Energy-dependent uptake of ochratoxin A by mitochondria

doi:10.1016/0003-9861(76)90243-5

Archives of Biochemistry and Biophysics

Volume 173, Issue 1, March 1976, Pages 132-140

https://doi.org/10.1016/0003-9861(76)90243-5 Get rights and content

Abstract

The interaction of ochratoxin A, a mycotoxin produced by Aspergillus ochraceus, with isolated rat liver mitochondria and plasma membranes has been studied. Cell membranes bind [¹⁴C]ochratoxin A poorly and do not show saturation in the concentration range examined. The uptake of the toxin by mitochondria is saturable, with an apparent K_m at 0 °C of 30 nmol/mg of protein. Sonication or freeze-thawing reduces the extent of incorporation by 88%. Ochratoxin A uptake is energy dependent, resulting in a depletion of intramitochondrial ATP. Uncouplers such as m-chlorocarbonylcyanide phenylhydrazone or the respiratory inhibitors rotenone and antimycin A inhibit uptake 60–85%, while ATP reverses the antimycin and rotenone inhibition. Phosphate transport is sensitive to inhibition by the toxin, as measured by Ca²⁺ plus P_istimulated respiration and [³²P]P_i incorporation. In turn, phosphate inhibits nearly completely [¹⁴C]ochratoxin A uptake at 22 °C and causes a concomitant mitochondrial swelling yet is not incorporated into the matrix space. Thus, the saturable uptake of ochratoxin A is accompanied by a decrease in the energy state and inhibition of P_i transport, which results in deteriorative changes of the mitochondria, as evidenced by large-amplitude swelling.

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The Parkinson's disease-related genes act in mitochondrial homeostasis
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It has been suggested that Parkin possesses anti-oxidant function in neuronal to affect mitochondrial function (Conn et al., 2002). Several reports have indicated the connections between mitochondrial dysfunction and oxidative damage in Parkin-deficient mice (Batenburg and Olson, 1976; Meisner, 1976; Raikhinshtein et al., 1976; Sandri et al., 1976). Sensitivity to oxidative stress and severe structural mitochondrial abnormalities were increased in Drosophila lacking Parkin (Batenburg and Olson, 1976; Sattler et al., 2000).
Neurons are metabolically active cells with high energy demands. Thus, neurons are particularly reliant on mitochondrial function, especially on the homeostasis properties of mitochondria. This is reflected by the observation that mitochondrial abnormalities have been well recognized to contribute to neurodegenerative diseases, like Parkinson's disease (PD). Mitochondria are highly complex and dynamic organelles continuously undergoing different alterations. The dynamic property of mitochondria is named as mitochondrial homeostasis. Imbalance of mitochondrial homeostasis is associated with neurodegenerative disease, such as Parkinson's diseases. Recently, the related genes of PD-familial, such as alpha-synuclein, Parkin, PINK1, DJ-1 and LRRK2, are observed to be associated with mitochondria, and capable of modulating normal mitochondrial integrity and functions under certain conditions. Therefore, in this review, we will focus on the action of PD-related genes in mitochondrial homeostasis.
Toxicokinetics and toxicodynamics of ochratoxin A, an update
2006, Chemico-Biological Interactions
Citation Excerpt :
Although information on the combined effects of mycotoxins is limited, most of it is related to OTA. Regarding the effects of OTA and OTB combination, additive effects were obtained when examining yeast phenylalanyl-tRNA synthetase activities and protein synthesis in hepatoma cells [214], as well as mitochondrial respiration [215]. By contrast, antagonistic interactions have been observed at the immunotoxic and nephrotoxic levels, as shown by the measurement of the immunosuppresion of human lymphocytes [216] and of the histological damage of the proximal tubules in rats [217].
Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunotoxic to several species of animals and to cause kidney and liver tumours in mice and rats. Because of differences in the physiology of animal species, wide variations are seen in the toxicokinetic patterns of absorption, distribution and elimination of the toxin. Biotransformation of OTA has not been entirely elucidated. At present, data regarding OTA metabolism are controversial. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. Several major mechanisms have been shown as involved in the toxicity of OTA: inhibition of protein synthesis, promotion of membrane peroxidation, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage. The contribution of metabolites in OTA genotoxicity and carcinogenicity is still unclear. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian tests, notably regarding the formation of DNA adducts. More recent studies are focused on the OTA ability to disturb cellular signalling and regulation, to modulate physiological signals and thereby to influence cells viability and proliferation. The present paper offers an update on these different issues. In addition since humans and animals are likely to be simultaneously exposed to several mycotoxins, especially through their diet, the little information available on the combined effects of OTA and other mycotoxins has also been reviewed.
Induction of free radicals in hepatocytes, mitochondria and microsomes of rats by ochratoxin A and its analogs
1997, Biochimica et Biophysica Acta - Molecular Cell Research
Oxidative damage may be one of the manifestations of cellular damage in the toxicity of ochratoxin A (OA). OA; its three natural analogs, OB, OC and Oα; and three synthetic analogs, the ethyl amide of OA (OE-OA), O-methylated OA (OM-OA), and the lactone-opened OA (OP-OA) were used to study free radical generation in hepatocytes, mitochondria and microsomes from rats. Electron paramagnetic resonance spectroscopy (EPR) using α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN) as a spin trapping agent showed an enhanced free radical generation due to the addition of NADPH to the microsomes. An EPR signal was not observed in the mitochondria and hepatocyte samples when they were treated with a variety of agents. Addition of OM-OA together with NADPH and Fe³⁺ to the microsomes resulted in a strong EPR signal compared with the other analogs, whereas the signal could be quenched by the addition of catalase. OM-OA does not have a dissociable phenolate group and does not chelate Fe³⁺. The spin adduct hyperfine splitting constants indicated the presence of α-hydroxyethyl radicals resulting from generated hydroxyl radicals, which were trapped by 4-POBN. The results also suggested that the production of hydroxyl radicals by OA does not require a dissociable phenolate group or the prior formation of an OA-Fe complex.
Accumulation of ochratoxin A in rat kidney in vivo and in cultivated renal epithelial cells in vitro
1996, Toxicology
In this study we determined the distribution of ochratoxin A (OTA) in renal tissue as well as its content and binding pattern in different cell types stemming from the proximal tubule (OK cells) and collecting duct (MDCK cells) of the kidney. To obtain the net amount of OTA in renal tissue, the relative amount in the vascular compartment was calculated and subtracted. After acute administration of OTA to male Wistar rats, the highest concentrations were detected in the papilla and inner medulla. Concentrations in the outer medulla and in the cortical tissue were 50% lower. Sub-chronic (6 day) exposure to OTA resulted in a similar distribution in young rats (6 weeks old) but in a different distribution in adult rats (2 year old). Cultured MDCK-C11 cells (representing intercalated cells) showed a higher OTA content after 48 h of exposure to 1 μmol/1 OTA than another MDCK cell subtype (MDCK-C7, representing principal cells) and OK cells. Additionally, the capability of cell extracts to bind OTA was the highest in MDCK-C11 cells followed by cell extracts of OK cells and cell extracts of MDCK-C7 cells. In two cell types studied, OK and MDCK-C11 cells, OTA was bound preferentially by organellar components and less by cytosolic ones.
Free radical generation as induced by ochratoxin A and its analogs in bacteria (Bacillus brevis)
1996, Journal of Biological Chemistry
Lipid peroxidation is considered as one of the manifestations of cellular damage in the toxicity of ochratoxin A (OA). OA; its three natural analogs, OB, OC, and Oα; and four synthetic analogs, d-OA, the ethylamide of OA (OE-OA), O-methylated OA (OM-OA), and the lactone-opened OA (OP-OA) were used to study free radical generation in bacteria with Bacillus brevis as a model system. The uptake of the different ochratoxins by B. brevis varied substantially depending on the molecular structures. Electron paramagnetic resonance spectroscopy using α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone as a spin trapping agent showed an enhanced free radical generation due to the addition of OA and most of the analogs. The EPR signals could be further enhanced by the addition of Ca²⁺, a calcium ionophore and an ATPase uncoupler, whereas they were eliminated by incubating the growing cells with vitamin E. The spin adduct hyperfine splitting constants indicate the presence of α-hydroxyethyl radicals resulting from generated hydroxyl radicals, which are trapped by α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone. The results further suggest that OA induces free radical production in this model system by enhancing the permeability of the cellular membrane to Ca²⁺.
Role of ochratoxin in disease causation
1992, Food and Chemical Toxicology
Under experimental conditions renal damage has been induced by alimentary exposure to ochratoxin A in all single-stomach animals tested so far, including rodents, dogs, pigs and birds, and even in young ruminants still functioning as single-stomach animals. Most information on ochratoxin-induced nephropathy has been obtained in pigs during experimental studies comprising structural as well as functional changes. The renal damage is characterized morphologically by atrophy of the proximal tubules, interstitial cortical fibrosis and sclerotized glomeruli, and functionally by impairment of tubular function indicated by a decrease in Tm_PAH/C_in and reduced ability to produce concentrated urine. The renal effect has been observed using exposure levels of ochratoxin A in the range 200 to 4000 μg/kg feed. Field cases of ochratoxin-induced nephropathy in pigs have been encountered in many countries, and the disease mycotoxic porcine nephropathy (MPN) is recognized as an endemic disease entity in several northern and central European countries. Epidemics of MPN have been reported, closely related to excessive climatic conditions in periods preceding harvest. Ochratoxin A is a recognized renal carcinogen in the mouse. In female pigs exposed to alimentary ochratoxin A for 2 years, no renal cancer was observed. Ochratoxin A is metabolized and excreted relatively fast in animals, with an RL₅₀ (residue elimination) in the pig of a few days for various tissues. Past exposure data is a requirement in retrospective epidemiological studies, but because of the short RL₅₀ values tissue analysis for ochratoxin A is unlikely to provide that kind of data, in animals or in humans. In order to meet this demand a procedure has been developed, using renal biopsy material for activity analysis of two renal tubular enzymes, phosphoenolpyruvate carboxykinase and γ-glutamyl transpeptidase. In pigs exposed to ochratoxin A for 1 week a 40% reduction of the enzyme activity was observed. The dose-related activity decrease of the two enzymes was accompanied by a dose-related aggravation of renal impairment, as measured by a reduction of Tm_PAH/C_in, suggesting that these enzymes are sensitive indicators of ochratoxin A-induced nephropathy.

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^☆: This research was supported by USPHS Grant No. ES 00838.

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Energy-dependent uptake of ochratoxin A by mitochondria☆

Abstract

Food Cosmet. Toxicol

Toxicol. Appl. Pharmacol

Biochim. Biophys. Acta

Biochem. Biophys. Res. Commun

J. Biol. Chem

Biochim. Biophys. Acta

Biochim. Biophys. Acta

Arch. Biochem. Biophys

C.R.C. Crit. Rev. Toxicol

Brit. J. Cancer