Metabolic Bone Disease in Viral Cirrhosis: A Prospective Study

Bone-organ axes: bidirectional crosstalk

In addition to its recognized role in providing structural support, bone plays a crucial role in maintaining the functionality and balance of various organs by secreting specific cytokines (also known as osteokines). This reciprocal influence extends to these organs modulating bone homeostasis and development, although this aspect has yet to be systematically reviewed. This review aims to elucidate this bidirectional crosstalk, with a particular focus on the role of osteokines. Additionally, it presents a unique compilation of evidence highlighting the critical function of extracellular vesicles (EVs) within bone-organ axes for the first time. Moreover, it explores the implications of this crosstalk for designing and implementing bone-on-chips and assembloids, underscoring the importance of comprehending these interactions for advancing physiologically relevant in vitro models. Consequently, this review establishes a robust theoretical foundation for preventing, diagnosing, and treating diseases related to the bone-organ axis from the perspective of cytokines, EVs, hormones, and metabolites.

Caring for the Bone Health Among Liver Transplant Recipients

Liver transplant outcomes have improved over the years, and currently, the quality of life and long-term well-being of these patients needs to be improved. Improving bone health goes a long way toward achieving this objective. Poor bone health (osteopenia and osteoporosis) although prevalent, is often overlooked owing to its asymptomatic nature. It can be complicated by debilitating fracture affecting quality of life. It is recommended to assess and optimize bone health prior to liver transplant. Multiple factors contribute to poor bone health in a liver transplant recipient and it is vital to understand and ameliorate these. A careful and targeted approach with inputs from multidisciplinary team involving transplant physician, endocrinologist, occupational therapist, nutritionist, and nursing personnel may often be required. In this review, we aim to concisely discuss the various aspects related to prevalence, pathophysiology, evaluation, treatment, and follow-up of bone disease among liver transplant recipients.

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

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

The Impact of Tenofovir Disoproxil Fumarate on Reduced Bone Mineral Density and Fractures in Liver Transplant Recipients

BACKGROUND

Tenofovir disoproxil fumarate (TDF) is associated with reduced bone density in patients with human immunodeficiency virus, but the effect of TDF on bone density in liver transplant (LT) recipients is unknown.

METHODS

We performed a single-center, retrospective study of LT recipients with hepatitis B taking TDF compared to a control group with non-hepatitis B virus viral hepatitis. The primary outcome was reduced bone density, defined as femoral neck or lumbar T-score less than -1. Other outcomes included mean T-score and fractures.

RESULTS

Three hundred ninety-three patients were studied: 52 patients in the TDF group and 341 patients in the control group; 64.3% patients in the TDF group had reduced bone density vs 71.4% in the control group (P = .58) before LT, compared to 75% and 81.5% (P = .57), respectively, after LT. Mean posttransplant lumbar T-scores were lower in the TDF group (-1.74 vs -0.75, P = .04). There was no difference between the 2 groups for the other outcomes. In a multivariate Cox proportional hazards model, TDF use did not affect the risk of post-LT reduced bone density (hazard ratio = 0.99; 95% confidence interval, 0.56-1.76; P = .97).

CONCLUSION

TDF use was not associated with reduced bone mineral density or increased rates of fractures in LT recipients compared to controls in this study.

Hepatic Osteodystrophy-Molecular Mechanisms Proposed to Favor Its Development

Almost all patients with chronic liver diseases (CLD) show altered bone metabolism. Depending on the etiology, this manifests in a severe osteoporosis in up to 75% of the affected patients. Due to high prevalence, the generic term hepatic osteodystrophy (HOD) evolved, describing altered bone metabolism, decreased bone mineral density, and deterioration of bone structure in patients with CLD. Once developed, HOD is difficult to treat and increases the risk of fragility fractures. Existing fractures affect the quality of life and, more importantly, long-term prognosis of these patients, which presents with increased mortality. Thus, special care is required to support the healing process. However, for early diagnosis (reduce fracture risk) and development of adequate treatment strategies (support healing of existing fractures), it is essential to understand the underlying mechanisms that link disturbed liver function with this bone phenotype. In the present review, we summarize proposed molecular mechanisms favoring the development of HOD and compromising the healing of associated fractures, including alterations in vitamin D metabolism and action, disbalances in transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signaling with histone deacetylases (HDACs) as secondary regulators, as well as alterations in the receptor activator of nuclear factor kappa B ligand (RANKL)–osteoprotegerin (OPG) system mediated by sclerostin. Based on these mechanisms, we give an overview on the limitations of early diagnosis of HOD with established serum markers.