to affect the sensitivity of the tyrosyl radical of R2 differently than wild type protein R1 does. Our results clearly show that the susceptibility of the tyrosyl radical in R2 to inactivation by hydroxyurea can be used as an efficient probe for the regulatory state of the holoenzyme complex.

Escherichia coli↗
PubMed1992

Caracemide, a site-specific irreversible inhibitor of protein R1 of Escherichia coli ribonucleotide reductase.

The anticancer drug caracemide, N-acetyl-N,O- di(methylcarbamoyl)hydroxylamine, and one of its degradation products, N-acetyl-O-methylcarbamoyl-hydroxylamine, were found to inhibit the enzyme ribonucleotide reductase of Escherichia coli by specific interaction with its larger component protein R1. No effect on the smaller protein R2 was observed. The effect of the degradation product was about 30 times lower than that of caracemide itself. The caracemide inactivation of R1 is irreversible, with an apparent second-order rate constant of 150 M-1 s-1. The R1R2 holoenzyme was approximately 30 times more sensitive to caracemide inactivation than the isolated R1 protein. The ribonucleotide reductase substrates were potent competitors of the caracemide inhibition, with a Kdiss for GDP binding to R1 of 80 microM. The reducing agent dithiothreitol was also found to be a potent competitor of caracemide inactivation. These results indicate that caracemide inactivates R1 by covalent modification at the substrate-binding site. By analogy with the known interaction between caracemide and acetylcholinesterase or choline acetyltransferase, we propose that the modification of R1 occurs at an activated cysteine or serine residue in the active site of the enzyme.

Aerobiosis↗
PubMed1992

Homologous collagen-induced arthritis in rats and mice are associated with structurally different major histocompatibility complex DQ-like molecules.

Collagen-induced arthritis (CIA) in rats, induced with homologous type II collagen (CII), is a genetically more restricted disease and has better resemblance to rheumatoid arthritis by its chronic disease course, than CIA induced with heterologous CII. The DA strain is highly susceptible to CIA induced with homologous CII, while the Lewis strain is resistant. (DAxLew)F1 is susceptible and backcrossing to Lewis reveals a close, but not complete, association of both arthritis and CII responsiveness to the RT1a haplotype. Analyses of congenic strains on DA and Lewis backgrounds suggest that expression of a major histocompatibility complex class II Ba molecule, encoded from the RT1Ba locus, is associated with arthritis susceptibility and CII responsiveness. The second exons coding for the first domains of the alpha and beta chains of both the RT1a and RT1l haplotypes were sequenced and the deduced amino acid sequences compared with the corresponding molecule associated with susceptibility to CIA in the mouse (H-2 Aq). The sequences of the respective alleles revealed no obvious structural homology explaining the extensive similarities in the development of chronic autoimmune arthritis. Instead, this finding implies that different trimolecular constituents (i.e. class II, T cell receptor, and CII peptides) may yield an antigen presentation event that is able to trigger a similar autoaggressiveness in the two rodent species.

Amino Acid Sequence↗
PubMed1992

Liquid chromatographic determination of a new catechol-O-methyltransferase inhibitor, entacapone, and its Z-isomer in human plasma and urine.

Assay procedures for analysis of entacapone, (E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)-propenamide++ +, and its Z-isomer in human plasma and urine are described. The methods were based on reversed-phase liquid chromatography with amperometric detection. Entacapone and its Z-isomer were extracted with n-hexane-ethyl acetate mixtures after acidification with hydrochloric acid. From urine extracts the analytes were back-extracted into phosphate buffer (pH 7.2). During sample treatment 1-2% of entacapone was changed to the Z-isomer. With recoveries exceeding 75% the relative standard deviations for within-day precision were less than 11% for plasma and less than 6% for urine at the quantitation limit (10 ng ml-1) and less than 6% for both methods at higher concentrations (20-2000 ng ml-1). The assays were specific with respect to all known metabolites and selective, sensitive and precise enough for determination of entacapone and its Z-isomer in plasma and urine down to 10 ng ml-1. The methods are thus suitable for the kind of pharmacokinetic studies exemplified in this paper.

Catechol O-Methyltransferase Inhibitors↗
PubMed1992

Occupational and other environmental factors and multiple myeloma: a population based case-control study.

Epidemiological studies on the aetiology of multiple myeloma are reviewed as a background to this population based case-control study performed in an area with a high incidence of multiple myeloma. The purpose was to identify and evaluate several suspected environmental factors in relation to this disease. A total of 275 confirmed cases diagnosed in four counties in northern Sweden during four years were compared with the same number of control subjects drawn from population registries. The controls were matched for age, sex, county, and vital status. Occupations and work associated exposures to chemicals and other potential carcinogens were assessed by an extensive questionnaire that also included questions on smoking habits, residential building materials, vicinity to electrical power lines, and leisure time contact with animals, electrical equipment, and chemicals. Information obtained from the questionnaires was completed by telephone interviews when necessary. Univariate analysis and multivariate logistic regression were performed. The study confirmed an association found earlier between farming and multiple myeloma. Some domestic animals (cattle, horses, and goats) and two types of pesticides (phenoxyacetic acids and DDT) were indicated as risk factors within farming. Exposure to electromagnetic fields, asbestos, and organic solvents were negatively associated with myeloma in this study.

Agricultural Workers' Diseases↗
PubMed1992

Fractionated irradiation and early changes in noradrenaline induced potassium efflux (86Rb+) in rat parotid gland.

The effects of fractionated irradiation on the electrolyte fluid secretion from rat parotid gland were studied. Secretion was measured as noradrenaline stimulated potassium efflux in vitro with 86Rb+ as tracer for potassium. The irradiation was delivered either as a five-day schedule (total dose 20, 25, 30, 35, 40, 45 Gy) or a two-day schedule (total dose 24, 32 Gy). The noradrenaline stimulated efflux was decreased in comparison with contralateral controls 10 days after the last irradiation. The effect was dose-dependent. Based on the data available, alpha/beta ratio of the used system was calculated to about 20 Gy, which corresponds to other results regarding early radiation effects.

Animals↗
PubMed1992

Relative biological effectiveness of 50-MV X rays on jejunal crypt survival in vivo.

Earlier in vitro studies of relative biological effectiveness (RBE) of 50-MV X rays show an RBE of approximately 1.1 compared to 4 MV. No difference in RBE has been found for 20-MV X rays or 50-MeV electrons. The higher RBE for 50 MV can be explained to some extent by the small high linear energy transfer contribution from photonuclear reactions at high X-ray energies. To investigate the validity of the results in vitro, a study of the RBE of 50-MV X rays has been performed in vivo using the jejunal crypt microcolony assay in mice. The reference radiation used in this case was 20-MV X rays. The results confirm the earlier in vitro studies. The RBE for 50-MV X rays was estimated to be 1.06, calculated as the ratio between the slopes of the response curves.

Animals↗
PubMed1991

Fibre composition of the ventral roots L7 and S1 in the owl monkey (Aotus trivirgatus).

The ventral roots L7 and S1 of the owl monkey Aotus trivirgatus, were examined by electron microscopy. On average, these roots contain 2950 and 1837 myelinated axons respectively. In both roots the myelinated axons have bimodal size distributions, but the S1 root contains more small myelinated axons. Both roots contain a substantial proportion of unmyelinated axon profiles (UAP). In the L7 root the proportion of UAP decreases as the spinal cord is approached, from 19% distally to 5% in the juxtamedullary rootlets. Unmyelinated and very small myelinated CNS-type axons have not been observed in the L7 transitional region. The average S1 root contains some 40% unmyelinated axons at all examined proximo-distal levels. Unmyelinated/very small myelinated axons are easily found on the CNS side of the S1 transitional region, in direct relation to motoraxon bundles. Bundles of unmyelinated and small myelinated axons occur in the ventral pia mater of both segments. The unmyelinated axons in the L7 root of the owl monkey appear to be arranged like those in the feline L7 ventral root, possibly representing afferents. It is likely that most unmyelinated and small myelinated axons in the ventral root S1 are autonomic efferents.

Animals↗
PubMed1991

Antibody response against autologous and heterologous isolates of Borrelia burgdorferi in four patients with Lyme neuroborreliosis.

Serum and cerebrospinal fluid (CSF) samples from four patients with Lyme neuroborreliosis were analyzed for IgM and IgG antibodies by an indirect enzyme immunoassay with the four patients' own CSF isolate of Borrelia burgdorferi and two tick isolates, strains STG152 and B31, as antigens. No major differences in the antibody response were found comparing autologous and heterologous strains as sonicate antigens, although a tendency towards a stronger response to the autologous isolates was noted in samples from two patients.

Antibodies, Bacterial↗
PubMed1990

Structures on the I-A molecule predisposing for susceptibility to type II collagen-induced autoimmune arthritis.

The susceptibility to type II collagen (CII)-induced arthritis (CIA) in mice is profoundly influenced by major histocompatibility complex (MHC) class II genes in the H-2 region. Analyses of MHC-congenic strains on the B10 background show that only strains developing an anti-CII antibody response after immunization with autologous CII develop arthritis after induction with CII from various species. The susceptible haplotypes have been found to be H-2q, H-2r, H-2w3 and H-2w17. In addition, these haplotypes respond to different patterns of CII derived from various species suggesting that T cell receptors and CII peptides interact. In contrast, certain haplotypes closely related to H-2q, such as the H-2p and H-2w5 haplotypes, are resistant to induction of CIA and are nonresponders to CII. We have earlier shown that a critical structure on the I-A beta molecule determines the susceptibility differences between the p and q haplotypes. We have now determined the structure of exon 2 of the A beta as well as some of the A alpha genes of the remaining haplotypes in the p, q and r families. The sequences show similarities between the CIA-susceptible haplotypes in the A beta C-terminal part and the A alpha N-terminal part of the first domains forming a large part of the antigenic peptide-binding site. Among the wild mouse-derived haplotypes, the w5 haplotype showed an A beta sequence identical to that of the p haplotype consistent with its nonresponder nature to CII immunization. These findings suggest that (a) structures shared between different class II molecules are of importance for the susceptibility to disease in mouse strains and (b) most likely recognition of different CII peptides is important for development of disease.

Amino Acid Sequence↗
PubMed1990

Comparison of flagellum and sonicate antigens for serological diagnosis of Lyme borreliosis.

A sonicate antigen and two concentrations of a purified flagellum antigen of Borrelia burgdorferi were compared for serological diagnosis of Lyme borreliosis by an enzyme immunoassay (EIA). Generally, the higher concentration of flagellum antigen was found to be superior to the lower concentration, which was diluted eight times compared to the higher concentration. The diagnostic sensitivity for IgG antibody detection increased from 13% in the sonicate EIA to 31% in the best flagellum EIA assay (p = 0.01) in sera from patients with erythema migrans (n = 70), and from 34% to 55% (p = 0.01) in sera from patients with neuroborreliosis (n = 77). However, the sensitivity for IgG in sera from patients with acrodermatitis chronica atrophicans (n = 20) was high in both assays: 90% in the sonicate EIA compared to 95% in the flagellum EIA. Regarding IgM, there was no significant difference between the sensitivity of the assays in sera from any of the patient groups. The sensitivity values for IgM and IgG in cerebrospinal fluid (CSF) from patients with neuroborreliosis were also without significant differences. Sera and CSF from patients with meningitis/encephalitis of non-Borrelia etiology (n = 35), multiple sclerosis (n = 9) or syphilis (n = 24), served as controls. The flagellum EIA showed a significantly improved specificity for IgG in CSF from controls with syphilis (p less than 0.01). It is concluded that purified Borrelia burgdorferi flagellum antigen is superior to a sonicate antigen, especially for serodiagnosis of the early stages of Lyme borreliosis.

Acrodermatitis↗
PubMed1990

Cultivation and characterization of spirochetes from cerebrospinal fluid of patients with Lyme borreliosis.

Attempts were made to culture spirochetes from cerebrospinal fluid samples of 105 patients suspected of having Lyme borreliosis with neurological complications. At the final evaluation, only 38 patients fulfilled the criteria of neuroborreliosis. Spirochetes were cultured from cerebrospinal fluid samples of four of these patients. All four patients had pleocytosis in their cerebrospinal fluid and a history of neurological symptoms of only 4 to 10 days in duration. Two of them had no detectable antibodies against any of the isolated spirochetes in their cerebrospinal fluid, both when tested with an enzyme-linked immunosorbent assay and when tested by immunoblotting. An antibody reaction against the homologous isolate that was distinctly stronger than that against the heterologous isolates was found in the serum and cerebrospinal fluid samples from one patient. The cells of the isolates were morphologically similar and showed a very similar protein pattern when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cells of all isolates reacted with the monoclonal antibodies H5332 and H9724, which also react with Borrelia burgdorferi B31, the type strain. One isolate lost a major protein of 23 kilodaltons after subcultivation for 4 months. We conclude that isolation of spirochetes from cerebrospinal fluid might prove successful in clinically selected cases of Lyme borreliosis.

Adult↗
PubMed1990

Western immunoblot and flagellum enzyme-linked immunosorbent assay for serodiagnosis of Lyme borreliosis.

Western immunoblot with a whole-cell lysate was compared with an enzyme-linked immunosorbent assay with a purified flagellum antigen of Borrelia burgdorferi for serodiagnosis of Lyme borreliosis. The assays showed similar sensitivities and specificities in detecting immunoglobulin M and/or immunoglobulin G antibodies in sera from 68 patients with neuroborreliosis and 44 controls with meningitis and encephalitis or with multiple sclerosis. Flagellum enzyme-linked immunosorbent assay is more easily standardized and seems to be a more suitable diagnostic test in a routine laboratory.

Antibodies, Bacterial↗