A study was conducted to assess benzo(a)pyrene (BP) binding to DNA in different tissues in iron deficiency. Benzo(a)pyrene administration to control and deficient groups of rats maintained on iron adequacy or deficiency showed that (a) there was a significantly increased binding of carcinogen to DNA in iron deficiency especially in liver and intestinal mucosa and (b) supplementation of iron proved to be beneficial in reversing this phenomenon. Activation and binding of carcinogens to DNA is considered a central event in chemical carcinogenesis (1). There are, however, very few studies on the effect of nutrient deficiency on carcinogen-DNA binding. Our earlier studies in food restriction (2) and in riboflavin deficiency (3) as well as another study on vitamin A deficiency (4) have all indicated an increase in adduct formation, suggesting an elevated risk of such populations to cancer. Presently, we are reporting our results in experimental iron deficiency, with possible implication to human situation. Any beneficial effect of iron supplementation was also investigated. Male weanling Fischer rats were divided into three groups and labeled "control" receiving an iron-sufficient diet (220 ppm Fe), "iron deficient" (<10 ppm Fe), and "supplemented." The details of diet preparation and animal maintenance are given in our publication (5). The supplemented group initially received an iron-deficient diet for a period of 6 weeks followed by iron repletion through dietary means for 2 subsequent weeks. The food intakes were monitored daily, and body weights were taken at weekly intervals. Hematological indices at the termination of the experiment attested to the development of iron deficiency. After 6 weeks of feeding the respective diets, 3H-labeled benzo(a)pyrene (Amersham, UK, Sp. activity 55-70 Ci/mmol) was administered intravenously through the tail vein in a solution of DMSO-saline combination (1.5:2.5) at a dose of 150 uCi/100 g body weight/rat. Before administration, the radioactive BP was suitably diluted with cold BP, so that the final administered volume contained 2 μg of BP. After injection, rats were kept in metabolic cages and sacrificed after 17 hours (5 p.m. to 10 a.m. the next day). Liver, lungs, kidneys, and proximal parts of the intestines, which are the major sites of xenobiotic metabolism, were quickly removed and processed for DNA bound radioactivity. In brief, it involved the isolation of DNA, followed by phenol extraction, enzymic digestions, and liquid scintillation counting of bound radioactivity. The results are expressed as fmol BP bound to mg DNA. The hematological studies revealed that the Hb levels in control as well as supplemented groups were higher than deficient groups (15.0 ± 0.5 vs. 5.3 ± 0.6 g/dL), respectively. The body weights also did not show any appreciable differences among the three groups. BP-DNA binding was maximum in kidneys among the tissues studied followed by the intestines, liver, and lungs (Table 1). There was a significantly higher binding in intestines and liver in iron deficiency compared to controls, to the extent of 106% and 24%, respectively. There was a dramatic reversal of this increased binding on iron supplementation. In both tissues, where significantly elevated binding was observed in deficiency, a considerable lowering of DNA bound activity was noted. Compared to deficient levels, the reduction was to the extent of 30% in the case of liver and 56% in the case of intestines, which was significant. Most of the carcinogens are known to undergo metabolic activation, which can bind to cellular macromolecules like DNA (1). If the adducted DNA is not repaired in time, this might result in aberration during cell multiplication and cancer (6). Both in vitro and in vivo studies are commonly employed using a model carcinogen like benzo(a)pyrene to assess the extent of activation and macromolecular binding in different experimental situations as well as to assess the effect of anticancer agents. Iron deficiency is quite widespread in the developing world. Epidemiological and experimental studies have suggested an increased risk of gastrointestinal (GI) tract cancer and liver abnormality in iron deficiency (7,8). In order to explain the mechanisms of chemical carcinogenesis in such nutrient inadequacy, this study was undertaken. Our results show a significant elevation in BP-DNA binding in the liver and intestines in iron deficiency. This would imply a greater predilection for tumor at these sites if repair and removal of the adducts is not achieved immediately. In our earlier studies, we have demonstrated that the activities of carcinogen metabolizing enzymes, both activating as well as conjugating, are impaired in iron deficiency (5). It is reasonable to surmise that reactive metabolites of carcinogens formed during biotransformation are inefficiently detoxified in an iron-deficient host, resulting in increased DNA binding. This could be deleterious from a human point of view. In the supplemented group, the findings were significant. The increased binding that was observed in an iron-deficient diet was reversed on feeding a diet sufficient in iron to levels almost similar to controls. This effect was particularly striking in the liver and intestines. Thus, the beneficial effect of iron in decreasing carcinogen-DNA adduct formation could be unequivocally demonstrated. The results of the present study thus indicate that iron deficiency in the human situation might render the host to a greater risk of chemical carcinogenesis, emphasizing the need for adequate iron nutrition. © 1996 John Wiley & Sons, Inc.