Possible protective role of pregnenolone-16α-carbonitrile in lithocholic acid-induced hepatotoxicity through enhanced hepatic lipogenesis

Habitual intakes of sugar-sweetened beverages associated with gut microbiota-related metabolites and metabolic health outcomes in young Chinese adults

BACKGROUND AND AIMS

Reducing consumption of sugar-sweetened beverages (SSBs) is a global public health priority because of their limited nutritional value and associations with increased risk of obesity and metabolic diseases. Gut microbiota-related metabolites emerged as quintessential effectors that may mediate impacts of dietary exposures on the modulation of host commensal microbiome and physiological status.

METHODS AND RESULTS

This study assessed the associations among SSBs, circulating microbial metabolites, and gut microbiota-host co-metabolites, as well as metabolic health outcomes in young Chinese adults (n = 86), from the Carbohydrate Alternatives and Metabolic Phenotypes study in Shaanxi Province. Five principal component analysis-derived beverage drinking patterns were determined on self-reported SSB intakes, which were to a varying degree associated with 143 plasma levels of gut microbiota-related metabolites profiled by untargeted metabolomics. Moreover, carbonated beverages, fruit juice, energy drinks, and bubble tea exhibited positive associations with obesity-related markers and blood lipids, which were further validated in an independent cohort of 16,851 participants from the Regional Ethnic Cohort Study in Northwest China in Shaanxi Province. In contrast, presweetened coffee was negatively associated with the obesity-related traits. A total of 79 metabolites were associated with both SSBs and metabolic markers, particularly obesity markers. Pathway enrichment analysis identified the branched-chain amino acid catabolism and aminoacyl-tRNA biosynthesis as linking SSB intake with metabolic health outcomes.

CONCLUSION

Our findings demonstrate the associations between habitual intakes of SSBs and several metabolic markers relevant to noncommunicable diseases, and highlight the critical involvement of gut microbiota-related metabolites in mediating such associations.

Atypical functions of xenobiotic receptors in lipid and glucose metabolism

Xenobiotic receptors are traditionally defined as xenobiotic chemical-sensing receptors, the activation of which transcriptionally regulates the expression of enzymes and transporters involved in the metabolism and disposition of xenobiotics. Emerging evidence suggests that "xenobiotic receptors" also have diverse endobiotic functions, including their effects on lipid metabolism and energy metabolism. Dyslipidemia is a major risk factor for cardiovascular disease, diabetes, obesity, metabolic syndrome, stroke, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH). Understanding the molecular mechanism by which transcriptional factors, including the xenobiotic receptors, regulate lipid homeostasis will help to develop preventive and therapeutic approaches. This review describes recent advances in our understanding the atypical roles of three xenobiotic receptors: aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR), in metabolic disorders, with a particular focus on their effects on lipid and glucose metabolism. Collectively, the literatures suggest the potential values of AhR, PXR and CAR as therapeutic targets for the treatment of NAFLD, NASH, obesity and diabetes, and cardiovascular diseases.

Serum Bile Acid Profiles Improve Clinical Prediction of Nonalcoholic Fatty Liver in T2DM patients

Background: The present study aimed to assess the ability of serum bile acid profiles to predict the development of nonalcoholic fatty liver (NAFL) in type 2 diabetes mellitus (T2DM) patients. Methods: Using targeted ultraperformance liquid chromatography (UPLC) coupled with triple quadrupole mass spectrometry (TQ/MS), we compared serum bile acid levels in T2DM patients with NAFL (n = 30) and age- and sex-matched T2DM patients without NAFL (n = 36) at the first time. Second, an independent cohort study of T2DM patients with NAFL (n = 17) and age- and sex-matched T2DM patients without NAFL (n = 20) was used to validate the results. The incremental benefits of serum biomarkers, clinical variables alone, or with biomarkers were then evaluated using receiver operating characteristic (ROC) curves and decision curve analysis. The area under the curve (AUC), integrated discrimination improvement (IDI), and net reclassification improvement (NRI) were used to evaluate the biomarker predictive abilities. Results: The serum bile acid profiles in T2DM patients with NAFL were significantly different from T2DM patients without NAFL, as characterized by the significant elevation of LCA, TLCA, TUDCA, CDCA-24G, and TCDCA, which may be potential biomarkers for the identification of NAFL in T2DM patients. Based on the improvement in AUC, IDI, and NRI, the addition of 5 bile acids to a model with clinical variables statistically improved its predictive value. Similar results were found in the validation cohort. Conclusions: These results highlight that the detected biomarkers may contribute to the progression of NAFL in T2DM patients, and these biomarkers particularly in combination may help in the diagnosis of NAFL and allow earlier intervention in T2DM patients.

Selenoneine Ameliorates Hepatocellular Injury and Hepatic Steatosis in a Mouse Model of NAFLD

Selenoneine is a novel organic selenium compound markedly found in the blood, muscles, and other tissues of fish. This study aimed to determine whether selenoneine attenuates hepatocellular injury and hepatic steatosis in a mouse model of non-alcoholic fatty liver disease (NAFLD). Mice lacking farnesoid X receptor (FXR) were used as a model for fatty liver disease, because they exhibited hepatomegaly, hepatic steatosis, and hepatic inflammation. Fxr-null mice were fed a 0.3 mg Se/kg selenoneine-containing diet for four months. Significant decreases in the levels of hepatomegaly, hepatic damage-associated diagnostic markers, hepatic triglycerides, and total bile acids were found in Fxr-null mice fed with a selenoneine-rich diet. Hepatic and blood clot total selenium concentrations were 1.7 and 1.9 times higher in the selenoneine group than in the control group. A marked accumulation of selenoneine was found in the liver and blood clot of the selenoneine group. The expression levels of oxidative stress-related genes (heme oxygenase 1 (Hmox1), glutathione S-transferase alpha 1 (Gsta1), and Gsta2), fatty acid synthetic genes (stearoyl CoA desaturase 1(Scd1) and acetyl-CoA carboxylase 1 (Acc1)), and selenoprotein (glutathione peroxidase 1 (Gpx1) and selenoprotein P (Selenop)) were significantly decreased in the selenoneine group. These results suggest that selenoneine attenuates hepatic steatosis and hepatocellular injury in an NAFLD mouse model.

Fish oil feeding reverses hepatomegaly and disrupted hepatic function due to the lack of FXR signaling

Mice lacking farnesoid X receptor (FXR) are used as a model for nonalcoholic fatty liver disease because their livers exhibit hepatomegaly, hepatic steatosis, and hepatic inflammation. The influence of fish oil feeding on hepatomegaly and disrupted hepatic function was investigated using female Fxr-null mice and wild-type mice fed a fish oil diet (2% fish oil and 2% corn oil) or a control diet (4% corn oil) for 4 weeks. Hepatic n-3 polyunsaturated fatty acid (PUFA) levels, including 22:6 n-3 docosahexaenoic acid (DHA) and 20:5 n-3 eicosapentaenoic acid (EPA) were significantly higher in the fish oil group than those in the control group of Fxr-null mice and wild-type mice. Fxr-null mouse livers of the control group showed a whitish brown coloration, whereas Fxr-null mouse livers of the fish oil group showed a dark brown coloration similar to that of wild-type mice. The liver in Fxr-null mice of the fish oil group was smaller than that of the control group. There was a significant decrease in the levels of hepatic damage-associated diagnostic markers, hepatic and serum bile acids, triglycerides, free fatty acids, and total cholesterol levels in Fxr-null mice because of fish oil feeding. It also reversed elevated mRNA levels of oxidative stress-related genes (Hmox1, Gsta1, and Gsta2) and reduced mRNA levels of transcriptional factors (Pparα and Shp) in Fxr-null mice. These results suggest that fish oil feeding reverses hepatomegaly and disrupted hepatic function due to the lack of FXR signaling.

TGF-β-SMAD3 signaling mediates hepatic bile acid and phospholipid metabolism following lithocholic acid-induced liver injury

Transforming growth factor-β (TGFβ) is activated as a result of liver injury, such as cholestasis. However, its influence on endogenous metabolism is not known. This study demonstrated that TGFβ regulates hepatic phospholipid and bile acid homeostasis through MAD homolog 3 (SMAD3) activation as revealed by lithocholic acid-induced experimental intrahepatic cholestasis. Lithocholic acid (LCA) induced expression of TGFB1 and the receptors TGFBR1 and TGFBR2 in the liver. In addition, immunohistochemistry revealed higher TGFβ expression around the portal vein after LCA exposure and diminished SMAD3 phosphorylation in hepatocytes from Smad3-null mice. Serum metabolomics indicated increased bile acids and decreased lysophosphatidylcholine (LPC) after LCA exposure. Interestingly, in Smad3-null mice, the metabolic alteration was attenuated. LCA-induced lysophosphatidylcholine acyltransferase 4 (LPCAT4) and organic solute transporter β (OSTβ) expression were markedly decreased in Smad3-null mice, whereas TGFβ induced LPCAT4 and OSTβ expression in primary mouse hepatocytes. In addition, introduction of SMAD3 enhanced the TGFβ-induced LPCAT4 and OSTβ expression in the human hepatocellular carcinoma cell line HepG2. In conclusion, considering that Smad3-null mice showed attenuated serum ALP activity, a diagnostic indicator of cholangiocyte injury, these results strongly support the view that TGFβ-SMAD3 signaling mediates an alteration in phospholipid and bile acid metabolism following hepatic inflammation with the biliary injury.

Fibroblast growth factor 19 treatment ameliorates disruption of hepatic lipid metabolism in farnesoid X receptor (Fxr)-null mice

Human fibroblast growth factor 19 (FGF19) is an enterohepatic hormone that is involved in the regulation of hepatic metabolism of bile acids, lipids, and glucose. Farnesoid X receptor (Fxr)-null mice exhibit steatosis-like symptoms, showing higher hepatic lipid levels than with the wild-type mice. We investigated the influence of FGF19 treatment on hepatic lipogenesis in Fxr-null mice. Recombinant FGF19 treatment (400 µg/kg/d) for 3 d prevented the accumulation of lipid droplets and decreased serum alanine aminotransferase activity and hepatic lipid levels, including those of triglycerides and free fatty acids. The treatment significantly decreased the hepatic mRNA levels of acetyl-CoA carboxylase 1 (Acc1), Cd36, and sterol regulatory element-binding protein-1c (Srebp-1c) as well as those of acetyl-CoA carboxylase 2 (Acc2), stearoyl CoA desaturase 1 (Scd1), and Cyp7a1. FGF19 treatment (4 µg/kg/d) for 3 d also decreased the hepatic free fatty acid levels and mRNA levels of Acc1, Cd36, and Srebp-1c. These results indicate that FGF19-mediated signaling ameliorates disrupted hepatic lipogenesis in Fxr-null mice.

Constitutive androstane receptor transactivates the hepatic expression of mouse Dhcr24 and human DHCR24 encoding a cholesterogenic enzyme 24-dehydrocholesterol reductase

Phenobarbital treatment has long been known to influence serum and hepatic cholesterol levels in rodents and humans. Constitutive androstane receptor (CAR), a member of the nuclear receptor superfamily, mediates various biological actions of phenobarbital. We have thus investigated whether CAR transactivates cholesterogenic genes in livers. Activation of CAR in mouse livers and cultured human hepatocytes increased mRNA levels of mouse Dhcr24 and human DHCR24, both of which encode 24-dehydrocholesterol reductase (DHCR24) catalyzing the last step of cholesterol biosynthesis. CAR transactivated the expression of these genes in reporter assays with cultured hepatoma cells. Furthermore, we have identified a DR4 (direct repeat separated by 4 nucleotides) motif in the human DHCR24 distal promoter as a binding site of CAR/retinoid X receptor α (RXRα) heterodimer. We have also demonstrated that the heterodimer of pregnane X receptor (PXR)/ RXRα binds to the DR4 motif and that human DHCR24 reporter gene is transactivated by the ligand-activated PXR. These results suggest a role of xenobiotic-responsive nuclear receptor CAR, and also possibly PXR, in cholesterol biosynthesis in the liver of mice and humans.

Lithocholic acid disrupts phospholipid and sphingolipid homeostasis leading to cholestasis in mice

Lithocholic acid (LCA) is an endogenous compound associated with hepatic toxicity during cholestasis. LCA exposure in mice resulted in decreased serum lysophosphatidylcholine (LPC) and sphingomyelin levels due to elevated lysophosphatidylcholine acyltransferase (LPCAT) and sphingomyelin phosphodiesterase (SMPD) expression. Global metabolome analysis indicated significant decreases in serum palmitoyl-, stearoyl-, oleoyl-, and linoleoyl-LPC levels after LCA exposure. LCA treatment also resulted in decreased serum sphingomyelin levels and increased hepatic ceramide levels, and induction of LPCAT and SMPD messenger RNAs (mRNAs). Transforming growth factor-β (TGF-β) induced Lpcat2/4 and Smpd3 gene expression in primary hepatocytes and the induction was diminished by pretreatment with the SMAD3 inhibitor SIS3. Furthermore, alteration of the LPCs and Lpcat1/2/4 and Smpd3 expression was attenuated in LCA-treated farnesoid X receptor-null mice that are resistant to LCA-induced intrahepatic cholestasis.

CONCLUSION

This study revealed that LCA induced disruption of phospholipid/sphingolipid homeostasis through TGF-β signaling and that serum LPC is a biomarker for biliary injury.

Pregnane X receptor and constitutive androstane receptor at the crossroads of drug metabolism and energy metabolism

The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are two closely related and liver-enriched nuclear hormone receptors originally defined as xenobiotic receptors. PXR and CAR regulate the transcription of drug-metabolizing enzymes and transporters, which are essential in protecting our bodies from the accumulation of harmful chemicals. An increasing body of evidence suggests that PXR and CAR also have an endobiotic function that impacts energy homeostasis through the regulation of glucose and lipids metabolism. Of note and in contrast, disruptions of energy homeostasis, such as those observed in obesity and diabetes, also have a major impact on drug metabolism. This review will focus on recent progress in our understanding of the integral role of PXR and CAR in drug metabolism and energy homeostasis.