Kathleen C. M. Campbell

d-Methionine provides excellent protection from cisplatin ototoxicity in the rat

Cisplatin (CDDP) is a widely used chemotherapeutic agent. Unfortunately, CDDP is highly ototoxic. We tested D-methionine (D-Met), a sulfur containing compound, as an otoprotectant in male Wistar rats. Complete data sets were obtained for five groups of five animals each, including a treated control group (16 mg/kg CDDP), an untreated control group (administered an equivalent volume of saline) and three groups that received either 75, 150, or 300 mg/kg D-Met 30 min prior to the 16 mg/kg CDDP dosing. Auditory brainstem response (ABR) thresholds were obtained in response to clicks, and 1 kHz, 4 kHz, 8 kHz, and 14 kHz toneburst stimuli, before and 3 days after drug administration. Scanning electron microscopy (SEM) was used to examine the outer hair cells of the apical, middle and basal turns of the cochlea. Animal weight was measured on the first and final day. D-Met provided excellent otoprotection even at the lowest level with complete otoprotection obtained for the 300 mg/kg dosing as measured by both ABR and SEM. D-Met also markedly reduced weight loss and mortality. All animals receiving D-Met (15/15) survived to the end of the study period as opposed to only 5/10 of the treated controls.

Prevention of noise- and drug-induced hearing loss with d-methionine ☆

A number of otoprotective agents are currently being investigated. Various types of agents have been found in animal studies to protect against hearing loss induced by cisplatin, carboplatin, aminoglycosides, or noise exposure. For over a decade we have been investigating D-methionine (D-met) as an otoprotective agent. Studies in our laboratory and others around the world have documented D-mets otoprotective action, in a variety of species, against a variety of ototoxic insults including cisplatin-, carboplatin-, aminoglycoside- and noise-induced auditory threshold elevations and cochlear hair cell loss. For cisplatin-induced ototoxicity, protection of the stria vascularis has also been documented. Further D-met has an excellent safety profile. D-met may act as both a direct and indirect antioxidant. In this report, we provide the results of three experiments, expanding findings in D-met protection in three of our translational research areas: protection from platinum based chemotherapy-, aminoglycoside- and noise-induced hearing loss. These experiments demonstrate oral D-met protection against cisplatin-induced ototoxicity, D-met protection against amikacin-induced ototoxicity, and D-met rescue from permanent noise-induced hearing loss when D-met is initiated 1h after noise exposure. These studies demonstrate some of the animal experiments needed as steps to translate a protective agent from bench to bedside.

Platinum-Induced Ototoxicity in Children: A Consensus Review on Mechanisms, Predisposition, and Protection, Including a New International Society of Pediatric Oncology Boston Ototoxicity Scale

PURPOSE The platinum chemotherapy agents cisplatin and carboplatin are widely used in the treatment of adult and pediatric cancers. Cisplatin causes hearing loss in at least 60% of pediatric patients. Reducing cisplatin and high-dose carboplatin ototoxicity without reducing efficacy is important. PATIENTS AND METHODS This review summarizes recommendations made at the 42nd Congress of the International Society of Pediatric Oncology (SIOP) in Boston, October 21-24, 2010, reflecting input from international basic scientists, pediatric oncologists, otolaryngologists, oncology nurses, audiologists, and neurosurgeons to develop and advance research and clinical trials for otoprotection. RESULTS Platinum initially impairs hearing in the high frequencies and progresses to lower frequencies with increasing cumulative dose. Genes involved in drug transport, metabolism, and DNA repair regulate platinum toxicities. Otoprotection can be achieved by acting on several these pathways and generally involves antioxidant thiol agents. Otoprotection is a strategy being explored to decrease hearing loss while maintaining dose intensity or allowing dose escalation, but it has the potential to interfere with tumoricidal effects. Route of administration and optimal timing relative to platinum therapy are critical issues. In addition, international standards for grading and comparing ototoxicity are essential to the success of prospective pediatric trials aimed at reducing platinum-induced hearing loss. CONCLUSION Collaborative prospective basic and clinical trial research is needed to reduce the incidence of irreversible platinum-induced hearing loss, and optimize cancer control. Wide use of the new internationally agreed-on SIOP Boston ototoxicity scale in current and future otoprotection trials should help facilitate this goal.

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 N‐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.

D-Methionine protects against cisplatin damage to the stria vascularis.

D-Methionine (D-met) protects against cisplatin (CDDP)-induced hearing loss and outer hair cell loss (Campbell et al., 1996). However, D-mets protective effects on the stria vascularis has not been previously investigated. The purpose of this study was to examine, using semi-quantitative analysis, whether D-met also protects the stria vascularis. We removed a basal turn section of the stria vascularis from five groups of five male Wistar rats each: (1) a CDDP-treated control group receiving a 30 min i.p. infusion of 16 mg/kg CDDP, (2) a saline-injected control group receiving an equivalent volume of saline, and (3) three groups injected with either 75, 150, or 300 mg/kg D-methionine (D-met) i.p. 30 min prior to receiving the 16 mg/kg CDDP dosing. Using transmission electron microscopy and light microscopy, we analyzed strial volume (i.e. edema), marginal cell damage classification (bulging and/or compression), and relative optical density (ROD) ratios (i.e. depletion of marginal cell cytoplasmic organelles). All three levels of D-met provided complete protection against marginal cell bulging and/or compression but only partial protection against strial edema. At 300 mg/kg, D-met significantly reduced ROD ratio degradation in the spiral prominence and middle stria vascularis regions. In Reissners membrane region, values from the D-met pretreated group were not significantly different from either the treated or untreated control groups suggesting only partial protection for that area. Protection of marginal cell cytoplasmic organelles was also noted. In summary, D-met partially or fully protects the stria vascularis from several types of CDDP-induced damage.

A semiquantitative analysis of the effects of cisplatin on the rat stria vascularis

Cisplatin (CDDP) is a very effective chemotherapeutic agent but is highly ototoxic. Most studies have focused on the effects of CDDP on the outer hair cells. The purpose of this study was to examine changes in the stria vascularis in cisplatin treated male Wistar rats and to provide semiquantitative analysis of the results. We removed a section of the stria vascularis from the basal turn of five control and five CDDP (16 mg/kg) treated rats. Using transmission electron microscopy (TEM) we analyzed: (1) changes to the strial tissue as a whole; and (2) intracellular changes in the marginal cells. We also subjected the samples to semiquantitative analysis using the MCID, focusing on three aspects of strial profile abnormalities; the number of abnormal marginal cells in CDDP treated tissue, intracellular strial edema and densitometry. Controls appeared normal, but many pathologic changes were apparent in the experimental group. Results from the semiquantitative analysis indicate cisplatin has a deleterious effect on the stria vascularis including strial edema; bulging, rupture and/or compression of the marginal cells and depletion of the cytoplasmic organelles.

A Unique Point Mutation in the PMP22 Gene Is Associated with Charcot-Marie-Tooth Disease and Deafness

Charcot-Marie-Tooth disease (CMT) with deafness is clinically distinct among the genetically heterogeneous group of CMT disorders. Molecular studies in a large family with autosomal dominant CMT and deafness have not been reported. The present molecular study involves a family with progressive features of CMT and deafness, originally reported by Kousseff et al. Genetic analysis of 70 individuals (31 affected, 28 unaffected, and 11 spouses) revealed linkage to markers on chromosome 17p11.2-p12, with a maximum LOD score of 9.01 for marker D17S1357 at a recombination fraction of .03. Haplotype analysis placed the CMT-deafness locus between markers D17S839 and D17S122, a approximately 0.6-Mb interval. This critical region lies within the CMT type 1A duplication region and excludes MYO15, a gene coding an unconventional myosin that causes a form of autosomal recessive deafness called DFNB3. Affected individuals from this family do not have the common 1.5-Mb duplication of CMT type 1A. Direct sequencing of the candidate peripheral myelin protein 22 (PMP22) gene detected a unique G-->C transversion in the heterozygous state in all affected individuals, at position 248 in coding exon 3, predicted to result in an Ala67Pro substitution in the second transmembrane domain of PMP22.

Strategies for prevention of toxicity caused by platinum-based chemotherapy: review and summary of the annual meeting of the Blood-Brain Barrier Disruption Program, Gleneden Beach, Oregon, March 10, 2001.

Objectives To summarize the findings relevant to otolaryngology from the annual meeting of the Blood–Brain Barrier Disruption Consortium in Gleneden Beach, Oregon, March 10, 2001.

Interpretation of Electrocochleography in Meniere's Disease and Normal Subjects

Electrocochleographic recordings were obtained from 20 subjects with normal hearing and 10 subjects with Menieres disease by using an eardrum electrode. Stimuli included clicks and 6,000-Hz tone bursts. Results were not significantly different between the two groups for summating potential (SP) amplitude, action potential (AP) amplitude, or the SP/AP amplitude ratio. Interpreting the results in light of symptoms on the date of assessment or hearing threshold did not appear to improve separation between the two groups. Various SP/AP amplitude ratio criteria have been proposed in order to separate normal patients from those with Menieres disease. Applying these proposed criteria to our data did not successfully separate the two groups.

Digital music exposure reliably induces temporary threshold shift in normal-hearing human subjects.

Objectives: One of the challenges for evaluating new otoprotective agents for potential benefit in human populations is the availability of an established clinical paradigm with real-world relevance. These studies were explicitly designed to develop a real-world digital music exposure that reliably induces temporary threshold shift (TTS) in normal-hearing human subjects. Design: Thirty-three subjects participated in studies that measured effects of digital music player use on hearing. Subjects selected either rock or pop music, which was then presented at 93 to 95 (n = 10), 98 to 100 (n = 11), or 100 to 102 (n = 12) dBA in-ear exposure level for a period of 4 hr. Audiograms and distortion product otoacoustic emissions (DPOAEs) were measured before and after music exposure. Postmusic tests were initiated 15 min, 1 hr 15 min, 2 hr 15 min, and 3 hr 15 min after the exposure ended. Additional tests were conducted the following day and 1 week later. Results: Changes in thresholds after the lowest-level exposure were difficult to distinguish from test–retest variability; however, TTS was reliably detected after higher levels of sound exposure. Changes in audiometric thresholds had a “notch” configuration, with the largest changes observed at 4 kHz (mean = 6.3 ± 3.9 dB; range = 0–14 dB). Recovery was largely complete within the first 4 hr postexposure, and all subjects showed complete recovery of both thresholds and DPOAE measures when tested 1 week postexposure. Conclusions: These data provide insight into the variability of TTS induced by music-player use in a healthy, normal-hearing, young adult population, with music playlist, level, and duration carefully controlled. These data confirm the likelihood of temporary changes in auditory function after digital music-player use. Such data are essential for the development of a human clinical trial protocol that provides a highly powered design for evaluating novel therapeutics in human clinical trials. Care must be taken to fully inform potential subjects in future TTS studies, including protective agent evaluations, that some noise exposures have resulted in neural degeneration in animal models, even when both audiometric thresholds and DPOAE levels returned to pre-exposure values.