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Richard A Johnston

Publications and source records attributed to Richard A Johnston.

12 recordsLinked to original sources
PubMed2006

Pulmonary responses to acute ozone exposure in fasted mice: effect of leptin administration.

Leptin is a satiety hormone that also has proinflammatory effects, including augmentation of ozone-induced pulmonary inflammation. The purpose of this study was to determine whether reductions in endogenous levels of leptin can attenuate pulmonary responses to ozone. To reduce serum leptin, we fasted mice overnight before ozone exposure. Fasting caused a marked reduction in serum leptin to approximately one-sixth the levels observed in fed mice, and continuous infusion of leptin via Alzet micro-osmotic pumps restored serum leptin to, but not above, fed levels. Ozone exposure (2 ppm for 3 h) caused a significant, approximately 40% increase in pulmonary resistance (P < 0.01) and increased airway responsiveness in fasted but not in fed mice. The increased effect of ozone on pulmonary mechanics and airway responsiveness in fasted mice was not observed when leptin was restored via continuous infusion. Ozone exposure caused pulmonary inflammation, as evident by increases in bronchoalveolar lavage cells, protein, and soluble tumor necrosis factor receptors. There was no effect of fasting status on ozone-induced changes in the bronchoalveolar lavage inflammatory profile, and leptin treatment did not alter these responses. Our results indicate that fasting augments ozone-induced changes in pulmonary mechanics and airway responsiveness in mice. These effects of fasting are the result of declines in serum leptin. The mechanistic basis for this protective effect of leptin in fasted mice remains to be determined but is not related to effects on ozone-induced inflammation.

Airway Resistance↗
PubMed2005

Increased pulmonary responses to acute ozone exposure in obese db/db mice.

Epidemiological studies indicate the incidence of asthma is increased in obese and overweight humans. Responses to ozone (O(3)), an asthma trigger, are increased in obese (ob/ob) mice lacking the satiety hormone leptin. The long form of leptin receptor (Ob-R(b)) is required for satiety; mice lacking this receptor (db/db mice) are also substantially obese. Here, wild-type (WT) and db/db mice were exposed to air or O(3) (2 ppm) for 3 h. Airway responsiveness, measured by the forced oscillation technique, was greater in db/db than WT mice after air exposure. O(3)-induced increases in pulmonary resistance and airway responsiveness were also greater in db/db mice. BALF eotaxin, IL-6, KC, and MIP-2 increased 4 h after O(3) exposure and subsided by 24 h, whereas protein and neutrophils continued to increase through 24 h. For each outcome, the effect of O(3) was significantly greater in db/db than WT mice. Previously published results obtained in ob/ob mice were similar except for O(3)-induced neutrophils and MIP-2, which were not different from WT mice. O(3) also induced pulmonary IL-1beta and TNF-alpha mRNA expression in db/db but not ob/ob mice. Leptin was increased in serum of db/db mice, and pulmonary mRNA expression of short form of leptin receptor (Ob-R(a)) was similar in db/db and WT mice. These data confirm obese mice have innate airway hyperresponsiveness and increased pulmonary responses to O(3). Differences between ob/ob mice, which lack leptin, and db/db mice, which lack Ob-R(b) but not Ob-R(a), suggest leptin, acting through Ob-R(a), can modify some pulmonary responses to O(3).

Animals↗
PubMed2005

Obesity and asthma.

Obesity is an important public health problem. An increasing body of data supports the hypothesis that obesity is a risk factor for asthma. These data include numerous large cross-sectional and prospective studies performed in adults, adolescents, and children throughout the world. With few exceptions, these studies indicate an increased relative risk of asthma in the obese and overweight and demonstrate that obesity antedates asthma. Obesity appears to be a particularly important issue for severe asthma. Studies showing improvements in asthma in subjects who lose weight, as well as studies showing that obese mice have innate airway hyperresponsiveness (AHR) as well as increased responses to certain asthma triggers also suggest a causal relationship between obesity and asthma. The mechanistic basis for this relationship has not been established. It may be that obesity and asthma share some common etiology, such as a common genetic predisposition, common effects of in utero conditions, or that obesity and asthma are both the result of some other predisposing factor such as physical activity or diet. However, there are also plausible biological mechanisms whereby obesity could be expected to either cause or worsen asthma. These include co-morbidities such as gastroesophageal reflux, complications from sleep-disordered breathing (SDB), breathing at low lung volume, chronic systemic inflammation, and endocrine factors, including adipokines and reproductive hormones. Understanding the mechanistic basis for the relationship between obesity and asthma may lead to new therapeutic strategies for treatment of this susceptible population.

Animals↗
PubMed2005

Augmented responses to ozone in obese carboxypeptidase E-deficient mice.

We reported previously that mice obese as a result of leptin deficiency (ob/ob) have enhanced ozone (O3)-induced airway hyperresponsiveness (AHR) and inflammation compared with wild-type (C57BL/6) controls. To determine whether this increased response to O3 was independent of the modality of obesity, we examined O3-induced AHR and inflammation in Cpe(fat) mice. These mice are obese as a consequence of a mutation in the gene encoding carboxypeptidase E (Cpe), an enzyme important in processing prohormones and proneuropeptides involved in satiety and energy expenditure. Airway responsiveness to intravenous methacholine, measured by forced oscillation, was increased in Cpe(fat) vs. wild-type mice after air exposure. In addition, compared with air exposure, airway responsiveness was increased 24 h after O3 exposure (2 ppm for 3 h) in Cpe(fat) but not in wild-type mice. Compared with air-exposed controls, O3 exposure increased bronchoalveolar lavage fluid (BALF) protein, IL-6, KC, MIP-2, MCP-1, and soluble TNF receptors (sTNFR1 and sTNFR2) as well as BALF neutrophils. With the exception of sTNFR1 and sTNFR2, all of these outcome indicators were greater in Cpe(fat) vs. wild-type mice. Serum sTNFR1, sTNFR2, MCP-1, leptin, and blood leukocytes were elevated in Cpe(fat) compared with wild-type mice even in the absence of O3 exposure, similar to the chronic systemic inflammation observed in human obesity. These results indicate that increased O3-induced AHR and inflammation are consistent features of obese mice, regardless of the modality of obesity. These results also suggest that chronic systemic inflammation may enhance airway responses to O3 in obese mice.

Animals↗
PubMed2005

Effect of leptin on allergic airway responses in mice.

BACKGROUND: Epidemiologic data indicate that the incidence of asthma is increased in obese patients. OBJECTIVE: Because the serum levels of the satiety hormone and proinflammatory cytokine leptin are increased in obese individuals, we sought to determine whether leptin can augment allergic airway responses. METHODS: We sensitized and challenged BALB/cJ mice with ovalbumin. Alzet micro-osmotic pumps were implanted in the mice to deliver a continuous infusion of either saline or leptin (1.75 mug/g/d). Two days later, the mice were challenged with either aerosolized saline or ovalbumin once per day for 3 days. We measured airway responsiveness, performed bronchoalveolar lavage, and obtained blood to measure serum leptin and IgE 24 or 48 hours after the last challenge. RESULTS: Leptin infusion increased serum leptin concentrations, which were increased further after ovalbumin sensitization and challenge. Ovalbumin challenge increased bronchoalveolar lavage fluid cells and cytokines, serum IgE, lung cytokine mRNA expression, and responses to inhaled, aerosolized methacholine. It is important to note that the changes in methacholine responsiveness and IgE were augmented in leptin- versus saline-infused mice. CONCLUSIONS: These results indicate that serum leptin is increased during allergic reactions in the airways and may play a role in the relationship between obesity and asthma.

Administration, Cutaneous↗
PubMed2004

Role of interleukin-6 in murine airway responses to ozone.

This study sought to examine the role of interleukin-6 (IL-6) in ozone (O(3))-induced airway injury, inflammation, and hyperresponsiveness (AHR). Subacute (72 h) exposure to 0.3 ppm O(3) significantly elevated bronchoalveolar lavage fluid (BALF) protein, neutrophils, and soluble TNF receptors (sTNFR1 and sTNFR2) in wild-type C57BL/6 (IL-6(+/+)) mice; however, all four outcome indicators were significantly reduced in IL-6-deficient (IL-6(-/-)) compared with IL-6(+/+) mice. Acute O(3) exposure (2 ppm for 3 h) increased BALF protein, KC, macrophage inflammatory protein(MIP)-2, eotaxin, sTNFR1, and sTNFR2 in IL-6(+/+) mice. However, MIP-2 and sTNFR2 were not significantly increased following O(3) exposure in IL-6(-/-) mice. Increases in BALF neutrophils induced by O(3) (2 ppm for 3 h) were also significantly reduced in IL-6(-/-) vs. IL-6(+/+) mice. Airway responsiveness to methacholine was measured by whole body plethysmography before and following acute (3 h) or subacute (72 h) exposure to 0.3 ppm O(3). Acute O(3) exposure caused AHR in both groups of mice, but there was no genotype-related difference in the magnitude of O(3)-induced AHR. AHR was absent in mice of either genotype exposed for 72 h. Our results indicate that IL-6 deficiency reduces airway neutrophilia, as well as the levels of BALF sTNFR1 and sTNFR2 following acute high dose and/or subacute low-dose O(3) exposure, but has no effect on O(3)-induced AHR.

Animals↗
PubMed2004

CXCR2 is essential for maximal neutrophil recruitment and methacholine responsiveness after ozone exposure.

Ozone (O(3)), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O(3) exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O(3)-induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O(3) exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O(3) exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O(3) exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O(3) exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O(3) exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O(3) exposure.

Animals↗
PubMed2003

Hyperosmolar solution effects in guinea pig airways. II. Epithelial bioelectric responses to relative changes in osmolarity.

Osmotic challenge of airways alters the bioelectric properties of the airway epithelium and induces the release of factors that modulate smooth muscle tone. Recent studies in our laboratory suggested that methacholine-contracted airways relax in response to incremental increases in osmolarity, rather than from cell shrinkage or absolute solute concentration. In the present study, guinea pig tracheae were mounted in Ussing chambers to elucidate the bioelectric effects of challenge of the epithelium with hyperosmolar and isosmolar solutions. Transepithelial short-circuit current (Isc) across tracheae stimulated with basolateral methacholine was inhibited by apical amiloride, apical 5-nitro-2-(3-phenylpropylamino)benzoic acid, basolateral bumetanide, basolateral ouabain, and Cl(-)-free solution, but not by basolateral iberiotoxin. Apical hyperosmolar challenge with NaCl variably decreased or increased Isc, but D-mannitol (D-M) always inhibited Isc; bumetanide attenuated decreases in Isc. The effects of the transport blockers depended upon whether Isc was initially decreased or increased. Unique concentration-dependent changes in Isc and transepithelial resistance (Rt) were observed when ionic (NaCl and KCl), nonionic impermeant (D-M and sucrose), and nonionic permeant (urea) osmolytes were added to the apical and basolateral baths. At concentrations that doubled the osmolarity of the apical bath, D-M, urea, and N-methyl-D-glucamine-gluconate (NMDG-Glu) decreased Isc. Apical isosmolar NMDG-Glu solution decreased Isc, and additional NMDG-Glu caused a further decrease in Isc. Inclusion of one permeant ion, either Na+,K+, or Cl-, reversed the response to apical isosmolar and hyperosmolar solutions. Thus, bioelectric responses of the airway epithelium to hyperosmolar solution are induced by incremental increases in osmolarity.

Amiloride↗
PubMed2003

Hyperosmolar solution effects in guinea pig airways. III. Studies on the identity of epithelium-derived relaxing factor in isolated perfused trachea using pharmacological agents.

Hyperosmolar challenge of airway epithelium stimulates the release of epithelium-derived relaxing factor (EpDRF), but the identity of EpDRF is not known. We examined the effects of pharmacological agents on relaxant responses of methacholine (3 x 10(-7) M)-contracted guinea pig perfused trachea to mucosal hyperosmolar challenge using D-mannitol. Responses were inhibited by gossypol (5 x 10(-6) M), an agent with diverse actions, by the carbon monoxide (CO) scavenger hemoglobin (10(-6) M), and by the heme oxygenase (HO) inhibitor zinc (II) protoporphyrin IX (10(-4) M). The HO inhibitor chromium (III) mesoporphyrin IX (10(-4) M) was not inhibitory, and the HO activator heme-L-lysinate (3 x 10(-4) M) did not evoke relaxant responses. The CO donor tricarbonyldichlororuthenium (II) dimer (2.2 x 10(-4) M) elicited small relaxation responses. Other agents without an effect on responses included: apyrase, adenosine, 6-anilino-5,8-quinolinequinone (LY83583), proadifen, (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), diphenhydramine, glibenclamide, HgCl2, tetrodotoxin, nystatin, alpha-hemolysin, 8-bromoguanosine 3',5'-cyclic monophosphothioate, Rp-isomer, 12-O-tetradecanoylphorbol-13-acetate, cholera toxin, pertussis toxin, thapsigargin, nifedipine, Ca(2+)-free mucosal solution, hydrocortisone, and epidermal growth factor. Cytoskeleton inhibitors, includingerythro-9-(2-hydroxyl-3-nonyl)adenine, colchicine, nocodazole, latrunculin B, and cytochalasins B and D, had no effect on relaxation responses. The results suggest provisionally that a portion of EpDRF activity may be due to CO and that the release of EpDRF does not involve cytoskeletal reorganization.

Animals↗
PubMed2003

Hyperosmolar solution effects in guinea pig airways. IV. Lipopolysaccharide-induced alterations in airway reactivity and epithelial bioelectric responses to methacholine and hyperosmolarity.

We investigated the in vivo and in vitro effects of lipopolysaccharide (LPS) treatment (4 mg/kg i.p.) on guinea pig airway smooth muscle reactivity and epithelial bioelectric responses to methacholine (MCh) and hyperosmolarity. Hyperosmolar challenge of the epithelium releases epithelium-derived relaxing factor (EpDRF). Using a two-chamber, whole body plethysmograph 18 h post-treatment, animals treated with LPS were hyporeactive to inhaled MCh aerosol. This could involve an increase in the release and/or actions of EpDRF, because LPS treatment enhanced EpDRF-induced smooth muscle relaxation in vitro in the isolated perfused trachea apparatus. In isolated perfused tracheas the basal transepithelial potential difference (Vt) was increased after LPS treatment. The increase in Vt was inhibited by amiloride and indomethacin. Concentration-response curves for changes in Vt in response to serosally and mucosally applied MCh were biphasic (hyperpolarization, <3 x 10(-7)M; depolarization, >3 x 10(-7)M); MCh was more potent when applied serosally. The hyperpolarization response to MCh, but not the depolarization response, was potentiated after LPS treatment. In both treatment groups, mucosally applied hyperosmolar solution (using added NaCl) depolarized the epithelium; this response was greater in tracheas from LPS-treated animals. The results of this study indicate that airway hyporeactivity in vivo after LPS treatment is accompanied by an increase in the release and/or actions of EpDRF in vitro. These changes may involve LPS-induced bioelectric alterations in the epithelium.

Amiloride↗
PubMed2003

Hyperosmolar solution effects in guinea pig airways. I. Mechanical responses to relative changes in osmolarity.

In the guinea pig isolated perfused trachea contracted with serosal methacholine (MCh), increasing the osmolarity of the mucosal bathing solution elicits relaxation of smooth muscle mediated by epithelium-derived relaxing factor (EpDRF). The present study was undertaken to determine whether a specific modality of the hyperosmolar stimulus induced the relaxation response. Mucosal hyperosmolar challenge with D-mannitol, N-methyl-D-glucamine (NMDG)-chloride, NMDG-gluconate (NMDG-Glu), or urea elicited relaxation with equal potency. In contrast, hyperosmolar solutions at the serosal surface induced diverse, osmolyte-specific responses. In tracheae contracted with MCh, abrupt replacement of the mucosal modified Krebs-Henseleit solution (MKHS) with isosmolar osmolyte solutions to stimulate cell shrinkage elicited five discrete response patterns related to the membrane permeance of the solute, but increasing the osmolarity of the isosmolar solution via the further addition of the same solute always induced relaxation. Similarly, perfusion of the lumen with water induced a transient contraction, but subsequent addition of MKHS, or isosmolar D-mannitol, urea, NMDG-Glu, NaCl, or KCl induced relaxation. Subsequent hyperosmolar addition of the same osmolyte-evoked relaxation. Compatible osmolytes had no effect on smooth muscle tone and did not affect responses to hyperosmolar challenge. The results suggest that the airway epithelium acts as an osmolarity sensor, which communicates with airway smooth muscle through EpDRF. The mechanical responses of the smooth muscle resulting from changes in the osmotic environment are associated with discrete modalities of the osmolar stimulus, including membrane reflection of the particles, incremental change in osmolarity and directionality, but not cell shrinkage.

Animals↗