Characterization of endogenous folate and incorporation of labelled folates into the brain of the South African fruit bat.

Folate in the brain of the South African fruit bat consists of 10-formyltetrahydropteroyglutamic acid and the tri-, tetra- and penta- forms of 5-methyltetrahydropteroylglutamic acid. Following parenteral injection, only 5-[3H]-methyltetrahydropteroylglutamic acid was taken up by the brain, but none of a dose of 14C-labelled tetrahydropteroylglutamic acid was detectable. Only trace smounts of the 5-methyltetrahydropteroylglutamic acid were converted into the formyl compounds and a small amount of methyltetrahydropteroyltriglutamic acid appeared after 96 h. There was no significant difference in vitamin B-12-deficient animals.

Utilization of [2-14C]tetrahydropteroylglutamic acid and 5-[G-3H]methyltetrahydropteroylglutamic acid as substrates for folate polyglutamate synthesis in fruit bats: effect of vitamin B-12-deficiency.

[2-14C]Tetrahydropteroylglutamic acid and 5-[G-3H]methyltetrahydropteroylglutamic acid were given intraperitoneally to fruit bats. Folate polyglutamates were formed in the liver from both substrates in different amounts and at different rates. The methylfolate pool appeared to remain separate from the tetrahydrofolate pool. More polyglutamate was formed from tetrahydropteroylglutamic acid than from 5-methyltetrahydropteroylglutamic acid. There was a fall in the folate content of the liver in the vitamin B-12-deficient bat and a more rapid incorporation of folates into polyglutamates but thereafter a more rapid loss of the labelled folate from liver.

A comparison of serum transcobalamin levels in white and black subjects.

Serum transcobalamins (TC) have been measured in 82 white and 79 Black healthy adults, 170 white and 73 Black pregnant subjects and in cord blood samples from 33 whites and 13 Blacks. Healthy Black adults had significantly higher mean TC I, TC II, and TC III levels than white adults of the same sex. These differences in mean TC levels persisted at all stages of pregnancy. Mean cord blood levels of TC II and TC III were significantly higher in Blacks than in whites. No environmental factors could be identified to account for these differences, which are probably genetically determined.

Levels of transcobalamins I, II, and III during pregnancy and in cord blood.

The levels of unsaturated serum transcobalamins (TC I, TC II, and TC III) of 193 women at various stages of pregnancy and the puerperium, and of 33 specimens of cord blood, have been measured. In addition, seven subjects were studied serially through pregnancy. The pattern of changes was similar in both groups. TC I and TC III rose steadily during pregnancy and fell in the puerperium, while TC II decreased in the 2nd trimester, rose sharply in the 3rd and fell in the puerperium. The changes in the individual TCs probably result from a complex of hormonally induced changes in binder production, release, or catabolism, and the effect of hydraemia.

A sex difference in serum cobalamin and transcobalamin levels.

In healthy young adults, serum levels of cobalamin, unsaturated and total cobalamin binding capacity, and transcobalamin (TC) II are significantly higher in females, while TC III is higher in males. These findings have relevance to the reference values in normals for these tests.

Prevention of folate deficiency by food fortification. VII. The use of bread as a vehicle for folate supplementation.

Bread fortified to contain a daily dose of 900 mug folic acid was administered to patients in late pregnancy. The patients receiving the bread showed significant rise in red cell folate concentration. The rise was similar to that observed in women receiving a daily dose of 300 mug of folic acid in tablet form. It is concluded that bread may be used as a vehicle for folic acid fortification.

Transition from a hunter-gatherer to a settled lifestyle in the !Kung San: effect on iron, folate, and vitamin B12 nutrition.

In 1969 a group of hunter-gatherer San were studied (Am J Clin Nutr 1971;24:229-42). Their state of hematological nutrition was excellent with a negligible incidence of iron, folate, or vitamin B12 deficiency. A genetically and linguistically similar San community who have been settled for the past 15 yr were the subjects of the present study. Anemia, due in the main to iron and/or folate deficiency, has become more common. Alcoholism has become rife in both sexes and all age groups. Our findings show that a settled lifestyle has resulted in a significant deterioration in the San's hematological nutrition.

Cobalamin inactivation by nitrous oxide produces severe neurological impairment in fruit bats : protection by methionine and aggravation by folates.

Nitrous oxide, which inactivates cobalamin when administered to fruit bats, results in severe neurological impairment leading to ataxia, paralysis and death. This occurs after about 6 weeks in animals depleted of cobalamin by dietary restriction, and after about 10 weeks in cobalamin replete bats. Supplementation of the diet with pteroylglutamic acid caused acceleration of the neurological impairment - the first unequivocal demonstration of aggravation of the neurological lesion in cobalamin deficiency by pteroylglutamic acid. The administration of formyltetrahydropteroylglutamic acid produced similar aggravation of the neurological lesion. Supplementation of the diet with methionine protected the bats from neurological impairment, but failed to prevent death. Methionine supplementation protected against the exacerbating effect of folate, preventing the development of neurological changes. These findings lend support to the hypothesis that the neurological lesion in cobalamin deficiency may be related to a deficiency in the methyl donor S-adenosylmethionine which follows diminished synthesis of methionine.

Ferritin in breast milk of black urban and rural mothers.

Ferritin levels in serum and milk were investigated in series of 15 urban and 18 rural black mothers. No mother was anaemic. Mean serum ferritin levels in the urban and rural groups were 57 +/- 55 ug/l and 25 +/- 28 ug/l (mean +/- SD). Corresponding milk ferritin concentrations were 21 +/- 22 ug/l and 29 +/- 30 ug/l respectively. The significance of ferritin in human milk is discussed.

Role of serum folate binders in the delivery of folate to tissues and to the fetus.

Specific folate binding protein (FBP) and non-specific binding protein have been prepared from pooled serum from patients in late pregnancy. The two classes of folate binder were labelled with 75Se-selenofolate and injected into non-pregnant and pregnant rabbits. Selenofolate bound to specific FBP was delivered predominantly to the liver, in both pregnant and non-pregnant animals. Fetal tissue took up selenofolate from non-specific FBP only. Specific FBP thus functions to deliver folate to stores and represents a storage pool of folate. The non-specific FBP are responsible for the delivery of folate to the fetus, and probably also to sites of utilization.

Vitamin B12 binders (transcobalamins) in serum.

The measurement of plasma or serum vitamin B12 (B12) binders is important in the diagnosis of congenital megaloblastic anemias, the myeloproliferative disorders and perhaps in other malignancies. Two classes of binders circulate in plasma, Transcobalamin II (TC II) and R-binders. The latter have been divided by some authors into transcobalamin I (TC I) and transcobalamin III (TC III), and the validity of this division is discussed. R-binders and TC II differ in their apparent molecular weight on gel filtration chromatography, by which method they can be separated reliably. However, the technique is time-consuming and cumbersome and a variety of rapid separation methods have been described in the literature. These are discussed and compared to the standard gel filtration separation method. TC I and III are separable on the basis of their differing charges, and the methods which have been described for accomplishing this are compared and critically reviewed. There has been some controversy in the literature as to whether plasma or serum should be used to measure circulating B12 binders. Leukocytes, which contain R-binders, release these in vitro and this release is greatest when blood is allowed to clot and the serum separated. Consequently, the use of plasma, sometimes with agents added to prevent leukocytic release of binder, has been advocated. Yet, none of the agents used eliminates artifact totally, and this aspect, too, is reviewed. Lastly, several techniques for the purification of B12 binders have been described. Some techniques result in pure binder preparations, while others result in preparations which are free of other binders but contaminated with non-B12 binding proteins. Both approaches have advantages and disadvantages, and these are discussed.

Transplacental transport in the rabbit of vitamin B12 bound to human transcobalamin I, II and III.

Transcobalamins I, II and III (TCI, TCII, TCIII) were purified from human serum, saturated with 57Co-vitamin B12 (57Co-B12), and injected into pregnant rabbits. Whole body retention of the 57Co-B12 averaged 91% and was similar for each of the three vitamin B12 binders. A maximum of 62% of the injected 57Co-B12 was found in fetal tissues when the vitamin was injected bound to TCII, but only 6--7% when bound to TCI or TCIII. Thus TCII is responsible for the delivery of vitamin B12 to the fetus.

A comparison of methods for the rapid quantitation of unsaturated transcobalamin II and the R-binding proteins.

Methods for the rapid quantitation on unsaturated transcobalamin II (TC II) and R-binders in serum following separation of these binders using a) adsorption by uncoated charcoal, b) adsorption by Quso G32, c) precipitation with ammonium sulphate, and d) acidification of serum, have been compared with the standard gel filtration technique. In serum from healthy subjects and patients with elevated R-binders, the serum acidification and Quso methods yielded results in closest agreement with those obtained by gel filtration. When TC II was markedly elevated, the recommended concentration of Quso failed to remove all TC II from serum. Both the serum acidification and Quso methods are suitable for routine use, providing that with the latter method the concentration of Quso is increased when elevated levels of TC II are anticipated, as, eg, in severe jaundice. All the rapid methods tested yielded clinically significant results in patients with myeloproliferative disorders.

Binding of methylfolate and pteroylglutamic acid by the specific serum folate binder.

The binding sites for methylfolate of the FABP in serum are fully saturated in the physiological state. When the FABP of serum from pregnant subjects is stripped of its endogenous folate, it is capable of binding an average of 549 +/- 12 pg/ml (range 464 to 723) of 14C-methylfolate, compared with 736 +/- 57 pg/ml (range 491 to 1610) of 3H-PGA. When 3H-PGA is added to untreated serum, an average of 258 +/- 6 pg/ml (range 218 to 325) is bound by FABP; this binding represents sites available to PGA but not to methylfolate, as well as sites from which methylfolate is displaced by 3H-PGA. This displacement averages 71 +/- 10 pg/ml (range 9 to 142), the amount which the standard technique for measurement of the UFBC for 3H-PGA overestimates the true UFBC for PGA.

Increased erythrocytic diphosphoglycerate in megaloblastic anaemia. A compensatory mechanism?

The levels of erythrocytic 2,3-diphosphoglyceric acid (2,3-DPG) in a group of patients with megaloblastic anaemia were compared with levels in an iron-deficient subject. The megaloblastic cells appeared to have 2 mumol more 2,3-DPG per g Hb than the iron-deficient cells, at the average haemoglobin level found in the megaloblastic group. The anticipated adaptive decrease in the oxygen affinity of the blood was not apparent when the relationship of P50 (7,4) to haemoglobin level was examined. This was shown to be due to a decreased mean corpuscular haemoglobin concentration (MCHC), which counteracted the effect of the increased 2,3-DPG.

Normal values for haemoglobin concentration and red cell indices in preschool children on the Highveld.

Data on haemoglobin concentration, red cell count, packed cell volume, mean cell volume, mean cell haemoglobin and mean cell haemoglobin concentration for 'normal' children aged 1-4 years living on the Highveld (altitude 1400-1800 m) are presented in yearly age groups. The children were defined as normal on the basis of having growth attainment and iron, folate and vitamin B12 nutrition within accepted normal limits. The results obtained differ from the standard reference values published for children resident at sea level. It is suggested that the mean (+/- 2 SD) ranges presented be used as normal ranges in the population studied.