Susan F Travis

Metabolic alterations in the human erythrocyte produced by increases in glucose concentration: The role of the polyol pathway

Human erythrocytes incubated in medium containing 50 mM glucose have increased intracellular sorbitol and fructose concentrations as compared with samples incubated with 5 mM glucose. Increased medium glucose concentration did not significantly alter total glucose consumption or lactate production. However, the intracellular lactate:pyruvate ratio rose, the concentrations of fructose diphosphate, and triose phosphates increased, and the 2,3-diphosphoglycerate concentration fell. [(14)C]O(2) production from glucose-1-(14)C also increased with increased medium glucose concentration. These changes are believed to reflect changes in the redox states of the diphosphopyridine nucleotide/reduced form of diphosphopyridine nucleotide (NAD/NADH) and nicotinamide-adenine dinucleotide phosphate/reduced form of nicotinamide-adenine dinucleotide phosphate (NADP/NADPH) couples resulting from increased activity of the polyol pathway. Addition of pyruvate to the incubation media prevented these changes. These studies illustrate that an increase in the red cells normal substrate, glucose, can produce changes in red cell metabolism.

Epidural hematoma of the cauda equina in a child with hemophilia A

Purpose: The presenting signs, treatment, and outcome of an epidural hematoma of the cauda equina in a child with severe hemophilia are reported for the first time. Patients and Methods: A 20-month-old boy with severe hemophilia A (factor VIII < 0.01 U/ml) presented with a 12-day history of refusal to stand and constipation of 5–7 days duration. He had normal deep tendon reflexes with normal sensation and withdrawal to pinprick of his lower extremities bilaterally. He stood on his right leg, but had inversion of his left foot and refused to bear weight on his left leg. MRI revealed an epidural hematoma of the cauda equina and a distended bladder. Factor VIII replacement therapy and lumbosacral laminectomy with evacuation of the hematoma resulted in recovery of a normal gait, but bladder dysfunction persisted for 11 months. Clean intermittent catheterization (CIC) was required until bladder function returned. Results: Complete neurologic recovery occurred 11 months after presentation. Conclusions: This case demonstrates the following points: (a) an epidural hematoma of the cauda equina in a child with severe hemophilia can present with neurologic findings that are as subtle as those seen in normal children; (b) CIC can be performed safely over an extended period without factor VIII replacement; and (c) complete recovery is possible, despite prolonged bladder dysfunction and a 12-day interval between the onset of symptoms and treatment.

Red Cell Metabolic Alterations in Postnatal Life in Term Infants: Glycolytic Intermediates and Adenosine Triphosphate

Summary: Red cell glycolytic intermediates and adenosine triphosphate were evaluated in term infants from birth to one year of age and compared to values obtained from normal adults and subjects with a population of a similar mean cell age. The concentration of glycolytic intermediates, with the exception of phosphoenolpyruvate were elevated at birth when compared to normal subjects, consistent with a young mean red cell population. The mean levels of red cell glucoses-phosphate, fnictose-6-phosphate, and “total triose phosphate” were elevated on days 1 and 4 of life when compared to both red cells from normal adults and subjects with a similar young mean red cell age. Glucose-6-phosphate steadily increased in concentration, peaked at 3 to 4 wk of age, and then progressively decreased in value. Total triose phosphate declined to a mildly elevated concentration by 3 to 4 wk of age. The mean concentrations of 2,3-diphosphoglycerate and adenosine triphosphate were normal on day 1, increased on day 4, and then declined by 3 to 4 wk to normal values, until 5 to 6 months when both increased. The mean phosphoenolpyruvate concentration was decreased on day 1 of age when compared to red cells of a similar mean age, but this decrease was not significant (P > 0.05).The mean concentrations of 3-phosphoglycerate and 2-phosphoglycerate were normal for mean red cell age on day 1 of life. The concentration of 2-phosphoglycerate increased at 3 to 4 wk of age and remained elevated for cell age at 11 to 12 months but this increase was not statistically significant (P > 0.05). 3-Phosphoglycerate levels did not change significantly throughout the first year of life. At one year of age, all red cell glycolytic intermediates and adenosine triphosphate were elevated when compared to red cells from normal adults, but were comparable to those observed in subjects with a red cell population of a similar mean cell age, consistent with the persistence of a young red cell population throughout the first year of life.Speculation: The pattern of glycolytic intermediates in the first year of life is suggestive of a relative “block” in glycolysis at the phosphofructokinase step. This block appears to result from factors other than decreased enzyme activity alone and may be secondary to an enzyme with altered kinetic properties and/or the influence of extracellular factors on enzyme activity at the in vivo level.

In vivo lability of red cell phosphofructokinase in term infants: the possible molecular basis of the relative phosphofructokinase deficiency in neonatal red cells.

Summary: Cord blood erythrocytes from nine term infants were separated rated by density gradient centrifugation into cohorts of intact cells of progressively increasing density and compared with red cells treated in a similar manner from four healthy adults. Pyruvate kinase (PK), an age-dependent enzyme, progressively decreased in activity from the lightest to the heaviest fractions, in both neonatal and adult red cells, indicating that red cells from newborn infants exhibit the same relationship between red cell age and density that had previously been demonstrated in red cells from adults. The rate of decline of red cell PK activity was essentially the same in neonates and adults, whereas phosphofructokinase (PFK) activity in cord erythrocytes decreased at a significantly faster rate when compared to adults. These data suggest that PFK has an accelerated rate of in vivo decay in neonatal red cells and is an unstable enzyme in the newborn.Speculation: The finding that PFK from cord blood has an accelerated rate of in vivo decay suggests that the relative PFK deficiency that exists in neonatal red cells is secondary to normal synthesis of an unstable enzyme, and leads to the speculation that red cell PFK in newborn infants is an isozyme (a “fetal” PFK).

Sequential changes in red cell glycolytic enzymes and intermediates and possible control mechanisms in the first two months of postnatal life in lambs.

ABSTRACT: The sequential changes in several glycolytic enzymes, glucose-6-phosphate dehydrogenase, glycolytic intermediates, and adenosine triphosphate, as well as intracellular pH and plasma inorganic phosphorus were followed simultaneously in eight lambs from birth to 2 months of age. The activities of all glycolytic enzymes and glucose- 6-phosphate dehydrogenase were elevated at birth. The 2,3-diphosphoglycerate concentration increased markedly postnatally and was associated with a simultaneous increase in the concentrations of red cell glucose-6-phosphate and total triose phosphate and a decrease in intracellular pH. Inorganic phosphorus also increased and correlated with the 2,3-diphosphoglycerate concentration in the first 10 days of postnatal life. The content of red cell 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, and ATP increased slightly. These results suggested increased glycolytic flux through the diphosphoglycerate mutase reaction which resulted in net synthesis of 2,3- diphosphoglycerate. The red cell total triose phosphate peaked and fell initially, followed by glucose-6-phosphate and 2,3-diphosphoglycerate suggesting inhibition of phosphofructokinase activity and a decrease in glycolysis secondary to decreased red cell intracellular pH. After 10 days of postnatal life all glycolytic intermediates fell simultaneously, which correlated with a decrease in activity of the glycolytic enzymes.

Red cell glycolytic intermediates and adenosine triphosphate in preterm infants on the first day of life.

ABSTRACT: Red cell glycolytic intermediates and ATP were evaluated in 47 appropriate for gestational age preterm infants on the 1st day of life who were divided into three groups on the basis of gestational age: 28-30, 31- 33, and 34-36 wk. The results were compared to those previously obtained in term infants. The concentrations of glucose-6-phosphate, total triose phosphates, and ATP were significantly higher than in term infants but appeared to be appropriately elevated for the young mean age of the red cell population. The concentration of red cell 2,3- diphosphoglycerate (2,3-DPG) was significantly decreased when compared to term infants and was lowest at 28-30 wk gestation. The content of red cell 3-phosphoglycerate was increased in term infants and was inappropriately elevated for the age of the red cell population at 28-30 wk gestation. This pattern of glycolytic intermediates was suggestive of a young red cell population metabolizing at an increased glycolytic rate with increased flow through the phosphoglycerate kinase step rather than the 2,3-DPG bypass in “normal” preterm infants. Two preterm infants of 28-30 wk gestation with low red cell intracellular pH were also evaluated and had markedly decreased concentrations of red cell 2,3-DPG and ATP and all phosphorylated intermediates distal to the phosphofructokinase reaction, indicative of a cross-over at the phosphofructokinase step secondary to acidosis. These studies demonstrate that the “normal” preterm infant has a decreased concentration of red cell 2,3-DPG in the steady state and in the presence of acidosis additional red cell metabolic perturbations occur which lead to a further fall in red cell 2,3- DPG and a decrease in the concentration of red cell ATP.

Red Cell Metabolic Alterations in Postnatal Life in Term Infants: Possible Control Mechanisms

Summary: Red cell glycolytic intermediates and enzymes in term infants in the first year of life were correlated with the fetal hemoglobin concentration (%F), intra- and extracellular venous pH, plasma inorganic phosphorus (Pi) and pyruvate kinase (PK) activity. Changes in the non-age-dependent enzymes phosphoglycerate kinase, enolase, and phosphofructokinase correlated most significantly with the postnatal decline in %F (P < 0.001), not the age of the red cell population, as reflected in PK activity. The age-dependent enzymes, hexokinase and glucose-6-phosphate dehydrogenase, however, correlated well with PK activity (P < 0.001). The concentration of glucose-6-phosphate did not correlate significantly with the postnatal decline in %F (P > 0.05) or PK (P > 0.10), but correlated significantly with the plasma Pi concentration (P < 0.001). “Total triose phosphate” and 2,3-diphosphoglycerate did not correlate with Pi.It appears from these studies that an extracellular factor, Pi, alters the pattern of glycolytic intermediates in term infants and that the postnatal changes in phosphoglycerate kinase, enolase, and phosphofructokinase are unique to the “fetal” red cell and reflect passage from fetal to “adult” erythropoiesis.Speculation: It is proposed that the rise in the glucose-6-phosphate concentration in red cells from term infants previously reported is secondary to a combination of stimulation of hexokinase activity by plasma inorganic phosphorus and a relative block in glycolysis at the phosphofructokinase (PFK) step secondary to both decreased enzyme activity and decreased activation of PFK by plasma inorganic phosphorus. It is speculated from these studies that the relative block in glycolysis at the PFK step previously described in term infants is probably greater at the in vivo level than that predicted from enzyme activity under optimal in vitro conditions.

884 GLYCOLYTIC ENZYMES IN PREMATURE INFANTS ON THE FIRST DAY OF LIFE

Prior studies of RBC glycolytic enzymes in term infants on the first day of life have revealed elevated levels of phosphoglycerate kinase (PGK) and enolase (ENO) and decreased activity of phosphofructokinase (PFK) when compared to both RBCs from normal adults and subjects with a RBC population of a similar young mean cell age, as reflected in pyruvate kinase (PK) activity. In the present study, 25 premature infants were studied on the first day of life to determine whether this increase in RBC PGK and ENO and decrease in PFK activities are greater in the preterm infant and vary with gestational age. There were 3 groups: 9 infants 28-30 wks of age; 9 of 31-33 wks and 7 of 34-36 wks. The age-dependent enzymes PK, hexokinase and aldolase were higher in premature infants than term infants indicating a RBC population of a younger mean cell age. The mean activities of both PGK and ENO were also higher in the premature infants than in term infants but did not differ significantly between 28-30 wks to 34-36 wks. Mean PFK activity, however, was higher, not lower in premature infants than in term infants. In contrast to term infants, PFK activity correlated well with the age-dependent enzyme, PK (r=0.73; p<0.001). Thus, it appears that the young mean RBC population present in the premature infant on the first day of life significantly influences PFK activity, resulting in higher levels than those anticipated at such a young gestational age.

1612 BRAINSTEM AUDITORY EVOKED POTENTIALS IN NEWBORNS: Peripheral and Central Conduction Time

Forty low risk newborn infants were studied with conceptual ages between 28 and 42 weeks. They were distinguished from high risk infants on the basis of neonatal medical complications. Brainstem auditory evoked potentials (BAEP) were recorded from vertex-ipsilateral and contralateral ear reference sites. Monaural 70 dBHL rarefaction clicks were presented at a repetition rate of 11 per second. Both ears were tested. The peak and interpeak latencies of waves I, III and V were measured in term and preterm infants. These intervals were analyzed in relationship to conceptual age in order to assess the relative contributions of the peripheral and central portions of the auditory system to the process of infant development.Since it is expected that BAEPs will have increasing diagnostic and prognostic significance for the neurologic and otologic outcome of newborns, a short term study of these responses in relationship to risk factors is underway in our laboratory. This data forms, in part, a basis for comparison of auditory brainstem function in low and high risk infants. (Supported by USPHS Grant NS15254).

INTERDEPENDENCE OF RED CELL HEXOKINASE, INORGANIC PHOSPHORUS(Pi)AND 2, 3-DIPHOSPHOCLYCERATE(2, 3-DPG)IN THE DEVELOPING FETAL LAMB

Previous studies have demonstrated that 2, 3-DPG inhibits red cell hexokinase activity in vitro and that the concentration of red cell 2, 3-DPG may be influenced by serum Pi in vivo. Since the developing fetal lamb exhibits wide variation in its red cell 2, 3-DPG content, hexokinase activity and serum Pi were studied in 7 lambs that were followed sequentially from birth until 8 weeks of life. The mean 2, 3-DPG concentration on day 1 of life was 4389±994 mumoles/ml RBC. There was a significant increase(p<0.005) in 2, 3-DPG from day 4 of iife(mean:8249±1754) through days 10-11 (mean:7577±1670). By day 17 of life the mean 2, 3-DPG concentration decreased to 4242±1832 mμmoles/ml RBC, and thereafter fell rapidly; by day 45 of life, 2, 3-DPG was not detected. No measurable 2, 3-DPG was found in 6 adult sheep. Red cell hexokinase activity appeared to be modulated by changes in the 2, 3-DPG content: Hexokinase was 1.18±0.33 units/gm hemoglobin on day 1, fell to 0.94±0.05 by days 10-11, and increased to 1.16±0.13 on day 17. From days 1 through 60 of life, changes in red cell 2, 3-DPG content correlated directly with the serum Pi(r = 0.82; p<0.001). These data demonstrate an in vivo confirmation of inhibition of red cell hexokinase activity by 2, 3-DPG and the regulation of red cell 2, 3-DPG concentration by serum Pi in the developing fetal lamb.