Hydrolysis kinetics of propylene glycol monomethyl ether acetate in rats in vivo and in rat and human tissues in vitro.

The kinetic equivalency of propylene glycol monomethyl ether (PGME), derived from propylene glycol monomethyl ether acetate (PGMEA), as well as the parent compound (PGME) following intravenous administration to Fischer 344 rats was evaluated. In addition, in vitro hydrolysis rates of PGMEA in blood and liver tissue from rats and humans were determined. The blood kinetics were determined following iv administration to rats of PGME and PGMEA of low [10 and 14.7 mg/kg body weight (bw)] or high (100 and 147 mg/kg) equimolar dosages of PGME and PGMEA, respectively. The blood time courses of PGME elimination for both dosages of both compounds were identical. Half-lives of PGMEA elimination following iv administration of 14.7 or 147 mg PGMEA/kg bw were calculated to be 1.6 and 2.3 min, respectively. Rat and human in vitro hydrolysis rates of PGMEA were determined by incubation of 5 or 50 microg PGMEA/ml in whole blood or liver homogenate. The rate of loss of PGMEA was more rapid in rat blood than in human blood, with hydrolysis half-lives of 36 and 34 min in human blood and 16 and 15 min in rat blood for the 5 and 50 microg/ml concentrations of PGMEA, respectively. In contrast the rate of loss of PGMEA in human and rat liver homogenate incubations was similar, 27-30 min and 34 min, respectively. These data demonstrate the rapid hydrolysis of PGMEA in vivo to its parent glycol ether, PGME and that, once hydrolyzed, the kinetics for PGME derived from PGMEA are identical to that for PGME. This study supports the use of the toxicological database on PGME as a surrogate for PGMEA.     

Propylene oxide in blood and soluble nonprotein thiols in nasal mucosa and other tissues of male Fischer 344/N rats exposed to propylene oxide vapors--relevance of glutathione depletion for propylene oxide-induced rat nasal tumors.

High concentrations of propylene oxide (PO) induced inflammation in the respiratory nasal mucosa (RNM) of rodents. Concentrations > or =300 ppm caused nasal tumors. In order to investigate if glutathione depletion could be relevant for these effects, we determined in PO exposed male Fischer 344/N rats PO in blood and soluble nonprotein SH-groups (NPSH) in RNM and other tissues. Rats were exposed once (6 h) to PO concentrations between 0 and 750 ppm, and repeatedly for up to 20 days (6 h, 5 days/week) to concentrations between 0 and 500 ppm. At the end of the exposures, PO in blood and NPSH in tissues were determined. PO in blood was dependent on concentration and duration of exposure. After the 1-day exposures, NPSH depletion was most distinctive (RNM > liver > lung). Compared to controls, NPSH levels were 43% at 50 ppm PO in RNM and 16% at > or =300 ppm in both RNM and liver. Lung NPSH fell linearly to 20% at 750 ppm. After repeated exposures over 3 and 20 days to 5, 25, 50, 300, and 500 ppm, NPSH losses were less pronounced. At both time points, NPSH were 90%, 70%, 50%, 30%, and 30% of the control values in RNM. Liver NPSH decreased to 80% and 50% at 300 and 500 ppm, respectively. After 20 days, lung NPSH declined to 70% (300 ppm) and 50% (500 ppm). We conclude that continuous, severe perturbation of GSH in RNM following repeated high PO exposures may lead to inflammatory lesions and cell proliferation, critical steps on the path towards tumorigenicity.     

A physiological toxicokinetic model for inhaled propylene oxide in rat and human with special emphasis on the nose.

Chronic exposure to high concentrations of PO induced inflammation in the respiratory nasal mucosa (RNM) of rodents and, for concentrations >or= 300 ppm, caused nasal tumors. Considering the nose to be the most relevant target organ for PO-induced tumorigenicity, we developed a physiological toxicokinetic model for PO in rats and humans. It includes compartments for arterial, venous, and pulmonary blood, liver, muscle, fat, richly perfused tissues, lung, and nose. It simulates inhalation of PO, its distribution into tissues by blood flow, and its elimination by exhalation and metabolism. In nose, lung, and liver of rats, PO conjugation with glutathione (GSH), PO-induced GSH depletion, and formation of PO adducts to DNA are described. Also modeled are PO adducts to hemoglobin of rats and humans. Required partition coefficients and metabolic parameters were derived experimentally or from publications. In rats, simulated PO concentrations in blood and GSH levels in tissues agreed with measured data. If compared with reported values, levels of adducts with hemoglobin were underpredicted up to a factor of about 2. Adducts with DNA differed up to a factor of 3. Hemoglobin adducts predicted for PO-exposed workers were 1.5-1.9 times higher than the reported ones. Considering identical conditions of PO exposure, similar PO concentrations in RNM were modeled for rats and humans. Also, PO concentrations in blood, about 1/30th of those in RNM, were similar in both species. Since the model was evaluated on all available data in rats and humans, we consider it to be useful for estimating the risk from inhalation exposure to PO.     

Effects of propylene oxide exposure on rat nasal respiratory cell proliferation.

Long-term exposure of rodents to propylene oxide (PO) induced inflammation, respiratory cell hyperplasia, and nasal tumors at concentrations >/= 300 ppm, suggesting a possible role for cytotoxicity and compensatory cell proliferation in PO carcinogenesis. In this study, the effects of PO exposure on histopathology and cell proliferation in nasal and hepatic tissues were studied in male F344 rats exposed by inhalation for 3 or 20 days (0, 5, 25, 50, 300, and 500 ppm). Histopathology revealed an increase in mucous cell hyperplasia in the anterior nasal passages after 20 days of exposure (>/=300 ppm). This was associated with the formation of goblet cell nests. Cell proliferation was measured in the respiratory epithelium (NRE; mucociliary and transitional) lining the anterior nasal passages, the nasopharyngeal meatus (NPM), and the liver using BrdU administered with 3-day osmotic pumps. Significant increases in cell proliferation occurred (>3.6-fold) in the mucociliary epithelium lining the anterior nasal cavity at and above 300 ppm for both exposure periods. In the mucociliary epithelium, the 20-day labeling was commonly associated with nests of goblet cells. Significant increases in cell proliferation (>2.3-fold) were observed in the transitional epithelium at 500 ppm after 3 days of exposure and at 300 and 500 ppm after 20 days of exposure. Significant increases in cell proliferation in the NPM (>2.8-fold) were evident at 500 ppm PO after 3 days and at 300 and 500 ppm PO after 20 days of exposure. No exposure-related changes in cell proliferation were observed in the liver. These studies demonstrate a clear concordance between the site and exposure concentration for tumor induction and those causing significant increases in cell proliferation in the rat nose.     

Uptake of inspired propylene oxide in the upper respiratory tract of the f344 rat.

Propylene oxide (1,2-epoxypropane) is a nasal toxicant and weak site-of-contact carcinogen in the rodent. The current study was aimed at providing quantitative information on upper respiratory tract (URT) dosimetry of this vapor. Since depletion of nasal non-protein sulfhydryls (NPSH) may be important in the toxicity of this vapor and may serve as a biomarker for delivery of propylene oxide to nasal tissues, measurements of respiratory and olfactory NPSH content after propylene oxide exposure were also made. Towards these ends, uptake of this vapor was measured in the surgically isolated URT of the F344 rat at constant velocity inspiratory flow rates of 50 or 200 ml/min throughout a 60-min exposure. Immediately after exposure, nasal respiratory and olfactory tissues were removed and analyzed for NPSH content. Propylene oxide was scrubbed from the airstream with moderate efficiency in the isolated URT. Similar uptake efficiencies were observed at inspired concentrations of 25, 50, 100, and 300 ppm, averaging 25 and 11% at flow rates of 50 and 200 ml/min, respectively. After 1-h exposure to concentrations of 100 ppm or more, statistically significant depletion of nasal respiratory mucosal NPSH was observed. Nasal respiratory mucosal NPSH levels averaged approximately 90, 70, 50, 40, and 15% of control levels after 1-h exposure to 25, 50, 100, 300, or 500 ppm propylene oxide. Olfactory mucosal NPSH levels also generally decreased at 300 or 500 ppm propylene oxide, but did not demonstrate statistically significant, consistent changes after propylene oxide exposure.     

Nasal NPSH depletion and propylene oxide uptake in the upper respiratory tract of the mouse.

Propylene oxide is a nasal toxicant and weak site-of-contact carcinogen in the mouse and rat. To aid in inhalation risk assessment of this vapor and to provide data for comparison to the rat, the current study was aimed at providing quantitative information on upper respiratory tract (URT) dosimetry of this vapor in the mouse. Toward this end, uptake efficiencies of propylene oxide were measured in the surgically isolated URT of the male B6C3F1 mouse under constant velocity inspiratory flow conditions at flow rates of 12 and 50 ml/min and exposure concentrations of 25, 50, 100, 300, or 500 ppm. URT uptake efficiencies were measured continuously during 1 h exposure; mice were terminated immediately after exposure and nasal respiratory and olfactory mucosal nonprotein sulfhydryl (NPSH) levels were determined. Propylene oxide was scrubbed with moderate efficiency in the URT, with uptake efficiencies of < or = 33 and < or = 16% at the low and high inspiratory flow rates, respectively. Uptake efficiencies were slightly (approximately 5%) higher at low (25 or 50 ppm) than high (300 or 500 ppm) exposure concentrations, suggesting that a saturable uptake pathway may exist. Nasal tissue NPSH levels were significantly depleted at exposure concentrations of 300 and 500 ppm but not at concentrations of 100 ppm or lower. Similar levels of NPSH depletion were observed in both nasal respiratory and olfactory mucosa. These data from mouse show some key differences when compared with those reported for the rat.     

Evaluation of effects from repeated inhalation exposure of F344 rats to high concentrations of propylene.

Chronic exposure to propylene does not result in any increased incidence of tumors, yet does increase N7-hydroxypropylguanine (N7-HPGua) adducts in tissue DNA. To investigate any potential for genotoxicity (mutagenicity or clastogenicity), male F344 rats were exposed via inhalation to up to 10,000 ppm propylene for 1, 3, or 20 days (6 h/day, 5 days/week). The endpoints examined included gene (Hprt, splenocytes) and chromosomal (bone marrow micronucleus [MN]) mutations, hemoglobin (hydroxypropylvaline, HPVal) adducts in systemic blood, and DNA adducts (N7-HPGua) in several tissues. Similarly exposed female and male F344 rats, implanted with bromodeoxyuridine (BrdU) minipumps, were evaluated for nasal effects (irritation via histopathology and cell proliferation via BrdU). Internal dose measures provided clear evidence for propylene exposure, with HPVal increased for all exposures; N7-HPGua was increased in all tissues from rats exposed for more than 1 day (except lymphocytes). Saturation of propylene conversion to propylene oxide was apparent from the adduct dose-response curves. There were no biologically significant genotoxic effects demonstrated at any exposure level, with no increase in Hprt mutant frequency or in bone marrow MN formation. In addition, no histopathological changes were noted in rodent nasal tissues nor any induction of cell proliferation in nasal tissues. These results demonstrate that repeated exposure of rats to high concentrations of propylene (< or = 10,000 ppm) does not produce evidence of local nasal cavity toxicity or evidence of systemic genotoxicity to hematopoietic tissue, despite the formation of N7-HPGua adducts. In addition, these data indicate that formation of N7-HPGua does not correlate with any measure of genotoxic effect, neither mutagenic nor clastogenic.     

The effect of ethylene exposure on ethylene oxide in blood and on hepatic cytochrome p450 in Fischer rats.

Ethylene (74-85-1) is an important petrochemical and is produced endogenously. It is metabolized to ethylene oxide (EO) by cytochrome P450. We studied the inhibition of cytochrome P450 activity during exposure to ethylene, and verified that this inhibition was reflected in the concentration of EO in the blood. Male F344 rats were exposed to 1000, 600, and 300 ppm ethylene by nose-only inhalation for up to 6 h. Blood samples were obtained during exposure. On exposure to 600 ppm ethylene, blood EO concentration increased during the first hour of exposure and then decreased to approximately half of the peak blood concentration. A less pronounced decrease was observed at 300 ppm, and at 1000 ppm little change was observed between 10 min and 6 h of exposure. For the analysis of cytochrome P450 and isozyme-specific substrate activities, groups of four male F344 rats were removed for the collection of liver at various times after exposure to 300, 600, or 1000 ppm ethylene. At all concentrations, liver microsomal cytochrome P450 decreased during exposure. Of the various monooxygenase activities measured, 4-nitrophenol hydroxylase was the one most consistently altered, with maximal inhibition (approximately 50%) at 2 h of exposure to 1000 ppm ethylene, 4 h at 600 ppm, and 6 h at 300 ppm. Activity recovered to control levels by 6 h after exposure. Cytochrome P450 2E1 appears to be the major isoform of cytochrome P450 inhibited by exposure to ethylene, and this may explain in part the observed alteration in EO blood kinetics.     

环氧丙烷染毒对视觉诱发电位的急性作用

选用４０只雄性Ｗｉｓｔａｒ大鼠,随机分成环氧丙烷（ＰＯ）染毒组与对照组,采用静式吸入染毒,以５档计算浓度分别为３００,５００,１０００,２０００,５０００ｍｇ／ｍ３,对实验组大鼠每次染毒２小时,染毒结束后,立即测定闪光视觉诱发电位（ＦＥＰ）和模式翻转视觉诱发电位（ＰＲＥＰ）,分析各波（Ｐ１、Ｎ１、Ｐ２,Ｎ２和Ｎ１、Ｐ１、Ｎ２）潜伏期及其波幅（Ｎ１－Ｐ２、Ｐ２－Ｎ２和Ｎ１－Ｐ１、Ｐ１－Ｎ２）。大鼠在２０００ｍｇ／ｍ３染毒时,ＰＲＥＰ测定中Ｎ２波潜伏期显著延长。５０００ｍｇ／ｍ３浓度时,ＰＲＥＰ和ＦＥＰ各波潜伏期均有显著延长,于第２天已部分恢复,但波幅未见改变。这说明ＰＯ对中枢神经系统产生功能性抑制作用。然而低浓度ＰＯ染毒时就出现呼吸道刺激症状,远早于诱发电位的变化;高浓度时有明显呼吸系统刺激症状,出现呼吸困难。因此,急性ＰＯ染毒对中枢神经的抑制作用较小,主要为呼吸系统刺激作用     

布地奈德对哮喘大鼠中性粒细胞诱导型一氧化氮合酶表达的影响

目的：观察诱导型一氧化氮合酶（iNOS）蛋白在哮喘大鼠血中性粒细胞（PMN）中的表达,探讨PMN参与哮喘炎症的可能机制,并研究布地奈德的影响。方法：采用卵白蛋白（OVA）和Al（OH）3制备大鼠哮喘模型,分离纯化血PMN,免疫细胞化学法检测PMN中iNOS蛋白的表达水平,比色法测定支气管肺泡灌洗液（BALF）中NO浓度。结果：哮喘组大鼠PMN中iNOS蛋白的表达水平显著高于正常对照组（P〈0.01）,布地奈德治疗组PMN中iNOS蛋白的表达水平显著低于哮喘组（P〈0.01）;哮喘组支气管壁iNOS蛋白的表达水平显著高于正常对照组（P〈0.01）,布地奈德治疗组支气管壁iNOS蛋白的表达水平显著低于哮喘组且高于正常对照组（均P〈0.01）;哮喘组BALF中NO浓度显著高于正常对照组（P〈0.01）,布地奈德治疗组BALF中NO浓度显著低于哮喘组（P〈0.01）;PMN中iNOS蛋白的表达水平与BALF中NO浓度呈显著正相关（n=29,r=0.754,P〈0.01）;支气管壁iNOS蛋白的表达水平与BALF中NO浓度呈显著正相关（n=29,r=0.760,P〈0.01）。结论：哮喘大鼠PMN合成iN-OS蛋白的功能增加,PMN可能部分通过iNOS参与哮喘的发病,这种功能可以部分被布地奈德所抑制。     

In vitro and in vivo phase II metabolism of combretastatin A-4: Evidence for the formation of a sulphate conjugate metabolite

1. Combretastatin A-4 (CA-4), is a natural compound with a potent tubulin polymerization and cell growth inhibitor properties. For these reasons CA-4 is one of the most potent anti-vascular agents that shows strong cytotoxicity against a variety of human cancer cells, including multi-drug-resistant cancer cell lines. In order to complete the knowledge of metabolic fate of CA-4, the in vitro and in vivo phase II metabolism was investigated.

2. Both in incubation with rat and human liver S9 preparation in the presence of 39-phosphoadenosine-5´-phosphosulfate (PAPS) as a cofactor the formation of a previously no reported sulphate metabolite was demonstrated through liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) data and comparison with a synthetic reference sample.

3. In incubation of CA-4 using rat and human liver microsomes, the formation of CA-4 glucuronide was observed and chromatographic and mass spectral properties of the metabolite were achieved and compared with those of a synthetic reference sample.

4. Incubation of CA-4 with rat and human liver S9 preparation in the presence of uridine-5´-diphosphoglucuronic acid trisodium salt (UDPGA) and an β-nicotinamide adenine dinucleotide phosphate, reduced form (NADPH)-regenerating system as cofactors resulted in the formation of glucuronides arising from phase I CA-4 metabolites.

5. When CA-4 was administered intraperitoneally to rat at a dose of 30 mg kg^?1, both glucuronide and sulphate metabolites were observed in LC-ESI-MS-MS chromatograms and their mass spectral data were identical to those obtained from synthetic standards.

     

Nitric oxide and reactive oxygen species production causes progressive damage in rats after cessation of silica inhalation.

Our laboratory has previously reported results from a rat silica inhalation study which determined that, even after silica exposure ended, pulmonary inflammation and damage progressed with subsequent fibrosis development. In the present study, the relationship between silica exposure, nitric oxide (NO) and reactive oxygen species (ROS) production, and the resultant pulmonary damage is investigated in this model. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were sacrificed at 0 days postexposure, while another portion was maintained without further exposure for 36 days to examine recovery or progression. The major findings of this study are: (1) silica-exposed rat lungs were in a state of oxidative stress, the severity of which increased during the postexposure period, (2) silica-exposed rats had significant increase in lung NO production which increased in magnitude during the postexposure period, and (3) the presence of silica particle(s) in an alveolar macrophage (AM) was highly associated with inducible nitric oxide synthase (iNOS) protein. These data indicate that, even after silica exposure has ended, and despite declining silica lung burden, silica-induced pulmonary NO and ROS production increases, thus producing a more severe oxidative stress. A quantitative association between silica and expression of iNOS protein in AMs was also determined, which adds to our previous observation that iNOS and NO-mediated damage are associated anatomically with silica-induced pathological lesions. Future studies will be needed to determine whether the progressive oxidative stress, and iNOS activation and NO production, is a direct result of silica lung burden or a consequence of silica-induced biochemical mediators.     

Carcinogenic and toxicologic effects of inhaled ethylene oxide and propylene oxide in F344 rats

The chronic inhalation toxicity and carcinogenicity of ethylene oxide (EO) and propylene oxide (PO) were evaluated in a 2-year inhalation bioassay. Five groups of male weanling Fischer 344 rats, 80 per group, were exposed at 0 ppm (shared control; filtered air), 50 ppm EO, 100 ppm EO, 100 ppm PO, or 300 ppm PO (7 hr/day, 5 days/week) for 104 weeks. Body weights from rats exposed to EO and PO at all exposure concentrations were significantly reduced compared to controls. A statistically significant increase in mortality was observed in all groups of exposed rats compared to controls. Skeletal muscle atrophy in the absence of any sciatic nerve neuropathology was found in rats exposed at 100 ppm EO and 300 ppm PO. Statistically significant associations between EO exposure and an increased incidence of the following rat neoplasms were observed: mononuclear cell leukemia, peritoneal mesothelioma, and mixed cell brain glioma. Among rats exposed to PO there was a dose-dependent increase in the incidence of complex epithelial hyperplasia in the nasal passages, and two adenomas were detected in the nasal passages of rats exposed at 300 ppm PO. The incidence of adrenal pheochromocytomas was elevated in both PO exposure groups, but not in a dose-related manner. All rat groups were affected by an outbreak of Mycoplasma pulmonis infection which occurred about 16 months into the study. This infection alone and in combination with the epoxide exposures affected the survival of rats in this study, and influenced the development of the proliferative lesions in the nasal mucosa of the PO-exposed rats. No treatment-related changes in any clinical chemistry or urinalysis indices were detected. PO exposure did not increase the incidence of the three neoplasms associated with EO exposure; however, adrenal pheochromocytomas and proliferative lesions of the nasal cavity were increased in rats exposed to PO.     

诱导型一氧化氮合酶在哮喘大鼠肺组织及中性粒细胞中的表达及地塞米松对其的影响

目的：观察诱导型一氧化氮合酶（iNOS）在哮喘大鼠肺组织及血中性粒细胞（PMN）中的表达,探讨PMN参与哮喘炎症的可能作用机制。方法：采用大鼠哮喘模型,随机分成哮喘组、对照组、地塞米松干预组,分离纯化血PMN,免疫组织化学法检测iNOS蛋白的表达水平,测定支气管肺泡灌洗液（BALF）中NO浓度。结果：哮喘组PMNiNOS蛋白光密度（OD）值（0.122±0.017）的表达水平显著高于对照组OD值（0.076±0.014）（P〈0.01）,地塞米松干预组OD值（0.089±0.013）PMNiNOS蛋白的表达水平显著低于哮喘组OD值（P〈0.01）,但与对照组相比差异无统计学意义。哮喘组支气管壁iNOS蛋白OD值（0.243±0.039）的表达水平显著高于对照组（0.119±0.016）（P〈0.01）,地塞米松干预组OD值（0.164±0.016）支气管壁iNOS蛋白的表达水平显著低于哮喘组且高于对照组（P均〈0.01）。哮喘组BALFNO浓度（8.59±1.07）ng/mL显著高于对照组（3.69±1.00）ng/mL（P〈0.01）,地塞米松干预组BALFNO浓度（4.28±0.89）ng/mL显著低于哮喘组（P〈0.01）,但与对照组相比差异无统计学意义。PMNiNOS蛋白的表达水平与BALFNO浓度呈显著正相关（n=29,r=0.770,P〈0.01）。支气管壁iNOS蛋白的表达水平与BALFNO浓度呈显著正相关（n=29,r=0.802,P〈0.01）。结论：哮喘大鼠PMN合成iNOS蛋白的功能增加,PMN可能通过iNOS参与哮喘的发病机制,这种功能可以部分被地塞米松所抑制。     

PBPK modeling of the percutaneous absorption of perchloroethylene from a soil matrix in rats and humans.

Perchloroethylene (PCE) is a widely used volatile organic chemical. Exposures to PCE are primarily through inhalation and dermal contact. The dermal absorption of PCE from a soil matrix was compared in rats and humans using real-time MS/MS exhaled breath technology and physiologically based pharmacokinetic (PBPK) modeling. Studies with rats were performed to compare the effects of loading volume, concentration, and occlusion. In rats, the percutaneous permeability coefficient (K(P)) for PCE was 0.102 +/- 0.017, and was independent of loading volume, concentration, or occlusion. Exhaled breath concentrations peaked within 1 h in nonoccluded exposures, but were maintained over the 5 h exposure period when the system was occluded. Three human volunteers submerged a hand in a container of PCE-laden soil for 2 h and their exhaled breath was continually monitored during and for 2.5 h following exposure. The absorption and elimination kinetics of PCE were slower in these subjects than initially predicted based upon the PBPK model developed from rat dermal kinetic data. The resulting K(P) for humans was over 100-fold lower than for the rat utilizing a single, well-stirred dermal compartment. Therefore, two additional PBPK skin compartment models were evaluated: a parallel model to simulate follicular uptake and a layered model to portray a stratum corneum barrier. The parallel dual dermal compartment model was not capable of describing the exhaled breath kinetics, whereas the layered model substantially improved the fit of the model to the complex kinetics of dermal absorption through the hand. In real-world situations, percutaneous absorption of PCE is likely to be minimal.     

Cardiovascular effects of chronic nitric oxide synthase inhibition in genetically hypertensive rats

1. The possible role of an endothelial defect in the hypertension of the New Zealand genetically hypertensive (GH) rat strain was assessed by examining cardiovascular responses to the nitric oxide synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) and the endothelium-dependent depressor agent acetylcholine (ACh). The vascular sensitivity of the hindquarter to nitric oxide (NO) was examined using the NO donor sodium nitroprusside (SNP). 2. NG-Nitro-L-arginine methyl ester (10 mg/kg per day in drinking water) was given to GH and normotensive (N) rats from age 7-9 weeks, with GH and N untreated control groups. Systolic blood pressure (tail-cuff) was monitored weekly from age 5-9 weeks. At age 9 weeks, pressure responses to various vasoactive agents were measured in vivo and in the rat isolated hindquarter. Left ventricular (LV) mass was measured at the time of death. 3. NG-Nitro-L-arginine methyl ester induced a greater hypertensive effect in GH (P < 0.001) compared with N (P < 0.05) rats and caused a significant increase in hindquarter perfusion pressure in GH rats only (P < 0.01). 4. Genetically hypertensive rats had LV hypertrophy that was exacerbated by L-NAME (P < 0.01). Left ventricular hypertrophy was not induced by L-NAME in N rats. 5. The normalized response to ACh did not differ between GH and N control rats and was unaffected by L-NAME treatment in vivo and in vitro except at the highest ACh dose (3 micrograms/kg) in GH hindquarters (P < 0.01). The response to SNP was similar in GH and N hindquarters and enhanced by L-NAME in GH (0.1 microgram; P < 0.05) and N rats (0.01 microgram, P < 0.01; 0.01 microgram, P < 0.001). 6. These results suggest that the L-arginine/NO system is not deficient in GH rats and that endothelial function in the GH hindquarter is preserved. They confirm that NO is involved in mediating blood pressure in GH and N rats and raise the possibility that a non-NO-mediated mechanism may underlie ACh-induced vasodilation in GH and N.     

Two-week aerosol inhalation study in rats of ethylene oxide/propylene oxide copolymers.

Previous studies have shown that aerosols of an ethylene oxide/propylene oxide copolymer (UCON 50-HB-5100) produced an inflammatory response in lungs of rats in short-term repeated exposures at relatively low concentrations. This study was carried out on related polyalkylene glycols (EO/PO copolymers) to determine if similar effects would occur upon short-term repeated exposure. Rats were treated by whole body liquid droplet aerosol exposures of six hours per day, five days per week for two consecutive weeks to each of five EO/PO copolymers. The exposure level for the positive control (UCON 50-HB-5100) was 55 mg/m3, while the remaining 4 test copolymers were evaluated at 100 mg/m3. Each exposure group consisted of ten male albino rats. After three exposures, nine of ten rats exposed to UCON 50-HB-5100, and six of ten rats exposed to UCON 50-HB-2000 had died. At necropsy, congestion, consolidation and red discoloration of the lungs were noted. A moderate to severe alveolitis, characterized by intraalveolar edema, hemorrhage and fibrin deposition, was observed after five days of exposure. At necropsy, these rats exhibited elevated lung weights and similar macroscopic and microscopic lesions. Rats exposed to the other test materials (UCON 75-H-1400, Pluronic L17R1, Pluronic L31, and Pluronic L64) survived with essentially no signs of toxicity through the ten exposure days. Body weights, organ weights, hematological evaluation, pharmacotoxic signs, and macroscopic and microscopic evaluation after necropsy were similar between groups and when compared to the negative control group. Only a slight alveolitis was noted after two weeks of exposure which subsided by two-weeks post exposure.     

Nonmonotonic dose-response relationships: mechanistic basis, kinetic modeling, and implications for risk assessment.

Dose-response curves for the first interaction of a chemical with a biochemical target molecule are usually monotonic; i.e., they increase or decrease over the entire dose range. However, for reactions of a complex biological system to a toxicant, nonmonotonic (biphasic) dose-effect relationships can be observed, showing a decrease at low dose followed by an increase at high dose, or vice versa. We present four examples to demonstrate that nonmonotonic dose-response relationships can result from superimposition of monotonic dose responses of component biological reactions. Examples include (i) a membrane-receptor model with receptor subtypes of different ligand affinity and opposing downstream effects (adenosine receptors A1 vs. A2), (ii) androgen receptor-mediated gene expression driven by homodimers, but not mixed-ligand dimers, (iii) repair of background DNA damage by enzymatic activity induced by adducts formed by a xenobiotic, (iv) rate of mutation as a consequence of DNA damage times rate of cell division, the latter being modulated by cell-cycle delay at low-level DNA damage, and cell-cycle acceleration due to regenerative hyperplasia at cytotoxic dose levels. Quantitative analyses based on biological models are shown, and factors that affect the degree of nonmonotonicity are identified. It is noted that threshold-type dose-response curves could in fact be nonmonotonic. Our analysis should promote a scientific discussion of biphasic dose responses and the concept termed "hormesis," and of default procedures for low-dose extrapolation in toxicological risk assessment.     

2,4,6-Trinitrotoluene inhibits endothelial nitric oxide synthase activity and elevates blood pressure in rats

2,4,6-Trinitrotoluene (TNT), which is widely used in explosives, is an important occupational and environmental pollutant. Human exposure to TNT has been reported to be associated with cardiovascular dysfunction, but the mechanism is not well understood. In this study, we examine the endothelial nitric oxide synthase (eNOS) activity and blood pressure value following TNT exposure. With a crude enzyme preparation, we found that TNT inhibited the enzyme activity of eNOS in a concentration-dependent manner (IC₅₀ value=49.4 μM). With an intraperitoneal administration of TNT (10 and 30 mg/kg) to rats, systolic blood pressure was significantly elevated 1 h after TNT exposure (1.2- and 1.3-fold of that of the control, respectively). Under the conditions, however, experiments with the inducible NOS inhibitor aminoguanidine revealed that an adaptive response against hypertension caused by TNT occurs. These results suggest that TNT is an environmental chemical that acts as an uncoupler of constitutive NOS isozymes, resulting in decreased nitric oxide formation associated with hypertension in rats.     

Species differences in the pharmacokinetics of KW-7158 [(2S)-(+)-3,3,3-Trifluoro-2-hydroxy-2-methyl-N-(5,5,10-trioxo-4,10-dihydrothieno[3,2-c][1]benzothiepin-9-yl)propanamide]: formation of hydrolyzed metabolite in human and animals

1. Species differences in the pharmacokinetics of KW-7158 [(2S)-(+)-3,3,3-Trifluoro-2-hydroxy-2-methyl-N-(5,5,10-trioxo-4,10-dihydrothieno[3,2-c][1]benzothiepin-9-yl)propanamide] were studied in in vivo and in vitro experiments.

2. The exposure ratio of hydrolyzed metabolite (M2, primary metabolite in human plasma)/KW-7158 was higher than the ratio of thiophen-to-furan converted metabolite (M1)/KW-7158 in human subjects after oral administration, but the mouse, rat and dog studies gave opposite results.

3. M2 was produced in the highest amount by the 9000g supernatant of small intestine, followed by that of liver and kidney in human subjects. After correction for protein contents, the results obtained suggested that the small intestine plays a major role in the metabolism to M2 for the first pass effect after oral administration of KW-7158.

4. The formation of M2 was independent of the presence of NADPH and was inhibited by various esterase inhibitors.

5. These observations suggested that the predominant enzymes or isozymes involved in the formation of M2 are esterases, which differ between humans and animals. Such differences may be one of the reasons for the species differences in the pharmacokinetics of KW-7158 between humans and animals.