Pain relievers containing N-acetyl-para-aminophenol, also called APAP, acetaminophen or paracetamol, in combination with opioid narcotics are top-selling pharmaceuticals in the U.S. Individuals who abuse these drugs for as little as sixty days can develop tinnitus and progressive bilateral sensorineural hearing loss. Recently published studies indicate that APAP and its metabolic product N-acetyl-p-benzoquinoneimine (NAPQI) are the primary ototoxic agents in this type of pain relievers. However, the mechanisms underlying the deleterious effects of these drugs on auditory cells remain to be fully characterized. In this study, we report cellular, genomic, and proteomic experiments revealing that cytotoxicity by APAP and NAPQI involves two different pathways in Immortomouse™-derived HEI-OC1 cells, implicating ROS overproduction, alterations in ER morphology, redistribution of intra-cisternal chaperones, activation of the eIF2α-CHOP pathway, as well as changes in ER stress and protein folding response markers. Thus, both oxidative and ER stress are part of the cellular and molecular mechanisms that contribute to the cytotoxic effects of APAP and NAPQI in these cells. We suggest that these in vitro findings should be taken into consideration when designing pharmacological strategies aimed at preventing the toxic effects of these drugs on the auditory system.

Deiters cells extend from the basilar membrane to the reticular lamina and, together with pillar cells and outer hair cells, structurally define the micro-architecture of the organ of Corti. Studying vibrotome sections of the mouse organ of Corti with confocal and scanning electron microscopy we found that the basal pole of every Deiters cell, independently of their position in the organ of Corti and along the cochlear spiral, attached to the basilar membrane within a 15.1±0.3 µm-wide stripe running the length of the cochlear spiral adjacent to the row of outer pillar cells. All Deiters cells’ basal poles had similar diameter and general morphology, and distributed on the stripe in a precise arrangement with a center-to-center distance of 7.1±0.3 µm between neighbor cells of the same row and 5.9±0.4 µm for neighbor cells in adjacent rows. Complete detachment of Deiters cells revealed an elliptical imprint on the top surface of the basilar membrane consisting of a smaller central structure with a very smooth surface surrounded by a rougher area, suggesting the presence of two different anchoring junctions. These previously unidentified morphological features of Deiters cells could be critical for the mechanical response of the organ of Corti.

Delta-9-tetrahydrocannabinol (Δ9-THC), the psychoactive component of marijuana, is known to suppress the immune responses to bacterial, viral and protozoan infections, but its effects on fungal infections have not been studied. Therefore, we investigated the effects of chronic Δ9-THC treatment on mouse resistance to systemic Candida albicans (C. albicans) infection. To determine the outcome of chronic Δ9-THC treatment on primary, acute systemic candidiasis, c57BL/6 mice were given vehicle or Δ9-THC (16 mg/kg) in vehicle on days 1–4, 8–11 and 15–18. On day 19, mice were infected with 5×105 C. albicans. We also determined the effect of chronic Δ9-THC (4–64 mg/kg) treatment on mice infected with a non-lethal dose of 7.5×104 C. albicans on day 2, followed by a higher challenge with 5×105 C. albicans on day 19. Mouse resistance to the infection was assessed by survival and tissue fungal load. Serum cytokine levels were determine to evaluate the immune responses. In the acute infection, chronic Δ9-THC treatment had no effect on mouse survival or tissue fungal load when compared to vehicle treated mice. However, Δ9-THC significantly suppressed IL-12p70 and IL-12p40 as well as marginally suppressed IL-17 versus vehicle treated mice. In comparison, when mice were given a secondary yeast infection, Δ9-THC significantly decreased survival, increased tissue fungal burden and suppressed serum IFN-γ and IL-12p40 levels compared to vehicle treated mice. The data showed that chronic Δ9-THC treatment decreased the efficacy of the memory immune response to candida infection, which correlated with a decrease in IFN-γ that was only observed after the secondary candida challenge.