Inhibition of mitochondrial oxidative phosphorylation with anidulafungin

Purpose: In previous ex vivo live-heart studies, anidulafungin (ANID) was found to cause cardiac toxicity. Because similar chemicals are known to inhibit mitochondrial respiration, the purpose of this study was to elucidate the effect of ANID on oxidative phosphorylation in mitochondria.

Methods: Liver mitochondria were isolated from Harlan Sprague-Dawley rats by homogenization of 1-2g of tissues followed by differential centrifugation. Mitochondrial respiration was measured as O₂ consumption using a Clark-type electrode and initiated with 5 uM succinate (S), 10 uM glutamate/5 uM malate (G), or 5 uM pyruvate (P). After establishing the rates of state 2 and 3 (+ 1060 uM ADP) respiration,  ANID was added in  concentrations ranging from 0.2 to 19.9 uM and compared to 1) state 3 respiration (S3R) in the absence of ANID and 2) state 4 respiration induced by oligomycin (OLIG) 4.9 uM, a known mitochondrial toxin, in the absence of ANID.  A one-sided Student t-test was used to determine the significance of comparisons.

Results: ANID decreased S3R by 64.5 ± 13.7% and 70.3 ± 16.4%, 65.7 ± 15.2% and 72.6 ± 18.9%, and 44.8 ± 6.7% and  39.7 ± 13.5% at 0.2, 2.0, and 19.9 uM, respectively, with S and G-driven respiration (p<0.0001 for all). With P, ANID decreased S3R by 11.9 ± 0.7%, 12.0 ± 2.2%, and 30.8 ± 3.2%, for 0.2, 2.0, and 19.9 ug/mL, respectively (p<0.0001 for all). OLIG 4.9 uM decreased oxygen consumption by 51.0 ± 21.6%, 51.1 ± 22.8%, and 76.2% ± 7.1% with S,G, and P, respectively (p<0.0001 for all). 

Conclusion: ANID inhibits mitochondrial oxidative phosphorylation more than OLIG with S and G.  Since the respiration of substrate producing ubiquinol (S) is inhibited as much by ANID as substrates producing NADH (G,P), it seems unlikely that ANID inhibits Complex I.  Studies to locate the molecular target are underway.