Description
6PPD-quinone is an oxidized derivative of the tire antiozonant and substituted p-phenylenediamine 6-PPD. It is toxic to rainbow trout (O. mykiss) and brook trout (S. fontinalis; LC50s = 0.59 and 1.96 μg/L, respectively) but not to arctic char (S. alpinus) and white sturgeon (A. transmontanus; LC50s = >12.7 μg/L for both). 6PPD-quinone (10 μg/L) induces cell death and germline DNA damage and decreases the number of mitotic cells in C. elegans gonads. Urine levels of 6-PPD-quinone are increased in pregnant women compared to non-pregnant adults and children.
Biochem/physiol Actions
Studies have shown that 6PPD/6PPD-quinone can interact with human serum albumin (HSA). It spontaneously inserts into the I-site of HSA, forming a binary complex that induces changes in the secondary structure of HSA. However, their effects on the esterase-like activity of HSA are polarised. 6PPD activates the esterase-like activity of HSA, whereas 6PPD-quinone inhibits it. Molecular docking analyses showed that 6PPD and 6PPD-quinone interact with many amino acid residues on HSA, including TRP214, ARG222, ARG218, ALA291, and PHE211. π-electrons on the benzene ring of 6PPD/6PPD-quinone play a key role in maintaining the stability of the complex. In addition, the stronger binding affinity between 6PPD and HSA compared to 6PPD-quinone could be attributed to the greater negative surface potential of 6PPD.
Safety
6PPD-quinone (6PPD-q) is an oxidation product of the antioxidant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) present in rubber. Studies have shown that 6PPD and 6PPD- q are also present in human urine, including adults, children, and pregnant women, and that urinary 6PPD- q concentrations were significantly higher than 6PPD; pregnant women had significantly higher concentrations of 6PPD and 6PPD- q (median 0.068 and 2.91 ng/mL, respectively) than adults (0.018 and 0.40 ng/mL) and children (0.015 and 0.076 ng/mL). The high daily urinary excretion of 6PPD-Q in pregnant women was estimated to be 273 (ng/kg bw)/day. 6PPD-Q is a lethal toxicant to a wide range of aquatic species, and its potential risk to human health from long-term exposure requires urgent attention.
