Further studies of trans-sobrerol metabolism: rat, dog and human urine

Herbal monoterpene alcohols inhibit propofol metabolism and prolong anesthesia time

2,6-Diisopropylphenol (Propofol) is a short-acting intravenous anesthetic that is rapidly metabolized by glucuronidation and ring hydroxylation catalyzed by cytochrome P450. The goal of this research was to determine whether dietary monoterpene alcohols (MAs) could be used to prolong the anesthetic effect of propofol by inhibiting propofol metabolism in animals. Mice were injected intraperitoneally (i.p.) with MAs (100-200) mg/kg followed by the administration of 100 mg/kg propofol 40 min later via an i.p. injection. The time of the anesthesia of each mouse was recorded. It was found that (+/-)-borneol, (-)-carveol, trans-sobrerol, and menthol significantly extended the anesthetic effect of propofol (>3 times). The concentration of propofol in the mouse blood over time (up to 180 min) also increased in mice pre-treated with (-)-borneol, (-)-carveol, and trans-sobrerol. The volume of distribution of propofol decreased in the (-)-borneol (p<0.05), pre-treated group as compared to the propofol control group. Moreover, the maximum blood concentration of propofol and the concentration of propofol in the blood as indicated by the area under the curve were significantly increased in (-)-borneol and (-)-carveol pre-treated groups. Additional evidence using rat hepatocytes showed that (-)-borneol inhibited propofol glucuronidation whereas trans-sobrerol and (-)-carveol inhibited cytochrome P450 dependent microsomal aminopyrine N-demethylation. These results suggest that (-)-borneol extends propofol-induced anesthesia by inhibiting its glucuronidation in the mouse whereas trans-sobrerol (-)-carveol extends propofol-induced anesthesia by inhibiting P450 catalyzed propofol metabolism.

COMPARATIVE METABOLISM OF GERANYL NITRILE AND CITRONELLYL NITRILE IN MOUSE, RAT, AND HUMAN HEPATOCYTES

Geranyl nitrile (GN) and citronellyl nitrile (CN) are fragrance components used in consumer and personal care products. Differences in the clastogenicity of these two terpenes are postulated to result from differential biotransformation, presumably involving the conjugated nitrile moiety. The metabolic clearance and biotransformation of GN and CN were compared in primary hepatocytes from mice, rats, and humans. For determination of intrinsic clearance, GN and CN were incubated with hepatocytes in sealed vials, and the headspace was sampled periodically by solid-phase microextraction and analyzed by gas chromatography/mass spectrometry. For metabolite identification, GN and CN were incubated with hepatocytes from each species for 60 min, and reaction mixtures were extracted and analyzed by mass spectroscopy. Both GN and CN were rapidly metabolized in hepatocytes from all species (T1/2, 0.7-11.6 min). Within a species, intrinsic clearance was similar for both compounds and increased in the order human < rat << mouse. Major common pathways for biotransformation of GN and CN involved 1) epoxidation of the 6-alkenyl moiety followed by conjugation with glutathione, 2) hydroxylation of the terminal methyl group(s) followed by direct conjugation with glucuronic acid in rodents or further oxidation to the corresponding acid in human cells, and 3) hydroxylation of the allylic C5 position. No evidence for either phase I or phase II metabolism of the conjugated nitrile moiety was obtained. Thus, the presumed metabolic basis for differences in genotoxicity remains elusive.

In vivo studies on the metabolism of the monoterpenes S-(+)- and R-(-)-carvone in humans using the metabolism of ingestion-correlated amounts (MICA) approach

The major in vivo metabolites of S-(+)- and R-(-)-carvone in a metabolism of ingestion correlated amounts (MICA) experiment were newly identified as alpha,4-dimethyl-5-oxo-3-cyclohexene-1-acetic acid (dihydrocarvonic acid), alpha-methylene-4-methyl-5-oxo-3-cyclohexene-1-acetic acid (carvonic acid), and 5-(1,2-dihydroxy-1-methylethyl)-2-methyl-2-cyclohexen-1-one (uroterpenolone) on the basis of mass spectral analysis in combination with syntheses and NMR experiments. Minor metabolites were identified as reduction products of carvone, namely, the alcohols carveol and dihydrocarveol. The previously identified major in vivo metabolite in rabbits, 10-hydroxycarvone, could not be detected, indicating either concentration effects or interspecies differences. Metabolic pathways for carvone in humans including oxidation of the double bond in the side chain and, to a minor extent 1,2- and 1,4 + 1,2-reduction of carvone, are discussed. No differences in metabolism between S-(+)- and R-(-)-carvone were detected.

The FEMA GRAS assessment of alicyclic substances used as flavour ingredients

For over 35 years, an independent panel of expert scientists has served as the primary body for evaluating the safety of flavour ingredients. This group, the Expert Panel of the Flavor and Extract Manufacturers' Association (FEMA), has achieved international recognition from the flavour industry, government regulatory bodies including the Food and Drug Administration, and the toxicology community for its unique contributions. To date, the Expert Panel has evaluated the safety of more than 1700 flavour ingredients and determined the vast majority to be "generally recognized as safe" (GRAS). Elements that are fundamental to the safety evaluation of flavour ingredients include exposure, structural analogy, metabolism, pharmacokinetics and toxicology. Flavour ingredients are evaluated individually taking into account the available scientific information on the group of structurally related substances. The elements of the GRAS assessment program as they have been applied by the Expert Panel to the group of 119 alicyclic substances used as flavour ingredients, and the relevant scientific data which provide the basis for the GRAS status of these substances, are described herein.

Metabolism of (-)-6(S)-hydroxy-4(R)-(1-hydroxy-1-methylethyl)-1- cyclohexene-1-ethanol in rat and dog

1. The metabolism of a new mucoactive drug, chemically (-)-6(S)-hydroxy-4(R)- (1-hydroxy-1-methylethyl)-1-cyclohexene-1-ethanol (CO/1408), has been studied in rat and dog after a single oral dose; eight metabolites were identified. 2. Oxidation of the primary and secondary alcohol groups, hydroxylation in allylic positions and conjugation with glucuronic acid occurred in both species. Products of oxidation on the double bond have not been identified. 3. Using reversed-phase h.p.l.c. and beta-cyclodextrin in the eluent it was found that the glucuronide metabolites varied with species and with the biological fluid examined.

Effect of a terpenoid, (-)-6-hydroxy-4-(1-hydroxy-1-methylethyl)-1-cyclohexene-1-ethanol, on drug-metabolizing enzymes and glutathione content in rat liver and lung

1. Chronic treatment of Sprague-Dawley rats with the new terpenoid mucoregulating drug (I) did not modify activities of the drug-metabolizing enzymes (phase I and phase II) of liver and lung. 2. Acute treatment of rats with I did not affect the GSH content of liver and lung, but administration of the corresponding alpha, beta-unsaturated ketone (II) produced considerable GSH depletion in both tissues, the original GSH levels being restored after a few hours. 3. The results are discussed in comparison with those previously obtained with the structurally related drug trans-sobrerol (III).

Effects of trans-sobrerol on drug metabolizing enzymes in the rat

1. Metabolism of 14C-trans-sobrerol (I) by Sprague-Dawley rat liver microsomes did not result in covalent binding to proteins, lipid peroxidation or cytochrome P-450 destruction. 2. Subacute and chronic treatment of Sprague-Dawley rats with (I) resulted only in an increase in liver cytosolic GSH-S-transferase. 3. Acute treatment of rats with trans-sobrerol or its metabolite, 8-hydroxycarvotanacetone (II) produced considerable GSH depletion, faster in the case of II, in both liver and lung; the original GSH levels were restored within 24 h. No significant increase in lipid peroxidation was found even when GSH was at its lowest level. 4. UDP-glucuronyltransferase and GSH-S-transferase conjugation occurred with trans-sobrerol and some of its metabolites although at low rates.

Biotransformation of trans-sobrerol. III. Metabolites of 8-hydroxycarvotanacetone in the rat

The metabolism of 8-hydroxycarvotanacetone (HCA), a major metabolite of trans-sobrerol, was studied in female rats after a single oral dose. The metabolic pathways include hydroxylation, reduction to cis- and trans-sobrerol, glucuronylation and Michael addition with glutathione giving rise to mercapturic acids which then undergo reduction. Biological reduction appears to occur more readily for the alicyclic-saturated ketones (Michael adducts) than for the alpha, beta unsaturated ketones (HCA and hydroxylated metabolites). This is in agreement with the chemical reactivity of the compounds.