Significantly decreased hypoxanthine levels in bone marrow plasma of aplastic anemia patients revealed by 800 MHz NMR based metabolomics analysis

Background: Compared to plasma, the hypoxanthine (HX) concentration is three times higher in the human bone marrow [R1] and its availability is crucial to regulate the de novo purine synthesis in human bone marrow in vivo [R1]. Studies have shown that circulatory HX levels in the plasma increase in patients with solid tumors and leukemia [R2]. Aplastic anemia (AA) is rare disorder of bone marrow failure characterized by hypocellularity and peripheral cytopenias. As purine biosynthesis is essential for normal cell growth and proliferation, we hypothesized that bone marrow HX levels will be decreased in aplastic anemia (AA) patients and may reset back partially in AA patients showing clinical improvement. 

Aim: To compare the HX levels in bone marrow plasma samples of AA patients and control subjects and further to check its metabolic reprogramming in AA patients showing clinical improvement. 

Methods: The HX levels of bone marrow plasma metabolites were estimated for 56 AA patients and 20 control subjects using 800 MHz NMR spectroscopy. The NMR spectra were analyzed using NMR suite of commercial software (CHENOMX). The levels of altered metabolites in AA patients w.r.t control were estimated and the values are reported as Mean ± SD (SD is standard deviation). The diagnostic potential is evaluated employing standard receiver operating characteristic (ROC) curve analysis.

Results: The present study aims to compare the bone marrow plasma metabolic profiles of hypoxanthine between age and sex matched AA patients (N=40; mean age 32.31±16.03, male/female ratio of 22/18) and follow-up AA patients (N=16) with respect to age matched control subjects (N=20, mean age=39.5±18.48 years, male/female ratio of 11/9). The comparison revealed that the HX levels are significantly decreased in AA patients (HX=3.62 ± 3.17) compared to NC subjects (HX = 20.89 ± 12.73) and improved slightly in follow-up patients (HX=6.21 ±4.77, however no statistically significant change compared to AA patients). Further, the circulatory HX levels exhibit significant diagnostic potential with area under ROC (AUROC) curve values equal to 0.96 [95%CI = 0.92–1.00].

Concluding remarks: The depleted HX levels in the bone marrow plasma suggested altered/compromised purine biosynthesis/metabolism in AA patients and future studies are warranted to underscore its role in the disease pathobiology.

Reference:

[R1] King, M.E., Honeysett, J.M. and Howell, S.B., 1983. Regulation of de novo purine synthesis in human bone marrow mononuclear cells by hypoxanthine. The Journal of clinical investigation, 72(3), pp.965-970.

[R2] Wung WE, Howell SB. Hypoxanthine concentrations in normal subjects and patients with solid tumors and leukemia. Cancer research. 1984 Jul;44(7):3144-8.