Stemona alkaloids such as (±)-stemonamine/ (±)-isostemonamine, have a unique structure, possibly coupled with potential biological activities. The establishment of effective total synthesis protocols for stemonamine alkaloids has been a challenge for synthetic chemists so far. These stemonamine alkaloids are isolated as racemates and there is no report concerning their asymmetric total synthesis. It is generally understood that any pair of enantiomers have physically and chemically indistinguishable properties. However, stereochemistry is a critical point in biological systems because most biological reactions, such as those mediated by enzymes and receptors, are stereospecific. We have successfully established the methods of asymmetric total synthesis of the stemonamine alkaloids, (–)-stemonamine/(–)-isostemonamine. We studied the potential application of these Stemona alkaloids as anti-proliferative agents. Experiments were conducted by using two representative human breast cancer cell lines, MCF-7 and MDA-MB-231, and our results indicated that i) (–)-isostemonamine displays strong cytotoxic effects on the highly aggressive estrogen receptor α (ERα)-negative MDA-MB-231 cell line, but not on the ERα-positive MCF-7 cells, with an IC50 value (9.3 ± 1.9 μM), which is comparable to that of etoposide (IC50 = 7.1 μM ± 1.4 μM), and ii) the thioamide derivative of (–)-isostemonamine does not suppress the growth of MDA-MB-231 cells.
Staphylococcal superantigen-like 10 (SSL10) is one of the immunoglobulin G (IgG) binding proteins produced by Staphylococcus aureus (S. aureus). SSL10 is reported to bind to Fc region of human IgG and interfere its effector functions. As SSL10 shows no homology with other staphylococcal IgG binding proteins, the mechanism of interaction between SSL10 and IgG remains to clear. In this study we attempted to identify the regions of SSL10 that are responsible for binding to human IgG (hIgG) by analyzing the binding ability of chimeras between SSL10 and its paralog, SSL7. The chimeras that retained either β1-β3 or β10-β12 of SSL10 bound to immobilized hIgG. On the other hand, chimeras that lacked both of these regions did not show binding activity to hIgG. In far western analysis, biotinylated hIgG interacted with SSL10 and chimera that retained β1-β3 and β10-β12 of SSL10. Collectively, SSL10 has two responsible regions for binding to hIgG, one is located in N-terminal half of oligonucleotide/oligosaccharide-binding (OB)-fold domain and the other is in C-terminal half of β-grasp domain. These findings would contribute to understand the mechanism of immune evasion of S. aureus and also to develop vaccines and drugs against S. aureus.
Elemental selenium, an essential element for humans and animals is totally obtained from foods and used for the synthesis of selenoproteins, such as glutathione peroxidases (GPx). Fish and shellfish are selenium-rich foodstuffs, and are the major dietary source of selenium for the Japanese population. However, the chemical structure and bioavailability of selenium species from seafood materials have hardly been elucidated. The Japanese littleneck clam (Asari) is the most popular consumed seawater bivalve in Japan. In this study, the selenium species in Asari were separated and assessed as a nutritional selenium source using cultured cells. The selenium content in the lyophilized Asari edible meat was 4.34±0.49 μg/g. The selenium extraction rate into water was 17−24% (1.07±0.14 μg/g-dry Asari). Based on the results that selenium in the Asari water-extract was mostly retained on both cationic Q Sepharose and anionic SP Sepharose columns, the selenium species in the Asari water-extract appeared to possess an amphoteric character. Selenium in the Asari water-extract mostly passed through a membrane with the molecular mass cutoff of 5000. After lyophilization, the resulting filtrate was subjected to in vitro assessment of the selenium bioavailability. HepG2 and HeLa cells were cultured in a basal medium containing the filtrate. The selenium content and GPx activity of the HepG2 cells increased with the increasing selenium content in the medium and incubation time, which suggested that the selenium species in the Asari water-extract were utilized for the synthesis of the GPxs. Overall, these results demonstrated that Asari contains nutritionally effective selenium species.