PET imaging of the dopamine transporter with 18F-FECNT: a polar radiometabolite confounds brain radioligand measurements.

18F-2beta-Carbomethoxy-3beta-(4-chlorophenyl)-8-(2-fluoroethyl)nortropane (18F-FECNT), a PET radioligand for the dopamine transporter (DAT), generates a radiometabolite that enters the rat brain. The aims of this study were to characterize this radiometabolite and to determine whether a similar phenomenon occurs in human and nonhuman primate brains by examining the stability of the apparent distribution volume in DAT-rich (striatum) and DAT-poor (cerebellum) regions of the brain. METHODS: Two rats were infused with 18F-FECNT and sacrificed at 60 min. Extracts of brain and plasma were analyzed by high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometric (LC-MS) techniques. Two human participants and 3 rhesus monkeys were injected with 18F-FECNT and scanned kinetically, with serial arterial blood analysis. RESULTS: At 60 min after the injection of rats, 18F-FECNT accumulated to levels about 7 times higher in the striatum than in the cortex and cerebellum. The radiometabolite was distributed at equal concentrations in all brain regions. The LC-MS techniques identified N-dealkylated FECNT as a major metabolite in the rat brain, and reverse-phase HPLC detected an equivalent amount of radiometabolite eluting with the void volume. The radiometabolite likely was 18F-fluoroacetaldehyde, the product expected from the N-dealkylation of 18F-FECNT, or its oxidation product, 18F-fluoroacetic acid. The distribution volume in the cerebellum increased up to 1.7-fold in humans between 60 and 300 min after injection and 2.0 +/- 0.1-fold (mean +/- SD; n = 3) in nonhuman primates between 60 and 240 min after injection. CONCLUSION: An 18F-fluoroalkyl metabolite of 18F-FECNT originating in the periphery confounded the measurements of DAT in the rat brain with a reference tissue model. Its uniform distribution across brain regions suggests that it has negligible affinity for DAT (i.e., it is an inactive radiometabolite). Consistent with the rodent data, the apparent distribution volume in the cerebellum of both humans and nonhuman primates showed a continual increase at late times after injection, a result that may be attributed to entry of the radiometabolite into the brain. Thus, reference tissue modeling of 18F-FECNT will be prone to more errors than analysis with a measured arterial input function.     

Reversal of pulmonary hypertension and subsequent repair of atrial septal defect after treatment with continuous intravenous epoprostenol.

We report the first case in the world literature of a patient with an atrial septal defect, severe pulmonary hypertension, and equalization of pulmonary and systemic pressures, who underwent successful closure of an ASD following prolonged therapy with the intravenous vasodilator epoprostenol. Judicious use of continuous prostacyclin in apparently inoperable patients with congenital heart disease may be associated with significant reversal of pulmonary hypertension, and conversion to an operable state.     

Stimulation of β-adrenoceptors inhibits store-operated channel currents via a cAMP-dependent protein kinase mechanism in rabbit portal vein myocytes

Previously we have described the properties of store-operated channel currents (SOCs) in freshly dispersed rabbit portal vein smooth muscle cells. In addition to Ca²⁺ store depletion these SOCs could also be activated by α-adrenoceptor stimulation and diacylglycerol (DAG) via a protein kinase C (PKC)-dependent mechanism. In the present study we have investigated the effect of β-adrenoceptor stimulation on SOCs in rabbit portal vein myocytes. With whole-cell recording the selective β-adrenoceptor agonist isoprenaline reduced the current evoked by cyclopiazonic acid (CPA, sarcoplasmic/endoplasmic reticulum ATPase inhibitor) by over 85%. With cell-attached patch recording, bath application of isoprenaline produced a pronounced inhibition of SOC activity evoked by either CPA or the acetoxymethyl ester form of BAPTA (BAPTA-AM). SOC activity evoked by CPA, the DAG analogue, 1-oleoyl-acetyl- sn -glycerol (OAG) or the phorbol ester, phorbol-12,13-dibutyrate (PDBu) was also markedly inhibited by the adenylate cyclase activator, forskolin, and the cell-permeable non-hydrolysable analogue of cyclic adenosine monophosphate (cAMP), 8-Br-cAMP. With inside-out patches, bath application of PDBu evoked channel currents with similar properties to SOCs which were inhibited by over 90% by a catalytic subunit of protein kinase A (PKA) and by 8-Br-cAMP. Moreover bath application of PKA inhibitors, H-89, KT5720 and an inhibitory peptide to quiescent cell-attached or inside-out patches, activated channel currents with similar properties to SOCs. These data suggest that in rabbit portal vein myocytes, stimulation of β-adrenoceptors inhibits SOC activity via a cAMP-dependent protein kinase signal transduction cascade. In addition it is concluded that constitutive PKA activity has a profound inhibitory effect on SOC activity in this vascular preparation.     

Cloning and developmental expression analysis of the murine homolog of the spinocerebellar ataxia type 1 gene (Sca1)

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by the expansion of a CAG trinucleotide repeat which encodes glutamine in the novel protein ataxin-1. In order to characterize the developmental expression pattern of SCA1 and to identify putative functional domains in ataxin-1, the murine homolog (Sca1) was isolated. Cloning and characterization of the murine Sca1 gene revealed that the gene organization is similar to that of the human gene. The murine and human ataxin-1 are highly homologous but the CAG repeat is virtually absent in the mouse sequence suggesting that the polyglutamine stretch is not essential for the normal function of ataxin-1 in mice. Cellular and developmental expression of the murine homolog was examined using RNA in situ hybridization. During cerebellar development, there is a transient burst of Sca1 expression at postnatal day 14 when the murine cerebellar cortex becomes physiologically functional. There is also marked expression of Sca1 in mesenchymal cells of the intervertebral discs during development of the spinal column. These results suggest that the normal Sca1 gene, has a role at specific stages of both cerebellar and vertebral column development.      

A de novo X;3 translocation in Rett syndrome

Rett syndrome is a neurodegenerative disorder that occurs exclusively in females. The syndrome is sporadic in most cases with the exception of a few familial cases with an inheritance pattern through maternal lines. These observations raised the possibility that Rett syndrome may be due to an X-linked dominant mutation which is lethal in the male. To evaluate this hypothesis, we have systematically performed high-resolution chromosome analysis on 28 patients with Rett syndrome searching for deletions and/or translocations. In one patient, a de novo balanced translocation was observed with the chromosome constitution of 46,X,t(X;3) (p22.11;q13.31). This finding supports the hypothesis of an X-linked dominant mutation and suggests that the Rett gene might map to distal Xp21 or proximal Xp22.