Saturated Fat Is More Metabolically Harmful for the Human Liver Than Unsaturated Fat or Simple Sugars.

OBJECTIVE: Nonalcoholic fatty liver disease (i.e., increased intrahepatic triglyceride [IHTG] content), predisposes to type 2 diabetes and cardiovascular disease. Adipose tissue lipolysis and hepatic de novo lipogenesis (DNL) are the main pathways contributing to IHTG. We hypothesized that dietary macronutrient composition influences the pathways, mediators, and magnitude of weight gain-induced changes in IHTG. RESEARCH DESIGN AND METHODS: We overfed 38 overweight subjects (age 48 ± 2 years, BMI 31 ± 1 kg/m2, liver fat 4.7 ± 0.9%) 1,000 extra kcal/day of saturated (SAT) or unsaturated (UNSAT) fat or simple sugars (CARB) for 3 weeks. We measured IHTG (1H-MRS), pathways contributing to IHTG (lipolysis ([2H5]glycerol) and DNL (2H2O) basally and during euglycemic hyperinsulinemia), insulin resistance, endotoxemia, plasma ceramides, and adipose tissue gene expression at 0 and 3 weeks. RESULTS: Overfeeding SAT increased IHTG more (+55%) than UNSAT (+15%, P < 0.05). CARB increased IHTG (+33%) by stimulating DNL (+98%). SAT significantly increased while UNSAT decreased lipolysis. SAT induced insulin resistance and endotoxemia and significantly increased multiple plasma ceramides. The diets had distinct effects on adipose tissue gene expression. CONCLUSIONS: Macronutrient composition of excess energy influences pathways of IHTG: CARB increases DNL, while SAT increases and UNSAT decreases lipolysis. SAT induced the greatest increase in IHTG, insulin resistance, and harmful ceramides. Decreased intakes of SAT could be beneficial in reducing IHTG and the associated risk of diabetes.

Predictors of Liver Fat and Stiffness in Non-Alcoholic Fatty Liver Disease (NAFLD) - an 11-Year Prospective Study.

Liver fat can be non-invasively measured by proton magnetic resonance spectroscopy (1H-MRS) and fibrosis estimated as stiffness using transient elastography (FibroScan). There are no longitudinal data on changes in liver fat in Europids or on predictors of liver stiffness using these methods. We determined liver fat (1H-MRS) and clinical characteristics including features of insulin resistance at baseline and after a median follow-up period of 11.3 (range 7.3-13.4) years in 97 Finnish subjects. Liver stiffness was measured at 11.3 years. Liver fat content decreased by 5% (p < 0.05) over time. Values at baseline and 11.3 years were closely interrelated (r = 0.81, p < 0.001). Baseline liver fat (OR 1.32; 95%CI: 1.15-1.50) and change in BMI (OR 1.67; 95%CI: 1.24-2.25) were independent predictors of liver fat at 11.3 years (AUROC 0.90; 95%CI: 0.83-0.96). Baseline liver fat (AUROC 0.84; 95%CI: 0.76-0.92) predicted liver fat at 11.3 years more accurately than routinely available parameters (AUROC 0.76; 95%CI: 0.65-0.86, p = 0.02). At 11.3 years, 29% of the subjects had increased liver stiffness. Baseline liver fat (OR 2.17; 95%CI: 1.05-4.46) was an independent predictor of increased liver stiffness. These data show that liver fat is more important than the associated metabolic abnormalities as the predictor of future liver fat and fibrosis.

Obesity/insulin resistance rather than liver fat increases coagulation factor activities and expression in humans.

Increased liver fat may be caused by insulin resistance and adipose tissue inflammation or by the common I148M variant in PNPLA3 at rs738409, which lacks both of these features. We hypothesised that obesity/insulin resistance rather than liver fat increases circulating coagulation factor activities. We measured plasma prothrombin time (PT, Owren method), activated partial thromboplastin time (APTT), activities of several coagulation factors, VWF:RCo and fibrinogen, and D-dimer concentration in 92 subjects divided into groups based on insulin sensitivity [insulin-resistant ('IR') versus insulin-sensitive ('IS')] and PNPLA3 genotype (PNPLA3148MM/MI vs PNPLA3148II). Liver fat content (1H-MRS) was similarly increased in 'IR' (13 ± 1 %) and PNPLA3148MM/MI (12 ± 2 %) as compared to 'IS' (6 ± 1 %, p<0.05) and PNPLA3148II (8 ± 1 %, p<0.05), respectively. FVIII, FIX, FXIII, fibrinogen and VWF:RCo activities were increased, and PT and APTT shortened in 'IR' versus 'IS', in contrast to these factors being similar between PNPLA3148MM/MI and PNPLA3148II groups. In subjects undergoing a liver biopsy and entirely lacking the I148M variant, insulin-resistant subjects had higher hepatic expression of F8, F9 and FGG than equally obese insulin-sensitive subjects. Expression of pro-inflammatory genes in adipose tissue correlated positively with PT (% of normal), circulating FVIII, FIX, FXI, VWR:RCo and fibrinogen, and expression of anti-inflammatory genes negatively with PT (%), FIX and fibrinogen. We conclude that obesity/insulin resistance rather than an increase in liver fat is associated with a procoagulant plasma profile. This reflects adipose tissue inflammation and increased hepatic production of coagulation factors and their susceptibility for activation.

Altered miRNA processing disrupts brown/white adipocyte determination and associates with lipodystrophy.

miRNAs are important regulators of biological processes in many tissues, including the differentiation and function of brown and white adipocytes. The endoribonuclease dicer is a major component of the miRNA-processing pathway, and in adipose tissue, levels of dicer have been shown to decrease with age, increase with caloric restriction, and influence stress resistance. Here, we demonstrated that mice with a fat-specific KO of dicer develop a form of lipodystrophy that is characterized by loss of intra-abdominal and subcutaneous white fat, severe insulin resistance, and enlargement and "whitening" of interscapular brown fat. Additionally, KO of dicer in cultured brown preadipocytes promoted a white adipocyte-like phenotype and reduced expression of several miRNAs. Brown preadipocyte whitening was partially reversed by expression of miR-365, a miRNA known to promote brown fat differentiation; however, introduction of other miRNAs, including miR-346 and miR-362, also contributed to reversal of the loss of the dicer phenotype. Interestingly, fat samples from patients with HIV-related lipodystrophy exhibited a substantial downregulation of dicer mRNA expression. Together, these findings indicate the importance of miRNA processing in white and brown adipose tissue determination and provide a potential link between this process and HIV-related lipodystrophy.

A population-based study on the prevalence of NASH using scores validated against liver histology.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease in Western countries. Diagnosis of NASH requires a liver biopsy. We estimated the prevalence of NASH non-invasively in a population-based study using scores validated against liver histology. METHODS: Clinical characteristics, PNPLA3 genotype at rs738409, and serum cytokeratin 18 fragments were measured in 296 consecutive bariatric surgery patients who underwent a liver biopsy to discover and validate a NASH score ('NASH score'). We also defined the cut-off for NASH for a previously validated NAFLD liver fat score to diagnose NASH in the same cohort ('NASH liver fat score'). Both scores were validated in an Italian cohort comprising of 380, mainly non-bariatric surgery patients, who had undergone a liver biopsy for NASH. The cut-offs were utilized in the Finnish population-based D2D-study involving 2849 subjects (age 45-74 years) to estimate the population prevalence of NASH. RESULTS: The final 'NASH Score' model included PNPLA3 genotype, AST and fasting insulin. It predicted NASH with an AUROC 0.774 (0.709, 0.839) in Finns and 0.759 (0.711, 0.807) in Italians (NS). The AUROCs for 'NASH liver fat score' were 0.734 (0.664, 0.805) and 0.737 (0.687, 0.787), respectively. Using 'NASH liver fat score' and 'NASH Score', the prevalences of NASH in the D2D study were 4.2% (95% CI: 3.4, 5.0) and 6.0% (5.0, 6.9%). Sensitivity analysis was performed by taking into account stochastic false-positivity and false-negativity rates in a Bayesian model. This analysis yielded population prevalences of NASH of 3.1% (95% stimulation limits 0.2-6.8%) using 'NASH liver fat score' and 3.6% (0.2-7.7%) using 'NASH Score'. CONCLUSIONS: The population prevalence of NASH in 45-74 year old Finnish subjects is ∼ 5%.