Attenuation of Age-Related Hearing Impairment in Senescence-Accelerated Mouse Prone 8 (SAMP8) Mice Treated with Fatty Acid Synthase Inhibitor CMS121

Journal of Molecular Neuroscience https://doi.org/10.1007/s12031-023-02119-w RESEARCH Attenuation of Age‑Related Hearing Impairment in Senescence‑Accelerated Mouse Prone 8 (SAMP8) Mice Treated with Fatty Acid Synthase Inhibitor CMS121 Tammy B. Pham1 · Ely Cheikh Boussaty1 · Antonio Currais2 · Pamela Maher2 · David R. Schubert2 · Uri Manor3 · Rick A. Friedman1 Received: 12 July 2022 / Accepted: 17 April 2023 © The Author(s) 2023 Abstract In the senescence-accelerated mouse prone 8 (SAMP8) mouse model, oxidative stress leads to premature senescence and age-related hearing impairment (ARHI). CMS121 inhibits oxytosis/ferroptosis by targeting fatty acid synthase. The aim of our study was to determine whether CMS121 is protective against ARHI in SAMP8 mice. Auditory brainstem responses (ABRs) were used to assess baseline hearing in sixteen 4-week-old female SAMP8 mice, which were divided into two cohorts. The control group was fed a vehicle diet, while the experimental group was fed a diet containing CMS121. ABRs were measured until 13 weeks of age. Cochlear immunohistochemistry was performed to analyze the number of paired ribbon-receptor synapses per inner hair cell (IHC). Descriptive statistics are provided with mean ± SEM. Two-sample t-tests were performed to compare hearing thresholds and paired synapse count across the two groups, with alpha = 0.05. Baseline hearing thresholds in the control group were statistically similar to those of the CMS121 group. At 13 weeks of age, the control group had significantly worse hearing thresholds at 12 kHz (56.5 vs. 39.8, p = 0.044) and 16 kHz (64.8 vs. 43.8, p = 0.040) compared to the CMS121 group. Immunohistochemistry showed a significantly lower synapse count per IHC in the control group (15.7) compared to the CMS121 group (18.4), p = 0.014. Our study shows a significant reduction in ABR threshold shifts and increased preservation of IHC ribbon synapses in the mid-range frequencies among mice treated with CMS121 compared to untreated mice. Keywords Age-related hearing impairment · Hearing loss · SAMP8 · ABR · CMS121 Introduction Age-related hearing impairment (ARHI) is the most common cause of hearing loss. It has been shown to be associated with cognitive decline, dementia, and depression and results in an estimated annual economic burden of over $3 billion in medical expenditures (Deal et al. 2017, 2018; Lin * Rick A. Friedman 1 Department of Otolaryngology‑Head and Neck Surgery, University of California San Diego Health, 92037 La Jolla, CA, USA 2 Cellular Neurobiology Laboratory, Salk Institute for Biological Studies, 92037 La Jolla, CA, USA 3 Waitt Advanced Biophotonics Center, Salk Institute for Biological Studies, 92037 La Jolla, CA, USA and Albert 2014). Although the use of hearing aids and/or cochlear implants may improve these associated conditions, ARHI remains significantly undertreated, and to date, there are no targeted therapies (Deal et al. 2018). SAMP8 Mouse Model Laboratory mouse models are invaluable resources for hearing research (Ohlemiller et al. 2016), as mouse and human ears are functionally and genetically homologous. As age is the greatest risk factor for hearing loss, mouse models of aging such as the senescence-accelerated mouse prone (SAMP) strains, which were derived from AKR/J mice and selected for senescence acceleration (Takeda et al. 1981), are excellent resources for the study of ARHI. Specifically, the senescence-accelerated mouse prone 8 (SAMP8) strain has been shown to develop premature ARHI (Menardo et al. 2012; Peixoto Pinheiro et al. 2021) and 13 Vol.:(0123456789) Journal of Molecular Neuroscience exhibit early increased oxidative stress (Benkafadar et al. 2019), which leads to chronic inflammation and the triggering of cell death, resulting in premature ARHI and senescence (Menardo et al. 2012). Functional studies using auditory brainstem response (ABR) have shown SAMP8 mice to be a fast and robust model for the study of aging-related diseases such as ARHI (Marie et al. 2017), and thus, this mouse model provides opportunities to investigate potential ARHI drug candidates. The Oxytosis/Ferroptosis Pathway and CMS121 Given the common cellular pathways leading to age-related dysfunction in the brain and cochlea, there is a significant precedent to study compounds for their ability to not only improve cognitive function but also attenuate ARHI. For example, EUK-207, a synthetic superoxide dismutase/catalase mimetic which suppresses oxidative stress, has been shown to both decrease age-related cognitive impairment in C57BL/6N mice (Liu et al. 2003; Clausen et al. 2010) and slow down ARHI in SAMP8 mice (Benkafadar et al. 2019). N-acetylcysteine (NAC) is another antioxidant which has been associated with improved memory performance as well as improved hearing in SAMP8 mice (Marie et al. 2018). In the study of neuronal cell death pathways and their relationships with age-related neurological disease, the oxytosis/ferroptosis pathway, a regulated cell-death pathway involving glutathione depletion, lipoxygenase activation, reactive oxygen species accumulation, and mitochondrial and calcium dysregulation, has emerged as a potential key driver of pathology in neurodegenerative diseases (Lewerenz et al. 2018; Maher et al. 2020). Although oxytosis/ferroptosis has not been widely studied in the field of hearing loss, this pathway has been associated with neurodegeneration of the auditory cortex in ARHI (Chen et al. 2020). As glutathione depletion is a key step in the oxytosis/ ferroptosis pathway, Maher et al. (2020) identified the flavonol fisetin as a compound of interest in the study of neurodegenerative diseases due to its ability to maintain glutathione levels in the presence of oxidative stress (Ishige et al. 2001; Maher 2009). Importantly, fisetin has been shown to enhance memory in normal animals (Maher et al. 2006), APPswe/PS1dE9 transgenic AD mice (Currais et al. 2014), and SAMP8 mice (Currais et al. 2018). Further pharmacokinetic studies into fisetin derivatives revealed CMS121 as a promising candidate with enhanced neuroprotective activity and good oral bioavailability (Chiruta et al. 2012). CMS121 reduces lipid peroxidation through activation of AMPK and inhibition of fatty acid synthase. It has since been shown to reduce metabolic and gene transcription markers of aging in SAMP8 mouse brains (Currais et al. 2019) and reduce neuroinflammation and cognitive decline in APPswe/PS1dE9 transgenic AD mice (Ates 13 et al. 2020). Given the potent neuroprotective effects of CMS121 in SAMP8 mice in the context of aging, we hypothesized that it would likewise be protective against ARHI in SAMP8 mice. In this study, we investigated the changes in ABR thresholds and suprathreshold wave I amplitudes in SAMP8 mice treated with CMS121 compared to untreated SAMP8 mice. As disruption in ribbon synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs) is an early pathologic (...truncated)