Inhibiting neutral amino acid transport for the treatment of phenylketonuria

Abstract

The neuropathological effects of phenylketonuria (PKU) stem from the inability of the body to metabolize excess phenylalanine (Phe), resulting in accumulation of Phe in the blood and brain. Since the kidney normally reabsorbs circulating amino acids with high efficiency, we hypothesized that preventing the renal uptake of Phe might provide a disposal pathway that could lower systemic Phe levels. SLC6A19 is a neutral amino acid transporter responsible for absorption of the majority of free Phe in the small intestine and reuptake of Phe by renal proximal tubule cells. Transgenic KO mice lacking SLC6A19 have elevated levels of Phe and other amino acids in their urine but are otherwise healthy. Here, we crossed the Pahenu2 mouse model of PKU with the Slc6a19-KO mouse. These mutant/KO mice exhibited abundant excretion of Phe in the urine and an approximately 70% decrease in plasma Phe levels. Importantly, brain Phe levels were decreased by 50%, and the levels of key neurotransmitters were increased in the mutant/KO mice. In addition, a deficit in spatial working memory and markers of neuropathology were corrected. Finally, treatment of Pahenu2 mice with Slc6a19 antisense oligonucleotides lowered Phe levels. The results suggest that inhibition of SLC6A19 may represent a novel approach for the treatment of PKU and related aminoacidopathies.

Novel Chemical Scaffolds to Inhibit the Neutral Amino Acid Transporter B0AT1 (SLC6A19), a Potential Target to Treat Metabolic Diseases

“…Most SLC6A19ko animals showed a significant protection against NASH, suggesting a potential of B 0 AT1 inhibitors to treat this metabolic disorder. Moreover, they could also be used to remediate amino acid imbalance in rare inherited disorders such as phenylketonuria (Belanger et al, 2018).…”

“…Similar to humans, plasma phenylalanine levels in the Pah enu2 mouse model of PKU are highly elevated. This translates into elevated levels of phenylalanine in the brain and reduced levels of neurotransmitters serotonin, dopamine, and norepinephrine (Belanger et al, 2018). Elevated levels of reactive astrocytes were found, replicating human PKU.…”

“…More recently, B 0 AT1 has also been suggested as a target to normalize amino acid imbalance in specific inherited disorders such as phenylketonuria (PKU) and urea cycle disorders (Belanger et al, 2018). In phenylketonuria, plasma levels of phenylalanine are highly elevated due to mutation of the enzyme phenylalanine hydroxylase, which initiates the degradation of the amino acid by converting it to tyrosine.…”

Amino acid transporters in the regulation of insulin secretion and signalling

“…Our lab and others have proposed the effects of dietary protein restriction in the B 0 AT1 KO mouse could be replicated by inhibiting B 0 AT1, making it a potential target for the alleviation of metabolic disorders that would benefit from dietary restriction of neutral amino acids, such as TIIDM (78) and phenylketonuria (79). Several inhibitors of B 0 AT1 have been identified but none yet with clinical significance (78)(79)(80)(81). B 0 AT1 (-/-) mice displayed hyper-excretion of neutral amino acids in urine and both major substrates of B 0 AT1 but plasma levels remained normal, perhaps as a result of decreased oxidation of amino acids (1,61).…”

Development of Biomarkers for Inhibition of SLC6A19 (B0AT1)—A Potential Target to Treat Metabolic Disorders

“…Because of the role of this transporter in the homeostasis of BCAA and methionine levels, we have postulated that pharmacological inhibition of the transporter may induce similar metabolic effects as protein restriction and could be used as a treatment for metabolic diseases [ 28 ]. The transporter has also been suggested as a target to treat specific disturbances of amino acid homeostasis such as phenylketonuria [ 29 ].…”