Biomedical subjects

H Stangl

Publications and source records attributed to H Stangl.

14 recordsLinked to original sources

PubMed2006

Apolipoprotein AV does not contribute to hypertriglyceridaemia or triglyceride lowering by dietary fish oil and rosiglitazone in obese Zucker rats.

AIMS/HYPOTHESIS: Apolipoprotein AV (apoAV) is a recently discovered apolipoprotein with a triglyceride-lowering effect in genetically modified mice. Transcription of the human gene encoding apoAV (APOA5) is suppressed by insulin and stimulated by fibrates. Our goal was to study the expression of Apoa5, in comparison with Apoa4 and Apoc3, in hypertriglyceridaemic, obese and insulin-resistant Zucker rats receiving the insulin sensitiser rosiglitazone and/or a fish oil diet to lower triglycerides. METHODS: Hepatic Apoa5, Apoa4 and Apo3 mRNA and liver and plasma apoAV were measured in lean and obese Zucker rats receiving rosiglitazone while on a coconut oil or fish oil diet. RESULTS: Basal hepatic Apoa5 expression was similar in obese and lean Zucker rats. Unexpectedly, obese Zucker rats tended to have higher plasma apoAV levels despite their hypertriglyceridaemic state. Both rosiglitazone and the fish oil diet significantly increased Apoa5 mRNA, by about 70%, but tended to lower liver and plasma apoAV. Rosiglitazone had no effect on Apoa5 mRNA in cultured rat hepatocytes. No intact PPAR (peroxisome proliferator-activated receptor) response element was identified in the rat Apoa5 promoter. CONCLUSIONS/INTERPRETATION: Our data indicate that apoAV does not contribute to the hypertriglyceridaemia of obese Zucker rats or to the hypolipidaemic effect of rosiglitazone or a fish oil diet. The divergent changes of Apoa5 mRNA and apoAV levels suggest co- or post-translational regulation. The increase in Apoa5 mRNA induced by rosiglitazone is not directly mediated by peroxisome proliferator-activated receptor gamma.

Animals↗

PubMed2004

Decrease of plasma apolipoprotein A-IV during weight reduction in obese adolescents on a low fat diet.

OBJECTIVE: Apolipoprotein (apo) A-IV is an antiatherogenic apolipoprotein, which may be involved in the regulation of food intake. Plasma apoA-IV is elevated in human obesity and apoA-IV polymorphisms have been associated with the extent of obesity. Our aim was to determine the effects of weight loss on plasma apo-IV in obese adolescents and to examine the relation of apoA-IV with the degree of obesity. DESIGN: Longitudinal intervention study of a low fat hypocaloric diet conducted in a dietary camp. SUBJECTS: Two groups of obese adolescents (n=47 and n=29), age: 12.7+/-1.7 and 11.7+/-2.6 y, relative body mass index (RBMI): 168+/-24 and 175+/-34%, respectively. MEASUREMENTS: Plasma total apoA-IV, apoA-I, apoB, plasma distribution of apoA-IV, leptin, lipids, and lipoproteins before and after 3 weeks of weight reduction. RESULTS: Plasma apoA-IV decreased from 11.5+/-4.1 mg/dl before to 6.7+/-2.2 mg/dl after weight reduction in the first group (P<0.001) and to a similar extent in the second group. The relative amount of lipid-free apoA-IV and apoA-IV associated with apoA-I increased slightly, whereas apoA-IV associated with lipoproteins devoid of apoA-I decreased. ApoA-IV levels before and after weight reduction and the changes in plasma apoA-IV did not independently correlate with RBMI, weight loss, or plasma leptin. CONCLUSION: Plasma apoA-IV decreases markedly in overweight adolescents undergoing short-term weight reduction. The decrease is not directly related to the degree of weight loss and the mechanisms underlying this reduction remain to be clarified.

Adolescent↗

PubMed2002

Effect of estrogen on scavenger receptor BI expression in the rat.

High-dose 17alpha-ethinyl estradiol treatment is associated with increased adrenal and decreased hepatic levels of scavenger receptor class B type 1 (SR-BI) in rats. In this paper we explored the mechanisms responsible for the differential regulation of SR-BI by estrogen in these two tIssues. Previously it was shown that estrogen-treated rats are profoundly hypolipidemic due to increased hepatic low density lipoprotein receptor (LDLR) activity, and that this effect is not maintained with hypophysectomy. To determine if the reduction in hepatic SR-BI was a direct or indirect effect of estrogen, we treated hypophysectomized rats with high-dose estrogen; the levels of SR-BI expression did not change in the livers or adrenals of these animals. To determine if the absence of response to estrogen in the adrenals of hypophysectomized animals was due to the absence of adrenocorticotropic hormone (ACTH), we examined the effect of estrogen treatment on SR-BI expression in animals treated with dexamethasone, which inhibits endogenous ACTH production. The administration of dexamethasone completely inhibited the increase in SR-BI expression in the adrenals of estrogen-treated rats. From these studies we conclude that estrogen does not have a direct effect on SR-BI expression in either the liver or the adrenals. In the liver, the decrease in SR-BI is dependent on the estrogen-induced increase in LDLR activity, and in the adrenal glands, ACTH is required for the estrogen-associated increase in expression of SR-BI.

Adrenal Glands↗

PubMed2001

Localization of mRNAs encoding peroxisomal proteins in cell culture by non-radioactive in situ hybridization. Comparison of rat and human hepatoma cells and their responses to two divergent hypolipidemic drugs.

A non-radioactive in situ hybridization (ISH) protocol for localization of mRNAs encoding peroxisomal proteins in hepatoma cell lines from humans (HepG2) and rats (MH1C1) is presented. In comparison to a similar procedure reported for tissue sections, the cell culture preparations require only brief fixation in 4% paraformaldehyde and their permeabilization is achieved by a very low concentration (1 microg/ml) of proteinase K. The exclusive localization of transcripts in the cytoplasm of hepatoma cells with the absence of nuclear staining and the completely negative sense controls confirm the specificity of the method. The marked differences in signal intensity between the results of albumin and beta-actin mRNAs which are of high abundance in contrast to moderate to low abundance of peroxisomal mRNAs show the high sensitivity and the wide range of applicability of our protocol. This is also confirmed by divergent results of treatment of hepatoma cell lines with clofibrate and cetaben on mRNA levels of catalase and acyl-CoA oxidase. The ISH results of drug treatment of cell lines are confirmed also by slot blot analysis of total RNA extracts using 32P-labeled probes. Thus the protocol presented here provides a sensitive tool for ISH localization of mRNAs encoding peroxisomal proteins. In combination with immunocytochemistry it may be useful to monitor intercellular differences in expression levels of specific mRNAs in correlation with the abundance of structurally divergent forms of peroxisomes (tubular versus spherical) and their importance in the biogenesis of peroxisomes.

4-Aminobenzoic Acid↗

PubMed2001

Cetaben-induced changes on the morphology and peroxisomal enzymes in MH1C1 rat hepatoma cells and HepG2 human hepatoblastoma cells.

Human HepG2 and rat MH1C1 hepatoma cell lines were examined for their response to cetaben, an exceptional type of peroxisome proliferator. Shape change and proliferation of peroxisomes as well as induction of selected peroxisomal enzymes catalase, acyl-CoA oxidase, and peroxisomal bifunctional enzyme, were assessed in response to cetaben. In MH1C1 cells, peroxisomes were seen in clusters displaying typical features of microperoxisomes. Cetaben caused little but reversible proliferation and morphological heterogeneity with the occurrence of dumbbell-shaped and cup-shaped peroxisomal profiles. Peroxisomes in HepG2 cells showed marked variation in size and shape. Cetaben treatment of HepG2 cells caused disintegration of Golgi regions and augmented mitochondrial matrix. Interestingly, MH1C1 cells showed different subunit composition of acyl-CoA oxidase in immunoblot analysis: only subunit A at 72 kDa was detected but not the cleavage products. In situ hybridization underlined the marked morphological heterogeneity observed, and both cell lines revealed different stages of gene expression. Our results indicate that cetaben represents an extraordinary type of peroxisomal proliferator with pleiotropic effects on human and rat hepatoma cells, and, at least in the human hepatoma cell line HepG2, these effects are not restricted to peroxisome proliferation.

4-Aminobenzoic Acid↗

PubMed1999

Transport of lipids from high and low density lipoproteins via scavenger receptor-BI.

The scavenger receptor-BI (SR-BI) delivers sterols from circulating lipoproteins to tissues, but the relative potency of individual lipoproteins and the transported cholesterol has not been studied in detail. In this study, we used Chinese hamster ovary cells that express recombinant mouse SR-BI but have no functional low density lipoprotein (LDL) receptors (ldlA7-SRBI cells) to compare the fate of lipids transferred from high or low density lipoproteins to cells by SR-BI. HDL and LDL were equally effective in mediating the transfer of [(3)H]cholesterol to cells. Only 5% of the free cholesterol transferred to cells was esterified, in direct contrast to the findings in the cells that express LDL receptors in which 50% of the transported cholesterol was esterified. Almost all the free cholesterol transferred from lipoproteins to cells was rapidly excreted when the ldlA7-SRBI cells were switched to media containing unlabeled lipoproteins. SR-BI expression was associated with an increase in selective cholesteryl ester uptake from both lipoproteins, but HDL was a more effective donor. HDL and LDL were equally effective in delivering cholesterol to the intracellular regulatory pool via SR-BI. These data indicate that SR-BI is able to exchange cholesterol rapidly between lipoproteins and cell membranes and can mediate the uptake of cholesteryl esters from both classes of lipoproteins.

Animals↗

PubMed1999

Developmental and hormonal regulation of murine scavenger receptor, class B, type 1.

The scavenger receptor, class B, type I (SR-BI), is the predominant receptor that supplies plasma cholesterol to steroidogenic tissues in rodents. We showed previously that steroidogenic factor-1 (SF-1) binds a sequence in the human SR-BI promoter whose integrity is required for high-level SR-BI expression in cultured adrenocortical tumor cells. We now provide in vivo evidence that SF-1 regulates SR-BI. During mouse embryogenesis, SR-BI mRNA was initially expressed in the genital ridge of both sexes and persisted in the developing testes but not ovary. This sexually dimorphic expression profile of SR-BI expression in the gonads mirrors that of SF-1. No SR-BI mRNA was detected in the gonadal ridge of day 11.5 SF-1 knockout embryos. Both SR-BI and SF-1 mRNA were expressed in the cortical cells of the nascent adrenal glands. These studies directly support SF-1 participating in the regulation of SR-BI in vivo. We examined the effect of cAMP on SR-BI mRNA and protein in mouse adrenocortical (Y1-BS1) and testicular carcinoma Leydig (MA-10) cells. The time courses of induction were strikingly similar to those described for other cAMP- and SF-1-regulated genes. Addition of lipoproteins reduced SR-BI expression in Y1-BS1 cells, an effect that was reversed by administration of cAMP analogs. SR-BI mRNA and protein were expressed at high levels in the adrenal glands of knockout mice lacking the steroidogenic acute regulatory protein; these mice have extensive lipid deposits in the adrenocortical cells and high circulating levels of ACTH. Taken together, these studies suggest that trophic hormones can override the suppressive effect of cholesterol on SR-BI expression, thus ensuring that steroidogenesis is maintained during stress.

Adrenal Glands↗

PubMed1998

Scavenger receptor, class B, type I-dependent stimulation of cholesterol esterification by high density lipoproteins, low density lipoproteins, and nonlipoprotein cholesterol.

Scavenger receptor, class B, type I (SR-BI) is a cell surface glycoprotein that mediates selective uptake and efflux of sterols from high density lipoproteins (HDL) to cells. A Chinese hamster ovary cell line that is deficient in functional LDL receptors, but has high expression levels of recombinant SR-BI (ldlA7-SR-BI), was used to examine the effect of SR-BI on the trafficking of sterols between lipoproteins and cells. To monitor the fate of sterols transported by SR-BI into cells, we measured the incorporation of [14C]oleate into cholesterol esters by acyl-CoA:cholesteryl acyltransferase in the endoplasmic reticulum. We show that incubation of ldlA7-SRBI cells with either LDL or HDL resulted in an equally dramatic increase in the formation of [14C]oleate-labeled cholesterol esters. The lipoprotein-stimulated, SR-BI-dependent increase in cholesterol esterification was inhibited by chloroquine. The uptake of sterols and their incorporation into cholesterol esters by SR-BI from LDL was largely a selective process. The addition of free cholesterol to ldlA7-SRBI cells also stimulated cholesterol ester formation in a chloroquine-sensitive fashion. We also show that SR-BI mediates the efflux of endogenously synthesized sterols from the cell membrane. From these studies we conclude that, in the absence of the LDL receptor, overexpression of SR-BI can mediate significant transport of sterols between lipoproteins and the endoplasmic reticulum of cells.

Acids↗

PubMed1996

Effects of prenatal treatment with betamethasone, L-carnitine, or betamethasone-L-carnitine combinations on the phosphatidylcholine content and composition of the foetal and maternal rat lung.

Pregnant rats received 0.10 or 0.20 mg/kg body weight betamethasone, or 100 mg/kg body weight L-carnitine, or L-carnitine 100 mg/kg plus betamethasone 0.05 or 0.10 mg/kg body weight, or saline (controls) for three days before delivery of foetuses at day 19 of gestation. Dose-related effects on the dipalmitoyl phosphatidylcholine content and the phosphatidylcholine species composition of foetal and maternal lungs were determined. Betamethasone (0.10 and 0.20 mg/kg) or L-carnitine (100 mg/kg) significantly increased (p < 0.05) the dipalmitoyl phosphatidylcholine content in the foetal lungs, while only small changes were found in relative terms. Combinations of betamethasone (0.05 or 0.10 mg/kg) with L-carnitine (100 mg/kg) also significantly increased the dipalmitoyl phosphatidylcholine content of the foetal lungs above control values (p < 0.01) and above the values achieved with betamethasone alone (p < 0.05). In the maternal lungs a significant increase of the dipalmitoyl phosphatidylcholine content above the control values was only found after treatment with betamethasone-carnitine combinations, whereas compared with the foetal lung the relative increase of dipalmitoyl phosphatidylcholine as a fraction of total phosphatidylcholine was more pronounced after betamethasone treatment. The gas chromatographic method used separates two monoenoic phosphatidylcholine species with 32 carbon atoms in the acyl residues. These two phosphatidylcholine species showed striking differences between adult and foetal lungs. Palmitoleyl palmitoyl phosphatidylcholine predominates in the maternal lung, whereas palmitoyl palmitoleyl phosphatidylcholine is the major monoenoic phosphatidylcholine species with 32 carbon atoms in the foetal lung. These two species were not affected in maternal or foetal lung by betamethasone or L-carnitine treatment. In contrast, after treatment with betamethasone-carnitine combinations, a significant increase of the fraction of palmitoyl palmitoleyl phosphatidylcholine was found in foetal but not in the maternal lung. The results of the present study demonstrate that maternal glucocorticoid and carnitine treatment affects the maternal as well as the foetal lung but with different effects on the dipalmitoyl phosphatidylcholine content and phosphatidylcholine species composition.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1996

[Pleiotrophic peroxisome induction by hypolipidemic agents in primates and rodents].

Hyperlipoproteinemia is the most important public health risk factor for ischemic heart disease and is still responsible for a high proportion of the annual deaths in Austria. Clofibrate and other structurally related compounds are hypolipidemic drugs used in the treatment of hyperlipoproteinemia. Peroxisome proliferators enhance peroxisomal enzyme activities and increase mRNA levels of the corresponding genes. Some of these effects may be mediated by peroxisome proliferator activated receptors (PPARs). Subchronic treatment of rodents with hypolipidemic drugs produces profound hepatomegaly and increases the incidence of hepatocellular carcinomas, which has not been found in primates. Up to now hypolipidemic drugs have been administered with caution in view of these results. In order to evaluate the interspecies differences in the regulation of the peroxisomal enzyme system we are establishing a cell model system.

Animals↗

PubMed1995

Nitric oxide regulates peroxisomal enzyme activities.

We have previously shown that peroxisomes are involved in the production and detoxification of reactive oxygen species and that peroxisomal functions are damaged by such oxygen species. Since nitric oxide is not only a cellular messenger, but also a free radical, it would be interesting to detect a connection between nitric oxide levels and peroxisomal enzyme activities. To determine if nitric oxide has an effect on the activities of peroxisomal functions and whether this effect is based solely on its chemical properties as reactive oxygen species or its action as a second messenger, effectors of the cellular nitric oxide level were applied to a cell model (human skin fibroblasts in culture) or directly to the enzymatic assays or both. If applied to the monolayer at non-cytotoxic concentrations, N-nitro-L-arginine methyl ester hydrochloride, an inhibitor of nitric oxide synthase (EC 1.14.13.39), increased catalase (EC 1.11.1.6) activity by more than 10% and decreased the activity of the peroxisomal fatty acid oxidation system by more than 10%. The effect was concentration-dependent. L-Arginine had the contrary effect. Combinations of L-arginine and N-nitro-L-arginine methyl ester hydrochloride compensated one another. If applied directly to the assays, S-nitroso-N-acetylpenicillamine and sodium nitroprusside inhibited catalase activity in a concentration-dependent manner. Sodium nitro-prusside had no effect on the peroxisomal beta-oxidation system unless cells were pretreated with N-nitro-L-arginine methyl ester overnight (50% inhibition). The results show a differential effect for the application of nitric oxide-effectors on fibroblast monolayers, cell suspensions and under assay conditions. Depending on the conditions of the incubation, nitric oxide applied to the cell monolayer at low doses acts as a second messenger in cells rather than as reactive oxygen species. Under assay conditions the effect of nitric oxide is more likely that of a reactive oxygen species because it inhibits all measured enzyme activities.

Arginine↗

PubMed1995

Differential induction of peroxisomal enzymes by hypolipidaemics in human (HepG2) and rat (MH1C1) hepatoma cell lines.

Human (HepG2) and rat (MH1C1) hepatoblastoma cells were incubated with different concentrations of the hypolipidaemics cetaben, clofibrate and thyroxine. The enzymatic activities of catalase, peroxisomal bifunctional enzyme, succinate dehydrogenase, and 3-oxoacyl-CoA thiolase were measured. In order to determine the point of regulation of the enzymatic activities Northern and Slot blot experiments with probes for peroxisomal bifunctional enzyme, catalase and fatty acyl CoA oxidase were performed on total RNA. Catalase activity was enhanced in HepG2 cells treated with 3 mmol/l clofibric acid to 135% of control and the mRNA value to 2.6 fold, whereas in cetaben treated cells the enhancement (up to 119% of control) was less pronounced. In MH1C1 cells catalase activity was not changed by any of the drugs. The activity of the peroxisomal bifunctional enzyme was not affected in HepG2 cells by clofibric acid and cetaben, whereas the mRNA level was elevated to 2.3 fold by 10 micromol/l cetaben. At high concentrations of cetaben all enzyme activities were decreased in both cell lines due to its high cytotoxicity. Our data show that, due to the differences in the genomic organisation, the regulation of the enzyme activities is different in human and rat, but the results from the human and rat hepatoblastoma cells correlate with the findings in whole man and rat, so that a human in vitro system is more suitable for pharmacological tests. These results suggest that the human hepatoma cell line HepG2 may be a useful model system for studies of the influence of hypolipidaemics on the peroxisomal enzyme system.

4-Aminobenzoic Acid↗

PubMed1995

[Peroxisomal diseases--oxygen and free radicals].

Peroxisomes were the latest subcellular organelles to be discovered. For a long time, due to limited knowledge of their function, peroxisomes were considered to play only a supporting role for other organelles in cellular metabolism. The discovery of specific metabolic pathways carried out exclusively in peroxisomes and, in particular, the description of genetically determined peroxisomal disorders such as the Zellweger syndrome and X-linked adrenoleukodystrophy, established the importance of these organelles in playing an essential role in cellular metabolism. Recently, their participation in the metabolism of reactive oxygen species and free radicals was found to be one of the important functions of peroxisomes. The fact that peroxisomal disorders are well defined biochemically and that peroxisomes consume a significant amount of the total cellular oxygen uptake, make cells from patients suffering from these disorders a suitable cell model for studying peroxisomal participation in the detoxification of reactive oxygen species.

Energy Metabolism↗

PubMed1993

Characterization of the Trichoderma reesei cbh2 promoter.

A 613-bp fragment of the 5' upstream region of the Trichoderma reesei cbh2 gene (coding for the cellulolytic enzyme cellobiohydrolase II) has been isolated and sequenced. Fusion of this fragment to the E. coli uidA gene (coding for beta-glucuronidase) leads to--albeit low--expression of beta-glucuronidase activity in the presence of cellulose and upon the addition of low molecular weight inducers (sophorose, lactose) of cellobiohydrolase II. It also governed the formation of beta-glucuronidase activity during sporulation and its transport to the conidial surface. However, despite the presence of a signal peptide in the cbh2:uidA fusion, beta-glucuronidase was not secreted in T. reesei. Defined fragments of the 613-bp promoter region were isolated and used to identify areas involved in the regulation of cbh2 expression by protein-DNA binding assays. At least two binding areas--between -443/-363 and -363/-173, respectively--were identified. In both areas, the DNA-protein complex observed was appreciably larger when cell-free extracts from sophorose-induced mycelia were used. This suggests that at least one of the proteins regulating cbh2 transcription is itself induced by cellulose.

Base Sequence↗