Different mechanisms underlie the effects of acute and long-term inhibition of nitric oxide synthases in antigen-induced pulmonary eosinophil recruitment in BALB/C mice

Effects of nitric oxide inhibitors in mice with bladder outlet obstruction

PURPOSE

To investigate the lower urinary tract changes in mice treated with L-NAME, a non-selective competitive inhibitor of nitric oxide synthase (NOS), or aminoguanidine, a competitive inhibitor of inducible nitric oxide synthase (iNOS), after 5 weeks of partial bladder outlet obstruction (BOO), in order to evaluate the role of constitutive and non-constitutive NOS in the pathogenesis of this experimental condition.

MATERIALS AND METHODS

C57BL6 male mice were partially obstructed and randomly allocated into 6 groups: Sham, Sham + L-NAME, Sham + aminoguanidine, BOO, BOO + L-NAME and BOO + aminoguanidine. After 5 weeks, bladder weight was obtained and cystometry and tissue bath contractile studies were performed.

RESULTS

BOO animals showed increase of non-voiding contractions (NVC) and bladder capacity, and also less contractile response to Carbachol and Electric Field Stimulation. Inhibition of NOS isoforms improved bladder capacity and compliance in BOO animals. L-NAME caused more NVC, prevented bladder weight gain and leaded to augmented contractile responses at muscarinic and electric stimulation. Aminoguanidine diminished NVC, but did not avoid bladder weight gain in BOO animals and did not improve contractile responses.

CONCLUSION

It can be hypothesized that chronic inhibition of three NOS isoforms in BOO animals leaded to worsening of bladder function, while selective inhibition of iNOS did not improve responses, what suggests that, in BOO animals, alterations are related to constitutive NOS.

Downregulation of L-arginine metabolism in dendritic cells induces tolerance to exogenous antigen

Dendritic cells (DC) are potential tools for therapeutic applications and several strategies to generate tolerogenic DCs are under investigation. When activated by cytokines and microbial products, DCs express mediators that modulate immune responses. In this regard, the metabolites generated by the activities of inducible nitric oxide synthase (iNOS) and arginase in DCs seem to play important roles. Here, we evaluated the effects of adoptive transfer of DCs generated in vitro from bone marrow precursors (BMDC) modulated with L-NAME (Nω-nitro-L-arginine methyl ester) and NOHA (NG-Hydroxy-L-arginine), inhibitors of iNOS and arginase, respectively, upon the immune response of the wild type (BALB/c) and OVA-TCR transgenic (DO11.10) mice. The modulation with L-NAME increased CD86 expression in BMDC, whereas treatment with NOHA increased both CD80 and CD86 expression. Adoptive transfer of either L-NAME- or NOHA-modulated BMDCs to BALB/c mice reduced the plasma levels of ovalbumin-specific antibody as well as proliferation and cytokine secretion in cultures of spleen cells in comparison adoptive transfer of non-modulated DCs. Conversely, transfer of both modulated and non-modulated BMDCs had no effect on immune response of DO11.10 mice. Together, these results show that the treatment with iNOS and Arg inhibitors leads to increased expression of co-stimulatory molecules in DCs, and provides evidences that L-arginine metabolism may be an important therapeutic target for modulating immune responses in inflammatory disorders.

Metformin attenuates the exacerbation of the allergic eosinophilic inflammation in high fat-diet-induced obesity in mice

A positive relationship between obesity and asthma has been well documented. The AMP-activated protein kinase (AMPK) activator metformin reverses obesity-associated insulin resistance (IR) and inhibits different types of inflammatory responses. This study aimed to evaluate the effects of metformin on the exacerbation of allergic eosinophilic inflammation in obese mice. Male C57BL6/J mice were fed for 10 weeks with high-fat diet (HFD) to induce obesity. The cell infiltration and inflammatory markers in bronchoalveolar lavage (BAL) fluid and lung tissue were evaluated at 48 h after ovalbumin (OVA) challenge. HFD obese mice displayed peripheral IR that was fully reversed by metformin (300 mg/kg/day, two weeks). OVA-challenge resulted in higher influx of total cell and eosinophils in lung tissue of obese mice compared with lean group. As opposed, the cell number in BAL fluid of obese mice was reduced compared with lean group. Metformin significantly reduced the tissue eosinophil infiltration and prevented the reduction of cell counts in BAL fluid. In obese mice, greater levels of eotaxin, TNF-α and NOx, together with increased iNOS protein expression were observed, all of which were normalized by metformin. In addition, metformin nearly abrogated the binding of NF-κB subunit p65 to the iNOS promoter gene in lung tissue of obese mice. Lower levels of phosphorylated AMPK and its downstream target acetyl CoA carboxylase (ACC) were found in lung tissue of obese mice, which were restored by metformin. In separate experiments, the selective iNOS inhibitor aminoguanidine (20 mg/kg, 3 weeks) and the anti-TNF-α mAb (2 mg/kg) significantly attenuated the aggravation of eosinophilic inflammation in obese mice. In conclusion, metformin inhibits the TNF-α-induced inflammatory signaling and NF-κB-mediated iNOS expression in lung tissue of obese mice. Metformin may be a good pharmacological strategy to control the asthma exacerbation in obese individuals.

Grape skin extract reduced pulmonary oxidative response in mice exposed to cigarette smoke

BACKGROUND

Oxidative stress has been implicated in the pathogenesis and progression of chronic obstructive pulmonary disease (COPD), and cigarette smoke (CS) is known to be one of the major sources of oxidants in the lungs. We postulated that acute administration of GSE (grape skin extract) would either reduce or protect the ALI (acute lung inflammation) produced by CS via NO release.

MATERIAL/METHODS

We adopted a nutritional approach by investigating the inflammatory cells, metalloproteinase 9 (MMP-9) activity, and oxidative stress markers (superoxide dismutase - SOD; catalase - CAT; glutathione peroxidase (GPx) activities and malondialdehyde - MDA - levels) that play a role in the development of acute lung inflammation (ALI). Therefore, we tested an orally active antioxidant produced from grape skin manipulation (grape skin extract - GSE), in mice exposed to CS from 6 cigarettes a day for 5 days. In addition, we used a separate group treated with NG-nitro-L-arginine methyl ester (an NO inhibitor) to confirm nitric oxide (NO) involvement in GSE effects.

RESULTS

We showed for the first time that administration of GSE inhibited ALI and oxidative damage induced by CS. This is associated with decreased MMP-9 activity, decreased number of inflammatory cells in the bronchoalveolar lavage fluid, and reduced levels of lipid peroxidation. Our results indicate that beneficial effects of GSE are NO-dependent.

CONCLUSIONS

The study indicates that alteration of the oxidant-antioxidant balance is important in the pathogenesis of CS-induced ALI and suggests lung protective effects of GSE treatment in the mouse.

Nitric oxide in both bronchoalveolar lavage fluid and serum is associated with pathogenesis and severity of antigen-induced pulmonary inflammation in rats

BACKGROUND

Nitric oxide (NO) is considered as a hallmark for allergic airway inflammation in asthmatics and animal models. But the correlation between NO and antigen-induced pulmonary inflammation (AIPI), a rat model for asthma, in varying genetic background population has not been completely understood.

OBJECTIVE

The objective in this study is to observe the different responsiveness to AIPI in two commonly used inbred rat strains and verify the correlation between NO from different sources and pathological parameters of AIPI by using Dark Agouti (DA), E3, F1 (E3 x DA), and F2 rat populations.

METHODS

AIPI was induced by systemically immunizing and intranasally challenging E3, DA, F1 (DA x E3), and F2 rats with ovalbumin (OVA). Pathological changes and mucus secretion in lungs were observed after hematoxylin and eosin (HE) and periodic acid Schiff (PAS) staining, whereas eosinophils in bronchoalveolar lavage fluid (BALF) were counted after Giemsa staining. Delayed-type hyperresponsiveness was determined by subcutaneous injection of OVA in ear. Total immunoglobulin E (IgE) and OVA-specific IgG1 were detected with enzyme-linked immunosorbent assay (ELISA). NO concentration was measured by the Griess method.

RESULTS

DA rats were unresponsive to OVA treatment, whereas E3 rats were susceptible to AIPI. F1 rats manifested the same responsiveness to OVA treatment as DA rats, and individual F2 rats showed the variable severity of AIPI. NO concentration in BALF and serum was significantly elevated in E3 rats but not in DA and F1 rats after OVA treatment. In F2 rats, NO concentration in serum was positively correlated with eosinophils in BALF, total IgE, and pathological scores, whereas NO concentration in BALF correlated only with eosinophils in BALF and total IgE.

CONCLUSION

DA and F1 rats are resistant, whereas E3 rats are sensitive, to AIPI. NO in serum can represent the severity of allergic inflammation and pathological changes in lungs in F2 population.