Clin. Lab. Haem. 1998, 20, 239–244 Carnosine and anserine as modulators of neutrophil function K.M.L. TAN Department of Biochemistry, Faculty of Medicine, J.K. CANDLISH National University of Singapore, Singapore Summary Carnosine and anserine, the bioactive peptides found in most meats and fish, were tested for their ability to modulate neutrophil and U937 cell function, specifically with respect to respiratory burst, interleukin-1b production and apoptosis. Both peptides increased the respiratory burst and interleukin-1b production of human neutrophils but not of U937 cells. They suppressed apoptosis of human neutrophils but enhanced apoptosis of U937 cells as assessed by DNA strand breaks. These results suggest that carnosine and anserine have the capacity to modulate the immune response at least in human neutrophils. Keywords Carnosine, neutrophils, superoxide, interleukin-1b, apoptosis Introduction Carnosine (N-b-alanyl-L-histidine) and anserine (N-b-ala- nyl-1-methyl-L-histidine) are found in skeletal muscle of most vertebrates, including those used for food; for exam- ple, 100 g of chicken breast contains 400 mg (17.6 mmol/L) of carnosine and 1020 mg (33.6 mmol/l) of anser- ine (Crush 1970). In humans, carnosine and related dipep- tides have been detected in skeletal muscle, cardiac muscle and brain and are primarily associated with the myofibrils (Jackson & Lenney 1995). The concentration of carnosine is approximately 20 mmol/l in human skeletal muscle (Decker 1995). Many actions of carnosine have been reported. It is a pH buffer in skeletal muscle (Babizhayev et al. 1994) and has antioxidant activity (Boldyrev et al. 1995). It is thought to be a neuromodulator in the olfactory system (Davidson & Sittman 1994), has been shown to inhibit the growth of neoplastic cells (Holliday & McFarland 1996) and is also known to have effects on vascular smooth muscle tone (O’Dowd, O’Dowd & Miller 1996). However, the precise physiological role of carnosine remains unclear. Anserine, not being found in humans, has been less studied. Bioactive constituents of foods have been shown to regu- late aspects of immune responses (Kitts et al. 1993). This prompted us to examine the effects of carnosine and anser- ine on human neutrophils and the U937 promonocytic human cell line. Because carnosine and anserine are anti- oxidants, the leucocytes tested were those that generate reactive oxygen intermediates. The neutrophil is a chemo- tactic, phagocytic, polymorphonuclear cell which is the Accepted for publication 27 November 1997 Correspondence Author: Dr J.K. Candlish, Department of Biochem- istry, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore. © 1998 Blackwell Science Limited first cell type to migrate to the site of infection (Smith 1994). Being the most abundant phagocyte, it has an important role in acute inflammation. The U937 cell line is a promonocytic cell line that can be induced to express macrophage-like characteristics by a variety of stimuli (Sundstrom & Nilsson 1976). In this study, it was used as a comparator to the terminally differentiated, end-stage neutrophils. The three functions of these cells examined were the respiratory burst, interleukin-1b (IL-1b) production, and apoptosis. Cell surface stimulation of neutrophils and monocytes leads to a respiratory burst in which oxygen consumption increases markedly and superoxide radicals are formed; in addition, there is a mechanism called priming whereby dormant neutrophils acquire a state of pre- activation that enables a more powerful response to be generated once microbicidal activity is activated (Smith 1994). In this study we examined whether the dipeptides carnosine and anserine can stimulate neutrophils to increase superoxide anion production in the oxidative res- piratory burst. IL-1 is an inflammatory cytokine that is synthesized and released by human neutrophils (Lloyd & Oppenheim 1992) and stimulated U937 cells (Palacios et al. 1982). IL-1a and IL-1b are ligands for the same receptors and have indistinguishable functions, including chemotactic attrac- tion of neutrophils and macrophages (Dinarello 1991). During the inflammatory process, IL-1 produced by human neutrophils may stimulate the synthesis and release of acute phase reactants, augment T- and B-cell activation and induce other regulatory cytokines such as interleukin- 6 (IL-6), interleukin-8 (IL-8) and granulocyte-macrophage colony stimulating factor (GM-CSF) (Lloyd & Oppenheim 239