José Antonio Arranz

Safety of ornithine phenylacetate in cirrhotic decompensated patients: an open-label, dose-escalating, single-cohort study.

Aims: Confirm in patients with cirrhosis and gastrointestinal bleeding the safety of ornithine phenylacetate (OP) and assess the pharmacokinetic profile of OP and its effects on plasma ammonia. Background: OP is a drug that has shown experimentally to decrease hyperammonemia and improve hepatic encephalopathy. OP is safe in healthy subjects and in stable patients with cirrhosis, but there are no data in decompensated cirrhosis. Methods: We performed a study to assess safety and tolerance of OP in cirrhotic patients after an episode of upper gastrointestinal bleeding.Ten patients were included within 24 hours of an upper gastrointestinal bleeding. OP was administered as a continuous infusion up to a maximum of 10 g/24 h (0.42 g/h) for 5 days. The infusion was started at 33% of the target dose and increased at 12-hour intervals achieving target dose at 24 hours. Ammonia was also assessed in control group of 10 patients. Results: No severe adverse events were observed. Mild adverse events were reported in 4 patients. Plasma ammonia (baseline: 80±43 &mgr;mol/L) showed a progressive drop between baseline and 36 hours (42±15 &mgr;mol/L), 72 hours (44±15 &mgr;mol/L), 96 hours (40±24 &mgr;mol/L), and 120 hours (33±14 &mgr;mol/L). Plasma ammonia at 24 hours was significantly higher in the control group. Plasma glutamine showed a significant decrease (−37% at day 5) and its excretion in urine as phenylacetylglutamine, a progressive rise (52±35 mmol at day 5). Conclusions: OP is a safe and well-tolerated drug in decompensated cirrhotics that may decrease plasma ammonia by inducing its appearance as phenylacetylglutamine in urine.

Estimation of the total number of disease-causing mutations in ornithine transcarbamylase (OTC) deficiency. Value of the OTC structure in predicting a mutation pathogenic potential

Ornithine transcarbamylase deficiency (OTCD), the X-linked, most frequent urea cycle error, results from mutations in the OTC gene, encoding a 354-residue polypeptide. To date 341 OTCD clinical mutations, including 222 missense single nucleotide changes (mSNCs), have been compiled (Hum Mutat 2006;27:626). OTCD mutation detection might be simplified if the entire repertoire of OTCD-causing mutations were known. We estimate the size of this repertoire from 23 new OTCD patients exhibiting 22 different mutations, of which 9, including 4 mSNCs, are novel. The complete repertoire of OTCD-causing mutations is estimated as 560 mutations (95% confidence interval, 422–833 mutations), including 290 mSNCs (95% confidence interval, 230–394 mSNCs). Thus, OTCD diagnosis based on the screening for known mutations might attain ˜90% sensitivity in <5 years. Since disease-causing mSNCs represent <20% of the 2064 possible OTC mSNCs, simple approaches are essential for discrimination between causative and trivial mSNCs. Observation of the OTC structure appears a simple approach for such discrimination, comparing favourably in our sample with three formalized structure-based and/or sequence-based in silico assessment methods, and supporting the causation of complete deficiency by the mutations p.Pro305Arg and p.Ser96Phe, and of partial deficiency by p.Asp41Gly, p.Glu122Gly, p.Leu179Phe, p.Pro220Thr and p.Glu273del. Five non-mSNC novel mutations (p.Gly71X, a 7-nucleotide and a 10-nucleotide duplication and deletion in exon 5, G>A transitions at bases +1 and +5 of introns 4 and 9, respectively) are obviously pathogenic. The previously reported mSNCs p.Arg26Gln, p.Arg40His, p.Glu52Lys, pLys88Asn, p.Arg129His, p.Asn161Ser, p.Thr178Met, p.His202Tyr, p.Ala208Thr and p.His302Arg, found in our cohort, are also discussed.

Protein expression profiles in patients carrying NFU1 mutations. Contribution to the pathophysiology of the disease

Cofactor disorders of mitochondrial energy metabolism are a heterogeneous group of diseases with a wide variety of clinical symptoms, particular metabolic profiles and variable enzymatic defects. Mutations in NFU1 were recently identified in patients with fatal encephalopathy displaying a biochemical phenotype consistent with defects in lipoic acid-dependent enzymatic activities and respiratory chain complexes. This discovery highlighted the molecular function of NFU1 as an iron-sulfur(Fe-S) cluster protein necessary for lipoic acid biosynthesis and respiratory chain complexes activities. To understand the pathophysiological mechanisms underlying this disease we have characterized the protein expression profiles of patients carrying NFU1 mutations. Fibroblasts from patients with the p.Gly208Cys mutation showed complete absence of protein-bound lipoic acid and decreased SDHA and SDHB subunits of complex II. In contrast, subunits of other respiratory chain complexes were normal. Protein lipoylation was also decreased in muscle and liver but not in other tissues available (brain, kidney, lung) from NFU1 patients. Although levels of the respiratory chain subunits were unaltered in tissues, BN-PAGE showed an assembly defect for complex II in muscle, consistent with the low enzymatic activity of this complex. This study provides new insights into the molecular bases of NFU1 disease as well as into the regulation of NFU1 protein in human tissues. We demonstrate a ubiquitous expression of NFU1 protein and further suggest that defects in lipoic acid biosynthesis and complex II are the main molecular signature of this disease, particularly in patients carrying the p.Gly208Cys mutation.

Neuropsychiatric Manifestations in Late-Onset Urea Cycle Disorder Patients

Inherited urea cycle disorders represent one of the most common groups of inborn errors of metabolism. Late-onset urea cycle disorders caused by partial enzyme deficiencies may present with unexpected clinical phenotypes. We report 9 patients followed up in our hospital presenting late-onset urea cycle disorders who initially manifested neuropsychiatric/neurodevelopmental symptoms (the most prevalent neuropsychiatric/neurodevelopmental diagnoses were mental retardation, attention-deficit hyperactivity disorder [ADHD], language disorder, and delirium). Generally, these clinical pictures did not benefit from pharmacological treatment. Conversely, dietary treatment improved the symptoms. Regarding biochemical data, 2 patients showed normal ammonium but high glutamine levels. This study highlights the fact that neuropsychiatric/neurodevelopmental findings are common among the initial symptomatology of late-onset urea cycle disorders. The authors recommend that unexplained or nonresponsive neuropsychiatric/neurodevelopmental symptoms appearing during childhood or adolescence be followed by a study of ammonia and amino acid plasmatic levels to rule out a urea cycle disorder.

Ornithine phenylacetate prevents disturbances of motor-evoked potentials induced by intestinal blood in rats with portacaval anastomosis

BACKGROUND & AIMS Ornithine phenylacetate (OP) is a new drug that has been proposed for the treatment of hepatic encephalopathy (HE) because it decreases plasma ammonia. We performed a study to assess if OP would impact on neuronal function. METHODS Motor-evoked potentials (MEP), a surrogate of hepatic encephalopathy, were assessed (without anesthesia) in rats with portacaval anastomosis (PCA) that received gastrointestinal blood (GIB). Rats were pre-treated with OP prior to GIB. Ammonia and related metabolites (plasma, urine, and brain microdialysis) were assessed by HPLC and mass spectroscopy. RESULTS OP (one dose or 3 days) prevented disturbances in MEP induced by GIB in PCA rats. In rats treated with OP for 3 days, the amplitude and latency of MEP remained stable (-1% and +1%), while in the control group the amplitude decreased -21% and the latency increased +12% (p<0.01). OP attenuated the rise of ammonia in plasma by 45%, ammonia in brain microdialysate by 48%, induced a faster glutamine rise and the appearance of phenylacetylglutamine in plasma and urine. In addition, OP was associated with a lower concentration of ammonia and glutamate in brain microdialysate (approx. 50%). CONCLUSIONS OP prevents abnormalities in MEP precipitated by GIB in a model of HE. This is probably due to the enhancement of glutamine synthesis and metabolism, which results in a lower rise of plasma ammonia and the prevention of changes in glutamate in microdialysate. Thus, OP may be a good drug to prevent HE precipitated by gastrointestinal bleeding.

Progressive vacuolating glycine leukoencephalopathy with pulmonary hypertension.

To report two unrelated patients with a new phenotype of nonketotic hyperglycinemia associated with idiopathic pulmonary hypertension. Clinical findings included rapidly progressive neurological deterioration with onset in the first year of life characterized by developmental regression without seizures or electroencephalogram abnormalities during follow‐up. Both patients died before the age of 18 months. Glycine cleavage system deficiency was confirmed by enzymatic studies in frozen liver. Molecular analysis in the related genes showed no pathogenic mutation. Radiological and pathological findings were consistent with progressive vacuolating encephalopathy. Our patients with biochemical and enzymatic parameters consistent with atypical nonketotic hyperglycinemia. The clinical and radiological evolution, as progressive vacuolating leukoencephalopathy and the association with pulmonary hypertension constitute a previously unrecognized variant. Ann Neurol 2006;60:148–152

Orotic aciduria and plasma urea cycle-related amino acid alterations in short bowel syndrome, evoked by an arginine-free diet.

BACKGROUND The small bowel is believed to play a crucial role in endogenous arginine synthesis. Therefore, an insufficient arginine supply in the situation of massive intestinal resection might impede normal arginine metabolism. This study sought to determine the clinical and metabolic effects of an arginine-free diet in stable short-bowel patients. METHODS Four patients, mean age 49 years (range: 26-67), mean time from intestinal resection 46 m (range: 15-97), and remnant small bowel of 30 to 100 cm consumed an L-amino acid arginine-free diet (egg pattern) for 5 days (0.9 g protein equivalent/kg/d plus malabsorption adjustments). Fasting plasma amino acids, ammonium, and blood chemistries were assessed at days 0, 3, and 5. Urinary orotate, orotidine, uric acid, urea, creatinine, and total nitrogen were evaluated daily. RESULTS Significant decreases in plasma levels of arginine, ornithine, and hydroxyproline occurred at day 5. A decreasing trend in plasma citrulline and a significant plasma glutamine increase were also observed in the same period. Conversely, ammonium concentrations remained normal. Regarding urine compounds, striking orotic aciduria with a peak at day 4 (14-fold vs baseline) and significant decreases in uric acid and urea excretion were found. There were no relevant clinical events. CONCLUSIONS Despite the limited number of patients in our work and their relative heterogeneity, our results support the idea of the indispensability of an exogenous arginine supply in humans under short bowel syndrome conditions. Studies in larger series are needed to further investigate these findings.

Motor‐evoked potentials in awake rats are a valid method of assessing hepatic encephalopathy and of studying its pathogenesis

Experimental models of hepatic encephalopathy (HE) are limited by difficulties in objectively monitoring neuronal function. There are few models that examine a well‐defined neuronal pathway and lack the confounding effects of anesthetics. Motor‐evoked potentials (MEPs) assess the function of the motor tract, which has been shown to be impaired in patients with cirrhosis. MEPs were elicited by cranial stimulation (central) and compound motor action potential by sciatic nerve stimulation (peripheral) in several models of HE in the rat. The experiments were performed using subcutaneous electrodes without anesthetics. Brain water content was assessed by gravimetry, brain metabolites were measured by magnetic resonance spectroscopy, and amino acids in microdialysates from the frontal cortex were analyzed by high‐performance liquid chromatography. Abnormalities of MEP were observed in acute liver failure (ALF) induced by hepatic devascularization in relation to the progression of neurological manifestations. Similar disturbances were seen in rats with portocaval anastomosis after the administration of blood or lipopolysaccharide, but were absent in rats with biliary duct ligation. Hypothermia (≤35°C) and mannitol prevented the development of brain edema in acute liver failure, but only hypothermia avoided the decrease in the amplitude of MEP. Disturbances of MEP caused by the administration of blood into the gastrointestinal tract in rats with portocaval anastomosis were associated with an increase in ammonia, glutamine, and glutamate in brain microdialysate. Conclusion: Assessment of MEP in awake rats is a valid method to monitor HE in models of ALF and precipitated HE. This method shows the lack of efficacy of mannitol, a therapy that decreases brain edema, and relates disturbances of the function of the motor tract to ammonia and its metabolites. (HEPATOLOGY 2010)

A leaky splicing mutation in NFU1 is associated with a particular biochemical phenotype. Consequences for the diagnosis

Mutations in NFU1 were recently identified in patients with fatal encephalopathy. NFU1 is an iron-sulfur cluster protein necessary for the activity of the mitochondrial respiratory chain complexes I-II and the synthesis of lipoic acid. We report two NFU1 compound heterozygous individuals with normal complex I and lipoic acid-dependent enzymatic activities and low, but detectable, levels of lipoylated proteins. We demonstrated a leaky splicing regulation due to a splice site mutation (c.545+5G>A) that produces small amounts of wild type NFU1 mRNA that might result in enough protein to partially lipoylate and restore the activity of lipoic acid-dependent enzymes and the assembly and activity of complex I. These results allowed us to gain insights into the molecular basis underlying this disease and should be considered for the diagnosis of NFU1 patients.

Impact of ornithine phenylacetate (OCR-002) in lowering plasma ammonia after upper gastrointestinal bleeding in cirrhotic patients

Background: Ornithine phenylacetate (OP) has been proven effective in lowering ammonia plasma levels in animals, and to be well tolerated in cirrhotic patients. A trial to assess OP efficacy in lowering plasma ammonia levels versus placebo in cirrhotic patients after an upper gastrointestinal bleeding was performed. The primary outcome was a decrease in venous plasma ammonia at 24 hours. Methods: A total of 38 consecutive cirrhotic patients were enrolled within 24 hours of an upper gastrointestinal bleed. Patients were randomized (1:1) to receive OP (10 g/day) or glucosaline for 5 days. Results: The primary outcome was not achieved. A progressive decrease in ammonia was observed in both groups, being slightly greater in the OP group, with significant differences only at 120 hours. The subanalysis according to Child–Pugh score showed a statistically significant ammonia decrease in Child–Pugh C-treated patients at 36 hours, as well as in the time-normalized area under the curve (TN-AUC) 0–120 hours in the OP group [40.16 μmol/l (37.7–42.6); median (interquartile range) (IQR)] versus placebo group [65.5 μmol/l (54–126);p = 0.036]. A decrease in plasma glutamine levels was observed in the treated group compared with the placebo group, and was associated with the appearance of phenylacetylglutamine in urine. Adverse-event frequency was similar in both groups. No differences in hepatic encephalopathy incidence were observed. Conclusions: OP failed to significantly decrease plasma ammonia at the given doses (10 g/day). Higher doses of OP might be required in Child–Pugh A and B patients. OP appeared well tolerated.