Effects of asbetos, iron oxide, silica, and carbon black on the microsomal availability of benzo\[a\]pyrene

Our plain-English summary of Effects of asbetos, iron oxide, silica, and carbon black on the microsomal availability of benzo[a]pyrene, by J.R. Lakowicz, D.R. Bevan (Biochemistry, 1979).

The study

• Authors: J.R. Lakowicz, D.R. Bevan
• Journal: Biochemistry
• Published: 1979;18(23):5170-6
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Particulate matter and polynuclear aromatic hydrocarbons are known to be cocarcinogenic. Using fluorescence spectroscopy, we determined that adsorption of benzoic] pyrene (BP) to iron oxide, silica, and asbestos (anthophyllite and Canadian chrysotile) results in a greatly enhanced rate of BP uptake into rat liver microsomes when compared to uptake from aqueous dispersions of BP microcrystals. Simple mixtures of BP microcrystals and particulates do not display enhanced microsomal uptake rates, an observation which indicates that adsorption of BP to the surface of the particle is necessary for enhanced microsomal uptake. BP was not released into microsomes from carbon black. Most importantly, the data indicate that asbestos particles are more effective than silica and iron oxide in enhancing the microsomal availability of BP. These observations suggest that particles, and especially the fibrous mineral particulates, could be cocarcinogenic as a result of their ability to adsorb polynuclear aromatic hydrocarbons and to transport these carcinogens into cells. Except for chrysotile, the particles did not disrupt microsomal integrity as determined by NADPH-dependent lipid peroxidation activity. Binding of the microsomes to the particles did not affect the BP uptake rates. In addition, these BP uptake rates were independent of both the concentrations of microsomes and of particles. These observations are consistent with the mechanism of particle-enhanced transport being an increased rate of BP solubilization from the adsorbed state into the aqueous phase, followed by rapid partitioning of BP into the microsomal membranes.

In plain English

This was a laboratory study, not a study of people. The authors used fluorescence to track how quickly benzo[a]pyrene (BP), a cancer-causing chemical, moved into microsomes from rat livers. Microsomes are where cells activate such chemicals. BP was coated onto two asbestos types (anthophyllite and Canadian chrysotile), amorphous silica, iron oxide (hematite) and carbon black. These were compared with BP in tiny crystals in water. BP coated onto all four minerals entered microsomes faster than BP from crystals. Uptake was highest from chrysotile and anthophyllite; silica and hematite were less effective. No BP was released into the microsomes from carbon black. Simply mixing particles with BP crystals did not speed uptake; the authors took this to mean BP must be stuck to the particle surface. Chrysotile, but not anthophyllite, silica or hematite, significantly reduced a test of microsomal integrity. The authors concluded that fibrous minerals were better than nonfibrous minerals at carrying carcinogens into microsomes. They suggested this may partly explain the combined cancer effect of asbestos and smoking in humans, but noted other mechanisms may also be involved.

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: Laboratory (in vitro) experiment using fluorescence spectroscopy
• Who was studied: Liver microsomes from rats pretreated with Aroclor 1254; the number of rats is not given
• Exposure: Benzo[a]pyrene adsorbed onto anthophyllite and Canadian chrysotile (standard samples from the International Union Against Cancer), amorphous silica, iron oxide (hematite) and carbon black, at 0.3 mg of BP per gram of particle (16.7 mg of particles carrying 5 micrograms of BP per test). This was compared with BP microcrystals, alone or mixed with particles.
• Main results:
  • BP adsorbed to all four mineral particles (anthophyllite, chrysotile, silica, hematite) entered microsomes faster than BP from the microcrystalline state.
  • Chrysotile- and anthophyllite-adsorbed BP showed the highest uptake rates. Silica and hematite also enhanced uptake but were less effective than the asbestos particles.
  • BP was not released into the microsomes from carbon black.
  • When particles were added to already-formed BP crystals, uptake rates were the same as for BP crystals alone, within experimental error.
  • Chrysotile significantly inhibited microsomal lipid peroxidation activity, the test used for microsomal integrity. Anthophyllite, silica and hematite had no significant effect.
  • Microsomes bound to the particles: 16.7 mg of anthophyllite, chrysotile or iron oxide bound essentially all of them, and silica bound about half. Binding did not change BP uptake rates.
  • Doubling both the particle and microsome concentrations did not change uptake rates for any particle. The authors took this to mean that release of BP from the particle surface was probably the rate-limiting step.
• The authors' conclusion: The authors concluded that fibrous minerals were superior to nonfibrous minerals in transporting carcinogens into microsomes. They suggested this may partly explain the combined cancer effects of asbestos inhalation and cigarette smoking in humans.
• Limitations the authors state:
  • Mechanisms other than particle-enhanced transport may be involved in combined particle and chemical cancer effects.
  • Conclusions drawn from the fluorescence of BP stuck to particle surfaces are tentative until better measurement methods exist.
  • The BP crystal preparations varied, which produced experimental error.
  • The conclusion about microsome binding would not hold if microsomes rapidly redistributed between particles with and without BP.

Topics

Medical terms in this study, explained in our Lexicon: Anthophyllite, Chrysotile.

Related studies

• Effect of chrysotile asbestos and silica on the microsomal metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1983)
• Presentation of benzo(a)pyrene to microsomal enzymes by asbestos fibers in the Salmonella/mammalian microsome mutagenicity test — K. Szyba, A. Lange (1983)
• Benzo[a]pyrene uptake into rat liver microsomes: effects of adsorption of benzo[a]pyrene to asbestos and non-fibrous mineral particulates — J.R. Lakowicz, D.R. Bevan (1980)
• Effects of asbestos on membrane transport and metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1980)
• Effect of particulates on metabolism and mutagenicity of benzo[a]pyrene — D.R. Bevan, W.E. Manger (1985)
• Asbestos-mediated membrane uptake of benzo[a]pyrene observed by fluorescence spectroscopy — J.R. Lakowicz, J.L. Hylden (1978)

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