Nitric oxide modulates cardiac and mast cell anaphylaxis

Anaphylaxis in the isolated guinea-pig heart was associated with a sudden release of histamine with a long-lasting release of nitrite (NO ⁻₂ ), an oxidation product of NO.N ^G-monomethyl-l-arginine (MeArg, 300 μM) increased the severity of cardiac anaphylaxis, as shown by the decrease in the coronary flow and by a prolonged duration of antigen-induced arrhythmias. Concomitantly, MeArg increased the release of histamine while decreasing the release of nitrite. Sodium nitroprusside (NaNP, 10⁻⁵–10⁻⁴ M) reduced the severity of cardiac anaphylaxis by increasing coronary flow and shortening the duration of antigen-induced arrhythmias. Concomitantly, NaNP decreased the release of histamine while increasing the release of nitrite. In mast cells isolated from actively sensitized guinea-pigs, the release of histamine elicited by specific antigen was increased by MeArg and decreased by NaNP.

In conclusion, endogenous and exogenous NO antagonizes the effect of vasoconstrictor mediators released after antigen challenge and plays a protective role in anaphylactic reactions “in vitro”,

     

Nitric oxide: a regulator of mast cell activation and mast cell-mediated inflammation

Nitric oxide (NO) plays diverse roles in physiological and pathological processes. During immune and inflammatory responses, for example in asthma, NO is generated at relatively high and sustained levels by the inducible form of nitric oxide synthase (NOS-2). NOS-2 derived NO regulates the function, growth, death and survival of many immune and inflammatory cell types. In the case of mast cells, NO suppresses antigen-induced degranulation, mediator release, and cytokine expression. The action of NO on mast cells is time dependent, requiring several hours, and noncGMP mediated, most probably involving chemical modification of proteins. NO inhibits a number of mast cell-dependent inflammatory processes in vivo, including histamine mediated vasodilatation, vasopermeation and leucocyte-endothelial cell attachment. In human asthma and animal models of lung inflammation the role of NO is harder to define. However, although there are conflicting data, the balance of evidence favours a predominantly protective role for NO. Mimicking or targeting NO dependent pathways may prove to be a valuable therapeutic approach to mast cell mediated diseases.     

Nitric oxide synthase and nitric oxide production in in vivo-derived mast cells

Nitric oxide (NO) is a potent mediator synthesized by a variety of cells involved in inflammatory reactions. We investigated the expression of NO synthase (NOS) in rat peritoneal mast cells (PMC). Small amounts of eNOS mRNA were detected basally, whereas neither mRNA for iNOS nor nNOS was detected in unstimulated PMC. Following stimulation by antigen, interferon-gamma (IFN-gamma), or anti-CD8 antibody, PMC up-regulated iNOS mRNA expression. In situ RT-PCR confirmed that iNOS mRNA originated from PMC. Production of iNOS protein was confirmed in stimulated PMC by immunohistochemistry. Upon stimulation with antigen, IFN-gamma, or anti-CD8, nitrite production was increased significantly (8.4+/-0.6, 7.6+/-0.9, and 6.6+/-0.9 microM/2x10(5) cells/48 h NO2-, respectively; P<0.01), whereas unstimulated PMC released 2.1 +/- 0.3 microM/2 x 10(5) cells/48 h NO2-. These findings demonstrate that in vivo-derived PMC transcribe and translate mRNA for NOS and produce NO.     

Nitric oxide scavenging modulates an experimental vasoplesia in-vitro

Endogenous overproduction of nitric oxide (NO) is believed to be a primary cause of refractory hypotension in septic shock. Under this condition, effectiveness of vasopressors is diminished due to hyporeactivity of blood vessels, a condition termed as vasoplesia. Effective reduction of NO levels should alleviate the condition. In this study, we investigated whether NO scavenging could modulate the endotoxin mediated vasoplesia in-vitro. Further, we explored whether NO scavenging in combination with a moderate NO synthase (NOS) inhibition would also be effective in modulating NO mediated vasoplesia. Experimental vasoplesia was produced in-vitro by incubating isolated rat thoracic aortic rings with lipopolysaccharide (LPS). Vessel rings were then treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor), human hemoglobin (Hb; a NO scavenger), or both L-NAME and Hb. Vascular reactivity was assessed by measuring vessel ring isometric tension changes to norepinephrine (NE) doses; the median effective doses (logEC50) of NE before and after each experimental treatment were compared. Following a 6-hour LPS treatment, vascular reactivity logEC50 values for NE were significantly increased compared with control vessel rings incubated without LPS. Treatment with either L-NAME alone or Hb alone significantly improved the vessel ring reactivity to NE. When both L-NAME and Hb were used concomitantly, vascular reactivity was also significantly improved. These results indicate that NO scavenging with Hb is as effective as NO synthesis inhibition with NAME in modulating the endotoxin induced vasoplesia. In conclusion, NO scavenging, alone or in combination with a moderate NOS inhibition, may render an alternative therapeutic approach to NOS synthesis inhibition in modulating the vasoplesia in septic shock.     

Nitric oxide modulates and adenosine mediates the tubuloglomerular feedback mechanism

The tubuloglomerular feedback (TGF) mechanism is an important regulator of the glomerular filtration rate (GFR) and urine excretion rate. It operates by sensing the distal delivery of fluid at the macula densa site and adjusting the tone of the glomerular arterioles to control GFR. We found evidence that nitric oxide is an important modulator of the setting of the sensitivity of the TGF mechanism. Studies on adenosine A1 receptor deficient mice have shown that these animals lack the TGF response and have an increased renin release. These findings show the important role of adenosine as a mediator of the signal for the TGF mechanism and as an inhibitor of renin release.     

Relaxin generates nitric oxide and provides protection against cardiac anaphylaxis

Inflammation Research -     

Rosette-forming mast cells in rat anaphylaxis. Immunological characteristics of mast cell rosettes.

Peritoneal mast cells from immunized rats can form rosettes with antigen-coated sheep red blood cells. The receptor responsible for this active rosette formation is shown to be IgE cytophilic antibody: rosettes are inhibited by previous contact of mast cells with antigen, or with anti-IgE antiserum; the kinetics of mast cell rosettes following a primary immunization with ovalbumin and Bordetella pertussis vaccine is similar to the kinetics of reaginic antibody response. Furthermore, a reaginic serum can induce passive rosette formation. There is no correlation between cell-bound and circulating IgE.     

Nitric oxide modulates vascular disease in the remnant kidney model

A loss of the microvascular endothelium occurs in the remnant kidney model of renal disease and may play an important role in progression (Kang et al, J Am Soc Nephrol, 12:1434, 2001). Given that nitric oxide (NO) is a potent endothelial cell survival factor, we hypothesized that stimulating (with L-arginine) or blocking (with nitro-L-arginine methyl ester, (L-NAME)) NO synthesis could modulate the integrity of the microvasculature and hence affect progression of renal disease. Rats underwent 5/6 nephrectomy (RK) and then were randomized at 4 weeks to receive vehicle, L-NAME, or L-arginine for 4 weeks. Systolic blood pressure and renal function was measured, and tissues were collected at 8 weeks for histological and molecular analyses. The effect of modulation of NO on vascular endothelial growth factor (VEGF) expression in rat aortic vascular smooth muscle cells (SMC) and mouse medullary thick ascending limb tubular epithelial cells (mTAL) was also studied. Inhibition of NO with L-NAME was associated with more rapid progression compared to RK alone, with worse blood pressure, proteinuria, renal function, glomerulosclerosis, and tubulointerstitial fibrosis. The injury was also associated with more glomerular and peritubular capillary endothelial cell loss in association with an impaired endothelial proliferative response. Interestingly, the preglomerular endothelium remained intact or was occasionally hyperplastic, and this was associated with a pronounced proliferation of the vascular SMCs with de novo expression of VEGF. Cell culture studies confirmed a divergent effect of NO inhibition on VEGF expression, with inhibition of VEGF synthesis in mTAL cells and stimulation of VEGF in vascular SMC. In contrast to the effects of NO inhibition, stimulation of NO with L-arginine had minimal effects in this rat model of progressive renal disease. These studies confirm that blockade of NO synthesis accelerates progression of renal disease in the remnant kidney model, and support the hypothesis that one of the pathogenic mechanisms may involve accelerated capillary loss and impaired angiogenesis of the renal microvasculature. Interestingly, inhibition of NO synthesis did not lead to a loss of the preglomerular endothelium, which may relate to the effect of NO blockade to stimulate VEGF synthesis in the adjacent vascular smooth muscle cell.     

Lack of correlation between mast cell response and active anaphylaxis in mice

Mast cell-competent mice, sensitized to lysozyme, were examined for their mast cell and anaphylactic responses to determine whether anaphylactic shock could occur independent of mast cell participation. Tissues (cremaster muscle, subdermal connective tissue and mesentery), taken a short time after intravenous antigenic challenge, showed no evidence of mast cell degranulation above control tissues. Data obtained from a quantitative comparison of the onset and increase in local and systemic anaphylactic and mast cell sensitivities to the antigen provide strong support for the view that mast cells are not the major effector cells for systemic anaphylaxis in mice. The significant increase in blood pressure that occurred immediately after infusion with the antigen also indicates that other cells within the blood stream are involved.     

Nitric oxide differentially modulates ON and OFF responses of retinal ganglion cells

Several lines of evidence suggest that nitric oxide (NO) can regulate diverse retinal functions, but whether this gas is capable of modulating the visual responses of retinal output neurons has not been established. In the present study the effects of NO on rod-driven responses of retinal ganglion cells were tested by making whole cell patch-clamp recordings from morphologically identified ganglion cells in the isolated ferret retina. Bath application of L-arginine, the substrate of nitric oxide synthase, and S-nitroso-N-acetylpenicillamine, the NO donor, was found to differentially affect on and off discharge patterns. The introduction of these drugs significantly decreased visual responses of retinal ganglion cells, but the effects were more pronounced on off than on on discharges. The peak discharge rates of on responses were usually reduced by about 40%, but not completely blocked. In contrast, off responses were completely blocked in most cells. These differential effects were observed in on-off cells as well as in cells that yielded just on or off discharges. The off responses that were blocked by NO were also blocked by DL-2-amino-phosphonobutyric acid (APB) and strychnine, suggesting the involvement of the APB-sensitive rod pathway.     

Auranofin modulates mast cell histamine and polymorphonuclear leukocyte collagenase release

Auranofin, an orally gold preparation, effective in the treatment of rheumatoid arthritis, was found to be a potent noncytotoxic inhibitor of histamine and collagenase release from mast cells and polymorphonuclear (PMN) leukocytes respectively.Histamine release has been inhibited by auranofin in dose-dependent fashion. Auranofin at concentration of 10^–5 M inhibited 100% of the release, lower concentration 10^–6 M and 10^–7 M produced 80 and 40% decrease.The exposure of PMN-leukocytes to auranofin caused also dose-dependent inhibition of collagenase release. Auranofin at a concentration of 10^–4 M produced a marked reduction (75–100%) of enzyme release from human and rat blood PMN-leukocytes. The modest inhibition 40 and 15–20% at a concentration of 10^–5 M and 10^–6 M respectively was obtained. Auranofin more significantly suppressed collagenase release from leukocytes isolated from inflammatory exudate. Decrease of 100, 80 and 60% were observed upon addition of 10^–4 M, 10^–5 M and 10^–6 M of auranofin.These results suggest that therapeutic action of auranofin may be caused, at least in part, by the inhibition of cellular release of histamine and collagenase in the course of inflammation.