Biomedical subjects

Hideyuki Hyogo

Publications and source records attributed to Hideyuki Hyogo.

At least 19 recordsLinked to original sources

PubMed2006

Anti-fibrogenic function of angiotensin II type 2 receptor in CCl4-induced liver fibrosis.

The renin-angiotensin system (RAS) contributes to fibrogenesis in a variety of organs. We recently showed that a lack of angiotensin (Ang) II type 1 (AT1) receptor activity reduces liver fibrosis. In this study, we investigated whether the Ang II type 2 (AT2) receptor is implicated in the development of liver fibrosis. A comparison was made between AT2-receptor knockout (AT2KO) and wild type (WT) mice after 4 weeks of treatment with carbon tetrachloride (CCl4). Fibrosis was assessed by Azan-Mallory staining and hepatic hydroxyproline (HP) content. The expression of fibrogenic mRNA was measured by real-time quantitative reverse-transcription polymerase chain reaction (PCR). Liver fibrosis evaluated by regular histological analyses and immunohistochemical alpha-SMA staining was observed in both groups of mice. The extent of fibrosis was greatest in the AT2KO mice. Fibrosis was associated with increases in hepatic HP content and mRNA expression for TGF-beta1 and alpha-SMA, as well as an increase in hepatic TBARS. These findings suggest that CCl4 induces oxidative stress which leads to activation of hepatic stellate cells (HSCs). These changes were considerably more pronounced in the AT2KO mice than the WT mice. Taken together, we conclude that AT2 signal has anti-fibrogenic and/or cytoprotective effects on oxidative stress-induced liver fibrosis. We therefore suggest that RAS-associated liver fibrogenesis may be determined by the balance between AT1 and AT2 signals.

Animals↗

PubMed2005

Glycochenodeoxycholate plays a carcinogenic role in immortalized mouse cholangiocytes via oxidative DNA damage.

Bile acids have been suggested to be involved in biliary carcinogenesis, although the underlying mechanisms are yet to be established. The aim of this study was to investigate the carcinogenic effect of bile acids in the biliary tract in relation to oxidative stress. Immortalized mouse cholangiocytes were incubated with various bile acids, followed by measurement of reactive oxygen species (ROS) and the glutathione (GSH) level. As a marker of oxidative DNA damage, 8-hydroxydeoxyguanosine (8-OHdG) expression in cholangiocytes was analyzed by flow cytometry. Then the expression of oxidative DNA repair enzymes in cholangiocytes was examined by real-time PCR. In addition, the long-term effect of bile acid-induced oxidative DNA damage on cholangiocytes was investigated using a mouse oligo DNA microarray. It was found that glycochenodeoxycholate (GCDC) induced the generation of ROS and the depletion of GSH. In contrast, no marked changes were induced by the other bile acids. The percentage of 8-OHdG-positive cells was also increased by GCDC, but the expression of oxidative DNA repair enzymes was not up-regulated. DNA microarray analysis showed marked changes of various genes associated with carcinogenesis (genes related to cell proliferation, angiogenesis, invasion, and metastasis). In conclusion, the long-term effect of oxidative DNA damage due to GCDC may promote carcinogenesis in the biliary tract. Furthermore, accumulation of 8-OHdG due to GCDC might contribute to the dysfunction of oxidative DNA repair enzymes.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2005

A biphasic response of hepatobiliary cholesterol metabolism to dietary fat at the onset of obesity in the mouse.

Human obesity is associated with abnormal hepatic cholesterol homeostasis and resistance to leptin action. Because leptin administration to rodents promotes the biliary elimination of plasma cholesterol, this study was designed to elucidate a pathophysiological role for leptin during the development of obesity. We fed mice diets containing high or low saturated fat contents. Before and after the onset of obesity, we measured downstream targets of leptin action and evaluated plasma, hepatic, and biliary cholesterol metabolism. Although not obese at 28 days, mice fed a high fat diet became hyperleptinemic. Sensitivity to leptin was evidenced by downregulation of both hepatic stearoyl CoA desaturase-1 and fatty acid synthase. Due principally to upregulation of adenosine triphosphate-binding cassette proteins A1 and G5, plasma high density lipoprotein (HDL) cholesterol concentrations increased, as did relative secretion rates of biliary cholesterol. A smaller, more hydrophilic bile salt pool decreased intestinal cholesterol absorption. In this setting, hepatic cholesterol synthesis was downregulated, indicative of increased uptake of plasma cholesterol. After 56 days of high fat feeding, obesity was associated with leptin resistance, as evidenced by marked hyperleptinemia without downregulation of stearoyl CoA desaturase-1 or fatty acid synthase and by upregulation of hepatic cholesterol and bile salt synthesis. Hypercholesterolemia was attributable to overproduction and decreased clearance of large HDL(1) particles. In conclusion, before the onset of obesity, preserved leptin sensitivity promotes biliary elimination of endogenous cholesterol in response to dietary fat. Leptin resistance due to obesity leads to a maladaptive response whereby newly synthesized cholesterol in the liver is eliminated via bile.

Animals↗

PubMed2005

A nuclear receptor ligand down-regulates cytosolic phospholipase A2 expression to reduce bile acid-induced cyclooxygenase 2 activity in cholangiocytes: implications of anticarcinogenic action of farnesoid X receptor agonists.

Bile acids are considered to be involved in the development of biliary tract carcinoma, although the underlying mechanisms are yet to be established. The aims of this study were (1) to investigate the carcinogenic role of bile acids in the biliary system based on the arachidonate-prostanoid pathway and (2) to clarify the therapeutic role of a farnesoid X receptor (FXR) ligand that modifies bile acid metabolism. Immortalized mouse cholangiocytes were incubated with glycochenodeoxycholate (GCDC), taurocholate, taurochenodeoxycholate, taurodeoxycholate, and tauroursodeoxycholate. GCDC induced cyclooxygenase 2 (COX-2) expression (Western blotting, 1.7-fold; RT-PCR, 2.3-fold) and prostaglandin (PG) production (PGE2, 6.3-fold; PGF2alpha, 8.5-fold), whereas cytosolic phospholipase A2 (cPLA2) expression and activity were reduced. In contrast, no marked changes were induced by the other bile acids. When the same experiment was performed in the presence of a synthetic FXR ligand (GW4064), cPLA2 expression and activity were reduced, although COX-2 expression was unchanged. GW4064 also suppressed PG generation by 40%. In conclusion, the present findings suggest a carcinogenic potential of GCDC. A synthetic FXR ligand (GW4064) inhibited the induction of COX-2 activity (detected as PG production) by GCDC, suggesting its anticarcinogenic potential. This effect seemed to be due to down-regulation of cPLA2. FXR ligands may have therapeutic potential against biliary carcinogenesis, but a delivery system for these agents is still to be developed.

Animals↗

PubMed2005

Angiotensin II participates in hepatic inflammation and fibrosis through MCP-1 expression.

In this study, we assessed the hypothesis that angiotensin (Ang) II could modulate inflammatory cell recruitment into the liver through hepatic expression of monocyte chemoattractant protein (MCP)-1 during liver injury. For in vivo study, Ang II type la knockout (ATla KO) mice and wild-type (WT) mice were treated with CCl4 for 4 weeks. After CCl4 treatment, ATla KO mice showed lower expression of MCP-1 and fewer CD68-positive cells in the liver compared with WT mice. For in vitro study, Ang II was added to LI90 cells. Ang II enhanced MCP-1 mRNA together with RhoA mRNA and also induced secretion of MCP-1 into the culture medium. This change was strongly blocked by Y-27632, a specific Rho-kinase inhibitor. These results suggest that Ang II modulates hepatic inflammation via production of MCP-1 by hepatic stellate cells, and the effect of Ang II on MCP-1 production is, at least partly, mediated by the Rho/Rho-kinase pathway.

Angiotensin II↗

PubMed2005

Hepatitis C virus core protein modulates fatty acid metabolism and thereby causes lipid accumulation in the liver.

We studied the roles of hepatitis C virus (HCV) core protein in hepatic steatosis and changes in hepatic lipid metabolism. HCV core protein expression plasmid was transfected in HepG2. Triacylglyceride (TG) and mRNA level associated with lipid metabolism were measured. Male C57BL/6 mice were infected with HCV core recombinant adenovirus and used for lipids and mRNA studies. In HCV core protein-expressing cells, peroxisome proliferator-activated receptor (PPAR)alpha, multidrug resistance protein (MDR) 3, and microsomal triglyceride transfer protein (MTP) were down-regulated 48 hr after transfection. In HCV core protein-expressing mice, hepatic TG content and hepatic thiobarbituric acid-reactive substances increased. PPARalpha, MDR2, acyl-CoA oxidase (AOX), and carnitine palmitoyl transferase-1 (CPT-1) were down-regulated. HCV core protein down-regulated lipid metabolism-associated gene expression, Mdr2, CPT, and AOX, accompanied by down-regulation of PPARalpha. There findings may contribute to the understanding of HCV-related steatosis, induction of reactive oxygen species, and carcinogenesis.

Animals↗

PubMed2005

Therapeutic effect of repeated natural killer T cell stimulation in mouse cholangitis complicated by colitis.

Primary sclerosing cholangitis is often complicated by ulcerative colitis. Recently, we reported on Th1-dominant cholangitis associated with experimental colitis, and natural killer T (NKT) cells might play an important role in this model. The aim of this study was to clarify the immunopathogenic role of NKT cells in this model using alpha-galactosylceramide. CD-1 mice were administered 2.0% dextran sulfate sodium for 29 days and injection of alpha-galactosylceramide was performed every 5 days, then inflammation was assessed. Mononuclear cells from the liver were analyzed with respect to cytokine production and the surface marker. alpha-Galactosylceramide improved survival rate, weight gain, and inflammation score. Also, interferon-gamma release from MNC, CD4/CD8 ratio, NKT cell population, and NK cell population were decreased by this treatment. These findings indicate that repeated stimulation of NKT cells modifies the Th1/Th2 balance to reduce Th1 dominance, and this may be a mechanism by which alpha-galactosylceramide has a therapeutic effect.

Animals↗

PubMed2005

Prevalence of Helicobacter pylori infection, endoscopic gastric findings and dyspeptic symptoms among a young Japanese population born in the 1970s.

BACKGROUND: With the prevalence of Helicobacter pylori (H. pylori) infection rapidly decreasing in Japan, endoscopic findings and dyspeptic symptoms need to be re-evaluated. METHODS: In a health check-up program, endoscopy was performed on 530 young Japanese subjects (371 men and 159 women) born in the 1970s. Helicobacter pylori infection was evaluated using serology and a rapid urease test. Endoscopic gastritis was classified according to the Sydney classification system, in addition to nodular gastritis. Dyspeptic symptoms were also recorded before endoscopy. RESULTS: Of the 530 subjects, 87 (16.4%) were H. pylori positive. Of the 443 H. pylori-negative subjects, 349 (78.8%) were considered to have endoscopically normal gastric mucosa. However, of the 87 H. pylori-positive subjects, only 19 (21.8%) tested normal (P < 0.001). The prevalence of several types of gastritis was significantly higher in H. pylori-positive subjects compared with H. pylori-negative subjects: atrophic gastritis (37.9% vs 1.1%, P < 0.001), flat erosive gastritis (29.9% vs 7.2%, P < 0.001), rugal hyperplastic gastritis (12.6% vs 0.0%, P < 0.001), and nodular gastritis (13.8% vs 0.0%, P < 0.001). Other types of gastritis were not related to H. pylori status. The prevalence of subjects with dyspeptic symptoms was significantly higher in H. pylori-positive subjects compared with H. pylori-negative ones (28.7% vs 6.5%, P < 0.001). CONCLUSION: It is suggested that in consideration of its recent low prevalence and the slow increase in its infection, the prevalence of H. pylori-related gastritis will gradually decrease in Japan. Further studies will be required to ascertain if there is a need for H. pylori eradication in this young population.

Adult↗

PubMed2005

Gastric acidity in patients with follicular gastritis is significantly reduced, but can be normalized after eradication for Helicobacter pylori.

BACKGROUND: Follicular gastritis is thought to be caused by Helicobacter pylori infection. However, the pathophysiology of it remains unclear. MATERIALS AND METHODS: We assessed gastric acidity in 15 patients with follicular gastritis, aged 20-37 years, using a 24-hour intragastric pH-metry, as well as by histologic and serologic evaluations; and compared it with that in other age-matched groups: 18 cases of H. pylori-positive antrum-predominant gastritis, 12 of pangastritis, and 24 H. pylori-negative normals. In eight cases with follicular gastritis, it was re-assessed 6 months after the eradication therapy for H. pylori. RESULTS: During nighttime, the percentage of time with intragastric pH above 3.0 in follicular gastritis was significantly higher than that in normals (p<.0001), and in antrum-predominant gastritis (p<.001), but was comparable with that in pangastritis. In the daytime period, this parameter in follicular gastritis was significantly higher than that in normal (p<.001), in antrum-predominant gastritis (p<.001), and in pangastritis (p<.05). Marked mononuclear cell and neutrophil infiltration but no apparent glandular atrophy were observed in both the antrum and corpus. Serum pepsinogen I/II ratio was significantly lower in follicular gastritis than that in normals (p<.0001) and in antrum-predominant gastritis (p<.001), whereas serum gastrin was significantly higher than that in normals (p<.0001), in antrum-predominant gastritis (p<.01) and in pangastritis (p<.05). After eradication for H. pylori, all of the parameters in follicular gastritis were altered to the same ranges as those in normals. CONCLUSIONS: In follicular gastritis, gastric acidity is significantly reduced, but can be normalized by eradication of H. pylori. It can thus be speculated that inflammatory cytokines or H. pylori-infection-induced prostaglandins might strongly inhibit gastric acid secretion in follicular gastritis.

Adult↗

PubMed2005

A nuclear receptor-mediated choleretic action of fibrates is associated with enhanced canalicular membrane fluidity and transporter activity mediating bile acid-independent bile secretion.

Fibrates are commonly used lipid-lowering agents that act via PPARalpha, a member of the nuclear hormone receptor superfamily. The mechanism(s) of fibrate-induced changes in the hepatic canalicular membrane and bile lipids are still unknown. Therefore, the aim of this study was to investigate the influence of fibrates on hepatic lipid metabolism and to assess the hepatocellular cytoprotective effect on hepatocyte canalicular membrane. Male ICR mice were fed standard chow with or without bezafibrate (100 mg/kg) for 6 days. The expression of canalicular membrane transporters (Mdr2 and Mrp2) was evaluated by RT-PCR and Western blotting. Canalicular membrane fluidity was also investigated. Canalicular membrane fluidity was markedly increased by fibrates. The expression of mdr 2 and mrp2 mRNA and protein showed a significant increase in fibrate-treated mice. These results suggested that fibrates improve liver function by enhancing bile secretion. The mechanism of the choleretic action of fibrate therapy might involve the enhancement of bile acid-independent bile secretion, since increased expression of Mdr2 and Mrp2 was found in fibrate-treated animals. These changes were very likely mediated by PPARalpha, and the increase of canalicular membrane fluidity may have been partly associated with enhancement of this transporter activity.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2004

Impaired response of biliary lipid secretion to a lithogenic diet in phosphatidylcholine transfer protein-deficient mice.

Phosphatidylcholine transfer protein (PC-TP) is a cytosolic lipid transfer protein that is highly expressed in liver and catalyzes intermembrane transfer of phosphatidylcholines in vitro. To explore a role for PC-TP in the hepatocellular trafficking of biliary phosphatidylcholines, we characterized biliary lipid secretion using Pctp(-/-) and wild-type littermate control mice with C57BL/6J and FVB/NJ genetic backgrounds, which express PC-TP at relatively high and low levels in liver, respectively. Eight-week-old male Pctp(-/-) and wild-type mice were fed a chow diet or a lithogenic diet, which served to upregulate biliary lipid secretion. In chow-fed mice, the absence of PC-TP did not reduce biliary phospholipid secretion or alter the phospholipid composition of biles. However, the responses in secretion of biliary phospholipids, cholesterol, and bile salts to the lithogenic diet were impaired in Pctp(-/-) mice from both genetic backgrounds. Alterations in biliary lipid secretion could not be attributed to transcriptional regulation of the expression of canalicular membrane lipid transporters, but possibly to a defect in their trafficking to the canalicular membrane. These findings support a role for PC-TP in the response of biliary lipid secretion to a lithogenic diet, but not specifically in the hepatocellular transport and secretion of phosphatidylcholines.

Animals↗

PubMed2004

Role of CYP27A in cholesterol and bile acid metabolism.

The CYP27A gene encodes a mitochondrial cytochrome P450 enzyme, sterol 27-hydroxylase, that is expressed in many different tissues and plays an important role in cholesterol and bile acid metabolism. In humans, CYP27A deficiency leads to cerebrotendinous xanthomatosis. To gain insight into the roles of CYP27A in the regulation of cholesterol and bile acid metabolism, cyp27A gene knockout heterozygous, homozygous, and wild-type littermate mice were studied. In contrast to homozygotes, heterozygotes had increased body weight and were mildly hypercholesterolemic, with increased numbers of lipoprotein particles in the low density lipoprotein size range. Cyp7A expression was not increased in heterozygotes but was in homozygotes, suggesting that parts of the homozygous phenotype are secondary to increased cyp7A expression and activity. Homozygotes exhibited pronounced hepatomegaly and dysregulation in hepatic cholesterol, bile acid, and fatty acid metabolism. Hepatic cholesterol synthesis and synthesis of bile acid intermediates were increased; however, side chain cleavage was impaired, leading to decreased bile salt concentrations in gallbladder bile. Expression of Na-taurocholate cotransporting polypeptide, the major sinusoidal bile salt transporter, was increased, and that of bile salt export pump, the major canalicular bile salt transporter, was decreased. Gender played a modifying role in the homozygous response to cyp27A deficiency, with females being generally more severely affected. Thus, both cyp27A genotype and gender affected the regulation of hepatic bile acid, cholesterol, and fatty acid metabolism.

Animals↗

PubMed2003

Restoration of gallstone susceptibility by leptin in C57BL/6J ob/ob mice.

The absence of leptin due to the ob mutation leads to obesity and confers resistance to diet-induced cholesterol gallstone formation in otherwise susceptible C57BL/6J mice. To investigate contributions of obesity and leptin to gallstone susceptibility, C57BL/6J ob/ob mice were treated daily with i.p. saline or recombinant murine leptin at low (1 microgram/g bw) or high (10 microgram/g bw) doses and were pair-fed a lithogenic diet (15% dairy fat, 1.25% cholesterol, 0.5% cholic acid). Weight loss in ob/ob mice increased in proportion to leptin dose, indicating that the lithogenic diet did not impair leptin sensitivity. In a dose-dependent manner, leptin promoted cholesterol crystallization and gallstone formation, which did not occur in saline-treated mice. Notwithstanding, leptin decreased biliary lipid secretion rates without enriching cholesterol in bile. Leptin did not affect bile salt hydrophobicity, but did increase the biliary content of the most abundant molecular species of phosphatidylcholine, 16:0-18:2. Treatment with leptin down-regulated 3-hydroxy-3-methylglutaryl CoA reductase and prevented cholesterol from accumulating in liver. Consistent with increased hepatic clearance, leptin decreased plasma HDL cholesterol concentrations. This was accommodated in liver without up-regulation of cholesterol 7alpha-hydroxylase or Acat. These data suggest that despite the lithogenic diet, endogenous sources constitute a significant proportion of biliary cholesterol during leptin-induced weight loss. Kinetic factors related to cholesterol nucleation, gallbladder contractility, or mucin secretion may have accounted for leptin-induced gallstone formation.

Animals↗

PubMed2003

Hypercholesterolemia and changes in lipid and bile acid metabolism in male and female cyp7A1-deficient mice.

Cholesterol 7alpha-hydroxylase, a rate-limiting enzyme for bile acid synthesis, has been implicated in genetic susceptibility to atherosclerosis. The gene, CYP7A1, encoding a protein with this activity, is expressed normally only in hepatocytes and is highly regulated. Our cyp7A1 gene knockout mouse colony, as young adults on a chow diet, is hypercholesterolemic. These mice were characterized extensively to understand how cyp7A1 affects lipid and bile acid homeostasis in different tissue compartments and whether gender plays a modifying role. Both male and female cyp7A1-deficient mice had decreased hepatic LDL receptors, unchanged hepatic cholesterol synthesis, increased intestinal cholesterol synthesis and bile acid transporters, and decreased fecal bile acids but increased fecal sterols. In females, cyp7A1 deficiency also caused changes in hepatic fatty acid metabolism, decreased hepatic canalicular bile acid transporter, Bsep, and gallbladder bile composition altered to a lithogenic profile. Taken together, the data suggest that cyp7A1 deficiency results in a proatherogenic phenotype in both genders and leads to a prolithogenic phenotype in females.

Animals↗

PubMed2003

Unique inhibition of bile salt-induced apoptosis by lecithins and cytoprotective bile salts in immortalized mouse cholangiocytes.

Bile duct epithelium is physiologically exposed to high concentrations of bile salts, suggesting the presence of a cytoprotective mechanism(s). The aim of this study was to clarify whether bile salts cause bile duct cell damage and to elucidate the mechanism(s) providing protection against such an action of bile salts. Immortalized mouse cholangiocytes were incubated with taurocholate, taurochenodeoxycholate, glycochenodeoxycholate (GCDC), taurodeoxycholate, and tauroursodeoxycholate (TUDC), followed by flow-cytometric analysis and caspase activity assay to evaluate the induction of apoptosis. GCDC time-dependently induced caspase 3 (3.4-fold)- and caspase 9 (1.4-fold)-mediated apoptosis of cholangiocytes, but this was inhibited by lecithins and TUDC. Further, expression of cholangiocyte bile salt transporters (apical sodium-dependent bile salt transporter [Asbt] and multidrug resistance protein 3 [Mrp3]) was examined by RT-PCR and western blotting, and cholangiocyte bile salt uptake was determined using radiolabeled bile salts. Expression of cholangiocyte Asbt and Mrp3 was increased by bile salts, whereas lecithins interestingly reduced bile salt uptake to inhibit cholangiocyte apoptosis. In conclusion, bile salts themselves cause cholangiocyte apoptosis when absorbed by and retained inside the cell, but this is inhibited by washing out cytotoxic bile salts according to Mrp3, a rescue exporting molecule. Biliary lecithin is seemingly another cytoprotective player against cytotoxic bile salts, reducing their uptake, and this is associated with a reduced expression of Mrp3.

Animals↗

PubMed2003

Impaired gallbladder mucosal function in aged gallstone patients suppresses gallstone recurrence after successful extracorporeal shockwave lithotripsy.

BACKGROUND: Absorption of water, as well as emptying of bile, are important functions of the gallbladder. We studied the changes of gallbladder function with age in gallstone patients and their influence on the outcome of extracorporeal shockwave lithotripsy (ESWL). METHODS: (i) A total of 123 consecutive patients with complete stone clearance by ESWL were examined. Gallbladder emptying was assessed before treatment using intravenous cholecystography. After stone clearance, the recurrence of gallstones was monitored by using ultrasonography. Cox regression analysis was used to determine the risk factors associated with stone recurrence. (ii) Gallbladder bile was sampled from 59 gallstone patients during surgery. Biliary cholesterol, phospholipids, and total bile acids were simultaneously quantified by using gas-liquid chromatography. RESULTS: Impaired gallbladder function, but not gallstone recurrence, was more frequently observed in older patients (>/=65 years old) than in younger patients (<65 years old). Cox regression analysis revealed that poor gallbladder emptying was an independent predictor of stone recurrence after ESWL in the total study population, but not in the older patients (>/=65 years old). Analysis of bile from surgically treated patients with cholesterol stones showed a significantly higher total lipid concentration and a shorter nucleation time in the younger group (<65 years old), but the cholesterol saturation index did not differ between the younger and older groups. CONCLUSIONS: Our data suggest that the reduced concentrating function of the gallbladder in elderly gallstone patients helps to counteract stone recurrence despite their abnormal gallbladder motility. Therefore, aged gallstone patients may be preferentially treated by a non-surgical strategy.

Age Factors↗

PubMed2002

Hepatic overexpression of sterol carrier protein-2 inhibits VLDL production and reciprocally enhances biliary lipid secretion.

We examined in vivo a role for sterol carrier protein-2 (SCP-2) in the regulation of lipid secretion across the hepatic sinusoidal and canalicular membranes. Recombinant adenovirus Ad.rSCP2 was used to overexpress SCP-2 in livers of mice. We determined plasma, hepatic, and biliary lipid concentrations; hepatic fatty acid (FA) and cholesterol synthesis; hepatic and biliary phosphatidylcholine (PC) molecular species; and VLDL triglyceride production. In Ad.rSCP2 mice, there was marked inhibition of hepatic fatty acids and cholesterol synthesis to <62% of control mice. Hepatic triglyceride contents were decreased, while cholesterol and phospholipids concentrations were elevated in Ad.rSCP2 mice. Hepatic VLDL triglyceride production fell in Ad.rSCP2 mice to 39% of control values. As expected, biliary cholesterol, phospholipids, bile acids outputs, and biliary PC hydrophobic index were significantly increased in Ad.rSCP2 mice. These studies indicate that SCP-2 overexpression in the liver markedly inhibits lipid synthesis as well as VLDL production, and alters hepatic lipid contents. In contrast, SCP-2 increased biliary lipid secretion and the proportion of hydrophobic PC molecular species in bile. These effects suggest a key regulatory role for SCP-2 in hepatic lipid metabolism and the existence of a reciprocal relationship between the fluxes of lipids across the sinusoidal and canalicular membranes.

Adenoviridae↗

PubMed2002

Microvascular hyperpermeability in caveolin-1 (-/-) knock-out mice. Treatment with a specific nitric-oxide synthase inhibitor, L-NAME, restores normal microvascular permeability in Cav-1 null mice.

Microvascular permeability is mediated by (i) the caveolar transcytosis of molecules across endothelial cells and (ii) the paracellular movement of ions and nutrients. Recently, we derived Cav-1 (-/-) knock-out mice using standard homologous recombination techniques. These mice are viable but show a loss of endothelial cell caveolae and striking defects in caveolae-mediated endocytosis. Thus, a compensatory mechanism must be operating in these mice. One possible compensatory response would be an increase in the paracellular pathway, resulting in increased microvascular permeability. To test this hypothesis directly, we studied the microvascular permeability of Cav-1 null mice using a variety of complementary in vivo approaches. Radio-iodinated bovine serum albumin was injected into Cav-1-deficient mice, and its rate of clearance from the circulatory system was compared with that of wild type control mice. Our results indicate that iodinated bovine serum albumin is removed from the circulatory system of Cav-1-deficient mice at a substantially faster rate. To determine whether this defect is restricted to the paracellular movement of albumin, lungs from Cav-1-deficient mice were next perfused with the electron dense dye Ruthenium Red. Micrographs of lung endothelial cells from Cav-1-deficient mice demonstrate that the paracellular movement of Ruthenium Red is dramatically increased. In addition, electron micrographs of Cav-1-deficient lung capillaries reveal defects in tight junction morphology and abnormalities in capillary endothelial cell adhesion to the basement membrane. This defect in cell-substrate attachment is consistent with the postulated role of caveolin-1 in positively regulating integrin signaling. Because loss of caveolin-1 expression results in constitutive activation of eNOS activity, we also examined whether these increases in microvascular permeability are NO-dependent. Interestingly, treatment with l-NAME (a well established nitric-oxide synthase inhibitor) successfully reversed the microvascular hyperpermeability phenotype of Cav-1 knock-out mice. Thus, caveolin-1 plays a dual regulatory role in controlling microvascular permeability: (i) as a structural protein that is required for caveolae formation and caveolar transcytosis and (ii) as a tonic inhibitor of eNOS activity to negatively regulate the paracellular pathway.

Animals↗