Effect of cigarette smoke on CYP1A1, CYP1A2 and CYP2B1/2 of nasal mucosae in F344 rats.

Enzymes of the nasal tissue, one of the first tissues to contact inhaled toxicants, are relatively resistant to induction by traditional inducers. Because tobacco smoke has been shown to induce cytochrome P450 1A1 (CYP1A1) in rat and human lung tissue, we hypothesized that it would also alter levels of xenobiotic-metabolizing enzymes in nasal mucosae. In the present study, the effect of mainstream cigarette smoke (MCS) on nasal CYP1A1, CYP1A2 and CYP2B1/2 was explored. Four groups of 30 F344 rats were exposed to MCS (100 mg total particulate matter/m3) or filtered air for 2 or 8 weeks. Western analysis of microsomes from nasal tissue of MCS-exposed rats showed an induction of CYP1A1 in respiratory and olfactory mucosae, as well as liver, kidney and lung. Relative to controls, CYP1A2 levels increased slightly in the liver and olfactory mucosa. CYP2B1/2, which increased in the liver, appeared to decrease in upper and lower respiratory tissues. Little to no immunoreactivity with CYP1A1 antibody was observed in fixed nasal sections of control rats, yet intense immunoreactivity was seen in epithelia throughout the nasal cavity of MCS-exposed rats. Ethoxyresorufin O-deethylase activity (associated with CYP1A1/2) decreased approximately 2-fold in olfactory mucosa, but increased in non-nasal tissues of rats exposed to MCS. Methoxy- and pentoxyresorufin O-dealkylase activities (associated with CYP1A2 and CYP2B1/2, respectively) decreased in olfactory and respiratory mucosae, as well as lung (CYP2B1/2), yet increased in liver. These data suggest that xenobiotic-metabolizing enzymines of the nasal mucosae may be regulated differently than other tissues.

An isotope-dilution gas chromatography-mass spectrometry method for trace analysis of xylene metabolites in tissues.

A gas chromatography-mass spectrometry (GC-MS) method using isotope dilution was developed to measure trace levels of xylene metabolites in brain tissues. The primary metabolites of xylene are dimethylphenol (DMP), methylbenzyl alcohol (MBA), toluic acid (TA), and methylhippuric acid (MHA). The internal standard was a mixture of deuterated DMP-d3, TA-d7, and MHA-d7. DMP-d3 was commercially available and was used as the internal standard for both DMP and MBA. TA-d7 and MHA-d7 were biosynthesized by administering xylene-d10 to rats and collecting their urine. Based on the noise peaks in 10 blank samples, the on-column limits of quantitation (mean +10 SD of noise peaks) were approximately 305, 1220, 545, and 386 pg for DMP, MBA, TA, and MHA, respectively. Analyte detection and recovery tests from brain tissues of control rats were conducted by spiking the tissues with 32 nmol/g of each analyte, together with the deuterated metabolites. The tissues were homogenized, extracted with ethyl acetate, and derivatized by trimethylsilylation. One microliter of the sample was injected into the GC-MS. The recoveries of the analytes were 104 +/- 8%, 80 +/- 9%, 93 +/- 10%, and 92 +/- 11% (mean +/- SD, n = 7) for DMP, MBA, TA, and MHA, respectively. The tissue preparation efficiency, which was indicated by absolute recoveries of internal standards, was approximately 33% for DMP, MBA, and TA and approximately 80% for MHA. No metabolites were detected in untreated control tissues. This simple and sensitive method to simultaneously detect major xylene metabolites in brain tissues could also be used for the analysis of blood and urine samples from workers to monitor p-xylene exposure.

Induction of nasal carboxylesterase in F344 rats following inhalation exposure to pyridine.

Carboxylesterases (CEs) in the nasal mucosa metabolize some inhaled esters, including industrially important acrylates and acetates, to toxic acid metabolites that produce site-specific lesions in the nasal epithelium. The metabolic capacity of CEs in the normal nasal mucosa is theoretically sufficient to protect the lower respiratory tract from toxicant-induced injury at concentrations of acrylates and acetates likely to be inhaled in industrial environments. Thus, alterations in the metabolism and toxicity of these substrates would be predicted with changes in the amount or activity of CE in the nasal mucosa. Although many other nasal enzymes have been reported to be relatively refractory to induction, the amount of CE in the nasal mucosa can be increased by inhalant exposure. In the liver, expression of CEs may be elevated in response to exposure to P450 inducers. To examine this phenomenon in the nose with the widely used industrial solvent pyridine, we examined the effect of pyridine inhalation at the threshold limit value concentration of 5 ppm, or at 444 ppm, 6 hr/day for 4 days on the localization and amount of immunoreactive CE in olfactory mucosas of F344/N rats. CE immunoreactivity was increased in Bowman's glands following exposure to 5 or 444 ppm pyridine, and in sustentacular cells most notably following the 5 ppm exposure. Quantitative densitometry showed a statistically significant, dose-related increase in the density of immunoreactive CE in Bowman's glands of pyridine-exposed rats. These results indicate pyridine, and possibly other solvents, can induce nasal CE, an enzyme not directly involved in the metabolism of those solvents, following low-dose, short-term exposure.(ABSTRACT TRUNCATED AT 250 WORDS)