Ayelet Gamliel

A hyperpolarized choline molecular probe for monitoring acetylcholine synthesis

Choline as a reporter molecule has been investigated by in vivo magnetic resonance for almost three decades. Accumulation of choline metabolites (mainly the phosphorylated forms) had been observed in malignancy in preclinical models, ex-vivo, in vivo and in patients. The combined choline metabolite signal appears in (1) H-MRS of the brain and its relative intensity had been used as a diagnostic factor in various conditions. The advent of spin hyperpolarization methods for in vivo use has raised interest in the ability to follow the physiological metabolism of choline into acetylcholine in the brain. Here we present a stable-isotope labeled choline analog, [1,1,2,2-D(4) ,2-(13) C]choline chloride, that is suitable for this purpose. In this analog, the (13) C position showed 24% polarization in the liquid state, following DNP hyperpolarization. This nucleus also showed a long T(1) (35 s) at 11.8 T and 25 °C, which is a prerequisite for hyperpolarized studies. The chemical shift of this (13) C position differentiates choline and acetylcholine from each other and from the other water-soluble choline metabolites, namely phosphocholine and betaine. Enzymatic studies using an acetyltransferase enzyme showed the synthesis of the deuterated-acetylcholine form at thermal equilibrium conditions and in a hyperpolarized state. Analysis using a comprehensive model showed that the T(1) of the formed hyperpolarized [1,1,2,2-D(4) ,2-(13) C]acetylcholine was 34 s at 14.1 T and 37 °C. We conclude that [1,1,2,2-D(4) ,2-(13) C]choline chloride is a promising new molecular probe for hyperpolarized metabolic studies and discuss the factors related to its possible use in vivo.

In vitro visualization of betaine aldehyde synthesis and oxidation using hyperpolarized magnetic resonance spectroscopy

Real-time monitoring of betaine aldehyde metabolism at high temporal resolution was accomplished using a hyperpolarized choline analog and (13)C-NMR. This represents the first observation of an aldehyde intermediate on hyperpolarized MR and opens the way for kinetic studies of oxidase/dehydrogenase enzymes in vitro and in vivo.

Biochemical phosphates observed using hyperpolarized 31 P in physiological aqueous solutions

The dissolution-dynamic nuclear polarization technology had previously enabled nuclear magnetic resonance detection of various nuclei in a hyperpolarized state. Here, we show the hyperpolarization of 31P nuclei in important biological phosphates (inorganic phosphate and phosphocreatine) in aqueous solutions. The hyperpolarized inorganic phosphate showed an enhancement factor >11,000 (at 5.8 T, 9.3% polarization) in D2O (T1 29.4 s). Deuteration and the solution composition and pH all affected the lifetime of the hyperpolarized state. This capability opens up avenues for real-time monitoring of phosphate metabolism, distribution, and pH sensing in the live body without ionizing radiation. Immediate changes in the microenvironment pH have been detected here in a cell-free system via the chemical shift of hyperpolarized inorganic phosphate. Because the 31P nucleus is 100% naturally abundant, future studies on hyperpolarized phosphates will not require expensive isotope labeling as is usually required for hyperpolarization of other substrates.Real-time monitoring of phosphate metabolism and distribution in the live body without ionizing radiation is highly desirable. Here, the authors show dissolution-dynamic nuclear polarization technology can enable nuclear magnetic resonance detection of hyperpolarized 31P of important biological phosphates in aqueous solutions.

Transaldolase Deficiency: A New Case Expands the Phenotypic Spectrum

Transaldolase (TALDO) deficiency has various clinical manifestations including liver dysfunction, hepatosplenomegaly, anemia, thrombocytopenia, and dysmorphic features. We report a case presenting prenatally with hyperechogenic bowel and intrauterine growth restriction. The infant was born small for gestational age, with cutis laxa and hypertrichosis. Postnatally, meconium plug was identified, complicated with intestinal obstruction necessitating laparotomy, partial resection of the intestine, and ileostomy. Liver biopsy revealed cholangiolar proliferation and portal fibrosis. He also suffered from persistent congenital thrombocytopenia requiring platelet transfusions and severe hypothyroidism with normal anatomical and structural gland responding only to the combination of T3 and T4 treatment. Neurologically, severe hypotonia and anisocoria were noted at the age of 2 months. Brain MRI was normal. Shortly after the abdominal surgery, a rapid liver failure ensued, which eventually led to his death. Specific metabolic tests ruled out glycosylation disorders, yet urine analysis using 1H NMR showed accumulation of sedoheptulose which was previously described in patients with transaldolase deficiency. Sequencing of the gene-encoding transaldolase (TALDO1) revealed a homozygous stop mutation c.669C>G; p.Tyr223*. In conclusion, we present an infant with a novel homozygous mutation in TALDO1, causing TALDO deficiency, and extend the clinical characteristics of this rare syndrome.

Higher levels of myelin phospholipids in brains of neuronal α-Synuclein transgenic mice precede myelin loss

Abstractα-Synuclein is a protein involved in the pathogenesis of synucleinopathies, including Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). We investigated the role of neuronal α-Syn in myelin composition and abnormalities. The phospholipid content of purified myelin was determined by 31P NMR in two mouse lines modeling PD, PrP-A53T α-Syn and Thy-1 wt-α-Syn. Significantly higher levels of phospholipids were detected in myelin purified from brains of these α-Syn transgenic mouse models than in control mice. Nevertheless, myelin ultrastructure appeared intact. To further investigate the effect of α-Syn on myelin abnormalities, we systematically analyzed the striatum, a brain region associated with neurodegeneration in PD. An age and disease-dependent loss of myelin basic protein (MBP) signal was detected by immunohistochemistry in striatal striosomes (patches). The age-dependent loss of MBP signal was associated with lower P25α levels in oligodendrocytes. In addition, we found that α-Syn inhibited oligodendrocyte maturation and the formation of membranous sheets in vitro. Based on these results we concluded that neuronal α-Syn is involved in the regulation and/or maintenance of myelin phospholipid. However, axonal hypomyelination in the PD models is evident only in progressive stages of the disease and associated with α-Syn toxicity.

Real-time ex-vivo measurement of brain metabolism using hyperpolarized [1- 13 C]pyruvate

The ability to directly monitor in vivo brain metabolism in real time in a matter of seconds using the dissolution dynamic nuclear polarization technology holds promise to aid the understanding of brain physiology in health and disease. However, translating the hyperpolarized signal observed in the brain to cerebral metabolic rates is not straightforward, as the observed in vivo signals reflect also the influx of metabolites produced in the body, the cerebral blood volume, and the rate of transport across the blood brain barrier. We introduce a method to study rapid metabolism of hyperpolarized substrates in the viable rat brain slices preparation, an established ex vivo model of the brain. By retrospective evaluation of tissue motion and settling from analysis of the signal of the hyperpolarized [1-13C]pyruvate precursor, the T1s of the metabolites and their rates of production can be determined. The enzymatic rates determined here are in the range of those determined previously with classical biochemical assays and are in agreement with hyperpolarized metabolite relative signal intensities observed in the rodent brain in vivo.

Author Correction: Biochemical phosphates observed using hyperpolarized 31 P in physiological aqueous solutions

The original version of the Supplementary Information associated with this Article contained an error in Supplementary Figure 2 and Supplementary Figure 5 in which the 31P NMR spectral lines were missing. The HTML has been updated to include a corrected version of the Supplementary Information.

Long-lived 15N Hyperpolarization and Rapid Relaxation as a Potential Basis for Repeated First Pass Perfusion Imaging - Marked Effects of Deuteration and Temperature

Deuteration of the exchangeable hydrogens of [15 N2 ]urea was found to prolong the T1 of the 15 N sites to more than 3 min at physiological temperatures. This significant increase in the lifetime of the hyperpolarized state of [15 N2 ]urea, compared to [13 C]urea - a pre-clinically proven perfusion agent, makes [15 N2 ]urea a promising perfusion agent. The molecular parameters that may lead to this profound effect were assessed by investigating small molecules with different molecular structures containing 15 N sites bound to labile protons and determining the hyperpolarized 15 N T1 in H2 O and D2 O. Dissolution in D2 O led to marked prolongation for all of the selected sites. In whole human blood, the T1 of [15 N2 ]urea was shortened. We present a general strategy for exploiting the markedly longer T1 outside the body and the quick decay in blood for performing multiple hyperpolarized perfusion measurements with a single hyperpolarized dose. Improved storage of the generated [15 N2 ]urea polarization prior to the contact with the blood is demonstrated using higher temperatures due to further T1 prolongation.