Editor: Dae Won Jun, Hanyang University College of Medicine, Korea
The initial presentation of non-alcoholic steatohepatitis (NASH) is hepatic steatosis. The dysfunction of lipid metabolism within hepatocytes caused by genetic factors, diet, and insulin resistance causes lipid accumulation. Lipotoxicity, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress would further contribute to hepatocyte injury and death, leading to inflammation and immune dysfunction in the liver. During the healing process, the accumulation of an excessive amount of fibrosis might occur while healing. During the development of NASH and liver fibrosis, the gut-liver axis, adipose-liver axis, and renin-angiotensin system (RAS) may be dysregulated and impaired. Translocation of bacteria or its end-products entering the liver could activate hepatocytes, Kupffer cells, and hepatic stellate cells, exacerbating hepatic steatosis, inflammation, and fibrosis. Bile acids regulate glucose and lipid metabolism through Farnesoid X receptors in the liver and intestine. Increased adipose tissue-derived non-esterified fatty acids would aggravate hepatic steatosis. Increased leptin also plays a role in hepatic fibrogenesis, and decreased adiponectin may contribute to hepatic insulin resistance. Moreover, dysregulation of peroxisome proliferator-activated receptors in the liver, adipose, and muscle tissues may impair lipid metabolism. In addition, the RAS may contribute to hepatic fatty acid metabolism, inflammation, and fibrosis. The treatment includes lifestyle modification, pharmacological therapy, and non-pharmacological therapy. Currently, weight reduction by lifestyle modification or surgery is the most effective therapy. However, vitamin E, pioglitazone, and obeticholic acid have also been suggested. In this review, we will introduce some new clinical trials and experimental therapies for the treatment of NASH and related fibrosis.
Non-alcoholic fatty liver disease (NAFLD) is currently the most prevalent type of liver disease worldwide. NAFLD is a wide hepatic spectrum, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH), which leads to progressive fibrosis, cirrhosis, and hepatocellular carcinoma (HCC) [
High-fat diet can result in hepatic steatosis in humans. Liver fat increased by 35% in overweight non-diabetic women after a 2-week isocaloric high-fat diet (56% total energy from fat) [
NAFLD patients have low level of physical activity compared to normal controls. Gerber et al. [
NAFLD is strongly associated with reduced whole body insulin sensitivity, as well as increased hepatic and adipose tissue insulin resistance [
There are several gene variants associated with NAFLD and NASH. The first fatty liver gene identified by Romeo et al. [
Using an epigenome-wide association study in peripheral blood cells, 22 CpGs were found to be associated with hepatic fat in European participants; 19 CpGs were annotated to 18 unique genes upregulated in the liver, including DHCR24, SLC43A1, CPT1A, SREBF1, SC4MOL, and SLC9A3R1 [
The ER is responsible for protein folding, and the accumulation of misfolded or unfolded proteins leads to stress and the activation of the unfolded protein response (UPR) [
Increased hepatic fat would increase hepatic fat oxidation with increased mitochondrial respiration [
It has been shown that hepatic activity of lysosomal acid lipase and lysosomal acidification, which are markers of lysosomal dysfunction, are decreased in patients with NAFLD [
The main mechanisms of fatty acid-induced damage are oxidative stress and increased pro-inflammatory cytokines [
Liver fibrosis is the most important risk factor for liver cancer in patients with NAFLD and decompensated cirrhosis [
Lipotoxic damage in hepatocytes would release cytokines and chemokines, and then activate innate and adaptive immune cells, including macrophages, dendritic cells, lymphocytes, and neutrophils, leading to an inflammation cascade [
Toxic fatty acids were able to directly affect Kupffer cells (KCs) and HSCs, which may contribute to the activation of inflammation and fibrosis. Palmitic acids activated toll-like receptor (TLR) 2 and TLR4 in macrophages with the induction of inflammatory signaling [
Insulin exerts profibrogenic activity. Insulin itself induces HSC mitogenesis and collagen synthesis [
HSCs express PNPLA3 and membrane-bound O-acyltransferase domain-containing protein 7 (MBOAT7) [
Hypomethylation or hypermethylation of genes involved in the wound-healing process in NAFLD could be used to distinguish between patients with mild fibrosis from those with severe fibrosis in NAFLD. Hypermethylation at specific CpGs within TGFβ1 and PDGF, and hypomethylation at specific CpGs within peroxisome proliferator-activated receptor (PPAR) α and PPARδ in patients with mild fibrosis, were found [
Compared with healthy adults, patients with NAFLD had a higher proportion of Firmicutes in the intestine, and the relative numbers of Bacteroidetes, Enterobacteriaceae, and Ruminococcaceae families were reduced [
Some metabolites in the blood and feces have been found to rely on bacterial synthesis, including choline and choline-related metabolites, bile acids, short-chain fatty acids (SCFAs), and ethanol, which may contribute to the pathogenesis of fatty liver. In animal experiments, the gut microbiota of mice fed with high-fat diet could convert choline into trimethylamine, reduce the bioavailability of choline, and produce a phenomenon similar to choline-deficient diet, leading to decreased excretion of VLDL from liver cells and increased liver fat accumulation [
Adipose tissues secrete adiponectin, leptin, and some proinflammatory cytokines, such as IL-6 and TNFα, which would influence the liver. Adiponectin binds to adiponectin receptors 1 and 2, respectively activates AMPK and PPAR-alpha pathways in the liver, and stimulate glucose use and fatty acid oxidation [
Hypertensive patients with biopsy-proven NAFLD on baseline RAS blockers had less advanced hepatic fibrosis [
NASH is now the most common risk factor for HCC in the United States [
Lifestyle changes by eating less and exercising more to achieve weight loss remain the cornerstone of clinical care. Hypocaloric diet with a reduction of body weight decreased total body fat, visceral fat, and intrahepatic lipid content [
Bariatric surgery provides sustained and durable weight loss and improving obesity-related diseases [
Endoscopic bariatric therapies, including intragastric balloons (IGB), endoscopic sleeve gastroplasty (ESG), duodenal mucosal resurfacing (DMR), and duodenal-Jejunal bypass liner (DJBL), were recently introduced as less invasive modalities to treat obesity and metabolic comorbidities. In a meta-analysis, improvement in steatosis and NAS were seen in 79.2% and 83.5% of patients receiving IGB, respectively [
Some studies have suggested that fecal transplantation helps ameliorate steatohepatitis [
The pharmacological agents predominantly target the following four mechanisms: 1) hepatic fat accumulation; 2) oxidative stress, inflammation, and apoptosis; 3) gut-liver axis, including bile acids, gut microbiomes, and metabolic endotoxemia; and 4) hepatic fibrosis [
Pioglitazone, a PPAR γ agonist, improved hepatic steatosis, inflammation, and hepatocellular ballooning [
GLP-1 agonists increase insulin secretion, inhibit glucagon secretion, delay gastric emptying, and decrease appetite. NASH resolution was observed in 39% of patients who received liraglutide for 48 weeks and in 59% of patients who received semaglutide for 72 weeks [
Sodium-glucose cotransporter 2 (SGLT2) inhibitors increase the urinary excretion of glucose. A meta-analysis of 10 RCTs showed that SGLT2 inhibitors can reduce aminotransferases and hepatic fat [
FGF19 and FGF21 are endocrines that regulate energy homeostasis. Aldafermin, a FGF19 analogue, led to reductions of liver fat content and a trend toward fibrosis improvement [
Two phase IIa trials investigated the effects of acetyl-coenzyme A carboxylase (ACC) inhibitor monotherapy (PF-05221304) and combination with a diacylglycerol O-acyltransferase 2 (DGAT2) inhibitor (PF-06865571). Both PF-05221304 monotherapy and co-administration with PF-06865571 reduced liver fat content [
Stearoyl-coenzyme A desaturase 1 (SCD-1) is a key enzyme that catalyzes the biosynthesis of monounsaturated fatty acids. A phase IIb trial (ARREST trial) showed that aramchol (a liver-targeted SCD-1 inhibitor) 600 mg did not cause a significant reduction in liver fat content. Nevertheless, the observed change in liver histology and biochemical improvement suggests a potential role of aramchol in treating NASH and fibrosis [
Thyroid hormone receptor-β (THR-β) is predominantly expressed in the hepatocytes. Resmetirom, a selective THR-β agonist, significantly reduced more than 30% of hepatic fat after 12 and 36 weeks of treatment in patients with NASH in phase II trial [
Vitamin E, an antioxidative agent, demonstrated benefits on hepatic decompensation and transplant-free survival in patient with NASH [
Apoptosis signaling kinase 1 (ASK1) promotes apoptosis, inflammation, and fibrosis in the liver. However, selonsertib, an ASK1 inhibitor, failed to improve fibrosis in NASH patients with bridging fibrosis or compensated cirrhosis [
Berberine ursodeoxycholate is an ionic salt of berberine and ursodeoxycholic acid. It reduced 4.8% of liver fat and improved glycemic control as well as liver enzymes in patients with NASH and diabetes [
In a phase IIb study, obeticholic acid (OCA), a FXR agonist, improved liver histology in 21% of NASH patients [
Caspase is a protease that is associated with apoptosis and inflammation in the liver. However, emricasan, a pan-caspase inhibitor, did not improve fibrosis or resolution of NASH [
In a phase IIb CENTAUR trial, a 2-year study, cenicriviroc, a dual C-C chemokine receptor types 2 and 5 antagonist, achieved ≥1-stage of fibrosis improvement without worsening of NASH after 1 year of treatment compared to placebo (20% vs. 10%) [
Belapectin, a galectin-3 inhibitor, did not significantly reduce HVPG or fibrosis in patients with NASH, cirrhosis, and portal hypertension; however, in a subgroup of patients without esophageal varices, belapectin reduced HVPG as well as the development of esophageal varices [
Information about the ongoing phase III clinical trials of promising drugs on phase II studies are listed in
NAFLD is a multifactorial disease, and combining therapies with different targets may have synergistic effects [
As understanding of mechanisms of NASH and its fibrosis increases, more therapies will be introduced and tested in clinical trials. The pathogenesis of NASH and fibrosis is complex; therefore, it would be difficult to treat the disease using just one therapy. Combination therapy is the focus in the future development of treatment. Furthermore, better care of extra-hepatic complications of NASH, novel biomarkers for diagnosis, risk stratification and treatment responses, and more clinical trials in Asian groups should also be well researched and developed.
KC Lee and PS Wu drafted the manuscript and HC Lin revised the manuscript. All the authors read and approved the final version.
The authors have no conflicts to disclose.
This study was supported in part by the grants from the Ministry of Science and Technology (110-2628-B-075-016; 111-2314-B-075-051-MY3) Taiwan.
acetyl-coenzyme A carboxylase
AMP-activated protein kinase
angiotensin
apoptosis signaling kinase 1
C/EBP homologous protein
diacylglycerol O-acyltransferase 2
duodenal-Jejunal bypass liner
duodenal mucosal resurfacing
de novo lipogenesis
endoplasmic reticulum
endoscopic sleeve gastroplasty
free fatty acid
fibroblast growth factor
fecal microbiota transplantation
farnesoid X receptor
glucokinase regulatory protein
glucagon-like peptide-1
hepatocellular carcinoma
hedgehog
hepatic stellate cell
hydroxysteroid 17- beta dehydrogenase 13
hepatic venous pressure gradient
intragastric balloons
interleukin
inositol-requiring enzyme 1
immunity-related GTPase M
Kupffer cell
laparoscopic sleeve gastrectomy
membrane-bound O-acyltransferase domain-containing protein 7
microRNA
non-alcoholic fatty liver disease
NAFLD activity score
non-alcoholic steatohepatitis
non-esterified fatty acid
obeticholic acid
plasminogen activator inhibitor-1
protein kinase R (double-stranded RNA-activated protein kinase)-like ER kinases
patatin-like phospholipase domaincontaining 3
proliferator-activated receptor
(pro)renin receptor
polyunsaturated fatty acid
renin-angiotensin system
randomized controlled trial
stearoyl-coenzyme A desaturase 1
short-chain fatty acid
saturated fatty acid
sodium-glucose cotransporter 2
single nucleotide polymorphism
sterol receptor binding protein 1-c
triglyceride
transforming growth factor
thyroid hormone receptor-β
toll-like receptor
transmembrane 6 superfamily 2
tumor necrosis factor
TNF receptor 1
unfolded protein response
very-low-density lipoprotein
X-box-binding protein 1
omega-6
Progression of hepatic steatosis to inflammation and fibrosis in liver. Both metabolic and genetic factors contribute to the formation of hepatic steatosis. Fat accumulation in hepatocytes leads to organelles dysfunction and lipotoxicity. Then, oxidative stress species or signaling molecules are transmitted through extracellular vesicles or diffusion, activating other parenchymal and non-parenchymal cells, which subsequently causes inflammatory cascades, steatohepatitis, and liver fibrosis. On the other hand, gut-derived bacterial end-products, metabolites, gut hormones, adipose tissue-derived cytokines or adipokines, and renin-angiotensin-system all contribute to the progression from steatosis to inflammation and fibrosis. SFA, saturated fatty acid; TG, triglyceride; ER, endoplastic reticulum; HH-OPN, Hedgehog-osteopontin; KC, Kupffer cell; HSC, hepatic stellate cell.
Promising pharmacological therapies for NAFLD or NASH
Type of drug | Mechanism of action | Drug name | Study design | Study outcome | Reference |
---|---|---|---|---|---|
PPAR agonist | PPAR-γ: ↑ insulin sensitivity modulates adipose tissue distribution | Pioglitazone (PPAR-γ agonist) | RCT; NASH, prediabetes/DM | ↓ ALT/AST | [ |
Pioglitazone vs. placebo | ↓ Steatosis, ballooning necrosis, and inflammation | [ |
|||
PPAR-α: ↑ fatty acid β-oxidation | Fibrosis not improved | ||||
PPAR-δ: anti-inflammatory | RCT; NASH | ↓ ALT/GGT | |||
Pioglitazone vs. placebo | Histology improvement, including liver injury and fibrosis | ||||
Pemafibrate (SPPARMα) | Phase II RCT; NAFLD and ↑ ALT | ↓ ALT | [ |
||
↓ Liver stiffness | |||||
Pemafibrate vs. placebo | No significant change of liver fat | ||||
Lanifibranor (Pan-PPAR agonist) | Phase IIb RCT; NASH (SAF-A ≥3) | ↓ SAF-A score ≥2 points in lanifibranor 1,200 mg group | [ |
||
Lanifibranor vs. placebo | |||||
GLP-1 agonist | ↑ Insulin secretion | Liraglutide | Phase II RCT; NASH, obesity | ↑ Resolution of NASH without worsening of fibrosis | [ |
↓ Glucagon secretion | Liraglutide vs. placebo | No difference in fibrosis improvement | |||
↓ Gastric emptying | Semaglutide | RCT, phase II; NASH (F1–F3 fibrosis) | ↑ Resolution of NASH without worsening of fibrosis in semaglutide 0.4 mg group | [ |
|
↓ Appetite | Semaglutide vs. placebo | No difference in fibrosis improvement | |||
SGLT2 inhibitor | ↑ Urinary excretion of glucose | SGLT2 inhibitors | Meta-analysis of 10 RCTs; NAFLD, DM | ↓ ALT/AST | [ |
SGLT2 inhibitor vs. other antidiabetic drugs | ↓ Liver fat content, visceral fat, and subcutaneous fat areas | ||||
FGF-19 analogue | ↓ Bile acids synthesis | Aldafermin | Phase II RCT; NASH (NAS ≥4, F2–F3 fibrosis, and liver fat content ≥8%) | ↓ ALT/AST | [ |
↓ Hepatic gluconeogenesis | ↓ Liver fat fraction on MRI-PDFF | ||||
↓ DNL | Aldafermin vs. placebo | ||||
↑ Fatty acid oxidation | |||||
FGF-21 analogue | ↓ Hepatic gluconeogenesis | Pegbelfermin | Phase IIa RCT; NASH (F1–F3 fibrosis, and liver fat content ≥10%), obesity | ↓ Liver fat fraction on MRI-PDFF | [ |
↑ Insulin sensitivity | |||||
↑ Energy expenditure | Pegbelfermin vs. placebo | ||||
↑ Mitochondria beta-oxidation in hepatocytes | Efruxifermin | Phase IIa RCT; NASH | ↓ Liver fat fraction on MRI-PDFF | [ |
|
Efruxifermin vs. placebo | |||||
Acetyl-CoA carboxylase inhibitor | ↓ DNL | PF-05221304 | 2 phase IIa RCTs; NAFLD/NASH | PF-05221304 monotherapy: | [ |
↑ Fatty acid oxidation | PF-05221304 monotherapy vs. placebo | ↓Liver fat on MRI-PDFF, but ↑ TG | |||
Diacylglycerol acyltransferase 2 inhibitor | ↓ Synthesis of fatty acids into TGs | PF-06865571 | PF-05221304 and PF-06865571 co-administration vs. placebo | Co-administration therapy: ↓ liver fat and mitigated ACC inhibitormediated effect on TG | |
Stearoyl-CoA desaturase 1 inhibitor | ↓ DNL | Aramchol | Phase IIb RCT; NASH | ↓ Liver fat content in aramchol 600 mg group, but not significant | [ |
Aramchol vs. placebo | |||||
Selective thyroid hormone receptor-β agonist | ↓ LDL, cholesterol, and TG | Resmetirom | Phase II RCT; NASH (F1–F3 fibrosis, and liver fat content ≥10%) | ↓ Liver fat on MRI-PDFF | [ |
↑ Fatty acid oxidation | Resmetirom vs. placebo | ||||
Anti-oxidant | Anti-oxidative stress | Vitamin E | RCT; NASH, no DM | ↓ ALT/AST for both vitamin E and pioglitazone groups | [ |
Vitamin E vs. pioglitazone vs. placebo | NASH improvement in vitamin E group, but not in pioglitazone group | ||||
Fibrosis not improved in vitamin E and pioglitazone groups | |||||
Bile acid analogue | Anti-inflammation | Berberine ursodeoxycholate | Phase II RCT; NAFLD, DM | ↓ Liver fat content on MRI-PDFF | [ |
Berberine ursodeoxycholate vs. placebo | |||||
↓ DNL | Obeticholic acid (FXR agonist) | Phase III RCT; NASH (NAS ≥4, F2–F3 fibrosis or F1 with ≥1 accompanying comorbidity) | ↓ Fibrosis | [ |
|
↑ Fatty acid β-oxidation | No significant resolution of NASH | ||||
↑ Cholesterol excretion | Obeticholic acid vs. placebo |
NAFLD, non-alcoholic fatty liver disease; NASH, non-alcoholic steatohepatitis; PPAR, proliferator-activated receptor; SPPARMα, selective peroxisome proliferator-activated receptor α modulator; RCT, randomized controlled trial; ALT, alanine aminotransferase; SAF-A, steatosis-activity-fibrosis activity; GLP-1, glucagon-like peptide-1; SGLT2, sodium-glucose cotransporter 2; DM, diabetes mellitus; AST, aspartate aminotransferase; FGF, fibroblast growth factor; DNL, de novo lipogenesis; NAS, NAFLD activity score; MRI, magnetic resonance imaging; PDFF, proton density fat fraction; TG, triglyceride; ACC, acetyl-coenzyme A carboxylase; LDL, low density lipoprotein; FXR, farnesoid X receptor.
Ongoing phase III clinical trials of pharmacological agents in patients with NAFLD or NASH
Agent | Mechanism | Patient | Outcome | Status | ClinicalTrials.gov identifier |
---|---|---|---|---|---|
Lanifibranor | Pan-PPAR agonist | NASH with stage 2–3 fibrosis without cirrhosis | NASH resolution; fibrosis improvement; liver-related events | Recruiting | NCT04849728 |
Semaglutide | GLP-1 agonist | NASH with stage 2–3 fibrosis | NASH resolution; fibrosis improvement; liver-related events | Recruiting | NCT04822181 |
Dapagliflozin | SGLT2 inhibitor | NASH and type 2 DM without cirrhosis | Histology improvement | Recruiting | NCT03723252 |
Resmetirom | Selective thyroid hormone receptor-β agonist | NASH without cirrhosis | NASH resolution; liver-related events | Recruiting | NCT03900429 |
Aramchol | Stearoyl-CoA desaturase 1 inhibitor | NASH with stage 2–3 fibrosis without cirrhosis; type 2 DM or prediabetes | NASH resolution; fibrosis improvement | Recruiting | NCT04104321 |
Belapectin | Galectin-3 inhibitor | NASH cirrhosis without esophageal or gastric varices | Newly developed esophageal varices | Recruiting | NCT04365868 |
Oltipraz | Liver X receptor alpha-inhibitor | NAFLD without cirrhosis | Liver fat | Recruiting | NCT04142749 |
NAFLD, non-alcoholic fatty liver disease; NASH, non-alcoholic steatohepatitis; PPAR, proliferator-activated receptor; GLP-1, glucagon-like peptide-1; SGLT2, sodium-glucose cotransporter 2; DM, diabetes mellitus.