Effects of extracochlear gacyclidine perfusion on tinnitus in humans: a case series

Targeting NMDA receptors with an antagonist is a promising therapeutic strategy for treating neurological disorders

Glutamate activates the NMDARs, significantly affecting multiple processes such as learning, memory, synaptic integration, and excitatory transmission in the central nervous system. Uncontrolled activation of NMDARs is a significant contributor to synaptic dysfunction. Having a properly functioning NMDAR and synapse is crucial for maintaining neuronal communication. In addition, the dysfunction of NMDAR and synapse function could contribute to the development of neurological disorders at the neuronal level; hence, targeting NMDARs with antagonists in the fight against neurological disorders is a promising route. Recently published results from the animal study on different kinds of brain diseases like stroke, epilepsy, tinnitus, ataxia, Alzheimer's disease, Parkinson's disease, and spinal cord injury have demonstrated promising therapeutic scopes. Several NMDA receptor antagonists, such as memantine, MK801, ketamine, ifenprodil, gacyclidine, amantadine, agmatine, etc., showed encouraging results against different brain disease mouse models. Given the unique expression of different subunits of the well-organized NMDA receptor system by neurons. It could potentially lead to the development of medications specifically targeting certain receptor subtypes. For a future researcher, conducting more targeted research and trials is crucial to fully understand and develop highly specific medications with good clinical effects and potential neuroprotective properties.

A randomized, double-blind, placebo-controlled phase 2 study of intratympanic OTO-313 in patients with moderate to severe subjective tinnitus

PURPOSE

This was a randomized, double-blind, placebo-controlled Phase 2 study to evaluate the efficacy and safety of intratympanic OTO-313 in patients with subjective unilateral tinnitus.

METHODS

Patients with moderate to severe unilateral tinnitus of 2-12 months duration were enrolled. A single intratympanic injection of OTO-313 or placebo was administered to the affected ear and patients were evaluated during a 16-weeks follow-up period. Efficacy was assessed using the Tinnitus Functional Index (TFI), daily ratings of tinnitus loudness and annoyance, and Patient Global Impression of Change (PGIC).

RESULTS

Intratympanic administration of OTO-313 and placebo produced reductions in tinnitus with a similar percentage of TFI responders at Weeks 4, 8, 12, and 16. Reductions in daily ratings of tinnitus loudness and annoyance, and PGIC scores were also similar between OTO-313 and placebo groups. No significant differences in mean TFI scores between OTO-313 and placebo were observed for pre-specified strata regarding tinnitus duration (≥ 2 to ≤ 6 months and > 6 to ≤ 12 months) and TFI baseline scores (≥ 32 to ≤ 53 points and ≥ 54 to 100 points), although the results numerically favored OTO-313 in patients in the ≥ 2 to ≤ 6 months strata. These results also demonstrated an unexpectedly high placebo response particularly amongst patients with chronic tinnitus, despite training implemented to mitigate placebo response. OTO-313 was well-tolerated with a similar incidence of adverse events compared to placebo.

CONCLUSIONS

OTO-313 did not demonstrate a significant treatment benefit relative to placebo due in part to a high placebo response. OTO-313 was safe and well-tolerated.

Approaches for Ear-targeted Delivery Systems in Neurosensory Disorders to avoid Chronic Hearing Loss Mediated Neurological Diseases

BACKGROUND AND OBJECTIVE

Hearing loss is a common audio-vestibular-related neurosensory disability of inner ears, in which patients exhibit clinical symptoms of dizziness, gait unsteadiness, and oscillopsia, at an initial stage. While, if such disorders are untreated for a prolonged duration then the progression of disease into a chronic state significantly decreases GABA level as well as an alteration in the neurotransmission of CNS systems. Hence, to control the progression of disease into a chronic approaches for timely and targeted delivery of the drugs at the site of action in the ear is now attracting the interest of neurologists for effective and safe treatment of such disorders. Among delivery systems, owing to small dimension, better penetration, rate-controlled release, higher bioavailability; nanocarriers are preferred to overcome delivery barriers, improvement in residence time, and enhanced the performance of loaded drugs. Subsequently, these carriers also stabilize encapsulated drugs while also provide an opportunity to modify the surface of carriers to favor guided direction for site-specific targeting. Contrary to this; conventional routes of drug delivery such as oral, intravenous, and intramuscular are poorer in performance because of inadequate blood supply to the inner ear and limited penetration of blood-inner ear barrier.

CONCLUSION

This review summarized novel aspects of non-invasive and biocompatible nanoparticles- based approaches for targeted delivery of drugs into the cochlea of the ear to reduce the rate, and extent of the emergence of any hearing loss mediated neurological disorders.

Intratympanic Administration of OTO-313 Reduces Tinnitus in Patients With Moderate to Severe, Persistent Tinnitus: A Phase 1/2 Study

OBJECTIVE

To evaluate the safety and exploratory efficacy of intratympanic administration of OTO-313 in patients with tinnitus.

STUDY DESIGN

Single intratympanic injection of OTO-313 evaluated in a randomized, double-blind, placebo-controlled Phase 1/2 clinical study.

SETTING

Tertiary referral centers.

PATIENTS

Patients with unilateral tinnitus (moderate-severe) with tinnitus duration 1 to 6 months.

INTERVENTIONS

Intratympanic OTO-313.

MAIN OUTCOME MEASURES

Safety and change from baseline in tinnitus functional index (TFI), daily ratings of tinnitus loudness and annoyance, and patient global impression of change (PGIC).

RESULTS

OTO-313 was well-tolerated with lower incidence of adverse events than placebo. Mean TFI reduction from baseline favored OTO-313 at Week 2, 4, and 8. A clinically meaningful, 13-point improvement on the TFI was observed in 43% (6/14) of OTO-313 patients at both Weeks 4 and 8 versus 13% (2/16) of placebo patients (ad hoc responder analysis, p-value < 0.05). Reductions in daily ratings of tinnitus loudness and annoyance favored OTO-313 compared with placebo. In OTO-313 responders, a strong correlation existed between change from baseline in TFI score and changes in tinnitus loudness, tinnitus annoyance, and PGIC.

CONCLUSIONS

OTO-313 was well-tolerated and demonstrated a higher proportion of responders than placebo across consecutive visits (Weeks 4 and 8) supporting further clinical development of OTO-313 for the treatment of tinnitus.

Local Drug Delivery for the Treatment of Neurotology Disorders

Neurotology disorders such as vertigo, tinnitus, and hearing loss affect a significant proportion of the population (estimated 39 million in the United States with moderate to severe symptoms). Yet no pharmacological treatments have been developed, in part due to limitations in effective drug delivery to the anatomically protected inner ear compartment. Intratympanic delivery, a minimally invasive injection performed in the office setting, offers a potential direct route of administration. Currently, off-label use of therapeutics approved to treat disorders via systemic administration are being injected intratympanically, mostly in the form of aqueous solutions, but provide variable levels of drug exposure for a limited time requiring repeated injections. Hence, current drug delivery approaches for neurotology disorders are sub-optimal. This review, following a description of pharmacokinetic considerations of the inner ear, explores the merits of novel delivery approaches toward the treatment of neurotology disorders. Methodologies employing local delivery to the inner ear are described, including direct intracochlear delivery as well as intratympanic methods of infusion and injection. Intratympanic injection delivery formulation strategies including hydrogels, polymers and nanoparticulate systems are explored. These approaches represent progress toward more effective delivery options for the clinical treatment of a variety of neurotology disorders.

Otic drug delivery systems: formulation principles and recent developments

Disorders of the ear severely impact the quality of life of millions of people, but the treatment of these disorders is an ongoing, but often overlooked challenge particularly in terms of formulation design and product development. The prevalence of ear disorders has spurred significant efforts to develop new therapeutic agents, but perhaps less innovation has been applied to new drug delivery systems to improve the efficacy of ear disease treatments. This review provides a brief overview of physiology, major diseases, and current therapies used via the otic route of administration. The primary focuses are on the various administration routes and their formulation principles. The article also presents recent advances in otic drug deliveries as well as potential limitations. Otic drug delivery technology will likely evolve in the next decade and more efficient or specific treatments for ear disease will arise from the development of less invasive drug delivery methods, safe and highly controlled drug delivery systems, and biotechnology targeting therapies.

A Surgical Procedure for the Administration of Drugs to the Inner Ear in a Non-Human Primate Common Marmoset (Callithrix jacchus)

Hearing research has long been facilitated by rodent models, although in some diseases, human symptoms cannot be recapitulated. The common marmoset (Callithrix jacchus) is a small, easy-to-handle New World monkey which has a similar anatomy of the temporal bone, including the middle ear ossicular chains and inner ear to humans, than in comparison with that of rodents. Here, we report a reproducible, safe, and rational surgical approach to the cochlear round window niche for the drug delivery to the inner ear of the common marmoset. We adopted posterior tympanotomy, a procedure used clinically in human surgery, to avoid manipulation of the tympanic membrane that may cause conductive hearing loss. This surgical procedure did not lead to any significant hearing loss. This approach was possible due to the large bulla structure of the common marmoset, although the lateral semicircular canal and vertical portion of the facial nerve should be carefully considered. This surgical method allows us to perform the safe and accurate administration of drugs without hearing loss, which is of great importance in obtaining pre-clinical proof of concept for translational research.

Tinnitus: Prospects for Pharmacological Interventions With a Seesaw Model

Chronic tinnitus, the perception of lifelong constant ringing in ear, is one capital cause of disability in modern society. It is often present with various comorbid factors that severely affect quality of life, including insomnia, deficits in attention, anxiety, and depression. Currently, there are limited therapeutic treatments for alleviation of tinnitus. Tinnitus can involve a shift in neuronal excitation/inhibition (E/I) balance, which is largely modulated by ion channels and receptors. Thus, ongoing research is geared toward pharmaceutical approaches that modulate the function of ion channels and receptors. Here, we propose a seesaw model that delineates how tinnitus-related ion channels and receptors are involved in homeostatic E/I balance of neurons. This review provides a thorough account of our current mechanistic understanding of tinnitus and insight into future direction of drug development.

Altered mental status and end organ damage associated with the use of gacyclidine: a case series

INTRODUCTION

Over the past decade, there has been a sharp increase in the number of newly identified synthetic drugs. These new drugs are often derivatives of previously abused substances but have unpredictable toxicity. One of these drugs is gacyclidine, a derivative of phencyclidine (PCP). Gacyclidine has been studied as a neuroprotective agent in trauma and as a therapy of soman toxicity. There are no previous reports of its use as a drug of abuse.

CASE REPORTS

During a two-month period in the summer of 2013, a series of patients with severe agitation and end-organ injury were identified in an urban academic Emergency Department (ED). A urine drug of abuse screen was performed on all patients, and serum samples were sent for comprehensive toxicology analysis. A total of five patients were identified as having agitation, rhabdomyolysis, and elevated troponin (Table 1). Three of the five patients reported use of methamphetamine, and all five patients had urine drug screens positive for amphetamine. Comprehensive serum analysis identified methamphetamine in three cases, cocaine metabolites in one case, and a potential untargeted match for gacyclidine in all five cases. No other drugs of abuse were identified.

DISCUSSION

This is the first series of cases describing possible gacyclidine intoxication. The possible source of the gacyclidine is unknown but it may have been an adulterant in methamphetamine as all patients who were questioned reported methamphetamine use. These cases highlight the importance of screening for new drugs of abuse when patients present with atypical or severe symptoms. Gacyclidine has the potential to become a drug of abuse both by itself and in conjunction with other agents and toxicity from gacyclidine can be severe. It is the role of the medical toxicology field to identify new agents such as gacyclidine early and to attempt to educate the community on the dangers of these new drugs of abuse.

Recent advances in local drug delivery to the inner ear

Inner ear diseases are not adequately treated by systemic drug administration mainly because of the blood-perilymph barrier that reduces exchanges between plasma and inner ear fluids. Local drug delivery methods including intratympanic and intracochlear administrations are currently developed to treat inner ear disorders more efficiently. Intratympanic administration is minimally invasive but relies on diffusion through middle ear barriers for drug entry into the cochlea, whereas intracochlear administration offers direct access to the colchlea but is rather invasive. A wide range of drug delivery systems or devices were evaluated in research and clinic over the last decade for inner ear applications. In this review, different strategies including medical devices, hydrogels and nanoparticulate systems for intratympanic administration, and cochlear implant coating or advanced medical devices for intracoclear administration were explored with special attention to in vivo studies. This review highlights the promising systems for future clinical applications as well as the current hurdles that remain to be overcome for efficient inner ear therapy.

Revisiting the cochlear and central mechanisms of tinnitus and therapeutic approaches

This short review aims at revisiting some of the putative mechanisms of tinnitus. Cochlear-type tinnitus is suggested to result from aberrant activity generated before or at the cochlear nerve level. It is proposed that outer hair cells, through their role in regulating the endocochlear potential, can contribute to the enhancement of cochlear spontaneous activity. This hypothesis is attractive as it provides a possible explanation for cochlear tinnitus of different aetiologies, such as tinnitus produced by acute noise trauma, intense low-frequency sounds, middle-ear dysfunction or temporomandibular joint disorders. Other mechanisms, namely an excitatory drift in the operating point of the inner hair cells and activation of NMDA receptors, are also briefly reported. Central-type tinnitus is supposed to result from aberrant activity generated in auditory centres, i.e. in these patients, the tinnitus-related activity does not pre-exist in the cochlear nerve. A reduction in cochlear activity due to hearing loss is suggested to produce tinnitus-related plastic changes, namely cortical reorganisation, thalamic neuron hyperpolarisation, facilitation of non-auditory inputs and/or increase in central gain. These central changes can be associated with abnormal patterns of spontaneous activity in the auditory pathway, i.e. hyperactivity, hypersynchrony and/or oscillating activity. Therapeutic approaches aimed at reducing cochlear activity and/or tinnitus-related central changes are discussed.

Expression of immediate-early genes in the inferior colliculus and auditory cortex in salicylate-induced tinnitus in rat

Tinnitus could be associated with neuronal hyperactivity in the auditory center. As a neuronal activity marker, immediate-early gene (IEG) expression is considered part of a general neuronal response to natural stimuli. Some IEGs, especially the activity-dependent cytoskeletal protein (Arc) and the early growth response gene-1 (Egr-1), appear to be highly correlated with sensory-evoked neuronal activity. We hypothesize, therefore, an increase of Arc and Egr-1 will be observed in a tinnitus model. In our study, we used the gap prepulse inhibition of acoustic startle (GPIAS) paradigm to confirm that salicylate induces tinnitus-like behavior in rats. However, expression of the Arc gene and Egr-1 gene were decreased in the inferior colliculus (IC) and auditory cortex (AC), in contradiction of our hypothesis. Expression of N-methyl d-aspartate receptor subunit 2B (NR2B) was increased and all of these changes returned to normal 14 days after treatment with salicylate ceased. These data revealed long-time administration of salicylate induced tinnitus markedly but reversibly and caused neural plasticity changes in the IC and the AC. Decreased expression of Arc and Egr-1 might be involved with instability of synaptic plasticity in tinnitus.

Developments in delivery of medications for inner ear disease

INTRODUCTION

Hearing loss, tinnitus and balance disturbance represent common diseases that have tremendous impact on quality of life. Despite the high incidence of inner ear disease in the general population, there are currently no dedicated pharmacologic interventions available to treat these problems.

AREAS COVERED

This review will focus on how treatment of inner ear disease is moving toward local delivery at the end organ level. The authors will discuss current practice, ongoing clinical trials and potential areas of development such as hair cell regeneration and neurotrophin therapy.

EXPERT OPINION

The inner ear is accessible through the middle ear via the oval and round windows allowing diffusion of drugs into the perilymph. With a better understanding of the physiology of the inner ear and the underlying molecular causes of inner ear disease there is great potential for the development of novel therapeutics that can be locally administered. At present, there is a rapid development of drugs to target diverse inner ear diseases that cause sensorineural hearing loss and balance dysfunction.

Drug delivery to the ear

Drug delivery to the ear is used to treat conditions of the middle and inner ear such as acute and chronic otitis media, Ménière’s disease, sensorineural hearing loss and tinnitus. Drugs used include antibiotics, antifungals, steroids, local anesthetics and neuroprotective agents. A literature review was conducted searching Medline (1966–2012), Embase (1988–2012), the Cochrane Library and Ovid (1966–2012), using search terms ‘drug delivery’, ‘middle ear’, ‘inner ear’ and ‘transtympanic’. There are numerous methods of drug delivery to the middle ear, which can be categorized as topical, systemic (intravenous), transtympanic and via the Eustachian tube. Localized treatments to the ear have the advantages of targeted drug delivery allowing higher therapeutic doses and minimizing systemic side effects. The ideal scenario would be a carrier system that could cross the intact tympanic membrane loaded with drugs or biochemical agents for the treatment of middle and inner ear conditions.

Expression of COX-2 and NMDA receptor genes at the cochlea and midbrain in salicylate-induced tinnitus

OBJECTIVE/HYPOTHESIS

The expression of the genes for cyclooxygenase (COX) and NMDA receptor (NR) has seldom been reported in tinnitus. We hypothesized that expression of COX-2 and NR was altered in the cochlea and midbrain in salicylate-induced tinnitus.

STUDY DESIGN

Experimental study on mice.

METHODS

We evaluated the tinnitus score and mRNA expression levels of COX-2 and NR subtype 2B (NR2B) in the cochlea and midbrain in response to intraperitoneal injections of salicylate for 4 days.

RESULTS

At day 4 of tinnitus induction, the mean weights of the whole body and midbrain did not change greatly in both control and salicylate groups. The tinnitus score was not elevated from day 1 to day 4 in the control group, but increased day by day in the salicylate group. The mRNA expression level of COX-2 decreased slightly in the salicylate group in the cochlea (1.1 ± 0.33 vs. 1.3 ± 0.49, P = .0752) and in the midbrain (0.9 ± 0.10 versus 1.0 ± 0.35, P = .0489). Inversely, the expression levels of the NR2B gene increased moderately in the salicylate group in the cochlea (3.7 ± 0.47 versus 2.3 ± 1.13, P < 0.0001) and in the midbrain (1.6 ± 0.64 versus 1.0 ± 0.44, P = .0007).

CONCLUSIONS

Salicylate induced tinnitus and altered the expression of the COX-2 and NR2B genes in the cochlea and midbrain of mice. These findings might contribute to further understanding of pathophysiology and therapy of tinnitus.

Evidence of key tinnitus-related brain regions documented by a unique combination of manganese-enhanced MRI and acoustic startle reflex testing

Animal models continue to improve our understanding of tinnitus pathogenesis and aid in development of new treatments. However, there are no diagnostic biomarkers for tinnitus-related pathophysiology for use in awake, freely moving animals. To address this disparity, two complementary methods were combined to examine reliable tinnitus models (rats repeatedly administered salicylate or exposed to a single noise event): inhibition of acoustic startle and manganese-enhanced MRI. Salicylate-induced tinnitus resulted in wide spread supernormal manganese uptake compared to noise-induced tinnitus. Neither model demonstrated significant differences in the auditory cortex. Only in the dorsal cortex of the inferior colliculus (DCIC) did both models exhibit supernormal uptake. Therefore, abnormal membrane depolarization in the DCIC appears to be important in tinnitus-mediated activity. Our results provide the foundation for future studies correlating the severity and longevity of tinnitus with hearing loss and neuronal activity in specific brain regions and tools for evaluating treatment efficacy across paradigms.