benzyloxycarbonylvalyl-alanyl-aspartyl-fluoromethyl-ketone and Hearing-Loss--Sensorineural

We recently showed that acute energy failure in the rat cochlea induced by local administration of the mitochondrial toxin 3-nitropropionic acid (3-NP) causes hearing loss mainly due to degeneration of cochlear lateral-wall fibrocytes. In the present study, we analyzed the effect of the pan-caspase inhibitor z-Val-Ala-Asp(Ome)-fluoromethylketone (Z-VAD-FMK) on 3-NP-induced hearing loss in a model showing temporary threshold shifts at low frequencies and permanent threshold shifts at high frequencies. The model rats received an intraperitoneal injection of either Z-VAD-FMK or vehicle for 3 days starting 1 day prior to 3-NP treatment. One day after the administration of 3-NP, the auditory brain-stem response (ABR) threshold at 20 kHz was elevated to 70 dB in the Z-VAD-FMK group and to 85 dB in controls. The Z-VAD-FMK group completely recovered to the preoperative level within 14 days, whereas in the controls, the ABR threshold remained elevated at 50 dB even 28 days after the administration of 3-NP. Treatment with Z-VAD-FMK also improved recovery of hearing at 8 kHz but did not change recovery at 40 kHz. Histological examination demonstrated that treatment with Z-VAD-FMK inhibited progressive degeneration of the lateral-wall fibrocytes in the cochlear basal turn, as well as apoptosis of these fibrocytes. These results clearly indicate that caspase-dependent apoptosis of fibrocytes in the cochlear lateral wall plays an important role in hearing loss in the present animal model. Moreover, the results of the present study suggest that systemic administration of a caspase inhibitor may be an effective therapy for sensorineural hearing loss caused by acute energy failure such as that observed in cochlear ischemia.

Topics: Acoustic Stimulation; Amino Acid Chloromethyl Ketones; Animals; Apoptosis; Auditory Threshold; Caspase 3; Cochlea; Disease Models, Animal; Dose-Response Relationship, Radiation; Evoked Potentials, Auditory, Brain Stem; Gene Expression Regulation; Hearing Loss, Sensorineural; Male; Neuroprotective Agents; Nitro Compounds; Propionates; Rats; Rats, Sprague-Dawley; Recovery of Function; Spiral Ganglion; Time Factors

In renal-coloboma syndrome (RCS), null mutations of the PAX2 gene cause renal hypoplasia due to a congenital deficit of nephrons; affected individuals may develop renal insufficiency in childhood. During normal kidney development, PAX2, is expressed at high levels throughout the arborizing ureteric bud (UB); recent observations suggest that one of its key roles is to suppress apoptosis in this collecting duct lineage. The authors hypothesized that increased UB cell apoptosis due to PAX2 haploinsufficiency must directly influence the rate of branching morphogenesis in developing kidney and the number of nephrons that can be formed before birth, when nephrogenesis in humans comes to an end. If so, the authors reasoned that caspase inhibitors might be used to suppress unwanted UB cell apoptosis during kidney development in Pax2(1Neu) mutant mice and rescue the genetic UB branching defect. E17.5 kidneys from Pax2(1Neu) mutant mice had smaller (-25%) longitudinal cross-sectional area and 3.5-fold increase in collecting duct cell apoptosis versus wild-type littermates; mutant E13.5 kidney explants allowed to arborize for 50 h in vitro had 18% fewer terminal branches than wild-types. However, exposure to the caspase inhibitor, Z-VAD-fmk (25 micro M), significantly increased terminal branch number in mutant explants (23%). It also increased branching in wild-type explants, apparently reflecting an effect of Z-VAD-fmk on basal apoptosis induced by ex vivo culture conditions. Similarly, when pregnant mice were injected daily with Z-VAD-fmk (10 micro g/g weight from E10.5 to E17.5), apoptosis of Pax2(1Neu) fetal collecting duct cells was suppressed to 40% of untreated mutants; by E14, terminal branch number was increased to 152% that of untreated litters. These studies support the hypothesis that PAX2 normally optimizes the rate of branching morphogenesis in fetal kidney by suppressing UB apoptosis. Furthermore, it suggests that caspase inhibitors can rescue the branching defect caused by PAX2 mutations.

Topics: Amino Acid Chloromethyl Ketones; Animals; Apoptosis; Caspase Inhibitors; Coloboma; DNA-Binding Proteins; Hearing Loss, Sensorineural; Kidney; Mice; Mice, Mutant Strains; Mutation; Nephrons; PAX2 Transcription Factor; Syndrome; Transcription Factors