The effect of parenteral vitamin B12 treatment on its plasma metabolomic profile and on functional biomarkers of its deficiency.

Diagnosis of vitamin B12 (B12) deficiency is hampered by the low specificity cut-offs of blood-based biomarkers, like serum B12 and holo-transcobalamin (HoloTc), or B12-associated metabolites like methylmalonic acid (MMA) and homocysteine (Hcy) concentrations, or their combinations computed as combined B12 (cB12). We assessed B12 deficiency through non-invasive [13C]-propionate oxidation breath test to derive functional cut-off and tested its sensitivity in response to acute change in B12 status in low B12 adult male participants by parenterally administering 3 mg hydroxocobalamin and profiling through untargeted and targeted B12 related metabolites. The functional deficiency cut-off, based on a breakpoint analysis of [13C]-propionate oxidation with B12 concentrations, was 144 pmol/L [95% CI 106.4-182.4, p = 0.02] for B12 deficiency. Untargeted metabolomic analyses revealed potential functional B12 metabolites that are known to be associated with mitochondrial function, oxidative stress, lipids, bile acids and 1-carbon metabolism. Parenteral B12 treatment increased [13C]-propionate oxidation (14.9%, range 1.1 to 66.9) significantly and was also associated with significant alterations (p < 0.05) in B12, HoloTc, MMA, Hcy concentrations, cB12, and associated functional metabolites like propionylcarnitine (C3), its ratio to acetylcarnitine (C3/C2) and palmitoylcarnitine (C3/C16). This study explores the clinical utility of propionate breath test to define functional B12 deficiency and associated metabolites through omics-based approach.This study was registered in Clinical Trials Registry of India (CTRI) with the registration number CTRI/2018/04/012957 (registered on 03/04/2018), available from https://ctri.nic.in/Clinicaltrials/pmaindet2.php?EncHid=MjQwNDc=&Enc=&userName .