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Role of Cytochrome P450s in Isoniazid bioactivation

Chen, J (2019) Role of Cytochrome P450s in Isoniazid bioactivation. Master's Thesis, University of Pittsburgh. (Unpublished)

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uberculosis (TB) is an infectious disease caused by bacteria Mycobacterium Tuberculosis. With a huge population infected worldwide and millions of new cases reported on an annual basis, TB is a serious threat to global health. TB chemotherapy is a crucial strategy and isoniazid (INH) is one of the most potent anti-TB drugs that is heavily used in both TB chemoprophylaxis and treatment.
One of the biggest concerns in INH therapy is INH-induced liver injury (I-ILI). Marked by persistent elevation of serum alanine aminotransferase (Alanine Aminotransferase and Aspartate aminotransferase), usually ten times above upper limit of normal (ULN), it is characterized as hepatocellular injury of a phenotype happened in 0.5-1.0% of patients on INH treatment. These patients are facing a high risk of fatal liver failure. INH associated hepatoxicity was identified as early as its introduction to the clinical use but the mechanism remains elusive. As numerous studies propose myriads of potential mechanisms, immune-medicated response was considered important contributing factor towards INH associated hepatotoxicity recently.
Since small molecules like INH and its metabolites are less likely to trigger the immune response, complexes of INH or its metabolites with endogenous macromolecules are hypothesized as antigens in this case. The study targeted on INH-human serum albumins (HSAs) adducts showed that this complex did get recognized by the immune system, but auto-antibodies for this antigen was undetectable even with highly sensitive radioimmunoassay. Subsequently, attention was switched to the CYP-bioactivated INH-CYP adducts and its association with I-ILI. In this case, auto-antibodies of these adducts were detectable, but the products of CYP-mediated INH bioactivation along with isoforms of CYP involved remains unclear. To further address this question, we developed in vitro incubation systems to identify the existence of CYP-mediated INH bioactivation products and the CYP isoforms responsible for the bioactivation.
To detect bioactivation products, we introduced N-α-acetyl-l-lysine (NAL) as a trapping agent to stabilize them and make them detectable as INH-NAL adducts. Results from incubation shown INH went through CYP-independent auto-oxidation, and no bioactivation products were observed in three individual CYP isoforms and human liver microsomes we evaluated. Thus, our results do not support the hypothesis of I-ILI that is mediated by the immune response from CYP-bioactivated INH-CYP adducts.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Chen, Jjic110@pitt.edujic110
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMa, XC
Committee MemberXie, W
Committee MemberLi, S
Date: 15 April 2019
Date Type: Publication
Defense Date: 4 April 2019
Approval Date: 15 April 2019
Submission Date: 12 April 2019
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 36
Institution: University of Pittsburgh
Schools and Programs: School of Pharmacy > Pharmaceutical Sciences
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Cytochrome P450s, Isoniazid, Liver injury, Bioactivation
Date Deposited: 15 Apr 2019 18:23
Last Modified: 15 Apr 2019 18:23


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