TRACE METALS, NEUROTRANSMITTERS AND OXIDATIVE STRESS MARKERS IN THE PATHOGENESIS OF AUTISM SPECTRUM DISORDERS AND CEREBRAL PALSY IN CHILDREN

Abstract

Autism Spectrum Disorders (ASD) and Cerebral Palsy (CP) are Neurodevelopmental Disorders (NDDs) with inconclusive genetic profiling. Currently, focus is on gene modulation in NDDs by environmental toxicants such as trace metals which induces oxidative stress. However, interrelationship between oxidative stress and neurotransmitters in the pathogenesis of NDDs is unclear. This study was conducted to assess in-utero placenta transfer of trace metals from occupationally-exposed pregnant mothers and effect on neurotransmitters in the pathophysiology of ASD and CP in children. Ethical approvals were obtained from UI/UCH Ethics Committee (UI/EC/15/0087) and Oyo State Ministry of Health. This case-control study had 180 participants; 50 pregnant women occupationally-exposed to metals (cases), 55 unexposed (controls), 25 each clinicallydiagnosed ASD, CP and Neuro-typical (NT) children, respectively. Maternal and cord blood obtained at parturition and blood samples from ASD, CP and NT were analysed for trace metals (selenium, zinc, copper, calcium, magnesium), lead, cadmium using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Samples from ASD, CP and NT were also assayed for neurotransmitters (glutamine, glutamate, GABA) using ELISA. Malondialdehyde (MDA), Total Antioxidant Capacity (TAC) and Total Plasma Peroxide (TPP) were spectrophotometrically determined, while Oxidative Stress Index (OSI) was calculated (TPP/TAC). Data were analysed using ANOVA and Pearsons’ correlation at α0.05. Maternal selenium, zinc, copper, lead, cadmium, calcium, magnesium levels in exposed (10.2±1.2, 370.8±193.0, 328.0±110.0, 11.0±1.4, 96.7±15.6 µg/dL; 8.6±0.9, 1.5±0.3 mg/dL) and unexposed (9.0±1.2, 416.8±277.0, 348.3±150.6, 10.0±1.9, 70.0±30.0 µg/dL; 8.6±0.9, 1.5±0.4 mg/dL) pregnant women were not significantly different. In the fetus cord-blood, selenium, zinc, copper and calcium levels were not significantly different, magnesium level (1.51±0.3 vs 1.6±0.1) was significantly reduced in exposed compared with unexposed, while lead and cadmium were not detectable. In ASD and CP, compared with NT, plasma calcium (7.9±1.4; 7.7±1.0 vs 9.8±1.3 mg/dL), magnesium (2.5±0.5; 2.8±0.6 vs 3.1±0.4 mg/dL), selenium (40.8±7.9; 27.6±6.8 vs 59.0±5.3 µg/dL), zinc (222.3±63.8; 233.8±105.3 vs 438.5±185.5 µg/dL) and copper (4.3±1.0; 4.0±0.8 vs 4.9±0.9 µg/dL) were significantly reduced, while lead level (9.5±4.0; 11.1±5.8 vs 5.4±2.05 µg/dL) was significantly elevated. The Zn/Cu ratio (55.3±22.0; 60.6±27.8 vs 92.3±44.6) was significantly reduced in ASD and CP compared with NT. Glutamine level (379.2±53.1; 296.3±59.6 vs 419.1±71.8 µmol/L) was decreased significantly in ASD and CP compared with NT. Glutamate (1.9±0.1; 1.8±0.3 vs 1.7±0.3 nmol/mL) and GABA (2.1±0.3; 1.8±0.4 vs 1.8±0.3 µmol/L) levels in CP and NT were comparable, and significantly elevated in ASD compared with NT. The OSI (0.6±0.2 vs 0.4±0.1; 0.4±0.1) and TPP (115.1±8.5 vs 105.9±2.3; 110.4±7.9) levels were significantly higher and TAC (209.8±57.9 vs 280.2±34.4; 303.8±33.1) was significantly reduced in CP compared with ASD and NT. The MDA (2.3±0.2; 2.1±0.2 vs 1.4±0.1) level was significantly elevated in ASD and CP compared with NT. Copper correlated positively with GABA and glutamine, while magnesium correlated negatively with GABA in ASD. Copper correlated positively with glutamate in CP. Transfer and imbalance of trace metals in-utero was established. Oxidative stress observed in autism spectrum disorders and cerebral palsy can be ascribed to imbalance in trace metals resulting in abnormal glutamatergic and GABAergic neuron activities in children with these disorders.