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Biomedical subjects

T M Allen

Publications and source records attributed to T M Allen.

At least 127 records · Page 7Linked to original sources
PubMed1987

Characterization of the phospholipid and fatty acid composition of Sendai virus.

The lipid composition of Sendai virus, propagated in chicken eggs, was analyzed by high performance liquid chromatography (HPLC), thin-layer chromatography (TLC), and gas-liquid chromatography (GLC). Phosphatidylcholine was found to be the dominant phospholipid (37.3%) with phosphatidylethanolamine (26.8%) and phosphatidylserine (12.0%) also present in significant amounts. Analysis of the fatty acid methyl esters revealed that the dominant fatty acids in total phospholipid were: C16:0 (17.6%), C18:0 (15.4%), C18:1 (n-9) (22.0%), and C24:0 (6.0%). Cardiolipin, phosphatidylserine, and sphingomyelin contained higher levels of saturated fatty acids relative to phosphatidylinositol, phosphatidylethanolamine, and phosphatidylcholine.

Cardiolipins↗
PubMed1986

Effect of long-term Intralipid administration in mice.

Intralipid was administered intravenously to mice at a level of 2 g kg-1 day-1 for 23 days. No alterations in phagocytic index, liver or spleen size were observed in the chronically injected mice as compared with control mice that received saline injections. Tissue distribution of 0.45 micron multilamellar liposomes of egg phosphatidylcholine:cholesterol (2:1) was similar in mice that had been chronically injected with Intralipid to that in control mice. Mice chronically given the same total amount of phospholipid in the form of 0.2 micron liposomes of phosphatidylcholine:cholesterol (2:1) rather than as a lipid-triglyceride emulsion showed altered tissue distribution of entrapped label with decreased liver uptake and increased splenic uptake, which is indicative of reticuloendothelial blockade. Tissue distribution of [14C]dipalmitoylphosphatidylcholine Intralipid was compared with that of [14C]dipalmitoylphosphatidylcholine 0.2 micron MLV of phosphatidylcholine:cholesterol (2:1). Intralipid was taken up 2- to 3-fold less by liver and 5- to 10-fold less by spleen than liposomes. Blood levels of Intralipid were higher than those of liposomes. [14C]dipalmitoylphosphatidylcholine Intralipid was eliminated from the body at a faster rate than [14C]dipalmitoylphosphatidylcholine liposomes. The lack of reticuloendothelial blockade caused by Intralipid as compared with liposomes appears to be related to its diminished uptake into reticuloendothelial tissues. This diminished uptake may be related to differences in apolipoprotein uptake of Intralipid, which is primarily in the form of a phospholipid monolayer, and liposomes, which have their phospholipid organized into a bilayer.

Absorption↗
PubMed1985

Gangliosides reduce leakage of aqueous-space markers from liposomes in the presence of human plasma.

We have studied the role of glycolipids in reducing leakage of aqueous-space markers from liposomes, composed primarily of egg phosphatidylcholine, in the presence of human plasma. Liposomes were either small unilamellar (SUV) or large unilamellar (LUV). Leakage of liposome contents as affected by the incorporation into the liposomal bilayer of mono-, di-, or trisialogangliosides (GM, GD, GT) at different molar ratios in the presence or absence of cholesterol was examined. Leakage from liposomes decreased with increasing ganglioside sialic acid. Asialogangliosides had no effect on calcein leakage in the presence of plasma. The stabilizing effect of gangliosides and cholesterol was synergistic, and SUV containing 10 mol% GT and 33 mol% cholesterol had a half-life for leakage of calcein in plasma at 37 degrees C approaching 24 hours. LUV in the presence of plasma retained their contents longer than SUV, and gangliosides had an additional stabilizing effect. Phosphatidylserine and sulfatides were also capable of substituting for gangliosides in stabilizing liposomes to plasma-induced leakage. It appears that gangliosides stabilize liposomes in plasma at least in part through their ability to impart surface negative charge.

Blood Proteins↗
PubMed1985

Liver pathology accompanying chronic liposome administration in mouse.

Particulate drug carriers have a pronounced tendency to localize in the mononuclear phagocyte system and chronic administration of such carriers can result in reticuloendothelial (RE) blockade. In a previous study (Allen et al., J. Pharmacol. Exp. Therap., 229, 267, 1984) we have examined the ability of chronic i.v. administration of liposomes of a variety of compositions to cause RE blockade in mice. In this communication we report on the time course of histological changes in liver accompanying chronic liposome administration in samples collected at the time of our previous studies. The predominant histological feature was the appearance of a granulomatous reaction in liver. Granulomas were frequent in liver tissue of mice receiving 2 or more injections of sphingomyelin:phosphatidylcholine, 4:1 or distearoylphosphatidylcholine:cholesterol, 1:1 liposomes, but disappeared shortly after termination of liposome injections. In mice receiving phosphatidylcholine:cholesterol, 2:1 liposomes no granulomas in liver were apparent during the injection course (10 injections of 2 mg phospholipid each over 25 days) but granulomatous inflammation of the liver became apparent 2 weeks after the last injection and had not resolved by 9 weeks post-injection. The appearance of granulomas was correlated with depression of phagocytic index and their disappearance was correlated with normalization or stimulation of reticuloendothelial function. These observations may be related to the rate of phospholipid metabolism for the various phospholipid types or to the nature of phospholipid metabolites.

Animals↗
PubMed1985

alpha-Glucosidase-albumin conjugates: effect of chronic administration in mice.

Enzyme albumin conjugates have been proposed as a means of increasing the efficacy of enzyme use in vivo and decreasing immune response to the enzyme. Particulate drug carriers, however, have a pronounced tendency to localize in the mononuclear phagocyte (reticuloendothelial) system. We have examined in mice the effect on phagocytic index, tissue distribution and organ size of continued administration of conjugates of alpha-glucosidase with either homologous or heterologous albumin. Mice received 10 X 2-mg injections of bovine serum albumin (BSA) or mouse serum albumin (MSA), either free, polymerized or conjugated with alpha-glucosidase. Experiments involving BSA had to be terminated before the end of the experiment because of anaphylaxis, but these reactions were less severe to the polymerized albumin than to free albumin. Free BSA, BSA polymer and BSA-enzyme conjugates all caused a decrease in phagocytic index after six injections. Mice receiving MSA showed no evidence of anaphylaxis, but mice receiving six or more injections of free MSA, MSA polymer or MSA-enzyme conjugate had significantly decreased phagocytic indices as compared to controls. Phagocytic indices had returned to normal by 7 days after the final injection. Tissue distribution of 125-I-labeled albumin preparations was determined in either naive or chronically injected mice.

Animals↗
PubMed1984

Chronic liposome administration in mice: effects on reticuloendothelial function and tissue distribution.

Liposomes have a pronounced tendency to localize in the reticuloendothelial (RE) system, a major host defense system. We have examined, in mice, the effect of chronic i.v. administration of low to moderate liposome doses on drug metabolism, phagocytic index and spleen and liver size. Little effect on the rate of pentobarbital metabolism was noted, except when mice received 80 mg/kg of sphingomyelin-containing liposomes in a series of 10 injections over 3.5 weeks. Impairment of RE phagocytic function was found to be related to liposome size and composition, size and frequency of liposome dose and the presence of lipid peroxides. The effects on tissue distribution of liposome-entrapped [14C]sucrose was also determined in mice receiving chronic liposome injections. In RE blockaded mice there was a consistent trend in favor of decreased liver uptake and increased spleen uptake. No significant uptake of liposome contents was seen in non-RE tissues even in mice with severe RE blockade, indicating that the induction of RE blockade by predosing with empty liposomes may not be a successful strategy for increasing liposome uptake to non-RE tissues. Liver to spleen ratios of [14C]sucrose appeared to be a sensitive method for quantitating RE blockade. Sphingomyelin-containing liposomes produced the greatest RE blockade, distearoylphosphatidylcholine-cholesterol liposomes were intermediate and egg phosphatidylcholine-cholesterol liposomes produced the least impairment in RE function. Liposomes which contained 1% vitamin E as an antioxidant had slightly less effect on RE function than liposomes not containing vitamin E.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Lipid-protein interactions of reconstituted membrane-associated adenosinetriphosphatases. Use of a gel-filtration procedure to examine phospholipid-activity relationships.

A gel-filtration procedure is described for the reconstitution of partially delipidated membrane adenosinetriphosphatases (Mg2+-ATPase and (Na+ + K+)-ATPase) into liposomes of defined composition. After detergent solubilization of membrane enzyme preparations, reconstitution of these ATPases was achieved by the rapid removal of deoxycholate by Sephadex G-50 chromatography. Proteoliposomes were separated from unincorporated enzyme by chromatography on Sepharose CL-4B. Sedimentation characteristics in sucrose density gradients and electron microscopy confirmed that both Mg2+-ATPase and (Na+ + K+)-ATPase were reconstituted into liposomes of phosphatidylcholine and yielded preparations having high recoveries of enzyme activity by comparison with the control membrane preparations. Reconstitution of (Na+ + K+)-ATPase into synthetic phosphatidylcholines of defined fatty acid composition reveals an inverse relationship between enzyme activity and the chain length of the saturated fatty acids DMPC, DPPC and DSPC. Higher recoveries were obtained when one or more fatty acid chains was unsaturated. Full reactivation occurred with DOPC (18:1/18:1). There was a positive correlation between the specific activity of reconstituted (Na+ + K+)-ATPase and the temperature of the thermal phase transition of the synthetic phosphatidyl cholines studied. This was not seen with Mg2+-ATPase. It is suggested that 'membrane fluidity' influences the catalytic activity of (Na+ + K+)-ATPase but not that of Mg2+-ATPase.

Adenosine Triphosphatases↗
PubMed1983

Effect of liposome size and drug release properties on pharmacokinetics of encapsulated drug in rats.

The organ distribution and half-life in blood of liposome-entrapped [14C]sucrose was examined in rats for two compositions of liposomes having widely differing drug release properties as determined by an in vitro assay in the presence of serum at 37 degrees C. The liposomes were composed of 1) egg phosphatidylcholine-cholesterol, 2:1 molar ratio and of 2) bovine brain sphingomyelin-phosphatidylcholine, 4:1 molar ratio. The two types of liposome were determined to have half-lives for release of contents in vitro in the presence of serum of 2.6 and 35 hr, respectively. Organ distribution and blood values were followed with time for small unilamellar, multilamellar and reverse-phase evaporation liposomes of both compositions. Free [14C]sucrose was almost totally eliminated from rats within 0.5 hr of injection. Liposome-entrapment increased the circulation time of sucrose in vivo in the following order: small unilamellar greater than reverse-phase evaporation greater than multilamellar liposomes. For all sizes of liposomes, the composition with slower leakage as determined by in vitro assay (sphingomyelin-phosphatidylcholine, 4:1) resulted in significantly longer half-lives in blood and in whole body. Liposomes containing sphingomyelin were taken up by liver to a lesser extent and by spleen to a greater extent than phosphatidylcholine-cholesterol liposomes of all sizes.

Animals↗
PubMed1982

Skeletal changes associated with copper deficiency.

Copper deficiency has been described in premature infants on hyperalimentation. The bony abnormalities are generalized and are usually associated with anemia and neutropenia. These changes present with normal serum levels of iron, ascorbic acid, calcium, phosphorus, and magnesium, as well as with depressed levels of copper and ceruloplasmin. They appear at about three to nine months of age in infants with a low birth weight who are receiving total parenteral nutrition, but can be prevented by greater than normal maintenance levels of copper supplements. Established bone changes improve rapidly after the administration of therapeutic supplements.

Copper↗
PubMed1981

Liposome-cell interactions. A study of the interactions of liposomes containing entrapped anti-cancer drugs with the EMT6, S49 and AE1 (transport-deficient) cell lines.

A study has been made to determine if the cytotoxicity observed when cells in culture were exposed to liposome-entrapped cytotoxic drugs was liposome mediated or resulted from leakage of drug from the liposomes with subsequent uptake of free drugs by the cells. In preliminary experiments with the EMT6 cell line in monolayer culture, the cytotoxicity observed when the cells were exposed to a range of concentrations of liposome-entrapped methotrexate, actinomycin D and cytosine arabinoside for a variety of liposome compositions was somewhat less than that observed when the cells were exposed to similar concentrations of free drug. We suspected that the cytotoxicity was mediated via uptake of free drug leaked from liposomes. This was confirmed in experiments involving the EMT6 and S49 cell lines in monolayer or suspension culture, respectively, in the absence and presence of the nucleoside transport inhibitor, 6-(4-nitrobenzyl)thio)-9-beta-D-ribofuranosylpurine. Additional experiments were performed in a transport-deficient mutant of the S49 cell line, the AE1 cell line. No evidence for liposome-mediated cell death could be found in these cell lines when tubercidin 5'-monophosphate was entrapped in either large or small unilamellar liposomes composed of egg phosphatidylcholine/cholesterol (2 : 1), bovine brain phosphatidylserine/egg phosphatidylcholine/cholesterol (8 : 2 : 5) or egg phosphatidylcholine/stearylamine/cholesterol (10 : 1 : 5). Considerable toxicity due to empty liposomes of a variety of compositions was observed in the S49 cell line at high lipid concentrations.

Animals↗
PubMed1981

A study of phospholipid interactions between high-density lipoproteins and small unilamellar vesicles.

Previous observations on serum-induced leakage of liposome contents from egg phosphatidylcholine liposomes (Allen, T.M. and Cleland, L.G. (1980) Biochim. Biophys, Acta 597, 418--426) have been extended in order to examine the role of the phase transition and phospholipid backbone in leakage. The high-density lipoprotein (HDL) fraction has been purified from human serum and the rate of transfer of radioactively labelled phospholipids from sonicated liposomes to high-density lipoproteins has been examined. Results obtained from the calcein dequenching method for serum-induced leakage of liposome contents showed that as the proportion of solid phospholipid (distearoyl phosphatidylcholine, Tc = 56 degrees C) increased, relative to the proportion of egg phosphatidylcholine, the half-time for retention of liposome contents at 37 degrees C in the presence of serum also increased. Including increasing amounts of bovine brain sphingomyelin (Tc = 30 degrees C) in egg phosphatidylcholine liposomes also substantially decreased leakage from liposomes in the presence of serum at 37 degrees C. 14C-labelled egg phosphatidylcholine was found to transfer readily from liposomes to purified HDL, as did 14C-labelled dioleoyl phosphatidylcholine. Including cholesterol in egg phosphatidylcholine liposomes decreased the rate of transfer of phospholipid to HDL. 14C-labelled distearoyl phosphatidylcholine did not exchange readily with HDL. These results are consistent with the interpretation that tightening bilayer packing prevents the apolipoprotein-mediated transfer of phospholipid to HDL and slows the leakage of liposome contents associated with this transfer. [14C]Sphingomyelin also did not exchange readily with HDL. This does not appear to be a phase transition effect as the majority of sphingomyelin is above its phase transition at 37 degrees C. The failure of sphingomyelin to exchange readily with HDL is interpreted as being due to intermolecular hydrogen bonding between the sphingosine backbones of the sphingomyelin molecule.

Animals↗
PubMed1980

Studies of synthetic peptide analogs of the amphipathic helix. Effect of charged amino acid residue topography on lipid affinity.

The amphipathic helix hypothesis for plasma lipoproteins was investigated using synthetic peptides. The lipid-associating properties of two potentially amphipathic model peptides and two analogs were studied by incubating synthetic peptides with small unilamellar vesicles and protein-lipid association examined by equilibrium density centrifugation, leakage of liposome-entrapped fluorescence compounds, intrinsic tryptophan fluorescence, and circular dichroism spectroscopy. The analog peptides were designed to determine the significance of the number and specific location of the charged residues in amphipathic domains of plasma lipoproteins to protein-lipid association. Based on the four procedures used to examine protein-lipid interactions, the two model peptides (18Aa, 18As) were found to associate strongly with liposomes; the two analog peptides (18As1, 18Asr), differing only with respect to the number and/or position of their charged residues, failed to demonstrate similar lipid binding properties. These findings support the earlier suggestions of the importance of the charged residues, but do not define the precise mechanisms involved. Such amino acids may help initiate the lipid-protein association by electrostatic interactions, contribute to the hydrophobicity of the nonpolar face of the helix by the acyl portion of lysine and arginine, and/or complement the charge distribution in the polar head regions of the phospholipid molecules.

Amino Acid Sequence↗
PubMed1980

Detergent removal during membrane reconstitution.

Efficiency of detergent removal during the course of several different procedures for membrane protein reconstitution was examined. Reconstitution methods studied include ethanol injection-dialysis, detergent dialysis and detergent-gel filtration. In the ethanol injection-dialysis method, approx. 70 molecules of ethanol per 1000 molecules of phospholipid are retained even after extensive (150 h) dialysis. Efficiency of detergent removal by dialysis depends on the detergent. However, even for sodium deoxycholate, a detergent possessing a large critical micelle concentration, there are approx. 7 molecules of deoxycholate per 1000 molecules of phospholipid retained by the bilayer even after extensive (310 h) dialysis. Detergent removal by gel filtration (Sephadex G-200 or G-50) of deoxycholate, cholic acid and Triton X-100 is more efficient than removal by dialysis; as few as 10 molecules of deoxycholate are retained per 100 molecules of phospholipid after one column passage, taking only a few hours. Ethanol was less efficiently removed by one passage over a Sephadex column than by extensive dialysis. Removal of Triton X-100 by passage over, or dialysis against, Biobeads SM-2 resulted in a similar level of detergent retention to that found by passage over Sephadex G-200 or G-50. Utilizing gel-filtration techniques, we have examined the competition for the hydrophobic peptide of glycophorin, T(is), between sodium deoxycholate and a series of phospholipids as a possible means of obtaining a quantitative measure of protein-lipid affinity. On the basis of these preliminary studies we conclude that the T(is) peptide has a relative lipid affinity of phosphatidylinositol > phosphatidylcholine > phosphatidylserine.

Chromatography, Gel↗
PubMed1980

Serum-induced leakage of liposome contents.

Efflux of contents from small unilamellar vesicles of various compositions, conaining a highly quenched fluorescent compound (calcein, 175 mM) was determined as a function of temperature in the presence and absence of human serum. Efflux of calcein from the liposomes was monitored as an increase in fluorescence as calcein became dequenched upon release from the liposomes. The presence of serum significantly increased liposome leakage in all cases. Incorporation of increasing molar ratios of cholesterol into liposomes reduced leakage of calcein from liposomes incubated with buffer and with serum. Leakage was significantly faster from liposomes with an osmotic gradient across the membrane (higher inside) than from equiosmolar liposomes. The leakage of [14C]sucrose from egg lecithin liposomes at 37 degrees C was also dramatically increased in the presence of serum.

Blood↗
PubMed1975

Scanning electron microscopy of the electric tissue of Narcine brasiliensis.

The anatomy of electroplaques of Narcine brasiliensis has been studied by scanning electron microscopy. The ventral faces of the plaques are innervated with an abundance of branching nerves in close contact with the underlying (postsynaptic) membrane. Large numbers of troughs and evaginations of the postsynaptic membrane serve to increase its surface area. Fibroblasts are closely associated with the dorsal faces which appear covered with a matrix of fibrous material. Well-washed dorsal surfaces of single electroplaques are free of this matrix. The dorsal surface area is considerably increased by tubules extending into, and projections out of, the surface.

Animals↗