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Until recently, the characterization of adenosine A2B receptors has been hampered by the lack of high affinity radioligands. This study describes the synthesis and in vitro characterization of the radiolabeled derivative of OSIP339391, a novel, potent, and selective pyrrolopyrimidine A2B antagonist. OSIP339391 had a selectivity of greater than 70-fold for A2B receptors over other human adenosine receptor subtypes. The radiolabel was introduced by hydrogenation of the acetylenic precursor with tritium gas resulting in the incorporation (on average) of three tritium atoms in the molecule, yielding a ligand with specific activity of 87 Ci/mmol (3.2 TBq/mmol). Using membranes from HEK-293 cells expressing the human recombinant A2B receptor, [3H]OSIP339391 was characterized in kinetic, saturation, and competition binding experiments. From the association and dissociation rate studies, the affinity was 0.41 nM and in close agreement with that found in saturation binding experiments (0.17 nM). In competition, binding studies using 0.5 nM [3H]OSIP339391, the affinity of a range of agonists and antagonists was consistent with previously reported data. Thus, [3H]OSIP339391 is a novel, selective, and high affinity radioligand that can be a useful tool in the further exploration and characterization of recombinant and endogenous adenosine A2B receptors. [Copyright &y& Elsevier]

Glutamatergic neurotransmission, important for learning and memory, is disrupted in different ways in patients with Alzheimer's disease (AD) and frontotemporal dementia (FTD) tauopathies. We have previously reported that two tau transgenic mouse models, L1 and L66, produce different phenotypes resembling AD and FTD, respectively. The AD-like L1 model expresses the truncated core aggregation domain of the AD paired helical filament (PHF) form of tau (tau296–390) whereas the FTD-like L66 model expresses full-length tau carrying two mutations at P301S/G335D. We have used synaptosomes isolated from these mice to investigate K+-evoked glutamate release and, if abnormal, to determine responsiveness to hydromethylthionine, a tau aggregation inhibitor previously shown to reduce tau pathology in these models. We report that the transgenes in these two mouse lines cause opposite abnormalities in glutamate release. Over-expression of the core tau unit in L1 produces a significant reduction in glutamate release and a loss of Ca2+-dependency compared with wild-type control mice. Full-length mutant tau produces an increase in glutamate release that retains normal Ca2+-dependency. Chronic pre-treatment with hydromethylthionine normalises both reduced (L1) and excessive glutamate (L66) and restores normal Ca2+-dependency in L1 mice. This implies that both patterns of impairment are the result of tau aggregation, but that the direction and Ca2+-dependency of the abnormality is determined by expression of the disease-specific transgene. Our results lead to the conclusion that the tauopathies need not be considered a single entity in terms of the downstream effects of pathological aggregation of tau protein. In this case, directionally opposite abnormalities in glutamate release resulting from different types of tau aggregation in the two mouse models can be corrected by hydromethylthionine. This may help to explain the activity of hydromethylthionine on cognitive decline and brain atrophy in both AD and behavioural-variant FTD. • Tau protein aggregation is an underlying feature of multiple forms of dementia. • These tauopathies were modelled in two mouse models. • Glutamate release from neuro-synaptosomes was abnormal in Tau transgenic models. • HMTM, a Tau aggregation inhibitor fully reversed this condition in both models. • Treatment appeared to mitigate imbalances in the calcium homeostasis of the pre-synapses. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we examined the temporal changes of terrestrially-derived particulate organic carbon (POC) in the lower Mississippi River (MR) and in a very limited account, the upper tributaries (Upper MR, Ohio River, and Missouri River). We used for the first time a combination of lignin-phenols, bulk stable carbon isotopes, and compound-specific isotope analyses (CSIA) to examine POC in the lower MR and upper tributaries. A lack of correlation between POC and lignin phenol abundances (Λ 8) was likely due to dilution effects from autochthonous production in the river, which has been shown to be considerably higher than previously expected. The range of δ13C values for p-hydroxycinnamic and ferulic acids in POC in the lower river do support that POM in the lower river does have a significant component of C4 in addition to C3 source materials. A strong correlation between δ13C values of p-hydroxycinnamic, ferulic, and vanillyl phenols suggests a consistent input of C3 and C4 carbon to POC lignin while a lack of correlation between these same phenols and POC bulk δ13C further indicates the considerable role of autochthonous carbon in the lower MR POC budget. Our estimates indicate an annual flux of POC of 9.3×108 kgy−1 to the Gulf of Mexico. Total lignin fluxes, based on Λ 8 values of POC, were estimated to be 1.2×105 kgy−1. If we include the total dissolved organic carbon (DOC) flux (3.1×109 kgy−1) reported by [Bianchi T. S., Filley T., Dria K. and Hatcher, P. (2004) Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochim. Cosmochim. Acta 68, 959–967.], we get a total organic carbon flux of 4.0×109 kgy−1. This represents 0.82% of the annual total organic carbon supplied to the oceans by rivers (4.9×1011 kg). [Copyright &y& Elsevier]