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M Rudling

Publications and source records attributed to M Rudling.

At least 55 records · Page 3Linked to original sources
PubMed1995

Studies on lipoprotein metabolism in a family with jejunal chylomicron retention.

We describe two siblings with fat malabsorption and jejunal chylomicron retention. Plasma lipoproteins were studied in the patients and their first-degree relatives. The patients were a 14-year-old girl and her 8-year-old brother. Compared to healthy controls, they both had low fasting plasma concentrations of plasma total, HDL, and LDL cholesterol, as well as of apolipoproteins A-I and B. No increase in plasma lipoprotein levels or detectable apo B-48 was observed following an oral fat load. Histological studies of jejunal biopsy specimens obtained during fasting and 1 h postprandially showed severe steatosis, and an apparent block of chylomicron secretion from the endoplasmic reticulum into the Golgi apparatus was observed by electron microscopy. Liver biopsy specimens showed moderate steatosis and ultrastructural changes similar to those in the enterocytes. One healthy sister had a normal plasma lipoprotein pattern, and showed increased plasma triglyceride levels as well as the presence of apo B-48 following an oral fat load. Both parents had normal plasma total cholesterol levels, but clearly reduced fasting concentrations of HDL cholesterol and apo A-I. At least in this family, determination of plasma apo A-I levels might thus prove useful in the identification of heterozygotes.

Adolescent↗
PubMed1995

Growth hormone specifically stimulates the expression of low density lipoprotein receptors in human hepatoma cells.

Human GH (hGH) has been shown to stimulate hepatic low density lipoprotein (LDL) receptor expression in man in vivo. To further characterize this effect in vitro, we determined the expression of LDL receptors in cultured human hepatoma (HepG2) cells exposed to hGH. After incubation with hGH, stimulation of LDL receptors appeared at a concentration of 0.25 nM hGH. The presence of hGH receptors on HepG2 cells could be demonstrated by immunocytochemistry using a hGH receptor-specific monoclonal antibody. Binding studies, using 125I-labeled hGH, revealed high affinity binding with the appropriate somatogenic specificity. The LDL receptor induction was specific for hGH, as both bovine GH and recombinant human PRL were without effect. The LDL receptor stimulation occurred in parallel with increased levels of LDL receptor messenger RNA. Inclusion of dexamethasone and thyroid hormone in the incubation medium enhanced the LDL receptor stimulation by hGH. Although incubation with insulin-like growth factor-I (IGF-I) stimulated LDL receptor expression, the hGH-induced stimulation was unaltered after preincubation of cells with a monoclonal mouse anti-IGF-I antibody, suggesting that the release of IGF-I is not involved in LDL receptor stimulation by hGH. We conclude that hGH specifically induces the LDL receptor in cultured HepG2 cells at both the protein and the messenger RNA level, and that the induction is independent of IGF-I release.

Carcinoma, Hepatocellular↗
PubMed1995

Effects of stigmastanyl-phosphocholine (Ro 16-6532) and lovastatin on lipid and lipoprotein levels and lipoprotein metabolism in the hamster on different diets.

Previous studies from our laboratory have shown that oral administration of stigmastanyl-phosphocholine (Ro 16-6532) reduces plasma cholesterol levels in experimental animals on diets free of added cholesterol. In the present study, effects of Ro 16-6532 and lovastatin on lipoprotein levels and metabolism were investigated in male golden Syrian hamsters. In hamsters fed a standard diet, Ro 16-6532 (1 mmol/kg/day) lowered cholesterol in all lipoprotein fractions, as well as apoB-100 and apoA-I. In contrast, lovastatin (25 mumol/kg/day) lowered high density lipoprotein (HDL)-cholesterol but had no effect on low density lipoprotein (LDL)-cholesterol or on apoB-100 or apoA-I while triglycerides and very low density lipoprotein (VLDL)-cholesterol increased. In hamsters fed a coconut fat-supplemented diet, Ro 16-6532 reduced all lipoproteins, with a stronger effect on VLDL- and LDL- than on HDL-cholesterol. Also apoB-100 was reduced. Lovastatin (50 mumol/kg/day) reduced LDL-cholesterol, HDL-cholesterol, and apoA-I while triglycerides and VLDL-cholesterol increased. The drop in LDL-cholesterol seen with both drugs in hamsters fed the diet supplemented with coconut fat occurred without any effect on the plasma removal rate of homologous LDL, or on the content of hepatic LDL-receptors. In contrast, the first phase of removal of homologous radioiodinated VLDL from plasma was markedly increased by both compounds, paralleled with an increased uptake of label in the liver and a decreased appearance of labeled apoB-100 in the LDL-fraction. Furthermore, retinyl ester-labeled chylomicrons were also cleared more rapidly in hamsters treated with Ro 16-6532. Hepatic uptake of label from VLDL and chylomicrons was strongly decreased by pre-injection of lactoferrin. In addition, Ro 16-6532 slightly decreased the secretion rate of VLDL in hamsters fed the coconut fat-supplemented diet. Taken together, these results indicate that the reduction of LDL-cholesterol after treatment with Ro 16-6532 and lovastatin observed in the hamster is mainly due to decreased conversion of VLDL into LDL, consequent to an increased hepatic removal of VLDL remnants. Ro 16-6532 also increased the liver uptake of chylomicron remnants. The hepatic uptake system implicated in this remnant removal can be completely blocked by lactoferrin. The nature of this uptake system is still unknown.

Animals↗
PubMed1994

Presence of cholesterol 7 alpha-hydroxylase enzyme protein in COS-cells leads to increased HMG CoA reductase activity.

Transfection of COS-cells with a cDNA coding for human cholesterol 7 alpha-hydroxylase resulted in significant production of cholesterol 7 alpha-hydroxylase enzyme and intracellular accumulation of the product, 7 alpha-hydroxycholesterol. Presence of this enzyme activity was always associated with increased HMG CoA reductase activity. In five different independent transfection experiments resulting in a cholesterol 7 alpha-hydroxylase activity of 0.26 +/- 0.05 pmol/min/mg in the transfected cells, the HMG CoA reductase activity increased to 158 +/- 14% of that of the control cells (p < 0.01). This change was not associated with significant changes in the cholesterol content or LDL-receptor expression of the COS-cells. It is evident that the two key enzymes in cholesterol synthesis and degradation interact with each other also in extra-hepatic cells that are unable to degrade cholesterol into bile acids. Possible mechanisms for the finding is discussed.

Animals↗
PubMed1994

Growth hormone and hepatic lipoprotein metabolism.

Growth hormone (GH) has significant effects on hepatic lipoprotein metabolism, stimulating triglyceride biosynthesis, secretion of VLDL, apolipoprotein (apo)E, and the editing of apoB while simultaneously increasing the expression of LDL receptors. Clinical observations support the concept that GH may have a protective role in the prevention of atherosclerosis, and treatment with GH could thus be beneficial in states of GH deficiency.

Animals↗
PubMed1993

Loss of resistance to dietary cholesterol in the rat after hypophysectomy: importance of the presence of growth hormone for hepatic low density lipoprotein-receptor expression.

This investigation was undertaken to determine the role of pituitary function and, in particular, the possible influence of growth hormone (GH) on hepatic low density lipoprotein (LDL)-receptor expression in response to dietary cholesterol. Feeding normal rats with 2% cholesterol for 5 or 6 days did not alter LDL-receptor numbers, LDL-receptor mRNA levels, or plasma cholesterol, although hepatic cholesterol increased 5-fold. When hypophysectomized rats received the same diet, the LDL-receptor number and its mRNA levels were reduced by 75%, plasma cholesterol increased 6-fold, and hepatic cholesterol increased 12-fold. Stepwise hormonal substitution of cholesterol-fed, hypophysectomized rats revealed that substitution with GH was important to restore hepatic LDL-receptor number and mRNA levels. The presence of GH was also important to reduce the hypercholesterolemia in cholesterol-fed hypophysectomized rats. We conclude that the presence of GH is important for hepatic LDL-receptor expression, both at the protein and the mRNA level. The resistance to suppression of rat hepatic LDL receptors by dietary cholesterol depends, at least in part, on the presence of GH.

Animals↗
PubMed1993

Effect of 3-thiadicarboxylic acid on lipid metabolism in experimental nephrosis.

The effect of the sulfur-substituted fatty acid analogue 1,10 bis(carboxymethylthio)decane, also known as 3-thiadicarboxylic acid, on puromycin aminonucleoside-induced nephrotic hyperlipidemia was studied in rats. Treatment with 3-thiadicarboxylic acid (250 mg/kg) for 5 days reduced plasma levels of triglycerides from 5.8 to 2.7 mmol/L and cholesterol from 11.0 to 7.7 mmol/L. This was accounted for by decreases in very-low-density lipoprotein triglycerides, very-low-density lipoprotein cholesterol, and low-density lipoprotein cholesterol, without any major changes in the composition of plasma lipoproteins. The activities of two enzymes involved in fatty acid synthesis (ATP:citrate lyase and fatty acid synthetase) were inhibited by 3-thiadicarboxylic acid treatment, whereas acetyl-coenzyme A carboxylase activity was unchanged. In contrast, treatment with the sulfur-substituted fatty acid analogue induced the peroxisomal beta-oxidation of fatty acids ninefold and the mitochondrial beta-oxidation by 54% to 73%, depending on the substrate used. This was accompanied by a 26% reduction in hepatic triglyceride secretion rate. The hepatic phosphatidate phosphohydrolase activity was unchanged. 3-Thiadicarboxylic acid treatment suppressed the activity of the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, by 58%, whereas hepatic LDL receptor expression was unaltered. The activities of lipoprotein lipase and hepatic lipase were unchanged by treatment. These results demonstrated that treatment with 3-thiadicarboxylic acid ameliorates hyperlipidemia in experimental nephrosis primarily by decreasing the overproduction of very-low-density lipoprotein present. The data also indicate that hepatic very-low-density lipoprotein synthesis and secretion is strongly influenced by the availability of the fatty acid substrate under the same hyperlipidemic conditions.

ATP Citrate (pro-S)-Lyase↗
PubMed1993

Stimulation of rat hepatic low density lipoprotein receptors by glucagon. Evidence of a novel regulatory mechanism in vivo.

We studied the influence of glucagon on hepatic LDL receptors and plasma lipoproteins in rats. A dose-dependent (maximum, threefold) increase in LDL-receptor binding was evident already at a dose of 2 x 4 micrograms, and detectable 3 h after injection; concomitantly, cholesterol and apolipoprotein (apo) B and apoE within LDL and large HDL decreased in plasma. LDL receptor mRNA levels were however unaltered or reduced. Hepatic microsomal cholesterol was increased and the enzymatic activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase in hepatic microsomes were reduced. Insulin alone increased receptor binding and receptor mRNA levels twofold, but plasma cholesterol was unchanged and plasma apoE and apoB increased. Administration of insulin to glucagon-treated animals reduced the LDL-receptor binding to control levels and apoB appeared in LDL particles. Estrogen treatment increased LDL-receptor binding and mRNA levels five- and eightfold, respectively. Combined treatment with glucagon and estrogen reduced the stimulation of LDL-receptor mRNA levels by 80% although LDL-receptor binding was unchanged. Immunoblot analysis showed that glucagon increased the number of hepatic LDL receptors. We conclude that glucagon induces the number of hepatic LDL receptors by a mechanism not related to increased mRNA levels, suggesting the presence of a posttranscriptional regulatory mechanism present in the liver in vivo.

Animals↗
PubMed1992

Importance of growth hormone for the induction of hepatic low density lipoprotein receptors.

This investigation was undertaken to determine the possible role of growth hormone (GH) in the hormonal regulation of hepatic low density lipoprotein (LDL) receptor expression. Treatment of normal rats with estrogen (ethynylestradiol, 5 mg/kg per day) increased the number of hepatic LDL receptors, and the LDL receptor mRNA levels were increased 2.4-fold. However, when hypophysectomized rats were treated with estrogen, the hepatic LDL receptor number and the mRNA levels only increased slightly. Treatment with GH was important to restore the induction of hepatic LDL receptors in hypophysectomized estrogen-treated rats. Further, the hypocholesterolemic effect of estrogen was abolished in hypophysectomized rats, and GH reversed this effect. To assess the effect of GH in humans, hepatic LDL receptor binding activity was determined in liver biopsy specimens from gallstone patients pretreated with GH (12 international units/day) prior to operation. GH administration induced hepatic LDL receptors approximately 2-fold, and this was accompanied by a 25% decrease in serum cholesterol. The LDL receptor stimulation caused by GH treatment was of similar magnitude as that observed upon 3 weeks of treatment with an established hypolipidemic drug (pravastatin or simvastatin). The data show that GH has an important role in the regulation of hepatic LDL receptors and suggest that GH secretion may be important for the control of plasma LDL levels in humans.

Adult↗
PubMed1992

Hepatic cholesterol metabolism in estrogen-treated men.

Operative liver biopsies were obtained from two male patients who developed gallstone disease during estrogen treatment of metastatic prostatic carcinoma. The heparin-sensitive binding of 125I-low-density lipoprotein (LDL) to liver homogenates (reflecting the expression of the LDL receptor) was determined, together with the activities of the rate-limiting enzymes in cholesterol synthesis [3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase], bile acid production (cholesterol 7 alpha-hydroxylase), and cholesterol esterification (acyl CoA:cholesterol acyl transferase). The results were related to data available in 18 patients (5 male, 13 female) who underwent cholecystectomy because of gallstone disease. The hepatic 125I-LDL-binding activity was increased threefold compared with five controls, and the activity of HMG-CoA reductase was increased twofold. There was no major difference in the activities of cholesterol 7 alpha-hydroxylase or acyl CoA:cholesterol acyl transferase. The concentration of free and total cholesterol in liver microsomes was approximately 30% lower in the estrogen-treated men than in 11 controls. The results indicate that estrogen at pharmacological doses stimulates hepatic LDL-receptor expression and HMG-CoA reductase activity in men. The increased LDL-receptor expression could in part explain the enhanced plasma clearance of injected 125I-LDL and hence the reduction in plasma LDL cholesterol previously shown to occur in estrogen-treated men.

Aged↗
PubMed1992

Effects of growth hormone on low-density lipoprotein metabolism.

GH appears to play an important role in mediating the increase in hepatic LDL receptor expression that occurs in response to pharmacological oestrogen treatment. Furthermore, in normal individuals there is evidence of an increased number of hepatic LDL receptors in response to GH, resulting in an accelerated elimination rate of the LDL particle and a subsequent lowering of LDL cholesterol. Further studies on lipoprotein metabolism in patients with GH deficiency, and also in patients with hypercholesterolaemia, would therefore be of interest.

Biological Transport, Active↗
PubMed1992

Hepatic mRNA levels for the LDL receptor and HMG-CoA reductase show coordinate regulation in vivo.

A sensitive solution hybridization assay using autologous cRNA probes was developed with the aim to study the simultaneous regulation of hepatic mRNA levels, on a quantitative basis, for the LDL receptor (LDLr), HMG-CoA reductase, and cholesterol 7 alpha-hydroxylase (Cho-7-hx) in C57BL/6J mice. With the purpose to suppress and stimulate transcript levels respectively, animals received established high fat diets, cholesterol-enriched diets, and a diet supplemented with mevinolin and colestipol. One hundred nineteen animals were investigated in six separate experiments. In spite of an eightfold increase in hepatic cholesterol induced by a high fat diet, the LDLr and the HMG-CoA reductase mRNA levels were only reduced to 60-70% and 25-50% of control values, respectively. When the data from all animals were analyzed, a strong positive correlation was obtained between the mRNA levels for the LDLr and HMG-CoA reductase (r = 0.79, P less than 0.001). A significant relation remained when control animals only were analyzed (n = 42, r = 0.59, P less than 0.001). Cho-7-hx mRNA showed a regulatory pattern that differed from that of the LDLr and HMG-CoA reductase; feeding cholesterol at 1.7% and 5% but not at 0.4% elevated the mRNA levels for Cho-7-hx while the LDLr and HMG-CoA reductase mRNA levels were maximally suppressed already at 0.4% of dietary cholesterol. The results show that the mRNA levels for the LDLr and HMG-CoA reductase are regulated in parallel in the liver in vivo during various metabolic perturbations as well as at normal physiologic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Molecular aspects of human lipid metabolism.

The application of molecular biology and genetics in the field of cholesterol and lipoprotein metabolism has resulted in a tremendous expansion of knowledge during the past decade. In this short review, the normal metabolism of lipoproteins is first discussed briefly, and several clinically important examples of genetic disorders which have recently been characterized are discussed: hypobetalipoproteinaemia, familial defective apo B-100, type III hyperlipoproteinaemia, and familial hypercholesterolaemia. New data on the molecular regulation of cholesterol metabolism are summarized, and the impact of this knowledge for our future therapeutic possibilities in hypercholesterolaemia and certain malignant diseases is discussed.

Apolipoproteins B↗
PubMed1991

[Lipid metabolism in man--new knowledge on molecular level gives hope for better therapy].

Application of the techniques of molecular biology to the study of cholesterol and lipoprotein metabolism in recent years has led to a dramatic increase in our knowledge of this field. This brief review provides a general outline of normal lipoprotein and cholesterol metabolism; some recent advances in research are discussed, and the molecular defects present in hypobetalipoproteinaemia, familial apo B-100 deficiency, type III hyperlipoproteinaemia, and familial hypercholesterolaemia are described and their clinical relevance is discussed. New aspects are presented of the finely tuned regulation of cholesterol synthesis, and its importance in treatment of hypercholesterolaemia is discussed, as is its possible involvement in oncogen expression.

Cholesterol↗
PubMed1991

[Effect of pravastatin on hepatic cholesterol metabolism].

BACKGROUND: Inhibitors of the rate-limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are now used frequently to treat hypercholesterolemia. We studied the effects of specific inhibition of cholesterol synthesis by one of these agents (pravastatin) on the hepatic metabolism of cholesterol in patients with gallstone disease who were scheduled to undergo cholecystectomy. METHODS: Ten patients were treated with pravastatin (20 mg twice a day) for three weeks before cholecystectomy; 20 patients not treated served as controls. A liver specimen was obtained from each patient at operation, and the activities of rate-determining enzymes in cholesterol metabolism as well as low-density-lipoprotein (LDL)-receptor binding activity were determined. RESULTS: Pravastatin therapy reduced plasma total cholesterol by 26 percent and LDL cholesterol by 39 percent (p less than 0.005). Serum levels of free lathosterol, a precursor of cholesterol whose concentration reflects the rate of cholesterol synthesis in vivo, decreased by 63 percent (p less than 0.005), indicating reduced de novo biosynthesis of cholesterol. Microsomal HMG-CoA reductase activity, when analyzed in vitro in the absence of the inhibitor, was increased 11.8-fold (1344 +/- 311 vs. 105 +/- 14 pmol per minute per milligram of protein in the controls; p less than 0.001). The expression of LDL receptors was increased by 180 percent (p less than 0.005), whereas the activities of cholesterol 7 alpha-hydroxylase (which governs bile acid synthesis) and of acyl-coenzyme A: cholesterol O-acyltransferase (which regulates cholesterol esterification) were unaffected by treatment. CONCLUSIONS: Inhibition of hepatic HMG-CoA reductase by pravastatin results in an increased expression of hepatic LDL receptors, which explains the lowered plasma levels of LDL cholesterol.

Adult↗
PubMed1991

Hepatic metabolism of cholesterol in Crohn's disease. Effect of partial resection of ileum.

To study cholesterol metabolism in Crohn's disease and especially the effect of ileum resection, liver biopsy specimens were obtained from patients undergoing partial ileal resection because of Crohn's disease (n = 17) and patients with Crohn's colitis undergoing colectomy (n = 3). Gallstone-free patients (n = 16) undergoing cholecystectomy because of adenomyomas or polyps of the gallbladder served as controls. The mean levels of cholesterol 7 alpha-hydroxylase activity and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, rate-determining enzymes in bile acid, and cholesterol synthesis, respectively, were twofold to threefold higher in the ileum-resected patients than in the controls. Significant positive correlations were obtained between length of resected ileum and cholesterol 7 alpha-hydroxylase activity. Provided patients who had received total parenteral nutrition preoperatively were excluded from analysis, a significant correlation was also observed between length of resected ileum and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. Significant positive correlations were also obtained between length of resected ileum and serum levels of 7 alpha-hydroxycholesterol (a marker for bile acid biosynthesis) and lathosterol (a marker for cholesterol synthesis). The plasma levels of total and low-density lipoprotein cholesterol were negatively correlated to the length of resected ileum. The expression of hepatic low-density lipoprotein-receptor binding activity was determined in five of the patients and in three of the controls. A significant positive correlation was observed between 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and low-density lipoprotein-receptor binding activity. The results show that malabsorption of bile acids leads to parallel stimulation of cholesterol synthesis, cholesterol degradation, and low-density lipoprotein-receptor expression in human liver. The resulting effect in the present patients was a significant reduction in low-density lipoprotein cholesterol.

Adult↗