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At least 19 recordsLinked to original sources
PubMed1993

Fumonisin B1 inhibits sphingosine (sphinganine) N-acyltransferase and de novo sphingolipid biosynthesis in cultured neurons in situ.

Fumonisins, mycotoxins produced by Fusarium moniliforme and a number of other fungi, cause neuronal degeneration, liver and renal toxicity, cancer, and other injury to animals. Recent work with rat hepatocytes (Wang, E., Norred, W. P., Bacon, C. W., Riley, R. T., and Merrill, A. H., Jr. (1991) J. Biol. Chem. 266, 14486-14490) found that fumonisins block sphingosine biosynthesis by inhibiting the conversion of sphinganine to dihydroceramides, which precedes introduction of the 4,5-trans-double bond of sphingosine. The current study utilized mouse cerebellar neurons in culture to evaluate how this affects the distribution of newly synthesized ceramides among different complex sphingolipids. Fumonisin B1 inhibited ceramide synthase in mouse brain microsomes with a competitive-like kinetic behavior with respect to both sphinganine and stearoyl-CoA. Fumonisin B1 inhibited sphingolipid biosynthesis in cultured cerebellar neurons in situ as reflected by accumulation of free sphinganine, a reduction in the mass of total sphingolipids, reductions in the incorporation of [14C]serine into glucosylceramide, lactosylceramide, sphingomyelin, and gangliosides (GM1, GD3, GD1a, GD1b, GT1b, and GQ1b), and inhibition of the incorporation of [14C]galactose and [3H]sphinganine into complex sphingolipids. Dose-response studies revealed that the labeling of sphingomyelin (IC50 of 0.7 microM) was more sensitive to inhibition by fumonisin B1 than was glycolipid formation (IC50 of approximately 7 microM) in these cells. A similar effect was seen when beta-fluoroalanine was added to inhibit the activity of serine palmitoyltransferase, the first enzyme of the pathway. The inhibition of complex sphingolipid synthesis was reversible, and nearly normal labeling profiles were obtained 48 h after removing the mycotoxin. These studies establish that fumonisin B1 inhibits de novo sphingolipid biosynthesis by neuronal cells and, moreover, that limiting ceramide synthesis differentially affects the formation of sphingomyelin versus glycosphingolipids.

Acyltransferases↗
PubMed1995

Ceramide triggers meiotic cell cycle progression in Xenopus oocytes. A potential mediator of progesterone-induced maturation.

The role of sphingomyelin-derived second messengers in progesterone-induced reinitiation of the meiotic cell cycle of Xenopus laevis oocytes was investigated. A brief treatment of defolliculated oocytes with sphingomyelinase (Staphylococcus aureus) was sufficient to induce maturation as measured by H1 kinase activity and germinal vesicle breakdown (GVBD). Pretreatment with cycloheximide inhibited sphingomyelinase-induced GVBD demonstrating a requirement for protein synthesis. Microinjection of ceramide or sphingosine, potential products of sphingomyelin hydrolysis, were capable of inducing GVBD in the absence of hormone. Metabolic labeling studies suggested the conversion of sphingosine to ceramide was necessary for sphingosine-induced GVBD. Additionally, fumonisin b1, an inhibitor of sphingosine N-acyltransferase, blocked sphingosine-induced GVBD demonstrating that ceramide is the more proximal biologically active metabolite. Treatment of oocytes with progesterone, the physiological inducer of oocyte maturation, resulted in a time- and concentration-dependent increase in the mass of ceramide and decrease in the mass of sphingomyelin through activation of a Mg(2+)-dependent neutral sphingomyelinase. These observations suggest that the generation of ceramide from sphingomyelin is part of the signal transduction pathway activated in response to progesterone and that the increase in ceramide is likely to be functionally important in resumption of the meiotic cell cycle.

Amino Acid Sequence↗
PubMed1991

Inhibition of sphingolipid biosynthesis by fumonisins. Implications for diseases associated with Fusarium moniliforme.

Culture materials and grains contaminated with certain isolates of Fusarium moniliforme cause equine leucoencephalomalacia, porcine pulmonary edema syndrome, and liver cancer in rats. The causative agents are thought to be a family of compounds called fumonisins, which bear considerable structural similarity to the long-chain (sphingoid) base backbones of sphingolipids. Incubation of rat hepatocytes with fumonisins inhibited incorporation of [14C]serine into the sphingosine moiety of cellular sphingolipids with an IC50 of 0.1 microM for fumonisin B1. In contrast, fumonisin B1 increased the amount of the biosynthetic intermediate sphinganine, which suggests that fumonisins inhibit the conversion of [14C]sphinganine to N-acyl-[14C]sphinganines, a step that is thought to precede introduction of the 4,5-trans double bond of sphingosine (Merrill, A.H., Jr. and Wang, E. (1986) J. Biol. Chem. 261, 3764-3769). In agreement with this mechanism, fumonisin B1 inhibited the activity of sphingosine N-acyltransferase (ceramide synthase) in rat liver microsomes with 50% inhibition at approximately 0.1 microM and reduced the conversion of [3H]sphingosine to [3H]ceramide by intact hepatocytes. As far as we are aware, this is the first discovery of a naturally occurring inhibitor of this step of sphingolipid metabolism. These findings suggest that disruption of the de novo pathway of sphingolipid biosynthesis may be a critical event in the diseases that have been associated with consumption of fumonisins.

Acyltransferases↗
PubMed1996

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.

Animals↗
PubMed1995

Fumonisin B1 alters sphingolipid metabolism and disrupts the barrier function of endothelial cells in culture.

Fumonisins are responsible for at least two diseases of veterinary importance (equine leukoencephalomalacia and porcine pulmonary edema) and are carcinogenic for experimental animals and, perhaps, humans. They have been found to disrupt sphingolipid metabolism in many types of cells, including hepatocytes, neurons, and renal cells. In this study, endothelial cells form porcine pulmonary arteries were cultured on micropore filters as a model for the endothelial barrier, and barrier function was quantitated as the movement of albumin across the endothelial monolayers. Fumonisin B1 increased the amount of free sphinganine by 20- to 30-fold within 3 hr, as expected for inhibition of sphinganine (sphingosine) N-acyltransferase by this mycotoxin. At 30 to 50 microM, fumonisin B1 doubled the rate of albumin transfer across endothelial monolayers; however, there was no loss of cell viability based on morphology or trypan blue exclusion. When 15 microM D-erythro-sphinganine was added to the cells, the rate of albumin transfer also doubled (after 24 hr incubation) without a loss of viability; however, this treatment increased the cellular level of sphinganine by > 100-fold. Addition of 25 microM sphinganine caused even greater albumin transfer, but also resulted in significant cell death. These results establish that fumonisin B1 and D-erythro-sphinganine allow accelerated passage of macromolecules across the endothelium. Fumonisin B1 alters sphingolipid biosynthesis with an elevation of sphinganine in the cells which may, at least in part, explain the observed disruption of endothelial barrier function.

Albumins↗
PubMed1995

Sphingolipid biosynthesis de novo by rat hepatocytes in culture. Ceramide and sphingomyelin are associated with, but not required for, very low density lipoprotein secretion.

Sphingolipids are constituents of liver and lipoproteins, but relatively little is known about their synthesis and secretion. Incubation of rat hepatocytes with [14C]- or [3H]serine labeled the long-chain base backbones of mainly ceramide and sphingomyelin. Most of the labeled sphingolipids were associated with the cells; however, 1-5% (the majority of which was ceramide) was released into the medium as part of very low density lipoproteins (VLDL). Since this is the first report that lipoproteins contain ceramide, lipoproteins were isolated from rat plasma, and the ceramide contents were (per mg of protein): 6.5 nmol for VLDL (d < 1.018), 0.6 nmol for low density lipoproteins (1.018 < d < 1.063), 0.2 nmol for high density lipoproteins (1.063 < d < 1.18), and 0.1 nmol for the albumin fraction; the lipoproteins also contained 0.1-0.4 nmol of free sphingosine/mg of protein. A number of factors affected the secretion of radiolabeled sphingolipids: 1) addition of palmitic acid, but not stearic or oleic acid, enhanced secretion due to an increase in long-chain base synthesis de novo. 2) Choline deficiency caused a 42% reduction in the secretion of radiolabeled sphingomyelin, but this was due to an effect on VLDL secretion rather than a decrease in sphingolipid synthesis. Removal of choline was examined because previous studies (Yao, Z. M., and Vance, D. E. (1988) J. Biol. Chem. 263, 2998-3004) have shown that choline deficiencies depress phosphatidylcholine synthesis and lipoprotein secretion. 3) Incubation of the cells with fumonisin B1, a mycotoxin inhibitor of sphinganine (sphingosine) N-acyltransferase, reduced overall sphingolipid synthesis and secretion by 90%, but had no effect on the secretion of apoB, phosphatidylcholine, or cholesterol. All together, these findings demonstrate that rat hepatocytes synthesize ceramide and sphingomyelin de novo and incorporate them into both cellular membranes and secreted VLDL, but normal sphingolipid synthesis is not required for lipoprotein secretion.

Animals↗
PubMed1994

Disruption of sphingolipid metabolism and stimulation of DNA synthesis by fumonisin B1. A molecular mechanism for carcinogenesis associated with Fusarium moniliforme.

Consumption of grains contaminated with Fusarium moniliforme (Sheldon) causes liver cancer in rats and has been correlated with esophageal cancer in humans. The causative agents are believed to be a family of compounds known as fumonisins, which bear remarkable structural resemblances to sphingosine and sphinganine, the long-chain (sphingoid) base backbones of sphingolipids. Recently, fumonisin B1 has been shown to block de novo synthesis of sphingolipids by inhibiting sphingosine (sphinganine) N-acyltransferase, which leads to accumulation of sphingoid bases. Because the exogenous addition of sphingosine and sphingosine 1-phosphate to Swiss 3T3 cells has been shown to stimulate DNA synthesis (Zhang, H., Buckley, N.E., Gibson, K., and Spiegel, S. (1990) J. Biol. Chem. 265, 76-81; Zhang, H., Desai, N.N., Olivera, A., Seki, T., Brooker, G., and Spiegel, S. (1991) J. Cell Biol. 114, 155-167), we hypothesized that fumonisins might stimulate DNA synthesis by disrupting sphingolipid metabolism. Fumonisin B1 caused accumulation of sphinganine and sphingosine in Swiss 3T3 fibroblasts and, as occurred when these sphingoid bases were added exogenously, stimulated thymidine incorporation into DNA and augmented the mitogenic effect of insulin in a concentration-dependent manner. The mechanism underlying the mitogenic effect of fumonisin B1 was further investigated by using beta-fluoroalanine to block the initial step of sphingolipid biosynthesis catalyzed by serine palmitoyltransferase. beta-Fluoroalanine reduced sphingoid base accumulation in fumonisin B1-treated fibroblasts and inhibited fumonisin B1-stimulated DNA synthesis, but had no effect on mitogenesis when added alone. Fumonisin B1 did not cause accumulation of sphinganine 1-phosphate; therefore, it appears that sphingoid bases per se can stimulate DNA synthesis. To prove that the 1-phosphate is not obligatory, a 1-deoxysphinganine was synthesized, and it was as potent as sphinganine in stimulating DNA synthesis. These results establish that fumonisin B1 is mitogenic via accumulation of sphingoid bases rather than inhibition of complex sphingolipid biosynthesis per se. Because mitogens can often affect cell transformation, this provides a plausible molecular mechanism to explain the carcinogenicity of fumonisins.

3T3 Cells↗
PubMed1992

Increases in serum sphingosine and sphinganine and decreases in complex sphingolipids in ponies given feed containing fumonisins, mycotoxins produced by Fusarium moniliforme.

Consumption of food contaminated with Fusarium moniliforme causes leucoencephalomalacia and hepatotoxicity in horses, pulmonary edema in pigs and liver cancer in rats, and has been correlated with esophageal cancer in humans. The causative agents are thought to be a family of compounds called fumonisins, which have recently been shown to be potent inhibitors of sphingosine (sphinganine) N-acyltransferase. Because inhibition at this step blocks the formation of complex sphingolipids while leading to accumulation of sphinganine, we hypothesized that exposure of animals to fumonisin-contaminated feed might be detected by analyses of serum sphingolipids. Within days of giving ponies feed contaminated with 15 to 44 micrograms/g fumonisin B1, there was an increase in the amount of free sphinganine (and sometimes sphingosine) and a reduction in complex sphingolipids. Free sphinganine and sphingosine decreased when ponies consumed less of the contaminated feed, and increased again when they consumed more fumonisin. When toxicosis was evident as indicated by other serum markers, complex sphingolipids as well as free sphingosine and sphinganine were elevated, probably due to loss of sphingolipids from dying cells. These findings establish that consumption of fumonisin-contaminated feed disrupts sphingolipid metabolism. Because the changes in sphinganine and sphingosine were seen before liver enzymes were noticeably elevated, they may be an early marker of exposure to fumonisins.

Animal Feed↗
PubMed1985

Sphingomyelin synthesis in Hymenolepis diminuta (Cestoda).

Adult Hymenolepis diminuta incorporated label from L[U-14C]serine, [1-14C]palmitic acid, [1-14C]palmitoyl-CoA and cytidine-5'-diphospho[methyl-14C]choline into the various intermediates of sphingomyelin synthesis (ketosphingosine, dihydrosphingosine, sphingosine, ceramide and sphingomyelin). From the results it was concluded that H. diminuta possessed the five enzymes involved in sphingomyelin synthesis, namely serine palmitoyl-transferase, 3-oxosphinganine reductase, flavoprotein dihydrosphingosine reductase, sphingosine acyltransferase and ceramide choline-phosphotransferase.

Acyltransferases↗
PubMed1993

The long-chain sphingoid base of sphingolipids is acylated at the cytosolic surface of the endoplasmic reticulum in rat liver.

Ceramide, a key intermediate in sphingolipid metabolism, is synthesized by acylation of sphinganine followed by dehydrogenation of dihydroceramide to ceramide. Using radioactive sphinganine, we have examined the site and topology of dihydroceramide synthesis in well-characterized subcellular fractions from rat liver. [4,5-3H]Sphinganine was introduced as a complex with BSA and was metabolized to [4,5-3H]dihydroceramide upon incubation of rat liver homogenates or microsomes with fatty acyl CoA. Conditions were established in a detergent-free system in which dihydroceramide synthesis was not limited by either substrate availability or by amounts of microsomal protein or reaction time. The distribution of dihydroceramide synthesis was found to exactly parallel that of an endoplasmic reticulum (ER) marker upon subfractionation of microsomes, and no endogenous activity was detected in either purified Golgi apparatus or plasma membrane fractions. Limited protease digestion demonstrated that sphinganine N-acyltransferase is localized at the cytosolic surface of intact ER-derived vesicles. These results are discussed with regard to the subsequent transport of (dihydro)-ceramide from the ER to sites of further metabolism in a pre-Golgi apparatus compartment and in the cis and medial cisternae of the Golgi apparatus.

Acyl Coenzyme A↗
PubMed1991

Sphingolipid biosynthesis in cultured neurons. Down-regulation of serine palmitoyltransferase by sphingoid bases.

Addition of exogenous sphingosine homologues (D-erythro configuration) with different alkyl chain lengths (12 and 18 carbon atoms) to the medium of primary cultured cerebellar cells resulted in a decrease of serine palmitoyltransferase activity in a time- and concentration-dependent manner. This enzyme catalyzes the first committed step in sphingolipid biosynthesis. Half-maximal reduction of enzyme activity occurred after a 4-h treatment with 25 microM sphingoid bases. Maximal decrease (approx. 80%) was obtained after treating the cells for 4-8 h with 50 microM long-chain bases. When a biosynthetically inert sphingoid, azidosphingosine (10-50 microM), was fed to the cells, decrease of 3-ketosphinganine formation was much slower, reaching its maximum (approx. 80%) after 24 h. In contrast to D-erythro-sphingosine, L-threo-C18-sphingosine did not yield any decrease of serine palmitoyltransferase activity when added to the cells under identical experimental conditions. Decrease of serine palmitoyltransferase activity was fully reversible after removal of the long-chain bases from the culture medium. Activities of other enzymes of lipid metabolism, ceramide synthase, long-chain acyl-CoA synthase and choline phosphotransferase, were not affected by the addition of sphingoid bases, indicating that the down regulation of serine palmitoyltransferase is quite specific.

Acyltransferases↗
PubMed1995

Fatty acyl-Co A: sphingosine acyltransferase in bovine brain mitochondria: its solubilization and reconstitution onto the membrane lipid liposomes.

Fatty acyl-Co A: sphingosine acyltransferase (ceramide synthase, EC 2.3.1.24) is mainly localized in the microsomal and mitochondrial membranes. Attempts to isolate the enzyme have failed, largely because there has been little or no detection of the enzyme activity in detergent extracts. In this study, we solubilized the membrane-bound enzyme from bovine brain mitochondria with a Tris-HCl buffer containing 2% Triton X-100 and, after removal of the detergent, reconstituted it with the membrane lipid liposomes. The specific activity of the reconstituted enzyme was approx. 8 times higher than that of the solubilized enzyme. We next examined the lipid dependence of the enzyme, using various phospholipid liposomes. The ability of phospholipids to enhance the activity of solubilized ceramide synthase was specific and structure-related. The most potent stimulator was phosphatidylserine liposomes, suggesting an important role of the net negative charges. This paper also describes a highly reproducible high-performance liquid chromatographic (HPLC) procedure for the determination of ceramide synthase activity. Combination of the HPLC method with the reconstituted enzyme system appears to be suitable for elucidating the characteristics of this enzyme.

Acyltransferases↗
PubMed1992

Subcellular localization and membrane topology of serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase in mouse liver.

Serine palmitoyltransferase, 3-dehydrosphinganine reductase and sphinganine N-acyltransferase are responsible for the first steps in sphingolipid biosynthesis forming 3-oxosphinganine, sphinganine, and dihydroceramide, respectively. We confirmed the localization of these enzymes in the endoplasmic reticulum (ER) using highly purified mouse liver ER and Golgi preparations. Mild digestion of sealed "right-side out" mouse liver ER derived vesicles with different proteolytic enzymes under conditions where latency of mannose-6-phosphatase was 90% produced approximately 60-80% inactivation of serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase activities. These sphingolipid biosynthetic activities (serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase) are not latent, indicating that they face the cytosolic side of the ER, so that substrates have free access to their active sites. Moreover, the membrane-impermeable compound, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, which binds to a large number of ER proteins, inhibits serine palmitoyltransferase and sphinganine N-acyltransferase activities by 30-70%.

Acyltransferases↗
PubMed1986

Solubilization and partial characterization of fatty acyl-CoA:sphingosine acyltransferase (ceramide synthetase) from rat liver and brain.

Lignoceroyl-CoA:sphingosine lignoceroyltransferase, which catalyzes synthesis of lignoceroylsphingosine, the ceramide that is a major component of sphingolipids in mammalian tissues, has been solubilized from microsomes of rat brain and liver and partially purified. The microsomes were treated with 1 M sodium thiocyanate in N,N-bis(2-hydroxyethyl)glycine (Bicine) buffer containing 20% glycerol. The supernatant fraction obtained after centrifugation was fractionated by Sepharose CL-4B gel filtration. The ceramide synthetase activity was recovered in a small fraction containing high molecular weight proteins. Analysis of proteins and lipids indicated that the fraction was not simply a fragment of microsomes. The activity for synthesis of lignoceroylsphingosine, which is abundant in nervous system, was compared with that for the synthesis of stearoylsphingosine, which is more enriched in extraneural sphingolipids, in brain and liver microsomes. Despite the difference in relative abundance of molecular species of ceramides in these tissues, the activity for lignoceroylsphingosine synthesis was not more enriched in brain than in liver.

Acyl Coenzyme A↗
PubMed1993

Alteration of tissue and serum sphinganine to sphingosine ratio: an early biomarker of exposure to fumonisin-containing feeds in pigs.

Fumonisins are a group of naturally occurring compounds produced by the fungus Fusarium moniliforme. They are believed to be the etiologic agent of several animal diseases associated with consumption of corn-based feeds including porcine pulmonary edema. Recently it was shown in vitro that fumonisins are specific inhibitors of sphingosine and sphinganine N-acyltransferases. Inhibition of these enzymes in cultured cells results in the accumulation of free long chain sphingoid bases, specifically sphingosine and sphinganine, and the depletion of complex sphingolipids. In this study, tissues and serum from male SPF pigs fed a nutritionally balanced diet containing corn or corn screenings naturally contaminated with fumonisins for up to 14 days were analyzed for free sphingoid bases and complex sphingolipids. Total fumonisins (B1 and B2) in the diets were analyzed at 0 (< 1), 5, 23, 39, 101, and 175 ppm. Pulmonary edema only occurred at 175 ppm, while histologic liver damage was present at > or = 23 ppm, and serum liver enzymes were significantly elevated at > or = 101 ppm. The results of this study show that free sphinganine is elevated in liver, lung, and kidney, from pigs consuming feeds containing fumonisins at total fumonisin concentrations of 23 ppm or greater. Sphingosine is also elevated in a dose-dependent manner, but to a lesser extent than sphinganine. The consequence of this differential inhibition is that the ratio of sphinganine to sphingosine increases, suggesting that sphinganine N-acyltransferase is the preferred target for fumonisins. Elevation of free sphinganine and free sphingosine in serum paralleled the increases in tissues. Statistically significant increases in the ratio were observed at feed concentrations as low as 5 ppm total fumonisins and in pigs (at higher concentrations) in which other serum biochemistry parameters and tissue morphology were not altered. Elevated ratios were also observed in serum from pigs fed pure fumonisin B1. The sensitivity of the ratio indicates that it could serve as an effective biomarker for consumption of fumonisin-containing feeds. In addition, the data supports the hypothesis that inhibition of sphingosine and sphinganine N-acyltransferase plays an important role in the pathogenesis of animal diseases associated with consumption of feed containing fumonisins.

Animal Feed↗
PubMed1992

Fumonisin inhibition of de novo sphingolipid biosynthesis and cytotoxicity are correlated in LLC-PK1 cells.

Fumonisins are a group of structurally related compounds produced by Fusarium moniliforme. Recently, it has been shown that fumonisins B1 and B2 are the first naturally occurring inhibitors of sphingosine and sphinganine N-acyltransferase (ceramide synthase) in rat primary hepatocytes (Wang et al. J. Biol. Chem. 266, 14, 486-14, 490, 1991). These enzymes are key components in the pathways for de novo sphingolipid biosynthesis and sphingolipid turnover. The results of the present study show that fumonisins B1 and B2 inhibit proliferation and are cytotoxic to LLC-PK1 cells. Concentrations of fumonisin B1 and B2 between 10 and 35 microM inhibited cell proliferation, whereas higher concentrations (greater than 35 microM) killed cells. Inhibition of cell proliferation and cell death were preceded by a lag period of at least 24 hr during which cells appeared to be functioning normally. Cells exposed to fumonisin B1 exhibited normal growth kinetics and morphology soon after fumonisin B1 was removed; thus, the effects of fumonisin B1 were reversible. The EC50 for alterations in sphingolipid biosynthesis was 10 to 15 microM. Inhibition of de novo sphingolipid biosynthesis occurred before inhibition of cell proliferation or cytotoxicity, and the dose response for the decrease in the [3H]sphingosine to [3H]sphinganine ratio at 7 hr closely paralleled the dose response for effects on proliferation and cytotoxicity at 3-5 days. In addition, the level of free sphinganine, and to a lesser extent sphingosine, increased in fumonisin-treated cells in a dose-dependent manner. During the 24-hr lag period preceding inhibition of cell proliferation, the free sphinganine content increased by 12,800% in cells exposed to 35 microM fumonisin B1. Whereas a mechanistic relationship between the inhibition of de novo sphingolipid biosynthesis and inhibition of proliferation and cell death has not been demonstrated, the results of this study support the hypothesis that inhibition of de novo sphingolipid biosynthesis is an early event in the toxicity of fumonisins to LLC-PK1 cells.

Acyltransferases↗
PubMed1995

Effects of intravenous fumonisin B1 in rabbits: nephrotoxicity and sphingolipid alterations.

Fumonisin B1 is hepatotoxic in all species, but nephrotoxicity has only been reported in rats. It is a specific inhibitor of sphinganine N-acyltransferase. Our objective was to determine the target organs for fumonisin toxicosis in the rabbit. We administered fumonisin B1 ( > 95% pure) intravenously to adult rabbits and examined selected clinical, biochemical, and histological parameters for up to 5 days. In a pilot study, rabbits were given fumonisin B1 at 1, 0.5, 0.3, 0.15, or 0 mg/kg daily for 4 or 5 days and then euthanized. Additional rabbits were given a single dose of fumonisin B1 at 1 mg/kg and euthanized on day 2 or 4. In the formal time-course study, rabbits were given a single dose of fumonisin B1 at 0 or 1.25 mg/kg and euthanized on days 1, 3, or 5. Rabbits given multiple doses of fumonisin B1 were lethargic and anorectic, and had decreased urine production. Liver- and renal-associated clinical chemistry parameters were elevated. Renal lesions consisted of severe proximal tubular necrosis. Liver lesions were variable and consisted of mild necrosis, hepatocyte vacuolation, and bile stasis. The sphinganine-to-sphingosine ratio, in both target and nontarget tissues, was markedly elevated in treated rabbits. A single dose of fumonisin B1 induced renal but not hepatic injury. Therefore, the target organs for fumonisin B1 toxicity in rabbits are kidney and liver, with the kidney being more sensitive.

Animals↗