Ceramides mediate cigarette smoke-induced metabolic disruption in mice

Chronic aryl hydrocarbon receptor activity impairs muscle mitochondrial function with tobacco smoking

BACKGROUND

Accumulating evidence has demonstrated that chronic tobacco smoking directly contributes to skeletal muscle dysfunction independent of its pathological impact to the cardiorespiratory systems. The mechanisms underlying tobacco smoke toxicity in skeletal muscle are not fully resolved. In this study, the role of the aryl hydrocarbon receptor (AHR), a transcription factor known to be activated with tobacco smoke, was investigated.

METHODS

AHR related gene (mRNA) expression was quantified in skeletal muscle from adult controls and patients with chronic obstructive pulmonary disease (COPD), as well as mice with and without cigarette smoke exposure. Utilizing both skeletal muscle-specific AHR knockout mice exposed to chronic repeated (5 days per week for 16 weeks) cigarette smoke and skeletal muscle-specific expression of a constitutively active mutant AHR in healthy mice, a battery of assessments interrogating muscle size, contractile function, mitochondrial energetics, and RNA sequencing were employed.

RESULTS

Skeletal muscle from COPD patients (N = 79, age = 67.0 ± 8.4 years) had higher levels of AHR (P = 0.0451) and CYP1B1 (P < 0.0001) compared to healthy adult controls (N = 16, age = 66.5 ± 6.5 years). Mice exposed to cigarette smoke displayed higher expression of Ahr (P = 0.008), Cyp1b1 (P < 0.0001), and Cyp1a1 (P < 0.0001) in skeletal muscle compared to air controls. Cigarette smoke exposure was found to impair skeletal muscle mitochondrial oxidative phosphorylation by ~50% in littermate controls (Treatment effect, P < 0.001), which was attenuated by deletion of the AHR in muscle in male (P = 0.001), but not female, mice (P = 0.37), indicating there are sex-dependent pathological effects of smoking-induced AHR activation in skeletal muscle. Viral mediated expression of a constitutively active mutant AHR in the muscle of healthy mice recapitulated the effects of cigarette smoking by decreasing muscle mitochondrial oxidative phosphorylation by ~40% (P = 0.003).

CONCLUSIONS

These findings provide evidence linking chronic AHR activation secondary to cigarette smoke exposure to skeletal muscle bioenergetic deficits in male, but not female, mice. AHR activation is a likely contributor to the decline in muscle oxidative capacity observed in smokers and AHR antagonism may provide a therapeutic avenue aimed to improve muscle function in COPD.

Long-term exposure to varying-sized particulate matters and kidney disease in middle-aged and elder adults: A 8-year nationwide cohort study in China

Evidence for the causal relationship of particulate matters (PMs) exposure with kidney disease, especially PM1, PM1-2.5 and PM2.5-10, remained scarce among developing countries with severe pollution. We conducted a longitudinal cohort study involving 13,041 adults with free kidney disease from 150 Chinese counties. PMs concentrations were generated using a well-established satellite-based spatiotemporal model. And the time-varying Cox regression model along with stratified analyses were performed to determine the association and potential modifiers, respectively. We also calculated the population-attributable fraction to evaluate the burden of kidney disease attributable to PMs pollution. Between Jan 2011 and Dec 2018, 985 kidney disease incidents were identified with an incidence rate of 12.69 per 1000 person-years. Significant dose-response relationships were observed for all 5 kinds PMs. Specifically, an increased risk of kidney disease was associated with per 10 μg/m3 increment of PM1 (HR = 1.187, 95%CI: 1.114 to 1.265), PM1-2.5 (1.326, 1.212 to 1.452), PM2.5 (1.197, 1.139 to 1.258), PM2.5-10 (1.297, 1.240 to 1.357), and PM10 (1.137, 1.108 to 1.166). A mixture analysis method of weighted quantile regression model revealed that PM2.5-10 predominated the PMs mixture index (57.1 %), and followed with PM10 (26.4 %). Stratified analyses indicated the elder, overweight persons, smokers, respiratory patients and urban residents were more vulnerable to PMs pollution than their counterparts. Calculated population attributable fractions of kidney disease attributable to PMs pollution was 16.67-39.47 %. Higher PMs pollution was associated with the increased risk of kidney disease development in China. Acceleration of efforts to reduce PMs pollution was therefore urgently needed to alleviate kidney disease burden.

Tissue-specific mitochondrial toxicity of cigarette smoke concentrate: consequence to oxidative phosphorylation

Cigarette smoke exposure is a well-known risk factor for developing numerous chronic health conditions, including pulmonary disease and cardiometabolic disorders. However, the cellular mechanisms mediating the toxicity of cigarette smoke in extrapulmonary tissues are still poorly understood. Therefore, the purpose of this study was to characterize the acute dose-dependent toxicity of cigarette smoke on mitochondrial metabolism by determining the susceptibility and sensitivity of mitochondrial respiration from murine skeletal (gastrocnemius and soleus) and cardiac muscles, as well as the aorta to cigarette smoke concentrate (CSC). In all tissues, exposure to CSC inhibited tissue-specific respiration capacity, measured by high-resolution respirometry, according to a biphasic pattern. With a break point of 451 ± 235 μg/mL, the aorta was the least susceptible to CSC-induced mitochondrial respiration inhibition compared with the gastrocnemius (151 ± 109 μg/mL; P = 0.008, d = 2.3), soleus (211 ± 107 μg/mL; P = 0.112; d = 1.7), and heart (94 ± 51 μg/mL; P < 0.001; d = 2.6) suggesting an intrinsic resistance of the vascular smooth muscle mitochondria to cigarette smoke toxicity. In contrast, the cardiac muscle was the most susceptible and sensitive to the effects of CSC, demonstrating the greatest decline in tissue-specific respiration with increasing CSC concentration (P < 0.001, except the soleus). However, when normalized to citrate synthase activity to account for differences in mitochondrial content, cardiac fibers' sensitivity to cigarette smoke inhibition was no longer significantly different from both fast-twitch gastrocnemius and slow-twitch soleus muscle fibers, thus suggesting similar mitochondrial phenotypes. Collectively, these findings established the acute dose-dependent toxicity of cigarette smoke on oxidative phosphorylation in permeabilized tissues involved in the development of smoke-related cardiometabolic diseases.NEW & NOTEWORTHY Despite numerous investigations into the mechanisms underlying cigarette smoke-induced mitochondrial dysfunction, no studies have investigated the tissue-specific mitochondrial toxicity to cigarette smoke. We demonstrate that, while aorta is least sensitive and susceptible to cigarette smoke-induced toxicity, the degree of cigarette smoke-induced toxicity in striated muscle depends on the tissue-specific mitochondrial content. We conclude that while the mitochondrial content influences cigarette smoke-induced toxicity in striated muscles, aorta is intrinsically protected against cigarette smoke-induced mitochondrial toxicity.

Effects of acute cigarette smoke concentrate exposure on mitochondrial energy transfer in fast- and slow-twitch skeletal muscle

The mechanisms underlying cigarette smoke-induced mitochondrial dysfunction in skeletal muscle are still poorly understood. Accordingly, this study aimed to examine the effects of cigarette smoke on mitochondrial energy transfer in permeabilized muscle fibers from skeletal muscles with differing metabolic characteristics. The electron transport chain (ETC) capacity, ADP transport, and respiratory control by ADP were assessed in fast- and slow-twitch muscle fibers from C57BL/6 mice (n = 11) acutely exposed to cigarette smoke concentrate (CSC) using high-resolution respirometry. CSC decreased complex I-driven respiration in the white gastrocnemius (CONTROL:45.4 ± 11.2 pmolO₂.s^-1.mg^-1 and CSC:27.5 ± 12.0 pmolO₂.s^-1.mg^-1; p = 0.01) and soleus (CONTROL:63.0 ± 23.8 pmolO₂.s^-1.mg^-1 and CSC:44.6 ± 11.1 pmolO₂.s^-1.mg^-1; p = 0.04). In contrast, the effect of CSC on Complex II-linked respiration increased its relative contribution to muscle respiratory capacity in the white gastrocnemius muscle. The maximal respiratory activity of the ETC was significantly inhibited by CSC in both muscles. Furthermore, the respiration rate dependent on the ADP/ATP transport across the mitochondrial membrane was significantly impaired by CSC in the white gastrocnemius (CONTROL:-70 ± 18 %; CSC:-28 ± 10 %; p < 0.001), but not the soleus (CONTROL:47 ± 16 %; CSC:31 ± 7 %; p = 0.08). CSC also significantly impaired mitochondrial thermodynamic coupling in both muscles. Our findings underscore that acute CSC exposure directly inhibits oxidative phosphorylation in permeabilized muscle fibers. This effect was mediated by significant perturbations of the electron transfer in the respiratory complexes, especially at complex I, in both fast and slow twitch muscles. In contrast, CSC-induced inhibition of the exchange of ADP/ATP across the mitochondrial membrane was fiber-type specific, with a large effect on fast-twitch muscles.

Effects of cigarette smoke on in situ mitochondrial substrate oxidation of slow- and fast-twitch skeletal muscles

Epidemiological and clinical evidence suggests that cigarette smoke exposure alters glucose and fatty acid metabolism, leading to greater susceptibility to metabolic disorders. However, the effects of cigarette smoke exposure on mitochondrial substrate oxidation in the skeletal muscle are still poorly understood. Accordingly, this study aimed to examine the acute effects of cigarette smoke on mitochondrial respiratory capacity, sensitivity, and concurrent utilization of palmitoylcarnitine (PC), a long-chain fatty acid, and pyruvate, a product of glycolysis, in permeabilized gastrocnemius and soleus muscle fibers exposed to an acute (1 h) dose (4 %) of cigarette smoke concentrate. Cigarette smoke decreased both mitochondrial respiratory capacity (CONTROL: 50.4 ± 11.8 pmol_O2/s/mg_wt and SMOKE: 22.3 ± 4.4 pmol_O2/s/mg_wt, p < 0.01) and sensitivity for pyruvate (CONTROL: 0.10 ± 0.04 mM and SMOKE: 0.11 ± 0.04 mM, p < 0.01) in the gastrocnemius muscle. In the soleus, only the sensitivity for pyruvate-stimulated mitochondrial respiration trended toward a decrease (CONTROL: 0.11 ± 0.04 mM and SMOKE: 0.23 ± 0.15 mM, p = 0.08). In contrast, cigarette smoke did not significantly alter palmitoylcarnitine-stimulated mitochondrial respiration in either muscle. In the control condition, pyruvate-supported respiration was inhibited by the concurrent addition of palmitoylcarnitine in the fast-twitch gastrocnemius muscle (-27.1 ± 19.7 %, p < 0.05), but not in the slow-twitch soleus (-9.2 ± 17.0 %). With cigarette smoke, the addition of palmitoylcarnitine augmented the maximal respiration rate stimulated by the concurrent addition of pyruvate in the gastrocnemius (+18.5 ± 39.3 %, p < 0.05). However, cigarette smoke still significantly impaired mitochondrial respiratory capacity with combined substrates compared to control (p < 0.05). Our findings underscore that cigarette smoke directly impairs mitochondrial respiration of carbohydrate-derived substrates and is a primary mechanism underlying cigarette smoke-induced muscle dysfunction, which leads to a vicious cycle involving excess glucose conversion into fatty acids and lipotoxicity.

Skeletal muscle mitochondrial adaptations induced by long-term cigarette smoke exposure

Because patients with chronic obstructive pulmonary disease (COPD) are often physically inactive, it is still unclear whether the lower respiratory capacity in the locomotor muscles of these patients is due to cigarette smoking per se or is secondary to physical deconditioning. Accordingly, the purpose of this study was to examine mitochondrial alterations in the quadriceps muscle of 10 mice exposed to 8 mo of cigarette smoke, a sedentary mouse model of emphysema, and 9 control mice, using immunoblotting, spectrophotometry, and high-resolution respirometry in permeabilized muscle fibers. Mice exposed to smoke displayed a twofold increase in the oxidative stress marker, 4-HNE, (P < 0.05) compared with control mice. This was accompanied by significant decrease in protein expression of UCP3 (65%), ANT (58%), and mitochondrial complexes II-V (∼60%-75%). In contrast, maximal ADP-stimulated respiration with complex I and II substrates (CON: 23.6 ± 6.6 and SMO: 19.2 ± 8.2 ρM·mg-1·s-1) or octanoylcarnitine (CON: 21.8 ± 9.0 and SMO: 16.5 ± 6.6 ρM·mg-1·s-1) measured in permeabilized muscle fibers, as well as citrate synthase activity, were not significantly different between groups. Collectively, our findings revealed that sedentary mice exposed to cigarette smoke for 8 mo, which is typically associated with pulmonary inflammation and emphysema, exhibited a preserved mitochondrial respiratory capacity for various substrates, including fatty acid, in the skeletal muscle. However, the mitochondrial adaptations induced by cigarette smoke favored the development of chronic oxidative stress, which can indirectly contribute to augment the susceptibility to muscle fatigue and exercise intolerance.NEW & NOTEWORTHY It is unclear whether the exercise intolerance and skeletal muscle mitochondrial dysfunction observed in patients with COPD is due to cigarette smoke exposure, per se, or if they are secondary consequences to inactivity. Herein, while long-term exposure to cigarette smoke induces oxidative stress and an altered skeletal muscle phenotype, cigarette smoke does not directly contribute to mitochondrial dysfunction. With this evidence, we demonstrate the critical role of physical inactivity in cigarette smoke-related skeletal muscle dysfunction.

Two Weeks of Smoking Cessation Reverse Cigarette Smoke-Induced Skeletal Muscle Atrophy and Mitochondrial Dysfunction in Mice

INTRODUCTION

Apart from its adverse effects on the respiratory system, cigarette smoking also induces skeletal muscle atrophy and dysfunction. Whether short-term smoking cessation can restore muscle mass and function is unknown. We, therefore, studied the impact of 1- and 2-week smoking cessation on skeletal muscles in a mouse model.

METHODS

Male mice were divided into four groups: Air-exposed (14 weeks); cigarette smoke (CS)-exposed (14 weeks); CS-exposed (13 weeks) followed by 1-week cessation; CS-exposed (12 weeks) followed by 2 weeks cessation to examine exercise capacity, physical activity levels, body composition, muscle function, capillarization, mitochondrial function and protein expression in the soleus, plantaris, and diaphragm muscles.

RESULTS

CS-induced loss of body and muscle mass was significantly improved within 1 week of cessation due to increased lean and fat mass. Mitochondrial respiration and protein levels of the respiratory complexes in the soleus were lower in CS-exposed mice, but similar to control values after 2 weeks of cessation. Exposing isolated soleus muscles to CS extracts reduced mitochondrial respiration that was reversed after removing the extract. While physical activity was reduced in all groups, exercise capacity, limb muscle force, fatigue resistance, fiber size and capillarization, and diaphragm cytoplasmic HIF-1α were unaltered by CS-exposure. However, CS-induced diaphragm atrophy and increased capillary density were not seen after 2 weeks of smoking cessation.

CONCLUSION

In male mice, 2 weeks of smoking cessation reversed smoking-induced mitochondrial dysfunction, limb muscle mass loss, and diaphragm muscle atrophy, highlighting immediate benefits of cessation on skeletal muscles.

IMPLICATIONS

Our study demonstrates that CS-induced skeletal muscle mitochondrial dysfunction and atrophy are significantly improved by 2 weeks of cessation in male mice. We show for the first time that smoking cessation as short as 1 to 2 weeks is associated with immediate beneficial effects on skeletal muscle structure and function with the diaphragm being particularly sensitive to CS-exposure and cessation. This could help motivate smokers to quit smoking as early as possible. The knowledge that smoking cessation has potential positive extrapulmonary effects is particularly relevant for patients referred to rehabilitation programs and those admitted to hospitals suffering from acute or chronic muscle deterioration yet struggling with smoking cessation.

Cigarette smoke exposure impairs β-cell function through activation of oxidative stress and ceramide accumulation

OBJECTIVES

Epidemiological studies indicate that first- and second-hand cigarette smoke (CS) exposure are important risk factors for the development of type 2 diabetes (T2D). Additionally, elevated diabetes risk has been reported to occur within a short period of time after smoking cessation, and health risks associated with smoking are increased when combined with obesity. At present, the mechanisms underlying these associations remain incompletely understood. The objective of this study was to test the impact of CS exposure on pancreatic β-cell function using rodent and in vitro models.

METHODS

Beginning at 8 weeks of age, C57BL/6 J mice were concurrently fed a high-fat diet (HFD) and exposed to CS for 11 weeks, followed by an additional 11 weeks of smoking cessation with continued HFD. Glucose tolerance testing was performed during CS exposure and during the cessation period. Cultured INS-1 β-cells and primary islets were exposed ex vivo to CS extract (CSE), and β-cell function and viability were tested. Since CS increases ceramide accumulation in the lung and these bioactive sphingolipids have been implicated in pancreatic β-cell dysfunction in diabetes, islet and β-cell sphingolipid levels were measured in islets from CS-exposed mice and in CSE-treated islets and INS-1 cells using liquid chromatography-tandem mass spectrometry.

RESULTS

Compared to HFD-fed, ambient air-exposed mice, HFD-fed and CS-exposed mice had reduced weight gain and better glucose tolerance during the active smoking period. Following smoking cessation, CS-mice exhibited rapid weight gain and had accelerated worsening of their glucose tolerance. CS-exposed mice had higher serum proinsulin/insulin ratios, indicative of β-cell dysfunction, significantly lower β-cell mass (p = 0.017), reduced β-cell proliferation (p = 0.006), and increased islet ceramide content compared to non-smoking control mice. Ex vivo exposure of isolated islets to CSE was sufficient to increase islet ceramide levels, which was correlated with reduced insulin gene expression and glucose-stimulated insulin secretion, and increased β-cell oxidative and endoplasmic reticulum (ER) stress. Treatment with the antioxidant N-acetylcysteine markedly attenuated the effects of CSE on ceramide levels, restored β-cell function and survival, and increased cyclin D2 expression, while also reducing activation of β-cell ER and oxidative stress.

CONCLUSIONS

Our results indicate that CS exposure leads to impaired insulin production, processing, secretion and reduced β-cell viability and proliferation. These effects were linked to increased β-cell oxidative and ER stress and ceramide accumulation. Mice fed HFD continued to experience detrimental effects of CS exposure even during smoking cessation. Elucidation of the mechanisms by which CS exposure impairs β-cell function in synergy with obesity will help design therapeutic and preventive interventions for both active and former smokers.

Diesel Exhaust Particle Exposure Compromises Alveolar Macrophage Mitochondrial Bioenergetics

Diesel exhaust particles (DEPs) are known pathogenic pollutants that constitute a significant quantity of air pollution. Given the ubiquitous presence of macrophages throughout the body, including the lungs, as well as their critical role in tissue and organismal metabolic function, we sought to determine the effect of DEP exposure on macrophage mitochondrial function. Following daily DEP exposure in mice, pulmonary macrophages were isolated for mitochondrial analyses, revealing reduced respiration rates and dramatically elevated H₂O₂ levels. Serum ceramides and inflammatory cytokines were increased. To determine the degree to which the changes in mitochondrial function in macrophages were not dependent on any cross-cell communication, primary pulmonary murine macrophages were used to replicate the DEP exposure in a cell culture model. We observed similar changes as seen in pulmonary macrophages, namely diminished mitochondrial respiration, but increased H₂O₂ production. Interestingly, when treated with myriocin to inhibit ceramide biosynthesis, these DEP-induced mitochondrial changes were mitigated. Altogether, these data suggest that DEP exposure may compromise macrophage mitochondrial and whole-body function via pathologic alterations in macrophage ceramide metabolism.

The Overlap of Lung Tissue Transcriptome of Smoke Exposed Mice with Human Smoking and COPD

Genome-wide mRNA profiling in lung tissue from human and animal models can provide novel insights into the pathogenesis of chronic obstructive pulmonary disease (COPD). While 6 months of smoke exposure are widely used, shorter durations were also reported. The overlap of short term and long-term smoke exposure in mice is currently not well understood, and their representation of the human condition is uncertain. Lung tissue gene expression profiles of six murine smoking experiments (n = 48) were obtained from the Gene Expression Omnibus (GEO) and analyzed to identify the murine smoking signature. The "human smoking" gene signature containing 386 genes was previously published in the lung eQTL study (n = 1,111). A signature of mild COPD containing 7 genes was also identified in the same study. The lung tissue gene signature of "severe COPD" (n = 70) contained 4,071 genes and was previously published. We detected 3,723 differentially expressed genes in the 6 month-exposure mice datasets (FDR <0.1). Of those, 184 genes (representing 48% of human smoking) and 1,003 (representing 27% of human COPD) were shared with the human smoking-related genes and the COPD severity-related genes, respectively. There was 4-fold over-representation of human and murine smoking-related genes (P = 6.7 × 10^-26) and a 1.4 fold in the severe COPD -related genes (P = 2.3 × 10^-12). There was no significant enrichment of the mice and human smoking-related genes in mild COPD signature. These data suggest that murine smoke models are strongly representative of molecular processes of human smoking but less of COPD.

MALAT1 via microRNA-17 regulation of insulin transcription is involved in the dysfunction of pancreatic β-cells induced by cigarette smoke extract

Cigarettes contain various chemicals with the potential to influence metabolic health. Exposure to cigarette smoke causes a dysfunction in pancreatic β-cells and impairs insulin production. However, the mechanisms for cigarette smoke-induced reduction of insulin remain largely unclear. Data from 558 patients with diabetes showed that, with smoking pack-years, homeostatic model assessment (HOMA)-β (a method for assessing β-cell function) decreased and that HOMA of insulin resistance increased. For β-cells (MIN6), cigarette smoke extract (CSE) increased the levels of thioredoxin-interacting protein (TXNIP) and the long noncoding (lnc)RNA, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), and downregulated the levels of the transcription factor, mafA, and microRNA (miR)-17. MALAT1, one of four lncRNAs predicted to regulate miR-17, was knocked down by small interfering RNA (siRNA). For these cells, an miR-17 mimic inhibited TXNIP and enhanced the production of insulin. Knockdown of MALAT1 induced an increase in miR-17, which suppressed TXNIP and promoted the production of insulin. In the sera of patients with diabetes who smoked, there were higher MALAT1 levels and lower miR-17 levels than in the sera of nonsmokers. Thus, CSE inhibits insulin production by upregulating TXNIP via MALAT1-mediated downregulation of miR-17, which provides an understanding of the processes involved in the reduced β-cells function caused by cigarette smoke.

A critical review of assays for hazardous components of air pollution

Increased mortality and diverse morbidities are globally associated with exposure to ambient air pollution (AAP), cigarette smoke (CS), and household air pollution (HAP). The AAP-CS-HAP aerosols present heterogeneous particulate matter (PM) of diverse chemical and physical characteristics. Some epidemiological models have assumed the same health hazards by PM weight for AAP, CS, and HAP regardless of the composition. While others have recognized that biological activities and toxicity will vary with components, we focus particularly on oxidation because of its major role in assay outcomes. Our review of PM assays considers misinterpretations of some chemical measures used for oxidative activity. Overall, there is low consistency across chemical and cell-based assays for oxidative and inflammatory activity. We also note gaps in understanding how much airborne PM of various sizes enter cells and organs. For CS, the body burden per cigarette may be much below current assumptions. Synergies shown for health hazards of AAP and CS suggest crosstalk in detoxification pathways mediated by AHR, NF-κB, and Nrf2. These complex genomic and biochemical interactions frustrate resolution of the toxicity of specific AAP components. We propose further strategies based on targeted gene expression based on cell-type differences.

β-Hydroxybutyrate improves β-cell mitochondrial function and survival

Pharmacological interventions aimed at improving outcomes in type 2 diabetes and achieving normoglycaemia, including insulin therapy, are increasingly common, despite the potential for substantial side effects. Carbohydrate-restricted diets that result in increased ketogenesis have effectively been used to improve insulin resistance, a fundamental feature of type 2 diabetes. In addition, limited evidence suggests that states of ketogenesis may also improve β-cell function in type 2 diabetics. Considering how little is known regarding the effects of ketones on β-cell function, we sought to determine the specific effects of β-Hydroxybutyrate (βHB) on pancreatic β-cell physiology and mitochondrial function. βHB treatment increased β-cell survival and proliferation, while also increasing mitochondrial mass, respiration and adenosine triphosphate (ATP) production. Despite these improvements, were unable to detect an increase in β-cell or islet insulin production and secretion. Collectively, these findings have two implications. Firstly, they indicate that β-cells have improved survival and proliferation in the midst of βHB, the circulating form of ketones. Secondly, insulin secretion does not appear to be directly related to apparent improvements in mitochondrial function and cellular proliferation.

Exercise Training Reverses Extrapulmonary Impairments in Smoke-exposed Mice

PURPOSE

Cigarette smoking is the main risk factor for chronic obstructive pulmonary disease and emphysema. However, evidence on the extrapulmonary effects of smoke exposure that precede lung impairments remains unclear at present, as are data on nonpharmacological treatments such as exercise training.

METHODS

Three groups of mice, including control (n = 10), smoking (n = 10), and smoking with 6 wk of high-intensity interval treadmill running (n = 11), were exposed to 20 wk of fresh air or whole-body cigarette smoke. Exercise capacity (peak oxygen uptake) and lung destruction (histology) were subsequently measured, whereas the heart, peripheral endothelium (aorta), and respiratory (diaphragm) and limb (extensor digitorum longus and soleus) skeletal muscles were assessed for in vivo and in vitro function, in situ mitochondrial respiration, and molecular alterations.

RESULTS

Smoking reduced body weight by 26% (P < 0.05) without overt airway destruction (P > 0.05). Smoking impaired exercise capacity by 15% while inducing right ventricular dysfunction by ~20%, endothelial dysfunction by ~20%, and diaphragm muscle weakness by ~15% (all P < 0.05), but these were either attenuated or reversed by exercise training (P < 0.05). Compared with controls, smoking mice had normal limb muscle and mitochondrial function (cardiac and skeletal muscle fibers); however, diaphragm measures of oxidative stress and protein degradation were increased by 111% and 65%, respectively (P < 0.05), but these were attenuated by exercise training (P < 0.05).

CONCLUSIONS

Prolonged cigarette smoking reduced exercise capacity concomitant with functional impairments to the heart, peripheral endothelium, and respiratory muscle that preceded the development of overt emphysema. However, high-intensity exercise training was able to reverse these smoke-induced extrapulmonary impairments.

High-Mobility Group Box 1 Disrupts Metabolic Function with Cigarette Smoke Exposure in a Ceramide-Dependent Manner

We have previously found that cigarette smoke disrupts metabolic function, in part, by increasing muscle ceramide accrual. To further our understanding of this, we sought to determine the role of the cytokine high-mobility group box 1 (HMGB1), which is increased with smoke exposure, in smoke-induced muscle metabolic perturbations. To test this theory, we determined HMGB1 from lungs of human smokers, as well as from lung cells from mice exposed to cigarette smoke. We also treated cells and mice directly with HMGB1, in the presence or absence of myriocin, an inhibitor of serine palmitoyltransferase, the rate-limiting enzyme in ceramide biosynthesis. Outcomes included assessments of insulin resistance and muscle mitochondrial function. HMGB1 was significantly increased in both human lungs and rodent alveolar macrophages. Further testing revealed that HMGB1 treatment elicited a widespread increase in ceramide species and reduction in myotube mitochondrial respiration, an increase in reactive oxygen species, and reduced insulin-stimulated Akt phosphorylation. Inhibition of ceramide biosynthesis with myriocin was protective. In mice, by comparing treatments of HMGB1 injections with or without myriocin, we found that HMGB1 injections resulted in increased muscle ceramides, especially C16 and C24, which were necessary for reduced muscle mitochondrial respiration and compromised insulin and glucose tolerance. In conclusion, HMGB1 may be a necessary intermediate in the ceramide-dependent metabolic consequences of cigarette smoke exposure.

LPS from P. gingivalis Negatively Alters Gingival Cell Mitochondrial Bioenergetics

OBJECTIVE

Oral inflammatory pathologies are linked to increased oxidative stress, thereby partly explaining their relevance in the etiology of systemic disorders. The purpose of this work was to determine the degree to which LPS from Porphyromonas gingivalis, the primary pathogen related to oral inflammation, altered gingival mitochondrial function and reactive oxygen species generation.

METHODS

Human gingival fibroblast (HGF-1) cells were treated with lipopolysaccharide of P. gingivalis. Mitochondrial function was determined via high-resolution respirometry.

P GINGIVALIS

Mitochondrial function was determined via high-resolution respirometry.

RESULTS

LPS-treated HGF-1 cells had significantly higher mitochondrial complex IV and higher rates of mitochondrial respiration. However, this failed to translate into greater ATP production, as ATP production was paradoxically diminished with LPS treatment. Nevertheless, production of the reactive H2O2 was elevated with LPS treatment.

CONCLUSIONS

LPS elicits an increase in gingival cell mitochondria content, with a subsequent increase in reactive oxygen species production (i.e., H2O2), despite a paradoxical reduction in ATP generation. These findings provide an insight into the nature of oxidative stress in oral inflammatory pathologies.

Plausible Roles for RAGE in Conditions Exacerbated by Direct and Indirect (Secondhand) Smoke Exposure

Approximately 1 billion people smoke worldwide, and the burden placed on society by primary and secondhand smokers is expected to increase. Smoking is the leading risk factor for myriad health complications stemming from diverse pathogenic programs. First- and second-hand cigarette smoke contains thousands of constituents, including several carcinogens and cytotoxic chemicals that orchestrate chronic inflammatory responses and destructive remodeling events. In the current review, we outline details related to compromised pulmonary and systemic conditions related to smoke exposure. Specifically, data are discussed relative to impaired lung physiology, cancer mechanisms, maternal-fetal complications, cardiometabolic, and joint disorders in the context of smoke exposure exacerbations. As a general unifying mechanism, the receptor for advanced glycation end-products (RAGE) and its signaling axis is increasingly considered central to smoke-related pathogenesis. RAGE is a multi-ligand cell surface receptor whose expression increases following cigarette smoke exposure. RAGE signaling participates in the underpinning of inflammatory mechanisms mediated by requisite cytokines, chemokines, and remodeling enzymes. Understanding the biological contributions of RAGE during cigarette smoke-induced inflammation may provide critically important insight into the pathology of lung disease and systemic complications that combine during the demise of those exposed.

Early exposure to thirdhand cigarette smoke affects body mass and the development of immunity in mice

Thirdhand smoke (THS) is the fraction of cigarette smoke that persists in indoor environments after smoking. We investigated the effects of neonatal and adult THS exposure on bodyweight and blood cell populations in C57BL/6 J mice. At the end of neonatal exposure, THS-treated male and female mice had significantly lower bodyweight than their respective control mice. However, five weeks after neonatal exposure ended, THS-treated mice weighed the same as controls. In contrast, adult THS exposure did not change bodyweight of mice. On the other hand, both neonatal and adult THS exposure had profound effects on the hematopoietic system. Fourteen weeks after neonatal THS exposure ended, eosinophil number and platelet volume were significantly higher, while hematocrit, mean cell volume, and platelet counts were significantly lower compared to control. Similarly, adult THS exposure also decreased platelet counts and increased neutrophil counts. Moreover, both neonatal and adult THS exposure caused a significant increase in percentage of B-cells and significantly decreased percentage of myeloid cells. Our results demonstrate that neonatal THS exposure decreases bodyweight and that THS exposure induces persistent changes in the hematopoietic system independent of age at exposure. These results also suggest that THS exposure may have adverse effects on human health.

Early exposure to thirdhand cigarette smoke affects body mass and the development of immunity in mice

Thirdhand smoke (THS) is the fraction of cigarette smoke that persists in indoor environments after smoking. We investigated the effects of neonatal and adult THS exposure on bodyweight and blood cell populations in C57BL/6 J mice. At the end of neonatal exposure, THS-treated male and female mice had significantly lower bodyweight than their respective control mice. However, five weeks after neonatal exposure ended, THS-treated mice weighed the same as controls. In contrast, adult THS exposure did not change bodyweight of mice. On the other hand, both neonatal and adult THS exposure had profound effects on the hematopoietic system. Fourteen weeks after neonatal THS exposure ended, eosinophil number and platelet volume were significantly higher, while hematocrit, mean cell volume, and platelet counts were significantly lower compared to control. Similarly, adult THS exposure also decreased platelet counts and increased neutrophil counts. Moreover, both neonatal and adult THS exposure caused a significant increase in percentage of B-cells and significantly decreased percentage of myeloid cells. Our results demonstrate that neonatal THS exposure decreases bodyweight and that THS exposure induces persistent changes in the hematopoietic system independent of age at exposure. These results also suggest that THS exposure may have adverse effects on human health.

Lipopolysaccharide Disrupts Mitochondrial Physiology in Skeletal Muscle via Disparate Effects on Sphingolipid Metabolism

Lipopolysaccharides (LPS) are prevalent pathogenic molecules that are found within tissues and blood. Elevated circulating LPS is a feature of obesity and sepsis, both of which are associated with mitochondrial abnormalities that are key pathological features of LPS excess. However, the mechanism of LPS-induced mitochondrial alterations remains poorly understood. Herein we demonstrate the necessity of sphingolipid accrual in mediating altered mitochondrial physiology in skeletal muscle following LPS exposure. In particular, we found LPS elicited disparate effects on the sphingolipids dihydroceramides (DhCer) and ceramides (Cer) in both cultured myotubes and in muscle of LPS-injected mice. Although LPS-treated myotubes had reduced DhCer and increased Cer as well as increased mitochondrial respiration, muscle from LPS-injected mice manifested a reverse trend, namely elevated DhCer, but reduced Cer as well as reduced mitochondrial respiration. In addition, we found that LPS treatment caused mitochondrial fission, likely via dynamin-related protein 1, and increased oxidative stress. However, inhibition of de novo sphingolipid biosynthesis via myriocin protected normal mitochondrial function in spite of LPS, but inhibition of DhCer desaturase 1, which increases DhCer, but not Cer, exacerbated mitochondrial respiration with LPS. In an attempt to reconcile the incongruent effects of LPS in isolated muscle cells and whole muscle tissue, we incubated myotubes with conditioned medium from treated macrophages. In contrast to direct myotube LPS treatment, conditioned medium from LPS-treated macrophages reduced myotube respiration, but this was again mitigated with sphingolipid inhibition. Thus, macrophage sphingolipid production appears to be necessary for LPS-induced mitochondrial alterations in skeletal muscle tissue.

Functional Effects of Cigarette Smoke-Induced Changes in Airway Smooth Muscle Mitochondrial Morphology

Long-term exposure to cigarette smoke (CS) triggers airway hyperreactivity and remodeling, effects that involve airway smooth muscle (ASM). We previously showed that CS destabilizes the networked morphology of mitochondria in human ASM by regulating the expression of mitochondrial fission and fusion proteins via multiple signaling mechanisms. Emerging data link regulation of mitochondrial morphology to cellular structure and function. We hypothesized that CS-induced changes in ASM mitochondrial morphology detrimentally affect mitochondrial function, leading to CS effects on contractility and remodeling. Here, ASM cells were exposed to 1% cigarette smoke extract (CSE) for 48 h to alter mitochondrial fission/fusion, or by inhibiting the fission protein Drp1 or the fusion protein Mfn2. Mitochondrial function was assessed via changes in bioenergetics or altered rates of proliferation and apoptosis. Our results indicate that both exposure to CS and inhibition of mitochondrial fission/fusion proteins affect mitochondrial function (i.e., energy metabolism, proliferation, and apoptosis) in ASM cells. In vivo, the airways in mice chronically exposed to CS are thickened and fibrotic, and the expression of proteins involved in mitochondrial function is dramatically altered in the ASM of these mice. We conclude that CS-induced changes in mitochondrial morphology (fission/fusion balance) correlate with mitochondrial function, and thus may control ASM proliferation, which plays a central role in airway health. J. Cell. Physiol. 232: 1053-1068, 2017. © 2016 Wiley Periodicals, Inc.

Oral Gingival Cell Cigarette Smoke Exposure Induces Muscle Cell Metabolic Disruption

Cigarette smoke exposure compromises health through damaging multiple physiological systems, including disrupting metabolic function. The purpose of this study was to determine the role of oral gingiva in mediating the deleterious metabolic effects of cigarette smoke exposure on skeletal muscle metabolic function. Using an in vitro conditioned medium cell model, skeletal muscle cells were incubated with medium from gingival cells treated with normal medium or medium containing suspended cigarette smoke extract (CSE). Following incubation of muscle cells with gingival cell conditioned medium, muscle cell mitochondrial respiration and insulin signaling and action were determined as an indication of overall muscle metabolic health. Skeletal muscle cells incubated with conditioned medium of CSE-treated gingival cells had a profound reduction in mitochondrial respiration and respiratory control. Furthermore, skeletal muscle cells had a greatly reduced response in insulin-stimulated Akt phosphorylation and glycogen synthesis. Altogether, these results provide a novel perspective on the mechanism whereby cigarette smoke affects systemic metabolic function. In conclusion, we found that oral gingival cells treated with CSE create an altered milieu that is sufficient to both disrupted skeletal muscle cell mitochondrial function and insulin sensitivity.

A Standardized Method for the Preparation of a Gas Phase Extract of Cigarette Smoke

The gas phase of cigarette smoke is important from the viewpoint of human health, because it can pass through alveolar epithelium and enter the circulation. There is no standard method for the preparation of a gas phase extract of cigarette smoke (CSE), although CSE is widely used for research instead of whole cigarette smoke. We have established a standard method for the preparation of CSE. One cigarette per trial is continuously combusted under a reduced pressure generated by an aspiration pump with a velocity of 1.050 L/min: the main stream of the smoke is passed through a Cambridge filter to remove tar, and subsequently, bubbled through a glass ball filter (pore size, 20-30 µm) into 15 mL of phosphate-buffered saline (PBS). To express the concentration of CSE, a virtual tar concentration is introduced, which is calculated assuming that tar trapped on the Cambridge filter is dissolved in the PBS. CSEs prepared from smaller numbers of cigarettes (original virtual tar concentration≤15 mg/mL) show similar concentration-response curves for cytotoxicity versus virtual tar concentrations. CSEs prepared from various brands of cigarettes and by different smoking regimes (continuous and puff smoking) show similar cytotoxic potency if the virtual tar concentrations are the same. In conclusion, using the standardized method for CSE preparation in combination with the virtual tar concentration, it becomes possible to simply and rapidly prepare standard CSEs with defined concentrations from any brand of cigarettes, which are toxicologically equivalent to CSE prepared by puff smoking.

Cardiomyocyte mitochondrial respiration is reduced by receptor for advanced glycation end-product signaling in a ceramide-dependent manner

Cigarette smoke exposure is associated with an increased risk of cardiovascular complications. The role of advanced glycation end products (AGEs) is already well established in numerous comorbidities, including cardiomyopathy. Given the role of AGEs and their receptor, RAGE, in activating inflammatory pathways, we sought to determine whether ceramides could be a mediator of RAGE-induced altered heart mitochondrial function. Using an in vitro model, we treated H9C2 cardiomyocytes with the AGE carboxy-methyllysine before mitochondrial respiration assessment. We discovered that mitochondrial respiration was significantly impaired in AGE-treated cells, but not when cotreated with myriocin, an inhibitor of de novo ceramide biosynthesis. Moreover, we exposed wild-type and RAGE knockout mice to secondhand cigarette smoke and found reduced mitochondrial respiration in the left ventricular myocardium from wild-type mice, but RAGE knockout mice were protected from this effect. Finally, conditional overexpression of RAGE in the lungs of transgenic mice elicited a robust increase in left ventricular ceramides in the absence of smoke exposure. Taken together, these findings suggest a RAGE-ceramide axis as an important contributor to AGE-mediated disrupted cardiomyocyte mitochondrial function.

Cigarette smoke increases cardiomyocyte ceramide accumulation and inhibits mitochondrial respiration

Background

Cigarette smoking is a common and lethal worldwide habit, with considerable mortality stemming from its deleterious effects on heart function. While current theories posit altered blood lipids and fibrinogen metabolism as likely mediators, none have explored the role of the sphingolipid ceramide in exacerbating heart function with smoke exposure. Ceramide production is a consequence of cigarette smoke in the lung, and considering ceramide’s harmful effects on mitochondrial function, we sought to elucidate the role of ceramide in mediating smoke-induced altered heart mitochondrial respiration.

Methods

Lung cells (A549) were exposed to cigarette smoke extract (CSE) and heart cells (H9C2) were exposed to the lung-cell conditioned medium. Adult male mice were exposed sidestream cigarette smoke for 8 wk with dietary intervention and ceramide inhibition. Ceramides and heart cell or myocardial mitochondrial respiration were determined.

Results

Lung cell cultures revealed a robust response to cigarette smoke extract in both production and secretion of ceramides. Heart cells incubated with lung-cell conditioned medium revealed a pronounced inhibition of myocardial mitochondrial respiration, though this effect was mitigated with ceramide inhibition via myriocin. In vivo, heart ceramides increased roughly 600% in adult mice with long-term sidestream cigarette smoke exposure. This resulted in a significant ceramide-dependent reduction in left myocardial mitochondrial respiration, as heart mitochondria from the mice exposed to both smoke and myriocin injections respired normally.

Conclusions

These results suggest ceramide to be an important mediator of altered myocardial mitochondrial function with cigarette smoke exposure. Thus, anti-ceramide therapies might be considered in the future to protect heart mitochondrial function with smoke exposure.