Telomerase modulation in therapeutic approach

Telomerase is a specialized enzymatic complex responsible for the synthesis of telomeric repeats 5'-TTAGGG-3' localized at the ends of eukaryotic chromosomes. This mechanism prevents shortening of telomeres after each cell division. The enzyme is detected in about 85% of human tumors, but it is not expressed in normal cells or its expression is significantly lower. Consequently, it provides the cancer cells immortality. Thus, since showing cancer cell specificity (to a certain extent), the enzyme became a target for an adjuvant cancer therapy. So far, in vitro studies and preclinical studies seem to be promising. This work focuses on the pathways and mechanisms that are targeted in order to eliminate telomerase with consequence of cancer cell death. The anti-telomerase strategy may be beneficial especially in the context of sensitization of tumor cell to chemotherapeutic agents. We also indicate potential side effects and consequences of telomerase downregulation that should be considered when anti-telomerase strategy is undertaken. Alternatively, we also emphasize potential useful application of telomerase induction.

[Senescence of mesothelial cells]

The mesothelium is a specific group of cells having characteristics of both mesenchymal and epithelial cells. One of the most unique properties of these cells is a low proliferative capacity and a small number of achievable division. The purpose of this paper was to present the current state of knowledge on the causes of premature senescence of peritoneal mesothelial cells and to discuss the molecular events involved in this process. Particular attention was paid to the role of telomeres, the activity of senescence effectors at the level of the cell cycle, and the action of oxidative stress and transforming growth factor beta1. Moreover, the relationship between senescence of mesothelial cells and the aging of the organism as a whole, as well as the participation of senescent cells in the development of the intraperitoneal cancer metastasis was addressed.

Bacterial aging: from mechanistic basis to evolutionary perspective

Aging-defined as the progressive impairment of an organism's functional capacity, resulting from deleterious changes in cells, organs, and biological systems-is one of the most fundamental features of Eukaryotes, from humans to the unicellular budding yeast Saccharomyces cerevisiae. It has recently been reported that this may also be the case for certain (if not all) types of bacteria. In this paper, the current view on the mechanistic background and evolutionary significance of bacterial kind of aging is presented, with particular emphasis on the role of asymmetric cell division, the characteristics of stationary growth phase, and the role of oxidative protein damage.

Oxidative stress-dependent increase in ICAM-1 expression promotes adhesion of colorectal and pancreatic cancers to the senescent peritoneal mesothelium

Intercellular adhesion molecule-1 (ICAM-1) has been implicated in adhesion of colorectal and pancreatic cancer cells (of the SW480 and PSN-1 line, respectively) to the peritoneal mesothelium. It has been demonstrated that ICAM-1 expression increases with senescence in some cell types, however, the significance of this phenomenon in the context of malignant dissemination remains elusive. In this report we show that the adherence of SW480 and PSN-1 cells to senescent human omentum-derived mesothelial cells (HOMCs) in vitro is greater than to early-passage cells and that the effect is mediated by ICAM-1. Senescent HOMCs display increased expression of ICAM-1 mRNA and cell surface protein. The development of this phenotype is related to increased oxidative stress in senescent cells. The augmented ICAM-1 expression in HOMCs can be reduced by culturing cells with antioxidants; in contrast, exposure of HOMCs to an oxidant, t-BHP, leads to cellular senescence and increased ICAM-1 expression. The effect is partly mediated by activation of p38 MAPK and AP-1 signaling pathways. Finally, culture of HOMCs in the presence of a strong antioxidant, PBN, significantly reduces the senescence-associated increase in SW480 and PSN-1 cancer cell binding. These results indicate that increased oxidative stress and increased expression of ICAM-1 in senescent HOMCs may facilitate peritoneal adhesion of selected colorectal and pancreatic cancers.

[Oxidative stress as an universal cause of aging--from human somatic cells to the unicellular yeast and bacteria]

Oxidative stress is one of the major causes of aging considered at both the cellular and organismal levels. There is evidence that this agent may also constitute a common element connecting the aging of cells of higher organisms with a similar process occurring in eukaryotic and prokaryotic unicellulars. The aim of this paper was to present the current state of knowledge on the role of oxidative stress in aging of human somatic cells, human as a whole as well as the yeast Saccharomyces cerevisiae and bacteria Caulobacter crescentus, and Escherichia coli.

A comprehensive review on mesenchymal stem cell growth and senescence

In recent years mesenchymal stem cells (MSCs) have generated a great deal of excitement as an attractive alternative to embryonic stem cells (ESCs) in cell-based regenerative medicine. In contrast to cells of embryonic origin, however, the clinical application of MSCs is heavily restricted by their finite ability of self-renewal, in which they resemble the rest of the somatic cells. Yet the mechanisms controlling MSC proliferation and senescence remain unclear. This review summarizes recent advances in our understanding of the factors affecting MSC expansion in vitro and discusses the pattern of their senescence with particular emphasis on the role of telomere shortening, activation of effectory pathways, and oxidative stress. The issues associated with MSC growth and senescence will be shown in the context of other somatic cells, and all of the parallels and disparities will be delineated precisely.

Senescent peritoneal mesothelial cells promote ovarian cancer cell adhesion: the role of oxidative stress-induced fibronectin

Adhesion of ovarian cancer cells to the peritoneal mesothelium is a key step in the malignant progression of the disease. In an in vitro study, we showed that the adherence of ovarian cancer cells (of the OVCAR-3, SKOV-3, and A2780 cell lines) to senescent human omentum-derived peritoneal mesothelial cells (HOMCs) was greater than to early passage cells. The process was mediated primarily by the increased interaction of the alpha5beta1 integrin on cancer cells with HOMC-associated fibronectin (FN). In comparison with early passage HOMCs, senescent cells exhibited increased FN mRNA expression levels and produced significantly more FN. To assess the effect of senescence-associated oxidative stress on FN release, HOMCs were rendered senescent by exposure to an oxidant, tert-butyl hydroperoxide. Treatment with tert-butyl hydroperoxide resulted in a significant increase in HOMC FN mRNA and protein expression levels. The effect of oxidative stress on FN synthesis was found to be mediated by transforming growth factor-beta1, whose signaling pathway was controlled at upstream and downstream levels by p38 MAPK. The activity of p38 MAPK increased markedly in senescent HOMCs. Treatment of HOMCs with antioxidants significantly attenuated senescence-associated increases in p38 MAPK activity, production of both transforming growth factor-beta1 and FN, and ovarian cancer cell adhesion. These data indicate that oxidative stress that accompanies senescence may increase FN production by HOMCs and thus facilitate binding and dissemination of ovarian cancer cells.

Vulnerability to oxidative stress and different patterns of senescence in human peritoneal mesothelial cell strains

Both the ascites fluid-derived mesothelial cell line LP-9 and primary cultures of human omentum-derived mesothelial cells (HOMCs) are commonly used in experimental studies. However, they seem to have a different replicative potential in vitro. In the present study, we have attempted to determine the causes of this discrepancy. HOMCs were found to divide fewer times and enter senescence earlier than LP-9 cells. This effect was coupled with earlier increases in the expression of senescence-associated-beta-galactosidase and cell cycle inhibitors p16INK4a and p21WAF1. Moreover, almost 3 times as many early-passage HOMCs as LP-9 cells bore senescence-associated DNA damage foci. In sharp contrast to LP-9 cells, the foci present in HOMCs localized predominantly outside the telomeres, and the HOMC telomere length did not significantly shorten during senescence. Compared with LP-9 cells, HOMCs were found to enter senescence with significantly lower levels of lipofuscin and damaged DNA, and markedly decreased glutathione contents. In addition, early-passage HOMCs generated significantly more reactive oxygen species either spontaneously or in response to exogenous oxidants. These results indicate that compared with LP-9 cells, HOMCs undergo stress-induced telomere-independent premature senescence, which may result from increased vulnerability to oxidative DNA injury.

Senescence induces a proangiogenic switch in human peritoneal mesothelial cells

The incidence of cancers that metastasize to the peritoneum increases with age. Intraperitoneal cancer dissemination depends largely on angiogenesis and interactions with the peritoneal mesothelium. We assessed the proangiogenic potential of human peritoneal mesothelial cells. Conditioned media collected from these cells at senescence stimulated proliferation of endothelial cells to a significantly greater extent compared to media from early-passage cells. The effect was accompanied by a significantly increased release of proangiogenic mediators -- VEGF, CXCL1/GROalpha, CXCL8/IL-8, and CCL2/MCP-1. These results indicate that the senescent mesothelium exhibits increased angiogenic activity, which may contribute to accelerated intraperitoneal cancer progression in the aged.

Oxidative stress-mediated early senescence contributes to the short replicative life span of human peritoneal mesothelial cells

The replicative life span of cells in culture is thought to be determined by the gradually rising pool of senescent cells rather than by the simultaneous loss of proliferative capacity by all cells in the population. We found that early-passage cultures of human peritoneal mesothelial cells (HPMCs) contained a significant fraction of senescent-like cells. Furthermore, early-passage populations with a high percentage of senescent cells had a reduced subsequent life span in culture compared with populations consisting of the same number of apparently young cells but containing no senescent cells. The exposure of early-passage HPMCs to the conditioned medium from cultures containing senescent cells resulted in the retardation of growth and the induction of senescence-associated beta-galactosidase (SA-beta-Gal). This effect could be partly reduced by neutralizing TGF-beta1 activity. The timely treatment with N-tert-butyl-alpha-phenylnitrone (PBN) reduced oxidative stress, the number of early senescent cells, TGF-beta1 secretion, and ultimately extended the population life span. The effect was evident only when PBN was introduced at a very early, but not at a late, phase of tissue culture history. These results indicate that a sudden onset of senescence in early-passage HPMCs is related to oxidative stress and may influence the replicative life span of the population as a whole.

[Impaired insulin signaling and human ageing]

Human ageing is associated with impaired insulin activity, which may lead to alterations in energy homeostasis and type 2 diabetes. In addition, increasing evidence suggests that type 2 diabetes-associated hyperglycemia and hyperinsulinemia may accelerate cellular senescence. On the other hand, impaired insulin signaling in animal models extends organismal lifespan and interventions that promote longevity prevent metabolic alterations and diabetes. Here, we review the mechanisms underlying the development of age-associated hyperglycemia, its impact on cellular senescence and the effect of insulin-signaling pathways on energy balance and ageing.

Comparison of icodextrin- and glucose-based peritoneal dialysis fluids in their acute and chronic effects on human peritoneal mesothelial cells

BACKGROUND

Icodextrin-based peritoneal dialysis fluids (PDFs) display several features that may potentially improve their biocompatibility compared to conventional glucose-containing solutions. So far, however, the studies assessing the biocompatibility profile of icodextrin toward human peritoneal mesothelial cells (HPMC) has produced mixed results. The present study was performed to examine the acute and chronic impact of icodextrin on HPMC in vitro in comparison with standard glucose-based PDF.

METHODS

Omentum-derived HPMC were either acutely pre-exposed to or incubated chronically (for up to 10 days) in the presence of icodextrin-PDF. Parallel cultures were treated with conventional PDFs containing either 1.5% or 4.25% glucose. All fluids were tested at neutral pH. HPMC were assessed for viability, proliferation, IL-6 secretion and generation of reactive oxygen species (ROS).

RESULTS

Incubation in the presence of icodextrin-PDF significantly reduced HPMC proliferation in a manner similar to that of 1.5% glucose-PDF. In addition, exposure to icodextrin-PDF impaired viability and IL-6 release from HPMC. This effect occurred both after the short pre-treatment with neat icodextrin-PDF for 1-4 hours and after prolonged incubation (up to 10 days) in media supplemented with icodextrin-PDF (1:1). The dysfunction of icodextrin-treated HPMC was of the magnitude that was between the effects exerted by 1.5%- and 4.25%-glucose PDF. Furthermore, exposure of HPMC to icodextrin-PDF induced a dose-dependent increase in ROS generation which was comparable to that produced by 1.5%-glucose PDF.

CONCLUSION

Exposure to icodextrin-PDF may impair viability and function of HPMC. The detrimental effects of icodextrin-PDF are at least as serious as those produced by conventional heat-sterilized low glucose-based PDF.

New insights into the biology of peritoneal mesothelial cells: the roles of epithelial-to-mesenchymal transition and cellular senescence

Ultrafiltration failure due to dysfunction of the peritoneum as a dialyzing organ is a major clinical limitation of peritoneal dialysis. It is increasingly clear that mesothelial cells play an important role in fibrogenesis and vasculopathy that underlie peritoneal membrane dysfunction. New and extensively studied aspects of peritoneal mesothelial cell biology include epithelial-to-mesenchymal transition and cellular senescence. We discuss the potential significance of these processes for the peritoneal membrane function.

Premature senescence of mesothelial cells is associated with non-telomeric DNA damage

Human peritoneal mesothelial cells (HPMCs) senesce in vitro after barely few population doublings. In this report, we show that senescence of HPMCs is associated with increased accumulation of gamma-H2A.X foci, which reveal DNA double-strand breaks. Of note, already early-passage cultures contain a considerable fraction (44+/-10%) of cells bearing gamma-H2A.X foci. The gamma-H2A.X foci localize predominantly to non-telomeric DNA, either in young or senescent cells. Moreover, HPMCs seem to have unusually short telomeres (approximately 3.5 kbp) despite the presence of active telomerase. These telomeres do not shorten during senescence, but the activity of telomerase decreases to undetectable levels. In addition, senescence of HPMCs is associated with mitochondrial dysfunction, as manifested by increased production of reactive oxygen species and reduced mitochondrial membrane potential. These results may indicate that premature senescence of HPMCs is largely related to oxidative stress-induced DNA damage in non-telomeric regions of the genome.

Correlation between the donor age and the proliferative lifespan of human peritoneal mesothelial cells in vitro: Is TGF-β1 a link?

In the present study we have examined the relationship between calendar age of the donor and the proliferative lifespan and TGF-beta1 production by human peritoneal mesothelial cells (HPMC) in culture. The experiments were performed on primary omentum-derived HPMC isolated from patients undergoing elective abdominal surgery. There was an inverse relationship between the calendar age of the tissue donor and the replicative lifespan of HPMC in vitro (n=49, r=-0.3991, p<0.005). There was also a positive correlation between the donor's age and the magnitude of TGF-beta1 production by first-passage HPMC (n=28, r=0.5400, p<0.004). In turn, the TGF-beta1 levels correlated inversely with the proliferative lifespan of HPMC in vitro (n=28, r=-0.4671, p<0.02). These findings indicate that the reduced proliferative capacity of HPMC isolated from older donors may be associated with increased TGF-beta1 release, which may, in turn, result from the age-related accumulation of senescent HPMC in the peritoneum.

Accelerated senescence of human peritoneal mesothelial cells exposed to high glucose: the role of TGF-beta1

Cellular senescence can be activated in response to noxious environmental stimuli. A senescent-like phenotype has been detected in the peritoneal mesothelium of mice exposed to high intraperitoneal glucose. We have sought to examine whether high glucose (HG) can induce the senescence program in human peritoneal mesothelial cells (HPMC) in vitro. Senescence of omentum-derived HPMC was induced by serial passages. Cells were cultured in media containing either 5 mM glucose, 30 mM glucose, or 5 mM glucose and 25 mM mannitol (M) for osmotic control. Compared with HPMC cultured in low glucose, the growth rate of cells exposed to HG was significantly decreased so that the cells reached fewer population doublings before entering senescence. Exposure to HG led to increased expression of senescence-associated beta-galactosidase (SA-beta-Gal) and of the cell cycle inhibitors p21(Waf1) and p27(Kip1). Late-passage HPMC exposed to HG displayed marked hypertrophy and released increased amounts of fibronectin and TGF-beta1. These effects were absent from HPMC treated with equimolar M. Exposure of early-passage HPMC to exogenous recombinant TGF-beta1 induced a senescence marker SA-beta-Gal in a dose-dependent manner and mimicked other senescence-associated alterations induced by HG. The addition of anti-TGF-beta1 neutralizing antibody partially reduced the activation of HG-induced SA-beta-Gal. These results indicate that chronic exposure to elevated glucose may result in TGF-beta1-mediated accelerated senescence of HPMC in vitro, which may hypothetically contribute to the peritoneal membrane dysfunction during peritoneal dialysis in vivo.

Oxidative stress contributes to accelerated development of the senescent phenotype in human peritoneal mesothelial cells exposed to high glucose

Increasing evidence indicates that cells exposed to high glucose exhibit shortened proliferative lifespan and enter the state of senescence earlier. However, the contribution of hyperglycemia-induced oxidative stress to premature cell senescence is not entirely clear. In the current study we have examined the role of oxidative stress in cellular senescence of human peritoneal mesothelial cells (HPMC) exposed to high glucose. The experiments were performed on primary omental-derived HPMC grown into senescence in the presence of normal (5 mM) and high (30 mM) glucose. Senescence of HPMC was associated with increased generation of reactive oxygen species (ROS) and decreased cellular glutathione (GSH). Exposure to high glucose significantly exacerbated these effects and increased the level of senescence-associated beta-galactosidase (SA-beta-Gal) and 8-hydroxy-2'-deoxyguanosine (8-OH-dG) expression. Furthermore, high glucose markedly increased senescence-related HPMC hypertrophy. The addition of L-2-oxothiazolidine-4-carboxylic acid, a GSH precursor, restored partially GSH levels and decreased ROS release. This effect was associated with reduced levels of SA-beta-Gal and 8-OH-dG, diminished TGF-beta1 and fibronectin release, and less pronounced hypertrophy of aged HPMC. These results indicate that the accelerated senescence response in HPMC exposed to high glucose is strongly related to oxidative stress.

Role of mesothelial cell-derived granulocyte colony-stimulating factor in interleukin-17-induced neutrophil accumulation in the peritoneum

Recent studies suggest that peritoneal CD4(+) T lymphocytes may control recruitment of polymorphonuclear leukocytes (PMN) during peritonitis by an interleukin-17 (IL-17)-dependent mechanism. IL-17 and granulocyte colony-stimulating factor (G-CSF) have been proposed to form an axis that regulates PMN transmigration. Here we report on the role of G-CSF released by human peritoneal mesothelial cells (HPMCs) in IL-17A-mediated peritoneal PMN accumulation. In vitro exposure of HPMCs to IL-17A resulted in a time- and dose-dependent release of G-CSF. This effect was related to the induction of G-CSF mRNA and mediated through the nuclear factor-kappaB (NF-kappaB) pathway. The novel observation was that IL-17A-stimulated NF-kappaB activation in HPMCs followed a biphasic profile, with an early induction (45 min), followed by the return to basal levels (90 min), and a delayed induction (3 h). Tumor necrosis factor alpha synergistically amplified IL-17A-induced G-CSF production by enhanced NF-kappaB activation and through stabilization of G-CSF mRNA. Intraperitoneal (i.p.) administration of IL-17A in Balb/c mice resulted in increased local levels of G-CSF and selective PMN accumulation. Administration of anti-G-CSF blocking antibody before IL-17A injection significantly reduced the IL-17A-triggered PMN infiltration. This effect occurred despite increased i.p. levels of PMN-specific chemokines KC and macrophage inflammatory protein-2 seen in animals treated with anti-G-CSF antibody. These data demonstrate that the mesothelium-derived G-CSF plays an important role in IL-17A-induced PMN recruitment into the peritoneum.

Effect of heparin on blood vascular endothelial growth factor levels in patients with ST-elevation acute myocardial infarction undergoing primary percutaneous coronary intervention

It has been demonstrated that high blood vascular endothelial growth factor (VEGF) levels in patients with myocardial infarction decrease rapidly after reperfusion, possibly in response to heparin administration. We measured serum VEGF concentration before and after heparin infusion in 105 patients with ST-elevation acute myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PCI). Serum VEGF concentration in patients with STEMI was significantly higher than in healthy controls. After PCI, the concentration of VEGF decreased by approximately 70%, with the greatest decrease seen in patients with the highest initial VEGF levels. To determine whether heparin could decrease VEGF concentration by sequestering VEGF in the endothelium, a fixed dose of recombinant VEGF was incubated for 40 minutes with EA.hy926 endothelial cells in vitro. Recovery of VEGF from medium after culture was decreased by up to 15% with increasing doses of heparin. Concentration of VEGF did not change in the absence of heparin and/or endothelial cells. In conclusion, these results suggest that a rapid decrease in blood VEGF after PCI may be related to the administration of heparin, which binds simultaneously to VEGF and endothelial cells.

Early loss of proliferative potential of human peritoneal mesothelial cells in culture: the role of p16INK4a-mediated premature senescence

Much has been learned about the mechanisms underlying cellular senescence. The pathways leading to senescence appear to vary, depending on the cell type and cell culture conditions. In this respect, little is known about senescence of human peritoneal mesothelial cells (HPMC). Previous studies have significantly differed in the reported proliferative lifespan of HPMC. Therefore, in the present study, we have examined how HPMC enter state of senescence under conditions typically used for HPMC culture. HPMC were isolated from omentum and grown into senescence. The cultures were assessed for the growth rate, the presence of senescence markers, activation of cell-cycle inhibitors, and the oxidative stress. HPMC were found to reach, on average, six population doublings before senescence. The terminal growth arrest was associated with decreased expression of Ki67 antigen, increased percentage of cells in the G1 phase, reduced early population doubling level cDNA-1 mRNA expression, and the presence of senescence-associated beta-galactosidase. Compared with early-passage cells, the late-passage HPMC exhibited increased expression of p16INK4a but not of p21Cip1. In addition, these cells generated more reactive oxygen species and displayed increased presence of oxidatively modified DNA (8-hydroxy-2'-deoxyguanosine). These results demonstrate that early onset of senescence in omentum-derived HPMC may be associated with oxidative stress-induced upregulation of p16INK4a.

[Mechanisms and medical implications of replicative senescence]

Normal somatic cells divide in vitro only for a limited number of times, and then enter a state of replicative senescence. In most human cells replicative senescence is triggered by critical shortening and uncapping of telomeres, which leads to the up-regulation of p53 and/or p16 suppressor proteins that inhibit cell divisions. Because both reconstruction of telomeres and inactivation of suppressor proteins enables the cells to grow further or even immortalize, it has been hypothesized that replicative senescence acts as a natural barrier against neoplastic transformation. On the other hand, however, recent reports suggest that the accumulation of senescent cells may jeopardize tissue integrity and create a specific microenvironment that promotes tumorogenesis in elderly people. In this review we describe recent advances in our knowledge on the mechanisms of replicative senescence and discuss its medical implications.

Peritoneal dialysis with solutions low in glucose degradation products is associated with improved biocompatibility profile towards peritoneal mesothelial cells

BACKGROUND

In vitro experiments point to a better biocompatibility profile of new pH-neutral peritoneal dialysis fluids (PDFs) containing low levels of glucose degradation products (GDPs). The present study examines the impact on human peritoneal mesothelial cells (HPMCs) of equilibrated dialysates obtained during dialysis with either conventional or new PDFs.

METHODS

Peritoneal dialysate was collected from 17 patients participating in a randomized, controlled, cross-over trial comparing a pH-neutral low-GDP solution (Balance) to a conventional solution (S-PDF). All patients were treated sequentially for 3 months with both PDFs. At the end of each treatment phase, peritoneal effluent was drained after a timed 10 h dwell. Samples of dialysate were then mixed with standard culture medium and added to in vitro cultures of HPMCs from healthy donors. Cells were assessed for proliferation, viability and cytokine release.

RESULTS

Proliferation and viability of HPMCs were better preserved in the presence of effluent obtained during dialysis with Balance (P<0.046 and P<0.035, respectively). The proliferative response of HPMCs correlated with the concentration of fibronectin in dialysates (P = 0.0024). Effluent drained following a 3 month dialysis with Balance contained significantly increased levels of fibronectin (P = 0.004) and CA125 antigen (P = 0.0004) compared with S-PDF. There was no significant difference in constitutive and stimulated cytokine (IL-6, MCP-1, VEGF) synthesis by HPMCs treated with either Balance- or S-PDF-derived effluents.

CONCLUSIONS

These results suggest that therapy with new pH-neutral low-GDP solutions contribute to an intraperitoneal milieu that improves mesothelial cell proliferation and viability. It may positively impact on the preservation of the peritoneal membrane integrity during long-term dialysis.

Mesothelial Toxicity of Peritoneal Dialysis Fluids is Related Primarily to Glucose Degradation Products, Not to Glucose Per Se

♦ Objectives

High concentrations of glucose and/or formation of glucose degradation products (GDPs) during heat sterilization of peritoneal dialysis fluids (PDFs) are believed to be key factors in the limited biocompatibility of PDFs. We have previously shown that several identified GDPs can specifically impair human peritoneal mesothelial cell (HPMC) function. In the present study we aimed at differentiating the respective roles of glucose and GDPs in the toxicity of PDF to mesothelial cells.

♦ Methods

HPMCs were acutely pre-exposed to or incubated chronically in the presence of pH-neutral PDF sterilized by either heat (H-PDF) or filtration (F-PDF). In addition, HPMCs were treated with commercially available H-PDF manufactured either conventionally, that is, in single-chamber containers, or using novel dual-chamber bags that help to substantially decrease GDP formation. Functional assessment of HPMCs included viability, release of interleukin (IL)-6, and proliferation.

♦ Results

Viability and release of IL-6 from HPMCs pretreated with H-PDF (pH 7.3) for 1 to 4 hours were significantly reduced compared to cells exposed to corresponding F-PDF. Incubation in medium mixed (1:1) with H-PDF considerably impaired growth of HPMCs, and over a period of 10 days gradually decreased both the viability of HPMCs and their ability to generate IL-6. These effects were either absent from or significantly less in HPMCs exposed to F-PDF. Similar differences were observed when commercial GDP-containing H-PDFs were compared with newly designed H-PDFs free of GDPs.

♦ Conclusions

Impaired viability and function of HPMCs exposed to glucose-containing pH-neutral PDF is related predominantly to the presence of GDP and, to a significantly lesser extent, to the presence of glucose per se. Prevention of GDP formation during auto-claving markedly improves the biocompatibility of H-PDF with HPMCs.

Mesothelial toxicity of peritoneal dialysis fluids is related primarily to glucose degradation products, not to glucose per se

OBJECTIVES

High concentrations of glucose and/or formation of glucose degradation products (GDPs) during heat sterilization of peritoneal dialysis fluids (PDFs) are believed to be key factors in the limited biocompatibility of PDFs. We have previously shown that several identified GDPs can specifically impair human peritoneal mesothelial cell (HPMC) function. In the present study we aimed at differentiating the respective roles of glucose and GDPs in the toxicity of PDF to mesothelial cells.

METHODS

HPMCs were acutely pre-exposed to or incubated chronically in the presence of pH-neutral PDF sterilized by either heat (H-PDF) or filtration (F-PDF). In addition, HPMCs were treated with commercially available H-PDF manufactured either conventionally, that is, in single-chamber containers, or using novel dual-chamber bags that help to substantially decrease GDP formation. Functional assessment of HPMCs included viability, release of interleukin (IL)-6, and proliferation.

RESULTS

Viability and release of IL-6 from HPMCs pretreated with H-PDF (pH 7.3) for 1 to 4 hours were significantly reduced compared to cells exposed to corresponding F-PDF. Incubation in medium mixed (1:1) with H-PDF considerably impaired growth of HPMCs, and over a period of 10 days gradually decreased both the viability of HPMCs and their ability to generate IL-6. These effects were either absent from or significantly less in HPMCs exposed to F-PDF. Similar differences were observed when commercial GDP-containing H-PDFs were compared with newly designed H-PDFs free of GDPs.

CONCLUSIONS

Impaired viability and function of HPMCs exposed to glucose-containing pH-neutral PDF is related predominantly to the presence of GDP and, to a significantly lesser extent, to the presence of glucose per se. Prevention of GDP formation during autoclaving markedly improves the biocompatibility of H-PDF with HPMCs.

Glucose degradation products in peritoneal dialysis fluids: do they harm?

BACKGROUND

Severe limitations in biocompatibility of conventional peritoneal dialysis fluids (PDF) can be partially attributed to the presence of glucose degradation products (GDP), which are generated during autoclaving of PDF. Formation of GDP can be significantly reduced by the use of multi-chamber bag systems. Recent clinical studies have revealed increased dialysate levels of pro-collagen I C-terminal peptide (PICP) in patients dialyzed with these solutions. Here, we briefly review the current knowledge on various aspects of GDP toxicity toward peritoneal cells and analyze the impact of GDP on PICP release by human peritoneal mesothelial cells (HPMC) in vitro.

METHODS

HPMC were exposed to a mixture of known GDP added to culture medium at clinically relevant doses. After 12 days, the amount of PICP released was measured using an immunoassay. Furthermore, the protein synthesis was assessed by 3H-proline incorporation in HPMC exposed to peritoneal effluent obtained from patients after three months of CAPD with either conventional PDF or low-GDP solution.

RESULTS

Exposure to GDP resulted in a significant decrease in PICP release by HPMC. In addition, the synthesis of new proteins secreted by HPMC was preserved significantly better in HPMC treated with effluent obtained when patients were dialyzed with low-GDP solutions rather than conventional PDF.

CONCLUSIONS

Exposure to GDP may impair protein synthesis and secretion by HPMC. Therefore, increased dialysate PICP levels in response to GDP-free PDF may be viewed as evidence of improved mesothelial cell function.

Glucose suppresses peritoneal inflammatory reactions and mesothelial hyperplasia caused by intraperitoneal saline infusion

In the past, we had observed that infusion of normal saline into the peritoneal cavity stimulates an inflammatory response. In the present study, we examined what effect the addition of glucose to normal saline would have on the peritoneal inflammatory response and change in peritoneal morphology. After catheter implantation, rats were infused intraperitoneally (i.p.) for 3 days with Dianeal 1.36% (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.). Dialysate samples were collected on day 3 after a 4-hour dwell. Next, rats were exposed to either NaCl (n = 7) or NaCl with glucose 250 mmol/L (Glu, n = 7) twice daily for 4 weeks. After 2 weeks and 4 weeks of the study, dialysate samples were collected after a 4-hour dwell to analyze the activity of inflammatory reaction. At the end of the experiment, imprints of peritoneal mesothelium were taken. Control animals (C, n = 6) did not undergo catheter implantation or the dialysis procedure. The inflammatory reaction--cell count, cell differentiation, nitric oxide production, protein loss, and monocyte chemoattractant protein-1 (MCP-1) concentration in dialysate expressed as a percentage of the initial value--did not change during the study in rats exposed to NaCl. On the other hand, in Glu-treated animals, the protein concentration was decreased after 4 weeks of the study (74% +/- 23%, p < 0.05), as was MCP-1 (24% +/- 12%, p < 0.05). The nitrites concentration was decreased after 2 weeks (72% +/- 19%; p < 0.05). Intraperitoneal adhesions were found in 6 rats of the NaCl group (86%) and in only 4 rats (57%) of Glu group. In the NaCl rats, a higher density of mesothelial cells was observed (2792 +/- 510 cells/mm2) as compared with Glu rats (2028 +/- 561 cells/mm2; p < 0.05) and with control rats (1629 +/- 422 cells/mm2, p < 0.05). The NaCl group also showed a higher nucleus: cytoplasm surface ratio (0.25 +/- 0.03) as compared with the Glu group (0.18 +/- 0.02, p < 0.01) and with the control group (0.14 +/- 0.01, p < 0.01). Addition of glucose to normal saline suppresses the peritoneal inflammatory response and mesothelial hyperplasia occurring with intraperitoneal infusion of NaCl solution alone.

[Dual role of nitric oxide in the pathogenesis of diabetic nephropathy]

Nitric oxide (NO) is a key mediator in renal physiology and pathology. In diabetic nephropathy, NO may exert destructive effects (hyperfiltration, peroxynitrate-mediated tissue injury) as well as exhibit certain protective properties (reduced TGF-beta expression and extracellular matrix expansion, inhibition of platelet aggregation). Here, we briefly review the biochemistry and pathophysiology of NO, and discuss the mechanisms underlying the contrasting effects of NO in diabetic nephropathy.

[The role of glucose and reactive oxygen species in the development of vascular complications of diabetes mellitus]

Several mechanisms seem to be involved in the development of oxidative stress in the presence of elevated glucose concentrations, namely glucose autoxidation, protein glycation, and the polyol pathway. In diabetes patients reactive oxygen species and advanced glycation end products are able to alter vascular function and disturb cellular homeostasis especially by lipid peroxidation, changes in extracellular matrix and inhibiting synthesis and action of nitric oxide.

[Aquaporin water channels in water balance regulation in the kidney]

The aquaporins (AQP) are a family of small transmembrane water channels. The discovery of AQP has provided insight into molecular mechanisms underlying renal water absorption and its regulation by vasopressin. Seven types of AQP have been identified in the kidney. AQP1 has been localized in the proximal tubule and descending thin limb, while AQP2, AQP3, and AQP4 are expressed in the collecting duct. Of these isoforms, AQP2 expression and intracellular trafficking is tightly regulated by vasopressin. Decreased expression of renal AQP has been detected in several disorders associated with polyuria and impaired ability to concentrate urine, as exemplified by nephrogenic diabetes insipidus or renal failure. In contrast, increased expression of AQP is seen in conditions leading to water retention, such as congestive heart failure, liver cirrhosis, and syndrome of inappropriate antidiuretic hormone secretion. Thus, the understanding of molecular structure and function of aquaporins may have important implications for therapy of water balance disorders.

[The role of PKC isoforms in tumorigenicity and apoptotic cell death]

Protein kinase C comprises a family of at least 13 distinct serine/threonine kinase isoenzymes that have important actions in transmembrane signal transduction pathways and have been reported to regulate cell proliferation, differentiation, cell-to-cell interaction, cytoskeletal functions, gene transcription, apoptosis and drug resistance. The results of investigations show differential redistribution isoenzymes in each organ and their specific activity in determined diseases.