Double-blind, crossover, placebo-controlled clinical trial with L-acetylcarnitine in patients with degenerative cerebellar ataxia

L-Carnitine in the Treatment of Psychiatric and Neurological Manifestations: A Systematic Review

OBJECTIVE

L-carnitine (LC), a vital nutritional supplement, plays a crucial role in myocardial health and exhibits significant cardioprotective effects. LC, being the principal constituent of clinical-grade supplements, finds extensive application in the recovery and treatment of diverse cardiovascular and cerebrovascular disorders. However, controversies persist regarding the utilization of LC in nervous system diseases, with varying effects observed across numerous mental and neurological disorders. This article primarily aims to gather and analyze database information to comprehensively summarize the therapeutic potential of LC in patients suffering from nervous system diseases while providing valuable references for further research.

METHODS

A comprehensive search was conducted in PubMed, Web Of Science, Embase, Ovid Medline, Cochrane Library and Clinicaltrials.gov databases. The literature pertaining to the impact of LC supplementation on neurological or psychiatric disorders in patients was reviewed up until November 2023. No language or temporal restrictions were imposed on the search.

RESULTS

A total of 1479 articles were retrieved, and after the removal of duplicates through both automated and manual exclusion processes, 962 articles remained. Subsequently, a meticulous re-screening led to the identification of 60 relevant articles. Among these, there were 12 publications focusing on hepatic encephalopathy (HE), while neurodegenerative diseases (NDs) and peripheral nervous system diseases (PNSDs) were represented by 9 and 6 articles, respectively. Additionally, stroke was addressed in five publications, whereas Raynaud's syndrome (RS) and cognitive disorder (CD) each had three dedicated studies. Furthermore, migraine, depression, and amyotrophic lateral sclerosis (ALS) each accounted for two publications. Lastly, one article was found for other symptoms under investigation.

CONCLUSION

In summary, LC has demonstrated favorable therapeutic effects in the management of HE, Alzheimer's disease (AD), carpal tunnel syndrome (CTS), CD, migraine, neurofibromatosis (NF), PNSDs, RS, and stroke. However, its efficacy appears to be relatively limited in conditions such as ALS, ataxia, attention deficit hyperactivity disorder (ADHD), depression, chronic fatigue syndrome (CFS), Down syndrome (DS), and sciatica.

Apparent Opportunities and Hidden Pitfalls: The Conflicting Results of Restoring NRF2-Regulated Redox Metabolism in Friedreich's Ataxia Pre-Clinical Models and Clinical Trials

Friedreich's ataxia (FRDA) is an autosomal, recessive, inherited neurodegenerative disease caused by the loss of activity of the mitochondrial protein frataxin (FXN), which primarily affects dorsal root ganglia, cerebellum, and spinal cord neurons. The genetic defect consists of the trinucleotide GAA expansion in the first intron of FXN gene, which impedes its transcription. The resulting FXN deficiency perturbs iron homeostasis and metabolism, determining mitochondrial dysfunctions and leading to reduced ATP production, increased reactive oxygen species (ROS) formation, and lipid peroxidation. These alterations are exacerbated by the defective functionality of the nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor acting as a key mediator of the cellular redox signalling and antioxidant response. Because oxidative stress represents a major pathophysiological contributor to FRDA onset and progression, a great effort has been dedicated to the attempt to restore the NRF2 signalling axis. Despite this, the beneficial effects of antioxidant therapies in clinical trials only partly reflect the promising results obtained in preclinical studies conducted in cell cultures and animal models. For these reasons, in this critical review, we overview the outcomes obtained with the administration of various antioxidant compounds and critically analyse the aspects that may have contributed to the conflicting results of preclinical and clinical studies.

Placebo response in degenerative cerebellar ataxias: a descriptive review of randomized, placebo-controlled trials

Placebo response in degenerative cerebellar ataxias (CAs) has never been studied despite the large number of randomized controlled trials (RCTs) that have been conducted. In this descriptive review, we aimed to examine the placebo response in patients with CAs. We performed a literature search on PubMed for RCTs on CAs that were published from 1977 to January 2020 and collected data on the changes from the baseline to the endpoint on various objective ataxia-associated clinical rating scales. We reviewed 56 clinical trials, finally including 35 parallel-group studies and excluding 21 cross-over studies. The included studies were categorized as follows: (1) studies showing significant improvements in one or more ataxia scales in the placebo groups (n = 3); (2) studies reporting individual placebo responders with improvements in one or more ataxia scales in the placebo groups (n = 5)-the overall proportion of placebo responders was 31.9%; (3) studies showing mean changes in the direction of improvement in at least one ataxia scale in the placebo groups, though not statistically significant (n = 19); (4) studies showing no placebo response in any of the ataxia scales in the placebo groups (n = 4); (5) studies where data on the placebo groups were unavailable (n = 9). This review demonstrated the placebo response in patients with CAs on various objective ataxia scales. Our study emphasizes that the placebo response should be considered when designing, analyzing, and interpreting clinical trials and in clinical practice in CA patients.

Metabolic profiling and novel plasma biomarkers for predicting survival in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is one of the most lethal gynecological malignancies around the world, and patients with ovarian cancer always have an extremely poor chance of survival. Therefore, it is meaningful to develop a highly efficient model that can predict the overall survival for EOC. In order to investigate whether metabolites could be used to predict the survival of EOC, we performed a metabolic analysis of 98 plasma samples with follow-up information, based on the ultra-performance liquid chromatography mass spectrometry (UPLC/MS) systems in both positive (ESI+) and negative (ESI-) modes. Four metabolites: Kynurenine, Acetylcarnitine, PC (42:11), and LPE(22:0/0:0) were selected as potential predictive biomarkers. The AUC value of metabolite-based risk score, together with pathological stages in predicting three-year survival rate was 0.80. The discrimination performance of these four biomarkers between short-term mortality and long-term survival was excellent, with an AUC value of 0.82. In conclusion, our plasma metabolomics study presented the dysregulated metabolism related to the survival of EOC, and plasma metabolites could be utilized to predict the overall survival and discriminate the short-term mortality and long-term survival for EOC patients. These results could provide supplementary information for further study about EOC survival mechanism and guiding the appropriate clinical treatment.

Comprehensive systematic review summary: Treatment of cerebellar motor dysfunction and ataxia: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology

OBJECTIVE

To systematically review evidence regarding ataxia treatment.

METHODS

A comprehensive systematic review was performed according to American Academy of Neurology methodology.

CONCLUSIONS

For patients with episodic ataxia type 2, 4-aminopyridine 15 mg/d probably reduces ataxia attack frequency over 3 months (1 Class I study). For patients with ataxia of mixed etiology, riluzole probably improves ataxia signs at 8 weeks (1 Class I study). For patients with Friedreich ataxia or spinocerebellar ataxia (SCA), riluzole probably improves ataxia signs at 12 months (1 Class I study). For patients with SCA type 3, valproic acid 1,200 mg/d possibly improves ataxia at 12 weeks. For patients with spinocerebellar degeneration, thyrotropin-releasing hormone possibly improves some ataxia signs over 10 to 14 days (1 Class II study). For patients with SCA type 3 who are ambulatory, lithium probably does not improve signs of ataxia over 48 weeks (1 Class I study). For patients with Friedreich ataxia, deferiprone possibly worsens ataxia signs over 6 months (1 Class II study). Data are insufficient to support or refute the use of numerous agents. For nonpharmacologic options, in patients with degenerative ataxias, 4-week inpatient rehabilitation probably improves ataxia and function (1 Class I study); transcranial magnetic stimulation possibly improves cerebellar motor signs at 21 days (1 Class II study). For patients with multiple sclerosis-associated ataxia, the addition of pressure splints possibly has no additional benefit compared with neuromuscular rehabilitation alone (1 Class II study). Data are insufficient to support or refute use of stochastic whole-body vibration therapy (1 Class III study).

[The use of acetyl-L-carnitine in gerontological practice]

An analysis of literature data on the acetyl-L-carnitine treatment in gerontological practice is performed. This review describes the range of biochemical activity and mechanism of action of the drug. The profile and specificity of acetyl-L-carnitine action and the possibility of combining nicergoline with other drugs is discussed. The results of preclinical and clinical studies on the application of acetyl-L-carnitine in the world medical practice are analyzed. The analysis of the studies demonstrates the high efficacy and a broad spectrum of acetyl-L-carnitine treatment.

Emerging therapies in Friedreich's ataxia

Friedreich's ataxia (FRDA) is an inherited, progressive neurodegenerative disease that typically affects teenagers and young adults. Therapeutic strategies and disease insight have expanded rapidly over recent years, leading to hope for the FRDA population. There is currently no US FDA-approved treatment for FRDA, but advances in research of its pathogenesis have led to clinical trials of potential treatments. This article reviews emerging therapies and discusses future perspectives, including the need for more precise measures for detecting changes in neurologic symptoms as well as a disease-modifying agent.

Treatment of cerebellar ataxia

SUMMARY 

Symptoms of cerebellar degeneration include ataxia or wide-based gait, visual and speech dysfunction, dysmetria, and dyscoordination. The etiology of cerebellar degeneration is vast and often complex, and requires neuroimaging, lab assessments, and a thorough family history to delineate its cause. There is currently no accepted treatment of hereditary cerebellar degeneration, although several pharmaceutical agents have shown potential promise.

Mitochondrial modulators for bipolar disorder: a pathophysiologically informed paradigm for new drug development

OBJECTIVES

Bipolar patients frequently relapse within 12 months of their previous mood episode, even in the context of adequate treatment, suggesting that better continuation and maintenance treatments are needed. Based on recent research of the pathophysiology of bipolar disorder, we review the evidence for mitochondrial dysregulation and selected mitochondrial modulators (MM) as potential treatments.

METHODS

We reviewed the literature about mitochondrial dysfunction and potential MMs worthy of study that could improve the course of bipolar disorder, reduce subsyndromal symptoms, and prevent subsequent mood episodes.

RESULTS

MM treatment targets mitochondrial dysfunction, oxidative stress, altered brain energy metabolism and the dysregulation of multiple mitochondrial genes in patients with bipolar disorder. Several tolerable and readily available candidates include N-acetyl-cysteine (NAC), acetyl-L-carnitine (ALCAR), S-adenosylmethionine (SAMe), coenzyme Q(10) (CoQ10), alpha-lipoic acid (ALA), creatine monohydrate (CM), and melatonin. The specific metabolic pathways by which these MMs may improve the symptoms of bipolar disorder are discussed and combinations of selected MMs could be of interest as well.

CONCLUSIONS

Convergent data implicate mitochondrial dysfunction as an important component of the pathophysiology of bipolar disorder. Clinical trials of individual MMs as well as combinations are warranted.

Longitudinal tracking of gait and balance impairments in cerebellar disease

Cerebellar damage typically results in ataxia and can be caused by stroke, tumor, or one of many forms of degenerative disease. Since few pharmacological options are available, most treatments rely heavily on rehabilitation therapy. Little data exist on methods for tracking the progression of ataxia, which is critical for assessing the efficacy of current and newly developing treatments. Here, we tracked the severity of ataxia, with a particular emphasis on gait and balance dysfunction, in a group of individuals with cerebellar damage using the International Cooperative Ataxia Rating Scale (ICARS) and several instrumented laboratory measures of gait and balance impairments over 1 year. We found that the ICARS was able to distinguish between subjects with static lesions and those with degenerative disorders, was sensitive to increases in ataxia severity occurring over 1 year, and correlated well with specific instrumented measures of gait in persons with cerebellar degeneration. These results suggest the ICARS is a valuable tool for clinicians and investigators to document and track long-term changes in gait and balance performance in individuals with cerebellar degenerative disorders.

Effectiveness and safety of treatments for degenerative ataxias: a systematic review

The aim of this study was to determine the effectiveness and safety of available treatment alternatives for degenerative ataxias (DA). We systematically reviewed studies that assess pharmacological, rehabilitative, or psychological treatments in patients with DA. Studies were included if they fulfilled prespecified criteria. All included clinical trials were scored for methodological quality. Main outcome measures were clinical status of neurological disorder, adverse events, and patient-based factors. Twenty-five studies were included. Most studies were of small sample sizes, wide age variations, and low scientific validity. Only one study gave information on physical rehabilitation and none on psychological therapy. The remaining 24 studies reported on the effects of different pharmacological treatments. Outcomes such as functional capacity and psychological functioning of patients were evaluated by few studies. Some evidence supports that 5-hydroxytryptophan is more effective than placebo improving neurological symptoms in patients with Friedreich ataxia (FA), olivopontocerebellar atrophy, or cerebellar atrophy. Idebenone is more effective than placebo for halting and reversing the hypertrophic cardiomyopathy associated with FA, but it seems unable to improve neurological semiology. Limited evidence for other therapies was found. No relevant side effects for drugs that shown some degree of effectiveness were reported. Availability of quality studies to evaluate the safety and efficacy of treatments for most DA is scarce. No valid information on the actual value of physical rehabilitation and psychological support as treatments for DA is available. Further investigations with improved trial designs are necessary.

Diagnosis and treatment of Friedreich ataxia: a European perspective

Friedreich ataxia is the most frequent hereditary ataxia, with an estimated prevalence of 3-4 cases per 100,000 individuals. This autosomal-recessive neurodegenerative disease is characterized by progressive gait and limb ataxia, dysarthria, lower-limb areflexia, decreased vibration sense, muscular weakness in the legs, and a positive extensor plantar response. Non-neurological signs include hypertrophic cardiomyopathy and diabetes mellitus. Symptom onset typically occurs around puberty, and life expectancy is 40-50 years. Friedreich ataxia is usually caused by a large GAA-triplet-repeat expansion within the first intron of the frataxin (FXN) gene. FXN mutations cause deficiencies of the iron-sulfur cluster-containing subunits of the mitochondrial electron transport complexes I, II, and III, and of the iron-sulfur protein aconitase. Mitochondrial dysfunction has been addressed in several open-label, non-placebo-controlled trials, which indicated that treatment with idebenone might ameliorate hypertrophic cardiomyopathy; a well-designed phase II trial suggested concentration-dependent functional improvements in non-wheelchair-bound children and adolescents. Other current experimental approaches address iron-mediated toxicity, or aim to increase FXN expression through the use of erythropoietin and histone deacetylase inhibitors. This Review provides guidelines, from a European perspective, for the diagnosis of Friedreich ataxia, differential diagnosis of ataxias and genetic counseling, and treatment of neurological and non-neurological symptoms.

Oxidative stress pathways in the potentiation of noise-induced hearing loss by acrylonitrile

We hypothesize that the disruption of antioxidant defenses is a key mechanism whereby chemical contaminants can potentiate noise-induced hearing loss (NIHL). This hypothesis was tested using acrylonitrile (ACN), a widely used industrial chemical whose metabolism is associated with glutathione (GSH) depletion and cyanide (CN) generation. CN, in turn, can inhibit Cu/Zn superoxide dismutase (SOD). We have shown previously that ACN potentiates NIHL, even with noise exposure approaching permissible occupational levels. However, the relative involvement of GSH depletion and/or CN production in this potentiation is still unknown. In this study, we altered these metabolic pathways pharmacologically in order to further delineate the role of specific antioxidants in the protection of the cochlea. We investigated the effects of sodium thiosulfate (STS), a CN inhibitor, 4-methylpyrazole (4MP), a drug that blocks CN generation by competing with CYP2E1, and l-N-acetylcysteine (l-NAC), a pro-GSH drug, in order to distinguish between GSH depletion and CN production as the mechanism responsible for potentiation of NIHL by ACN. Long-Evans rats were exposed to an octave-band noise (97 dB SPL, 4h/day, 5 days) and ACN (50 mg/kg). Separate pre-treatments with STS (150 mg/kg), 4MP (100 mg/kg) and l-NAC (4 x 400 mg/kg) all dramatically reduced blood CN levels, but only l-NAC significantly protected GSH levels in both the liver and the cochlea. Concurrently, only l-NAC treatment decreased the auditory loss and hair cell loss resulting from ACN + noise, suggesting that GSH is involved in the protection of the cochlea against reactive oxygen species generated by moderate noise levels. On the other hand, CN does not seem to be involved in this potentiation.

Risk assessment for carnitine

Carnitine is a conditionally essential amino acid-like compound involved in the transport of long-chain fatty acids into the mitochondria during the beta-oxidation process. Carnitine has become an increasingly popular ingredient in dietary supplements, especially weight loss and some sports nutrition products. A number of clinical trials have been conducted examining the effect of carnitine supplementation on weight loss and energy balance. Regarding safety, systematic evaluation of the research designs and data do not provide a basis for risk assessment and the usual safe upper level of intake (UL) derived from it unless the newer methods described as the observed safe level (OSL) or highest observed intake (HOI) are utilized. The OSL risk assessment method indicates that the evidence of safety is strong at intakes up to 2000mg/day l-carnitine equivalents for chronic supplementation, and this level is identified as the OSL. Although much higher levels have been tested without adverse effects and may be safe, the data for intakes above 2000mg/day are not sufficient for a confident conclusion of long-term safety.

Prevention of impulse noise-induced hearing loss with antioxidants

CONCLUSION

These findings indicate a strong protective effect of ALCAR and NAC on impulse noise-induced cochlear damage, and suggest the feasibility of using clinically available antioxidant compounds to protect the ear from acute acoustic injury.

OBJECTIVE

Reactive oxygen species have been shown to play a significant role in noise-induced hearing loss. In the current study, the protective effects of two antioxidants, acetyl-L-carnitine (ALCAR) and N-L-acetylcysteine (NAC), were investigated in a chinchilla model of hearing loss resulting from impulse noise. It was hypothesized that pre- and post-treatment with these antioxidants would ameliorate the effects of impulse noise compared to saline-treated controls.

MATERIAL AND METHODS

Eighteen animals were randomly assigned to 1 of 3 groups and exposed to impulse noise at a level of 155 dB peak SPL for 150 repetitions. ALCAR or NAC were administered twice daily (b.i.d.) for 2 days and 1 h prior to and 1 h following noise exposure, and then b.i.d. for the following 2 days. For the control group, saline was injected at the same time points. Auditory brainstem responses (ABRs) were recorded. Cochlear surface preparations were made to obtain cytocochleograms.

RESULTS

Three weeks after exposure, permanent threshold shifts for the experimental groups were significantly reduced to approximately = 10-30 dB less than that for the control group (p < 0.01). Less hair cell loss was also observed in the ALCAR and NAC groups than in the control group.

Therapeutic strategies in Friedreich’s ataxia

Friedreich's ataxia is caused by a pronounced lack of frataxin, a mitochondrial protein of not fully understood function. Lack of frataxin homologues in yeast and mice leads to increased sensitivity to oxidative stress, depletion of proteins with iron-sulfur clusters like respiratory chain complexes I-III and aconitase, and to iron accumulation in mitochondria. Similar effects have been demonstrated in human disease with increased markers of oxidative DNA damage in urine and impaired oxidative phosphorylation in in vivo exercise studies using 31 Phosphorus magnetic resonance spectroscopy (31P-MRS). Therapeutical trials mainly focus on antioxidative treatment with coenzyme Q10 or its short-chain variant idebenone. Promising effects on cardiac hypertrophy in uncontrolled preliminary studies contrast with minor effects in controlled trials and no effect of antioxidants on neurological deficits has been established. Preliminary encouraging 31P-MRS data exist for the treatment with L-carnitine but not with creatine. However, all these interventions may take effect too late in the pathogenic process. Alternative strategies aiming at an enhancement of frataxin by stem cell transplantation, gene transfer or frataxin supplementation are desirable. Additionally, more efficient biomarkers are needed to monitor treatment effects.

Primary sensory neuronal rescue with systemic acetyl-l-carnitine following peripheral axotomy. A dose-response analysis

The loss of a large proportion of primary sensory neurons after peripheral nerve axotomy is well documented. As a consequence of this loss, the innervation density attained on completion of regeneration will never be normal, regardless of how well the individual surviving neurons regenerate. Acetyl-L-carnitine (ALCAR), an endogenous peptide in man, has been demonstrated to protect sensory neurons, thereby avoiding loss after peripheral nerve injury. In this study we examined the dose-response effect of ALCAR on the primary sensory neurons in the rat dorsal root ganglia (DRG) 2 weeks after sciatic nerve axotomy. Six groups of adult rats (n=5) underwent unilateral sciatic nerve axotomy, without repair, followed by 2 weeks systemic treatment with one of five doses of ALCAR (range 0.5-50 mg/kg/day), or normal saline. L4 and L5 dorsal root ganglia were then harvested bilaterally and sensory neuronal cell counts obtained using the optical disector technique. ALCAR eliminated neuronal loss at higher doses (50 and 10 mg/kg/day), while lower doses did result in loss (12% at 5 mg/kg/day, p<0.05; 19% at 1 mg/kg/day, p<0.001; 23% at 0.5 mg/kg/day, p<0.001) compared to contralateral control ganglia. Treatment with normal saline resulted in a 25% (p<0.001) loss, demonstrating no protective effect in accordance with previous studies.ALCAR preserves the sensory neuronal cell population after axotomy in a dose-responsive manner and as such, has potential for improving the clinical outcome following peripheral nerve trauma when doses in excess of 10 mg/kg/day are employed.

Reversal of biochemical and behavioral parameters of brain aging by melatonin and acetyl L-carnitine

The potential utility of dietary supplementation in order to prevent some of the oxidative and inflammatory changes occurring in the brain with age, has been studied. The cerebral cortex of 27-month-old male B6C3F1 mice had elevated levels of nitric oxide synthase 1 (EC 1.14.13.39) (nNOS) and peptide nitrotyrosine relative to cortices of younger (4-month-old) animals. After 25-month-old mice received basal diet together with 300 mg/l acetyl L-carnitine in the drinking water for 8 weeks, these levels were fully restored to those found in younger animals. A partial restoration was found when old animals received basal diet supplemented with 200 ppm melatonin in the diet. Levels of mRNA (messenger RNA) for nNOS were unchanged following these treatments implying translational regulation of nNOS activity. Behavioral indices indicative of exploratory behavior were also depressed in aged animals. Dietary supplementation with melatonin or acetyl L-carnitine partially reversed these changes. These findings suggest that dietary supplementation cannot merely arrest but indeed reverse some age-related increases in markers of oxidative and inflammatory events occurring with the cortex.

Candidate's thesis: enhancing intrinsic cochlear stress defenses to reduce noise-induced hearing loss

OBJECTIVES/HYPOTHESIS

Oxidative stress plays a substantial role in the genesis of noise-induced cochlear injury that causes permanent hearing loss. We present the results of three different approaches to enhance intrinsic cochlear defense mechanisms against oxidative stress. This article explores, through the following set of hypotheses, some of the postulated causes of noise-induced cochlear oxidative stress (NICOS) and how noise-induced cochlear damage may be reduced pharmacologically. 1) NICOS is in part related to defects in mitochondrial bioenergetics and biogenesis. Therefore, NICOS can be reduced by acetyl-L carnitine (ALCAR), an endogenous mitochondrial membrane compound that helps maintain mitochondrial bioenergetics and biogenesis in the face of oxidative stress. 2) A contributing factor in NICOS injury is glutamate excitotoxicity, which can be reduced by antagonizing the action of cochlear -methyl-D-aspartate (NMDA) receptors using carbamathione, which acts as a glutamate antagonist. 3) Noise-induced hearing loss (NIHL) may be characterized as a cochlear-reduced glutathione (GSH) deficiency state; therefore, strategies to enhance cochlear GSH levels may reduce noise-induced cochlear injury. The objective of this study was to document the reduction in noise-induced hearing and hair cell loss, following application of ALCAR, carbamathione, and a GSH repletion drug D-methionine (MET), to a model of noise-induced hearing loss.

STUDY DESIGN

This was a prospective, blinded observer study using the above-listed agents as modulators of the noise-induced cochlear injury response in the species chinchilla langier.

METHODS

Adult chinchilla langier had baseline-hearing thresholds determined by auditory brainstem response (ABR) recording. The animals then received injections of saline or saline plus active experimental compound starting before and continuing after a 6-hour 105 dB SPL continuous 4-kHz octave band noise exposure. ABRs were obtained immediately after noise exposure and weekly for 3 weeks. After euthanization, cochlear hair cell counts were obtained and analyzed. RESULTS ALCAR administration reduced noise-induced threshold shifts. Three weeks after noise exposure, no threshold shift at 2 to 4 kHz and <10 dB threshold shifts were seen at 6 to 8 kHz in ALCAR-treated animals compared with 30 to 35 dB in control animals. ALCAR treatment reduced both inner and outer hair cell loss. OHC loss averaged <10% for the 4- to 10-kHz region in ALCAR-treated animals and 60% in saline-injected-noise-exposed control animals. Noise-induced threshold shifts were also reduced in carbamathione-treated animals. At 3 weeks, threshold shifts averaged 15 dB or less at all frequencies in treated animals and 30 to 35 dB in control animals. Averaged OHC losses were 30% to 40% in carbamathione-treated animals and 60% in control animals. IHC losses were 5% in the 4- to 10-kHz region in treated animals and 10% to 20% in control animals. MET administration reduced noise-induced threshold shifts. ANOVA revealed a significant difference (P <.001). Mean OHC and IHC losses were also significantly reduced (P <.001).

CONCLUSIONS

These data lend further support to the growing body of evidence that oxidative stress, generated in part by glutamate excitotoxicity, impaired mitochondrial function and GSH depletion causes cochlear injury induced by noise. Enhancing the cellular oxidative stress defense pathways in the cochlea eliminates noise-induced cochlear injury. The data also suggest strategies for therapeutic intervention to reduce NIHL clinically.