The induction and persistence of altered sphingolipid biosynthesis in rats treated with fumonisin B1

Evaluation of sphingolipids in Wistar rats treated to prolonged and single oral doses of fumonisin b₁

The objective of the present study was to evaluate sphingolipid levels (sphingosine-So and sphinganine-Sa) and to compare the Sa/So ratio in liver, serum and urine of Wistar rats after prolonged administration (21 days) of fumonisin B(1) (FB(1)). In parallel, the kinetics of sphingolipid elimination in urine was studied in animals receiving a single dose of FB(1). Prolonged exposure to FB(1) caused an increase in Sa levels in urine, serum and liver. The most marked effect on sphingolipid biosynthesis was observed in animals treated with the highest dose of FB(1). Animals receiving a single dose of FB(1) presented variations in Sa and So levels and in the Sa/So ratio.

Fumonisin exposure and the sphinganine/sphingosine ratio in urine, serum and buccal cells in adults from Burkina Faso, West Africa

Fumonisins are mycotoxins that frequently contaminate maize, a dietary staple in Burkina Faso. Fumonisins have been linked with both the incidence of oesophageal cancer, and to neural tube defects. However, epidemiological studies of these associations are hampered by lack of validated exposure biomarkers. One candidate biomarker is the sphinganine/sphingosine (Sa/So) ratio in biological samples. Twenty husband-wife pairs aged 20-40 were recruited from Dingasso-1, western Burkina Faso. Plate ready food was sampled over three consecutive days (day one to three) for fumonisin B1 and B2, to provide a measure of total fumonisin intake. The Sa/So ratio was determined in (1) first morning urines taken on days two to four, (2) buccal cells and (3) serum on days one and four only. Fumonisin intake was moderate (mean 0.81 µg/kg bw/day (range 0.01-2.40 µg/kg bw/day) compared to exposures reported in China and South Africa. For each person the mean fumonisin intake over three days was compared to the mean Sa, So and Sa/So ratio in urine, buccal cells and serum. A modest positive trend between mean fumonisin intake and mean serum Sa/So was observed (P=0.067). When individuals were dichotomised based on the median fumonisin intake (<0.75 µg/kg bw/day), the serum Sa/So ratio was moderately higher (P=0.044) in the high intake group (geometric mean 0.64; 95% CI: 0.54, 0.75) compared to the low intake group (0.49; 95% CI: 0.41, 0.59). Neither urinary nor buccal cell Sa/So ratio was associated with mean fumonisin intake. Neither mean individual Sa nor So level for urine, buccal cells or urine was associated with mean individual fumonisin intake. The study population was exposed to moderate levels of fumonisin with limited evidence of altered Sa/So ratio. Further work on serum Sa/So ratio is merited in comparison with other biomarker approaches such as urinary fumonisin B1 or sphingolipid 1-phosphate metabolites.

Validation of fumonisin biomarkers in F344 rats

Fumonisins (FNs) are ubiquitous contaminants of cereal grains. Fumonisin B(1) (FB(1)) was linked to several animal and human diseases. To validate FB(1) biomarkers for studying human disease risks, F344 rats were administered by gavage with either a single dose of 0, 10 or 25 mg FB(1)/kg body weight (BW) or repeated doses of 0, 1.0, or 2.5 mg FB(1)/kg BW/day for 5 weeks. FB(1) excretion and FB(1)-induced metabolic alterations of sphingolipids in rat urine, feces and serum were assessed. Dose-dependent urinary and fecal excretion of free FB(1) were found in both single-dose- and repeat-dose-treated rats. In the single-dose study, urinary sphinganine (Sa) to sphingosine (So) ratio (Sa/So) reached a maximum at day 7 for the high-dose group and at day 5 for the low-dose group, whereas serum Sa/So showed only marginal changes. In the repeat-dose study, urinary Sa/So was persistently elevated at 2 weeks, while serum Sa/So was unchanged. Time course changes of sphinganine 1-phosphate (SaP) and sphingosine 1-phosphate (SoP) were also examined. Although serum Sa/So and SaP/SoP ratios showed no signs of time- or dose-dependent changes, a 10-fold increase in urinary SaP/SoP was observed, suggesting that urinary SaP/SoP is a more sensitive biomarker for FB(1) exposure. The accumulation of SaP and SoP was evident in the time course of SaP/Sa and SoP/So, which may reflect activity changes of enzymes closely related to the metabolism and catabolism of SaP and SoP. These results provide concrete evidence towards the practical use of excreted FB(1), Sa/So and SaP/SoP as biomarkers of exposure to FNs.

Effects of fumonisins on liver and kidney sphinganine and the sphinganine to sphingosine ratio during chronic exposure in ducks

Sa and the Sa/So ratio are very sensitive biomarkers of exposure to fumonisins in several species. We previously demonstrated that increases in Sa and in the Sa/So ratio in serum were less pronounced when ducks ingested fumonisins for more than 7 weeks than when animals were exposed for only 1-2 weeks [S.T. Tran, D. Tardieu, A. Auvergne, J.D. Bailly, R. Babilé, S. Durand, G. Benard, P. Guerre, Serum sphinganine and the sphinganine to sphingosine ratio as biomarker of dietary fumonisins during chronic exposure in ducks, Chem. Biol. Interact., in press]. The aim of this study was to investigate the kinetics of Sa and of the Sa/So in both liver and kidney of ducks that have been previously tested for Sa and the Sa/So ratio in serum. Analysis were performed on treatment days 0, 7, 14, 28 and 77 in five groups of ducks fed fumonisins obtained from an extract of Fusarium verticillioides culture material by daily gavage to obtain an exposure equal to 0, 2, 8, 32 and 128 mg FB1/kg feed. Sa and the Sa/So ratio in tissues were then correlated with Sa and the Sa/So ratio previously obtained in serum. The amounts on sphinganine 1-phosphate (Sa1P) and sphingosine1-phosphate (So1P) in the liver were also investigated. On day 7 of treatment, 2mg/kg FB1 in the feed were sufficient to increase Sa and the Sa/So ratio in liver (by 165 and 148%, respectively) and kidney (by 193 and 104%, respectively). At a rate of 128 mg/kg FB1 in the feed, a very high increase in Sa concentration was observed in both liver and kidney without mortality and/or signs of necrosis (respective increase of 2034 and 3768%). Although the precise mechanism of the resistance of ducks to fumonisin-induced hepatotoxicity is still uncertain, it might be linked to the rate at which the sphingoid bases sphinganine and sphingosine are converted to their 1-phosphate or other metabolite and eliminated from target tissues.

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.