Excretion and tissue disposition of dichloroacetonitrile in rats and mice

The excretion and tissue distribution of [1-14C]dichloroacetonitrile and [2-14C]dichloroacetonitrile were studied in male Fischer 344 rats and male B6C3F1 mice. Three dose levels of dichloroacetonitrile (DCAN) (0.2, 2, or 15 mg/kg) were administered to rats and two dose levels of DCAN (2 or 15 mg/kg) to mice. Daily excreta including exhaled volatiles and radiolabeled carbon dioxide (14CO2) were analyzed for radiolabeled carbon (14C) until greater than 70% of the radioactivity was excreted. At that time the animals were sacrificed and tissues were collected. Tissues and excreta were analyzed for 14C by combustion and liquid scintillation counting. Rats administered [1-14C]DCAN excreted 62 to 73% of the 14C in 6 days, with 42 to 45% in urine, 14 to 20% in feces, and 3 to 8% as CO2. Rats administered [2-14C]DCAN excreted 82 to 86% of the 14C in 48 hr, with 35 to 40% in urine, 33 to 34% as CO2, and 10 to 13% in feces. Mice administered [1-14C]DCAN excreted 83 to 85% of the 14C in 24 hr, with 64 to 70% in urine, 9 to 13% in feces, and 5 to 6% as CO2. Mice administered [2-14C]DCAN excreted 84 to 88% of the 14C in 24 hr with 42 to 43% in urine, 8 to 11% in feces, and 31 to 37% as CO2. Liver tissues retained the most 14C in all studies except the study of [1-14C]DCAN in rats, where blood contained the most 14C. These results indicate that DCAN was absorbed rapidly after oral administration in water. The differences in the route of excretion of [1-14C]DCAN compared to [2-14C]DCAN indicated that the molecule was being cleaved in the body and metabolized by different mechanisms.

Examination of the differential hepatotoxicity of diallyl phthalate in rats and mice

In this study we confirmed that diallyl phthalate (DAP) is more hepatotoxic to rats than to mice, and we demonstrated the same species difference in toxicity for allyl alcohol (AA). The data suggest that the toxicity of DAP probably results from AA cleaved from DAP. To determine if the species difference in susceptibility to hepatotoxicity resulted from differences in the disposition and metabolism of DAP, Fischer-344 rats and B6C3F1 mice were given [14C]DAP, 1, 10, or 100 mg/kg po or 10 mg/kg iv, and placed in metabolism cages for 24 hr. In rats, 25-30% of the DAP was excreted as CO2, and 50-70% appeared in the urine within 24 hr. In mice, 6-12% of the DAP was excreted as CO2, and 80-90% was excreted in the urine within 24 hr. Monoallyl phthalate (MAP), allyl alcohol, 3-hydroxypropylmercapturic acid (HPMA), and an unidentified polar metabolite (PM) were found in the urine of rats and mice dosed with DAP. The polar metabolite was present in the urine of rats dosed with DAP or AA, indicating that the compound is a metabolite of AA. There was no difference between the species in the quantity of AA excreted, but mice excreted more MAP (39 vs 33%), HPMA (28 vs 17%), and PM (20 vs 8%) than rats. Because DAP is metabolized to AA, a potent periportal hepatotoxicant, and because the mouse produced more HPMA than rats, we postulate that the differential hepatotoxicity of DAP is related to the extent of glutathione conjugation with allyl alcohol or acrolein (the active metabolite of AA).

Comparative pulmonary toxicity of gallium arsenide, gallium(III) oxide, or arsenic(III) oxide intratracheally instilled into rats

The relative toxicity of gallium arsenide (GaAs) and its metal oxides was assessed by intratracheally instilling particulate suspensions of GaAs (100 mg/kg), equimolar gallium as Ga2O3 (65 mg/kg), or a maximally tolerated nonlethal dose of arsenic as As2O3 (17 mg/kg). Two weeks after dosing, five rats from each group were randomly selected for the biochemical determination of lung lipid, protein, DNA, and collagen (4-hydroxyproline; 4-HP) content. The pulmonary retention of gallium and/or arsenic and the concentration of these metals in blood were also determined. Lungs from the remaining rats (n = 3) were examined histopathologically. Pulmonary exposure to Ga2O3 particulates significantly (p less than 0.05) increased the total lipid content of lungs relative to that observed in the vehicle-treated control animals. This response appeared to be associated with the pulmonary retention of gallium particulates (means = 36% of the gallium dose). In contrast, As2O3 particulates were not retained in the lung. Blood arsenic concentrations were 36 ppm which represented 20% of the total arsenic administered. Treatment with As2O3 significantly elevated lung dry weight as well as protein, DNA, and 4-HP content. These data suggest that As2O3 induced an acute fibrogenic response. The intratracheal instillation of GaAs particulates produced effects similar to those observed with the individual oxides. The total lung content of lipids, protein, and DNA was significantly elevated. These biochemical changes were accompanied by significant increases in lung dry weight and lung wet weight. Lungs from rats receiving GaAs particulates retained 44% of the dose as gallium and 28% of the dose as arsenic at the end of the 14-day study. Blood arsenic concentrations were 44 ppm (7% of the arsenic dose) while gallium was not detected in blood at this time. The primary histopathological observations 14 days after the intratracheal instillation of all metal particulates were an inflammatory response and pneumonocyte hyperplasia. The biological severity of these lesions, in descending order, was GaAs greater than As2O3 much greater than Ga2O3. It must be noted, however, that As2O3 was dosed at 0.25 X moles of GaAs.

Distribution, excretion, and metabolism of butylbenzyl phthalate in the rat

The disposition of butylbenzyl phthalate (BBP), a widely used plasticizer, was evaluated after oral and iv administration to rats. Male Fischer-344 rats were dosed with [14C]BBP at 2, 20, 200, or 2000 mg/kg po or 20 mg/kg iv to determine the effects of dose on rates and routes of excretion. In 24 h, 61-74% of the dose was excreted in the urine and 13-19% in the feces at 2-200 mg/kg. At the 2000-mg/kg dose, 16% of the 14C was excreted in the urine and 57% in the feces. Urinary 14C was composed of monophthalate derivatives (MP: 10-42% of the dose) and glucuronides of these monophthalate derivatives (2-21% of the dose). At 4 h after iv administration of BBP (20 mg/kg), 53-58% of the dose was excreted in the bile of anesthetized rats. No parent compound was found in the bile, but monobutyl phthalate-glucuronide and monobenzyl phthalate-glucuronide (26% and 13% of the dose, respectively) and trace amounts of free monoesters (2% of the dose) and unidentified metabolites (14% of the dose) were present. Although BBP is an asymmetric diester with the potential of forming equal amounts of monobutyl phthalate (MBuP) and monobenzyl phthalate (MBeP), larger quantities of MBuP were formed (MBuP = 44% versus MBeP = 16% of the dose). The half-lives of BBP, MP, and total 14C in blood (20 mg/kg, iv) were 10 min, 5.9 h, and 6.3 h, respectively. This study indicates that BBP is rapidly metabolized and that the major route of excretion of metabolites is biliary. These metabolites are reabsorbed and ultimately eliminated in the urine.

Pharmacokinetics of o-nitroanisole in Fischer 344 rats

The pharmacokinetics and metabolism of o-nitroanisole (ONA) were studied in male Fischer 344 rats. Three dose levels of [14C]ONA (5.0, 50, or 500 mg/kg) were administered orally to rats and daily excreta were analyzed for 14C. Since the highest dose altered the urinary excretion rate of ONA, a dose of 25 mg/kg was used for subsequent pharmacokinetic studies. Following a single 25 mg/kg iv dose of [14C]ONA, blood, tissues, and excreta were collected at times ranging from 15 min to 7 days. Urinary excretion accounted for 82% of the dose by 24 hr and 86% by 7 days. Fecal excretion was 7.5% in 24 hr and 9.0% by 7 days. Fifteen min after ONA administration, most of the 14C content was found in muscle (20%), skin (10%), adipose tissue (6.8%), and blood (6.5%). All other tissues contained less than 5% of the dose. Within 8 hr, less than 1% of the dose was present in any tissue. The initial elimination t1/2 for 14C in all tissues was 1-2 hr and the terminal t1/2 was approximately 4 days. The elimination of parent ONA from blood followed first order biphasic elimination kinetics (initial t1/2 = 30 min; terminal t1/2 = 2.2 hr). Parent ONA was rapidly eliminated from all other tissues in a monophasic manner (t1/2 = 15 min to 2 hr). Skin and fat demonstrated an uptake phase prior to the elimination of parent. Only 0.5% of the dose was excreted as ONA in the urine. Urinary metabolites of ONA were predominantly conjugated compounds (63% as sulfates; 11% as glucuronides).

Pharmacokinetics of 14C-isotretinoin in healthy volunteers and volunteers with biliary T-tube drainage

The pharmacokinetics of isotretinoin and 4-oxoisotretinoin in blood, as well as the blood concentrations and urinary, biliary, and fecal excretion of carbon-14 were studied using liquid scintillation counting techniques and reverse phase HPLC methods following a single 80-mg oral suspension dose of 14C-isotretinoin to four healthy male subjects and two patients with biliary T-tube drainage. Approximately 80% of the dose was recovered as 14C in excreta during the course of the study of which about equal fractions were in the urine and feces. Secondary peaks in blood concentrations of 14C were observed in the healthy subjects whereas they were not seen in the patients with T-tubes. The harmonic mean apparent half-life for isotretinoin in the blood of the healthy subjects was 13.6 hr, whereas the corresponding value for the 14C was 90 hr. Although a rigorous comparison of pharmacokinetic parameters between healthy subjects and T-tube patients was not feasible due to the limited number of subjects studied, comparisons of certain trends in the pharmacokinetic profiles gave some possible insights into the role of biliary excretion and enterohepatic cycling on the disposition of isotretinoin. The data for isotretinoin and 4-oxoisotretinoin coupled with the total carbon-14 data suggest that the oral dose of 14C-isotretinoin is absorbed to a similar extent by the healthy subjects and T-tube patients, whereas T-tube patients clear the drug more rapidly. The biliary excretion and possible enterohepatic circulation of isotretinoin and its metabolites may have significant impact on the pharmacokinetic profile of isotretinoin in man.

In vitro solubility and in vivo toxicity of gallium arsenide

The in vitro solubilities of gallium arsenide (GaAs) and its metal oxides were arsenic(III) oxide greater than GaAs much greater than gallium(III) oxide. GaAs dissolution was also dependent upon the type and concentration of buffer anion. The amount of arsenic dissolved in 12 hr by various aqueous media was 0.2 M phosphate buffer greater than or equal to 0.1 M phosphate buffer greater than Krebs-Hensleit buffer greater than distilled H2O greater than HCl-KCl buffer. GaAs was apparently soluble under in vivo conditions. Blood arsenic concentrations in rats 14 days after intratracheal instillation of 10, 30, or 100 mg/kg GaAs were 5.5, 14.3, and 53.6 micrograms/ml, respectively; gallium was not detected at any doses. An increase in lung wet weight at 14 days was dose dependent with these organs retaining 17 to 42% of the dose as gallium or arsenic. Excretion of gallium and arsenic was limited to the feces. Urinary porphyrin concentrations and body weight, monitored as indices of toxicity, were significantly altered over the 14-day study. The analysis of porphyrins revealed that uroporphyrin replaced coproporphyrin as the primary urinary metabolite. Rats receiving 10, 100, or 1000 mg/kg GaAs po exhibited similar signs of toxicity. Blood arsenic concentrations at 14 days were 3.5, 6.8, and 17.6 micrograms/ml, respectively. Porphyria was increased, and body weight was decreased at 1000 mg/kg GaAs. These values were equivalent to those obtained with an intratracheal dose of 10 to 30 mg/kg GaAs. Our results showed that pulmonary and po exposure to GaAs resulted in systemic arsenic intoxication. The finding that urinary uroporphyrin concentrations were greater than coproporphyrin concentrations may serve as a sensitive indicator for GaAs exposure.

N-(2,3-dimercaptopropyl)phthalamidic acid: protection, in vivo and in vitro, against arsenic intoxication

The ip LD50s of N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) and British Anti-Lewisite (BAL) were 0.819 and 1.48 mmol/kg, respectively, in male albino mice. The ip ED50 of DMPA and BAL for prevention of the lethal effects of 0.15 mmol NaAsO2/kg was 0.022 and 0.169 mmol/kg, respectively. DMPA increased the LD50 of sodium arsenite by approximately 2.5-fold following two ip injections of 0.20 mmol DMPA/kg. The effectiveness of DMPA in reducing the toxicity of NaAsO2 was further demonstrated by its reversal of the sodium arsenite inhibition of pyruvate dehydrogenase multienzyme complex (PDH) activity in vitro. Similarly, in an in vivo experiment in which mice received 0.10 mmol NaAsO2/kg, and 30 min later were given 0.05 or 0.10 mmol/kg DMPA, there was a rapid recovery of PDH activity. The distribution of 74As in the tissues of male New Zealand rabbits was altered following im injection of 0.20 mmol/kg DMPA. Under these conditions, the tissue concentration of 74As was significantly decreased. For all tissues tested, the 74As content decreased by at least 50% as compared to that of untreated controls. DMPA was effective also in increasing both urinary and fecal excretion of arsenic. The stability of aqueous solutions of DMPA varies with the pH of the solution. DMPA is more stable in acid solution.

Disposition of 1,2,3-trichloropropane in the Fischer 344 rat: conventional and physiological pharmacokinetics

To investigate the disposition of 1,2,3-trichloropropane (TCP), [14C]-TCP was administered iv to male Fischer 344 rats. Unchanged TCP and total radiolabel were determined in tissues and excreta at varying intervals after administration. The compound was distributed and eliminated rapidly. Initial and terminal half-lives of unchanged TCP in the blood were 0.29 and 23 hr. Adipose tissue accumulated 37% of the dose within 15 min and retained more of the dose than any other tissue until 4 hr; most (69%) of the radiolabel in adipose tissue through 4 hr was unchanged TCP. After 4 hr, the liver contained the largest fraction of the dose, primarily as metabolites. Thus TCP disappeared from adipose tissue while metabolites appeared in liver and other tissues. Excretion was nearly complete (90% of the dose) in 24 hr and was predominantly via the urine (47% of the dose). Expiration was the only route by which unchanged TCP (5% of the dose) was excreted. In addition, 25% of the dose was expired as carbon dioxide. There were numerous other metabolites, none accounting for more than 10% of the dose. Nonvolatile metabolites were longer lived than the parent compound. On the basis of high water solubility, reaction with 2,4-dinitrofluorobenzene, and diminished radiolabel in bile of glycidol-treated rats, glutathione conjugation is suggested as an important metabolic route for TCP. A physiological pharmacokinetic model was developed to describe the time course of trichloropropane concentration in tissues. The model demonstrates the possibility of using physiological and pharmacokinetic data to predict concentration-time relations for toxic compounds.

An improved wet digestion procedure for the analysis of total arsenic in biological samples by direct hydride atomic absorption spectrophotometry

The presence of dimethylarsinic acid (DMAA) in biological samples can cause an underestimation of total arsenic content when analyzed relative to an inorganic arsenic standard by direct hydride flame atomic absorption spectrophotometry. An acid digestion procedure is described that quantitatively recovers DMAA as well as monomethylarsonic acid, inorganic arsenic(III), and arsenic(V) from aqueous and biological samples. Methylated arsenicals are converted to inorganic arsenic by wet digestion with HNO3, H2SO4, and K2Cr2O7 and subsequently reduced to arsenic(III) with Nal. Arsine is generated with NaBH4 and converted to atomic arsenic following immediate introduction into a nitrogen-entrained air-hydrogen flame. This method produces a linear relationship to absorbance within a mass range of 50 to 300 ng arsenic/arsine reaction. A sensitivity of 2 ng arsenic and a detection limit of 7 ng arsenic/arsine reaction were also obtained. Recovery of DMAA from water, urine, feces, or whole blood ranged from 92 to 105% with a coefficient of variation of 5 to 10%.

DMSA, DMPS, and DMPA--as arsenic antidotes

meso-Dimercaptosuccinic acid (DMSA), 2,3-dimercapto-1-propanesulfonic acid, Na salt (DMPS), and N-(2,3- dimercaptopropyl )- phthalamidic acid (DMPA) are water soluble analogs of 2,3-dimercapto-1-propanol (BAL). The relative effectiveness or therapeutic index of these dimercapto compounds in protecting mice from the lethal effects of an LD99 of sodium arsenite is DMSA greater than DMPS greater than DMPA greater than BAL in the magnitude of 42:14:4:1, respectively. DMPS, DMPA, or DMSA will mobilize tissue arsenic. BAL, however, increases the arsenic content of the brain of rabbits injected with sodium arsenite. These results raise the question as to the appropriateness of BAL as the treatment for systemic arsenic poisoning. Either DMSA or DMPS, when given sc or po, will protect rabbits against the lethal systemic effects of subcutaneously administered Lewisite . DMPS and DMSA have promise as prophylactics for the prevention of the vesicant action of Lewisite . The sodium arsenite inhibition of the pyruvate dehydrogenase (PDH) complex can be prevented and reversed in vitro or in vivo by DMPS, DMSA, DMPA, or BAL. Of them all, DMPS is most potent and BAL appears to be the least potent. The usefulness of all these dimercapto compounds would be enhanced by a careful study of their metabolism and biotransformation. These dimercapto compounds are in a great many respects orphan drugs. At this stage of their development, it is very difficult for the clinician to obtain funds to study them clinically even though they appear to be useful for treatment of poisoning by any one of the heavy metals.

Comparison of 2,2',4,4',5,5'-hexachloro[14C]biphenyl levels in different adipose tissues of dogs and monkeys

The polychlorinated biphenyl isomer, 2,2',4,4',5,5'-hexachloro[14C]biphenyl (2,4,5-HCB) was administered as a single iv dose at 0.6 mg/kg to dogs and monkeys. Adipose tissue, which included omentum, pericardial, perirenal, peritesticular, and subcutaneous fat, and blood were collected at various termination times and analyzed for total 14C and the parent hexachlorobiphenyl (HCB). Significant differences (p less than 0.0005) in the total hexachlorobiphenyl concentration as measured by total radioactivity (14C equivalents) were noted in the various adipose tissues and in the same adipose tissues with time. Peritesticular fat was consistently lower in the concentration of 14C equivalents than the other adipose tissues, which were nearly equal. The concentrations in subcutaneous fat samples were inconsistent. Total 14C equivalent concentrations in the adipose tissues either peaked or reached a maximum at Day 1 and Day 4 for dog and monkey, respectively. However, parent HCB fat/blood ratios continually increased over the time course of the experiment, because concentrations in blood decreased more rapidly than those in adipose tissue.

Toxicity of a phthalate ester in the diet of a penaied shrimp

The toxicity of di-2-ethylhexyl phthalate (DEHP), a ubiquitous environmental pollutant, was measured experimentally as a contaminant in shrimp aquaculture feeds. Diets containing 40 to 50,000 ppm DEHP were fed to Penaeus vannamei for 14 d at 4% body weight/d. DEHP concentrations in shrimp, diet, and water were measured by electron-capture gas chromatography. Whole-body residues in shrimp were 18 ppm at the highest dose, and bioconcentration factors were inversely proportional to dose. DEHP in water was less than or equal to 1.7 ppb for all dose levels. No increased mortality or histopathological alterations were observed at any dose. Absorption of DEHP by P. vannamei was measured in static 24- and 96-h bioassays. Diets enriched with [14C]DEHP to levels of 60, 600, and 6000 ppm were fed at 2% body weight/d. At all dose levels, 3.7% of total radioactivity was measured as body burden in shrimp and 40% as polar species in test water after 96 h. DEHP by oral administration was absorbed, metabolized, and excreted, and this process was linear with dose for the dose range studied.

The effect of intestinal esterase inhibition on the in vivo absorption and toxicity of Di-n-butyl phthalate

Inhibition of intestinal mucosal esterases by S,S,S-tributylphosphorotrithioate (DEF) did not alter the gastro-intestinal absorption of di-n-butyl phthalate (DBP) in the rat. After intragastric administration of [14C]DBP to control and esterase-inhibited animals, the disappearance of 14C from the small intestine and the levels of 14C in the blood were not significantly different in the two groups over the first 4 hr. Peak blood levels of 14C occurred 2 hr after dosing in both groups of rats. The circulating [14C]butyl phthalate in the diester form accounted for less than 5% of the total 14C at 2 hr, regardless of intestinal esterase activity. The remaining 14C was associated with mono-n-butyl phthalate or more polar metabolites. These data suggest an important role for pancreatic esterases, which may be protected from DEF-mediated inhibition by storage in zymogen granules, in the metabolism and absorption of DBP.

The role of food consumption and amino acid uptake in the action of methylmercury on protein synthesis

The effect of methylmercury (MM) on protein synthesis was examined with respect to nutritional deficiency due to decreased food intake, method of amino acid administration, and amino acid uptake. Female rats were administered orally 40 mg MM hydroxide/kg and were compared with both ad libitum and pair-fed control groups. Synthesis of blood, liver, kidney, and cerebellar proteins of pair-fed controls was significantly lower than for ad libitum-fed controls. Relative to ad libitum-fed controls, MM transiently increased synthesis of blood proteins and then decreased it for blood and liver proteins. In contrast, using pair-fed controls, MM increased synthesis of blood and liver proteins. Comparison with either control showed MM to increase protein synthesis in the kidney and decrease it in the cerebellum. Intraperitoneal and intravenous administration of the [14C]amino acids showed similar results. The action of MM on protein synthesis seemed independent of its action on amino acid uptake, since MM did not affect aminoisobutyric acid uptake in the liver and cerebellum and decreased it in the kidney. In summary, we found that the effect of MM on food intake plays a significant role in the action of MM on protein synthesis and must be accounted for with pair-fed controls.

Early indices of methyl mercury toxicity and their use in treatment evaluation

Mercury distribution, food consumption, body weight, and in vivo protein synthesis were compared as criteria for evaluating the efficacy of D-penicillamine (DPA) in treating experimental methyl mercury (MM) intoxication. Female rats were orally administered MM hydroxide at 40 mg/kg and, after a 7- to 8-d latency period, displayed characteristic neurological signs of MM intoxication. Within 24 h of MM exposure food consumption decreased 75% causing a 12-g drop in body weight, and synthesis of whole blood and kidney protein increased. Protein synthesis in liver was increased 39% by MM after 3 d, and that in cerebellum was decreased 15% after 7 d. Treatment with DPA (1.2 g/kg.d sc on d 2, 3, and 4) prevented the appearance of neurological signs. DPA lowered the Hg content of all tissues; restored food consumption of control levels; increased the onset and amount of body weight gain; returned synthesis of blood, liver, and kidney proteins to control levels; and prevented the decrease in protein synthesis in cerebellum. By itself, DPA produced a transitory decrease in both food consumption and body weight, which could be prevented with vitamin B6. Vitamin B6 antagonized DPA's reversal of MM's action on protein synthesis. Furthermore, DPA and/or vitamin B6 had a variety of effects on protein synthesis in control rats. Thus it was not possible to use protein synthesis to predict the efficacy of the combination of DPA and vitamin B6 as found for the parameters of food consumption, body weight, and Hg distribution. Since changes in body weight and food consumption were the earliest and most pronounced and consistent responses to MM and effective DPA treatment, they were considered the best criteria for evaluating treatment efficacy in experimental MM poisoning in rats.

Isolation and identification of the polar metabolites of chlorpheniramine in the dog

The metabolites of chlorpheniramine were isolated from dog urine. After daily repeated dosing with chlorpheniramine, [methylene-14C]chlorpheniramine maleate was given as a tracer and urine was collected until less than 1% of the labeled dose was excreted daily. An average of 54% of the oral radioactive dose was recovered in the urine. In addition to the N-demethylated metabolites, one very polar metabolite accounting for about 18% and two less polar metabolites accounting for a total of about 30% of the total urine radioactivity were isolated. Hydrolysis studies of the most polar metabolite indicated that it was a conjugate, though not a glucuronide or sulfate. The metabolite identified after hydrolysis was 3-(p-chlorobenzyl)-3-(2-pyridyl)propionic acid. One of the two less polar metabolites was identified as the corresponding alcohol. The least abundant metabolite could not be identified.