Adrian J. Ryan

The Metabolism and Excretion of Curcumin (1,7-Bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) in the Rat

Curcumin labelled with deuterium and tritium was prepared. Oral and intraperitoneal doses of [3H]curcumin led to the faecal excretion of most of the radioactivity. 2. Intravenous and intraperitoneal doses of [3H]curcumin were well excreted in the bile of cannulated rats. 3. The major biliary metabolites were glucuronides of tetrahydrocurcumin and hexahydrocurcumin. A minor biliary metabolite was dihydroferulic acid together with traces of ferulic acid. Metabolites were identified using chemical ionization mass spectrometry.

Pharmacokinetic model for the successive demethylation and biliary secretion of methyl orange in the rat

1 A one‐compartment pharmacokinetic model was developed in which a drug underwent two successive metabolical reactions (for example, metabolism followed by conjugation) and free drug and both metabolites were excreted. 2 Techniques were described whereby graphical estimates of the first‐order rate constants may be derived from cumulative excretion data on the drug and its metabolites. Computer simulation techniques were used to show that the experimental data permit reasonably accurate estimation of the rate constants of the model by graphical and computer methods. 3 Tritiated methyl orange (2 mg) was administered to five groups of six rats with biliary cannulation. The bile produced by each animal was collected at hourly intervals for 6 h and the amounts of methyl orange and its metabolites, 4′sulpho‐4‐methylaminoazobenzene and 4′sulpho‐4‐aminoazobenzene, determined by thin layer chromatography and radioactive counting techniques. 4 The data were analysed graphically and with an iterative digital computer programme to yield the first‐order rate constants for the successive demethylation steps in the metabolism of methyl orange. The removal of the first methyl group had a rate constant of 0·684 ± 0·142 h−1 (± s.d.) and the second methyl group 1·00 ± 0·302 h−1. The rate constant for biliary excretion of the free methyl orange was 0·164 ± 0·042 h−1, for the monomethyl derivative 0·672 ± 0·461 h−1 and for the demethylated metabolite 6·413 ± 3.222 h−1.

The kinetics of inhibition of drug metabolism in vitro by some naturally occurring compounds

Abstract Kinetic studies with two naturally occurring ketones, leptospermone and grandiflorone, which inhibit oxidative metabolism of drugs in liver homogenates together with parallel studies with SKF-525A and piperonyl butoxide have been carried out. The inhibition appears to be competitive. However, except for leptospermone, the Lineweaver-Burk plots show a downward curvature. This is attributed to metabolism of the inhibitor. Rapid inactivation of the inhibitor was shown to occur when inhibitor and enzyme were incubated together for varying times before addition of substrate. This effect did not take place with leptospermone which may not be metabolised by liver homogenates.

The biliary metabolism of butylated hydroxytoluene (3, 5‐di‐t‐butyl‐4‐hydroxy‐toluene) and its derivatives in the rat

The biliary metabolism of 3, 5‐di‐t‐butyl‐4‐hydroxybenzyl alcohol (BHT‐CH2OH), 3, 5‐di‐t‐butyl‐4‐hydroxybenzaldehyde (BHT‐CHO) and 3, 5‐di‐t‐butyl‐4‐hydroxybenzoic acid (BHT‐COOH) after parenteral administration has been examined in the rat and compared to that of 3, 5‐di‐t‐butyl‐4‐hydroxytoluene. Quantitative excretion and chemical examination of bile showed that in the enterohepatic circulation BHT‐COOH or its ester glucuronide is the recirculating compound from the four compounds studied. Biliary excretion data are also presented for 1, 2‐bis(3, 5‐di‐t‐butyl‐4‐hydroxyphenyl)ethane.

The metabolism of 2-phenylazo-1-naphthol-4-and -5-sulphonic acids in the rat

Abstract After intraperitoneal injection of the title compounds into rats the major metabolite found in the urine was 2-(-4-hydroxyphenylazo-)-1-naphthol-4 or 5-sulphonate and the corresponding glucuronide. No reduction of the dye was found to take place. This was confirmed using 2-phenylazo-14C-1-naphthol-5- sulphonate. Radioactivity was quantitatively excreted in the urine after 48 hr and was associated only with whole dye metabolites. Some enterophepatic circulation of the dyes took place but did not lead to reduction of the dyes in the gastro-intestinal tract. The reasons for the failure of the dye to be reduced in vivo are discussed. The hydroxylation of these compounds appears to be the first example of such a reaction in vivo with a non-lipid soluble molecule and has been shown to take place in the microsomal fraction of rat liver.

Studies in the metabolism of carcinogenic polycyclic heteroaromatic compounds: I. The hepatic microsomal metabolism of 7-methylbenz[c]acridine

Abstract An enzyme assay for the metabolism of the carcinogenic aza-aromatic polycyclic compound 7-methylbenz[c]acridine has been developed using a modification of a radiochemical assay described for the polycyclic aromatic hydrocarbon benzo[a]pyrene by DePierre et al. [J. W. DePierre, M. S. Moron, K. A. M. Johannesen and L. Ernster, Analyt. Biochem. 63, 470 (1975)]and Van Cantfort et al. [J. Van Cantfort, J. DeGraeve and J. E. Gielen, Biochem. biophys. Res. Commun. 79, 505 (1977)]. When the activities of control microsomes and microsomes of phenobarbital-, 3-methylcholanthrene-and 7-methylbenz[c]acridine-pretreated animals were compared, strong similarities were displayed toward oxidation of benzo[a]pyrene and 7-methylbenz[c]acridine. These similarities were seen in turnover numbers, Michaelis constants, and inducibility of both enzyme systems. 7-Methylbenz[c]acridine afforded a type I difference spectrum with 3-methylcholanthrene-pretreated microsomes. It is suggested that 7-methylbenz[c]acridine is oxidized by the same or a similar set of enzymes which is responsible for benzo[a]pyrene metabolism.

The metabolism of butylated hydroxytoluene, (3, 5‐di‐t‐butyl‐4‐hydroxytoluene) in man

The urinary metabolites of [14C]-3,5-di-t-butyl-4-hydroxytoluene (BHT) in man have been estimated by Daniel, Gage & others (1967), who found that over 50% of a 40 mg oral dose is excreted in the urine during the 24 h after dosing. The major metabolite (present to the extent of 35% of the dose) was later identified as a glucuronide of 4-carboxy-2-( 1 -carboxy-I -methylethyl)-6-( 1 -formyl-1 -methylethyl)-

The inhibition of drug metabolism enzymes by some naturally occurring compounds

Abstract The ability of a series of naturally occurring pyrethrin synergists to inhibit various pathways of drug metabolism has been studied in the rat and mouse. These compounds were effective in vitro inhibitors of the oxidative metabolism of aniline, aminopyrine, diphenyl and hexobarbital by liver preparations. Reduction of the azo dye neoprontosil was not inhibited. In vivo inhibition of hexobarbital oxidation in the mouse, as shown by an increase in sleeping times, was also observed. Some considerations of structure-activity relationships are discussed. Several of the compounds studied produced dilation of the endoplasmic reticulum and the Golgi apparatus of liver cells as well as depleting glycogen deposits. These effects did not appear to be related to inhibitory power. These substances can alter membrane permeability, as shown by measurements of glucose exit from red blood cells. The effects on the liver and red blood cell may be a function of lipid solubility or, more likely, ability to bind to protein.

Further studies on the metabolism of isopropyl N-phenylcarbamate (propham) in the rat

Abstract The metabolic fate of [ 14 C]-isopropyl N -phenylcarbamate ([ 14 C]IPC) was investigated in the rat. After both oral and intraperitoneal doses approximately 80% of the administered radioactivity appeared in the urine over 4 days, with much smaller amounts appearing in the faeces and respired air. Of the urinary radioactivity, about 80% was present as the sulphate ester of isopropyl N -(4-hydroxyphenyl)carbamate. Little or no isopropyl N -(2-hydroxyphenyl)carbamate was formed. Neomycin feeding studies suggested that the small amount of hydrolysis which occurred was mediated by the animal rather than by its gut microflora. Biliary elimination of [ 14 C]IPC was also examined, about 30% of an intravenous dose being excreted in the bile in 6 hr.

Rat liver microsomal metabolites of 7-methylbenz[c]acridine

The metabolism of the weak carcinogen 7-methylbenz[c]acridine (7MBAC) was examined in rat liver microsomes from 3-methylcholanthrene(MC)-induced animals by the use of mixed 14C- and 2H-labelled substrate. The three metabolites identified by spectroscopic and chromatographic examination were 7-OHMBAC and two dihydrodiols. The dihydrodiols were assigned structures consisted with attack on the 8,9- and 5,6- or K-region of the aromatic system.