Pharmacokinetics of ethylene glycol. II. Tissue distribution, dose-dependent elimination, and identification of urinary metabolites following single intravenous, peroral or percutaneous doses in female Sprague-Dawley rats and CD-1 mice

Glycolate is a Novel Marker of Vitamin B2 Deficiency Involved in Gut Microbe Metabolism in Mice

Microbes in the human gut play a role in the production of bioactive compounds, including some vitamins. Although several studies attempted to identify definitive markers for certain vitamin deficiencies, the role of gut microbiota in these deficiencies is unclear. To investigate the role of gut microbiota in deficiencies of four vitamins, B₂, B₆, folate, and B₁₂, we conducted a comprehensive analysis of metabolites in mice treated and untreated with antibiotics. We identified glycolate (GA) as a novel marker of vitamin B₂ (VB2) deficiency, and show that gut microbiota sense dietary VB2 deficiency and accumulate GA in response. The plasma GA concentration responded to reduced VB2 supply from both the gut microbiota and the diet. These results suggest that GA is a novel marker that can be used to assess whether or not the net supply of VB2 from dietary sources and gut microbiota is sufficient. We also found that gut microbiota can provide short-term compensation for host VB2 deficiency when dietary VB2 is withheld.

Acute and 28-Day Repeated Inhalation Toxicity Study of Glycolic Acid in Male Sprague-Dawley Rats

BACKGROUND/AIM

The use of glycolic acid is present in a variety of consumer products, including medicines, cleaners, cosmetics, and paint strippers. It has recently led to concerns about toxicity from inhalation exposure. Herein, the pulmonary toxicity of glycolic acid was investigated in rats.

MATERIALS AND METHODS

We conducted acute (~458 mg/m³) and sub-acute (~49.5 mg/m³) inhalation tests to identify the potential toxicities of glycolic acid.

RESULTS

Inhalation exposure to glycolic acid in the acute and subacute inhalation tests did not cause any specific changes in clinical examinations, including body weight, organ weight, hematology, serum biochemistry, and histopathology. The polymorphonuclear neutrophils (PMNs) and inflammatory cytokines in Bronchoalveolar lavage fluid (BALF) increased in rats exposed to single and repeated inhalations. In the sub-acute test, the changes induced by glycolic acid were minor or returned to normal during the recovery period.

CONCLUSION

The No Observed Adverse Effect Concentration (NOAEC) for the nasal and pulmonary toxicity of glycolic acid was determined to be over 50 mg/m³ at the end of a 28-day inhalation test in male rats.

A toxicological review of the ethylene glycol series: Commonalities and differences in toxicity and modes of action

This review summarizes the hazards, exposure and risk that are associated with ethylene glycols (EGs) in their intended applications. Ethylene glycol (EG; CAS RN 107-21-1) and its related oligomers include mono-, di-, tri-, tetra-, and penta-EG. All of the EGs are quickly and extensively absorbed following ingestion and inhalation, but not by the dermal route. Metabolism involves oxidation to the mono- and dicarboxylic acids. Elimination is primarily through the urine as the parent compound or the monoacid, and, in the case of EG, also as exhaled carbon dioxide. All EGs exert acute toxicity in a similar manner, characterized by CNS depression and metabolic acidosis in humans and rodents; the larger molecules being proportionally less acutely toxic on a strict mg/kg basis. Species differences exist in the metabolism and distribution of toxic metabolites, particularly with the formation of glycolic acids and oxalates (OX) from EG and diethylene glycol (DEG); OX are not formed to a significant degree in higher ethylene glycols. Among rodents, rats are more sensitive than mice, and males more sensitive than females to the acute and repeated-dose toxicity of EG. The metabolic formation of glycolic acid (GA), diglycolic acid (DGA), and OX are associated with nephrotoxicity in humans and rodents following single and repeated exposures. However, physiological and metabolic differences in the rate of formation of GA, DGA and OX and their distribution result in EG and DEG causing embryotoxicity in rats, but not rabbits. This rodent-specific sensitivity indicates that EG and its higher oligomers are not anticipated to be embryotoxic in humans at environmentally relevant doses. None of the compounds present developmental toxicity concerns at doses that do not also cause significant maternal toxicity, nor do any of the EGs cause adverse effects on fertility. The EGs are neither genotoxic nor carcinogenic. A read-across matrix is presented, which considers the common and distinct toxicological properties of each compound. It is concluded that EGs pose no risk to human health as a result of their intended use patterns.

Dermal penetration of ethylene glycol through human skin in vitro

This study was conducted to determine the in vitro dermal absorption of ethylene glycol (EG) through dermatomed human abdominal skin (containing epidermis and dermis), obtained from cadavers within 24 hours of death and kept frozen until processed. Three formulations of EG (neat, 50%, and 10% aqueous solutions) were applied in triplicate to skin samples from 6 donors, and placed in Teflon Bronaugh flow-through diffusion cells. Barrier integrity of each sample was evaluated with (3)H-H(2)O prior to applying EG and only data from samples passing the test were used. A physiological receptor fluid was pumped beneath the skin samples and collected in a fraction collector at predetermined time points through 24 hours. Possible volatilized EG was trapped in a charcoal basket located above each skin sample. Each skin sample was treated with an infinite dose of 500 microL of EG formulation/cm(2). At the end of 24 hours, volatilized EG trapped in the headspace was collected, the unabsorbed dose was removed from the skin and the skin was rinsed, tape stripped, and solubilized along with a rinse of the flow-through cells, and total radioactivity was determined. Only a small fraction (</=1%) of the applied EG was absorbed in 24 hours, of which <0.7% penetrated through the skin and ~0.4% remained in the skin. Recovery (mass balance) of the applied EG was between 93% and 99%, which further validated the observed low dermal penetration of EG. The net penetration of the applied EG over 24 hours was concentration proportional, comprising 2.97 +/- 0.78, 1.75 +/- 0.62, and 0.23 +/- 0.12 mg/cm(2) of the neat, 50%, and 10% formulations, respectively. The steady-state flux of EG was established between 16 and 24 hours. The mean steady-state flux of EG through dermatomed skin was 217, 129, and 15 microg/cm(2)h for the neat, 50%, and 10% aqueous formulations, respectively, consistent with concentration-proportional penetration of EG. The steady-state permeation coefficient (Kp) for EG was low, between 1.5 x 10(-4) and 2.6 x 10(-4) cm/h. These findings demonstrate that EG dermal penetration is expected to be very low and to be slow, indicating very limited systemic or internal dose of EG due to dermal exposure.

Comparison of the metabolism of ethylene glycol and glycolic acidin vitroby precision-cut tissue slices from female rat, rabbit and human liver

1. The metabolism of [1,2-(14)C]-ethylene glycol and [1,2-(14)C]-glycolic acid was studied in vitro using precision-cut tissue slices prepared from the livers of female Sprague-Dawley rats, New Zealand white rabbits and humans. The time-course for production of metabolites formed from ethylene glycol at concentrations from 3 to 40 mM was determined to compare quantitatively the differences between species in the rates and amounts of formation of glycolic acid, the presumed developmental toxicant of ethylene glycol. The rates of metabolism of glycolic acid to glyoxylic acid at concentrations from 0.05 to 16 mM by liver tissue from the different species were also determined. The apparent V(max)/K(m) for the metabolic conversions of ethylene glycol to glycolic acid and for glycolic acid to glyoxylic acid in liver tissue from the different species were obtained. 2. There were qualitative differences in the metabolic profiles and quantitative differences in the formation of glycolic acid between the mammalian liver systems. There was an average of 10-fold less glycolic acid produced by liver slices from rabbits compared with rats. With the human liver, the formation of glycolic acid was not detectable using tissue from three of four human donors. A low level of glycolic acid was detected in one liver slice incubation from one of the four subjects, but only at one extended time point; glyoxylate was detected with liver slices from all four humans. 3. Liver slices prepared from female Sprague-Dawley rats, female New Zealand White rabbits and three female human subjects all metabolized glycolic acid to glyoxylic acid. Human liver tissue was the most effective at further metabolizing glycolic acid to glyoxylic acid. The ratios of V(max)/K(m), representing the relative clearance of glycolic acid from liver tissue, were approximately 14:9:1 for human, rat and rabbit liver, respectively. 4. Precision-cut liver slices maintained in dynamic organ culture are good predictors of metabolism by liver tissue in vivo. The results of the present study therefore indicate that levels of glycolic acid, if formed in vivo, following exposures to similar concentrations of ethylene glycol, would be lower in humans than in rabbits and rats.

Strain differences in urinary factors that promote calcium oxalate crystal formation in the kidneys of ethylene glycol-treated rats

Ethylene glycol (EG)-induced hyperoxaluria is the most commonly employed experimental regimen as an animal model of calcium oxalate (CaOx) stone formation. The variant sensitivity to CaOx among different rat strains has not been fully explored, although the Wistar rat is known to accumulate more CaOx in kidney tissue after low-dose EG exposure than in the Fischer 344 (F344) rats. Supersaturation of CaOx in tubular fluid contributes to the amount of CaOx crystal formation in the kidney. We hypothesized that the urinary supersaturation of CaOx in Wistar rats is higher than that of F344 rats, thereby allowing for greater CaOx crystal deposition in the Wistar rat. Age-matched male Wistar and F344 rats were treated with 0.75% EG or drinking water for 8 wk. Twenty-four-hour urine was collected at 0, 2, 4, 6, and 8 wk for analysis of key electrolytes to calculate the CaOx supersaturation. Plasma oxalate level was also measured. Our data confirmed the different sensitivity to renal toxicity from EG between the two rat strains (Wistar > F344). After EG treatment, the plasma oxalate level and urine oxalate excretion were markedly greater in the Wistar rats than in the F344 rats, while urine calcium was slightly decreased in Wistars. Thus, the CaOx supersaturation in urine of Wistar rats was higher, which led to a greater crystal deposition in kidney in Wistar rats. These studies suggest that during EG treatment, changes in urine electrolytes and in CaOx supersaturation occur to a greater extent in the Wistar rat, in agreement with its greater sensitivity to EG toxicity.

Species-specificity of ethylene glycol-induced developmental toxicity: toxicokinetic and whole embryo culture studies in the rabbit

High-dose gavage exposure to ethylene glycol (EG) is teratogenic in rats, but not rabbits. To investigate the reason for this species difference, toxicokinetic and whole embryo culture (WEC) studies were conducted in gestation day 9 New Zealand White rabbits, and the data compared to very similar data previously generated in pregnant rats. In the toxicokinetic study, maximal levels of unchanged EG in rabbits were comparable to those reported for rats. However, maximal levels of EG's teratogenic metabolite, glycolic acid (GA), in rabbit maternal blood and embryo were only 46% and 10% of the respective levels in rats. The toxicokinetic profile suggested that the lower GA levels in rabbits were due to a slower rate of maternal metabolism of EG to GA, slow uptake of GA into the yolk sac cavity fluid which surrounds the embryo, and negligible transfer via the visceral yolk sac (VYS) placenta. In the WEC study, exposure of rabbit conceptuses to high concentrations (< or = 12.5 mM) of GA was without effect, which contrasts with reported effects in rat WEC at > or = 3 mM. Overall, these data implicate toxicokinetics as an important factor underlying the species difference, although intrinsic insensitivity of the rabbit embryo might also be involved. Integration of these findings with published human data suggest that the rabbit is the more relevant model for human EG exposure, based on the negligible role of the rabbit VYS in placental transfer (humans lack a VYS) and similar rates of EG metabolism and extraembryonic fluid turnover.

Mode of Action: Oxalate Crystal-Induced Renal Tubule Degeneration and Glycolic Acid-Induced Dysmorphogenesis—Renal and Developmental Effects of Ethylene Glycol

Ethylene glycol can cause both renal and developmental toxicity, with metabolism playing a key role in the mode of action (MOA) for each form of toxicity. Renal toxicity is ascribed to the terminal metabolite oxalic acid, which precipitates in the kidney in the form of calcium oxalate crystals and is believed to cause physical damage to the renal tubules. The human relevance of the renal toxicity of ethylene glycol is indicated by the similarity between animals and humans of metabolic pathways, the observation of renal oxalate crystals in toxicity studies in experimental animals and human poisonings, and cases of human kidney and bladder stones related to dietary oxalates and oxalate precursors. High-dose gavage exposures to ethylene glycol also cause axial skeletal defects in rodents (but not rabbits), with the intermediary metabolite, glycolic acid, identified as the causative agent. However, the mechanism by which glycolic acid perturbs development has not been investigated sufficiently to develop a plausible hypothesis of mode of action, nor have any cases of ethylene glycol-induced developmental effects been reported in humans. Given this, and the variations in sensitivity between animal species in response, the relevance to humans of ethylene glycol-induced developmental toxicity in animals is unknown at this time.

Inhalation and epidermal exposure of volunteers to ethylene glycol: kinetics of absorption, urinary excretion, and metabolism to glycolate and oxalate

Ethylene glycol (EG) is a widely used liquid. Limited data are published regarding inhaled EG and no data regarding transdermal EG uptake in humans. In order to gain information on the quantitative fate of EG, four male volunteers inhaled between 1340 and 1610 micromol vaporous 13C-labeled EG (13C2-EG) for 4h. Separately, three of these subjects were epidermally exposed for up to 6h to liquid 13C2-EG (skin area 66 cm2). Plasma concentrations and urinary amounts of 13C2-EG were determined by gas chromatography with mass selective detection. Additionally, plasma was assayed for 13C-labeled glycolic acid 13C2-GA) and urine for 13C2-GA and 13C-labeled oxalic acid (13C2-OA). Both EG metabolites were nephrotoxic in animals and humans and embryotoxic in rodents. 13C-labels enabled to differentiate from also determined endogenous EG, glycolic acid (GA), and oxalic acid (OA). Of 13C2-EG inhaled, 5.5+/-3.0%, 0.77+/-0.15%, and 0.10+/-0.12% were detected in urine as 13C2-EG, 13C2-GA, and 13C2-OA, respectively. The skin permeability constant of liquid EG was 2.7 x 10(-5)+/-0.5 x 10(-5)cm/h. Of the dose taken up transdermally, 8.1+/-3.2% and up to 0.4% were excreted in urine as 13C2-EG and 13C2-GA, respectively. It is calculated that equally long-lasting exposure to 10 ppm vaporous EG or wetting of both hands by liquid EG leads to about the same body burden by EG and metabolites. The amounts of GA and OA excreted daily in urine as a result of exposure (8h/day) to 10 ppm EG are about 15% and 2%, respectively, of those excreted from naturally occurring endogenous GA and OA.

Ethylene glycol induces hyperoxaluria without metabolic acidosis in rats

Ethylene glycol (EG) consumption is commonly employed as an experimental regimen to induce hyperoxaluria in animal models of calcium oxalate nephrolithiasis. This approach has, however, been criticized because EG overdose induces metabolic acidosis in humans. We tested the hypothesis that EG consumption (0.75% in drinking water for 4 wk) induces metabolic acidosis by comparing arterial blood gases, serum electrolytes, and urinary chemistries in five groups of Sprague-Dawley rats: normal controls (CON), those made hyperoxaluric (HYP) with EG administration, unilaterally nephrectomized controls (UNI), unilaterally nephrectomized rats fed EG (HRF), and a metabolic acidosis (MA) reference group imbibing sweetened drinking water (5% sucrose) containing 0.28 M NH4Cl. Arterial pH, plasma bicarbonate concentrations, anion gap, urinary pH, and the excretion of titratable acid, ammonium, phosphate, citrate, and calcium in HYP rats were not significantly different from CON rats, indicating that metabolic acidosis did not develop in HYP rats with two kidneys. Unilateral nephrectomy alone (UNI group) did not significantly affect arterial pH, plasma bicarbonate, anion gap, or urinary pH compared with CON rats; however, HRF rats exhibited some signs of a nascent acidosis in having an elevated anion gap, higher phosphate excretion, lower urinary pH, and an increase in titratable acid. Frank metabolic acidosis was observed in the MA rats: decreased arterial pH and plasma HCO3−concentration with lower urinary pH and citrate excretion with elevated excretion of ammonium, phosphate and, hence, titratable acid. We conclude that metabolic acidosis does not develop in conventional EG treatments but may ensue with renal insufficiency resulting from an oxalate load.

Development of a Physiologically Based Pharmacokinetic Model for Ethylene Glycol and Its Metabolite, Glycolic Acid, in Rats and Humans

An extensive database on the toxicity and modes of action of ethylene glycol (EG) has been developed over the past several decades. Although renal toxicity has long been recognized as a potential outcome, in recent years developmental toxicity, an effect observed only in rats and mice, has become the subject of extensive research and regulatory reviews to establish guidelines for human exposures. The developmental toxicity of EG has been attributed to the intermediate metabolite, glycolic acid (GA), which can become a major metabolite when EG is administered to rats and mice at high doses and dose rates. Therefore, a physiologically based pharmacokinetic (PBPK) model was developed to integrate the extensive mode of action and pharmacokinetic data on EG and GA for use in developmental risk assessments. The resulting PBPK model includes inhalation, oral, dermal, intravenous, and subcutaneous routes of administration. Metabolism of EG and GA were described in the liver with elimination via the kidneys. Metabolic rate constants and partition coefficients for EG and GA were estimated from in vitro studies. Other biochemical constants were optimized from appropriate in vivo pharmacokinetic studies. Several controlled rat and human metabolism studies were used to validate the resulting PBPK model. When internal dose surrogates were compared in rats and humans over a broad range of exposures, it was concluded that humans are unlikely to achieve blood levels of GA that have been associated with developmental toxicity in rats following occupational or environmental exposures.

Ethylene glycol: an estimate of tolerable levels of exposure based on a review of animal and human data

Upon ingestion ethylene glycol (EG, monoethylene glycol) is rapidly absorbed from the gastrointestinal tract, and depending on the severity of exposure signs of toxicity may progress through three stages. Neurological effects characterize the first step consisting of central nervous depression (intoxication, lethargy, seizures, and coma). The second stage, usually 12-24 h after ingestion, is characterized by metabolic acidosis due to the accumulation of acidic metabolites of EG, primarily glycolic acid (GA), contributing to the ensuing osmolal and anion gaps. Stage 3, generally 24-72 h after ingestion, is determined mainly by oxalic acid excretion, nephropathy, and eventual renal failure. Because the toxicity of EG is mediated principally through its metabolites, adequate analytical methods are essential to provide the information necessary for diagnosis and therapeutic management. The severe metabolic acidosis and multiple organ failure caused by ingestion of high doses of EG is a medical emergency that usually requires immediate measures to support respiration, correct the electrolyte imbalance, and initiate hemodialysis. Since metabolic acidosis is not specific to EG, whenever EG intoxication is suspected, every effort should be made to determine EG as well as its major metabolite GA in plasma to confirm the diagnosis and to institute special treatment without delay. A number of specific and sensitive analytical methods (GC, GC-MS, or HPLC) are available for this purpose. Due to the rapid metabolism of EG, the plasma concentration of GA may be higher than that of EG already upon admission. As toxicity is largely a consequence of metabolism of EG to GA and oxalic acid, the simultaneous quantification of EG and GA is important. Formation of calcium oxalate monohydrate in the urine may be a useful indicator of developing oxalate nephrosis although urine crystals can result without renal injury. The pathways involved in the metabolism of EG are qualitatively similar in humans and laboratory animals, although quantitative differences have been reported. Comparison between species is difficult, however, because the information on humans is derived mainly from acute poisoning cases whereas the effects of repeated exposures have been investigated in animal experiments. Based on published data the minimum human lethal dose of EG has been estimated at approx. 100 ml for a 70-kg adult or 1.6 g/kg body weight (calculation of dose in ml/kg to mg/kg based in EG density=1.11 g/l). However, human data from case reports are generally insufficient for the determination of a clear dose-response relationship and quantification of threshold doses for systemic toxicity, in particular renal effects, is limited. As toxicity is largely a consequence of metabolism of EG to GA, it is important to note that no signs of renal injury have developed at initial plasma glycolate concentrations of up to 10.1 mM (76.7 mg/dl). Plasma EG levels of 3.2 mM (20 mg/dl) are considered the threshold of toxicity for systemic exposure, if therapeutic strategy is based on the EG concentration alone.

Principles of risk assessment for determining the safety of chemicals: recent assessment of residual solvents in drugs and di(2-ethylhexyl) phthalate

Risk assessment of chemicals is essential for the estimation of chemical safety, and animal toxicity data are typically used in the evaluation process, which consists of hazard identification, dose-response assessment, exposure assessment, and risk characterization. Hazard identification entails the collection of all available toxicity data and assessment of toxicity endpoints based on findings for repeated dose toxicity, carcinogenicity or genotoxicity and species-specificity. Once a review is compiled, the allowable lifetime exposure level of a chemical is estimated from a dose-response assessment based on several measures. For non-carcinogens and non-genotoxic carcinogens, the no-observed-adverse-effect-level (NOAEL) is divided by uncertainty factors (e.g. with environmental pollutants) or safety factors (e.g. with food additives) to derive a tolerable daily intake (TDI) or acceptable daily intake (ADI), respectively. These factors include interspecies and individual differences, duration of exposure, quality of data, and nature of toxicity such as carcinogenicity or neurotoxicity. For genotoxic carcinogens, low dose extrapolation is accomplished with mathematical modeling (e.g. linearized multistage model) from the point of departure to obtain exposure levels that will be associated with an excess lifetime cancer risk of a certain level. Data for levels of chemicals in food, water and air, are routinely used for exposure assessment. Finally, risk characterization is performed to ensure that the established 'safe' level of exposure exceeds the estimated level of actual exposure. These principles have led to the evaluation of several existing chemicals. To establish a guideline for residual solvents in medicine, the permitted daily exposure (PDE), equivalent to TDI, of N,N-dimethylformamide was derived on the basis of developmental toxicity (malformation) and of N-methylpyrrolidone on the basis of the developmental neurotoxicity. A TDI for di(2-ethylhexyl)phthalate was derived from assessment of testicular toxicity.

Expression of osteopontin in rat kidneys: induction during ethylene glycol induced calcium oxalate nephrolithiasis

PURPOSE

Osteopontin is a well-known component of stone matrix and a strong inhibitor of the nucleation, growth and aggregation of calcium oxalate crystals in vitro. To understand its involvement in vivo in calcium oxalate nephrolithiasis we investigated the renal expression and urinary excretion of osteopontin in normal rats, and rats with hyperoxaluria and calcium oxalate crystal deposits in the kidneys.

MATERIALS AND METHODS

Calcium oxalate nephrolithiasis was induced by administering ethylene glycol. Immunohistochemistry and in situ hybridization were done to localize osteopontin and osteopontin messenger RNA in the kidneys, while sensitive reverse transcriptase quantitative competitive template polymerase chain reaction was performed to detect and quantify osteopontin messenger RNA expression. Urinary excretion was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis, and then quantified by densitometry of the Western blots.

RESULTS

Osteopontin expression in the kidneys was significantly increased after hyperoxaluria and it increased further after the deposition of calcium oxalate crystals in the kidneys. Urinary excretion of osteopontin increased concomitantly. The results reveal differences in renal responses after exposure to oxalate and calcium oxalate crystals. In normal kidneys osteopontin expression was limited to a small number of cells of the thin limbs of the loop of Henle and papillary surface epithelium. During hyperoxaluria osteopontin expression in the kidneys was increased but still mostly limited to cells of the thin limb and papillary surface epithelium. However, after calcium oxalate crystal deposition osteopontin expression was observed throughout the kidneys, including segments of the proximal tubules.

CONCLUSIONS

In response to exposure to oxalate and calcium oxalate crystals renal epithelial cells increase the production of osteopontin, which may have a significant role in calcium oxalate nephrolithiasis.

Hepatic distribution of a phosphorothioate oligodeoxynucleotide within rodents following intravenous administration

The pharmacokinetics of ISIS 1082, a 21-base heterosequence phosphorothioate oligodeoxynucleotide, were characterized within rodent whole liver, and cellular and subcellular compartments. Cross-species comparisons were performed using Sprague-Dawley rat and CD-1 mouse strains. Although whole liver oligonucleotide deposition and the proportion of drug found within parenchymal and nonparenchymal cells were similar between the two rodent species as a function of both time and dose, dramatic differences in subcellular pharmacokinetics were observed. Specifically, within murine hepatocyte nuclei, drug was observed at the 10 mg/kg dose, whereas in the rat nuclear-associated levels required the administration of 25 mg/kg. Under all experimental regimens, murine hepatic nuclear-associated drug concentrations were at least 2-fold higher than those found in rat liver cells. More detailed metabolic analysis was also performed using high performance liquid chromatography/electrospray-mass spectrometry (HPLC/ES-MS) and demonstrated that although the extent of metabolism was similar for rat and mouse, the pattern of n-1 metabolites varied as a function of both species and cell type. While rat and mouse hepatocytes and rat nonparenchymal cellular metabolites were predominantly products of 3'-exonuclease degradation, mouse nonparenchymal cells contained a majority of n-1 metabolites produced by 5'-exonucleolytic activity. Based upon these data, it would appear that subcellular oligonucleotide disposition and metabolism among rodent species are more divergent than whole organ pharmacokinetics might predict.

Dose-dependent nonlinear pharmacokinetics of ethylene glycol metabolites in pregnant (GD 10) and nonpregnant Sprague-Dawley rats following oral administration of ethylene glycol

The kinetics of orally administered ethylene glycol (EG) and its major metabolites, glycolic acid (GA) and oxalic acid (OX), in pregnant (P; gestation day 10 at dosing, GD 10) rats were compared across doses, and between pregnant and nonpregnant (NP) rats. Groups of 4 jugular vein-cannulated female rats were administered 10 (P and NP), 150 (P), 500 (P), 1000 (P), or 2500 (P and NP) mg (13)C-labelled EG/kg body weight. Serial blood samples and urine were collected over 24-hr postdosing, and analyzed for EG, GA, and OX using GC/MS techniques. Pharmacokinetic parameters including Cmax, Tmax, AUC, and betat((1/2)) were determined for EG and GA. Pregnancy status (GD 10-11) had no impact on the pharmacokinetic parameters investigated. Blood levels of GA were roughly dose-proportional from 10 to 150 mg EG/kg, but increased disproportionately from 500 to 1000 mg EG/kg. EG and GA exhibited dose-dependent urinary elimination at doses > or = 500 mg EG/kg, probably due to saturation of metabolic conversion of EG to GA, and of GA to downstream metabolites. The shift to nonlinear kinetics encompassed the NOEL (500 mg EG/kg) and LOEL (1000 mg EG/kg) for developmental toxicity of EG in rats, providing additional evidence for the role of GA in EG developmental toxicity. The peak maternal blood concentration of GA associated with the LOEL for developmental toxicity in the rat was quite high (363 microg/g or 4.8 mM blood). OX was a very minor metabolite in both blood and urine at all dose levels, suggesting that OX is not important for EG developmental toxicity.