ANALYSIS

Fetal exposure to dietary carcinogens and risk of childhood cancer Jos Kleinjans and colleagues summarise the evidence from the NewGeneris project, a European study using biomarkers to assess how maternal diet affects the child BLEND IMAGES/ALAMY BLEND

KEY MESSAGES ancer in childhood is rare. Glob- cause. Diet is an important source of carcino- ally, there are around 175 000 genic compounds because of the accumula- • An estimated 175 000 new cancer new cancer cases a year among tion of environmental carcinogens within the cases occur globally among children children aged 0-14 years.1 How- food chain (dioxins, polychlorinated biphe- aged 0-14 ever, in Europe, since the 1950s nyls (PCBs), polycyclic aromatic hydrocarbons • The fetus is exposed to dietary Cthe incidence of cancer in this age group has (PAHs)), as well as of formation of carcino- carcinogens consumed by the increased by about 1% a year, with leukaemia, gens such as PAHs, heterocyclic amines, and mother during pregnancy brain tumours, and lymphomas accounting acrylamide during baking, frying, and grill- • Exposure of the fetus causes for most cases.2 The increases in incidence ing of food.6 The NewGeneris (Newborns and perturbations of the molecular of lymphoid leukaemia, in particular, are Genotoxic Exposure Risks) project therefore pathways linked with functional more apparent in European than in Asian or set out to investigate whether intake of dietary markers of carcinogenicity African children.3 The development of child- carcinogens by the pregnant mother leads to • Genetic polymorphisms and male hood cancer thus seems to be affected by both exposure of the fetus and initiates adverse sex may predispose to susceptibility genetic and environmental factors. Given that biological responses that can induce cancer to carcinogen exposure before birth the highest incidences of childhood leukae- in later childhood. and increase risks of developing mia are reported in children younger than 6-7 Investigation of this hypothesis in an leukaemia, in particular years, that the latency period of leukaemia in e­pidemiological study would require a huge 4 • Fetal exposure to dietary children is relatively short, and that adverse sample size because of the relatively low inci- carcinogens may also affect genetic events in utero have been shown dence of childhood cancer (about 140 cases 5 2 3 birth weight and cause immune to give rise to leukaemia in childhood, we per million children). Case-control studies suppression hypothesised that fetal exposure to environ- have been informative but also have limita- mental carcinogens may be an underlying tions.7 Instead, we designed a biomarker­

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Overall, fetal exposure to selected dietary carcinogens seems to induce molecular events that indicate increased cancer risks

based study.8 We used umbilical cord blood Does fetal exposure induce potentially Subsequently, from these gene expression pro- samples from 1151 newborns from mother- carcinogenic events? files, we selected 36 genes and developed a high child birth cohorts and biobanks in Crete, To assess the cancer risks potentially associated throughput screen based on polymerase chain Denmark, Norway, Spain, and UK to inves- with fetal exposures to selected dietary carcino- reaction technology. This allowed us to evaluate tigate biochemical and cytogenetic markers gens, we measured the numbers of micronuclei the associations of these genes with established indicative of prenatal exposure to chemical in lymphocytes from 467 umbilical cord blood fetal exposures in all 1151 newborns for whom c­arcinogens and longer term cancer risk. samples. Micronuclei are a cytogenetic bio- we had umbilical cord blood. Compared with the We focused on fetal exposure to the follow- marker for chromosomal damage and have been lowest exposure groups, expression of five genes ing dietary carcinogens: acrylamide, PAHs, prospectively associated with cancer risks in was significantly higher in those with highest nitrosamines, fat oxidation metabolites adults occupationally exposed to carcinogenic exposure to polycyclic aromatic hydrocarbons (malondialdehyde), and xenoestrogens compounds.15 We found significant associations and six genes for those with highest exposure to (d­ioxins and dioxin-like PCBs). Here, we between particular features of micronuclei and fat metabolites. Expression levels were signifi- summarise the major findings.­ exposure to oxidative fat metabolites and diox- cantly lower for seven genes in those with high- ins and PCBs, predominantly in the highest est exposure to dioxins compared with the lowest Do dietary carcinogens pass the placenta? quarters of exposure.11 category.11 The affected genes have roles in cell For fetal exposure to occur, dietary car- To investigate further the molecular mecha- cycle regulation and apoptosis, which are generic cinogens taken in by the mother have to nisms underlying carcinogenic events in utero processes involved in carcinogenesis. pass through the placenta. We investigated we determined global gene expression levels Overall, fetal exposure to selected dietary this using perfusion methods on placen- in 120 Norwegian neonates in relation to fetal carcinogens seems to induce molecular events tas donated by 93 healthy mothers without exposure to acrylamide and dioxins. While that indicate increased cancer risks, thus sup- any reported complications of pregnancy.9 exposure did not seem to differ between the porting the hypothesis that childhood cancer, Although the transfer rates of the different sexes, we discovered important sex-specific in particular leukaemia among boys, is causally compounds varied, all tested carcinogens differences in genomic responses, in particu- related to the dietary intake of carcinogenic sub- readily crossed the placental barrier. Nitros- lar associated with effects on cell cycle and the stances by their mothers during pregnancy. amines—for example, nitrosodimethylamine— immune system.16 Specifically in boys, dioxin passed through most rapidly, followed by exposure was associated with activation of Are particular children more susceptible to acrylamide and PAHs such as benzo(a)pyr- the proinflammatory transcription regulator cancer risks? ene, with PCB 52 and dioxin being the slow- tumour necrosis factor α, which then induces Childhood cancer remains uncommon despite est.9 However, since placental morphology the nuclear factor-κB; acrylamide exposure widespread exposure to dietary carcinogens profoundly changes throughout gestation, was associated with activation of the Wnt path- in utero. This suggests that particular children data on carcinogen transfer rates from term way, which is associated with uncontrolled cell may be more susceptible to the cancerous placenta may not be representative of transfer growth. This may explain the higher incidence effects of toxic chemicals.17 Such increased occurring earlier in gestation.10 We concluded of leukaemia2 and cancer overall among boys.3 susceptibility may be genetically predisposed— that the placenta does not protect the fetus against exposure to dietary carcinogens. Median (range) exposure to dietary (pre)carcinogens in newborns and maternal dietary intake during pregnancy Cord blood Maternal daily dietary Is the fetus actually exposed to dietary Carcinogen (biomarker) biomarker level intake* Foods with high levels Acrylamide (acrylamide- 14.4 (4.4-124.8) 22 (1-135) µg Deep fried potato products carcinogens? haemoglobin adducts) pmol/g Hb (crisps, french fries) We quantified the presence of selected dietary Crisp breads, biscuits, crackers carcinogens in umbilical cord blood samples Coffee taken from 1151 newborns. For nitrosamines, Polycyclic aromatic 8.4 (0.6-116.6) 180 (42-717) ng Grilled/barbecued meats acrylamide, oxidative fat metabolites, and hydrocarbons (bulky DNA 10-8 nucleotides Smoked and processed fish adducts) PAHs we assessed exposure by measuring Smoked and processed meat levels of reactive metabolites bound to macro- Oxidative fat metabolites 34.2 (0.5-324.7) Omega 6 fatty acids Vegetable oils (soya, rape, sunflower) molecules such as DNA and haemoglobin. (M1dG-DNA adducts) 10-9 nucleotides 11.3 (1.2-77.0) g Fatty meat Plasma levels of dioxins and dioxin-like PCBs Eggs 6 were measured with a validated bioassay (DR Nitrosamines (O -MG-DNA 0.40 (0.08-3.03) N-nitrosodimethylamine Processed meat adducts) 10-8 nucleotides 82 (2-547) ng CALUX). The table shows the levels of these Preserved fish biomarkers of exposure in cord blood. In most Smoked meat infants, fetal exposure was confirmed. We Smoked fish Dioxin/PCBs (plasma DR 0.13 (0.01-104) 77.2 (5.1-945.5) pg† Fatty meat noticed large variations in all biomarkers, with CALUX) pg/ml† Fatty fish a skewed distribution of exposure across new- Full fat milk and dairy products borns (for instance, acrylamide-haemoglobin *Derived from the NewGeneris database on dietary consumption patterns taken from food frequency questionnaires and data on adducts ranged from 4.4 to 124.8 pmol/g chemical levels in food.12-14 Hb).11 †2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalency quotients. the bmj | 5 September 2015 17 ANALYSIS

thebmj.com ЖЖResearch: Maternal obesity during pregnancy and premature mortality from cardiovascular event in adult offspring BMJ( 2013;347:f4539) ЖЖResearch: Maternal dietary patterns and preterm delivery (BMJ 2014;348:g1446)

some people may lack the gene activity for, say, childhood and later life. We observed higher detoxifying carcinogens or repairing induced susceptibilities among boys, as well as among DNA damage, or express a higher activity in carriers of particular gene polymorphisms, metabolic transformation of carcinogens into suggesting that genetic predisposition may DNA damaging daughter compounds. Relevant contribute to health risks. Such risks can be genes may be polymorphic in the general popu- reduced by decreasing the intake of dietary lation, being non-homogeneously distributed carcinogens. Although pregnant women can at frequencies of 5-40%. Carriers of such sin- limit consumption by avoiding foods such as gle nucleotide polymorphisms (SNPs) may be processed meats and fried and grilled food, prone to increased cancer risks after exposure eliminating carcinogens altogether is difficult to carcinogenic agents.18 because of their ubiquity in the diet. To investigate whether genetic predisposi- Food manufacturers could have a role in tion increased susceptibility to fetal exposure reducing the presence of carcinogenic agents. to carcinogens, we analysed cord blood DNA For instance, manufacturers of French fries from 435 subjects using a genome-wide asso- and crisps could switch to low sugar potato ciation method.19 We found a strong signal that varieties to reduce the presence of acryl- the folate hydrolase 1 (FOLH1) gene interacted amide, which is formed during deep frying with the association between fetal exposure to by the reaction of asparagine and reducing dioxin related androgens and frequencies of sugars (both naturally occurring in potatoes). micronuclei. The FOLH1 polymorphism may Reduction of use of nitrite for curing meat cause low serum levels of folate thus lead- products would also lead to less formation of ing to chromosome instability and formation We propose that national nitrosamines in the stomach. For carcinogens of micronuclei. In addition, polymorphisms food safety agencies consider that are present in multiple types of food, such in the epoxyhydrolase 1/2 (EPHX1/2) and exposure risks in more detail as dioxin-like PCBs which are generically pre- cytochrome p450 2E1 (CYP2E1) genes coding and implement policy measures sent in meat and fish as well as in milk and for metabolic enzymes, which may bioactivate where appropriate milk products,13 food manufacturers could precarcinogenic chemicals, seem to be associ- be required to assess the levels of these com- ated with the micronuclei frequencies.11 Furthermore, we showed that maternal pounds in raw products and take preventive In conclusion, although the evidence is still intake of dioxin and PCBs estimated from food measures. We propose that national food limited, our data suggest some genetic predis- frequency questionnaires is associated with safety agencies consider exposure risks in position to risk of childhood cancer associated immunotoxic events during early childhood. more detail and implement policy measures with fetal exposure to dietary carcinogens. In 111 newborns from the Norwegian cohort, where appropriate. dioxin exposure was associated with gene In general, our findings support the recom- Are there other effects on health? expression responses in cord blood cells and mendation to pregnant mothers to eat a well We also investigated the effect of fetal expo- with reduced measles vaccination responses balanced diet. Such a diet also has benefits sure to dietary carcinogens on birth weight, at age 3 years.24 Overall, the functions of for the child by reducing the risks of preterm head circumference, and gestational age. Fetal affected genes—for instance, those belonging delivery,26 low birth weight,27 childhood leu- exposure to acrylamide seemed associated with to the HLA system related to antibody produc- kaemia,7 and adult cardiovascular disease.28 a reduction in birth weight and head circum- tion25—pointed towards immunosuppression, It should also not be forgotten that smoking ference (n=1101).20 Biomarkers of exposure girls showing more immune related genes and alcohol intake during pregnancy pose the to PAHs (n=612) were associated with lower deregulated in association with dioxin and largest health risks to the unborn child. birth weight only in newborns from Denmark, PCB exposure than boys. Jos Kleinjans professor of environmental health science, E­ngland, and Norway.21 In addition, birth Based on the above results, fetal exposure Department of Toxicogenomics, Maastricht University, weight was lower in infants in the medium and to dietary carcinogens may have other adverse Maastricht, Netherlands high thirds of dioxin and dioxin-like PCB levels effects on health in addition to cancer risk. Maria Botsivali research associate, Institute of Biology, Medicinal Chemistry and Biotechnology, National in cord blood (n=967) compared with those in Hellenic Research Foundation, Athens, Greece 12 the lowest third. Furthermore, gestational age Can pregnant women reduce their risk of Manolis Kogevinas professor, Center for Research in was shorter by about half a week in the highest exposure? Environmental Epidemiology (CREAL), Barcelona, Spain compared with the lowest exposure levels; this The NewGeneris project suggests that pregnant Domenico Franco Merlo senior epidemiologist, IRCCS association seemed to be stronger for boys than women’s consumption of carcinogens present AOU San Martino-IST- Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy, on behalf of the NewGeneris for girls. Reduced birth weight is regarded as in the European diet results in measurable fetal consortium a risk factor for cardiovascular disease, type 2 exposures. Furthermore, such exposure seems Correspondence to: J Kleinjans diabetes, and osteoporosis in later life,22 while to result in molecular and functional changes [email protected] reduced head circumference at birth may be that are thought to be biomarkers for the risk Cite this as: BMJ 2015;351:h4501 23 related to delayed neurodevelopment. of developing cancer and other diseases during ЖЖEDITORIAL, p 9

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