The effect of a single gavage dose of fumonisin B(1) on the sphinganine and sphingosine levels in vervet monkeys

Development and Limitations of Exposure Biomarkers to Dietary Contaminants Mycotoxins

Mycotoxins are toxic secondary fungal metabolites that frequently contaminate cereal crops globally, presenting exposure hazards to humans and livestock in many settings. The heterogeneous distribution of mycotoxins in food restricts the usefulness of food sampling and intake estimates for epidemiological studies, making validated exposure biomarkers better tools for informing epidemiological investigations. While biomarkers of exposure have served important roles for understanding the public health impact of mycotoxins such as aflatoxins (AF), the science of biomarkers must continue advancing to allow for better understanding of mycotoxins' roles in the etiology of disease and the effectiveness of mitigation strategies. This review will discuss mycotoxin biomarker development approaches over several decades for four toxins of significant public health concerns, AFs, fumonisins (FB), deoxynivalenol (DON), and ochratoxin A (OTA). This review will also highlight some knowledge gaps, key needs and potential pitfalls in mycotoxin biomarker interpretation.

Mycotoxicological research in South Africa 1910-2011

The British mycologist, I.B. Pole-Evans, was appointed as the first South African government mycologist in 1905 following the Anglo-Boer War (1899-1902). The Onderstepoort Veterinary Research Institute was founded in 1908 with the Swiss veterinarian, Arnold Theiler, as the first director. Thus, the stage was set for the commencement of mycotoxicological research when the Union of South Africa came into being in 1910. The first accounts of this pioneering research appeared in the 'Seventh and eight reports of the Director of Veterinary Research, Union of South Africa. 1918' in which D.T. Mitchell reported on the experimental reproduction of the neurotoxic syndrome, diplodiosis, in cattle with pure cultures of Stenocarpella maydis (= Diplodia zea) isolated by P.A. Van der Bijl and grown on sterile maize kernels. This is the first report of the experimental reproduction of a veterinary mycotoxicosis with a pure culture of a fungus in South Africa and possibly in the world. This seminal research was followed by a great deal of multidisciplinary research on veterinary mycotoxicoses as well as human syndromes in which fungal toxins are suspected to be involved, taxonomy of mycotoxigenic fungi and chemistry of mycotoxins in South Africa. The mycotoxicoses studied in South Africa include the following (more or less in chronological order): diplodiosis, Paspalum staggers, aflatoxicosis, human hepatocellular carcinoma, ochratoxicosis, lupinosis, facial eczema, tremorgenic mycotoxicosis, hyperoestrogenism, stachybotryotoxicosis, ergotism, leukoencephalomalacia and human oesophageal cancer. A major breakthrough in mycotoxicological research was made in South Africa in 1988 with the isolation and chemical characterisation of the carcinogenic fumonisins produced by Fusarium verticillioides in maize. Current research at the PROMEC Unit of the South African Medical Research Council on the risk assessment of fumonisins and intervention methods to reduce fumonisin intake by rural populations on a maize staple diet is highlighted. This paper concludes with a selected list of mycotoxicological publications by South African mycologists/plant pathologists, veterinarians and chemists/biochemists.

Fumonisin exposure and the sphinganine/sphingosine ratio in urine, serum and buccal cells in adults from Burkina Faso, West Africa

Fumonisins are mycotoxins that frequently contaminate maize, a dietary staple in Burkina Faso. Fumonisins have been linked with both the incidence of oesophageal cancer, and to neural tube defects. However, epidemiological studies of these associations are hampered by lack of validated exposure biomarkers. One candidate biomarker is the sphinganine/sphingosine (Sa/So) ratio in biological samples. Twenty husband-wife pairs aged 20-40 were recruited from Dingasso-1, western Burkina Faso. Plate ready food was sampled over three consecutive days (day one to three) for fumonisin B1 and B2, to provide a measure of total fumonisin intake. The Sa/So ratio was determined in (1) first morning urines taken on days two to four, (2) buccal cells and (3) serum on days one and four only. Fumonisin intake was moderate (mean 0.81 µg/kg bw/day (range 0.01-2.40 µg/kg bw/day) compared to exposures reported in China and South Africa. For each person the mean fumonisin intake over three days was compared to the mean Sa, So and Sa/So ratio in urine, buccal cells and serum. A modest positive trend between mean fumonisin intake and mean serum Sa/So was observed (P=0.067). When individuals were dichotomised based on the median fumonisin intake (<0.75 µg/kg bw/day), the serum Sa/So ratio was moderately higher (P=0.044) in the high intake group (geometric mean 0.64; 95% CI: 0.54, 0.75) compared to the low intake group (0.49; 95% CI: 0.41, 0.59). Neither urinary nor buccal cell Sa/So ratio was associated with mean fumonisin intake. Neither mean individual Sa nor So level for urine, buccal cells or urine was associated with mean individual fumonisin intake. The study population was exposed to moderate levels of fumonisin with limited evidence of altered Sa/So ratio. Further work on serum Sa/So ratio is merited in comparison with other biomarker approaches such as urinary fumonisin B1 or sphingolipid 1-phosphate metabolites.

Validation of fumonisin biomarkers in F344 rats

Fumonisins (FNs) are ubiquitous contaminants of cereal grains. Fumonisin B(1) (FB(1)) was linked to several animal and human diseases. To validate FB(1) biomarkers for studying human disease risks, F344 rats were administered by gavage with either a single dose of 0, 10 or 25 mg FB(1)/kg body weight (BW) or repeated doses of 0, 1.0, or 2.5 mg FB(1)/kg BW/day for 5 weeks. FB(1) excretion and FB(1)-induced metabolic alterations of sphingolipids in rat urine, feces and serum were assessed. Dose-dependent urinary and fecal excretion of free FB(1) were found in both single-dose- and repeat-dose-treated rats. In the single-dose study, urinary sphinganine (Sa) to sphingosine (So) ratio (Sa/So) reached a maximum at day 7 for the high-dose group and at day 5 for the low-dose group, whereas serum Sa/So showed only marginal changes. In the repeat-dose study, urinary Sa/So was persistently elevated at 2 weeks, while serum Sa/So was unchanged. Time course changes of sphinganine 1-phosphate (SaP) and sphingosine 1-phosphate (SoP) were also examined. Although serum Sa/So and SaP/SoP ratios showed no signs of time- or dose-dependent changes, a 10-fold increase in urinary SaP/SoP was observed, suggesting that urinary SaP/SoP is a more sensitive biomarker for FB(1) exposure. The accumulation of SaP and SoP was evident in the time course of SaP/Sa and SoP/So, which may reflect activity changes of enzymes closely related to the metabolism and catabolism of SaP and SoP. These results provide concrete evidence towards the practical use of excreted FB(1), Sa/So and SaP/SoP as biomarkers of exposure to FNs.

Maternal fumonisin exposure and risk for neural tube defects: mechanisms in an in vivo mouse model

BACKGROUND

Fumonisin B1 (FB1) is a mycotoxin produced by the fungus Fusarium verticillioides, a common contaminant of corn worldwide. FB1 disrupts sphingolipid biosynthesis by inhibiting the enzyme ceramide synthase, resulting in an elevation of free sphingoid bases and depletion of downstream glycosphingolipids. A relationship between maternal ingestion of FB1-contaminated corn during early pregnancy and increased risk for neural tube defects (NTDs) has recently been proposed in human populations around the world where corn is a dietary staple. The current studies provide an in vivo mouse model of FB1 teratogenicity.

METHODS

Pregnant LM/Bc mice were injected with increasing doses of FB1 on GD 7.5 and 8.5, and exposed fetuses were examined for malformations. Sphingolipid profiles and (3)H-folate concentrations were measured in maternal and fetal tissues. Immunohistochemical expression of the GPI-anchored folate receptor (Folbp1) and its association with the lipid raft component, ganglioside GM1, were characterized. Rescue experiments were performed with maternal folate supplementation or administration of gangliosides.

RESULTS

Maternal FB1 administration (20 mg/kg of body weight) during early gestation resulted in 79% NTDs in exposed fetuses. Sphingolipid profiles were significantly altered in maternal and embryonic tissues following exposure, and (3)H-folate levels and immunohistochemical expression of Folbp1 were reduced. Maternal folate supplementation partially rescued the NTD phenotype, whereas GM1 significantly restored folate concentrations and afforded almost complete protection against FB1-induced NTDs.

CONCLUSIONS

Maternal FB1 exposure altered sphingolipid metabolism and folate concentrations in LM/Bc mice, resulting in a dose-dependent increase in NTDs that could be prevented when adequate folate levels were maintained.

Fumonisins disrupt sphingolipid metabolism, folate transport, and neural tube development in embryo culture and in vivo: a potential risk factor for human neural tube defects among populations consuming fumonisin-contaminated maize

Fumonisins are a family of toxic and carcinogenic mycotoxins produced by Fusarium verticillioides (formerly Fusarium moniliforme), a common fungal contaminant of maize. Fumonisins inhibit ceramide synthase, causing accumulation of bioactive intermediates of sphingolipid metabolism (sphinganine and other sphingoid bases and derivatives) as well as depletion of complex sphingolipids, which interferes with the function of some membrane proteins, including the folate-binding protein (human folate receptor alpha). Fumonisin causes neural tube and craniofacial defects in mouse embryos in culture. Many of these effects are prevented by supplemental folic acid. Recent studies in LMBc mice found that fumonisin exposure in utero increases the frequency of developmental defects and administration of folate or a complex sphingolipid is preventive. High incidences of neural tube defects (NTD) occur in some regions of the world where substantial consumption of fumonisins has been documented or plausibly suggested (Guatemala, South Africa, and China); furthermore, a recent study of NTD in border counties of Texas found a significant association between NTD and consumption of tortillas during the first trimester. Hence, we propose that fumonisins are potential risk factors for NTD, craniofacial anomalies, and other birth defects arising from neural crest cells because of their apparent interference with folate utilization.

Screening toxicity study in young carp (Cyprinus carpio L.) on feed amended with fumonisin B1

Fumonisin B1 (FB1) is one of several mycotoxins produced by Fusarium moniliforme, a major fungal pathogen of corn and widely spread throughout the world. FB1 produces a wide range of biological effects, some of which are specific for particular organs or species and some are common to all investigated animals. In this study we have evaluated subchronic toxicosis features in young carp (Cyprinus carpio L.) exposed to 0.5 and 5.0 mg FB1 kg(-1) body weight for 42 days through nutritionally balanced diet. During the trial we observed loss of body weight in both treated groups, together with higher incidence of infective bacterial dermatological lesions erythrodermatitis cyprini (Aeromonas salmonicida subsp. nova) in the group treated with the higher FB1 dose. Several hematological parameters (erythrocyte count, platelet count) and serum chemical concentrations (creatinin, total bilirubin) and activities (aspartate aminotransferase, AST and alanine aminotransferase, ALT) were greater in the fumonisin treated groups than in the control group. Our results indicate that long-term dietary exposure to 0.5 and 5.0 mg FB1 kg(-1) body weight is not lethal to young carp, but can produce adverse physiological effects. These findings also suggest that primary target organs of FB1 in the carp are kidney and liver, as it has already been observed in other animal species tested. Specifically changed red blood cell- parameters reveal that FB1 probably causes erythrocyte membrane defect or interferes with carp's respiratory process.

Fumonisin B(1) induces apoptosis in LLC-PK(1) renal epithelial cells via a sphinganine- and calmodulin-dependent pathway

Fumonisins are a family of mycotoxins produced by Fusarium moniliforme, which is the most common mold found on corn throughout the world. These compounds are both toxic and carcinogenic for animals, and perhaps humans, with the kidney being the most sensitive organ to fumonisin toxicity. The molecular mechanism of fumonisin toxicity appears to involve disruption of de novo biosynthesis of sphingolipids and accumulation of sphinganine. The goals of this study were to determine whether fumonisin B(1) kills LLC-PK(1) renal kidney epithelial cells by inducing apoptosis and to identify genes affected by sphinganine that mediate fumonisin B(1)-induced cell death. Fumonisin B(1) produced morphological changes (i.e., cell shrinkage, membrane blebbing) and time-dependent increases in DNA fragmentation demonstrating that the toxin induces apoptosis. Simultaneously, fumonisin B(1) blocked sphingolipid biosynthesis and caused accumulation of sphinganine. To further investigate the role of sphinganine in fumonisin B(1)-induced apoptosis, beta-fluoroalanine (betaFA) was used to inhibit serine palmitoyltransferase, which catalyzes an earlier step in the sphingolipid biosynthetic pathway. betaFA blocked sphinganine accumulation and prevented fumonisin B(1)-induced DNA fragmentation, confirming that apoptosis induced by fumonisin B(1) is dependent upon accumulation of sphinganine. To examine gene expression, differential display reverse transcriptase polymerase chain reaction (DDRT-PCR) was applied to RNA isolated after 16 h of exposure to fumonisin B(1). Differential expression in response to fumonisin B(1) of a gene identified as calmodulin has been verified by Northern analysis. Sphinganine appears to mediate the effect because betaFA reduces induction of calmodulin mRNA by fumonisin B(1). Fumonisin B(1) also increases calmodulin protein in a concentration-dependent manner and the calmodulin antagonist W7 blocks fumonisin B(1)-induced DNA fragmentation, supporting a role for calmodulin in fumonisin B(1)-induced apoptosis. In contrast, fumonisin B(1) had no effect on expression of bcl-2 family genes (bax, bcl-2, and bcl-x). These findings demonstrate that fumonisin B(1) kills LLC-PK(1) kidney cells by inducing apoptosis. Further, the results establish a sequence of events for fumonisin B(1)-induced apoptosis involving initial disruption of sphingolipid metabolism and accumulation of sphinganine (or a metabolite), which, in turn, induces expression of calmodulin.

The effect of repeated gavage doses of fumonisin B1 on the sphinganine and sphingosine levels in vervet monkeys

Fumonisins occur widely around the world in maize products intended for human and animal consumption posing a health hazard. Direct measurement of fumonisins in physiological fluids as a biomarker of exposure is not practicable, however fumonisins disrupt sphingoid metabolism by inhibition of sphinganine N-acyltransferase. In this study the disruption in sphinganine (Sa) and sphingosine (So) levels in plasma and urine was measured in vervet monkeys (Cercopithecus aethiops) dosed with repeated gavages of 1mg fumonisin B1 (FB1)/kg body weight three times/week continuously over a 51-day period. The plasma Sa/So ratio reached a maximum (mean of 4.3) after 30 days in the dosed monkeys with a three-fold increase above the ratio of the control monkeys and then declined slowly to double the value in controls after 51 days. The lack of a clear elevation in urinary Sa/So ratios after 51 days of multiple exposure in the dosed monkeys indicates that the plasma ratio is more sensitive than urinary changes in monkeys. This is confirmed by the plasma levels of liver function enzymes of which aspartate transaminase, glutamyl-transferase and lactate dehydrogenase were increased in the dosed monkeys, while the plasma indicators of renal function were not increased above the levels in the control monkeys. Thus repeated low doses of FB1 can cause sustained disruption of sphingoid metabolism.

The effect of a single gavage dose of fumonisin B(2) on the sphinganine and sphingosine concentrations in vervet monkeys

The disruption in sphinganine (Sa) and sphingosine (So) concentrations in plasma and urine of vervet monkeys (Cercopithecus aethiops) was measured following a single gavage dose of either 1 (low dose) or 10 mg (high dose) fumonisin B(2) (FB(2))/kg body weight. Blood and urine were collected over a 51-day period. In the low-dose monkeys, none of the parameters measured increased significantly above the control values. In the high-dose monkeys the plasma Sa/So ratios were significantly increased (P< 0.05) above the corresponding control ratios after 3 days and continued to be significantly raised for another 27 days, whereafter the ratios declined to control values after 51 days. The plasma aspartate transaminase (AST) activities increased significantly above their control values from day 5 to day 23 and the gamma-glutamyl transferase (GGT) activities from day 7 until the end of the study period. The plasma cholesterol concentration and alanine transaminase (ALT) and lactate dehydrogenase (LDH) activities increased transiently, but not significantly, and returned to control values within the study period. The urinary Sa/So ratio, plasma creatinine and urea values in both groups of monkeys did not increase above the control values. This study demonstrated that a single large dose of FB(2) can cause transient disruption of sphingoid metabolism in vervet monkeys.