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Biomedical subjects

R Blomhoff

Publications and source records attributed to R Blomhoff.

117 records · Page 7Linked to original sources
PubMed1983

Enhanced stability of beta-galactosidase in parenchymal and nonparenchymal liver cells by conjugation with dextran.

In order to enhance the stability of beta-galactosidase, we conjugated the enzyme with dextran T-10 (Mr approx. 10 000). The conjugate contained 9-10 mol dextran/mol protein (beta-galactosidase, Mr 68 000), and the specific activity retained after conjugation was 90 +/- 4% (n = 3) of the initial activity. Uptake and degradation of native and conjugated beta-galactosidase in isolated hepatocytes and nonparenchymal liver cells was studied. There was a marked increase in stability against degradation in both cell types when beta-galactosidase was conjugated with Dextran. The degradation of dextran-conjugated enzyme was reduced by 35% in hepatocytes and by 43% in nonparenchymal cells, after 80 and 40 min, respectively, as compared with the free enzyme. However, there was insignificant difference between the uptake of native and conjugated enzyme into the liver cells. Upon intravenous infusion into rats, native and conjugated enzyme were cleared from plasma with only a slight difference in the clearance rate. The observed stability of dextran-conjugated beta-galactosidase towards cellular degradation was in accordance with the in vitro experiments. The conjugate showed marked thermal stability at 50 degrees C and enhanced resistance towards proteolysis by the broad specific protease subtilopeptidase A. This demonstrates that dextran conjugation may be used as a means of stabilizing lysosomal enzymes for therapeutic purposes.

Animals↗
PubMed1982

Binding of calcium ions to the isolated asialo-glycoprotein receptor. Implications for receptor function in suspended hepatocytes.

The binding of calcium ions by the isolated asialoglycoprotein receptor of hepatocytes and the inter-relationship between the calcium ion concentration and receptor function have been studied. The isolated receptor binds calcium ions only in the presence of asialoglycoprotein. The asialo-glycoprotein receptor complex binds 4 calcium ions; the binding exhibits marked positive cooperativity, and the association constant at half-saturation of the binding sites was of the order of 10*5) M-1 as determined from a Hill plot. The isolated receptor was almost saturated at a calcium ion concentration of 0.1 mM. The binding capacity of isolated hepatocytes for asialo-glycoproteins increased, however, even when the calcium concentration was increased above this level. This may be explained by the exposure of increasing numbers of functional receptors on the surface of the cell with increasing membrane potential, and this explanation is supported by analogous observations in the presence of 5 mM La3+.

Animals↗
PubMed1982

In vivo uptake of chylomicron [3H]retinyl ester by rat liver: evidence for retinol transfer from parenchymal to nonparenchymal cells.

We have studied hepatic uptake of chylomicron retinyl ester. Chylomicrons were obtained from intestinal lymph of rats that were given retinol in groundnut oil by intraduodenal injection. When lymph was injected intravenously into normal rats, the radioactivity was cleared from blood with t1/2 approximately equal to 10 min. Retinyl ester was taken up initially by the liver, which, after 30 min, contained 80-90% of the radioactivity injected. Initially, most of the radioactivity was in hepatocytes, but after 30 min it disappeared from these cells and reappeared in nonparenchymal liver cells. After 2 hr these cells contained more radioactivity than the hepatocytes. When lymph was injected into vitamin A-deficient rats or rats given vitamin A in the form of retinoic acid, the plasma clearance and initial hepatic uptake of radioactivity were similar to that found in control animals. However, the nonparenchymal cells in these animals did not accumulate radioactivity. The current data suggest that vitamin A (in chylomicron remnants) is taken up initially by hepatocytes and then is released from these cells and delivered mainly to nonparenchymal liver cells in normal animals. In vitamin A-deficient rats, the vitamin is transferred from the hepatocytes to extrahepatic tissues.

Animals↗
PubMedDate not supplied

Vitamin A deficiency impairs colonic healing but not adhesion formation in germ-free and conventional rats.

Vitamin A is well recognized as a factor of major importance in epithelial and connective tissue repair mechanisms. Recently it was shown that vitamin A deficiency caused overgrowth and translocation of intestinal bacteria in rats. The aim of this study was to investigate the healing of colonic anastomoses and formation of postsurgical adhesions in vitamin A-deficient germ-free and conventional rats. Fourteen germ-free and 10 conventional rats were allocated to four groups: germ-free rats not given vitamin A, germ-free rats given vitamin A, conventional rats not given vitamin A, and conventional rats given vitamin A. All rats underwent surgery for colonic anastomosis. Seven days afterward, they were euthanized, and the bursting pressure of colonic anastomosis and formation of peritoneal adhesions were evaluated. The bursting pressures in groups not given vitamin A were lower than in groups given vitamin A. The adhesion scores in germ-free groups were lower than in conventional groups. These findings demonstrated that vitamin A had an important role in healing of colonic anastomoses whether in the presence or absence of intestinal flora, and that intestinal bacteria had a greater effect than vitamin A on formation of postsurgical adhesions. This may suggest that the mechanism of healing of colonic anastomoses differs from that of postsurgical adhesion formation.

Animals↗
PubMedDate not supplied

Cytotoxic effect of TNF-alpha and abnormal regulation of cAMP in the retinoid resistant cell line U937/GTB.

We have studied the effect of retinoids, forskolin and TNF-alpha on two sublines of U937 cells, U937/clone 4 and U937/GTB. Retinoids induced differentiation of U937/clone 4, while the U937/GTB cells were resistant to induction of differentiation by retinoids. Retinoids effectively reduced the proliferation of both U937/clone 4 and U937/GTB, and decreased the steady state levels of c-myc mRNA in both sublines. Furthermore, the retinoid resistant U937/GTB cells were hypersensitive to the cytotoxic effect of TNF-alpha. Forskolin increased the cAMP level in the U937/clone 4 cells 14 times above basal level, but did not change the cAMP concentration in the U937/GTB cells.

Cell Differentiation↗
PubMedDate not supplied

Effects of antiepileptics on the hepatic storage of retinol.

The effect of various antiepileptics on the retinol storage in rat liver was tested. We observed a dose- and time-dependent reduction in the hepatic storage of retinol after the administration of several of these drugs. Administration for 11 weeks of phenobarbital, primidone and carbamazepine in doses comparable to those used in humans reduced the retinol concentration in the Liver by 17-33% compared to control rats. The plasma retinol levels remained unaffected in all the rats. Plasma retinol from 31 epileptic children had plasma levels between 0.7 and 2.4 nmol/ml, which is regarded as normal.

Animals↗