Residents of Qidong, People's Republic of China, are at high risk for development of hepatocellular carcinoma, in part from consumption of foods contaminated with aflatoxins. Chlorophyllin, a mixture of semisynthetic, water-soluble derivatives of chlorophyll that is used as a food colorant and over-the-counter medicine, has been shown to be an effective inhibitor of aflatoxin hepatocarcinogenesis in animal models by blocking carcinogen bioavailability. In a randomized, double-blind, placebo-controlled chemoprevention trial, we tested whether chlorophyllin could alter the disposition of aflatoxin. One hundred and eighty healthy adults from Qidong were randomly assigned to ingest 100 mg of chlorophyllin or a placebo three times a day for 4 months. The primary endpoint was modulation of levels of aflatoxin-N 7 -guanine adducts in urine samples collected 3 months into the intervention measured by using sequential immunoaffinity chromatography and liquid chromatography-electrospray mass spectrometry. This aflatoxin-DNA adduct excretion product serves as a biomarker of the biologically effective dose of aflatoxin, and elevated levels are associated with increased risk of liver cancer. Adherence to the study protocol was outstanding, and no adverse events were reported. Aflatoxin-N 7 -guanine could be detected in 105 of 169 available samples. Chlorophyllin consumption at each meal led to an overall 55% reduction (P ‫؍‬ 0.036) in median urinary levels of this aflatoxin biomarker compared with those taking placebo. Thus, prophylactic interventions with chlorophyllin or supplementation of diets with foods rich in chlorophylls may represent practical means to prevent the development of hepatocellular carcinoma or other environmentally induced cancers.

No abstract

Progress over the past 30 years has revealed many strengths of the rainbow trout as an alternative model for environmental carcinogenesis research. These include low rearing costs, an early life-stage ultrasensitive bioassay, sensitivity to many classes of carcinogen, a well-described tumor pathology, responsiveness to tumor promoters and inhibitors, and a mechanistically informative nonmammalian comparative status. Low-cost husbandry, for example, has permitted statistically challenging tumor study designs with up to 10,000 trout to investigate the quantitative interrelationships among carcinogen dose, anticarcinogen dose, DNA adduct formation, and final tumor outcome. The basic elements of the trout carcinogen bioassay include multiple exposure routes, carcinogen response, husbandry requirements, and pathology. The principal known neoplasms occur in liver (mixed hepatocellular/cholangiocellular adenoma and carcinoma, hepatocellular carcinoma), kidney (nephroblastoma), swim bladder (adenopapilloma), and stomach (adenopapilloma). Trout possess a complex but incompletely characterized array of cytochromes P450, transferases, and other enzymic systems for phase and phase 11 procarcinogen metabolism. In general, trout exhibit only limited capacity for DNA repair, especially for removal of bulky DNA adducts. This factor, together with a high capacity for P450 bioactivation and negligible glutathione transferase-mediated detoxication of the epoxide, accounts for the exceptional sensitivity of trout to aflatoxin B1 carcinogenesis. At the gene level, all trout tumors except nephroblastoma exhibit variable and often high incidences of oncogenic Ki-ras gene mutations. Mutations in the trout p53 tumor suppressor gene have yet to be described. There are many aspects of the trout model, especially the lack of complete organ homology, that limit its application as a surrogate for human cancer research. Within these limitations, however, it is apparent that trout and other fish models can serve as highly useful adjuncts to conventional rodent models in the study of environmental carcinogenesis and its modulation. For some problems, fish models can provide wholly unique approaches.Environ Health Perspect 104(Suppl 1): 5-21 (1996)

Using zebrafish, Danio

Lymphoma and leukemia are the most common cancers in children and young adults; in utero carcinogen exposure may contribute to the etiology of these cancers. A polycyclic aromatic hydrocarbon (PAH), dibenzo [a,l]pyrene (DBP), was given to pregnant mice (15 mg/kg body weight, gavage) on gestation day 17. Significant mortalities in offspring, beginning at 12 weeks of age, were observed due to an aggressive T-cell lymphoblastic lymphoma. Lymphocytes invaded numerous tissues. All mice surviving 10 months, exposed in utero to DBP, exhibited lung tumors; some mice also had liver tumors. To assess the role of the aryl hydrocarbon receptor (AHR) in DBP transplacental cancer, B6129SF1/J (AHR b-1/d , responsive) mice were crossed with strain 129S1/SvIm (AHR d/d , nonresponsive) to determine the effect of maternal and fetal AHR status on carcinogenesis. Offspring born to nonresponsive mothers had greater susceptibility to lymphoma, irrespective of offspring phenotype. However, when the mother was responsive, an AHR-responsive phenotype in offspring increased mortality by 2-fold. In DBP-induced lymphomas, no evidence was found for TP53, B-catenin, or Ki-ras mutations but lung adenomas of mice surviving to 10 months of age had mutations in Ki-ras codons 12 and 13. Lung adenomas exhibited a 50% decrease and a 35-fold increase in expression of Rb and p19/ARF mRNA, respectively. This is the first demonstration that transplacental exposure to an environmental PAH can induce a highly aggressive lymphoma in mice and raises the possibility that PAH exposures to pregnant women could contribute to similar cancers in children and young adults. (Cancer Res 2006; 66(2): 755-62)

We exposed embryos (83 hours postfertilizaton) and fry (3 weeks posthatch) to N -methyl-N' -nitro-N -nitrosoguanidine (MNNG) by immersion in aqueous solutions of 0-10 ppm for 1 hour (embryo) or 0-2 ppm for 24 hours (fry). Zebrafish

Chlorophyll (Chla) and chlorophyllin (CHL) were shown previously to reduce carcinogen bioavailability, biomarker damage, and tumorigenicity in trout and rats. These findings were partially extended to humans, where CHL reduced excretion of aflatoxin B1 (AFB1)-DNA repair products in Chinese unavoidably exposed to dietary AFB1. However, neither AFB1 pharmacokinetics nor Chla effects were examined. We conducted an unblinded crossover study to establish AFB1 pharmacokinetic parameters among four human volunteers, and to explore possible effects of CHL or Chla cotreatment in three of those volunteers. For protocol 1, fasted subjects received an Institutional Review Board–approved dose of 14C-AFB1 (30 ng, 5 nCi) by capsule with 100 mL water, followed by normal eating and drinking after 2 hours. Blood and cumulative urine samples were collected over 72 hours, and 14C- AFB1 equivalents were determined by accelerator mass spectrometry. Protocols 2 and 3 were similar except capsules also contained 150 mg of purified Chla or CHL, respectively. Protocols were repeated thrice for each volunteer. The study revealed rapid human AFB1 uptake (plasma ka, 5.05 ± 1.10 h−1; Tmax, 1.0 hour) and urinary elimination (95% complete by 24 hours) kinetics. Chla and CHL treatment each significantly impeded AFB1 absorption and reduced Cmax and AUCs (plasma and urine) in one or more subjects. These initial results provide AFB1 pharmacokinetic parameters previously unavailable for humans, and suggest that Chla or CHL co-consumption may limit the bioavailability of ingested aflatoxin in humans, as they do in animal models.

No abstract