Does aflatoxin B1 play a role in the etiology of hepatocellular carcinoma in the United States?

Fungal infections and the fungal microbiome in hepatobiliary disorders

Liver and biliary diseases affect more than a billion people worldwide, with high associated morbidity and mortality. The impact of the intestinal bacterial microbiome on liver diseases has been well established. However, the fungal microbiome, or mycobiome, has been overlooked for a long time. Recently, several studies have shed light on the role of the mycobiome in the development and progression of hepatobiliary diseases. In particular, the fungal genus Candida has been found to be involved in the pathogenesis of multiple hepatobiliary conditions. Herein, we compare colonisation and infection, describe mycobiome findings in the healthy state and across the various hepatobiliary conditions, and point toward communalities. We detail how quantitation of immune responses to fungal antigens can be employed to predict disease severity, e.g. using antibodies to Saccharomyces cerevisiae or specific anti-Candida albicans antibodies. We also show how fungal products (e.g. beta-glucans, candidalysin) activate the host's immune system to exacerbate liver and biliary diseases. Finally, we describe how the gut mycobiome can be modulated to ameliorate hepatobiliary conditions.

Prevalence of Aflatoxin-Associated TP53R249S Mutation in Hepatocellular Carcinoma in Hispanics in South Texas

We aimed to determine whether aflatoxin dietary exposure plays a role in the high incidence of hepatocellular carcinoma (HCC) observed among Hispanics in South Texas. We measured TP53R249S somatic mutation, hallmark of aflatoxin etiology in HCC, using droplet digital PCR and RFLP. TP53R249S mutation was detected in 3 of 41 HCC tumors from Hispanics in South Texas (7.3%). We also measured TP53R249S mutation in plasma cell-free DNA (cfDNA) from 218 HCC patients and 96 Hispanic subjects with advanced fibrosis or cirrhosis, from South Texas. The mutation was detected only in Hispanic and Asian HCC patients, and patients harboring TP53R249S mutation were significantly younger and had a shorter overall survival. The mutation was not detected in any Hispanic subject with advanced fibrosis or cirrhosis. Genes involved in cell-cycle control of chromosomal replication and in BRCA1-dependent DNA damage response were enriched in HCCs with TP53R249S mutation. The E2F1 family members, E2F1 and E2F4, were identified as upstream regulators. TP53R249S mutation was detected in 5.7% to 7.3% of Hispanics with HCC in South Texas. This mutation was associated with a younger age and worse prognosis. TP53R249S was however not detected in Hispanics in South Texas with cirrhosis or advanced fibrosis. Aflatoxin exposure may contribute to a small number of HCCs in Hispanics in South Texas, but the detection of TP53R249S mutation in plasma cfDNA is not a promising biomarker of risk assessment for HCC in subjects with cirrhosis or advanced fibrosis in this population. Cancer Prev Res; 11(2); 103-12. ©2017 AACR.

Prevalence of aflatoxin induced p53 mutation at codon 249 (R249s) in hepatocellular carcinoma patients with and without hepatitis B surface antigen (HBsAg)

BACKGROUND

A missense mutation in exon 7 (R249S) of the p53 tumor suppressor gene is characteristic of aflatoxin B1 (AFB1) exposure. AFB1 is believed to have a synergistic effect on hepatitis virus B (HBV) carcinogenesis. However, results of studies comparing R249S prevalence among patients are conflicting. The aim of this study was to determine the prevalence of the R249S mutation in hepatocellular carcinoma (HCC) patients with or without positive HBsAg.

MATERIALS AND METHODS

Paraffin embedded liver tissues were obtained from 124 HCC patients who underwent liver resection and liver biopsy in King Chulalongkorn Memorial Hospital. Restriction fragment length polymorphism (RFLP) was utilized to detect the R249S mutation. Positive results were confirmed by direct sequencing.

RESULTS

Sixty four (52%) patients were positive for HBsAg and 18 (15%) were anti-HCV positive. 12 specimens tested positive by RFLP. Ten HCC patients (8.1%) were confirmed to be R249S positive by Sanger sequencing (AGG to AGT). Out of these 10, six were HBsAg positive, and out of the remaining 4, two were anti-HCV positive. The R249S prevalence among HCC patients with positive HBsAg was 9.4% compared to 6.7% for HBsAg negative samples. Patients with the R249S mutation were younger (55±10 vs 60±13 year-old) and tended to have a more advanced Edmonson-Steiner grade of HCC, although differences did not reach statistical significance.

CONCLUSIONS

Our study shows moderate prevalence of aflatoxin B1-related p53 mutation (R249S) in HCC with or without HBsAg. HBsAg positive status was not associated with R249S prevalence.

The molecular epidemiology of chronic aflatoxin driven impaired child growth

Aflatoxins are toxic secondary fungal metabolites that contaminate dietary staples in tropical regions; chronic high levels of exposure are common for many of the poorest populations. Observations in animals indicate that growth and/or food utilization are adversely affected by aflatoxins. This review highlights the development of validated exposure biomarkers and their use here to assess the role of aflatoxins in early life growth retardation. Aflatoxin exposure occurs in utero and continues in early infancy as weaning foods are introduced. Using aflatoxin-albumin exposure biomarkers, five major studies clearly demonstrate strong dose response relationships between exposure in utero and/or early infancy and growth retardation, identified by reduced birth weight and/or low HAZ and WAZ scores. The epidemiological studies include cross-sectional and longitudinal surveys, though aflatoxin reduction intervention studies are now required to further support these data and guide sustainable options to reduce the burden of exposure. The use of aflatoxin exposure biomarkers was essential in understanding the observational data reviewed and will likely be a critical monitor of the effectiveness of interventions to restrict aflatoxin exposure. Given that an estimated 4.5 billion individuals live in regions at risk of dietary contamination the public health concern cannot be over stated.

Environmental Exposures and Hepatocellular Carcinoma

Infection with hepatitis B and/or hepatitis C virus is a well-established risk factor for the development of hepatocellular carcinoma (HCC). However, it is now clear that certain occupational, environmental, and lifestyle factors also play a role in cancer development. Among these factors are smoking, alcohol consumption, workplace exposure to vinyl chloride, and exposure to polycylic aromatic hydrocarbons and aflatoxins. There is also evidence that several other chemical and infectious agents have a role in inducing HCC in humans. Epidemiologic studies and the use of biomarkers have provided essential data to demonstrate the importance of some of these factors in human risk, while animal studies have suggested that other chemicals may also play a role. Although immunization against hepatitis B virus infection remains the primary method of preventing HCC in regions of the world where this virus is a primary etiologic agent, there is currently no vaccine for hepatitis C virus. Thus, limiting exposure to other known risk factors remains an important mechanism in preventing HCC.

Aflatoxin and PAH exposure biomarkers in a U.S. population with a high incidence of hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) is significantly elevated in a Hispanic community in Bexar County, Texas. Chronic exposure to dietary aflatoxins (AFs) is a major risk factor for HCC; increased risk has been linked to polycyclic aromatic hydrocarbon (PAH) co-exposure and hepatitis virus infection. The aims of this study were to assess AF and PAH exposures, investigate dietary factors that may contribute to increased AF exposure, and determine the prevalence of hepatitis virus infection in Bexar Co. Blood and urine samples were collected from 184 volunteers for biomarker analyses and hepatitis screening. Serum AFB(1)-lysine adduct, urinary AFM(1) and 1-hydroxypyrene (1-OHP) levels were measured using high-performance liquid chromatography. The average AFB(1)-lysine adduct level detected in 20.6% of serums was 3.84 ± 3.11 pg/mg albumin (range 1.01-16.57 pg/mg). AFM(1) was detected in 11.7% of urines, averaging 223.85 ± 250.56 pg/mg creatinine (range 1.89-935.49 pg/mg). AFM(1) detection was associated with increased consumption of corn tortillas (p=0.009), nuts (p=0.033) and rice (p=0.037). A significant difference was observed between mean 1-OHP values of non-smokers (0.07 ± 0.13) and smokers (0.80 ± 0.68) μmol/mol creatinine (p<0.01). A high hepatitis C virus positivity rate (7.1%) was observed. Findings suggest that the incidence and level of AF and PAH exposure were less than those observed in a high-risk population; however, participants consuming higher amounts of foods prone to AF contamination may be more vulnerable to exposure and interactions with other environmental/biological factors (i.e., HCV).

249 TP53 mutation has high prevalence and is correlated with larger and poorly differentiated HCC in Brazilian patients

Background

Ser-249 TP53 mutation (249^Ser) is a molecular evidence for aflatoxin-related carcinogenesis in Hepatocellular Carcinoma (HCC) and it is frequent in some African and Asian regions, but it is unusual in Western countries. HBV has been claimed to add a synergic effect on genesis of this particular mutation with aflatoxin. The aim of this study was to investigate the frequency of 249^Ser mutation in HCC from patients in Brazil.

Methods

We studied 74 HCC formalin fixed paraffin blocks samples of patients whom underwent surgical resection in Brazil. 249^Ser mutation was analyzed by RFLP and DNA sequencing. HBV DNA presence was determined by Real-Time PCR.

Results

249^Ser mutation was found in 21/74 (28%) samples while HBV DNA was detected in 13/74 (16%). 249^Ser mutation was detected in 21/74 samples by RFLP assay, of which 14 were confirmed by 249^Ser mutant-specific PCR, and 12 by nucleic acid sequencing. All HCC cases with p53-249ser mutation displayed also wild-type p53 sequences. Poorly differentiated HCC was more likely to have 249^Ser mutation (OR = 2.415, 95% CI = 1.001 – 5.824, p = 0.05). The mean size of 249^Ser HCC tumor was 9.4 cm versus 5.5 cm on wild type HCC (p = 0.012). HBV DNA detection was not related to 249^Ser mutation.

Conclusion

Our results indicate that 249^Ser mutation is a HCC important factor of carcinogenesis in Brazil and it is associated to large and poorly differentiated tumors.

The epidemiology of hepatocellular cancer: from the perspectives of public health problem to tumor biology

The epidemiology of hepatocellular cancer (HCC) can be viewed from several important perspectives. The conventional perspective includes the overall public health impact of HCC, which is increasing in incidence in many regions of the world. The epidemiology of HCC can also be viewed from the perspective of variation in underlying disease associations such as viral hepatitis or the recently recognized link to nonalcoholic fatty liver disease (NAFLD). Of perhaps increasing importance with recent advances in therapy of HCC, the epidemiology of HCC can also be viewed from the perspective of variation in HCC biology. This lesser known perspective may depend in part on the underlying liver disease and the cell origin of the cancer, whether of hepatocyte or stem cell origin. This aspect is likely to become central to diagnosis and management of HCC with the further development of targeted therapeutics. The relative efficacy of these agents will likely depend on the biochemical pathways active in a given hepatocellular malignancy. This, in turn, is likely to be related to the epidemiological associations of HCC.

Quantitative analysis and chronic dosimetry of the aflatoxin B1 plasma albumin adduct Lys-AFB1 in rats by isotope dilution mass spectrometry

Aflatoxin B1 (AFB1) is a major risk factor in the pathogenesis of liver cancer in Asia and sub-Saharan Africa. Biomarkers reflecting exposure will facilitate disease risk assessment and the efficacy of protective interventions in these populations. The Lys-AFB1 adduct in plasma albumin is a candidate biomarker for this role. Although aflatoxin albumin adducts are most frequently measured in epidemiological studies using an enzyme-linked immunosorbent assay, a more specific and 10-fold more sensitive isotopic dilution mass spectrometric assay for Lys-AFB1 has recently become available. Here, the dosimetry of chronically administered AFB1 at lower doses than have been previously studied was explored using this assay. AFB1 was administered to rats for nine consecutive days at eight dose levels ranging from 50 pg to 55 microg/kg body wt. Plasma samples were enzymatically digested and processed by solid phase extraction. Lys-AFB1 was isolated by HPLC and detected via selected reaction monitoring. The dose-response relationship was linear-quadratic exhibiting upward curvature at higher doses. The adduct yield [(pg Lys-AFB1/mg albumin)/(microg AFB1/kg body wt)] increased nonlinearly with the dose by 6-fold between the 0.05 and 55 microg AFB1/kg body wt groups and exhibited the onset of saturation in the highest dose group where the adduct yield was approximately 2%. Incomplete knowledge of the timing of exposure and the complexity of the underlying biology confound the precise determination of prior AFB1 exposures in humans; however, the dosimetry of AFB1 observed in chronically dosed rats conceptually suggests that measurements in humans may underestimate exposure if a constant fraction of the AFB1 dose, approximately 2%, is assumed to be converted to Lys-AFB1 without regard to the dose.

Genetic alterations in cancer knowledge system: analysis of gene mutations in mouse and human liver and lung tumors

Mutational incidence and spectra for genes examined in both human and mouse lung and liver tumors were analyzed using the National Institute of Environmental Health Sciences (NIEHS) Genetic Alterations in Cancer (GAC) knowledge system. GAC is a publicly available, web-based system for evaluating data obtained from peer-reviewed studies of genetic changes in tumors associated with exposure to chemical, physical, or biological agents, as well as spontaneous tumors. In mice, mutations in Kras2 and Hras-1 were the most common events reported for lung and liver tumors, respectively, whether chemically induced or spontaneous. There was a significant difference in Kras2 mutation incidence for spontaneous versus induced mouse lung tumors and in Hras-1 mutation incidence and spectrum for spontaneous versus induced mouse liver tumors. The major gene changes reported for human lung and liver tumors were in KRAS2 (lung only) and TP53. The KRAS2 mutation incidence was similar for spontaneous and asbestos-induced human lung tumors, while the TP53 mutation incidence differed significantly. Aflatoxin B1, hepatitis B virus, hepatitis C virus, and vinyl chloride all caused TP53 mutations in human liver tumors, but the mutation spectrum for each agent differed. The incidence of KRAS2 mutations in human compared to mouse lung tumors differed significantly, as did the incidence of Hras and p53 gene mutations in human compared to mouse liver tumors. Differences observed in the mutation spectra for agent-induced compared to spontaneous tumors and similarities in spectra for structurally similar agents support the concept that mutation spectra can serve as a "fingerprint" of exposure based on chemical structure.

Environmental factors and risk for hepatocellular carcinoma

Chronic infections with hepatitis B virus (HBV) and hepatitis C virus (HCV) are the most important risk factors for the development of hepatocellular carcinoma (HCC) in humans. HBV is the primary cause of HCC in high-risk areas including China and Africa, whereas in developed countries such as the United States, HCV plays a more prominent role and is at least partially responsible for the increase in HCC incidence in this country. Humans are exposed to hepatocarcinogenic aflatoxins through ingestion of moldy foods, a consequence of poor storage of susceptible grains. Highly exposed populations are primarily in sub-Sahara Africa and Asia, where dietary aflatoxins significantly enhance the carcinogenic effects of viral hepatitis. Heavy, long-term alcohol use is a risk factor for HCC, whereas moderate use (1-3 drinks/day) is not. Constituents of cigarette smoke are hepatic carcinogens in animals, and there is mounting evidence that the liver is an organ susceptible to tobacco carcinogenicity. Diabetic patients are at risk for HCC probably as a result of the hepatic injury, fibrosis, and eventual cirrhosis resulting from fatty liver disease. Given the current epidemic of obesity and diabetes in the United States, this risk factor will be increasingly important. Increased risk for HCC is evident in young noncirrhotic users of oral contraceptives in the United States and Europe. In summary, risk factors for HCC are identifiable in most patients and primarily are associated with chronic hepatic injury.