Relationship between pinocytic rate and uptake of transferrin by suspended rat hepatocytes

Summary The aim of this study was to compare quantitatively the capacity to transcytose (i.e. to uptake and release) transferrin (Tf) with the pinocytic activity of suspended adult rat hepatocytes. An oligodisperse preparation of¹³¹I-polyvinylpyrrolidone (PVP;M r 36000) was used to measure the inward and outward aspects of the pinocytic process in separate experiments. Cell association of rat¹²⁵I-Tf was measured at Tf concentrations approaching physiological, where⁵⁹Fe uptake obeyed first-order kinetics. Release studies with both PVP and Tf were carried out under conditions which minimized the probability ofde novo endocytosis of a molecule already released. Sets of experimental points representing cell-associated radioactivities were converted into continuous algebraic functions by fitting with two-term (release studies) or three-term (uptake studies) exponential equations. Transport of PVP and Tf through the cells was computed from these equations by deconvolution. This analysis showed that, under the present experimental conditions, the fractional transcytosis rates of Tf and PVP by hepatocytes were in the ratio of I:0.77. These values imply that, in the physiological range of Tf concentrations, about 75% of the Fe taken up by hepatocytes may be due to a pinocytic mechanism (fluid-phase or mixed). Inclusion of chloroquine (1 mM) in the suspending medium, both in uptake and release experiments, resulted in more PVP and Tf passing through the cells, while Fe uptake was reduced. It is suggested that the base probably exerted its enhancing effect on transcytosis by shunting the subcellular transport of PVP and Tf to the outward leg through a shorter circuit.Abbreviations BSA bovine serum albumin - HBSS Hank's balanced salt solution - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - MEM minimal essential medium - PVP polyvinylpyrrolidone - Tf transferrin     

Adsorption of endogenous polyphenols relieves the inhibition by fruit juices and fresh produce of immuno-PCR detection of Escherichia coli O157:H7

The immuno-polymerase chain reaction (PCR) approaches facilitate rapid (8 h) detection of Escherichia coli O157:H7 in contaminated dairy products and ground beef samples with detection sensitivities approaching 1 colony forming unit (cfu) g-1 ml-1. However, no PCR products were obtained when the method was applied to identify E. coli O157:H7 in tainted apple juice. Enzyme-linked immuno-assay (ELISA) results suggested non-specific binding of endogenous polyphenols (ubiquitous in plant products) to antibodies present on the surface of the immunobeads, making the latter unavailable for capturing the target bacteria Treatment of the test sample, prior to IMS, with a synthetic fining agent, polyvinylpyrrolidone, restored the full function and sensitivity of the immuno-PCR. The study demonstrates the suitability of the improved method as a generic strategy for rapid screening of fruit juices and plant produce for E. coli O157:H7.     

Preservation of Oligodendroglial Cytoplasm in Cryopreservative-Pretreated Frozen White Matter

Abstract: Various cryoprotective agents [glycerol, dimethylsulphoxide, polyvinylpyrrolidone (PVP 40)], all dissolved in Krebs phosphate medium were tested for their effects on cytoplasmic preservation in oligodendroglia isolated from bovine white matter stored at -30°C. Of these agents, only PVP 40 (15% wt/vol) produced a significant improvement in recovery of oligodendroglial cytoplasm compared with untreated frozen brain. Cells isolated after PVP 40 pretreatment contained levels of membrane-bound enzymes similar to those found in cells isolated from fresh white matter. There was, however, some loss of soluble protein. Studies of galactocerebroside synthesis in neuronal and oligodendroglial perikarya have shown that the glial cells contain ceramide galactosyltransferase at much higher specific activity than the neurones.     

Effect of carbopol and polyvinylpyrrolidone on the mechanical, rheological, and release properties of bioadhesive polyethylene glycol gels

This study examined the mechanical (hardness, compressibility, adhesiveness, and cohesiveness) and rheological (zero-rate viscosity and thixotropy) properties of polyethylene glycol (PEG) gels that contain different ratios of Carbopol 934P (CP) and polyvinylpyrrolidone K90 (PVP). Mechanical properties were examined using a texture analyzer (TA-XT2), and rheological properties were examined using a rheometer (Rheomat 115A). In addition, lidocaine release from gels was evaluated using a release apparatus simulating the buccal condition. The results indicated that an increase in CP concentration significantly increased gel compressibility, hardness, and adhesiveness, factors that affect ease of gel removal from container, ease of gel application onto mucosal membrane, and gel bioadhesion. However, CP concentration was negatively correlated with gel cohesiveness, a factor representing structural reformation. In contrast, PVP concentration as negatively correlated with gel hardness and compressibility, but positively correlated with gel cohesiveness. All PEG gels exhibited pseudoplastic flow with thixotropy, indicating a general loss of consistency with increased shearing stress. Drug release T_50% was affected by the flow rate of the simulated saliva solution. A reduction in the flow rate caused a slower drug release and hence a higher T_50% value. In addition, drug release was significantly reduced as the concentrations of CP and PVP increased because of the increase in zero-rate viscosity of the gels. Response surfaces and contour plots of the dependent variables further substantiated that various combinations of CP and PVP in the PEG gels offered a wide range of mechanical, rheological, and drug-release characteristics. A combination of CP and PVP with complementary physical properties resulted in a prolonged buccal drug delivery.