Aryl Hydrocarbon Hydroxylase Activity In Lung Research Articles

Monoclonal Antibody-Directed Analysis of Benzo[

Monoclonal antibody (MAb) 1-7-1 against 3-methylcholanthrene (MC)-induced forms of cytochrome P-450 (CYP) was used to characterize benzo[a]pyrene (B[a]P) metabolism in rat liver and extrahepatic tissues and its modulation by phenolic antioxidants, propyl and octyl gallates. Male Wistar rats were treated with these food additives (50 mg/kg body wt ip) twice weekly for 14 days alone or in combination with MC. Immunochemical inhibition of aryl hydrocarbon hydroxylase (AHH) and [<O*>14C]B[a]P metabolism (analyzed by high-performance liquid chromatography) were measured in liver, kidney, and lung microsomes. Organ-specific changes in levels of MAb-mediated inhibition of microsomal metabolism of B[a]P were observed. In liver microsomes from untreated rats, AHH was not affected by MAb, but in kidney and lung, there was 70% and 50% inhibition, respectively. In MC-treated rats, MAb reduced AHH activity by 43% in liver. Kidney and lung AHH was inhibited up to 80% by this MAb. Formation of B[a]P metabolites in MC-induced microsomes from liver and kidney was affected by MAb in a similar way. In lung, the total metabolism was inhibited by 50% by MAb treatment, but significant differences in inhibition of individual metabolites were observed. Treatment with propyl or octyl gallate alone had no effect on MAb inhibition of AHH activity in liver and lung but decreased the level of inhibition in kidney. Combined treatment with MC and propyl or octyl gallate slightly reduced the effect of MAb on AHH activity in liver and significantly reduced the level of inhibition in kidney but did not affect AHH activity in lung. The same treatment regimen dramatically reduced MAb inhibition of B[a]P metabolism in kidney but had no effect on B[a]P metabolite formation in liver. Inhibition by MAb of renal 3-hydroxy-B[a]P, 7,8-B[a]P-dihydrodiol, and 1,6-quinone-B[a]P was the most affected. In lung, treatment with gallates affected only formation of 7,8-B[a]P-dihydrodiol. These results suggest that treatment with gallates affects the CYP 1A and may change the CYP isozyme composition and, thus, alter the tissues' susceptibility to tumor induction by B[a]P.

Aryl Hydrocarbon Hydroxylase Activity in Human Lung Tissue: In Relation to Cigarette Smoking and Lung Cancer

In order to investigate the relationship between aryl hydrocarbon hydroxylase (AHH) activity and smoking or lung cancer, AHH activities in fresh lungs (normal tissue, tumorous tissue, and surrounding tissue of tumor) obtained from lung cancer patients and non-lung cancer patients were measured. There were no differences in lung AHH activity in the lung lobes. In the non-lung cancer patients, AHH activities ranged from 0.13 to 2.37 (pmol 3 hydroxybenzo[ a]pyrene/20 min/mg protein), and whereas in the normal tissues of the lung cancer patients they ranged from 0.19 to 5.05. Lung AHH activities showed normal distribution, and a large variation (26 times) was observed in normal tissues in the lung cancer patients. In most cases, AHH activities in the tumorous tissues and the surrounding tissue of the tumor were lower than those in the normal tissues of the lung cancer patients. In the non-lung cancer group, the means of AHH activity of the nonsmoker subgroup (NN) and the smoker subgroup (SN) were 0.62 and 0.96, respectively. On the other hand, in the lung cancer group the means of AHH activity of the nonsmoker subgroup (NC) and smoker subgroup (SC) were 0.85 and 1.05, respectively. Statistically significant differences were observed between NN and SN, NN and NC, and NN and SC. These results suggest that human lung AHH activity was increased by cigarette smoke as in rodent lungs, and the distribution of basal AHH activity in lung tissue of the nonsmokers group in the lung cancer patients shifted toward high levels compared to the nonsmokers group in the non-lung cancer group. The effect of the histological cell types of the lung cancer on the AHH activity was not observed in this study.

Enzyme induction in rat lung and liver by condensates and fractions from main-stream and side-stream cigarette smoke

Aryl hydrocarbon hydroxylase (AHH) and dimethylnitrosamine demethylase (DMND) activities in pulmonary and hepatic tissues of male Sprague-Dawley rats were assayed following pretreatment with known inducers (benzo[a]pyrene, 3-methylcholanthrene, Aroclor 1254, phenobarbital) and with main-stream (MS) and side-stream (SS) cigarette smoke condensates and their related fractions. Biochemical assays by spectrophotofluorimetry (AHH activity) and spectrophotometry (DMND activity) and by a biological assay (Ames test) were performed to detect AHH and DMND induction. Ames test proved to be much less sensitive than the spectrophotofluorimetric analysis for AHH determination. Both main-stream and side-stream cigarette smoke condensates and some fractions, containing water-soluble bases, water-insoluble bases, and polycyclic aromatic hydrocarbons, were found to induce AHH activity in lung and liver, the lung being induced to the greatest extent. The highest levels of AHH inducibility were found for the SS-smoke condensate and related fractions. In particular, the insoluble bases fractions gave the highest induction. On the contrary, pulmonary DMND activity was not affected by pretreatment with the same materials, while hepatic DMND response was only minimally induced by Aroclor and phenobarbital treatment.

Lung aryl hydrocarbon hydroxylase: Inhibition following cadmium chloride inhalation

Polycyclic hydrocarbon metabolism in male Spraque-Dawley rats following inhalation of aerosolized cadmium chloride (CdCl 2) was examined. Constitutive activity of microsomal aryl hydrocarbon hydroxylase (AHH) (benzo( a)pyrene substrate) was monitored in lung and liver homogenates up to 10 days after exposure. Lung AHH activity was reduced by 85% during the first 2 days following cadmium inhalation, and did not return to normal levels until 7 days after exposure. Enzyme activity in the livers of cadmium-treated animals was similarly depressed (by 65%) within 24 hr. Cadmium inhalation also inhibited (by 50%) 3-methylcholanthrene (MC) induction of lung AHH when compared with MC-treated controls. No significant effect on AHH inducibility by MC was noted in liver homogenates from cadmium-exposed animals. Nonspecific microsomal damage appeared not to occur since glucose-6-phosphatase activity in lung was unaffected by cadmium treatment. Although the mechanism of cadmium's action remains unclear, it appears not to involve a direct interaction of the metal with enzyme. The alteration of AHH activity by cadmium may result from injury to a specific cell type within the lung, which may be a major site of pulmonary AHH activity, or may result from modulation of synthesis and/or degradation of heme proteins in the lung. These results suggest that cadmium, under these conditions, markedly reduces the constitutive and inducible activity of AHH in the lung.

Chronic cigarette smoke exposure adversely alters 14C-arachidonic acid metabolism in rat lungs, aortas and platelets

Male rats were exposed to freshly generated cigarette smoke once daily, 5 times a week for 10 weeks. Inhalation of smoke was verified by elevated carboxyhemoglobin in blood sampled immediately after smoke exposure and by increased lung aryl hydrocarbon hydroxylase activity 24 hours after the last smoke exposure. Aortic rings isolated from smoke-exposed rats synthesized less prostacyclin (PGI 2) from 14C-arachidonic acid than rings from sham rats. Platelets from smoke-exposed rats synthesized more thromboxane (TXA 2) from 14C-arachidonic acid than platelets from room controls but not those from sham rats. Lung microsomes from smoke-exposed rats synthesized more TXA 2 and had a lower PGI 2/TXA 2 ratio than lung microsomes from room controls and shams. It is concluded that chronic cigarette smoke exposure alters arachidonic acid metabolism in aortas, platelets and lungs in a manner resulting in decreased PGI 2 and increased TXA 2, thereby creating a condition favoring platelet aggregation and a variety of cardiovascular diseases.

Pulmonary aryl hydrocarbon hydroxylase: Tobacco smoke-exposed guinea pigs

Exposure of various species of laboratory animals (rats, hamsters, and mice) to tobacco smoke or tobacco smoke condensate usually results in increased activity of aryl hydrocarbon hydroxylase (AHH) in the lung. In an ongoing study on tobacco smoke toxicity, guinea pigs were exposed to smoke from five regular Canadian flue-cured tobacco cigarettes. The activity of AHH was measured 1, 3, 6, 12, and 24 hr after smoke exposure. Contrary to what has been observed in other species, cigarette smoke did not enhance AHH activity in the guinea pig lung, but rather depressed it. Exposure to the vapor phase of cigarette smoke did not depress AHH activity in the lung, while exposure to whole smoke from nicotine-free cigarettes resulted in a depression of AHH activity similar to that obtained with regular flue-cured tobacco cigarettes. 3-Methylcholanthrene injected ip at 50 mg/kg also failed to induce benzo(a)pyrene hydroxylase in the lung of guinea pigs 18 hr later, and Arochlor 1254 (500 mg/kg, ip) produced even a marked depression of AHH activity. In contrast, benzo(a)pyrene injected ip at 50 mg/kg did induce pulmonary AHH 18 hr later. All three chemicals were inducers of hepatic AHH. Treatment of Sprague-Dawley rats with the same chemicals produced a marked induction of this enzyme in both the lung and the liver. The present study suggests that this species difference in the inducibility of pulmonary AHH will have to be taken into account in future studies on acute and chronic toxicity of tobacco smoke.

Induction by cigarette smoke of aryl hydrocarbon hydroxylase activity in the rat kidney and lung.

In both the rat kidney and lung, inhalation of cigarette smoke diluted with air (1/15) for a limited period of time (15 min) specifically induces aryl hydrocarbon hydroxylase (AHH)2 in less than 4 h. Up to four successive inhalations administered at 2-h intervals activities. The maximal effect corresponds to about 10 times the control value. Compared to the kidney enzyme, the lung AHH activity is about three or four time more sensitive to small concentrations of cigarette smoke. The biological half-life of the lung AHH activity is longer than 24 h, while it is only 3-4 h in the kidney. In both tissues, the induced enzyme presents the same in vitro thermolability and sensitivity to various inhibitors. For the establishment of the AHH induction, protein synthesis is continuously required, while RNA synthesis is only necessary during the first 2 h following the smoke treatment.

Organ specificity of the sex dependent regulation of aryl hydrocarbon hydroxylase (AHH) in rat

Aryl hydrocarbon hydroxylase (AHH) activity was measured in liver, kidneys and lungs of control and gonadectomized Sprague-Dawley rats. There was a six-fold difference in hepatic AHH activity between male and female rat. Activity in male was highest, castration reduced this activity by about 50%, whereas ovariectomy had little effect on activity in female. No sex difference in lung AHH activity was discernable; on the other hand kidney AHH activity was higher in females than in males. These data suggest that, at least in the rat, sex dependent regulation of microsomal mixed function oxygenases is organ specific.