Aflatoxin Exposure and Associated Human Health Effects, a Review of Epidemiological Studies

Aflatoxins are fungal toxins that possess acute life threatening toxicity, carcinogenic properties and other potential chronic adverse effects. Dietary exposure to aflatoxins is considered a major public health concern, especially for subsistence farming communities in sub-Saharan Africa and South Asia, where dietary staple food crops such as groundnuts and maize are often highly contaminated with aflatoxin due to hot and humid climates and poor storage, together with low awareness of risk and lack of enforcement of regulatory limits. Biomarkers have been developed and applied in many epidemiological studies assessing aflatoxin exposure and the associated health effects in these high-risk population groups. This review discusses the recent epidemiological evidence for aflatoxin exposure, co-exposure with other mycotoxins and associated health effects in order to provide evidence on risk assessment, and highlight areas where further research is necessary. Aflatoxin exposure can occur at any stage of life and is a major risk factor for hepatocellular carcinoma, especially when hepatitis B infection is present. Recent evidence suggests that aflatoxin may be an underlying determinant of stunted child growth, and may lower cell-mediated immunity, thereby increasing disease susceptibility. However, a causal relationship between aflatoxin exposure and these latter adverse health outcomes has not been established, and the biological mechanisms for these have not been elucidated, prompting further research. Furthermore, there is a dearth of information regarding the health effects of co-exposure to aflatoxin with other mycotoxins. Recent developments of biomarkers provide opportunities for important future research in this area.

A mini review on aflatoxin exposure in Malaysia: past, present and future

This mini review article described the exposure of aflatoxin in Malaysia, including its presence in the foodstuffs and the detection of aflatoxin biomarkers in human biological samples. Historically, the exposure of aflatoxin in Malaysia can be dated in 1960s where an outbreak of disease in pig farms caused severe liver damage to the animals. Later, an aflatoxicosis case in Perak in 1988 was reported and caused death to 13 children, as up to 3 mg of aflatoxin was present in a single serving of contaminated noodles. Since then, extensive research on aflatoxin has been conducted in Malaysia. The food commodities such as peanuts, cereals, spices, and their products are the main commodities commonly found to be contaminated with aflatoxin. Surprisingly, some of the contaminated foods had levels greater than the permissible limit adopted by the Malaysian Food Regulation 1985. Besides, exposure assessment through the measurement of aflatoxin biomarkers in human biological samples is still in its infancy stage. Nevertheless, some studies had reported the presence of these biomarkers. In fact, it is postulated that Malaysians are moderately exposed to aflatoxin compared to those high risk populations, where aflatoxin contamination in the diets is prevalent. Since the ingestion of aflatoxin could be the integral to the development of liver cancer, the incidence of cancer attributable by dietary aflatoxin exposure in Malaysia has also been reported and published in the literatures. Regardless of these findings, the more important task is to monitor and control humans from being exposed to aflatoxin. The enforcement of law is insufficient to minimize human exposure to aflatoxin. Preventive strategies include agricultural, dietary, and clinical measures should be implemented. With the current research on aflatoxin in Malaysia, a global networking for research collaboration is needed to expand the knowledge and disseminate the information to the global scientific community.

The microRNAs as potential biomarkers for predicting the onset of aflatoxin exposure in human beings: a review

The identification of aflatoxins as human carcinogens has stimulated extensive research efforts, which continue to the present, to assess potential health hazards resulting from contamination of the human food supply and to minimize exposure. The use of biomarkers that are mechanistically supported by toxicological studies will be important tools for identifying stages in the progression of development of the health effects of environmental agents. miRNAs are small non-coding mRNAs that regulate post-transcriptional gene expression. Also, they are molecular markers of cellular responses to various chemical agents. Growing evidence has demonstrated that environmental chemicals can induce changes in miRNA expression. miRNAs are good biomarkers because they are well defined, chemically uniform, restricted to a manageable number of species, and stable in cells and in the circulation. miRNAs have been used as serological markers of HCC and other tumors. The expression patterns of different miRNAs can distinguish among HCC-hepatitis viruses related, HCC cirrhosis-derivate, and HCC unrelated to either of them. The main objective of this review is to find unreported miRNAs in HCC related to other causes, so that they can be used as specific molecular biomarkers in populations exposed to aflatoxins and as early markers of exposure, damage/presence of HCC. Until today specific miRNAs as markers for aflatoxins-exposure and their reliability are currently lacking. Based on their elucidated mechanisms of action, potential miRNAs that could serve as possible markers of HCC by exposure to aflatoxins are miR-27a, miR-27b, miR-122, miR-148, miR-155, miR-192, miR-214, miR-221, miR-429, and miR-500. Future validation for all of these miRNAs will be needed to assess their prognostic significance and confirm their relationship with the induction of HCC due to aflatoxin exposure.

The influence of local market and household factors on aflatoxin presence in maize and symptoms of its exposure to children in Guatemala

Recent evidence supports the hypothesis that aflatoxin exposure from maize can influence malnutrition rates among children. Therefore, in Guatemala we investigated two questions; which maize sources exposed households to higher risk of aflatoxin exposure symptoms and what the risk factors were for each maize source, pre- and post-maize harvest. Survey data and household maize samples were collected in October 2016 (pre-harvest) and February 2017 (post-harvest) in San Vicente, Guatemala. Structural equation modeling (SEM) and odds ratios were used to assess the data. The results suggested that households which purchased maize from the market had 3.64 higher odds of high levels of aflatoxin. The models identified that good market purchase habits were significant for market-based maize sources while improved post-harvest practices and improved types of maize storage were significant for subsistence-based maize sources. Cumulative results suggest multiple interventions may be effective but are dependent on time of year and source of maize.

The effect of an intervention to reduce aflatoxin consumption from 6 to 18 mo of age on length-for-age z-scores in rural Tanzania: a cluster-randomized trial

BACKGROUND

Linear growth faltering continues to negatively affect children in low- and middle-income countries and is associated with poor cognitive, developmental, and educational outcomes. Laboratory and observational data suggest that aflatoxin (AF) is a contributor to stunting.

OBJECTIVE

The Mycotoxin Mitigation Trial was a cluster-randomized, community-based 2-group trial conducted in Kongwa District, Tanzania, between 2018 and 2020. The trial assessed whether a 12-mo intervention to reduce AF consumption increased length-for-age z-scores (LAZ) at 18 mo.

METHODS

Low-AF maize and groundnut flours were provided to the intervention group each month; skin lotion was distributed to the control group monthly. Infant and young child feeding education was delivered equally in 52 health facilities (clusters). Anthropometry and the AF blood biomarker serum AF-albumin (AF-alb) were assessed at 6, 12, and 18 mo of age. Outcomes were analyzed as intention-to-treat and per-protocol using linear mixed-effects models.

RESULTS

Two thousand eight hundred forty-two maternal-infant dyads were recruited into the study. The intervention did not create a contrast in AF-alb. At 18 mo, 36% (n = 186/520) of infants had detectable levels of AF-alb compared with 54% (n = 195/364) at baseline, with no difference between groups. Mean LAZ in the intervention group at 18 mo was -1.83 (n = 1231, 95% CI: -1.93, -1.73) compared to -1.90 (n = 1287, 95% CI: -1.99, -1.82) in the control group (P = 0.28).

CONCLUSIONS

An intervention to reduce AF exposure did not alter AF-alb nor anthropometric measures between treatment groups. Drought and agricultural data indicated less favorable conditions for toxin production, resulting in low levels of exposure in both trial arms. Annual, seasonal, and geographic heterogeneity of AF contamination make it difficult to study in an ethically designed trial. Our formative research and early trial data indicate that stunting and intermittent AF exposure continue to be a problem in this region. However, the low-AF exposure levels during the trial led to inconclusive results.

TRIAL REGISTRATION NUMBER

NCT03940547 (ClinicalTrials.org).