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.
