Interactions between hepatitis B virus infection and exposure to aflatoxins in the development of hepatocellular carcinoma: a molecular epidemiological approach

Prevalence of HIV and Viral Hepatitis Markers among Healthcare Workers in the Republic of Guinea

Healthcare workers are much more likely to be infected with HIV and hepatitis viruses compared to the general population. Although healthcare workers are more aware of HIV and hepatitis viruses, several countries in Africa lack a comprehensive grasp of disease routes and transmission risks. The aim of this study was to assess the prevalence of the serological and molecular biological markers of HIV and viral hepatitis among healthcare workers in the Republic of Guinea. The study material was 74 blood serum samples collected from healthcare workers who received additional training at the Institute of Applied Biological Research of Guinea (IRBAG, Kindia, Republic of Guinea). The markers examined included HBsAg, HBeAg, anti-HBs IgG, anti-HBcore IgG, anti-HCV qualitative determination, anti-HEV IgM and IgG, anti-HAV IgM and IgG, and anti-HIV. For viral DNA and RNA detection, nucleic acids were extracted from blood serum, and viral presence was inferred using real-time PCR with hybridization fluorescence detection. A high prevalence of viral hepatitis B markers was shown, and significantly fewer cases of viral hepatitis C and HIV were detected. Almost all examined medical workers had anti-HAV IgG antibodies, but no antibodies to hepatitis E virus. Apparently, the identified markers depend on the general prevalence of certain pathogens in the region and are associated with the traditions and characteristics of the country's residents.

Applying the health capability profile to empirically study chronic hepatitis B in rural Senegal: a social justice mixed-methods study protocol

INTRODUCTION

Despite the early implementation of hepatitis B vaccination and the ongoing decentralisation of chronic hepatitis B (CHB) care, over 10% of the Senegalese adult population lives with CHB and liver cancer remains a main cause of death. Investigating factors associated with CHB infection, prevention of CHB-related morbidity, and prevention and treatment of mortality secondary to CHB calls for a holistic and multidimensional approach. This paper presents the adaptation of the health capability profile (HCP) to a specific epidemiological issue and empirical setting: it seeks to identify and analyse inter-related abilities and conditions (health capabilities) in relation to the CHB epidemic in the rural area of Niakhar, Senegal.

METHODS AND ANALYSIS

This ongoing study relies on a sequential social justice mixed-methods design. The HCP is comprehensively adapted to CHB in rural Senegal and guides the design and conduct of the study. Objective and subjective data are collected at the individual level following a mixed-methods explanatory core design. The quantitative module, embedded in the ANRS12356 AmBASS cross-sectional survey (exhaustive sampling), is used to select a purposeful sampling of participants invited for one-on-one qualitative interviews. Additional data are collected at the institutional and community level through health facility surveys and an ethnography (in-depth interviews) of local and national CHB stakeholders. Data analysis adopts a synergistic approach to produce a multilayered analysis of individual HCPs and crosscutting analysis of the 15 health capabilities. The data integration strategy relies on a mixed-methods convergent core design, and will use 0-100 health capability scores as well as flow diagrams to measure and characterise levels of development and interactions among health capabilities, respectively.

ETHICS AND DISSEMINATION

This study was approved by Senegalese and French authorities. Results dissemination through local workshops and scientific publications aim at fuelling effective policy change towards CHB-related health capability.

Detection and Concentration of Plasma Aflatoxin is Associated with Detection of Oncogenic Human Papillomavirus in Kenyan Women

BACKGROUND

Cervical cancer is common in Kenyan women. Cofactors in addition to infection with oncogenic human papillomavirus (HPV) are likely to be important in causing cervical cancer, as only a small percentage of HPV-infected women will develop this malignancy. Kenyan women are exposed to dietary aflatoxin, a potent carcinogen and immunosuppressive agent, which may be such a co-factor.

METHODS

Demographics, behavioral data, plasma, and cervical swabs were collected from 88 HIV-uninfected Kenyan women without cervical dysplasia. HPV detection was compared between women with or without plasma AFB1-lys and evaluated in relation to AFB1-lys concentration.

RESULTS

Valid HPV testing results were available for 86 women (mean age 34.0 years); 49 women (57.0%) had AFB1-lys detected and 37 (43.0%) had none. AFB1-lys detection was not associated with age, being married, having more than secondary school education, home ownership, living at a walking distance to health care ≥60 minutes, number of lifetime sex partners, or age of first sex. AFB1-lys detection and plasma concentrations were associated with detection of oncogenic HPV types.

CONCLUSIONS

AFB1-lys-positivity and higher plasma AFB1-lys concentrations were associated with higher risk of oncogenic HPV detection in cervical samples from Kenya women. Further studies are needed to determine if aflatoxin interacts with HPV in a synergistic manner to increase the risk of cervical cancer.

Association between aflatoxin-albumin adduct levels and tortilla consumption in Guatemalan adults

Aflatoxin B₁ (AFB₁) is a known human hepatocarcinogen and a recent study reported elevated AFB₁ levels, measured by serum albumin biomarkers, among Guatemalan adults. While AFB₁ can contaminate a variety of foodstuffs, including maize, Guatemala's main dietary staple, the relationship of maize intake to serum AFB₁-albumin adducts levels in Guatemala has not been previously examined. As a result, a cross-sectional study was conducted among 461 Guatemalan adults living in five geographically distinct departments of the country. Participants provided a serum sample and completed a semi-quantitative food frequency questionnaire and a sociodemographic questionnaire. Multiple linear regression analysis was used to estimate the least square means (LSQ) and 95% confidence intervals (95% CI) of log-transformed AFB₁-albumin adducts by quintiles of maize consumption in crude and adjusted models. Additionally, analyses of tortilla consumption and levels of maize processing were conducted. The median maize intake was 344.3 g per day [Interquartile Range (IQR): 252.2, 500.8], and the median serum AFB₁-albumin adduct level was 8.4 pg/mg albumin (IQR: 3.8, 22.3). In adjusted analyses, there was no association between overall maize consumption and serum AFB₁-albumin levels. However, there was a statistically significant association between tortilla consumption and AFB₁-albumin levels (p_trend = 0.01). The LSM of AFB₁-albumin was higher in the highest quintile of tortilla consumption compared to the lowest quintile [LSM:9.03 95%CI: 7.03,11.70 vs 6.23, 95%CI: 4.95,8.17, respectively]. These findings indicate that tortilla may be an important source of AFB₁ exposure in the Guatemalan population. Therefore, efforts to control or mitigate AFB₁ levels in contaminated maize used for tortillas may reduce overall exposure in this population.

Dietary exposure to aflatoxin and micronutrient status among young children from Guinea

SCOPE

Aflatoxin exposure coincides with micronutrient deficiencies in developing countries. Animal feeding studies have postulated that aflatoxin exposure may be exacerbating micronutrient deficiencies. Evidence available in human subjects is limited and inconsistent. The aim of the study was to investigate the relationship between aflatoxin exposure and micronutrient status among young Guinean children.

METHODS AND RESULTS

A total of 305 children (28.8 ± 8.4 months) were recruited at groundnut harvest (rainy season), of which 288 were followed up 6 months later postharvest (dry season). Blood samples were collected at each visit. Aflatoxin-albumin adduct levels were measured by ELISA. Vitamin A, vitamin E and β-carotene concentrations were measured using HPLC methods. Zinc was measured by atomic absorption spectroscopy. Aflatoxin exposure and micronutrient deficiencies were prevalent in this population and were influenced by season, with levels increasing between harvest and postharvest. At harvest, children in the highest aflatoxin exposure group, compared to the lowest, were 1.98 (95%CI: 1.00, 3.92) and 3.56 (95%CI: 1.13, 11.15) times more likely to be zinc and vitamin A deficient.

CONCLUSION

Although children with high aflatoxin exposure levels were more likely to be zinc and vitamin A deficient, further research is necessary to determine a cause and effect relationship.

Aflatoxin M1in breast-milk of UAE women

A study was undertaken to determine whether breast-milk of mothers from the United Arab Emirates (UAE) contained aflatoxins. One hundred and forty lactating mothers, 55 who had delivered premature infants (<2500 g, </=37 wk gestational age) and 85 who had full-term infants, agreed to participate in the study. Breast-milk was collected during regular feeding of infants in the special care baby unit and postnatal wards using an electric breast pump and ten ml of milk was siphoned off into a zinc-free plastic container for analysis. Aflatoxin M(1) concentration in the breast-milk samples was measured by HPLC. Samples were collected between January 1999 and December 2000. Approximately 66% of the mothers were expatriates and 34% were UAE nationals. Babies' weight, postnatal age, sex, birthweight and gestational age, and mothers' nationality, age and parity were recorded. Overall, 92% of the breast-milk samples contained aflatoxin M(1). Both univariate and multivariate logistic regression analysis failed to show significant correlation between aflatoxin M(1) and gestational age, postnatal age, gender, nationality and clinical condition. Levels of lactose, protein and lipids did not correlate significantly with levels of aflatoxin M(1). The public should be educated about storing food and the hazards of aflatoxin ingestion to reduce the unacceptably frequent presence of aflatoxin in breast-milk.

Hepatitis B and C viruses and survival from hepatocellular carcinoma in the Arkhangelsk region: a Russian registry-based study

Introduction

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. The prevalence of hepatitis B (HBV) and C (HCV) in Russia was 7.6 and 5.4 per 100,000, respectively. The aim of this study was to assess the proportion of HCV and HBV infection among HCC patients, to evaluate associations between HCV, HBV and stage of HCC and to compare survival of HCC patients by their HBV/HCV status in the Arkhangelsk region of northwest Russia.

Materials and methods

A retrospective cohort study was conducted using data on all histologically confirmed HCC cases. Proportions of infected and non-infected HCC cases were calculated by Wilson's method. The associations between HBV, HCV and severity of HCC were assessed by Pearson's Chi-squared test. Survival data were presented using Kaplan–Meier curves and median survival. Survival time between the groups was compared using log-rank tests. Adjustment for potential confounders (sex, age groups, stage of HCC and cirrhosis stage by Child-Paquet scale) was performed using Cox regression.

Results

There were 583 histologically confirmed HCC cases. The viral status was registered in 311 of patients with pre-mortem diagnosis, where 124 or 39.9% (95% confidence interval (CI), 34.4–45.4) had HBV, 54 or 17.4% (95% CI, 13.5–21.9) had HCV and 16 or 5.1% (95% CI, 3.2–8.2) were infected with both HBV and HCV. The median survival rates of patients were 3 months (95% CI, 2.3–3.8), 3 months (95% CI, 2.0–3.9) and 1 month (95% CI, 0.0–0.6) for patients with HBV, HCV and HBV and HCV, respectively. For virus-free patients, it was 5 months (95% CI, 3.5–6.5), log-rank test=10.74, df=3, p=0.013. Crude Cox regression showed increased risk of death for HBV and HBV and HCV groups in comparison with virus-free patients, and not reaching the level of statistical significance for HCV. After adjustment, the hazard ratios (HRs) decreased to non-significant levels or even reversed, with only exception for the group of patients infected with both hepatitis viruses.

Conclusions

We found that more than half of HCC patients were infected with HBV or HCV. The study did not reveal an association between viral status of HCC patients and stage of HCC. The viral hepatitis may have an impact on survival of HCC patients.

The role of biomarkers in evaluating human health concerns from fungal contaminants in food

Mycotoxins are toxic secondary metabolites that globally contaminate an estimated 25 % of cereal crops and thus exposure is frequent in many populations. Aflatoxins, fumonisins and deoxynivalenol are amongst those mycotoxins of particular concern from a human health perspective. A number of risks to health are suggested including cancer, growth faltering, immune suppression and neural tube defects; though only the demonstrated role for aflatoxin in the aetiology of liver cancer is widely recognised. The heterogeneous distribution of mycotoxins in food restricts the usefulness of food sampling and intake estimates; instead biomarkers provide better tools for informing epidemiological investigations. Validated exposure biomarkers for aflatoxin (urinary aflatoxin M(1), aflatoxin-N7-guaunine, serum aflatoxin-albumin) were established almost 20 years ago and were critical in confirming aflatoxins as potent liver carcinogens. Validation has included demonstration of assay robustness, intake v. biomarker level, and stability of stored samples. More recently, aflatoxin exposure biomarkers are revealing concerns of growth faltering and immune suppression; importantly, they are being used to assess the effectiveness of intervention strategies. For fumonisins and deoxynivalenol these steps of development and validation have significantly advanced in recent years. Such biomarkers should better inform epidemiological studies and thus improve our understanding of their potential risk to human health.

Host genetic factors in hepatitis B infection, liver cancer and vaccination response: a review with a focus on Africa

The disease burden due to hepatitis B virus (HBV) infection remains significant; 350 million people are infected world-wide, and around half a million deaths each year are due to HBV-related liver disease and hepatocellular carcinoma (HCC). Infant immunisation against infection was introduced in the early 1980s, the vaccine is routinely administered across regions where the disease is endemic and has been shown to be safe and effective. However, the large number of older individuals with persistent infection means that disease will not be reduced significantly for several decades. Furthermore, failure to respond to the vaccination has been observed in about 5% of vaccinees and to date we have limited information on the durability of vaccine protection against infection. Hepatitis B infection and disease pathogenesis are known to be influenced by a number of factors including host genetics factors. This review aims to give an overview of the role of genetic variation in persistent HBV infection and the development of liver disease including HCC. Vaccine-induced immunity is, at least in part, heritable and we also discuss findings on the genetic control of responses to HBV vaccination. The epidemiology of HBV infection differs by world region, as does the genetic makeup of individuals originating from different regions. This review focuses on the situation in Africa, where hepatitis B is highly endemic.

Interactions between hepatitis B virus and aflatoxin B1: effects on p53 induction in HepaRG cells

Infection by hepatitis B virus (HBV) and dietary exposure to aflatoxin B1 (AFB1) are the main risk factors for the development of chronic liver disease and hepatocellular carcinoma (HCC). How these factors cooperate is still largely unknown. AFB1 activation leads to DNA adduction and mutagenesis, with a specific mutation at codon 249 in TP53 (p.R249S). So far, only limited studies have addressed the effects of AFB1 on HBV replication. We have analysed the effects of both risk factors on p53 induction during HBV infection in HepaRG, a cell line with hepatocyte-like morphology that metabolizes AFB1 and supports HBV infection. Exposure to AFB1 up to 5 µM induced a downregulation of HBV replication after 48 h, as measured by a decrease in viral antigens in the culture medium (HBsAg, HBeAg and large envelope protein) and in intracellular levels of HBV transcripts, DNA and HBsAg. Conversely, HBV infection did not significantly modify AFB1-DNA adduct formation or repair as assessed by immunodot-blot assay, and the induction of p53 in response to AFB1 was similar in infected and non-infected HepaRG cells. Overall, our results suggest that AFB1 exposure decreases HBV replication, whereas DNA damage by AFB1 and subsequent p53 induction is not affected by the presence of the virus. Thus, in HepaRG cell line, AFB1 and HBV do not cooperate to increase DNA damage by AFB1. Further studies on the effects of both factors in a context of chronicity are needed to better understand synergistic effects.

Present and future directions of translational research on aflatoxin and hepatocellular carcinoma. A review

The aflatoxins were discovered in toxic peanut meal causing "turkey X" disease, which killed large numbers of turkey poults, ducklings and chicks in the UK in the early 1960s. Extracts of toxic feed induced the symptoms in experimental animals, and purified metabolites with properties identical to aflatoxins B(1) and G(1) (AFB(1) and AFG(1)) were isolated from Aspergillus flavus cultures. Structure elucidation of aflatoxin B(1) was accomplished and confirmed by total synthesis in 1963. AFB(1) is a potent liver carcinogen in rodents, non-human primates, fish and birds, operating through a genotoxic mechanism involving metabolic activation to an epoxide, formation of DNA adducts and, in humans, modification of the p53 gene. Aflatoxins are unique among environmental carcinogens, in that elucidation of their mechanisms of action combined with molecular epidemiology provides a foundation for quantitative risk assessment; extensive evidence confirms that contamination of the food supply by AFB(1) puts an exposed population at increased risk of developing hepatocellular carcinoma (HCC). Molecular biomarkers to quantify aflatoxin exposure in individuals were essential to link aflatoxin exposure with liver cancer risk. Biomarkers were validated in populations with high HCC incidence in China and The Gambia, West Africa; urinary AFB(1)-N (7)-Guanine excretion was linearly related to aflatoxin intake, and levels of aflatoxin-serum albumin adducts also reflected aflatoxin intake. Two major cohort studies employing aflatoxin biomarkers identified their causative role in HCC etiology. Results of a study in Shanghai men strongly support a causal relationship between HCC risk and the presence of biomarkers for aflatoxin and HBV infection, and also show that the two risk factors act synergistically. Subsequent cohort studies in Taiwan confirm these results. IARC classified aflatoxin as a Group 1 human carcinogen in 1993, based on sufficient evidence in humans and experimental animals indicating the carcinogenicity of naturally occurring mixtures of aflatoxins, aflatoxin B(1), G(1) and M(1). Aflatoxin biomarkers have also been used to show that primary prevention to reduce aflatoxin exposure can be achieved by low-technology approaches at the subsistence farm level in sub-Saharan Africa. Also, in residents of Qidong, China, oral dosing with chlorophyllin, a chlorophyll derivative, prior to each meal led to significant reduction in aflatoxin-DNA biomarker excretion, supporting the feasibility of preventive measures to reduce HCC risk in populations experiencing unavoidable aflatoxin exposure. The systematic, comprehensive approach used to create the total aflatoxin database justifies optimism for potential success of preventive interventions to ameliorate cancer risk attributable to aflatoxin exposure. This strategy could serve as a template for the development, validation and application of molecular and biochemical markers for other carcinogens and cancers as well as other chronic diseases resulting from environmental exposures.

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.

Understanding mechanisms in the health sciences

This article focuses on the assessment of mechanistic relations with specific attention to medicine, where mechanistic models are widely employed. I first survey recent contributions in the philosophical literature on mechanistic causation, and then take issue with Federica Russo and Jon Williamson's thesis that two types of evidence, probabilistic and mechanistic, are at stake in the health sciences. I argue instead that a distinction should be drawn between previously acquired knowledge of mechanisms and yet-to-be-discovered knowledge of mechanisms and that both probabilistic evidence and manipulation are essential with respect to newly discovered mechanisms.

Cooperation of tumor-derived HBx mutants and p53-249(ser) mutant in regulating cell proliferation, anchorage-independent growth and aneuploidy in a telomerase-immortalized normal human hepatocyte-derived cell line

Hepatocellular carcinoma (HCC) is a common cancer, and hepatitis B virus (HBV) is a major etiological agent. Convincing epidemiological and experimental evidence also links HCC to aflatoxin, a naturally occurring mycotoxin that produces a signature p53-249(ser) mutation. Recently, we have reported that tumor-derived HBx variants encoded by HBV exhibited attenuated transactivation and proapoptotic functions but retained their ability to block p53-mediated apoptosis. These results indicate that mutations in HBx may contribute to the development of HCC. In this study, we determined whether tumor-derived HBx mutants along, or in cooperation with p53-249(ser), could alter cell proliferation and chromosome stability of normal human hepatocytes. To test this hypothesis, we established a telomerase immortalized normal human hepatocycte line HHT4 that exhibited a near diploid karyotype and expressed many hepatocyte-specific genes. We found that overexpression one of the tumor-derived HBx mutants, CT, significantly increased colony forming efficiency (CFE) while its corresponding wild-type allele CNT significantly decreased CFE in HHT4 cells. p53-249(ser) rescued CNT-mediated inhibition of colony formation. Although HHT4 cells lacked an anchorage independent growth capability as they did not form any colonies in soft agar, the CT-expressing HHT4 cells could form colonies, which could be significantly enhanced by p53-249(ser). Induction of aneuploidy could be observed in HHT4 cells expressing CT, but additionally recurring chromosome abnormalities could only be detected in cells coexpressing CT and p53-249(ser). Our results are consistent with the hypothesis that certain mutations in HBx and p53 at codon 249 may cooperate in contributing to liver carcinogenesis.

Molecular pathogenesis and early detection of hepatocellular carcinoma--perspectives from West Africa

This article reviews mechanisms involved in development of hepatocellular carcinoma and how host and environmental factors interact at a molecular level to cause cancer. These processes are intimately linked with strategies for early detection since molecular intermediates on the carcinogenesis pathway can now be detected with increasing levels of sensitivity. Similarly host factors influencing response to environmental agents, together with substances produced by early cancers, can be assayed in fine detail with new and emerging technologies. These advances in the field of biomarkers may lead to more rapid diagnosis and ultimately to improved survival as novel therapeutic strategies are adopted.

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.

A longitudinal assessment of aflatoxin M1 excretion in breast milk of selected Egyptian mothers

Aflatoxins are potent toxins and carcinogens which can be excreted in the milk of exposed lactating mothers mainly in the form of aflatoxin M(1) (AFM(1)). We previously evaluated the level and frequency of AFM(1) in breast milk in a group of Egyptian mothers attending the New El-Qalyub Hospital, Qalyubiyah governorate, Egypt. In this study, fifty of those women who were AFM(1) positive were revisited monthly for 12 months to assess the temporal variation in breast milk AFM(1). AFM(1) was detected in 248 of 443 (56%) samples. In a multilevel model of the data there was a highly significant (p<0.001) effect of month of sampling on the frequency of AFM(1) detection with summer months having the highest frequency (>80%) and winter months the lowest frequency (<20%) of detection. AFM(1) was observed most frequently in June [OR 63, 95% CI (7.6, 522)]. The level of AFM(1) detection also followed this seasonal pattern with highest mean level in July (64 pg/ml milk, range 6.3-497 pg/ml milk) and the lowest mean level in January (8 pg/ml milk, range 4.2-108 pg/ml milk). The duration of lactation [p=0.0035, OR=1.08, 95% CI (1.02, 1.13)], and peanut consumption [p=0.06, OR=1.69, 95% CI (0.9, 2.9)] also contributed to the model. The identification and understanding of factors determining the presence of toxicants in human milk is important and may provide a knowledge driven basis for controlling the transfer of chemicals to infants.

Absence of TP53 codon 249 mutations in young Guinean children with high aflatoxin exposure

Infection with hepatitis viruses and chronic exposure to high levels of dietary aflatoxins are the major etiologic agents for hepatocellular carcinoma in west Africa. A challenge for the prevention of hepatocellular carcinoma in this region is that both hepatitis B virus and aflatoxin exposures start early in life; indeed, aflatoxin exposures can start in utero and continue unabated throughout childhood. A mutation in the TP53 tumor suppressor gene at codon 249 (TP53 Ser249 mutation) has been reported previously for hepatocellular carcinoma tumors and matched plasma DNA samples in individuals from areas with high aflatoxin exposure. We examined whether the TP53 Ser249 mutation could be observed in DNA found in plasma of young children (ages 2-5 years) from Guinea, west Africa, a region of high aflatoxin exposure. Plasma aflatoxin-albumin adducts were present in 119 of 124 (96%) of the children, geometric mean of positives 9.9 pg/mg albumin (95% confidence interval, 8.8-11.0 pg/mg). This is the level and prevalence of exposure observed previously in adults. Following PCR amplification of plasma-derived DNA and detection using mass spectrometry, none of the samples were found to contain the TP53 Ser249 mutation. Because approximately 50% of the hepatocellular carcinomas in adults in west Africa have this specific TP53 Ser249 mutation, a lack of detection in samples from children ages <5 years may indicate that a window of opportunity for intervention exists that could be exploited to lower hepatocellular carcinoma risk.

p53 Mutations in human cholangiocarcinoma: a review

The reported mortality from intrahepatic bile duct tumours is increasing markedly in industrialised countries, for reasons that remain unknown. Inactivation of the tumour suppressor gene p53, is the commonest genetic abnormality in human cancer and has been implicated in the genesis of cholangiocarcinoma in various immunohistochemical and molecular epidemiological investigations, including gene sequencing studies. The structure and function of p53 and its role in linking cancer to specific carcinogens by way of mutational signatures is reviewed. The findings of previous p53 studies and their relevance in human cholangiocarcinoma are summarised.

Reduction in exposure to carcinogenic aflatoxins by postharvest intervention measures in west Africa: a community-based intervention study

BACKGROUND

Aflatoxins are fungal metabolites that frequently contaminate staple foods in much of sub-Saharan Africa, and are associated with increased risk of liver cancer and impaired growth in young children. We aimed to assess whether postharvest measures to restrict aflatoxin contamination of groundnut crops could reduce exposure in west African villages.

METHODS

We undertook an intervention study at subsistence farms in the lower Kindia region of Guinea. Farms from 20 villages were included, ten of which implemented a package of postharvest measures to restrict aflatoxin contamination of the groundnut crop; ten controls followed usual postharvest practices. We measured the concentrations of blood aflatoxin-albumin adducts from 600 people immediately after harvest and at 3 months and 5 months postharvest to monitor the effectiveness of the intervention.

FINDINGS

In control villages mean aflatoxin-albumin concentration increased postharvest (from 5.5 pg/mg [95% CI 4.7-6.1] immediately after harvest to 18.7 pg/mg [17.0-20.6] 5 months later). By contrast, mean aflatoxin-albumin concentration in intervention villages after 5 months of groundnut storage was much the same as that immediately postharvest (7.2 pg/mg [6.2-8.4] vs 8.0 pg/mg [7.0-9.2]). At 5 months, mean adduct concentration in intervention villages was less than 50% of that in control villages (8.0 pg/mg [7.2-9.2] vs 18.7 pg/mg [17.0-20.6], p<0.0001). About a third of the number of people had non-detectable aflatoxin-albumin concentrations at harvest. At 5 months, five (2%) people in the control villages had non-detectable adduct concentrations compared with 47 (20%) of those in the intervention group (p<0.0001). Mean concentrations of aflatoxin B1 in groundnuts in household stores in intervention and control villages were consistent with measurements of aflatoxin-albumin adducts.

INTERPRETATION

Use of low-technology approaches at the subsistence-farm level in sub-Saharan Africa could substantially reduce the disease burden caused by aflatoxin exposure.

Human aflatoxicosis in developing countries: a review of toxicology, exposure, potential health consequences, and interventions

Aflatoxins are well recognized as a cause of liver cancer, but they have additional important toxic effects. In farm and laboratory animals, chronic exposure to aflatoxins compromises immunity and interferes with protein metabolism and multiple micronutrients that are critical to health. These effects have not been widely studied in humans, but the available information indicates that at least some of the effects observed in animals also occur in humans. The prevalence and level of human exposure to aflatoxins on a global scale have been reviewed, and the resulting conclusion was that approximately 4.5 billion persons living in developing countries are chronically exposed to largely uncontrolled amounts of the toxin. A limited amount of information shows that, at least in those locations where it has been studied, the existing aflatoxin exposure results in changes in nutrition and immunity. The aflatoxin exposure and the toxic affects of aflatoxins on immunity and nutrition combine to negatively affect health factors (including HIV infection) that account for >40% of the burden of disease in developing countries where a short lifespan is prevalent. Food systems and economics render developed-country approaches to the management of aflatoxins impractical in developing-country settings, but the strategy of using food additives to protect farm animals from the toxin may also provide effective and economical new approaches to protecting human populations.

Viruses, chemicals and co-carcinogenesis

The etiology of cancers appears to be complex and multifactorial. Peyton Rous and others demonstrated the process of co-carcinogenesis by exposing rabbits to a virus and tars. Epidemiologists have proposed virus-chemical interactions to cause several cancers. For example, one might propose that the etiology of cervical cancer results from a complex interplay between oncogenic viruses and cervical tar exposures through tar-based vaginal douching, cigarette smoking, and/or long-term cooking over wood-burning stoves in poorly ventilated kitchens. Hepatocellular carcinoma may result from the joint effects of viruses and hepatotoxic chemical carcinogens. Kaposi's sarcoma might happen following reciprocal actions of human herpes virus-8 infection, immunosuppression, and chemical exposures, such as nitrite radicals and alumino-silicates. Use of Koch's postulates will not help one prove or disprove a multifactorial causation of disease; new criteria are needed. Delineating the web of causation may lead to additional strategies for prevention and treatment of several cancers.

A novel diagnostic marker, p28GANK distinguishes hepatocellular carcinoma from potential mimics

PURPOSE

To investigate the sensitivity, specificity, and spatial distribution of the product of p28 gene (p28(GANK) protein) in human hepatocellular carcinoma (HCC) and nonhepatocellular carcinomas in relation to immunostaining with Cytokeratin 18 (CK18), alpha-fetoprotein (AFP), and Hepatocyte paraffin 1 (HepPar1).

METHOD

In this retrospective study, formalin-fixed paraffin-embedded tissues from 24 HCCs, five intrahepatic cholangiocarcinomas (ICC), five combined hepatocellular cholangiocarcinomas (C-HCC-CC) and mine metastatic hepatic carcinomas (MHC) were immunostained for p28(GANK) as well as CK18, AFP and HepPar1. Only cases with more intensified staining in carcinoma contrast to the adjacent liver tissues were accepted as positive.

RESULT

In HCC, p28(GANK) was expressed restrictively in hepatocytes of both para-lesion and carcinoma liver tissues, while absent in the bile duct epithelial cells, Kupffer cells, and other interstitial cells. The positive staining of p28(GANK) was noted in 16 (66.7%) specimens of HCC and three (60.0%) specimens of C-HCC-CC, and no specific lesion staining was found in all tested specimens of ICC and MHC. Sensitivity and specificity for hepatocyte-originated carcinoma were, respectively, 65.5% and 100% for p28(GANK), 79.3% and 85.2% for CK18, 20.7% and 100% for AFP, 79.3% and 92.0% for HepPar1.

CONCLUSION

The hepatocytic staining for p28(GANK) is clearly useful in differentiating hepatocyte-originated carcinoma from non-HCC. p28(GANK) may be used as an ancillary marker for the diagnosis of HCC.

Ser-249TP53 mutation in tumour and plasma DNA of hepatocellular carcinoma patients from a high incidence area in the Gambia, West Africa

Hepatocellular carcinoma (HCC) is frequent in areas of high exposure to aflatoxin and high prevalence of HBV infection, such as western Africa and south-east China. A selective mutation in TP53 (AGG-->AGT at codon 249, Arg-->Ser) has been identified as a hotspot in HCCs from such areas, reflecting DNA damage caused by aflatoxin metabolites. Recent studies have shown that circulating free DNA can be retrieved from human plasma, and it is hypothesised that plasma DNA may serve as a source for biomarkers of tumorigenic processes. In our study, we have determined the prevalence of Ser-249 mutation, using a PCR-restriction digestion method, with selective use of short oligonucleotide mass spectrometry analysis (SOMA), in a series of 29 biopsy specimens of HCC from The Gambia in West Africa. Overall, we identified the Ser-249 mutation in 35% (10/29) of the tumours. In parallel, we tested 17 plasma samples from HCC patients with matching tumour tissue. The 249 status concordance between tumour tissues and matched plasma was 88.5%. These results indicate that the Ser-249 mutation is common in HCC in The Gambia (35%), although a higher prevalence has been reported in other regions with high population exposure to aflatoxin (e.g., eastern China: >50%). Moreover, our studies indicate that plasma is a convenient source of liver tumour-derived DNA, thus holding promise for earlier detection and diagnosis of cancer.

Transgenic mouse models of hepatitis B virus-associated hepatocellular carcinoma

The multi-factorial and multi-step nature of cancer development makes analysis difficult in cell culture and non-genetic animal models. Recent progress in technology has allowed the development of several transgenic animal models addressing various aspects of liver diseases caused by hepatitis B virus in human patients. The experimental data from these studies in vivo highlight the importance of HBV gene products that alone or in conjunction with other host cellular protein(s) can deregulate the cell cycle control checkpoints in the hepatocytes of transgenic mice leading to the development of hepatocellular carcinoma. Moreover, these models are extremely useful in analysing and ascertaining the stages of malignant transformation linked to multiple genetic and non-genetic events of cancer development and in developing novel strategies of intervention.

The role of aflatoxins and hepatitis viruses in the etiopathogenesis of hepatocellular carcinoma: A basis for primary prevention in Guinea-Conakry, West Africa

Aflatoxins and hepatitis B virus (HBV) are major risk factors for hepatocellular carcinoma (HCC) in South-east Asia and Africa, parts of the world where this cancer is most prevalent. Exposure to both factors is endemic, occurring from early in life. There is evidence from both epidemiological studies and animal models that the two factors can act synergistically to increase the risk of HCC, but the underlying cellular and molecular mechanisms of interaction are as yet undefined. One possibility suggested by studies in HBV transgenic mice is that chronic liver injury alters the expression of carcinogen metabolizing enzymes, thus modulating the level of binding of aflatoxin to DNA. Primary prevention of HCC in high incidence areas of the world should primarily be focused on provision of the safe, effective vaccine against HBV. However, measures to reduce the high levels of aflatoxin exposure, where chronic HBV infection is currently epidemic, would also significantly contribute to reducing HCC incidence. In Guinea-Conakry, West Africa, surveys of HBV infection and aflatoxin exposure have established baseline data for the implementation of a community-based intervention study. This study will evaluate the effectiveness of improving the post-harvest processing and storage of the groundnut crop, a major source of aflatoxins, using aflatoxin-albumin adducts as the outcome measurement.

Determinants of formation of aflatoxin-albumin adducts: a seven-township study in Taiwan

Dietary exposure to aflatoxins is one of the major risk factors for hepatocellular carcinoma. Individual susceptibility to aflatoxin-induced hepatocarcinogenesis may be modulated by both genetic and environmental factors affecting metabolism. A cross-sectional study was performed to evaluate determinants of the formation of aflatoxin covalently bound to albumin (AFB1-albumin adducts). A total of 474 subjects who were free of liver cancer and cirrhosis and were initially selected as controls for previous case-control studies of aflatoxin-induced hepatocarcinogenesis in Taiwan, were employed in this study. Aflatoxin-albumin adducts were determined by competitive enzyme-linked immunosorbent assay, hepatitis B surface antigen and antibodies to hepatitis C virus by enzyme immunoassay, as well as genotypes of glutathione S-transferase M1-1 and T1-1 by polymerase chain reaction. The detection rate of AFB1-albumin adducts was significantly higher in males (42.5%) than in females (21.6%) (multivariate-adjusted odds ratio=2.6, 95% confidence interval=1.4-5.0). The formation of detectable albumin adducts was moderately higher in hepatitis B surface antigen carriers (42.8%) than in non-carriers (36.6%) (multivariate-adjusted odds ratio=1.4, 95% confidence interval=1.0-2.1). In addition, the detection rate of AFB1-albumin adducts tended to increase with the increasing number of null genotypes of glutathione S-transferase M1-1 and glutathione S-transferase T1-1. In conclusion, this cross-sectional study has assessed the relative contributions of environmental exposure and host susceptibility factors in the formation of AFB1-albumin adducts in a well characterised Chinese adult population. This study further emphasises the necessity to reduce aflatoxin exposure in people living in an area endemic for chronic hepatitis B virus infection.

Overexpression of p28/gankyrin in human hepatocellular carcinoma and its clinical significance

AIM: To investigate the expression of p28/gankyrin gene and its role in the carcinogenetic process of human hepatocellular carcinoma (HCC).

METHODS: 64 specimens of HCC and para-carcinoma tissues, 22 specimens of non-tumor liver tissues (7 normal, 15 cirrhosis), 10 specimens of normal human tissues and 5 hepatoma cell lines were studied for the expression of p28/gankyrin by Northern blot. The expression of p28/gankyrin protein was detected immunohistochemically by using the specific polyclonal antibody.

RESULTS: Northern blot analysis indicated that the expression of p28/gankyrin mRNA was intensively distributed in brain and heart, weakly in lung, spleen and muscle, undetectable in digestive system including liver, pancreas, stomach, small and large intestines. p28/gankyrin mRNA was absent in normal liver, weakly detected in liver cirrhosis and in 18 of 64 para-carcinoma liver tissues. In contrast, the expression of p28/gankyrin mRNA was intensively detected in all 5 hepatoma cell lines tested, markedly increased in 57 of 64 and moderately increased in 5 of 64 HCC samples. In comparison with liver cirrhosis and para-carcinoma liver tissues, the average expression of p28/gankyrin mRNA in HCC was increased 3.6- (2.901 ± 0.507 vs 0.805 ± 0.252, P < 0.05) and 5.2-fold (2.901 ± 0.507 vs 0.557 ± 0.203, P < 0.01), respectively. In addition, p28/gankyrin mRNA expression level was higher in HCC with portal vein tumor thrombus and microscopic hepatic vein involvement (P = 0.021 and P = 0.047, respectively). The overexpression of p28/gankyrin protein in HCC was targeted in hepatic tumor cells, not in bile duct cells and other interstitial cells.

CONCLUSION: Overexpression of p28/gankyrin in HCC plays an important role and contributes to the metastasis potential in the process of carcinogenesis. p28/gankyrin may become a specific biological tissue marker for the pathological diagnosis of HCC.

Hepatitis B infection and aflatoxin biomarker levels in Gambian children

OBJECTIVES

To examine the relationship between hepatitis B virus (HBV) infection and biomarkers of aflatoxin exposure in West African children.

METHODS

Sera from 444 children aged 3-4 years who were selected to be representative of their communities were analysed for aflatoxin-albumin (AF-alb) adducts and markers of hepatitis B infection.

RESULTS

There was large interindividual variation in adduct levels (range: 2.2 to 459 pg AF-lysine eq./mg albumin). Adduct level was strongly correlated with season, with an approximately twofold higher mean level in the dry season than the wet. Geometric mean adduct levels in uninfected children, chronic carriers and acutely infected children were 31.6 (n = 404), 44.9 (n = 34) and 96.9 (n = 6) pg/mg, respectively. The relationship of AF-alb level to ethnicity, month of sampling and HBV status was examined in a multiple regression model. Month of obtaining the blood sample (P = 0.0001) and HBV status (P = 0.0023) each made a highly significant contribution to the model; the high AF-alb levels were particularly associated with acute infection. Elevated serum transaminase levels were significantly (P < 0.002) associated with HBV status, with acutely infected children having the highest levels. Ethnicity was not significantly associated with AF-alb adduct levels in the model (P = 0.09).

CONCLUSIONS

HBV infection and month of sampling both significantly influence AF-alb adduct levels. The effect of seasonality on adducts was also observed in a previous study of 347 Gambian adults, although there was no correlation between adduct level and HBV status in that population. This difference between children and adults may reflect a more severe effect of HBV infection, particularly acute infection, in childhood on hepatic AF metabolism.

Genetics of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the human cancers clearly linked to viral infections. Although the major viral and environmental risk factors for HCC development have been unravelled, the oncogenic pathways leading to malignant transformation of liver cells have long remained obscure. Recent outcomes have been provided by extensive allelotype studies which resulted in a comprehensive overview of the main genetic abnormalities in HCC, including DNA copy gains and losses. The differential involvement of the p53 tumor-suppressor gene in tumors associated with various risk factors has been largely clarified. Evidence for a crucial role of the reactivation of the Wnt/beta-catenin pathway, through mutations in the beta-catenin and axin genes in 30-40% of liver tumors, represents a major breakthrough. It has also been shown that the Rb pathway is frequently disrupted by methylation-dependent silencing of the p16INK4A gene and stimulation of Rb degradation by a proteosomal subunit. Presently, the identification of candidate oncogenes and tumor suppressors in the most frequently altered chromosomal regions is a major challenge. Great insights will come from integrating the signals from different pathways operating at preneoplastic and neoplastic stages. This search might, in time, permit an accurate evaluation of the major targets for therapeutic treatments.