Host resistance to Trypanosoma cruzi infection is enhanced in mice fed Fusarium verticillioides (=F. moniliforme) culture material containing fumonisins.

Fumonisins, metabolites of Fusarium verticillioides (=F. moniliforme) and related fungi that occur naturally on corn, elicit various organ- and species-specific toxicities. However, immunologic effects of fumonisins are not well characterized. BALB/c mice were fed diets containing F. verticillioides culture material (CM) providing 50 (LD) or 150 (HD) ppm fumonisins (FB(1)+FB(2)) beginning 1 week before and continuing 5 weeks after challenge with the myotropic Brazil strain of T. cruzi. A control group (ZD) was fed a diet lacking CM. The LD and HD diets caused increases in tissue sphinganine/sphingosine ratios and minimum to mild hepatotoxicity, both of which are typically induced by fumonisins. Nitric oxide (NO) production by peritoneal macrophages from HD mice was significantly higher than by peritoneal macrophages from ZD mice on day 14 after challenge. NO production also was stimulated in macrophages from ZD mice, but the peak response did not occur until day 26 after challenge. Compared with ZD mice, LD and HD mice exhibited reduced parasitemia and decreased numbers of pseudocysts in cardiac muscle. Thus, the CM increased host resistance to T. cruzi by accelerating NO production by macrophages or otherwise enhancing the immune response. The findings provide additional evidence that fumonisins modulate immune function.

Persistence and reversibility of the elevation in free sphingoid bases induced by fumonisin inhibition of ceramide synthase.

These studies determined (1) the time course for sphingoid base elevation in the small intestines, liver, and kidney of mice following a single 25 mg/kg body weight (bw) oral dose (high dose) of fumonisin B(1) (FB(1)), (2) the minimum threshold dose of FB(1) that would prolong the elevated sphingoid base concentration in kidney following the single high dose, and (3) the importance of the balance between the rate of sphingoid base biosynthesis and degradation in the persistence of sphingoid base accumulation. Following the high dose of FB(1), there was an increase in sphinganine in intestinal cells and liver that peaked at 4 to 12 h and declined to near the control level by 48 h. In kidney, sphinganine peaked at 6-12 h but remained elevated until 72 h, approaching control levels at 96-120 h. Oral administration of 0.03 mg FB(1)/kg bw (low dose) for 5 days had no effect on the sphingoid bases in kidney. However, following an initial high dose, daily administration of the low dose prolonged the elevation in kidney sphinganine compared to mice receiving a single high dose. Thus, a single exposure to a high dose of FB(1) followed by daily exposure at low levels will prolong the elevation of sphinganine in kidney. In cultured renal cells FB(1) was rapidly eliminated, but elevated sphinganine was persistent. This persistence in renal cells was rapidly reversed in the presence of the serine palmitoyltransferase inhibitor (ISP-1), indicating that the persistence was due to differences in the rates of sphinganine biosynthesis and degradation. The in vivo persistence in kidney may be due to similar differences.

Temporal expression of fumonisin B(1)-induced tumor necrosis factor-alpha and interferon gamma in mice.

Fumonisin B(1) (FB(1)), a toxic metabolite of Fusarium verticillioides, is a carcinogen and causative agent of various animal diseases. Our previous studies indicated the involvement of tumor necrosis factor-alpha (TNF alpha) in FB(1)-induced toxic responses. To further investigate the time-course of TNF alpha production and signaling, mice (four/group) were treated subcutaneously (s.c.) or per os (p.o.) with either vehicle or 25 mg/kg of FB(1) as a single dose and sacrificed at 0, 2, 4, 8, 12 and 24 h after treatment. The TNF alpha expression was increased in liver and kidney after both routes of FB(1) exposure without any alterations in spleen. The p.o.-route FB(1) treatment caused greater hepatotoxicity compared to the s.c. route, as depicted by increased alanine aminotransferase and aspartate aminotransferase level in plasma, observed only after p.o. FB(1) treatment. The increase in enzymes at 8 h after p.o. treatment correlated with the highest TNF alpha expression, also noted at 8 h after p.o. treatment, thus further confirming the involvement of TNF alpha in FB(1) toxicity. The interferon (IFN)-gamma expression was increased in liver at 4 h after p.o. FB(1) treatment, suggesting a possible combined role of TNF alpha and IFN gamma in their induction and hepatotoxicity.

Sphingolipid perturbations as mechanisms for fumonisin carcinogenesis.

There is a great deal of evidence that altered sphingolipid metabolism is associated with fumonisin-induced animal diseases including increased apoptotic and oncotic necrosis, and carcinogenesis in rodent liver and kidney. The biochemical consequences of fumonisin disruption of sphingolipid metabolism most likely to alter cell regulation are increased free sphingoid bases and their 1-phosphates, alterations in complex sphingolipids, and decreased ceramide (CER) biosynthesis. Because free sphingoid bases and CER can induce cell death, the fumonisin inhibition of CER synthase can inhibit cell death induced by CER but promote free sphingoid base-induced cell death. Theoretically, at any time the balance between the intracellular concentration of effectors that protect cells from apoptosis (decreased CER, increased sphingosine 1-phosphate) and those that induce apoptosis (increased CER, free sphingoid bases, altered fatty acids) will determine the cellular response. Because the balance between the rates of apoptosis and proliferation is important in tumorigenesis, cells sensitive to the proliferative effect of decreased CER and increased sphingosine 1-phosphate may be selected to survive and proliferate when free sphingoid base concentration is not growth inhibitory. Conversely, when the increase in free sphingoid bases exceeds a cell's ability to convert sphinganine/sphingosine to dihydroceramide/CER or their sphingoid base 1-phosphate, then free sphingoid bases will accumulate. In this case cells that are sensitive to sphingoid base-induced growth arrest will die and insensitive cells will survive. If the cells selected to die are normal phenotypes and the cells selected to survive are abnormal, then cancer risk will increase.

Disruption of sphingolipid metabolism in small intestines, liver and kidney of mice dosed subcutaneously with fumonisin B(1).

Fumonisin B(1) is a fungal inhibitor of ceramide synthase, a key enzyme in the de novo biosynthesis of sphingolipids. The resulting increase in tissue free sphinganine (and sometimes sphingosine) is used as a biomarker for fumonisin exposure. This study determined whether a single subcutaneous injection of fumonisin B(1) could cause an increase in free sphingoid bases in the intestinal epithelial cells of mice over 24 hr. It was hypothesized that fumonisin administered subcutaneously would be excreted into the small intestine via biliary excretion, and this should be detectable by increased sphingoid bases in the intestine. A significant time-dependent increase in sphingoid bases occurred in the intestine and liver peaking at 4-8 hr and declining to control levels by 24 hr. In the kidney the increase in free sphinganine was persistent. The parallel time course of the change in sphinganine in the intestine and liver suggested fumonisin B(1) was rapidly excreted into the small intestine. Rapid cell turnover in the intestine could account for the reversal of the sphinganine increase. The rapid return to the control level in liver was unexpected since ceramide synthase inhibition in cultured cells is persistent suggesting that liver handles fumonisin B(1) or sphingoid bases quite differently than kidney.