Liver-bone crosstalk in non-alcoholic fatty liver disease: Clinical implications and underlying pathophysiology

Exploring the Bone-Liver Axis: Impact of Acute Ethanol Intoxication on Post-Traumatic Liver Inflammation and Damage Following Femur Fracture

Bone fracture activates the immune system and induces inflammation crucial for fracture healing but may also affect trauma-distant organs like the liver. Acute alcohol intoxication (AAI) dysregulates immune responses and affects organ damage post-trauma. However, the bone-liver axis and alcohol's role in this process remain poorly understood. This study explores liver inflammation and damage following fracture, with and without prior AAI. Twenty-four male C57BL/6J mice were randomly assigned to four groups (n = 6) and received either NaCl (control) or 35% ethanol via gavage. Mice underwent femur osteotomy with external fixation or sham surgery. After 24 h, liver damage was assessed using hematoxylin-eosin and activated caspase-3 staining. Liver inflammation was evaluated through CXCL1 and polymorphonuclear leukocyte (PMNL) immunostaining, cytokine gene and protein expression analyses, and immune cell profiling in the liver via flow cytometry. Western blotting assessed NF-κB and Wnt signaling. Neither fracture alone nor with AAI caused significant liver damage. However, fracture significantly increased PMNL infiltration and altered monocyte populations, effects that were amplified by AAI. The hepatic neutrophil-to-monocyte ratio significantly decreased after fracture and was absent in the fracture AAI group. CXCL1 increased post-fracture, while MCP-1 and IL-10 decreased significantly, with AAI further significantly amplifying these changes. Wnt1 and Wnt3a levels increased significantly after fracture and were further strongly elevated by AAI. AAI completely abolished fracture-induced significant β-catenin reduction and significantly increased its phosphorylation, effects that potentially involve an AAI-induced β-catenin stabilization as well as its increased degradation. NF-κB activation was significantly decreased, while A20 expression significantly increased after fracture and AAI. Fracture influences the inflammatory liver response and signaling pathways, effects which were further modulated by AAI.

Oxidative stress-induced circSOD2 inhibits osteogenesis through sponging miR-29b in metabolic-associated fatty liver disease

BACKGROUND

Metabolic-associated fatty liver disease (MAFLD) is characterized by lipid accumulation in hepatocytes and is closely associated with oxidative stress. Increasing clinical evidence indicates that MAFLD is linked to bone metabolic disorders, including osteoporosis. Recent studies indicate that the expression profiles of liver circular RNAs (circRNAs) are altered in MAFLD. However, the effects of these changes on bone metabolism remain poorly understood.

AIM

To investigate the effects and mechanism of differently expressed circRNAs secreted by the liver on osteogenic differentiation in MAFLD.

METHODS

RNA sequencing was performed to identify highly expressed circRNAs in the liver, validated by quantitative real-time reverse transcription polymerase chain reaction, and localized using fluorescence in situ hybridization (FISH). A mouse model induced by a high-fat diet was used to simulate MAFLD.

RESULTS

CircSOD2 was significantly upregulated in liver tissues and primary hepatocytes from subjects with MAFLD. CircSOD2 was induced by oxidative stress and attenuated by antioxidants in the mouse model. In addition, circSOD2 was delivered from hepatocytes to bone marrow mesenchymal stem cells (BMSCs). Furthermore, circSOD2 inhibited the osteogenic differentiation of BMSCs and in vivo bone formation by sponging miR-29b. Moreover, miR-29b inhibition reversed the stimulatory effect of circSOD2 silencing on osteogenic differentiation of BMSCs and in vivo bone formation. Mechanistically, the interaction between circSOD2 and miR-29b confirmed through a luciferase reporter assay and the co-localization in the cytoplasm evidenced by FISH indicated that circSOD2 acted as a sponge for miR-29b.

CONCLUSION

This study provides a novel mechanism underlying the liver-bone crosstalk, demonstrating that circSOD2 upregulation in hepatocytes, induced by oxidative stress, inhibits osteogenic differentiation of BMSCs by sponging miR-29b. These findings offer a better understanding of the relationship between MAFLD and osteoporosis.

Liver function linked to bone health: A bibliometric of the liver-bone axis

BACKGROUND

The liver exerts profound influence on skeletal health, while osseous tissues reciprocally modulate hepatic function. This bidirectional metabolic axis between these two organ systems plays a pivotal role in both physiological homeostasis and pathological states.

AIM

To investigate and analyze the literatures on liver-bone axis using bibliometrics.

METHODS

A comprehensive literature search pertaining to the liver-bone axis was conducted using the Science Citation Index Expanded within the Web of Science Core Collection. Subsequently, visualization and bibliometric analyses were performed utilizing VOSviewer (version 1.6.20), Citespace (version 6.2.R4), and the R programming language.

RESULTS

This comprehensive analysis encompasses 855 publications, comprising 694 articles and 161 reviews, authored by 4988 researchers from 425 institutions across 61 countries. The United States and China emerge as the leading nations in terms of publication volume. The University of California system stands out as the most influential institution in liver-bone axis research. Guanabens N is identified as the most prolific author in this field. The annual increase in publications related to the liver-bone axis underscores its growing prominence as a research focus. The study highlights key areas of investigation, including osteoporosis, bone metabolism, non-alcoholic fatty liver disease, and insulin-like growth factor-1, which represent both current and prospective hot topics within this domain.

CONCLUSION

This investigation employs bibliometric methodologies to conduct a systematic analysis of liver-bone axis literature spanning from 2001 to 2024. The exponential growth in publications over the past two decades underscores the significance of synthesizing research outcomes in this domain. Through rigorous statistical analyses, we delineate fundamental contributions to the field while providing strategic direction for emerging scholars. Furthermore, we illuminate current research trajectories and identify promising future investigative directions. Investigation of the liver-bone axis enhances our comprehension of inter-organ communication networks. Conceptualizing these organs as an integrated system provides profound insights into pathophysiological mechanisms and disease management strategies. This paradigm not only facilitates the development of sophisticated diagnostic modalities but also catalyzes the discovery of novel therapeutic agents targeting these mechanistic pathways, thereby advancing our capacity to diagnose and treat hepatic and skeletal disorders.

Inter-organ metabolic interaction networks in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multisystem metabolic disorder, marked by abnormal lipid accumulation and intricate inter-organ interactions, which contribute to systemic metabolic imbalances. NAFLD may progress through several stages, including simple steatosis (NAFL), non-alcoholic steatohepatitis (NASH), cirrhosis, and potentially liver cancer. This disease is closely associated with metabolic disorders driven by overnutrition, with key pathological processes including lipid dysregulation, impaired lipid autophagy, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and local inflammation. While hepatic lipid metabolism in NAFLD is well-documented, further research into inter-organ communication mechanisms is crucial for a deeper understanding of NAFLD progression. This review delves into intrahepatic networks and tissue-specific signaling mediators involved in NAFLD pathogenesis, emphasizing their impact on distal organs.

Fine particulate matter and osteoporosis: evidence, mechanisms, and emerging perspectives

Air pollution, particularly fine particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5), has been recognized for its adverse effects on multiple organs beyond the lungs. Among these, the bone began to garner significant attention. This review covers epidemiological, animal, and cell studies on PM2.5 exposure and bone health as well as studies on PM2.5-induced diseases with skeletal complications. Emerging evidence from epidemiological studies indicates a positive association between PM2.5 exposure and the incidence of osteoporosis and fractures, along with a negative association with bone mineral density. Experimental studies have demonstrated that PM2.5 can disrupt the metabolic balance between osteoclasts and osteoblasts through inflammatory responses, oxidative stress, and endocrine disruption, thereby triggering bone loss and osteoporosis. Additionally, this review proposes a secondary mechanism by which PM2.5 may impair bone homeostasis via pathological alterations in other organs, offering new perspectives on the complex interactions between environmental pollutants and bone health. In conclusion, this contemporary review underscores the often-overlooked risk factors of PM2.5 in terms of its adverse effects on bone and elucidates the mechanisms of both primary and secondary toxicity. Further attention should be given to exploring the molecular mechanisms of PM2.5-induced bone impairment and developing effective intervention strategies.

Osteokines in Nonalcoholic Fatty Liver Disease

PURPOSE OF REVIEW

To critically summarize evidence on the potential role of osteokines in the pathogenesis and progression of nonalcoholic fatty liver disease (NAFLD).

RECENT FINDINGS

There are emerging data supporting that certain osteokines, which are specific bone-derived proteins, may beneficially or adversely affect hepatic metabolism, and their alterations in the setting of osteoporosis or other bone metabolic diseases may possibly contribute to the development and progression of NAFLD. There is evidence showing a potential bidirectional association between NAFLD and bone metabolism, which may imply the existence of a liver-bone axis. In this regard, osteocalcin, osteoprotegerin, bone morphogenic protein 4 (BMP4) and BMP6 appear to have a positive impact on the liver, thus possibly alleviating NAFLD, whereas osteopontin, receptor activator of nuclear factor kappa Β ligand (RANKL), sclerostin, periostin, BMP8B, and fibroblast growth factor 23 (FGF23) appear to have a negative impact on the liver, thus possibly exacerbating NAFLD. The potential implication of osteokines in NAFLD warrants further animal and clinical research in the field that may possibly result in novel therapeutic targets for NAFLD in the future.

Sexual dimorphism of MASLD-driven bone loss

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is highly prevalent with major risk of progression to Metabolic Dysfunction-Associated Steatohepatitis (MASH) and Hepatocellular Carcinoma (HCC). Recently, osteoporosis and bone fracture have emerged as sexually-dimorphic comorbidities of MASLD yet the mechanisms of this bone loss are unknown. Herein, we address these knowledge gaps using DIAMOND mice which develop MASLD, MASH, and HCC via Western diet exposure. We examined the skeletal phenotype of male DIAMOND mice after 16, 36, and 48 weeks of exposure to Western or control diet. At 16 weeks, male DIAMOND mice with MASLD lose trabecular bone but retain mechanical bone integrity. At 48 weeks, males lose cortical bone and mechanical integrity, indicating severe skeletal weakening. Female DIAMOND mice were protected from cortical and trabecular MASLD-associated bone loss and skeletal fragility at all timepoints. Using NicheNet, a publicly available database of hepatic mRNA expression in DIAMOND mice, and a PTH-induced model of bone loss, we suggest Ctgf, Rarres2, Anxa2, Fgf21, and Mmp13 are liver-secreted ligands inducing bone resorption. This study is the first preclinical investigation of bone loss in MASLD, and the first to suggest the role of Ctgf, Rarrest2, Anxa2, Fgf21, and Mmp13 as drivers of this pathology.

Association between Chronic Hepatitis B/C and Incidence of Osteoporosis and Bone Fractures: Results from a Retrospective Cohort Study

Background: Osteoporosis and bone fractures affect health and quality of life. Since bone disease is multifactorial, identifying risk factors is key in prevention. There are multiple reports on how viral hepatitis, especially chronic hepatitis B (CHB) and chronic hepatitis C (CHC), are affecting bone disease, but results vary. Here, we analyzed the potential association between CHB/CHC and osteoporosis or bone fractures in a large outpatient cohort in Germany. Methods: We included 3136 outpatients with CHB and 15,608 matched non-hepatitis individuals as well as 2867 outpatients with CHC and 14,335 matched non-hepatitis individuals from the Disease Analyzer Database between 2005 and 2022. The main outcome was the 5-year cumulative incidence of osteoporosis and bone fractures as a function of either CHB or CHC. Results: Within 5 years of the index date, 2.9% vs. 1.6% of patients with and without CHB were diagnosed with osteoporosis (p = 0.001) and 1.0% vs. 0.4% were diagnosed with bone fractures (p < 0.001). Moreover, 3.3% of CHC patients and 2.2% of individuals without hepatitis C were diagnosed with osteoporosis (p = 0.002). In Cox regression analyses, CHB was significantly associated with an increased risk for osteoporosis (HR: 1.76) and fractures (HR:2.43) and CHC with osteoporosis (HR: 1.54). For both CHB and CHC, the association with osteoporosis was restricted to the female subgroup. Conclusions: CHB and CHC are associated with osteoporosis in women. CHB in male patients is associated with a higher risk of fractures. More research is needed to understand the underlying pathophysiological mechanisms.

Effects of FGF21 overexpression in osteoporosis and bone mineral density: a two-sample, mediating Mendelian analysis

Objective

Fibroblast growth factor 21 (FGF21) is a secreted protein that regulates body metabolism. In recent years, many observational studies have found that FGF21 is closely related to bone mineral density and osteoporosis, but the causal relationship between them is still unclear. Therefore, this study used two-sample, mediated Mendelian randomization (MR) analysis to explore the causal relationship between FGF21 and osteoporosis and bone mineral density.

Methods

We conducted a two-sample, mediator MR Analysis using genetic data from publicly available genome-wide association studies (GWAS) that included genetic variants in the inflammatory cytokine FGF21, and Total body bone mineral density, Heel bone mineral density, Forearm bone mineral density, Femoral neck bone mineral density, osteoporosis. The main analysis method used was inverse variance weighting (IVW) to investigate the causal relationship between exposure and outcome. In addition, weighted median, simple median method, weighted median method and MR-Egger regression were used to supplement the explanation, and sensitivity analysis was performed to evaluate the reliability of the results.

Results

MR Results showed that FGF21 overexpression reduced bone mineral density: Total body bone mineral density (OR=0.920, 95%CI: 0.876-0.966), P=0.001), Heel bone mineral density (OR=0.971, 95%CI (0.949-0.993); P=0.01), Forearm bone mineral density (OR=0.882, 95%CI(0.799-0.973); P=0.012), Femoral neck bone mineral density (OR=0.952, 95%CI(0.908-0.998), P=0.039); In addition, it also increased the risk of osteoporosis (OR=1.003, 95%CI (1.001-1.005), P=0.004). Sensitivity analysis supported the reliability of these results. The effect of FGF21 overexpression on osteoporosis may be mediated by type 2 diabetes mellitus and basal metabolic rate, with mediating effects of 14.96% and 12.21%, respectively.

Conclusions

Our study suggests that the overexpression of FGF21 may lead to a decrease in bone mineral density and increase the risk of osteoporosis, and the effect of FGF21 on osteoporosis may be mediated through type 2 diabetes and basal metabolic rate. This study can provide a reference for analyzing the potential mechanism of osteoporosis and is of great significance for the prevention and treatment of osteoporosis.

Liver-based inter-organ communication: A disease perspective

Inter-organ communication through hormones, cytokines and extracellular vesicles (EVs) has emerged to contribute to the physiological states and pathological processes of the human body. Notably, the liver coordinates multiple tissues and organs to maintain homeostasis and maximize energy utilization, with the underlying mechanisms being unraveled in recent studies. Particularly, liver-derived EVs have been found to play a key role in regulating health and disease. As an endocrine organ, the liver has also been found to perform functions via the secretion of hepatokines. Investigating the multi-organ communication centered on the liver, especially in the manner of EVs and hepatokines, is of great importance to the diagnosis and treatment of liver-related diseases. This review summarizes the crosstalk between the liver and distant organs, including the brain, the bone, the adipose tissue and the intestine in noticeable situations. The discussion of these contents will add to a new dimension of organismal homeostasis and shed light on novel theranostics of pathologies.

Prediction of Osteoporotic Hip Fracture Outcome: Comparative Accuracy of 27 Immune-Inflammatory-Metabolic Markers and Related Conceptual Issues

Objectives: This study, based on the concept of immuno-inflammatory-metabolic (IIM) dysregulation, investigated and compared the prognostic impact of 27 indices at admission for prediction of postoperative myocardial injury (PMI) and/or hospital death in hip fracture (HF) patients. Methods: In consecutive HF patient (n = 1273, mean age 82.9 ± 8.7 years, 73.5% females) demographics, medical history, laboratory parameters, and outcomes were recorded prospectively. Multiple logistic regression and receiver-operating characteristic analyses (the area under the curve, AUC) were used to establish the predictive role for each biomarker. Results: Among 27 IIM biomarkers, 10 indices were significantly associated with development of PMI and 16 were indicative of a fatal outcome; in the subset of patients aged >80 years with ischaemic heart disease (IHD, the highest risk group: 90.2% of all deaths), the corresponding figures were 26 and 20. In the latter group, the five strongest preoperative predictors for PMI were anaemia (AUC 0.7879), monocyte/eosinophil ratio > 13.0 (AUC 0.7814), neutrophil/lymphocyte ratio > 7.5 (AUC 0.7784), eosinophil count < 1.1 × 109/L (AUC 0.7780), and neutrophil/albumin × 10 > 2.4 (AUC 0.7732); additionally, sensitivity was 83.1-75.4% and specificity was 82.1-75.0%. The highest predictors of in-hospital death were platelet/lymphocyte ratio > 280.0 (AUC 0.8390), lymphocyte/monocyte ratio < 1.1 (AUC 0.8375), albumin < 33 g/L (AUC 0.7889), red cell distribution width > 14.5% (AUC 0.7739), and anaemia (AUC 0.7604), sensitivity 88.2% and above, and specificity 85.1-79.3%. Internal validation confirmed the predictive value of the models. Conclusions: Comparison of 27 IIM indices in HF patients identified several simple, widely available, and inexpensive parameters highly predictive for PMI and/or in-hospital death. The applicability of IIM biomarkers to diagnose and predict risks for chronic diseases, including OP/OF, in the preclinical stages is discussed.

Association of chronic liver disease with bone diseases and muscle weakness

The liver is a vital organ involved in nutrient metabolism, hormone regulation, immunity, cytokine production, and gut homeostasis. Impairment in liver function can result in malnutrition, chronic inflammation, decreased anabolic hormone levels, and dysbiosis. These conditions eventually cause an imbalance in osteoblast and osteoclast activities, resulting in bone loss. Osteoporosis is a frequent complication of chronic liver disease (CLD) that adversely affects quality of life and increases early mortality. Sarcopenia is another common complication of CLD characterized by progressive loss of skeletal muscle mass and function. Assessment criteria for sarcopenia specific to liver disease have been established, and sarcopenia has been reported to be associated with an increase in the risk of liver disease-related events and mortality in patients with CLD. Owing to their similar risk factors and underlying pathophysiological mechanisms, osteoporosis and sarcopenia often coexist (termed osteosarcopenia), progress in parallel, and further exacerbate the conditions mentioned above. Therefore, comprehensive management of these musculoskeletal disorders is imperative. This review summarizes the clinical implications and characteristics of osteoporosis, extending to sarcopenia and osteosarcopenia, in patients with CLD caused by different etiologies.

The associations of alcoholic liver disease and nonalcoholic fatty liver disease with bone mineral density and the mediation of serum 25-Hydroxyvitamin D: A bidirectional and two-step Mendelian randomization

BACKGROUND

Reduced bone mineral density (BMD) and osteoporosis are common in chronic liver diseases. However, the causal effect of alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) on BMD remains uncertain.

OBJECTIVES

This study uses a two-sample Mendelian randomization (MR) design to evaluate the genetically predicted effect of ALD and NAFLD on BMDs using summary data from publically available genome-wide association studies (GWASs).

METHODS

The GWAS summary statistics of ALD (1416 cases and 213,592 controls) and NAFLD (894 cases and 217,898 controls) were obtained from the FinnGen consortium. BMDs of four sites (total body, n = 56,284; femoral neck, n = 32,735; lumbar spine, n = 28,498; forearm, n = 8143) were from the GEnetic Factors for OSteoporosis Consortium. Data for alcohol consumption (n = 112,117) and smoking (n = 33,299) and serum 25-Hydroxyvitamin D (25-OHD) level (n = 417,580) were from UK-biobank. We first performed univariate MR analysis with the Inverse Variance Weighted (IVW) method as the primary analysis to investigate the genetically predicted effect of ALD or NAFLD on BMD. Then, multivariate MR and mediation analysis were performed to identify whether the effect was mediated by alcohol consumption, smoking, or serum 25-OHD level.

RESULTS

The MR results suggested a robust genetically predicted effect of ALD on reduced BMD in the femoral neck (FN-BMD) (IVW beta = -0.0288; 95% CI: -0.0488, -0.00871; P = 0.00494) but not the other three sites. Serum 25-OHD level exhibited a significant mediating effect on the association between ALD and reduced FN-BMD albeit the proportion of mediation was mild (2.21%). No significant effects of NAFLD, alcohol consumption, or smoking on BMD in four sites, or reverse effect of BMD on ALD or NAFLD were detected.

CONCLUSION

Our findings confirm the genetically predicted effect of ALD on reduced FN-BMD, and highlight the importance of periodic BMD and serum 25-OHD monitoring and vitamin D supplementation as needed in patients with ALD. Future research is required to validate our results and investigate the probable underlying mechanisms.