. measured for 8 days. The feces were collected every 2 days for 8 days. Ileal and fecal lipids were extracted as described in the Supplemental Methods. Triglycerides were measured with a triglyceride colorimetric assay kit (Bioassay Systems). Free fatty acids (FFAs) were measured using reagents from Wako.Statistics. Experimental values are presented as the mean ± SD. Statistical analyses were performed using the 2-tailed Student's t test and 1-way ANOVA with Tukey's confirmation. Weighted UniFrac analysis to assess changes in bacterial abundance was performed on the Galaxy web-based platform. Statistical models including PCA, PLS-DA, and OPLS-DA were established to represent the major latent variables in the data matrix. P values of less than 0.05 were considered significant. Study approval. All animal studies were performed in accordance with the Institute of Laboratory Animal Resources guidelines and approved by the IACUC of the NCI.

Bile acids play a pivotal role in the pathological development of inflammatory bowel disease (IBD). However, the mechanism of bile acid dysregulation in IBD remains unanswered. Here we show that intestinal peroxisome proliferator-activated receptor α (PPARα)-UDP-glucuronosyltransferases (UGTs) signalling is an important determinant of bile acid homeostasis. Dextran sulphate sodium (DSS)-induced colitis leads to accumulation of bile acids in inflamed colon tissues via activation of the intestinal peroxisome PPARα-UGTs pathway. UGTs accelerate the metabolic elimination of bile acids, and thereby decrease their intracellular levels in the small intestine. Reduced intracellular bile acids results in repressed farnesoid X receptor (FXR)-FGF15 signalling, leading to upregulation of hepatic CYP7A1, thus promoting the de novo bile acid synthesis. Both knockout of PPARα and treatment with recombinant FGF19 markedly attenuate DSS-induced colitis. Thus, we propose that intestinal PPARα-UGTs and downstream FXR-FGF15 signalling play vital roles in control of bile acid homeostasis and the pathological development of colitis.

Bile acid synthesis is the major pathway for catabolism of cholesterol. Cholesterol 7α-hydroxylase (CYP7A1) is the rate-limiting enzyme in the bile acid biosynthetic pathway in the liver and plays an important role in regulating lipid, glucose and energy metabolism. Transgenic mice overexpressing CYP7A1 (CYP7A1-tg mice) were resistant to high-fat diet (HFD)-induced obesity, fatty liver, and diabetes. However the mechanism of resistance to HFD-induced obesity of CYP7A1-tg mice has not been determined. In this study, metabolomic and lipidomic profiles of CYP7A1-tg mice were analyzed to explore the metabolic alterations in CYP7A1-tg mice that govern the protection against obesity and insulin resistance by using ultra-performance liquid chromatography-coupled with electrospray ionization quadrupole time-of-flight mass spectrometry combined with multivariate analyses. Lipidomics analysis identified seven lipid markers including lysophosphatidylcholines, phosphatidylcholines, sphingomyelins and ceramides that were significantly decreased in serum of HFD-fed CYP7A1-tg mice. Metabolomics analysis identified 13 metabolites in bile acid synthesis including taurochenodeoxycholic acid, taurodeoxycholic acid, tauroursodeoxycholic acid, taurocholic acid, and tauro-β-muricholic acid (T-β-MCA) that differed between CYP7A1-tg and wild-type mice. Notably, T-β-MCA, an antagonist of the farnesoid X receptor (FXR) was significantly increased in intestine of CYP7A1-tg mice. This study suggests that reducing 12α-hydroxylated bile acids and increasing intestinal T-β-MCA may reduce high fat diet-induced increase of phospholipids, sphingomyelins and ceramides, and ameliorate diabetes and obesity.

Fibrates, such as fenofibrate, are peroxisome proliferator-activated receptor-α (PPARα) agonists and have been used for several decades as hypolipidemic agents in the clinic. However, contradictory observations exist on the role of fibrates in host response to acute inflammation, with unclear mechanisms. The role of PPARα in colitis was assessed using fenofibrate and Ppara-null mice. Wild-type or Ppara-null mice were subjected to acute colitis under three distinct protocols, dextran sulfate sodium, trinitrobenzenesulfonic acid, and Salmonella Typhi. Serum and colon lipidomics were analyzed to characterize the metabolic profiles by ultra-performance liquid chromatography-coupled with electrospray ionization quadrupole time-of-flight mass spectrometry. Messenger RNAs of PPARα target genes and genes involved in inflammation were determined by qunatitative PCR analysis. Fenofibrate treatment exacerbated inflammation and tissue injury in acute colitis, and this was dependent on PPARα activation. Lipidomics analysis revealed that bioactive sphingolipids, including sphingomyelins (SM) and ceramides, were significantly increased in the colitis group compared with the control group; this was further potentiated following fenofibrate treatment. In the colon, fenofibrate did not reduce the markedly increased expression of mRNA encoding TNFα found in the acute colitis model, while it decreased hydrolysis and increased synthesis of SM, upregulated RIPK3-dependent necrosis, and elevated mitochondrial fatty acid β-oxidation, which were possibly related to the exacerbated colitis.

Celastrol is well known for its anti-inflammatory and anti-cancer effects. In this study, the efficacy of celastrol against dextran sulfate sodium (DSS)-induced inflammatory bowel disease (IBD) in mice was established and the mechanism was investigated using lipidomics. Celastrol treatment significantly alleviated DSS-induced colitis in mice, as revealed by the body weight, colon length, scores of rectal bleeding and diarrhea, serum TNF-α level, and histological analysis results. Lipidomics analysis based on UPLC/MS revealed characteristic changes in the metabolic profiles of the colitis mice, with altered levels of lipid markers associated with IBD, including LPC18 : 0, LPC18 : 1, LPC18 : 2, sphingomyelin (SM), and increased LPC18 : 0/LPC18 : 1 and LPC18 : 0/LPC18 : 2 ratios. For the celastrol-treated colitis mice, however, levels of the above lipid markers were restored, together with recovered saturated LPC/unsaturated LPC ratios. Accordingly, using GC-MS analysis, increased stearic acid (C18 : 0)/oleic acid (C18 : 1) and stearic acid (C18 : 0)/linoleic acid (C18 : 2) ratios were observed in colitis mice, which were later recovered after celastrol treatment. Quantitative real-time PCR analysis revealed that the liver expression of stearoyl-coenzyme A desaturase 1 (SCD1), the key enzyme controlling the desaturation of saturated fatty acid, was dramatically inhibited in IBD mice, and was obviously recovered after celastrol treatment. These results suggest that the increased saturated LPC/unsaturated LPC (and saturated fatty acid/unsaturated fatty acid) ratios associated with SCD1 down-regulation could be regarded as biomarkers of colitis, and celastrol alleviates DSS-induced colitis partially via up-regulation of SCD1, restoring the altered balance between stearic acid- and oleic acid-derived lipid species, which plays an important role in alleviating colitis. In all, this study provided the scientific basis for further development of celastrol in treating IBD.

No abstract

Fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist, was found to exacerbate inflammation and tissue injury in experimental acute colitis mice. Through lipidomics analysis, bioactive sphingolipids were significantly up-regulated in the colitis group. In this study, to provide further insight into the PPARα-dependent exacerbation of colitis, gas chromatography-mass spectrometry (GC/MS) based metabolomics was employed to investigate the serum and colon of dextran sulfate sodium (DSS)-induced colitis mice treated with fenofibrate, with particular emphasis on changes in low-molecular-weight metabolites. With the aid of multivariate analysis and metabolic pathway analysis, potential metabolite markers in the amino acid metabolism, urea cycle, purine metabolism, and citrate cycle were highlighted, such as glycine, serine, threonine, malic acid, isocitric acid, uric acid, and urea. The level changes of these metabolites in either serum or colons of colitis mice were further potentiated following fenofibrate treatment. Accordingly, the expression of threonine aldolase and phosphoserine aminotransferase 1 was significantly up-regulated in colitis mice and further potentiated in fenofibrate/DSS-treated mice. It was revealed that beyond the control of lipid metabolism, PPARα also shows effects on the above pathways, resulting in enhanced protein catabolism and energy expenditure, increased bioactive sphingolipid metabolism and proinflammatory state, which were possibly related to the exacerbated colitis.

The present results indicate that LPCs and sphingolipids are significantly altered in patients with AAD, and several sphingolipids, such as sphinganine, phytosphingosine, and ceramide, were dramatically decreased in patients with Stanford type A AAD. A combination of these two families of metabolites could serve as a potential biomarker for the diagnosis of AAD and distinguishing between Stanford type A and Stanford type B.