Intracellular acidification enhances neutrophil phagocytosis in chronic haemodialysis patients: possible role of CD11b/CD18.

BACKGROUND: We have demonstrated that uraemic neutrophils that exhibit a low intracellular pH (pHi) display enhanced phagocytosis. However, the underlying cellular mechanism is unclear. METHODS: We used neutrophils from three groups of haemodialysis (HD) patients before dialysis (Groups A, B and C) and also from age- and sex-matched healthy individuals to determine pHi, phagocytosis and expression of CD11b, CD18, CD14 and toll-like receptors (TLR)-2 and TLR-4. The patients were categorized based on three consecutive monthly pre-dialysis plasma bicarbonate concentrations(P(HCO3)) and pH values; Groups A, B and C had a constant pre-dialysis P(HCO3) of /=26 mmol/L (mEq/L), respectively. We also studied the effects induced by the correction of metabolic acidosis and monoclonal antibodies (mAbs) against CD11b/CD18 on neutrophils in Group A. Furthermore, we investigated the effect of intracellular acidification on uraemic neutrophils ex vivo. RESULTS: We observed that the neutrophils in Group A exhibited significantly increased phagocytosis and expression of CD11b/CD18 compared with those in Groups B and C. Additionally, our ex vivo studies demonstrated that the mAbs against CD11b/CD18 partially blocked the enhancement of neutrophil phagocytosis in Group A. Moreover, the pHi of uraemic neutrophils is inversely correlated with phagocytosis and expression of CD11b/CD18. CONCLUSIONS: HD patients with a low P(HCO3) exhibited low neutrophil pHi that in turn increased the expression of CD11b/CD18 compared with neutrophils with a normal or high pHi. This increased expression of CD11b/CD18 on the uraemic neutrophils may contribute to the pHi-mediated phagocytosis.

Neutrophils in acidotic haemodialysed patients have lower intracellular pH and inflamed state.

BACKGROUND: The effect of intracellular pH (pHi) on neutrophils has not been clearly defined. METHODS: We used pre-dialysis neutrophils from three groups of haemodialysis (HD) patients having different levels of pre-dialysis plasma bicarbonate concentrations (PHCO3) and pH values (pre-dialysis PHCO3 of groups A, B and C were consistentlyor=26 mmol/l [mEq/l], respectively) and neutrophils from age- and sex-matched healthy controls to determine pHi, apoptosis, phagocytosis and oxidative burst reactions in vivo. We also studied, in group A, the effect of metabolic acidosis correction on neutrophil function. Furthermore, we investigated the effect of intracellular acidification on neutrophil functioning in vitro. RESULTS: Neutrophils from the HD patients in group A exhibited significantly lower pHi than those in groups B and C. In addition, group A neutrophils had significantly delayed apoptosis, enhanced phagocytosis and increased oxidative burst reactions compared with those in groups B and C. These alterations in neutrophil function in group A were reduced by correcting metabolic acidosis over a period of 1 month. Moreover, our in vitro studies demonstrated that the pHi of neutrophils is positively correlated with apoptosis and inversely correlated with phagocytosis and oxidative burst reactions. CONCLUSION: HD patients having low PHCO3 exhibited low neutrophil pHi. This intracellular acidification may contribute to the delayed apoptosis, enhanced phagocytosis and increased oxidative burst reactions observed in these neutrophils compared with neutrophils having normal or higher pHi.

Enhanced expression of glucose transporter 1 on erythrocyte membrane in hemodialysis patients: the possible role in erythrocyte ascorbate recycling.

BACKGROUND: Human erythrocytes can take up dehydroascorbate on the glucose transporter 1 (GLUT 1) and reduce it to ascorbate. Intraerythrocyte ascorbate was proved to be directly responsible for decreased oxidation of extraerythrocytic ascorbate. In addition to spontaneous and irreversible loss of ascorbate in plasma, the hemodialysis (HD) process itself consumes plasma ascorbate. However, intraerythrocyte ascorbate status in uremic patients during HD has yet to be reported. METHODS: Plasma and intraerythrocyte ascorbate, dehydroascorbate, GLUT 1 expression on erythrocyte membranes, and in vitro studies of "erythrocyte ascorbate recycling" were investigated in age- and sex-matched healthy subjects (control group) and HD patients (HD group). RESULTS: Intraerythrocyte ascorbate concentrations decreased after 1 HD session compared with pre-HD and recovered to pre-HD values 2 days later, whereas plasma ascorbate concentrations did not recover. In vitro studies suggested that erythrocytes of HD patients have a stronger ability to maintain intracellular ascorbate concentrations compared with healthy subjects. This ability could be inhibited by cytochalasin B (GLUT 1 inhibitor). We also found increased GLUT 1 expression (P = 0.002) on erythrocyte membranes in the HD group compared with the control group. CONCLUSION: Erythrocytes of uremic patients lost large amounts of ascorbate during HD, but regained it to the pre-HD level 2 days later. Enhanced GLUT 1 expression on erythrocyte membranes for HD patients may contribute to better preservation of intracellular ascorbate compared with healthy subjects.