James M. Mathews

Pharmacokinetic, Neurochemical, Stereological and Neuropathological Studies on the Potential Effects of Paraquat in the Substantia Nigra Pars Compacta and Striatum of Male C57BL/6J Mice

The pharmacokinetics and neurotoxicity of paraquat dichloride (PQ) were assessed following once weekly administration to C57BL/6J male mice by intraperitoneal injection for 1, 2 or 3 weeks at doses of 10, 15 or 25 mg/kg/week. Approximately 0.3% of the administered dose was taken up by the brain and was slowly eliminated, with a half-life of approximately 3 weeks. PQ did not alter the concentration of dopamine (DA), homovanillic acid (HVA) or 3,4-dihydroxyphenylacetic acid (DOPAC), or increase dopamine turnover in the striatum. There was inconsistent stereological evidence of a loss of DA neurons, as identified by chromogenic or fluorescent-tagged antibodies to tyrosine hydroxylase in the substantia nigra pars compacta (SNpc). There was no evidence that PQ induced neuronal degeneration in the SNpc or degenerating neuronal processes in the striatum, as indicated by the absence of uptake of silver stain or reduced immunolabeling of tyrosine-hydroxylase-positive (TH(+)) neurons. There was no evidence of apoptotic cell death, which was evaluated using TUNEL or caspase 3 assays. Microglia (IBA-1 immunoreactivity) and astrocytes (GFAP immunoreactivity) were not activated in PQ-treated mice 4, 8, 16, 24, 48, 96 or 168 h after 1, 2 or 3 doses of PQ. In contrast, mice dosed with the positive control substance, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 10mg/kg/dose×4 doses, 2 h apart), displayed significantly reduced DA and DOPAC concentrations and increased DA turnover in the striatum 7 days after dosing. The number of TH(+) neurons in the SNpc was reduced, and there were increased numbers of degenerating neurons and neuronal processes in the SNpc and striatum. MPTP-mediated cell death was not attributed to apoptosis. MPTP activated microglia and astrocytes within 4 h of the last dose, reaching a peak within 48 h. The microglial response ended by 96 h in the SNpc, but the astrocytic response continued through 168 h in the striatum. These results bring into question previous published stereological studies that report loss of TH(+) neurons in the SNpc of PQ-treated mice. This study also suggests that even if the reduction in TH(+) neurons reported by others occurs in PQ-treated mice, this apparent phenotypic change is unaccompanied by neuronal cell death or by modification of dopamine levels in the striatum.

Reaction of the Butter Flavorant Diacetyl (2,3-Butanedione) with N-α-Acetylarginine: A Model for Epitope Formation with Pulmonary Proteins in the Etiology of Obliterative Bronchiolitis

The butter flavorant diacetyl (2,3-butanedione) is implicated in causing obliterative bronchiolitis in microwave popcorn plant workers. Because diacetyl modifies arginine residues, an immunological basis for its toxicity is under investigation. Reaction products of diacetyl with N-α-acetylarginine (AcArg) were determined as a model for hapten formation, with characterization by mass spectrometry, NMR, and HPLC with UV detection and radiodetection. Four products were identified by LC-MS, each with a positive ion of m/z 303 (diacetyl + AcArg); one pair displayed an additional ion at m/z 217 (AcArg), the other pair at m/z 285 (- H(2)O). Their (1)H-(13)C NMR correlation spectra were consistent with the addition of one or two of the guanidine nitrogens to form aminols. Open-chain pairs interconverted at pH 2, as did the cyclized, but all four interconverted at neutral pH. This is the first structural characterization of the covalent adducts between diacetyl and an arginine moiety.

Metabolism and disposition of GTS-21, a novel drug for Alzheimer's disease

1. GTS-21, a novel drug for Alzheimers disease, is currently under clinical development. In the current study, the metabolism and disposition of GTS-21 have been evaluated in rat and dog after single oral and intravenous administration. 2. Following oral administration of [14C]GTS-21 to rat, radioactivity was primarily excreted in the faeces (67%) via the bile with possible enterohepatic circulation. Urinary excretion of radioactivity in rat and dog was 20 and 19% respectively. 3. GTS-21 was rapidly and extensively absorbed after oral administration and rapidly cleared from plasma. The maximum concentration ratio of GTS-21 to total radioactivity in plasma was low, indicating first-pass or pre-systemic biotransformation. 4. In rat, GTS-21 showed linear pharmacokinetics over doses ranging from 1 to 10 mg/kg with an absolute bioavailability of 23%. In dog, the absolute bioavailability was 27% at an oral dose of 3 mg/kg. 5. GTS-21 was O-demethylated to yield compounds that were then subject to glucuronidation. Three of the metabolites in rat urine were isolated and characterized as 4-OH-GTS-21, 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. The major urinary metabolites were 4-OH-GTS-21 glucuronide and 2-OH-GTS-21 glucuronide. 6. In vitro chemical inhibition of cytochrome P450 in human liver microsomes indicated that CYPIA2 and CYP2E1 were the isoforms primarily responsible for the O-demethylation of GTS-21, with some contribution from CYP3A.

Metabolism and distribution of bromodichloromethane in rats after single and multiple oral doses

The disposition of [14C]bromodichloromethane (BDCM) was studied in male Fischer rats after single oral doses of 1, 10, 32, or 100 mg/kg and 10-d repeat oral dosing of 10 or 100 mg/kg/d. Methods were developed to quantitate exhaled 14CO and 14CO2. Bromodichloromethane was extensively (approximately 80-90%) metabolized within 24 h postdosing with approximately 70-80% of the administered dose appearing as 14CO2 and approximately 3-5% as 14CO. Urinary and fecal elimination were low, accounting for 4-5% and 1-3% of the dose, respectively. Oral administration of BDCM at a level of 10 mg/kg/d for 10 d did not result in the bioaccumulation or altered disposition of the test chemical, but during the course of the repeat 100 mg/kg/d dosing the rate of production of 14CO2 increased, suggesting that this dose of BDCM induced its own metabolism. Persistence of radiolabeled residues in tissues collected 24 h after single-dose administration was low (3-4% of dose), with the most marked accumulation (1-3% of dose) in liver. Kidney tissue, particularly the cortical region, also contained significant concentrations of residues.

The effect of repeat administration of GTS-21 on mixed-function oxidase activities in rat

The effect of repeat administration of GTS-21 on hepatic microsomal enzymes was determined in rats administered the drug at levels of 3, 60 and 300 mg/kg/day for 7 days. Liver weight and cytochrome P450 (CYP) contents were not changed. Cytochrome b5 contents were increased at the mid and high doses of GTS-21, as the contents increased with increasing dose, but were unchanged at the low dose. Five selective activities of CYP isoforms, acetanilide hydroxylase (CYP1A2), tolbutamide hydroxylase (CYP2C6), dextromethorphan O-demethylase (CYP2D1), p-nitrophenol hydroxylase (CYP2E1) and erythromycin N-demethylase (CYP3A) were examined. Enzyme activities were changed only at the highest dose; the activity of CYP1A2 was increased by 71% and the activities of CYP2C6 and CYP2D1 were decreased by 37 and 19%, respectively. At low and mid doses of GTS-21, all activities were unchanged. These data indicate that GTS-21 is not a strong modulator of the mixed-function oxidase system.

The influence of cytochrome P450 enzyme activity on the composition and quantity of volatile organics in expired breath

Abstract We have previously described a method to capture, identify and quantify volatile components in expired breath. The purpose of this research is to provide a non-invasive means to measure biomarkers of metabolism in vivo. In the present studies, the effect of 1-aminobenzotriazole (ABT), an inhibitor of diverse cytochrome P450 (P450) enzymes, on the composition of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with the catalytic activities and total content of hepatic P450. lntraperitoneal administration of ABT (100 mg kg-(1)) to rats resulted in markedly diminished hepatic microsomal P450 content and activities. The extent of inhibition was near maximal at 4 h, at which time approximately 50% of the total P450 content, about 65% of the CYPlA2 activity, 55% of the CYP2E1 activity, and about 80% of CYP2B activity were lost. Inhibition was maintained to 48 h post-dosing, but P450 content and activities had largely been restored by day 7. Concomitant with the inhibition of P450 were corresponding increases (up to several hundred-fold) in the molar amount of volatiles appearing in the breath of ABT-treated animals, and the rebound of P450 levels was attended by corresponding decreases in the appearance of breath volatiles. These studies indicate that P450 plays a major role in the metabolism of VOCs appearing in breath, and that these chemicals can serve as markers on P450 activity in vivo.

Disposition of bisphenol AF, a bisphenol A analogue, in hepatocytes in vitro and in male and female Harlan Sprague-Dawley rats and B6C3F1/N mice following oral and intravenous administration

Abstract 1. Bisphenol AF (BPAF) is used as a crosslinking agent for polymers and is being considered as a replacement for bisphenol A (BPA). 2. In this study, comparative clearance and metabolism of BPAF and BPA in hepatocytes and the disposition and metabolism of BPAF in rodents following oral administration of 3.4, 34 or 340 mg/kg [14C]BPAF were investigated. 3. BPAF was cleared more slowly than BPA in hepatocytes with the rate: rat > mouse > human. 4. [14C]BPAF was excreted primarily in feces by 72 h after oral administration to rats (65–80%) and mice (63–72%). Females excreted more in urine (rat, 15%; mouse, 24%) than males (rat, 1–4%; mouse, 10%). Residual tissue radioactivity was <2% of the dose at 72 h. Similar results were observed following intravenous administration. 5. In male rats, 52% of a 340 mg/kg oral dose was excreted in 24 h bile and was mostly comprised of BPAF glucuronide. However, >94% of fecal radioactivity was present as BPAF, suggesting extensive deconjugation in the intestine. 6. Metabolites identified in bile were BPAF-glucuronide, -diglucuronide, -glucuronide sulfate and -sulfate. 7. In conclusion, BPAF was well absorbed following gavage administration and highly metabolized and excreted mostly in the feces as BPAF.

Metabolism and disposition of [14C]n-butyl-p-hydroxybenzoate in male and female Harlan Sprague Dawley rats following oral administration and dermal application

n-Butyl-p-hydroxybenzoate (n-butylparaben, BPB) is an antioxidant used in foods, pharmaceuticals and cosmetics. This study investigated the disposition of ring-labelled [14C]BPB in Harlan Sprague Dawley rats, and in rat and human hepatocytes. BPB was rapidly cleared in hepatocytes from rat (t1/2 = 3–4 min) and human (t1/2 = 20–30 min). The major metabolites detected in rat hepatocytes were hydroxybenzoic acid and in human hepatocytes were hydroxybenzoic acid and hydroxyhippuric acid. [14C]BPB was administered to male rats orally at 10, 100 or 1000 mg/kg, intravenously at 10 mg/kg and dermally at 10 and 100 mg/kg; female rats were administered oral doses at 10 mg/kg. Oral doses of BPB were well-absorbed (>83%) and eliminated chiefly in urine (83–84%); ≤1% of the radioactivity remained in tissues at 24 h or 72 h after dosing. About 4% and 8%, respectively, of 100 mg/kg dermal doses were absorbed in 24 h and 72 h, and about 50% of a 10 mg/kg dose was absorbed in 72 h. Metabolites detected in urine included those previously reported, BPB-glucuronide, BPB-sulfate, hydroxybenzoic acid and hydroxyhippuric acid, but also novel metabolites arising from ring hydroxylation followed by glucuronidation and sulfation.

Inhibition of Paclitaxel Metabolism In Vitro in Human Hepatocytes by Ginkgo biloba Preparations

Since the late 1980s, chemotherapy-induced cognitive impairment, also known as “chemobrain”, has been a recognized side effect in patients undergoing cancer treatment (). Although products containing Ginkgo biloba may be used by patients undergoing chemotherapy with paclitaxel and other agents, the potential for an herb–drug interaction with this combination has not been adequately explored. This report describes the inhibition of paclitaxel metabolism by Ginkgo preparations in vitro in human hepatocytes. Hydrolyzate of Ginkgo extract (10–100 mM in terpene lactone concentration) caused a dose-dependent inhibition of the 6α -hydroxylation of paclitaxel, the enzymatic activity responsible for the majority of the clearance of that drug in clinical applications; parent extract had no effect. Contrary to the assumed therapeutic benefit of Ginkgo, its concomitant use with paclitaxel could result in elevated blood levels of the chemotherapeutic, with attendant exacerbation of cognitive impairment and other toxic effects associated with cancer therapy.

Metabolism and disposition of [14C]dibromoacetonitrile in rats and mice following oral and intravenous administration

Tissue distribution, metabolism, and disposition of oral (0.2–20 mg/kg) and intravenous (0.2 mg/kg) doses of [2-14C]dibromoacetonitrile (DBAN) were investigated in male rats and mice. [14C]DBAN reacts rapidly with rat blood in vitro and binds covalently. Prior depletion of glutathione (GSH) markedly diminished loss of DBAN. Chemical reaction with GSH readily yielded glutathionylacetonitrile. About 90% of the radioactivity from orally administered doses of [14C]DBAN was absorbed. After intravenous administration, 10% and 20% of the radioactivity was recovered in mouse and rat tissues, respectively, at 72 h. After oral dosing, three to four times less radioactivity was recovered, but radioactivity in stomach was mostly covalently bound. Excretion of radioactivity into urine exceeded that in feces; 9–15% was exhaled as labeled carbon dioxide and 1–3% as volatiles in 72 h. The major urinary metabolites were identified by liquid chromatography-mass spectrometry, and included acetonitrile mercaptoacetate (mouse), acetonitrile mercapturate, and cysteinylacetonitrile. The primary mode of DBAN metabolism is via reaction with GSH, and covalent binding may be due to reaction with tissue sulphydryls.