Studies on the folic acid activity of human serum

A method for the measurement of serum folic acid activity is described, which is a modification of previous methods. The material in serum with activity for L. casei is made up of a stable and a labile component. The amount of stable component in normal subjects and patients with megaloblastic anaemia is similar. The amount of labile component varies. In patients with folic acid deficiency none is present; in normal subjects it constitutes between 65 and 94% of the total serum L. casei activity. The labile component appears to be an index of folic acid metabolism, and the assay of total serum L. casei activity is therefore a valuable method for differentiating patients requiring treatment with folic acid from normal subjects and patients with primary vitamin B(12) deficiency. Normal subjects had serum folic acid levels from 5.9 to 21.0 mmug./ml. (mean 9.9 mmug./ml. +/- 0.3 mmug./ml. S.E.). In patients with megaloblastic anaemia requiring treatment with folic acid, other than megaloblastic anaemia of pregnancy, the levels were less than 4.0 mmug./ml. Patients with uncomplicated pernicious anaemia had levels from 6.0 to 27.0 mmug./ml. (mean 16.6 mmug./ml. +/- 1.1 mmug./ml. S.E.). The mean level in this group was higher than in normal subjects, and the highest levels of all were found in patients with subacute combined degeneration of the cord with minimal anaemia (range 14.4 to 36.8 mmug./ml.; mean 24.8 mmug./ml. +/- 2.4 mmug./ml. S.E.). The L. casei activity of the labile component is lost during autoclaving or storage at -20 degrees C. This loss can be prevented during autoclaving by using adequate amounts of ascorbic acid in the phosphate buffer used to dilute the serum for assay and by adding ascorbic acid to serum that is to be stored. Moreover, the activity lost during the storage of serum not protected by ascorbic acid could be restored, for periods up to three months, by adding ascorbic acid to this serum before assay.

Urinary excretion of histidine derivatives in megaloblastic anaemia and other conditions and comparison with the folic acid clearance test

Urinary excretion of urocanic acid and formimino-glutamic acid in abnormal amounts following oral doses of histidine has been observed not only in most cases of megaloblastic anaemia, but in iron-deficiency anaemia, haemolytic anaemia, and neoplastic disease. The urinary excretion of these substances is increased in those disease states in which an abnormally rapid rate of removal from the plasma of intravenously injected folic acid has been demonstrated.

Stimulatory effects of hepatocyte growth factor on hemopoiesis of SCF/c-kit system-deficient mice

In this study, we report that W/W mutant mice, which have severe macrocytic anemia caused by a deficit of extracellular domain in c-kit molecules and therefore die perinatally, have hemopoietic stem cells (HSCs) and mature hematolymphoid cells in the bone marrow (BM), thymus, and spleen, although there are significant decreases in cell counts. Moreover, the mitogen-induced proliferative response, mixed lymphocyte reaction, and anti-SRBC plaque formation of spleen cells in W/W mice are similar to those in age-matched +/? littermates and normal mice, suggesting that the SCF/c-kit system is necessary for cell proliferation but not essential for HSCs to differentiate. We next examine the stimulatory effects of hepatocyte growth factor (HGF) on hemopoiesis in W/W mice. HGF has a stimulatory effect on the colony formation (CFU-C) of W/W BM cells when cultured using either a methylcellulose assay (containing cytokines) or a long-term culture (LTC) assay. A similar stimulatory effect of HGF is observed in the other W or SI locus-mutant mice (W/Wv and SI/SId mice), which show less severe anemia than W/W. The numbers of nonadherent cells and cobblestone colonies significantly increase in the LTCs using their BM cells. In addition, in vivo administration of HGF shows a transient increase in the CFU-C counts in BM cells and peripheral blood cells. RBC, WBC, and platelet counts also increased. These results suggest that the SCF/c-kit system is not essential to hemopoiesis but that a compensatory system such as the HGF/c-met system functions in the SCF/c-kit system-deficient mice.

Folic acid fortification of the food supply. Potential benefits and risks for the elderly population

OBJECTIVE

To estimate the potential benefits and risks of food folic acid fortification for an elderly population. Benefits are expected through the improvement of folate and homocysteine status, but there is also a risk of masking or precipitating clinical manifestations related to vitamin B12 deficiency with increasing exposure to folic acid.

DESIGN

Cross-sectional analysis, with projected change at various levels of folic acid fortification.

SETTING

Participants in the Framingham Heart Study original cohort.

PARTICIPANTS

A total of 747 subjects aged 67 to 96 years who both completed usable food frequency questionnaires and had blood concentrations of B vitamins and homocysteine measured.

MAIN OUTCOME MEASURES

Projected blood folate and homocysteine concentrations and combined high folate intake and low plasma vitamin B12 concentration.

RESULTS

Percentages of this elderly population with folate intake below 400 microg/d are projected to drop from 66% at baseline to 49% with 140 microg of folate per 100 g of cereal-grain product, to 32% with 280 microg, to 26% with 350 microg, and to 11% with 700 microg. Percentages with elevated homocysteine concentrations (>14 micromol/L) are projected to drop from 26% at baseline to 21% with 140 microg of folate per 100 g, to 17% with 280 microg, to 16% with 350 microg, and to 12% with 700 microg. Without fortification, the prevalence of combined high folate intake (>1000 microg/d) and low plasma vitamin B12 concentration (<185 pmol/L [<250 pg/mL]) was 0.1%. This is projected to increase to 0.4% with folate fortification levels of 140 to 350 microg/100 g and to 3.4% with 700 microg.

CONCLUSION

The evidence suggests that, at the level of 140 microg/100 g of cereal-grain product mandated by the Food and Drug Administration, the benefits of folate fortification, through projected decreases in homocysteine level and heart disease risk, greatly outweigh the expected risks. However, quantification of the actual risks associated with vitamin B12 deficiency remains elusive. Before higher levels of folic acid fortification are implemented, further research is needed to better understand the clinical course of various forms of vitamin B12 deficiency, to measure the potential effect of high folate intake on this course, and to identify cost-effective approaches to the identification and treatment of all forms of vitamin B12 deficiency.

PRACTICAL EVALUATION OF THE FIGLU TEST IN PREGNANCY WITH SPECIAL REFERENCE TO THE WHITE CELL CHANGES

Using slight modifications to the method of Kohn, Mollin, and Rosenbach (1961) the histidine loading test has been carried out in 210 pregnant women. Seventy per cent. of the cases showed complete haematological correlation and this rose to 87% when marrow puncture was performed. False positive results occurred in some cases showing active erythropoiesis in response to iron therapy. False negative results were noted when other complications in addition to anaemia were present, and it was felt that these might interfere with the metabolism of histidine. In some cases the histidine test anticipated the haematological change.Seventy-seven per cent. of women with multiple pregnancies showed evidence of folic acid deficiency. Only in a few cases was the test positive before the 25th week of pregnancy. These were either cases of multiple pregnancy, haemolytic anaemia, malabsorption syndrome, or women with a recent history of megaloblastic anaemia of pregnancy. The test appears to confirm the significance of white cell changes as an indication of folic acid deficiency in pregnancy.

FOLIC ACID AND VITAMIN B12 LEVELS IN PREGNANCY AND THEIR RELATION TO MEGALOBLASTIC ANAEMIA

There is a significant fall in the serum folic acid level during pregnancy, reaching its lowest level at term. This is most pronounced in twin pregnancies. A similar but less spectacular fall occurs in the vitamin B(12) concentration. In megaloblastic anaemia both folic acid and vitamin B(12) levels are lower than in other pregnant women. The degree of megaloblastic change in the bone marrow, as measured by the type and number of megaloblasts, is reflected in the vitamin levels, cases with florid megaloblastosis showing the most marked depression of vitamin B(12) and folic acid activity. Although there is a significant difference in the mean folic acid levels between megaloblastic and normoblastic pregnant women, a considerable overlap exists between individual values in the two groups. When the labile folic-acid factor is determined separately the test becomes much more specific. In the present series, all cases of megaloblastic anaemia yielded labile-factor levels below 1.0 mmug. per ml., while a similar value was encountered in only one of 35 normal pregnancies. In five women with megaloblastic anaemia the vitamin B(12) concentration was less than 100 mumug. per ml. but rose to normal levels on folic acid therapy alone.