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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

Staphylococcus aureus growth in fluid secretions from H441 monolayers. (A) S aureus growth over 7 h in fluid secretions (with glucose concentration normalised to 10 mM) obtained from the apical surface of H441 epithelial monolayers after exposure to different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin (MF) pretreatment (1 mM; 18 h pretreatment; hatched bars), n=4, or (B) in the presence of heat-killed bacteria, and different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin pretreatment (hatched bars) n=4. (C) S aureus growth over 7 h across H441 airway epithelial monolayers, after pretreatment with different concentrations of metformin (all in the presence of 10 mM basolateral glucose), n=5. (D) S aureus growth in culture media only (without cells) containing varying concentrations of metformin, n=4. All data are shown as percentage of control *p<0.05, ***p<0.001, ****p<0.0001.
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THORAXJNL2012203178F4: Staphylococcus aureus growth in fluid secretions from H441 monolayers. (A) S aureus growth over 7 h in fluid secretions (with glucose concentration normalised to 10 mM) obtained from the apical surface of H441 epithelial monolayers after exposure to different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin (MF) pretreatment (1 mM; 18 h pretreatment; hatched bars), n=4, or (B) in the presence of heat-killed bacteria, and different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin pretreatment (hatched bars) n=4. (C) S aureus growth over 7 h across H441 airway epithelial monolayers, after pretreatment with different concentrations of metformin (all in the presence of 10 mM basolateral glucose), n=5. (D) S aureus growth in culture media only (without cells) containing varying concentrations of metformin, n=4. All data are shown as percentage of control *p<0.05, ***p<0.001, ****p<0.0001.

Mentions: Epithelial cells secrete a number of proteins and substances on their apical surface.29 Some have antimicrobial properties; others could promote the growth of bacteria. Therefore, we tested whether basolateral glucose-induced changes in H441 fluid secretions influenced apical bacterial growth. No effect on S aureus growth was seen in fluid secretions (normalised for glucose concentration) produced by different hyperglycaemic conditions in the absence (figures 4A) or presence of heat-killed bacteria (figure 4B). These data are consistent with basolateral glucose, not other glucose-dependent factors, as a determinant of apical S aureus growth.


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)

Staphylococcus aureus growth in fluid secretions from H441 monolayers. (A) S aureus growth over 7 h in fluid secretions (with glucose concentration normalised to 10 mM) obtained from the apical surface of H441 epithelial monolayers after exposure to different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin (MF) pretreatment (1 mM; 18 h pretreatment; hatched bars), n=4, or (B) in the presence of heat-killed bacteria, and different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin pretreatment (hatched bars) n=4. (C) S aureus growth over 7 h across H441 airway epithelial monolayers, after pretreatment with different concentrations of metformin (all in the presence of 10 mM basolateral glucose), n=5. (D) S aureus growth in culture media only (without cells) containing varying concentrations of metformin, n=4. All data are shown as percentage of control *p<0.05, ***p<0.001, ****p<0.0001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3756442&req=5

THORAXJNL2012203178F4: Staphylococcus aureus growth in fluid secretions from H441 monolayers. (A) S aureus growth over 7 h in fluid secretions (with glucose concentration normalised to 10 mM) obtained from the apical surface of H441 epithelial monolayers after exposure to different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin (MF) pretreatment (1 mM; 18 h pretreatment; hatched bars), n=4, or (B) in the presence of heat-killed bacteria, and different concentrations of basolateral glucose (10, 20, 40 mM glucose; black bars) or 40 mM glucose + metformin pretreatment (hatched bars) n=4. (C) S aureus growth over 7 h across H441 airway epithelial monolayers, after pretreatment with different concentrations of metformin (all in the presence of 10 mM basolateral glucose), n=5. (D) S aureus growth in culture media only (without cells) containing varying concentrations of metformin, n=4. All data are shown as percentage of control *p<0.05, ***p<0.001, ****p<0.0001.
Mentions: Epithelial cells secrete a number of proteins and substances on their apical surface.29 Some have antimicrobial properties; others could promote the growth of bacteria. Therefore, we tested whether basolateral glucose-induced changes in H441 fluid secretions influenced apical bacterial growth. No effect on S aureus growth was seen in fluid secretions (normalised for glucose concentration) produced by different hyperglycaemic conditions in the absence (figures 4A) or presence of heat-killed bacteria (figure 4B). These data are consistent with basolateral glucose, not other glucose-dependent factors, as a determinant of apical S aureus growth.

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