Blood soluble drag-reducing polymers prevent lethality from hemorrhagic shock in acute animal experiments

Over the past several decades, blood-soluble drag reducing polymers (DRPs) have been shown to significantly enhance hemodynamics in various animal models when added to blood at nanomolar concentrations. In the present study, the effects of the DRPs on blood circulation were tested in anesthetized rats exposed to acute hemorrhagic shock. The animals were acutely resuscitated either with a 2.5% dextran solution (Control) or using the same solution containing 0.0005% or 5 parts per million (ppm) concentration of one of two blood soluble DRPs: high molecular weight (MW=3500 kDa) polyethylene glycol (PEG-3500) or a DRP extracted from Aloe vera (AVP). An additional group of animals was resuscitated with 0.0075% (75 ppm) polyethylene glycol of molecular weight of 200 kDa (PEG-200), which possesses no drag-reducing ability. All of the animals were observed for two hours following the initiation of fluid resuscitation or until they expired. We found that infusion of the DRP solutions significantly improved tissue perfusion, tissue oxygenation, and two-hour survival rate, the latter from 19% (Control) and 14% (PEG-200) to 100% (AVP) and 100% (PEG-3500). Furthermore, the Control and PEG-200 animals that survived required three times more fluid to maintain their blood pressure than the AVP and PEG-3500 animals. Several hypotheses regarding the mechanisms underlying these observed beneficial hemodynamic effects of DRPs are discussed. Our findings suggest that the drag-reducing polymers warrant further investigation as a potential clinical treatment for hemorrhagic shock and possibly other microcirculatory disorders.     

Cowpea mosaic virus chimeric particles bearing the ectodomain of matrix protein 2 (M2E) of the influenza a virus: Production and characterization

The epitope presentation system for the ectodomain of the M2 protein (M2e) of the influenza A virus was constructed on the basis of the cowpea mosaic virus (CPMV) for expression in the plant Vigna unguiculata. CPMV is widely used as a vector to produce immunogenic chimeric virus particles (CVPs) bearing epitopes of various infectious human and animal pathogens. To produce chimeric CPMV particles in plants, two binary vectors were constructed to bear a modified gene coding for the CPMV S-coat protein with insertions of M2e epitopes of human influenza and bird influenza viruses. Antigenic and immunogenic properties of CVPs were investigated in mice immunization experiments. CVPs were shown to induce anti-M2e IgG production and to partly protect mice against a challenge with low doses of the influenza virus. However, low infectivity and immunogenicity of chimeric CPMV particles indicate that the plant virus-based systems for M2e epitope presentation requires further optimization in order to use plants as a possible source of flu vaccines.     

Post-translational modification of low molecular mass GTP-binding proteins by isoprenoid

Several proteins in mammalian cells are modified post-translationally by the isoprenoid, farnesol. Incubation of cultured cells with [3H]mevalonate, an isoprenoid precursor, results in the labeling of multiple polypeptides, the most prominent of which migrate in the range of 21-26 kDa on sodium dodecyl sulfate-polyacrylamide gels. In Rat-6 fibroblasts transformed by H-ras, one of the farnesylated proteins was identified as p21ras by two-dimensional immunoblotting. However, this protein accounted for only a small proportion of the [3H]mevalonate-derived radioactivity incorporated into 21-26-kDa proteins. Murine erythroleukemia cells, which did not express immunodetectable quantities of p21ras, contained several 21-26-kDa farnesylated proteins distributed in both the cytosolic and particulate fractions. At least eight of these proteins were capable of binding [alpha-32P]GTP on nitrocellulose membranes. Pulse-chase studies showed that the isoprenoid modification did not necessarily result in the translocation of the cytosolic proteins to the cell membrane. A prominent group of carboxyl-methylated proteins in murine erythroleukemia cells overlapped with the 21-26-kDa farnesylated proteins on one-dimensional sodium dodecyl sulfate gels. Methylation of this group of proteins was selectively abolished when cells were treated with lovastatin, an inhibitor of isoprenoid synthesis. Addition of exogenous mevalonate to the lovastatin-treated cells fully restored carboxyl methylation. These studies suggest that the 21-26-kDa farnesylated proteins in mammalian cells are members of a recently discovered family of low molecular mass GTP-binding proteins which, although ras-related, appear to be distinct structurally and possibly functionally from the products of the ras genes. The observed isoprenoid-dependent carboxyl methylation of a group of 21-26-kDa proteins suggests that the low molecular mass GTP-binding proteins may undergo a series of post-translational C-terminal cysteine modifications (i.e. farnesylation, carboxyl methylation) analogous to those recently elucidated for p21ras.     

Post-translational isoprenylation of cellular proteins is altered in response to mevalonate availability

Cells incorporate isoprenoid products derived from mevalonate (MVA) into several unique proteins. The aim of this study was to delineate the effects of blocking MVA synthesis on the covalent isoprenylation of these proteins in murine erythroleukemia cells. Inhibition of protein synthesis with cycloheximide prevented the incorporation of [3H]MVA into proteins, suggesting that isoprenylation normally occurs immediately after synthesis of the polypeptides. However, incubation of cells with lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, for as little as 1 h prior to addition of cycloheximide rendered the isoprenylation step insensitive to cycloheximide. Lovastatin had no apparent effect on the stability of the isoprenylated proteins, but the development of cycloheximide insensitivity during the lovastatin preincubation was dependent on synthesis of new protein during that period. Addition of 50-200 microM MVA to the culture medium eliminated the effects of preincubation with lovastatin. Preincubation of cells with 25-hydroxycholesterol, which suppresses the synthesis and enhances the degradation of HMG-CoA reductase but is not a competitive enzyme inhibitor, did not induce cycloheximide-insensitivity of the isoprenylation reaction. The results suggest that blocking MVA synthesis with lovastatin causes a rapid depletion of isoprenoid groups available for protein modification. Consequently, there is an accumulation of non-isoprenylated substrate proteins. Shifts in the ratio of modified vs. unmodified proteins in response to MVA availability may have implications for the changes in cell morphology, cell proliferation and HMG-CoA reductase gene expression that occur when cells are subjected to MVA deprivation.