Mononuclear leucocyte function tests in the assessment of the biocompatibility of peritoneal dialysis fluids

Steviol glycosides as an alternative osmotic agent for peritoneal dialysis fluid

Background: Peritoneal dialysis (PD) is a renal replacement technique that requires repeated exposure of the peritoneum to hyperosmolar PD fluids (PDFs). Unfortunately, it promotes alterations of the peritoneal membrane (PM) that affects its functionality, including mesothelial-mesenchymal transition (MMT) of mesothelial cells (MCs), inflammation, angiogenesis, and fibrosis. Glucose is the most used osmotic agent, but it is known to be at least partially responsible, together with its degradation products (GDP), for those changes. Therefore, there is a need for more biocompatible osmotic agents to better maintain the PM. Herein we evaluated the biocompatibility of Steviol glycosides (SG)-based fluids.

Methods: The ultrafiltration and transport capacities of SG-containing and glucose-based fluids were analyzed using artificial membranes and an in vivo mouse model, respectively. To investigate the biocompatibility of the fluids, Met-5A and human omental peritoneal MCs (HOMCs) were exposed in vitro to different types of glucose-based PDFs (conventional 4.25% glucose solution with high-GDP level and biocompatible 2.3% glucose solution with low-GDP level), SG-based fluids or treated with TGF-β1. Mice submitted to surgery of intraperitoneal catheter insertion were treated for 40 days with SG- or glucose-based fluids. Peritoneal tissues were collected to determine thickness, MMT, angiogenesis, as well as peritoneal washings to analyze inflammation.

Results: Dialysis membrane experiments demonstrated that SG-based fluids at 1.5%, 1%, and 0.75% had a similar trend in weight gain, based on curve slope, as glucose-based fluids. Analyzing transport capacity in vivo, 1% and 0.75% SG-based fluid-exposed nephrectomized mice extracted a similar amount of urea as the glucose 2.3% group. In vitro, PDF with high-glucose (4.25%) and high-GDP content induced mesenchymal markers and angiogenic factors (Snail1, Fibronectin, VEGF-A, FGF-2) and downregulates the epithelial marker E-Cadherin. In contrast, exposition to low-glucose-based fluids with low-GDP content or SG-based fluids showed higher viability and had less MMT. In vivo, SG-based fluids preserved MC monolayer, induced less PM thickness, angiogenesis, leukocyte infiltration, inflammatory cytokines release, and MMT compared with glucose-based fluids.

Conclusion: SG showed better biocompatibility as an osmotic agent than glucose in vitro and in vivo, therefore, it could alternatively substitute glucose in PDF.

The Effects of Peritoneal Dialysis Solutions on Peritoneal Host Defense

Conventional peritoneal dialysis fluid (PDF) is a bioincompatible solution owing to the acidic pH, the high glucose concentrations and the associated hyperosmolarity, the high lactate concentrations, and the presence of glucose degradation products (GDPs). This unphysiologic composition adversely affects peritoneal host defense and may thus contribute to the development of PD-related peritonitis. The viability of polymorphonuclear leukocytes, monocytes, peritoneal macrophages, and mesothelial cells is severely depressed in the presence of conventional PDF. In addition, the production of inflammatory cytokines and chemoattractants by these cells is markedly affected by conventional PDF. Further, conventional PDF hampers the recruitment of circulating leukocytes in response to an infectious stimulus. Finally, phagocytosis, respiratory burst, and bacterial killing are markedly lower when polymorphonuclear leukocytes, monocytes, and peritoneal macrophages are exposed to conventional PDF. Although there are a few discrepant results, all major PDF components have been implicated as causative factors. Generally, novel PDF with alternative osmotic agents or with alternative buffers, neutral pH, and low GDP content have much milder inhibitory effects on peritoneal host defense. Clinical studies, however, still need to demonstrate their superiority with respect to the incidence of PD-related peritonitis.

Addition of Alanyl-Glutamine to Dialysis Fluid Restores Peritoneal Cellular Stress Responses - A First-In-Man Trial

BACKGROUND

Peritonitis and ultrafiltration failure remain serious complications of chronic peritoneal dialysis (PD). Dysfunctional cellular stress responses aggravate peritoneal injury associated with PD fluid exposure, potentially due to peritoneal glutamine depletion. In this randomized cross-over phase I/II trial we investigated cytoprotective effects of alanyl-glutamine (AlaGln) addition to glucose-based PDF.

METHODS

In a prospective randomized cross-over design, 20 stable PD outpatients underwent paired peritoneal equilibration tests 4 weeks apart, using conventional acidic, single chamber 3.86% glucose PD fluid, with and without 8 mM supplemental AlaGln. Heat-shock protein 72 expression was assessed in peritoneal effluent cells as surrogate parameter of cellular stress responses, complemented by metabolomics and functional immunocompetence assays.

RESULTS

AlaGln restored peritoneal glutamine levels and increased the primary outcome heat-shock protein expression (effect 1.51-fold, CI 1.07-2.14; p = 0.022), without changes in peritoneal ultrafiltration, small solute transport, or biomarkers reflecting cell mass and inflammation. Further effects were glutamine-like metabolomic changes and increased ex-vivo LPS-stimulated cytokine release from healthy donor peripheral blood monocytes. In patients with a history of peritonitis (5 of 20), AlaGln supplementation decreased dialysate interleukin-8 levels. Supplemented PD fluid also attenuated inflammation and enhanced stimulated cytokine release in a mouse model of PD-associated peritonitis.

CONCLUSION

We conclude that AlaGln-supplemented, glucose-based PD fluid can restore peritoneal cellular stress responses with attenuation of sterile inflammation, and may improve peritoneal host-defense in the setting of PD.

The effects of arginine glutamate, a promising excipient for protein formulation, on cell viability: Comparisons with NaCl

The effects of an equimolar mixture of l-arginine and l-glutamate (Arg·Glu) on cell viability and cellular stress using in vitro cell culture systems are examined with reference to NaCl, in the context of monoclonal antibody formulation. Cells relevant to subcutaneous administration were selected: the human monocyte cell line THP-1, grown as a single cell suspension, and adherent human primary fibroblasts. For THP-1 cells, the mechanism of cell death caused by relatively high salt concentrations was investigated and effects on cell activation/stress assessed as a function of changes in membrane marker and cytokine (interleukin-8) expression. These studies demonstrated that Arg·Glu does not have any further detrimental effects on THP-1 viability in comparison to NaCl at equivalent osmolalities, and that both salts at higher concentrations cause cell death by apoptosis; there was no significant effect on measures of THP-1 cellular stress/activation. For adherent fibroblasts, both salts caused significant toxicity at ~400 mOsm/kg, although Arg·Glu caused a more precipitous subsequent decline in viability than did NaCl. These data indicate that Arg·Glu is of equivalent toxicity to NaCl and that the mechanism of toxicity is such that cell death is unlikely to trigger inflammation upon subcutaneous injection in vivo.

Dual reporter gene imaging for tracking macrophage migration using the human sodium iodide symporter and an enhanced firefly luciferase in a murine inflammation model

PURPOSE

The purpose of this study is to visualize the migration of reporter macrophages expressing both the human sodium iodide symporter (hNIS) and enhanced firefly luciferase (effluc) gene in mice with chemically induced inflammation.

PROCEDURES

A macrophage cell line expressing both hNIS and effluc genes (Raw264.7/hNIS-effluc, herein referred to as a Raw264.7/NF) was established by cotransduction of two genes into a murine macrophage cell line (Raw264.7), and cell proliferation and phagocytic activity were compared between parental Raw264.7 and Raw264.7/NF cells. Both serial bioluminescence imaging (BLI) and small animal positron emission tomography (PET) imaging with I-124 were performed in inflammation-induced mice at various time points after intravenous injection of either Raw264.7 or Raw264.7/NF cells.

RESULTS

There was no significant difference in cellular proliferation and phagocytic activity between parental Raw264.7 and Raw264.7/NF cells. Early distribution of Raw264.7/NF cells was successfully visualized in the lung and spleen by BLI, but not by I-124 PET imaging. BLI signals, but not PET signals, were observed from the inflammation site at day 4 after the injection of Raw264.7/NF cells, and the signal intensity gradually increased until day 8. In contrast, focal uptake of I-124 was first detected at the site of inflammation at postinjection day 8, and signal intensity from the inflamed lesion was highest at that time point. While visualization of the inflamed lesion was possible by both BLI and PET imaging until day 14, it was only possible by BLI until day 21 after injection.

CONCLUSIONS

Tracking of macrophage migration toward inflammation foci was successfully achieved in vivo from early time points by dual reporter gene imaging with a combination of nuclear and optical reporters. Multimodal reporter imaging of macrophages might successfully overcome the limitations of single reporter gene imaging in preclinical models of inflammation.

Trafficking macrophage migration using reporter gene imaging with human sodium iodide symporter in animal models of inflammation

The aim of this study was to investigate the feasibility of nuclear molecular imaging using the human sodium iodide symporter (hNIS) as a reporter gene to monitor macrophage migration toward the inflammatory foci.

METHODS

A stable macrophage cell line coexpressing hNIS and green fluorescent protein (GFP) genes (RAW264.7/hNIS-GFP and R(NIS) cell) was established from an immortalized macrophage cell line (RAW264.7 cells). (125)I uptake was determined (for hNIS protein functional activity), and flow cytometry analysis (to examine GFP gene expression), a cell proliferation assay, a cytokine assay, and a phagocytic activity assay were performed. (99m)Tc-pertechnetate images were acquired at 1 d after subcutaneous inoculation of R(NIS) cells in nude mice. Chemical inflammation was induced for in vivo imaging in the thigh of nude mice by turpentine oil injection. Small-animal PET with (18)F-FDG and (124)I was performed with an intravenous administration of RAW264.7 or R(NIS) cells in inflammation-induced animals.

RESULTS

The expression of hNIS and GFP genes was confirmed in R(NIS) cells by flow cytometry and immunofluorescent staining. (125)I uptake was about 67 times higher in R(NIS) cells than in RAW264.7 cells. No significant difference was observed in cell proliferation, cytokine production, and phagocytic activity between RAW264.7 and R(NIS) cells. (99m)Tc-pertechnetate imaging revealed increased tracer uptake at the inoculation site. PET with (124)I demonstrated a donut-shaped uptake, correlating with uptake shown by the (18)F-FDG PET images, at the inflammation site of mice administered R(NIS) cells. (124)I uptake (percentage injected dose per gram) was about 2.12 times higher at the inflammation site in the R(NIS) mice than in RAW264.7 mice. By immunohistochemistry, the migration of macrophages was further confirmed by positive staining for GFP and hNIS at the inflammation site of R(NIS) mice.

CONCLUSION

These data support the feasibility of hNIS reporter gene imaging to monitor the macrophage migration toward an inflammatory lesion. Macrophages expressing hNIS may provide a new strategy to investigate the cellular behavior seen with inflammatory response in a preclinical model.

Effects of new peritoneal dialysis solutions on leukocyte recruitment in the rat peritoneal membrane

OBJECTIVES

Peritonitis remains a principal cause of dropout in peritoneal dialysis (PD). The physiological host response to a peritoneal infection involves a rise in numbers of circulating leukocytes to the peritoneal cavity. We evaluated the effects of (1) conventional peritoneal dialysis fluid (PDF), (2) bicarbonate-based PDF, low in glucose degradation products, and (3) non-glucose PDF on peritoneal leukocyte recruitment in response to an inflammatory stimulus using intravital microscopy.

METHODS

The visceral peritoneum was exposed to EBSS, conventional lactate-buffered and bicarbonate/lactate-buffered glucose-based PDF and three lactate-buffered non-glucose PDF-icodextrin, amino acid-based PDF and amino acid/glycerol-based PDF. The number of rolling, adhering and extravasated leukocytes and leukocyte rolling velocity was assessed at different time intervals after stimulation with lipopolysaccharide (LPS).

RESULTS

Exposure to LPS dissolved in EBSS dramatically increased the number of rolling, adhering and extravasated leukocytes and decreased leukocyte rolling velocity. Conventional PDF completely abolished LPS-induced leukocyte recruitment. Bicarbonate/lactate-buffered PDF only minimally affected the process of leukocyte recruitment, whereas icodextrin PDF resulted in partial inhibition of the immune response. The amino acid-based and the amino acid/glycerol-based PDF inhibited leukocyte recruitment to a similar extent as conventional PDF.

CONCLUSIONS

Bicarbonate/lactate-buffered PDF has superior biocompatibility towards peritoneal host defense, in spite of its high glucose concentrations. Lactate-buffered non-glucose containing PDF has substantial inhibitory effects on leukocyte recruitment, indicating that the bioincompatibility of high lactate concentrations and/or low pH may not be underestimated.

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions. Patients treated with peritoneal dialysis (PD) are at risk for development of ultrafiltration failure and peritonitis. These two significant complications can result in the termination of PD treatment. The relative unphysiologic composition of the currently used standard peritoneal dialysis fluids (PDF) is considered to be a major cause for the development of morphologic changes of the peritoneal membrane, ultimately resulting in ultrafiltration failure and probably contributing to changes in local defense mechanisms with the associated increased risk of peritonitis. In recent years, a major research focus has become the development of new and improved PD solutions. This has resulted in the development of an amino-acid-based PDF, a glucose polymer-based PDF, and several bicarbonate-buffered PDF. Typically, the first phase of biocompatibility testing of new PD solutions involves in vitro testing, employing isolated cells such as peritoneal macrophages or cell culture systems using human peritoneal mesothelial cells. The results of such evaluations are useful in providing insights into the biocompatibility performance of any given formulation, but suffer from several disadvantages, which can be better addressed using animal models. In vivo studies using animals permit the analysis of biocompatibility under conditions that allow for cell-to-cell interactions and dynamic changes in solution composition that more closely mimic the clinical situation. In this paper, we will review the use of animal models for the study of PDF biocompatibility and their application to the assessment of bicarbonate-buffered PDF.