Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders.

HIV-associated neurocognitive disorders (HAND) have been linked to dysregulation of glutamate metabolism in the central nervous system (CNS) culminating in elevated extracellular glutamate and disrupted glutamatergic neurotransmission. Increased glutamate synthesis via upregulation of glutaminase (GLS) activity in brain immune cells has been identified as one potential source of excess glutamate in HAND. However, direct evidence for this hypothesis in an animal model is lacking, and the viability of GLS as a drug target has not been explored. In this brief report, we demonstrate that GLS inhibition with the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) can reverse cognitive impairment in the EcoHIV-infected mouse model of HAND. However, due to peripheral toxicity DON is not amenable to clinical use in a chronic disease such as HAND. We thus tested JHU083, a novel, brain penetrant DON prodrug predicted to exhibit improved tolerability. Systemic administration of JHU083 reversed cognitive impairment in EcoHIV-infected mice similarly to DON, and simultaneously normalized EcoHIV-induced increases in cerebrospinal fluid (CSF) glutamate and GLS activity in microglia-enriched brain CD11b + cells without observed toxicity. These studies support the mechanistic involvement of elevated microglial GLS activity in HAND pathogenesis, and identify JHU083 as a potential treatment option. Graphical Abstract Please provide Graphical Abstract caption.Glutamine Antagonist JHU083 Normalizes Aberrant Glutamate Production and Cognitive Deficits in the EcoHIV Murine Model of HIV-Associated Neurocognitive Disorders .

Non-physiological amino acid (NPAA) therapy targeting brain phenylalanine reduction: pilot studies in PAHENU2 mice.

Transport of large neutral amino acids (LNAA) across the blood brain barrier (BBB) is facilitated by the L-type amino acid transporter, LAT1. Peripheral accumulation of one LNAA (e.g., phenylalanine (phe) in PKU) is predicted to increase uptake of the offending amino acid to the detriment of others, resulting in disruption of brain amino acid homeostasis. We hypothesized that selected non-physiological amino acids (NPAAs) such as DL-norleucine (NL), 2-aminonorbornane (NB; 2-aminobicyclo-(2,1,1)-heptane-2-carboxylic acid), 2-aminoisobutyrate (AIB), and N-methyl-aminoisobutyrate (MAIB), acting as competitive inhibitors of various brain amino acid transporters, could reduce brain phe in Pah (enu2) mice, a relevant murine model of PKU. Oral feeding of 5 % NL, 5 % AIB, 0.5 % NB and 3 % MAIB reduced brain phe by 56 % (p < 0.01), -1 % (p = NS), 27 % (p < 0.05) and 14 % (p < 0.01), respectively, compared to untreated subjects. Significant effects on other LNAAs (tyrosine, methionine, branched chain amino acids) were also observed, however, with MAIB displaying the mildest effects. Of interest, MAIB represents an inhibitor of the system A (alanine) transporter that primarily traffics small amino acids and not LNAAs. Our studies represent the first in vivo use of these NPAAs in Pah (enu2) mice, and provide proof-of-principle for their further preclinical development, with the long-term objective of identifying NPAA combinations and concentrations that selectively restrict brain phe transport while minimally impacting other LNAAs and downstream intermediates.

Dual mechanism of brain injury and novel treatment strategy in maple syrup urine disease.

Maple syrup urine disease (MSUD) is an inherited disorder of branched-chain amino acid metabolism presenting with life-threatening cerebral oedema and dysmyelination in affected individuals. Treatment requires life-long dietary restriction and monitoring of branched-chain amino acids to avoid brain injury. Despite careful management, children commonly suffer metabolic decompensation in the context of catabolic stress associated with non-specific illness. The mechanisms underlying this decompensation and brain injury are poorly understood. Using recently developed mouse models of classic and intermediate maple syrup urine disease, we assessed biochemical, behavioural and neuropathological changes that occurred during encephalopathy in these mice. Here, we show that rapid brain leucine accumulation displaces other essential amino acids resulting in neurotransmitter depletion and disruption of normal brain growth and development. A novel approach of administering norleucine to heterozygous mothers of classic maple syrup urine disease pups reduced branched-chain amino acid accumulation in milk as well as blood and brain of these pups to enhance survival. Similarly, norleucine substantially delayed encephalopathy in intermediate maple syrup urine disease mice placed on a high protein diet that mimics the catabolic stress shown to cause encephalopathy in human maple syrup urine disease. Current findings suggest two converging mechanisms of brain injury in maple syrup urine disease including: (i) neurotransmitter deficiencies and growth restriction associated with branched-chain amino acid accumulation and (ii) energy deprivation through Krebs cycle disruption associated with branched-chain ketoacid accumulation. Both classic and intermediate models appear to be useful to study the mechanism of brain injury and potential treatment strategies for maple syrup urine disease. Norleucine should be further tested as a potential treatment to prevent encephalopathy in children with maple syrup urine disease during catabolic stress.