Nonalcoholic fatty liver disease and sarcopenia: pathophysiological connections and therapeutic implications

The relationship between sarcopenia and metabolic dysfunction-associated fatty liver disease among the young and middle-aged populations

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed as a new term for diagnosing fatty liver disease, which is considered to be a multi-systemic disease with multiple extrahepatic manifestations, including sarcopenia. The link between sarcopenia and MAFLD remains uncertain, especially among young and middle-aged adults. Thus, we examined the relationship between MAFLD and sarcopenia in young and middle-aged individuals in this study.

METHODS

A total of 2214 individuals with laboratory tests, dual-energy X-ray absorptiometry and ultrasound transient elastography from NHANES 2017-2018 were selected for this study. MAFLD was diagnosed as fatty liver disease with any one of the situations: overweight/obesity, diabetes mellitus, presence of metabolic dysregulation. Sarcopenia was defined by appendicular lean mass adjusted for body mass index (BMI). Multivariable logistic regression and restricted cubic spline (RCS) model were applied to explore the relationship between MAFLD and sarcopenia, and the mediation analyses were also conducted. Moreover, subgroup analyses stratified by BMI and lifestyles were done.

RESULTS

The prevalence of MAFLD was 47.85%, and nearly 8.05% of participants had sarcopenia. The prevalence of sarcopenia was higher in participants with MAFLD (12.75%; 95% CI 10.18-15.31%) than in the non-MAFLD (3.73%; 95% CI 2.16-5.31%). MAFLD was significantly positively associated with sarcopenia after adjustments [OR = 2.87 (95% CI: 1.62-5.09)]. Moreover, significant positive associations were observed between liver fibrosis and sarcopenia prevalence in MAFLD patients (OR = 2.16; 95% CI 1.13-4.15). The RCS curve revealed that MAFLD was linearly associated with sarcopenia. The relationship between the MAFLD and sarcopenia were mediated by C-reactive protein (mediation proportion: 15.9%) and high-density lipoprotein cholesterol (mediation proportion: 18.9%). Subgroup analyses confirmed the association between MAFLD and sarcopenia differed in different lifestyle groups.

CONCLUSIONS

Both MAFLD prevalence and severity was significantly associated with sarcopenia. Thus, clinicians should advise comorbidity screening and lifestyle changes to young and middle-aged patients.

Muscle strength and non-alcoholic fatty liver disease/metabolic-associated fatty liver disease

This editorial comments on an article published in a recent issue of World Journal of Gastroenterology, entitled “Association of low muscle strength with metabolic dysfunction-associated fatty liver disease: A nationwide study”. We focused on the association between muscle strength and the incidence of non-alcoholic fatty liver disease (NAFLD) and metabolic-associated fatty liver disease (MAFLD), as well as the mechanisms underlying the correlation and related clinical applications. NAFLD, which is now redefined as MAFLD, is one of the most common chronic liver diseases globally with an increasing prevalence and is characterized by malnutrition, which may contribute to decreased muscle strength. Reduction of muscle strength reportedly has a pathogenesis similar to that of NAFLD/ MAFLD, including insulin resistance, inflammation, sedentary behavior, as well as insufficient vitamin D. Multiple studies have focused on the relationship between sarcopenia or muscle strength and NAFLD. However, studies investigating the relationship between muscle strength and MAFLD are limited. Owing to the shortage of specific medications for NAFLD/MAFLD treatment, early detection is essential. Furthermore, the relationship between muscle strength and NAFLD/MAFLD suggests that improvements in muscle strength may have an impact on disease prevention and may provide novel insights into treatments including dietary therapy, as well as tailored physical activity.

Lifestyle interventions in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a dynamic chronic liver disease that develops in close association with metabolic irregularities. Between 2016 and 2019, the global prevalence among adults was reported as 38% and among children and adolescents it was about 10%. NAFLD can be progressive and is associated with increased mortality from cardiovascular disease, extrahepatic cancers and liver complications. Despite these numerous adverse outcomes, no pharmacological treatments currently exist to treat nonalcoholic steatohepatitis, the progressive form of NAFLD. Therefore, the main treatment is the pursuit of a healthy lifestyle for both children and adults, which includes a diet rich in fruits, nuts, seeds, whole grains, fish and chicken and avoiding overconsumption of ultra-processed food, red meat, sugar-sweetened beverages and foods cooked at high heat. Physical activity at a level where one can talk but not sing is also recommended, including leisure-time activities and structured exercise. Avoidance of smoking and alcohol is also recommended. Policy-makers, community and school leaders need to work together to make their environments healthy by developing walkable and safe spaces with food stores stocked with culturally appropriate and healthy food items at affordable prices as well as providing age-appropriate and safe play areas in both schools and neighbourhoods.

Impact of skeletal muscle mass evaluating methods on severity of metabolic associated fatty liver disease in non-elderly adults

The study aimed to explore the relationships of skeletal muscle mass with disease severity in metabolic-associated fatty liver disease (MAFLD) patients with different methods. Consecutive subjects undergoing bioelectrical impedance analysis were included. The steatosis grade and liver fibrosis were evaluated by MRI-derived proton density fat fraction and two-dimensional shear wave elastography. The appendicular skeletal muscle mass (ASM) was adjusted by height2 (ASM/H2), weight (ASM/W) and BMI (ASM/BMI). Overall, 2223 subjects (50·5 %, MAFLD; 46·9 %, male) were included, with the mean age 37·4 ± 10·6 years. In multivariate logistic regression analysis, the subjects with the lowest quartile (Q1) of ASM/W or ASM/BMI had higher risk ratios for MAFLD (OR (95 % CI) in male: 2·57 (1·35, 4·89), 2·11(1·22, 3·64); in female: 4·85 (2·33, 10·01), 4·81 (2·52, 9·16), all P < 0·05, all for Q1 v. Q4). The MAFLD patients with lower quartiles of ASM/W had the higher risk OR for insulin resistance (IR), both in male and female (2·14 (1·16, 3·97), 4·26 (1·29, 14·02) for Q4 v. Q1, both P < 0·05). While the significant OR were not observed when ASM/H2 and ASM/BMI were used. There were significant dose-dependent associations between decreased ASM/W as well as ASM/BMI and moderate-severe steatosis (2·85(1·54, 5·29), 1·90(1·09, 3·31), both P < 0·05) in male MAFLD patients. In conclusion, ASM/W is superior to ASM/H2 and ASM/BMI in predicting the degree of MAFLD. A lower ASM/W is associated with IR and moderate-severe steatosis in non-elderly male MAFLD.

Sarcopenia Among Patients With Nonalcoholic Fatty Liver Disease (NAFLD) Is Associated With Advanced Fibrosis

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) and sarcopenia can be associated with advanced liver disease. Our aim was to assess the association between sarcopenia and the risk of fibrosis among patients with NAFLD.

METHODS

We used the National Health and Nutrition Examination Survey (2017-2018). NAFLD was defined by transient elastography without other causes of liver disease or excessive alcohol use. Significant fibrosis (SF) and advanced fibrosis (AF) were defined by liver stiffness greater than 8.0 kPa and greater than 13.1 kPa, respectively. Sarcopenia was defined using the Foundation for the National Institutes of Health definition.

RESULTS

Of the total cohort (N = 2422), 18.9% had sarcopenia, 9.8% had obese sarcopenia, 43.6% had NAFLD, 7.0% had SF, and 2.0% had AF. Moreover, 50.1% had neither sarcopenia nor NAFLD, 6.3% had sarcopenia without NAFLD, 31.1% had NAFLD without sarcopenia, and 12.5% had NAFLD with sarcopenia. Compared with individuals without NAFLD or sarcopenia, individuals with sarcopenic NAFLD had higher rates of SF (18.3% vs 3.2%) and AF (7.1% vs 0.2%). In the absence of sarcopenia, compared with individuals without NAFLD, individuals with NAFLD have a significantly increased risk of SF (odds ratio, 2.18; 95% CI, 0.92-5.19). In the presence of sarcopenia, NAFLD was associated with an increased risk of SF (odds ratio, 11.27; 95% CI, 2.79-45.56). This increase was independent of metabolic components. The proportion of SF that is attributable to the interaction of NAFLD and sarcopenia was 55% (attributable proportion, 0.55; 95% CI, 0.36-0.74). Increased leisure time physical activity was associated with a lower risk of sarcopenia.

CONCLUSIONS

Patients with sarcopenic NAFLD are at risk for SF and AF. Increased physical activity and a healthy diet targeted to improve sarcopenic NAFLD could reduce the risk of significant fibrosis.

Metabolic-Associated Fatty Liver Disease and Sarcopenia

The current evidence indicates a strong association between sarcopenia, the loss of muscle mass and strength, and metabolic-associated fatty liver disease (MAFLD). The two entities share many common pathophysiologic mechanisms, and their coexistence may result in higher rates of morbidity and mortality. Therefore, given their increasing incidence in the modern world, there is a need for a better understanding of the liver-muscle axis for early identification of sarcopenia in patients with MAFLD and vice versa. This review aims at presenting current data regarding the correlation between sarcopenia and MAFLD, the associated comorbidities, and the need for effective therapies.

The relationship between metabolic dysfunction-associated fatty liver disease and low muscle mass in an asymptomatic Korean population

BACKGROUND

Metabolic (dysfunction)-associated fatty liver disease (MAFLD) emphasizes the metabolic dysfunction in nonalcoholic fatty liver disease (NAFLD). Although the relationship between low muscle mass and NAFLD has been suggested, the effect of MAFLD on low muscle mass is yet to be investigated. In this study, we examined the relationship between MAFLD and low muscle mass in an asymptomatic Korean population.

METHODS

Examinees who underwent FibroScan® and bioelectrical impedance analyses on the same day during the period of June 2017 to December 2019 were included. Hepatic steatosis was diagnosed using controlled attenuation parameter (CAP) with two cut-off values of 248 and 294 dB/m. Low muscle mass was defined based on appendicular skeletal muscle mass/body weight (wt) or body mass index (BMI) ratios of two standard deviations below the sex-specific mean for healthy young adults. Subjects were divided into four subgroups: diabetic MAFLD (presence of diabetes mellitus [DM]), metabolic dysfunction (MD) MAFLD (≥2 metabolic abnormalities without DM), overweight MAFLD (overweight/obese without DM and <2 metabolic abnormalities) and no MAFLD.

RESULTS

Among all of the 6414 subjects (mean 53.9 years of age; 85.4% male), the prevalence of MAFLD was 49.9% and 22.7% for CAP cut-off values of 248 and 294 dB/m, respectively. In the multivariate analysis, MAFLD was associated with an increased risk of both low muscle mass_wt (odds ratio [OR] 1.80, 95% confidence interval [CI] 1.38-2.35, P < 0.001) and low muscle mass_BMI (OR 1.31, 95% CI 1.01-1.70, P = 0.042). The risk of low muscle mass_wt and low muscle mass_BMI increased the most in the diabetic MAFLD subgroup compared with the no-MAFLD group (OR 2.11, 95% CI 1.51-2.96, P < 0.001 and OR 1.51, 95% CI 1.08-2.13, P = 0.017). There was an increased risk of low muscle mass_wt in the MD MAFLD subgroup (OR 1.73, 95% CI 1.31-2.28, P < 0.001). Comparable results were observed when the CAP cut-off value of 294 dB/m was applied.

CONCLUSIONS

The presence of MAFLD is significantly associated with increased risk of low muscle mass with varying risks according to the MAFLD subgroups. Clinicians should be aware of the differentiated risk of low muscle mass across the subgroups of MAFLD.

Metabolic aspects of hepatitis C virus

Many metabolic factors are associated with chronic hepatitis C virus (HCV) infection and can influence the course of the illness and impact the progression of liver and non-liver-related diseases through complex interactions. Several of these factors impact the course of chronic HCV (CHC) and result in the conceptual translation of CHC from a localized to systemic disease. Besides the traditional liver manifestations associated with CHC infection, such as cirrhosis and hepatocellular carcinoma, various extrahepatic disorders are associated with HCV infection, including atherosclerosis, glucose and lipid metabolic disturbances, alterations in the iron metabolic pathways, and lymphoproliferative diseases. The coexistence of metabolic disorders and CHC is known to influence the chronicity and virulence of HCV and accelerates the progression to liver fibrosis and hepatocellular carcinoma. Insulin resistance is one of the key factors that have a tremendous metabolic impact on CHC. Therefore, there is a great need to properly evaluate patients with CHC infection and correct the modifiable metabolic risk factors. Furthermore, patients with HCV who achieved a sustained virological response showed an overall improvement in glucose metabolism, but the exact evidence still requires further studies with long-term follow-up. This review delineates the most recent evidence on the main metabolic factors associated with CHC and the possible influence of chronic HCV infection on metabolic features.

Prevalence of frailty in patients with non-cirrhotic non-alcoholic fatty liver disease

OBJECTIVE

End-stage chronic liver disease is associated with accelerated ageing and increased frailty. Frailty measures have provided clinical utility in identifying patients at increased risk of poor health outcomes, including those awaiting liver transplantation. However, there is limited data on the prevalence and severity of frailty in patients with non-cirrhotic non-alcoholic fatty liver disease (NAFLD). The aim of this study was to evaluate the prevalence of frailty and prefrailty in patients with non-cirrhotic NAFLD and correlate with severity of liver disease.

DESIGN

A cross-sectional analysis of functional and laboratory frailty assessments, including the Fried frailty index (FFI), a self-reported frailty index (SRFI) and a lab-based frailty index (FI-LAB), was performed in a cohort of 109 patients with NAFLD, and results compared with fibrosis staging based on transient elastography.

RESULTS

Patients with NAFLD had a high prevalence of prefrailty and frailty, with a median SRFI score of 0.18 (IQR: 0.18), FFI of 1 (IQR: 1) and FI-LAB of 0.18 (IQR: 0.12). Using the SRFI, 45% of F0/F1 patients were classified as prefrail and 20% were classified as frail, while in F2/F3 patients this increased to 36% and 41%, respectively. SRFI, 30 s sit-to-stand and FI-LAB scores increased with increasing liver fibrosis stages (p=0.001, 0.006 and <0.001, respectively). On multivariate linear regression, female gender was identified as a significant predictor of elevated frailty scores.

CONCLUSION

This study identifies a high prevalence of frailty in individuals with non-cirrhotic NAFLD. Addressing frailty through early rehabilitation interventions may reduce overall morbidity and mortality in this population.

Insights into Nonalcoholic Fatty-Liver Disease Heterogeneity

The acronym nonalcoholic fatty-liver disease (NAFLD) groups a heterogeneous patient population. Although in many patients the primary driver is metabolic dysfunction, a complex and dynamic interaction of different factors (i.e., sex, presence of one or more genetic variants, coexistence of different comorbidities, diverse microbiota composition, and various degrees of alcohol consumption among others) takes place to determine disease subphenotypes with distinct natural history and prognosis and, eventually, different response to therapy. This review aims to address this topic through the analysis of existing data on the differential contribution of known factors to the pathogenesis and clinical expression of NAFLD, thus determining the different clinical subphenotypes observed in practice. To improve our understanding of NAFLD heterogeneity and the dominant drivers of disease in patient subgroups would predictably impact on the development of more precision-targeted therapies for NAFLD.

Management of non-alcoholic fatty liver disease in patients with sarcopenia

INTRODUCTION

Sarcopenia usually occurs with aging, sedentary lifestyle, unhealthy dietary habits, and chronic disorders pathophysiologically and bi-directionally linked to obesity and nonalcoholic fatty liver disease (NAFLD). Because of the global increase in aging and obesity populations, patients with concomitant sarcopenia and NAFLD are common, accompanied by various disorders relevant to obesity and sarcopenia, with across-the-board impact on socio-economic and public health life worldwide. Therefore, developing effective and practical management of these patients has become a pressing clinical issue.

AREAS COVERED

The authors searched literature from PubMed and Ovid MEDLINE up until Feb 2020. Emerging data on the management of sarcopenia and nonalcoholic fatty liver disease were examined and discussed.

EXPERT OPINION

Although NAFLD in patients with sarcopenia has become a critical problem worldwide, we still don't know much about the management of such patients. Based on theoretical speculations, we can recommend lifestyle intervention, including diet control with adequate protein intake, exercise intervention, and weight reduction as the mainstay of management at the first stage. More studies are needed in the future to identify the most suitable treatment and solve this important problem.

An Overview of the Molecular Mechanisms Contributing to Musculoskeletal Disorders in Chronic Liver Disease: Osteoporosis, Sarcopenia, and Osteoporotic Sarcopenia

The prevalence of osteoporosis and sarcopenia is significantly higher in patients with liver disease than in those without liver disease and osteoporosis and sarcopenia negatively influence morbidity and mortality in liver disease, yet these musculoskeletal disorders are frequently overlooked in clinical practice for patients with chronic liver disease. The objective of this review is to provide a comprehensive understanding of the molecular mechanisms of musculoskeletal disorders accompanying the pathogenesis of liver disease. The increased bone resorption through the receptor activator of nuclear factor kappa (RANK)-RANK ligand (RANKL)-osteoprotegerin (OPG) system and upregulation of inflammatory cytokines and decreased bone formation through increased bilirubin and sclerostin and lower insulin-like growth factor-1 are important mechanisms for osteoporosis in patients with liver disease. Sarcopenia is associated with insulin resistance and obesity in non-alcoholic fatty liver disease, whereas hyperammonemia, low amount of branched chain amino acids, and hypogonadism contributes to sarcopenia in liver cirrhosis. The bidirectional crosstalk between muscle and bone through myostatin, irisin, β-aminoisobutyric acid (BAIBA), osteocalcin, as well as the activation of the RANK and the Wnt/β-catenin pathways are associated with osteosarcopenia. The increased understandings for these musculoskeletal disorders would be contributes to the development of effective therapies targeting the pathophysiological mechanism involved.

Role of Oxidative Stress in Hepatic and Extrahepatic Dysfunctions during Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is a pathology that contains a broad liver dysfunctions spectrum. These alterations span from noninflammatory isolated steatosis until nonalcoholic steatohepatitis (NASH), a more aggressive form of the disease characterized by steatosis, inflammatory status, and varying liver degrees fibrosis. NAFLD is the most prevalent chronic liver disease worldwide. The causes of NAFLD are diverse and include genetic and environmental factors. The presence of NASH is strongly associated with cirrhosis development and hepatocellular carcinoma, two conditions that require liver transplantation. The liver alterations during NAFLD are well described. Interestingly, this pathological condition also affects other critical tissues and organs, such as skeletal muscle and even the cardiovascular, renal, and nervous systems. Oxidative stress (OS) is a harmful state present in several chronic diseases, such as NAFLD. The purpose of this review is to describe hepatic and extrahepatic dysfunctions in NAFLD. We will also review the influence of OS on the physiopathological events that affect the critical function of the liver and peripheral tissues.