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Biomedical subjects

G Bengtsson

Publications and source records attributed to G Bengtsson.

At least 37 records · Page 2Linked to original sources
PubMed1987

Radiation doses in Europe after the Chernobyl accident.

In the course of the reactor accident at Chernobyl in 1986, large amounts of radioactive materials were released and spread over all of Europe and the rest of the world. A comprehensive analysis of the resulting radiation doses is still in progress through the United Nations Scientific Committee on the Effects of Atomic Radiations. This review lists the most significant nuclides involved and the most significant pathways of exposure. Preliminary estimates of radiation doses made by various organisations are presented. Particular emphasis is given to the collective effective dose equivalent which is important for the assessment of the possible future incidence of leukemia and cancer from the accident. This quantity amounted to about 200,000 mansievert for Europe outside of the Soviet Union, and about twice as much for the European part of the Soviet Union, for the first 50 years after the accident. The uncertainty in these estimates should be less than a factor of three up or down. According to the hypothesis of a linear dose-effect relationship this dose could be calculated to result in 6000 extra cases of cancer and hereditary disease, 4000 of which would be fatal, during 100 years in Europe outside the Soviet Union.

Accidents↗
PubMed1987

Effect of phenobarbital on the distribution of drug metabolizing enzymes between periportal and perivenous rat hepatocytes prepared by digitonin-collagenase liver perfusion.

Intact periportal (pp) or perivenous (pv) hepatocytes were prepared by digitonin-collagenase liver perfusion. The degree of separation was indicated by significant differences between the pp and pv cells in their activity of the pp markers, alanine aminotransferase (pp/pv = 2.1), gamma-glutamyltranspeptidase (3.4) and lactate dehydrogenase (1.3), and of the pv markers, glutamate dehydrogenase (0.73) and pyruvate kinase (0.81). This pattern was not altered by a 3-day pretreatment with phenobarbital (PB). The hepatocytes isolated from the pv area contained higher activities of microsomal NADPH-cytochrome c reductase, 7-ethoxycoumarin O-deethylase, 7-ethoxyresorufin O-deethylase and benzo(a)pyrene hydroxylase, and of cytosolic glutathione transferase. Cytochrome P-450 and UDP-glucuronosyltransferase were slightly higher in pv cells. Treatment with PB induced NADPH-cytochrome c reductase, glutathione transferase, cytochrome P-450 and UDP-glucuronosyltransferase but the degree of induction was found to be at least as strong in pp cells as in pv cells. The induction of 7-ethoxyresorufin O-deethylase and 7-ethoxycoumarin O-deethylase was clearly more prominent in pp cells. On the other hand, PB reduced the activities of benzo(a)pyrene hydroxylase and alcohol dehydrogenase in both cell types. These results demonstrate by direct enzyme assay of separated cells the dominance of the pv-region for metabolizing drugs in the normal liver. Contrary to several other studies, however, our data indicate that induction by PB occurs panacinarily, i.e., relatively more in the pp region, thus diminishing rather than exaggerating the original pv dominance.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1984

Ethanol effects on protein synthesis in nonparenchymal liver cells, hepatocytes, and density populations of hepatocytes.

Rats were given ethanol chronically (20-30% of the energy) in a nutritionally sufficient diet regimen. Controls received lipid as an isoenergetic substitute for ethanol. Protein synthesis in hepatocytes isolated from ethanol-fed rats was decreased compared with controls, but not in isolated nonparenchymal liver cells. Ethanol added in vitro inhibited protein synthesis in hepatocytes by 30%, but not in nonparenchymal cells for both ethanol-fed and control rats. Protein export and protein degradation in isolated hepatocytes were not affected by long-term ethanol treatment. Isolated hepatocytes were separated according to their buoyant density in linear metrizamide gradients. They were distributed in a bell-shaped manner regardless of donor rat treatment. Cells of low density contained three times as much lipid as high density cells. They were probably enriched in periportal cells, since histologic examination indicated a predominantly periportal localization of cells containing lipid droplets. Distribution of the intra-acinar marker alanine aminotransferase supported this conclusion. Protein synthesis was similar in the low-density hepatocyte populations of the respective groups of rats, whereas it was inhibited in a high-density population of ethanol-treated rats compared to the controls. Inhibition of protein synthesis by 80 mM ethanol was lower in the low-density hepatocytes of ethanol-fed rats.

Alanine Transaminase↗
PubMed1984

Value of serum-5-nucleotidase, alkaline phosphatase and gamma-glutamyl transferase for prediction of liver metastases preoperatively in colorectal cancer.

In 133 patients laparotomized for colorectal cancer the serum-5-nucleotidase, alkaline phosphatase and gamma-glutamyltransferase were analysed preoperatively. The presence of liver metastases was established at laparotomy by palpation (prevalence 19%). The serum enzyme levels were elevated in 10-18% of patients without liver metastases and in 48-64% of patients with liver metastases. A comparison of the estimated tumor volume in the liver and the serum enzyme levels was performed. The predictive values of the three tests were computed at different reference limits. It was concluded that none of the tests used had any advantage of the other. To increase the diagnostic yield another reference limit than the normal at the laboratory can be used.

5'-Nucleotidase↗
PubMed1983

Immunochemical properties of lipoprotein lipase. Development of an immunoassay applicable to several mammalian species.

The reaction of bovine lipoprotein lipase with its antibodies was found to be conformation-dependent. One aspect of this was that most antisera were more reactive with denatured than with native 125I-labeled lipoprotein lipase. Another aspect was that denatured lipase did not compete effectively with native lipase for those antibodies which caused inhibition of the enzyme's activity. This latter observation leads to the conclusion that the inhibiting antibodies recognize conformation-dependent determinants on the native enzyme. Fab fragments prepared from an inhibiting antiserum blocked the binding of the lipase to triacylglycerol/phospholipid droplets. This suggests that the inhibition results from reaction of the antibodies with the enzyme as it exists in solution, either covering the lipid-binding site on the enzyme or making it impossible for the enzyme to go through the conformational transitions necessary for binding to lipid. Most rabbit antisera did not react with rat or mouse lipoprotein lipase, but some sera showed a weak cross-reaction. Antisera raised in hens showed a much stronger cross-reaction, enough to be useful for heterologous immunoassays. An immunoassay for the bovine lipase was developed. For reproducible results it was necessary to have tracer, standard and samples in denatured form. This was accomplished by heating them in SDS, and running the immunoreaction in a Triton X-100-containing medium.

Animals↗
PubMed1983

The effects of pH and salt on the lipid binding and enzyme activity of lipoprotein lipase.

This paper demonstrates a striking difference between the effects of salt and pH on the activity of lipoprotein lipase against two different substrates: Intralipid and bovine milk fat droplets. With the former substrate 1 M NaCl caused only a slight reduction in enzyme activity and the stimulation by apolipoprotein C-II was the same from 0.1 to 1.1 M NaCl. In contrast, 0.5 M or more NaCl virtually abolished the enzyme activity in the milk system. In this system the salt also abolished binding of the enzyme to the lipid droplets, whereas in the Intralipid system most of the enzyme remained bound even at 1 M NaCl. A similar picture was obtained with respect to effects of pH. In the milk system the activity decreased sharply at pH values above 8.5, whereas in the Intralipid system it continues to rise to pH 10, and the stimulation by activator protein is the same at all pH values. Correlating with this, the binding of the enzyme to the lipid droplets was highly dependent on pH values in the milk systems, with optimum binding around pH 8, whereas in the Intralipid system most of the enzyme remained bound to the lipid droplets at all pH values. These studies demonstrate that apolipoprotein C-II can activate lipoprotein lipase at a wide range of salt concentrations and of pH. They suggest that the well-known effects of high salt concentrations and of high pH to decrease lipoprotein lipase activity are exerted primarily on the enzyme itself.

Animals↗
PubMed1983

Activity of lipoprotein lipase in thyroidectomized rats.

Total plasma postheparin lipolytic activity as well as lipoprotein lipase activity in plasma was higher after heparin injection in thyroidectomized rats than in controls. In contrast, the activity of liver lipase was lower in thyroidectomized rats. Adipose tissue from thyroidectomized rats contained more lipoprotein lipase activity than adipose tissue from controls as measured both in extracts of tissue homogenates and medium from in vitro incubations of tissue pieces. There were no differences between control and hypothyroid rats in the disappearance of intravenously injected 125I-labeled lipoprotein lipase, but when a low dose of heparin was injected before the labeled enzyme, the disappearance of 125I-labeled lipoprotein lipase was more retarded in thyroidectomized rats. The elimination of heparin itself was slightly retarded by thyroidectomy.

Adipose Tissue↗
PubMed1982

On the pH dependency of lipoprotein lipase activity.

The relation between pH and activity for lipoprotein lipase against emulsions of long-chain triacylglycerols has previously been studied in several laboratories and found to be a bell-shaped curve with optimum activity between pH 8 and 9. In contrast, using short-chain triacylglycerols or monoacylglycerols as substrates we had found that the activity rises continuously with pH to at least pH 10.5. This suggested that some factor other than the active site mechanism limited the activity at high pH in traditional assay systems. We, therefore, reinvestigated the activity against long-chain triacylglycerols under conditions where binding of the enzyme to the emulsion droplets and enzyme stability was not limiting. Under these conditions the activity continued to rise from pH 8 to pH 10, and the degree of stimulation by apolipoprotein C-II was found to be the same over the whole range studied (pH 6.5-10.5).

Animals↗
PubMed1982

Purification and properties of lipoprotein lipase in guinea pig milk.

Lipoprotein lipase was purified from guinea pig milk by chromatography on heparin-Sepharose followed by chromatography on an immobilized preparation of heparin that had been N-desulphated and then acetylated. This second step was necessary to separate a plasma protein, presumably antithrombin, from the lipase. The guinea pig enzyme turned out to be quite similar to lipoprotein lipase from bovine milk with respect to composition and molecular size. Furthermore, the specific activities and the dose-response relations for activation by apolipoprotein C-II were quite similar for the two enzymes. Antibodies raised against the guinea pig milk enzyme inhibited not only this enzyme but also the lipoprotein lipase activity in post-heparin plasma and in homogenates from adipose tissue and heart.

Amino Acids↗
PubMed1982

Protein synthesis in different populations of rat hepatocytes separated according to density.

Hepatocytes were isolated from fasted rats by a two-step CA++-free/collagenase perfusion method. The cells were subjected to centrifugation under mild conditions at 12 degrees C in a linear metrizamide gradient (1.075-1.12 gm/cm3). The cells were distributed in the gradient in a bell-shaped manner. According to their position in the gradient the cells were divided in five different populations. The heaviest population was omitted from the subsequent evaluation because it contained a high proportion of dead cells. The activity of alanine aminotransferase increased with increasing cell density indicating that the lightest cell population was enriched in perivenous cells, whereas the heaviest cell population had an excess of periportal cells. Protein synthesis was more rapid in the light (perivenous) cell population than in the heavy (periportal) cell population as measured by means of incorporation of radioactively labeled valine into protein. The distribution measured in vitro indicated approximately 80% higher rates in perivenous cells. On the other hand, the synthesis and secretion of export proteins were similar in all cell populations regardless of their density. Protein degradation measured as appearance of free valine in cell media was higher in the light (perivenous) cell population than in the other populations. Thus protein metabolism seemed to be faster in the light cell population.

Alanine Transaminase↗
PubMed1982

Activator proteins for lipoprotein lipase from bovine plasma: preparation by adsorption to Intralipid.

A method has been developed for preparation from bovine plasma of the apolipoproteins which activate lipoprotein lipase. The method is based on the known ability of these proteins to transfer from the plasma lipoproteins to the lipid droplets of Intralipid. The protein lipid complexes were harvested and washed by low speed centrifugation, the proteins were then delipidated and separated by gel filtration in 6 M guanidine hydrochloride followed by anion exchange chromatography in 6 M urea. By this method batches of 5-1. bovine plasma can readily be processed, yielding about 20 mg of purified activators. These separated into three fractions, the properties of which suggest that they are isoproteins.

Adsorption↗
PubMed1982

Molecular properties of lipoprotein lipase. Effects of limited trypsin digestion on molecular weight and secondary structure.

The monomer molecular size of bovine lipoprotein lipase was evaluated by sedimentation equilibrium measurements and by gel permeation chromatography in 6 M guanidinium chloride. To establish molecular weight unequivocally we determined the partial specific volume (v) experimentally. This was done by analyzing equilibrium concentration profiles from analytical ultracentrifugation in 6 M guanidinium chloride using buffers made up in H2O and 2H2O. The combined results gave a v of 0.71 +/- 0.007 ml/g and a molecular weight of 41,700 +/- 1000 for monomeric bovine lipoprotein lipase. This value did not change upon mild tryptic digestion; the elution volume upon gel permeation chromatography in 6 M guanidinium chloride was also unaffected by treatment with trypsin. Sedimentation equilibrium measurements of the trypsin-treated material in the presence of reducing agents gave limiting molecular weights of 19,000 and 23,000, demonstrating that mild trypsin digestion cleaved lipoprotein lipase into two polypeptide chains of similar size held together by disulfide bonds. Mild trypsin digestion also resulted in a loss of secondary structure as determined by circular dichroic measurements. Discussion centers around the correlation between these effects of trypsin on the molecular properties of lipoprotein lipase and the previously reported effects on the kinetic properties of the enzyme.

Animals↗
PubMed1982

Transfer of human lymph chylomicron constituents to other lipoprotein density fractions during in vitro lipolysis.

To ascertain whether chylomicron constituents would be transferred to low density lipoprotein (LDL, d 1.019-1.063 g/ml) and high density lipoprotein (HDL, d 1.063-1.21 g/ml) density fractions during lipolysis in the absence of other lipoproteins, the in vitro effect of bovine milk lipoprotein lipase on human thoracic duct lymph chylomicrons in the presence of albumin was examined. In incubations without lipase, over 90% of chylomicron constituents remained in the 1.006 g/ml supernate, and large particles ranging in diameter mainly from 750-6000 A were observed by electron microscopy. After the addition of lipase, lipolysis ranged from 69.0-94.6% and numerous collapsed particles with redundant surface were seen, as well as smaller particles within the LDL and HDL density region. With lipolysis, the majority of chylomicron cholesterol and phospholipid mass was transferred to LDL and HDL, while chylomicron apolipoprotein (apo) A-I, A-II, and C-II mass was transferred mainly to HDL. Utilizing either radioiodinated apoA-I and apoA-II reassociated with chylomicrons or radiolabeled chylomicrons, a similar redistribution of apoA-I and apoA-II radioactivity was noted with lipolysis. In contrast, chylomicron apoB (mainly B-48) radioactivity was transferred predominantly to LDL with lipolysis. These data are consistent with the concept that during lymph chylomicron triglyceride hydrolysis, chylomicron apolipoproteins, cholesterol, and phospholipid can be transferred to the LDL and HDL density regions in the absence of acceptor particles.

Animals↗
PubMed1981

Demonstration of hepatic heparin-releasable lipase in the guinea-pig.

It was recently reported by Yamada et al. (Yamada, N., Murase, T., Akanuma, Y., Ikakura, H. and Kosaka, K. (1979) Biochim. Biophys. Acta 575, 128-134) that the guinea-pig has no hepatic heparin-releasable lipase. We have, however, found a low but definite lipase activity in guinea-pig post-heparin plasma with the characteristics of the hepatic lipase. This activity, as measured in our assay, is only about one-tenth of that in rat post-heparin in plasma. Although the activity is thus much lower than in some other animals, its presence demonstrates that the guinea-pig is not qualitatively but only quantitatively different in this respect.

Animals↗