Temporal aspects of DNA and RNA synthesis during human immunodeficiency virus infection: evidence for differential gene expression

The kinetics of retroviral DNA and RNA synthesis are parameters vital to understanding viral growth, especially for human immunodeficiency virus (HIV), which encodes several of its own regulatory genes. We have established a single-cycle growth condition for HIV in H9 cells, a human CD4+ lymphocyte line. The full-length viral linear DNA is first detectable by 4 h postinfection. During a one-step growth of HIV, amounts of viral DNA gradually increase until 8 to 12 h postinfection and then decrease. The copy number of unintegrated viral DNA is not extraordinarily high even at its peak. Most strikingly, there is a temporal program of RNA accumulation: the earliest RNA is greatly enriched in the 2-kilobase subgenomic mRNA species, while the level of 9.2-kilobase RNA which is both genomic RNA and mRNA remains low until after 24 h of infection. Virus production begins at about 24 h postinfection. Thus, viral DNA synthesis is as rapid as for other retroviruses, but viral RNA synthesis involves temporal alteration in the species that accumulate, presumably as a consequence of viral regulatory genes.

SOCS-1, a negative regulator of the JAK/STAT pathway, is silenced by methylation in human hepatocellular carcinoma and shows growth-suppression activity

Hepatocellular carcinoma (HCC) is a major cause of cancer death, but the molecular mechanism for its development beyond its initiation has not been well characterized. Suppressor of cytokine signaling (SOCS-1; also known as JAB and SSI-1) switches cytokine signaling 'off' by means of its direct interaction with Janus kinase (JAK). We identified aberrant methylation in the CpG island of SOCS-1 that correlated with its transcription silencing in HCC cell lines. The incidence of aberrant methylation was 65% in the 26 human primary HCC tumor samples analyzed. Moreover, the restoration of SOCS-1 suppressed both growth rate and anchorage-independent growth of cells in which SOCS-1 was methylation-silenced and JAK2 was constitutively activated. This growth suppression was caused by apoptosis and was reproduced by AG490, a specific, chemical JAK2 inhibitor that reversed constitutive phosphorylation of STAT3 in SOCS-1 inactivated cells. The high prevalence of the aberrant SOCS-1 methylation and its growth suppression activity demonstrated the importance of the constitutive activation of the JAK/STAT pathway in the development of HCC. Our results also indicate therapeutic strategies for the treatment of HCC including use of SOCS-1 in gene therapy and inhibition of JAK2 by small molecules, such as AG490.

Aflatoxin: a 50-year odyssey of mechanistic and translational toxicology

Since their discovery 50 years ago, the aflatoxins have become recognized as ubiquitous contaminants of the human food supply throughout the economically developing world. The adverse toxicological consequences of these compounds in populations are quite varied because of a wide range of exposures leading to acute effects, including rapid death, and chronic outcomes such as hepatocellular carcinoma. Furthermore, emerging studies describe a variety of general adverse health effects associated with aflatoxin, such as impaired growth in children. Aflatoxin exposures have also been demonstrated to multiplicatively increase the risk of liver cancer in people chronically infected with hepatitis B virus (HBV) illustrating the deleterious impact that even low toxin levels in the diet can pose for human health. The public health impact of aflatoxin exposure is pervasive. Aflatoxin biomarkers of internal and biologically effective doses have been integral to the establishment of the etiologic role of this toxin in human disease through better estimates of exposure, expanded knowledge of the mechanisms of disease pathogenesis, and as tools for implementing and evaluating preventive interventions.

Urinary aflatoxin biomarkers and risk of hepatocellular carcinoma

Aflatoxins have long been suspected to be human hepatic carcinogens but no direct study was feasible until assays to measure individual aflatoxin exposure became available. We have used assays for urinary aflatoxin B1, its metabolites AFP1 and AFM1, and DNA-adducts (AFB1-N7-Gua) to assess the relation between aflatoxin exposure and liver cancer, as part of an ongoing prospective study of 18,244 middle-aged men in Shanghai, People's Republic of China. After 35,299 person-years of follow-up, 22 cases of liver cancer had been identified. For each case, 5 or 10 controls were randomly selected from cohort members without liver cancer on the date the disorder was diagnosed in the case and matched to within 1 year for age, within 1 month for sample collection, and for neighbourhood of residence. Subjects with liver cancer were more likely than were controls to have detectable concentrations of any of the aflatoxin metabolites (relative risk 2.4, 95% confidence interval 1.0-5.9). The highest relative risk was for aflatoxin P1 (6.2, 1.8-21.5). In an analysis adjusting for the effects of hepatitis B surface antigen seropositivity, level of education, cigarette smoking, and alcohol consumption, the relative risk for the presence of aflatoxin metabolites was 3.8 (1.2-12.2). There was a strong interaction between serological markers of chronic hepatitis B infection and aflatoxin exposure in liver-cancer risk. Reduction of aflatoxin exposure may be a useful intermediate goal in prevention of liver cancer, since the benefits of wide-scale hepatitis B vaccination will not be apparent for many years.

Workgroup report: public health strategies for reducing aflatoxin exposure in developing countries

Consecutive outbreaks of acute aflatoxicosis in Kenya in 2004 and 2005 caused > 150 deaths. In response, the Centers for Disease Control and Prevention and the World Health Organization convened a workgroup of international experts and health officials in Geneva, Switzerland, in July 2005. After discussions concerning what is known about aflatoxins, the workgroup identified gaps in current knowledge about acute and chronic human health effects of aflatoxins, surveillance and food monitoring, analytic methods, and the efficacy of intervention strategies. The workgroup also identified public health strategies that could be integrated with current agricultural approaches to resolve gaps in current knowledge and ultimately reduce morbidity and mortality associated with the consumption of aflatoxin-contaminated food in the developing world. Four issues that warrant immediate attention were identified: a) quantify the human health impacts and the burden of disease due to aflatoxin exposure; b) compile an inventory, evaluate the efficacy, and disseminate results of ongoing intervention strategies; c) develop and augment the disease surveillance, food monitoring, laboratory, and public health response capacity of affected regions; and d) develop a response protocol that can be used in the event of an outbreak of acute aflatoxicosis. This report expands on the workgroup's discussions concerning aflatoxin in developing countries and summarizes the findings.

Keap1-nrf2 signaling: a target for cancer prevention by sulforaphane

Sulforaphane is a promising agent under preclinical evaluation in many models of disease prevention. This bioactive phytochemical affects many molecular targets in cellular and animal models; however, amongst the most sensitive is Keap1, a key sensor for the adaptive stress response system regulated through the transcription factor Nrf2. Keap1 is a sulfhydryl-rich protein that represses Nrf2 signaling by facilitating the polyubiquitination of Nrf2, thereby enabling its subsequent proteasomal degradation. Interaction of sulforaphane with Keap1 disrupts this function and allows for nuclear accumulation of Nrf2 and activation of its transcriptional program. Enhanced transcription of Nrf2 target genes provokes a strong cytoprotective response that enhances resistance to carcinogenesis and other diseases mediated by exposures to electrophiles and oxidants. Clinical evaluation of sulforaphane has been largely conducted by utilizing preparations of broccoli or broccoli sprouts rich in either sulforaphane or its precursor form in plants, a stable β-thioglucose conjugate termed glucoraphanin. We have conducted a series of clinical trials in Qidong, China, a region where exposures to food- and air-borne carcinogens has been considerable, to evaluate the suitability of broccoli sprout beverages, rich in either glucoraphanin or sulforaphane or both, for their bioavailability, tolerability, and pharmacodynamic action in population-based interventions. Results from these clinical trials indicate that interventions with well characterized preparations of broccoli sprouts may enhance the detoxication of aflatoxins and air-borne toxins, which may in turn attenuate their associated health risks, including cancer, in exposed individuals.

Effects of glucosinolate-rich broccoli sprouts on urinary levels of aflatoxin-DNA adducts and phenanthrene tetraols in a randomized clinical trial in He Zuo township, Qidong, People's Republic of China

Residents of Qidong, People's Republic of China, are at high risk for development of hepatocellular carcinoma, in part due to consumption of aflatoxin-contaminated foods, and are exposed to high levels of phenanthrene, a sentinel of hydrocarbon air toxics. Cruciferous vegetables, such as broccoli, contain anticarcinogens. Glucoraphanin, the principal glucosinolate in broccoli sprouts, can be hydrolyzed by gut microflora to sulforaphane, a potent inducer of carcinogen detoxication enzymes. In a randomized, placebo-controlled chemoprevention trial, we tested whether drinking hot water infusions of 3-day-old broccoli sprouts, containing defined concentrations of glucosinolates, could alter the disposition of aflatoxin and phenanthrene. Two hundred healthy adults drank infusions containing either 400 or < 3 micromol glucoraphanin nightly for 2 weeks. Adherence to the study protocol was outstanding; no problems with safety or tolerance were noted. Urinary levels of aflatoxin-N(7)-guanine were not different between the two intervention arms (P = 0.68). However, measurement of urinary levels of dithiocarbamates (sulforaphane metabolites) indicated striking interindividual differences in bioavailability. An inverse association was observed for excretion of dithiocarbamates and aflatoxin-DNA adducts (P = 0.002; R = 0.31) in individuals receiving broccoli sprout glucosinolates. Moreover, trans, anti-phenanthrene tetraol, a metabolite of the combustion product phenanthrene, was detected in urine of all participants and showed a robust inverse association with dithiocarbamate levels (P = 0.0001; R = 0.39), although again no overall difference between intervention arms was observed (P = 0.29). Understanding factors influencing glucosinolate hydrolysis and bioavailability will be required for optimal use of broccoli sprouts in human interventions.

Intrahepatic Cholangiocarcinoma: Continuing Challenges and Translational Advances

Intrahepatic cholangiocarcinoma (iCCA) has over the last 10-20 years become the focus of increasing concern, largely due to its rising incidence and high mortality rates worldwide. The significant increase in mortality rates from this primary hepatobiliary cancer, particularly over the past decade, has coincided with a rapidly growing interest among clinicians, investigators, and patient advocates to seek greater mechanistic insights and more effective biomarker-driven targeted approaches for managing and/or preventing this challenging liver cancer. In addition to discussing challenges posed by this aggressive cancer, this review will emphasize recent epidemiological, basic, and translational research findings for iCCA. In particular, we will highlight emerging demographic changes and evolving risk factors, the critical role of the tumor microenvironment, extracellular vesicle biomarkers and therapeutics, intertumoral and intratumoral heterogeneity, and current and emerging targeted therapies regarding iCCA. Specifically, recent evidence linking non-bile duct medical conditions, such as nonalcoholic fatty liver disease and nonspecific cirrhosis, to intrahepatic cholangiocarcinogenesis together with geographic and ethnic variation will be assessed. Recent developments concerning the roles played by transforming growth factor-β and platelet-derived growth factor D in driving the recruitment and expansion of cancer-associated myofibroblasts within cholangiocarcinoma (CCA) stroma as well as their therapeutic implications will also be discussed. In addition, the potential significance of extracellular vesicles as bile and serum biomarkers and therapeutic delivery systems for iCCA will be described. An integrated systems approach to classifying heterogeneous iCCA subtypes will be further highlighted, and recent clinical trials and emerging targeted therapies will be reviewed, along with recommendations for future translational research opportunities. Established international CCA networks are now facilitating collaborations aimed at advancing iCCA translational and clinical research.

DNA damage by mycotoxins

Mycotoxins are toxic fungal metabolites which are structurally diverse, common contaminants of the ingredients of animal feed and human food. To date, mycotoxins with carcinogenic potency in experimental animal models include aflatoxins, sterigmatocystin, ochratoxin, fumonisins, zearalenone, and some Penicillium toxins. Most of these carcinogenic mycotoxins are genotoxic agents with the exception of fumonisins, which is currently believed to act by disrupting the signal transduction pathways of the target cells. Aflatoxin B1 (AFB1), a category I known human carcinogen and the most potent genotoxic agent, is mutagenic in many model systems and produces chromosomal aberrations, micronuclei, sister chromatid exchange, unscheduled DNA synthesis, and chromosomal strand breaks, as well as forms adducts in rodent and human cells. The predominant AFB1-DNA adduct was identified as 8, 9-dihydro-8-(N7-guanyl)-9-hydroxy-AFB1 (AFB1-N7-Gua), which derives from covalent bond formation between C8 of AFB1-8,9-epoxides and N7 of guanine bases in DNA. Initial AFB1-N7-guanine adduct can convert to a ring-opened formamidopyrimidine derivative, AFB1-FAPY. The formation of AFB1-N7-guanine adduct was linear over the low-dose range in all species examined, and liver, the primary target organ, had the highest level of the adduct. Formation of initial AFB1-N7-guanine adduct was correlated with the incidence of hepatic tumor in trout and rats. The AFB1-N7-guanine adduct was removed from DNA rapidly and was excreted exclusively in urine of exposed rats. Several human studies have validated the similar correlation between dietary exposure to AFB1 and excretion of AFB1-N7-guanine in urine. Replication of DNA containing AFB1-N7-guanine adduct-induced G-->T mutations in an experimental model. Activation of ras protooncogene has been found in AFB1-induced tumors in mouse, rat, and fish. More strikingly, the relationship between aflatoxin exposure and development of human hepatocellular carcinoma (HHC) was demonstrated by the studies on the p53 tumor suppressor gene. High frequency of p53 mutations (G-->T transversion at codon 249) was found to occur in HHC collected from populations exposed to high levels of dietary aflatoxin in China and Southern Africa. Furthermore, AFB1-induced DNA damage and hepatocarcinogenesis in experimental models can be modulated by a variety of factors including nutrients, chemopreventive agents, and other factors such as food restriction and viral infection, as well as genetic polymorphisms.

Quantitative changes in T helper or T suppressor/cytotoxic lymphocyte subsets that distinguish acquired immune deficiency syndrome from other immune subset disorders

Quantitative measurements of the immune cell subgroups, T helper (Leu 3+/OKT4+) cells and T suppressor/cytotoxic (Leu 2+/OKT8+) cells, were made in patients having acquired immune deficiency syndrome (AIDS) with Kaposi's sarcoma and in patients with AIDS and opportunistic infection, as well as in three other relevant populations. These included patients with lymphadenopathy syndrome, e.g., homosexually active males with lymphadenopathy who sought medical care for additional symptoms, and healthy male homosexuals, as well as a control population. Decrease in the number of T helper cells is characteristic of AIDS with Kaposi's sarcoma or opportunistic infection. Augmentation of the T suppressor/cytotoxic cell population is rare in AIDS with Kaposi's sarcoma but is more frequent in AIDS with opportunistic infection. Augmentation of the T suppressor/cytotoxic cell population, however, may occur in a variety of circumstances, including cytomegalovirus and other viral infections, in healthy, homosexually active males, and in otherwise healthy hemophiliac subjects receiving factor VIII treatment. Reduced T helper:T suppressor/cytotoxic cell ratio can be caused by either decrease in the number of T helper cells or augmentation of the T suppressor/cytotoxic cell population. Lowered T helper:T suppressor/cytotoxic cell ratio does not, by itself, help to distinguish between AIDS and other causes of reduced ratios. Quantitative measurements are needed to define the T subset changes. AIDS is characterized by decrease in the number of T helper cells and reduced T helper:T suppressor/cytotoxic cell ratio. The T helper (Leu 3+) and T suppressor/cytotoxic (Leu 2+) cell subpopulations can change independently. Identification of decrease in the number of T helper cells as an alteration that occurs independently of numerical change in other lymphoid subpopulations, such as T suppressor/cytotoxic cells and B cells, and the close association of the decrease in the number of T helper cells with AIDS are consistent with a distinct pathogenesis (and cause) for AIDS.

Protective alterations in phase 1 and 2 metabolism of aflatoxin B1 by oltipraz in residents of Qidong, People's Republic of China

BACKGROUND

Residents of Qidong, People's Republic of China, are at high risk for development of hepatocellular carcinoma, in part due to consumption of foods contaminated with aflatoxins, which require metabolic activation to become carcinogenic. In a randomized, placebo-controlled, double-blind phase IIa chemoprevention trial, we tested oltipraz, an antischistosomal drug that has been shown to be a potent and effective inhibitor of aflatoxin-induced hepatocarcinogenesis in animal models.

METHODS

In 1995, 234 adults from Qidong were enrolled. Healthy eligible individuals were randomly assigned to receive by mouth 125 mg oltipraz daily, 500 mg oltipraz weekly, or a placebo. Sequential immunoaffinity chromatography and liquid chromatography coupled to mass spectrometry or to fluorescence detection were used to identify and quantify phase 1 and phase 2 metabolites of aflatoxin B1 in the urine of study participants. Reported P values are two-sided.

RESULTS

One month of weekly administration of 500 mg oltipraz led to a 51% decrease in median levels of the phase 1 metabolite aflatoxin M1 excreted in urine compared with administration of a placebo (P = .030), but it had no effect on levels of a phase 2 metabolite, aflatoxin-mercapturic acid (P = .871). By contrast, daily intervention with 125 mg oltipraz led to a 2.6-fold increase in median aflatoxin-mercapturic acid excretion (P = .017) but had no effect on excreted aflatoxin M1 levels (P = .682).

CONCLUSIONS

Intermittent, high-dose oltipraz inhibited phase 1 activation of aflatoxins, and sustained low-dose oltipraz increased phase 2 conjugation of aflatoxin, yielding higher levels of aflatoxin-mercapturic acid. While both mechanisms can contribute to protection, this study highlights the feasibility of inducing phase 2 enzymes as a chemopreventive strategy in humans.

Chlorophyllin intervention reduces aflatoxin-DNA adducts in individuals at high risk for liver cancer

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.

Lack of a negative influence on viral growth by the nef gene of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) contains an open reading frame called nef at the 3' end of its genome. The nef gene product has been reported to down-regulate viral growth by suppressing viral transcription through interaction with the long terminal repeat region. We have compared two isogenic HIV-1 (HIV-1-WI3) strains, one of which lacks nef expression, and found little difference between them in in vitro growth. We tested effects on viral entry, DNA synthesis, and RNA expression by measuring HIV-specific low molecular weight DNA and RNA after infection. The qualitative and quantitative aspects of DNA and RNA synthesis were comparable between the nef+ and nef- strains. The effects on viral growth were also examined by following changes in reverse transcriptase activity during the course of infection. The presence of the nef gene product failed to slow viral growth in several different cell types tested, including the human T-lymphocyte cell lines H9 and CEM-SS, human primary T cells enriched for CD4+ cells, and human monocytic cell lines U-937 and THP-1. On the contrary, the nef+ strain grew more efficiently in some cell types than the nef- strain. The same results were obtained with nef+ and nef- strains of a different virus, HIV-1-432, whose Nef had been reported to have a negative effect on viral growth. Our data suggest that the Nef protein does not act as a negative factor, at least in the experimental systems employed in our studies.

Protective interventions to prevent aflatoxin-induced carcinogenesis in developing countries

The public health impact of aflatoxin exposure is pervasive in economically developing countries; consequently, we need to design intervention strategies for prevention that are practicable for these high-risk populations. The adverse health consequences of aflatoxins in populations are quite varied, eliciting acute effects, such as rapid death, and chronic outcomes, such as hepatocellular carcinoma. Furthermore, a number of epidemiological studies describe a variety of general adverse health effects associated with aflatoxin, such as impaired growth in children. Thus, the magnitude of the problem is disseminated across the entire spectrum of age, gender, and health status in the population. The aflatoxins multiplicatively increase the risk of liver cancer in people chronically infected with hepatitis B virus (HBV), which illustrates the deleterious impact that even low toxin levels in the diet can pose for human health. Thus other aflatoxin interactions, which likely contribute to the disease burden, still remain to be identified. Therefore, many diverse and appropriate strategies for disease prevention are needed to decrease the incidence of aflatoxin carcinogenesis in developing countries.

Role of phase 2 enzyme induction in chemoprotection by dithiolethiones

One of the major mechanisms of protection against carcinogenesis, mutagenesis, and other forms of toxicity mediated by carcinogens is the induction of enzymes involved in their metabolism, particularly phase 2 enzymes such as glutathione S-transferases (GSTs), UDP-glucuronosyl transferases, and quinone reductases. Animal studies indicate that induction of phase 2 enzymes is a sufficient condition for obtaining chemoprevention and can be achieved by administering any of a diverse array of naturally-occurring and synthetic chemopreventive agents. Indeed, monitoring of enzyme induction has led to the recognition or isolation of novel, potent chemopreventive agents such as 1,2-dithiole-3-thiones, terpenoids and the isothiocyanate sulforaphane. For example, oltipraz, a substituted 1,2-dithiole-3-thione originally developed as an antischistosomal agent, possesses chemopreventive activity against different classes of carcinogens targeting multiple organs. Mechanistic studies in rodent models for chemoprevention of aflatoxin B(1) (AFB(1))-induced hepatocarcinogenesis by oltipraz indicates that increased expression of phase 2 genes is of central importance, although inhibition of phase 1 activation of AFB(1) can also contribute to protection. Exposure of rodents to 1,2-dithiole-3-thiones triggers nuclear accumulation of the transcription factor Nrf2 and its enhanced binding to the "antioxidant response element" (ARE), leading to transcriptional activation of a score of genes involved in carcinogen detoxication and attenuation of oxidative stress. Nrf2-deficient mice fail to induce many of these genes in response to dithiolethiones; moreover, basal expression of these genes is typically repressed. To test the hypothesis that enzyme induction is a useful strategy for chemoprevention in humans, three key elements are necessary: a candidate agent, an at-risk population and modulatable intermediate endpoints. Towards this end, a placebo-controlled, double blind clinical trial of oltipraz was conducted in residents of Qidong, PR China who are exposed to dietary aflatoxins and who are at high risk for the development of liver cancer. Oltipraz significantly enhanced excretion of a phase 2 product, aflatoxin-mercapturic acid, a derivative of the aflatoxin-glutathione conjugate, in the urine of study participants administered 125 mg oltipraz by mouth daily. Administration of 500 mg oltipraz once a week led to a significant reduction in the excretion of the primary oxidative metabolite of AFB(1), AFM(1), when measured shortly after drug administration. While this study highlighted the general feasibility of inducing phase 2 enzymes in humans, a longer term intervention is addressing whether protective alterations in aflatoxin metabolism can be sustained for extended periods of time in this high-risk population.

Simian virus 40 large tumor antigen-immortalized normal human liver epithelial cells express hepatocyte characteristics and metabolize chemical carcinogens

Normal human liver tissue and cultured human hepatocytes are valuable models to study xenobiotic metabolism and toxicity, but they only have a limited in vitro life-span and are not readily available. This report describes the establishment of replicative cultures of human adult liver epithelial cells in serum-free medium. The longevity of three of these cultures, derived from different donors, was extended by introduction of the simian virus 40 large T antigen gene. Two cell lines, THLE-2 and -3, established with a recombinant simian virus 40 large T antigen virus have undergone > 100 population doublings, are nontumorigenic when injected into athymic nude mice, have near-diploid karyotypes, and do not express alpha-fetoprotein. The cells express cytokeratin 18 and albumin in early passage, whereas higher-passage cells in logarithmic-phase growth also express cytokeratin 19. THLE-2 and -3 cells metabolize benzo[a]pyrene, N-nitrosodimethylamine, and aflatoxin B1 to their ultimate carcinogenic metabolites that adduct DNA, which indicates functional cytochrome P450 pathways. Other enzymes involved in metabolism of chemical carcinogens, such as epoxide hydrolase, NADPH cytochrome P450 reductase, superoxide dismutase, catalase, glutathione S-transferases, and glutathione peroxidase are also retained by THLE cells. Thus, these immortalized human liver cells constitute an in vitro model for pharmacotoxicological studies and for the investigation of etiology and pathogenesis of human hepatocellular carcinoma.

The related adhesion focal tyrosine kinase is tyrosine-phosphorylated after beta1-integrin stimulation in B cells and binds to p130cas

Integrin ligation initiates intracellular signaling events, among which are the activation of protein tyrosine kinases. The related adhesion focal tyrosine kinase (RAFTK), also known as PYK2 and CAKbeta, is a tyrosine kinase that is homologous to the focal adhesion kinase (FAK) p125FAK. The structure of RAFTK is similar to p125FAK in that it lacks a transmembrane region, does not contain Src homology 2 or 3 domains, and has a proline-rich region in its C terminus. Here we report that RAFTK is a target for beta1-integrin-mediated tyrosine phosphorylation in both transformed and normal human B cells. Ligation of the B cell antigen receptor also induced tyrosine phosphorylation of RAFTK. Phosphorylation of RAFTK following integrin- or B cell antigen receptor-mediated stimulation was decreased by prior treatment of cells with cytochalasin B, indicating that this process was at least partially cytoskeleton-dependent. One of the tyrosine-phosphorylated substrates after integrin stimulation in fibroblasts is p130cas, which can associate with p125FAK. RAFTK also interacted constitutively with p130cas in B cells, since p130cas was detected in RAFTK immunoprecipitates. Although the function of RAFTK remains unknown, these data suggest that RAFTK may have a significant function in integrin-mediated signaling pathways in B cells.

Potent protection against aflatoxin-induced tumorigenesis through induction of Nrf2-regulated pathways by the triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole

Synthetic triterpenoid analogues of oleanolic acid are potent inducers of the phase 2 response as well as inhibitors of inflammation. We show that the triterpenoid, 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im), is a highly potent chemopreventive agent that inhibits aflatoxin-induced tumorigenesis in rat liver. The chemopreventive potency of CDDO-Im was evaluated by measuring inhibition of formation of putative preneoplastic lesions (glutathione S-transferase P positive foci) in the liver of rats exposed to aflatoxin B1. CDDO-Im produces an 85% reduction in the hepatic focal burden of preneoplastic lesions at 1 micromol/kg body weight and a >99% reduction at 100 micromol/kg body weight. CDDO-Im treatment reduces levels of aflatoxin-DNA adducts by approximately 40% to 90% over the range of 1 to 100 micromol/kg body weight. Additionally, changes in mRNA levels of genes involved in aflatoxin metabolism were measured in rat liver following a single dose of CDDO-Im. GSTA2, GSTA5, AFAR, and EPHX1 transcripts are elevated 6 hours following a 1 micromol/kg body weight dose of CDDO-Im. Microarray analysis using wild-type and Nrf2 knockout mice confirms that many phase 2 and antioxidant genes are induced in an Nrf2-dependent manner in mouse liver following treatment with CDDO-Im. Thus, low-micromole doses of CDDO-Im induce cytoprotective genes, inhibit DNA adduct formation, and dramatically block hepatic tumorigenesis. As a point of reference, oltipraz, an established modulator of aflatoxin metabolism in humans, is 100-fold weaker than CDDO-Im in this rat antitumorigenesis model. The unparalleled potency of CDDO-Im in vivo highlights the chemopreventive promise of targeting Nrf2 pathways with triterpenoids.

Bioavailability of Sulforaphane from two broccoli sprout beverages: results of a short-term, cross-over clinical trial in Qidong, China

One of several challenges in design of clinical chemoprevention trials is the selection of the dose, formulation, and dose schedule of the intervention agent. Therefore, a cross-over clinical trial was undertaken to compare the bioavailability and tolerability of sulforaphane from two of broccoli sprout-derived beverages: one glucoraphanin-rich (GRR) and the other sulforaphane-rich (SFR). Sulforaphane was generated from glucoraphanin contained in GRR by gut microflora or formed by treatment of GRR with myrosinase from daikon (Raphanus sativus) sprouts to provide SFR. Fifty healthy, eligible participants were requested to refrain from crucifer consumption and randomized into two treatment arms. The study design was as follows: 5-day run-in period, 7-day administration of beverages, 5-day washout period, and 7-day administration of the opposite intervention. Isotope dilution mass spectrometry was used to measure levels of glucoraphanin, sulforaphane, and sulforaphane thiol conjugates in urine samples collected daily throughout the study. Bioavailability, as measured by urinary excretion of sulforaphane and its metabolites (in approximately 12-hour collections after dosing), was substantially greater with the SFR (mean = 70%) than with GRR (mean = 5%) beverages. Interindividual variability in excretion was considerably lower with SFR than with GRR beverage. Elimination rates were considerably slower with GRR, allowing for achievement of steady-state dosing as opposed to bolus dosing with SFR. Optimal dosing formulations in future studies should consider blends of sulforaphane and glucoraphanin as SFR and GRR mixtures to achieve peak concentrations for activation of some targets and prolonged inhibition of others implicated in the protective actions of sulforaphane. Cancer Prev Res; 4(3); 384-95. ©2011 AACR.

Translational strategies for cancer prevention in liver

Unlike many other types of human cancer, the aetiology of liver cancer is well understood. Infection with hepatitis viruses, coupled with dietary exposure to the fungal toxin aflatoxin, increases the risk of the disease. Although primary prevention, based on vaccination and avoiding exposure to these agents, is an appealing option, such strategies will require considerable investment of time and resources to be successful. In the developing world--where the burden of liver cancer is highest--immediate, practical and economical approaches are essential. So, targeted chemoprevention might be most appropriate for the present generation of individuals at risk.

Diet and carcinogenesis

In summary there is a wealth of information on dietary and nutritional effects on carcinogenesis in laboratory rodents. Experimental studies based on epidemiological evidence, earlier experimental studies and known or predicted cellular, biochemical and molecular effects of nutrients have produced clear evidence that carcinogenesis in laboratory rodents is influenced by dietary intake of calories, fat, lipotropes (choline, methionine), vitamin A and related retinoids, Se, calcium, zinc, fiber, ethanol and a large number of non-nutrient components of foods. For these substances or groups of substances mechanistic hypotheses supported by experimental data and are leading to further research. The information provided will contribute to understanding of basic processes in carcinogenesis as well as of the specific interactions studied, and should contribute to significant advances in preventive medicine. Restriction of caloric intake of rodents by amounts > 10% over a significant portion of their lifetime reduces tumorigenesis. That level of restriction reduces the rate of growth and maturation, and most experiments in this area employ greater restrictions that virtually abolish growth from a young age. Therefore, the observations are of interest in mechanistic studies, but their applicability to preventive medicine requires better definition of the degree and duration of restriction required for a significant effect and the age at which it must be imposed. Restriction of total fat intake and modifications to increase the intake of omega-3 fats have a reasonably consistent effect on tumorigenesis in rodents but a much less consistently demonstrable effect in humans. Again, the observations in rodents are providing a major stimulus to mechanistic studies. The lipotropes are extremely valuable as tools for investigating mechanisms of carcinogenesis in rodents. Their importance in the epidemiology of human cancer has yet to be demonstrated clearly and is a subject of research at present. The naturally occurring vitamins and minerals, as well as fiber, derive their importance in this context from investigations to explain the consistent epidemiological demonstrations of reduction of tumor risk with increased consumption of fruits and vegetables. The activity of the isolated nutrients as anticarcinogens in rodents has generally not matched the activity expected from epidemiological studies. The anticarcinogenic activity of many of the non-nutrient components of fruits and vegetables is remarkable in particular models, however, as is the activity of natural and synthetic retinoids. At present the results must be interpreted to indicate an important effect of combinations of the whole foods with identification of particular nutrients or non-nutrients in specific cases.(ABSTRACT TRUNCATED AT 400 WORDS)

Aflatoxin B1-induced DNA adduct formation and p53 mutations in CYP450-expressing human liver cell lines

Epidemiological evidence has been supporting a relationship between dietary aflatoxin B1 (AFB1) exposure, development of human primary hepatocellular carcinoma (HCC) and mutations in the p53 tumor suppressor gene. However, the correlation between the observed p53 mutations, the AFB1 DNA adducts and their activation pathways has not been elucidated. Development of relevant cellular in vitro models, taking into account species and tissue specificity, could significantly contribute to the knowledge of cytotoxicity and genotoxicity mechanisms of chemical procarcinogens, such as AFB1, in humans. For this purpose a non-tumorigenic SV40-immortalized human liver epithelial cell line (THLE cells) which retained most of the phase II enzymes, but had markedly reduced phase I activities was used for stable expression of the human CYP1A2, CYP2A6, CYP2B6 and CYP3A4 cDNA. The four genetically engineered cell lines (T5-1A2, T5-2A6, T5-2B6 and T5-3A4) produced high levels of the specific CYP450 proteins and showed comparable or higher catalytic activities related to the CYP450 expression when compared to human hepatocytes. The T5-1A2, T5-2A6, T5-2B6 and T5-3A4 cell lines exhibited a very high sensitivity to the cytotoxic effects of AFB1 and were approximately 125-, 2-, 2- and 15-fold, respectively, more sensitive than the control T5-neo cells, transfected with an expressing vector which does not contain CYP450 cDNA. In the CYP450-expressing cells, nanomolar doses of AFB1-induced DNA adduct formation including AFB1-N7-guanine, -pyrimidyl and -diol adducts. In addition, the T5-1A2 cells showed AFM1-DNA adducts. At similar levels of total DNA adducts, both the T5-1A2 and T5-3A4 cells showed, at codon 249 of the p53 gene, AGG to AGT transversions at a relative frequency of 15x10(-6). In contrast, only the T5-3A4 cells showed CCC to ACC transversion at codon 250 at a high frequency, whereas the second most frequent mutations found in the T5-1A2 cells were C to T transitions at the first and second position of the codon 250. No significant AFB1-induced p53 mutations could be detected in the T5-2A6 cells. Therefore, the differential expression of specific CYP450 genes in human hepatocytes can modulate the cytotoxicity, DNA adduct levels and frequency of p53 mutations produced by AFB1.

Rapid and sustainable detoxication of airborne pollutants by broccoli sprout beverage: results of a randomized clinical trial in China

Broccoli sprouts are a convenient and rich source of the glucosinolate, glucoraphanin, which can generate the chemopreventive agent, sulforaphane, an inducer of glutathione S-transferases (GST) and other cytoprotective enzymes. A broccoli sprout-derived beverage providing daily doses of 600 μmol glucoraphanin and 40 μmol sulforaphane was evaluated for magnitude and duration of pharmacodynamic action in a 12-week randomized clinical trial. Two hundred and ninety-one study participants were recruited from the rural He-He Township, Qidong, in the Yangtze River delta region of China, an area characterized by exposures to substantial levels of airborne pollutants. Exposure to air pollution has been associated with lung cancer and cardiopulmonary diseases. Urinary excretion of the mercapturic acids of the pollutants, benzene, acrolein, and crotonaldehyde, were measured before and during the intervention using liquid chromatography tandem mass spectrometry. Rapid and sustained, statistically significant (P ≤ 0.01) increases in the levels of excretion of the glutathione-derived conjugates of benzene (61%), acrolein (23%), but not crotonaldehyde, were found in those receiving broccoli sprout beverage compared with placebo. Excretion of the benzene-derived mercapturic acid was higher in participants who were GSTT1-positive than in the null genotype, irrespective of study arm assignment. Measures of sulforaphane metabolites in urine indicated that bioavailability did not decline over the 12-week daily dosing period. Thus, intervention with broccoli sprouts enhances the detoxication of some airborne pollutants and may provide a frugal means to attenuate their associated long-term health risks.

Mouse embryonic stem cells carrying one or two defective Msh2 alleles respond abnormally to oxidative stress inflicted by low-level radiation

Chronic oxidative stress may play a critical role in the pathogenesis of many human cancers. Here, we report that mouse embryonic stem (ES) cells deficient in DNA mismatch repair responded abnormally when exposed to low levels of ionizing radiation, a stress known to generate oxidative DNA damage. ES cells derived from mice carrying either one or two disrupted Msh2 alleles displayed an increased survival following protracted exposures to low-level ionizing radiation as compared with wild-type ES cells. The increases in survival exhibited by ES cells deficient in DNA mismatch repair appeared to have resulted from a failure to efficiently execute cell death (apoptosis) in response to radiation exposure. For each of the ES cell types, prolonged low-level radiation treatment generated oxidative genome damage that manifested as an accumulation of oxidized bases in genomic DNA. However, ES cells from Msh2(+/-) and Msh2(-/-) mice accumulated more oxidized bases as a consequence of low-level radiation exposure than ES cells from Msh2(+/+) mice. The propensity for normal cells with mismatch repair enzyme deficiencies, including cells heterozygous for inactivating mismatch repair enzyme gene mutations, to survive promutagenic genome insults accompanying oxidative stresses may contribute to the increased cancer risk characteristic of the hereditary nonpolyposis colorectal cancer syndrome.