ln vitro enantioselective studies of metabolism, cytotoxicity and genotoxicity of the nematicide fenamiphos

Author(s)

Nayara Cristina Perez de Albuquerque

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2019-02-08

Examining board members

Anderson Rodrigo Moraes de Oliveira; Quezia Bezerra Cass; Danielle Palma de Oliveira; Jonas Augusto Rizzato Paschoal

• Advisor: Anderson Rodrigo Moraes de Oliveira; Lusania Maria Greggi Antunes

Abstract

Human exposition to pesticides can occur in several ways, as occupational exposure or chronic exposure by ingestion of food and water contaminated with pesticide residue. So, the risks of human exposition to these pesticides should be assessed. For that, it is necessary information about metabolism, such as the metabolic pathway, the possible interactions with other xenobiotics, and evaluate the possible cytotoxicity and genotoxicity. Fenamiphos, the target pesticide of the present work, stands out due to its wide use to control of nematodes in more than 60 countries, including Brazil. Despite of its chirality and evidences of stereoselectivity with respect its activity and toxicity, fenamiphos is still sold as a racemic mixture. Given that, this work proposed to carry out an extensive in vitro stereoselective study of phase I metabolism of the chiral pesticide fenamiphos using human liver microsomes and evaluate the drug-pesticide interactions through in vitro inhibition assays of major cytochrome P450 (CYP450) enzymes. ln addition, the stereoselective cytotoxicity and genotoxicity of this pesticide were evaluated in human peripheral blood mononuclear cells. The in vitro results showed the phase I metabolism of fenamiphos by CYP450 enzymes, and the oxidation of fenamiphos to fenamiphos sulfoxide. The Michaelis-Menten model was used to describe the enzyme kinetics of fenamiphos metabolism. The kinetic parameters (KM e VMAX) were determined and used to perform in vitro-in vivo extrapolations. Hepatic clearance and hepatic extraction rate evidenced the role of liver on fenamiphos clearance, although this process does not occur completely during the first passage of the pesticide by the organ. The phenotyping assays showed the significant participation of CYP3A, CYP2B6 and CYP2E1 isoforms on fenamiphos sulfoxide formation. Regarding the evaluation of the inhibitory potential of fenamiphos of the main isoforms of CYP450, the results suggest that this pesticide inhibits by reversible and competitive mechanisms CYP1A2, CYP2C19 and CYP3A isoforms, highlighting the strongly stereoselectivity in inhibition of the CYP1A2 isoform. ln vitro-in vivo extrapolation suggests that the inhibition caused by fenamiphos to these isoforms should not be ignored, and that this pesticide has significant potential to cause drug-pesticide interactions. Cytotoxicity and genotoxicity assays have demonstrated that fenamiphos does not appear to be toxic to human peripheral blood mononuclear cells, at least at the concentrations evaluated (0.10 to 102.40 µmol L-1) during 24 hours of exposure. However, although fenamiphos does not exhibit cytotoxicity and genotoxicity to evaluated cells, the risks of human exposure to this compound should not be neglected. Fenamiphos presents a significant potential to cause drug-pesticide interactions by the inhibition of cytochrome P450 isoforms. Thus, the results presented in this study highlight the risks to which the Brazilian population is exposed. (AU)

• FAPESP's process: 15/02533-1 - In vitro enantioselective studies of metabolism , cytotoxicity and genotoxicity of the nematicide fenamiphos
• Grantee: Nayara Cristina Perez de Albuquerque
• Support Opportunities: Scholarships in Brazil - Doctorate