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Biomedical subjects

M J Poznansky

Publications and source records attributed to M J Poznansky.

At least 55 records · Page 3Linked to original sources
PubMed1983

Phospholipid synthesis in the squid giant axon: enzymes of phosphatidylinositol metabolism.

We examined the properties of several enzymes of phospholipid metabolism in axoplasm extruded from squid giant axons. The following synthetic enzymes, CDP-diglyceride: inositol transferase (EC 2.7.8.11), ATP:diglyceride phosphotransferase, diglyceride kinase (EC 2.7.2.-), and phosphatidylinositol kinase (EC 2.7.1.67), were all present in axoplasm. Phospholipid exchange proteins, which catalyzed the transfer of phosphatidylinositol and phosphatidylcholine between membrane preparations and unilamellar lipid vesicles, were also found. However, we did not find conditions under which the synthesis of CDP-diglyceride, phosphatidylserine, and phosphatidylinositol-4,5-diphosphate could be measured. Subcellular fractionation by differential centrifugation showed that the axoplasmic inositol transferase and phosphatidylinositol kinase activities were largely "microsomal," while the diglyceride kinase and exchange protein activities were primarily "cytosolic."

1-Phosphatidylinositol 4-Kinase↗
PubMed1982

Cholesterol movement between human skin fibroblasts and phosphatidylcholine vesicles.

Cholesterol readily exchanges between human skin fibroblasts and unilamellar phospholipid vesicles. Only a fraction of the exchangeable cholesterol and only 10-15% of the total cellular free cholesterol is available for net movement or depletion to cholesterol-free phosphatidylcholine vesicles. [14C]Cholesterol introduced into the fibroblast plasma membrane by exchange from lipid vesicles does not readily equilibrate with fibroblast cholesterol labelled endogenously from [3H]mevalonic acid. While endogenously-synthesized [3H]cholesterol readily becomes incorporated into a pool of esterified cholesterol, little, if any, of the [14C]cholesterol introduced into the fibroblast membrane by exchange from lipid vesicles becomes available for esterification. We interpret these findings as suggesting that: (1) net cholesterol movement from fibroblasts to an acceptor membrane is limited to a small percentage of the plasma membrane cholesterol, and (2) separate pools of cholesterol exist in human skin fibroblasts, one associated with the plasma membrane and the second associated with intracellular membranes, and equilibration of cholesterol between the two pools is a very limited process.

Carbon Radioisotopes↗
PubMed1982

Advantages in the use of L-asparaginase-albumin polymer as an antitumor agent.

Polymeric conjugates of L-asparaginase and an excess of homologous albumin were compared with free L-asparaginase for antitumor activity using a mouse model 6C3HED lymphosarcoma and a human pancreatic tumor cell line, PANC-1. The asparaginase-albumin polymer is more resistant to proteolytic degradation compared to equivalent amounts of free enzyme and is more effective as an antitumor agent in prolonging survival of C3H/HeJ mice receiving 6C3HED lymphosarcoma. In terms of antitumor activity, the enzyme is approximately 20 times more effective, compared to free enzyme, when given in polymeric form with albumin. Similarly, the polymeric form of L-asparaginase is more effective in inhibiting cell growth of human pancreatic tumor cells grown in tissue culture. The increased effectiveness of the polymeric form of L-asparaginase is probably related to its resistance to biodegradation. The use of cell surface-specific monoclonal antibodies to target the polymer to tumor cells is also demonstrated.

Albumins↗
PubMed1981

Antibody-mediated targeting of alpha-1,4-glucosidase-albumin polymers to rat hepatocytes. A model for enzyme therapy.

Chemically cross-linking alpha-1,4-glucosidase, homologous albumin and antibody (immunoglobulin G, IgG) molecules raised against isolated rat hepatocytes yields an active and stable soluble enzyme-polymer complex of mol.wt. approx. 10(6). After intravenous injection, the 125I-labelled complex is seen to be preferentially associated with hepatocytes when compared with labelled free alpha-1,4-glucosidase, enzyme-albumin polymers without IgG or polymer linked to a non-specific IgG molecule, all of which are associated to a much larger extent with the Kupffer cells. The procedure offers several advantages for targeting of enzymes to specific tissues and cells and for the possible lowering of hepatocyte glycogen content in Type II glycogenesis (Pompe's disease).

Animals↗
PubMed1981

Transbilayer movement of 24Na in sonicated phosphatidylcholine vesicles exposed to frequency-modulated microwave radiation.

Sonicated egg phosphatidylcholine vesicles loaded with 24Na+ were exposed at 20mW to a frequency-modulated (3 Hz) microwave field in the range of 2350 to 2550 MHz, or at 80 mW to a 2450-MHz CW (continuous wave) field, in a waveguide. The vesicle suspension absorbed microwaves at about 1 mW/ml and 25 mW/ml (CW experiment). The average temperature change of the irradiated suspension was less than 0.1 degree C from ambient. Leakage of 24Na+ from the vesicles for up to 19 hours was measured. No difference was noted in the movement of 24Na+ from the vesicles in the irradiated and control dispersions.

Animals↗
PubMed1981

Lipid vesicle-mediated alterations of membrane cholesterol levels: effects on Na+ and K+ currents in squid axon.

We demonstrate that cholesterol can exchange from sonicated lipid vesicles to a perfused squid axon membrane and that vesicles with varying cholesterol/phospholipid (C/P) mole ratios can be used to achieve either net loading or net depletion of axon membrane cholesterol. Two types of evidence were obtained which show that net loading or depletion of cholesterol was achieved: (i) changes in the cholesterol/phospholipid (C/P) mole ratios of axons, and (ii) visualization of cholesterol depleted from the preparation by cholesterol-free vesicles by thin-layer chromatography. The C/P mole ratios indicate that cholesterol levels in the preparation were increased or decreased by 30-40%. Increasing or decreasing membrane cholesterol levels were ineffective in altering the Na+ or K+ occurrents in voltage-clamped axons. In addition, we determined that cholesterol "flip-flop" across the axonal membrane occurred with a t 1/2 of 7.3 to 15.3 min.

Animals↗
PubMed1980

Enhanced anti-inflammatory effect and reduced immunogenicity of bovine liver superoxide dismutase by conjugation with homologous albumin.

Bovine liver superoxide dismutase (SOD) can be cross-linked to albumin to form soluble conjugates with up to 70% retention of original enzyme activity. These conjugates have markedly prolonged plasma half-times of enzymatic activity (15 h) compared to native SOD (6 min). The conjugates have potent anti-inflammatory effects in vivo and reduced immunogenicity and antigenicity compared to native SOD. These conjugates provide new possibilities for the study of inflammation and its treatment.

Albumins↗
PubMed1980

alpha1,4-Glucosidase-albumin polymers: in vitro properties and advantages for enzyme replacement therapy.

Soluble polymers of rat (or human) albumin and alpha-1,4-glucosidase are prepared using the cross-linking agent glutaraldehyde. The resulting polymer has an average molecular weight of 800 000 indicating an average composition of 12 albumin molecules for each enzyme molecule. Compared with an equivalent amount of free enzyme, the enzyme-albumin polymer has an increased resistance to heat denaturation (half-life of 15 h compared with 1 h for free enzyme at 37 degrees C) and to proteolysis by trypsin (half-life of 180 min compared with 10 min). The high degree of resistance to bioinactivation of the enzyme-albumin polymer is discussed in relation to requirements for enzyme replacement therapy in a range of metabolic diseases including type II glycogenosis (Pompe's disease) where alpha-1,4-glucosidase is the defective enzyme.

Animals↗
PubMed1979

Cholesterol exchange as a function of cholesterol/phospholipid mole ratios.

The activation energy (Ea) for cholesterol exchange between dioleoyl phosphatidylcholine vesicles and erythrocyte 'ghosts' is measured as a function of molar percentage of cholesterol in both donor and acceptor membranes. A sharp increase in Ea occurs (from 39.9kJ/mol to 84kJ/mol) when the molar percentage of cholesterol decreases from 30 to 20%.

Cholesterol↗
PubMed1979

Liposomes: a new approach to gold therapy?

Gold sodium thiomalate (GST) can be encapsulated in egg phophatidyl choline (and cholesterol) vesicles. Leakage from vesicles at room temperature is negligible allowing storage for at least 6 days prior to use. Intravenous injection of GST encapsulated in egg phosphatidyl choline vesicles results in: 1) delayed blood clearance, 2) enhanced uptake by the liver and spleen, 3) reduced uptake by the kidney, 4) reduced 24 hr urine excretion, and 5) enhanced uptake by inflamed tissues compared to free GST given by the same route. Thus, our preliminary findings suggest that egg phosphatidyl choline vesicles may be a suitable carrier of GST for parenteral administration.

Animals↗
PubMed1978

Immunogenicity and antigenicity of soluble cross-linked enzyme/albumin polymers: Advantages for enzyme therapy.

Soluble cross-linked polymers of hog-liver uricase and an excess of either rabbit or dog albumin were injected repeatedly into rabbits in order to determine their antigenicity and immunogenicity. Whereas the enzyme in its free form induces antibody production, homologous albumin polymerised with the enzyme renders the complex non-immunogenic and non-antigenic. Dog-albumin/uricase polymers injected into rabbits induce antibody formation against the dog albumin but not against the uricase. The results suggest an important advantage of these soluble enzyme polymers in enzyme-replacement therapy.

Albumins↗
PubMed1978

Transbilayer movement of cholesterol in phospholipid vesicles under equilibrium and non-equilibrium conditions.

1. The exchange of [3H] cholesterol between phospholipid: cholesterol vesicles and an excess of red cell ghosts is examined. 2. Using a number of different phophatidylcholines, only the cholesterol thought to be associated with the outer half of the bilayer (about 70 percent) is available for exchange, suggesting that at least at equilibrium the transbilayer movement of cholesterol or "flip-flop", occurs very slowly, if it occurs at all. 3. The rate of exchange of cholesterol between the vesicles and the ghosts is dependent on the nature of the fatty acid chain of the phospholipids, being a function of both the fatty acid chain length and the degree of unsaturation. 4. Under non-equilibrium conditions, when cholesterol is being both exchanged and depleted from the lipid vesicles to red cell ghosts, the previously non-exchangeable vesicle cholesterol becomes available for exchange, suggesting that under these conditions "flip-flop" can occur.

Biological Transport↗
PubMed1977

Transmembrane movement of cholesterol in human erythrocytes.

We studied the exchange of cholesterol between radioactively labeled plasma and human erythrocytes. Results from experiments in which [3H]cholesterol and [14C]-cholesterol were exchanged sequentially into the cells and back out into unlabeled plasma, showed that transmembrane movement of cholesterol occurred with a half-time that was either less than 50 min or greater than 10 days. To obtain further information about the transmembrane movement of cholesterol, we used a technique [Jacobson, B. S. & Branton, D. (1977) Science 195, 302-304] for exposure of the cytoplasmic surface of erythrocyte membranes. This method involved the ionic attachment of erythrocytes to derivatized glass beads followed by disruption of the cells, leaving the beads covered by membrane with the cytoplasmic surface exposed [3H]Cholesterol was exchanged into intact erythrocytes which then were attached to beads. The beads with attached membrane were incubated with phospholipid-cholesterol vesicles and the exchange of cholesterol between the membrane cytoplasmic surface and vesicles was studied. We found that [3H]cholesterol was present at the cytoplasmic surface, indicating that transmembrane movement of cholesterol had occurred within the 2.5 hr required to complete the experiment. This result suggests that the more rapid rate of transmembrane cholesterol movement, inferred from the experiments described above, is the one that applies.

Biological Transport↗