الفهرس 
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Abstract
The liver is a particular target for drug toxicity because of its role in clearing and metabolizing chemicals. Drug induced hepatotoxicity is a common cause of acute liver injury that may be presented by jaundice, pruritus, and marked increase in alkaline phosphatase level, as well as increase in alanine transaminase (ALT) levels. The pathophysiology and intrinsic mechanisms underlying paracetamol (APAP) induced hepatotoxicity are different because aetiologies and mechanisms vary between oxidative stress, inflammation and cell death including apoptosis, necrosis and necroptosis .
This study is a trial to explore the pathophysiology and different mechanisms involved in hepatotoxicity induced by APAP as a common model in rats. In our study we used different antioxidant, anti-inflammatory, anti-apoptotic and anti-necroptotic drugs (vitamin E, NaHS (H2S donor), necrostatin-1) to evaluate their role in prevention of hepatotoxicity.
The present study was conducted on 50 adult male albino rats weighing 150-250 gram. Rats were left to acclimatize to the lab environment for two weeks before the start of the experiments. Rats were randomly classified into the following groups:
1-Control groups: consisted of 10 rats
A- Control group (4rats/group): in which rats didn’t receive medications and were left freely wandering throughout the period of the experiment.
B- Control groups treated with vehicle (3rats/group): in which rats received the vehicles such as dimethyl sulfoxide (DMSO) vehicle for necrostatin-1 and olive oil vehicle for vitamin E.
There is no significant difference between control groups treated by vehicles or not.
2- paracetamol treated group(APAP group): consisted of 10 male rats. Each rat of this group received paracetamol(APAP) dissolved in saline at a dose level of 2 gm/kg body weight given as a single dose orally by oral gavage.
3- group treated by parcetamol + Vitamin E (α-tocopherol) (APAP+ vitamin E group): consisted of 10 Male rats. Each rat of this group received pretreatment of α-tocopherol diluted in olive oil with a dose of 100mg/kg body weight that is received as a single dose that is received by intraperitoneal injection 24 hours before receiving APAP.
4- group treated by paracetamol + sodium hydrosulfide (NaHS as a donor of H2S) (APAP+H2S group): consisted of 10 Male rats. Each rat of this group received pretreatment of NaHSdissolved in salinewith a dose level of56µmole/kg once a day for 2 days by intraperitoneal injection. The second dose is given 1 hour before receiving APAP.
5- group treated by paracetamol + necrostatin-1(RIPK1 inhibitor) (APAP+Necrostatin-1 group): consisted of 10 Male rats. Each rat of this group received pretreatment of necrostatin-1 dissolved in 2% DMSO in a phosphate buffered saline at a dose level of 1.8 mg/kg taken as a single dose intraperitoneal injection 1 hour beforereceiving APAP with the previous dose.
At the end of the experiment, rats were sacrificed by decapitation after an overnight fasting and blood samples were collected, allowed to clot at room temperature, and then centrifuged at 3000 rpm for 15 min. The serum layer was then withdrawn into identified eppendorf tubes, labeled and stored at - 20 °C till the time of assay of:
Serum liver enzymes including alanine transaminase (ALT) and aspartate transaminase (AST), serum lipid profile including total cholesterol, (TC), low density lipoprotein (LDL), high density lipoprotein (HDL) and triglycerides (TGs), serum reduced glutathione (GSH), serum tumor necrosis factor alpha (TNF-α) and serum interleukin-33 (IL-33). The abdomen was dissected, and then liver was removed and sent for histopathology. Parts of rat livers were used for Hematoxylin and eosin (H&E) staining using standard techniques. Other sections were immune-stained for caspase-3 measurement.
The results obtained clearly demonstrated that:
• In APAP group, in comparison with the Control group, serum levels of ALT, AST, TNF-α, TGs, TC, and LDL were significantly increased associated with a significant decrease in serum HDL and GSH. It showed positive Caspase-3 immune reactions.
• In (APAP+vitamin E) group, in comparison with the APAP group, serum levels of ALT, AST, TNF-α, TGs, TC, and LDL were significantly decreased associated with a significant increase in serum HDL and GSH. It showed decreased positive immune Caspase-3 reactions.
• In (APAP+H2S) group, in comparison with the APAP group, serum levels of ALT, AST, TNF-α, TGs, TC, and LDL were significantly decreased associated with a significant increase in serum HDL and GSH. It showed no positive immune Caspase-3 reactions.
• In (APAP+Necrostatin-1) group, in comparison with the APAP group, serum levels of ALT, AST, TNF-α, TGs, TC, and LDL were significantly decreased associated with a significant increase in serum HDL and GSH. It showed decreased positive immune Caspase-3 reactions.
• Microscopic examination of the liver revealed that (APAP+H2S) group showed best protective effects to the liver and improvement of liver enzymes level. (APAP+vitamin E) group showed moderate improvement. The least protective effect on the liver was detected in (APAP+Necrostatin-1) group.