Recent advances in the understanding and management of hepatorenal syndrome

Enteronephrohepatic Circulation of Bile Acids and Therapeutic Potential of Systemic Bile Acid Transporter Inhibitors

Together with carriers in liver and small intestine, kidney transporters function to conserve and compartmentalize bile acids in the enteronephrohepatic circulation. In patients with liver disease, systemic bile acid levels are elevated, undergo increased renal glomerular filtration, and contribute to the pathogenesis of cholemic nephropathy and acute kidney injury. In this review, we describe mechanisms for renal bile acid transport and highlight very recent discoveries that challenge current paradigms for the pathogenesis of cholemic nephropathy and renal tubule cast formation. We also discuss the therapeutic potential of inhibiting the kidney apical sodium-dependent bile acid transporter (ASBT) to redirect bile acids into urine for elimination, reduce hepatobiliary accumulation and systemic levels of bile acids, and treat cholemic nephropathy. In conclusion, a deeper understanding of the enteronephrohepatic bile acid axis is providing insights into novel strategies to protect both liver and kidney in patients with liver disease.

Bile acid metabolism and signalling in liver disease

Bile acids (BAs) serve as signalling molecules, efficiently regulating their own metabolism and transport, as well as key aspects of lipid and glucose homeostasis. BAs shape the gut microbial flora and conversely are metabolised by microbiota. Disruption of BA transport, metabolism and physiological signalling functions contribute to the pathogenesis and progression of a wide range of liver diseases including cholestatic disorders and MASLD (metabolic dysfunction-associated steatotic liver disease), as well as hepatocellular and cholangiocellular carcinoma. Additionally, impaired BA signalling may also affect the intestine and kidney, thereby contributing to failure of gut integrity and driving the progression and complications of portal hypertension, cholemic nephropathy and the development of extrahepatic malignancies such as colorectal cancer. In this review, we will summarise recent advances in the understanding of BA signalling, metabolism and transport, focusing on transcriptional regulation and novel BA-focused therapeutic strategies for cholestatic and metabolic liver diseases.

Validation of NBD-coupled taurocholic acid for intravital analysis of bile acid transport in liver and kidney of mice

Fluorophore-coupled bile acids (BA) represent an important tool for intravital analysis of BA flux in animal models of cholestatic diseases. However, addition of a fluorophore to a BA may alter transport properties. We developed and validated a 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole-coupled taurocholic acid (3β-NBD-TCA) as a probe for intravital analysis of BA homeostasis. We compared transport of 3β-NBD-TCA to [3H]-TCA in HEK293 cells stably expressing the mouse hepatic or renal BA carriers mNtcp or mAsbt, respectively. We also studied distribution kinetics intravitally in livers and kidneys of anesthetized wildtype and mOatp1a/1b cluster knockout mice (OatpKO) with and without administration of the Ntcp inhibitor Myrcludex B and the ASBT inhibitor AS0369. In vitro, 3β-NBD-TCA and [3H]-TCA showed comparable concentration- and time-dependent transport via mNtcp and mAsbt as well as similar inhibition kinetics for Myrcludex B and AS0369. Intravital analysis in the livers of wildtype and OatpKO mice revealed contribution of both mNtcp and mOatp1a/1b in the 3β-NBD-TCA uptake from the sinusoidal blood into hepatocytes. Combined deletion of mOatp1a/1b and inhibition of mNtcp by Myrcludex B blocked the uptake of 3β-NBD-TCA from sinusoidal blood into hepatocytes. This led to an increase of 3β-NBD-TCA signal in the systemic circulation including renal capillaries, followed by strong enrichment in a subpopulation of proximal renal tubular epithelial cells (TEC). The enrichment of 3β-NBD-TCA in TEC was strongly reduced by the systemic ASBT inhibitor AS0369. NBD-coupled TCA has similar transport kinetics as [3H]-TCA and can be used as a tool to study hepatorenal BA transport. See also the graphical abstract(Fig. 1).

Long-Circulating Vasoactive 1,18-Octadecanedioic Acid-Terlipressin Conjugate

Hepatorenal syndrome (HRS) is a life-threatening complication of end-stage liver disease first reported over a century ago, but its management still poses an unmet challenge. A therapeutic agent found to stabilize the condition is a short cyclic peptide, vasopressin analogue, terlipressin (TP). While TP is commonly prescribed for HRS patients in most parts of the world, it was only recently approved for use in the United States. TP exhibits short circulation half-lives and adverse side effects associated with the dose required. Herein, we present a 1,18-octadecanedioic acid (ODDA) conjugate of the cyclic peptide (ODDA-TP), which enables noncovalent binding to serum albumin via native fatty acid binding modes. ODDA-TP is demonstrated to outperform TP alone in studies including in vitro cellular receptor activation, stability in plasma, pharmacokinetics, and performance in vivo in rats. Specifically, ODDA-TP had an elimination half-life 20 times that of TP alone while exhibiting a superior safety profile.

Inhibition of the renal apical sodium dependent bile acid transporter prevents cholemic nephropathy in mice with obstructive cholestasis

BACKGROUND & AIMS

Cholemic nephropathy (CN) is a severe complication of cholestatic liver diseases for which there is no specific treatment. We revisited its pathophysiology with the aim of identifying novel therapeutic strategies.

METHODS

Cholestasis was induced by bile duct ligation (BDL) in mice. Bile flux in kidneys and livers was visualized by intravital imaging, supported by MALDI mass spectrometry imaging and liquid chromatography-tandem mass spectrometry. The effect of AS0369, a systemically bioavailable apical sodium-dependent bile acid transporter (ASBT) inhibitor, was evaluated by intravital imaging, RNA-sequencing, histological, blood, and urine analyses. Translational relevance was assessed in kidney biopsies from patients with CN, mice with a humanized bile acid (BA) spectrum, and via analysis of serum BAs and KIM-1 (kidney injury molecule 1) in patients with liver disease and hyperbilirubinemia.

RESULTS

Proximal tubular epithelial cells (TECs) reabsorbed and enriched BAs, leading to oxidative stress and death of proximal TECs, casts in distal tubules and collecting ducts, peritubular capillary leakiness, and glomerular cysts. Renal ASBT inhibition by AS0369 blocked BA uptake into TECs and prevented kidney injury up to 6 weeks after BDL. Similar results were obtained in mice with humanized BA composition. In patients with advanced liver disease, serum BAs were the main determinant of KIM-1 levels. ASBT expression in TECs was preserved in biopsies from patients with CN, further highlighting the translational potential of targeting ASBT to treat CN.

CONCLUSIONS

BA enrichment in proximal TECs followed by oxidative stress and cell death is a key early event in CN. Inhibiting renal ASBT and consequently BA enrichment in TECs prevents CN and systemically decreases BA concentrations.

IMPACT AND IMPLICATIONS

Cholemic nephropathy (CN) is a severe complication of cholestasis and an unmet clinical need. We demonstrate that CN is triggered by the renal accumulation of bile acids (BAs) that are considerably increased in the systemic blood. Specifically, the proximal tubular epithelial cells of the kidney take up BAs via the apical sodium-dependent bile acid transporter (ASBT). We developed a therapeutic compound that blocks ASBT in the kidneys, prevents BA overload in tubular epithelial cells, and almost completely abolished all disease hallmarks in a CN mouse model. Renal ASBT inhibition represents a potential therapeutic strategy for patients with CN.

INFUSE: Rationale and design of a multi-center, open label, collaborative study to treat HRS-AKI with continuous terlipressin infusion

Background

Hepatorenal syndrome-acute kidney injury (HRS-AKI) carries significant morbidity and mortality among those with end-stage liver disease. Bolus terlipressin for treatment of HRS-AKI received FDA approval in September 2022. US implementation of terlipressin, however, is hindered by the paucity of local data on the optimal patient population and administration mode, as well as the effect on transplant priority. The INFUSE study is designed to evaluate the use of continuous terlipressin infusion among transplant candidates with advanced liver disease and HRS-AKI.

Methods

Fifty prospective patients with HRS-AKI will receive a single bolus of terlipressin 0.5 mg followed by continuous infusions of terlipressin from 2 to 8 mg/day for up to 14 days. The cohort will be enriched with those listed, in evaluation, or eligible for liver transplantation, while those with ACLF grade 3, MELD ≥35, and serum creatinine >5.0 mg/dL will be excluded. Fifty patients who received midodrine plus octreotide or norepinephrine for HRS-AKI will serve as a retrospective comparator cohort.

Conclusion

The INFUSE study aims to assess the safety and efficacy of continuous terlipressin infusion among largely transplant-eligible patients with HRS-AKI, and to provide US-based data on transplant outcomes. This novel study design simultaneously mitigates terlipressin adverse events while providing renal benefits to patients, thus addressing the unmet medical need of those with HRS-AKI who have limited treatment options and are awaiting liver transplantation in the US.

A Comprehensive Systematic Review of the Latest Management Strategies for Hepatorenal Syndrome: A Complicated Syndrome to Tackle

Hepatorenal syndrome (HRS), defined by the extreme manifestation of renal impairment in patients with cirrhosis, is characterized by reduced renal blood flow and glomerular filtration rate. It is diagnosed with reduced kidney function confirming the absence of intrinsic kidney disease, such as hematuria or proteinuria. HRS is potentially reversible with liver transplantation or vasoconstrictor drugs. The condition carries a poor prognosis with high mortality rates, particularly in patients with advanced cirrhosis. The latest management for HRS involves a combination of pharmacological and non-pharmacological interventions, aiming to improve renal function and reduce the risk of mortality. Pharmacological treatments include vasoconstrictors, such as terlipressin and midodrine, and albumin infusion, which have been shown to improve renal function and reduce mortality in HRS patients. Non-pharmacological interventions, including invasive procedures such as transjugular intrahepatic portosystemic shunt (TIPS), plasma exchange, liver transplantation, and renal replacement therapy, may also be considered. Though TIPS has been shown to be effective in improving renal function in HRS patients, liver transplantation remains at the top of the consideration for the treatment of end-stage liver disease and HRS. Recent studies have placed importance on early recognition and prompt intervention in HRS patients, as delaying treatment can result in poorer outcomes. Although there are numerous reviews that summarize various aspects of HRS, the recent advancements in the management and pathophysiology of HRS are still insufficient. Therefore, in this review, we summarized a brief pathophysiology and highlighted recent advancements in the management of HRS with a quick review of the latest articles.

Obeticholic Acid Reduces Kidney Matrix Metalloproteinase Activation following Partial Hepatic Ischemia/Reperfusion Injury in Rats

We have previously demonstrated that the farnesoid X receptor (FXR) agonist obeticholic acid (OCA) protects the liver via downregulation of hepatic matrix metalloproteinases (MMPs) after ischemia/reperfusion (I/R), which can lead to multiorgan dysfunction. The present study investigated the capacity of OCA to modulate MMPs in distant organs such as the kidney. Male Wistar rats were dosed orally with 10 mg/kg/day of OCA (5 days) and were subjected to 60-min partial hepatic ischemia. After 120-min reperfusion, kidney biopsies (cortex and medulla) and blood samples were collected. Serum creatinine, kidney MMP-2, and MMP-9-dimer, tissue inhibitors of MMPs (TIMP-1, TIMP-2), RECK, TNF-alpha, and IL-6 were monitored. MMP-9-dimer activity in the kidney cortex and medulla increased after hepatic I/R and a reduction was detected in OCA-treated I/R rats. Although not significantly, MMP-2 activity decreased in the cortex of OCA-treated I/R rats. TIMPs and RECK levels showed no significant differences among all groups considered. Serum creatinine increased after I/R and a reduction was detected in OCA-treated I/R rats. The same trend occurred for tissue TNF-alpha and IL-6. Although the underlying mechanisms need further investigation, this is the first study showing, in the kidney, beneficial effects of OCA by reducing TNF-alpha-mediated expression of MMPs after liver I/R.