p-Phenylenediamine dihydrochloride: comparative disposition in male and female rats and mice

The absorption, distribution, metabolism, and excretion of p-phenylenediamine (PDA) was studied in both sexes of F344 rats and B6C3F1 mice. Absorption of PDA from the gastrointestinal tract was nearly complete in both species, and tissue distribution and excretion were not affected by the route of administration or dose in the range studied. The highest PDA-derived radioactivity was present in muscle, skin, and liver in both species at all time points examined. Both sexes of either species cleared radioactivity from all tissues rapidly, so that in 24 h only 10-15% of the total dose administered was still present in the animal body. Clearance of PDA-derived radioactivity was primarily through urine (68-86%) and secondarily through feces (10-19%). Over 95% of the radioactivity excreted in urine of both species was in the form of metabolites. The major metabolites in male and female rat urine were qualitatively and quantitatively similar, while major quantitative differences were observed between urinary metabolites of male and female mice. Variability in urinary metabolites was observed between the two species. Supplementary experiments have shown that PDA and/or metabolites do not bind covalently to hepatic DNA. However, PDA-derived radioactivity was found to bind with hepatic protein of both sexes of each species.     

2,6-Dichloro-p-phenylenediamine: comparative disposition in male and female rats and mice

2,6-Dichloro-p-phenylenediamine (DPA) was recently reported to induce hepatocellular adenomas and carcinomas in male and female B6C3F1 mice but not in F344 rats. The present investigation of comparative disposition in both sexes of each species was designed to detect species-related variations in DPA disposition that might explain variations in toxicity. Mouse tissues retained higher concentrations of radioactivity at the early time points (15 min and 2 h) than the corresponding rat tissues but were readily cleared at later time points. Elimination of DPA-derived radioactivity by each species was primarily in urine (56-63% of an intravenous dose of 600 mumol/kg body weight) and secondarily in feces (23-31%). Metabolites were qualitatively similar, but varied quantitatively with species. Rats excreted three major and eight minor metabolites in urine, while mice excreted one major and nine minor metabolites. The major metabolite present in mouse urine (61-78% of radioactivity) was approximately two-fold higher than the corresponding major metabolite in rat urine. Efforts to detect covalent binding of DPA and/or metabolites with hepatic DNA indicated no detectable binding in either species. The present study indicates that quantitative variations in disposition and metabolism exist between the two species but does not identify a likely source of species variation in susceptibility to DPA toxicity.     

Comparative disposition and elimination of chlordane in rats and mice

The absorption, distribution and elimination of orally administered cis-[14C]chlordane (1.0 mg/kg) was determined in male Sprague-Dawley rats and C57BL/6JX mice. Absorption appeared somewhat slower in mice, but total [14C]chlordane equivalents at peak blood concentration (113 ng/ml at 8 h) exceeded the maximum which occurred in rats (81 ng/ml at 2 h). Peak tissue residues in both species were observed within 4 h, suggesting that the radiocarbon responsible for the latent peak blood levels in mice was eliminated rather than sequestered by the tissues. This was supported by the findings that peak tissue residue levels were lower in mice, and that the initial fecal elimination rate was higher than in rats. At 12 h, 34% and 7% of the doses were excreted in mouse and rat feces, respectively; by 3 days, both species had voided 83% of the dose in the feces. Clearance rates of tissue residues were markedly faster in the rat, and consequently, the total body burden resulting from chronic exposure to chlordane will be far greater in mice than in rats.     

Metabolic disposition study of chlorinated hydrocarbons in rats and mice

Chlorinated hydrocarbons found in a bioassay to be carcinogenic to both B6C3F1 mice and Osborne-Mendel rats (1,2-dichloroethane), carcinogenic only to mice (1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, hexachloroethane, trichloroethylene, and tetrachloroethylene), and noncarcinogenic to either species (1,1-dichloroethane and 1,1,1-trichloroethane) were used to investigate the biochemical bases for tumorigenesis. Studies were conducted after chronic oral dosing of adult mice and rats with the MTD and 1/4 MTD of each compound. The extent to which the compounds were metabolized in 48 hr, hepatic protein binding, and urinary metabolite patterns were examined. Metabolism of the compounds (mmoles per kg body weight) was 1.7 to 10 times greater in mice than in rats. Hepatic protein binding (nanomole equivalents bound to 1 mg of liver protein) was 1.2 to 8.3 times higher in mice than in rats except for 1,2-dichloroethane and 1,1,1-trichloroethane. The noncarcinogens 1,1-dichloroethane and 1,1,1-trichloroethane exhibited 2 to 18 times more binding in mice than did the carcinogens 1,2-dichloroethane and 1,1,2-trichloroethane. Urinary metabolite patterns of the compounds were similar in both species. The biochemical parameters measured provided no clue to differentiate the carcinogens from the noncarcinogens.     

Metabolism and disposition of 4-t-butylcatechol in rats and mice.

4-t-Butylcatechol (TBC) is an antioxidant used primarily as a polymerization inhibitor for reactive monomers. Annual production and use of TBC in the United States is approximately 1.5 million pounds. The absorption, tissue distribution, metabolism, and excretion of [(14)C]TBC, labeled in the methine carbon, was investigated in male Fischer 344 rats and B6C3F(1) mice after i.v., oral, and dermal administration. Oral (2 and 200 mg/kg in rats; 3 and 300 mg/kg in mice) and dermal (0.6, 6, and 63 mg/kg in rats; 1.3 and 157 mg/kg in mice) doses of TBC were well absorbed, then rapidly metabolized and excreted primarily in urine. Dermal absorption of the highest dose in the rat (87% of the 63 mg/kg dose) was significantly higher than that of the two lower doses (0.6 and 6 mg/kg, 44 and 57%, respectively). Dermally administered TBC was also well absorbed in the mouse (72-86%). Polar metabolites of TBC comprise all of the radioactivity in the urine of both species after all routes of administration. These were shown to consist mostly of the sulfate conjugates (and lesser amounts of the glucuronides) of TBC and of a less polar metabolite. The deconjugated metabolite was isolated and determined by mass spectrometry and (1)H-NMR to be mono-O-methylated TBC.     

Allyl isothiocyanate regulates caspase-1/receptor interacting protein-2 expression

Isothiocyanates can inhibit nuclear factor-kappaB (NF-kappaB) activation. Interleukin (IL)-1β activates the NF-kappaB, which in turn activates proteins involved in inflammation. IL-1β is directly associated with caspase-1 activation. We tested the anti-inflammatory effect of allyl isothiocyanate (AITC) in mast cells. AITC suppressed the intracellular calcium level in the phorbol myristate acetate (PMA) plus calcium ionophore A23187-stimulated human mast cell line. AITC decreased PMA plus A23187-induced cystein-aspartic acid protease (caspase)-1 activity. Particularly, AITC decreased PMA plus A23187-induced caspase-1/receptor interacting protein-2 expression as well as the mRNA expression and production of IL-1β. An in-depth research of the cellular targets of the AITC is warranted.     

Comparative disposition and metabolism of 1,2,3-trichloropropane in rats and mice.

1,2,3-Trichloropropane (TCP) has been used as a solvent and degreasing agent and as an intermediate in pesticide manufacture. TCP is currently the subject of a National Toxicology Program chronic toxicity study. The present study is part of a larger effort to characterize the toxicity of TCP. Following acute oral exposure of male and female F344 rats (30 mg/kg) and male B6C3F1 mice (30 and 60 mg/kg), TCP was rapidly absorbed, metabolized, and excreted. The major route of excretion of TCP was in the urine. By 60 hr postdosing, rats had excreted 50% and mice 65% of the administered dose by this route. Exhalation as 14CO2 and excretion in the feces each accounted for 20% of the total dose in 60 hr rats and 20 and 15%, respectively, in mice. No apparent sex-related differences were observed in the ability of the rats to excrete TCP-derived radioactivity. At 60 hr, TCP-derived radioactivity was most concentrated in the liver, kidney, and forestomach in both rats and male mice. Male mice eliminated TCP-derived radioactivity more rapidly than rats and lower concentrations of radioactivity were found in tissues 60 hr after dosing in mice. Two urinary metabolites were isolated and identified by NMR, mass spectroscopy, and comparison with synthetic standards, as N-acetyl- and S-(3-chloro-2-hydroxypropyl)cysteine. Analyses of the early urine (0-6 hr) showed this mercapturic acid to be the major metabolite in rat urine and was only a minor component in mouse urine. 2-(S-Glutathionyl)malonic acid was identified by NMR and mass spectrometry and by chemical synthesis as the major biliary metabolite in rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

The comparative disposition and metabolism of dolutegravir,a potent HIV-1 integrase inhibitor,in mice,rats, and monkeys

Abstract

1.?Plasma clearance of dolutegravir, an unboosted HIV-1 integrase inhibitor, was low in rat and monkey (0.23 and 2.12?mL/min/kg, respectively) as was the volume of distribution (0.1 and 0.28?L/kg, respectively) with terminal elimination half-life approximately 6?h. Dolutegravir was rapidly absorbed from oral solution with a high bioavailability in rat and monkey (75.6 and 87.0% respectively), but solubility or dissolution rate limited when administered as suspension.

2.?Dolutegravir was highly bound (>99%) to serum proteins in rat and monkey, similar to binding to plasma and serum proteins in human. Radioactivity was associated with the plasma versus cellular components of blood across all species.

3.?Following oral administration to rats, [¹⁴C]dolutegravir-related radioactivity was distributed to most tissues, due in part to high permeability; however, because of high plasma protein binding, tissue to blood ratios were low. In mouse, rat and monkey, the absorbed dose was extensively metabolized and secreted into bile, with the majority of the administered radioactivity eliminated in feces within 24?h.

4.?The primary route of metabolism of dolutegravir was through the formation of an ether glucuronide. Additional biotransformation pathways: benzylic oxidation followed by hydrolysis to an N-dealkylated product, glucose conjugation, oxidative defluorination, and glutathione conjugation.     

Interaction of the isothiocyanate sulforaphane with drug disposition and metabolism: pharmacological and toxicological implications

Isothiocyanates (ITCs) are sulfur-containing compounds that are broadly distributed among cruciferous vegetables such as cabbages and broccoli. The consumption of ITCs is expected to rise due to the use of dietary supplements and public health initiatives promoting the consumption of more fruits and vegetables. Sulforaphane (SFN) is by far the most widely studied and characterized ITC. SFN is extensively metabolized and can therefore compete with other substrates of Phases I, II, III enzymes and transporters. In addition, it has an unusually high potency as an inducer of phase II enzymes and regulates the expression and function of different cytochrome P-450 genes. Such effects can be beneficial and may indicate a mechanism for the preventive role that SFN is believed to play against the degenerative events of aging and chronic diseases. Furthermore, these gene induction effects and the interaction with detoxification responses can modify bioavailability and in vivo bioactivity of drugs. This review will discuss 1) the metabolism of ITCs using SFN as an example, 2) inhibition of drug metabolism by SFN, and 3) induction of drug metabolizing enzymes by SFN. The potential pharmacological and toxicological implications of these effects on drug metabolism will also be discussed.     

Pharmacokinetics of alpha-naphthyl isothiocyanate in rats

Many naturally occurring and synthetic isothiocyanates can inhibit chemical carcinogenesis in animal models. Recently, we found that alpha-naphthyl isothiocyanate (1-NITC) inhibited P-glycoprotein- and multidrug resistance associated protein 1-mediated efflux, indicating the potential application of 1-NITC as a chemosensitizing agent for cancer chemotherapy. The objective of this study was to explore the pharmacokinetic characteristics of 1-NITC in rats. A single dose of 10, 25, 50, or 75 mg/kg of 1-NITC was administered intravenously or orally to female Sprague-Dawley rats (n = 4 for each group). Dose-normalized concentration-time profiles were not superimposable following intravenous or oral dosing, indicating that the disposition of 1-NITC in rats was nonlinear. As doses increased from 10 to 75 mg/kg following iv administration, the total clearance decreased from 2.2 +/- 0.9 to 0.8 +/- 0.3 L/h/kg; oral availability averaged 0.46 for oral doses of 10-75 mg/kg. A nonlinear two-compartment open model with capacity-limited absorption and capacity-limited elimination from the central compartment best fit the data, based on goodness-of-fit criteria. The mechanism underlying the nonlinear elimination of 1-NITC in rats is most likely due to the capacity-limited metabolism of 1-NITC. This study represents the first report of the pharmacokinetics of 1-NITC.     

The disposition of the local anaesthetic, pentacaine, in rats and mice

The pharmacokinetics of pentacaine, a new local anaesthetic agent from the group of carbanilates, was investigated in the rat at a dose of 2 mg kg-1 i.v. and per os. A three-compartment open model gave the best fit to the data. The model parameters are: t1/2 99.0 +/- 14.1 min, Vss 7411.1 ml kg-1, Cl 77.9 ml min-1 kg-1; after oral administration t1/2ab 4.9 +/- 1.9 min, bioavailability 59.1 per cent, and extent of absorption 79.3 per cent. Pentacaine is eliminated almost entirely by metabolism. The metabolites are excreted equally in the urine and faeces at a relatively slow rate. The pharmacokinetics of pentacaine was linear in the dose range 0.008-4 mg kg-1. The whole-body autoradiography in mice showed rapid transfer of 3H radioactivity from the vessels to tissues and a markedly heterogeneous disposition pattern in organs.     

The comparative pharmacokinetics of carboplatin and cisplatin in mice and rats

The plasma, urinary and biliary clearances of cisplatin and its non-nephrotoxic analogue, Carboplatin (cis-diammine-1,1-cyclobutane dicarboxylate platinum II, CBDCA, JM8) have been determined in mice and rats following intravenous administration of the compounds. The plasma concentration-time curves were biphasic during the time period studied (0-60 min), with t1/2 alpha of 2-3 min for both platinum complexes and t1/2 beta of 10-15 min for cisplatin and 25-26 min for Carboplatin. The kinetic rate constants, k12 and k21, were similar for both Carboplatin and cisplatin, indicating that there was no appreciable net accumulation of the compounds in the peripheral tissues. Immediately after administration, Carboplatin became reversibly bound to plasma proteins in vivo to the extent of about 20%. Appreciable irreversible binding appeared after the first 60 min and increased steadily, so that by 4 hr only 34% of the compound was present in the plasma as the free drug. In comparison, binding of cisplatin to plasma was exclusively irreversible and, after the first 10 min, free drug disappeared rapidly, such that by 60 min free platinum was not detectable. The plasma clearance of free cisplatin (26.1 ml/min/kg) was significantly greater than that of either Carboplatin (10.3 ml/min/kg) or insulin (10.1 ml/min/kg). The main route of excretion of the two platinum complexes was via the urine, with 80-90% of Carboplatin and 43-48% of cisplatin being excreted within 4 hr. In the rat, the Carboplatin excreted in the urine was predominantly as the unchanged compound. The renal clearance of cisplatin (12.3 ml/min/kg) was significantly greater than that of either Carboplatin (9.3 ml/min/kg) or insulin (9.6 ml/min/kg), suggesting that cisplatin was excreted by an active renal secretory mechanism whilst Carboplatin was eliminated by glomerular filtration alone. Biliary excretion of the two compounds was only 0.4-1.2% of the administered dose in 6 hr, with biliary clearance of cisplatin (0.27 ml/min/kg) being fivefold greater than that of Carboplatin (0.053 ml/min/kg). The results indicate that the major pharmacokinetic differences between Carboplatin and cisplatin relate to their renal handling and their reactivity with macromolecules. These differences may well underline the substantial lack of Carboplatin nephrotoxicity in comparison with cisplatin.     

Metabolism and disposition of 1-bromopropane in rats and mice following inhalation or intravenous administration

Workplace exposure to 1-bromopropane (1-BrP) can potentially occur during its use in spray adhesives, fats, waxes, and resins. 1-BrP may be used to replace ozone depleting solvents, resulting in an increase in its annual production in the US, which currently exceeds 1 million pounds. The potential for human exposure to 1-BrP and the reports of adverse effects associated with potential occupational exposure to high levels of 1-BrP have increased the need for the development of biomarkers of exposure and an improved understanding of 1-BrP metabolism and disposition. In this study, the factors influencing the disposition and biotransformation of 1-BrP were examined in male F344 rats and B6C3F1 mice following inhalation exposure (800 ppm) or intravenous administration (5, 20, and 100 mg/kg). [1,2,3-(13)C]1-BrP and [1-(14)C]1-BrP were administered to enable characterization of urinary metabolites using NMR spectroscopy, LC-MS/MS, and HPLC coupled radiochromatography. Exhaled breath volatile organic chemicals (VOC), exhaled CO(2), urine, feces, and tissues were collected for up to 48 h post-administration for determination of radioactivity distribution. Rats and mice exhaled a majority of the administered dose as either VOC (40-72%) or (14)CO(2) (10-30%). For rats, but not mice, the percentage of the dose exhaled as VOC increased between the mid ( approximately 50%) and high ( approximately 71%) dose groups; while the percentage of the dose exhaled as (14)CO(2) decreased (19 to 10%). The molar ratio of exhaled (14)CO(2) to total released bromide, which decreased as dose increased, demonstrated that the proportion of 1-BrP metabolized via oxidation relative to pathways dependent on glutathione conjugation is inversely proportional to dose in the rat. [(14)C]1-BrP equivalents were recovered in urine (13-17%, rats; 14-23% mice), feces (<2%), or retained in the tissues and carcass (<6%) of rats and mice administered i.v. 5 to 100 mg/kg [(14)C]1-BrP. Metabolites characterized in urine of rats and mice include N-acetyl-S-propylcysteine, N-acetyl-3-(propylsulfinyl)alanine, N-acetyl-S-(2-hydroxypropyl)cysteine, 1-bromo-2-hydroxypropane-O-glucuronide, N-acetyl-S-(2-oxopropyl)cysteine, and N-acetyl-3-[(2-oxopropyl)sulfinyl]alanine. These metabolites may be formed following oxidation of 1-bromopropane to 1-bromo-2-propanol and bromoacetone and following subsequent glutathione conjugation with either of these compounds. Rats pretreated with 1-aminobenzotriazole (ABT), a potent inhibitor of P450 excreted less in urine (down 30%), exhaled as (14)CO2 (down 80%), or retained in liver (down 90%), with a concomitant increase in radioactivity expired as VOC (up 52%). Following ABT pretreatment, rat urinary metabolites were reduced in number from 10 to 1, N-acetyl-S-propylcysteine, which accounted for >90% of the total urinary radioactivity in ABT pretreated rats. Together, these data demonstrate a role for cytochrome P450 and glutathione in the dose-dependent metabolism and disposition of 1-BrP in the rat.     

A comparative study of the disposition of nicotine and its metabolites in three inbred strains of mice

The disposition of nicotine, cotinine, and nicotine N-oxide was investigated in male C57BL, DBA, and C3H mice following an ip injection of nicotine (1.0 mg/ml). The half-lives (t1/2) of nicotine in blood were 5.9 to 6.9 min. The rapid elimination of nicotine was accompanied by a rapid accumulation of metabolites; maximal concentrations of cotinine in blood (204 to 364 ng/ml) were achieved in 10 min and nicotine N-oxide (23 ng/ml in C3H mice) in 15 min. The t1/2 in blood was 20.1 to 39.8 min for cotinine and 18.4 min for nicotine N-oxide. The t1/2 values for nicotine in brain were similar to those in blood, but the values for liver were slightly larger (6.3 to 9.2 min) and interstrain differences were significant. A large strain-related difference in the t1/2 for cotinine was found; the metabolite was eliminated from the blood of DBA mice at only about one-half the rate determined for the other strains. The t1/2 for nicotine N-oxide in liver ranged from 12.7 to 27.3 min; the values were significantly different with C57BL greater than DBA greater than C3H. Strain-related differences were also observed in response to chronic exposure to cigarette smoke. The t1/2 of injected nicotine appeared to be slightly decreased in C57BL and DBA mice but was increased by 60% in livers of C3H mice compared to a control group.     

Comparative metabolism and disposition of 1-chloro- and 3-chloro-2-methylpropene in rats and mice

A recent 2-year carcinogenicity study found that gavage administration of 3-chloro-2-methylpropene (CMP), containing 5% 1-chloro-2-methylpropene (dimethylvinyl chloride, DMVC), caused forestomach neoplasms in rats and mice. Similar chronic studies revealed that DMVC caused forestomach neoplasms in both rats and mice; neoplasms of the nasal and oral cavities were observed in rats but not in mice. In the current studies we have investigated the metabolic basis of these differences. Daily doses of 150 mg/kg of 2-[14C]DMVC or 2-[14C]CMP were administered to rats for 1, 2, or 4 consecutive days. One daily dose of 150 mg/kg of DMVC was administered to mice. Both DMVC and CMP were rapidly metabolized; however, CMP was cleared at a slightly lower rate. Rats exhaled approximately 25 and 10% of the DMVC and CMP as CO2, respectively. Mice exhaled 25% of the DMVC as CO2. Rats expired 30% of the administered DMVC unchanged in the 24 hr after dosing compared to only 7% of the administered CMP. Mice expired 5% of the administered DMVC in the same time period. This observation may explain the occurrence of tumors in the nasal and oral cavities of rats treated with DMVC but not in rats treated with CMP or in mice treated with DMVC in 2-year carcinogenicity studies. The 24-hr urinary excretion in rats was 35% of the administered DMVC compared to 58% of CMP. Mice excreted 47% of the administered DMVC in 24 hr in the urine. An unusual urinary metabolite of DMVC, 2-amino-6-methyl-4-thia-5-heptene-1,7-dioic acid, was identified.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ethosuximide disposition kinetics in rats

1. Single and multiple dose disposition kinetics of ethosuximide were studied in male Sprague-Dawley rats following intravenous administration. 2. The plasma disappearance of a single 35 mg/kg dose followed for 75 h was not linear. A dose-ranging study suggested that the apparent non-linearity of ethosuximide's plasma disappearance might be due to enzyme induction over time with the drug exhibiting a faster elimination from 24 h onward. 3. Ethosuximide, after only two daily doses of 35 mg/kg/day, shortened pentobarbital-induced sleep in rats. The clearance of ethosuximide was also significantly faster after four daily 35 mg/kg doses than after a single 35 mg/kg dose. 4. Single sample clearance estimates calculated from ethosuximide concentrations prior to enzyme induction, viz. up to 24 h post-dose, were practically identical to multiple sample clearance values. Both single and multiple sample clearances were calculated assuming linear rather than non-linear elimination.     

Long-term disposition of phencyclidine in mice

The disposition of 3H-phencyclidine (PCP), as well as total metabolites, was studied in mice up to 21 days after either iv or po administration. Thirty minutes after either iv or po administration the highest concentrations of 3H-PCP were found in stomach. The next highest levels were in fat (iv), liver (po), and intestines (po) and the lowest levels were found in brain and plasma (iv and po). Twenty-four hours later, the levels of 3H-PCP in all tissues were less than 2% of the concentrations after 30 min. After 3 days, the only detectable levels were in fat, and were less than 1% of the 30-min levels. Trace quantities of 3H-PCP were detected in fat at 7, 14, and 21 days. The disposition of total metabolites differed from that of 3H-PCP in that total metabolite levels were highest in stomach, liver, and intestines 30 min after administration of 3H-PCP by both routes. After 24 hr the concentration of total metabolites in all tissues far exceeded that of 3H-PCP. The highest concentration of metabolites remained in liver, stomach, and intestines for 24 hr, but after 3 days the levels in stomach and intestines fell considerably. Metabolite levels were sustained in lung and liver up to 14 days and in lung up to 21 days. Mice were also treated with seven daily gavages of 3H-PCP to determine the extent of 3H-PCP and metabolite accumulation. 3H-PCP was found only in fat 7, 14, and 21 days after the last treatment, but these levels were quite low. Metabolite levels in lung and liver at all time points were 5-10 times greater than those following acute treatment. 3H-PCP does not appear to be sequestered to an appreciable extent in any tissue in mice, whereas metabolites do accumulate in lung and liver for long periods of time.