Tumor Necrosis Factor-α as a Predictor for the Development of Nonalcoholic Fatty Liver Disease: A 4-Year Follow-Up Study

Metabolic Health Is More Important than Obesity in the Development of Nonalcoholic Fatty Liver Disease: A 4-Year Retrospective Study

BACKGROUND

The aim of this study is to compare the risk for future development of nonalcoholic fatty liver disease (NAFLD) according to different status of metabolic health and obesity.

METHODS

A total of 3,045 subjects without NAFLD and diabetes at baseline were followed for 4 years. Subjects were categorized into four groups according to the following baseline metabolic health and obesity statuses: metabolically healthy, non-obese (MHNO); metabolically healthy, obese (MHO); metabolically unhealthy, non-obese (MUHNO); and metabolically unhealthy, obese (MUHO). Being metabolically healthy was defined as having fewer than two of the following five components: high blood pressure, high fasting blood glucose, high triglyceride, low high density lipoprotein cholesterol, and being in the highest decile of the homeostasis model assessment-insulin resistance index. Obesity was defined as a body mass index >25 kg/m². The presence of NAFLD was assessed by ultrasonography.

RESULTS

The proportions of subjects included in the MHNO, MHO, MUHNO, and MUHO groups were 71.4%, 9.8%, 13.0%, and 5.8%, respectively. The proportions of subjects who developed NAFLD were 10.5%, 31.4%, 23.2%, and 42% in the MHNO, MHO, MUHNO, and MUHO groups, respectively. The risk for developing NAFLD was highest in subjects who were metabolically unhealthy both at baseline and after 4 years compared with subjects who were consistently metabolically healthy during the follow-up period (odds ratio, 2.862). Using the MHNO group as reference, the odds ratios for the MHO, MUHNO, and MUHO groups were 1.731, 1.877, and 2.501, respectively.

CONCLUSION

The risk for NAFLD was lower in MHO subjects than in MUNO subjects.

Exogenous administration of DLK1 ameliorates hepatic steatosis and regulates gluconeogenesis via activation of AMPK

BACKGROUND/OBJECTIVES

Activation of Notch signaling pathologically enhances lipogenesis and gluconeogenesis in the liver causing non-alcoholic fatty liver disease (NAFLD) and diabetes. Delta-like 1 homolog (DLK1), an imprinted gene that can modulate adipogenesis and muscle development in mice, was found as an inhibitory regulator of Notch signaling. Therefore, we investigated the metabolic effect of exogenous DLK1 in vitro and in vivo.

SUBJECTS/METHODS

A soluble DLK1 peptide was generated with fusion between a human Fc fragment and extracellular domain of DLK1. Male db/db mice were randomly assigned to two groups: vehicle treated and DLK1-treated group (25 mg kg(-1), intraperitoneal injection, twice a week for 4 weeks). Primary mice hepatocytes and HepG2 cells were used for in vitro experiments.

RESULTS

After 4 weeks of DLK1 administration, hepatic triglyceride content and lipid droplets in liver tissues, as well as serum levels of liver enzymes, were markedly decreased in db/db mice. DLK1 treatment induced phosphorylation of AMPK and ACC and suppressed nuclear expression of SREBP-1c in the mouse liver or hepatocytes, indicating regulation of fatty acid oxidation and synthesis pathways. Furthermore, DLK1-treated mice showed significantly lower levels of fasting and random glucose, with improved glucose and insulin tolerance compared with the vehicle-treated group. Macrophage infiltration and proinflammatory cytokine levels in the epididymal fat were decreased in DLK1-treated db/db mice. Moreover, DLK1 suppressed glucose production from hepatocytes, which was blocked after co-administration of an AMPK inhibitor, compound C. DLK1-treated hepatocytes and mouse liver tissues showed lower PEPCK and G6Pase expression. DLK1 triggered AKT phosphorylation followed by cytosolic translocation of FOXO1 from the nucleus in hepatocytes.

CONCLUSIONS

The present study demonstrated that exogenous administration of DLK1 reduced hepatic steatosis and hyperglycemia via AMPK activation in the liver. This result suggests that DLK1 may be a novel therapeutic approach for treating NAFLD and diabetes.

Relationship between waist circumference level and new onset of non-alcoholic fatty liver disease

AIM: To investigate the relationship between different waist circumference (WC) levels and new onset of non-alcoholic fatty liver disease (NAFLD).

METHODS: A total of 55358 subjects without NAFLD were initially recruited from people who underwent health examination between 2006 and 2007 for this community-based prospective cohort study, and 36978 subjects were finally included in the analysis. According to the baseline WC measurement and its quartile, the subjects were divided into four groups. The incidence of NAFLD in 2012-2013 was compared in the four groups, and multiple Logistic regression analysis was used to test the relationship between different WC levels and new onset of NAFLD.

RESULTS: Along with increasing WC in the four quartile groups, the incidence of NAFLD progressively increased, being13.5%, 26.0%, 31.6% and 38.4%, respectively, of the total population (13.4%, 24.7%, 30.3% and 38.9% in males, and 13.6%, 28.8%, 36.5% and 36.0% in females). Multiple Logistic regression analysis showed that compared with the first quartile group, the second, third, and forth quartile groups had increased risk of NAFLD after adjusting age, gender and other risk factors, with the OR values being 1.72, 1.91 and 2.04, respectively (1.66, 1.87 and 2.19 in males, and 1.60, 1.80 and 1.46 in females).

CONCLUSION: The incidence of NAFLD increases with increasing WC.

Comparison of Serum Adipocytokine Levels according to Metabolic Health and Obesity Status

BACKGROUND

Metabolic health is an emerging concept that is highly correlated with various metabolic complications, and adipocytokines have been causally linked to a wide range of metabolic diseases. Thus, this study compared serum adipocytokine levels according to metabolic health and obesity status.

METHODS

Four hundred and fifty-six nondiabetic subjects (mean age, 40.5 years) were categorized into four groups according to metabolic health and obesity status: metabolically healthy nonobese (MHNO), metabolically healthy obese (MHO), metabolically unhealthy nonobese (MUHNO), and metabolically unhealthy obese (MUHO). Being metabolically healthy was defined as the presence of fewer than two of the following five metabolic abnormalities: high blood pressure, high fasting blood glucose, high triglyceride, low high density lipoprotein cholesterol, and being in the highest decile of the homeostatic model assessment of insulin resistance index. Obesity status was assessed using body mass index (BMI), with obesity defined as a BMI higher than 25 kg/m². Levels of serum interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor α (TNF-α), and adipocyte fatty acid binding protein (A-FABP) were also evaluated.

RESULTS

Of the 456 subjects, 247 (54.2%) were in the MHNO group, 66 (14.5%) were in the MHO group, 66 (14.5%) were in the MUHNO group, and 77 (16.9%) were in the MUHO group. There were no significant differences in IL-6 or MCP-1 levels among the groups, but levels of TNF-α and A-FABP were significantly higher in the MUHNO group compared to the MHNO group.

CONCLUSION

High TNF-α and A-FABP levels are significantly associated with metabolically unhealthiness in nonobese Korean individuals.

Adipokines and proinflammatory cytokines, the key mediators in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a condition in which excess fat accumulates in the liver of a patient with no history of alcohol abuse or other causes for secondary hepatic steatosis. The pathogenesis of NAFLD and nonalcoholic steatohepatitis (NASH) has not been fully elucidated. The “two-hit“ hypothesis is probably a too simplified model to elaborate complex pathogenetic events occurring in patients with NASH. It should be better regarded as a multiple step process, with accumulation of liver fat being the first step, followed by the development of necroinflammation and fibrosis. Adipose tissue, which has emerged as an endocrine organ with a key role in energy homeostasis, is responsive to both central and peripheral metabolic signals and is itself capable of secreting a number of proteins. These adipocyte-specific or enriched proteins, termed adipokines, have been shown to have a variety of local, peripheral, and central effects. In the current review, we explore the role of adipocytokines and proinflammatory cytokines in the pathogenesis of NAFLD. We particularly focus on adiponectin, leptin and ghrelin, with a brief mention of resistin, visfatin and retinol-binding protein 4 among adipokines, and tumor necrosis factor-α, interleukin (IL)-6, IL-1, and briefly IL-18 among proinflammatory cytokines. We update their role in NAFLD, as elucidated in experimental models and clinical practice.