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At least 829 records · Page 46Linked to original sources
PubMed1998

Induction of islet cell neogenesis in the adult pancreas: the partial duct obstruction model.

The proliferative capacity of adult pancreatic islet cells is limited, although the formation of new islets from cells associated with the ductal epithelium is achievable even in the adult gland. Understanding the mechanism whereby proliferation and subsequent differentiation of putative precursor cells leads the appearance of new islets, i.e., islet neogenesis, may be important as a modality for treatment of both Type I and type II diabetes, in which there is an absolute or relative deficiency of insulin. It appears that certain genes and their protein products are essential to the initiation of the initial step in the pathway. We have shown that partial obstruction of the hamster pancreas is able to reverse streptozotocin-induced diabetes more than 50% of the time. An extract, termed ilotropin, prepared from obstructed pancreata, also reverses the diabetes, whereas extracts of control non-obstructed pancreata do not. Ilotropin contains a protein that is heat and acid stable with MW around 20-45 kDa that is capable of stimulating the proliferation of isolated duct cells in culture. Using mRNA and a differential display technique, 20 genes were found to be expressed in the partially obstructed (regenerating), but not the non-obstructed (non-regenerating) pancreas. One of these islet neogenesis-associated proteins (INGAP) proved to be unique to the obstructed pancreas, and a peptide contained within the sequence was capable of stimulating the proliferation of ductal cells in culture. INGAP was found to be expressed early in the neogenic process before the onset of ductal cell proliferation, and was capable of stimulating tritiated thymidine uptake into protodifferentiated epithelial cells, compatible with the notion that it might be involved in initiating the process of islet neogenesis.

Animals↗
PubMed1992

The partial isolation and characterization of ilotropin, a novel islet-specific growth factor.

In this series of studies, we have presented evidence for a novel, pancreatic islet-specific growth factor, which we call ilotropin. Ilotropin is acid stable, heat stable, ethanol-precipitable, and sensitive to trypsin digestion. It appears to have a molecular weight between 29 - 44,000, and preliminary data not presented here suggests that it has a relatively basic pI. Unlike many other growth factors, ilotropin does not bind to heparin. Ilotropin is distinguishable from most of the known growth factors on the basis of at least one of the characteristics established in these studies. The apparent molecular weight of 29 - 44,000 eliminates all but the larger growth factors such as PDGF and hepatic growth factor. The fact that ilotropin is acid stable rules out identity with hepatic growth factor, and its lack of binding to heparin and apparent basic pI rules out identity with PDGF. Thus, the combination of characteristics described in these studies eliminates most of the known growth factors as candidates for the role of ilotropin. Certain growth factor precursor molecules (e.g. TGF-a) and several interleukins and cytokines (e.g. pro-IL-1 and melanocyte growth factor) also fall into this molecular weight range. Whether these proteins might be related to ilotropin or play a role in its biological activity remains to be determined. Current studies of ilotropin include further purification to homogeneity, determination of the peptide sequence of ilotropin, and development of an in vitro bioassay using trophic responses of primary cultures of pancreatic duct cells as an indicator of ilotropin activity. With purified material we ought to be able to identify the cells of origin and the target cells for the action of ilotropin, and establish assays to determine the relationship to failure of beta-cell regeneration that accompanies diabetes. Ultimately we hope that ilotropin may lead to new ways of approaching aspects of the problems presented in pancreatic beta-cell failure.

Animals↗
PubMed1991

Kinetics of water sorption in packaging materials for food.

The water content of paper and its time dependence are of great importance for the use of paper and cardboard as packaging materials. The physical process of water sorption and the mechanisms of water "binding" in paper, as fundamental principles of the kinetics, are discussed. Water exists in up to four different "states" (i.e. domains of mobility) in paper: the first layer at the primary sites on the surface of the fibers; the multimolecular layers, with less "binding" energy, on these inner surfaces; condensed water in the voids; and dissolved water in the cellulose fibers. All these "states" influence the shape of the sorption isotherm and correspond to a different water content and to different transport mechanisms. The various types of water "binding" on paper were studied by measuring the transversal relaxation rate, T2, using a pulsed Nuclear Magnetic Resonance spectrometer (minispec pc 120). In addition, a non-destructive, fast method of determining the water content in packaging materials with NMR spectroscopy is described.

Adsorption↗
PubMed1983

Rapid, economical qualitative method for separation of aflatoxins B-1, B-2 & G-1, G-2 by dry column chromatography.

A good correlation of four components of aflatoxins was accomplished by using the dry column chromatography method. The decolorization process of interfering substances, by 0.01 N KOH and defatting the extract with petroleum ether yields a clean residue for DCC separation. It is clear that the dry column chromatography is a very simple and time-saving procedure for separation of aflatoxins. DCC columns are more economical than precoated 'thick layer' preparative plates and, in DCC, no large developing tanks need to be used. Hazards associated with the use of large volumes of flammable solvents are greatly reduced.

Aflatoxin B1↗
PubMed1988

The migration of propylene glycol, mono-, di-, and triethylene glycols from regenerated cellulose film into food.

Chocolates, boiled sweets, toffees, cakes and meat pies were wrapped in regenerated cellulose films (with or without coatings) that contained various mixtures of glycol softeners and which had been specially formulated for particular food applications. Samples were unwrapped at intervals (up to the end of the usual maximum shelf-life for the food) and analysed for their glycol content. Analysis involved homogenization of the food in hot water, removal of fats with hexane, precipitation of sugars with calcium hydroxide and analysis of the glycols by capillary gas chromatography with flame ionization detection (GC/FID) after trimethylsilyl (TMS) derivatization. Triethylene glycol was analysed by selected ion monitoring GC/mass spectrometry (GC/MS) as interference problems occurred with the GC/FID approach. The results of the study showed that higher levels of migration occurred for propylene glycol than for triethylene glycol and the presence of a coating reduced the migration of both softeners. Generally, mono- and diethylene glycol levels in the food samples were below 10 mg/kg, although some samples wrapped in polyethylene glycol-softened films contained levels approaching the current statutory limit of 50 mg/kg.

Cellophane↗
PubMed2000

Differential complementation of a Neurospora crassa Galpha(i) mutation using mammalian Galpha protein genes.

Heterotrimeric (alphabetagamma) G proteins interact with sensory receptors to transduce signals to downstream effectors in eukaryotes. We previously reported that GNA-1 from Neurospora crassa is a microbial member of the Galphai family found in higher organisms. Deletion of gna-1 leads to female sterility, slower growth rates on normal and hyperosmotic solid medium, and increased resistance to heat and oxidative stress. In this study we compare mammalian genes for proteins of the Galphai sub-family (Galphai, Galphao, Galphat and Galphaz), and Galphas (which is not a member of the Galphai family) with the N. crassa gna-1 gene with respect to their ability to complement deltagna-1 phenotypes. Northern analysis detected full-length transcripts of all these genes, except that for Galphai, in N. crassa transformants. Measurements of pertussis toxin-catalyzed ADP-ribosylation and Western analysis showed that the GNA-1, Galphaz, Galphao and Galphas proteins were present in the respective transformed strains. Strains in which the mammalian Galpha protein could be detected were subjected to phenotypic testing. During the vegetative cycle, none of the mammalian Galpha genes complemented the thermotolerance phenotype of deltagna-1. However, the three expressed mammalian Galpha genes achieved at least partial complementation of the defects in vegetative apical extension rate. cAMP levels did not correlate with restoration of vegetative growth rate by the mammalian genes. During the sexual cycle, Galphao was the only mammalian Galpha gene that rescued the defect in female fertility characteristic of deltagna-1 strains. Alignment of GNA-1, Galphaz, Galphao and Galphas protein sequences revealed correlations between the observed complementation pattern and the degree of identity to GNA-1 in various functional motifs. The finding that Galphac gave the best restoration of vegetative growth but could not restore normal female fertility implies that GNA-1 regulates different pathways that are important for vegetative and sexual growth in N. crassa.

Amino Acid Sequence↗