Nitric oxide production and inducible nitric oxide synthase expression in peritoneal macrophages of cirrhotic patients

Abstract

The present study assessed whether peritoneal macrophages isolated from cirrhotic patients produce nitric oxide (NO) and express NO The description of endogenous production of nitrates by human beings 1 was the starting point of a series of discoveries attributing an important antimicrobial role to nitric oxide (NO). A major contribution along this track includes the realization that, under proper stimulus, rodent macrophages produce huge amounts of NO 2 as a result of the expression of an inducible form of nitric oxide synthase (NOS II). 3 This enzyme is responsible for the high-output pathway of NO production, uses molecular oxygen and L-arginine as cosubstrates, is Ca 2ϩ /calmodulin-independent, and its activity can be competitively inhibited by several L-arginine analogues such as N -nitro-L-arginine (NNA).Because macrophages are of central importance in the initiation and regulation of the nonspecific and specific immune responses, 4 it is considered that NO from these cells is implicated in the nonspecific defense against parasitic diseases and participates in the production of free radicals that are toxic to bacteria and parasites. 5 However, whereas bacterial lipopolysaccharide and/or proinflammatory cytokines are extremely efficacious at inducing NOS II in rodent macrophages, their ability to promote NOS II expression and NO production in human macrophages in vitro is almost nonexistent. 6 This, in turn, casts serious doubts on the role of this system in human beings. 7 This controversy has further been fueled by the demonstration of some degree of NOS II activity and/or expression in human macrophages when taken from patients with infectious or inflammatory diseases. [8][9][10] Spontaneous bacterial peritonitis (SBP) is a relatively common complication of patients with cirrhosis and ascites consisting of bacterial infection of ascitic fluid without any intraabdominal, surgically treatable source of infection. 11 Previous investigations have shown that the intraperitoneal administration of a selective inhibitor of NOS II to cirrhotic rats with ascites provokes bacterial peritonitis in these animals. 12 This finding indicates that NOS II is an important component of the rat armamentarium to fight against bacterial peritonitis in experimental cirrhosis. However, as to whether this also occurs in cirrhotic patients is not clear because, as previously discussed, NO production in human macrophages by the high-output NOS II pathway is controversial and does not seem to be controlled as in rodent macrophages. Therefore, in the present investigation, peritoneal macrophages of patients with cirrhosis and ascites, with and without SBP, were collected after therapeutic paracentesis to assess whether these cells produce NO and express NOS II mRNA and protein. The results indicate that peritoneal macrophages of most patients express NOS II within 8 days after the diagnosis of SBP. PATIENTS AND METHODSPatients. Ascites was collected by therapeutic paracentesis from 23 cirrhotic patients (6 women and 17 men). The me...

A randomized unblinded pilot study comparing albumin versus hydroxyethyl starch in spontaneous bacterial peritonitis

“…31,38 There is, therefore, a clear dissociation between the time course of cytokines in plasma and ascitic fluid, the concentration of which decreases markedly after the resolution of the infection, and the plasma and ascitic fluid levels of nitrates and nitrites, which reach the highest levels several days after SBP resolution. 2,31,38 This dissociation is not surprising considering that the inducible form of NO synthase is expressed in many cell types and that the production of NO is maintained over relatively long periods after challenging the cells with immunological or inflammatory stimuli. 38 In our patients treated with HES 200/0.5, we observed a significant increase in the serum levels of nitrates and nitrites despite the resolution of the infection.…”

“…2,31,38 This dissociation is not surprising considering that the inducible form of NO synthase is expressed in many cell types and that the production of NO is maintained over relatively long periods after challenging the cells with immunological or inflammatory stimuli. 38 In our patients treated with HES 200/0.5, we observed a significant increase in the serum levels of nitrates and nitrites despite the resolution of the infection. In contrast, in patients receiving albumin, no significant increase in the serum levels of nitrates and nitrites was observed.…”

Hypoxia is an inducer of vasodilator agents in peritoneal macrophages of cirrhotic patients

“…These cells are ubiquitously distributed, may produce a variety of vasoactive factors in response to microenvironmental changes, and several investigations have shown that circulating monocytes or peritoneal macrophages of patients and rats with cirrhosis may differentially produce vasoactive substances, including NO, anandamide, prostaglandins, and VEGF. [7][8][9][20][21][22] In the present study we were interested in assessing whether decreased O 2 tension is a further stimulus for the production of vasoactive peptides in monocytes/macrophages of patients with advanced liver disease because there are a number of vasoactive genes regulated by hypoxia and abnormalities of arterial oxygenation are common in cirrhotic patients.…”

“…6 In this regard, we have shown recently that peritoneal macrophages of cirrhotic patients may produce important amounts of vasodilator/ vasopermeabilizing agents under proper in vitro stimuli or in determined pathologic circumstances. [7][8][9] In the present study we considered the hypothesis that focal areas of low oxygen tension could be an additional stimulus for the production of vasoactive substances by resident macrophages of patients with advanced liver disease. Thus, we assessed whether hypoxia may induce the secretion of vasoactive factors in peritoneal macrophages of patients with cirrhosis and ascites.…”

New challenge of hepatorenal syndrome: Prevention and treatment

“…83 Sepsis decreases both spontaneous and agonist-induced vascular contractile activity in the cirrhotic rat. 84 Sort et al 85 postulated that sepsis in cirrhosis induces an increased production of various cytokines and endotoxins, which in turn stimulate the production of nitric oxide and other vasodilators 86 causing further arterial vasodilatation. Indeed, intestinal decontamination with oral antibiotics in cirrhotic patients was associated with improvement in systemic hemodynamics and reduction in systemic arterial vasodilatation, 87 probably as a result of a reduction of nitric oxide-induced systemic arterial vasodilatation.…”