Relative spatial positions of tryptophan and cationic residues in helical membrane-active peptides determine their cytotoxicity.

The cytotoxic activity of 10 analogs of the idealized amphipathic helical 21-mer peptide (KAAKKAA)3, where three of the Ala residues at different positions have been replaced with Trp residues, has been investigated. The peptide's cytotoxic activity was found to be markedly dependent upon the position of the Trp residues within the hydrophobic sector of an idealized α-helix. The peptides with Trp residues located opposite the cationic sector displayed no antitumor activity, whereas those peptides with two or three Trp residues located adjacent to the cationic sector exhibited high cytotoxic activity when tested against three different cancer cell lines. Dye release experiments revealed that in contrast to the peptides with Trp residues located opposite the cationic sector, the peptides with Trp residues located adjacent to the cationic sector induced a strong permeabilizing activity from liposomes composed of a mixture of zwitterionic phosphatidylcholine and negatively charged phosphatidylserine (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS)) (2:1) but not from liposomes composed of zwitterionic phosphatidylcholine, POPC. Fluorescence blue shift and quenching experiments revealed that Trp residues inserted deeper into the hydrophobic environment of POPC/POPS liposomes for peptides with high cytotoxic activity. Through circular dichroism studies, a correlation between the cytotoxic activity and the α-helical propensity was established. Structural studies of one inactive and two active peptides in the presence of micelles using NMR spectroscopy showed that only the active peptides adopted highly coiled to helical structures when bound to a membrane surface.

Exposure of chromatin and not high affinity for dsDNA determines the nephritogenic impact of anti-dsDNA antibodies in (NZBxNZW)F1 mice.

Recent studies have demonstrated that the nephritogenicity of antibodies to dsDNA and nucleosomes confers to binding of glomerular membrane-associated nucleosomes, and not to cross-reacting glomerular antigens. There is no known parameter that determines antibody pathogenicity aside from specificity for dsDNA/nucleosomes, and systemic lupus erytheomatosus (SLE) patients may have high titer anti-dsDNA antibodies irrespective whether they have lupus nephritis or not. One parameter may be antibody affinity, as theoretically only high affinity antibodies may bind in vivo in a stable way. This was analyzed in (NZB x NZW)F1 mice with full-blown lupus nephritis. These mice had serum antibodies to dsDNA, and IgG autoantibodies bound in situ in glomerular membrane-associated electron dense structures as determined by immune electron microscopy (IEM). Intrinsic affinity of purified circulating and glomerular IgG anti-dsDNA antibodies was determined by surface plasmon resonance. The results demonstrate that affinity of glomerular-bound anti-dsDNA antibodies was higher than for those in circulation. However, affinity of glomerular in situ-bound antibodies from different mice varied considerably, from K(D) in the range from 10(- 8) to 10(- 13). These results indicate that antibody affinity is not a decisive pathogenic factor, but rather that availability of chromatin fragments may be the factor that determines whether an anti-dsDNA antibody binds in glomeruli or not.

Synthetic antimicrobial peptidomimetics with therapeutic potential.

A series of synthetic antimicrobial peptidomimetics (SAMPs) have been prepared and found to be highly active against several Gram-negative and Gram-positive bacterial strains. These derivatives comprise the minimal structural requirements for cationic antimicrobial peptides and showed high selectivity for Gram-negative and/or Gram-positive bacteria compared to human red blood cells. We have found that SAMPs share many of the attractive properties of cationic antimicrobial peptides inasmuch that a representative SAMP was found to insert into the bilayers of large unilamellar vesicles, permeabilized both the outer and cytoplasmic membrane of Escherichia coli ML-35p, and displayed an extremely rapid bacterial killing for Staphylococcus aureus. However, while antimicrobial peptides are prone to proteolytic degradation, high in vitro stability in human blood plasma was shown for SAMPs. A combination of high antibacterial activity against methicillin-resistant staphylococci and low toxicity against human erythrocytes makes these molecules promising candidates for novel antibacterial therapeutics.

Glomerular expression of large polyomavirus T antigen in binary tet-off regulated transgenic mice induces apoptosis, release of chromatin and initiates a lupus-like nephritis.

Binary tetracycline-regulated polyomavirus large T antigen transgenic mice were generated to study immunological tolerance for nucleosomes. Expression of T antigen resulted in binding of the protein to chromatin, and released T antigen-nucleosome complexes from dying cells maintained anti-dsDNA and anti-nucleosome antibody-production by activating autoimmune nucleosome-specific B cells and CD4+ and CD8+ T antigen specific T cells. Glomerular T antigen expression was observed in these mice. Here, we demonstrate that this expression was linked to glomerular cell apoptosis, release of nucleosomes and association of nucleosomes with glomerulus basement membranes, detected as electron dense structures. Immune electron microscopy (IEM) revealed that these structures were glomerular targets for induced anti-dsDNA and anti-T antigen antibodies. Co-localization IEM demonstrated that in vivo-bound auto-antibodies co-localized with experimental monoclonal antibodies to dsDNA and to T antigen. A comparative analysis of glomeruli from nephritic (NZWxNZB)F1 and T antigen expressing transgenic mice revealed deposition of nucleosomes in glomerular capillary and mesangial matrix membranes and binding of anti-nucleosome antibodies in both mice strains. A controlled experimental model that may elucidate the initial events accounting for nucleosome-mediated nephritis has not been available. The transgenic mouse may be important to describe early immunological and cellular events accounting for the enigmatic lupus nephritis.

Alpha-actinin-binding antibodies in relation to systemic lupus erythematosus and lupus nephritis.

This study investigated the overall clinical impact of anti-alpha-actinin antibodies in patients with pre-selected autoimmune diseases and in a random group of anti-nuclear antibody (ANA)-positive individuals. The relation of anti-alpha-actinin antibodies with lupus nephritis and anti-double-stranded DNA (anti-dsDNA) antibodies represented a particular focus for the study. Using a cross-sectional design, the presence of antibodies to alpha-actinin was studied in selected groups, classified according to the relevant American College of Rheumatology classification criteria for systemic lupus erythematosus (SLE) (n = 99), rheumatoid arthritis (RA) (n = 68), Wegener's granulomatosis (WG) (n = 85), and fibromyalgia (FM) (n = 29), and in a random group of ANA-positive individuals (n = 142). Renal disease was defined as (increased) proteinuria with haematuria or presence of cellular casts. Sera from SLE, RA, and Sjøgren's syndrome (SS) patients had significantly higher levels of anti-alpha-actinin antibodies than the other patient groups. Using the geometric mean (+/- 2 standard deviations) in FM patients as the upper cutoff, 20% of SLE patients, 12% of RA patients, 4% of SS patients, and none of the WG patients were positive for anti-alpha-actinin antibodies. Within the SLE cohort, anti-alpha-actinin antibody levels were higher in patients with renal flares (p = 0.02) and correlated independently with anti-dsDNA antibody levels by enzyme-linked immunosorbent assay (p < 0.007) but not with other disease features. In the random ANA group, 14 individuals had anti-alpha-actinin antibodies. Of these, 36% had SLE, while 64% suffered from other, mostly autoimmune, disorders. Antibodies binding to alpha-actinin were detected in 20% of SLE patients but were not specific for SLE. They correlate with anti-dsDNA antibody levels, implying in vitro cross-reactivity of anti-dsDNA antibodies, which may explain the observed association with renal disease in SLE.

Nephritogenic lupus antibodies recognize glomerular basement membrane-associated chromatin fragments released from apoptotic intraglomerular cells.

Antibodies to dsDNA represent a classification criterion for systemic lupus erythematosus. Subpopulations of these antibodies are involved in lupus nephritis. No known marker separates nephritogenic from non-nephritogenic anti-dsDNA antibodies. It is not clear whether specificity for glomerular target antigens or intrinsic antibody-affinity for dsDNA or nucleosomes is a critical parameter. Furthermore, it is still controversial whether glomerular target antigen(s) is constituted by nucleosomes or by non-nucleosomal glomerular structures. Previously, we have demonstrated that antibodies eluted from murine nephritic kidneys recognize nucleosomes, but not other glomerular antigens. In this study, we determined the structures that bind nephritogenic autoantibodies in vivo by transmission electron microscopy, immune electron microscopy, and colocalization immune electron microscopy using experimental antibodies to dsDNA, to histones and transcription factors, or to laminin. The data obtained are consistent and point at glomerular basement membrane-associated nucleosomes as target structures for the nephritogenic autoantibodies. Terminal deoxynucleotidyl-transferase-mediated dUTP nick end-labeling or caspase-3 assays demonstrate that lupus nephritis is linked to intraglomerular cell apoptosis. The data suggest that nucleosomes are released by apoptosis and associate with glomerulus basement membranes, which may then be targeted by pathogenic anti-nucleosome antibodies. Thus, apoptotic nucleosomes may represent both inducer and target structures for nephritogenic autoantibodies in systemic lupus erythematosus.

Critical comparative analyses of anti-alpha-actinin and glomerulus-bound antibodies in human and murine lupus nephritis.

OBJECTIVE: Although anti-double-stranded DNA (anti-dsDNA) antibodies are important in lupus nephritis, the question regarding which glomerular structures (alpha-actinin, nucleosomes, or others) are recognized by nephritogenic anti-dsDNA antibodies is still controversial. In this study, we determined which glomerular structures are recognized by monoclonal and in vivo-bound nephritogenic antibodies. METHODS: Western blotting was used to analyze the ability of nephritogenic anti-dsDNA antibodies to recognize glomerular and nucleosomal structures. Sera from patients with lupus nephritis, sera from random antinuclear antibody-positive patients, and paired antibodies from sera and kidney eluates from nephritic (NZB x NZW)F(1) mice were analyzed for activity against proteins identified by monoclonal nephritogenic antibodies, and against alpha-actinin, dsDNA, nucleosomes, histone H1, heparan sulfate, DNase I, and type IV collagen. Immunoelectron microscopy was used to determine the glomerular localization of alpha-actinin and in vivo-bound autoantibodies in nephritic (NZB x NZW)F1 mouse kidneys. RESULTS: Anti-alpha-actinin antibodies were observed in human and murine lupus nephritis sera and in sera from patients without systemic lupus erythematosus and were not detected in kidney eluates from nephritic mice. Antibodies to dsDNA and histone H1 were detected in all eluates. Western blot analyses revealed that nephritogenic anti-dsDNA antibodies recognized a 32-kd band, identified as histone H1. Competitive enzyme-linked immunosorbent assay demonstrated that nephritogenic monoclonal antibodies, and dominant antibodies eluted from nephritic kidneys, cross-reacted with dsDNA and H1. This cross-reactive anti-H1 specificity was largely absent in sera from those mice. Immunoelectron microscopic analysis of nephritic (NZB x NZW)F1 mouse kidneys revealed that antibodies eluted from kidneys, but not anti-alpha-actinin antibodies, bound to distinct nephritis-associated electron-dense structures linked to glomerular basement membranes. CONCLUSION: Cross-reactive anti-dsDNA/anti-histone H1 antibodies, but not anti-alpha-actinin antibodies, are central among those deposited in nephritic glomeruli.