Taurine attenuates aminoglycoside ototoxicity by inhibiting inducible nitric oxide synthase expression in the cochlea

Antibiotic Therapy and Athletes: Is the Mitochondrial Dysfunction the Real Achilles’ Heel?

It is widely recognized that athletes consume oral antibiotics almost twice as often as observed in the non-sports population in order to reduce as much as possible the period of inactivity due to bacterial diseases. However, increasing evidences have demonstrated the ability of some classes of antibiotics to induce muscle weakness, pain, and a feeling of fatigue upon resuming physical activity conditions that considerably limit the athletic performance of athletes, ascribable to alterations in the biochemical mechanisms underlying normal musculoskeletal activity, such as mitochondrial respiration. For this reason, tailoring a treatment plan for effective antibiotics that limit an athlete’s risk is paramount to their safety and ability to maintain adequate athletic performance. The present review illustrates and critically analyzes the evidence on the use of antibiotics in sports, deepening the molecular mechanisms underlying the onset and development of muscle–tendon alterations in athletes as well as delineating the pharmacological strategies aimed at counteracting such adverse events.

Use of the guinea pig in studies on the development and prevention of acquired sensorineural hearing loss, with an emphasis on noise

Guinea pigs have been used in diverse studies to better understand acquired hearing loss induced by noise and ototoxic drugs. The guinea pig has its best hearing at slightly higher frequencies relative to humans, but its hearing is more similar to humans than the rat or mouse. Like other rodents, it is more vulnerable to noise injury than the human or nonhuman primate models. There is a wealth of information on auditory function and vulnerability of the inner ear to diverse insults in the guinea pig. With respect to the assessment of potential otoprotective agents, guinea pigs are also docile animals that are relatively easy to dose via systemic injections or gavage. Of interest, the cochlea and the round window are easily accessible, notably for direct cochlear therapy, as in the chinchilla, making the guinea pig a most relevant and suitable model for hearing. This article reviews the use of the guinea pig in basic auditory research, provides detailed discussion of its use in studies on noise injury and other injuries leading to acquired sensorineural hearing loss, and lists some therapeutics assessed in these laboratory animal models to prevent acquired sensorineural hearing loss.

Taurine enhances mouse cochlear neural stem cell transplantation via the cochlear lateral wall for replacement of degenerated spiral ganglion neurons via sonic hedgehog signaling pathway

The aim of this paper is to investigate the potential beneficial effects of taurine in cochlear neural stem cell (NSC) transplantation and elucidate the underlying molecular mechanism. The NSC cells were isolated from neonatal Balb/c mice and an auditory neuropathy gerbil model was established by microinjection of ouabain. The spiral ganglion neurons (SGN) were characterized with immunofluorescence stained with Tuj1 antibody. Cell proliferation was determined by BrdU incorporation assay and the morphologic index was measured under the light microscope. The relative protein level was determined by immunoblotting. The hearing of the animal model was scored by click- and tone burst-evoked auditory brainstem response (ABR). Here we consolidated our previous finding that taurine stimulated SGN density and the proliferation index, which were completely abolished by Shh inhibitor, cyclopamine. Transplantation of cochlear NSCs combined with taurine significantly improved ouabain-induced auditory neuropathy in gerbils. In addition, cyclopamine antagonized taurine's effect on glutamatergic and GABAergic neuron population via suppression of VGLUT1 and GAT1 expression. Mechanistically, taurine evidently activated the Sonic HedgeHog pathway and upregulated Shh, Ptc-1, Smo and Gli-1 proteins, which were specifically blockaded by cyclopamine. Here, for the first time demonstrated we that co-administration with taurine significantly improved NSC transplantation and the Shh pathway was identified in this beneficial effect.

Taurine enhances mouse cochlear neural stem cells proliferation and differentiation to sprial gangli through activating sonic hedgehog signaling pathway

To investigate the molecular mechanism underlying taurine-stimulated proliferation and differentiation of cochlear neural stem cells (NSCs) and potential involvement of Sonic Hedgehog (Shh) pathway. The NSCs were characterized with immunofluorescence stained with nestin antibody. Cell viability was determined by MTT assay. The relative proliferation was measured by BrdU incorporation assay. The morphologic index was measured under light microscope. The relative protein level was determined by immunoblotting. Here we presented our findings that taurine stimulated proliferation and neurite outgrowth of NSCs, which was completely abolished by Shh inhibitor cyclopamine. In addition, cyclopamine antagonized taurine's effect on glutamatergic and GABAergic neuron population via suppressing expressions of Ptc-1, Smo and Gli-1. Our data supported the critical role of Shh pathway underlying the protective effect of taurine on auditory neural system.

Aminoglycoside Increases Permeability of Osseous Spiral Laminae of Cochlea by Interrupting MMP-2 and MMP-9 Balance

The spiral ganglion neurons (SGNs) located in the Rosenthal's canal of cochlea are essential target for cochlear implant. Previous studies found that the canaliculi perforantes, small pores on the surface of the osseous spiral lamina (OSL) of the scala tympanic (ST) of cochlea, may provide communication between the cochlear perilymph and SGNs. In this study, we found that chronic treatment of aminoglycosides antibiotics, which is well known to cause sensory cell damage in the cochlea, induced significant damage of bone lining cells on the OSLs and increased the permeability of the Rosenthal's canal. The pores among the bone lining cells became significantly wider after chronic treatment of amikacin (100 mg/kg/day for 3-7 days). Injection of Evans Blue in the ST resulted in significant increase in its migration in the modulus in the amikacin-treated cochlea compared to the control ears, suggesting increased permeability of these passages. Treatment of amikacin with oxytetracycline, an inhibitor of matrix metalloproteases (MMPs), significantly reduced the amount of dye migrated from the ST to the modiolus. These results suggest that amikacin enhanced the permeability between the ST and SGNs by increasing MMPs. Aggregating the permeability of the bone lining cells on the OSLs may benefit gene and stem cell delivery to the SGNs in the cochlea.

The beneficial effect of Hangesha-shin-to (TJ-014) in gentamicin-induced hair cell loss in the rat cochlea

OBJECTIVE

Ototoxic damage caused by aminoglycosides (AG) leads to the loss of cochlear hair cells (HCs). In mammals, mature cochlear HCs are unable to regenerate, and their loss results in permanent hearing deficits. Our objective was to protect the inner ear from damage after an AG challenge. The generation of reactive oxygen species (ROS), one of the earliest events in the process of AG ototoxicity, is considered to play a key role in the initiation of HC death. We examined whether Hangesha-shin-to (TJ-014), a traditional Japanese Kampo medicine considered to be a potent antioxidant, protects HCs from gentamicin (GM)-induced damage.

METHODS

Organ of Corti explants removed from postnatal day 3-5 rats were maintained in tissue culture and exposed to 50μM GM for up to 48h. The effects of TJ-014 on GM-induced ototoxicity were assessed by HC counts and immunohistochemistry against cleaved caspase-3, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and a probe reacting to mitochondrial function changes.

RESULTS

TJ-014 treatments significantly reduced GM-induced HC loss and immunoreactivities for cleaved caspase-3 and 8-OHdG; these effects were correlated with increasing TJ-014 concentrations. Moreover, TJ-014 protected the mitochondrial membrane potential from GM ototoxicity.

CONCLUSION

These findings indicate the potential of TJ-014 to prevent GM-induced cochlear damage involving ROS.

Neurotrophic effects of taurine on spiral ganglion neurons in vitro

Taurine is an ubiquitary expressed aminosulfonic acid known to play an important role in the development and maintenance of the nervous system. It is distributed in the inner ear, contributing toward the protection of hair cells against aminoglycoside-induced or bilirubin-induced ototoxicity. Thus, the question arises whether taurine also has an influence on the cellular integrity of the auditory neurons. To test this hypothesis, isolated cells of the spiral ganglion were cocultured with taurine or the neurotrophic factors brain derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) as controls. The analysis included cellular survival rate and neurite outgrowth. With application of taurine, the survival of glial cells and neurons was stimulated in a similar pattern, whereas BDNF and NT-3 only effected neuronal survival. Furthermore, administration of taurine resulted in enhanced neurite outgrowth comparable with the effect of the neurotrophic factors. These new insights on the neuromodulatory effects of taurine on auditory neurons suggest the use of this aminosulfonic acid to reduce the degeneration of auditory neurons in sensorineural hearing loss. Consecutively, a new therapeutical approach for the therapy of hearing impairment could be discussed.

Cell-specific accumulation patterns of gentamicin in the guinea pig cochlea

Intratympanic gentamicin therapy has become a popular treatment modality for Ménière's disease (MD) through controlled elimination of vertigo spells caused by the balance organ. However, the known ototoxic properties of aminoglycosides lead to cochlear damage. In order to gain more information about cellular preferences for aminoglycoside accumulation within the cochlea, gentamicin was immuno histochemically localized by light microscopy in male guinea pigs 1 and 7 days after intratympanic application (n = 8 ears/incubation time). Differences in the gentamicin-specific cellular storage capacities were quantified by determination of the local immuno staining intensities. Gentamicin was detected in every cochlear cell type, but with spatiotemporal variability. One day after application, an intense staining reaction was found in all cell types except the spiral ganglion cells and the stria vascularis. Six days later, gentamicin staining intensities were additionally reduced in the nerve fibers and the spiral ligament. Statistic analysis revealed strong cellular associations in respect to aminoglycoside accumulation. Furthermore, associations with recorded hearing losses were identified comparing the cellular gentamicin content in the organ of Corti, in the stria vascularis, in the spiral ganglion cells and in fibrocytes of the Limbus. In the lateral wall, clear differences in cellular gentamicin accumulation were found between type I fibrocytes of the spiral ligament compared with basal and intermediate cells of the stria vascularis. This finding was unexpected as these three cell types belong to a well-developed gap-junction system which normally enables unhampered cell communication. Cellular differences in local gentamicin storage capacities, transport processes and inherent diffusion barriers are discussed.

New trends in aminoglycosides use

Despite their inherent toxicity and the acquired bacterial resistance that continuously threaten their long-term clinical use, aminoglycosides (AGs) still remain valuable components of the antibiotic armamentarium. Recent literature shows that the AGs' role has been further expanded as multi-tasking players in different areas of study. This review aims at presenting some of the new trends observed in the use of AGs in the past decade, along with the current understanding of their mechanisms of action in various bacterial and eukaryotic cellular processes.

The protective effect of Salvia miltiorrhiza on gentamicin-induced ototoxicity

OBJECTIVE

The clinical use of aminoglycoside antibiotics is limited in most countries because of auditory toxicity side effects. However, their use is common in developing countries because they are inexpensive and convenient. Salvia miltiorrhiza extracts are used clinically in China for their antioxidant properties. We investigated the effect of a clinically approved injectable S. miltiorrhiza solution on inducible nitric oxide synthase (iNOS) generation induced by the aminoglycoside antibiotic gentamicin and an ototoxicity protective mechanism.

METHODS

Sixty adult guinea pigs were used in this study and divided into four groups. Auditory brainstem response (ABR) testing was performed before and after treatments and animals were sacrificed for morphological and immunostaining assays after determining threshold shifts in ABR. The cochleae were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to observe ultrastructural changes. In addition, hair cell loss, iNOS and caspase-3 expression, and apoptosis were measured.

RESULTS

The result showed that hearing loss, iNOS overexpression accompanied with disorganization in the cochlea, and terminal deoxynucleotidyl transferase- mediated dUTP- biotin nick end labeling (TUNEL)-stained positive cells in animals treated with gentamicin. However, pretreatment with S. miltiorrhiza (3g/kg/day for 10 days) decreased gentamicin-induced hearing loss, attenuated iNOS and caspase-3 expression, and decreased the number of apoptotic cells. Furthermore, it also reduced the ultrastructural damage due to ototoxicity as observed by SEM and TEM.

CONCLUSIONS

These findings indicate that S. miltiorrhiza protects against gentamicin-induced ototoxicity and could apply to the protection of ototoxicity.

Pomegranate extract: a potential protector against aminoglycoside ototoxicity

OBJECTIVE

To investigate the effectiveness of pomegranate extract as protection against aminoglycoside ototoxicity.

DESIGN

Prospective, randomised, controlled, experimental study.

SUBJECTS

Eighteen Wistar albino rats were randomly allocated to 5 days of either: saline injections; gentamicin injections; or pomegranate extract (100 µl/day via gavage) plus gentamicin injections. Distortion product otoacoustic emissions were tested before treatment and on day 3. After treatment, reactive oxygen species levels were measured in each rat's right cochlea and right kidney via chemiluminescence.

RESULTS

Baseline emission amplitudes were similar. Post-treatment emissions differed significantly in the two treatment groups (p < 0.001). Cochlear reactive oxygen species levels were significantly higher in the gentamicin group (mean ± standard deviation, 316.6 ± 36.5 relative light units per mg) than the gentamicin plus pomegranate extract group (240 ± 24.6 relative light units per mg) (p = 0.004); control group levels were 119.1 ± 10.3 relative light units per mg. Renal reactive oxygen species levels were similar for the control and gentamicin plus pomegranate extract groups (p = 0.59) but much higher in the gentamicin group (p = 0.004).

CONCLUSION

Concurrent systemic pomegranate extract administration reduced reactive oxygen species level increases and otoacoustic emission changes, following aminoglycoside injection.

Nitric oxide--a versatile key player in cochlear function and hearing disorders

Nitric oxide (NO) is a signaling molecule which can generally be formed by three nitric oxide synthases (NOS). Two of them, the endothelial nitric oxide synthase (eNOS) and the neural nitric oxide synthase (nNOS), are calcium/calmodulin-dependent and constitutively expressed in many cell types. Both isoforms are found in the vertebrate cochlea. The inducible nitric oxide synthase (iNOS) is independent of calcium and normally not detectable in the un-stimulated cochlea. In the inner ear, as in other tissues, NO was identified as a multitask molecule involved in various processes such as neurotransmission and neuromodulation. In addition, increasing evidence demonstrates that the NO-dependent processes of cell protection or, alternatively, cell destruction seem to depend, among other things, on changes in the local cochlear NO-concentration. These alterations can occur at the cellular level or within a distinct cell population both leading to an NO-imbalance within the hearing organ. This dysfunction can result in hearing loss or even in deafness. In cases of cochlear malfunction, regulatory systems such as the gap junction system, the blood vessels or the synaptic region might be affected temporarily or permanently by an altered NO-level. This review discusses potential cellular mechanisms how NO might contribute to different forms of hearing disorders. Approaches of NO-reduction are evaluated and the transfer of results obtained from experimental animal models to human medication is discussed.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Glycine and taurine equally prevent fatty livers from Kupffer cell-dependent injury: an in vivo microscopy study

BACKGROUND

IRI still is a major problem in liver surgery due to warm ischemia and organ manipulation. Steatosis is not only induced by diabetes, hyperalimentation, alcohol and toxins, but also chemotherapy given before resection. Since steatotic livers are prone to Kupffer cell-dependent IRI, protection of steatotic livers is of special interest. This study was designed to compare the effect of taurine and glycine on IRI in steatotic livers.

MATERIALS AND METHODS

Steatosis was induced with ethanol (7 g/kg b.w.; p.o.) in female SD rats. Ten minutes after inactivation of Kupffer cells with taurine or glycine (300 mM; i.v.), left liver lobes underwent 60 minutes of warm ischemia. Controls received the same volume of valine (300 mM; i.v.) or normal saline. After reperfusion, white blood cell-endothelial interactions and latex-bead phagocytosis by Kupffer cells were investigated. Liver enzymes were measured to estimate injury. For statistical analysis, ANOVA and Student's t-test were used.

RESULTS

Glycine and taurine significantly decreased leukocyte- and platelet-endothelium interactions and latex-bead phagocytosis (p < 0.05). Liver enzymes were significantly lower after glycine and taurine (p < 0.05).

CONCLUSIONS

This study shows that preconditioning with taurine or glycine is equally effective in preventing injury to fatty livers most likely via Kupffer cell-dependent mechanisms.

Korean red ginseng prevents gentamicin-induced hearing loss in rats

OBJECTIVES

To evaluate the preventive effects of Korean red ginseng (KRG) on gentamicin (GM)-induced ototoxicity and to identify the effective components of KRG.

STUDY DESIGN

In vivo and in vitro studies.

METHODS

Thirty-five Sprague-Dawley rats were divided into four groups. The GM group (n = 15) received intraperitoneal injections (IPI) of GM (160 mg/kg) for 5 days. The KRG + GM group (n = 12) was treated with intragastric feeding of KRG (500 mg/kg) for 12 days with 5 days of IPIs of GM. KRG (n = 4) and control (n = 4) groups were treated with KRG and saline, respectively. Auditory brainstem response (16 or 32 kHz) and Rotarod treadmill tests were done before and after treatments. Cochleas were evaluated by a scanning electron microscope (SEM) and phalloidin staining. Ginsenosides Rb1, Rb2, Rg1, and Re were evaluated as the water-soluble terazolium salt assay, annexin V/propidium iodide assay, and Western blots in HEI-OC1 cells.

RESULTS

Posttreatment hearing thresholds in GM, KRG + GM, KRG, and control groups were: 27.7 ± 7.2 dB, 23.1 ± 4.1 dB, 16.9 ± 2.6 dB, and 21.3 ± 3.5 dB, respectively, for 16 kHz, 30.5 ± 6.6 dB, 25.2 ± 4.3 dB, 22.5 ± 2.7 dB, and 22.5 ± 3.8 dB, respectively for 32 kHz. The KRG + GM group had significantly better hearing than the GM group (P < .05). On SEM and phalloidin staining, the GM group showed severe loss of stereocilia in the basal outer hair cells and a few losses in the middle turns, whereas the KRG + GM group showed relatively intact hair cells. Balance impairment in treadmill tests was not definite in any group. Rb1 and Rb2 showed more effective protection than other components.

CONCLUSIONS

KRG protects against GM-induced hearing loss and hair cell death in rats. Laryngoscope, 2011.

Glucocorticoids reduce nitric oxide concentration in middle ear effusion from lipopolysaccharide induced otitis media

OBJECTIVE

Otitis media with effusion (OME) is a common childhood disease that is characterized by an accumulation of fluid in the middle ear. Chronic OME can also lead to sensorineural hearing loss (SNHL). Nitric oxide (NO), an inflammatory mediator (IM) of OME, is a free radical known to regulate cell proliferation, cell death, and angiogenesis. Previous studies have shown that nitric oxide may cause SNHL through outer hair cell (OHC) cytotoxicity. This experiment was designed to determine whether glucocorticoids, dexamethasone, fluticasone propionate, or rimexolone, can reduce the concentration of NO in middle ear effusion (MEE).

METHODS

Fifty-three chinchillas were divided into 7 groups, vehicle vs. each glucocorticoid at 0.1% and 1.0% concentrations. Due to anesthesia complications, N ranged from 6 to 9 per group. Two hundred microlitres of each test article was injected into the bullae of each animal. Two hours later, lipopolysaccharide (LPS) (0.3mg in solution) was added. Test articles were re-administered at 24 and 48h post-LPS induction. After 96h, animals were euthanized and the MEE was collected.

RESULTS

All three glucocorticoids numerically reduced NO concentration in the middle ear when administered at 0.1%, but only FP showed a significant reduction. At 1.0% concentrations, all 3 steroids significantly reduced NO concentration.

CONCLUSION

This study suggests that glucocorticoid treatment reduces NO concentration in the MEE and may protect the ear from the SNHL caused by NO.