EFFECT OF PARTIALLY MODIFIED RETRO-INVERSO ANALOGS DERIVED FROM C-REACTIVE PROTEIN ON THE INDUCTION OF NITRIC-OXIDE SYNTHESIS IN PERITONEAL-MACROPHAGES

1 The ability of three modified tetrapeptides, representing fragments of the C-reactive protein (CRP) sequence and stabilized in the first p eptide bond by retro-inverso modification, to affect the secretion of nitric oxide (NO) was studied in macrophages of BALB/c mice. 2 These t etrapeptides, resembling the aminoacid sequence of tuftsin (CRP I, H-g Thr-(R,S)mLys-Pro-Leu-OH, ITF 1192; CRP II, H-gGly-(R, S)mLys-Pro-Arg- OH, ITF 1127; CRP III, H-gThr-(R,S)mLys-Pro-Gln-OH, ITF 1193), were ab le to induce NO synthesis by peritoneal macrophages in a dose-dependen t manner; the most stimulating dose was 1000 ng ml(-1) for CRP II and 100 ng ml(-1) for CRP I and CRP III. NO synthesis was not strictly dep endent on lipopolysaccharide (LPS) activation. 3 The enhanced effect o f retro-inverso CRP-related analogues on the expression of iNOS (induc ible NO synthase) was confirmed by higher levels of iNOS activity in t he cytosol and by the increase in iNOS protein, as evaluated by Wester n blot analysis, in macrophages stimulated by CPR compared with untrea ted ones.4 The production of NO by retro-inverso CRP-peptide analogues was significantly inhibited by dexamethasone (20 mu M), N-G-monomethy l-L-arginine (L-NMMA) (500 mu M) and pyrrolidine dithiocarbamate (PDTC ) (100 mu M). 5 Retro-inverso CRP-peptide analogues stimulated macroph ages to produce high levels of interleukin-1 (IL-1) and tumour necrosi s factor-alpha (TNF-alpha) in the presence of LPS. 6 Retro-inverso CRP -peptide analogues stimulated NO synthesis by the enhancement of endog enously produced IL-1 and TNF-alpha, as the treatment of peritoneal ma crophages with LPS in the presence of neutralizing anti-IL-1 and anti- TNF monoclonal antibodies (mAbs) reduced retro-inverso analogue-induce d NO secretion. Data indicate a predominant role for IL-1 alpha in the induction of NO secretion by retro-inverso analogues. 7 These results suggest that retro-inverso CRP derived analogues act as costimulators of NO and cytokine synthesis in macrophages. The mechanisms by which they cause iNOS induction appear to be strongly dependent on the activ ation of nuclear factor-kappa B (NF-kappa B).