The gut microbiome, a diverse microbial community in the gastrointestinal tract, plays a pivotal role in the maintenance of health. The gut microbiome metabolizes dietary and host-derived molecules to produce bioactive metabolites, which have a wide array of effects on host metabolism and immunity. 'Dysbiosis' of the gut microbiome, commonly considered as perturbation of microbiome diversity and composition, has been associated with intestinal and extra-intestinal diseases, including nonalcoholic fatty liver disease (NAFLD). A number of endogenous and exogenous factors, such as nutritional intake and xenobiotic exposure, can alter the gut microbiome. We will review the evolving methods for studying the gut microbiome and how these profiling techniques have been utilized to further our understanding of the gut microbial community composition and functional potential in the clinical spectrum of NAFLD. We will highlight microbiome-host interactions that may contribute to the pathogenesis of NAFLD, with a primary focus on mechanisms related to the metabolic output of the gut microbiome. Finally, we will discuss potential therapeutic implications of the gut microbiome in NAFLD.

The gut microbiome, a diverse microbial community in the gastrointestinal tract, plays a pivotal role in the maintenance of health. The gut microbiome metabolizes dietary and host-derived molecules to produce bioactive metabolites, which have a wide array of effects on host metabolism and immunity. 'Dysbiosis' of the gut microbiome, commonly considered as perturbation of microbiome diversity and composition, has been associated with intestinal and extra-intestinal diseases, including nonalcoholic fatty liver disease (NAFLD). A number of endogenous and exogenous factors, such as nutritional intake and xenobiotic exposure, can alter the gut microbiome. We will review the evolving methods for studying the gut microbiome and how these profiling techniques have been utilized to further our understanding of the gut microbial community composition and functional potential in the clinical spectrum of NAFLD. We will highlight microbiome-host interactions that may contribute to the pathogenesis of NAFLD, with a primary focus on mechanisms related to the metabolic output of the gut microbiome. Finally, we will discuss potential therapeutic implications of the gut microbiome in NAFLD.

The gut microbiome, the multispecies community of microbes that exists in the gastrointestinal tract, encodes several orders of magnitude more functional genes than the human genome. It also plays a pivotal role in human health, in part due to metabolism of environmental, dietary, and host-derived substrates, which produce bioactive metabolites. Perturbations to the composition and associated metabolic output of the gut microbiome have been associated with a number of chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD). Here, we review the rapidly evolving suite of next-generation techniques used for studying gut microbiome composition, functional gene content, and bioactive products and discuss relationships with the pathogenesis of NAFLD.

Background

The proportion of older patients awaiting liver transplantation (LT) is rising. Although increased age and LT-MELD are known to increase the risk of graft loss, no studies have explored whether there is a synergistic effect between LT-age and LT-MELD.

Methods

All US adult, non-Status 1 recipients of primary deceased donor LT from 2/05 to 1/10 without MELD exceptions were included (n=15,677). Recipients were categorized by LT-age [18-59 yr (n=11,966), 60-64 yr (n=2181), 65-69 yr (n=1177), and ≥70 yr (n=343)] and LT-MELD [low (<20, n=5290), mid (20-27, n=5112), and high (≥28, n=5265)]. Adjusted Cox models evaluated the independent and combined effects of LT-age and LT-MELD on graft loss (death or re-LT).

Results

LT-age ≥70 yr (HR=1.65, 95% CI 1.08-1.82) and LT-MELD ≥28 (HR=1.46, 95% CI 1.02-1.47) were independently associated with increased risk of graft loss (P<0.001). In a model allowing for the interaction between LT-age and LT-MELD, the risk of graft loss for recipients ≥70 years with MELD ≥28 was higher than predicted by the additive model (HR=2.38, 95% CI 1.73-3.27, P<0.001) resulting in 1-year graft survival of 56%. However, the increased risk of graft loss in recipients ≥70 years was attenuated at lower LT-MELD <28. Furthermore, the interaction term was not significant for any other LT-age and LT-MELD combination.

Conclusion

Our analyses suggest that recipients should not be excluded solely based on age; however, LT for recipients ≥70 years at high LT-MELD scores should be undertaken cautiously.

Background

Longitudinal studies are needed to decipher mechanistic links between the gut microbiome and nonalcoholic steatohepatitis (NASH). We examined shifts in the gut microbiome in persons with NASH with improvement in liver stiffness measurement (LSM) by magnetic resonance (MR) elastography.

Methods

Gut microbial profiling was performed at baseline and study completion (24 weeks) using 16 S rRNA gene sequencing in 69 adults with biopsy-confirmed NASH and significant fibrosis (stages 2-3) enrolled in a multi-center randomized controlled trial evaluating selonsertib alone or in combination with simtuzumab. Differential abundance of bacterial taxa at baseline and end of study were examined in participants with and without longitudinal improvement in LSM. Gut microbial shifts that correlated with secondary outcomes, including reduction in MR imaging-derived proton density fat faction (MRI-PDFF) and histologic fibrosis regression were evaluated. Fecal samples from 32 healthy adults were profiled and genus-level multidimensional scaling was used to determine if microbial shifts in persons with NASH improvement represented a shift toward a healthy gut microbiome.

Results

Shifts in abundance of 36 bacterial taxa including Lactobacillus (log2_FC = -4.51, FDR < 0.001), Enterococcus (log2_FC = -6.72, FDR < 0.001), and Megasphaera (log2_FC = 7.74, FDR < 0.001) were associated with improvement in LSM. Improvement in LSM was associated with microbial shifts toward healthy reference (p = 0.05). Significant shifts in 10 and 12 bacterial taxa were associated with improvement in LSM in addition to MRI-PDFF and fibrosis regression, respectively, indicating consistent taxonomic changes across multiple clinical endpoints.

Conclusion

Longitudinal changes in the gut microbiota are observed in adults with NASH and clinical improvement and represent a shift toward a healthy microbiome.

Background

Magnetic resonance elastography (MRE) is an accurate biomarker of liver fibrosis; however, limited data characterize its association with outcomes. We aimed to evaluate the association between liver stiffness (LS) on MRE and liver-related outcomes.

Methods

This is a longitudinal, retrospective analysis of subjects at risk of NAFLD who had MRE assessment. LS was estimated using MRE, and liver fat was assessed using magnetic resonance imaging proton density fat fraction. Univariable and multivariable survival and regression analyses were used to assess the association between LS on MRE and liver-related outcomes including a cumulative primary outcome of hepatic decompensation, hepatocellular carcinoma (HCC), or death.

Results

In all, 265 patients (68% women) with a mean age of 50 (±18) years and 44% Hispanic ethnicity and 45.3% with NAFLD were included. A total of 76 liver-related events or death occurred, and there was 453 person-years of follow-up time in 97 patients with available follow-up. Each 1-kPa increase in LS was associated with 2.20-fold (95% CI: 1.70-2.84, p < 0.001) increased odds of prevalent hepatic decompensation or HCC. A positive MEFIB index, a combination of MRE ⩾ 3.3 kPa and FIB-4 ⩾ 1.6, had a strong association with the primary outcome compared with those without, HR = 21.8 (95% CI: 4.28-111.4, p < 0.001). The MEFIB index had a sensitivity of 75% and specificity of 90%, and a negative score was associated with 98% negative predictive value for incident liver-related events or death.

Conclusion

LS assessed by MRE is associated with hepatic decompensation and death, and the MEFIB combination of MRE with FIB-4 may have high negative predictive value for liver-related events.

Background and aims

Whether hepatocellular carcinoma (HCC) increases the familial risk for hepatic fibrosis has not been thoroughly explored, particularly in Mexican Americans who are disproportionately affected by obesity and metabolic syndrome. We evaluated the risk of significant hepatic fibrosis in first-degree relatives of Mexican American adults with HCC.

Methods

We performed a cross-sectional analysis of a prospective cohort of Mexican American probands with HCC and first-degree relatives enrolled in the Hispanic Liver Cancer Cohort study. We evaluated the prevalence of hepatic fibrosis in first-degree relatives, defined by liver stiffness measurement (LSM) >= 7.0 kPa with transient elastography (TE). Secondary outcomes included the prevalence of definite hepatic steatosis, defined by controlled attenuation parameter >=288 dB/m.

Results

We identified 70 probands diagnosed with HCC; 47% were female and the mean age was 62 years (±13 years). Among 112 first-degree relatives with a mean age of 43 years (±14 years), 19 (17%) had significant fibrosis and 47 (42%) had definite hepatic steatosis, respectively. The prevalence of significant fibrosis was 20% in first-degree relatives 40 years of age or older. Regression analysis revealed that diabetes (OR 3.2, 95% CI: 1.1-9.2, p = 0.03) and aspartate aminotransferase >=30 units/L (OR 4.0, 95% CI: 1.4-11.7, p = 0.01) were predictors of significant fibrosis in first-degree relatives.

Conclusions

Using a well-phenotyped familial cohort, we found that the prevalence of significant fibrosis and definite hepatic steatosis are high in first-degree relatives of Mexican Americans with HCC, particularly those with diabetes, suggesting that this population may benefit from screening for liver disease.

Introduction

Two-dimensional shear wave elastography (2D-SWE) and vibration-controlled transient elastography (VCTE) provide noninvasive assessment of hepatic fibrosis. We compared performance of 2D-SWE and VCTE for fibrosis detection in nonalcoholic fatty liver disease (NAFLD).

Methods

We performed a prospective study of adults with NAFLD who underwent 2D-SWE, VCTE, and liver biopsy analysis (using Nonalcoholic Steatohepatitis Clinical Research Network scoring system). The primary outcome was hepatic fibrosis (stage ⩾ 1); secondary outcomes included dichotomized fibrosis stages. Area under receiver operating characteristic curve (AUROC) analyses were used to compare 2D-SWE and VCTE performance.

Results

A total of 114 adults with a median BMI of 31.2 kg/m² were included. The VCTE was better than 2D-SWE for the detection of fibrosis (AUROC: 0.81 versus 0.72, p = 0.03). The VCTE detected fibrosis stage 2, 3, or 4 with AUROCs of 0.86 (95% CI, 0.80-0.93), 0.91 (95% CI, 0.82-0.99), and 0.96 (95% CI, 0.91-1.00). The 2D-SWE detected fibrosis stage 2, 3, or 4 with AUROCs of 0.84 (95% CI, 0.76-0.92), 0.88 (95% CI, 0.81-0.96), and 0.93 (95% CI, 0.86-0.99).

Conclusion

In a prospective study including more than 100 adults with NAFLD, we found VCTE to be more accurate than 2D-SWE in detecting fibrosis; these modalities, however, are comparable in assessing for higher stages of fibrosis.

Background

There are limited data on the diagnostic accuracy of gut microbial signatures for predicting hepatic decompensation in patients with cirrhosis.

Aims

To determine whether a stool metagenome-derived signature accurately detects hepatic decompensation and mortality risk in cirrhosis secondary to non-alcoholic fatty liver disease (NAFLD) METHODS: Shotgun metagenomic sequencing was performed on faecal samples collected at study entry from a prospective cohort of adults with NAFLD-related cirrhosis. A Random Forest machine learning algorithm was utilised to identify a metagenomic signature of decompensated cirrhosis (defined by ascites, hepatic encephalopathy or variceal haemorrhage) and subsequently validated in an external cohort. A Cox proportional hazards regression model was used to examine predictors of all-cause mortality.

Results

In all, 25 adults with NAFLD-related cirrhosis (training cohort) were included. Among the 16 participants with decompensated cirrhosis, 33% had ascites, 56% had hepatic encephalopathy and 22% had experienced a variceal haemorrhage (not mutually exclusive). We identified a stool metagenomic signature comprising 13 discriminatory species that reliably distinguished decompensated NAFLD-related cirrhosis (diagnostic accuracy, 0.97, 95% confidence interval [CI] 0.96-0.99). Diagnostic accuracy of the 13-species signature remained high after adjustment for lactulose (area under the curve [AUC] 0.99) and rifaximin use (AUC 0.93). The discriminative ability of 13-species metagenomic signature was robust in an independent test cohort (AUC 0.95, 95% CI 0.81-1.00). The 13-species metagenomic signature (hazard ratio [HR] 1.54, 95% CI 1.10-2.15, p = 0.01) was a stronger predictor of mortality than the Model for End-Stage Liver Disease score (HR 1.25, 95% CI 1.03-1.53, p = 0.03).

Conclusions

This study provides evidence for a gut metagenome-derived signature with high diagnostic accuracy for hepatic decompensation that predicts risk of mortality in NAFLD-related cirrhosis.

Background and aims

Patients with NAFLD with significant hepatic fibrosis (Stage ≥ 2) are at increased risk of liver-related morbidity and are candidates for pharmacologic therapies. In this study, we compared the diagnostic accuracy of MEFIB (the combination of magnetic resonance elastography [MRE] and Fibrosis-4 [FIB-4]) and FAST (FibroScan-aspartate aminotransferase; combined liver stiffness measurement by vibration-controlled transient elastography, controlled attenuation parameter, and aspartate aminotransferase) for detecting significant fibrosis.

Approach and results

This prospective cohort study included 234 consecutive patients with NAFLD who underwent liver biopsy, MRE, and FibroScan at the University of California San Diego (UCSD cohort) and an independent cohort (N = 314) from Yokohama City University, Japan. The primary outcome was diagnostic accuracy for significant fibrosis (Stage ≥ 2). The proportions of significant fibrosis in the UCSD and Yokohama cohorts were 29.5% and 66.2%, respectively. Area under the receiver operating characteristic curve (95% CI) of MEFIB (0.860 [0.81-0.91]) was significantly higher than that of FAST (0.757 [0.69-0.82]) in the UCSD cohort (p = 0.005), with consistent results in the Yokohama cohort (AUROC, 0.899 [MEFIB] versus 0.724 [FAST]; p < 0.001). When used as the rule-in criteria (MEFIB, MRE ≥ 3.3 kPa and FIB-4 ≥ 1.6; FAST ≥ 0.67), the positive predictive value for significant fibrosis was 91.2%-96.0% for MEFIB and 74.2%-89.2% for FAST. When used as the rule-out criteria (MEFIB, MRE < 3.3 kPa and FIB-4 < 1.6; FAST ≤ 0.35), the negative predictive value for significant fibrosis was 85.6%-92.8% for MEFIB and 57.8%-88.3% for FAST.

Conclusions

MEFIB has higher diagnostic accuracy than FAST for significant fibrosis in NAFLD, and our results support the utility of a two-step strategy for detecting significant fibrosis in NAFLD.