Inhibition of virus-induced cell fusion by apolipoprotein A-I and its amphipathic peptide analogs

HDL-based therapeutics: A promising frontier in combating viral and bacterial infections

Low levels of high-density lipoprotein (HDL) and impaired HDL functionality have been consistently associated with increased susceptibility to infection and its serious consequences. This has been attributed to the critical role of HDL in maintaining cellular lipid homeostasis, which is essential for the proper functioning of immune and structural cells. HDL, a multifunctional particle, exerts pleiotropic effects in host defense against pathogens. It functions as a natural nanoparticle, capable of sequestering and neutralizing potentially harmful substances like bacterial lipopolysaccharides. HDL possesses antiviral activity, preventing viruses from entering or fusing with host cells, thereby halting their replication cycle. Understanding the complex relationship between HDL and the immune system may reveal innovative targets for developing new treatments to combat infectious diseases and improve patient outcomes. This review aims to emphasize the role of HDL in influencing the course of bacterial and viral infections and its and its therapeutic potential.

The Influence of SARS-CoV-2 Infection on Lipid Metabolism—The Potential Use of Lipid-Lowering Agents in COVID-19 Management

Several studies have indicated lipid metabolism alterations during COVID-19 infection, specifically a decrease in high-density lipoprotein (HDL) and low-density lipoprotein (LDL) concentrations and an increase in triglyceride (TG) levels during the infection. However, a decline in triglycerides can also be observed in critical cases. A direct correlation can be observed between a decrease in serum cholesterol, HDL-C, LDL-C and TGs, and the severity of the disease; these laboratory findings can serve as potential markers for patient outcomes. The transmission of coronavirus increases proportionally with rising levels of cholesterol in the cell membrane. This is due to the fact that cholesterol increases the number of viral entry spots and the concentration of angiotensin-converting enzyme 2 (ACE2) receptor, crucial for viral penetration. Studies have found that lower HDL-C levels correspond with a higher susceptibility to SARS-CoV-2 infection and infections in general, while higher HDL-C levels were related to a lower risk of developing them. However, extremely high HDL-C levels in serum increase the risk of infectious diseases and is associated with a higher risk of cardiovascular events. Low HDL-C levels are already accepted as a marker for risk stratification in critical illnesses, and higher HDL-C levels prior to the infection is associated with a lower risk of death in older patients. The correlation between LDL-C levels and disease severity is still unclear. However, TG levels were significantly higher in non-surviving severe patients compared to those that survived; therefore, elevated TG-C levels in COVID-19 patients may be considered an indicator of uncontrolled inflammation and an increased risk of death.

Multifaced Roles of HDL in Sepsis and SARS-CoV-2 Infection: Renal Implications

High-density lipoproteins (HDLs) are a class of blood particles, principally involved in mediating reverse cholesterol transport from peripheral tissue to liver. Omics approaches have identified crucial mediators in the HDL proteomic and lipidomic profile, which are involved in distinct pleiotropic functions. Besides their role as cholesterol transporter, HDLs display anti-inflammatory, anti-apoptotic, anti-thrombotic, and anti-infection properties. Experimental and clinical studies have unveiled significant changes in both HDL serum amount and composition that lead to dysregulated host immune response and endothelial dysfunction in the course of sepsis. Most SARS-Coronavirus-2-infected patients admitted to the intensive care unit showed common features of sepsis disease, such as the overwhelmed systemic inflammatory response and the alterations in serum lipid profile. Despite relevant advances, episodes of mild to moderate acute kidney injury (AKI), occurring during systemic inflammatory diseases, are associated with long-term complications, and high risk of mortality. The multi-faceted relationship of kidney dysfunction with dyslipidemia and inflammation encourages to deepen the clarification of the mechanisms connecting these elements. This review analyzes the multifaced roles of HDL in inflammatory diseases, the renal involvement in lipid metabolism, and the novel potential HDL-based therapies.

Host Defence Cryptides from Human Apolipoproteins: Applications in Medicinal Chemistry

Several eukaryotic proteins with defined physiological roles may act as precursors of cryptic bioactive peptides released upon protein cleavage by the host and/or bacterial proteases. Based on this, the term "cryptome" has been used to define the unique portion of the proteome encompassing proteins with the ability to generate bioactive peptides (cryptides) and proteins (crypteins) upon proteolytic cleavage. Hence, the cryptome represents a source of peptides with potential pharmacological interest. Among eukaryotic precursor proteins, human apolipoproteins play an important role, since promising bioactive peptides have been identified and characterized from apolipoproteins E, B, and A-I sequences. Human apolipoproteins derived peptides have been shown to exhibit antibacterial, anti-biofilm, antiviral, anti-inflammatory, anti-atherogenic, antioxidant, or anticancer activities in in vitro assays and, in some cases, also in in vivo experiments on animal models. The most interesting Host Defence Peptides (HDPs) identified thus far in human apolipoproteins are described here with a focus on their biological activities applicable to biomedicine. Altogether, reported evidence clearly indicates that cryptic peptides represent promising templates for the generation of new drugs and therapeutics against infectious diseases.

High-Density Lipoproteins Are Bug Scavengers

Lipoproteins were initially defined according to their composition (lipids and proteins) and classified according to their density (from very low- to high-density lipoproteins—HDLs). Whereas their capacity to transport hydrophobic lipids in a hydrophilic environment (plasma) is not questionable, their primitive function of cholesterol transporter could be challenged. All lipoproteins are reported to bind and potentially neutralize bacterial lipopolysaccharides (LPS); this is particularly true for HDL particles. In addition, HDL levels are drastically decreased under infectious conditions such as sepsis, suggesting a potential role in the clearance of bacterial material and, particularly, LPS. Moreover, "omics" technologies have unveiled significant changes in HDL composition in different inflammatory states, ranging from acute inflammation occurring during septic shock to low-grade inflammation associated with moderate endotoxemia such as periodontal disease or obesity. In this review, we will discuss HDL modifications associated with exposure to pathogens including bacteria, viruses and parasites, with a special focus on sepsis and the potential of HDL therapy in this context. Low-grade inflammation associated with atherosclerosis, periodontitis or metabolic syndrome may also highlight the protective role of HDLs in theses pathologies by other mechanisms than the reverse transport of cholesterol.

Liver Transcriptome and miRNA Analysis of Silver Carp (Hypophthalmichthys molitrix) Intraperitoneally Injected With Microcystin-LR

Next-generation sequencing was used to analyze the effects of toxic microcystin-LR (MC-LR) on silver carp (Hypophthalmichthys molitrix). Silver carps were intraperitoneally injected with MC-LR, and RNA-seq and miRNA-seq in the liver were analyzed at 0.25, 0.5, and 1 h. The expression of glutathione S-transferase (GST), which acts as a marker gene for MC-LR, was tested to determine the earliest time point at which GST transcription was initiated in the liver tissues of the MC-LR-treated silver carps. Hepatic RNA-seq/miRNA-seq analysis and data integration analysis were conducted with reference to the identified time point. Quantitative PCR (qPCR) was performed to detect the expression of the following genes at the three time points: heme oxygenase 1 (HO-1), interleukin-10 receptor 1 (IL-10R1), apolipoprotein A-I (apoA-I), and heme binding protein 2 (HBP2). Results showed that the liver GST expression was remarkably decreased at 0.25 h (P < 0.05). RNA-seq at this time point revealed that the liver tissue contained 97,505 unigenes, including 184 significantly different unigenes and 75 unknown genes. Gene Ontology (GO) term enrichment analysis suggested that 35 of the 145 enriched GO terms were significantly enriched and mainly related to the immune system regulation network. KEGG pathway enrichment analysis showed that 18 of the 189 pathways were significantly enriched, and the most significant was a ribosome pathway containing 77 differentially expressed genes. miRNA-seq analysis indicated that the longest miRNA had 22 nucleotides (nt), followed by 21 and 23 nt. A total of 286 known miRNAs, 332 known miRNA precursor sequences, and 438 new miRNAs were predicted. A total of 1,048,575 mRNA–miRNA interaction sites were obtained, and 21,252 and 21,241 target genes were respectively predicted in known and new miRNAs. qPCR revealed that HO-1, IL-10R1, apoA-I, and HBP2 were significantly differentially expressed and might play important roles in the toxicity and liver detoxification of MC-LR in fish. These results were consistent with those of high-throughput sequencing, thereby verifying the accuracy of our sequencing data. RNA-seq and miRNA-seq analyses of silver carp liver injected with MC-LR provided valuable and new insights into the toxic effects of MC-LR and the antitoxic mechanisms of MC-LR in fish.

The RNA/miRNA data are available from the NCBI database Registration No. : SRP075165.

Molecular Characterization and Growth Association of Two Apolipoprotein A-Ib Genes in Common Carp (Cyprinus carpio)

Apolipoprotein A-I (ApoA-I) is functionally involved in the transportation and metabolism of lipids in vertebrates. In this study, two isoforms of apoA-Ib in common carp (Cyprinus carpio L.) were characterized. Sequence comparison and phylogenetic analysis showed that C. carpio ApoA-Ib is relatively conserved within cyprinid fishes. During embryonic development, C. carpioapoA-Ib was first expressed at the stage of multi-cells, and the highest mRNA level was observed at the stage of optic vesicle. A ubiquitous expression pattern was detected in various tissues with extreme predominance in the liver. Significantly different expression levels were observed between light and heavy body weight groups and also in the compensatory growth test. Seventeen and eight single-nucleotide polymorphisms (SNPs) were identified in matured mRNA of the C. carpioapoA-Ib.1 and apoA-Ib.2, respectively. Two of these SNPs (apoA-Ib.2-g.183A>T and apoA-Ib.2-g.1753C>T) were significantly associated with body weight and body length in two populations of common carp. These results indicate that apoA-Ib may play an important role in the modulation of growth and development in common carp.

Apolipoprotein A-I in Labeo rohita: Cloning and functional characterisation reveal its broad spectrum antimicrobial property, and indicate significant role during ectoparasitic infection

Apolipoprotein A-I (ApoA-I) is the most abundant and multifunctional high-density lipoprotein (HDL) having a major role in lipid transport and potent antimicrobial activity against a wide range of microbes. In this study, a complete CDS of 771 bp of Labeo rohita (rohu) ApoA-I (LrApoA-I) encoding a protein of 256 amino acids was amplified, cloned and sequenced. Tissue specific transcription analysis of LrApoA-I revealed its expression in a wide range of tissues, with a very high level of expression in liver and spleen. Ontogenic study of LrApoA-I expression showed presence of transcripts in milt and 3 h post-fertilization onwards in the larvae. The expression kinetics of LrApoA-I was studied upon infection with three different types of pathogens to elucidate its functional significance. Its expression was found to be up-regulated in the anterior kidney of L. rohita post-infection with Aeromonas hydrophila. Similarly following poly I:C (poly inosinic:cytidylic) stimulation, the transcript levels increased in both the anterior kidney and liver tissues. Significant up-regulation of LrApoA-I expression was observed in skin, mucous, liver and anterior kidney of the fish challenged with the ectoparasite Argulus siamensis. Immunomodulatory effect of recombinant LrApoA-I (rApoA-I) produced in Escherichia coli was demonstrated against A. hydrophila challenge in vivo. L. rohita administered with rApoA-I at a dose of 100 μg exhibited significantly higher protection (∼55%) upon challenge with A. hydrophila 12 h post-administration of the protein, in comparison to that observed in control group, along with higher level of expression of immune-related genes. The heightened expression of ApoA-I observed post-infection reflected its involvement in immune responses against a wide range of infections including bacterial, viral as well as parasitic pathogens. Our results also suggest the possibility of using rApoA-I as an immunostimulant, particularly rendering protection against A. hydrophila.

Expression of apolipoprotein A-I and A-II in rainbow trout reproductive tract and their possible role in antibacterial defence

Antimicrobial proteins such as apolipoproteins A (ApoA-I and ApoA-II) play an important role in the primary defence barrier in vertebrates including fish. The aims of the present study were to isolate and characterise rainbow trout seminal plasma ApoA-I and ApoA-II, to examine the mRNA expression of each apolipoprotein in testis and spermatic ducts, and to test the antibacterial properties of the apolipoproteins. Using a three-step isolation procedure consisting of ion-exchange chromatography, gel filtration and preparative SDS-PAGE, apolipoproteins were purified and identified as ApoA-I and ApoA-II. Both apolipoproteins were represented by several proteoforms. The expression of ApoA-I and ApoA-II mRNA in the reproductive tract and their antibacterial properties against Escherichia coli suggest that seminal apolipoproteins play an important role in innate immunity in the rainbow trout reproductive tract. The functions of seminal ApoA can be related to protection of sperm and reproductive tissue from microbial attack and to the maintenance of sperm membrane integrity.

Isolation and function analysis of apolipoprotein A-I gene response to virus infection in grouper

Apolipoproteins, synthesized mainly in liver and intestine and bounded to lipids, play important roles in lipid transport and uptake through the circulation system. In this study, an apolipoprotein A-I gene homologue was cloned from orange-spotted grouper Epinephelus coioides (designed as Ec-ApoA-I) by rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA of Ec-ApoA-I was comprised of 1278 bp with a 792 bp open reading frame (ORF) that encodes a putative protein of 264 amino acids. Quantitative real-time PCR (qPCR) analysis revealed that Ec-ApoA-I was abundant in liver and intestine, and the expression in liver was significantly (P < 0.01) up-regulated after the stimulation of LPS, Poly(I:C), Vibrio alginolyticus, and Singapore grouper iridovirus (SGIV). Recombinant Ec-ApoA-I (rEc-ApoA-I) was produced in Escherichia coli BL21 (DE3) expression system exhibited bacteriolyticactivity against Microcococcus lysodeikticus and Aeromonas hydrophila. Intracellular localization revealed that Ec-ApoA-I distributed in both cytoplasm and nucleus, and predominantly in the cytoplasm. Overexpression of Ec-ApoA-I in grouper Brain (GB) cells could inhibit the replication of SGIV. These results together indicated that Ec-ApoA-I perhaps is involved in the responses to bacterial and viral challenge.

Characterization, expression and antibacterial properties of apolipoproteins A from carp (Cyprinus carpio L.) seminal plasma

Apolipoproteins A are multifunctional proteins that, in addition to contributing to lipid metabolism and transport, are associated with the innate immune system in fish. Using a three step isolation procedure consisting of affinity chromatography on Blue-Sepharose, delipidation and reverse phase HPLC we isolated apolipoproteins from carp seminal plasma and identified them as ApoA-I and Apo-14 kDa. Moreover, we provided the full-length cDNA sequence of ApoA-I encoding 257 amino acids including a 18 amino acid signal peptide and a 4 amino acid propeptide. Apolipoproteins corresponded to the most abundant proteins in carp seminal plasma. Both ApoA-I and Apo-14 kDa were represented by several proteoforms that differ both in molecular mass and isoelectric point. The proteoforms of ApoA-I characteristic for seminal plasma were distinguished from those of blood. Carp seminal plasma ApoA-I and Apo-14 kDa showed a high immunologic similarity to their counterparts in carp blood and seminal plasma of other Cyprinid species. The mRNA expression analysis and immunohistochemical study suggest synthesis and secretion of ApoA-I and Apo-14 kDa in the fish reproductive tract and suggest a role in spermatogenesis and the stabilization of sperm membrane. Moreover, ApoA-I displayed bactericidal activity against Escherichia coli and bacteriostatic activity against Aeromonas hydrophila which suggests that ApoA-I is associated with innate immune system of the fish reproductive tract.

Animal models and the tumor microenvironment: studies of tumor-host symbiosis

The contributions of murine models to elucidation of processes central to tumor growth are reviewed. Localized acidosis, increased interstitial pressure, perturbations in structure and function of the extracellular matrix, hypoxia, angiogenesis, and co-optation of the immune response are all phenomena that promote tumor survival and metastasis. The use of animal models is critical to understanding the pathophysiology of these processes and the development of more effective cancer therapies.

Molecules that mimic apolipoprotein A-I: potential agents for treating atherosclerosis

Certain amphipathic α-helical peptides can functionally mimic many of the properties of full-length apolipoproteins, thereby offering an approach to modulate high-density lipoprotein (HDL) for combating atherosclerosis. In this Perspective, we summarize the key findings and advances over the past 25 years in the development of peptides that mimic apolipoproteins, especially apolipoprotein A-I (apoA-I). This assemblage of information provides a reasonably clear picture of the state of the art in the apolipoprotein mimetic field, an appreciation of the potential for such agents in pharmacotherapy, and a sense of the opportunities for optimizing the functional properties of HDL.

The cardioprotective protein apolipoprotein A1 promotes potent anti-tumorigenic effects

Here, we show that apolipoprotein A1 (apoA1), the major protein component of high density lipoprotein (HDL), through both innate and adaptive immune processes, potently suppresses tumor growth and metastasis in multiple animal tumor models, including the aggressive B16F10L murine malignant melanoma model. Mice expressing the human apoA1 transgene (A1Tg) exhibited increased infiltration of CD11b(+) F4/80(+) macrophages with M1, anti-tumor phenotype, reduced tumor burden and metastasis, and enhanced survival. In contrast, apoA1-deficient (A1KO) mice showed markedly heightened tumor growth and reduced survival. Injection of human apoA1 into A1KO mice inoculated with tumor cells remarkably reduced both tumor growth and metastasis, enhanced survival, and promoted regression of both tumor and metastasis burden when administered following palpable tumor formation and metastasis development. Studies with apolipoprotein A2 revealed the anti-cancer therapeutic effect was specific to apoA1. In vitro studies ruled out substantial direct suppressive effects by apoA1 or HDL on tumor cells. Animal models defective in different aspects of immunity revealed both innate and adaptive arms of immunity contribute to complete apoA1 anti-tumor activity. This study reveals a potent immunomodulatory role for apoA1 in the tumor microenvironment, altering tumor-associated macrophages from a pro-tumor M2 to an anti-tumor M1 phenotype. Use of apoA1 to redirect in vivo elicited tumor-infiltrating macrophages toward tumor rejection may hold benefit as a potential cancer therapeutic.

High-throughput sequence analysis of turbot (Scophthalmus maximus) transcriptome using 454-pyrosequencing for the discovery of antiviral immune genes

Background

Turbot (Scophthalmus maximus L.) is an important aquacultural resource both in Europe and Asia. However, there is little information on gene sequences available in public databases. Currently, one of the main problems affecting the culture of this flatfish is mortality due to several pathogens, especially viral diseases which are not treatable. In order to identify new genes involved in immune defense, we conducted 454-pyrosequencing of the turbot transcriptome after different immune stimulations.

Methodology/Principal Findings

Turbot were injected with viral stimuli to increase the expression level of immune-related genes. High-throughput deep sequencing using 454-pyrosequencing technology yielded 915,256 high-quality reads. These sequences were assembled into 55,404 contigs that were subjected to annotation steps. Intriguingly, 55.16% of the deduced protein was not significantly similar to any sequences in the databases used for the annotation and only 0.85% of the BLASTx top-hits matched S. maximus protein sequences. This relatively low level of annotation is possibly due to the limited information for this specie and other flatfish in the database. These results suggest the identification of a large number of new genes in turbot and in fish in general. A more detailed analysis showed the presence of putative members of several innate and specific immune pathways.

Conclusions/Significance

To our knowledge, this study is the first transcriptome analysis using 454-pyrosequencing for turbot. Previously, there were only 12,471 EST and less of 1,500 nucleotide sequences for S. maximus in NCBI database. Our results provide a rich source of data (55,404 contigs and 181,845 singletons) for discovering and identifying new genes, which will serve as a basis for microarray construction, gene expression characterization and for identification of genetic markers to be used in several applications. Immune stimulation in turbot was very effective, obtaining an enormous variety of sequences belonging to genes involved in the defense mechanisms.

Alzheimer's Disease: APP, Gamma Secretase, APOE, CLU, CR1, PICALM, ABCA7, BIN1, CD2AP, CD33, EPHA1, and MS4A2, and Their Relationships with Herpes Simplex, C. Pneumoniae, Other Suspect Pathogens, and the Immune System

Alzheimer's disease susceptibility genes, APP and gamma-secretase, are involved in the herpes simplex life cycle, and that of other suspect pathogens (C. pneumoniae, H. pylori, C. neoformans, B. burgdorferri, P. gingivalis) or immune defence. Such pathogens promote beta-amyloid deposition and tau phosphorylation and may thus be causative agents, whose effects are conditioned by genes. The antimicrobial effects of beta-amyloid, the localisation of APP/gamma-secretase in immunocompetent dendritic cells, and gamma secretase cleavage of numerous pathogen receptors suggest that this network is concerned with pathogen disposal, effects which may be abrogated by the presence of beta-amyloid autoantibodies in the elderly. These autoantibodies, as well as those to nerve growth factor and tau, also observed in Alzheimer's disease, may well be antibodies to pathogens, due to homology between human autoantigens and pathogen proteins. NGF or tau antibodies promote beta-amyloid deposition, neurofibrillary tangles, or cholinergic neuronal loss, and, with other autoantibodies, such as anti-ATPase, are potential agents of destruction, whose formation is dictated by sequence homology between pathogen and human proteins, and thus by pathogen strain and human genes. Pathogen elimination in the ageing population and removal of culpable autoantibodies might reduce the incidence and offer hope for a cure in this affliction.

Conformational transitions in the membrane scaffold protein of phospholipid bilayer nanodiscs

Phospholipid bilayer nanodiscs are model membrane systems that provide an environment where membrane proteins are highly stable and monodisperse without the use of detergents or liposomes. Nanodiscs consist of a discoidal phospholipid bilayer encircled by two copies of an amphipathic alpha helical membrane scaffold protein, which is modeled from apolipoprotein A-1. Hydrogen exchange mass spectrometry was used to probe the structure and dynamics of the scaffold protein in the presence and absence of lipid. On nanodisc self-assembly, the entire scaffold protein gained significant protection from exchange, consistent with a large, protein-wide, structural rearrangement. This protection was short-lived and the scaffold protein was highly deuterated within 2 h. Several regions of the scaffold protein, in both the lipid-free and lipid-associated states, displayed EX1 unfolding kinetics. The rapid deuteration of the scaffold protein and the presence of correlated unfolding events both indicate that nanodiscs are dynamic rather than rigid bodies in solution. This work provides a catalog of the expected scaffold protein peptic peptides in a nanodisc-hydrogen exchange mass spectrometry experiment and their deuterium uptake signatures, data that can be used as a benchmark to verify correct assembly and nanodisc structure. Such reference data will be useful control data for all hydrogen exchange mass spectrometry experiments involving nanodiscs in which transmembrane or lipid-associated proteins are the primary molecule(s) of interest.

High density lipoprotein: it's not just about lipid transport anymore

Plasma levels of high density lipoprotein cholesterol (HDL-C) have long been associated with protection against cardiovascular disease (CVD) in large populations. However, HDL-C has been significantly less useful for predicting CVD risk in individual patients. This has ignited a new debate on the merits of measuring HDL quantity versus quality in terms of protective potential. In addition, numerous recent studies have begun to uncover HDL functions that vary surprisingly from traditional lipid transport roles. In this paper, we review recent findings that point to important functions for HDL that go well beyond lipid transport. These discoveries suggest that HDL might be a platform that mediates protection from a host of disease states ranging from CVD to diabetes to infectious disease.

Spotlight on Human LL-37, an Immunomodulatory Peptide with Promising Cell-Penetrating Properties

Cationic antimicrobial peptides are major components of innate immunity and help control the initial steps of the infectious process. They are expressed not only by immunocytes, but also by epithelial cells. They share an amphipathic secondary structure with a polar cationic site, which explains their tropism for prokaryote membranes and their hydrophobic site contributing to the destructuration of these membranes. LL-37 is the only cationic antimicrobial peptide derived from human cathelicidin. LL-37 can also cross the plasma membrane of eukaryotic cells, probably through special domains of this membrane called lipid rafts. This transfer could be beneficial in the context of vaccination: the activation of intracellular toll-like receptors by a complex formed between CpG oligonucleotides and LL-37 could conceivably play a major role in the building of a cellular immunity involving NK cells.

Anti-infective activity of apolipoprotein domain derived peptides in vitro: identification of novel antimicrobial peptides related to apolipoprotein B with anti-HIV activity

Background

Previous reports have shown that peptides derived from the apolipoprotein E receptor binding region and the amphipathic α-helical domains of apolipoprotein AI have broad anti-infective activity and antiviral activity respectively. Lipoproteins and viruses share a similar cell biological niche, being of overlapping size and displaying similar interactions with mammalian cells and receptors, which may have led to other antiviral sequences arising within apolipoproteins, in addition to those previously reported. We therefore designed a series of peptides based around either apolipoprotein receptor binding regions, or amphipathic α-helical domains, and tested these for antiviral and antibacterial activity.

Results

Of the nineteen new peptides tested, seven showed some anti-infective activity, with two of these being derived from two apolipoproteins not previously used to derive anti-infective sequences. Apolipoprotein J (151-170) - based on a predicted amphipathic alpha-helical domain from apolipoprotein J - had measurable anti-HSV1 activity, as did apolipoprotein B (3359-3367) dp (apoBdp), the latter being derived from the LDL receptor binding domain B of apolipoprotein B. The more active peptide - apoBdp - showed similarity to the previously reported apoE derived anti-infective peptide, and further modification of the apoBdp sequence to align the charge distribution more closely to that of apoEdp or to introduce aromatic residues resulted in increased breadth and potency of activity. The most active peptide of this type showed similar potent anti-HIV activity, comparable to that we previously reported for the apoE derived peptide apoEdpL-W.

Conclusions

These data suggest that further antimicrobial peptides may be obtained using human apolipoprotein sequences, selecting regions with either amphipathic α-helical structure, or those linked to receptor-binding regions. The finding that an amphipathic α-helical region of apolipoprotein J has antiviral activity comparable with that for the previously reported apolipoprotein AI derived peptide 18A, suggests that full-length apolipoprotein J may also have such activity, as has been reported for full-length apolipoprotein AI. Although the strength of the anti-infective activity of the sequences identified was limited, this could be increased substantially by developing related mutant peptides. Indeed the apolipoprotein B-derived peptide mutants uncovered by the present study may have utility as HIV therapeutics or microbicides.

Homologue of mammalian apolipoprotein A-II in non-mammalian vertebrates

Although apolipoprotein with molecular weight 14 kDa (apo-14 kDa) is associated with fish plasma high-density lipoproteins (HDLs), it remains to be determined whether apo-14 kDa is the homologue of mammalian apoA-II. We have obtained the full cDNA sequences that encode Japanese eel and rainbow trout apo-14 kDa. Homologues of Japanese eel apo-14 kDa sequence could be found in 14 fish species deposited in the DDBJ/EMBL/GenBank or TGI database. Fish apo-14 kDa lacks propeptide and contains more internal repeats than mammalian apoA-II. Nevertheless, phylogenetic analysis allowed fish apo-14 kDa to be the homologue of mammalian apoA-II. In addition, in silico cloning of the TGI, Ensembl, or NCBI database revealed apoA-IIs in dog, chicken, green anole lizard, and African clawed frog whose sequences had not so far been available, suggesting both apoA-I and apoA-II as fundamental constituents of vertebrate HDLs.

Apolipoprotein A-I from striped bass (Morone saxatilis) demonstrates antibacterial activity in vitro

HDL and apolipoprotein A-I from teleostean fishes demonstrate in vitro activity against gram-positive and gram-negative bacteria. In this study, we purified ApoA-1 from striped bass (Morone saxatilis) plasma and examined its in vitro antibacterial activity against Streptococcus sp., Escherichia coli, and Mycobacterium marinum. In addition, we obtained sequence for a putative striped bass ApoA-1 gene, which when translated contained the identical sequence generated from N-terminal sequencing of the purified ApoA-1. The predicted secondary and tertiary structures contained the characteristic proline residues and high alpha-helical content conserved between mammals and fishes. Purified ApoA-1 exhibited antibacterial activity against the bacteria assayed. Concentrations of 125 microg/mL for E. coli, 250 microg/mL for Streptococcus sp., and 250 microg/mL for M. marinum, inhibited bacterial growth by 50% compared to control. ApoA-1 plasma concentrations in experimental and wild fish ranged from undetectable levels to greater than 5 mg/mL, indicating that striped bass ApoA-1 is an effective antibacterial agent at concentrations below the range of physiological concentrations in striped bass plasma. We therefore conclude that ApoA-1 could play a role in innate defense against bacterial pathogens in striped bass.

Interactions between the products of the Herpes simplex genome and Alzheimer's disease susceptibility genes: relevance to pathological-signalling cascades

The products of the Herpes simplex (HSV-1) genome interact with many Alzheimer's disease susceptibility genes or proteins. These in turn affect those of the virus. For example, HSV-1 binds to heparan sulphate proteoglycans (HSPG2), or alpha-2-macroglobulin (A2M), and enters cells via nectin receptors, which are cleaved by gamma-secretase (APH1B, PSEN1, PSEN2, PEN2, NCSTN). The virus also binds to blood-borne lipoproteins and apolipoprotein E (APOE) is able to modify its infectivity. Viral uptake is cholesterol- and lipid raft-dependent (DHCR24, HMGCR, FDPS, RAFTLIN, SREBF1). The virus is transported to the nucleus via the dynein and kinesin (KNS2) motors associated with the microtubule network (MAPT). Amyloid precursor protein (APP) plays a role in this transport. Nuclear export is mediated via disruption of the nuclear lamina and binding to LMNA. Herpes simplex activates kinases (CDC2 and casein kinase 2) whose substrates include APOE, APP, MAPT, PSEN2, and SREBF1. A viral protein is also able to delete mitochondrial DNA, a situation prevalent in Alzheimer's disease. The virus binds to the host transcription factors transcription factor CP2 (TFCP2) and POU2F1 that control many other genes associated with Alzheimer's disease. Viral latency is controlled by IL6 and IL1B and at different stages of its life cycle the virus can either promote or attenuate apoptosis via Fas and tumor necrosis factor pathways (FAS, TNF, DAPK1, PARP1). Viral evasion strategies include inhibition of the antigen processor TAP2, the production of an Fc immunoglobulin receptor mimic (FCER1G) and inhibition of the viral-activated kinase EIF2AK2. These and other host/viral interactions, targeted to certain Alzheimer's disease susceptibility genes, support the idea that some form of synergy between the pathogen and genetic factors may play a role in the pathology of late-onset Alzheimer's disease.

The exchangeable apolipoprotein ApoC-I promotes membrane fusion of hepatitis C virus

Cell entry of hepatitis C virus (HCV) is strikingly linked to lipoproteins and their receptors. Particularly, high density lipoprotein (HDL) enhances infectivity of HCV by involving the lipid-transfer function of the scavenger receptor BI, a receptor for both HDL and HCV. Here, we demonstrate that apoC-I, an exchangeable apolipoprotein that predominantly resides in HDL, specifically enhances HCVcc and HCVpp infectivity and increases the fusion rates between viral and target membranes via a direct interaction with the HCV surface. We identify the hypervariable region 1, located at the N terminus of the HCV E2 glycoprotein, as an essential viral component that modulates apoC-I-mediated enhancement of HCV fusion properties. The affinity of apoC-I for the HCV membrane may predispose it for fusion with a target membrane via alterations of its outer phospholipid layer. Conversely, we found that excess apoC-I provided as lipoprotein-free protein induces the disruption of the HCV membrane and subsequent loss of infectivity. Furthermore, our data indicate that HDL neither interacts nor spontaneously exchanges apoC-I with HCV virions. Because apoC-I is not present in serum as a lipoprotein-free form, our results suggest that HDL-embedded apoC-I could be released from the lipoprotein particle through a fine-tuned mechanism regulated via a triple interplay between hypervariable region 1, HDL, and scavenger receptor BI, resulting in optimal apoC-I recruitment on the viral membrane. These results provide the first description of a host serum factor helping the fusion process of an enveloped virus.

Transcriptomic approach to the study of osmoregulation in the European eel Anguilla anguilla

In euryhaline teleosts, osmoregulation is a fundamental and dynamic process that is essential for the maintenance of ion and water balance, especially when fish migrate between fresh water (FW) and sea water (SW) environments. The European eel has proved to be an excellent model species to study the molecular and physiological adaptations associated with this osmoregulatory plasticity. The life cycle of the European eel includes two migratory periods, the second being the migration of FW eels back to the Sargasso Sea for reproduction. Various anatomical and physiological changes allow the successful transition to SW. The aim of this study was to use a microarray approach to screen the osmoregulatory tissues of the eel for changes in gene expression following acclimation to SW. Tissues were sampled from fish at selected intervals over a 5-mo period following FW/SW transfer, and RNA was isolated. Suppressive subtractive hybridization was used for enrichment of differentially expressed genes. Microarrays comprising 6,144 cDNAs from brain, gill, intestine, and kidney libraries were hybridized with appropriate targets and analyzed; 229 differentially expressed clones with unique sequences were identified. These clones represented the sequences for 95 known genes, with the remaining sequences (59%) being unknown. The results of the microarray analysis were validated by quantification of 28 differentially expressed genes by Northern blotting. A number of the differentially expressed genes were already known to be involved in osmoregulation, but the functional roles of many others, not normally associated with ion or water transport, remain to be characterized.

Different isoforms of apolipoprotein AI present heterologous post-translational expression in HIV infected patients

Human immunodeficiency virus (HIV) is rapidly becoming a global health concern. Proteomics technology was employed to examine HIV infected plasma samples in an attempt to identify disease-associated proteins. By comparison with normal and HIV positive plasma samples, at least eight proteins were significantly changed in HIV infected plasma. In particular, apolipoprotein AI presents a heterogeneous change in expression level with different isoforms. Apolipoprotein AI could be a useful biomarker for HIV diagnosis.

Effects of amino acid substitutions at glycine 420 on SR-BI cholesterol transport function

Scavenger receptor class B type I (SR-BI) facilitates the uptake of HDL cholesteryl esters (CEs) in a two-step process involving binding of HDL to its extracellular domain and transfer of HDL core CEs to a metabolically active membrane pool, where they are subsequently hydrolyzed by a neutral CE hydrolase. Recently, we characterized a mutant, G420H, which replaced glycine 420 in the extracellular domain of SR-BI with a histidine residue and had a profound effect on SR-BI function. The G420H mutant receptor exhibited a reduced ability to mediate selective HDL CE uptake and was unable to deliver HDL CE for hydrolysis, despite the fact that it retained the ability to bind HDL. This did not hold true if glycine 420 was replaced with an alanine residue; G420A maintained wild-type HDL binding and cholesterol transport activity. To further understand the role that glycine 420 plays in SR-BI function and why there was a disparity between replacing glycine 420 with a histidine versus an alanine, we generated a battery of point mutants by substituting glycine 420 with amino acids possessing side chains that were charged, hydrophobic, polar, or bulky and tested the resulting mutants for their ability to support HDL binding, HDL cholesterol transport, and delivery for hydrolysis. The results indicated that substitution with a negatively charged residue or a proline impaired cell surface expression of SR-BI or its interaction with HDL, respectively. Furthermore, substitution of glycine 420 with a positively charged residue reduced HDL CE uptake as well as its subsequent hydrolysis.

Kinetic stabilization and fusion of apolipoprotein A-2:DMPC disks: comparison with apoA-1 and apoC-1

Denaturation studies of high-density lipoproteins (HDL) containing human apolipoprotein A-2 (apoA-2) and dimyristoyl phosphatidylcholine indicate kinetic stabilization. Circular dichroism (CD) and light-scattering melting curves show hysteresis and scan rate dependence, indicating thermodynamically irreversible transition with high activation energy E(a). CD and light-scattering data suggest that protein unfolding triggers HDL fusion. Electron microscopy, gel electrophoresis, and differential scanning calorimetry show that such fusion involves lipid vesicle formation and dissociation of monomolecular lipid-poor protein. Arrhenius analysis reveals two kinetic phases, a slower phase with E(a,slow) = 60 kcal/mol and a faster phase with E(a,fast) = 22 kcal/mol. Only the fast phase is observed upon repetitive heating, suggesting that lipid-poor protein and protein-containing vesicles have lower kinetic stability than the disks. Comparison of the unfolding rates and the melting data recorded by differential scanning calorimetry, CD, and light scattering indicates the rank order for the kinetic disk stability, apoA-1 > apoA-2 > apoC-1, that correlates with protein size rather than hydrophobicity. This contrasts with the tighter association of apoA-2 than apoA-1 with mature HDL, suggesting different molecular determinants for stabilization of model discoidal and plasma spherical HDL. Different effects of apoA-2 and apoA-1 on HDL fusion and stability may reflect different metabolic properties of apoA-2 and/or apoA-1-containing HDL.

The structure and interactions of human apolipoprotein C-II in dodecyl phosphocholine

The structure of human apolipoprotein C-II (apoC-II) in the presence of dodecyl phosphocholine (DPC) micelles has been investigated by NMR spectroscopy. The resulting structural information is compared to that available for apoC-II in the presence of sodium dodecyl sulfate, revealing a high level of overall similarity but several significant differences. These findings further our understandings of the structural basis for apoC-II function. The interactions of the protein with the detergent micelle are probed using intermolecular nuclear Overhauser effects (NOEs) and paramagnetic agents. These interactions are seen across almost the full length of apoC-II and show the periodicity expected for an amphipathic helix interacting with the amphipathic surface of the DPC micelle. Furthermore, we observe specific contacts between lysine residues of apoC-II and protons near the phosphate group of DPC, consistent with the predictions of the so-called "snorkel hypothesis" of the structural basis for the apolipoprotein/lipid interaction (Segrest, J. P., Jackson, R. L., Morrisett, J. D., and Gotto, A. M., Jr. (1974) A molecular theory of lipid-protein interactions in the plasma lipoproteins, FEBS Lett 38, 247-258.). These findings offer the most detailed structural information available for the interaction between an apolipoprotein and the phospholipids of the lipoprotein surface and provide the first direct structural support for the snorkel hypothesis.

Model class A and class L peptides increase the production of apoA-I-containing lipoproteins in HepG2 cells

Class A peptides inhibit atherosclerosis and protect cells from class L peptide-mediated lysis. Because the cytolytic process is concentration dependent, we hypothesized that at certain concentrations both classes of peptides exert similar effect(s) on cells. To test this hypothesis, we studied the effects of a class L peptide (18L = GIKKFLGSIWKFIKAFVG) and a class A peptide, 18A-Pro-18A (18A = DWLKAFYDKVAEKLKEAF) (37pA), on apolipoprotein and lipoprotein production in HepG2 cells. Secretion of (35)S-labeled apolipoprotein A-I (apoA-I) was stimulated by both 18L (110%) and 37pA (135%) at 10 and 20 nM of peptides, respectively. Both peptides enhanced the secretion of (3)H-labeled phospholipids by 140% and (14)C-labeled HDL-cholesterol (HDL-C) by 35% but had no significant effect on the total cholesterol mass or secretion. These results indicate that class L and class A peptides cause redistribution of cholesterol among lipoproteins in favor of HDL-C. Both peptides remodeled apoA-I-containing particles forming prebeta- as well as alpha-HDL. This study suggests that increased secretion of phospholipids and apoA-I and the formation of prebeta-HDL particles might contribute to the antiatherogenic properties of these peptides.

Apolipoproteins A-I and A-II are potentially important effectors of innate immunity in the teleost fish Cyprinus carpio

We have previously shown that high density lipoprotein is the most abundant protein in the carp plasma and displays bactericidal activity in vitro. Therefore the aim of this study was to analyze the contribution of its principal apolipoproteins, apoA-I and apoA-II, in defense. Both apolipoproteins were isolated by a two step procedure involving affinity and gel filtration chromatography and were shown to display bactericidal and/or bacteriostatic activity in the micromolar range against Gram-positive and Gram-negative bacteria, including some fish pathogens. In addition, a cationic peptide derived from the C-terminal region of carp apoA-I was synthesized and shown to possess antimicrobial activity (EC(50) = 3-6 micro m) against Planococcus citreus. This peptide was also able to potentiate the inhibitory effect of lysozyme in a radial diffusion assay at subinhibitory concentrations of both effectors. Finally, limited proteolysis of HDL-associated apoA-I with chymotrypsin in vitro was shown to generate a major truncated fragment, which indicates that apoA-I peptides liberated in vivo through a regulated proteolysis could also be involved in innate immunity.

Poly(ethylene glycol)-Induced Fusion and Destabilization of Human Plasma High-Density Lipoproteins†

High-density lipoproteins (HDL) are macromolecular complexes of specific proteins and lipids that mediate the removal of cholesterol from peripheral tissues. Chemical unfolding revealed that HDL fusion and rupture are the two main kinetic steps in HDL denaturation. Here we test the hypothesis that lipid fusogens such as poly(ethylene glycol) (PEG) may promote lipoprotein fusion and rupture and thereby destabilize HDL. We analyze thermal disruption of spherical HDL in 0-15% PEG-8000 by calorimetric, spectroscopic, electron microscopic, and light scattering techniques. We demonstrate that the two irreversible high-temperature endothermic HDL transitions involve particle enlargement and show a heating rate dependence characteristic of kinetically controlled reactions with high activation energy. The first calorimetric transition reflects HDL fusion and dissociation of lipid-poor apolipoprotein A-1 (apoA-1), and the second transition reflects HDL rupture and release of the apolar lipid core. Neither transition involves substantial protein unfolding; thus, the transition heat originates from lipid and/or protein dissociation and repacking. At room temperature, PEG-8000 induces HDL fusion that is distinct from the heat-, denaturant-, or enzyme-induced fusion since it leads to formation of larger particles and does not involve apoA-1 dissociation. Increasing the PEG concentration in solution from 0 to 15% leads to low-temperature shifts by approximately -18 degrees C in the two calorimetric HDL transitions without altering their nature. Thus, consistent with our hypothesis, PEG-8000 induces fusion and reduces the thermal stability of HDL. Our results suggest that PEG is useful for the analysis of the molecular events involved in metabolic HDL remodeling and fusion.

Effects of innate immunity on herpes simplex virus and its ability to kill tumor cells

Several clinical trials have or are being performed testing the safety and efficacy of different strains of oncolytic viruses (OV) for malignant cancers. OVs represent either naturally occurring or genetically engineered strains of viruses that exhibit relatively selective replication in tumor cells. Several types of OV have been derived from herpes simplex virus 1 (HSV1). Tumor oncolysis depends on the processes of initial OV infection of tumor, followed by subsequent propagation of OV within the tumor itself. The role of the immune responses in these processes has not been extensively studied. On the contrary, effects of the immune response on the processes of wild-type HSV1 infection and propagation in the central nervous system have been studied and described in detail. The first line of defense against a wild-type HSV1 infection in both naive and immunized individuals is provided by innate humoral (complement, cytokines, chemokines) and cellular (macrophages, neutrophils, NK cells, gammadelta T cells, and interferon-producing cells) responses. These orchestrate the lysis of virions and virus-infected cells as well as provide a link to effective adaptive immunity. The role of innate defenses in curtailing the oncolytic effect of genetically engineered HSV has only recently been studied, but several of the same host responses appear to be operative in limiting anticancer effects by the replicating virus. The importance of this knowledge lies in finding avenues to modulate such initial innate responses, in order to allow for increased oncolysis of tumors while minimizing host toxicity.

High-density lipoprotein concentrations relate to the clinical course of HIV viral load in patients undergoing antiretroviral therapy

OBJECTIVE

To determine whether levels of HDL are associated with viral load response in HIV-treated patients, and to seek an explanation based on amino acid sequence similarity between the key apolipoprotein A1 and HIV proteins concerned in viral replication.

DESIGN

The major HDL lipoprotein is apolipoprotein A1, which is able to inhibit HIV-induced syncytium formation. This retrospective clinical study assessed the relationship between the response to antiretroviral treatment (time of undetectable viral load/duration of viral suppression below the limit of detection) and HDL-cholesterol levels on commencing antiretroviral treatment.

PATIENTS AND METHODS

HIV-treated patients with undetectable HIV viral loads were followed every 3 months for 36 months. We measured total cholesterol, HDL-cholesterol, triglycerides, previous responses to antiretroviral treatment, opportunistic infections, sex and age. These variables were assessed in relation to the time of undetectable viral load until viral rebound. Amino acid sequence alignment was performed with HIV proteins and apolipoprotein A1 to detect shared similarity.

RESULTS

The Cox proportional hazards model showed a significant association between HDL-cholesterol and the time of undetectable viral load. The other variables studied were not associated. There was 30% sequence similarity in an area of 50 amino acids shared between apolipoprotein A1 and p17 Gag-HIV protein.

CONCLUSION

High levels of HDL-cholesterol are associated with a better viral response in treated HIV patients. This association could be related to the sequence similarity and structure homology between apolipoprotein A1 and p17 Gag-HIV protein, which raises the intriguing clinical possibility that inducing an increase in HDL could assist HIV therapy.

Complement depletion facilitates the infection of multiple brain tumors by an intravascular, replication-conditional herpes simplex virus mutant

Intravascular routes of administration can provide a means to target gene- and virus-based therapies to multiple tumor foci located within an organ, such as the brain. However, we demonstrate here that rodent plasma inhibits cell transduction by replication-conditional (oncolytic) herpes simplex viruses (HSV), replication-defective HSV, and adenovirus vectors. In vitro depletion of complement with mild heat treatment or in vivo depletion by treatment of athymic rats with cobra venom factor (CVF) partially reverses this effect. Without CVF, inhibition of cell infection by HSV is observed at plasma dilution as high as 1:32, while plasma from CVF-treated animals displays anti-HSV activity at lower dilutions (1:8). When applied to the therapy of intracerebral brain tumors, in vivo complement depletion facilitates the initial infection (assayed at the 2-day time point) by an intra-arterial replication-conditional HSV of tumor cells, located within three separate and distinct human glioma masses. However, at the 4-day time point, no propagation of HSV from initially infected tumor cells could be observed. Previously, we have shown that the immunosuppressive agent, cyclophosphamide (CPA), facilitates the in vivo propagation of an oncolytic HSV, delivered intravascularly, within infected multiple intracerebral masses, by inhibition of both innate and elicited anti-HSV neutralizing antibody response (K. Ikeda et al., Nat. Med. 5:881-889, 1999). In this study, we thus show that the addition of CPA to the CVF treatment results in a significant increase in viral propagation within infected tumors, measured at the 4-day time period. The concerted action of CVF and CPA significantly increases the life span of athymic rodents harboring three separate and large glioma xenografts after treatment with intravascular, oncolytic HSV. Southern analysis of viral genomes analyzed by PCR reveals the presence of the oncolytic virus in the brains, livers, spleens, kidneys, and intestine of treated animals, although none of these tissues displays evidence of HSV-mediated gene expression. In light of clinical trials of oncolytic HSV for malignant brain tumors, these findings suggest that antitumor efficacy may be limited by the host innate and elicited humoral responses.

Gene therapy of brain tumors: problems presented by physiological barriers

The explosion of molecular techniques for gene discovery and their application to a variety of diseases has uncovered numerous gene abnormalities that can result in disease. These discoveries have provided the needed understanding and genetic materials to apply gene therapy approaches in the treatment of several diseases, including those of the central nervous system. A variety of different anticancer complementary DNAs (cDNA) have been shown to possess biological efficacy when used in the appropriate experimental setting. However, efficient and effective delivery of these cDNAs remains a major obstacle for future clinical applications. The focus of this review will be to describe the obstacles that impede the process of gene therapy and oncolytic viral therapy of brain tumors and to describe how important new discoveries derived from other disciplines are being used to address problems encountered in the gene/ viral therapy of this disease.

Role of the Arg123-Tyr166 paired helix of apolipoprotein A-I in lecithin:cholesterol acyltransferase activation

The Arg123-Tyr166 central and Ala190-Gln243 carboxyl-terminal pairs of helices of apoA-I were substituted with the pair of helices of apoA-II, resulting in the apoA-I(Delta(Arg123-Tyr166), nablaA-II(Ser12-Ala75)) and apoA-I(Delta(Ala190-Gln243), nablaA-II(Ser12-Gln77)) chimeras, respectively. The structures of these chimeras in aqueous solution and in reconstituted high density lipoproteins (rHDL) and the lecithin:cholesterol acyltransferase (LCAT) activation properties of the rHDL were studied. Recombinant human apoA-I and the chimeras were expressed in Escherichia coli and purified from the periplasmic space. Binding of the apolipoproteins with palmitoyloleoylphosphatidylcholine was associated with a similar shift of Trp fluorescence maxima from 337 to 332 nm, from 339 to 334 nm, and from 337 to 333 nm, respectively. All rHDL had a Stokes radius of 4.8 nm and contained 2 apolipoprotein molecules/particle. Circular dichroism measurements revealed eight alpha-helices per apoA-I and per chimera molecule. The catalytic efficiencies of LCAT activation were 1.5 +/- 0.33 (mean +/- S.D.; n = 3), 0.054 +/- 0.009 (p < 0.001 versus apoA-I), and 1.3 +/- 0.32 (p = not significant versus apoA-I) nmol of cholesteryl ester/h/microM, respectively. The lower LCAT activity of the central domain chimera was due to a 27-fold reduced Vmax with unaltered Km. Binding of radiolabeled LCAT to rHDL of apoA-I and apoA-I(Delta(Arg123-Tyr166), nablaA-II(Ser12-Ala75)) was very similar. In conclusion, although substitution of the Arg123-Tyr166 central or Ala190-Gln243 carboxyl-terminal pair of helices of apoA-I with the pair of helices of apoA-II yields chimeras with structure similar to that of native apoA-I, exchange of the central domain (but not the carboxyl-terminal domain) of apoA-I reduces the rate of LCAT activity that is independent of binding to rHDL.

In vivo characterization of Gd(BME-DTTA), a myocardial MRI contrast agent: tissue distribution of its MRI intensity enhancement, and its effect on heart function

We have determined an LD50 of 0.56 +/- 0.05 mmol/kg for liposomal Gd(BME-DTTA) in mice and also shown that liposomal Gd(BME-DTTA) has no deleterious effects on heart rate, blood pressure, left ventricular force and AV conductance in ferret hearts in vivo at the magnetic resonance imaging (MRI)-effective dose of 0.05 mmol/kg body weight. In MRI images, a 1H signal intensity enhancement is observed in the following organs in decreasing order of the effect: heart approximately spleen > kidney > liver. This enhancement is stable for over 3 h in all organs. The results of 1H MRI and electron micrographs indicate that the lipophilic fatty acyl groups in the ligand BME structure and the particle sizes of liposomal Gd(BME-DTTA) are two important factors for tissue specificity of liposomal Gd(BME-DTTA) in the intensity enhancement. In vitro relaxivity of a liposomal Gd(BME-DTTA) sample, stored at 4 degrees C, remained stable for over 4 months of observation, but a significant decrease in relaxivity was observed in a sample stored at room temperature, most likely reflecting some deterioration in liposome chemistry.

Inhibitors of human immunodeficiency virus type 1 derived from gp41 transmembrane protein: structure--activity studies

We synthesized analogues of gp41 (553-590), 1, and evaluated them for their inhibitory activity against HIV-1 in MT4 cell assay (IC50(1) = 2.7 microM). (The numbering scheme for gp41 (e.g., gp41(553-590) for 1) adapted throughout the text is from ref 6.) Gradual truncation of either the N- or C-terminal end of gp41 (553-590) resulted in a substantial loss of inhibitory properties of resulting compounds. Unexpectedly, simultaneous truncations of both N- and C-termini of gp41(553-590) resulted in a potent heptadecamer, 13, IC50 = 10.4 microM. Coupling of a racemic alpha-aminotetradecanoic acid (Atd) to gp41 fragments afforded diastereomeric conjugates, most of which were chromatographically separable. In this series, pentadecamer 27 had an IC50 of 8.9 microM, while its Atd diastereomer 28 was much less inhibitory. This finding is consistent with relative inhibitory potencies of other Atd-containing diastereomeric pairs and could reflect a chiral sense of Atd residue interacting with the receptor. Compounds 13 and 27, which are practically equipotent to 1, represent minimalistic fragments of the leucine-zipper region of gp41 and constitute a basis for design of a second generation of gp41-based inhibitors. Circular dichroism studies suggested that compounds in this series are likely to inhibit HIV-1 replication by virtue of their alpha-helical character. The observed structure-activity relationship supports impairment of viral gp41 as a possible mechanism of action of 1.

Mechanisms for the modulation of membrane bilayer properties by amphipathic helical peptides

The amphipathic helix, in which hydrophobic and hydrophilic residues are grouped on opposing faces, is a structural motif found in many peptides and proteins that bind to membranes. One of the physical properties of membranes that can be altered by the binding of amphipathic helices is membrane monolayer curvature strain. Class A amphipathic helices, which are present in exchangeable plasma lipoproteins, can stabilize membranes by reducing negative monolayer curvature strain; proline-punctuated class A amphipathic helical segments are particularly effective in this regard. This property is suggested to be associated with some of the beneficial biological effects of this protein. On the other hand, lytic amphipathic helical peptides can act by increasing negative curvature strain or by forming pores composed of helical clusters. Thus, different amphipathic helical peptides can be membrane stabilizing or be lytic to membranes, depending on the structural motif of the helix, which in turn determines the nature of its association with membranes. Features of these peptides that are responsible for their specific properties are discussed.