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Biomedical subjects

G Eggertsen

Publications and source records attributed to G Eggertsen.

At least 55 records · Page 3Linked to original sources
PubMed1994

Lack of association between apolipoprotein E allele epsilon 4 and sporadic Alzheimer's disease.

Apolipoprotein E (apoE) is a protein involved in the transport of lipids and a component of Alzheimer's disease (AD) plaques. There are three common alleles of the apoE gene, designated epsilon 2, epsilon 3 and epsilon 4. An association between familial and sporadic AD and the epsilon 4 allele was recently reported. We have investigated Swedish Alzheimer patients and controls. The epsilon 4 allele frequency in familial and sporadic cases and in controls was 47, 22 and 18%, respectively. There was no significant difference between sporadic AD and controls but in familial cases the increased epsilon 4 allele frequency previously reported was confirmed.

Aged↗
PubMed1994

Cloning and expression of cDNA of human delta 4-3-oxosteroid 5 beta-reductase and substrate specificity of the expressed enzyme.

The enzyme delta 4-3-oxosteroid 5 beta-reductase (3-oxo-5 beta-steroid: NADP+ oxidoreductase and 4,5 beta-dihydrocortisone: NADP+ delta 4-oxidoreductase) catalyzes the reduction of the delta 4 double bond of bile acid intermediates and steroid hormones carrying the delta 4-3-one structure in the A/B cis configuration. Human delta 4-3-oxosteroid 5 beta-reductase cDNA was isolated from a liver cDNA library by cross hybridization with a previously cloned rat cDNA, which was used as a probe [Onishi, Y. Noshiro, M., Shimosato, T. & Okuda, K.-I. (1991) FEBS Lett. 283, 215-218]. DNA sequence analysis of a hybridization-positive clone predicted the human delta 4-3-oxosteroid 5 beta-reductase to contain 326 amino acids. The amino acid sequence of the human delta 4-3-oxosteroid 5 beta-reductase had 79% overall identity to the rat enzyme sequence. It also showed 54% and 50% overall identity with rat 3 alpha-hydroxysteroid dehydrogenase and human aldose reductase, respectively. RNA blotting analysis demonstrated the existence of a single delta 4-3-oxosteroid 5 beta-reductase mRNA of approximately 2.7 kb in human liver. Transfection of the cDNA into COS cells resulted in the expression of an active enzyme with a high activity toward the bile acid intermediates 7 alpha,12 alpha-dihydroxy-4-cholesten-3-one and 7 alpha-hydroxy-4-cholesten-3-one. In addition, the expressed enzyme showed a small but significant 5 beta-reduction activity toward 11 beta,17 alpha,21-trihydroxy-delta 4-pregnene-3,20-dione (cortisol) and 17 beta-hydroxy-delta 4-androsten-3-one (testosterone) whereas no activity was observed toward delta 4-pregnene-3,20-dione (progesterone) or delta 4-androstene-3-17-dione (androstenedione). The substrate specificity of the human enzyme is considerably narrower than that of the rat enzyme, and the enzyme seems to be more important for bile acid biosynthesis than for metabolism of steroid hormones.

Amino Acid Sequence↗
PubMed1994

Stimulation of HMG-CoA reductase as a consequence of phenobarbital-induced primary stimulation of cholesterol 7 alpha-hydroxylase in rat liver.

Among nine strains of rat, two were found that responded to phenobarbital treatment with increased activity of hepatic cholesterol 7 alpha-hydroxylase. This effect was maximal after 2-3 days of treatment and was then reduced. Interestingly the increased cholesterol 7 alpha-hydroxylase activity was associated with increased activity of hepatic HMG-CoA reductase in the two responding strains but not in the non-responding strains. In tissues other than the liver, HMG-CoA reductase activity was unaffected in responding rats. Most of the above stimulation occurred at a pretranslatory level and the mRNA levels corresponding to the two enzymes paralleled the activities. The phenobarbital treatment resulted in decreased content of free cholesterol in liver microsomes in a strain of rat that responded with increased cholesterol 7 alpha-hydroxylase activity. It was shown that depletion of cholesterol in the responding strain of rats by lymph fistulation also was associated with a parallel increase in levels of HMG-CoA reductase activity and mRNA. The findings are discussed in relation to the link between HMG-CoA reductase and cholesterol 7 alpha-hydroxylase. A primary upregulation of the cholesterol 7 alpha-hydroxylase by the cytochrome P450 inducer phenobarbital can be expected to lead to increased consumption of cholesterol substrate. This consumption may result in a compensatory increase in the activity of the HMG-CoA reductase. It is suggested that such a mechanism is responsible for part of the covariation of the two enzyme systems under different conditions.

Animals↗
PubMed1994

Identification of new mutations in sterol 27-hydroxylase gene in Japanese patients with cerebrotendinous xanthomatosis (CTX).

Cerebrotendinous xanthomatosis (CTX) is a hereditary sterol storage disease associated with accumulation of cholesterol and cholestanol in various tissues, especially tendons and neural tissues. The biochemical defect that causes CTX is a deficiency of the mitochondrial sterol 27-hydroxylase which oxidizes the side chain of cholesterol in connection with formation of bile acids. Japan has a relatively high prevalence of CTX and more cases of the disease are found here than in any other country. In the present study two new different point mutations are described in the heme-ligand binding domain of the sterol 27-hydroxylase gene in three Japanese CTX patients and one CTX heterozygote. Two of the homozygotes as well as the heterozygote subject have a single base substitution of A for G at codon 441 [CGG (Arg) to CAG (Gln)]. Another homozygote has a transition of C to T at codon 441 [CGG (Arg) to TGG (Trp)]. These two different mutations result in two restriction fragment length polymorphisms (RFLPs) for the enzymes StuI or HpaII. We also assayed sterol 27-hydroxylase activity using skin fibroblasts derived from three CTX patients, one CTX heterozygote, and normal subjects. While two of the homozygous subjects have undetectable levels of the enzyme activity, one homozygous subject and one heterozygous subject have decreased levels of the enzyme activity, about 1.4% and 10% of normal, respectively. The results suggest that the newly identified point mutations in the sterol 27-hydroxylase gene could account for the sterol 27-hydroxylase deficiency in the Japanese CTX patients.

Adult↗
PubMed1994

Time-resolved fluorometry in the genetic diagnosis of familial defective apolipoprotein B-100.

A novel technique for screening point mutations has been developed for diagnosis of familial defective apolipoprotein (apo) B-100 (FDB). In FDB, an amino acid exchange occurs at position 3500 in apoB-100 due to a point mutation. Polymerase chain reaction (PCR) was performed on the appropriate region of the apoB gene, and the PCR products were hybridized in solution with europium-labeled oligonucleotides, complementary to either the wildtype or the mutant genome. The presence or absence of the apoB-3500 mutation was monitored by time-resolved fluorescence of the europium chelate. The method allows a larger number of samples to be processed simultaneously, and the detection system displays a high level of sensitivity without the hazards connected to the use of radioactivity. When 127 Swedish patients, clinically diagnosed as suffering from heterozygous familial hypercholesterolemia, were screened for the presence of the apoB-3500 mutation, two patients, unrelated to each other, were found to be heterozygotes. These patients are the first reported cases of FDB from Sweden, and the frequency rate observed among hypercholesterolemic patients, 1.6%, is in accordance with the figures reported for several other patient population in Europe and the United States.

Adult↗
PubMed1993

Cholesterol 7 alpha-hydroxylase is up-regulated by the competitive inhibitor 7-oxocholesterol in rat liver.

Rats of the Sprague-Dawley strain were infused intravenously with a fat emulsion (Intralipid, trademark of Kabi Pharmacia, Uppsala, Sweden) containing 7-oxocholesterol. This resulted in an increased cholesterol 7 alpha-hydroxylase activity in liver microsomes as compared to controls and was accompanied by increased levels of cholesterol 7 alpha-hydroxylase mRNA and microsomal cholesterol 7 alpha-hydroxylase protein. Rats were also fed a cholestyramine-supplemented diet and infused with 7-oxocholesterol. These animals excreted about half as much bile acids in faeces as cholestyramine-fed controls. Addition of 7-oxocholesterol to liver microsomes from normal rats in amounts corresponding to those present in microsomes from 7-oxocholesterol-treated rats inhibited the cholesterol 7 alpha-hydroxylase activity by about 75%. Cholesterol induced a type-I binding spectrum when added to a purified bacterial-expressed cholesterol 7 alpha-hydroxylase (P-450c7 delta 2-24). 7-Oxocholesterol competitively inhibited the cholesterol binding spectrum, while 7 beta-hydroxycholesterol did not interfere with binding of cholesterol to the enzyme. It is concluded that treatment with the competitive inhibitor 7-oxocholesterol leads to a reduced bile acid biosynthesis and, as a consequence of reduced bile acid inhibition, a compensatory increase in cholesterol 7 alpha-hydroxylase synthesis. The high enzyme activity measured in microsomal preparations from 7-oxocholesterol-treated rats may be due to a continuous conversion of 7-oxocholesterol into less inhibitory metabolites, e.g. 7 beta-hydroxycholesterol. The latter compound was found in high concentrations in liver microsomes from rats treated with 7-oxocholesterol. The physiological importance of these results is discussed in relation to the previous findings that 7-oxocholesterol is accumulated in liver after cholesterol feeding and that 7-oxocholesterol is formed from cholesterol during lipid peroxidation.

Animals↗
PubMed1993

Structural characterization of the gene encoding rat 25-hydroxyvitamin D3 24-hydroxylase.

The structural gene encoding 25-hydroxyvitamin D3 24-hydroxylase (P-450cc24) was isolated from the rat genomic DNA. It spans approximately 15 kb, is composed of 12 exons, and was demonstrated by Southern blot analysis to be present as a single copy. One major T residue was identified at the cap site, a putative TATA (ATAAATA) box was located at position -30, and a putative CCAAT box was at -58. Four possible vitamin D responsive elements that may be involved in regulation of 24-hydroxylase expression were found in the 5'-flanking region. Alignment with mitochondrial P-450 proteins showed that 7 out of 11 intron insertion sites of P-450cc24 gene occupied positions identical with those in the CYP11 family (P-450scc, P-450(11 beta)). The structure of the gene is discussed in relation to present knowledge about the mechanism of regulation of the 25-hydroxyvitamin D3 24-hydroxylase and calcium homeostasis.

Amino Acid Sequence↗
PubMed1993

Apolipoprotein E phenotypes in familial hypercholesterolaemia: importance for expression of disease and response to therapy.

To study the possible importance of variation at the apolipoprotein (apo) E gene locus for the clinical expression of heterozygous familial hypercholesterolaemia (FH), we determined apo E phenotype and serum lipoprotein pattern in 120 patients with FH. The allele frequency of the patients studies were: epsilon 2 0.033, epsilon 3 0.733, and epsilon 4 0.233. There was no influence of apo E phenotype on the serum concentrations of total. VLDL, LDL or HDL cholesterol, triglycerides, or of apo AI, B or (a). Serum concentrations of apo E were significantly higher in patients with the apo E 3/3 phenotype compared to those with apo E 4/3 or 4/4, and the highest concentrations were found in patients carrying the epsilon 2-allele. The cholesterol-lowering response to therapy with cholestyramine or pravastatin was not related to apo E phenotype. It is concluded that variation at the apo E gene locus is not of major importance for the expression of heterozygous FH.

Apolipoproteins E↗
PubMed1993

Studies on the link between HMG-CoA reductase and cholesterol 7 alpha-hydroxylase in lymph-fistula rats: evidence for both transcriptional and post-transcriptional mechanisms for down-regulation of the two enzymes by bile acids.

The mechanism of down-regulation of hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase by cholic acid (CA) and chenodeoxycholic acid (CDCA) was investigated in rats with a lymph fistula. In accordance with the contention that bile acids are able to down-regulate HMG-CoA reductase by a mechanism independent of their effect on cholesterol absorption, inclusion of the above bile acids in diet (1%, wt/wt) reduced the HMG-CoA reductase specific activity by about 80%. The levels of mRNA were reduced by about 50% and the transcription rate (nuclear run-on) by 27% and 35%, respectively. Thus, HMG-CoA reductase appears to be regulated at both a transcriptional and a post-transcriptional level by bile acids. The cholesterol 7 alpha-hydroxylase activity as well as the corresponding mRNA levels were both reduced by about 50% by the same treatments. The transcription rate of the cholesterol 7 alpha-hydroxylase was not significantly affected by the treatment with CDCA, whereas the CA treatment reduced the transcription rate by about 24%. It is evident that bile acids regulate these two enzymes by different mechanisms in this model, in spite of the fact that the levels of mRNA were affected to about the same degree. The most obvious difference was the marked suppression of HMG-CoA reductase activity by cholic acid with relatively modest effects on transcription rate and level of mRNA. The latter finding is interesting in view of recent reports that dietary cholesterol also seems to down-regulate HMG-CoA reductase predominantly by a post-transcriptional mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Apolipoprotein E polymorphism in a healthy Swedish population: variation of allele frequency with age and relation to serum lipid concentrations.

We analyzed blood samples from 407 healthy Swedish individuals, 244 men and 163 women, ages 17 to 86 years, for apolipoprotein (apo) E isoforms and serum triglycerides, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and total cholesterol. Parallel genotyping by means of polymerase chain reaction (PCR)-amplified DNA was performed in 200 subjects. Identical results were obtained by genotyping and phenotyping in 95% of all subjects analyzed. The apo E allelic frequencies were 7.8% for epsilon 2, 71.9% for epsilon 3, and 20.3% for epsilon 4. Compared with other Caucasian populations, the present population had a high relative allelic frequency of epsilon 4. The epsilon 4 frequency decreased with increasing age and was significantly lower in individuals > 60 years of age (14.7%). When controlling for age and sex, there were strong correlations between total serum and LDL cholesterol and the various epsilon alleles. The epsilon 4 and epsilon 3 alleles correlated positively with serum cholesterol and the epsilon 4 allele correlated positively with LDL cholesterol. In contrast, HDL cholesterol and serum triglycerides did not show any correlation to the allele types. Thus, the results demonstrate a considerable age variation of the epsilon allele frequency among healthy Swedes and an influence of apo E alleles on serum and LDL cholesterol concentrations.

Adolescent↗
PubMed1991

On the mechanism of stimulation of cholesterol 7 alpha-hydroxylase by dietary cholesterol.

In agreement with previous work, treatment of rats with cholesterol, 2% in diet, stimulated the cholesterol 7 alpha-hydroxylase activity more than 2-fold. With less than 1% in diet, no significant effect was obtained. Intravenous infusion of cholesterol-enriched Intralipid had no stimulatory effect. In accordance with some recent work by other groups, it was shown that the stimulation of the cholesterol 7 alpha-hydroxylase by dietary cholesterol was associated with elevated levels of mRNA corresponding to the enzyme. Most of the stimulation of the activity induced by dietary cholesterol could not be prevented by lymphatic drainage. Feeding lymph fistulated rats with 2% cholesterol in diet stimulated the cholesterol 7 alpha-hydroxylase almost 2-fold, indicating that under the conditions employed, a major part of the cholesterol-induced stimulation of the activity was due to factor(s) unrelated to the flux of cholesterol from the intestine to the liver. There was a good correlation between the amount of cholesterol excreted in faeces and the activity of the cholesterol 7 alpha-hydroxylase. The half-life of intraperitoneally administered labelled cholic acid was significantly shorter in rats treated with 2% cholesterol in diet (t1/2 = 1.2 +/- 0.1 days) than in control rats (t1/2 = 1.9 +/- 0.18 days). A notable finding was that the weight of faeces was considerably higher in rats fed cholesterol than in the controls. It is hypothesized that a high dietary load of cholesterol causes increased binding of bile acids in the intestine and increased loss of bile acids in faeces. This leads to a reduced suppression of the cholesterol 7 alpha-hydroxylase by the bile acids. The results support the contention that the flux of bile acids rather than the flux of cholesterol from the intestine is the major direct regulator of bile acid biosynthesis.

Animals↗
PubMed1991

Effect of n-3 fatty acids on the key enzymes involved in cholesterol and triglyceride turnover in rat liver.

The effect of long-chain n-3 fatty acids on hepatic key enzymes of cholesterol metabolism and triglyceride biosynthesis was investigated in two rat models. In the first model, rats were intravenously infused for two weeks with a fat emulsion containing 20% of triglycerides in which either n-6 or n-3 fatty acids predominated. The treatment with n-3 fatty acids led to a reduction primarily of serum cholesterol (45%), but also of serum triglycerides (18%). HMG-CoA reductase activity and cholesterol 7 alpha-hydroxylase activity were reduced by 45% and 36%, respectively. There were no significant effects on diacylglycerol acyltransferase (DGAT) or phosphatidate phosphohydrolase (PAP) activities. In the second model, rats were fed a diet enriched with sucrose, coconut oil and either sunflower oil (n-6 fatty acids) or fish oil (long-chain n-3 fatty acid ethyl esters). The treatment with n-3 fatty acids decreased serum triglycerides (41%) and, to a lesser extent, serum cholesterol (17%). Neither glycerol 3-phosphate acyltransferase (GPAT) or DGAT were affected by n-3 fatty acids. In contrast, PAP activity was reduced by 26%. HMG-CoA reductase was not significantly affected, whereas cholesterol 7 alpha-hydroxylase activity was reduced by 36%. The results indicate that part of the TG-lowering effect of long-chain n-3 fatty acids may be mediated by inhibition of the soluble phosphatidate phosphohydrolase. The effect on serum cholesterol may be partly due to inhibition of HMG-CoA reductase.

Acyltransferases↗
PubMed1991

Sequence of rat alpha 1-macroglobulin, a broad-range proteinase inhibitor from the alpha-macroglobulin-complement family.

The alpha-macroglobulin-complement family of plasma proteins includes at least three different alpha-macroglobulins in rats, alpha 2-macroglobulin (alpha 2M), alpha 1 inhibitor III (alpha 1I3), and alpha 1-macroglobulin (alpha 1M). These high molecular weight polypeptides (Mr 160,000 to 200,000) are broad-range proteinase inhibitors. They utilize an internal thiolester function to trap proteinases that cleave their bait regions. The amino acid sequences of alpha 2M and two variants of alpha 1I3 are known. The isolation of alpha 1M cDNA clones and the determination of their cDNA and derived amino acid sequences are reported here. Alpha 1M shares 57.2% and 53.0% overall amino acid sequence identity with alpha 2M and alpha 1I3, respectively, but differs significantly from both in its bait region, suggesting that each inhibitor addresses a different spectrum of proteinases. The disulfide bridge structure of alpha 1M was deduced from its sequence and showed extensive similarities with the experimentally determined structures of other alpha-macroglobulins, suggesting similar overall tertiary structures. Alpha 1M mRNA was detected in 13 different rat tissues tested, whereas alpha 2M and alpha 1I3 mRNAs showed a far more restricted tissue distribution. While alpha 2M and alpha 1I3 mRNA and protein concentrations are significantly altered during acute and chronic inflammations, alpha 1M plasma concentrations are changed only twofold. Thus, in contrast with alpha 2M and alpha 1I3, the functions provided by alpha 1M may be ubiquitously and constitutively required in a broad range of tissues.

Amino Acid Sequence↗
PubMed1989

Elevated NK-mediated lysis of Raji and Daudi cells carrying fixed iC3b fragments.

Raji and Daudi cells were opsonized with C3b, iC3b, and C3d fragments by using purified complement components. The sensitivity of C3-opsonized cells to lysis mediated by low density blood lymphocytes was studied. Raji and Daudi cells carrying C3b or C3d fragments were lysed with similar efficiencies as the nonopsonized cells. The presence of iC3b on the target surface imposed elevated NK sensitivity. The iC3b-mediated enhancement of NK lysis was inhibited when iC3b fragments or rabbit anti-human C3 antibodies were included into the lytic assays. These results indicate that the iC3b fragments fixed on the targets bind to the CR3 on the lymphocytes. Results obtained in immobilized conjugate-lytic assays showed that iC3b-opsonized targets interact more readily with the lymphocytes. This was reflected by the elevated proportion of lymphocytes that were bound to the iC3b-carrying targets. The proportions of conjugates in which target damage occurred were similar with the control and with the iC3b-carrying cells. It seems therefore that opsonization of targets with iC3b leads to recruitment of effector lymphocytes due to contact with their CR3. However, once the effector-target contact is established, the triggering of lytic function does not seem to be influenced by the iC3b/CR3 bridge.

Burkitt Lymphoma↗
PubMed1988

Relationships between the gene and protein structure in human complement component C9.

Human complement component C9 is a multidomain protein for which a large number of surface topographical features have been determined. We have analyzed the exon-intron boundaries of the human C9 gene and find a good correlation between splice sites and surface features of the protein but little correlation with the putative protein domain structure, even in the cysteine-rich sequence homology with the low-density lipoprotein (LDL) receptor which is likely to be an independently folded structural motif. This is surprising because in the LDL receptor the same sequence is precisely bounded by introns, and it has been assumed that this sequence is present in both proteins as a result of exon shuffling. We deduce that substantial rearrangement of the exon-intron structure of the C9 gene must have occurred before the exchange of cysteine-rich domains, possibly linked to the process of exon duplication which was required to generate the repeats in the LDL receptor.

Amino Acid Sequence↗