Emerging therapeutic options for non-alcoholic fatty liver disease: A systematic review

Jasmine Tidwell, Natalie Balassiano, Anjiya Shaikh, Mahmoud Nassar

Abstract

Key Words: Non-alcoholic fatty liver disease; Non-alcoholic steatohepatitis; Cyclophilin inhibitors; Fibroblast growth factor 21 analogs; Dual peroxisome proliferator-activated receptor agonists; Pan peroxisome proliferator-activated receptor agonists

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is a prevalent chronic liver disease affecting approximately 30% of the world's population[1].It is characterized by the buildup of more than 5% of fat in hepatocyte histology[1].NAFLD encompasses a range of conditions, such as non-alcoholic fatty liver (NAFL), non-alcoholic steatohepatitis (NASH), and cirrhosis[2].NAFL is defined as hepatic steatosis without inflammation, based on liver biopsy histology[2].

Approximately 20% of patients with NAFL will develop NASH, which is the presence of hepatic steatosis, lobular inflammation, and hepatocyte ballooning[1,2].This persistent liver cell injury leads to progressive fibrosis and cirrhosis in approximately 10%–20% of patients, converting NAFLD into the quickest-growing cause of hepatocellular carcinoma (HCC)[1,3].NAFLD is currently liver transplantation's third most common cause[1].Unlike other causes of HCC, which start with fibrosis, up to one-third of patients with NASH and HCC are non-cirrhotic and are more advanced, making treatment difficult[3].

NAFLD is a liver condition that is closely linked with metabolic syndrome[1].It is often seen in people who have type 2 diabetes, are insulin resistant, have high levels of triglycerides and cholesterol, and are obese[1].The main risk factors for developing NAFLD are a diet high in fats and sugars and a sedentary lifestyle[1].Some experts have started using metabolic-associate fatty liver disease to describe this condition because of its strong link with metabolic dysfunction.Still, for clarity purposes, we will stick with the NAFLD nomenclature throughout this review[4].

Approximately 70% of diabetics, overweight patients, and 90% of patients with dyslipidemia and morbid obesity will develop NAFLD[1,4].NAFLD is also associated with systemic pathologies such as chronic kidney disease, cardiovascular disease, and reduced mineral density[1].Cardiovascular disease is the most common cause of death in NAFLD patients; however, they also have an increased overall mortality rate compared to the general population[1].It is of utmost concern that there is an increase in the prevalence of adolescents with NAFLD, leading to earlier end-stage liver disease[5].

In the United States alone, $100 billion of annual medical costs are attributed to NAFLD.Searching for an approved medical therapy for NAFLD is a pressured race[4].The lack of an authorized agent could be secondary to the limited understanding of a multifactorial disease process and the absence of dependable non-invasive biomarkers[4].Due to the acknowledgment of an increasing epidemic and the severity of NAFLD, several trials are ongoing to identify possible pharmacologic agents[3].Most of the agents target the known metabolic associations with NAFLD, such as adipose tissue dysfunction, insulin resistance, de novo lipogenesis, lipid exportation in the liver, and imbalance between energy intake and expenditure[5].

There is growing interest in future combined medications targeting multiple critical pathways involved in developing NAFLD[5].Precise identification of the drivers of this disease is crucial for developing new agents, and it is hoped that registered therapy for NAFLD will become available in the next few years[2].Clinicians must be aware of the emerging agents for the treatment of NAFLD and the need for further human research to characterize better the efficacy, dosage, length of treatment,etc.This systematic review will delve into the scientific data behind four innovative therapeutic classes currently being studied for treating NAFLD: Cyclophilin inhibitors, fibroblast growth factor 21 analogs (FGF21), and dual and pan peroxisome proliferator-activated receptor (PPAR) agonists.

移动式筛分站集成度高，输送机长度较短，安装空间小，而且需要完成折叠旋转等动作。传统的滚筒安装方式轴向尺寸大，机构布置困难。本文介绍了一种新型的半内藏式输送机滚筒，可快速拆卸，节省安装空间，缩短输送机整体宽度。并利用Workbench对设计的滚筒进行了静力分析和疲劳分析，验证了滚筒设计质量和性能的可靠性。

MATERIALS AND METHODS

This review analyzed animal and human research, case reports, and published articles in English from all countries with patients aged 18 and above.Only articles with a five or higher National Institutes of Health (NIH) Quality Assessment score were included.Articles that were narrative or systematic reviews, abstracts, not in English, focused on patients under 18 years old, did not measure outcomes of interest, were inaccessible, or had a low NIH Quality Assessment score were excluded.

A comprehensive literature search using broad search criteria was conducted in five databases: PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science (October 29, 2022).Our search terms were as follows: (rencofilstat OR "cyclophilin inhibitor" OR "cyclophilin inhibition" OR lanifibranor OR "PPAR agonist" OR "peroxisome proliferator activated receptor agonist" OR "pan-ppar agonist" OR "pan-peroxisome proliferator activated receptor agonist" OR efruxifermin OR "FGF-21 inhibitor" OR "fibroblast growth factor-21 inhibitor" OR "fibroblast growth factor 21 inhibitor" OR "FGF21 inhibitor" OR "FGF21 inhibition" OR "FGF-21 inhibition") AND (NASH or "fatty liver" or "hepatic steatosis" or steatohepatitis OR NAFLD OR "non-alcoholic fatty liver disease" OR "Non-alcoholic Fatty Liver Disease" OR "Fatty Liver, Non-alcoholic" OR "Fatty Livers, Non-alcoholic" OR "Liver, Non-alcoholic Fatty" OR "Non-alcoholic Fatty Liver" OR "Non-alcoholic Fatty Livers" OR "Non-alcoholic Steatohepatitis" OR "Non-alcoholic Steatohepatitides" OR "Steatohepatitides, Non-alcoholic" OR "Steatohepatitis, Non-alcoholic" OR "liver, fatty" OR "steatosis of liver" OR "visceral steatosis" OR "steatosis, visceral" OR "steatoses, visceral" OR "visceral steatosis" OR "liver steatosis" OR "liver steatoses" OR "steatosis, liver" OR "steatoses liver").

For the study selection process, Covidence was used, a platform that facilitates the importation of citations and screening of titles, abstracts, and full text.Each article was initially screened by title and abstract by two independent researchers (J.T.and N.B.) to exclude studies irrelevant to our aim.Next, each article was screened by full text by the same two independent researchers (J.T.and N.B.) to exclude studies that were finally irrelevant to our aim.Once both researchers completed all screening stages, any conflicts were registered in Covidence, and the discrepancies were reviewed and resolved.

The following data were collected separately by J.T.and N.B.from all eligible studies and recorded in Excel: First author, digital object identifier, study design, number of participants, name of therapy, mechanism of action, side effects, and statistical data about liver enzymes, cholesterol panels, weight reduction, NAFLD activity score (NAS), Fibroscan controlled attenuation parameter (CAP) and kPa, fibrosis stage, fibrotic markers, and quality assessment scores.J.T.and N.B.resolved all discrepancies in the collected data.The quality of included studies was assessed by the NIH Quality Assessment tool.We included articles with a score greater than or equal to five out of eight points.

RESULTS

Records were identified from 5 databases: PubMed, EMBASE, Cochrane Library, Scopus, and Web of Science.One hundred twenty-two duplicate records were removed before the screening.Six hundred eighty-one records were screened, out of which eighty-two were excluded by an automation tool.Five hundred fifty-nine reports were sought for retrieval, out of which three hundred were not retrieved.Two hundred fifty-nine reports were assessed for eligibility, out of which two hundred and thirty were excluded.The most common reason for exclusion was review articles (156) followed by irrelevant articles (31), abstracts (18), duplicates (16), foreign language (5), and unable to be accessed (4).Twenty-nine of the two hundred and fifty-nine records assessed for eligibility were included (Figure 1).Most studies, including human and animal participants, were small (n< 100).Some studies enrolled patients with NAFLD and others with NASH.Articles were included when the NIH Quality Assessment Score was greater than or equal to five points.The majority of articles included were scored as six or seven points.Reasons for lower scores included unknown publication bias and no rating by two independent reviewers.Most studies did not report harmful outcomes.

Four studies evaluated cyclophilin inhibitors (Table 1), four evaluated FGF analogs (Table 2), eleven evaluated pan-PPAR agonists (Table 3), and ten evaluated dual-PPAR agonists (Table 4).Different investigational products were assessed; the most common for cyclophilin inhibitors was NV556, for FGF agonists/analogs was Efruxifermin (EFX), forpan-PPAR agonists was Lanifibranor, and for dual-PPAR agonists was Saroglitazar.

Table 1 Studies of cyclophilin inhibitors in the treatment of non-alcoholic fatty liver disease

In terms of cyclophilin inhibitors, four animal studies demonstrated significant improvement in fibrosis on liver biopsy weeks after product use (P< 0.05).The randomized controlled trial (RCT) performed in humans (n= 49) noted similar results, with a reduction in ALT and Pro-C3 levels (P< 0.01), as well as steatosis and fibrosis as measured on FibroScan (P< 0.01).

The three animal studies using FGF analogs demonstrated significant improvement in both steatosis and fibrosis measured on liver biopsy (P< 0.05).The RCT performed in humans (n= 80) measured the change in hepatic fat fraction (HFF) on magnetic resonance imaging at 12 wk of treatment.It noted a greater than 50% reduction in HFF in all treatment dosage groups (P< 0.0001).

Eight animal studies using pan-PPAR agonists evidenced a significant reduction in steatosis on biopsy as measured by the decrease in triglyceride or lipid accumulation in hepatocytes (P< 0.05).There was also a reduction in fibrosis and collagen deposition on liver biopsy (P< 0.05).The human studies included three RCTs that examined the metabolic effects and/or steatosis markers (steatosis activity score) and concluded improved metabolic function, resolution of steatosis, and fibrosis improvement (P< 0.05).

In terms of dual-PPAR agonists, six animal studies reported improvement in steatosis, reduction in fibrosis or progression to fibrosis, and improvement in lipid metabolism and insulin sensitivity (P< 0.05).Two human in-vitro studies on hepatic cells were performed, which demonstrated a reduction in hepatic lipid accumulation, secretion of inflammatory chemokines, and profibrotic gene expression.Four additional human studies, including prospective design and RCTs, showed improved metabolic parameters such as insulin sensitivity, hemoglobin A1c, and lipid profiles (P< 0.05).Additionally, FibroScan results showed improved liver stiffness and steatosis (P< 0.05).

DISCUSSION

Cyclophilin inhibitors

Cyclophilins are thought to contribute to the development of liver fibrosis and cancer.Among these, Cyclophilin B is known to play a role in collagen production, leading to fibrosis.To treat NASH, several investigational products havebeen developed to target Cyclophilins[6].The main cyclophilin inhibitors reviewed here are CRV431[6], NV556[7,8], and Rencofilstat[9].

Table 2 Studies of fibroblast growth factor analogs/agonists in the treatment of non-alcoholic fatty liver disease

Studies conducted on animals, mainly mice that were administered a cyclophilin inhibitor, have shown positive results in improving liver fibrosis during biopsy[6-8].In particular, Kuoet al's research indicated a reduction of over 37% in liver fibrosis with CRV431 treatment compared to control on various mouse models[6,8].Likewise, NV556 also demonstrated a significant decrease in collagen production and liver fibrosis[7,8].

Due to these promising results, researchers conducted a phase 2a RCT with 49 patients who received Rencofilstat (75, 225 mg) or a placebo[9].The results showed that patients with high baseline Pro-C3 levels (> 15) experienced a decrease in collagen biomarkers, which are predictors for collagen deposition (P< 0.01)[9].This aligns with previous animal studies, suggesting that cyclophilin inhibitor treatment may reduce liver fibrosis.The patients generally tolerated Rencofilstat well, with only mild side effects reported, such as constipation, diarrhea, back pain, dizziness, and headache[9].Animal and human studies have shown that various investigational products that inhibit cyclophilin effectively treat patients with NASH.These agents are also well-tolerated and have anti-fibrotic properties that are beneficial.

FGF21 analogs or agonists

FGF21 is an active component of organ metabolism.Different variants have been studied for treating fatty liver disease, diabetes, and obesity due to their effect on glucose and lipid metabolism[10].The main FGF21 analogs and agonists reviewed here are LY2405319[11], PsTag600[12], BMS-986171[13], and EFX[10].Multiple animal studies involving FGF21 analogs and agonists have demonstrated improved glucose metabolism and reductions in markers of liver injury and fibrosis[11,12].Leet al[11] performed an animal study using LY2405319 (FGF21 analog), which attenuated increased collagen type 1, alpha-smooth muscle actin, and GPR91 protein levels[11].These results align with research on PsTag600 (long-acting FGF21) and BMS-986171 (FGF21 agonist)[12,13].

又由比尔-朗博定律可知，待测物质浓度C与吸光度A的关系如图2所示，从图中可以看出，当待测物质浓度超过一定范围时，浓度与吸光度将不再满足线性关系[6]，因此，在对待测气体进行定量分析时，要尽量选择待测物质浓度在其线性范围内。

A phase 2a study included 80 patients treated with a placebo or EFX 28 mg, 50 mg, or 70 mg (FGF21 analog) for 12 wk[10].The results indicated a significant decrease in HFF, with 78% of patients showing a positive response to NAS with an increase of at least 2 points and 48% of patients showing a resolution of NASH[10].There was also a statisticallysignificant reduction in alanine transaminase (ALT), aspartate aminotransferase (AST), and total cholesterol levels[10].Compared to Resmetirom, a selective thyroid hormone receptor-β agonist in phase 3 trials, FGF21 analogs/agonists showed similar reductions in HFF and fibrosis[10].The side effects reported for EFX were mild and included diarrhea, nausea, vomiting, abdominal pain, frequent bowel movements, and fatigue[10].In conclusion, FGF21 analogs and agonists have numerous benefits for NAFLD, including improved glucose and lipid metabolism, reduced markers of liver injury, and liver fibrosis.They effectively reduce hepatic steatosis and fibrosis, making them a promising treatment for NAFL and NASH.

Table 3 Studies of pan peroxisome proliferator-activated receptor agonists in the treatment of non-alcoholic fatty liver disease

ALT: Alanine transaminase; NASH: Non-alcoholic steatohepatitis; n: Number; TG: Triglycerides; CCL4: Carbon tetrachloride; SAF: Steatosis activity fibrosis; NAFLD: Non-alcoholic fatty liver disease; NAS: NAFLD activity score; IHC: Immunohistochemistry.

Figure 1 PRISMA flow diagram.

Table 4 Studies of dual-pan peroxisome proliferator-activated receptor agonists in the treatment of non-alcoholic fatty liver disease

N/A: Not applicable; NASH: Non-alcoholic steatohepatitis; n: Number; TG: Triglycerides; CCL4: Carbon tetrachloride; NFS: NAFLD fibrosis score; CAP: Controlled attenuation parameter; HbA1c: Hemoglobin A1c; NAFLD: Non-alcoholic fatty liver disease; GIR: Glucose infusion rate; CDHFD: Cholinedeficient high-fat diet; BMI: Body mass index; ALT: Alanine transaminase; AST: Aspartate aminotransferase; US: Ultrasound; MRI: Magnetic resonance imaging; CT: Computerized tomography.

Pan-PPAR agonists

There are three different isoforms of PPAR, α, γ, δ[14].PPARα mainly regulates genes that participate in lipid transport, beta-oxidation, gluconeogenesis, and ketogenesis[15].PPARγ regulates adiponectin, glucose metabolism, adipocyte differentiation, and lipogenesis[15].PPARδ limits inflammation and regulates hepatic fatty acid oxidation[15].Single PPAR agonists have had unwanted adverse effects and less effective results, for which investigational products that act on several isoforms have been attractive[15].

The main pan-PPAR agonists reviewed here are Benzafibrate[16,17], Lanifibranor[14,15,18-21], and MHY2013[22,23].Multiple animal studies involving pan-PPAR agonists have demonstrated increased plasma adiponectin, improvement in hepatic steatosis, and markers of liver injury[15,17,19,20,22-24].In alignment with the mechanism of pan-PPAR agonists, MHY2013[22,25] and Lanifibranor[19,20,24] also led to a decrease in hepatic steatosis, hepatic inflammation, serum triglycerides, profibrotic and fibrotic genes.In addition to the previously mentioned effects of Lanifibranor, Møllerhøjet al[20] revealed that Lanifibranor resulted in progressive weight loss, a 23% decrease at eight weeks and a 30% decrease at 12 wk[20].

In line with results from animal studies, a study of 45 patients using Lanifibranor (400 mg, 800 mg, or 1200 mg) or placebo for four weeks revealed an increase in adiponectin, a decrease in triglycerides, and ALT[25].Shortly after, a more significant phase 2b trial was performed on 247 patients with NASH that were randomly assigned to Lanifibranor (800 or 1200 mg) or a placebo daily for 24 wk[18].Participants had at least a 2-point decrease in the Steatosis, Activity, and Fibrosis score[18].A comparison of pan-PPAR agonistsvssingle agents revealed that pan-PPAR agonists were more potent in counteracting fibrosis by combining specific mechanisms of single PPAR agonists[15].Lanifibranor was generally well tolerated with mild reported side effects, including diarrhea, nausea, peripheral edema, anemia, and weight gain[18].Based on initial data, pan-PPAR agonists are more effective in improving the histological features of fatty liver disease with fewer adverse side effects than single PPAR agonists.This makes them a desirable option for the treatment of fatty liver disease.

Dual-PPAR agonists

Like pan-PPAR agonists, these agents act on two isoforms of PPAR, allowing for a more targeted effect.Saroglitazar has already been Federal Drug Administration (FDA)-approved for diabetic dyslipidemia and hypertriglyceridemia and has been shown to improve NAFLD, which piqued interest.

The main dual-PPAR agonists reviewed here are Ragaglitazar (α/γ)[23], GFT505 (α/δ)[26,27], Saroglitazar (α/γ)[28-32] and Elafibranor (α/δ)[33,34].Multiple animal studies involving dual-PPAR agonists have demonstrated promising results, including reduced triglycerides and liver injury markers[23,29].Ragaglitazar revealed an 88% reduction in triglycerides, increased adiponectin, counteracted an increase in visceral fat mass, and enhanced insulin suppressibility of hepatic glucose output[23].These outcomes correlate with results seen with GFT505[26] and Saroglitazar[20,29].Furthermore, Saroglitazar completely normalized AST and ALT, reduced serum TNF-α level by 47.6% and leptin by 58.6%[29].

Human research showed promising results in line with the aforementioned animal studies.GFT505 80 mg/day revealed a statistically significant reduction of fasting plasma triglycerides, LDL, and liver enzyme levels[27].However, the most studied investigational product is Saroglitazar.A more extensive study in 85 patients revealed reduced ALT and triglycerides[28].Furthermore, a study of Saroglitazar in 91 patients showed that 57 patients (63%) could reduce ≥ 5% of their weight[31].There has been discussion regarding pan-PPAR agonistsvsdual agents; Boeckmanset al[33] compared ElafibranorvsLanifibranor (pan-PPAR agonist), which identified Elafibranor as having higher anti-NASH properties[33].In general, dual-PPAR agonists are safe and effective in treating NAFLD and obesity.Research suggests that Elafibranor may be more effective than pan-PPAR agonists in treating these conditions.

CONCLUSION

NAFLD has become one of the most common causes of chronic liver disease globally.It's troubling that no FDAapproved treatments are currently available for this condition.Patients are limited to lifestyle changes and managing any concurrent diseases associated with fatty liver.However, there are promising developments in the form of investigational products that are being studied through clinical trials.These products include cyclophilin inhibitors, FGF21 agonists, and pan and dual PPAR agonists.The data analyzed in this review show clinically significant improvement in individual histological features of NAFLD in both animal and human trials for all four classes.These agents were generally well tolerated, with minimal side effects.We believe this compilation of information will have positive clinical implications in obtaining an FDA-approved therapy for NAFLD.However, more extensive trials are needed to further determine their efficacy, proper dosage, duration of therapy, and potential side effects for patients with NAFLD, including those with hepatic steatosis and fibrosis.

ARTICLE HIGHLIGHTS

FOOTNOTES

Author contributions: Tidwell J and Balassiano N performed the screening of articles, extraction of data and wrote the manuscript; Tidwell J and Shaikh A contributed to the results and discussion section; Nassar M contributed to editing, formatting and reviewing; All authors have read and approve the final manuscript.

Conflict-of-interest statement: The authors declare that they have no conflict of interest.

PRISMA 2009 Checklist statement:The authors have read the PRISMA 2009 Checklist, and the manuscript was prepared and revised according to the PRISMA 2009 Checklist.

Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers.It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial.See: https://creativecommons.org/Licenses/by-nc/4.0/

Country/Territory of origin: United States

ORCID number: Jasmine Tidwell 0009-0004-0560-672X; Natalie Balassiano 0000-0003-2476-0218; Anjiya Shaikh 0000-0002-4252-7404; Mahmoud Nassar 0000-0002-5401-9562.

S-Editor: Fan JR

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P-Editor: Cai YX