A hybrid computational fluid dynamics and physiologically based pharmacokinetic model for comparison of predicted tissue concentrations of acrylic acid and other vapors in the rat and human nasal cavities following inhalation exposure.

To assist in interspecies dosimetry comparisons for risk assessment of the nasal effects of organic acids, a hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of inhaled vapors in the rat and human nasal cavity. Application to a specific vapor would involve the incorporation of the chemical-specific reactivity, metabolism, partition coefficients, and diffusivity (in both air and tissue phases) of the vapor. This report describes the structure of the CFD-PBPK model and its application to a representative acidic vapor, acrylic acid, for interspecies tissue concentration comparisons to assist in risk assessment. By using the results from a series of short-term in vivo studies combined with computer modeling, regional nasal tissue dose estimates were developed and comparisons of tissue doses between species were conducted. To make these comparisons, the assumption was made that the susceptibilities of human and rat olfactory epithelium to the cytotoxic effects of organic acids were similar, based on similar histological structure and common mode of action considerations. Interspecies differences in response were therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The results of simulations with the seven-compartment CFD-PBPK model suggested that the olfactory epithelium of the human nasal cavity would be exposed to tissue concentrations of acrylic acid similar to that of the rat nasal cavity when the exposure conditions are the same. Similar analysis of CFD data and CFD-PBPK model simulations with a simpler one-compartment model of the whole nasal cavities of rats and humans provides comparable results to averaging over the compartments of the seven-compartment model. These results indicate that the general structure of the hybrid CFD-PBPK model applied in this assessment would be useful for target tissue dosimetry and interspecies dose comparisons for a wide variety of vapors. Because of its flexibility, this CFD-PBPK model is envisioned to be a platform for the construction of case-specific inhalation dosimetry models to simulate in vivo exposures that do not involve significant histopathological damage to the nasal cavity.

Gender differences in adolescents' behavior during conflict resolution tasks with best friends.

This study examined gender differences in adolescents' behavior during conflict resolution tasks with their best friends. It also examined gender differences in adolescents' descriptions of those friendships. Thirty-nine adolescents were videotaped while discussing unresolved problems with their best friends. In addition, adolescents completed the Friendship Questionnaire (Furman & Adler, 1982). The results indicated that there were significant gender differences. On the conflict resolution tasks, females were rated lower in withdrawal and higher in communication skills and support-validation than were males. On the Friendship Questionnaire, males rated their relationships with best friends higher in conflict than did females. Methodological considerations are discussed.

Breastfeeding the high risk infant: implications for midwifery management.

The mother of a high risk infant is confronted with numerous parenting challenges, not the least of which is the decision about how to nourish her vulnerable newborn. Successful breastfeeding depends on overcoming obstacles posed by infant condition, maternal health, and the neonatal intensive care environment. These obstacles include maternal separation from the nursing infant during hospitalization, delayed initiation of the expression of breast milk due to maternal illness and/or surgery, the inability to suckle her infant or feed on demand, and the lack of sufficient maternal follow-up after discharge. This article reviews the benefits of providing breast milk to high risk infants, problems that may be encountered by mothers of high risk infants, and the interventions that may be used by the midwife to facilitate the breastfeeding process.

Application of a hybrid computational fluid dynamics and physiologically based inhalation model for interspecies dosimetry extrapolation of acidic vapors in the upper airways.

This study provides a scientific basis for interspecies extrapolation of nasal olfactory irritants from rodents to humans. By using a series of short-term in vivo studies, in vitro studies with nasal explants, and computer modeling, regional nasal tissue dose estimates were made and comparisons of tissue doses between species were conducted. To make these comparisons, this study assumes that human and rodent olfactory epithelium have similar susceptibility to the cytotoxic effects of organic acids based on similar histological structure and common mode of action considerations. Interspecies differences in susceptibility to the toxic effects of acidic vapors are therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The acute, subchronic, and in vitro studies have demonstrated that the nasal olfactory epithelium is the most sensitive tissue to the effects of inhalation exposure to organic acids and that the sustentacular cells are the most sensitive cell type of this epithelium. A hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of organic acids in the rodent and human nasal cavity. The CFD-PBPK model simulations indicate that the olfactory epithelium of the human nasal cavity is exposed to two- to threefold lower tissue concentrations of a representative inhaled organic acid vapor, acrylic acid, than the olfactory epithelium of the rodent nasal cavity when the exposure conditions are the same. The magnitude of this difference varies somewhat with the specific exposure scenario that is simulated. The increased olfactory tissue dose in rats relative to humans may be attributed to the large rodent olfactory surface area (greater than 50% of the nasal cavity) and its highly susceptible location (particularly, a projection of olfactory epithelium extending anteriorly in the dorsal meatus region). In contrast, human olfactory epithelium occupies a much smaller surface area (less than 5% of the nasal cavity), and it is in a much less accessible dorsal posterior location. In addition, CFD simulations indicate that human olfactory epithelium is poorly ventilated relative to rodent olfactory epithelium. These studies suggest that the human olfactory epithelium is protected from irritating acidic vapors significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy and nasal air flow. Furthermore, the general structure of the hybrid CFD-PBPK model used for this study appears to be useful for target tissue dosimetry and interspecies dose comparisons for a wide range of inhaled vapors.

Autonomy in practice: are nurse practitioner students being prepared for reality?

This article reports on a study examining the relationship between nurse practitioner students' expectations of future professional autonomy and the level of autonomy experienced by certified nurse practitioners. The findings indicate that practicing nurse practitioners experience a greater sense of autonomy than student nurse practitioners perceive. As autonomy is an issue of continuing importance in nursing, and for advanced practice, further research is needed to assist schools of nursing in devising reality-based curricula for nurse practitioner programs.

Disposition and metabolism of acrylic acid in C3H mice and Fischer 344 rats after oral or cutaneous administration.

Acrylic acid (AA) is used in large amounts to produce acrylic esters and polymers. Here we report on the disposition and metabolism of [1-14C]AA in male C3H mice and Fischer 344 (F344) rats after oral (40 and 150) mg/kg) or cutaneous (10 and 40 mg/kg) administration. Although these and other strains of rodents have been used frequently in toxicity studies of AA, results of pharmacokinetic studies are available for only the Sprague-Dawley rat. In the current study, C3H mice rapidly absorbed and metabolized orally administered AA, with about 80% of the dose exhaled as 14CO2 within 24 h. Excretion in urine and feces accounted for approximately 3% and 1% of the dose, respectively. Elimination of 14C from plasma, liver, and kidney was rapid but was slower from fat. The disposition of orally administered AA in F344 rats was similar to the results obtained from mice. After cutaneous administration to C3H mice, about 12% of the dose was absorbed, while the remainder apparently evaporated. Approximately 80% of the absorbed fraction of the dose was metabolized to 14CO2 within 24 h. Excretion in urine and feces each accounted for less than 0.5% of the dose. Elimination of radioactivity from plasma, liver, and kidney was rapid; however, levels in fat were higher at 72 h than at 1 or 8 h. After cutaneous administration to F344 rats, 19-26% of the dose was absorbed, and the rest apparently evaporated. Disposition of the absorbed fraction of the dose was similar to results found in mice. Results from an in vitro experiment with rat skin showed that at least 60% of the applied dose evaporated and about 25% was absorbed, confirming the in vivo results. High-performance liquid chromatography (HPLC) analysis of rat urine and rat and mouse tissues indicated that absorbed AA was rapidly metabolized by the beta-oxidation pathway of propionate catabolism. In summary, rapid detoxification of systemically absorbed AA, as observed here in C3H mice and F344 rats, can explain findings that AA causes minimal systemic toxicity despite its causing irritation at portal-of-entry tissues.

Acrylic acid oxidation and tissue-to-blood partition coefficients in rat tissues.

We report rates of acrylic acid (AA) oxidation and tissue/blood partition coefficients in rat tissues. AA oxidation in Fischer 344 rat kidney and liver slices was described by saturable kinetics with maximal velocities of about 4 and 2 mumol/h/g, respectively. AA oxidation rates in 11 additional tissues were 40% or less than in liver. AA oxidation rates in Sprague-Dawley rat liver and kidney were similar to those in Fischer rats. Partition coefficients varied within a narrow range, suggesting that a tissue's contribution to systemic detoxification of AA will depend much more strongly on its rate of AA oxidation and the proportion of the cardiac output that it receives.

Metabolism of acrylic acid to carbon dioxide in mouse tissues.

Acrylic acid (AA) is acutely irritating at sites of initial contact but causes little systemic toxicity probably due to its rapid metabolism to CO2 and acetyl-CoA via a secondary pathway of propionic acid catabolism. In this study, the rate of AA oxidation in 13 tissues of C3H mice was measured by incubating tissue slices with [1-14C]AA and collecting, 14CO2. Oxidation of AA followed pseudo-Michaelis-Menten kinetics in the liver, kidney, and skin. Pseudo-Km values were similar among these tissues and averaged 0.67 mM. The maximal rate of AA oxidation in kidney, liver, and skin was 2890 +/- 436 (mean +/- SE, N = 3), 616 +/- 62, and 47.9 +/- 5.8 nmol/hr/g, respectively. The remaining organs oxidized AA at rates less than 40% of the rate in liver. Rates of metabolism in tissues from male and female mice were similar. 3-Hydroxypropionic acid was the only metabolite detected by high-performance liquid chromatographic analysis following incubation of tissues with [1-14C]AA. Kidney and liver also oxidized [2,3-14C]AA and [1-14C]acetate well, thus providing for the complete metabolism of AA carbons to CO2. These results demonstrate that the rate of AA metabolism varies significantly among mouse tissues and suggest that the kidneys and liver are major sites of detoxification of AA.

Flow cytometric analysis of xenobiotic metabolism activity in isolated rat hepatocytes.

Flow cytometry offers great potential for the study of xenobiotic metabolism in intact cells. We explored this application by the use of ethoxyfluorescein ethyl ester (EFEE) and isolated rat hepatocytes, a classic system for studying such reactions. EFEE is only weakly fluorescent and it diffuses freely into viable cells, where it is metabolized to fluorescein by a process dependent upon mixed-function oxidase activity. In the current study, viable hepatocytes were first identified by flow cytometric assessment of fluorescein diacetate staining. The viable subpopulation was also identifiable on the basis of forward and right angle light scattering properties alone, and it was in this fraction that EFEE metabolism was measured. Metabolism of EFEE to fluorescein was quantified by flow cytometry. SKF 525A, alpha-naphthoflavone, and metyrapone, classic inhibitors of mixed-function oxidation, each inhibited the metabolism of EFEE. These results demonstrate the potential of EFEE for use in flow cytometric studies of drug metabolism, such as in multiparameter mechanistic assays of cellular xenobiotic metabolism and toxicity, and in the isolation by fluorescence-activated cell sorting of subpopulations which differ in this activity.

Application of confocal scanning laser microscopy in experimental pathology.

Confocal scanning laser microscopy (CSLM) represents an exciting new tool for scientific disciplines which focus on mechanistic studies such as experimental pathology. Enhanced resolution in the specimen plane and rejection of out-of-focus fluorescence flare allow analysis of specific nucleic acid sequences, enzymes, structural macromolecules, and cellular homeostasis utilizing fluorescent probes. Four different experimental applications are discussed which utilize CSLM to evaluate pathological processes at the subcellular, cellular, and tissue levels. Programmed cell death, or apoptosis, is a natural process of significance both during development and as a response to toxic stimuli. CSLM-imaging of nuclei of human B lymphoblastoid cells following exposure to a monofunctional alkylating agent suggests that the degradation of chromatin characteristic of apoptosis may occur in asymmetric patterns. Surfactant apoprotein-A is the major non-serum protein component of pulmonary surfactant and is essential for the extracellular function of surfactant. CSLM of alveolar type II cells suggests that apoprotein-A is present in both the cytoplasm, predominantly in lamellar bodies, and in the nucleus. The tumor promoter, phorbol myristate acetate, rapidly stimulated the formation of vacuoles in human neutrophils. CSLM using Lucifer Yellow as a probe suggests that cylindrical vacuoles are formed by fluid-phase pinocytosis. The blood-nerve barrier (BNB) in peripheral nerves may be an important target during toxin-induced neuropathies. Ricin-induced permeability of the BNB in the rat was rapidly visualized by CSLM as leakage of fluorescein isothiocynate (FITC)-dextran into the endoneurial compartment.

Intravenous regional administration of methylprednisolone in rheumatoid arthritis.

Intravenous regional administration of corticosteroid (IVRAS) in the treatment of rheumatoid arthritis of the hand has not been reported previously. The method is based on a modification of Bier's block, with substitution of corticosteroid for local anaesthetic. Twenty-two patients were assessed in this double-blind, placebo-controlled study. The technique was safe and effective in improving grip strength, with a group mean improvement of more than 50%. Because suppression of endogenous cortisol production 24 h after treatment was commensurate with the dose of methylprednisolone used (40 mg), we could not exclude that the response may have been due to systemic steroid. Further studies are required to define the real value of IVRAS as it may offer alternative treatment of the joints and tendons within the hand and wrist in some patients rather than more prolonged oral therapy or individual, multiple joint or sheath injections.

Effects of 4-nitroquinoline-1-oxide on population growth, cell-cycle compartmentalization and viability in human lymphoblastoid cells.

The mechanism by which the carcinogen 4-nitroquinoline-1-oxide (4-NQO) kills mammalian cells is unclear; however, damage to DNA is presumed to be involved. We examined the relationship between the kinetics of cell death and alteration of cell-cycle compartmentalization after exposure of T5-1 human lymphoblastoid cells to 4-NQO (50 to 500 ng/ml) to establish whether cytotoxicity was related to the perturbation of DNA replication. Dose-dependent reductions in cell proliferation and cell viability were present from 1 day after treatment. Maximal reductions in viability were observed 2 days after exposure. Concentrations of 4-NQO of up to 175 ng/ml did not affect cell-cycle compartmentalization, but 250 ng 4-NQO/ml caused a transient accumulation of cells in S phase after 1 day. Only after 500 ng 4-NQO/ml was a marked and prolonged S-phase block observed from 1 day onwards. The lack of a strong correlation between S-phase block and cell death after exposure to 4-NQO suggests that responses to DNA damage in addition to perturbation of DNA replication entrain 4-NQO-induced cell lethality.

S-phase block and cell death in human lymphoblasts exposed to benzo[a]pyrene diol epoxide or N-acetoxy-2-acetylaminofluorene.

The relationship between perturbation of the cell cycle and induction of cell death by benzo[a]pyrene diol epoxide (BPDE) or N-acetoxy-2-acetylaminofluorene (AcAAF) in exponentially proliferating T5-1 human lymphoblastoid cells was studied. Both BPDE and AcAAF caused cells to accumulate in the S phase of the cell cycle. Perturbation of the cell cycle preceded reduction of cell viability and was associated with inhibition of population growth. Effects on each of the three parameters were noted during the first population doubling, suggesting that they occurred during the first cell cycle after exposure. BPDE-exposed cells accumulated initially in early to mid-S phase and then moved parasynchronously through the remainder of this phase. In contrast, AcAAF-exposed cells accumulated uniformly at all points of the S phase. High doses of either compound froze cell cycle progression, completely inhibited population growth, and killed nearly all cells in the population. Our results suggest that perturbation of DNA replication mediates cell death after exposure to doses of either chemical that cause less than complete inhibition of cell proliferation. However, additional processes, such as perturbation of transcription, may be involved in lethality after exposure to doses that immediately and completely inhibit population growth.

Cell cycle perturbation and cell death after exposure of a human lymphoblastoid cell strain to N-methyl-N'-nitro-N-nitrosoguanidine.

The mechanisms involved in cell death caused by carcinogens that methylate DNA are poorly understood. In this study, the cytotoxicity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was studied in exponentially growing T5-1 human lymphoblastoid cells. MNNG exposure killed cells and inhibited proliferation of the remaining viable cells. Reduction in cell viability, which coincided with the accumulation of cells in the late S phase of the cell cycle, was not apparent until the population had completed one doubling. Fluorescence-activated cell sorting of fluorescein diacetate-stained, MNNG-treated cells into live and dead subpopulations revealed that all cycle phases were well represented in the live fraction, whereas the dead fraction consisted primarily of cells with a sub-G1 DNA content. Thus, cell death after MNNG exposure occurred during the second cell cycle after treatment apparently as a consequence of perturbation of DNA replication and the degradation of nuclear DNA.

Effect of the suicide substrate 3,5-diethoxycarbonyl-2,6-dimethyl-4-ethyl-1,4-dihydropyridine on the metabolism of xenobiotics and on cytochrome P-450 apoproteins.

Treatment of rats with the cytochrome P-450 suicide substrate, 3,5-diethoxycarbonyl-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP), produced a 95% inhibition of the in vivo demethylation of either aminopyrine or morphine within 2 hr. One-carbon metabolism of formaldehyde or formate to carbon dioxide was not altered. DDEP also produced a time-dependent decrease in total hepatic microsomal cytochrome P-450 but had no effect on either NADPH-cytochrome c reductase or p-nitrophenol glucuronyl-transferase activities up to 24 hr after administration. A rapid decrease in rat liver microsomal aniline hydroxylation and ethoxyresorufin deethylation was observed in vitro following DDEP administration. Although in vitro testosterone metabolism to 16 alpha-, 16 beta-, and 2 alpha-hydroxy metabolites was depressed profoundly by DDEP in microsomes from untreated and 3-methylcholanthrene-treated animals, 7 alpha-hydroxylation of testosterone was much less affected. Immunochemical quantification of various microsomal cytochrome P-450 protein moieties showed that cytochromes P-450 beta NF-B, P-450UT-A, P-450PCN-E, and P-450PB-C were decreased in hepatic microsomes from DDEP-treated rats. However, the protein moiety of cytochrome P-450UT-H was not diminished and the immunoreactive protein for cytochromes P-450UT-F, P-450PB-B, and P-450ISF-G was only slightly decreased. These results show that DDEP treatment leads to marked decreases in holoprotein and apoproteins of many but not all hepatic microsomal cytochrome P-450 isozymes.

Role of hepatic tetrahydrofolate in the species difference in methanol toxicity.

The susceptibility of various species to methanol toxicity is inversely related to the rate of tetrahydrofolate (H4folate)-dependent formate oxidation to carbon dioxide. Thus, the levels of various folate derivatives and folate-dependent enzyme activities present in the livers of monkeys, which are sensitive to methanol, and rats, which are not, were compared in order to investigate the biochemical basis of this species difference. Hepatic H4folate levels in monkeys were 60% of those in rats, and formylated-H4folate derivatives were 2-fold higher in monkeys than in rats. No significant difference between monkeys and rats in the levels of total hepatic folate or 5-methyl-H4folate was observed. The activities of formyl-H4folate synthetase (EC 6.3.4.3) and formyl-H4folate dehydrogenase (EC 1.5.1.6) were 4- and 2-fold higher, respectively, in monkeys than in rats. There was no significant difference between monkeys and rats in methionine synthetase activity (EC 2.1.1.13). Dihydrofolate reductase activity (EC 1.5.1.3) in monkeys was 20% of that in rats. 5,10-Methylene-H4folate reductase (NADPH) activity (EC 1.1.1.171) in monkeys was 40% and 25% of that in rats when the rates of the forward and reverse reactions, respectively, were compared. Serine hydroxymethyltransferase activity (EC 2.1.2.1) was 2-fold higher in monkeys than in rats. The differences in the activities of methylene-H4folate reductase and serine hydroxymethyl-transferase between monkeys and rats may have contributed to the difference in hepatic H4folate levels. The 40% lower level of hepatic H4folate in monkeys, as compared to rats, relates well to the 50% lower maximal rate of formate oxidation in monkeys. Thus, the species difference in susceptibility to methanol may be explained by the difference in the level of hepatic H4folate.

Reduction of hepatic tetrahydrofolate and inhibition of exhalation of 14CO2 formed from [dimethylamino-14C]aminopyrine in nitrous oxide-treated rats.

The exhalation of 14CO2 after the administration of [dimethylamino-14C]aminopyrine to an organism is assumed to reflect the demethylation of aminopyrine by hepatic mixed-function oxidase activity. The formaldehyde formed as a result of the demethylation of aminopyrine is then sequentially oxidized to formic acid and CO2. The last step in the pathway, i.e., formate oxidation, is dependent upon tetrahydrofolate; thus, factors which alter hepatic tetrahydrofolate potentially may modify 14C-aminopyrine metabolism to 14CO2 in vivo. Exposure of rats to nitrous oxide (N2O) produces a significant reduction in hepatic tetrahydrofolate as a result of the inhibition of 5-methyltetrahydrofolate:homocysteine methyltransferase activity (E.C. 2.1.1.13). In the present study, exposure of rats to N2O/O2 (1:1) for 4 hr prior to the administration of 14C-aminopyrine (40 or 400 mumoles per kg) produced a 60% reduction in the peak rate of 14CO2 exhalation and a 45% decrease in the total 14CO2 exhaled within 2 hr. In control experiments, exposure of rats to nitrogen/O2 (1:1) produced no effect on 14C-aminopyrine metabolism to 14CO2. Administration of methionine (1.3 mmoles per kg) 30 min prior to 14C-aminopyrine administration reversed the inhibition of 14CO2 exhalation and reduction in hepatic tetrahydrofolate observed in N2O-exposed animals. Aminopyrine (400 mumoles per kg) administration to air-breathing rats did not affect the level of urinary formate, but exposure to N2O produced a 40-fold increase. Aminopyrine administration to N2O-exposed rats produced a 75% increase in urinary formate as compared to rats treated with N2O alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Methanol toxicity in the monkey: effects of nitrous oxide and methionine.

Methanol poisoning in monkeys and humans is characterized by the development of formic acidemia, metabolic acidosis and ocular toxicity. Formate, the metabolite associated with the toxicity of methanol, is oxidized to carbon dioxide by a tetrahydrofolate-dependent pathway. Nitrous oxide treatment was used to inhibit the tetrahydrofolate-generating enzyme, 5-methyltetrahydrofolate homocysteine methyltransferase (methionine synthetase, E.C. 2.1.1.13.), to delineate the role of this enzyme in regulating formate oxidation in the monkey. The importance of methionine in the regulation of formate oxidation in the monkey also was evaluated. Nitrous oxide inhibited the oxidation of formate generated from the metabolism of methanol (1 g/kg i.p.) in the monkey, resulting in the development of severe metabolic acidosis and high blood formate levels in these animals compared with air-breathing monkeys administered the same dose of methanol. Treatment of nitrous oxide-exposed monkeys with repetitive doses of methionine (100 mg/kg 10, 12 and 14 hr after methanol) reversed the effects of nitrous oxide on formate oxidation, resulting in a marked decrease in blood formate levels and an increase in the rate of [14C]O2 formation from methanol. Methionine treatment also reversed the development of metabolic acidosis and bicarbonate depletion observed in nitrous oxide-exposed monkeys. These results indicate that hepatic methionine synthetase is important in the regulation of tetrahydrofolate-dependent metabolism in the monkey and that the generation of tetrahydrofolate by this enzyme is a major factor in determining the sensitivity of a species to methanol poisoning.