The common indoor air pollutant α-pinene is metabolised to a genotoxic metabolite α-pinene oxide.

α-Pinene caused a concentration-responsive increase in bladder hyperplasia and decrease in sperm counts in rodents following inhalation exposure. Additionally, it formed a prospective reactive metabolite, α-pinene oxide.To provide human relevant context for data generated in animal models and explore potential mechanism, we undertook studies to investigate the metabolism of α-pinene to α-pinene oxide and mutagenicity of α-pinene and α-pinene oxide.α-Pinene oxide was formed in rat and human microsomes and hepatocytes with some species differences. Based on area under the concentration versus time curves, the formation of α-pinene oxide was up to 4-fold higher in rats than in humans.While rat microsomes cleared α-pinene oxide faster than human microsomes, the clearance of α-pinene oxide in hepatocytes was similar between species.α-Pinene was not mutagenic with or without induced rat liver S9 in Salmonella typhimurium or Escherichia coli when tested up to 10 000 µg/plate while α-pinene oxide was mutagenic at ≥25 µg/plate.α-Pinene was metabolised to α-pinene oxide under the conditions of the bacterial mutation assay although the concentration was approximately 3-fold lower than the lowest α-pinene oxide concentration that was positive in the assay, potentially explaining the lack of mutagenicity observed with α-pinene.

Oral administration of TiO2 nanoparticles during early life impacts cardiac and neurobehavioral performance and metabolite profile in an age- and sex-related manner.

BACKGROUND: Nanoparticles (NPs) are increasingly incorporated in everyday products. To investigate the effects of early life exposure to orally ingested TiO2 NP, male and female Sprague-Dawley rat pups received four consecutive daily doses of 10 mg/kg body weight TiO2 NP (diameter: 21 ± 5 nm) or vehicle control (water) by gavage at three different pre-weaning ages: postnatal day (PND) 2-5, PND 7-10, or PND 17-20. Cardiac assessment and basic neurobehavioral tests (locomotor activity, rotarod, and acoustic startle) were conducted on PND 20. Pups were sacrificed at PND 21. Select tissues were collected, weighed, processed for neurotransmitter and metabolomics analyses. RESULTS: Heart rate was found to be significantly decreased in female pups when dosed between PND 7-10 and PND 17-20. Females dosed between PND 2-5 showed decrease acoustic startle response and when dosed between PND 7-10 showed decreased performance in the rotarod test and increased locomotor activity. Male pups dosed between PND 17-20 showed decreased locomotor activity. The concentrations of neurotransmitters and related metabolites in brain tissue and the metabolomic profile of plasma were impacted by TiO2 NP administration for all dose groups. Metabolomic pathways perturbed by TiO2 NP administration included pathways involved in amino acid and lipid metabolism. CONCLUSION: Oral administration of TiO2 NP to rat pups impacted basic cardiac and neurobehavioral performance, neurotransmitters and related metabolites concentrations in brain tissue, and the biochemical profiles of plasma. The findings suggested that female pups were more likely to experience adverse outcome following early life exposure to oral TiO2 NP than male pups. Collectively the data from this exploratory study suggest oral administration of TiO2 NP cause adverse biological effects in an age- and sex-related manner, emphasizing the need to understand the short- and long-term effects of early life exposure to TiO2 NP.

Development and Validation of an Analytical Method for Quantitation of Alpha-Pinene Oxide in Rodent Blood and Mammary Glands by GC-MS.

Alpha-pinene is a monoterpene found in the oil of coniferous trees and has a wide variety of applications. Alpha-pinene oxide (APO) is a potential reactive metabolite of alpha-pinene in rodents. The objective of this work is to validate a gas chromatography-mass spectrometry method to quantitate APO in rat and mouse blood and mammary glands in support of studies investigating the toxicity and toxicokinetic behavior of alpha-pinene. The method was validated in male Sprague Dawley rat blood over the concentration range of 5-250 ng/mL. Matrix standard curves were linear (r ≥ 0.99), and accuracy (percent relative error, %RE) was ≤±15% for standards at all levels. Intra- and interday precision (percent relative standard deviation, %RSD) and accuracy (%RE) were evaluated at three concentration levels (10, 50 and 200 ng/mL) and were ≤6.3% and ≤±5.4%, respectively. The limit of detection, determined from the SD of the limit of quantitation (5 ng/mL), was 1.06 ng/mL. Standards as high as 25,000 ng/mL could be accurately quantified after diluting to the validated range (%RE ≤ ±7.1%; %RSD ≤ 5.8%). APO was stable in rat blood for at least 70 days in frozen storage (-80°C). APO could accurately be quantified in male and female Hsd:Sprague Dawley® SD® rat and B6C3F1 mouse blood (mean %RE ≤ ±5.3%; %RSD ≤ 7.8%) and female B6C3F1 and Sprague Dawley rat mammary glands (mean %RE ≤ ±14.6%; %RSD ≤ 8.1%) using a primary matrix standard curve. These results demonstrate that the method is suitable for the analysis of APO in rodent blood and mammary glands generated from toxicokinetic and toxicology studies.

Simulated Gastric Digestion and In Vivo Intestinal Uptake of Orally Administered CuO Nanoparticles and TiO2 E171 in Male and Female Rat Pups.

Oral exposure to nanoparticles (NPs) during early life is an understudied area. The goals of this study were to evaluate the effect of pre-weaned rat gastric fluids on 50 nm CuO NPs and TiO2 E171 in vitro, and to evaluate uptake in vivo. The NP uptake was studied in vivo in male and female Sprague-Dawley rat pups following oral administration of four consecutive daily doses of 10 mg/kg CuO NPs, TiO2 E171, or vehicle control (water) between postnatal day (PND) 7-10. Rat pups were sacrificed on either PND10 or PND21. Simulated digestion led to dissolution of CuO NPs at the later ages tested (PND14 and PND21, but not PND7). In vivo intestinal uptake of CuO NPs and TiO2 E171 was observed by hyperspectral imaging of intestinal cross sections. Brightfield microscopy showed that the number of immune cells increased in the intestinal tissue following NP administration. Orally administered NPs led to low intestinal uptake of NPs and an increase in immune cells in the small and large intestine, suggesting that oral exposure to NPs during early life may lead to irritation or a low-grade inflammation. The long-term impact of increased immune cells in the intestinal tract during early life is unknown.

Toxicokinetic evaluation of the common indoor air pollutant, α-pinene, and its potential reactive metabolite, α-pinene oxide, following inhalation exposure in rodents.

The toxicokinetic behavior of α-pinene and its potential reactive metabolite, α-pinene oxide, was investigated following whole body inhalation exposure to 50 and 100 ppm α-pinene in rats and mice for 6 h per day for 7d. In both species and sexes, the maximum blood concentration (Cmax) increased more than proportionally while the increase in area under the concentration time curve (AUC) was proportional to the exposure concentration. When normalized to the calculated dose (D), both Cmax/D (male rats, 12.2-54.5; female rats, 17.4-74.1; male mice, 7.41-14.2; female mice, 6.59-13.0 (ng/mL)/(mg/kg)) and AUC/D (male rats, 28.9-31.1; female rats, 55.8-56.8; male mice, 18.1-19.4; female mice, 19.2-22.5 (h*ng/mL)/(mg/kg)) in rats were higher than in mice and in female rats were higher than in male rats; no sex difference was observed in mice. α-Pinene was eliminated from blood with half-lives between 12.2 and 17.4 h in rats and 6.18-19.4 h in mice. At the low dose, the ratio of α-pinene oxide to α-pinene, based on Cmax and AUC, respectively, was 0.200-0.237 and 0.279-0.615 in rats and 0.060-0.086 and 0.036-0.011 in mice demonstrating lower formation of the oxide in mice than in rats. At the high dose, the ratio decreased considerably in both species pointing to saturation of pathways leading to the formation of α-pinene oxide. α-Pinene and the oxide were quantified in the mammary glands of rats and mice with tissue to blood ratios of ≥23 demonstrating retention of these analytes in mammary glands. The findings of epoxide formation and species- and sex-differences in systemic exposure may be important in providing context and relating animal findings to human exposures.

Alpha-pyrrolidinopentiophenone and mephedrone self-administration produce differential neurochemical changes following short- or long-access conditions in rats.

Stimulant-induced neurochemical changes may occur at different times for different brain regions or neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of extended access to α-pyrrolidinopentiophenone (α-PVP) and 4-methylmethcathinone (4MMC). Male and female Sprague-Dawley rats were trained to self-administer α-PVP (0.1 mg/kg/infusion) or 4MMC (0.5 mg/kg/infusion) through autoshaping, and then self-administered for 21 days during 1 h (short access; ShA) or 6 h (long access; LgA) sessions. Separate rats were assigned to a naïve control group. Amygdala, hippocampus, hypothalamus, prefrontal cortex (PFC), striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Rats acquired self-administration of α-PVP and 4MMC, and LgA rats showed more escalation of self-administration than ShA rats. Synthetic cathinone administration produced several effects on neurotransmitters. LgA self-administration of α-PVP increased 5-HIAA levels in all brain regions, compared to control. In contrast, both LgA and ShA 4MMC self-administration decreased 5-HT and 5-HIAA levels in most brain regions. LgA exposure to both synthetic cathinones increased DOPAC levels in hypothalamus and striatum, and increased HVA levels in striatum compared to control. LgA self-administration of either synthetic cathinone produced region-specific increases in NE levels, whereas ShA self-administration lowered NE levels in select locations compared to control. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse, and that 21 days of self-administration only models the beginning stages of dysregulated drug intake.

Biodistribution, cardiac and neurobehavioral assessments, and neurotransmitter quantification in juvenile rats following oral administration of aluminum oxide nanoparticles.

Little is known about the uptake, biodistribution, and biological responses of nanoparticles (NPs) and their toxicity in developing animals. Here, male and female juvenile Sprague-Dawley rats received four consecutive daily doses of 10 mg/kg Al2 O3 NP (diameter: 24 nm [transmission electron microscope], hydrodynamic diameter: 148 nm) or vehicle control (water) by gavage between postnatal days (PNDs) 17-20. Basic neurobehavioral and cardiac assessments were performed on PND 20. Animals were sacrificed on PND 21, and selected tissues were collected, weighed, and processed for histopathology or neurotransmitter analysis. The biodistribution of Al2 O3 NP in tissue sections of the intestine, liver, spleen, kidney, and lymph nodes were evaluated using enhanced dark-field microscopy (EDM) and hyperspectral imaging (HSI). Liver-to-body weight ratio was significantly increased for male pups administered Al2 O3 NP compared with control. HSI suggested that Al2 O3 NP was more abundant in the duodenum and ileum tissue of the female pups compared with the male pups, whereas the abundance of NP was similar for males and females in the other tissues. The abundance of NP was higher in the liver compared with spleen, lymph nodes, and kidney. Homovanillic acid and norepinephrine concentrations in brain were significantly decreased following Al2 O3 NP administration in female and male pups, whereas 5-hydroxyindoleacetic acid was significantly increased in male pups. EDM/HSI indicates intestinal uptake of Al2 O3 NP following oral administration. Al2 O3 NP altered neurotransmitter/metabolite concentrations in juvenile rats' brain tissues. Together, these data suggest that orally administered Al2 O3 NP interferes with the brain biochemistry in both female and male pups.

Disposition and metabolism of antibacterial agent, triclocarban, in rodents; a species and route comparison.

Triclocarban is a residue-producing antibacterial agent used in a variety of consumer products. These studies investigated the disposition and metabolism of [14C]triclocarban. In male rats following a single gavage administration of 50, 150, and 500 mg/kg, excretion was primarily via feces (feces, 85-86%; urine, 3-6%) with no apparent dose-related effect. In male rats, 29% of the administered dose was excreted in bile suggesting some of the fecal excretion is from the absorbed dose which was excreted to the intestine via bile. The tissue retention of radioactivity was low in male rats (24 h, 3.9%; 72 h, 0.1%). Disposition pattern following gavage administration of 50 mg/kg in female rats and male and female mice were similar to male rats. Plasma elimination half-life of triclocarban in rats following gavage administration was shorter (∼2 h) compared to that based on total radioactivity (≥9 h) which included all products of triclocarban. Absorption following a single dermal application of 1.5 or 3% was low (≤3%) in rodents. Hydroxylated and conjugated metabolites of triclocarban predominated in bile. In hepatocytes, clearance of triclocarban in mouse and human was similar and was faster than in rat.

Disposition and metabolism of sulfolane in Harlan Sprague Dawley rats and B6C3F1/N mice and in vitro in hepatocytes from rats, mice, and humans.

Sulfolane has been found as a ground water contaminant near refining sites. These studies investigated the in vitro hepatic clearance and in vivo disposition of [14C]sulfolane in rats and mice following a single oral administration (30, 100, or 300 mg/kg) and dermal application (100 mg/kg).[14C]Sulfolane was well-absorbed in male rats following oral administration and excreted extensively in urine (≥93%). Total radioactivity in tissues at 24 and 48 h was ∼7% and <2%. Disposition pattern was similar in female rats and male and female mice at 100 mg/kg oral dose.Dermally applied [14C]Sulfolane (covered dose site, 100 mg/kg) was poorly absorbed in male (∼16%) and female (∼19%) rats; absorption increased to 59% when the dose site was uncovered in male rats suggesting ingestion of dose via grooming of the dose site. Dermally applied [14C]sulfolane (100 mg/kg, covered dose site) was well absorbed in male (∼70%) and female (∼80%) mice.Urinary radiochemical profiles were similar between routes, species, and sexes; the main analytes present in urine were sulfolane and 3-hydroxysulfolane.Sulfolane was not cleared in hepatocytes from rodents or human suggesting sites other than liver might be involved in metabolism of sulfolane in vivo.

Disposition and metabolism of N-butylbenzenesulfonamide in Sprague Dawley rats and B6C3F1/N mice and in vitro in hepatocytes from rats, mice, and humans.

N-Butylbenzenesulfonamide (NBBS) is a plasticizer detected in the environment suggesting potential human exposure. These studies investigated the in vitro hepatic clearance and disposition of [14C]NBBS in rodents following a single gavage (2, 20 or 200 mg/kg) or intravenous (IV) administration (20 mg/kg). NBBS was cleared slower in hepatocytes from humans compared to rodents. [14C]NBBS was well-absorbed in male rats following gavage administration and excreted extensively in urine (70-76 %) and feces (11-15 %) 72 h following administration. Following a 20 mg/kg gavage dose in male rats, 25 % of the dose was excreted in bile by 24 h suggesting that observed fecal excretion was due to biliary excretion. The radioactivity was distributed to tissues with 14 % and 8 % of the administered dose remaining in tissues at 24 and 72 h, respectively. There was no apparent dose-dependent effect in disposition in male rats. Disposition patterns were similar in female rats (urine, 83 %; feces, 14 %) and male (urine, 69 %; feces, 11 %) and female (urine, 72 %; feces, 9 %) mice following gavage administration of 20 mg/kg. The disposition following IV administration was similar to that of gavage. Urinary radiochemical profiles were similar between doses, routes, species, and sexes. Among numerous metabolites identified, oxidative metabolites of NBBS predominated.

Synthetic cathinone self-administration in female rats modulates neurotransmitter levels in addiction-related brain regions.

Synthetic cathinones are used for their stimulant-like properties. Stimulant-induced neurochemical changes are thought to occur at different times in different brain regions and neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of α-pyrrolidinopentiophenone (α-PVP) and mephedrone (4MMC) in female rats. Methods probed the chronology of effects of synthetic cathinone exposure. Female rats were trained to self-administer α-PVP, 4MMC, or saline. Drug exposure ceased after 7 days of autoshaping for half of each drug group; the other half self-administered for another 21 days. Amygdala, hippocampus, hypothalamus, PFC, striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Responding was minimal during autoshaping; thus, most infusions were delivered noncontingently in the autoshaping phase. Rats acquired self-administration of α-PVP and 4MMC. Synthetic cathinone administration, and duration of exposure produced several effects on neurotransmitters. α-PVP primarily increased serotonin, 5-hydroxy-3-acetic acid (5-HIAA), norepinephrine, and glutamate in hypothalamus. In contrast, 4MMC decreased serotonin and 5-HIAA in several brain regions. Longer durations of exposure to both synthetic cathinones increased 5-HIAA, norepinephrine, and glutamate in multiple brain regions compared to the short exposure during autoshaping. Notably, both α-PVP and 4MMC produced minimal changes in dopamine levels, suggesting that the dopaminergic effects of these synthetic cathinones are transient. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse.

Toxicokinetics and bioavailability of sulfolane, a ground water contaminant, following oral and intravenous administration in rodents: A dose, species, and sex comparison.

Sulfolane is a ground water contaminant near refinery sites. The objective of this work was to investigate the toxicokinetics and bioavailability of sulfolane in male and female Harlan Hsd:Sprague Dawley® SD® rats and B6C3F1/N mice following a single oral administration of 10, 30, or 100 mg/kg. Sulfolane was rapidly absorbed in rats with the maximum plasma concentration, Cmax, reached at ≤1.47 h. Although Cmax increased proportionally to the dose, the half-life of elimination increased with the dose and the area under the concentration versus time curve (AUC) increased more than proportionally to the dose. In male and female rats, plasma elimination half-life increased with the dose from 1.97 to 6.33 h. Absorption of sulfolane in mice following oral administration was more rapid than in rats with Cmax reached at ≤0.55 h. In addition, mice had a shorter half-life (≤ 1.25 h) and a lower AUC than rats. In male and female mice, both Cmax and AUC increased more than proportionally to the dose. Bioavailability of sulfolane was higher in rats (81-83%) than mice (59-63%) at 10 mg/kg; at 30 and 100 mg/kg, bioavailability >100% in both species and sexes suggesting that the saturation of metabolism and clearance processes of sulfolane may begin at a single oral dose of ~30 mg/kg. There was no apparent sex difference in toxicokinetic parameters of sulfolane in rats and mice. These data demonstrate that sulfolane was well-absorbed following oral administration with high bioavailability in rats and mice with some species differences, but no sex difference.

Disposition of tris(4-chlorophenyl)methanol and tris(4-chlorophenyl)methane in male and female Harlan Sprague Dawley rats and B6C3F1/N mice following oral and intravenous administration.

Tris(4-chlorophenyl)methane (TCPME) and tris(4-chlorophenyl)methanol (TCPMOH) have been detected in various biota and human tissues. The current studies were undertaken to investigate the disposition and metabolism of TCPME and TCPMOH in rats and mice. [14C]TCPME was well absorbed (≥66%) in male rats and mice following a single oral administration of 1, 10, or 100 mg/kg. The excretion of [14C]TCPME-derived radioactivity in urine (≤2.5%) and feces (≤18%) was low. The administered dose was retained in tissues (≥ 64%) with adipose containing the highest concentrations. The metabolism of TCPME was minimal. The disposition and metabolism of [14C]TCPME in females was similar to males. The time to reach maximum concentration was ≤7 h, the plasma elimination half-life was ≥31 h, and the bioavailability was ≥82% following a 10 mg/kg oral dose of [14C]TCPME in male rats and mice. The disposition of [14C]TCPMOH was similar to that of [14C]TCPME. Following an intravenous administration of [14C]TCPME or [14C]TCPMOH in male rats and mice, the pattern of disposition was similar to that of oral administration. In conclusion, both TCPME and TCPMOH are readily absorbed and highly bioavailable following a single oral administration pointing to importance of assessing the toxicity of these chemicals.

Metabolism of 4-methylimidazole in Fischer 344 rats and B6C3F1 mice.

4-Methylimidazole (4-MeI) is a widely used chemical, also identified as a by-product of heating foods. In cancer bioassays, 4-MeI induced lung tumors in mice, but not in rats. To establish if metabolic differences could explain species difference in carcinogenicity, this study investigated metabolism of 4-MeI in rat and mouse lung and liver microsomes and S-9 fractions, and in vivo in rats and mice. No metabolites were detected in rat or mouse lung and liver microsomes, or lung S-9 fractions. Male and female F-344 rats and B6C3F1 mice were administered 50 and 150 mg/kg [14C] 4-MeI by gavage. Excreta, exhaled CO2 and volatiles were collected for 48 h. Elimination was mainly via urine, with 79-89% of the radioactivity in urine in rats and 41-70% in mice. Most of the radioactivity (71-88%) in urine was unchanged 4-MeI. Additional radioactive peaks (the largest metabolite was 8-18%) were characterized by LC-MS/MS as 4-hydroxymethylimidazole, its glucuronide, and other oxidized products, including methylhydantoin. 4-MeI was largely excreted unchanged in rats and mice with limited oxidative metabolism and conjugation. 4-MeI was not oxidized in subcellular fractions from rat and mouse lung and liver. Overall, the metabolism of 4-MeI appeared similar between rats and mice.

Disposition and metabolism of the bisphenol analogue, bisphenol S, in Harlan Sprague Dawley rats and B6C3F1/N mice and in vitro in hepatocytes from rats, mice, and humans.

With the removal of bisphenol A (BPA) from many consumer products, the potential use of alternatives such as bisphenol S (BPS) and its derivatives is causing some concerns. These studies investigated the comparative in vitro hepatic clearance and metabolism of BPS and derivatives and the disposition and metabolism of BPS in rats and mice following gavage and intravenous administration. The clearance of BPS and its derivatives was slower in human hepatocytes than in rodents. In male rats following gavage administration of 50, 150, and 500 mg/kg [14C]BPS the main route of excretion was via urine; the urinary excretion decreased (72 to 48%) and the fecal excretion increased (16 to 30%) with increasing dose. The disposition was similar in female rats and male and female mice following gavage administration. Radioactivity remaining in tissues at 72 h in both species and sexes was ≤2.4%. In bile duct cannulated rats 53% of a gavage dose was secreted in bile suggesting extensive enterohepatic recirculation of [14C]BPS. Following an intravenous dose in rats and mice, the pattern of excretion was similar to gavage. These data suggest that the dose excreted in feces folowing gavage administration is likely the absorbed dose. Urinary metabolites included the glucuronide and sulfate conjugates with a moderate amount of parent. The pattern of in vitro hepatic metabolsim was similar to in vivo with some difference among derivatives. These data suggest that similar to other bisphenol analogues, BPS was well absorbed following oral expsosure and extensively excreted with minimal tissue retention.

Metabolism and disposition of 2-ethylhexyl-p-methoxycinnamate following oral gavage and dermal exposure in Harlan Sprague Dawley rats and B6C3F1/N mice and in hepatocytes in vitro.

1. 2-Ethylhexyl-p-methoxycinnamate (EHMC) is commonly used as an ingredient in sunscreens, resulting in potential oral and dermal exposure in humans. 2. Clearance and metabolism of EHMC in hepatocytes and disposition and metabolism of EHMC in rodents following oral (8-800 mg/kg) intravenous (IV) (8 mg/kg) or dermal (0.8-80 mg/kg representing 0.1-10% formulation concentration) exposure to [14C]EHMC were investigated in rats and mice. 3. EHMC was rapidly cleared from rat and mouse hepatocytes (half-life ≤3.16 min) and less rapidly (half-life ≤48 min) from human hepatocytes. 4. [14C]EHMC was extensively absorbed and excreted primarily in urine by 72 h after oral administration to rats (65-80%) and mice (63-72%). Oral doses to rats were excreted to a lesser extent (3-8%) in feces and as CO2 (1-4%). Radioactive residues in tissues were <1% of the dose. There were no sex or species differences in disposition in rats. 5. Following dermal application, 34-42% of an 8-mg/kg dose was absorbed in rats, and 54-62% in mice in 72-h. 6. Among numerous urinary metabolites associated with hydrolysis of the ester, two potential reproductive and developmental toxicants, 2-ethylhexanol and 2-ethylhexanoic acid were produced by metabolism of EHMC.

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

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. [14 C]HQ administered (0.5, 5 or 50 mg/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 72 h was <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% [14 C]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 5 mg/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.

Dietary administration of diquat for 13 weeks does not result in a loss of dopaminergic neurons in the substantia nigra of C57BL/6J mice.

Male and female C57BL/6J mice were administered diquat dibromide (DQ∙Br2) in their diets at concentrations of 0 (control), 12.5 and 62.5 ppm for 13 weeks to assess the potential effects of DQ on the nigrostriatal dopaminergic system. Achieved dose levels at 62.5 ppm were 6.4 and 7.6 mg DQ (ion)/kg bw/day for males and females, respectively. A separate group of mice was administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) ip as a positive control. The comparative effects of DQ and MPTP on the substantia nigra pars compacta (SNpc) and/or striatum were assessed using neurochemical, neuropathological and stereological endpoints. Morphological and stereological assessments were performed by investigators who were "blinded" to dose group. DQ had no effect on striatal dopamine concentration or dopamine turnover. There was no evidence of neuronal degeneration, astrocytic or microglial activation, or a reduction in the number of tyrosine hydroxylase positive (TH(+)) neurons in the SNpc or neuronal processes in the striatum of DQ-treated mice. These results are consistent with the rapid clearance of DQ from the brain following a single dose of radiolabeled DQ. In contrast, MPTP-treated mice exhibited decreased striatal dopamine concentration, reduced numbers of TH(+) neurons in the SNpc, and neuropathological changes, including neuronal necrosis, as well as astrocytic and microglial activation in the striatum and SNpc.

Systemic uptake, albumin and hemoglobin binding of [(14)C]2,3-butanedione administered by intratracheal instillation in male Harlan Sprague Dawley rats and oropharyngeal aspiration in male B6C3F1/N mice.

2,3-Butanedione (BD) is a reactive diketone in artificial butter flavors that is thought to cause bronchiolitis obliterans in workers in microwave popcorn manufacturing. Bronchiolitis obliterans is generally not diagnosed until irreversible damage has occurred; therefore a biomarker of early exposure is needed. The potential systemic uptake of BD from inhalation exposure has not been evaluated. The objective here was to evaluate the systemic exposure of BD and binding to hemoglobin and albumin. [(14)C]BD was administered to male Harlan Sprague Dawley rats (100 mg/kg, intratracheal instillation) and B6C3F1/N mice (157 mg/kg, oropharyngeal aspiration). Blood and plasma was collected 24 h after administration and analyzed for (14)C content. At 24h, 0.88±0.07% of the administered dose was in rat blood, 0.66±0.06% in rat plasma, 0.38±0.13% in mouse blood and 0.17±0.05% in mouse plasma. Albumin binding in rats was 269±24.2 ng equiv./mg, which accounts for 38% of the radioactivity in plasma. In mice, binding was 85.0±22.3 ng equiv./mg albumin, which accounts for 51% of the radioactivity in plasma. The binding to hemoglobin in rats was 38.2±17.6 ng equiv./mg, and to globin was 29.1±3.96 ng equiv./mg. In mice, the binding to hemoglobin was 16.2±9.0 ng equiv./mg. The site(s) of adduction on hemoglobin and albumin was investigated by mass spectrometry. In rat globin, arginine adducts were detected at R-30 and R-104 of the beta chain in vitro and in vivo. In rat albumin, adducts were detected in vitro on R-219/221, R-360, and R-368, and in vivo on a variety of arginine residues. This study demonstrated that BD enters the systemic circulation and reacts with arginine on hemoglobin and albumin. These results indicate that hemoglobin and albumin adducts may be useful as biomarkers of BD exposure in humans.

Metabolism and disposition of [(14)C]dimethylamine borane in male Harlan Sprague Dawley rats following gavage administration, intravenous administration and dermal application.

1. Dimethylamine borane (DMAB) is used as a reducing agent in the manufacturing of a variety of products and in chemical synthesis. National Toxicology Program is evaluating the toxicity of DMAB in rodents following dermal application. The objective of this study was to evaluate the metabolism and disposition of DMAB in male Harlan Sprague Dawley (HSD) rats. 2. Disposition of radioactivity was similar between gavage and intravenous administration of 1.5 mg/kg [(14)C] DMAB, with nearly 84%-89% of the administered radioactivity recovered in urine 24 h post dosing. At 72 h, only 1% or less was recovered in feces, 0.3% as CO2, and 0.5%-1.4% as volatiles and 0.3%-0.4 % in tissues. 3. The absorption of [(14)C]DMAB following dermal application was moderate; percent dose absorbed increased with the dose, with 23%, 32% and 46% of dose absorbed at 0.15, 1.5 and 15 mg/kg, respectively. Urinary and fecal excretion ranged from 18%-37% and 2%-4% of dose, respectively, and 0.1%-0.2% as CO2, and 1%-3% as volatiles. Tissue retention of the radiolabel was low ∼1%, but was higher than following the gavage or intravenous administration. 4. Following co-adminsitration of DMAB and sodium nitrite by gavage, N-nitrosodimethylamine was not detected in blood or urine above the limit of quantitation of the analytical method of 10 ng/mL. 5. Absorption of DMAB in fresh human skin in vitro was ∼41% of the applied dose: the analysis of the receptor fluid shows that the intact DMAB complex can be absorbed through the skin.