Resistance in Maize Inbred Lines to Fusarium verticillioides and Fumonisin Accumulation in South Africa.

Fusarium ear rot of maize, caused by Fusarium verticillioides, is an important disease affecting maize production worldwide. Apart from reducing yield and grain quality, F. verticillioides produces fumonisins which have been associated with mycotoxicoses of animals and humans. Currently, no maize breeding lines are known with resistance to F. verticillioides in South Africa. The objective of this study, therefore, was to evaluate 24 genetically diverse maize inbred lines as potential sources of resistance to Fusarium ear rot and fumonisin accumulation in field trials at Potchefstroom and Vaalharts in South Africa. After artificial silk channel inoculation with F. verticillioides, Fusarium ear rot development was determined at harvest and fumonisins B1, B2, and B3 quantified. A significant inbred line by location effect was observed for Fusarium ear rot severity (P ≤ 0.001), although certain lines proved to be consistently resistant across both locations. The individual inbred lines also differed considerably in fumonisin accumulation between Potchefstroom and Vaalharts, with differentiation between susceptible and potentially resistant inbred lines only being possible at Vaalharts. A greenhouse inoculation trial was then also performed on a subset of potentially resistant and highly susceptible lines. The inbred lines CML 390, CML 444, CML 182, VO 617Y-2, and RO 549 W consistently showed a low Fusarium ear rot (<5%) incidence at both Potchefstroom and Vaalharts and in the greenhouse. Two of these inbred lines, CML 390 and CML 444, accumulated fumonisin levels <5 mg kg-1. These lines could potentially act as sources of resistance for use within a maize breeding program.

Cancer initiating properties of fumonisin B1 in a short-term rat liver carcinogenesis assay.

The nature of cancer initiation by fumonisin B(1) (FB(1)) was investigated in rat liver by monitoring the effect of phenobarbital (PB) as cancer promoter and evaluating the involvement of spontaneously initiated cells. A PB promoting regimen (0.05% in the diet) stimulated the outgrowth of FB(1)-induced placental glutathione S-transferase (GSTP) positive initiated hepatocytes. Reversion of the FB(1)-induced GSTP(+) foci was noticed in the absence of a promoting regimen. Younger rats were shown to be more sensitive to the induction of GSTP(+) foci by FB(1). Cancer initiation by FB(1) was associated with a hepatotoxic effect, which was less pronounced in older rats presumably due to a reduced intake. A specific role of spontaneously initiated cells and their promotion by FB(1) into the development of eosinophilic clear cell foci could not be established under the present experimental conditions. The ability of different stimuli to selectively promote the outgrowth of FB(1) initiated cells further verifies the cancer initiating potency of this apparent non-genotoxic mycotoxin. The underlying mechanism(s) involved in the genesis of the initiated hepatocytes is not known at present.

Mango malformation disease and the associated fusarium species.

ABSTRACT Mango malformation disease (MMD) occurs in Asia, Africa, and the Americas and was first reported in India in 1891. The vegetative form of MMD was first reproduced in 1966 with Fusarium moniliforme and the floral form with isolates of F. moniliforme var. subglutinans from both vegetative shoots and floral tissue. The fungi were subsequently recognized as F. subglutinans. In 2002, a new species, F. mangiferae, was established based on nuclear and mitochondrial DNA sequences; it included strains of F. subglutinans from Egypt, Florida, Israel, Malaysia, and South Africa, some of which had been shown to cause MMD by artificial inoculation. At least three additional taxa have been associated with MMD: F. sterilihyphosum from Brazil and South Africa, and Fusarium sp. nov. and F. proliferatum (teleomorph: Gibberella intermedia) from Malaysia. To date, Koch's postulates have not been completed with them. In the future, gene sequencing will be essential to identify the Fusarium spp. that are associated with MMD. Work remains to be done on the morphology, sexual compatibility, pathogenicity, and toxigenicity of these taxa.

Cytopathology of the esophagus in Transkei.

Esophageal brush biopsy capsules were used to prepare exfoliative cytologic smears of 1,000 residents of low-, intermediate-, and high-risk areas for esophageal cancer in Transkei, southern Africa. Satisfactory smears were obtained from 96.4% of the persons screened. The technique used was rapid, simple, inexpensive, safe, and effective in the determination of the prevalence of dysplasia and early carcinoma and the progression rate of dysplasia to carcinoma. In the high-risk area, precursor lesions (esophagitis and cellular atypia) were detected in 24% of adults older than 35 years, dysplastic changes in 9%, and carcinoma in 2%. Dysplastic changes were also present in 7% of young adults (25-34 yr of age) and in 1.5% of persons 15-24 years old. Precursor lesions were detected in 16% of the population group between 15 and 24 years old. Dysplastic changes and other precursor lesions were significantly less frequent in the population from the low-risk areas. A total of 14 malignant cases were detected in 8 females and 6 males. Of these, 9 were histologically confirmed squamous cell carcinomas in various stages of differentiation. The progression of dysplastic changes to carcinoma was observed in 5 of the total 14 cases. Three early cancers were successfully treated by esophagectomy. Seasonal variation occurred in the prevalence of mild cytologic changes.

Carcinogenicity of Fusarium moniliforme culture material in rats.

Two isolates of Fusarium moniliforme from corn were used in a chronic study with groups of 30 inbred male BD IX rats fed a semipurified diet that was marginally adequate nutritionally. Group 1 served as the controls and received the semipurified diet containing 5% cornmeal, group 2 received 5% of strain MRC 1069 culture material that was nontoxic to rats, and group 3 received 0.5% of strain MRC 826 culture material that was highly toxic to rats. The amount of the mutagen fusarin C detected in the culture material of strains MRC 826 and MRC 1069 was 104 and 364 mg/kg, respectively. Survival up to 2 years was good in all groups. Pathologic examination showed that many rats in group 2 had mild ductular cell hyperplasia. Almost all rats in group 3 had neoplastic nodules, gamma-glutamyltransferase-positive foci, adenofibrosis, and esophageal basal cell hyperplasia. Whereas no tumors were induced in groups 1 and 2, the 21 long-term survivors in group 3 developed 8 cholangiocarcinomas, 2 hepatocellular carcinomas, 4 carcinomas of the forestomach epithelium, and 1 esophageal papilloma. Since neoplastic lesions were confined to rats in group 3 and the diet of these rats contained much less fusarin C than that of group 2, it is highly unlikely that fusarin C was responsible for the carcinogenicity of the MRC 826 culture material. It appears that the toxicity of F. moniliforme strains may be related to their carcinogenicity, but the chemical nature of the toxic and carcinogenic metabolite(s) produced by F. moniliforme MRC 826 remains unknown.

Natural occurrence of Fusarium and subsequent fumonisin contamination in preharvest and stored maize in Benin, West Africa.

The natural occurrence of Fusarium and fumonisin contamination was evaluated from 1999 to 2003 in both preharvest and stored maize produced by small-scale farmers in four agroecological zones of Benin. Mycological analyses revealed a predominance of both Fusarium and Aspergillus in maize samples compared to other genera. The two Fusarium species most commonly isolated from maize were Fusarium verticillioides (68%) and Fusarium proliferatum (31%). Atypical isolates of F. verticillioides with some characteristics of Fusarium andiyazi but apparently closer to F. verticillioides, because the isolates were all high fumonisin producers, were also found only on preharvest maize. Study of F. verticillioides strains showed the presence of extremely high fumonisin producers in Benin with total fumonisin levels ranging from 8240 to 16,690 mg/kg. Apart from 2002-2003, Fusarium occurrence was not significantly different from one zone to another, although a slight decrease was observed from south, humid, to north, drier. Fusarium occurrence varied somewhat from one season to another. It significantly decreased over the 6 months of storage. Widespread fumonisin occurrence in maize was observed. Most of the maize samples collected were found positive for fumonisin with levels ranging from not detected to 12 mg/kg in 1999-2000, 6.7 mg/kg in 2000-2001 and 6.1 mg/kg in 2002-2003. Fumonisin levels in maize were found to be significantly higher in the two southern zones during all the surveys. The highest mean total fumonisin level was detected in 1999-2000 in maize samples from the southern Guinea Savannah (SGS) (12 mg/kg), whereas in both 2000-2001 and 2002-2003, it was in samples from the forest mosaic savannah (FMS) (6.7 and 6.1 mg/kg, respectively). Fumonisin levels varied from one season to another and, throughout the storage time, showing a decreasing trend in each zone. However, this decrease was not significant every season. An increasing trend was observed during some seasons in the SGS and northern Guinea Savannah (NGS) zones. The results of this study emphasise that farmers and consumers, not only in Benin but also in other West African countries, should be alerted to the danger of fumonisin contamination in maize.

Fate of aflatoxins and fumonisins during the processing of maize into food products in Benin.

The fate of aflatoxins and fumonisins, two mycotoxins that cooccur in maize, was studied through the traditional processing of naturally contaminated maize in mawe, makume, ogi, akassa, and owo, maize-based foods common in Benin, West Africa. Levels of total aflatoxin and fumonisin were measured at the main unit operations of processing, and the unit operations that induce significant reduction of mycotoxin level were identified. Overall reduction of mycotoxin level was more significant during the preparation of makume (93% reduction of aflatoxins, 87% reduction of fumonisins) and akassa (92% reduction of aflatoxins, 50% reduction of fumonisins) than that of owo (40% reduction of aflatoxins, 48% reduction of fumonisins). Sorting, winnowing, washing, crushing combined with dehulling of maize grains were the unit operations that appeared very effective in achieving significant mycotoxin removal. Aflatoxins and fumonisins were significantly recovered in discarded mouldy and damaged grains and in washing water. Fermentation and cooking showed little effect. During the preparation of ogi and akassa, reduction of fumonisin levels measured in food matrix was lower (50%) compared to mawe and makume, probably due to significant fumonisin release in ogi supernatant. Consequently, the use of ogi supernatant for preparing beverages or traditional herbal medicines could be harmful as it is likely to be contaminated with mycotoxin from the raw maize.

Atherogenic effects in a non-human primate of Fusarium moniliforme cultures added to a carbohydrate diet.

Adding less than 0.5% w/w of culture material of strain MRC 826 of the fungus Fusarium moniliforme to a carbohydrate diet low in fat resulted in an atherogenic plasma lipid profile in a non-human primate. Simultaneously increased plasma fibrinogen and activity of blood coagulation factor VII could enhance atherogenesis. This unique potential for promotion of atherosclerosis was probably secondary to chronic hepatotoxicity as indicated by liver fibrosis and elevated cholesterol, albumin and the enzymes AST, ALT, LD, GGT and ALP in serum. The cholesterol and enzymes responded in proportion to the calculated doses of fumonisin mycotoxins in the F. moniliforme MRC 826 cultures. Fumonisins are water soluble and heat stable. Thrombotic, hepatotoxic, carcinogenic and cerebral effects of MRC 826 culture material and fumonisins are well known in non-primates. The estimated fumonisin concentrations tested fall within a range due to natural contamination of human foods. The results suggest that all maize grain products should be analysed for fumonisins.

Cancer initiation by fumonisin B(1) in rat liver--role of cell proliferation.

Fumonisin B(1) (FB(1)), a carcinogenic mycotoxin produced by the fungus Fusarium verticillioides in corn, causes cancer initiation in rat liver in a similar manner to genotoxic carcinogens although apparently with different kinetics. The present experiment was designed to evaluate the role of regenerative cell proliferation, effected by partial hepatectomy (PH) and carbontetrachloride (CCl(4)) and direct mitogen-induced hyperplasia, induced by lead nitrate (PbNO(3)), on FB(1)-induced cancer initiation. Initiation was effected over a period of 14 days by gavage administration of FB(1) at different daily doses ranging from 0.14 to 3.5 mg FB(1)/100 g body weight while the stimuli for cell proliferation were introduced 7 days after the start of the FB(1) treatment. Based on the proliferative stimulus used, cancer promotion was effected 3 weeks after completion of the initiating treatment by 2-acetylaminofluorene (2-AAF) treatment followed by PH or carbon tetrachloride CCl(4) on day 4. Cancer initiation by FB(1) was associated with a hepatotoxic effect and an increase in lipid peroxidation. In contrast to compensatory liver cell proliferation induced by PH and CCl(4), mitogen-induced hyperplasia (PbNO(3)) failed to enhance the cancer initiating potential of FB(1) suggesting that cancer induction by a non-genotoxic carcinogen is supported by regenerative cell proliferation. Cognizance of the enhancing role of cell proliferation during cancer initiation by FB(1) is required in assessing the risks posed by this mycotoxin to humans.

The cancer-promoting potential of fumonisin B1 in rat liver using diethylnitrosamine as a cancer initiator.

The cancer-promoting potential of fumonisin B1 (FB1) was investigated by feeding different dietary levels (10, 50, 100, 250, 500 mg FB1/kg) to diethynitrosamine (DEN)-initiated rats for 21 days. Dietary levels containing 50 mg FB1/kg and higher, markedly increased the number and size of the placental form of glutathione-S-transferase-positive (GSTP+) foci in the liver of the rats. The cancer-promoting activity of FB1 was associated with an inhibitory effect on partial hepatectomy (PH)-induced regenerative hepatocyte proliferation, as the incorporation of 3H-labelled thymidine was significantly (P < 0.05) reduced by those FB1-containing diets that exhibited cancer promotion. In vitro studies on the mitogenic activity of epidermal growth factor (EGF) in primary rat hepatocytes further supported the in vivo data in that FB1, similar to other cancer promoters such as phenobarbital and 2-acetylaminofluorene (2-AAF), alters growth stimulatory responses in primary hepatocytes. No significant (P > 0.05) changes in the sphinganine/sphingosine (Sa/So) ratio were observed in the liver of the rats fed the lowest FB1-containing diet (50 mg FB1/kg diet) that effected cancer promotion. The present study indicated that FB1 exhibited cancer-promoting activity in the absence of adverse hepatotoxic effects and at dietary levels that failed to effect cancer initiation.

The effects of dietary iron overload on fumonisin B1-induced cancer promotion in the rat liver.

The present study was performed to determine whether excess hepatic iron modulates the cancer-initiating and promoting properties of FB1. Thirty-eight male F344 rats were divided into four dietary treatment groups: (i) control diet (AIN, n = 8); (ii) FB1 250 mg/kg diet (FB1, n = 10); (iii) 1-2% carbonyl iron (CI, n = 10); or (iv) FB1 plus iron loading (FB1/CI, n = 10) for 5 weeks (2 x 2 factorial design). Hepatic iron concentrations in iron-loaded animals at 5 weeks were 444 +/- 56 (CI) and 479 +/- 80 micromol/g dry weight (FB1/CI) (mean +/- SEM). All the FB1-fed rats, in the presence or absence of CI, developed a toxic hepatitis with a 4-fold rise in serum alanine transaminase (ALT) levels. FB1 appeared to augment iron-induced hepatic lipid peroxidation, as measured by the generation of thiobarbituric acid reacting substances (TBARS) in liver homogenates (P < 0.0001). Morphometric analysis showed that FB1 caused a significantly greater mean +/- SEM number of 'enzyme-altered' foci and nodules per cm2 (5.34 +/- 1.42 vs. 1.50 +/- 0.52, P < 0.05), as well as a greater area (%) of liver occupied by foci and nodules (0.33 +/- 0.12% vs. 0.05 +/- 0.03%, P < 0.001), compared with FB1/CI. The addition of FB1 to dietary iron loading caused a shift in distribution of iron from hepatocytes to Kupffer cells, probably due to phagocytosis of necrotic iron-loaded hepatocytes. In conclusion, (i) FB1 appears to cause toxicity in the liver independently from effects on lipid peroxidation; (ii) FB1 has a potentiating effect on iron-induced lipid peroxidation; and (iii) dietary iron loading appears to protect against the cancer promoting properties of FB1, possibly due to a stimulatory effect of iron on hepatocyte regeneration.

Discovery and occurrence of the fumonisins: a historical perspective.

This article describes the events leading to the discovery of the fumonisins in South Africa in 1988 and highlights the first 10 years (1988-1998) of fumonisin research. The predominant fungus isolated from moldy corn implicated in a field outbreak of equine leukoencephalomalacia (ELEM) in South Africa in 1970 was Fusarium verticillioides (F. moniliforme). This fungus was also prevalent in moldy home-grown corn consumed by people in high-incidence areas of esophageal cancer (EC) in the Transkei region of South Africa. Culture material on corn of F. verticillioides strain MRC 826, which was isolated from moldy corn in Transkei, was shown to cause ELEM in horses, porcine pulmonary edema (PPE) syndrome in pigs, and liver cancer in rats. A short-term cancer initiation/promotion assay in rat liver was used to purify the carcinogen(s) in the culture material. These efforts finally met with success when fumonisins B1 and B2 novel mycotoxins with cancer-promoting activity in rat liver, were isolated from culture material of F. verticillioides MRC 826 at the Programme on Mycotoxins and Experimental Carcinogenesis of the Medical Research Council in Tygerberg, South Africa. Following the elucidation of the chemical structure of the fumonisins, these carcinogenic mycotoxins were shown to occur naturally in moldy corn in Transkei. Shortly thereafter, high levels of fumonisins in the 1989 U.S. corn crop resulted in large-scale field outbreaks of ELEM and PPE in horses and pigs, respectively, in the United States. Subsequently the fumonisins were found to occur naturally in corn worldwide, including corn consumed as the staple diet by people at high risk for EC in Transkei and China. These findings, together with the fact that the fumonisins cause field outbreaks of mycotoxicoses in animals, are carcinogenic in rats, and disrupt sphingolipid metabolism, have resulted in much worldwide interest in these compounds during the first 10 years after the discovery of the fumonisins in 1988.

Toxicity of culture material of Fusarium verticillioides strain MRC 826 to nonhuman primates.

We conducted a chronic feeding study in vervet monkeys (Cercopithecus aethiops) over 13.5 years. The experimental design consisted of two dietary treatment groups, each including males and females, fed varying levels of culture material of Fusarium verticillioides (Sacc.) Nirenberg (= F. moniliforme Sheldon) strain MRC 826 mixed into their daily food ration. Two females were included as treatment controls. We conducted blood chemical analyses bimonthly and recorded all clinical signs during the course of the experiment. We took liver biopsies at various stages during the initial phase of the experiment. Several monkeys were terminated in extremis during the experiment. Detailed feed intake profiles were determined 5 years after the experiment began, and the fumonisin B (FB) mycotoxin content of the feed was determined during the final stages of the experiment. The apparent FB consumption patterns were related to changes observed in the biochemical parameters in the blood and urine, including the liver function enzymes and creatinine clearance as well as differential blood counts and sphingolipid levels in the serum and urine. An apparent no-effect threshold for kidney and liver damage is estimated to be between 0.11 and 0.18 mg FB/kg body weight (bw)/day, which corresponds to a feed contamination level of between 8.21 and 13.25 mg FB/kg bw diet. Apart from the effects on the liver and kidney, a wide variety of parameters, including cholesterol and creatine kinase, were also adversely affected. Several blood parameters, including white and red blood cells, also significantly decreased in the treated animals. The serum sphinganine level and the sphingosine/sphinganine ratio, monitored toward the end of the experiment, significantly increased in both the low-dose and high-dose animals. The present study provides important information about the diversity of lesions induced by culture material of F. verticillioides in vervet monkeys and the dosage levels of fumonisins to be used in long-term studies in nonhuman primates.

Fumonisin-induced hepatocarcinogenesis: mechanisms related to cancer initiation and promotion.

We review the hepatocarcinogenic effects of fungal cultures of Fusarium verticillioides(= Fusarium moniliforme) strain MRC 826 in male BD IX rats. Subsequent chemical analyses of the fumonisin B (FB) mycotoxin content in the culture material used and long-term carcinogenesis studies with purified FB1 provide information about dose-response effects, relevance of hepatotoxicity during FB1-induced carcinogenesis, and the existence of a no-effect threshold. Fumonisin intake levels of between 0.08 and 0.16 mg FB/100 g body weight (bw)/day over approximately 2 years produce liver cancer in male BD IX rats. Exposure levels < 0.08 mg FB/100 g bw/day fail to induce cancer, although mild toxic and preneoplastic lesions are induced. The nutritional status of the diets used in the long-term experiments was marginally deficient in lipotropes and vitamins and could have played an important modulating role in fumonisin-induced hepatocarcinogenesis. Short-term studies in a cancer initiation/promotion model in rat liver provided important information about the possible mechanisms involved during the initial stages of cancer development by this apparently nongenotoxic mycotoxin. These studies supported the findings of long-term investigations indicating that a cytotoxic/proliferative response is required for cancer induction and that a no-effect threshold exists for cancer induction. The mechanisms proposed for cancer induction are highlighted and include the possible role of oxidative damage during initiation and the disruption of lipid metabolism, integrity of cellular membranes, and altered growth-regulatory responses as important events during promotion.

Soil fertility factors in relation to oesophageal cancer risk areas in Transkei, southern Africa.

Soil samples were collected during certain years for the period 1982-89 from high- and low-risk areas for oesophageal cancer in Transkei, southern Africa. These samples were taken either from cultivated soils under maize monoculture, or from uncultivated soils (1989 only) adjacent to the maize fields. Analyses of mineral elements in the soil samples were performed at two independent laboratories. Furthermore, soil and maize leaf samples, from field trials in a high- and a low-risk area for oesophageal cancer were analysed. The results from this study do not agree with those reported previously for Transkei. Cultivated soils in both high- and low-risk areas were found to be highly fertile. The levels of Mn, Ni, Mg, Ca, K and soil pH were significantly higher, and Al, Fe and organic matter significantly lower in the high-risk compared with the low-risk area. Leaf analysis, although not tested statistically, indicated higher levels of Mn K, Ca and Fe, and lower levels of P, in the high-risk area.

A mutagen produced by Fusarium moniliforme.

A mutagenic compound produced by Fusarium moniliforme on maize was isolated by CHCl3--iso-PrOH extraction, solvent partitioning and liquid chromatography on silica gel and Sephadex LH-20. HPLC studies showed that different mutagenic and non-mutagenic forms can be derived from the mutagen (P3) and that prolonged exposure to longwave u.v. light and to high temperatures causes a total loss of its u.v. absorption and mutagenic characteristics. Spectral data presented for P3 include u.v., i.r., mass spectra as well as 1H NMR and 13C NMR. Mass spectral data indicated a molecular formula of C23H29NO7.

Disruption of sphingolipid metabolism in non-human primates consuming diets of fumonisin-containing Fusarium moniliforme culture material.

The fumonisin mycotoxins are produced by Fusarium moniliforme Sheldon, a contaminant of corn worldwide. The two most abundant analogues (fumonisins B1 and B2) are known to be potent inhibitors of sphingosine N-acyltransferase (ceramide synthase) and hence to disrupt de novo sphingolipid biosynthesis. The sphingoid bases, sphingosine and sphinganine (and hence their ratio), were measured at varying intervals over a period of 60 weeks in the serum of non-human primates (vervet monkeys; Cercopithecus aethiops) which were consuming diets containing 'low' and 'high' amounts of F. moniliforme culture material, such that their total daily fumonisin intake was approximately 0.3 and 0.8 mg/kg body weight/day, respectively. Although no significant differences were found in the serum levels of sphingosine compared to controls, serum sphinganine levels in the experimental groups (mean of 219 nM and 325 nM, respectively) were significantly (P = 0.02) elevated above the levels in controls (mean 46 nM). As a consequence, the ratio sphinganine:sphingosine was significantly (P = 0.003) elevated from a mean of 0.43 in the control group to 1.72 and 2.57 in the experimental groups, respectively. Similar changes in sphingolipid profiles were also measured in urine with an increase of the ratio from 0.87 in controls to 1.58 and 2.17 in the experimental groups, although the differences were not statistically significant. Hence, the disruption of sphingolipid biosynthesis in vervet monkeys by fumonisins in culture material added to their diet can effectively be monitored in the serum as an elevation of the sphinganine:sphingosine ratio.

Interaction of fumonisin B(1) and aflatoxin B(1) in a short-term carcinogenesis model in rat liver.

The co-existence of the fumonisin and aflatoxin mycotoxins in corn merited studies to investigate their possible synergistic toxicological and carcinogenic effects. When utilising a short-term carcinogenesis model in rat liver, both the compounds exhibited slow cancer initiating potency as monitored by the induction of foci and nodules stained positively for the placental form of gluthatione-S-transferase (GSTP(+)). However, when rats were treated in a sequential manner with AFB(1) and FB(1) the number and size of GSTP(+) lesions significantly increased as compared to the separate treatments. Histopathological analyses indicated that the individual treatments showed far less toxic effects, including occasional hepatocytes with dysplastic nuclei, oval cell proliferation and, in the case of FB(1), a few apoptotic bodies in the central vein regions. The sequential treatment regimen induced numerous foci and dysplastic hepatocyte nodules, and with oval cells extending from the periportal regions into the centrilobular regions. This would imply that, in addition to the cancer promoting activity of FB(1) of AFB(1)-initiated hepatocytes, the AFB(1) pre-treatment enhanced the FB(1) initiating potency, presumably by rendering the liver more susceptible to the toxic effects of FB(1). The co-occurrence of AFB(1) and FB(1) in corn consumed as a staple diet could pose an increased risk and should be included in establishing risk assessment parameters in humans.

Toxicological effects in rats chronically fed low dietary levels of fumonisin B(1).

The toxicity of low dietary levels of fumonisin B(1) (FB(1)), i.e. 1, 10 and 25 mg FB(1)/kg diet, were monitored in rats over a period of 24 months. No effects on the body weight gain and feed intake profiles were noticed, while the relative liver weight was significantly (P<0.05) reduced in the FB(1)-treated rats. Mild toxic effects, including single cell necrosis (apoptosis), proliferation of bile duct epithelial cells (DEC), and early signs of fibrosis, bile duct hyperplasia and in one case, adenofibrosis, were noticed in the liver of the rats fed the highest (25 mg/FB(1)/kg diet) dietary level. A significant (P<0.05) increase in the level of oxidative damage was also noticed in the liver of the rats of high dosage dietary group. The toxic effects were less severe in the 10 mg FB(1)/kg dietary group, whilst only a few ground glass foci were observed in the 1 mg FB(1)/kg dietary group. Hepatocyte nodules, staining positively for glutathione-S-transferase (placental form, PGST), were observed macroscopically in the 25 mg FB(1)/kg treated group and to a lesser extent in the 10 mg FB(1)/kg treated rats. The most prominent toxic lesions by FB(1) (10 and 25 mg FB(1)/kg dietary groups) in the kidneys were restricted to the tubular epithelium manifesting as granular cast, necrosis, apoptosis, calcification and the presence of regenerative foci in the proximal convoluted tubules. The existence of a cytotoxic/proliferative threshold with respect to cancer induction by FB(1) in rat liver became apparent, with a dietary level of <10-mg FB(1)/kg diet as a no effect threshold for the induction of hepatocyte nodules.