Energy Metabolism in Human Erythrocytes: I. EFFECTS of SODIUM FLUORIDE
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Energy Metabolism in Human Erythrocytes: I. EFFECTS OF SODIUM FLUORIDE Stephen A. Feig, … , Stephen B. Shohet, David G. Nathan J Clin Invest. 1971;50(8):1731-1737. https://doi.org/10.1172/JCI106662. Exposure of red cells to fluoride produces a variety of metabolic alterations, most of which are based upon the secondary effects of enolase inhibition, which reduces pyruvate synthesis and interferes with the regeneration of diphosphopyridine nucleotide (NAD). Adenosine triphosphate (ATP) is consumed in the hexokinase and phosphofructokinase reactions but is not regenerated since the deficiency of NAD limits glyceraldehyde phosphate dehydrogenase. ATP depletion in the presence of fluoride and calcium induces a massive loss of cations and water. Of the other known sites of ATP utilization, membrane-bound ATPase is inhibited by fluoride, but the incorporation of fatty acids into membrane phospholipids is unaffected until ATP is depleted. The addition of methylene blue to fluoride-treated red cells regenerates NAD, permitting triose oxidation and the generation of 3-phosphoglycerate and 2,3-diphosphoglycerate. Enolase inhibition is then partially overcome by mass action, and sufficient glycolysis proceeds to maintain the concentration of ATP. This in turn prevents the massive cation and water loss, and permits membrane phospholipid renewal to proceed. Membrane ATPase activity is not restored by the oxidant so that normal cation leakage remains unopposed by cation pumping in red cells exposed to the combination of fluoride and methylene blue. Find the latest version: https://jci.me/106662/pdf Energy Metabolism in Human Erythrocytes I. EFFECTS OF SODIUM FLUORIDE STEPHEN A. FEIG, STEPHEN B. SHOHET, and DAvm G. NATHAN From the Division of Hematology of the Department of Medicine, Children's Hospital Medical Center, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115 A B S T R A C T Exposure of red cells to fluoride pro- model system with particular reference to inherited duces a variety of metabolic alterations, most of which erythrocyte pyruvate kinase deficiency (2). This paper are based upon the secondary effects of enolase inhibi- presents an analysis of the metabolic perturbations pro- tion, which reduces pyruvate synthesis and interferes duced by fluoride in the red cell and also describes their with the regeneration of diphosphopyridine nucleotide partial correction by the introduction of an oxidant, (NAD). Adenosine triphosphate (ATP) is consumed methylene blue. in the hexokinase and phosphofructokinase reactions but is not regenerated since the deficiency of NAD limits METHODS glyceraldehyde phosphate dehydrogenase. ATP deple- Human blood samples were obtained from nonfasting nor- tion in the presence of fluoride and calcium induces a mal subjects and patients with young red cell populations. massive loss of cations and water. These included patients recovering from iron deficiency, Of the other known sites of ATP utilization, mem- pernicious anemia, and acute hemorrhage, as well as a pa- ATPase is inhibited by fluoride, but the tient with an unstable hemoglobin hemolytic anemia and brane-bound another with an acquired hemolytic anemia. They were col- incorporation of fatty acids into membrane phospho- lected in preservative-free heparin (0.1 mg/ml) and washed lipids is unaffected until ATP is depleted. three times at 4VC in Krebs-Henseleit buffer containing al- The addition of methylene blue to fluoride-treated bumin (1 g/100 ml). The final hematocrit was adjusted to red cells regenerates NAD, permitting triose oxidation approximately 30%7 with the same buffer. Measurements of packed cell volume, red cell count, hemoglobin concentra- and the generation of 3-phosphoglycerate and 2,3-di- tion, and reticulocyte count were performed by standard phosphoglycerate. Enolase inhibition is then partially methods (3) and in a Coulter model S counter. Glutamic overcome by mass action, and sufficient glycolysis pro- oxaloacetic transaminase activity of hemolysates was per- ceeds to maintain the concentration of ATP. This in formed by the method of Karmen, Wroblewski, and LaDue turn prevents the massive cation and water loss, and (4). Cell suspensions (3-8 ml in 25-ml Erlenmeyer flasks) permits membrane phospholipid renewal to proceed. were gassed with a mixture of air and 5% C02 to bring the Membrane ATPase activity is not restored by the oxi- pH to 7.5 +0.1. Additives were prepared to provide desired dant so that normal cation leakage remains unopposed final concentrations by the addition of 10 ul to the incubation by cation pumping in red cells exposed to the combina- flask. Incubations were carried out in a 37'C water bath blue. at 60 oscillations/min. NaH2P04 was added to give a final tion of fluoride and methylene concentration of 10 mmoles/liter of incubation mixture. The pH was measured when samples were obtained. If the pH had changed by more than 0.1 U, the samples were gassed INTRODUCTION with 5% CO2 or left open briefly to bring the pH back to In the search for improved methods of management of 7.5. Filtrates were prepared at 4°C in two volumes of 1 N anemia, the cor- perchloric acid before and during the incubations. These patients with congenital hemolytic were centrifuged at 4'C twice to remove the sediment, neu- rection of induced disorders of erythrocyte metabolism tralized with 5 M K2C0, and frozen within 2 hr. These may be instructive. The inhibition of glycolysis at the were later analyzed for ATP (5), glucose (6), lactate (7), level of enolase by fluoride (1) has been used as a and 2,3-diphosphoglycerate (2,3-DPG) (8) .1 Dr. Shohet is a Fellow of the Medical Foundation Inc. 1Abbreviationis used in this paper: DHAP, dihydroxy ace- Dr. Nathan is the recipient of U. S. Public Health Service' tone phosphate; 2,3-DPG, 2,3-diphosphoglycerate; FDP, Research Career Development Award K3-AM 35361. fructose diphosphate; G3P, glyceraldehyde-3-phosphate; Received for publication 25 November 1970 and in revised GPD, glyceraldehyde-3-phosphate dehydrogenase; 2PG, 2- form 24 February 1971. phosphoglycerate; 3PG, 3-phosphoglyceric acid. The Journal of Clinical Investigation Volume 50 1971 1731 Other glycolytic intermediates in the filtrates were mea- had no discernible effect on ATP and 2,3-DPG concen- sured in assays of 1 ml final volume by modifications of trations when used alone, and NaCN increased lactate the fluorometric methods of Lowry, Passonneau, Hassel- less than The rate berger, and Schulz (9) with an Eppendorf Fluorimeter, production in immature cells 10%. model 1100 M. For hexose monophosphates, 0.1-0.4 ml of of ATP decline seemed faster in immature cells, but the neutralized filtrate was used in a system containing 100 mat difference was not statistically significant. Stable levels Tris buffer (pH 8.0), 80 AM NADP, and 10 mM MgCl2. The were attained in both in less than 1 hr. No further de- increase in fluorescence was always less than that produced cline was noted at 3 or 4 hr. The final ATP concentra- by a standard of 4 mptmoles of NADPH. For fructose di- phosphate (FDP), dihyroxy acetone phosphate (DHAP), tion, 0.49 +0.13 mmoles/liter cells, was approximately and glyceraldehyde-3-phosphate (G3P), 0.05-0.2 ml of neu- one-third of the initial value. tralized filtrate was used in a system containing 16 mm imid- Fig. 1 also shows the rate of loss of potassium from azol buffer (pH 7.0) and 4-16 /LM NADH. For 3-phospho- fluoride-treated cells. After a lag period, during which glyceric acid (3 PG), 0.2 ml of neutralized filtrate was used ensued, especially in a system containing 16 mar imidazol buffer (pH 7.0), 5 ATP fell, a dramatic loss of potassium mM 2-mercaptoethanol, 5 mat MgC12, 0.3 mm ATP, and 4 in immature cells. We also confirmed earlier findings /Lm NADH. For pyruvate, perchloric acid filtrates were (16-19) that this massive effect on potassium perme- prepared from buffer, the red cells having been eliminated ability was inhibited by 5 mM EDTA and was not ob- by centrifugation (10). 0.05-0.2 ml of a neutralized filtrate free buffer (data not shown). In spite of this protec- was used in a system containing a final concentration of 40 mm phosphate buffer (pH 7.0), 4 mm MgCl2 and 4-16 tion against potassium loss, ATP stability was unaf- ILM NADH. With the methodology used, fluoride interfered served when the incubation was performed in a calcium- with the accurate measurement of 2-phosphoglycerate fected, confirming previous observations (15). The ad- (2PG), and this intermediate was not estimated. Neither dition of 2 mM ATP to the incubation mixture did not fluoride nor methylene blue interfered with the other en- protect fluoride-treated cells against potassium loss. zymatic determinations. The release of potassium from incubated red cells was estimated by the change in the po- Since the effect of fluoride is known to be dependent tassium ion concentration in the incubation medium measured upon phosphate concentration (20), cells were incu- with an internally standardized flame photometer (model bated in 10 mm sodium fluorophosphate to determine 143; Instrumentation Laboratory Inc., Watertown, Mass.). whether that complex might be directly involved in the All of the above concentrations were expressed per liter of red cells based upon the initial hematocrit of the cell sus- massive potassium loss. Neither potassium loss nor in- pension. hibition of lactate production were observed under The activity of membrane-bound ATPase (11) was mea- these conditions.2 sured in ghosts prepared by the Nakao, Kurashina, and Na- kao (12) modification of the method of Dodge, Mitchell, The effect of fluoride on ATP metabolism and Hanahan (13). The incorporation of radioactive fatty acid into red The dramatic loss of red cell ATP encouraged an cell membrane phospholipid was also measured.