Gestational Valproic Acid Alters Polyamine Metabolism in the Mouse Placenta: Implications for Autism Spectrum Disorders Causation

Background:  Currently ~40% of Autism Spectrum Disorders (ASD) risk is attributed to non-genomic factors.  Gestational use of the antiepileptic drug valproic acid (VPA) is one such factor that is associated with substantial increase in offspring risk of ASD. In the mouse, mid-gestational administration of VPA results in ASD-like anatomy and behavior in offspring. Although ASD-promoting effects of VPA are commonly considered to operate by histone deacetylase inhibition, VPA impacts many signaling pathways leaving unresolved the molecular mechanism(s) by which VPA promotes an ASD phenotype. 

Objectives:  We have realized that many maternal risk factors for ASD correlate with dysregulation of polyamine (PA) metabolism (e.g., rheumatoid arthritis, diabetes) implicating PA dysregulation in ASD causation. To our knowledge it is not known whether VPA can disrupt PA metabolism and thus whether the effects of gestational VPA might be mediated by dysregulation of PA metabolism. As a first-test of a VPA-PA link we here ask whether gestational administration of VPA in the mouse can cause dysregulation of placental PA metabolism. 

Methods:  Pregnant CD1 mice were injected subcutaneously with 600 mg/kg VPA or with equivalent volume physiological saline on gestational days 12, 13 and 14 and tissue was harvested ~4 hours post-final treatment.  Placentas were dissected and assigned to analysis by (1) qRT-PCR of mRNA of polyamine pathway enzymes ornithine decarboxylase 1 (ODC), adenosylmethionine decarboxylase 1 (AMD1) and spermidine/spermine N1-acetyltransferase 1 (SAT1), (2) SDS-PAGE-Western of ODC protein or (3) Hematoxylin-Eosin histochemistry for determination of placenta mid-sagittal cross-sectional area (following cryostat sectioning). 

Results:  Compared to controls, mRNA of all PA enzymes was elevated by 1.38±0.09x (ODC, average±SD), 1.90±0.10x (AMD1) and 1.59±0.57x (SAT1) by VPA. By Western, ODC protein was elevated 1.6x by VPA. Placenta cross-sectional area was decreased following VPA treatment (10.8± 2.2 mm² VPA versus 14.4± 2.0 mm² Control). 

Conclusions:  These results demonstrate that gestational VPA can alter placental PA metabolism with morphological consequence. Whether VPA impacts PA metabolism in maternal and fetal compartments and in the placenta at other developmental time points awaits further investigation.