Structure-activity studies of a series of dipyrazolo[3,4-b:3',4'-d]pyridin-3-ones binding to the immune regulatory protein B7.1

The interaction of co-stimulatory molecules on T cells with B7 molecules on antigen presenting cells plays an important role in the activation of naive T cells. Consequently, agents that disrupt these interactions should have applications in treatment of transplant rejection as well as autoimmune diseases. To this end, specific small molecule inhibitors of human B7.1 were identified and characterized. Herein, we report the identification of potent small molecule inhibitors of the B7.1-CD28 interaction. In a high-throughput screen we identified several leads that prevented the interaction of B7.1 with CD28 with activities in the nanomolar to low micromolar range. One of these, the dihydrodipyrazolopyridinone 1, was subsequently shown to bind the V-like domain of human B7.1 at equimolar stoichiometry. With this as a starting point, we report here the synthesis and initial in vitro structure-activity relationships of a series of these compounds.     

Measuring mast seeding behavior: relationships among population variation,individual variation and synchrony

Mast seeding, or masting, is the variable production of flowers, seeds, or fruit across years more or less synchronously by individuals within a population. A critical issue is the extent to which temporal variation in seed production over a collection of individuals can be viewed as arising from a combination of individual variation and synchrony among individuals. Studies of masting typically quantify such variation in terms of the coefficient of variation (CV). In this paper we examine mathematically how the population CV relates to the mean individual CV and synchrony, concluding that the relationship is a complex one which cannot isolate an overall measure of synchrony, and involves additional factors, principally the number of plants sampled and the mean productivity per plant. Our development suggests some simple approximate relationships of population CV to individual variability, synchrony and the number of individuals. These were found to fit quite well when applied to data from 59 studies which included seed production at the individual level.     

Snow tussocks, chaos, and the evolution of mast seeding

One hitherto intractable problem in studying mast seeding (synchronous intermittent heavy flowering by a population of perennial plants) is determining the relative roles of weather, plant reserves, and evolutionary selective pressures such as predator satiation. We parameterize a mechanistic resource-based model for mast seeding in Chionochloa pallens (Poaceae) using a long-term individually structured data set. Each plant's energy reserves were reconstructed using annual inputs (growing degree days), outputs (flowering), and a novel regression technique. This allowed the estimation of the parameters that control internal plant resource dynamics, and thereby allowed different models for masting to be tested against each other. Models based only on plant size, season degree days, and/or climatic cues (warm January temperatures) fail to reproduce the pattern of autocovariation in individual flowering and the high levels of flowering synchrony seen in the field. This shows that resource-matching or simple cue-based models cannot account for this example of mast seeding. In contrast, the resource-based model pulsed by a simple climate cue accurately describes both individual-level and population-level aspects of the data. The fitted resource-based model, in the absence of environmental forcing, has chaotic (but often statistically periodic) dynamics. Environmental forcing synchronizes individual reproduction, and the models predict highly variable seed production in close agreement with the data. An evolutionary model shows that the chaotic internal resource dynamics, as predicted by the fitted model, is selectively advantageous provided that adult mortality is low and seeds survive for more than 1 yr, both of which are true for C. pallens. Highly variable masting and chaotic dynamics appear to be advantageous in this case because they reduce seed losses to specialist seed predators, while balancing the costs of missed reproductive events.     

High mutation rates in human and ape pseudoautosomal genes

It has been suggested that recombination may be mutagenic, which, if true, would inflate intraspecies diversity and interspecies silent divergence in regions of high recombination. Here, we test this hypothesis comparing human/orangutan genome-wide non-coding divergence (K) to that in the pseudoautosomal genes which were reported to recombine much more frequently than the rest of the genome. We demonstrate that, compared to the average human/orangutan non-coding divergence (K=3%), the substitution rate is significantly elevated in the introns of SHOX (K=5.7%), PPP2R3L (K=8.7%) and ASMT (K=6.5%) genes located in the human and orangutan Xp/Yp pseudoautosomal region (p-PAR), where recombination is over 20-fold higher than the genomic average. On the other hand, human/orangutan non-coding divergence at the Xp/Yp pseudoautosomal boundary (K=3.5%) and in the SYBL1 gene (K=2.7%), located in the human Xq/Yq pseudoautosomal region (q-PAR), where recombination is known to be less frequent than in p-PAR, was not significantly higher than the genome average. The data are consistent with the hypothesis that recombination may be mutagenic.     

Mast cells: an unexpected finding in the modulation of cutaneous wound repair by charged beads

Increased numbers of mast cells are affiliated with a broad spectrum of pathologic skin conditions, including ulcers, atopic dermatitis, neurofibromatosis, hemangiomas, keloids, and hypertrophic scars. It has been proposed that mast cells play a primary pathophysiologic role in these disorders and that their presence represents not merely a secondary event. While investigating their recent hypothesis that positively charged cross-linked diethylaminoethyl dextran (CLDD) beads potentiate cutaneous wound healing, the authors serendipitously observed increased numbers of mast cells in the deep dermis of wounds treated with CLDD beads. The authors propose that mast cells may play an important role in the modulation of healing seen with CLDD beads. Incisional wounds were studied in 30 Sprague-Dawley rats partitioned into two groups that were killed 7 or 14 days after wounding. The wounds were treated with positively, negatively, or neutrally charged CLDD beads. Physiologic saline served as a control. At the designated times after incisional wounding, biopsy specimens were tested for wound breaking strength or processed for histologic testing, fixed in 4% paraformaldehyde, and stained with Giemsa and Goldner-Masson trichrome. Mast cells were counted under light microscopy in a blinded fashion and were expressed as the number of cells per millimeter squared. Significant increases in the number of mast cells were observed in the deep dermis of incisional wounds after implantation with positively or negatively charged CLDD beads. In contrast, neutrally charged beads had no effect on mast cell numbers. At 7 days, the incisions treated with positively charged beads averaged 2.1 times more mast cells compared with those treated with physiologic saline or neutrally charged beads, whereas the incisions treated with negatively charged beads displayed 3.2 times more mast cells. By day 14, the incisions treated with positively charged beads averaged 2.5 times more mast cells than those wounds treated with saline or neutrally charged beads; the incisions treated with negatively charged CLDD beads had 3.4 times more mast cells. The 7-day tensiometric data indicated that wounds treated with negatively charged CLDD beads had increased breaking strength compared with wounds treated with neutrally charged beads or saline (1.8 and 1.7 times, respectively; p = 0.01 and p = 0.02). Wounds treated with positively charged beads also showed increased breaking strength compared with wounds treated with neutrally charged beads or saline (1.5 and 1.4 times greater); however, this did not reach statistical significance. There was no apparent difference in breaking strength when neutrally charged beads were compared with those treated with saline. At 14 days, there was no statistically significant difference in wound breaking strength between different treatments. These findings are clinically germane to the assessment of proposed therapeutic applications of CLDD beads for a variety of impaired wound-healing states. Furthermore, if increased mast cell populations are intimately linked to hypertrophic scar and keloid formation, the results of the authors' study suggest that CLDD bead therapy of cutaneous wounds may lead to pathologic wound healing in humans.     

Tissue cholinesterases. A comparative study of their kinetic properties

The substrate saturation and temperature-dependent kinetic properties of soluble and membrane-bound forms of acetylcholinestarase (AChE) from brain and butyrylcholinesterase (BChE) from heart and liver were examined. In simultaneous studies these parameters were also measured for AChE in erythrocyte membranes and for BChE in the serum from rat and humans. For both soluble and membrane-bound forms of the enzyme from the three tissues, two components were discernible. In the brain, Km of component I (high affinity) and component II (low affinity) was somewhat higher in membrane-bound form than that of the soluble form components, while the Vmax values were significantly higher by about five fold. In the heart, Km of component II was lower in membrane-bound form than in the soluble form, while Vmax for both the components was about four to six fold higher in the membrane-bound form. In the liver, Vmax was marginally higher for the two components of the membrane-bound enzyme; the Km only of component I was higher by a factor of 2. In the rat erythrocyte membranes three components of AChE were present showing increasing values of Km and Vmax. In contrast, in the human erythrocyte membranes only two components could be detected; the one corresponding to component II of rat erythrocyte membranes was absent. In the rat serum two components of BChE were present while the human serum was found to possess three components. Component I of the human serum was missing in the rat serum. Temperature kinetics studies revealed that the Arrhenius plots were biphasic for most of the systems except for human serum. Membrane binding of the enzyme resulted in decreased energy of activation with shift in phase transition temperature (Tt) to near physiological temperature.     

The Discovery of orally available thrombin inhibitors : Studies towards the optimisation of CGH1668

The chemical optimisation of CGH1668 1 is described employing an in vivo model of absorption to determine the influence on bioavailability of single point modifications to five key molecular templates. The discovery of an orally bioavailable and selective thrombin inhibitor, 24, highlights the utility of this approach.     

Signal transduction in isolated fat body from the cockroach Blaptica dubia exposed to hypertrehalosaemic neuropeptide

Hypertrehalosaemic hormones stimulate trehalogenesis while inhibiting glycolysis in cockroach fat body. Signal transduction of the hypertrehalosaemic peptide Bld HrTH was examined in isolated fat body of the Argentine cockroach Blaptica dubia with respect to its effects on the increase in trehalose production and decrease in the content of the glycolytic activator fructose 2,6-bisphosphate in the tissue. Cyclic AMP does not seem to be involved in these processes as the cAMP analogue cpt-cAMP and the phosphodiesterase inhibitor IBMX, which both permeate cell membranes, had no effect on either parameter. Octopamine at physiological concentrations (10⁻⁷ mol · l⁻¹) was also ineffective, but at 10⁻⁵ mol · l⁻¹ or above, octopamine stimulated trehalose production although the content of fructose 2,6-bisphosphate in fat body was not affected. Both calcium entry and the release of Ca²⁺ from intracellular stores seem to be involved in the action of the hormone. If Ca²⁺ was omitted from the incubation medium, the hormone stimulated trehalose production less, though still significantly, whereas the hormone effect on fructose 2,6-bisphosphate was completely abolished in the absence of extracellular Ca²⁺. With Ca²⁺ present in the medium, the effect of the hormone on fructose 2,6-bisphosphate could be fully mimicked by the calcium ionophore A23187, suggesting that calcium entry is a␣decisive step in this signalling pathway. Trehalose production, on the other hand, was increased by thimerosal and thapsigargin which increase cytosolic Ca²⁺ from intracellular stores, whereas thimerosal in the absence of extracellular Ca²⁺ increased rather than decreased the content of fructose 2,6-bisphosphate, thus dissociating the two effects, which are normally coordinated by the hormone. Trehalose production and the content of fructose 2,6-bisphosphate were not significantly affected by mepacrine and mellitin, which are known to inhibit, respectively stimulate, phospholipase A₂. Our data suggest that the effects of Bld HrTH on the stimulation of trehalose production and reduction of fructose 2,6-bisphosphate content in fat body are mediated by Ca²⁺, but that different signalling pathways are involved, suggesting that the two processes, although they are functionally linked, could be regulated separately. Accepted: 10 November 1997