Polymorphonuclear leukocyte injury by methylglyoxal and hydrogen peroxide: A possible pathological role for enhanced oxidative stress in chronic kidney disease

Background. Accelerated burst of polymorphonuclear leukocytes (PMNs) may be involved in the primary pathology of enhanced oxidative stress in patients with chronic kidney disease (CKD); however, the precise mechanism remains unknown. Methylglyoxal (MGO), an α-oxoaldehyde reportedly elevated in CKD, could induce apoptosis in several cell lines, and generates radicals by the reaction with hydrogen peroxide (H₂O₂). Thus, we tested if a high MGO of uraemic milieu could play a role in PMN injury by interaction with H ₂O₂. Method. Cellular viability of PMNs, isolated from healthy volunteers, was tested by ATP chemiluminescence levels under MGO and/or H₂O₂, or 4-β phorbol 12-β-myristate 13-α-acetate (PMA). Superoxide anion (O₂^-) generation and apoptosis were measured by the reduction of ferricytochrome C and fluorocytometric analysis, respectively. Plasma MGO levels were measured by mass spectometry in 29 CKD patients. Results. At low levels of MGO (1-10 μM) and H₂O₂ (12.5 μM), no differences were found in cellular viability as compared to controls, whereas their combination significantly decreased PMN viability. PMA stimulation enhanced cellular injury of MGO by a function of MGO levels and preincubation with 5,5-dimethyl-1- pyrroline-N-oxide (free radical trap agent) attenuated it. MGO suppressed O ₂^- generation by PMA, while it accelerated apoptotic ratios in PMNs. Significant increases of plasma MGO and C-reactive protein levels were found by a function of CKD stage, and clinical level of MGO could induce PMN injury in combination with H₂O₂. Conclusion. These results indicate the combinatory effect of MGO and H₂O ₂ on PMN oxidative injury, and this pathology may be linked to enhanced oxidative stress in CKD.