Megaloblastic anaemia in vitamin B12 deficiency

Dietary-derived vitamin B12 protects Caenorhabditis elegans from thiol-reducing agents

Background

One-carbon metabolism, which includes the folate and methionine cycles, involves the transfer of methyl groups which are then utilised as a part of multiple physiological processes including redox defence. During the methionine cycle, the vitamin B12-dependent enzyme methionine synthetase converts homocysteine to methionine. The enzyme S-adenosylmethionine (SAM) synthetase then uses methionine in the production of the reactive methyl carrier SAM. SAM-binding methyltransferases then utilise SAM as a cofactor to methylate proteins, small molecules, lipids, and nucleic acids.

Results

We describe a novel SAM methyltransferase, RIPS-1, which was the single gene identified from forward genetic screens in Caenorhabditis elegans looking for resistance to lethal concentrations of the thiol-reducing agent dithiothreitol (DTT). As well as RIPS-1 mutation, we show that in wild-type worms, DTT toxicity can be overcome by modulating vitamin B12 levels, either by using growth media and/or bacterial food that provide higher levels of vitamin B12 or by vitamin B12 supplementation. We show that active methionine synthetase is required for vitamin B12-mediated DTT resistance in wild types but is not required for resistance resulting from RIPS-1 mutation and that susceptibility to DTT is partially suppressed by methionine supplementation. A targeted RNAi modifier screen identified the mitochondrial enzyme methylmalonyl-CoA epimerase as a strong genetic enhancer of DTT resistance in a RIPS-1 mutant. We show that RIPS-1 is expressed in the intestinal and hypodermal tissues of the nematode and that treating with DTT, β-mercaptoethanol, or hydrogen sulfide induces RIPS-1 expression. We demonstrate that RIPS-1 expression is controlled by the hypoxia-inducible factor pathway and that homologues of RIPS-1 are found in a small subset of eukaryotes and bacteria, many of which can adapt to fluctuations in environmental oxygen levels.

Conclusions

This work highlights the central importance of dietary vitamin B12 in normal metabolic processes in C. elegans, defines a new role for this vitamin in countering reductive stress, and identifies RIPS-1 as a novel methyltransferase in the methionine cycle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01415-y.

The predictive value of vitamin B12 concentrations and hyperhomocysteinaemia for cardiovascular disease

BACKGROUND

Cardiovascular disease has been associated with both homocysteine and vitamin B12 levels. However, little information is available about the mutual relation in cardiovascular patients. The aim of this study was to assess the prevalence of vitamin B12 deficiency in patients with cardiovascular disease, and to study the correlation with homocysteine levels.

METHODS

Blood samples were taken from 229 patients who had been admitted to the Coronary Care Unit of the Heart-Lung Centre of the Radboud University Medical Centre in Nijmegen, the Netherlands. Patient demographics and clinical characteristics were assessed from medical files. Adjusted logistic regression was used to study the associations between vitamin B12, homocysteine and ischaemic heart disease.

RESULTS

In 70 patients (33%) serum vitamin B12 levels were below the lower limit of normal (<203 ng/l). Sixty-nine patients (33%) had vitamin B12 concentrations in the lower normal range (between 203 and 339 ng/l). Plasma homocysteine levels above the upper limit of normal were found in 83 out of the 229 patients (36%). Adjusted odds ratios for both vitamin B12 (0.76, 95% CI 0.44-1.30) and homocysteine (1.27, 95% CI 0.74-2.18) levels did not show a statistical association with ischaemic heart disease. No association was found between serum vitamin B12 levels and plasma homocysteine.

CONCLUSION

Our data suggest that hyperhomocysteinaemia and low serum vitamin B12 concentrations are independent and cannot be used as a diagnostic tool for ischaemic heart disease. (Neth Heart J 2007;15:291-4.).

Tromboembolia venosa e hiperhomocisteinemia como primera manifestación de una anemia perniciosa

INTRODUCTION AND OBJECTIVE

Hyperhomocysteinemia is associated to thrombosis and atherosclerosis. Vitamin B12 is among its main causes and may be due to a pernicious anemia. This study aimed to know the prevalence of this disease in patients who have venous thromboembolism and hyperhomocysteinemia.

PATIENTS AND METHODS

A total of 80 consecutive patients (55 men and 25 women; age: mean [standard deviation] 63 [15] years) with pulmonary embolism and/or venous thrombosis and elevated values of homocysteine (> 12 micromol/l) were studied.

RESULTS

Pernicious anemia was diagnosed (positive Schilling test, presence of anti-intrinsic factor antibodies and/or anti-parietal cells and fundal atrophic gastritis) in 5 patients (6.25% with range of age: 42-73 years. Only one of them had macrocytic anemia and there were no alterations in any of them in the thrombophilia study. The patients were treated with vitamin B12, administering it orally (1 mg/day) in 4 of them. The homocysteine and vitamin B12 values were normalized in every case at 6 months.

CONCLUSIONS

Although the prevalence of pernicious anemia is not elevated in patients with venous thromboembolism and hyperhomocysteinemia, its existence must be ruled out to avoid other thrombotic and neurological complications.