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Karlsson, Maria
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Publications (10 of 11) Show all publications
Karlsson, M. & Laitila, T. (2014). Finite mixture modeling of censored regression models. Statistical papers, 55(3), 627-642
Open this publication in new window or tab >>Finite mixture modeling of censored regression models
2014 (English)In: Statistical papers, ISSN 0932-5026, E-ISSN 1613-9798, Vol. 55, no 3, p. 627-642Article in journal (Refereed) Published
Abstract [en]

A finite mixture of Tobit models is suggested for estimation of regression models with a censored response variable. A mixture of models is not primarily adapted due to a true component structure in the population; the flexibility of the mixture is suggested as a way of avoiding non-robust parametrically specified models. The new estimator has several interesting features. One is its potential to yield valid estimates in cases with a high degree of censoring. The estimator is in a Monte Carlo simulation compared with earlier suggestions of estimators based on semi-parametric censored regression models. Simulation results are partly in favor of the proposed estimator and indicate potentials for further improvements.

Keywords
Finite mixture models, Censoring, Tobit, EM-algorithm
National Category
Probability Theory and Statistics
Research subject
Statistics; Mathematics
Identifiers
urn:nbn:se:oru:diva-36166 (URN)10.1007/s00362-013-0509-y (DOI)000339339100004 ()2-s2.0-84903907361 (Scopus ID)
Available from: 2014-09-03 Created: 2014-08-28 Last updated: 2018-06-09Bibliographically approved
Bang, C. S., Kinnunen, A., Karlsson, M., Önnberg, A., Söderquist, B. & Persson, K. (2014). The antibacterial effect of nitric oxide against ESBL-producing uropathogenic E-coli is improved by combination with miconazole and polymyxin B nonapeptide. BMC Microbiology, 14, Article ID 65.
Open this publication in new window or tab >>The antibacterial effect of nitric oxide against ESBL-producing uropathogenic E-coli is improved by combination with miconazole and polymyxin B nonapeptide
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2014 (English)In: BMC Microbiology, ISSN 1471-2180, E-ISSN 1471-2180, Vol. 14, article id 65Article in journal (Refereed) Published
Abstract [en]

Background: Nitric oxide (NO) is produced as part of the host immune response to bacterial infections, including urinary tract infections. The enzyme flavohemoglobin, coded by the hmp gene, is involved in protecting bacterial cells from the toxic effects of NO and represents a potentially interesting target for development of novel treatment concepts against resistant uropathogenic bacteria. The aim of the present study was to investigate if the in vitro antibacterial effects of NO can be enhanced by pharmacological modulation of the enzyme flavohemoglobin.

Results: Four clinical isolates of multidrug-resistant extended-spectrum beta-lactamase (ESBL)-producing uropathogenic E. coli were included in the study. It was shown that the NO-donor substance DETA/NO, but not inactivated DETA/NO, caused an initial growth inhibition with regrowth noted after 8 h of exposure. An hmp-deficient strain showed a prolonged growth inhibition in response to DETA/NO compared to the wild type. The imidazole antibiotic miconazole, that has been shown to inhibit bacterial flavohemoglobin activity, prolonged the DETA/NO-evoked growth inhibition. When miconazole was combined with polymyxin B nonapeptide (PMBN), in order to increase the bacterial wall permeability, DETA/NO caused a prolonged bacteriostatic response that lasted for up to 24 h.

Conclusion: An NO-donor in combination with miconazole and PMBN showed enhanced antimicrobial effects and proved effective against multidrug-resistant ESBL-producing uropathogenic E. coli.

Place, publisher, year, edition, pages
London: BioMed Central, 2014
Keywords
Uropathogenic E. coli, Extended-spectrum beta-lactamase, Nitric oxide, Polymyxin B nonapeptide
National Category
Microbiology Medical and Health Sciences
Research subject
Microbiology
Identifiers
urn:nbn:se:oru:diva-35214 (URN)10.1186/1471-2180-14-65 (DOI)000335406100001 ()24629000 (PubMedID)2-s2.0-84899073270 (Scopus ID)
Note

Funding Agencies:

Swedish Council for Working Life and Social Research (FAS)

Nyckelfonden at Örebro University Hospital

Örebro University

Available from: 2014-06-03 Created: 2014-06-02 Last updated: 2018-06-07Bibliographically approved
Pradhan, A., Khalaf, H., Ochsner, S. A., Sreenivasan, R., Koskinen, J., Karlsson, M., . . . Olsson, P.-E. (2012). Activation of NF-kappa B Protein Prevents the Transition from Juvenile Ovary to Testis and Promotes Ovarian Development in Zebrafish. Journal of Biological Chemistry, 287(45), 37926-37938
Open this publication in new window or tab >>Activation of NF-kappa B Protein Prevents the Transition from Juvenile Ovary to Testis and Promotes Ovarian Development in Zebrafish
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2012 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 287, no 45, p. 37926-37938Article in journal (Refereed) Published
Abstract [en]

Testis differentiation in zebrafish involves juvenile ovary to testis transformation initiated by an apoptotic wave. The molecular regulation of this transformation process is not fully understood. NF-kappa B is activated at an early stage of development and has been shown to interact with steroidogenic factor-1 in mammals, leading to the suppression of anti-Mullerian hormone (Amh) gene expression. Because steroidogenic factor-1 and Amh are important for proper testis development, NF-kappa B-mediated induction of anti-apoptotic genes could, therefore, also play a role in zebrafish gonad differentiation. The aim of this study was to examine the potential role of NF-kappa B in zebrafish gonad differentiation. Exposure of juvenile zebrafish to heat-killed Escherichia coli activated the NF-kappa B pathways and resulted in an increased ratio of females from 30 to 85%. Microarray and quantitative real-time-PCR analysis of gonads showed elevated expression of NF-kappa B-regulated genes. To confirm the involvement of NF-kappa B-induced anti-apoptotic effects, zebrafish were treated with sodium deoxycholate, a known inducer of NF-kappa B or NF-kappa B activation inhibitor (NAI). Sodium deoxycholate treatment mimicked the effect of heat-killed bacteria and resulted in an increased proportion of females from 25 to 45%, whereas the inhibition of NF-kappa B using NAI resulted in a decrease in females from 45 to 20%. This study provides proof for an essential role of NF-kappa B in gonadal differentiation of zebrafish and represents an important step toward the complete understanding of the complicated process of sex differentiation in this species and possibly other cyprinid teleosts as well.

Place, publisher, year, edition, pages
The American Society for Biochemistry and Molecular Biology, 2012
National Category
Developmental Biology
Research subject
Biology
Identifiers
urn:nbn:se:oru:diva-32903 (URN)10.1074/jbc.M112.386284 (DOI)000310642200028 ()2-s2.0-84868315208 (Scopus ID)
Funder
Swedish Research CouncilKnowledge Foundation
Note

Funding Agency: Orebro University; Agri-Food and Veterinary Authority; Temasek Life Sciences Laboratory, Singapore (se även Forskningsfinansiärer)

Available from: 2014-01-02 Created: 2014-01-02 Last updated: 2018-11-29Bibliographically approved
Karlsson, M. & Laitila, T. (2008). A semiparametric regression estimator under left truncation and right censoring. Statistics and Probability Letters, 78(16), 2567-2571
Open this publication in new window or tab >>A semiparametric regression estimator under left truncation and right censoring
2008 (English)In: Statistics and Probability Letters, ISSN 0167-7152, E-ISSN 1879-2103, Vol. 78, no 16, p. 2567-2571Article in journal (Refereed) Published
Abstract [en]

An estimator is proposed for semiparametric linear regression models with left truncated and right censored dependent variables. The estimator is derived from a moment condition following the principles of Newey [Newey, W.K., 2001. Conditional moment restrictions in censored and truncated regression models. Econometric Theory 17, 863–888] on conditional moment conditions. Consistency of the estimator is shown and simulation is used for illustration of the small sample properties.

National Category
Probability Theory and Statistics
Research subject
Statistics
Identifiers
urn:nbn:se:oru:diva-5996 (URN)10.1016/j.spl.2008.06.009 (DOI)
Available from: 2009-03-11 Created: 2009-03-11 Last updated: 2017-12-13Bibliographically approved
Karlsson, M., Julander, A., van Bavel, B. & Hardell, L. (2007). Levels of brominated flame retardants in blood in relation to levels in household air and dust. Environment International, 33(1), 62-69
Open this publication in new window or tab >>Levels of brominated flame retardants in blood in relation to levels in household air and dust
2007 (English)In: Environment International, ISSN 0160-4120, E-ISSN 1873-6750, Vol. 33, no 1, p. 62-69Article in journal (Refereed) Published
Abstract [en]

Levels of tri- to decabrominated diphenyl ethers (BDEs), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and 1,2-bis(pentabromophenyl)ethane (DeBDethane) were determined in air, sedimentary dust and human plasma from five households in Sweden. The levels of the individual BDEs in the plasma samples were in the same order of magnitude as in other studies of the general population in Scandinavia, and varied between non-detectable (< 0.41 ng g− 1 l.w.) to 17 ng g− 1 (l.w.). BDE#28 and #47 were present in all air samples, with mean values of 0.015 and 0.12 ng m− 3, respectively, except for one sample where the BDE#47 concentration was below the limit of detection (< 0.17 ng m− 3). BDE#209 was found in one of the five air samples at a concentration of 0.26 ng m− 3. DeBDethane was also detected in one sample, in which the BDE#209 level was below LOD (< 0.021 ng m− 3), at a level of 0.023 ng m− 3. All the target compounds were found in the sedimentary dust samples at levels from 0.51 to 1600 ng g− 1, the highest concentration representing BDE#209. The most abundant components in plasma, air and dust were BDE#47, #99 and #209. In the plasma samples BDE#207 and #206 were also present at similar concentrations as BDE#47. In the sedimentary dust samples, DeBDethane was also among the most abundant BFRs. A positive relationship was found for the sumBDE concentrations in dust and plasma, although the relationship was strongly dependent on one of the five observations. BFR levels in dust and air were not dependent on the house characteristics such as living area, floor material or number of electronic devices.

National Category
Chemical Sciences Environmental Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3146 (URN)10.1016/j.envint.2006.06.025 (DOI)
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
Karlsson, M. (2006). Levels of brominated flame retardants in humans and their environment: occupational and home exposure. (Doctoral dissertation). Örebro: Örebro universitetsbibliotek
Open this publication in new window or tab >>Levels of brominated flame retardants in humans and their environment: occupational and home exposure
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plasma from workers at an electronic dismantling plant were analysed for tri- to heptaBDEs (brominated diphenyl ethers), during 18 months. The different exposed groups showed concentrations ranging from 0.06to 2.8 ng g-1 (l.w.). Only BDE #153 and #183 showed elevated levels compared to the general population in Sweden. The levels in the workers were approximately one order of magnitude higher. No clear trend of increased BDE levels was seen during the study period, nor was there a reduction of the plasma concentration during and after the vacation.

Air levels of tri- to decaBDEs, BTBPE (1,2-bis(2,4,6-tribromophenoxy)-ethane) and DeBDethane (1,2-bis(pentabromophenyl)ethane) ranging from 0.082 to 370 ng m-3 were determined at the same electronic dismantling facility. A comparison was made to the levels reported in this facility before an increase of the production volume. The levels of tri- to hexaBDEs, the main compounds in the commercial PentaBDE mixture, were very similar 2001-02 and 2005. Hepta- to decaBDEs, which are the main components in the Octa- and DecaBDE mixtures, were about three to five times higher in 2005 than in 2001-02. The mean level for BTBPE was two times higher 2001-02 while the concentration of DeBDethane measured 73 times higher 2005.

Levels of tri- to decaBDEs, BTBPE and DeBDethane were also determined in air, dust and human plasma from households. The levels of the individual BDEs in the plasma samples varied between <0.41 ng g-1 (l.w.) to 17 ng g-1 (l.w). BDE #28 and #47 were present in all air samples, with mean values of 0.015 and 0.12 ng m-3, respectively. BDE #209 was only found in one air sample at a concentration above the detection limit. DeBDethane was detected in only one sample, at a level of 0.023 ng m-3. All the analytes were found in the dust samples at levels ranging from 0.51 to 1600 ng g-1, the highest concentrations were found for BDE #209. DeBDethane was among the most abundant BFRs in the dust at a mean concentration of 47 ng g-1. The concentrations of the sumBDE showed a positive relationship in dust and plasma.

Eggs from Northern fulmars (Fulmarus glacialis) in the Faroe Islands were sampled for BFRs to establish the levels in remote regions. . The content of tri- to heptaBDEs, BDE #209 and BTBPE were determined in nine samples in concentrations ranging from non-detectable (< 0.02 ng g−1 l.w.) to 7 ng g−1(l.w.). BTBPE was detected in eight samples at a mean level of 0.11 ng g−1 (l.w).

All work included substantial method development and adaption of existing methods. Validation of a solid phase extraction (SPE) method to analyse tri- to heptabrominated diphenyl ethers in human plasma was performed. The SPE extraction method was found to be faster and less solvent- and sample-demanding, compared to the previously used open column extraction based method.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek, 2006. p. 75
Series
Örebro Studies in Chemistry, ISSN 1651-4270 ; 7
Keywords
PBDE, BTBPE, DeBDethane, plasma, air, dust, Northern fulmar, egg, household, occupational exposure
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-694 (URN)91-7668-499-7 (ISBN)
Public defence
2006-11-03, Hörsal P1, Prismahuset, Örebro universitet, Örebro, 13:00
Opponent
Supervisors
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-10-18Bibliographically approved
Karlsson, M., Ericson, I., van Bavel, B., Jensen, J.-K. & Dam, M. (2006). Levels of brominated flame retardants in Northern Fulmar (Fulmarus glacialis) eggs from the Faroe Islands. Science of the Total Environment, 367(2-3), 840-846
Open this publication in new window or tab >>Levels of brominated flame retardants in Northern Fulmar (Fulmarus glacialis) eggs from the Faroe Islands
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2006 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 367, no 2-3, p. 840-846Article in journal (Refereed) Published
Abstract [en]

Eggs from Northern Fulmars (Fulmarus glacialis) were sampled in the Faroe Islands. The content of the brominated flame retardants tri- to decabromodiphenyl ethers (BDEs) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) were determined in nine samples in concentrations ranging from non-detectable to 7 ng g− 1(l.w.). The BDE levels were similar as in an earlier study of BDE levels in the fulmar eggs from the Faroe Islands but 10–1000 times lower compared to studies of eggs from seabirds and birds of prey from Europe. The two hexaBDEs #153 and #154 were the most abundant congeners, which represented around 50% of the total mean BDE concentration. The levels of BDE #209 were below the limit of detection (1.24 ng g− 1 l.w.) except for one sample, which showed a concentration of 7.18 ng g− 1 l.w. BTBPE was detected in eight samples and the mean level was 0.11 ng g− 1 l.w. This concentration was 150 times lower than the average total BDE concentration (including BDEs #28, #47, #100, #99, #154, #153, #183, #209). BTBPE has only been detected once before in biota. Also other bromo-containing compounds were detected in the fulmar eggs. One group identified was the polybrominated biphenyls (PBBs), but because of the absence of reference standards in the lab, these could not be quantified.

National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3147 (URN)10.1016/j.scitotenv.2006.02.050 (DOI)
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
Julander, A., Karlsson, M., Hagström, K., Ohlson, C.-G., Engwall, M., Bryngelsson, I.-L., . . . van Bavel, B. (2005). Polybrominated diphenyl ethers: plasma levels and thyroid status of workers at an electronic recycling facility. International Archives of Occupational and Environmental Health, 78(7), 584-592
Open this publication in new window or tab >>Polybrominated diphenyl ethers: plasma levels and thyroid status of workers at an electronic recycling facility
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2005 (English)In: International Archives of Occupational and Environmental Health, ISSN 0340-0131, E-ISSN 1432-1246, Vol. 78, no 7, p. 584-592Article in journal (Refereed) Published
Abstract [en]

Objectives: Personnel working with electronic dismantling are exposed to polybrominated diphenyl ethers (PBDEs), which in animal studies have been shown to alter thyroid homeostasis. The aim of this longitudinal study was to measure plasma level of PBDEs in workers at an electronic recycling facility and to relate these to the workers’ thyroid status. Methods: PBDEs and three thyroid hormones: triiodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH) were repeatedly analysed in plasma from 11 workers during a period of 1.5 years.Results: Plasma levels of PBDEs at start of employment were <0.5–9.1 pmol/g lipid weight (l.w.). The most common congener was PBDE #47 (median 2.8 pmol/g l.w.), followed by PBDE #153 (median 1.7 pmol/g l.w.), and PBDE #183 had a median value of <0.19 pmol/g l.w. After dismantling the corresponding median concentrations were: 3.7, 1.7 and 1.2 pmol/g l.w., respectively. These differences in PBDE levels were not statistically significant. PBDE #28 showed a statistically significantly higher concentration after dismantling than at start of employment (P=0.016), although at low concentrations (start 0.11 pmol/g l.w. and dismantling 0.26 pmol/g l.w.). All measured levels of thyroid hormones (T3, T4 and TSH) were within the normal physiological range. Statistically significant positive correlations were found between T3 and #183 in a worker, between T4 and both #28 and #100 in another worker and also between TSH and #99 and #154 in two workers. Conclusions: The workers’ plasma levels of PBDEs fluctuated during the study period. Due to small changes in thyroid hormone levels it was concluded that no relevant changes were present in relation to PBDE exposure within the workers participating in this study.

National Category
Environmental Sciences Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3144 (URN)10.1007/s00420-005-0627-5 (DOI)15902483 (PubMedID)
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
Karlsson, M., Julander, A., van Bavel, B. & Lindström, G. (2005). Solid-phase extraction of polybrominated diphenyl ethers in human plasma: comparison with an open column extraction method. Chromatographia, 61(1-2), 67-73
Open this publication in new window or tab >>Solid-phase extraction of polybrominated diphenyl ethers in human plasma: comparison with an open column extraction method
2005 (English)In: Chromatographia, ISSN 0009-5893, E-ISSN 1612-1112, Vol. 61, no 1-2, p. 67-73Article in journal (Refereed) Published
Abstract [en]

A solid phase extraction (SPE) method in combination with silica gel cleanup to analyse tri-to heptabrominated diphenyl ethers in human plasma was validated. All congeners showed recoveries over 70% except for BDE #183, which showed recoveries around 45%. The method was tested on 21 individual plasma samples which were extracted with both the SPE method and an open column extraction method using Hydromatrix. Method detection limits were of the same order of magnitude for both methods, ranging from 0.0076 to 0.13 ng g−1 (l.w.) depending on the congener. The SPE extraction method meets the demand for a faster, less solvent-and sample-demanding method with lower contamination risk due to fewer steps compared to the open column extraction.

National Category
Chemical Sciences Natural Sciences
Research subject
Chemistry; Enviromental Science
Identifiers
urn:nbn:se:oru:diva-3143 (URN)10.1365/s10337-004-0461-z (DOI)
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-12-14Bibliographically approved
Karlsson, M., Julander, A. & van Bavel, B. Air levels of brominated flame retardants in an electronic dismantling facility after a production increase.
Open this publication in new window or tab >>Air levels of brominated flame retardants in an electronic dismantling facility after a production increase
(English)Manuscript (preprint) (Other academic)
National Category
Environmental Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3145 (URN)
Available from: 2006-10-13 Created: 2006-10-13 Last updated: 2017-10-18Bibliographically approved
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