Benzo(a)pyrene quinone metabolism in tracheal organ cultures

The adjuvant effect of ambient particulate matter is closely reflected by the particulate oxidant potential

BACKGROUND

It has been demonstrated that ambient particulate matter (PM) can act as an adjuvant for allergic sensitization. Redox-active organic chemicals on the particle surface play an important role in PM adverse health effects and may determine the adjuvant effect of different particle types according to their potential to perturb redox equilibrium in the immune system.

OBJECTIVES

We determined whether the adjuvant effect of ambient fine particles versus ultrafine particles (UFPs) is correlated to their prooxidant potential.

METHODS

We have established an intranasal sensitization model that uses ambient PM as a potential adjuvant for sensitization to ovalbumin (OVA), which enhances the capacity for secondary OVA challenge to induce allergic airway inflammation.

RESULTS

UFPs with a greater polycyclic aromatic hydrocarbon (PAH) content and higher oxidant potential enhanced OVA sensitization more readily than did fine particles. This manifests as enhanced allergic inflammation upon secondary OVA challenge, leading to eosinophilic inflammation and mucoid hyperplasia starting at the nasal turbinates all the way down to the small pulmonary airways. The thiol antioxidant N-acetyl cysteine was able to suppress some of these sensitization events.

CONCLUSIONS

The adjuvant effects of ambient UFP is determined by their oxidant potential, which likely plays a role in changing the redox equilibrium in the mucosal immune system.

Effects of superoxide generated in vitro on glucuronidation of benzo[a]pyrene metabolites by mouse liver microsomes

Glucuronidation of benzo[a]pyrene (B[a]P) metabolites, generated in situ by oxidative pathways, was studied using mouse liver uninduced microsomes. No coupling was evident between UDP-glucuronyltransferase and oxygenation of B[a]P. UDPGA protected microsomal macromolecules against binding of reactive B[a]P metabolites. Superoxide, and other reactive oxygen species decreased both the overall B[a]P metabolism and glucuronidation of some B[a]P metabolic products, and caused more extensive binding to macromolecules; UDPGA was less protective in this condition. Peroxidation of microsomes differentially affected glucuronidation of various metabolites of B[a]P, and of various model substrates, indicating that multiple glucuronyltransferases are involved in the conjugation of hydroxylated metabolites of B[a]P.

Somatic mutation, DNA damage and cytotoxicity induced by benzo[a]pyrenedione/benzo[a]pyrenediol redox couples in cultured mammalian cells

BP-3,6-dione was found to be mutagenic, cytotoxic and to induce DNA damage in a transformed line of Syrian hamster fibroblasts at low concentrations, 2 micrograms/ml and less. Inhibition of sulfate and glucuronic acid conjugating enzymes with salicylamide potentiated the above effects of BP-3,6-dione. Diminishing cellular capacity to scavenge superoxide anion radicals also potentiated the mutagenic and cytotoxic action of the dione. The presence of dicumarol, a specific inhibitor of the two-electron reduction of quinones by DT-diaphorase, afforded some protection against cytotoxicity. The results indicate that BP-3,6-dione undergoes two-electron reduction to an unstable hydroquinone, BP-3,6-diol, or one-electron reduction to a semiquinone radical intermediate and that both of these reduced forms undergo rapid univalent oxidation to generate active reduced oxygen species. The data are consistent with the hypothesis that active oxygen species generated by BP-dione/BP-diol redox cycling are responsible, at least in part, for the mutagenic and cytotoxic effects observed with BP-3,6-dione.

Biochemical studies of the tracheobronchial epithelium

Tracheobronchial epithelium has been a focus of intense investigation in the field of chemical carcinogenesis. We have reviewed some biochemical investigations that have evolved through linkage with carcinogenesis research. These areas of investigation have included kinetics of carcinogen metabolism, identification of carcinogen metabolites, levels of carcinogen binding to DNA, and analysis of carcinogen-DNA adducts. Such studies appear to have provided a reasonable explanation for the susceptibilities of the respiratory tracts of rats and hamsters to carcinogenesis by benzo(a)pyrene. Coinciding with the attempts to understand the initiation of carcinogenesis in the respiratory tract has also been a major thrust aimed at effecting its prevention both in humans and in animal models for human bronchogenic carcinoma. These studies have concerned the effects of derivatives of vitamin A (retinoids) and their influence on normal cell biology and biochemistry of this tissue. Recent investigations have included the effects of retinoid deficiency on the synthesis of RNA and the identification of RNA species associated with this biological state, and also have included the effects of retinoids on the synthesis of mucus-related glycoproteins. Tracheal organ cultures from retinoid-deficient hamsters have been used successfully to indicate the potency of synthetic retinoids by monitoring the reversal of squamous metaplasia. Techniques applied to this tissue have also served to elucidate features of the metabolism of retinoic acid using high pressure liquid chromatography. In brief, formidable strides have been made in biochemistry specific to this important target tissue, despite the inability to acquire tracheobronchial epithelium in large quantities.

Influence of sulfur dioxide on metabolism and distribution of benzo[a]pyrene in isolated perfused rabbit lung

An isolated perfused lung [IPL) preparation was used to investigate the effects of SO2 (1-2 ppm) on the metabolism of benzo[a]pyrene (BaP), a ubiquitous potent carcinogen that has been associated with the increased incidence of a human bronchiogenic carcinoma in occupational and urban populations. [14C]BaP, with and without crude air particulate (CAP), was administered intratracheally to the IPL in conjunction with SO2 or after pretreatment of the whole animal with SO2. Metabolites were isolated from serial blood samples up to 3 h after the administration of [14C]BaP to the IPL. Metabolites were also isolated from lung tissue, washout fluid, macrophage, and trachea and bronchi at the end of the perfusion at 180 min. Patterns of BaP metabolites were determined by thin-layer and high-performance liquid chromatography and scintillation counting. SO2 given in conjunction with BaP on the IPL or given to the whole animal followed by BaP on the IPL, in comparison with BaP only on the IPL, resulted in a twofold increase in the total rate of appearance of metabolites of BaP in the blood with changes in the metabolic pattern. SO2 given in conjunction with BaP and CAP on the IPL, in comparison with BaP plus SO2 on the IPL, resulted in a threefold decrease in the total rate of appearance of metabolites of BaP in the blood with changes in the metabolic pattern.

Benzo[a]pyrene metabolism in organ cultures of human endometrium

Twenty-six specimens of normal human endometrium were obtained for studies of [3H]benzo[alpha]pyrene metabolism in short-term organ culture. The tissues were capable of converting benzo[alpha]pyrene (BP) to oxygenated derivatives which co-chromatographed with dihydrodiols, quinones and monohydroxy derivatives of BP. A sulfate conjugate of a monohydroxy BP was also found among the acetone/ethyl acetate soluble products. When the acetone/ethyl acetate soluble metabolites were analyzed using high-pressure liquid chromatography (HPLC), the proportion of metabolites were found to vary greatly from specimen to specimen. Eight women smoked cigarettes but the BP metabolite profiles from organ cultures of endometrial tissue from these women did not differ from those who did not smoke. The average value for sulfate conjugates of monohydroxy BP was significantly lower in endometrial tissue from three postmenopausal women (ages 49, 57 and 58) than among premenopausal women. Specimens from premenopausal women which had been in organ culture for 2 weeks prior to the addition of [3H] BP produced metabolite profiles similar to those of specimens from postmenopausal women with a greatly reduced proportion of BP-phenol sulfate conjugates. These data suggest that the absence of hormonal stimulus (i.e., advanced age or conditions of organ culture) may affect the metabolism of BP in human endometrial tissue.