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B Angelin

Publications and source records attributed to B Angelin.

At least 37 records · Page 2Linked to original sources
PubMed1999

Endogenous histamine reduces plasma insulin-like growth factor I via H1 receptor-mediated pathway in the rat.

Endotoxin has been recently shown to reduce plasma insulin-like growth factor I. As it was reported that histamine can induce gut-derived endotoxemia, we wanted to determine whether histamine has a similar effect on plasma insulin-like growth factor I. Compound 48/80 (a histamine releaser) was injected subcutaneously into rats, then blood was taken for plasma insulin-like growth factor I assay and the livers were assayed for insulin-like growth factor I mRNA. Like endotoxin, injection of compound 48/80 significantly reduced plasma insulin-like growth factor I. Six hours post-injection, plasma insulin-like growth factor I was reduced by 61% (P < 0.001), and 24 h post-injection, it was still lower (by 35% P < 0.001) than in the control group. Hepatic insulin-like growth factor I mRNA was not reduced by this treatment. The effect of compound 48/80 on plasma insulin-like growth factor I was significantly attenuated by oral administration of the histamine H1 receptor antagonist (chlorpheniramine), but not by the histamine H2 receptor antagonists (cimetidine and ranitidine). Oral administration of polymyxin B (an antiendotoxin antibiotic) did not attenuate the effect of compound 48/80 on plasma insulin-like growth factor I at all. In conclusion, endogenous histamine reduces plasma insulin-like growth factor I via H1 receptor-mediated pathway. Our study suggests a novel role of histamine in the regulation of insulin-like growth factor I metabolism in vivo.

Animals↗
PubMed1999

Endotoxin suppresses mouse hepatic low-density lipoprotein-receptor expression via a pathway independent of the toll-like receptor 4.

Endotoxin provokes an inflammatory state in the infected host. C3H/HeJ mice are tolerant to endotoxin because of an Lps gene mutation. Recent studies have identified that this gene encodes the Toll-like receptor 4. Endotoxin also induces hyperlipidemia and suppresses hepatic low-density lipoprotein (LDL)-receptor expression. In the current study, we investigated whether a defective Lps gene would impair the hepatic LDL-receptor response to endotoxin in C3H/HeJ mice. Eighteen hours after an intraperitoneal injection of endotoxin, the hepatic LDL-receptor expression and the plasma lipoprotein pattern were analyzed. Endotoxin increased plasma triglyceride and apoE in very low-density lipoproteins (VLDL) and intermediate-density lipoproteins, and decreased apoAI in high-density lipoproteins (HDL) in the endotoxin-sensitive mice (C3H/HeN), but not in the endotoxin-resistant mice (C3H/HeJ). These data indicate that a defective Lps gene impairs the endotoxin signaling to alter these lipoproteins. However, the hepatic LDL-receptor response to endotoxin in the endotoxin-resistant mice was similar to that in the endotoxin-sensitive mice. Thus, at a dose of 5 microg/mouse, endotoxin reduced hepatic LDL-receptor expression by 35% in C3H/HeN mice and by 52% in C3H/HeJ mice. At a dose of 50 microg/mouse, endotoxin reduced hepatic LDL-receptor expression by 61% in C3H/HeN mice and by 63% in C3H/HeJ mice. It is concluded that endotoxin suppresses hepatic LDL-receptor expression in vivo via a pathway independent of the Toll-like receptor 4.

Animals↗
PubMed1999

Evidence of circadian rhythm in low-density lipoprotein apoB catabolism and its impact on the estimation of kinetic parameters.

BACKGROUND: Compartmental models with constant parameters are commonly used in kinetic analysis of low-density lipoproteins (LDLs). Recent studies in animals have demonstrated the existence of circadian rhythms (CRs) in cholesterol synthesis and LDL catabolism. In this study, we investigated the possible existence of a CR in the fractional catabolic rate (FCR) of LDL apoB in man. MATERIALS AND METHODS: Radioactivity data from 45 turnover studies using 125I-labelled LDL apoB were analysed. In a preliminary analysis the pattern of radioactivity decay was investigated. Kinetic analysis was performed by using one- and two-compartment models with constant parameters (steady-state, SS, analysis). Parameters were estimated by the use of the whole data set, which included frequent sampling during the first day of the turnover study, or the once-a-day data, taken at 08.00 h. The selection of once-a-day data allowed elimination of the impact of a CR on parameter evaluation. Furthermore, non-steady-state (NSS) analysis was performed in which the FCR of LDL apoB was calculated as a function of time. In one additional subject, the FCR of LDL apoB was calculated separately for the day and the night using the urine-to-plasma (U/P) radioactivity ratio. RESULTS: The presence of a CR in LDL apoB catabolism, with higher FCR values during the day than during the morning, was demonstrated by the NSS analysis and confirmed by LDL apoB calculation from the U/P ratio. The SS analysis with the whole and the once-a-day data sets resulted in similar average FCR of apoB values (0.329 +/- 0.076 and 0.321 +/- 0.071 respectively) when the two-compartment model was used. Thus, a CR appeared to have little impact on the average FCR of apoB estimation. However, frequent sampling used in the hope of improving parameter estimation accuracy actually resulted in deterioration of the intercompartmental parameter estimators. CONCLUSION: The fractional catabolic rate of LDL apoB exhibited a circadian rhythm with higher FCR values during the day than during the morning. The presence of a CR had, however, a limited impact on the overall FCR of apoB values.

Apolipoproteins B↗
PubMed1999

Deoxycholic acid treatment in patients with cholesterol gallstones: failure to detect a suppression of cholesterol 7alpha-hydroxylase activity.

UNLABELLED: Hillebrant C-G, Nyberg B, Angelin B, Axelson M, Björkhem I, Rudling M, Einarsson C (Huddinge University Hospital and Karolinska Hospital, Karolinska Institute, Stockholm, Sweden). Deoxycholic acid treatment in patients with cholesterol gallstones: failure to detect a suppression of cholesterol 7alpha-hydroxylase activity. J Intern Med 1999; 246: 399-407. OBJECTIVES: Based on animal studies, hydrophobic bile acids have been postulated to be particularly strong inhibitors of bile acid synthesis. The present study was undertaken to characterize in humans the effects of one of the most hydrophobic of the common bile acids, deoxycholic acid (DCA), on the transcriptional regulation and activity of the cholesterol 7alpha-hydroxylase, on hepatic cholesterol metabolism and on biliary lipid metabolism and plasma lipids. DESIGN, SUBJECTS AND SETTINGS: Thirteen patients with cholesterol gallstone disease were treated with DCA (750 mg day-1) for 3 weeks prior to cholecystectomy. Blood samples were collected before and during treatment. At operation, a liver biopsy and gallbladder bile were obtained. Twenty-eight untreated gallstone patients undergoing cholecystectomy served as controls. The study was carried out at a university hospital. RESULTS: Deoxycholic acid comprised 72 +/- 6% (mean +/- SEM) of total biliary bile acids in DCA-treated patients (n = 8), and 21 +/- 2% in the controls (n = 16; P < 0.001). Cholesterol saturation of gallbladder bile averaged 102% in both treated (n = 7) and untreated (n = 16) patients. Cholesterol 7alpha-hydroxylase and HMG CoA reductase activities and mRNA levels were not different between DCA-treated and untreated gallstone patients. The LDL receptor mRNA levels were similar in both groups of patients. Plasma levels of total cholesterol were lowered by 10% upon DCA treatment (P < 0.05). CONCLUSIONS: Treatment with DCA did not significantly affect mRNA levels and activity of hepatic cholesterol 7alpha-hydroxylase or HMG CoA reductase in patients with cholesterol gallstones. There was no effect on the saturation of gallbladder bile, Thus, the present study could not verify that the hydrophobicity of the bile acid pool is a major factor regulating human hepatic cholesterol 7alpha-hydroxylase activity.

Adult↗
PubMed1999

Heme oxygenase inhibitors transiently increase serum ferritin concentrations without altering other acute-phase reactants in man.

Sn protoporphyrin (SnPP) and Sn mesoporphyrin (SnMP), potent inhibitors of heme oxygenase (HO), significantly suppress bilirubin production, lower serum and biliary bilirubin levels and increase biliary heme output in animals and man. In this study, 20 healthy volunteers, 7 patients with primary biliary cirrhosis and 4 patients with idiopathic hemochromatosis were treated with SnPP and 4 healthy volunteers with SnMP. In all cases, serum ferritin levels increased substantially but transiently after administration of these HO inhibitors. Values returned to baseline within a few days. Infusion of hematin in 4 healthy volunteers did not significantly affect ferritin levels. No increases occurred in 7 other acute-phase reactants. The observation that these HO inhibitors transiently increase serum ferritin levels implies a link between ferritin, iron metabolism and HO activity which may be usefully explored in disorders of iron metabolism.

Acute-Phase Proteins↗
PubMed1999

Cholesterol and lipoprotein metabolism in aging: reversal of hypercholesterolemia by growth hormone treatment in old rats.

Plasma cholesterol levels increase with age, as does the incidence of coronary heart disease. The mechanisms responsible for the age-related hypercholesterolemia are not well understood. An interesting hypothesis suggests that the relative deficiency in growth hormone (GH), which occurs with aging, contributes to the development of the age-related hypercholesterolemia, because GH has beneficial effects on cholesterol metabolism. In the present work, we tested this hypothesis by the administration of GH to normal rats of varying ages. Plasma lipids and hepatic cholesterol metabolism were characterized in 2-, 12-, and 18-month-old male Sprague-Dawley rats. In 2-month-old rats, GH specifically stimulated the hepatic low density lipoprotein (LDL) receptor expression in a dose-dependent way, both at the protein level and at the mRNA level. Concomitantly, plasma cholesterol increased by approximately 30% within the large high density lipoprotein and LDL fractions. In 12-month-old animals, cholesterol 7alpha-hydroxylase (C7alphaOH) activity was reduced, whereas hepatic LDL receptors and plasma total cholesterol were unchanged. GH treatment (1 mg. kg-1. d-1) normalized the activity of C7alphaOH and had effects on plasma cholesterol and LDL receptors similar to those seen in 2-month-old animals. In 18-month-old rats, plasma cholesterol was increased 2-fold, whereas hepatic LDL receptor expression and C7alphaOH activity were similar to those of the 12-month-old animals. Infusion of GH to 18-month-old rats had similar effects on hepatic C7alphaOH and LDL receptors as seen in 12-month-old rats. However, GH treatment strongly reduced the hypercholesterolemia in 18-month-old animals. We conclude that the age-dependent increase of plasma cholesterol in rats can be reversed by the administration of GH, presumably through the pleiotropic effects of this hormone on lipoprotein metabolism.

Aging↗
PubMed1999

Acute and short-term effects of growth hormone on insulin-like growth factors and their binding proteins: serum levels and hepatic messenger ribonucleic acid responses in humans.

We investigated the acute (4-5 h) and short-term (5 days) effects of GH treatment on hepatic messenger RNA (mRNA) levels of the genes for the insulin-like growth factors (IGFs), insulin-like growth factor binding protein-1, -2, and -3 (IGFBPs), and the acid labile subunit (ALS), as well as serum levels of these proteins in humans. At the mRNA level, we observed an increase in IGF-1 transcription (+173%) following GH treatment in the acute group, which remained elevated in the short-term treatment group. IGFBP-2 mRNA decreased after short-term GH treatment, without changes in IGFBP-1 or -3 expression. The ALS transcript level increased after 5 days. In serum, we found increased levels of IGF-I and insulin, and decreased levels of IGF-II, in the short-term treatment group. IGFBP-1 decreased in both treatment groups, whereas IGFBP-2 was reduced after 5 days treatment. ALS increased in the short-term group. We observed increased IGFBP-3 serum levels after 5 days of GH treatment, likely due to increased formation of the ternary complex. Our results show that the metabolic effects by GH on the IGF axis are complex. In addition to a direct stimulation of IGF-I and ALS expression, GH inhibits IGFBP-1 serum levels and IGFBP-2 expression in an indirect manner, possibly facilitating enhanced IGF bioavailability to target tissues.

Adult↗
PubMed1999

VLDL activation of plasminogen activator inhibitor-1 (PAI-1) expression: involvement of the VLDL receptor.

The potential role of the very low density lipoprotein (VLDL) receptor in mediating VLDL-induced plasminogen activator inhibitor-1 (PAI-1) expression was studied in vitro. Cultured endothelial cells incubated with VLDL showed an increased secretion of PAI-1. This response to VLDL could be completely prevented by the receptor-associated protein (RAP) and partially blocked by rabbit polyclonal anti-VLDL receptor IgG. Furthermore, Chinese hamster ovary (CHO) control cells and cells overexpressing the VLDL receptor were transiently transfected with a PAI-1 promoter-reporter construct and incubated with VLDL. The PAI-1 promoter activity in response to VLDL was significantly higher in the VLDL receptor overexpressing cells compared to the control cells. Addition of RAP completely blocked the VLDL-activated PAI-1 transcription. Electromobility shift assay was performed to investigate whether the enhanced PAI-1 promoter activity seen in the VLDL receptor overexpressing cells in response to VLDL involved induction of the previously described VLDL-inducible factor(s) binding to the -675 to -653 region of the PAI-1 promoter. We found that the binding of the VLDL-inducible factor in VLDL receptor overexpressing cells was markedly enhanced by addition of VLDL as compared to control cells where no increased binding could be seen in response to VLDL. In summary, these results indicate that the VLDL receptor is a strong candidate for mediating VLDL effects on PAI-1 synthesis and secretion in cells expressing this receptor.

Animals↗
PubMed1998

The level of 7-dehydrocholesterol in plasma reflects the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in the human liver.

Plasma levels of the cholesterol precursor 7-dehydrocholesterol (7-DHC) were compared with activities of the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase assayed in liver biopsies from patients undergoing cholecystectomy. Some patients were treated with cholestyramine, deoxycholic acid or chenodeoxycholic acid prior to surgery in order to alter the activity of the enzyme. The median level of 7-DHC and the activity of HMG-CoA reductase in the untreated group were 55 ng/ml and 98 pmol/min/mg protein, respectively. The sterol levels and enzyme activities were increased in patients treated with cholestyramine (85 ng/ml and 439 pmol/min/mg protein) and deoxycholic acid (86 ng/ml and 173 pmol/min/mg protein) and decreased in patients treated with chenodeoxycholic acid (38 ng/ml and 51 pmol/min/mg protein). There was a strong positive correlation (rs=0.75, P<0.0005) between the plasma levels of 7-DHC and the activities of hepatic HMG-CoA reductase in these patients. This correlation was further improved when the plasma levels of 7-DHC were expressed relative to those of cholesterol (rs=0.90, P<0.0001). The results show that the level of 7-DHC in plasma reflects the activity of HMG-CoA reductase in the liver.

Adult↗
PubMed1998

Lipoprotein receptors in acute myelogenous leukemia: failure to detect increased low-density lipoprotein (LDL) receptor numbers in cell membranes despite increased cellular LDL degradation.

The high-affinity degradation of low-density lipoprotein (LDL) is enhanced 3- to 100-fold in leukemic blood cells from patients with acute myelogenous leukemia (AML), suggesting an increased cellular LDL receptor expression. There are, however, inconsistencies regarding the published properties of LDL receptor regulation in AML cells, and previous data on this are indirect. In the present study the aim was to determine whether the LDL receptor number is increased in AML cells. The LDL receptor number was assayed by ligand blot with rabbit 125I-labeled beta-very-low-density lipoprotein (beta-VLDL) of transferred, SDS-polyacrylamide-gel-electrophoresis-separated AML cell membranes. Samples from 10 patients, six with AML, one with chronic myelogenous leukemia in blast crisis, and three with acute lymphoblastic leukemia, were investigated. The LDL receptor expression was strongly suppressed in all samples to levels lower than that of normal mononuclear cells. This was despite the fact that cells from one patient with AML of M4 subtype had a 50- to 100-fold higher 125I labeled LDL degradation compared with normal cells. Immunoblots with antibodies against gp330/megalin and the LDL-receptor-related protein (LRP) and ligand blot using 125I-labeled 39-kd receptor-associated protein (RAP) could not detect gp330/megalin or VLDL receptors. The LRP was abundant in AML samples of M4 and M5b subtype, as determined from both RAP ligand blot and immunoblot using an LRP-specific antibody. It is concluded that LDL receptors are suppressed in AML cells. It is possible that the high degradation of 125I-labeled LDL present in type M4 and M5 AML cells may involve another lipoprotein receptor.

Adolescent↗
PubMed1998

Gemfibrozil-induced decrease in serum ubiquinone and alpha- and gamma-tocopherol levels in men with combined hyperlipidaemia.

BACKGROUND: Low blood levels of antioxidants are associated with an increased risk of developing coronary artery disease. Lipophilic antioxidants are transported in lipoproteins, and hypolipidaemic therapy may therefore alter their blood concentrations. METHODS: The present randomized, placebo-controlled cross-over study of 21 men with combined hyperlipidaemia examines whether 10-12 weeks of gemfibrozil treatment affects the serum concentrations of the antioxidants ubiquinone-10 or alpha- or gamma-tocopherol. RESULTS: Gemfibrozil treatment lowered plasma triglycerides and both total and very low-density lipoprotein (VLDL)-cholesterol (P < 0.001 for all by ANOVA), whereas high-density lipoprotein (HDL)-cholesterol increased (P < 0.001). The median serum levels of ubiquinone-10 decreased from 1.30 mumol L-1 (interquartile range 0.87-1.71 mumol L-1) with placebo to 0.76 mumol L-1 (0.66-0.95) with gemfibrozil treatment (P < 0.001). Corresponding levels for alpha- and gamma-tocopherol were: 68.5 mumol L-1 (51.1-84.7) vs. 40.8 mumol L-1 (30.3-55.0) and 8.6 mumol L-1 (5.2-16.7) vs. 4.3 mumol L-1 (3.5-7.0) respectively (P < 0.001 for both). The decrease in serum antioxidants was also evident when standardized for total cholesterol (P < 0.05) or LDL-cholesterol (P < 0.001). Normolipaemic control subjects had significantly lower antioxidant levels than placebo-treated patients: ubiquinone 0.63 mumol L-1 (0.41-1.05), alpha-tocopherol 34.3 mumol L-1 (27.3-45.6) and gamma-tocopherol 3.2 mumol L-1 (2.5-4.2) (P < 0.001 for all). The association of antioxidants with lipoprotein lipids was further established by positive correlations between the levels of antioxidants and those of total cholesterol (r = 0.64, P < 0.001) or total triglycerides (r = 0.71, P < 0.001). CONCLUSION: Gemfibrozil treatment of men with combined hyperlipidaemia reduces serum antioxidant levels to the levels seen in healthy normolipidaemic men. The mechanisms and the relevance of this finding remain unclear and need to be addressed in further studies.

Adult↗
PubMed1998

Low frequency of the common Norwegian and Finnish LDL-receptor mutations in Swedish patients with familial hypercholesterolaemia.

OBJECTIVE: To evaluate the frequency of the common Finnish and Norwegian mutations in the low density lipoprotein (LDL) receptor gene in Swedish patients with familial hypercholesterolaemia (FH), and to start screening for other mutations in these patients. In contrast to the situation in Norway and Finland, where the frequency of common mutations causing the disease has been determined, very little about the mutation spectrum is known in Sweden. SETTINGS AND SUBJECTS: In total, 182 unrelated Swedish patients fulfilling clinical criteria for FH were investigated. Of these, 112 were identified at Huddinge University Hospital in Stockholm, and 70 at Sahlgren's Hospital in Göteborg. They were screened by single-strand conformation polymorphism (SSCP) for mutations in exons 3, 4, 6 and 9 of the LDL-receptor gene and by polymerase chain reaction (PCR) for the most common FH mutations occurring in Finland. and the prevailing mutation causing familial defective apolipoprotein B-100 (FDB). RESULTS: Mutations in the LDL receptor were identified in 25 of the 182 patients. Of these, 10 represented FH-Helsinki and one FH-North Karelia. Other mutations identified were FH-Svartor (four patients), FH-Elverum (one patient), FH-Padova (two patients), FH-Morocco (one patient) and FH-Algeria-1 (one patient). One patient was simultaneously positive for two mutations formerly described in Sweden: E256K (exon 6) and 1402T (exon 9). Another mutation caused replacement of one amino acid residue in exon 6 (C292Y). Two new mutations were found, both in exon 6: one nonsense mutation in the codon #275 for cysteine (FH-Huddinge, two patients), and one deletion of two base-pairs in the codon for leucine in position 254 (FH-Göteborg, one patient). The mutation for FDB was found in three patients. CONCLUSIONS: The mutation pattern in Swedish FH patients differs considerably from that in Finland and Norway. The two new mutations discovered will probably cause serious functional disturbances in the LDL-receptor function. Thus far, no predominant mutation was seen in Swedish FH-patients.

Adult↗
PubMed1998

Degradation of urokinase plasminogen activator (UPA) in endometrial stromal cells requires both the UPA receptor and the low-density lipoprotein receptor-related protein/alpha2-macroglobulin receptor.

Primary cultures of human endometrial stromal cells expressed a single class of specific high-affinity binding sites for urokinase plasminogen activator (UPA) with a dissociation constant KD 1.0 nmol/l and saturation at 2.0 nmol/l. Similar binding data and number of free binding sites, about 200 fmol/mg protein, were found for UPA in complex with its inhibitor plasminogen activator inhibitor-1 (PAI-1). These binding data agree with those reported for the specific cell surface receptor for UPA, and stromal cell expression of UPA receptor mRNA was identified in Northern blots. Cell surface-bound UPA was degraded at 37 degrees C. Degradation of complexed UPA was more efficient than that of free UPA. Degradation of free UPA did not require prior binding to endogenous PAI-1. Degradation of both free and complexed UPA was reduced by 70% by colchicine, chloroquine and methylamine, indicating that degradation involved both internalization and lysosomal enzymes. Furthermore, degradation was independently inhibited by about 70% with anti-UPA receptor antibodies and receptor-associated protein, indicating that the UPA receptor as well as one or more receptors of the low-density lipoprotein (LDL) receptor supergene family were involved in the degradation process. Receptor-associated protein ligand blotting demonstrated a major band co-migrating with the LDL receptor-related protein or glycoprotein 330/megalin, and a minor band co-migrating with the very low-density lipoprotein receptor. Immunoblotting positively demonstrated expression of LDL receptor-related protein, but not glycoprotein 330.

Adult↗
PubMed1998

Platelet activity in vivo in hyperlipoproteinemia--importance of combined hyperlipidemia.

Platelet hyperactivity in vitro is found in patients with isolated hypercholesterolemia. It is, however, less well established if platelet activity in vivo is enhanced, and if there are differences between various types of hyperlipoproteinemia. Platelet function in vivo was studied at rest and during mental stress in men with isolated hypercholesterolemia (phenotype IIa; n = 21) or combined hyperlipidemia (phenotype IIb; n = 29), and age-matched normolipidemic controls (n = 41). The urinary excretion of 11-dehydrothromboxane B2 was elevated in patients compared to controls (IIa, p <0.05; IIb, p <0.001), and higher in type IIb than in IIa patients (p <0.05). Platelet secretion, assessed as plasma beta-thromboglobulin levels, was higher in type IIb patients compared to controls (p <0.01) and type IIa patients (p <0.05) during mental stress. The urinary excretion of beta-thromboglobulin was also elevated in type IIb patients compared to controls (p <0.05). Platelet aggregability at rest, as measured by filtragometry ex vivo was, however, reduced in both patient groups compared to controls (p <0.05). No correlations were found between plasma lipoprotein levels and markers of platelet function in vivo. Type IIb patients had higher plasma fibrinogen levels and higher leukocyte counts than controls (p <0.05 and p <0.001) and type IIa patients (p <0.05 and p = 0.06). Thromboxane excretion was positively related to fibrinogen levels and leukocyte counts (p <0.01 for both). Preliminary data regarding serum TNF-alpha also indicated an elevation of this inflammatory cytokine in type IIb patients (p <0.05 vs controls). In conclusion, thromboxane generation and platelet secretion in vivo are enhanced in patients with hypercholesterolemia, and particularly so among patients with concomitant elevation of plasma triglycerides. The mechanism is unknown, but inflammatory mediators may be involved. The present findings are of interest in relation to the role of triglycerides in coronary artery disease.

Adult↗
PubMed1998

Bovine aortic endothelial cells express a variant of the very low density lipoprotein receptor that lacks the O-linked sugar domain.

The very low density lipoprotein (VLDL) receptor is a member of the low density lipoprotein supergene family of receptors in which differential splicing of mRNA has been reported. We present several lines of evidence showing that bovine aortic endothelial cells exclusively express a VLDL receptor isoform that lacks the O-linked sugar domain i) Western and receptor-associated protein (RAP) ligand blotting gave a single band of about 99 kDa in membrane extracts of bovine aortic endothelial cells (BAEC). ii) Screening of the BAEC cDNA library with the previously characterized human VLDL receptor cDNA as a probe gave several C-terminal-positive clones; all lacked the 84 nucleotides corresponding to exon 16. Polymerase chain reaction (PCR) confirmed that VLDL receptor cDNA encoding exon 16 was absent from the library. iii) Reverse transcription (RT)-PCR analysis of the BAEC mRNA using a pair of oligonucleotide primers that flank the deletion gave only one band of 136 nt. iv) Semiquantitative RT-PCR analysis showed that only the non-O-glycosylated variant was expressed in BAEC. Cell-binding studies with antibodies against the N-terminal domain showed that the BAEC VLDL receptor is present at the plasma membrane, suggesting that the non-glycosylated variant could be functional. In addition, RT-PCR performed in bovine tissues showed that the variant containing the O-linked sugar domain is preferentially expressed in heart, brain, and skeletal muscle, whereas the non-O-glycosylated spliced variant is found in all tissues analyzed. Taken together these results suggest that the differential splicing of the VLDL receptor is cell- and tissue-specific and that the functions of the receptor could depend on the cell type.

Alternative Splicing↗
PubMed1997

Growth hormone and bile acid synthesis. Key role for the activity of hepatic microsomal cholesterol 7alpha-hydroxylase in the rat.

Growth hormone (GH) has an important role in the regulation of hepatic LDL receptor expression and plasma lipoprotein levels. This investigation was undertaken to characterize the effects of GH on hepatic cholesterol and bile acid metabolism in the rat. In hypophysectomized (Hx) rats, the activities of the rate-limiting enzymes in cholesterol and bile acid biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and cholesterol 7alpha-hydroxylase (C7alphaOH), were reduced by 71 and 64%, respectively. HMG CoA reductase mRNA levels were reduced by 37%, whereas C7alphaOH mRNA was increased by 81%. LDL receptor expression was reduced by 18% in Hx rats, without any change in the LDL receptor mRNA levels. Although the normal diurnal variation of C7alphaOH activity was preserved in Hx rats, the activity of C7alphaOH was much reduced both at midday and midnight. Total hepatic cholesterol was increased by 14% in Hx animals whereas microsomal cholesterol was unchanged. The rate of cholesterol esterification was enhanced (by 38%) in liver microsomes from Hx rats. Stepwise hormonal substitution of Hx rats showed that GH, but not thyroid hormone or cortisone, was essential to normalize the enzymatic activity of C7alphaOH. GH also normalized the altered plasma lipoprotein pattern in Hx rats, and increased the fecal output of bile acids. The latter effect was particularly evident when GH was combined with cortisone and thyroid hormone. Also in normal rats, GH stimulated C7alphaOH activity. In conclusion, GH has an essential role to maintain a normal enzymatic activity of C7alphaOH, and this, at least in part, explains the effects of GH on hepatic cholesterol metabolism. GH is also of critical importance to normalize the altered plasma lipoprotein pattern in Hx rats.

Animals↗