Activation of farnesoid X receptor attenuates liver injury in systemic lupus erythematosus

Urinary metabolomic profiling of a cohort of Colombian patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune and multisystem disease with a high public health impact. Lupus nephritis (LN), commonly known as renal involvement in SLE, is associated with a poorer prognosis and increased rates of morbidity and mortality in patients with SLE. Identifying new urinary biomarkers that can be used for LN prognosis or diagnosis is essential and is part of current active research. In this study, we applied an untargeted metabolomics approach involving liquid and gas chromatography coupled with mass spectrometry to urine samples collected from 17 individuals with SLE and no kidney damage, 23 individuals with LN, and 10 clinically healthy controls (HCs) to identify differential metabolic profiles for SLE and LN. The data analysis revealed a differentially abundant metabolite expression profile for each study group, and those metabolites may act as potential differential biomarkers of SLE and LN. The differential metabolic pathways found between the LN and SLE patients with no kidney involvement included primary bile acid biosynthesis, branched-chain amino acid synthesis and degradation, pantothenate and coenzyme A biosynthesis, lysine degradation, and tryptophan metabolism. Receiver operating characteristic curve analysis revealed that monopalmitin, glycolic acid, and glutamic acid allowed for the differentiation of individuals with SLE and no kidney involvement and individuals with LN considering high confidence levels. While the results offer promise, it is important to recognize the significant influence of medications and other external factors on metabolomics studies. This impact has the potential to obscure differences in metabolic profiles, presenting a considerable challenge in the identification of disease biomarkers. Therefore, experimental validation should be conducted with a larger sample size to explore the diagnostic potential of the metabolites found as well as to examine how treatment and disease activity influence the identified chemical compounds. This will be crucial for refining the accuracy and effectiveness of using urine metabolomics for diagnosing and monitoring lupus and lupus nephritis.

Exploring the causal correlations between 486 serum metabolites and systemic lupus erythematosus: a bidirectional Mendelian randomization study

Objective: The observational association between circulating metabolites and systemic lupus erythematosus (SLE) has been well documented. However, whether the association is causal remains unclear. In this study, bidirectional Mendelian randomization (MR) was introduced to analyse the causal relationships and possible mechanisms. Methods: We conducted a two-sample bidirectional MR study. A genome-wide association study (GWAS) with 7,824 participants provided data on 486 human blood metabolites. Outcome information was obtained from a large-scale GWAS summary, which contained 5,201 single nucleotide polymorphisms (SNPs) cases and 9,066 control cases of Europeans and yielded a total of 7,071,163 SNPs. The inverse variance weighted (IVW) model was recruited as the primary two-sample MR analysis approach, followed by sensitivity analyses such as the heterogeneity test, horizontal pleiotropy test, leave-one-out analysis, and linkage disequilibrium score (LDSC) regression. Results: In this study, we discovered that 24 metabolites belonging to the lipid, carbohydrate, xenobiotic and amino acid superpathways may increase the risk of SLE occurrence (p < 0.05). In addition, the metabolic disorders of 51 metabolites belonging to the amino acid, energy, xenobiotics, peptide and lipid superpathways were affected by SLE (p < 0.05). Palmitoleate belonging to the lipid superpathway and isobutyrylcarnitine and phenol sulfate belonging to the amino acid superpathway were factors with two-way causation. The metabolic enrichment pathway of bile acid biosynthesis was significant in the forward MR analysis (p = 0.0435). Linolenic acid and linoleic acid metabolism (p = 0.0260), betaine metabolism (p = 0.0314), and glycerolipid metabolism (p = 0.0435) were the significant metabolically enriched pathways in the reverse MR analysis. Conclusion: The levels of some specific metabolites may either contribute to the immune response inducing SLE, or they may be intermediates in the development and progression of SLE. These metabolites can be used as auxiliary diagnostic tools for SLE and for the evaluation of disease progression and therapeutic effects.

Investigating the Mechanisms of Jieduquyuziyin Prescription Improves Lupus Nephritis and Fibrosis via FXR in MRL/lpr Mice

Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE) and one of the leading causes of death. An alternative effective treatment to ameliorate and relieve LN and delay the process of renal tissue fibrosis is urgently needed in the clinical setting. Jieduquyuziyin prescription (JP) has been successfully used to treat SLE, but its potential mechanisms are not sufficiently understood. In this study, we treated MRL/lpr mice with JP for 8 weeks and treated human renal tubular epithelial cells (human kidney 2 (HK-2)) with drug-containing serum to observe the antagonistic effects of JP on inflammation and fibrosis, as well as to investigate the possible mechanisms. Results demonstrated that JP significantly reduced urinary protein and significantly improved pathological abnormalities. Metabolomics combined with ingenuity pathway analysis illustrated that the process of kidney injury in lupus mice may be closely related to farnesoid X receptor (FXR) pathway abnormalities. Microarray biomimetic analysis and LN patients indicated that FXR may play a protective role as an effective therapeutic target for LN and renal fibrosis. JP significantly increased the expression of FXR and inhibited the expression of its downstream targets, namely, nuclear transcription factor κB (NF-κB) and α-smooth muscle actin (α-SMA), in the kidney of MRL/lpr mice and HK-2 cells, as confirmed by in vitro and in vivo experiments. In conclusion, JP may mediate the activation of renal FXR expression and inhibit NF-κB and α-SMA expression to exert anti-inflammatory and antifibrotic effects for LN prevention and treatment.

Gut Microbiome and Metabolites in Systemic Lupus Erythematosus: Link, Mechanisms and Intervention

Systemic lupus erythematosus (SLE), often considered the prototype of autoimmune diseases, is characterized by over-activation of the autoimmune system with abnormal functions of innate and adaptive immune cells and the production of a large number of autoantibodies against nuclear components. Given the highly complex and heterogeneous nature of SLE, the pathogenesis of this disease remains incompletely understood and is presumed to involve both genetic and environmental factors. Currently, disturbance of the gut microbiota has emerged as a novel player involved in the pathogenesis of SLE. With in-depth research, the understanding of the intestinal bacteria-host interaction in SLE is much more comprehensive. Recent years have also seen an increase in metabolomics studies in SLE with the attempt to identify potential biomarkers for diagnosis or disease activity monitoring. An intricate relationship between gut microbiome changes and metabolic alterations could help explain the mechanisms by which gut bacteria play roles in the pathogenesis of SLE. Here, we review the role of microbiota dysbiosis in the aetiology of SLE and how intestinal microbiota interact with the host metabolism axis. A proposed treatment strategy for SLE based on gut microbiome (GM) regulation is also discussed in this review. Increasing our understanding of gut microbiota and their function in lupus will provide us with novel opportunities to develop effective and precise diagnostic strategies and to explore potential microbiota-based treatments for patients with lupus.

Immunoregulatory Functions of Nuclear Receptors: Mechanisms and Therapeutic Implications

Members of the nuclear receptor superfamily serve as master regulators in signaling by either positively or negatively regulating gene expression. Accumulating evidence has suggested that nuclear receptors are actively involved in immune responses, with specific roles in different immune cell compartments that contribute to both normal function and to disease development. The druggable properties of nuclear receptors have made them ideal modulatory therapeutic targets. Here, we revisit nuclear receptor biology, summarize recent advances in our understanding of the immunological functions of nuclear receptors, describe cell-type-specific roles and specific nuclear receptors in disease pathogenesis, and explore their potential as novel therapeutic targets. These nuclear receptor-dependent alterations in the immune system are amenable to pharmacological manipulation and suggest novel therapeutic strategies.

Metabolic profiling of endogenous bile acids: a novel method to assess hepatoprotective effect of Tanreqing capsule on carbon-tetrachloride-induced liver injury in rats

Tanreqing (TRQ), a traditional Chinese medicine (TCM) formula, can alleviate liver injury and improve liver function. Its pharmacological mechanisms of actions are still unclear due to its complex components and multi-target natures. Metabolomic study is an effective approach to investigating drug pharmacological actions, new diagnostic markers, and potential mechanisms of actions. In the present study, a new strategy was used to evaluate the protective effect of TRQ capsule against carbon tetrachloride (CCl₄)-induced hepatotoxicity in rats, by analyzing metabolic profiling of endogenous bile acids (BAs) along with biochemical and histological analyses. BAs concentrations were determined by ultra-performance liquid chromatography coupled with quadrupole mass spectrometry (UPLC-MS). Principal component analysis and partial least squares discriminant analysis were then employed to analyze the UPLC-MS results and compare the hepatoprotective effect of TRQ capsule in different groups at the doses of 0.36, 1.44, and 2.88 g·kg^-1 body weight, respectively. Moreover, our results suggested that taurocholic acid (TCA) and taurohyodesoxycholic acid (THDCA) were the most important biochemical markers, which were indicative of CCl₄-induced acute hepatic damage and hepatoprotective effect of TRQ capsule. Therefore, this new strategy would be an excellent alternative method for evaluating hepatoprotective effect and proposing potential mechanisms of action for other drugs as well.

The farnesoid-X-receptor in myeloid cells controls CNS autoimmunity in an IL-10-dependent fashion

Innate immune responses by myeloid cells decisively contribute to perpetuation of central nervous system (CNS) autoimmunity and their pharmacologic modulation represents a promising strategy to prevent disease progression in Multiple Sclerosis (MS). Based on our observation that peripheral immune cells from relapsing-remitting and primary progressive MS patients exhibited strongly decreased levels of the bile acid receptor FXR (farnesoid-X-receptor, NR1H4), we evaluated its potential relevance as therapeutic target for control of established CNS autoimmunity. Pharmacological FXR activation promoted generation of anti-inflammatory macrophages characterized by arginase-1, increased IL-10 production, and suppression of T cell responses. In mice, FXR activation ameliorated CNS autoimmunity in an IL-10-dependent fashion and even suppressed advanced clinical disease upon therapeutic administration. In analogy to rodents, pharmacological FXR activation in human monocytes from healthy controls and MS patients induced an anti-inflammatory phenotype with suppressive properties including control of effector T cell proliferation. We therefore, propose an important role of FXR in control of T cell-mediated autoimmunity by promoting anti-inflammatory macrophage responses.

Fatty liver diseases, bile acids, and FXR

The prevalence of nonalcoholic fatty liver disease (NAFLD) worldwide has increased at an alarming rate, which will likely result in enormous medical and economic burden. NAFLD presents as a spectrum of liver diseases ranging from simple steatosis, nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and even to hepatocellular carcinoma (HCC). A comprehensive understanding of the mechanism(s) of NAFLD-to-NASH transition remains elusive with various genetic and environmental susceptibility factors possibly involved. An understanding of the mechanism may provide novel strategies in the prevention and treatment to NASH. Abnormal regulation of bile acid homeostasis emerges as an important mechanism to liver injury. The bile acid homeostasis is critically regulated by the farnesoid X receptor (FXR) that is activated by bile acids. FXR has been known to exert tissue-specific effects in regulating bile acid synthesis and transport. Current investigations demonstrate FXR also plays a principle role in regulating lipid metabolism and suppressing inflammation in the liver. Therefore, the future determination of the molecular mechanism by which FXR protects the liver from developing NAFLD may shed light to the prevention and treatment of NAFLD.