N6-Acetyl-L-Lysine and p-Cresol as Key Metabolites in the Pathogenesis of COVID-19 in Obese Patients

Abstract

Despite the growing number of the vaccinated population, COVID-19, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a global health burden. Obesity, a metabolic syndrome affecting one-third of the population, has proven to be a major risk factor for COVID-19 severe complications. Several studies have identified metabolic signatures and disrupted metabolic pathways associated with COVID-19, however there are no reports evaluating the role of obesity in the COVID-19 metabolic regulation. In this study we highlight the involvement of obesity metabolically in affecting SARS-CoV-2 infection and the consequent health complications, mainly cardiovascular disease. We measured one hundred and forty-four (144) metabolites using ultra high-performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC-QTOF-MS) to identify metabolic changes in response to SARS-CoV-2 infection, in lean and obese COVID-19 positive (n=82) and COVID-19 negative (n=24) patients. The identified metabolites are found to be mainly correlating with glucose, energy and steroid metabolisms. Further data analysis indicated twelve (12) significantly yet differentially abundant metabolites associated with viral infection and health complications, in COVID-19 obese patients. Two of the detected metabolites, n6-acetyl-l-lysine and p-cresol, are detected only among the COVID-19 cohort, exhibiting significantly higher levels in COVID-19 obese patients when compared to COVID-19 lean patients. These metabolites have important roles in viral entry and could explain the increased susceptibility of obese patients. On the same note, a set of six metabolites associated with antiviral and anti-inflammatory functions displayed significantly lower abundance in COVID-19 obese patients. In conclusion, this report highlights the plasma metabolome of COVID-19 obese patients as a metabolic feature and signature to help improve clinical outcomes. We propose n6-acetyl-l-lysine and p-cresol as potential metabolic markers which warrant further investigations to better understand their involvement in different metabolic pathways in COVID-19.

Keywords: COVID-19; SARS-CoV-2; metabolomics; obesity; ultra-high-performance liquid chromatography-mass spectrometry.

Figure 1

Summary of Metabolomic Set Enrichment Analysis Plot. Metabolomic Set Enrichment Analysis (MSEA) showing the most altered functional metabolic pathways in COVID-19 patients. The graph was obtained using the online tool MSEA by plotting on the y-axis the -log of p values from pathway enrichment analysis.

Figure 2

Alteration in plasma metabolite levels of COVID-19 lean and obese patients compared to non-COVID-19 lean and obese patients. Plasma levels of different metabolites (A) m-Coumaric acid (B) Cinnamic acid (C) Phosphatidylcholine [PC (16:0/16:0)] and (D) Benzocaine, were significantly different in COVID-19 lean and overweight-obese patients when compared to controls (non-COVID-19). Analysis was performed using one-way ANOVA with Dunn’s multiple comparison and Kruskal-Walis tests; *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. The y axis in the dot plots indicates arbitrary units of median intensity.

Figure 3

Upregulated levels of plasma metabolites as markers of viral function and adverse complications in COVID-19 obese patients. Plasma levels of (A) N6-Acetyl-L-Lysine were significantly upregulated when comparing COVID-19 obese and overweight patients to COVID-19 lean patients. Similarly, significant increase in plasma levels of (B) p-Cresol in COVID-19 overweight-obese patients. Analysis was performed using Mann Whitney t-test with or without Welch’s correction test. (C) Plasma metabolite levels of N6-acetyl-l-lysine displayed altered levels that correlated with the occurrence of symptoms in COVID-19 overweight-obese patients. Analysis was performed using one-way ANOVA followed by Dunn’s multiple comparison and Kruskal-Wallis testpost hoc; *P < 0.05; **P < 0.01; ****P < 0.0001.

Figure 4

Downregulation of plasma metabolites as markers of COVID-19 health complications in obese patients. Plasma levels of (A) Mevalonic acid, (B) 3,4-Dihydroxymandelic acid, (C) Gallic acid, (D) Homo-L-Arginine, (E) Phenol, and (F) Tricosanoic acid displayed significantly lower levels in COVID-19 overweight-obese patients compared to COVID-19 lean patients. Analysis was performed using Mann Whitney t-test with or without Welch’s correction test; *P < 0.05.

Figure 5

Summary of the proposed involvement of N6-Acetyl-L-Lysine and p-Cresol as key metabolites of COVID-19 pathogenesis observed in COVID-19 overweight-obese patients. (1) SARS-CoV-2 access the airway of an overweight-obese patient by binding to the host cell. (2) The virus utilizes ACE2 receptor for its entry and the serine protease TMPRSS2 for S protein priming, contributing to rapid spread of the virus in infected patients. (3) Inside the host cell, SARs-CoV-2 influence epigenetic factors that manipulates viral survival and replication, leading to metabolic dysregulation. (4) The increase of N6-Acetyl-L-Lysine, as a key metabolite of COVID-19 pathogenesis in overweight-obese patients, induces molecular alterations in SARS-CoV-2 Nucleoplasmid and RNA at functional interacting sites. This in turn creates a positive feedback loop through the induction of viral replication and infectivity. In another mechanism, (5) and (6) SARS-CoV-2 invasion of epithelial cells, leads to the (7) degradation of proteins and thus accumulating as a by-product toxin. Of these, is the uremic toxin (8) P-Cresol, another key metabolite involved in the pathogenesis of COVID-19 disease, displayed increased intensity in overweight-obese COVID-19 patients. Elevated p-Cresol (9) is shown to inhibit macrophage activity and leukocyte cell adhesion, which leads to decrease of immune response, as seen in COVID-19 patients. (10) In another mechanism, p-Cresol increases the expression of ACE2 receptor and TMPRSS2, thus enhancing viral entry and load. (11) The increase of N6-Acetyl-L-Lysine and p-Cresol resulted in the induction of inflammation, cytokine storm and reactive oxygen species (ROS) production. This subsequently led to the development of (12) severe health complications which involves pulmonary fibrosis, cardiovascular diseases and kidney failure, and possibly admission to intensive care unit (ICU).