Evidence on neurodevelopmental effects of co-exposure to heavy metals and plasticisers is continuously growing, yet there is also a marked lack of mechanistic interpretation to date.
Phthalate and heavy metal (Pb and Hg) prenatal exposure was determined in mothers during the third trimester of pregnancy (prenatal exposure) and from their children at the 24th month of age (postnatal exposure). Urine untargeted metabolomics analysis was also carried out in both a Thermo Orbitrap LC/MS-MS and NMR. Psychomotor development was assessed in children at the age of 2 years using the Bayley Scale. Associations were investigated using the linkage disequilibrium method of the exposome-wide association study paradigm (EWAS), while pathway analysis was mapped with the Mass Profiler Pro (Agilent Technologies).
Based on our results, co-exposure to phthalates and metals is highly associated with the metabolism of citrate (Krebs cycle). Plasma untargeted metabolomics analysis using NMR led to the detection of pyruvate, 2-oxo-glutarate, and succinate, while urinary untargeted metabolomics using LC/MS/MS led to the detection of citrate, and (s) - malate. These compounds are main metabolites of the Krebs cycle. Perturbations of the TCA cycle may result in altered ATP levels, affecting in this way mitochondrial function. In addition, NMR plasma untargeted metabolomics resulted in the detection of L-arginine, and Fumarate, while urinary untargeted metabolomics using LC/MS/MS led to the detection of L-aspartate. These three compounds (L-aspartate, L-arginine, and Fumarate) are the main compounds of the urea cycle. Regarding the links between the urea cycle and the Krebs cycle, the generation of aspartate from fumarate is well known. Also, the flux of acetyl-CoA through the TCA cycle can indirectly affect the urea cycle by altering the levels of N-acetyl glutamate.
Overall, although phthalates and metals affect mitochondrial respiration through different mechanisms (endocrine disruption and oxidative stress respectively), this synergistic effect is essential for the expression of neurodevelopmental defects.