Nell I. Mock

Circulating RBC volume, measured with biotinylated RBCs, is superior to the Hct to document the hematologic effects of delayed versus immediate umbilical cord clamping in preterm neonates

BACKGROUND: One problem assessing the hematologic physiology of preterm infants after delivery and/or the efficacy and toxicity of therapeutic interventions affecting RBC measurements is the inability of blood Hct values to accurately reflect circulating RBC volume—owing to changes in plasma volume that influence Hct (i.e., a fall in plasma volume concentrates RBCs to increase Hct; a rise in plasma volume dilutes RBCs to decrease Hct).

Disturbances in biotin metabolism in children undergoing long-term anticonvulsant therapy.

BACKGROUND In subjects undergoing long-term therapy with carbamazepine and/or phenytoin, reduced plasma concentrations of biotin have been reported. However, the diagnostic value of plasma biotin is unclear, in part because of the presence of significant plasma concentrations of biotin metabolites. Pathologic organic aciduria has also been reported with long-term anticonvulsant therapy, suggesting biotin deficiency, but no mechanism leading to deficiency has yet been determined. METHODS In the current study, we sought to determine whether biotin catabolism was accelerated in children receiving long-term treatment with certain anticonvulsants and to assess biotin status as judged by urinary excretion of biotin and 3-hydroxyisovaleric acid, an organic acid that is an indicator of deficiency of a biotin-dependent enzyme. Seven children treated with carbamazepine and/or phenytoin and six treated with phenobarbital provided untimed urine samples. Sixteen healthy children receiving no anticonvulsants served as controls. Biotin and biotin metabolites were determined by high-performance liquid chromatography/avidin-binding assay. Urinary excretion of 3-hydroxyisovaleric acid was determined using gas chromatography/mass spectrometry. RESULTS Bisnorbiotin excretion was increased significantly in the carbamazepine/phenytoin group and in the phenobarbital group. Biotin sulfoxide excretion was significantly increased in the carbamazepine/phenytoin group but not in the phenobarbital group. 3-Hydroxyisovaleric acid excretion was increased significantly in the carbamazepine/phenytoin group. However, only one child (carbamazepine/phenytoin group) had a decreased urinary excretion of biotin. CONCLUSION These data provide evidence that long-term administration of some anticonvulsants can accelerate biotin catabolism, but the indicators of biotin status conflict.

Effects of biotin deficiency on plasma and tissue fatty acid composition: evidence for abnormalities in rats.

ABSTRACT: Abnormalities of fatty acid composition have been detected in the plasma of patients who developed frank biotin deficiency during parenteral nutrition. We sought to determine which abnormalities of fatty acid composition, if any, would be replicated in the biotindeficient rat and to determine the relative temporal relationships of these abnormalities to biotin nutritional status. We measured fatty acid compositions of the phospholipids extracted from plasma, heart, and liver and assessed biotin nutritional status longitudinally in biotin-deficient and biotin-treated rats during progressive biotin deficiency. In the biotin-deficient group, significant increases relative to the biotin-treated group were detected in all three tissues in the odd-chain fatty acids 15:0 and 17:0. In the biotindeficient rats, significant increases in 18:2ω6 in liver and 18:3ω6 in plasma and liver and significant decreases in 22:5ω6 were detected in plasma and liver. The constellation of fatty acid abnormalities observed in the biotin-deficient rats was not identical to that observed in biotin-deficient patients, but abnormalities in composition of odd-chain fatty acids were detected in both human and rat and therefore are attributable to biotin deficiency per se. The abnormalities in fatty acid composition were already present by wk 4 on the egg white diet; the cutaneous findings appeared between wk 3 and 6. These observations are consistent with the hypothesis that an abnormality in fatty acid metabolism may play a pathogenetic role in the cutaneous manifestations of biotin deficiency.

Concentrations of biotin metabolites in human milk

Because estimates of the biotin requirement for infants currently are based on the biotin concentration in human milk, we sought to determine whether inactive biotin metabolites are present. Samples were collected for 7 weeks post partum from 15 healthy women. Biotin and the inactive metabolites bisnorbiotin and biotin sulfoxide were measured by means of a high-performance liquid chromatography avidin-binding assay. At 8 days post partum the proportion of biotin was 44%, bisnorbiotin 48%, and biotin sulfoxide 8%. Although biotin content increased post partum (p < 0.003), the metabolites remained an important portion of the total providing evidence that accurate measurement of biotin in human milk requires an assay that is specific for biotin.

Lymphocyte propionyl-CoA carboxylase and accumulation of odd-chain fatty acid in plasma and erythrocytes are useful indicators of marginal biotin deficiency

BACKGROUND: Recent studies indicate marginal biotin deficiency is more common than previously thought. That conclusions validity rests on two indicators of biotin status that depend on renal function.OBJECTIVE: Assessing the validity of two indicators of biotin status that do not depend upon renal function: 1) activity of the biotin-dependent enzyme propionyl-CoA carboxylase (PCC) in lymphocytes and 2) accumulation of odd-chain fatty acids in the lipids of plasma and erythrocytes.DESIGN: Marginal biotin deficiency was induced in 11 healthy adults by egg-white feeding for 28 days. Blood and 24-h urine samples were collected before commencing the diet and twice weekly thereafter. After depletion, biotin status was restored with a general diet with or without 80 &mgr;g/day or 328 nmol/day biotin supplement. Activity of PCC was determined by an optimized NaH 14CO(3) incorporation assay. Fatty acid composition was determined by gas chromatography.RESULTS: With time on the egg-white diet, lymphocyte PCC activity decreased significantly (P <0.0001); C15:0 and C17:0 content increased significantly in the lipids of plasma and erythrocytes (P <0.015). In eight of 11 subjects, lymphocyte PCC activity returned to normal within three weeks of resuming general diets with or without biotin supplement. With repletion, C15:0 and C17:0 in plasma lipids decreased (P <0.02), but odd-chain content of erythrocytes did not decrease significantly.CONCLUSIONS: Lymphocyte PCC activity is an early and sensitive indicator of marginal biotin deficiency. Odd-chain fatty acids accumulate in blood lipids more gradually during marginal deficiency and return to normal more gradually after biotin repletion.

Lymphocyte propionyl-CoA carboxylase and its activation by biotin are sensitive indicators of marginal biotin deficiency in humans

BACKGROUND Marginal biotin deficiency may be a human teratogen. A biotin status indicator that is not dependent on renal function may be useful in studies of biotin status during pregnancy. A previous study of experimental biotin deficiency suggested that propionyl-coenzyme A carboxylase (PCC) activity in peripheral blood lymphocytes (PBLs) is a sensitive indicator of biotin status. OBJECTIVE We examined the utility of measuring PCC activity and the activation of PCC by biotin in detecting marginal biotin deficiency. DESIGN Marginal biotin deficiency was induced in 7 adults (3 women) by egg-white feeding for 28 d. Blood and urine were obtained on days 0, 14, and 28 (depletion phase) and 44 and 65 (repletion phase). PBLs were incubated with (activated) or without (control) biotin before PCC assay. The activation coefficient of PCC is the ratio of PCC activity in activated PBLs to that in control PBLs. The significance of differences for all measurements was tested by repeated-measures analysis of variance with Fishers post hoc test and Bonferroni correction. RESULTS Changes in the urinary excretion of biotin and of 3-hydroxyisovaleric acid confirmed that marginal biotin deficiency was successfully induced. By day 14, PCC activity had decreased (P < 0.0001) to below the lower limit of normal in all subjects. By day 28, the activation coefficient of PCC had increased significantly (P = 0.003) and was above the upper limit of normal in 6 of 7 subjects. CONCLUSION PCC activity is the most sensitive indicator of biotin status tested to date. In future pregnancy studies, the use of lymphocyte PCC activity data should prove valuable in the assessment of biotin status.

Red cell volume can be accurately determined in sheep using a nonradioactive biotin label.

The sheep has served as an informative animal model for investigation of human fetal and newborn erythropoiesis and red blood cell (RBC) kinetics. We previously validated the permanent label (14C)cyanate for measuring red cell volume (RCV) in sheep. Here, we validate biotin labeling of RBCs as a nonradioactive method for measuring RCV in sheep with the anticipation that it can be applied in studies of human infants. The RCV was determined simultaneously using two techniques for quantitation of the biotin label. The first one quantified total blood concentration of biotin label on biotin-labeled RBCs using (125I)streptavidin. The second one enumerated biotin-labeled RBCs by flow cytometry after incubation with fluorescein-conjugated avidin. RCV measurements made using the two biotin quantitation techniques were validated against both (14C)cyanate and 51Cr as reference methods. Both biotin techniques produced RCV values that agreed well with the reference methods and with each other, producing correlation coefficients averaging ≥0.93. Sequential repetitive measurements in the same animal also agreed with the (14C)cyanate method and each other (average difference <10%). These results establish biotin-labeled RBCs as an accurate method for performing RCV measurements in sheep. This biotin method can be applied in studies that model neonatal erythropoiesis.

The proportion of mitochondrial isoenzyme of aspartate aminotransferase is not elevated in Reye's syndrome.

Summary: We reexamined a previously reported, highly specific increase in the relative proportion of the mitochondrial isoenzyme of asparate aminotransferase (AST) in the serum of patients with Reyes Syndrome. Using ion exchange chromatography, we measured mitochondrial, cytosolic, and total AST in serum samples from (1) 10 patients early in the course of Reyes Syndrome; (2) nine controls with normal serum AST; and (3) seven controls with other diseases causing an increase in serum AST. The mitochondrial percentage (2.8 ± 2.0%) in Reyes Syndrome was significantly lower (P < 0.05) than that of both the normal control group (6.1 ± 7.1%) and the group with increased AST (5.6 ± 4.0%). We thus failed to confirm the previous report of a specific increase in the % of mitochondrial isoenzyme in Reyes Syndrome, and conclude that the % of mitochondrial isoenzyme is not likely to be a useful marker of (or predictor for progression to) Reyes Syndrome.

Requirements for biotin are not affected by the combination of copper deficiency and fructose feeding.

OBJECTIVE The objective of the present study was to establish whether copper (Cu)-deficient rats fed a diet containing fructose as their sole carbohydrate source require more biotin than the recommended 2 mg/kg diet when egg-white serves as the dietary protein. METHODS Eighty weanling male Sprague-Dawley rats were randomly divided into 8 groups according to type of dietary carbohydrate (starch or fructose), level of Cu (0.6 micrograms Cu/g diet or 6.0 micrograms Cu/g diet) and level of biotin (2 mg/kg diet or 10 mg/kg diet). RESULTS Regardless of the level of dietary biotin, Cu-deficient rats fed a fructose-containing diet exhibited growth retardation, anemia, atrophied pancreata, enlarged hearts and similar death rates. The remaining Cu-deficient rats fed fructose were emaciated and sick regardless of dietary biotin levels. The concentration of biotin in serum and biotin content of liver of rats fed fructose were higher than corresponding values from rats fed starch. CONCLUSION Cu-deficient rats fed fructose are not deficient in biotin compared to published normal values. Supplementation of 10 mg/biotin/kg diet did not improve morbidity or mortality and therefore was not beneficial.