الفهرس 
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Abstract
Hepatic fibrosis (HF) is a wound healing response to chronic liver injury including chronic infection by hepatitis B, C viruses and parasite schistosoma, chronic alcoholism, non-alcoholic steatohepatitis (NASH), auto-immune hepatitis, biliary diseases, metabolic disorders or exposure to certain drugs and toxins. Progressive HF is the final common pathway for most chronic liver injuries, leading to cirrhosis with risk of liver failure and hepatocellular carcinoma. Initial stages of liver fibrosis may be reversible, but liver cirrhosis is irreversible. Therefore, it is of practical significance to seek a drug that can inhibit or delay the progression of liver fibrosis.
Chronic carbon tetrachloride (CCl4) intoxication is a well-known model for producing oxidative stress and chemical hepatic injury and it is used as a model for the screening of anti-hepatotoxic and/or hepatoprotective drugs.
Irbesartan is considered one of long-acting angiotensin II receptor blocker. Its main action is to prevent binding of angiotensin II, thereby it inhibits the renin angiotensin system and lowers blood pressure. Sildenafil citrate is selective inhibitor of cGMP-specific PDE5. The drug was first approved for the treatment of erectile dysfunction and for treatment of pulmonary arterial hypertension. Atorvastatin is a selective, competitive inhibitor of HMG-CoA reductase. Statins have anti-inflammatory effects.
In view of such considerations, the design of the current work was set to compare the efficacy of sildenafil, irbesartan and atorvastatin on oxidative stress, some inflammatory and fibrotic markers, as well as hepatic function tests in CCl4 induced hepatic fibrosis in rats, in an attempt to achieve better therapeutic management of HF and to examine the possible mechanisms of action of the probed drugs.
In the present study, 40 adult male albino rats were used. Rats were divided into 5 groups (n=8). Eight rats served as normal controls. HF was induced in rats with intraperitoneally injection of 1 ml/kg CCl4. HF was progressed in all animals after 8 weeks. Rats were then divided into 5 groups:
Group 1: untreated HF rats (normal control group).
Group 2: rats treated with an intraperitoneal injection of 1 ml/kg CCl4, twice a week for 8 weeks (positive control group).
Group 3: HF rats treated with a subcutaneous dose of sildenafil citrate (10 mg / kg), daily for 14 days.
Group 4: HF rats treated with an oral dose of irbesartan (15mg/kg), daily for 4 weeks.
Group 5: HF rats treated with an oral dose of atorvastatin (15mg/kg), daily for 4 weeks.
At the end of the experiment, rats of all groups were sacrificed by cervical dislocation. Blood samples were collected from posterior vena cava and serum was separated, kept at -80 °C and used for estimation of the following parameters:
1- Tumor necrosis factor alpha (TNF-α).
2- Transforming growth factor- TGF-β1 (TGF-β1)
3- Alanine aminotransferase (ALT).
4- Aspartate aminotransferase (AST).
5- gamma glutamyl transaminase (γ-GT).
6- Total bilirubin
Livers of all groups were excised and cut into two sections. The first liver section will be fixed in 10% neutral buffered formaldehyde to be used for histopathological examination, while the second liver section was kept at -80 °C used for the estimation for following parameters:
1. Malondialdehyde (MDA).
2. Reduced glutathione (GSH) concentration.
3. Glutathione peroxidase activity.
Tumor necrosis factor-α (TNF-α) is a cytokine that plays a role in various pathological and physiological situations such as metabolic, inflammatory, proliferative but also necrotic effect. Transforming growth factor-β1 (TGF-β1), a major fibrotic growth factor in liver fibrosis, plays a pivotal role in the phenotypical activation of hepatic stellate cells that increase production of ECM proteins leading to fibrosis progression. In untreated HF rats, a significant rise in these cytokines was observed in comparison to normal controls. There was a reduction in the level of TNF-α and TGF-β in the treated groups. The highest significant decrease in the levels of TNF-α, TGF-β in the current study has occurred in the irbesartan group, thus demonstrating a potent anti-inflammatory and antifibrotic effect.
Estimation of the level of malondialdehyde, reduced glutathione and glutathione peroxidase activity were used for the assessment of oxidative status which is considered one of the pathways leading to fibrosis development and progression. Significant changes were noticed in values of MDA, GSH and GSHpx activity in fibrotic rat model compared to normal controls, as the level of MDA increased while GSH and GSHpx activity decreased in the fibrotic rat model.
Treatment of the HF rats with each of the probed drugs, decreased the MDA level and elevated the GSH and GSHpx activity. Both Irbesartan and sildenafil exert a strong antioxidative property and free radical scavenging properties.
In addition, hepatic fibrosis was confirmed by ALT, AST, γ-GT and total bilirubin level in rat sera and histopathological examination of the liver tissue of rats in positive control group. Hepatic enzymes showed significant reduction in both irbesartan and sildenafil therapy in comparison to untreated HF and atorvastatin treated rats. Noteworthy, atorvastatin showed non significant decrease in ALT and γ-GT levels compared to positive control group. This is indicating the clear adverse effect of the drug.
Consistent with the results of liver enzymes, the histopathological examination of liver tissue in untreated HF rats expressed prominent fibrous tissue proliferation in the portal tracts with formation of porto-portal or porto-central septae as well as marked lymphocytic infiltration in the portal tracts. Treatment with either irbesartan or with sildenafil presented with a nearly similar degree in the reduction of fibrous tissue deposition.While, in atorvastatin treated group still showed both lymphocytic infiltration and fibrous tissue deposition compared to the other treated groups. Histopathological data confirmed the antifibriotic effect of either irbesartan or sildenafil.
Collectively, these results referred to variable contribution of the proposed targeted pathways on the anti-fibrotic action exerted by the tested drugs. Thus, the antfibrotic action of both irbesartan and sildenafil were documented to be mediated not only by anti inflammatory action, but also by decreasing oxidative stress, modulating liver injury and preventing the progression of fibrosis. However, atorvastatin exerted the least therapeutic effect in hepatic fibrosis treatment.