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L W Whitehouse

Publications and source records attributed to L W Whitehouse.

At least 19 recordsLinked to original sources
PubMed2001

A quantitative analysis for the ADP-ribosylation activity of pertussis toxin: an enzymatic-HPLC coupled assay applicable to formulated whole cell and acellular pertussis vaccine products.

The majority of the biological effects of pertussis toxin (PT) are the result of a toxin-catalyzed transfer of an adenosine diphosphate-ribose (ADP-ribose) moiety from NAD(+)to the alpha-subunits of a subset of signal-transducing guanine-nucleotide-binding proteins (G-proteins). This generally leads to an uncoupling of the modified G-protein from the corresponding receptor and the loss of effector regulation. This assay is based on the PT S1 subunit enzymatic transfer of ADP-ribose from NAD to the cysteine moiety of a fluorescent tagged synthetic peptide homologous to the 20 amino acid residue carboxyl-terminal sequence of the alpha-subunit of the G(i3)protein. The tagged peptide and the ADP-ribosylated product were characterized by HPLC/MS and MS/MS for structure confirmation. Quantitation of this characterized ADP-ribosylated fluorescently tagged peptide was by HPLC fluorescence using Standard Addition methodology. The assay was linear over a five hr incubation period at 20 degrees C at PT concentrations between 0.0625 and 4.0 microg/ml and the sensitivity of the assay could be increased several fold by increasing the incubation time to 24 h. Purified S1 subunit of PT exhibited 68.1+/-10.1% of the activity of the intact toxin on a molar basis, whereas the pertussis toxin B oligomer, the genetically engineered toxoid, (PT-9K/129G), and several of the other components of the Bordetella pertussis organism possessed little (<0.6%) or no detectable ribosylation activity. Commonly used pertussis vaccine reference materials, US PV Lot #11, BRP PV 66/303, and BRP PV 88/522, were assayed by this method against Bordetella pertussis Toxin Standard 90/518 and demonstrated to contain, respectively, 0.323+/-0.007, 0.682+/-0.045, and 0.757+/-0.006 microg PT/ml (Mean+/-SEM) or in terms of microg/vial: 3.63, 4.09 and 4.54, respectively. A survey of several multivalent pertussis vaccine products formulated with both whole cell as well as acellular components indicated that products possessed a wide range of ribosylation activities. The pertussis toxin S1 subunit catalyzed ADP- ribosylation of the FAC-Galpha(i3)C20 peptide substrate and its subsequent quantitation by HPLC was demonstrated to be a sensitive and quantitative method for measuring intrinsic pertussis toxin activity. This methodology not only has the potential to be an alternative physicochemical method to replace existing bioassay methodology, but has the added advantage of being a universal method applicable to the assay of pertussis toxin in both whole cell and acellular vaccines as well as bulk and final formulated vaccine products. Acceptance of this method by regulatory agencies and industry as a credible alternative to existing methods would, however, require validation in an international collaborative study against the widely accepted bioassay methods.

Adenosine Diphosphate Ribose↗
PubMed1999

Detection of quantitative trait loci affecting caffeine metabolism by interval mapping in a genome-wide scan of C3H/HeJ x APN F(2) mice.

Caffeine metabolite ratios have been widely used to measure cytochrome P-450 1A2 activity in humans. Serum paraxanthine/caffeine ratio is one such index of this activity. We had previously demonstrated genetic variation of this trait among inbred mouse strains. In the present study, we have undertaken a genome-wide scan for quantitative trait loci affecting this trait with an interval mapping approach on an F(2) intercross population of acetaminophen nonsusceptible and C3H/HeJ inbred mice. A statistically significant association (log-likelihood ratio = 25.0) between a locus on chromosome 9, which colocalized with the murine Cyp1a2 locus, and the plasma paraxanthine/caffeine ratio was identified. This result suggested the presence of an expression polymorphism affecting this gene. A second locus was identified on chromosome 1 (log-likelihood ratio = 9.7) for which no obvious candidate gene has been identified. The influence of this locus on the paraxanthine/caffeine index was more significant among males (log-likelihood ratio = 6.3) than females (log-likelihood ratio = 3.6). A third locus was identified on chromosome 4 with a less statistically robust association (log-likelihood ratio = 3.4) to the paraxanthine/caffeine phenotype. Collectively, these three loci accounted for 63.2% of the variation observed in the F(2) population for this phenotype. These results demonstrate the potential for genetic variation arising from factors other than CYP1A2 activity to influence the plasma paraxanthine/caffeine ratio in mice. This study demonstrates the utility of quantitative genetics in the analysis of polygenic drug metabolism.

Animals↗
PubMed1997

Differences in caffeine 3-demethylation activity among inbred mouse strains: a comparison of hepatic Cyp1a2 gene expression between two inbred strains.

The 3-demethylation of caffeine can be used as an index of cytochrome P450 CYP1A2 activity in vivo. We compared the plasma levels of caffeine and the 3-demethylated metabolite. 1,7-dimethylxanthine, in six common inbred strains (A/J, P/J, BALB/cJ, C3H/HeJ, AKR/J, and SWR/J) and one inbred strain (APN) derived in our laboratory from outbred Swiss-Webster mice on the basis of its relative susceptibility to acetaminophen-induced hepatotoxicity. We found significant variations between a number of the common strains, all of which produced significantly higher caffeine 3-demethylation indices than our APN strain. In three of the six common strains, there was a significant difference between males and females, with the females having consistently lower 1,7-xanthine/caffeine ratios. Hepatic Cyp1a2 expression was compared between APN and C3H/HeJ males. Microsomal methoxyresorufin O-demethylation, acetanilide 4-hydroxylation, and CYP1A2 immunoreactive protein levels were significantly higher in C3H/HeJ relative to APN mice, as were hepatic CYP1A2 mRNA levels. These results indicate the importance of strain and gender to the outcome of pharmacological or toxicological studies involving CYP1A2-mediated metabolism, as well as the suitability of the plasma 1,7-dimethylxanthine/caffeine ratio as a marker of CYP1A2 activity in the mouse. The striking differences observed between the APN and C3H/HeJ mice suggest that these strains may be suitable for a genetic analysis of the regulation of the basal expression of CYP1A2, a key enzyme in procarcinogen activation.

Acetaminophen↗
PubMed1997

Increased basal expression of hepatic Cyp1a1 and Cyp1a2 genes in inbred mice selected for susceptibility to acetaminophen-induced hepatotoxicity.

Susceptibility to acetaminophen-induced hepatotoxicity was found to vary widely in an outbred colony of Swiss Webster mice. Some acetaminophen-treated male mice showed a significant elevation in serum levels of the hepatic enzyme alanine aminotransferase at a normally non-hepatotoxic oral dose. A selective breeding program over 17 generations produced inbred mice which were either susceptible or nonsusceptible to the hepatotoxic effects of acetaminophen. Liver microsomes from the susceptible group showed a statistically significant increase in the ability to metabolize acetaminophen to a reactive intermediate which covalently binds N-acetylcysteine. Microsomal cytochrome P450 activities associated with CYP1A2 (acetanilide 4-hydroxylation and methoxyresorufin O-demethylase) were significantly increased in the susceptible group. Ethoxyresorufin O-deethylase activity, associated with both CYP1A1 and CYP1A2, was also significantly elevated in this group. Further examination of both CYP1A isoforms revealed that hepatic CYP1A1 and CYP1A2 mRNA and protein levels were significantly elevated in animals from the susceptible group. In vivo caffeine 3-demethylation, which is associated with CYP1A2 activity, co-segregated with acetaminophen susceptibility and showed a significant positive correlation (r = 0.626, p < 0.005) with CYP1A2 mRNA expression in animals from both the susceptible and nonsusceptible groups. The co-segregation of elevated basal Cyp1a1 and CYP1a2 gene expression levels in animals selected for susceptibility to acetaminophen-induced hepatotoxicity suggested a common heritable basis for regulation of basal expression of both of these CYP1A isoforms. This was supported by the correlated expression of both CYP1A mRNAs within individual mice (r = 0.644, p < 0.02).

Acetaminophen↗
PubMed1996

Cytotoxicity of unsaturated metabolites of valproic acid and protection by vitamins C and E in glutathione-depleted rat hepatocytes.

Valproic acid (VPA) and the unsaturated metabolites, 2-ene VPA and (E)-2,(Z)-3'-diene VPA, demonstrated dose-dependent cytotoxicity in primary cultures of rat hepatocytes, as evaluated by lactate dehydrogenase (LDH) leakage. Cellular glutathione (GSH) was depleted by adding buthionine sulfoximine (BSO) to the culture medium. Induction of cytochrome P450 by pretreatment of rats with phenobarbital or pregnenolone-16 alpha-carbonitrile enhanced the cytotoxicity of parent VPA in BSO-treated hepatocytes. The cytotoxicity of 4-ene VPA was apparent in BSO-treated hepatocytes with detectable loss of cell viability at 1 microM of added 4-ene VPA. Depletion of cellular GSH also increased the cytotoxicities of 2-ene VPA and (E)-2,(Z)-3'-diene VPA. The cytotoxicity of 2-ene VPA was comparable to or higher than that of VPA, producing loss of viability at concentrations > or = 5 mM. Time-course evaluation of hepatocyte response to 4-ene VPA in the GSH-depleted state revealed a delayed cytotoxicity with no effect during the first 12 h of exposure followed by a pronounced toxicity between 12 and 14 h. Two major GSH conjugates of 4-ene VPA metabolites, namely 5-GS-4-hydroxy VPA lactone and 5-GS-3-ene VPA, were detected in 4-ene VPA treated hepatocytes. Consistent with this finding, a 50% decrease in cellular GSH levels was observed following 4-ene VPA treatment. Under similar conditions, neither toxicity nor the GSH conjugated metabolite were detected in cells treated with the alpha-fluorinated 4-ene VPA analogue (alpha-F-4-ene VPA). The antioxidants, vitamin C and vitamin E, demonstrated a cytoprotective effect against 4-ene VPA-induced injury in GSH-depleted hepatocytes. These results are in support of hepatocellular bioactivation of VPA via 4-ene VPA to highly reactive species, which are detoxified by GSH. The susceptibility of hepatocytes to VPA metabolite-mediated cytotoxicity depends on cellular GSH homeostasis.

Analysis of Variance↗
PubMed1994

Mouse hepatic metabolites of ketoconazole: isolation and structure elucidation.

Oxidation, cleavage and degradation of the imidazole and piperazine rings, O-dealkylation, and aromatic hydroxylation are the reported pathways of ketoconazole (KC) metabolism. Metabolites were examined in hepatic extracts from male Swiss Webster mice treated with KC (350 mg kg-1 po x 7 days) in a 0.25% gum tragacanth suspension at 10 ml kg-1. Livers were collected 24 h after the last dose and stored at -70 degrees C. A mixture of chloroform/methanol extracts of liver homogenates were dried under vacuum and methanol extracts of the residue were chromatographed by a series of preparative and analytical HPLC techniques. Structure assignments were made by NMR and MS/MS techniques. It was demonstrated that KC was biotransformed to a number of products. Nine were isolated and seven identified as exclusive products of the biotransformation of the 1-acetylpiperazine moiety of KC. This substituent was biotransformed to the following: piperazine (de-N-acetyl ketoconazole, DAKC), N-carbamylpiperazine, N-formylpiperazine, 2,3-piperazinedione, 2-formamidoethylamine, ethylenediamine and amine. The 1H-NMR and MS data suggested that the remaining two metabolites were products resulting from the oxidation of the imidazole ring.

Animals↗
PubMed1994

Reversed-phase LC assay method for deoxycholate in influenza vaccine.

Sodium deoxycholate is used for the disruption of particles in the manufacturing of some influenza vaccines. Residual deoxycholate in inactivated vaccines is currently determined using a labour-intensive colorimetric method which lacks complete specificity. An alternative assay method for residual deoxycholate in vaccine preparations was developed using reversed-phase LC. Cholic acid was used as internal standard and the ratio of internal standard to test solute was used for all calculations. Prior to LC analysis, deoxycholic acid was concentrated by solid-phase extraction, a procedure that also removed proteinaceous material in vaccine samples. The clean-up/concentration procedure recovery was examined using untreated samples and was found to be quantitative. The linearity range of the LC method was between 3 and 200 micrograms ml-1, with a limit of detection of approximately 0.4 micrograms on column, and a lower limit of quantitation of 1.6 micrograms on column. Replicate assays during intra-and inter-day experiments gave acceptable levels of variability. The DCA content of samples from three lots of influenza vaccine varied between 10 and 16 micrograms ml-1. These values were appreciably lower than those measured spectrophotometrically, indicating the higher specificity of the LC method.

Cholic Acid↗
PubMed1993

Metabolism and disposition of phenazopyridine in rat.

1. The blood profile, tissue distribution, biliary and urinary excretion, and metabolism of 14C-phenazopyridine (PAP) was studied in male Wistar rats. 2. Based on the blood profile of 14C the absorption of PAP from the gastrointestinal tract was rapid; the t1/2 of elimination was 7.35 h. 3. Biliary excretion was a major route of elimination with 40.7% dose excreted by this route in bile duct-cannulated rats over the 0-8 h period. The predominant metabolite was conjugated 4'-hydroxy-PAP. 4. Liver and kidney showed the highest tissue levels of PAP-derived 14C, and significant covalent binding was found in these two tissues. 5. The major urinary metabolite of PAP was 4-acetylaminophenol (NAPA) followed in order by 5,4'-dihydroxy-PAP, 5-hydroxy-PAP, 4'-hydroxy-PAP and 2'-hydroxy-PAP; unchanged PAP accounted for < 1% dose. 6. Doubling the dose of PAP to 200 mg/kg caused a proportionate decrease in urinary NAPA excretion and an increase in 5-hydroxy-PAP.

Animals↗
PubMed1992

Biotransformation of tri-substituted methoxyamphetamines by Cunninghamella echinulata.

1. Four trimethoxyamphetamine analogues were incubated with the filamentous fungus Cunninghamella echinulata. 2. 2,4,5-Trimethoxyamphetamine and 2,5-dimethoxy-4-ethoxyamphetamine were poorly metabolized by C. echinulata ATCC 9244 and C. echinulata var. elegans ATCC 9245. 2,5-Dimethoxy-4-(n)-propoxyamphetamine was mainly metabolized through N-acetylation and O-dealkylation with minor amounts of several aliphatic hydroxylation metabolites formed. 2,5-Dimethoxy-4-methylthioamphetamine was extensively metabolized to the corresponding sulphoxide. 3. 2,5-Dimethoxy-4-methylthioamphetamine metabolism was inhibited by ethanol and quinidine. Sparteine did not inhibit the formation of the sulphoxide and may have shunted the substrate through alternate metabolic pathways. 4. Incubation conditions can affect the rate and extent of fungal biotransformation of 2,5-dimethoxy-4-methylthioamphetamine, and influence dextrose utilization, ammonia formation and pH.

Amphetamines↗
PubMed1990

Dextran sulfate disposition in the rat.

Comparative studies of oral and intravenous administration of tritiated dextran sulfate in rats showed markedly different distribution patterns. Following IV dosing about 50 per cent of the radioactivity was recovered in feces and urine within 24 h. The major portion of the recoverable dose was eliminated in the urine as dextran sulfate within 3 h after administration. In orally treated rats only about 32 per cent of the 3H was recovered in the feces and urine, the major fraction being associated with unabsorbed dextran sulfate in the feces. The remainder of the dose in both treatment groups has apparently distributed throughout the rat body with some accumulation in the liver, kidney and spleen. Consequently, the disposition of about 67 per cent or the oral dose could not be fully accounted for by these excretion routes. However, separation with Sephadex columns showed similarities in the 24 h plasma and urine profiles of the IV and orally dosed rats which suggest that while the oral dose was absorbed as dextran sulfate, it underwent rapid metabolism to small molecular weight products prior to entering the systemic circulation which were then widely distributed within the rat.

Administration, Oral↗
PubMed1990

Excretion of phenazopyridine and its metabolites in the urine of humans, rats, mice, and guinea pigs.

The metabolism of the urinary tract analgesic phenazopyridine [2,6-diamino-3-(phenylazo)pyridine; PAP] was studied in the urine of humans, rats, mice, and guinea pigs. Urinary excretion was rapid in human and guinea pig, but in the rat and mouse it was slower and there was significant fecal excretion. Metabolism of PAP was extensive in all four species, and there were marked quantitative differences in the routes of metabolism. The extent of azo bond cleavage was high in the mouse and guinea pig, moderate in the rat, and low in humans. Hydroxylation of both the phenyl and pyridyl rings of PAP was observed in all species. In the human, 5-hydroxyl PAP was the major metabolite (48.3% of the dose). It was concluded that there are marked species differences in the metabolism of PAP, and that none of the species studied resembles the human; the rat comes closest, but cannot be considered a particularly good model.

Aminopyridines↗
PubMed1990

Antinociceptive activity of propionyl esters of morphine: a reevaluation.

The antinociceptive activity of the propionyl homologues of 3-O- and 6-O-acetyl- and 3,6-O-diacetylmorphine was re-investigated using materials of unequivocally established structure. Testing was in male Wistar rats at 60 min following subcutaneous administration by the rat tail-flick method. Results indicate that the antinociceptive activity of 3-O-propionylmorphine was similar to that of 3-O-acetylmorphine. 6-O-Propionylmorphine and 3,6-O-dipropionylmorphine had similar antinociceptive activity and, like 6-O-acetylmorphine, 6-O-propionylmorphine may be the pharmacologically active principle responsible for the antinociceptive activity of its disubstituted homologue.

Analgesics↗
PubMed1990

Hepatic effects of ketoconazole in the male Swiss Webster mouse: temporal changes in drug metabolic parameters.

There have been conflicting observations regarding the effects of ketoconazole on hepatic metabolism. The objectives of these studies were to determine whether ketoconazole was an enzyme inducer or inhibitor in the mouse and then to establish the time frame of these ketoconazole-induced enzyme changes. Ketoconazole was administered (150 mg/kg p.o. X 4 days) to male Swiss Webster mice. Biochemical observations over a period of 6 days following treatment indicated that ketoconazole had a temporal biphasic effect on the liver. Although liver weight and microsomal protein were elevated, all other parameters monitored were lower at 2 h following ketoconazole treatment. At 24 h after the last dose of ketoconazole, hepatic biochemical parameters (liver wt., % liver wt./body wt., microsomal protein, and cytochrome P-450) were statistically elevated, while enzyme activities (benzphetamine N-demethylation, 6 beta- and 7 alpha-hydroxylation of testosterone, formation of androstenedione and UDP-glucuronyltransferase) were inhibited. At 72 h the ketoconazole-induced changes in the hepatic biochemical parameters were comparable to those observed at 24 h, and enzymatic parameters generally appeared to be induced by ketoconazole, with the exception of benzphetamine N-demethylase and UDP-glucuronyltransferase, which exhibited lower enzyme activities. Ethoxyresorufin O-deethylase, 7 alpha-hydroxylation of testosterone and glutathione S-transferase, on the other hand, were unaltered by ketoconazole treatment. The opposing effects of ketoconazole on benzphetamine N-demethylase and ethylmorphine N-demethylase at 72 h were further examined. Enzyme kinetics studies indicated that ketoconazole did not effect the Michaelis constants (Km) of the two substrates, but the maximum velocity (Vmax) of the reactions was altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Plasma sorbitol dehydrogenase determination in experimental hepatotoxicity using the Abbott Bichromatic Analyzer.

An automated single reagent micro-assay for the determination of sorbitol dehydrogenase (EC 1.1.1.14) catalytic activity concentration in mouse plasma was developed for the Abbott Bichromatic Analyzer (ABA-100). The kinetic rate determination was linear up to 250 U/l, had a CV of 2.65%, and required only 25 microliters of sample. Experimentally induced hepatotoxicity in the mouse by acetaminophen produced a dose dependent increase in blood sorbitol dehydrogenase activity.

Acetaminophen↗
PubMed1987

Effect of rifampin, phenobarbital pretreatment, and acetylator phenotype on acetylisoniazid metabolism in the rabbit.

The metabolism of [14C]acetylisoniazid was studied in male New Zealand White rabbits. Pretreatment of the rabbits with the microsomal enzyme inducers rifampin and phenobarbital had little effect on acetylisoniazid metabolism. Rifampin appears to produce some inhibition of acetylation of the metabolite acetylhydrazine to diacetylhydrazine. Acetylation phenotype was an important factor. Covalent binding of 14C to hepatic protein increased as the acetylation rate decreased. In plasma and urine acetylhydrazine levels were negatively correlated with acetylation rate and diacetylhydrazine levels were positively correlated as one would expect. It was concluded that in the rabbit covalent binding to hepatic protein was more dependent on the acetylation rate than on induction of microsomal oxidase.

Acetylation↗
PubMed1985

Postabsorption antidotal effects of N-acetylcysteine on acetaminophen-induced hepatotoxicity in the mouse.

Male Swiss Webster mice, treated with N-acetylcysteine (NAC, 500 mg/kg po) 1 h following acetaminophen (NAPA, 350 mg/kg po) administration, had control levels of transaminases indicating that NAC protects against NAPA-induced hepatotoxicity by postabsorption antidotal mechanism(s). Hepatic congestion induced by NAPA was reduced by NAC. Significantly higher elimination rate constants (K) for indocyanine green (500 micrograms/kg, iv) in mice treated with NAPA and NAC (K = 0.676 +/- 0.062) than in animals receiving NAPA alone (0.341 +/- 0.105) suggested NAC improved or preserved the hepatic circulation of the compromised liver. This NAC-induced improvement and (or) preservation of hepatic circulation was reflected in biliary and urinary excretion of acetaminophen and its metabolites by a general increase in elimination during the first 6 h (70.2 +/- 2.6 vs. 32.6 +/- 7.1%), and in the repletion of glutathione (GSH) in the liver by a return to control levels more quickly (3 vs. greater than 5 h) following depletion by NAPA. The metabolic consequences of the postabsorption antidotal effect of NAC in the compromised liver was a preferential excretion of sulphydryl-derived metabolites in the 1-4 h bile (GSH conjugate 11.30 +/- 1.25 vs. 7.25 +/- 0.39%) which was subsequently observed in the urine by preferential excretion of glutathione degradation products.

Acetaminophen↗
PubMed1984

Metabolism of [14C]acetylisoniazid and [14C]acetylhydrazine by the rat and rabbit.

Male rats and rabbits were singly dosed with either 1-[14C]acetyl isoniazid (acetylisonicotinoylhydrazine, acetyl-INH, 200 mg/kg po) or 1-[14C]acetylhydrazine (50 or 100 mg/kg ip). Urine and expired 14CO2 were collected, and after 6 hr the animals were killed for the analysis of tissue 14C concentrations and covalent binding of 14C to hepatic protein. Rats excreted proportionately more 14C in urine and had lower 14C levels in their tissues compared to rabbits. When acetyl-INH was administered, covalent hepatic protein binding of the acetyl moiety was greater in the rabbit than the rat, but the opposite was observed when acetylhydrazine was administered. Analysis of blood and urine by TLC revealed that the rabbit more rapidly metabolized both acetyl-INH to acetylhydrazine, and acetylhydrazine to diacetylhydrazine than did the rat. These observations suggest that higher amidase activity in the rabbit compared to the rat leads to faster conversion of acetyl-INH to acetylhydrazine which in turn leads to greater covalent binding and hepatotoxicity.

Animals↗