Neurotransmitter and their metabolite concentrations in different areas of the HPRT knockout mouse brain.

Lesch-Nyhan syndrome (LNS) is characterized by uric acid overproduction and severe neurobehavioral symptoms, such as recurrent self-mutilative behavior. To learn more about the pathophysiology of the disease, we quantified neurotransmitters and their metabolites in the cerebral hemisphere, cerebellum and the medulla oblongata of HPRT knockout mice, an animal model for LNS, in comparison to the corresponding wild-type. Our analyses included l-glutamate, 4-aminobutanoic acid (GABA), acetylcholine, serotonin, 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine, l-normetanephrine, epinephrine and l-metanephrine and were conducted via high performance liquid chromatography (HPLC) coupled to tandem mass spectrometry (MS/MS). Among these neurotransmitter systems, we did not find any abnormalities in the HPRT knockout mouse brains. On one side, this might indicate that HPRT deficiency most severely affects dopamine signaling, while brain functioning based on other neurotransmitters is more or less spared. On the other hand, our findings may reflect a compensating mechanism for impaired purine salvage that protects the brain in HPRT-deficient mice but not in LNS patients.

Non-targeted metabolomics by high resolution mass spectrometry in HPRT knockout mice.

AIMS: Lesch-Nyhan disease (LND) is characterized by hyperuricemia as well as neurological and neuropsychiatric symptoms including repetitive self-injurious behavior. Symptoms are caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) as a result of a mutation on the X chromosome. To elucidate the pathophysiology of LND, we performed a metabolite screening for brain and serum extracts from HPRT knockout mice as an animal model for LND. MAIN METHODS: Analyses were performed by high performance liquid chromatography (HPLC)-coupled quadrupole time-of-flight mass spectrometry (QTOF-MS). KEY FINDINGS: In brain extracts, we found six metabolites with significantly different contents in wild-type and HPRT-deficient mice. Two compounds we could identify as 5-aminoimidazole-4-carboxamide ribotide (AICAR) and 1-methylimidazole-4-acetic acid (1-MI4AA). Whereas AICAR was accumulated in brains of HPRT knockout mice, 1-MI4AA was decreased in these mice. SIGNIFICANCE: Both metabolites play a role in histidine metabolism and, as a consequence, histamine metabolism. AICAR, in addition, is part of the purine metabolism. Our findings may help to better understand the mechanisms leading to the behavioral phenotype of LND.

Altered histamine neurotransmission in HPRT-deficient mice.

Lesch-Nyhan syndrome (LNS) is an X-chromosomal disorder with congenital deficiency of the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) as underlying defect. We determined the concentrations of dopamine, histamine and their metabolites in brains of HPRT knockout mice, which serve as an animal model for LNS, and compared the results to those obtained from wild-type controls. Analyses were performed by high performance liquid chromatography (HPLC)-coupled tandem mass spectrometry (MS/MS). Besides a decrease of dopamine and 3-methoxytyramine (3-MT) concentrations in the cerebral hemisphere, HPRT-deficient mice also exhibited significantly reduced 1-methylhistamine (1-MH) and 1-methylimidazole-4-acetic acid (1-MI4AA) concentrations in the brain hemisphere and medulla. Moreover, the amount of 1-MI4AA was significantly decreased in the cerebellum. Our findings show that neuronal perturbations caused by HPRT deficiency are not restricted to the dopamine system but also affect histaminergic neurotransmission. These new insights into the brain metabolism of an LNS mouse model may help to find new therapeutic strategies to improve the quality of life of LNS patients.