Excretion Of 14C Research Articles

Abstract P322: Absorption, Metabolism, And Elimination Of Nonsteroidal Mineralocorticoid Receptor Antagonist Ocedurenone In Humans

Objective: Ocedurenone is a novel nonsteroidal mineralocorticoid receptor antagonist under development for the treatment of uncontrolled/resistant hypertension in patients with advanced chronic kidney disease. A phase 1, open-label study was conducted to determine absorption, metabolism, and excretion of 14 C labeled Ocedurenone following a single oral dose in healthy male subjects. Methods: A total of seven healthy subjects between 18 and 55 years of age with a body mass index between 18.0 and 32.0 kg/m 2 were selected and received a single oral dose ocedurenone (5 mg, 100 μCi of [ 14 C]-ocedurenone). Blood, urine and feces samples were collected for determination of ocedurenone in plasma, total radioactivity in whole blood and plasma, and metabolite profiling and identification. Results: Fecal excretion was the predominant route and mean cumulative percent of total radioactivity eliminated via feces was 84.2% (4.23 of 5). Urine excretion was the minor route, only 6.91% (0.347 of 5) of total radioactivity was collected. Ocedurenone geometric mean Cmax, AUC0-tlast and AUC0-∞ were 92.7 ng/mL, 6510 h*ng/mL and 6560 h*ng/mL, respectively. The geometric mean Cmax of total radioactivity in plasma and whole blood was 123 and 71.5 ngEq/g, respectively. The geometric mean AUC0-tlast and AUC0-∞ of total radioactivity in plasma and whole blood were 9660 and 9910 h*ngEq/g and 5240 and 5570 h*ngEq/g, respectively. Mean whole blood/plasma ratio for total radioactivity was 0.562 for AUC0-∞, indicating little association of radioactivity with red blood cells. In addition to parent drug, 12 metabolites were detected in various matrices. Unchanged ocedurenone was major circulating entities, oxidation and dehydrogenation were the major metabolic pathways. One subject experienced 1 mild adverse event. No serious adverse event and all events resolved without intervention. Conclusion: Ocedurenone appears to be safe and well-tolerated after single oral 0.5 mg dose in humans. The primary route of elimination was fecal after steadily absorbed and extensively metabolized primarily through oxidation and dehydrogenation.

A Phase I, Open-Label Trial to Assess the Absorption, Metabolism, and Excretion of (14C)-OPC-61815 in Healthy Male Japanese Subjects

A Phase I, Open-Label Trial to Assess the Absorption, Metabolism, and Excretion of (14C)-OPC-61815 in Healthy Male Japanese Subjects

Vitamin B12 added as a fortificant to flour retains high bioavailability when baked in bread

Vitamin B12 deficiency and depletion are common world-wide, particularly in populations that consume low amounts of animal source foods. WHO and the Food Fortification Initiative recommend that wheat flour be fortified with vitamin B12 in regions where intake of B12 is low. The purpose of this pilot study in five participants was to determine if fortification of flour with B12 produced a bread product with intact B12 still present and to determine if healthy elderly absorb sufficient B12 from bread fortified in this manner. High-purity crystalline 14C-B12 was dissolved in water and added to flour (2 µg B12/100 g flour) in a bread maker and made into rolls (average 1.17 kBq (31.5 nCi) 14C-B12 in a total of 0.8 µg B12 per roll). Excess 14C first appeared in plasma 4 h after ingestion of the 14C fortified bread and plasma levels returned almost to background by 72 h. Measurement of 14C in plasma verified that the dose was absorbed into the systemic circulation. The cumulative % dose recovered in urine was 4.8–37.0% (mean = 20.1%). Most of the 14C label in the stool appeared by day 4, and the cumulative % dose recovered in stool was 24.5–43.0% (mean = 31.8%). Bioavailability among the 5 participants, calculated by subtracting the sum of urinary and fecal 14C excretion from the administered dose, was 28.4–63.7% (mean = 48.0%). This study showed that when B12 is added as a fortificant to flour it survives the fermentation and baking processes, and retains ∼50% bioavailability when fed in small doses to healthy subjects. The Recommended Dietary Allowance of B12 for adults is 2.4 µg/d. This recommendation assumes that usual bioavailability of low doses of the vitamin in the crystalline form is 60%, while for the same amount in foods such as meat and fish it is 50%. Our pilot study shows that B12 added to bread as a fortificant in flour was absorbed as well as it is from endogenous food sources such as meat and fish.

Disposition, profiling and identification of emixustat and its metabolites in humans

1. Emixustat is a small molecule that potently inhibits retinal pigment epithelium 65 isomerohydrolase. Emixustat is in clinical development for the treatment of various retinopathies (i.e. Stargardt disease and diabetic retinopathy).2. A human absorption, distribution, metabolism, and excretion (ADME) study was conducted with a single dose of [14C]-emixustat in healthy male subjects. Total 14C content in plasma, urine, and faeces was determined using accelerator mass spectrometry (AMS), and metabolic profiles in pooled plasma and urine were investigated by both HPLC-AMS and 2D LC-MS/MS.3. After a single, oral 40-mg dose of [14C]-emixustat, recovery of total 14C was nearly complete within 24 h. Urine was the major route of 14C elimination; accounting for > 90% of the administered dose.4. Biotransformation of emixustat occurred primarily at two structural moieties; oxidation of the cyclohexyl moiety and oxidative deamination of the 3R-hydroxypropylamine, both independently and in combination to produce secondary metabolites. Metabolite profiling in pooled plasma samples identified 3 major metabolites: ACU-5124, ACU-5116 and ACU-5149, accounting for 29.0%, 11.5%, and 10.6% of total 14C, respectively. Emixustat was metabolized in human hepatocytes with unchanged emixustat accounting for 33.7% of sample radioactivity and predominantly cyclohexanol metabolites observed.

Human mass balance study and metabolite profiling of 14C-niraparib, a novel poly(ADP-Ribose) polymerase (PARP)-1 and PARP-2 inhibitor, in patients with advanced cancer

SummaryNiraparib is an investigational oral, once daily, selective poly(ADP-Ribose) polymerase (PARP)-1 and PARP-2 inhibitor. In the pivotal Phase 3 NOVA/ENGOT/OV16 study, niraparib met its primary endpoint of improving progression-free survival (PFS) for adult patients with recurrent, platinum sensitive, ovarian, fallopian tube, or primary peritoneal cancer in complete or partial response to platinum-based chemotherapy. Significant improvements in PFS were seen in all patient cohorts regardless of biomarker status. This study evaluates the absorption, metabolism and excretion (AME) of 14C–niraparib, administered to six patients as a single oral dose of 300 mg with a radioactivity of 100 μCi. Total radioactivity (TRA) in whole blood, plasma, urine and faeces was measured using liquid scintillation counting (LSC) to obtain the mass balance of niraparib. Moreover, metabolite profiling was performed on selected plasma, urine and faeces samples using liquid chromatography – tandem mass spectrometry (LC-MS/MS) coupled to off-line LSC. Mean TRA recovered over 504 h was 47.5% in urine and 38.8% in faeces, indicating that both renal and hepatic pathways are comparably involved in excretion of niraparib and its metabolites. The elimination of 14C–radioactivity was slow, with t1/2 in plasma on average 92.5 h. Oral absorption of 14C–niraparib was rapid, with niraparib concentrations peaking at 2.49 h, and reaching a mean maximum concentration of 540 ng/mL. Two major metabolites were found: the known metabolite M1 (amide hydrolysed niraparib) and the glucuronide of M1. Based on this study it was shown that niraparib undergoes hydrolytic, and conjugative metabolic conversions, with the oxidative pathway being minimal.

Fate and uptake of pharmaceuticals in soil-earthworm systems.

Pharmaceuticals present a potential threat to soil organisms, yet our understanding of their fate and uptake in soil systems is limited. This study therefore investigated the fate and uptake of 14C-labeled carbamazepine, diclofenac, fluoxetine, and orlistat in soil–earthworm systems. Sorption coefficients increased in the order of carbamazepine < diclofenac < fluoxetine < orlistat. Dissipation of 14C varied by compound, and for orlistat, there was evidence of formation of nonextractable residues. Uptake of 14C was seen for all compounds. Depuration studies showed complete elimination of 14C for carbamazepine and fluoxetine treatments and partial elimination for orlistat and diclofenac, with greater than 30% of the 14C remaining in the tissue at the end of the experiment. Pore-water-based bioconcentration factors (BCFs), based on uptake and elimination of 14C, increased in the order carbamazepine < diclofenac < fluoxetine and orlistat. Liquid chromatography–tandem mass spectrometry and liquid chromatography–Fourier transform mass spectrometry indicated that the observed uptake in the fluoxetine and carbamazepine treatments was due to the parent compounds but that diclofenac was degraded in the test system so uptake was due to unidentifiable transformation products. Comparison of our data with outputs of quantitative structure−activity relationships for estimating BCFs in worms showed that these models tend to overestimate pharmaceutical BCFs so new models are needed.

Metabolism of propyrisulfuron: 14C excretion, 14C concentration in plasma and tissues, and amount of metabolites in rats

1. Metabolism of a novel sulfonylurea herbicide, propyrisulfuron [1-(2-chloro-6-propylimidazo[1,2-b]pyridazin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea] labeled at the C-1 position of the propyl group and C-5 position of the pyrimidine ring with 14C was investigated after a single oral administration in male and female rats.2. Administered 14C was excreted into the urine (5.7–29.8%) and feces (64.6–97.4%), respectively. 14C concentration in plasma reached a maximum level at 4 to 12 h post-administration and then decreased rapidly with a biological half-life of approximately 23 to 32 h. Total 14C residues in the whole body were <0.1–1.4%, suggesting that the residues were not accumulated in the tissues.3. The amount of metabolites in urine, feces, and bile were quantified using high-performance liquid chromatography (HPLC). There were no differences in metabolites found between male and female rats.4. The absorption for the low dose (5 mg/kg) and the high dose (1000 mg/kg) was estimated to be approximately 90% and 20%, respectively, suggesting a saturable absorption.5. The plasma protein binding in male and female rats was ≥98.8%, suggesting that propyrisulfuron had a strong affinity to plasma proteins.

Disposition of the New Potent Acetylcholinesterase Inhibitor 8-[3-[1-[(3-fluorophenyl)methyl]-4-piperidiny]-1-oxopropyl]-1, 2, 5, 6-tetrahydro-4H-pyrrolo [3, 2, 1-ij] quinolin-4-one (TAK-802) in Rats, Dogs and Monkeys

The pharmacokinetics of TAK-802, a potential agent of amelioration for voiding dysfunction, were investigated in rats, dogs and monkeys after a single oral administration of 14C-labeled TAK-802. The values of the bioavailability for the compound ranged from 10.2 to 19.9% and the extent of absorption of 14C were higher than the values for the bioavailability in the tested animals. TAK-802 and its related compounds distributed widely in the tissues including the target organ, the urinary bladder, in rats. TAK-802 was highly bound to the plasma proteins and the protein-binding % was independent of the spiked concentrations in all the species tested. Meanwhile, the erythrocyte distribution decreased significantly with the increase in the TAK-802 concentrations. After oral dosing, the dosed 14C was predominantly excreted into the feces of the test animals and the hepato-biliary route mainly contributed to the excretion of 14C in rats. The major components of 14C in the plasma and excreta were unidentified polar metabolites in the test animals. These results indicated that TAK-802 was extensively metabolized by first-pass metabolism during the absorption process and its related metabolites were excreted predominantly into the feces via the bile in the test animals. The concentration-dependent erythrocyte distribution was characterized as the most influential property on the pharmacokinetics of TAK-802. For the clinical safety in the development of TAK-802, the effect of the concentration-dependent erythrocyte distribution on the pharmacokinetics of TAK-802 in animals and humans should be addressed.

Absorption, distribution and excretion of 14C-pilocarpine following oral administration to rats.

The absorption, distribution and excretion of pilocarpine (CAS 92-13-7) were studied after single oral doses of 14C-pilocarpine hydrochloride (CAS 54-71-7) to the Sprague-Dawley rat, administered in aqueous solution mainly at a dose level of 0.3 mg/kg. Rats also received single intravenous doses at 0.3 mg/kg so as to compare 14C pharmacokinetics and excretion. The oral 14C-dose was rapidly and almost completely absorbed from the duodenum and small intestine within 30 min in the male rat and 14C concentrations in plasma declined biexponentially with a terminal half-life of about 9 h. Over the oral dosage range studied, i.e. 0.1-1.0 mg/kg, there was no evidence of significant non-proportionality for Cmax of 14C, whereas there was some such evidence for AUG24. Tissue 14C concentrations in male and pregnant female (Day 18) rats peaked at 0.5 h and mostly declined in parallel with those in the plasma. Excluding tissues concerned with drug absorption and elimination, 14C concentrations in most tissues were similar to, or lower than, those in the plasma. The extent of placental transfer of 14C was small and less than 0.09% of a maternal dose reached a foetus. 14C diffused into maternal milk at concentrations similar to those in the plasma. The 14C-dose was rapidly excreted in male rats, mostly in the urine (about 80%) during 6 h post dose. Recoveries of 14C in mass balance (excretion) studies were in the range 96-100%. There were no apparent gender differences in the disposition of 14C-pilocarpine in the rat.

COMPARATIVE BIOKINETICS OF RADIOCARBON INGESTED AS COMPOUNDS OR FOODS IN RATS

The biokinetics of radiocarbon (¹⁴C) in rats continuously ingested in the forms of amino acids (glycine and leucine) or as foods (wheat and rapeseed) were examined and compared with each other. The differences in the biokinetics between ¹⁴C-amino acids and ¹⁴C-foods were observed in the excretion of ¹⁴C in feces and in the incorporation and retention of ¹⁴C in the rat tissues. At the 10 week of continuous ingestion of ¹⁴C-amino acids, the integrated activities of ¹⁴C in all the tissues were within 5% of the ingested activity. The integrated activities in each tissue coming from ¹⁴C-food ingestion were higher by a factor of more than 2 compared to those coming from ¹⁴C-amino acid ingestion. Radiation dose rates estimated at the 10 week showed that the dose rates to the individual tissues coming from ¹⁴C-food ingestion were 2-5 times higher than those coming from ¹⁴C-amino acid ingestion. The difference in the dose rate between ¹⁴C-amino acid and ¹⁴C-food was more significant in adipose tissue by a factor of 7-30.

Organic acid metabolism and root excretion of malate in wheat cultivars under aluminium stress

The effects of aluminium (Al) on the metabolism of organic acids synthesised via nonphotosynthetic carbon fixation in the roots and on malate exudation were investigated in Al-tolerant Shirosanjyaku (SH) and Al-sensitive Chikushikomugi (CK) wheat cultivars labelled with bicarbonate-(14)C. Aluminum triggered the excretion of (14)C into the solution, especially in the SH that excreted 2.5 times more (14)C than the CK. The loss of radioactivity (about 10%) into the solution represented a small drain in the (14)C reserve found in the roots. In the organic acid fraction within the roots, malate contained the greatest amount of (14)C, and this amount decreased rapidly with time in both cultivars. The disappearance of radioactivity in the malate resulted from metabolism and translocation rather than to root efflux. Aluminium decreased the malate concentrations in roots of both cultivars. The Al-sensitive cultivar had higher concentrations of malate regardless of the presence of Al. It was therefore assumed that the decrease of malate concentration in roots under Al stress did not result from the decline in malate synthesis but due to an increase in malate decomposition. This response was interpreted as the result of the Al-induced stress and not as the cause of a differential Al-tolerance between the wheat cultivars. An important component of the differential Al tolerance between SH and CK is the greater ability of the Al-tolerant cultivar to excrete malate from the roots, which is independent of its internal concentration in the roots.

Metabolism of 2,6-Dichloro-4-(3,3-dichloroallyloxy)phenyl 3-[5-(trifluoromethyl)-2-pyridyloxy]propyl Ether (Pyridalyl) in Rats after Repeated Oral Administration and a Simple Physiologically Based Pharmacokinetic Modeling in Brown and White Adipose Tissues

Male and female Sprague-Dawley rats received repeated oral administration of 14C-2,6-dichloro-4-(3,3-dichloroallyloxy)phenyl 3- [5-(trifluoromethyl)-2-pyridyloxy]propyl ether (14C-pyridalyl) at 5 mg/kg/day for 14 consecutive days, and 14C excretion, 14C concentration in tissues, and the metabolic fate were determined. Most 14C was excreted into feces. The 14C concentrations in the blood and tissues attained steady-state levels at days 6 to 10, whereas those in white adipose tissues increased until day 14. Tissue 14C concentrations were highest in brown and white adipose tissue (38.37-57.50 ppm) but were 5.60 ppm or less in all the other tissues. Total 14C residues in blood and tissues on the 27th day after the first administration accounted for 2.6 to 3.2% of the total dose. A major fecal metabolite resulted from O-dealkylation. Analysis of metabolites in tissues revealed that the majority of 14C in perirenal adipose tissue and lungs was pyridalyl, accounting for greater than 90 and 60%, respectively, of the total, whereas a major metabolite in whole blood, kidneys, and liver was a dehalogenated metabolite. The experimental data were simulated with simple physiologically based pharmacokinetics using four-compartment models with assumption of lymphatic absorption and membrane permeability in adipose tissues. The different kinetics in brown and white adipose tissues was reasonably predicted in this model, with large distribution volume in adipose tissues and high hepatic clearance in liver. Sex-related difference of pyridalyl concentration in liver was considered to be a result of different unbound fraction times the hepatic intrinsic clearance (f x CL(int)) of 1.8 and 12 l/h for male and female, respectively.

Oral Administration of Carbon-14 Labeled Cyanocobalamin (14C-Cbl) Reveals Variable Degradation of Vitamin B12 in the Gastrointestinal Tract That Impacts Vitamin B12 Absorption and Status.

Abstract 3018Poster Board II-994Recent evidence from our laboratory and others suggests that a variable portion of ingested cobalamin (Cbl), either crystalline or from food, is degraded in the gastrointestinal tract. We have developed a biosynthetic method to incorporate 14C into the lower axial ligand of cobalamin that has made it possible to study the fate of this vitamin during its passage through the gastrointestinal tract and to assess the presence of Cbl or its breakdown products in biological samples. Following oral administration of an aqueous physiological tracer dose of 14C-Cbl (1.3 μg, 50 nCi), blood, urine, and feces are analyzed for 14C by accelerator mass spectrometry. In 9 subjects, the plasma response was consistent with the expected behavior of peroral Cbl: 14C-Cbl first appeared in the plasma 3h post-dose reaching a peak level within 6-8h. Confirmation that this dose appears bound to the physiological transport protein transcobalamin (TC) was obtained in a subset of subjects by an immunoaffinity method using anti-human TC antibody-coated magnetic beads which selectively bound 95-98% of plasma 14C. Urinary excretion of 14C was maximal in the first 24h, with 14C first appearing in urine as early as 1.5h after dosing. Fecal excretion occurred variably over several days. The amount of 14C found in the urine (10-50% of the dose) was 100-fold greater than in previous reports using 57Co-labeled cyanocobalamin (0.1-0.5%), and fecal excretion was lower than expected (10-20% vs 30-70%). Urinary excretion of 14C was inversely correlated with the peak plasma level of 14C attained (r2=0.610; p<0.001). The bulk of urinary 14C was not associated with intact Cbl and first appeared in the urine before peak 14C levels were attained in the plasma. The peak plasma level of 14C attained also showed a strong positive correlation with plasma holotranscobalamin concentration measured before administration of the 14C-Cbl (r2=0.571; p<0.001). No such correlation was found with total plasma Cbl. In additional experiments on normal volunteers using eggs endogenously labeled with 14C Cbl following intramuscular injection of hens with 14C Cbl, comparably high urinary excretion of 14C was also observed. We conclude that a variable fraction of ingested Cbl is degraded in the gastrointestinal tract of normal individuals. This may be an important determinant of the amount of Cbl absorbed from food or supplement sources. Additionally, our findings suggest that the concentration of holoTC in the plasma reflects absorptive capacity and may therefore be a good surrogate for Cbl absorptive status. Our findings also have implications regarding the bioavailability of Cbl and may inform pending considerations to fortify food supplies with Cbl in order to mitigate the incidence of Cbl deficiency, particularly among the elderly. Intestinal degradation, either microbial or through the action of digestive enzymes, may also be a source of Cbl analogues that have previously been detected in the plasma and tissues. Cbl analogues may interfere with the physiological function of cobalamin, resulting in some of the manifestations of cobalamin deficiency. Disclosures:Green:Vitalea Science: Research Funding. Miller:Vitalea Science: Research Funding. Lee:Vitalea Science: Research Funding. Sutter:Vitalea Science: Research Funding. Allen:Vitalea Science: Research Funding. Dueker:Vitalea Science: Employment.

A Minute Dose of 14C-β-Carotene Is Absorbed and Converted to Retinoids in Humans1–3

Our objective was to quantify the absorption and conversion to retinoids of a 1.01-nmol, 3.7-kBq oral dose of 14C-β-carotene in 8 healthy adults. The approach was to quantify, using AMS, the elimination of 14C in feces for up to 16 d after dosing and in urine for up to 30 d after dosing. The levels of total 14C in undiluted serial plasma samples were measured for up to 166 d after dosing. Also, the levels of 14C in the retinyl ester (RE), retinol (ROH), and β-carotene fractions that were isolated from undiluted plasma using HPLC were measured. The apparent digestibility of the 14C was 53 ± 13% (mean ± SD), based on the mass balance data, and was generally consistent with the area under the curve for zero to infinite period of 14C that was eliminated in the feces collections made up to 7.5 d after dosing. Metabolic fecal elimination, calculated as the slope per day (% 14C-dose/collection from d 7.5 to the final day), was only 0.05 ± 0.02%. The portion of the 14C dose eliminated via urine was variable (6.5 ± 5.2%). Participants [except participant 6 (P6)] had a distinct plasma peak of 14C at 0.25 d post-dose, preceded by a shoulder at ∼0.1 d, and followed by a broad 14C peak that became indistinguishable from baseline at ∼40 d. Plasma 14C-RE accounted for most of the absorbed 14C early after dosing and P1 had the longest delay in the first appearance of 14C-RE in plasma. The data suggest that plasma RE should be considered in estimating the ROH activity equivalent of ingested β-carotene.

Estimation of absorption, retention, and urinary elimination of a single oral high‐dose vitamin A (HD‐VA) supplement or a single oral dose of stable isotope‐labeled (SI‐labeled VA), in 3–4 y old Zambian boys

A recent survey indicates that HD‐VA supplements have no apparent effect on vitamin A (VA) status of Zambian children &lt;5 y of age. We assessed absorption, retention, and urinary elimination of a single HD‐VA supplement (60 mg), or a smaller dose of SI‐labeled VA (5 mg), used to measure vitamin A pool size, in 3–4 y old Zambian boys (n=8), by co‐administering a tracer dose of 14C‐labeled VA (25 nCi) with the HD‐VA or SI‐labeled VA, and collecting 24‐hr stool and urine for 3 and 7 consecutive days respectively, and 24‐hr urine at 4 later time points.Accelerator mass spectrometry was used to measure the cumulative excretion of 14C in stool 2‐d after dosing to estimate absorption, and in urine 3‐d after dosing to estimate retention. The urinary elimination rate (UER) was estimated by plotting 14C in urine vs. time, and fitting an exponential equation to the data; the 2nd coefficient of the final exponential term was used as an estimate of the UER.Estimated absorption, retention and UER of the HD‐VA supplement were 92.0 ± 5.5%, 84.7 ± 4.9%, and 1.8 ± 1.2 %/d respectively (n=4). Estimated absorption, retention, and UER of the SI‐labeled VA were 88.4 ± 4.6%, 82.2 ± 4.6%, and 1.9 ± 0.5 %/d , respectively (n=4). These estimates did not differ in boys who received the HD‐VA supplement or the smaller dose of SI‐labeled VA

Tissue Distribution and Excretion of N-Methyl-2-Pyrrolidone in Male and Female Rats

N-methyl-2-pyrrolidone (NMP) belongs to solvents widely used in the petrochemical industry a well as in the production of pesticides, veterinary drugs and paint removers. NMP is easily absorbed from the respiratory tract, digestive system and through the skin. It is a compound of slight acute toxicity that also displays moderate irritating activity. The aim of this study was to assess tissue distribution and excretion following a single intraperitoneal NMP administration. Tissue distribution and excretion of NMP following administration of a single dose of 250 mg/kg body weight (350 kBq/rat) was investigated using 14C. Blood plasma (6 rats per time point) were sampled up to 72 h after administration and determination of radioactivity. Male and female rats (4 animals per time point) were decapitated at appropriate time intervals and examined tissues were removed for determination of radioactivity. Excretion of 14C in urine and feces were also measured. All radioactivity measurements were carried out using a Rackbetta 1209 (LKB, Sweden) liquid scintillation counter. The highest 14C activity in tissues and internal organs of female and male rats was observed 4 h after administration of the compound. The highest accumulation was detected in the muscles and fat tissue as well as in the liver and testicles. During 72 h following administration, approximately 80% of the dose was excreted in urine. Elimination of the compound in feces was far less significant: only about 5% of the dose was excreted at once. The results of the study indicate that there are no significant differences in 14C-NMP tissue distribution between male and female rats; NMP absorption from the peritoneal cavity to blood is rapid, disappearance from plasma is monophase and kidneys are the main route of excretion of NMP and/or its metabolites from the rat body after administration of a dose equal to 10% of LD50. The ability to accumulate NMP and/or its metabolites in testes and seminal vesicles may be the reason for fertility impairment in male rats observed after repeated exposure to this compound.

Effects of yo-yo diet, caloric restriction, and olestra on tissue distribution of hexachlorobenzene

Chlorinated hydrocarbons are lipophilic, toxic, and persistent in the environment and animal tissues. They enter the body in food and are stored in adipose tissue. Loss of body fat through caloric restriction mobilizes stored lipophilic xenobiotics and results in distribution to other tissues. We have studied the reversibility of this process in mice that followed a regimen of body weight cycling. Weight gain was followed by weight loss, a second gain, and a second loss ("yo-yo diet regimen"). We measured the distribution of orally gavaged [14C]hexachlorobenzene, which is sparingly metabolized. We found that weight cycling has different effects in different organs. Continued weight loss resulted in a threefold increase of 14C amount and concentration in the brain. After weight regain, 14C in the brain decreased but then increased again after a second weight loss. Weight loss resulted in an increase in the concentration of 14C in adipose tissue without changing the total amount in that tissue. Weight loss and regain resulted in an increase of 14C in the liver, which reflected an increase of fat in the liver. The regimen of weight gain and loss was repeated in mice gavaged with [14C]hexachlorobenzene, with one group receiving the nonabsorbable fat olestra in the diet. Combined dietary olestra and caloric restriction caused a 30-fold increase in the rate of excretion of 14C relative to an ad libitum diet or a reduced caloric diet alone. Distribution of 14C into the brain resulting from the restricted diet was reduced by 50% by dietary olestra.

Absorption, distribution, metabolism and excretion of the cholecystokinin-1 antagonist dexloxiglumide in the rat.

Single oral doses of 14C-dexloxiglumide were rapidly and extensively absorbed in rats, and eliminated more slowly by females than by males. The respective half-lives were about 4.9 and 2.1 h. Following single intravenous doses, dexloxiglumide was characterised as a drug having a low clearance (6.01 and about 1.96 ml/min/kg in males and females respectively), a moderate volume of distribution (Vss, 0.98 and about 1.1 L/kg in males and females respectively) and a high systemic availability. It was extensively bound to plasma proteins (97%). Dexloxiglumide is mainly cleared by the liver. Its renal clearance was minor. In only the liver and gastrointestinal tract, were concentrations of 14C generally greater than those in plasma. Peak 14C concentrations generally occurred at 1-2 h in males and at 2-4 h in females. Tissue 14C concentrations then declined by severalfold during 24 h although still present in most tissues at 24 h but only in a few tissues (such as the liver and gastrointestinal tract) at 168 h. Decline of 14C was less rapid in the tissues of females than in those of males. Single intravenous or oral doses were mainly excreted in the faeces (87-92%), mostly during 24 h and more slowly from females than from males. Urines contained less than 11% dose. Mean recoveries during 7 days when 14C was not detectable in the carcass except in one female rat ranged between 93-101%. Biliary excretion of 14C was prominent (84-91% dose during 24 h) in the disposition of 14C which was also subjected to facile enterohepatic circulation (74% dose). Metabolite profiles in plasma and selected tissues differed. In the former, unchanged dexloxiglumide was the major component whereas in the latter, a polar component was dominant. Urine, bile and faeces contained several 14C-components amongst which unchanged dexloxiglumide was the most important (eg. up to 63% dose in bile). LC-MS/MS showed that dexloxiglumide was metabolised mainly by hydroxylation in the N-(3-methoxypropyl)pentyl sidechain and by O-demethylation followed by subsequent oxidation of the resulting alcohol to a carboxylic acid.

The absorption, distribution and excretion of 1- and 2-[ 14C]palmitoyl triacyglycerols in the rat

Human breast milk is rich in 2-palmitoyl 1,3 unsaturated triacyglycerols and during the neonatal period, when milk is the sole source of nutrients, their role could be particularly important. Betapol is a novel triacylglycerol mix resembling human breast milk in its high palmitic acid content and positional distribution. The total fat absorption from Betapol has been shown to be higher than fat from conventional infant milk formulas and closer to human breast milk in infants. However, the relative fate of purified palmitic acid esterified to glycerol in the 1-, 3- and 2-positions in neonatal and young animals has not previously been established. Therefore, the fate of orally administered 1-[1- 14C]palmitoyl, 2,3 dioleoyl glycerol ([ 14C]POO) and 1,3 dioleoyl,2-[1- 14C]palmitoyl glycerol (O[ 14C]PO) was investigated in suckling and weanling rats using liquid scintillation counting of tissues and expired air and whole-body autoradiography. The results obtained indicate that orally administered [ 14C]POO and O[ 14C]PO are extensively absorbed from the gut, probably either as palmitic acid or as a palmitoyl glyceride in both suckling and weanling rats. Radioactivity initially concentrated in brown fat with apparent migration to the white fat of weanling rats by 96 h. Levels of 14C were low in blood, brain and other tissues. Excretion of 14C was mainly by expiration of CO 2 (approximately 72% in 96 h), indicating β-oxidation as a major route of metabolism. Urine and faeces accounted for only approximately 6% of the excreted radioactivity. The design and size of the experiment did not allow tests of statistical significance between the absorption and excretion of OPO and POO to be conducted. However, the absorption, distribution, β-oxidation and excretion appeared to be similar.

Placental transfer and pharmacokinetics of a single oral dose of [14C]p-nitrophenol in rats.

The pharmacokinetics and placental transfer of a single oral dose of 100 mg/kg (10 microCi/kg, 16% of acute oral LD50) of uniformly phenyl-labeled [14C]p-nitrophenol were investigated in pregnant Sprague-Dawley rats at 14-18 days of gestation. Three animals were killed on gestation day 18, at 0.5, 1, 2, 4, 12, 24, and 48 h after dosing. Radioactivity was rapidly absorbed and distributed throughout the maternal and fetal tissues. The gastrointestinal tract contents retained 20% and 2% of the dose at 0.5 h and 4 h after dosing. The peak maternal plasma concentration of radioactivity (microg p-nitrophenol equivalent/ml) was 7.17 compared with 0.37 for fetal plasma at 0.5 h. Maximum concentration of radioactivity (microg p-nitrophenol equivalent/g fresh tissue) was detected in most tissues 0.5 h after dosing and was in descending order: kidney 23.27, liver 12.37, placenta 3.56, fetus 2.17, and brain 1.99. Radioactivity was eliminated from plasma and all tissues beiexponentially. The half-lives of elimination of 14C were 34.65 h and 69.30 h for maternal and fetal plasma, respectively. p-Nitrophenol, detected by HPLC, was the major compound identified in plasma and tissues. While p-nitrophenol disappeared biphasically from maternal plasma and kidney, it was eliminated monophasically from brain, placenta, and liver. p-Nitrocatechol and p-aminophenol were detected in the liver with peak concentrations at 0.5 h of 1.13 and 1.00 microg/g fresh tissue, respectively. While the change in the concentration of p-nitrocatechol with time was monophasic, that of p-aminophenol showed a biphasic pattern with elimination half-lives of 1.93 h and 4.95 h, respectively. Radioactivity was rapidly excreted in the urine mostly as polar metabolites, while only 3% of the dose was recovered in the feces. Radioactive materials excreted in the urine comprised: glucuronides 4%, sulfates 8%, hot-acid hydrolysates 11%, nonconjugated compounds 16%, and water-soluble metabolites 61%. This study demonstrated that although orally administered p-nitrophenol is a rapidly absorbed and excreted compound, it is transported to the maternal brain and the fetus and may pose a health risk following exposure to toxic doses during pregnancy.