A novel mouse model for pyridoxine-dependent epilepsy due to antiquitin deficiency

Abstract

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disease caused by mutations in the ALDH7A1 gene leading to blockade of the lysine catabolism pathway. PDE is characterized by recurrent seizures that are resistant to conventional anticonvulsant treatment but are well-controlled by pyridoxine (PN). Most PDE patients also suffer from neurodevelopmental deficits despite adequate seizure control with PN. To investigate potential pathophysiological mechanisms associated with ALDH7A1 deficiency, we generated a transgenic mouse strain with constitutive genetic ablation of Aldh7a1. We undertook extensive biochemical characterization of Aldh7a1-KO mice consuming a low lysine/high PN diet. Results showed that KO mice accumulated high concentrations of upstream lysine metabolites including ∆1-piperideine-6-carboxylic acid (P6C), α-aminoadipic semialdehyde (α-AASA), and pipecolic acid (PIP) both in brain and liver tissues, similar to the biochemical picture in ALDH7A1-deficient patients. We also observed preliminary evidence of a widely deranged amino acid profile and increased levels of methionine sulfoxide, an oxidative stress biomarker, in the brains of KO mice, suggesting that increased oxidative stress may be a novel pathobiochemical mechanism in ALDH7A1 deficiency. KO mice lacked epileptic seizures when fed a low lysine/high PN diet. Switching mice to a high lysine/low PN diet led to vigorous seizures and a quick death in KO mice. Treatment with PN controlled seizures and improved survival of high-lysine/low PN fed KO mice. This study expands the spectrum of biochemical abnormalities that may be associated with ALDH7A1 deficiency and provides a proof-of-concept for the utility of the model to study PDE pathophysiology and to test new therapeutics.

Identification of novel biomarkers for pyridoxine-dependent epilepsy using untargeted metabolomics and infrared ion spectroscopy - biochemical insights and clinical implications

“…In brain extracts of four non-PDE controls, 2-OPP and 6-oxoPIP levels were below the detection limit of our quantitative assay. In a recently described Aldh7a1 knock-out (KO) mouse model (32), we were also able to detect increased concentrations of 2-OPP and 6-oxoPIP in plasma (Fig 5A-B) and brain extracts (Figure 5E-F) of KO mice, supporting our findings from the human situation. The known PDE-ALDH7A1 markers P6C, α-AASA and pipecolic acid (Figure 5C-D,G) were also found to be increased in brain tissue of Aldh7a1 KO mice, with pipecolic acid accumulating in remarkably high levels.…”

“…The Aldh7a1 KO mouse model used in this study was generated in accordance with guidelines of the Canadian Council on Animal Care and under an approved protocol from the University of British Columbia Animal Care Committee (Animal Protocols # A15-0200, A15-0180, A14-0031 and A18-0117), and was previously published (32). For collection of body fluids and tissues from Aldh7a1 KO and WT mice for metabolite analysis, mice were anesthetized by Avertin (2,2,2-tribromoethanol) injection or isoflurane inhalation.…”

“…and was previously published (32). For collection of body fluids and tissues from Aldh7a1 KO and WT mice for metabolite analysis, mice were anesthetized by Avertin (2,2,2-tribromoethanol) injection or isoflurane inhalation.…”

Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy

“…In brain extracts of four non-PDE controls, 2-OPP and 6-oxoPIP levels were below the detection limit of our quantitative assay. In a recently described aldh7a1 knock-out (KO) mouse model (33), we were also able to detect increased concentrations of 2-OPP and 6-oxoPIP in plasma (Fig 5A-B) and brain extracts (Figure 5E-F) of KO mice, supporting our findings from the human situation. The known PDE-ALDH7A1 markers P6C, α-AASA and pipecolic acid (Figure 5C-D,G) were also found to be increased in brain tissue of aldh7a1 KO mice, with pipecolic acid accumulating in remarkably high levels.…”

“…The aldh7a1 KO mouse model used in this study was generated in accordance with guidelines of the Canadian Council on Animal Care and was previously published (33). Mice used in this study were housed in a pathogen-free barrier facility at the Centre for Molecular Medicine and Therapeutics, University of British Columbia, Canada and were given free access to food and water.…”