Effect of diet on serum albumin and hemoglobin adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in humans

Abstract

2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) is the most abundant heterocyclic amine formed in meat and fish during cooking and can be used as a model compound for this class of chemicals possibly involved in human carcinogenesis. Knowing the exposure to heterocyclic amines is important for establishing their role in human diseases. Serum albumin (SA) and globin (Gb) adducts were first tested as biomarkers of exposure to PhIP in male Fischer 344 rats given oral doses of 0.1, 0.5, 1 and 10 mg/kg. Blood samples were collected 24 hr after treatment and PhIP released from SA and Gb after acidic hydrolysis was analyzed by gas chromatography‐mass spectrometry or liquid chromatography‐tandem mass spectrometry. PhIP‐SA and Gb adducts increased linearly with the dose. Studies on 35 volunteers with different dietary habits exhibited that diet was a major determinant in the formation of both adducts. PhIP‐SA adducts were significantly higher in meat consumers than in vegetarians (6.7 ± 1.6 and 0.7 ± 0.3 fmol/mg SA; respectively, mean ± SE; p = 0.04, Mann‐Whitney U test). The Gb adduct pattern was quantitatively lower but paralleled SA (3 ± 0.8 in meat consumers and 0.3 ± 0.1 in vegetarians). PhIP‐SA adducts were no different in smokers and in non‐smokers. The results show for the first time that PhIP‐blood protein adducts are present in humans not given the synthetic compound. Both biomarkers appear to be suitable for assessing dietary exposure and internal PhIP dose and may be promising tools for studying the role of heterocyclic amines in the etiology of colon cancer and other diseases. Int. J. Cancer 88:1–6, 2000. © 2000 Wiley‐Liss, Inc.

Meat-derived carcinogens, genetic susceptibility and colorectal adenoma risk

“…These three compounds have been detected in beef, lamb, pork, chicken and fish, especially when chargrilled, fried or roasted (Gooderham et al 2001;Turesky 2007). PhIP and MeIQx are potent mutagens in bacterial and mammalian cell genotoxicity assays and induce colon tumors in rats; less genotoxicity data are available for DiMeIQx Magagnotti et al 2000;Nishikawa et al 2005;Turteltaub et al 1999).…”

Acid-labile protein-adducted heterocyclic aromatic amines in human blood are not viable biomarkers of dietary exposure: A systematic study

“…It is generally thought that total HCA adduction to albumin in vivo is substantially greater than to haemoglobin (Turesky and Le Marchand, 2011); however, one study (Magagnotti et al, 2000) demonstrated acid labile PhIP-Hb adducts to be only two-fold lower than albumin adducts. Our protein adducts prepared in vitro contain HCAs at concentrations approximately four orders of magnitude greater than PhIPprotein adducts described in vivo in the few studies which have quantified albumin or haemoglobin adducts in people consuming conventional diets (Magagnotti et al, 2000) or dietary-relevant doses of radiolabelled PhIP (Dingley et al, 1999). This high level of adduction is similar to that reported for in vitro adduction of reactive metabolites of PhIP to albumin (Peng and Turesky, 2011).…”

“…Residues of HCAs adducted to blood proteins have been postulated for some years as potential medium-term biomarkers of carcinogenic HCA exposure (Peng and Turesky, 2011;Magagnotti et al, 2000;Dingley et al, 1999). However, the viability of quantifying HCAs following their release from such adducts in vivo has not been proven in people consuming diets encompassing the normal range of HCA intakes.…”

“…Serum from the same participant contained acid-labile PhIP at 8.1 pg/ml. The paucity of acid-labile HCAs led us to revisit the sample preparation method of Magagnotti et al (2000) who isolated serum albumin by precipitation before hydrolysis with 0.1M HCl for 1h at 80°C followed by liquid-liquid extraction with ethyl acetate and clean up by immunoaffinity chromatography (as opposed to solid phase extraction used in the current study). We purified 75mg albumin from a pool of serum from high HCA intake participants (mean intake 1.8 µg/d) using ammonium sulphate/acetic acid precipitation before hydrolysis under Magagnotti's conditions and extraction by our described method.…”

“…The concentration of adducts in such in vitro studies may be significantly greater than would be expected in vivo, and the efficacy of hydrolysis procedures to release protein-adducted HCAs is unknown in those studies which employ only fortification with free HCAs. Only one study (Magagnotti et al, 2000) has claimed to quantify an HCA adducted to blood proteins following its release by hydrolysis from the blood of human subjects consuming normal diets.…”