Pulmonary metabolism of benzo(a) pyrene : effect of asbestos

Our plain-English summary of Pulmonary metabolism of benzo(a) pyrene : effect of asbestos, by C. Kandaswami, P.J. O'Brien (Biochemical Pharmacology, 1981).

The study

• Authors: C. Kandaswami, P.J. O'Brien
• Journal: Biochemical Pharmacology
• Published: 1981;30(7):811-4
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This preliminary communication examined whether asbestos affects the activity of aryl hydrocarbon hydroxylase, the enzyme system that metabolizes the carcinogen benzo(a)pyrene, in rat lung. The authors noted that asbestos and polycyclic aromatic hydrocarbons in cigarette smoke appear to act synergistically in causing lung cancer. Male Sprague-Dawley rats (200-250 g) were pretreated with 3-methylcholanthrene (40 mg/kg i.p. daily for 4 days), and lung microsomal fractions were isolated. Standard asbestos samples were supplied by the International Union Against Cancer. In one procedure, microsomes were preincubated with 2 mg of asbestos for 1 hour at 37°C. In another, benzo(a)pyrene was preincubated with a small amount of asbestos (50 µl of a 0.5 mg/ml suspension) for 10 minutes before microsomes were added. Enzyme activity was measured by fluorescence of phenolic products. With microsomal preincubation, activity relative to the asbestos-free control was 34% with crocidolite, 46% with Canadian chrysotile B, 38% with amosite and 40% with anthophyllite (averages of 3 experiments). Pretreating benzo(a)pyrene with asbestos also lowered activity, to 58% with crocidolite and 64% with chrysotile. The metal chelator EDTA did not affect inhibition by asbestos, although it protected the enzyme against copper. The authors concluded that asbestos could prevent benzo(a)pyrene from being metabolized in lung tissue. This might slow its clearance and prolong its retention. The inhibition did not appear to be due to trace metals associated with asbestos.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This preliminary communication reported a test-tube experiment on whether asbestos affects aryl hydrocarbon hydroxylase. This is an enzyme system in rat lung that breaks down benzo(a)pyrene, a cancer-causing chemical found in cigarette smoke. The authors mixed lung microsome fractions from male Sprague-Dawley rats, pre-treated with 3-methylcholanthrene injections, with standard samples of crocidolite, Canadian Chrysotile B, amosite or anthophyllite asbestos for one hour. Compared with samples without asbestos, enzyme activity fell to 34% with crocidolite, 46% with chrysotile, 38% with amosite and 40% with anthophyllite, averaged over 3 experiments. The article's text said crocidolite caused the least inhibition, which does not match these table figures. When benzo(a)pyrene was first mixed with a smaller amount of asbestos, activity fell to 58% with crocidolite and 64% with chrysotile. Adding EDTA, a metal-binding chemical, did not change the inhibition. The authors concluded that asbestos could prevent benzo(a)pyrene from being metabolized in the tissue. Asbestos was added in the test tube, not breathed in, and cancer was not measured.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Preliminary communication reporting an in vitro (test-tube) biochemical experiment on rat lung microsomes
• Who was studied: Lung microsomal fractions from male Sprague-Dawley rats weighing 200 to 250 g, pre-treated with daily injections of 3-methylcholanthrene for 4 days. The number of rats was not stated. Department of Biochemistry, Memorial University of Newfoundland, Canada.
• Exposure: Standard asbestos samples from the International Union Against Cancer: crocidolite, Canadian Chrysotile B, amosite and anthophyllite. These were added to the test mixture in one of two ways: 2 mg of asbestos preincubated with the microsomes for 1 hour, or benzo(a)pyrene first preincubated with 50 microlitres of a suspension containing 0.5 mg asbestos per ml.
• Main results:
  • When asbestos was preincubated with the lung microsomes, enzyme activity relative to the no-asbestos control (100%) was 34% (range 32-36) with crocidolite, 46% (42-50) with Canadian Chrysotile B, 38% (35-41) with amosite, and 40% (36-43) with anthophyllite. These are averages of 3 separate experiments. Control specific activity was 15 pmoles/minute/mg of protein.
  • When benzo(a)pyrene was first preincubated with asbestos, enzyme activity relative to control (100%) was 58% with crocidolite and 64% with Canadian Chrysotile B (averages of 3 experiments). The authors noted that relatively small amounts of asbestos inhibited the activity in this setup.
  • The metal-chelating agent EDTA did not affect inhibition by asbestos, though it protected the enzyme against inhibition by copper. The authors stated that the inhibition does not seem to be due to trace metals associated with asbestos.
• The authors' conclusion: The authors concluded that asbestos could prevent benzo(a)pyrene from being metabolized in the tissue. They suggested this might slow pulmonary clearance of the carcinogen and could have consequences in living animals.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Crocidolite, Chrysotile, Amosite, Anthophyllite.

Related studies

• Effects of asbestos on membrane transport and metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1980)
• Effect of chrysotile asbestos and silica on the microsomal metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1983)
• Studies on in vitro chrysotile-pleural mesothelial cell interaction: morphological aspects and metabolism of benzo-3,4-pyrene — M.C. Jaurand, I. Bastie-Sigeac, et al. (1983)
• Effects of crocidolite and chrysotile asbestos on cellular uptake and metabolism of benzo(a)pyrene in hamster tracheal epithelial cells — B.T. Mossman, A. Eastman, et al. (1983)
• Study of the cell-transforming ability of amosite and crocidolite asbestos and the ability to induce changes in the metabolism and macromolecular binding of benzo(a)pyrene in C3H10T1/2 cells — A. Poole, R.C. Brown, et al. (1983)
• Presentation of benzo(a)pyrene to microsomal enzymes by asbestos fibers in the Salmonella/mammalian microsome mutagenicity test — K. Szyba, A. Lange (1983)

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