Biochemical and morphological effects of fumonisin B(1) on primary cultures of rat cerebrum

Fumonisin B1 neurotoxicity: Preclinical evidence, biochemical mechanisms and therapeutic strategies

The neurotoxic effects of fungal toxins in both humans and animals have been well documented. Fumonisin B1 (FB1), a mycotoxin produced by fungi of the Fusarium species, is the most toxic fumonisin variant whose neurotoxic effect is still being elucidated. This review highlights the biochemical aspects of FB1 neurotoxicity, such as its mechanisms of action as well as therapeutic strategies. Both in vitro and in vivo studies have demonstrated that alteration in sphingolipid metabolism is a major event in FB-induced neurotoxicity. Studies have also shown that neurotoxicity due to FB1 involves dysregulation of several biochemical events in the brain, such as induction of oxidative stress and inflammation, mitochondrial dysfunction and associated programmed cell death, inhibition of acetylcholinesterase and alteration of neurotransmitter levels, decreased activity of Na+K+ ATPase, as well as disruption of blood-brain barrier. This review highlights the potential public health effects of FB1-induced neurotoxicity and the need to limit human and animal exposure to FB1in order to prevent its neurotoxic effect. Moreover, it is hoped that this review would stimulate studies aimed at filling the current research gaps such as delineating the effect of FB1 on the blood-brain barrier and appropriate therapies for neurotoxicity caused by FB1.

FB1 causes barrier damage to vascular endothelial cells through ferroptosis by a PINK1/Parkin mediated mitophagy-dependent mechanism

Fumonisin B1 (FB1) is an environmental mycotoxin produced mainly by fungi of the genus Fusarium. Exposure to FB1 can lead to pulmonary edema in pigs, likely caused by damage to vascular endothelial cells, but the mechanism of FB1-induced damage was unknown. Here, we found that FB1 damages vascular endothelial cells through ferroptosis, marked by iron-dependent membrane lipid peroxidation, and through mitophagy, a selective autophagy that targets mitochondria. FB1 exposure reduced barrier-related gene expression and increased pro-inflammatory factors. Ferroptosis was evidenced by elevated iron, ROS, lipid peroxidation, and ferroptotic markers (TFR, ACSL4), alongside decreased GSH, SLC7A11, and GPX-4 levels in vascular endothelial cells. Importantly, the ferroptosis inhibitor, Ferrostatin-1, reversed the vascular endothelial cells' barrier damage, inflammation, and ferroptosis caused by FB1. FB1-induced mitophagy was demonstrated by detecting decreased mitochondrial membrane potential and increased levels of mitophagy-related proteins. Surprisingly, silencing PINK1 using siRNA not only diminished mitophagy, cellular damage, and inflammatory responses induced by FB1, but also mitigated FB1-induced ferroptosis. In conclusion, this study demonstrates that FB1 causes vascular endothelial cell damage by ferroptosis in a mitophagy-dependent manner. This study thus lays a mechanistic foundation for the study of FB1 causing pulmonary edema in pigs and for exploring options for therapeutic intervention in conditions caused by this mycotoxin, which causes substantial harm to both human and animal health.

The role of mycotoxins in neurodegenerative diseases: current state of the art and future perspectives of research

Mycotoxins are fungal metabolites that can cause various diseases in humans and animals. The adverse health effects of mycotoxins such as liver failure, immune deficiency, and cancer are well-described. However, growing evidence suggests an additional link between these fungal metabolites and neurodegenerative diseases. Despite the wealth of these initial reports, reliable conclusions are still constrained by limited access to human patients and availability of suitable cell or animal model systems. This review summarizes knowledge on mycotoxins associated with neurodegenerative diseases and the assumed underlying pathophysiological mechanisms. The limitations of the common in vivo and in vitro experiments to identify the role of mycotoxins in neurotoxicity and thereby in neurodegenerative diseases are elucidated and possible future perspectives to further evolve this research field are presented.

Study on Fungi Inhabiting Indoor Woods and their Eco-Friendly Management

Biodeterioration of indoor wood and microbial pollution inside buildings is one of important problem in humid areas. Number of fungi are associated with indoor wood and many of them are responsible for its deterioration by causing decay and stain. Some of them may release mycotoxins, which have hazardous impact on human health. In present study, fifteen fungi associated with wood surface were isolated and out of which genus Aspergillus dominate with four species. A. flavus was recorded from all locations. The potential of leaf extracts of nine tree species on the growth of A. flavus was evaluated by amending culture media. Considerable growth inhibition of A. flavus in the range of 1.14-45.45% was recorded on solid media and 9.37-86.66% in liquid media. Amendment of culture media @ 30% concentration of the leaf extract of Corymbia torelliana have recorded maximum growth inhibition irrespective of the media used.

Study on Fungi Inhabiting Indoor Woods and their Eco-Friendly Management

Biodeterioration of indoor wood and microbial pollution inside buildings is one of important problem in humid areas. Number of fungi are associated with indoor wood and many of them are responsible for its deterioration by causing decay and stain. Some of them may release mycotoxins, which have hazardous impact on human health. In present study, fifteen fungi associated with wood surface were isolated and out of which genus Aspergillus dominate with four species. A. flavus was recorded from all locations. The potential of leaf extracts of nine tree species on the growth of A. flavus was evaluated by amending culture media. Considerable growth inhibition of A. flavus in the range of 1.14-45.45% was recorded on solid media and 9.37-86.66% in liquid media. Amendment of culture media @ 30% concentration of the leaf extract of Corymbia torelliana have recorded maximum growth inhibition irrespective of the media used.

Mechanisms of mycotoxin-induced neurotoxicity through oxidative stress-associated pathways

Among many mycotoxins, T-2 toxin, macrocyclic trichothecenes, fumonisin B(1) (FB(1)) and ochratochin A (OTA) are known to have the potential to induce neurotoxicity in rodent models. T-2 toxin induces neuronal cell apoptosis in the fetal and adult brain. Macrocyclic trichothecenes bring about neuronal cell apoptosis and inflammation in the olfactory epithelium and olfactory bulb. FB(1) induces neuronal degeneration in the cerebral cortex, concurrent with disruption of de novo ceramide synthesis. OTA causes acute depletion of striatal dopamine and its metabolites, accompanying evidence of neuronal cell apoptosis in the substantia nigra, striatum and hippocampus. This paper reviews the mechanisms of neurotoxicity induced by these mycotoxins especially from the viewpoint of oxidative stress-associated pathways.

The ribotoxin deoxynivalenol affects the viability and functions of glial cells

Glial cells are responsible for maintaining brain homeostasis. Modification of the viability and functions of glial cells, including astrocytes and microglia, are associated with neuronal death and neurological diseases. Many toxins (heavy metals, pesticides, bacterial or viral toxins) are known to impact on brain cell viability and functions. Although recent publications suggest a potential link between environmental exposure of humans to mycotoxins and neurological diseases, data regarding the effects of fungal toxins on brain cells are scarce. In the present study, we looked at the impact of deoxynivalenol (DON), a fungal ribotoxin, on glial cells from animal and human origin. We found that DON decreased the viability of glial cells with a higher toxicity against microglial cells compared with astrocytes. In addition to cellular toxicity, DON affected key functions of glial cells. Thus, DON caused a biphasic effect on the neuroinflammatory response of microglia to lipopolysaccharide (LPS), while sublethal doses of DON increased the LPS-induced secretion of TNF-α and nitric oxide, toxic doses inhibited it. In addition to affecting microglial functions, sublethal doses of DON also suppressed the uptake of L-glutamate by astrocytes. This inhibition was associated with a modification of the expression of the glutamate transporters at the plasma membrane. Our results suggest that environmental ribotoxins such as DON could, at low doses, cause modifications of brain homeostasis and possibly participate in the etiology of neurological diseases in which alterations of the glia are involved.

Fumonisin B1 inhibits mitochondrial respiration and deregulates calcium homeostasis--implication to mechanism of cell toxicity

Fumonisin B(1) (FB(1)) is a neurodegenerative mycotoxin produced by Fusarium verticiloides mould that contaminates maize worldwide. FB(1) toxicity has been connected with deregulation of sphingolipid metabolism, but the mechanism of cytotoxicity remains controversial. In cell cultures of rat primary astrocytes and human neuroblastoma (SH-SY5Y), we found that FB(1) inhibits mitochondrial complex I, which leads to a decrease in the rate of mitochondrial and cellular respiration, depolarisation of the mitochondrial membrane, induction of reactive oxygen species (ROS) production in mitochondria and deregulation of calcium signalling. Despite the increase in ROS production, the intracellular level of glutathione (GSH) was significantly increased. After 24h of FB(1) exposure, no cell death was observed. Thus, mitochondria appear to be the primary target of FB(1), which leads to sustained deregulation of calcium homeostasis and presumably to cell death.

Effects of fumonisin B1 on HLA class I antigen presentation and processing pathway in GES-1 cells in vitro

Fumonisin B1 (FB1) is a food-borne mycotoxin produced by genus Fusarium and was classified as possible carcinogen to humans by the International Agency for Research on Cancer (IARC). Human leukocyte antigen (HLA) class I antigen presentation pathway plays an important role in immunosurveillance. Defects in HLA class I antigen presentation pathway can down-regulate the expression of HLA class I antigen on the surface of nucleated cells that will confer a survival advantage to randomly mutant cells and may lead to malignant transformation. In the present study, we analyzed the effects of FB1 on the expression of HLA class I heavy chain (classical HLA-A, -B and -C genes included), beta2-microglobulin (β2m), LMP2 and TAP1 genes in human gastric epithelial immortalized GES-1 cells in vitro using semi-quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR), Western blot and immunocytochemical methods in dose- and time-effect studies. Our results revealed that FB1 have an effect on HLA class I antigen presentation pathway via the decreased expression of HLA class I heavy chain and/or defects of LMP2 and TAP1 expression. However, the importance of this effect in carcinogenesis needs further investigation.

Fumonisin B1-induced apoptosis in neuroblastoma, glioblastoma and hypothalamic cell lines

Fumonisin B(1) (FB(1)) is a mycotoxin produced by Fusarium verticilliodes, which commonly infects corn across the world. Fusarium fungi may also be found in moisture-damaged buildings. In this study, we investigated the role of apoptosis in the toxicity of FB(1) in four different cell lines. Activation of caspase-3-like protease, DNA fragmentation and expression of p53 and Bcl-2 family proteins were studied in mouse GT1-7 hypothalamic, rat C6 glioblastoma, human U-118MG glioblastoma, and human SH-SY5Y neuroblastoma cells exposed to 0.1-100microM FB(1) for 0-144h. Caspase-3-like protease activity increased in all cell lines, except SH-SY5Y, at 48-144h, and internucleosomal DNA fragmentation occurred in all of the cell lines, pointing to a role for apoptosis in the toxicity of FB(1). However, the expressions of p53 or pro- or antiapoptotic Bcl-2 family proteins (Bax, Bcl-2, Bcl-X(L) and Mcl-1) were not affected in any of the cell lines even after prolonged exposure to FB(1) at high doses. The results of this study, together with the results of our previous studies, provide evidence that FB(1) is a potential neurotoxin, but that the toxicity of FB(1) varies between different cell lines. The sensitivity of these cell lines towards FB(1) is as follows: U-118MG>GT1-7>C6>SH-SY5Y cells. These results are consistent with the assumption that cells of glial origin may be more sensitive towards FB(1) than cells of neural origin.

Fumonisin B1 Induces Necrotic Cell Death in BV-2 Cells and Murine Cultured Astrocytes and is Antiproliferative in BV-2 Cells While N2A Cells and Primary Cortical Neurons are Resistant

Fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, causes equine leukoencephalomalacia, impairs myelination, and inhibits neuronal growth in vitro. Intact mice do not show brain damage after systemic administration of FB1. We recently reported that intracerebroventricular administration of FB1 in mice caused neurodegeneration in the cortex and activation of astrocytes in the hippocampal area; results suggested that the neuronal damage may be secondary to activation of immunocompetent non-neuronal cells. Current study investigated effects of FB1 upon murine microglial (BV-2) and neuroblastoma (N2A) cell lines, and primary astrocytes and cortical neurons. BV-2 and N2A cultures and cells prepared from neonatal and postnatal brains of BALB/c mice were exposed to various concentrations of FB1 for 4 (BV-2 and N2A) or 4 and 8 (astrocytes and cortical neurons) days. FB1 at 25 microM decreased viability in BV-2 cells, whereas at 50 microM caused necrotic but not apoptotic cell death in both BV-2 and primary astrocytes (at day 8 only), assessed by lactic dehydrogenase release, and pripidium iodide and annexin V staining. Thymidine incorporation indicated that 2.5 microM FB1 decreased proliferation in BV-2 cells. DNA analysis by flow cytometry showed that the inhibition was not caused by cell cycle arrest. The mitochondrial activity decreased dose-dependently in BV-2 cells and was significantly elevated at 25 microM FB1, but not at 50 microM at days 4 or 8 in astrocytes. In BV-2 cells and primary astrocytes, the expression of TNFalpha and IL-1beta analyzed by real-time polymerase chain reaction was downregulated at 6 or 24 h. In all cell types tested the FB1 treatment caused accumulation of free sphinganine and decrease in free sphingosine levels at selected time points. Results indicated that primary and established murine brain immunocompetent cells are vulnerable to the FB1-dependent cytotoxicity in vitro whereas neuronal cells are not. The toxic effects on the neuronal tissue may therefore be secondary to modulation of astrocyte or glial cell function.

Endotoxin exposure alters brain and liver effects of fumonisin B1 in BALB/c mice: implication of blood brain barrier

Fumonisin B(1) (FB(1)), a mycotoxin produced by Fusarium verticillioides, causes equine leukoencephalomalacia and hepatotoxicity. We studied the modulation of FB(1) toxicity in brain and liver of female BALB/c mice after endotoxin administration to compromise the blood-brain barrier (BBB) integrity. Mice were injected intraperitoneally with saline or 3 mg/kg of lipopolysaccharide (LPS) followed 2 h later by either a single or three daily subcutaneous doses of 2.25 mg/kg of FB(1). After 4h of a single FB(1) injection the inhibition of sphingolipid biosynthesis occurred in liver. Circulating alanine aminotransferase increased by LPS alone at this time. In brain LPS triggered inflammation increasing the expression of tumor necrosis factor (TNF) alpha, interferon (IFN) gamma, interleukin (IL)-1beta, IL-6, and IL-12; no effect of FB(1) was observed. In liver LPS+FB(1) attenuated the expression TNFalpha and IFNgamma compared to LPS alone. One day after the 3-day FB(1) treatment the biosynthesis of sphingolipids was markedly reduced in brain and liver and it was further inhibited when LPS was given before FB(1). FB(1) induced hepatotoxicity, as measured by circulating liver enzymes, was reduced after the combined treatment with LPS+FB(1) compared to FB(1) alone. FB(1) decreased the LPS-induced brain expression of IFNgamma and IL-1beta, whereas the expression of IL-6 and IL-12 was augmented. In liver FB(1) also reduced the expression of IL-1beta and IFNgamma compared to LPS alone. Results indicated that endotoxemia concurrent with FB(1) intoxication facilitated the permeability of fumonisin in brain indicated by increased accumulation of sphinganine and endotoxin modified the effects of FB(1) in both brain and liver.

Fumonisin B1-Induced Neurodegeneration in Mice after Intracerebroventricular Infusion is Concurrent with Disruption of Sphingolipid Metabolism and Activation of Proinflammatory Signaling

Fumonisin B1 (FB1), a mycotoxin produced by Fusarium verticillioides, causes equine leukoencephalomalacia, a condition not reproduced in any other species. We hypothesized that direct exposure of murine brain to FB1 will result in neurotoxicity, characterized by biochemical and pathological alterations. The present study compared the toxicity of FB1 in mouse brain after an intracerebroventricular (icv) or subcutaneous (sc) infusion. Female BALB/c mice (5/group) were infused (0.5 microl/h) with total doses of 0, 10 or 100 microg FB1 in saline over 7 days via osmotic pumps implanted either via icv cannulation of the ventricle or via the sc route. One day after the last day of treatment, brains were dissected either fresh or after intracardiac paraformaldehyde fixation. In mice given 100 microg of FB1 icv, FluoroJade B staining revealed neurodegeneration in the cortex, and anti-glial fibrillary acidic protein staining detected activated astrocytes in the hippocampus. High performance liquid chromatography indicated accumulation of free sphinganine in animals given FB1 icv in all brain regions and increased free sphingosine after the 100 microg FB1 in the cortex. The concentration of cortical sphingomyelin and complex sphingolipids remained unchanged. The icv administration of FB1 induced expression of tumor necrosis factor alpha, interleukin-1beta, interleukin-6 and interferon gamma after both doses, assayed by the real-time polymerase chain reaction. The sc administration of 100 microg FB1 caused slight sphinganine accumulation and increased IL-1beta expression in cortex only. Results indicated that icv injection of FB1 caused neurodegeneration with simultaneous inhibition of de novo ceramide synthesis, stimulation of astrocytes, and upregulation of pro-inflammatory cytokines in the murine brain. A relative lack of FB1 availability into the brain could be responsible for the absence of its neurotoxicity in mouse.

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.