Regulation of phospholipid metabolism in differentiating cells from rat brain cerebral hemispheres in culture: ontogenesis of carrier-specific transport of choline and N-methyl-substituted choline analogs

PET and PET/CT with radiolabeled choline in prostate cancer: a critical reappraisal of 20 years of clinical studies

We here aim to provide a comprehensive and critical review of the literature concerning the clinical applications of positron emission tomography/computed tomography (PET/CT) with radiolabeled choline in patients with prostate cancer (PCa). We will initially briefly summarize the historical context that brought to the synthesis of [¹¹C]choline, which occurred exactly 20 years ago. We have arbitrarily grouped the clinical studies in three different periods, according to the year in which they were published and according to their relation with their applications in urology, radiotherapy and oncology. Studies at initial staging and, more extensively, studies in patients with biochemical failure, as well as factors predicting positive PET/CT will be reviewed. The capability of PET/CT with radiolabeled choline to provide prognostic information on PCa-specific survival will also be examined. The last sections will be devoted to the use of radiolabeled choline for monitoring the response to androgen deprivation therapy, radiotherapy, and chemotherapy. The accuracy and the limits of the technique will be discussed according to the information available from standard validation processes, including biopsy or histology. The clinical impact of the technique will be discussed on the basis of changes induced in the management of patients and in the evaluation of the response to therapy. Current indications to PET/CT, as officially endorsed by guidelines, or as routinely performed in the clinical practice will be illustrated. Emphasis will be made on methodological factors that might have influenced the results of the studies or their interpretation. Finally, we will briefly highlight the potential role of positron emission tomography/magnetic resonance and of new radiotracers for PCa imaging.

A fully-automated one-pot synthesis of [18F]fluoromethylcholine with reduced dimethylaminoethanol contamination via [18F]fluoromethyl tosylate

INTRODUCTION

A novel one-pot method for preparing [(18)F]fluoromethylcholine ([(18)F]FCH) via in situ generation of [(18)F]fluoromethyl tosylate ([(18)F]FCH2OTs), and subsequent [(18)F]fluoromethylation of dimethylaminoethanol (DMAE), has been developed.

METHODS

[(18)F]FCH was prepared using a GE TRACERlab FXFN, although the method should be readily adaptable to any other fluorine-(18) synthesis module. Initially ditosylmethane was fluorinated to generate [(18)F]FCH2OTs. DMAE was then added and the reaction was heated at 120 °C for 10 min to generate [(18)F]FCH. After this time, reaction solvent was evaporated, and the crude reaction mixture was purified by solid-phase extraction using C(18)-Plus and CM-Light Sep-Pak cartridges to provide [(18)F]FCH formulated in USP saline. The formulated product was passed through a 0.22 µm filter into a sterile dose vial, and submitted for quality control testing. Total synthesis time was 1.25 h from end-of-bombardment.

RESULTS

Typical non-decay-corrected yields of [(18)F]FCH prepared using this method were 91 mCi (7% non-decay corrected based upon ~1.3 Ci [(18)F]fluoride), and doses passed all other quality control (QC) tests.

CONCLUSION

A one-pot liquid-phase synthesis of [(18)F]FCH has been developed. Doses contain extremely low levels of residual DMAE (31.6 µg/10 mL dose or ~3 ppm) and passed all other requisite QC testing, confirming their suitability for use in clinical imaging studies.

Uptake rates of 18F-fluorodeoxyglucose and 11C-choline in lung cancer and pulmonary tuberculosis: a positron emission tomography study

STUDY OBJECTIVE

The purpose of this study was to examine the uptake rates of (18)F-fluorodeoxyglucose (FDG) and (11)C-choline in patients with lung cancer, pulmonary tuberculosis, and atypical mycobacterial infection of the lung by positron emission tomography (PET) scanning with relation to their tumor size.

DESIGN

Ninety-seven patients with untreated lung cancer, 14 patients with untreated pulmonary tuberculosis, and 5 patients with untreated atypical mycobacterial infection were examined. The diagnosis of lung cancer was confirmed pathologically after biopsy and surgery. The diagnosis of tuberculosis and atypical mycobacterial infection was confirmed by bacterial culture. The uptake rates of FDG and (11)C-choline were presented quantitatively as the standardized uptake value (SUV).

SETTING

International Medical Center of Japan.

RESULTS

In lung cancer patients, the SUV of FDG increased with increasing tumor size, whereas the SUV of (11)C-choline was almost constant at around 3.5 for every tumor size. In tuberculosis patients, the SUV of FDG increased with increasing tumor size, whereas the SUV of (11)C-choline was almost constant at around 2 for every tumor size. In atypical mycobacterial infection patients, the SUV of FDG and the SUV of (11)C-choline were equally low at around < or = 2.

CONCLUSION

The differences in the SUVs of FDG and (11)C-choline in patients with lung cancer, tuberculosis, and atypical mycobacterial infection for the same tumor size (tumor size, > 1.5 cm) were distinct. In lung cancer patients, the SUVs of both FDG and (11)C-choline were high. In tuberculosis patients, the SUV of FDG was high, but the SUV of (11)C-choline was low. In atypical mycobacterial infection patients, the SUVs of both FDG and (11)C-choline were low. It may be possible to apply this principle to make a presumptive diagnosis of a solitary pulmonary nodule if it is too small to make a definitive diagnosis pathologically and bacteriologically.

Differential development of cholinergic nerve terminal markers in rat brain regions: implications for nerve terminal density, impulse activity and specific gene expression

During critical developmental periods, cholinergic activity plays a key role in programming the development of target cells. In the current study, ontogeny of cholinergic terminals and their activity were contrasted in 4 brain regions of the fetal and neonatal rat using choline acetyltransferase activity, which is unresponsive to changes in impulse flow, and [3H]hemicholinium-3 binding, which labels the high-affinity choline transporter that upregulates in response to increased neuronal stimulation. In all 4 regions (cerebral cortex, midbrain + brainstem, striatum, hippocampus) choline acetyltransferase activity increased markedly from late gestation through young adulthood, but generally did so in parallel with the expansion of total membrane protein, reflective of axonal outgrowth and synaptic proliferation. In contrast, [3H]hemicholinium-3 binding was extremely high in late gestation and immediately after birth, declined in the first postnatal week and then rose again into young adulthood. The ontogenetic changes reflected alterations primarily in the number of binding sites (Bmax) and not in binding affinity. Only the latter phase of development of [3H]hemicholinium-3 binding corresponded to the ontogenetic changes in choline acetyltransferase activity; in the hippocampus, there were disparities even in young adulthood, where [3H]hemicholinium-3 binding showed a spike of activity centered around the 5th to 6th postnatal week, whereas choline acetyltransferase did not. Correction of binding for membrane protein development did not eliminate any of the major differences in developmental patterns between the two markers. These results suggest that development of the choline transporter binding site is regulated independently of the outgrowth of the bulk of cholinergic nerve terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic but not GABAergic neuronal markers are decreased in primary neuronal cultures treated with choline mustard

Nitrogen mustard analogues of choline are potent irreversible inhibitors of high-affinity choline transport at the cholinergic presynaptic nerve terminal in vitro. Ethylcholine mustard aziridinium ion, and to a lesser extent choline mustard aziridinium ion, have been used as tools to chemically lesion cholinergic neurons in the central nervous system. The selectivity of these compounds as neurotoxins for cholinergic neurons in vivo has been questioned and the mechanism by which they mediate neuronal death has not been elucidated. The objective of the present study was to investigate the selectivity of choline mustard aziridinium ion on embryonic rat brain neurons maintained in primary culture. The effect of choline mustard aziridinium ion on levels of cholinergic neuronal markers was compared with markers for GABAergic neurons as a measure of neuronal specificity. Choline mustard aziridinium ion at 10 and 30 microM irreversibly inhibited hemicholinium-sensitive, high-affinity choline transport into the cultured neurons without altering sodium-dependent, high-affinity GABA transport. Similarly, incubation of the neurons for 30 min in the presence of 10 microM choline mustard aziridinium ion led to a decrease in choline acetyltransferase activity of the cultures which was maintained for 72 h; glutamic acid decarboxylase activity was not altered under the same experimental conditions. Protein and DNA content and DNA-to-protein ratios of the choline mustard aziridinium ion-treated cultures were monitored as indicators of generalized cellular damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine synthesis and secretion by LA-N-2 human neuroblastoma cells

We have investigated the rates of acetylcholine (ACh) synthesis and release in LA-N-2 cells in order to characterize them as a potential model of cholinergic neurons. When grown in a serum-containing medium the cells extend few neurites. In the absence of serum most cells develop processes. ACh content of the cells (determined by a radioenzymatic assay) varies with extracellular choline concentration in a saturable fashion, reaching a maximum of approximately 25 nmol/mg protein. Radiolabeled choline is taken up by the cell and converted to ACh or phosphocholine, as determined by purification from cell extracts by HPLC, in a saturable manner which is described by a single rectangular hyperbola. Hemicholinium-3 (100 microM) inhibits this uptake. The cells release ACh spontaneously and this release is enhanced upon depolarization with potassium or veratridine (the latter effect is blocked by tetrodotoxin). The data demonstrate that LA-N-2 cells exhibit some properties similar to cholinergic neurons and may therefore be useful for studies of ACh synthesis and release.

Cholinotoxicity of the ethylcholine aziridinium ion in primary cultures from rat central nervous system

The cytotoxic effects of ethylcholine aziridinium ion (AF64A) were studied in primary cultures prepared from either whole brain, septum, or midbrain of fetal rats. AF64A, at concentrations up to 22.5 microM, significantly reduced the number of acetylcholinesterase-stained cells without affecting the number of dopaminergic neurons or their ability to take up and release [3H]dopamine. Many of the survived acetylcholinesterase-stained cells appeared with intact somata but damaged processes, indicating a retrograde degeneration starting at the nerve terminal. Higher concentrations of AF64A (greater than 22.5 microM), caused general toxicity which was expressed by degeneration of various neuronal and glial cells. Choline (500 microM), significantly protected the cells from AF64A induced cytotoxicity. The results are consistent with a previously described kinetic model, that predicted a dual action of AF64A: selective cholinotoxicity at low concentrations and non-selective cytotoxicity at higher concentrations.

The incorporation of monomethylethanolamine and dimethylethanolamine in fetal brain aggregating cell culture

Fetal rat brain aggregating cell cultures were exposed to varying concentrations of [3H]monomethylethanolamine (MME) and [3H] dimethylethanolamine (DME). The rate of labeling of water-soluble compounds was more rapid and the amount of radioactivity present was greater than in the lipids. After a 72 hour incubation in the presence of millimolar concentrations of these nitrogenous bases, the major water-soluble products were the phosphorylated form of the bases. Little label was associated with the free bases or their cytidyl derivative. In the phospholipids, 97% of the radioactivity was recovered in phosphatidylmonomethylethanolamine (PMME) and 3% in phosphatidyldimethylethanolamine (PDME) or 95% in PDME and 5% in phosphatidylcholine (PC) after growth in presence of [3H]MME and [3H]DME respectively. The rate of formation of the radioactive products increased as function of the concentration of the nitrogenous base added up to 4 mM, the highest concentration employed. There was no significant difference in the pattern of labeling with cells grown in media devoid of methionine or choline. The turnover of the water-soluble metabolites was more rapid than in the phospholipids where an apparent half-life of 24 hours was calculated.

Polar head group decarboxylation and methylation of phospholipids: an alternate route for phosphatidylcholine formation in cultured neuronal cells

Decarboxylation of phosphatidylserine (SPG) and methionine-dependent, stepwise methylation of phosphatidylethanolamine (EPG) to form phosphatidylcholine (CPG) were examined in monolayer cultures of rat cerebral cells. Ethanolamine, monomethylaminoethanol, or dimethylaminoethanol nitrogenous bases (N-bases) added to culture medium at millimolar level result each in synthesis of the corresponding phospholipid via a de novo pathway at initial rates of 0.18, 0.30, and 0.36 nmol/h/micrograms DNA, respectively. Addition of methyl-labeled methionine to culture medium at tracer levels or at millimolar concentration enabled measurements of the rates of phospholipid methylation from EPG phosphatidylmonomethylaminoethanol (Me1EPG) and phosphatidyldimethylaminoethanol (Me2EPG) precursors. At tracer doses, the rates of methylation from the above respective phospholipids are 0.45, 1.17, and 1.70 pmol/h/micrograms DNA. At 1 mM methionine, synthesis of CPG proceeds from [14C]EPG or [14C]Me2EPG at initial rates of 8 and 17 pmol/h/micrograms DNA, respectively. Although the latter phospholipid analog can be generated from its monomethyl precursor, methylation of EPG does not result in the accumulation of Me2EPG, suggesting two segregated and metabolically distinct pathways. In the presence of N-bases, of the total [3H]serine incorporated into cellular phospholipids 30-36.5% of labelled SPG is converted into decarboxylation products. The decarboxylation and methylation routes contribute a significant portion of choline from endogenous sources, most likely through conversion of SPG.

Choline and cholinergic neurons

Mammalian neurons can synthesize choline by methylating phosphatidylethanolamine and hydrolyzing the resulting phosphatidylcholine. This process is stimulated by catecholamines. The phosphatidylethanolamine is synthesized in part from phosphatidylserine; hence the amino acids methionine (acting after conversion to S-adenosylmethionine) and serine can be the ultimate precursors of choline. Brain choline concentrations are generally higher than plasma concentrations, but depend on plasma concentrations because of the kinetic characteristics of the blood-brain-barrier transport system. When cholinergic neurons are activated, acetylcholine release can be enhanced by treatments that increase plasma choline (for example, consumption of certain foods).