Browsing by Subject "Aflatoxin"
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Item Biomarkers of Exposure to Foodborne and Environmental Carcinogens: Enterosorbent Intervention in a High Risk Population(2011-10-21) Johnson, Natalie MalekThe need to assess human exposures to foodborne and environmental carcinogens, particularly in populations at high risk for cancer and disease, has led to the development of chemical-specific biomarkers. Sensitive biomarkers for aflatoxin and polycyclic aromatic hydrocarbons (PAHs) have been useful in providing information on population exposure and reducing associated public health impacts. Aflatoxins are fungal metabolites found in a variety of foods. Among these toxins, aflatoxin B1 (AFB1) is the most predominant and hepatocarcinogenic. Acutely, AFB1 can cause disease and death, necessitating safe and effective intervention strategies. Inclusion of NovaSil (NS) clay in the diet represents a practical, sustainable approach. NS has been shown to prevent aflatoxicosis in multiple animal species by binding aflatoxins in the gastrointestinal tract, reducing toxin bioavailability. Co-exposure to PAHs, hazardous environmental contaminants, has been shown to increase the risk for hepatocellular carcinoma (HCC). Therefore, objectives of this research were to utilize biomarkers to assess aflatoxin and PAH exposures in susceptible populations in Ghana and the U.S. and to evaluate the safety and efficacy of NS intervention in Ghana (a population at risk for aflatoxicosis). After 3-month intervention with 3.0g NS/day, median aflatoxin M1 (an AFB1 metabolite) was significantly reduced (up to 58 percent) compared to the placebo group. Furthermore, no significant differences were found in levels of nutrient minerals between NS and placebo groups at baseline and 3-months suggesting NS can be used to effectively sorb AFB1 without affecting serum concentrations of important minerals. PAH biomarker results showed participants in Ghana were significantly exposed to high levels of PAHs based on the presence of 1-hydroxypyrene (1-OHP) in the majority of urines (98.9 percent). NS treatment had no effect on 1-OHP levels, further confirming the preferential binding of aflatoxins by NS. U.S. population data from a Hispanic community in Texas with an elevated incidence of HCC demonstrated a lower percentage and level of aflatoxin and PAH biomarkers. Aflatoxin M1 excretion, however, was associated with increased consumption of certain foods prone to aflatoxin contamination; thus, some individuals may be more vulnerable to exposure and associated interactions that increase the risk for HCC (e.g., PAHs or hepatitis infection).Item Human Exposure to Foodborne Toxins in Ghana: Intervention Strategy for Reduction of Aflatoxin and Fumonisin Bioavailability(2013-08-30) Mitchell, Nicole JeanInternational health has typically focused on remediation of infectious diseases in developing countries. However, recent reports from the International Agency for Research on Cancer (IARC) have highlighted the importance of cancer incidence/ mortality in the developing world. Foodborne mycotoxins produced by fungi, called aflatoxin (AF) and fumonisin (FB), have been associated with hepatocellular and esophageal carcinomas among other deleterious effects, such as growth faltering and immune dysfunction. Exposure to these toxins in Ghana is particularly high due to food insecurity, climate, and lack of regulatory infrastructures. Work to alleviate AF and FB contamination in Africa has focused on instituting good agricultural and storage practices however, exposures remain inextricable in many communities. Utilization of a calcium montmorillonite clay, UPSN, shows promise of tightly binding both AF and FB in the gastrointestinal tract, thereby reducing their bioavailability. The objectives of this research were to determine exposure susceptibility in Ghana and to assess efficacy and safety of UPSN treatment within vulnerable populations. Cross-sectional data from six different regions of Ghana indicated that AF exposure is associated with maize consumption and region of residence. However, food preparation practices were not correlated to AF levels in the present study. Therefore, future intervention strategies were focused on the end point of the food consumption chain by reducing AF exposure from maize immediately prior to ingestion (i.e. UPSN treatment). In a three-month trial an encapsulated montmorillonite clay was efficacious in reducing AF exposure. However, concern for sustainability and its applicability for children led to an effort to alter the dose dissemination form. Inclusion of UPSN in common Ghanaian foods retained the efficacy of the clay, reducing a short-term biomarker (AFM_(1)) by 55%, and was determined to be safe in children (ages 3-9). Importantly, daily assessment of AFM_(1) levels was successful in providing statistical significance of intervention effects within only five days of treatment. Initial results indicate that UPSN could efficiently to bind both AF and FB in the gastrointestinal tract, reducing biomarkers for both toxins in animal models. Thus, UPSN could positively impact health in developing communities at risk for AF and FB exposure.Item Improving Maize by QTL Mapping, Agronomic Performance and Breeding to Reduce Aflatoxin in Texas(2012-07-16) Mayfield, Kerry LucasAflatoxins are potent carcinogens produced by the fungus Aspergillus flavus Link:Fr and are a significant preharvest problem in maize production in Texas, the southern US, and subtropical climates. Several sources of maize germplasm are available which reduce preharvest aflatoxin accumulation, but many of these sources lack agronomic performance for direct use as a parent in commercial hybrids. Tropical germplasm is a source of both resistance to aflatoxin accumulation resistance and agronomic performance traits. The goal of this study was to investigate germplasm for traits to reduce preharvest aflatoxin accumulation. The specific objectives of this research were: 1) to validate QTL estimates previously identified in lines per se and estimate new QTL associated with reduced aflatoxin accumulations and agronomic traits; 2) to evaluate agronomic characteristics of selections from a RIL population in testcrosses at multiple locations across Texas; and (3) to release agronomically desirable germplasm sources with reduced risk to preharvest aflatoxin accumulation. A total of 96 QTLs were detected across fourteen measured traits using an RIL population of 130 individuals in testcross hybrids evaluated in five environments. Three QTL detected in per se analyses were also detected in hybrid testcrosses. Previously unreported QTL were detected on chromosomes 3, 4, 8 and 9. Within each of the two years, neither subset of the RIL testcross hybrids produced grain yields equal to commercial hybrid checks in these trials, but one testcross in 2008 produced grain yield within 10 percent of commercial check hybrids and in 2009, five RIL testcrosses produced grain yield within 17 percent of the commercial check hybrids. Although RIL testcrosses did not yield more than the commercial checks, they will be a source of germplasm for reduced aflatoxin. Improved sources of maize germplasm lines Tx736, Tx739, and Tx740 have been selected for adaptation to southern US and Texas growing environments with traits that reduce aflatoxin accumulation. Each of the lines in testcross accumulated significantly fewer aflatoxins than commercial hybrids in the trial.Item Phenotypic and genotypic characterization of white maize inbreds, hybrids and synthetics under stress and non-stress environments(Texas A&M University, 2006-10-30) Makumbi, DanMaize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield under drought and well-watered conditions. Heterosis estimates were highest in stress environments. Clustering based on genetic distance calculated using marker data from AFLP, RFLP, and SSRs grouped lines according to origin. Genetic distance was positively correlated with grain yield and specific combining ability. In the second study, synthetic hybrids were evaluated at seven locations in three countries to estimate GCA and SCA effects under low N stress and optimal conditions and investigate genotype x environment interaction. GCA effects were significant for all traits across low N stress and optimal conditions. The highest yielding synthetic hybrids involved synthetics developed from stress tolerant lines. Synthetics 99SADVIA-# and SYNA00F2 had good GCA for grain yield across low N stress conditions. Heterosis was highly correlated with grain yield. Optimal environments explained more variation than stress environments. The third study evaluated the agronomic performance and aflatoxin accumulation of single and three-way cross white maize hybrids at five locations in Texas. Inbreds CML343, Tx601W, and Tx110 showed positive GCA effects for grain yield. Significant GCA effects for reduced aflatoxin concentration were observed in lines CML269, CML270, and CML78 across locations. Differences in performance between single and three-way crosses hybrids were dependent mostly on the inbred lines.Item Phenotypic and genotypic evaluation of generations and recombinant inbred lines for response to aflatoxin(2009-05-15) Bello, Halima ThelmaAspergillus flavus is a fungus pathogen of maize that causes contamination of maize with aflatoxin. Aflatoxin is a carcinogenic toxin that can cause harm to human and animal health. Several management practices have been developed, such as cultural, chemical, biological and breeding, for host resistance. Development of host plant resistance has been the most desirable but this has been hampered by several factors, such as environmental influence, time consuming phenotyping and costly inoculation and field evaluations. Because of the problems associated with breeding for aflatoxin resistance, heritability estimates along with genetic correlations for aflatoxin and its secondary traits were estimated in this study. This experiment was conducted in two Texas locations (College Station and Weslaco) and phenotypic data were collected for aflatoxin concentration, maturity, endosperm texture, percentage of rotten ears and grain yield per ear. The heritability was moderate to high for aflatoxin and secondary traits such as endosperm texture and percentage of rotten ears. Aflatoxin was observed to be negatively correlated to grain yield and positively correlated to percentage of rotten ears. A population of recombinant inbred line derived from a cross between CML161 and B73o2 were evaluated in replicated trials in two environments for resistance to aflatoxin contamination. The families were genotyped using simple sequence repeat (SSR) markers. The mapping Recombinant Inbred Line population was used to detect and characterize Quantitative Trait Loci associated with aflatoxin accumulation. Alleles for reducing aflatoxin contamination came from both parents across the chromosomes. Thirty-eight epistatic interactions were detected for aflatoxin resistance. Several other QTLs were identified for other traits such as grain yield, endosperm texture, and percentage of rotten ears. The QTLs reported in this experiment are promising and need to be validated in other environment and genetic backgrounds for further use in marker assisted selection. Inheritance studies using generation mean analysis in six crosses showed additive and dominance effects to be mainly responsible for aflatoxin resistance. Two inbreds, CML176 and CML161, were identified as sources of resistance in breeding programs and use for selection.Item Preharvest aflatoxin in maize genotypes under inoculation with Aspergillus flavus(2009-05-15) Mayfield, Kerry L.Pre-harvest aflatoxin contamination is a major limitation to maize production in Texas and the southern United States, causing major economic loss and severe health problems worldwide. Screening for resistance to aflatoxin accumulation is commonly conducted through inoculation with a highly concentrated solution of Aspergillus flavus FR: Link spores, a naturally occurring fungus which infects maize and produces a toxic metabolite (aflatoxin) to humans and animals consuming the grain. No commercial hybrids exist with full resistance to aflatoxin accumulation; however, sources exist to reduce susceptibility. These sources commonly lack good agronomic characteristics for use in commercial hybrids. Exotic germplasm with favorable traits for reduced aflatoxin accumulations are introgressed with temperate and locally adapted lines. This program utilizes only one isolate of A. flavus even though many isolates exist in the environment. The objectives of this thesis are i) to evaluate the progress of the Maize Breeding and Genetics Program?s accomplishments of breeding maize for the reduction in susceptibility of aflatoxin accumulation in yellow inbreds through analysis of hybrid and inbred per se trials and ii) to determine whether interaction exists between geneticallydifferent isolates of A. flavus and several genotypes of maize. Response to aflatoxin accumulation for hybrids and inbreds was measured at up to three environments across Texas. Significant differences were detected for most years and environments. Maize lines CML285, CML288, CML323, CML325, CML326, CML338, Tx601y and lines derived from Population 69 and from Tx772 crosses in hybrid combinations tended to accumulate less aflatoxin than commercial hybrid checks. Significant differences were detected at each environment aflatoxin accumulation was measured for inbred lines per se. Inbreds Tx772, Tx601y, CML289, CML294, CML323 and derived lines from Population 69 show reduced aflatoxin accumulations. Interaction between genetically different isolates of A. flavus and several genotypes of maize were not detected in hybrid or inbred trials at two or three environments, across locations and across years. Introgression of exotic germplasm into locally adapted germplasm has improved agronomic characteristics for use in the Southern U.S. and brought sources for decreased aflatoxin accumulation.