Preclinical and clinical otoprotective applications of cell-penetrating peptide D-JNKI-1 (AM-111).

There is a growing interest in the auditory community to develop novel prophylactic and therapeutic drugs to prevent permanent sensorineural hearing loss following acute cochlear injury. The jun-N-terminal protein kinase (JNK) pathway plays a crucial role in acute sensory hearing loss. Blocking the JNK pathway using the cell-penetrating peptide D-JNKI-1 (AM-111/brimapitide) has shown promise as both a prophylactic and therapeutic agent for acute cochlear injury. A number of pre-clinical and clinical studies have determined the impact of D-JNKI-1 on acute sensorineural hearing loss. Given the inner-ear selective therapeutic profile, local route of administration, and ability to diffuse across cellular membranes rapidly using both active and passive transport makes D-JNK-1 a promising oto-protective drug. In this review article, we discuss the application of D-JNKI-1 in various auditory disorders as well as its pharmacological properties and distribution in the cochlea.

Low-dose D-methionine and N-acetyl-L-cysteine for protection from permanent noise-induced hearing loss in chinchillas.

OBJECTIVE: Despite efforts at public health awareness and stringent industrial standards for hearing protection, noise-induced hearing loss (NIHL) remains a formidable public health concern. Although many antioxidants have proven to be beneficial in the laboratory for prevention of permanent NIHL, low-dose combinations of compounds with different biochemical mechanisms of action may allow long-term administration with fewer side effects and equal efficacy. The mixture of D-methionine and N-acetyl-L-cysteine administered at levels less than 10% of standard dosing has not been previously reported. STUDY DESIGN: Twenty-six female adult Chinchilla laniger were placed in 4 study groups, consisting of (1) a group receiving combination 12.5 mg/kg each D-methionine and N-acetyl-L-cysteine (DMET/NAC group), (2) a group receiving 12.5 mg/kg D-methionine (DMET-only group), (3) a group receiving 12.5 mg/kg N-acetyl-L-cysteine (NAC-only group), and (4) saline controls. SETTING: Laboratory. SUBJECTS AND METHODS: All groups received twice-daily intraperitoneal injections 2 days prior to noise exposure, 1 hour before and after exposure on day 3, and for 2 days subsequently, totaling 10 doses of 125 mg/kg for each antioxidant over 5 days. RESULTS: Although NAC-only animals paralleled saline control recovery during 3 weeks, the DMET-only group revealed gradual improvement with statistically significant recovery in the middle frequencies. The DMET/NAC group showed significant improvement at most frequencies compared with controls (P < .001 and P < .05). CONCLUSION: Significant recovery of hearing was observed following continuous noise exposure with either DMET only or a combination of low-dose DMET/NAC, demonstrating a considerably lower dose of antioxidants required than previously reported for hearing recovery following acoustic trauma.

Noise protection with N-acetyl-l-cysteine (NAC) using a variety of noise exposures, NAC doses, and routes of administration.

CONCLUSION: These studies extend previous work on N-acetyl-l-cysteine (NAC) and noise, showing protection with NAC against a high-kurtosis noise, showing protection with NAC at low doses, as well as protection by oral gavage. The studies further reveal the potential for the use of NAC in a clinical population exposed to noise. OBJECTIVE: To extend previous work on NAC protection from noise, the current study examined the effectiveness of NAC against a high-kurtosis noise that combined continuous and impact noise, tested the effectiveness of NAC at varying doses, and tested NAC when administered by gavage. MATERIALS AND METHODS: Chinchillas were tested for auditory brainstem responses (ABRs) at five frequencies before and at three time points after one of three noise exposures: high-kurtosis (2 h, 108 dB L(eq)), impulse (75 pairs of 155 dB pSPL impulses), or continuous (4 kHz octave band, 105 dB SPL for 6 h). Animals were treated with NAC or saline vehicle before and after noise. RESULTS: The NAC was protective against the high-kurtosis noise both at low doses and when given orally by gavage.

NAC for noise: from the bench top to the clinic.

Noise-induced hearing loss (NIHL) is an important etiology of deafness worldwide. Hearing conservation programs are in place and have reduced the prevalence of NIHL, but this disorder is still far too common. Occupational and recreational pursuits expose people to loud noise and ten million persons in the US have some degree of noise-induced hearing impairment. It is estimated that 50 million in the US and 600 million people worldwide are exposed to noise hazards occupationally. Noise deafness is still an important and frequent cause of battlefield injury in the US military. A mainstay of hearing conservation programs is personal mechanical hearing protection devices which are helpful but have inherent limitations. Research has shown that oxidative stress plays an important role in noise-induced cochlear injury resulting in the discovery that a number of antioxidant and cell death inhibiting compounds can ameliorate deafness associated with acoustic trauma. This article reviews one such compound, N-acetylcysteine (NAC), in terms of its efficacy in reducing hearing loss in a variety of animal models of acute acoustic trauma and hypothesizes what its therapeutic mechanisms of action might be based on the known actions of NAC. Early clinical trials with NAC are mentioned.

AM-111 protects against permanent hearing loss from impulse noise trauma.

The otoprotective peptide AM-111, a cell-permeable inhibitor of JNK mediated apoptosis, was tested for its efficacy as a rescue agent following impulse noise trauma. Single dose administrations of AM-111 at 1h or 4h post-impulse noise exposure (155 dB peak SPL) via systemic or local routes were evaluated with a total of 48 chinchillas. The animals received the compound either by IP injection or locally onto the round window membrane (hyaluronic acid gel formulation or osmotic mini-pump). Efficacy was determined by auditory brainstem responses (ABR) as well as cytocochleograms. Three weeks after impulse noise exposure, permanent threshold shifts (PTS) were significantly lower for AM-111 treated ears compared to controls, regardless of the drug administration route and the time point of drug delivery. Even the treatments which started 4h post-noise exposure, reduced hearing loss in the 2-8 kHz range compared to controls by up to 16-25 dB to a PTS as low as 6-17 dB, demonstrating significant protection against permanent hearing loss from impulse noise trauma. These findings suggest a key role for JNK mediated cochlear sensory cell death from oxidative stress.

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.

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.