Farnesoid X receptor ligand prevents cisplatin-induced kidney injury by enhancing small heterodimer partner

The NF-κB/FXR/TonEBP pathway protects renal medullary interstitial cells against hypertonic stress

Farnesoid X receptor (FXR), a ligand-activated transcription factor, plays an important role in maintaining water homeostasis by up-regulating aquaporin 2 (AQP2) expression in renal medullary collecting ducts; however, its role in the survival of renal medullary interstitial cells (RMICs) under hypertonic conditions remains unclear. We cultured primary mouse RMICs and found that the FXR was expressed constitutively in RMICs, and that its expression was significantly up-regulated at both mRNA and protein levels by hypertonic stress. Using luciferase and ChIP assays, we found a potential binding site of nuclear factor kappa-B (NF-κB) located in the FXR gene promoter which can be bound and activated by NF-κB. Moreover, hypertonic stress-induced cell death in RMICs was significantly attenuated by FXR activation but worsened by FXR inhibition. Furthermore, FXR increased the expression and nuclear translocation of hypertonicity-induced tonicity-responsive enhance-binding protein (TonEBP), the expressions of its downstream target gene sodium myo-inositol transporter (SMIT), and heat shock protein 70 (HSP70). The present study demonstrates that the NF-κB/FXR/TonEBP pathway protects RMICs against hypertonic stress.

Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Farnesoid X receptor (FXR) activation reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). The signaling lipid sphingosine-1-phosphate (S1P) stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of NETosis via repressing S1P signaling. We determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase (APRT) deficiency and Alport syndrome, both genetic disorders that cause chronic kidney disease. Renal FXR activity is greatly reduced in both models, and FXR agonism reduces disease severity. Renal NETosis and sphingosine kinase 1 (Sphk1) expression are increased in diseased mice, and they are reduced by OCA in both models. Genetic deletion of FXR increases Sphk1 expression, and Sphk1 expression correlates with NETosis. Importantly, kidney S1P levels in Alport mice are two-fold higher than controls, and FXR agonism restores them back to baseline. Short-term inhibition of sphingosine synthesis in Alport mice with severe kidney disease reverses NETosis, establishing a causal relationship between S1P signaling and renal NETosis. Finally, extensive NETosis is present in human Alport kidney biopsies (six male, nine female), and NETosis severity correlates with clinical markers of kidney disease. This suggests the potential clinical relevance of the newly identified FXR-S1P-NETosis pathway. In summary, FXR agonism represses kidney Sphk1 expression. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis.NEW & NOTEWORTHY Many preclinical studies have shown that the farnesoid X receptor (FXR) reduces renal inflammation, but the mechanism is poorly understood. This report identifies FXR as a novel regulator of neutrophilic inflammation and NETosis via the inhibition of sphingosine-1-phosphate signaling. Additionally, NETosis severity in human Alport kidney biopsies correlates with clinical markers of kidney disease. A better understanding of this signaling axis may lead to novel treatments that prevent renal inflammation and chronic kidney disease.

Bile acid receptors and renal regulation of water homeostasis

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2 L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

Farnesoid X Receptor Plays a Key Role in Ochratoxin A-Induced Nephrotoxicity by Targeting Ferroptosis In Vivo and In Vitro

The mycotoxin ochratoxin A (OTA) causes nephrotoxicity, hepatotoxicity, and immunotoxicity in animals and humans. The farnesoid X receptor (FXR) is a member of the NR family and is highly expressed in the kidney, which has an antilipid production function. Ferroptosis is an iron-dependent form of regulated cell death involved in several pathophysiological cell death and kidney injury. The present study aims to evaluate the role of FXR and ferroptosis in OTA-induced nephrotoxicity in mice and HK-2 cells. Results showed that OTA induced nephrotoxicity as demonstrated by inducing the histopathological lesions and neutrophil infiltration of the kidney, increasing serum BUN, CRE, and UA levels, increasing Ntn-1, Kim-1, and pro-inflammatory cytokine expression, and decreasing IL-10 expression and the cell viability of HK-2 cells. OTA treatment also induced FXR deficiency, ROS release, MDA level increase, GSH content decrease, and 4-HNE production in the kidney and HK-2 cells. OTA treatment induced ferroptosis as demonstrated by increasing labile iron pool and lipid peroxidation levels as well as Acsl4, TFR1, and HO-1 mRNA and protein levels, decreasing GPX4 and FTH mRNA and protein expressions, and inducing mitochondrial injury. The FXR activator (GW4064) rescued the accumulation of lipid peroxides, intracellular ROS, and Fe2+, inhibited ferroptosis, and alleviated OTA-induced nephrotoxicity. The ferroptosis inhibitor (Fer-1) prevented ferroptosis and attenuated nephrotoxicity. Collectively, this study elucidates that FXR played a critical role in OTA-induced nephrotoxicity via regulation of ferroptosis, which provides a novel strategy against OTA-induced nephrotoxicity.

Hepatic and renal improvements with FXR agonist vonafexor in individuals with suspected fibrotic NASH

BACKGROUND & AIMS

The LIVIFY trial investigated the safety, tolerability, and efficacy of vonafexor, a second-generation, non-bile acid farnesoid X receptor agonist in patients with suspected fibrotic non-alcoholic steatohepatitis (NASH).

METHODS

This double-blind phase IIa study was conducted in two parts. Patients were randomised (1:1:1:1) to receive placebo, vonafexor 100 mg twice daily (VONA-100BID), vonafexor 200 mg once daily (VONA-200QD), or 400 mg vonafexor QD (VONA-400QD) in Part A (safety run-in, pharmacokinetics/pharmacodynamics) or placebo, vonafexor 100 mg QD (VONA-100QD), or VONA-200QD (1:1:1) in Part B. The primary efficacy endpoint was a reduction in liver fat content (LFC) by MRI-proton density fat fraction, while secondary endpoints included reduced corrected T1 values and liver enzymes, from baseline to Week 12.

RESULTS

One hundred and twenty patients were randomised (Part A, n = 24; Part B, n = 96). In Part B, there was a significant reduction in least-square mean (SE) absolute change in LFC from baseline to Week 12 for VONA-100QD (-6.3% [0.9]) and VONA-200QD (-5.4% [0.9]), vs. placebo (-2.3% [0.9], p = 0.002 and 0.012, respectively). A >30% relative LFC reduction was achieved by 50.0% and 39.3% of patients in the VONA-100QD and VONA-200QD arms, respectively, but only in 12.5% in the placebo arm. Reductions in body weight, liver enzymes, and corrected T1 were also observed with vonafexor. Creatinine-based glomerular filtration rate improved in the active arms but not the placebo arm. Mild to moderate generalised pruritus was reported in 6.3%, 9.7%, and 18.2% of participants in the placebo, VONA-100QD, and VONA-200QD arms, respectively.

CONCLUSIONS

In patients with suspected fibrotic NASH, vonafexor was safe and induced potent liver fat reduction, improvement in liver enzymes, weight loss, and a possible renal benefit.

CLINICAL TRIAL NUMBER (EUDRACT)

2018-003119-22.

CLINICALTRIALS

GOV IDENTIFIER

NCT03812029.

IMPACT AND IMPLICATIONS

Non-alcoholic steatohepatitis (NASH) has become a leading cause of chronic liver disease worldwide. Affected patients are also at higher risk of developing chronic kidney disease. There are no approved therapies and only few options to treat this population. The phase IIa LIVIFY trial results show that single daily administration of oral vonafexor, an FXR agonist, leads in the short term to a reduction in liver fat, liver enzymes, fibrosis biomarkers, body weight and abdominal circumference, and a possible improvement in kidney function, while possible mild moderate pruritus (a peripheral FXR class effect) and an LDL-cholesterol increase are manageable with lower doses and statins. These results support exploration in longer and larger trials, with the aim of addressing the unmet medical need in NASH.

A perspective study of the possible impact of obeticholic acid against SARS-CoV-2 infection

The causative agent of CoV disease 2019 is a new coronavirus CoV type 2, affecting the respiratory tract with severe manifestations (SARS-CoV-2). Covid-19 is mainly symptomless, with slight indications in about 85% of the affected cases. Many efforts were done to face this pandemic by testing different drugs and agents to make treatment protocols in different countries. However, the use of these proposed drugs is associated with the development of adverse events. Remarkably, the successive development of SARS-CoV-2 variants which could affect persons even they were vaccinated, prerequisite wide search to find efficient and safe agents to face SARS-CoV-2 infection. Obeticholic acid (OCA), which has anti-inflammatory effects, may efficiently treat Covid-19. Thus, the goal of this perspective study is to focus on the possible medicinal effectiveness in managing Covid-19. OCA is a powerful farnesoid X receptor (FXR) agonist possessing marked antiviral and anti-inflammatory effects. FXR is dysregulated in Covid-19 resulting in hyper-inflammation with concurrent occurrence of hypercytokinemia. Interestingly, OCA inhibits the reaction between this virus and angiotensin-converting enzyme type 2 (ACE2) receptors. FXR agonists control the expression of ACE2 and the inflammatory signaling pathways in this respiratory syndrome, which weakens the effects of Covid-19 disease and accompanied complications. Taken together, FXR agonists like OCA may reveal both direct and indirect impacts in the modulation of immune reaction in SARS-CoV-2 conditions. It is highly recommended to perform many investigations regarding different phases of the discovery of new drugs.

The role of the farnesoid X receptor in kidney health and disease: a potential therapeutic target in kidney diseases

The prevalence of kidney diseases has been increasing worldwide due to the aging population and has results in an increased socioeconomic burden as well as increased morbidity and mortality. A deep understanding of the mechanisms underlying the physiological regulation of the kidney and the pathogenesis of related diseases can help identify potential therapeutic targets. The farnesoid X receptor (FXR, NR1H4) is a primary nuclear bile acid receptor that transcriptionally regulates bile acid homeostasis as well as glucose and lipid metabolism in multiple tissues. The roles of FXR in tissues other than hepatic and intestinal tissues are poorly understood. In studies over the past decade, FXR has been demonstrated to have a protective effect against kidney diseases through its anti-inflammatory and antifibrotic effects; it also plays roles in glucose and lipid metabolism in the kidney. In this review, we discuss the physiological role of FXR in the kidney and its pathophysiological roles in various kidney diseases, including acute kidney injury and chronic kidney diseases, diabetic nephropathy, and kidney fibrosis. Therefore, the regulatory mechanisms involving nuclear receptors, such as FXR, in the physiology and pathophysiology of the kidney and the development of agonists and antagonists for modulating FXR expression and activation should be elucidated to identify therapeutic targets for the treatment of kidney diseases.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

Interplay between metabolic dysfunction-associated fatty liver disease and chronic kidney disease: Epidemiology, pathophysiologic mechanisms, and treatment considerations

The recently proposed nomenclature change from non-alcoholic fatty liver disease to metabolic dysfunction-associated fatty liver disease (MAFLD) has resulted in the reappraisal of epidemiological trends and associations with other chronic diseases. In this context, MAFLD appears to be tightly linked to incident chronic kidney disease (CKD). This association may be attributed to multiple shared risk factors including type 2 diabetes mellitus, arterial hypertension, obesity, dyslipidemia, and insulin resistance. Moreover, similarities in their molecular pathophysiologic mechanisms can be detected, since inflammation, oxidative stress, fibrosis, and gut dysbiosis are highly prevalent in these pathologic states. At the same time, lines of evidence suggest a genetic predisposition to MAFLD due to gene polymorphisms, such as the PNPLA3 rs738409 G allele polymorphism, which may also propagate renal dysfunction. Concerning their management, available treatment considerations for obesity (bariatric surgery) and novel antidiabetic agents (glucagon-like peptide 1 receptor agonists, sodium-glucose co-transporter 2 inhibitors) appear beneficial in preclinical and clinical studies of MAFLD and CKD modeling. Moreover, alternative approaches such as melatonin supplementation, farnesoid X receptor agonists, and gut microbiota modulation may represent attractive options in the future. With a look to the future, additional adequately sized studies are required, focusing on preventing renal complications in patients with MAFLD and the appropriate management of individuals with concomitant MAFLD and CKD.

Farnesoid X receptor protects against cisplatin-induced acute kidney injury by regulating the transcription of ferroptosis-related genes

The side effects of cisplatin, a widely used chemotherapeutic agent, include nephrotoxicity. Previous studies have reported that cisplatin induces ferroptosis and lipid peroxide accumulation. Ferroptosis, a type of regulated cell death, is characterized by iron-dependent lipid peroxidation. Although previous studies have examined the regulation of ferroptosis in acute kidney injury (AKI), the regulatory mechanism of ferroptosis has not been elucidated. Here, the ability of activated farnesoid X receptor (FXR) to attenuate cisplatin-induced AKI through the regulation of ferroptosis was examined. FXR deficiency exhibited more ferroptosis responses, such as increase in lipid peroxidation, iron content and heme oxygenase 1 protein, and a decrease in glutathione/glutathione disulfide ratio and glutathione peroxidase 4 levels in HK2 cells and mice. Increased blood urea nitrogen, serum creatinine, and ferroptotic responses in the cisplatin-induced AKI mouse model were mitigated upon treatment with the FXR agonist GW4064 but were exacerbated in FXR knockout mice. RNA sequencing analysis revealed that ferroptosis-associated genes were novel targets of FXR. FXR agonist upregulated the expression of lipid and glutathione metabolism-related genes and downregulated cell death-related genes. Additionally, chromatin immunoprecipitation assays, using mice renal tissues, revealed that agonist-activated FXR could bind to its known target genes (Slc51a, Slc51b, Osgin1, and Mafg) and ferroptosis-related genes (Aifm2, Ggt6, and Gsta4). Furthermore, activated FXR-dependent MAFG, a transcriptional repressor, could bind to Hmox1, Nqo1, and Tf in the renal tissues of FXR agonist-treated mice. These findings indicate that activated FXR regulates the transcription of ferroptosis-related genes and protects against cisplatin-induced AKI.

Knockout of farnesoid X receptor gene aggravates cisplatin-induced kidney injury

OBJECTIVES

Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of ligand activated transcription factors and belongs to bile acid receptor. Studies have shown that the expression of FXR in renal tissue can reduce renal injury via regulation of glucose and lipid metabolism, inhibition of inflammatory response, reduction of oxidative stress and renal fibrosis. However, it is unclear whether FXR is involved in autophagy in renal diseases. This study aims to investigate the role of FXR in cisplatin-induced acute renal injury and whether its mechanism is related to autophagy regulation.

METHODS

Twelve male WT or FXR-KO mice at 12 weeks were randomly divided into a WT group, a WT+cisplatin group, a FXR-KO group, and a FXR-KO+cisplatin group, with 6 mice in each group. The WT+cisplatin group and the FXR-KO+cisplatin group were intraperitoneally injected with cisplatin (20 mg/kg), and the WT group and the FXR-KO group were intraperitoneally injected with equal volume of cisplatin solvent. Seventy-two hours later, the mice were killed and blood and renal tissue samples were collected. The levels of SCr and BUN were detected by immunoturbidimetry. After the staining, the pathological changes of renal tissue were observed under optical microscope. The protein levels of LC3 and p62 were detected by Western blotting and immunohistochemistry. The clearance of damaged mitochondria and the accumulation of lysosomal substrate were observed under electron microscope. The apoptosis of renal tubular epithelial cells was detected by TUNEL.

RESULTS

Compared with the WT group or the FXR-KO group, both SCr and BUN levels in the WT+cisplatin group or the FXR-KO+cisplatin group were significantly increased (P<0.01 or P<0.001), and SCr and BUN levels in the FXR-KO+cisplatin group were significantly higher than those in the WT+cisplatin group (both P<0.05). Under the light microscope, there were no obvious pathological changes in the renal tissue of mice in the WT group and the FXR-KO group. Both the WT+cisplatin group and the FXR-KO+cisplatin group had vacuolar or granular degeneration of renal tubular epithelial cells, flat cells, lumen expansion, brush edge falling off, and even exposed basement membrane and tubular formation. The scores of renal tubular injury in the WT+cisplatin group and the FXR-KO+cisplatin group were significantly higher than those in the WT group and the FXR-KO group, respectively (both P<0.001), and the score in the FXR-KO+cisplatin group was significantly higher than that in the WT+cisplatin group (P<0.05). Under the transmission electron microscope, the mitochondria of mouse tubular epithelial cell in the WT+cisplatin group and the FXR-KO+cisplatin group was swollen, round, vacuolated, cristae broken or disappeared; the lysosome was uneven and high-density clumps, and the change was more obvious in the FXR-KO+cisplatin group. Western blotting showed that the ratio of LC3-II to LC3-I was decreased and the expression of p62 was increased in the WT+cisplatin group compared with the WT group and the FXR-KO+cisplatin group compared with FXR-KO group (P<0.05 or P<0.01); compared with the FXR-KO group, the ratio of LC3-II to LC3-I was decreased and the expression of p62 was increased significantly in the FXR-KO+cisplatin group (both P<0.05). Immunohistochemistry results showed that the expression of total LC3 and p62 in renal cortex of the WT+cisplatin group and the FXR-KO+cisplatin group was increased significantly, especially in the FXR-KO+cisplatin group. TUNEL results showed that the mice in the WT group and the FXR-KO group had negative staining or only a few apoptotic tubular epithelial cells, and the number of apoptotic cells in the WT+cisplatin group and the FXR-KO+cisplatin group were increased. The apoptosis rates of renal tubular epithelial cells in the WT+cisplatin group and the FXR-KO+cisplatin group were significantly higher than those in the WT group and the FXR-KO group, respectively (both P<0.001), and the apoptosis rate in the FXR-KO+cisplatin group was significantly higher than that in the WT+cisplatin group (P<0.05).

CONCLUSIONS

Knockout of FXR gene aggravates cisplatin induced acute renal injury, and its mechanism may be related to inhibiting autophagy and promoting apoptosis.

Lower bile acids as an independent risk factor for renal outcomes in patients with type 2 diabetes mellitus and biopsy-proven diabetic kidney disease

AIMS

Abnormalities of glucolipid metabolism are critical mechanisms involved in the progression of diabetic kidney disease (DKD). Bile acids have an essential role in regulating glucolipid metabolism. This study investigated the clinicopathological characteristics of DKD patients with different bile acid levels and explored the relationship between bile acids and renal outcomes of DKD patients.

METHODS

We retrospectively reviewed and evaluated the histopathological features and clinical features of our cohort of 184 patients with type 2 diabetes mellitus and biopsy-proven DKD. Patients were divided into the lower bile acids group (≤2.8 mmol/L) and higher bile acids group (>2.8 mmol/L) based on the cutoff value of bile acids obtained using the time-dependent receiver-operating characteristic curve. Renal outcomes were defined as end-stage renal disease (ESRD). The influence of bile acids on renal outcomes and correlations between bile acids and clinicopathological indicators were evaluated.

RESULTS

Bile acids were positively correlated with age (r = 0.152; P = 0.040) and serum albumin (r = 0.148; P = 0.045) and negatively correlated with total cholesterol (r = -0.151; P = 0.041) and glomerular class (r = -0.164; P =0.027). During follow-up, 64 of 184 patients (34.78%) experienced progression to ESRD. Lower levels of proteinuria, serum albumin, and bile acids were independently associated with an increased risk of ESRD (hazard ratio, R=5.319; 95% confidence interval, 1.208-23.425).

CONCLUSIONS

Bile acids are an independent risk factor for adverse renal outcomes of DKD patients. The serum level of bile acids should be maintained at more than 2.8 mmol/L in DKD patients. Bile acid analogs or their downstream signaling pathway agonists may offer a promising strategy for treating DKD.

Vincamine protects against cisplatin induced nephrotoxicity via activation of Nrf2/HO-1 and hindering TLR4/ IFN-γ/CD44 cells inflammatory cascade

Cisplatin is a commonly prescribed chemotherapeutic agent for the treatment of different types of solid tumors. However, the high incidence of cisplatin-induced nephrotoxicity largely restricts its clinical efficacy in absence of both preventive and treatment options to combat its serious and life-threatening effects. Therefore, the current study investigated the reno-protective molecular mechanisms of vincamine against cisplatin nephrotoxicity. Vincamine (40 mg/kg P.O.) was given for 7 days, cisplatin was injected as single dose (10 mg/kg i.p.) at the seven day of the experiments. Animals were sacrificed after 72 h of cisplatin injection to allow nephrotoxicity. Vincamine pretreatment improved kidney functions and decreased kidney function tests as urea, creatinine and kidney injury molecule-1 (KIM-1), as well as it exhibited antioxidant properties by restoring balance between pro and anti-oxidants of malondialdehyde (MDA), myeloperoxidase (MPO), nuclear factor erythroid 2-related factor 2 (Nrf2) and hemeoxygenase-1 (HO-1). Moreover, vincamine hindered the inflammatory cascade via mediating Toll like receptor 4 (TLR4)- interferon gamma (IFNγ)-CD44 cells pathway and transforming growth factor beta (TGFβ1). Additionally, vincamine retained DNA fragmentation. In conclusion, vincamine represents a promising intervention in limiting cisplatin nephrotoxicity by its anti-oxidant, anti-inflammatory, antiapoptotic mechanistic activities. Therefore, vincamine can be used as adjunct therapy with cisplatin to mitigate cisplatin-induced-AKI.

Nuclear receptors in the kidney during health and disease

Over the last 30 years, nuclear receptors (NRs) have been increasingly recognized as key modulators of systemic homeostasis and as contributing factors in many diseases. In the kidney, NRs play numerous important roles in maintaining homeostasis-many of which continue to be unraveled. As "master regulators", these important transcription factors integrate and coordinate many renal processes such as circadian responses, lipid metabolism, fatty acid oxidation, glucose handling, and inflammatory responses. The use of recently-developed genetic tools and small molecule modulators have allowed for detailed studies of how renal NRs contribute to kidney homeostasis. Importantly, while NRs are intimately involved in proper kidney function, they are also implicated in a variety of renal diseases such as diabetes, acute kidney injury, and other conditions such as aging. In the last 10 years, our understanding of renal disease etiology and progression has been greatly shaped by knowledge regarding how NRs are dysregulated in these conditions. Importantly, NRs have also become attractive therapeutic targets for attenuation of renal diseases, and their modulation for this purpose has been the subject of intense investigation. Here, we review the role in health and disease of six key renal NRs including the peroxisome proliferator-activated receptors (PPAR), estrogen-related receptors (ERR), the farnesoid X receptors (FXR), estrogen receptors (ER), liver X receptors (LXR), and vitamin D receptors (VDR) with an emphasis on recent findings over the last decade. These NRs have generated a wealth of data over the last 10 years that demonstrate their crucial role in maintaining normal renal homeostasis as well as their capacity to modulate disease progression.

Farnesoid X Receptor Activation Stimulates Organic Cations Transport in Human Renal Proximal Tubular Cells

Farnesoid X receptor (FXR) is a ligand-activated transcription factor highly expressed in the liver and kidneys. Activation of FXR decreases organic cation transporter (OCT) 1-mediated clearance of organic cation compounds in hepatocytes. The present study investigated FXR regulation of renal clearance of organic cations by OCT2 modulation and multidrug and toxin extrusion proteins (MATEs). The role of FXR in OCT2 and MATEs functions was investigated by monitoring the flux of ³H-MPP⁺, a substrate of OCT2 and MATEs. FXR agonists chenodeoxycholic acid (CDCA) and GW4064 stimulated OCT2-mediated ³H-MPP⁺ uptake in human renal proximal tubular cells (RPTEC/TERT1 cells) and OCT2-CHO-K1 cells. The stimulatory effect of CDCA (20 µM) was abolished by an FXR antagonist, Z-guggulsterone, indicating an FXR-dependent mechanism. CDCA increased OCT2 transport activity via an increased maximal transport rate of MPP⁺. Additionally, 24 h CDCA treatment increased MATEs-mediated ³H-MPP⁺ uptake. Moreover, CDCA treatment increased the expression of OCT2, MATE1, and MATE2-K mRNA compared with that of the control. OCT2 protein expression was also increased following CDCA treatment. FXR activation stimulates renal OCT2- and MATE1/2-K-mediated cation transports in proximal tubules, demonstrating that FXR plays a role in the regulation of OCT2 and MATEs in renal proximal tubular cells.

The farnesoid X receptor: a potential target for expanding the therapeutic arsenal against kidney disease

INTRODUCTION

Farnesoid X receptor (FXR) is a nuclear bile acid (BA) receptor widely distributed among tissues, a major sensor of BA levels, primary suppressor of hepatic BA synthesis and secondary regulator of lipid metabolism and inflammation. Chronic kidney disease is a common, multifactorial condition with metabolic and inflammatory causes and implications. An array of natural and synthetic FXR agonists has been developed, but not yet studied clinically in kidney disease. Areas covered: Following a summary of FXR's physiological functions in the kidney, we discuss its effects in renal disease with emphasis on chronic and acute kidney disease, chemotherapy-induced nephrotoxicity, and renal neoplasia. Most information is derived from animal models; no relevant clinical study has been conducted to date. Expert opinion: Most available preclinical data indicates a promising outlook for clinical research in this direction. We believe FXR agonism to be an auspicious approach to treating renal disease, considering that multifactorial diseases call for ideally wide-reaching therapies.

Histone deacetylase inhibitor, CG200745 attenuates renal fibrosis in obstructive kidney disease

Tubulointerstitial fibrosis is a common feature of kidney disease. Histone deacetylase (HDAC) inhibitors have been reported to attenuate renal fibrosis progression. Here, we investigated the effect of CG200745, a novel HDAC inhibitor, on renal fibrosis development in a mouse model of unilateral ureteral obstruction (UUO). To examine the effects of CG200745 on renal fibrosis in UUO, C57BL/6 J male mice were divided into three groups: control, UUO, and CG200745 (30 mg/kg/day)-treated UUO groups. CG 200745 was administered through drinking water for 1 week. Human proximal tubular epithelial (HK-2) cells were also treated with CG200745 (10 µM) with or without TGF-β (2 ng/mL). Seven days after UUO, plasma creatinine did not differ among the groups. However, plasma neutrophil gelatinase-associated lipocalin (NGAL) levels were markedly increased in the UUO group, which were attenuated by CG200745 treatment. UUO kidneys developed marked fibrosis as indicated by collagen deposition and increased α-smooth muscle actin (SMA) and fibronectin expression. CG200745 treatment attenuated these fibrotic responses and suppressed UUO-induced production of transforming growth factor-beta1 (TGF-β) and phosphorylation of Smad-2/3. CG200745 treatment also attenuated UUO-induced inflammation as indicated by the expression of inflammatory markers. Furthermore, CG200745 attenuated phosphorylation of p38 mitogen-activated protein kinase in UUO kidneys. In HK-2 cells, TGF-β induced the expression of α-SMA and fibronectin, which were attenuated by CG200745 cotreatment. These results demonstrate that CG200745, a novel HDAC inhibitor, has a renoprotective effect by suppressing renal fibrosis and inflammation in a UUO mouse model.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

Bile acid receptors and the kidney

PURPOSE OF REVIEW

Bile acids act as activating signals of endogenous renal receptors: the nuclear receptor farnesoid X receptor (FXR) and the membrane-bound G protein-coupled bile acid receptor 1 (GPBAR1, also known as TGR5). In recent years, bile acids have emerged as important for renal pathophysiology by activating FXR and TGR5 and transcription factors relevant for lipid, cholesterol and carbohydrate metabolism, as well as genes involved in inflammation and renal fibrosis.

RECENT FINDINGS

Activation of bile acid receptors has a promising therapeutic potential in prevention of diabetic nephropathy and obesity-induced renal damage, as well as in nephrosclerosis. During the past decade, progress has been made in understanding the biology and mechanisms of bile acid receptors in the kidney and in the development of specific bile acid receptor agonists.

SUMMARY

In this review, we discuss current knowledge on the roles of FXR and TGR5 in the physiology of the kidney and the latest advances made in development and characterization of bile acid analogues that activate bile acid receptors for treatment of renal disease.

Farnesoid X Receptor Activation Attenuates Intestinal Ischemia Reperfusion Injury in Rats

INTRODUCTION

The farnesoid X receptor (FXR) is abundantly expressed in the ileum, where it exerts an enteroprotective role as a key regulator of intestinal innate immunity and homeostasis, as shown in pre-clinical models of inflammatory bowel disease. Since intestinal ischemia reperfusion injury (IRI) is characterized by hyperpermeability, bacterial translocation and inflammation, we aimed to investigate, for the first time, if the FXR-agonist obeticholic acid (OCA) could attenuate intestinal ischemia reperfusion injury.

MATERIAL AND METHODS

In a validated rat model of intestinal IRI (laparotomy + temporary mesenteric artery clamping), 3 conditions were tested (n = 16/group): laparotomy only (sham group); ischemia 60min+ reperfusion 60min + vehicle pretreatment (IR group); ischemia 60min + reperfusion 60min + OCA pretreatment (IR+OCA group). Vehicle or OCA (INT-747, 2*30mg/kg) was administered by gavage 24h and 4h prior to IRI. The following end-points were analyzed: 7-day survival; biomarkers of enterocyte viability (L-lactate, I-FABP); histology (morphologic injury to villi/crypts and villus length); intestinal permeability (Ussing chamber); endotoxin translocation (Lipopolysaccharide assay); cytokines (IL-6, IL-1-β, TNFα, IFN-γ IL-10, IL-13); apoptosis (cleaved caspase-3); and autophagy (LC3, p62).

RESULTS

It was found that intestinal IRI was associated with high mortality (90%); loss of intestinal integrity (structurally and functionally); increased endotoxin translocation and pro-inflammatory cytokine production; and inhibition of autophagy. Conversely, OCA-pretreatment improved 7-day survival up to 50% which was associated with prevention of epithelial injury, preserved intestinal architecture and permeability. Additionally, FXR-agonism led to decreased pro-inflammatory cytokine release and alleviated autophagy inhibition.

CONCLUSION

Pretreatment with OCA, an FXR-agonist, improves survival in a rodent model of intestinal IRI, preserves the gut barrier function and suppresses inflammation. These results turn FXR into a promising target for various conditions associated with intestinal ischemia.

Identification of functional farnesoid X receptors in brain neurons

Farnesoid X receptor (FXR) has been confirmed to sense bile acids in various tissues. However, its expression in brain neurons remains obscure. In this study, we identified FXR mRNA and protein expression in mouse brain neurons and in mouse/human brain tissues. FXR was predominantly localized in the nucleus in cultured neurons, but in neurons in vivo, it mainly appeared in the cytoplasm. In nuclear compartments, the neuronal FXR exhibited a punctate distribution. Activation of FXR increased the small heterodimer partner (SHP) mRNA and protein expression levels in cultured neurons and in brain tissues. These findings will help explore new functions of FXR in the brain.

Farnesoid X Receptor Agonists and Other Bile Acid Signaling Strategies for Treatment of Liver Disease

The intracellular nuclear receptor farnesoid X receptor (FXR) and the transmembrane G protein-coupled receptor 5 (TGR5) respond to bile acids (BAs) by activating transcriptional networks and/or signaling cascades. These cascades affect the expression of a great number of target genes relevant for BA, cholesterol, lipid and carbohydrate metabolism, as well as genes involved in inflammation, fibrosis and carcinogenesis. FXR activation in the liver tissue and beyond, such as the gut-liver axis, kidney and adipose tissue, plays a role in metabolic diseases. These BA receptors activators hold promise to become a new class of drugs to be used in the treatment of chronic liver disease, hepatocellular cancer and extrahepatic inflammatory and metabolic diseases. This review discusses the relevant BA receptors, the new drugs that target BA transport and signaling and their possible applications.

FXR agonists enhance the sensitivity of biliary tract cancer cells to cisplatin via SHP dependent inhibition of Bcl-xL expression

Chemoresistance is common in patients with biliary tract cancer (BTC) including gallbladder cancer (GBC) and cholangiocarcinoma (CC). Therefore, it is necessary to identify effective chemotherapeutic agents for BTC. In the present study, we for the first time tested the effect of farnesoid X receptor (FXR) agonists GW4064 and CDCA (chenodeoxycholic acid) in combination with cisplatin (CDDP) on increasing the chemosensitivity in BTC. Our results show that co-treatment of CDDP with FXR agonists remarkably enhance chemosensitivity of BTC cells. Mechanistically, we found that activation of FXR induced expression of small heterodimer partner (SHP), which in turn inhibited signal transducer and activator of transcription 3 (STAT3) phosphorylation and resulted in down-regulation of Bcl-xL expression in BTC cells, leading to increased susceptibility to CDDP. Moreover, the experiments on tumor-bearing mice showed that GW4064/CDDP co-treatment inhibited the tumor growth in vivo by up-regulating SHP expression and down-regulating STAT3 phosphorylation. These results suggest CDDP in combination with FXR agonists could be a potential new therapeutic strategy for BTC.

Activation of farnesoid X receptor downregulates visfatin and attenuates diabetic nephropathy

Visfatin, a recently discovered adipocytokine, has been shown to have an important role in the pathogenesis of diabetic nephropathy (DN). The farnesoid X receptor (FXR), a ligand-activated nuclear receptor, plays a protective role in DN. The regulation between FXR and visfatin and their interaction in DN has not been well established. In this study, we reported that FXR agonist GW4064 reduced high glucose induced human mesangial cells (HMCs) inflammation, fibrosis and proliferation by downregulating visfatin expression, which can be blunted by exogenous visfatin treatment. Moreover, luciferase reporter assay showed FXR regulated visfatin transcription activity probably by binding to the -1607 bp and -1192 bp region of the visfatin promoter. In vivo study also showed that GW4064 ameliorated the progression of DN in db/db mice with a decreased visfatin expression. These findings suggest that FXR activation delayed the progression of diabetic nephropathy and this effect is through downregulating visfatin.

FXR expression is associated with dysregulated glucose and lipid levels in the offspring kidney induced by maternal obesity

Background

Maternal obesity is associated with dysregulation of glucose and lipid metabolism with consequent exposure of the fetus to an abnormal metabolic milieu. It is recognized that maternal obesity predisposes offspring to chronic kidney disease (CKD). We aimed to determine whether the nuclear Farnesoid X receptor (FXR), known to play a role in maintaining homeostasis of glucose and lipid metabolism, is involved in renal injury in offspring of obese mothers.

Methods

Maternal obesity was established in a rat model by feeding dams with high-fat diet prior to and during pregnancy and lactation. The offspring’s kidneys were examined at postnatal Day 1and Day 20. Human kidney 2 (HK2) cells were exposed to high glucose with or without the FXR agonist GW4064 or when FXR mRNA was silenced.

Results

Glucose intolerance in the offspring of obese mothers was evident at weaning, with associated downregulation of renal FXR expression and upregulation of monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-β1 (TGF-β1). HK2 cells exposed to high glucose had reduced FXR expression and increased MCP-1, TGF-β1, fibronectin and collagen IV expression, which was reversed in the presence of GW4064. FXR-silenced HK2 cells had amplified pro-inflammatory and pro-fibrotic markers under high glucose conditions.

Conclusions

Maternal obesity influences renal expression of pro-inflammatory and fibrotic factors that predispose the offspring to CKD. This was associated with the downregulation of the renal FXR expression suggesting a potential protective role for FXR.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-015-0032-3) contains supplementary material, which is available to authorized users.

Cisplatin-induced apoptosis in auditory, renal, and neuronal cells is associated with nitration and downregulation of LMO4

Cytotoxic effects of cisplatin occur primarily through apoptosis. Though several pro- and anti-apoptotic signaling molecules have been identified to play an important role in mediating the ototoxic, nephrotoxic, and neurotoxic side effects of cisplatin, the underlying mechanism is yet to be fully characterized. We reported that nitration of LIM domain-only 4 (LMO4), a transcriptional regulator, facilitates cochlear apoptosis in cisplatin-induced ototoxicity. However, its role in cisplatin-mediated nephrotoxicity and neurotoxicity is poorly understood. Therefore, HK2 and SH-SY5Y cells were used along with UBOC1 cells, to investigate the perturbations of LMO4 in cisplatin-induced cytotoxicity, in renal, neuronal, and auditory cells, respectively. Cisplatin induced an increase in the expression of active caspase-3, indicating cellular apoptosis, and increased the nitration of proteins, 24 h post treatment. Immunostaining with anti-nitrotyrosine and anti-LMO4 indicated that nitrotyrosine co-localized with LMO4 protein in cisplatin-treated cells. Immunoblotting with anti-LMO4 indicated that cisplatin induced a decrease in LMO4 protein levels. However, a corresponding decrease in LMO4 gene levels was not observed. Inhibition of protein nitration with SRI110, a peroxynitrite decomposition catalyst, attenuated cisplatin-induced downregulation of LMO4. More importantly, overexpression of LMO4 mitigated the cytotoxic effects of cisplatin in UBOC1 cells while a dose-dependent decrease in LMO4 protein strongly correlated with cell viability in UBOC1, HK2, and SH-SY5Y cells. Collectively, these findings suggested a potential role of LMO4 in facilitating the cytotoxic effects of cisplatin in auditory, renal, and neuronal cells.