Dietary Carbohydrates and Fat Induce Distinct Surfactant Alterations in Mice

Magnitude of obesity alone does not alter the alveolar lipidome

Obesity may lead to pulmonary dysfunction through complex and incompletely understood cellular and biochemical effects. Altered lung lipid metabolism has been identified as a potential mechanism of lung dysfunction in obesity. Although murine models of obesity demonstrate changes in pulmonary surfactant phospholipid composition and function, data in humans are lacking. We measured untargeted shotgun lipidomes in two bronchoalveolar lavages (BALs) from apical and anteromedial pulmonary subsegments of 14 adult subjects (7 males and 7 females) with body mass indexes (BMIs) ranging from 24.3 to 50.9 kg/m2. The lipidome composition was characterized at the class, species, and fatty acyl/alkyl level using total lipid molecular ion signal intensities normalized to BAL protein concentration and epithelial lining fluid volumes. Multivariate analyses were conducted to identify potential changes with increasing BMI. The alveolar lipidomes contained the expected composition of surfactant-associated phospholipids, sphingolipids, and sterols in addition to cardiolipin and intracellular signaling lipid species. No significant differences in lipidomes were detected between the two BAL regions. Though a small number of lipid species were associated with BMI in multivariate analyses, no robust differences in lipidome composition or specific lipid species were identified over the range of body habitus. The magnitude of obesity alone does not substantially alter the alveolar lipidome in patients without lung disease. Differences in lung function in patients with obesity and no lung disease are unlikely related to changes in alveolar lipid composition.NEW & NOTEWORTHY Altered lung lipid metabolism has been identified as a potential mechanism of lung dysfunction in obesity, but data in humans are lacking. We measured the alveolar lipidome in bronchoalveolar lavages from subjects with healthy lungs with a wide range of body mass index. There were no differences in lipidome composition in association with the magnitude of obesity. In patients with healthy lungs, obesity alone does not alter the alveolar lipidome.

Preoperative Atelectasis in Patients with Obesity Undergoing Bariatric Surgery: A Cross-Sectional Study

BACKGROUND

Pulmonary atelectasis is present even before surgery in patients with obesity. We aimed to estimate the prevalence and extension of preoperative atelectasis in patients with obesity undergoing bariatric surgery and to determine if variation in preoperative Spo2 values in the seated position at room air is explained by the extent of atelectasis coverage in the supine position.

METHODS

This was a cross-sectional study in a single center specialized in laparoscopic bariatric surgery. Preoperative chest computed tomographies were reassessed by a senior radiologist to quantify the extent of atelectasis coverage as a percentage of total lung volume. Patients were classified as having atelectasis when the affection was ≥2.5%, to estimate the prevalence of atelectasis. Crude and adjusted prevalence ratios (aPRs) and odds ratios (aORs) were obtained to assess the relative prevalence of atelectasis and percentage coverage, respectively, with increasing obesity category. Inverse probability weighting was used to assess the total, direct (not mediated), and indirect (mediated through atelectasis) effects of body mass index (BMI) on preoperative Spo2, and to quantify the magnitude of mediation (proportion mediated). E-values were calculated, to represent the minimum magnitude of association that an unmeasured confounder with the same directionality of the effect should have to drive the observed point estimates or lower confidence intervals (CIs) to 1, respectively.

RESULTS

In 236 patients with a median BMI of 40.3 kg/m2 (interquartile range [IQR], 34.6-46.0, range: 30.0-77.3), the overall prevalence of atelectasis was 32.6% (95% CI, 27.0-38.9) and by BMI category: 30 to 35 kg/m2, 12.7% (95% CI, 6.1-24.4); 35 to 40 kg/m2, 28.3% (95% CI, 17.2-42.6); 40 to 45 kg/m2, 12.3% (95% CI, 5.5-24.3); 45 to 50 kg/m2, 48.4% (95% CI, 30.6-66.6); and ≥50 units, 100% (95% CI, 86.7-100). Compared to the 30 to 35 kg/m2 group, only the categories with BMI ≥45 kg/m2 had significantly higher relative prevalence of atelectasis-45 to 50 kg/m2, aPR = 3.52 (95% CI, 1.63-7.61, E-value lower bound: 2.64) and ≥50 kg/m2, aPR = 8.0 (95% CI, 4.22-15.2, E-value lower bound: 7.91)-and higher odds of greater atelectasis percentage coverage: 45-50 kg/m2, aOR = 7.5 (95% CI, 2.7-20.9) and ≥50 kg/m2, aOR = 91.5 (95% CI, 30.0-279.3). Atelectasis percent alone explained 70.2% of the variation in preoperative Spo2. The proportion of the effect of BMI on preoperative Spo2 values <96% mediated through atelectasis was 81.5% (95% CI, 56.0-100).

CONCLUSIONS

The prevalence and extension of atelectasis increased with higher BMI, being significantly higher at BMI ≥45 kg/m2. Preoperative atelectasis mediated the effect of BMI on Spo2 at room air in the seated position.

Chronic hypoxia-induced alterations of the right ventricular myocardium are not aggravated by alimentary obesity in the mouse

BACKGROUND AND AIMS

Obesity is a risk factor of cardiopulmonary disorders including left and right ventricular dysfunction and pulmonary hypertension (PH), and PH is associated with right ventricular (RV) hypertrophy and failure. Here, we tested the hypothesis that alterations of the RV capillary network under PH induced by chronic hypoxia are aggravated by alimentary obesity, thereby representing a predisposition for subsequent RV dysfunction.

METHODS AND RESULTS

Male, 6-week-old C57BL/6N mice were assigned to one of the following groups: control diet (CD), CD/hypoxia (CD-Hyp), high-fat diet (HFD), HFD/hypoxia (HFD-Hyp). Mice were fed CD or HFD for 30 weeks, CD-Hyp and HFD-Hyp mice were exposed to normobaric hypoxia (13 % O2) during the last 3 weeks of the experiments. Hearts were prepared for light and electron microscopy and right atria and RVs were analyzed by design-based stereology. HFD and hypoxia independently increased RV and cardiomyocyte volume. These changes were further enhanced in HFD-Hyp. The ratio between RV and body weights was similar in CD and HFD but enhanced in both hypoxia groups to a similar extent. The total length of capillaries was elevated in proportion with the RV hypertrophy, thus the area of myocardium supplied by an average capillary was similar in all groups. Similarly, the thickness of the capillary endothelium was not altered by HFD or hypoxia.

CONCLUSION

In conclusion, in experimental PH capillaries of the RV myocardium showed similar adaptations in lean and obese mice. Thus, under chronic hypoxic conditions, obesity had no adverse effect on the capillarization of the right ventricle.

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Obesity impacts hypoxia adaptation of the lung

Obesity is mostly associated with adverse health consequences, but may also elicit favorable effects under chronic conditions. This "obesity paradox" is under debate for pulmonary diseases. As confounding factors complicate conclusions from human studies, this study used a controlled animal model combining diet-induced obesity and chronic hypoxia as a model for pulmonary hypertension and chronic obstructive pulmonary disease. Male C57BL/6 mice were fed control or high-fat diet for 30 wk, and half of the animals were exposed to chronic hypoxia (13% O2) for 3 wk. Hypoxia induced right ventricular hypertrophy, thickening of pulmonary arterial and capillary walls, higher lung volumes, and increased hemoglobin concentrations irrespective of the body weight. In contrast, lung proteomes differed substantially between lean- and obese-hypoxic mice. Many of the observed changes were linked to vascular and extracellular matrix (ECM) proteins. In lean-hypoxic animals, circulating platelets were reduced and abundances of various clotting-related proteins were altered, indicating a hypercoagulable phenotype. Moreover, the septal ECM composition was changed, and airspaces were significantly distended pointing to lung hyperinflation. These differences were mostly absent in the obese-hypoxic group. However, the obesity-hypoxia combination induced the lowest blood CO2 concentrations, indicating hyperventilation for sufficient oxygen supply. Moreover, endothelial surface areas were increased in obese-hypoxic mice. Thus, obesity exerts differential effects on lung adaptation to hypoxia, which paradoxically include not only adverse but also rather protective changes. These differences have a molecular basis in the lung proteome and may influence the pathogenesis of lung diseases. This should be taken into account for future individualized prevention and therapy.NEW & NOTEWORTHY An "obesity paradox" is discussed for pulmonary diseases. By linking lung proteome analyses to pulmonary structure and function, we demonstrate that diet-induced obesity affects lung adaptation to chronic hypoxia in various ways. The observed changes include not only adverse but also protective effects and are associated with altered abundances of vascular and extracellular matrix proteins. These results highlight the existence of relevant differences in individuals with obesity that may influence the pathogenesis of lung diseases.

Postnatal growth restriction impairs rat lung structure and function

The negative impact of nutritional deficits in the development of bronchopulmonary dysplasia is well recognized, yet mechanisms by which nutrition alters lung outcomes and nutritional strategies that optimize development and protect the lung remain elusive. Here, we use a rat model to assess the isolated effects of postnatal nutrition on lung structural development without concomitant lung injury. We hypothesize that postnatal growth restriction (PGR) impairs lung structure and function, critical mediators of lung development, and fatty acid profiles at postnatal day 21 in the rat. Rat pups were cross-fostered at birth to rat dams with litter sizes of 8 (control) or 16 (PGR). Lung structure and function, as well as serum and lung tissue fatty acids, and lung molecular mediators of development, were measured. Male and female PGR rat pups had thicker airspace walls, decreased lung compliance, and increased tissue damping. Male rats also had increased lung elastance, increased lung elastin protein abundance, and lysol oxidase expression, and increased elastic fiber deposition. Female rat lungs had increased conducting airway resistance and reduced levels of docosahexaenoic acid in lung tissue. We conclude that PGR impairs lung structure and function in both male and female rats, with sex-divergent changes in lung molecular mediators of development.

Type 1 diabetes and diet-induced obesity predispose C57BL/6J mice to PM2.5-induced lung injury: a comparative study

BACKGROUND

Pre-existing metabolic diseases may predispose individuals to particulate matter (PM)-induced adverse health effects. However, the differences in susceptibility of various metabolic diseases to PM-induced lung injury and their underlying mechanisms have yet to be fully elucidated.

RESULTS

Type 1 diabetes (T1D) murine models were constructed by streptozotocin injection, while diet-induced obesity (DIO) models were generated by feeding 45% high-fat diet 6 weeks prior to and throughout the experiment. Mice were subjected to real-ambient PM exposure in Shijiazhuang City, China for 4 weeks at a mean PM2.5 concentration of 95.77 µg/m3. Lung and systemic injury were assessed, and the underlying mechanisms were explored through transcriptomics analysis. Compared with normal diet (ND)-fed mice, T1D mice exhibited severe hyperglycemia with a blood glucose of 350 mg/dL, while DIO mice displayed moderate obesity and marked dyslipidemia with a slightly elevated blood glucose of 180 mg/dL. T1D and DIO mice were susceptible to PM-induced lung injury, manifested by inflammatory changes such as interstitial neutrophil infiltration and alveolar septal thickening. Notably, the acute lung injury scores of T1D and DIO mice were higher by 79.57% and 48.47%, respectively, than that of ND-fed mice. Lung transcriptome analysis revealed that increased susceptibility to PM exposure was associated with perturbations in multiple pathways including glucose and lipid metabolism, inflammatory responses, oxidative stress, cellular senescence, and tissue remodeling. Functional experiments confirmed that changes in biomarkers of macrophage (F4/80), lipid peroxidation (4-HNE), cellular senescence (SA-β-gal), and airway repair (CCSP) were most pronounced in the lungs of PM-exposed T1D mice. Furthermore, pathways associated with xenobiotic metabolism showed metabolic state- and tissue-specific perturbation patterns. Upon PM exposure, activation of nuclear receptor (NR) pathways and inhibition of the glutathione (GSH)-mediated detoxification pathway were evident in the lungs of T1D mice, and a significant upregulation of NR pathways was present in the livers of T1D mice.

CONCLUSIONS

These differences might contribute to differential susceptibility to PM exposure between T1D and DIO mice. These findings provide new insights into the health risk assessment of PM exposure in populations with metabolic diseases.

Oral Supplementation with the Polyamine Spermidine Affects Hepatic but Not Pulmonary Lipid Metabolism in Lean but Not Obese Mice

The polyamine spermidine is discussed as a caloric restriction mimetic and therapeutic option for obesity and related comorbidities. This study tested oral spermidine supplementation with regard to the systemic, hepatic and pulmonary lipid metabolism under different diet conditions. Male C57BL/6 mice were fed a purified control (CD), high sucrose (HSD) or high fat (HFD) diet with (-S) or without spermidine for 30 weeks. In CD-fed mice, spermidine decreased body and adipose tissue weights and reduced hepatic lipid content. The HSD induced hepatic lipid synthesis and accumulation and hypercholesterolemia. This was not affected by spermidine supplementation, but body weight and blood glucose were lower in HSD-S compared to HSD. HFD-fed mice showed higher body and fat depot weights, prediabetes, hypercholesterolemia and severe liver steatosis, which were not altered by spermidine. Within the liver, spermidine diminished hepatic expression of lipogenic transcription factors SREBF1 and 2 under HSD and HFD and affected the expression of other lipid-related enzymes. In contrast, diet and spermidine exerted only minor effects on pulmonary parameters. Thus, oral spermidine supplementation affects lipid metabolism in a diet-dependent manner, with significant reductions in body fat and weight under physiological nutrition and positive effects on weight and blood glucose under high sucrose intake, but no impact on dietary fat-related parameters.

Starch and Fiber Contents of Purified Control Diets Differentially Affect Hepatic Lipid Homeostasis and Gut Microbiota Composition

Background

Interpretation of results from diet-induced-obesity (DIO) studies critically depends on control conditions. Grain-based chows are optimized for rodent nutrition but do not match the defined composition of purified diets used for DIO, severely limiting the comparability. Purified control diets are recommended but often contain high starch and only minor fiber amounts. It is unknown whether this composition leads to metabolic alterations compared with chow and whether the addition of refined fibers at the expense of starch affects these changes.

Methods

In this experiment, 6-week-old C57BL/6N mice were fed (i) a conventional purified control diet (high-starch, low-fiber; Puri-starch), (ii) an alternative, custom-made purified control diet containing pectin and inulin (medium-starch, higher-fiber; Puri-fiber), or (iii) grain-based chow for 30 weeks (N = 8–10).

Results

Puri-starch feeding resulted in significantly elevated levels of plasma insulin (p = 0.004), cholesterol (p < 0.001), and transaminases (AST p = 0.002, ALT p = 0.001), hepatic de novo lipogenesis and liver steatosis, and an altered gut microbiota composition compared with chow-fed mice. In contrast, Puri-fiber exerted only minor effects on systemic parameters and liver lipid homeostasis, and promoted a distinct gut microbiota composition.

Conclusion

Carbohydrate-rich purified diets trigger a metabolic status possibly masking pathological effects of nutrients under study, restricting its use as control condition. The addition of refined fibers is suited to create purified, yet physiological control diets for DIO research.

A recipe for a good clinical pulmonary surfactant

The lives of thousands premature babies have been saved along the last thirty years thanks to the establishment and consolidation of pulmonary surfactant replacement therapies (SRT). It took some time to close the gap between the identification of the biophysical and molecular causes of the high mortality associated with respiratory distress syndrome in very premature babies and the development of a proper therapy. Closing the gap required the elucidation of some key questions defining the structure–function relationships in surfactant as well as the particular role of the different molecular components assembled into the surfactant system. On the other hand, the application of SRT as part of treatments targeting other devastating respiratory pathologies, in babies and adults, is depending on further extensive research still required before enough amounts of good humanized clinical surfactants will be available. This review summarizes our current concepts on the compositional and structural determinants defining pulmonary surfactant activity, the principles behind the development of efficient natural animal-derived or recombinant or synthetic therapeutic surfactants, as well as a the most promising lines of research that are already opening new perspectives in the application of tailored surfactant therapies to treat important yet unresolved respiratory pathologies.

Techniques to evaluate surfactant activity for a personalized therapy of RDS neonates

According to both European and American Guidelines, preterm neonates have to be treated by nasal continuous air pressure (CPAP) early in the delivery room. The administration of surfactant should be reserved only for babies with respiratory distress syndrome (RDS) with increased oxygen requirement, according to different thresholds of FiO₂. However, these oxygenation thresholds do not fully take into consideration the lung physiopathology and mechanics or the lung surfactant biology of RDS neonates. Since surfactant replacement therapy (SRT) seems to be more effective if it is initiated within the first 3 hours after birth, the use of a reliable bench-to-bedside biological test able to predict as soon as possible the necessity of SRT will help optimise individualised therapies and personalise the actual collective strategy used to treat RDS neonates. With this in mind, in the present review several quantitative and qualitative biological tests to assess the surfactant status in RDS neonates are introduced as potential candidates for the early prediction of SRT requirement, summarising the state-of-the-art in the evaluation of surfactant activity.

Association of Triglyceride-Glucose Index and Lung Health: A Population-based Study

BACKGROUND

Metabolic syndrome and insulin resistance are associated with worsened outcomes of chronic lung disease. The triglyceride-glucose index (TyG), a measure of metabolic dysfunction, is associated with metabolic syndrome and insulin resistance, but its relationship to lung health is unknown.

RESEARCH QUESTION

What is the relationship of TyG to respiratory symptoms, chronic lung disease, and lung function?

STUDY DESIGN AND METHODS

This study analyzed data from the National Health and Nutrition Examination Survey from 1999 to 2012. Participants included fasting adults age ≥ 40 years (N = 6,893) with lung function measurements in a subset (n = 3,383). Associations of TyG with respiratory symptoms (cough, phlegm production, wheeze, and exertional dyspnea), chronic lung disease (diagnosed asthma, chronic bronchitis, and emphysema), and lung function (FEV₁, FVC, and obstructive or restrictive spirometry pattern) were evaluated, adjusting for sociodemographic variables, comorbidities, and smoking. TyG was compared vs insulin resistance, represented by the homeostatic model assessment of insulin resistance (HOMA-IR), and vs the metabolic syndrome.

RESULTS

TyG was moderately correlated with HOMA-IR (Spearman ρ = 0.51) and had good discrimination for metabolic syndrome (area under the receiver-operating characteristic curve, 0.80). A one-unit increase in TyG was associated with higher odds of cough (adjusted OR [aOR], 1.28; 95% CI, 1.06-1.54), phlegm production (aOR, 1.20; 95% CI, 1.01-1.43), wheeze (aOR, 1.18; 95% CI, 1.03-1.35), exertional dyspnea (aOR, 1.21; 95% CI, 1.07-1.38), and a diagnosis of chronic bronchitis (aOR, 1.21; 95% CI, 1.02-1.43). TyG was associated with higher relative risk of a restrictive spirometry pattern (adjusted relative risk ratio, 1.45; 95% CI, 1.11-1.90). Many associations were maintained with additional adjustment for HOMA-IR or metabolic syndrome.

INTERPRETATION

TyG was associated with respiratory symptoms, chronic bronchitis, and a restrictive spirometry pattern. Associations were not fully explained by insulin resistance or metabolic syndrome. TyG is a satisfactory measure of metabolic dysfunction with relevance to pulmonary outcomes. Prospective study to define TyG as a biomarker for impaired lung health is warranted.