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Biomedical subjects

M Ingelman-Sundberg

Publications and source records attributed to M Ingelman-Sundberg.

At least 91 records · Page 5Linked to original sources
PubMed1998

Ultrarapid metabolism of sparteine: frequency of alleles with duplicated CYP2D6 genes in a Danish population as determined by restriction fragment length polymorphism and long polymerase chain reaction.

CYP2D6 is a polymorphically expressed enzyme with two phenotypes. Poor metabolizers lack the enzyme caused by inactivating mutations in the CYP2D6 gene and extensive metabolizers have at least one active CYP2D6 gene. Extensive metabolizers with very high capacity for CYP2D6 dependent drug metabolisms are termed ultrarapid metabolizers and carry alleles with duplicated, multi duplicated or amplified CYP2D6 genes. In the present study, we examined the frequency of CYP2D6 gene duplications in a Danish population and validated a long polymerase chain reaction method for identification of ultrarapid metabolizers. Sixty individuals having a metabolic ratio for sparteine at or below 0.15 were selected and a control group of 53 individuals with a metabolic ratio between 0.16 and 12.4 was used. Based on EcoRI restriction fragment length polymorphism analysis, eight individuals were found with a duplicated CYP2D6 gene, whereas using a long polymerase chain reaction method, nine individuals with a 3.6 kb fragment indicative of two CYP2D6 genes in tandem were found among the 60 individuals with a low metabolic ratio. No gene duplication was found in the control group or in any individuals with a metabolic ratio > 0.14. Based on these results, we estimate the frequency of individuals with CYP2D6 duplication in the Danish population to be 0.8%, which is comparable to the frequency in the Swedish and the German populations, but considerably lower than in Spanish or African populations. We conclude that the long polymerase chain reaction assay is simple and reliable for detection of duplications of the CYP2D6 gene.

Alleles↗
PubMed1997

Pretranslational and posttranslational regulation of rat hepatic CYPs 3A2 and 2E1 by disulfiram.

The aldehyde dehydrogenase inhibitor disulfiram (DS) has been used to deter drinking in alcoholics, but it also precipitates pharmacokinetic interactions with coadministered drugs. From previous experiments conducted in vitro, it has been proposed that the ethanol-inducible cytochrome P450 2E1 (CYP2E1) is the major target for inhibition by DS, but the inference from reported drug interactions is that the drug inhibits multiple CYPs. The aim of the present study was to evaluate the inhibition of major constitutive CYPs in rat liver by DS. Thus, the effects of DS on activities mediated by CYPs 2A1/2, 2C11, 2E1, and 3A, which constitute approximately 80% of total CYPs in male rat liver, were evaluated. It was found that CYP2E1-mediated aniline 4-hydroxylase activity was weakly inhibited by DS in vitro, but that preincubation of the drug with NADPH-supplemented microsomes to generate metabolites of DS enhanced the extent of inhibition somewhat. In contrast, constitutive testosterone hydroxylases were inhibited effectively at low concentrations of DS (20 microM decreased the activities of all hydroxylation pathways to 40-60% of control), and a preincubation step between DS and NADPH-fortified microsomes enhanced the inhibition of CYP2C11 and 3A2 activities. In vivo studies were undertaken in which a single dose of DS (100 mg/kg, i.p.) was administered to rats; 24 hr later, CYP2E1-mediated aniline 4-hydroxylase activity was decreased to about 50% of the activity in untreated control rats. CYP2E1 apoprotein and mRNA were also decreased to 38% of the respective control, and CYP3A apoprotein and CYP3A2 mRNA responded similarly. In contrast, CYP2C11 apoprotein was decreased to 66% of control after DS administration, and CYP2A1 expression was unchanged. These findings establish that multiple CYPs are targets for inhibition by DS and provide a basis for clinically significant drug interactions involving CYPs other than 2E1. In addition, the in vivo modulation of CYP function by DS administration is not restricted to enzyme inactivation and may also include down-regulatory effects mediated at a pretranslational level.

Alcohol Deterrents↗
PubMed1997

Signal transduction-mediated activation of the aryl hydrocarbon receptor in rat hepatoma H4IIE cells.

We have investigated mechanisms of omeprazole (OME)-mediated induction of CYP1A1 and CYP3A, using the rat hepatoma H4IIE cell line, in comparison with mechanisms exerted by traditional aryl hydrocarbon receptor (AhR) ligands such as benso(a)pyrene (B(a)P) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). OME did not bind specifically to AhR, and it could not activate the AhR complex in rat cytosol to a xenobiotic-responsive element (XRE)-binding form in vitro. Genistein, a tyrosine kinase inhibitor, and daidzein, an inhibitor of casein kinase II, efficiently inhibited OME-mediated but not B(a)P- or TCDD-mediated induction of CYP1A1, as monitored at the transcriptional, mRNA, and protein levels as well as by analysis of activation of XRE-luciferase reporter constructs transfected into H4IIE cells. The protease inhibitor Nalpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and lavendustin A also had similar OME-specific effects. In addition, insulin pretreatment caused an almost complete inhibition of OME-dependent CYP1A1 induction but only partially affected TCDD and B(a)P-mediated induction of CYP1A1. Staurosporine, an inhibitor of protein kinase C, impaired the induction by both B(a)P and OME. OME caused an approximately 2-fold increase in the level of CYP3A expression, but all inhibitors used were ineffective in preventing this induction. Gel shift analysis with radiolabeled XRE and specific peptide antibodies toward AhR and aryl hydrocarbon receptor nuclear translocator protein (Arnt) revealed an OME-mediated translocation of the AhR.Arnt complex into the nuclei. Genistein inhibited the specific nuclear XRE binding caused by OME, but it potentiated the formation of the TCDD-induced XRE.AhR complex. Although daidzein was able to effectively inhibit the OME-stimulated CYP1A1 gene transcription, it did not influence the OME-dependent AhR.XRE complex formation. The data are consistent with a mechanism for OME-mediated induction of CYP1A1 that involves activation of the AhR complex via intracellular signal transduction systems and that is distinct from induction mediated by AhR ligands.

Animals↗
PubMed1997

Detection of cytochrome P4503A (CYP3A) in human hepatic stellate cells.

In this study we have investigated the occurrence of cytochrome P450 isoforms and of related cytochrome P450 reductase in human hepatic stellate cells (hHSC), a type of cell having relevant roles in physiopathological conditions of the liver. By performing immunoblotting of hHSC microsomes and immunofluorescence analysis associated to confocal laser microscopy we detected only P450 enzymes belonging to the cytochrome P450 3A subfamily (CYP3A) as well as cytochrome P450 reductase. The presence of CYP3A was further indicated by detection of testosterone 6beta-hydroxylase activity in hHSC microsomes. Other important human P450 forms were either undetectable (CYP1A2, CYP2E1, CYP2C8/9/19 and CYP4A) or bearly detectable (CYP1A1) in hHSC. This is the first study showing existence of active cytochrome P450 isoforms in human HSC.

Adipocytes↗
PubMed1997

Selective fast degradation of cytochrome P-450 2E1 in serum-deprived hepatoma cells by a mechanism sensitive to inhibitors of vesicular transport.

Cytochrome P-450 2E1 (CYP2E1) is characterized by a rapid turnover in the liver and some cell lines and the ability of substrates and heme iron ligands to inhibit significantly enzyme degradation. In the Fao hepatoma cell line, CYP2E1 was found to be fairly stable (half-life of 26 h), but serum withdrawal resulted in its rapid disappearance from the microsomal fraction (half-life of about 7 h) as evaluated using cycloheximide chase. The effect of serum withdrawal could be partially reversed by the addition of albumin to the culture medium, whereas insulin and the insulin-like growth factor IGF-I had no additional effect. The effect of serum withdrawal was specific for CYP2E1 since (a) no concomitant fast degradation of CYP2B1 and NADPH-cytochrome P-450 reductase was observed and (b) the CYP2E1 ligands ethanol and imidazole prevented the fast degradation of the enzyme. The lysosomotropic agent ammonium chloride and the inhibitor of autophagocytosis 3-methyladenine slowed down CYP2E1 degradation by about 30%, while leupeptin had no effect. Under the same conditions, the degradation of total long-lived cell protein showed the same sensitivity to ammonium chloride, but was significantly less sensitive to 3-methyladenine and serum and not sensitive to ethanol and imidazole. CYP2E1 degradation was inhibited by combined treatment with brefeldin A and nocodazole, which blocks both anterograde and retrograde vesicular transport between endoplasmic reticulum and the Golgi apparatus. The data point to the existence of a selective mechanism for the degradation of membrane proteins in serum-deprived cells in addition to nonselective autophagocytosis. The selective degradation of CYP2E1 may be attained by means of its selective vesicular transport to an acidic post-endoplasmic reticulum compartment.

Animals↗
PubMed1997

In vitro kinetics of two human CYP1A1 variant enzymes suggested to be associated with interindividual differences in cancer susceptibility.

A genetic polymorphism (A4889-->G) in the human CYP1A1 gene which creates an Ile462-->Val amino acid substitution has been suggested to cause altered enzymatic properties of CYP1A1. Since several epidemiological studies have shown an association between the CYP1A1-Val allele and lung cancer, we considered it of importance to evaluate the in vitro kinetic properties of the two CYP1A1 variants after expression of each cDNA in yeast. No differences were found in K(m) or Vmax for CYP1A1 dependent O-dealkylation of ethoxyresorufin and 3-hydroxylation of benzo(a)pyrene between the two variants. The data indicate that the Ile/Val polymorphism in human CYP1A1 is not functionally important.

Benzo(a)pyrene↗
PubMed1997

Purification and characterization of hepsin from rat liver microsomes.

Hepsin, a putative cell-surface serine proteinase, has been isolated from the microsomal membranes of rat liver and purified to homogeneity by hydroxyapatite, DEAE-Sepharose, and benzamidine-Sepharose chromatography. The course of purification was monitored using antibodies raised against a 20-mer peptide at the C-terminus of rat hepsin, and the identity of the purified protein was confirmed by partial amino-acid sequencing. A single-chain precursor of ca. 50 kDa found in the microsomes underwent spontaneous maturation in the course of purification so that the last, affinity chromatography, step recovered only the mature form which dissociated to subunits of 31 and 19 kDa under reducing SDS-PAGE. Proteinase digestion experiments with microsomal vesicles are consistent with the luminal orientation of the precursor C-terminus, which would result in its extracellular orientation upon transportation to the cell surface. [3H]diisopropylfluorophosphate covalently binds to the large subunit showing it to be the catalytic one. The N-terminal sequencing of this subunit demonstrates that the zymogen is converted to the active serine proteinase by cleavage at the Arg161-Ile162 site. Activity measurements with short synthetic peptides show that the enzyme cleaves after basic amino-acid residues, Arg being preferable to Lys. The inhibition pattern is typical of trypsin-like serine proteinases. The pH-dependence of activity within the range pH 6-9 has no maximum, the activity increasing continuously with pH. These results are consistent with the earlier predictions based on hepsin amino-acid sequence and elucidate the specificity and other earlier unknown enzymatic and molecular properties of the enzyme.

Amino Acid Sequence↗
PubMed1997

Plasma membrane hydroxyethyl radical adducts cause antibody-dependent cytotoxicity in rat hepatocytes exposed to alcohol.

BACKGROUND & AIMS: We reported previously that patients with alcoholic liver disease (ALD) have circulating immunoglobulins reacting with cytochrome P4502E1 (CYP2E1) complexed with hydroxyethyl free radicals. The aim of this study was to investigate whether hydroxyethyl radical adducts are present on the plasma membranes of ethanol-treated hepatocytes and their role in antibody-dependent cytotoxicity. METHODS: Immunofluorescence confocal laser microscopy, Western blotting, and antibody-dependent cell-mediated cytotoxicity assay were used. RESULTS: Isolated rat hepatocytes incubated in vitro with ethanol or obtained from ethanol-treated animals showed strong surface fluorescence when exposed to rabbit anti-hydroxyethyl radical serum or sera from patients with ALD. No surface fluorescence was evident on control hepatocytes or after scavenging hydroxyethyl radicals with 4-pyridyl-1-oxide-t-butyl nitrone. The presence of CYP2E1-hydroxyethyl radical adducts on hepatocyte plasma membranes was shown by Western blot and by immunofluorescence using double staining for human and rabbit anti-CYP2E1 immunoglobulin G. Cytotoxicity was observed in ethanol-treated hepatocytes incubated with immunoglobulin G from patients with ALD and normal human blood mononuclear cells. This effect was blocked by preabsorbing the sera with human albumin complexed with hydroxyethyl radicals, which also eliminated the antibody reaction with the plasma membranes. CONCLUSIONS: Hydroxyethyl radicals bound to CYP2E1 on hepatocyte plasma membranes can target immune reactions triggered by alcohol abuse.

Animals↗
PubMed1997

Lipid peroxidation, CYP2E1 and arachidonic acid metabolism in alcoholic liver disease in rats.

The role of cytochrome P450 metabolism of fatty acids and lipid peroxidation in the alterations of the fatty acid composition of the liver and liver pathology was investigated. The CYP2E1 inhibitors partially prevented CYP2E1 induction by ethanol and completely blocked lipid peroxidation. However, the liver pathology induced by ethanol was only partially prevented as was the decrease in arachidonic acid in total liver lipid, triglycerides and cholesterol esters. This means that liver peroxidation induced by ethanol can not completely account for the liver pathology or the decrease in arachidonic acid caused by ethanol. Lauric acid omega-1 hydroxidation by the liver microsomes in vitro was increased by ethanol and partially blocked by CYP2E1 inhibitors. However, although ethanol feeding increased the total hydroxidation and epoxidation of arachidonic acid, these were not inhibited by CYP2E1 inhibitors. Thus the ethanol-induced arachidonic acid depletion is not likely due to CYP2E1 metabolism of arachidonic acid, since the severity of liver pathology correlated negatively with the decrease in arachidonic acid in the ethanol-fed rats. The increase in its metabolism by microsomes and decrease in synthesis may be an important mechanism of ethanol-induced liver injury.

Animals↗
PubMed1997

Frequent occurrence of CYP2D6 gene duplication in Saudi Arabians.

The polymorphic cytochrome P450 2D6 (CYP2D6) causing poor, extensive or ultrarapid metabolism of several clinically important drugs exhibits pronounced interethnic variation. Ultrarapid metabolism is caused by multiple copies of active CYP2D6 genes and recently 29% of an Ethiopian population has been shown to carry duplicated or multiduplicated CYP2D6 genes, whereas the corresponding frequency in other black, Oriental and European populations investigated is 1-2%. In order to characterize the distribution of alleles with multiple CYP2D6 copies in a neighbouring population and to characterize the CYP2D locus in general among Saudi Arabians, the CYP2D6 genotype of a Saudi Arabian population was examined using restriction fragment length polymorphism (RFLP) analysis and allele-specific polymerase chain reaction (PCR) amplification. Of 101 Saudi Arabians studied, 21 subjects had an EcoRI fragment indicative of CYP2D6 gene duplication. In contrast, only two individuals were heterozygous for a deletion of the whole gene (CYP2D6*5). The allele frequency of CYP2D6*4, the most common defective allele among Caucasians, was only 3.5% in the Saudi population. Two other alleles, CYP2D6*10 and *17, common in certain populations and which cause diminished enzyme activity, were found only at low allele frequencies of 3.0% each. These findings are in agreement with earlier Saudi Arabian phenotyping studies which reported a low frequency (1-2%) of poor metabolizers for CYP2D6 probe drugs. In conclusion, the Saudi Arabian population studied exhibited very few defective alleles and a large number of subjects carried duplicated CYP2D6 genes, implying a high conservation on functional CYP2D6 genes possibly due to dietary reasons and reveal the Saudi Arabians as an unique population in comparison with others examined.

Adult↗
PubMed1997

A combination of mutations in the CYP2D6*17 (CYP2D6Z) allele causes alterations in enzyme function.

In many black African populations, the capacity for CYP2D6-dependent drug metabolism is generally reduced. A specific variant of the CYP2D6 gene (CYP2D6*17) that carries three functional mutations (T107I, R296C, and S486T) has been found to be present in Zimbabwean subjects with impaired CYP2D6-dependent hydroxylase activity. To evaluate whether the CYP2D6*17 allele was the major cause behind the decreased rate of drug metabolism and to examine the role of the different mutations, CYP2D6 cDNAs containing all eight combinations of the mutations were created. Expression of the cDNAs in COS-1 cells revealed that the CYP2D6 17 enzyme displayed only 20% of the wild-type (CYP2D6 1) activity, whereas the T107I substitution on its own had no significant effect on enzyme function. Expression in yeast showed that the three possible single amino-acid mutant CYP2D6 variants all had properties similar to CYP2D6 1 when the kinetics of bufuralol hydroxylation was examined. However, enzymes containing both the T107I and R296C mutations exhibited a more than 5-fold higher K(m) for bufuralol than the wild-type enzyme, whereas the S486T mutation was of little importance. In contrast, when codeine was used as a substrate, the T107I substitution alone was sufficient to cause a significant increase in the apparent K(m), indicating a differential effect for this substitution depending on the CYP2D6 substrate. In conclusion, the CYP2D6*17 allele represents the first human cytochrome P450 polymorphic variant in which a combination of substitutions is required to alter the enzyme's catalytic properties and is the first case in which a decreased CYP2D6 activity, as monitored in vivo, has been documented to be caused by an enzyme with altered affinity for CYP2D6 substrates.

Adrenergic beta-Antagonists↗
PubMed1997

Characterization of a human glutathione S-transferase mu cluster containing a duplicated GSTM1 gene that causes ultrarapid enzyme activity.

The mu class glutathione S-transferase gene GSTM1 is polymorphic in humans, with approximately half of the Caucasian population being homozygous deleted for this gene. GSTM1 enzyme deficiency has been suggested to predispose people to lung and bladder cancer. Some people in a Saudi Arabian population, however, have been described previously with ultrarapid GSTM1 enzyme activity. Here we have evaluated the molecular genetic basis for this observation. Genomic DNA from two Saudi Arabian subjects exhibiting ultrarapid enzyme activity and from 13 Swedish subjects having null, one, or two GSTM1 genes were subjected to restriction fragment length polymorphism analysis using the restriction enzymes EcoRI, EcoRV, and HindIII and combinations thereof. Hybridization was carried out using a full-length GSTM1 cDNA or the 5' and 3' parts of the cDNA. The restriction mapping data revealed the presence of a GST mu cluster with two GSTM1 genes in tandem situated between the GSTM2 and GSTM5 genes. A quantitative multiplex polymerase chain reaction method, which simultaneously amplified a fragment of the GSTM1 gene and the beta-globin gene, was developed, and the genomic GSTM1 copy number was determined from the GSTM1/beta-globin ratio. This method clearly separated GSTM1 +/- subjects (ratios between 0.4 and 0.7) from GSTM1 +/+ subjects (ratios between 0.8 and 1.2). The two Saudi Arabians with ultrarapid GSTM1 activities had ratios of approximately 1.5, indicating that they carried three GSTM1 genes. These results demonstrate the existence of a novel mu class GST cluster containing a duplicated active GSTM1 gene causing ultrarapid enzyme activity.

Binding Sites↗
PubMed1997

Selective centrilobular expression of the aryl hydrocarbon receptor in rat liver.

The aryl hydrocarbon receptor (AHR) is a transcriptional activator of genes encoding a group of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1), glutathione S-transferase, tumor-associated aldehyde dehydrogenase and quinone reductase. Both the constitutive and inducible expression of these genes in the liver is zonated, i.e., dominant in hepatocytes of the centrilobular region, a poorly understood position-dependent phenomenon. By comparing cell lysates obtained from opposite acinar regions we observed that immunoreactive AHR protein was almost exclusively confined to centrilobular cells. The AHR mRNA, as analyzed from cell lysates by reverse transcriptase polymerase chain reaction, exhibited a similar, although somewhat less pronounced zonation. By contrast, only slight zonation of the AHR nuclear translocator mRNA was observed. Treatment of rats with omeprazole, an atypical nonligand activator of the AHR, caused a zone-specific induction of CYP1A1 in the centrilobular region similar to that seen after pretreatment with the AHR ligand 3-methylcholanthrene. Our results suggest that the zone-restricted expression of AHR protein will allow the constitutive and inducible expression of AHR-regulated genes in the centrilobular region, but will limit their expression in the periportal region.

Animals↗
PubMed1997

Genetic polymorphism of human CYP2E1: characterization of two variant alleles.

Ethanol-inducible CYP2E1 is an enzyme of major toxicological interest because it metabolizes several precarcinogens, drugs, and solvents to reactive metabolites. CYP2E1 has also been implicated in alcohol liver disease because of its contribution to oxidative stress. Previously, polymorphic alleles with mutations in introns and in the 5'-flanking regulatory region have been described, and their presence has been related to the incidence of alcohol liver disease and lung cancer. In the present investigation, we investigated whether any functional mutations are linked to the above-mentioned rare alleles and also screened for mutations in the open reading frame using single-stranded conformation polymorphism and genomic DNA from almost 200 individuals belonging to either a Chinese, an Italian, or a Swedish population. Two new CYP2E1 gene variants were found with functional mutations: one (CYP2E1*2) in which a G1168A point mutation in exon 2 caused an R76H amino acid substitution, and the other (CYP2E1*3) in which a G10059A base substitution in exon 8 yielded a V3891 amino acid exchange. The corresponding CYP2E1 cDNAs were constructed, subcloned into the pCMV4 expression vector, and expressed in COS-1 cells. The cellular levels of CYP2E1 mRNA, CYP2E1 protein, and rate of chlorzoxazone hydroxylation were monitored. The CYP2E1*3 cDNA variant was indistinguishable from the wild-type cDNA on all variables investigated, whereas CYP2E1*2 cDNA, although yielding similar amounts of mRNA, only caused 37% of the protein expression and 36% of the catalytic activity compared with the wild-type cDNA. Complete screening by single-stranded conformation polymorphism of the three populations studied revealed that these variant alleles were rare. We conclude that the human CYP2E1 gene is functionally surprisingly well conserved compared with other cytochrome P450 enzymes active in drug metabolism, which suggests an important endogenous function in humans.

Alleles↗
PubMed1996

Enzyme-specific transport of rat liver cytochrome P450 to the Golgi apparatus.

It has been reported that cytochrome P450 is expressed in the plasma membrane of hepatocytes isolated from human and rat. Cytochrome P450s expressed on the cell surface are potential targets for the immune response of drug-induced and autoimmune hepatitis. However, the mechanisms behind transport of cytochrome P450 to the plasma membrane are obscure. The present investigation aimed at identifying cytochrome P450 expressed in the Golgi apparatus. Golgi membrane fractions from rat liver were prepared and characterized: one enriched with cis-Golgi, one highly enriched with trans-Golgi, and one intermediate Golgi fraction representing medial-Golgi. In these three fractions, significant amounts of cytochrome P450 and NADPH cytochrome P450 reductase were present, which could not be accounted for by contamination with endoplasmic reticulum. A marked difference between the relative content of different cytochrome P450 enzymes was found. CYP4A1 was found at the highest concentration, CYP2E1 at an intermediary level, and CYP1A2 at low levels, whereas no Golgi-specific CYP3A1 was detectable. It was also shown that the CYP2E1 present in the Golgi fractions was catalytically active. It is suggested that various forms of hepatic cytochrome P450 are transported to the plasma membrane through the Golgi apparatus in an enzyme-specific manner.

Animals↗