Tracer Levels Research Articles

Time series measurements of transient tracers and tracer-derived transport in the Deep Western Boundary Current between the Labrador Sea and the subtropical Atlantic Ocean at Line W

Time series measurements of the nuclear fuel reprocessing tracer, 129I and the gas ventilation tracer, CFC-11 were undertaken on the AR7W section in the Labrador Sea (1997-2014) and on Line W (2004-2014), located over the US continental slope off Cape Cod, to determine advection and mixing time scales for the transport of Denmark Strait Overflow Water (DSOW) within the Deep Western Boundary Current (DWBC). Tracer measurements were also conducted in 2010 over the continental rise southeast of Bermuda to intercept the equator-ward flow of DSOW by interior pathways. The Labrador Sea tracer and hydrographic time series data were used as input functions in a boundary current model that employs transit time distributions to simulate the effects of mixing and advection on downstream tracer distributions. Model simulations of tracer levels in the boundary current core and adjacent interior (shoulder) region with which mixing occurs were compared with the Line W time series measurements to determine boundary current model parameters. These results indicate that DSOW is transported from the Labrador Sea to Line W via the DWBC on a time scale of 5-6 y corresponding to a mean flow velocity of 2.7 cm/s while mixing between the core and interior regions occurs with a time constant of 2.6 y. A tracer section over the southern flank of the Bermuda rise indicates that the flow of DSOW that separated from the DWBC had undergone transport through interior pathways on a time scale of 9 y with a mixing time constant of 4 y. This article is protected by copyright. All rights reserved.

Determining the timepoint when 14C tracer accurately reflect photosynthate use in the plant-soil system

Only the carbon (C) isotope pulse labeling approach can provide time-resolved data concerning the input and turnover of plant-derived C in the soil, which are urgently needed to improve the performance of terrestrial C cycle models. However, there is currently very limited information about the point in time after pulse labeling at which the distribution of tracer C accurately represents the usage of photosynthates in different components of the plant-soil system. This should be the case as soon as the tracer has disappeared from the mobile C pool due to respiration, incorporation into the structural C pool of shoot and root tissue and exudation into the soil (rhizodeposition). Following $^{14} {CO}_{2}$ pulse labeling in laboratory and outdoor experiments with spring rye, the 14C dilution rates of soluble fractions and different substances from the structural C pool of the shoot (molecular level), the release of labeled CO2 by belowground respiration (component level), and the 14C kinetics of shoot respiration and 14C remaining in the plant-soil-soil gas continuum (system level) were analyzed during different stages of plant development. At all three levels investigated, 14C kinetics indicated that the C tracer levels changed very little between 15 and 21 days after labeling. Results also showed increasing tracer depletion in the mobile C pool. Consequently, only 0.42 % and 0.06 % of all 14C was still available for shoot respiration 15 and 21 days after labeling, respectively. The similarities between 14C tracer kinetics at the three investigated levels indicate that tracer disappearance from the mobile pool and distribution throughout the plant-soil system was nearly complete between 15 and 21 days after labeling. Therefore, this appears to be the point at which the pulse labeling approach provides sufficiently precise data concerning the use of C (assimilated during labeling) for root growth, rhizodeposition, root respiration and the microbial turnover of rhizodeposits.

Seasonal variation of secondary organic aerosol tracers in Central Tibetan Plateau

Abstract. Secondary organic aerosol (SOA) affects the earth's radiation balance and global climate. High-elevation areas are sensitive to global climate change. However, at present, SOA origins and seasonal variations are understudied in remote high-elevation areas. In this study, particulate samples were collected from July 2012 to July 2013 at the remote Nam Co (NC) site, Central Tibetan Plateau and analyzed for SOA tracers from biogenic (isoprene, monoterpenes and β-caryophyllene) and anthropogenic (aromatics) precursors. Among these compounds, isoprene SOA (SOAI) tracers represented the majority (26.6 ± 44.2 ng m−3), followed by monoterpene SOA (SOAM) tracers (0.97 ± 0.57 ng m−3), aromatic SOA (SOAA) tracer (2,3-dihydroxy-4-oxopentanoic acid, DHOPA, 0.25 ± 0.18 ng m−3) and β-caryophyllene SOA tracer (β-caryophyllenic acid, 0.09 ± 0.10 ng m−3). SOAI tracers exhibited high concentrations in the summer and low levels in the winter. The similar temperature dependence of SOAI tracers and isoprene emission suggested that the seasonal variation of SOAI tracers at the NC site was mainly influenced by the isoprene emission. The ratio of high-NOx to low-NOx products of SOAI (2-methylglyceric acid to 2-methyltetrols) was highest in the winter and lowest in the summer, due to the influence of temperature and relative humidity. The seasonal variation of SOAM tracers was impacted by monoterpenes emission and gas-particle partitioning. During the summer to the fall, temperature effect on partitioning was the dominant process influencing SOAM tracers' variation; while the temperature effect on emission was the dominant process influencing SOAM tracers' variation during the winter to the spring. SOAM tracer levels did not elevate with increased temperature in the summer, probably resulting from the counteraction of temperature effects on emission and partitioning. The concentrations of DHOPA were 1–2 orders of magnitude lower than those reported in the urban regions of the world. Due to the transport of air pollutants from the adjacent Bangladesh and northeastern India, DHOPA presented relatively higher levels in the summer. In the winter when air masses mainly came from northwestern India, mass fractions of DHOPA in total tracers increased, although its concentrations declined. The SOA-tracer method was applied to estimate secondary organic carbon (SOC) from these four precursors. The annual average of SOC was 0.22 ± 0.29 μgC m−3, with the biogenic SOC (sum of isoprene, monoterpenes and β-caryophyllene) accounting for 75 %. In the summer, isoprene was the major precursor with its SOC contributions of 81 %. In the winter when the emission of biogenic precursors largely dropped, the contributions of aromatic SOC increased. Our study implies that anthropogenic pollutants emitted in the Indian subcontinent could be transported to the TP and have an impact on SOC over the remote NC.

208 Arterial Inflammation and Calcification in Patients with Lower Limb Atherosclerosis using PET/CT Analysis: A Proof-of-Principle Study

<h3>Introduction</h3> Lower limb peripheral arterial disease (PAD) is common. Atherosclerotic development is linked with inflammatory and calcific processes occurring at the vessel wall, having been evaluated in the coronary and carotid circulation using PET/CT analysis with the 18F FDG (inflammation) and 18F NaF (calcification) tracers. <h3>Methods</h3> 8 patients (16 legs; 5 men, median age 74.5 years; IQR (69.5–77.5)) with a diagnosis of intermittent claudication were prospectively recruited to the study. PET/CT analysis was undertaken in each patient using both tracers. The lower limb arterial tree was examined from the aortic bifurcation to the ankle. The degree of arterial calcification (AC) was measured using a modified Agatston score. Arterial 18F-NaF and 18F-FDG uptake was determined using standard protocols and measured by drawing regions of interest and normalised to tracer levels in the common femoral vein to obtain the arterial target-to-background ratio (TBR). Correlation between tracer uptake and AC was determined using Pearson’s correlation. <h3>Results</h3> The overall whole limb median (IQR) TBR levels for 18F NaF was 1.30 (0.98–1.74) and for 18F FDG was 1.42 (1.11–1.75). The median limb AC score was 1954.5 (1198–3216). A positive correlation was observed when arterial 18F FDG uptake was correlated with 18F NaF uptake (p = 0.000, r = 0.611) and AC score (p = 0.009, r = 0.654). An inverse correlation was found when correlating 18F NaF tracer uptake with AC score (p = 0.004, r=–0.765). <h3>Conclusion</h3> Lower limb disease progression will lead to increased atherosclerotic burden with a potential risk of amputation. This study is the first to determine the inter-relationship between inflammation and calcification within the lower limb arterial tree. Further studies are required to look at longer-term sequelae of atherosclerotic progression/development.

Quantifying the contribution of grape hexoses to wine volatiles by high-precision [U¹³C]-glucose tracer studies.

Many fermentation volatiles important to wine aroma potentially arise from yeast metabolism of hexose sugars, but assessing the relative importance of these pathways is challenging due to high endogenous hexose substrate concentrations. To overcome this problem, gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) was used to measure high-precision (13)C/(12)C isotope ratios of volatiles in wines produced from juices spiked with tracer levels (0.01-1 APE) of uniformly labeled [U-(13)C]-glucose. The contribution of hexose to individual volatiles was determined from the degree of (13)C enrichment. As expected, straight-chain fatty acids and their corresponding ethyl esters were derived almost exclusively from hexoses. Most fusel alcohols and their acetate esters were also majority hexose-derived, indicating the importance of anabolic pathways for their formation. Only two compounds were not derived primarily from hexoses (hexanol and isobutyric acid). This approach can be extended to other food systems or substrates for studying precursor-product relationships.

Ezetimibe enhances macrophage reverse cholesterol transport in hamsters: Contribution of hepato–biliary pathway

Reverse cholesterol transport (RCT) is pivotal in the return of excess cholesterol from peripheral tissues to the liver for excretion in bile and eventually feces. RCT from macrophages is a critical anti-atherogenicity mechanism of HDL. As the cholesterol absorption inhibitor ezetimibe promoted RCT in mice, which lack cholesterol ester transfer protein (CETP), we investigated its effects in hamsters, which have CETP.A high-cholesterol diet (HC) increased cholesterol levels throughout lipoprotein fractions and ezetimibe markedly reduced VLDL/LDL cholesterol levels under both normal chow (NC) and HC. However, ezetimibe did not affect and reduced HDL-cholesterol levels under NC and HC, respectively. Intraperitoneal injection of 3H-cholesterol pre-labeled macrophages in an in vivo RCT assay increased tracer accumulation in the liver but reduced it in bile under HC, and these changes were completely cancelled by ezetimibe. Under both NC and HC, ezetimibe reduced tracer levels in the liver but increased them in feces, indicating promotion of RCT in vivo. We performed a RCT assay using hamsters subjected to bile duct ligation (BDL) to clarify whether a transintestinal cholesterol efflux (TICE) pathway contributes to ezetimibe's enhancement of RCT. BDL markedly inhibited macrophage-derived 3H-cholesterol excretion to feces and cancelled ezetimibe's stimulatory effect on RCT, suggesting that biliary cholesterol excretion is a major contributor in RCT promotion by ezetimibe but the contribution of the TICE pathway is minimal.In conclusions, ezetimibe exerts an additive anti-atherogenic property by enhancing RCT in hamsters. Our findings suggest that this property is independent of the TICE pathway.

SHP-1 regulates neuroinvasion of neurotropic virus into the CNS (VIR5P.1035)

Abstract Viral infections in the central nervous system (CNS) may have devastating clinical consequences to the host. Neurotropic virus infections often begin in peripheral tissues, which then spread to the CNS via peripheral nerves following entry into nerve terminals by receptor-mediated endocytosis and subsequent retrograde axonal transport into the CNS compartment. In our lab, a possible novel role for the protein tyrosine phosphatase, SHP-1, in regulating neuroinvasion via peripheral nerves of a neurotropic virus (Theiler’s Murine Encephalomyelitis Virus, TMEV) is being investigated. Preliminary data using immunohistochemistry of TMEV showed extensive staining of spinal cord neurons after intraperitoneal inoculation in mice with a null mutation in the SHP-1 gene (me/me mice) compared to wild type mice. Further, intramuscular (IM) inoculations of TMEV caused virus infection in spinal cord neurons and subsequent paralysis of SHP-1-deficient mice but not of wild type mice. IM and intraperitoneal injections (IP) of retrograde axonal transport tracers fluorogold and horseradish peroxidase showed increased tracer levels in the spinal cords of SHP-1-deficient mice compared to wild type mice. Therefore, we propose SHP-1 may play a role in regulating viral neuroinvasion by controlling retrograde axonal transport from peripheral sites of infection. In this sense, SHP-1 may play novel roles in antiviral responses including inhibition of virus invasion and spreading in the CNS.

Neurovascular coupling to D2/D3 dopamine receptor occupancy using simultaneous PET/functional MRI

This study employed simultaneous neuroimaging with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to demonstrate the relationship between changes in receptor occupancy measured by PET and changes in brain activity inferred by fMRI. By administering the D2/D3 dopamine receptor antagonist [(11)C]raclopride at varying specific activities to anesthetized nonhuman primates, we mapped associations between changes in receptor occupancy and hemodynamics [cerebral blood volume (CBV)] in the domains of space, time, and dose. Mass doses of raclopride above tracer levels caused increases in CBV and reductions in binding potential that were localized to the dopamine-rich striatum. Moreover, similar temporal profiles were observed for specific binding estimates and changes in CBV. Injection of graded raclopride mass doses revealed a monotonic coupling between neurovascular responses and receptor occupancies. The distinct CBV magnitudes between putamen and caudate at matched occupancies approximately matched literature differences in basal dopamine levels, suggesting that the relative fMRI measurements reflect basal D2/D3 dopamine receptor occupancy. These results can provide a basis for models that relate dopaminergic occupancies to hemodynamic changes in the basal ganglia. Overall, these data demonstrate the utility of simultaneous PET/fMRI for investigations of neurovascular coupling that correlate neurochemistry with hemodynamic changes in vivo for any receptor system with an available PET tracer.

In Vivo Visualization and Quantification of (Disturbed) Oatp-Mediated Hepatic Uptake and Mrp2-Mediated Biliary Excretion of 99mTc-Mebrofenin in Mice

Hepatic transport of (99m)Tc-mebrofenin through organic anion transport protein 1a and 1b (Oatp1a/1b) and multidrug resistance protein 2 (Mrp2) was investigated by small-animal SPECT. On the basis of the results, a noninvasive method to visualize and quantify disturbances in hepatic transport is proposed. Friend virus B wild-type mice (untreated, bile duct-ligated, vehicle- or rifampicin-treated) and strain-matched knockout mice unable to express the uptake transporters Oatp1a/1b (Slco1a/1b(-/-)/(-/-)) or the efflux transporter Mrp2 (Abcc2(-/-)) were intravenously injected with (99m)Tc-mebrofenin (n = 3 per group). After dynamic small-animal SPECT and short CT acquisitions, time-activity curves of the liver and of the gallbladder and intestines were obtained and correlated with direct blood samples. Normal hepatobiliary clearance of (99m)Tc-mebrofenin was severely impaired in the bile duct-ligated animal, as evidenced by elevated hepatic tracer levels. In Slco1a/1b(-/-)/(-/-) mice, a lower area under the curve (AUC) for the liver (P = 0.014) was obtained and no activity was detected in the gallbladder and intestines. Renal rerouting was observed, along with an increase in the blood AUC (P = 0.01). Abcc2(-/-) mice had a higher liver AUC (P = 0.009), a delayed emergence time of (99m)Tc-mebrofenin in the gallbladder (P = 0.009), and a lower AUC for the gallbladder and intestines (P = 0.001). The blood curve was similar to that of wild-type mice. (99m)Tc-mebrofenin disposition was altered after rifampicin treatments. We observed a dose-dependent delayed time point at which tracer maximized in liver, an increased AUC for liver, and a lower AUC for gallbladder and intestines (P = 0.042, 0.034, and 0.001, respectively, highest dose). Emergence in the gallbladder occurred later (P = 0.009, highest dose), and blood AUC was higher (P = 0.006). The current study visualized and quantified hepatic uptake and biliary efflux of (99m)Tc-mebrofenin. Our results demonstrated the possibility of discriminating, on a quantitative level, between lack of functional activity of sinusoidal uptake versus that of biliary efflux transporters.

Sustained levels of antibodies against Aβ in amyloid-rich regions of the CNS following intravenous dosing in human APP transgenic mice

Passive immunization with anti-Aβ antibodies leads to the reduction of AD-like neuropathology in transgenic mice. Previously we showed that anti-Aβ antibodies enter the brain and bind to amyloid plaques. Now using 125I-labeled 3D6, the mouse parent antibody of the clinical candidate bapineuzumab, we further characterized the pharmacokinetic profile of this antibody in the brain and serum. Our studies demonstrated that following a single intravenous injection, the labeled antibody accumulates and persists in plaque rich regions of the brain in transgenic PDAPP mice. Accumulation was specific to amyloid since it did not occur in non-transgenic animals lacking human APP, could not be measured in transgenic animals prior to plaque deposition, and correlated with the level of plaque burden in aging transgenic mice. After a single intravenous injection, CNS levels of 125I‐labeled 3D6 continued to increase for 14days even as serum levels of the antibody declined. The calculated half-life of antibody in the circulation was 6days, while antibody levels in the CNS remained stable for nearly a month. When given at supra-therapeutic levels, unlabeled antibody did not compete with tracer levels of labeled antibody for accumulation in the CNS, indicating that the binding capacity of plaques was very high. Our results demonstrate that even when administered in the periphery at very low (tracer) doses, 3D6 and bapineuzumab cross the blood brain barrier to accumulate in plaque rich regions of the brain. CNS clearance is markedly slower than in the serum and correlates with binding to deposited amyloid in a transgenic model of Alzheimer's disease.

In vivo receptor occupancy assay of histamine H3 receptor antagonist in rats using non-radiolabeled tracer

IntroductionRapid and reliable preclinical receptor occupancy measurement at the target organ in relevant species is critical in accelerating the drug hunting process. The aim of this study was to develop in vivo receptor occupancy assay for histamine H3 receptors (H3R) using the non-radiolabeled GSK189254 as a tracer and to correlate the occupancy–exposure relationship for H3R antagonists in the rats. MethodsIn vivo tracer characterization studies like brain regional distribution, dose and time dependent uptake were carried out for GSK189254 in the male Wistar rats after intravenous administration. The tracer specificity was validated by pretreatment with H3 antagonists like ciproxifan, thioperamide, and GSK334429. The brain regional tracer levels and H3R antagonist concentrations in plasma and brain were quantified using liquid chromatography tandem mass spectrometry. Receptor occupancy was calculated using the ratio of total binding (striatum or frontal cortex) to the nonspecific binding (cerebellum) of the tracer in animals pretreated with H3R antagonist. ResultsHigh degree of selective distribution of GSK189254 was found in striatum, frontal cortex, and low level in the cerebellum. Regional distribution of GSK189254 in the rat brain was consistent to that of H3R distribution mapped using 3H or 11C-GSK189254 in human, porcine, and rat. The calculated occupancy ED50 values in the frontal cortex were 0.14, 1.58, and 0.14mg/kg for ciproxifan, thioperamide, and GSK334429, respectively. The plasma EC50 values (ng/mL) were found to be 2.33, 292.2, and 3.54 for ciproxifan, thioperamide and GSK334429, respectively. DiscussionResults from mass spectroscopy based approach to determine H3R occupancy in rat brain is comparable with reported radiolabeled method by scintillation spectroscopy. In conclusion, non-radiolabeled GSK189254 was successfully employed as a tracer for assessing the H3R occupancy in rats and it can be used as a preclinical tool for evaluation of novel H3R ligands in the drug discovery.

Iron Levels Change in Larval Heliothis virescens Tissues Following Baculovirus Infection

Inductively coupled plasma mass spectrometry and (59)Fe radiotracers were used to investigate changes in levels of Fe in the tissues of 4th instar Heliothis virescens larvae following infection with Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) or with Autographa californica multiple nucleopolyhedrovirus. Baculovirus infection led to significant changes in hemolymph Fe levels late in infection. (24)Na radiotracer ingested by 4th instar larvae was rapidly cleared to nearly undetectable levels 6 h post-ingestion. In contrast, (59)Fe radiotracer fed to 4th instar larvae declined within the first few hours of ingestion and then remained constant at approximately 60% of the initial tracer activity. While Fe radiotracer levels among larval tissues changed, whole insect tracer levels did not decline from 6 to 60 h post-ingestion. Tissues from HzSNPV larvae had higher radiotracer levels in the hemolymph and midgut 36 and 60 h post-infection. The protein-bound/free ratio of (59)Fe was significantly higher in baculovirus infected hemolymph than in uninfected hemolymph at 60 h post-infection, indicating that Fe released from damaged cells is protein-bound. In both studies, hemolymph Fe levels were higher in HzSNPV infected larvae. This first study of tissue Fe levels during viral infection of an insect clearly demonstrates that Fe homeostasis is substantially disrupted.

A model to measure lymphatic drainage from the eye

Intraocular pressure (IOP) is the most important risk factor for glaucoma development and progression. Most anti-glaucoma treatments aim to lower IOP by enhancing aqueous humor drainage from the eye. Aqueous humor drainage occurs via well-characterized trabecular meshwork (TM) and uveoscleral (UVS) pathways, and recently described ciliary body lymphatics. The relative contribution of the lymphatic pathway to aqueous drainage is not known. We developed a sheep model to quantitatively assess lymphatic drainage along with TM and UVS outflows. This study describes that model and presents our initial findings.Following intracameral injection of 125I-bovine serum albumin (BSA), lymph was continuously collected via cannulated cervical lymphatic vessels and the thoracic lymphatic duct over either a 3-h or 5-h time period. In the same animals, blood samples were collected from the right jugular vein every 15 min. Lymphatic and TM drainage were quantitatively assessed by measuring 125I-BSA in lymph and plasma, respectively. Radioactive tracer levels were also measured in UVS and “other” ocular tissue, as well as periocular tissue harvested 3 and 5 h post-injection. Tracer recovered from UVS tissue was used to estimate UVS drainage. The amount of 125I-BSA recovered from different fluid and tissue compartments was expressed as a percentage of total recovered tracer. Three hours after tracer injection, percentage of tracer recovered in lymph and plasma was 1.64% ± 0.89% and 68.86% ± 9.27%, respectively (n = 8). The percentage of tracer in UVS, other ocular and periocular tissues was 19.87% ± 5.59%, 4.30% ± 3.31% and 5.32% ± 2.46%, respectively. At 5 h (n = 2), lymphatic drainage was increased (6.40% and 4.96% vs. 1.64%). On the other hand, the percentage of tracer recovered from UVS and other ocular tissue had decreased, and the percentage from periocular tissue showed no change. Lymphatic drainage increased steadily over the 3 h post-injection period, while TM drainage increased rapidly – reaching a plateau at 30 min.This quantitative sheep model enables assessment of relative contributions of lymphatic drainage, TM and UVS outflows, and may help to better understand the effects of glaucoma agents on outflow pathways.

Uptake, depuration, and radiation dose estimation in zebrafish exposed to radionuclides via aqueous or dietary routes

Understanding uptake and depuration of radionuclides in organisms is necessary to relate exposure to radiation dose and ultimately to biological effects. We investigated uptake and depuration of a mixture of radionuclides to link bioaccumulation with radiation dose in zebrafish, Danio rerio. Adult zebrafish were exposed to radionuclides ( 54Mn, 60Co, 65Zn, 75Se, 109Cd, 110mAg, 134Cs and 241Am) at tracer levels (< 200 Bq g −1) for 14 d, either via water or diet. Radioactivity concentrations were measured in whole body and excised gonads of exposed fish during uptake (14 d) and depuration phases (47 d and 42 d for aqueous and dietary exposures respectively), and dose rates were modelled from activity concentrations in whole body and exposure medium (water or diet). After 14-day aqueous exposure, radionuclides were detected in decreasing activity concentrations: 75Se > 65Zn > 109Cd > 110mAg > 54Mn > 60Co > 241Am > 134Cs (range: 175–8 Bq g 1). After dietary exposure the order of radionuclide activity concentration in tissues (Bq g −1) was: 65Zn > 60Co > 75Se > 109Cd > 110mAg > 241Am > 54Mn > 134Cs (range: 91–1 Bq g −1). Aqueous exposure resulted in higher whole body activity concentrations for all radionuclides except 60Co. Route of exposure did not appear to influence activity concentrations in gonads, except for 54Mn, 65Zn, and 75Se, which had higher activity concentrations in gonads following aqueous exposure. Highest gonad activity concentrations (Bq g −1) were for 75Se (211), 109Cd (142), and 65Zn (117), and highest dose rates (μGy h −1) were from 241Am (aqueous, 1050; diet 242). This study links radionuclide bioaccumulation data obtained in laboratory experiments with radiation dose determined by application of a dosimetry modelling tool, an approach that will enable better linkages to be made between exposure, dose, and effects of radionuclides in organisms.

A preclinical 188Re tumor therapeutic investigation using MORF/cMORF pretargeting and an antiTAG-72 antibody CC49

The utility of MORF/cMORF pretargeting for the radiotherapy of cancer requires further validation in tumored mice before clinical trials. We now report on a therapeutic study in mice pretargeted with MORF-CC49 (an anti-TAG-72 antibody CC49 conjugated with MORF, a phosphorodiamidate morpholino oligomer) and then targeted by 188Re-cMORF (a 188Re labeled complementary MORF). Before the dose-escalating therapeutic study, a pretargeting study in LS174T tumored mice was performed at tracer levels. By both necropsy and imaging, the tracer study showed that the whole body radioactivity was largely restricted to tumor in the mice pretargeted 48 h earlier with MORF-CC49 and the tumor radioactivity was retained over 90 h. After decay correction, a best-fit to the biodistribution provided the areas under the radioactivity curves (AUCs) used for the radiation dose estimates. The tumor to normal organ AUC ratios in all cases were greater than unity and ranged from 3 (kidneys) to 48 (muscle). Tumor growth was inhibited in the therapy study. At the highest 188Re dose of 1.40 mCi, a complete but temporary tumor remission was evident in 3 out of the 5 animals. Histological examination of tissues from these animals showed no evidence of cytotoxicity to normal tissues but obvious radiation damage to tumor. In conclusion, effective radiotherapy was achieved in a mouse model by MORF/cMORF pretargeting using 188Re as the therapeutic radionuclide and CC49 as the pretargeting antibody.

Small Amounts of Zinc from Zinc Oxide Particles in Sunscreens Applied Outdoors Are Absorbed through Human Skin

Metal oxide nanoparticles are commonly used in personal-care formulations as protective agents against exposure to ultraviolet radiation. Although previous research has concluded that nanoparticles do not penetrate healthy skin, it remains contentious whether this conclusion holds under normal conditions of sunscreen use. Humans (n = 20) were exposed to sunscreens containing zinc oxide (ZnO) particles to determine if Zn from the particles was absorbed through skin over five consecutive days under outdoor conditions. Two sunscreens were tested-"nano sunscreen" containing 19-nm nanoparticles and "bulk sunscreen" containing > 100-nm particles. Venous blood and urine samples were collected 8 days before exposure, twice daily during the trial, and 6 days post-exposure. As the first application in nanotechnology studies, stable isotope tracing was used where the ZnO, enriched to > 99% with the stable isotope (68)Zn, allowed dermally absorbed zinc to be distinguished from naturally occurring zinc. The overwhelming majority of applied (68)Zn was not absorbed, although blood and urine samples from all subjects exhibited small increases in levels of tracer (68)Zn. The amount of tracer detected in blood after the 5-day application period was ∼1/1000 th that of total Zn in the blood compartment. Tracer levels in blood continued to increase beyond the 5-day application phase in contrast to those in urine. Levels of (68)Zn in blood and urine from females receiving the nano sunscreen appeared to be higher than males receiving the same treatment and higher than all subjects receiving the bulk sunscreen. It is not known whether (68)Zn has been absorbed as ZnO particles or soluble Zn or both.

Nitrogen dynamics in a small arctic watershed: retention and downhill movement of15N

We examined short‐ and long‐term nitrogen (N) dynamics and availability along an arctic hillslope in Alaska, USA, using a stable isotope of nitrogen (15N), as a tracer. Tracer levels of15NH4+were sprayed once onto the tundra at six sites in four tundra types: heath (crest), tussock with high and low water flux (mid‐ and footslope), and wet sedge (riparian).15N in vegetation and soil was monitored to estimate retention and loss over a 3‐year period.Nearly all15NH4+was immediately retained in the surface moss–detritus–plant layer, and &gt;57% of the15N added remained in this layer at the end of the second year. Organic soil was the second largest15N sink. By the end of the third growing season, the moss–detritus–plant layer and organic soil combined retained ≥87% of the15N added except at the Midslope site with high water flux, where recovery declined to 68%. At all sites, non‐extractable and non‐labile‐N pools were the principal sinks for added15N in the organic soil.Hydrology played an important role in downslope movement of dissolved15N. Crest and Midslope with high‐water‐flux sites were most susceptible to15N losses via leaching, perhaps because of deep permeable mineral soil (crest) and high water flow (Midslope with high water flux). Late spring melt season also resulted in downslope dissolved‐15N losses, perhaps because of an asynchrony between N release into melt water and soil immobilization capacity. We conclude that separation of the rooting zone from the strong sink for incoming N in the moss–detritus–plant layer, rapid incorporation of new N into relatively recalcitrant‐soil‐N pools within the rooting zone, and leaching loss from the upper hillslope would all contribute to the strong N‐limitation of this ecosystem. An extended snow‐free season and deeper depth of thaw under warmer climate may significantly alter current N dynamics in this arctic ecosystem.

Competition between selenomethionine and methionine absorption in the intestinal tract of green sturgeon ( Acipenser medirostris)

l-Selenomethionine (SeMet) is a dominant form of selenium (Se) found in organisms at all levels of aquatic food chains and a key source of Se bioaccumulation and ecotoxicity. In mammals, intestinal absorption of SeMet is at least partly via the Na +-dependent neutral amino acid transporter. The mechanism of SeMet absorption and competitive effects of other dietary components on SeMet absorption in fish are unknown. Thus the in vitro uptake rates of l-methionine (Met) and the competitive effect of SeMet on Met absorption, an indicator that SeMet uses the same nutrient transporter(s) for absorption, in the various regions of the green sturgeon ( Acipenser medirostris) intestine were investigated using intact tissues (a modified everted sleeve method). Intestinal tissue was incubated in Ringer's solution containing 0–10 mmol L −1 Met or SeMet ( n = 5 for each substrate's concentration and intestinal region), respectively, as well as constant tracer levels of isotope-labeled Met. The data indicate that SeMet uptake was mediated by the same transporter(s) as Met and that the absorption kinetics were similar for both substrates. When there were differences in absorption they appeared to be mostly due to higher permeability (passive uptake) of the tissue for Met than for SeMet, particularly in the pyloric caeca (PC) and distal intestine (DI). Maximum rates of absorption, on the other hand, tended to be higher for SeMet than Met in the mid intestine and DI, whereas differences in affinity for the transporters varied between these tissues but were very similar in the PC. These differences may be due to differences in regional intestinal characteristics such as amount of mucus secreted and degree of tissue contraction, and/or substrate differences regarding solubility in and movement through the mucus, influence on tissue contraction, permeability through membranes or between cells, intracellular metabolism, as well as basolateral transport. Interestingly, an increasing proximal-to-distal gradient for rates of methionine and putative SeMet absorption was observed in green sturgeon which differs from the declining gradient usually observed for substrate absorption in other fish species and mammals.

Determination of dissociation kinetics of 188Re(I)-pharmaceuticals by free-ion selective radiotracer extraction

Due to physical decay properties commonly associated with therapeutic radionuclides, 188Re (t1/2 = 16.98 h, Emax = 2.12 MeV) is of high interest for endovascular brachytherapy and endoradiotherapy in general. Rhenium precursors in the low oxidation state +I, such as the organometallic fac-[Re(H2O)3(CO)3]+ are promising lead compounds compared to those with oxidation states +III and +V since they can be prepared under mild conditions and do not tend to reoxidize to oxidation state +VII while multidentate ligands can be attached under substitution of coordinated water molecules. This study comprises the application of the Free-Ion Selective Radiotracer Extraction (FISRE) technique in order to determine dissociation rate constants of complexes bearing the [188Re(CO)3]+-core at tracer levels in vitro with regards to their time-dependent kinetic speciation. As ligands, the tridentate l-histidine as well as the dipeptides l-carnosine (β-alanyl-l-histidine) and glycyl-l-histidine were chosen in order to study the effects of different moieties attached to the primary amine of l-histidine.

High temporal resolution tracing of photosynthate carbon from the tree canopy to forest soil microorganisms

Half of the biological activity in forest soils is supported by recent tree photosynthate, but no study has traced in detail this flux of carbon from the canopy to soil microorganisms in the field. Using (13)CO(2), we pulse-labelled over 1.5 h a 50-m(2) patch of 4-m-tall boreal Pinus sylvestris forest in a 200-m(3) chamber. Tracer levels peaked after 24 h in soluble carbohydrates in the phloem at a height of 0.3 m, after 2-4 d in soil respiratory efflux, after 4-7 d in ectomycorrhizal roots, and after 2-4 d in soil microbial cytoplasm. Carbon in the active pool in needles, in soluble carbohydrates in phloem and in soil respiratory efflux had half-lives of 22, 17 and 35 h, respectively. Carbon in soil microbial cytoplasm had a half-life of 280 h, while the carbon in ectomycorrhizal root tips turned over much more slowly. Simultaneous labelling of the soil with (15)NH(+)(4) showed that the ectomycorrhizal roots, which were the strongest sinks for photosynthate, were also the most active sinks for soil nitrogen. These observations highlight the close temporal coupling between tree canopy photosynthesis and a significant fraction of soil activity in forests.