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Recently, interest in small peptide molecules as potential drug candidates has revived. In this review, two series of synthetic peptides and their selective effects on the inflammatory response have been described, focusing on the intracellular pathways involved and on their therapeutic potential. A series of F(D)LF(D)LF analogs has been synthesized, including either N- t-Boc or different N-ureido substituents. The free acid derivatives as they are good candidates as antiinflammatory drugs are able to antagonize the multiple neutrophil functions evoked by N-formyl-L-methionyl-L-leucyl-Lphenylalanine (fMLF), i.e. chemotaxis, superoxide anion production and lysozyme release. Their methyl-ester derivatives are ineffective. The second series of peptides derives from the endogenous protein kinase C (PKC) inhibitor PKI55, a 55-amino acid protein, whose synthesis is induced by PKC activation, so that a feedback loop of inhibition is established. In vitro experiments showed that PKI55 inhibits recombinant PKC isoforms α, β1, β2, γ, δ, ζ, ; to identify the minimal amino acid sequence of PKI55 protein maintaining the inhibitory effects on PKC, peptides derived from both C- and N-terminal sequences have been synthesized. The N-terminal peptides 5 (MLYKLHDVCRQLWFSC), 8 (CRQLWFSC) and 9 (CRQLW), that in human neutrophils retain the inhibitory activity on PKC, decrease the chemotaxis, and, in mice, display anti-inflammatory and analgesic action, after both central and peripheral administration of very low doses. Furthermore, the peptide 5 shows neuroprotective activity in a model of cerebral ischemia in vitro, favouring the recovery of synaptic function. These findings suggest interesting possible therapeutic applications for these peptides.

Abstract: In order to explore the properties of chemotactic N-formylpeptides containing isopeptide bonds within their backbones, a group of lysine-containing analogs of the prototypical chemotactic tripeptide N-formylmethionyl-leucyl-phenylalanine (fMLF) was synthesized. The new analogs were designed by adding to the HCO-Met or Boc-Met residue a dipeptide fragment made up of Lys and Phe residues joined through Lys N[sup α] or N[sup ε] bonds, in all possible combinations. Thus, the following six pairs of tripeptides were synthesized and examined for their bioactivity: RCO-Met-Lys(Z)-Phe-OMe (2a, b), RCO-Met-Lys(Z-Phe)-OMe (3a, b), Z-Lys(RCO-Met)-Phe-OMe (4a, b), Z-Phe-Lys(RCO-Met)-OMe (5a, b), RCO-Met-Phe-Lys(Z)-OMe (6a, b) and Z-Lys(RCO-Met-Phe)-OMe (7a, b), with R=OC(CH[sub 3])[sub 3] and R=H for compounds a and b, respectively. All the new models were characterized fully and their activity (chemotaxis, superoxide anion production and lysozyme release) on human neutrophils determined as agonists (compounds b) and antagonists (compounds a). All N-formyl derivatives 2b-7b are less potent than fMLF-OMe as chemoattractants, but compound 7b exhibits selective activity as superoxide anion producer. Derivatives 2a-7a do not show antagonistic activity towards fMLF induced chemotaxis and O[sub 2][sup -] production, however, all these compounds except 4a antagonize lysozyme release by 60%. [ABSTRACT FROM AUTHOR]

The human erythroid myeloid leukaemia cell line K562 was used as target for human neutrophil cytotoxicity. Neutrophils demonstrated cytotoxicity against K562 only in the presence of a second stimulus, tetradecanoil phorbol acetate (TPA), a result consistent with previous observations.We now demonstrate that antibody-coated K562 (using OKT9 and 345 monoclonal antibodies) are similarly only sensitive to neutrophils when TPA is added. The presence of both antibody and TPA in the cytotoxic assay resulted in significantly higher levels of cytotoxicity than in the absence of antibody; the result being consistent with a synergistic action between protein kinase C activation and Fe receptor perturbation in the neutrophil. The cytotoxicity against non-coated and antibody-coated targets was markedly inhibited, particularly against the former, by the protein kinase C inhibitor, l-(5-isoquinollne-sulfonyl)-2-methyl piperazine (H-7). There were marked differences in the extra-cellular calcium dependency of the two types of cytotoxicity reactions. TPA-activated respiratory burst was unaffected by the presence of non-coated and OKT9-coated targets, whereas TPA-induced lysosomal enzyme release was significantly increased by non-coated targets and a further increase occurred in the presence of OKT9-coated K562. [ABSTRACT FROM AUTHOR]

Abstract: We previously reported the structural and biological properties of the C-terminal sequence (REGDPSSSQHLPSTPSSPRV) coded by the rarely expressed exon 26A of human elastin. It assumes a stable type II β-turn structure spanning the REGD sequence and possesses chemotactic and immunological properties. Here the structural characterization of the sequence coded by this exon was completed. Nuclear magnetic resonance and circular dichroism studies on the N-terminal amino acid sequence (GADEGVRRSLSPELREGD) showed the presence of an α-helix within VRRSL and a type II β-turn within SPEL. The smaller peptides GADEGVRRSLSP and LSPELREGD revealed structural features similar to those identified in the parent peptide. No β-turn was found in the REGD sequence of these peptides and no chemotactic activity was detected, thereby demonstrating that this biological activity is conformation dependent. Structural studies on additional peptides such as LREGD, ELREGD and LSPELREGDPSS showed that the presence of a Glu residue two positions before the Arg residue inhibits the β-turn formation in the REGD sequence. [ABSTRACT FROM AUTHOR]