Biomedical subjects

Lavinia M Proctor

Publications and source records attributed to Lavinia M Proctor.

10 recordsLinked to original sources

PubMed2006

Complement mediators in ischemia-reperfusion injury.

BACKGROUND: Ischemia-reperfusion (I/R) injury occurs when a tissue is temporarily deprived of blood supply and the return of the blood supply triggers an intense inflammatory response. Pathologically, increased complement activity can cause substantial damage to blood vessels, tissues and also facilitate leukocyte activation and recruitment following I/R injury. Herein, previously published studies are reported and critically reviewed. METHODS: Medline and the World Wide Web were searched and the relevant literature was classified under the following categories: (1) Complement pathways; (2) The complement system and the inflammatory response; (3) Complement in ischemia-reperfusion injuries; and (4) Therapeutic approaches against complement in I/R injuries. RESULTS AND CONCLUSIONS: I/R injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient and is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. Complement activation leads to the release of biologically active potent inflammatory complement substances including the anaphylatoxins (C3a and C5a) and the cytolytic terminal membrane attack complement complex C5b-9 (MAC). The use of specific complement inhibitors to block complement activation at various levels of the cascade has been shown to prevent or reduce local tissue injury after I/R. Several agents that inhibit all or part of the complement system, such as soluble complement receptor type 1 (sCR1), C1 inhibitor (C1-INH), C5a monoclonal antibodies, a C5a receptor antagonist and soluble CD59 (sCD59) have been shown to reduce I/R injury of various organs. The novel inhibitors of complement products may eventually find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Animals↗

PubMed2006

Complement inhibitors selectively attenuate injury following administration of cobra venom factor to rats.

Systemic activation of complement is a pathophysiological response common to severe disturbances such as hemorrhagic shock, major burn injury and sepsis. Intravenous infusion of cobra venom factor (CVF) has been used as an animal model of acute respiratory distress syndrome (ARDS), and reliably and selectively induces rapid intravascular activation of the complement system, leading to acute organ damage. In the present study, we have used different complement inhibitors to investigate the roles of complement products in CVF-induced responses in the rat. Rats were treated with either a C5a receptor antagonist (C5aRA, AcF-[OP(d-Cha)WR], 1 mg/kg i.v. or 10 mg/kg p.o.), a C3a receptor antagonist (C3aRA, N(2)-[(2,2-diphenylethoxy)acetyl]-l-arginine, 0.1 mg/kg i.v.) or a convertase inhibitor, rosmarinic acid (RMA, 10 mg/kg i.v.), prior to CVF-induced complement challenge. Intravenous CVF resulted in hallmark events evident in the development of ARDS, including systemic neutropenia followed by neutrophil migration to the lung and bronchoalveolar vascular leakage, blood pressure alterations, and an increase in TNFalpha levels in both serum and bronchoalveolar lavage fluid. These hemodynamic changes were differentially inhibited by antagonism of C5a receptors, C3a receptors or by inhibition of the entire complement cascade using RMA. This evidence strongly implicates complement factors in the development of lung injury associated with systemic complement activation and identifies complement inhibition as a potential therapeutic target for acute syndromes such as ARDS and other severe systemic shock states mediated by activation of complement.

Administration, Oral↗

PubMed2006

Transdermal pharmacology of small molecule cyclic C5a antagonists.

Overproduction or underregulation of the proinflammatory complement component C5a has been implicated in numerous immune and inflammatory conditions. Therefore, targeting the C5a receptor (C5aR) has become an innovative strategy for antiinflammatory drug development. The novel cyclic peptide C5aR antagonist, AcF-[OP(D-Cha)WR] (PMX53), attenuates injury in numerous animal models of inflammation following intravenous, subcutaneous, intraperitoneal, and oral administration. In the present study the transdermal pharmacology of PMX53 and three analogs designed with increased lipophilicity, hydrocinnamate-[OP(D-Cha)WCit] (PMX200), AcF-[OP(D-Cha)WCit] (PMX201) and hydrocinnamate-[OP(D-Cha)WR] (PMX205), have been examined in order to assess their transdermal permeability and inhibitory effect on C5a-mediated lipopolysaccharide (LPS)-induced systemic responses. In the rat, PMX53, PMX201, and PMX205, were bioavailable following topical dermal administration (10 mg/50 cm2 site/rat). All analogs functionally antagonized neutropenia and hypotension induced by systemic challenge with LPS (1 mg/kg i.v.). Interestingly, PMX200 attenuated LPS-induced neutropenia more effectively than other analogs, despite undetectable (<5 ng/ml) circulating levels following topical administration. In conclusion, we have demonstrated that cyclic peptide C5aR antagonists can penetrate transdermally sufficiently to have systemic effects. However, increasing lipophilicity in these compounds did not result in increased blood levels. Nonetheless, topical application of C5aR antagonists produced circulating levels of the drugs that antagonized the LPS-induced systemic responses of neutropenia and hypotension. This suggests that these small-molecule C5aR antagonists may be developed for topical administration for the treatment of local and systemic inflammatory conditions in the human and veterinary pharmaceutical markets.

Administration, Cutaneous↗

PubMed2006

Therapeutic activity of C5a receptor antagonists in a rat model of neurodegeneration.

The complement system is thought to be involved in the pathogenesis of numerous neurological diseases, although its precise role remains controversial. In this study we used orally active C5a receptor antagonists (PMX53 and PMX205) developed in our laboratories in a rat model of 3-nitropropionic acid (3-NP) -induced Huntington's disease. Administration of the C5a antagonists (10 mg/kg/day, oral) either 48 h pre- or 48 h post-toxin significantly reduced body weight loss, anorexia, and behavioral and motor deficits associated with 3-NP intoxication. Striatal lesion size, apoptosis, neutrophil infiltration, and hemorrhage were also significantly reduced in C5a antagonist-treated rats. Immunohistochemical analysis demonstrated marked deposition of C3 and C9, and up-regulation of C5a receptors on neuronal cells at the time of lesion formation. Inhibition of prostaglandins or TNF-alpha with ibuprofen or infliximab had no effect in this model. The C5a antagonists did not affect 3-NP-induced cell death when added directly to rat striatal neuronal cultures, indicating a secondary mechanism of action in vivo. Our findings demonstrate for the first time that complement activation in the brain, particularly C5a, is a key event in the pathogenesis of this disease model, and suggest a future role for inhibitors of C5a in the treatment of neurodegenerative diseases.

Animals↗

PubMed2005

Increased potency of a novel complement factor 5a receptor antagonist in a rat model of inflammatory bowel disease.

We have previously shown that complement factor 5a (C5a) plays a role in the pathogenesis of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats by using the selective, orally active C5a antagonist AcF-[OP(d-Cha)WR]. This study tested the efficacy and potency of a new C5a antagonist, hydrocinnamate (HC)-[OP(d-Cha)WR], which has limited intestinal lumenal metabolism, in this model of colitis. Analogs of AcF-[OP(d-Cha)WR] were examined for their susceptibility to alimentary metabolism in the rat using intestinal mucosal washings. One metabolically stable analog, HC-[OP(d-Cha)WR], was then evaluated pharmacokinetically and investigated at a range of doses (0.03-10 mg/kg/day p.o.) in the 8-day rat TNBS-colitis model, against the comparator drug AcF-[OP(d-Cha)WR]. Using various amino acid substitutions, it was determined that the AcF moiety of AcF-[OP(d-Cha)WR] was responsible for the metabolic instability of the compound in intestinal mucosal washings. The analog HC-[OP(d-Cha)WR], equiactive in vitro to AcF-[OP(d-Cha)WR], was resistant to intestinal metabolism, but it displayed similar oral bioavailability to AcF-[OP(d-Cha)WR]. However, in the rat TNBS-colitis model, HC-[OP(d-Cha)WR] was effective at reducing mortality, colon edema, colon macroscopic scores, and increasing food consumption and body weights, at 10- to 30-fold lower oral doses than AcF-[OP(d-Cha)WR]. These studies suggest that resistance to intestinal metabolism by HC-[OP(d-Cha)WR] may result in increased local concentrations of the drug in the colon, thus affording efficacy with markedly lower oral doses than AcF-[OP(d-Cha)WR] against TNBS-colitis. This large increase in potency and high efficacy of this compound makes it a potential candidate for clinical development against intestinal diseases such as inflammatory bowel disease.

Animals↗

PubMed2005

Comparative agonist/antagonist responses in mutant human C5a receptors define the ligand binding site.

The C terminus is responsible for all of the agonist activity of C5a at human C5a receptors (C5aRs). In this report we have mapped the ligand binding site on the C5aR using a series of agonist and antagonist peptide mimics of the C terminus of C5a as well as receptors mutated at putative interaction sites (Ile(116), Arg(175,) Arg(206), Glu(199), Asp(282), and Val(286)). Agonist peptide 1 (Phe-Lys-Pro-d-cyclohexylalanine-cyclohexylalanine-d-Arg) can be converted to an antagonist by substituting the bulkier Trp for cyclohexylalanine at position 5 (peptide 2). Conversely, mutation of C5aR transmembrane residue Ile(116) to the smaller Ala (I116A) makes the receptor respond to peptide 2 as an agonist (Gerber, B. O., Meng, E. C., Dotsch, V., Baranski, T. J., and Bourne, H. R. (2001) J. Biol. Chem. 276, 3394-3400). However, a potent cyclic hexapeptide antagonist, Phe-cyclo-[Orn-Pro-d-cyclohexylalanine-Trp-Arg] (peptide 3), derived from peptide 2 and which binds to the same receptor site, remains a full antagonist at I116AC5aR. This suggests that although the residue at position 5 might bind near to Ile(116), the latter is not essential for either activation or antagonism. Arg(206) and Arg(175) both appear to interact with the C-terminal carboxylate of C5a agonist peptides, suggesting a dynamic binding mechanism that may be a part of a receptor activation switch. Asp(282) has been previously shown to interact with the side chain of the C-terminal Arg residue, and Glu(199) may also interact with this side chain in both C5a and peptide mimics. Using these interactions to orient NMR-derived ligand structures in the binding site of C5aR, a new model of the interaction between peptide antagonists and the C5aR is presented.

Binding Sites↗

PubMed2004

Comparative anti-inflammatory activities of antagonists to C3a and C5a receptors in a rat model of intestinal ischaemia/reperfusion injury.

1. Complement activation is implicated in the pathogenesis of intestinal ischaemia-reperfusion injury (I/R), although the relative importance of individual complement components is unclear. A C3a receptor antagonist N(2)-[(2,2-diphenylethoxy)acetyl]-l-arginine (C3aRA) has been compared with a C5a receptor antagonist (C5aRA), AcF-[OPdChaWR], in a rat model of intestinal I/R. 2. C3aRA (IC(50)=0.15 microm) and C5aRA (IC(50)=0.32 microm) bound selectively to human polymorphonuclear leukocyte (PMN) C3a and C5a receptors, respectively. Effects on circulating neutrophils and blood pressure in the rat were also assessed. 3. Anaesthetised rats, subjected to intestinal ischaemia (30 min) and reperfusion (120 min), were administered intravenously with either (A) the C3aRA (0.1-1.0 mg x kg(-1)); the C5aRA (1.0 mg x kg(-1)); the C3aRA+C5aRA (each 1.0 mg x kg(-1)); or vehicle, 45 min prior, or (B) the C3aRA (1.0 mg x kg(-1)) or vehicle, 120 min prior to reperfusion. 4. The C3aRA and C5aRA, administered 45 min prior to reperfusion, displayed similar efficacies at ameliorating several disease markers (increased oedema, elevated ALT levels and mucosal damage) of rat intestinal I/R. The combination drug treatment did not result in greater injury reduction than either antagonist alone. However, doses of the C3aRA (0.01-10 mg x kg(-1)) caused transient neutropaenia, and the highest dose (10 mg x kg(-1)) also caused a rapid and transient hypertension. 5. The C3aRA (1.0 mg x kg(-1)), delivered 120 min prior to reperfusion to remove the global effect of C3aRA-induced neutrophil sequestration, did not attenuate the markers of intestinal I/R, despite persistent C3aR antagonism at this time. 6. C3aR antagonism does not appear to be responsible for the anti-inflammatory actions of this C3aRA in intestinal I/R in the rat. Instead, C3aRA-mediated global neutrophil tissue sequestration during ischaemia and early reperfusion may account for the protective effects observed.

Alanine Transaminase↗

PubMed2004

Protective effect of a human C5a receptor antagonist against hepatic ischaemia-reperfusion injury in rats.

BACKGROUND/AIMS: Complement activation is induced by ischaemia-reperfusion (I/R) and the complement factor C5a plays an important role in organ specific I/R injuries. This study investigated the efficacy of a small molecule C5a receptor (C5aR) antagonist against hepatic I/R injury. METHODS: Total hepatic ischaemia or partial hepatic ischaemia were induced in rats, followed by a period of reperfusion. The C5aR antagonist, AcF-[OPdChaWR], was administered at 1 mg/kg i.v. or 10 mg/kg p.o. or s.c. before induction of ischaemia. Total hepatic I/R-induced mortality was measured and partial hepatic ischaemia injury was assessed by measuring the serum levels of liver enzymes, tissue or serum TNFalpha, liver and lung myeloperoxidase activity, the number of infiltrating neutrophils, neutrophilia and liver histopathology. RESULTS: C5aR antagonist treatment reduced total hepatic I/R-induced mortality. In partial hepatic I/R rats, treatment with the C5aR antagonist significantly attenuated the increases in liver enzymes, serum and tissue TNFalpha, myeloperoxidase activity, infiltrating neutrophils, neutrophilia, and also reduced liver histopathology. CONCLUSIONS: This study shows that an orally active, small molecule C5aR antagonist is effective in reducing the markers of tissue damage caused by I/R in the rat, suggesting an important role for C5a in I/R injuries in the liver.

Alanine Transaminase↗

PubMed2004

Potent cyclic antagonists of the complement C5a receptor on human polymorphonuclear leukocytes. Relationships between structures and activity.

Human C5a is a plasma protein with potent chemoattractant and pro-inflammatory properties, and its overexpression correlates with severity of inflammatory diseases. C5a binds to its G protein-coupled receptor (C5aR) on polymorphonuclear leukocytes (PMNLs) through a high-affinity helical bundle and a low-affinity C terminus, the latter being solely responsible for receptor activation. Potent and selective C5a antagonists are predicted to be effective anti-inflammatory drugs, but no pharmacophore for small molecule antagonists has yet been developed, and it would significantly aid drug design. We have hypothesized that a turn conformation is important for activity of the C terminus of C5a and herein report small cyclic peptides that are stable turn mimics with potent antagonism at C5aR on human PMNLs. A comparison of solution structures for the C terminus of C5a, small acyclic peptide ligands, and cyclic antagonists supports the importance of a turn for receptor binding. Competition between a cyclic antagonist and either C5a or an acyclic agonist for C5aR on PMNLs supports a common or overlapping binding site on the C5aR. Structure-activity relationships for 60 cyclic analogs were evaluated by competitive radioligand binding with C5a (affinity) and myeloperoxidase release (antagonist potency) from human PMNLs, with 20 compounds having high antagonist potencies (IC(50), 20 nM-1 microM). Computer modeling comparisons reveal that potent antagonists share a common cyclic backbone shape, with affinity-determining side chains of defined volume projecting from the cyclic scaffold. These results define a new pharmacophore for C5a antagonist development and advance our understanding of ligand recognition and receptor activation of this G protein-coupled receptor.

Binding, Competitive↗

PubMed2003

Comparative protection against rat intestinal reperfusion injury by a new inhibitor of sPLA2, COX-1 and COX-2 selective inhibitors, and an LTC4 receptor antagonist.

(1) A new group IIa sPLA2 inhibitor was compared with selective inhibitors of COX-1, COX-2 and an LTC4 antagonist for effects on local and remote tissue injuries following ischaemia and reperfusion (I/R) of the small intestine in rats. (2) In an acute model of ischaemia (30 min) and reperfusion (150 min) injury in the absence of inhibitors, there was significant intestinal haemorrhage, oedema and mucosal damage, neutropenia, elevated serum levels of aspartate aminotransferase (AST) and hypotension. (3) Preischaemic treatment with the inhibitor of sPLA2 (Group IIa), at 5 mg kg-1 i.v. or 10 mg kg-1 p.o. significantly inhibited I/R-induced neutropenia, the elevation of serum levels of AST, intestinal oedema and hypotension. (4) Pretreatment with the COX-2 inhibitor celebrex (10 mg kg-1 i.v.) and the LTC4 antagonist zafirlukast (1 mg kg-1 i.v.) also showed marked improvement with I/R-induced AST, oedema and neutropenia. Hypotension was only reduced by the LTC4 antagonist. The COX-1 inhibitor flunixin (1 mg kg-1 i.v.) did not effect improvement in the markers of tissue injury. (5) Histological examination of rat I/R injury showed that all of the drugs offered some protection to the mucosal layer damage compared to no drug treatment. Given i.v., the sPLA2 inhibitor was more effective than either the COX-1 or COX-2 inhibitors in preventing rat I/R injury. (6) These results indicate that a potent new inhibitor of sPLA2 (group IIa) protects the rat small intestine from I/R injury after oral or intravenous administration. COX-2 and LTC4 inhibitors also showed some beneficial effects against intestinal I/R injury. Our study suggests that sPLA2 (Group IIa) may have a pathogenic role in intestinal I/R in rats.

Animals↗