An experimental study on the progressiveness of cochlear damage by aminoglycoside drug

Influence of chronic kanamycin administration on basement membrane anionic sites in the labyrinth

We studied the effect of chronic treatment with kanamycin on the basement membrane (BM) anionic sites in the cochlea and endolymphatic sac using polyethyleneimine (PEI) as a cationic tracer. Albino guinea pigs weighing 250-300 g received kanamycin (400 mg/kg/day, i.m.) for 10 or 17 consecutive days. The number of BM anionic sites as derived from the PEI area was not affected in Reissner's membrane, spiral prominence, basilar membrane or endolymphatic sac, whereas it was significantly decreased in the stria vascularis and spiral limbus, being more marked in the guinea pigs treated for 17 days than in those treated for 10 days. The number of BM anionic sites in these regions did not recover until 6 weeks after kanamycin treatment. These findings suggest that chronically administered kanamycin may selectively and progressively affect the BM anionic sites in the stria vascularis and spiral limbus, resulting in disruption of a barrier function in the cochlea, and that severely impaired BM anionic sites in the cochlea may not recover.

Partial hearing loss in the macaque following the co-administration of kanamycin and ethacrynic acid

Co-administration of kanamycin (KA) with the loop diuretic ethacrynic acid (EA) rapidly produces a profound hearing loss in the cat while maintaining normal renal function [Xu et al., Hear. Res. 70, 205-215 (1993)]. In the present paper we have applied this deafening procedure to the old world monkey Macaca fascicularis (macaque). Following the co-administration of KA and EA, the hearing loss in the macaque developed far slower than we observed in the cat. Moreover, unlike the cat, there was evidence of a partial recovery in the animal's hearing, resulting in a bilaterally symmetrical high frequency hearing loss. The extent of this hearing loss was dependent on the dose of the EA administered. Finally, the most unexpected result of the present study was the degree of acute nephrotoxicity experienced by these animals following the drug administration. The sensitivity of this species to renal failure restricted the dose of EA that could be safely administered. In conclusion, the co-administration of KA and EA cannot reliably produce a profound hearing loss in the macaque. While it can produce a dose dependent high frequency hearing loss the animal will also experience acute renal failure that requires careful management.

Inner ear damage due to lipoid nephrosis

Inner ear pathology was studied in adult rats with lipoid nephrosis induced by puromycin aminonucleoside. Although no abnormality was observed in auditory brain-stem responses, significant changes were noted in the stria vascularis. The most striking observation was that intermediate cells were markedly swelled, there-by pressing adjacent marginal cells. Severely affected marginal cells have vacuoles and increased lysosomes and protruded toward the endolymphatic space. The organ of Corti remained virtually intact. Although the vestibular maculae were relatively normal, type I hair cells in the semicircular canal underwent a conspicuous vaculolization. These findings support a postulate that the inner ear is liable to damage in lipoid nephrosis.

Circadian rhythm dependent kanamycin-induced hearing loss in rodents assessed by auditory brainstem responses

An antimicrobial agent, kanamycin, has been shown to produce as an untoward effect, ototoxicity. The purpose of this study was to investigate differential effects of kanamycin ototoxicity as a function of Rx timing with regard to circadian rhythms. Four groups of comparable weight Sprague-Dawley rats received a daily subcutaneous dosage of 225 mg/kg kanamycin sulfate with each receiving the antibiotic at a different time: 8 AM (8A), 2 PM (2P), 8 PM (8P), and 2 AM (2A). The rats were housed in separate cages, in a room on a light-dark (12:12) illumination cycle with light between 6 AM and 6 PM. Hearing loss was assessed with the auditory brainstem response (ABR) using pure tone stimuli at 8, 16, 24, and 32 kHz. ABR measures were obtained before dosing began and 2, 4, and 6 weeks after the initial dosing. Kanamycin produced a hearing loss which reflected the total dosage given to each group. Significant differences in physiologic thresholds were observed for both timing of the daily dosage (p less than 0.05), and the 2, 4 and 6 week testings (p less than 0.001). After 2 weeks, the 8A group showed an average hearing loss of 11.5 dB at 32 kHz, with the other timed treatment groups exhibiting minimal effects (3.0-6.5 dB). For the 8A group at this frequency, the loss progressed at 4 (19.5 dB) and 6 (22.5 dB) weeks. The 2P group after 4 weeks exhibited similar losses as the 8A group for this frequency, with the loss at 6 weeks being even greater (34.0 dB). The 8P and 2A groups exhibited only slight losses over all frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic status of regenerated hair cells in the avian inner ear following aminoglycoside ototoxicity

Regeneration of avian inner ear hair cells has been demonstrated after administration of aminoglycoside and after acoustic trauma. However, no published study to date has documented functional recovery of these regenerated sensory receptor cells. Newborn chicks were treated with gentamicin sulfate (50 mg/kg/day) for a total of either 5 (n = 10) or 10 (n = 76) days. Evoked potential thresholds were obtained one day after the 5-day treatment, or at intervals between one day and 20 weeks after the 10-day treatment course, and compared to thresholds of age-matched control animals. A significant hearing loss, predominantly in the high frequencies, was present after as few as 5 days of drug administration. The magnitude of hearing loss continued to increase, especially at lower frequencies, as survival increased from 1 day to 5 weeks after gentamicin treatment. Sixteen-to-20 weeks after treatment, partial recovery of thresholds was evident. These findings demonstrate that functional recovery does occur in the avian inner ear following aminoglycoside administration. Recovery occurs at all frequencies, but predominantly at low and middle frequencies, leaving significant residual high-frequency threshold elevation. Recovery lags 14 to 18 weeks behind anatomic evidence of hair cell regeneration, which was demonstrated in one study by 2 weeks after comparable administration of gentamicin.

Delay in hearing loss following drug administration. A consistent feature of amikacin ototoxicity

The time course of threshold increase in the VIII nerve compound action potential was studied in guinea pigs following amikacin administration at four different constant infusion rates. Despite the wide range of dosing durations required to achieve drug ototoxicity (2-24 days), the full development of both high and low frequency hearing loss was invariably found to be delayed with respect to the time of drug removal. The greatest degree of delayed hearing loss generally occurred within the first 7 days after drug removal, with smaller losses occurring during later time intervals. The delay showed a tendency to decrease as the ototoxic dose was increased. Using the data from the two highest dosing rates, it was estimated that a minimum of 4 days had to elapse before any hearing loss could be detected, once an ototoxic amount of drug had been administered. These data suggest that hearing loss is always substantially delayed with respect to the receipt of an ototoxic dose of amikacin, and that this must be taken into account when conducting animal experiments and when monitoring hearing in patients for the early detection of ototoxicity.

Furosemide-induced alteration of drug pathway to cochlea

The ototoxicity of aminoglycosides is known to be enhanced by post-treatment with loop diuretics. The present experimental study was undertaken to elucidate the mechanism of this enhancement immunohistologically. Intravenously administered kanamycin (KM) reached the organ of Corti rapidly (within 10 min) via the capillaries of the basilar membrane and spiral limbus. Besides this direct pathway, KM penetrated through the perilymphatic space pathway. This penetration, however, took a much longer time (90 min). In contrast, in the case when KM was followed by intravenous furosemide (FM), KM reached the perilymphatic region within a short time (1-5 min). The KM content of the organ of Corti ascertained 1-5 min after FM injection seemed almost equivalent to that determined 90 min after injection of KM alone. This FM-induced change in the time-course penetration pattern of KM might have a bearing on the enhancement of its otoxicity.

Drug permeability of the endolymphatic sac

Intravenously injected kanamycin sulfate (KM) was located in the endolymphatic sac (ES) of guinea pigs by an immunohistologic method. Kanamycin sulfate had passed through the capillaries in the subepithelial layer and reached the epithelial layer as early as 1 minute after injection. The amount of KM in the epithelial layer gradually increased with time (until 30 minutes after injection). The KM also accumulated in floating cells in the ES. These results tend to indicate that the ES is rather easily permeable to systemically administered drugs, which readily get into the regional endolymph. In conclusion, much more attention should be paid to the ES and drug ototoxicity associated with drug therapy in the management of patients with inner ear disturbances.

Morphological changes to the stereociliary bundles in the guinea pig cochlea after kanamycin treatment

Pigmented guinea pigs were treated with 400 mg/kg of kanamycin for 8 days and sacrificed 13 days later. The upper surface structures of the organ of Corti were studied using high resolution scanning electron microscopy to reveal fine details of stereociliary fusion and damage to the reticular lamina. Outer hair cell stereocilia showed from partial to complete fusion and loss whilst the inner hair cells showed very little evidence of any damage. In particular, the possible effects of kanamycin on the cross-links between the stereocilia have been investigated. The cross-links are found to be present on all outer and inner hair cell bundles which show no fusion of stereocilia. Partially-fused stereocilia which have free tips still possess the upward-pointing links, and the remaining undamaged stereocilia in these bundles possess the normal cross-links. Where fusion occurs along the sides of the stereocilia, the side-to-side links are missing although whether their absence either results in, or else is caused by, the fusion is not known.

Effects of X-ray irradiation on hearing in guinea pigs

Effects of X-ray irradiation on the hearing with CM and ABR to both air- and bone-conduction stimuli were studied continuously from immediately after the irradiation to a few weeks later. At 2, 4, and 6 krad, only slight conductive hearing impairment was found, but at 8 krad or more, CM and ABR disappeared abruptly, after having increased briefly. Advanced sensorineural hearing loss appeared at about 10 hours after irradiation ended at 8 krad, at about 6 hours at 10 krad, and at about 3 hours at 12 krad. More severe hearing impairment was observed at higher frequencies and the endocochlear d.c. potential (EP) decreased at about 7 hours after 10 krad irradiation. Histologically, no discernible changes in the hair cells or sensory hairs were found with a scanning electron microscope at about 6 hours after 10 krad irradiation, while with a transmission electron microscope, the outer hair cells in the basal coil of the cochlea were found to be mostly destroyed. However, no changes could be found in the inner hair cells or other supporting cells.

Progressive ototoxicity of neomycin monitored using derived brainstem response audiometry

Progressive hearing loss following the systemic administration of neomycin was investigated using derived brainstem response audiometry. Cats were given three to five times the maximum recommended clinical dose of neomycin over a period of 10 days. Their hearing was monitored prior to and during the administration of the drug, and periodically following its completion. The results of this study showed that the induced hearing loss generally proceeded from high to low frequencies as an advancing lesion, with regions apical to the lesion functioning normally. Although considerable variability in response to the drug existed among animals, the evoked responses from both ears of each animal showed close bilateral symmetry during the deafening process. Furthermore, the present results highlight the long-term ongoing ototoxicity associated with neomycin, and the importance of monitoring high frequencies for initial signs of an aminoglycoside induced hearing loss.

Alteration of strial capillary transport in kanamycin-treated guinea pigs

Ferritin transport through the strial capillary during kanamycin intoxication was examined under a transmission electron microscope. Twelve guinea pigs were treated intramuscularly with kanamycin (400 mg/kg/day) for 2-3 weeks. When full hearing loss was recognized by estimating the Preyer reflex or auditory brain-stem response (ABR), ferritin was given intravenously and animals were sacrificed 1/3, 1, and 2 h later. At 1/3 h, ferritin was present diffusely not only in the endothelial cell but also in the basal lamina and within vesicles in the strial cell. Alternatively, it was discharged into the endolymphatic space. At 2 h, ferritin was seen on the luminal surface and in the cytoplasm of the endolymphatic cells of Reissner's membrane. These results suggest that the basal lamina of the strial capillary was altered qualitatively by kanamycin administration.

"Is magnesium depletion the reason for ototoxicity caused by aminoglycosides?"

Aminoglycoside antibiotic drugs may cause ototoxicity and nephrotoxicity. Our hypothesis postulates that aminoglycosides cause ototoxicity by a mechanism of magnesium depletion in the hair cells of the cochlea. The same mechanism maybe responsible for nephrotoxicity caused by aminoglycosides.

Ototoxic effect of an aminoglycoside drug on an immature inner ear

In order to investigate to what extent an immature inner ear is injured by external causes, the effect of Kanamycin on an immature cochlea was studied in mice by using scanning and transmission electron microscopes. Our results showed that immature cochleae are more highly susceptible to injury than mature cochleae, especially when the Nuel's space and the Corti tunnel open. It is suggested that in humans, during the stage corresponding to the above period, that is, in about the third gestational month, the inner ear is highly susceptible to injury by external causes.

Application of loop diuretics for treatment of sensorineural hearing impairment. Experimental and clinical study

In a series of animal experiments on guinea pigs and rats, conducted in an attempt to find a better solution for the treatment of sensorineural hearing impairment and tinnitus-known as diseases almost impossible to heal-it was revealed electrophysiologically, biochemically and electronmicroscopically that loop diuretics, referred to as ototoxic drugs, cause an increased amount of the therapeutic preparation to transfer to the inner ear fluid. It is concluded, on the basis of the encouraging results of these experiments, that combined medication with metabolic activator, steroid hormone and loop diuretics is significantly more effective in improving the symptoms of patients with inner ear deafness and tinnitus.