Carcinogenicity and mechanism of action of fumonisin B1: a mycotoxin produced by Fusarium moniliforme (= F. verticillioides)

Systemic Infection by Fusarium verticillioides in Maize Plants Grown Under Three Temperature Regimes

Fusarium verticillioides causes seedling decay, stalk rot, ear rot, and mycotoxin contamination (primarily fumonisins) in maize. Systemic infection of maize plants by F. verticillioides can lead to kernel infection, but the frequency of this phenomenon has varied widely among experiments. Variation in the incidence of systemic infection has been attributed to environmental factors. In order to better understand the influence of environment, we investigated the effect of temperature on systemic development of F. verticillioides during vegetative and reproductive stages of plant development. Maize seeds were inoculated with a green fluorescent protein-expressing strain of F. verticillioides, and grown in growth chambers under three different temperature regimes. In the vegetative-stage and reproductive-stage experiments, plants were evaluated at tasseling (VT stage), and at physiological maturity (R6 stage), respectively. Independently of the temperature treatment, F. verticillioides was reisolated from nearly 100% of belowground plant tissues. Frequency of reisolation of the inoculated strain declined acropetally in aboveground internodes at all temperature regimes. At VT, the high-temperature treatment had the highest systemic development of F. verticillioides in aboveground tissues. At R6, incidence of systemic infection was greater at both the high- and low-temperature regimes than at the average-temperature regime. F. verticillioides was isolated from higher internodes in plants at R6, compared to stage VT. The seed-inoculated strain was recovered from kernels of mature plants, although incidence of kernel infection did not differ significantly among treatments. During the vegetative growth stages, temperature had a significant effect on systemic development of F. verticillioides in stalks. At R6, the fungus reached higher internodes in the high-temperature treatment, but temperature did not have an effect on the incidence of kernels (either symptomatic or asymptomatic) or ear peduncles infected with the inoculated strain. These results support the role of high temperatures in promoting systemic infection of maize by F. verticillioides, but plant-to-seed transmission may be limited by other environmental factors that interact with temperature during the reproductive stages.

Subchronic mycotoxicoses in rats. Histopathological changes and modulation of the sphinganine to sphingosine (Sa/So) ratio imbalance induced by Fusarium verticillioides culture material, due to the coexistence of aflatoxin B1 in the diet

Mycotoxicoses are diseases caused by consumption of diets contaminated with mycotoxins, a special class of fungal secondary metabolites. Fumonisin B1 (FB1) and aflatoxin B1 (AFB1), the main toxins synthesized by toxicogenic stocks of Fusarium spp. and Aspergillus spp., respectively, can coexist in grains and in its by-products. We investigated a probable synergism of a fumonisins-containing Fusarium verticillioides culture material and AFB1 in the induction of hepatocyte apoptosis in rats subchronically fed on a mixture of them. Furthermore, the possibility of modifications in the fumonisins-induced Sa/So ratio imbalance in tissues and urine from rats poisoned with this mycotoxin, due to the presence of AFB1 in the diet, was evaluated. The co-exposure to fumonisins and AFB1 produced a higher liver toxicity, with respect to their individual administration, inducing apoptosis and mitotic hepatocytes. There was an inversion of the typical Sa/So ratio in rats fed on the culture material as well as in those subjected to a diet co-contamined with fumonisins and AFB1. Moreover, the later had a synergistic effect in the induction of Sa/So variations in kidneys. Therefore, the mixture of fumonisins and AFB1 induced toxic responses which could not be considered a sum of the effects caused individually by these mycotoxins.

Toxic effects of Fusarium mycotoxin butenolide on rat myocardium and primary culture of cardiac myocytes

Mycotoxin toxicosis has been implicated in the etiopathogenesis of Keshan disease (KD), an endemic cardiomyopathy prevailing in some regions of China. Butenolide (4-acetamido-4-hydroxy-2-butenoic acid gamma-lactone, CAS No. 16275-44-8), a mycotoxin produced by several Fusarium species such as Fusarium tricinctum and Fusarium graminearum, is frequently detected from the cereals in the endemic areas of KD. The present study is undertaken to investigate whether this mycotoxin can induce myocardial damage. Exposure of primary culture of cardiac myocytes to butenolide resulted in significant cytotoxicity, manifested by changes in cell morphology and decreases in cell viability. Consistent with the in vitro findings, distinct myocardial toxicity in vivo was observed after administration of rats by gavage with butenolide (10 and 20 mg/kg/day) for 2 months, and the myocardial injuries were characterized by focal necrosis of myocardium and fragmentation of myofiber. Butenolide also induced significant oxidative damage to the myocardium in vitro evidenced by a concentration-dependent lipid peroxidation in the myocardial homogenates, whereas antioxidants superoxide dismutase (SOD), N-acetylcysteine (NAC) and glutathione (GSH) provided significant protections against this oxidative effect. Taken together, these results clearly reveal that butenolide possesses the potential to induce myocardial toxicity. The present findings may reinforce the hypothesis that toxicosis by mycotoxins is one of the etiological factors for KD.

In vitromicrobial metabolism of fumonisin B1

There is a lack of information on the effect of swine caecal microbiota on fumonisin metabolism. In this in vitro study, the biotransformation of fumonisin B(1) (FB(1)) by the gut microbiota of adult, healthy pigs was examined. Suspensions of caecal contents and McDougall buffer solution were incubated anaerobically with pure FB(1) for 0, 12, 24, 48 and 72 h. After 48 h, the conversion of FB(1) to partially hydrolysed FB(1) (46%) was nearly equal to the percentage ratio of FB(1), while by 72 h it was 49%. In vitro, the conversion of fumonisin B(1) to aminopentol was less than 1%. The results show that the caecal microbiota are capable of transforming fumonisin B(1) to the above metabolites. Further studies on FB(1) metabolism in the small intestine are clearly justified.

Palmitate and oleate have distinct effects on the inflammatory phenotype of human endothelial cells

Free fatty acids may create a state of continuous and progressive damaging to the vascular wall manifested by endothelial dysfunction. In this study we determine the mechanisms by which fatty acids palmitate (C16:0) and oleate (C18:1) affect intracellular long chain acyl-CoA (LCAC) content, energy metabolism, cell survival and proliferation and activation of NF-kappaB in cultured endothelial cells. A 48-h exposure of human umbilical vein endothelial cells (HUVEC) to 0.5 mM palmitate or 0.5 mM oleate increased total long chain acyl-CoA (LCAC) content 1.7 and 2 fold, respectively and decreased ATP(total)/ADP(total) ratio by 26+/-5% (mean+/-SEM) and 15+/-2%, respectively, which was prevented by the acyl-CoA synthetase inhibitor triacsin C. Furthermore, palmitate inhibited cell proliferation by 34+/-5%, while oleate stimulated it by 12+/-2%. alpha-Tocopherol fully and triacsin C partially abolished the effect of palmitate on cell proliferation. Palmitate and oleate increased caspase-3 activity 3.2 and 1.4 fold, respectively. Palmitate-induced caspase-3 activation was prevented by triacsin C and slightly reduced by alpha-tocopherol and by the de novo ceramide synthesis inhibitor fumonisin B(1). Both fatty acids induced antioxidant-sensitive nuclear translocation of NF-kappaB after 72 h, but not after 48 h. In conclusion, we showed that fatty acids influence different aspects of HUVEC function resulting in amongst other activation of apoptotic and inflammatory pathways. Our results indicate that the effects depend on the fatty acid type and may be related to accumulation of LCAC.

Involvement of de novo ceramide synthesis in radiocontrast-induced renal tubular cell injury

We reported previously that various radiocontrast media cause apoptosis in porcine proximal tubular (LLC-PK(1)) cells, in which reduction in B-cell lymphoma (Bcl)-2 expression and caspase-3 activation are implicated. In the present study, we investigated a role for ceramide in radiocontrast media-induced apoptosis in renal tubular cells. LLC-PK(1) cells were exposed to radiocontrast media for 30 min, followed by incubation for 24 h in normal medium. Cell viability was assessed by 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt assay, while apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling stain. Immunofluorescent stains were performed using antibodies against phosphorylated Akt (pAkt) and cAMP response element binding protein (CREB) (pCREB), and ceramide. The mRNA expression and protein content of Bcl-2 were determined by reverse transcriptase-polymerase chain reaction and enzyme immunoassay, respectively. In vivo model of contrast-induced renal injury was induced in mice with unilateral renal occlusion. The cell injury induced by the nonionic radiocontrast medium ioversol was reversed by inhibiting de novo ceramide synthesis with fumonisin B(1) (FB(1)) and L-cycloserine, but not by suppressing sphingomyelin breakdown with D609. FB(1) reversed ioversol-induced decrease in the immunoreactivities of pAkt and pCREB, reduction in Bcl-2 expression and caspase-3 activation. Like ioversol, C2 ceramide and the Akt inhibitor Src homology-6 induced apoptosis by reducing pAkt and pCREB-like immunoreactivities, lowering Bcl-2 expression and enhancing caspase-3 activity. Indeed, various radiocontrast media, excluding iodixanol which showed the least nephrotoxicity, enhanced ceramide-like immunoreactivity. The role for de novo ceramide synthesis was also shown in the in vivo model of radiocontrast nephropathy. We demonstrated here for the first time that the enhancement of de novo ceramide synthesis contributes to radiocontrast nephropathy.

Effects of ceramide inhibition on experimental radiation-induced oral mucositis

OBJECTIVE

Oral mucositis (OM) is a common toxicity of ionizing radiation (IR), which is used as treatment for head and neck cancer. Ceramide-mediated apoptosis may contribute to the pathogenesis of mucositis. In response to IR or other cellular stresses, ceramide production occurs either by the hydrolytic action of sphingomyelinase (SMase) or de novo via ceramide synthase.

STUDY DESIGN

Male golden Syrian hamsters (10 per group) exposed to a single dose of 40 Gy ionizing radiation (day 0) were treated with subcutaneous 0.2 mL injections of either neutral SMase, acidic SMase, or ceramide synthase inhibitor (5 mmol/L glutathione, 5 micromol/L desipramine, or 1 micromol/L fumonisin B1, respectively) from day -1 to day 16. A control group was treated with saline. Two blinded examiners assessed clinical OM development from day 6 to day 26. Two animals per group were killed on days 3, 10, and 16 for immunohistochemical detection of ceramide expression in both the epithelium and in the connective tissue.

RESULTS

The group exposed to fumonisin B1 exhibited a statistically significant reduction in mean daily weight gain, mean mucositis score, duration of mucositis, and expression of ceramide in the epithelium on day 3 as well as in the connective tissue on days 10 and 16 relative to control. Immunohistologic analysis also revealed significant differences in ceramide expression on days 3 and 16 for animals treated with glutathione in both the epithelial and connective tissue when compared to the control.

CONCLUSIONS

These results suggest that IR triggers early de novo ceramide production and that inhibition of this process attenuates OM on a clinical level.

Natural variation of ascospore and conidial germination by Fusarium verticillioides and other Fusarium species

Fusarium verticillioides and other Fusarium species were examined for their spore germination phenotypes. In general, germinating spores of F. verticillioides formed germ tubes that immediately penetrated into agar. Such invasive germination was the predominant growth phenotype among 22 examined field isolates of F. verticillioides from a broad range hosts and locations. However, two of the field isolates were unique in that they formed conidial germ tubes and hyphae that grew along the surface of agar before penetration eventually occurred. Conidia of 22 other Fusarium species were assessed for their germination phenotypes, and only some strains of F. annulatum, F. fujikuroi, F. globosum, F. nygamai, and F. pseudoanthophilum had the surface germination phenotype (21% of the strains assessed). Sexual crosses and segregation analyses involving one of the F. verticillioides surface germination strains, NRRL 25059, indicated a single locus, designated SIG1 (surface vs. invasive germination), controlled the germ tube growth phenotypes exhibited by both conidia and ascospores. Perfect correlation was observed between an ascospore germination phenotype and the germination phenotype of the conidia produced from the resulting ascospore-derived colony. Recombination data suggested SIG1 was linked ( approximately 7% recombination frequency) to FPH1, a recently described locus necessary for enteroblastic conidiogenesis. Corn seedling blight assays indicated surface germinating strains of F. verticillioides were less virulent than invasively germinating strains. Assays also indicated pathogenicity segregated independently of the FPH1 locus. Invasive germination is proposed as the dominant form of spore germination among Fusarium species. Furthermore, conidia were not necessary for corn seedling disease development, but invasive germination may have enhanced the virulence of conidiating strains.

Serum sphinganine and the sphinganine to sphingosine ratio as a biomarker of dietary fumonisins during chronic exposure in ducks

Sphinganine concentration (Sa) and sphinganine to sphingosine ratio (Sa/So) are sensitive biomarkers of fumonisin B1 (FB1) exposure in animals and have been proposed to reveal FB1 exposure in humans. They correlate with liver and kidney toxicity and often precede signs of toxicity. However, the use of Sa and Sa/So is confusing during chronic exposure. Indeed, some authors report altered sphingolipids metabolism, whereas others fail to demonstrate significant effect. The aim of this study was to investigate the kinetics of Sa and Sa/So in the serum of ducks over a 77-day exposure to 0, 2, 8, 32 and 128 mg FB1/kg feeds. Serum biochemistry was also investigated to reveal hepatotoxicity. The results obtained indicate that the kinetics of sphingolipids and serum biochemistry are closely linked with the duration of the exposure. After a strong and rapid increase Sa and Sa/So decrease then stabilize. The lowest investigated dose able to determine a detectable effect is 2 mg/kg feeds, the Sa/So ratio being the most sensitive biomarker of FB1 exposure.

A time-series study of sick building syndrome: chronic, biotoxin-associated illness from exposure to water-damaged buildings

The human health risk for chronic illnesses involving multiple body systems following inhalation exposure to the indoor environments of water-damaged buildings (WDBs) has remained poorly characterized and the subject of intense controversy. The current study assessed the hypothesis that exposure to the indoor environments of WDBs with visible microbial colonization was associated with illness. The study used a cross-sectional design with assessments at five time points, and the interventions of cholestyramine (CSM) therapy, exposure avoidance following therapy, and reexposure to the buildings after illness resolution. The methodological approach included oral administration of questionnaires, medical examinations, laboratory analyses, pulmonary function testing, and measurements of visual function. Of the 21 study volunteers, 19 completed assessment at each of the five time points. Data at Time Point 1 indicated multiple symptoms involving at least four organ systems in all study participants, a restrictive respiratory condition in four participants, and abnormally low visual contrast sensitivity (VCS) in 18 participants. Serum leptin levels were abnormally high and alpha melanocyte stimulating hormone (MSH) levels were abnormally low. Assessments at Time Point 2, following 2 weeks of CSM therapy, indicated a highly significant improvement in health status. Improvement was maintained at Time Point 3, which followed exposure avoidance without therapy. Reexposure to the WDBs resulted in illness reacquisition in all participants within 1 to 7 days. Following another round of CSM therapy, assessments at Time Point 5 indicated a highly significant improvement in health status. The group-mean number of symptoms decreased from 14.9+/-0.8 S.E.M. at Time Point 1 to 1.2+/-0.3 S.E.M., and the VCS deficit of approximately 50% at Time Point 1 was fully resolved. Leptin and MSH levels showed statistically significant improvement. The results indicated that CSM was an effective therapeutic agent, that VCS was a sensitive and specific indicator of neurologic function, and that illness involved systemic and hypothalamic processes. Although the results supported the general hypothesis that illness was associated with exposure to the WDBs, this conclusion was tempered by several study limitations. Exposure to specific agents was not demonstrated, study participants were not randomly selected, and double-blinding procedures were not used. Additional human and animal studies are needed to confirm this conclusion, investigate the role of complex mixtures of bacteria, fungi, mycotoxins, endotoxins, and antigens in illness causation, and characterize modes of action. Such data will improve the assessment of human health risk from chronic exposure to WDBs.

Augmented fumonisin B1 toxicity in co-cultures: evidence for crosstalk between macrophages and non-parenchymatous liver epithelial cells involving proinflammatory cytokines

Fumonisin B1, a common mycotoxin produced by Fusarium verticillioides found in corn, causes several fatal animal diseases. Liver and kidney are target organs of fumonisin B1 in laboratory animals, but primary rodent hepatocytes and liver slices were resistant to fumonisin B1-induced cytotoxic effects. We have shown that fumonisin B1 induces expression of tumor necrosis factor (TNF)alpha, interferon (IFN)gamma, and interleukine (IL) 12, in mouse liver. In various models of acute liver injury, a positive amplification loop involving TNFalpha, IFNgamma, and IL-12 has been implied that involves Kupffer cells (macrophages), hepatic lymphocytes and non-parenchymatous liver epithelial cells (NPECs). In the current study, cellular interactions in fumonisin B1-induced toxicity were investigated, using co-cultures of murine macrophages (J774A.1) and NPECs (NMuLi). Treatment of the co-cultures with fumonisin B1-produced cytotoxicity, whereas either J774A.1 or NMuLi cultures alone showed no response to the mycotoxin. Accumulation of sphinganine occurred to the similar extent in individual cultures as well as co-cultures. Expression of TNFalpha and IL-12 was increased in co-cultures but not in individual cultures. Transfer of conditioned medium from fumonisin B1-treated J774A.1 cells to NMuLi cultures produced an increase in IFNgamma expression in NMuLi cells. Results indicated that macrophages and liver epithelial cells interact in response to fumonisin B1 and potentiate the cytokines expression, which may have implications in making hepatocytes responsive to cytotoxicity of fumonisin B1.

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.