Tactile friction of topical creams and emulsions: Friction measurements on excised skin and VitroSkin® using ForceBoard™.

Tactile perception can be investigated through ex vivo friction measurements using a so-called ForceBoard™, providing objective assessments and savings in time and money, compared to a subjective human panel. In this work we aim to compare excised skin versus VitroSkin® as model substrates for tactile friction measurements. A further aim is to detect possible differences between traditional surfactant-based creams, and a particle-stabilized (Pickering) cream and investigate how the different substrates affect the results obtained. It was found that the difference in tactile friction between excised skin and VitroSkin® was small on untreated substrates. When topical creams were applied, the same trends were observed for both substrates, although the frictional variation over time relates to the difference in surface structure between the two substrates. The results also confirmed that there is a difference between starch-based Pickering formulations and surfactant-based creams after application, indicating that the latter is greasier than Pickering cream. It was also shown that the tactile friction of Pickering emulsions was consistently high even with high amounts of oil, indicating a non-greasy, and non-sticky formulation. The characteristics of starch-stabilized Pickering formulations make them promising candidates in the development of surfactant-free topical formulations with unique tactile properties.

Relationship between sensorial and physical characteristics of topical creams: A comparative study on effects of excipients.

Rising consumer demands for safer, more natural, and sustainable topical products have led to increased interest in finding alternative excipients, while retaining functionality and cosmetic appeal. Particle-stabilized Pickering creams have emerged as possible alternatives to replace traditional surfactant-stabilized creams and are thus one of the focuses in this study. The aim of this paper was to study relationships between sensorial characteristics and physical properties to understand how different excipients affect these aspects, comparing one starch particle-stabilized and three surfactant-stabilized formulations. A human panel was used to evaluate sensorial perception, while physical properties were deduced by rheology and tactile friction, together with in vivo and ex vivo skin hydration measurements. The results show that sensorial attributes related to the application phase can be predicted with rheology, while afterfeel attributes can be predicted with tactile friction studies. Differences in rheological and sensory properties among surfactant-based creams could mainly be attributed to the type of emollients used, presence of thickeners and surfactant composition. Differences between surfactant-based creams and a Pickering cream were more evident in relation to the afterfeel perception. Presence of starch particles in the residual film on skin results in high tactile friction and low perception of residual coating, stickiness, greasiness, and slipperiness in sensorial afterfeel.

Novel fibrillar structure confers adhesive property to malaria-infected erythrocytes.

Infections with the malaria parasite Plasmodium falciparum are characterized by sequestration of erythrocytes infected by mature forms of the parasite. Sequestration seems critical for the survival of the parasite, but may lead to excessive binding in the microvasculature and death of the human host. We report here that a novel electrondense fibrillar structure, containing immunoglobulins M or M and G, is found at the surface of infected erythrocytes that adhere to host cells. In cases of cerebral malaria, fibrillar strands are also seen in the microvasculature at autopsy. Our findings may explain the adhesive mechanism by which malaria-infected erythrocytes cause the vascular obstruction seen in complicated malaria infections.

PECAM-1/CD31, an endothelial receptor for binding Plasmodium falciparum-infected erythrocytes.

Excessive binding of Plasmodium falciparum-infected red blood cells (pRBCs) to the vascular endothelium (cytoadherence) and to uninfected erythrocytes (rosetting) may lead to occlusion of the microvasculature and thereby contribute directly to the acute pathology of severe human malaria. A number of endothelial receptors have been identified as targets for the pRBCs, including CD36, intercellular adhesion molecule-1 (ICAM-1) and chondroitin-4-sulfate (CSA). In vitro, CD36 is the most frequent target of strains from patients with mild as well as severe P. falciparum malaria, but is expressed at low levels on the cerebral microvasculature and therefore seems unlikely to be involved in the evolution of cerebral disease. Strains of P. falciparum that form rosettes are associated both with the occurrence of cerebral malaria and severe anemia. Here we report that malaria-infected RBCs adhere to platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31) on the vascular endothelium. pRBCs bind to endothelial cells, to PECAM-1/CD31 transfected cells, and directly to recombinant PECAM-1/CD31 absorbed onto plastic. Soluble PECAM-1/CD31 and monoclonal antibodies specific for the amino-terminal segment of PECAM-1/CD31 (domains 1-4) blocked the binding. Interferon-gamma (IFN-gamma)-essential for the development of cerebral malaria in the mouse-was found to augment adhesion of human pRBCs to PECAM-1/CD31 on endothelial cell monolayers. Our results suggest that PECAM-1/CD31 is a virulence-associated endothelial receptor of P. falciparum-infected RBCs.

Plasmodium falciparum erythrocyte rosetting is mediated by promiscuous lectin-like interactions.

Herein we describe an assay that was developed to quantitate the binding of normal red blood cells (RBC), labeled with carboxy fluorescein diacetate (C-FDA), to rosetting Plasmodium falciparum-infected RBC. The binding of RBC obtained from various animal species or humans to different strains or clones of rosetting P. falciparum-infected RBC was studied. A strain-specific preference of rosetting was observed for either blood group A/AB or B/AB RBC for all parasites tested. The higher affinity of rosette binding of blood group A, B, or AB vs. O RBC was reflected in larger rosettes when a given parasite was grown in RBC of the preferred blood group. The small size of the rosettes formed when P. falciparum was grown in blood group O RBC may be the in vitro correlate of the relative protection against cerebral malaria afforded by belonging to blood group O rather than to blood group A or B. Rosettes of a blood group A-preferring parasite could be completely disrupted by heparin only when grown in blood group O or B RBC, but not when grown in blood group A RBC. Similarly, the rosettes of a blood group B-preferring parasite could be more easily disrupted by heparin when grown in blood group O or A RBC than when grown in blood group B RBC. Several different saccharides inhibited rosetting of group O RBC, including two monosaccharides that are basic components of heparin. The rosetting of the same parasites grown in blood group A or B RBC was less sensitive to heparin and was specifically inhibited only by the terminal mono- and trisaccharides of the A and the B blood group antigens, the H disaccharide, and fucose. Our results suggest that rosetting is mediated by multiple lectin-like interactions, the usage of which rely on the parasite phenotype and whether the receptors are present on the host cell or not.

Small, clonally variant antigens expressed on the surface of the Plasmodium falciparum-infected erythrocyte are encoded by the rif gene family and are the target of human immune responses.

Disease severity in Plasmodium falciparum infections is a direct consequence of the parasite's efficient evasion of the defense mechanisms of the human host. To date, one parasite-derived molecule, the antigenically variant adhesin P. falciparum erythrocyte membrane protein 1 (PfEMP1), is known to be transported to the infected erythrocyte (pRBC) surface, where it mediates binding to different host receptors. Here we report that multiple additional proteins are expressed by the parasite at the pRBC surface, including a large cluster of clonally variant antigens of 30-45 kD. We have found these antigens to be identical to the rifins, predicted polypeptides encoded by the rif multigene family. These parasite products, formerly called rosettins after their identification in rosetting parasites, are prominently expressed by fresh isolates of P. falciparum. Rifins are immunogenic in natural infections and strain-specifically recognized by human immune sera in immunoprecipitation of surface-labeled pRBC extracts. Furthermore, human immune sera agglutinate pRBCs digested with trypsin at conditions such that radioiodinated PfEMP1 polypeptides are not detected but rifins are detected, suggesting the presence of epitopes in rifins targeted by agglutinating antibodies. When analyzed by two-dimensional electrophoresis, the rifins resolved into several isoforms in the pI range of 5.5-6.5, indicating molecular microheterogeneity, an additional potential novel source of antigenic diversity in P. falciparum. Prominent polypeptides of 20, 22, 76-80, 140, and 170 kD were also detected on the surfaces of pRBCs bearing in vitro-propagated or field-isolated parasites. In this report, we describe the rifins, the second family of clonally variant antigens known to be displayed by P. falciparum on the surface of the infected erythrocyte.

The semiconserved head structure of Plasmodium falciparum erythrocyte membrane protein 1 mediates binding to multiple independent host receptors.

Erythrocytes infected with mature forms of Plasmodium falciparum do not circulate but are withdrawn from the peripheral circulation; they are bound to the endothelial lining and to uninfected erythrocytes in the microvasculature. Blockage of the blood flow, hampered oxygen delivery, and severe malaria may follow if binding is excessive. The NH(2)-terminal head structure (Duffy binding-like domain 1 [DBL1alpha]-cysteine-rich interdomain region [CIDR1alpha]) of a single species of P. falciparum erythrocyte membrane protein 1 (PfEMP1) is here shown to mediate adherence to multiple host receptors including platelet-endothelial cell adhesion molecule 1 (PECAM-1)/CD31, the blood group A antigen, normal nonimmune immunoglobulin M, three virulence-associated receptor proteins, a heparan sulfate-like glucosaminoglycan, and CD36. DBL2delta was found to mediate additional binding to PECAM-1/CD31. The exceptional binding activity of the PfEMP1 head structure and its relatively conserved nature argues that it holds an important role in erythrocyte sequestration and therefore in the virulence of the malaria parasite.

Antibodies in malarial sera to parasite antigens in the membrane of erythrocytes infected with early asexual stages of Plasmodium falciparum.

Monolayers of human erythrocytes (E) infected with Plasmodium falciparum were briefly fixed with 1% glutaraldehyde and air dried. They were then exposed to sera from patients with P. falciparum malaria or from donors immune to this parasite and tested in an indirect immunofluorescence assay (IFA). Parasites in infected E were made visible by counterstaining with ethidium bromide. Immunofluorescence (IF) was restricted to the surface of infected E. No antibody binding was detected unless the E were dried, suggesting that the relevant antigens were not available on the outer layers of the E surface. Staining over large parts of the E surface was seen already when the merozoite penetrated noninfected cells and was strong in E containing early stages of the parasite (rings, trophozoites). It was weak or absent from E containing schizonts. Antibodies in sera from different parts of Africa, Colombia, or Sweden reacted similarly with E infected with a Tanzanian P. falciparum strain kept in culture for many years and with parasitized E freshly drawn from African, Swedish, or Colombian patients. All sera from residents of a holoendemic area (Liberia) were IFA positive. In contrast, some sera from Colombian or Swedish patients with primary infection gave negative results. The results of the IFA and of an enzyme-linked immunosorbent assay in which fixed and dried E were the targets were well-correlated, suggesting that the same antibodies were detected by these assays. The antigens involved in the IFA were susceptible to pronase but not to trypsin or neuraminidase. E surface IF was inhibited by lysates of infected E, merozoite extracts, or soluble antigens present in P. falciparum culture supernatants but not by lysates of normal E or ghost extracts. The inhibitory antigens were heat stable (100 degrees C, 5 min). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by immunoblotting of either antigen-enriched preparations from culture supernatants or merozoite extracts showed that antibodies eluted from monolayers of infected E reacted consistently with a predominant polypeptide of Mr 155,000 and two to four minor polypeptides of lower molecular weights. Metabolic labeling of the parasites with 75Se-methionine indicated that these antigens were parasite derived. We conclude that the antigens involved in these reactions are released from bursting schizonts or merozoites and are deposited in the E membrane in the course of invasion.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasmodium falciparum-infected erythrocytes form spontaneous erythrocyte rosettes.

Erythrocytes infected with trophozoites or schizonts of Plasmodium falciparum bind uninfected erythrocytes, leading to rosette formation. Both established laboratory strains and fresh isolates from patients form such rosettes, but at widely different frequencies. IgG preparations from the serum of some P. falciparum-immune donors and heparin inhibited rosette formation. The results indicate that cytoadherence of infected erythrocytes to endothelial cells and rosetting represent distinct genetic traits.

Identification of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) as the rosetting ligand of the malaria parasite P. falciparum.

Severe Plasmodium falciparum malaria is characterized by excessive sequestration of infected and uninfected erythrocytes in the microvasculature of the affected organ. Rosetting, the adhesion of P. falciparum-infected erythrocytes to uninfected erythrocytes is a virulent parasite phenotype associated with the occurrence of severe malaria. Here we report on the identification by single-cell reverse transcriptase PCR and cDNA cloning of the adhesive ligand P. falciparum erythrocyte membrane protein 1 (PfEMP1). Rosetting PfEMP1 contains clusters of glycosaminoglycan-binding motifs. A recombinant fusion protein (Duffy binding-like 1-glutathione S transferase; Duffy binding-like-1-GST) was found to adhere directly to normal erythrocytes, disrupt naturally formed rosettes, block rosette reformation, and bind to a heparin-Sepharose matrix. The adhesive interactions could be inhibited with heparan sulfate or enzymes that remove heparan sulfate from the cell surface whereas other enzymes or similar glycosaminoglycans of a like negative charge did not affect the binding. PfEMP1 is suggested to be the rosetting ligand and heparan sulfate, or a heparan sulfate-like molecule, the receptor both for PfEMP1 binding and naturally formed erythrocyte rosettes.

Role of nonimmune IgG bound to PfEMP1 in placental malaria.

Infections with Plasmodium falciparum during pregnancy lead to the accumulation of parasitized red blood cells (infected erythrocytes, IEs) in the placenta. IEs of P. falciparum isolates that infect the human placenta were found to bind immunoglobulin G (IgG). A strain of P. falciparum cloned for IgG binding adhered massively to placental syncytiotrophoblasts in a pattern similar to that of natural infections. Adherence was inhibited by IgG-binding proteins, but not by glycosaminoglycans or enzymatic digestion of chondroitin sulfate A or hyaluronic acid. Normal, nonimmune IgG that is bound to a duffy binding-like domain beta of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) might at the IE surface act as a bridge to neonatal Fc receptors of the placenta.

Human monoclonal antibodies to Pf 155, a major antigen of malaria parasite Plasmodium falciparum.

Pf 155, a protein of the human malaria parasite Plasmodium falciparum, is strongly immunogenic in humans and is believed to be a prime candidate for the preparation of a vaccine. Human monoclonal antibodies to Pf 155 were obtained by cloning B cells that had been prepared from an immune donor and transformed with Epstein-Barr virus. When examined by indirect immunofluorescence, these antibodies stained the surface of infected erythrocytes, free merozoites, segmented schizonts, and gametocytes. They bound to a major polypeptide with a relative molecular weight of 155K and to two minor ones (135K and 120K), all having high affinity for human glycophorin. The antibodies strongly inhibited merozoite reinvasion in vitro, suggesting that they might be appropriate reagents for therapeutic administration in vivo.

Protein adsorption to solid surfaces.

The phenomenon of protein adsorption to solid surfaces affects the performance of many materials and processes, in areas ranging from medicine to biochemical engineering. Controlling protein adsorption, from solutions of single proteins as well as from more complex mixtures, requires an understanding of the mechanism(s) by which it occurs. This, in turn, entails detailed characterization of both the protein and the solid surface and identification of those factors controlling the adsorption process.

A protease inhibitor associated with the surface of Toxoplasma gondii.

Toxoplasma gondii has a broad host-range including man and a variety of warm-blooded animals. The ability to infect and survive in this wide spectrum of hosts suggests highly evolved mechanisms to handle the harsh environments encountered. Here we show that extracellular tachyzoites are resistant to milligram levels of trypsin and describe the presence of an inhibitor of trypsin associated with the surface of T. gondii, TgTI. TgTI has an estimated molecular mass of 37000 dalton and is encoded by the TgTI-gene which is found at low abundance as an expressed sequence tag (EST) in both the bradyzoite and tachyzoite stages. The inhibitory binding region was found to be in the N-terminus of TgTI where aminoacid-alignment to earlier described protease inhibitors demonstrates 75% similarity. In functional analysis, recombinant TgTI-protein inhibits the activity of trypsin approximately 10 times more efficiently than an inhibitor isolated from soybean. In contrast to other known trypsin inhibitors, TgTI also possesses a predicted membrane-binding region. Polyclonal antibodies raised against recombinant TgTI bind to the surface of the tachyzoite stage as seen both by immunofluorescence and immunoprecipitation of surface labelled parasite proteins. The high survival rate of the parasite in the upper gastrointestinal tract may be enhanced by the presence of the TgTI-molecule.

Enhancement or inhibition of Plasmodium falciparum erythrocyte reinvasion in vitro by antibodies to an asparagine rich protein.

A clone encoding a recombinant protein which reacted strongly with human antibodies from a donor clinically immune to malaria, was isolated from a genomic Plasmodium falciparum library. Mice injected with this protein, designated 10b, produced antibodies which reacted with all developmental stages of erythrocytic asexual parasites in indirect immunofluorescence. In immunoblotting, the same antibodies recognized two P. falciparum polypeptides of 36 kDa and 33 kDa. Of three monoclonal antibodies raised against the 10b recombinant protein, two inhibited parasite reinvasion of erythrocytes in an isolate specific manner. Surprisingly, however, the third was found to significantly enhance reinvasion of erythrocytes and also to induce a more rapid maturation of intraerythrocytic parasites in all isolates tested. Nucleotide sequence analysis of the 1124 bp insert revealed that it encodes a protein which consists of 30% asparagine and contains three asparagine rich, imperfect tandem repeats: Lys-Lys-Asn-Asn (3x), Met-Asn-His/Gln-Pro-Asn-Asn (14x), and Lys-Asn-Asn-Asn-Asn (7x).

Monoclonal antibodies to a synthetic peptide corresponding to a repeated sequence in the Plasmodium falciparum antigen Pf155.

Mouse monoclonal antibodies were prepared against a synthetic peptide (EENVEHDA) corresponding to a tandemly repeated sequence in the C-terminus of the Plasmodium falciparum antigen Pf155. One antibody (IgG1) producing hybridoma was studied in detail. The specificity of the antibody was determined by enzyme-linked immunosorbent assays using bovine serum albumin-conjugated or free peptides as solid phase antigens and various synthetic peptides for inhibition. The antibody reacted with Pf155 as detected by immunofluorescence and immunoblotting. It was also an efficient inhibitor of merozoite invasion in P. falciparum in vitro cultures indicating that it defines a biologically important epitope present on the native Pf155 molecule.

A comparison of knobby (K+) and knobless (K-) parasites from two strains of Plasmodium falciparum.

Erythrocytes infected with Plasmodium falciparum develop knob-like protrusions on their membranes. Knobby (K+) parasites of the FCR-3 (Gambian) strain have been shown to possess a histidine-labelled protein of apparent molecular weight 80 000 which is absent from knobless (K-) variants of the same strain. Here we report similar findings with K+ and K- parasites of another strain, the Malayan Camp strain, and also with cloned K+ and K- parasites of the FCR-3 strain. A histidine-labelled protein unique to the two K+ parasites was identified as a broad band with an apparent molecular weight of 89 000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The presence of this protein in both K+ Malayan Camp parasites and K+ FCR-3 (Gambian) parasites and its absence from K- parasites of both strains is consistent with this protein being a major component of knobs.

The squirrel monkey as an experimental model for Plasmodium falciparum erythrocyte rosette formation.

Experimental cerebral malaria was recently found to occur in the squirrel monkey Saimiri sciureus when infected with the human malaria parasite Plasmodium falciparum. This report is concerned with the existence of spontaneous rosette formation ex vivo (infected blood samples) and in vitro (cultured parasites) between red blood cells (RBC) infected with squirrel monkey-adapted P. falciparum isolates and normal squirrel monkey RBC. Transfer of P. falciparum with high rosette formation tendencies (90-100 R+) from one donor monkey to several recipients gave rise to parasites that varied extensively in their ex vivo rosette formation capacity (4-96% R+). However, all individual parasites readily form rosettes after 24 hr of in vitro culture (60-95% R+). Host factors may be involved in the modulation of rosette formation, although it is found to occur both in splenectomized and spleen-intact animals. Cross-rosette formation is seen between parasitized human RBC and normal squirrel monkey RBC and vice versa, and rosettes formed by RBC of the two hosts are similarly affected by pH, temperature, EDTA, trypsin, as well as squirrel monkey and African human hyperimmune IgG. These characteristics of rosette formation are preserved after long-term in vitro culture in human RBC. Rosettes formed by some isolates are highly sensitive to heparin while others are not, suggesting at least two distinct mechanisms of rosette formation. This idea is also supported by the observation that specific squirrel monkey antisera to heparin-sensitive strains does not dissociate rosettes formed by a heparin-resistant strain. The results suggest that rosettes and anti-rosette formation antibodies formed by squirrel monkeys and humans exhibited similar characteristics, and that the squirrel monkey is therefore a good experimental model to study erythrocyte rosette formation and cerebral malaria.