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Biomedical subjects

A Johnsson

Publications and source records attributed to A Johnsson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Agravitropic behaviour of roots of rapeseed (Brassica napus L.) transformed by Agrobacterium rhizogenes.

Transgenic hairy roots of Brassica napus (cv. Omega) have been developed, using Agrobacterium rhizogenes strain AR 25, for use as a model system in the investigation of physiological and morphological differences between transgenic and normal roots. The basic parameters of growth and normal or altered gravitropical behaviour of hairy roots are for the first time presented in this paper together with an ultrastructural and morphological analysis of the root statocytes. The results obtained also represented the basis for the TRANSF0RM-experiment on the IML-2 mission performed onboard the Space Shuttle Columbia. Typical hairy root traits such as hormone-autonomous growth high growth rate, lateral branching, and changed/absence of gravitropism were detected. The transformed nature of the roots was confirmed by Southern blot analyses. The gravitropical behaviour of apices from hairy root cultures of this clone has been compared with root tips from normal seedlings. While the wild type roots curved progressively with increasing stimulation angles, the transformed roots showed no curvature when stimulated at 45 degrees, 90 degrees or 135 degrees on the ground. The morphology and ultrastructure of the root tip regions were examined by light microscopy and transmission electron microscopy. At the ultrastructural level no major differences could be detected between the roots studied. There was, however, a slight reduction in the starch content of most of the amyloplasts of the transgenic root tips, and the root cap was more V-shaped in the transgenic roots than in the wild type. Preliminary results from the Shuttle experiment TRANSFORM show a random distribution of amyloplasts in the root cells of both transformed and wild type root caps after 14 h on a 1xg centrifuge followed by 37 h in microgravity.

Agrobacterium tumefaciens↗
PubMed1996

Dynamics of root growth in microgravity.

An experiment to study the growth of garden cress roots in microgravity is described. The experiment, denoted RANDOM, was an ESA Biorack experiment in the IML-2 flight in July 1994. In the absence of gravity, it can be anticipated that the roots would show random growth, changing their direction randomly. The hypothesis that such random growth movements occur according to random walk theory, leads to predictions as to the detailed manner in which deviations increase with time. The experiment was designed to test this random walk hypothesis. The paper concentrates on the technological aspects of studying the roots in microgravity. The development of suitable plant chambers, fitting containers developed by ESA, is described as well as the techniques used to grow the seeds between agar slices. hardware was developed to record photographically root movements between the agar slices. Photos were taken once per hour. Some plant chambers were designed to allow fixation of plant material in space. The practical solutions found using glutaraldehyde for prefixation in the Spacelab, within the restrictions given, are described. The experimental results show that the growth pattern in fact followed the prediction from the random walk approach. The average changes in the growth direction stayed constant and equal to zero during the experiment while the squared angular deviations increased proportional to time. Furthermore, plant material prefixed in orbit was permanently fixed after the flight. Light microscopy and electron microscopy pictures are shown as examples of the results achieved. The long prefixation period meant a drawback for the quality of the fixation process. However, sections suitable for study were achieved. The main goals of the RANDOM experiment were therefore achieved.

Environment, Controlled↗
PubMed1996

The behaviour of normal and agravitropic transgenic roots of rapeseed (Brassica napus L.) under microgravity conditions.

In the TRANSFORM experiment for IML-2 on the Space Shuttle Columbia, normal (wild type = WT) and genetically transformed agravitropic rapeseed roots were tested under microgravity conditions. The aim of the experiment was to determine if the wild-type roots behaved differently (growth, morphology, gravitropical sensitivity) from the transgenic roots. The appearance of the organelles and distribution of statoliths (i.e. amyloplasts with starch grains) in the gravitropic reactive cells (statocytes) under weightlessness was compared for the two types of roots. Attempts have also been made to regenerate new plants from the root material tested in space. Both the WT and the transgenic root types showed the expected increase in length during 36 h of photorecording. Contrary to the results of the ground controls, no significant difference in elongation rates was found between the WT and transgenic roots grown in orbit. However, there are indications that the total growth both in the WT and the transgenic roots was higher in the ground control than for roots in orbit. After a 60 min 1 x g stimulation of the roots on board the Shuttle, no detectable curvatures were obtained in either the transgenic or the WT roots. However, it cannot be excluded that a minute curvature development occurs in the root tips but was not detected due to technical reasons. The ultrastructure was well preserved in both the WT and the transgenic roots, despite the fact that the tissue was kept in the prefixative for over 3 weeks. No marked differences in ultrastructure were observed between the transformed root statocyte cells and the equivalent cells in the wild type. There were no obvious differences in root morphology during the orbital period. Light micrographs and morphometrical analysis indicate that the amyloplasts of both the wild type and transformed root statocytes are randomly distributed over the cells kept under micro-g conditions for 37 h after a 14 h stimulation on the 1 x g centrifuge. The main scientific conclusion from the TRANSFORM experiment is that the difference in growth found in the ground control between the WT and the transgenic root types seems to be eliminated under weightlessness. Explanations for this behaviour cannot be found in the root ultrastructure or in root morphology.

Brassica↗
PubMed1996

Circadian locomotor activity of Musca flies: recording method and effects of 10 Hz square-wave electric fields.

Musca domestica flies that were exposed to a uniform vertical 10 Hz electric square-wave field of 1 kVm(-1) changed the period length of their circadian locomotor activity rhythm. Under constant conditions, the clock of short-period flies was slowed down by the field, whereas the clock of long-period flies either was affected only scarcely (experiments at about 19 degrees C) or ran faster (experiments at 25 degrees C). If the field was applied for only 12 h daily, then 30-40 percent of the flies were synchronized. Thus, the field could function as a weak "Zeitgeber" (synchronizer). If the field was increased to 10 kVm(-1), then 50-70 percent of the flies were synchronized. Flies avoided becoming active around the onset of the 12 h period of exposure to a 10 Hz field. The results of these experiments are discussed with respect to similar experiments by Wever on the effects of exposure to a 10 Hz field on the circadian system of man.

Animals↗
PubMed1996

Cisplatin pharmacokinetics and pharmacodynamics in patients with squamous-cell carcinoma of the head/neck or esophagus.

The pharmacokinetics of total platinum (Pt) in plasma and cisplatin (CDDP)-DNA adducts in different cell types were described in ten patients with squamous-cell carcinoma of the head/neck or esophagus after their first cycle of chemotherapy containing a CDDP dose of 100 mg/m2. Nephrotoxicity was studied in terms of urinary excretion of marker proteins (protein HC, IgG, and albumin). Pharmacodynamic relationships between pharmacokinetic parameters and toxicity were investigated. A population-based model with limited sampling was found feasible for producing pharmacokinetic information, in accordance with literature data. The kinetics of two normal cell types with different turnover (lymphocytes and buccal cells) appeared to have different kinetic profiles of CDDP-DNA adducts. Analysis of urinary excretion of marker proteins (protein HC, albumin, and IgG) showed that the nephrotoxicity was displayed first as tubular damage and later as impaired glomerular barrier function. There were indications that tubular nephrotoxicity may be predicted by pharmacokinetic parameters of plasma Pt. We found older patients to have a lower Pt clearance and more extensive early tubular damage. There was no correlation between CDDP-DNA adducts in normal cells and nephrotoxicity. Larger studies are warranted to define the pharmacokinetic window of CDDP. Limited sampling for analysis of CDDP pharmacokinetics may then be a possible avenue for individualizing the dose and, thus, improving the clinical use of the drug.

Adult↗
PubMed1996

A topographic study on the distribution of cisplatin in xenografted tumors on nude mice.

The intratumoral distribution of cisplatin was studied in terms of platinum concentrations in tissue pieces and immunohistochemically detected cisplatin-DNA adducts in xenografted tumors on nude mice. Heterogeneities in drug distribution were calculated as standard deviations and coefficients of variation. A three-dimensional image of adduct distribution was produced which showed regions with low adduct levels to be topographically connected also in three dimensions. A model was presented for investigating the potential influence of vascularization and cell proliferation on intratumoral adduct distribution by using different immunohistochemical stainings of parallel tissue sections. A weak but significant correlation was found between cisplatin-DNA adducts and proliferation, which might indicate that the drug uptake and adduct formation is increased in proliferating cells.

Animals↗
PubMed1996

Metoclopramide as a modulator of cisplatin: effects on pharmacokinetcs and cisplatin-DNA adducts in tumor and normal tissue.

The antiemetic drug metoclopramide (MCA) has previously been shown to cause DNA damage, to inhibit DNA repair and to enhance the effect of the chemotherapeutic agent cisplatin. Cisplatin acts by binding to DNA and thus forming cisplatin-DNA adducts. The present study was designed to investigate whether MCA affects the pharmacokinetics of cisplatin and the levels of cisplatin-DNA adducts in tumor and kidney. The effect on kidney is of special interest since cisplatin is highly nephrotoxic. Nude mice with xenografted squamous cell carcinoma where injected with cisplatin 5 mg/kg i.p. alone or in combination with MCA 2 mg/kp i.p. MCA was given 8 h after cisplatin. Total platinum was measured in serum and cisplatin-DNA adducts were analyzed in tumor and kidney with quantitative immunohistochemistry at 1, 9 and 24 h after cisplatin administration. The efficacy after treatment with cisplatin, MCA or cisplatin + MCA was studied in terms of tumor size measurements during 3 weeks following treatment and our previous observation that MCA enhances the cisplatin cytotoxicity was confirmed. The addition of MCA to cisplatin resulted in a slight increase in serum-platinum concentrations at 9 h and increased levels of adducts in tumors at 24 h. There was a tendency, however, not statistically significant, for increased adducts also in kidney. Thus, our findings may indicate that the sensitization of MCA on the cytotoxicity of cisplatin is mediated by increased formation, maybe accompanied by inhibited repair, of cisplatin-DNA adducts.

Animals↗
PubMed1996

Fifty-Hertz magnetic field exposures of premature infants in a neonatal intensive care unit.

In this study the magnetic flux density in and around incubators of a neonatal intensive care unit was registered and mapped. The mean 50-Hz magnetic flux densities in an incubator were typically in the range of 0.2-1 microT, with maximum values around 1.5 microT. For 1 incubator, harmonics contributed to the field substantially. The field levels varied depending on the type of equipment, the positioning of the electronics and the position of the 240-volt main plugs. The positioning of the infant in the incubator and the precise mattress position in the incubator affected the magnetic flux density to a great extent, as did the positioning of the electronic monitoring and treatment equipment. The flux density values found were fairly low as compared to magnetic field levels present at some work places where high electric currents are used. In intensive care units, however, the duration of exposure can be very long, especially for premature infants. The fields can also be compared with the magnetic field levels of residences and are then approximately 100 times higher. Further studies are necessary -it seems important to record magnetic fields and attempt to reduce the levels. Such a reduction can be achieved by reducing the field from the incubators but also by changing the electronic equipment around the incubators or increasing the distance to the incubator. Further research should of course also study any mechanism by which magnetic fields can affect cells and organisms. Compared to the risks many of these infants are exposed to, it is difficult to say whether the magnetic field levels measured can represent a significant additional risk factor. However, this is an area where one should adopt a prudent avoidance strategy, particulary considering how easily these fields can be reduced, mainly through redesign of the various equipment.

Environmental Exposure↗
PubMed1996

Random root movements in weightlessness.

The dynamics of root growth was studied in weightlessness. In the absence of the gravitropic reference direction during weightlessness, root movements could be controlled by spontaneous growth processes, without any corrective growth induced by the gravitropic system. If truly random of nature, the bending behavior should follow so-called 'random walk' mathematics during weightlessness. Predictions from this hypothesis were critically tested. In a Spacelab ESA-experiment, denoted RANDOM and carried out during the IML-2 Shuttle flight in July 1994, the growth of garden cress (Lepidium sativum) roots was followed by time lapse photography at 1-h intervals. The growth pattern was recorded for about 20 h. Root growth was significantly smaller in weightlessness as compared to gravity (control) conditions. It was found that the roots performed spontaneous movements in weightlessness. The average direction of deviation of the plants consistently stayed equal to zero, despite these spontaneous movements. The average squared deviation increased linearly with time as predicted theoretically (but only for 8-10 h). Autocorrelation calculations showed that bendings of the roots, as determined from the 1-h photographs, were uncorrelated after about a 2-h interval. It is concluded that random processes play an important role in root growth. Predictions from a random walk hypothesis as to the growth dynamics could explain parts of the growth patterns recorded. This test of the hypothesis required microgravity conditions as provided for in a space experiment.

Brassicaceae↗
PubMed1995

Pharmacokinetics and tissue distribution of cisplatin in nude mice: platinum levels and cisplatin-DNA adducts.

The pharmacokinetics of platinum (Pt) and cisplatin (CDDP)-DNA adducts were studied in nude mice after single-dose CDDP treatments. Whole blood, serum, kidney, lever, testis, brain, and tumor were collected at different intervals after injection of CDP at different dose levels. Pt was measured with flameless atomic absorption spectrometry (FAAS) or adsorptive voltammetry (AdV) and CDDP-DNA adducts with quantitative immunohistochemistry. The drug was immediately absorbed into the blood circulation (peak serum Pt levels were reached within 5 min) after i.p. CDDP administration, and distribution into most tissues also occurred rapidly (tissue Pt levels peaked at 15 min). With a sampling period of 7 days there was a biphasic elimination of Pt from blood, serum, and tissues. In the brain the pharmacokinetics differed with a gradual accumulation of Pt occurring during the 1st week. Formation of CDDP-DNA adducts in tissues was a slower process, with maximal levels being achieved at between 30 min and 4 h after drug administration, followed by a steady state lasting for at least 24 h. Each tissue type had its specific immunohistochemical staining pattern of adducts. With escalating CDDP doses there was a linear, or almost linear, increase in Pt concentrations and CDDP-DNA adduct levels in all sample types examined. These results suggest that a fair estimation of the amount of drug in tumor and normal tissues can be made from analysis of serum Pt at a fixed time point after a single dose of CDDP.

Animals↗
PubMed1995

Intracellular pH changes induced in Propionibacterium acnes by UVA radiation and blue light.

The intracellular pH changes induced in the Gram-positive skin bacterium Propionibacterium acnes by blue light and UVA radiation were studied. Two methods (31P nuclear magnetic resonance (NRM) spectroscopy and fluorescence spectroscopy using a pH-sensitive fluoroprobe (2',7'-bis-(2-carboxyethyl)-5-(and -6-)-carboxyfluorescein)) were used to determine the intracellular pH. The pH changes induced by irradiation were found to be a function of cell survival. These changes as a function of cell survival followed the same pattern for blue light and UVA radiation. A reduction of the pH gradient across the cell membrane (inside alkaline) was found for lethal doses (less than 15% survival). This reduction corresponded to a decrease in intracellular pH and may indicate a proton influx. An increase in the pH gradient, which corresponded to an increase in the intracellular pH, was observed for sublethal doses. This increase appears to be reversible. Thus two separate mechanisms, which appear to be the same in UVA and blue light regions, may be responsible for the irradiation-induced pH alterations.

Fluoresceins↗
PubMed1995

Can ultraviolet erythema be used to identify the basal cell carcinoma phenotype?

Since a prolonged duration of a strong UVB erythema has been suggested as a marker for propensity to develop skin cancer, we objectively followed the duration and intensity of erythemas induced by UVB and UVA radiation for 28 days in 18 patients with basal cell carcinoma (BCC), and in 15 healthy controls using reflectance spectrophotometry. The erythema index, defined as the difference in redness between UV-exposed skin and normal, adjacent skin on the lower abdomen, did not differ significantly between the two groups at 24 h, when the reaction was maximal, following a dose of 6 MED of UVB. Erythema values after 7 and 14 days were slightly higher in the BCC group, but this difference did not reach statistical significance. At day 7 some patients in the BCC group showed very strong erythemas. At days 21 and 28 the two groups had almost identical erythemal reactions. Following a standard dose of UVA of 100 J/cm2, patients with BCC and healthy controls both showed weak erythemal reactions, which declined somewhat over the study period. No significant differences in pigmentary response were noted between the BCC and the control group, neither following UVB nor UVA. Although individual patients with BCC deviate from the normal erythemal curve for UVB, the UVB response is not a suitable predictive instrument in screening patients with the basal cell carcinoma phenotype.

Basal Cell Carcinoma↗
PubMed1995

Gravitropic responses of the Avena coleoptile in space and on clinostats. I. Gravitropic response thresholds.

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g-force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow-speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.l and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostat experiments on earth using the same apparatus. Characteristic gravitropistic response patterns of Atuena were not substantially different from those observed in ground-based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than 0.1 g.

Acceleration↗
PubMed1995

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time. Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g-stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided. Plants at two stages of coleoptile development were tested. Plant responses were obtained using time-lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g-doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g-doses, chiefly because the data were more variable. It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm x t) with m-values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well-defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.

Acceleration↗
PubMed1994

Evaluation of a method for quantitative immunohistochemical analysis of cisplatin-DNA adducts in tissues from nude mice.

The reproducibility of an immunohistochemical method for visualization and quantitation of the cytotoxic drug cisplatin (CDDP) in its active position, bound to nuclear DNA, was investigated in tissues from CDDP-treated nude mice. Kidney, liver, and tumor sections were stained with a PAP technique using an antiserum elicited against CDDP-DNA adducts. The resulting brown nuclear precipitate was quantitated using a CAS 200 image analyzer. The variance components of the errors in the staining procedure and in the image analysis were estimated. The method was found to be feasible for comparisons between slides of the same type of tissue, stained in the same batch, and measured by one observer on one occasion. The method should be a valuable tool for studies of CDDP pharmacodynamics, sensitivity prediction, and the effects of interactions between CDDP and other drugs and chemomodulators.

Animals↗
PubMed1994

A study of the singularities in a mathematical model for circadian rhythms.

One of the models that has been suggested for describing circadian rhythms mathematically is an extension of the van der Pol equation given by ÿ + 0.5(y2 + y-2 - 3)y + (1 + 0.6 y) y = z + z + z, where y is the oscillating variable, and z is the light intensity assumed to excite the oscillator. In order for the equation to exhibit self-sustained oscillations, z has to be within the oscillatory range (0.847 < z < 3.189). This equation has been shown to simulate several of the features possessed by circadian systems (Wever, R., 1984, Toward a mathematical model of circadian rhythmicity, in: Mathematical Models of the Circadian Sleep-Wake Cycle, M.C. Moore-Ede and C.A. Czeisler (eds.) (Raven Press, New York) pp. 17-79). Physiological experiments have been performed which show that circadian rhythms can have stable singularities. Therefore, it was of interest to investigate whether or not the equation given above also has this property. We have studied the stability of the two singularities of the model system above. One of the singularities is unstable and corresponds to non-physiological conditions. The other one is an unstable spiral point if the light conditions are such that oscillations can occur in the system. We conclude that the model mentioned above is unsuitable to describe circadian systems which have stable singularities. The model has been simulated, and pulses have been applied to the system by temporarily changing the value of z to find appropriate conditions forcing the system into its singularity. The strategy to find such pulses is discussed.

Animals↗
PubMed1994

Using fura-2 to measure intracellular free calcium in Propionibacterium acnes.

The fluorescent probe fura-2 was used to measure the intracellular free calcium concentration [Ca2+]i in the Gram-positive skin bacterium Propionbacterium acnes. Three methods for loading the probe into P. acnes were used. Two consisted of using the membrane permeable acetoxymethyl ester of fura-2, fura-2/AM, whereas in the third method, fura-2 was loaded directly into the bacteria by means of an acid shock procedure. One method using fura-2/AM was found to be satisfactory. In this case, a statistical experimental design (2(4-1)IV) was used to devise a suitable loading procedure. [Ca2+]i of P. acnes was dependent upon the external calcium concentration. At low external concentrations (0.2 < [Ca2+]o < 5 muM), [Ca2+]i was 135 +/- 13 nM (n = 20). An increase in [Ca2+]o to 1mM resulted in an increase in [Ca2+]i to approximately 280 +/- 40 nM whereas in a Ca-free solution ([Ca2+]o < 5 nM), [Ca2+]i decreased to a lower resting value of 70 +/- 7 nM. The time constants for calcium regulation upon step changes in the external concentration were of the order of 10 min. Intracellular alkalinization induced by changes in the external pH (pHo) resulted in an increase in [Ca2+]i when [Ca2+]o was in the range 0.2-5 muM. [Ca2+]i was approximately constant in the range pHo 5.5-7.7 but increased when pHo > 8.0. This increase was partially reversed when pHo was again lowered to below 8.0. In a Ca-free solution, little or no increase in [Ca2+]i was observed when pHo > 8.0.

Calcium↗