Chronology of patulin-induced alterations in membrane function of cultured renal cells, LLC-PK

Patulin suppresses α1-adrenergic receptor expression in HEK293 cells

Patulin (PAT) is a common mycotoxin contaminant of apple products linked to impaired metabolic and kidney function. Adenosine monophosphate activated protein kinase (AMPK), abundantly expressed in the kidney, intercedes metabolic changes and renal injury. The alpha-1-adrenergic receptors (α₁-AR) facilitate Epinephrine (Epi)-mediated AMPK activation, linking metabolism and kidney function. Preliminary molecular docking experiments examined potential interactions and AMPK-gamma subunit 3 (PRKAG3). The effect of PAT exposure (0.2-2.5 µM; 24 h) on the AMPK pathway and α₁-AR was then investigated in HEK293 human kidney cells. AMPK agonist Epi determined direct effects on the α₁-AR, metformin was used as an activator for AMPK, while buthionine sulphoximine (BSO) and N-acetyl cysteine (NAC) assessed GSH inhibition and supplementation respectively. ADRA1A and ADRA1D expression was determined by qPCR. α₁-AR, ERK1/2/MAPK and PI3K/Akt protein expression was assessed using western blotting. PAT (1 µM) decreased α₁-AR protein and mRNA and altered downstream signalling. This was consistent in cells stimulated with Epi and metformin. BSO potentiated the observed effect on α₁-AR while NAC ameliorated these effects. Molecular docking studies performed on Human ADRA1A and PRKAG3 indicated direct interactions with PAT. This study is the first to show PAT modulates the AMPK pathway and α₁-AR, supporting a mechanism of kidney injury.

Overnutrition Determines LPS Regulation of Mycotoxin Induced Neurotoxicity in Neurodegenerative Diseases

Chronic neurodegenerative diseases are now associated with obesity and diabetes and linked to the developing and developed world. Interests in healthy diets have escalated that may prevent neurodegenerative diseases such as Parkinson's and Alzheimer's disease. The global metabolic syndrome involves lipoprotein abnormalities and insulin resistance and is the major disorder for induction of neurological disease. The effects of bacterial lipopolysaccharides (LPS) on dyslipidemia and NAFLD indicate that the clearance and metabolism of fungal mycotoxins are linked to hypercholesterolemia and amyloid beta oligomers. LPS and mycotoxins are associated with membrane lipid disturbances with effects on cholesterol interacting proteins, lipoprotein metabolism, and membrane apo E/amyloid beta interactions relevant to hypercholesterolemia with close connections to neurological diseases. The influence of diet on mycotoxin metabolism has accelerated with the close association between mycotoxin contamination from agricultural products such as apple juice, grains, alcohol, and coffee. Cholesterol efflux in lipoproteins and membrane cholesterol are determined by LPS with involvement of mycotoxin on amyloid beta metabolism. Nutritional interventions such as diets low in fat/carbohydrate/cholesterol have become of interest with relevance to low absorption of lipophilic LPS and mycotoxin into lipoproteins with rapid metabolism of mycotoxin to the liver with the prevention of neurodegeneration.

Patulin in apple juice and its risk assessments on albino mice

The contamination of apple juice with patulin mycotoxin is a major risk factor in food safety. This study focuses to assess the biochemical and histopathological effects of patulin in apple juice samples collected from different outlets retailing in Jeddah, Kingdom of Saudi Arabia. On the basis of the selected dose level, 152.5 ppb patulin/ml was administered daily orally for up to 6 weeks to male albino mice. The exposure to contaminated samples revealed significant elevation of all the studied blood parameters (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities as well as creatinine, urea and uric acid contents). On the other hand, and with regard to the accumulated neuronal toxicity of the tested dose level, the toxic signs were recorded as significant increase in the aggressive and locomotor behavioral changes. In addition, the brain areas monoamines concentration revealed variable increased changes. The potential maximal changes in norepinephrine, dopamine and serotonin5-hydroxytryptamine levels attained in cortex, hypothalamus, striatum, hippocampus, midbrain and pons and medulla were assessed. Moreover, the histological examination revealed degeneration and necrosis in liver tissues and degenerated glomeruli and hemorrhage between the tubules of the cortical region in kidney tissues. The study declared that patulin-contaminated (152.5 ppb) apple juice exhibited liver, kidney and neurotoxicological effects in 6 weeks orally administered mice.

Regulation of patulin-induced oxidative stress processes in the fission yeast Schizosaccharomyces pombe

Patulin (PAT), is one of the most widely disseminated mycotoxins found in agricultural products. In this study the PAT-induced accumulation of reactive oxygen species (ROS) and the regulation of the specific activities of antioxidant enzymes were investigated in the single cell eukaryotic organism Schizosaccharomyces pombe. In comparison with the untreated cells, 500 μM PAT treatment caused a 43% decrease in the concentration of the main intracellular antioxidant, glutathione (GSH); this depletion of GSH initiated a 2.44- and a 2.6-fold accumulation of superoxide anion and hydrogen peroxide, respectively, but did not increase the concentration of hydroxyl radicals; the reduction of ROS-induced adaptation processes via the activation of Pap1 transcription factor resulted in significantly increased specific activities of Cu/Zn superoxide dismutase, catalase and glutathione S-transferase to protect the cells against the ROS-induced unbalanced redox state. However, no change was measured in the activities of glutathione reductase, glutathione peroxidase and glucose-6-phosphate dehydrogenase. It seems reasonable to assume that the temporary PAT-induced ROS accumulation plays a crucial role in adaptation processes. The adverse effects of PAT may be exerted mainly through the destruction of cellular membranes and protein/enzyme functions.

In vitro investigation of individual and combined cytotoxic effects of ochratoxin A and other selected mycotoxins on renal cells

Hundreds of mycotoxins are known to date and many of them are of great interest with regard to human and animal health since they are detected frequently in plant-derived products. Various mycotoxins may occur simultaneously, depending on the environmental and substrate conditions. Considering this coincident production, it is very likely, that humans and animals are always exposed to mixtures rather than to individual compounds. Therefore, future risk assessments should consider mixture toxicity data. This is particularly true for ochratoxin A (OTA), ochratoxin B (OTB), citrinin (CIT) and occasionally for patulin (PAT) as they are all produced by a number of Penicillium and Aspergillus species. Therefore, these four toxins were chosen to study the interactive effects in vitro, using the well-established porcine renal cell line LLC-PK1 and the MTT reduction test as a cytotoxicity endpoint. By application of a step-wise approach to test combination toxicity, using various full factorial as well as a central composite experimental designs, the interactive (synergistic) cytotoxic effects of the these four toxins were assessed. The results obtained in this study confirm a potential for interactive (synergistic) effects of CIT and OTA and possibly other mycotoxins in cells of renal origin.

Patulin reduces glutathione level and enzyme activities in rat liver slices

In the present study, an attempt was made to identify glutathione (GSH) adducts of patulin in precision-cut rat liver slices, which were used as a model system to study the metabolism and biological effects of this mycotoxin. Patulin disappeared in the slices but none of the GSH adducts, previously demonstrated in the chemical reaction of patulin with GSH, could be detected by HPLC. After incubation with various concentrations of patulin, a concentration-dependent decline of the GSH level was observed in the slices. For example, only 25% of the GSH of controls was found with 200 microM patulin. The activities of glutathione-S-transferase (GST) and of drug metabolizing phase I and phase II enzymes, assayed by the hydroxylation and conjugation of testosterone, were also reduced. On the other hand, incubation with patulin markedly increased lipid peroxidation in the slices. The effects of patulin on enzyme activities and lipid peroxidation may be a consequence of the GSH decline, which cannot be accounted for by a direct reaction of patulin with GSH due to the high concentration of GSH in hepatocytes. The decrease of GSH level and GST activity may be related to the putative mutagenic and carcinogenic potential of patulin.

Patulin-induced cellular toxicity: a vital fluorescence study

The mechanisms of patulin-induced cellular toxicity in an immortalized rat granulosa cell line were examined using several vital fluorescence bioassays. Monochlorobimane and 5-chloromethylfluorescein diacetate were used to monitor cellular glutathione (GSH) levels and revealed dose- and time-dependent depletion of GSH by patulin. A significant reduction in the fluorescence of the monochlorobimane-GSH conjugate by 0.1 microM patulin was observed between 1 and 2 hr. Similar GSH depletion by the mycotoxin was also observed in parallel studies on a liver (Clone 9) and a renal (LLC-PK1) cell line, although reduction of fluorescence occurred within 1 hr at the same dosage. Analysis of the electrical potential-dependent partitioning of rhodamine 123 into mitochondria also revealed significant effects of patulin within 1 hr at 0.1 microM. An initial dose-dependent reduction in mitochondrial fluorescence was followed by loss of selective partitioning of the fluorophore into mitochondria at higher doses and/or a longer exposure of cells to patulin. The reduction in mitochondrial fluorescence was paralleled by a dose-dependent decrease in intracellular pH detected with 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein. Analysis of [Ca2+]i with indo-1 and fluo-3 revealed a significant dose-dependent influx of Ca2+ at 10 microM and an alteration of the pattern of ionomycin-induced Ca2+ influx at 1.0 microM following patulin treatment. A carboxyfluorescein fluorescence photobleaching assay was used to examine the effects of patulin on gap junction-mediated intercellular communication. Dose-dependent reduction in intercellular communication was observed within 2 hr with 1.0 microM patulin. These observations indicate that the fluorescence assays used in this study provide a sensitive index of toxicity caused by exposure to patulin. Further, the toxic effects of patulin may involve direct effects on cellular glutathione levels and mitochondrial function in addition to direct effects on the plasma membrane.

The mechanism of patulin's cytotoxicity and the antioxidant activity of indole tetramic acids

In LLC-PK1 cells exposed to patulin (50 microM), lipid peroxidation, abrupt calcium influx, extensive blebbing, and total LDH release appeared to be serially connected events with each representing a step in the loss of structural integrity of the plasma membrane. The aforementioned patulin-induced events were prevented by concurrent incubation with butylated hydroxytoluene, deferoxamine, and cyclopiazonic acid, a fungal metabolite. Patulin also caused depletion of nonprotein sulfhydryls, increased 86Rb+ efflux, dome collapse, and eventually the loss of cell viability. These events were not prevented by antioxidants, results consistent with the hypothesis that they were also serially connected but occurring parallel to those previously mentioned. The earliest events observed in patulin-treated cells were the decrease in nonprotein sulfhydryls and increase in 86Rb+ efflux (5 min) which occurred before statistically significant alterations in protein-bound sulfhydryls. The increased potassium efflux (86Rb+ efflux) occurred via a pathway distinct from BaCl2, quinine, or tetraethylammonium sensitive potassium channels. This is the first published report of the antioxidant activity of indole tetramic acids (cyclopiazonic acid and cyclopiazonic acid imine). The protective effect of tetramic acids in LLC-PK1 cells was restricted to indole tetramic acids, and their prevention of lipid peroxidation did not involve iron chelation. The results of this study demonstrate that cyclopiazonic acid is a potent inhibitor of azide-insensitive, ATP-dependent, a23187-sensitive calcium uptake by the lysate of LLC-PK1 cells. This result is consistent with the hypothesis that the endoplasmic reticulum calcium transport ATPase is a sensitive target for cyclopiazonic acid in LLC-PK1 cells. These findings raise the interesting possibility that the antioxidant activity of indole tetramic acids may involve multiple novel mechanisms: surface charge alterations on the cytoplasmic surface of plasma membranes, alterations in calcium permeability in the plasma and endoplasmic reticulum membrane, and inhibition of the calcium-dependent ATPase of the endoplasmic reticulum.