Glutathione redox potential is low and glutathionylated and cysteinylated hemoglobin levels are elevated in maintenance hemodialysis patients

Abstract

Glutathione (GSH), the most abundant intracellular low molecular mass thiol, protects cells from oxidative damage and regulates their function. Available information is inconsistent regarding levels of GSH and its disulfide (GSSG) in maintenance hemodialysis patients (HD). In addition, very limited data are available in HD about the relationship of GSH and GSSG with other measures of thiol metabolism and with the clinical profile. We tested the hypothesis that erythrocyte GSH/GSSG redox potential (Eh) is lower in HD than in healthy controls (C), and that Eh correlates with posttranslational thiolation of hemoglobin (Hb) and with standard clinical parameters in HD. In cross-sectional comparison of 33 stable HD and 21 C, we found a net loss of reducing capacity in HD as indicated by low erythrocyte GSH/GSSG Eh (-257 ± 5.5 vs -270 ± 5.6 mV, P = 0.002). Glutathionylated Hb (HbSSG) was 46% higher in HD than C (19.3 ± 4.80 vs 13.2 ± 2.79 pmol/mg Hb; P = 0.001) and cysteinylated Hb (HbSSCy) was >3-fold higher in HD than C [38.3 (29.0-63.3) vs 11.5 (9.6-17.2) pmol/mg Hb; P = 0.001]. In multiple regression analysis of the HD cases, statistically significant associations were found between the GSH/GSSG Eh and the blood urea nitrogen (P = 0.001), creatinine (P = 0.015) and normalized protein catabolic rate (P = 0.05), after adjusting for age, race/ethnicity, and etiology of end-stage renal disease. In conclusion, accurate and precise analysis of GSH, GSSG, and mixed disulfides reveals loss of erythrocyte GSH/GSSG Eh, rise of both HbSSG and HbSSCy, and correlation of these thiols with measures of uremia and dietary protein intake.

Conflict of interest statement

All authors have read the journal’s policy on disclosure of potential conflict of interest and they declare of having no conflict of interest to disclose.

Copyright © 2013 Mosby, Inc. All rights reserved.

Figures

Figure 1

(a.) Glutathione (GSH, nmol/mg Hb); (b.) glutathione disulfide (GSSG, nmol/mg Hb); (c.) ratio between reduced and oxidized glutathione (GSH/GSSG ratio, ×102); and (d.) GSH/GSSG redox power (Eh, mV × 102) in RBCs from 21 healthy Control subjects (C) and 33 Maintenance HD Patients (HD); mean ± SD. (*) indicates p=0.002 and (**) indicates p<0.001.

Figure 2

(a.) Glutathionylated Hb (HbSSG, pmol/mg Hb) and (b.) cysteinylated Hb (HbSSCy, pmol/mg Hb) in RBCs from 21 healthy Control subjects (C) and 33 Maintenance HD Patients (HD); box-and-whisker diagram (median, 25th–75th percentile). (**) indicates p<0.001.

Figure 3

Scatter plot of HbSSG (pmol/mg Hb) with (a.) glutathione (GSH, nmol/mg Hb); (b.) glutathione disulfide (GSSG, nmol/mg Hb); and (c.) ratio between glutathione and glutathione disulfide (GSH/GSSG ratio, ×102) in RBCs from 33 Maintenance HD Patients (multiple regression models with age, race and diabetes as covariates).

Figure 4

Scatter plot of RBC GSH/GSSG redox power (Eh, mV × 102) with (a) serum blood urea nitrogen (BUN, mg/dL); (b) creatinine (Creat, mg/dL); and (c.) normalized protein catabolic rate (nPCR, g/kg per day) in 33 Maintenance HD Patients (multiple regression models with age, race and diabetes as covariates).

Appendix Figure A1

Scatter plot of HbSSCy (pmol/mg Hb) with (a.) glutathione (GSH, pmol/mg Hb), (b) glutathione disulfide (GSSG, pmol/mg Hb), and (c) ratio between glutathione and glutathione disulfide (GSH/GSSG ratio, x102) in RBCs from 33 Maintenance HD Patients (multiple regression models with age, race and diabetes as covariates).

Appendix Figure A2

Scatter plot of RBC HbSSCy (pmol/mg Hb) with (a) serum blood urea nitrogen (BUN, mg/dL); (b.) Creatinine (Creat, mg/dL); and (c) normalized protein catabolic rate (nPCR, g/kg per day) in 33 Maintenance HD Patients (multiple regression models with age, race and diabetes as covariates).

Appendix Figure A3

1Scatter plot of HbSSG (pmol/mg Hb) with (a.) serum blood urea nitrogen (BUN, mg/dL); (b.) Creatinine (Creat, mg/dL); and (c.) normalized protein catabolic rate (nPCR, g/kg per day) in 33 Maintenance HD Patients (multiple regression models with age, race and diabetes as covariates).