Proteoglycans of CAPD-dialysate fluid and mesothelium

Dialysate Markers of Peritoneal Tissue during Peritonitis and in Stable Capd

Objective

To investigate whether dialysateconcentrations of substances that are locally produced within the peritoneal cavity can be used to study the effects of inflammation on peritoneal tissue.

Design

We followed the appearance rates (AR) of concentrations of cancer antigen (CA) 125, phospholipids (PHL), hyaluronan (HA), and the procollagen peptides PICP (procollagen 1 C-terminal) and PIIINP (procollagen 3 N-terminal) in dialysate during peritonitis (8 consecutive days) and after recovery. Data were compared with the stable situation.

Setting

CAPD (continuous ambulatory peritoneal dialysis) unit in the Academic Medical Center in Amsterdam.

Patients

Twelve CAPD patients with a total of 16 episodes of peritonitis and 10 clinically stable CAPD patients were studied.

Results

All substances showed temporal increments in dialysate during peritonitis compared to control. No difference was found between the control day of peritonitis and the stable patients. Maximum AR were reached in the acute phase of peritonitis for CA 125, PHL, and HA and on day 4 for both PICP and P111NP. A second increment in CA125 occurred on days 4 to 6. These findings indicate acute damage to the mesothelium (CA 125) and other cells (PHL) by the infection. HA may reflect stromal changes. Subsequently, peritoneal healing (PICP, PIIINP) and remesothelialization (second peak CA125) are likely to occur.

Conclusions

Dialysate concentrations of these substances can be used as markers for the effects of peritonitis on the peritoneum of CAPD patients in vivo. The similarity between the marker concentrations in the effluent after recovery from peritonitis and those in stable CAPD patients implies that complete peritoneal healing is likely to occur after uncomplicated peritonitis.

Synthesis of Hyaluronic Acid by Human Peritoneal Mesothelial Cells: Effect of Cytokines and Dialysa Te

Objective

To assess effects of the inflammatory cytokines (IL-1-beta, TNF-alpha, TGF-beta 1) and dialysate effluent on synthesis of hyaluronic acid by human peritoneal mesothelial cells (HMC) in in vitro culture.

Methods

Dialysate effluent was collected after the overnight dwell of DianeaI 1.5% from patients during CAPD training. HMC were obtained from omentum from nonuremic donors or were harvested from the dialysate effluent from CAPD patients. Synthesis of hyaluronic acid was studied on monolayers of HMC, which were deprived of serum 48 hours priortoexperiment. Effects of cytokines were tested in a medium with low serum concentration (0.1%) or in medium mixed (1:1 v/v) with the autologous dialysate. Hyaluronic acid level in medium was measured with radioimmunoassay.

Results

Cytokines enhanced synthesis of hyaluronic acid by HMC, and the strongest effect was induced by IL-1. Effluent dialysate stimulates synthesis of hyaluronic acid stronger than 10% FCS. Effluent dialysate and IL-1 synergistically enhance synthesis of hyaluronic acid by HMC.

Conclusion

Effluent dialysate from CAPD patients stimulates production of hyaluronic acid by HMC and acts synergistically with cytokines.

Dialysate Markers of Peritoneal Tissue during Peritonitis and in Stable CAPD

Objective

To investigate whether dialysate concentrations of substances that are locally produced within the peritoneal cavity can be used to study the effects of inflammation on peritoneal tissue.

Design

We followed the appearance rates (AR) of concentrations of cancer antigen (CA) 125, phospholipids (PHL), hyaluronan (HA), and the procollagen peptides PICP (procollagen 1 C-terminal) and PIIINP (procollagen 3 N-terminal) in dialysate during peritonitis (8 consecutive days) and after recovery. Data were compared with the stable situation.

Setting

CAPD (continuous ambulatory peritoneal dialysis) unit in the Academic Medical Center in Amsterdam.

Patients

Twelve CAPD patients with a total of 16 episodes of peritonitis and 10 clinically stable CAPD patients were studied.

Results

All substances showed temporal increments in dialysate during peritonitis compared to control. No difference was found between the control day of peritonitis and the stable patients. Maximum AR were reached in the acute phase of peritonitis for CA 125, PHL, and HA and on day 4 for both PICP and P111NP. A second increment in CA125 occurred on days 4 to 6. These findings indicate acute damage to the mesothelium (CA 125) and other cells (PHL) by the infection. HA may reflect stromal changes. Subsequently, peritoneal healing (PICP, PIIINP) and remesothelialization (second peak CA125) are likely to occur.

Conclusions

Dialysate concentrations of these substances can be used as markers for the effects of peritonitis on the peritoneum of CAPD patients in vivo. The similarity between the marker concentrations in the effluent after recovery from peritonitis and those in stable CAPD patients implies that complete peritoneal healing is likely to occur after uncomplicated peritonitis.

The Biology of the Mesothelium during Peritoneal Dialysis

Substantial derangements of mesothelial biology are observed during experimental simulations of dialysis conditions, inferred from the content of human dialysis effluent and visualized by microscopy of human mesothelial biopsies. Canosmotically active solutions be made biocompatible with the osmoregulatory system of the mesothelium? Can the contributions of the mesothelium to host defenses against inflammation and/or infection be supported during CAPD? Do underlying metabolic derangements present in various kidney diseases and end-stage renal disease, regardless of cause, require customized CAPD protocols and solutions? Use of dialysis solutions less directly toxic to the mesothelium is a necessary step toward some day manipulating peritoneal biology by pharmacological and therapeutic modalities.

Peritoneal Proteoglycans: Much more than Ground Substance

Recent advances in the field of glycobiology have exposed a multitude of biological processes that are controlled or influenced by proteoglycans, in both physiological and pathological conditions ranging from early embryonic development, inflammation, and fibrosis to tumor invasion and metastasis. The first part of this article reviews the biosynthesis of proteoglycans and their multifunctional roles in health and disease; the second part of this review focuses on their putative roles in peritoneal homeostasis and peritoneal inflammation and fibrosis in the context of chronic peritoneal dialysis and peritonitis.

Peritoneal changes in patients on long-term peritoneal dialysis

Long-term peritoneal dialysis can lead to morphological and functional changes in the peritoneum. Although the range of morphological alterations is known for the peritoneal dialysis population as a whole, these changes will not occur in every patient in the same sequence and to the same extent. Longitudinal studies are therefore required to help identify which patients might develop the changes. Although longitudinal studies using peritoneal biopsies are not possible, analyses of peritoneal effluent biomarkers that represent morphological alterations could provide insight. Longitudinal studies on peritoneal transport have been performed, but follow-up has often been too short and an insufficient number of parameters have been investigated. This Review will firstly describe peritoneal morphology and structure and will then focus on peritoneal effluent biomarkers and their changes over time. Net ultrafiltration will also be discussed together with the transport of small solutes. Data on the peritoneal transport of serum proteins show that serum protein levels do not increase to the same extent as levels of small solutes with long-term peritoneal dialysis. Early alterations in peritoneal transport must be distinguished from alterations that only develop with long-term peritoneal dialysis. Early alterations are related to vasoactive mediators, whereas later alterations are related to neoangiogenesis and fibrosis. Modern peritoneal dialysis should focus on the early detection of long-term membrane alterations by biomarkers--such as cancer antigen 125, interleukin-6 and plasminogen activator inhibitor 1--and the improved assessment of peritoneal transport.

Pathophysiological changes to the peritoneal membrane during PD-related peritonitis: the role of mesothelial cells

The success of peritoneal dialysis (PD) is dependent on the structural and functional integrity of the peritoneal membrane. The mesothelium lines the peritoneal membrane and is the first line of defense against chemical and/or bacterial insult. Peritonitis remains a major complication of PD and is a predominant cause of technique failure, morbidity and mortality amongst PD patients. With appropriate antibiotic treatment, peritonitis resolves without further complications, but in some PD patients excessive peritoneal inflammatory responses lead to mesothelial cell exfoliation and thickening of the submesothelium, resulting in peritoneal fibrosis and sclerosis. The detrimental changes in the peritoneal membrane structure and function correlate with the number and severity of peritonitis episodes and the need for catheter removal. There is evidence that despite clinical resolution of peritonitis, increased levels of inflammatory and fibrotic mediators may persist in the peritoneal cavity, signifying persistent injury to the mesothelial cells. This review will describe the structural and functional changes that occur in the peritoneal membrane during peritonitis and how mesothelial cells contribute to these changes and respond to infection. The latter part of the review discusses the potential of mesothelial cell transplantation and genetic manipulation in the preservation of the peritoneal membrane.

Pathophysiology of the peritoneal membrane during peritoneal dialysis: the role of hyaluronan

During peritoneal dialysis (PD), constant exposure of mesothelial cells to bioincompatible PD solutions results in the denudation of the mesothelial monolayer and impairment of mesothelial cell function. Hyaluronan, a major component of extracellular matrices, is synthesized by mesothelial cells and contributes to remesothelialization, maintenance of cell phenotype, and tissue remodeling and provides structural support to the peritoneal membrane. Chronic peritoneal inflammation is observed in long-term PD patients and is associated with increased hyaluronan synthesis. During inflammation, depolymerization of hyaluronan may occur with the generation of hyaluronan fragments. In contrast to native hyaluronan which offers a protective role to the peritoneum, hyaluronan fragments exacerbate inflammatory and fibrotic processes and therefore assist in the destruction of the tissue. This paper will discuss the contribution of mesothelial cells to peritoneal membrane alterations that are induced by PD and the putative role of hyaluronan in these processes.

Peritoneal fluid markers of mesothelial cells and function

Peritoneal structural changes are likely to result in functional deterioration of the peritoneal membrane. For the purpose of early detection of these changes, markers of mesothelial cells that can be measured in peritoneal effluent could provide easily accessible information in individual peritoneal dialysis (PD) patients. In this review, current knowledge on a number of these markers is summarized, such as cancer antigen (CA) 125, phospholipids, hyaluronan, and factors involved in the coagulation system. Although only analyzed in limited studies so far, this approach to understanding changes in the peritoneal membrane seems to be valid and warrants further evaluation in the future, especially in combination with functional studies and peritoneal biopsies.

Characterization of proteoglycans produced by rat pleural mesothelial cells in vitro

The mesothelial cell envelopes the surface of the parietal and visceral pleura. These cells are known to synthesize most of the protein constituents of the pleural basement membrane and interstitium. This study examined the ability of a rat pleural mesothelial cell line to synthesize proteoglycans in vitro. Cells were labeled with inorganic 35SO4 to label the glycosaminoglycan moiety of proteoglycans. The medium and combined cell membrane/extracellular matrix fractions contained 73 and 25% of the proteoglycan radioactivity, respectively. The medium contained a single chondroitin/dermatan sulfate proteoglycan of approximately 190 kDa, consistent with biglycan. As determined by Northern analysis of steady-state levels of messenger RNA, the cells contained message for biglycan. Stimulation of the cells with epidermal growth factor resulted in the appearance of a second chondroitin/dermatan sulfate proteoglycan of approximately 97 kDa, characteristic of decorin. The cell membrane/matrix contained a biglycan-like chondroitin/dermatan proteoglycan and several heparan sulfate proteoglycans. Pleural mesothelial cells in vitro are capable of synthesizing a variety of interstitial and basement membrane proteoglycans.