Aflatoxins and growth impairment: a review

Effects of β-glucan on some environmental toxins: An overview

BACKGROUND

Beta-glucans are naturally occurring polysaccharides and constituents of the cell wall of certain pathogenic bacteria and fungi. They have proven healing and immunostimulating properties, linked to enhanced macrophage and natural killer cell function which likely involves specific interaction with several cell surface receptors, such as lactosylceramide, selected scavenger receptors, and dectin-1 (betaGR). In particular, glucan reduces the immunosuppressive effects of a number of agents including chemo therapy and radiation. More recent studies suggest a positive function for glucan in the immunosuppression caused by toxic agents in the environment.

AIM

An overview of the effects of glucan on the mycotoxin, aflotoxin and other environmental toxins (mercury-thimerosal, depleted uranium).

CONCLUSION

Glucan is effective as a natural immunomodulator and could be used as an inexpensive solution to reducing the adverse effects of some environmental toxins.

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.

Evaluation of the bright greenish yellow fluorescence test as a screening technique for aflatoxin-contaminated maize in Malawi

The bright greenish yellow fluorescence (BGYF) test has been used with varying success in screening for aflatoxins in maize. This test was applied to 180 maize samples collected from different markets within 12 districts of Malawi in order to evaluate its performance against high performance liquid chromatographic analysis. The number of BGYF grains in 2.5 kg unground samples ranged from 0 to 35 and about 49% of all tested samples had aflatoxin concentrations ranging from 1 to 382 μg/kg. A total of 65 (36%) of the examined unground samples showed no BGYF. The European Commission recommends a false negative rate of less than 5% for a screening technique to be acceptable. In this study, four BGYF grains per 2.5 kg unground maize sample successfully indicated an aflatoxin contamination of >10 μg/kg (10 μg/kg being the maxium tolerable level proposed by the Common Market for Eastern and Southern Africa), with a 4.4% false negative rate. In this case, the amount of confirmatory analyses would be reduced by 63%, if the BGYF test was employed as a screening method. The screening technique therefore offers a practical tool for Malawi and possibly for the Sub-Saharan region.

Contextualising complementary feeding in a broader framework for stunting prevention

An estimated 165 million children are stunted due to the combined effects of poor nutrition, repeated infection and inadequate psychosocial stimulation. The complementary feeding period, generally corresponding to age 6-24 months, represents an important period of sensitivity to stunting with lifelong, possibly irrevocable consequences. Interventions to improve complementary feeding practices or the nutritional quality of complementary foods must take into consideration the contextual as well as proximal determinants of stunting. This review presents a conceptual framework that highlights the role of complementary feeding within the layers of contextual and causal factors that lead to stunted growth and development and the resulting short- and long-term consequences. Contextual factors are organized into the following groups: political economy; health and health care systems; education; society and culture; agriculture and food systems; and water, sanitation and environment. We argue that these community and societal conditions underlie infant and young child feeding practices, which are a central pillar to healthy growth and development, and can serve to either impede or enable progress. Effectiveness studies with a strong process evaluation component are needed to identify transdisciplinary solutions. Programme and policy interventions aimed at preventing stunting should be informed by careful assessment of these factors at all levels.

The World Health Organization's global target for reducing childhood stunting by 2025: rationale and proposed actions

In 2012, the World Health Organization adopted a resolution on maternal, infant and young child nutrition that included a global target to reduce by 40% the number of stunted under-five children by 2025. The target was based on analyses of time series data from 148 countries and national success stories in tackling undernutrition. The global target translates to a 3.9% reduction per year and implies decreasing the number of stunted children from 171 million in 2010 to about 100 million in 2025. However, at current rates of progress, there will be 127 million stunted children by 2025, that is, 27 million more than the target or a reduction of only 26%. The translation of the global target into national targets needs to consider nutrition profiles, risk factor trends, demographic changes, experience with developing and implementing nutrition policies, and health system development. This paper presents a methodology to set individual country targets, without precluding the use of others. Any method applied will be influenced by country-specific population growth rates. A key question is what countries should do to meet the target. Nutrition interventions alone are almost certainly insufficient, hence the importance of ongoing efforts to foster nutrition-sensitive development and encourage development of evidence-based, multisectoral plans to address stunting at national scale, combining direct nutrition interventions with strategies concerning health, family planning, water and sanitation, and other factors that affect the risk of stunting. In addition, an accountability framework needs to be developed and surveillance systems strengthened to monitor the achievement of commitments and targets.

Analysis of the contrast between natural occurrence of toxigenic Aspergilli of the Flavi section and aflatoxin B1 in cassava

Aflatoxin B1 (AFB1) is a carcinogenic mycotoxin produced by Aspergilli of the section Flavi that may contaminate food, in the field or during storage. Cassava represents an important staple food in sub-Saharan Africa. The analysis of aflatoxigenic fungi in 36 cassava samples obtained from producers in Benin indicated that 40% were contaminated by Aspergilli of the section Flavi. Upon morphological and molecular characterization of the 20 isolates, 16 belonged to Aspergillus flavus, 2 to Aspergillus parvisclerotigenus and 2 to Aspergillus novoparasiticus. This is the first time that this latter species is isolated from food. Although most of these isolates were toxigenic on synthetic media, no AFB1 contamination was observed in these cassava samples. In order to determine the action of cassava on AFB1 synthesis, a highly toxigenic strain of A. flavus, was inoculated onto fresh cassava and despite a rapid development, no AFB1 was produced. The anti-aflatoxin property was observed with cassava from different geographical origins and on other aflatoxigenic strains of the section Flavi, but it was lost after heating, sun drying and freezing. Our data suggest that fresh cassava is safe regarding AFB1 contamination, however, processing may alter its ability to block toxinogenesis leading to secondary contamination.

De-novo design of antimicrobial peptides for plant protection

This work describes the de-novo design of peptides that inhibit a broad range of plant pathogens. Four structurally different groups of peptides were developed that differ in size and position of their charged and hydrophobic clusters and were assayed for their ability to inhibit bacterial growth and fungal spore germination. Several peptides are highly active at concentrations between 0,1 and 1 µg/ml against plant pathogenic bacteria, such as Pseudomonas syringae, Pectobacterium carotovorum, and Xanthomonas vesicatoria. Importantly, no hemolytic activity could be detected for these peptides at concentrations up to 200 µg/ml. Moreover, the peptides are also active after spraying on the plant surface demonstrating a possible way of application. In sum, our designed peptides represent new antimicrobial agents and with the increasing demand for antimicrobial compounds for production of “healthy” food, these peptides might serve as templates for novel antibacterial and antifungal agents.

Exposure to food contaminants during pregnancy

During pregnancy, the fetus is exposed to contaminants from its mother's diet. This work provides an assessment of the dietary exposure of pregnant women to inorganic contaminants (aluminum, mercury, lead, inorganic arsenic, cobalt), polychlorodibenzodioxins, polychlorodibenzofurans, dioxin-like and non-dioxin-like polychlorobiphenyls (DL-PCBs, NDL-PCBs), polybromodiphenyl ethers (PBDEs), perfluoroalkyl acids, mycotoxins (zearalenone, patulin, trichothecenes), and heat-generated compounds (acrylamide and polycyclic aromatic hydrocarbons). Consumption data of 2002 pregnant women aged 18 to 45 from the EDEN cohort study were combined with contamination data from the second French total diet study to assess the exposure before pregnancy (n=1861) and during the third trimester of pregnancy (n=1775). Exposure was also assessed considering the season during which the third trimester of pregnancy occurred. Significant changes in consumptions during pregnancy and between seasons were associated with differences in exposures for some substances. Some contaminant exposures appeared to be of health concern. Margins of exposure to acrylamide (635 to 1094 for mean), inorganic arsenic, lead, and BDE-99 (≤100) were too low to exclude all risks. For NDL-PCBs, T-2 and HT-2 toxins, and deoxynivalenol, significant exceedings of toxicological reference values were found before pregnancy, but there was no significant exceeding in the third trimester.

Human aflatoxin exposure in Kenya, 2007: a cross-sectional study

Aflatoxins contaminate approximately 25% of agricultural products worldwide. They can cause liver failure and liver cancer. Kenya has experienced multiple aflatoxicosis outbreaks in recent years, often resulting in fatalities. However, the full extent of aflatoxin exposure in Kenya has been unknown. Our objective was to quantify aflatoxin exposure across Kenya. We analysed aflatoxin levels in serum specimens from the 2007 Kenya AIDS Indicator Survey – a nationally representative, cross-sectional serosurvey. KAIS collected 15,853 blood specimens. Of the 3180 human immunodeficiency virus-negative specimens with ≥1 mL sera, we randomly selected 600 specimens stratified by province and sex. We analysed serum specimens for aflatoxin albumin adducts by using isotope dilution MS/MS to quantify aflatoxin B1-lysine, and normalised with serum albumin. Aflatoxin concentrations were then compared by demographic, socioeconomic and geographic characteristics. We detected serum aflatoxin B1-lysine in 78% of serum specimens (range = <LOD-211 pg/mg albumin, median = 1.78 pg/mg albumin). Aflatoxin exposure did not vary by sex, age group, marital status, religion or socioeconomic characteristics. Aflatoxin exposure varied by province (p < 0.05); it was highest in Eastern (median = 7.87 pg/mg albumin) and Coast (median = 3.70 pg/mg albumin) provinces and lowest in Nyanza (median = <LOD) and Rift Valley (median = 0.70 pg/mg albumin) provinces. Our findings suggest that aflatoxin exposure is a public health problem throughout Kenya, and it could be substantially impacting human health. Wide-scale, evidence-based interventions are urgently needed to decrease exposure and subsequent health effects.

Global risk assessment of aflatoxins in maize and peanuts: are regulatory standards adequately protective?

The aflatoxins are a group of fungal metabolites that contaminate a variety of staple crops, including maize and peanuts, and cause an array of acute and chronic human health effects. Aflatoxin B1 in particular is a potent liver carcinogen, and hepatocellular carcinoma (HCC) risk is multiplicatively higher for individuals exposed to both aflatoxin and chronic infection with hepatitis B virus (HBV). In this work, we sought to answer the question: do current aflatoxin regulatory standards around the world adequately protect human health? Depending upon the level of protection desired, the answer to this question varies. Currently, most nations have a maximum tolerable level of total aflatoxins in maize and peanuts ranging from 4 to 20ng/g. If the level of protection desired is that aflatoxin exposures would not increase lifetime HCC risk by more than 1 in 100,000 cases in the population, then most current regulatory standards are not adequately protective even if enforced, especially in low-income countries where large amounts of maize and peanuts are consumed and HBV prevalence is high. At the protection level of 1 in 10,000 lifetime HCC cases in the population, however, almost all aflatoxin regulations worldwide are adequately protective, with the exception of several nations in Africa and Latin America.

Assessment of aflatoxin contamination of maize, peanut meal and poultry feed mixtures from different agroecological zones in Cameroon

Mycotoxins affect poultry production by being present in the feed and directly causing a negative impact on bird performance. Carry-over rates of mycotoxins in animal products are, in general, small (except for aflatoxins in milk and eggs) therefore representing a small source of mycotoxins for humans. Mycotoxins present directly in human food represent a much higher risk. The contamination of poultry feed by aflatoxins was determined as a first assessment of this risk in Cameroon. A total of 201 samples of maize, peanut meal, broiler and layer feeds were collected directly at poultry farms, poultry production sites and poultry feed dealers in three agroecological zones (AEZs) of Cameroon and analyzed for moisture content and aflatoxin levels. The results indicate that the mean of the moisture content of maize (14.1%) was significantly (P < 0.05) higher than all other commodities (10.0%–12.7%). Approximately 9% of maize samples were positive for aflatoxin, with concentrations overall ranging from <2 to 42 µg/kg. Most of the samples of peanut meal (100%), broiler (93.3%) and layer feeds (83.0%) were positive with concentrations of positive samples ranging from 39 to 950 µg/kg for peanut meal, 2 to 52 µg/kg for broiler feed and 2 to 23 µg/kg for layer feed. The aflatoxin content of layer feed did not vary by AEZ, while the highest (16.8 µg/kg) and the lowest (8.2 µg/kg) aflatoxin content of broiler feed were respectively recorded in Western High Plateau and in Rainforest agroecological zones. These results suggest that peanut meal is likely to be a high risk feed, and further investigation is needed to guide promotion of safe feeds for poultry in Cameroon.

Nutrient environments influence competition among Aspergillus flavus genotypes

The population dynamics of Aspergillus flavus, shaped in part by intraspecific competition, influence the likelihood and severity of crop aflatoxin contamination. Competition for nutrients may be one factor modulating intraspecific interactions, but the influences of specific types and concentrations of nutrients on competition between genotypes of A. flavus have not been investigated. Competition between paired A. flavus isolates on agar media was affected by varying concentrations of carbon (sucrose or asparagine) and nitrogen (nitrate or asparagine). Cocultivated isolate percentages from conidia and agar-embedded mycelia were quantified by measurements of isolate-specific single-nucleotide polymorphisms with quantitative pyrosequencing. Compositions and concentrations of nutrients influenced conidiation resulting from cocultivation, but the percentages of total conidia from each competing isolate were not predicted by sporulation of isolates grown individually. Success during sporulation did not reflect the outcomes of competition during mycelial growth, and the extents to which isolate percentages from conidia and mycelia differed varied among both isolate pairs and media. Whether varying concentrations of sucrose, nitrate, or asparagine increased, decreased, or had no influence on competitive ability was isolate dependent. Different responses of A. flavus isolates to nutrient variability suggest genotypes are adapted to different nutrient environments that have the potential to influence A. flavus population structure and the epidemiology of aflatoxin contamination.

Integrative toxicopathological evaluation of aflatoxin B₁ exposure in F344 rats

In this study, male F344 rats were orally exposed to a single dose of aflatoxin B₁ (AFB₁) at 0, 50, 250, or 1,000 µg/kg body weight (BW) or repeated dose of 0, 5, 10, 25, or 75 µg/kg BW for up to 5 weeks. Biochemical and histological changes were assessed together with the formation of AFB1-lysine adduct (AFB-Lys) and liver foci positive for placental form glutathione S transferase (GST-P⁺). In single-dose protocol, serum aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) showed dose-related elevation, with maximal changes observed (>100-fold) at day 3 after treatment. Animals that received 250 µg/kg AFB₁ showed concurrent bile duct proliferation, necrosis, and GST-P⁺ hepatocytes at 3 day, followed by liver GST-P⁺ foci appearance at 1 week. In repeated-dose protocol, bile duct proliferation and liver GST-P⁺ foci co-occurred after 3-week exposure to 75 µg/kg AFB₁, followed by proliferation foci formation after 4 week and dramatic ALT, AST, and CK elevations after 5 weeks. Liver GST-P⁺ foci were induced temporally and in a dose-related manner. Serum AFB-Lys increased temporally at low doses (5-25 µg/kg), and reached the maximum after 2-week exposure at 75 µg/kg. This integrative study demonstrated that liver GST-P⁺ cells and foci are sensitive biomarkers for AFB₁ toxic effect and correlated with bile duct proliferation and biochemical alterations in F344 rats.

Aflatoxin regulations in a network of global maize trade

Worldwide, food supplies often contain unavoidable contaminants, many of which adversely affect health and hence are subject to regulations of maximum tolerable levels in food. These regulations differ from nation to nation, and may affect patterns of food trade. We soughtto determine whether there is an association between nations' food safety regulations and global food trade patterns, with implications for public health and policymaking. We developed a network model of maize trade around the world. From maize import/export data for 217 nations from 2000–2009, we calculated basic statistics on volumes of trade; then examined how regulations of aflatoxin, a common contaminant of maize, are similar or different between pairs of nations engaging in significant amounts of maize trade. Globally, market segregation appears to occur among clusters of nations. The United States is at the center of one cluster; European countries make up another cluster with hardly any maize trade with the US; and Argentina, Brazil, and China export maize all over the world. Pairs of nations trading large amounts of maize have very similar aflatoxin regulations: nations with strict standards tend to trade maize with each other, while nations with more relaxed standards tend to trade maize with each other. Rarely among the top pairs of maize-trading nations do total aflatoxin standards (standards based on the sum of the levels of aflatoxins B₁, B₂, G₁, and G₂) differ by more than 5 µg/kg. These results suggest that, globally, separate maize trading communities emerge; and nations tend to trade with other nations that have very similar food safety standards.

Food chain mycotoxin exposure, gut health, and impaired growth: a conceptual framework

Childhood stunting is an important and intractable public health problem that underlies ~20% of deaths among children aged <5 y in developing countries. Environmental enteropathy (EE), a subclinical condition of the small intestine characterized by reduced absorptive capacity and increased intestinal permeability, is almost universal among children in developing countries and may mediate stunting. However, the etiology of EE is poorly understood. Mycotoxins are metabolites of fungi that frequently contaminate the staple foods of children living in developing countries. We review evidence from human and animal studies that exposure to mycotoxins, particularly aflatoxin (AF), fumonisin (FUM), and deoxynivaenol (DON), may impair child growth. Although these toxins have distinct actions, they all mediate intestinal damage through: 1) inhibition of protein synthesis (AF, DON); 2) an increase in systemic proinflammatory cytokines (DON); and 3) inhibition of ceramide synthase (FUM). The intestinal pathology that arises from mycotoxin exposure is very similar to that of EE. We propose that future studies should address the role of mycotoxins in the pathogenesis of EE and evaluate interventions to limit mycotoxin exposure and reduce childhood stunting.

Quality and safety aspects of infant nutrition

Quality and safety aspects of infant nutrition are of key importance for child health, but oftentimes they do not get much attention by health care professionals whose interest tends to focus on functional benefits of early nutrition. Unbalanced diets and harmful food components induce particularly high risks for untoward effects in infants because of their rapid growth, high nutrient needs, and their typical dependence on only one or few foods during the first months of life. The concepts, standards and practices that relate to infant food quality and safety were discussed at a scientific workshop organized by the Child Health Foundation and the Early Nutrition Academy jointly with the European Society for Paediatric Gastroenterology, Hepatology and Nutrition, and a summary is provided here. The participants reviewed past and current issues on quality and safety, the role of different stakeholders, and recommendations to avert future issues. It was concluded that a high level of quality and safety is currently achieved, but this is no reason for complacency. The food industry carries the primary responsibility for the safety and suitability of their products, including the quality of composition, raw materials and production processes. Introduction of new or modified products should be preceded by a thorough science based review of suitability and safety by an independent authority. Food safety events should be managed on an international basis. Global collaboration of food producers, food-safety authorities, paediatricians and scientists is needed to efficiently exchange information and to best protect public health.