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Hexamethylene bisacetamide protects peritoneal mesothelial cells from glucose.

BACKGROUND
Peritoneal dialysis causes damage to peritoneal mesothelial cells primarily because dialysis fluids have a high glucose concentration. This study examined the abnormalities of gap junctional intercellular communication (GJIC) in human peritoneal mesothelial cells (HPMCs) exposed to relatively high levels of glucose. Also, ability of hexamethylene bisacetamide (HMBA) to up-regulate GJIC in HPMCs exposed to high levels of glucose was measured.


METHODS
An assay that monitors the recovery of fluorescence after photobleaching was used to measure GJIC in primary cultured HPMCs. The cells were exposed to a low (10 mmol/L) or high (50 or 90 mmol/L) glucose level for a total of six days, and some cells were also incubated with or without HMBA (1 or 6 mmol/L) from day 4. The effects of incubation in these various environments on expression of the connexin 43 (Cx43) gene were investigated by the reverse transcription-polymerase chain reaction (to detect Cx43 mRNA) or by immunofluorescence and Western blotting (to detect Cx43 protein). To evaluate the influence of protein kinase C (PKC) or mitogen-activated protein kinase (MAPK) on GJIC, specific inhibitors were added to cultures in a high glucose medium.


RESULTS
Gap junctional intercellular communication was inhibited in a concentration- and time-dependent manner when cells were exposed to high glucose. The addition of 6 mmol/L HMBA to cultures significantly enhanced GJIC despite the presence of a high glucose concentration. High glucose also down-regulated Cx43 mRNA and protein expression, with the dose-dependent decrease of Cx43 protein at gap junctions paralleled by a decrease in the phosphorylation of this protein. As expected, treatment of cells with 6 mmol/L HMBA increased both Cx43 mRNA and protein levels despite exposure to high glucose. The addition of PKC or MAPK inhibitors to high glucose cultures did not restore GJIC, and there was no significant change of Cx43 phosphorylation in the presence of these inhibitors.


CONCLUSIONS
High glucose down-regulates GJIC in human peritoneal mesothelial cells. It also decreases the levels of both Cx43 mRNA and Cx43 protein, with the latter becoming hypophosphorylated. HMBA appears to reverse all of these changes. These results are consistent with our hypothesis that HMBA protects HPMCs from the adverse effects of high glucose by reversing various processes that would otherwise lead to harmful loss of GJIC.