Kidney Week

Abstract: SA-PO1023

Acetazolamide Inhibits Ammoniagenesis and Prevents the Correction of Metabolic Acidosis in Rat

Session Information

• Fluid and Electrolytes: Basic - II
  October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid and Electrolytes

• 901 Fluid and Electrolytes: Basic

Authors

• Amlal, Hassane, University of Cincinnati, Cincinnati, Ohio, United States

Hassane Amlal,

• Amlal, Sihame, University of Cincinnati, Cincinnati, Ohio, United States

Sihame Amlal,

• Alam, Perwez, University of Cincinnati, Cincinnati, Ohio, United States

Perwez Alam,

Background

Acetazolamide (ACTZ), a potent inhibitor of carbonic anhydrases (CA), increases renal bicarbonate wasting and causes metabolic acidosis. Intracellular acidic pH, per se, upregulates the glutamine transporter SNAT3 and the ammoniagenic enzymes (glutaminase or GA and glutamate dehydrogenase or GDH). CAII binds to the basolateral Na⁺:HCO₃^- cotransporter (NBCe1) and facilitates HCO₃^- reabsorption across the proximal tubule. However, whether ACTZ alters NBCe1 activity and interferes with the ammoniagenesis pathway during the onset of ACTZ-induced metabolic acidosis remains elusive.

Methods

We compared male Sprague Dawley rats treated with ACTZ or its vehicle (control) to those subjected to NH₄Cl loading inthe drinking water . The animals were housed in metabolic cages for daily measurements of urine volume, Na⁺ excretion, NH₄⁺ excretion and urine pH. The animals were sacrificed after 6 days or 2 weeks. Blood composition was analyzed and the protein abundance of SNAT3, GA and GDH in the kidney cortex was examined.

Results

ACTZ-treated rats exhibited a significant increase in urine flow, natriuresis and bicarbonaturia (urine pH = 8.1 vs. 6.8 in controls). NH₄Cl-loaded rats showed a significant decrease in urine pH (5.6 vs. 6.7 in controls) with no change in Na⁺ excretion or urine flow. ACTZ caused a significant and sustained metabolic acidosis for up to 2 weeks (serum [HCO₃^-] = 20 and 21 mM for 6 days and 2 weeks, respectively, vs. 30mM in controls). Whereas in NH₄Cl loaded rats, metabolic acidosis was developed in 6 days but was fully corrected after 2 weeks of treatment ( serum [HCO₃^-] = 20 and 28 mM for 6 days and 2 weeks, respectively, vs. 29 mM in controls). NH₄⁺ excretion increased by 4-fold in NH₄Cl-loaded rats but only slightly (0.6-flod) in ACTZ-treated rats for 6 days despite similar degree of metabolic acidosis. Immunoblotting studies showed that the protein abundance of GA (4-fold), GDH (06-fold) and SN1 (8-fold) increased significantly in NH₄Cl-loaded rats, but remained unchanged in ACTZ-treated animals.

Conclusion

1- We propose that ACTZ binds to CAII and inactivates NBCe1. This alkalinizes proximal tubule cells and therefore suppresses the ammoniagenesis pathway despite systemic metabolic acidosis. 2- Metabolic acidosis of ACTZ is generated by renal HCO₃^- wasting and maintained by the inhibition of ammoniagenesis pathway in the proximal tubule.

Funding

• NIDDK Support