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Metformin reduces airway glucose permeability and hyperglycaemia-induced Staphylococcus aureus load independently of effects on blood glucose.

Garnett JP, Baker EH, Naik S, Lindsay JA, Knight GM, Gill S, Tregoning JS, Baines DL - Thorax (2013)

Bottom Line: S aureus reduced transepithelial electrical resistance (RT) and increased paracellular glucose flux.Metformin did not decrease blood glucose but reduced paracellular flux across ex vivo murine tracheas.Metformin might, therefore, be of additional benefit in the prevention and treatment of respiratory infection.

View Article: PubMed Central - PubMed

Affiliation: Division of Biomedical Sciences, Centre for Cell Physiology and Pharmacology, St George's, University of London, London, UK.

ABSTRACT

Background: Diabetes is a risk factor for respiratory infection, and hyperglycaemia is associated with increased glucose in airway surface liquid and risk of Staphylococcus aureus infection.

Objectives: To investigate whether elevation of basolateral/blood glucose concentration promotes airway Staphylococcus aureus growth and whether pretreatment with the antidiabetic drug metformin affects this relationship.

Methods: Human airway epithelial cells grown at air-liquid interface (±18 h pre-treatment, 30 μM-1 mM metformin) were inoculated with 5×10(5) colony-forming units (CFU)/cm(2) S aureus 8325-4 or JE2 or Pseudomonas aeruginosa PA01 on the apical surface and incubated for 7 h. Wild-type C57BL/6 or db/db (leptin receptor-deficient) mice, 6-10 weeks old, were treated with intraperitoneal phosphate-buffered saline or 40 mg/kg metformin for 2 days before intranasal inoculation with 1×10(7) CFU S aureus. Mice were culled 24 h after infection and bronchoalveolar lavage fluid collected.

Results: Apical S aureus growth increased with basolateral glucose concentration in an in vitro airway epithelia-bacteria co-culture model. S aureus reduced transepithelial electrical resistance (RT) and increased paracellular glucose flux. Metformin inhibited the glucose-induced growth of S aureus, increased RT and decreased glucose flux. Diabetic (db/db) mice infected with S aureus exhibited a higher bacterial load in their airways than control mice after 2 days and metformin treatment reversed this effect. Metformin did not decrease blood glucose but reduced paracellular flux across ex vivo murine tracheas.

Conclusions: Hyperglycaemia promotes respiratory S aureus infection, and metformin modifies glucose flux across the airway epithelium to limit hyperglycaemia-induced bacterial growth. Metformin might, therefore, be of additional benefit in the prevention and treatment of respiratory infection.

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Related in: MedlinePlus

Comparison of Staphylococcus aureus numbers in BAL fluid of infected db/db and wild-type (WT) mice. Leptin receptor deficient (db/db) or WT C57BL/6 mice were inoculated with 107 CFU of S aureus strain 8325-4 intranasally. (A) Blood glucose concentration on the day of infection. (B) Weight measured over the time of the experiment. (C) Number of cells; (D) number of neutrophils; (E) IL-6 concentration in BAL fluid on day 1 after infection. (F) Percentage weight loss measured during the experiment. (G) Bacterial CFU recovered from BAL fluid on day 1 after infection. Individual mice are shown as data points, the horizontal bars represent mean ± SEM of n=9–13 (pooled experiments). *p<0.05, **p<0.01, ****p<0.0001. (H) Correlation of blood glucose concentration with CFU recovered from BAL fluid, n=18. BAL, bronchoalveolar lavage; IL, interleukin.
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THORAXJNL2012203178F1: Comparison of Staphylococcus aureus numbers in BAL fluid of infected db/db and wild-type (WT) mice. Leptin receptor deficient (db/db) or WT C57BL/6 mice were inoculated with 107 CFU of S aureus strain 8325-4 intranasally. (A) Blood glucose concentration on the day of infection. (B) Weight measured over the time of the experiment. (C) Number of cells; (D) number of neutrophils; (E) IL-6 concentration in BAL fluid on day 1 after infection. (F) Percentage weight loss measured during the experiment. (G) Bacterial CFU recovered from BAL fluid on day 1 after infection. Individual mice are shown as data points, the horizontal bars represent mean ± SEM of n=9–13 (pooled experiments). *p<0.05, **p<0.01, ****p<0.0001. (H) Correlation of blood glucose concentration with CFU recovered from BAL fluid, n=18. BAL, bronchoalveolar lavage; IL, interleukin.

Mentions: Mice deficient for the leptin receptor (db/db) exhibited significantly higher blood glucose concentrations (17.7±1.6 vs 7.4±0.1 mM; p<0.01; n=10; figure 1A) and were heavier (p<0.001; n=10; figure 1B) than WT mice. Twenty-four hours after infection with S aureus 8325-4, there were more inflammatory cells, neutrophils and cytokines (IL-6) present in the airways of db/db than WT mice or naïve mice (non-infected WT mice) (p<0.05; n=10–13; figure 1C, D and E). All infected mice lost weight after infection (figure 1F). Crucially, db/db mice had significantly more bacteria in their airways after infection than WT mice (p<0.01; n=9; figure 1G), and there was a direct correlation between blood glucose and CFU (r2=0.8, p<0.0001; n=18; figure 1H) supporting clinical observations in humans.


Metformin reduces airway glucose permeability and hyperglycaemia-induced Staphylococcus aureus load independently of effects on blood glucose.

Garnett JP, Baker EH, Naik S, Lindsay JA, Knight GM, Gill S, Tregoning JS, Baines DL - Thorax (2013)

Comparison of Staphylococcus aureus numbers in BAL fluid of infected db/db and wild-type (WT) mice. Leptin receptor deficient (db/db) or WT C57BL/6 mice were inoculated with 107 CFU of S aureus strain 8325-4 intranasally. (A) Blood glucose concentration on the day of infection. (B) Weight measured over the time of the experiment. (C) Number of cells; (D) number of neutrophils; (E) IL-6 concentration in BAL fluid on day 1 after infection. (F) Percentage weight loss measured during the experiment. (G) Bacterial CFU recovered from BAL fluid on day 1 after infection. Individual mice are shown as data points, the horizontal bars represent mean ± SEM of n=9–13 (pooled experiments). *p<0.05, **p<0.01, ****p<0.0001. (H) Correlation of blood glucose concentration with CFU recovered from BAL fluid, n=18. BAL, bronchoalveolar lavage; IL, interleukin.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC3756442&req=5

THORAXJNL2012203178F1: Comparison of Staphylococcus aureus numbers in BAL fluid of infected db/db and wild-type (WT) mice. Leptin receptor deficient (db/db) or WT C57BL/6 mice were inoculated with 107 CFU of S aureus strain 8325-4 intranasally. (A) Blood glucose concentration on the day of infection. (B) Weight measured over the time of the experiment. (C) Number of cells; (D) number of neutrophils; (E) IL-6 concentration in BAL fluid on day 1 after infection. (F) Percentage weight loss measured during the experiment. (G) Bacterial CFU recovered from BAL fluid on day 1 after infection. Individual mice are shown as data points, the horizontal bars represent mean ± SEM of n=9–13 (pooled experiments). *p<0.05, **p<0.01, ****p<0.0001. (H) Correlation of blood glucose concentration with CFU recovered from BAL fluid, n=18. BAL, bronchoalveolar lavage; IL, interleukin.
Mentions: Mice deficient for the leptin receptor (db/db) exhibited significantly higher blood glucose concentrations (17.7±1.6 vs 7.4±0.1 mM; p<0.01; n=10; figure 1A) and were heavier (p<0.001; n=10; figure 1B) than WT mice. Twenty-four hours after infection with S aureus 8325-4, there were more inflammatory cells, neutrophils and cytokines (IL-6) present in the airways of db/db than WT mice or naïve mice (non-infected WT mice) (p<0.05; n=10–13; figure 1C, D and E). All infected mice lost weight after infection (figure 1F). Crucially, db/db mice had significantly more bacteria in their airways after infection than WT mice (p<0.01; n=9; figure 1G), and there was a direct correlation between blood glucose and CFU (r2=0.8, p<0.0001; n=18; figure 1H) supporting clinical observations in humans.

Bottom Line: S aureus reduced transepithelial electrical resistance (RT) and increased paracellular glucose flux.Metformin did not decrease blood glucose but reduced paracellular flux across ex vivo murine tracheas.Metformin might, therefore, be of additional benefit in the prevention and treatment of respiratory infection.

View Article: PubMed Central - PubMed

Affiliation: Division of Biomedical Sciences, Centre for Cell Physiology and Pharmacology, St George's, University of London, London, UK.

ABSTRACT

Background: Diabetes is a risk factor for respiratory infection, and hyperglycaemia is associated with increased glucose in airway surface liquid and risk of Staphylococcus aureus infection.

Objectives: To investigate whether elevation of basolateral/blood glucose concentration promotes airway Staphylococcus aureus growth and whether pretreatment with the antidiabetic drug metformin affects this relationship.

Methods: Human airway epithelial cells grown at air-liquid interface (±18 h pre-treatment, 30 μM-1 mM metformin) were inoculated with 5×10(5) colony-forming units (CFU)/cm(2) S aureus 8325-4 or JE2 or Pseudomonas aeruginosa PA01 on the apical surface and incubated for 7 h. Wild-type C57BL/6 or db/db (leptin receptor-deficient) mice, 6-10 weeks old, were treated with intraperitoneal phosphate-buffered saline or 40 mg/kg metformin for 2 days before intranasal inoculation with 1×10(7) CFU S aureus. Mice were culled 24 h after infection and bronchoalveolar lavage fluid collected.

Results: Apical S aureus growth increased with basolateral glucose concentration in an in vitro airway epithelia-bacteria co-culture model. S aureus reduced transepithelial electrical resistance (RT) and increased paracellular glucose flux. Metformin inhibited the glucose-induced growth of S aureus, increased RT and decreased glucose flux. Diabetic (db/db) mice infected with S aureus exhibited a higher bacterial load in their airways than control mice after 2 days and metformin treatment reversed this effect. Metformin did not decrease blood glucose but reduced paracellular flux across ex vivo murine tracheas.

Conclusions: Hyperglycaemia promotes respiratory S aureus infection, and metformin modifies glucose flux across the airway epithelium to limit hyperglycaemia-induced bacterial growth. Metformin might, therefore, be of additional benefit in the prevention and treatment of respiratory infection.

Show MeSH
Related in: MedlinePlus