Benzbromarone

Benzbromarone is a CYP2C9 inhibitor, it binds to CYP2C9 with K_i value of 19.3 nM.

Identification of novel glutathione adducts of benzbromarone in human liver microsomes.[Pubmed:28131653]

Drug Metab Pharmacokinet. 2017 Feb;32(1):46-52.

Benzbromarone (BBR) is a potent uricosuric drug that can cause serious liver injury. Our recent study suggested that 1'-hydroxy BBR, one of major metabolites of BBR, is metabolized to a cytotoxic metabolite that could be detoxified by glutathione (GSH). The aim of this study was to clarify whether GSH adducts are formed from 1'-hydroxy BBR in human liver microsomes (HLM). Incubation of 1'-hydroxy BBR with GSH in HLM did not result in the formation of GSH adducts, but 1',6-dihydroxy BBR was formed. In addition, incubation of 1',6-dihydroxy BBR with GSH in HLM resulted in the formation of three novel GSH adducts (M1, M2 and M3). The structures of M1 and M2 were estimated to be GSH adducts in which the 1-hydroxyethyl group at the C-2 position and the hydroxyl group at the C-1' position of 1',6-dihydroxy BBR were substituted by GSH, respectively. We also found that the 6-hydroxylation of 1'-hydroxy BBR is mainly catalyzed by CYP2C9 and that several CYPs and/or non-enzymatic reaction are involved in the formation of GSH adducts from 1',6-dihydroxy BBR. The results indicate that 1'-hydroxy BBR is metabolized to reactive metabolites via 1',6-dihydroxy BBR formation, suggesting that these reactive metabolites are responsible for BBR-induced liver injury.

A study comparing the safety and efficacy of febuxostat, allopurinol, and benzbromarone in Chinese gout patients: a retrospective cohort study.[Pubmed:27936522]

Int J Clin Pharmacol Ther. 2017 Feb;55(2):163-168.

OBJECTIVE: To evaluate and compare the safety and efficacy of three urate lowering agents: febuxostat, allopurinol, and Benzbromarone, when used to treat Chinese gout patients. METHODS: A total of 120 patients treated in our department from November 2011 to December 2014 were randomly selected and divided into four groups: febuxostat (40 mg per day), febuxostat (80 mg per day), allopurinol (100 mg, 3 x per day) or Benzbromarone (50 mg per day), (n = 30 patients/group). The serum uric acid (UA) concentrations of the patients in each group were recorded and compared from week 2 through week 24 after the treatments, and all adverse events were evaluated to determine the safety of the various treatment regimens. RESULTS: Treatment with febuxostat (40 mg) significantly reduced serum UA levels to those achieved with allopurinol or Benzbromarone treatment. The treatment with febuxostat (80 mg) produced the best therapeutic effect and achieved the targeted UA level as early as week 2. However, the total number of patients experiencing adverse events was significantly higher in the febuxostat 80-mg group. The incidences of abnormal liver function, hyperlipidemia, and gout flare were higher in both febuxostat treatment groups. The allopurinol group had a higher incidence of hypersensitivity, and the Benzbromarone group had a higher incidence of renal dysfunction. CONCLUSION: Chinese patients treated with the 40-mg dose of febuxostat experienced a treatment effect and total rate of adverse events similar to those produced by allopurinol or Benzbromarone. To achieve a better therapeutic effect, the dose of febuxostat can be elevated to 80 mg per day; however, patients receiving the higher dose must be closely monitored for signs of liver dysfunction. Febuxostat is an alternative treatment for Chinese gout patients who are at a much higher risk for severe cutaneous adverse reactions as well as for patients with a history of kidney stones..

Cysteine-Based Protein Adduction by Epoxide-Derived Metabolite(s) of Benzbromarone.[Pubmed:27989145]

Chem Res Toxicol. 2016 Dec 19;29(12):2145-2152.

Benzbromarone (BBR) is a therapeutically useful uricosuric agent but can also cause acute liver injury. The hepatotoxicity of BBR is suggested to be associated with its metabolic activation. Our recent metabolic study demonstrated that BBR was metabolized to epoxide intermediate(s) by cytochrome P450 3A, and the intermediate(s) was reactive to N-acetylcysteine. The objectives of the present study were to determine the chemical identity of the interaction of protein with the epoxide intermediate(s) of BBR and to define the association of the protein modification with hepatotoxicity induced by BBR. Microsomal incubation study showed that the reactive intermediate(s) covalently modified microsomal protein at cysteine residues. Such adduction was also observed in hepatic protein obtained from liver of mice given BBR. The protein covalent binding occurred in time- and dose-dependent manners. Pretreatment with ketoconazole attenuated BBR-induced protein modification and hepatotoxicity, while pretreatment with dexamethasone or buthionine sulfoximine potentiated the protein adduction and hepatotoxicity induced by BBR. A good correlation was observed between BBR-induced hepatotoxicity and the epoxide-derived hepatic protein modification in mice. The present study provided in-depth mechanistic insight into BBR-induced hepatotoxicity.

Allopurinol, benzbromarone and risk of coronary heart disease in gout patients: A population-based study.[Pubmed:28202260]

Int J Cardiol. 2017 Apr 15;233:85-90.

BACKGROUND: The effect of gout on the risk of developing coronary artery disease (CAD) is uncertain. Some studies have found that gout is a risk factor for acute myocardial infarction. This study examined the changes in risk of CAD in gout patients taking allopurinol and/or Benzbromarone, and analyzed the dose-response relationship of both drugs with CAD incidence. METHODS: The medical records of one million subjects from 2000 to 2011 were provided by the Taiwan National Health Insurance Research Database. Cox proportional hazard ratio was used to compare the risk of CAD in gout patients taking allopurinol or/and Benzbromarone with those taking neither drug. Hazard ratios (HR) were adjusted for possible confounding factors, including age, gender, hypertension, hyperlipidemia, diabetes mellitus, chronic kidney disease, and relevant medications. RESULTS: Of 8047 gout patients, 1422 were treated with allopurinol (Group A), 4141 with Benzbromarone (Group B), and 2484 with both drugs (Group A/B) during the follow-up period. Our results showed the incidence of CAD after adjusting for covariates for Group A, Group B, and Group A/B did not significantly differ from the comparison group. However, after adjustment for covariates in dose-response analyses, treatment with over 270 defined daily doses (DDDs) of allopurinol, and over 360 DDDs of Benzbromarone, was associated with a significantly reduced risk of CAD. CONCLUSION: We found that the use of allopurinol and Benzbromarone, whether alone or in combination, had a linear dose-response relationship between the numbers of defined daily doses and the risk of CAD, especially in higher DDDs.

Functional expression of the TMEM16 family of calcium-activated chloride channels in airway smooth muscle.[Pubmed:23997176]

Am J Physiol Lung Cell Mol Physiol. 2013 Nov 1;305(9):L625-34.

Airway smooth muscle hyperresponsiveness is a key component in the pathophysiology of asthma. Although calcium-activated chloride channel (CaCC) flux has been described in many cell types, including human airway smooth muscle (HASM), the true molecular identity of the channels responsible for this chloride conductance remains controversial. Recently, a new family of proteins thought to represent the true CaCCs was identified as the TMEM16 family. This led us to question whether members of this family are functionally expressed in native and cultured HASM. We further questioned whether expression of these channels contributes to the contractile function of HASM. We identified the mRNA expression of eight members of the TMEM16 family in HASM cells and show immunohistochemical evidence of TMEM16A in both cultured and native HASM. Functionally, we demonstrate that the classic chloride channel inhibitor, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), inhibited halide flux in cultured HASM cells. Moreover, HASM cells displayed classical electrophysiological properties of CaCCs during whole cell electrophysiological recordings, which were blocked by using an antibody selective for TMEM16A. Furthermore, two distinct TMEM16A antagonists (tannic acid and Benzbromarone) impaired a substance P-induced contraction in isolated guinea pig tracheal rings. These findings demonstrate that multiple members of this recently described family of CaCCs are expressed in HASM cells, they display classic electrophysiological properties of CaCCs, and they modulate contractile tone in airway smooth muscle. The TMEM16 family may provide a novel therapeutic target for limiting airway constriction in asthma.

Calcium-activated chloride channel TMEM16A modulates mucin secretion and airway smooth muscle contraction.[Pubmed:22988107]

Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):16354-9.

Mucous cell hyperplasia and airway smooth muscle (ASM) hyperresponsiveness are hallmark features of inflammatory airway diseases, including asthma. Here, we show that the recently identified calcium-activated chloride channel (CaCC) TMEM16A is expressed in the adult airway surface epithelium and ASM. The epithelial expression is increased in asthmatics, particularly in secretory cells. Based on this and the proposed functions of CaCC, we hypothesized that TMEM16A inhibitors would negatively regulate both epithelial mucin secretion and ASM contraction. We used a high-throughput screen to identify small-molecule blockers of TMEM16A-CaCC channels. We show that inhibition of TMEM16A-CaCC significantly impairs mucus secretion in primary human airway surface epithelial cells. Furthermore, inhibition of TMEM16A-CaCC significantly reduces mouse and human ASM contraction in response to cholinergic agonists. TMEM16A-CaCC blockers, including those identified here, may positively impact multiple causes of asthma symptoms.

Benzbromarone is a highly effective and well tolerated non-competitive inhibitor of xanthine oxidase, used as an uricosuric agent, used in the treatment of gout.

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