2011 Annual Report
1a.Objectives (from AD-416)
1. Determine the biochemical and molecular basis for the species specificity of fumonisins using animal models.
2. Determine the dietary “no observed effect” and “lowest observed effect levels” for neural tube defect induction and determine the dose-response thresholds for elevation in sphingolipid biomarkers in blood spots and fumonisins in urine using animal models.
3. Determine the relationship between fumonisin consumption, urinary fumonisin (exposure biomarker) and changes in sphingolipids in blood spots (effect biomarker) in human populations consuming corn.
4. Determine the specific mechanism(s) by which fumonisins are readily taken up by corn plant roots and yet have limited translocation into above ground vegetative tissues.
5. Determine the effectiveness of alkaline cooking for reducing the toxic potential of fumonisin-contaminated whole kernel corn.
1b.Approach (from AD-416)
1. Conduct dose-response studies to determine the minimum oral dose of FB1 that disrupts sphingolipid metabolism and induces toxicity (increased apoptosis) in rat kidney and mouse liver.
2. Conduct dose-response studies in susceptible mouse strains to determine the thresholds for changes in biomarkers of exposure and effect and induction of neural tube defects.
3. Conduct epidemiological studies to identify humans consuming large amounts of corn-based foods in communities where FB is infrequently detected and frequently detected and sample and analyze urine (FBs) and blood spots (sphingolipids).
4. Conduct dose response studies to determine FB1 affects on plant transpiration and levels of sphingoid bases and their 1-phosphates in roots and aerial tissues in FB1-sensitive and -insensitive genotypes of corn.
5. Utilize FB-contaminated whole kernel corn to determine the processing conditions that maximize FB1 reduction using chemical analysis and in vivo animal bioassays.
This report is the first for the project which replaces 6612-42000-038-00D; terminated 02/07/2011.
Objectives 1 and 2: Study was conducted in collaboration with Creighton University in female mice to determine the oral doses for a larger study to determine the threshold for fumonisin B1 (FB1)-induction of neural tube defects (NTD), maternal toxicity, urinary FB1 and sphingoid bases and sphingoid base 1-phosphates in maternal kidney, liver, blood and in the embryos. We showed that elevation in urinary FB1 and elevated sphingoid base 1-phosphates in red blood cells (blood spots) was detected at doses that did not induce NTDs in mice. NTDs were-induced at all doses > 5 mg/kg body weight per day. The elevation in FB1 in urine (exposure biomarker) and sphinganine 1-phosphate in blood spots (mechanism biomarker) was dose-dependent. Elevation in 1-deoxysphingoid bases was easily detected in mouse liver but was not detected in the liver or kidney of male rats.
Objective 2: We showed that NTD induction by intraperitoneal injection of FB1 was significantly reduced in mice fed folate deficient diets beginning five weeks prior to pregnancy. In groups fed folate sufficient diets, fifteen and 90 percent of litters from mice given the low and high doses of FB1 had one or more NTD-affected fetuses. Corresponding values in the groups fed the folate deficient diet were zero and 36 percent.
Objective 3: Biomarkers for FB exposure (urinary FB1) and effects (changes in sphingoid base 1-phosphates in blood spots) are being used in Independent Review Board approved studies in humans in collaboration with Guatemalan scientists through the Centro de Investigaciones en Nutricion y Salud in Guatemala (CIENSA). In the human studies approximately 450 urine and blood spot samples have been collected and analyzed from three locations in rural Guatemala. Maize samples (n=27) from the same locations have been collected and analyzed. The results show that FB1 in urine is correlated with the level of FB in the maize collected from each locality and the urinary FB1 is significantly correlated with evidence indicating elevated levels of sphingoid base 1-phosphates in blood spots.
Objective 4: Studies are in progress to address our hypothesis that water uptake and transpiration processes in corn plants are modulated during the plant-Fusarium interaction. Plant transpiration may be negatively impacted by increased concentrations of sphingoid base 1-phosphates, which accumulate as a result of fumonisin inhibition of the corn plant’s ceramide synthase. Since such inhibition of ceramide synthase is dependent upon the concentration of FB that accumulates in the seedlings, we have developed growth chamber assays to address transpiration responses when the plant is treated with either FB alone or with F. verticillioides. These studies will address the potential negative physiological effects of FBs on corn growth and development.
Objective 5: Institutional Animal Care and Use Committee approval was obtained, corn for use in experiment identified, and the protocol for cooking and bioassay was developed. Feeding trial is anticipated to begin in September.
Evidence for fumonisin-induced disruption of sphingolipid metabolism. The studies conducted in Guatemala in collaboration with the Centro de Investigaciones en Nutricion y Salud in Guatemala (CIENSA), Creighton University and Duke University show for the first time that fumonisin exposure, based on the levels of urinary fumonisin B1, is significantly correlated with the level of sphingoid base 1-phosphates in blood spots and the increase in the sphinganine 1-phosphate to sphingosine 1-phosphate ratio. This finding is consistent with the hypothesis that high levels of fumonisin exposure in humans can lead to disruption of sphingolipid metabolism through inhibition of ceramide synthase. This is a significant finding because every animal disease known to be caused by fumonisin has been shown to be closely correlated with and preceded by evidence of disruption of sphingolipid metabolism. The impact of this finding is that it provides a research tool for assessing the threshold for disruption of sphingolipid metabolism in humans and for designing epidemiological studies to evaluate the potential of fumonisin exposure as a contributing factor to human disease.
Myung, K., Zitomer, N.C., Duvall, M., Glenn, A.E., Riley, R.T., Calvo, A.M. 2011. The conserved global regulator veA is necessary for symptom production and mycotoxin synthesis in maize seedlings by Fusarium verticillioides. Plant Pathology. (2012) 61:152-160. DOI: 10.1111/j.1365-3059.2011.02504.x.
Zitomer, N.C., Riley, R.T. 2011. Extraction and analyses of fumonisins and compounds indicative of fumonisin exposure in plant and mammalian tissues and cultured cells. In: Holst, O., editor. Microbial Toxins: Methods and Protocols. New York, NY: Humana Press. 739:171-185.