Comprehensive metabolome analyses reveal N-acetylcysteine-responsive accumulation of kynurenine in systemic lupus erythematosus: implications for activation of the mechanistic target of rapamycin.

Andras Perl,Rebecca Borsuk,Ryan Kelly,John M Asara,Zhi-Wei Lai,Zachary Oaks,Robert Hanczko,Paul E Phillips

doi:10.1007/s11306-015-0772-0

Abstract

Systemic lupus erythematosus (SLE) patients exhibit depletion of the intracellular antioxidant glutathione and downstream activation of the metabolic sensor, mechanistic target of rapamycin (mTOR). Since reversal of glutathione depletion by the amino acid precursor, N-acetylcysteine (NAC), is therapeutic in SLE, its mechanism of impact on the metabolome was examined within the context of a double-blind placebo-controlled trial. Quantitative metabolome profiling of peripheral blood lymphocytes (PBL) was performed in 36 SLE patients and 42 healthy controls matched for age, gender, and ethnicity of patients using mass spectrometry that covers all major metabolic pathways. mTOR activity was assessed by western blot and flow cytometry. Metabolome changes in lupus PBL affected 27 of 80 KEGG pathways at FDR p < 0.05 with most prominent impact on the pentose phosphate pathway (PPP). While cysteine was depleted, cystine, kynurenine, cytosine, and dCTP were the most increased metabolites. Area under the receiver operating characteristic curve (AUC) logistic regression approach identified kynurenine (AUC = 0.859), dCTP (AUC = 0.762), and methionine sulfoxide (AUC = 0.708), as top predictors of SLE. Kynurenine was the top predictor of NAC effect in SLE (AUC = 0.851). NAC treatment significantly reduced kynurenine levels relative to placebo in vivo (raw p = 2.8 × 10−7, FDR corrected p = 6.6 × 10−5). Kynurenine stimulated mTOR activity in healthy control PBL in vitro. Metabolome changes in lupus PBL reveal a dominant impact on the PPP that reflect greater demand for nucleotides and oxidative stress. The PPP-connected and NAC-responsive accumulation of kynurenine and its stimulation of mTOR are identified as novel metabolic checkpoints in lupus pathogenesis.Electronic supplementary materialThe online version of this article (doi:10.1007/s11306-015-0772-0) contains supplementary material, which is available to authorized users.

Highlights

Systemic lupus erythematosus (SLE) is a potentially fatal autoimmune inflammatory disease of unknown etiology
Quantitative metabolome profiling of peripheral blood lymphocytes (PBL) was performed in 36 SLE patients and 42 healthy controls matched for age, gender, and ethnicity of patients using mass spectrometry that covers all major metabolic pathways. mechanistic target of rapamycin (mTOR) activity was assessed by western blot and Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users
The pathway changes were driven by the accumulation of 32 among 34 metabolites altered in lupus PBL (Fig. 1b) 0.11 of these metabolites are involved in multiple pathways, with 4/11 being substrates in the phosphate pathway (PPP) (Fig. 1b)

Summary

Introduction

Systemic lupus erythematosus (SLE) is a potentially fatal autoimmune inflammatory disease of unknown etiology. Dysfunction of T and B cells drives anti-nuclear antibody production through the release of oxidized immunogenic nuclear materials from necrotic rather than apoptotic cells (Perl 2013). Lupus T cells exhibit mitochondrial dysfunction, which is characterized by elevated mitochondrial transmembrane potential (Dwm) or persistent mitochondrial hyperpolarization (MHP) that mediates diminished activation-induced apoptosis and predisposes T cells to pro-inflammatory death via necrosis (Gergely et al 2002; Lai et al 2013).

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