Treatment of nonalcoholic fatty liver disease: from adult trials to perspectives in the management of children and adolescents

KEYWORDS:

• Children
• nonalcoholic fatty liver disease
• nonalcoholic steatohepatitis
• pharmacotherapy
• drugs

1. Introduction

Nonalcoholic fatty liver disease (NAFLD) is associated with the metabolic syndrome (MetS a cluster of interrelated conditions including obesity, hypertension, type 2 diabetes mellitus (T2DM), insulin resistance (IR) and dyslipidemia [1]), is considered the most predominant form of chronic liver disease in childhood/adolescence and its prevalence ranges from 7.6% to 34.2% [2]. Several factors contribute to disease development, supporting, therefore, a multifactorial etiology; obesity, race/ethnicity (Black non-Hispanic children are less susceptible), genetic influences (e.g. patatin like phospholipase domain–coding protein gene), environmental exposures (e.g. sedentary lifestyle) and disturbed gut microbiota [increased gut permeability, translocation of bacteria and their products (pathogen-associated molecular pattern such as lipopolysaccharide) from the gut to the liver, thereby contributing to the inflammatory process observed in NAFLD] [3]. An additional risk factor is male sex, since females are less susceptible, at least till menopause, a phenomenon attributed to a protective role to estrogens [4]. NAFLD encompasses a diversity of phenotypes, starting from steatosis (nonalcoholic fatty liver, NAFL) that might progress to nonalcoholic steatohepatitis (NASH), which may subsequently advance to hepatic fibrosis, cirrhosis and hepatocellular carcinoma [5,6]. During the progression of NAFL to NASH, a low-grade chronic inflammation of the liver is observed, which is orchestrated by alterations in adipokines, produced mainly by adipocytes and cytokines, predominantly induced by immune cells infiltrating the adipose tissue and the liver [7]. These alterations aggravate IR, lipotoxicity and mitochondrial dysfunction, all considered key players for the disease progression [8]. Regarding the natural history of pediatric NAFLD, although it remains largely unknown, some authors reported progression to end-stage liver disease, even in children [9,10].

Table 1. A summary of selected ongoing clinical trials on NASH.

Drug	Properties	Clinical Trial Phase (possible completion date*)	Trial ID
Targeting liver steatosis
Gemcabene	Dialkyl ether dicarboxylic acid with antihyperlipidemic activity	2 (8/2019)**	NCT03436420
Liraglutide	Glucagon-like peptide-1 analogue, injectable drug, with shown efficacy to induce weight loss and lower glucose in obese patients; approved for T2DM and obesity	3 (12/2017) 4 (9/2023)	NCT02654665 NCT03648554
NGM282 (M70)	Non-tumorigenic, engineered variant of fibroblast growth factor 21 (Receptors 1c, 4) reducing steatosis and lipotoxicity	2 (9/2020) 2 (9/2019)	NCT03912532 NCT02443116
Pemafibrate (K-877)	Selective PPAR-α modulator	2 (2/2020)	NCT03350165
Targeting oxidative stress/inflammation/apoptosis
BI 1,467,335	Promoter of leukocyte recruitment in the liver, with monoamine oxidase activity, insulin-like effects, and initiation of oxidative stress	2 (6/2019)	NCT03166735
Cilofexor (GS-9674)	Selective non-bile acid FXR agonist, designed to avoid the side effects of obeticholic acid	2 (8/2019) 2 (10/2019)	NCT02781584 NCT03449446
Elafibranor (GFT505)	PPAR α/δ agonist, insulin sensitizer, ameliorating hepatic inflammation, steatosis and fibrosis	2 (11/2020)**	NCT03883607
Emricasan	Irreversible pan-caspase inhibitor	2 (8/2019)	NCT03205345
Losartan	Angiotensin II receptor antagonist; approved for arterial hypertension	2 (04/2020)**	NCT03467217
Metadoxine	Antioxidant, source of glutathione, capable of inhibiting adipocyte differentiation, limiting hepatic lipid accumulation and exerting antifibrotic properties	4 (1/2020)	NCT02051842
Pentoxifylline	Anti-oxidant/anti-inflammatory properties	Not applicable (6/2016)	NCT02231333
Pioglitazone	PPARγ activator, attenuating IR, steatosis, lobular inflammation, and fibrosis; approved for T2DM	4 (2/2019) 4 (9/2020) Cohort (7/2021)	NCT03796975 NCT03910361 NCT02815891
Tipelukast (MN-001)	A leukotriene receptor antagonist, which inhibits phosphodiesterase, 5-lipoxygenase and exhibits antifibrotic, anti-inflammatory activity in preclinical models	2 (5/2018)	NCT0268105
Targeting gut microbiota
Fecal microbiota transplantation	Modulator of intestinal microbiome	1 (1/2021)	NCT03803540
IMM-124E	IgG-rich extract from cows immunized against lipopolysaccharide, which reduces the hepatic exposure to gut-derived bacterial products	2 (12/2019)**	NCT03042767
Targeting liver fibrosis
BMS-986,036	Pegylated analogue of fibroblast growth factor 21	2 (1/2020) 2 (1/2020)	NCT03486912 NCT03486899
GR-MD-02	Galectin-3 inhibitor, resulting in improvement in liver histology with a significant reduction in NASH activity and collagen deposition	2 (9/2016)	NCT02421094
GS0976 acetyl-CoA carboxylase (Firsocostat)	Fatty acid metabolism key regulator, controlling the balance between de novo lipogenesis and fatty acid oxidation	2 (6/2020) 2 (10/2019)	NCT03987074 NCT03449446
Saroglitazar	PPAR-α/γ dual agonist; approved for hypertriglyceridemia in T2DM	2 (4/2020) 2 (10/2019) 2 (8/2019) 2 (9/2020)	NCT03639623 NCT03617263 NCT03061721 NCT03863574

* estimated date (month/year) of primary completion

** pediatric clinical trial

Abbreviations: FXR; farnesoid X receptor, IR; insulin resistance, NAFLD; nonalcoholic fatty liver disease, NASH; nonalcoholic steatohepatitis, PPAR; peroxisome proliferator-activator receptors

The histopathological hallmarks of NASH in adults include the following triad: hepatic lipid accumulation (macrovesicular steatosis with displacement of nucleus), inflammation (mainly lobular and even portal) [11] and accompanying ballooning, indicative of injury. Fibrosis (perisinusoidal) is not a required diagnostic feature of NASH, though it is usually present [12]. Pediatric NAFLD patients, however, appear to display more steatosis with fewer ballooning in hepatocytes and more prominent portal inflammation/fibrosis [13,14].

Beyond the initially recommended conservative measures with life-style modifications, which often fail to achieve or maintain long term, due to incompliance [1,5,15], the necessity for developing effective medications is urgent. However, there is no specific approved pharmacotherapy for NAFLD in the US, Europe or Asia [6,16–18].

2. Pharmacotherapy in childhood and adolescence

Several medications have been introduced to treat NAFLD [5,16,19]. They are classified into certain categories, depending on the mechanism of action and/or the pharmacological target. A heterogenic category of agents targets liver fat accumulation (peroxisome proliferator-activator receptors [PPAR], farnesoid X receptor [FXR] agonists, inhibitors of the de novo lipogenesis and fibroblast growth factor-21 analogues). Another category includes drugs targeting oxidative stress, apoptosis and inflammation. A third category includes medications targeting gut microbiota dysbiosis and metabolic endotoxemia. Furthermore, agents against liver fibrosis are important therapeutic targets, since fibrosis is the main prognostic histological endpoint and a hard to reverse condition [5,19].

Current guidelines recommend that pharmacotherapy should be reserved for NASH patients with fibrosis (at least fibrosis stage F2) or for those with many risk factors that potentially contribute to the disease progression [5,6]. Therefore, most clinical trials focus on NASH. However, it still remains an unanswered scientific question, why not all patients, but only a subset of them have a reported disease progression [20].

Importantly, since longitudinal studies of NAFLD/NASH in pediatric populations are mostly lacking [10,14], its management is extrapolated from adult studies.

Beyond lifestyle modifications (diet and physical activity), the cornerstone of pediatric NAFLD treatment [6,21], numerous medications and supplements have been introduced for the management of pediatric NAFLD [21,22]; the most commonly studied agents include vitamin E and metformin [21,23].

Metformin is an insulin sensitizer, constituting a first-line medication in the treatment of type 2 diabetes mellitus (T2DM). Although metformin decreases IR, it is not recommended by the guidelines for adults, since it failed to show a significant improvement in liver histology [6,18]. Worth mentioning is the TONIC trial (NCT00063635), a two-year randomized control trial (RCT) with 173 patients, which compared vitamin E (800 UI) or metformin (1000 mg) with placebo in the management of children/adolescents NAFLD, with liver biopsies obtained at baseline and at 2-year follow-up period of time. Although no ALT improvement was noticed between drug and placebo arms, vitamin E treatment led to statistically significant improvement in histology, demonstrated by a lower NAFLD activity score (NAS) (−0.7 NAS for placebo and −1.8 for vitamin E) [23]. However, the use of long-term high-dose vitamin E, at least in adults, has raised concern for increased all-cause mortality and risk of cardio-cerebrovascular events and malignancy [5,6,18,19]. The same trial reported no effect of metformin on ALT reduction or NAS score compared with placebo.

Pioglitazone, another insulin sensitizer, is a thiazolidinedione acting as PPARγ activator, approved for the treatment of T2DM. Contrary to metformin, pioglitazone ameliorates liver histopathology in NASH patients and thus, may be considered for biopsy-proven adult NASH patients according to American and European guidelines [1,6,18]. However, the adverse effect of pioglitazone on weight gain, bone metabolism and a potential minimal effect on bladder cancer should be considered before its treatment initiation [18].

Other common tested drugs in clinical trials of pediatric NAFLD are omega-3 polyunsaturated fatty acids including docosahexaenoic acid (DHA) and probiotics, though without resulting in resolving histopathology that would justify their usage [21]. For example, in a RCT, 41 children/adolescents with biopsy-proven NAFLD and vitamin D deficiency were placed on DHA (500 mg) and vitamin D (800 UI) supplementation versus placebo (NCT02098317). When compared with placebo, the combined regimen demonstrated improved ALT (40 vs. 25 UI/l, respectively), triglycerides (175 vs. 102 mg/dl, respectively), IR, the key component of MetS, and NASH Activity Score (5.4 vs 1.9, respectively) [24]. Another RCT with 58 included children with NAFLD, reported no improvement in ALT when DHA was compared with placebo. Nevertheless, there was a reduction in visceral (7.8%), epicardial (14.2%) and liver fat (53.4%) and improvement in MetS parameters [25]. Of note, recent data indicate that vitamin D deficiency is related to suspected NAFLD, independent of obesity and MetS in children/adolescents [26]. Nevertheless, although no noteworthy adverse events have been reported to date, the major concern regarding the use of vitamin D at treatment dose appears to be the risk of hypercalcemia, especially in children with high calcium consumption [27]. In obese children with NAFLD, some RCTs also reported improvement in ALT, body and liver fat and MetS parameters, by probiotic consumption [22]. However, definite conclusions could not be currently made, largely owing to the fact that different probiotic combinations in different doses have been used in different studies.

Another category of widely prescribed medications is statins. Six of them have a clinical relevance; atorvastatin, lovastatin, fluvastatin, simvastatin, pravastatin, and rosuvastatin. Statins have shown favorable effects on steatosis in adult patients with NAFLD, albeit their effect on inflammation and fibrosis remains questionable [6,28]. Thus, they are suggested by the guidelines for the reduction of cardiovascular risk, as necessary, in adult NAFLD patients. It is highlighted that cardiovascular disease is the main cause of death in adult NAFLD patients. Their benefit in reducing the cardiovascular risk outweighs the smaller risk of idiopathic hepatotoxicity of statins. There is also evidence supporting that statins may also decrease the risk of liver cirrhosis decompensation and its complications [29].

3. Future perspectives mainly based on adult trials

A quite impressive number of new drugs from all the above-mentioned categories are currently being tested in RCT. The future is promising and recommendation-approval of more pharmacological agents specific for NAFLD is anticipated. The most important of them are briefly reported, as well as their mechanism of action.

Losartan, an angiotensinogen II receptor blocker, failed to be tested in an adult NASH RCT, due to slower recruitment than anticipated [5]. A pediatric RCT with losartan 100 mg for 6 months is, however, ongoing (NCT03467217), recruiting children and adolescents of 8–17 years. The primary aim of this RTC is ALT reduction, which may presumably occur via a downregulation of plasminogen activator inhibitor-1 and blockage of renin-angiotensin-aldosterone system.

Ursodeoxycholic acid has been tested to treat pediatric NAFLD and showed no improvement in ALT or liver ultrasound [22]. Obeticholic acid (Intercept Pharmaceuticals, New York, NY, USA) is an FXR agonist, approved for the treatment of primary biliary cholangitis (PBC). This nuclear receptor is expressed in the liver and modulates bile acid, lipid, and glucose metabolism. Obeticholic acid provided favorable preclinical results and positive effects on hepatic steatosis, inflammation, and fibrosis in adults. The main side effects included high rates of pruritus and an adverse effect on lipid profile. A phase III RCT (REGENERATE, NCT02548351) is ongoing in NASH. The estimated number of patients is 2370 and obeticholic acid is administered in a dosage of 10 or 25 mg. Its main aim is the long-term (7 years) efficacy of obeticholic acid versus placebo on hepatic histopathology of NASH patients with fibrosis scores 2 and 3 [30].

Aramchol, a synthetic bile acid (cholic-arachidic acid conjugate), inhibits stearoyl-CoA desaturase 1, the rate-limiting enzyme in monounsaturated fatty acid synthesis, leading to downregulation of hepatic fat accumulation. Beyond its original production aimed at gallstone therapy, studies in animal models also exhibited an improvement in liver steatosis [5,21].

Elafibranor (GFT505) is a PPAR-α/δ dual agonist acting as an insulin sensitizer. In murine models of NAFLD, elafibranor ameliorated hepatic inflammation, steatosis, and fibrosis [31]. In a phase II RCT (NCT01694849) with 274 NASH patients, elafibranor 120 mg for 52 weeks resolved NASH without worsening of fibrosis in a higher proportion than placebo (19% vs 12%, respectively) [32]. It is also under phase III evaluation for NASH (RESOLVE-IT, NCT02704403) and PBC [5,16,21]. A pediatric RCT is also ongoing (NCT03883607), targeting to evaluate mainly safety and pharmacokinetics of 3-month elafibranor 80 and 120 mg in 20 children with NASH [33].

Selonsertib (GS-4997) is an inhibitor of apoptosis signal-regulating kinase 1, which is activated by intracellular oxidative and endoplasmic reticulum stress as well as by extracellular tumor necrosis factor-α, leading to hepatic apoptosis and fibrosis. In a phase II RCT, selonsertib ameliorated NAS and fibrosis [5,16,21]. However, two recently completed phase III RCTs for selonsertib in NASH (STELLAR 3, NCT03053063 and STELLAR 4, NCT03053050) showed no efficacy [34].

Cenicriviroc is a dual C–C motif chemokine receptor-2/5 antagonist (CCR2/5), primarily targeting inflammation, and also exhibiting antifibrotic effects. In a phase IIb RCT (CENTAUR, NCT02217475) [32], cenicriviroc 150 mg attenuated liver fibrosis in a sample of 289 patients without worsening NASH compared with placebo (20% vs 10%, respectively). It has also been shown to improve insulin sensitivity. Currently, it is under further evaluation in other two phase II RCTs (NCT03059446, NCT03517540) [5,16,21].

Another interesting agent is resmetirom (MGL-3196, Madrigal Pharmaceuticals), which is a selective agonist of thyroid hormone receptor in the liver [1]. It binds the main hepatic thyroxine (T4) receptor, leading to increased cholesterol excretion through bile. Resmetirom has been designed to treat dyslipidemia and has been demonstrated to reduce liver steatosis in high fat-fed rats [5]. A phase II RCT has been completed (NCT02912260) and the NASH patients received 80 mg (±20-mg adjustment) of resmetirom for 12 weeks. It showed that resmetirom caused a 27% relative reduction in liver fat (both from baseline, placebo adjusted) [1]. Currently, a phase III RCT is ongoing (MAESTRO-NASH NCT03900429).

Other medications worth mentioning, which are also under evaluation in clinical trials are summarized in Table 1.

Interestingly, recent experimental data indicate that blockade of receptor-interacting serine/threonine protein kinase 1 (RIPK1) signaling (crucial for protection from hepatocellular damage in a steatotic liver undergoing ischemia reperfusion injury but not in the lean liver) results in augmented caspase 8 activity and reduces mitochondrial viability, thereby recommending as a new target for drug therapy to inhibit hepatocellular injury in NAFLD [35].

Beyond the plethora of previous agents, regarding the mentioned recommendation of life-style modifications, the importance of changing eating habits, especially in children, and adopting a healthier diet was recently demonstrated in an RCT with 40 NAFLD adolescent boys (NCT02513121) receiving a low free sugar diet for 8 weeks, which resulted in ameliorating liver steatosis (25% to 17% vs. 21% to 20% observed in usual diet) [36]. There is also evidence suggesting an association between Helicobacter pylori infection (Hp-I) and NAFLD as well as between Hp-I and IR or MetS and associated morbidity [17,37]. Hp eradication might contribute to a more integrated management of this multifactorial disease. However, further large-scale studies are necessitated, before its recommendation and integration in guidelines can be made.

4. Expert opinion

Since NAFLD is a multifactorial disease, NAFLD management may need a multiple-step approach, thus targeting several contributing pathogenetic factors [38]. In this respect, in a recent proof-of-concept study, only the combined vitamin E/pioglitazone therapy was able to improve histological scores in patients with NASH and T2DM [39]. A close collaboration among diverse specialties (hepatologist/diabetologist/dietician/cardiologist) may be important to improve outcomes. The contribution of a pathologist is regarded also fundamental, since the histological diagnosis quantifies the presence of steatosis/inflammation/fibrosis and establishes NAFLD diagnosis. Lifestyle modifications are the first-line, substantial and effective measure, though, it often fails, due to incompliance in lifelong term [1,5,15]. Bariatric surgery, although non-pharmacological treatment, plays a well-established role in adult NAFLD. Limited data show that bariatric surgery may be more efficient in reducing NASH and liver fibrosis compared to lifestyle modifications in obese adolescences [22].

In clinical practice, diabetologists should consider NAFLD in patients with T2DM, a disease with high NAFLD prevalence and higher rates of NASH than the general population [7]. Patients with biopsy-proven NASH and/or significant fibrosis currently qualify for pharmacotherapy. Vitamin E and pioglitazone are currently recommended, albeit as off-label treatment, for specific NASH patients, especially those with fibrosis stage (F)≥2 [6]. However, given the variety of pharmacological agents under investigation, the therapeutic future of NAFLD seems to be promising.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

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