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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 across airway epithelial monolayers is dependent on basolateral glucose levels and is inhibited by metformin. Airway epithelia–bacteria co-cultures were grown in the presence of varying concentrations of basolateral glucose (10, 20, 40 mM glucose) or 10 mM bilateral glucose (10/10) without (black bars) or with pretreatment with metformin (1 mM; 18 h pre-treatment; hatched bars). Bacterial CFU were measured 7 h after infection (percentage compared with growth in the presence of 10 mM basolateral glucose). (A) H441 and S aureus 8325-4 co-culture, n=9–12; (B) primary human bronchial epithelial cells and S aureus 8325-4 co-culture, n=4; (C) H441 and S aureus JE2 co-culture, n=4; (D) H441 and Pseudomonas aeruginosa co-culture, n=12. *p<0.05, ****p<0.0001, †p<0.05 compared to 10mM glucose pretreated with metformin.
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THORAXJNL2012203178F3: Staphylococcus aureus growth across airway epithelial monolayers is dependent on basolateral glucose levels and is inhibited by metformin. Airway epithelia–bacteria co-cultures were grown in the presence of varying concentrations of basolateral glucose (10, 20, 40 mM glucose) or 10 mM bilateral glucose (10/10) without (black bars) or with pretreatment with metformin (1 mM; 18 h pre-treatment; hatched bars). Bacterial CFU were measured 7 h after infection (percentage compared with growth in the presence of 10 mM basolateral glucose). (A) H441 and S aureus 8325-4 co-culture, n=9–12; (B) primary human bronchial epithelial cells and S aureus 8325-4 co-culture, n=4; (C) H441 and S aureus JE2 co-culture, n=4; (D) H441 and Pseudomonas aeruginosa co-culture, n=12. *p<0.05, ****p<0.0001, †p<0.05 compared to 10mM glucose pretreated with metformin.

Mentions: Increasing basolateral glucose from 10 to 20 or 40 mM in H441 airway epithelial co-cultures produced a stepwise increase in apical S aureus 8325-4 growth (2.7±0.4×107 to 13.0±2.4×107 CFU/ml in 10 and 40 mM, respectively, p<0.01; n=9, figure 3A). Similarly, apical S aureus 8325-4 growth was also increased by increasing basolateral glucose from 10 mM to 20 mM in primary HBE monolayers (1.8±0.2×107 to 2.5±0.2×107 CFU/ml respectively; p<0.05; n=4, figure 3B). Application of 10 mM glucose to apical and basolateral solutions significantly increased apical S aureus growth compared with 10 mM (basolateral only) control (p<0.05; n=12; figure 3A). No S aureus colonies were seen under any condition, in basolateral fluid suggesting that the bacteria did not cross the epithelial barrier over the 7 h time course. Elevation of basolateral glucose promoted the growth of S aureus JE2 (p<0.05; n=3; figure 3C). Furthermore, the growth of P aeruginosa (PA01), was also promoted by increasing basolateral glucose from 10 to 40 mM (p<0.05; n=6; figure 3D).


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 across airway epithelial monolayers is dependent on basolateral glucose levels and is inhibited by metformin. Airway epithelia–bacteria co-cultures were grown in the presence of varying concentrations of basolateral glucose (10, 20, 40 mM glucose) or 10 mM bilateral glucose (10/10) without (black bars) or with pretreatment with metformin (1 mM; 18 h pre-treatment; hatched bars). Bacterial CFU were measured 7 h after infection (percentage compared with growth in the presence of 10 mM basolateral glucose). (A) H441 and S aureus 8325-4 co-culture, n=9–12; (B) primary human bronchial epithelial cells and S aureus 8325-4 co-culture, n=4; (C) H441 and S aureus JE2 co-culture, n=4; (D) H441 and Pseudomonas aeruginosa co-culture, n=12. *p<0.05, ****p<0.0001, †p<0.05 compared to 10mM glucose pretreated with metformin.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

THORAXJNL2012203178F3: Staphylococcus aureus growth across airway epithelial monolayers is dependent on basolateral glucose levels and is inhibited by metformin. Airway epithelia–bacteria co-cultures were grown in the presence of varying concentrations of basolateral glucose (10, 20, 40 mM glucose) or 10 mM bilateral glucose (10/10) without (black bars) or with pretreatment with metformin (1 mM; 18 h pre-treatment; hatched bars). Bacterial CFU were measured 7 h after infection (percentage compared with growth in the presence of 10 mM basolateral glucose). (A) H441 and S aureus 8325-4 co-culture, n=9–12; (B) primary human bronchial epithelial cells and S aureus 8325-4 co-culture, n=4; (C) H441 and S aureus JE2 co-culture, n=4; (D) H441 and Pseudomonas aeruginosa co-culture, n=12. *p<0.05, ****p<0.0001, †p<0.05 compared to 10mM glucose pretreated with metformin.
Mentions: Increasing basolateral glucose from 10 to 20 or 40 mM in H441 airway epithelial co-cultures produced a stepwise increase in apical S aureus 8325-4 growth (2.7±0.4×107 to 13.0±2.4×107 CFU/ml in 10 and 40 mM, respectively, p<0.01; n=9, figure 3A). Similarly, apical S aureus 8325-4 growth was also increased by increasing basolateral glucose from 10 mM to 20 mM in primary HBE monolayers (1.8±0.2×107 to 2.5±0.2×107 CFU/ml respectively; p<0.05; n=4, figure 3B). Application of 10 mM glucose to apical and basolateral solutions significantly increased apical S aureus growth compared with 10 mM (basolateral only) control (p<0.05; n=12; figure 3A). No S aureus colonies were seen under any condition, in basolateral fluid suggesting that the bacteria did not cross the epithelial barrier over the 7 h time course. Elevation of basolateral glucose promoted the growth of S aureus JE2 (p<0.05; n=3; figure 3C). Furthermore, the growth of P aeruginosa (PA01), was also promoted by increasing basolateral glucose from 10 to 40 mM (p<0.05; n=6; figure 3D).

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