Sulforaphane Improved Social Communication Impairment with Upregulation of Gabaergic Pathway in Cerebral Cortex of Valproic Acid Induced Autism

Background: Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder that is characterized by deficits in social communication, and restricted repetitive pattern of behavior. The etiology of ASD has not yet been defined due to its multiple factors. Valproic acid (VPA), which is for treating epilepsy and depression, has been reported to induce ASD by prenatal exposure in clinical cases and animal model. Current pharmacotherapies are still in clinical trial stages. Sulforaphane (SFN), which is an isothiocyanate derived from vegetables like broccoli, has been showed to ameliorate the social communication impairment in clinical trial. Our previous research demonstrated that that SFN can ameliorate of social impairment in VPA induced mouse model. However, the possible mechanism has not been realized yet.

Objectives: This study aimed to investigate the mechanism of SFN effects on VPA mouse model. Besides, the pathway will be studied in respect to the pathogenesis and treatment of ASD.

Methods: Pregnant BALB/c albino mice were injected intraperitoneally with VPA (600 mg/kg) on embryonic day 12.5, while the PBS group mothers were given with PBS as control group. On postnatal day 28, male pups from VPA-injected mothers were verified the autistic feature by three chambers sociability test. Mice with autistic feature were randomly assigned into SFN treatment group and VPA group. The SFN treatment group (VPA-SFN) mice was given with SFN (3.854 mg/kg/day) by oral gavage; while the VPA and PBS group were fed with saline (VPA-SAL). All groups were fed daily for 22 days. All mice were euthanized on postnatal day 50 and the cerebral cortices were harvested to perform Western Blot and immunohistochemistry analysis of presynaptic glutamic decarboxylase GAD67 and GABAergic receptors including GABRα1, GABRα5 and GABRβ2.

Results: For presynaptic protein, the protein levels of GAD67 were significantly repressed by 77.1% (p < 0.05) in VPA mice as compared with PBS group. SFN group showed up-regulation of GAD67 (26.4%, p < 0.05) respective to VPA mice. For postsynaptic receptors, expression levels of GABRα1, GABRα5 and GABRβ2 were down-regulated by 29.2% (p < 0.05), 15.4% (p < 0.01) and 33.0% (p < 0.05) significantly in VPA group, while in SFN treatment group, expression levels were rescued by 17.7% (p< 0.05), 71.9% (p<0.05) (comparable to PBS group), and 44.3% (p<0.01) respectively. In the fluorescent histochemistry, SFN treated mice showed intense signals of GAD67, GABRA1 GABRA5 GABRB2 in cerebral cortex, similar to PBS group but less signals in VPA group.

Conclusions: Sulforaphane ameliorates the inhibition of GABAergic proteins in valproic acid induced autistic mice.