Role of Enzymatic N -Hydroxylation and Reduction in Flutamide Metabolite-Induced Liver Toxicity

ABSTRACT:Flutamide, an antiandrogen drug, is widely used for the treatment of prostate cancer. The initial metabolic pathways of flutamide are hydroxylation and hydrolysis. It was recently reported that the hydrolyzed product, 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1), is further metabolized to N-hydroxy FLU-1, an assumed hepatotoxicant. However, the esterase responsible for the flutamide hydrolysis has not been characterized. In the present study, we found that human arylacetamide deacetylase (AADAC) efficiently hydrolyzed flutamide using recombinant AADAC expressed in COS7 cells. In contrast, carboxylesterase1 (CES1) and CES2, which are responsible for the hydrolysis of many drugs, could not hydrolyze flutamide. AADAC is specifically expressed in the endoplasmic reticulum. Flutamide hydrolase activity was highly detected in human liver microsomes (K m , 794 ؎ 83 M; V max , 1.1 ؎ 0.0 nmol/min/mg protein), whereas the activity was extremely low in human liver cytosol. The flutamide hydrolase activity in human liver microsomes was strongly inhibited by bis-(nonylphenyl)-phenylphosphate, diisopropylphosphorofluoride, and physostigmine sulfate (eserine) but moderately inhibited by sodium fluoride, phenylmethylsulfonyl fluoride, and disulfiram. The same inhibition pattern was obtained with the recombinant AADAC. Moreover, human liver and jejunum microsomes showing AADAC expression could hydrolyze flutamide, but human pulmonary and renal microsomes, which do not express AADAC, showed slight activity. In human liver microsomal samples (n ‫؍‬ 50), the flutamide hydrolase activities were significantly correlated with the expression levels of AADAC protein (r ‫؍‬ 0.66, p < 0.001). In conclusion, these results clearly showed that flutamide is exclusively hydrolyzed by AADAC. AADAC would be an important enzyme responsible for flutamideinduced hepatotoxicity.Flutamide (3Ј-trifluoro-2-methyl-4Ј-nitro-2-methyl-propinoylanilide) is a nonsteroidal antiandrogen drug used for the treatment of prostate cancer. The combination of luteinizing hormone-releasing hormone agonist results in prolonged survival in prostate cancer patients (Crawford et al., 1989). However, flutamide occasionally causes severe hepatotoxicity (Thole et al., 2004). Flutamide itself is not toxic when used at the appropriate clinical dose, but bioactivation of flutamide has been considered to be the cause of flutamide-induced hepatotoxicity (Fau et al., 1994).Flutamide is mainly metabolized to 2-hydroxyflutamide by human CYP1A2. It has been suggested that 2-hydroxyflutamide is associated with the therapeutic effect of flutamide (Katchen and Buxbaum, 1975). Flutamide is also hydrolyzed to 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1) by esterase (Katchen and Buxbaum, 1975;Schulz et al., 1988). FLU-1 is considered to have no therapeutic effect (Aizawa et al., 2003). Goda et al. (2006) recently reported that FLU-1 is further metabolized to N-hydroxyl FLU-1 by human CYP3A4. Many researchers have reported on the relationship between the toxicity and metabolism...

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Human Arylacetamide Deacetylase Is a Principal Enzyme in Flutamide Hydrolysis

Watanabe

Fukami²,

Nakajima³

et al. 2009

“…Thus, there may be inter-or intraindividual variations in CES2 expression and function that affect the flutamide pharmacokinetics. The flutamide-hydrolyzed metabolite, FLU-1, is further metabolized to N-hydroxy FLU-1 by human CYP3A4, and N-hydroxy FLU-1 is thought to be associated with hepatotoxicity (Ohbuchi et al, 2009). Further study is needed to clarify the association of CES2 and AADAC with flutamide-induced hepatotoxicity.…”

Section: Resultsmentioning

confidence: 99%

“…It has been suggested that 2-hydroxyflutamide is associated with the therapeutic effect of flutamide (Katchen and Buxbaum, 1975), whereas FLU-1 is considered to have no therapeutic effect (Aizawa et al, 2003). FLU-1 is further metabolized to N-hydroxy FLU-1 by human CYP3A4, and N-hydroxy FLU-1 is considered to be associated with hepatotoxicity (Ohbuchi et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Contributions of Arylacetamide Deacetylase and Carboxylesterase 2 to Flutamide Hydrolysis in Human Liver

Kobayashi

Fukami²,

Shimizu³

et al. 2012

ABSTRACT:Flutamide, an antiandrogen drug, is widely used for the treatment of prostate cancer. The major metabolic pathways of flutamide are hydroxylation and hydrolysis. The hydrolyzed metabolite, 5-amino-2-nitrobenzotrifluoride (FLU-1), is further metabolized to N-hydroxy FLU-1, an assumed hepatotoxicant. Our previous study demonstrated that arylacetamide deacetylase (AADAC), one of the major serine esterases expressed in the human liver and gastrointestinal tract, catalyzes the flutamide hydrolysis. However, the enzyme kinetics in human tissue microsomes were not consistent with the kinetics by recombinant human AADAC. Thus, it seemed that AADAC is not the sole enzyme responsible for flutamide hydrolysis in human. In the present study, we found that recombinant carboxylesterase (CES) 2 could hydrolyze flutamide at low concentrations of flutamide. In the inhibition assay, the flutamide hydrolase activities at a flutamide concentration of 5 M in human liver and jejunum microsomes were strongly inhibited by a selective CES2 inhibitor, 10 M loperamide, with the residual activities of 22.9 ؎ 3.5 and 18.6 ؎ 0.7%, respectively. These results suggest that CES2 is also involved in the flutamide hydrolysis in human tissues. Using six individual human livers, the contributions of AADAC and CES2 to flutamide hydrolysis were estimated by using the relative activity factor. The relative contribution of CES2 was approximately 75 to 99% at the concentration of 5 M flutamide. In contrast, the relative contribution of AADAC increased in parallel with the concentration of flutamide. Thus, CES2, rather than AA-DAC, largely contributed to the flutamide hydrolysis in clinical therapeutics.

“…Flutamide induced severe hepatic dysfunction. Ohbuchi et al (2008) suggested that CYP3A4 catalyzed the N-oxidation of the amino metabolite of flutamide, which had hepatotoxic effects. Although the bioactivation pathways of nitrobenzodiazepines still remain unclear, they may undergo metabolic activation similar to that of other drugs.…”

Section: Metabolic Activation Of Nitrobenzodiazepinesmentioning

confidence: 99%

Metabolic Activation of Benzodiazepines by CYP3A4

Mizuno¹,

Katoh²,

Okumura³

et al. 2008

ABSTRACT:Cytochrome P450 3A4 is the predominant isoform in liver, and it metabolizes more than 50% of the clinical drugs commonly used. However, CYP3A4 is also responsible for metabolic activation of drugs, leading to liver injury. Benzodiazepines are widely used as hypnotics and sedatives for anxiety, but some of them induce liver injury in humans. To clarify whether benzodiazepines are metabolically activated, 14 benzodiazepines were investigated for their cytotoxic effects on HepG2 cells treated with recombinant CYP3A4. By exposure to 100 M flunitrazepam, nimetazepam, or nitrazepam, the cell viability in the presence of CYP3A4 decreased more than 25% compared with that of the control. In contrast, in the case of other benzodiazepines, the changes in the cell viability between CYP3A4 and control Supersomes were less than 10%.These results suggested that nitrobenzodiazepines such as flunitrazepam, nimetazepam, and nitrazepam were metabolically activated by CYP3A4, which resulted in cytotoxicity. To identify the reactive metabolite, the glutathione adducts of flunitrazepam and nimetazepam were investigated by liquid chromatography-tandem mass spectrometry. The structural analysis for the glutathione adducts of flunitrazepam indicated that a nitrogen atom in the side chain of flunitrazepam was conjugated with the thiol of glutathione. Therefore, the presence of a nitro group in the side chain of benzodiazepines may play a crucial role in the metabolic activation by CYP3A4. The present study suggested that metabolic activation by CYP3A4 was one of the mechanisms of liver injury by nitrobenzodiazepines.