Metabolism of isosafrole and dihydrosafrole in the rat

Formation and Biological Targets of Quinones: Cytotoxic versus Cytoprotective Effects

Quinones represent a class of toxicological intermediates, which can create a variety of hazardous effects in vivo including, acute cytotoxicity, immunotoxicity, and carcinogenesis. In contrast, quinones can induce cytoprotection through the induction of detoxification enzymes, anti-inflammatory activities, and modification of redox status. The mechanisms by which quinones cause these effects can be quite complex. The various biological targets of quinones depend on their rate and site of formation and their reactivity. Quinones are formed through a variety of mechanisms from simple oxidation of catechols/hydroquinones catalyzed by a variety of oxidative enzymes and metal ions to more complex mechanisms involving initial P450-catalyzed hydroxylation reactions followed by two-electron oxidation. Quinones are Michael acceptors, and modification of cellular processes could occur through alkylation of crucial cellular proteins and/or DNA. Alternatively, quinones are highly redox active molecules which can redox cycle with their semiquinone radical anions leading to the formation of reactive oxygen species (ROS) including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can alter redox balance within cells through the formation of oxidized cellular macromolecules including lipids, proteins, and DNA. This perspective explores the varied biological targets of quinones including GSH, NADPH, protein sulfhydryls [heat shock proteins, P450s, cyclooxygenase-2 (COX-2), glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1, (NQO1), kelch-like ECH-associated protein 1 (Keap1), IκB kinase (IKK), and arylhydrocarbon receptor (AhR)], and DNA. The evidence strongly suggests that the numerous mechanisms of quinone modulations (i.e., alkylation versus oxidative stress) can be correlated with the known pathology/cytoprotection of the parent compound(s) that is best described by an inverse U-shaped dose-response curve.

The prevention of ferric nitrilotriacetate-induced nephro- and hepatotoxicity by methylenedioxybenzene antioxidants

Previously it was shown that methylenedioxybenzenes (MDBs), particularly isosafrole, were highly effective at preventing CCl4-induced liver necrosis in vivo (Z.S. Zhao, P.J. O'Brien, The prevention of CCl4-induced liver necrosis in mice by naturally occurring methylenedioxybenzenes, Toxicol. Appl. Pharmacol., 140 (1996) 411-421), probably as a result of forming metabolic intermediate complexes with cytochrome P450. In the following it was shown that pretreatment of mice with isosafrole also completely prevented ferric nitrilotriacetate (FeNTA)-induced renal necrosis and lipid peroxidation, even though metabolic activation by cytochrome P450 is not involved. The naturally occurring or synthetic MDBs that prevented CCl4 hepatotoxicity also prevented hepatocyte lipid peroxidation. induced by FeNTA, but other cytochrome P450 inhibitors were ineffective. These compounds, in decreasing order of antioxidant effectiveness, were sesamol, 4-t-butyl-methylenedioxybenzene, isosafrole, piperonyl butoxide and 4-bromo-methylenedioxybenzene and safrole, whereas, benzodioxole, 3,4-(methylenedioxy)-toluene and 1,2-(methylenedioxy)-4-nitrobenzene were ineffective. Pre-incubating the hepatocytes with P450 inhibitors decreased the protective effects of isosafrole, suggesting that the catecholic metabolites of MDBs were responsible for the antioxidant activity. A greater inhibition of FeNTA-induced lipid peroxidation by catecholic metabolites was observed. Since cytochrome P450 did not participate in FeNTA-induced hepatocyte or microsomal lipid peroxidation, it is likely that the antioxidant properties of MDBs or their catecholic metabolites also contribute to their in vivo protection against CCl4 or FeNTA-induced hepato- or nephrotoxicity.

Metabolism of dopamine analogues in rat

1. The metabolism of dopamine analogues, differing in their ring substituents and length of side chain, has been examined in rat. 2. Both benzylamines and phenethylamines were converted to their analogous acids. Where sought, the corresponding alcohols were present only in minute traces, or were undetectable. 3. Benzylamines were largely excreted as such, possibly conjugated, and this output, together with acid metabolites, accounts for most of the dose. In contrast, only a minor part of the phenethylamine dose was excreted unchanged, and much of what was given remains unaccounted for. 4. With increasing chain length the proportion of the dose found as urinary metabolites decreases markedly; long-chain (hydrophobic) amines may be sequestered in fat depots rendering them largely unavailable for metabolism. 5. beta-Oxidation of long-chain aromatic acids is observed. 6. Catechols showed evidence of O-methylation, and some O-methyl compounds were demethylated. N-methylation and N-demethylation were, at best, very minor pathways. 7. No overall pattern emerged between the position of substituents and the extent of oxidation by monoamine oxidase. No pattern at all was apparent with the benzylamines. Phenethylamines showed a trend towards a lower rate of metabolism for secondary and tertiary amines. Phenethylamines and propylamines with ortho substituents exhibited a lower rate of metabolite excretion than did their analogues.

In vivo metabolism of nasally instilled dihydrosafrole [1-(3,4-methylenedioxyphenyl)propane] in dogs and monkeys

Nasal metabolism of inhaled material may influence its biological fate and toxicity. The purpose of this study was to investigate, in a noninvasive and qualitative manner, the in vivo nasal metabolic activity towards 1-(3,4-methylenedioxyphenyl)propane (dihydrosafrole). Dihydrosafrole was the compound of choice as a representative of the methylenedioxyphenyl compounds. Methylenedioxyphenyl compounds, inhaled as essences or insecticide synergists, have complex interactions with cytochrome P-450-dependent monooxygenases, causing both inhibition and induction. Clearance of dihydrosafrole and its metabolites from both the ethmoid (olfactory) and maxillary (respiratory) turbinate regions of Beagle dogs and Cynomolgus monkeys was examined. Nasopharyngeal mucus was collected at frequent intervals during periodic instillation of dihydrosafrole (and, for the dogs, 24 h after instillation). Blood, urine and feces were collected to examine dihydrosafrole clearance from the nose during instillations and up to 48 h after completion of the nasal instillations of [3H]dihydrosafrole. Analysis of mucus for dihydrosafrole metabolites was by HPLC. Most of the recovered radioactivity was in urine and blood samples over the first 24 h. Radioactivity was recovered from the nasopharyngeal mucus in both organic extractable and water soluble forms. HPLC of the organic extracts demonstrated that [3H]dihydrosafrole instilled in either turbinate region was metabolized to 2-methoxy-4-propylphenol, 2-methoxy-4-propenylphenol and 1-(3,4-methylenedioxyphenyl)propan-1-ol. A number of minor metabolites were produced in both species. One mucus sample from an ethmoid-instilled dog contained 1-(3,4-methylenedioxyphenyl)propene (isosafrole) as a metabolite. Results from this study indicate that interspecies, inter-individual, and inter-regional differences occur in the metabolism of nasally deposited dihydrosafrole in monkeys and dogs.

The metabolic sulfonation and side-chain oxidation of 3'-hydroxyisosafrole in the mouse and its inactivity as a hepatocarcinogen relative to 1'-hydroxysafrole

The chemically synthesized sulfuric acid esters of 1'-hydroxysafrole and 3'-hydroxyisosafrole, 1'-sulfooxysafrole and 3'-sulfooxyisosafrole, respectively, are both strong electrophiles. Each ester reacted with deoxyguanosine (dGuo) in aqueous solution to form both safrol-1'-yl- and isosafrol-3'-yl-deoxyguanosine adducts. Both 1'-hydroxysafrole and 3'-hydroxyisosafrole were also formed from each ester in the presence of water. When either 1'-[3H]hydroxysafrole or 3'-[3H]hydroxyisosafrole was incubated with mouse liver cytosols fortified with 3'-phosphoadenosine-5'-phosphosulfate (PAPS) and RNA, similar levels of RNA- and protein-bound adducts were formed; thus, the hepatic sulfotransferase activities for these two substrates appear to be similar. In contrast, the levels of hepatic nucleic acid and protein adducts formed after administration of 3'-[3H]hydroxyisosafrole to mice were only 2-4% and 8-14%, respectively, of those obtained after an equimolar dose of 1'-[3H]hydroxysafrole. Likewise, when 3'-hydroxyisosafrole was injected into 12-day-old male B6C3F1 mice at a level of 0.1 or 2.5 mumol/g body wt., the average numbers of hepatomas per mouse (0.2 and 0.4, respectively) were not significantly increased over the average number for mice treated only with the solvent (0.2). By contrast, mice that received 0.1 mumol of 1'-hydroxysafrole/g body wt. developed about 2 hepatomas per mouse. The metabolism of 3'-hydroxyisosafrole in the rat and mouse differed markedly from that of 1'-hydroxysafrole. 3'-Hydroxyisosafrole rapidly underwent side-chain oxidation to yield 3,4-methylenedioxycinnamic acid and 3,4-methylenedioxybenzoic acid. In the first 4 h, 3,4-methylenedioxybenzoyl glycine and 3,4-methylenedioxycinnamoyl glycine, the major urinary metabolites, together accounted for 39% and 63% of the dose administered to rats and mice, respectively. The glucuronide of 3'-hydroxyisosafrole was not detected in the urine, whereas urinary excretion of the glucuronide of 1'-hydroxysafrole at 2 h accounted for approx. 40% of a dose of 1'-hydroxysafrole.

Metabolism of safrole in the rat

The urinary metabolites of safrole (4-allyl-1,2-methylenedioxybenzene) in the rat were identified using gas chromatographic - mass spectrometric methods. The amounts of the individual metabolites excreted were determined gas chromatographically. Metabolite excretion was 93% in 72 hrs and most of this material (86%) consisted of metabolites formed via demethylenation of the methylenedioxy moiety. The other metabolic routes observed were allylic hydroxylation and the epoxide-diol pathway.