Combinatorial targeting of G-protein-coupled bile acid receptor 1 and cysteinyl leukotriene receptor 1 reveals a mechanistic role for bile acids and leukotrienes in drug-induced liver injury

Revealing the anti-inflammatory ingredients in wine-processed Radix et Rhizoma Rhei using immobilized cysteinyl leukotriene receptor type 1 as the stationary phase

Despite the tremendous progress of wine-processed Radix et Rhizoma Rhei (Jiudahuang, JDH) in removing toxic heat from the blood in the upper portion of the body for hundreds of years, the deep understanding of its functional material basis of the anti-inflammatory ingredients remains unclear due to the lack of high specific and efficient methods. Herein, taking Cysteinyl leukotriene receptor type 1(CysLT1R) as the target protein, we established a chromatographic method based on the immobilized CysLT1R using haloalkane dehalogenases (Halo) at the C-terminus of the receptor in one step. After careful characterization by X-ray photoelectronic spectroscopy, immune-fluorometric analysis, and chromatographic investigations, the immobilized receptor was used to screen the anti-inflammatory ingredients in JDH. Aloe-emodin, rhein, emodin, chrysophanol, and physcion were identified as the main anthraquinone exerting anti-inflammatory effects in the drug. The association constants for the five compounds to bind with the receptor were calculated as (0.30 ± 0.06)× 105, (0.35 ± 0.03)× 105, (0.46 ± 0.05)× 105, (1.05 ± 0.14)× 105, and (1.66 ± 0.17)× 105 M-1 by injection amount-dependent method. Meanwhile, hydrogen bonds were identified as the main driving force for the five compounds to bind with CysLT1R by molecular docking. Based on these results, we believe that the immobilized receptor chromatography preserves historic significance in revealing the functional material basis of the complex matrices.

XIAP-mediated degradation of IFT88 disrupts HSC cilia to stimulate HSC activation and liver fibrosis

Activation of hepatic stellate cells (HSCs) plays a critical role in liver fibrosis. However, the molecular basis for HSC activation remains poorly understood. Herein, we demonstrate that primary cilia are present on quiescent HSCs but exhibit a significant loss upon HSC activation which correlates with decreased levels of the ciliary protein intraflagellar transport 88 (IFT88). Ift88-knockout mice are more susceptible to chronic carbon tetrachloride-induced liver fibrosis. Mechanistic studies show that the X-linked inhibitor of apoptosis (XIAP) functions as an E3 ubiquitin ligase for IFT88. Transforming growth factor-β (TGF-β), a profibrotic factor, enhances XIAP-mediated ubiquitination of IFT88, promoting its proteasomal degradation. Blocking XIAP-mediated IFT88 degradation ablates TGF-β-induced HSC activation and liver fibrosis. These findings reveal a previously unrecognized role for ciliary homeostasis in regulating HSC activation and identify the XIAP-IFT88 axis as a potential therapeutic target for liver fibrosis.

Mechanism of action of the bile acid receptor TGR5 in obesity

G protein-coupled receptors (GPCRs) are a large family of membrane protein receptors, and Takeda G protein-coupled receptor 5 (TGR5) is a member of this family. As a membrane receptor, TGR5 is widely distributed in different parts of the human body and plays a vital role in regulating metabolism, including the processes of energy consumption, weight loss and blood glucose homeostasis. Recent studies have shown that TGR5 plays an important role in glucose and lipid metabolism disorders such as fatty liver, obesity and diabetes. With the global obesity situation becoming more and more serious, a comprehensive explanation of the mechanism of TGR5 and filling the gaps in knowledge concerning clinical ligand drugs are urgently needed. In this review, we mainly explain the anti-obesity mechanism of TGR5 to promote the further study of this target, and show the electron microscope structure of TGR5 and review recent studies on TGR5 ligands to illustrate the specific binding between TGR5 receptor binding sites and ligands, which can effectively provide new ideas for ligand research and promote drug research.

Macrophage metabolism in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) and its inflammatory and often progressive subtype nonalcoholic steatohepatitis (NASH), have emerged as significant contributors to hepatic morbidity worldwide. The pathophysiology of NAFLD/NASH is multifaceted, variable, and remains incompletely understood. The pivotal role of liver-resident and recruited macrophages in the pathogenesis of NAFLD and NASH is widely acknowledged as a crucial factor in innate immunity. The remarkable plasticity of macrophages enables them to assume diverse activation and polarization states, dictated by their immunometabolism microenvironment and functional requirements. Recent studies in the field of immunometabolism have elucidated that alterations in the metabolic profile of macrophages can profoundly influence their activation state and functionality, thereby influencing various pathological processes. This review primarily focuses on elucidating the polarization and activation states of macrophages, highlighting the correlation between their metabolic characteristics and the transition from pro-inflammatory to anti-inflammatory phenotypes. Additionally, we explore the potential of targeting macrophage metabolism as a promising therapeutic approach for the management of NAFLD/NASH.

Development of bile acid activated receptors hybrid molecules for the treatment of inflammatory and metabolic disorders

The farnesoid-x-receptor (FXR) and the G protein bile acid activated receptor (GPBAR)1 are two bile acid activated receptors highly expressed in entero-hepatic, immune, adipose and cardiovascular tissues. FXR and GPBAR1 are clinically validated targets in the treatment of metabolic disorders and FXR agonists are currently trialled in patients with non-alcoholic steato-hepatitis (NASH). Results of these trials, however, have raised concerns over safety and efficacy of selective FXR ligands suggesting that the development of novel agent designed to impact on multiple targets might have utility in the treatment of complex, multigenic, disorders. Harnessing on FXR and GPBAR1 agonists, several novel hybrid molecules have been developed, including dual FXR and GPBAR1 agonists and antagonists, while exploiting the flexibility of FXR agonists toward other nuclear receptors, dual FXR and peroxisome proliferators-activated receptors (PPARs) and liver-X-receptors (LXRs) and Pregnane-X-receptor (PXR) agonists have been reported. In addition, modifications of FXR agonists has led to the discovery of dual FXR agonists and fatty acid binding protein (FABP)1 and Leukotriene B4 hydrolase (LTB4H) inhibitors. The GPBAR1 binding site has also proven flexible to accommodate hybrid molecules functioning as GPBAR1 agonist and cysteinyl leukotriene receptor (CYSLTR)1 antagonists, as well as dual GPBAR1 agonists and retinoid-related orphan receptor (ROR)γt antagonists, dual GPBAR1 agonist and LXR antagonists and dual GPBAR1 agonists endowed with inhibitory activity on dipeptidyl peptidase 4 (DPP4). In this review we have revised the current landscape of FXR and GPBAR1 based hybrid agents focusing on their utility in the treatment of metabolic associated liver disorders.

Angiocrine Signaling in Sinusoidal Health and Disease

Liver sinusoidal endothelial cells (LSECs) are key players in maintaining hepatic homeostasis. They also play crucial roles during liver injury by communicating with liver cell types as well as immune cells and promoting portal hypertension, fibrosis, and inflammation. Cutting-edge technology, such as single cell and spatial transcriptomics, have revealed the existence of distinct LSEC subpopulations with a clear zonation in the liver. The signals released by LSECs are commonly called "angiocrine signaling." In this review, we summarize the role of angiocrine signaling in health and disease, including zonation in healthy liver, regeneration, fibrosis, portal hypertension, nonalcoholic fatty liver disease, alcohol-associated liver disease, aging, drug-induced liver injury, and ischemia/reperfusion, as well as potential therapeutic advances. In conclusion, sinusoidal endotheliopathy is recognized in liver disease and promising preclinical studies are paving the path toward LSEC-specific pharmacotherapies.

Distribution of the cysteinyl leukotriene system components in the human, rat and mouse eye

The cysteinyl leukotrienes (CysLTs) have important functions in the regulation of inflammation and cellular stress. Blocking the CysLT receptors (CysLTRs) with specific antagonists is beneficial against progression of retinopathies (e.g. diabetic retinopathy, wet AMD). However, the exact cellular localization of the CysLTRs and their endogenous ligands in the eye have not been elucidated in detail yet. It is also not known whether the expression patterns differ between humans and animal models. Therefore, the present study aimed to describe and compare the distribution of two important enzymes in CysLT biosynthesis, 5-lipoxygenase (5-LOX) and 5-lipoxygenase-activating protein (FLAP), and of CysLTR1 and CysLTR2 in healthy human, rat and mouse eyes. Human donor eyes (n = 10) and eyes from adult Sprague Dawley rats (n = 5) and CD1 mice (n = 8) of both sexes were collected. The eyes were fixed in 4% paraformaldehyde and cross-sections were investigated by immunofluorescence with specific antibodies against 5-LOX, FLAP (human tissue only), CysLTR1 and CysLTR2. Flat-mounts of the human choroid were prepared and processed similarly. Expression patterns were assessed and semiquantitatively evaluated using a confocal fluorescence microscope (LSM710, Zeiss). We observed so far unreported expression sites for CysLT system components in various ocular tissues. Overall, we detected expression of 5-LOX, CysLTR1 and CysLTR2 in the human, rat and mouse cornea, conjunctiva, iris, lens, ciliary body, retina and choroid. Importantly, expression profiles of CysLTR1 and CysLTR2 were highly similar between human and rodent eyes. FLAP was expressed in all human ocular tissues except the lens. Largely weak immunoreactivity of FLAP and 5-LOX was observed in a few, yet unidentified, cells of diverse ocular tissues, indicating low levels of CysLT biosynthesis in healthy eyes. CysLTR1 was predominantly detected in ocular epithelial cells, supporting the involvement of CysLTR1 in stress and immune responses. CysLTR2 was predominantly expressed in neuronal structures, suggesting neuromodulatory roles of CysLTR2 in the eye and revealing disparate functions of CysLTRs in ocular tissues. Taken together, we provide a comprehensive protein expression atlas of CysLT system components in the human and rodent eye. While the current study is purely descriptive and therefore does not allow significant functional conclusions yet, it represents an important basis for future studies in diseased ocular tissues in which distribution patterns or expression levels of the CysLT system might be altered. Furthermore, this is the first comprehensive study to elucidate expression patterns of CysLT system components in human and animal models that will help to identify and understand functions of the system as well as mechanisms of action of potential CysLTR ligands in the eye.

Montelukast prevents mice against carbon tetrachloride- and methionine-choline deficient diet-induced liver fibrosis: Reducing hepatic stellate cell activation and inflammation

AIMS

Montelukast is an antagonist of cysteinyl leukotriene receptor 1 (CysLTR1) that protects against inflammation and oxidative stress. However, the function of montelukast in liver fibrosis remains unknown. In this study, we examined whether the pharmacological inhibition of CysLTR1 could protect mice against hepatic fibrosis.

MATERIALS AND METHODS

Carbon tetrachloride (CCl₄) and methionine-choline deficient (MCD) diet models were used in this study. The expression of CysLTR1 in liver were detected by RT-qPCR and Western blot analysis. Liver hydroxyproline levels, fibrotic genes expression, serum biochemical indexes and inflammatory factors were used to evaluate the effect of montelukast on liver fibrosis, injury, and inflammation. In vitro, we used the RT-qPCR and Western blot analysis to assess CysLTR1 in mouse primary hepatic stellate cell (HSC) and human LX-2 cell line. The role of montelukast on HSC activation and the underlying mechaisms were determined using RT-qPCR analysis, Western blot and immunostaining assays.

KEY FINDINGS

Chronic stimulation from CCl₄ and MCD diet upregulated the mRNA and protein levels of CysLTR1 in the liver. Pharmacological inhibition of CysLTR1 by montelukast ameliorated liver inflammation and fibrosis in both models. Mechanistically, montelukast suppressed HSC activation by targeting the TGFβ/Smad pathway in vitro. The hepatoprotective effect of montelukast was also associated with reduced liver injury and inflammation.

SIGNIFICANCE

Montelukast suppressed CCl₄- and MCD-induced chronic hepatic inflammation and liver fibrosis. CysLTR1 might be a therapeutic target for treating liver fibrosis.