The Effect of Vitamin B12 Deficiency on Methylfolate Metabolism and Pteroylpolyglutamate Synthesis in Human Cells

Abstract

1. The uptake of 14C from [methyl-14C]methyltetrahydrofolate was significantly reduced in the phytohaemagglutinin (PHA)-stimulated lymphocytes from nine patients with untreated pernicious anaemia compared with the uptake in seven normal subjects.2. The uptake of I4C from [14C]methyltetrahydrofolate by the lymphocytes from seven of the patients with pernicious anaemia was consistently increased by addition of vitamin B,, in vitro.3. The proportion of 14C taken up from ['4C]methyltetrahydrofolate transferred to non-folate compounds was found to be significantly reduced in the PHA-stimulated lymphocytes from nine patients with untreated pernicious anaemia compared with the proportion transferred in the PHA-stimulated lymphocytes from seven normal subjects. Addition of vitamin BIZ in vitro consistently increased the transfer in vitamin B,,-deficient cells but had no consistent effect in normal cells. Normal and vitamin B,,-deficient PHA-stimulated lymphocytes took up[3H]folic acid and after 72 h incubation converted this largely into pteroylpolyglutamate forms.5. The proportion of labelled lymphocyte folate as pteroylpolyglutamate after incubation with [3H]folic acid was the same in vitamin B,,-deficient as in normal lymphocytes and the proportion of pteroylpolyglutamates formed in vitamin BIZdeficient lymphocytes was unaffected by addition of vitamin B,, in uitro. 6. No radioactivity could be decteted in pteroylpolyglutamates after incubating normal PHA-stimulated lymphocytes with [14C]methyltetrahydrofolate for 72 h, suggesting that pteroylpolyglutamate forms of folate cannot be made directly from methyltetrahydrofolate. 7. These results are consistent with the 'methyltetrahydrofolate trap' hypothesis Correspondence: Professor A. V. Hoffbrand, Department of Haematology, The Royal Free Hospital, Pond Street, Hampstead, London NW3 2QG. 617

Metabolic evidence of vitamin B-12 deficiency, including high homocysteine and methylmalonic acid and low holotranscobalamin, is more pronounced in older adults with elevated plasma folate

“…The monoglutamate can more easily pass out of the cell back into the circulation. Thus, in vitamin B-12 deficiency, an elevation in plasma folate with a concomitant fall in RBC folate often occurs because of a lack of intracellular retention of the vitamin (38,39). Arguing against the proposition that our low vitamin B-12/ elevated-folate group simply selected for individuals with more severe vitamin B-12 deficiency is our finding that RBC folate concentrations were actually significantly higher in the low vitamin B-12-elevated plasma folate group than in the low vitamin B-12-nonelevated plasma folate group.…”

Biochemical mechanisms in the Killmann experiment: critique of the deoxyuridine suppression test.

“…This hypothesis has occasioned much debate (7)(8)(9)(10)(11), some of it centering on the merits of an experiment by Killmann (12), which later workers made the basis of the deoxyuridine suppression test (13)(14)(15)(16)(17). With ra-dioautographic methods Killmann showed that exogenous deoxyuridine strongly inhibits (or suppresses) the uptake of labeled thymidine into normal bone marrow cells, but does so by a smaller percentage in bone marrow cells from cobalamin-deficient subjects.…”

The Deoxyuridine Suppression Test and Cobalamin‐folate Interrelations

“…Studies in nitrous oxide treated rats may not be equivalent to those in vitamin B12 deficient humans. For instance, the nitrous oxide treated rat apparently does not make folate polyglutamates from pteroylglutamic acid (Perry et al, 1985), whereas the cells from vitamin BI2 deficient humans can (Lavoie et al, 1974 …”