Formation of 4-hydroxyochratoxin A from ochratoxin A by rat liver microsomes

Abstract

Hydroxyochratoxin A was isolated and identified from the urine of rats after injection with ochratoxin A. By incubating ochratoxin A with rat liver microsomes and reduced nicotinamide adenine dinucleotide phosphate, one major (90%) and two minor metabolites, more polar than ochratoxin A, were formed. Thin-layer chromatography revealed that the major metabolite had Rf values identical to those of hydroxyochratoxin A in six different solvent systems. Formation of the metabolites in vitro was inhibited by carbon monoxide and by metyrapone, and the rate of formation increased after pretreatment of the rats with phenobarbital. A type I spectrum appeared upon binding of ochratoxin A to microsomes with a spectral dissociation constant (Ks) of 37.6 microM. These findings strongly suggest the involvement of a cytochrome P-450 in the hydroxylation of ochratoxin A by rat liver microsomes. Apparent Km and Vmax values for the formation of hydroxyochratoxin A were determined to 50 microM and 5.5 nmol/mg of protein per h, respectively.

Ochratoxin A: An overview on toxicity and carcinogenicity in animals and humans

“…The metabolism of OTA has been extensively studied by the team of Størmer during the past 25 years [291] using in vitro and in vivo assays in liver of different animals [292][293][294][295]. The major metabolites are shown in Fig.…”

“…Formation of the OH-OTA derivatives is modulated by inducers or inhibitors of CYP450, and prostaglandin synthase, which has similar activity to COX and LOX. Indeed, pretreatment of animal with phenobarbital (PB) increased 4(R)-OH-OTA production in hepatocytes [308], rat liver [292,319], rabbit kidney, and in BEAS-2B cells [305]. We have also observed these hydroxylated metabolites in kidney of pig fed OTA [301] and have noted that inhibition of the LOX pathway increases formation of 10-OH-OTA [306].…”

Detoxification of Mycotoxins through Biotransformation

“…Toxins 2020, 12, 121 3 of 37 (4R)-4-Hydroxyochratoxin A (24), or 4-hydroxyochratoxin A, was isolated from the urine of rats after injection with OTA (21), which indicated that OTA (21) was converted to (4R)-4-hydroxyochratoxin A (24) ( Figure S8) [29].…”

“…7-Carboxy-(2 -hydroxy-1phenylalanine-amide)-5-chloro-8-hydroxy-3,4-dihydro-3Rmethylisocoumarin (22) Phenylobacterium immobile (bacterium) [28] Dihydrodiol derivative of ochratoxin A (23) Phenylobacterium immobile (bacterium) [28] (4R)-4-Hydroxyochratoxin A (24) Rat liver microsomes [29] Cell cultures of wheat and maize [29] Rabbit liver microsomes [30] (4S)-4-Hydroxyochratoxin A (25) Cell cultures of wheat and maize [31] Rabbit liver microsomes [30] 10-Hydroxyochratoxin A (26) Rabbit liver microsomes [30] Ochratoxin B (OTB, 27) Hydroquinone metabolite of ochratoxin (OTHQ, 28) Horse radish peroxidase (HPR) [32] Sterigmatocystin (29) 9-Hydroxy sterigmatocystin (30) Human and rat hepatic microsomes [34] T-2 toxin (31) 19-OH T-2 toxin = 3'-OH T-2 toxin (32) Chicken CYP3A37 (enzyme) [35] Zearalenone (ZEN, 33) (5S)-5-Hydroxy ZEN (34) Cunninghamella bainieri (fungus) [38] 13-Hydroxy ZEN (35) Human liver microsomes [40] 15-Hydroxy ZEN (36) Human liver microsomes [40] Toxins 2020, 12, x FOR PEER REVIEW 4 of 37 hydroxy-3,4-dihydro-3Rmethylisocoumarin (22) Dihydrodiol derivative of ochratoxin A (23) Phenylobacterium immobile (bacterium) [28] (4R)-4-Hydroxyochratoxin A (24) Rat liver microsomes [29] Cell cultures of wheat and maize [29] Rabbit liver microsomes [30] (4S)-4-Hydroxyochratoxin A (25) Cell cultures of wheat and maize [31] Rabbit liver microsomes [30] 10-Hydroxyochratoxin A (26) Rabbit liver microsomes [30] Ochratoxin B (OTB,…”

“…It was considered as an important detoxification step made by the host plant [24,25].Fusaric acid (FA, 19), also called 5-butylpicolinic acid, is a host non-specific phytotoxin produced by the fungi from the genus Fusarium [26]. FA (19) was converted to 8-hydroxyfusaric acid (20) with hydroxylation by the fungus Mucor rouxii ( Figure S6) [27].Ochratoxin A (OTA, 21) consists of a chlorinated dihydroisocoumarin linked through a 7-carboxyl group to L-phenylalanine by an amide bond.OTA (21) was hydroxylated into 7-carboxy-(2 -hydroxy-1-phenylalanine-amide)-5-chloro-8-hydroxy-3,4-dihydro-3R-methylisocoumarin (22) and a dihydrodiol derivative (23) by a Gram-negative bacterium Phenylobacterium immobile ( Figure S7) [28].Toxins 2020, 12, 121 3 of 37 (4R)-4-Hydroxyochratoxin A (24), or 4-hydroxyochratoxin A, was isolated from the urine of rats after injection with OTA (21), which indicated that OTA (21) was converted to (4R)-4-hydroxyochratoxin A (24) ( Figure S8) [29].OTA (21) was hydroxylated into (4R)-4-hydroxyochratoxin A (24) and (4S)-4-hydroxyochratoxin A (25) as well as 10-hydroxyochratoxin A (26) by rabbit liver microsomes ( Figure S9) [30,31].When ochratoxin B (OTB, 27) was incubated with horse radish peroxidase (HPR), the high level of the hydroquinone metabolite of ochratoxin (OTHQ, 28) was produced ( Figure S10). It indicated that the hydroquinone redox couple played a significant role in OTB-mediated toxicity [32].Sterigmatocystin (STC, 29) was found to be produced by more than 30 fungal species, particularly by Aspergillus species such as A. flavus, A. parasiticus, A. versicolor and A. nidulans [33].…”