Evaluation of a bolus/infusion protocol for 11C-ABP688, a PET tracer for mGluR5

(11)C-ABP-688 is a selective tracer for the mGluR5 receptor. Its kinetics is fast and thus favourable for an equilibrium approach to determine receptor-related parameters. The purpose of this study was to test the hypothesis that the pattern of the (11)C-ABP688 uptake using a bolus-plus-infusion (B/I) protocol at early time points corresponds to the perfusion and at a later time point to the total distribution volume. METHODS: A bolus and a B/I study (1 h each) was performed in five healthy male volunteers. With the B/I protocol, early and late scans were normalized to gray matter, cerebellum and white matter. The same normalization was done on the maps of the total distribution volume (Vt) and K(1) which were calculated in the study with bolus only injection and the Logan method (Vt) and a two-tissue compartment model (K(1)). RESULTS: There was an excellent correlation close to the identity line between the pattern of the late uptake in the B/I study and Vt of the bolus-only study for all three normalizations. The pattern of the early uptake in the B/I study correlated well with the K(1) maps, but only when normalized to gray matter and cerebellum, not to white matter. CONCLUSION: It is demonstrated that with a B/I protocol the (11)C-ABP688 distribution in late scans reflects the pattern of the total distribution volume and is therefore a measure for the density pattern of mGluR5. The early scans following injection are related to blood flow, although not in a fully quantitative manner. The advantage of the B/I protocol is that no arterial blood sampling is required, which is advantageous in clinical studies.

Activation of a PAK-MEK signalling pathway in malaria parasite-infected erythrocytes

Merozoites of malaria parasites invade red blood cells (RBCs), where they multiply by schizogony, undergoing development through ring, trophozoite and schizont stages that are responsible for malaria pathogenesis. Here, we report that a protein kinase-mediated signalling pathway involving host RBC PAK1 and MEK1, which do not have orthologues in the Plasmodium kinome, is selectively stimulated in Plasmodium falciparum-infected (versus uninfected) RBCs, as determined by the use of phospho-specific antibodies directed against the activated forms of these enzymes. Pharmacological interference with host MEK and PAK function using highly specific allosteric inhibitors in their known cellular IC50 ranges results in parasite death. Furthermore, MEK inhibitors have parasiticidal effects in vitro on hepatocyte and erythrocyte stages of the rodent malaria parasite Plasmodium berghei, indicating conservation of this subversive strategy in malaria parasites. These findings have profound implications for the development of novel strategies for antimalarial chemotherapy.

Characterization of canine dendritic cells in healthy, atopic, and non-allergic inflamed skin

Atopic dermatitis in humans and dogs is a chronic relapsing allergic skin disease. Dogs show a spontaneous disease similar to the human counterpart and represent a model to improve our understanding of the immunological mechanisms, the pathogenesis of the disease, and new therapy development. The aim of the study was to determine the frequency and phenotype of dendritic cells (DC) in the epidermis and dermis of healthy, canine atopic dermatitis lesional, and non-allergic inflammatory skin to further validate the model and to obtain insights into the contribution of DC to the pathogenesis of skin diseases in dogs. We first characterized canine skin DC using flow-cytometric analysis of isolated skin DC combined with an immunohistochemical approach. A major population of canine skin dendritic cells was identified as CD1c(+)CD11c(+)CD14(-)CD80(+)MHCII(+)MAC387(-) cells, with dermal DC but not Langerhans cells expressing CD11b. In the epidermis of lesional canine atopic dermatitis and non-allergic inflammatory skin, we found significantly more dendritic cells compared with nonlesional and control skin. Only in canine atopic dermatitis skin did we find a subset of dendritic cells positive for IgE, in the epidermis and the dermis. Under all inflammatory conditions, dermal dendritic cells expressed more CD14 and CD206. MAC387(+) putative macrophages were absent in healthy but present in inflamed skin, in particular during non-allergic diseases. This study permits a phenotypic identification and differentiation of canine skin dendritic cells and has identified markers and changes in dendritic cells and macrophage populations related to allergic and non-allergic inflammatory conditions. Our data suggest the participation of dendritic cells in the pathogenesis of canine atopic dermatitis similar to human atopic dermatitis and further validate the only non-murine spontaneous animal model for this disease.

Neuregulin-1 beta attenuates doxorubicin-induced alterations of excitation-contraction coupling and reduces oxidative stress in adult rat cardiomyocytes

Treatment of metastatic breast cancer with doxorubicin (Doxo) in combination with trastuzumab, an antibody targeting the ErbB2 receptor, results in an increased incidence of heart failure. Doxo therapy induces reactive oxygen species (ROS) and alterations of calcium homeostasis. Therefore, we hypothesized that neuregulin-1 beta (NRG), a ligand of the cardiac ErbB receptors, reduces Doxo-induced alterations of EC coupling by triggering antioxidant mechanisms. Adult rat ventricular cardiomyocytes (ARVM) were isolated and treated for 18-48 h. SERCA protein was analyzed by Western blot, EC coupling parameters by fura-2 and video edge detection, gene expression by RT-PCR, and ROS by DCF-fluorescence microscopy. At clinically relevant doses Doxo reduced cardiomyocytes contractility, SERCA protein and SR calcium content. NRG, similarly as the antioxidant N-acetylcystein (NAC), did not affect EC coupling alone, but protected against Doxo-induced damage. NRG and Doxo showed an opposite modulation of glutathione reductase gene expression. NRG, similarly as NAC, reduced peroxide- or Doxo-induced oxidative stress. Specific inhibitors showed, that the antioxidant action of NRG depended on signaling via the ErbB2 receptor and on the Akt- and not on the MAPK-pathway. Therefore, NRG attenuates Doxo-induced alterations of EC coupling and reduces oxidative stress in ARVM. Inhibition of the ErbB2/NRG signaling pathway by trastuzumab in patients concomitantly treated with Doxo might prevent beneficial effects of NRG in the myocardium.