Protein adducts from the anti-HIV drug abacavir – possible biomarkers of drug toxicity

• Author(s): Grilo, Nádia Filipa Marques
• Date: 2012
• Persistent ID: http://hdl.handle.net/10362/8203
• Origin: Repositório Institucional da UNL
• Subject(s): Abacavir; Aldehyde metabolite; Biomarker; Cardiotoxicity; Drug bioactivation; Hypersensitivity
• Document Type: Master thesis
• Language: English
• Advisor(s): Pereira, Sofia; Antunes, Alexandra
• Contributor(s): RUN

Description

Dissertação para obtenção do Grau de Mestre em Genética Molecular e Biomedicina

While the benefits of combined antiretroviral therapy have revolutionized the life expectancy of patients infected with the human immunodeficiency virus, treatment-associated toxicity is frequently observed. Abacavir is a nucleoside reverse transcriptase inhibitor associated with acute toxic events,such as hypersensitivity reactions. In addition, its long-term use has increasingly been recognized as associated with an increased risk of myocardial infarction. While the mechanisms underlying abacavirinduced hypersensitivity and cardiotoxicity are not fully understood, abacavir bioactivation to a reactive aldehyde metabolite is thought to play a crucial role in this context. However, as a short lived specie,in vivo, its formation has so far eluded detection. Our initial hypothesis was that it could be efficiently trapped by N-terminal valine of hemoglobin, forming N-terminal-valine-abacavir adducts. With the ultimate goal of gain insight into the role of abacavir metabolism in abacavir-induced toxicity, the present work was focused on obtaining evidence for the abacavir bioactivation to a reactive aldehyde metabolite, in human immunodeficiency virus - infected patients, and on the evaluation of this reactive metabolite ability to undergo protein modification. To address these issues: 1) abacavir-Edman standards were prepared to monitor the presence of these adducts in vivo; 2) the presence of abacavir-Edman adduct was screened in Wistar rats, for optimization of analytical method; and 3) in patients infected with the human immunodeficiency virus. The experimental approach used, involving N-Alkyl Edman degradation, for specific detachment of N-terminal-valineabacavir adducts from protein, followed by liquid chromatography-electrospray ionization tandem mass spectrometry analysis of detached abacavir-Edman adducts, upon comparison with standards prepared in vitro, allowed the unequivocal identification of these adducts in animal and human samples. These results represent the first report on the involvement of a conjugated aldehyde intermediate in the metabolic activation of abacavir in man. Whereas this evidence does not imply an exclusive relation between abacavir-Edman adducts and abacavir toxicity, the search for causal relationships between the formation of abacabir-derived protein adducts and the occurrence of abacavir-induced toxic events in patients is worth pursuing, and is currently underway, towards the clarification of mechanism(s) of abacavir-induced toxicity.