Osteoclastogenesis during Infective Exacerbations in Patients with Cystic Fibrosis

Changes in bone turnover after high-dose vitamin D supplementation during acute pulmonary exacerbation in cystic fibrosis

In people with cystic fibrosis (CF), chronic inflammation and infection increase the risk for low bone mineral density and CF-related bone disease. During acute pulmonary exacerbations (APE), people with CF have increases in markers of bone resorption. Vitamin D has been proposed as a potential nutrient to lower inflammation. In this ancillary analysis of the Vitamin D for the Immune System in CF study, we hypothesized that vitamin D administered at the time of APE would have favorable changes on bone turnover markers compared to placebo. Participants with CF were randomized to receive a single dose of 250,000 IU of vitamin D or placebo during an APE and followed for 1 year for the primary outcome of APE or death after randomization. Bone turnover markers: C-terminal telopeptide (CTX-1) and procollagen type 1 intact N-terminal propetide (P1NP) were assessed at randomization (during APE) and after recovery from the APE in 45 participants. Participants randomized to vitamin D had significant decreases in markers of bone turnover; participants who received placebo had non-significant increases in markers of bone turnover. Vitamin D supplementation during an APE may help reduce the risk for CF-related bone disease.

Future Comorbidities in an Aging Cystic Fibrosis Population

Cystic fibrosis (CF) is an autosomal recessive disease due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. With the advent of highly effective modulator therapy targeting the abnormal CFTR protein, people with CF (PwCF) are living more than 40 years longer than the pre-modulator therapy era. As a result, PwCF are facing new challenges of managing similar comorbidities affecting the average aging population. While CF is notoriously identified as a chronic respiratory disease, the multisystem presence of the CFTR gene can contribute to other organ-related complications acutely, but also heighten the likelihood of chronic conditions not routinely encountered in this cohort. In this overview, we will focus on risk factors and epidemiology for PwCF as they relate to cardiovascular disease, dyslipidemia, CF-related diabetes, pulmonary hypertension, obstructive sleep apnea, CF-liver disease, bone health and malignancy. With increased awareness of diseases affecting a newly aging CF population, a focus on primary and secondary prevention will be imperative to implementing a comprehensive care plan to improve long-term morbidity and mortality.

Cystic Fibrosis Bone Disease: The Interplay between CFTR Dysfunction and Chronic Inflammation

Cystic fibrosis is a monogenic disease with a multisystemic phenotype, ranging from predisposition to chronic lung infection and inflammation to reduced bone mass. The exact mechanisms unbalancing the maintenance of an optimal bone mass in cystic fibrosis patients remain unknown. Multiple factors may contribute to severe bone mass reduction that, in turn, have devastating consequences in the patients' quality of life and longevity. Here, we will review the existing evidence linking the CFTR dysfunction and cell-intrinsic bone defects. Additionally, we will also address how the proinflammatory environment due to CFTR dysfunction in immune cells and chronic infection impairs the maintenance of an adequate bone mass in CF patients.

Endocrine Complications of Cystic Fibrosis

Endocrine comorbidities have become increasingly important medical considerations as improving cystic fibrosis (CF) care increases life expectancy. Although the underlying pathophysiology of CF-related diabetes remains elusive, the use of novel technologies and therapeutics seeks to improve both CF-related outcomes and quality of life. Improvements in the overall health of those with CF have tempered concerns about pubertal delay and short stature; however, other comorbidities such as hypogonadism and bone disease are increasingly recognized. Following the introduction of highly effective modulator therapies there are many lessons to be learned about their long-term impact on endocrine comorbidities.

Osteoporosis in nontuberculous mycobacterial pulmonary disease: a cross-sectional study

Background

Since nontuberculous mycobacterial pulmonary disease (NTM-PD) is common in middle-aged/elderly slender women at risk of osteoporosis, we hypothesized that NTM-PD could be associated with osteoporosis. The study aimed to evaluate the prevalence of osteoporosis in patients with NTM-PD compared with that in the general population and determine the factors associated with osteoporosis in the subjects, including the serum estradiol (E₂) and 25-hydroxyvitamin D (25OHD) levels.

Methods

We have recruited 228 consecutive adult patients with NTM-PD from a prospective cohort study at the Keio University Hospital, who had no history of osteoporosis or osteoporosis-associated bone fracture but underwent dual-energy X-ray absorptiometry-based bone mineral density (BMD) evaluation from August 2017–September 2019. The E₂ and 25OHD levels were measured in 165 patients with available stored serum samples. We performed multivariable logistic regression analyses for osteopenia and osteoporosis.

Results

Osteoporosis (T-score ≤  − 2.5) and osteopenia (T-score − 1 to − 2.5) were diagnosed in 35.1% and 36.8% of patients with NTM-PD, respectively. Compared with the general population, the proportion of osteoporosis was significantly higher in 50–59-, 60–69-, and 70–79-year-old women with NTM-PD. Multivariable analysis revealed that older age (adjusted odds ratio [aOR] for 1-year increase = 1.12; 95% confidence interval [CI] = 1.07–1.18), female sex (aOR = 36.3; 95% CI = 7.57–174), lower BMI (aOR for 1 kg/m² decrease = 1.37; 95% CI = 1.14–1.65), and chronic Pseudomonas aeruginosa (PA) infection (aOR = 6.70; 95% CI = 1.07–41.8) were independently associated with osteoporosis. Additionally, multivariable analysis in 165 patients whose serum E₂ and 25OHD levels were measured showed that both low E₂ levels (< 10 pg/mL) and lower 25OHD levels were independently associated with osteoporosis.

Conclusions

Middle-aged/elderly women with NTM-PD have a higher prevalence of osteoporosis than the general population. BMD screening should be considered in NTM-PD, especially in older females with severe diseases such as chronic PA infection and lower BMI, and low serum E₂ and 25OHD levels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-01991-3.

IL-8 correlates with reduced baseline femoral neck bone mineral density in adults with cystic fibrosis: a single center retrospective study

Cystic fibrosis (CF) is a multi-system disease that is characterized by lung disease due to recurrent airway infection and inflammation. Endocrine complications, such as CF bone disease (CFBD), are increasingly identified as patients are living longer. The cause of CFBD is multifactorial with chronic systemic inflammation theorized to be a contributing factor. Thus, we attempted to identify inflammatory biomarkers that are associated with CFBD. We conducted a retrospective observational study of 56 adult patients with CF with an average percentage predictive forced expiratory volume in one second (ppFEV₁) of 73.7% (standard deviation: 30.0) who underwent baseline serum analysis for osteoprotegerin (OPG) and pro-inflammatory biomarkers (IL-1β, IL-6, IL-8 and TNF-α), and had repeated dual-energy x-ray absorptiometry (DXA) scans separated by at least 2 years to examine correlations between serum biomarkers and bone mineral density (BMD) measurements. Univariate linear regression model analysis demonstrated that serum IL-1β and IL-8, but not other pro-inflammatory markers, were negatively correlated with baseline BMD results. However, after accounting for confounding variables, only the relationship between IL-8 and left femoral neck BMD remained statistically significant. Additionally, IL-8 level was associated with BMD decline over time. These results suggest that IL-8 might play a unique role in the pathophysiology of CFBD relative to other pro-inflammatory cytokines but further study is warranted before firm conclusions can be made.

Cystic fibrosis bone disease treatment: Current knowledge and future directions

Bone disease is a frequent complication in adolescents and adults with cystic fibrosis (CF). Early detection and monitoring of bone mineral density and multidisciplinary preventive care are necessary from childhood through adolescence to minimize CF-related bone disease (CFBD) in adult CF patients. Approaches to optimizing bone health include ensuring adequate nutrition, particularly intake of calcium and vitamins D and K, addressing other secondary causes of low bone density such as hypogonadism, encouraging weight bearing exercise, and avoiding bone toxic medications. Of the currently available anti-resorptive or anabolic osteoporosis medications, only bisphosphonates have been studied in individuals with CF. Future studies are needed to better understand the optimal approach for managing CFBD.

Understanding the interplay between factors that influence bone mineral density in CF

BACKGROUND AND OBJECTIVES

Multiple factors affect bone mineral density (BMD) in cystic fibrosis (CF). Our aim was to perform comprehensive analyses of parameters potentially contributing to BMD.

METHODS

A prospective single-center study assessing BMD, and correlations with multiple parameters including pancreatic status, lung functions, 6-minute walk test (6MWT), clinical score (modified Shwachman-Kulczycki [SK] score), vitamin D, nutritional intake, hand grip strength (HGS), habitual physical activity (smart watches), and quality of life (SF-36 questionnaire).

RESULTS

Forty CF patients, mean age 18.3 ± 8.1 years, forced expiratory volume in 1 second 74.7% ± 17.9% predicted. Fifteen (37.5%) and 11 (27.5%) had osteopenia and osteoporosis, respectively. BMD was similar in pancreatic sufficient (pancreatic sufficient [PS], n = 15) and insufficient (pancreatic insufficient [PI], n = 25); median hip z score -1.5 ((-2.7)-(+0.2)) vs -1.5 ((-3.5)-(+0.7)), P = .79; spine -0.8 ((-2.2)-(+2)) vs -1.2 ((-4.4)-(+1.5)), P = .39 in PS vs PI, respectively. BMD correlated with HGS (r = .72, P < .001 hip; r = .52, P = .001 spine) and fat-free mass index (r = .81, P < .001 hip; r = .63, P < .001 spine). BMD z score correlated weakly with SK score and moderately with SF-36 general health. Data from smart watches, nutrition questionnaires, and 6MWT did not correlate with BMD. In a multivariate model, age and SK score predicted spine z score BMD.

CONCLUSIONS

A substantial number of CF patients have low BMD. Similar rates in PS and PI suggest that other factors, such as disease severity, may contribute to low BMD. SK and age, which can easily be obtained even with limited resources, were the best predictors of low BMD. Further larger multicenter studies are warranted to evaluate the contribution of multifactorial etiologies to low BMD in CF.

Lung-Specific Risk Factors Associated With Incident Hip Fracture in Current and Former Smokers

Hip fractures are associated with significant morbidity and mortality in smokers with lung disease, but whether lung-specific factors are associated with fracture risk is unknown. Our goal was to determine whether lung-specific factors associate with incident hip fracture and improve risk discrimination of traditional fracture risk models in smokers. The analysis consisted of a convenience sample of 9187 current and former smokers (58,477 participant follow-up years) participating in the Genetic Epidemiology of chronic obstructive pulmonary disease (COPD) longitudinal observational cohort study. Participants were enrolled between 2008 and 2011 with follow-up data collection through July 2018. Traditional risk factors associated with incident hip fracture (n = 361) included age, female sex, osteoporosis, prevalent spine and hip fracture, rheumatoid arthritis, and diabetes. Lung-specific risk factors included post-bronchodilator percent forced expiratory volume in 1 s (FEV₁ %) predicted (OR, 0.95; 95% CI, 0.92-0.99 for each 10% increase), Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification (OR, 1.09; 95% CI, 1.002-1.19 for each higher stage), presence of CT-determined emphysema (OR, 1.34; 95% CI, 1.06-1.69), symptom scores (OR, 1.10; 95% CI, 1.03-1.19 for each higher unit score), 6-min walk distance (OR, 0.92; 95% CI, 0.90-0.95 for each 30-m increase), body mass index, airflow obstruction, dyspnea, and exercise (BODE) index (OR, 1.07; 95% CI, 1.01-1.13 for each higher unit score), total exacerbations (OR, 1.13; 95% CI, 1.10-1.16 per exacerbation), and annual exacerbations (OR, 1.37; 95% CI, 1.21-1.55 per exacerbation). In multivariable modeling, age, black race, osteoporosis, prevalent hip and spine fracture, rheumatoid arthritis, and diabetes were associated with incident hip fracture. The presence of emphysema, 6-min walk distance, and total number of exacerbations added to traditional models improved risk discrimination (integrated discrimination improvement [IDI] values 0.001 [95% CI, 0.0003-0.002], 0.001 [95% CI, 0.0001-0.002], and 0.008 [95% CI, 0.003-0.013], corresponding to relative IDIs of 12.8%, 6.3%, and 34.6%, respectively). These findings suggest that the incorporation of lung-specific risk factors into fracture risk assessment tools may more accurately predict fracture risk in smokers. © 2020 American Society for Bone and Mineral Research.

Prevention of osteoporosis in cystic fibrosis

PURPOSE OF REVIEW

The increased life span of patients with cystic fibrosis has lead to the detection of new complications. Osteopenia is present in up to 50% of adult patients with cystic fibrosis, and osteoporosis in 10-34% and can cause a difficult management problem.

RECENT FINDINGS

In children, defects in bone health become apparent generally at adolescence because of suboptimall bone peak mass achievement. Malnutrition, inflammation, vitamin D and vitamin K deficiency, altered sex hormone production, glucocorticoid therapy, and physical inactivity potentiate poor bone health.

SUMMARY

Monitoring bone mineral density and preventive care of osteoporosis are necessary from childhood to minimize cystic fibrosis-related bone disease in adult cystic fibrosis patients.

Analysis of Bone Metabolism in Children with Cystic Fibrosis

One of the most important CF-related conditions is the bone disease, which is nowadays acknowledged as a significant clinical complication of CF. Imbalance between bone formation and degradation in cystic fibrosis (CF) has become an important issue for developing osteopenia. The aim of the study was to assess bone formation and resorption process with bone markers in children with cystic fibrosis (CF). Materials and methods: The study included 35 clinically stable children with CF who regularly attended the Cystic fibrosis center at the University Pediatric Clinic in Skopje, R. Macedonia. The control group was presented with 21 healthy children at the same age. Serum osteocalcin (OC), β cross laps, 25OHD and PTH were determined by ELISA assays in the CF group (mean age 8.25±SD1.9 y.) and in age-match controls (7.5±1.9 y.). Results: Vitamin D in the CF group was (23.83±10.9 ng/ml versus 25.6±11.53 in the control group, p=0.57), OC (70.88±34.24 ng/ml v.100.02±47.98, p=0.01) βcrosslaps (1.35±0.72 ng/ml v.1.54±0.73, p=0.37) and PTH (37.39±25.5 pg/ml v. 36.76±25.73, p=0.92). In the study, we did not find a significant difference for 25OHD between CF and healthy controls. OC in children with CF correlates significantly with the control and indicates a decreased formation rate whereas resorption rate is normal. Conclusion: Our results suggest that bone turnover in CF is impaired in childhood. Serum markers for bone formation can be used for predicting osteopenia in children with CF.

Osteoporosis Is Associated with Deteriorating Clinical Status in Adults with Cystic Fibrosis

BACKGROUND

Cystic fibrosis (CF) patients are in increased risk of osteoporosis. We aimed to determine the osteoporosis prevalence in an adult CF cohort and investigate calcium metabolic parameters and clinical status' association with bone mineral density evaluated by dual X-ray absorptiometry scan.

METHODS

We performed a cross section database study of adults at a tertiary CF Center. Z scores were applied for patients < 50 years of age and T scores for patients > 50 years of age.

RESULTS

One hundred twenty-five patients were included. Compared to nonosteoporotic patients, osteoporotic patients (15%) had significantly lower percent predicted forced expiratory volume in 1 second (ppFEV1), lower body mass index, higher frequency of CF-related diabetes and chronic lung infection, and higher high-sensitive C-reactive protein and glycated hemoglobin levels. Vitamin D was not associated with any outcome. In multivariate analyses, only ppFEV1 and female gender were independently associated with Z scores.

CONCLUSIONS

Osteoporosis in CF occurs with deteriorating clinical status while the role of calcium metabolism seems minor. Gender specific and dysglycemic impact on bone status should be investigated further.

Overexpression of RANKL in osteoblasts: a possible mechanism of susceptibility to bone disease in cystic fibrosis

Bone fragility and loss are a significant cause of morbidity in patients with cystic fibrosis (CF), and the lack of effective therapeutic options means that treatment is more often palliative rather than curative. A deeper understanding of the pathogenesis of CF-related bone disease (CFBD) is necessary to develop new therapies. Defective CF transmembrane conductance regulator (CFTR) protein and chronic inflammation in bone are important components of the CFBD development. The receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) drive the regulation of bone turnover. To investigate their roles in CFBD, we evaluated the involvement of defective CFTR in their production level in CF primary human osteoblasts with and without inflammatory stimulation, in the presence or not of pharmacological correctors of the CFTR. No major difference in cell ultrastructure was noted between cultured CF and non-CF osteoblasts, but a delayed bone matrix mineralization was observed in CF osteoblasts. Strikingly, resting CF osteoblasts exhibited strong production of RANKL protein, which was highly localized at the cell membrane and was enhanced in TNF (TNF-α) or IL-17-stimulated conditions. Under TNF stimulation, a defective response in OPG production was observed in CF osteoblasts in contrast to the elevated OPG production of non-CF osteoblasts, leading to an elevated RANKL-to-OPG protein ratio in CF osteoblasts. Pharmacological inhibition of CFTR chloride channel conductance in non-CF osteoblasts replicated both the decreased OPG production and the enhanced RANKL-to-OPG ratio. Interestingly, using CFTR correctors such as C18, we significantly reduced the production of RANKL by CF osteoblasts, in both resting and TNF-stimulated conditions. In conclusion, the overexpression of RANKL and high membranous RANKL localization in osteoblasts are related to defective CFTR, and may worsen bone resorption, leading to bone loss in patients with CF. Targeting osteoblasts with CFTR correctors may represent an effective strategy to treat CFBD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Reduced bone volumetric density and weak correlation between infection and bone markers in cystic fibrosis adult patients

In our current adult CF population, low BMD prevalence was only 20 %, lower than that historically described. We found a mild increase of serum RANK-L levels, independent from the bone resorption level. The increased fracture risk in CF may be explained by a lower tibial cortical thickness and total vBMD.

INTRODUCTION

Bone disease is now well described in cystic fibrosis (CF) adult patients. CF bone disease is multifactorial but many studies suggested the crucial role of inflammation. The objectives of this study were, in a current adult CF population, to assess the prevalence of bone disease, to examine its relationship with infections and inflammation, and to characterize the bone microarchitecture using high resolution peripheral scanner (HR-pQCT).

METHODS

Fifty-six patients (52 % men, 26 ± 7 years) were assessed in clinically stable period, during a respiratory infection, and finally 14 days after the end of antibiotic therapy. At each time points, we performed a clinical evaluation, lung function tests, and biochemical tests. Absorptiometry and dorso-lumbar radiographs were also performed. A subgroup of 40 CF patients (63 % men, 29 ± 6 years) underwent bone microarchitecture assessment and was age- and gender-matched with 80 healthy controls.

RESULTS

Among the 56 CF patients, the prevalence of low areal BMD (T-score < -2 at any site), was 20 % (95 % CI: [10.2 %; 32.4 %]). After infections, serum RANK-L (+24 %, p = 0.08) and OPG (+13 %, p = 0.04) were increased with a stable ratio. Microarchitectural differences were mostly observed at the distal tibia, with lower total and cortical vBMD and trabecular thickness (respectively -9.9, -3.0, and -5 %, p < 0.05) in CF patients compared to controls, after adjustment for age, gender, weight, and height.

CONCLUSIONS

In this study, bone disease among adult CF patients was less severe than that previously described with only 20 % of CF patients with low BMD. We found a mild increase of biological marker levels and an impaired volumetric density of the tibia that may explain the increased fracture risk in CF population.

Bone health and disease in cystic fibrosis

Low bone mineral density is common in children and adults with CF. It has a multifactorial aetiology that includes direct effects of CFTR dysfunction on bone cell activity, as well as the secondary effects of CFTR dysfunction including pancreatic insufficiency (leading to malnutrition/malabsorption of fat soluble vitamins) and pulmonary infection (leading to systemic inflammation and increased bone resorption). Strategies to improve bone health in CF include optimising general CF nutritional and pulmonary care and the judicious use of bisphosphonates in selected patients. CFTR correctors/potentiators may have positive impact on bone metabolism in people with CF.

Bone disease in cystic fibrosis: new pathogenic insights opening novel therapies

Mutations within the gene encoding for the chloride ion channel cystic fibrosis transmembrane conductance regulator (CFTR) results in cystic fibrosis (CF), the most common lethal autosomal recessive genetic disease that causes a number of long-term health problems, as the bone disease. Osteoporosis and increased vertebral fracture risk associated with CF disease are becoming more important as the life expectancy of patients continues to improve. The etiology of low bone density is multifactorial, most probably a combination of inadequate peak bone mass during puberty and increased bone losses in adults. Body mass index, male sex, advanced pulmonary disease, malnutrition and chronic therapies are established additional risk factors for CF-related bone disease (CFBD). Consistently, recent evidence has confirmed that CFTR plays a major role in the osteoprotegerin (OPG) and COX-2 metabolite prostaglandin E2 (PGE2) production, two key regulators in the bone formation and regeneration. Several others mechanisms were also recognized from animal and cell models contributing to malfunctions of osteoblast (cell that form bone) and indirectly of bone-resorpting osteoclasts. Understanding such mechanisms is crucial for the development of therapies in CFBD. Innovative therapeutic approaches using CFTR modulators such as C18 have recently shown in vitro capacity to enhance PGE2 production and normalized the RANKL-to-OPG ratio in human osteoblasts bearing the mutation F508del-CFTR and therefore potential clinical utility in CFBD. This review focuses on the recently identified pathogenic mechanisms leading to CFBD and potential future therapies for treating CFBD.

Emerging therapeutic concepts for muscle and bone preservation/building

Loss of muscle or bone mass occurs with ageing, immobility and in association with a variety of systemic diseases. The interaction of these two processes is most evident in the major contribution of falls to the risk of fractures in the elderly population. Exercise and nutrition are key common physiological variables that allow for preservation or formation of greater muscle or bone mass. However, although several pharmacological approaches have the potential to benefit both muscle and bone health, for example vitamin D, selective androgen receptor modulators and ghrelin mimetics, clinical trials with appropriate primary outcomes are lacking. Conventional approaches to address muscle loss are being extended to include stem cell biology and conserved molecular mechanisms of atrophy/hypertrophy. Pharmacological interventions to reduce fracture risk are exploring new mechanisms of action, in particular the uncoupling of bone resorption and formation. Emerging key issues for clinical trial design include adequate phenotyping of patients (personalised medicine), optimisation of the physiological background (multimodal approach) and the use of meaningful and robust outcomes relevant to daily clinical practice. At present, effective treatments that combine beneficial effects on both muscle and bone are lacking, although this is an important target for the future. This review therefore considers current and developing strategies to improve muscle function and bone strength in separate sections.

Cystic fibrosis-related bone disease: insights into a growing problem

PURPOSE OF REVIEW

This review will describe the clinical significance, pathogenesis and treatment of cystic fibrosis related bone disease (CFBD).

RECENT FINDINGS

CFBD continues to increase as the life expectancy of individuals with cystic fibrosis increases. According to clinical guidelines, individuals with cystic fibrosis should be initially screened at the age of 18 years via dual-energy x-ray absorptiometry, if not done so previously. The underlying pathogenesis of CFBD appears to be multifactorial, but increasing data imply a direct impact by the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR deficiency and/or dysfunction impair osteoblast activity and differentiation, and indirectly promote osteoclast formation. Unfortunately, once diagnosed with CFBD, few cystic fibrosis tested medical therapies exist.

SUMMARY

CFBD is an increasingly recognized complication that has a significant impact on the overall health of the individual. Recommendations to identify patients with cystic fibrosis who are at risk for fracture using dual-energy x-ray absorptiometry have been established. Therapeutic agents directly studied in patients with cystic fibrosis are limited to bisphosphonates, although other potential treatment agents exist. Finally, an improved understanding of the pathologic mechanisms will aid in the study and development of therapies.

Cystic fibrosis: what to expect now in the early adult years

As a testimony to advances in patient care, more individuals with cystic fibrosis are surviving into their adult years than ever before. The clinical epidemiology of this complex multi-organ disease is evolving and has changed dramatically over the past two to three decades. This article discusses the emergence of chronic disease-related co-morbidities such as CF-related diabetes, chronic kidney disease, bone disease, arthropathy, and depression. It also provides an overview of the many challenges confronted by adult CF care providers.

Does radiographic emphysema correlate with low bone mineral density?

PURPOSE OF REVIEW

Several large epidemiologic studies have shown an association between chronic obstructive pulmonary disease (COPD) and osteoporosis. Recent studies have further implied an emphysema-specific association with low bone mineral density independent of obstruction severity.

RECENT FINDINGS

This review will outline the studies demonstrating an independent association between radiographic emphysema and decreased bone mineral density and will discuss potential disease mechanisms, including systemic inflammation and immune-mediated factors, linking these disease processes.

SUMMARY

Radiographic emphysema should be considered an independent risk factor in studies examining the mechanisms underlying COPD-related bone loss. Future research focused on the relationship between emphysema and low bone mineral density could provide mechanistic insight and result in the development of targeted therapies designed to halt progression of both disease processes.

Osteoporosis and inflammation

Several inflammatory diseases such as rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, celiac disease, cystic fibrosis and chronic obstructive pulmonary disease have been associated to bone resorption. The link between osteoclast, macrophage colony stimulating factor and pro-inflammatory cytokines, especially tumor necrosis factor-alpha and interleukin-1 explain the association between inflammation and osteoporosis. These diseases are related to osteoporosis and high fracture risk independent of other risk factors common to inflammatory diseases such as reduced physical activity, poor nutritional status, hypovitaminosis D, decrease in calcium intake and glucocorticoid treatment. Erythrocyte sedimentation rate and C-reactive protein should always be performed, but the indication about when to perform the densitometry test should be analyzed for each disease. Bisphosphonates are nowadays the best choice of therapy but new medications such as denosumab, IL-1 receptor antagonist, and TNF-alpha antibody have risen as new potential treatments for osteoporosis secondary to inflammation.

Prevalence of bone loss in a population with cystic fibrosis

The adverse effect of an increased life expectancy for people with cystic fibrosis (CF) is the increased risk of complications, such as CF-related low bone mineral density (BMD). Diagnosis of CF-related low BMD is confirmed by a dual-energy X-ray absorptiometry (DXA) scan. This study reports the results of an audit of DXA scans in 108 adults with CF in our clinic. The most common risk factors for bone loss were vitamin D deficiency (89%), CF-related diabetes (53%), low body mass index (39%) and post-lung transplant (25%); half of those with bone loss were genotype homozygous DF508. Overall fracture incidence was 5.5%; low BMD was not associated with high fracture rates. Thus BMD may not be a good predictor of fracture risk. Treatment includes bisphosphonates, which are difficult to take and have uncertain long-term effects. It is unknown whether bisphosphonate therapy is justified in this already overburdened group.

Cystic fibrosis transmembrane conductance regulator (CFTR) regulates the production of osteoprotegerin (OPG) and prostaglandin (PG) E2 in human bone

Bone loss is an important clinical issue in patients with cystic fibrosis (CF). Whether the cystic fibrosis transmembrane conductance regulator (CFTR) plays a direct role in bone cell function is yet unknown. In this study, we provide evidence that inhibition of CFTR-Cl(-) channel function results in a significant decrease of osteoprotegerin (OPG) secretion accompanied with a concomitant increase of prostaglandin (PG) E(2) secretion of primary human osteoblast cultures (n=5). Our data therefore suggest that in bone cells of CF patients, the loss of CFTR activity may result in an increased inflammation-driven bone resorption (through both the reduced OPG and increased PGE(2) production), and thus might contribute to the early bone loss reported in young children with CF.

Update on cystic fibrosis-related bone disease: a special focus on children

A high prevalence of low bone mineralization is documented in adult patients with cystic fibrosis (CF). Osteopenia is present in up to 85% of adult patients and osteoporosis in 10% to 34%. In children, study results are discordant probably because of comparisons to different control populations and corrections for bone size in growing children. Malnutrition, inflammation, vitamin D and vitamin K deficiency, altered sex hormone production, glucocorticoid therapy, and physical inactivity are well known risk factors for poor bone health. Puberty is a critical period for bone mineralization and requires a careful follow-up to achieve optimal bone peak mass. Strategies for optimizing bone health, such as monitoring bone mineral density (BMD) and providing preventive care are necessary from childhood through adolescence to minimize CF-related bone disease in adult CF patients.

Relation of bone mineral density with clinical and laboratory parameters in pre-pubertal children with cystic fibrosis

To study bone mineral density (BMD) of pre-pubertal cystic fibrosis (CF) children, and its relation with clinical and laboratory parameters, we enrolled 16 CF (8 girls) (4-8 years), and 16 control children (8 girls) (4-8 years). After anthropometric measurements, BMD, serum calcium, phosphorus, total alkaline phosphatase (ALP), 25-hydroxy vitamin D (25-OHD), parathyroid hormone, osteocalcin, tumor necrosis factor (TNF)-alpha, soluble TNF-alpha receptor 2 (sTNFR2), and soluble IL-2 receptor (sIL-2R) levels, and urinary calcium and hydroxyproline excretions were assessed. Disease severity of CF patients was determined with Shwachman-Kulczycki clinical and Brasfield radiological scoring systems.The mean Shwachman-Kulczycki and Brasfield scores of CF patients were indicating well-controlled disease. The anthropometric measurements, mean BMD values, and serum calcium, phosphorus and parathyroid hormone levels were within normal range and similar in both groups. Serum osteocalcin levels were lower, and ALP and 25-OHD levels were higher in CF. Although 24-hr urinary calcium excretions was higher in CF patients, hydroxyproline excretions were similar in both groups. There was no difference between two groups for the serum levels of sIL-2R, TNF-alpha and sTNFR2. Children with low vertebral z-scores had higher serum sIL-2R levels in both groups, but the same relation could not be shown for TNF-alpha and sTNFR2.We may speculate that younger, healthier and well-nourished patients with CF may have normal BMD, but the bone disease develop as patients get older because of the other contributing factors. Future well-designed longitudinal studies with large cohorts might show a relation with BMD and cytokines in CF.

Murine model for cystic fibrosis bone disease demonstrates osteopenia and sex-related differences in bone formation

As the incidence of cystic fibrosis (CF) bone disease is increasing, we analyzed CF transmembrane conductance regulator (CFTR) deficient mice (CF mice) to gain pathogenic insights. In these studies comparing adult (14 wk) CF and C57BL/6J mice, both bone length and total area were decreased in CF mice. Metaphyseal trabecular and cortical density were also decreased, as well as diaphyseal cortical and total density. Trabecular bone volume was diminished in CF mice. Female CF mice revealed decreased trabecular width and number compared with C57BL/6J, whereas males demonstrated no difference in trabecular number. Female CF mice had reduced mineralizing surface and bone formation rates. Conversely, male CF mice had increased mineralizing surface, mineral apposition, and bone formation rates compared with C57BL/6J males. Bone formation rate was greater in males compared with female CF mice. Smaller bones with decreased density in CF, despite absent differences in osteoblast and osteoclast surfaces, suggest CF transmembrane conductance regulator influences bone cell activity rather than number. Differences in bone formation rate in CF mice are suggestive of inadequate bone formation in females but increased bone formation in males. This proanabolic observation in male CF mice is consistent with other clinical sex differences in CF.

Alendronate once weekly for the prevention and treatment of bone loss in Canadian adult cystic fibrosis patients (CFOS trial)

BACKGROUND

Patients with cystic fibrosis (CF) are at risk for early bone loss, and demonstrate increased risks for vertebral fractures and kyphosis. A multicenter, randomized, controlled trial was conducted to assess the efficacy, tolerability, and safety of therapy with oral alendronate (FOSAMAX; Merck; Whitehouse Station, NJ) in adults with CF and low bone mass.

METHODS

Participants received placebo or alendronate, 70 mg once weekly, for 12 months. All participants received 800 IU of vitamin D and 1,000 mg of calcium daily. Adults with confirmed CF with a bone mineral density (BMD) T score of < - 1.0 were eligible for inclusion. Participants who had undergone organ transplantation or had other reported contraindications were excluded from the study. The primary outcome measure was the mean (+/- SD) percentage change in lumbar spine BMD after 12 months. Secondary measures included the percentage change in total hip BMD, the number of new vertebral fractures (grade 1 or 2), and changes in quality of life.

RESULTS

A total of 56 participants were enrolled in the study (mean age, 29.1 +/- 8.78 years; 61% male). The absolute percentage changes in lumbar spine and total hip BMDs at follow-up were significantly higher in the alendronate therapy group (5.20 +/- 3.67% and 2.14 +/- 3.32%, respectively) than those in the control group (- 0.08 +/- 3.93% and - 1.3 +/- 2.70%, respectively; p < 0.001). At follow-up, two participants (both in the control group) had a new vertebral fracture (not significant), and there were no differences in quality of life or the number of adverse events (including serious and GI-related events).

CONCLUSION

Alendronate therapy was well tolerated and produced a significantly greater increase in BMD over 12 months compared with placebo.

Osteoporosis in chronic obstructive pulmonary disease patients

PURPOSE OF REVIEW

The purpose of this review is to examine the state of knowledge and clinical practice in the association of chronic obstructive pulmonary disease to osteoporosis and fracture incidence.

RECENT FINDINGS

There is a clear association between chronic obstructive pulmonary disease and excessive bone loss/risk of fractures. Little is known about the pathophysiological processes involved in the bone loss, but recent reports point to a continuous systemic inflammatory state in patients with chronic obstructive pulmonary disease. This inflammation involves the release of inflammatory cytokines such as tumour necrosis factor-alpha and interleukin-1. During the course of chronic obstructive pulmonary disease, a protein catabolic process takes place, including increased production of catalytic enzymes (matrix metalloproteinases etc.), which together with the inflammatory cytokines induces bone resorption.

SUMMARY

Patients with chronic obstructive pulmonary disease are at increased risk of osteoporosis and fractures. Risk factors such as smoking, advanced age, physical inactivity, malnutrition, and low weight may be responsible, but a number of pathophysiological explanations including the presence of a chronic inflammatory state with increased levels of proinflammatory cytokines and protein catalytic enzymes may also be involved. The use of oral glucocorticoids is also a significant risk factor. Increased awareness is highly warranted to diagnose osteoporosis at an early stage, and professionals should be aware of the risk of osteoporosis in this patient population.

Shwachman-Diamond syndrome is associated with low-turnover osteoporosis

INTRODUCTION

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterized by exocrine pancreatic insufficiency and bone marrow dysfunction. These result in malabsorption and hematological abnormalities. A skeletal dysplasia is also an integral feature of SDS. The present study assessed prevalence and determinants of osteopenia and osteoporosis in patients with SDS and disease-causing mutations in the SBDS gene.

MATERIALS AND METHODS

Eleven patients (8 males) aged from 5 to 37 years (median 16.7 years) with a genetically confirmed diagnosis of SDS were assessed for fracture history, bone mineral content (BMC), lean tissue mass (LTM) and bone mineral density (BMD) (Hologic Discovery A), osteoporotic vertebral changes, and for blood biochemistry and hematological parameters. Iliac crest bone biopsies were obtained from four patients for histology and histomorphometry.

RESULTS

The main findings were: (1) markedly reduced BMD Z-scores at the lumbar spine (median -2.1, range -4.4 to -0.8), proximal femur (median -1.3, range -2.2 to -0.7) and, whole body (median -1.0, range -2.8 to +0.6), and reduced Z-scores for height-adjusted BMC/LTM ratio (median -0.9, range -3.6 to +1.1); (2) vertebral compression fractures in three patients; and (3) blood biochemistry suggestive of mild vitamin D and vitamin K deficiency. Bone biopsies in four patients showed significant low-turnover osteoporosis with reduced trabecular bone volume, low numbers of osteoclasts and osteoblasts, and reduced amount of osteoid.

CONCLUSIONS

The results suggest that in addition to the skeletal dysplasia, SDS is associated with a more generalized bone disease characterized by low bone mass, low bone turnover and by vertebral fragility fractures. Osteoporosis may result from a primary defect in bone metabolism, and could be related to the bone marrow dysfunction and neutropenia.

Update on maintaining bone health in cystic fibrosis

PURPOSE OF REVIEW

The high prevalence of decreased bone density in adults with cystic fibrosis is now well recognized, and guidelines for screening and treatment of cystic fibrosis-related bone disease have recently been published. This review summarizes the current best practices for optimizing bone health in cystic fibrosis and highlight recent findings that provide insight into the etiology of cystic fibrosis-related bone disease.

RECENT FINDINGS

Recent research suggests that cystic fibrosis-related bone disease actually starts during childhood, when individuals with cystic fibrosis fail to demonstrate normal bone calcium accretion. The failure to reach peak bone mass is made worse by increased osteoclast activity and bone resorption. This combination results in decreased bone density and an increased risk of fracture. Recent clinical studies suggest that multiple contributing factors need to be addressed in cystic fibrosis to optimize bone health: malnutrition, vitamin and mineral malabsorption, recurrent infections, inadequate sex hormones, and lack of exercise. Oral bisphosphonates have been demonstrated to be effective in cystic fibrosis and should be used when osteoporosis or progressive osteopenia is present.

SUMMARY

Research suggests cystic fibrosis-related bone disease actually begins during childhood, and guidelines now exist to aid in identifying and treating those with decreased bone density.