A 90-day subchronic toxicity study and reproductive toxicity studies on ACE-inhibiting lactotripeptide.

In recent years there has been an increasing body of literature describing the antihypertensive effects of peptides produced from milk protein. The tripeptides isoleucine-proline-proline (IPP) and valine-proline-proline (VPP), isolated from hydrolysed casein have been shown to lower blood pressure by inhibiting angiotensin I-converting enzyme (ACE). This has led to the use of these tripeptides, collectively referred to as lactotripeptide (LTP) as ingredients of functional foods intended to help control blood pressure. A programme of studies including a 90-day repeat-dose oral gavage toxicity study in the rat and an embryo-fetal (pre-natal) development study in the rabbit was conducted to ensure the safety of this ACE-inhibiting ingredient. In addition, a non-standard pre- and post-natal development study in the rat was performed. This study included direct dosing of the neonates, and was designed specifically to investigate renal development and to ensure that the bioactive peptides were not associated with the same type of fetopathy exhibited by ACE inhibiting drugs. These studies showed that there were no adverse effects of treatment at the highest doses tested.

Sources of uncertainty in pharmacokinetic prediction.

Assessment of the hazard associated with residues in food animals must be based on an accurate estimate of the residue levels present in the final food product, as well as animal toxicology studies to determine the potential untoward effects of these residues. Extrapolation of residue levels or toxic effects produced by the administration of a chemical in one species to predict residue levels or toxicology that may be produced by lower doses in the same species or by equivalent or lower doses in another species is associated inextricably with knowledge of the pharmacokinetics of the chemical. There are several factors that may influence the pharmacokinetics of xenobiotics which, if left unconsidered, may introduce uncertainty in the predictions of toxicity following any chemical exposure. Two of these factors are dose level and species differences. Because initial toxicity studies are designed to characterize the type of toxicity and to elucidate target organ effects the use of high doses is the accepted practice. However, because biotransformation and excretion of many chemicals are capacity-limited processes, extrapolation of toxicity to lower doses, without adequate pharmacokinetic information at those lower dose levels may result in overestimation of predicted toxicity. Furthermore, determination of tissue residue levels following administration of doses that saturate these processes may result in an overestimation of residues remaining following lower doses. Finally extrapolation of toxicity results across species may result in an over or underestimation of hazard without adequate information on the pharmacokinetics of the chemical in both species.

Pharmacokinetics of 2,4,5-T PGBE ester applied dermally to rats.

The pharmacokinetic profile of the herbicide 2,4,5-T PGBE ester (propylene glycol butyl ether esters of 2,4,5-trichlorophenoxyacetic acid) 14C-labeled in the ring was examined in rats given a single dermal application of 5 mg/kg. The rate of absorption of the ester through the skin was lower than the rate of hydrolysis to 2,4,5-T acid and the rate of excretion of 2,4,5-T in the urine. Urinary excretion of radioactivity was apparently first order with a half-life of approximately 24 h. Clearance of radioactivity from blood plasma, liver kidneys, and the remaining carcass was also apparently first order with half-life values ranging from 25 to 37 h. Six days (144 h) after application of the dose, an average of 98.7 +/- 5.1% of the applied radioactivity was recovered in he urine, and approximately 97% of the urinary radioactivity was identified as 2,4,5-T acid. The tissue-to-plasma ratios of 14C activity in liver and kidney were similar to those observed previously in rats given a single iv dose of 5 mg/kg 2,4,5-T acid. The results of this study indicate that the pharmacokinetic model for 2,4,5-T PGBE ester in rats is similar to that for 2,4,5-T acid. This similarity suggests the chronic exposures to 2,4,5-T acid and its PGBE ester would be toxicologically comparable. The low rate of absorption of the ester through the skin suggests that removal of the ester from the skin by washing after exposure might substantially reduce the dose of 2,4,5-T received by this route. Since the urinary excretion rate of 2,4,5-T in humans is known, a similar pharmacokinetic model for humans may be developed to calculate the absorbed dose of 2,4,5-T based on urinary excretion data.

Quantitative determination of 1,2-dibromo-3-chloropropane in whole rat blood and drinking water by gas chromatography.

1,2-Dibromo-3-chloropropane (DBCP) in an amber-colored liquid that has been used as a soil fumigant for nematodes since 1957 in agricultural cropland. Formulations containing DBCP have been primarily sold under the trademarks Fumazone (Dow Chemical, Midland, MI, U.S.A.) and Nemagon (Shell, THe Hague, The Netherlands). Recent reports have associated exposure to DBCP with disruption of spermatogenesis and azoospermia or oligospermia in male workers. Tests on laboratory animals have indicated that DBCP has an adverse effect on spermatogenesis and leads to testicular atrophy. In support of DBCP studies in animals, an analytical method was developed to determine low-level concentrations of DBCP in whole blood. Previous analytical methods for DBCP in blood required extensive sample preparation and steam distillation which limits the number of analysis per time period. This paper describes a simple gas chromatographic-electron-capture detection (GC-ECD) method that is both specific and sensitive to DBCP blood levels at concentrations as low as 2.28 x 10(-1) ng/ml DBCP. In addition, a quantitative analytical method was developed to measure levels of DBCP in drinking water which parallels the method in blood.

Identification of the major urinary metabolites of acrylonitrile in the rat.

The metabolism of acrylonitrile (AN) in rats was studied in conjunction with toxicological and pharmacokinetic studies to help assess the potential hazard of exposure to AN in the workplace. Rats were administered 30 mg/kg [1-14C] AN or [2,3-14C] AN orally. Radiolabeled metabolites excreted in the urine during the first 16 h were separated by ion-exclusion liquid chromatography and identified (after derivatization) by gas chromatography-infrared spectroscopy and/or gas chromatography-mass spectrometry. Two major urinary metabolites were identified as thiocyanate and N-acetyl-S-(2-cyanoethyl)cysteine. A third was tentatively identified as 4-acetyl-3-carboxy-5-cyanotetrahydro-1,4-2H-thiazine. AN was not detected in the urine. One possible scheme for the AN metabolic pathways is proposed.

The dose-dependent fate of 1,4-dioxane in rats.

A pharmacokinetic study was conducted to determine the fate of dioxane in rats at doses equivalent to those given in toxicological studies conducted previously. The results show that the fate of dioxane in rats is markedly dose-dependent due to a limited capacity to metabolize dioxane to beta-hydroxyethoxyacetic acid (HEAA). The pharmacokinetic data collected in support of these conclusions include plasma concentration-time curves for dioxane given to rats intravenously at dose levels from 3 to 1000 mg/kg and an inhalation study of 50 ppm dioxane vapors for 6 hr. The plasma curves at low doses by each route were linear, with half life values of about 1 hr. As the dose was increased above 10 mg/kg the plasma clearance rate decreased, the fraction of the dose excreted as HEAA decreased, and the fraction of the dose excreted as dioxane per se in the urine and expired in the breath increased. These data could be described by a one-compartment open system model with parallel first order (urinary and pulmonary excretion) and Michaelis-Menten (metabolism) type elimination kinetics. At saturation, the maximum velocity of the metabolism of dioxane ato HEAA was about 18 mg/kg/hr. Multiple daily oral doses of 1000 mg/kg, but not 10 mg/kg, were excreted more rapidly than equivalent single doses, indicating that at high daily doses dioxane induced its own metabolism. The correlation of the dose-dependent fate of dioxane with the results of toxicological studies in rats supports the conclusion that there is an apparent threshold for the toxic effects of dioxane which coincides with saturation of the metabolic pathway for its detoxification.

Quantitative determination of styrene in biological samples and expired air by gas chromatography-mass spectrometry (selected ion monitoring).

Styrene, phenylethylene, is an oily liquid of commercial importance in the manufacture of various plastics, rubbers, resins, and insulating materials. A gas chromatographic-mass spectrometric method is described for the determination of low levels of styrene in biological samples. The procedure utilizes an internal standard and specificity is gained by monitoring selected ions.

Dose-dependent fate of 1,4-dioxane in rats.

A pharmacokinetic study was conducted to determine the fate of dioxane in rats at doses equivalent to those given in toxicological studies conducted previously. The results show that the fate of dioxane in rats is markedly dose-dependent because of a limited capacity to metabolize dioxane to beta-hydroxyethoxyacetic acid (HEAA). The pharmacokinetic data collected in support of these conclusions include plasma concentration-time curves for dioxane given to rats iv at dose levels of 3-1000 mg/kg and for an inhalation study of 50 ppm dioxane vapors for 6 h. The plasma curves at low doses by each route were linear with half-life values of about 1 h. As the dose was increased above 10 mg/kg the plasma clearance rate decreased, the fraction of the dose excreted as HEAA decreased, and the fraction of the dose excreted as dioxane per se in the urine and expired in the breath increased. These data could be described by a one-compartment open system model with parallel first-order (urinary and pulmonary excretion) and Michaelis-Menten (metabolism) elimination kinetics. At saturation, the maximum velocity of metabolism of dioxane to HEAA was about 18 mg/kg . h. Multiple daily oral doses of 1000 mg/kg, but not 10 mg/kg, were excreted more rapidly than equivalent single doses, indicating that at high daily doses dioxane induced its own metabolism. The correlation of the dose-dependent fate of dioxane with the results of toxicological studies in rats supports the conclusion that there is an apparent threshold for the toxic effects of dioxane that coincides with saturation of the metabolic pathway for its detoxification.

Pharmacokinetic and toxicological evaluation of dogs fed 1,2,4,5-tetrachlorobenzene in the diet for two years.

1,2,4,5-Tetrachlorobenzene (TCB), an intermediate in several industrial processes, was administered in the diet to dogs at 5 mg/kg . d for 2 yr, followed by a 20-mo recovery phase. The animals were examined periodically for toxicity; the concentration of TCB in the plasma and fat was measured during the 2 yr of exposure and 20 mo of recovery. After 18 mo of exposure, all clinical chemistry parameters were normal; however, after 24 mo, serum alkaline phosphatase activity and total bilirubin levels were slightly elevated in the dogs dosed with TCB. Both clinical chemistry parameters returned to normal levels within 3 mo of the cessation of exposure. After the 20-mo recovery, gross and histopathologic examination of tissues revealed no morphological changes considered related to the ingestion of TCB. At the end of 2 yr of exposure, TCB had reached 98 and 97% of the calculated steady-state concentrations in fat and plasma, respectively. TCB was eliminated from the fat and plasma with half-life values of 111 and 104 d, respectively. Although there were only small differences in the approach to steady state, differences in the rate of elimination of TCB from fat and plasma resulted in dramatic changes in the fat/plasma ratio of TCB throughout the entire study.

Fate of silvex following oral administration to humans.

The fate of silvex [2-(2,4,5-trichlorophenoxy)propionic acid] was defined in seven men and in one woman following oral administration of 1 mg/kg. No adverse effects were observed. Samples of blood plasma, urine, and feces were collected at designated time intervals through 168 hr. Plasma samples were analyzed for silvex only, while samples of urine and feces were analyzed for silvex, silvex conjugate(s), 2,4,5-trichlorophenol, and 2,4,5-trichlorophenol conjugate(s). Apparent first-order kinetics described the biphasic clearance of silvex from plasma and excretion in urine. The half-life values for clearance of silvex from plasma were 4.0 +/- 1.9 and 16.5 +/- 7.3 hr for the initial and terminal phases, respectively. Peak plasma levels of silvex occurred within 2-4 hr after dosage. Within 24 hr after administration, 65% of the administered dose had been excreted in urine. Silvex was excreted in urine as silvex and silvex conjugate(s). The half-life values for excretion of silvex per se in urine were 5.0 +/- 1.8 and 25.9 +/- 6.3 hr for the two phases, respectively. Small amounts (3.2% or less) of silvex and/or silvex conjugate(s) were eliminated in feces. Recovery of silvex and its conjugate(s) in urine and feces through 168 hr ranged from 66.6 to 95.1% of the administered dose, with a mean value and standard deviation of 80.3 +/- 10.5%. In humans, silvex is readily absorbed after ingestion and subsequently readily excreted, predominantly via the urine.

The fate of 2,4-dichlorophenoxyacetic acid (2,4-D) following oral administration to man.

The pharmacokinetic profile of 2,4-D is defined in man. Five male human volunteers ingested a single dose of 5 mg/kg 2,4-D without detectable clinical effects. Concentration of 2,4-D were determined in plasma in 3 of 5 subjects and in urine in all subjects at intervals after ingestion. The elimination of 2,4-D from plasma in all subjects occurred by an apparent first-order rate process with an average half-life (t1/2) of 11.6 h. All subjects excreted 2,4-D in the urine with an average t1/2 of 17.7 h. Excretion occurred mainly as 2,4-D (82.3%) with smaller amounts excreted as a 2,4-D conjugate (12.8%). Essentially all of the 2,4-D was absorbed from the gastrointestinal tract in man. Clearance of 2,4-D from the plasma and excretion from the body are first-order rate processes. There was no evidence that 2,4-D would accumulate following repeated administration.