Kerttuli Helariutta

Phloem-Transported Cytokinin Regulates Polar Auxin Transport and Maintains Vascular Pattern in the Root Meristem

Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture [1-3]. Long-distance transport of cytokinin is supported by the discovery of cytokinins in xylem and phloem sap [4] and by grafting experiments between wild-type and cytokinin biosynthesis mutants [5]. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching [6]. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling [7]. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem.

Translating the concept of peptide labeling with 5-deoxy-5-[18F]fluororibose into preclinical practice: 18F-labeling of Siglec-9 peptide for PET imaging of inflammation.

Peptide glycosylation with 5-deoxy-5-[(18)F]fluororibose was translated into preclinical settings. The novel (18)F-labeled Siglec-9 peptide was produced using an automated synthesis procedure. The (18)F-labeled Siglec-9 peptide showed favorable binding in the animal model of inflammation in vivo.

A New Highly Reactive and Low Lipophilicity Fluorine-18 Labeled Tetrazine Derivative for Pretargeted PET Imaging.

A new (18)F-labeled tetrazine derivative was developed aiming at optimal radiochemistry, fast reaction kinetics in inverse electron-demand Diels-Alder cycloaddition (IEDDA), and favorable pharmacokinetics for in vivo bioorthogonal chemistry. The radiolabeling of the tetrazine was achieved in high yield, purity, and specific activity under mild reaction conditions via conjugation with 5-[(18)F]fluoro-5-deoxyribose, providing a glycosylated tetrazine derivative with low lipophilicity. The (18)F-tetrazine showed fast reaction kinetics toward the most commonly used dienophiles in IEDDA reactions. It exhibited excellent chemical and enzymatic stability in mouse plasma and in phosphate-buffered saline (pH 7.41). Biodistribution in mice revealed favorable pharmacokinetics with major elimination via urinary excretion. The results indicate that the glycosylated (18)F-labeled tetrazine is an excellent candidate for in vivo bioorthogonal chemistry applications in pretargeted PET imaging approaches.

Comparison of Somatostatin Receptor 2-Targeting PET Tracers in the Detection of Mouse Atherosclerotic Plaques

PurposeRupture-prone atherosclerotic plaques are characterized by accumulation of macrophages, which have shown to express somatostatin type 2 receptors. We aimed to investigate whether somatostatin receptor-targeting positron emission tomography (PET) tracers, [68Ga]DOTANOC, [18F]FDR-NOC, and [68Ga]DOTATATE, can detect inflamed atherosclerotic plaques.ProceduresAtherosclerotic IGF-II/LDLR−/−ApoB100/100 mice were studied in vivo and ex vivo for tracer uptake into atherosclerotic plaques. Furthermore, [68Ga]DOTANOC and [68Ga]DOTATATE were compared in a head-to-head setting for in vivo PET/X-ray computed tomography (CT) imaging characteristics.ResultsEx vivo uptake of [68Ga]DOTANOC and [68Ga]DOTATATE in the aorta was higher in atherosclerotic mice compared to control C57Bl/6N mice, while the aortic uptake of [18F]FDR-NOC showed no genotype difference. Unlike [18F]FDR-NOC, [68Ga]DOTANOC and [68Ga]DOTATATE showed preferential binding to atherosclerotic plaques with plaque-to-wall ratio of 1.7 ± 0.3 and 2.1 ± 0.5, respectively. However, the aortic uptake and aorta-to-blood ratio of [68Ga]DOTANOC were higher compared to [68Ga]DOTATATE in in vivo PET/CT imaging.ConclusionOur results demonstrate superior applicability for [68Ga]DOTANOC and [68Ga]DOTATATE in the detection of atherosclerotic plaques compared to [18F]FDR-NOC.

Using 5-deoxy-5-[18F]fluororibose to glycosylate peptides for positron emission tomography

So far seven peptide-based 18F-radiopharmaceuticals for diagnostic applications with positron emission tomography (PET) have entered into clinical trials. Three candidates out of these seven are glycosylated peptides, which may be explained by the beneficial influence of glycosylation on in vivo pharmacokinetics of peptide tracers. This protocol describes the method for labeling peptides with 5-deoxy-5-[18F]fluororibose ([18F]FDR) as a prosthetic group. The synthesis of [18F]FDR is effected by a nucleophilic fluorination step by using dried Kryptofix 2.2.2-K2CO3-K18F complex and a subsequent HCl-catalyzed hydrolysis. The conjugation of [18F]FDR to the N-terminus aminooxy (-ONH2)-functionalized peptides is carried out in anilinium buffer at pH 4.6 and at room temperature (RT, 21–23 °C), with the concentration of peptide precursors being 0.3 mM. The procedure takes about 120 min and includes two cartridge isolation steps and two reversed-phase (RP) HPLC purification steps. The quaternary methyl amine (QMA) anion exchange cartridge and the hydrophilic-lipophilic balanced (HLB) cartridge are used for the isolation of 18F-fluoride and [18F]FDR-conjugated peptides, respectively. The first HPLC purification provides the 18F-fluorinated precursor of [18F]FDR and the second HPLC purification is to separate labeled peptides from their unlabeled precursors. The final product is formulated in PBS ready for injection, with a radiochemical purity of >98% and a radiochemical yield (RCY) of 27–37% starting from the end of bombardment (EOB). The carbohydrate nature of [18F]FDR and the operational convenience of this protocol should facilitate its general use.

Production of 234,235Np and 236Pu in bombardment of 236U with protons in the energy range from 17 to 40 MeV

Abstract The production of 235Np and 236Pu by the reactions 236U(p,2n) 235Np and 236U(p,nβ−) 236Pu using the K-130 cyclotron of the University of Jyväskylä was investigated. The cross sections for the reactions were determined. Thick-target yield curves were derived based on the cross sections. The results are discussed and compared with previous data on other reactions leading to the formation of the same end products. The thick-target yield of 235Np in the 236U(p,2n) reaction is about 50 percent higher than the yield obtained in the 238U(p,4n) reaction leading to this nuclide at comparable particle energies. The purity of 236Pu produced in the 236U(p,nβ−) reaction is more than ten times better than for earlier known as the purest reaction 237Np(p,2n+pnβ−) 236Pu.

The effects of proton-induced radiation damage on compound-semiconductor x-ray detectors

We report the results of a series of experiments designed to assess the relative radiation hardness of a range of compound semiconductor X-ray detectors. The specific compounds tested were GaAs, InP, CdZnTe, HgI2 and TlBr, along with an elemental Si device. To allow meaningful comparisons, all devices were of a similar size and, with the exception of the InP detector, had sub-keV energy resolution at 5.9 keV. The irradiations were carried out using the University of Helsinki’s Cyclone 10/5 10 MeV proton cyclotron. Each detector was given six consecutive exposures - the integral fluences being; 2.66 x 109 p cm-2, 7.98 x 109 p cm-2, 2.65 x 1010 p cm-2, 7.97 x 1010 p cm-2, 1.59 x 1011 p cm-2, and 2.65 x 1011 p cm-2, respectively. In Si, these correspond to absorbed radiation doses of 2, 6, 20, 60, 120 and 200 krads. During the exposures, the detectors were kept unbiased and at room temperature. After each irradiation, the effects of the exposure were assessed, both at room temperature and at a reduced temperature using 55Fe, 109Cd and 241Am radioactive sources. It was found that with the exception of the HgI2 and TlBr detectors all materials showed varying degrees of damage effects.

A comparative study on the effect of solvent on nucleophilic fluorination with [18F]fluoride: protic solvents as co-solvents in SN2 and SNAr reactions

Abstract The effect of solvent on nucleophilic substitution with cyclotron-produced [18F]fluoride was studied in polar aprotic (CH3CN and DMF) and protic solvent (t-BuOH and t-amyl alcohol) mixtures (CH3CN/co-solvent, 2:8) in a series of model compounds, 4-(R1-methyl)benzyl R2-benzoates, using a K2.2.2/[ 18F]KF phase transfer system (R1=–Cl, –OMs or –OH; R2=–Cl, –I or –NO2). 18F-fluorination of compounds 1–3, with chloride or mesylate as a leaving group in the benzylic position (R1), afforded the desired 4-([ 18F]fluoromethyl)benzyl analogues in all solvents during 15ߙmin reaction time. The highest radiochemical yields (RCY) in all the studied reaction temperatures (80, 120 and 160ºC) were achieved in CH3CN. Radiochemical yields in protic solvents were comparable to RCY in CH3CN only with the sulfonate ester 3 as a starting material. 18F-Fluorination of the benzylic halides 1 and 2 was not promoted in the same extent; in addition, labelled side-products were detected at higher reaction temperatures. Radiofluorination in tert-alcohols was also studied using [18F]CsF with and without added phase transfer catalyst, resulting in both conditions lower RCY when compared to K2.2.2/[18F]KF system. Protic solvents were not able to promote aromatic 18F-fluorination. 18F-Fluorination of compound 5, having para-activated nitro group in the aromatic position (R2), failed in tert-alcohols even at the highest temperature, but it was labelled successfully in DMF and to some extent in CH3CN.

Migration kinetics of ion-implanted beryllium in ZnO and GaN

Migration kinetics of ion-implanted beryllium in ZnO and GaN has been studied using the modified radiotracer technique utilizing 7Be tracers. For ZnO the studies were carried out in the temperature range 650–750 °C. Clear Be migration following Arrhenius type behaviour was noted. The process is suggested to be limited due to formation of the BeZnO compound. An activation enthalpy of EA = (2.9 ± 0.3) eV and pre-exponential factor of D0 = 4 × 10−3 m2 s−1 were deduced for Be diffusion in ZnO. In the case of GaN two annealing temperatures were employed, 850 and 950 °C. Distinct trapping of Be in defects induced via implantation was noted. The activation enthalpy for Be diffusion in GaN free of implantation induced defects is estimated to be ~4 eV in agreement with theoretical predictions presented in the literature.

Analysis of 3H, 36Cl, 133Ba, 134Cs and 22Na from synthetic granitic groundwater: an in situ through diffusion experiment at ONKALO

AbstractA method for analyzing 3H, 36Cl, 22Na, 133Ba and 134Cs from simulated groundwater (SGW) samples was introduced. Gamma emitting radionuclides 22Na, 133Ba and 134Cs were measured by using an HPGe-detector. Beta emitting 3H and 36Cl were separated from gamma emitting 22Na, 133Ba and 134Cs. AgCl precipitation was used for the separation of 36Cl from SGW samples with yields of 98 ± 2%. 3H was separated by distillation with recoveries of 97 ± 3%. This method was used for the determination of activity concentrations of 3H, 36Cl, 22Na, 133Ba and 134Cs in SGW samples collected from an in situ through diffusion experiment.