Elsevier

Sleep Medicine

Volume 13, Issue 10, December 2012, Pages 1254-1260
Sleep Medicine

Original Article
Obesity and intermittent hypoxia increase tumor growth in a mouse model of sleep apnea

https://doi.org/10.1016/j.sleep.2012.08.012Get rights and content

Abstract

Background

Intermittent hypoxia and obesity which are two pathological conditions commonly found in patients with obstructive sleep apnea (OSA), potentially enhance cancer progression.

Objective

To investigate whether obesity and/or intermittent hypoxia (IH) mimicking OSA affect tumor growth.

Methods

A subcutaneous melanoma was induced in 40 mice [22 obese (40–45 g) and 18 lean (20–25 g)] by injecting 106 B16F10 cells in the flank. Nineteen mice (10 obese/9 lean) were subjected to IH (6 h/day for 17 days). A group of 21 mice (12 obese/9 lean) were kept under normoxia. At day 17, tumors were excised, weighed and processed to quantify necrosis and endothelial expression of vascular endothelial growth factor (VEGF) and CD-31. VEGF in plasma was also assessed.

Results

In lean animals, IH enhanced tumor growth from 0.81 ± 0.17 to 1.95 ± 0.32 g. In obese animals, a similar increase in tumor growth (1.94 ± 0.18 g) was observed under normoxia, while adding IH had no further effect (1.69 ± 0.23 g). IH only promoted an increase in tumoral necrosis in lean animals. However, obesity under normoxic conditions increased necrosis, VEGF and CD-31 expression in tumoral tissue. Plasma VEGF strongly correlated with tumor weight (ρ = 0.76, p < 0.001) in the whole sample; it increased in lean IH-treated animals from 66.40 ± 3.47 to 108.37 ± 9.48 pg/mL, p < 0.001), while the high baseline value in obese mice (106.90 ± 4.32 pg/mL) was unaffected by IH.

Conclusions

Obesity and IH increased tumor growth, but did not appear to exert any synergistic effects. Circulating VEGF appeared as a crucial mediator of tumor growth in both situations.

Introduction

Obstructive sleep apnea (OSA) is characterized by recurrent disruptions of ventilation caused by an abnormal increase in upper airway collapsibility [1]. These repetitive obstructive apneas induce intermittent hypoxia, increased inspiratory efforts and sleep disruption which have been widely associated with several neurological and cardiovascular consequences [2], [3]. Interestingly, it is well known that hypoxia (a hallmark challenge in OSA) enhances tumor growth [4], [5], [6], [7]. More specifically, a recent report has indicated that intermittent hypoxia potentiates cancer progression in an animal model of OSA [8]. Similarly, data from some epidemiological studies also suggested a possible relationship between cancer death and severity of OSA [9], [10]. Moreover, a very recent analysis of a 22-year follow-up of a population-based sample cohort has provided evidence of an association between cancer mortality and OSA [11]. Obesity, a common finding associated with OSA, is known to increase the risk of several types of neoplasia [12] and enhances tumor growth [13], [14], [15]. As for the potential mechanism(s) involved, both intermittent hypoxia and obesity can contribute to increase the vascular endothelial growth factor (VEGF) [13], [16], [17], [18], [19], [20], which promotes angiogenesis and plays an important role in tumor growth [13], [21], [22].

To better understand the potential mechanisms involved in cancer growth in OSA, the aim of this work was to investigate the contribution of intermittent hypoxia and obesity to the enhancement of tumor progression in an animal model. To this end, we implanted melanoma tumor cells subcutaneously in both lean and obese mice and subjected them to a chronic pattern of intermittent hypoxia mimicking OSA. Given that intermittent hypoxia could induce some degree of sleep loss [23], we carried out an independent set of experiments to assess whether sleep deprivation could affect tumor growth, as this could be a potential confounding factor. Besides assessing tumor growth and necrosis, we also investigated the potential mechanisms involved by determining the levels of circulating VEGF and the expression of VEGF and CD-31 in the tumor tissue as markers of angiogenesis and vascularization, respectively.

Section snippets

Animals

This study, which was approved by the Ethical Committee for Animal Research of the University of Barcelona, was conducted on 60 pathogen-free, 10-week-old male mice. To assess the effects of IH and obesity, we used 40 mice from a recently established metabolic syndrome mouse model (The Pound Mouse; Charles River Laboratories, Saint Germain sur L’arbresle, France; http://www.criver.com/en-US/ProdServ/ByType/ResModOver/ResMod/Pages/PoundMouse.aspx) characterized by a deletion of the exon 2 in

Tumor growth

Seventeen days after the injection of melanoma cells, the tumor weight of control non-obese animals was enhanced in a similar manner by intermittent hypoxia (p = 0.006, F = 8.51) and by obesity (p = 0.003, F = 10.02). Specifically, the tumor weight was 0.81 ± 0.17 g in normoxic lean mice, 1.95 ± 0.32 g (p < 0.001) in lean mice subjected to intermittent hypoxia and 1.94 ± 0.18 g (p < 0.001) in normoxic obese animals. In obese mice, however, tumor growth was not affected by intermittent hypoxia (1.69 ± 0.23 g) (Fig. 2).

Discussion

The application of intermittent hypoxia with a frequency and relative duration that mimic OSA increased the growth of melanoma tumors in lean mice, but not in obese ones. In fact, the increased tumor growth induced by obesity was not enhanced by adding the intermittent hypoxia stimulus. The effect of intermittent hypoxia on tumoral necrosis and vascular density was smaller than the effect of obesity. Plasma levels of VEGF presented a similar behavior to that of tumor weight, resulting in a

Conflict of interest

The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2012.08.012.

. ICMJE Form for Disclosure of Potential Conflicts of Interest form.

Acknowledgments

The authors thank Esteve-Teijin for kindly providing the oxygen concentrators used to prepare the gas mixtures. The authors wish to thank Rocio Nieto and Miguel A. Rodríguez for their technical assistance. Sources of support: This work was supported in part by Ministerio de Economía y Competitividad (SAF2011-22576, FIS-PI11/00089, FIS-PI11/01892), SEPAR and FUCAP.

References (43)

  • M. Yamauchi et al.

    Oxidative stress in obstructive sleep apnea

    Chest

    (2005)
  • D. Eckert et al.

    Pathophysiology of adult obstructive sleep apnea

    Proc Am Thorac Soc

    (2008)
  • S. Redline et al.

    Obstructive sleep apnea–hypopnea and incident stroke: The Sleep Heart Health Study

    Am J Respir Crit Care Med

    (2010)
  • L. Kheirandish-Gozal et al.

    Endothelial progenitor cells and vascular dysfunction in children with obstructive sleep apnea

    Am J Respir Crit Care Med

    (2010)
  • E.B. Rankin et al.

    The role of hypoxia-inducible factors in tumorigenesis

    Cell Death Differ

    (2008)
  • S. Toffoli et al.

    Intermittent hypoxia is a key regulator of cancer cell and endothelial cell interplay in tumours

    FEBS J

    (2008)
  • E.K. Rofstad et al.

    Tumors exposed to acute cyclic hypoxic stress show enhanced angiogenesis, perfusion and metastatic dissemination

    Int J Cancer

    (2010)
  • P. Martinive et al.

    Preconditioning of the tumor vasculature and tumor cells by intermittent hypoxia: implications for anti-cancer therapies

    Acta Clin Belg

    (2008)
  • I. Almendros et al.

    Intermittent hypoxia enhances cancer progression in a mouse model of sleep apnoea

    Eur Respir J

    (2012)
  • T. Young et al.

    Sleep disordered breathing and mortality: eighteen-year follow-up of the Wisconsin Sleep Cohort

    Sleep

    (2008)
  • F.J. Nieto et al.

    Sleep-disordered breathing and cancer mortality: results from the Wisconsin Sleep Cohort Study

    Am J Respir Crit Care Med.

    (2012)
  • Cited by (0)

    View full text