Comparative analysis of combination kanamycin-furosemide versus kanamycin alone in the mouse cochlea

Abstract

Combinations of aminoglycosides and loop diuretics have been known to have a synergistic effect in ototoxic injury. Because murine hair cells are relatively resistant to ototoxicity compared to those of other mammals, investigators have turned to combination therapies to create ototoxic lesions in the mouse inner ear. In this paper, we perform a systematic comparison of hearing thresholds, hair cell damage and monocyte migration into the mouse cochlea after kanamycin versus combined kanamycin/furosemide and explore the pathophysiology of enhanced hair cell loss in aminoglycoside ototoxicity in the presence of loop diuretic. Combined kanamycin-furosemide resulted in elevation of threshold not only in the high frequencies, but across all frequencies with more extensive loss of outer hair cells when compared to kanamycin alone. The stria vascularis was severely atrophied and stellate cells in the spiral limbus were missing in kanamycin-furosemide exposed mice while these changes were not observed in mice receiving kanamycin alone. Monocytes and macrophages were recruited in large numbers to the spiral ligament and spiral ganglion in these mice. Combination therapy resulted in a greater number of macrophages in total, and many more macrophages were present further apically when compared to mice given kanamycin alone. Combined kanamycin-furosemide provides an effective method of addressing the relative resistance to ototoxicity that is observed in most mouse strains. As the mouse becomes increasingly more common in studies of hearing loss, and combination therapies gain popularity, recognition of the overall effects of combined aminoglycoside-loop diuretic therapy will be critical to interpretation of the interventions that follow.

Deafness Induction in Mice

“…Only in 2 studies by Wu et al (15) and Hirose and Sato (19), in which a more time consuming regimen (15 consecutive days of several kanamycin injections per day) was used for deafening, ABR measurements were performed. The threshold shifts we determined lie in between those described by Wu et al (15) who found an average shift of 55 to 65 dB at 20 kHz pure tone, and Hirose and Sato (19) who found an 80 dB shift at 24 kHz pure tone. Although there is obviously a difference in click response and pure tone ABR, there does not seem to be a large difference between the threshold shifts acquired after several injections per day for 15 consecutive days and those acquired with our single procedure.…”

“…Wu et al (15) described severe OHC damage with exception of the apex. Similarly, Hirose and Sato (19) described marked OHC destruction as well, with survival at the apex in 40% of cases. With respect to IHC destruction: Wu et al (15) did not describe this, whereas Hirose and Sato (19), who used a tenfold lower dose of furosemide, describe IHC survival rates of 20% yet confined to the base.…”

“…We also managed to induce more IHC loss when compared with the more complex multidose regimens of Wu et al (15) and Hirose and Sato (19). Wu et al (15) described severe OHC damage with exception of the apex.…”

“…Although these results are promising, for future experiments with mouse models, it is desirable to assure reliable reproducibility and severity. Furthermore, the use of larger studies with many experimental animals would benefit from rapid hearing loss induction as realized by a single administration of both an aminoglycoside and a loop diuretic (18), instead of more complex regimens using several administrations per day for several consecutive days (15,19).…”

Auditory nerve impulses induced by 980 nm laser

“…There were several effective ototoxic deafening protocols to eliminate hair cell fuction. [30][31][32] In conclusion, stimulation with a laser of 980 nm wavelength can successfully induce CAPs outside the cochlea. Furthermore, the results of our research into the effects of pulse duration, laser power, and radiant exposure provide information about optical parameters relevant to improving the design of optical cochlear implants toward their eventual application in the human cochlea.…”