A specific method for measurement of nitric oxide synthase enzymatic activity in peritoneal biopsies

The pathophysiology of Post SSRI Sexual Dysfunction - Lessons from a case study

BACKGROUND

Although Post-SSRI Sexual Dysfunction (PSSD) has finally been recognized by the European Medicines Agency as a medical condition that can outlast discontinuation of SSRI and SNRI antidepressants, this condition is still largely unknown by patients, doctors, and researchers, and hence, poorly understood, underdiagnosed, and undertreated.

OBJECTIVE

Becoming familiar with the symptomatology of PSSD and understanding the underlying mechanisms and treatment options.

METHOD

We applied a design thinking approach to innovation to 1) provide insights into the medical condition as well as the personal needs and pains of a targeted patient; and 2) generate ideas for new solutions from the perspective of this particular patient. These insights and ideas informed a literature search on the potential pathophysiological mechanisms that could underlie the patient's symptoms.

RESULTS

The 55-year-old male patient developed symptoms of low libido, delayed ejaculation, erectile dysfunction, 'brain zaps', overactive bladder and urinary inconsistency after discontinuation of the SNRI venlafaxine. In many of these symptoms a dysregulation in serotonergic activity has been implicated, with an important role of 5-HT_1A receptor downregulation and possible downstream effects on neurosteroid and oxytocin systems.

CONCLUSIONS

The clinical presentation and development of symptoms are suggestive of PSSD but need further clinical elaboration. Further knowledge of post-treatment changes in serotonergic - and possibly noradrenergic - mechanisms is required to improve our understanding of the clinical complaints and to inform appropriate treatment regimes.

Ameliorate impacts of scopoletin against vancomycin-induced intoxication in rat model through modulation of Keap1-Nrf2/HO-1 and IκBα-P65 NF-κB/P38 MAPK signaling pathways: Molecular study, molecular docking evidence and network pharmacology analysis

Nephrotoxicity is an indication for the damage of kidney-specific detoxification and excretion mechanisms by exogenous or endogenous toxicants. Exposure to vancomycin predominantly results in renal damage and losing the control of body homeostasis. Vancomycin-treated rats (200 mg/kg/once daily, for seven consecutive days, i.p.) revealed significant increase in serum pivotal kidney function, oxidative stress, and inflammatory biomarkers. Histologically, vancomycin showed diffuse acute tubular necrosis, denudation of epithelium and infiltration of inflammatory cells in the lining tubular epithelium in cortical portion. In the existing study, the conservative consequences of scopoletin against vancomycin nephrotoxicity was investigated centering on its capacity to alleviate oxidative strain and inflammation through streamlining nuclear factor (erythroid-derived-2) like 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling and prohibiting the nuclear factor kappa B (NF-κB)/mitogen-activated protein kinase (p38 MAPK) pathway. With respect to vancomycin group, scopoletin pretreatment (50 mg/kg/once daily, i.p.) efficiently reduced kidney function, oxidative stress biomarkers and inflammatory mediators. Moreover, histological and immunohistochemical examination of scopoletin-treated group showed remarkable improvement in histological structure and reduced vancomycin-induced renal expression of iNOS, NF-κB and p38 MAPK. In addition, scopoletin downregulated (Kelch Like ECH Associated Protein1) Keap1, P38MAPK and NF-κB expression levels while upregulated renal expression levels of regulatory protein (IκBα), Nrf2 and HO-1. Furthermore, molecular docking and network approach were constructed to study the prospect interaction between scopoletin and the targeted proteins that streamline oxidative stress and inflammatory pathways. The present investigations elucidated that scopoletin co-treatment with vancomycin may be a rational curative protocol for mitigation of vancomycin-induced renal intoxication.

Using diaminofluoresceins (DAFs) in nitric oxide research

Diaminofluoresceins (DAFs) are fluorescent probes widely applied to measure nitric oxide (NO) formation in cells and tissues. The main advantages of these compounds are their availability and low cost, and the general availability of instruments able to detect green fluorescence in all laboratories; these include fluorimeters, flow cytometers, and fluorescent microscopes. What made these molecules particularly interesting for many scientists approaching the NO field is that they are apparently very easy to use, as compared with other techniques requiring specific instrumentation and knowledge like chemiluminescence and electron paramagnetic resonance. However, the reactivity and biological chemistry of these probes in the cellular environment is rather complex and still not fully understood. Moreover, secondary reactions with ascorbate, or interference with thiols occur in cells. Therefore, the use of DAFs requires specific experimental planning and a careful interpretation of the results obtained. In this methodological review, we described in detail what is known about the reactivity of DAFs, their application in biological assays, list some principles to help experimental planning, including the necessary controls, and list the caveats concerning result interpretation. These guiding principles will help to understand the "Method behind our DAF-madness".

Amino Acid-Based Peritoneal Dialysis Solution Stimulates Mesothelial Nitric Oxide Production

Objective

Ultrafiltration failure is a common problem in continuous ambulatory peritoneal dialysis. Recent work has indicated a role of enhanced expression of nitric oxide synthase (NOS) in ultrafiltration failure. However, the conditions predisposing to increased generation of NO by the peritoneum have not been studied in detail and the cell types potentially involved have not been tested individually.

Design

We performed experiments in human peritoneal mesothelial cells (HPMC) in culture. Amino acid-based dialysis solution (Nutrineal; Baxter Deutschland GmbH, München, Germany), L-arginine, and glucose-containing control solutions were used and we observed the effects on the HPMC. We reasoned that amino acid-based dialysis solutions containing L-arginine, the substrate of NOS, might influence mesothelial NO generation. Nitric oxide production was measured in the supernatant using the Griess reaction. We studied the effect of the combined NOS inhibitor L-NMMA and specified the isoform of NOS involved.

Results

In serum-free control medium, the cells exhibited baseline generation of nitrite at a rate of 5.4 ± 0.5 μmol/g protein. Addition of 6 mmol/L L-arginine to the control medium increased nitrite significantly (11.8 ± 0.66 μmol/g protein, p < 0.002), as did amino acid-based dialysis solution (15.7 ± 1.3 μmol/g protein, p < 0.002); L-NMMA caused a significant reduction of this nitrite. HPMC expressed eNOS (NOSIII) when grown in L-arginine-supplemented medium, shown by immunocytochemistry and by reverse transcriptase-polymer chain reaction. Biochemical exposure to a calcium ionophore in 1 μmol/L concentration approximately doubled the nitrite production by L-arginine-incubated cells.

Conclusion

Peritoneal mesothelial cells generate NO in vitro. Generation of NO increased further in response to L-arginine supplementation of the culture medium and to amino acid-containing dialysis solution. Mesothelial cells express eNOS, which was likely involved in the observed peritoneal NO generation.

Transgenic Mouse Models

The development of peritoneal dialysis has been paralleled by a growing interest in establishing suitable experimental models to better understand the functional and structural processes operating in the peritoneal membrane. Thus far, most investigations have been performed in rat and rabbit models, with mechanistic insights essentially based on intervention studies using pharmacological agents, blocking antibodies, or transient expression systems. Since the body size of a species is no longer a limiting factor in the performance of in vivo studies related to peritoneal dialysis, it has been considered that mice, particularly once they have been genetically modified, could provide an attractive tool to investigate the molecular mechanisms operating in the peritoneal membrane. The purpose of this review is to illustrate how investigators in peritoneal dialysis research, catching up with other fields of biomedical research, are increasingly taking advantage of mouse models to provide direct evidence of basic mechanisms involved in the major complications of peritoneal dialysis.

Аrginase/NO-synthase system сharacteristics in blood lymphocytes under effect of fluoroquinolones

Antibiotics of the fluoroquinolone series are highly effective synthetic drugs of a wide range of antimicrobial activity. They have a specific mechanism of action on bacterial cells to inhibit the DNA-gyrase enzyme of mostly gram-negative and the topoisomerase IV of gram-positive bacterial cells, which leads to a decrease in the activity of enzymes, disruption of DNA and RNA biosyntheses, and the impossibility of chromosome superspilarization, as a result of which its division is broken and the cell dies. Fluoroquinolones also have an immunomodulatory effect, which is very important in terms of the pathogenesis of many infectious and inflammatory diseases. We assume that fluoroquinolones also act on cells of the body of patients, in particular on such regulatory mechanisms as the arginase-NO-synthase system. In this regard, peripheral blood lymphocytes can be a convenient and adequate model for studying the mechanism of the effect of fluoroquinolones. It is shown that under the influence of various generations of fluoroquinolones, arginase activity increases, depending on the dose, in the following sequence: control → ciprofloxacin → levofloxacin → moxifloxacin. The highest activity is observed under the effects of moxifloxacin, belonging to generation IV. The increase in arginase activity in blood lymphocytes under the influence of fluoroquinolones occurs due to the growth of turnover number of the enzymes (Vmax increases), although the affinity of enzyme to the substrate decreases (KL-arg increases). At the same time, all fluoroquinolones reduce the activity of the constitutive isoforms of NO-synthase, depending on the dose. It has been established that a slight activity of iNOS of blood lymphocytes in practically healthy women was detected, almost on the verge of error. When studying the influence of fluoroquinolones on the activation of iNOS lymphocytes isolated from the blood of practically healthy women, we did not observe its activity, and the inhibitive effect could not be determined due to its low activity. Oxidative stress was used to induce iNOS activity in blood lymphocytes, with H2O2 lymphocytes preincubation. The preincubation of lymphocytes with 0.2 mM H2O2 leads to increase of iNOS activity by 31.30 times. By activation of iNOS with hydrogen peroxide, 10–5 M concentration of ciprofloxin leads to inhibition of enzyme activity by 1.22 times, levofloxacin by 1.45 and moxifloxacin by 2.34 times. The obtained kinetic parameters suggest that in the blood lymphocytes under the influence of fluoroquinolones, the synthesis of NO with the participation of cNOS is inhibited, and the hyperproduction of NO is inhibited by the activation of iNOS, which is characteristic for pathological conditions.

Development of novel FP-based probes for live-cell imaging of nitric oxide dynamics

Nitric oxide () is a free radical with a wide range of biological effects, but practically impossible to visualize in single cells. Here we report the development of novel multicoloured fluorescent quenching-based probes by fusing a bacteria-derived -binding domain close to distinct fluorescent protein variants. These genetically encoded probes, referred to as geNOps, provide a selective, specific and real-time read-out of cellular dynamics and, hence, open a new era of bioimaging. The combination of geNOps with a Ca(2+) sensor allowed us to visualize and Ca(2+) signals simultaneously in single endothelial cells. Moreover, targeting of the probes was used to detect signals within mitochondria. The geNOps are useful new tools to further investigate and understand the complex patterns of signalling on the single (sub)cellular level.

Analysis of the Expression and Activity of Nitric Oxide Synthase from Marine Photosynthetic Microorganisms

Nitric oxide (NO) functions as a signaling molecule in many biological processes in species belonging to all kingdoms of life. In animal cells, NO is synthesized primarily by NO synthase (NOS), an enzyme that catalyze the NADPH-dependent oxidation of L-arginine to NO and L-citrulline. Three NOS isoforms have been identified, the constitutive neuronal NOS (nNOS) and endothelial NOS (eNOS) and one inducible (iNOS). Plant NO synthesis is complex and is a matter of ongoing investigation and debate. Despite evidence of an Arg-dependent pathway for NO synthesis in plants, no plant NOS homologs to animal forms have been identified to date. In plants, there is also evidence for a nitrate-dependent mechanism of NO synthesis, catalyzed by cytosolic nitrate reductase. The existence of a NOS enzyme in the plant kingdom, from the tiny single-celled green alga Ostreococcus tauri was reported in 2010. O. tauri shares a common ancestor with higher plants and is considered to be part of an early diverging class within the green plant lineage.In this chapter we describe detailed protocols to study the expression and characterization of the enzymatic activity of NOS from O. tauri. The most used methods for the characterization of a canonical NOS are the analysis of spectral properties of the oxyferrous complex in the heme domain, the oxyhemoglobin (oxyHb) and citrulline assays and the NADPH oxidation for in vitro analysis of its activity or the use of fluorescent probes and Griess assay for in vivo NO determination. We further discuss the advantages and drawbacks of each method. Finally, we remark factors associated to the measurement of NOS activity in photosynthetic organisms that can generate misunderstandings in the interpretation of results.

The impact of human and mouse differences in NOS2 gene expression on the brain's redox and immune environment

BACKGROUND

Mouse models are used in the study of human disease. Despite well-known homologies, the difference in immune response between mice and humans impacts the application of data derived from mice to human disease outcomes. Nitric oxide synthase-2 (NOS2) is a key gene that displays species-specific outcomes via altered regulation of the gene promoter and via post-transcriptional mechanisms in humans that are not found in mice. The resulting levels of NO produced by activation of human NOS2 are different from the levels of NO produced by mouse Nos2. Since both tissue redox environment and immune responsiveness are regulated by the level of NO and its interactions, we investigated the significance of mouse and human differences on brain oxidative stress and on immune activation in HuNOS2tg/mNos2-/- mice that express the entire human NOS2 gene and that lack a functional mNos2 compared to wild type (WT) mice that express normal mNos2.

METHODS/RESULTS

Similarly to human, brain tissue from HuNOS2tg/mNos2-/- mice showed the presence of a NOS2 gene 3'UTR binding site. We also identified miRNA-939, the binding partner for this site, in mouse brain lysates and further demonstrated reduced levels of nitric oxide (NO) typical of the human immune response on injection with lipopolysaccharide (LPS). HuNOS2tg/mNos2-/- brain samples were probed for characteristic differences in redox and immune gene profiles compared to WT mice using gene arrays. Selected genes were also compared against mNos2-/- brain lysates. Reconstitution of the human NOS2 gene significantly altered genes that encode multiple anti-oxidant proteins, oxidases, DNA repair, mitochondrial proteins and redox regulated immune proteins. Expression levels of typical pro-inflammatory, anti-inflammatory and chemokine genes were not significantly different with the exception of increased TNFα and Ccr1 mRNA expression in the HuNOS2tg/mNos2-/- mice compared to WT or mNos2-/- mice.

CONCLUSIONS

NO is a principle factor in establishing the tissue redox environment and changes in NO levels impact oxidative stress and immunity, both of which are primary characteristics of neurodegenerative diseases. The HuNOS2tg/mNos2-/- mice provide a potentially useful mechanism to address critical species- specific immune differences that can impact the study of human diseases.

Aquaporin-1 in the peritoneal membrane: implications for peritoneal dialysis and endothelial cell function

PD (peritoneal dialysis) is an established mode of renal replacement therapy, based on the exchange of fluid and solutes between blood in peritoneal capillaries and a dialysate that has been introduced into the peritoneal cavity. The dialysis process involves diffusive and convective transports and osmosis through the PM (peritoneal membrane). Computer simulations predicted that the PM contains ultrasmall pores (radius <3 A, 1 A=10(-10) m), responsible for up to 50% of UF (ultrafiltration), i.e. the osmotically driven water movement during PD. Several lines of evidence suggest that AQP1 (aquaporin-1) is the ultrasmall pore responsible for transcellular water permeability during PD. Treatment with corticosteroids induces the expression of AQP1 in the PM and improves water permeability and UF in rats without affecting the osmotic gradient and permeability for small solutes. Studies in knockout mice provided further evidence that osmotically driven water transport across the PM is mediated by AQP1. AQP1 and eNOS (endothelial nitric oxide synthase) show a distinct regulation within the endothelium lining the peritoneal capillaries. In acute peritonitis, the up-regulation of eNOS and increased release of nitric oxide dissipate the osmotic gradient and prevent UF, whereas AQP1 expression is unchanged. These results illustrate the usefulness of the PM to investigate the role and regulation of AQP1 in the endothelium. The results also emphasize the critical role of AQP1 during PD and suggest that manipulation of AQP1 expression may be used to increase water permeability across the PM.

Nitric oxide synthase isoforms play distinct roles during acute peritonitis

Background. Acute peritonitis is the most frequent complication of peritoneal dialysis (PD). Increased nitric oxide (NO) release by NO synthase (NOS) isoforms has been implicated in acute peritonitis, but the role played by the NOS isoforms expressed in the peritoneum is unknown.

Methods. We investigated the structural and functional consequences of acute peritonitis induced by LPS in wild-type (WT) mice versus knockout mice (KO) for the endothelial NOS (eNOS), the inducible NOS (iNOS) or the neuronal NOS (nNOS).

Results. The level of NO metabolites (NOx) in the dialysate was maximal 18 h after LPS injection. LPS induced a significant increase in the transport of small solutes and decreased ultrafiltration in WT mice. These changes, which occurred without vascular proliferation, were paralleled by the upregulation of nNOS and eNOS, and the induction of iNOS. The transport modifications induced by LPS were significantly reversed in eNOS KO mice, but not modified in mice lacking iNOS or nNOS. In contrast, the increase of dialysate NOx was abolished in iNOS KO mice and significantly reduced in eNOS KO mice, but left unchanged in mice lacking nNOS. Mice lacking iNOS also showed more severe inflammatory changes, and a trend towards increased mortality following LPS.

Conclusion. These data demonstrate specific roles for NOS isoforms in the peritoneal membrane and suggest that selective eNOS inhibition may improve peritoneal transport during acute peritonitis.

Protective effects of EPA and deleterious effects of DHA on eNOS activity in Ea hy 926 cultured with lysophosphatidylcholine

Oxidized low density lipoprotein (Ox-LDL) is a well-established risk factor in atherosclerosis and lysophosphatidylcholine (LysoPtdCho) is considered to be one of the major atherogenic component of Ox-LDL. The purpose of this work was to investigate the effects of two membrane n-3 long chain polyunsaturated fatty acids (n-3 PUFAs), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) compared to n-6 PUFA, ARA (arachidonic acid), on the activation of endothelial NO synthase (eNOS) by histamine in Ea hy 926 endothelial cells incubated during 24 h in the presence or the absence of LysoPtdCho. DHA (50 muM) produced a ROS induction in cells and aggravated the LysoPtdCho-induced oxidative stress. It did not modify the basal eNOS activity but impaired the stimulation of eNOS induced by histamine and was unable to correct the deleterious effect of LysoPtdCho on histamine-stimulated eNOS activity or phosphorylation of Ser 1177. In contrast, EPA (90 muM) did not modify the ROS level produced in the presence or absence of LysoPtdCho or basal eNOS activity and the stimulating effect of histamine on eNOS. However, it diminished the deleterious effect of LysoPtdCho as well as on the histamine-stimulated eNOS activity on the phosphorylation on Ser 1177 of eNOS. The beneficial effect of EPA but not DHA on endothelial eNOS activity in Ea hy 926 could be also partially due to a slight decrease in membrane DHA content in EPA-treated cells. Consequently, the equilibrium between NO generated by eNOS and ROS due to oxidative stress could explain, in part, the beneficial effect of EPA on the development of cardiovascular diseases. By contrast ARA an n-6 PUFA was devoid of any effect on ROS generation or eNOS activity in the basal state or after histamine-induced stimulation. In vivo experiments should be undertaken to confirm these results.

Clinical application of aquaporin research: aquaporin-1 in the peritoneal membrane

Peritoneal dialysis (PD) is an established mode of renal replacement therapy based on the exchange of fluid and solutes between blood and a dialysate that has been instilled in the peritoneal cavity. The dialysis process involves osmosis, as well as diffusive and convective transports through the highly vascularized peritoneal membrane. Computer simulations predicted that the membrane contains ultrasmall pores responsible for the selective transport of water across the capillary endothelium during crystalloid osmosis. The distribution of the water channel aquaporin-1 (AQP1), as well as its molecular structure ensuring an exquisite selectivity for water, fit with the characteristics of the ultrasmall pore. Peritoneal transport studies using AQP1 knockout mice demonstrated that the osmotic water flux across the peritoneal membrane is mediated by AQP1. This water transport accounts for 50% of the ultrafiltration during PD. Treatment with high-dose corticosteroids upregulates the expression of AQP1 in peritoneal capillaries, resulting in increased water transport and ultrafiltration in rats. AQP1 may also play a role during inflammation, as vascular proliferation and leukocyte recruitment are both decreased in mice lacking AQP1. These data illustrate the potential of the peritoneal membrane as an experimental model in the investigation of the role of AQP1 in the endothelium at baseline and during inflammation. They emphasize the critical role of AQP1 during PD and suggest that manipulating AQP1 expression could be clinically useful in PD patients.

Aquaporin-1 in the peritoneal membrane: Implications for water transport across capillaries and peritoneal dialysis

Peritoneal dialysis (PD) is an established mode of renal replacement therapy, based on the exchange of fluid and solutes between blood in peritoneal capillaries and a dialysate that has been introduced in the peritoneal cavity. The dialysis involves diffusive and convective transports and osmosis through the highly vascularized peritoneal membrane. Computer simulations predicted that the membrane contains ultrasmall pores (radius < 3 A) responsible for the transport of solute-free water across the capillary endothelium during crystalloid osmosis. The distribution of the water channel aquaporin-1 (AQP1), as well as its molecular structure ensuring an exquisite selectivity for water perfectly fit with the characteristics of the ultrasmall pore. Treatment with corticosteroids induces the expression of AQP1 in peritoneal capillaries and increases water permeability and ultrafiltration in rats, without affecting the osmotic gradient and the permeability for small solutes. Studies in knockout mice provided further evidence that osmotically-driven water transport across the peritoneal membrane is mediated by AQP1. AQP1 and endothelial NO synthase (eNOS) show a distinct regulation within the endothelium lining peritoneal capillaries. In acute peritonitis, the upregulation of eNOS and increased release of NO dissipate the osmotic gradient and result in ultrafiltration failure, despite the unchanged expression of AQP1. These data illustrate the potential of the peritoneal membrane to investigate the role and regulation of AQP1 in the endothelium. They also emphasize the critical role of AQP1 during peritoneal dialysis and suggest that manipulating AQP1 expression may be used to increase water permeability across the peritoneal membrane.

Genetic and clinical factors influence the baseline permeability of the peritoneal membrane

BACKGROUND

Patients starting peritoneal dialysis (PD) show a significant variability in small solute transport across the peritoneal membrane (PM). The latter parameter determines dialysis prescription and survival. Clinical factors probably influence solute transport across the PM, but the putative role of genetic variants is unknown.

METHODS

We have investigated the influence of functional polymorphisms of VEGF, ENOS, and IL-6, together with clinical and biological factors, on baseline peritoneal equilibration test (PET) parameters in a homogeneous population of 152 unrelated Caucasian PD patients from Belgium and the North of France.

RESULTS

The distribution of the 21 alleles (7 polymorphisms) and linkage disequilibrium parameters were similar in PD patients and healthy subjects. Univariate and multivariate analyses identified comorbidity, serum albumin, and the -174G/C polymorphism of IL-6 as independent predictors of small solute transport. The -174G/C polymorphism of IL-6 was associated with significantly higher IL-6 mRNA levels in the PM and higher plasma and dialysate IL-6 concentrations, suggesting a dominant effect of the C allele. Patients harboring the CC and GC genotypes (N= 92) were characterized by significantly higher permeability parameters and inflammatory markers than patients harboring the GG genotype (N= 60). In contrast with IL-6, VEGF and ENOS polymorphisms had no influence on baseline peritoneal permeability.

CONCLUSION

These data (1) show that, together with clinical parameters, the functionally relevant -174G/C polymorphism of IL-6 contributes to the interpatient variability in small solute transport rate at the start of PD; and (2) substantiate the critical role played by IL-6 in the PM.

Zymosan induces nitric oxide production by peritoneal mesothelial cells

INTRODUCTION

The production of nitric oxide is an important peritoneal defense mechanism. We have evaluated the effect of various putative stimulants on nitric oxide production by peritoneal mesothelial cells.

METHODS

Wistar rats were randomized to either a control group or a peritonitis group (5 mg zymosan intraperitoneally). Groups of five animals were sacrificed at 4, 18, 24, 48 and 96 h after the induction of peritonitis and their peritoneal fluid was harvested for assay. Cultures of peritoneal mesothelial cells were stimulated with lipopolysaccharide, myeloperoxidase, TNFalpha, zymosan, peritoneal fluid from a control animal and peritoneal fluid from a peritonitis animal. Supernatants were collected after incubation for 4, 24 and 48 h for assay. The assay for nitric oxide was based upon the nitrite content of the samples.

RESULTS

The intraperitoneal administration of zymosan was associated with an increased production of nitric oxide (NO) when compared with control animals (P < 0.01). In cultures of peritoneal mesothelial cells, zymosan, but not the other putative stimulants, was associated with a marked output of nitric oxide (P < 0.001).

CONCLUSION

Zymosan has a direct effect on peritoneal mesothelial cells, which are able to generate nitric oxide in the absence of co-stimulatory molecules. This suggests that it may be possible to use some form of external stimulation to up-regulate the NO response by peritoneal mesothelial cells.

Mice that Lack Endothelial Nitric Oxide Synthase Are Protected against Functional and Structural Modifications Induced by Acute Peritonitis

ABSTRACT. Pharmacologic studies suggest that the release of nitric oxide (NO) by endothelial NO synthase (eNOS) contributes to functional alterations of the peritoneal membrane (PM) induced by acute peritonitis. In this study, peritoneal permeability parameters in a mouse model of peritoneal dialysis were characterized, and the effects of eNOS deletion on the PM structure and permeability at baseline and after catheter-induced bacterial peritonitis were examined. Exposure of C57BL/6 mice to standard dialysate yielded a transport of urea and glucose, a sodium sieving, and a net ultrafiltration that were remarkably similar to the values obtained in rats. In comparison with controls, mice with catheter-induced peritonitis were characterized by structural changes in the PM (mononuclear cells infiltrate, vascular proliferation), upregulation of endothelial and inducible NOS, increased permeability for urea and glucose, decreased ultrafiltration, and increased protein loss in the dialysate. Comparison of eNOS wild-type and knockout mice revealed that the permeability modifications and structural changes induced by acute peritonitis were significantly reversed in eNOS knockout mice, resulting in a net increase in ultrafiltration. In contrast, the deletion of eNOS in mouse peritoneum was not reflected by permeability modifications or structural changes at baseline. These results are the first to take advantage of a knockout mouse model to demonstrate directly the crucial importance of eNOS in the permeability and structural modifications caused by acute peritonitis. The characterization of this mouse model suggests that genetically modified mice represent useful tools to investigate the molecular bases of the peritoneal changes during peritoneal dialysis.

Experimental diabetes induces functional and structural changes in the peritoneum

BACKGROUND

Peritoneal dialysis (PD) is an established renal replacement therapy in diabetic patients, but the influence of diabetes on the peritoneal membrane (PM) remains debated. We have used functional, biochemical and molecular studies in vivo and in vitro to substantiate the changes induced by diabetes and hyperglycemia in the PM.

METHODS

Peritoneal equilibration tests were performed 2, 4, and 6 weeks after induction of diabetes with streptozotocin (STZ) in rats. Morphological analyses, determination of nitric oxide synthase (NOS) activities, and expression studies for NOS isoforms and advanced glycation end products (AGE) were performed in parallel. Additional studies were conducted in diabetic rats treated with insulin, non-diabetic rats fed with urea, and cultured bovine aortic endothelial cells (BAEC).

RESULTS

In comparison with controls, diabetic rats were characterized by: increased permeability for small solutes and decreased sodium sieving; capillary proliferation; increased endothelial NOS (eNOS) and AGE immunoreactivity; up-regulation of eNOS and down-regulation of neuronal NOS; and increased NOS activity in the PM. The changes, which culminated at week 6, were prevented by chronic insulin treatment in diabetic rats. In contrast to hyperglycemia, hyperosmolality alone did not induce functional or structural changes in the PM. Studies in BAEC showed that high glucose incubation led to increased activity and expression of eNOS, a prerequisite for vascular proliferation.

CONCLUSIONS

These data demonstrate that chronic hyperglycemia is associated with functional and structural changes in the peritoneum that parallel with selective regulation of NOS isoforms and AGE deposits. The alterations are prevented by insulin treatment, which suggests that adequate control of diabetes can preserve PM integrity in diabetic patients prior to PD.

Inhibition of nitric oxide synthase reverses changes in peritoneal permeability in a rat model of acute peritonitis

BACKGROUND

Acute peritonitis is the most frequent complication of peritoneal dialysis (PD), and nitric oxide (NO) is thought to play a role in the structural and permeability changes observed in this condition. We have used a combination of expression, enzymatic and pharmacological studies to substantiate the potential role(s) played by NO during peritonitis.

METHODS

The peritoneal equilibration test was performed in control rats and rats with acute peritonitis (originating from skin flora), using standard dialysate supplemented or not with the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). In parallel, peritoneal NOS enzymatic activities were measured and expression studies for NOS isoforms and S-nitrosocysteine reactivity performed in the peritoneum.

RESULTS

In comparison with controls, rats with acute peritonitis were characterized by inflammatory changes, increased S-nitrosocysteine immunoreactivity, and increased NOS activities in the peritoneum, due to the up-regulation of endothelial and inducible NOS. In parallel, rats with acute peritonitis showed increased permeability for small solutes; decreased sodium sieving; loss of ultrafiltration (UF); and increased protein loss in the dialysate. Addition of L-NAME to the dialysate did not induce permeability changes in control rats, but significantly improved UF and reversed permeability modifications in rats with peritonitis. The effect of L-NAME was reflected by a mild but consistent increase in blood pressure during PD exchange.

CONCLUSIONS

Our results demonstrate that local generation of NO, secondary to up-regulation of NOS isoforms, plays an important role in the regulation of peritoneal permeability during acute peritonitis in rats. By itself, NOS inhibition improves UF and reverses permeability changes, which might offer new therapeutic perspectives in acute peritonitis.

Chronic uremia induces permeability changes, increased nitric oxide synthase expression, and structural modifications in the peritoneum

Advanced glycation end products (AGE), growth factors, and nitric oxide contribute to alterations of the peritoneum during peritoneal dialysis (PD). These mediators are also involved in chronic uremia, a condition associated with increased permeability of serosal membranes. It is unknown whether chronic uremia per se modifies the peritoneum before PD initiation. A rat model of subtotal nephrectomy was used to measure peritoneal permeability after 3, 6, and 9 wk, in parallel with peritoneal nitric oxide synthase (NOS) isoform expression and activity and structural changes. Uremic rats were characterized by a higher peritoneal permeability for small solutes and an increased NOS activity due to the up-regulation of endothelial and neuronal NOS. The permeability changes and increased NOS activities correlated with the degree of renal failure. Focal areas of vascular proliferation and fibrosis were detected in uremic rats, in relation with a transient up-regulation of vascular endothelial growth factor and basic fibroblast growth factor, as well as vascular deposits of the AGE carboxymethyllysine and pentosidine. Correction of anemia with erythropoietin did not prevent the permeability or structural changes in uremic rats. Thus, in this rat model, uremia induces permeability and structural changes in the peritoneum, in parallel with AGE deposits and up-regulation of specific NOS isoforms and growth factors. These data suggest an independent contribution of uremia in the peritoneal changes during PD and offer a paradigm to better understand the modifications of serosal membranes in uremia.