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Abstract: TH-PO492

Metabolic Acidosis Increases Susceptibility of Mice to Uropathogenic E. coli (UPEC)-Induced Pyelonephritis (PN)

Session Information

Category: Fluid and Electrolytes

  • 901 Fluid and Electrolytes: Basic

Authors

  • Purkerson, Jeffrey M., University of Rochester Med Ctr, Rochester, New York, United States
  • Peng, Hu, University of Rochester Med Ctr, Rochester, New York, United States
  • Schwartz, George J., University of Rochester Med Ctr, Rochester, New York, United States
Background

Carbonic anhydrase 2-deficient mice show metabolic acidosis with deficient urine acidification, and are more susceptible to UPEC-induced PN (Hains, AJP 307:F869, 2014). Whether the susceptibility to PN is due to H+ transport abnormalities or acidosis is unclear. In this study we examined the impact of acidosis on susceptibility of refluxing C3H-HEouJ mice to PN.

Methods

Metabolic acidosis was induced in C3H-HEouJ mice via NH4Cl (2% w/w) supplementation of food±I.P. administration of acetazolamide (ACZ 100 mg/kg). Acid-base state was assessed by blood gas using an iSTAT® G3+ and pH of urine collected under water-saturated mineral oil in metabolic cages housing 2-4 mice. Collecting duct (CD) fragments were enriched from collagenase-digested mouse kidney by DBA-lectin magnetic sorting. Relative abundance of SDF1 and antimicrobial peptide (AMP) mRNAs (cathelicidin [Camp]; beta defensin-2 [BD2]) in CDs was determined by qRT-PCR via ΔΔCt. Female C3H-HEouJ mice were infected with UPEC strain CFT073 @ 107 cfu/50 µl via transurethral inoculation. Bacterial burden (cfu/g) in bladder and kidney was determined by culture of tissue homogenates. Statistical significance utilized T-test or Mann-Whitney Test.

Results

NH4Cl-fed mice were acidotic (s[HCO3] 18.2±0.65*, Ur pH 5.8±0.02*; N=8 ) compared to normal (NL) (s[HCO3] 22.2±0.68; Ur pH 6.8±0.01, *p<0.05, N=24 ); co-administration of ACZ resulted in severe acidosis and reduced urine acidification (s[HCO3] 12.8±0.7**; Ur pH 6.9±0.05, p<0.001 versus NL, N=5-9). UPEC infection alone did not induce SDF1 mRNA; however acidosis+UPEC infection induced SDF1 expression 3.5±0.4 fold over NL (p<0.01). Severe acidosis (NH4Cl+ACZ) increased Camp (2.1±0.11) and BD2 (2.3±0.36) mRNA, whereas expression of SDF-1 mRNA was induced 10.5±1.0 compared to NL (p<0.01). Acidotic mice were more susceptible to PN than NL (kidney mean cfu/g: NL 4.1x103; Acidosis 2.6x108, p<0.001; N=7-8). UPEC burden was also higher in bladders from acidotic mice compared to normal (mean cfu/g: NL 6.8x105; Acidosis 8.6x108, p<0.001).

Conclusion

Metabolic acidosis increases the susceptibility of C3H-HEouJ mice to PN. Increases in AMP expression with acidosis do not compensate for an apparent loss of barrier function, manifested as increased production of SDF1, a key mediator of the kidney response to metabolic stress (e.g. hypoxia, acidosis).