Marta Torres

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

To the Editors: Obstructive sleep apnoea (OSA) is a very prevalent syndrome that induces or aggravates cardiovascular, metabolic and neurocognitive disorders. Among the various challenges imposed on a patient by OSA as a consequence of apnoeas (sleep disruption, increased inspiratory efforts and recurrent hypoxaemia), intermittent hypoxia plays a major role in the pathophysiology of this sleep breathing disorder. It has been well established that hypoxia plays an important role in regulating the various stages of tumour formation and progression [1]. Accordingly, the aim of the experimental study reported here was to test the hypothesis that high-rate intermittent hypoxia with a time course similar to that found in OSA (one or more hypoxic event per minute) enhances tumour growth. To avoid the interaction of any comorbidity, this investigation was carried out in a well-controlled animal model where the main variable under study was intermittent hypoxia. This study, which was approved by the Ethical Committee for Animal Research of the University of Barcelona (Barcelona, Spain), was conducted in 15 pathogen-free male C57BL/6J mice (25–30 g) using a conventional murine melanoma model consisting of tumour induction by subcutaneous injection of 106 B16F10 melanoma cells (ATCC-CRL-6475; American Type Culture Collection, Manassas, VA, USA) in the left flank region of the mouse [2]. This is a widely used cancer model in experimental research [3, 4], which has a response to hypoxia that is representative of a variety of cancer types …

Intermittent hypoxia increases melanoma metastasis to the lung in a mouse model of sleep apnea

Obstructive sleep apnea (OSA) has recently been associated with an increased risk of cancer incidence and mortality in humans. Experimental data in mice have also shown that intermittent hypoxia similar to that observed in OSA patients enhances tumor growth. The aim of this study was to test the hypothesis that intermittent hypoxia mimicking OSA enhances lung metastasis. A total of 75 C57BL/6J male mice (10-week-old) were subjected to either spontaneous or induced melanoma lung metastasis. Normoxic animals breathed room air and intermittent hypoxic animals were subjected to cycles of 20s of 5% O2 followed by 40s of room air for 6h/day. Spontaneous and induced lung metastases were studied after subcutaneous and intravenous injection of B16F10 melanoma cells, respectively. Compared with normoxia, intermittent hypoxia induced a significant increase in melanoma lung metastasis. These animal model results suggest that intermittent hypoxia could contribute to cancer metastasis in patients with OSA.

Tissue Oxygenation in Brain, Muscle, and Fat in a Rat Model of Sleep Apnea: Differential Effect of Obstructive Apneas and Intermittent Hypoxia

STUDY OBJECTIVES To test the hypotheses that the dynamic changes in brain oxygen partial pressure (PtO(2)) in response to obstructive apneas or to intermittent hypoxia differ from those in other organs and that the changes in brain PtO(2) in response to obstructive apneas is a source of oxidative stress. DESIGN Prospective controlled animal study. SETTING University laboratory. PARTICIPANTS 98 Sprague-Dawley rats. INTERVENTIONS Cerebral cortex, skeletal muscle, or visceral fat tissues were exposed in anesthetized animals subjected to either obstructive apneas or intermittent hypoxia (apneic and hypoxic events of 15 s each and 60 events/h) for 1 h. MEASUREMENTS AND RESULTS Arterial oxygen saturation (SpO(2)) presented a stable pattern, with similar desaturations during both stimuli. The PtO(2) was measured by a microelectrode. During obstructive apneas, a fast increase in cerebral PtO(2) was observed (38.2 ± 3.4 vs. 54.8 ± 5.9 mm Hg) but not in the rest of tissues. This particular cerebral response was not found during intermittent hypoxia. The cerebral content of reduced glutathione was decreased after obstructive apneas (46.2% ± 15.2%) compared to controls (100.0% ± 14.7%), but not after intermittent hypoxia. This antioxidant consumption after obstructive apneas was accompanied by increased cerebral lipid peroxidation under this condition. No changes were observed for these markers in the other tissues. CONCLUSIONS These results suggest that cerebral cortex could be protected in some way from hypoxic periods caused by obstructive apneas. The increased cerebral PtO(2) during obstructive apneas may, however, cause harmful effects (oxidative stress). The obstructive apnea model appears to be more adequate than the intermittent hypoxia model for studying brain changes associated with OSA.

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

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 (40-45g) and 18 lean (20-25g)] by injecting 10(6) B16F10 cells in the flank. Nineteen mice (10 obese/9 lean) were subjected to IH (6h/day for 17days). 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±0.32g. In obese animals, a similar increase in tumor growth (1.94±0.18g) was observed under normoxia, while adding IH had no further effect (1.69±0.23g). 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±9.48pg/mL, p<0.001), while the high baseline value in obese mice (106.90±4.32pg/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.

Intermittent hypoxia alters gut microbiota diversity in a mouse model of sleep apnoea

We assessed whether intermittent hypoxia, which emulates one of the hallmarks of obstructive sleep apnoea (OSA), leads to altered faecal microbiome in a murine model. In vivo partial pressure of oxygen was measured in colonic faeces during intermittent hypoxia in four anesthetised mice. 10 mice were subjected to a pattern of chronic intermittent hypoxia (20 s at 5% O2 and 40 s at room air for 6 h·day−1) for 6 weeks and 10 mice served as normoxic controls. Faecal samples were obtained and microbiome composition was determined by 16S rRNA pyrosequencing and bioinformatic analysis by Quantitative Insights into Microbial Ecology. Intermittent hypoxia exposures translated into hypoxia/re-oxygenation patterns in the faeces proximal to the bowel epithelium (<200 μm). A significant effect of intermittent hypoxia on global microbial community structure was found. Intermittent hypoxia increased the α-diversity (Shannon index, p<0.05) and induced a change in the gut microbiota (ANOSIM analysis of β-diversity, p<0.05). Specifically, intermittent hypoxia-exposed mice showed a higher abundance of Firmicutes and a smaller abundance of Bacteroidetes and Proteobacteria phyla than controls. Faecal microbiota composition and diversity are altered as a result of intermittent hypoxia realistically mimicking OSA, suggesting the possibility that physiological interplays between host and gut microbiota could be deregulated in OSA. Faecal microbiota composition and diversity are altered due to intermittent hypoxia mimicking OSA in a murine model http://ow.ly/ERjA9

A Bayesian cost-effectiveness analysis of a telemedicine-based strategy for the management of sleep apnoea: a multicentre randomised controlled trial

Background Compliance with continuous positive airway pressure (CPAP) therapy is essential in patients with obstructive sleep apnoea (OSA), but adequate control is not always possible. This is clinically important because CPAP can reverse the morbidity and mortality associated with OSA. Telemedicine, with support provided via a web platform and video conferences, could represent a cost-effective alternative to standard care management. Aim To assess the telemedicine impact on treatment compliance, cost-effectiveness and improvement in quality of life (QoL) when compared with traditional face-to-face follow-up. Methods A randomised controlled trial was performed to compare a telemedicine-based CPAP follow-up strategy with standard face-to-face management. Consecutive OSA patients requiring CPAP treatment, with sufficient internet skills and who agreed to participate, were enrolled. They were followed-up at 1, 3 and 6 months and answered surveys about sleep, CPAP side effects and lifestyle. We compared CPAP compliance, cost-effectiveness and QoL between the beginning and the end of the study. A Bayesian cost-effectiveness analysis with non-informative priors was performed. Results We randomised 139 patients. At 6 months, we found similar levels of CPAP compliance, and improved daytime sleepiness, QoL, side effects and degree of satisfaction in both groups. Despite requiring more visits, the telemedicine group was more cost-effective: costs were lower and differences in effectiveness were not relevant. Conclusions A telemedicine-based strategy for the follow-up of CPAP treatment in patients with OSA was as effective as standard hospital-based care in terms of CPAP compliance and symptom improvement, with comparable side effects and satisfaction rates. The telemedicine-based strategy had lower total costs due to savings on transport and less lost productivity (indirect costs). Trial register number NCT01716676.

Changes in oxygen partial pressure of brain tissue in an animal model of obstructive apnea

BackgroundCognitive impairment is one of the main consequences of obstructive sleep apnea (OSA) and is usually attributed in part to the oxidative stress caused by intermittent hypoxia in cerebral tissues. The presence of oxygen-reactive species in the brain tissue should be produced by the deoxygenation-reoxygenation cycles which occur at tissue level during recurrent apneic events. However, how changes in arterial blood oxygen saturation (SpO2) during repetitive apneas translate into oxygen partial pressure (PtO2) in brain tissue has not been studied. The objective of this study was to assess whether brain tissue is partially protected from intermittently occurring interruption of O2 supply during recurrent swings in arterial SpO2 in an animal model of OSA.MethodsTwenty-four male Sprague-Dawley rats (300-350 g) were used. Sixteen rats were anesthetized and non-invasively subjected to recurrent obstructive apneas: 60 apneas/h, 15 s each, for 1 h. A control group of 8 rats was instrumented but not subjected to obstructive apneas. PtO2 in the cerebral cortex was measured using a fast-response oxygen microelectrode. SpO2 was measured by pulse oximetry. The time dependence of arterial SpO2 and brain tissue PtO2 was carried out by Friedman repeated measures ANOVA.ResultsArterial SpO2 showed a stable periodic pattern (no significant changes in maximum [95.5 ± 0.5%; m ± SE] and minimum values [83.9 ± 1.3%]). By contrast, brain tissue PtO2 exhibited a different pattern from that of arterial SpO2. The minimum cerebral cortex PtO2 computed during the first apnea (29.6 ± 2.4 mmHg) was significantly lower than baseline PtO2 (39.7 ± 2.9 mmHg; p = 0.011). In contrast to SpO2, the minimum and maximum values of PtO2 gradually increased (p < 0.001) over the course of the 60 min studied. After 60 min, the maximum (51.9 ± 3.9 mmHg) and minimum (43.7 ± 3.8 mmHg) values of PtO2 were significantly greater relative to baseline and the first apnea dip, respectively.ConclusionsThese data suggest that the cerebral cortex is partially protected from intermittently occurring interruption of O2 supply induced by obstructive apneas mimicking OSA.

Biological consequences of oxygen desaturation and respiratory effort in an acute animal model of obstructive sleep apnea (OSA)

BACKGROUND An animal model mimicking all the factors involved in obstructive sleep apnea (OSA) is useful for investigating mechanisms because the associated comorbidity usually present in such patients is an important limitation. AIM To test the hypothesis that hypoxia/normoxia and respiratory effort have different effects on the induction of inflammatory response and endothelial dysfunction in an acute rat model of OSA. METHODS Four groups of anesthetized rats were studied (n=8): (1) sham; (2) apnea: obstructions (15s each, 60/h, for 3h); (3) apnea+O(2): obstructions and breathing oxygen-enriched air to avoid hypoxia and (4) intermittent hypoxia/normoxia. Inflammatory and endothelial mediators were measured as outcomes along with NF-kappaB in the lung and diaphragm. RESULTS TNF-alpha and IL-1beta significantly increased in all groups compared with sham. NF-kappaB in the lung was increased in apnea and hypoxia/normoxia groups, but not in apnea+O(2) group. In diaphragm tissue, NF-kappaB was only significant in apnea compared to sham. Significant differences were found in the ratio thromboxane-B2/6-keto-Prostaglandin-F1alpha between apnea and hypoxia/normoxia compared to sham but not in apnea+O(2). CONCLUSIONS Oxygen desaturations and respiratory efforts play a role in the induction of systemic inflammation but only hypoxia/normoxia induces endothelial dysfunction. These data suggest a potential role for oxygen therapy in patients with OSA.

Effect of CPAP on Cognition, Brain Function, and Structure Among Elderly Patients With OSA: A Randomized Pilot Study

BACKGROUND Despite the increasing aging population and the high prevalence of OSA in elderly adults, little is known about cognitive effects of OSA and the effectiveness of CPAP treatment. Therefore, this study investigated whether elderly patients with OSA present cognitive deficits and functional and structural alterations of the brain that could be improved by CPAP treatment. METHODS This randomized, evaluator-blinded, parallel-group, single-center pilot study involved patients aged ≥ 65 years with newly-diagnosed severe OSA syndrome. Thirty-three patients were assigned to receive either conservative care (CC) or CPAP plus CC for 3 months. At baseline and 3 months after treatment, patients underwent a neuropsychologic evaluation and a functional and structural MRI study of connectivity within the default mode network (DMN) and of cortical thickness. RESULTS Neuropsychologic evaluation revealed no differences in cognitive performance between OSA groups at baseline. By contrast, after CPAP treatment, patients showed a significant improvement in episodic (between-group difference in change, 7.60; 95% CI, 1.66-13.55; P = .014) and short-term memory (between-group difference in change, 1.06; 95% CI, 0.10-2.01; P = .032) and in executive function (speed of mental processing, 5.74; 95% CI, 1.69-9.79; P = .007; mental flexibility, -47.64; 95% CI, -81.83 to -13.45; P = .008), whereas no changes were observed in the CC group. Neuroimaging revealed an increase in the connectivity in the right middle frontal gyrus after 3 months of CPAP treatment and a higher percentage of cortical thinning in the CC group. No association was seen between cognition and brain functional connectivity changes within the DMN. CONCLUSIONS Elderly patients with severe OSA who present with cognitive difficulties could benefit from CPAP treatment. Moreover, CPAP treatment increases the connectivity of the DMN and attenuates cortical thinning. TRIAL REGISTRY ClinicalTrials.gov; No.: NCT01826032; URL: www.clinicaltrials.gov.

Multivariate curve resolution analysis of voltammetric data obtained at different time windows: study of the system Cd2+–nitrilotriacetic acid

The system Cd2+–nitrilotriacetic acid (NTA) has been studied by voltammetric techniques with different time windows (long drop time direct current polarography, differential pulse polarography and differential pulse anodic stripping voltammetry), in a way that, depending on the technique, the 1:1 complex behaves mainly labile or mainly inert. The corresponding signals have been treated by using two different approaches: hard modelling (i.e., the usual strategy in electrochemistry which requires a priori postulated models) and soft modelling (i.e., by means of purely mathematical data analysis using a family of factor analysis techniques). The results have been compared with each other and also with the values in the literature. It was found that soft modelling is especially accurate in the case of inert complexes, even when a small fraction of the complex dissociates during the voltammetric measurement. However, for systems that are closer to lability (i.e., with an important fraction of complex dissociation) soft modelling just provides rough estimations of the complexation parameters that, anyway, can be useful when a basis for the hard model approach is not available.