Lithocholic acid downregulates vitamin D effects in human osteoblasts

Obesity and lipid metabolism in the development of osteoporosis (Review)

Osteoporosis is a common bone metabolic disease that causes a heavy social burden and seriously threatens life. Improving osteogenic capacity is necessary to correct bone mass loss in the treatment of osteoporosis. Osteoblasts are derived from the differentiation of bone marrow mesenchymal stem cells, a process that opposes adipogenic differentiation. The peroxisome proliferator‑activated receptor γ and Wnt/β‑catenin signaling pathways mediate the mutual regulation of osteogenesis and adipogenesis. Lipid substances play an important role in the occurrence and development of osteoporosis. The content and proportion of lipids modulate the activity of immunocytes, mainly macrophages, and the secretion of inflammatory factors, such as IL‑1, IL‑6 and TNF‑α. These inflammatory effectors increase the activity and promote the differentiation of osteoclasts, which leads to bone imbalance and stronger bone resorption. Obesity also decreases the activity of antioxidases and leads to oxidative stress, thereby inhibiting osteogenesis. The present review starts by examining the bidirectional differentiation of BM‑MSCs, describes in detail the mechanism by which lipids affect bone metabolism, and discusses the regulatory role of inflammation and oxidative stress in this process. The review concludes that a reasonable adjustment of the content and proportion of lipids, and the alleviation of inflammatory storms and oxidative damage induced by lipid imbalances, will improve bone mass and treat osteoporosis.

Microbiota metabolites in bone: Shaping health and Confronting disease

The intricate interplay between the gut microbiota and bone health has become increasingly recognized as a fundamental determinant of skeletal well-being. Microbiota-derived metabolites play a crucial role in dynamic interaction, specifically in bone homeostasis. In this sense, short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, indirectly promote bone formation by regulating insulin-like growth factor-1 (IGF-1). Trimethylamine N-oxide (TMAO) has been found to increase the expression of osteoblast genes, such as Runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP2), thus enhancing osteogenic differentiation and bone quality through BMP/SMADs and Wnt signaling pathways. Remarkably, in the context of bone infections, the role of microbiota metabolites in immune modulation and host defense mechanisms potentially affects susceptibility to infections such as osteomyelitis. Furthermore, ongoing research elucidates the precise mechanisms through which microbiota-derived metabolites influence bone cells, such as osteoblasts and osteoclasts. Understanding the multifaceted influence of microbiota metabolites on bone, from regulating homeostasis to modulating susceptibility to infections, has the potential to revolutionize our approach to bone health and disease management. This review offers a comprehensive exploration of this evolving field, providing a holistic perspective on the impact of microbiota metabolites on bone health and diseases.

Bile Acid Network and Vascular Calcification-Associated Diseases: Unraveling the Intricate Connections and Therapeutic Potential

Bile acids play a crucial role in promoting intestinal nutrient absorption and biliary cholesterol excretion, thereby protecting the liver from cholesterol accumulation and bile acid toxicity. Additionally, bile acids can bind to specific nuclear and membrane receptors to regulate energy expenditure and specific functions of particular tissues. Vascular calcification refers to the pathological process of calcium-phosphate deposition in blood vessel walls, which serves as an independent predictor for cardiovascular adverse events. In addition to aging, this pathological change is associated with aging-related diseases such as atherosclerosis, hypertension, chronic kidney disease, diabetes mellitus, and osteoporosis. Emerging evidence suggests a close association between the bile acid network and these aforementioned vascular calcification-associated conditions. Several bile acids have been proven to participate in calcium-phosphate metabolism, affecting the transdifferentiation of vascular smooth muscle cells and thus influencing vascular calcification. Targeting the bile acid network shows potential for ameliorating these diseases and their concomitant vascular calcification by regulating pathways such as energy metabolism, inflammatory response, oxidative stress, and cell differentiation. Here, we present a summary of the metabolism and functions of the bile acid network and aim to provide insights into the current research on the profound connections between the bile acid network and these vascular calcification-associated diseases, as well as the therapeutic potential.

Bile acid metabolism regulatory network orchestrates bone homeostasis

Bile acids (BAs), synthesized in the liver and modified by the gut microbiota, have been widely appreciated not only as simple lipid emulsifiers, but also as complex metabolic regulators and momentous signaling molecules, which play prominent roles in the complex interaction among several metabolic systems. Recent studies have drawn us eyes on the diverse physiological functions of BAs, to enlarge the knowledge about the "gut-bone" axis due to the participation about the gut microbiota-derived BAs to modulate bone homeostasis at physiological and pathological stations. In this review, we have summarized the metabolic processes of BAs and highlighted the crucial roles of BAs targeting bile acid-activated receptors, promoting the proliferation and differentiation of osteoblasts (OBs), inhibiting the activity of osteoclasts (OCs), as well as reducing articular cartilage degradation, thus facilitating bone repair. In addition, we have also focused on the bidirectional effects of BA signaling networks in coordinating the dynamic balance of bone matrix and demonstrated the promising effects of BAs on the development or treatment for pathological bone diseases. In a word, further clinical applications targeting BA metabolism or modulating gut metabolome and related derivatives may be developed as effective therapeutic strategies for bone destruction diseases.

Prenatal and Neonatal Bone Health: Updated Review on Early Identification of Newborns at High Risk for Osteopenia

Bone health starts with maternal health and nutrition, which influences bone mass and density already in utero. The mechanisms underlying the effect of the intrauterine environment on bone health are partly unknown but certainly include the 'foetal programming' of oxidative stress and endocrine systems, which influence later skeletal growth and development. With this narrative review, we describe the current evidence for identifying patients with risk factors for developing osteopenia, today's management of these populations, and screening and prevention programs based on gestational age, weight, and morbidity. Challenges for bone health prevention include the need for new technologies that are specific and applicable to pregnant women, the foetus, and, later, the newborn. Radiofrequency ultrasound spectrometry (REMS) has proven to be a useful tool in the assessment of bone mineral density (BMD) in pregnant women. Few studies have reported that transmission ultrasound can also be used to assess BMD in newborns. The advantages of this technology in the foetus and newborn are the absence of ionising radiation, ease of use, and, above all, the possibility of performing longitudinal studies from intrauterine to extrauterine life. The use of these technologies already in the intrauterine period could help prevent associated diseases, such as osteoporosis and osteopenia, which are characterised by a reduction in bone mass and degeneration of bone structure and lead to an increased risk of fractures in adulthood with considerable social repercussions for the related direct and indirect costs.

The association between total bile acid and bone mineral density among patients with type 2 diabetes

Objective

Bile acids have underlying protective effects on bones structure. Long-term diabetes also causes skeletal disorders including osteoporosis, Charcot arthropathy and renal osteodystrophy. Nevertheless, few studies have reported whether bile acid is associated with bone metabolism in diabetics. This study aimed to explore the relationship between total bile acid (TBA) and bone mineral density (BMD) among patients with type 2 diabetes mellitus (T2DM).

Methods

We retrospectively included 1,701 T2DM patients who were hospitalized in Taian City Central Hospital (TCCH), Shandong Province, China between January 2017 to December 2019. The participants were classified into the osteopenia (n = 573), osteoporosis (n= 331) and control groups (n= 797) according to BMD in the lumbar spine and femoral. The clinical parameters, including TBA, bilirubin, vitamin D, calcium, phosphorus and alkaline phosphatase were compared between groups. Multiple linear regression was used to analyze the relationship between TBA and BMD in lumbar spine, femoral, trochiter, ward's triangle region. A logistic regression was conducted to develop a TBA-based diagnostic model for differentiating abnormal bone metabolism from those with normal BMD. We evaluated the performance of model using ROC curves.

Results

The TBA level was significantly higher in patients with osteoporosis (Median[M]= 3.300 μmol/L, interquartile range [IQR] = 1.725 to 5.250 μmol/L) compared to the osteopenia group (M = 3.200 μmol/L, IQR = 2.100 to 5.400 μmol/L) and control group (M = 2.750 μmol/L, IQR = 1.800 to 4.600 μmol/L) (P <0.05). Overall and subgroup analyses indicated that TBA was negatively associated with BMD after adjusted for the co-variates (i.e., age, gender, diabetes duration, BMI, total bilirubin, direct bilirubin, indirect bilirubin) (P <0.05). Logistic regression revealed that higher TBA level was associated with increased risk for abnormal bone metabolism (OR = 1.044, 95% CI = 1.005 to 1.083). A TBA-based diagnostic model was established to identify individuals with abnormal bone metabolism (T-score ≤ -1.0). The area under ROC curve (AUC) of 0.767 (95% CI = 0.730 to 0.804).

Conclusion

Our findings demonstrated the potential role of bile acids in bone metabolism among T2DM patients. The circulating TBA might be employed as an indicator of abnormal bone metabolism.

Bacillus subtilis Modulated the Expression of Osteogenic Markers in a Human Osteoblast Cell Line

Several in vivo trials have previously demonstrated the beneficial effects of the administration of various probiotic forms on bone health. In this study, we explored the potency of two probiotics, Bacillus subtilis and Lactococcus lactis, alone or in combination with vitamin D (VD), to modulate the transcription of genes involved in the ossification process in a human osteoblast cell line. Genes that mark the "osteoblast proliferation phase", such as RUNX2, TGFB1, and ALPL, "extracellular matrix (ECM) maturation", such as SPP1 and SPARC, as well as "ECM mineralization", such as BGN, BGLAP, and DCN, were all highly expressed in osteoblasts treated with B. subtilis extract. The observed increase in the transcription of the ALPL mRNA was further in agreement with its protein levels as observed by Western blot and immunofluorescence. Therefore, this higher transcription and translation of alkaline phosphatase in osteoblasts treated with the B. subtilis extract, indicated its substantial osteogenic impact on human osteoblasts. Although both the probiotic extracts showed no osteogenic synergy with VD, treatment with B. subtilis alone could increase the ECM mineralization, outperforming the effects of L. lactis and even VD. Furthermore, these results supported the validity of employing probiotic extracts rather than live cells to investigate the effects of probiotics in the in vitro systems.

The Role of Vitamin D and Vitamin D Binding Protein in Chronic Liver Diseases

Vitamin D (calciferol) is a fat-soluble vitamin that has a significant role in phospho-calcium metabolism, maintaining normal calcium levels and bone health development. The most important compounds of vitamin D are cholecalciferol (vitamin D3, or VD3) and ergocalciferol (vitamin D2, or VD2). Besides its major role in maintaining an adequate level of calcium and phosphate concentrations, vitamin D is involved in cell growth and differentiation and immune function. Recently, the association between vitamin D deficiency and the progression of fibrosis in chronic liver disease (CLD) was confirmed, given the hepatic activation process and high prevalence of vitamin D deficiency in these diseases. There are reports of vitamin D deficiency in CLD regardless of the etiology (chronic viral hepatitis, alcoholic cirrhosis, non-alcoholic fatty liver disease, primary biliary cirrhosis, or autoimmune hepatitis). Vitamin D binding protein (VDBP) is synthesized by the liver and has the role of binding and transporting vitamin D and its metabolites to the target organs. VDBP also plays an important role in inflammatory response secondary to tissue damage, being involved in the degradation of actin. As intense research during the last decades revealed the possible role of vitamin D in liver diseases, a deeper understanding of the vitamin D, vitamin D receptors (VDRs), and VDBP involvement in liver inflammation and fibrogenesis could represent the basis for the development of new strategies for diagnosis, prognosis, and treatment of liver diseases. This narrative review presents an overview of the evidence of the role of vitamin D and VDBP in CLD, both at the experimental and clinical levels.

Bilirubin increases viability and decreases osteoclast apoptosis contributing to osteoporosis in advanced liver diseases

Bilirubin and bile acids have deleterious effects on osteoblasts, which may explain the low bone formation of liver diseases with cholestasis. Although there is some clinical evidence of increased bone resorption in this condition, the effects of these substances on osteoclasts are unknown. The objective was to analyze the effects of bilirubin and bile acids -lithocholic acid (LCA) and ursodeoxycholic acid (UDCA)- on osteoclast viability and apoptosis, and on the expression of osteoclast-related microRNAs (miRNAs). RAW 264.7 cells and human PBMCs were differentiated into osteoclasts. Success in differentiation was assessed by TRAP stain and osteoclast-specific gene expression; osteoclast activity was detected by the resorption pits in Corning® Osteo Assay Surface Plates. Cells were treated with camptothecin (CAM) or with bilirubin, LCA or UDCA, at several concentrations and combinations, including non-treated cells as control. Cell viability was measured using WST-1 assay and apoptosis assessing Caspase-3 by Western blot. Expression of miR-21a, miR-29b, miR-31, miR-148a, miR-155 and miR-223 were analyzed by Real Time. Viability increased gradually in osteoclasts differentiated from RAW 264.7 cells, as the concentration of bilirubin increased, being particularly high with bilirubin 100 μM (61 %) as compared to the untreated control (p < 0.007). Viability decreased significantly with CAM, LCA and UDCA (80 %, 62 % and 27 %, respectively), effects which were abolished by bilirubin. Moreover, bilirubin increased viability in osteoclasts derived from human PBMCs (p < 0.03). Caspase-3 decreased by 46 % with bilirubin 50 μM and increased 10-fold with LCA 100 μM and CAM (p < 0.01). Bilirubin increased miR-21 and miR-148a expression as compared to controls (115 % and 59 %, respectively; p < 0.007). In conclusion, bilirubin increases viability and decreases apoptosis of osteoclasts, and overexpresses the osteoclastogenic miR-21 and miR-148a. The effects of bilirubin counteract the actions of LCA and UDCA. Therefore, bilirubin may contribute to the increased bone resorption and to the development of osteoporosis in advanced liver diseases.

Activation of farnesoid X receptor signaling by geniposidic acid promotes osteogenesis

BACKGROUND

New targets and strategies are urgently needed for the identification and development of anabolic drugs for osteoporosis. Farnesoid X receptor (FXR) is a promising novel therapeutic target for bone metabolism diseases. Although used clinically, FXR agonists have obvious side effects; therefore, the development of new FXR agonists for the treatment of osteoporosis would be welcomed. Geniposidic acid (GPA) is a bioactive compound extracted from Eucommiae cortex, which is used for treating arthritis, osteoporotic fractures, and hypertension. However, the therapeutic effects of GPA against osteoporosis remain underexplored.

PURPOSE

This study aims to reveal the potential osteogenic effects of FXR and to explore the effect of GPA on bone formation, osteoporosis treatment, and FXR signaling.

STUDY DESIGN & METHODS

The role of FXR in promoting bone formation was evaluated in Fxr knockout (Fxr^-/-) mice and cell models. GPA activation of FXR was evaluated by molecular docking and luciferase reporter gene assays. Thirty female C57BL/6J mice were randomly assigned into a sham operation group (Sham) and four ovariectomized (OVX) groups (n=6 each) and were treated with vehicle or different doses of GPA (25, 50, and 100 mg/kg/day). The therapeutic effect of GPA on osteoporosis was systematically analyzed by performing bone histomorphometry and measuring serum biochemical parameters, and the molecular mechanism was also evaluated. Furthermore, the action of GPA in Fxr^-/- mice was evaluated to investigate its dependency on FXR in promoting bone formation and treating osteoporosis.

RESULTS

We found that FXR was highly expressed in bone tissues and enriched in osteoblasts. Notably, deletion of FXR significantly reduced the bone formation rate and bone mass of the Fxr^-/- mice compared with wild-type mice. Furthermore, using a high throughput drug screening strategy based on fluorescent reporter genes, we found that GPA functions as a natural agonist of FXR. We confirmed the activities of GPA on FXR activation and osteogenesis in both osteoblast differentiation models and OVX-induced osteoporosis models. We revealed that GPA strongly promotes bone formation by activating FXR/RUNX2 signaling. Moreover, the osteoporotic therapeutic effect of GPA was abolished in Fxr^-/- mice.

CONCLUSION

This study demonstrated that FXR is a promising target for treating osteoporosis and that GPA promotes bone formation in OVX-induced osteoporosis by activating FXR signaling. These findings provide novel insight into the mechanism by which GPA promotes bone formation and more evidence for its application in the treatment of osteoporosis.

Risk factors for metabolic bone disease of prematurity: A meta-analysis

Objective

To investigate the risk factors for metabolic bone disease of prematurity (MBDP), and to provide a reference for the prevention of MBDP.

Methods

The databases including China Biomedical Literature Service System, China National Knowledge Infrastructure, Wanfang Data, and Weipu Periodical Database, PubMed, Web of Science, Embase, Cochrane Library and other databases were searched for studies on the risk factors for MBDP published up to June 18, 2021. RevMan 5.3 and Stata 14.1 software were used to perform a Meta analysis.

Results

A total of 15 articles were included, including 13 case-control studies, 1 current investigation, and 1 retrospective cohort study. There were 1,435 cases in the case group and 2,057 cases in the control group, with a total sample size of 3,492 cases. Meta analysis showed that risk factors for MBDP include birth weight <1000g (OR = 6.62, 95%CI: 2.28–19.25), gestational age <32 weeks (OR = 2.73, 95%CI: 1.07–6.95), septicemia (OR = 2.53, 95%CI: 1.69–3.79), parenteral nutrition time (OR = 4.04, 95%CI: 1.72–9.49), cholestasis (OR = 3.50, 95%CI: 1.49–8.23), intrauterine growth retardation (OR = 6.89, 95%CI: 3.81–12.44), while the birth weight(OR = 0.44, 95%CI: 0.21–0.90) and gestational age (OR = 0.57, 95%CI: 0.44–0.73)are the protective factors of MBDP.

Conclusion

Factors like birth weight <1000g, gestational age <32 weeks, septicemia, parenteral nutrition time, cholestasis, and intrauterine growth retardation may increase the risk of metabolic bone disease of prematurity.

Decreasing Rates of Fracture-Related Hospitalization With Primary Biliary Cholangitis: Insights From the Nationwide Inpatient Sample

Introduction

Primary biliary cholangitis (PBC) is associated with an increased risk of developing fractures. Current guidelines recommend measures that can help prevent the development of fractures in these patients. The purpose of this study was to trend the rates of hospitalizations related to fractures and their burden on healthcare.

Methods

We performed a retrospective, cohort study of adults hospitalized in the United States with PBC between 2010 and 2014. Patients were identified using the Nationwide Inpatient Sample (NIS). Temporal analysis of PBC patients with a co-diagnosis of hip, vertebral, or wrist fractures (the study group) was performed with regards to the total number of inpatient admissions, inpatient mortality, length of stay, and total charges associated with hospitalization. Descriptive analyses were performed using the t-test for continuous data and the chi-square test for categorical data.

Results

During the five-year study period, there were 308,753 hospitalizations for PBC. There has been a downward trend (p=0.02) in fracture-related admissions among patients with PBC during this study period. Length of stay was higher in the PBC-fracture group (10.85 days vs 7.36 days; p<0.001). Total hospitalization charges were higher among the PBC-fracture patients when compared to the control group ($98,444 vs $72,964; p=0.004).

Conclusion

There has been a gradual reduction in the rate of fracture-related hospitalizations in patients with PBC. However, patients with PBC who have fractures have increased the utilization of health care resources as compared to their cohort admitted for reasons other than for a fracture.

Osteosarcopenia in autoimmune cholestatic liver diseases: Causes, management, and challenges

Primary biliary cholangitis and primary sclerosing cholangitis (PSC) are the most common cholestatic liver diseases (CLD) in adults and are both characterized by an immune pathogenesis. While primary biliary cholangitis is a model autoimmune disease, with over 90% of patients presenting very specific autoantibodies against mitochondrial antigens, PSC is considered an immune mediated disease. Osteoporosis is the most common bone disease in CLD, resulting in frequent fractures and leading to significant morbidity. Further, sarcopenia is emerging as a frequent complication of chronic liver diseases with a significant prognostic impact and severe implications on the quality of life of patients. The mechanisms underlying osteoporosis and sarcopenia in CLD are still largely unknown and the association between these clinical conditions remains to be dissected. Although timely diagnosis, prevention, and management of osteosarcopenia are crucial to limit the consequences, there are no specific guidelines for management of osteoporosis and sarcopenia in patients with CLD. International guidelines recommend screening for bone disease at the time of diagnosis of CLD. However, the optimal monitoring strategies and treatments have not been defined yet and vary among centers. We herein aim to comprehensively outline the pathogenic mechanisms and clinical implications of osteosarcopenia in CLD, and to summarize expert recommendations for appropriate diagnostic and therapeutic approaches.

Gut microbiota and bone metabolism

Osteoporosis is the most common metabolic skeletal disease. It is characterized by the deterioration of the skeletal microarchitecture and bone loss, leading to ostealgia, and even bone fractures. Accumulating evidence has indicated that there is an inextricable relationship between the gut microbiota (GM) and bone homeostasis involving host-microbiota crosstalk. Any perturbation of the GM can play an initiating and reinforcing role in disrupting the bone remodeling balance during the development of osteoporosis. Although the GM is known to influence bone metabolism, the mechanisms associated with these effects remain unclear. Herein, we review the current knowledge of how the GM affects bone metabolism in health and disease, summarize the correlation between pathogen-associated molecular patterns of GM structural components and bone metabolism, and discuss the potential mechanisms underlying how GM metabolites regulate bone turnover. Deciphering the complicated relationship between the GM and bone health will provide new insights into the prevention and treatment of osteoporosis.

The Role of Intestinal Flora in the Regulation of Bone Homeostasis

Intestinal flora located within the intestinal tract comprises a large number of cells, which are referred to as the second gene pool of the human body and form a complex symbiotic relationship with the host. The knowledge of the complex interaction between the intestinal flora and various life activities of the host is a novel and rapidly expanding field. Recently, many studies are being conducted on the relationship between the intestinal flora and bone homeostasis and indicate that the intestinal flora can regulate bone homeostasis via the host immune, metabolic, and endocrine systems. What’s more, based on several clinical and preclinical pieces of evidence, changing the composition and function of the host intestinal flora through the application of probiotics, prebiotics, and fecal microbiota transplantation is being considered to be a potential novel target for the regulation of bone homeostasis. Here, we searched relevant literature and reviewed the role of the intestinal flora in the regulation of bone homeostasis and its modulating interventions.

Bilirubin and bile acids in osteocytes and bone tissue. Potential role in the cholestatic-induced osteoporosis

BACKGROUND AND AIMS

Osteoporosis is a common complication in patients with primary biliary cholangitis. Both bilirubin and lithocholic acid (LCA) result in detrimental effects on osteoblastic cells, and ursodeoxycholic acid (UDCA) counteracts these outcomes. However, there is no information on the consequences of these retained substances of cholestasis and sera from cholestatic patients in osteocytes.

METHODS

The impact of bilirubin, LCA, UDCA and serum from jaundiced patients on viability, differentiation, mineralization and apoptosis has been assessed in MLO-Y4 and MLO-A5 osteocyte cell lines. Effects on gene expression were assessed in these cells and in human bone fragments.

RESULTS

Lithocholic acid 10 μmol/L and bilirubin 50 μmol/L decreased viability in MLO-Y4 and MLO-A5 cells (11% and 53% respectively; P ≤ .01). UDCA alone or combined with LCA or bilirubin increased cell viability. Jaundiced sera decreased cell viability (56%), an effect which was reverted by UDCA. Bilirubin decreased differentiation by 47% in MLO-Y4 (P ≤ .01) and mineralization (87%) after 21 days in MLO-A5 (P ≤ .03). Both bilirubin and LCA increased apoptosis in MLO-Y4, and UDCA diminished the apoptotic effect. Moreover, bilirubin down-regulated RUNX2 and up-regulated RANKL gene expression in bone tissue, MLO-Y4 and MLO-A5 cells, and LCA up-regulated RANKL expression in bone tissue. UDCA 100 μmol/L increased the gene expression of all these genes in bone tissue and MLO-Y4 cells and neutralized the decreased RUNX2 expression induced by bilirubin.

CONCLUSION

Bilirubin and LCA have damaging consequences in osteocytes by decreasing viability, differentiation and mineralization, increasing apoptosis and modifying gene expression, effects that are neutralized by UDCA.

The role of gut microbiota in bone homeostasis

The gut microbiota (GM) is referred to as the second gene pool of the human body and a commensal, symbiotic, and pathogenic microorganism living in our intestines. The knowledge of the complex interaction between intestinal microbiota and health outcomes is a novel and rapidly expanding the field. Earlier studies have reported that the microbial communities affect the cellular responses and shape many aspects of physiology and pathophysiology within the body, including muscle and bone metabolism (formation and resorption). GM influences the skeletal homeostasis via affecting the host metabolism, immune function, hormone secretion, and the gut-brain axis. The premise of this review is to discuss the role of GM on bone homeostasis and skeletal muscle mass function. This review also opens up new perspectives for pathophysiological studies by establishing the presence of a 'microbiota-skeletal' axis and raising the possibility of innovative new treatments for skeletal development.

The Pharmacologic Management of Osteoporosis in Primary Biliary Cholangitis: A Systematic Review and Meta-Analysis

INTRODUCTION

Osteoporosis is a common complication of primary biliary cholangitis (PBC) yet evidence for effective therapy is lacking. We sought to review all randomized controlled trials evaluating pharmacotherapy against placebo or no intervention for treatment of osteoporosis in PBC.

METHODOLOGY

A comprehensive database search was conducted from inception through 29 March 2017. The primary outcome was incidence of fractures; secondary outcomes were change in bone mineral density (BMD) and adverse events. We assessed studies for risk of bias, graded quality of evidence, and used meta-analysis to obtain overall effect by pooling studies of the same drug class.

RESULTS

We identified 11 randomized controlled trials evaluating bisphosphonates (3), hormone replacement therapy (2), ursodeoxycholic acid (1), obeticholic acid (1), cyclosporin A (1), vitamin K (1), calcitriol (1), and sodium fluoride (1). No intervention significantly reduced fractures compared to control. Although significant improvement in BMD was seen in one study with alendronate, a third-generation bisphosphonate, no significant improvement was seen on pooled analysis of all bisphosphonates including first-generation bisphosphonates (standard mean difference 0.41, p = 0.68). On pooled analysis, hormone replacement therapy modestly improved lumbar BMD (standard mean difference 0.69, p = 0.02), but with significantly increased adverse events (odds ratio 8.82, p = 0.01).

CONCLUSIONS

There is a lack of high-quality evidence supporting the efficacy of any treatment of osteoporosis in PBC. This may be explained by lack of power in the included studies. However, our current understanding of PBC-related osteoporosis indicates that it results from decreased bone formation, which may explain the attenuated effect of traditional antiresorptive agents. Future studies should investigate newer anabolic bone agents.

Bone Health in Patients With Liver Diseases

Osteoporosis is the most common bone disease in chronic liver disease (CLD) resulting in frequent fractures and leading to significant morbidity in this population. In addition to patients with cirrhosis and chronic cholestasis, patients with CLD from other etiologies may be affected in the absence of cirrhosis. The mechanism of osteoporosis in CLD varies according to etiology, but in cirrhosis and cholestatic liver disease it is driven primarily by decreased bone formation, which differs from the increased bone resorption seen in postmenopausal osteoporosis. Direct toxic effects from iron and alcohol play a role in hemochromatosis and alcoholic liver disease, respectively. Chronic inflammation also has been proposed to mediate bone disease in viral hepatitis and nonalcoholic fatty liver disease. Treatment trials specific to osteoporosis in CLD are small, confined to primary biliary cholangitis and post-transplant patients, and have not consistently demonstrated a benefit in this population. As it stands, prevention of osteoporosis in CLD relies on the mitigation of risk factors such as smoking and alcohol use, treatment of underlying hypogonadism, and encouraging a healthy diet and weight-bearing exercise. The primary medical intervention for the treatment of osteoporosis in CLD remains bisphosphonates though a benefit in terms of fracture reduction has never been shown. This review outlines what is known regarding the pathogenesis of bone disease in CLD and summarizes current and emerging therapies.

Vitamin D status among preterm infants with cholestasis and metabolic bone disease

BACKGROUND

Metabolic bone disease of prematurity (MBD) is a common problem among preterm infants. Our previous study identified cholestasis as an important risk factor for the development of MBD. We conducted this study to determine the vitamin D status in preterm infants with MBD and cholestasis.

METHODS

We retrospectively reviewed medical record of preterm infants evaluated in NICU at Holtz Children's/Jackson Memorial Hospital between June 2014 and May 2016. Demographic, biochemical data, and vitamin D intake were collected and analyzed.

RESULTS

We identified 58 preterm infants (median gestational age 25 weeks) with MBD during this period. Twenty five infants also developed cholestasis. Median serum 25-hydroxyvitamin D level at the time of diagnosis of MBD was similar in cholestasis (C), (29.1 ng/ml, IQR 24.4-33.5), and non-cholestasis (NC), (28.7 ng/ml, IQR 22.7-34.6), group (p = 0.41). At the second measurement, average 6 weeks after the first measurement; median serum 25-hydroxyvitamin D level was lower (p = 0.02) in the C group (31.2 ng/ml, IQR 23.0-38.8) than in the NC group (36.5 ng/ml, IQR 28-45). However, the actual percentage of infants with vitamin D deficiency was similar in both the groups.

CONCLUSION

Most preterm infants with cholestasis and MBD had normal vitamin D status.

Bile acids and bilirubin effects on osteoblastic gene profile. Implications in the pathogenesis of osteoporosis in liver diseases

Osteoporosis in advanced cholestatic and end-stage liver disease is related to low bone formation. Previous studies have demonstrated the deleterious consequences of lithocholic acid (LCA) and bilirubin on osteoblastic cells. These effects are partially or completely neutralized by ursodeoxycholic acid (UDCA). We have assessed the differential gene expression of osteoblastic cells under different culture conditions. The experiments were performed in human osteosarcoma cells (Saos-2) cultured with LCA (10 μM), bilirubin (50 μM) or UDCA (10 and 100 μM) at 2 and 24 h. Expression of 87 genes related to bone metabolism and other signalling pathways were assessed by TaqMan micro fluidic cards. Several genes were up-regulated by LCA, most of them pro-apoptotic (BAX, BCL10, BCL2L13, BCL2L14), but also MGP (matrix Gla protein), BGLAP (osteocalcin), SPP1 (osteopontin) and CYP24A1, and down-regulated bone morphogenic protein genes (BMP3 and BMP4) and DKK1 (Dickkopf-related protein 1). Parallel effects were observed with bilirubin, which up-regulated apoptotic genes and CSF2 (colony-stimulating factor 2) and down-regulated antiapoptotic genes (BCL2 and BCL2L1), BMP3, BMP4 and RUNX2. UDCA 100 μM had specific consequences since differential expression was observed, up-regulating BMP2, BMP4, BMP7, CALCR (calcitonin receptor), SPOCK3 (osteonectin), BGLAP (osteocalcin) and SPP1 (osteopontin), and down-regulating pro-apoptotic genes. Furthermore, most of the differential expression changes induced by both LCA and bilirubin were partially or completely neutralized by UDCA. Conclusion: Our observations reveal novel target genes, whose regulation by retained substances of cholestasis may provide additional insights into the pathogenesis of osteoporosis in cholestatic and end-stage liver diseases.

Microbial osteoporosis: The interplay between the gut microbiota and bones via host metabolism and immunity

The complex relationship between intestinal microbiota and host is a novel field in recent years. A large number of studies are being conducted on the relationship between intestinal microbiota and bone metabolism. Bone metabolism consisted of bone absorption and formation exists in the whole process of human growth and development. The nutrient components, inflammatory factors, and hormone environment play important roles in bone metabolism. Recently, intestinal microbiota has been found to influence bone metabolism via influencing the host metabolism, immune function, and hormone secretion. Here, we searched relevant literature on Pubmed and reviewed the effect of intestinal microbiota on bone metabolism through the three aspects, which may provide new ideas and targets for the clinical treatment of osteoporosis.

Osteoporosis in primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune cholestatic liver disease with multiple debilitating complications. Osteoporosis is a common complication of PBC resulting in frequent fractures and leading to significant morbidity in this population, yet evidence for effective therapy is lacking. We sought to summarize our current understanding of the pathophysiology of osteoporosis in PBC, as well as current and emerging therapies in order to guide future research directions. A complete search with a comprehensive literature review was performed with studies from PubMed, EMBASE, Web of Science, Cochrane database, and the Countway Library. Osteoporosis in PBC is driven primarily by decreased bone formation, which differs from the increased bone resorption seen in postmenopausal osteoporosis. Despite this fundamental difference, current treatment recommendations are based primarily on experience with postmenopausal osteoporosis. Trials specific to PBC-related osteoporosis are small and have not consistently demonstrated a benefit in this population. As it stands, prevention of osteoporosis in PBC relies on the mitigation of risk factors such as smoking and alcohol use, as well as encouraging a healthy diet and weight-bearing exercise. The primary medical intervention for the treatment of osteoporosis in PBC remains bisphosphonates though a benefit in terms of fracture reduction has never been shown. This review outlines what is known regarding the pathogenesis of bone disease in PBC and summarizes current and emerging therapies.

Lithocholic Acid Is a Vitamin D Receptor Ligand That Acts Preferentially in the Ileum

The vitamin D receptor (VDR) is a nuclear receptor that mediates the biological action of the active form of vitamin D, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], and regulates calcium and bone metabolism. Lithocholic acid (LCA), which is a secondary bile acid produced by intestinal bacteria, acts as an additional physiological VDR ligand. Despite recent progress, however, the physiological function of the LCA−VDR axis remains unclear. In this study, in order to elucidate the differences in VDR action induced by 1,25(OH)₂D₃ and LCA, we compared their effect on the VDR target gene induction in the intestine of mice. While the oral administration of 1,25(OH)₂D₃ induced the Cyp24a1 expression effectively in the duodenum and jejunum, the LCA increased target gene expression in the ileum as effectively as 1,25(OH)₂D₃. 1,25(OH)₂D₃, but not LCA, increased the expression of the calcium transporter gene Trpv6 in the upper intestine, and increased the plasma calcium levels. Although LCA could induce an ileal Cyp24a1 expression as well as 1,25(OH)₂D₃, the oral LCA administration was not effective in the VDR target gene induction in the kidney. No effect of LCA on the ileal Cyp24a1 expression was observed in the VDR-null mice. Thus, the results indicate that LCA is a selective VDR ligand acting in the lower intestine, particularly the ileum. LCA may be a signaling molecule, which links intestinal bacteria and host VDR function.

Primary biliary cholangitis and bone disease

Osteoporosis, characterized by compromised bone strength leading to fragility fractures, is a common event in patients with primary biliary cholangitis (PBC). Osteomalacia, defined by poor bone mineralization is very uncommon. The pathogenesis of osteoporosis is not well clarified, but it mainly results from low bone formation. Few reports have revealed increased bone resorption, particularly in end-stage disease. The prevalence of osteoporosis is about 35% in the most significant studies, and it depends on the diagnostic criteria and severity of liver damage. Osteoporosis is associated with age, postmenopausal status, duration of PBC and advanced histological stage. Bone densitometry is the common method for the diagnosis of osteoporosis and should be performed in all patients with PBC. Lateral X-rays of the dorsal and lumbar spine should also be carried out to disclose vertebral fractures. There is no specific treatment but bisphosphonates, especially alendronate and ibandronate, efficiently increases bone mass and prevents bone loss. Despite these positive effects on bone mass no clear results on decreasing the fracture rate have been demonstrated, probably because the low number of patients included in the trials. The potential value of new agents requires further evaluation.

Metabolic alterations in the bone tissues of aged osteoporotic mice

Age-related osteoporosis is characterized by reduced bone mineralization and reduced bone strength, which increases the risk of fractures. We examined metabolic changes associated with age-related bone loss by profiling lipids and polar metabolites in tibia and femur bone tissues from young (5 months old) and old (28 months old) male C57BL/6J mice using ultra-performance liquid chromatography quadrupole-time-of-flight mass spectrometry. Partial least-squares discriminant analysis showed clear differences in metabolite levels in bone tissues of young and old mice. We identified 93 lipid species, including free fatty acids, sphingolipids, phospholipids, and glycerolipids, that were significantly altered in bone tissues of old mice. In addition, the expression of 26 polar metabolites differed significantly in bone tissues of old mice and young mice. Specifically, uremic toxin metabolite levels (p-cresyl sulfate, hippuric acid, and indoxylsulfate) were higher in bone tissues of old mice than in young mice. The increase in p-cresyl sulfate, hippuric acid, and indoxylsulfate levels were determined using targeted analysis of plasma polar extracts to determine whether these metabolites could serve as potential osteoporosis biomarkers. This study demonstrates that LC-MS-based global profiling of lipid and polar metabolites can elucidate metabolic changes that occur during age-related bone loss and identify potential biomarkers of osteoporosis.

Osteoporosis in chronic liver disease

Osteoporosis is a frequent complication in patients with chronic liver disease, especially in end-stages and in chronic cholestasis, in addition to non-alcoholic fatty liver disease, haemochromatosis and alcoholism. Mechanisms underlying osteoporosis are poorly understood, but osteoporosis mainly results from low bone formation. In this setting, sclerostin, a key regulator of the Wnt/β-catenin signalling pathway which regulates bone formation, in addition to the effects of the retained substances of cholestasis such as bilirubin and bile acids on osteoblastic cells, may influence the decreased bone formation in chronic cholestasis. Similarly, the damaging effects of iron and alcohol on osteoblastic cells may partially explain bone disease in haemochromatosis and alcoholism. A role for proinflammatory cytokines has been proposed in different conditions. Increased bone resorption may occur in cholestatic women with advanced disease. Low vitamin D, poor nutrition and hypogonadism, may be contributing factors to the full picture of bone disorders in chronic liver disease.

Association between primary biliary cholangitis and osteoporosis: meta-analysis

The relationship between primary biliary cholangitis (PBC, previously termed primary biliary cirrhosis) and risks of osteoporosis remains controversial. This meta-analysis was designed to comprehensively analyze the association between PBC and osteoporosis. We conducted a systematic literature search of the PubMed, EMBASE, and Web of Science. Either fixed or random effects models were applied to assess bone mineral density (BMD), osteoporosis rates, and fractures in PBC patients and normal controls. A total of eight studies were included (including 1643 PBC patients and 10,921 controls). PBC patients had a relative risk (RR) of 2.79 (95% CI 1.26 to 6.16) for the development of osteoporosis, lower lumbar spine BMD (95% CI - 0.13 to - 0.04, P = 0.0002), hip BMD (95% CI - 0.13 to - 0.03, P = 0.002), and lumbar spine t score (95% CI - 1.69 to - 1.02, P < 0.00001) than controls. Moreover, PBC patients had an OR of 1.86 (95%CI 1.54 to 2.24, P < 0.00001) for the development of fractures. Collectively, this meta-analysis indicates that PBC patients were more likely to suffer from osteoporosis. Given the limited literature available, better designed and larger scale primary studies will be required to confirm our conclusion.

Risk factors of metabolic bone disease of prematurity

OBJECTIVE

To identify the factors that increase risk of metabolic bone disease of prematurity (MBD).

STUDY DESIGN

A retrospective case-control study of infants born between January 2013-April 2014 with gestation age <30weeks and birth weight <1000g. MBD was defined as serum alkaline phosphatase above 500U/L and characteristic radiographic changes. Information was obtained on the presence of specific comorbidities.

RESULTS

Of 76 infants evaluated, 40 met criteria for MBD. Median gestational age was 25weeks in both groups (p=0.512). Median birth weight of infants with MBD was significantly lower than that of controls (560 vs. 765g, p<0.01). Longer period of parenteral nutrition and dexamethasone use was observed in MBD group. Cholestasis was associated with the highest likelihood of MBD (OR 16.6, 95% CI 4.8-56.9). Seizures (OR 5.2, 95% CI 1.3-20.5) and the prolonged use of diuretics (OR 2.6, 95% CI 1.0-7.0) also significantly increased the likelihood of MBD. Only cholestasis remained significant (OR 9.6, 95% CI 2.1-45.3) after multiple regression analysis.

CONCLUSION

Cholestasis is a significant risk factor for the development of MBD. Our future studies will be directed towards determining the causal relationship between cholestasis and MBD.

Vitamin D in liver disease: Current evidence and potential directions

Consistent with its multifaceted nature, growing evidence links vitamin D with hepatic disease. In this review, we summarise the roles of vitamin D in different liver pathologies and explore the clinical utility of vitamin D-based treatments in hepatology. We find that the small number of clinical trials coupled with the profound heterogeneity of study protocols limits the strength of evidence needed to ascribe definite clinical value to the hormone in liver disease. Nevertheless, the experimental data is promising and further bench and bedside studies will likely define a clearer role in hepatic therapeutics.

Diagnosis and Management of Cirrhosis-Related Osteoporosis

Management of cirrhosis complications has greatly improved, increasing survival and quality of life of the patients. Despite that, some of these complications are still overlooked and scarcely treated, particularly those that are not related to the liver. This is the case of osteoporosis, the only cirrhosis complication that is not solved after liver transplantation, because bone loss often increases after immunosuppressant therapy. In this review, the definitions of bone conditions in cirrhotic patients are analyzed, focusing on the more common ones and on those that have the largest impact on this population. Risk factors, physiopathology, diagnosis, screening strategies, and treatment of osteoporosis in cirrhotic patients are discussed, presenting the more striking data on this issue. Therapies used for particular conditions, such as primary biliary cirrhosis and liver transplantation, are also presented.

Metabolic Bone Disease in Primary Biliary Cirrhosis

Primary biliary cirrhosis (PBC) is a liver-specific autoimmune disease that primarily affects women (female-to-male ratio, 10:1) between 40 and 60 years of age. Metabolic bone disease is a common complication of PBC, affecting 14% to 52% of patients, depending on the duration and severity of liver disease. The osteoporosis seen in PBC seems mainly due to low bone formation, although increased bone resorption may contribute. Treatment of osteoporosis consists primarily of antiresorptive agents. Additional large prospective, long-term studies in patients with PBC are needed to determine efficacy in improving bone density as well as reducing fracture risk.

Association between nutritional screening via the Controlling Nutritional Status index and bone mineral density in chronic liver disease of various etiologies

AIM

Bone density disorders are prevalent in patients with chronic liver disease (CLD), who commonly present with hepatic osteodystrophy. However, the relationship between nutritional status and bone mineral density (BMD) has been scarcely studied in CLD.

METHODS

This single-center, cross-sectional study included outpatients consecutively diagnosed with CLD during a 1.5-year period. The nutritional status was assessed with the Controlling Nutritional Status (CONUT) index; dual-energy X-ray absorptiometry scans and parameters of bone mineral metabolism were carried out. Bone fracture risk was estimated with the World Health Organization FRAX tool.

RESULTS

Among the 126 patients recruited (58.7% male), osteopenia and osteoporosis were present in 31.1% and 10.7%, respectively. The 10-year fracture risk was significantly higher among women. Malnutrition estimated with the CONUT index was present in 29.9% of patients and was significantly more frequent in cirrhotic patients, 63.4% of whom were malnourished. Malnutrition stage directly correlated with hepatic function as expressed by the Model for End-Stage Liver Disease index. A non-significant relationship between CONUT-assessed nutritional status and BMD was documented. 25-Hydroxyvitamin-D3 (25[OH]-D3) and fracture risk correlated positively with the CONUT stage, and total cholesterol had an inverse relationship with BMD.

CONCLUSION

Malnutrition assessed by the CONUT was very frequent in patients with liver cirrhosis. The CONUT score inversely correlated with liver function, while malnutrition stage directly correlated with BMD, fracture risk and 25(OH)-D3. Total cholesterol showed a negative association with BMD in this population.

Ursodeoxycholic acid decreases bilirubin-induced osteoblast apoptosis

BACKGROUND

Low bone turnover osteoporosis is common in cholestatic diseases. Ursodeoxycholic acid (UDCA) counteracts the damaging effects of bilirubin or lithocholic acid (LCA) on osteoblast viability, proliferation and mineralisation. UDCA is anti-apoptotic in various cell lines, but this effect in bone cells is unknown. Therefore, the consequences of bilirubin and LCA on apoptosis, and whether UDCA has anti-apoptotic effects have been assessed on osteoblasts.

MATERIALS AND METHODS

Human osteoblasts (hOB) and osteosarcoma cell line (Saos-2) were treated with camptothecin as a pro-apoptotic agent, and UDCA, LCA and bilirubin. Apoptosis was determined by DNA fragmentation, flow cytometry, caspase-3 activity and expression of pro-apoptotic (Bcl-2-associated X protein BAX) and anti-apoptotic (BCL2 and BCL2-like 1 protein, BCL2L) genes.

RESULTS

Both LCA (10 μM) and bilirubin (50 μM) induced apoptosis as indicated by DNA fragmentation (4·7- and 3·7-fold, respectively, P < 0·001), caspase-3 activity and flow cytometry in Saos-2 and hOB. UDCA (10 μM) reduced the apoptotic effects of camptothecin (0·5 μM) by 61%, (P < 0·001) and counteracted the apoptotic effects of LCA and bilirubin determined by DNA fragmentation (56% and 60%, respectively, P < 0·001), cytometry and caspase-3 activity in Saos-2, with lower effects in hOB. UDCA (10 μM) downregulated BAX (75%), upregulated BCL2L (10-fold, P < 0·01) genes, and neutralised BAX upregulation (P < 0·01) and BCL2L downregulation (P < 0·01) induced by LCA and bilirubin.

CONCLUSIONS

Bilirubin and LCA induce apoptosis in osteoblastic cells. UDCA counteracts the apoptotic consequences of these two substances, and therefore, it may have further beneficial effects on the decreased bone formation in the cholestasis.

Primary Biliary Cirrhosis and Primary Sclerosing Cholangitis: a Review Featuring a Women's Health Perspective

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are two major types of chronic cholestatic liver disease. Each disorder has distinguishing features and variable progression, but both may ultimately result in cirrhosis and hepatic failure. The following offers a review of PBC and PSC, beginning with a general overview of disease etiology, pathogenesis, diagnosis, clinical features, natural course, and treatment. In addition to commonly associated manifestations of fatigue, pruritus, and fat-soluble vitamin deficiency, select disease-related topics pertaining to women's health are discussed including metabolic bone disease, hyperlipidemia and cardiovascular risk, and pregnancy-related issues influencing maternal disease course and birth outcomes. This comprehensive review of PBC and PSC highlights some unique clinical considerations in the care of female patients with cholestatic liver disease.

Vitamin D modulates biliary fibrosis in ABCB4-deficient mice

Purpose

Impaired vitamin D receptor signaling represents an aggravating factor during liver injury, and recent studies suggest that vitamin D might exert a protective role in chronic hepatobiliary diseases. We hypothesized that vitamin D supplementation would ameliorate liver fibrosis in ATP-binding cassette transporter B4 knockout (Abcb4^−/−) mice as a preclinical model of sclerosing cholangitis.

Methods

Abcb4^−/− and wild-type mice were fed a regular chow diet (600 IU vitamin D/kg food) or diets with lower (100 IU/kg) and higher (2,400 IU/kg) vitamin D concentrations for 12 weeks. Serum 25-hydroxyvitamin D concentrations were measured by chemiluminescence immunoassays. Liver injury and biliary fibrosis were assessed by liver enzyme activities, histopathology and hepatic collagen contents. Hepatic mRNA expression of markers for fibrosis, vitamin D and bile acid metabolism were analyzed by quantitative PCR.

Results

Different vitamin D concentrations were observed depending on genotype and diet group, with Abcb4^−/− mice on the control diet showing lower vitamin D concentrations compared to wild-type mice. Abcb4^−/− animals on the low vitamin D diet demonstrated the most advanced liver fibrosis and highest hepatic collagen contents. Feeding Abcb4^−/− mice a high vitamin D diet enriched serum vitamin D levels, lowered liver enzyme activities, altered expression levels of profibrogenic genes and ameliorated, in part, liver injury.

Conclusions

This is the first report to demonstrate that fibrogenesis in the established Abcb4^−/− model is influenced by vitamin D supplementation. Since vitamin D modulates sclerosing cholangitis in vivo, we speculate that sufficient vitamin D intake might improve liver damage and induce antifibrotic effects in chronic cholestasis in humans.

Electronic supplementary material

The online version of this article (doi:10.1007/s12072-014-9548-2) contains supplementary material, which is available to authorized users.

Ursodeoxycholic acid increases differentiation and mineralization and neutralizes the damaging effects of bilirubin on osteoblastic cells

BACKGROUND

Osteoporosis resulting from decreased bone formation is a common complication in patients with chronic cholestasis. Lithocholic acid (LCA) and bilirubin may play a role in osteoporosis given that both substances have detrimental effects on survival of human osteoblasts, the cells involved in bone formation.

AIMS

As ursodeoxycholic acid (UDCA) improves cholestasis, we have assessed if this bile acid may neutralize the harmful effects of LCA, bilirubin and sera from jaundiced patients on osteoblastic cells.

METHODS

The experiments were performed in primary human osteoblasts and human osteosarcoma cell line (Saos-2) at different times and concentrations of UDCA, LCA, cholic acid (CA), bilirubin and sera from jaundiced patients to assess cell viability, differentiation and mineralization.

RESULTS

UDCA significantly decreased cell survival at concentrations 10 times higher (1 mM) than that observed with LCA, whereas CA did not decrease osteoblast survival. UDCA (100 μM) neutralized the damaging effects of bilirubin (50 μM) and sera from jaundiced patients on survival. Moreover, UDCA (1 μM and 10 μM) increased osteoblast differentiation in cells treated with harmful concentrations of LCA or bilirubin. UDCA (100 μM) increased cell differentiation in osteoblasts cultured with a mix of serum from cholestatic patients by 23%. Furthermore, UDCA increased osteoblast mineralization by 35% and neutralized the negative consequences of 50 μM bilirubin.

CONCLUSIONS

UDCA increases osteoblast differentiation and mineralization, and neutralizes the detrimental effects of lithocholic acid, bilirubin and sera from jaundiced patients on osteoblastic cells. Therefore, UDCA may exert a favourable effect on bone in patients which chronic cholestasis.

Modeling hepatic osteodystrophy in Abcb4 deficient mice

Hepatic osteodystrophy (HOD) denotes the alterations in bone morphology and metabolism frequently observed in patients with chronic liver diseases, in particular in case of cholestatic conditions. The molecular mechanisms underlying HOD are only partially understood. In the present study, we characterized the bone phenotypes of the ATP-binding cassette transporter B4 knockout mouse (Abcb4(-/-)), a well-established mouse model of chronic cholestatic liver disease, with the aim of identifying and characterizing a mouse model for HOD. Furthermore, we investigated the influence of vitamin D on bone quality in this model. The bone morphology analyses revealed reduced bone mineral contents as well as changes in trabecular bone architecture and decreased cortical bone densities in Abcb4(-/-) mice with severe liver fibrosis. We observed dysregulation of genes involved in bone remodeling (osteoprotegerin, osteocalcin, osteopontin) and vitamin D metabolism (7-dehydrocholesterol reductase, Gc-globulin, Cyp2r1, Cyp27a1) as well as alterations in calcium and vitamin D homeostasis. In addition, serum RANKL and TGF-β levels were increased in Abcb4(-/-) mice. Vitamin D dietary intervention did not restore the bone phenotypes of Abcb4(-/-) animals. We conclude that the Abcb4(-/-) mouse provides an experimental framework and a preclinical model to gain further insights into the molecular pathobiology of HOD and to study the systemic effects of therapeutic interventions.

Nuclear receptors as drug targets in cholestatic liver diseases

Cholestatic liver diseases encompass a wide spectrum of disorders with different causes, resulting in impaired bile flow and accumulation of bile acids and other potentially hepatotoxic cholephils. The understanding of the molecular mechanisms of bile formation and cholestasis has recently improved significantly through new insights into nuclear receptor (patho)biology. Nuclear receptors are ligand-activated transcription factors, which act as central players in the regulation of genes responsible for elimination and detoxification of biliary constituents accumulating in cholestasis. They also control other pathophysiologic processes such as inflammation, fibrogenesis, and carcinogenesis involved in the pathogenesis and disease progression of cholestasis liver diseases.

Microarray analysis of 1,25(OH)₂D₃ regulated gene expression in human primary osteoblasts

Though extensive studies have been conducted, questions regarding the molecular effectors and pathways underlying the regulatory role of 1,25(OH)(2)D(3) in human osteoblasts other than cell differentiation and matrix protein production remain unanswered. This study aims to identify genes and pathways that are modulated by 1,25(OH)(2)D(3) treatment in human osteoblasts. Primary osteoblast cultures obtained from human bone tissue samples were treated with 1,25(OH)(2)D(3) (10(-7)  M) for 24 h and their transcritptomes were profiled by microarray analysis using the Affymetrix GeneChip. Statistical analysis was conducted to identify genes whose expression is significantly modulated following 1,25(OH)(2)D(3) treatment. One hundred and fifty-eight genes were found to be differentially expressed. Of these, 136 were upregulated, indicating clear transcriptional activation by 1,25(OH)(2)D(3). Biostatistical evaluation of microarray data by Ingenuity Pathways Analysis (IPA) revealed a relevant modulation of genes involved in vitamin D metabolism (CYP24), immune functions (CD14), neurotransmitter transporters (SLC1A1, SLC22A3), and coagulation [thrombomodulin (THBD), tissue plasminogen activator (PLAT), endothelial protein C receptor (PROCR), thrombin receptor (F2R)]. We identified a restricted number of highly regulated genes and confirmed their differential expression by real-time quantitative PCR (RT qPCR). The present genome-wide microarray analysis on 1,25(OH)(2)D(3) -treated human osteoblasts reveals an interplay of critical regulatory and metabolic pathways and supports the hypothesis that 1,25(OH)(2)D(3) can modulate the coagulation process through osteoblasts, activates osteoclastogenesis through inflammation signaling, modulates the effects of monoamines by affecting their reuptake.

Effects of bilirubin and sera from jaundiced patients on osteoblasts: contribution to the development of osteoporosis in liver diseases

Low bone formation is considered to be the main feature in osteoporosis associated with cholestatic and end-stage liver diseases, although the consequences of retained substances in chronic cholestasis on bone cells have scarcely been studied. Therefore, we analyzed the effects of bilirubin and serum from jaundiced patients on viability, differentiation, mineralization, and gene expression in the cells involved in bone formation. The experiments were performed in human primary osteoblasts and SAOS-2 human osteosarcoma cells. Unconjugated bilirubin or serum from jaundiced patients resulted in a dose-dependent decrease in osteoblast viability. Concentrations of bilirubin or jaundiced serum without effects on cell survival significantly diminished osteoblast differentiation. Mineralization was significantly reduced by exposure to 50 μM bilirubin at all time points (from -32% to -55%) and jaundiced sera resulted in a significant decrease on cell mineralization as well. Furthermore, bilirubin down-regulated RUNX2 (runt-related transcription factor 2) gene expression, a basic osteogenic factor involved in osteoblast differentiation, and serum from jaundiced patients significantly up-regulated the RANKL/OPG (receptor activator of nuclear factor-κB ligand/osteoprotegerin) gene expression ratio, a system closely involved in osteoblast-induced osteoclastogenesis.

CONCLUSION

Besides decreased cell viability, unconjugated bilirubin and serum from jaundiced patients led to defective consequences on osteoblasts. Moreover, jaundiced serum up-regulates the system involved in osteoblast-induced osteoclastogenesis. These results support the deleterious consequences of increased bilirubin in advanced chronic cholestasis and in end-stage liver diseases, resulting in disturbed bone formation related to osteoblast dysfunction.

Management of osteoporosis in liver disease

Osteoporosis resulting in a high risk for fracture is a common complication in patients with liver disease, particularly in those with chronic cholestasis and with end-stage cirrhosis. The pathogenesis of bone loss in liver patients is poorly understood but it mainly results from low bone formation as a consequence of cholestasis or the harmful effects of alcohol or iron on osteoblasts. Increased bone resorption has also been described in cholestatic women with advanced disease. The management of bone disease in liver patients is addressed to reduce or avoid the risk factors for osteoporosis and fracture. Bisphosphonates associated with supplements of calcium and vitamin D are safe and effective for increasing bone mass in patients with chronic cholestasis and after liver transplantation, though no clear achievements in descreasing the incidence of fractures have been described, probably because of the low number of patients included in the therapeutic trials. Randomized studies assessing bisphosphonates in larger series of patients, the development of new drugs for osteoporosis and the improvement in the management of liver transplant recipients may change the future.

Liver and bone

Osteoporosis is a frequent complication in patients with chronic liver disease, especially in end-stages and in cases with chronic cholestasis, hemochromatosis and alcohol abuse. The problem is more critical in transplant patients when bone loss is accelerated during the period immediately after transplantation, leading to a greater incidence of fractures. Advanced age, low body mass index and severity of the liver disease are the main risk factors for bone disease in patients with cholestasis. Mechanisms underlying osteoporosis in chronic liver disease are complex and poorly understood, but osteoporosis mainly results from low bone formation, related to the effects of retained substances of cholestasis, such as bilirubin and bile acids, or to the effects of alcohol on osteoblastic cells. Increased bone resorption has also been described in cholestatic women with advanced disease. Although there is no specific treatment, bisphosphonates associated with supplements of calcium and vitamin D are effective for increasing bone mass in patients with chronic cholestasis and after liver transplantation. The outcome in reducing the incidence of fractures has not been adequately demonstrated essentially because of the low number of patients included in the therapeutic trials. Randomized studies assessing bisphosphonates in larger series of patients, the development of new drugs for osteoporosis and the improvement in the management of liver transplant recipients may change the future.

Low bone mass and severity of cholestasis affect fracture risk in patients with primary biliary cirrhosis

BACKGROUND & AIMS

The influence of osteoporosis and liver disease on fracture risk is not well characterized in patients with primary biliary cirrhosis (PBC). We studied a large series of women with PBC to assess the prevalence and risk factors for fractures and the fracture threshold.

METHODS

In female patients with PBC (n = 185; age, 55.7 +/- 0.7 years; range 28-79 years), age, duration of PBC, menopausal status, and histologic stage and severity of liver disease were assessed. Vertebral and non-vertebral fractures were recorded in 170 and 172 patients, respectively. Osteoporosis and osteopenia were diagnosed based on densitometry analysis.

RESULTS

The prevalences of vertebral, non-vertebral, and overall fractures were 11.2%, 12.2%, 20.8%, respectively. Osteoporosis was significantly more frequent in patients with PBC than in normal women. Osteoporosis was associated with age, weight, height, histologic stage, severity, and duration of liver damage; fractures were associated with osteoporosis, menopause, age, and height but not with severity of PBC. Osteoporosis was a risk factor for vertebral fracture (odds ratio [OR], 8.48; 95% confidence interval [CI]: 2.67-26.95). Lumbar T score <-1.5 (OR, 8.27; 95% CI: 1.84-37.08) and femoral neck T score <-1.5 (OR, 6.83; 95% CI: 1.48-31.63) were significant risk factors for vertebral fractures.

CONCLUSIONS

Fractures, particularly vertebral fractures, are associated with osteoporosis, osteopenia, and T scores less than -1.5, whereas osteoporosis and osteopenia are associated with the severity of liver damage. Patients with T scores less than -1.5 might require additional monitoring and be considered for therapy to prevent fractures.