Shigetada Fujii

Microencapsulation of pancreatic islets: A technique and its application to culture and transplantation

Hamster pancreatic islets were encapsulated by a biocompatible membrane composed of the molecular sequence of alginate-polylysine-alginate. The encapsulated islets released insulin into the culture medium in response to secretagogues in short-term incubation. In long-term culture, the encapsulated islets maintained their insulin-releasing capacity for 28 days at a level similar to that of the unencapsulated islets. No overgrowth of fibroblastic cells was observed inside the capsule even after 70 days of culture. Further, the encapsulated hamster islets were xenotransplanted to streptozotocin-induced diabetic rats intraperitoneally. Some of the encapsulated islets, which were recovered from a recipient 27 days after transplantation, were found to be viable, although prolonged normalization of fasting plasma glucose levels of the recipients could not been achieved. On the contrary, the unencapsulated islets were replaced by massive connective tissue elements and insulin-positive B cells were hardly detected within the grafts 22 days after transplantation. The results of this study seem to confirm the potential of the application of the encapsulating technique to primary culture of parenchymal cells and to transplantation of pancreatic islets.

Effect of poly(α-D-glutamic acid) on the polarographic reduction of 3,6-diaminoacridines

The effect of poly(α-D-glutamic acid) (PGA) on the Tast polarographic reduction of trypaflavine (TrFl) as a representative of the 3,6-diaminoacridines was studied. In the polarograms of 0.1 mM TrFl, two reduction waves were observed. The first wave corresponded to the formation of a TrFl radical. In the presence of PGA in acid solutions, the half-wave potential of the first wave of TrFl shifted towards negative values, while the limiting current decreased. The absorption spectra and drop time curves for the TrFl solution with and without PGA were also examined. It is concluded that the TrFl molecule is bound to a PGA molecule in the bulk to form a complex. At appropriate concentrations of the complex, an adsorption layer was formed on the electrode. The second wave corresponds to the formation of acridan by one-electron reduction accompanied by protonation. Upon addition of PGA to the solution, the half-wave potential of this wave shifted remarkably towards positive values with the PGA concentration, although a considerable decrease was observed in the limiting current. This behaviour was pronounced in the pH region where the PGA-H+ chelate complex is formed. It is deduced that in the electroreduction of TrFl in the second step, the H+ ion is supplied mainly from the PGA-H+ complex, which is present in close proximity to the TrFl radical on the electrode.

Polarographic study of poly(α-D-glutamic acid) in acid solutions

Abstract A reduction wave with a half-wave potential of about −1.45V ( versus n.h.e.) was observed for the first time in tast polarographic measurement of poly(α-D-glutamic acid), poly(Glu), in acid solutions. This wave was diffusion-controlled and its height increased with increasing H + ion concentration. The reduction wave was examined in detail by carrying out polarographic measurements both for carboxyl-containing compounds such as malonic acid, EDTA, and poly-acrylic acid, and for poly(L-ornithine), a polypeptide which does not contain any carboxyl groups. Cyclic voltammetry was also performed for poly(Glu) in acid solutions. The present experiments strongly indicated that poly(Glu) forms a proton chelate complex in acid solution. This complex is responsible for the appearance of a polarographic reduction wave at about −1.45 V ( versus n.h.e.). The concept of intramolecular proton chelates was also supported by analysis of the limiting current with the aid of the Ilkovic equation, from which the diffusion coefficient of poly(Glu) was obtained. The correlation between the limiting current at −1.45 V and the helix-coil transition curve of poly(Glu) was examined. The reduction waves at −1.45 V appeared in the pH region where the helix-coil transition of poly(Glu) takes place. On the basis of these results, a possible chelated structure of poly(Glu) in acid solution is discussed.