Development and validation of a liquid chromatography–tandem mass spectrometry assay for the analysis of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and its metabolite 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP) in plasma, urine, bile, intestinal contents, faeces and eight selected tissues from mice

doi:10.1016/j.jchromb.2010.07.012

Journal of Chromatography B

Volume 878, Issue 25, 1 September 2010, Pages 2353-2362

https://doi.org/10.1016/j.jchromb.2010.07.012 Get rights and content

Abstract

The development and validation of a bioanalytical assay is described for the simultaneous analysis of 2-amino-1-methyl-6-phenylimidazo[4-5-b]pyridine (PhIP) and its main metabolite 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP) in plasma, urine, faeces, bile, liver, kidney, testis, spleen, brain, as well as colon-, cecum- and small intestinal tissue and contents from mice. The effect of the matrix on the accuracy of the method was extensively investigated. The bioanalytical assay is based on reversed phase liquid chromatography coupled with tandem mass spectrometry in the positive ion mode using multiple reaction monitoring for analyte quantification. The assay is validated from 1 to 250 ng/mL and the sample pretreatment consists of protein precipitation with acetonitrile using only 100 μL matrix (plasma, bile diluted in 4% (m/v) BSA, intestinal contents, faeces and tissue samples homogenized in 4% (m/v) BSA). The measured concentrations of PhIP and N-OH-PhIP in homogenates were expressed in ng/mL. Based on the weight of the isolated intestinal contents, faeces or tissue the amount of PhIP and N-OH-PhIP per mass unit intestinal content, faeces or tissue was calculated. The validated range for PhIP in urine is from 10 to 1000 ng/mL using 20 μL urine. For N-OH-PhIP quantification, mouse urine was diluted 100× in blank human urine to compensate for matrix effects. The developed method is simple, robust and reproducible. The applicability of the method was demonstrated and the assay could be successfully used to support in vivo toxicokinetics studies of PhIP and N-OH-PhIP in mice.

Introduction

Heterocyclic amines are a large group of carcinogenic compounds found in proteinaceous foods such as cooked meats and fish, coffee, alcohol beverages, cigarette smoke, air, river and rainwater [1]. The most abundant of these heterocyclic amines, 2-amino-1-methyl-6-phenylimidazo[4-5-b]pyridine (PhIP), has been shown to specifically induce tumors of the colon, breast and prostate in rodents [2], [3], [4]. PhIP is formed as a by-product of the Maillard reaction during cooking or frying of protein-rich foods at high temperatures [5]. Shioya et al. suggested phenylalanine, creatinine and glucose to be the most probable precursors of PhIP [6]. For PhIP to exert its carcinogenic effect, a multiple metabolism pathway has been suggested [7], [8], [9], starting with N-hydroxylation at the amine group by CYP1A1 and CYP1A2 [10], [11], [12] resulting in 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP).

The hydroxyl group can be sulphated by SULT1A1 enzymes [13], [14], [15], [16], [17] or acetylated by NAT1 or NAT2 enzymes [13], [17], [18]. Heterolytic cleavage of this sulphate or acetate group results in a reactive radical cation which can form adducts with DNA purines [19], [20]. PhIP and N-OH-PhIP are precursors for this multiple metabolism pathway which stresses the importance of the ability to quantify PhIP and N-OH-PhIP in biological samples in order to understand the distribution of PhIP and the formation and distribution of its carcinogenic metabolite N-OH-PhIP.

The enzymes that are mainly responsible for the metabolism of PhIP are found in different organs and therefore biotransformation of PhIP is not restricted to specific tissues such as the liver [10], [21], [22], [23], [24], [25], [26]. As it has been shown that PhIP induces tumors in numerous organs such as the colon, breast and prostate, the distribution profile of PhIP may be very relevant. This could provide further insight into the carcinogenic potential of PhIP.

A partially validated assay for the analysis of PhIP and N-OH-PhIP in human liver was published in 2001 by Prabhu et al. [27]. A fully validated bioanalytical liquid chromatography–tandem mass spectrometry method for the quantification of PhIP and its metabolite N-OH-PhIP in plasma, urine, bile, faeces, intestinal contents and eight selected tissues from mice has, to the best of our knowledge, not been published hitherto. We designed such an assay with the purpose to support preclinical toxicokinetic studies.

Section snippets

Chemicals

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and its deuterated internal standard 2-amino-1-(trideuteromethyl)-6-phenylimidazo[4,5-b]pyridine (PhIP-D3) were purchased from Toronto Research Chemicals (North York, Ontario, Canada). 2-Hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine was purchased from the National Cancer Institute Chemical Carcinogen Reference Standard Repository at the Midwest Research Institute (Kansas City, USA). 2-Amino-1-methyl-6-phenylimidazo[4,5-b]-5-hydroxypyridine

Linearity

Eight non-zero calibration standards in plasma, urine and 4% (m/v) BSA were prepared in duplicate for each run and analyzed in three independent runs. Calibration curves (area ratio with the internal standard versus nominal concentration) were fitted by least-squares linear regression using the reciprocal of the squared concentration (1/x²) as a weighting factor. To assess linearity, deviations from the mean calculated concentrations over three runs should be within ±15% of nominal

HPLC-MS/MS

To obtain high sensitivity, a triple quadrupole mass spectrometer was chosen as a detector. An analytical column was selected with a stationary phase endcapped with polar groups to provide retention of both hydrophobic as well as hydrophilic compounds.

The protonated molecular ions ([M+H]⁺) were used as precursor ions to generate product-ion spectra (Fig. 1A and B). The most intense product ions were optimized and used as MRM transitions to ensure high sensitivity and selectivity. Ionization and

Toxicokinetic study

The applicability of the assay was demonstrated by i.v. administration of 1 mg/kg PhIP into the tail vein of a male mouse. After 0.5 h plasma, urine, intestinal contents and tissues were collected and analyzed. Bile was obtained in a separate experiment where gall bladder cannulation in a male mouse was performed. After cannulation, 1 mg/kg PhIP was administered i.v. and bile was collected in 15 min fractions. Faeces were collected for 24 h in a metabolic cage after i.v. administration of 1 mg/kg

Conclusion

We have developed an assay for the sensitive analysis of PhIP and N-OH-PhIP in murine plasma, urine, bile, intestinal contents, faeces and tissue homogenates. The influence of matrix effects on the quantification of analytes is described. Two LC-gradients were developed: a step gradient and a linear gradient.

For the analysis of PhIP, a stable isotope labelled internal standard was available to compensate for matrix effects. Both gradients can be used for the quantitative analysis of this

Acknowledgement

Abadi Gebretensae is acknowledged for his excellent technical assistance.

References (29)

N.J. Gooderham et al.
Toxicol. Lett.
(2007)
T. Shirai et al.
Cancer Res.
(1997)
M. Murkovic
J. Chromatogr. B: Analyt. Technol. Biomed. Life Sci.
(2004)
M. Shioya et al.
Mutat. Res.
(1987)
H. Frandsen
Food Chem. Toxicol.
(2007)
H. Glatt
Chem. Biol. Interact.
(2000)
R.F. Minchin et al.
Biochem. Biophys. Res. Commun.
(1992)
E.L. Jamin et al.
J. Am. Soc. Mass Spectrom.
(2007)
L. Vanhaecke et al.
Food Chem. Toxicol.
(2008)
S. Prabhu et al.
Anal. Biochem.
(2001)

A.M. Sanz et al.

J. Chromatogr. B: Analyt. Technol. Biomed. Life Sci.

(2008)

W. Zheng et al.

J. Natl. Cancer Inst.

(1998)

R. Reistad et al.

Carcinogenesis

(1994)

N.J. Gooderham et al.

Drug Metab. Dispos.

(2001)

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Abstract

Introduction

Section snippets

Chemicals

Linearity

HPLC-MS/MS

Toxicokinetic study

Conclusion

Acknowledgement

Toxicol. Lett.

Cancer Res.

J. Chromatogr. B: Analyt. Technol. Biomed. Life Sci.

Mutat. Res.

Food Chem. Toxicol.

Chem. Biol. Interact.

Biochem. Biophys. Res. Commun.

J. Am. Soc. Mass Spectrom.

Food Chem. Toxicol.

Anal. Biochem.

J. Chromatogr. B: Analyt. Technol. Biomed. Life Sci.

J. Natl. Cancer Inst.

Carcinogenesis

Drug Metab. Dispos.