Despite the contribution of changes in pancreatic β-cell mass to the development of all forms of diabetes mellitus, few robust approaches currently exist to monitor these changes prospectively in vivo. Although magnetic-resonance imaging (MRI) provides a potentially useful technique, targeting MRI-active probes to the β cell has proved challenging. Zinc ions are highly concentrated in the secretory granule, but they are relatively less abundant in the exocrine pancreas and in other tissues. We have therefore developed functional dual-modal probes based on transition-metal chelates capable of binding zinc. The first of these, Gd⋅1, binds ZnII directly by means of an amidoquinoline moiety (AQA), thus causing a large ratiometric Stokes shift in the fluorescence from λem=410 to 500 nm with an increase in relaxivity from r1=4.2 up to 4.9 mM−1 s−1. The probe is efficiently accumulated into secretory granules in β-cell-derived lines and isolated islets, but more poorly by non-endocrine cells, and leads to a reduction in T1 in human islets. In vivo murine studies of Gd⋅1 have shown accumulation of the probe in the pancreas with increased signal intensity over 140 minutes.

Background Many translational MR biomarkers derive from measurements of the water proton longitudinal relaxation rate R 1 , but evidence for between-site reproducibility of R 1 in small-animal MRI is lacking. Objective To assess R 1 repeatability and multi-site reproducibility in phantoms for preclinical MRI. Methods R 1 was measured by saturation recovery in 2% agarose phantoms with five nickel chloride concentrations in 12 magnets at 5 field strengths in 11 centres on two different occasions within 1–13 days. R 1 was analysed in three different regions of interest, giving 360 measurements in total. Root-mean-square repeatability and reproducibility coefficients of variation (CoV) were calculated. Propagation of reproducibility errors into 21 translational MR measurements and biomarkers was estimated. Relaxivities were calculated. Dynamic signal stability was also measured. Results CoV for day-to-day repeatability ( N = 180 regions of interest) was 2.34% and for between-centre reproducibility ( N = 9 centres) was 1.43%. Mostly, these do not propagate to biologically significant between-centre error, although a few R 1 -based MR biomarkers were found to be quite sensitive even to such small errors in R 1 , notably in myocardial fibrosis, in white matter, and in oxygen-enhanced MRI. The relaxivity of aqueous Ni 2+ in 2% agarose varied between 0.66 s −1 mM −1 at 3 T and 0.94 s −1 mM −1 at 11.7T. Interpretation While several factors affect the reproducibility of R 1 -based MR biomarkers measured preclinically, between-centre propagation of errors arising from intrinsic equipment irreproducibility should in most cases be small. However, in a few specific cases exceptional efforts might be required to ensure R 1 -reproducibility.

The conformation of actinomycin D in acetone and chloroform solution at different temperatures has been studied by 'H NMR spectroscopy.At lower temperature the resonances due to the two chromophoric amino protons were observed. These signals exhibit very different resonance positions indicating a severely hindered rotation of the 2-amino group and the presence of a hydrogen-bond connecting the 2-amino and the I-carbonyl groups.In 'H NMR spectra of partially "N-enriched actinomycin D, the lJN.fl coupling constants at the 2-amino group were determined and a strong sp2 character for the 2-amino nitrogen was deduced. The strong amide character of the 2-amino group is caused by mesomerism involving the I-carbonyl group.The amino proton signals are sensitive indicators for differences in the spatial relationship of the diverse parts of the actinomycin molecule.At lower temperatures a simultaneous and selective broadening of the CI ring threonine and valine amide proton signals as well as of the 2-amino group resonance was observed, indicating the presence of one dynamic process in the molecule which slows down upon temperature reduction. A swinging motion of the N(10) nitrogen through the chromophore plane would explain this observation.The interpretation of these results requires the presence of a non-planar chromophoric system in the actinomycin molecule in acetone and chloroform solution. The possible implications of this non-planarity for the intercalation process and for the biological activity of the drug are discussed.Actinomycin D is the best studied representative of a family of chromopeptides of bacterial origin, which has aroused interest because of its antineoplastic activity [I, 21. The biological activity seems to be correlated with the ability of actinomycins to form intercalation complexes with DNA, whereby the DNA-dependent RNA synthesis is inhibited. The formation of the DNA-actinomycin complex requires the presence of certain structural features in the actinomycin molecule (cf. Fig. I), e.g. both lactone rings have to be intact [2].Actinomycin derivatives in which the 2-amino group on the

Cartilage-binding bimodal MRI and fluorescent probes were developed to monitor osteoarthritic damage in animal models over extended periods of time.

Using the noninvasive method of 31P nuclear magnetic resonance (NMR) spectroscopy, the influence of hypoxia on intracellular pH (pH,) and on the energy metabolism was studied in the lugworm Arenicola marina.1. During hypercapnic hypoxia (induced by the animal itself), pH, dropped from 7.3 +-0.1 (n = 6) to 6.5 k 0.1 (n = 4) within 24 hours, whereas during hypocapnic hypoxia pHi decreased by only 0.3 units (n = 4). The change in pH, (pH of the ambient water) was similar: strong acidification from about 8.1 to 6.1 during hypercapnic and moderate acidification to 7.8 during hypocapnic hypoxia.2. Mobilization of phosphagen (phosphotaurocyamine) occurred faster during hypercapnic than hypocapnic hypoxia. Anaerobic end products (propionate and acetate), however, accumulated to a greater extent during hypocapnic than hypercapnic hypoxia.3. Conclusion: The severe acidosis found during hypercapnic hypoxia depends on the amount of C 0 2 accumulation rather than on the amount of glycolytic end products. On the other hand, the lower accumulation of glycolytic end products and the faster mobilization of phosphagen with severe acidosis seem to reflect a regulatory effect of pHi on anaerobic metabolism.Several invertebrates belonging to different phyla have been shown to survive prolonged periods of experimental and environmental hypoxia; i.e., they are facultative anaerobes (for review, see de Zwaan and van den Thillart, '85; Zebe and Schottler, '86). The pathways of energy production during prolonged anaerobiosis have been studied thoroughly, particularly in the sea mussel Mytilus edulis (for review, see de Zwaan and van den Thillart, '85) and in the lugworm ArenicoZa marina (Grieshaber and Kreutzer, '86; Schottler, '86). From these studies it is evident that a sufficient energy supply for surviving prolonged periods of hypoxia depends on two mechanisms: 1) the depression of the metabolic rate and 2) the switch of the glycolytic pathway toward the formation of volatile fatty acids resulting in a yield of adenosine triphosphate ( ATP) substantially higher than from formation of lactic acid.Several hypotheses have been published to explain how depression of the metabolic rate may be attained and which regulatory mechanisms could bring about the switch of glycolysis at the phosphoerolpyruvate (PEP) branchpoint during the first hours of hypoxia. In this respect, the role of 0 1989 ALAN R. LISS, INC.