Maternal fumonisin exposure as a risk factor for neural tube defects

Mycotoxins in a changing global environment--a review

Mycotoxins are toxic metabolites produced by fungal species that commonly contaminate staple foods and feeds. They represent an unavoidable problem due to their presence in globally consumed cereals such as rice, maize and wheat. Most mycotoxins are immunosuppressive agents and some are carcinogens, hepatotoxins, nephrotoxins, and neurotoxins. Worldwide trends envision a stricter control of mycotoxins, however, the changing global environment may not be the ideal setting to control and reduce the exposure to these toxins. Although new technologies allow us to inspect the multi-mycotoxin presence in foods, new sources of exposure, gaps in knowledge of mycotoxins interactions, appearance of "emergent" mycotoxins and elucidation of consequent health effects can complicate their control even more. While humans are adapting to cope with environmental changes, such as food scarcity, decreased food quality, mycotoxin regulations, crop production and seasonality, and other climate related modifications, fungal species are also adapting and increased cases of mycotoxin adverse health effects are likely to occur in the future. To guarantee access to quality food for all, we need a way to balance global mycotoxin standards with the realistic feasibility of reaching them, considering limitations of producers and designing strategies to reduce mycotoxin exposure based on sound research.

Constitutive expression of fluorescent protein by Aspergillus var. niger and Aspergillus carbonarius to monitor fungal colonization in maize plants

Aspergillus niger and Aspergillus carbonarius are two species in the Aspergillus section Nigri (black-spored aspergilli) frequently associated with peanut (Arachis hypogea), maize (Zea mays), and other plants as pathogens. These infections are symptomless and as such are major concerns since some black aspergilli produce important mycotoxins, ochratoxins A, and the fumonisins. To facilitate the study of the black aspergilli-maize interactions with maize during the early stages of infections, we developed a method that used the enhanced yellow fluorescent protein (eYFP) and the monomeric red fluorescent protein (mRFP1) to transform A. niger and A. carbonarius, respectively. The results were constitutive expressions of the fluorescent genes that were stable in the cytoplasms of hyphae and conidia under natural environmental conditions. The hyphal in planta distribution in 21-day-old seedlings of maize were similar wild type and transformants of A. niger and A. carbonarius. The in planta studies indicated that both wild type and transformants internally colonized leaf, stem and root tissues of maize seedlings, without any visible disease symptoms. Yellow and red fluorescent strains were capable of invading epidermal cells of maize roots intercellularly within the first 3 days after inoculation, but intracellular hyphal growth was more evident after 7 days of inoculation. We also tested the capacity of fluorescent transformants to produce ochratoxin A and the results with A. carbonarius showed that this transgenic strain produced similar concentrations of this secondary metabolite. This is the first report on the in planta expression of fluorescent proteins that should be useful to study the internal plant colonization patterns of two ochratoxigenic species in the Aspergillus section Nigri.

Geographic and urban-rural disparities in the total prevalence of neural tube defects and their subtypes during 2006-2008 in China: a study using the hospital-based birth defects surveillance system

BACKGROUND

Previous reports on the prevalence of neural tube defects (NTDs) in China did not include cases of NTDs that were less than 28 weeks of gestational age (GA) and hence did not accurately reflect the total prevalence of NTDs or the geographic and urban-rural disparities in their prevalence. This article includes cases of NTDs that were less than 28 weeks of GA.

METHODS

Data used in this study were collected from 2006 to 2008 using a nationwide hospital-based registry, the Chinese Birth Defects Monitoring Network. The total prevalence ratio (PR) of NTDs and their subtypes, the ratios of PR (PRR), and 95% confidence intervals (CI) were used to analyse geographic disparities at both the regional (north, south) and provincial levels and to analyse disparities between rural and urban areas.

RESULTS

Overall, the total PR of NTDs was 14.0 per 10,000 births. The PRR of NTDs of rural women between the north and south region was 2.26 (95% CI: 2.04-2.52), which was much higher than that of urban women (PRR: 1.56, 95% CI: 1.41-1.72). The three subtypes of NTDs had different geographic distribution at the level of province. The urban-rural PRR of NTDs was 2.14 (95% CI: 1.94-2.34) in the north but only 1.47 (95% CI: 1.31-1.66) in the south.

CONCLUSIONS

There is a high total prevalence of NTDs, which remains one of the major public health concerns in China. Eliminating the geographic and urban-rural disparities in the disease burden is a priority for future intervention.

Mouse as a model for multifactorial inheritance of neural tube defects

Neural tube defects (NTDs) such as spina bifida and anencephaly are some of the most common structural birth defects found in humans. These defects occur due to failures of neurulation, a process where the flat neural plate rolls into a tube. In spite of their prevalence, the causes of NTDs are poorly understood. The multifactorial threshold model best describes the pattern of inheritance of NTDs where multiple undefined gene variants interact with environmental factors to cause an NTD. To date, mouse models have implicated a multitude of genes as required for neurulation, providing a mechanistic understanding of the cellular and molecular pathways that control neurulation. However, the majority of these mouse models exhibit NTDs with a Mendelian pattern of inheritance. Still, many examples of multifactorial inheritance have been demonstrated in mouse models of NTDs. These include null and hypomorphic alleles of neurulation genes that interact in a complex fashion with other genetic mutations or environmental factors to cause NTDs. These models have implicated several genes and pathways for testing as candidates for the genetic basis of NTDs in humans, resulting in identification of putative pathogenic mutations in some patients. Mouse models also provide an experimental paradigm to gain a mechanistic understanding of the environmental factors that influence NTD occurrence, such as folic acid and maternal diabetes, and have led to the discovery of additional preventative nutritional supplements such as inositol. This review provides examples of how multifactorial inheritance of NTDs can be modeled in the mouse.

Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain

Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, β-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.

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.

Neural tube defects--disorders of neurulation and related embryonic processes

Neural tube defects (NTDs) are severe congenital malformations affecting 1 in every 1000 pregnancies. 'Open' NTDs result from failure of primary neurulation as seen in anencephaly, myelomeningocele (open spina bifida), and craniorachischisis. Degeneration of the persistently open neural tube in utero leads to loss of neurological function below the lesion level. 'Closed' NTDs are skin-covered disorders of spinal cord structure, ranging from asymptomatic spina bifida occulta to severe spinal cord tethering, and usually traceable to disruption of secondary neurulation. 'Herniation' NTDs are those in which meninges, with or without brain or spinal cord tissue, become exteriorized through a pathological opening in the skull or vertebral column (e.g., encephalocele and meningocele). NTDs have multifactorial etiology, with genes and environmental factors interacting to determine individual risk of malformation. While over 200 mutant genes cause open NTDs in mice, much less is known about the genetic causation of human NTDs. Recent evidence has implicated genes of the planar cell polarity signaling pathway in a proportion of cases. The embryonic development of NTDs is complex, with diverse cellular and molecular mechanisms operating at different levels of the body axis. Molecular regulatory events include the bone morphogenetic protein and Sonic hedgehog pathways which have been implicated in control of neural plate bending. Primary prevention of NTDs has been implemented clinically following the demonstration that folic acid (FA), when taken as a periconceptional supplement, can prevent many cases. Not all NTDs respond to FA, however, and adjunct therapies are required for prevention of this FA-resistant category.

Exposure to toxic chemicals in the diet: is the Brazilian population at risk?

In Brazil, in the last 20 years, dietary risk assessments have been conducted on pesticides, mycotoxins, food additives, heavy metals (mainly mercury), environmental contaminants (mainly DDT) and acrylamide, a compound formed during food processing. The objectives of this paper were to review these studies, discuss their limitations and uncertainties and identify the most critical chemicals that may pose a health risk to Brazilian consumers. The studies have shown that the cumulative intake of organophosphorus and carbamate pesticides by high consumers of fruits and vegetables may represent a health concern (up to 169% of the ARfD), although the benefits of consuming large portions of those foods most probably overcome the risks. High consumers of maize products may also be at risk due to the presence of fumonisin (355% of the PMTDI), a mycotoxin present at high levels in Brazilian maize. The studies conducted in the Brazilian Amazon have shown that riparian fish consumers are exposed to unsafe levels of mercury. However, this is a more complex issue, as mercury levels in the region are naturally high and the health benefits of a fish-based diet are well known. Studies conducted both in Brazil and internationally on acrylamide have shown that the exposure to this genotoxic compound, mainly from the consumption of French fries and potato chips, is of health concern. Reducing the population dietary exposure to toxic chemicals is a challenge for government authorities and food producers in all countries. Management strategies aimed at decreasing exposure to the critical chemicals identified in this review involve limiting the use or eliminating highly toxic pesticides, implementing good agricultural practices to decrease maize contamination by fumonisins, educating local fish-eating communities toward a fish diet less contaminated by mercury, and changing dietary habits concerning the consumption of fried potatoes, the main processed food containing acrylamide.

Distinct generation, pharmacology, and distribution of sphingosine 1-phosphate and dihydrosphingosine 1-phosphate in human neural progenitor cells

In vivo and in vitro studies suggest a crucial role for Sphingosine 1-phosphate (S1P) and its receptors in the development of the nervous system. Dihydrosphingosine 1-phosphate (dhS1P), a reduced form of S1P, is an agonist at S1P receptors, but the pharmacology and physiology of dhS1P has not been widely studied. The mycotoxin fumonisin B1 (FB(1)) is a potent inhibitor of ceramide synthases and causes selective accumulation of dihydrosphingosine and dhS1P. Recent studies suggest that maternal exposure to FB(1) correlates with the development of neural tube defects (NTDs) in which the neural epithelial progenitor cell layers of the developing brain fail to fuse. We hypothesize that the altered balance of S1P and dhS1P in neural epithelial cells contributes to the developmental effects of FB(1). The goal of this work was first to define the effect of FB(1) exposure on levels of sphingosine and dh-sphingosine and their receptor-active 1-phosphate metabolites in human embryonic stem cell-derived neural epithelial progenitor (hES-NEP) cells; and second, to define the relative activity of dhS1P and S1P in hES-NEP cells. We found that dhS1P is a more potent stimulator of inhibition of cAMP and Smad phosphorylation than is S1P in neural progenitors, and this difference in apparent potency may be due, in part, to more persistent presence of extracellular dhS1P applied to human neural progenitors rather than a higher activity at S1P receptors. This study establishes hES-NEP cells as a useful human in vitro model system to study the mechanism of FB(1) toxicity and the molecular pharmacology of sphingolipid signaling. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Fumonisin elimination and prospects for detoxification by enzymatic transformation

A technology to efficiently reduce the concentration of carcinogenic and toxic fumonisins in food and feed would be desirable. This class of mycotoxins is produced by the maize pathogen Fusarium verticillioides and other fungi. Fumonisins are frequently found in maize from the warm growing regions of the world, sometimes in considerable concentrations. Their molecular similarity with sphingolipids enables their binding to mammalian ceramide synthase, and the resulting interference with sphingolipid metabolism. Recently, we reported on a cluster of genes of Sphingopyxis sp. MTA144 which enables this alphaproteobacterium to degrade fumonisins. These and the previously known fumonisin catabolism genes and enzymes from the black yeast Exophiala spinifera and from bacterium ATCC 55552 allow the consideration of prospects for enzymatic detoxification of fumonisins in food and feed. All the known fumonisin catabolism pathways start by hydrolytic release of the two tricarballylic acid side chains, followed by removal of the 2-amino group from the core chain by different enzymatic mechanisms. The potential for application of feed enzymes for fumonisin detoxification in the gastrointestinal tract of animals is discussed, and possible applications in processing of maize for feed or food are also considered. To be able to evaluate the requirement for, and potential of, a new, enzyme-based fumonisin detoxification technology, an overview of the state of the art of fumonisin elimination and the known chemical reactions of fumonisins in processing or decontamination is also given. There is a special focus on the toxicity of hydrolysed fumonisins, because they can be generated from fumonisins both by an established, traditional method of maize processing, nixtamalisation, and by enzymatic biotransformation. As a complement to other approaches, enzymatic degradation of fumonisins to ameliorate the health risk of contaminated maize for animals, and possibly also for humans, seems feasible.