Role of human organic anion transporter 4 in the transport of ochratoxin A.
(25/282)
The purpose of this study was to investigate the characteristics of ochratoxin A (OTA) transport by multispecific human organic anion transporter 4 (hOAT4) using mouse proximal tubule cells stably transfected with hOAT4 (S(2) hOAT4). Immunohistochemical analysis revealed that hOAT4 protein was localized to the apical side of the proximal tubule. S(2) hOAT4 expressed hOAT4 protein in the apical side as well as basolateral side and the cells were cultured on the plastic dish for experiments. S(2) hOAT4 exhibited a time- and concentration-dependent, and a saturable increase in OTA uptake, with an apparent K(m) value of 22.9+/-2.44 microM. The OTA uptakes were inhibited by several substrates for the OATs. Probenecid, piroxicam, octanoate and citrinin inhibited OTA uptake by hOAT4 in a competitive manner (K(i)=44.4-336.4 microM), with the following order of potency: probenecid > piroxicam > octanoate >citrinin. The efflux of OTA by S(2) hOAT4 was higher than that by mock. Addition of OTA resulted in slight decrease in viability of S(2) hOAT4 compared with mock. These results indicate that hOAT4 mediates the high-affinity transport of OTA on the apical side of the proximal tubule, whereas the transport characteristics of OTA are distinct from those by basolateral OATs. (+info)
Aristolochic acid as a probable human cancer hazard in herbal remedies: a review.
(26/282)
The old herbal drug aristolochic acid (AA), derived from Aristolochia spp., has been associated with the development of a novel nephropathy, designated aristolochic acid nephropathy (AAN), and urothelial cancer in AAN patients. There is clear evidence that the major components of the plant extract AA, aristolochic acid I (AAI) and aristolochic acid II (AAII), both nitrophenanthrene carboxylic acids, are genotoxic mutagens forming DNA adducts after metabolic activation through simple reduction of the nitro group. Several mammalian enzymes have been shown to be capable of activating both AAI and AAII in vitro and in cells. The activating metabolism has been elucidated and is consistent with the formation of a cyclic nitrenium ion with delocalized charge leading to the preferential formation of purine adducts bound to the exocyclic amino groups of deoxyadenosine and deoxyguanosine. The predominant DNA adduct in vivo, 7-(deoxyadenosin-N(6)-yl)aristolactam I (dA-AAI), which is the most persistent of the adducts in target tissue, is a mutagenic lesion leading to AT-->TA transversions in vitro. This transversion mutation is found at high frequency in codon 61 of the H-ras oncogene in tumours of rodents induced by AAI, suggesting that dA-AAI might be the critical lesion in the carcinogenic process in rodents. DNA-binding studies confirmed that both AAs bind to the adenines of codon 61 in the H-ras mouse gene and preferentially to purines in the human p53 gene. In contrast, the molecular mechanism of renal interstitial fibrosis in humans after chronic administration of AA remains to be explored. However, preliminary findings suggest that DNA damage by AA is not only responsible for the tumour development but also for the destructive fibrotic process in the kidney. It is concluded that there is significant evidence that AA is a powerful nephrotoxic and carcinogenic substance with an extremely short latency period, not only in animals but also in humans. In particular, the highly similar metabolic pathway of activation and resultant DNA adducts of AA allows the extrapolation of carcinogenesis data from laboratory animals to the human situation. Therefore, all products containing botanicals known to or suspected of containing AA should be banned from the market world wide. (+info)
Fate of ochratoxin A in brewing.
(27/282)
The fate of ochratoxin A in brewing was investigated by adding (3H)ochratoxin A to the raw materials at 1- and 10-mug/g levels during mashing in a conventional microbrewing process. The results indicated that large portions (28 to 39%) of the added toxin were recovered in spent grains, with less recovery in the yeast (8 to 20%) and beer (14 to 18%). About 38 and 12% of the added toxin at levels of 1 and 10 mug/g, respectively, were degraded during brewing. (+info)
The role of oxidative stress in the ochratoxin A-mediated toxicity in proximal tubular cells.
(28/282)
Balkan endemic nephropathy (BEN), a disease characterized by progressive renal fibrosis in human patients, has been associated with exposure to ochratoxin A (OTA). This mycotoxin is a frequent contaminant of human and animal food products, and is toxic to all animal species tested. OTA predominantly affects the kidney and is known to accumulate in the proximal tubule (PT). The induction of oxidative stress is implicated in the toxicity of this mycotoxin. In the present study, primary rat PT cells and LLC-PK(1) cells, which express characteristics of the PT, were used to investigate the OTA-mediated oxidative stress response. OTA exposure of these cells resulted in a concentration-dependent elevation of reactive oxygen species (ROS) levels, depletion of cellular glutathione (GSH) levels and an increase in the formation of 8-oxoguanine. The OTA-induced ROS response was significantly reduced following treatment with alpha-tocopherol (TOCO). However, this chain-braking anti-oxidant did not reduce the cytotoxicity of OTA and was unable to prevent the depletion of total GSH levels in OTA-exposed cells. In contrast, pre-incubation of the cell with N-acetyl-L-cysteine (NAC) completely prevented the OTA-induced increase in ROS levels as well as the formation of 8-oxoguanine and completely protected against the cytotoxicity of OTA. In addition, NAC treatment also limited the GSH depletion in OTA-exposed PT- and LLC-PK(1) cells. From these data, we conclude that oxidative stress contributes to the tubular toxicity of OTA. Subsequently, cellular GSH levels play a pivotal role in limiting the short-term toxicity of this mycotoxin in renal tubular cells. (+info)
Depletion of intracellular Ca2+ stores sensitizes the flow-induced Ca2+ influx in rat endothelial cells.
(29/282)
Hemodynamic shear stress elicits a rise in endothelial [Ca2+]i, which may serve as a key second messenger to regulate many flow-associated physiological and biochemical processes. In the present study, we used Mn2+ quenching of fluorescent dye Fluo3 as an assay to investigate the Ca2+ influx of rat aortic endothelial cells in response to flow. We found that the Ca2+ signaling in response to flow could be greatly influenced by the status of intracellular Ca2+ stores. Depletion of intracellular Ca2+ stores by thapsigargin (4 micromol/L) or cyclopiazonic acid (10 micromol/L) drastically sensitized the Ca2+ influx in response to flow. Ca2+-mobilizing agonist bradykinin (100 nmol/L) or ATP (100 micromol/L) had similar sensitizing effect. The effect of bradykinin or ATP was blocked by Xestospongin C and U73122, suggesting that the sensitization was related to the IP3-mediated store depletion. On the other hand, the Mn2+ quenching in response to flow was greatly reduced by ochratoxin A (100 nmol/L), an agent that could increase the filling state of intracellular Ca2+ stores. In addition, we found that depletion-sensitized Ca2+ influx in response to flow was mediated by a PKG-inhibitable cation channel and that the influx was affected by membrane potential and K+ channel activity. In conclusion, the present study argues for a critical role of intracellular Ca2+ status in determining the Ca2+ signaling in response to flow and it provides a general mechanistic explanation for the stimulatory role of blood-borne agonists on flow-induced Ca2+ influx. (+info)
A new approach to studying ochratoxin A (OTA)-induced nephrotoxicity: expression profiling in vivo and in vitro employing cDNA microarrays.
(30/282)
Ochratoxin A (OTA) is a mycotoxin often found in cereals as a contaminant, and it is known to cause severe nephrotoxicity in animals and humans. There have been several investigations studying the mode of action of this toxicant, suggesting inhibition of protein synthesis, formation of DNA adducts, and provocation of DNA single-strand breaks as a result of oxidative stress, but little is known about the transcriptional alterations underlying OTA-derived nephrotoxicity so far. We carried out DNA microarray analyses to assess OTA-specific expression profiles in vivo and in vitro. Cultures of primary rat proximal tubular cells and male Wistar rats were treated with a low dose (5 microM and 1 mg/kg, respectively) or a high dose (12.5 microM and 10 mg/kg, respectively) of OTA for 24 or 72 h. Microarray experiments were carried out after dual fluorescent labeling of sample cDNA, and data analysis was performed utilizing different statistical methods. Validity of selected microarray data was confirmed by quantitative real-time PCR. We were able to demonstrate that microarray data derived from our proximal tubule cell (PTC) culture model were highly comparable to the in vivo situation. Marked treatment-specific transcriptional changes were detected for genes involved in DNA damage response and apoptosis (upregulation of GADD 153, GADD 45, annexin V), response to oxidative stress (differential expression of hypoxia-inducible factor 1 and catalase), and inflammatory reactions (upregulation of alpha 2 macroglobulin, ceruloplasmin, and cathepsin S). We conclude that our results provide a molecular basis for interpretation of OTA-induced nephrotoxicity. (+info)
Levels of ochratoxin A and IgG against conidia of Penicillium verrucosum in blood samples from healthy farm workers.
(31/282)
Ochratoxin A (OTA) is a mycotoxin frequently found in human blood and milk samples in the colder climatic zones. In addition to dietary intake, exposure may occur by inhalation of toxin containing fungal conidia. The purpose of this work was to investigate the level of OTA in blood samples from farm workers and non-farm working controls, and to examine if serum levels of OTA were related to inhalatory exposure to conidia of Penicillium verrucosum, the main OTA producer in temperate climates. Blood samples from 210 participants were analysed for the presence of OTA and IgG antibodies against P. verrucosum conidia. The concentration of OTA was determined by HPLC (DL 10 ng/l), and the IgG level was determined by ELISA. All serum samples contained OTA (mean 397 ng/l, range 21-5534 ng/l). The OTA level in serum was unrelated to farm working, gender, age, and IgG level. The mean IgG level was significantly higher among farm workers than controls. Farm working, or increased inhalatory exposure to P. verrucosum, was not related to higher OTA serum levels. Inhalatory exposure to OTA from farm working seems to be of minor importance compared to dietary intake. (+info)
Mycotoxins and reproduction in domestic livestock.
(32/282)
Molds are parasitic plants that are ubiquitous in livestock feedstuffs. Even though molds themselves reduce the quality of grains, their synthesis of chemical substances termed mycotoxins causes the greatest monetary loss to the animal industry. Five major mycotoxins that impair growth and reproductive efficiency in North America are aflatoxins, zearalenone, deoxynivalenol, ochratoxin, and ergot. Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus. Consumption of grains containing aflatoxins by swine affects reproduction indirectly by reducing feed intake and growth. In swine, aflatoxins impair liver and kidney function, delay blood clotting, increase susceptibility to bruising, and interfere with cellular humoral immune systems. Ruminants are comparatively resistant to aflatoxicosis, but presence of aflatoxins in milk of dairy cows is closely monitored for human safety. Depending on environmental conditions, Fusarium roseum can produce either zearalenone or deoxynivalenol. Days 7 to 10 postmating seem to be a critical period of gestation for zearalenone to exert its detrimental actions on early embryonic development. Presence of deoxynivalenol in swine feedstuffs decreases feed intake, causes feed refusal, and induces occasional vomiting. Several species of Penicillium and Aspergillus produce ochratoxin, a mycotoxin that causes necrosis of kidney tissue. Ergot alkaloids produced by Claviceps purpurea on wheat can cause reproductive problems and are associated with lactational failure in swine. Various methods have been developed to remove mycotoxins from infected feedstuffs. Chemical analyses in laboratories as well as diagnostic kits suitable for use at the elevator or farm can be used successfully to identify which mycotoxins are present in suspect feedstuffs. (+info)