Serum levels of osteoprotegerin in the spectrum of nonalcoholic fatty liver disease

Osteoprotegerin is an Early Marker of the Fibrotic Process and of Antifibrotic Treatment Responses in Ex Vivo Lung Fibrosis

BACKGROUND

Lung fibrosis is a chronic lung disease with a high mortality rate with only two approved drugs (pirfenidone and nintedanib) to attenuate its progression. To date, there are no reliable biomarkers to assess fibrosis development and/or treatment effects for these two drugs. Osteoprotegerin (OPG) is used as a serum marker to diagnose liver fibrosis and we have previously shown it associates with lung fibrosis as well.

METHODS

Here we used murine and human precision-cut lung slices to investigate the regulation of OPG in lung tissue to elucidate whether it tracks with (early) fibrosis development and responds to antifibrotic treatment to assess its potential use as a biomarker.

RESULTS

OPG mRNA expression in murine lung slices was higher after treatment with profibrotic cytokines TGFβ1 or IL13, and closely correlated with Fn and PAI1 mRNA expression. More OPG protein was released from fibrotic human lung slices than from the control human slices and from TGFβ1 and IL13-stimulated murine lung slices compared to control murine slices. This OPG release was inhibited when murine slices were treated with pirfenidone or nintedanib. OPG release from human fibrotic lung slices was inhibited by pirfenidone treatment.

CONCLUSION

OPG can already be detected during the early stages of fibrosis development and responds, both in early- and late-stage fibrosis, to treatment with antifibrotic drugs currently on the market for lung fibrosis. Therefore, OPG should be further investigated as a potential biomarker for lung fibrosis and a potential surrogate marker for treatment effect.

Anti-osteoporotic treatments in the era of non-alcoholic fatty liver disease: friend or foe

Over the last years non-alcoholic fatty liver disease (NAFLD) has grown into the most common chronic liver disease globally, affecting 17-38% of the general population and 50-75% of patients with obesity and/or type 2 diabetes mellitus (T2DM). NAFLD encompasses a spectrum of chronic liver diseases, ranging from simple steatosis (non-alcoholic fatty liver, NAFL) and non-alcoholic steatohepatitis (NASH; or metabolic dysfunction-associated steatohepatitis, MASH) to fibrosis and cirrhosis with liver failure or/and hepatocellular carcinoma. Due to its increasing prevalence and associated morbidity and mortality, the disease-related and broader socioeconomic burden of NAFLD is substantial. Of note, currently there is no globally approved pharmacotherapy for NAFLD. Similar to NAFLD, osteoporosis constitutes also a silent disease, until an osteoporotic fracture occurs, which poses a markedly significant disease and socioeconomic burden. Increasing emerging data have recently highlighted links between NAFLD and osteoporosis, linking the pathogenesis of NAFLD with the process of bone remodeling. However, clinical studies are still limited demonstrating this associative relationship, while more evidence is needed towards discovering potential causative links. Since these two chronic diseases frequently co-exist, there are data suggesting that anti-osteoporosis treatments may affect NAFLD progression by impacting on its pathogenetic mechanisms. In the present review, we present on overview of the current understanding of the liver-bone cross talk and summarize the experimental and clinical evidence correlating NAFLD and osteoporosis, focusing on the possible effects of anti-osteoporotic drugs on NAFLD.

Osteoprotegerin/Receptor Activator of Nuclear Factor-Kappa B Ligand/Receptor Activator of Nuclear Factor-Kappa B Axis in Obesity, Type 2 Diabetes Mellitus, and Nonalcoholic Fatty Liver Disease

PURPOSE OF REVIEW

To summarize evidence on the potential involvement of the osteoprotegerin (OPG)/receptor activator of nuclear factor-kappa B (NF-κΒ) ligand (RANKL)/receptor activator of NF-κΒ (RANK) axis in the pathogenesis of metabolic diseases.

RECENT FINDINGS

The OPG-RANKL-RANK axis, which has been originally involved in bone remodeling and osteoporosis, is now recognized as a potential contributor in the pathogenesis of obesity and its associated comorbidities, i.e., type 2 diabetes mellitus and nonalcoholic fatty liver disease. Besides bone, OPG and RANKL are also produced in adipose tissue and may be involved in the inflammatory process associated with obesity. Metabolically healthy obesity has been associated with lower circulating OPG concentrations, possibly representing a counteracting mechanism, while elevated serum OPG levels may reflect an increased risk of metabolic dysfunction or cardiovascular disease. OPG and RANKL have been also proposed as potential regulators of glucose metabolism and are potentially involved in the pathogenesis of type 2 diabetes mellitus. In clinical terms, type 2 diabetes mellitus has been consistently associated with increased serum OPG concentrations. With regard to nonalcoholic fatty liver disease, experimental data suggest a potential contribution of OPG and RANKL in hepatic steatosis, inflammation, and fibrosis; however, most clinical studies showed reduction in serum concentrations of OPG and RANKL. The emerging contribution of the OPG-RANKL-RANK axis to the pathogenesis of obesity and its associated comorbidities warrants further investigation by mechanistic studies and may have potential diagnostic and therapeutic implications.

Bone disease in patients with cirrhosis of different etiology and severity; are Klotho protein and osteoprotegerin potential biomarkers?

BACKGROUND AND AIMS

Cirrhosis is associated with increased risk for osteoporosis and osteopenia. This study aims to further investigate this relationship by examining if etiology and severity of cirrhosis are independent predictors of bone mineral density (BMD) loss. Furthermore we examined the serum levels of osteoprotegerin (OPG) and Klotho proteins that have been involved in bone metabolism.

METHODS

Seventy-four patients with cirrhosis of different etiology and 25 matched healthy controls were included in this study. Bone mineral densitometry at both lumbar spine and femoral neck was measured. Serum total OPG, Klotho protein and vitamin D levels were also determined. Comparisons were performed according to etiology and severity of cirrhosis.

RESULTS

Decreased bone density was observed in cirrhotic patients compared to healthy controls with T = -1.46 and T = -1.37 in lumbar spine and femoral bone respectively compared to T = -0.396 and T = -0.672 in the control group. In the cirrhotic group, osteopenia was observed in 46% in lumbar spine and 51% in femoral bone whereas osteoporosis was observed in 20% in lumbar spine and 9% in femoral bone. Decreased bone density was confirmed, regardless of cirrhosis etiology or stage of liver function. Patients were found to have higher levels of OPG than the control group (136 pg/ml vs. 67 pg/ml, p < 0.001), but lower levels of Klotho protein (1051 pg/ml vs. 1842 pg/ml, p < 0.001) regardless etiology and severity of cirrhosis. High OPG levels were found to be associated with low femoral bone density.

CONCLUSIONS

BMD is lower in cirrhotic patients regardless etiology and severity of liver disease with osteopenia and osteoporosis be present in 50% and 20%, respectively. Higher levels of OPG and lower levels of Klotho protein were observed in cirrhotic patients regardless etiology and severity in comparison to matched healthy group.

RANKL Is Independently Associated with Increased Risks of Non-Alcoholic Fatty Liver Disease in Chinese Women with PCOS: A Cross-Sectional Study

Women with polycystic ovarian syndrome (PCOS) are more likely to have non-alcoholic fatty liver disease (NAFLD) than non-PCOS women; however, the exact mechanism underlying this trend is unknown. The receptor activator of NF-κB ligand (RANKL) is strongly involved in bone metabolism and has multiple functions. Recent studies suggest that RANKL is implicated in hepatic insulin resistance (IR), which is the highest risk factor for NAFLD. This study aimed to assess the role of RANKL in NAFLD in Chinese women with PCOS. A cross-sectional observational study was conducted on women newly diagnosed with PCOS, which included 146 patients with NAFLD and 142 patients without NAFLD. Sex hormones, glucose, insulin, and lipids were measured, and anthropometric data were collected. The concentration of serum total RANKL was measured using commercial ELISA kits. PCOS patients with NAFLD had a significantly higher mean age, body mass index (BMI), waist circumference (WC), and worsened metabolic profile than non-NAFLD subjects. The concentrations of high-sensitivity C-reactive protein, total cholesterol, and low-density lipoprotein cholesterol increased with the RANKL tertile (p for trend = 0.023, 0.026, and 0.035, respectively). A significantly positive association was found between RANKL (per SD change) and the risks of NAFLD (OR = 1.545, 95% CI = 1.086−2.199) after adjusting for confounders, including demographic factors, metabolic markers, and sex hormones. Subgroup multivariate logistic analyses stratified by age, BMI, and WC showed the same tendency. In addition, the positive association between RANKL and NAFLD seemed more prominent in lean patients with a BMI < 24 kg/m2 (OR = 1.70, 95% CI = 1.06−2.75) when compared to overweight/obesity subjects. Therefore, this study suggests that RANKL is positively associated with the increased risk of NAFLD in Chinese women with PCOS, independent of metabolic and reproductive factors.

Obesity and Bone Health: A Complex Relationship

Recent scientific evidence has shown an increased risk of fractures in patients with obesity, especially in those with a higher visceral adipose tissue content. This contradicts the old paradigm that obese patients were more protected than those with normal weight. Specifically, in older subjects in whom there is a redistribution of fat from subcutaneous adipose tissue to visceral adipose tissue and an infiltration of other tissues such as muscle with the consequent sarcopenia, obesity can accentuate the changes characteristic of this age group that predisposes to a greater risk of falls and fractures. Other factors that determine a greater risk in older subjects with obesity are chronic proinflammatory status, altered adipokine secretion, vitamin D deficiency, insulin resistance and reduced mobility. On the other hand, diagnostic tests may be influenced by obesity and its comorbidities as well as by body composition, and risk scales may underestimate the risk of fractures in these patients. Weight loss with physical activity programs and cessation of high-fat diets may reduce the risk. Finally, more research is needed on the efficacy of anti-osteoporotic treatments in obese patients.

Relationship Between Non-Alcoholic Fatty Liver Disease and Degree of Hepatic Steatosis and Bone Mineral Density

BACKGROUND

The liver and bones are both active endocrine organs that carry out several metabolic functions. However, the link between non-alcoholic fatty liver disease (NAFLD) and bone mineral density (BMD) is still controversial. The goal of this study was to discover if there was a link between non-alcoholic fatty liver disease and bone mineral density in US persons aged 20 to 59 years of different genders and races.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES) 2017-2018, multivariate logistic regression models were utilized to investigate the association between NAFLD and lumbar BMD. Fitted smoothing curves and generalized additive models were also used.

RESULTS

The analysis included a total of 1980 adults. After controlling for various variables, we discovered that NAFLD was negatively linked with lumbar BMD. The favorable connection of NAFLD with lumbar BMD was maintained in subgroup analyses stratified by sex, race and age in men, other race and aged 20-29 years. The relationship between NAFLD and lumbar BMD in blacks and people aged 40-49 years was a U-shaped curve with the inflection point: at 236dB/m and 262dB/m. Furthermore, we discovered that liver advanced fibrosis and liver cirrhosis were independently connected with higher BMD, while no significant differences were detected in severe liver steatosis and BMD.

CONCLUSIONS

Our study found an independently unfavorable relationship between NAFLD and BMD in persons aged 20 to 59. We also discovered a positive link between BMD and advanced fibrosis and cirrhosis. More research is needed to back up the findings of this study and to look into the underlying issues.

The role of osteoprotegerin (OPG) in fibrosis: its potential as a biomarker and/or biological target for the treatment of fibrotic diseases

Fibrosis is defined by excessive formation and accumulation of extracellular matrix proteins, produced by myofibroblasts, that supersedes normal wound healing responses to injury and results in progressive architectural remodelling. Fibrosis is often detected in advanced disease stages when an organ is already severely damaged and can no longer function properly. Therefore, there is an urgent need for reliable and easily detectable markers to identify and monitor fibrosis onset and progression as early as possible; this will greatly facilitate the development of novel therapeutic strategies. Osteoprotegerin (OPG), a well-known regulator of bone extracellular matrix and most studied for its role in regulating bone mass, is expressed in various organs and functions as a decoy for receptor activator of nuclear factor kappa-B ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Recently, OPG has been linked to fibrosis and fibrogenesis, and has been included in a panel of markers to diagnose liver fibrosis. Multiple studies now suggest that OPG may be a general biomarker suitable for detection of fibrosis and/or monitoring the impact of fibrosis treatment. This review summarizes our current understanding of the role of OPG in fibrosis and will discuss its potential as a biomarker and/or novel therapeutic target for fibrosis.

The potential of biomarkers of fibrosis in chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) is the major long-term cause of morbidity and mortality after lung transplantation. Both bronchiolitis obliterans syndrome and restrictive lung allograft syndrome, two main types of CLAD, lead to fibrosis in either the small airways or alveoli and pleura. Pathological pathways in CLAD and other types of fibrosis, for example idiopathic pulmonary fibrosis, are assumed to overlap and therefore fibrosis biomarkers could aid in the early detection of CLAD. These biomarkers could help to differentiate between different phenotypes of CLAD and could, in comparison to biomarkers of inflammation, possibly distinguish an infectious event from CLAD when a decline in lung function is present. This review gives an overview of known CLAD specific biomarkers, describes new promising fibrosis biomarkers currently investigated in other types of fibrosis, and discusses the possible use of these fibrosis biomarkers for CLAD.

Prevalence and Trends in Low Bone Density, Osteopenia and Osteoporosis in U.S. Adults With Non-Alcoholic Fatty Liver Disease, 2005-2014

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is suggested to be associated with bone mineral density (BMD) alterations; however, this has not been ascertained. The current study aimed to investigate the changes in BMD and the prevalence of osteopenia/osteoporosis in US adults with or without NAFLD and to evaluate their association.

METHODS

The study was conducted based on data collected from the U.S. National Health and Nutrition Examination Survey (NHANES) during the period 2005-2014. A total of 13 837 and 6 177 participants aged > 20 years were eligible for conducting the Hepatic Steatosis Index (HSI) and the US Fatty Liver Index (USFLI) analysis, respectively.

RESULTS

From 2005-2014, a downward trend in femoral neck BMD was observed in subjects with NAFLD aged ≥ 40. After adjustment for potential confounders, an upward shift occurred in the prevalence of osteopenia/osteoporosis at the femoral neck in adults aged ≥ 40, particularly in women ≥ 60 years old and men below the age of 60. Moreover, a negative association was found between BMD and NAFLD markers (USFLI, HSI), whereas NAFLD with advanced fibrosis was positively associated with the prevalence of spine fractures.

CONCLUSIONS

There was a trend toward lower BMD and higher prevalence of osteopenia/osteoporosis at the femoral neck in US adults with NAFLD aged ≥ 40 years during the period of 2005-2014. NAFLD with advanced fibrosis was positively associated with a higher risk of spine fracture. More research is required to fully investigate the mechanism and consequence of poor bone health in NAFLD patients and consider optimum management of osteopenia/osteoporosis for this population.

Circulating mRNA and plasma levels of osteoprotegerin and receptor activator of NF-κB ligand in nonalcoholic fatty liver disease

Pathogenesis of the beginning and progression of nonalcoholic fatty liver disease (NAFLD) has not been clarified exactly. The osteoprotegerin (OPG)/receptor activator of NF-κB ligand (RANKL) axis seems to play an imperative function in the onset and progression of this disease. The goal of the present study was to investigate the peripheral blood mononuclear cell (PBMC) expression and plasma levels of RANKL and OPG cytokines in NAFLD patients and compare them with healthy group. Plasma levels of OPG and RANKL were determined with ELISA kits in 57 men with NAFLD and 25 healthy men as controls. Biochemical and anthropometric parameters tests were also evaluated in the study groups. RANKL and OPG mRNA contents were evaluated by quantitative RT-PCR. OPG contents were markedly decreased in NAFLD patients as compared with healthy patients [1.43 (1.05-5.45)] versus [2.94 (1.76-4.73)] ng/mL; P = 0.007). The levels of RANKL were significantly reduced in NAFLD patients [74.00 (56.26-203.52) ng/mL] than in healthy patients [119.37 (83.71-150.13) ng/mL]; (P = 0.03). Also, OPG and RANKL gene expression were significantly decreased in NAFLD patients in comparison with the control group (P < 0.05). Moreover, receiver operating characteristic curve indicated that OPG may have a good capability to discriminate between NAFLD patients and normal individuals. A positive correlation was observed between OPG and RANKL in plasma sample (r = 0.495) (P = 0.000). Decreased plasma levels and gene expression of RANKL and OPG cytokines in NAFLD patients indicate that there is a relationship between these cytokines and the pathology of NAFLD disease. Confirmation of this association as well as the mechanism and role of these cytokines in NAFLD require further studies.

Bone morphogenetic protein 8B promotes the progression of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is characterized by lipotoxicity, inflammation and fibrosis, ultimately leading to end-stage liver disease. The molecular mechanisms promoting NASH are poorly understood, and treatment options are limited. Here, we demonstrate that hepatic expression of bone morphogenetic protein 8B (BMP8B), a member of the transforming growth factor beta (TGFβ)-BMP superfamily, increases proportionally to disease stage in people and animal models with NASH. BMP8B signals via both SMAD2/3 and SMAD1/5/9 branches of the TGFβ-BMP pathway in hepatic stellate cells (HSCs), promoting their proinflammatory phenotype. In vivo, the absence of BMP8B prevents HSC activation, reduces inflammation and affects the wound-healing responses, thereby limiting NASH progression. Evidence is featured in primary human 3D microtissues modelling NASH, when challenged with recombinant BMP8. Our data show that BMP8B is a major contributor to NASH progression. Owing to the near absence of BMP8B in healthy livers, inhibition of BMP8B may represent a promising new therapeutic avenue for NASH treatment.

Osteoprotegerin is More than a Possible Serum Marker in Liver Fibrosis: A Study into its Function in Human and Murine Liver

Osteoprotegerin (OPG) serum levels are associated with liver fibrogenesis and have been proposed as a biomarker for diagnosis. However, the source and role of OPG in liver fibrosis are unknown, as is the question of whether OPG expression responds to treatment. Therefore, we aimed to elucidate the fibrotic regulation of OPG production and its possible function in human and mouse livers. OPG levels were significantly higher in lysates of human and mouse fibrotic livers compared to healthy livers. Hepatic OPG expression localized in cirrhotic collagenous bands in and around myofibroblasts. Single cell sequencing of murine liver cells showed hepatic stellate cells (HSC) to be the main producers of OPG in healthy livers. Using mouse precision-cut liver slices, we found OPG production induced by transforming growth factor β1 (TGFβ1) stimulation. Moreover, OPG itself stimulated expression of genes associated with fibrogenesis in liver slices through TGFβ1, suggesting profibrotic activity of OPG. Resolution of fibrosis in mice was associated with decreased production of OPG compared to ongoing fibrosis. OPG may stimulate fibrogenesis through TGFβ1 and is associated with the degree of fibrogenesis. It should therefore be investigated further as a possible drug target for liver fibrosis or biomarker for treatment success of novel antifibrotics.

Osteoprotegerin Promotes Liver Steatosis by Targeting the ERK-PPAR-γ-CD36 Pathway

Previous cross-sectional studies have established that circulating osteoprotegerin (OPG) levels are associated with nonalcoholic fatty liver disease (NAFLD). However, the role of OPG in metabolic diseases, such as diabetes and NAFLD, is still unclear. In the current study, we demonstrated that hepatic OPG expression was downregulated in NAFLD individuals and in obese mice. OPG deficiency decreased lipid accumulation and expression of CD36 and peroxisome proliferator-activated receptor-γ (PPAR-γ) in the livers of OPG^-/- mice and cultured cells, respectively, whereas OPG overexpression elicited the opposite effects. The stimulatory role of OPG in lipid accumulation was blocked by CD36 inactivation in hepatocytes isolated from CD36^-/- mice. The overexpression of OPG led to a decrease in extracellular signal-regulated kinase (ERK) phosphorylation in the livers of OPG^-/- mice and in cultured cells, while OPG deficiency resulted in the opposite effect. The inhibition of PPAR-γ or the activation of ERK blocked the induction of CD36 expression by OPG in cultured cells. Mechanistically, OPG facilitated CD36 expression by acting on PPAR response element (PPRE) present on the CD36 promoter. Taken together, our study revealed that OPG signaling promotes liver steatosis through the ERK-PPAR-γ-CD36 pathway. The downregulation of OPG in NAFLD might be a compensatory response of the body to dampen excess hepatic fat accumulation in obesity.

NAFLD and Extra-Hepatic Comorbidities: Current Evidence on a Multi-Organ Metabolic Syndrome

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide and its incidence is definitely increasing. NAFLD is a metabolic disease with extensive multi-organ involvement, whose extra-hepatic manifestations include type 2 diabetes mellitus, cardiovascular disease, obstructive sleep apnea, chronic kidney disease, osteoporosis, and polycystic ovarian syndrome. Recently, further evidence has given attention to pathological correlations not strictly related to metabolic disease, also incorporating in this broad spectrum of systemic involvement hypothyroidism, psoriasis, male sexual dysfunction, periodontitis, and urolithiasis. The most common cause of mortality in NAFLD is represented by cardiovascular disease, followed by liver-related complications. Therefore, clinicians should learn to screen and initiate treatment for these extra-hepatic manifestations, in order to provide appropriate multidisciplinary assessments and rigorous surveillance. This review evaluates the current evidence regarding extra-hepatic associations of NAFLD, focusing on the pathogenic hypothesis and the clinical implications.

Nonalcoholic fatty liver disease and alcoholic liver disease: metabolic diseases with systemic manifestations

The progression of liver disease is portrayed by several common, overarching signs and symptoms. Classically, these include findings such as spider angiomata, jaundice, palmar erythema, and as cirrhosis decompensates, ascites, variceal hemorrhage (VH), hepatic encephalopathy (HE), and hepatocellular carcinoma (HCC). Aside from these universal hallmarks among cirrhotics, patients with nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) harbor their own distinct systemic associations and manifestations. NAFLD is tightly linked to metabolic syndrome, which appears to be a driving force for a multitude of comorbidities, such as insulin resistance, cardiovascular disease, chronic kidney disease (CKD), obstructive sleep apnea (OSA), as well as increased malignancy risk. ALD also maintains a variety of comorbidities congruent with systemic effects of chronic alcohol use. These findings are highlighted by cardiovascular conditions, neuronal damage, myopathy, nutritional deficiencies, chronic pancreatitis, in addition to increased malignancy risk. While a general, guideline-driven management for all cirrhotic patients remains imperative for minimizing risk of complications, a tailored treatment strategy is useful for patients with NAFLD and ALD who entertain their own constellation of unique systemic manifestations.

Relationship between nonalcoholic fatty liver disease and bone mineral density in adolescents with obesity: a meta-analysis

PURPOSE

Many studies have reported the relationship between nonalcoholic fatty liver disease (NAFLD) and bone mineral density (BMD) among adults. However, fewer studies on this topic have been reported in adolescents. We thus conducted a meta-analysis to show the association between NAFLD and BMD in adolescents with obesity.

MATERIALS AND METHODS

Computer retrieval was carried out via PubMed, Embase, Cochrane Library and the Cochrane Central Register of Controlled Trials from inception to September 2018. Six published case-control studies that assessed the relationship between NAFLD and BMD were included.

RESULTS

The six studies included 217 obese adolescents with NAFLD and 236 controls. The meta-analysis indicated that obese children with NAFLD had a lower BMD and Z-score than the control group (weighted mean difference [WMD]-0.03, 95% CI [-0.05, -0.02], P=0.000; [WMD] -0.26, 95% CI [-0.37, -0.14], P=0.000). However, we analyzed the factor of bone mineral content, and there was no correlation between the two groups ([WMD]-55.99, 95% CI [-132.16, 20.18], P=0.150).

CONCLUSION

Obese children with NAFLD are more susceptible to osteoporosis than children with only obesity. Because of the limitations related to the quantity and quality of the included literature, further studies are still needed.

Mechanisms Involved in Childhood Obesity-Related Bone Fragility

Childhood obesity is one of the major health problems in western countries. The excessive accumulation of adipose tissue causes inflammation, oxidative stress, apoptosis, and mitochondrial dysfunctions. Thus, obesity leads to the development of severe co-morbidities including type 2 diabetes mellitus, liver steatosis, cardiovascular, and neurodegenerative diseases which can develop early in life. Furthermore, obese children have low bone mineral density and a greater risk of osteoporosis and fractures. The knowledge about the interplay bone tissue and between adipose is still growing, although recent findings suggest that adipose tissue activity on bone can be fat-depot specific. Obesity is associated to a low-grade inflammation that alters the expression of adiponectin, leptin, IL-6, Monocyte Chemotactic Protein 1 (MCP1), TRAIL, LIGHT/TNFSF14, OPG, and TNFα. These molecules can affect bone metabolism, thus resulting in osteoporosis. The purpose of this review was to deepen the cellular mechanisms by which obesity may facilitate osteoporosis and bone fractures.

Novel insights into the relationship between nonalcoholic fatty liver disease and osteoporosis

Excess fat deposition and insulin resistance are considered the main risk factors for nonalcoholic fatty liver disease (NAFLD), and therefore, not surprisingly, the global prevalence of NAFLD increases in parallel with both obesity and type 2 diabetes. Although deterioration of bone homeostasis in patients with NAFLD is commonly observed, its etiology has not been fully elucidated yet. It was shown in several studies that bone tissue seems to be independently associated with NAFLD. A mechanistic perspective puts the liver at the center of mutual interdependencies obviously involving adipose tissue and muscles and also the bone matrix and bone cells, which are relatively novel. In this review, various pathophysiological mechanisms and possible mediating molecules that may interplay between NAFLD and bone tissue are described. Chronic inflammation, vitamin D3, growth hormone, insulin-like growth factor 1, osteopontin, fetuin-A, irisin, osteocalcin, and osteoprotegerin from osteoblasts have been proposed as mediators of mutual interactions among the skeleton, fatty tissue, and liver. Although to date there are still many issues that have not been elucidated, growing evidence suggests that screening and surveillance of bone mineral density in patients with NAFLD should be considered in future strategies and guidelines for NAFLD management.

Noninvasive Tests Do Not Accurately Differentiate Nonalcoholic Steatohepatitis From Simple Steatosis: A Systematic Review and Meta-analysis

BACKGROUND & AIMS

Nonalcoholic fatty liver disease is a rapidly increasing health problem. Liver biopsy analysis is the most sensitive test to differentiate between nonalcoholic steatohepatitis (NASH) and simple steatosis (SS), but noninvasive methods are needed. We performed a systematic review and meta-analysis of noninvasive tests for differentiating NASH from SS, focusing on blood markers.

METHODS

We performed a systematic search of the PubMed, Medline and Embase (1990-2016) databases using defined keywords, limited to full-text papers in English and human adults, and identified 2608 articles. Two independent reviewers screened the articles and identified 122 eligible articles that used liver biopsy as reference standard. If at least 2 studies were available, pooled sensitivity (sens_p) and specificity (spec_p) values were determined using the Meta-Analysis Package for R (metafor).

RESULTS

In the 122 studies analyzed, 219 different blood markers (107 single markers and 112 scoring systems) were identified to differentiate NASH from simple steatosis, and 22 other diagnostic tests were studied. Markers identified related to several pathophysiological mechanisms. The markers analyzed in the largest proportions of studies were alanine aminotransferase (sens_p, 63.5% and spec_p, 74.4%) within routine biochemical tests, adiponectin (sensp, 72.0% and spec_p, 75.7%) within inflammatory markers, CK18-M30 (sens_p, 68.4% and spec_p, 74.2%) within markers of cell death or proliferation and homeostatic model assessment of insulin resistance (sens_p, 69.0% and spec_p, 72.7%) within the metabolic markers. Two scoring systems could also be pooled: the NASH test (differentiated NASH from borderline NASH plus simple steatosis with 22.9% sens_p and 95.3% spec_p) and the GlycoNASH test (67.1% sens_p and 63.8% spec_p).

CONCLUSION

In the meta-analysis, we found no test to differentiate NASH from SS with a high level of pooled sensitivity and specificity (≥80%). However, some blood markers, when included in scoring systems in single studies, identified patients with NASH with ≥80% sensitivity and specificity. Replication studies and more standardized study designs are urgently needed. At present, no marker or scoring system can be recommended for use in clinical practice to differentiate NASH from simple steatosis.

Role of osteoprotegerin/receptor activator of nuclear factor kappa B/receptor activator of nuclear factor kappa B ligand axis in nonalcoholic fatty liver disease

Concomitantly with the increase in the prevalences of overweight/obesity, nonalcoholic fatty liver disease (NAFLD) has worldwide become the main cause of chronic liver disease in both adults and children. Patients with fatty liver display features of metabolic syndrome (MetS), like insulin resistance (IR), glucose intolerance, hypertension and dyslipidemia. Recently, epidemiological studies have linked obesity, MetS, and NAFLD to decreased bone mineral density and osteoporosis, highlighting an intricate interplay among bone, adipose tissue, and liver. Osteoprotegerin (OPG), an important symbol of the receptor activator of nuclear factor-B ligand/receptor activator of nuclear factor kappa B/OPG system activation, typically considered for its role in bone metabolism, may also play critical roles in the initiation and perpetuation of obesity-related comorbidities. Clinical data have indicated that OPG concentrations are associated with hypertension, left ventricular hypertrophy, vascular calcification, endothelial dysfunction, and severity of liver damage in chronic hepatitis C. Nonetheless, the relationship between circulating OPG and IR as a key feature of MetS as well as between OPG and NAFLD remains uncertain. Thus, the aims of the present review are to provide the existent knowledge on these associations and to discuss briefly the underlying mechanisms linking OPG and NAFLD.

Association of Nonalcoholic Fatty Liver Disease With Osteoporotic Fractures: A Cross-Sectional Retrospective Study of Chinese Individuals

Objective: Nonalcoholic fatty liver disease (NAFLD) is related to several inflammatory or metabolic diseases. However, findings of previous studies investigating the association between NAFLD and BMD are inconsistent. Only one study reported a potential association between NAFLD and osteoporotic fracture. This study investigated whether NAFLD in older participants (>55 years) was associated with osteoporotic fracture risk. Materials and Methods: This cross-sectional, observational study included 2,695 participants (35.7% men, 614 cases of NAFLD, and 383 fractures). Standardized questionnaires, laboratory tests, and physical and ultrasonic examinations were completed. Results: After adjusting for various factors including serum triglycerides (TG), high-density cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C), multivariate logistic regression models revealed a marginal association between NAFLD and osteoporotic fracture risk in men (odds ratio [OR], 1.86; 95% confidence interval [CI], 1.06-3.27; P = 0.030) but no association in women (OR, 1.05; 95% CI, 0.74-1.48; P = 0.800). Further stratified analyses showed a significant association between NAFLD and osteoporotic fracture risk in men without high TG, low HDL-C, and high LDL-C. Conclusions: There was a significant association between NAFLD and osteoporotic fracture risk in older Chinese men, particularly men without dyslipidemia.

Novel circulating biomarkers for non-alcoholic fatty liver disease: A systematic review

Currently, a liver biopsy remains the only reliable way to precisely diagnose non-alcoholic fatty liver disease (NAFLD) and establish the severity of liver injury, presence of fibrosis, and architecture remodeling. However, the cost and the intrinsic invasive procedure of a liver biopsy rules it out as a gold standard diagnostic test, and the imaging test are not the best choice due to the price, and currently is being refined. The lack of a biomarker of NAFLD pushes to develop this new line of research. The aim of the present systematic review is to clarify and update all the NAFLD biomarkers described in the literature until recently. We highlight α-ketoglutarate and CK18-F as currently the best potential biomarker of NAFLD. However, due to methodological differences, we propose the implementation of international, multicenter, multiethnic studies with larger population size, and biopsy proven NAFLD diagnosis to analyze and compare α-ketoglutarate and CK18-F as potential biomarkers of the silent evolution of NAFLD.

Non-alcoholic fatty liver disease connections with fat-free tissues: A focus on bone and skeletal muscle

The estimates of global incidence and prevalence of non-alcoholic fatty liver disease (NAFLD) are worrisome, due to the parallel burden of obesity and its metabolic complications. Indeed, excess adiposity and insulin resistance represent two of the major risk factors for NAFLD; interestingly, in the last years a growing body of evidence tended to support a novel mechanistic perspective, in which the liver is at the center of a complex interplay involving organs and systems, other than adipose tissue and glucose homeostasis. Bone and the skeletal muscle are fat- free tissues which appeared to be independently associated with NAFLD in several cross-sectional studies. The deterioration of bone mineral density and lean body mass, leading to osteoporosis and sarcopenia, respectively, are age-related processes. The prevalence of NAFLD also increases with age. Beyond physiological aging, the three conditions share some common underlying mechanisms, and their elucidations could be of paramount importance to design more effective treatment strategies for the management of NAFLD. In this review, we provide an overview on epidemiological data as well as on potential contributors to the connections of NAFLD with bone and skeletal muscle.

Association of Osteoprotegerin with Obesity, Insulin Resistance and Non-Alcoholic Fatty Liver Disease in Children

BACKGROUND

Osteoprotegerin (OPG) is a member of the tumor necrosis factor superfamily. Reduced OPG levels are related to obesity, insulin resistance, and non-alcoholic fatty liver disease (NAFLD).

OBJECTIVES

The aim of this study was to evaluate the relationship between OPG levels, obesity, insulin resistance, and NAFLD in pediatric patients.

METHODS

This was a prospective, cross-sectional, controlled study that was conducted in the department of pediatrics at Bagcilar training and research hospital in Istanbul, Turkey, between April and August 2015. The study was performed on 107 children with obesity and 37 controls aged 5 - 17 years. In the obese subset, 62 patients had NAFLD. Homeostatic model assessment-insulin resistance (HOMA-IR) was used to calculate insulin resistance. Insulin resistance was defined as a HOMA-IR value greater than 2.5. Plasma OPG levels were measured using enzyme-linked immunosorbent assays. NAFLD was diagnosed by hepatic ultrasound.

RESULTS

The mean age was 11.25 ± 3.38 years in the patient group and 10.41 ± 3.15 years in the control group. The OPG level in the obese group with the mean of 55.20 ± 24.55 pg/mL (median = 48.81 pg/mL) was significantly lower than that in the control group with the mean of 70.78 ± 33.41 pg/mL (median = 64.57 pg/mL) (P = 0.0001). The optimal cut-off point (sensitivity, specificity) of the OPG level for the diagnosis of obesity was ≤ 46, 19 pg/mL. According to logistic regression analysis, fasting insulin (P = 0.036) and OPG (P = 0.01) levels were most affected by obesity. In the obese patients, who had HOMA-IR < 2.5, the mean level of OPG was 58.91 ± 6.88729 pg/mL (median = 49.55). In the obese patients, who had HOMA-IR ≥ 2.5, the mean level of OPG was 54.19 ± 22.21 pg/mL (median = 48.47). No significant correlations were found between OPG and HOMA-IR (P = 0.791). No statistically significant difference was observed in the mean OPG between patients with hepatosteatosis (mean = 54.55 ± 25.01 pg/mL) (median = 49.46) and those without the disease (56.30 ± 24.02 pg/mL) (mean = 48.34) (P = 0.089).

CONCLUSIONS

We confirmed that serum OPG concentrations reduce in obese children. However, no correlation was identified between OPG and insulin resistance. OPG levels are not meaningful in the diagnosis of NAFLD in children with obesity.

Concentrations of fetuin-A, osteoprotegerin and α-Klotho in patients with alcoholic liver cirrhosis

The aim of the present study was to evaluate the concentrations of fetuin-A, osteoprotegerin (OPG) and α-Klotho protein in patients with alcoholic cirrhosis at different stages of the disease, and to demonstrate that fetuin-A, osteoprotegin and α-Klotho may be used as markers of the severity of cirrhosis. A total of 54 patients with alcoholic liver cirrhosis treated in various hospitals in the Lublin region of Poland were randomly enrolled. The control group consisted of 18 healthy individuals without liver disease, who did not drink alcohol. Serum levels of fetuin-A, OPG and α-Klotho were measured by ELISA kits. Levels of fetuin-A were significantly reduced in patients with alcoholic liver cirrhosis compared with the control group. OPG levels were higher in patients with alcoholic liver cirrhosis than in the controls, whereas the levels of α-Klotho were comparable in the cirrhosis and control groups. No statistically significant differences in the concentrations of fetuin-A, OPG and α-Klotho protein were demonstrated according to type of liver cirrhosis. The findings of the present study revealed a significant negative correlation between the level of α-Klotho protein and C-reactive protein in the patients with alcoholic liver cirrhosis. Concentrations of fetuin-A were lower, whereas those of OPG were higher, in the alcoholic liver cirrhosis group compared with the control group. Fetuin-A, OPG and α-Klotho may not be good indicators of liver cirrhosis severity. In conclusion, fetuin-A and OPG may be used in the diagnosis of liver cirrhosis.

Plasma osteoprotegerin levels are inversely associated with nonalcoholic fatty liver disease in patients with type 2 diabetes: A case-control study in China

OBJECTIVE

Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor (TNF) receptor superfamily, is a decoy receptor for the receptor activator of nucleus factor-κB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). OPG has an effect on systemic insulin sensitivity and glucose homeostasis. The objective of this study was to evaluate the relationship between plasma osteoprotegerin (OPG) levels and nonalcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes.

MATERIALS/METHODS

A case-control study was performed with 746 patients with type 2 diabetes. Of the study population, 367 patients had B-mode ultrasound-proven NAFLD and 379 were controls. The plasma OPG levels were measured using ELISA methods. NAFLD was diagnosed by hepatic ultrasound after the exclusion of alcohol abuse and other liver diseases.

RESULTS

The OPG levels were significantly decreased in patients with NAFLD (2.3±1.1μg/L vs. 2.8±1.3μg/L, p=3.75×10(5)) compared to controls. Pearson correlation analysis showed that the OPG levels were associated with age and systolic blood pressure (both p<0.05). The participants in the lowest OPG quartile had a significantly increased risk for NAFLD (OR=3.49, 95% CI 1.86-6.94) after adjusting for potential cofounders.

CONCLUSIONS

The plasma OPG level is negatively associated with NAFLD independent of potential cofounders.

Association of osteoprotegerin with impaired glucose regulation and microalbuminuria: the REACTION study

BACKGROUND

High osteoprotegerin (OPG) has been reported in association with insulin resistance and type 2 diabetes. We aimed to evaluate the association of serum OPG with impaired glucose regulation (IGR) and microalbuminuria among middle-aged and older Chinese.

METHODS

Serum OPG was measured in 599 individuals with normal glucose regulation, 730 with impaired glucose regulation and 327 newly diagnosed patients with diabetes. Serum OPG was measured using ELISA methods and urine albumin/creatinine ratio was used to determine the urinary albumin excretion.

RESULTS

Serum OPG levels were significantly higher in subjects with isolated impaired fasting glucose, isolated impaired glucose tolerance, combined impaired fasting glucose/impaired glucose tolerance and diabetes than in those with normal glucose regulation, whereas serum OPG levels were not different in the four groups with dysregulation of glucose metabolism. OPG was associated with a higher risk for IGR (OR 1.108 for each 0.1 μg/l increase in OPG, 95% CI 1.009-1.117, p = 0.01) after adjustment for gender, age, BMI, current smoking and alcohol intake, family history of diabetes, homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile; the corresponding OR of combined impaired glucose regulation and type 2 diabetes was 1.121 (95% CI 1.101-1.141, p = 0.0005). OPG was associated with the risk of microalbuminuria (OR 1.025, 95% CI 1.006-1.044, p = 0.02) after adjustment for gender, age, current smoking, current alcohol intake, family history of diabetes, BMI, waist/hip ratio, HOMA-IR, eGFR and lipid profile.

CONCLUSIONS

Serum OPG level is closely and independently associated with IGR and is an independent risk factor for microalbuminuria.

Nonalcoholic fatty liver disease and decreased bone mineral density: is there a link?

PURPOSE

Liver diseases are associated with decreased bone mineral density (BMD) and evidence suggests that nonalcoholic fatty liver disease (NAFLD) affects several extra-hepatic organs, interacting with the regulation of multiple endocrine and metabolic pathways. This review focuses on the rapidly expanding body of evidence that supports a strong association between NAFLD and the risk of decreased BMD, expression of low bone mass (osteoporosis), or reduced mineralization (osteomalacia).

METHODS

We identified studies by searching PubMed for original articles published in English through March 2015 using the keywords "nonalcoholic fatty liver disease" or "fatty liver" combined with "bone mineral density", "osteoporosis", or "osteomalacia".

RESULTS

Recent cross-sectional and case-control studies involving both adults and children have consistently shown that patients with NAFLD exhibit a greater prevalence of decreased BMD compared with age-, sex-, and body mass index-matched healthy controls. Accumulating clinical and experimental evidence suggests that NAFLD may contribute to the pathophysiology of low BMD, possibly through the direct contribution of NAFLD to whole-body and hepatic insulin resistance and/or the systemic release of multiple pro-inflammatory, pro-coagulant, and pro-fibrogenic mediators.

CONCLUSIONS

Although more research is needed before firm conclusions can be drawn, it appears that there is a non-chance, statistical association between NAFLD and low BMD. This finding argues for more careful monitoring and evaluation of BMD among patients with NAFLD. The potential contribution of NAFLD itself to the development and progression of decreased BMD warrants further study.

Increased Serum Levels of LIGHT/TNFSF14 in Nonalcoholic Fatty Liver Disease: Possible Role in Hepatic Inflammation

OBJECTIVES

The tumor necrosis factor superfamily member 14, LIGHT (homologous to lymphotoxin, exhibits inducible expression, and competes with HSV glycoprotein D for herpes virus entry mediator (HVEM), a receptor expressed by T lymphocytes), has been involved in various autoimmune disorders and has been shown to influence hepatic lipid metabolism. We hypothesized that LIGHT could also have a pathogenic role in nonalcoholic fatty liver disease (NAFLD).

METHODS

Serum levels of LIGHT in NAFLD patients and control subjects, as well as LIGHT and interleukin (IL)-8 released from Huh7 (human hepatoma cell line) hepatocytes, were determined by enzyme-linked immunosorbent assay. The mRNA expression of LIGHT in the liver tissue and mRNA levels of LIGHT and IL-8 in Huh7 hepatocytes were assessed by real-time quantitative reverse transcription-PCR.

RESULTS

(i) Serum levels of LIGHT were significantly elevated in NAFLD patients (n=66) as compared with healthy controls (n=16), with no differences between simple steatosis (n=34) and nonalcoholic steatohepatitis (NASH) (n=32). (ii) Within the liver, NAFLD patients (n=14) had significantly increased mRNA levels of the two LIGHT receptors, herpes virus entry mediator and lymphotoxin β receptor (LTβR), as compared with controls (n=7), with no difference between simple steatosis (n=8) and NASH (n=6). (iii) LIGHT markedly increased the release of IL-8 in Huh7 hepatocytes in a time- and dose-dependent manner. (iv) The reactive oxygen species (ROS) H2O2 (hydrogen peroxide) enhanced the LIGHT-mediated release of IL-8 in Huh7 hepatocytes.

CONCLUSION

We show increased levels of LIGHT and its two membrane-bound receptors in NAFLD, potentially promoting hepatic inflammation through ROS interaction. Our findings should encourage further studies on the role of LIGHT in NAFLD development and progression.

Combined Serum Biomarkers in Non-Invasive Diagnosis of Non-Alcoholic Steatohepatitis

BACKGROUND

Non-alcoholic steatoheaptitis (NASH), the critical stage of non-alcoholic fatty liver disease (NAFLD), is of chronic progression and can develop cirrhosis even hepatocellular carcinoma (HCC). However, non-invasive biomarkers for NASH diagnosis remain poorly applied in clinical practice. Our study aims at testing the accuracy of the combination of cytokeratin-18 M30 fragment (CK-18-M30), fibroblast growth factor 21 (FGF-21), interleukin 1 receptor antagonist (IL-1Ra), pigment epithelium-derived factor (PEDF) and osteoprotegerin (OPG) in diagnosing NAFLD and NASH.

METHODS

179 patients with biopsy-proven NAFLD were enrolled as training group, 91 age- and gender-matched healthy subjects were recruited at the same time as controls. 63 other NAFLD patients were separately collected as validation group. 45 alcoholic fatty liver disease (AFLD) patients, 50 hepatitis B virus (HBV) patients, 52 hepatitis C virus (HCV) patients were also included. Serum biomarker levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Serum levels of CK-18-M30, FGF-21, IL-1Ra and PEDF increased, while OPG decreased in a stepwise fashion in controls, non-NASH NAFLD patients and NASH patients (P < 0.01). The area under receiver-operating characteristics curve to diagnose NASH was 0.86 for CK-18-M30, 0.89 for FGF-21, 0.89 for IL-1Ra, 0.89 for PEDF and 0.89 for OPG. CK-18-M30 had 70% negative predictive value (NPV) and 79% positive predictive value (PPV) to diagnose NASH. A 5-step approach measuring CK-18-M30 followed by FGF21, IL-1Ra, PEDF and OPG gradually improved the NPV to 76% and PPV to 85%, which reached 80% and 76% respectively in the validation cohort.

CONCLUSION

Compared to single biomarker, stepwise combination of CK-18-M30, FGF-21, IL-1Ra, PEDF and OPG can further improve the accuracy in diagnosing NASH.

The Wide and Complex Field of NAFLD Biomarker Research: Trends

Background. Nonalcoholic fatty liver disease is now acknowledged as a complex public health issue linked to sedentary lifestyle, obesity, and related disorders like type 2 diabetes and metabolic syndrome. Aims. We aimed to retrieve its trends out of the huge amount of published data. Therefore, we conducted an extensive literature search to identify possible biomarker and/or biomarker combinations by retrospectively assessing and evaluating common and novel biomarkers to predict progression and prognosis of obesity related liver diseases. Methodology. We analyzed finally 62 articles accounting for 157 cohorts and 45,288 subjects. Results. Despite the various approaches, most cohorts were considerably small and rarely comparable. Also, we found that the same standard parameters were measured rather than novel biomarkers. Diagnostics approaches appeared incomparable. Conclusions. Further collaborative investigations on harmonizing ways of data acquisition and identifying such biomarkers for clinical use are necessary to yield sufficient significant results of potential biomarkers.

Interactions among bone, liver, and adipose tissue predisposing to diabesity and fatty liver

Growing epidemiological evidence connects obesity and its complications, including metabolic syndrome, diabetes, and nonalcoholic fatty liver disease (NAFLD) to reduced bone health and osteoporosis. Parallel to human studies, experimental data disclosed a complex network of interaction among adipose tissue, the liver, and the bone, which reciprocally modulate the function of each other. The main mediators of such crosstalk include hormonal/cytokine signals from the bone (osteopontin, osteocalcin, and osteoprotegerin), the liver (fetuin-A), and adipose tissue [leptin, tumor necrosis factor-α (TNF-α), and adiponectin]. Dysregulation of this network promotes the development of diabesity, NAFLD, and osteoporosis. We will review recent advances in understanding the mechanisms of bone-liver-adipose tissue interaction predisposing to obesity, diabetes, NAFLD, and osteoporosis and their potential clinical implications.

Identification of a support vector machine-based biomarker panel with high sensitivity and specificity for nonalcoholic steatohepatitis

BACKGROUND

Although liver biopsy remains the best diagnostic standard for nonalcoholic steatohepatitis (NASH), non-invasive tests are eagerly awaited. In this study, we sought to develop a support vector machine (SVM) algorithm to discriminate with high accuracy between subjects with NASH and controls using a blood-based biomarker panel.

METHODS

A total of 17 biomarkers were measured by commercially available enzyme-linked immunosorbent assays in 136 serum samples from patients with biopsy-proven NASH (n = 60) and subjects with normal ALT and no evidence of fatty liver on ultrasound (n = 76). The database was randomly divided (1:1 fashion) into a discovery set for classification training and in a validation set of the chosen biomarkers in blinded samples. Multivariate analysis was performed by means of SVM.

RESULTS

After the identification of a group of three most discriminative biomarkers (osteoprotegerin, fibroblast growth factor 21, and M30) in the discovery set, the application of SVM to the validation test resulted in a 92.5% sensitivity and 84.1% specificity for distinguishing subjects with NASH from controls.

CONCLUSIONS

A targeted biomarker profiling combined with a SVM-based pattern identification approach may allow the identification of patients with NASH with clinically relevant accuracy and validity.

Review article: non-alcoholic fatty liver disease and osteoporosis--clinical and molecular crosstalk

BACKGROUND

Low bone mineral density (BMD) has been reported in both paediatric and adult patients with non-alcoholic fatty liver disease (NAFLD). The mechanisms behind the reduced BMD in NAFLD are still not completely understood.

AIM

To provide a critical overview of the pathophysiological pathways linking NAFLD, reduced BMD and osteoporosis, with a special focus on the alterations of soluble mediators which could link fat accumulation in the liver with bone health. The MEDLINE database was searched by a combination of keywords: non-alcoholic fatty liver disease OR hepatic steatosis OR metabolic syndrome OR insulin resistance AND bone mineral density OR osteoporosis OR bone AND biomarkers OR serum marker.

RESULTS

Several factors that may influence bone mineralisation and the increased risk of osteoporosis in NAFLD can be discussed. These include the release of cytokines from the inflamed liver which may influence the bone microenvironment, vitamin D deficiency, and limited physical activity. Circulating markers of bone metabolism, including osteopontin, osteoprotegerin, osteocalcin and fetuin-A, have been found to be altered in patients with NAFLD.

CONCLUSION

A better understanding of the mechanisms that link bone metabolism and the liver may open a new frontier to fight two highly prevalent conditions like NAFLD and osteoporosis.