Risk factors for progression of and treatment options for NAFLD in children

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Abbreviations

ALT

alanine aminotransferase

BMI

body mass index

EtOH

ethanol

LPS

lipopolysaccharide

NAFLD

nonalcoholic fatty liver disease

NASH

nonalcoholic steatohepatitis

PNPLA3

patatin‐like phospholipase domain‐containing 3

Nonalcoholic fatty liver disease (NAFLD) is a common disease and can affect both adults and children. It is defined as a long‐standing hepatic steatosis that is not due to genetic or metabolic disorders, infections, side effects of medication, alcohol consumption, or malnutrition. Pediatric NAFLD occurs in children 18 years or younger. Alanine aminotransferase (ALT) cutoffs for the diagnosis of NAFLD have been determined to be 22 mg/dL for girls and 26 mg/dL for boys in the United States. NAFLD is linked to obesity and insulin resistance, but also to dyslipidemia with high triglyceride, high low‐density lipoprotein (LDL), and low high‐density lipoprotein (HDL) cholesterol levels. NAFLD can be subgrouped into several entities, with the main pathologies being nonalcoholic fatty liver (NAFL), nonalcoholic steatohepatitis (NASH), and end‐stage cirrhosis, which can be associated with similar complications in children as seen in adults (see Table 1 for definitions).1 This review highlights several risk factors for NAFLD progression to NASH in children, examines novel treatment options, and investigates the role of the intestinal microbiome in NAFLD.

Table 1.

Spectrum of Nonalcoholic Fatty Liver Disease

Type	Definition
NAFLD	Wide spectrum of conditions, all with long‐standing hepatic steatosis, not due to genetic or metabolic disorders, infections, side effects of medication, alcohol consumption, or malnutrition
NAFL	At least 5% of hepatic fat by imaging or histology, without inflammation, with or without fibrosis
NASH	Hepatic steatosis and liver inflammation (“‐hepatitis”), with or without fibrosis
Cirrhosis	End‐stage liver disease in the setting of NAFLD

Spectrum of Non‐Alcoholic Fatty Liver Disease (NAFLD). NAFLD encompasses non‐alcoholic fatty liver (NAFL) with ≥ 5% fat content; non‐alcoholic steatohepatitis (NASH) with fatty liver and liver inflammation (both entities with or without fibrosis); and NAFLD with cirrhosis which represents hepatic end‐stage disease.

Based on data from Vos et al.1

Demographic and Clinical Factors Associated With NAFLD and Progression to NASH in Children

Several factors determine the risk for NAFLD progression to NASH in children (Fig. 1).

Figure 1.

Risk Factors for Progression of Non‐Alcoholic Fatty Liver Disease (NAFLD) to Non‐Alcoholic Steatohepatitis (NASH) in Children. Multiple risk factors for progression to NASH have been identified, such as diet (e.g., fructose) and metabolic factors, for example, metabolic syndrome, in particular dyslipidemia, hyperuricemia, diabetes mellitus type 2, and possibly an increased BMI z score. Specific ethnicities and genetic setups have been found to be more susceptible to NASH, for example, Hispanic subjects and subjects with polymorphisms in the PNPLA3 gene. Other risk factors for the progression to NASH, such as physical inactivity, older pediatric age, or high birth weight, are conceivable or have been suggested by single studies, but robust scientific evidence is still lacking. Abbreviations: NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohepatitis; PNPLA3, patatin‐like phospholipase domain‐containing 3.

Demographics

Pediatric NAFLD is more likely to be present in boys than in girls and more likely in adolescents than in toddlers. The risk for NAFLD is directly proportional to the body mass index (BMI), with obese children being most at risk for NAFLD. The Hispanic population has a higher risk for NAFLD than Asian or white children. Black children are least likely to experience NAFLD (Table 2).2 Hispanic children have also been found to be more at risk for NASH. Interestingly, a single‐nucleotide polymorphism in the patatin‐like phospholipase domain‐containing 3 (PNPLA3) gene (SN rs738409 C>G), involved in lipid metabolism, is more common in Hispanic individuals and has been independently associated with NAFLD and NASH.3

Table 2.

Prevalence of Nonalcoholic Fatty Liver Disease (NAFLD) in Children

Variable	Group	Prevalence of NAFLD (%)
Gender	Male	11.1
	Female	7.9
Age	2‐4 years	0.7
	5‐9 years	3.3
	10‐14 years	11.3
	15‐19 years	17.3
Ethnicity	Black	1.5
	White	8.6
	Asian	10.2
	Hispanic	11.8
BMI	≤5%	0
	>5% to < 85%	5
	85% to < 95%	16
	≥95%	38

Based on data from Schwimmer et al.2

Diet

Fructose consumption has been associated with NAFLD severity in both cross‐sectional and interventional studies. There is evidence that fructose consumption was independently associated with NASH in obese children with NAFLD; it also showed that fructose intake was independently linked to hyperuricemia.4 An intervention with a low‐fructose diet in pediatric NAFLD demonstrated that fructose intake correlated strongly with plasma ALT, aspartate aminotransferase (AST), and insulin resistance, independently of weight loss.5 Furthermore, a recent study showed that a 9‐day‐long fructose restriction led to significantly decreased liver fat, visceral fat, and hepatic de novo lipogenesis in obese children.6

Metabolic Syndrome

Individual features of metabolic syndrome, in particular central obesity and insulin resistance, were found to be associated with severity of NAFLD in children.7 In addition, dyslipidemia, hyperuricemia, prediabetes, and diabetes were associated with a higher risk for pediatric NASH.4, 8

Novel Treatments

Currently, pediatric NAFLD is mostly managed by lifestyle modifications including a healthy, well‐balanced diet without sugar‐sweetened beverages, daily moderate‐ to high‐intensity exercise, and less than 2 hours of screen time per day.1

Only a relatively small number of pediatric drug trials have been conducted for NAFLD/NASH and have thus far focused on hepatic lipid metabolism, insulin resistance, and/or liver inflammation/oxidative stress. A few studies have shown that vitamin E (with lifestyle interventions) results in an improvement of ALT levels in pediatric patients with NAFLD similar to controls. One study demonstrated that high‐dose vitamin E over 2 years resulted in significantly better NAFLD activity scores and greater resolution of NASH when compared with controls despite similar ALT levels.1 A few short‐term studies with probiotics, or living nonpathogenic microorganisms such as Lactobacilli and Bifidobacteria that have a favorable impact on the host,9 showed improvement of pediatric NAFLD/NASH either with regard to ALT levels or hepatic steatosis. Fifty‐two weeks of cysteamine bitartrate delayed release (CBDR), a potent antioxidant, led to significant reductions in serum aminotransferase levels and lobular inflammation, but not to significant improvement of overall histological markers of NAFLD compared with placebo. Several studies demonstrated that omega‐3 fatty acids (docosahexaenoic acid [DHA]/eicosapentaenoic acid [EPA]) ameliorate liver steatosis on ultrasound and insulin sensitivity, improve liver and visceral fat, fasting insulin and/or lipid serum levels relative to placebo; however only one showed modest improvement of ALT levels. and improve liver and visceral fat, fasting insulin, and/or.1

In summary, several drugs have been tested in pediatric NAFLD/NASH trials and resulted in some improvement with regard to systemic ALT levels, hepatic steatosis on ultrasound, and/or liver histology. However, most have not led to significantly better outcomes in relation to placebo/lifestyle intervention only.

Association Between the Intestinal Microbiome and NAFLD

Children with NASH harbor significantly higher intestinal amounts of the gram‐negative bacteria Proteobacteria, Enterobacteriaceae, and ethanol (EtOH)‐producing Escherichia than healthy children.10 Intriguingly, children with NASH have also been shown to have significantly higher serum levels of EtOH, which can promote gut permeability.9, 10 In addition, they harbor fewer of the beneficial Bifidobacteria than healthy children.10 This is an example of intestinal dysbiosis, or a microbial imbalance with its associated deleterious effects on the colonized host.9 Dysbiosis is linked to translocation of bacterial products, for example, lipopolysaccharides (LPS) from gram‐negative bacteria, into the bloodstream. The latter is facilitated by increased intestinal permeability (“leaky gut”) and is a hallmark event in the development of NAFLD/NASH, with subsequent hepatic steatosis and inflammation.11 Antibiotics, prebiotics (complex carbohydrates nondegradable by humans promoting the growth of beneficial bacteria), and probiotics are aiming at preventing this translocation9 (for more details, refer to Fig. 2, as well as Hartmann et al.9 and Schnabl and Brenner11). Given the likelihood that resistant pathogenic bacteria could be selected, no antibiotic trials for pediatric NAFLD have been conducted. Despite promising results from studies with rodents (using oligo‐fructose or lactulose), clinical trials for pediatric NAFLD/NASH with prebiotics have not been carried out yet. A few encouraging interventions with probiotics in children with liver disease have been completed (see above). However, longer trials with larger sample sizes are necessary to confirm these results and possibly demonstrate robust improvement of both liver steatosis and ALT levels in pediatric NAFLD before routine use can be recommended.

Figure 2.

Simplified model of intestinal Stages in the development of nonalcoholic fatty liver disease (NAFLD) and ways probiotics can intervene. Adverse environmental, metabolic and genetic factors such as diet rich in fat or fructose can cause intestinal dysbiosis with reduction of beneficial bacteria and increase of deleterious bacteria. Dysbiosis results in increased intestinal permeability, or “leaky gut”, by disruption of tight junction proteins such as zonula occludens‐1 and occludin. Associated metabolic changes in the bacteria lead to ‐ amongst others ‐ depletion of choline (which is metabolized to trimethylamine [TMA]), and production of ethanol (EtOH). EtOH and microbial products, e.g. lipopolysaccharides (LPS), translocate from the intestine into the blood circulation and travel to the liver. In the liver, choline deficiency promotes steatosis, and EtOH and LPS cause more liver inflammation and finally NAFLD/nonalcoholic steatohepatitis (NASH). Probiotics (living non‐pathogenic microorganisms such as Lactobacilli and Bifidobacteria that have a favorable impact on the host) work on several levels. They attenuate intestinal dysbiosis and metabolic changes, and ameliorate the “leaky gut” by preventing inflammation and apoptosis of the enterocytes, and by inducing tight junction proteins. Probiotics thereby decrease translocation of bacterial products and metabolites into the blood stream, which eventually alleviates liver injury. Abbreviations: EtOH, ethanol; LPS, lipopolysaccharide; NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohepatitis; TMA, trimethylamine.

In conclusion, lifestyle intervention including diet and physical exercise regimens remains the most important intervention for NAFLD for now. However, our understanding of the role of the intestinal microbiome in the development of NAFLD/NASH is evolving and supports a potential role of probiotics and possibly prebiotics in pediatric NAFLD/NASH, also in light of a favorable side effect profile.