Evaluation of spindle inhibiting effects of metals by chromosome length measurements†

Presented at the 2nd IAEAC Workshop on Carcinogenic and/or Mutagenic Metal Compounds, CH‐1884 Villars‐sur‐Ollon, 21st January 1986.

Aneuploidy due to meiotic nondisjunction is the cause of several severe genetic diseases as well as a significant fraction of fetal losses and early infant mortality. Mitotic nondisjunction during early embryogenesis may cause the same effects, and recent research indicates that mitotic nondisjunction may play a role in the development of certain types of cancer.

Despite several suggestive epidemiological investigations it remains controversial whether human exposure to chemical or physical agents may increase the rate of aneuploidy. However, the severe human and social consequences of genetic diseases caused by aneuploidy warrant efforts toward development of short term tests for aneuploidy induction and identification of agents capable of inducing nondisjunction.

The present paper describes an indirect method for assessing spindle inhibiting effects of chemicals by chromosome length measurements combined with evaluation of spindle structure, and the use of this technique for evaluation of spindle inhibiting effects of several metal compounds in human lymphocytes in vitro. As positive controls, the well characterized spindle inhibitors colchicine and parafluorophenyl‐alanine were used. This technique could identify the threshold concentration for spindle inhibition for several compounds. Furthermore, partial spindle inhibition, leading to a high risk of chromosomal malsegregation, was observed at the threshold concentration.

Cd⁺⁺ and Hg⁺⁺ induced transient reductions in average chromosome length, indicating intracellular detoxification by metallothionein induction. This was confirmed by demonstration of intracellular ¹⁰⁹Cd‐metallothionein complex formation. Chromosome length reduction induced by CH₃Hg⁺ was stable, suggesting that CH₃Hg⁺ is not detoxified by metallothionein. Also organic and inorganic lead compounds, Ni⁺⁺, Co⁺⁺, Mn⁺⁺, AsO₂ ^–, and SeO₃ ^‐ significantly reduced the average chromosome length, indicating spindle inhibiting potency of these compounds. Fe^{+ + +}, Zn ^{+ +} and Cu⁺⁺ did not reduce the average chromosome length.

The results indicate that chromosome length measurements offer an indirect, but sensitive test for evaluation of spindle inhibition, able to identify the threshold concentration of effect on the spindle, thus allowing direct study of aneuploidy induction at the most relevant concentration.

Key words:

• Genotoxicity
• short term test
• aneuploidy
• spindle inhibition
• chromosome length measurement
• cadmium
• methylmercury
• arsenite
• HS‐groups in proteins

Notes

Presented at the 2nd IAEAC Workshop on Carcinogenic and/or Mutagenic Metal Compounds, CH‐1884 Villars‐sur‐Ollon, 21st January 1986.