Bad and good growth factors in the peritoneal cavity (Review Article)

Progressive peritoneal membrane fibrosis, and associated loss of ultrafiltration and dialysis capacity, is an increasingly limiting problem with time on peritoneal dialysis. The primary culprit is the composition of the peritoneal dialysate, although episodes of peritonitis can hasten the process. At a molecular level, there is increasing evidence that several growth factors play key roles in the development of peritoneal membrane fibrosis. Transforming growth factor (TGF)-beta is widely implicated in pathological fibrosis, and a considerable body of evidence favours a similar role in the peritoneal membrane. Connective tissue growth factor (CTGF), a downstream mediator of TGF-beta-induced fibrosis, has more recently been implicated in peritoneal membrane scarring. In contrast to the pleiotropic effects of TGF-beta, CTGF more specifically targets the fibrosis pathway, and so is an attractive candidate for inhibiting the damage to the membrane. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has also been found in the peritoneal cavity, but its effect on peritoneal mesothelial cells suggests that it has a positive role in guiding membrane repair and avoiding pathological fibrosis. In the future, it is hoped that changes in peritoneal dialysis technology will create a better balance between the bad and good effects of these growth factors, which in turn will lead to more successful long-term outcomes for this major renal replacement therapy.

Impact of hemodialysis on endogenous plasma and muscle carnitine levels in patients with end-stage renal disease

BACKGROUND

End-stage renal disease (ESRD) patients undergoing hemodialysis treatment have reduced plasma L-carnitine levels; however, the relationship between dialysis age and carnitine status is poorly understood. This study examined the relationship between duration of dialysis and plasma and skeletal muscle concentrations of L-carnitine and its esters in ESRD patients.

METHODS

Blood samples were collected from 21 patients at baseline and throughout the first 12 months of hemodialysis. In 5 patients, muscle samples were obtained after 0, 6, and 12 months of hemodialysis. Blood and muscle samples were collected from an additional 20 patients with a mean dialysis age of 5.10 years. L-carnitine, acetyl-L-carnitine, and total L-carnitine were measured by high-performance liquid chromatography (HPLC).

RESULTS

The mean +/- SD plasma L-carnitine concentration in ESRD patients who had not yet started hemodialysis was 50.6 +/- 20.0 micromol/L. Significantly lower concentrations were observed after 12 months (29.7 +/- 10.5 micromol/L) and >12 months (22.0 +/- 5.4 micromol/L) of hemodialysis treatment. Acetyl-L-carnitine also declined with dialysis age, while plasma nonacetylated acylcarnitines continued to increase with the progression of hemodialysis therapy. An inverse relationship between dialysis age and muscle L-carnitine concentrations was observed.

CONCLUSION

Long-term hemodialysis treatment is associated with a significant reduction in endogenous plasma and muscle L-carnitine levels and a significant increase in plasma acylcarnitines. The majority of the change in plasma L-carnitine concentrations occurs within the first few months of hemodialysis, while muscle levels continue to decline after 12 months of treatment.

Connective tissue growth factor and its regulation in the peritoneal cavity of peritoneal dialysis patients

BACKGROUND

Connective tissue growth factor (CTGF) is a fibrogenic cytokine that is highly expressed in wound healing and fibrotic lesions. The role of transforming growth factor-beta (TGF-beta) in fibrosis is well documented, and the emerging understanding that its fibrogenic actions are mediated through CTGF has provided an attractive target molecule for the modulation of matrix overproduction in fibrotic disease. The involvement of CTGF in the pathogenesis of peritoneal membrane fibrosis in peritoneal dialysis (PD) patients has not been investigated, and so the aim of this study was to ascertain whether CTGF is produced in the peritoneal cavity of PD patients and to investigate its regulation by cytokines.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), Northern blotting, and Western blotting were used to study CTGF expression by cultured human peritoneal mesothelial cells (HPMC) from peritoneal dialysis patients. Western blotting was used to detect CTGF expression in spent peritoneal dialysate from patients with and without peritonitis.

RESULTS

RT-PCR analysis demonstrated the expression of CTGF mRNA in cultured primay HPMCs isolated from spent peritoneal effluent. The production of the major 36 to 38 kD CTGF protein doublet by HPMC in addition to a 23 to 25 kD proteolytically processed form was confirmed by Western blotting. Several molecular weight forms of CTGF (18 to 38 kD) were also detected by Western blotting in peritoneal dialysate, with levels markedly elevated during episodes of peritonitis. Northern and Western blot analysis revealed that CTGF mRNA and protein production by HPMC was up-regulated by TGF-beta, with mRNA levels significantly increasing above the control (P < 0.01). In contrast, platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and tumor necrosis factor-alpha (TNF-alpha) had no measurable effects on CTGF mRNA expression.

CONCLUSION

These results are the first to demonstrate the production of CTGF by HPMC and its presence in the peritoneal cavity of PD patients. The marked increase in CTGF levels by factors implicated in the development of peritoneal membrane fibrosis suggests its involvement in the underlying pathophysiologic mechanism(s).

Laparoscopic placement of peritoneal dialysis catheters: 7 years experience

BACKGROUND

Since 1994 we have placed all peritoneal dialysis (Tenckhoff) catheters at our hospital laparoscopically using a technique that incorporates suture fixation into the pelvis. The purpose of this study was to determine the long-term outcome of this approach.

METHOD

Perioperative and follow-up data for all patients undergoing placement of a peritoneal dialysis catheter at the Royal Adelaide Hospital were collected prospectively and managed on unit specific and hospital wide computerized databases. A total of 148 procedures were carried out in 123 patients from March 1994 to November 2001. Follow-up ranged from 3 to 68 months (median, 42 months). All procedures were undertaken or supervised by one surgeon, and catheters were routinely sutured into the pelvis at laparoscopy.

RESULTS

There was no perioperative mortality in this series, and only one catheter could not be placed laparoscopically. This was in a patient with extensive intra-abdominal adhesions. Mean operative time was 27 min (range, 10-100 min), and mean postoperative stay was 2.8 days (range, 1-12 days). Seven (5%) patients experienced peri/postoperative haemorrhage, and four of these underwent surgical re-exploration. Twenty-five (17%) catheters are still used for dialysis. Thirty-four (23%) catheters were removed when the recipient received a subsequent renal transplant, and 42 (28%) patients died during follow-up. Forty-six (31%) patients required catheter revision or removal because of technical problems; 26 (18%) recurrent peritonitis or exit site infection; and 20 (14%) catheter blockage. Twenty-eight reinsertion procedures were carried out in 25 patients. Ten (7%) patients developed port site hernias at late follow-up, and required hernioplasty. Catheter migration leading to malfunction (poor drainage) occurred in eight (5%) patients only.

CONCLUSIONS

Laparoscopic placement of peritoneal dialysis catheters is a safe and effective procedure. The majority of patients will dialyse successfully using this technique. Suturing the catheter tip into the pelvis is associated with a low rate of catheter migration.

Expression of defensin antimicrobial peptides in the peritoneal cavity of patients on peritoneal dialysis

OBJECTIVE

To investigate the expression and regulation of defensins in the peritoneal cavity of peritoneal dialysis (PD) patients.

DESIGN

The presence of defensins in the peritoneal cavity was assessed using reverse transcription polymerase chain reaction (RT-PCR). In vivo defensin expression was analyzed in human peritoneal membrane biopsies and in peritoneal cavity leukocytes isolated from spent dialysate. Defensin expression in vitro was assessed in cultured human peritoneal mesothelial cells (HPMC) and confirmed with PCR Southern blot and DNA sequencing. The effect of tumor necrosis factor alpha (TNFalpha) and epidermal growth factor (EGF) on beta2 defensin expression in HPMC was analyzed by Northern blot analysis and RT-PCR respectively.

RESULTS

Both alpha and beta classes of defensins are expressed in the peritoneal cavity of PD patients. Messenger RNA for the alpha-defensin human neutrophil peptide 3 and for beta-defensin-1 (hbetaD-1) were found in preparations containing predominantly peritoneal leukocytes, whereas beta-defensin-2 (hbetaD-2) is expressed by HPMC. HPMC isolated from different individuals displayed variability in both basal hbetaD-2 expression and in response to stimulation by TNFalpha. Conversely, EGF consistently downregulated the level of hbetaD-2 message in HPMC.

CONCLUSION

Alpha- and beta-defensins are expressed in the peritoneal cavity, and hbetaD-2 is the main defensin present in the peritoneal membrane. Variable levels of expression of hbetaD-2 by mesothelial cells were seen, with evidence of regulation by cytokines and growth factors. This provides evidence for a previously unknown mechanism of innate immunity at that site.

HB-EGF is produced in the peritoneal cavity and enhances mesothelial cell adhesion and migration

BACKGROUND

The mesothelial cell monolayer lining the peritoneal membrane needs constant repair in response to peritonitis and to the toxicity of peritoneal dialysate. In many continuous ambulatory peritoneal dialysis (CAPD) patients, the repair process progressively fails, and membrane dysfunction and fibrosis occur. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has an important role in wound repair and is also fibrogenic, and thus may be involved in these processes in the peritoneal cavity.

METHODS

The presence of HB-EGF, its receptors, and its associated proteins was determined in peritoneal membrane biopsies, cultured human peritoneal mesothelial cells (HPMCs), and peritoneal macrophages from CAPD patients by reverse transcription-polymerase chain reaction, flow cytometry, and immunofluorescence immunocytochemistry with confocal microscopy. HB-EGF effects on HPMC adhesion were measured by a static adhesion assay, on integrin expression by flow cytometry, and on migration by wound healing and chemotaxis assays.

RESULTS

HB-EGF, its receptors HER-1 and HER-4, and the associated proteins CD9, CD44, and integrin alpha(3)beta(1) were expressed by HPMCs and peritoneal macrophages. HB-EGF colocalized with HER-1 and HER-4 in HPMCs and induced their adhesion to collagen type I, expression of beta 1 integrins, and migration.

CONCLUSIONS

HB-EGF is produced by cells in the peritoneal cavity of CAPD patients and has functional effects on HPMCs that would facilitate repair of the mesothelial layer.

Excellent long-term graft survival in low risk, primary renal allografts treated with prednisolone-avoidance immunosuppression

Primary avoidance of oral corticosteroids for renal transplant recipients is uncommon. The South Australian renal transplant service used a double therapy (DT) regimen of cyclosporin and azathioprine from August 1986 to July 1996 for low risk (first graft, PRA < 50%) allografts. Oral corticosteroid, prednisolone (P), was reserved for severe rejection or two mild rejection episodes, but could be later withdrawn at the physician's discretion. This regimen is associated with more early acute rejection (Russ et al., Clin Transplant 1990: 4: 26). We have now analysed long-term patient survival (PS) and graft survival (GS) for this group. Of 448 transplants in South Australia between August 1986 and July 1996, 295 commenced DT regimen. Ninety-four (31.8%) never received P at any stage post-transplantation (group 1), 96 (32.5%) were placed on P and later weaned (group 2), and 97 (33%) remained on long-term P (group 3). Technical losses, eight (2.7%), within 30 d of transplantation, were excluded from sub-group analysis. PS for the total DT cohort at 1, 5 and 9 yr post-transplantation was 97, 88 and 74%, respectively. GS over the same time period was 88, 75 and 55%, respectively. There was no statistically significant difference in survival compared to other 'low risk' grafts in the rest of Australia during the same time period. Mean serum creatinine concentration (CrC) for the DT group at 3 and 6 months and 1, 3, 5 and 10 yr was not significantly different to the rest of the Australian 'low risk' grafts. In the DT cohort, there were 334 acute rejections ( < 90 d) in 206 patients (70%), but only 42 (12.5%) required anti-lymphocyte antibody therapy (OKT3 or ATG) for rejection. PS at 9 yr was not statistically significantly different between groups 1 and 2, but both groups survived better than group 3 (p < 0.0043). GS for group 1 at 1, 5 and 9 yr post-transplantation was 90, 81 and 73%, respectively; for group 2, 98, 87 and 66%, respectively; and for group 3, 84, 63 and 29%, respectively. Statistical significance was reached in group 1 versus 3 (p < 0.001) and group 2 versus 3 (p < 0.001). In summary, a DT regimen in low risk, first renal allografts gives excellent long-term patient and GS and minimises long-term P, despite a high rate of early acute rejection.

Clozapine-induced acute interstitial nephritis

Drug hypersensitivity reactions commonly cause acute interstitial nephritis (AIN). Clozapine, a new antipsychotic, can cause fatal bone-marrow toxicity. We report clozapine-induced AIN as another serious adverse drug reaction.

Epidermal growth factor modifies the expression and function of extracellular matrix adhesion receptors expressed by peritoneal mesothelial cells from patients on CAPD

BACKGROUND

Efficient peritoneal dialysis depends on an intact layer of mesothelial cells that line the peritoneal membrane. This layer is disrupted in patents on continuous ambulatory peritoneal dialysis during episodes of peritonitis (acute injury) and replaced by fibrous tissue during extended dialysis (chronic injury). Little is understood of human peritoneal mesothelial cell (HPMC) responses to wounding and episodes of peritonitis.

METHODS

HPMC were harvested from spent peritoneal dialysis effluent and maintained under defined in vitro conditions. Adhesive interactions with extracellular matrix (ECM) molecules and chemotactic and wound-healing responses were measured in vitro using purified ECM molecules.

RESULTS

HPMC express multiple functional cell receptors recognizing and binding to ECM molecules, including several members of the integrin family. HPMC exhibit directed migration in wound healing and chemotaxis assays with ECM molecules. Epidermal growth factor (EGF) stimulates a reversible change to a fibroblastic phenotype, accompanied by increased expression of beta1 integrins, particularly alpha2beta1, increased adhesion to type I collagen, and significantly greater HPMC migration on type I collagen in wound healing and chemotaxis assays.

CONCLUSIONS

HPMC possess the migratory capacity to contribute to the efficient repair of damaged peritoneal membrane after acute injury, and growth factors, such as EGF, facilitate peritoneal membrane healing by augmenting cell adhesion and migration.

During human thymic development, beta 1 integrins regulate adhesion, motility, and the outcome of RHAMM/hyaluronan engagement

During human thymic differentiation, interactions between fibronectin (Fn)/beta1 integrins and hyaluronan (HA)/RHAMM control motility and Fn/beta1 integrins mediate spontaneous Fn-dependent adhesion. Multinegative (MN, CD3-4-8-) thymocytes exhibit strong spontaneous adherence to Fn (75%) that was efficiently inhibited by anti-alpha5beta1 and only weakly inhibited by anti-alpha4beta1. The relatively weak adherence of unfractionated thymocytes to Fn required both alpha4beta1 and alpha5beta1. Video time-lapse microscopy indicates that a subset of thymocytes also undergo spontaneous Fn-dependent motility mediated by alpha5beta1, alpha4beta1, and the HA-receptor RHAMM, but not by CD44. The loss of motility after hyaluronidase treatment of thymocytes indicated that motility is strongly dependent on HA. Of motile cells, 55% were DP, 19% were DN, and 24% were CD4+SP, but only 1% were CD8+SP. Overall, for MN thymocytes, beta1 integrin mediated Fn-adhesion, but after expression of CD4/CD8, beta1 integrins mediated Fn-dependent motility. Treatment with the activating anti-beta1 mAb QE.2E5 inhibited thymic motility and converted otherwise nonadherent thymocytes to an adherent state. High-avidity interactions via integrins appear to supercede the motogenicity of RHAMM and HA, suggesting that integrin avidity may regulate RHAMM. During thymic development, changes in adhesion or motility appear to be mediated by integrin avidity modulation.

A novel activating anti-beta1 integrin monoclonal antibody binds to the cysteine-rich repeats in the beta1 chain

The functional status of an integrin depends on the conformation of its extracellular domain, which is controlled by the cell expressing that receptor. The transmission of regulatory signals from within the cell is considered to be via propagated conformational changes from the receptor's cytoplasmic tails to the extracellular ligand binding "pocket." The end result is increased accessibility of the ligand binding pocket in the high affinity ("active") form of integrins. We report a novel monoclonal antibody (QE.2E5) that binds within the cysteine-rich repeats in the integrin beta1 chain and induces high affinity binding of fibronectin to the integrin alpha5beta1. The QE.2E5 epitope is located approximately 200 residues both from the predicted binding site for fibronectin and from the epitopes recognized by other activating anti-beta1 monoclonal antibodies. It is also expressed on beta1 integrins from a number of nonhuman species. Although they have the same functional effects, the binding of QE.2E5 and another activating antibody (8A2) to the receptor have contrasting effects on the expression of an activation-dependent epitope in the beta1 chain. We propose that the cysteine-rich repeats contain a regulatory region that is distinct from those previously described in the integrin beta1 chain.

Changes in the expression of adhesion molecules as peripheral blood monocytes differentiate into peritoneal macrophages

Peritoneal macrophages, derived from peripheral blood monocytes, are the chief cellular defenders against invasion of the peritoneal cavity by infectious organisms. Monocyte migration into the peritoneal cavity depends upon a coordinated series of adhesive events, utilizing cell surface receptors known as adhesion molecules. In order to better understand the mechanisms of leucocyte infiltration of the peritoneum during peritonitis, we studied the relative expression of adhesion molecules on monocytes and peritoneal macrophages from patients on continuous ambulatory peritoneal dialysis (CAPD). Peripheral blood and spent peritoneal dialysis fluid were obtained from patients undergoing CAPD, and the level of expression of various adhesion molecules on the monocytes/macrophages analysed by flow cytometry using receptor-specific monoclonal antibodies. Monocytes were also purified from the peripheral blood of volunteer donors, cultured in vitro for varying periods, and analysed in the same manner. Consistent differences in expression of certain adhesion molecules were found between monocytes and peritoneal macrophages, and similar changes occurred on monocytes cultured in vitro. Concurrent infection had no clear effect. Several receptors (integrins alpha 4 beta 1, alpha 6 beta 1, alpha L beta 2 and alpha IIb beta 3, and platelet endothelial cell adhesion molecule-1) were significantly decreased on peritoneal macrophages, while only the integrin alpha v beta 5 increased. It is concluded that monocyte differentiation into peritoneal macrophages is accompanied by characteristic alterations in the adhesion molecule repertoire on the cell surface, emphasizing the different adhesive requirements of these two cell types.

Inside-out signaling through integrins

Rapid and yet precisely controlled changes in cell adhesion are a hallmark of a number of basic physiological processes. Many of these processes directly impact upon nephrology, including: (1) cell migration, which occurs during leukocyte infiltration into inflammatory sites (e.g., in glomerulonephritis, interstitial nephritis, and renal transplant rejection) and during embryogenesis (e.g., in development of the genitourinary system): and (2) platelet aggregation at sites of clot formation (e.g., in glomerulonephritis). The integrins are a family of adhesion molecules whose function is controlled by the cells that express them, and this properly makes them eminently suitable receptors for those situations that demand flexibility of the cellular adhesive phenotype. The control of integrin function occurs via regulatory signals that originate within the cell cytoplasm and are then transmitted to the external ligand-binding domain of the receptor. The generation and transmission of these "inside-out" signals are the subjects of intensive research that will be summarized in this review article.

Dynamic regulation of integrins

Dynamic regulation of receptor function is a distinguishing feature of the integrin family of adhesion molecules and makes a significant contribution to alterations in cellular adhesive properties. The best characterized example is that of the platelet receptor alpha IIb beta 3 (glycoprotein IIb-IIIa), which does not bind soluble fibrinogen on resting platelets. Following platelet activation, the alpha IIb beta 3 binds soluble fibrinogen with moderately high affinity and platelet aggregation ensues. Similar regulation of receptor function has also been directly demonstrated for alpha 5 beta 1 and alpha M beta 2, and it is likely that it is a general property of all members of the family. The altered ligand binding affinity is due to a change in the conformation of the external domain of the receptor, in response to intracellular signals that are transmitted the length of the molecule. The cytoplasmic tails of the integrins are active participants in this regulation, and they also mediate interactions with the cytoskeleton. A number of anti-integrin monoclonal antibodies have been described which induce high affinity ligand binding, and certain of these preferentially bind to the high affinity conformation of the receptor. The alteration in conformation allows better access for macromolecular ligands to the ligand binding pocket, which has been mapped (in alpha IIb beta 3) to the amino terminal globular head of the receptor. The precise mechanism by which the activating signal is transferred from within the cell to the distal external domain remains the subject of active research.

Stimulation of integrin-mediated adhesion of T lymphocytes and monocytes: two mechanisms with divergent biological consequences

We show that the adhesion of T lymphoid cells to immobilized fibronectin can be increased by two distinct mechanisms. The first is by increasing the affinity of the fibronectin receptor/ligand interaction using the anti-beta 1 integrin monoclonal antibody 8A2. The second is by treating the cells with phorbol 12-myristate 13-acetate (PMA), which alters events that occur after receptor occupancy (e.g., cell spreading) without affecting receptor affinity. The effects of these two mechanisms on adhesion in the presence of physiological concentrations of soluble fibronectin suggest that they have different biological consequences. Under these conditions, the net effect of increasing the affinity of the fibronectin receptors is to decrease cell adhesion, whereas the increase in adhesion induced by PMA is unaffected. This suggests that the high affinity receptors are not primarily available for cell adhesion under these circumstances, and that they have an alternative function. We further show that high affinity binding of soluble fibronectin can be induced by either differentiation of the monocytic cell line THP-1 or by cross-linking the T cell receptor complexes on the T lymphoid cell line HUT-78. The differentiated monocytic cells express two populations of fibronectin receptors: a minority in a high affinity state, and the majority in a low affinity state. Thus they will both continue to adhere in the presence of physiological concentrations of soluble fibronectin and bind significant amounts of soluble fibronectin at the cell surface.