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Biomedical subjects

Ulrika Nilsson

Publications and source records attributed to Ulrika Nilsson.

12 recordsLinked to original sources
PubMed2005

Investigation of a cylindrical chemosorptive denuder for sampling and phase separation of toluene diisocyanate aerosols.

A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100-500 mL min(-1), the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley-Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour-particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 microg m(-3), 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m(-3) for both the vapour and the aerosol phases when LC-ESI-MS-MS was used for chemical analysis.

Adsorption↗
PubMed2005

A chemosorptive cylindrical denuder designed for personal exposure measurements of isocyanates-evaluation on generated aerosols of 4,4'-methylenediphenyl diisocyanate.

A denuder/filter system constructed for solvent-free personal exposure measurements was evaluated for separation of vapour and particulate 4,4'-methylenediphenyl diisocyanate (4,4'-MDI) generated from heated PUR-foam. The two different phases were collected in the denuder and on the filter, respectively, by chemosorption on a polydimethylsiloxane (SE-30)-dibutylamine (DBA) stationary phase. Both repeatability and the total mass concentration of 4,4'-MDI were similar to that obtained from the reference method, in this case an impinger/filter system. The penetration of particles through the denuder at 300 ml min(-1) was nearly 100% in the particle size range 25 to 700 nm, which fits well with the Gormley-Kennedy equation. Denuder/filter sampling of the 4,4'-MDI aerosol at 500 ml min(-1) yielded a phase distribution that was in accordance with the results from the reference method. The method limit of detection was 6 ng m(-3) and 4 ng m(-3) for the denuder and filter, respectively, when using an air sampling flow rate of 300 ml min(-1) and a sampling period of 15 min. This is well below the Swedish occupational exposure limit (OEL) of 50 and 100 microg m(-3) for an 8-hour working day and a 5-min period, respectively.

Adsorption↗
PubMed2004

Investigation of matrix effects of urine on a molecularly imprinted solid-phase extraction.

This study investigates matrix effects on a molecularly imprinted solid-phase extraction (MISPE) method developed for the clean-up of diphenyl phosphate (a hydrolysis product of the commonly used flame retardant and plasticizer, triphenyl phosphate) in urine samples. The influence of potentially interfering compounds that naturally occur in urine was examined with respect to extraction recovery, repeatability and selectivity. The components tested were NaCl, urea, creatinine and hippuric acid. The imprinted polymer was prepared using 2-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as crosslinker and a structural analogue of the analyte as the template molecule. The recovery of diphenyl phosphate from water standards was over 90% using MISPE, compared to less than 25% using a non-imprinted SPE (NISPE) counterpart. The selectivity of MISPE compared to NISPE was achieved in a wash step with a basic modifier in methanol. The recovery and repeatability of the MISPE method were affected most by NaCl in the tested concentrations, while urea, creatinine and hippuric acid had no significant influence. NaCl most likely weakens the binding during the loading of the sample. This effect could be suppressed by diluting the sample with a citrate buffer at pH 4.0.

Creatinine↗
PubMed2004

Dynamic field sampling of airborne organophosphate triesters using solid-phase microextraction under equilibrium and non-equilibrium conditions.

A simple setup for dynamic air sampling using a solid-phase microextraction (SPME) device designed for use in the field was evaluated for organophosphate triester vapour under both equilibrium and non-equilibrium conditions. The effects of varying the applied airflows in the sampling device were evaluated in order to optimise the system with respect to the Reynolds number and magnitude of the boundary layer that developed near the surface. Further, the storage stability of the analytes was studied for both capped and uncapped 100-microm PDMS fibres. Organophosphate triesters are utilized on large scales as flame-retardants and/or plasticizers, for instance in upholstered furniture. In indoor working environments these compounds have become common components in the surrounding air. Measurements were performed in a recently furnished working environment and the concentration of tris(2-choropropyl) phosphate was found to be 7 microg m(-3).

Air Pollutants, Occupational↗
PubMed2004

Evaluation of solid-phase microextraction with PDMS for air sampling of gaseous organophosphate flame-retardants and plasticizers.

As an inexpensive, simple, and low-solvent consuming extraction technique, the suitability of solid-phase microextraction (SPME) with polydimethylsiloxane (PDMS) sorbent was investigated as a quantitative method for sampling gaseous organophosphate triesters in air. These compounds have become ubiquitous in indoor air, because of their widespread use as additive flame retardants/plasticizers in various indoor materials. Results obtained by sampling these compounds at controlled air concentrations using SPME and active sampling on glass fibre filters were compared to evaluate the method. A constant linear airflow of 10 cm s(-1) over the fibres was applied to increase the extraction rate. For extraction of triethyl phosphate with a 100-microm PDMS fibre, equilibrium was achieved after 8 h. The limit of detection was determined to be less than 10 pg m(-3). The PDMS-air partition coefficients, Kfs, for the individual organophosphate triesters were determined to be in the range 5-60 x 10(6) at room temperature (22-23 degrees C). Air measurements were performed utilising the determined coefficients for quantification. In samples taken from a lecture room four different airborne organophosphate esters were identified, the most abundant of which was tris(chloropropyl) phosphate, at the comparatively high level of 1.1 microg m(-3). The results from SPME and active sampling had comparable repeatability (RSD less than 17%), and the determined concentrations were also similar. The results suggest that the investigated compounds were almost entirely associated with the gaseous phase at the time and place sampled.

Adsorption↗
PubMed2004

Air sampling of organophosphate triesters using SPME under non-equilibrium conditions.

Solid phase micro-extraction (SPME) was used to collect air samples of semi-volatile organophosphate triesters, a group of compounds that are commonly used as flame retardants/plasticisers and have therefore become ubiquitous indoor air pollutants. SPME is a simple sampling technique with several major advantages, including time-efficiency and low solvent consumption. Analyte losses also tend to be relatively low. In quantitative SPME, measurements are normally taken after the analyte has reached partitioning equilibrium between the fibre and the sample matrix. However, equilibrium sampling of semi-volatile compounds in air with SPME often takes several hours. Clearly, time-weighted average (TWA) sampling using SPME under non-equilibrium conditions could be considerably faster. So, in this study, the possibility of sampling organophosphate triesters under non-equilibrium conditions was tested. The most important variables proved to be the fibre coating and the air velocity during sampling. The highest uptake rate was obtained with polydimethylsiloxane (PDMS, 100 microm). The rate for this fibre was 150-fold higher than obtained with PDMS/DVB and Carbowax/DVB, both 65 microm. Contrary to theoretical expectations, the uptake rate appeared to be constant for all tested air velocities over the fibre surface >7 cm/s. These findings suggest that the uptake rate for non-equilibrium SPME sampling is independent of the sampling flow above this flow rate, which would considerably enhance the robustness and flexibility of the method. Applying this method for TWA sampling, with sampling periods of 1 h, detection limits lower than 2 ng/m(3) for individual organophosphate esters were obtained.

Journal Article↗
PubMed2004

Selective determination of organophosphate flame retardants and plasticizers in indoor air by gas chromatography, positive-ion chemical ionization and collision-induced dissociation mass spectrometry.

Gas chromatography/ion trap mass spectrometry with in-source ionization and dissociation was used in positive-ion chemical ionization (PICI) mode for the determination of organophosphate triesters in indoor air. These compounds are widely used as additive flame retardants and plasticizers in different types of materials and have become ubiquitous pollutants in indoor environments. When using collision-induced dissociation in PICI mode the fragmentation of the organophosphate triesters can be performed in a more controllable way than in electron ionization (EI) mode. The developed selected-reaction monitoring method provided high selectivity for the investigated compounds. For 8-h air measurements (corresponding to 1.5 m3 of sampled air) the limit of detection of the method was determined to be in the range 0.1-1.4 ng m(-3), which is comparable with nitrogen-phosphorus detection and about 50-fold lower than when using EI in selected-ion monitoring mode. The presented method was applied to samples from three common indoor environments, in which a number of organophosphate triesters were identified and quantified. The dominating compound was found to be tris(2-chloropropyl) phosphate, which occurred at levels up to 0.8 microg m(-3).

Journal Article↗
PubMed2003

Effects of aging and ischemia on adenosine receptor transcription in mouse myocardium.

The well-documented age-related change in ischemic tolerance may result from impaired adenosine-mediated cardioprotection. Additionally, ischemia itself may potentially modify adenosine signalling, contributing to the post-ischemic phenotype. This study investigates age- and ischemia-dependent changes in adenosine receptor transcript levels (Adora) for the A(1), A(2A), A(2B), and A(3) receptor subtypes in mouse myocardium. Hearts from young (2-4 months) and moderately aged (16-18 months) mice were subjected to 20-min ischemia and 45-min reperfusion. Ischemic tolerance was impaired in aged hearts, which recovered less than 30% ventricular pressure development (compared with approximately 70% in young hearts), and lost 2-fold higher levels of lactate dehydrogenase during reperfusion (reflecting cellular disruption). Real-time PCR analyses revealed an age-related decline in Adora3 levels and induction of Adora2B. Curiously, this effect was mimicked by ischemia, which acutely reduced Adora3 levels and induced Adora2B in young (but not old) hearts. In contrast, in aged hearts ischemia selectively reduced levels of Adora1 transcript ( approximately 2-fold) without altering transcript levels for the other receptors. These results demonstrate selective modulation of cardioprotective adenosine receptor transcription by both aging and ischemia. Reduced A(3) adenosine receptor transcription may contribute to impaired ischemic tolerance in aged hearts, whereas changes in Adora transcription induced by ischemia may impact on the post-ischemic phenotype at later time points.

Adaptation, Physiological↗
PubMed2003

Determination of a flame retardant hydrolysis product in human urine by SPE and LC-MS. Comparison of molecularly imprinted solid-phase extraction with a mixed-mode anion exchanger.

Diphenyl phosphate is a hydrolysis product and possible metabolite of the flame retardant and plasticiser additive triphenyl phosphate. A molecularly imprinted polymer solid-phase extraction (MISPE) method for extracting diphenyl phosphate from aqueous solutions has been developed and compared with SPE using a commercially available mixed-mode anion exchanger. The imprinted polymer was prepared using 2-vinylpyridine (2-Vpy) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, and a structural analogue of the analyte as the template molecule. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with both aqueous standards and spiked urine samples, by comparing recovery and breakthrough data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from aqueous solutions resulted in more than 80% recovery. Adsorption by the molecularly imprinted polymer (MIP) was non-selective, but selectivity was achieved by selective desorption in the wash steps. Diphenyl phosphate could also be selectively extracted from urine samples, although the urine matrix reduced the capacity of the MISPE cartridges. Recoveries from urine extraction were higher than 70%. It was important to control pH during sample loading. The MISPE method was found to yield a less complex LC-ESI-MS chromatogram of the urine extracts compared with the mixed-mode anion-exchanger method. An LC-ESI-MS method using a Hypercarb LC column with a graphitised carbon stationary phase was also evaluated for organophosphate diesters. LC-ESI-MS using negative-ion detection in selected ion monitoring (SIM) mode was shown to be linear for diphenyl phosphate in the range 0.08-20 ng microL(-1).

Anion Exchange Resins↗
PubMed2002

Low striatal and extra-striatal D2 receptor occupancy during treatment with the atypical antipsychotic sertindole.

RATIONALE: Sertindole is a new atypical antipsychotic drug. Preclinical pharmacology suggests that sertindole has a preferential effect on the activity of limbic and cortical dopaminergic neurons. Clinical trials have shown antipsychotic efficacy and very few extrapyramidal symptoms (EPS) with sertindole at 20 mg/day. OBJECTIVES: This positron emission tomography (PET) study aimed to measure D(2) receptor occupancy in striatal and extra-striatal regions induced by clinically representative doses of sertindole in patients with schizophrenia. METHOD: Four stabilized schizophrenic out-patients received sertindole 20 mg/day for 6-8 weeks. PET was performed using [(11)C]raclopride to measure D(2) receptor occupancy in the striatum and [(11)C]FLB457 to measure occupancy in the neocortex and thalamus, i.e. regions with very low D(2) receptor density. RESULTS: Striatal D(2) receptor occupancy was 52-68%. Similar occupancies were found in the thalamus, and the temporal and frontal cortices. CONCLUSIONS: Sertindole appears efficacious at a low D(2) receptor occupancy, comparable to that produced by clozapine. This finding could explain the low risk of EPS. The functional limbic selectivity of sertindole was not reflected in regional differences in receptor occupancy.

Adult↗
PubMed2001

Genetic localization and regulation of the maltose phosphorylase gene, malP, in Lactococcus lactis.

Maltose phosphorylase (MP) from Lactococcus lactis was purified and the corresponding gene was cloned and expressed in Escherichia coli. The isoelectric point of the pure enzyme was determined to be 7.0. According to zymogram analysis and SDS-PAGE, the native MP was shown to be a monomeric enzyme with a molecular mass of 75 kDa. A polyclonal antiserum was produced to assess the regulation of the gene encoding MP in LC: lactis. According to immunoblot analysis, synthesis of the enzyme was markedly repressed by both glucose and lactose in the growth medium. When the lactococci were cultivated in the presence of other sugars, including maltose, trehalose or galactose, there was a pronounced expression of the MP gene. In addition, when the cells were grown in media without any added sugar, there was also pronounced expression of the enzyme, according to immunoblot analysis and specific activity data. These results indicated that no particular sugar specifically induces the gene encoding MP. However, an effect of glucose on MP expression was demonstrated by performing fermentations in the presence of both maltose and glucose. When glucose was added to maltose-grown lactococci in the mid-exponential growth phase, both the specific activity and amount of MP per millilitre of cell extract decreased rapidly. The genetic locus for the MP gene was found to be in the vicinity of the region encoding a possible regulator belonging to the LacI-GalR family of transcriptional regulators. Furthermore, this genetic location was separated from the previously characterized maltose-inducible and glucose-repressible beta-phosphoglucomutase (beta-PGM) gene. The different genetic loci for the genes encoding MP and beta-PGM explains the different gene regulation behaviour.

Amino Acid Sequence↗