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.

Nutritional status, glutathione levels, and ototoxicity of loop diuretics and aminoglycoside antibiotics

Chinchillas deprived of food for 48 h prior to the administration of a combined dose of ethacrynic acid (10 mg/kg) and kanamycin (100 mg/kg) suffered a profound hearing loss. Fed animals did not demonstrate any hearing loss at the same dose levels. Drug metabolism may be the common pathway by which ototoxic agents interact, by a mechanism which is common to both the cochlea and the kidney. Glutathione (GSH) is a tripeptide which is involved in several pathways in the detoxification of active oxygen and reactive species formed during xenobiotic metabolism. The enhanced auditory dysfunction was paralleled by one-third decline in hepatic glutathione levels in the food-deprived animals. Manipulation of endogenous GSH levels may mitigate the toxicities of many of these drugs, which otherwise limit their clinical usefulness. These results also indicate that nutritional status may have important clinical implications during drug therapy.

Intratympanic ototoxicity: influence of post-injection survival period

Many studies have been reported on the intratympanic ototoxicity of different drugs in animal models. The recovery periods of the animals following intratympanic drug applications varied among these studies. The present study compares the cochlear damage caused by intratympanic kanamycin following short (4 days) and long (30 days) post-injection survival periods, using the guinea pig as the animal model. The degree of cochlear damage 4 days after kanamycin injection was consistent among the tested animals. The degeneration was mainly confined to the outer hair cells and almost all inner hair were spared. The change 30 days after kanamycin injection was more variable among the animals and both inner and outer hair cells were damaged. This shows that, although the damage to the cochlea after intratympanic aminoglycoside injection is progressive, a short post-injection recovery period is suitable for comparative intratympanic ototoxicity studies.

The effect of chronic application of kanamycin on stereocilia and their tip links in hair cells of the guinea pig cochlea

Albino guinea pigs were treated with kanamycin (400 mg/kg i.p.) daily for 10 days. After a 2-week recovery period their cochleae were analyzed by scanning electron microscopy. Attention was paid to those outer hair cells which had been less severely damaged. Stereocilia of the outer hair cells were often constricted at the root, and in some cases had become detached at the root. In stereocilia showing any degree of abnormality, the tip links were usually missing. However, in a few exceptional cases, tip links could remain on stereocilia showing other abnormalities, such as constriction at the root. Where hair cells were otherwise apparently unaffected, a much higher proportion of tip links remained, even on cells situated in an area of extensive hair cell loss. The results give further information on the process of kanamycin poisoning. They also suggest that substantial loss of tip links, and therefore perhaps of transduction, is one of the preliminary consequences of kanamycin poisoning.

Sound perception in the ultrasonic region

The mechanism of ultrasonic perception was investigated electrocochleographically in guinea pigs (1) to compare AP responses in normal animals with those in kanamycin-poisoned animals with a damaged outer hair cell system; (2) and to analyse the masking property of continuous ultrasonic sound upon the AP evoked by burst stimuli within the auditory field. The study revealed several facts indicating the breakdown of cochlear sharp frequency analysis in the transduction of ultrasonic sound. We concluded that the sound perception in the ultrasonic region could be performed by the inner hair cell system without any enhancement or modulation of the outer hair cell system, which was regarded as an important process in a recent model of cochlear micromechanics.

Comparative ototoxicity of kanamycin A and kanamycin B in the guinea pig

It has previously been shown that simple compounds with multiple amine groups are ototoxic, the degree of ototoxicity depending on the number of amine groups in the molecule. The relationship between the number of amino groups and ototoxicity in aminoglycoside was studied using kanamycin A and kanamycin B, which contain 4 and 5 amino groups respectively. Forty-five pigmented guinea pigs were injected intratympanically with 0.1 ml of different concentrations of kanamycin A and kanamycin B. The animals were sacrificed 4 days after injection and the organ of Corti was studied by scanning electron microscopy. It was found that on an equimolar basis, kanamycin B (with 5 amino groups) is more cochleotoxic than kanamycin A (with 4 amino groups). The greater cochleotoxic potential of kanamycin B may be explained by the higher cationic nature of the molecule due to protonation of the amino--NH2 groups at physiological pH, resulting in a greater affinity between the drug and the cell membrane.

Aminoglycoside toxicity in infants and children

The aminoglycosides are frequently prescribed for infants and children, especially newborn infants with suspected or documented sepsis or meningitis. In older infants and children, the aminoglycosides are commonly used to treat acute respiratory exacerbations in patients with cystic fibrosis, intra-abdominal sepsis, complicated urinary tract infections, and other infections caused by gram-negative enteric bacilli. Although these drugs are generally well tolerated and efficacious, there is relatively little information on toxicity in pediatric patients. The potential for ototoxicity from the aminoglycosides, especially streptomycin, kanamycin, and gentamicin, was evaluated in seven prospective, controlled studies of 1,321 newborn infants. Although the designs and follow-up periods were different among the studies, the audiometric tests were similar and appropriate for age. Three studies measured auditory brain stem response during the neonatal and early infancy periods. With the exception of one study, ototoxicity occurred less frequently in aminoglycoside-treated patients than it did in untreated control patients. One study from Canada demonstrated abnormal brain stem response audiograms in gentamicin- or tobramycin-treated neonates compared with normal brain stem response audiograms in untreated control subjects. That study, however, was flawed by the small number of patients evaluated and the lack of follow-up of any patients. Nephrotoxicity appears to be rare in neonates, although one study in this age group showed an elevated N-acetyl-beta-glucosaminidase excretion rate in gentamicin-treated infants compared with rates in infants treated with amikacin or chloramphenicol. In that study, no attempt was made to correlate lysosomal injury with clinical or conventional laboratory evidence of nephrotoxicity. The toxicity of the aminoglycosides in older infants and children has not been adequately assessed. The broadest experience with these compounds has been in patients with cystic fibrosis, and most open studies in these patients have indicated a relative lack of ototoxicity and nephrotoxicity. It should be emphasized, however, that the standard dosage of aminoglycosides in patients with cystic fibrosis frequently results in serum concentrations that are lower than anticipated because of a relatively larger volume of drug distribution and a greater urinary excretion rate. The lack of reports on aminoglycoside-associated toxic effects in children suggests that these compounds are safe and well tolerated in this age group.

Ototoxicity of kanamycin in albino and pigmented guinea pigs. I. A morphologic and electrophysiologic study

Ototoxic drugs of the aminoglycoside type have been shown to accumulate to melanin, suggesting a possible mechanism for their ototoxicity. The present study was undertaken by combining electrophysiologic and morphologic methods to investigate whether the ototoxicity of kanamycin is different in pigmented and albino guinea pigs. In pigmented animals a kanamycin dose of 200 mg per kilogram of body weight per day resulted in hearing loss together with loss of both inner and outer hair cells. The albino animals in the same dose group showed significantly less hearing loss and hair cell degeneration. With daily doses of 20 and 60 mg/kg/day, no difference in ototoxicity was found between the pigmented and albino animals. The results support the hypothesis that affinity of kanamycin to inner ear melanin might be responsible for the difference in ototoxicity between albino and pigmented guinea pigs.

[Measurement of an auditory impairment induced by aminoglycosides using a shuttle box method in newborn rats]

To investigate the auditory impairment induced by the administration of aminoglycosides in the newborn, the shuttle box method was employed to measure the auditory threshold of rats. Five groups of newborn rats were administered kanamycin sulfate, 250 and 500 mg/kg, streptomycin sulfate, 250 and 500 mg/kg, or 1 ml/kg saline, subcutaneously, from the 10th to the 15th day of birth. The auditory threshold of the control group could be measured by the shuttle box method at the age of 100 days. The auditory threshold of the control group was 52.1 +/- 1.0 dB (N = 14). The auditory thresholds of the animals treated with kanamycin 250 mg/kg and streptomycin 250 mg/kg groups were measured in only 1 (61.0 dB) and 4 (64.8 +/- 4.6 dB), respectively, since the auditory toxicity of these drugs in newborn rats was stronger than adult rats. Auditory threshold of the 250 mg/kg streptomycin group was significantly higher than that of the control group. The animals which could not be measured for the auditory threshold had the ability to acquire conditioned avoidance response when both conditioned stimuli (tone and light) were presented. However, after differentiation of the stimuli, the percent avoidance to tone in these animals was significantly decreased and did not recover by the following trainings, while the percent avoidance to light was similar to that before the differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex modification as a test for sensory function

Reflex modification is a versatile procedure for the assessment of sensory function because it can provide information about the responses of several sensory systems to both weak and intense stimuli. The procedure has two elements: The elicitation of some reflex, such as the acoustic startle reflex, and the modification of that reflex by preliminary stimuli. In these experiments we used reflex modification and reflex elicitation procedures to examine the normal development of auditory function in rats and to evaluate alterations in auditory function produced by physical and toxic insult. Adult rats exposed to octave bands of noise demonstrated frequency-specific deficits on a test of reflex modification, but not reflex elicitation. In the studies of developing rats, reflex elicitation appeared by postnatal day 12 and modification around day 14. Frequency-specific increases in both measures suggested that the phenomena were sensitive to auditory development and, not simply, motor development. Exposure to kanamycin on postnatal days 8 to 16 produced dose-related deficits in the ability to detect stimuli at 32 and 16 kHz, but not 4 and 0.8 kHz. These effects were observed in the absence of changes in reflex elicitation. The results demonstrate that reflex modification procedures provide more sensitive and specific information than that provided by the use of reflex elicitation alone.

[Toxicity and antimicrobial properties of the new aminoglycoside antibiotic 535]

LD50 of antibiotic 535 (3'-desoxykanamycin C) on its intravenous, subcutaneous and oral administration to albino mice was 225, 1150 and at least 5000 mg/kg respectively. After a single subcutaneous administration to rabbits in a dose of 10 mg/kg antibiotic 535 was rapidly absorbed and detected in the blood and organs of the animals for 24 hours. The antibiotic was mainly excreted with the urine. Comparative investigation of the pharmacokinetics of antibiotic 535, tobramycin and kanamycin in rabbits revealed no significant differences. Antibiotic 535 showed a broad antibacterial spectrum and inhibited both grampositive and gramnegative bacteria. It was highly active against infections caused by S. aureus, E. coli and Pr. vulgaris and somewhat less active against infections caused by Ps. aeruginosa. In treatment of experimental tuberculosis of albino mice antibiotic 535 and tobramycin were inferior by their efficacy to kanamycin.

Ventral cochlear nucleus neural discharge characteristics in the absence of outer hair cells

The role of the cochlear outer hair cell (OHC) in auditory processing remains poorly understood. The OHCs possess an independent afferent innervation which constitutes 5-10% of cochlear afferent neurons and which appears to project to the cochlear nucleus (CN). Whether the OHCs contribute to the processing of auditory signals in the CN has not been determined. To address this question, kanamycin ototoxicity was used to produce selective OHC loss while leaving the inner hair cell (IHC) population largely intact, in the basal portion of the cochlea of chinchillas. Single unit responses were then recorded in the ventral cochlear nucleus (VCN), and compared to responses in untreated subjects. Many of the changes observed in VCN neural responses reflected changes which have previously been reported in the VIIIth nerve. However, frequency tuning curve tip segments which were normal in both bandwidth and length were observed in approximately 22% of the units associated with regions of complete OHC loss and preservation of IHCs. This has not been reported in previous OHC lesion studies. Also, first spike latency was found to be significantly lengthened for units associated with the OHC free regions. Those features of VCN neural responses which first arise within the CN, such as non-primary-like post-stimulus-time histogram response patterns, were unaffected by OHC loss. These results suggest that afferent fibers associated with OHCs do not play a major role in signal processing in the VCN.

Comparative toxicity of intravitreal aminoglycoside antibiotics

We compared the toxicity of the aminoglycoside antibiotics (tobramycin, amikacin, netilmicin, and kanamycin) by ophthalmoscopy, light and electron microscopy, and electro-retinography after intravitreal injection in rabbits in doses ranging from 100 to 3,000 micrograms. The earliest manifestations of toxicity were confined to the outer retina with each drug, with lamellar lysosomal inclusions in the retinal pigment epithelium as the earliest finding. However, the aminoglycosides displayed marked differences in the threshold dose required to produce toxic reactions, permitting the following ordering of toxicity: (most toxic) gentamicin greater than netilmicin = tobramycin greater than amikacin = kanamycin (least toxic).

[Frequency selectivity of the normal guinea pig cochlea and in experimental hearing loss]

The frequency selectivity of the cochlea was measured in pigmented guinea pigs with implanted electrodes using simultaneous masking paradigm. In animals with experimentally induced deafness, AP tuning curves are broadened by a factor of 2-3 as compared with normal animals. The deterioration of frequency selectivity is thought to correlate with extent of the outer hair cells loss. The deterioration of threshold and tuning properties of the cochlea seem to be induced by the loss of the functional integrity of the outer hair cells.

Topical antimicrobial toxicity

Three topical antibiotics and four antiseptics (1% povidone-iodine, 0.25% acetic acid, 3% hydrogen peroxide, and 0.5% sodium hypochlorite) were directly applied to cultured human fibroblasts to quantitatively assess their cytotoxicity. The four antiseptics were found to be cytotoxic; all of the cytotoxic agents except hydrogen peroxide were subsequently found to adversely affect wound healing in an animal model. Comparison of bactericidal and cytotoxic effects of serial dilutions of these four topical agents indicated the cellular toxicity of hydrogen peroxide and acetic acid exceeded their bactericidal potency. Bactericidal noncytotoxic dilutions of povidone-iodine and sodium hypochlorite were identified. These experiments provide evidence that 1% povidone-iodine, 3% hydrogen peroxide, 0.5% sodium hypochlorite, and 0.25% acetic acid are unsuitable for use in wound care. This sequence of experiments could be used to identify bactericidal, noncytotoxic agents prior to their clinical use.

Results of an ultrastructural study comparing stria vascularis with organ of Corti in guinea pigs treated with kanamycin

Ultrastructural study of ototoxicity is well documented with two points of interest: organ of Corti for aminoglycosides and stria vascularis for loop diuretics. As a previous study suggested initial lesions of stria vascularis, an attempt of comparison and of chronological study was made between the organ of Corti and stria vascularis lesions by kanamycin intoxication. The method was devised by J. M. ARAN, with electrophysiological control. We failed to find in the stria vascularis a radial or longitudinal pattern of lesions. We could not discern a chronological injury between the organ of Corti and stria vascularis because both were damaged even in the less deafened animals. Nevertheless, two facts were clarified: hair cell lesions are lysosomial as for the kidney lesions, while stria vascularis lesions are mitochondrial, melanine granulations play a part in drug metabolism (increased number, secretory aspect) and deserve further study.

DNA sequences specifying the transcription of the streptococcal kanamycin resistance gene in Escherichia coli and Bacillus subtilis

The gene conferring resistance to kanamycin, aphA, and originating from the streptococcal plasmid pJH1 was inserted into a shuttle vector. Full expression of aphA was obtained in Escherichia coli and Bacillus subtilis. The starting point for aphA transcription, determined by S1 nuclease mapping, was located 340 base pairs upstream from the ATG translational initiator codon. The sequence of the promoter consists of the hexanucleotides TTGACA and TATCTT, with a spacing of 17 base pairs. The stability profile of a 600 base-pair-long DNA fragment containing the aphA promoter and the translational initiation site indicated that, as already reported for Escherichia coli, both structures are located in domains of weak stability.

Low ototoxicity and its mechanism of netilmicin

The ototoxicity and nephrotoxicity of netilmicin were compared with those of dibekacin, kanamycin and amikacin using rabbits. Groups of 5 rabbits each were given doses of 50 or 100 mg/kg of either one of the four drugs for 30 days, and 10 days after the last injection, all animals were prepared for histopathological studies. Results show the least ototoxicity of netilmicin in comparison to the other three antibiotics. It has been concluded that the low ototoxicity of netilmicin is due not to its lack of accumulation in the perilymph but to its low toxicity to the hair cells.

Single-neuron labeling and chronic cochlear pathology. III. Stereocilia damage and alterations of threshold tuning curves

Tuning curves were obtained from 100 to 150 auditory-nerve fibers spanning the range of characteristic frequencies (CFs) in each of eight cases of permanent noise-induced and three cases of permanent kanamycin-induced threshold shift. In each ear, from one to six neurons were intracellularly labeled with horseradish peroxidase. Locating the labeled terminals in plastic-embedded surface preparations of the cochlea enabled us to accurately correlate particular tuning-curve abnormalities with the condition of the sensory cells generating them. The correlations between structural and functional changes suggest that a normal tuning-curve tip requires that the stereocilia on both the IHCs and OHCs (especially those from the first row) be normal. Selective damage to the OHCs is associated with elevation of the tips and hypersensitivity of the tuning-curve tails. This tuning-curve pattern also originates from cochlear regions at the basal border of hair cell lesions where the local hair cells (and their stereocilia) appear completely normal at the light-microscopic level. Total destruction of the OHCs in a region in which the IHCs appear normal (as can happen in cases of kanamycin poisoning) is associated with bowl-shaped tuning curves which appear to lack a tip. Combined damage to the IHCs and OHCs (as typically happens in cases of acoustic trauma) is invariably associated with elevation of both tips and tails on the tuning curve. A framework for the interpretation of the results is suggested in which the activity of the OHCs is transmitted via the tectorial membrane to the tall row of stereocilia on the IHCs.

Enzymatic and nucleotide sequence studies of a kanamycin-inactivating enzyme encoded by a plasmid from thermophilic bacilli in comparison with that encoded by plasmid pUB110

The product of a kanamycin resistance gene encoded by plasmid pTB913 isolated from a thermophilic bacillus was identified as a kanamycin nucleotidyltransferase which is similar to that encoded by plasmid pUB110 from a mesophile, Staphylococcus aureus. The enzyme encoded by pTB913 was more thermostable than that encoded by pUB110. In view of a close resemblance of restriction endonuclease cleavage maps around the BglII site in the structural genes of both enzymes, ca. 1,200 base pairs were sequenced, followed by amino-terminal amino acid sequencing of the enzyme. The two nucleotide sequences were found to be identical to each other except for only one base in the midst of the structural gene. Each structural gene, initiating from a GUG codon as methionine, was composed of 759 base pairs and 253 amino acid residues (molecular weight, ca. 29,000). The sole difference was transversion from a cytosine (pUB110) to an adenine (pTB913) at a position + 389, counting the first base of the initiation codon as + 1. That is, a threonine at position 130 for the pUB110-coded kanamycin nucleotidyltransferase was replaced by a lysine for the pTB913-coded enzyme. The difference in thermostability between the two enzymes caused by a single amino acid replacement is discussed in light of electrostatic effects.

Dissociation of maximum concentration of kanamycin in plasma and perilymph from ototoxic effect

Kanamycin was administered in total daily doses of 0 (vehicle), 100, 200 or 300 mg/kg to different groups of guinea pigs for two weeks. These total daily doses were administered according to three different dosing schedules, either as a single injection given once a day, divided into two equal doses and given twice a day, or divided into four equal doses and administered four times a day. It was found that the magnitude of the ototoxicity resulting from kanamycin administration was related to the total daily dose alone and not the dosing schedule. This lack of relationship between the dosing schedule and the magnitude of the ototoxicity due to kanamycin is the reverse of that reported for the nephrotoxicity resulting from gentamicin, tobramycin and netilmicin.

Conduction of nonconjugative plasmids by F' lac is not necessarily associated with transposition of the gamma delta sequence

A nonconjugative kanamycin-resistant (Kmr) recombinant plasmid, pNR5311, transferred at a low frequency from an Hfr or F' lac Escherichia coli donor to an F- lac- recipient. Among the transconjugants, two types of Kmr plasmids were found: one was indistinguishable from pNR5311 (type A), and the other was a recombinant between pNR5311 and the gamma delta sequence (type B). When the F' lac strain was used as a donor, 5% of lactose-fermenting (Lac+) and 75% of lactose-nonfermenting (Lac-) transconjugants had type A plasmids. A kinetic study revealed that type A plasmids were transferred more readily in short mating periods than were type B plasmids. Involvement of Tn903, which is present in pNR5311, in transfer of type A plasmids was unlikely since there was no discernible change in the F' lac molecule coexisting with the type A plasmid in the transconjugant cells. The non-gamma delta-associated conduction of pNR5311 by F' lac did not require the recA+ function of the donor. Conduction of pBR322 by F' lac was also carried out, and two types of plasmids with and without gamma delta were found, as with pNR5311. These findings suggest that the transfer of nonconjugative plasmids is conducted by a novel pathway which is not associated with translocation of transposable elements into either plasmid.

Transposon Tn5 encodes streptomycin resistance in nonenteric bacteria

Strains of Caulobacter crescentus, Pseudomonas putida, Acinetobacter calcoaceticus, Rhizobium meliloti, and Rhodopseudomonas sphaeroides carrying the kanamycin resistance-encoding transposon Tn5 were 15 to 500 times more resistant to streptomycin than transposon-free strains. The streptomycin resistance determinant, which is separable from the kanamycin resistance determinant of Tn5, was not expressed in Escherichia coli or Klebsiella aerogenes.

Effects of nephrotoxic compounds on active uptake of drugs in isolated renal tubules in rabbits

The uptake of sulfonamides and phenolsulfonphthalein (PSP) was examined in vitro using isolated renal proximal tubule suspension, and the effects of nephrotoxic compounds on the uptake of sulfamethizole (SMZ) were studied. The uptake of SMZ and PSP was energy dependent and was inhibited competitively by iodopyracet (IP), which is transported actively by the p-aminohippurate mechanism. The uptake of sulfamethoxazole was also reduced by IP but that of sulfanilamide was negligible. The present results correspond well with those of in vitro experiments reported previously. Nephrotoxic compounds, mercuric chloride, neomycin, viomycin and kanamycin, decreased the uptake of SMZ non-competitively. The inhibitory action of the three antibiotics corresponds with in vivo potency, suggesting that this renal tubule preparation may provide a simple method for predicting the nephrotoxicity of drugs.

Histopathological study of the cochlea with altered perilymph metabolism

In 41 guinea pigs an experiment was conducted to determine the effect of kanamycin on ears with or without blockage of the cochlear aqueduct. In 24 animals the cochlear aqueduct was blocked on one side, and after 1 to 21 days, kanamycin (300 mg/kg) was given daily and subcutaneously until the pinna reflex began to decrease. The remaining animals were used for controls: exposure of and trauma to the aperture of the cochlear aqueduct and kanamycin administration (8), blockage of the cochlear aqueduct only (3 plus 17 previous cases), and kanamycin administration to normal animals (6). The survival time of all these animals was four months. The results showed that ears with blockage of the cochlear aqueduct and kanamycin administration consistently demonstrated a more severe and extensive atrophy of the cochlear sensory cells. The lesions occurred primarily at the basal end and spread toward the apical turn, although the lesions in some specimens jumped from the basal to apical turn. The outer hair cells were more extensively affected than the inner hair cells. Proteinaceous precipitates were often found to be slightly greater in the perilymph of cochleae with blocked cochlear aqueducts. From these observations, it is concluded that the decrease in patency of the cochlear aqueduct will impair perilymph metabolism, causing the cochlear sensory cells at the basal turn to become more vulnerable to noxious substances.

Tn4001: a gentamicin and kanamycin resistance transposon in Staphylococcus aureus

We describe a 4.5 kilobase transposon, Tn4001, which mediates resistance to gentamicin, tobramycin and kanamycin in Staphylococcus aureus. Originally detected in plasmid pSK1, Tn4001 was shown to undergo rec-independent transposition to the chromosome from this plasmid and from an inserted derivative of the plasmid pII147. Heteroduplexes between plasmids with and without Tn4001 demonstrated a characteristic stem and loop structure with inverted repeats of approx. 1.3 kilobases.

Genetic structure and stability of a copy number mutant of IncFI group plasmid ColV-K94 in Escherichia coli K-12

Mutants pWS10, pWS11 and pWS12 were derived from an IncFI group plasmid ColV-K94 by the insertion of a transposon Tn903 (Kmr). These plasmids were all approximately 130 kb in length. The plasmid pWS12 resembled the wild type ColV-K94 in transmissibility, incompatibility and stable maintenance. Cells harboring pWS11 were poor conjugal donors but resistant to the same level of kanamycin as pWS12 containing hosts. In contrast, pWS10 conferred a higher resistance to kanamycin and exhibited reduced incompatibility properties in comparison with pWS12. The higher drug resistance associated with pWS10 appeared to be a consequence of an increase in its copy number and the generation of miniplasmids of varying sizes. Electron microscope analysis of the copy mutant pWS10 revealed that Tn903 was located at a site adjacent to a region 32.6F to 35.3F. The latter region appears to be the primary replicon of ColV-K94 and is homologous with the secondary replicon of F. The insertional mutagenesis with Tn903 brought about an extensive DNA rearrangement including the duplication and translocation of the stems of two inverted repeat structures. The DNA alterations of pWS10 were distinguishable through comparison of its EcoRI digestion patterns with those of pWS11 and pWS12.

Ototoxic and nephrotoxic effects of combined treatment with cis-diamminedichloroplatinum and kanamycin in the guinea pig

Ototoxic and nephrotoxic potentiation with concomitant cis-diamminedichloroplatinum, or cis-platinum II (CSP), and aminoglycoside therapy was investigated in the guinea pig. We evaluated possible potentiation of the toxic effects of CSP and kanamycin compared with CSP alone in the inner ear and kidney and quantitatively localized CSP in the cochlea with gamma emission analysis of 195mPt. Kanamycin-treated animals demonstrated cytocochleograms and ABR waveforms, absolute latencies, and interwave latencies for waves I, II, and III similar to control animals at our maximum level of acoustic stimulation. CSP treatment produced 60% to 70% mean outer hair cell (OHC) loss in the basal turn of the cochlea, a reduction in ABR waveform and amplitude, and an increase in latencies of ABR waves I, II, and III. Combined CSP and kanamycin treatment produced 90% to 100% mean OHC loss in all rows of the basal turn of the cochlea, with no discernible ABR waveform corresponding to the region stimulated by a 4500 to 7000 Hz acoustic click. Combined treatment produced the most significant cortical medullary tubular necrosis and interstitial nephritis. Furthermore, this study reports for the first time localization of platinum in the inner ear.

Morphologic study of effects of kanamycin on the developing cochlea of the rat

The development of the rat inner ear starts about day 9 of a 22-day gestational period. The sensory and supporting cells are morphologically identifiable by day 18 of gestation; however, auditory function is not evident until day 9 postnatally. The organ of Corti attains adult maturity about day 16 postnatally. Morphologic and physiologic studies have shown that administration of sublethal doses of aminoglycosidic antibiotics, including kanamycin, damages the sensory and supporting cells of the inner ear in mammals. This results in the impairment of auditory function. This study was designed to determine the earliest stage in cochlear duct development at which kanamycin toxicity can be morphologically detected. A sublethal dose of kanamycin was administered to pregnant rats on days 10 through 20 of gestation and to neonates from days 1 to 8 or from days 8 to 16 postnatally. The inner ears were dissected and processed for light microscopic and ultrastructural observations. The cochlear ducts of fetuses exposed in utero to kanamycin and those of neonates exposed from days to 1 to 8 postnatally were unaffected. Kanamycin toxicity was evident in the cochlear ducts of neonates exposed from days 8 to 16 postnatally. The most severe damage occurred in the basal coil of the cochlea where in many instances sensory cells were totally absent. The sensory cells in the middle and apical coils exhibited abnormal morphology. These results suggest: (1) kanamycin does not have any permanent toxic effects on the rat cochlear duct during gestation and the first week of postnatal life. This provides a basis for further studies into the possible pharmacologic application of this finding in humans. (2) A correlation exists between the initiation of auditory function and the vulnerability of the organ of Corti to kanamycin toxicity.

Nephrotoxic effects of aminoglycoside treatment on renal protein reabsorption and accumulation

To quantify the effects of gentamicin, kanamycin and netilmicin on renal protein reabsorption and accumulation, these drugs were administered to rats intraperitoneally (30 mg/kg/day) for 7, 14 or 21 days. Scanning electron microscopy of the glomerular endothelia, urinary measurements of sodium, potassium, endogenous lysozyme, N-acetyl-beta-D-glucosaminidase (NAG) as well as clearance and accumulation experiments after i.v. administration of egg-white lysozyme and measurements of inulin clearance (GFR) were done in each treatment group. Gentamicin administration decreased diameter, density and shape of endothelial fenestrae. Kanamycin and netilmicin appeared to have no effect at the dose used. All three aminoglycosides decreased GFR and increased urinary excretion of sodium and potassium. While gentamicin and kanamycin decreased the percentage reabsorption and accumulation of lysozyme after i.v. administration of egg-white lysozyme netilmicin had no effect. Daily excretion of total protein, endogenous lysozyme and NAG increased only after treatment with kanamycin and gentamicin. Thus, aminoglycosides may act as nephrotoxicants at glomerular and/or tubular level inducing impairment of renal reabsorption and accumulation of proteins.

Transposable element IS50 improves growth rate of E. coli cells without transposition

Insertion sequence IS50R, which encodes the transposase and an inhibitor of transposition of the kanamycin-resistance transposon Tn5, increases the growth rate of E. coli K12 cells relative to that of their otherwise isogenic counterparts during competition in continuous culture. Most clones isolated from chemostats in which selection had occurred retain their original number of copies of IS50R at their original genomic locations, implying that the increased growth rate is not mediated by transposition. The selective advantage due to a single IS50R element averages about 5% per hour. When the number of copies of IS50R is small, the growth-rate advantage is approximately proportional to the number of copies of IS50R. These results imply that IS50R has effects on cells that are independent of both position and transposition and may be important in the initial selection leading to the appearance of such elements in bacterial populations.

[Ocular and auditory organs of Ochotona rufescens]

Ochotona rufescens is an animal species native to Afghanistan, and is among many new animal species currently being raised for use in experimental research in Japan. In the present paper, we report morphological findings on ocular and auditory character of Ochotona rufescens examined first under normal conditions and then under the influence of various agents, and the results were compared with those on other experimental animals used in this study. On histological examination, the cochlear portion of the labyrinth was found to consist of a coiled canal making two and one half turns from its basal end to the upper turn, and was identical to those of cats and rabbits. Moreover, triple rows of outer sensory hair cells and a single row of inner sensory hair cells were observed. Kanamycin and furosemide (Lasix), a diuretic, were administered 10 min. apart to determine the effects of these drugs on pinna reflex, however, as a result of these administration, none of the Ochotona rufescens tested showed any appreciable depression of this reflex. By funduscopic observation with photographic records, principal retinal arteries were hardly demonstrable except for extremely vague chorioidal vessels, in the layer of the pigmented epithelium which had a puce-like color. Ay contrast, retinal veins were seen in the fundus oculi, as well as whitish optic nerves. The amplitude of the "a" wave in the electroretinogram (ERG) of Ochotona rufescens was only 1/6 that of albino rats or albino rabbits, but the "b" wave was similar in amplitude for all these three species.(ABSTRACT TRUNCATED AT 250 WORDS)

The sensitive period for ototoxicity of kanamycin in mice: morphological evidence

The ototoxicity of kanamycin was investigated in mice treated with the drug either from 6 to 9, 10 to 13, or 15 to 18 days of age. The results showed extensive damage to the outer-hair-cell (OHC) receptors of the cochlea in the 10-13-day group; some less severe damage to the OHC was found in the 6-9-day group, and little damage was observed in the 15-18 day group. The present finding is consistent with the view that the mouse cochlea is most vulnerable to the ototoxic effect of kanamycin during the period of its rapid development, i.e., between 10 and 13 days of age.

A possible method to study transient effects of ototoxic agents on the vestibular system

A method is described in which the direct influence of anoxia and ototoxic agents on the vestibular system can be studied. After fenestration of the lateral semicircular canal in pigeons, a vestibular whole nerve action potential (VAP) could be recorded during acoustic stimulation. The cochlear whole nerve action potential (CAP) was recorded simultaneously. The influence of ototoxic agents and anoxia upon the amplitude of these action potentials was studied.

Damage to sensory hairs of inner hair cells after exposure to noise in rabbits without outer hair cells

We investigated if the noise-induced damage to the stereocilia of inner hair cells (IHCs) was dependent on the integrity of the outer hair cells (OHCs) in rabbit. Prior to the noise exposure a total loss of OHCs in the basal 1.5 to 2 turns was induced by administration of kanamycin (400 mg/kg for 10 days). This left the IHCs apparently normal as observed in the scanning electron microscope. These animals exhibited a 20-60 dB hearing loss before noise exposure. In spite of this pronounced hearing loss, the fusion and inclination of the IHC stereocilia were extensive in these noise-exposed ears. The stereocilia damage occurred at the same noise exposure and was as prominent or even more pronounced than has been noted in ears exposed to noise only. Under the assumption that kanamycin causes selective destruction of OHCs, the results can be interpreted as evidence that the OHCs facilitate the IHCs at low sound levels without being involved in the process which damages IHC stereocilia at high levels of noise.

Transplacental kanamycin ototoxicity in the guinea pig

The effect of kanamycin on the cochlear sensory epithelium of albino guinea pig fetuses was studied histologically following the administration of 200 or 400 mg/kg body weight kanamycin sulfate to the pregnant mothers for 8 consecutive days at different stages of gestation. Surface view analysis of Corti's organ revealed slight damage following treatment in the middle trimester of gestation and marked damage due to treatment in the last trimester. The pattern of hair cell loss induced during and after the functional differentiation of the cochlea resembled the pattern of ototoxic lesions in the adult ear. The assumed mechanisms for induction of teratogenesis by kanamycin in the fetal organ of Corti are discussed.

Aminoglycoside ototoxicity in the chick (Gallus domesticus) inner ear: I. The effects of kanamycin and netilmicin on the basilar papilla

A single dose (100 mg/kg of egg weight) of kanamycin or netilmicin was injected into the yolk sacs of 7-day-old chick (Gallus domesticus) embryos. Embryos were collected every 24 hours and processed for light and transmission electron microscopy. Morphologic study of the medial basilar papilla disclosed that both kanamycin and netilmicin are toxic to the hair cells in this region. Intoxication was manifested by an increased number of dense osmiophilic bodies, swollen mitochondria, agglomerated chromatin, and occasional disorganization of the kinocilium basal bodies. The cytologic changes observed in the hair cells of embryos injected with netilmicin and kanamycin were similar. However, mitochondrial damage was more severe in the chicks after kanamycin than after netilmicin injection. Some of the cytologic alterations described here are comparable to those already reported for aminoglycoside-intoxicated hair cells in several mammalian species. This study and previous work indicate that the chick embryo provides a satisfactory developmental model for testing ototoxicity of drugs in vivo.

Effect of furosemide on aminoglycoside-induced nephrotoxicity and auditory toxicity in humans

We analyzed data from three prospective, controlled, randomized, double-blind clinical trails to determine whether furosemide increases the nephrotoxicity and auditory toxicity of aminoglycosides. All patients who received at least 72 h of treatment and who had no other cause for nephrotoxicity or auditory toxicity were included in the analysis. Nephrotoxicity developed in 10 of 50 (20.0%) patients given furosemide and in 38 of 222 (17.1%) patients not given furosemide (P greater than 0.3). Auditory toxicity developed in 5 of 23 patients (21.7%) given furosemide and in 28 of 119 patients (23.5%) not given furosemide (P greater than 0.3). In each case, the groups receiving and not receiving furosemide did not differ in mean age, initial creatinine, duration of aminoglycoside therapy, mean change in auditory acuity or creatinine, mean number of days to the development of toxicity, the frequency with which gentamicin, tobramycin, amikacin, or cephalothin was administered, or the mean predose and 1-h postdose plasma aminoglycoside levels. We conclude that furosemide use should not be considered a major risk factor for the development of aminoglycoside-induced nephrotoxicity or auditory toxicity.

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.

Ultrastructural changes in the cochlear sensory epithelium following damage to the organ of Corti

The repair pattern of the reticular lamina of the organ of Corti was studied after idiophatic hair-cell loss and ototoxic damage. The present report examines the repairing capacities of the inner and outer pillars of Corti and Deiters' cells in guinea pigs that received aminoglycosides for 21 days. By means of scanning electron microscopy, the defects of the reticular lamina, the hypertrophic processes of the supporting cells, and numerical increase of microvilli were observed.

Evaluation of ototoxicity of amino-glycoside antibiotics in rabbits

It is generally accepted that the ototoxicity of aminoglycoside antibiotics is gentamicin (GM) greater than dibekacin (DKB) greater than kanamycin (KM) greater than amikacin (AMK) based on the results of animal experiments. However, clinical data reveals that the ototoxicity caused by each of the aminoglycoside antibiotics does not coincide with the ototoxicity in the animals. The present study was intended histopathologically for comparative evaluation of above-mentioned antibiotics using rabbits. The ototoxicity was GM greater than DKB greater than KM greater than AMK with the dose of 100 mg/kg, which coincide with many of the conventional reports on animal experiments. However, with the dose of 50 mg/kg, the order was GM greater than AMK greater than KM greater than DKB. With the dose of 30 mg/kg, hardly any differences were noted between the ototoxicity of GM and that of AMK. It was found out that the evaluation of the ototoxicity of drugs in high doses does not always correspond to that of lower doses. Therefore, the ototoxicity should be evaluated in strict consideration of dose of drugs. Usually, the doses of drugs used in the ototoxicity studies with animals are more than 10 times higher than those used clinically. Consequently, problems still exist in infering the ototoxicity of drugs in humans directly from the results obtained from animal experiments.