Subchronic JP-8 jet fuel exposure enhances vulnerability to noise-induced hearing loss in rats.

Both laboratory and epidemiological studies published over the past two decades have identified the risk of excess hearing loss when specific chemical contaminants are present along with noise. The objective of this study was to evaluate the potency of JP-8 jet fuel to enhance noise-induced hearing loss (NIHL) using inhalation exposure to fuel and simultaneous exposure to either continuous or intermittent noise exposure over a 4-wk exposure period using both male and female Fischer 344 rats. In the initial study, male (n = 5) and female (n = 5) rats received inhalation exposure to JP-8 fuel for 6 h/d, 5 d/wk for 4 wk at concentrations of 200, 750, or 1500 mg/m³. Parallel groups of rats also received nondamaging noise (constant octave band noise at 85 dB(lin)) in combination with the fuel, noise alone (75, 85, or 95 dB), or no exposure to fuel or noise. Significant concentration-related impairment of auditory function measured by distortion product otoacoustic emissions (DPOAE) and compound action potential (CAP) threshold was seen in rats exposed to combined JP-8 plus noise exposure when JP-8 levels of 1500 mg/m³ were presented with trends toward impairment seen with 750 mg/m³ JP-8 + noise. JP-8 alone exerted no significant effect on auditory function. In addition, noise was able to disrupt the DPOAE and increase auditory thresholds only when noise exposure was at 95 dB. In a subsequent study, male (n = 5 per group) and female (n = 5 per group) rats received 1000 mg/m³ JP-8 for 6 h/d, 5 d/wk for 4 wk with and without exposure to 102 dB octave band noise that was present for 15 min out of each hour (total noise duration 90 min). Comparisons were made to rats receiving only noise, and thosereceiving no experimental treatment. Significant impairment of auditory thresholds especially for high-frequency tones was identified in the male rats receiving combined treatment. This study provides a basis for estimating excessive hearing loss under conditions of subchronic JP-8 jet fuel exposure.

A Post Hoc Exploratory Analysis: Induced Abortion Complications Mistaken for Miscarriage in the Emergency Room are a Risk Factor for Hospitalization.

Introduction: Previous research indicates that an increasing number of women who go to an emergency room for complications following an induced abortion are treated for a miscarriage, meaning their abortion is miscoded or concealed. Objective: To determine if the failure to identify a prior induced abortion during an ER visit is a risk factor for higher rates of subsequent hospitalization. Methods: Post hoc analysis of hospital admissions following an induced abortion and ER visit within 30 days: 4273 following surgical abortion and 408 following chemical abortion; abortion not miscoded versus miscoded or concealed at prior ER visit. Results: Chemical abortion patients whose abortions are misclassified as miscarriages during an ER visit subsequently experience on average 3.2 hospital admissions within 30 days. 86% of the patients ultimately have surgical removal of retained products of conception (RPOC). Chemical abortions are more likely than surgical abortions (OR 1.80, CL 1.38-2.35) to result in an RPOC admission, and chemical abortions concealed are more likely to result (OR 2.18, CL 1.65-2.88) in a subsequent RPOC admission than abortions without miscoding. Surgical abortions miscoded/concealed are similarly twice as likely to result in hospital admission than those without miscoding. Conclusion: Patient concealment and/or physician failure to identify a prior abortion during an ER visit is a significant risk factor for a subsequent hospital admission. Patients and ER personnel should be made aware of this risk.

Partition coefficients for nonane and its isomers in the rat.

Jet Fuel 8 (JP-8) is a major fuel source used by US and NATO military. JP-8 is a complex mixture of aliphatic and aromatic isomers of hydrocarbons. Tissue/blood partition coefficient (PC) values are chemical-specific parameters used in modeling the kinetic behavior of chemicals. The partition coefficient values for n-alkanes tend to increase with the increasing carbon number, but less is known about the trend for isomers of n-alkanes. PC values were obtained for the n-alkane nonane (C9) and five of its isomers, namely 3-methyloctane, 4-ethylheptane, 2,3-dimethylheptane, 2,2,4-trimethylhexane, 2,2,4,4-tetramethylpentane. The blood:air and tissue:air PC values correlated with the published log octanol/water (O:W) PC values for n-nonane and its isomers. Experimentally determined blood:air and tissue:air PC values for n-nonane with the largest O:W value were greatest and smallest for the isomer 2,2,4,4-tetramethylpentane with the lowest O:W value. As expected the fat tissue had the highest PC values and muscle the lowest for n-nonane and its isomers. For each tissue, a linear relationship was observed between the tissue/blood PC values for the isomers of n-nonane and n-nonane. This suggests that tissue/blood PC values for all isomers of an alkane could be estimated using data collected from only a sub-set of alkanes of equal carbon number. These reported tissue/blood PC values will support the development of a jet fuel physiologically-based pharmacokinetic (PBPK) model.

Evaluation of potassium iodide (KI) and ammonium perchlorate (NH4ClO4) to ameliorate 131I- exposure in the rat.

Nuclear reactor accidents and the threat of nuclear terrorism have heightened the concern for adverse health risks associated with radiation poisoning. Potassium iodide (KI) is the only pharmaceutical intervention that is currently approved by the Food and Drug Administration for treating (131)I(-) exposure, a common radioactive fission product. Though effective, KI administration needs to occur prior to or as soon as possible (within a few hours) after radioactive exposure to maximize the radioprotective benefits of KI. During the Chernobyl nuclear reactor accident, KI was not administered soon enough after radiation poisoning occurred to thousands of people. The delay in administration of KI resulted in an increased incidence of childhood thyroid cancer. Perchlorate (ClO(4)(-)) was suggested as another pharmaceutical radioprotectant for 131I- poisoning because of its ability to block thyroidal uptake of iodide and discharge free iodide from the thyroid gland. The objective of this study was to compare the ability of KI and ammonium perchlorate to reduce thyroid gland exposure to radioactive iodide (131I-). Rats were dosed with 131I- tracer and 0.5 and 3 h later dosed orally with 30 mg/kg of either ammonium perchlorate or KI. Compared to controls, both anion treatments reduced thyroid gland exposure to 131I- equally, with a reduction ranging from 65 to 77%. Ammonium perchlorate was more effective than stable iodide for whole-body radioprotectant effectiveness. KI-treated animals excreted only 30% of the (131)I(-) in urine after 15 h, compared to 47% in ammonium perchlorate-treated rats. Taken together, data suggest that KI and ammonium perchlorate are both able to reduce thyroid gland exposure to 131I- up to 3 h after exposure to 131I-. Ammonium perchlorate may offer an advantage over KI because of its ability to clear 131I- from the body.

Interaction of nitric oxide and cyclic guanosine 3',5'-monophosphate in erythropoietin production.

The present study was designed to investigate whether in vivo and in vitro erythropoietin (EPO) production is modulated by nitric oxide (NO) and cyclic guanosine 3',5'-monophosphate (cGMP). Serum levels of EPO in ex-hypoxic polycythemic mice were significantly increased after injections of 200 micrograms/kg sodium nitroprusside for 4 d. One injection of NG-nitro-L-arginine methyl ester (L-NAME) produced a significant dose-related decrease in serum levels of EPO in ex-hypoxic polycythemic mice in response to hypoxia. When EPO producing Hep3B cells were incubated in 1% O2 for 30 min, cGMP levels in the Hep3B cells were significantly elevated, compared with cells incubated in 20% O2. The elevation of cGMP by hypoxia was inhibited by L-NAME (100 microM). Sodium nitroprusside (10 and 100 microM) and NO (2 microM) also significantly increased cGMP levels in Hep3B cells. L-NAME, LY 83583 (6-Anilino-5,8-quinolinedione, a soluble guanylate cyclase inhibitor), and Rp-8-Bromo-cGMPS (Rp-8-Bromo-guanosine 3',5'-cyclic monophosphothioate, a cGMP-dependent protein kinase inhibitor) significantly inhibited the hypoxia-induced increase in medium levels of EPO in Hep3B cells. 8-Bromo-cGMPS produced a dose-dependent decrease in EPO messenger RNA levels in Hep3B cells in response to hypoxia. 8-Bromo-cGMP (10(-3) M) produced significant increases in medium levels of EPO in Hep3B cell cultures incubated under normoxic conditions, which was enhanced by the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (0.2 mM). These results suggest that NO and cGMP may interact in modulating hypoxic stimulation of EPO production.

Role of endogenous prostaglandin E2 in erythropoietin production and dome formation by human renal carcinoma cells in culture.

Studies were carried out on the role of endogenous prostaglandin E2 (PGE2) in erythropoietin (Ep) production and dome formation in primary monolayer cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted into BALB/c athymic nude mice. The metabolism of [14C]arachidonic acid (14C-AA) by cultured renal carcinoma cells, which were plated in 25-cm2 flasks at a density of 2 X 10(4) cells/cm2 and grown for 6, 12 (confluence, 13 X 10(4) cells/cm2), 16, 24, and 30 d in Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum, was examined by using radiometric thin-layer chromatography (TLC). TLC revealed PGE2 to be the major metabolite of 14C-AA produced by the cultured cells throughout the 30 d of cultivation. In addition, the cultured cells at each time period were incubated for 24 h in 5 ml of serum-free Eagle's MEM and the levels of PGE2 and Ep in the incubated media were measured via radioimmunoassay. PGE2 levels in the serum-free media incubated with the cultured cells grown for 6 d were significantly (P less than 0.001) elevated (174 +/- 2.5 pg/ml, n = 5), compared with the unincubated control media (1.5 +/- 0.19 pg/ml, n = 5) and gradually decreased at each time period to 97.6 +/- 4.4 pg/ml (n = 5) at 30 d. On the other hand, the levels of Ep in the incubated media of the cells grown for 6 d were 11.5 +/- 0.52 mU/ml (n = 5) compared with 7.6 +/- 0.62 mU/ml (n = 5) in the control media. However, after the cultured cells became confluent, the levels of Ep in the incubated media showed a marked increase to 222.9 +/- 5.26 mU/ml (n = 5) at 30 d of cultivation. Multicellular hemicysts (domes) developed after the cultured cells reached confluence and their numbers increased with increasing time in confluence in parallel with the increase in Ep. Meclofenamate (MF) (3 X 10(-6)-3 X 10(-5) M), a prostaglandin synthesis inhibitor, produced a significant dose-related decrease in PGE2, Ep, and dome formation without producing a significant effect on cell viability in the 30-d cells. This inhibitory effect of MF on Ep production and dome formation was completely abolished by the addition of 10(-8) M PGE2 to the incubation medium. In conclusion, endogenous PGE2 plays an important role in supporting and/or stimulating Ep production and dome formation in cultured renal carcinoma cells.

Identification of spermine as an inhibitor of erythropoiesis in patients with chronic renal failure.

Fetal mouse liver and normal human bone marrow cell cultures were used for studies on the inhibition of erythroid colony formation (CFU-E) by sera from anemic patients with end-stage renal failure and the polyamine spermine. Sera from each of eight predialysis uremic anemic patients with end-stage renal failure produced a significant (P < 0.001) inhibition of erythroid colony formation in the fetal mouse liver cell cultures when compared to sera from normal human volunteers. In vivo or in vitro dialysis of the uremic sera with a 3,500-dalton exclusion limit membrane removed the inhibitor from uremic sera. The uremic serum dialysate provided by the membrane fractionation was significantly inhibitory in the erythroid cell cultures. When this dialysate was applied to gel filtration chromatography (Bio-Gel P-2) the inhibitor was found to be in the same molecular weight range as [(14)C]spermine. The polyamine spermine produced a dose-related inhibition of erythroid colony formation (CFU-E) in fetal mouse liver and normal human bone marrow cultures. Thus, the following evidence is provided that the in vitro inhibitor of erythropoiesis found in chronic renal failure patients' sera is identical with the polyamine spermine: (a) the inhibitor and radiolabeled spermine appeared in identical Bio-Gel P-2 effluent fractions; (b) when spermine was added to normal human sera at concentrations reported in sera of uremic patients, and studied in both the fetal mouse liver cell culture and normal human bone marrow cultures, a dose-related inhibition of erythroid colony (CFU-E) formation was noted; and (c) the inhibitory effects of crude uremic serum, uremic serum dialysate, and fractions of uremic serum dialysate from a Bio-Gel column, on erythroid colony formation were completely abolished by the addition of a specific rabbit antiserum to spermine.

Protein kinase C alpha protein expression is necessary for sustained erythropoietin production in human hepatocellular carcinoma (Hep3B) cells exposed to hypoxia.

Although protein kinase C (PKC) has been implicated as an effector of erythropoietin (EPO) production, its exact role is still uncertain. Hep3B human hepatocellular carcinoma cells were used for this study and were depleted of PKC in three different ways: long-term treatment with phorbol 12-myristate 13-acetate (PMA), selective inhibition with calphostin C, and treatment with PKCalpha antisense oligonucleotides. When EPO-producing Hep3B cells were incubated in 1% O2 (hypoxia) for 24 h, PMA treatment resulted in significant decreases in medium levels of EPO in Hep3B cell cultures at concentrations higher than 10 nM. The specific PKC inhibitor, calphostin C, significantly inhibited medium levels of EPO and EPO mRNA levels in Hep3B cells exposed to 1% O2. Western blot analysis revealed that Hep3B cells express the classical PKCalpha and gamma isoforms, as well as novel PKCepsilon and delta and the atypical zeta isoform. Preincubation with PMA for 6 h specifically down-regulated PKCalpha protein expression. Phosphorothioate modified antisense oligonucleotides specific for PKCalpha also decreased EPO production in Hep3B cells exposed to hypoxia for 20 h when compared to PKCalpha sense treatment. The translocation of PKCalpha from the soluble to particulate fractions was increased in Hep3B cells incubated under hypoxia compared with normoxia (21% O2) controls. These results suggest that the PKCalpha isoform plays an important role in sustaining hypoxia-regulated EPO production.

Role of erythropoietin and cyclic nucleotides in erythroid cell proliferation in fetal liver.

Cyclic AMP and cyclic GMP have been implicated as regulators of proliferation and differentiation in a variety of tissues including erythroid cells. Present studies indicate that erythropoietin is capable of stimulating an accumulation of cyclic GMP in fetal liver cultures. Erythropoietin (Ep) decreases the duration of the G1 phase of the cell cycle, diminishing the total cell cycle time by approximately 40%. In proliferating cells to which no Ep was added, concentrations of cyclic AMP and cyclic GMP changed as cells progressed through the cycle. Increases in cyclic GMP levels are associated with DNA synthesis and mitosis. On the other hand, cyclic AMP levels are associated with the G1 and G2 phases of the cycle. When Ep was included in cultures, the same cyclic nucleotide pattern relative to phases of the cell cycle was maintained. Thus, it is likely that cyclic GMP and cyclic AMP exert a regulatory influence on proliferation and differentiation of developing erythroid cells.

Prostaglandins activation of erythropoietin production and erythroid progenitor cells.

A model is presented postulating a role for prostaglandins E and prostacyclin in kidney generation of erythropoietin and the activation of the erythroid progenitor cell (CFU-E) compartment by erythropoietin (Ep). Several criteria have been met to prove that prostanoids mediate erythropoiesis: 1) several E-type prostaglandins (PGE2, 15-methyl prostaglandin E2, 16,16-dimethyl E2, 6-keto-E1 and PGE1) produced a significant increase in radioiron incorporation in red cells of exhypoxic polycythemic mice; 2) prostaglandin E2 increased kidney production of erythropoietin in the isolated perfused dog kidney; 3) arachidonic acid, a precursor for all bisenoic prostaglandins, increased kidney production of erythropoietin in the isolated perfused dog kidney which was blocked by pretreatment with the cyclo-oxygenase inhibitor drug indomethacin; 4) hypoxemic perfusion of the isolated perfused dog kidney increased kidney production of erythropoietin and produced an elevation in prostacyclin in the perfusates; 5) albuterol, a beta-2 adrenergic agonist, produced a significant increase in perfusate levels of erythropoietin and PGE in the isolated perfused dog kidney; 6) renal ischemia increased Ep and PGE levels in renal venous plasma which was blocked by pretreatment with indomethacin; 7) prostaglandin E2 and arachidonic acid produced a significant increase in erythroid colonies (CFU-E) in vitro in normal mouse bone marrow; 8) E-type prostaglandins (15-methyl E2) increased in vivo erythroid colony (CFU-E) formation in bone marrows of post-hypoxic polycythemic mice; and 9) injections of 15-methyl E2 daily for six weeks in normal and hypoxic mice produced a significant elevation in the total circulating red cell mass. These studies indicate that hypoxic stimulation of kidney production of erythropoietin may be related to the generation of prostacyclin (PGI2). On the other hand, albuterol and ischemic (reduction in renal blood flow) stimulation of kidney production of erythropoietin involves prostaglandins of the E type. In addition, E-type prostaglandins were found to enhance the effects of erythropoietin in activating erythroid progenitor cells (CFU-E) in the bone marrow. We postulate from our model that prostaglandins E and prostacyclins are involved in the mechanism of kidney production of erythropoietin as well as the activation of the Ep-responsive cell (ERC) compartment.

Decreased erythroid colony-forming cell response of XTfm/Y mice to testosterone and 5 beta-dihydrotestosterone.

Although certain tissue of XTfm/Y mice are known to be deficient in androgen-binding sites, the defect has not been documented for bone marrow. To study the bone marrow response to testosterone and its metabolites, we compared the responses of the erythroid colony-forming cell (CFU-E) in these mice and their wild counter-parts, XTa/Y mice, using an in vitro methyl cellulose system in the presence of erythropoietin. Testosterone or 5 beta-dihydrotestosterone (5 beta-DHT) treatment (5 mg/kg) of Ta/Y mice in vivo before femoral bone marrow culture resulted in a significant increase in CFU-E colonies. However, similar in vivo treatment of Tfm/Y mice with testosterone or 5 beta-DHT had no effect on CFU-E colony formation. 5 alpha-DHT had no significant effect on Ta/Y or Tfm/Y mouse bone marrow. Testosterone or 5 beta-DHT added directly to Ta/Y marrow cultures caused an enhancement of CFU-E colony numbers compared with erythropoietin alone. 5 alpha-DHT inhibited colony formation at high concentrations. Testosterone had no effect on Tfm/Y erythroid colonies, whereas 5 beta-DHT and 5 alpha-DHT significantly inhibited colony formation. These results indicate that Tfm/Y erythroid bone marrow colonies may have an altered response to testosterone and its metabolites compared to that of Ta/Y erythroid colonies. We postulate that the pattern of androgen receptors in the erythroid progenitor cell compartment of Tfm/Y mice is different from that of Ta/Y mice.

Von Hippel-Lindau disease and erythrocytosis: radioimmunoassay of erythropoietin in cyst fluid from a brainstem hemangioblastoma.

A 59-year-old woman with von Hippel-Lindau disease developed erythrocytosis and a recurrent intracranial hemangioblastoma. Radioimmunoassay showed an elevated level of erythropoietin in her serum. Cyst fluid from the tumor also contained erythropoietin, concentrated a thousandfold relative to the serum level. Production of erythropoietin by hemangioblastomas may explain the erythrocytosis present in some patients with von Hippel-Lindau disease.

The role of renal adenosine 3',5'-monophosphate in the control of erythropoietin production.

A regulatory role for adenosine 3',5'-monophosphate (cyclic AMP) in the production of the renal hormone rythropoietin following erythropoietic stimulation with cobaltous chloride hexahydrate is proposed. Studies in rates reveal a temporal relationship between renal cyclic AMP levels and plasma titers of erythropoietin. In addition, cobalt increases the activity of an erythropoietin-generating enzyme (renal erythropoietic factor) with maximal enzyme activity occurring after the rise in cyclic AMP levels but before the increase in erythropoietin titers. This increase in renal cyclic AMP is localized to the renal cortex. Cobalt stimulates renal cortical adenylate cyclase but has no effect on renal cyclic nucleotide phosphodiesterase. The addition of cyclic AMP (3 time 10-6 M) and a partially purified cyclic AMP-dependent protein kinase from rat kidney to an inactive preparation of renal erythropoietic factor increases the ability of renal erythropoietic factor to generate erythropoietin. Data from the polycythemic mouse assay, a bioassay used to quantitate erythropoietic activity of test substances, indicate that dibutyryl cyclic AMP is erythropoietically active with respect to its ability to increase radioactive-labelled iron (59Fe) incorporation into heme of newly formed red blood cells. Theophylline, which by itself is erythropoietically inactive, potentiated the erythropoietic effect of cobalt in polycythemic mice. These results suggest that cyclic AMP plays a significant role in the renal production of erythropoietin following cobalt administration. It is postulated that cobalt stimulates renal cortical adenyoate cyclase, thus increasing renal cyclic AMP levels. Cyclic AMP then activates a protein kinase which subsequently stimulates renal erythropoietic factor to generate erythropoietin. A similar cyclic AMP mechanism may be operative after erythropoietic stimulation by exposure to hypoxia or prostaglandin treatment.

Physiologically based pharmacokinetic models for trichloroethylene and its oxidative metabolites.

Trichloroethylene (TCE) pharmacokinetics have been studied in experimental animals and humans for over 30 years. Compartmental and physiologically based pharmacokinetic (PBPK) models have been developed for the uptake, distribution, and metabolism of TCE and the production, distribution, metabolism, and elimination of P450-mediated metabolites of TCE. TCE is readily taken up into systemic circulation by oral and inhalation routes of exposure and is rapidly metabolized by the hepatic P450 system and to a much lesser degree, by direct conjugation with glutathione. Recent PBPK models for TCE and its metabolites have focused on the major metabolic pathway for metabolism of TCE (P450-mediated metabolic pathway). This article briefly reviews selected published compartmental and PBPK models for TCE. Trichloroacetic acid (TCA) is considered a principle metabolite responsible for TCE-induced liver cancer in mice. Liver cancer in mice was considered a critical effect by the U.S. Environmental Protection Agency for deriving the current maximum contaminant level for TCE in water. In the literature both whole blood and plasma measurements of TCA are reported in mice and humans. To reduce confusion about disparately measured and model-predicted levels of TCA in plasma and whole blood, model-predicted outcomes are compared for first-generation (plasma) and second-generation (whole blood) PBPK models published by Fisher and colleagues. Qualitatively, animals and humans metabolize TCE in a similar fashion, producing the same metabolites. Quantitatively, PBPK models for TCE and its metabolites are important tools for providing dosimetry comparisons between experimental animals and humans. TCE PBPK models can be used today to aid in crafting scientifically sound public health decisions for TCE.

Trichloroethene levels in human blood and exhaled breath from controlled inhalation exposure.

The organic constituents of exhaled human breath are representative of bloodborne concentrations through gas exchange in the blood/breath interface in the lungs. The presence of specific compounds can be an indicator of recent exposure or represent a biological response of the subject. For volatile organic compounds, sampling and analysis of breath is preferred to direct measurement from blood samples because breath collection is noninvasive, potentially infectious waste is avoided, the sample supply is essentially limitless, and the measurement of gas-phase analytes is much simpler in a gas matrix rather than in a complex biological tissue such as blood. However, to assess the distribution of a contaminant in the body requires a reasonable estimate of the blood level. We have investigated the use of noninvasive breath measurements as a surrogate for blood measurements for (high) occupational levels of trichloroethene in a controlled exposure experiment. Subjects were placed in an exposure chamber for 24 hr; they were exposed to 100 parts per million by volume trichloroethene for the initial 4 hr and to purified air for the remaining 20 hr. Matched breath and blood samples were collected periodically during the experiment. We modeled the resulting concentration data with respect to their time course and assessed the blood/breath relationship during the exposure (uptake) period and during the postexposure (elimination) period. Estimates for peak blood levels, compartmental distribution, and time constants were calculated from breath data and compared to direct blood measurements to assess the validity of the breath measurement methodology. Blood/breath partition coefficients were studied during both uptake and elimination. At equilibrium conditions at the end of the exposure, we could predict actual blood levels using breath elimination curve calculations and a literature value partition coefficient with a mean ratio of calculated:measured of 0.98 and standard error (SE) = 0.12 across all subjects. blood/breath comparisons at equilibrium resulted in calculated in vivo partition coefficients with a mean of 10.8 and SE = 0.60 across all subjects and experiments and 9.69 with SE = 0.93 for elimination-only experiments. We found that about 78% of trichloroethene entering the body during inhalation exposure is metabolized, stored, or excreted through routes other than exhalation.

Metabolism of trichloroethylene.

A major focus in the study of metabolism and disposition of trichloroethylene (TCE) is to identify metabolites that can be used reliably to assess flux through the various pathways of TCE metabolism and to identify those metabolites that are causally associated with toxic responses. Another important issue involves delineation of sex- and species-dependent differences in biotransformation pathways. Defining these differences can play an important role in the utility of laboratory animal data for understanding the pharmacokinetics and pharmacodynamics of TCE in humans. Sex-, species-, and strain-dependent differences in absorption and distribution of TCE may play some role in explaining differences in metabolism and susceptibility to toxicity from TCE exposure. The majority of differences in susceptibility, however, are likely due to sex-, species-, and strain-dependent differences in activities of the various enzymes that can metabolize TCE and its subsequent metabolites. An additional factor that plays a role in human health risk assessment for TCE is the high degree of variability in the activity of certain enzymes. TCE undergoes metabolism by two major pathways, cytochrome P450 (P450)-dependent oxidation and conjugation with glutathione (GSH). Key P450-derived metabolites of TCE that have been associated with specific target organs, such as the liver and lungs, include chloral hydrate, trichloroacetate, and dichloroacetate. Metabolites derived from the GSH conjugate of TCE, in contrast, have been associated with the kidney as a target organ. Specifically, metabolism of the cysteine conjugate of TCE by the cysteine conjugate ss-lyase generates a reactive metabolite that is nephrotoxic and may be nephrocarcinogenic. Although the P450 pathway is a higher activity and higher affinity pathway than the GSH conjugation pathway, one should not automatically conclude that the latter pathway is only important at very high doses. A synthesis of this information is then presented to assess how experimental data, from either animals or from (italic)in vitro (/italic)studies, can be extrapolated to humans for risk assessment. (italic)Key words(/italic): conjugate beta-lyase, cysteine glutathione, cytochrome P450, glutathione (italic)S(/italic)-transferases, metabolism, sex dependence, species dependence, tissue dependence, trichloroethylene.

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. III: pharmacokinetic and pharmacodynamic considerations.

We review pharmacokinetic and pharmacodynamic factors that should be considered in the design and interpretation of developmental neurotoxicity studies. Toxicologic effects on the developing nervous system depend on the delivered dose, exposure duration, and developmental stage at which exposure occurred. Several pharmacokinetic processes (absorption, distribution, metabolism, and excretion) govern chemical disposition within the dam and the nervous system of the offspring. In addition, unique physical features such as the presence or absence of a placental barrier and the gradual development of the blood--brain barrier influence chemical disposition and thus modulate developmental neurotoxicity. Neonatal exposure may depend on maternal pharmacokinetic processes and transfer of the xenobiotic through the milk, although direct exposure may occur through other routes (e.g., inhalation). Measurement of the xenobiotic in milk and evaluation of biomarkers of exposure or effect following exposure can confirm or characterize neonatal exposure. Physiologically based pharmacokinetic and pharmacodynamic models that incorporate these and other determinants can estimate tissue dose and biologic response following in utero or neonatal exposure. These models can characterize dose--response relationships and improve extrapolation of results from animal studies to humans. In addition, pharmacologic data allow an experimenter to determine whether exposure to the test chemical is adequate, whether exposure occurs during critical periods of nervous system development, whether route and duration of exposure are appropriate, and whether developmental neurotoxicity can be differentiated from direct actions of the xenobiotic.

Diagnostic use of CFU-E formation from peripheral blood in polycythemia vera.

Peripheral blood mononuclear cells from five patients with polycythemia vera (P. vera) and three with other polycythemias were cultured in a methylcellulose system. Colony-forming unit-erythroid (CFU-E) colonies appeared after seven days in the absence of added erythropoietin (Ep) in all P. vera cultures. A pattern of growth similar to the one seen for P. vera patients occurred in the culture from a patient in whom that disease was suspected. In the cultures from two of the patients with other polycythemias, erythroid colonies did not appear even in the presence of Ep. These findings emphasize the potential value of culturing peripheral blood for CFU-E colonies in diagnosing polycythemia vera.

External messengers and erythropoietin production.

We have presented a model for the role of external messenger substances in hypoxic stimulation of kidney production of erythropoietin. These autacoids probably act in concert to activate the adenylate cyclase system to enhance production and/or secretion of erythropoietin. The phosphoproteins generated in this system could act at the level of transcription and translation of erythropoietin as well as at the level of release of erythropoietin from the cell. Even though eicosanoids and beta-2-adrenergic agonists may be involved in mild to moderate hypoxia, it seems more likely that adenosine is more involved in erythropoietin production with increasing severity of hypoxia. Adenosine may play a very early role in hypoxia following the decrease in ATP to trigger erythropoietin production, and hydrogen peroxide may be generated from hypoxanthine, a metabolite of adenosine, during reoxygenation and regional changes in blood flow in the normal kidney and perhaps in certain renal and hepatic tumors. Further work is necessary in vivo to completely clarify the role of adenosine and oxygen free radicals in regulating kidney production of erythropoietin.

Analysis of respiratory exchange of methanol in the lung of the monkey using a physiological model.

A physiologically based pharmacokinetic (PBPK) model was developed for the monkey, to account for fractional systemic uptake of inhaled methanol vapors in the lung. Fractional uptake of inhaled [14C]-methanol was estimated using unreported exhaled breath time course measurements of [14C]-methanol from the D.C. Dorman et al. (1994, Toxicol Appl Pharmacol. 128, 229-238) lung-only exposure study. The cumulative amount of [14C]-methanol exhaled was linear with respect to exposure duration (0.5 to 2 h) and concentration (10 to 900 ppm). The model estimated that forty to eighty-one percent of the of inhaled [14C]-methanol delivered to the lung was taken into systemic circulation in female Cynomolgus monkeys exposed for two h to 10-900 ppm of [14C]-methanol. There was no apparent trend between the percent of inhaled [14C]-methanol absorbed systemically and the [14C]-methanol exposure concentration. Model simulations were conducted using a single saturable Michaelis-Menten equation with Vmaxc, the metabolic capacity set to 15.54 mg/kg/h and Km, the affinity constant, to 0.66 mg/l. The [14C]-methanol blood concentrations were variable across [14C]-methanol exposure groups and the PBPK model tended to over-predict systemic clearance of [14C]-methanol. Accounting for fractional uptake of inhaled polar solvents is an important consideration for risk assessment of inhaled polar solvents.