Effect of ascorbic acid administration in hemodialysis patients on in vitro oxidative stress parameters: influence of serum ferritin levels.
BACKGROUND
Ascorbic acid supplementation has been recommended to circumvent resistance to erythropoietin, which sometimes occurs in iron-overloaded uremic patients. In considering the pro-oxidant effect of ascorbic acid, the authors hypothesize that adjuvant therapy with larger doses of ascorbic acid in hemodialysis patients with iron overload may raise the risk of increasing free radical generation. The oxidative stress of intravenous ascorbic acid supplementation in hemodialysis patients was evaluated in this study.


METHODS
Six healthy subjects and 29 hemodialysis patients were enrolled. Chemical scavenging activity of various compounds was measured by in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Free radical generation was determined in vitro by lucigenin-enhanced chemiluminescence (LucCL) assay on blood samples. Blood biochemistries were also measured simultaneously in hemodialysis patients 1 minute before and 5 minutes later in the presence or absence of intravenous injection of 300 mg ascorbic acid.


RESULTS
Ascorbic acid presented a strong antioxidant effect in DPPH chemical reaction. On the contrary, it exerted pro-oxidant effect when mixed with plasma or whole blood of healthy subjects and hemodialysis patients. The pro-oxidant effect of ascorbic acid detected by LucCL was attenuated by various iron chelators and superoxide dismutase. In hemodialysis patients, the changes of LucCL intensity were significantly higher in the ascorbic acid-treated group than those in the control group (1261.0 +/- 401.9 v 77.4 +/- 62.5 relative light unit [RLU]; P < 0.05). Adjuvant ascorbic acid therapy resulted in significantly higher LucCL intensity in hemodialysis patients with ferritin > or =600 ng/mL (1,348.2 pmol/L) than those with ferritin less than 600 ng/mL (2,296.0 +/- 763.8 v 414.3 +/- 88.0 RLU; P<0.05). The changes of LucCL intensity were positively correlated with serum ferritin level (R2=0.8673; P<0.05). However, there was no significant correlation between the responses of LucCL intensity to ascorbic acid administration and transferrin saturation (R2=0.195; P=0.0665).


CONCLUSIONS
Persons with excess ascorbic acid supplement in the blood or plasma generate iron-chelator-suppressible chemiluminescents suggestive of free radical formation. Whether the findings occur in vivo or that the free radicals generated in vitro lead to toxicity in patients is not known from this study. These results suggest that either lower parenteral dose or lower infusion rate of ascorbic acid may be more appropriate for adjuvant therapy in iron-overloaded uremic patients.
Chen
Wei-Teing
WT
Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan, ROC, China.
Lin
Yuh-Feng
YF
Yu
Fu-Chiu
FC
Kao
Woei-Yau
WY
Huang
Wen-Hsin
WH
Yan
Horng-Chin
HC
D000368:Aged; D000975:Antioxidants / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology* / Q000627:therapeutic use; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology* / Q000627:therapeutic use; D001713:Biphenyl Compounds / Q000032:analysis; D005260:Female; D005293:Ferritins / Q000097:blood*; D016166:Free Radical Scavengers / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology / Q000627:therapeutic use; D005609:Free Radicals / Q000097:blood*; D006801:Humans; D006834:Hydrazines / Q000032:analysis; D066298:In Vitro Techniques; D007275:Injections, Intravenous; D007501:Iron / Q000097:blood* / Q000493:pharmacokinetics; D019190:Iron Overload / Q000097:blood* / Q000188:drug therapy / Q000209:etiology; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000628:therapy; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D018384:Oxidative Stress; D010851:Picrates; D006435:Renal Dialysis / Q000009:adverse effects
D000975:Antioxidants; D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D005609:Free Radicals; D006834:Hydrazines; D010851:Picrates; D005293:Ferritins; C004931:1,1-diphenyl-2-picrylhydrazyl; D007501:Iron; D001205:Ascorbic Acid