Biomedical subjects

J T Slattery

Publications and source records attributed to J T Slattery.

111 records · Page 7Linked to original sources

PubMedDate not supplied

Activation of acetaminophen-reactive metabolite formation by methylxanthines and known cytochrome P-450 activators.

Previous in vitro studies suggested that caffeine enhanced acetaminophen (APAP) oxidation to N-acetyl-p-benzoquinone imine (NAPQI) by selectively activating the male-specific constitutive cytochrome P-450IIIA2. Monomethylxanthine and dimethylxanthine analogs of caffeine (also metabolites) were studied for their potential effect to accelerate NAPQI formation in various preparations of rat liver microsomes. In contrast to caffeine, none of the mono- and dimethylxanthines (2.5 mM) activated P-450. Rather, the analogs either inhibited NAPQI formation or had no effect; 1-methylxanthine (2.5 mM) was the only compound which consistently inhibited (25-70%) APAP oxidation in all microsomal preparations. Thus, all three methyl groups appear to be required for P-450 activation by methylxanthines. Because of the highly selective activation effect of caffeine, it was of particular interest to determine whether other known P-450 activators could enhance APAP oxidation. Both acetone (400 mM) and flavone (50 microM) accelerated NAPQI formation in all microsomal preparations, whereas metyrapone caused only inhibition. Flavone (50 microM) caused a pattern of activation similar to that observed with 5 mM caffeine (maximal activation of 125-300%), except that NAPQI formation was increased approximately 40% by flavone in microsomes prepared from adult females, whereas no activation was caused by caffeine. Acetone yielded a pattern of P450 activation very different from that of either caffeine or flavone; the maximal degree of activation (3 times control) was observed in microsomes prepared from adult females. In contrast to caffeine and flavone, the degree of activation by acetone in microsomes prepared from juvenile animals was considerably lower (50%) than that observed in adult microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗

PubMedDate not supplied

Partial characterization of biliary metabolites of pulegone by tandem mass spectrometry. Detection of glucuronide, glutathione, and glutathionyl glucuronide conjugates.

The hepatotoxic monoterpene pulegone is a major constituent of the herbal abortifacient pennyroyal oil. An approximately equimolar mixture of 2H3- and 14C-labeled pulegone was administered to rats to study its phase II metabolism. Radioactive conjugates that were excreted into the bile were isolated by selective derivatization and HPLC separation, and subsequently characterized from the daughter ion mass spectra of protio- and deutero-analogs of each metabolite. The biliary metabolites characterized were glucuronide and glutathione (GSH) conjugates, accounting for approximately 3% of the radioactivity excreted in bile. The glucuronides, which were 2-fold more abundant than GSH conjugates, were mainly of hydroxylated pulegone and hydroxylated, reduced pulegone. The three GSH conjugates contained xenobiotic moieties that varied in their oxidation state; one of these was tentatively identified as the GSH conjugate of the proximate oxygenated metabolite, menthofuran. The two other GSH conjugates apparently underwent subsequent glucuronidation since novel glutathionyl glucuronide conjugates were identified that contained nonhydroxylated xenobiotic moieties. The results indicate that pulegone is bioactivated via at least three distinct pathways, each marked by a different GSH conjugate. Characterization of these conjugates represents a first step in the identification of the reactive metabolites from which they are derived.

Animals↗

PubMedDate not supplied

The formation and toxicity of catechol metabolites of acetaminophen in mice.

Acetaminophen is metabolized to a catechol, 3'-hydroxy-4'-hydroxyacetanilide (3-hydroxyacetaminophen), by mouse liver microsomes, and to both catechol and methylated catechol metabolites by the mouse in vivo. Although 3-hydroxyacetaminophen is less hepatotoxic in mice than acetaminophen itself, 3-methoxyacetaminophen is as hepatotoxic as acetaminophen and is subject to a glutathione threshold effect. However, neither metabolite is formed in sufficient amounts to account for the hepatotoxicity caused by acetaminophen in the mouse. Mouse liver microsomes catalyze the oxidation of acetaminophen to the catechol in an apparent cytochrome P-450-mediated reaction that is induced by phenobarbital and inhibited by piperonyl butoxide, but is surprisingly not altered by cobaltous chloride. Lineweaver-Burk analysis of the oxidation carried out by liver microsomes from control animals gave curvilinear plots that may indicate catalysis by two enzyme sites with apparent Km values of 0.011 and 0.271 mM, and apparent Vmax values of 87 and 162 pmol/mg/min, respectively. Neither an isotope effect nor an NIH shift were measurable in the microsomal metabolism of selectively deuterated analogs of acetaminophen to 3-hydroxyacetaminophen. These results, coupled with results of previous investigations with 18O2 and epoxide hydrolase, indicate that a mechanism different from either direct insertion or epoxidation is involved in the formation of the catechol metabolite of acetaminophen.

Acetaminophen↗