Sarcopenia Contributes to the Progression of Nonalcoholic Fatty Liver Disease- Related Fibrosis: A Meta-Analysis

The Story of Ammonia in Liver Disease: An Unraveling Continuum

Hyperammonemia and liver disease are closely linked. Most of the ammonia in our body is produced by transamination and deamination activities involving amino acid, purine, pyrimidines, and biogenic amines, and from the intestine by bacterial splitting of urea. The only way of excretion from the body is by hepatic conversion of ammonia to urea. Hyperammonemia is associated with widespread toxicities such as cerebral edema, hepatic encephalopathy, immune dysfunction, promoting fibrosis, and carcinogenesis. Over the past two decades, it has been increasingly utilized for prognostication of cirrhosis, acute liver failure as well as acute on chronic liver failure. The laboratory assessment of hyperammonemia has certain limitations, despite which its value in the assessment of various forms of liver disease cannot be negated. It may soon become an important tool to make therapeutic decisions about the use of prophylactic and definitive treatment in various forms of liver disease.

The effects of exposure to and timing of a choline-deficient diet during pregnancy and early postnatal life on the skeletal muscle transcriptome of the offspring

BACKGROUND & AIMS

Nonalcoholic fatty liver disease (NAFLD) is related to muscle loss, but the precise mechanism underlying this association remains unclear. The aim of the present study was thus to determine the influence of maternal fatty liver and dietary choline deficiency during pregnancy and/or lactation periods on the skeletal muscle gene expression profile among 24-day-old male rat offspring.

METHODS

Histological examination of skeletal muscle tissue specimens obtained from offspring of dams suffering from fatty liver, provided with proper choline intake during pregnancy and lactation (NN), fed a choline-deficient diet during both periods (DD), deprived of choline only during pregnancy (DN), or only during lactation (ND), was performed. The global transcriptome pattern was assessed using a microarray approach (Affymetrix® Rat Gene 2.1 ST Array Strip). The relative expression of selected genes was validated by real-time PCR (qPCR).

RESULTS

Morphological differences in fat accumulation in skeletal muscle related to choline supply were observed. The global gene expression profile was consistent with abnormal morphological changes. Mettl21c gene was overexpressed in all choline-deficient groups compared to the NN group, while two genes, Cdkn1a and S100a4, were downregulated. Processes of protein biosynthesis were upregulated, and processes related to cell proliferation and lipid metabolism were inhibited in DD, DN, and ND groups compared to the NN group.

CONCLUSIONS

Prenatal and early postnatal exposure to fatty liver and dietary choline deficiency leads to changes in the transcriptome profile in skeletal muscle of 24-day old male rat offspring and is associated with muscle damage, but the mechanism of it seems to be different at different developmental stages of life. Adequate choline intake during pregnancy and lactation can prevent severe muscle disturbance in the progeny of females suffering from fatty liver.

Metabolic-associated fatty liver disease and sarcopenia: A double whammy

The prevalence of metabolic-associated fatty liver disease (MAFLD) has increased substantially in recent years because of the global obesity pandemic. MAFLD, now recognized as the number one cause of chronic liver disease in the world, not only increases liver-related morbidity and mortality among sufferers but also worsens the complications associated with other comorbid conditions such as cardiovascular disease, type 2 diabetes mellitus, obstructive sleep apnoea, lipid disorders and sarcopenia. Understanding the interplay between MAFLD and these comorbidities is important to design optimal therapeutic strategies. Sarcopenia can be either part of the disease process that results in MAFLD (e.g., obesity or adiposity) or a consequence of MAFLD, especially in the advanced stages such as fibrosis and cirrhosis. Sarcopenia can also worsen MAFLD by reducing exercise capacity and by the production of various muscle-related chemical factors. Therefore, it is crucial to thoroughly understand how we deal with these diseases, especially when they coexist. We explore the pathobiological interlinks between MAFLD and sarcopenia in this comprehensive clinical update review article and propose evidence-based therapeutic strategies to enhance patient care.

Sarcopenia, sarcopenic obesity and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), sarcopenia and sarcopenic obesity (SO) are highly prevalent conditions that may coexist, especially in the aging population, without any approved pharmacologic treatment for all of them. There are multiple pathophysiologic mechanisms suggested to explain an association between NAFLD and sarcopenia or SO, including alterations in the adipokines, cytokines, hepatokines and myokines, which may interplay with other factors, such as aging, diet and physical inactivity. In clinical terms, most observational studies support an association between NAFLD and sarcopenia or SO; importantly, there are few cohort studies indicating higher mortality in patients with NAFLD and sarcopenia. Their association also bears some treatment considerations: for example, pioglitazone or vitamin E, suggested as off label treatment for selected patients with nonalcoholic steatohepatitis, may be recommended in the coexistence of sarcopenia or SO, since limited evidence did not show adverse effects of them on sarcopenia and abdominal obesity. In this review, evidence linking sarcopenia and SO with NAFLD is summarized, with a special focus on clinical data. A synopsis of the major pathophysiological links between NAFLD and sarcopenia/SO is initially presented, followed by selected clinical studies and, finally, treatment considerations in patients with NAFLD and sarcopenia or SO are discussed.

Lean nonalcoholic fatty liver disease: Age-dependent differences in pathology, prognosis, and liver-related events

AIM

This study aimed to evaluate the age-specific characteristics, prognosis, and complications of patients with lean nonalcoholic fatty liver disease (NAFLD).

METHODS

Background factors (age, sex, diabetes, dyslipidemia, hypertension, and PNPLA3 gene polymorphism), blood test results, liver histology findings, muscle mass, and grip strength were investigated in 782 patients with NAFLD who underwent liver biopsy. Prognosis and complications were compared among 549 patients with nonlean or lean NAFLD who were followed up for 6.5 years. Additionally, background factors, blood test results, liver histology findings, prognosis, and complications were compared according to age (≥60 years vs. <60 years) in patients with lean NAFLD.

RESULTS

Lean NAFLD patients showed lower aspartate aminotransferase, alanine aminotransferase, homeostasis model assessment-insulin resistance, high-sensitivity C-reactive protein, ferritin, and leptin but higher adiponectin and hemoglobin A1c (HbA1c) levels than patients with nonlean NAFLD. Furthermore, lean NAFLD patients showed less liver fibrosis, inflammation, steatosis, and ballooning. Among lean NAFLD patients, those aged 60 years and older were more frequently female, showed higher rates of hypertension, diabetes, and dyslipidemia, had higher HbA1c and type IV collagen 7S levels, lower platelet count, higher liver fibrosis and inflammation grades, and lower muscle mass and grip strength. Lean NAFLD was associated with a worse prognosis in patients aged 60 years and over than in those younger than 60 years of age and with a higher incidence of liver-related disease, cerebrocardiovascular events, and nonliver cancer.

CONCLUSIONS

Age is an important consideration in patients with lean NAFLD. Compared with nonlean NAFLD, lean NAFLD was associated with a worse prognosis and higher risk of complications in patients aged 60 years and older.

[Sarcopenia in chronic liver diseases]

BACKGROUND

Sarcopenia is a progressive and generalized disorder of the skeletal musculature that involves the loss of skeletal muscle mass and function. Patients with chronic liver disease frequently have sarcopenia in advanced stages of the disease; however, there is an increased prevalence of sarcopenia not only in liver cirrhosis but also in earlier stages of disease, e.g., in non-alcoholic fatty liver disease (NAFLD).

RESULTS

Sarcopenia is an independent prognostic risk factor for morbidity and mortality in patients with liver cirrhosis. The pathogenesis of sarcopenia is multifactorial and in chronic liver diseases a lower oral energy intake, altered ammonia metabolism, hormonal imbalances and a chronic low-grade inflammatory state are important. When the screening test is positive, determination of the muscle strength, e.g., measurement of hand grip strength, is recommended for the diagnostic approach. Lower muscle strength leads to further measurement of muscle mass to confirm the diagnosis of sarcopenia. In patients with chronic liver disease abdominal imaging by computed tomography or magnetic resonance imaging is particularly suitable for this. The severity of sarcopenia is classified by the physical performance. Therapeutic strategies for the treatment of sarcopenia include nutritional therapy as well as exercise therapy.

CONCLUSION

Patients with chronic liver diseases frequently have sarcopenia. This is an independent prognostic risk factor. Therefore, sarcopenia should be considered in the diagnostics and therapeutic approaches.

Clinics in Liver Disease: Update on Nonalcoholic Steatohepatitis: Sarcopenia and Nonalcoholic Fatty Liver Disease

Dual diagnoses of sarcopenia and nonalcoholic fatty liver disease (NAFLD) increase the risk of all cause mortality and severe liver disease, regardless of nationality. General agreement about diagnostic criteria for sarcopenia includes loss of skeletal muscle mass, weakness, and reduced physical performance. Histopathology demonstrates loss of type 2 muscle fibers, more than type 1 fibers and myosteatosis, a risk factor for severe liver disease. Low skeletal mass and NAFLD are inversely related; the mechanism is through decreased insulin signaling and insulin resistance, critical for metabolic homeostasis. Weight loss, exercise, and increased protein intake have been effective in reducing NAFLD and sarcopenia.

Non-Alcoholic Fatty Liver Disease with Sarcopenia and Carotid Plaque Progression Risk in Patients with Type 2 Diabetes Mellitus

BACKGROUND

We aimed to evaluate whether non-alcoholic fatty liver disease (NAFLD) with or without sarcopenia is associated with progression of carotid atherosclerosis in patients with type 2 diabetes mellitus (T2DM).

METHODS

We investigated 852 T2DM patients who underwent abdominal ultrasonography, bioelectrical impedance analysis, and carotid artery ultrasonography at baseline and repeated carotid ultrasonography after 6 to 8 years. NAFLD was confirmed by abdominal ultrasonography, and sarcopenia was defined as a sex-specific skeletal muscle mass index (SMI) value <2 standard deviations below the mean for healthy young adults. SMI was calculated by dividing the sum of appendicular skeletal mass by body weight. We investigated the association between NAFLD with or without sarcopenia and the progression of carotid atherosclerosis.

RESULTS

Of the 852 patients, 333 (39.1%) were classified as NAFLD without sarcopenia, 66 (7.7%) were classified as sarcopenia without NAFLD, and 123 (14.4%) had NAFLD with sarcopenia at baseline. After 6 to 8 years, patients with both NAFLD and sarcopenia had a higher risk of atherosclerosis progression (adjusted odds ratio, 2.20; P<0.009) than controls without NAFLD and sarcopenia. When a subgroup analysis was performed on only patients with NAFLD, female sex, absence of central obesity, and non-obesity were significant factors related to increased risk of plaque progression risk in sarcopenic patients.

CONCLUSION

NAFLD with sarcopenia was significantly associated with the progression of carotid atherosclerosis in T2DM patients.

Interaction between sarcopenia and nonalcoholic fatty liver disease

Sarcopenia and nonalcoholic fatty liver disease (NAFLD) are common health problems related to aging. Despite the differences in their diagnostic methods, several cross-sectional and longitudinal studies have revealed the close link between sarcopenia and NAFLD. Sarcopenia and NAFLD are linked by several shared pathogenetic mechanisms, including insulin resistance, hormonal imbalance, systemic inflammation, myostatin and adiponectin dysregulation, nutritional deficiencies, and physical inactivity, thus implicating a bidirectional relationship between sarcopenia and NAFLD. However, there is not sufficient data to support a direct causal relationship between sarcopenia and NAFLD. Moreover, it is currently difficult to conclude whether sarcopenia is a risk factor for nonalcoholic steatohepatitis (NASH) or is a consequence of NASH. Therefore, this review intends to touch on the shared common mechanisms and the bidirectional relationship between sarcopenia and NAFLD.

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.

Nutrition in the prevention and management of sarcopenia - A special focus on Asian Indians

Sarcopenia, characterized by loss of muscle mass and strength, is common in advanced old age but can be accelerated by chronic disease, malnutrition and physical inactivity. Early initiation of intervention to achieve and maintain a higher peak muscle mass and strength may allow for prevention or delay of sarcopenia and facilitate independent living even in old age. In this context, malnutrition, a significant contributor to sarcopenia, is often overlooked among the Indian population. Maintenance of an optimal energy and protein balance with adequate physical activity level is essential to preserve physical function in the aging population. However, research on the role of micronutrients in muscle maintenance, is still in its infancy. This narrative review, therefore, aims to explore the current status of International and Indian research on the role of nutrition in sarcopenia mitigation and the way forward.

Lipid metabolism in sarcopenia

Sarcopenia is an age-related disease associated with loss of muscle mass and strength. This geriatric syndrome predisposes elderly individuals to a disability, falls, fractures, and death. Fat infiltration in muscle is one of the hallmarks of sarcopenia and aging. Alterations in fatty acid (FA) metabolism are evident in aging, type 2 diabetes, and obesity, with the accumulation of lipids inside muscle cells contributing to muscle insulin resistance and ceramide accumulation. These lipids include diacylglycerol, lipid droplets, intramyocellular lipids, intramuscular triglycerides, and polyunsaturated fatty acids (PUFAs). In this review, we examine the regulation of lipid metabolism in skeletal muscle, including lipid metabolization and storage, intervention, and the types of lipases expressed in skeletal muscle responsible for the breakdown of adipose triglyceride fats. In addition, we address the role of FAs in sarcopenia and the potential benefits of PUFAs.

Prevalence of sarcopenia using different methods in patients with non-alcoholic fatty liver disease

BACKGROUND

Sarcopenia is a clinical condition associated with several liver diseases and it includes non-alcoholic fatty liver disease (NAFLD) in its broad spectrum as steatosis, steatohepatitis and fibrosis. However, the criteria to define sarcopenia are diverse, and even those established in consensus have been discussed regarding their performance in making an accurate diagnosis.

AIM

To evaluate the prevalence of sarcopenia, using different methods, in patients with NAFLD, and its association with clinical-anthropometric parameters.

METHODS

This was an observational study of outpatients with NAFLD. Sarcopenia was defined by the European Working Group Consensus on Sarcopenia in Older People of 2010 (EWGSOP1) and 2018 (EWGSOP2). The skeletal muscle index was used to estimate muscle mass, handgrip strength was assessed using the dynamometer and physical performance by walking a distance of four meters at usual walking speed. The non-invasive fibrosis scores, fibrosis-4 (FIB-4) index and Aspartate aminotransferase to platelet ratio index (APRI), were used to assess the absence and presence of fibrosis.

RESULTS

Fifty-seven individuals with NAFLD were evaluated, the mean age (SD) was 52.7 (11.3) years and 75.4% were female. Fibrosis assessed by FIB-4 and APRI was observed in 3.7% and 16.6% of patients with NAFLD, respectively. The diagnosis of sarcopenia was identified only by EWGSOP1 in 3.5% of NAFLD patients, and the prevalence of probable/pre-sarcopenia was higher using the EWGSOP2 consensus at 26.3%, when compared to 1.8% with EWGSOP1. Sarcopenia defined by EWGSOP1, was associated with grade I steatosis, but without overweight (P < 0.05). An association between sarcopenia and fibrosis was not observed (P > 0.05). EWGSOP2 showed a greater number of patients with probable sarcopenia, and who were overweight (12 (80.0%)), with a higher degree of steatosis [11 (73.3%) and presence of fibrosis (1 (6.7%), FIB-4 and 3 (20.0%), APRI] compared to EWGSOP1 [1 (100%), 0 (0.0%), 0 (0.0%), FIB-4 and 0 (0.0%), APRI, respectively].

CONCLUSION

The present study showed that sarcopenia in NAFLD was not predominant in patients without fibrosis, by both diagnostic methods. In addition, the prevalence of probable sarcopenia also depends on the method applied.

Benefits of Physical Exercise as Approach to Prevention and Reversion of Non-Alcoholic Fatty Liver Disease in Children and Adolescents with Obesity

Non-alcoholic fatty liver disease (NAFLD) is an important health concern during childhood; indeed, it is the most frequent cause of chronic liver diseases in obese children. No valid pharmacological therapies for children affected by this condition are available, and the recommended treatment is lifestyle modification, usually including nutrition and exercise interventions. In this narrative review, we summarized up-to-date information on the benefits of physical exercise on NAFLD in children and adolescents with obesity. The role of exercise as non-pharmacological treatment was emphasized in order to provide recent advances on this topic for clinicians not deeply involved in the field. Several studies on obese children and adults confirm the positive role of physical activity (PA) in the treatment of NAFLD, but to date, there are no pediatric randomized clinical trials on exercise versus usual care. Among the pathogenic mechanisms involved in the PA effects on NAFLD, the main players seem to be insulin resistance and related inflammation, oxidative stress, and gut dysbiosis, but further evaluations are necessary to deeply understand whether these factors are correlated and how they synergistically act. Thus, a deeper research on this theme is needed, and it would be extremely interesting.

Low skeletal muscle mass is associated with more severe histological features of non-alcoholic fatty liver disease in male

BACKGROUND/PURPOSE OF THE STUDY

Although low skeletal muscle mass is associated with non-alcoholic fatty liver disease (NAFLD), it is currently uncertain whether there are associations between weight-adjusted appendicular skeletal muscle (ASM%), severity of histological features of NAFLD, and the patatin-like phospholipase domain-containing 3 (PNPLA3) rs738409 polymorphism. Our aim was to test for a possible influence of the PNPLA3 rs738409 variant on the association between ASM% and severity of NAFLD histological features.

METHODS

We enrolled 401 Chinese male with biopsy-proven NAFLD. Using a bioelectrical-impedance body composition analyzer (BIA, Inbody 720, Japan Inc., Tokyo), we calculated the ASM% as the percentage of total appendicular skeletal muscle mass (ASM, kg)/total body mass (kg) × 100.

RESULTS

Compared to those with high ASM%, patients with low ASM% (≤ 30.6, i.e., the median value of distribution of the whole sample) had a greater severity of individual histological features of NAFLD. These patients also had a higher risk of severe steatosis and non-alcoholic steatohepatitis (NASH) (adjusted-odds ratio [OR] 2.34, 95% CI 1.39-3.93, and adjusted-OR 2.22, 95% CI 1.30-3.77) even after adjusting for age, body mass index, diabetes, and serum creatinine levels. Carriage of the G allele of PNPLA3 rs738409 plus low ASM% was associated with a higher risk of severe steatosis and presence of liver fibrosis (OR 3.02, 95% CI 1.46-6.26, p = 0.003 and OR 2.18, 95% CI 1.03-4.60, p = 0.041 respectively), and there was a non-significant but borderline increased risk of NASH (OR 2.00, 95% CI 0.98-4.06, p = 0.056).

CONCLUSIONS

Low ASM% and the presence of a G allele within PNPLA3 rs738409 is associated with more severe histological features of NAFLD.

Lifestyle Interventions for Non-Obese Patients Both with, and at Risk, of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease occurring in non-obese subjects (the so-called non-obese NAFLD) is a highly prevalent but neglected liver condition, which is closely associated with metabolic disorders and suboptimal lifestyles. Landmark studies have shown that lifestyle interventions are potentially beneficial in decreasing the risk of developing non-obese NAFLD and in ameliorating NAFLD in non-obese individuals with pre-existing NAFLD. Lifestyle interventions usually refer to changes in eating habits and physical activity, both of which have a powerful effect on non-obese NAFLD and on risk factors for non-obese NAFLD. However, to date, patients and health-care professionals have a poor awareness and understanding of non-obese NAFLD and the beneficial effects of lifestyle interventions in this patient population. The aim of this narrative review is to briefly discuss the evidence for the effects of lifestyle changes and what changes are needed amongst medical personnel and other stakeholders in order to raise awareness of non-obese NAFLD.

Impact of Sarcopenia on the Severity of the Liver Damage in Patients With Non-alcoholic Fatty Liver Disease

An extensive body of the literature shows a strong interrelationship between the pathogenic pathways of non-alcoholic fatty liver disease (NAFLD) and sarcopenia through the muscle-liver-adipose tissue axis. NAFLD is one of the leading causes of chronic liver diseases (CLD) affecting more than one-quarter of the general population worldwide. The disease severity spectrum ranges from simple steatosis to non-alcoholic steatohepatitis (NASH), cirrhosis, and its complications: end-stage chronic liver disease and hepatocellular carcinoma. Sarcopenia, defined as a progressive loss of the skeletal muscle mass, reduces physical performances, is associated with metabolic dysfunction and, possibly, has a causative role in NAFLD pathogenesis. Muscle mass is a key determinant of the whole-body insulin-mediated glucose metabolism and impacts fatty liver oxidation and energy homeostasis. These mechanisms drive the accumulation of ectopic fat both in the liver (steatosis, fatty liver) and in the muscle (myosteatosis). Myosteatosis rather than the muscle mass per se, seems to be closely associated with the severity of the liver injury. Sarcopenic obesity is a recently described entity which associates both sarcopenia and obesity and may trigger worse clinical outcomes including hepatic fibrosis progression and musculoskeletal disabilities. Furthermore, the muscle-liver-adipose tissue axis has a pivotal role in changes of the body composition, resulting in a distinct clinical phenotype that enables the identification of the "sarcopenic NAFLD phenotype." This review aims to bring some light into the complex relationship between sarcopenia and NAFLD and critically discuss the key mechanisms linking NAFLD to sarcopenia, as well as some of the clinical consequences associated with the coexistence of these two entities: the impact of body composition phenotypes on muscle morphology, the concept of sarcopenic obesity, the relationship between sarcopenia and the severity of the liver damage and finally, the future directions and the existing gaps in the knowledge.

Impact of Sarcopenia and Myosteatosis in Non-Cirrhotic Stages of Liver Diseases: Similarities and Differences across Aetiologies and Possible Therapeutic Strategies

Sarcopenia is defined as a loss of muscle strength, mass and function and it is a predictor of mortality. Sarcopenia is not only a geriatric disease, but it is related to several chronic conditions, including liver diseases in both its early and advanced stages. Despite the increasing number of studies exploring the role of sarcopenia in the early stages of chronic liver disease (CLD), its prevalence and the relationship between these two clinical entities are still controversial. Myosteatosis is characterized by fat accumulation in the muscles and it is related to advanced liver disease, although its role in the early stages is still under researched. Therefore, in this narrative review, we firstly aimed to evaluate the prevalence and the pathogenetic mechanisms underlying sarcopenia and myosteatosis in the early stage of CLD across different aetiologies (mainly non-alcoholic fatty liver disease, alcohol-related liver disease and viral hepatitis). Secondly, due to the increasing prevalence of sarcopenia worldwide, we aimed to revise the current and the future therapeutic approaches for the management of sarcopenia in CLD.

Waist and hip circumference are independently associated with the risk of liver disease in population-based studies

BACKGROUND & AIMS

While several anthropometric measures predict liver disease, the waist-hip ratio (WHR) has shown superiority in previous studies. We analysed independent and joint associations of waist circumference (WC) and hip circumference (HC) with liver disease and liver-related risk factors.

METHODS

Cross-sectional study (n = 6619) and longitudinal cohort (n = 40 923) comprised individuals from Health 2000 and FINRISK 1992-2012 studies. Prevalent and viral liver diseases were excluded. Longitudinal cohort was linked with national healthcare registers for severe incident liver disease. Linear regression and Cox proportional hazards models were used to analyse anthropometric, lifestyle, metabolic and bioimpedance-related parameters; liver enzymes; and 59 liver-related genetic risk variants.

RESULTS

WC and HC showed independent and opposite associations with both liver enzymes and incident liver disease among men (HR for liver disease: WC, 1.07, 95% CI 1.03-1.11; HC, 0.96, 95% CI 0.92-0.99; P-range .04 to <.001) and women (HR for liver diseases: WC, 1.06, 95% CI 1.02-1.10; HC, 0.93, 95% CI 0.89-0.98; P-range .005 to .004). HC modified associations between WC and liver enzymes, and between WC and incident liver disease, particularly among men. Liver enzymes and risk of liver disease increased with increasing WC, more so among individuals with high WHR compared to with low WHR. WC and HC jointly reflected both body fat distribution and muscle mass, which was largely mirrored by WHR.

CONCLUSIONS

WC and HC exhibit independent and joint associations with liver disease, which are largely reflected by WHR. Both body fat distribution and muscle mass contribute to these anthropometric measures.

Metabolic Syndrome and Sarcopenia

Skeletal muscle is a major organ of insulin-induced glucose metabolism. In addition, loss of muscle mass is closely linked to insulin resistance (IR) and metabolic syndrome (Met-S). Skeletal muscle loss and accumulation of intramuscular fat are associated with a variety of pathologies through a combination of factors, including oxidative stress, inflammatory cytokines, mitochondrial dysfunction, IR, and inactivity. Sarcopenia, defined by a loss of muscle mass and a decline in muscle quality and muscle function, is common in the elderly and is also often seen in patients with acute or chronic muscle-wasting diseases. The relationship between Met-S and sarcopenia has been attracting a great deal of attention these days. Persistent inflammation, fat deposition, and IR are thought to play a complex role in the association between Met-S and sarcopenia. Met-S and sarcopenia adversely affect QOL and contribute to increased frailty, weakness, dependence, and morbidity and mortality. Patients with Met-S and sarcopenia at the same time have a higher risk of several adverse health events than those with either Met-S or sarcopenia. Met-S can also be associated with sarcopenic obesity. In this review, the relationship between Met-S and sarcopenia will be outlined from the viewpoints of molecular mechanism and clinical impact.

The Association between Low Muscle Mass and Hepatic Steatosis in Asymptomatic Population in Korea

Background: An association between low muscle mass and nonalcoholic fatty liver disease (NAFLD) has been suggested. We investigated this relationship using controlled attenuation parameter (CAP). Methods: A retrospective cohort of subjects had liver FibroScan^® (Echosens, Paris, France) and bioelectrical impedance analyses during health screening exams. Low muscle mass was defined based on appendicular skeletal muscle mass/body weight ratios of one (class I) or two (class II) standard deviations below the sex-specific mean for healthy young adults. Results: Among 960 subjects (58.1 years; 67.4% male), 344 (45.8%, class I) and 110 (11.5%, class II) had low muscle mass. After adjusting for traditional metabolic risk factors, hepatic steatosis, defined as a CAP ≥ 248 dB/m, was associated with low muscle mass (class I, odds ratio (OR): 1.96, 95% confidence interval (CI): 1.38–2.78; class II, OR: 3.33, 95% CI: 1.77–6.26). A dose-dependent association between the grade of steatosis and low muscle mass was also found (class I, OR: 1.88, for CAP ≥ 248, <302; OR: 2.19, in CAP ≥ 302; class II, OR: 2.33, for CAP ≥ 248, <302; OR: 6.17, in CAP ≥ 302). High liver stiffness was also significantly associated with an increased risk of low muscle mass (class I, OR: 1.97, 95% CI: 1.31–2.95; class II, OR: 2.96, 95% CI: 1.51–5.78). Conclusion: Hepatic steatosis is independently associated with low muscle mass in a dose-dependent manner. The association between hepatic steatosis and low muscle mass suggests that particular attention should be given to subjects with NAFLD for an adequate assessment of muscle mass.

Relationship Between Protein Intake and Sarcopenia in the Elderly with Nonalcoholic Fatty Liver Disease Based on the Fourth and Fifth Korea National Health and Nutrition Examination Survey

Background: The association between sarcopenia and protein intake has been well studied. However, limited data are available on the association between sarcopenia and protein intake in people with nonalcoholic fatty liver disease (NAFLD). This study aimed to investigate the association between protein intake and sarcopenia among elderly participants with NAFLD using the Korea National Health and Nutrition Examination Survey (KNHANES). Methods: Data of 4179 participants (1576 men and 2603 women, age ≥60 years) who participated in the KNHANES during 2008-2011 were obtained. Sarcopenia was defined as appendicular skeletal muscle mass/wt (%) of 1 standard deviation below the gender-specific mean for healthy adults and NAFLD as liver fat score using the fatty liver prediction models. According to their daily protein intake, participants were grouped into the high protein intake group (>1.2 g/kg/day), middle protein intake group (0.8-1.2 g/kg/day), and low protein intake group (<0.8 g/kg/day). Generalized linear models and logistic regression models were used. Results: The overall prevalence of sarcopenia in participants with NAFLD was 16.53%. Compared with the highest protein intake group, the low protein intake group had a significantly higher risk of sarcopenia (adjustment odds ratio = 1.707; 95% confidence interval = 1.009-2.886). In the fully adjusted model, the highest protein intake group had significantly lower levels of insulin, total body fat, vitamin B, and fat intake, whereas muscle proportions, energy, carbohydrates, vitamin A, and vitamin C intake of high protein intake participants were significantly higher than other groups. Conclusion: The prevalence of sarcopenia and sarcopenia-related factors were significantly lower in NAFLD elderly participants with high protein intake. These results suggest that high protein intake can help prevent and manage sarcopenia in people with NAFLD.

Sarcopenic Obesity in Non-Alcoholic Fatty Liver Disease-The Union of Two Culprits

Non-alcoholic fatty liver disease (NAFLD) continues to rise and has become the most common cause of chronic liver disease among all ages and ethnicities. Metabolic disorders, such as obesity and insulin resistance, are closely associated with sarcopenia and NAFLD. Sarcopenic obesity is a clinical disorder characterized by the simultaneous loss of skeletal muscle and gain of adipose tissue. It is associated with worse outcomes in individuals with NAFLD. It is projected that NAFLD and sarcopenia will rise as the prevalence of obesity continues to increase at an unparallel rate. Recently, sarcopenia and sarcopenic obesity have gained considerable interest, but we still lack a well-defined definition and a management approach. Therefore, it is imperative to continue shining the light on this topic and better understand the underlying mechanism as well as treatment options. In this review article, we aimed to address the pathophysiology, impact, and outcomes of sarcopenic obesity on NAFLD.

The muscle to bone axis (and viceversa): An encrypted language affecting tissues and organs and yet to be codified?

Skeletal muscles and bone tissue form the musculoskeletal apparatus, a complex system essential for the voluntary movement. The loss of muscle mass and muscle strength is often associated with a loss of bone mass, in a "hazardous duet" which implies the co-existence of sarcopenia-osteoporosis and exposes patients to a deterioration in quality of life and increased mortality. From the mechanostat theory to the recent definition of the osteosarcopenia syndrome, many aspects of muscle-bone interaction have been investigated in recent decades. The mechanical interaction is now accepted, considering the close anatomical relationship between the two tissues, however, much remains to be discovered regarding the biochemical muscle-bone interaction. Skeletal muscle has been defined as an endocrine organ capable of exerting an action on other tissues. Myokines, bioactive polypeptides released by the muscle, could represent the encrypted message in the communication between muscle and bone. These two tissues have a reciprocal influence on their metabolisms and respond in a similar way to the multiple external factors. The aim of this review is to stimulate the understanding of the encrypted language between muscle and bone, highlighting the role of catabolic pathways and oxidative stress in the musculoskeletal apparatus to elucidate the shared mechanisms and the similarity of response to the same stimuli by different tissues. Our understanding of muscle-bone interactions it could be useful to identify and develop new strategies to treat musculoskeletal diseases, together with pharmacological, nutritional and exercise-based approaches, which are already in use for the treatment of these pathologies.

Harnessing Muscle-Liver Crosstalk to Treat Nonalcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) has reached epidemic proportions, affecting an estimated one-quarter of the world's adult population. Multiple organ systems have been implicated in the pathophysiology of NAFLD; however, the role of skeletal muscle has until recently been largely overlooked. A growing body of evidence places skeletal muscle-via its impact on insulin resistance and systemic inflammation-and the muscle-liver axis at the center of the NAFLD pathogenic cascade. Population-based studies suggest that sarcopenia is an effect-modifier across the NAFLD spectrum in that it is tightly linked to an increased risk of non-alcoholic fatty liver, non-alcoholic steatohepatitis (NASH), and advanced liver fibrosis, all independent of obesity and insulin resistance. Longitudinal studies suggest that increases in skeletal muscle mass over time may both reduce the incidence of NAFLD and improve preexisting NAFLD. Adverse muscle composition, comprising both low muscle volume and high muscle fat infiltration (myosteatosis), is highly prevalent in patients with NAFLD. The risk of functional disability conferred by low muscle volume in NAFLD is further exacerbated by the presence of myosteatosis, which is twice as common in NAFLD as in other chronic liver diseases. Crosstalk between muscle and liver is influenced by several factors, including obesity, physical inactivity, ectopic fat deposition, oxidative stress, and proinflammatory mediators. In this perspective review, we discuss key pathophysiological processes driving sarcopenia in NAFLD: anabolic resistance, insulin resistance, metabolic inflexibility and systemic inflammation. Interventions that modify muscle quantity (mass), muscle quality (fat), and physical function by simultaneously engaging multiple targets and pathways implicated in muscle-liver crosstalk may be required to address the multifactorial pathogenesis of NAFLD/NASH and provide effective and durable therapies.

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

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is currently one of the most common liver diseases worldwide. Recent data suggest that loss of skeletal muscle mass and function (i.e. sarcopenia) is highly prevalent and frequently overlooked in NAFLD patients. Experimental and clinical data suggest that the relationship between NAFLD and sarcopenia is pathophysiologically complex and bi-directional and there is a growing interest in unveiling how sarcopenia could influence NAFLD development and progression.

AREAS COVERED

PubMed/MEDLINE was searched for articles related to concomitant occurrence of NAFLD and sarcopenia between January 2013 and April 2020. Areas covered in this review include: (1) updated sarcopenia diagnosis strategy, (2) discussion of current data on pathophysiological connections between NAFLD and sarcopenia, and (3) analysis of current and future therapeutic implications of this knowledge.

EXPERT OPINION

Clinical studies describe a consistent association between NAFLD and sarcopenia, although a cause-effect relation remains to be determined. Active implementation of current diagnosis algorithms and optimized treatment can prevent sarcopenia related complications in subjects with NAFLD. Pathogenic pathways implicated in this relation are multiple and complex, a better understanding of them can provide novel biomarkers and targeted therapies that will hopefully have an important impact in NAFLD management.

Sarcopenia and adverse health-related outcomes: An umbrella review of meta-analyses of observational studies

OBJECTIVE

The purpose of this umbrella review was to assess the associations between sarcopenia and adverse health-related outcomes.

DESIGN

An umbrella review of meta-analyses of observational studies.

SETTING AND PARTICIPANTS

Patients with sarcopenia and controls without sarcopenia were included.

MEASURES

The PubMed, Web of Science and Embase were searched for relevant systematic review and meta-analysis. AMSTAR and GRADE system were used for methodological quality and evidence quality assessments, respectively.

RESULTS

Totally 54 outcomes extracted from 30 meta-analyses were analyzed. Twenty out of 21 prognostic outcomes indicated that sarcopenia was significantly associated with poorer prognosis of gastric cancer, hepatocellular cancer, urothelial cancer, head and neck cancer, hematological malignancy, pancreatic cancer, breast cancer, colorectal cancer, lung cancer, esophageal cancer, and ovarian cancer. Besides, 10 out of 16 postoperative outcomes suggested that sarcopenia significantly increased the risk of multiple postoperative complications and prolonged the length of hospitalization of patients with digestive cancer. In age-related outcomes, sarcopenia significantly increased the risk of dysphagia, cognitive impairment, fractures, falls, hospitalization, and all-cause mortality of elderly populations. Moreover, sarcopenia was also associated with higher level of albuminuria, risk of depression, and several metabolic diseases.

CONCLUSIONS AND IMPLICATIONS

Sarcopenia significantly affected a wide range of adverse health-related outcomes, particularly in patients of tumor and elderly populations. Because evidences of most outcomes were rated as "low" and "very low," more prospective cohort studies are required in the future.

Adverse muscle composition is linked to poor functional performance and metabolic comorbidities in NAFLD

Background & Aims

Sarcopenia and frailty are recognised as important factors in later stages of liver disease. However, their role in non-alcoholic fatty liver disease (NAFLD) is not yet fully understood. In this study we investigate the associations of MRI-measured adverse muscle composition (AMC: low muscle volume and high muscle fat) with poor function, sarcopenia, and metabolic comorbidity within NAFLD in the large UK Biobank imaging study.

Methods

A total of 9,545 participants were included. Liver fat, fat-tissue free muscle volume, and muscle fat infiltration were quantified using a rapid MRI protocol and automated image analysis (AMRA® Researcher). For each participant, a personalised muscle volume z-score (sex- and body size-specific) was calculated and combined with muscle fat infiltration for AMC detection. The following outcomes were investigated: functional performance (hand grip strength, walking pace, stair climbing, falls) and metabolic comorbidities (coronary heart disease, type 2 diabetes). Sarcopenia was detected by combining MRI thresholds for low muscle quantity and low hand grip strength according to the European working group definition.

Results

The prevalence of sarcopenia in NAFLD (1.6%) was significantly lower (p <0.05) compared with controls without fatty liver (3.4%), whereas the prevalence of poor function and metabolic comorbidity was similar or higher. Of the 1,204 participants with NAFLD, 169 (14%) had AMC and showed 1.7–2.4× higher prevalence of poor function (all p <0.05) as well as 2.1× and 3.3× higher prevalence of type 2 diabetes and coronary heart disease (p <0.001), respectively, compared with those without AMC.

Conclusions

AMC is a prevalent and highly vulnerable NAFLD phenotype displaying poor function and high prevalence of metabolic comorbidity. Sarcopenia guidelines can be strengthened by including cut-offs for muscle fat, enabling AMC detection.

Lay summary

Today, it is hard to predict whether a patient with fatty liver disease will progress to more severe liver disease. This study shows that measuring muscle health (the patient's muscle volume and how much fat they have in their muscles) could help identify the more vulnerable patients and enable early prevention of severe liver disease.

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The role of sarcopenia and frailty in NAFLD is not yet fully understood.

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Magnetic resonance imaging enables quantification of muscle composition.

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Myosteatosis in combination with low muscle volume characterises an adverse muscle composition.

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Adverse muscle composition is a novel NAFLD phenotype associated with poor function and metabolic comorbidity.

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Sarcopenia guidelines can be strengthened by including cut-offs for muscle fat.

A Critical Appraisal of the Definition of Sarcopenia in Patients with Non-Alcoholic Fatty Liver Disease: Pitfall of Adjusted Muscle Mass by Body Weight

Traditionally, sarcopenia has defined as amount of absolute muscle mass adjusted by height in the elderly people. However, relative muscle mass adjusted by weight has been used extensively in most non-alcoholic fatty liver disease (NAFLD) studies. Here, we attempted to investigate the pitfall of adjusted muscle mass by weight to evaluate association between sarcopenia and NAFLD. Adult subjects (n = 1343) who underwent a health check-up were finally included for analysis. The weight-adjusted skeletal muscle mass index (wSMI) and height-adjusted SMI (hSMI) calculated by dividing the total appendicular skeletal muscle (ASM) by weight or the square of height, respectively. Prevalence of sarcopenia defined by wSMI in the NAFLD group was significantly higher than in the control group (1.3% vs. 8.8%, p < 0.001). However, there was no difference in the prevalence of sarcopenia defined by hSMI between the control and NAFLD groups (2.0% vs. 0.8%, p = 0.055). Since body weight was the most potent independent risk factor for NAFLD in multivariable logistic regression analysis, abnormal rates (<-1 SD) of almost all parameters increased in the NAFLD population, after weight adjustment. However, abnormal rates of non-metabolic parameter did not increase in NAFLD, after height adjustment. Only metabolic parameters showed relationship with NAFLD, after height adjustment. As NAFLD is highly associated with body weight, careful attention should be given in the case of studying the relationship of NAFLD with sarcopenia adjusted by body weight.

Dysregulated Autophagy Mediates Sarcopenic Obesity and Its Complications via AMPK and PGC1α Signaling Pathways: Potential Involvement of Gut Dysbiosis as a Pathological Link

Sarcopenic obesity (SOB), which is closely related to being elderly as a feature of aging, is recently gaining attention because it is associated with many other age-related diseases that present as altered intercellular communication, dysregulated nutrient sensing, and mitochondrial dysfunction. Along with insulin resistance and inflammation as the core pathogenesis of SOB, autophagy has recently gained attention as a significant mechanism of muscle aging in SOB. Known as important cellular metabolic regulators, the AMP-activated protein kinase (AMPK) and the peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) signaling pathways play an important role in autophagy, inflammation, and insulin resistance, as well as mutual communication between skeletal muscle, adipose tissue, and the liver. Furthermore, AMPK and PGC-1α signaling pathways are implicated in the gut microbiome-muscle axis. In this review, we describe the pathological link between SOB and its associated complications such as metabolic, cardiovascular, and liver disease, falls and fractures, osteoarthritis, pulmonary disease, and mental health via dysregulated autophagy controlled by AMPK and/or PGC-1α signaling pathways. Here, we propose potential treatments for SOB by modulating autophagy activity and gut dysbiosis based on plausible pathological links.

Implications of Nonalcoholic Steatohepatitis as the Cause of End-Stage Liver Disease Before and After Liver Transplant

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease. Nonalcoholic steatohepatitis (NASH) is the clinically aggressive variant of NAFLD and has a propensity for fibrosis progression and cirrhosis. The prevalence of NAFLD and NASH is projected to increase rapidly in the near future and dramatically add to the already substantial health care burden. Cirrhosis and end-stage liver disease resulting from NASH is now the fastest growing indication for liver transplant (LT) in the United States. Patients with NASH cirrhosis have higher prevalence of cardiometabolic diseases. Following LT, recurrence of NAFLD and NASH is common.

Impact of Skeletal Muscle Mass on Metabolic Health

Skeletal muscle is regarded as an endocrine and paracrine organ. Muscle-derived secretory proteins, referred to as myokines, mediate interactions between skeletal muscle mass and other organs such as the liver, adipose tissue, pancreas, bone, and the cardiovascular system. As individuals age, reduced levels of physical activity and sarcopenia (loss of skeletal muscle mass and strength) are associated with physical frailty and disability. Recently, several studies have suggested that the loss of skeletal muscle mass may contribute to metabolic disease. Therefore, herein, we focus on the relationships between skeletal muscle mass and metabolic diseases, including metabolic syndrome and non-alcoholic fatty liver disease.

Sarcopenia and fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease which may progress to non-alcoholic steatohepatitis. The prevalence of sarcopenia, which is the loss of muscle mass and strength, is increasing in the aging society. Recent studies reported the relationship between NAFLD and sarcopenia. The skeletal muscle is the primary organ for glucose disposal. Loss of muscle mass can cause insulin resistance, which is an important risk factor for NAFLD. Moreover, obesity, chronic low-grade inflammation, vitamin D deficiency, physical inactivity, hepatokines, and myokines might be involved in the pathophysiologic mechanism of sarcopenia and NAFLD. Although most of the previous studies have demonstrated the positive correlation between sarcopenia and NAFLD, the difference in diagnostic methods of sarcopenia and NAFLD leads to difficulties in interpretation and application. This review discusses the concept and diagnosis of sarcopenia and NAFLD, common pathophysiology, and clinical studies linking sarcopenia to NAFLD. The presentation of the association between sarcopenia and NAFLD may provide an opportunity to prevent the deterioration of fatty liver disease.

Sarcopenic obesity in fatty liver

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steato hepatitis have an increasing prevalence among liver diseases. Overweight and obesity are frequently associated conditions in patients with fatty liver. Skeletal muscle mass depletion may also coexist with chronic liver disease even in obese patients. This review will focus on the relationship between sarcopenic obesity and fatty liver.

RECENT FINDINGS

Obesity and sarcopenia are frequently encountered in patients with NAFLD. Adipose tissue is able to release molecules (adipokines) that regulate lipid metabolism, interact with insulin sensitivity and may contribute to induce fibrogenesis in the liver. Skeletal muscle tissue is able to secrete myokines regulating muscle metabolism and insulin sensitivity. Myokines perturbation has been reported to influence adipose tissue mass and fat deposition in the liver. Sarcopenia has been reported as independent risk factor for the development of NAFLD, and for a more severe liver fibrosis in patients with NAFLD.

SUMMARY

The interaction between skeletal muscle, adipose tissue and the liver may play a role in the development of NAFLD. Sarcopenia and sarcopenic obesity are risk factors for the development of fatty liver and associated with more severe liver fibrosis. Management is not standardized, but dietary counseling and physical training have been proposed as promising strategies. Bariatric surgery may be considered in patients with severe 'resistant' obesity.