Fumonisins

Fumonsisins are produced by F. verticilloides (formerly moniliforme), F. proliferatum, and several uncommon fu-saria (83,84). Fumonisins were discovered in 1988 by two groups working independently. One was investigating the cause of human esophageal cancer in parts of southern Africa (85). The other was attempting to find the cause of a disease of horses known since 1850, equine leucoence-phalomalacia (ELEM) (86). There are at least three naturally occurring fumonisins—B1; B2, and B3; FBX occurs at highest concentration followed by B2 and B3. Fumonisins have been found as a very common contaminant of corn-based food and feed in the United States, China, Europe, southern Africa, South America, and Southeast Asia (5,17,87). In addition, there are a number of minor fumo-nonisins. F. verticilloides also produces fusarin C, heat-and light-unstable compounds, and fusaric acid. F. proliferatum produces fumonisins, fusarins, fusaric acid, and moniliformin (88,89). Moniliformin is toxic to poultry species (6) and can occur in food (90).

F. verticilloides and F. proliferatum are the most common fungi associated with corn. For many years, F. moniliforme has been known to occur systematically in leaves, stems, roots, and kernels (91). These fungi can be recovered from virtually all corn kernels including those that are healthy, which suggests that it may be an endopyte that is, a mutualistic relationship (28). F. verticillioides and F. proliferatum cause a "disease" called fusarium kernel rot. In parts of the United States and lowland tropics, this is one of the most important ear diseases and is associated with warm, dry years and insect damage and fu-monisin (92,93). Corn plant disease-stress also promotes the growth of F. verticillioides and fumonisin formation (94).

Fumonisins are toxic in all types of cells (yeast, plant, animal, human) due to their effects on sphinglolipid synthesis (95). Alteration in sphingolipid base ratios occurs almost immediately after exposure because fumonisin inhibits ceraminde synthetase. There are also many changes in the amounts and ratios of complex ceramides. In addition, fumonisins induce apoptosis leading to cell proliferation, which may explain their carcinogenic properties (96,97). Fumonisins B2 and B3 have similar toxic properties to Bj but are less potent (98).

Pure fumonisin was demonstrated to cause equine leu-cocencephalomalia (ELEM) in 1988 (99). ELEM involves a massive liquefactive necrosis of the cerebral hemispheres; hence, the disease involves neurological manifestations including abnormal movements, aimless circling, lameness, and so on. At high exposures, death can occur within hours after the onset of visible symptoms. Damage to liver and kidneys in horses, features of fumonisins exposure in other animals, is poorly characterized in horses (6).

As in equine species, alterations of sphingolipid base ratios are indicative of fumononisin exposure in swine

(95). At high exposures, porcine pulmonary edema (PPE) has been shown to be caused by both pure fumonosin and F. moniliforme culture material and maize containing fu-monisin (6). This is thought to be caused by fumonisin-induced heart failure (100). At lower exposures, both liver and kidney damage has been reported in swine (101). Fu-monisin causes feed refusal and changes in carcass quality at dietary concentrations in the low mg/kg range (102,103). Feeder calves were reported to be unaffected by fumonisin (6).

Exposure to F. verticilloides-contaminated maize has been linked to the elevated rates of esophageal cancer in the Transkei for 25 years, and this has since been directly linked to fumonisin exposure (17,87,104). Fumonisin Bj has been demonstrated to exhibit cancer-promoting activity in diethylnitrosamine-initiated rats (105). Fumonisin Bj has been also shown to be hepatotoxic and hepatocar-cinogenic in rats fed 50 mg/kg (90% purity) (106). Very pure fumonisin produced tumors in male and female mice and rats in the U.S. National Toxicology two-year bioassay (NTP TR 496; http://www.ntp.gov). In Fisher 344 rats, fumonisin B, exposure resulted in tumors at doses about 10 times less than aflatoxin. IARC (17) examined the human carcinogenicity of grain contaminated with F. verti-cillioides containing fumonisins and fusarin C and found them to be possible human carcinogens. There is an enormous amount known about the rodent toxicities of fumonisins from the just-noted NTP assay. An exhaustive treatment of the toxicology of fumonisins can be found in WHO (87).

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