Gavage administration of the fungal toxin fumonisin B1 to female Sprague-Dawley rats

A 65-Day Fumonisin B Exposure at High Dietary Levels Has Negligible Effects on the Testicular and Spermatological Parameters of Adult Rabbit Bucks

A 65-day study was undertaken to test the effects of two doses (10 and 20 mg/kg) of dietary fumonisin Bs (FB) on the rabbit male reproduction system. Body and testicular weight was not affected by the intoxication, neither the fatty acid composition of the testicular total phospholipids; the testis histological analysis failed to reveal any toxic effect. The FBs increased the testicular concentration and activity of reduced glutathione and glutathione peroxidase and decreased initial phase lipid peroxidation (conjugated dienes and trienes) in a dose dependent manner. Sperm morphology and chromatin condensation were monitored on Feulgen-stained smears. No significant differences were observed between the treatment groups and between sampling time points. The live cell ratio in the sperm (as assessed with flow cytometry) was not different among groups at any of the five sampling timepoints and was also identical within groups. Similarly, the spermatozoa membrane lipid profile was also identical in all three groups after the total intoxication period. In summary, it was demonstrated that FBs in an unrealistic and unjustified high dose still do not exert any drastic harmful effect on the leporine, male reproduction system, meanwhile slightly augmenting testicular antioxidant response.

Dose and Exposure Time-Dependent Renal and Hepatic Effects of Intraperitoneally Administered Fumonisin B₁ in Rats

Male Wistar rats were treated intraperitoneally (i.p.) with fumonisin B₁ (FB₁; 0, 20, 50 and 100 mg/kg dietary dose equivalent) for 5 and 10 days (n = 24⁻24 in each setting) to gain dose- and time-dependent effects on antioxidant status and oxidative stress response, clinical chemical endpoints and liver, kidney and lung histopathology and lymphocyte damage (genotoxicity). FB₁ decreased feed intake, body weight gain and absolute liver weight, irrespective of the toxin dose. Relative kidney weight increased in the 10-day setting. Linear dose response was found for plasma aspartate aminotransferase, alanine aminotransferase, total cholesterol, urea and creatinine, and exposure time-dependence for plasma creatinine level. The latter was coupled with renal histopathological findings, tubular degeneration and necrosis and the detachment of tubular epithelial cells. The pronounced antioxidant response (reduced glutathione accretion, increasing glutathione peroxidase activity) referred to renal cortical response (5⁻10 days exposure at 50⁻100 ppm FB₁). Hepatic alterations were moderate, referring to initial phase lipid peroxidation (exposure time dependent difference of conjugated diene and triene concentrations), and slight functional disturbance (↑ total cholesterol). Lymphocyte DNA damage was moderate, supporting a mild genotoxic effect of FB₁.

Possible Role of Phosphatidylcholine and Sphingomyelin on Fumonisin B1-mediated Toxicity

A major corn-related mycotoxin, fumonisin B1 (FB1), continues to attract attention of researchers as well as risk-assessors due to the diverse toxicological characteristics, including distinct target tissues in different animal species and opposite susceptibility in males and females in mice and rats. More than thirty years passed since the structure identification as a sphingoid-like chemical, but the causal mechanism of the toxicity remains obscure in spites of extensive studies. Considerable amounts of knowledge have been accumulated on the biochemical/toxicological actions of FB1, but the influence on lipid dynamics and mobilization in the body has not been focused well in relation to the FB1-mediated toxicity. Considerable influences of this toxin on mobilization of sphingolipids and phospholipids and also on adaptive changes in their compositions in tissues are implicated from recent studies on FB1-interacting ceramide synthases. Accumulated patho-physiological data also suggest a possible role of hepatic phospholipid on FB1-mediated toxicity. Thus, a mechanism of FB1-mediated toxicity is discussed in relation to the mobilization of phospholipids and sphingolipids in the body in this context.

Effects of dietary fumonisin B1 on the onset of puberty, semen quality, fertility rates and testicular morphology in male rabbits

The influences of dietary fumonisin B(1) (FB(1)), a metabolite of Fusarium verticillioides, on the onset of puberty, semen quality, fertility rates and testicular morphology in male rabbits (bucks) were studied. Forty male rabbits were randomly assigned and fed four diets containing 0.13, 5.0, 7.5 and 10.0 mg FB(1)/kg, constituting diets 1 (control), 2, 3 and 4 respectively, for a period of 175 days in a completely randomized design. During the last week of the feeding trial, two untreated female rabbits were mated to each of the four treated bucks per treatment to assess the fertility rate of the treated bucks. Onset of puberty in animals fed diets 3 and 4 was significantly (P<0.05) delayed by some 9-12 days. The weight at puberty, sperm concentration and total sperm/ejaculate were not significantly influenced by the dietary FB(1). Sperm mass activities, motility and live spermatozoa of the rabbits' semen significantly (P<0.05) declined with an increase in the dietary FB(1). The highest sperm cell abnormalities were recorded in the animals fed 10.0 mg/kg FB(1), while the least was observed in the control animals. The conception rate, litter size and embryo survival rate were statistically the same among the dietary treatments. Embryo mortality was significantly (P<0.05) higher in rabbits fed diets 3 and 4 than in others. Testicular elements were significantly (P<0.05) impaired by the toxin in rabbits fed 7.5 and 10.0 mg FB(1)/kg. This suggests that LOAEL of 7.50 mg/kg FB(1) delayed puberty, impaired semen quality and spermatogenesis and induced embryo mortality without a statistically adverse effect on the fertility rates of male rabbits.

A review of the toxic effects and mechanisms of action of fumonisin B1

Fumonisin B(1) (FB(1)) is a mycotoxin produced by the fungus Fusarium verticillioides, which commonly infects corn and other agricultural products. Fusarium species can also be found in moisture-damaged buildings, and, therefore, exposure of humans to Fusarium mycotoxins including FB(1) may take place. FB(1) bears a clear structural similarity to the cellular sphingolipids, and this similarity has been shown to disturb the metabolism of sphingolipids by inhibiting the enzyme ceramide synthase leading to accumulation of sphinganine in cells and tissues. FB(1) is neurotoxic, hepatotoxic, and nephrotoxic in animals, and it has been classified as a possible carcinogen to humans. The cellular mechanisms behind FB(1)-induced toxicity include the induction of oxidative stress, apoptosis, and cytotoxicity, as well as alterations in cytokine expression. The effects of FB(1) on different parameters vary markedly depending on what types of cells are studied or what species they originate from. These aspects are important to consider when evaluating the toxic potential of FB(1).

Altered de novo sphingolipid biosynthesis is involved in the serum deprivation-induced cell death in LLC-PK1 cells

Fumonisin B1, a specific inhibitor of ceramide synthase, and ISPI (Myriocin), a serine palmitoyltransferase inhibitor, modulate the de novo sphingolipid biosynthesis pathway. This study was conducted to determine whether serum deprivation-induced cell death is regulated by de novo sphingolipid biosynthesis in pig kidney LLC-PK1 cells. Serum withdrawal from the culture medium produced cell death in LLC-PK1 cells. Fumonisin B1 at concentrations ranging from 5 M to 30 M delayed until 48 h this cell death resulting from the absence of fetal bovine serum (FBS) in cell culture. Pretreatment of cultured cells with fumonisin B1 in the presence of serum for 24 h increased by approximately 70% this cytoprotective activity of fumonisin B1 against serum deprivation-induced cell death. Serum deprivation increased sphingolipid biosynthesis threefold compared to 5% serum-enriched culture. Fumonisin B1 at 5-30 M lowered the content of total complex sphingolipids to levels of 50% and 77% of the content in serum-enriched culture, although the concentration of intracellular free sphinganine was elevated. ISP1 alone at greater than 1 nM concentration reduced total complex sphingolipid content to values in LLC-PK1 cells grown in the presence of 5% FBS. The results suggest that the de novo complex sphingolipid biosynthesis modulated by either fumonisin B1 or ISP1 may regulate serum deprivation-induced cell death in LLC-PK1 cells.

Residue formation of fumonisin B1 in porcine tissues

The residues derived from the uptake of fumonisin B1, a toxic metabolite of Fusarium verticillioides frequently occurring in corn and corn products, were determined in growing pigs. After oral administration of 100 mg FB(1)/animal/day for 5-11 days, serum, bile, lung, liver, kidney, brain, spleen, pancreas, heart, muscle, eye, and fat samples were collected immediately and analysed by LC-MS. The highest values were measured in kidney (833 +/- 1329 microg kg(-1), mean +/- SD), liver (231 +/- 163 microg kg(-1)), lung (170 +/- 311 microg kg(-1)) and spleen (854 +/- 2212 microg kg(-1)). Muscle contained 26 +/- 41 microg kg(-1), while in fat only 2 +/- 3 microg kg(-1) were traceable. Despite the potential accumulation over extended feeding periods as well as the large variations in the residue formation of FB(1), a carry-over in edible tissues from swine was considered not to be of toxicological relevance.

Nerve conduction velocity and spinal reflexes may change in rats after fumonisin B1 exposure

Mycotoxin fumonisin B1 (FB1) a natural inhibitor of ceramide synthase contaminating mainly the corn-based food and feed may cause dysfunctions in the nervous system. In the present study peripheral neural dysfunctions were biomonitored after dietary FB1 exposure in rats. Daily oral doses of 6.2 mg/kg body weight/day FB1 were applied in rats for 2 weeks. Before and after FB1 treatment nerve conduction velocities of tibial and sciatic nerves and spinal reflexes were analyzed in vivo. Electrophysiological recordings of biphasic plantar EMG (M and H components) and evaluation of sensory and motor nerve conduction velocities were carried out. Nerve conduction velocities revealed decreasing tendencies after FB1 exposure. The flexor reflex and the H-components of the extensor reflex were significantly reduced. The proposed in vivo biomonitoring can reveal functional impairment of the peripheral nervous system caused by mycotoxin exposure. Reduction of conduction velocity and altered reflexes after FB1 exposure are suspected to be associated with modified signal transmission due to toxic systemic effects and possible changes in sphingolipid metabolism.

Rat kidney pathology induced by chronic exposure to fumonisin B1 includes rare variants of renal tubule tumor

The carcinogenicity of fumonisin B1 (FB1), a worldwide contaminant of corn produced by Fusaria species of fungi, has been tested recently in 2-year feeding studies in Fischer F344 rats and B6C3F1 mice. Inclusion of FB1 at 50 and 80 ppm in the diet induced liver tumors in female mice, and at 50 and 150 ppm induced renal tumors in male rats (22). In the present study, the kidneys from the rat bioassay were examined to characterize the various histopathological changes associated with renal tumor induction. In all high-dose (150 ppm) and mid-dose (50 ppm) male rats, and to a lesser extent in high-dose (100 ppm) female rats, there was evidence of sustained nephrotoxicity manifested as basophilia, apoptosis, cell regeneration, and simple tubule hyperplasia, affecting proximal convoluted tubules in the deep cortex, extending into the outer region of the outer stripe of outer medulla. A further alteration consisted of sporadic areas of interstitial hyalinization in deep cortex, suggestive of expanded basement membrane, coupled with tubule atrophy. The continued presence of nephrotoxicity throughout chronic exposure to FB1 suggested that renal tumor development may have been an outcome of sustained cell loss and compensatory regeneration. In some cases, preneoplastic tubules or incipient renal tumors presented an immature or fetal form in association with interstitial hyalinization. The renal tubule tumors induced by FB1 were typified by a rare, highly malignant, anaplastic variant capable of growth by infiltration. Of the 10 renal tubule tumors diagnosed in the mid-dose males, and the 16 in the high-dose males, 8 and 10, respectively, were graded as carcinomas. Anaplastic variants represented 50% of the mid-dose carcinomas and 80% of the high-dose carcinomas. One of the anaplastic carcinomas in a mid-dose male was a true sarcomatoid phenotype not previously recorded in the rodent. Metastatic invasion of the lung occurred with 25% of the mid-dose carcinomas and 50% of the high-dose carcinomas. It was speculated that FB1 may have been influencing the growth characteristics of the induced renal tumors via its inhibitory action on the synthesis of sphingolipids, which in turn, participate in regulating cell contact, growth, and differentiation, or alternatively by affecting cell adhesion molecules.

A comparison of clinical, histopathological and cell-cycle markers in rats receiving the fungal toxins fumonisin B1 or fumonisin B2 by intraperitoneal injection

Fumonisins B1 and B2 (FB1 and FB2) are fungal secondary metabolites produced by members of the genus Fusarium. Although FB1 is usually detected in greater quantities, FB2 frequently co-occurs in contaminated feeds and foods and contributes to the total toxin load. In the present study, the comparative toxicity of FB1 and FB2 was examined in male Sprague-Dawley rats administered toxin (0.75 mg/kg body weight) or vehicle control intraperitoneally (ip) for 2, 4 or 6 consecutive days. Clinical changes, including elevated serum cholesterol, alanine aminotransferase (ALT), creatinine and protein, were slightly more pronounced in FB1-treated rats. The most consistent hematological change was an increase in vacuolated bone marrow cells, which was more pronounced in FB1-treated rats. Histopathological changes were similar in FB1- and FB2-treated rats and included single cell necrosis in kidneys and liver, cytoplasmic vacuolation in adrenal cortex and lymphocytolysis in thymus. In the liver mRNA expression for the cyclin kinase inhibitor p21 gene was significantly increased in FB1- and FB2-treated rats, compared to controls. Expression of mRNA for the cyclin D1 gene was significantly depressed in FB2-treated rats. Hepatic cyclin E mRNA was elevated in response to FB1 and FB2 compared to controls. In FB2-treated animals this corresponded with decreased liver p27 mRNA expression. Hepatic proliferating cell nuclear antigen (PCNA) transcription was elevated in FB1- but not FB2- treated rats. Changes in liver microsomal protein levels of p27, cyclin E and PCNA were similar to changes in gene expression. In contrast, cyclin D1 protein levels were elevated in rats treated with FB1 and, to a lesser extent, FB2. The data indicate that FB1 and FB2 can alter the expression of genes associated with the cell cycle, and indicate a need for a further understanding of the mechanistic basis of FB1 and FB2 toxicity.

Glutathione S-transferase-placental form expression and proliferation of hepatocytes in fumonisin B1-treated male and female Sprague-Dawley rats

Fumonisin B1 (FB1), a mycotoxin produced by a common corn contaminant Fusarium moniliforme and a hepatocarcinogen in rats, has been previously suggested to act as a poor initiator, but a better promoter of gamma-glutamyltranspeptidase (GGT)-positive rat liver preneoplastic lesions. Using glutathione S-transferase-placental form (GSTP) as a more sensitive marker of initiation, we have further evaluated the initiating capacity of various doses of purified FB1 administered (a) intraperitoneally (i.p.) to male Sprague-Dawley (SD) rats for 4 days and (b) orally (PO) to male and female SD rats for 11 days. Compared to their respective controls, significant increases in GSTP-positive hepatocytes were observed in male rats administered FB1 i.p. at 10 mg/kg body weight/day for 4 days, as well as in male and female rats treated with 35 and 75 mg/kg body weight/day FB1 p.o. for 11 days. The percentage section area of liver occupied by GSTP-positive mini-foci comprising of three to 12 cells was increased significantly in male rats given 10 mg/kg FB1 i.p., or in p.o.-treated males and females with 75 mg/kg FB1. Both i.p. and p.o. FB1 treatments resulted in dose-related enhanced hepatocyte proliferation as measured by proliferating cell nuclear antigen (PCNA) labeling with significant increases in the number of PCNA-positive nuclei at the same i.p. and p.o. dose levels where the number of GSTP-positive cells were elevated. In all studies, enhanced PCNA and GSTP expression occurred at FB1 doses which, based on serum biochemical and histopathological data previously reported from our laboratory, were shown to be hepatotoxic. Therefore, our data suggest that in a manner similar to known genotoxic carcinogens, FB1 has the capacity to initiate GSTP-positive hepatocytes with their subsequent development into GSTP mini-foci at exposure levels that induce enhanced hepatocyte proliferation in response to liver toxicity. In SD rats, this occurs as early as within 4 days of i.p. treatment or 11 days of p.o. treatment.