Avian forms of cytochrome P450

Area of Science:

• Environmental Toxicology
• Biochemistry
• Avian Biology

Background:

• Avian cytochrome P450 (P450) enzymes play a vital role in metabolizing environmental contaminants, yet remain understudied and poorly characterized.
• A P450 form, potentially belonging to family 1A, is inducible by planar molecules and used in field biomarker assays, though it differs catalytically from mammalian P450 1A1.
• Phenobarbital induces two purified P450 forms (2H1, 2H2) in chickens, resembling rat P450 2B1/2B2, alongside partially purified PB-A/PB-B and an acetone-inducible form similar to rodent P450 2E.

Purpose of the Study:

• To characterize avian cytochrome P450 (P450) forms and their responses to environmental inducers.
• To investigate the catalytic properties and antibody recognition of avian P450s in relation to mammalian forms.
• To explore the role of avian P450 induction in potentiating pesticide toxicity.

Main Methods:

• Purification and partial purification of induced avian P450 forms.
• Characterization of enzyme kinetics and substrate specificity.
• Use of antibodies against mammalian P450s for cross-reactivity studies.
• Analysis of P450 induction in avian liver in response to environmental pollutants (PCBs) and fungicides.

Main Results:

• An avian P450 1A-like form, inducible by planar molecules, shows distinct catalytic properties compared to mammalian P450 1A1.
• Phenobarbital treatment of domestic fowl yielded purified P450s 2H1 and 2H2, analogous to rat P450 2B1 and 2B2.
• Field studies indicated P450 induction in avian liver (adults and embryos) by environmental PCBs, recognized by antibodies to mammalian P450 1A1 and P450 2B.
• Ergosterol biosynthesis inhibitor (EBI) fungicides potentiate the toxicity of certain phosphorothionate pesticides in birds.

Conclusions:

• Avian P450s exhibit diverse forms with distinct inducibility and catalytic activities, differing from their mammalian counterparts.
• Environmental pollutants like PCBs induce specific P450 forms in birds, highlighting their role in xenobiotic metabolism.
• The potentiation of pesticide toxicity by EBI fungicides underscores the complex interactions between avian P450s, environmental chemicals, and toxicological outcomes.