Melanin concentrating hormone. IV. Development of a sensitive solid-phase radioimmunoassay for melanin-concentrating hormone

A two-step solid-phase radioimmunoassay for melanin-concentrating hormone (MCH) was developed for direct determination of the hormone in plasma samples. To this end, synthetic MCH was coupled to bovine thyreoglobulin and the complex was injected into rabbits. Specific antisera of high titer were obtained which did not crossreact with other hormones. The IgGs were chemically linked to immunobeads, an acrylamide/acrylic acid polymer matrix. In the first step, plasma MCH was immunoextracted by incubation of diluted plasma samples with anti-MCH immunobeads. In the second step, the washed polymer was incubated with radioiodinated MCH tracer for titration of non-occupied sites. This procedure made it possible to determine as little as 4 pg MCH per ml of plasma. Application of the radioimmunoassay to plasma levels of black or white background-adapted trout showed a marked difference in circulating MCH: while trout on a black background contained a mean value of 29 +/- 5.6 pg/ml, animals on a white background had 106 +/- 19 pg/ml. These findings strengthen the hypothesis that MCH is directly involved in the control of color change of teleost fishes. By contrast, there was no detectable salmonid MCH immunoreactivity in rat or human plasma.     

Synthesis and structure-activity relationship of novel RXR antagonists: orally active anti-diabetic and anti-obesity agents

A series of diazepinylbenzoic acid derivatives were synthesized and tested in the inhibition assay of the transactivation of RXR. Oral treatment of cyano derivatives (16f) was found to show anti-diabetic and anti-obesity effects in KK-A(y) mice.     

Synthesis and structure-activity relationship of RXR antagonists based on the diazepinylbenzoic acid structure

Synthesis and structure-activity relationship of RXR antagonists employing a diazepinylbenzoic acid scaffold are described. Of those antagonists, sulfonamide derivatives (6v and 6w) reveal a high antagonistic activity and good pharmacokinetic properties.     

Antibacterial activity of a virgatusin-related compound

The relationship between antibacterial activity of tetra-substituted tetrahydrofuran lignans (1-4) and their absolute configurations was tested. Only compound 4 among two virgatusins and two related compounds exhibited growth inhibitory activity against the Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus and Listeria denitrificans. Compound 4 affected the growth of B. subtilis in a bactericidic manner, and its ability to dissipate the cytoplasmic membrane potential was investigated using the fluorescence probe 3,3'-dipropylthiadicarbocyanine iodide. These results suggested that compound 4 damages cells by causing the loss of the proton motive force and disruption of the cellular integrity of the membrane, leading to cell death. In addition, it was shown that the antibacterial activity of a lignan was closely related to its absolute configuration and functional groups.     

Mechanism of dopachrome tautomerization into 5,6-dihydroxyindole-2-carboxylic acid catalyzed by Cu(II) based on quantum chemical calculations

Background

Tautomerization of dopachrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA) is a biologically crucial reaction relevant to melanin synthesis, cellular antioxidation, and cross-talk among epidermal cells. Since dopachrome spontaneously converts into 5,6-dihydroxyindole (DHI) via decarboxylation without any enzymes at physiologically usual pH, the mechanism of how tautomerization to DHICA occurs in physiological system is a subject of intense debate. A previous work has found that Cu(II) is an important factor to catalyze the tautomerization of dopachrome to DHICA. However, the effect of Cu(II) on the tautomerization has not been clarified at the atomic level.

Methods

We propose the reaction mechanism of the tautomerization to DHICA by Cu(II) from density functional theory-based calculation.

Results

We clarified that the activation barriers of α-deprotonation, β-deprotonation, and decarboxylation from dopachrome are significantly reduced by coordination of Cu(II) to quinonoid oxygens (5,6-oxygens) of dopachrome, with the lowest activation barrier of β-deprotonation among them. In contrast to our previous work, in which β-deprotonation and quinonoid protonation (O5/O6-protonation) were shown to be important to form DHI, our results show that the Cu(II) coordination to quinonoid oxygens inhibits the quinonoid protonation, leading to the preference of proton rearrangement from β-carbon to carboxylate group but not to the quinonoid oxygens.

Conclusion

Integrating these results, we conclude that dopachrome tautomerization first proceeds via proton rearrangement from β-carbon to carboxylate group and subsequently undergoes α-deprotonation to form DHICA.

General significance

This study would provide the biochemical basis of DHICA metabolism and the generalized view of dopachrome conversion which is important to understand melanogenesis.     

Feedback between size balance and consumption strongly affects the consequences of hatching phenology in size‐dependent predator–prey interactions

In many size‐dependent predator–prey systems, hatching phenology strongly affects predator–prey interaction outcomes. Early‐hatched predators can easily consume prey when they first interact because they encounter smaller prey. However, this process by itself may be insufficient to explain all predator–prey interaction outcomes over the whole interaction period because the predator–prey size balance changes dynamically throughout their ontogeny. We hypothesized that hatching phenology influences predator–prey interactions via a feedback mechanism between the predator–prey size balance and prey consumption by predators. We experimentally tested this hypothesis in an amphibian predator–prey model system. Frog tadpoles Rana pirica were exposed to a predatory salamander larva Hynobius retardatus that had hatched 5, 12, 19 or 26 days after the frog tadpoles hatched. We investigated how the salamander hatch timing affected the dynamics of prey mortality, size changes of both predator and prey, and their subsequent life history (larval period and size at metamorphosis). The predator–prey size balance favoured earlier hatched salamanders, which just after hatching could successfully consume more frog tadpoles than later hatched salamanders. The early‐hatched salamanders grew rapidly and their accelerated growth enabled them to maintain the predator‐superior size balance; thus, they continued to exert strong predation pressure on the frog tadpoles in the subsequent period. Furthermore, frog tadpoles exposed to the early‐hatched salamanders were larger at metamorphosis and had a longer larval period than other frog tadpoles. These results suggest that feedback between the predator‐superior size balance and prey consumption is a critical mechanism that strongly affects the impacts of early hatching of predators in the short‐term population dynamics and life history of the prey. Because consumption of large nutrient‐rich prey items supports the growth of predators, a similar feedback mechanism may be common and have strong impacts on phenological shifts in size‐dependent trophic relationships.     

Olfaction and brain size in the bowhead whale (Balaena mysticetus)

Although there are several isolated references to the olfactory anatomy of mysticetes, it is usually thought that olfaction is rudimentary in this group. We investigated the olfactory anatomy of bowhead whales and found that these whales have a cribriform plate and small, but histologically complex olfactory bulb. The olfactory bulb makes up approximately 0.13% of brain weight, unlike odontocetes where this structure is absent. We also determined that 51% of olfactory receptor genes were intact, unlike odontocetes, where this number is less than 25%. This suggests that bowheads have a sense of smell, and we speculate that they may use this to find aggregations of krill on which they feed.     

Novel functional biodegradable polymer II: fibroblast growth factor-2 activities of poly(gamma-glutamic acid)-sulfonate

Basic fibroblast growth factor (FGF-2) mitogenic activities of sulfonated poly(gamma-glutamic acid) (gamma-PGA-S) were investigated with chlorate-treated L929 fibroblast culture tests. When 72% of the carboxyl groups in gamma-PGA were sulfonated (gamma-PGA-S72), cell numbers reached a maximum. The activity of gamma-PGA-S72 was higher than that of gamma-PGA and synthetic heparinoids and was almost comparable to that of heparin. Cytotoxicity of gamma-PGA-S72 was not observed, regardless of the degree of sulfonation. FGF-2-protective effects of gamma-PGA-S72 against acid and thermal inactivation were also evaluated, and gamma-PGA-S72 showed higher FGF-2-protective effects in comparison to nonsulfonated gamma-PGA. The steric structures of various sulfonated gamma-PGA-Ss were analyzed by molecular modeling (molecular orbital method (MOPAC)) and indicated that gamma-PGA-Ss are helical in vacuo. Results from MOPAC and the molecular mechanics method (MM2) demonstrated that electrostatic interactions can take place between sulfonic and carboxyl groups of gamma-PGA-S and basic amino acid residues in FGF-2. gamma-PGA-S72 can interact with FGF-2 strongly.     

Electro-transfer of small interfering RNA ameliorated arthritis in rats

RNA interference provides the powerful means of sequence-specific gene silencing. Particularly, small interfering RNA (siRNA) duplexes may be potentially useful for therapeutic molecular targeting of human diseases, although novel delivery systems should be devised to achieve efficient and organ-specific transduction of siRNA. In the present study, we demonstrated that electro-transfer of a siRNA-polyamine complex made efficient and specific gene knockdown possible in the articular synovium. Targeted suppression of the tumor necrosis factor-alpha gene through this procedure significantly ameliorated collagen-induced arthritis in rats. Our results suggest the potential feasibility of therapeutic intervention with RNA medicines for treatment of rheumatoid and other locomotor diseases.