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      Osteoporosis in a Rat Model Co-Exposed to Cigarette Smoke and Intermittent Hypoxia

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          Abstract

          Purpose

          There are few studies on osteoporosis in chronic obstructive pulmonary disease-obstructive sleep apnea overlap syndrome, and the results obtained are inconsistent. The purpose of our study is to observe the occurrence of osteoporosis and its possible mechanism in rat model co-exposed to cigarette smoke and intermittent hypoxia.

          Materials and Methods

          The rats were randomly divided into four groups: air exposed group, cigarette smoke (CS) exposed group, 10% concentration of intermittent hypoxia exposed group, CS combined with 10% concentration of intermittent hypoxia exposed group. All animals completed lung function and lung tissue morphology assessment. The femurs were examined by microcomputer tomography (microCT). Tartrate-resistant acidic phosphatase (TRAP) staining was used to evaluate the osteoclasts. We also assessed the interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in peripheral blood.

          Results

          There was no difference in the femoral length between each group, but the quantitative analyses of microCT showed that compared with the air exposed group, the percent bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), cortical thickness (Ct.Th) and bone mineral density (BMD) decreased, and the trabecular separation (Tb.Sp) and the proportion of trap-positive cells increased significantly in the overlapping exposed group. There were higher levels of BV/TV in the overlapping group than CS exposed group. Compared with the intermittent hypoxia exposed group, there were lower levels of Tb.Th and Ct.Th and higher levels of Tb.Sp in the overlapping exposed group. However, there was no statistical difference of trap-positive cell between the overlapping exposed group and the CS exposed single group or the intermittent hypoxia exposed group. There were higher levels of IL-6 and TNF-α in the overlapping exposed group than those in the air-exposed group.

          Conclusion

          Bone destruction increased in the overlapping exposed rat model compared with the rat exposed to air, which may be related to the upregulation of inflammation.

          Related collections

          Most cited references 35

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          Bone marrow, cytokines, and bone remodeling. Emerging insights into the pathophysiology of osteoporosis.

          Both osteoblasts and osteoclasts are derived from progenitors that reside in the bone marrow; osteoblasts belong to the mesenchymal lineage of the marrow stroma, and osteoclasts to the hematopoietic lineage. The development of osteoclasts from their progenitors is dependent on stromal-osteoblastic cells, which are a major source of cytokines that are critical in osteoclastogenesis, such as interleukin-6 and interleukin-11. The production of interleukin-6 by stromal osteoblastic cells, as well as the responsiveness of bone marrow cells to cytokines such as interleukin-6 and interleukin-11, is regulated by sex steroids. When gonadal function is lost, the formation of osteoclasts as well as osteoblasts increases in the marrow, both changes apparently mediated by an increase in the production of interleukin-6 and perhaps by an increase in the responsiveness of bone marrow progenitor cells not only to interleukin-6 but also to other cytokines with osteoclastogenic and osteoblastogenic properties. The cellular activity of the bone marrow is also altered by the process of aging. Specifically, senescence may decrease the ability of the marrow to form osteoblast precursors. The association between the dysregulation of osteoclast or osteoblast development in the marrow and the disruption of the balance between bone resorption and bone formation, resulting in the loss of bone, leads to the following notion. Like homeostasis of other regenerating tissues, homeostasis of bone depends on the orderly replenishment of its cellular constituents. Excessive osteoclastogenesis and inadequate osteoblastogenesis are responsible for the mismatch between the formation and resorption of bone in postmenopausal and age-related osteopenia. The recognition that changes in the numbers of bone cells, rather than changes in the activity of individual cells, form the pathogenetic basis of osteoporosis is a major advance in understanding the mechanism of this disease.
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            Outcomes in patients with chronic obstructive pulmonary disease and obstructive sleep apnea: the overlap syndrome.

            Patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) (overlap syndrome) are more likely to develop pulmonary hypertension than patients with either condition alone. To assess the relation of overlap syndrome to mortality and first-time hospitalization because of COPD exacerbation and the effect of continuous positive airway pressure (CPAP) on these major outcomes. We included 228 patients with overlap syndrome treated with CPAP, 213 patients with overlap syndrome not treated with CPAP, and 210 patients with COPD without OSA. All were free of heart failure, myocardial infarction, or stroke. Median follow-up was 9.4 years (range, 3.3-12.7). End points were all-cause mortality and first-time COPD exacerbation leading to hospitalization. After adjustment for age, sex, body mass index, smoking status, alcohol consumption, comorbidities, severity of COPD, apnea-hypopnea index, and daytime sleepiness, patients with overlap syndrome not treated with CPAP had a higher mortality (relative risk, 1.79; 95% confidence interval, 1.16-2.77) and were more likely to suffer a severe COPD exacerbation leading to hospitalization (relative risk, 1.70; 95% confidence interval, 1.21-2.38) versus the COPD-only group. Patients with overlap syndrome treated with CPAP had no increased risk for either outcome compared with patients with COPD-only. The overlap syndrome is associated with an increased risk of death and hospitalization because of COPD exacerbation. CPAP treatment was associated with improved survival and decreased hospitalizations in patients with overlap syndrome.
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              Stimulation of bone resorption and inhibition of bone formation in vitro by human tumour necrosis factors.

              When leukocytes are exposed to mitogens or antigens in vitro, they release bone-resorbing activity into the culture supernatants which can be detected by bioassay. Like many lymphocyte-monocyte products, this activity has been difficult to purify because of its low abundance in activated leukocyte cultures and the unwieldy bioassay required to detect biological activity. Partially purified preparations of this activity inhibit bone collagen synthesis in organ cultures of fetal rat calvariae. Recent data suggest that both activated lymphocytes and monocytes release factors which could contribute to this activity. Recently, monocyte-derived tumour necrosis factor alpha (TNF-alpha) and lymphocyte-derived tumour necrosis factor beta (TNF-beta) (previously called lymphotoxin), two multifunctional cytokines which have similar cytotoxic effects on neoplastic cell lines, have been purified to homogeneity and their complementary DNAs cloned and expressed in Escherichia coli. As both of these cytokines are likely to be present in activated leukocyte supernatants, we tested purified recombinant preparations for their effects on bone resorption and bone collagen synthesis in vitro, and report here that both cytokines at 10(-7) to 10(-9) M caused osteoclastic bone resorption and inhibited bone collagen synthesis. These data suggest that at least part of the bone-resorbing activity present in activated leukocyte culture supernatants may be due to these cytokines.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                copd
                copd
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove
                1176-9106
                1178-2005
                05 November 2020
                2020
                : 15
                : 2817-2825
                Affiliations
                [1 ]Department of Respiratory and Critical Care Medicine, Tianjin Medical University General Hospital , Tianjin, People’s Republic of China
                Author notes
                Correspondence: Xia Yang; Jie Cao Department of Respiratory and Critical Care Medicine, Tianjin Medical University General Hospital , Tianjin300052, People’s Republic of ChinaTel +86 13682187319; +86 13132088076Fax +86 22 60361720 Email xiaoxia20050111@163.com; tjcaojie@sina.com
                Article
                276913
                10.2147/COPD.S276913
                7652222
                © 2020 Zhuang et al.

                This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 4, References: 37, Pages: 9
                Categories
                Original Research

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