Peter Mancuso

Leptin-Deficient Mice Exhibit Impaired Host Defense in Gram-Negative Pneumonia

Leptin is an adipocyte-derived hormone that is secreted in correlation with total body lipid stores. Serum leptin levels are lowered by the loss of body fat mass that would accompany starvation and malnutrition. Recently, leptin has been shown to modulate innate immune responses such as macrophage phagocytosis and cytokine synthesis in vitro. To determine whether leptin plays a role in the innate host response against Gram-negative pneumonia in vivo, we compared the responses of leptin-deficient and wild-type mice following an intratracheal challenge of Klebsiella pneumoniae. Following K. pneumoniae administration, we observed increased leptin levels in serum, bronchoalveolar lavage fluid, and whole lung homogenates. In a survival study, leptin-deficient mice, as compared with wild-type mice, exhibited increased mortality following K. pneumoniae administration. The increased susceptibility to K. pneumoniae in the leptin-deficient mice was associated with reduced bacterial clearance and defective alveolar macrophage phagocytosis in vitro. The exogenous addition of very high levels of leptin (500 ng/ml) restored the defect in alveolar macrophage phagocytosis of K. pneumoniae in vitro. While there were no differences between wild-type and leptin-deficient mice in lung homogenate cytokines TNF-α, IL-12, or macrophage-inflammatory protein-2 after K. pneumoniae administration, leukotriene synthesis in lung macrophages from leptin-deficient mice was reduced. Leukotriene production was restored by the addition of exogenous leptin (500 ng/ml) to macrophages in vitro. This study demonstrates for the first time that leptin-deficient mice display impaired host defense in bacterial pneumonia that may be due to a defect in alveolar macrophage phagocytosis and leukotriene synthesis.

Leukotrienes: underappreciated mediators of innate immune responses.

Leukotrienes are bronchoconstrictor and vasoactive lipid mediators that are targets in the treatment of asthma. Although they are increasingly recognized to exert broad proinflammatory effects, their role in innate immune responses is less well appreciated. These molecules are indeed synthesized by resident and recruited leukocytes during infection. Acting via cell surface G protein-coupled receptors and subsequent intracellular signaling events, they enhance leukocyte accumulation, phagocyte capacity for microbial ingestion and killing, and generation of other proinflammatory mediators. Interestingly, a variety of acquired states of immunodeficiency, such as HIV infection and malnutrition, are characterized by a relative deficiency of leukotriene synthesis. The data reviewed herein point to leukotrienes as underappreciated yet highly relevant mediators of innate immunity.

Leukotriene B4 augments neutrophil phagocytosis of Klebsiella pneumoniae

ABSTRACT Neutrophils play a critical role in the clearance of bacteria from the lung and other organs by their capacity for phagocytosis and killing. Previously, we identified an important role for the leukotrienes in rat alveolar macrophage phagocytosis ofKlebsiella pneumoniae. In this report, we explored the possibility that the leukotrienes play an important role in phagocytosis by neutrophils as well. Inhibition of endogenous leukotriene synthesis by 5-lipoxygenase knockout in mice or by pharmacologic means in human peripheral blood neutrophils attenuated phagocytosis of opsonized K. pneumoniae. Reduced phagocytosis was also observed in human neutrophils pretreated with a leukotriene B4 receptor but not a cysteinyl-leukotriene receptor antagonist. While leukotriene B4 reconstituted defective phagocytosis in leukotriene-deficient neutrophils and enhanced phagocytosis in neutrophils capable of leukotriene synthesis, leukotriene C4, leukotriene D4, 5-hydroperoxyeicosatetraenoic acid, and 5-oxo-eicosatetraenoic acid were ineffective. To determine the opsonin dependence of the leukotriene B4 augmentation of phagocytosis, we assessed the ability of leukotriene B4 to modulate neutrophil phagocytosis and the adherence of sheep erythrocytes opsonized with immunoglobulin G or the complement fragment C3bi. While leukotriene B4 augmented both Fc receptor- and complement receptor-mediated phagocytosis, increased adherence to leukotriene B4-treated neutrophils was limited to complement opsonized targets. In conclusion, we have identified a novel role for leukotriene B4 in the augmentation of neutrophil phagocytosis mediated by either the Fc or complement receptor.

Cigarette Smoke Exposure Impairs Pulmonary Bacterial Clearance and Alveolar Macrophage Complement-Mediated Phagocytosis of Streptococcus pneumoniae

ABSTRACT Cigarette smoke exposure increases the risk of pulmonary and invasive infections caused by Streptococcus pneumoniae, the most commonly isolated organism from patients with community-acquired pneumonia. Despite this association, the mechanisms by which cigarette smoke exposure diminishes host defense against S. pneumoniae infections are poorly understood. In this study, we compared the responses of BALB/c mice following an intratracheal challenge with S. pneumoniae after 5 weeks of exposure to room air or cigarette smoke in a whole-body exposure chamber in vivo and the effects of cigarette smoke on alveolar macrophage phagocytosis of S. pneumoniae in vitro. Bacterial burdens in cigarette smoke-exposed mice were increased at 24 and 48 h postinfection, and this was accompanied by a more pronounced clinical appearance of illness, hypothermia, and increased lung homogenate cytokines interleukin-1β (IL-1β), IL-6, IL-10, and tumor necrosis factor alpha (TNF-α). We also found greater numbers of neutrophils in bronchoalveolar lavage fluid recovered from cigarette smoke-exposed mice following a challenge with heat-killed S. pneumoniae. Interestingly, overnight culture of alveolar macrophages with 1% cigarette smoke extract, a level that did not affect alveolar macrophage viability, reduced complement-mediated phagocytosis of S. pneumoniae, while the ingestion of unopsonized bacteria or IgG-coated microspheres was not affected. This murine model provides robust additional support to the hypothesis that cigarette smoke exposure increases the risk of pneumococcal pneumonia and defines a novel cellular mechanism to help explain this immunosuppressive effect.

Leptin Modulates Neutrophil Phagocytosis of Klebsiella pneumoniae

ABSTRACT Leptin is a pleiotropic hormone-cytokine known to regulate energy homeostasis and immune function. Neutrophils from leptin-deficient mice exhibited impaired phagocytosis of Klebsiella pneumoniae opsonized with serum containing complement and reduced CD11b expression that could be restored with exogenous leptin. These results suggest that leptin is required for normal neutrophil complement-mediated phagocytosis of bacteria.

Perinatal bisphenol A exposure promotes hyperactivity, lean body composition, and hormonal responses across the murine life course

The development of adult‐onset diseases is influenced by perinatal exposure to altered environmental conditions. One such exposure, bisphenol A (BPA), has been associated with obesity and diabetes, and consequently labeled an obesogen. Using an isogenic murine model, we examined the effects of perinatal exposure through maternal diet to 50 ng (n=20), 50 μg (n=21), or 50 mg (n=18) BPA/kg diet, as well as controls (n=20) on offspring energy expenditure, spontaneous activity, and body composition at 3, 6, and 9 mo of age, and hormone levels at 9 and 10 mo of age. Overall, exposed females and males exhibited increased energy expenditure (P<0.001 and 0.001, respectively) throughout the life course. In females, horizontal and vertical activity increased (P=0.07 and 0.06, respectively) throughout the life course. Generally, body composition measures were not different throughout the life course in exposed females or males (all P>0.44), although body fat and weight decreased in exposed females at particular ages (all P<0.08). Milligram‐exposed females had improved glucose, insulin, adiponectin, and leptin profiles (all P<0.10). Thus, life‐course analysis illustrates that BPA is associated with hyperactive and lean phenotypes. Variability across studies may be attributable to differential exposure duration and timing, dietary fat and phytoestrogen content, or lack of sophisticated phenotyping across the life course.—Anderson, O.S., Peterson, K.E., Sanchez, B.N., Zhang, Z., Mancuso, P., Dolinoy, D.C. Perinatal bisphenol A exposure promotes hyperactivity, lean body composition, and hormonal responses across the murine life course. FASEB J. 27, 1784–1792 (2013). www.fasebj.org

Change in adipocytokines and ghrelin with menopause.

OBJECTIVES To determine if ghrelin and adipocytokine (leptin, adiponectin, resistin) levels vary with menopause stage or with estradiol (E2), testosterone (T), follicle-stimulating hormone (FSH) and sex hormone-binding globulin (SHBG) concentrations measured in three stages of the menopause transition. METHODS A study of adipocytokines and menopause was nested in a population-based, longitudinal study of Caucasian women [Michigan Bone Health and Metabolism Study (MBHMS)]. Annual serum and urine samples, available from the MBHMS repository, were selected to correspond to the pre-, peri-, and postmenopause stages of the menopause transition. Participants included forty women, stratified into obese versus non-obese groups based upon their baseline body mass index, who had specimens corresponding to the three menopause stages. RESULTS Mean resistin levels were approximately two times higher during premenopause compared to peri- or postmenopause. There were significantly lower adiponectin and higher ghrelin levels in the perimenopause stage, compared to either the pre- or postmenopause stage. Increases in FSH concentrations were significantly and positively associated with higher leptin in non-obese women (P<0.01) but not in obese women (P<0.23). Increases in FSH concentrations were also significantly (P<0.005) and positively associated with higher adiponectin concentrations but were negatively associated with ghrelin concentrations (P<0.005). Associations remained following adjustment for waist circumference, waist circumference change, chronological age, and time between measures. CONCLUSIONS Menopause stages and underlying FSH changes are associated with notable changes in levels of the metabolically active adipocytokines and ghrelin and these changes may be related to selected health outcomes observed in women at mid-life.

Race-ethnic differences in adipokine levels: the Study of Women's Health Across the Nation (SWAN).

Differences in adipose tissue secretory profile, as measured by adipokine levels, may play a role in race-ethnic disparities in cardiovascular disease (CVD). We examined race-ethnic differences in adipokine levels in a group of mid-life Caucasian, African American (AA), Chinese and Japanese women, after accounting for adiposity. Data on 1876 women from the Study of Womens Health Across the Nation were analyzed. In multivariable adjustment, including total fat mass, differences in total and high molecular weight (HMW) adiponectin, leptin and soluble leptin receptor (sOB-R) levels were examined. Despite intermediate levels of adiposity, Caucasian women had higher levels of both total and HMW adiponectin, when compared to both AA and Chinese and Japanese women. After multivariable adjustment, compared to Caucasian women, AA women had significantly lower total (β: -3.40; 95% CI: -4.29, -2.52; P<.001) and HMW adiponectin (β: -0.53; 95% CI: -0.64, -0.43; P<.001) levels, higher leptin levels (β: 3.26; 95% CI: 1.36, 5.16; P<.001) and lower sOB-R levels (β: -0.07; 95% CI: -0.11, -0.03; P<.001). Compared to Caucasian women, both Chinese and Japanese women had lower total (Chinese: β: -5.50; 95% CI: -7.07, -3.93; P<.001; Japanese: β: -5.48; 95% CI: -6.95, -4.02; P<.001) and HMW adiponectin (Chinese: β: -0.57; 95% CI: -0.75, -0.38; P<.001; Japanese: β: -0.61; 95% CI: -0.78, -0.44; P<.001) levels and lower sOB-R levels (Chinese: β: -0.13; 95% CI: -0.20, -0.06; P<.001; Japanese: β: -0.09; 95% CI: -0.15, -0.02; P=.008). Significant race-ethnic differences exist in circulating adipokines, even after accounting for adiposity. Further research is needed to explicitly determine if such differences contribute to known racial differences in CVD risk.

Intrapulmonary Administration of Leukotriene B4 Enhances Pulmonary Host Defense against Pneumococcal Pneumonia

ABSTRACT Leukotriene B4 (LTB4) is a potent lipid mediator of inflammation formed by the 5-lipoxygenase (5-LO)-catalyzed oxidation of arachidonic acid. We have previously shown that (i) LTB4 is generated during infection, (ii) its biosynthesis is essential for optimal antimicrobial host defense, (iii) LT deficiency is associated with clinical states of immunocompromise, and (iv) exogenous LTB4 augments antimicrobial functions in phagocytes. Here, we sought to determine whether the administration of LTB4 has therapeutic potential in a mouse model of pneumonia. Wild-type and 5-LO knockout mice were challenged with Streptococcus pneumoniae via the intranasal route, and bacterial burdens, leukocyte counts, and cytokine levels were determined. LTB4 was administered via the intraperitoneal, intravenous, and intranasal routes prior to pneumococcal infection and by aerosol 24 h following infection. Leukocytes recovered from mice given S. pneumoniae and treated with aerosolized LTB4 were evaluated for expression levels of the p47phox subunit of NADPH oxidase. Intrapulmonary but not systemic pretreatment with LTB4 significantly reduced the lung S. pneumoniae burden in wild-type mice. Aerosolized LTB4 was effective at improving lung bacterial clearance when administered postinoculation in animals with established infection and exhibited greater potency in 5-LO knockout animals, which also exhibited greater baseline susceptibility. Augmented bacterial clearance in response to LTB4 was associated with enhanced monocyte recruitment and leukocyte expression of p47phox. The results of the current study in an animal model serve as a proof of concept for the potential utility of treatment with aerosolized LTB4 as an immunostimulatory strategy in patients with bacterial pneumonia.

Leukotrienes: Mediators that have been typecast as villains

Abstract.As befalls many mediators that act upon the human stage, leukotrienes have become identified with their most powerful roles as villains of the immune system. They are well known for their leading roles in allergic diseases, including asthma. They also have gained recognition for their dramatic role as promoters of inflammation. As new roles for these lipid messengers are sought, it is becoming apparent that the leukotrienes have been typecast as bad guys of the immune system. As examples, their more recent roles have been in atherosclerosis, pulmonary fibrosis and cancer. However, upon further evaluation, we can begin to see their versatility. Thus, leukotrienes stimulate innate immunity against pathogens. In addition, they promote the expression of mediators, receptors and other molecules that are important for immune defense. In these lesser known roles, they lead the fight against bacterial, fungal and viral infection. This review is intended to shed light on the leukotrienes, where they come from and what we really know about them.