Effect OfN-Acetylcysteine on Carboplatin-Induced Ototoxicity and Nitric Oxide Levels in a Rat Model

Harderian gland-derived stem cells as a cytotherapy in a guinea pig model of carboplatin-induced hearing loss

BACKGROUND

Stem cells therapy of hearing loss is a challenging field due to lacking self-regenerative capacity of cochlea. Harderian gland of guinea pigs was thought to harbour a unique type of progenitors which could restore the damaged cochlear tissues.

THE AIM

of this study was to isolate Harderian gland derived stem cells (HG-SCs) and investigate their efficacy in restoring the damaged cochlear tissue in carboplatin-induced hearing loss.

METHODOLOGY

Sixty female and 10 male pigmented guinea pigs were used; the male animals were HG-SCs donors, while the females were assigned into 3 groups; control, hearing loss (HL) and HG-SC-treated groups. Auditory reflexes were assessed throughout the study. The animals were euthanized 35 days after HG-SCs transplantation, the cochleae were extracted and processed for assessment by light microscope and scanning electron microscope. Morphometric assessment of stria vascularis thickness, hair cells and spiral ganglia neuronal number and optical density of TLR4 expression were done.

RESULTS

The isolated HG-SCs had the same morphological and phenotypical character as mesenchymal stem cells. HL group revealed destruction of organ of Corti, stria vascularis and spiral ganglion with decreased morphometric parameters. Restoration of both cochlear structure and function was observed in HG-SC-treated group along with a significant increase in IHCs, OHCs numbers, stria vascularis thickness and spiral ganglionic cell count to be close to the values of control group.

CONCLUSION

The isolated HG-SCs were proved to restore structure and function of cochlea in guinea pig model of hearing loss.

Protective effect of N-acetylcysteine against cisplatin ototoxicity in rats: a study with hearing tests and scanning electron microscopy

INTRODUCTION

Ototoxicity is a health problem appearing after powerful treatments in serious health conditions. It is sometimes inevitable when treatment of the serious disease is required. Cisplatin is an antineoplastic agent which was investigated previously to reveal increased nitrogen and reactive oxygen radicals that damages hair cells, resulting in ototoxicity. N-acetylcysteine, previously shown to decrease ototoxicity caused by different agents, is known to be a powerful in vitro antioxidant. Probably N-acetylcysteine, in addition to its antioxidant effect, blocks a cascade where reactive oxygen species result in apoptosis in the cochlea.

OBJECTIVES

The possible preventive effect of N-acetylcysteine in cisplatin ototoxicity was studied with auditory brain stem responses, otoacoustic emissions, and histopathological investigation of the cochlea in a scanning electron microscopy.

METHODS

This study was conducted on 21 Wistar Albino rats in four groups. 1mL/kg/day three times in total intraperitoneal (i.p.) Saline (n=5), 500mg/kg/day i.p. three times in total N-acetylcysteine (n=5), i.p. 15mg/kg cisplatin alone (single dose) (n=5) and i.p. 15mg/kg cisplatin plus 500mg/kg/day N-acetylcysteine (n=6) were administered. The rats were anesthetized to study the hearing tests before and after the experiment. The rats were sacrificed to investigate the cochleas by scanning electron microscopy.

RESULTS

Auditory brain stem responses and otoacoustic emissions values were attenuated in the cisplatin group. The group that received N-acetylcysteine in addition to cisplatin had better auditory brain stem responses thresholds and otoacoustic emissions. The samples obtained from the cisplatin group showed surface irregularities, degeneration areas, and total or partial severe stereocilia losses. The changes were milder in the cisplatin+N-acetylcysteine group.

CONCLUSION

Cisplatin ototoxicity can be detected by auditory brain stem responses and otoacoustic emissions testing in rats. N-acetylcysteine may protect the cochlear cells from histopathological changes. We concluded that N-acetylcysteine given 4h after cisplatin injection has a potential otoprotective effect against cisplatin ototoxicity. which suggests it could be used in clinical trials.

The expression of oxidative stress response genes is modulated by a combination of resveratrol and N-acetylcysteine to ameliorate ototoxicity in the rat cochlea

Aminoglycoside antibiotics are used widely in medicine despite their ototoxic side-effects. Oxidative stress and inflammation are key mechanisms determining the extent and severity of the damage. Here we evaluate the protective effect of a treatment with resveratrol plus N-acetylcysteine on the ototoxic actions of kanamycin and furosemide in the rat. Resveratrol (10 mg/kg) and N-acetylcysteine (400 mg/kg) were administered together to Wistar rats on 5 consecutive days. The second day, a concentrated solution of kanamycin and furosemide was placed on the round window to induce ototoxicity. Hearing was assessed by recording auditory brainstem responses before and 5, 16 and 23 days after the beginning of the treatment. Cochlear samples were taken at day 5 (end of the treatment) and at day 23, and targeted PCR arrays or RT-qPCR were performed to analyze oxidative balance and inflammation related genes, respectively. In addition, the cytoarchitecture and the presence of apoptosis, oxidative stress and inflammation markers were evaluated in cochlear sections. Results indicate that administration of resveratrol plus N-acetylcysteine reduced the threshold shifts induced by ototoxic drugs at high frequencies (≈10 dB), although this protective effect fades after the cessation of the treatment. Gene expression analysis showed that the treatment modulated the expression of genes involved in the cellular oxidative (Gpx1, Sod1, Ccs and Noxa1) and inflammatory (Il1b, Il4, Mpo and Ncf) responses to injury. Thus, co-administration of resveratrol and NAC, routinely used individually in patients, could reduce the ototoxic secondary effects of aminoglycosides.

N-acetyl-cysteine prevents age-related hearing loss and the progressive loss of inner hair cells in γ-glutamyl transferase 1 deficient mice

Genetic factors combined with oxidative stress are major determinants of age-related hearing loss (ARHL), one of the most prevalent disorders of the elderly. Dwarf grey mice, Ggt1^dwg/dwg, are homozygous for a loss of function mutation of the γ-glutamyl transferase 1 gene, which encodes an important antioxidant enzyme critical for the resynthesis of glutathione (GSH). Since GSH reduces oxidative damage, we hypothesized that Ggt1^dwg/dwg mice would be susceptible to ARHL. Surprisingly, otoacoustic emissions and cochlear microphonic potentials, which reflect cochlear outer hair cell (OHC) function, were largely unaffected in mutant mice, whereas auditory brainstem responses and the compound action potential were grossly abnormal. These functional deficits were associated with an unusual and selective loss of inner hair cells (IHC), but retention of OHC and auditory nerve fibers. Remarkably, hearing deficits and IHC loss were completely prevented by N-acetyl-L-cysteine, which induces de novo synthesis of GSH; however, hearing deficits and IHC loss reappeared when treatment was discontinued. Ggt1^dwg/dwgmice represent an important new model for investigating ARHL, therapeutic interventions, and understanding the perceptual and electrophysiological consequences of sensory deprivation caused by the loss of sensory input exclusively from IHC.

In vitro analysis of a novel controlled release system designed for intratympanic administration of N-acetylcysteine: a preliminary report

The aim of this in-vitro experimental study was to design a novel drug delivery system that may permit controlled release of N-acetylcysteine (NAC) following intratympanic administration. The system was composed of two different solutions that attained a hydrogel form within seconds after getting into contact with each other. The authors performed swelling, pH and temperature tests and analysis of controlled release of NAC from this novel controlled release system. For the structure and porosity analysis of the hydrogel, an environmental scanning electron microscope (SEM) was used. The diameter of designed hydrogel showed an increase when pH was increased. In addition, in comparison to acidic values, the pore diameter of the hydrogel increased significantly especially in physiological level. The increase in the pore diameter was also directly proportional to the increase in temperature. Spectrophotometric analysis showed that the amount of NAC released into the medium was statistically significant (p=0.038, t=-2.18, 95% CI; DF: 27). SEM analysis of the samples revealed a smooth surface topography and numerous porous structures. The authors are of the opinion that the designed hydrogel may be used as an alternative method for intratympanic delivery of NAC for otoprotective purposes. The disadvantages of intratympanic injection of the drug in its liquid form, including leakage through eustachian tube, restraining the patient in an uncomfortable position, necessity for repetitive injections and dose dependent inflammation of the middle ear epithelium, may also be avoided. Further in vivo studies should be conducted to assess its tolerability and effectivity.

The Safety Pharmacology of Auditory Function

Safety pharmacology satisfies a key requirement in the process of drug development. Safety pharmacology studies are required to assess the impact of a new chemical entity (NCE) or biotechnology-derived product for human use on vital systems, such as those subserving auditory function. Safety pharmacology studies accordingly are defined as those studies that investigate the potential undesirable effects of a substance on auditory functions in relation to exposure in and above the therapeutic range. Auditory safety studies should be designed with the primary objective of determining how administration of a compound influences normal hearing. If an effect on hearing is identified, then it is necessary to determine through histopathology the underlying mechanism for the observed hearing loss. Since the auditory system contains a heterogeneous mixture of structural and cellular components that are organized in a very complex and integrated manner, it is necessary to clearly identify the underlying primary mechanism or target of the new chemical entity that produced the hearing loss. This chapter will highlight major components of auditory function with regard to potential opportunities for drug interaction. Aspects of designing ototoxicity studies will be discussed with an emphasis on standards deemed necessary by the US Food and Drug Administration. Additionally, classes of ototoxic compounds and their proposed mechanisms of action are described in depth.

Methylseleninic acid sensitizes Notch3-activated OVCA429 ovarian cancer cells to carboplatin

Ovarian cancer, the deadliest of gynecologic cancers, is usually not diagnosed until advanced stages. Although carboplatin has been popular for treating ovarian cancer for decades, patients eventually develop resistance to this platinum-containing drug. Expression of neurogenic locus notch homolog 3 (Notch3) is associated with chemoresistance and poor overall survival in ovarian cancer patients. Overexpression of NICD3 (the constitutively active form of Notch3) in OVCA429 ovarian cancer cells (OVCA429/NICD3) renders them resistance to carboplatin treatment compared to OVCA429/pCEG cells expressing an empty vector. We have previously shown that methylseleninic acid (MSeA) induces oxidative stress and activates ataxia-telangiectasia mutated and DNA-dependent protein kinase in cancer cells. Here we tested the hypothesis that MSeA and carboplatin exerted a synthetic lethal effect on OVCA429/NICD3 cells. Co-treatment with MSeA synergistically sensitized OVCA429/NICD3 but not OVCA429/pCEG cells to the killing by carboplatin. This synergism was associated with a cell cycle exit at the G2/M phase and the induction of NICD3 target gene HES1. Treatment of N-acetyl cysteine or inhibitors of the above two kinases did not directly impact on the synergism in OVCA429/NICD3 cells. Taken together, these results suggest that the efficacy of carboplatin in the treatment of high grade ovarian carcinoma can be enhanced by a combinational therapy with MSeA.

Infliximab has no apparent effect in the inner ear hearing function of patients with rheumatoid arthritis and ankylosing spondylitis

Animal studies suggest that tumor necrosis factor (TNF) alpha blockers may pass to the inner ear in adequate concentration. In this prospective study, we aimed to evaluate the effect of infliximab on the inner ear hearing function in patients with ankylosing spondylitis (AS) and rheumatoid arthritis (RA). The patients with high disease activity, who were planned to begin infliximab for therapy by physical medicine and rehabilitation department, were referred to ear-nose-throat clinic for consultation. After physical and otoscopic examination, audiological tests were performed. Air conduction thresholds between 250 and 8,000 Hz, bone conduction thresholds between 500 and 4,000 Hz, pure tone average, speech discrimination scores, distortion product otoacoustic emission (DPOAE) were used to evaluate the hearing function. The tests were repeated 2 and 6 months after the initiation of the drug "infliximab." A total of 44 ears of 22 patients (17 males and 5 females) were evaluated. Fifteen patients had a diagnosis of AS, and seven patients had RA. After initiation of infliximab therapy, statistically significant improvement was observed in disease activity scores [Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) for AS, Disease Activity Score 28 (DAS-28) for RA] after 2 and 6 months (p < 0.05). We did not find any statistically significant difference between the air conduction thresholds, bone conduction thresholds, pure tone average, speech discrimination scores, and measurements of DPOAE before the initiation of treatment and after 2 and 6 months (p > 0.05). Any problem about the balance, vertigo, or dizziness was not reported from the patients during the treatment period. As a result, our study showed that there was no notable change or deterioration in the hearing function of the patients with AS and RA who were treated with infliximab. Further studies with higher number of patients with AS and RA and also with different TNF alpha inhibitors are needed to make more valid conclusion.

OTOTOXIC EFFECTS OF CARBOPLATIN IN ORGANOTYPIC CULTURES IN CHINCHILLAS AND RATS

Carboplatin, a second-generation platinum chemotherapeutic drug, is considerably less ototoxic than cisplatin. While common laboratory species such as mice, guinea pigs and rats are highly resistant to carboplatin ototoxicity, the chinchilla stands out as highly susceptible. Moreover, carboplatin causes an unusual gradient of cell death in chinchillas. Moderate doses selectively damage type I spiral ganglion neurons (SGN) and inner hair cells (IHC) and the lesion tends to be relatively uniform along the length of the cochlea. Higher doses eventually damage outer hair cells (OHC), but the lesion follows the traditional gradient in which damage is more severe in the base than the apex. While carboplatin ototoxicity has been well documented in adult animals in vivo, little is known about its in vitro toxicity. To elucidate the ototoxic effects of carboplatin in vitro, we prepared cochlear and vestibular organotypic cultures from postnatal day 3 rats and adult chinchillas. Chinchilla cochlear and vestibular cultures were treated with carboplatin concentrations ranging from 50 µM to 10 mM for 48 h. Consistent with in vivo data, carboplatin selectively damaged IHC at low concentrations (50-100 µM). Surprisingly, IHC loss decreased at higher doses and IHC were intact at doses exceeding 500 µM. The mechanisms underlying this nonlinear response are unclear but could be related to a decrease in carboplatin uptake via active transport mechanisms (e.g., copper). Unlike the cochlea, the carboplatin dose-response function increased with dose with the highest dose destroying all chinchilla vestibular hair cells. Cochlear hair cells and auditory nerve fibers in rat cochlear organotypic cultures were unaffected by carboplatin concentrations <10 µM; however, the damage in OHC were more severe than IHC once the dose reached 100 µM. A dose at 500 µM destroyed all the cochlear hair cells, but hair cell loss decreased at high concentrations and nearly all the cochlear hair cells were present at the highest dose, 5 mM. Unlike the nonlinear dose-response seen with cochlear hair cells, rat auditory nerve fiber and spiral ganglion losses increased with doses above 50 µM with the highest dose destroying virtually all SGN. The remarkable species differences seen in vitro suggest that chinchilla IHC and type I SGN posse some unique biological mechanism that makes them especially vulnerable to carboplatin toxicity.

Well-defined, reversible disulfide cross-linked micelles for on-demand paclitaxel delivery

To minimize premature release of drugs from their carriers during circulation in the blood stream, we have recently developed reversible disulfide cross-linked micelles (DCMs) that can be triggered to release drug at the tumor site or in cancer cells. We designed and synthesized thiolated linear-dendritic polymers (telodendrimers) by introducing cysteines to the dendritic oligo-lysine backbone of our previously reported telodendrimers comprised of linear polyethylene glycol (PEG) and a dendritic cluster of cholic acids. Reversibly cross-linked micelles were then prepared by the oxidization of thiol groups to disulfide bond in the core of micelles after the self-assembly of thiolated telodendrimers. The DCMs were spherical with a uniform size of 28 nm, and were able to load paclitaxel (PTX) in the core with superior loading capacity up to 35.5% (w/w, drug/micelle). Cross-linking of the micelles within the core reduced their apparent critical micelle concentration and greatly enhanced their stability in non-reductive physiological conditions as well as severe micelle-disrupting conditions. The release of PTX from the DCMs was significantly slower than that from non-cross-linked micelles (NCMs), but can be gradually facilitated by increasing the concentration of reducing agent (glutathione) to an intracellular reductive level. The DCMs demonstrated a longer in vivo blood circulation time, less hemolytic activities, and superior toxicity profiles in nude mice, when compared to NCMs. DCMs were found to be able to preferentially accumulate at the tumor site in nude mice bearing SKOV-3 ovarian cancer xenograft. We also demonstrated that the disulfide cross-linked micellar formulation of PTX (PTX-DCMs) was more efficacious than both free drug and the non-cross-linked formulation of PTX at equivalent doses of PTX in the ovarian cancer xenograft mouse model. The anti-tumor effect of PTX-DCMs can be further enhanced by triggering the release of PTX on-demand by the administration of the FDA approved reducing agent, N-acetylcysteine, after PTX-DCMs have reached the tumor site.

N-acetylcysteine and N-nitroarginine methyl ester attenuate Carboplatin-induced ototoxicity in dissociated spiral ganglion neuron cultures

Objectives

Carboplatin, a platinum-containing anti-cancer drug used to treat a variety of cancers, induces ototoxicity. Since, reactive oxygen species (ROS) and nitric oxide (NO) seem to be responsible for this toxicity, the antioxidant, N-acetyl-L-cysteine (L-NAC), and NO synthetase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) were predicted to have protective effects against carboplatin ototoxicity. The aim of this study was to test for the protective effects of L-NAC and L-NAME on cochlear hair cells and spiral ganglion neurons (SGNs).

Methods

Cochlear organotypic cultures and dissociated spiral ganglion neuron cultures, from mice postnatal day 5 cultures were used in this study. The cultures were treated with carboplatin alone or in combination with L-NAC or L-NAME, and carboplatin-induced damage was monitored.

Results

Treatment with carboplatin induced a significant loss of outer hair cells, while inner hair cells were preserved in the cochlear organotypic cultures. Addition of L-NAC or L-NAME reduced the amount of carboplatin-induced hair cell damage; the differences did not reach statistical significance. However, carboplatin significantly decreased the number of surviving SGNs in dissociated cultures. The toxic effects were significantly reduced by addition of L-NAC or L-NAME. In addition, carboplatin induced the loss of neurites from the SGN somata, and this was not blocked with L-NAC or L-NAME.

Conclusion

The results of this study suggest that ROS and NO are involved in carboplatin-induced damage to hair cells and SGNs, and administration of L-NAC/L-NAME can be used to attenuate the toxicity.

Protective effects of fomepizole on 2-chloroethanol toxicity

2-Chloroethanol (2-CE) is a widely used industrial solvent. In Taiwan, Taiwanese farmers apply 2-CE on grape-vines to accelerate grape growth, a practice that in some cases have caused poisoning in humans. Thus, there is strong interest in identifying antidotes to 2-CE. This study examines the protective role in 2-CE intoxicated rats. Alcohol dehydrogenase and glutathione were hypothesized to be important in the metabolism of 2-CE. This study used fomepizole, an alcohol dehydrogenase inhibitor, and chemicals that affected glutathione metabolism to study 2-CE toxicity. Notably, fomepizole 5 mg/kg significantly increased median lethal dose (LD50) of 2-CE from 65.1 to 180 mg/kg and reduced the production of a potential toxic metabolite chloroacetaldehyde (CAA) in animal plasma. In contrast, disulfiram (DSF), an aldehyde dehydrogenase inhibitor, increased the toxicity of 2-CE on the lethality in rats. Additional or pretreatment with N-acetylcysteine (NAC) and fomepizole significantly reduced plasma CAA concentrations. Fomepizole also significantly reduced 2-CEinhibited glutathione activity. Otherwise, pretreatment with NAC for 4 days followed by co-treatment with fomepizole significantly decreased formation of the metabolic CAA. These results indicated that its catalytic enzyme might play a vital role during 2-CE intoxication, and the combination of fomepizole and NAC could be a protective role in cases of acute 2-CE intoxication.

Carnitine deficiency aggravates carboplatin nephropathy through deterioration of energy status, oxidant/anti-oxidant balance, and inflammatory endocoids

We have recently shown that carnitine deficiency could represent a risk factor in paracetamol hepatotoxicity. By the same token, d-carnitine-induced carnitine deficiency aggravated carboplatin nephropathy following challenge with a single dose (35mg/kg, IP) of the platinum drug in male Swiss albino rats. The combination modality induced marked degenerative changes and severe inflammation in kidney tissues that surpassed either carboplatin or d-carnitine given alone. The combined regimen synergistically increased the serum levels of creatinine, blood urea nitrogen (BUN), tumor necrosis factor alpha (TNF-alpha), palmitate, and kidney malondialdehyde (MDA), adenosine triphosphate (ATP), nitric oxide (NO) contents as well as kidney myeloperoxidase (MPO) activity. The only parameter that has been notably decreased was the kidney reduced glutathione (GSH) level. Exaggeration by carnitine deficit of the deleterious effects of carboplatin is most probably ascribed to energy starvation. The reduction in kidney content of ATP parcels was associated with elevation of serum palmitate level that reflected debilitated fatty acid oxidation, and this further deteriorated energy resources in kidney tissues. Compromising the oxidant/anti-oxidant balance and modulating the release of some inflammatory endocoids namely, TNF-alpha and NO could also possibly account for such combinatorial detrimental toxicity. The current study was further extended to elucidate any possible nephroprotective effects of l-carnitine. Interestingly, carnitine supplementation ahead of carboplatin challenge ameliorated and almost normalized all the biochemical parameters and also mitigated the injurious effects of the cytotoxic drug. Thus, one could conclude that carnitine deficiency, whether being a causative clue or a sequela, might represent a risk factor in carboplatin nephropathy.