EPR demonstration of iron-nitrosyl complex formation by cytotoxic activated macrophages.

Abstract

Activated macrophage cytotoxicity is characterized by loss of intracellular iron and inhibition of certain enzymes that have catalytically active nonheme-iron coordinated to sulfur. This phenomenon involves the oxidation of one of the terminal guanidino nitrogen atoms of L-arginine, which results in the production of citrulline and inorganic nitrogen oxides (NO-, NO5, and NO). We report here the results of an electron paramagnetic resonance spectroscopic study performed on cytotoxic activated macrophage (CAM) effector cells, which develop the same pattern of metabolic inhibition as their targets. Examination of activated macrophages from mice infected with Mycobacterium bovis (strain bacillus CalmetteGuerin) that were cultured in medium with lipopolysaccharide and L-arginine showed the presence of an axial signal at g = 2.039, which is similar to previously described iron-nitrosyl complexes formed from the destruction of iron-sulfur centers by nitric oxide (NO). Inhibition of the L-arginine-dependent pathway by addition of NG-monomethyl L-arginine (methyl group on a terminal guanidino nitrogen) inhibits the production of nitrite, nitrate, citrulline, and the g = 2.039 signal. Comparison of the hyperfine structure of the signal from cells treated with L-arginine with terminal guanidino nitrogen atoms of natural abundance N'4 atoms or labeled with N'5 atoms showed that the nitrosyl group in this paramagnetic species arises from one of these two atoms. These results show that loss of iron-containing enzyme function in CAM is a result of the formation of iron-nitrosyl complexes induced by the synthesis of nitric oxide from the oxidation of a terminal guanidino nitrogen atom of L-arginine.

NG-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthesis, ameliorates interleukin 2-induced capillary leakage and reduces tumour growth in adenocarcinoma-bearing mice

“…While NO may be required for tumoricidal function of certain effector cells, excessive NO production can also suppress lymphocyte activation. It has been shown that activated murine macrophages synthesise NO from L-arginine (Stuehr and Marletta, 1985), which may partly mediate the cytotoxic activity of these cells against tumour cells and bacteria (Lancaster and Hibbs, 1990). Mills et al (1992) reported that tumour growth in the peritoneal cavity of mice was associated with a marked decline in the production of NO by intra-tumour macrophages.…”

Nitric oxide and arthritis

“…NO has a high affinity for both heme and non-heme iron atoms present in the prosthetic groups of proteins (41). It is the binding of NO to the heme group of soluble guanylate cyclase that activates this enzyme, raising intracellular levels of cGMP in many (3), but not all (42), types of cells.…”

NO accounts completely for the oxygenated nitrogen species generated by enzymic l-arginine oxygenation

“…released from endothelial cells (the endothelium-derived relaxing factor, EDRF) [3] and the L-arginine-derived cytotoxic effector molecule released from macrophages and other cells is identical with NO [1][2][3][4][5][6][7][8], other investigators have proposed that hydroxylamine [9,10], a nitrosothiol [11] or a mixture of these [10] can also account for the activity of this NO.. This uncertainty derives mainly from the fact that the techniques used to quantify NO in oxygen-containing aqueous solutions are unable to discriminate between NO and labile NO donors.…”