1-Methylnicotinamide (MNA), a major metabolite of nicotinamide (NA), is known to exert anti-inflammatory effects in vivo. Treatment of inflammatory skin diseases by topical application of MNA provides certain advantages over the use of NA. However, in contrast to NA, the molecular mechanisms of the anti-inflammatory properties of MNA are not well known. In this study the influence of exogenous MNA and NA in vivo on the generation of inflammatory mediators by macrophages (Mϕ) was investigated. Peritoneal Mϕ of CBA/J mice were activated in vitro with lipopolysaccharide and incubated with MNA or NA. The effect of these compounds on biological functions of Mϕ was measured by evaluation of the production of reactive oxygen species (ROS) by luminol-dependent chemiluminescence, cytokines and prostaglandin E₂ (PGE₂) by ELISA, and nitric oxide (NO) by the Griess method. Moreover, the expressions of inducible NO synthase and cyclooxygenase-2 were measured by Western blotting. It was shown that at non-cytotoxic concentrations, NA inhibits the production of a variety of pro-inflammatory agents, such as tumor necrosis factor α, interleukin 6, NO, PGE₂, and the generation of ROS. In contrast to NA, exogenous MNA inhibited only the generation of ROS, while its effect on the synthesis of other mediators was negligible. These results indicate that the anti-inflammatory properties of MNA demonstrated previously in vivo do not depend on its capacity to suppress the functions of immune cells, but more likely may be related to its action on vascular endothelium. The authors suggest that the limited permeability for exogenous MNA, in contrast to that for NA, may be responsible for its lack of suppressor activity against Mϕ.

Adenosine deaminase (ADA) is an enzyme of purine metabolism that irreversibly converts adenosine to inosine or 2′deoxyadenosine to 2′deoxyinosine. ADA is active both inside the cell and on the cell surface where it was found to interact with membrane proteins, such as CD26 and adenosine receptors, forming ecto-ADA (eADA). In addition to adenosine uptake, the activity of eADA is an essential mechanism that terminates adenosine signaling. This is particularly important in cardiovascular system, where adenosine protects against endothelial dysfunction, vascular inflammation, or thrombosis. Besides enzymatic function, ADA protein mediates cell-to-cell interactions involved in lymphocyte co-stimulation or endothelial activation. Furthermore, alteration in ADA activity was demonstrated in many cardiovascular pathologies such as atherosclerosis, myocardial ischemia-reperfusion injury, hypertension, thrombosis, or diabetes. Modulation of ADA activity could be an important therapeutic target. This work provides a systematic review of ADA activity and anchoring inhibitors as well as summarizes the perspectives of their therapeutic use in cardiovascular pathologies associated with increased activity of ADA.

Aims Extracellular nucleotides and adenosine that are formed or degraded by membrane-bound ecto-enzymes could affect atherosclerosis by regulating the inflammation and thrombosis. This study aimed to evaluate a relation between ecto-enzymes that convert extracellular adenosine triphosphate to adenine dinucleotide phosphate, adenosine monophosphate, adenosine, and inosine on the surface of the vessel wall with the severity or progression of experimental and clinical atherosclerosis. Furthermore, we tested whether the inhibition of adenosine deaminase will block the development of experimental atherosclerosis. Methods and results Vascular activities of ecto-nucleoside triphosphate diphosphohydrolase 1, ecto-5’-nucleotidase, and ecto-adenosine deaminase (eADA) were measured in aortas of apolipoprotein E-/- low density lipoprotein receptor (ApoE-/-LDLR-/-) and wild-type mice as well as in human aortas. Plaques were analysed in the entire aorta, aortic root, and brachiocephalic artery by Oil-Red O and Orcein Martius Scarlet Blue staining and vascular accumulation of macrophages. The cellular location of ecto-enzymes was analysed by immunofluorescence. The effect of eADA inhibition on atherosclerosis progression was studied by a 2-month deoxycoformycin treatment of ApoE-/-LDLR-/- mice. The vascular eADA activity prominently increased in ApoE-/-LDLR-/- mice when compared with wild type already at the age of 1 month and progressed along atherosclerosis development, reaching a 10-fold difference at 10 months. The activity of eADA correlated with atherosclerotic changes in human aortas. High abundance of eADA in atherosclerotic vessels originated from activated endothelial cells and macrophages. There were no changes in ecto-nucleoside triphosphate diphosphohydrolase 1 activity, whereas ecto-5’-nucleotidase was moderately decreased in ApoE-/-LDLR-/- mice. Deoxycoformycin treatment attenuated plaque development in aortic root and brachiocephalic artery of ApoE-/-LDLR-/- mice, suppressed vascular inflammation and improved endothelial function. Conclusions This study highlights the importance of extracellular nucleotides and adenosine metabolism in the atherosclerotic vessel in both experimental and clinical setting. The increased eADA activity marks an early stage of atherosclerosis, contributes to its progression and could represent a novel target for therapy.