The in vitro porcine brain tubulin assembly assay: effects of a genotoxic carcinogen (aflatoxin B1), eight tumor promoters and nine miscellaneous substances

Our plain-English summary of The in vitro porcine brain tubulin assembly assay: effects of a genotoxic carcinogen (aflatoxin B1), eight tumor promoters and nine miscellaneous substances, by S. Albertini, U. Friederich, C. Holderegger, et al (Mutation Research, 1988).

The study

• Authors: S. Albertini, U. Friederich, C. Holderegger, F.E. Würgler
• Journal: Mutation Research
• Published: 1988;201(2):283-92
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Aflatoxin B1 (AFB1) had a reversible inhibitory effect on the assembly of porcine brain tubulin in vitro. The 30%-inhibition concentration was 0.3 mM AFB1. The 8 tumor promoters showed different effects. Five of them, anthralin, cholic acid, gamma-hexachlorocyclohexane (lindane, gamma-HCH), lithocholic acid and phenobarbital (PB), enhanced the in vitro assembly. The effect was reversible in the case of PB and anthralin, only partially reversible in the case of cholic acid and gamma-HCH, whereas the stimulating effects of lithocholic acid led to an irreversible modification of the tubulin structure, as shown by the insolubility of the microtubules at 0 degrees C. This could be confirmed by an electron microscopic study. The doses necessary for a 30% enhancement of the steady-state level were 3 mM (PB), 0.2 mM (anthralin), 6 mM (cholic acid), 0.7 mM (gamma-HCH) and less than 0.2 mM (lithocholic acid). The other 3 tumor promoters tested - diethylstilbestrol (DES), 4,4'-dichloro-diphenyl-trichloro-ethane (DDT) and saccharin - inhibited the assembly. The concentrations necessary for a 30% inhibition varied within a wide range: 0.025 mM, 0.4 mM and 7.5 mM for DES, DDT and saccharin, respectively. Five of the 9 miscellaneous compounds, namely asbestos (crocidolite), bavistan, colchicine, chloropropham and ethylacetate, showed inhibitory effects, whereas Fe2+ (a constituent of asbestos) and 5-azacytidine did not influence the assembly process. The 30%-inhibition concentrations for colchicine, ethylacetate and asbestos were 10 microM, 0.153 M and 0.19 mM, respectively. For bavistan and chloropropham the 30%-inhibition values were 0.7 mM and 2.0 mM, respectively. The inhibitory effects of chloropropham and asbestos were reversible. For colchicine and bavistan the reversibility of the effects was not assayed. In agreement with published data, dimethylsulfoxide (DMSO) and acetone enhanced the in vitro assembly of porcine brain tubulin. The doses needed for a 30% enhancement by DMSO and acetone were 0.4 mM and 0.136 M, respectively. The effect of DMSO was irreversible whereas acetone led to a reversible stimulation. Some compounds were tested for their influence on preformed microtubules (interaction with the equilibrium between assembly and disassembly). Anthralin, cholic acid, PB and DMSO showed no effect on the steady-state plateau. A slight reduction was induced by DDT and bavistan, whereas DES, colchicine and chloropropham led to a pronounced reduction.

In plain English

This was a laboratory test-tube study, not a study of people or animals. The authors, at the Institute of Toxicology in Schwerzenbach, Switzerland, were looking for possible ways that chemicals cause chromosomes to be shared out wrongly when cells divide. They tested 18 substances on the assembly of tubulin, the protein that builds microtubules, using tubulin purified from pig brain and measuring the cloudiness of the mixture. One substance was crocidolite asbestos (a UICC reference sample). Crocidolite inhibited tubulin assembly. The concentration giving 30% inhibition was reported as 0.19 mM in the text and 0.2 mM in Table 2. The inhibition was reversible after cooling. Iron (Fe2+), which the authors described as a constituent of asbestos, had no effect. Aflatoxin B1 and the tumor promoters DES, DDT and saccharin also inhibited assembly. Five other tumor promoters, including lindane and phenobarbital, enhanced it. The authors did not test asbestos on already-formed microtubules. They concluded that more detailed molecular investigations are needed. They noted that the data were too small for a full comparison with aneuploidy (chromosome-number) tests.

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: In vitro (test-tube) biochemical assay of tubulin assembly, measured by light absorbance
• Who was studied: Tubulin purified from pig (porcine) brain, tested with 18 compounds: aflatoxin B1, 8 tumor promoters and 9 miscellaneous substances including asbestos; Institute of Toxicology, Schwerzenbach, Switzerland
• Exposure: Crocidolite asbestos (UICC sample), suspended in phosphate-buffered saline, plus Fe2+ (as FeCl2) and other chemicals; effect expressed as the concentration giving 30% inhibition or enhancement of assembly
• Main results:
  • Crocidolite asbestos inhibited tubulin assembly; 30% inhibition concentration 0.19 mM (0.2 mM in Table 2)
  • The inhibition of tubulin assembly by asbestos was reversible
  • Fe2+, described as a constituent of asbestos, had no influence on tubulin assembly
  • Asbestos was not tested in the steady-state test on preformed microtubules (n.d., not determined)
  • Aflatoxin B1, DES, DDT and saccharin inhibited assembly; 30% inhibition concentrations were 0.025 mM (DES), 0.3 mM (AFB1), 0.4 mM (DDT) and 7.5 mM (saccharin)
  • Five tumor promoters (anthralin, cholic acid, gamma-HCH/lindane, lithocholic acid, phenobarbital) enhanced assembly
• The authors' conclusion: The authors concluded that more detailed investigations at the molecular level are needed to understand what stimulation or inhibition of tubulin assembly in vitro means for cell division and aneuploidy
• Limitations the authors state:
  • The authors stated that the data were too small for a comprehensive correlation between the tubulin assay results and the aneuploidy test results
  • The authors noted that interspecies differences in tubulin may determine species specificity of spindle-active chemicals

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite.

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