Biomedical subjects

S Skrede

Publications and source records attributed to S Skrede.

At least 37 records · Page 2Linked to original sources

PubMed1988

Content of sitosterol, cholestanol, and cholesterol in very low density lipoproteins of rat liver perfusate.

Sterol specificity in synthesis of very low density lipoproteins in the rat liver was studied by liver perfusion after injection in vivo of sterols as double isotopes. The amounts of sterols recovered in the very low density lipoprotein fraction of the perfusate were compared with the microsomal contents, using both double isotope ratio technique and quantitation by gas chromatography. The secretion of sitosterol and cholestanol was 0.72 and 0.88 of that of cholesterol, respectively. Variations of microsomal sterol concentrations did not affect the principal results. Relative to cholesterol, one-third more of injected sitosterol was present in the liver after 24 h. Sitosterol was excreted in the bile at one-fourth the rate of cholesterol and to a larger extent as free sterol compared with cholesterol.

Animals↗

PubMed1988

Hepatic 7 alpha-dehydroxylation of bile acid intermediates, and its significance for the pathogenesis of cerebrotendinous xanthomatosis.

The bile acid precursor 7 alpha-hydroxy-4-cholesten-3-one was found to be enzymatically dehydroxylated at a slow rate by liver tissues from the rat, human, and guinea pig. The rat liver enzyme is localized in the microsomal fraction, has a pH optimum of about 8.5, an apparent Km of 0.03-0.04 mM, and a Vmax of 10-15 nmoles.mg protein-1.hr-1. The product from 7 alpha-hydroxy-4-cholesten-3-one was identified as cholesta-4,6-dien-3-one by its chromatographic properties and by mass spectrometry. The reaction proceeded both in air and N2, and pyridine nucleotides were not required as cofactors. In addition to the enzymatic reaction, there was a significant nonenzymatic dehydroxylation of 7 alpha-hydroxy-4-cholesten-3-one, in particular at high pH and with high concentrations of protein. No 7 alpha-dehydroxylation occurred with various 7 alpha-hydroxylated 3 beta-hydroxy-delta 5-steroids. We have previously shown that at least part of the accumulation of cholestanol in cerebrotendinous xanthomatosis (CTX) is due to accelerated 7 alpha-dehydroxylation of bile acid intermediate(s), which are further converted into cholestanol. The capacity to dehydroxylate 7 alpha-hydroxy-4-cholesten-3-one was found to be about the same in homogenates of liver biopsies from two patients with CTX as in preparations from control subjects. It is suggested that increased levels of substrate (7 alpha-hydroxy-4-cholesten-3-one) in the liver, rather than increased amounts of 7 alpha-dehydroxylase is the explanation for the accelerated 7 alpha-dehydroxylation in CTX that leads to increased biosynthesis of cholestanol.

Animals↗

PubMed1987

Metabolism of the cholestanol precursor cholesta-4,6-dien-3-one in different tissues.

Cerebrotendinous xanthomatosis (CTX) is a lipid storage disease where the basic defect is a lack of the mitochondrial C27-steroid 26-hydroxylase involved in bile acid synthesis (EC 1.14.13.15). Cholestanol and cholesterol accumulate in all tissues. At least part of the accumulation of cholestanol is due to a 7 alpha-dehydroxylation of early bile acid intermediates. Cholesta-4,6-dien-3-one, a proposed intermediate in this pathway, is found in increased concentrations in serum of the patients. This study shows that cholesta-4,6-dien-3-one may be metabolized to 4-cholesten-3-one and cholestanol by liver, adrenals and brain. No conversion was found in intestinal mucosa or in kidneys. The capacity to convert cholesta-4,6-dien-3-one into 4-cholesten-3-one and cholestanol varied in different tissues as well as in different species. The results are discussed in relation to the cholestanol accumulation in CTX.

Animals↗

PubMed1987

Normal activity of C27-steroid 26-hydroxylase in cultured sitosterolaemia fibroblasts.

The primary defect in sitosterolaemia is unknown. In some patients excretion of bile alcohols is increased, and it has been suggested that the defect is located to some step in the biosynthesis of bile acids. The activity of C27-steroid 26-hydroxylase was measured in cultured skin fibroblasts from a sitosterolaemic patient. The same assay was used as before in demonstrating deficiency of this enzyme activity in cerebrotendinous xanthomatosis (CTX), a disease in which high excretion of bile alcohols is typical. The substrate, 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol, was 26-hydroxylated to the same extent in the patient cells as in those of healthy controls. Thus, the sitosterolaemia cells have a normal activity of this enzyme.

Brain Diseases↗

PubMed1986

Effects of thyroid state and fasting on the concentrations of CoA and malonyl-CoA in rat liver.

Liver CoA is markedly higher in hyperthyroid rats as compared to hypothyroid rats, and in fasted rats as compared to fed rats. In hyperthyroid rats the CoA is increased mainly in the cytosol, while in fasted rats the increase is mainly in the mitochondria. Malonyl-CoA is markedly higher in hypothyroid rats than in euthyroid and hyperthyroid rats. With fasting, malonyl-CoA drops 80-85% in all thyroid states. These findings are discussed in relation to the regulation of fatty acid oxidation in the liver.

Acyl Coenzyme A↗

PubMed1986

C-reactive protein as an indicator of infection in the immunosuppressed child.

C-reactive protein (CRP) concentrations were determined in a prospective fashion in 50 children with malignant disease. In 35 children with active and aggressive disease, but without signs of infection, no significant increase in CRP was detected. Neither did aggressive cytostatic therapy (70 courses) in non-infected children result in an increase. In bacteriologically proven, and in clinical sepsis-suspected cases, CRP values increased in all cases to levels above 100 mg/l (normal values less than 5 mg/l). Effective antibiotic therapy resulted in a prompt decline in CRP. Viral infections resulted in a much smaller increase. We conclude that serial measurements of CRP in these immunosuppressed children are of great help in monitoring infections and defining the group that needs antibiotic therapy. The measurement is also a good indicator of the effectiveness of the antibiotic therapy chosen.

Adolescent↗

PubMed1986

Long-term blood pressure and renal function in kidney donors.

We have reexamined 68 (92%) of 74 donors accepted at this center nine to 15 years ago. There was a moderate but significant increase in BP, and ten donors (15%) were hypertensive at the follow-up. Twenty-six donors (38%) had albumin excretion over 10 micrograms/min or excretion of total protein over 185 mg/24 hr. In four of 16 with increased excretion of total protein, this exceeded 400 mg/24 hr, and in three donors this could be due to an intercurrent disease. Ccr averaged 78.4% of preoperative values, and was less than 50% (range 32 to 49%) in eight donors. The compensatory increase (median 30.5 mliter/min/1.73m2) was inversely correlated with age and BP. Aspects of tubular function were assessed by the diluting capacity during water diuresis and by urinary excretion of beta 2-microglobulin and N-acetyl-beta-glucosaminidase. No consistent abnormalities were observed. A subgroup of donors (N = 32) was compared with a matched control group. Urinary albumin excretion among the donors was significantly higher compared to the controls, both in absolute terms (5.4 vs. 3.3 micrograms/min, P less than 0.002) and as percent of total protein excretion (7.6 vs. 5.7%, P less than 0.05). Otherwise no consistent differences were observed. The development of BP over time warrants further observations, but there is no evidence that uninephrectomy represents a long-term risk to the donors' health.

Acetylglucosaminidase↗

PubMed1986

Demonstration of 26-hydroxylation of C27-steroids in human skin fibroblasts, and a deficiency of this activity in cerebrotendinous xanthomatosis.

26-Hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and other C27-steroids was demonstrated in cultured skin fibroblasts from healthy individuals. Activities in skin fibroblasts were approximately 5-10% of those previously found in human liver homogenates, and were inhibited by CO. The apparent Km was lowest for 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol (1.3 mumol/liter) and highest for 5-cholestene-3 beta, 7 alpha-diol (12 mumol/liter). The rate of 26-hydroxylation was highest with 7 alpha-hydroxy-4-cholesten-3-one. These characteristics are similar to those of hepatic mitochondrial C27-steroid 26-hydroxylase. In skin fibroblasts from three patients with cerebrotendinous xanthomatosis (CTX), 26-hydroxylation of C27-steroids proceeded at a rate of only 0.2-2.5% of healthy controls. No accumulation of endogenous 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol could be demonstrated in these cells, and the lowered formation of radioactive, 26-hydroxylated products could not be explained by dilution of the labeled exogenous substrate. The present results add strong evidence to the concept that the primary metabolic defect in CTX is a deficiency of C27-steroid 26-hydroxylase.

Brain Diseases↗

PubMed1986

On the mechanism of biosynthesis of cholestanol from 7 alpha-hydroxycholesterol.

In a patient with cerebrotendinous xanthomatosis (CTX), a small part of i.v. administered [7 beta-3H]-7 alpha-hydroxycholesterol was converted into cholestanol. Traces of 3H were also found in plasma cholesterol, but its specific radioactivity was only about 1% of that of cholestanol. When [7 beta-3H]-7 alpha-hydroxycholesterol was given orally to rabbits, significant amounts of 3H were found in cholestanol in different organs. Much less 3H was found in cholesterol. Our results support the conclusion that the pathway from 7 alpha-hydroxycholesterol to cholestanol does not involve cholesterol, but 7 alpha-hydroxy-4-cholesten-3-one and cholesta-4,6-dien-3-one as intermediates.

Animals↗

PubMed1986

Metabolism of 24-ethyl-4-cholesten-3-one and 24-ethyl-5-cholesten-3 beta-ol (sitosterol) after intraperitoneal injection in the rat.

14C-labeled C29- and C27-steroids were injected in rats, which were killed after 14 days. Phytosterols (C29) were excreted mainly as such, whereas C27-steroids were recovered essentially as water soluble metabolites. The total 14C-excretion was lower from 3-oxo, delta 4-steroids (5 alpha-stanol precursors) than from 3 beta-hydroxy,delta 5-steroids. 14C-Phytosterols were accumulated more than C27-steroids in liver, serum (mainly in HDL) and especially in adrenal glands and ovaries. In relation to serum, particularly the 5 alpha-stanols were enriched in the adrenal glands and ovaries. No striking lysosomal accumulation of any of the steroids was found.

Animals↗

PubMed1985

The presence of 5 alpha-sitostanol in the serum of a patient with phytosterolemia, and its biosynthesis from plant steroids in rats with bile fistula.

The presence of 5 alpha-sitostanol (24-ethyl-5 alpha-cholestan-3 beta-ol) in serum of a patient with the rare genetic disease phytosterolemia was confirmed. This study aimed at clarifying the pathway(s) for the formation of 5 alpha-sitostanol, by use of rats with bile fistula. 5 alpha-Sitostanol was formed only slowly from sitosterol, but readily from 24-ethyl-4-cholesten-3-one. Some conversion was also obtained with 7 alpha-hydroxysitosterol as precursor. In view of the low rate of 7 alpha-hydroxylation of sitosterol, however, a pathway from sitosterol to 5 alpha-sitostanol involving 7 alpha-hydroxysitosterol as intermediate is probably of small physiological importance. Intestinal microorganisms are not essential for the above conversions, since the 5 alpha-sitostanol was found in bile from bile fistula rats. 5 alpha-Sitostanol was converted to water soluble metabolites (bile acids) much more slowly than was cholestanol (5 alpha-cholestan-3 beta-ol), and was accumulated serum to a much larger extent.

Adolescent↗

PubMed1985

On the structural specificity in the regulation of the hydroxymethylglutaryl-CoA reductase and the cholesterol-7 alpha-hydroxylase in rats. Effects of cholestanol feeding.

The effect of feeding 2% cholestanol or cholesterol on cholesterol-7 alpha-hydroxylase activity and hydroxymethylglutaryl (HMG)-CoA reductase activity was studied in rats. The rate of 7 alpha-hydroxylation of a trace amount of labelled cholesterol increased by about 80% after the cholestanol feeding, whereas the 7 alpha-hydroxylation of endogenous microsomal cholesterol increased by about 40%. The latter conversion was measured with an accurate technique based on isotope dilution-mass spectrometry. After cholesterol feeding, the corresponding figures were about 50 and 60%, respectively. The cholestanol feeding had no significant effect on the HMG-CoA reductase activity, whereas the cholesterol feeding decreased the activity by about 80%. From the results obtained, it is concluded that the increased 7 alpha-hydroxylation observed after cholesterol feeding can not be explained only by a simple expansion of the substrate pool. The similar effect of both cholesterol and cholestanol on the cholesterol 7 alpha-hydroxylase activity and the diverging effect on the HMG-CoA reductase activity show that there is no coupling between cholesterol synthesis and degradation under the conditions employed. The lack of effect of cholestanol on the HMG-CoA reductase activity indicates a high structural specificity of the receptor involved in regulation of the enzyme. If a receptor mechanism is involved in the stimulation of the cholesterol-7 alpha-hydroxylase by cholesterol and cholestanol, these receptor(s) must be different from those involved in the regulation of the HMG-CoA reductase.

Animals↗

PubMed1985

Biosynthesis of cholestanol from bile acid intermediates in the rabbit and the rat.

Biliary 7 alpha-hydroxy-4-cholesten-3-one (an intermediate in bile acid biosynthesis) may be 7 alpha-dehydroxylated in the gut and further metabolized to cholestanol (Skrede, S., and Björkhem, I. (1982) J. Biol. Chem. 257, 8363-8367). We have now evaluated the quantitative importance of pathway(s) to cholestanol with 7 alpha-hydroxylated C27 steroids as intermediates. After feeding conventionally fed rabbits or rats or germ-free rats with [7 alpha-3H]cholesterol and [4-14C]cholesterol, tissue cholestanol could be isolated with about a 20% lower 3H/14C ratio than present in cholesterol. We conclude that there is a pathway to cholestanol involving 7 alpha-hydroxylated intermediates. Intestinal microorganisms are not essential for this pathway, which accounts for at most 20% of the cholestanol formed in these species. In bile fistula rats, there was also a significant conversion of intraperitoneally injected [7 beta-3H]7 alpha-hydroxycholesterol and [4-14C]7 alpha-hydroxy-4-cholesten-3-one into cholestanol. The enzymes involved in the 7 alpha-hydroxylation/dehydroxylation pathway for the biosynthesis of cholestanol are probably located in the liver. Both 7 alpha-hydroxycholesterol and 7 alpha-hydroxy-4-cholesten-3-one may be intermediates.

Animals↗

PubMed1985

A novel pathway for biosynthesis of cholestanol with 7 alpha-hydroxylated C27-steroids as intermediates, and its importance for the accumulation of cholestanol in cerebrotendinous xanthomatosis.

A mixture of 7 alpha-3H- and 4-14C-labeled cholesterol was administered intravenously to rats. Cholestanol with 20-30% lower ratio between 3H and 14C than in cholesterol could be isolated from different organs. In a healthy human control, cholestanol isolated from feces had a 3H/14C ratio which was 28% lower than in administered cholesterol. Cholesterol and coprostanol reisolated in these experiments had the same ratio between 3H and 14C as in the precursor. A previously unknown pathway for formation of cholestanol, involving 7 alpha-hydroxylated intermediates, may explain these results. Under normal conditions, this pathway is responsible for at most 30% of the cholestanol synthesized from cholesterol. Intravenous administration of the 7 alpha-3H- and 4-14C-labeled cholesterol to a patient with cerebrotendinous xanthomatosis (CTX) resulted in formation of cholestanol which had 70-75% lower 3H/14C ratio. It is concluded that the novel pathway involving 7 alpha-hydroxylated intermediates is accelerated in patients with CTX. This acceleration may contribute essentially to the accumulation of cholestanol, which is a predominant feature of this disease. 7 alpha-Hydroxycholesterol and 7 alpha-hydroxy-4-cholesten-3-one might be intermediates in the novel pathway to cholestanol. After intravenous administration of 7 beta-3H-labeled 7 alpha-hydroxycholesterol in a patient with CTX, significant amounts of 3H were incorporated into plasma and fecal cholestanol. Only small amounts of 7 alpha-hydroxycholesterol and 7 alpha-hydroxy-4-cholesten-3-one are excreted into the intestine, and we therefore conclude that the 7 alpha-dehydroxylation step mainly occurs in the liver. In CTX, the synthesis of cholestanol may be accelerated because the concentrations of 7 alpha-hydroxylated bile acid intermediates in the liver are increased. A possible mechanism for the conversion of a minor fraction of 7 alpha-hydroxycholesterol into cholestanol is suggested.

Adult↗

PubMed1985

Fast atom bombardment mass spectrometry in the diagnosis of cerebrotendinous xanthomatosis.

Urine from a patient with cerebrotendinous xanthomatosis (CTX) was extracted with a Sep-Pak C18 cartridge and the extract was analysed by fast atom bombardment mass spectrometry. The spectra indicated the presence of glucuronidated bile alcohols with four to seven hydroxyl groups. The method is simple and rapid and is suggested as an aid in the diagnosis of CTX with possible application to prenatal diagnosis.

Adult↗

PubMed1985

Studies of the mechanism of the increased biosynthesis of cholestanol in cerebrotendinous xanthomatosis. The activity of delta 5-3 beta-hydroxysteroid dehydrogenase.

It was recently proposed that the increased biosynthesis of cholestanol in cerebrotendinous xanthomatosis (CTX) is due to increased activity of the delta 5-3 beta-hydroxysteroid dehydrogenase involved in bile acid biosynthesis, causing increased conversion of cholesterol into cholestanol through 4-cholesten-3-one. Our attempts to confirm this hypothesis have failed. Liver biopsy specimens from two patients with CTX did not have any increased capacity to catalyze conversion of 7 alpha-hydroxycholesterol into 7 alpha-hydroxy-4-cholesten-3-one. Further, we did not find any changes in the activity of liver microsomal delta 5-3 beta-hydroxysteroid dehydrogenase after feeding rabbits with cholestanol or cholesterol. The findings are discussed in relation to our hypothesis that the accelerated biosynthesis of cholestanol in CTX is due to an increased conversion of early bile acid intermediates into cholestanol.

3-Hydroxysteroid Dehydrogenases↗

PubMed1985

Follow-up and prospective studies of the classification of liver disease.

Two hundred patients with different liver diseases were observed during a period of 6-8 years. The diagnosis at the first hospitalization was based on morphological criteria (and, in some cases, additional clinical information). In 162 of the cases an initial 'specific' diagnosis could be made. By the time of the follow-up study the diagnosis was confirmed in 73% of them. In 22 of 38 patients who were initially unclassifiable, the diagnosis was made definite by the follow-up study. Eighty-five patients were hospitalized for re-examination 6-8 years after the initial study. Several of the liver diseases initially had quite typical patterns of clinical chemical data. Allocation by discriminant analysis was therefore in good agreement with the morphological classification. The follow-up study showed that several patients with initially atypical patterns of clinical chemical results had their diagnosis changed. In 35 patients with the final diagnosis of chronic active hepatitis (CAH) or primary biliary cirrhosis (PBC), laboratory data from the last hospitalization were used for discriminant analysis with teaching data from the initial study. Ninety-seven per cent were correctly allocated, and we conclude that these patients retain recognizable patterns of laboratory results for several years, even when given immunosuppressive treatment. The potential clinical usefulness of discriminant analysis of laboratory data for differential diagnosis was evaluated by a prospective study of 65 patients with the morphological diagnosis of CAH or PBC. Correspondence with the morphological classification system was found in almost 90% of the cases.

Chronic Disease↗

PubMed1985

A novel route for the biosynthesis of cholestanol, and its significance for the pathogenesis of cerebrotendinous xanthomatosis.

The main symptoms in cerebrotendinous xanthomatosis (CTX) are caused by increased synthesis of cholestanol (5 alpha-cholestan-3 beta-ol) and depositions of this steroid in brain and xanthomas. Previously, we have shown a deficiency in CTX of the mitochondrial C27-steroid 26-hydroxylase essential for normal degradation of the cholesterol side chain. Because of this defect, different 7 alpha-hydroxylated substrates for the 26-hydroxylase accumulate in the liver - among these 7 alpha-hydroxy-4-cholesten-3-one. The possibility that such accumulated 7 alpha-hydroxylated bile acid precursors can be converted into cholestanol was studied by administration of labelled 7 alpha-hydroxy-cholesterol to bile fistula rats and to a patient with CTX. Label was incorporated into cholestanol in the rats as well as in the CTX-patient. The quantitative significance of this 7 alpha-hydroxylation/dehydroxylation route for the biosynthesis of cholestanol was examined by administering a mixture of 7 alpha-3H and 4-14C-labeled cholesterol to rats, rabbits and a human volunteer. In all species, about 25% of 3H was lost during the conversion of cholesterol to cholestanol. In a patient with CTX, the flow through the 7 alpha-hydroxylation/dehydroxylation route was greatly increased, since 75% of 3H present in the precursor (cholesterol) had been removed in cholestanol isolated from bile, serum and faeces. Experiments with germfree rats and bile fistula rats indicate that the 7 alpha-dehydroxylation mainly occurs in the liver. The microsomal fraction of rat liver was found to 7 alpha-dehydroxylate 7 alpha-hydroxy-4-cholesten-3-one at a slow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗