Randle, LE 
ORCID: 0000-0002-7881-2979
(2005)
'Pharmacological and physiological protective mechanisms in chemical-induced hepatotoxicity.'.
PhD thesis, University of Liverpool.
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| Item Type: | Thesis (PhD) |
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| Additional Information: | Adverse drug reactions (ADRs) are a major complication to drug development with hepatotoxicity being the most cited reason for drug withdrawal from the market. This is because the liver plays a major role in xenobiotic metabolism with toxicity arising as the result of an imbalance between bioactivation, the metabolic conversion of a parent compound to a chemically reactive species, and bioinactivation, a detoxification and elimination process. Adrenergic modulation of hepatotoxicity was proposed during extensive studies by Calvert et al., (1960) into carbon tetrachloride (CCl4) hepatotoxicity. However, the ability for adrenergic compounds to protect against paracetamol (APAP) induced hepatotoxicity has not been investigated, and is the premise of this thesis. Histological and serological analysis confirmed the ability of the selective alpha1 antagonist, prazosin (PZ) to protect the murine liver from a toxic APAP insult. Serum ALTs remained at control values in PZ pre-treated mice 5 h post APAP dosing (U/L ± SEM; APAP alone: 1780 ± 662; APAP + PZ: 140 ± 50, P <0.01). However, multiple doses of PZ were required to maintain protection (¿normal¿ hepatic histology) at 24 h. PZ failed to prevent the APAP-induced decrease in hepatic GSH. The mechanistic basis behind this protection was further investigated. PZ did not alter APAP bioactivation with comparable levels of APAP protein adducts detected between groups at 1 and 5 h (% binding/mg protein ± SEM; 5 h APAP alone: 1.41 ± 0.23; 5 h APAP + PZ 1.3 ± 0.39). A difference was observed in the amount of hepatic APAP-glucuronide recovered at 1 h, however this was deemed to be the result of a lack of toxicity in the PZ pre-treated group and disappeared with low dose APAP (% dose hepatic APAP-Gluc. ± SEM; 1 mmol/kg APAP 7.69 ± 1.3; APAP + PZ 9.33 ± 1.52; 3.5 mmol/kg APAP 36.03 ± 13.29; APAP + PZ 55.83 ± 7.14, P <0.05). PZ also modulated toxicity when administered 30 min and 1 h post APAP (ALT U/L ± SEM; APAP alone: 1655 ± 937; APAP + PZ 30 min post: 228 ± 132; APAP + PZ 1 h post: 414 + 161). The role of Nrf2 nuclear translocation in the defence response initiated by APAP toxicity was also investigated. Western blot analysis confirmed a linear increase in hepatic Nrf2 levels at 1 h, with nuclear levels rising from 113  61 % control ± SD (50mg/kg) to 613  210 % control ± SD (1g/kg). Northern blots confirmed the functionality of this translocation and highlighted a hierarchy of gene induction (HO-1> GCS> mEH). The GSH depleting agent diethylmaleate was also capable of increasing nuclear Nrf2 levels (1h; DEM 7.05 mmol/kg 652 ± 55 % control ± SD, P <0.001), but not buthionine sulfoximine. To characterise the role of GSH depletion in chemical induced Nrf2 trans activation, the hepatotoxins bromobenzene (BB), CCl4 and furosemide (FS), each with differing mechanism of toxicity, were all capable of inducing Nrf2 nuclear translocation, within 1 h in vivo (% control ± SEM; BB: 209 ± 10; CCl4: 146 ± 3; FS: 254 ± 41), despite a lack of significant GSH depletion in the CCl4 and FS groups (% control ± SEM; 102 ± 20 % and 83 ± 14 %, respectively). The ability of PZ to protect against other forms of xenobiotic-induced toxicity was studied. BB depletes GSH within 1 h (40.4 ± 7.7 nmol/mg protein ± SEM, P <0.05) with significant toxicity developing at 5 h (161 ± 14 U/L ± SEM, P< 0.001), multiple doses of PZ were also required to protect against BB toxicity. PZ did not provide hepatoprotection against CCl4 and FS with moderate necrosis developing at 24 h (Histology grade; CCl4:1.9, CCl4 ± mPZ: 2.1; FS: 2.2, FS: + mPZ 2.2). In conclusion, the studies described in this thesis have demonstrated 1 antagonist-mediated hepatoprotection against certain forms of chemical stress within the murine liver. This protection is not due to modulation of the metabolism of the toxicant. Further characterisation of the physiological defence r |
| Uncontrolled Keywords: | hepatotoxicity, nrf2, defence, protection, paracetamol |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 20 Oct 2023 14:38 |
| Last Modified: | 20 Oct 2023 14:59 |
| DOI: | 10.17638/03174852 |
| Copyright Statement: | Copyright © and Moral Rights for this thesis and any accompanying data (where applicable) are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3174852 |
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