Nasal cavity enzymes involved in xenobiotic metabolism: effects on the toxicity of inhalants.

A decade ago, the ability of nasal tissues to metabolize inhalants was only dimly suspected. Since then, the metabolic capacities of nasal cavity tissues has been extensively investigated in mammals, including man. Aldehyde dehydrogenases, cytochrome P-450-dependent monooxygenases, rhodanese, glutathione transferases, epoxide hydrolases, flavin-containing monooxygenases, and carboxyl esterases have all been reported to occur in substantial amounts in the nasal cavity. The contributions of these enzyme activities to the induction of toxic effects from inhalants such as benzo-a-pyrene, acetaminophen, formaldehyde, cocaine, dimethylnitrosamine, ferrocene, and 3-trifluoromethylpyridine have been the subject of dozens of reports. In addition, the influence of these enzyme activities on olfaction and their contribution to vapor uptake is beginning to receive attention from the research community. Research in the next decade promises to provide answers to the many still unanswered questions posed by the presence of the substantial xenobiotic metabolizing capacity of the nasal cavity.

Isotopic sensitivity in the microsomal oxidation of the dihydropyridine calcium entry blocker nifedipine.

The primary deuterium isotope effect on Vm for the microsomal oxidation of the dihydropyridine calcium entry blocker nifedipine [4-(2-nitrophenyl)-2,6-dimethyl-3,5- bis(methoxycarbonyl)-1,4-dihydropyridine] has been measured. The magnitude of the kinetic isotope effect, 6.7, suggests that the rate-limiting step in the mechanism of microsomal oxidation of nifedipine involves the loss of a hydrogen atom rather than nitrogen oxidation. Thus the microsomal oxidation of nifedipine is mechanistically different from that of other 1,4-dihydropyridines.

Persistent suppression of humoral immunity produced by 7,12-dimethylbenz(A)anthracene (DMBA) in B6C3F1 mice: correlation with changes in spleen cell surface markers detected by flow cytometry.

The purpose of these studies was to examine the effects of DMBA on subpopulations of splenocytes obtained from B6C3F1 mice, using cell surface markers defined by monoclonal antibodies and multiparameter flow cytometry. Changes were correlated with alterations in humoral immune function assessed in vitro. Mice were treated for 10 days during a 2 week period by subcutaneous (s.c.) injections of DMBA in corn oil at doses of 0.5, 5 and 10 micrograms/g/day (5-100 micrograms/g total dose). Four mice from each exposure group and an additional corn oil control group of mice were studied at 4 and 8 weeks following the last injection with DMBA. These studies demonstrated a dose-dependent decrease in the total number and percentage of spleen cells expressing B-cell markers (mu heavy chain, kappa light chain and 14.8 antigen) as well as T-cell markers (Thy 1.2, Lyt-1 and Lyt-2). The percentage of splenocytes expressing Mac-1 was increased by DMBA. Helper T-cells appeared to be a very sensitive population of spleen cells to DMBA exposure, as suggested by a decrease in the number and percentage of Lyt-1 positive cells recovered from the spleen 4 weeks after exposure to DMBA. DMBA produced a dose-dependent suppression of the in vitro primary humoral immune responses to SRBC, TNP-Ficoll and TNP-LPS. The fact that a functional suppression of humoral immunity was accompanied by a decrease in the number of mature B-cells and T-cells in the spleen suggests that cell surface markers may be useful indicators of immunotoxicity in animals receiving DMBA in sub-chronic studies.

Five-month oral (diet) toxicity/infectivity study of Bacillus thuringiensis insecticides in sheep.

Bacillus thuringiensis insecticides (Bt) [Dipel (test substance D or Thuricide-HP (test substance T)] were administered in the diet for 5 months to castrated mixed rambouillet/merino sheep (24-34 kg at the beginning of the study) at a dose of 500 mg/kg/day (approximately 10(12) spores per day). No treatment-related effect was seen on weight gain or clinical chemistry parameters nor were significant gross clinical changes observed. Several blood and tissue samples taken just prior to the time the animals were killed or at necropsy were found to be positive for Bt when cultured. Detailed gross and microscopic pathologic examination of the sheep revealed several incidental lesions. However, the only lesion that may have been associated with the treatment was lymphocytic hyperplasia in Peyer's patches seen in the cecum of three sheep and it was not considered to be clinically significant.

Analysis of heavy metal immunotoxicity by multiparameter flow cytometry: correlation of flow cytometry and immune function data in B6CF1 mice.

Bone marrow and spleen cells obtained from female B6C3F1 mice given a single i.p. exposure to cadmium acetate (0.9 mg/kg), lead acetate (12 mg/kg), or sodium acetate (12 mg/kg), were studied using flow cytometry, immunologic, and hematologic assays. Significant changes were detected in subpopulations of bone marrow cells using multiparameter flow cytometry within 1 day following treatment with cadmium or lead. Bone marrow cells obtained from B6C3F1 mice 5 days after treatment with cadmium or lead were found to have a decreased number of cells expressing Mac-1, 55-7.2, 14.8, and Lyt-1 antigens, suggesting a shift to immature cell types. An increase in the number of progenitor cells (CFU-C) obtained from the bone marrow of mice treated with heavy metals was also noted 5 days after exposure to cadmium or lead. A time-dependent suppression of the in vitro primary humoral immune response of spleen cells to SRBCs, TNP-Ficoll and TNP-LPS was produced by cadmium or lead treatment. Suppression of the mitogenic response of spleen cells to Con A, PHA, and LPS was also found to be time-dependent. Spleen cell surface marker expression (Mac-1, Lyt-1, Lyt-2 and 14.8) was altered in response to cadmium or lead treatments, but these changes did not appear to correlate with the humoral immunity or mitogen-induced proliferation data. These studies demonstrate that changes in cell surface markers on discrete subpopulations of lymphoid cells present in the spleens of heavy metal exposed mice may not correlate with alterations in the functional activity of these cells. However, changes in murine bone marrow surface markers in response to cadmium or lead treatment predicts a shift to immature cell types, which appeared to correlate with the increase in CFU-C activity.

Flow cytometry Coulter volume analysis of lead- and cadmium-induced cellular alterations in bone marrow obtained from young adult and aged Balb/c mice.

Flow cytometry Coulter volume analysis was used to examine the effects of an acute exposure to cadmium or lead on subpopulations of Balb/c bone marrow cells. A significant shift in the volume of Balb/c bone marrow cells was detected in response to a single i.p. injection of cadmium acetate (Cd) or lead acetate (Pb) compared to sodium acetate (Na)-treated mice. An increase in the relative number or size of myeloid/monocytic cells was noted in the bone marrow of cadmium or lead-treated mice. This effect was more pronounced in aged Balb/c mice than in young adults. These studies suggest the flow cytometry Coulter volume analysis may be a useful and sensitive technique for the assessment of cellular changes that occur in the bone marrow in response to xenobiotic exposure.

Comparative distribution of misonidazole and its amine metabolite in female Swiss Webster mice.

The distribution of misonidazole and its terminal reduction product 1-(2-amino-1-imidazolyl)-3-methoxy-2-propanol (miso-amine) were compared in female Swiss Webster mice to determine if either misonidazole or miso-amine is distributed to peripheral nerves. Female Swiss Webster mice received a 100 mg/kg (5 microCi/mumole) i.p. dose of either 3H-misonidazole or 3H-miso-amine and the distribution of radioactivity was determined in various tissues including sciatic nerves and other myelinated nerves. Urine from misonidazole treated animals contained both miso-amine and misonidazole (8.4 and 20.4%, respectively, of the total radioactivity in the urine). Misonidazole produced higher initial tissue concentrations of radioactivity than did miso-amine. The relative tissue concentrations of radioactivity produced by misonidazole or miso-amine were similar, although not identical, 48 hours after administration of the drugs. Both sciatic and other myelinated nerves were found to retain radioactivity following the administration of either misonidazole or miso-amine.

Formaldehyde production promoted by rat nasal cytochrome P-450-dependent monooxygenases with nasal decongestants, essences, solvents, air pollutants, nicotine, and cocaine as substrates.

To identify compounds which might be metabolized to formaldehyde in the nasal cavity, 32 potential substrates for cytochrome P-450-dependent monooxygenases were screened with rat nasal and, for comparison, liver microsomes. Tested substrates included 6 nasal decongestants, cocaine, nicotine, 9 essences, 3 potential air pollutants, and 12 solvents. Each test substrate, with the possible exception of the air pollutants, contained one or more N-methyl, O-methyl, or S-methyl groups. Eighteen of the tested materials were metabolized to produce formaldehyde by nasal microsomes. Five substrates, namely, the solvents HMPA and dimethylaniline, cocaine, and the essences dimethyl anthranilate and p-methoxyacetophenone, were metabolized to produce formaldehyde at rates exceeding 1000 pmol/mg microsomal protein/min by nasal microsomes. Eight substrates, including four nasal decongestants, nicotine, and an extract of diesel exhaust particles, were metabolized to produce formaldehyde at rates of 200 to 1000 pmol/mg microsomal protein/min. Five other substrates were metabolized to formaldehyde at detectable rates. The results indicate that a variety of materials which often come in contact with the nasal mucosa can be metabolized to formaldehyde by nasal enzymes. The released formaldehyde may influence the irritancy of inhaled compounds and has been suggested to play a role in the tumorigenicity of some compounds.

Cytochrome P-450-dependent monooxygenases in olfactory epithelium of dogs: possible role in tumorigenicity.

The respiratory tract epithelium of dogs, from the nose to the lungs, was examined for cytochrome P-450 and associated biotransformation activities. In the ethmoturbinates, where olfactory epithelium is located, the amount of cytochrome P-450 was comparable to that in the liver, when measured on the basis of activity per milligram of microsomal protein. The rest of the nasal region also contained large quantities of cytochrome P-450. The presence of these enzymes in the nose may be important in chemical-induced tumorigenesis. The nasal carcinogen hexamethyl-phosphoramide was shown to be metabolized by nasal microsomal enzymes to another nasal carcinogen, formaldehyde.

Cytochrome P-450 dependent monooxygenase activity in rat nasal epithelial membranes.

Cytochrome P-450 was found in nasal epithelial membranes (NEM) of the rat. The quantity was 12% that of liver on a per mg of microsomal protein basis and 1.6 times that of lung on the same basis. Metabolism of p-nitroanisole was faster by microsomes from NEM than by microsomes from liver or lungs while the metabolism rate of aniline by microsomes from NEM was between that of microsomes from liver and lung.

Monitoring children on sustained-release therapy by salivary theophylline levels.

The serum-saliva theophylline level ratio was measured in 19 chronically asthmatic children after their conditions were stabilized on a sustained-release theophylline preparation. Simultaneous serum and saliva samples were collected at 0, 4, 6, and 10 hours after theophylline dose and measured by high-pressure liquid chromatography. The mean ratio for the group of 1.52 +/- 0.64 approximated the mean ratio from previous reports. However, the correlation coefficient (r = .80) was lower, and the interpatient and intrapatient variability (25% and 23%) much higher, than in previous reports. The possible mechanism of these findings in relation to sustained-release preparations are discussed. These data question the use of salivary theophylline determinations to monitor therapy. Dosage should be based on serum measurements.

Inhibition of in vitro cytochrome P-450-catalyzed reactions by substituted pyridines.

A series of substituted pyridines was investigated as inhibitors of cytochrome P-450-catalyzed reactions. The relative potencies for the in vitro inhibition of aminopyrine demethylation and aniline hydroxylation are reported for a series of 2-, 3-, and 4-substituted pyridines.

Determination of selenium in tissues, serum, and blood of wild rodents by graphite furnace atomic absorption spectrophotometry.

Selenium (Se) levels were determined in liver, kidney, blood, and serum of wild rodents using graphite furnace atomic absorption spectrophotometry. A simple wet digestion technique was used to prepare samples for analysis. Nickel nitrate was used to suppress volatilization of Se during the char stage. Compared to existing techniques this greatly reduces the effort and time required for sample preparation and allows use of the graphite furnace atomic absorption technique for Se determination.

The effect of large doses of atropine sulfate on heart rate and blood pressure in rats.

Atropine sulfate causes bradycardia in doses which are greater than the usual anticholinergic doses producing tachycardia (Shucard and Andrew, 1977, Res. Comm. Chem. Path. Pharmacol. 16, 401-410). The present study was designed to evaluate the effects of large doses of atropine sulfate on heart rate and systemic blood pressure in rats. Six groups of urethane anesthetized, male, Sprague Dawley rats (200-450 g) were injected with varying doses of atropine via the jugular vein. Groups I through IV received 5 mg/kg, 20 mg/kg, 40mg/kg and 80 mg/kg, respectively. Group V was bilaterally vagotomized before the injection of 80 mg/kg of atropine. Animals in Group VI were bilaterally vagotomized and pretreated with propranolol-HCl before injection of 40 mg/kg of atropine. Atropine caused a significant (p less than 0.005) dose-dependent reduction in both heart rate and blood pressure. The negative chronotropic property of atropine shown in these experiments is in agreement with recent in vitro and in vitro studies. The cause of bradycardia in these doses appears to be an intrinsic property of atropine rather than being centrally mediated. Possible direct action by atropine on peripheral vascular resistance is discussed.