Sherry R. Black

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.

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.

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.u2002Bisphenol AF (BPAF) is used as a crosslinking agent for polymers and is being considered as a replacement for bisphenol A (BPA). 2.u2002In 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 340u2009mg/kg [14C]BPAF were investigated. 3.u2002BPAF was cleared more slowly than BPA in hepatocytes with the rate: ratu2009>u2009mouseu2009>u2009human. 4.u2002[14C]BPAF was excreted primarily in feces by 72u2009h 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 72u2009h. Similar results were observed following intravenous administration. 5.u2002In male rats, 52% of a 340u2009mg/kg oral dose was excreted in 24u2009h bile and was mostly comprised of BPAF glucuronide. However, >94% of fecal radioactivity was present as BPAF, suggesting extensive deconjugation in the intestine. 6.u2002Metabolites identified in bile were BPAF-glucuronide, -diglucuronide, -glucuronide sulfate and -sulfate. 7.u2002In conclusion, BPAF was well absorbed following gavage administration and highly metabolized and excreted mostly in the feces as BPAF.

Disposition of intravenously or orally administered silver nanoparticles in pregnant rats and the effect on the biochemical profile in urine.

Few investigations have been conducted on the disposition and fate of silver nanoparticles (AgNP) in pregnancy. The distribution of a single dose of polyvinylpyrrolidone (PVP)‐stabilized AgNP was investigated in pregnant rats. Two sizes of AgNP, 20 and 110u2009nm, and silver acetate (AgAc) were used to investigate the role of AgNP diameter and particle dissolution in tissue distribution, internal dose and persistence. Dams were administered AgNP or AgAc intravenously (i.v.) (1u2009mgu2009kg−1) or by gavage (p.o.) (10u2009mgu2009kg−1), or vehicle alone, on gestation day 18 and euthanized at 24 or 48u2009h post‐exposure. The silver concentration in tissues was measured using inductively‐coupled plasma mass spectrometry. The distribution of silver in dams was influenced by route of administration and AgNP size. The highest concentration of silver (μg Ag g−1 tissue) at 48u2009h was found in the spleen for i.v. administered AgNP, and in the lungs for AgAc. At 48u2009h after p.o. administration of AgNP, the highest concentration was measured in the cecum and large intestine, and for AgAc in the placenta. Silver was detected in placenta and fetuses for all groups. Markers of cardiovascular injury, oxidative stress marker, cytokines and chemokines were not significantly elevated in exposed dams compared to vehicle‐dosed control. NMR metabolomics analysis of urine indicated that AgNP and AgAc exposure impact the carbohydrate, and amino acid metabolism. This study demonstrates that silver crosses the placenta and is transferred to the fetus regardless of the form of silver. Copyright

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 = 3–4u2009min) and human (t1/2 = 20–30u2009min). 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 1000u2009mg/kg, intravenously at 10u2009mg/kg and dermally at 10 and 100u2009mg/kg; female rats were administered oral doses at 10u2009mg/kg. Oral doses of BPB were well-absorbed (>83%) and eliminated chiefly in urine (83–84%); ≤1% of the radioactivity remained in tissues at 24u2009h or 72u2009h after dosing. About 4% and 8%, respectively, of 100u2009mg/kg dermal doses were absorbed in 24u2009h and 72u2009h, and about 50% of a 10u2009mg/kg dose was absorbed in 72u2009h. 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.

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

Tissue distribution, metabolism, and disposition of oral (0.2–20u2009mg/kg) and intravenous (0.2u2009mg/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 72u2009h. 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 72u2009h. 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.

[14C]bis(2-chloroethoxy)methane: comparative absorption, distribution, metabolism and excretion in rats and mice.

bis(2-Chloroethoxy)methane (BCM) is used primarily as a precursor in the synthesis of polysulfide elastomers. After administration of [14C]BCM, radioactivity is readily absorbed from the gastrointestinal tract and moderately absorbed through skin. Following absorption, BCM-derived radioactivity is rapidly distributed to all tissues, rapidly metabolized and excreted primarily in urine. Minimal effects of sex, species or dose in the range studied (0.1–10u2009mgu2009kg−1) were observed on the fate of BCM in rats and mice after all routes of administration. The major metabolite (about 40% of the dose) of BCM in rat was isolated and identified as thiodiglycolic acid (TDGA) indicating that the ether linkage of BCM is cleaved to form 2-chloroethyl fragments that may be further metabolized to 2-chloracetaldehyde, conjugated with glutathione and the latter subsequently metabolized to TDGA. 2-chloroacetaldehyde has also been shown to be cardiotoxic, possibly accounting for BCM cardiotoxicity observed in repeated dose studies.

Disposition of methyl ethyl ketoxime in the rat after oral, intravenous and dermal administration

1. The disposition of 14C-methyl ethyl ketoxime (MEKO) was determined in the male F344 rat following oral, intravenous (i.v.) and dermal administration. 2. Oral doses of 2.7, 27 and 270 mg/kg were primarily excreted as CO2 (71-49%) in decreasing percentage as the dose increased. Excretion in urine (13-26%) and as volatiles (5-18%) increased as the dose increased. Five to 6% of the dose remained in the major tissues after 72 h. 3. An i.v. dose of 2.7 mg/kg was also principally excreted as CO2 (48.8%) with excretion in urine and as expired volatiles accounting for 21.4 and 11.4%, respectively. About 7% of the administered radioactivity remained in the tissues after 72 h. 4. Following dermal administration, 13 and 26% of a 2.7 and 270 mg/kg dose, respectively, were absorbed. Volatilization from the dose site prior to placement in the metabolism cage may account for the low absorption. 5. MEKO was biotransformed to at least five polar metabolites that could only be partially resolved by anion exchange chromatography. Incubation with glucuronidase, but not sulphatase, changed the urinary metabolic profile. Methyl ethyl ketone was a major component in the volatiles.

Disposition of [14C]hydroquinone in Harlan Sprague-Dawley rats and B6C3F1/N mice: Species and route comparison

Abstract 1. Hydroquinone (HQ) is present in some foods and has varied industrial, medical and consumer uses. These studies were undertaken to investigate the disposition of HQ in rats and mice following gavage, intravenous (IV) and dermal exposure. 2. [14u2009C]HQ administered (0.5, 5 or 50u2009mg/kg) by gavage or IV routes to male and female Harlan Sprague-Dawley (HSD) rats and B6C3F1/N mice was well absorbed and rapidly excreted primarily in urine. Radioactivity remaining in tissues at 72u2009h wasu2009<1% for both species at all dose levels and routes. No sex, species or route related differences in disposition were found. 3. With dermal application of 2, 10 or 20% [14u2009C]HQ, mice absorbed higher percentages of the dose than rats (37, 12, 12% versus 18.6, 4.43 and 1.79%, respectively). The HQ mass absorbed by mice increased with dose, while in rats it was more constant over the dose range. Absorbed HQ was rapidly excreted in urine of both species and urinary excretion indicated continued absorption over the exposure period. No sex differences in disposition were found. 4. The oral bioavailability of HQ at 5u2009mg/kg was low in both rats (1.6%) and mice (3.9%) demonstrating significant first pass metabolism. Dermal bioavailability in mice was 9.4% following application of 2% formulation. 5. Urinary metabolites for both species and all routes included the glucuronide and sulfate conjugates; no parent was found in urine.

Evaluating in vitro-in vivo extrapolation of toxicokinetics

Prioritizing the risk posed by thousands of chemicals potentially present in the environment requires exposure, toxicity, and toxicokinetic (TK) data, which are often unavailable. Relatively high throughput, in vitro TK (HTTK) assays and in vitro-to-in vivo extrapolation (IVIVE) methods have been developed to predict TK, but most of the in vivo TK data available to benchmark these methods are from pharmaceuticals. Here we report on new, in vivo rat TK experiments for 26 non-pharmaceutical chemicals with environmental relevance. Both intravenous and oral dosing were used to calculate bioavailability. These chemicals, and an additional 19 chemicals (including some pharmaceuticals) from previously published in vivo rat studies, were systematically analyzed to estimate in vivo TK parameters (e.g., volume of distribution [Vd], elimination rate). For each of the chemicals, rat-specific HTTK data were available and key TK predictions were examined: oral bioavailability, clearance, Vd, and uncertainty. For the non-pharmaceutical chemicals, predictions for bioavailability were not effective. While no pharmaceutical was absorbed at less than 10%, the fraction bioavailable for non-pharmaceutical chemicals was as low as 0.3%. Total clearance was generally more under-estimated for nonpharmaceuticals and Vd methods calibrated to pharmaceuticals may not be appropriate for other chemicals. However, the steady-state, peak, and time-integrated plasma concentrations of nonpharmaceuticals were predicted with reasonable accuracy. The plasma concentration predictions improved when experimental measurements of bioavailability were incorporated. In summary, HTTK and IVIVE methods are adequately robust to be applied to high throughput in vitro toxicity screening data of environmentally relevant chemicals for prioritizing based on human health risks.