Cigarette smoke worsens lung inflammation and impairs resolution of influenza infection in mice.

BACKGROUND: Cigarette smoke has both pro-inflammatory and immunosuppressive effects. Both active and passive cigarette smoke exposure are linked to an increased incidence and severity of respiratory virus infections, but underlying mechanisms are not well defined. We hypothesized, based on prior gene expression profiling studies, that upregulation of pro-inflammatory mediators by short term smoke exposure would be protective against a subsequent influenza infection. METHODS: BALB/c mice were subjected to whole body smoke exposure with 9 cigarettes/day for 4 days. Mice were then infected with influenza A (H3N1, Mem71 strain), and analyzed 3 and 10 days later (d3, d10). These time points are the peak and resolution (respectively) of influenza infection. RESULTS: Inflammatory cell influx into the bronchoalveolar lavage (BALF), inflammatory mediators, proteases, histopathology, viral titres and T lymphocyte profiles were analyzed. Compared to smoke or influenza alone, mice exposed to smoke and then influenza had more macrophages, neutrophils and total lymphocytes in BALF at d3, more macrophages in BALF at d10, lower net gelatinase activity and increased activity of tissue inhibitor of metalloprotease-1 in BALF at d3, altered profiles of key cytokines and CD4+ and CD8+ T lymphocytes, worse lung pathology and more virus-specific, activated CD8+ T lymphocytes in BALF. Mice smoke exposed before influenza infection had close to 10-fold higher lung virus titres at d3 than influenza alone mice, although all mice had cleared virus by d10, regardless of smoke exposure. Smoke exposure caused temporary weight loss and when smoking ceased after viral infection, smoke and influenza mice regained significantly less weight than smoke alone mice. CONCLUSION: Smoke induced inflammation does not protect against influenza infection.In most respects, smoke exposure worsened the host response to influenza. This animal model may be useful in studying how smoke worsens respiratory viral infections.

Long-term cigarette smoke exposure increases uncoupling protein expression but reduces energy intake.

The appetite suppressing effect of tobacco is a major driver of smoking behaviour; however few studies have addressed the effects of chronic cigarette smoke exposure (SE) on appetite, body weight and metabolic markers. We compared the effects of SE to equivalent food restriction (pair-fed, PF), against sham-exposure, on body weight, adiposity, cytokines, and levels of uncoupling proteins (UCP) and brain neuropeptide Y (NPY) in male Balb/C mice. SE rapidly induced anorexia, and after 12 weeks, SE and PF groups were lighter than control animals (23.9+/-0.2, 25.5+/-0.5, 26.8+/-0.4 g respectively, P<0.05). White fat (WAT) masses were reduced by both SE and PF. Plasma leptin and insulin were reduced in SE mice; insulin was further reduced by PF. Brown fat UCP1 and 3 mRNA were increased in SE animals relative to PF animals, possibly promoting thermogenesis. WAT mRNA expression of the inflammatory cytokine, TNFalpha was doubled by SE, while IL-6 was reduced by both PF and SE. Hypothalamic NPY content was increased by SE (89.3+/-2.8 vs. 75.9+/-2.4 ng control, P<0.05), and more by PF (100.7+/-3.4 ng, P<0.05 compared to both groups), suggesting disinhibition due to reduced adipose derived leptin. In contrast to equivalent food restriction, cigarette smoke exposure reduced body weight and total hypothalamic NPY, and increased thermogenesis and markers of inflammation. The suppressed hypothalamic NPY and increased UCPs may contribute to the spontaneous hypophagia and extra weight loss in SE animals. These findings contribute to our understanding of weight loss in smoking-related lung disease, suggesting a greater impact than that due to anorexia alone.

Granulocyte-CSF links destructive inflammation and comorbidities in obstructive lung disease.

Chronic obstructive pulmonary disease (COPD) is an incurable inflammatory lung disease that afflicts millions of people worldwide, and it is the fourth leading cause of death. Systemic comorbidities affecting the heart, skeletal muscle, bone, and metabolism are major contributors to morbidity and mortality. Given the surprising finding in large prospective clinical biomarker studies that peripheral white blood cell count is more closely associated with disease than inflammatory biomarkers, we probed the role of blood growth factors. Using the SHIP-1-deficient COPD mouse model, which manifests a syndrome of destructive lung disease and a complex of comorbid pathologies, we have identified a critical and unexpected role for granulocyte-CSF (G-CSF) in linking these conditions. Deletion of G-CSF greatly reduced airway inflammation and lung tissue destruction, and attenuated systemic inflammation, right heart hypertrophy, loss of fat reserves, and bone osteoporosis. In human clinical translational studies, bronchoalveolar lavage fluid of patients with COPD demonstrated elevated G-CSF levels. These studies suggest that G-CSF may play a central and unforeseen pathogenic role in COPD and its complex comorbidities, and identify G-CSF and its regulators as potential therapeutic targets.

Therapeutic prospects to treat skeletal muscle wasting in COPD (chronic obstructive lung disease).

Chronic obstructive pulmonary disease (COPD) is an incurable group of lung diseases characterised by progressive airflow limitation and loss of lung function, which lead to profound disability. It is mostly caused by cigarette smoke. Although COPD is one of the most prevalent diseases worldwide and its incidence is increasing, current therapies do little to improve the condition. Much current research focuses on strategies to halt the accelerated rate of decline in lung function that occurs in the disease. However, as most symptoms occur when the lungs are already extensively and irreversibly damaged, it is uncertain whether an agent able to slow or halt decline in lung function would actually provide relief to COPD patients. As lung function worsens, systemic comorbidities contribute markedly to disability. Loss of lean body mass (skeletal muscle) has recently been identified as a major determinant of disability in COPD and an independent predictor of mortality. In contrast to lung structure damage, skeletal muscle retains regenerative capacity in COPD. In this review, we discuss mechanisms of wasting in COPD, focusing on therapeutic strategies that might improve the health and productive life expectancy of COPD patients by improving skeletal muscle mass and function. Single or combination approaches exploiting the suppression of procatabolic inflammatory mediators, inhibition of ubiquitin ligases, repletion of anabolic hormones and growth factors, inhibition of myoblast apoptosis, remediation of systemic oxidative stress and promotion of repair, and regeneration via stimulation of satellite cell differentiation hold considerable therapeutic promise.

Regulation of hypothalamic NPY by diet and smoking.

Appetite is regulated by a number of hypothalamic neuropeptides including neuropeptide Y (NPY), a powerful feeding stimulator that responds to feeding status, and drugs such as nicotine and cannabis. There is debate regarding the extent of the influence of obesity on hypothalamic NPY. We measured hypothalamic NPY in male Sprague-Dawley rats after short or long term exposure to cafeteria-style high fat diet (32% energy as fat) or laboratory chow (12% fat). Caloric intake and body weight were increased in the high fat diet group, and brown fat and white fat masses were significantly increased after 2 weeks. Hypothalamic NPY concentration was only significantly decreased after long term consumption of the high fat diet. Nicotine decreases food intake and body weight, with conflicting effects on hypothalamic NPY reported. Body weight, plasma hormones and brain NPY were investigated in male Balb/c mice exposed to cigarette smoke for 4 days, 4 and 12 weeks. Food intake was significantly decreased by smoke exposure (2.32+/-0.03g/24h versus 2.71+/-0.04g/24h in control mice (non-smoke exposed) at 12 weeks). Relative to control mice, smoke exposure led to greater weight loss, while pair-feeding the equivalent amount of chow caused an intermediate weight loss. Chronic smoke exposure, but not pair-feeding, was associated with decreased hypothalamic NPY concentration, suggesting an inhibitory effect of cigarette smoking on brain NPY levels. Thus, consumption of a high fat diet and smoke exposure reprogram hypothalamic NPY. Reduced NPY may contribute to the anorexic effect of smoke exposure.

Emerging therapies for the treatment of skeletal muscle wasting in chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease that constitutes a major global health burden. A significant proportion of patients experience skeletal muscle wasting and loss of strength as a comorbidity of their COPD, a condition that severely impacts on their quality of life and survival. At present, the lung pathology is considered to be largely irreversible; however, the inherent adaptability of muscle tissue offers therapeutic opportunities to tackle muscle wasting and potentially reverse or delay the progression of this aspect of the disease, to improve patients' quality of life. Muscle wasting in COPD is complex, with contributions from a number of factors including inflammatory cytokines, oxidative stress, growth and anabolic hormones, nutritional status, and physical activity. In this review, we discuss current and emerging therapeutic approaches to treat muscle wasting in COPD, including a number of pharmacological therapies that are in development for muscle atrophy in other pathological states that could be of relevance for treating muscle wasting in COPD patients.

Serum Amyloid A Induces Toll-Like Receptor 2-Dependent Inflammatory Cytokine Expression and Atrophy in C2C12 Skeletal Muscle Myotubes.

BACKGROUND: Skeletal muscle wasting is an important comorbidity of Chronic Obstructive Pulmonary Disease (COPD) and is strongly correlated with morbidity and mortality. Patients who experience frequent acute exacerbations of COPD (AECOPD) have more severe muscle wasting and reduced recovery of muscle mass and function after each exacerbation. Serum levels of the pro-inflammatory acute phase protein Serum Amyloid A (SAA) can rise more than 1000-fold in AECOPD and are predictively correlated with exacerbation severity. The direct effects of SAA on skeletal muscle are poorly understood. Here we have examined SAA effects on pro-inflammatory cachectic cytokine expression (IL-6 and TNFα) and atrophy in C2C12 myotubes. RESULTS: SAA increased IL-6 (31-fold) and TNFα (6.5-fold) mRNA levels compared to control untreated cells after 3h of SAA treatment, and increased secreted IL-6 protein at 24h. OxPAPC, a dual TLR2 and TLR4 inhibitor, reduced the response to SAA by approximately 84% compared to SAA alone, and the TLR2 neutralising antibody T2.5 abolished SAA-induced expression of IL-6, indicating that SAA signalling in C2C12 myotubes is primarily via TLR2. SAA also reduced myotube width by 10-13% and induced a 2.5-fold increase in the expression of the muscle atrophy gene Atrogin-1, suggesting direct effects of SAA on muscle wasting. Blocking of TLR2 inhibited the SAA-induced decrease in myotube width and Atrogin-1 gene expression, indicating that SAA induces atrophy through TLR2. CONCLUSIONS: These data demonstrate that SAA stimulates a robust pro-inflammatory response in skeletal muscle myotubes via the TLR2-dependent release of IL-6 and TNFα. Furthermore, the observed atrophy effects indicate that SAA could also be directly contributing to the wasting and poor recovery of muscle mass. Therapeutic strategies targeting this SAA-TLR2 axis may therefore ameliorate muscle wasting in AECOPD and a range of other inflammatory conditions associated with loss of muscle mass.

Feeding responses to a melanocortin agonist and antagonist in obesity induced by a palatable high-fat diet.

Hypothalamic melanocortins are critical for the control of food intake, and alterations in POMC mRNA have been described in genetic models of obesity. However, the time course of changes in brain transmitters over the development of dietary obesity is less clear. Therefore, we examined the effect of diet-induced obesity on hypothalamic alpha-MSH content and feeding responsiveness to synthetic melanocortins. Male Sprague-Dawley rats fed a high-fat cafeteria diet (30% fat) or chow (5% fat) for 4 or 12 weeks were implanted with intracerebroventricular cannulae and feeding responses to the MC3/4R agonist MTII (0.5 nmol) and the selective MC4R antagonist HS014 (0.8 nmol) were determined. MTII had a long-lasting inhibitory effect on food intake. Chronically overfed animals had a significantly exaggerated inhibitory feeding response 15 and 24 h after MTII injection and lost more body weight (15 +/- 3 g) compared to control rats (4 +/- 4 g; P < 0.05). Daytime administration of HS014 significantly increased food intake in all rats to the same extent (P < 0.05). No change in hypothalamic alpha-MSH content was observed after 2 or 12 weeks of high-fat diet. The observation of increased responsiveness to the melanocortin agonist, in the face of a high-fat diet, suggests melanocortin analogues may have potential for the pharmacological treatment of obesity.

IL-17A and serum amyloid A are elevated in a cigarette smoke cessation model associated with the persistence of pigmented macrophages, neutrophils and activated NK cells.

While global success in cessation advocacy has seen smoking rates fall in many developed countries, persistent lung inflammation in ex-smokers is an increasingly important clinical problem whose mechanistic basis remains poorly understood. In this study, candidate effector mechanisms were assessed in mice exposed to cigarette smoke (CS) for 4 months following cessation from long term CS exposure. BALF neutrophils, CD4+ and CD8+ T cells and lung innate NK cells remained significantly elevated following smoking cessation. Analysis of neutrophil mobilization markers showed a transition from acute mediators (MIP-2α, KC and G-CSF) to sustained drivers of neutrophil and macrophage recruitment and activation (IL-17A and Serum Amyoid A (SAA)). Follicle-like lymphoid aggregates formed with CS exposure and persisted with cessation, where they were in close anatomical proximity to pigmented macrophages, whose number actually increased 3-fold following CS cessation. This was associated with the elastolytic protease, MMP-12 (macrophage metallo-elastase) which remained significantly elevated post-cessation. Both GM-CSF and CSF-1 were significantly increased in the CS cessation group relative to the control group. In conclusion, we show that smoking cessation mediates a transition to accumulation of pigmented macrophages, which may contribute to the expanded macrophage population observed in COPD. These macrophages together with IL-17A, SAA and innate NK cells are identified here as candidate persistence determinants and, we suggest, may represent specific targets for therapies directed towards the amelioration of chronic airway inflammation.

The lung inflammation and skeletal muscle wasting induced by subchronic cigarette smoke exposure are not altered by a high-fat diet in mice.

Obesity and cigarette smoking independently constitute major preventable causes of morbidity and mortality and obesity is known to worsen lung inflammation in asthma. Paradoxically, higher body mass index (BMI) is associated with reduced mortality in smoking induced COPD whereas low BMI increases mortality risk. To date, no study has investigated the effect of a dietary-induced obesity and cigarette smoke exposure on the lung inflammation and loss of skeletal muscle mass in mice. Male BALB/c mice were exposed to 4 cigarettes/day, 6 days/week for 7 weeks, or sham handled. Mice consumed either standard laboratory chow (3.5 kcal/g, 12% fat) or a high fat diet (HFD, 4.3 kcal/g, 32% fat). Mice exposed to cigarette smoke for 7 weeks had significantly more inflammatory cells in the BALF (P<0.05) and the mRNA expression of pro-inflammatory cytokines and chemokines was significantly increased (P<0.05); HFD had no effect on these parameters. Sham- and smoke-exposed mice consuming the HFD were significantly heavier than chow fed animals (12 and 13%, respectively; P<0.05). Conversely, chow and HFD fed mice exposed to cigarette smoke weighed 16 and 15% less, respectively, compared to sham animals (P<0.05). The skeletal muscles (soleus, tibialis anterior and gastrocnemius) of cigarette smoke-exposed mice weighed significantly less than sham-exposed mice (P<0.05) and the HFD had no protective effect. For the first time we report that cigarette smoke exposure significantly decreased insulin-like growth factor-1 (IGF-1) mRNA expression in the gastrocnemius and tibialis anterior and IGF-1 protein in the gastrocnemius (P<0.05). We have also shown that cigarette smoke exposure reduced circulating IGF-1 levels. IL-6 mRNA expression was significantly elevated in all three skeletal muscles of chow fed smoke-exposed mice (P<0.05). In conclusion, these findings suggest that a down-regulation in local IGF-1 may be responsible for the loss of skeletal muscle mass following cigarette smoke exposure in mice.

Detrimental metabolic effects of combining long-term cigarette smoke exposure and high-fat diet in mice.

Obesity and cigarette smoking are both important risk factors for insulin resistance, cardiovascular disease, and cancer. Smoking reduces appetite, which makes many people reluctant to quit. Few studies have documented the metabolic impact of combined smoke exposure (se) and high-fat-diet (HFD). Neuropeptide Y (NPY) is a powerful hypothalamic feeding stimulator that promotes obesity. We investigated how chronic se affects caloric intake, adiposity, plasma hormones, inflammatory mediators, and hypothalamic NPY peptide in animals fed a palatable HFD. Balb/c mice (5 wk old, male) were exposed to smoke (2 cigarettes, twice/day, 6 days/wk, for 7 wk) with or without HFD. Sham-exposed mice were handled similarly without se. Plasma leptin, hypothalamic NPY, and adipose triglyceride lipase (ATGL) mRNA were measured. HFD induced a 2.3-fold increase in caloric intake, increased adiposity, and glucose in both sham and se cohorts. Smoke exposure decreased caloric intake by 23%, with reduced body weight in both dietary groups. Fat mass and glucose were reduced only by se in the chow-fed animals. ATGL mRNA was reduced by HFD in se animals. Total hypothalamic NPY was reduced by HFD, but only in sham-exposed animals; se increased arcuate NPY. We conclude that although se ameliorated hyperphagia and reversed the weight gain associated with HFD, it failed to reverse fat accumulation and hyperglycemia. The reduced ATGL mRNA expression induced by combined HFD and se may contribute to fat retention. Our data support a powerful health message that smoking in the presence of an unhealthy Western diet increases metabolic disorders and fat accumulation.

Cigarette smoke exposure reprograms the hypothalamic neuropeptide Y axis to promote weight loss.

RATIONALE: Despite irrefutable epidemiologic evidence, cigarette smoking remains the major preventable cause of lung disease morbidity worldwide. The appetite-suppressing effect of tobacco is a major behavioral determinant of smoking, but the underlying molecular and neuronal mechanisms are not understood. Neuropeptide Y (NPY) is an orexigenic neuropeptide, whose activity in the hypothalamic paraventricular nucleus governs appetite. OBJECTIVES: To compare the effects of smoke exposure and equivalent food restriction on body weight, organ mass, cytokines, and brain NPY in Balb/c mice. METHODS: A pair-feeding study design compared smoke exposure (4 wk; 1 cigarette, 3 x /d, 5 d/wk) to equivalent food restriction (pair-fed) and sham-exposed control mice. RESULTS: Smoke exposure rapidly induced mild anorexia. After 4 wk, smoke-exposed and pair-fed groups were lighter than control mice (22.0 +/- 0.2, 23.2 +/- 0.5, 24.9 +/- 0.4 g, respectively; p < 0.05). Brown and white fat masses were only reduced by smoke exposure, relative to control mice. NPY concentration in the paraventricular nucleus was significantly and paradoxically reduced by smoke exposure, despite lower plasma leptin concentrations; this was not observed in the pair-fed group experiencing 19% food restriction. Adipose mRNA expression of uncoupling proteins, inflammatory cytokines interleukin 6 and tumor necrosis factor alpha, and adipose triglyceride lipase was decreased by smoke exposure, and even lower in pair-fed mice. CONCLUSIONS: In contrast to food restriction, smoke exposure caused a reduction in hypothalamic NPY and fat mass, and regulated adipose cytokines. These findings may contribute to understanding weight loss in smoking-related lung disease and in the design of more effective smoking cessation strategies.

Adaptive responses in hypothalamic neuropeptide Y in the face of prolonged high-fat feeding in the rat.

While a dysregulation in neuropeptide Y (NPY) signaling has been described in rodent models of obesity, few studies have investigated the time-course of changes in NPY content and responsiveness during development of diet-induced obesity. Therefore we investigated the effect of differing lengths (2-17 weeks) of high-fat diet on hypothalamic NPY peptide content, release and NPY-induced hyperphagia. Male Sprague-Dawley rats (211 +/- 3 g) were fed either a high-fat diet (30% fat) or laboratory chow (5% fat). Animals were implanted with intracerebroventricular cannulae to investigate feeding responses to NPY (0.5 nmol, 1 nmol) after 4 or 12 weeks of diet. At the earlier stage of obesity, NPY-induced hyperphagia was not altered; however, animals maintained on the high-fat diet for the longer duration were hyper-responsive to NPY, compared to chow-fed control rats (p < 0.05). Overall, hypothalamic NPY peptide content tended to be decreased from 9 to 17 weeks of diet (p < 0.05). Total hypothalamic NPY content was negatively correlated with plasma leptin concentration (p < 0.05), suggesting the hypothalamic NPY system remains responsive to leptin's inhibitory signal. In addition, hypothalamic NPY overflow was significantly reduced in high-fat fed animals (p < 0.05). Together these results suggest a reduction in hypothalamic NPY activity in high-fat fed animals, perhaps in an attempt to restore energy balance.

Inhibitory effect of apelin-12 on nocturnal food intake in the rat.

Apelin, the endogenous peptide ligand of the APJ receptor, is expressed in brain regions implicated in food and water intake. This study reports for the first time, the effect of apelin-12, one of the most potent apelin peptides, on spontaneous (nocturnal) feeding. Randomised intracerebroventricular injection of 1, 3 and 10 nmol apelin-12 or saline vehicle, 10 min prior to lights out, led to dose-dependent reductions in food intake 2-4 h after injection (n = 7; p < 0.05). This suggests that apelin-12 exerts a delayed inhibitory effect on nocturnal feeding. Relative to saline, no effect was observed on total 24-h food intake post injection. In contrast, day-time administration of 10 nmol apelin-12 to satiated rats stimulated feeding (n = 5-11; p < 0.05); lower doses had no effect. No changes in water intake were observed after apelin-12. These results suggest that apelin is involved in the central control of feeding.