Methylmalonic acid and coenzyme A concentrations in the livers of pair-fed vitamin B12-deficient and vitamin B12-treated sheep

The concentrations of CoA in the livers of severely vitamin B(12)-deficient ewes were about 2.6 times those in pair-fed animals treated with vitamin B(12). When the feeding rates of the pair-fed animals were closely similar, the concentrations of methylmalonic acid in deficient livers were about twice those in vitamin B(12)-sufficient livers. The molar concentrations of CoA present were more than three times those of methylmalonic acid in both deficient and treated animals, and it is concluded that the elevated concentrations of CoA in the deficient livers were not primarily due to accumulation of methylmalonyl-CoA.     

Polyamine concentrations in the brain of vitamin B12-deficient rats

To study the pathophysiology of the neuronal degeneration in vitamin B12 deficiency, we investigated the concentrations of the polyamines putrescine, spermidine, and spermine in brain regions and liver using high-performance liquid chromatography with fluorescence detection. Male Wistar rats were fed either a control or vitamin B12-deficient diet for 20 weeks. No remarkable behavioral changes were observed. Serum vitamin B12 and hepatic methionine concentrations were significantly lower and hepatic homocysteine was elevated in rats fed vitamin B12-deficient diet than in controls. Vitamin B12 deficiency was associated with decreased concentrations of spermidine, spermidine in liver and some regions of brain, although there were no observed abnormalities in behavior. These results suggest that vitamin B12 deficiency may play a role in neuronal degeneration through the disturbance of polyamine concentrations in rat brain.     

Vitamin B 12 plasma concentrations in Alzheimer disease

In this contribution we investigated the correlation between plasma vitamin B12 levels and cognitive impairment in Alzheimer's disease. We could demonstrate a significant inverse correlation when the MMSE scores of those patients with the lowest 10% Vitamin B12 plasma levels (<184 ng/ml) were compared with the upper 10% Vitamin B12 plasma levels (>598 ng/ml): p=0.008, Spearman-Rho= -0.36. MMSE in the upper percentile of plasma B12 levels was 20.0 +/- 4.6 and in the lower percentile 15.7 +/- 6.1, resulting in a difference of 4.3 MMSE points. We conclude, that vitamin B12 deficiency could aggravate or accelerate the course of Alzheimer disease as vitamin B12 possesses neuroprotective and anti-inflammatory properties.     

Nutritional value of meat: the influence of nutrition and physical activity on vitamin B12 concentrations in ruminant tissues

An important nutritional characteristic of ruminant meat is its high content in vitamin B12. The variability of these contents is not known. Three studies were been set up in order to test the influence of the animal species (2 studies on Charolais steers slaughtered at 30-32 months of age, n = 24 and n = 30 and a third one on lambs slaughtered at 4.5 months of age, n = 21), of the nature of the diet (grass vs. maize silage, lucerne or concentrate diets) and of physical activity (without or with walking) on the vitamin B12 contents of different muscle types (rather oxidative (Rectus Abdominis, RA), intermediate (Longissimus Dorsi, LD), or glycolytic (Semi Tendinosus, ST)) and on the liver. The animals were supplemented in macro and trace minerals according to usual feeding practices in France in order to theoretically avoid any risk of deficiency. For this reason, cobalt allowances, which are necessary for the ruminal synthesis of vitamin B12, could differ among treatments. The results indicate the following: (1) cobalt allowances varied widely among treatments, from (sub-)deficient to plethoric allowances, influencing vitamin B12 contents of the liver, and muscles (only in case of deficiency), (2) the effects of dietary treatments or of physical exercise were essentially related to differences in cobalt allowances, (3) the oxidative type muscle (RA) showed contents which were double those in glycolytic type muscle (RA 10.8 vs. ST 5.0 ng.g(-1)) and (4) vitamin B12 contents of raw muscles were lower than the values indicated in tables of feed composition for humans for cooked meat (0.5 to 1 vs. 2 to 3 microg.100 g(-1)).     

The effect of vitamin B12 and biotin on the metabolism of vitamin B12 in biotin-deficient rats

1. The effect of the administration of vitamin B₁₂ and biotin on the metabolic pattern of vitamin B₁₂ in biotin-deficient rats was studied. 2. No significant changes in the absorption and excretion of orally administered [⁵⁸Co]vitamin B₁₂ were noted either in vitamin B₁₂-treated and or in biotin-fed rats. A significant decrease of the uptake of orally given [⁵⁸Co]vitamin B₁₂ was observed in the liver and kidneys of biotin-treated rats, whereas an increase of uptake in the kidneys of vitamin B₁₂-treated rats was noted as compared with biotin-deficient animals. 3. No significant difference in the excretion of radioactivity was noted between biotin deficient and biotin-fed rats when [⁵⁸Co]vitamin B₁₂ was administered by injection. A small decrease was observed in vitamin B₁₂-treated rats. The retention of injected [⁵⁸Co]vitamin B₁₂ by major organs of biotin-treated rats was lower than that of biotin-deficient rats. A lower content of [⁵⁸Co]vitamin B₁₂ was also detected in the organs, with the exception of the kidneys, of vitamin B₁₂-treated rats. 4. These results are discussed in terms of an interrelationship between biotin and vitamin B₁₂.     

The anaerobic biosynthesis of vitamin B12

Vitamin B12 (cobalamin) is a cobalt-containing modified tetrapyrrole that is an essential nutrient for higher animals. Its biosynthesis is restricted to certain bacteria and requires approximately 30 enzymatic steps for its complete de novo construction. Remarkably, two distinct biosynthetic pathways exist, which are termed the aerobic and anaerobic routes. The anaerobic pathway has yet to be fully characterized due to the inherent instability of its oxygen-sensitive intermediates. Bacillus megaterium, a bacterium previously used for the commercial production of cobalamin, has a complete anaerobic pathway and this organism is now being used to investigate the anaerobic B12 pathway through the application of recent advances in recombinant protein production. The present paper provides a summary of recent findings in the anaerobic pathway and future perspectives.     

The biosynthesis of vitamin B12.

The use of 13C-Fourier transform nuclear magnetic resonance (F.t.-n.m.r.) has led to the observation that while 8 molecules of [2-13C]ALA are incorporated into vitamin B12 in P. shermanii, [5-13C]ALA labels only seven of the carbon atoms of cyanocobalamin, i.e. one of the amino methyl groups of ALA is "lost" in the process. It has also been confirmed that seven of the methyl groups of B12 are derived from 13CH3-enriched methionine and further that the chirality of the gemdimethyl grouping at C12 labelled with [13CH3]methionine is R. A soluble enzyme mixture from the 37000 or 100000 g supernatant of disrupted cells of P. shermanii converts both 14 C-labelled ALA and [14C]uro'gen III to cobyrinic acid, the simplest corrinoid material on the pathway to vitamin B12 and the coenzyme, in presence of NADPH, Co2+, Mg2+, S-adenosyl-methionine and glutathione. Multiply-labelled uro'gens (13C, 14C and 3H) have been used to show that incorporation takes place without randomization. A sequence for corrin synthesis from uro'gen III is presented.     

The diagnosis of vitamin B 12 deficiency]

In 5 normal persons, 1 patient with pernicious anemia, 5 patients with renal insufficiency in the state of compensation, and in one patient with chronic hemodialysis Schilling tests, activity of 57Co and vitamin B12 serum levels were measured. It was obvicous that activity of 57Co in serum 8 hours after oral application of 0.5 muCi 57Co-vitamin B12 showed reliable results to clear the problem of vitamin B12 malresorption. This method is easier than the Schilling test because the collection of 24-hour-urine is not necessary and an insufficiency of renal function does not influence the result.     

Biosynthesis of vitamin B12

Radioactivity from [1-¹⁴C]riboflavin was incorporated into the 5,6-dimethylbenzimidazole moiety of Vitamin B₁₂ in the aerobes Bacillus megaterium, Nocardia rugosa and Streptomyces sp. as well as in the aerotolerant anaerobe Propionibacterium freudenreichii, but not in the anaerobe Eubacterium limosum.As recently published for E. limosum, also in the anaerobe Clostridium barkeri radioactivity from [1-¹⁴C]glycine and [2-¹⁴C]glycine was found in the 5,6-dimethylbenzimidazole moiety, but not in the corrin moiety. The addition of l-[methyl-¹⁴C]methionine to C. barkeri led to the labeling of the corrin moiety and the 5,6-dimethylbenzimidazole moiety, showing that the seven extra methyl groups in the corrin ring as well as the two methyl groups of the base part originate from this precursor.In Clostridium thermoaceticum, forming the vitamin B₁₂ analog 5-methoxybenzimidazolylcobamide, [1-¹⁴C]glycine and [2-¹⁴C]glycine were also incorporated into the 5-methoxybenzimidazole moiety, but not into the corrin ring.In E. limosum l-[U-¹⁴C]glutamate led to the labeling of the corrin ring of vitamin B₁₂, but not of its base moiety.There results together with data from the literature indicate that a common biosynthetic pathway might exist for the corrinoid biosynthesis in aerobic microorganisms, and in those aerotolerant anaerobes like the Propionibacteria, which form the 5,6-dimethylbenzimidazole moiety of vitamin B₁₂ only under aerobic conditions. They also show that this pathway differs from the pathway found in anaerobic bacteria.