Immunohistochemical fate of ochratoxin A in mice

Modulation of mucin mRNA (MUC5AC and MUC5B) expression and protein production and secretion in Caco-2/HT29-MTX co-cultures following exposure to individual and combined Fusarium mycotoxins

Intestinal epithelial cells (IECs) are a critical component of the innate local immune response. In order to reduce the risk of pathogen infection or xenobiotic intoxication, different host defense mechanisms have been evolved. Evidence has shown that upon ingestion of food or feed contaminated with toxins (e.g., mycotoxins), IECs respond by regulating mucin secretions, which act as a physical barrier inhibiting bacterial attachment and subsequent infection-related processes. However, the effect of Fusarium mycotoxins on mucin production remains unclear. Consequently, the aim of this study was to evaluate individual and interactive effects of four common Fusarium mycotoxins, deoxynivalenol, nivalenol, zearalenone, and fumonisins B1 on mRNA expression and secretion of mucins, MUC5AC, and MUC5B, as well as total mucin-like glycoprotein secretion, using Caco-2 (absorptive-type) and HT29-MTX (secretive-type) cells and their co-cultures (initial seeding ratios Caco-2/HT29-MTX: 90/10 and 70/30). Our results showed that individual and mixtures of mycotoxins significantly modulated MUC5AC and MUC5B mRNA and protein, and total mucin-like glycoprotein secretion as measured by quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and enzyme-linked lectin assay, respectively. Additive effects were not always observed for mixtures. Also, the present study showed that in co-cultures, lower MUC5AC and MUC5B mRNA, protein and total mucin production occurred following exposure, which might suggest higher intestinal permeability and susceptibility to toxin exposure. This study demonstrates the importance of selecting an appropriate cell model for the in vitro investigation of Fusarium mycotoxin effects either alone or in combinations on the immunological defense mechanisms of IECs, and will contribute to improved toxin risk assessments.

Ochratoxin A in avicultural meat production: chemical and histological effects

Ochratoxins are fungal secondary metabolites that may contaminate various foods and beverages. Ochratoxins may undergo bio-concentration in some animal tissues/organs and reach concentrations in meat products that are not acceptable for human consumption. The intake of ochratoxins by humans may result in typical syndromes (nephrotoxicity, carcinogenicity, teratogenicity and immunotoxicity) and has been associated with Balkan Endemic Nephropathy. In this study we evaluated the effects and the dynamics of accumulation of ochratoxin A in the organs and tissues after prolonged exposure (40 days) in broilers through their productive cycle. Cytological and histological examinations revealed severe alterations in the hepatic and renal tissues only in animals fed with high dosages (200 µg/kg) of ochratoxin A. But the toxin was detected at levels of 0.78-2.15 µg/kg at day 10 in the tissues of animals that were given feed containing 100 µg/kg, a dosage of ochratoxin A admitted by the current EU recommendation and Italian legislation, and that did not display gross or histo-pathological lesions. Consumption of ochratoxin A-contaminated avian meat, containing such ochratoxin concentrations, could pose a health risk for some human categories. Intensification of surveillance for fungal toxins in animal feeds is advisable in order to understand and prevent this risk.

Expression of COX-2 and hsp72 in peritoneal macrophages after an acute ochratoxin A treatment in mice

Ochratoxin A (OTA) is a secondary fungal metabolite produced by Aspergillus and Penicillium strains that elicits a broad spectrum of toxicological effects in animals and man. A single oral OTA administration (10 mg/kg) in mice induced after 24 h oxidative damage and polymorphonuclear leukocyte (PMN) infiltration in parenchymal organs. In fact, OTA treatment increased lipid peroxidation (via malondialdehyde formation) in kidney and liver and PMN accumulation in duodenum, as shown by myeloperoxidase activity. Following in vivo OTA treatment an increase of cyclooxygenase-2 and of heat shock protein 72 expression was evidenced in peritoneal macrophage lysates by Western blot. That OTA modulates these proteins involved in the inflammatory process indicates that the mycotoxin is able to activate immune cells. This study suggests that the oxidative stress, the neutrophil accumulation in parenchymal tissues and the modulation of inflammatory parameters in peritoneal macrophages induced by OTA are involved in its toxicity, and represent early events related to several aspects of OTA mycotoxicosis.

The effects of mycotoxins, fungal food contaminants, on the intestinal epithelial cell-derived innate immune response

Mycotoxins are structurally diverse fungal metabolites that can contaminate a variety of dietary components consumed by animals and humans. It is considered that 25% of the world crop production is contaminated by mycotoxins. The clinical toxicological syndromes caused by ingestion of moderate to high amounts of mycotoxins and their effect on the immune system have been well characterized. However, no particular attention has been focused on the effects of mycotoxins on the local intestinal immune response. Because of their location, intestinal epithelial cells (IECs) could be exposed to high doses of mycotoxins. As a component of the innate local immune response, intestinal epithelial cells have developed a variety of mechanisms which act to reduce the risk of infection by microorganisms or intoxication by toxic compounds. This review summarises the innate immune response developed by intestinal epithelial cells and reports the literature concerning the effects of mycotoxins on them. Particularly, the effects of mycotoxins on the maintenance of a physical barrier by epithelial cells will be discussed together with their effect on extrinsic protective components of the innate intestinal immunity: mucus secretion, antimicrobial peptide generation, IgA and pro-inflammatory cytokine release.

The role of alpha2u-globulin in ochratoxin A induced renal toxicity and tumors in F344 rats

The mycotoxin ochratoxin A (OTA) was shown to be a potent kidney carcinogen in rats demonstrating a marked sex difference in the response. Compared to female rats, male rats had a 10-fold higher incidence of kidney carcinomas. The objective of this study was to investigate whether this sex difference in tumor response is due to an exacerbation of effect resulting from the interaction of the male rat specific urinary protein alpha2u-globulin (alpha2u) with OTA. Male and female rats were treated by oral gavage with OTA (1 mg/kg per day), D-limonene (dL; 1650 mg/kg per day) as a positive control or corn oil for 7 consecutive days. OTA induced severe renal lesions predominantly in the P3 region of the proximal tubules. The lesions consisted of necrotic cells and cell exfoliations. No hyaline droplets were found in the P2 segment following OTA treatment, whereas dL induced the expected accumulation of droplets. The results suggest that OTA induced kidney lesions are in all characteristic points different from the known alpha2u-nephropathy induced by dL. Based on these experiments the male rat specific protein alpha2u does not seem to be involved in the mechanism(s) leading to the high tumor incidence observed in OTA exposed male rats.

Nephrotoxicity assessment by measuring cellular ATP content. II. Intranephron site of ochratoxin A nephrotoxicity

To clarify the nephrotoxic site and potency of ochratoxin A (OCTA), we measured cellular ATP contents in nine nephron segments incubated with or without OCTA in vitro. Cellular ATP contents of nephron segments isolated under stereomicroscopic observation after treatment of renal slices with 0.1% collagenase were measured by the microchemiluminescence method. OCTA decreased cellular ATP content in a dose-dependent manner. A concentration-response study of OCTA showed that the minimum concentration of OCTA needed to cause a significant decrease in ATP was 10(-8) M in the middle portion of the proximal tubule (S2; p less than 0.05) and 5 x 10(-4) M in the medullary collecting tubule (MCT; p less than 0.01). Among nine nephron segments, OCTA at 5 x 10(-5) M significantly decreased cellular ATP content in only S2 and the terminal portion of the proximal tubule (S3; p less than 0.01). ATP synthesis in mitochondria isolated from the renal cortex was significantly inhibited by 10(-6) M OCTA (p less than 0.05). Probenecid at 4 x 10(-4) M protected against the OCTA-induced cellular ATP decrease. These results suggest that OCTA might enter the plasma membrane in S2 and S3 through the organic anion transport pathway and inhibit mitochondrial oxidative phosphorylation. This newly established method would be applicable to evaluation of the intrarenal toxic site and potency of various chemical compounds.