Isoprene: background and issues

Area of Science:

• Toxicology
• Environmental Chemistry
• Polymer Science

Background:

• Isoprene, a petroleum-derived monomer, is crucial for manufacturing polyisoprene and rubber copolymers.
• Naturally occurring isoprene in plants and mammals contributes to atmospheric levels.
• Structural similarity to butadiene raises questions about isoprene's toxicological profile.

Purpose of the Study:

• To compare the toxicological properties of isoprene with those of butadiene.
• To investigate the metabolic pathways and species-specific differences in isoprene toxicity.
• To evaluate the mutagenic and carcinogenic potential of isoprene and its metabolites.

Main Methods:

• Comparative analysis of acute toxicity and biotransformation pathways with butadiene.
• Pharmacokinetic studies to assess species differences in metabolic elimination rates (mice vs. rats).
• In vitro mutagenicity tests (Salmonella strains) and in vivo cytogenetic assays (mice) for isoprene and its metabolites.
• Long-term inhalation studies in rats and mice to evaluate tumorigenicity.

Main Results:

• Isoprene shares qualitative similarities in acute toxicity and biotransformation to mono- and diepoxides with butadiene.
• Significant species differences in metabolic elimination rates were observed, with mice metabolizing isoprene faster than rats.
• Isoprene diepoxide showed mutagenic activity in Salmonella TA100; in vivo tests indicated increased SCEs and micronuclei.
• Long-term studies revealed species-specific tumor responses, with isoprene demonstrating lower potency than butadiene.

Conclusions:

• Isoprene is less potent than butadiene regarding mutagenicity and carcinogenicity.
• Species-specific metabolism plays a crucial role in determining isoprene's toxicological effects.
• Findings aid in refining risk assessments for occupational exposure and chemical regulations.