Transport of a carcinogen, benzo\[a\]pyrene, from particulates to lipid bilayers: a model for the fate of particle-adsorbed polynuclear aromatic hydrocarbons which are retained in the lungs

Our plain-English summary of Transport of a carcinogen, benzo[a]pyrene, from particulates to lipid bilayers: a model for the fate of particle-adsorbed polynuclear aromatic hydrocarbons which are retained in the lungs, by J.R. Lakowicz, D.R. Bevan, S.C. Riemer (Biochimica et Biophysica Acta, 1980).

The study

• Authors: J.R. Lakowicz, D.R. Bevan, S.C. Riemer
• Journal: Biochimica et Biophysica Acta
• Published: 1980;629(2):243-58
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fluorescence spectroscopic methods were used to investigate the effects of adsorption of benzo[a]pyrene to particulate matter on its rate of uptake into model membranes composed of dipalmitoyl L-alpha-phosphatidylcholine. From these experiments we conclude the following: 1. Adsorption of benzo[a]pyrene to four types of asbestos (anthophyllite, crocidolite, chrysotile, and amosite) and a variety of non-fibrous particles (hematite, silica, titanium dioxide, porous glass and talc) results in increased rates of membrane uptake when compared with aqueous suspensions of benzo[a]pyrene microcrystals. Benzo[a]pyrene was not released from carbon black. 2. Asbestos-adsorbed benzo[a]pyrene was transferred to the membranes most rapidly. 3. Adsorption of benzo[a]pyrene to the surface of the particles is necessary for its enhanced transport into membranes. That is, simple mixtures of benzo[a]pyrene microcrystals and particulates do not show enhanced transport. 4. Particle-enhanced transport of benzo[a]pyrene is not correlated with the effects of the particles on vesicle integrity, binding of vesicles to the particles, or the concentrations of either particles or vesicles. The rate limiting step for transport of benzo[a]pyrene into vesicles appears to be its rate of desorption from the surface of the particle. Following desorption, membrane uptake of benzo[a]pyrene is rapid.

In plain English

This was a laboratory study, not a study of people. The authors coated benzo[a]pyrene, a cancer-causing chemical, onto four types of asbestos (amosite, anthophyllite, Canadian chrysotile and crocidolite) and onto non-fibrous particles including hematite, silica, porous glass, talc, glass beads, titanium dioxide and carbon black. They used fluorescence to measure how fast the chemical moved into artificial membranes made of DPPC, the main ingredient of lung surfactant. Within 30 minutes, 74% to 90% of the chemical moved into the membranes from the asbestos samples, compared with 21% from loose crystals of the chemical. Titanium dioxide gave 27%, and none was released from carbon black. Simply mixing particles with the crystals did not speed transfer. The speed of transfer was not linked to membrane damage (0 to 9.5%) or to membranes sticking to particles. The authors proposed that the slow step is the chemical leaving the particle surface. They concluded that coating onto particles speeds membrane uptake. They called their results consistent with the asbestos-smoking link in lung cancer but stressed that other mechanisms may be operative.

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 and model lipid membranes (vesicles)
• Who was studied: No people or animals. Particles were studied: four UICC asbestos samples (amosite, anthophyllite, Canadian chrysotile, crocidolite) and non-fibrous particles (hematite, silica, Partisil, porous glass, talc, glass beads, carbon black, titanium dioxide), together with model membranes (vesicles) of dipalmitoyl phosphatidylcholine (DPPC). DPPC was chosen because lung surfactant contains at least 70% DPPC.
• Exposure: Benzo[a]pyrene adsorbed onto the particles. Uptake experiments used 16.7 mg of particles carrying 5 micrograms of adsorbed benzo[a]pyrene, or 5 micrograms of benzo[a]pyrene microcrystals alone, with 10 mg of DPPC vesicles, monitored for 30 minutes.
• Main results:
  • Asbestos samples: amount of benzo[a]pyrene taken up by the vesicles in 30 minutes was 85% from amosite, 90% from anthophyllite, 81% from Canadian chrysotile and 74% from crocidolite (Table III).
  • Comparison groups: uptake in 30 minutes was 21% from benzo[a]pyrene microcrystals alone, 27% from titanium dioxide and 0% from carbon black. Other non-fibrous particles ranged from 50% (glass beads) to 83% (porous glass).
  • The asbestos particles showed a greater enhancement of benzo[a]pyrene uptake than the non-fibrous particles.
  • Benzo[a]pyrene was not released from carbon black.
  • Simple mixtures of particles (amosite, hematite, Canadian chrysotile and the others tested) with benzo[a]pyrene microcrystals showed the same uptake rate as microcrystals alone. Adsorption onto the particle surface was needed for faster transport.
  • Vesicle disruption by the particles was small (0 to 9.5%) and was not correlated with uptake rates. Anthophyllite gave the greatest uptake with little disruption; titanium dioxide gave little enhancement with the most disruption.
  • Binding of vesicles to particles did not correlate with uptake. Porous glass and glass beads bound no vesicles, yet porous glass gave uptake similar to asbestos.
  • Varying the concentrations of porous glass particles and of vesicles did not change uptake rates.
  • Asbestos particles appeared better than silica at adsorbing benzo[a]pyrene as single molecules (monomers), even though the silica had a 30- to 60-fold greater surface area.
  • The particles could adsorb no more than about 3 mg of benzo[a]pyrene per g of particle.
• The authors' conclusion: The authors concluded that adsorption of benzo[a]pyrene to a wide variety of particles enhances its rate of uptake into lipid vesicles. They proposed that the rate-limiting step is the release of benzo[a]pyrene from the particle into water. They said their results are consistent with the human epidemiology on asbestos and smoking but emphasized that other mechanisms may be operative.
• Limitations the authors state:
  • The rates at which benzo[a]pyrene dissolves off the particles could not be measured directly.
  • A strict correlation between the fluorescence spectra of adsorbed benzo[a]pyrene and uptake rates could not be derived for all particles. One reason is that some particles, such as hematite, quench the fluorescence.
  • Comparison with animal studies is hindered by lack of knowledge of how much hydrocarbon was adsorbed to the particles and how fast it moves into animal tissues.
  • Comparison with the human asbestos-smoking lung cancer findings is more difficult because of the complexity of the human situation.

Topics

Medical terms in this study, explained in our Lexicon: Anthophyllite, Crocidolite, Chrysotile, Amosite, Hematite, Talc.

Related studies

• Effects of particulate matter on rates of membrane uptake of polynuclear aromatic hydrocarbons — D.R. Bevan, S.C. Riemer, et al. (1981)
• 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 asbetos, iron oxide, silica, and carbon black on the microsomal availability of benzo[a]pyrene — J.R. Lakowicz, D.R. Bevan (1979)
• A hypothesis concerning asbestos carcinogenicity: the migration of lipophilic carcinogens in adsorbed lipid bilayers — P. Gerde, P. Scholander (1987)
• Asbestos-mediated membrane uptake of benzo[a]pyrene observed by fluorescence spectroscopy — J.R. Lakowicz, J.L. Hylden (1978)
• Effects of asbestos on membrane transport and metabolism of benzo(a)pyrene — C. Kandaswami, P.J. O'Brien (1980)

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