Lack of efficacy of mTOR inhibitors and ACE pathway inhibitors as antifibrotic agents in evolving and established fibrosis in Mdr2⁻/⁻ mice

BACKGROUND & AIMS

Mammalian target of rapamycin and angiotensin-converting enzyme inhibition has been shown to have antifibrotic activity in models of liver fibrosis. The aim of our study was to determine the efficacy of rapamycin, everolimus, irbesartan and captopril, alone and in combination, as antifibrotic agents in the Mdr2(-/-) model of cholestasis both in early injury and established disease.

METHODS

Mdr2(-/-) mice were treated for 4 weeks with vehicle, rapamycin (1 mg/kg) or everolimus (5 mg/kg) every second day or with captopril (30 mg/kg/day), irbesartan (10 mg/kg/day) or vehicle. Further groups of 3-week-old Mdr2(-/-) mice were treated with rapamycin and irbesartan in combination (1 mg/kg/day and 10 mg/kg/day) or with rapamycin (2 mg/kg/day) for 4 weeks. Liver injury and fibrosis were compared between treated and untreated animals.

RESULTS

There were no significant improvements in liver injury, histology, hepatic hydroxyproline or profibrogenic gene expression following treatment with rapamycin, everolimus, captopril or irbesartan at any time point studied. Likewise, there were no improvements in liver histology or profibrogenic gene expression following combination therapy or high-dose rapamycin treatment.

CONCLUSIONS

The antifibrotic effects of rapamycin, everolimus, captopril and irbesartan seen in other models of fibrosis were not replicated in the Mdr2(-/-) model in this study. This highlights the clear need to test specific antifibrotic agents in a number of different animal models. We believe this animal model is ideal to study usefulness of antifibrotic agents in cholestatic liver disease because of the similarity in genetics and hepatic histopathology to human cholestatic liver disease.

A corn oil-based diet protects against combined ethanol and iron-induced liver injury in a mouse model of hemochromatosis

BACKGROUND

Combined iron overload and alcohol may promote synergistic chronic liver injury and toxicity. The role of specific dietary fats in influencing the development of co-toxic alcoholic liver disease needs further evaluation and is investigated in this study.

METHODS

Wild-type (WT) and the iron-loaded Hfe-null (Hfe(-/-) ) mice were fed chow (CC), a AIN-93G standard control (SC), or a corn oil-modified, AIN-93G-based (CO) diet with or without the addition of 20% ethanol (EtOH) in the drinking water for 8 weeks and assessed for liver injury.

RESULTS

WT mice on CC, SC, and CO diets had no liver injury, although mild steatosis developed in the SC and CO groups. The addition of EtOH resulted in mild steatohepatitis in WT mice fed SC but not those on a CO diet. EtOH administration in Hfe(-/-) animals on the CC and SC diets caused marked oxidative stress, inflammatory activity, and subsinusoidal and portal-portal tract linkage fibrosis with significant up-regulation of genes involved in cellular stress signaling and fibrogenic pathways. These effects were abrogated in the CO-fed mice, despite elevated serum EtOH levels and hepatic iron concentrations, reduced hepatic glutathione and mitochondrial superoxide dismutase activities. Feeding with the CO diet led to increased hepatic glutathione peroxidase and catalase activities and attenuated alcohol-induced hepatic steatosis in the Hfe(-/-) animals. Iron and EtOH feeding markedly reduced p-STAT3 and p-AMPK protein levels, but this effect was significantly attenuated when a CO diet was consumed.

CONCLUSIONS

A CO-based diet is protective against combined EtOH- and iron-induced liver toxicity, likely via attenuation of hepatic steatosis and oxidative stress and may have a role in the prevention of fibrosis development in chronic liver disease.

The serum hepcidin:ferritin ratio is a potential biomarker for cirrhosis

BACKGROUND

Serum hepcidin concentration is potentially affected by inflammation and iron stores in chronic liver disease (CLD), but little is known about the relationship between hepcidin and the degree of hepatic fibrosis. We investigated the potential role of serum hepcidin as a biomarker of advanced liver disease.

METHODS

Serum hepcidin was measured in 332 adults with CLD of varying aetiologies, 45 healthy and 50 non-liver disease patient controls. Liver biopsy data were available for 228 CLD subjects.

RESULTS

Hepcidin was decreased in CLD patients compared with non-liver disease patient controls (P < 0.0001) but not healthy controls, and was lowest in those with cirrhosis (P < 0.0001). Serum hepcidin correlated with hepatic hepcidin mRNA expression in 91 biopsy samples available for genetic analysis (r = 0.68, P < 0.0001). Hepcidin also correlated positively with serum ferritin concentration, transferrin saturation, ALT, serum albumin and haemoglobin, but negatively with serum bilirubin. The hepcidin:ferritin ratio was significantly lower in CLD subjects compared with healthy and disease controls, and decreased with each increase in the stage of fibrosis and siderosis. The hepcidin:ferritin ratio was associated with progressive fibrosis on linear regression, and a value of less than 0.1 was independently associated with cirrhosis on logistic regression analyses (OR 5.54, P < 0.001). Receiver operating characteristic analysis showed the hepcidin:ferritin ratio was able to distinguish between F0 and F4 stages of fibrosis (area under receiver operating characteristic curve = 0.86).

CONCLUSIONS

The hepcidin:ferritin ratio is reduced in relation to increasing fibrosis in CLD and the use of this ratio may have potential future diagnostic implications as a marker of cirrhosis.

Altered lipid metabolism in Hfe-knockout mice promotes severe NAFLD and early fibrosis

The HFE protein plays a crucial role in the control of cellular iron homeostasis. Steatosis is commonly observed in HFE-related iron-overload disorders, and current evidence suggests a causal link between iron and steatosis. Here, we investigated the potential contribution of HFE mutations to hepatic lipid metabolism and its role in the pathogenesis of nonalcoholic fatty liver disease. Wild-type (WT) and Hfe knockout mice (Hfe(-/-)) were fed either standard chow, a monounsaturated low fat, or a high-fat, high-carbohydrate diet (HFD) and assessed for liver injury, body iron status, and markers of lipid metabolism. Despite hepatic iron concentrations and body weights similar to WT controls, Hfe(-/-) mice fed the HFD developed severe hypoxia-related steatohepatitis, Tnf-α activation, and mitochondrial respiratory complex and antioxidant dysfunction with early fibrogenesis. These features were associated with an upregulation in the expression of genes involved in intracellular lipid synthesis and trafficking, while transcripts for mitochondrial fatty acid β-oxidation and adiponectin signaling-related genes were significantly attenuated. In contrast, HFD-fed WT mice developed bland steatosis only, with no inflammation or fibrosis and no upregulation of lipogenesis-related genes. A HFD led to reduced hepatic iron in Hfe(-/-) mice compared with chow-fed mice, despite higher serum iron, decreased hepcidin expression, and increased duodenal ferroportin mRNA. In conclusion, our results demonstrate that Hfe(-/-) mice show defective hepatic-intestinal iron and lipid signaling, which predispose them toward diet-induced hepatic lipotoxicity, accompanied by an accelerated progression of injury to fibrosis.