Treatment of portal hypertension with NCX-1000, a liver-specific NO donor. A review of its current status

Current and investigational drugs in early clinical development for portal hypertension

Introduction

The development of portal hypertension leads to a majority of complications associated with chronic liver disease. Therefore, adequate treatment of portal hypertension is crucial in the management of such patients. Current treatment options are limited and consist mainly of medications that decrease the hyperdynamic circulation, such as non-selective beta blockers, and treatment of hypervolemia with diuretics. Despite these options, mortality rates have not improved over the last two decades. Newer, more effective treatment options are necessary to help improve survival and quality of life in these patients.

Areas covered

Multiple preclinical models and clinical studies have demonstrated potential efficacy of a variety of new treatment modalities. We introduce treatment options including the use of vasodilation promotors, vasoconstriction inhibitors, anticoagulants, antiangiogenics, and anti-inflammatory drugs. We examine the most recent studies for treatment options within these drug classes and offer insights as to which show the most promise in this field.

Methodology

Published studies that identified novel medical treatment options of portal hypertension were searched using PubMed (https://pubmed.ncbi.nlm.nih.gov/). Clinical trials listed in Clinicaltrials.gov were also searched with a focus on more recent and ongoing studies, including those with completed recruitment. Searching with key terms including "portal hypertension" as well as individually searching specific treatment medications that were listed in other publications was carried out. Finally, current societal guidelines and recent review articles relevant to the management of portal hypertension were evaluated, and listed references of interest were included.

Conclusion

Many ongoing early phase studies demonstrate promising results and may shape the field of portal hypertension management in future. As concrete results become available, larger RCTs will be required before making definitive conclusions regarding safety and efficacy and whether or not they can be incorporated into routine clinical practice. Statins, anticoagulants, and PDE inhibitors have been among the most studied and appear to be most promising.

Liver-targeted delivery of asiatic acid nanostructured lipid carrier for the treatment of liver fibrosis

Liver fibrosis is a major global health concern. Management of chronic liver disease is severely restricted in clinics due to ineffective treatment approaches. However, a lack of targeted therapy may aggravate this condition. Asiatic acid (AA), a pentacyclic triterpenoid acid, can effectively protect the liver from hepatic disorders. However, the pharmaceutical application of AA is limited by low oral bioavailability and poor targeting efficiency. This study synthesized a novel liver-targeting material from PEG-SA, chemically linked to ursodeoxycholic acid (UA), and utilized it to modify AA nanostructured lipid carriers (UP-AA-NLC) with enhanced targeting and improved efficacy. The formulation of UP-AA-NLC was optimized via the Box–Behnken Experimental Design (BBD) and characterized by size, zeta potential, TEM, DSC, and XRD. Furthermore, in vitro antifibrotic activity and proliferation of AA and NLCs were assessed in LX-2 cells. The addition of UP-AA-NLC significantly stimulated the TGF-beta1-induced expression of α-SMA, FN1, and Col I α1. In vivo near-infrared fluorescence imaging and distribution trials in rats demonstrated that UP-AA-NLC could significantly improve oral absorption and liver-targeting efficiency. Oral UP-AA-NLC greatly alleviated carbon tetrachloride-induced liver injury and fibrosis in rats in a dosage-dependent manner, as reflected by serum biochemical parameters (AST, ALT, and ALB), histopathological features (H&E and Masson staining), and antioxidant activity parameters (SOD and MDA). Also, treatment with UP-AA-NLC lowered liver hydroxyproline levels, demonstrating a reduction of collagen accumulation in the fibrotic liver. Collectively, optimized UP-AA-NLC has potential application prospects in liver-targeted therapy and holds great promise as a drug delivery system for treating liver diseases.

A long way to go: caspase inhibitors in clinical use

Caspases are an evolutionary conserved family of cysteine-dependent proteases that are involved in many vital cellular processes including apoptosis, proliferation, differentiation and inflammatory response. Dysregulation of caspase-mediated apoptosis and inflammation has been linked to the pathogenesis of various diseases such as inflammatory diseases, neurological disorders, metabolic diseases, and cancer. Multiple caspase inhibitors have been designed and synthesized as a potential therapeutic tool for the treatment of cell death-related pathologies. However, only a few have progressed to clinical trials because of the consistent challenges faced amongst the different types of caspase inhibitors used for the treatment of the various pathologies, namely an inadequate efficacy, poor target specificity, or adverse side effects. Importantly, a large proportion of this failure lies in the lack of understanding various caspase functions. To overcome the current challenges, further studies on understanding caspase function in a disease model is a fundamental requirement to effectively develop their inhibitors as a treatment for the different pathologies. Therefore, the present review focuses on the descriptive properties and characteristics of caspase inhibitors known to date, and their therapeutic application in animal and clinical studies. In addition, a brief discussion on the achievements, and current challenges faced, are presented in support to providing more perspectives for further development of successful therapeutic caspase inhibitors for various diseases.

An insight into primary biliary cholangitis and its recent advances in treatment: semi-synthetic analogs to combat ursodeoxycholic-acid resistance

INTRODUCTION

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease which on progression causes cirrhosis; various studies also suggested that several diseases can co-exist in patients. In existing depiction of disease PBC, apart from entire use of ursodeoxycholic acid (UDCA), several patients need to step forward to liver-transplantation or death due to resistance or non-responder with UDCA monotherapy.

AREAS COVERED

To overcome this non-respondent treatment, novel bile acid semi-synthetic analogs have been identified which shows their potency against for farnesoid X receptor and transmembrane G protein-coupled receptor-5 which are identified as target for many developing analogs which have desirable pharmacokinetic profiles.

EXPERT OPINION

A range of studies suggests that adding semisynthetic analogs in therapeutic regime improves liver biochemistries in patients with suboptimal response to UDCA. Thus, the aspire of this review is to abridge and compare therapeutic value and current markets affirm of various bile acids semi-synthetic analogs which certainly are having promising effects in PBC monotherapy or in pooled treatment with UDCA for PBC.

Phosphodiesterases in the Liver as Potential Therapeutic Targets of Cirrhotic Portal Hypertension

Liver cirrhosis is a frequent condition with high impact on patients' life expectancy and health care systems. Cirrhotic portal hypertension (PH) gradually develops with deteriorating liver function and can lead to life-threatening complications. Other than an increase in intrahepatic flow resistance due to morphological remodeling of the organ, a functional dysregulation of the sinusoids, the smallest functional units of liver vasculature, plays a pivotal role. Vascular tone is primarily regulated by the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, wherein soluble guanylate cyclase (sGC) and phosphodiesterase-5 (PDE-5) are key enzymes. Recent data showed characteristic alterations in the expression of these regulatory enzymes or metabolite levels in liver cirrhosis. Additionally, a disturbed zonation of the components of this pathway along the sinusoids was detected. This review describes current knowledge of the pathophysiology of PH with focus on the enzymes regulating cGMP availability, i.e., sGC and PDE-5. The results have primarily been obtained in animal models of liver cirrhosis. However, clinical and histochemical data suggest that the new biochemical model we propose can be applied to human liver cirrhosis. The role of PDE-5 as potential target for medical therapy of PH is discussed.

Semisynthetic bile acids: a new therapeutic option for metabolic syndrome

Bile acids are endogenous emulsifiers synthesized from cholesterol having a peculiar amphiphilic structure. Appreciation of their beneficial effects on human health, recognized since ancient times, has expanded enormously since the discovery of their role as signaling molecules. Activation of farnesoid X receptor (FXR) and Takeda G-protein receptor-5 (TGR5) signaling pathways by bile acids, regulating glucose, lipid and energy metabolism, have become attractive avenue for metabolic syndrome treatment. Therefore, extensive effort has been directed into the research and synthesis of bile acid derivatives with improved pharmacokinetic properties and high potency and selectivity for these receptors. Minor modifications in the structure of bile acids and their derivatives may result in fine-tuning modulation of their biological functions, and most importantly, in an evasion of undesired effect. A great number of semisynthetic bile acid analogues have been designed and put in preclinical and clinical settings. Obeticholic acid (INT-747) has achieved the biggest clinical success so far being in use for the treatment of primary biliary cholangitis. This review summarizes and critically evaluates the key chemical modifications of bile acids resulting in development of novel semisynthetic derivatives as well as the current status of their preclinical and clinical evaluation in the treatment of metabolic syndrome, an aspect that is so far lacking in the scientific literature. Taking into account the balance between therapeutic benefits and potential adverse effects associated with specific structure and mechanism of action, recommendations for future studies are proposed.

AMPK agonist AICAR ameliorates portal hypertension and liver cirrhosis via NO pathway in the BDL rat model

Recent studies have indicated that the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway is closely involved in liver fibrosis and other fibrotic diseases. However, whether targeting the AMPK pathway can rescue liver fibrosis and its complications, such as portal hypertension, is unknown. This study aimed to explore the therapeutic value of AICAR (5-aminoimidazole-4-carboxyamide ribonucleoside), an agonist of the AMPK pathway, on liver fibrosis and portal hypertension in bile duct ligation (BDL) rats. In vitro experiments showed that the gene expression levels of TGF-b, a-SMA, and collagen 1 in primary rat hepatic stellate cells (HSCs) were significantly decreased after AICAR treatment. The p-eNOS expression and nitric oxide (NO) production were increased by AICAR administration in sinusoidal endothelial cells (SECs). For in vivo animal studies, AICAR acutely decreased portal pressure in the BDL and CCL4 fibrotic rats, but not in the partial portal vein ligation (PVL) rats, without changes in systemic hemodynamics. It was also observed by using intravital fluorescence microscopy that AICAR led to sinusoidal vasodilation in situ experiment. We propose that the relevant mechanisms may be related to the activation of the AMPK/NO pathway in SECs and that this activation promoted NO production in the liver, thereby promoting hepatic sinusoid microcirculation and decreased intrahepatic resistance. The results were verified using the NO inhibitor L-NAME. Chronic AICAR treatment also showed profound beneficial effects on the BDL model rats. The hemodynamic condition was greatly improved, but the positive effect could be partially blocked by L-NAME. Moreover, AICAR also decreased hepatic fibrogenesis in the BDL rats. KEY MESSAGES: Acute and chronic use of AICAR could alleviate portal pressure without changing systemic hemodynamics. AICAR induced sinusoidal vasodilation by improving NO bioavailability and ameliorating endothelial dysfunction in vivo and in vitro. AICAR could alleviate liver cirrhosis in the BDL model rats.

Small Molecule Active Site Directed Tools for Studying Human Caspases

Caspases are proteases of clan CD and were described for the first time more than two decades ago. They play critical roles in the control of regulated cell death pathways including apoptosis and inflammation. Due to their involvement in the development of various diseases like cancer, neurodegenerative diseases, or autoimmune disorders, caspases have been intensively investigated as potential drug targets, both in academic and industrial laboratories. This review presents a thorough, deep, and systematic assessment of all technologies developed over the years for the investigation of caspase activity and specificity using substrates and inhibitors, as well as activity based probes, which in recent years have attracted considerable interest due to their usefulness in the investigation of biological functions of this family of enzymes.

Future therapy of portal hypertension in liver cirrhosis - a guess

In patients with chronic liver disease, portal hypertension is driven by progressive fibrosis and intrahepatic vasoconstriction. Interruption of the initiating and perpetuating etiology—mostly leading to necroinflammation—is possible for several underlying causes, such as autoimmune hepatitis, hepatitis B virus (HBV) infection, and most recently hepatitis C virus (HCV) infection. Thus, in the long run, lifestyle-related liver damage due to chronic alcoholism or morbid obesity will remain the main factor leading to portal hypertension. Both causes are probably more easily countered by socioeconomic measures than by individual approaches. If chronic liver injury supporting fibrogenesis and portal hypertension cannot be interrupted, a wide variety of tools are available to modulate and reduce intrahepatic resistance and therewith portal hypertension. Many of these have been evaluated in animal models. Also, some well-established drugs, which are used in humans for other indications (for example, statins), are promising if applied early and concomitantly to standard therapy. In the future, more individually tailored strategies must also be considered in line with the spectrum of portal hypertensive complications and risk factors defined by high-throughput analysis of the patient’s genome, transcriptome, metabolome, or microbiome.

Poly-s-nitrosated albumin as a safe and effective multifunctional antitumor agent: characterization, biochemistry and possible future therapeutic applications

Nitric oxide (NO) is a ubiquitous molecule involved in multiple cellular functions. Inappropriate production of NO may lead to disease states. To date, pharmacologically active compounds that release NO within the body, such as organic nitrates, have been used as therapeutic agents, but their efficacy is significantly limited by unwanted side effects. Therefore, novel NO donors with better pharmacological and pharmacokinetic properties are highly desirable. The S-nitrosothiol fraction in plasma is largely composed of endogenous S-nitrosated human serum albumin (Mono-SNO-HSA), and that is why we are testing whether this albumin form can be therapeutically useful. Recently, we developed SNO-HSA analogs such as SNO-HSA with many conjugated SNO groups (Poly-SNO-HSA) which were prepared using chemical modification. Unexpectedly, we found striking inverse effects between Poly-SNO-HSA and Mono-SNO-HSA. Despite the fact that Mono-SNO-HSA inhibits apoptosis, Poly-SNO-HSA possesses very strong proapoptotic effects against tumor cells. Furthermore, Poly-SNO-HSA can reduce or perhaps completely eliminate the multidrug resistance often developed by cancer cells. In this review, we forward the possibility that Poly-SNO-HSA can be used as a safe and effective multifunctional antitumor agent.

Molecular mechanisms of liver preconditioning

Ischemia/reperfusion (I/R) injury still represents an important cause of morbidity following hepatic surgery and limits the use of marginal livers in hepatic transplantation. Transient blood flow interruption followed by reperfusion protects tissues against damage induced by subsequent I/R. This process known as ischemic preconditioning (IP) depends upon intrinsic cytoprotective systems whose activation can inhibit the progression of irreversible tissue damage. Compared to other organs, liver IP has additional features as it reduces inflammation and promotes hepatic regeneration. Our present understanding of the molecular mechanisms involved in liver IP is still largely incomplete. Experimental studies have shown that the protective effects of liver IP are triggered by the release of adenosine and nitric oxide and the subsequent activation of signal networks involving protein kinases such as phosphatidylinositol 3-kinase, protein kinase C δ/ε and p38 MAP kinase, and transcription factors such as signal transducer and activator of transcription 3, nuclear factor-κB and hypoxia-inducible factor 1. This article offers an overview of the molecular events underlying the preconditioning effects in the liver and points to the possibility of developing pharmacological approaches aimed at activating the intrinsic protective systems in patients undergoing liver surgery.

Efficacy and cytotoxicity of a liver-targeted nitric oxide-releasing drug in the treatment of liver injury in mice

AIM: To evaluate the efficacy and cytotoxicity of NO-040527, a new liver-targeted nitric oxide-releasing drug, in the treatment of liver injury induced with carbon tetrachloride, acetaminophen or D-galactosamine in mice.

METHODS: Liver injury was induced in mice by intraperitoneal injection of carbon tetrachloride, acetaminophen or D-galactosamine. NO-040527 was orally administered to animals 1 h before and 12 h after the induction of liver injury. The animals were killed 24 h after drug delivery, and blood samples were taken to determine serum ALT and AST levels using an automatic biochemical analyzer. The cytotoxicity of the targeted conjugate was determined by methyl thiazol tetrazolium (MTT) assay.

RESULTS: NO-040527 could significantly inhibit carbon tetrachloride-induced elevation of ALT and AST in mice (both P < 0.01) in a dose-dependent manner. At the same dose (55 mg/kg), NO-040527 exhibited better efficacy than control drug NCX-1000 (P < 0.05) in lowering carbon tetrachloride-induced elevation of serum ALT and AST levels. Similarly, NO-040527 could also significantly inhibit acetaminophen-induced elevation of ALT and AST (both P < 0.01) though no dose-dependent effect was noted. At the same dose (55 mg/kg), NO-040527 exhibited similar efficacy to NCX-1000 in lowering acetaminophen-induced elevation of serum ALT and AST levels. NO-040527 showed no protective effects against liver injury induced with D-galactosamine. No significant differences were noted in serum ALT and AST levels between untreated mice with D-galactosamine-induced liver injury and those treated with medium- or low-dose NO-040527. However, the levels of serum ALT and AST in mice with D-galactosamine-induced liver injury treated with high-dose NO-040527 was higher than those in untreated ones. NO-040527 at a dose of 500 μmol/L began to show cytotoxicity (cell viability rate: 45.96% ± 29.46%; P = 0.058). Significant cytotoxicity was noted when the dose of NO-040527 rose to 1000 μmol/L (P < 0.005). NO-040527 at 50 and 100 μmol/L could accelerate cell growth (cell viability rate: 137.67% ± 8.47% and 152.65% ± 10.084%, respectively; both P < 0.05).

CONCLUSION: NO-040527 has good protective effects against carbon tetrachloride- or acetaminophen-induced liver injury in mice. NO-040527 is cytotoxic when used at high dose.

Future expectations in the prophylaxis of intestinal bleeding

Prophylaxis of gastrointestinal bleeding is attempted in widely varying situations. In NSAID-induced peptic ulcer, the advantage of selective cyclooxygenase 2 inhibitors with regard to gastrointestinal damage has yet to be translated into an advantage in overall morbidity. Strategies for primary and secondary prevention of variceal bleeding have been established. Therapy tailored to hepatic venous pressure gradient has the potential to achieve clinical relevance. Several methods have been developed to prevent postpolypectomy bleeding, but their optimal risk-tailored application has yet to be demonstrated. Although octreotide treatment seems to be beneficial in reducing the blood loss from angiodysplasias, controlled studies to determine its optimal use are awaited. Stress-ulcer prophylaxis is commonly applied in critically ill patients. Although data indicate that H2-receptor antagonists and omeprazole are effective in preventing clinically significant bleeding, evidence for an advantage with respect to length of hospital or intensive-care-unit stay, as well as mortality, is still lacking. Since there is misuse of acid-suppressing drugs on regular wards, in-house guidelines may offer the potential for saving costs and reducing inappropriate prescription.

Molecular mechanisms of increased intrahepatic resistance in portal hypertension

Portal hypertension is associated with changes in the intrahepatic, systemic, and portosystemic collateral circulation. Alterations in vasoreactivity (vasodilation and vasoconstriction) play a central role in the pathogenesis of portal hypertension by contributing to increased intrahepatic resistance, hyperdynamic circulation, and expansion of the collateral circulation. Portal hypertension is also importantly characterized by changes in vascular structure; termed vascular remodeling, which is an adaptive response of the vessel wall that occurs in response to chronic changes in the environment such as shear stress. These complementary processes of vasoreactivity and vascular remodeling contribute importantly to increased intrahepatic resistance and represent important targets in the treatment of portal hypertension. This review will focus on these processes within the intrahepatic circulation, a circulatory bed whose study, that Dr Roberto Groszmann has pioneered.