Context Nonalcoholic fatty liver disease (NAFLD) is the most common cause of liver disease, affecting approximately 3 in 10 obese children worldwide. Objective We aimed to investigate the potential relationship between gut microbiota and NAFLD in obese youth, while considering the role of PNPLA3 rs738409, a strong genetic contributor to NAFLD. Design In this cross-sectional study, participants completed abdominal MRI to measure hepatic fat fraction (HFF), oral glucose tolerance test, and PNPLA3 rs738409 genotyping. Fecal samples were collected to analyze the V4 region of the 16S rRNA gene for intestinal bacteria characterization. Setting Yale Pediatric Obesity Clinic. Participants Obese youth (BMI > 95th percentile) with NAFLD (HFF ≥ 5.5%; n=44) and without NAFLD (HFF < 5.5%; n=29). Main Outcome Measure Shannon-Wiener diversity index values and proportional bacterial abundance by NAFLD status and PNPLA3 genotype. Results Subjects with NAFLD had decreased bacterial alpha-diversity compared to those without NAFLD (p=0.013). Subjects with NAFLD showed a higher Firmicutes to Bacteroidetes (F/B) ratio (p=0.019) and lower abundance of Bacteroidetes (p=0.010), Prevotella (p=0.019), Gemmiger (p=0.003), and Oscillospira (p=0.036). F/B ratio, Bacteroidetes, Gemmiger, and Oscillospira were associated with HFF when controlling for group variations. We also observed an additive effect on HFF by PNPLA3 rs738409 and Gemmiger, and PNPLA3 rs738409 and Oscillospira. Conclusions Obese youth with NAFLD have a different gut microbiota composition than those without NAFLD. These differences were still statistically significant when controlling for factors associated with NAFLD, including PNPLA3 rs738409.

ABSTRACT Background Recent literature suggests that the Western diet's imbalance between high ω-6 (n–6) and low ω-3 (n–3) PUFA intake contributes to fatty liver disease in obese youth. Objectives We tested whether 12 wk of a low n–6:n–3 PUFA ratio (4:1) normocaloric diet mitigates fatty liver and whether the patatin-like containing domain phospholipase 3 (PNPLA3) rs738409 variant affects the response. Methods In a single-arm unblinded study, obese youth 9–19 y of age with nonalcoholic fatty liver disease were treated with a normocaloric low n–6:n–3 PUFA ratio diet for 12 wk. The primary outcome was change in hepatic fat fraction (HFF%), measured by abdominal MRI. Metabolic parameters included alanine aminotransferase (ALT), lipids, measures of insulin sensitivity, and plasma oxidized linoleic acid metabolites (OXLAMs). Outcomes were also analyzed by PNPLA3 rs738409 genotype. Wilcoxon's signed rank test, the Mann–Whitney U test, and covariance pattern modeling were used. Results Twenty obese adolescents (median age: 13.3 y; IQR: 10.5–16.4 y) were enrolled and 17 completed the study. After 12 wk of dietary intervention, HFF% decreased by 25.8% (P = 0.009) despite stable weight. We observed a 34.4% reduction in ALT (P = 0.001), 21.9% reduction in triglycerides (P = 0.046), 3.28% reduction in LDL cholesterol (P = 0.071), and a 26.3% improvement in whole body insulin sensitivity (P = 0.032). The OXLAMs 9-hydroxy-octadecandienoic acid (9-HODE) (P = 0.011), 13-HODE (P = 0.007), and 9-oxo-octadecadienoic acid (9-oxoODE) (P = 0.024) decreased after 12 wk. HFF% declined in both the not-at-risk (CC/CG) and at-risk (GG) PNPLA3 rs738409 genotype groups, with significant (P = 0.016) HFF% reduction in the GG group. Changes in 9-HODE (P = 0.023), 9-oxoODE (P = 0.009), and 13-oxoODE (P = 0.003) differed between the 2 genotype groups over time. Conclusions These data suggest that, independently of weight loss, a low n–6:n–3 PUFA diet ameliorates the metabolic phenotype of adolescents with fatty liver disease and that response to this diet is modulated by the PNPLA3 rs738409 genotype. This trial was registered at clinicaltrials.gov as NCT01556113.

Patterns of abdominal fat distribution (for example, a high vs. low visceral adipose tissue [VAT]/[VAT + subcutaneous adipose tissue (SAT)] ratio), independent of obesity, during adolescence carry a high risk for insulin resistance and type 2 diabetes. Longitudinal follow-up of a cohort of obese adolescents has recently revealed that a high ratio (high VAT/[VAT + SAT]) is a major determinant of fatty liver and metabolic impairment over time, with these effects being more pronounced in girls than in boys. To unravel the underlying metabolic alterations associated with the unfavorable VAT/(VAT + SAT) phenotype, we used the 2H2O labeling method to measure the turnover of adipose lipids and cells in the subcutaneous abdominal and gluteal/femoral adipose tissue (SAT) of weight-stable obese adolescent girls with a similar level of obesity but discordant VAT/(VAT + SAT) ratios. Girls with the unfavorable (high VAT/[VAT + SAT]) phenotype exhibited higher in vivo rates of triglyceride (TG) turnover (representing both lipolysis and synthesis at steady state), without significant differences in de novo lipogenesis in both abdominal and gluteal depots, compared with obese girls with the favorable phenotype. Moreover, mature adipocytes had higher turnover, with no difference in stromal vascular cell proliferation in both depots in the metabolically unfavorable phenotype. The higher TG turnover rates were significantly correlated with higher intrahepatic fat stores. These findings are contrary to the hypothesis that impaired capacity to deposit TGs or proliferation of new mature adipocytes are potential mechanisms for ectopic fat distribution in this setting. In summary, these results suggest that increased turnover of TGs (lipolysis) and of mature adipocytes in both abdominal and gluteal SAT may contribute to metabolic impairment and the development of fatty liver, even at this very early stage of disease.

AimTo evaluate whether intrahepatic fat accumulation contributes to impaired insulin clearance and hepatic insulin resistance across different ethnic groups.MethodsThe intrahepatic fat content (HFF%) was quantified by magnetic resonance imaging in a multi‐ethnic cohort of 632 obese youths aged 7‐18 years at baseline and after a 2‐year follow‐up. Insulin secretion rate (ISR), endogenous insulin clearance (EIC) and hepatic insulin resistance index (HIRI) were estimated by modelling glucose, insulin and C‐peptide data during 3‐hour, 9‐point oral glucose tolerance tests.ResultsAfrican American youths exhibited the lowest HFF% and a prevalence of non‐alcoholic fatty liver disease (NAFLD) less than half of that shown by Caucasians and Hispanics. Furthermore, African Americans had lower EIC and glucose‐stimulated ISR, despite similar HIRI and plasma insulin levels, compared with Caucasians and Hispanics. EIC and HIRI were markedly reduced in individuals with NAFLD and declined across group‐specific HFF% tertiles in all ethnic groups. Consistently, the HFF% correlated with EIC and HIRI, irrespective of the ethnic background, after adjustment for age, sex, ethnicity, adiposity, waist‐hip ratio, pubertal status and plasma glucose levels. An increased HFF% at follow‐up was associated with decreased EIC and increased HIRI across all groups.ConclusionsIntrahepatic lipid accumulation is associated with reduced insulin clearance and hepatic insulin sensitivity in obese youths, irrespective of their ethnic background.

Nonalcoholic fatty liver disease (NAFLD) is the most common form of liver disease and is often the precursor for more serious liver conditions such as nonalcoholic steatohepatitis and cirrhosis. Although the gut microbiome has been implicated in the development of NAFLD, the strong association of obesity with NAFLD and its effect on microbiome structure has made interpreting study outcomes difficult. In the present study, we examined the taxonomic and functional differences between the microbiomes of youth with obesity and with and without NAFLD. Shotgun metagenome sequencing was performed to profile the microbiomes of 36 subjects, half of whom were diagnosed with NAFLD using abdominal magnetic resonance imaging. Beta diversity analysis showed community‐wide differences between the groups (p = 0.002). Specific taxonomic differences included increased relative abundances of the species Fusicatenibacter saccharivorans (p = 0.042), Romboutsia ilealis (p = 0.046), and Actinomyces sp. ICM47 (p = 0.0009), and a decrease of Bacteroides thetaiotamicron (p = 0.0002), in the NAFLD group as compared with the non‐NAFLD group. At the phylum level, Bacteroidetes (p < 0.0001) was decreased in the NAFLD group. Functionally, branched‐chain amino acid (p = 0.01343) and aromatic amino acid (p = 0.01343) synthesis pathways had increased relative abundances in the NAFLD group along with numerous energy use pathways, including pyruvate fermentation to acetate (p = 0.01318). Conclusion: Community‐wide differences were noted based on NAFLD status, and individual bacterial species along with specific metabolic pathways were identified as potential drivers of these differences. The results of the present study support the idea that the NAFLD phenotype displays a differentiated microbial and functional signature from the obesity phenotype.

The risk genotype for the common variant rs7903146 of the transcription factor 7-like-2 (TCF7L2) gene has been found to affect the incretin response in healthy and obese adults; however, whether a similar functional defect is also present in obese adolescents remains unexplored. Herein, we examined the functional effect of the rs7903146 variant in the TCF7L2 gene on the incretin effect and determined its translational metabolic manifestation by performing deep phenotyping of the incretin system, b-cell function relative to insulin sensitivity, the gastrointestinalinduced glucose disposal (GIGD) in obese youth with normal and impaired glucose tolerance. RESEARCH DESIGN AND METHODSThirty-nine obese adolescents without diabetes (median age 15 [25th, 75th percentile 14, 18] years; BMI 37 [33,43] kg/m 2 ) were genotyped for the rs7903146 variant of TCF7L2 and underwent a 3-h oral glucose tolerance test (OGTT) followed by an isoglycemic intravenous glucose infusion (iso-intravenous glucose tolerance test [IVGTT]) to match the plasma glucose concentrations during the OGTT and a hyperglycemic clamp with arginine stimulation. The incretin effect was measured as 100 * (AUC-SR OGTT 2 AUC-SR iso-IVGTT ) / AUC-SR OGTT , where AUC-SR 5 area under the curve of C-peptide secretion rate.Participants were grouped into tertiles according to the percentage incretin effect (high, moderate, and low) to describe their metabolic phenotype. RESULTSThe presence of T risk allele for TCF7L2 was associated with a markedly reduced incretin effect compared with the wild-type genotype (0.3% [27.2, 14] vs. 37.8% [12.5, 52.4], P < 0.002). When the cohort was stratified by incretin effect, the high, moderate, and low incretin effect groups did not differ with respect to anthropometric features, while the low incretin effect group exhibited higher 1-h glucose (P 5 0.015) and a reduced disposition index, insulin sensitivity, and insulin clearance compared with the high incretin effect group. GIGD was reduced in the low incretin effect group (P 5 0.001). The three groups did not differ with respect to intravenous glucose-induced insulin secretion and arginine response during the hyperglycemic clamp. CONCLUSIONSA reduced incretin effect and its association with the TCF7L2 variant rs7903146 identify an early metabolic phenotype in obese youth without diabetes, featuring a higher plasma glucose peak at 1 h; lower insulin secretion, sensitivity, and clearance; and GIGD.

Objective Growth differentiation factor 15 (GDF15) has been associated with food intake and weight regulation in response to metabolic stress. In animal models, it has been noted that it may play a role in the progression of non-alcoholic fatty liver disease (NAFLD), the leading cause of chronic liver disease in children. Design In the current study, we explored the association of circulating plasma concentrations of GDF15 with NAFLD in youth with overweight/obesity, and whether changes in plasma concentrations in GDF15 parallel the changes in intrahepatic fat content (HFF%) over time. Methods Plasma GDF15 concentrations were measured by ELISA in 175 youth with overweight/obesity who underwent an oral glucose tolerance test (OGTT) and magnetic resonance imaging (MRI) to assess intrahepatic, visceral, and subcutaneous fat. Baseline fasting GDF15 concentrations were measured in twenty-two overweight/obese youth who progressed (n = 11) or regressed (n = 11) in HFF% by more than 30% of original over a 2-year period. Results Youth with NAFLD had significantly higher plasma concentrations of GDF15 than those without NAFLD, independent of age, sex, ethnicity, BMI z-score (BMIz), and visceral fat (P = 0.002). During the OGTT, there was a decline in plasma GDF15 concentrations from 0 to 60 min, but GDF15 concentrations returned to basal levels by the end of the study. There was a statistically significant association between change in HFF% and change in GDF15 (P = 0.008; r2 = 0.288) over ~2 years of follow-up. Conclusions These data suggest that plasma GDF15 concentrations change with change in intrahepatic fat content in youth with overweight/obesity and may serve as a biomarker for NAFLD in children.

Background In the last few years, there has been a growing interest in the role of gut microbiota in the development of obesity and its complications. Objectives In this study, we tested the following hypotheses: 1) lean youth and youth with obesity experience a different capability of their gut microbiota to ferment carbohydrates and produce acetate; and 2) colonic acetate may serve as a substrate for hepatic de novo lipogenesis (DNL). Methods Nineteen lean youth [mean ± SE BMI (in kg/m2): 21.8 ± 0.521] and 19 youth with obesity (BMI: 35.7 ± 1.66), ages 15–21 y, frequency-matched by age and sex, underwent a fasting 10-h sodium [d3]-acetate intravenous infusion to determine the rate of appearance of acetate (Raacet) into the peripheral circulation before and after an oral dose of 20 g of lactulose. Pre- and post-lactulose Raacet values were determined at a quasi-steady state and changes between groups were compared using a quantile regression model. Acetate-derived hepatic DNL was measured in 11 subjects (6 youth with obesity) and its association with Raacet was assessed using Spearman correlation. Results Mean ± SE Raacet was not different before lactulose ingestion between the 2 groups (7.69 ± 1.02 μmol · kg−1 · min−1 in lean youth and 7.40 ± 1.73 μmol · kg−1 · min−1 in youth with obesity, P = 0.343). The increase in mean ± SE Raacet after lactulose ingestion was greater in lean youth than in youth with obesity (14.7 ± 2.33 μmol · kg−1 · min−1 and 9.29 ± 1.44 μmol · kg−1 · min−1, respectively, P = 0.001). DNL correlated with Raacet, calculated as changes from the pre- to the post-lactulose steady state (ρ = 0.621; P = 0.046). Conclusions These data suggest that youth with obesity ferment lactulose to a lesser degree than youth without obesity and that colonic acetate serves as a substrate for hepatic DNL. This trial was registered at clinicaltrials.gov as NCT03454828.