Structural and functional comparisons of pH-sensitive liposomes composed of phosphatidylethanolamine and three different diacylsuccinylglycerols

The titratable, double-chain amphiphiles 1,2-dipalmitoyl-sn-3-succinylglycerol (1,2-DPSG), 1,2-dioleoyl-sn-3-succinylglycerol (1,2-DOSG) and 1,3-dipalmitoylsuccinylglycerol (1,3-DPSG) have been used in combination with phosphatidylethanolamine (PE) to form pH-sensitive liposomes. The effect of the compounds on dielaidoyl PE bilayer stabilization was examined by differential scanning calorimetry. Only 1,2-DPSG showed bilayer stabilization activity; whereas the other two are destabilizers at pH 7.4. All three amphiphiles became strong destabilizers at pH 5.0. The ability of the amphiphiles to stabilize DOPE liposomes was examined by light scattering and calcein entrapment. In general, 1,2-DPSG is the most potent stabilizer of PE bilayers while 1,3-DPSG is the weakest liposome stabilizer. All three compounds can be combined with DOPE to generate liposomes which are stable at neutral and basic pH. At weakly acidic pH, the liposomes are leaky and exhibit extensive lipid mixing, with protons and calcium showing synergistic effects on lipid mixing. DOPE/1,2-DPSG liposomes are stable in human plasma and remain acid-sensitive even after prolonged plasma incubation. Immunoliposomes prepared from either DOPE/1,2-DPSG or DOPE/1,2-DOSG can deliver diphtheria toxin A fragment to the cytoplasm of cultured cells in a process which involves endocytosis of the liposomes. Immunoliposomes prepared with 1,2-DPSG are more effective drug carriers than those prepared with 1,2-DOSG. These results indicate that the bilayer- and, hence the liposome-stabilization activity of the diacylsuccinylglycerol depends on the structure of the compounds. The potential drug delivery activity of the pH-sensitive liposomes composed of these lipids is discussed.

[Sedative-hypnotic effect of caulis Polygoni multiflori decoction]

The sedative-hypnotic effect of Caulis Polygoni multiflori decoction (CPMD) was studied by the rolling cylinder method in mice and by the somnopolygraphic recording method in rats. The result from the rolling method in mice showed that CPMD (9g/kg) did have synergic action with the subthreshold hypnotic dose of sodium pentobarbital (20mg/kg). The result from the somnopolygraphic recording experiment showed that the immediate hypnotic effect of an effective dose of CPMD (20g/kg) was basically similar to that of diazepam (5mg/kg) used under the same experimental condition, chiefly an increase in the duration of slow wave sleep phase (SWS) and a decrease in the duration of paradoxical sleep phase (PS). By the end of a three-day session in dose of twice a day the hypnotic effect appeared more prominent and the reduction of SWS latency became significant.

Cellulose digestion and cellulase regulation and distribution in Fibrobacter succinogenes subsp. succinogenes S85

Fibrobacter succinogenes subsp. succinogenes S85 initiated growth on microcrystalline cellulose without a lag whether inoculated from a glucose, cellobiose, or cellulose culture. During growth on cellulose, there was no accumulation of soluble carbohydrate. When the growth medium contained either glucose or cellobiose in combination with microcrystalline cellulose, there was a lag in cellulose digestion until all of the soluble sugar had been utilized, suggesting an end product feedback mechanism that affects cellulose digestion. Cl-stimulated cellobiosidase and periplasmic cellodextrinase were produced under all growth conditions tested, indicating constitutive synthesis. Both cellobiosidases were cell associated until the stationary phase of growth, whereas proteins antigenically related to the Cl-stimulated cellobiosidase and a proportion of the endoglucanase were released into the extracellular culture fluid during growth, irrespective of the substrate. Immunoelectron microscopy of cells with a polyclonal antibody to Cl-stimulated cellobiosidase as the primary antibody and 10-nm-diameter gold particles conjugated to goat anti-rabbit antibodies as the second antibody revealed protrusions of the outer surface which were selectively labeled with gold, suggesting that Cl-stimulated cellobiosidase was located on the protrusions. These data support the contention that the protrusions have a role in cellulose hydrolysis; however, this interpretation is complicated by reactivity of the antibodies with a large number of other proteins that possess related antigenic epitopes.

Antigenic nature of the chloride-stimulated cellobiosidase and other cellulases of Fibrobacter succinogenes subsp. succinogenes S85 and related fresh isolates

Polyclonal and monoclonal antibodies to the Cl-stimulated cellobiosidase of Fibrobacter succinogenes subsp. succinogenes S85 reacted with numerous proteins of both higher and lower molecular weights from F. succinogenes subsp. succinogenes S85, but not with Escherichia coli proteins, and only one protein each from Butyrivibrio fibrisolvens and Ruminococcus albus. Different profiles were observed for Western blots (immunoblots) of peptide digests of both the purified enzyme from F. succinogenes and immunoreactive proteins of higher and lower molecular weights, demonstrating that they were different proteins. Therefore, F. succinogenes appeared to produce numerous proteins with one or more common antigenic determinants. However, with the exception of Cl-stimulated cellobiosidase, none were cellulases that have been characterized. An affinity-purified polyclonal antibody to Cl-stimulated cellobiosidase reacted with numerous proteins in cells of each of three fresh isolates of F. succinogenes subsp. succinogenes and one of F. succinogenes subsp. elongata when analyzed by Western blotting. Antibodies to periplasmic cellodextrinase, endoglucanase 2 (EG2), and EG3, when reacted in Western blots with the various cellulases, including Cl-stimulated cellobiosidase, revealed limited antigenic similarity among the different proteins and none with either B. fibrisolvens or R. albus proteins. The periplasmic cellodextrinase antibody reacted with an antigen with a size corresponding to cellodextrinase in each of the three F. succinogenes subsp. succinogenes isolates but not with any antigens from the F. succinogenes subsp. elongata isolate. The anti-EG2 antibody reacted with single antigens in each of the four isolates, while the anti-EG3 antibody reacted with only one of the four isolates.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions of serum proteins with small unilamellar liposomes composed of dioleoylphosphatidylethanolamine and oleic acid: high-density lipoprotein, apolipoprotein A1, and amphipathic peptides stabilize liposomes

Small unilamellar liposomes composed to dioleoylphosphatidylethanolamine (DOPE) and oleic acid (OA) are stabilized by incubation with normal human serum or plasma [Liu, D., & Huang, L. (1989) Biochemistry 28, 7700-7707]. The present report describes a systematic study of interactions of purified serum proteins and lipoproteins with these liposomes. Albumin destabilized liposomes by extracting OA from the liposomes, whereas immunoglobulins and lipoproteins (HDL, LDL, and VLDL) had no effect. However, HDL and, to some extent, VLDL showed a rapid stabilization activity against the lytic effect of albumin. HDL added together with or shortly after the addition of albumin completely abolished the liposome leakage and aggregation effects induced by albumin. SDS-PAGE analysis of the HDL-stabilized liposomes revealed that apolipoprotein A1 was associated with liposomes. Purified apolipoprotein A1, but not a lipid mixture resembling the lipid composition of HDL, showed comparable liposome stabilization activity as HDL. Furthermore, synthetic peptides resembling the amphipathic helices found in apolipoprotein A1 also showed strong liposome stabilization activity. Peptides which were able to form amphipathic helixes of a wedge shape were more effective stabilizers than those which could not. These data indicate that HDL plays a major role in human serum or plasma for the liposome stabilization activity. HDL exerts its activity probably by the interactions of the amphipathic helices of apolipoprotein A1 with the hydrophobic voids found on the outer surface of the highly curved, small liposomes.

pH-sensitive, plasma-stable liposomes with relatively prolonged residence in circulation

Acid-sensitive liposomes composed of unsaturated phosphatidylethanolamine (PE) are efficient vehicles for cytoplasmic delivery of the target cells. We have recently shown that liposomes composed of dioleoyl-PE (DOPE) and dipalmitoyl-succinylglycerol (DPSG) retain the acid-sensitivity after exposure to human plasma. In the present work, we have extended these observations to investigate the role of ganglioside GM1 on the blood residence time of these liposomes. Small (d approximately 100 nm) unilamellar liposomes composed of DOPE and DPSG (4:1, molar ratio) became progressively less acid-sensitive when increasing amounts of GM1 were included in the lipid composition. However, partial sensitivity to acid (40-50% release of entrapped contents at pH 4) could be retained up to 5% GM1, even for liposomes which had been exposed to human plasma. Inclusion of GM1 in the lipid composition only slightly increased the release of entrapped contents in the presence of human plasma. The biodistribution of i.v. injected GM1-containing liposomes was studied by following the entrapped 125I-labeled tyraminylinulin marker in Balb/c mice. Inclusion of up to 5% GM1 showed a transient increase in the blood level and a concomitant decrease of liver and spleen uptake of liposomes. Thus, these liposomes are pH-sensitive, plasma-stable and show a relatively prolonged residence time in circulation. They are potentially significant drug carriers in vivo.

[A preliminary study on the pharmacology of the compound prescription huangqin tang and its component drugs]

Results obtained from the pharmacological experiments demonstrated that the compound prescription Huangqin Tang and its component drugs, roots of Paeonia lactiflora, Scutellaria baicalensis and Glycyrrhiza uralensis, and the fruit of Ziziphus jujuba showed marked anti-inflammatory effect. The compound prescription and its component drugs, except the peony root, possessed significant antispastic effect. Antipyretic effect of Radix Scutellariae, Radix Glycyrrhizae and Huangqin Tang was suggested. Huangqin Tang, Radix Paeoniae alba, and Radix Glycyrrhizae showed marked analgesic effect. In addition, the experiments confirmed that both Huangqin Tang and single Radix Scutellariae have sedative effect.

Influence of peptide acylation, liposome incorporation, and synthetic immunomodulators on the immunogenicity of a 1-23 peptide of glycoprotein D of herpes simplex virus: implications for subunit vaccines

A peptide corresponding to residues 1 to 23 of glycoprotein D of herpes simplex virus type 1 was chemically synthesized and coupled to a fatty acid carrier by standard Merrifield synthesis procedures. The resulting peptide-palmitic acid conjugate (acylpeptide) exhibited enhanced immunogenicity in mice as compared with that exhibited by the free form of the peptide. Incorporation of the acylpeptide into liposomes further increased the immunogenicity of the peptide, while inclusion of the immunomodulators muramyl tripeptide phosphatidylethanolamine and monophosphoryl lipid A into the same liposome stimulated the strongest response. The humoral immune responses induced by the acylpeptide-liposome construct were greater than those induced by peptide in Freund complete adjuvant, and cellular responses were equal. The acylpeptide-immunomodulator-liposome formulation also induced significant levels of protective immunity, although the immunity was less than that induced by herpes simplex virus infection. Acylated peptides, especially in liposomes, were taken up more effectively by draining lymph nodes, which possibly accounts in part for the enhanced immunogenicity of the peptides. Since the acylpeptide-immunoliposome formulation used was nontoxic, it could represent a useful way to enhance immunogenicity of subunit peptides used for vaccine purpose in humans and animals.

Partitioning of teniposide into membranes and the role of lipid composition

We have examined the partitioning behavior of the anticancer agent teniposide (VM-26) into multilamellar vesicles composed of various phospholipid species. Partitioning was found to be sensitive to the composition of the liposomal membrane since changes in the head group or acyl chain constituents could dramatically alter the affinity of the drug for the bilayer. [3H]VM-26 partitioned most readily into 1,2-monounsaturated species of phosphatidylcholine (PC) with a molar partition coefficient (Kp) of 4290 for dioleoyl-PC at 37 degrees C. Inclusion of additional phospholipids having a different head group reduced partitioning in the order cardiolipin greater than phosphatidylglycerol greater than phosphatidylserine greater than phosphatidylethanolamine. The Kp for dioleoyl-PC with 33 mol% cardiolipin was reduced to 1370. Partitioning into completely saturated species of PC was much less than that for unsaturated species and was inversely proportional to the hydrocarbon chain length at temperatures either above or below the chain melting temperature. The Kp for fluid phase dimyristoyl-PC was 2300. Partitioning into dimyristoyl-PC or dioleoyl-PC at 37 degrees C (fluid) or dipalmitoyl-PC at 25 degrees C (gel) was reduced by the addition of 5-30 mol% cholesterol in proportion to its bilayer concentration. Etoposide (VP-16) at concentrations up to 10 mol% did not compete with [3H]VM-26 for association with dioleoyl-PC. Addition of calf serum or serum albumin could significantly reduce the association of [3H]VM-26 with the liposomes.

Regulation of 5-Aminolevulinic Acid (ALA) Synthesis in Developing Chloroplasts : III. Evidence for Functional Heterogeneity of the ALA Pool

Gabaculine and 4-amino-5-hexynoic acid (AHA) up to 3.0 millimolar concentration strongly inhibited 5-aminolevulinic acid (ALA) synthesis in developing cucumber (Cucumis sativus L. var Beit Alpha) chloroplasts, while they hardly affected protochlorophyllide (Pchlide) synthesis. Exogenous protoheme up to 1.0 micromolar had a similar effect. Exogenous glutathione also exhibited a strong inhibitory effect on ALA synthesis in organello but hardly inhibited Pchlide synthesis. Pchlide synthesis in organello was highly sensitive to inhibition by levulinic acid, both in the presence and in the absence of gabaculine, indicating that the Pchlide was indeed formed from precursor(s) before the ALA dehydratase step. The synthesis of Pchlide in the presence of saturating concentrations of glutamate was stimulated by exogenous ALA, confirming that Pchlide synthesis was limited at the formation of ALA. The gabaculine inhibition of ALA accumulation occurred whether levulinic acid or 4,6-dioxohepatonic acid was used in the ALA assay system. ALA overproduction was also observed in the absence of added glutamate and was noticeable after 10-minute incubation. These observations suggest that although Pchlide synthesis in organello is limited by ALA formation, it does not utilize all the ALA that is made in the in organello assay system. Gabaculine, AHA, and probably also protoheme, inhibit preferentially the formation of that portion of ALA that is not destined for Pchlide. A model proposing a heterogenous ALA pool is described.

Highly efficient immunoliposomes prepared with a method which is compatible with various lipid compositions

Monoclonal antibody was conjugated to N-glutaryl-phosphatidylethanolamine in the presence of octylglucoside by using N-hydroxysulfosuccinimide as a carboxyl-activation reagent. The conjugated antibody was then incorporated into liposomes by a simple dialysis method. The method is mild and is compatible with various lipid compositions of the liposomes. We have prepared immunoliposomes containing a lung endothelium-specific monoclonal antibody and showed excellent target binding (approximately 75% injected dose) of the immunoliposomes in mouse. Immunoliposomes can be prepared to contain other acidic lipids such as phosphatidylserine and various amounts of cholesterol. The presence of 20% or more cholesterol in liposomes resulted in high level of target binding. We have used in these experiments a new radioactive lipid-phase marker, 111In-DTPA-SA, which was very stable in vivo. The halflife of clearance in mouse exceeded 3 weeks.

Immunoliposomes with different acid sensitivities as probes for the cellular endocytic pathway

By combining dioleoylphosphatidylethanolamine (DOPE) with oleic acid (OA), palmitoylhomocysteine (PHC) or dipalmitoylsuccinylglycerol (DPSG) we have prepared pH-sensitive liposomes with different acid sensitivities. DOPE/OA liposomes are the most acid sensitive, while DOPE/DPSG liposomes are the least acid sensitive. Incubation of DOPE/OA liposomes with mouse L929 cells reduces the pH-sensitivity of these liposomes by altering the lipid composition. Using diphtheria toxin fragment A as a marker for cytoplasmic delivery, we find that the delivery kinetics of pH-sensitive immunoliposomes closely correlates with the modified acid sensitivities of the liposomes. Immunoliposomes encounter pH 6-6.2 with a t1/2 of 5-15 min after internalization. By contrast, acidification of the endosomes to pH 5.0 takes longer (t1/2 approximately 25 min). We also used a whole cell null point technique (Yamishiro and Maxfield (1987) J. Cell Biol. 105, 2713-2721) to directly determine the average pH encountered by the endocytosed immunoliposomes. We find that acidification determined by the null point method proceeds less rapidly than that estimated from DTA delivery data. This is likely due to the fact that the measured DTA delivery is done by those liposomes which first arrive at the endosomes with sufficient acidity. Our data suggests that DOPE/PHC immunoliposomes deliver at the early endosome while DOPE/DPSG immunoliposomes deliver at the late endosomes. The DOPE/OA immunoliposomes, with the altered composition and acid sensitivity, deliver with a kinetics intermediate between the other two immunoliposomes. Thus, pH-sensitive liposomes represent useful probes for studying the kinetics of endosome acidification.

[Clinical characteristics of silent myocardial ischemia and the effect of nifedipine treatment]

The characteristics of ischemic episodes in exercise test and daily activities were observed in a silent myocardial ischemia (SMI) group and an anginal group (23 patients each). 15 patients in the SMI group were treated with nifedipine. In exercise test, the time of onset of ischemia was earlier and the ischemic threshold was lower in SMI group. During daily activities, the frequency of SMI was high. The heart rate just before onset of SMI was lower than the mean heart rate in 24-hour Holter monitoring. The highest frequency of SMI was found between 5 AM and 12 noon. Postinfarction patients had a higher frequency and a longer duration of SMI than noninfarction patients. The frequency and duration of SMI decreased in the 15 patients treated with nifedipine in SMI group. It is concluded that silent ischemic episodes were frequent and occurred easily. They might be associated with poor prognosis in CAD patients. Nifedipine was effective in reducing the frequency and duration of SMI in our patients.

Highly efficient DNA delivery mediated by pH-sensitive immunoliposomes

We have previously shown that pH-sensitive immunoliposomes can mediate a target-specific delivery of plasmid DNA to tumor cells grown in a mouse model [Wang, C.-Y., & Huang, L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7851-7855]. The efficiency of delivery in terms of the target cell transformation frequency has now been characterized for both short- and long-term gene expression in a tissue culture system. Herpes simplex virus thymidine kinase (TK) gene was used as a reporter gene. It was placed under the control of the promoter for the rat phosphoenolpyruvate carboxykinase gene, which contains a cAMP regulatory element. Therefore, the expression of the exogenous gene in the target cell, mouse Ltk- cells, can be regulated by cAMP drugs. The plasmid DNA was encapsulated in liposomes using a detergent dialysis method. The efficiency of gene delivery was optimized with respect to the time course and dose of liposome-associated DNA. The existence of antibody of the liposomes was essential for the maximal level of DNA delivery. Delivery was also dependent on the lipid composition of the liposome. The pH-sensitive lipid composition gave 8-fold higher efficiency than the corresponding pH-insensitive composition. The transformation efficiency of the target cell also depended on the regulation of gene expression; cells incubated with dibutyryl-cAMP and theophylline showed a much higher level of transformation frequency than cells incubated without the drugs. When all liposome and incubation parameters are optimized, the Ltk- cells showed a 47% efficiency for the short-term transformation, and 2% for the long-term transformation.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of protein-linked oligosaccharide in the bilayer stabilization activity of glycophorin A for dioleoylphosphatidylethanolamine liposomes

The importance of the protein-linked carbohydrates for the stabilization of dioleoylphosphatidylethanolamine (DOPE) bilayers has been investigated using glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, as a stabilizer. Two major types of glycophorin, differing in the sialic acid content, were used in the study. Type MM contains 19.2 +/- 2.5 sialic residues per molecule of glycophorin, and type NN contains 10.8 +/- 1.2. Type MM could stabilize DOPE bilayers at 0.5 mol%, whereas type NN was unable to do so even at 1 mol%. The importance of the sialic acid content to the stabilization activity of glycophorin was further confirmed by the observation that the neuraminidase-treated type MM showed a lower stabilization activity than the untreated type. Since type NN had no stabilizing activity, we attempted to couple a trisaccharide, NeuNAc----Gal----Glc, to type NN by reductive amination. 2.5 +/- 0.8 saccharide chains were added per molecule of type NN. The trisaccharide-attached type NN showed a greater stabilization activity than the parent type NN molecule, indicating again that the sialic acid content of the stabilizer molecule determines the stabilization activity. Addition of wheat-germ agglutinin (WGA), which binds to the sialic acid residues of a glycoprotein, to type MM-stabilized liposomes caused rapid aggregation and destabilization of liposomes, resulting in leakage of an entrapped marker, calcein. The aggregation increased with increasing amount of the lectin; however, the leakage rate was maximum at an optimum concentration of WGA. These results are discussed in terms of the role of sialic acid in the interfacial hydration and charge repulsion which determines the DOPE bilayer stability.

Monoclonal antibody targeting of liposomes to mouse lung in vivo

A monoclonal antibody (MoAb), 273-34A, specifically binds to an epitope expressed almost exclusively on capillary endothelial cells of the lung. Within 15 min after i.v. injection, approximately 80 to 85% of the injected radioiodinated MoAb 273-34A accumulates in the lung. Approximately 90 to 95% of the recovered dose is found in the lung for up to 1 week postinjection. Ratios of MoAb 273-34A to a nonspecific, irrelevant MoAb 135-14 are 250 to 285 times higher in the lung than in the serum. When 273-34A was coupled with palmitic acid and incorporated into liposomes, the amount of 125I-labeled liposomes recovered per g of tissue was 12 times higher in the lung than in the liver at 15 min postinjection, and 22 times higher at 5 h postinjection. At 24 h postinjection the amount of liposomes per gram of lung tissue was still 6.0 times the amount per gram of liver tissue. Liposomes conjugated to MoAb 273-34A locate in the lung 20 and 15 times better than do liposomes conjugated to the nonspecific MoAb 135-14 at 15 min and 24 h postinjection, respectively. The results indicate that this immunoliposome system could be used as a model for enhanced drug delivery to the lung. The potential use for delivering anticancer drugs for therapy of lung tumors is discussed.

Use of a quaternary ammonium detergent in liposome mediated DNA transfection of mouse L-cells

Sonicated liposomes composed of dioleoylphosphatidylethanolamine (DOPE) and a quaternary ammonium detergent (dodecyl-, tetradecyl-, or cetyl-trimethylammonium bromide) mediates functional transfer of pSV2 CAT plasmid DNA to mouse L929 fibroblasts. Successful transfection was determined by assaying for chloramphenicol acetyltransferase activity in cell lysates collected 40 h after exposure to the lipid-DNA complexes. Liposomes prepared with the quaternary ammonium detergents were less toxic than the free detergents at the same concentrations and were more efficient in their delivery of the plasmid DNA to the cells. Analysis of the three detergents in combination with the lipid showed that cetyltrimethylammonium bromide was least toxic to the cells. This detergent, at a minimal concentration of 20 mol% in DOPE, allowed for stable liposome preparations and efficient transfection. Optimal efficiency of transfection occurred with 30 micrograms of DNA. Further increases in the DNA concentration caused a decrease in the transfection efficiency, perhaps due to charge repulsions between the liposomes now saturated with negatively charged DNA and the negatively charged cell surface. The transfection activity of the liposome was limited by its cytotoxicity at high liposome concentrations. These results are compared with that of the Lipofectin, another positively charged liposome preparation which is commercially available. Although the overall transfection activity of the liposome containing the quaternary ammonium detergent is somewhat lower than that of the Lipofectin, it may serve as an inexpensive and convenient alternative.

Structure and function relationship of phosphatidylglycerol in the stabilization of the phosphatidylethanolamine bilayer

Differential scanning calorimetry was used to examine the structure-function relationship of the phospholipids on the L alpha-phase stabilization of phosphatidylethanolamine (PE). Phosphatidylglycerol (PG) was chosen as a model stabilizer. Dielaidoylphosphatidylethanolamine (DEPE) was mixed with various PGs to study the effects of (i) chain length, (ii) chain unsaturation, and (iii) chain number of the stabilizer on the L alpha-phase stabilization. At low concentrations of stabilizer, both bilayer stabilization and destabilization were observed. Phase separations also were seen, as revealed by split peaks of the L beta----L alpha transition; these were particularly prone to occur in the destabilization cases. When saturated PGs were compared, shorter chains (C12:0 and C14:0) promoted bilayer stabilization whereas longer chains (C16:0 and C18:0) promoted bilayer destabilization. Unsaturated PG with larger hydrophobic volumes (C18:2) favored bilayer destabilization, relative to unsaturated PG with smaller hydrophobic volumes (C18:1). Lyso-PG (C14:0) showed higher bilayer stabilization activity than their double-chain counterparts. Thus, at low concentrations of stabilizer, the acyl chain composition plays a vital role in bilayer-phase stabilization. However, at higher concentrations (greater than or equal to 8 mol %), all PGs become active bilayer stabilizers. This is probably because the increased head-group hydration becomes the dominant factor in the stabilization. The effect of acyl chain composition of the stabilizer was also studied by using small unilamellar vesicles composed of dioleoylphosphatidylethanolamine (DOPE). Fluorescence quenching of calcein entrapped in liposomes was used to monitor the stability of the liposomes. Similar acyl chain effects on liposomal stabilization were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Small, but not large, unilamellar liposomes composed of dioleoylphosphatidylethanolamine and oleic acid can be stabilized by human plasma

Small unilamellar liposomes, composed of dioleoylphosphatidylethanolamine (DOPE) and oleic acid (OA), prepared by sonication, were incubated in the presence of human plasma at 37 degrees C. The release of entrapped calcein after 8-h incubation was about 15% in plasma, compared with about 70% in phosphate-buffered saline under the same conditions. In contrast, dioleoylphosphatidylcholine (DOPC)/OA liposomes under the same conditions release about 70% in plasma and only 10% in PBS. Total release of calcein from the DOPE/OA liposomes was observed in a PBS solution containing bovine serum albumin, and the release was completely blocked by preincubation of the liposomes with plasma. These results indicate that the unstable DOPE/OA liposomes are stabilized by incubation with plasma. The stabilization process was very fast, being completed within 1 min. Only relatively small liposomes (d less than or equal to 200 nm) were completely stabilized by plasma; larger liposomes were progressively less stabilizable. SDS-polyacrylamide gel electrophoresis of liposomes which had been incubated with plasma and then washed indicated that several proteins were tightly associated with liposomes. Using liposomes containing [14C]OA, it was found that about 70% of the original OA was extracted after 1-h incubation with human plasma at 37 degrees C. Thin-layer chromatographic analysis of the plasma-treated liposomes showed the presence of the plasma lipids in the liposomes. These results suggest that liposomes composed of DOPE/OA are stabilized by protein and/or lipid components from human plasma and that the composition of the liposomes is altered. The mechanism of stabilization is discussed in terms of the surface pressure of small vesicles with a high degree of curvature.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of plasma-stabilized liposomes composed of dioleoylphosphatidylethanolamine and oleic acid [published errtum appears in Biochem Biophys Res Commun 1989 Sep 29;163(3):1539]

We have previously reported that small unilamellar liposomes (d less than or equal to 200 nm) composed of dioleoylphosphatidylethanolamine and oleic acid can be stabilized by incubating with normal human plasma (Liu and Huang, Biochemistry 1989, in press). The stabilized liposomes were very stable even under relatively harsh conditions such as extreme pH, high salt and trypsin treatment. Fluorescence depolarization of diphenylhexatriene showed that the stabilized liposome had a high microviscosity in the lipid core, which did not decrease even after the majority of proteins were removed by trypsin. These data suggest that plasma proteins inserted into the lipid bilayer are probably responsible for the stabilization activity. After i.v. injection into mouse, stabilized liposomes showed a relatively low affinity to liver and spleen as compared to a conventional liposome composition.

Regulation of 5-Aminolevulinic Acid (ALA) Synthesis in Developing Chloroplasts : II. Regulation of ALA-Synthesizing Capacity by Phytochrome

When dark-grown cucumber (Cucumis sativus L.) seedlings previously exposed to white light for 20 hours were returned to darkness, the ability of isolated chloroplasts to synthesize 5-aminolevulinic acid dropped by approximately 70% within 1 hour. The seedlings were then exposed to light, and the synthetic ability of the isolated chloroplasts was determined. Restoration of the synthetic capacity was promoted by continuous white or red light of moderate intensity. Intermittent red light was also effective. Blue and far-red light did not restore the synthetic capability. Blue light given after a red pulse did not enhance the effect of the red light. Far-red light given immediately after each red pulse prevented the stimulation due to intermittent red light. Restoration of the biosynthetic activity by in vivo light treatments was inhibited by cycloheximide indicating the requirement for translation on 80 S ribosomes for the in vivo light response. These findings suggest that the majority of the plastidic 5-aminolevulinic acid synthesis is under phytochrome regulation.

Regulation of 5-aminolevulinic Acid synthesis in developing chloroplasts : I. Effect of light/dark treatments in vivo and in organello

Intact chloroplasts isolated from greening cucumber (Cucumis sativus L. var Beit Alpha) cotyledons regenerated protochlorophyllide (Pchlide) in the dark with added cofactors from either exogenous glutamate or endogenous substrates. No other intermediates of the chlorophyll biosynthetic pathway accumulated. When inhibitors of 5-aminolevulinic acid (ALA) dehydratase were added, the Pchlide that failed to form was replaced by an excessive amount of ALA. When greening seedlings were returned to the dark, ALA-synthesizing activity in the isolated chloroplasts decreased dramatically and recovered if the dark-treated seedlings were again exposed to continuous white light prior to chloroplast isolation. Both the decline and the recovery of ALA-synthesizing activity were complete in approximately 50 minutes. Changes in chloroplast structure during in vivo light to dark and dark to light transitions (as evidenced by electron microscopy) were much slower. Exposing isolated chloroplasts from dark-treated seedlings to short white flashes before incubation transformed nearly all the endogenous Pchlide, but hardly stimulated ALA synthesis, suggesting that Pchlide does not act as a feed-back inhibitor on ALA synthesis. Chloroplasts isolated from dark-treated tissue did not form Pchlide from glutamate when incubated in the dark with added cofactors; moreover, the endogenous Pchlide did not turn over in organello. However, these chloroplasts did synthesize Pchlide from added ALA at the normal rate and synthesized ALA from glutamate at a reduced, but still significant, rate. Mg chelation was not affected by in vivo dark treatment.

Role of cholesterol in the stability of pH-sensitive, large unilamellar liposomes prepared by the detergent-dialysis method

Large unilamellar liposomes prepared by an octyl glucoside-dialysis method were examined for stability at 37 degrees C in the presence or absence of human plasma, using the release of the entrapped calcein as a fluorescence marker. The liposomes were acid-sensitive as they were composed of dioleoylphosphatidylethanolamine, oleic acid and cholesterol. The stability of the liposomes in the absence of plasma was significantly enhanced with increasing cholesterol content. However, the maximal calcein release at pH 5 decreased linearly with increasing cholesterol content of the liposome, indicating that cholesterol had reduced the acid-sensitivity of the liposomes. In the presence of human plasma, calcein release exhibited a biphasic behavior with a fast (plasma-sensitive) and a slow (plasma-resistant) component. Inclusion of cholesterol in the liposomes resulted in an increased proportion of the plasma-resistant component. Liposomes pretreated with human plasma, after removal of excess plasma and the released calcein by gel-filtration, showed a remarkable stability both in the presence and absence of human plasma. The acid-sensitivity of the plasma-treated liposomes with 40% cholesterol was the same as that of the untreated liposomes. These results are discussed in terms of the mechanism by which these liposomes deliver their contents to the cytoplasm of the cells via the endocytic pathway, a known biological activity of the type of liposome described here.

Anterior ischemic optic neuropathy--recurrent attacks in one eye in a bilateral case

Subsequent involvement of the fellow eye is common in anterior ischemic optic neuropathy, but recurrent episodes in one eye are extremely rare. Our hypertensive patient had one eye attacked nine years before and two episodes in the second eye within ten days of each other. Visual-field examination revealed progressing field loss, and fluorescein angiography demonstrated an enlarged disc hypofluorescence area.

Insulin and a putative insulin metabolic mediator fraction from liver and muscle stimulate p33 messenger ribonucleic acid accumulation by apparently different mechanisms

We have previously shown that in rat H4 hepatoma cells insulin enhances the nuclear transcription of p33 mRNA in a dose- and time-dependent manner, with no alteration in mRNA half-time (t1/2). Presumably, this effect is mediated by the cell surface receptor. In this report, we have investigated the effect of putative insulin mediator fractions which act to control metabolic events on p33 mRNA accumulation in these cells. Initial experiments originally demonstrated an insulin-like effect of an added putative metabolic fraction to enhance p33 mRNA concentrations. However, when the fetal calf serum supply was changed, the effect of insulin remained, but that of added mediator was no longer observed. After a series of experimental approaches designed to alter the permeability of the cell membrane, it was found that in the presence of increased Ca2+, the effect of mediator could again be observed. The present data demonstrate that the partially purified cAMP-dependent protein kinase/adenylate cyclase inhibitory putative mediator fractions from liver and muscle enhance p33 mRNA accumulation in intact H4 hepatoma cells by a mechanism that is differentiated from that of insulin. The action of the putative mediator is inhibited by cycloheximide, while the action of insulin itself is not. These results suggest that insulin may control nuclear transcription by multiple signaling mechanisms. Alternatively, the added putative metabolic mediator may not enter the cell in the presence of cycloheximide or is inactive as such within the cell and must first be converted to an active species by a step requiring protein synthesis.

Gadolinium-labeled liposomes containing paramagnetic amphipathic agents: targeted MRI contrast agents for the liver

Unique paramagnetic liposomal contrast agents were synthesized and utilized for selective augmentation of T1 MR imaging of the livers of normal Balb/c mice. Amphipathic gadolinium complexes, which mimic phospholipids, were incorporated into the lamella of small unilamellar liposomes (SUV) such that they became an integral part of its surface. T1 signal enhancement of normal liver approached 150% after iv administration of the paramagnetic liposomes, determined by experiments performed on a 1.9-T, experimental whole-body MRI unit. Tracer studies utilizing gadolinium-153-tagged SUV revealed that the agents exhibited excellent in vivo stability, compared to liposomal preparations in which paramagnetic agents are simply entrapped in the aqueous core of the liposome vesicle.

Purification and characterization of a chloride-stimulated cellobiosidase from Bacteroides succinogenes S85

A cellobiosidase with unique characteristics from the extracellular culture fluid of the anaerobic gram-negative cellulolytic rumen bacterium Bacteroides succinogenes grown on microcrystalline cellulose (Avicel) in a continuous culture system was purified to homogeneity by column chromatography. The enzyme was a glycoprotein with a molecular weight of approximately 75,000 and an isoelectric point of 6.7. When assayed at 39 degrees C and pH 6.5, the activity of the enzyme with p-nitrophenyl-beta-D-cellobioside as the substrate was stimulated by chloride, bromide, fluoride, iodide, nitrate, and nitrite, with maximum activation (approximately sevenfold) occurring at concentrations ranging from 1.0 mM (Cl-) to greater than 0.75 M (F-). The presence of chloride (0.2 M) did not affect the Km but doubled the Vmax. In the presence of chloride (0.2 M), the pH optimum of the enzyme was broadened, and the temperature optimum was increased from 39 to 45 degrees C. The enzyme released terminal cellobiose from cellotriose and cellobiose and cellotriose from longer-chain-length cellooligosaccharrides and acid-swollen cellulose, but it had no activity on cellobiose. The enzyme showed affinity for cellulose (Avicel) but did not hydrolyze it. It also had a low activity on carboxymethyl cellulose.

beta-Galactosidase-induced destabilization of liposome composed of phosphatidylethanolamine and ganglioside GM1

A novel type of liposome bilayer destabilization catalyzed by the enzyme, beta-galactosidase, is described. Unsaturated phosphatidylethanolamine (PE), an HII-phase-forming lipid, does not form stable liposomes at physiological temperature and pH. However, stable unilamellar liposomes can be prepared by mixing PE with a minimum of 5 mol% ganglioside GM1, a micellar-phase-forming lipid. Treatment of these GM1/PE liposomes with beta-galactosidase induces a rapid leakage (3-6 min) of the entrapped fluorescent dye, calcein. The studies indicate that liposome destabilization is the result of catalytic degradation of GM1, rather than a stoichiometric binding of GM1 by beta-galactosidase. Kinetic data indicate that the destabilization takes place via liposome collision. This simple, rapid method of liposome destabilization by beta-galactosidase will be useful in designing a liposome-based signal amplification mechanism for assays involving enzymes.

A homogeneous, liposome-based signal amplification for assays involving enzymes

Exploiting the fact that phosphatidylethanolamine (PE) liposome can be stabilized by a membrane lipid or protein, and that destruction of this stabilizer leads to rapid lysis of the liposome, we have designed a liposome-based signal enhancement mechanism for assays that involve enzyme as the final read-out step. Stable liposomes with entrapped glucose-6-phosphate dehydrogenase (G6PDH) were prepared with unsaturated PE stabilized with 5 mol percent of ganglioside GM1. Addition of beta-galactosidase caused rapid (3-5 min) lysis of liposomes, revealing the latent G6PDH activity, owing to the enzymatic degalactosylation of GM1. We have used Microgenic's CEDIA assay for digoxin as an example. The magnitude of signal was 25 mA/min per microgram of digoxin per liter for the unamplified assay and 1000 mA/min per microgram of digoxin per liter for the liposome-enhanced assay--i.e., a 40-fold amplification. This simple, rapid, and homogeneous signal-amplification mechanism is likely to be useful in many enzyme-dependent assays, such as ELISA, CEDIA, gene-probe assays, and immunoliposome assays.

A homogeneous, liposome-based signal amplification for assays involving enzymes

Exploiting the fact that phosphatidylethanolamine (PE) liposome can be stabilized by a membrane lipid or protein, and that destruction of this stabilizer leads to rapid lysis of the liposome, we have designed a liposome-based signal enhancement mechanism for assays that involve enzyme as the final read-out step. Stable liposomes with entrapped glucose-6-phosphate dehydrogenase (G6PDH) were prepared with unsaturated PE stabilized with 5 mol percent of ganglioside GM1. Addition of beta-galactosidase caused rapid (3-5 min) lysis of liposomes, revealing the latent G6PDH activity, owing to the enzymatic degalactosylation of GM1. We have used Microgenic's CEDIA assay for digoxin as an example. The magnitude of signal was 25 mA/min per microgram of digoxin per liter for the unamplified assay and 1000 mA/min per microgram of digoxin per liter for the liposome-enhanced assay--i.e., a 40-fold amplification. This simple, rapid, and homogeneous signal-amplification mechanism is likely to be useful in many enzyme-dependent assays, such as ELISA, CEDIA, gene-probe assays, and immunoliposome assays.

Kinetic and ultrastructural studies of interactions of target-sensitive immunoliposomes with herpes simplex virus

The bilayer phase of dioleoylphosphatidylethanolamine (PE) can be stabilized with palmitoyl-IgG monoclonal antibody to the glycoprotein gD of the herpes simplex virus (HSV). Interactions of PE immunoliposomes with the target virions were characterized by analyzing the kinetics of lipid mixing, by liposomal content release, and by ultrastructural studies. As revealed by a resonance energy transfer assay, lipid mixing between PE immunoliposomes and virions was very rapid, with a second-order rate constant (kapp) of 0.173 (min)-1 (microgram/mL virus)-1. In comparison, content release from PE immunoliposomes was much slower and exhibited multiple-phase, mixed-order kinetics, indicating that liposome destabilization involved fusion of liposomes with HSV. The extent and the apparent rate of liposome destabilization were strongly dependent on liposome concentration. This was evident by the fact that only one to two liposomes were destabilized by each virus particle at low liposome concentration (0.1 microM). For higher liposome concentrations (1-10 microM), this value was 35-104. This finding implies that collision among the virus-bound liposomes is essential for the eventual collapse of PE immunoliposomes to form the hexagonal (HII) equilibrium phase which was observed using freeze-fracture electron microscopy. Studies employing soluble gD, immobilized on latex beads, indicated that a multivalent antigen source is essential for PE immunoliposome destabilization. Immediately after liposome-virus binding, fusion of liposome with the viral membrane then follows. Upon growth of the fusion complexes, which increase to 35-104 liposomes for each virus, an eventual collapse of the structure results, driving PE to its equilibrium structure of HII phase.

Electron microscopic observation on infected hairs of kerion caused by Microsporum nanum

Microsporum nanum can afflict human hair, although pigs are the usual focus of infection. Although this dermatophyte was thought to invade hair as an endothrix, electron microscopic studies show it to cause ectothrix infection due to its keratinolytic activities.

pH-sensitive immunoliposomes mediate target-cell-specific delivery and controlled expression of a foreign gene in mouse

A plasmid containing the Escherichia coli chloramphenicol acetyltransferase (CAT) gene under the control of a mammalian cAMP-regulated promoter was entrapped in H-2Kk antibody-coated liposomes composed of dioleoyl phosphatidylethanolamine, cholesterol, and oleic acid (pH-sensitive immunoliposomes). The entrapped or free DNA was injected intraperitoneally into immunodeficient (nude) BALB/c mice bearing ascites tumor generated by H-2Kk-positive RDM-4 lymphoma cells. About 20% of the injected immunoliposomes were taken up by the target RDM-4 cells. Uptake was much less when liposomes without antibody were used. The presence of the targeting antibody on liposomes also significantly decreased the nonspecific uptake of liposomes by the spleen. Significant CAT enzyme activity was detected in RDM-4 cells from mice treated with DNA entrapped in the pH-sensitive immunoliposomes. Furthermore, CAT expression in RDM-4 cells was under the control of cAMP, as only the cells from mice injected with 8-bromo-cAMP and 3-isobutyl-1-methylxanthine showed CAT activity. CAT activity in liver and spleen was much lower (by factors of 12 and 5, respectively) than in the RDM-4 cells, and the activities in these reticuloendothelial organs were not regulated by cAMP. CAT activity in RDM-4 cells from mice injected with DNA entrapped in pH-insensitive immunoliposomes (containing phosphatidylcholine in place of phosphatidylethanolamine) was approximately one-fourth that in RDM-4 cells from mice injected with pH-sensitive immunoliposomes, indicating the superior delivery efficiency of the pH-sensitive liposomes. These results are discussed in terms of the DNA-carrier potential of immunoliposomes in therapy of cancer and genetic diseases.

Interactions of target-sensitive immunoliposomes with herpes simplex virus. The foundation of a sensitive immunoliposome assay for the virus

Interactions between target-sensitive (TS) immunoliposomes and herpes simplex virus (HSV) were investigated. Target sensitivity of phosphatidylethanolamine (PE) immunoliposomes is a result of the ability of acylated monoclonal anti-HSV glycoprotein D (gD) to stabilize the bilayer phase of PE, whereas by itself, PE does not form stable liposomes (Ho, R. J. Y., Rouse, B. T., and Huang, L. (1986) Biochemistry 25, 5500-5506). Upon binding of these immunoliposomes to HSV antigen-containing gD, destabilization of PE immunoliposomes was observed. By encapsulating either a self-quenching fluorescent dye, calcein, or alkaline phosphatase inside the liposomal compartment, the HSV-induced destabilization of TS immunoliposomes was shown to be target-specific. Neither Sendai, Semliki Forest, nor Sindbis virus could significantly destabilize the TS immunoliposomes. Moreover, HSV-induced liposome destabilization could be inhibited by free anti-gD (the same antibody used in TS immunoliposomes) but not by monoclonal anti-HSV glycoprotein B, indicating that the interaction was antigen-specific. Destabilization could also be induced by binding to truncated gD (tgD), but only when in a multivalent form immobilized on latex beads. Truncated gD is a cloned, 312-amino acid fragment of HSV-gD that lacks the transmembrane segment. Preincubation of soluble tgD with the TS immunoliposomes failed to induce destabilization and, in addition, abolished the tgD-bead-induced destabilization. This finding strongly indicated that multivalent binding is essential for TS immunoliposome destabilization. Using alkaline phosphatase encapsulated in the liposomes, TS immunoliposomes could be used to detect HSV in fluid phase with 50% signal recorded at 5 microliters of 3.2 x 10(3) pfu/ml; at least 10-fold more sensitive than the standard double-antibody sandwich enzyme-linked immunosorbent assay. The interactions described here may be useful in designing a homogeneous and sensitive immunoliposome assay.

Target-sensitive immunoliposomes as an efficient drug carrier for antiviral activity

We have shown previously that target-sensitive immunoliposomes composed of palmitoyl antibody stabilized phosphatidylethanolamine bilayers could be destabilized by binding to the target cells (Ho, R. J. Y., Rouse, B. T., and Huang, L., Biochemistry (1986) 25, 5500-5506). Target-sensitive immunoliposome-encapsulated and free cytotoxic drugs of nucleoside analogs cytosine-beta-D-arabinoside (AraC) or acycloguanosine (acyclovir, ACV) were compared for their antiviral efficacy and cell cytotoxicity. Target-insensitive immunoliposomes and nontargeted liposomes were also investigated. When the mouse fibroblast L929 cells were infected at low multiplicity with herpes simplex virus, AraC encapsulated in target-sensitive immunoliposomes composed of transphosphatidylated egg phosphatidylethanolamine effectively inhibited virus replication and had far less cell cytotoxicity than free drug. As a measure of cytotoxicity, the drug concentration required to inhibit 50% of [3H]thymidine incorporation from 6 to 42 h (CD50) was determined. For free AraC, this value was 0.3 ng/ml, whereas for target-sensitive immunoliposome-encapsulated AraC, the CD50 exceeded 1 microgram/ml. However, target-sensitive immunoliposome-encapsulated AraC was virus inhibitory (50% effective dose = ED50) at 1.8 ng/ml. A free drug concentration of at least 1000-fold greater was required for comparable antiviral activity. A similar phenomenon was observed when ACV was administered via target-sensitive immunoliposomes. The CD50 values of the free and target-sensitive immunoliposome-encapsulated ACV were 12.5 ng/ml and 1.4 micrograms/ml, respectively, whereas the ED50 values of the free and target-sensitive immunoliposome-encapsulated ACV were 1.1 and 125 ng/ml, respectively. Consequently, our results indicated the superiority of target-sensitive immunoliposomes at drug delivery, especially when drugs were cytotoxic to cells. The use of liposomes of the target-insensitive variety provided some enhancement of activity, but this was several-fold less than that observed with target-sensitive immunoliposomes. In addition, the nucleoside transport inhibitors, p-nitrothiobenzylinosine and dipyridamole, were shown to inhibit the liposome-mediated antiviral activity of AraC. This finding indicated that site-specific cytosolic delivery of nucleoside analogs by target-sensitive immunoliposomes involved a cellular nucleoside transport system. A mechanism of action is proposed.

Plasmid DNA adsorbed to pH-sensitive liposomes efficiently transforms the target cells

We have previously reported that plasmid DNA entrapped in the pH-sensitive immunoliposomes effectively transforms the target cells (Proc. Natl. Acad. Sci. USA, in press). In the present study, we demonstrate that DNA adsorbed on the same liposome also transforms the target cells. The transformation activity is antibody dependent, as liposomes containing no targeting antibody had reduced activity. The activity could be significantly inhibited by excess non-specific DNA (salmon sperm). Since some DNA are likely adsorbed to the liposomes during the entrapment process, the activity of the entrapped DNA is partially accounted for by the adsorbed DNA. The possibility of developing a simple DNA-mediated transfection protocol using liposome adsorbed DNA is discussed.

L-652,469--a dual receptor antagonist of platelet activating factor and dihydropyridines from Tussilago farfara L

L-652,469, 14-acetoxy-7 beta-(3'-ethylcrotonoyloxy)-notonipetranone, isolated from the methylene chloride extracts of the buds of Tussilago farfara L, was found to inhibit both platelet activating factor (PAF) and Ca2+ entry blocker binding to membrane vesicles. It inhibits the [3H]PAF specific binding to rabbit platelet membranes with equilibrium inhibition constants (Ki) of 3.2 and 4.0 microM in the presence of 150 mM NaCl and 10 mM MgCl2 respectively. It is a competitive PAF receptor antagonist with an equilibrium dissociation constant (KB) of 5.16 microM. It also competitively inhibits the specific binding of Ca2+ channel blockers (e.g. [3H]nitrendipine; Ki = 1.2 microM) in cardiac sarcolemmal vesicles. At 10(-5) M, L-652,469 causes a 60% relaxation of Ca2+-induced contraction of rat thoracic aorta strips. Due to its dual antagonistic activities, L-652,469 potently inhibits the gel-filtered rabbit platelet aggregation with a pA2 of 5.79. It was also found to be orally active with a beneficial effect to inhibit the PAF-induced rat foot edema and the first phase of carrageenan-induced rat hindpaw edema.

Increased survival of skin flaps by scavengers of superoxide radical

Elevation of rat abdominal skin flaps, followed by ligation and division of the left inferior neurovascular pedicle, resulted in only a 40% survival of the area normally perfused by the ligated artery and vein. Superoxide dismutase (SOD) (EC 1.15.1.1) administered i.v. (20,000 U/kg) 30 min before flap elevation increased survival to 52%. SOD derivatized with polyethylene glycol, which increases circulating half-life, was more effective, increasing survival to 80%. This protective effect resulted from the catalytic activity of the derivatized enzyme because inactivation by treatment with H2O2 eliminated its effect on skin flap survival. An equimolar mixture of Desferal and MnCl2, which catalyzes the dismutation of O2- in vitro, improved survival to 72%. Desferal-Fe3+, which lacks in vitro SOD activity, or Mn2+ alone did not affect the survival of skin flaps, but Desferal alone was nearly as effective as the Desferal-Mn2+ mixture. This effect of Desferal may result from acquisition of and subsequent removal of iron in vivo. These results support the view that the superoxide radical or a product derived from it plays a role in limiting the survival of island skin flaps.

The role of multivalency in antibody mediated liposome targeting

We have investigated the role of multivalency in immunoliposome binding to cells displaying different amounts of surface antigen using liposomes with increasing numbers of palmitoyl anti-H2Kk antibodies incorporated into the bilayer. RDM-4 lymphoma cells were treated with proteinase k to generate a series of cells with various amounts of H2Kk antigen. Percent binding of immunoliposomes was related to the number of antigens displayed by the RDM-4 cell. Increasing liposome binding was observed with increasing number of antibody molecules per liposome. However, the ratio of binding of the high-antigen-density cells to that of the low-antigen-density cells was higher with immunoliposomes of lower antibody density than the ones with higher antibody density. This result suggests that for better discrimination between cells differing in antigen density, liposomes with lower numbers of antibody molecules per liposome may be more useful as a discriminatory tool for cells with a low level antigen expression than liposomes with greater antibody densities.

Thermodynamic and phase characterization of phosphatidylethanolamine and ganglioside GD1a mixtures

By employing diphenylhexatriene steady-state fluorescence anisotropy, pyrenedecanoic acid excimer formation, and high sensitivity scanning calorimetry we have demonstrated that the liposomes containing phosphatidylethanolamine (PE) and various mole fractions of ganglioside GD1a had a gel-liquid crystalline phase transition between 15 and 25 degrees C. Calorimetric measurements indicated that these phase transitions were broad and centered between 17 and 21 degrees C. The enthalpy change of the transition was linearly dependent on the ganglioside concentration up to 10.0 mol% and plateaued between 11.4-16.2 mol%. The high enthalpy change (37 kcal/mol of GD1a added into the PE bilayer) indicates the existence of PE-GD1a complex structure in the liposomal membrane. It is proposed that semi-fluid domains containing six PE and one ganglioside molecule are present in the PE-GD1a membranes at temperatures above gel-liquid crystalline phase transition. The Sendai virus induced leakage of PE-GD1a liposomes has been investigated by using an entrapped, self-quenching fluorescent dye, calcein. The leakage rate was dependent on the mole fraction of ganglioside GD1a and was maximal at 6.3 mol%. Arrhenius plots of the leakage rates showed breaks in the 20-25 degrees C temperature range, which correspond to the gel-liquid crystalline phase transition of the target liposomes. These data suggest that the rate of Sendai virus-induced leakage can be regulated via fluidity modulation by changing the PE to GD1a ratio at constant temperatures.

A putative mediator of insulin action which inhibits adenylate cyclase and adenosine 3',5'-monophosphate-dependent protein kinase: partial purification from rat liver: site and kinetic mechanism of action

A novel putative mediator of insulin action which acts to inhibit adenylate cyclase and cAMP-dependent protein kinase has been purified from livers of insulin-treated streptozotocin-diabetic rats. It was increased by short term (5-min) insulin injections in vivo and purified several thousand-fold by Sephadex and HPLC. Its mol wt was somewhat larger (2500) than previous mediators identified, and it was more hydrophobic in character. Its mechanism of action or adenylate cyclase was determined and found to be chiefly directed against the catalytic subunit. Its action on the cAMP-dependent protein kinase was found to be competitive with regard to protein substrate, but noncompetitive with regard to ATP and cAMP. Its relationship to other putative insulin mediators and the mechanism of insulin action is discussed.

Gadolinium-labeled liposomes: targeted MR contrast agents for the liver and spleen

A contrast agent for use in magnetic resonance (MR) imaging of the liver and spleen has been designed in which gadolinium-DTPA is chemically incorporated into the lamellar phase of liposome particles. This agent has excellent in vivo stability and is taken up by liver and spleen of normal mice after intravenous administration. The T1 increased by 110% in liver and 66% in spleen at 4 degrees C. At 37 degrees, the relaxation rate in the liver increased by 180%. This method is an attractive concept for the development of various organ-specific liposomal contrast agents that may be used for either MR imaging or nuclear medicine.