An Effect of Vitamin B12 Deficiency in Tissue Culture

Branched-chain amino acid catabolism fuels adipocyte differentiation and lipogenesis

Adipose tissue plays important roles in regulating carbohydrate and lipid homeostasis, though less is known about the regulation of amino acid metabolism in adipocytes. Here we applied isotope tracing to pre–adipocytes and differentiated adipocytes to quantify the contributions of different substrates to tricarboxylic acid metabolism and lipogenesis. In contrast to proliferating cells that use glucose and glutamine for acetyl–coenzyme A (AcCoA) generation, differentiated adipocytes increased branched chain amino acid (BCAA) catabolic flux such that leucine and isoleucine from media and/or protein catabolism accounted for as much as 30% of lipogenic AcCoA pools. Medium cobalamin deficiency caused methylmalonic acid accumulation and odd–chain fatty acid synthesis. B12 supplementation reduced these metabolites and altered the balance of substrates entering mitochondria. Finally, inhibition of BCAA catabolism compromised adipogenesis. These results quantitatively highlight the contribution of BCAAs to adipocyte metabolism and suggest that BCAA catabolism plays a functional role in adipocyte differentiation.

The biochemical basis of cobalamin deficiency

OBJECTIVE

In this report, our goal was to summarize the current knowledge of the biochemical basis for the impaired DNA synthesis and neuropathy associated with vitamin B12 deficiency.

MATERIAL AND METHODS

We reviewed the pertinent literature and our clinical experience with cobalamin deficiency.

RESULTS

Studies have established that the megaloblastic hematopoiesis associated with vitamin B12 and folate deficiency is secondary to impaired DNA synthesis. Two mechanisms of impairment of DNA synthesis have been proposed: the "methylfolate trap hypothesis" and the "formate starvation hypothesis." One possibility is that both hypotheses may be contributory--that is, incoming dietary folate may be inaccessible for polyglutamation in accordance with the methylfolate trap hypothesis, whereas the formate starvation hypothesis may explain the failure to use already polyglutamated forms of folate.

CONCLUSION

Although the pathophysiologic mechanisms of vitamin B12 and folate deficiency are not completely understood, nutritional anemias offer suitable models for the study of the biochemical basis of disease.

Vitamin B12 and brain development

This is a report of a 1 1/2-year-old male with megaloblastic anaemia and a progressive neurological disorder clinically resembling leucodystrophy. The child was exclusively breast fed and his mother had been a strict vegetarian for more than 4 years before the child was born. After Vitamin B12 therapy the anaemia disappeared and the neurological condition dramatically improved.

Developmental regression as an early manifestation of vitamin B12 deficiency

Loss of previously attained developmental milestones in an infant is often associated with central nervous system tumor, neuromuscular disease, or an inborn metabolic error. An infant with developmental regression and involuntary movements who was found to be vitamin B12 deficient on the basis of unrecognized maternal vitamin B12 deficiency is described. The infant had a dramatic neurologic recovery after receiving vitamin B12. The case and a review of similar cases is presented.

Optic atrophy in experimental vitamin B12 deficiency in monkeys

The clinical findings and pathological changes of the visual pathway of vitamin B12 deficient monkeys have been described. The cellular morphology and counts of the peripheral blood and bone marrow remained normal during the study (nine deficient, three controls: one still alive in each group). Visual impairment was noted in all seven of the deficient animals that were evaluated by clinical observations. Ophthalmoscopic examination disclosed optic atrophy in six of the seven deficient monkeys. Degeneration of the visual pathway was demonstrated by pathological examination in eight of the deficient group of nine (one is still alive). Loss of ganglion cells was noted in the maculae of two of three deficient animals with completed studies. In the three control animals there were neither visual disturbances nor ophthalmoscopic changes and in two animals autopsies disclosed no lesions in the visual pathways. The third animal is still alive and well.

Effects of vitamin B12 deficiency on lipid metabolism of the rat liver and nervous system

1. Rats bred from vitamin B12-depleted dams were fed on a vitamin B12-deficient diet for 12-15 months and developed a severe vitamin B12 deficiency, as judged from methylmalonic acid excretion and tissue vitamin B12 levels at slaughter. Control rats were supplemented with vitamin B12 in the drinking-water. 2. Neurological signs were recorded after 7 months but the motor nerve conduction velocities remained normal. Neuropathological examination revealed mild changes in the peripheral nerves but no changes in the central nervous system. 3. The amounts of total lipids and phospholipids were normal, but in all examined tissues the proportions of pentadecanoate (C15 fatty acid) and heptadecanoate (C17 fatty acid) were considerably increased in vitamin B12 deficiency. 4. 3H2O was incorporated to the same extent into the fatty acids of nervous tissue from vitamin B12-deficient and control rats after 48 h. Less 3H was found in the liver fatty acids of the vitamin B12-deficient rats. 5. Neurological dysfunction can be demonstrated in the vitamin B12-deficient rat; the relation of the biochemical and neuropathological changes to the neurological signs needs further study.

Fatty acid composition of myelin isolated from the brain of a patient with cellular deficiency of co-enzyme forms of vitamin B12

Myelin fractionation and subsequent lipid isolation have been carried out on a brain from a patient who suffered from a cellular deficiency of the adenosylcobalamin and methylcobalamin co-enzyme forms of vitamin B12. Examination of the fatty acid composition of choline and ethanolamine glycerophospholipids indicated a relative enrichment of odd-chain fatty acids which were identified by gas-liquid chromatography-mass spectroscopy as C15, C15:1, C17 and C17:1. A mixture of methyl branched C17 fatty acids was also identified. Odd-chain fatty acids accounted for 9.8% of the total fatty acid in the myelin choline phospholipid conpared to control values of 1.2%. The affected brain myelin phospholipids had a lower unsaturated fatty acid content. Examination of the myelin sphingolipids, sphingomyelin, cerebroside and sulfatide, yielded abnormal fatty acid profiles. The sphingomyelin contained only small amounts of C24:1 fatty acid. Both normal and hydroxy fatty acid containing cerebroside and sulfatide had reduced levels of C24 fatty acid. Determination of the relative hydroxy and normal fatty acid content of the galactolipids indicated an abnormally high hydroxy fatty acid level. Abnormal fatty acid profiles of brain cerebral sphingolipids have not been previously described in cases of vitamin B12 deficiency. Whether or not these alterations are characteristic will only be established by estimating sphingolipids in other such cases.

HLA phenotype A2;B12 in vitamin B12 neuromyelopathy

Severe neurological complications (either peripheral neuropathy, subacute combined degeneration of the cord or cerebral changes) are a characteristic feature in some patients with marked vitamin B12 deficiency. Although Addisonian pernicious anaemia (PA) is the major cause of this neurological syndrome, the disorder has been described in association with other conditions in which there is a profound depletion of vitamin B12 stores. Sixteen patients with vitamin B12 neuromyelopathy, associated with PA, have been HLA-typed for 27 alleles of the A and B loci and compared with 53 cases of PA without neurological damage and 60 controls of the same ethnic group. There is a significantly increased frequency of the HLA phenotype. A12;B12 (44% instead of 4% in PA patients without neurological damage) in the disease group studied (P less than 0.0005). The signficance of these findings in relation to the pathogenesis of vitamin B12 neuromyelopathy is discussed.

Intracellular localization of hepatic propionyl-CoA carboxylase and methylmalonyl-CoA mutase in humans and normal and vitamin B12 deficient rats

The intracellular localization of the enzymes in the vitamin B12 dependent pathway which involves the oxidation of propionate was studied in rat liver obtained from normal and vitamin B12 deficient rats as well as from man. The subcellular site of propionyl CoA carboxylase and the vitamin B12 dependent-methylmalonyl CoA mutase were determined. All of the activity of these two enzymes was demonstrated to be in the mitochondria and those enzymes were shown to be loosely bound to the inner membrane-matrix portion of the mitochondria. Vitamin B12 deficiency did not alter the subcellular localization. Finally, a rapid enzymatic assay for methylmalonyl-CoA mutase was described.

Changes in folate metabolism in baboons Papio cynocephalus treated with 2-methyl-2-aminopropanol-B12

After the intramuscular administration of the vitamin B12 analogue, 2-methyl-2-aminopropanol-B12, to vitamin B12-depleted baboons (Papio cynocephalus) the effects on vitamin B12 and folate metabolism have been studied. The 'apparent' serum vitamin B12 and the serum folate concentrations increased, the liver folate concentrations decreased, and the liver vitamin B12 concentrations were unchanged. The analogue caused a marked increase in the amount of formiminoglutamic acid excreted after a histidine load whereas the amount of methylmalonic acid excreted after a valine load decreased. The rate of red blood cell regeneration after venesection was normal in baboons treated with the analogue and there was no evidence of megaloblastic haemopoiesis. Two baboons given the analogue developed a partial loss of utilization and lack of co-ordination in the hind limbs.