Search PubMed⌕ Search

Biomedical subjects

C R Alving

Publications and source records attributed to C R Alving.

At least 145 records · Page 8Linked to original sources
PubMed1979

Interactions of C-reactive protein and complement with liposomes. II. Influence of membrane composition.

We found previoulsy that interaction of C-reactive protein (CRP) with liposomal model membranes resulted in complement(C)-dependent membrane damage. In the present study, we investigated the influence of membrane composition on the interactions of CRP and C with liposomes. Adsorption experiments showed that binding of CRP was greatest to strongly positive liposomes. A lesser, but still substantial, extent of CRP binding also was observed with negative liposomes, but negligible amounts of CRP bound to neutral or weakly positive liposomes. CRP-mediated consumption of hemolytic C, and C-dependent glucose release from liposomes both were strongly influenced by liposomal charge, positive being superior to negative. Glucose release and, to a lesser extent, consumption of hemolytic C were inversely related to phospholipid fatty acyl chain length. Phospholipid fatty acyl unsaturation and liposomal cholesterol concentration both had strong influences on C consumption and glucose release. The data suggest that CRP-mediated C consumption and membrane damage require an optimum membrane fluidity. Complement damage in the presence of CRP was enhanced by certain sphingolipids and also by digalactosyl diglyceride, but not by sphingomyelin. Our results thus demonstrate that CRP-mediated C consumption and C-dependent membrane damage both are influenced by the liposomal membrane composition.

Adsorption↗
PubMed1979

Activation of human complement by liposomes: a model for membrane activation of the alternative pathway.

Liposomal model membranes were found to activate the alternative pathway of human complement. Activation was measured by C3 conversion and component consumption in serum that had been incubated with liposomes. C3 conversion did not require C1 or C2 of the classical pathway, since it was observed in serum from a C1r-deficient patient, serum from a C2-dificient patient, and normal serum in buffer containing EGTA and MgCl2. The incubation of liposomes with C2-deficient serum resulted in consumption of components C3 through C9 with no consumption of C1 or C4 in a profile typical of alternative pathwya activation. The reaction was further shown to require alternative pathway factor D, and to be independent of antibody. Activation of the alterative pathway was dependent on the membrane composition of the liposomes. A positive charge was required for liposomes to produce C3 conversion. Liposomal cholesterol concentration and phospholipid fatty acyl chain length and unsaturation all influenced activation, suggesting the importance of membrane fluidity. Positively charged liposomes containing dimyristoyl phosphatidylcholine and cholesterol required the presence of certain glycolipids for C3 conversion. The activation of the alternative complement pathway by liposomes of defined membrane composition may provide a suitable model for the study of alternative pathway activation by cellular membranes.

Agammaglobulinemia↗
PubMed1978

Therapy of leishmaniasis: superior efficacies of liposome-encapsulated drugs.

Liposomes containing antimonial compounds trapped in the aqueous phase were tested in the treatment of experimental leishmaniasis. The rationale of this approach was based on the hypothesis that the liposomes and the parasite are taken up by the same cell, the reticuloendothelial cell, and we present electron microscopic evidence that supports this hypothesis. Suppression of leishmaniasis was quantified by determining the total number of parasites per liver from impression smears. When two antimonials, meglumine antimoniate and sodium stibogluconate, were encapsulated within liposomes, each was more than 700 times more active compared to either of the free (unencapsulated) drugs. After infection, if untreated, all of the hamsters eventually would die from the disease. Liposome-encapsulated meglumine antimoniate was about 330-640 times more effective in causing a drop in the death rate than was the free antimonial. The efficacy of treatment was influenced by the lipid composition and charge of the liposomes. For example, positively charged liposomes containing egg phosphatidylcholine were much less effective than negatively charged ones. In contrast, positively and negatively charged sphingomyelin liposomes were equally effective. Liposomes containing phosphatidylserine (which were negatively charged, but also had a much higher charge density) were among the less-effective preparations. Among those tested, the most consistently efficacious liposomes contained highly saturated long-chain phospholipids (eg., dipalmitoyl phosphatidylcholine), cholesterol, and a negative charge. We conclude that liposomes may be useful as carriers of drugs to treat infectious diseases involving the reticuloendothelial system. The toxicities of antimony are very similar to those of arsenic. Encapsulation of antimonial drugs and reduction of the dose required for effective therapy should minimize such systemic toxicities as acute cardiomyopathy and toxic nephritis.

Animals↗
PubMed1977

Effect of the A and B protomers of choleragen on release of trapped glucose from liposomes containing or lacking ganglioside GM1.

Liposomes containing trapped glucose were used to examine the interaction of the A and B protomers of choleragen with ganglioside GM1 and lipid model membranes. The B protomer (choleragenoid) was as effective as choleragen in causing release of trapped glucose from liposomes containing GM1; the A protomer did not release glucose from GM1 liposomes. Neither choleragen nor the A or B protomers caused release of trapped glucose from glycolipid-free liposomes. Anti-choleragen and complement, however, caused release of trapped glucose from ganlioside-free liposomes previously incubated with the A protomer but not from those incubated with the B protomer or choleragen. These results suggest that the A protomer, but not intact choleragen or B protomer, bound to ganglioside-free liposomes. Presumably, the A protomer must be freed of the constraints present in the intact choleragen in order to interact with the liposomal model membrane system.

Bacterial Proteins↗
PubMed1977

Interactions of C-reactive protein and complement with liposomes.

Interactions between C-reactive protein (CRP) and liposomal model membranes containing phosphatidylcholine were investigated. These interactions, in the presence of human serum, resulted in consumption of each of the components of the classical complement pathway (C1-C9) and also resulted in complement-dependent damage and release of trapped glucose from certain types of liposomes. CRP-initiated lysis of liposomes was strongly dependent upon membrane lipid composition. Optimal activity occurred with positively charged liposomes containing galactosylceramide (galactocerebroside); positively charged liposomes lacking galactocerebroside released much less glucose, while negatively charged liposomes, either with or without galactocerebroside, did not release glucose at all. Glucose release was inhibited by free phosphocholine. Lesser, but significant, "background" glucose release independent of the presence of CRP also was observed with positively charged liposomes containing galactocerebroside, and this was associated with marked preferential consumption of the later-acting complement components (C3-C9). C2-deficient human serum failed to support CRP-dependent glucose release, but glucose release was observed upon reconstitution of the serum with C2. Guinea pig complement also did not support CRP-mediated glucose release, but upon addition of human C1q substantial glucose release was observed. We conclude that (i) CRP can sensitize appropriate liposomes for complement-dependent damage via the primary complement pathway starting at the level of C1q; (ii) of those studied, liposomes that are most susceptible to membrane damage contain phosphatidylcholine, have a positive charge, and contain a ceramide glycolipid; and (iii) such liposomes also are sensitive, although to a much lesser degree, to complement-dependent lysis initiated in the absence of CRP and involving consumption of terminal in excess of early acting complement components.

C-Reactive Protein↗
PubMed1977

Cholesterol-dependent human complement activation resulting in damage to liposomal model membranes.

Human (but not guinea pig) complement-mediated damage. It was concluded that human complement was activated spontaneously by liposomes containing a high concentration (71 mol %) of cholesterol. This occurred in the absence of any recognizable antigen or antibody, and did not occur at a low concentration (43 mol %) of cholesterol. Activation of complement resulted in membrane damage and release of trapped liposomal glucose. The complement activity was inhibited by preheating (56 degrees C, 30 min), 10 mM Mg2EDTA3 or EGTA, and by prior adsorption with insoluble immune complexes. Almost all human sera had some reactivity, but it ranged from very low levels (less than 7% liposomal glucose release) to very high levels (greater than 50% glucose release). Complement activation appeared to be mediated by a serum factor which could be removed by adsorption and which was partially heat labile. The factor was transferred by adding heated high reacting human serum to unheated low reacting human serum, or to guinea pig serum. The serum factor, although quantitatively diminished in potency due to heat lability, caused equal activation of each of these two latter complement sources in the presence of high cholesterol liposomes. It did not cause activation of C4-deficient guinea pig complement. These data suggested that the classical complement pathway was activated. The liposomal membrane composition had an influence on this phenomenon. Activities of about half of the human sera were enhanced when galactosyl ceramide, or ceramide alone, was present in the liposomes. Activity was enhanced by longer fatty acyl chain lengths of lecithin when dimyristoyl-, dipalmitoyl-, or distearoyllecithin was employed in the liposomes. Liposomes containing sphingomyelin as the only phospholipid were not sensitive to cholesterol-dependent complement-mediated damage. It was concluded that human complement was activated in the presence of high concentrations of membrane cholesterol and that this was caused by an uncharacterized serum factor and was influenced by the lipid composition of the membrane.

Ceramides↗
PubMed1976

Choleragen-mediated release of trapped glucose from liposomes containing ganglioside GM1.

125I-Labeled choleragen was bound to liposomes containing galactosyl-N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosylglucosylceramide (GM1), but not in large amounts to ganglioside-free liposomes nor to those containing N-acetylneuraminylgalactosylglucosylceramide (GM3), N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosylglucosylceramide (GM2), or N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosylglucosylceramide (GD1a). Choleragen released trapped glucose only from GM1-liposomes. This choleragen-induced glucose release from GM1-liposomes was relatively rapid for the first few minutes, then continued more slowly. The amount of glucose released from liposomes in 30 min was dependent on both the GM1 content and choleragen concentration. Prior incubation of GM1-liposomes with anti-GM1 antiserum prevented the choleragen-dependent release of trapped glucose. After incubation of GM1-liposomes with choleragen, addition of anticholeragen antibodies and complement led to more extensive glucose release. Under these latter conditions a much smaller glucose release was observed also from liposomes containing GM1 or N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosylglucosylceramide in the absence of choleragen. These releases were attributed to naturally-occurring antiganglioside antibodies in the antiserum and complement. Ganglioside-free liposomes did not release glucose in response to anticholeragen and complement. It appears that choleragen in the absence of other proteins binds specifically to liposomes containing GM1 and can induce permeability changes.

Antigen-Antibody Reactions↗
PubMed1975

Vitamin A in liposomes. Inhibition of complement binding and alteration of membrane structure.

Incorporation of vitamin A aldehyde (retinal) into liposomes had an inhibitory effect on the amount of human complement protein bound in the presence of specific antiserum. The total membrane-bound protein was directly measured on liposomes which were washed after incubation in antiserum and fresh human serum (complement). At every concentration of complement, decreased protein binding was found with liposomes which contained retinal. Binding of the third component of complement (C3) was also measured directly on washed liposomes and was found to be decreased in the presence of retinal. The diminution in protein binding due to retinal was not caused by differences in the amount of antibody bound and this was shown by two experiments. First, specific antibody protein binding to liposomes was directly measured and was essentially unaffected by retinal. Second, liposomes were prepared from lipid extracts of sheep erythrocytes. These liposomes were used as as immunoadsorbants to remove antisheep erythrocyte antibodies. The immunoadsorbant capacity was the same in both the presence and the absence of retinal. A further conclusion from these experiments was that retinal did not change the number of liposomal glycolipid antigen molecules available for antibody binding and thus presumably did not change the total number of lipid molecules present on the outer surface of the liposomes. Retinal did have an effect on the geometric structure of the liposomes. Size distribution measurements were performed in the diameter range of 1-6.35 mum by using an electronic particle size analyzer (Coulter Counter). Liposomes containing retinal were shifted toward smaller sizes and had less total surface area and volume. It was suggested that retinal-containing liposomes may have had a tighter packing of the molecules in the phospholipid bilayer. This effect of retinal on liposomal structure may have been responsible for the observed decreased binding of C3 and total complement protein.

Animals↗
PubMed1975

Liposome spin immunoassay: a new sensitive method for detecting lipid substances in aqueous media.

A new sensitive immunoassay procedure is described for quantitative detection of glycolipids and other lipids in aqueous media. As with other immunoassays specific antiserum is first reacted with the free lipid hapten. The amount of antibody activity remaining is measured by assaying the release, in the presence of complement, of spin label marker from liposomes containing the same lipid hapten. Using this method, 2.6 pmol of aqueous Forssman hapten was detected, and the sensitivity could be increased further.

Antigen-Antibody Reactions↗
PubMed1975

Interaction of Sindbis virus with liposomal model membranes.

Radiolabeled Sindbis virus was found to bind to protein-free lipid model membranes (liposomes) derived from extracts of sheep erythrocytes. The virus interaction was dependent on initial pH, and the range of pH dependence (pH 6.0 to 6.8) was the same as the observed with virus-dependent hemagglutination. After the initial interaction, pH changes no longer influenced the virus binding to liposomes. Virus bound to liposomes prepared from a mixture of erythrocyte phospholipids, but the binding was greatly diminished when either cholesterol or phosphatidylethanolamine was omitted from the liposomal lipid mixture. It was concluded that phospholipids and cholesterol, in a bilayer configuration, may be sufficient for specific virus binding in the absence of membrane protein.

Adsorption↗
PubMed1975

Abnormal lipid composition of the red cell membrane in congenital dyserythropoietic anemia type II (HEMPAS).

The lipids derived from the erythrocytes of two siblings with clinical congenital dyserythropietic anemia Type II (CDA-II) and one sibling without clinical evidence of CDA-II underwent a detailed analysis. The total phospholipids, total cholesterol, and cholesterol: phosphate ratio were normal in all siblings. In the two clinically affected siblings there was a significant increase in the phosphatidyl choline with a concomitant decrease in the other phospholipids. The fatty acids of phosphatidyl choline from the CDA-II erythrocytes were normal. The total gylcosphingolipids were increased in all siblings. The glycosphingolipids, di- , tri-, and tetrahexosyl ceramides were increased 1.5- to 10-fold over controls in the clinically affected siblings. The increases were present but less striking in the clinically unaffected sibling. Gluococerebroside was not significantly increased in any of the siblings. The possible causes and significance of the lipid changes are discussed.

Anemia, Hemolytic, Congenital Nonspherocytic↗