Overexpression of hepatic plasminogen activator inhibitor type 1 mRNA in rabbits with fatty liver

Small leucine zipper protein negatively regulates liver fibrosis by suppressing the expression of plasminogen activator inhibitor-1

Liver fibrosis, which is caused by viral infection, toxic exposure, and autoimmune diseases, is a chronic liver disease. Plasminogen activator inhibitor-1 (PAI-1) is a serine protease inhibitor of tissue-type plasminogen activator (tPA) and urokinase plasminogen activator, which convert plasminogen into plasmin. Therefore, PAI-1 suppresses fibrinolysis by blocking plasmin synthesis and is involved in liver fibrosis via extracellular matrix deposition. Small leucine zipper protein (sLZIP) acts as a transcription factor and plays critical roles in many cellular processes. However, the role of sLZIP in liver fibrosis remains unclear. In this study, we investigated the role of sLZIP in regulating PAI-1 transcription and liver fibrosis. sLZIP knockdown enhanced the expression of PAI-1 at the mRNA and protein levels. sLZIP knockdown also increased PAI-1 secretion and suppressed blood clot lysis by blocking tPA activity. Moreover, conditioned medium derived from sLZIP knockdown cells downregulated the expression of matrix metalloprotease (MMP)-2 and MMP-9 in the presence of tPA in hepatic stellate cells (HSCs). Liver-specific sLZIP knockout mice showed deteriorated liver fibrosis compared to control mice in a bile duct ligation-induced fibrosis model. These findings demonstrate that sLZIP functions as a negative regulator of liver fibrosis by suppressing PAI-1 transcription and HSC activation.

Rosiglitazone attenuates atherosclerosis and increases high-density lipoprotein function in atherosclerotic rabbits

Rosiglitazone has been found to have anti-atherogenic effects and to increase serum high-density lipoprotein (HDL) cholesterol (HDL-C) levels. However, in vivo studies investigating the regulation of adenosine triphosphate-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI) by rosiglitazone are limited. Moreover, the effects of rosiglitazone on the function and levels of HDL are unclear. In the present study, we investigated the effects of rosiglitazone on HDL function and its mechanisms of action in atherosclerotic rabbits. Our results revealed that rosiglitazone induced a significant increase in serum HDL-C levels, paraoxonase 1 (PON1) activity, [³H]cholesterol efflux rates, and the expression of ABCA1 and SR-BI in hepatocytes and peritoneal macrophages. The expression of ABCA1 was also increased in aortic lesions. Rosiglitazone markedly reduced serum myeloperoxidase (MPO) activity, aortic intima-media thickness (IMT) and the percentage of plaque area in the aorta. It can thus be concluded that in atherosclerotic rabbits, rosigitazone increases the levels of HDL-C and hinders atherosclerosis. Thus, it improves HDL quality and function, as well as the HDL-induced cholesterol efflux, exerting anti-inflammatory and antioxidant effects.

Mechanisms linking nonalcoholic fatty liver disease with coronary artery disease

The most common cause of death in patients with nonalcoholic fatty liver disease (NAFLD) is coronary artery disease (CAD), not chronic liver disease. Fatty liver increases cardiovascular risk by classical (dyslipidemia, hypertension, diabetes) and by less conventional mechanisms. Common pathways involved in the pathogenesis of fatty liver and CAD includes hepatic insulin resistance and sub clinical inflammation. The hepatic insulin resistance state of fatty liver infiltration is characterized by increased FFA, which causes lipotoxicity and impairs endothelium-dependent vasodilatation, increases oxidative stress, and has a cardio toxic effect. Additional metabolic risk factors include leptin, adiponectin, pro inflammatory cytokines [such as IL-6, C-reactive protein and plasminogen activator inhibitor-1 (PAI-1)], which together lead to increased oxidative stress and endothelial dysfunction, finally promoting coronary artery disease (CAD). When classical risk factors are superimposed on fatty liver accumulation, they may further increase the new metabolic risk factors, exacerbating CAD. The clinical implication is that patients with NAFLD are at higher risk (steatohepatitis, diabetes, obesity, atherogenic dyslipidemia) and should undergo periodic cardiovascular risk assessment including the Framingham score, cardiac effort test, and measurement of intimae-media thickening of the carotids arteries. This may improve risk stratification for CAD.

Role of adipose tissue in haemostasis, coagulation and fibrinolysis

Obesity is associated with an increased incidence of insulin resistance (IR), type 2 diabetes mellitus and cardiovascular diseases. The increased risk for cardiovascular diseases could partly be caused by a prothrombotic state that exists because of abdominal obesity. Adipose tissue induces thrombocyte activation by the production of adipose tissue-derived hormones, often called adipokines, of which some such as leptin and adiponectin have been shown to directly interfere with platelet function. Increased adipose tissue mass induces IR and systemic low-grade inflammation, also affecting platelet function. It has been demonstrated that adipose tissue directly impairs fibrinolysis by the production of plasminogen activator inhibitor-1 and possibly thrombin-activatable fibrinolysis inhibitor. Adipose tissue may contribute to enhanced coagulation by direct tissue factor production, but hypercoagulability is likely to be primarily caused by affecting hepatic synthesis of the coagulation factors fibrinogen, factor VII, factor VIII and tissue factor, by releasing free fatty acids and pro-inflammatory cytokines (tumour necrosis factor-alpha, interleukin-1beta and interleukin-6) into the portal circulation and by inducing hepatic IR. Adipose tissue dysfunction could thus play a causal role in the prothrombotic state observed in obesity, by directly and indirectly affecting haemostasis, coagulation and fibrinolysis.

Relationships of PAI-1 levels to central obesity and liver steatosis in a sample of adult male population in southern Italy

To analyse the relationship of PAI-1 plasma levels to echographically determined liver steatosis and cardiometabolic risk factors in a randomly selected sample of 254 adult male participants of the Olivetti Heart Study. Accounting for age and ongoing pharmacological treatment, PAI-1 levels were directly (P < 0.005) associated with body mass index (BMI), waist circumference (WC), serum triglyceride (TG), total cholesterol, insulin, homeostasis model assessment index, gamma-glutamyl transpeptidase and peritoneal fat. At multiple linear regression (MLR) analysis, measures of adiposity and TG exerted significant and quantitatively similar effects on PAI-1 levels. A progressive rise in PAI-1 level was detected with increasing degree of steatosis. A stepwise MLR model was used to evaluate the relative power of cardiometabolic risk factors and liver steatosis on PAI-1 levels. Adjusting for alcohol intake, BMI, WC and peritoneal fat were alternatively included in the model with other variables found to be significantly associated with plasma PAI-1 level. Liver steatosis, serum TG and various indexes of adiposity each had a significant independent impact on PAI-1 plasma level and explained overall 23% of its variability. Abdominal fat, liver steatosis and serum TG levels were significant and independent determinants of PAI-1 plasma level in an unselected sample of adult male population upon adjustment for age and therapy.

Atorvastatin reduces plasminogen activator inhibitor-1 expression in adipose tissue of atherosclerotic rabbits

BACKGROUND

Plasminogen activator inhibitor-1 (PAI-1) expression are increased in adipose tissues/adipocytes of obese mice, which is associated with a hypofibrinolytic state that contributes to thrombosis. We recently demonstrated that PAI-1 expression increases in adipose tissues/adipocytes of cholesterol-fed rabbits. In this study, we evaluated the ability of atorvastatin to modulate PAI-1 expression in cholesterol-fed rabbits and the regulatory mechanism.

METHODS

Male rabbits were randomly fed with normal diet and high-cholesterol diet for 8 weeks, following 4 weeks, those fed high-cholesterol diet were randomly assigned to 2.5 mg/kg/day atorvastatin or starch. At the end of 12 weeks, subcutaneous adipose was collected, and culture adipocyte. PAI-1 mRNA was detected by RT-PCR. PAI-1 concentrations were determined with ELISA. The effect of atorvastatin and mevalonate (MVA) on PAI-1 production in adipocytes in vitro was observed.

RESULTS

Atorvastatin significantly reduced serum TC and LDL-C concentrations (p<0.05), and decreased plasma PAI-1 concentration and PAI-1 expression in adipose tissues/adipocytes from cholesterol-fed rabbits. In vitro, atorvastatin dose-dependently suppressed PAI-1 expression and protein secretion in adipocytes. MVA reversed the inhibitory effect of atorvastatin on PAI-1 expression in concentration-dependent manner.

CONCLUSIONS

Atorvastatin reduces plasma PAI-1 concentration and PAI-1 expression in adipose tissue and adipocyte of atherosclerotic rabbit, and inhibits PAI-1 expression and protein secretion in adipocytes in vitro, suggesting that it may have an antithrombtic effect. We also suggest that the mevalonate pathway may play an important role in PAI-1 expression in adipocyte.

Fenofibrate inhibits thrombogenic and fibrinolytic factors expression in adipose tissue of atherosclerotic rabbits

BACKGROUND

Tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1) activity and/or expression are upregulated in obesity. We investigated TF and PAI-1 mRNA expression in adipose tissues of cholesterol-fed rabbits, and the effects of fenofibrate.

METHODS

Male rabbits were fed either a normal or high-cholesterol diet for 8 weeks. After 4 weeks, those fed high-cholesterol diets were randomly assigned to 30 mg/kg/day fenofibrate and starch. At the end of 12 weeks, subcutaneous adipose was collected. The concentration of TF and PAI-1 mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR). The plasma activities of TF and PAI-1 were determined with ELISA and chromogenic substrate method, respectively.

RESULTS

The atherogenic diet caused a consistent increase in serum concentrations of total cholesterol (TC) (p<0.05) and did not significantly affect serum triglyceride (TG) concentrations, and increased TF and PAI-1 mRNA expression in adipose tissues (1.149+/-0.014 and 1.200+/-0.012, respectively) as compared to the normal diet (1.034+/-0.011 and 1.098+/-0.013, respectively) (p<0.01). The plasma activities of TF [(74.4+/-28.8) ng/l] and PAI-1 [(15.6+/-1.9) x 10(3) AU/l] in high-cholesterol diet group were higher than those of normal diet group [(33.1+/-10.7) ng/l and (6.9+/-0.9) x 10(3) AU/l, respectively, p<0.05]. Four-week fenofibrate treatment resulted in significant decrease of TF (1.017+/-0.010) and PAI-1 mRNA (1.061+/-0.011, p<0.01), the plasma activity of TF [(40.3+/-12.2) ng/l, p<0.05] and PAI-1 [(7.5+/-1.5) x 10(3) AU/l, p<0.01] also decreased significantly, and the concentrations of lipids were not changed.

CONCLUSION

TF and PAI-1 mRNA expression and plasma activities increased in adipose tissue of cholesterol-fed rabbits. Fenofibrate reduced TF and PAI-1 expression and plasma activity in adipose, suggesting that fenofibrate treatment reduces thrombosis risk, and may have an antithrombotic effect independent of its lipid-lowering.

Effects of low-calorie diet on steatohepatitis in rats with obesity and hyperlipidemia

AIM

To evaluate the effects of low calorie diet (LCD) on nonalcoholic steatohepatitis (NASH) in rats with obesity and hyperlipidemia.

METHODS

29 Sprague-Dawley (SD) rats were randomly divided into three groups. The animals in control (n=9) and NASH group (n=10) were fed on standard rat diet and high fat diet respectively for 12 weeks, ten rats in LCD group were fed on high fat diet for 10 weeks and then low calorie diet for 2 weeks. At the end of the experiment, body weight, abdominal adipose content, liver function, and hepatopathological changes were examined to evaluate the effect of different feeding protocols on the experimental animals.

RESULTS

There was no death of animal in the experimental period. All rats in the NASH group developed steatohepatitis according to liver histological findings. Compared with the control group, body weight (423.5+/-65.2 vs 351.1+/-43.0 g, P<0.05), abdominal adipose content (14.25+/-1.86 vs 9.54+/-1.43, P<0.05), liver index (3.784+/-0.533 vs 2.957+/-0.301 %, P<0.01), total serum cholesterol (1.60+/-0.41 vs 1.27+/-0.17 mmol/L,P<0.05) and free fatty acids (728.2+/-178.5 vs 429.2+/-96.7 mmol/L, P<0.01), serum alanine aminotransferase (1,257.51+/-671.34 vs 671.34+/-118.57 nkat/L, P<0.05) and aspartic aminotransferase (2,760.51+/-998.66 vs 1,648.29+/-414.16 nkat/L, P<0.01) were significantly increased in the NASH group. Whereas, when rats were fed on LCD protocol, their body weight (329.5+/-38.4 g, P<0.01), abdominal adipose content (310.21+/-1.52 g, P<0.05), liver index (3.199+/-0.552 %, P<0.05), and serum alanine aminotransferase (683.03+/-245.49 nkat/L, P<0.05) were significantly decreased, and the degree of hepatic steatosis (P<0.05) was markedly improved compared with those in the NASH group. However, no significant difference was found in serum lipid variables and hepatic inflammatory changes between the two groups.

CONCLUSION

LCD might play a role in the prevention and treatment of obesity and hepatic steatosis in SD rats, but it exerts no significant effects on both serum lipid disorders and hepatic inflammatory changes.

Plasma PAI-1 levels are more strongly related to liver steatosis than to adipose tissue accumulation

OBJECTIVE

Because obesity and insulin resistance (IR) are strongly associated with liver steatosis (LS), we investigated the relation between the degree of LS and plasminogen activator inhibitor-1 (PAI-1) in ob/ob mice, in C57/BL6 mice with alcoholic LS, and in severely obese humans.

METHODS AND RESULTS

In both mouse models, plasma PAI-1 levels were associated with PAI-1 expression in the liver and with the degree of LS. Liver PAI-1 antigen was associated with the tumor necrosis factor receptor-II (TNFRII) antigen, whereas association with TNF antigen content was found in ob/ob mice only. No significant correlation between plasma PAI-1 and PAI-1 expression in adipose tissue of ob/ob mice was observed. Furthermore, the relation between plasma PAI-1 levels and body weight was positive in ob/ob mice but negative in C57/BL6 mice (both P<0.001). In humans, PAI-1 levels were correlated with the degree of LS, and 26% of plasma PAI-1 activity was independently explained by LS and serum insulin levels.

CONCLUSIONS

Plasma PAI-1 levels are more closely related to fat accumulation and PAI-1 expression in the liver than in adipose tissue. In steatotic liver, PAI-1 antigen content is associated with those of TNF and TNFRII. Therefore, we suggest that TNF pathway dysregulation in LS could be involved in increased plasma PAI-1 in obesity with IR.

Regulation of plasma PAI-1 concentrations in HAART-associated lipodystrophy during rosiglitazone therapy

OBJECTIVE

Patients with highly active antiretroviral therapy-associated lipodystrophy (HAART+LD+) have high plasminogen activator inhibitor-1 (PAI-1) concentrations for unknown reasons. We determined whether (1). plasma PAI-1 antigen concentrations are related to liver fat content (LFAT) independently of the size of other fat depots and (2) rosiglitazone decreases PAI-1 and LFAT in these patients.

METHODS AND RESULTS

In the cross-sectional study, 3 groups were investigated: 30 HIV-positive patients with HAART+LD+, 13 HIV-positive patients without lipodystrophy (HAART+LD-), and 15 HIV-negative subjects (HIV-). In the treatment study, the HAART+LD+ group received either rosiglitazone (8 mg, n=15) or placebo (n=15) for 24 weeks. Plasma PAI-1 was increased in HAART+LD+ (28+/-2 ng/mL) compared with the HAART+LD- (18+/-3, P<0.02) and HIV- (10+/-3, P<0.001) groups. LFAT was higher in HAART+LD+ (7.6+/-1.7%) than in the HAART+LD- (2.1+/-1.1%, P<0.001) and HIV- (3.6+/-1.2%, P<0.05) groups. Within the HAART+LD+ group, plasma PAI-1 was correlated with LFAT (r=0.49, P<0.01) but not with subcutaneous or intra-abdominal fat or serum insulin or triglycerides. In subcutaneous adipose tissue, PAI-1 mRNA was 2- to 3-fold higher in the HAART+LD+ group than in either the HAART+LD- or HIV- group. Rosiglitazone decreased LFAT, serum insulin, and plasma PAI-1 and increased serum triglycerides but had no effect on intra-abdominal or subcutaneous fat mass or PAI-1 mRNA.

CONCLUSIONS

Plasma PAI-1 concentrations are increased in direct proportion to LFAT in HAART+LD+ patients. Rosiglitazone decreases LFAT, serum insulin, and plasma PAI-1 without changing the size of other fat depots or PAI-1 mRNA in subcutaneous fat. These data suggest that liver fat contributes to plasma PAI-1 concentrations in these patients.