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, cB_12, 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 .