Crosstalk between Gut Microbiota and Bile Acids in Cholestatic Liver Disease

Interkingdom signaling between gastrointestinal hormones and the gut microbiome

The interplay between the gut microbiota and gastrointestinal hormones plays a pivotal role in the health of the host and the development of diseases. As a vital component of the intestinal microecosystem, the gut microbiota influences the synthesis and release of many gastrointestinal hormones through mechanisms such as modulating the intestinal environment, producing metabolites, impacting mucosal barriers, generating immune and inflammatory responses, and releasing neurotransmitters. Conversely, gastrointestinal hormones exert feedback regulation on the gut microbiota by modulating the intestinal environment, nutrient absorption and utilization, and the bacterial biological behavior and composition. The distributions of the gut microbiota and gastrointestinal hormones are anatomically intertwined, and close interactions between the gut microbiota and gastrointestinal hormones are crucial for maintaining gastrointestinal homeostasis. Interventions leveraging the interplay between the gut microbiota and gastrointestinal hormones have been employed in the clinical management of metabolic diseases and inflammatory bowel diseases, such as bariatric surgery and fecal microbiota transplantation, offering promising targets for the treatment of dysbiosis-related diseases.

Caffeoylquinic acids from Silphium perfoliatum L. show hepatoprotective effects on cholestatic mice by regulating enterohepatic circulation of bile acids

ETHNOPHARMACOLOGICAL RELEVANCE

The incidence of cholestatic liver disease (CLD), which is primarily marked by abnormal bile acids (BAs) metabolism and can result in significant hepatic injury, is rising. Nevertheless, there remains a lack of effective treatments and drugs in clinical practice. Silphium perfoliatum L. (SP) is rich in various structural types of caffeoylquinic acid (CQA) compounds, and it is a traditional herb of North American Indians with hepatobiliary therapy effects. However, its therapeutic effect and mechanism of action on CLD have never been studied.

AIM OF THE STUDY

To determine if SP-8, an extract rich in CQAs from SP, protects against cholestatic liver injury induced by alpha-naphthylisothiocyanate (ANIT) and to clarify its mechanism based on the farnesoid x receptor (FXR) signaling pathway and enterohepatic circulation of BAs.

MATERIALS AND METHODS

The therapeutic efficacy of SP-8 was evaluated by assessing the serum biochemical indices, inflammatory factors, and liver histopathology. Targeted metabolomics of the BAs was studied in the feces, liver, serum, and bile using UPLC-MS/MS. Additionally, a Western blot analysis was used to examine the expression levels of the peroxisome proliferator-activated receptor γ (PPARγ), the FXR, and proteins related to the synthesis and transport of BAs. 16S rRNA gene sequencing was performed to evaluate the gut microbiota (GM). Finally, molecular docking simulations were conducted to assess the interaction between seven types of CQAs from SP-8 with FXR and PPARγ.

RESULTS

SP-8 significantly enhanced the health status of cholestatic mice induced by ANIT as evidenced by a notable reduction in the liver function indices and pro-inflammatory factors, restoration of liver pathological damage, and acceleration of BAs excretion through the feces. In addition, the levels of harmful secondary BAs in the liver and blood were significantly reduced by SP-8. Furthermore, the results of the study on the mechanism of action confirmed that SP-8 not only regulated FXR and PPARγ but also significantly ameliorated the GM structure, thereby promoting the enterohepatic circulation of BAs and achieving the homeostasis of the BAs in the blood and liver. In addition, SP-8 successfully reduced the inflammatory response by strongly suppressing the nuclear translocation of NF-κBp65. According to the molecular docking results, the extract's primary active ingredients could be the seven CQAs in SP-8, as they exhibited a strong affinity for both FXR and PPARγ. Finally, the Mantel test analysis revealed a significant correlation among cholestatic-associated parameters, the GM, and BAs.

CONCLUSION

It was confirmed for the first time that the SP-8 extract of Silphium perfoliatum L. that is rich in seven CQAs had a strong therapeutic effect on ANIT-induced CLD. Its mechanism may involve the regulation of the FXR signaling pathway and the amelioration of the GM structure to promote the homeostasis of BAs enterohepatic circulation. This study provides a potential candidate medicinal herb and its components for the development of CLD therapeutic drugs.

Probiotic interventions with highly acid-tolerant Levilactobacillus brevis strains improve lipid metabolism and gut microbial balance in obese mice

Many studies have shown that specific lactic acid bacteria (LAB) strains can delay obesity, offering a viable alternative to medications and surgeries. However, the mining and development of highly effective LAB strains for obesity control is still limited. In this study, the naturally highly acid-tolerant and gamma-aminobutyric acid-producing Levilactobacillus brevis D17 and its glnR deletion strain were used to investigate their anti-obesity effects. In an 8-week mouse experiment, L. brevis D17 and its glnR-deletion strain D17ΔglnR significantly reduced weight gain by 28.4% and 29.1%, respectively, improving abnormal serum indicators and glucose metabolism caused by a high-fat diet. Furthermore, L. brevis D17 and its glnR-deletion strain D17ΔglnR successfully colonized in the gut. Both D17 and D17ΔglnR interventions significantly restored the relative abundance of Muribaculaceae, Ileibacterium valens, Lactobacillus, Faecalibaculum, Bifidobacterium globosum, Akkermansia muciniphila, and Romboutsia ilealis, whereas they significantly reduced potentially harmful bacteria like Leptogranulimonas, Flintibacter, and Alistipes. Additionally, L. brevis intervention effectively decreased the levels of primary bile acids and increased secondary bile acids in the gut, thus balancing bile acid metabolism. The transcriptional analysis suggested that D17 and D17ΔglnR interventions may activate the AMPK signaling pathway in the liver to inhibit lipogenesis, activate the cAMP pathway to promote lipolysis, and inhibit pro-inflammatory macrophage infiltration to block inflammatory responses. These results indicate that L. brevis D17 and its glnR-deletion mutant strain D17ΔglnR show great potential in combating obesity. Moreover, these results also provide insights into the underlying mechanism behind their anti-obesity properties.

Bile acids as a key target: traditional Chinese medicine for precision management of insulin resistance in type 2 diabetes mellitus through the gut microbiota-bile acids axis

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease caused by insulin resistance (IR) and insufficient insulin secretion. Its characteristic pathophysiological processes involve the interaction of multiple mechanisms. In recent years, globally, the prevalence of T2DM has shown a sharp rise due to profound changes in socio-economic structure, the persistent influence of environmental factors, and the complex role of genetic background. It is worth noting that most T2DM patients show significant IR, which further exacerbates the difficulty of disease progression and prevention. In the process of extensively exploring the pathogenesis of T2DM, the dynamic equilibrium of gut microbes and its diverse metabolic activities have increasingly emphasized its central role in the pathophysiological process of T2DM. Bile acids (BAs) metabolism, as a crucial link between gut microbes and the development of T2DM, not only precisely regulates lipid absorption and metabolism but also profoundly influences glucose homeostasis and energy balance through intricate signaling pathways, thus playing a pivotal role in IR progression in T2DM. This review aims to delve into the specific mechanism through which BAs contribute to the development of IR in T2DM, especially emphasizing how gut microbes mediate the metabolic transformation of BAs based on current traditional Chinese medicine research. Ultimately, it seeks to offer new insights into the prevention and treatment of T2DM. Diet, genetics, and the environment intricately sculpt the gut microbiota and BAs metabolism, influencing T2DM-IR. The research has illuminated the significant impact of single herbal medicine, TCM formulae, and external therapeutic methods such as electroacupuncture on the BAs pool through perturbations in gut microbiota structure. This interaction affects glucose and lipid metabolism as well as insulin sensitivity. Additionally, multiple pathways including BA-FXR-SHP, BA-FXR-FGFR15/19, BA-FXR-NLRP3, BA-TGR5-GLP-1, BAs-TGR5/FXR signaling pathways have been identified through which the BAs pool significantly alter blood glucose levels and improve IR. These findings offer novel approaches for enhancing IR and managing metabolic disorders among patients with T2DM.

Fecal Bile Acids in Canine Chronic Liver Disease: Results from 46 Dogs

The concentrations of fecal and serum bile acids (BAs) are known to be altered in human patients with chronic liver diseases (CLDs), especially those with biliary tract involvement (BTD). Scarce literature is available regarding fecal BA modifications during canine CLDs. This study aimed to evaluate fecal BAs in canine CLDs according to different clinical and clinicopathological variables. Forty-six dogs were enrolled. Canine feces were analyzed by HPLC. Cholic Acid (CA), Chenodeoxycholic Acid (CDCA), Ursodeoxycholic Acid (UDCA), Deoxycholic Acid (DCA), and Lithocholic Acid (LCA) were measured, and primary BAs (CA + CDCA), secondary BAs (UDCA + DCA + LCA), and the primary/secondary (P/S) ratio were calculated. Primary BAs (p < 0.0001), CA (p = 0.0003), CDCA (p = 0.003), the P/S ratio (p = 0.002), and total BAs (p = 0.005) were significatively higher in BTD dogs (n = 18) compared to in non-BTD dogs (n = 28). Fecal secondary BAs did not statistically differ between BTD and non-BTD dogs. Gastrointestinal clinical signs (p = 0.028) and diarrhea (p = 0.03) were significantly more prevalent in BTD dogs compared to in non-BTD dogs, supporting the hypothesis of some pathological mechanisms assimilable to bile acid diarrhea (BAD). Our results could reflect imbalances of the fecal BA metabolism in dogs with CLDs. Further studies involving gut microbiome and metabolomic assessment are needed to better understand the possible clinical implications of BA metabolism disruption and their potential role in canine CLDs.

Effects of Synbiotic Administration on Gut Microbiome and Fecal Bile Acids in Dogs with Chronic Hepatobiliary Disease: A Randomized Case-Control Study

Alteration in the gut microbiome in human patients with chronic liver disease is a well-known pathophysiological mechanism. Therefore, it represents both a diagnostic and therapeutical target. Intestinal dysbiosis has also been identified in dogs with chronic liver disease, but clinical trials evaluating the effectiveness of synbiotic administration are lacking. Thirty-two dogs with chronic hepatobiliary disease were equally randomized into two groups: one treated with a synbiotic complex for 4-6 weeks (TG) and one untreated control group (CG). All dogs underwent clinical evaluation, complete anamnesis, bloodwork, abdominal ultrasound, fecal bile acids, and gut microbiome evaluation at T0-T1 (after 4-6 weeks). Treated dogs showed a significant reduction in ALT activity (p = 0.007) and clinical resolution of gastrointestinal signs (p = 0.026) compared to control dogs. The synbiotic treatment resulted in a lower increase in Enterobacteriaceae and Lachnospiraceae compared to the control group but did not affect the overall richness and number of bacterial species. No significant changes in fecal bile acids profile were detected with synbiotic administration. Further studies are needed to better evaluate the effectiveness of synbiotic administration in these patients and the metabolic pathways involved in determining the clinical and biochemical improvement.

Mechanistic studies on the alleviation of ANIT-induced cholestatic liver injury by Polygala fallax Hemsl. polysaccharides

ETHNOPHARMACOLOGICAL RELEVANCE

Polygala fallax Hemsl. is a traditional folk medicine commonly used by ethnic minorities in the Guangxi Zhuang Autonomous Region, and has a traditional application in the treatment of liver disease. Polygala fallax Hemsl. polysaccharides (PFPs) are of interest for their potential health benefits.

AIM OF THIS STUDY

This study explored the impact of PFPs on a mouse model of cholestatic liver injury (CLI) induced by alpha-naphthyl isothiocyanate (ANIT), as well as the potential mechanisms.

MATERIALS AND METHODS

A mouse CLI model was constructed using ANIT (80 mg/kg) and intervened with different doses of PFPs or ursodeoxycholic acid. Their serum biochemical indices, hepatic oxidative stress indices, and hepatic pathological characteristics were investigated. Then RNA sequencing was performed on liver tissues to identify differentially expressed genes and signaling pathways and to elucidate the mechanism of liver protection by PFPs. Finally, Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were used to verify the differentially expressed genes.

RESULTS

Data analyses showed that PFPs reduced the levels of liver function-related biochemical indices, such as ALT, AST, AKP, TBA, DBIL, and TBIL. PFPs up-regulated the activities of SOD and GSH, down-regulated the contents of MDA, inhibited the release of IL-1β, IL-6, and TNF-α, or promoted IL-10. Pathologic characterization of the liver revealed that PFPs reduced hepatocyte apoptosis or necrosis. The RNA sequencing indicated that the genes with differential expression were primarily enriched for the biosynthesis of primary bile acids, secretion or transportation of bile, the reactive oxygen species in chemical carcinogenesis, and the NF-kappa B signaling pathway. In addition, the results of qRT-PCR and Western blotting analysis were consistent with those of RNA sequencing analysis.

CONCLUSIONS

In summary, this study showed that PFPs improved intrahepatic cholestasis and alleviated liver damage through the modulation of primary bile acid production, Control of protein expression related to bile secretion or transportation, decrease in inflammatory reactions, and inhibition of oxidative pressure. As a result, PFPs might offer a hopeful ethnic dietary approach for managing intrahepatic cholestasis.

Exploring Advanced Therapies for Primary Biliary Cholangitis: Insights from the Gut Microbiota-Bile Acid-Immunity Network

Primary biliary cholangitis (PBC) is a cholestatic liver disease characterized by immune-mediated injury to small bile ducts. Although PBC is an autoimmune disease, the effectiveness of conventional immunosuppressive therapy is disappointing. Nearly 40% of PBC patients do not respond to the first-line drug UDCA. Without appropriate intervention, PBC patients eventually progress to liver cirrhosis and even death. There is an urgent need to develop new therapies. The gut-liver axis emphasizes the interconnection between the gut and the liver, and evidence is increasing that gut microbiota and bile acids play an important role in the pathogenesis of cholestatic diseases. Dysbiosis of gut microbiota, imbalance of bile acids, and immune-mediated bile duct injury constitute the triad of pathophysiology in PBC. Autoimmune cholangitis has the potential to be improved through immune system modulation. Considering the failure of conventional immunotherapies and the involvement of gut microbiota and bile acids in the pathogenesis, targeting immune factors associated with them, such as bile acid receptors, microbial-derived molecules, and related specific immune cells, may offer breakthroughs. Understanding the gut microbiota-bile acid network and related immune dysfunctions in PBC provides a new perspective on therapeutic strategies. Therefore, we summarize the latest advances in research of gut microbiota and bile acids in PBC and, for the first time, explore the possibility of related immune factors as novel immunotherapy targets. This article discusses potential therapeutic approaches focusing on regulating gut microbiota, maintaining bile acid homeostasis, their interactions, and related immune factors.