Immunomodulation by vitamin B12: augmentation of CD8+ T lymphocytes and natural killer (NK) cell activity in vitamin B12-deficient patients by methyl-B12 treatment

Cobalamin (vitamin B12) in subacute combined degeneration and beyond: traditional interpretations and novel theories

Subacute combined degeneration (SCD) is a neuropathy due to cobalamin (Cbl) (vitamin B(12)) deficiency acquired in adult age. Hitherto, the theories advanced to explain the pathogenesis of SCD have postulated a causal relationship between SCD lesions and the impairment of either or both of two Cbl-dependent reactions. We have identified a new experimental model, the totally gastrectomized rat, to reproduce the key morphological features of the disease [spongy vacuolation, intramyelinic and interstitial edema of the white matter of the central nervous system (CNS), and astrogliosis], and found new mechanisms responsible for the pathogenesis of SCD: the neuropathological lesions in TGX rats are not only due to mere vitamin withdrawal but also to the overproduction of the myelinolytic tumor necrosis factor (TNF)-alpha and the reduced synthesis of the two neurotrophic agents, epidermal growth factor (EGF) and interleukin-6. This deregulation of the balance between TNF-alpha and EGF synthesis induced by Cbl deficiency has been verified in the sera of patients with pernicious anemia (but not in those with iron-deficient anemia), and in the cerebrospinal fluid (CSF) of SCD patients. These new functions are not linked to the coenzyme functions of the vitamin, but it is still unknown whether they involve genetic or epigenetic mechanisms. Low Cbl levels have also been repeatedly observed in the sera and/or CSF of patients with Alzheimer's disease or multiple sclerosis, but whether Cbl deficit plays a role in the pathogenesis of these diseases is still unclear.

Folate deficiency inhibits the proliferation of primary human CD8+ T lymphocytes in vitro

Folate is required for one-carbon transfer reactions and the formation of purines and pyrimidines for DNA and RNA synthesis. Deficiency of folate can lead to many clinical abnormalities, including macrocytic anemia, cardiovascular diseases, birth defects, and carcinogenesis. The nucleotide imbalance due to folate deficiency causes cell cycle arrest in the S phase and uracil misincorporation into DNA, which may result in DNA double-strand breaks during repair. The role of folate in the immune system has not been fully characterized. We cultured PHA-activated human T lymphocytes in varying concentrations of folate, and measured proliferation, cell cycle, apoptosis, uracil misincorporation, and proportions of Th cells (CD4(+)) and cytotoxic T (CD8(+)) cells. Folate deficiency reduced proliferation of T lymphocytes, induced cell cycle arrest in the S phase, induced apoptosis, and increased the level of uracil in DNA. Folate deficiency also increased the CD4(+) to CD8(+) ratio due to a marked reduction of CD8(+) cell proliferation. Folate or nucleoside repletion of folate-deficient cells rapidly restored T lymphocyte proliferation and normal cell cycle, reduced the DNA uracil content, and lowered the CD4(+) to CD8(+) ratio. These data suggest that folate status may affect the immune system by reducing the capacity of CD8(+) cells to proliferate in response to activation.

Functional Vitamin B12 Deficiency and Determination of Holotranscobalamin in Populations at Risk

BACKGROUND

The prevalence of a sub-clinical functional vitamin B12 deficiency in the general population is higher than previously expected. Total serum vitamin B12 may not reliably indicate vitamin B12 status. To get more specificity and sensitivity in diagnosing vitamin B12 deficiency, the concept of measuring holotranscobalamin II (holoTC), a sub-fraction of vitamin B12, has aroused great interest. HoloTC as a biologically active vitamin B12 fraction promotes a specific uptake of its vitamin B12 by all cells. In this study we investigated the diagnostic value of storage (holoTC) of vitamin B12 and functional markers (methylmalonic acid (MMA)) of vitamin B12 metabolism in populations who are at risk of vitamin B12 deficiency.

SUBJECTS AND METHODS

Our study included 93 omnivorous German controls, 111 German and Dutch vegetarian subjects, 122 Syrian apparently healthy subjects, 127 elderly Germans and finally 92 German pre-dialysis renal patients. Serum concentrations of homocysteine (Hcy) and MMA were measured by gas chromatography-mass spectrometry, folate and vitamin B12 by chemiluminescence immunoassay, and holoTC by utilizing a RIA test.

RESULTS

High Hcy (>12 micromol/l), high MMA (>271 nmol/l) resp. low holoTC (vitamin B12) in serum were detected in 15%, 8% resp. 13% (1%) of German controls, 36%, 60%, resp. 72% (30%) of vegetarians, 42%, 48% resp. 50% (6%) of Syrians, 75%, 42%, resp. 21% (7%) of elderly subjects and 75%, 67% resp. 4% (2%) of renal patients. The lowest median levels of holoTC were observed in vegetarians, followed by the Syrian subjects (23 and 35 pmol/l, respectively). Renal patients had significantly higher levels of holoTC compared to the German controls (74 vs. 54 pmol/l). In the vitamin B12 range between 156 pmol/l (conventional cut-off level) and 241 pmol/l, both mean concentrations of holoTC and MMA were in the pathological range. HoloTC was the earliest marker for vitamin B12 deficiency followed by MMA. Vitamin B12 deficiency causes folate trapping. A higher folate level is required to keep Hcy normal. The relationship between MMA and holoTC seemed dependent on renal function. In renal patients with a glomerular filtration rate below 36 ml/min, a significantly lower mean level of MMA was detected within the highest tertile of holoTC concentration, compared to the lowest tertile. Thus, in renal patients, a higher serum concentration of circulating holoTC is required to deliver sufficient amounts of holoTC into the cells.

CONCLUSION

Our data support the concept that the measurement of holoTC and MMA provides a better index of cobalamin status than the measurement of total vitamin B12. HoloTC is the most sensitive marker, followed by MMA. The use of holoTC and MMA enables us to differentiate between storage depletion and functional vitamin B12 deficiency. Renal patients have a higher requirement of circulating holoTC. In renal dysfunction, holoTC cannot be used as a marker of vitamin B12 status.

The impact of vegetarianism on some haematological parameters

OBJECTIVE

Subjects adopting a vegetarian diet are liable to vitamin B12 and iron deficiencies. Co-existing vitamin B12 and iron deficiencies may give an equivocal haematological picture, which may, in turn, delay making an early diagnosis. The current work was undertaken to investigate some haematological parameters in relation to vitamin B12 and iron status in vegetarians.

SUBJECTS AND METHODS

Twenty-nine vegans, 64 lacto- and lacto-ovo-vegetarians, in addition to 20 occasional meat eaters, were enrolled for this study. The total group included 49 males and 64 females aged [mean (SD) = 46(15) yr]. Complete blood count, methylmalonic acid (MMA), homocysteine (HCY), ferritin, and transferrin concentrations and percentage transferrin saturation were assayed, using conventional methods.

RESULTS

Vegans displayed the highest MMA and HCY levels (median MMA = 708 nmol L(-1); HCY = 12.8 micromol L(-1)). A lower lymphocyte count and a higher mean corpuscular volume (MCV) were found in vegans compared with lacto- or lacto-ovo-vegetarians (median = 1.51 x 10(9) vs. 1.83 x 10(9) L(-1); 92 vs. 89 fL, respectively). Vitamin B12-deficient subjects in the higher range of transferrin saturation percentage had higher MCV than vitamin B12-deficient subjects in the lower transferrin saturation range (mean MCV = 92 vs. 89 fL). A lower platelet count was found in the highest quartile of MMA (mean = 211 x 10(9) L(-1)) and in the highest quartile of HCY (mean = 215 x 10(9) L(-1)), compared with the other quartiles. Lower lymphocyte and platelet counts and higher MCV were found in subjects with elevated MMA and HCY, compared to those with normal metabolites. Factors that explained the variations in MCV were red blood cell count, ferritin, transferrin saturation, and methylmalonic acid levels.

CONCLUSION

vitamin B12 and iron status were compromised by a vegetarian diet. Variations in mean corpuscular volume were determined by iron and vitamin B12 status. Lower lymphocyte and platelet count were accompanied by metabolic evidence that indicated vitamin B12 deficiency.

Modulation of intracellular Ca(2+) concentration by vitamin B12 in rat thymocytes

We have studied several novel effects of vitamin B12 (cyanocobalamin) on cellular Ca(2+) homeostasis in rat thymocytes. We determined the effect of various concentrations of vitamin B12 on intracellular Ca(2+) concentration ([Ca(2+)]i) and parameters of Ca(2+)in signaling using the fluorescent dye Fura-2. The basal [Ca(2+)]i in Ca(2+)-containing media was 115 +/- 5 nM but in vitamin B12 (10 nM)-treated thymocytes [Ca(2+)]i was decreased to 60 +/- 15 nM (mean +/- SEM) during the first 5 min. The decline in [Ca(2+)]i was accompanied by an increase in the endoplasmic reticulum Ca(2+) store, presumably as a result of Ca-ATPase activation. At the same time 100 nM-10 mM B12 induced the accumulation of Ca(2+) in mitochondria. Somewhat higher concentrations of B12 (1-10 microM) had no effect on [Ca(2+)]i. A further increase in B12 concentration with range from 50 microM to 1 mM caused a dose-dependent elevation of [Ca(2+)]i from the basal level (115 +/- 5 nM) up to 200 +/- 50 nM in thymocytes, and this elevation was partially blocked in Ca(2+)-free media. This high concentration of vitamin B12 caused a gradual decrease of endoplasmic reticulum Ca(2+) stores by means of Ca-ATPase inhibition. The B12-induced increase in [Ca(2+)]i was not observed after depletion of intracellular Ca(2+) stores, induced by addition of 2',5'-di(tert-butyl)-1,4-benzohydroquinone (BHQ), an inhibitor of endoplasmic reticulum Ca (2+)-ATPase, concanavalin A, or arachidonic acid. These studies show that vitamin B12 regulates [Ca(2+)]i via several different mechanisms at different B12 concentrations. Participation of G proteins and calmodulin activity in B12-mediated [Ca(2+)]i increase is discussed.

Hyperhomocysteinemia and elevated methylmalonic acid indicate a high prevalence of cobalamin deficiency in Asian Indians

BACKGROUND

In India, most people adhere to a vegetarian diet, which may lead to cobalamin deficiency.

OBJECTIVE

The objective was to examine indicators of cobalamin status in Asian Indians.

DESIGN

The study population included 204 men and women aged 27-55 y from Pune, Maharashtra, India, categorized into 4 groups: patients with cardiovascular disease (CVD) and diabetes, patients with CVD but no diabetes, patients with diabetes but no CVD, and healthy subjects. Data on medical history, lifestyle, and diet were obtained by interviews and questionnaires. Blood samples were collected for measurement of serum or plasma total cobalamin, holotranscobalamin (holoTC), methylmalonic acid (MMA), and total homocysteine (tHcy) and hemetologic indexes.

RESULTS

MMA, tHcy, total cobalamin, and holoTC did not differ significantly among the 4 groups; therefore, the data were pooled. Total cobalamin showed a strong inverse correlation with tHcy (r = -0.59) and MMA (r = -0.54). Forty-seven percent of the subjects had cobalamin deficiency (total cobalamin <150 pmol/L), 73% had low holoTC (<35 pmol/L), 77% had hyperhomocysteinemia (tHcy >15 micromol/L), and 73% had elevated serum MMA (>0.26 micromol/L). These indicators of impaired cobalamin status were observed in both vegetarians and nonvegetarians. Folate deficiency was rare and only 2.5% of the subjects were homozygous for the MTHFR 677C-->T polymorphism.

CONCLUSIONS

About 75% of the subjects had metabolic signs of cobalamin deficiency, which was only partly explained by the vegetarian diet. If impaired cobalamin status is confirmed in other parts of India, it may have important health implications.