Macrophage Cytotoxicity: Role for L-Arginine Deiminase and Imino Nitrogen Oxidation to Nitrite

Abstract

Previous studies have shown that cytotoxic activated macrophages cause inhibition of DNA synthesis, of mitochondrial respiration, and of aconitase activity in tumor target cells. An L-arginine-dependent biochemical pathway synthesizing L-citrulline and nitrite, coupled to an effector mechanism, is now shown to cause this pattern of metabolic inhibition. Murine cytotoxic activated macrophages synthesize L-citrulline and nitrite in the presence of L-arginine but not D-arginine. L-Citrulline and nitrite biosynthesis by cytotoxic activated macrophages is inhibited by NG-monomethyl-L-arginine, which also inhibits this cytotoxic effector mechanism. This activated macrophage cytotoxic effector system is associated with L-arginine deiminase activity, and the imino nitrogen removed from the guanido group of L-arginine by the deiminase reaction subsequently undergoes oxidation to nitrite. L-Homoarginine, an alternative substrate for this deiminase, is converted to L-homocitrulline with concurrent nitrite synthesis and similar biologic effects.

Selective Targeting of Nitric Oxide Synthase Inhibitors to System y+ in Activated Macrophages

“…In activated macrophages generation of NO by inducible NO synthase (iNOS) is critically dependent on extracellular arginine (2,4,5), despite reports that activated cells contain high intracellular arginine levels (1,6). N G -derivatized analogues of L-arginine are potent inhibitors of iNOS, and their rank order of potency has been attributed to different NOS isoforms and/or their differential rates of cellular uptake (7,8).…”

The role of nitric oxide in cancer

“…The mammalian immuno -defense network is involved in tumour suppression, and macrophages are an important part of this process because of their ability to destroy selectively a broad range of tumour types upon specific activation. The role of NO in macrophage cytotoxicity was first described by Hibbs and colleagues in 1987 [10], and since that time numerous studies have shown that cytokine activated rodent macrophages can generate large concentrations of NO by up-regulation of expression of the inducible nitric oxide synthase gene (iNOS) [11]. The NO generated by this process is capable of killing a range of tumour cells of differing origin and grade [11][12][13][14][15].…”

Differential nitric oxide (NO) production by macrophages from mice and guinea pigs infected with virulent and avirulent Legionella pneumophila serogroup 1

“…pneumophila produced significantly more nitrite than uninfected mice. The inhibition of nitrite production by NMMA, a competitive inhibitor of L-arginine [10,11], showed that this production was due to induction of NO synthase activity. In addition, macrophages from mice infected with the avirulent strain produced higher amounts of nitrite ex vivo than those infected with the virulent strain.…”

“…These authors have also shown that this bactericidal activity correlates with the depletion of intracellular iron in this cell line. Nitric oxide radicals generated by IFN--activated macrophages react with iron-sulphur prosthetic groups of the enzymes necessary for cellular functions such as (i) mitochondrial respiration, which may limit the ability of host cells to produce ATP [10,11]; (ii) DNA replication requiring ribonucleotide reductase [36]; and (iii) the citric acid cycle [12,37], and these radicals are released # 1996 Blackwell Science Ltd, Clinical and Experimental Immunology, 104:48-53 Fig. 3.…”

“…pneumophila by a murine macrophage cell line, RAW 264.7 in vitro [28]. NO is generated via nitric oxide synthase, which uses L-arginine as sole substrate to produce citrulline and NO, which gives rise to nitrate and nitrite [9][10][11].…”