Development of a caffeine breath test to measure cytochrome P450-1A activity in birds

Cytochrome P450-1A activity is induced by planar polyhalogenated diaromatic hydrocarbons, and is often used as a biomarker of exposure of wildlife to these compounds. P450-1A activity is usually measured ex vivo in liver tissue. The purpose of this study was to develop a less invasive breath test to measure P450-1A activity in birds. Such an assay would allow measurement of P450-1A activity without the need to kill birds, and on the same individual over time. Caffeine is specifically metabolized by P450-1A, and N-demethylation of (14)C-labelled caffeine to (14)CO(2) was used as indicator of whole-body P450-1A activity. The caffeine breath test (CBT) was performed by injecting (14)C-labelled caffeine i.v. and measuring the (14)C activity of respired (14)CO(2). The CBT was developed with domestic chickens (Gallus domesticus) using several (14)C-labelled caffeine isomers, and was also performed with three species of fish-eating birds in the North American Great Lakes. The CBT was an effective method for measuring P450-1A activity. Chickens treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) metabolized significantly more tri-labelled caffeine (1,3,7-[(14)C]trimethylxanthine) during the CBT than untreated chickens (p = 0.004). Tri-labelled caffeine and 3-methyl-[(14)C]caffeine were effective substrates in the CBT.