Non-alcoholic Fatty Liver Disease (NAFLD) Management in the Community

1. Introduction

As type 2 diabetes (T2D) increases the concentration of glucose in the blood of adult population, kidney and nerve damage as well as retinal complications will naturally ensue as its consequences. It can also cause serious cardiovascular complications (CVDs) such as peripheral vascular disease, stroke, angina, and /or myocardial infarction. In the long run, these all contributes to increase mortality and morbidity of diabetes patients and reduces their life expectancy. It was not until 1960, along with rapid modernization as well as social and economic growth with improved medical utilization patterns, the number of diabetes patients was found to increase explosively. From the epidemiological data implemented in Yonchon, Gyonggi-do in 1990, we now know 8 out of 100 adults in Korea have diabetes [1]. Consecutive follow up study, performed 2 years later at the same location proved that diabetes condition is expected to increase in the future [2]. Therefore, proper management plan in the community level should be employed knowing that diabetes is an important health issue in Korea.

Non-alcoholic fatty liver disease (NAFLD), which commonly co-associate with T2D, which has not been counted as an important bad companion yet, is also a chronic metabolic disease that reduces quality of life of the patients with T2D in the community [3]. NAFLD is the liver component of a cluster of conditions that are associated with metabolic syndrome (MS). NAFLD is known to have a bidirectional association with components of MS [4]. Although Koreans have a higher fraction of NAFLD patients who are lean, their illness has the same prognosis or worse than those who are obese. It is a disease with increased phlegm which is common in the community, especially in Korea [5]. Over the past four decades, NAFLD has become the most common chronic liver disorder (with a global prevalence of around 25% of the adult population) [4]. As around 10% of people with NAFLD develop liver-related complications, a crucial challenge is to identify those who are at the highest risk for these complications among the people affected by NAFLD. Due to its high prevalence, NAFLD is now the most rapidly increasing cause of liver-related morbidity and mortality and is emerging as an important cause of end-stage liver disease, hepatocellular carcinoma, and liver transplantation with higher medical costs [4,6,7,8]. Gradually, nonalcoholic steato-hepatitis (NASH) and cirrhosis have also emerged as causes for increased health care costs. Among community inhabitants of age 30s to 50s, the overall death rate due to chronic liver diseases, excluding hepatocellular carcinoma ranks 2nd to 4th in Korea [5]. Therefore, NAFLD is fathomed as a very important threat to the health of our people and regarded as emerging big health problems. The number of patients with NAFLD is very high, and so is the mortality rate due to its complications because of the expensive health costs. Despite the growing concern, NAFLD is underappreciated as an important chronic disease, and there are few national strategies or policies for NAFLD [5].

NAFLD is defined by the presence of steatosis in more than 5% of hepatocytes in association with metabolic risk factors (particularly, obesity and T2D) and in the absence of excessive alcohol consumption or other chronic liver diseases [7,9]. NAFLD is a diagnosis of exclusion and there is a debate about the limitations of this term. In 2020, an international panel of experts proposed the concept of metabolic dysfunction-associated fatty liver disease (MAFLD) to highlight the contribution of cardiometabolic risk factors to the development and progression of liver disease [10]. NAFLD encompasses a disease continuum that includes steatosis with or without mild inflammation and a necroinflammatory subtype (NASH), which is additionally characterized by the presence of hepatocellular injury (hepatocyte ballooning). However, the prime pathogenesis of disease can vary substantially among patients with NAFLD, which could be crucial hurdles to be managed appropriately in the community. Furthermore, disease progression and response to treatment are heterogeneous. Information about disease activity and, in particular, the extent of liver fibrosis is necessary to assess the severity of liver disease and provide prognostic information. Growing knowledge from metabolomics, genomics, and other areas will enable disease phenotyping and facilitate potential disease stratification in the future.

Diabetes and NAFLD is known to be the conditions often coexist in the community. Research on the cause and clinical significance of this correlation is rare. Generally, as the content of liver fat increases, the chances of lipid oxidation also increases accordingly. It has been known that in the circumstances of increased whole body lipid oxidation, the levels of endogenous glucose production increase and those of glucose disposal decrease [11]. Excess lipids might also induce glucose intolerance through an inhibitory effect on glucose storage [12]. According to one report of calorimetric experiment, in severe NAFLD patients, a more dramatic decrease in insulin-mediated suppression of whole-body lipid oxidation implicating deepened IR, which results in a less decrease in blood β-hydroxy butyrates (ketones) was observed [13]. Likewise, more marked decrease in insulin-mediated suppression of glycerol production was also found in severe NAFLD. Therefore, lesser degree of insulin-mediated suppression of glucose production as a whole occurs as the level of plasma nonesterified fatty acids (FA) increases, which might be fathomed as a primary driver of NAFLD.

In around half of people with cirrhosis, a devastating complication of NAFLD, therefore, abnormalities in glucose tolerance are observed. According to one report, 15-20% of liver cirrhosis newly develop diabetes over 5 years [5]. Detection of T2D among patients with NAFLD or NASH is important in part because improved glycemic control may improve NAFLD. Although there is no difference in the short-term prognosis between cirrhosis patients with and without diabetes, patients with diabetes have a more poor long-term prognosis. It is known that liver failure occurs frequently in patients with diabetes. Importantly, advanced liver fibrosis should be counted as a key prognostic marker for liver-related outcomes and can be assessed with combinations of non-invasive tests in the community. In the present review, we would first like to present a overviewing synopsis explaining pathogenesis, pathways of NAFLD progression, diagnostic modalities and assessing methods of disease severity, especially when combined with fibrosis. Then, we extend our discussion on viable prevention and management strategies in the community. Ultimately, we would like to appreciate NAFLD as an important chronic disease and suggest some strategies or policies to overcome it on a community level.

2. Pathogenesis in General

The principal mechanism for NAFLD development is overnutrition, which causes not only expansion of adipose tissue but also accumulation of ectopic fat in the liver. Meanwhile, macrophage infiltration of the visceral adipose tissue creates a proinflammatory state that promotes IR [14]. Inappropriate lipolysis under the influence of IR results in unabated delivery of fatty acids to the liver, which, along with increased de-novo lipogenesis (DNL), overwhelms its metabolic capacity. The imbalance in lipid metabolism leads to the formation of lipotoxic lipids that contribute to cellular stress (oxidative stress (OS) and endoplasmic reticulum (ER) stress), inflammasome activation and apoptotic cell death, and stimulation of inflammation, tissue regeneration, and fibrogenesis [7,15,16]. Inflammatory and profibrogenic macrophages are implicated in the progression of liver fibrosis and might also have a role in chronic inflammatory processes in other tissues as well [17] (Figure 1).

These pathogenic pathways of NAFLD are influenced by multiple metabolic, genetic, and microbiome-related factors that are not understood completely yet. NAFLD has a heritable component with variable penetrance estimates by 20–70% [7]. A single-nucleotide polymorphism (SNP) in the patatin-like phospholipase domain–containing 3 (PNPLA3) gene is the best characterized genetic variant associated with susceptibility to NAFLD, the importance of which have not yet been assessed properly in the Korean community. Moreover, all of known genetic variants account for a small proportion (10–20%) of overall heritability, although this proportion varies across populations. These genes might influence multiple traits such as those related with IR with divergent effects on NAFLD and cardiovascular comorbidities. Several genetic risk variants of NAFLD show a synergistic interaction with those of obesity. In addition, crosstalk between the liver and other organs (particularly, adipose tissue and the gut) via FGF19 and FGF21 might also contribute to metabolic dysregulation and inflammation in NAFLD [18,19,20,21,22] (Figure 1). Alterations in gut microbiota are seen in patients with NAFLD and some data suggest that there is a fecal-microbiome signature associated with advanced fibrosis [23,24]. However, confirmation of these bacterial signatures in different geographical regions controlling for environmental factors is required to determine their clinical significance and use for diagnostic purposes.

3. Molecular Pathways of NAFLD Progression

In around 15% of NAFLD patients, simple steatosis can evolve into NASH, a mixture of inflammation, hepatocellular injury, and fibrosis, often culminating in cirrhosis and even hepatocellular cancer [25]. Although the precise molecular mechanism underlying NAFLD progression is not completely understood, its pathogenesis on the whole has been assumed by the ‘double-hit hypothesis’ [26]. The first hit includes lipid accumulation in the liver, followed by a second hit in which proinflammatory mediators induce inflammation, hepatocellular injury, and fibrosis. Nowadays, a more complex model assumed by ‘multiple parallel hits hypothesis’ suggest that FAs and their metabolites might be truly lipotoxic and they might contribute to NAFLD progression [27,28]. It is certain that in NAFLD patients, IR leads to hepatic steatosis via multiple mechanisms [29]. Not only DNL is increased, but FAs are also taken up into liver excessively from the serum. Furthermore, a decrease in mitochondrial FA oxidation and secretion of very-low-density lipoproteins (VLDL) has been reported. It turns out that triglyceride (TG) accumulation in the cytoplasm of hepatocytes, as the hallmark of NAFLD, arises from an imbalance between lipid acquisition (FA uptake and DNL) and removal (mitochondrial FA oxidation and export) and accompanies multiple pathophysiological mechanisms in NASH [26].

The first process called DNL includes de novo synthesis of FAs through a continuing process of polymerization in the hepatocyte in which glucose is converted to acetyl-CoA by glycolysis and the oxidation of pyruvate in the beginning. Then, acetyl-CoA carboxylase (ACC1) converts acetyl-CoA into malonyl-CoA. Finally, FA synthase (FAS) catalyzes the formation of palmitic acid from malonyl-CoA and acetyl-CoA. Depending on the metabolic needs, FAs are then processed to TGs and stored or rapidly metabolized. On the whole, the rate of DNL is regulated primarily at the transcriptional level. Several nuclear transcription factors such as liver X receptor α (LXRα), sterol regulatory element-binding protein 1c (SREBP1c), carbohydrate-responsive element-binding protein (ChREBP), farnesoid X receptor (FXR), and several enzymes (ACC1, FAS, and steroyl CoA desaturase 1 (SCD1)) are involved. After the ingestion of meals, as plasma glucose and insulin levels rise, activation of lipogenesis through the activation of ChREBP and SREBP1c is promoted, respectively [26]. In humans, NAFLD has been associated with increased hepatic expression of several genes involved in DNL [26,30].

Oxidation of FAs occurs in the mitochondria, peroxisomes and the ER. It facilitates the degradation of activated FAs to acetyl-CoA. Activated long chain fatty acids (LCFAs) are shuttled across the membrane via carnitine palmitoyltransferase-1 (CPT1). Malonyl-CoA, an important intermediate of DNL, is an inhibitor of CPT1. In FA overload condition such as NAFLD and diabetes as well, cytochrome P450 (CYP4A)-dependent ω-oxidation of LCFAs occurs in the ER and induces ROS and lipid peroxidation. During the process of β-oxidation, electrons are indirectly donated to the electron transport chain (ETC) to drive ATP synthesis. Acetyl-CoA can be further processed via the tricarboxylic acid (TCA) cycle, or in the case of FA abundance, be converted into ketones. PPARα and insulin signaling are involved in the regulation of FA oxidation and the formation of ketones. In the liver, PPARα plays a pivotal role in FA metabolism by upregulating the expression of numerous genes involved in mitochondrial and peroxisome FA oxidation [30,31]. Therefore, activation of PPARα might prevent and decrease hepatic fat storage.

4. Diagnosis and Assessment of Disease Severity

NAFLD is frequently diagnosed by imaging, although it can be implicated from clinical risk scores such as fatty liver index (FLI) or identified histologically. In routine practice, the most commonly used test is abdominal ultrasonography (US) [32,33]. However, abdominal US has two important limitations: insensitivity and misdiagnosis. Advanced fibrosis can coarsen hepatic echotexture and blur vascular pattern and may lead to misdiagnosis. The sensitivity of US is low when steatosis is mild (< 30%). Instead, MRI-based measurements of hepatic steatosis can detect as little as 5% fat and are sensitive to dynamic change, but are often used in the research setting rather than in routine clinical practice in the community.

Detection of T2D among patients with NAFLD or NASH is important because improved glycemic control may improve NAFLD. NAFLD patients with T2D is associated with a more than 2 times increased risk of advanced fibrosis, cirrhosis-related complications, and liver disease mortality [7]. Obesity, dyslipidemia and hypertension are also associated with an increased risk of severe liver disease, although the effect sizes are smaller than for T2D [34,35]. Therefore, numbers of components of MS involved should be counted at first visit and could be used as an important prognostic information of NAFLD assessed easily in the routine care of NAFLD (Figure 2). Patients with NAFLD who are older than 65 years also have a higher prevalence of advanced fibrosis. A variant of the PNPLA3 gene encoding adiponutrin may be associated with NAFLD histological severity and development of hepatocellular carcinoma as well as liver-related and all-cause mortality. Recently, the PNPLA3 genotypes in addition to diabetes status were found to identify patients at a higher risk of cirrhosis among those at an indeterminate risk of NAFLD in two Caucasian cohorts [36], the clinical role of which has not been reproduced in a Korean biopsy-proven NAFLD cohort [37].

5. Non-Invasive Tests of Disease Severity

Liver enzymes (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)) may be a first-step to assess and monitor patients with liver diseases. However, serum liver enzyme concentrations can be normal in more than half of patients with NAFLD, and correlate poorly with the histological severity [38]. Traditionally, liver biopsy was used to characterize and quantify histological features of steatosis, inflammation, hepatocyte ballooning, and fibrosis. However, this invasive procedure is not suitable for widespread use to assess progression or response to therapy in the community. In addition to its risk and cost, liver biopsy is prone to sampling bias. Moreover, subjective variability in histological assessment is also documented. As fibrosis has consistently emerged as the most crucial histologic feature predicting clinical events, instead, researchers have developed several non-invasive tests estimating fibrosis. Simple fibrosis scores, such as the NAFLD fibrosis score (NFS), Fibrosis-4 (FIB-4) index and AST-to-platelet ratio index (APRI) composed of demographic, clinical, and routine laboratory parameters have been developed and are ready to be applied in the community. These are inexpensive to use and can be applied easily in the Korean community [39,40]. Although the overall sensitivity of these scores is assumed not to be high, they have high negative predictive values to exclude advanced liver fibrosis. Patients with low fibrosis scores are also at a low risk of developing liver-related complications.

Another way to estimate liver fibrosis in patients with NAFLD is to measure liver stiffness by US-based and MR elastography [41]. Transient elastography (Fibro-scan) has been most extensively evaluated, is widely available, and therefore, can be used in the community. It is also possible to estimate hepatic steatosis by controlled attenuation parameter measurement at the same time. The liver stiffness measurement (LSM) also correlates with future risk of hepatocellular carcinoma and cirrhotic complications.

In the community, we may start with inexpensive simple fibrosis scores (NFS or FIB-4) as a first step to identify individuals at low risk of advanced fibrosis who can be managed in the community. Numbers of components of MS involved could be another prognostic marker of NAFLD assessed easily in the routine care in the community. Individuals with high risk of advanced fibrosis require additional assessment with Fibro-scan, or might require referral to university hospitals (secondary care) for investigation of liver disease or management of advanced fibrosis. Patients without advanced fibrosis at initial assessment might require ongoing monitoring to identify progressive liver disease and retesting 3 years after initial assessment (Figure 2) [42].

6. Comorbid Conditions

Although the risk of liver disease progression is extensive, the main cause of death in patients with NAFLD is CVDs, followed by extrahepatic malignancy such as colorectal or breast cancer [7,25]. These might be resulted from increased cardiometabolic risk factors that are shared in NAFLD and CVDs. However, it is not known to what extent NAFLD has a direct causative role in the development of CVDs. In addition to the characteristic proatherogenic lipid profile, the bidirectional relationship between NAFLD and some MS features (T2D and hypertension) is one mechanism by which NAFLD might augment cardiovascular risk [43,44]. Patients with NAFLD have a 1.9 times higher risk of incident cancers than the general population, particularly cancers involving the liver, gastrointestinal tract and uterus [45]. It might be driven by the association of NAFLD with visceral adiposity and chronic low-grade inflammation, but this mechanism has not yet been determined.

7. Prevention & Management of NAFLD

Along with new strategies in the diagnosis, risk stratification, and management of NAFLD, a few studies have succeeded in evaluating primary prevention of NAFLD, which can be organized and managed easily in the community. It turns out that improved diet quality [46] and sustained physical activity [47] reduced the risk of developing NAFLD, even among individuals with high genetic risk. As a first start, clinicians can manage to implement comprehensive programs to promote and coordinate lifestyle interventions with dietary modification and exercise, accompanied by management of metabolic comorbidities. The team approaches to fulfil these activities can be easily organized and accessed in the community level via the holistic medicine pursuing multidisciplinay approach. Having various non-invasive tests to diagnose NAFLD and liver fibrosis at hand, to screen for NAFLD and NAFLD with fibrosis can be amenable, particularly when patients participate in secondary prevention programs for T2D or MS. However, data are inconsistent, partly reflecting the paucity of available effective therapeutic interventional measures [48]. Irrespective of the possibilities of over-diagnosing NAFLD, once NAFLD is diagnosed applying simple clinical indices or abdominal US in the community, practitioners recommend risk stratification by assessing for the presence of advanced fibrosis or cirrhosis, and the evaluation of cardiovascular risk and comorbid illnesses (Figure 2).

It is certain that those patients with T2D have a high prevalence of NAFLD (40–70%), and are more likely to develop advanced fibrosis, cirrhosis, and hepatocellular carcinoma [49]. Multi-morbidity and polypharmacy are commonly found in patients with T2D and NAFLD in several community hospitals of Korea, highlighting a need for multidisciplinary management to address the complicated health care needs [50]. In university diabetes clinics, the prevalence of advanced fibrosis among patients with NAFLD is around 2 ~ 4 times higher than in the community [51,52]. Because of the increasing need to assess NAFLD and liver fibrosis that should be incorporated into the routine care of patients with T2D, the American Diabetes Association now recommends that “Patients with T2D and elevated liver enzymes (ALT) or fatty liver on US should be evaluated for the presence of NASH and liver fibrosis [53].” However, since ALT measurements are inaccurate and are within the normal range in most people with T2D and NAFLD, many patients with clinically significant liver disease will not be diagnosed. Alternatively, we can rephrase them into a better recommendation implicating that “Patients with T2D with elevated FLI or fatty liver on US should be evaluated for the presence of NASH and liver fibrosis applying simple fibrosis scores.”

8. Management of NAFLD in the Community

Although the liver related burden of NASH is substantial and increasing, CVDs and malignancy are the leading causes of death in people with NAFLD [4,43,44,45,51]. Therefore, management of NASH deserves to stick to a holistic approach that strives to minimize CV risk and to reduce inducers of steatosis and systemic inflammation. Central obesity is an important driver of disease through the promotion of IR and proinflammatory signaling. Although the nutrient content and proportion of the fat in diet is important, weight loss inducing more than 5–7% of present body weight reduces hepatic fat content and NASH, while weight loss in excess of 10% brings about even fibrosis reduction in a large proportion of people, irrespective of method of weight loss [54]. However, sustained weight loss is challenging because it requires a transformation of behavior patterns. It is difficult to adhere to calorie restriction (CR), the most crucial step for weight loss, because calorie intake must be carefully monitored every day. Ultimate success requires substantial commitment in addition to clear and solid recommendations and support from the treatment team, which might be organized at the community level. Important hurdles to weight loss such as medical comorbidities, low education levels, and little access to healthy food should be considered when developing a treatment plan. While CR is a conventional recommendation to help people with NAFLD achieve their weight reduction goals, another optional approach that limits the timing of food intake has recently been introduced. Time-restricted eating may be an attractive alternative to CR for weight loss in patients with T2D as well as in NAFLD and can be utilized easily in the community [55,56]. Alternatively, despite surgical risk, bariatric surgery in NAFLD patients with severe obesity can lead to substantial (15–25%), durable weight reduction and improvement in liver histological features of NASH and fibrosis [57]. Weight loss improves NAFLD and all of cardio-metabolic comorbidities, which then favorably affects cardiovascular and malignancy related risk. There is an independent contribution of NASH to cardiovascular and cancer risk but we do not know yet if liver targeted treatment interventions will reduce them.

9. Optimizing Management with Existing Therapeutics

Irrespective of numerous researches and activities to treat NAFLD, there is only one FDA approved therapy for NASH until now. A combination of conservative treatment (lifestyle adjustments, increasing physical activity and smoking/ alcohol cessation) appears to be beneficial. Intriguingly, several drugs that are available for other indications have been studied for NAFLD treatment (Table 1). Similar to the experiences with several hepatotonics, ursodeoxycholic acid, ω-3 fatty acids and metformin have not shown any histological benefit. Metformin, an important diabetic treatment medicine relieving IR has no effect on NASH disease activity [58]. Vitamin E and pioglitazone have been endorsed by current guidelines as possible treatment in patients with NASH [59,60,62,63]. The benefits of vitamin E for NASH have been proved in several studies of patients without diabetes or cirrhosis. In a trial of patients with T2D and NASH, combination therapy of vitamin E with pioglitazone achieved improvement of NASH without worsening of fibrosis [62]. Nonetheless, vitamin E can only be used taking potential adverse effects (increased risk of bleeding and adverse cardiovascular outcomes in higher doses) into account. Although statins have no discernible histological benefit on NASH, they should be used for cardiovascular risk reduction.

Thiazolidinediones (TZDs), to which pioglitazone belong, activate PPARγ in adipose tissue and has been proposed to promote differentiation of adipocytes and storage of fat in adipose tissue, protecting peripheral tissues from lipotoxicity [73]. Fortunately, all TZDs are highly effective in improving NAFLD outcomes. Multiple trials in NASH patients with and without diabetes have shown that pioglitazone improves NASH activity with a some improvement in fibrosis [73,74]. Weight gain and the risk of bone loss are side effects. Accordingly, it appears unlikely that either vitamin E or pioglitazone will be studied in phase 3 studies. Alternatively, other drugs that modulate PPAR-γ and complementary mechanisms are being developed. GLP-1 receptor agonists [65,66,75,76] and SGLT2 inhibitors [66,77,78], antidiabetic medications that are cardioprotective and renoprotective are currently being studied in several trials to assess their efficacy in NASH resolution and improvement in fibrosis. These drugs have additional benefit of inducing weight loss. Several GLP-1 receptor agonists are being evaluated for the treatment of NASH with some success. In a phase 2 trial, s.c. semaglutide 0.4 mg daily proved NASH resolution without worsening of fibrosis [64]. Although it is difficult to discern if this effect is independent of weight loss, it shows the highest rate of NASH resolution ever reported in NASH therapeutic trials [77,78]. Interestingly, in a recent Korean study of T2D with NAFLD, SGLT2 inhibitors shows a higher NAFLD regression and lower adverse liver-related outcomes compared with other oral anti-diabetic drugs including TZDs [79].

10. Emerging Therapeutics of NASH

Numerous drugs of NASH treatment with different mechanisms of action, aiming to target lipid metabolism, inflammatory, or fibrotic pathways, are in development [80] (Figure 1). Trials utilizing potent FXR agonist has proven favorable results [67,81,82]. A trial of obeticholic acid [81] was implemented as the first phase 3 trial to prove an improvement in fibrosis without worsening of NASH, confirming the findings of the previous phase 2 trial [67,82]. However, the magnitude of response was modest, suggesting that combination therapy will be required to treat the majority of patients adequately. Although obeticholic acid failed to achieve complete NASH resolution, it did improve individual histological features. However, pruritus and increase in LDL concentration are side effects of obeticholic acid. Recently, the selective thyroid hormone receptor β (THR-β) agonists are found to be effective in the treatment of NAFLD [69,70], and approved by FDA. In addition, irrespective of multiple failures caused by disease heterogeneity, several other drugs are in advanced stages of development for NASH [68,71,72]. However, future treatment will require combination therapy since the modest effect and potential side effects in higher doses of these drugs. Several combination trials are also now underway. The ATLAS trial showed an improvement in fibrosis with cilofexor (a FXR agonist) and firsocostat (a ACC inhibitor) in patients with NASH and fibrosis [83]. Patients receiving this combination were more likely to have better improvement in the NAFLD activity score than those receiving monotherapy. Given the modest difference, more effective combinations will be needed.

11. MiRNA Targeting for NAFLD

NAFLD is associated with thorough reprogramming of hepatic metabolism. Research indicates that various metabolic pathways deregulated in NAFLD converge in the aberrant accumulation of lipids into hepatocytes. In recent years, microRNAs (miRs) have been proposed to halt the development and progression of NAFLD as alterations of epigenetic mechanisms may contribute to these hepatic metabolic changes [84]. As elevated glucose levels can lead to increased DNL, miR-dependent alterations of hepatic glycolysis, gluconeogenesis and glycogen metabolism are key pathological mechanisms contributing to NAFLD development. In addition, deregulated cellular processes, such as autophagy or ER stress and the UPR were also implicated in steatosis and shown to be under the control of several miRs. However, to develop an efficient miR-based therapeutic strategy, targeting common key transcription factors involved in hepatic glucose and lipid metabolism would be important to have a broader systemic effect on NAFLD [85]. MiR-192 and miR-29, which are both deregulated in the liver of patients with NAFLD, were reported to target SREBP1, while ChREBP is regulated by miR-1322 in hepatocytes. LXR, which can regulate the activity of both SREBP1 and ChREBP, was also found to be targeted by several miRs (miR-1, miR-155, miR-206 and miR-613). PPARγ, a lipogenic transcription factor, was found to be regulated by miR-27a, miR-34a, miR-128 and miR130. In addition, PPARγ is also involved in hepatic stellate cells activation repression, thereby negatively regulating hepatic fibrosis. MiR-696 and miR-130a are targeting its cofactor, PGC1α, while miR-16 and miR-100 are acting on its repressor, NCOR. Another strategy to alleviate steatosis in the liver is to activate lipid oxidation by derepressing expression of PPARα. PPARα was shown to be targeted by miR-9, miR-10b, miR-21, miR-33 and miR-199a. However, as all these transcription factors or cofactors are provisional potential targets to be regulated, which have been examined only in some cell lines and/ or in animal models, their real influence in NAFLD development and progression in man have not yet been determined.

12. Therapeutic Potential of a New Antioxidant Protein Delivery in NAFLD

Though diabetes and/ or NAFLD progression commonly associate with increased OS, only vitamin E, an important antioxidant, but not other antioxidants have been shown to improve the histology of NAFLD. These inconsistent effects of antioxidants might be resulted from diverse factors such as difficulty in maintaining a consistent circulating antioxidant level, inadequate tissue distribution, and lack of suitable exogenous antioxidants. Therapeutic antioxidants should be given in appropriate cellular concentration enough to tackle newly generating ROS levels without significant toxicity [86]. Therefore, a different way of delivering medicines having antioxidant properties has been studied [87]. If antioxidant in general are to improve the pathophysiology in various stages of NAFLD, steady delivery at required concentrations into the cells or into the cellular compartment where generates ROS would be most important. A strategy to induce an endogenous and nonspecific antioxidant or to deliver it in a more efficient way could be a more attractive approach. As NAFLD progression might be resulted from OS in mitochondria, ER and others (especially in hepatocyte as well as stellate cells) due to lipotoxicity, hypoxia and AGE accumulation, endogenous nonspecific antioxidant treatment may improve tissue repair in various stages of NAFLD. Therefore, nonspecific antioxidants such as metallothionein (MT), SOD and catalase have been exploited to combat increased ROS in various tissues applying intracellular delivery [86,87,88,89,90]. Taking advantage of the recently developed cell-penetrating peptide technologies, each of these antioxidants and their combination inhibited various OS and had the potential to protect cells and tissues against NAFLD progression as well as diabetes and its complications due to its anti-apoptotic and anti-oxidant effects either in vitro or in vivo [90]. Tat-MT and Tat-SOD given in combination intraperitoneally at regular interval were protective against various injuries and protected against steatosis as well as inflammatory condition in OLETF rats (unpublished data). This result is reminiscent of similar delay in development of NASH by vitamin E.

13. Challenges and Prospects

Although progress has been made during the past decades in investigating the natural history and underlying biology of NAFLD, there are still many areas of challenges and obstacles. NAFLD at large and NASH in particular are poorly understood and recognized by health care professionals working in the community, especially in Korea. Implementation of appropriate strategies to identify and manage at-risk patients of NAFLD with advanced fibrosis will ask for timely action by clinicians in community care, diabetes clinics, and other specialists who treat patients with metabolic risk factors. There is an increasing need for the awareness of a multi-pronged public health approaches to cope with increased NAFLD risk factors in rapidly modernizing community. When we consider liver fibrosis, a key prognostic marker for liver-related outcomes can be assessed with combinations of non-invasive tests in the routine care of the patients in the community, these challenges can be overcome irrespective of the obesogenic environment. In addition, there should be several obstacles to develop highly effective therapeutic measures of intervention. One of the most important challenges in the community hospital is a long-term necessity of liver biopsy for diagnosis and follow-up. Although reliable biomarkers that can accurately diagnose and stage NAFLD across the entire disease spectrum does not yet exist, a diagnostic biomarker, in conjunction with a prognostic biomarker, would allow the identification of high-risk individuals on whom resources should be concentrated. A second challenge is the substantial heterogeneity of NAFLD and the current limited understanding of disease phenotypes. The ability to phenotype patients would permit more accurate prognostication, selection of appropriate therapy, and prediction of treatment response than is currently possible. Lastly, the refinement of therapeutic strategies into thoughtful combination approaches, tailored to the patient’s individual disease inducers, are needed for increased response rates and a change in our attitude to screening. Finally, regardless of the progress that has been, or will be, made in diagnostic tests and drug treatments, healthy lifestyle and weight reduction remains crucial for the prevention and treatment of NAFLD, as obesity is the main driver of this common liver disease and its associated metabolic comorbidities.