Ruthenium red as measure of mast cell activation

The Roles of Complement Factor C5a and CINC-1 in Glucose Transport, Ultrafiltration, and Neutrophil Recruitment during Peritoneal Dialysis

Background

In a recent experimental study, we showed that low molecular weight heparin improved ultrafiltration and blocked complement activation and coagulation in a single peritoneal dialysis (PD) dwell.

Objective

The aim of the present study was to evaluate the possible contribution of the complement factor C5a and the potential interactions between C5a, the coagulation system, and cytokines of the interleukin (IL)-8 family (cytokine-induced neutrophil chemoattractant; CINC-1).

Methods

Nonuremic rats were exposed through an indwelling catheter to a single dose of 20 mL glucose- (2.5%) based filter-sterilized PD fluid, with or without the addition of anti-rat C5 antibody. The dwell fluid was analyzed 2 and 4 hours later concerning activation of the coagulation cascades, neutrophil recruitment, ultrafiltration volume; CINC-1, glucose, urea, and histamine concentrations; and ex vivo intraperitoneal chemotactic activity.

Results

The numbers of neutrophils and levels of thrombin–antithrombin complex (TAT) and CINC-1 increased significantly during the PD dwell. C5 blockade significantly reduced the levels of TAT and increased the ultrafiltration volumes at 2 hours. Glucose concentrations were significantly positively correlated to ultrafiltration volumes.

Conclusions

Blockade of C5 leads to an increase in ultra-filtration, probably by a mechanism that involves a reduction in glucose transport. This effect may form a basis for improving PD efficiency in situations where high glucose transport limits ultrafiltration. Mechanisms connected to complement activation during PD may involve coagulation. Further studies of the intraperitoneal cascade systems under conditions of PD are indicated.

Mast cells and histamine are triggering the NF-κB-mediated reactions of adult and aged perilymphatic mesenteric tissues to acute inflammation

This study aimed to establish mechanistic links between the aging-associated changes in the functional status of mast cells and the altered responses of mesenteric tissue and mesenteric lymphatic vessels (MLVs) to acute inflammation. We used an in vivo model of acute peritoneal inflammation induced by lipopolysaccharide treatment of adult (9-month) and aged (24-month) F-344 rats. We analyzed contractility of isolated MLVs, mast cell activation, activation of nuclear factor-κB (NF-κB) without and with stabilization of mast cells by cromolyn or blockade of all types of histamine receptors and production of 27 major pro-inflammatory cytokines in adult and aged perilymphatic mesenteric tissues and blood. We found that the reactivity of aged contracting lymphatic vessels to LPS-induced acute inflammation was abolished and that activated mast cells trigger NF-κB signaling in the mesentery through release of histamine. The aging-associated basal activation of mesenteric mast cells limits acute inflammatory NF-κB activation in aged mesentery. We conclude that proper functioning of the mast cell/histamine/NF-κB axis is necessary for reactions of the lymphatic vessels to acute inflammatory stimuli as well as for interaction and trafficking of immune cells near and within the collecting lymphatics.

Aging-associated shifts in functional status of mast cells located by adult and aged mesenteric lymphatic vessels

We had previously proposed the presence of permanent stimulatory influences in the tissue microenvironment surrounding the aged mesenteric lymphatic vessels (MLV), which influence aged lymphatic function. In this study, we performed immunohistochemical labeling of proteins known to be present in mast cells (mast cell tryptase, c-kit, prostaglandin D(2) synthase, histidine decarboxylase, histamine, transmembrane protein 16A, and TNF-α) with double verification of mast cells in the same segment of rat mesentery containing MLV by labeling with Alexa Fluor 488-conjugated avidin followed by toluidine blue staining. Additionally, we evaluated the aging-associated changes in the number of mast cells located by MLV and in their functional status by inducing mast cell activation by various activators (substance P; anti-rat DNP Immunoglobulin E; peptidoglycan from Staphyloccus aureus and compound 48/80) in the presence of ruthenium red followed by subsequent staining by toluidine blue. We found that there was a 27% aging-associated increase in the total number of mast cells, with an ∼400% increase in the number of activated mast cells in aged mesenteric tissue in resting conditions with diminished ability of mast cells to be newly activated in the presence of inflammatory or chemical stimuli. We conclude that higher degree of preactivation of mast cells in aged mesenteric tissue is important for development of aging-associated impairment of function of mesenteric lymphatic vessels. The limited number of intact aged mast cells located close to the mesenteric lymphatic compartments to react to the presence of acute stimuli may be considered contributory to the aging-associated deteriorations in immune response.

Mast cells mediate the microvascular inflammatory response to systemic hypoxia

Systemic hypoxia produces an inflammatory response characterized by increases in reactive O(2) species (ROS), venular leukocyte-endothelial adherence and emigration, and vascular permeability. Inflammation is typically initiated by mediators released from activated perivascular cells that generate the chemotactic gradient responsible for extravascular leukocyte accumulation. These experiments were directed to study the possible participation of mast cells in hypoxia-induced microvascular inflammation. Mast cell degranulation, ROS levels, leukocyte adherence and emigration, and vascular permeability were studied in the mesenteric microcirculation by using intravital microscopy of anesthetized rats. The main findings were 1) activation of mast cells with compound 48/80 in normoxia produced microvascular effects similar, but not identical, to those of hypoxia; 2) systemic hypoxia resulted in rapid mast cell degranulation; 3) blockade of mast cell degranulation with cromolyn prevented or attenuated the hypoxia-induced increases in ROS, leukocyte adherence/emigration, and vascular permeability; and 4) mast cell degranulation during hypoxia was prevented by administration of the antioxidant lipoic acid and of nitric oxide. These results show that mast cells play a key role in hypoxia-induced inflammation and suggest that alterations in the ROS-nitric oxide balance may be involved in mast cell activation during hypoxia.

Influence of serotonin-receptor antagonism on mast cell activation during endotoxemia

INTRODUCTION: Mast cells have been implicated in the aetiology of many diseases and are particularly important in evoking leukocyte-endothelial interactions during endotoxemia. Mast cell activity can be modified by histamine. There are only little data available whether serotonin (5-HT), another amine, is involved in alterations of mast cell activity, too. The aim of the study was to investigate the effects of the 5-HT-receptor antagonists methysergide (5-HT(1/2/7)-receptor antagonist), and ketanserin (5-HT(2A)-receptor antagonist) on mesenteric mast cell activation during endotoxemia. MATERIALS AND METHODS: In male Wistar rats, mast cell activity was determined in the mesentery using intravital microscopy. Rats were randomised in four groups of 12 animals each. Animals underwent laparotomy and the mesentery was exposed beneath an in-vivo videomicroscope. After baseline measurment endotoxemia was induced by continuous intravenous infusion of 2 mg/kg/h endotoxin (ETX group). Animals in the ETX/5-HT(1/2)-ANT group received methysergide (1 mg/kg body weight), animals in the ETX/5-HT(2A)-ANT group received ketanserin (1 mg/kg body weight) additionally prior to laparotomy and to the procedure described above. Animals in saline group served as controls and received equivalent volumes of NaCl 0.9%. Activated mast cells were stained by superfusion of the mesentery with ruthenium red. RESULTS: The relative mast cell activity to baseline value increased significantly in all groups. Values of the ETX-group versus the ETX/5-HT(1/2)-ANT group, the ETX/5-HT(2A)-ANT group, and the saline group were significantly higher at 120 min. CONCLUSIONS: Serotonin receptor antagonism using the 5-HT(1/2/7)-receptor antagonist methysergide or the 5-HT(2A)-receptor antagonist ketanserin reduces endotoxin-induced mast cell activation in-vivo, most probably via the 5-HT(2A)-receptor subtype.

Absence of mast cell involvement in active systemic anaphylaxis in rats

This study investigates the role of mast cells in the hypotension induced by antigen-mediated anaphylaxis, compound 48/80 and dextran in mast cell-deficient white spotting (Ws/Ws) and normal wild type (+/+) rats. Rats were sensitized with 10 microg of intraperitoneal ovalbumin in saline or saline alone (sham-sensitized). Sensitized rats, both Ws/Ws and +/+ but not sham-sensitized rats, challenged intravenously with ovalbumin exhibited hypotensive responses. There was no evidence of mast cell activation in rat mesentery 20 min after intravenous antigen challenge in sensitized +/+ rats. Hypotension induced by intravenous injection of dextran (Dextran-162, 6%, 2 ml kg(-1)) or compound 48/80 (1 mg kg(-1)) occurred in +/+ rats, but not in Ws/Ws rats, and was inhibited by pretreatment with a combination of chlorpheniramine and cimetidine. Taken together, these data indicate that the hypotensive response induced by antigen-mediated anaphylaxis is independent of mast cell activation, whereas mast cell amines play the main role in the hypotensive response induced by dextran or compound 48/80.