Phylogeny-guided Characterization of Bacterial Hydrazine Biosynthesis Mediated by Cupin/methionyl tRNA Synthetase-like Enzymes.

Cupin/methionyl-tRNA synthetase (MetRS)-like didomain enzymes catalyze nitrogen-nitrogen (N-N) bond formation between Nω-hydroxylamines and amino acids to generate hydrazines, key biosynthetic intermediates of various natural products containing N-N bonds. While the combination of these two building blocks leads to the creation of diverse hydrazine products, the full extent of their structural diversity remains largely unknown. To explore this, we herein conducted phylogeny-guided genome-mining of related hydrazine biosynthetic pathways consisting of two enzymes: flavin-dependent Nω-hydroxylating monooxygenases (NMOs) that produce Nω-hydroxylamine precursors and cupin/MetRS-like enzymes that couple the Nω-hydroxylamines with amino acids via N-N bonds. A phylogenetic analysis identified the largely unexplored sequence spaces of these enzyme families. The biochemical characterization of NMOs demonstrated their capabilities to produce various Nω-hydroxylamines, including those previously not known as precursors of N-N bonds. Furthermore, the characterization of cupin/MetRS-like enzymes identified five new hydrazine products with novel combinations of building blocks, including one containing non-amino acid building blocks: 1,3-diaminopropane and putrescine. This study substantially expanded the variety of N-N bond forming pathways mediated by cupin/MetRS-like enzymes.

Noninvasive estimation of quantitative myocardial blood flow with Tc-99m MIBI by a compartment model analysis in rat.

BACKGROUND: We aimed to investigate the use of dynamic cardiac planar images to estimate myocardial blood flow (MBF) by a compartment model analysis using time-to-peak (TP) map and compared it by the microsphere technique in rat. Positron emission tomography is considered the gold standard method, but is not available everywhere. By contrast, although myocardial perfusion imaging (MPI) with single-photon tracers is more widely available, it may be difficult to obtain adequate region of interest (ROI) settings. We proposed using the TP map to set the ROI, and hypothesized that this method could facilitate the measurement of absolute MBF by MPI in rat. METHODS: Twenty-one normal rats were studied. Dynamic planar images with Tc-99m MIBI were obtained, and input function and cardiac ROIs were set using the obtained TP map. MBF was estimated by a one-compartment model analysis with the Renkin-Crone model and by the microsphere technique. RESULTS: The MBFs from these two methods were significantly correlated. A negative proportional bias was observed, but no significant difference was observed between the mean MBFs calculated with each method. CONCLUSIONS: MBF estimation by a compartment model analysis using TP map could facilitate absolute MBF measurement in rats.

In vivo SPECT imaging of amyloid-ß deposition with radioiodinated imidazo[1,2-a]pyridine derivative DRM106 in a mouse model of Alzheimer's disease.

UNLABELLED: Noninvasive determination of amyloid-ß peptide (Aß) deposition has important significance for early diagnosis and medical intervention for Alzheimer's disease (AD). In the present study, we investigated the availability of radiolabeled DRM106 ((123/125)I-DRM106 [6-iodo-2-[4-(1H-3-pyrazolyl)phenyl]imidazo[1,2-a]pyridine]), a compound with sufficient affinity for the synthesis of human Aß fibrils and satisfactory metabolic stability, as a SPECT ligand in living brains. METHOD: The sensitivity of (125)I-DRM106 for detecting Aß deposition was compared with that of (125)I-IMPY (2-(4'-dimethylaminophenyl)-6-iodo-imidazo[1,2-a]pyridine), a well-known amyloid SPECT ligand, by ex vivo autoradiographic analyses in 18-mo-old amyloid precursor protein transgenic mice. To verify the sensitivity and quantitation of radiolabeled DRM106 for in vivo imaging, we compared the detectability of Aß plaques with (123)I-DRM106 and a well-known amyloid PET agent, (11)C-labeled Pittsburgh compound B ((11)C-PiB), in 29-mo-old transgenic mice and age-matched nontransgenic littermates. Additionally, we compared the binding characteristics of (125)I-DRM106 with those of (11)C-PiB and (11)C-PBB3, which selectively bind to Aß plaques and preferentially to tau aggregates, respectively, in postmortem AD brain sections. RESULTS: Ex vivo autoradiographic analysis showed that measurement with (125)I-DRM106 has a higher sensitivity for detecting Aß accumulation than with (125)I-IMPY in transgenic mice. SPECT imaging with (123)I-DRM106 also successfully detected Aß deposition in living aged transgenic mice and showed strong correlation (R = 0.95, P < 0.01) in quantitative analysis for Aß plaque detection by PET imaging with (11)C-PiB, implying that sensitivity and quantitation of SPECT imaging with (123)I-DRM106 are almost as good as (11)C-PiB PET for the detectability of Aß deposition. Further, the addition of nonradiolabeled DRM106 fully blocked the binding of (125)I-DRM106 and (11)C-PiB, but not (11)C-PBB3, to AD brain sections, and (125)I-DRM106 showed a lower binding ratio of the diffuse plaque-rich lateral temporal cortex to the dense-cored/neuritic plaque-rich hippocampal CA1 area, compared with (11)C-PiB. CONCLUSION: All of these data demonstrated the high potential of (123)I-DRM106 for amyloid imaging in preclinical and clinical application, and it might more preferentially detect dense-cored/neuritic amyloid deposition, which is expected to be closely associated with neuropathologic changes of AD.