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S D Nelson

Publications and source records attributed to S D Nelson.

At least 271 records · Page 15Linked to original sources
PubMedDate not supplied

Hepatotoxicity after 3'-hydroxyacetanilide administration to buthionine sulfoximine pretreated mice.

The administration of 3'-hydroxyacetanilide, a regioisomer of acetaminophen, to mice failed to produce hepatotoxicity even after the administration of diethyl maleate. In contrast, hepatotoxicity did occur when 3'-hydroxyacetanilide was administered to buthionine sulfoximine pretreated mice. Although the administration of 3'-hydroxyacetanilide in conjunction with either diethyl maleate or buthionine sulfoximine depleted total hepatic glutathione, only the combined buthionine sulfoximine-3'-hydroxyacetanilide treatment decreased hepatic mitochondrial glutathione concentrations to below 20% of control values. In addition, pretreatment with buthionine sulfoximine increased the amount of 3'-hydroxyacetanilide bound to mitochondrial proteins. These results, in conjunction without previous results on the involvement of mitochondrial damage in the pathogenesis of hepatotoxicity caused by acetaminophen, suggest a probable relationship between mitochondrial damage caused by the buthionine sulfoximine-3'-hydroxyacetanilide treatment and hepatotoxicity caused by this treatment.

Acetaminophen↗
PubMedDate not supplied

Effect of bromine and chlorine positioning in the induction of renal and testicular toxicity by halogenated propanes.

A series of halogenated propanes were studied for renal and testicular necrogenic effects in the rat and correlated to their ability to induce in vivo renal and testicular DNA damage and in vitro testicular DNA damage. 1,2-Dibromo-3-chloropropane (DBCP) and 1,2,3-tribromopropane were most potent in causing organ damage in both kidney and testes. Extensive necrosis was evident at 85 mumol/kg in kidney and at 170 mumol/kg in testis. The dibromomonochlorinated analogue 1,3-dibromo-2-chloropropane was less organ toxic than DBCP and 1,2,3-tribromopropane, but induced more organ damage than the dichloromonobrominated analogues 1-bromo-2,3-dichloropropane and 1,3-dichloro-2-bromopropane. Dihalogenated propanes were even less necrogenic. These observed differences in toxic potency between the halogenated propanes could not be explained by relative differences in tissue concentrations. The ability of the halogenated propanes to induce DNA damage in vivo correlated well with their ability to induce organ damage. However, DNA damage occurred at lower doses and at a shorter period of exposure than organ necrosis. This indicates that DNA damage might be an initial event in the development of organ necrosis by halogenated propanes in general. Further, testicular DNA damage induced by the halogenated propanes in vivo correlated well with the DNA damage observed in isolated testicular cells in vitro, showing that toxicity was due to in situ activation. The numbers, positions, and the types of halogen substituents appear to be important determinants in causing DNA damage and necrogenic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Reactive intermediates in the oxidation of menthofuran by cytochromes P-450.

Menthofuran, a naturally occurring hepatotoxin, is metabolically activated to chemically reactive intermediates that are capable of covalent binding to cellular proteins. Studies in vivo and in vitro with inhibitors and inducers of hepatic cytochromes P-450 demonstrated an association between hepatocellular damage caused by menthofuran and its metabolic activation and covalent binding to target organ proteins. The same gamma-ketoenal formed from the metabolic precursor of menthofuran, pulegone, is the major electrophilic metabolite of menthofuran as well. Diastereomeric mintlactones also are formed, and studies with H218O and 18O2 indicate that the gamma-ketoenal is a precursor to the mintlactones, as well as other reactive intermediates in the cytochrome P-450 mediated oxidation of menthofuran.

Acetaminophen↗
PubMedDate not supplied

Hepatotoxicity of germander (Teucrium chamaedrys L.) and one of its constituent neoclerodane diterpenes teucrin A in the mouse.

The hepatotoxicity of the herbal plant germander and that of one of its major furanoneoclerodane diterpenes, teucrin A, were investigated in mice. Teucrin A was found to cause the same midzonal hepatic necrosis as observed with extracts of the powedered plant material. Evidence that bioactivation of teucrin A by cytochromes P450 (P450) to a reactive metabolite(s) is required for initiation of the hepatocellular damage is provided by results of experiments on the induction and inhibition of P450 and from studies on the effects of glutathione depletion. Pretreatment of mice with the P450 inducer phenobarbital enhanced the hepatotoxic response, as indicated by an increase in plasma alanine aminotransferase (ALT) levels and hepatic necrosis, while pretreatment with the P450 inhibitor piperonyl butoxide markedly attenuated the toxic response. Hepatotoxicity of teucrin A also was increased following pretreatment with the inhibitor of glutathione synthesis buthionine sulfoximine. Most importantly, the tetrahydrofuran analog of teucrin A, obtained by selective chemical reduction of the furan ring, was not hepatotoxic, a result that provides strong evidence that oxidation of the furan ring moiety of the neoclerodane diterpenes is involved in the initiation of hepatocellular injury caused by germander.

Administration, Oral↗
PubMedDate not supplied

A comparative study of mouse liver proteins arylated by reactive metabolites of acetaminophen and its nonhepatotoxic regioisomer, 3'-hydroxyacetanilide.

Acetaminophen (4'-hydroxyacetanilide), a widely used analgesic/antipyretic drug, is hepatotoxic in large doses, whereas the m-hydroxy isomer of acetaminophen, 3'-hydroxyacetanilide, is not hepatotoxic. Both are oxidized by mouse liver cytochromes P-450 to reactive metabolites that bind covalently to hepatic proteins. Because previous studies have shown that peak levels of liver protein adducts formed after the administration of each of these compounds to mice are nearly equivalent, and because liver protein adduct formation correlates with hepatotoxicity caused by acetaminophen in mice, we investigated the abundance and patterns of protein adducts formed by acetaminophen and its regioisomer for significant differences. Hepatotoxic doses of acetaminophen to mice significantly altered the abundances of several liver proteins 2 h after dosing as revealed by densitometric analysis of two-dimensional electrophoretic patterns of these proteins. The same analysis after the administration to mice of 3'-hydroxyacetanilide indicated that this nonhepatotoxic regioisomer of acetaminophen caused several similar changes in protein patterns, but also revealed some significant differences. Binding of radiolabeled acetaminophen and 3'-hydroxyacetanilide to hepatic proteins corroborated and extended these results. Two hours after the administration of 14C-labeled analogs of these two compounds to mice, at a time when their extent of total covalent binding to hepatic proteins is approximately equivalent, there are many similarities but also some differences in selectivity of proteins that are adducted, as revealed by both one-dimensional and two-dimensional gel electrophoresis followed by phosphorimage analysis of radiolabel bound to protein bands. Moreover, protein adducts formed from 3'-hydroxyacetanilide were found to be less stable than those formed from acetaminophen under the conditions of electrophoretic analysis. Furthermore, a comparison of radiodetection and immunodetection of protein adducts formed from acetaminophen with an antibody specific for acetaminophen protein adducts indicates that the antibody detects most of the same proteins that are radiolabeled and that the relative quantitative contribution of various adducts to the overall covalent binding of acetaminophen to proteins is approximately the same by both methods. Thus, 3'-hydroxyacetanilide should prove to be a useful tool to aid in the discrimination of hepatic acetaminophen protein adducts that may be critical or noncritical to survival of hepatocytes.

Acetaminophen↗
PubMedDate not supplied

Human cytochrome P450 2E1 is a major autoantigen associated with halothane hepatitis.

Autoantibodies against specific human cytochrome P450s have been found in the sera of patients suffering from a variety of diseases, including those caused by drugs. In the cases of tienilic acid- and dihydralazine-induced hepatitis, patients have serum autoantibodies directed against cytochromes P450 2C9 and P450 1A2, respectively. In the present study, we have found that 25 of 56 (45%) patients diagnosed with halothane hepatitis have autoantibodies that react with human cytochrome P450 2E1 that was purified from a baculovirus expression system. The autoantibodies inhibited the activity of cytochrome P450 2E1 and appeared to be directed against mainly conformational epitopes. In addition, because cytochrome P450 2E1 became trifluoroacetylated when it oxidatively metabolized halothane, it is possible that the covalently altered form of cytochrome P450 2E1 may be able to bypass the immunologic tolerance that normally exists against cytochrome P450 2E1. A similar mechanism may explain the formation of autoantibodies that have been found against other cellular targets of the reactive trifluoroacetyl chloride metabolite of halothane.

Acetylation↗
PubMedDate not supplied

Investigations of mechanisms of reactive metabolite formation from (R)-(+)-pulegone.

1. (R)-(+)-Pulegone is a monoterpene that is oxidized by cytochromes P-450 to reactive metabolites that initiate events in the pathogenesis of hepatotoxicity in mice, rats and humans. 2. Selective labelling of (R)-(+)-pulegone with deuterium revealed that menthofuran was a proximate hepatotoxic metabolite formed by oxidation of the allylic methyl groups of pulegone. Incubations of pulegone with mouse liver microsomes in an atmosphere of 18O2 resulted in the formation of menthofuran that contained only oxygen-18 in the furan moiety. These results are consistent with oxidation of pulegone to an allylic alcohol that reacts intramolecularly with the ketone moiety to form a hemiketal that subsequently dehydrates to generate menthofuran. 3. Studies on the metabolism of menthofuran revealed that it is oxidized by cytochromes P-450 to an electrophilic gamma-ketoenal that reacts with nucleophilic groups on proteins to form covalent adducts. In addition, diastereomeric mintlactones are formed. Investigations with H2(18)O and 18O2 are indicative of a furan epoxide intermediate, or a precursor, in the formation of the gamma-ketoenal and mintlactones.

Animals↗
PubMedDate not supplied

Inhibition and activation of acetaminophen reactive metabolite formation by caffeine. Roles of cytochromes P-450IA1 and IIIA2.

Caffeine has previously been shown to diminish or potentiate acetaminophen (APAP) hepatotoxicity in rats, depending on induction state. To elucidate the P-450 forms involved in these divergent effects, rat liver microsomes, prepared after pretreatment with various inducers, were used to examine the effect of caffeine on N-acetyl-p-benzoquinone imine (NAPQI) formation. The addition of caffeine to incubations with 3-methylcholanthrene (MC)-induced microsomes resulted in a biphasic effect on the formation of NAPQI. A 43% decrease in NAPQI formation was observed as caffeine concentration was increased from 0 to 0.5 mM; however, NAPQI formation was accelerated as caffeine concentration increased, exceeding the control (no caffeine) value, at caffeine concentrations greater than 2.5 mM. Incubations with purified P-450IA1 showed that as caffeine concentration increased from 0 to 5 mM, a 50% inhibition was observed with no evidence of acceleration. In contrast to MC microsomes, the addition of caffeine to incubations with uninduced and phenobarbital-induced adult rat microsomes resulted in a marked (3- to 4-fold) acceleration of NAPQI formation with no evidence of inhibition. Caffeine (5 mM) also accelerated NAPQI formation in microsomes isolated from diabetic rats, but to a substantially lesser extent (120%), suggesting a modest (if any) effect on P-450IIE1, a form previously shown to form NAPQI from APAP. Interestingly, caffeine caused a 3- to 4-fold increase in NAPQI formation by juvenile male and female rat microsomes, but no activation was observed with adult female rat microsomes. These results suggested that caffeine activated a member of the cytochrome P-450IIIA subfamily.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
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

Hepatic protein arylation, glutathione depletion, and metabolite profiles of acetaminophen and a non-hepatotoxic regioisomer, 3'-hydroxyacetanilide, in the mouse.

The metabolism and disposition of acetaminophen (APAP) and a non-hepatotoxic regioisomer, 3'-hydroxyacetanilide (AMAP), were investigated in the mouse using 14C-labeled analogues. Covalent binding of metabolites of both compounds was observed on the order of 1 nmol/mg tissue protein. AMAP binding was much higher than that of APAP at 1 hr, but by 24 hr, AMAP binding was significantly lower than that of APAP. APAP binding peaked at 3 hr and did not decrease significantly thereafter. Despite the high early levels of covalent binding, AMAP was not as effective in causing glutathione depletion as was APAP. This was reflected in the urinary metabolite profiles of the two compounds. Approximately twice as much APAP was cleared through thioether conjugation compared to AMAP, based on an analysis of urinary metabolites. These results and results of other studies suggest that electrophilic metabolites of AMAP are more reactive than those of APAP, and do not diffuse as far from their site of formation, which may spare some critical target proteins from damage.

Acetaminophen↗
PubMedDate not supplied

Investigations of the N-hydroxylation of 3'-hydroxyacetanilide, a non-hepatotoxic positional isomer of acetaminophen.

The hydroxamic acid of 3'-hydroxyacetanilide (AMAP) was synthesized to test the hypothesis that different reactive metabolites of AMAP and acetaminophen account for similarities in covalent binding of the two positional isomers to hepatic proteins, but for differences in their ability to cause hepatotoxicity. N-OH-AMAP was found to be a relatively stable hydroxamic acid, but it was not detected as a metabolite of AMAP formed in vitro by mouse liver microsomes or in urine of mice administered AMAP. Therefore, metabolites other than N-OH-AMAP must be responsible for covalent binding observed with AMAP to mouse liver proteins.

Acetaminophen↗
PubMedDate not supplied

Stereoselectivity of naphthalene epoxidation by mouse, rat, and hamster pulmonary, hepatic, and renal microsomal enzymes.

Previous studies have demonstrated the formation of three glutathione conjugates during the hepatic and pulmonary microsomal metabolism of naphthalene in the presence of reduced glutathione and cytosolic enzymes containing the glutathione transferases. These glutathione conjugates now have been identified by negative ion fast atom bombardment mass spectrometry, by proton NMR spectroscopy, and by chemical synthesis from the (1S,2R)- and (1R, 2S)-naphthalene 1,2-oxide enantiomers as isomeric hydroxyglutathionyldihydronaphthalene derivatives. All three glutathione adducts yielded prominent mass spectral ions at m/z 450 (M-H)-, 432 (dehydration product), and 306 (glutathionyl moiety) which were consistent with the monoglutathionyl derivatives of hydroxydihydronaphthalene. Signals in the proton NMR spectra at 3.60 and 4.95 ppm (adduct 1) and 3.60 and 4.95 ppm (adduct 2) indicated that these conjugates were diastereomers of 1-hydroxy-2-glutathionyl-1,2-dihydronaphthalene. Corresponding signals for H1 and H2 at 4.22 and 4.45 ppm for adduct 3 showed that this isomer was generated from attack of glutathione at the 1 position of the naphthalene 1,2-oxide. Incubation of synthetic (1S, 2R)-naphthalene 1,2-oxide with glutathione in the presence of glutathione transferases resulted in the formation of adducts 1 and 3 in approximately equal proportions; under identical conditions, glutathione conjugate 2 was formed from (1R, 2S)-naphthalene 1,2-oxide. Incubation of naphthalene, glutathione, and glutathione transferases with pulmonary, hepatic, or renal microsomal preparations from mouse, rat, and hamster resulted in the formation of all three glutathione conjugates. Substantial differences in the rates of formation of the individual conjugates were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

The metabolism of the abortifacient terpene, (R)-(+)-pulegone, to a proximate toxin, menthofuran.

(R)-(+)-Pulegone, the major monoterpene component of the abortifacient mint oil, pennyroyal oil, is metabolized by hepatic microsomal monooxygenases of the mouse to a hepatotoxin. The formation of a toxic metabolite is apparently mediated by cytochromes P-450 of the phenobarbital class inasmuch as phenobarbital pretreatment of mice increases, whereas beta-naphthoflavone pretreatment decreases, the extent of hepatic necrosis caused by pulegone. Furthermore, two inhibitors of cytochromes P-450, cobaltous chloride and piperonyl butoxide, block toxicity. An analog of (R)-(+)-pulegone that was labeled with deuterium in the allylic methyl groups was found to be significantly less hepatotoxic than the parent compound. The results indicate that oxidation of an allylic methyl group is required for generation of a hepatotoxic metabolite. Menthofuran was identified as a proximate toxic metabolite of (R)-(+)-pulegone, and investigations with (R)-(+)-pulegone-d6 and 18O2 strongly indicate that menthofuran is formed by a sequence of reactions that involve: 1) oxidation of an allylic methyl group, 2) intramolecular cyclization to form a hemiketal, and 3) dehydration to form the furan.

Abortifacient Agents↗
PubMedDate not supplied

Linear relationship between cytochrome P-450 and carbamazepine clearance in rhesus monkey.

The effect of carbamazepine (CBZ) long-term (4-day) infusions on changes in liver cytochrome P-450 levels were examined in eight rhesus monkeys. Each animal received two treatments. Treatment I was a 4-hr CBZ infusion and treatment II was a 4-day CBZ infusion. At the end of each treatment, the monkey was anesthetized and a liver biopsy was taken. The tissue was homogenized and cytochrome P-450 and protein were determined in the crude liver homogenate. During treatment II, blood samples taken at 8 and 101 hr were assayed for CBZ and the clearance of CBZ at these times determined. The mean (+/- SD) CBZ clearance at 8 and 101 hr during treatment II was 0.88 +/- 0.17 and 1.35 +/- 0.34 liters/hr/kg, respectively. The mean (+/-SD) liver cytochrome P-450 level between treatment I and treatment II was 0.26 +/- 0.04 and 0.44 +/- 0.14 nmol/mg of protein, respectively. A high degree of correlation (r2 = 0.85) was observed between the percentage change in cytochrome P-450 and the percentage change in CBZ intrinsic clearance. Theoretical and experimental results suggest a direct quantitative relationship between these parameters.

Animals↗