Serum based clinical metabolomics analysis by NMR revealed abnormalities in mannose and myo-inositol metabolism in Scleroderma

Background and hypothesis

Systemic sclerosis (SSc) is a chronic autoimmune disorder characterized by fibrosis of the skin and internal organs, as well as vascular damage. Recent research has suggested that abnormal metabolism of certain sugars, such as mannose and myo-inositol, may contribute to the development and progression of SSc. Clinical studies have found that SSc patients have increased mannose and decreased myoinositol levels in their blood plasma/serum samples compared to those of healthy controls, suggesting that abnormal mannose and myoinositol metabolism may contribute to SSc pathogenesis. However, further research on patient cohorts of different ethnicity is imperative to validate these findings and understanding the mechanisms underlying these metabolic abnormalities and to develop new therapies that target these pathways. The present hypothesis-free NMR based clinical metabolomics study is an effort in this direction to compare the circulatory levels of mannose, myo-inositol and other endogenous metabolites in the sera of scleroderma patients and control subjects so that to validate the proposed abnormalities in mannose and myo-inositol metabolic pathways and association between them. The selected metabolic features and the metabolic ratio i.e. myo-inositol to mannose ratio (MMR) were further evaluated for their clinical potential in diagnostic and prognostic screening. Methods: The serum sample from 83 SSc patients meeting ACR 1980 criteria for Systemic Sclerosis, and 43 age and sex matched normal controls, were analyzed using one dimensional (1D) ¹H NMR spectroscopy coupled with multivariate statistical analysis such as Partial Least Square-Discriminate Analysis (PLS-DA). The NMR spectra were analysed using NMR suite of commercial software CHENOMX (www.chenomx.com/) and the metabolic concentrations were measured with respect to endogenous metabolite formate (as an internal calibration standard and concentration was set to 30 µM). For evaluating serum metabolic disparity between the study groups, the machine learning model was generated using random forest (RF) classification  method and the Mean decrease accuracy (MDA) scores were used to identify the distinctive metabolic abnormalities in SSc. Univariate receiver operator characteristic (ROC) curve analysis was used to evaluate the diagnostic potential of the selected metabolic features. Results: There was clear distinction between SSc and healthy controls on the PLS-DA score plots [R²= 0.98] and aberrant metabolic changes were evident in the sera of SSc patients. The sera of SSc patients were characterized by decreased serum levels of alanine, valine, myoinositol, creatinine, pyruvate, and lactate; whereas the serum levels of, acetate, and 3-hydroxybutyrate were found to be significantly elevated. Contrary to expectation, the serum levels of mannose found to be insignificantly different (SSc: 46.0 µM and NC: 43.8 µM). The majority of these metabolic alterations found to be well consistence with those reported previously in other clinical metabolomics studies [1,2]. The mean values for circulatory levels of Myoinositol in SSC patients and NC subjects were 29.2 µM and 67.4 µM, respectively. Further, the circulatory MMR levels were estimated as [Myo-inositol/ Mannose] and compared between the study groups. Like myo-inositol, the MMR levels were also found to be significantly decreased in SSc patients (mean value =0.71 ± 0.32 compared to 1.85 ± 0.73 as observed for NC subjects. Conclusion: The altered levels of myo-inositol and other endogenous metabolites in the sera of SSc patients suggested abnormalities in myo-inositol metabolism in SSc patients and future studies are warranted to underscore its role in the pathobiology of scleroderma.

References:

[1] Federica Murgia, Silvia Svegliati, Simone Poddighe, Milena Lussu, Aldo Manzin, Tatiana Spadoni, Colomba Fischetti, Armando Gabrielli, and Luigi Atzori. "Metabolomic profile of systemic sclerosis patients." Scientific Reports 8, no. 1 (2018): 7626.

[2]. Thomas Bögl, Franz Mlynek, Markus Himmelsbach, Norbert Sepp, Wolfgang Buchberger, and Marija Geroldinger-Simić. "Plasma metabolomic profiling reveals four possibly disrupted mechanisms in systemic sclerosis." Biomedicines 10, no. 3 (2022): 607.