[Research progress of acute kanamycin sulfate-induced deafness in guinea pig]

To present a summary of current knowledge regarding acute kanamycin sulfate-induced deafness in guinea pig, by reviewing the published literature. Animal model of acute deafness induced by a single dose of kanamycin sulfate in combination with ethacrynic acid or furosemide in guinea pig was usually used to investigate the mechanism of cochlear cell degeneration. There were different time sequences of cell degeneration of spiral ganglion cell and hair cell in different studies. The findings may result from different doses, order of two drugs administration or time point chosen. There remains scope for further research in chronic kanamycin-induced deafness, which more replicates the type of exposure to people than acute deafness.

Aryloxoalcanoic compounds induce resistance to antibiotic therapy in urinary tract infection caused by Escherichia coli

Clofibric acid (CL) is a compound used to control hypertriglyceridemia, and ethacrynic acid (ET) is administered to enhance diuresis. These compounds are structurally analogous to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), as they have a chlorinated phenoxy moiety. As these agents are mainly excreted by the renal route, they could potentially coexist with Escherichia coli in the urinary tract of infected patients. Induction of the in vitro resistance of E. coli to hydrophilic antibiotics was determined by increasing the values of the minimum inhibitory concentration (2-40-fold). These results correlated with drastically inhibited expression of the hydrophilic bacterial channel OmpF. In vivo assays were performed in ascending urinary tract infection in female BALB/c mice. Treatment with the hydrophilic antibiotic cephalexin 25 mg kg(-1) day(-1) by the oral route diminished renal infection. The CFU mean values in the kidneys were between 75% and 89% lower than those in animals without treatment. Simultaneous exposure to CL (at a therapeutic dose, 28.6 mg kg(-1) day(-1)) did not change the effect of the treatment. In contrast, ET at 2.9 mg kg(-1) day(-1) or 2,4-D at 70 mg kg(-1) day(-1) inhibited the antibiotic therapeutic effect. Moreover, 2,4-D dramatically increased bacterial infection after 9 days of exposure.

Ototoxic drugs and sensorineural hearing loss following severe neonatal respiratory failure

AIM

To determine relationships between ototoxic drugs and 4-y sensorineural hearing loss (SNHL) in near-term and term survivors of severe neonatal respiratory failure.

METHODS

All 81 survivors of the Canadian arm of the Neonatal Inhaled Nitric Oxide Study (mortality 32, loss to follow-up 9) received loop diuretics, aminoglycosides, and neuromuscular blockers (NMB), and 50 received vancomycin as neonates. Prospective, longitudinal secondary outcome using audiological tests diagnosed late-onset, progressive SNHL in 43 (53%); not flat (sloping) in 29, flat (severe to profound) in 14. Risk for SNHL was determined.

RESULTS

A combination of duration of diuretic use of >14 d and average NMB dose of >0.96 mg/kg/d contributed to SNHL among survivors (odds ratio 5.2; 95% CI 1.6, 16.7). Markers of illness severity did not contribute. Dosage or duration of aminoglycosides use did not relate to SNHL. Cumulative dosages and duration of use of diuretics; NMB; use of vancomycin; and overlap of diuretics with NMB, aminoglycosides, and vancomycin individually linked to SNHL (p<0.001).

CONCLUSION

Overuse of loop diuretics and/or NMB contributes to SNHL after neonatal respiratory failure; markers of illness severity or the appropriate administration of aminoglycosides do not.

Novel antiglaucoma prodrugs and codrugs of ethacrynic acid

The purpose of this study was to synthesize a novel prodrug of ethacrynic acid (ECA) with short chain polyethylene glycols (PEGs) and codrugs of ECA with the beta-adrenergic blocking agent atenolol (ATL) or timolol (TML) to overcome the adverse effects of ECA and to enhance its physicochemical properties.

Glial cell line-derived neurotrophic factor. Potential for otoprotection

Sensorineural hearing loss results from the degeneration of hair cells and/or auditory neurons in the cochlea of the inner ear. BDNF and NT-3 were shown to support survival of auditory neurons both in vitro and in vivo. Cochlea from P3-P4 rats were cultured as floating explants and hair cells in the organ of Corti were identified by phalloidin-FITC immunostaining. Treatment with cisplatin (35 micrograms/mL) or neomycin (0.6 mM) resulted in 21.2 +/- 6.0% and 7.4 +/- 4.7% surviving hair cells, respectively, after 3 days in culture. GDNF, added together with the ototoxins, increased their number to 46.7% and 37.4%, respectively. In cultures of dissociated cochlea from 4-week-old rat, cisplatin (5 mg/mL) added 24 h after seeding resulted in only 6.1 +/- 1.2% surviving neurons. However, when cisplatin was added together with GDNF (10 ng/mL), 32.8 +/- 1.0% of the neurons survived. The efficacy of GDNF in animal models of ototoxicity was tested next. Guinea pigs were pretreated with GDNF in one ear, delivered either by infusion into the inner ear (scala tympani) with Alzet minipumps (50 ng/mL at a 0.5 microL/h), or injected into the middle ear (120 microL at 1 mg/mL) through the tympanic membrane. The ear that did not receive GDNF always served as control. Ototoxicity was induced systemically either by intraperitoneal cisplatin injections (1 mg/kg/day for 15 days or two injections of 7.5 mg/kg at a 5-day interval or by a combination of kanamycin (200-300 mg/kg, administered subcutaneously) and ethacrinic acid (40 mg/kg, intravenous). It was found that the number of surviving hair cells in GDNF-treated ears was about twice that of control ears in animals exposed to the ototoxins. The transducing GDNF receptor (ret) is expressed in the inner ear.

Topical gentamicin and ethacrynic acid: effects on cochlear function

OBJECTIVE

To determine whether concurrent intravenous administration of the loop diuretic ethacrynic acid potentiates the toxicity of the aminoglycoside antibiotic gentamicin applied topically on the round window.

STUDY DESIGN

The authors studied the effects on cochlear sensitivity of co-administered intracardiac ethacrynic acid (40 mg/kg) and high-dose topical gentamicin solution (100%) applied to the round window. Comparisons were made with animals receiving ethacrynic acid plus systemic gentamicin (100 mg/kg); topical gentamicin alone; systemic gentamicin alone; and intravenous ethacrynic acid alone.

METHODS

Experiments were carried out on pigmented guinea pigs weighing 400 to 500 g. Changes in cochlear function were characterized by monitoring shifts in compound action potential (CAP) thresholds by use of chronic indwelling electrodes implanted at the round window, vertex, and contralateral mastoid.

RESULTS

After 20 days animals receiving ethacrynic acid in combination with topical gentamicin to the round window failed to demonstrate a significant deterioration in cochlear sensitivity, whereas all animals receiving systemic gentamicin plus ethacrynic acid experienced profound increases in CAP thresholds.

CONCLUSIONS

This study supports the contention that ethacrynic acid potentiates aminoglycoside ototoxicity by facilitating the entry of the antibiotics from the systemic circulation into the endolymph. In addition, this study answers important clinical concerns regarding the safety of the use of topical aminoglycoside agents in combination with loop diuretics.

Ototoxicity of loop diuretics

The loop diuretics are drugs that increase the excretion of water and electrolytes in the urine by their action on the cells in the loop of Henle. Clinical reports of ototoxicity of these agents are reviewed, and the results of a number of studies in experimental animals are discussed. These drugs can cause either a temporary, or in some cases, a permanent loss of hearing in patients. Animal experiments show that these drugs act on the stria vascularis, producing edema of these tissues and a temporary loss of function, resulting in a decrease of the endocochlear potential. This can result in secondary effects on sound-evoked measures of hearing. As new information unfolds about protective agents, it may be possible to preserve hearing and maintain the desired therapeutic effect.

The effect of intracameral ethacrynic acid on the intraocular pressure of living monkeys

Previous studies have shown that the sulfhydryl-reactive ethacrynic acid increases outflow facility in living monkeys when perfused via the anterior chamber. To study its potential clinical use further, living monkeys were intracamerally injected with 10 microliters of ethacrynic acid, with concentrations ranging from 0.5 to 7.5 mmol/l. The fellow control eye was injected with 10 microliters of diluent. The status of the anterior segment was monitored by slit-lamp biomicroscopy and the intraocular pressure was measured by pneumatonometry with the monkeys anesthetized with ketamine. The anterior segment of living monkeys tolerated injections up to 3.0-mmol/l ethacrynic acid without marked adverse effects. One of 13 monkey eyes injected with 3.0-mmol/l ethacrynic acid demonstrated mild reversible segmental corneal edema. The greatest mean intraocular pressure reduction in the 3.0- to 3.75-mmol/l group occurred at six hours, with the experimental intraocular pressure decreasing 2.9 mm Hg compared to a mean intraocular pressure increase of 0.1 mm Hg in the control group (n = 19). Concentrations of ethacrynic acid less than 3.0 mmol/l did not provide reliable reduction of intraocular pressure, whereas concentrations greater than 3.75 mmol/l caused a greater incidence and severity of corneal edema. We believe that the intracameral injection of ethacrynic acid can reliably and safely reduce intraocular pressure in living monkey eyes, and that this drug deserves further investigation as a potential antiglaucomatous agent.

Physiologic and rheologic effects of the antisickling agent ethacrynic acid and its N-butylated derivative on normal and sickle erythrocytes

Ethacrynic acid, a loop diuretic, has been shown to inhibit hemoglobin S polymerization. Until now, however, most studies were performed using purified solutions of hemoglobin S. The experiments reported here were designed to examine the effects of ethacrynic acid and its n-butryic acid derivative on the rheological and physiological properties of intact red blood cells. Using net and unidirectional flux measurements, both agents were shown to cause ion and water loss from normal and sickle erythrocytes. Since cell shrinkage adversely influences red cell rheology, it is unlikely that this class of compounds, despite its ability to inhibit hemoglobin S polymerization, will prove useful in the treatment of sickle cell disease.

[Deafness, induced by sodium ethacrynate in guinea pigs, alleviated by microwave treatment]

Microwave is used to treat temporal hearing loss caused by intravenous injection of the ethacrynic acid in guinea pigs. The recovery of hearing is much faster in the treated groups than in the control group. The article proposes possible mechanism of the effects against the ethacrynic acid induced deafness and assume that the result of this research can provide an experimental basis for treatment of some perceptive deafness due to ischemia of stria vascularis of the cochlea.

Phase I study of thiotepa in combination with the glutathione transferase inhibitor ethacrynic acid

The glutathione transferases comprise a family of isoenzymes, one or more of which are involved in the conjugation of alkylating agents to glutathione (GSH). Increased GSH transferase activity has been shown to underlie acquired resistance to several alkylating agents. Ethacrynic acid inhibits the isoenzymes of GSH transferase with 50% inhibitory concentration values ranging from 0.3 to 6.0 microM and has been shown to restore sensitivity to alkylating agents in drug-resistant animal tumor models. We entered 27 previously treated patients with advanced cancer on a study of ethacrynic acid (25 to 75 mg/m2 p.o. every 6 h for 3 doses) and thiotepa (30 to 55 mg/m2 i.v. 1 h after the second dose of ethacrynic acid). The major toxicity of ethacrynic acid was diuresis, which was observed at every dose level; in addition, severe metabolic abnormalities occurred at 75 mg/m2. At 50 mg/m2, the diuretic effects were manageable. Myelosuppression was the most important effect of the combination. Two of seven courses of ethacrynic acid, 50 mg/m2, and thiotepa, 55 mg/m2, were associated with grade 3 or 4 neutropenia and/or thrombocytopenia. Nausea/vomiting greater than or equal to grade 2 was observed in 16% of courses. GSH transferase activity was assayed spectrophotometrically in the peripheral mononuclear cells of all patients. At each dose level, activity decreased following ethacrynic acid administration, with recovery by 6 h. Administration of ethacrynic acid, 50 mg/m2, resulted in a mean nadir of transferase activity of 37% of control. The pharmacokinetics of thiotepa and its principal metabolite TEPA were studied in 23 patients. The plasma disappearance of thiotepa fit a two-compartment open model with a terminal half-life of approximately 2 h. Plasma TEPA levels peaked at a mean of 2.16 h following thiotepa administration. The harmonic mean terminal half-life of TEPA was 10.4 h, and the TEPA area under the curve (AUC) did not increase with increasing thiotepa dose. The AUC of thiotepa was approximately twice, and the clearance about one-half, of the values obtained in a previous study of single agent thiotepa. The AUC of TEPA was lower than that previously observed. The data suggest that ethacrynic acid inhibits enzymes involved in the metabolic disposition of thiotepa, including its oxidative desulfuration to TEPA. The severity of the platelet toxicity was correlated with the AUC of thiotepa, but not with that of TEPA. This combination of thiotepa and ethacrynic acid will be tested further in Phase II trials.

Protective effect of electrical stimulation in the deafened guinea pig cochlea

The effect of chronic intrascalar electrical stimulation on the spiral ganglion cell survival of the ototoxically deafened guinea pig was investigated. Immediately after ototoxic drug administration, unilateral sinusoidal (1 kHz) charge-balanced electrical stimulation on a 50% duty cycle was administered for 2 hours per day, 5 days per week, at intensities from 0 (control) to 400 microAmp via an implanted scala tympani electrode. The relationship of electrically evoked middle latency response (EMLR) to stimulation protocol and cell survival was studied. At 9 weeks post-drug treatment, the animals were killed and temporal bones were prepared for morphometric analysis of spiral ganglion cell density. The subjects showed essentially complete elimination of outer hair sensory cells, with minimal remaining inner hair cells confined to apical turns. Variable loss of spiral ganglion cell populations was observed, which related to electrical stimulation. In animals that received daily unilaterally electrical stimulation, statistically significant increases in survival of spiral ganglion cells were observed in the stimulated ear, compared to the nonstimulated ear-particularly in basal cochlear regions near the electrode. Spiral ganglion cell density was a function of stimulation current intensity level. Moreover, the slope of the amplitude input/output (I/O) function of the EMLR was found to be dependent on stimulating current level. The effect of stimulation on induced survival may be dependent on a number of mechanisms, including metabolic effects of direct activation of "deafferented" spiral ganglion cells. These data support the suggestion that implantation may provide optimal benefits when performed shortly after deafness.

[Synergism between noise and ototoxic drugs: new experimental data]

Results of experiments investigating, in the guinea pig, the effects of combinations of gentamicin (GM), ethacrynic acid (EA) and acoustic stimulations are reported. They indicate that functional and morphological alterations develop only after GM has penetrated specifically into the sensory cells, that this penetration is indirectly facilitated by EA, since it is known to increase GM concentration in endolymph, and directly by functional depolarization of the cell, as it occurs during normal acoustic stimulation.

Noise-induced hearing loss as influenced by other agents and by some physical characteristics of the individual

The interaction of noise with a variety of other agents and with some physical characteristics of the individual to produce noise-induced hearing loss is reviewed critically. The review is restricted, for the most part, to publications since 1970. Other agents interacting with steady-state noise that are reviewed here include: (1) ototoxic drugs (kanamycin, neomycin, ethacrynic acid, furosemide, and salicylates), (2) impulse noise, and (3) whole-body vibration. Physical characteristics of the individual that are reviewed are: (1) age, (2) presence of previous hearing loss from prior noise exposure, (3) eye color, and (4) race. Suggestions for future research in this general area are also made. Some of these suggestions are as follows: (1) to extend studies of the interaction of steady-state noise with impulse noise, salicylates, and whole-body vibration to encompass a broader range of exposure conditions, including exposure conditions typically encountered by the worker, (2) to develop an animal model of presbycusis to explore the interactions of noise-induced hearing loss and presbycusis, and (3) to explore the potential interactions resulting from concurrent exposure to multiple agents, such as impulse noise and ototoxic drugs, in younger, more susceptible animals.

A tubulo-cisternal endoplasmic reticulum system in the potassium transporting marginal cells of the stria vascularis and effects of the ototoxic diuretic ethacrynic acid

Sections of metal impregnated tissue and freeze-fracture have been used to examine intracellular membrane systems in marginal cells of the stria vascularis in mammalian cochleae. A continuous network of elements of the smooth endoplasmic reticulum was revealed. Notable features of this system were a series of flattened cisternae just inside and parallel with the lateral plasma membrane in continuity with an apical network of tubules, cisternae and sheets oriented in parallel with the luminal membrane. The whole system was closely associated with mitochondria. These characteristics suggest that the potassium transporting marginal cells possess a tubulo-cisternal endoplasmic reticulum (TER) like that found in many sodium transporting epithelial cells. The lateral elements of the TER dilated, appearing like vacuoles, and opened to the lateral extracellular space in response to the effects of ethacrynic acid. This diuretic impairs ion transport in the stria vascularis. It is suggested that the TER in marginal cells is involved in the transport of ions and fluid from the cell to the intercellular space when ion balance is disturbed and may play a role in cell volume regulation.

Potentiating effects of cisplatin and ethacrynic acid in ototoxicity

Seven milligrams per kilogram of body weight of cisplatin and 50 mg/kg of body weight of ethacrynic acid were given intravenously to guinea pigs. The threshold for Preyer's reflex, the cochlear microphonics (CM), and the endocochlear dc potential (EP) were measured during a four-day period after the injection. The changes in Preyer's reflex audiometry and the CM were more severe than that of the EP. These changes are greater than those that occur with the administration of each agent independently. The ototoxic interaction seemingly has a greater effect on the hair cells than on the stria vascularis. Baseline and periodic audiometry should be performed when both of these drugs are administered clinically.

Ultrastructural histopathology in a case of human ototoxicity due to loop diuretics

The temporal bones of a patient who suffered sudden deafness and ataxia after administration of both furosemide and ethacrynic acid, were prepared for light and electron microscopy. There was no loss of hair or supporting cells. However, some hair cells, in both the vestibular neuroepithelium and the organ of Corti, particularly in the basal turn, were more densely staining and more granular than normal. Membrane whorls also were common within mitochondria of such cells. The endoplasmic reticulum of some spiral ganglion cells was dilated. The major cytologic changes were found in the stria vascularis of the cochlea and dark cell areas of the vestibular system. There was marked dilatation of the intercellular fluid spaces, consistent with the biochemical observation that loop diuretics interfere first with enzyme systems responsible for fluid transport within the inner ear.

Drug-induced pancreatitis: a critical review

We critically reviewed the English language literature pertaining to drug-induced pancreatitis and attempted to determine whether the reported association between each drug and pancreatitis was valid. The following drugs seem to cause pancreatitis: azathioprine, thiazides, sulfonamides, furosemide, estrogens, and tetracycline. Less convincing, but suggestive evidence exists for: 1-asparaginase, iatrogenic hypercalcemia, chlorthalidine, corticosteroids, ethacrynic acid, phenformin, and procainamide. Evidence implicating other drugs is either inadequate or contradictory. Little is known about the pathogenesis of drug-induced pancreatitis. Ethanol was not considered in this review.

The endolymphatic surface of the stria vascularis in the guinea-pig and the effects of ethacrynic acid as shown by scanning electron microscopy

Examination of the endolymphatic surface of the stria vascularis showed, in agreement with previous studies, the marginal cells to be hexagonal in shape and that most possessed microvilli. However, the cells in the apical turns were more profusely covered with microvilli than those at the base and, particularly in the basal turns, there was some variation in the surface detail of the cells. These results may indicate differences in the physiological state of the cells. In the early period of ethacrynic acid intoxication (15-30 minutes post-injection), when rapid changes in endolymphatic potential and ion-fluxes occur, the surface of the marginal cells showed only slight distortion. The most dramatic changes were noted 1 hour post-injection, and involved swelling of the cells and loss of microvilli. This distortion persisted up to 2 hours post-injection. The possible explanation for these findings is discussed.