Definition
Small, anti-inflammatory peptides are useful to inhibit inflammation of a mammal's skin, mucous membranes, or lacerations of the musculature or injury to the brain or leakage of fluids into the air spaces of the lungs.
Discovery
Camussi G in 1986 described platelet-activating factor (PAF) as a phospholipid (1-0-alkyl-2-sn-acetyl-glycero-3-phosphocholine) mediator of inflammation and endotoxic shock. Polymorphonuclear neutrophils (PMN), peritoneal macrophages, vascular endothelial cells, basophils, and platelets synthesize PAF rapidly after appropriate stimuli 1. For example, TNF or phagocytosis promotes synthesis and release of PAF in PMN or macrophages within 10 min 2. These stimuli induce phospholipase A2 (PLA2) activity that cleaves membrane phospholipids into lyso-PAF and arachidonic acid. Thrombin stimulates PAFsynthesis in endothelial cells also within 10 min 3. Other proteinases, such as elastase, stimulate PAF synthesis rapidly in PMN, macrophages, and endothelial cells, and induce PLA2 and acetyltransferase activity. Conversely, different proteinase inhibitors block PAF synthesis induced by TNF. These findings led to the hypothesis that proteinases added to cells and cellular proteinases activated by TNF cleave proteins inhibitory for PLA2, such as lipocortins 4. Lipocortins belong to a family of related proteins that mediate the anti-inflammatory activity of corticosteroids.
Structural Characteristics
Cloning and sequencing of lipocortins cDNA has provided the amino acid sequence of anti-inflammatory proteins. Steroid induced protein with PLA2 inhibitory activity is uteroglobin, a rabbit secretory protein 5. Two identical subunits of 70 amino acids form uteroglobin; lipocortin I and II comprise four nonidentical repeats of 70 amino acids. Miele et al., have noticed a striking sequence similarity between amino acid residues 40-46 of uteroglobin and 247-253 of lipocortin I, repeat 3. Synthetic peptides designated "antiflammins" that correspond to such sequences show potent PLA2 inhibitory activity in vitro and an antiinflammatory effect on carrageenan induced rat foot pad edema in vivo 6, 7. SV-IV is a basic, thermostable, secretory protein of low Mr (9758) that is synthesized by rat seminal vesicle (SV) epithelium under strict androgen transcriptional control. By using two different experimental, data were obtained showing that in this protein: (a) the immunomodulatory activity is related to the structural integrity of the whole molecule; (b) the anti-inflammatory activity is located in the N-terminal region of the molecule, the 8-16 peptide fragment being the most active; (c) the identified anti-inflammatory peptide derivatives do not seem to possess pro-coagulant activity, even though this particular function has been located in the 1-70 segment of the molecule 8. The peptide HDMNKVLDL (antiflammin-2) inhibits the synthesis of PAF induced by TNF or phagocytosis in rat macrophages and human neutrophils, and by thrombin in vascular endothelial cells. The peptide MQMKKVLDS (antiflammin-1) is less inhibitory than antiflammin-2 for macrophages and not inhibitory for neutrophils after a 5-min preincubation 9.
Mode of Action
PLA2 are a family of esterases that initiate the arachidonic acid cascade, resulting in the production of numerous inflammatory mediators. Lipocortins are inhibitors of PLA2. Peptides corresponding to a region of high amino-acid sequence similarity between uteroglobin and lipocortin I have potent PLA2 inhibitory activity. Several synthetic peptides corresponding to the region of highest similarity were designed by Miele, L. et al., The most effective anti-inflammatory nonapeptides, termed antiflammins (AFs) correspond to uteroglobin residues 39–47 and lipocortin-1 residues 246–254. Both peptides are PLA2 inhibitors in-vitro and are effective in a classic model of acute inflammation in carrageenan-induced rat footpad edema. The nonapeptides have anti-inflammatory effects in-vitro and in-vivo 10. Antiflammin-1 is inactivated by neutrophils secretory products, possibly oxidizing agents. Synthesis of PAF is inhibited by antiflammin-2 without an appreciable lag, but this inhibition is reversed when neutrophils or macrophages are washed and incubated in fresh medium. Antiflammins must be continuously present to inhibit PAF synthesis. Antiflammins block activation of the acetyltransferase required for PAF synthesis, suggesting that this enzyme is another target for the inhibitory activity of antiflammins. These peptides inhibit neutrophil aggregation and chemotaxis induced by complement component C5a 9.
Functions
Bee venom, in a study of phospholipase-A2,3 nearly 1 kg of freeze-dried bee venom was fractionated and tested all the fractions for anti-inflammatory activity. Experiments showed activity to be associated with the basic peptide fraction 11.
PAF synthesis, anti-inflammatory peptides inhibit PAF synthesis in PMN, macrophages, and endothelial cells stimulated by TNF, phagocytosis, or proteinases 9.
PMN aggregation and chemotaxis, the antiflammins inhibit also PMN aggregation and chemotaxis, and suppress the inflammatory reaction induced in rat skin by in situ formation of immune complexes or by intradermal injection of TNF and complement component C5a 9.
References
1. Camussi G (1986). Potential role of platelet-activating factor in renal pathophysiology. Kidney Int., 29: 469-477.
2. Camussi G, Bussolino F, Salvidio G, Baglioni C (1987). Tumor necrosis factor/cachectin stimulates rat peritoneal macrophages and human endothelial cells to synthesize and release platelet activating factor. J. Exp. Med., 166:1390-1404.
3. Prescott SM (1984). Human endothelial cells in culture produce platelet-activating factor (1-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine) when stimulated with thrombin. PNAS., 81:3534-3538.
4. Camussi G, Tetta C, Bussolino F, Baglioni C (1988). Synthesis and release of platelet-activating factor is inhibited by plasma a,proteinase inhibitor or citantichymotrypsin and stimulated by proteinases . J. Exp. Med., 168:1293-1306.
5. Levin SW, Butler JD, Schumacher UK, Wightman PD, Mukherjee AB (1986). Uteroglobin inhibits phospholipase A2 activity. Life Sci., 38:1813-1819.
6. Morize I, Surcouf E, Vaney MC, Epelboin Y, Buehner M, Fridlansky F, Milgrom E, Mornon JP (1987) . Refinement of the C222 crystal formofoxidized uteroglobin at 1 .34 A resolution. J. Mol. Biol., 194:725-739.
7. Miele L, Cordella-Miele E, Facchiano A, Mukherjee AB (1988). Novel anti-inflammatory peptides from the region of highest similarity between uteroglobin and lipocortin I. Nature, 335:726-730.
8. Ialenti A, Santagada V, Caliendo G, Severino B, Fiorino F, Maffia P, Ianaro A, Morelli F, Di Micco B, Cartenì M, Stiuso P, Metafora V, Metafora S (2001). Synthesis of novel anti-inflammatory peptides derived from the amino-acid sequence of the bioactive protein SV-IV. FEBS Journal, 268(12):3399-3406.
9. Camussi G, Tetta C, Bussolino F, Baglioni C (1990). Antiinflamatory peptides (antiinflamins) inhibit synthesis of platelet-activating factor, neutrophil aggregation and chemotaxis, and interdermal inflammatory reactions. J. Exp. Med., 171:913-927.
10. Sohn J, Kim TI, Yoon YH, Kim JY, Kim SY (2003). Novel transglutaminase inhibitors reverse the inflammation of allergic conjunctivitis. J. Clin. Invest., 111(1):121-128.
11. Billingham ME, Morley J, Hanson JM, Shipolini RA, Vernon CA (1973). Letter: An anti-inflammatory peptide from bee venom. Nature, 245(5421):163-164.