α-Ketoglutaramate: an overlooked metabolite of glutamine and a biomarker for hepatic encephalopathy and inborn errors of the urea cycle.

Glutamine metabolism is generally regarded as proceeding via glutaminase-catalyzed hydrolysis to glutamate and ammonia, followed by conversion of glutamate to α-ketoglutarate catalyzed by glutamate dehydrogenase or by a glutamate-linked aminotransferase (transaminase). However, another pathway exists for the conversion of glutamine to α-ketoglutarate that is often overlooked, but is widely distributed in nature. This pathway, referred to as the glutaminase II pathway, consists of a glutamine transaminase coupled to ω-amidase. Transamination of glutamine results in formation of the corresponding α-keto acid, namely, α-ketoglutaramate (KGM). KGM is hydrolyzed by ω-amidase to α-ketoglutarate and ammonia. The net glutaminase II reaction is: L - Glutamine + α - keto acid + H2O → α - ketoglutarate + L - amino acid + ammonia. In this mini-review the biochemical importance of the glutaminase II pathway is summarized, with emphasis on the key component KGM. Forty years ago it was noted that the concentration of KGM is increased in the cerebrospinal fluid (CSF) of patients with hepatic encephalopathy (HE) and that the level of KGM in the CSF correlates well with the degree of encephalopathy. In more recent work, we have shown that KGM is markedly elevated in the urine of patients with inborn errors of the urea cycle. It is suggested that KGM may be a useful biomarker for many hyperammonemic diseases including hepatic encephalopathy, inborn errors of the urea cycle, citrin deficiency and lysinuric protein intolerance.

Management and classification of type II congenital portosystemic shunts.

BACKGROUND: Congenital portosystemic shunts (PSS) with preserved intrahepatic portal flow (type II) present with a range of clinical signs. The indications for and benefits of repair of PSS remain incompletely understood. A more comprehensive classification may also benefit comparative analyses from different institutions. METHODS: All children treated at our institution for type II congenital PSS from 1999 through 2009 were reviewed for presentation, treatment, and outcome. RESULTS: Ten children (7 boys) with type II PSS were identified at a median age of 5.5 years. Hyperammonemia with varying degrees of neurocognitive dysfunction occurred in 80%. The shunt arose from a branch of the portal vein (type IIa; n = 2), from the main portal vein (type IIb; n = 7), or from a splenic or mesenteric vein (type IIc; n = 1). Management included operative ligation (n = 6), endovascular occlusion (n = 3), or a combined approach (n = 1). Shunt occlusion was successful in all cases. Serum ammonia decreased from 130 ± 115 µmol/L preoperatively to 31 ± 15 µmol/L postoperatively (P = .03). Additional benefits included resolution of neurocognitive dysfunction (n = 3), liver nodules (n = 1), and vaginal bleeding (n = 1). CONCLUSION: Correction of type II PSS relieves a wide array of symptoms. Surgery is indicated for patients with clinically significant shunting. A refined classification system will permit future comparison of patients with similar physiology.