G. Visser

UPTAKE OF RADIOLIGANDS BY RAT-HEART AND LUNG INVIVO - CGP-12177 DOES AND CGP-26505 DOES NOT REFLECT BINDING TO BETA-ADRENOCEPTORS

The biodistribution of (-)-4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H-benzimidazol-2-one (CGP12177, a non-selective beta-adrenoceptor antagonist) and 1-[2-(3-carbamoyl-4-hydroxy)-(5-3H-phenoxy)]-2-propanol methanesulfonate, (CGP26505, a beta 1-adrenoceptor antagonist) was studied in rats pretreated with various alpha- and beta-adrenoceptor blocking drugs (5 min before 3H injection, in dosages at which the drugs demonstrated the expected selectivity). Cardiac and pulmonary radioactivity were measured after 10 min, when specific binding was maximal. Uptake of [3H]CGP12177 was linked to binding to beta-adrenoceptors since it was not affected by prazosin or yohimbine, and was equally well inhibited by propranolol, unlabelled CGP12177 and isoprenaline. Moreover, atenolol and CGP20712A inhibited [3H]CGP12177 uptake in heart (predominantly beta 1-adrenoceptors) more potently than ICI 118,551, while in lungs (predominantly beta 2-adrenoceptors) ICI 118,551 was more potent than atenolol or CGP20712A. In contrast, [3H]CGP26505 uptake in the target organs was equally effectively inhibited by propranolol and ICI 118,551, and significantly lowered by alpha-adrenoceptor antagonists. We conclude that [11C]CGP12177, but not [11C]CGP2605 will be suitable for positron emission tomography imaging of beta-adrenoceptors in animals.

Succinyl-CoA:acetoacetate transferase deficiency: identification of a new patient with a neonatal onset and review of the literature

AbstractWe describe the clinical symptoms and biochemical findings of a patient with succinyl-CoA:acetoacetate transferase deficiency who presented in the neonatal period and review the current literature on this subject. Our patient was initially suspected to have distal renal tubular acidosis, and subsequently, a fasting test revealed severe metabolic ketoacidosis with normal blood glucose after 13 h which suggest a defect in ketolysis. In his cultured skin fibroblasts succinyl-CoA:acetoacetate transferase was deficient (residual activity 15%). Treatment in the acute phase consisted of sodium bicarbonate. At the present age of 9 years, psychomotor and physical development are within normal limits. Conclusion Defects of ketolysis probably are underdi agnosed disorders and should be considered in infants and young children with persistent ketosis.

Neurotransmitter positron emission tomographic-studies in adults with phenylketonuria, a pilot study

Patients with phenylketonuria (PKU) may suffer from cognitive and neurological deficits which are related to reduced intracerebral concentrations of catecholamines. The function of phenylalanine (Phe) as an inhibitor of the uptake of the precursor amino acid tyrosine (Tyr) through the blood-brain barrier as well as an inhibitor of the expression of dopamine receptors in the brain is under investigation. Positron emission tomography (PET) is a method for quantitatively determining biochemical and physiological processes in vivo. In the current pilot study, l-[1-11C]-Tyr and 18F-fluoro-ethyl-spiperone (FESP) have been used. The metabolic pathway of carboxylic labelled Tyr is mainly incorporation into protein. From the measured tissue and plasma activity as a function of time in combination with a compartimentai model the Protein Synthesis Rate (PSR) for Tyr can be calculated. FESP is a ligand which binds irreversibly to the dopamine D2-receptor and has also a low non specific binding, although affinity to the serotonin receptor has been described. The ratio of FESP concentration in striatum and in cerebellum is a measure of the receptor status in vivo. In patients with plasma Phe levels above the maximum therapeutic concentration (>700 µmol/1) the PSR for Tyr was decreased as compared to controls and patients with plasma Phe concentrations within the therapeutic range, indicating a decreased availability of Tyr for neurotransmitter synthesis, and hence explaining the reduced cerebral concentration of catecholamines.

A convenient diagnostic function test of peripheral blood neutrophils in glycogen storage disease type Ib

Neutrophils from patients suffering from glycogen storage disease type Ib (GSD-Ib) show several defects, one of which is a decreased rate of glucose utilization. In this study, we established experimental conditions to show the stimulation of the neutrophil respiratory burst by extracellular glucose. With phorbol-myristate-acetate as stimulus of the burst, the activity of the NADPH oxidase in GSD-Ib neutrophils hardly increased on addition of glucose. In control and GSD-type Ia neutrophils, a clear increase was observed. The lack of response to extracellular glucose in GSD-Ib neutrophils is correlated with the inability to raise intracellular glucose-6-P levels on glucose addition, thereby limiting the activity of the generation of NADPH in the hexose-monophosphate shunt. Our study shows the usefulness of this test for the diagnosis of neutrophil function abnormality in GSD-Ib patients.

Elevated cholesterol precursors other than cholestanol can also be a hallmark for CTX

SummaryCerebrotendinous xanthomatosis (CTX) is an inborn error of bile acid synthesis in which hepatic conversion of cholesterol to cholic and chenodeoxycholic acids is impaired. Patients have abnormal bile alcohols in urine, normal to increased plasma cholesterol concentrations and increased concentrations of plasma cholestanol. Little is known about cholesterol precursors in CTX, however. We studied cholesterol and phytosterol profiles in two siblings with CTX during follow-up. While cholesterol concentrations were low in both patients, plasma cholestanol was 6-fold higher compared to control values. In addition, both siblings had a more than 100-fold increase in 7-dehydrocholesterol (7DHC) and 8-dehydrocholesterol (8DHC). Lathosterol, lanosterol and sitosterol were increased in both patients while concentrations of desmosterol and campesterol were normal. In addition, plasma lathosterol/cholesterol ratios were significantly elevated. After treatment with chenodeoxycholate, both patients showed a marked decrease in cholestanol, 7DHC, 8DHC, lathosterol, lanosterol and sitosterol. In addition, the lathosterol/cholesterol ratio normalized, indicating that overall cholesterol synthesis was sufficiently suppressed. This study shows that elevated cholesterol precursors, other than cholestanol, can be a hallmark for CTX.

Tyrosinaemia type I : considerations of treatment strategy and experiences with risk assessment, diet and transplantation

The rapid development of new modes of treatment including organ transplantation, enzyme inhibition, enzyme replacement, liver cell transplantation and gene therapy necessitates knowledge about the results of all modes of treatment to allow decisions on treatment strategies. In hereditary tyrosinaemia type I, apart from the dietary treatment, both orthotopic liver transplantation (OLT) and treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) have become available (Lindstedt et al 1992). However, this disease seems clinically very heterogeneous. Therefore, we should first attempt to categorize different clinical forms since treatment strategies may be quite different. Based on clinical heterogeneity, Halvorsen (1990) divided patients with tyrosinaemia into three forms - acute, subacute and chronic - but could not report the exact outcome on dietary treatment with possible consequences for treatment strategies. We have therefore investigated the clinical course on dietary treatment of our own patients and conducted an international survey on the clinical course of patients managed by dietary treatment and/or OLT, of which the results in part are described elsewhere (van Spronsen et al 1994). The results may enable us to compare the outcome on NTBC and to decide on treatment strategy in tyrosinaemia type I patients.

Synthesis and organ distribution of [18F]fluoro-org 6141 in the rat: A potential glucocorticoid receptor ligand for positron emission tomography

For the synthesis of [18F]Fluoro-Org 6141 via a nucleophilic substitution reaction with 18F-, the tosyl group was chosen as the leaving group because of its stability and excellent leaving group ability. The biodistribution of the high affinity and moderate lipophilicity (log P = 2.66, calculated value) ligand [18F]Fluoro-Org 6141 (specific activity 8.2 to 37 TBq/mmol, yield 10% at EOB) was examined in sham adrenalectomized (sADX) and adrenalectomized (ADX) male Wistar rats. Two days after ADX or sADX, the animals were anesthetized and 0.37 to 1.85 MBq of [18F]Fluoro-Org 6141 was administered intravenously. Kinetics of 18F activity uptake were monitored for 3 h using a stationary double-headed positron emission tomography (PET) camera, and the biodistribution was assessed by ex vivo determination of radioactivity in several tissues and different brain areas. One hour after injection of the radioligand, the bladder, kidney, liver, trachea, and bone of sADX animals contained more concentration on a wet weight basis than blood. Three hours post injection, radioactivity was retained in bladder, trachea, and bone. The accumulation of radioactivity in brain corresponded to the concentration of activity in the blood within the first hours after injection. ADX animals showed a higher uptake of 18F activity in spleen, testes, and brain areas (hippocampus and brainstem) but a lower uptake in bone than sADX rats. PET scans suggested that 18F activity uptake in the brain had not yet reached a maximum at this interval. Although [18F]Fluoro-Org 6141 is not useful for PET studies of glucocorticoid receptors (GRs), the results obtained with this compound indicate a synthetic strategy suitable for the synthesis of high-affinity radioligands for GRs.

Prolonged exercise testing in two children with a mild Multiple Acyl-CoA-Dehydrogenase deficiency

BackgroundMultiple Acyl-CoA-Dehydrogenase deficiency (MADD) is an inherited metabolic disorder characterized by impaired oxidation of fatty acids and some amino acids.MethodsWe were interested whether children with MADD could tolerate a prolonged low-intensity exercise test and if this test could have any additional diagnostic value. Therefore, we performed a maximal exercise test and a low-intensity prolonged exercise test in 2 patients with MADD and in 5 control subjects. During a prolonged exercise test the subjects exercised on a cycle ergometer at a constant workload of 30% of their maximum for 90 minutes and heart rate, oxygen uptake, fuel utilization and changes in relevant blood and urinary parameters were monitored.ResultsThe tests were tolerated well. During the prolonged exercise test the fatty acid oxidation (FAO) was quite low compared to 5 control subjects, while characteristic metabolites of MADD appeared in plasma and urine.ConclusionWe suggest that the prolonged exercise test could be of diagnostic importance and might replace the fasting test as a diagnostic procedure in some cases, particularly in patients with anamnestic signs of intolerance for prolonged exercise.

Comment on Zwickler et al.: Usefulness of biochemical parameters in decision-making on the start of emergency treatment in patients with propionic acidemia

Dear Editor, Treatment of patients with (acutely) decompensated propionic acidemia (PA) is a medical emergency. We read with great interest the paper by Zwickler et al. (2014), who reported that ammonia, acid–base balance, and anion gap are important biochemical parameters by which to identify an (impending) metabolic decompensation and can be used to assess its severity in PA patients. Moreover, Zwickler et al. suggested that presently available metabolic parameters, such as organic acids and acylcarnitines, were not discriminative and can be omitted. Based on our study results, we fully agree with this conclusion. In addition, we quantified methylcitrate (MCA) in plasma of patients with PA (n=54) using ultraperformance liquid chromatography–tandem mass spectrometry. The analysis of MCA in plasma was based on the method described by Fu et al. (2013), with some modifications. MCA in PA patients is formed as a consequence of propionyl–coenzyme A (CoA) accumulation and subsequent condensation with oxaloacetate. MCA was consistently increased in all patients, irrespective of their metabolic condition (range 6.7– 107.5 μmol/L, median 30.6 μmol/L, normal <0.4 μmol/ L). Our results further show that when metabolic control in patients with PA becomes unstable, ammonia levels increase concurrently with plasma MCA (Fig. 1, y=0.450x+ 1.184, r=0.75, P<0.0001, n=28). A direct link between ammonia and MCA has also been reported in the study by Jafari et al. (2013), who showed parallel changes in ammonium after exposure to MCA (dose–response studies in an in vitro model). The authors show that exposure to MCA causes morphological changes in neuronal and glial cells and suggest that ammonium accumulation is secondary to cell suffering and/ or death. We suggest further investigation of MCA in plasma as a marker for PA decompensation. This stable compound may be favorable, as plasma ammonia concentrations may artificially increase by contamination and deterioration of blood components during specimen handling and storage. In conclusion, MCA measurements in plasma, along with the other suggested parameters, may provide information on decompensation in PA.

Synthesis of [11C]methyl ketones via [11C]methylation of dithiane intermediates

Abstract A versatile synthetic route to obtain [ 11 C]methyl ketones from aldehydes is described. Test reactions with [ 11 C]CH 3 I on the model compounds 2-methyl- and 2-cyclohexyl- 1,3-dithiane followed by oxidation with N-bromosuccinimide gave almost quantitative radiochemical yields. Reaction of [ 11 C]CH 3 I with 2-phenylethyl-1,3-dithiane yielded the corresponding [ 11 C]methyl ketone in 80% radiochemical yield together with an unidentified side-product on oxidation with N-bromosuccinimide.