Chlorodibromomethane metabolism to bromide and carbon monoxide in rats

Abstract

The chlorodibromomethane (CDBM) metabolites bromide and CO were analysed as bromide level in plasma and carboxyhaemoglobin (COHb) level in blood of rats, respectively. The mean basic levels of bromide in plasma of rats receiving vehicle were 0.075 +/- 0.036 mmol/l (n = 27). After administration of CDBM at 0.4, 0.8, 1.6, and 3.1 mmol/kg p.o., the mean bromide levels rose to maximal values that were higher by a factor 27, 48, 69, and 135, respectively. Bromide elimination was slow and the plasma level was significantly increased following repeated administration in comparison to a single administration of CDBM. The CDBM concentrations in blood and in fat tissue 6 h after the last of 7 administrations of 0.8 mmol CDBM/ kg p.o., once a day for 7 consecutive days, were significantly lower than 6 h after a single gavage of this CDBM dose. The mean normal level of 0.45 +/- 0.32% COHb in rats (n = 30) was significantly increased following oral CDBM uptake. Initially higher COHb levels were measured after 7 consecutive applications of 0.8 mmol/kg CDBM. After a single administration of CDBM the level of glutathione disulphide in the liver was significantly increased; this effect was reversible. The oxidative CDBM metabolism was influenced by the glutathione (GSH) concentration in the liver. The rate of COHb and bromide formation was decreased after GSH depletion due to pretreatment of rats with buthionine sulphoximine (BSO) and increased following enhancement of the GSH concentration due to pretreatment of the animals with butylated hydroxyanisole (BHA). CDBM is a substrate for cytochrome P-450 2E1 (CYP2E1), as demonstrated by the inhibition of bromide and COHb formation due to simultaneous administration of CDBM and the CYP2E1 inhibitor diethyldithiocarbamate (DDTC); also by the initially higher levels of bromide in plasma and COHb in blood after gavage of CDBM pretreated with isoniazid (INH), an inducer of CYP2E1. The increase of bromide formation after CDBM administration in phenobarbital (PB)-pretreated rats indicated that cytochrome P-450 2B1 and 2B2 (CYP2B1 and CYP2B2) play a role as catalysts of the CDBM biotransformation. It is shown that m-xylene pretreatment, which activates CYP2E1 as well as CYP2Bs, leads to a higher bromide level after CDBM administration than the INH or PB pretreatment. In liver microsomes of rats treated with CDBM (0.8 mmol/kg p.o., seven daily applications), the p-nitrophenol hydroxylase (p-NPH) activity, a market of CYP2E1, was increased. It is concluded that CDBM may be an inducer of CYP2E1. These results combined with literature data demonstrate that the oxidation of CDBM was catalysed mainly by CYP2E1 and CYP2Bs and that there may be a risk of bromide accumulation following repeated uptake of the trihalomethane.

Carbon Monoxide Generation from Trihalomethane Metabolism in Rats

“…The increase of COHb forma- Table 1. GSSG concentration in the liver of male Wistar rats (mean ± SD; n = 3) after a single oral uptake of CDBM or TBM, 0.8 mmol ~ kg-~ (* p < 0.05 vs. control) tion after TBM administration and the increase of bromide concentration in plasma after CDBM administration observed previously [15] in PB-pretreated rats indicates that CYP2B]12 are involved in the trihalomethane oxidation.…”

“…The initial COHb levels were higher in rats after seven consecutive applications (once a day) in comparison with a single uptake of the corresponding dose. An increase of the p-nitrophenol hydroxylase activity, a marker of CYP2E] [16], was demonstrated in liver microsomes of rats after repeated CDBM uptake [ 15].…”

Carbon Monoxide Generation from Trihalomethane Metabolism in Rats

“…INH is an inducer of CYP2E1 [14]. The increase of COHb forma- Pankow/Damme tion after TBM administration and the increase of bromide concentration in plasma after CDBM administration observed previously [15] in PB-pretreated rats indicates that CYP2B1/2 are involved in the trihalomethane oxidation.…”

“…The initial COHb levels were higher in rats after seven consecutive applications (once a day) in comparison with a single uptake of the corresponding dose. An increase of the p-nitrophenol hydroxylase activity, a marker of CYP2E1 [16], was demonstrated in liver microsomes of rats after repeated CDBM uptake [15].…”

Characterization of the Metabolic Interaction between Trihalomethanes and Chloroacetic Acids using Rat Liver Microsomes

“…The main isozyme responsible for the metabolism of chloroform, BDCM and DBCM is CYP2E1 (Nakajima et al, 1995;Lilly et al, 1997;Pankow et al, 1997). THMs are also metabolized into an intermediate metabolite, dihalocarbonyl, which after hydrolysis becomes carbon dioxide (Amhed et al, 1980;Brown et al, 1974;Mathews et al, 1990).…”