New aspects in genotoxic risk assessment of styrene exposure--a working hypothesis

Styrene is one of the most important plastic monomers worldwide. Styrene-7,8-oxide (SO), the major in-vivo metabolite of styrene, is classified as probably carcinogenic to humans and carcinogenic in rodents. Biological monitoring of exposure to styrene is usually carried out by determination of mandelic acid and phenylglyoxylic acid, the two main styrene metabolites in urine. SO binds covalently to human plasma protein and haemoglobin. The ability of SO to induce DNA adducts and DNA strand-breaks has been well documented. Recently in-vitro results showed that SO may disrupt the pre-existing oxidative status in white blood cells. This disruption would alter the balance between oxidants and antioxidants in cells. Styrene exposure can also result in oxidative DNA damage. A significant increase of 8-hydroxy-2;-deoxyguanosine (8-OHdG) has been found in white blood cells of styrene-exposed workers. According to these findings we propose a new hypothesis for the genotoxic risk assessment of styrene. Depletion of glutathione and increase in lipid peroxidation, similarity in the decrease of high molecular weight (HMW) DNA fragments after SO exposure compared to hydrogen peroxide (H(2)O(2)) exposure, oxidative DNA damage (increased amounts of 8-OHdG and an increased level of DNA strand-breaks) following styrene or SO exposure are due to oxidative stress which can be a result of the imbalance between oxidants and antioxidants. Formation of protein-, RNA- and DNA-adducts, changes in DNA repair capacity and styrene metabolism following styrene exposure could cause this imbalance between oxidants and antioxidants. Oxidative stress seems to be the basis for genotoxic risk assessment of styrene.