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Biomedical subjects

A Berglund

Publications and source records attributed to A Berglund.

At least 37 records · Page 2Linked to original sources
PubMed1998

A new method for predicting the alignment of flexible molecules and orienting them in a receptor cleft of known structure.

It is not always easy to align flexible compounds with each other or with their binding cleft on a biological macromolecule, and the alignment of nine partly flexible molecules has now been studied. These compounds are heme analogues having either two or three flexible propionate side chains attached to a porphyrin core, and one compound is a close analogue of natural heme. The noncovalent interactions of each compound were predicted using a new version of the program Grid which can take account of the flexibility of the propionate side chains. The Grid results were then analyzed by hierarchical principal component analysis, and this allowed the molecules to be oriented with respect to each other. It also allowed each analogue to be correctly aligned with the receptor cleft for heme in myoglobin, because the alignment of natural heme in that cleft is already known. Factors influencing the predicted alignment are also considered.

Binding Sites↗
PubMed1998

Bolus injection (2-4 min) versus short-term (10-20 min) infusion of 5-fluorouracil in patients with advanced colorectal cancer: a prospective randomised trial. Nordic Gastrointestinal Tumour Adjuvant Therapy Group.

The use of bolus 5-fluorouracil (5-FU) as a short-term infusion over 10-30 min is increasing at the cost of a push injection, mainly due to practical advantages. Since even a short prolongation of the administration time results in lower 5-FU peak and area under the curve (AUC) levels, there might be a risk of decreased efficacy. The aim of this study was to compare a rapid intravenous (i.v.) 5-FU injection and a short-term 5-FU infusion with respect to objective responses and toxicity in patients with advanced colorectal cancer. 203 patients with measurable advanced colorectal cancer were randomised to bolus 5-FU either as an injection for 2-4 min or as a short-term infusion lasting 10-20 min. In both groups, the 5-FU dose was 500 mg/m2 and leucovorin 60 mg/m2 was given 40 min after the start of 5-FU. Treatment was given on two successive days every other week until progression. Objective tumour regression was seen in 27/100 (27%) in the injection group and in 13/103 (13%) in the infusion group (P = 0.02). Severe toxicity was rare and did not differ significantly between the groups. Progression-free survival tended to be longer in the injection group (P = 0.07), but overall survival did not differ between the groups. Bolus 5-FU should be administered as a rapid i.v. injection rather than as a short-term infusion, since the former rate of administration results in a higher response rate without being significantly more toxic.

Adult↗
PubMed1998

The impact of obstetric risk factors and socioeconomic characteristics on utilization of antenatal care.

BACKGROUND: The objective of the study is to assess the impact of obstetric risk status and defined risk factors on utilization of antenatal care in a Swedish county. METHODS: An area-based, population study was carried out with retrospective review of standardized patient records before (n = 2008) and after (n = 1874) the introduction of a reduced schedule for surveillance of pregnancy. For assessment of individual risk factors a multiple regression model is used. RESULTS: Overall the number of contacts per pregnancy decreased from 13.2 to 11.4. With the reduced routine programme the difference between low-risk and high-risk women increased from 1.1 to 2.7 visits on average. In the multiple regression model socioeconomic characteristics had little influence on the use of antenatal care. Previous obstetric complications increased compliance to the schedule after the programme change. Complications during current pregnancy were important for the number of extra visits planned by the staff. Self referrals were most influenced by symptoms but in-patient care was influenced by multiple factors. The total explanatory ability of the regression model was low for time of first visit to the antenatal care unit and referrals for ultrasound examinations. CONCLUSIONS: With a reduced routine programme the surveillance became better apportioned to obstetric risk. Even a combination of medical or obstetric risk factors with socioeconomic characteristics explain only part of the variation in utilization of antenatal care.

Adolescent↗
PubMed1998

Influence of low frequency magnetic fields on the intra-oral release of mercury vapor from amalgam restorations.

Since the results of a preliminary study have shown that the magnetic fields of some visual display units (VDUs) increased the release of mercury from amalgam specimens, the aim of the present study was to examine whether exposure to magnetic fields might affect the mercury vapor release from amalgam restorations in humans. The test group consisted of five subjects with an average of 31.4 amalgam surfaces (range 13-48). In each of the subjects tested, the intra-oral release of mercury vapor was measured during three 9-h periods at intervals of 30 to 90 min, using a standardized schedule and standardized food. During the first 9-h period which served as control, no intentional magnetic fields were applied. During the second and the third 9-h period, magnetic fields with flux densities of 20 microT at 30 kHz or 500 microT at 50 Hz, respectively, were applied. Although these flux densities were one thousand times higher than those caused by VDUs, no effects could be found on the release of mercury vapor from the amalgam restorations. The results of the present study do not support the assumption that exposure to magnetic fields increases the mercury vapor release from amalgam restorations in humans.

Adult↗
PubMed1997

Mercury levels in plasma and urine after removal of all amalgam restorations: the effect of using rubber dams.

OBJECTIVE: The aim of the present study was to determine whether removal of all amalgam restorations might significantly affect mercury levels in plasma and urine and whether the use of rubber dams might reduce patient exposure to mercury during amalgam removal. METHODS: All amalgam restorations were removed from 18 subjects during a single treatment session in which a rubber dam was used and from 10 subjects when a rubber dam was not used. All amalgam restorations were removed by the same dentist using high-speed cutting, water coolant, and high-volume evacuation. The levels of mercury in plasma and urine were analyzed both before and during the subsequent twelve months after amalgam removal. In order to determine whether removal of all amalgam restorations might cause an exposure large enough to significantly increase the mercury levels in two indicator media for mercury exposure, i.e., plasma and urine, and to determine if the removal might cause a significant decrease in the mercury levels found over time, the one-tailed, paired Students' t-test was used. For each individual, the pre-removal levels were compared with both the levels found in plasma on d 1 and in urine on d 10, and also with the levels found 1 y after removal. Furthermore, in order to examine whether the use of rubber dams had any effect on the mercury levels found after removal, the changes in the mercury levels found were compared between the groups using the Wilcoxon-Mann-Whitney rank sum test. RESULTS: After removal of all amalgam restorations, only the non-rubber dam group showed significant increases in the mercury levels found in plasma (p = 0.012) and urine (p = 0.037). However, one year later, the mercury levels in plasma and urine had sunk significantly below the pre-removal levels for both groups. When the changes in the mercury levels found were compared between the groups, the non-rubber dam group showed a significantly higher increase of mercury in plasma than the rubber dam group the day after removal (p = 0.0010). Compared to the pre-removal mercury levels in plasma and urine, the levels found 1 y after removal of all amalgam restorations were on average 52 +/- 23% (range 4-89%) lower in plasma and 76 +/- 21% (range 20-94%) lower in urine. SIGNIFICANCE: The study showed that dental amalgam had a statistically significant impact on the mercury levels found in plasma and urine in the patients tested, and that the use of a rubber dam during removal of all amalgam restorations significantly reduced the peak of mercury in plasma following removal.

Adult↗
PubMed1997

Alignment of flexible molecules at their receptor site using 3D descriptors and Hi-PCA.

Three categories of molecular flexibility are defined. A novel method of aligning partly flexible molecules with each other is described. The binding mode of one of these molecules to its receptor site was already well known from previous crystallographic studies, and this known binding mode was used to predict the binding mode of the other molecules at their receptor. The predictions were checked by comparison with previous observations, and were correct. Two novel methods were combined in this research. It was necessary to take account of the conformational changes which occur when each ligand molecule binds to the protein, and a new release of programme Grid was used for this. It was also necessary to analyse the Grid results in order to distinguish the role of each chemical group at the receptor site. This was done by applying hierarchical principal component analysis (Hi-PCA) methods to the descriptors obtained from Grid.

Binding Sites↗
PubMed1997

Neurophysiological effects of flickering light in patients with perceived electrical hypersensitivity.

An increasing number of people in Sweden are claiming that they are hypersensitive to electricity. These patients suffer from skin as well as neurological symptoms when they are near computer monitors, fluorescent tubes, or other electrical appliances. Provocation studies with electromagnetic fields emitted from these appliances have, with only one exception, all been negative, indicating that there are other factors in the office environment that can effect the autonomic and/or central nervous system, resulting in the symptoms reported. Flickering light is one such factor and was therefore chosen as the exposure parameter in this study. Ten patients complaining of electrical hypersensitivity and the same number of healthy voluntary control subjects were exposed to amplitude-modulated light. The sensitivity of the brain to this type of visual stimulation was tested by means of objective electrophysiological methods such as electroretinography and visual evoked potential. A higher amplitude of brain cortical responses at all frequencies of stimulation was found when comparing patients with the control subjects, whereas no differences in retinal responses were revealed.

Adult↗
PubMed1997

Connections between polarization curves and log(a[i]/a[ref])-pe diagram.

When reading papers concerning studies of corrosion of dental amalgam and its phases by means of polarization curves, one often finds it difficult to understand the reasons for the chemical reactions proposed from the form of the polarization curve. Thermodynamic data represented in the form of log(a[i]/a[ref])-pe diagrams, i.e., the logarithm of the activity of a metal or an alloy with reference to the activity of the corresponding metal ion, as a function of pe (a recalculated form of the potential), make it possible for one to determine which chemical reactions can occur on the specimen surface or in the solution within the potential difference used in the polarization experiment and to decide which of these reactions is the most probable. The hypothesis examined in this study is that a log(a[i]/a[ref])-pe diagram can be used in the interpretation of polarization curves. Potentiodynamic polarization curves and log(a[i]/a[ref])-pe diagrams were compared for the corrosion of Ag, Hg, and gamma 1 with and without Sn. It was found that there was a connection between the polarization curves and the log(a[i]/a[ref])-pe diagrams. From the composition of the specimens and the solution and by means of thermodynamic data, pe values for solid corrosion products and relative concentrations of soluble complexes at these pe values were obtained independently of the polarization curves. A much more reliable value for the nobility of metals and alloys was attained by use of the log(a[i]/a[ref])-pe diagrams than by use of the potential of the starting point of the polarization curves. It was found that pe corresponding to the potential of the starting point of the polarization curves in de-aerated synthetic saliva was obtained about two pe units before pe of the most insoluble solid compound formed on the specimen surface or in the solution.

Corrosion↗
PubMed1997

Mercury exposure from dental amalgam fillings: absorbed dose and the potential for adverse health effects.

This review examines the question of whether adverse health effects are attributable to amalgam-derived mercury. The issue of absorbed dose of mercury from amalgam is addressed first. The use of intra-oral Hg vapor measurements to estimate daily uptake must take into account the differences between the collection volume and flow rate of the measuring instrument and the inspiratory volume and flow rate of air through the mouth during inhalation of a single breath. Failure to account for these differences will result in substantial overestimation of the absorbed dose. Other factors that must be considered when making estimates of Hg uptake from amalgam include the accurate measurement of baseline (unstimulated) mercury release rates and the greater stimulation of Hg release afforded by chewing gum relative to ordinary food. The measured levels of amalgam-derived mercury in brain, blood, and urine are shown to be consistent with low absorbed doses (1-3 micrograms/day). Published relationships between the number of amalgam surfaces and urine levels are used to estimate the number of amalgam surfaces that would be required to produce the 30 micrograms/g creatinine urine mercury level stated by WHO to be associated with the most subtle, pre-clinical effects in the most sensitive individuals. From 450 to 530 amalgam surfaces would be required to produce the 30 micrograms/g creatinine urine mercury level for people without any excessive gum-chewing habits. The potential for adverse health effects and for improvement in health following amalgam removal is also addressed. Finally, the issue of whether any material can ever be completely exonerated of claims of producing adverse health effects is considered.

Absorption↗
PubMed1996

Mercury vapor release from dental amalgam in patients with symptoms allegedly caused by amalgam fillings.

The aim of this study was to determine whether a group of patients with symptoms, self-related to their amalgam restorations, experienced an exposure to mercury vapor from their amalgam restorations that reached the range at which subtle symptoms have been reported in the literature. Furthermore, the aim was to determine whether the mercury exposure for these patients was significantly higher than for controls with no reported health complaints. The symptom group consisted of 10 consecutively selected patients from a larger group, referred by their physicians for investigation into any correlation between subjective symptoms and amalgam restorations. The control group consisted of 8 persons with no reported health complaints. The intra-oral release of mercury vapor was measured between 7:45 a.m. and 9:00 p.m. at intervals of 30-45 min, following a standardized schedule. The mercury levels in plasma, erythrocytes, and urine were also determined. The calculated daily uptake of inhaled mercury vapor, released from the amalgam restorations, was less than 5% of the daily uptake calculated at the lower concentration range given by the WHO (1991), at which subtle symptoms have been found in particularly sensitive individuals. The symptom group had neither a higher estimated daily uptake of inhaled mercury vapor, nor a higher mercury concentration in blood and urine than in the control group. The study provides no scientific support for the belief that the symptoms of the patients examined originated from an enhanced mercury release from their amalgam restorations.

Adult↗
PubMed1995

CD45 phosphatase in Jurkat cells is necessary for response to applied ELF magnetic fields.

Oscillations of free intracellular calcium [Ca2+]i were seen in individual Jurkat cells as response to a 50 Hz, 0.15 mT magnetic field (MF). In contrast, a CD45-deficient Jurkat cell line was unable to respond to MF stimulation. The phosphatase activity of CD45 has been implicated to regulate p56lck tyrosine kinase activity by removing an inhibitory phosphate. By using Jurkat cells that expressed a chimeric molecule, comprising the cytoplasmic phosphatase domain of CD45, the MF induced calcium response was restored. This showed the necessity for an intact signal transduction pathway leading to a calcium increase as a result of stimulation of cells by MF. Thus, our data suggest that the target for the applied MF are molecules involved in early events in the signalling pathway from the T cell antigen receptor.

Antigens, CD↗
PubMed1995

Low frequency MFs increased inositol 1,4,5-trisphosphate levels in the Jurkat cell line.

We have earlier reported that when a weak 50 Hz MF (magnetic field) was applied, the leukemic T-cell line Jurkat responded with intracellular calcium oscillations [Lindström, et al., J. Cell Physiol., 156 (1993) 395-398]. The result suggested that the MF interfered with the signal transduction, although neither target molecules nor molecular mechanisms are at present known. In this study we found that application of a MF to Jurkat cells resulted in significant increase of inositol 1,4,5-trisphosphate (IP3) levels. Chelation of intracellular calcium ions by BAPTA/AM, did not block the increase of IP3 induced by MF. This result implied that MF-induced Ca2+ oscillations were not due to direct stimulation of the Ca(2+)-dependent phospholipase C-gamma 1 (PLC-gamma 1).

Calcium↗
PubMed1995

Intracellular calcium oscillations in a T-cell line after exposure to extremely-low-frequency magnetic fields with variable frequencies and flux densities.

Low-frequency magnetic fields (MF) can increase the cytosolic calcium concentration ([Ca2+]i) in lymphocytes in the same manner as a physiological stimulus such as antibodies directed towards the CD3 complex. In this study, MF with various frequencies and flux densities were used, while [Ca2+]i changes were recorded using microfluorometry with fura-2 as a probe. The applied sinusoidal MF induced oscillatory changes of [Ca2+]i in the leukemic cell line Jurkat in a manner similar to that seen with stimulation by antibodies. The response at 0.15 mT was over a frequency range from 5 to 100 Hz, with a fairly broad peak having its maximum at 50 Hz. The result of testing increasing flux densities at 50 Hz was a threshold response with no effect below 0.04 mT and a plateau at 0.15 mT. On the basis of the characteristic calcium pattern resulting from an applied MF, we suggest that MF influence molecular events in regular signal transduction pathways of T cells.

Antibodies↗