Pharmacokinetics and Metabolism of an .ALPHA.,.BETA.-Blocker, Amosulalol Hydrochloride, in Mice: Biliary Excretion of Carbamoyl Glucuronide

Abstract

Amosulalol hydrochloride is a combined a-and b-blocker that was selected from a series of sulphonamide-substituted phenylethylamines. It blocks both postsynaptic a 1 -and b 1 -adrenoceptors to almost the same extent. When administered to conscious, spontaneously hypertensive rats, it reduces blood pressure via its a 1 -blocking activity without causing reflex tachycardia because of its b 1 -blocking action.1) This drug exhibited dose-dependent hypotensive effects in healthy volunteers, 2) and is used for the treatment of essential hypertension.3) In contrast to a structurally related a-and bblocker, labetalol, 4) amosulalol's first-pass metabolism was almost negligible in humans.2) However, this drug was extensively metabolized in laboratory animals 5) yielding an order of total body clearance as follows: rats>dogs>monkeys>hu-mans. 2,6) The metabolites found in these animals were derived through the hydroxylation (M-1, M-3, M-4), demethylation (M-2), and oxidative cleavage of the C-N bond (M-5). Some of them were subsequently conjugated to their glucuronides or sulfates. In humans, only the sulfate of M-3 was quantified as the urinary metabolite. 7) In the present study, pharmacokinetic and metabolic studies of amosulalol hydrochloride in mice were undertaken, with amosulalol carbamoyl glucuronide being reported as a new amosulalol metabolite found in bile. MATERIALS AND METHODS ChemicalsAmosulalol hydrochloride and its metabolites, M-1, M-2, M-3, M-4 and M-6 (desmethyl metabolite at o-methoxyphenoxy group of M-1), were supplied by the Chemistry Laboratories of Astellas Pharma Inc. (Ibaraki, Japan). M-5 (o-methoxyphenoxy acetic acid) was purchased from Tokyo Kasei (Tokyo, Japan). 14 C-Amosulalol hydrochloride, labelled at both of the carbons in the ethyl group of the o-methoxyphenoxy ethyl moiety, was synthesized in our laboratories.8) All other reagents were of analytical grade. Animal Studies Male ICR mice (4-7 weeks) were purchased from Charles River Laboratories Japan or CLEA Japan, and used after a one-week period of acclimatization.Amosulalol hydrochloride was administered intravenously as a solution in saline and orally as an aqueous solution. Mice were fasted overnight before oral administration, and fed 4 h after dosing. Blood samples were taken from the inferior vena cava with heparinized syringes under diethyl ether anesthesia, and each animal was sacrificed at each sampling point. For urine and fecal sample collection, animals were kept in glass metabolic cages for 24 or 48 h after dosing. For the metabolite identification, bile samples were obtained from bile duct-cannulated mice during hours 0 and 24 after dosing. This research was conducted in accordance with the "Principles of Laboratory Animal Care" (NIH publication #85-23, revised 1985).Determination of Radioactivity The urine collected was diluted 10-fold with distilled water. Aquaol-2 (10 ml, New England Nuclear) was then added to a 0.1-ml aliquot of the diluted sample. In addition, about 100 mg of dried feces was combusted in a sample oxidiz...

Biotransformation of an α4β2 Nicotinic Acetylcholine Receptor Partial Agonist in Sprague-Dawley Rats and the Dispositional Characterization of Its N-Carbamoyl Glucuronide Metabolite

“…Dissimilarly, M6 was converted quantitatively to 1 by ␤-glucuronidase, paralleling the hydrolytic behavior of N-carbamoyl glucuronides (Tremaine et al, 1989;Schaefer, 1992;Shaffer et al, 2005). Furthermore, an N-carbamoyl glucuronide of 1 was generated in vitro; the CID spectra, whose fragmentation cascades mirrored those of known N-carbamoyl glucuronides (Shaffer et al, 2005;Schaefer, 2006;Suzuki and Kamimura, 2007), and LC t R values of the biosynthesized N-carbamoyl glucuronide and M6 were identical. NMR analyses of M6 purified from rat bile extracts unequivocally identified it as an N-carbamoyl glucuronide of 1.…”

Identification of a NovelN-Carbamoyl Glucuronide: In Vitro, In Vivo, and Mechanistic Studies

“…Of the earlier reports for N-carbamoyl glucuronidation few were for tocainide (Elvin et al, 1980;Ronfeld et al, 1982). Since then, such a metabolic pathway has been reported for rimantadine (Brown et al, 1990), carvedilol (Schaefer, 1992), mofegiline (Dow et al, 1994), and most recently for amosulalol (Suzuki and Kamimura, 2007), in addition to sitagliptin and sertraline.…”

“…N-Carbamoyl glucuronides have been reported not only in in vitro incubations but also in in vivo tissues or body fluids. For example, the N-carbamoyl glucuronide conjugate of mofegiline was identified in dog urine (Dow et al, 1994), that of amosulalol in mouse bile (Suzuki and Kamimura, 2007), that of varenicline in rat, monkey, and human plasma and urine (Obach et al, 2006), that of ropinirole in monkey and human urine (Ramji et al, 1999), and that of tocainide in urine of guinea pig, dog, cat, rabbit, and monkey (Gipple et al, 1982). We attempted to examine whether M1 was formed across multiple species and to measure the ratio of relative intensities of the N-carbamoyl glucuronide metabolite (M1/parent) across a variety of species.…”

“…N-Carbamoyl glucuronides of amino acids and certain xenobiotics have been reviewed by Schaefer (2006). Other xenobiotics that are reported to form N-carbamoyl glucuronide are tocainide (Elvin et al, 1980), rimantadine (Brown et al, 1990), carvedilol (Schaefer, 1992), mofegiline (Dow et al, 1994), sertraline , sitagliptin (Vincent et al, 2007), and amosulalol (Suzuki and Kamimura, 2007). Little is known about the mechanism of this reaction and the human UGTs that catalyze it.…”

Assessment of Chimeric Mice with Humanized Liver as a Tool for Predicting Circulating Human Metabolites

“…Major metabolic pathways of amosulalol in mice and humans M-3 sulfate, the major metabolite in humans, was found as one of the minor metabolites in mice. 45) …”