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Intracellular acidification mediates the inhibitory effect of peritoneal dialysate on peritoneal macrophages
A Douvdevani1, J Rapoport, A Konforty
1Department of Nephrology, Soroka Medical Center, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Abstract:
Commercial peritoneal dialysis solution (CDS) is known to have a detrimental effect on the capacity of peritoneal macrophages (PM phi) to kill bacteria and produce acute phase cytokines. This cytotoxic effect is largely caused by the low pH of CDS. Because the cytoplasmic pH (pHi) is an important determinant of cellular function, the effect of CDS on the pHi of PM phi from continuous ambulatory peritoneal dialysis patients was studied. The pHi of PM phi was measured fluorometrically in N-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered salt solution (HBSS) or CDS at pH values of 5.3, 6.5, and 7.0, values that represent the pH existing in dialysate during the first 30 min of dwell time. For any given pH of the experimental medium, the pHi was always more acidic in CDS than in HBSS. When PM phi were incubated with a lactate-containing HBSS, a cellular acidification was observed that was similar to that attained by exposure to CDS at the same pH. This supports the hypothesis that the decrease in pHi was due to the influx of lactic acid from the CDS into the PM phi. In order to demonstrate a causal association between the CDS-induced cellular acidification and a defect in phagocytosis and cytokine production, these functions were studied after pHi clamping by means of K+/nigericin. It was found that clamping pHi to values below 6.5 led to a markedly reduced tumor necrosis factor-alpha production and phagocytosis. However, at values of pHi > 6.5, these functions were normal. (ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Commercial peritoneal dialysis solution (CDS) lowers the pH within peritoneal macrophages (PM phi), impairing their ability to fight bacteria and produce cytokines. Restoring intracellular pH above 6.5 is crucial for normal macrophage function.
Area of Science:
- Peritoneal dialysis
- Immunology
- Cellular physiology
Background:
- Commercial peritoneal dialysis solutions (CDS) negatively impact peritoneal macrophage (PM phi) function, including bacterial killing and cytokine production.
- The low pH of CDS is a primary contributor to its cytotoxic effects on PM phi.
Purpose of the Study:
- To investigate the effect of CDS on the intracellular pH (pHi) of PM phi from continuous ambulatory peritoneal dialysis patients.
- To determine the relationship between CDS-induced pHi changes and impaired PM phi functions.
Main Methods:
- PM phi pHi was measured using a fluorometric method in various buffered solutions (HBSS and CDS) at different pH levels.
- The impact of lactic acid influx on PM phi acidification was assessed.
- Phagocytosis and tumor necrosis factor-alpha production were evaluated after pHi clamping using K+/nigericin.
Main Results:
- PM phi exhibited a more acidic pHi in CDS compared to HBSS at equivalent external pH values.
- Exposure to lactate-containing HBSS mimicked the cellular acidification caused by CDS, suggesting lactic acid influx.
- Clamping pHi below 6.5 significantly reduced tumor necrosis factor-alpha production and phagocytosis, while pHi above 6.5 maintained normal function.
Conclusions:
- The low pH of CDS leads to lactic acid influx into PM phi, causing cellular acidification.
- This acidification below a pHi of 6.5 impairs critical macrophage functions like phagocytosis and cytokine production.
- Maintaining an intracellular pH above 6.5 is essential for normal PM phi immune responses in patients undergoing peritoneal dialysis.