l-2-oxothiazolidine-4-carboxylic acid modulates function of peritoneal mesothelial cells in vitro

Changes in peritoneal mesothelial cells phenotype after chronic exposure to glucose or N-acetylglucosamine

Glucose is commonly used as an osmotic solute in peritoneal dialysis fluids despite vast knowledge about deleterious peritoneal and systemic effects of that solute. N-acetylglucosamine (NAG) is a solute of the comparable size to glucose, with strong anti-inflammatory properties. We compared the chronic in vitro effect of both solutes on phenotype of peritoneal mesothelial cells. Experiments were performed of primary cultures of human peritoneal mesothelial cells, which were cultured over 4 weeks in medium supplemented either with glucose 45 mmol/L (GLU) or with NAG 45 mmol/L (NAG). Generation of reactive oxygen species (ROS) in cells was studied, as well as their ability to proliferate, synthesis of cytokines, fibronectin, and factors regulating peritoneal fibrinolysis. Cells cultured in the presence of glucose 45 mmol/L generated more ROS (+73% vs control, P < 0.01), whereas NAG did not stimulate generation of ROS. GLU caused hypertrophy of mesothelial cells (+53% vs control, P < 0.001) and prolonged their population doubling time (+16% vs control, P < 0.01); NAG did not cause significant changes in these parameters. Healing of mesothelial monolayer after mechanical injury was impaired in GLU treated cells: (-48% vs control, P < 0.001 and -40% vs NAG, P < 0.05). Synthesis of Il-6, vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFbeta), and fibronectin was higher in GLU group as compared with control: + 86%, P < 0.001, +38%, P < 0.05, +51%, P < 0.001, +38%, P < 0.05, respectively. In the presence of NAG, these parameters were comparable with the control group, but at the same time NAG stimulated synthesis of hyaluronan: +116% versus control, P < 0.001 and + 96% versus GLU, P < 0.01. Treatment with GLU resulted in decline of tissue plasminogen activator/plasminogen activator inhibitor-1 (t-PA/PAI-1) ratio by 23% versus control, P < 0.001, whereas NAG increased that parameter by 43%, P < 0.01 versus control. Glucose, contrary to NAG, induces oxidative stress and proinflammatory and profibrotic changes in mesothelial cells. NAG seems to be more biocompatible osmotic solute than glucose.

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.