Acute oxidative stress induces peritoneal hyperpermeability, mesothelial loss, and fibrosis

Melatonin decreases GSDME mediated mesothelial cell pyroptosis and prevents peritoneal fibrosis and ultrafiltration failure

Peritoneal fibrosis together with increased capillaries is the primary cause of peritoneal dialysis failure. Mesothelial cell loss is an initiating event for peritoneal fibrosis. We find that the elevated glucose concentrations in peritoneal dialysate drive mesothelial cell pyroptosis in a manner dependent on caspase-3 and Gasdermin E, driving downstream inflammatory responses, including the activation of macrophages. Moreover, pyroptosis is associated with elevated vascular endothelial growth factor A and C, two key factors in vascular angiogenesis and lymphatic vessel formation. GSDME deficiency mice are protected from high glucose induced peritoneal fibrosis and ultrafiltration failure. Application of melatonin abrogates mesothelial cell pyroptosis through a MT1R-mediated action, and successfully reduces peritoneal fibrosis and angiogenesis in an animal model while preserving dialysis efficacy. Mechanistically, melatonin treatment maintains mitochondrial integrity in mesothelial cells, meanwhile activating mTOR signaling through an increase in the glycolysis product dihydroxyacetone phosphate. These effects together with quenching free radicals by melatonin help mesothelial cells maintain a relatively stable internal environment in the face of high-glucose stress. Thus, Melatonin treatment holds some promise in preserving mesothelium integrity and in decreasing angiogenesis to protect peritoneum function in patients undergoing peritoneal dialysis.

Network Pharmacology and In Vivo Analysis of Dahuang-Huangqi Decoction Effectiveness in Alleviating Renal Interstitial Fibrosis

Dahuang and Huangqi are the most frequently prescribed treatment methods for chronic kidney disease in China. Our study aimed to clarify the pharmacological mechanism of action of Dahuang-Huangqi decoction (DHHQD) in renal interstitial fibrosis (RIF). The intersection of genes targeted by DHHQD active ingredients and RIF target genes was searched using network pharmacology to build a chemical ingredient and disease target network. For in vivo analysis, Sprague–Dawley rats with unilateral urethral obstruction (UUO) were administered DHHQD, and their kidney function-related indicators and pathological indices were determined. The expression of core targets was quantified using real-time polymerase chain reaction and western blotting. A total of 139 common targets for DHHQD and RIF in chronic kidney disease were detected. Compared with the untreated UUO rats, the DHHQD-treated rats showed reductions in the following: blood urea nitrogen and serum creatinine levels, kidney tubular atrophy and necrosis, interstitial fibrosis, hyperplasia and abnormal deposition of extracellular matrix, and microstructural changes in the mesangial matrix and glomerular basement membrane. DHHQD treatment significantly regulated the levels of renal core proteins, such as eNOS, IL-6, EGFR, and VEGF and reduced the mRNA and protein expression of the core targets involved in inflammation pathways, such as PI3K/AKT and TLR4/NF-κB. DHHQD treatment ameliorated the severity of RIF by potentially regulating the AKT/PI3K and TLR4/NF-κB signaling pathways. Our study findings provide insights into the mechanisms associated with DHHQD action and essential data for future research.

Establishment of a novel mouse peritoneal dialysis-associated peritoneal injury model

BACKGROUND

Peritoneal fibrosis induced by various factors during peritoneal dialysis (PD) can eventually lead to ultrafiltration failure and termination of PD treatment. The existing animal models are caused by a single stimulus, and cannot accurately simulate complex pathogenesis of peritoneal injury and fibrosis. We aim to develop an efficient and realistic mouse model of PD-associated peritoneal injury using daily intraperitoneal injection (I.P.) of human peritonitis PD effluent.

METHODS

Eight-week-old male C57BL/6 mice were classified into six groups: saline control; 2.5% PD fluid; 2.5% PD fluid + lipopolysaccharide (LPS); 4.25% PD fluid; 4.25% PD fluid + LPS; and peritonitis effluent. Mice received daily I.P. for 6 weeks, and were sacrificed to determine peritoneal structural and functional damage, inflammation, and fibrosis.

RESULTS

Mice in the peritonitis effluent group had low mortality. The submesothelial thickness in the peritonitis effluent group was significantly greater than that in the 2.5% PD fluid group. The peritonitis effluent group had increased expression of fibrosis markers (α-SMA, Collagen I, etc.), neutrophil granulocytes (MPO), and macrophages (CD68, F4/80) in the peritoneum based on immunohistochemical staining; and significantly higher expression of inflammation markers (IL-1β, IL-6, etc.) and fibrosis markers (TGF-β1, α-SMA, etc.) based on real-time qPCR. Modified peritoneal equilibration tests (PET) demonstrated that I.P. of peritonitis effluent reduced peritoneal ultrafiltration.

CONCLUSION

Our novel animal model of PD-associated peritoneal injury faithfully simulates the clinical pathophysiological process. This animal model may be useful for study of the pathogenesis of PD-associated peritoneal injury and identification of novel treatments.

Increased risk of modality failure with higher serum uric acid level in continuous ambulatory peritoneal dialysis patients: a prospective cohort study

BACKGROUND

Peritoneal dialysis (PD) is one of the most important kidney replacement therapies for patients with end-stage kidney disease (ESKD). PD technique failure can lead to an escalated cost and increased infectious and cardiovascular risk, up and including to death. The accumulation of uric acid (UA) was associated with adverse outcomes in ESKD patients. However, the relationship between serum UA and technique failure is little explored.

METHODS

Here, a total of 266 continuous ambulatory peritoneal dialysis (CAPD) patients (age, 41.8 ± 12.6 years; 125 males) were enrolled and followed up for 31.7 months. Serum UA levels were examined at baseline and each visit. Subjects were divided into three groups according to their baseline serum UA concentrations. Multivariable Cox regression models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of PD technique failure.

RESULTS

The level of serum UA increased gradually as time prolonged. During the follow-up period, 77 (28.9%) patients occurred PD technique failure, of which 56 (21.1%) transferred to hemodialysis (HD) and 21 (7.9%) died. Compared to the lowest UA tertile, after adjusting for potential confounders, HRs of technique failure in tertile 2 and tertile 3 were 1.82 (95% CI: 0.95-3.49) and 2.03 (95% CI: 1.05-3.92), respectively, and p for trend was 0.043. Adjusted HRs of all-cause technique failure, transferring to HD and mortality with each 1 mg/dL increase in serum UA were 1.20 (95% CI: 1.03-1.40, p = 0.019), 1.22 (95% CI: 1.01-1.48, p = 0.039), and 1.25 (95% CI: 0.94-1.67, p = 0.128), respectively.

CONCLUSION

Higher serum UA level predicted higher risk of technique failure in CAPD patients.

The effect of laparoscopy on mast cell degranulation and mesothelium thickness in rats

Background

Laparoscopy induces adhesion due to ischemia-reperfusion injury. However, the detail pathomechanism is poorly understood. This study aimed to investigate the impact of laparoscopy on mast cell and mesothelium morphological changes in the rat.

Methods

Forty-nine males of Sprague-Dawley Rattus norvegicus were divided into four groups: a) control and b) intervention groups P1, P2, and P3 that underwent 60 min laparoscopic using carbon dioxide (CO₂) insufflation at 8, 10, and 12 mmHg groups, respectively. Serum hydrogen peroxide (H₂O₂), catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA), and oxidative stress index (OSI) levels were determined 24 h after laparoscopy. Histopathological analyses of mast cell infiltration and degranulation and mesothelium thickness in the liver, greater omentum, mesenterium, small intestine, and peritoneum were performed 7 days after the procedure.

Results

H₂O₂, MDA, and OSI levels were significantly increased in the intervention groups compared with the control (p<0.05), while the SOD and CAT levels were decreased in the intervention groups compared with the control (p<0.05). Mast cell infiltration and degranulation were higher in the intervention groups than in control (p<0.05), while the mesothelium thickness was significantly lower in the laparoscopic groups than in control (p<0.05). Interestingly, the decrease in mesothelium thickness was strongly associated with the increase in mast cell infiltration and degranulation (p<0.01).

Conclusions

Our study shows that laparoscopy in rats increases mast cell infiltration and degranulation, which also results in and correlates with a decrease in mesothelial thickness.

Osmotic Agents Hamper Mesothelial Repopulation as Seen in the Doughnut In Vivo Model

♦ Background

The problem of mesothelial cell injury derived from the use of peritoneal dialysis solutions has been explored deeply. Conversely, the eventual detrimental effects upon mesothelial cell regeneration have awaked less investigative efforts than those focused on injury.

♦ Objective

To evaluate in the in vivo and in situ rat “doughnut” model of mesothelial repopulation, the eventual effect of peritoneal lavage with Hank's Balanced Salt Solution (HBSS) as well as that of 4.25% glucose and 7.5% icodextrin dialysis solutions.

♦ Experimental Animals

100 Sprague–Dawley albino rats were included in the study. Animals were divided into five groups of 20 rats each: group 1: control at zero time; group 2: sham-injected rats; group 3: rats exposed to HBSS; group 4: rats treated with 4.25% glucose peritoneal dialysis solution; group 5: rats injected with 7.5% icodextrin.

♦ Methods

Selective exfoliation of a ring of mesothelium (width 0.8 mm, diameter 4 mm) covering the anterior surface of the liver was performed in 80 animals. The control zero-time group was used to evaluate the normal density distribution of the mesothelial cells forming the monolayer. The other groups were treated by means of daily sham injections or intraperitoneal infusion of each experimental solution for a period of 30 consecutive days. After a recovery period of 15 days, imprints and biopsies from the monolayer covering the exfoliated area were taken and processed for light microscopy.

♦ Results

Macroscopic observation of the abdominal cavity at the end of the 15-day recovery period showed that the prevalence of fibrotic adhesions between the peritoneal exfoliated area and the neighboring diaphragm was 10% for the sham-injected group, 5% for the HBSS-exposed animals, 85% for the rats injected with 4.25% glucose, and 95% for the icodextrin-treated group. Prevalence of fibrous adhesions in sham-injected animals and rats exposed to HBSS were devoid of statistically significant differences. Conversely, comparison of these groups with results observed in animals treated with the osmotic agents was significant, at the p < 0.0039 level. Regarding density distribution of mesothelial cells observed in imprints, there were no significant differences between the control zero-time and the sham-injected group. This parameter was marginally lower ( p < 0.05) in the HBSS-treated rats. Imprints were not taken from animals exposed to glucose or icodextrin because a dense layer of connective tissue replaced the exfoliated mesothelial area.

♦ Conclusions

Observations made in this study support the contention that both osmotic agents, 4.25% glucose and 7.5% icodextrin, substantially restrain the normal process of mesothelial cell repopulation and induce repair by means of connective tissue. The underlying mechanism is most likely sustained oxidative stress.

Agents that Modulate Peritoneal Membrane Structure and Function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

A Short Review of Experimental Peritoneal Sclerosis: From Mice to Men

Peritoneal sclerosis has been induced in rodents in vivo by exposing the membrane to a variety of experimental interventions: asbestos, 0.1% chlorexidine, iron dextran, glucose degradation products, AGE deposits derived from uremia per se, sodium hypochlorite, lypopolysaccharide, low pH, pure water, silica or zymosan. With a few exceptions (pure water, chlorhexidine and low pH), the other substances mentioned operate setting out different degrees of oxidative stress. This short review describes several experimental interventions in rodents, aimed at acute exfoliation or long-term, sustained injury of the mesothelial monolayer performed by means of intraperitoneal injections of different oxidant agents.

Acute exfoliation induced by deoxycholate resulted in a depopulated monolayer coincident with immediate alteration of the peritoneal permeability, evidenced by increased urea D/P ratio, higher glucose absorption rate, elevated albumin losses in the effluent and significant reduction of the ultrafiltration rate.

In the long term (30 days), these manifestations of membrane failure persisted and coincided with substantial peritoneal sclerosis.

Peritoneal sclerosis was also induced by IP injections of 0.125% trypsin and 6.6 mM/L solution of formaldehyde. Using the doughnut rat model of mesothelial regeneration, exposure to 4.25% glucose or 7.5% icodextrin solutions severely hampered repopulation of the monolayer, which was replaced by a thick sheet of fibrous tissue.

It is concluded that peritoneal sclerosis derives mostly from sustained oxidative injury to the peritoneal membrane. Loss of the mesothelial monolayer is the first step in the chain of events leading to this complication.

Effect of Hydrogen-Rich Saline on Postoperative Intra-Abdominal Adhesion Bands Formation in Mice

Background

Postsurgical peritoneal adhesions (PPAs) are pathologic fibrous bands within the peritoneal cavity. The aim of this study was to investigate the protective effect of hydrogen-rich saline (HRS) on PPAs formation in mice.

Material/Methods

Adhesions were induced in mice using the cecum rubbing model. The mice were allocated into 4 groups: control sham group without cecum rubbing; PPA group with saline applied intraperitoneally (i.p.) daily after cecum rubbing; PPA+HRS (5) group with 5 ml/kg of HRS applied i.p. daily after cecum rubbing; and PPA+HRS (10) group with 10 ml/kg of HRS applied i.p. daily after cecum rubbing. On the 1^st, 3^rd, and 7^th days after the operation, mice were killed and pathological adhesion bands were quantified to detect the effect of HRS on PPAs formation.

Results

HRS did not affect PPAs formation on the 1^st day, but did make a significant reduction on the 3^rd and 7^th days. A significant increase of t-PA and decrease of TGF-β1 and PAI-1 in the peritoneal fluids were observed in the HRS-treated groups. The levels of MDA and MPO in the HRS-treated groups were significantly lower than those in the PPA group. TNF-α and IL-6 levels in HRS-treated groups significantly decreased compared with those in the PPA group on postoperative day 3 and 7. Moreover, HRS decreased the mRNA levels of pro-inflammatory cytokines and TGF-β1 expression in the postsurgical adhesion bands.

Conclusions

These results showed that HRS had therapeutic potential for preventing PPAs formation, possibly through balancing the expression of TGF-β1, t-PA, and PAI-1, and inhibiting oxidative stress and inflammation.

Peripheral serotonin regulates postoperative intra-abdominal adhesion formation in mice

The aim of the present study is to investigate the role and potential mechanisms of peripheral serotonin in postoperative intra-abdominal adhesion formation in mice. The caecum-rubbing operations were conducted for intra-abdominal adhesion formation modelling in wild-type and Tph1−/− mice. The deficiency of serotonin significantly decreased the adhesion scores, weight loss, and adhesion thickness as well as levels of collagen fibres and hydroxyproline in the adhesive tissues. The Tph1−/− mice exhibited a milder inflammatory response and oxidative stress in the adhesive tissues than did the wild-type mice. Moreover, the deficiency of serotonin reduced the levels of PAI-1 and fibrinogen, and raised the t-PA and t-PA/PAI levels in the peritoneal fluids. Moreover, the expressions of CD34, VEGF, TGF-β and 5-HT_2B receptor in the adhesive tissues were significantly decreased in the Tph1−/− group mice. Furthermore, the Tph1−/− +5-HTP group showed more severe adhesions than did the Tph1−/− group mice, and the p-chlorophenylalanine (PCPA) could markedly alleviated the adhesion formation in the WT mice. In conclusion, the present study showed that peripheral serotonin regulated postoperative intra-abdominal adhesion formation by facilitating inflammation, oxidative stress, disorder of the fibrinolytic system, angiopoiesis and TGF-β1 expression via the 5-HT_2B receptor in the adhesive tissues.

Targeting cannabinoid signaling for peritoneal dialysis-induced oxidative stress and fibrosis

Long-term exposure to bioincompatible peritoneal dialysis (PD) solutions frequently results in peritoneal fibrosis and ultrafiltration failure, which limits the life-long use of and leads to the cessation of PD therapy. Therefore, it is important to elucidate the pathogenesis of peritoneal fibrosis in order to design therapeutic strategies to prevent its occurrence. Peritoneal fibrosis is associated with a chronic inflammatory status as well as an elevated oxidative stress (OS) status. Beyond uremia per se, OS also results from chronic exposure to high glucose load, glucose degradation products, advanced glycation end products, and hypertonic stress. Therapy targeting the cannabinoid (CB) signaling pathway has been reported in several chronic inflammatory diseases with elevated OS. We recently reported that the intra-peritoneal administration of CB receptor ligands, including CB₁ receptor antagonists and CB₂ receptor agonists, ameliorated dialysis-related peritoneal fibrosis. As targeting the CB signaling pathway has been reported to be beneficial in attenuating the processes of several chronic inflammatory diseases, we reviewed the interaction among the cannabinoid system, inflammation, and OS, through which clinicians ultimately aim to prolong the peritoneal survival of PD patients.

Relationship between uric acid and technique failure in patients on continuous ambulatory peritoneal dialysis: a long-term observational cohort study

OBJECTIVES

Uric acid (UA) is the product of purine or nucleotide metabolism via the pathway of xanthine oxidase or xanthine dehydrogenase. Although epidemiological studies assessing the role of UA in cardiovascular disease or mortality have produced inconsistent results, the correlation between UA and technique failure in patients on continuous ambulatory peritoneal dialysis (CAPD) remains to be assessed.

DESIGN

A retrospective cohort study.

SETTING

Patients starting CAPD between 2001 and 2009 in a single centre in Taiwan.

PARTICIPANTS

A total of 371 patients on CAPD.

PRIMARY OUTCOME MEASURES

All-cause and peritonitis-related technique failure.

RESULTS

A cohort of 371 participants (43.9% male) was enrolled in the study with a mean age of 55.7±15.9 years at the start of CAPD. During the study period, technique failure occurred in 41 (34.4%) patients in the hyperuricaemia group compared with 49 (19.4%) in the normouricaemia group (p=0.003). In the multivariate Cox regression models, hyperuricaemia at baseline was significantly associated with both a higher risk of technique failure (HR 1.24; 95% CI 1.09 to 1.42, p=0.001) and peritonitis-related technique failure (HR 1.29; 95% CI 1.07 to 1.57, p=0.008).

CONCLUSIONS

UA was shown to be associated with all-cause and peritonitis-related technique failure in our study. Patients on CAPD with hyperuricaemia should be closely monitored and strategies of increasing survival on CAPD should be taken.

Peritoneal adhesion prevention with a biodegradable and injectable N,O-carboxymethyl chitosan-aldehyde hyaluronic acid hydrogel in a rat repeated-injury model

Postoperative peritoneal adhesion is one of the serious issues because it induces severe clinical disorders. In this study, we prepared biodegradable and injectable hydrogel composed of N,O-carboxymethyl chitosan (NOCC) and aldehyde hyaluronic acid (AHA), and assessed its anti-adhesion effect in a rigorous and severe recurrent adhesion model which is closer to clinical conditions. The flexible hydrogel, which gelated in 66 seconds at 37 °C, was cross-linked by the schiff base derived from the amino groups of NOCC and aldehyde groups in AHA. In vitro cytotoxicity test showed the hydrogel was non-toxic. In vitro and in vivo degradation examinations demonstrated the biodegradable and biocompatibility properties of the hydrogel. The hydrogel discs could prevent the invasion of fibroblasts, whereas fibroblasts encapsulated in the porous 3-dimensional hydrogels could grow and proliferate well. Furthermore, the hydrogel was applied to evaluate the anti-adhesion efficacy in a more rigorous recurrent adhesion model. Compared with normal saline group and commercial hyaluronic acid (HA) hydrogel, the NOCC-AHA hydrogel exhibited significant reduction of peritoneal adhesion. Compared to control group, the blood and abdominal lavage level of tPA was increased in NOCC-AHA hydrogel group. These findings suggested that NOCC-AHA hydrogel had a great potential to serve as an anti-adhesion candidate.

A review of rodent models of peritoneal dialysis and its complications

This article reviews the available rodent models of peritoneal dialysis (PD) that have been developed over the past 20 years and the complications associated with their use. Although there are several methods used in different studies, the focus of this article is not to review or provide detailed summaries of these methods. Rather, this article reviews the most common methods of establishing a dialysis model in rodents, the assays used to observe function of the peritoneum in dialysis, and how these models are adapted to study peritonitis and peritoneal fibrosis. We compared the advantages and disadvantages of different methods, which should be helpful in studies of PD and may provide valuable data for further clinical studies.

Hyperbranched polyglycerol is an efficacious and biocompatible novel osmotic agent in a rodent model of peritoneal dialysis

OBJECTIVES

To enhance the effectiveness of peritoneal dialysis (PD), new biocompatible PD solutions may be needed. The present study was designed to test the efficacy and biocompatibility of hyperbranched polyglycerol (HPG)-a nontoxic, nonimmunogenic water-soluble polyether polymer-in PD.

METHODS

Adult Sprague-Dawley rats were instilled with 30 mL HPG solution (molecular weight 3 kDa; 2.5% - 15%) or control glucose PD solution (2.5% Dianeal: Baxter Healthcare Corporation, Deerfield, IL, USA), and intraperitoneal fluid was recovered after 4 hours. Peritoneal injury and cellular infiltration were determined by histologic and flow cytometric analysis. Human peritoneal mesothelial cells were assessed for viability in vitro after 3 hours of PD fluid exposure.

RESULTS

The 15% HPG solution achieved a 4-hour dose-related ultrafiltration up to 43.33 ± 5.24 mL and a dose-related urea clearance up to 39.17 ± 5.21 mL, results that were superior to those with control PD solution (p < 0.05). The dialysate-to-plasma (D/P) ratios of urea with 7.5% and 15% HPG solution were not statistically different from those with control PD solution. Compared with fluid recovered from the control group, fluid recovered from the HPG group contained proportionally fewer neutrophils (3.63% ± 0.87% vs 9.31% ± 2.89%, p < 0.0001). Detachment of mesothelial cells positive for human bone marrow endothelial protein 1 did not increase in the HPG group compared with the stain control (p = 0.1832), but it was elevated in the control PD solution group (1.62% ± 0.68% vs 0.41% ± 0.31%, p = 0.0031). Peritoneal biopsies from animals in the HPG PD group, compared with those from control PD animals, demonstrated less neutrophilic infiltration and reduced thickness. Human peritoneal mesothelial cell survival after HPG exposure was superior in vitro (p < 0.0001, 7.5% HPG vs control; p < 0.01, 15% HPG vs control). Exposure to glucose PD solution induced cytoplasmic vacuolation and caspase 3-independent necrotic cell death that was not seen with HPG solution.

CONCLUSIONS

Our novel HPG PD solution demonstrated effective ultrafiltration and waste removal with reduced peritoneal injury in a rodent model of PD.

NADPH oxidase-dependent formation of reactive oxygen species contributes to transforming growth factor β1-induced epithelial-mesenchymal transition in rat peritoneal mesothelial cells, and the role of astragalus intervention

OBJECTIVE

To investigate the role of nicotinamide-adenine dinucleotide phosphate (NADPH) oxidasedependent formation of reactive oxygen species (ROS) in the transforming growth factor β1 (TGF-β1)-induced epithelial-mesenchymal transition (EMT) in rat peritoneal mesothelial cells (RPMCs), and the effect of Astragalus injection (AGI) intervention.

METHODS

Primary RPMCs were cultured to the second generation in vitro. After synchronization for 24 h, the cells were randomly assigned to the following groups: control (Group A), AGI (2 g/mL; Group B), TGF-β1 (10 ng/mL; Group C), TGF-β1 (10 ng/mL) + AGI (2 g/mL; Group D; pretreated for 1 h with AGI before TGF-β1 stimulation). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis were employed to evaluate the mRNA and protein expression of the NADPH oxidase subunit p67phox, α-smooth muscle actin (α-SMA) and E-cadherin. The dichlorofluorescein-sensitive cellular ROS levels were measured by a fluorometric assay and confocal microscopy.

RESULTS

TGF-β1 significantly induced NADPH oxidase subunit p67phox mRNA and protein expression in RPMCs, as well as inducing the production of intracellular ROS. AGI inhibited this TGF-β1-induced up-regulation by 39.3% and 47.8%, respectively (P<0.05), as well as inhibiting the TGF-β1-induced ROS generation by 56.3% (P<0.05). TGF-β1 also induced α-SMA mRNA and protein expression, and down-regulated E-cadherin mRNA and protein expression (P<0.05). This effect was suppressed by AGI (P<0.05).

CONCLUSIONS

NADPH oxidase-dependent formation of ROS may mediate the TGF-β1-dependent EMT in RPMCs. AGI could inhibit this process, providing a theoretical basis for AGI in the prevention of peritoneal fibrosis.

Medical ozone therapy decreases postoperative uterine adhesion formation in rats

PURPOSE

Various studies have been performed to find out novel treatment strategies to prevent postoperative adhesion formation. Ozone therapy (OT) is shown to reduce inflammation in several pathological conditions. Therefore, we aimed to evaluate the efficacy of OT in a rat model of experimental uterine adhesion (EUA).

METHODS

Thirty female Wistar rats (200-250 g) were divided into three groups: sham, EUA and EUA+OT. EUA and EUA+OT groups were subjected to the postoperative adhesion procedure by bipolar coagulation on the uterine horns and corresponding pelvic sidewall parietal peritoneum. EUA+OT group received 0.7 mg/kg daily single dose for 3 days of ozone/oxygen mixture intraperitoneally after adhesion induction. All animals were killed on the 7th day and uterine adhesions were scored. Uterine tissues and peritoneal washing fluid were harvested for all analyses.

RESULTS

Uterine malondialdehyde levels in the EUA group were significantly higher compared to the other groups. However, in the EUA group, uterine superoxide dismutase and glutathione peroxidase activities were lower than in other groups. Peritoneal fluid TNF-α levels were found to be significantly different for all groups (p < 0.001). Macroscopic total adhesion score was significantly higher in the EUA group compared to the other groups (p < 0.001). But, total score in the EUA+OT group was lower than in the EUA group (p = 0.006).

CONCLUSIONS

Medical OT prevents postoperative uterine adhesions by modulating TNF-α levels and oxidative/antioxidative status in an experimental uterine adhesion model.

Level of 8-OHdG in drained dialysate appears to be a marker of peritoneal damage in peritoneal dialysis

PURPOSE

Peritoneal dialysis (PD) is a successful renal replacement therapy; however, long-term PD leads to structural and functional peritoneal damage. Therefore, the monitoring and estimation of peritoneal function are important in PD patients. Oxidative stress has been implicated as one possible mechanism of peritoneal membrane damage. The aim of this study was to evaluate the association between an oxidative stress marker, 8-hydroxydeoxyguanosine (8-OHdG), and peritoneal damage in PD patients.

METHODS

The authors evaluated 8-OHdG in drained dialysate by enzyme immunoassay to investigate the association between 8-OHdG and solute transport rate estimated by peritoneal equilibration test and matrix metalloproteinase-2 (MMP-2) level in 45 samples from 28 PD patients.

RESULTS

The 8-OHdG level was significantly correlated with dialysate:plasma creatine ratio (r = 0.463, P < 0.05) and significantly inversely correlated with D/D0 glucose (where D is the glucose level of peritoneal effluents obtained 4 hours after the injection and D0 is the glucose level obtained immediately after the injection) (r = -0.474, P < 0.05). The 8-OHdG level was also significantly correlated with MMP-2 level (r = 0.551, P < 0.05), but it was not correlated with the age of subjects, the duration of PD, or blood pressure.

CONCLUSION

The level of 8-OHdG in drained dialysate may be a useful novel marker of peritoneal damage in PD.

Role of mitochondrial respiratory chain complex III in high glucose peritoneal dialysate-induced hyperpermeability of HPMCs

BACKGROUND

High-glucose-based peritoneal dialysis solution (PDS) is considered to be one of the primary causes for the increase of ionic permeability in peritoneum as detected by transmesothelial electrical resistance (TER) measurements and claudin-1 expression. However, the mechanism is not clear. The aim of this study is to test the hypothesis that high-glucose PDS induces hyperpermeability in human peritoneal mesothelial cell (HPMC) monolayer by mitochondrial respiratory chain complex III pathway.

METHODS

HPMCs were cultured in a 1 : 1 mix of Dulbecco's modified Eagle's medium (DMEM) and PDS containing 1.5% and 4.25% glucose for 24 h. A 1 : 1 mixture of 160 mg/L glutathione and 4.25% glucose PDS was also added as an antioxidant group. TER measurement and immunostaining and western blot analysis of claudin-1 expression were examined for detection of permeability damage in HPMCs. MitoSOX™ Red staining and respiratory chain complexes' activities were determined for detection of mitochondrial reactive oxygen species (ROS) production and mitochondrial complexes' activities.

RESULTS

TER decreased in a time- and concentration-dependent manner after culture with high-glucose PDS for 24 h. Claudin-1 was also downregulated. Complex III activity was inhibited accompanied by increasing mitochondrial ROS generation. These changes were partially prevented by glutathione.

CONCLUSION

These findings demonstrate that mitochondrial respiratory complex III pathway has crucial importance in maintaining permeability of HPMCs, which might reveal a valuable target for novel therapies to fight hyperpermeability of peritoneum during the prolonged PD treatment.

Epithelial-mesenchymal transition of rat peritoneal mesothelial cells via Rhoa/Rock pathway

The objective of this study was to investigate the role of the RhoA/Rock signaling pathway in the epithelial-mesenchymal transition (EMT) of rat peritoneal mesothelial cells (RPMCs). Primary SD rat peritoneal mesothelial cells were cultured in vitro. RPMCs were randomly assigned to four groups: group A (control), group B (TGF-β1, 10 μg/L), group C (10 μg/L TGF-β1 + 10 μmol/L Y-27632, an inhibitor of Rock that was pre-applied for 2 h before TGF-β1 stimulation), and group D (Y-27632 alone, 10 μmol/L). Our results were as follows: (1) TGF-β1 stimulation elicited a robust increase in RhoA activity in a time-dependent manner; the increase was 2.57 ± 0.52 times larger than the activity observed for the control group (P < 0.05) after 10 min of stimulation. RhoA activity peaked at 1 h and was 4.35 ± 0.41 times the value observed for the control group (P < 0.05). (2) TGF-β1 up-regulated mRNA and/or protein expression of α-SMA, vimentin, and collagen and down-regulated mRNA and protein expression of E-cadherin in RPMCs. (3) The Rock inhibitor Y-27632 effectively reduced TGF-β1-induced expression of α-SMA, collagen, and vimentin; the mRNA levels of α-SMA and collagen decreased by 53.8% and 55.7%, respectively, and the protein levels of α-SMA, vimentin, and collagen decreased by 42.6%, 60.1%, and 58.1%, respectively, as compared to TGF-β1-stimulated groups (P < 0.05). However, the Rock inhibitor Y-27632 had no effect on the level of E-cadherin. In conclusion, the RhoA/Rock signaling pathway may mediate EMT induced by TGF-β1 in rat peritoneal mesothelial cells. The RhoA/Rock pathway may be a potential therapeutic target for the treatment of peritoneal fibrosis.

HSP-mediated cytoprotection of mesothelial cells in experimental acute peritoneal dialysis

BACKGROUND

Low biocompatibility of peritoneal dialysis solution (PDS) injures mesothelial cells but also induces heat shock proteins (HSP), the main effectors of the cellular stress response. This study investigated whether overexpression of HSP upon pharmacologic induction results in cytoprotection of mesothelial cells in experimental PD.

METHODS

Stress response of mesothelial cells upon exposure to PDS was pharmacologically manipulated using glutamine as a co-inducer. In vitro, HSP-mediated cytoprotection was assessed by simultaneous measurements of HSP expression using Western blot analysis and viability testing using release of lactic dehydrogenase in cultured human mesothelial cells. In vivo, detachment of mesothelial cells from their peritoneal monolayer was assessed following exposure to PDS with and without the addition of glutamine in the acute rat model of PD.

RESULTS

In vitro, mesothelial cell viability following exposure to PDS was significantly improved upon pharmacologic co-induction of HSP expression by glutamine (226% +/- 29% vs 190% +/- 19%, p = 0.001). In vivo, mesothelial cell detachment during exposure to PDS was reduced upon pharmacologic induction of HSP expression by glutamine (93 +/- 39 vs 38 +/- 38 cells, p = 0.044), resulting in reduced peritoneal protein loss (75 +/- 7 vs 65 +/- 4 mg, p = 0.045).

CONCLUSION

Our results represent the first study of pharmacologic manipulation of HSP expression for cytoprotection of mesothelial cells following acute in vitro and in vivo exposure to PDS. PDS with added glutamine might represent a promising therapeutic approach against low biocompatibility of PDS but needs validation in a chronic PD model.

Intraperitoneal Administration of Methylene Blue Attenuates Oxidative Stress, Increases Peritoneal Fibrinolysis, and Inhibits Intraabdominal Adhesion Formation

BACKGROUND

Mounting evidence indicates that postoperative oxidative stress may be linked to decreased fibrinolytic activity and, subsequently, the development of intraabdominal adhesions. The goal of this study was to determine if methylene blue, a highly redox active dye that has been shown to inhibit adhesion formation (1) acts as an antioxidant in the postoperative peritoneum, and (2) subsequently affects fibrinolytic activity.

MATERIALS AND METHODS

Intraabdominal adhesions were surgically induced in rats receiving methylene blue (30 mg/kg) or vehicle (sterile water) intraperitoneally at surgery. At 24 h and 7 d following surgery, adhesion formation, oxidative stress, and peritoneal fibrinolytic activity were assessed.

RESULTS

Methylene blue did not affect adhesion formation at 24 h, but did induce a >50% regression in adhesions after 7 d (P < 0.05). Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and myeloperoxidase (MPO) activities, and 8-isoprostane and thiobarbituric acid-reactive substances were all significantly increased in peritoneal tissue samples (P < 0.05) by 24 h following surgery. Methylene blue inhibited NADPH oxidase by 98% and MPO activity by 78% in the 24 h tissue samples, and blunted the corresponding surgery-induced increases in tissue lipid and protein oxidation. Furthermore, methylene blue significantly increased (P < 0.05) fibrinolytic activity in peritoneal fluid at 24 h.

CONCLUSIONS

Methylene blue acts as an antioxidant in this experimental system and may reduce intraabdominal adhesion formation by enhancing peritoneal fibrinolytic activity following surgery.

A neurokinin-1 receptor antagonist that reduces intra-abdominal adhesion formation decreases oxidative stress in the peritoneum

Oxidative stress has been implicated in intra-abdominal adhesion formation. Substance P, a neurokinin-1 receptor (NK-1R) ligand, facilitates leukocyte recruitment and reactive oxygen species (ROS) generation. We have shown in a rat model of adhesion formation that intraperitoneal administration of a NK-1R antagonist at the time of abdominal operation reduces postoperative adhesion formation. Thus we determined the effects of NK-1R antagonist administration on peritoneal leukocyte recruitment and oxidative stress within 24 h of surgery. Adhesions were induced in Wistar rats randomly assigned to receive the antagonist or vehicle intraperitoneally. Peritoneal tissue was isolated at 2, 4, 6, and 24 h after surgery for analysis of the oxidative stress biomarkers 8-isoprostane (8-IP), protein carbonyl, NADPH oxidase, myeloperoxidase (MPO), and ICAM-1 and VCAM-1 mRNAs. Total antioxidant capacity of peritoneal fluid was also determined. MPO, NADPH oxidase, 8-IP, and protein carbonyl were elevated (P < 0.05) by 6 h. ICAM-1 mRNA was elevated (P < 0.05) by 2 h, whereas VCAM-1 levels decreased (P < 0.05) at 24 h. The NK-1R antagonist delayed the MPO rise and reduced (P < 0.05) 8-IP levels by 6 h and ICAM-1 mRNA, VCAM-1 mRNA, and protein carbonyl at 2 h. The antagonist also increased (P < 0.05) the antioxidant capacity of peritoneal fluid at all time points. These data further support a role for oxidative stress in adhesion formation and suggest that the NK-1R antagonist may limit adhesions, in part, by reducing postoperative oxidative stress through an inhibition of neutrophil recruitment and an increase in peritoneal fluid antioxidant capacity.

Differently charged polypeptides in the prevention of post-surgical peritoneal adhesions

OBJECTIVE

Peritoneal adhesions develop after almost all surgical interventions in the abdomen. We have developed an efficient treatment against post-surgical adhesions consisting of a combination of positively charged poly-L-lysine and negatively charged poly-L-glutamate. The aim of the present study was to further develop the concept of applying oppositely charged polypeptides in the prevention of adhesion formation, by evaluating different doses of the peptides, alterations in the way of administration, and also testing alternative components.

MATERIAL AND METHODS

Eighty-five NMRI mice were divided into six groups. A standardized peritoneal injury model was used. The groups received physiologic sodium chlorine, poly-L-lysine+poly-L-glutamate, low molecular weight poly-L-lysine+poly-L-glutamate, locally administered poly-L-lysine+poly-L-glutamate, in vitro mixed poly-L-lysine+poly-L-glutamate and poly-L-arginine+poly-L-glutamate, respectively. After 7 days, the extent of adhesion formation was determined during relaparotomy and was expressed as the mean percentage of the total wound length.

RESULTS

A significant decrease (p <0.001) in the peritoneal adhesion rate was detected in all groups, with the exception of the group administered poly-L-arginine. Among those animals that received poly-L-lysine and poly-L-glutamate, the low dose of poly-L-lysine administration resulted in the most pronounced anti-adhesive effect.

CONCLUSIONS

The most effective polypeptide combination was poly-L-lysine and poly-L-glutamate, also showing effectiveness when used at low doses and by local application. The differences in adhesion prevention and the possible underlying mechanisms are discussed and the key role of poly-L-lysine is elucidated.

Evidence for HSP-mediated cytoskeletal stabilization in mesothelial cells during acute experimental peritoneal dialysis

Low biocompatibility of peritoneal dialysis fluid (PDF) injures mesothelial cells and activates their stress response. In this study, we investigated the role of heat shock proteins (HSP), the main cytoprotective effectors of the stress response, in cytoskeletal stabilization of mesothelial cells in experimental peritoneal dialysis. In cultured human mesothelial cells, cytoskeletal integrity was assessed by detergent extractability of marker proteins following in vitro PDF exposure. Effects of HSP on stabilization of ezrin were evaluated by a conditioning protocol (PDF pretreatment) and repair assay, based on coincubation of cytoskeletal protein fractions with recombinant HSP-72 or HSP-72 antibodies. In the rat model, detachment of mesothelial cells from their peritoneal monolayer during in vivo PDF exposure was assessed with and without overexpression of HSP-72 (by heat conditioning). In vitro, cytoskeletal disruption on sublethal PDF exposure was demonstrated by significantly altered detergent extractability of ezrin and ZO-1. Restoration was associated with significant induction and cytoskeletal redistribution of HSP during recovery. Both the conditioning protocol and in vitro repair assay provided evidence for HSP-72-mediated cytoskeletal stabilization. In the rat model, overexpression of HSP-72 following heat conditioning resulted in significantly reduced detachment of mesothelial cells on in vivo exposure to PDF. Our results establish an essential role of HSP in repair and cytoprotection of cytoskeletal integrity in mesothelial cells following acute in vitro and in vivo exposure to PDF. Repeated exposure to PDF, as is the rule in the clinical setting, may not only cause repeat injury to mesothelial cells but rather represents a kind of inadvertent conditioning treatment.

Icodextrin Peritoneal Transport In Vitro: Effect of Sodium Deoxycholate, Glucose, and Methylglyoxal

The aim of the in vitro studies was to examine the effect of sodium deoxycholate, glucose, and methylglyoxal on icodextrin peritoneal transfer. The rabbit peritoneum in a modified Ussing chamber was an experimental model. Transport and morphometric analyses were performed. In the first of them, the icodextrin (7.5 g/dL) diffusion from the mesothelial to the interstitial side of the membrane, expressed as a diffusive permeability coefficient (P), was evaluated in the control stage, after chemical modification of the membrane using sodium deoxycholate (104 mg/dL), after the addition of glucose (1.8 g/dL) and methylglyoxal (1 mg/dL), in the separate experimental series. In the second morphometric studies, the thickness and transverse cross-section surface area of native tissue, in 75 min of experiment and after application of sodium deoxycholate, were investigated. In the control conditions, the rate of glucose polymer passage remained constant. A mean value of P +/- SD was 0.194 +/- 0.126 (x10(-4), cm/s) during 120 min of the study. The transfer of icodextrin was enhanced by 224% after 3 min of incubation of the peritoneum with sodium deoxycholate. The introduction of glucose into the circulating medium with icodextrin caused the increase of P values for glucose polymer by 94% during 60 min. In the same conditions, the usage of methylglyoxal did not change transport parameters. Both thickness and transverse cross-section surface area of the native tissue in 75 min of the study did not differ. It was 4.87 microm and 12.50 x 10(2) microm(2) for the mesothelial layer, and 63.83 microm and 208.10 x 10(2) microm(2) for the whole peritoneal membrane. The application of sodium deoxycholate caused the decrease of mesothelium thickness by 20% but the increase of thickness and transverse cross-section surface area of the peritoneum by 37% in comparison with 75 min of experiment. In conclusion, sodium deoxycholate and glucose, but not methylglyoxal, intensify peritoneal transport of icodextrin in vitro. These modifications are probably connected with the exfoliation of the mesothelium and looseness of the interstitium caused by sodium deoxycholate as well as the physical and metabolic influence of glucose on the peritoneum.