Policy forum: public health. Reducing liver cancer--global control of aflatoxin

Ochratoxins: a global perspective

Ochratoxins have been overshadowed by better-known mycotoxins, but they are gaining importance. Here we consider ochratoxins in the context of aflatoxins, which are better understood than ochratoxins on many levels. We review recent work on taxonomic distribution, contamination of commodities, biosynthesis, toxicity and regulatory aspects of ochratoxins. We focus on ochratoxins in coffee, since coffee is becoming a key commodity in ochratoxin research and regulation.

Viral hepatitis and liver cancer: the case of hepatitis C

Chronic infection with the hepatitis C virus (HCV) is a major risk factor for the development of hepatocellular carcinoma (HCC) worldwide. The pathogenesis of HCC in HCV infection has extensively been analysed. Hepatitis C virus-induced chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation are considered as one of the major pathogenic mechanisms. Increasing experimental evidence suggests that HCV contributes to HCC by directly modulating pathways that promote the malignant transformation of hepatocytes. Hepatitis C virus is an RNA virus that does not integrate into the host genome but HCV proteins interact with many host-cell factors well beyond their roles in the viral life cycle and are involved in a wide range of activities, including cell signaling, transcription, cell proliferation, apoptosis, membrane rearrangements, vesicular trafficking and translational regulation. At least four of the HCV gene products, namely HCV core, NS3, NS4B and NS5A, have been shown to exhibit transformation potential in tissue culture and several potentially oncogenic pathways have been shown to be altered by the expression of HCV proteins. Both HCV core and NS5A induce the accumulation of wild-type beta-catenin and the Wnt-beta-catenin pathway emerges as a common target for HCV (and HBV) in human HCCs, also independently from axin/beta-catenin gene mutations. Induction of both endoplasmic reticulum stress and oxidative stress by HCV proteins might also contribute to HCV transformation. Most of the putative transforming functions of the HCV proteins have been defined in artificial cellular systems, which may not be applicable to HCV infection in vivo, and still need to be established in relevant infection and disease models.

Mycotoxin Reduction in Bt Corn: Potential Economic, Health, and Regulatory Impacts

Genetically modified (GM) Bt corn, through the pest protection that it confers, has lower levels of mycotoxins: toxic and carcinogenic chemicals produced as secondary metabolites of fungi that colonize crops. In some cases, the reduction of mycotoxins afforded by Bt corn is significant enough to have an economic impact, both in terms of domestic markets and international trade. In less developed countries where certain mycotoxins are significant contaminants of food, Bt corn adoption, by virtue of its mycotoxin reduction, may even improve human and animal health. This paper describes an integrated assessment model that analyzes the economic and health impacts of two mycotoxins in corn: fumonisin and aflatoxin. It was found that excessively strict standards of these two mycotoxins could result in global trade losses in the hundreds of millions US dollars annually, with the US, China, and Argentina suffering the greatest losses. The paper then discusses the evidence for Bt corn's lower levels of contamination of fumonisin and aflatoxin, and estimates economic impacts in the United States. A total benefit of Bt corn's reduction of fumonisin and aflatoxin in the US was estimated at 23 million dollars annually. Finally, the paper examines the potential policy impacts of Bt corn's mycotoxin reduction, on nations that are making a decision on whether to allow commercialization of this genetically modified crop.

Determinants of aflatoxin levels in Ghanaians: sociodemographic factors, knowledge of aflatoxin and food handling and consumption practices

Aflatoxins are among the most potent of carcinogens found in staple foods such as groundnuts, maize and other oil seeds. This study was conducted to measure the levels of aflatoxin B(1) (AFB(1)) albumin adducts in blood and aflatoxin M(1) (AFM(1)) metabolite in urine of people in a heavy peanut and maize consuming region of Ghana and to examine the association between aflatoxin levels and several socio-demographic factors and food handling and consumption practices. A cross-sectional study was conducted in four villages in the Ejura Sekyedumase district of Ghana. A socio-demographic survey was administered to 162 participants. Blood samples were collected from 140 and urine samples from 91 of the participants and AFB(1) albumin-adduct levels in blood and AFM(1) levels in urine were measured. High AFB(1) albumin-adduct levels were found in the plasma (mean+/-SD=0.89+/-0.46pmol/mg albumin; range=0.12-3.00pmol/mg; median=0.80pmol/mg) and high AFM(1) levels in the urine (mean+/-SD=1,800.14+/-2602.01pg/mg creatinine; range=non-detectable to 11,562.36pg/mg; median=472.67pg/mg) of most of the participants. There was a statistically significant correlation (r=0.35; p=0.007) between AFB(1)-albumin adduct levels in plasma and AFM(1) levels in urine. Several socio-demographic factors, namely, educational level, ethnic group, the village in which participants lived, number of individuals in the household, and number of children in the household attending secondary school, were found to be significantly associated with AFB(1) albumin-adduct levels by bivariate analysis. By multivariate analyses, ethnic group (p=0.04), the village in which participants live (p=0.02), and the number of individuals in the household (p=0.01), were significant predictors of high AFB(1) albumin-adducts. These findings indicate strongly that there is need for specifically targeted post-harvest and food handling and preparation interventions designed to reduce aflatoxin exposure among the different ethnic groups in this region of Ghana.

Effect of dietary honey on intestinal microflora and toxicity of mycotoxins in mice

BACKGROUND

Bee honey is a functional food which has a unique composition, antimicrobial properties and bifidogenic effect. In order to assess whether honey can inhibit the toxic effect of mycotoxins, the present study was undertaken.

METHODS

Production of biomass and toxins by Aspergillus parasiticus and Aspergillus ochraceus were followed in media without and with honey. Although aflatoxins and ochratoxin A. were administrated to male Swiss albino mice up to 1 mug and 10 ng/kg body weight/day respectively. The experimental animals were fed diets without our with 10% honey for two months. The changes in colonic probiotic bacteria, determintal colon enzyme glucuronidases, and genotoxicity were followed.

RESULTS

Addition of 32% in its media increased the biomass of A parasiticus, while the biomass of A. ochraceus decreased and Ochratoxin A. was not produced. When the honey was added at the ratio of 32 and 48% in the medium. No relationship was found between mycelium weight and production of mycotoxins. Oral administration of aflatoxins (mixture of B1, B2, G1 and G2) and Ochratoxin A. induced structural and numerical chromosomal aberrations in bone marrow and germ cells of male mice, whereas, honey treatment reduced the genotoxicity of mycotoxins. Also both toxins induced histopathological changes in liver and kidney. Feeding on diet supplemented with honey improved the histopathological changes in case of aflatoxin group, but not in the case of ochratoxin A. group (except of kidney in two cases). No significant differences were found in the activity of colon beta-glucuronidase between group fed diet with or without honey. On the other hand, the colon bifido bacteria and lactobacilli counts were increased markedly in group receiving diet supplemented with honey.

CONCLUSION

Substituting sugars with honey in processed food can inhibit the harmful and genotoxic effects of mycotoxins, and improve the gut microflora.

The function of breast cancer resistance protein in epithelial barriers, stem cells and milk secretion of drugs and xenotoxins

The breast cancer resistance protein [BCRP (also known as ABCG2)] belongs to the ATP binding cassette (ABC) family of transmembrane drug transporters. BCRP has a broad substrate specificity and actively extrudes a wide variety of drugs, carcinogens and dietary toxins from cells. Situated in the apical plasma membrane of epithelial cells of the small and large intestine and renal proximal tubules and in the bile canalicular membrane of hepatocytes, BCRP decreases the oral availability and systemic exposure of its substrates. In several blood-tissue barriers BCRP reduces tissue penetration of its substrates and it protects haematopoietic stem cells from cytotoxic substrates. Moreover, BCRP is expressed in mammary gland alveolar epithelial cells during pregnancy and lactation, where it actively secretes a variety of drugs, toxins and carcinogens into milk. In apparent contradiction with the detoxifying role of BCRP in mothers, this contamination of milk exposes suckling infants and dairy consumers to xenotoxins. BCRP thus affects many important aspects of pharmacology and toxicology.

Dietary fibres as "prebiotics": implications for colorectal cancer

A "prebiotic" is a nondigestible food ingredient whose beneficial effects on the host result from the selective stimulation of growth and/or activity of members of the bacterial community that inhabits the human bowel (the gut microbiota). Although much of the prebiotic literature focuses on nondigestible oligosaccharides, such as oligofructose, most dietary fibres that are fermentable carbohydrates could be considered as prebiotics. Early studies suggested that colonic bacteria were risk factors for colon cancer. However, altering the composition or metabolic activity of the bowel microbiota through the use of dietary fibre might be important in reducing the prevalence of colorectal cancer. Mechanisms for beneficial effects of prebiotics might include changing the activity of exogenous carcinogens through modulating metabolic activation and/or detoxification, or stimulating the production of the short-chain fatty acid, butyrate. However, modern analytical techniques suggest that an important consequence of a modified bacterial community could be a change in the expression not only of a range of different bacterial genes in bowel contents, but also in the bowel mucosa of the host. Analogous with observations with probiotics, the stimulation of cytokines and modification of immune responses could be important in producing beneficial effects. Compared with transitory effects of probiotics, the prebiotic action of fermentable carbohydrates potentially provide the opportunity for sustainable modulation of activity of the gut microbiota. However, their mechanisms of action in humans are speculative, and research aimed at providing an integrated view of the gut microbiota and dietary fibre nutrition of humans needs to be developed.

Breast cancer resistance protein (Bcrp1/Abcg2) reduces systemic exposure of the dietary carcinogens aflatoxin B1, IQ and Trp-P-1 but also mediates their secretion into breast milk

The breast cancer resistance protein (BCRP/ABCG2) usually protects the body from a wide variety of environmental and dietary xenotoxins by reducing their net uptake from intestine and by increasing their hepatobiliary, intestinal and renal elimination. BCRP is also highly expressed in lactating mammary glands in mice, and this expression is conserved in cows and humans. As a result, BCRP substrates can be secreted into milk. We investigated whether different classes of dietary carcinogens are substrates of Bcrp1/BCRP and the implications for systemic exposure and breast milk contamination. Using polarized cell lines, we found that Bcrp1 transports the heterocyclic amines 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and the potent human hepatocarcinogen aflatoxin B1, and decreases their cellular accumulation up to 10-fold. In vivo pharmacokinetic studies showed that [14C]IQ, [14C]Trp-P-1 and [3H]aflatoxin B1 plasma levels were substantially lower in wild-type compared with Bcrp1-/- mice, after both oral and intravenous administration, demonstrating that Bcrp1 restricts systemic exposure to these carcinogens. Moreover, Bcrp1 mediates transfer of [14C]IQ, [14C]Trp-P-1 and [3H]aflatoxin into milk, with 3.4+/-0.6, 2.6+/-0.3 and 3.8+/-0.5-fold higher milk to plasma ratios, respectively, in lactating wild-type versus Bcrp1-/- mice. We have thus identified Bcrp1/BCRP as one of the molecular mechanisms by which heterocyclic amines and aflatoxin are transferred into milk, thereby posing a health risk to breast-fed infants and dairy consumers. Paradoxically, Bcrp1/BCRP appears to have both protective and adverse roles with respect to exposure to dietary carcinogens.

Pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumours worldwide. The major aetiologies and risk factors for the development of HCC are well defined and some of the multiple steps involved in hepatocarcinogenesis have been elucidated in recent years. However, no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Malignant transformation of hepatocytes may occur as a consequence of various aetiologies, such as chronic viral hepatitis, alcohol, and metabolic disorders, in the context of increased cellular turnover induced by chronic liver injury, regeneration and cirrhosis. Activation of cellular oncogenes, inactivation of tumour suppressor genes, genomic instability, including DNA mismatch repair defects and impaired chromosomal segregation, overexpression of growth and angiogenic factors, and telomerase activation may contribute to the development of HCC. Overall, HCCs are genetically very heterogeneous tumours. New technologies, including gene expression profiling and proteomic analyses, should allow us to further elucidate the molecular events underlying HCC development and identify novel diagnostic markers as well as therapeutic targets.

Increased levels of aflatoxin-albumin adducts are associated with CYP3A5 polymorphisms in The Gambia, West Africa

OBJECTIVES

Major risk factors for hepatocellular carcinoma (HCC) are hepatitis viruses and exposure to aflatoxins, including aflatoxin B1 (AFB1). The mutagenic effect of AFB1 results from hepatic bioactivation to AFB1-exo-8,9-epoxide. This is in part catalysed by CYP3A5, an enzyme expressed polymorphically. We investigated the role of CYP3A5 polymorphisms in the formation of AFB1-exo-8,9-epoxide in The Gambia, a population exposed to high aflatoxin levels.

METHODS

Common CYP3A5 polymorphisms were identified in an African-American population. Subsequently, 288 Gambian subjects were genotyped and CYP3A5 activity predicted using haplotypes of the three variant loci (CYP3A5*3, *6 and *7) associated with decreases in protein expression. CYP3A5 expression was then compared to aflatoxin-albumin (AF-alb) adduct, a biomarker of AFB1 bioactivation; data were also analysed in relation to expression of other aflatoxin-metabolizing enzymes.

RESULTS

CYP3A5 haplotypes reflecting high CYP3A5 protein expression were associated with increased AF-alb. Compared to individuals with predicted low expression those predicted to express CYP3A5 from one allele displayed 16.1% higher AF-alb (95% CI: -2.5, 38.2, P = 0.093) and homozygous expressers displayed 23.2% higher AF-alb levels (95% CI: -0.01, 52.0, P = 0.051). The effect of the CYP3A5 polymorphism was strongest in individuals with low CYP3A4 activity with a 70.1% increase in AF-alb (95% CI: 11.8, 158.7, P < 0.05) in high compared to low expressers. A similar effect was observed for individuals with null alleles of GSTM1, which conjugates the AFB1-exo-8,9-epoxide to reduced glutathione.

CONCLUSIONS

The CYP3A5 polymorphism is associated with increased levels of the mutagenic AFB1-exo-8,9-epoxide, particularly in individuals with low CYP3A4, and this may modulate individual risk of HCC.

Immunogenicity in humans of an edible vaccine for hepatitis B

A double-blind placebo-controlled clinical trial evaluated the immunogenicity of hepatitis B surface antigen (HBsAg) expressed in potatoes and delivered orally to previously vaccinated individuals. The potatoes accumulated HBsAg at approximately 8.5 microg/g of potato tuber, and doses of 100 g of tuber were administered by ingestion. The correlate of protection for hepatitis B virus, a nonenteric pathogen, is blood serum antibody titers against HBsAg. After volunteers ate uncooked potatoes, serum anti-HBsAg titers increased in 10 of 16 volunteers (62.5%) who ate three doses of potatoes; in 9 of 17 volunteers (52.9%) who ate two doses of transgenic potatoes; and in none of the volunteers who ate nontransgenic potatoes. These results were achieved without the coadministration of a mucosal adjuvant or the need for buffering stomach pH. We conclude that a plant-derived orally delivered vaccine for prevention of hepatitis B virus should be considered as a viable component of a global immunization program.

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.

Inheritance of resistance to aflatoxin production and Aspergillus ear rot of corn from the cross of inbreds b73 and oh516

ABSTRACT Our objective was to determine the value of corn (Zea mays) inbred Oh516 as a source of resistance to Aspergillus ear rot and aflatoxin accumulation in grain. Types and magnitudes of gene action associated with resistance were determined with generation means analysis. Molecular markers associated with resistance were identified from BCP(1)S(1) families developed from the cross of the susceptible inbred B73 and Oh516. In 2001 and 2002, B73 (P(1)), Oh516 (P(2)), and the F(1), F(2), F(3), BCP(1), BCP(2), and BCP(1)S(1) generations were evaluated for aflatoxin concentration in grain, percent bright greenish yellow fluorescence (BGYF), and severity of Aspergillus ear rot following inoculation in Urbana, IL. BCP(1)S(1) families testcrossed with LH185 also were evaluated at three locations in 2002. Molecular marker-quantitative trait loci (QTL) associations with all traits were determined with single factor analysis of variance. Dominance gene action was associated with aflatoxin concentration in grain and percent BGYF. QTL associated with aflatoxin accumulation in grain were identified on chromosomes 2, 3, and 7 (bins 2.01 to 2.03, 2.08, 3.08, and 7.06). Alleles from inbred Oh516 on chromosomes 2, 3, and 7 should improve resistance of commercially used, B73-type inbreds.

Mycotoxin risk assessment for the purpose of setting international regulatory standards

The 2003 Council for Agricultural Science and Technology Mycotoxin report states that one 21st century goal is the development of uniform regulations worldwide for foodborne mycotoxin contamination. This study informs that endeavor by a risk assessment and economic analysis of two important mycotoxins: fumonisins and aflatoxins. The goals are to identify the nations that would be most heavily impacted by tighter mycotoxin regulations, examine costs and benefits as a function of regulatory stringency, and address risk-risk tradeoffs between health benefits and economic losses from compliance with those regulations. Among industrial nations, the United States would experience the heaviest economic losses from more precautionary mycotoxin standards. Environmental conditions in the developing world, however, are more conducive to mycotoxin accumulation in crops. Contrary to concerns expressed among policymakers, the less developed countries that would likely experience the greatest loss from tighter mycotoxin standards are not sub-Saharan African nations, but China and Argentina. If a fumonisin standard of 0.5 mg/kg were adopted worldwide, total export losses from fumonisins in corn may exceed 300 million dollars annually: 3-fold higher than if the less stringent U.S. standard of 2 mg/kg were adopted. Likewise, export losses from aflatoxins in peanuts may exceed 450 million dollars under the current EU regulatory standard of 4 microg/kg: almost 5-fold higher than if the U.S. standard of 20 microg/kg were adopted. Stricter standards are unlikely to improve health significantly. In developing nations such as China where hepatitis B and C are prevalent, tighter aflatoxin standards may increase health risks until improved control methods for aflatoxins are found, as high-quality crops may be exported instead of being consumed domestically.

Detection and identification of tumor-associated protein variants in human hepatocellular carcinomas

The proteomic approach is a valuable tool to detect and identify proteins that are associated with cancer. In previous investigations on experimentally induced rat hepatomas, we detected aldose reductase-like protein (ARLP) as a highly significant marker protein. Our present study was intended to look for the presence of similar tumor-associated marker proteins on human hepatocellular carcinomas (HCC). We found several novel tumor-associated protein variants that represent members of the aldo-keto reductase (AKR) superfamily. Human aldose reductase-like protein-1 (hARLP-1) was the most prominent tumor-associated AKR member detected in HCC by 2-dimensional electrophoresis (2-DE) and identified by mass spectrometric fingerprinting. The enzyme was found in 4 distinct forms (hARLP-1, 36/7.4 (kd/pI); hARLP-2, 36/7.2; hARLP-3, 36/6.4; and hARLP-4, 33/7.35). In addition, a human aldose reductase-like protein (hARLP-5, 36/7.6) was identified that differed from hARLP-1 by 1 amino acid (D313N), indicating 2 allelic forms of the human aldose reductase-like gene. A novel antibody directed against common parts of the hARLPs revealed hARLP reactivity in human HCC by immunohistochemistry. Furthermore, aldose reductase (AR) was identified and characterized as a tumor-associated variant. In conclusion, in all investigated human HCCs at least one of the various types of the described tumor-associated proteins of the AKR superfamily was clearly present. Of these HCC samples, 95% were positive for hARLPs as proven by 2-DE analysis and/or by use of the antibody directed against hARLP. Thus, hARLP is a strong candidate for use as an immunohistochemical diagnostic marker of human HCC.

Identification of genes differentially expressed during aflatoxin biosynthesis in Aspergillus flavus and Aspergillus parasiticus

A complex regulatory network governs the biosynthesis of aflatoxin. While several genes involved in aflatoxin production are known, their action alone cannot account for its regulation. Arrays of clones from an Aspergillus flavus cDNA library and glass slide microarrays of ESTs were screened to identify additional genes. An initial screen of the cDNA clone arrays lead to the identification of 753 unique ESTs. Many showed sequence similarity to known metabolic and regulatory genes; however, no function could be ascribed to over 50% of the ESTs. Gene expression analysis of Aspergillus parasiticus grown under conditions conducive and non-conductive for aflatoxin production was evaluated using glass slide microarrays containing the 753 ESTs. Twenty-four genes were more highly expressed during aflatoxin biosynthesis and 18 genes were more highly expressed prior to aflatoxin biosynthesis. No predicted function could be ascribed to 18 of the 24 genes whose elevated expression was associated with aflatoxin biosynthesis.

Mycotoxins

Mycotoxins are secondary metabolites produced by microfungi that are capable of causing disease and death in humans and other animals. Because of their pharmacological activity, some mycotoxins or mycotoxin derivatives have found use as antibiotics, growth promotants, and other kinds of drugs; still others have been implicated as chemical warfare agents. This review focuses on the most important ones associated with human and veterinary diseases, including aflatoxin, citrinin, ergot akaloids, fumonisins, ochratoxin A, patulin, trichothecenes, and zearalenone.

Paradoxical effects of chemicals in the diet on health

In 1992, Block et al. published a summary of 200 epidemiological investigations which indicated that a diet that was high in fruit and vegetables cut cancer risks approximately in half. These investigations used conventionally farmed produce that contained traces of synthetic pesticides and mycotoxins as well as an estimated 10,000 secondary products (i.e. natural pesticides). Dietary consumption of fruits and vegetables also reduces risks of cardiovascular disease, cataracts and brain dysfunction. Before genetic manipulation is undertaken to elevate or diminish any individual constituent of fruits and vegetables, the contribution of each of these constituents to health must be better understood, as in many cases their effects on health can be paradoxical.

Aspergillus on tree nuts: incidence and associations

California exports tree nuts to countries where they face stringent standards for aflatoxin contamination. Trade concerns have stimulated efforts to eliminate aflatoxins and Aspergillus flavus from almonds, pistachios and walnuts. Incidence of fungi on tree nuts and associations among fungi on tree nuts were studied. Eleven hundred pistachios, almonds, walnuts and brazil nuts without visible insect damage were plated on salt agar and observed for growth of fungi. Samples came both from California nut orchards and from supermarkets. To distinguish internal fungal colonization of nuts from superficial colonization, half the nuts were surface-sterilized before plating. The most common genera found were Aspergillus, Rhizopus and Penicillium. Each species of nut had a distinct mycoflora. Populations of most fungi were reduced by surface sterilization in all except brazil nuts, suggesting that they were present as superficial inoculum on (rather than in) the nuts. In general, strongly positive associations were observed among species of Aspergillus; nuts infected by one species were likely to be colonized by other species as well. Presence of Penicillium was negatively associated with A. niger and Rhizopus in some cases. Results suggest that harvest or postharvest handling has a major influence on nut mycoflora, and that nuts with fungi are usually colonized by several fungi rather than by single species.

Effects of some groundnut packaging methods and protection with Ocimum and syzygium powders on kernel infection by fungi

Powders from the leaves of Ocimum gratissimum and cloves of Syzygium aromaticum were used as protectants at 3% (w/w) in combination with various packaging methods to store 3.5 kg groundnut kernel samples (9.3% moisture) artificially inoculated with Aspergillus parasiticus. Phostoxin-protected and unprotected samples were the controls. Packaging was accomplished with (i) Jute bags; JB (ii) Interlaced polypropylene bags; IPPB (iii) Polyethylene bags; PB (iv) PB inserted into IPPB and (v) PB inserted into JB. Selected treatments were repeated concurrently with naturally infected kernels (6.6% moisture). With 9.3% moisture kernels, there was a highly significant protectant, packaging method, and protectant X packaging method effect on protection of kernels from fungal infection at 2, 4, and 6 months. Packaging with JB and IPPB with or without plant powders gave 100% protection against fungi but insect infestation was prevented only when the Syzygium powder was used. When PB was used either singly or in combination with JB and IPPB, 100% protection from fungi was achieved up to 2 months with the Ocimum and up to 4 months with the Syzygium powder. The phostoxin treatment also gave 100% protection with JB and IPPB packaging but was ineffective with PB packaging. Kernels packaged with PB without the powders were extensively mouldy. Kernels with natural mycoflora (6.6% moisture) were free from fungi at 6 months regardless of the protectant and packaging used. In further tests, the Syzygium powder, at 3% and in combination with JB-packaging, effectively suppressed cross infection of healthy kernels (12% moisture) by fungi from diseased kernels when both kernel types occurred in the same lot. At 18.5% kernel moisture and with identical packaging, the Syzygium powder at 3%, was not as effective.

Effect of processing on aflatoxin

Naturally occurring toxicant contamination of foods with mycotoxins is unavoidable and unpredictable and poses a unique challenge to food safety. Aflatoxins are toxic mold metabolites produced by toxigenic strains of Aspergillus species. Primary commodities susceptible to aflatoxin contamination include corn, peanuts and cottonseed and animal-derived foods such as milk when the animal is fed aflatoxin-contaminated feed. Risks associated with aflatoxin-contaminated foods can be reduced through the use of specific processing and decontamination procedures. Factors, which influence the effectiveness of a specific process or procedure, include the chemical stability of the mycotoxin(s), nature of the process, type and interaction with the food/feed matrix and interaction with multiple mycotoxins if present. Practical decontamination procedures must: 1) inactivate, destroy, or remove the toxin, 2) not produce or leave toxic residues in the food/feed, 3) retain the nutritive value of the food/feed, 4) not alter the acceptability or the technological properties of the product, and, if possible, 5) destroy fungal spores. For aflatoxins, multiple processing and/or decontamination schemes have been successful in reducing aflatoxin concentrations to acceptable levels. Physical cleaning and separation procedures, where the mold-damaged kernel/seed/nut is removed from the intact commodity, can result in 40-80% reduction in aflatoxins levels. Processes such as dry and wet milling result in the distribution of aflatoxin residues into less utilized fractions of the commodity. The ammoniation of aflatoxin-contaminated commodities has altered the concentrations as well as toxic and carcinogenic effects of aflatoxin by greater than 99%. Nonbiological materials such as selected anticaking agents covalently bind aflatoxins from aqueous suspensions, diminish aflatoxin uptake by animals, prevent acute aflatoxicosis, and decrease aflatoxin residues in milk. Ultimately, the best processing or decontamination process is one that is approved by regulatory agencies, cost-effective, and reduces the mycotoxin concentration to acceptable levels.

The Yakult International Conference, Probiotics & Health 2001, The Three Ages of Man. Was held at The Royal College of Physicians in London on 13-14 September 2001

The papers in these proceedings truly reflect the wide nature of research work that is being undertaken and the advances that have been achieved particularly in the therapeutic application of probiotics. All abstracts are available as pdf and html format.

Development of a fluorescence polarization assay for the determination of aflatoxins in grains

Aflatoxins produced by Aspergillus flavus are commonly found in human and animal foods including grains, cereals, peanut products, sorghum, and soy seeds. Exposure to aflatoxins has been associated with carcinogenicity. This paper reports a simple, portable, and rapid fluorescence polarization (FP) assay for aflatoxin determination in grains. This immunoassay is field portable, homogeneous, and without any washing and cleaning steps. The assay is based upon the competition between free aflatoxin and an aflatoxin-fluorescein tracer for an aflatoxin-specific monoclonal antibody in solution. A series of naturally contaminated corn, sorghum, peanut butter, and peanut paste samples were analyzed by FP and compared with HPLC results. Similarly, spiked popcorn samples were analyzed by FP. FP results of naturally contaminated samples correlated well with HPLC (r (2) = 0.97). FP analysis of spiked popcorn samples (with a mixture of B(1)/B(2)/G(1)/G(2), 7/1/3/1, w/w) gave a good correlation with spiked values (r (2) = 0.99). However, FP consistently underestimated the aflatoxin contents. This was perhaps due to low cross-reactivity of the antibody used toward B(2), G(1), and G(2) aflatoxins. These results combined with the portability and simplicity of the assay suggest that the assay can be used for screening total aflatoxin in grains.

Restriction fragment length polymorphism assessment of the heterogeneous nature of maize population GT-MAS:gk and field evaluation of resistance to aflatoxin production by Aspergillus flavus

Aflatoxin, produced by Aspergillus flavus, is one of the most toxic and carcinogenic substances known and contaminates many agricultural commodities such as corn, peanuts, cottonseed, and tree nuts. The challenge to breeders/plant pathologists is to identify lines that have resistance to aflatoxin production. Maize population GT-MAS:gk has been identified and released as a germplasm with resistance to aflatoxin contamination. In the present study, we assessed genetic divergence in the GT-MAS:gk population using restriction fragment length polymorphism (RFLP) DNA markers to survey 11 selfed inbred lines and conducted field evaluations for the dissimilarities in aflatoxin production among these inbred lines in comparison with a sister population, GT-MAS:pw.nf. The 11 selfed inbred lines were assayed for DNA polymorphism using 113 RFLP markers in 10 linkage groups covering 1,518.2 centimorgans (cM; unit of gene or chromosome size). Considerable variation among the inbreds was detected with RFLP markers, of which 42 probe-enzyme combinations gave 102 polymorphic bands. Cluster analysis based on genetic similarities revealed associations and variations among the tested lines. Three polymorphic groups were distinguished by cluster analysis. Two years of field evaluation data showed that aflatoxin concentrations among the lines were significantly different in both years (P < 0.001). Maturity data were also different. Thus, this study demonstrates that the maize population GT-MAS:gk is heterogeneous and that individuals may be different in resistance to A. flavus infection and aflatoxin production. Therefore, the most resistant lines should be inbred to increase homogeneity, and resistance should be confirmed through progeny testing.

The genetic determinants of the CYP3A5 polymorphism

CYP3A proteins comprise a significant portion of the hepatic cytochrome P450 (CYP) protein and they metabolize around 50% of drugs currently in use. The dissection of the individual contributions of the four CYP3A genes identified in humans to overall hepatic CYP3A activity has been hampered by sequence and functional similarities. We have investigated the expression of CYP3A5 and its genetic determinants in a panel of 183 Caucasian liver samples. CYP3A5 expression is increased in 10% of livers in this ethnic group. Using a high density map of CYP3A5 variants, we searched for genetic markers of the increased CYP3A5 expression. In agreement with an independent, recent study, we report that a SNP within intron 3 (g.6986G>A) is the primary cause of the CYP3A5 protein polymorphism. The frequencies of the g.6986A variant which allow for normal splicing of CYP3A5 transcripts are 5% in Caucasians, 29% in Japanese, 27% in Chinese, 30% in Koreans and 73% in African-Americans. In the last ethnic group, the expression of CYP3A5 in some individuals who carry the g.6986A variant is affected adversely by a frame shift mutation (CYP3A5*7, D348., q = 0.10). In summary, these results should add to efforts to identify clinically relevant, CYP3A5-specific reactions and to further elucidate traits responsible for variable expression of the entire CYP3A family.

Inhibitory effects of naturally occurring compounds on aflatoxin B(1) biotransformation

Effects of naturally occurring compounds from plants on biotransformation of a mycotoxin, aflatoxin B(1), were evaluated. Among 77 naturally occurring compounds tested, anthraquinones, coumarins, and flavone-type flavonoids were shown to be potent inhibitors of aflatoxin B(1)-8,9-epoxide formation. Addition of the flavonoids galangin, rhamnetin, and flavone strongly inhibited mouse liver microsomal conversion of aflatoxin B(1) to aflatoxin B(1)-8,9-epoxide, a metabolically activated mutagenic product. In contrast to these results, addition of isoflavonoids, catechins, terpenes, alkaloids, and quinones to mouse liver microsomes did not inhibit formation of aflatoxin B(1)-8,9-epoxide. Formation of the aflatoxin B(1) reductase product, aflatoxicol, by chicken liver cytosols was strongly inhibited by curcumin, the diferuloylmethane present in turmeric and other Curcuma species. Curcumin analogues also showed inhibitory effects, and a structure-activity study established that beta-diketone groups linked with two benzyl moieties were essential for inhibition of aflatoxicol formation. An additional 37 naturally occurring compounds tested did not inhibit formation of aflatoxicol. These results demonstrate that dietary constituents in certain fruits, vegetables, and spices may have significant inhibitory effects on metabolic transformation of aflatoxins to their hepatotoxic or carcinogenic derivatives or, alternatively, may promote their transformation into nontoxic products.

Surface binding of aflatoxin B(1) by lactic acid bacteria

Specific lactic acid bacterial strains remove toxins from liquid media by physical binding. The stability of the aflatoxin B(1) complexes formed with 12 bacterial strains in both viable and nonviable (heat- or acid-treated) forms was assessed by repetitive aqueous extraction. By the fifth extraction, up to 71% of the total aflatoxin B(1) remained bound. Nonviable bacteria retained the highest amount of aflatoxin B(1). Lactobacillus rhamnosus strain GG (ATCC 53103) and L. rhamnosus strain LC-705 (DSM 7061) removed aflatoxin B(1) from solution most efficiently and were selected for further study. The accessibility of bound aflatoxin B(1) to an antibody in an indirect competitive inhibition enzyme-linked immunosorbent assay suggests that surface components of these bacteria are involved in binding. Further evidence is the recovery of around 90% of the bound aflatoxin from the bacteria by solvent extraction. Autoclaving and sonication did not release any detectable aflatoxin B(1). Variation in temperature (4 to 37 degrees C) and pH (2 to 10) did not have any significant effect on the amount of aflatoxin B(1) released. Binding of aflatoxin B(1) appears to be predominantly extracellular for viable and heat-treated bacteria. Acid treatment may permit intracellular binding. In all cases, binding is of a reversible nature, but the stability of the complexes formed depends on strain, treatment, and environmental conditions.

Identification and functional characterization of eight CYP3A4 protein variants

The genetic component of the inter-individual variability in CYP3A4 activity has been estimated to be between 60% and 90%, but the underlying genetic factors remain largely unknown. A study of 213 Middle and Western European DNA samples resulted in the identification of 18 new CYP3A4 variants, including eight protein variants. A total of 7.5% of the population studied was found to be heterozygous for one of these variants. In a bacterial heterologous expression system, two mutants, R130Q and P416L, did not result in detectable P450 holoprotein. One mutant, T363M, expressed at significantly lower levels than wild-type CYP3A4. G56D, V170I, D174H and M445T were not significantly different when compared with wild-type CYP3A4 in expression or steroid hydroxylase activity. L373F displayed a significantly altered testosterone metabolite profile and a four-fold increase in the Km value for 1'-OH midazolam formation. The results suggest a limited contribution of CYP3A4 protein variants to the inter-individual variability of CYP3A4 activity in Caucasians. Some variants may, however, play a role in the atypical response to drugs or altered sensitivity to carcinogens.

In vitro metabolism of aflatoxin B1 by larvae of navel orangeworm, Amyelois transitella (Walker) (Insecta, Lepidoptera, Pyralidae) and codling moth, Cydia pomonella (L.) (Insecta, Lepidoptera, Tortricidae)

Larvae of the navel orangeworm (NOW), Amyelois transitella (Walker), a major pest of almonds and pistachios, and the codling moth (CM), Cydia pomonella (L.), the principal pest of walnuts and pome fruits, are commonly found in tree nut kernels that can be contaminated with aflatoxin, a potent carcinogen. The ability of larvae of these insects to metabolize aflatoxin B1 (AFB1) was examined. A field strain of NOW produced three AFB1 biotransformation products, chiefly aflatoxicol (AFL), and minor amounts of aflatoxin B2a (AFB2a) and aflatoxin M1 (AFM1). With AFL as a substrate, NOW larvae produced AFB1 and aflatoxicol M1 (AFLM1). A lab strain of CM larvae produced no detectable levels of AFB1 biotransformation products in comparison to a field strain which produced trace amounts of only AFL. Neither NOW nor CM produced AFB1-8,9-epoxide (AFBO), the principal carcinogenic metabolite of AFB1. In comparison, metabolism of AFB1 by chicken liver yielded mainly AFL, whereas mouse liver produced mostly AFM1 at a rate eightfold greater than AFL. Mouse liver also produced AFBO. The relatively high production of AFL by NOW compared to CM may reflect an adaptation to detoxify AFB1. NOW larvae frequently inhabit environments highly contaminated with fungi and, hence, aflatoxin. Only low amounts, if any, of this mycotoxin occur in the chief CM hosts, walnuts, and pome fruits. Characterizations of enzymes and co-factors involved in biotransformation of AFB1 are discussed.

Regulation of aflatoxin production by naphthoquinones of walnut (Juglans regia)

Walnuts are a valuable crop the sale and export potential of which may be severely limited by contamination with aflatoxins, metabolites produced on infection with Aspergillus flavus. The effect of a series of four naphthoquinones [1,4-naphthoquinone (1); juglone (5-hydroxy-1,4-naphthoquinone) (2); 2-methyl-1, 4-naphthoquinone (3); and, plumbagin (5-hydroxy-2-methyl-1, 4-naphthoquinone) (4)] (Figure 1), which occur in walnut husks, on fungal viability and aflatoxigenesis was studied in vitro. The quinones delayed germination of the fungus and were capable of completely inhibiting growth at higher concentrations. Their effect on aflatoxin levels was highly dependent on the concentration of individual naphthoquinones in the media. At higher concentrations, aflatoxin production was decreased or completely inhibited, but at lower concentrations there was a stimulatory effect on aflatoxin biosynthesis, with a >3-fold increase at 20 ppm of 3. Structural features associated with decreased fungal viability and greatest effect on aflatoxigenesis are the presence of a 5-hydroxyl or 2-methyl substituent, but there is no significant additive effect when both of these substituents are present.

Factors affecting the sequestration of aflatoxin by Lactobacillus rhamnosus strain GG

The interaction of a potent carcinogen, aflatoxin B(1) (AFB(1)), with a probiotic strain of lactic acid bacteria, Lactobacillus rhamnosus strain GG (GG), has been investigated. The binding of AFB(1) to GG in the late exponential-early stationary phase was studied for viable, heat-killed and acid-killed bacteria. In general, viable, heat-killed and acid-killed GG responded in a similar manner. The effects of pronase E, lipase and m-periodate on AFB(1) binding and release were consistent with AFB(1) binding predominantly to carbohydrate components of the bacteria. The effect of urea suggested hydrophobic interactions play a major role in binding. Increasing concentration (0.01-1 M) of NaCl or CaCl(2) had minor effects on AFB(1) binding suggesting some involvement of electrostatic interactions. An increase in pH from 2.5 to 8.5 had no effect on AFB(1) binding but decreased binding of AFB(2a), possibly due to hydrogen bonding interactions.