Associations between element mixtures and biomarkers of pathophysiologic pathways related to autism spectrum disorder

We previously documented that exposure to a spectrum of elements is associated with autism spectrum disorder (ASD). However, there is a lack of mechanistic understanding as to how elemental mixtures contribute to the ASD development.

Serum and urinary concentrations of 26 elements and six biomarkers of ASD-relevant pathophysiologic pathways including serum HIPK 2, serum p53 protein, urine malondialdehyde (MDA), urine 8-OHdG, serum melatonin, and urine carnitine, were measured in 21 ASD cases and 21 age-matched healthy controls of children aged 6-12 years. The Mann-Whitney U test was used to compare the differences in serum elemental levels between ASD and control groups. A principal component analysis (PCA) was used to reduce the dimensionality of multiple elements into uncorrelated predictors that may capture shared patterns. Associations of PC scores with ASD risk or pathway-specific biomarkers were examined using logistic or linear regressions, respectively. Robust linear regressions were conducted to explore the association between serum and urinary elements.

We observed significantly higher serum levels of chromium, titanium, lithium, vanadium, calcium, cobalt, magnesium, and arsenic, but lower levels of cadmium and palladium in ASD children. We identified four PCs. PC1 reflects a mixture of 14 elements that were significantly elevated in ASD. PC2 reflects a mixture of elements that were significantly affected by urinary excretion. PC3 reflects a mixture of 5 elements within the 14 elements in PC1. PC4 reflects barium and palladium, both lower in ASD children. PC1 and PC2 were differentially associated with pathway-specific biomarkers. Each interquartile range (IQR) increase in PC1 was associated with increases in HIPK2 (12.96 %, 95 % CI: 3.98 %, 21.94 %) and p53 (8.34 %, 95 % CI: 0.30 %, 16.38 %), and a decrease in urinary carnitine (-24.85 %, 95 % CI: -46.36 %, -3.34 %). An IQR increase in PC2 was associated with increased urinary carnitine by 19.27 % (95 % CI: 3.08 %, 35.47 %). PC4 was not associated with any biomarkers. No PCs were associated with oxidative stress biomarkers of 8-OHdG or MDA. Additionally, increased excretion of essential elements (e.g. phosphorus, calcium, zinc) and the accumulation of metals with higher molecular weight (lead, tin, molybdenum, palladium, and bismuth) were observed in ASD group.

Increased levels of element mixtures of chromium, calcium, magnesium, arsenic, and antimony were associated with pro-apoptotic increases in HIPK2 and p53, whereas increased levels of cobalt, lead, and cadmium were associated with carnitine excretion. Increased urinary excretion of essential elements may contribute to ASD risk through modulating blood elemental levels. The role of oxidative stress was not observed.