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Biomedical subjects

L Blomqvist

Publications and source records attributed to L Blomqvist.

53 records · Page 3Linked to original sources
PubMed1992

Endogenous hypercholecystokininemia model in the hamster: trophic effect on the exocrine pancreas.

Using Syrian golden hamsters, we studied the effect of pancreaticobiliary diversion (PBD) on plasma cholecystokinin (CCK) and exocrine pancreatic tissue over 5, 10, and 24 days. As compared with sham-operated controls, PBD-operated animals had increased plasma CCK concentrations by 228, 318, and 207% at 5, 10, and 24 days, respectively. Correspondingly, pancreatic wet weight increased by 24, 61, and 87%; total pancreatic protein by 6, 57, and 73%; and total pancreatic DNA by 35, 52, and 98%, respectively. At 5 days, but not at 10 and 24 days, there was a significant increase in the pancreatic tissue DNA concentration (p less than 0.01) and [3]H-thymidine incorporation into DNA (p less than 0.02). Autoradiography showed increased [3]H-thymidine labeling index in acinar cells at 5 and 10 days after PBD (p less than 0.01 and p less than 0.005). Although not significant, ductal cell labeling index was also increased at 5 and 10 days. These findings provide evidence that, as in the rat, PBD in the hamster induces hypercholecystokininemia with ensuing pancreatic hyperplasia and hypertrophy. The hamster model may be useful for studies on the effect of endogenous CCK on pancreatic ductal cell carcinogenesis and diseases of the gallbladder, neither of which can be studied in the rat.

Animals↗
PubMed1991

Extravasation of staphylococcal alpha-toxin in normal and injured CNS regions lacking blood-brain barrier function: observations after ventral root replantation.

Staphylococcus aureus plays an important role as a bacterial pathogen after traumatic injury. The majority of isolated strains produces alpha-toxin, a 33-kDa protein, with membrane-damaging and lethal effects. The central nervous system (CNS) has been considered as the possible target for the lethal action of this toxin. A transfer of alpha-toxin across an intact blood-brain barrier (BBB) is however unlikely. The aim of the present study was to determine if alpha-toxin is accumulated in CNS regions which lack the BBB function. The distribution of alpha-toxin after intravascular injections, in normal mice and rats as well as in rats subjected to ventral root replantation, was assessed using immunogold technique. The results show that, although alpha-toxin does not cross the BBB, alpha-toxin-like immunoreactivity could be detected in the area postrema and at the optic nerve-retinal junction. Extravasation of alpha-toxin was also shown to occur in the spinal cord even 22 months after ventral root replantation. This finding suggests that axon regeneration after ventral root replantation takes place in a macromolecular environment which is totally different from the normal CNS. The implications of vascular spread of alpha-toxin to regions devoid of BBB function are discussed in relation to the bacterial infections which might complicate severe spinal injuries.

Animals↗
PubMed1991

Oligomerisation of cell-bound staphylococcal alpha-toxin in relation to membrane permeabilisation.

We have studied the kinetics of staphylococcal alpha-toxin oligomerisation in relation to membrane permeabilisation, using as targets cultured adrenocortical Y1 cells, rabbit red blood cells (RRBC), human platelets, and liposomes prepared of lipids extracted from platelets. After isolation of membranes from toxin-treated cells, oligomeric toxin was detected (i) by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) followed by autoradiography or Western blotting, and (ii) by electron microscopy of negatively stained specimens. alpha-Toxin was found to oligomerise on all membranes independently of the temperature. On RRBC and Y1 cells most of the membrane associated toxin appeared converted to the oligomeric form. Hexamers were always present along with membrane permeabilisation. However, hexamers were also detected at conditions when membrane permeabilisation did not occur; at low temperature, in the presence of high concentrations of Ca2+, and after pretreatment of cells with concanavalin A (Con A). Addition of a neutralising monoclonal antibody (MAb) to cell-bound toxin collected it into aggregates much larger than the hexamers. By contrast hexameric toxin remained after addition of a non-neutralising MAb. Our data suggest that the active toxin species is not monomeric, and support the hypothesis that alpha-toxin permeabilises membranes by forming hexameric protein-lined transmembrane channels.

Animals↗
PubMed1990

Long-term adjuvant tamoxifen in early breast cancer: effect on bone mineral density in postmenopausal women.

The decrease in sex steroid hormone levels after the onset of menopause is associated with bone loss and subsequent osteoporosis. Tamoxifen has antiestrogenic properties and may thus theoretically decrease bone mineral density, particularly after long-term treatment. Bone mineral density (BMD) was assessed in 75 recurrence-free postmenopausal breast cancer patients included in a randomized trial of adjuvant tamoxifen (40 mg daily) for 2 or 5 years versus no adjuvant endocrine therapy. The measurements were done about 7 years after the initial randomization. BMD was measured with single-photon absorptiometry (SPA) at two levels of the distal forearm representing cortical and trabecular bone. The BMD was found to be similar among tamoxifen patients compared with the controls. For cortical bone, the BMD was 1.03 g/cm2 (95% confidence interval [Cl], 0.97 to 1.09) among tamoxifen patients and 1.03 g/cm2 (95% Cl, 0.96 to 1.11) in controls. For trabecular bone, the values were 0.74 g/cm2 (95% Cl, 0.70 to 0.79) and 0.73 g/cm2 (95% Cl, 0.68 to 0.79), respectively. The results thus did not indicate an accelerated postmenopausal bone loss with long-term adjuvant tamoxifen.

Aged↗
PubMed1990

Proliferative response of different exocrine pancreatic cell types to hormonal stimuli. I. Effects of long-term cerulein administration.

The trophic effect on the exocrine pancreas of the cholecystokinin analogue cerulein was studied in a long-term experiment (20 or 160 micrograms/kg/24 h for 14 days) in mice by measuring changes in pancreatic weight and protein, amylase, and DNA content. Further, the selective cell growth stimulation exerted by various doses of cerulein (4, 20, 54, 160 micrograms/kg/24 h) on different exocrine pancreatic cell types was studied by continuous administration of 3H-thymidine. In the first experiment animals given 20 micrograms/kg/24 h of cerulein had increased pancreatic weight and amylase and protein content, whereas the animals given the higher dose had unchanged weight and a less pronounced increase in amylase and protein content. The pancreatic DNA content was unaffected in the 20-micrograms group but was clearly decreased by the higher dose. In the second experiment a statistically significant increase over controls was found in the fraction of labeled ductal cells when 20, 54, and 160 micrograms of cerulein was administered. However, in the acinar cell population an increase was measured only in the 160-micrograms group. A tendency to nadir in cell labeling was observed in both acinar and ductal cell groups at less stimulation. Labeling of centroacinar cells increased in all cerulein-treated groups. The results show that all cell types of the exocrine pancreas can be forced into proliferation by the cholecystokinin analogue used and that there is preferential cell growth stimulation in the ductal and centroacinar cell populations.

Amylases↗
PubMed1990

Proliferative response of different exocrine pancreatic cell types to hormonal stimuli. II. Effects of long-term secretin administration.

The effect of graded doses of secretin on exocrine pancreatic growth and cell proliferation was studied in a long-term experiment. After 16.5 and 150 micrograms/kg/24 h of secretin, each administered as two subcutaneous injections daily for 14 days, the pancreatic wet weight decreased, whereas the protein and DNA content of the gland was uninfluenced. When administered as described above for 14 days, 16.5, 50, 150, and 450 micrograms/kg/24 h of secretin did not affect the proliferation rate of ductal, acinar, or centroacinar cells as measured by a labeling index after 7 days of continuous 3H-thymidine administration. In the control groups a higher labeling index was found for ductal cells (19.9%) than for acinar cells (11.0%). During the 7 days of 3H-thymidine administration 80-90% of ductal and acinar cells remained in the G0 phase. There was a significantly higher labeling index in interlobular than in intralobular duct cells.

Amylases↗
PubMed1988

Staphylococcal alpha toxin--recent advances.

The elucidation of the amino acid sequence of alpha toxin in 1984 has greatly promoted our understanding of the basic biochemistry and interaction of this toxin with membranes. These aspects are discussed and the concept of alpha toxin as a channel forming protein is critically evaluated. The lethal action of alpha toxin has not yet been clarified, but the previously postulated action as a neurotoxin is not supported by recent observations.

Bacterial Toxins↗
PubMed1988

Production and characterization of monoclonal antibodies against Staphylococcus aureus alpha-toxin.

Murine monoclonal antibodies against staphylococcal alpha-toxin were produced using a well-characterized alpha-toxin fragment preparation as immunizing agent. Three monoclonal antibodies were selected for anti-alpha-toxin activity in an ELISA using alpha-toxin as antigen. The monoclonal antibodies (MAbs) belonged to different immunoglobulin classes/subclasses and showed different abilities to neutralize the hemolytic, cell-membrane-damaging, dermonecrotizing and lethal action of alpha-toxin. One MAb was superior to mouse polyclonal antiserum in all test systems except for hemolysis, whereas another MAb neutralized essentially as the polyclonal serum. The third MAb did not neutralize the hemolytic or dermonecrotic effect but still inhibited the lethal and membrane-damaging effect of alpha-toxin. These results indicate that the three MAbs recognize different epitopes on the toxin molecule and that different biological activities might correspond to these epitopes.

Animals↗
PubMed1988

Oligomerization of 3H-labelled staphylococcal alpha-toxin and fragments on adrenocortical Y1 tumour cells.

Staphylococcus aureus alpha-toxin has previously been shown to bind to erythrocyte membranes and the isolated membranes contain the toxin in both monomeric and hexameric form. The hexamers are believed to form the ring-shaped structures observed by electron microscopy on toxin-treated erythrocytes. It has not previously been shown that hexamers are formed also on nucleated mammalian cells although it has been assumed that hexamers in both systems create transmembrane channels, responsible for the toxin-induced membrane damage. Here we demonstrate by autoradiography that 3H-alpha-toxin bound to and formed high molecular weight complexes-presumably hexamers-on cultured adrenocortical Y1 tumour cells. The binding kinetics suggested a non-specific association of alpha-toxin with the membrane, rather than specific receptor-binding. The pH during toxin binding did not influence the subsequently induced membrane damage. Non-membrane damaging alpha-toxin fragment preparations also bound firmly to the cell membranes. Upon contact with Y1 cells the fragments formed complexes of the same apparent molecular size as those generated from intact alpha-toxin. Two interpretations are possible: either the fragment oligomers are somehow defective i.e. not able to form transmembrane structures or the functional relevance of toxin oligomerization for alpha-toxin-induced membrane damage must be questioned.

Adrenal Cortex↗
PubMed1987

Characterization of domain borders and of a naturally occurring major fragment of staphylococcal alpha-toxin.

A naturally occurring staphylococcal alpha-toxin fragment with an apparent membrane-binding capacity but without toxic activities is shown to be derived from the C-terminal half of the intact polypeptide chain by cleavage between position 134 and 135 in the parent molecule. The resulting N-terminus is slightly ragged with a fragment start not only at position 135 but also at the adjacent position 136. Another naturally occurring fragment starts at position 9, derived from an original cleavage between position 8 and 9 in the parent molecule. Analysis of non-purified fragment mixtures confirmed these positions and established that only one further region, at positions 71-72, is partly sensitive to proteolysis under natural conditions. Trypsin treatment has limited effects on the native toxin molecule, giving essentially only two initial cleavages with resultant large fragments. One of these cleavages is at the peptide bond between position 131 and 132, thus only three residues away from the position of the major naturally occurring cleavage. The other bond sensitive to trypsin is between position 8 and 9, thus identically positioned to the cleavage occurring naturally. Together, all the cleavages define a region in a central segment of the polypeptide chain that has all the properties of an inter-domain segment. The C-terminal half appears to constitute a membrane-binding domain, and the N-terminal half a structure needed for full biological activity, functionally subdividing the parent polypeptide chain.

Amino Acid Sequence↗
PubMed1987

Distribution of 3H-labeled staphylococcal alpha-toxin and a toxin fragment in mice.

Staphylococcal alpha-toxin and a toxin fragment were labeled with N-succinimidyl[2,3-3H]propionate. The labeled compounds retained greater than 95% biological activity. The distribution of labeled staphylococcal alpha-toxin and alpha-toxin fragment after intravenous administration to BALB/c mice was studied with whole-body and microautoradiography. The animals were divided into three groups that received (i) labeled alpha-toxin only, labeled alpha-toxin after prior injection of unlabeled fragment, or labeled fragment only. After 5 min, the distribution patterns were similar in groups 1 and 2, with the highest amounts of radioactivity found in the blood vessels, liver, spleen, lungs, and kidneys, whereas the labeled fragment alone showed no initial accumulation in the lungs. The kidneys continued to show a high concentration of radioactivity, whereas the levels at 60 min had decreased in the other organs. The toxin showed continued stable binding to the proximal tubuli, whereas the toxin fragment seemed to dissociate and was found only in small amounts in the glomeruli. No radioactivity was found in the central nervous system.

Animals↗
PubMed1986

Early events in the action of staphylococcal alpha-toxin on the plasma membrane of adrenocortical Y1 tumor cells.

The early events in staphylococcal alpha-toxin action on mouse adrenocortical (Y1) tumor cells were studied. Cell-bound toxin could be partially neutralized by anti-alpha-toxin and inactivated by trypsin added within 10 min at 37 degrees C after the end of the binding step. Likewise, cell-bound toxin was capable of lysing rabbit erythrocytes (RRBC) added to the cells within 10 min after binding at 37 degrees C. After this time, the Y1 cells could not be rescued from intoxication by antibodies or trypsin, and the toxin was not accessible for lysis of RRBC. However, at 0 to 4 degrees C, the cell-bound toxin remained accessible to antibodies for at least 4 h. CaCl2 (30 mM) did not affect binding of the toxin to Y1 cells but completely prevented the intoxication if added within 10 min at 37 degrees C after the end of the binding step. The intoxication was independent of metabolic energy, active receptor clustering on the cell surface, and endocytosis of the toxin. Therefore, alpha-toxin interacted with the Y1 cell membrane in at least three separable steps: binding, a conformational change at the cell surface, and membrane damage. These early events appear to be similar to those occurring on RRBC treated with alpha-toxin.

Adrenal Cortex Neoplasms↗
PubMed1986

A staphylococcal alpha-toxin fragment. Its characterization and use for mapping biologically-active regions of alpha-toxin.

A fragment (alpha-13) of Staphylococcal alpha-toxin was compared with intact alpha-toxin as regards biochemical and biological properties, and the resulting information was used for mapping biologically-active regions of alpha-toxin. The alpha-13 fragment had an apparent Mr of 18,500, judged by sodium dodecylsulphate polyacrylamide gel electrophoresis. However, it showed the same relative mobility as alpha-toxin when subjected to gel filtration on Biogel P60, high pressure liquid chromatography or electrophoresis on polyacrylamide gradient gel. The fragment had roughly the same specific hemolytic activity as intact alpha-toxin. In contrast to intact alpha-toxin, the fragment was neither membrane-damaging to mouse adrenocortical (Y 1) tumour cells nor lethal to mice. However, a short treatment of Y 1 cells with the fragment completely blocked intoxication by subsequently-added alpha-toxin. Likewise, the lethal effect of alpha-toxin was inhibited when the fragment was injected prior to the toxin. Thus, the fragment had lost the active region(s) responsible for Y 1 cell intoxication and lethality, while the region(s) for binding to these targets, as well as the region responsible for hemolysis, were retained. On the basis of these findings and previous reports concerning tryptic fragments of alpha-toxin, a hypothetical map of the different biologically-active regions of alpha-toxin was established.

Animals↗