**3. Key factors involved in the progression of NAFLD**

#### **3.1 Lipid accumulation and insulin resistance**

Triglyceride accumulation in hepatocytes is a significant factor in the development of NAFLD. Glycerol and fatty acids undergo esterification to form triglycerides (TGs), which are usually stored or secreted. The fate of the fatty acids is to either undergo esterification or enter the β-oxidation pathway. Under normal conditions, TGs are not toxic; where they maintain free fatty acids [10]. Studies have shown increased de-novo lipogenesis and expression of transcription factors such as sterol regulatory element binding protein-1c (SREBP-1c), carbohydrate response element-binding protein (ChREBP) and peroxisome proliferator-activated receptor-γ (PPAR-γ) in NAFLD [11]. Insulin resistance is another critical factor in NAFLD that drive the activation of de-novo lipogenesis. Insulin receptor substrate-2 (IRS-2) is known to regulate SREBP-1c negatively. Insulin resistance also lead to decreased oxidation of free fatty acids; hence fat accumulate in the hepatocytes. Free fatty acids in hepatocytes also inhibit the insulin signaling through the serine-kinase pathway leading to insulin resistance [12]. Accumulation of fat in the liver also contribute to stress and dysfunction to mitochondria and endoplasmic reticulum (ER). Dysfunctional mitochondria lead to increased reactive oxygen species (ROS) generation and activation of inflammatory pathways leading to hepatic necro-inflammation and further damage of mitochondria (**Figure 1**) [13].

#### **3.2 Cytokines**

Studies have shown the involment of cytokines during liver inflammation, liver fibrosis, liver regeneration and hepatocyte apoptosis [14]. In obese individuals, adipose tissue is enlarged and release various adipokines, which further recruit macrophages resulting in the secretion of pro-inflammatory adipokines [15]. Increased leptin levels play a crucial role in NAFLD progression by inducing insulin resistance and steatosis development [16]. Adiponectin, an anti-inflammatory adipokine secreted exclusively by the adipocytes, plays a protective role in the liver by preventing lipid accumulation through enhanced β-oxidation of free fatty acids [17]. Lipid accumulation, insulin resistance, mitochondrial stress, ER stress

*Functional Foods for the Management of Non-Alcoholic Fatty Liver Disease DOI: http://dx.doi.org/10.5772/intechopen.96317*

and fatty dysfunction have contributed to the generation of pro-inflammatory cytokines. c-Jun N-terminal kinase/activator protein 1 (JNK/AP-1), tumor necrosis factor-α (TNF-α) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) are some of the crucial players in the development of inflammation in NAFLD. JNK pathway lead to apoptosis and progression of NAFL to NASH. NF-κB activation lead to chronic hepatocyte inflammation and insulin resistance [18].

#### **3.3 Genetic, epigenetic and dietary factors**

Gene mutations like single nucleotide polymorphisms (SNPs) influence the free fatty acids secreted from hepatocytes to release cytokines, further stimulating NAFLD progression [19]. An example of SNP that affect NAFLD progression is the patatin-like phospholipase 3 (PNPLA3) gene. Lipid accumulation in hepatocytes of a PNPLA3 gene mutant carrier is associated with lower lipoprotein secretion, which is rich in liver TGs [20]. Pirazzi et al. (2012) showed that humans with PNPLA3 mutation exhibited increased steatosis and fibrosis. Transmembrane 6 superfamily member 2 (TM6SF2) mutation is also associated with NAFLD [21]. Wild type TM6SF2 protein promote VLDL secretion, while its variant is associated with hepatic steatosis caused by lower VLDL secretion and high ALT levels [22].

Epigenetic modifications generally occur at the transcriptional levels, such as DNA methylation, histone modifications and microRNA (miRNA) expression. Studies have shown that aberration in epigenetics is known to increase susceptibility to NAFLD [23]. DNA methylation has a crucial epigenetic determinant in NAFLD progression, which is influenced by dietary methyl donor deficiency. Betaine, choline and folate are common methyl donors [24]. Sirtuins (SIRTs) are a group of proteins with deacetylase activity mainly involved in epigenetic modification. SIRTs have been implicated in regulating proteins involved in metabolic processes like lipid metabolism, oxidative stress, glucose metabolism and inflammatory pathways. Research findings in animal and human models showed that NAFLD is associated with lowered SIRT1 levels [25]. Recent studies demonstrated the association between miRNA levels and NAFLD pathogenesis. Krützfeldt et al. (2005) showed inhibition of miRNA-122 led to decreased plasma cholesterol levels and reduced expression of genes involved in hepatic cholesterol and fatty acid synthesis [26].

The pathogenesis of NAFLD is also dependent on dietary factors. The quantity of calorie intake and the diet's quality concerning nutrients decide a healthy diet. Diet rich in fructose is associated with NAFLD. Fructose is a lipogenic dietary factor with pro-inflammatory activity, causing oxidative stress and increased expression of TNF-α. Studies demonstrated that fructose intake in patients with NAFLD leads to increased fibrosis [27]. Diet rich in mono-unsaturated fatty acids showed protective effects by improving steatosis and insulin resistance in NAFLD patients [28]. Studies conducted in ob/ob mice showed less steatosis and lowered liver enzyme levels upon a moderate alcohol administration level [29].

#### **3.4 Gut microbiota**

Recent studies showed the involvement of the gut-liver axis in the pathogenesis of NAFLD [30]. Bacterial toxins like lipopolysaccharides (LPS) are the potent toxins released by gut bacteria. LPS activate inflammatory response by activating stressactivated protein kinase, JNK, p38 affecting insulin resistance, obesity, hepatic fat accumulation and NASH development [31]. Patients with NAFLD have increased gut permeability and higher bacterial growth than normal subjects [32].

### **4. Functional foods for NAFLD**

Human history's survival has always been highly reliant on food to avoid or battle the diseases. Hippocrates, the renowned physician, quoted, "Let food be thy medicine and medicine be thy food." Functional foods should not contradict the scientific advancements made to treat degenerative diseases over the last two centuries. Due to modern nomadic lifestyle and the shift in natural resources, traditional agricultural practices and dietary habits are not standard in this decade. Anti-NAFLD compounds, in general, must be discerning and innocuous. They should look at molecular and metabolic levels to reduce fat deposition in the liver. Flavones such as quercetin, hesperetin from onions and citrus fruits were shown to reduce fatty acid deposition in the liver. Anti-NAFLD compounds' mechanism must be reversible in the event NAFLD needs, for example, to promote the tissue darning subsequent injury. Most food-derived compounds show reversible activity [33]. The flavonoid, naringenin dose-dependently and reversibly inhibited transforming growth factor-β (TGF-β) and vascular endothelial growth factor (VEGF), thereby modulated the fatty acid oxidation and trafficking dependent liver inflammation [34].

Pre-clinical and clinical models have proven their worth to test natural compounds for anti-NAFLD activities. Many anti-NAFLD compounds such as flavones, anthraquinones, stilbenes, naphthols and polysaccharides showed potency at cellular levels, phase I and II clinical trials [35]. Epidemiological studies illustrated that populations gobble such bioactive substances have low disability rates as their main diets. Since these compounds are food endogenous, the fortifying meal is a relatively cheap way of delivering them throughout a lifetime, as many people tend to forget pills over long periods. It was suggested that the use of non-alcoholic steatohepatitis inhibitors might not prove relevant, as these inhibitors may be more efficient against the progression of disease at an early stage as comparing when a metastatic illness has progressed to advanced stages [36]. Meanwhile, the onset or evolution of the process of non-alcoholic steatohepatitis and cirrhosis generally take months or years; continual intake of anti-NAFLD compounds might be the ultimate approach to inhibit NAFLD-related molecular and metabolic stimulators chronically.

#### *Functional Foods for the Management of Non-Alcoholic Fatty Liver Disease DOI: http://dx.doi.org/10.5772/intechopen.96317*

Most NAFLD inhibitors of diet can inversely inactivate more than one stimulator of fatty liver disease, making them favorable over irreversible inhibitors with one specificity and substantial lethal side effects. Inhibitors of nutrition sources, such as silymarin and morin, are reversible and appear to target multiple activators and inhibitors of NAFLD [37]. NAFLD inhibitors seem immune or could delay drug resistance in standard therapy to develop drug resistance by prolonging cells [38]. These assets converse to these bioactive composites to bypass drug resistance and be effective against several types of non-alcoholic fatty liver dependent diseases. NAFLD is a widely down-regulated co-fetal mechanism in healthy populations. NAFLD targeting does not lead to side effects even after chronic exposure to naturally occurring and physiological anti-NAFLD compounds.

Low molecular weight anti-NAFLD functional foods such as antioxidants, pre- or probiotics, tangeritin and lycopene may offer novel strategies in NAFLD dependant insulin resistance, obesity and abnormal fatty acid metabolism-related hepatocellular carcinoma [39]. Orally administered lycopene was detected in the liver and plasma and brain cortex of the rat model of various diseases with numerous concentrations [40]. Reviews on the work of several types of research on a diversity of anti-NAFLD functional foods, the non-alcoholic fatty liver-associated enzymes they inhibit, the right sources of NAFLD compounds, the molecular mechanisms of inhibition and references for additional information. The list is not meticulous. Minerals have some negative role on NAFLD and the existed clinical data showed that Zinc (Zn), selenium (Se) and Copper (Cu) have some negative impact on anti-NAFLD [41].
