Reduced Systemic Toxicity and Preserved Vestibular Toxicity Following Co-treatment with Nitriles and CYP2E1 Inhibitors: a Mouse Model for Hair Cell Loss

Abstract

Several nitriles, including allylnitrile and ciscrotononitrile, have been shown to be ototoxic and cause hair cell degeneration in the auditory and vestibular sensory epithelia of mice. However, these nitriles can also be lethal due in large part to the microsomal metabolic release of cyanide, which is mostly dependent on the activity of the 2E1 isoform of the cytochrome P450 (CYP2E1). In this study, we co-administered mice with a nitrile and, to reduce their lethal effects, a selective CYP2E1 inhibitor: diallylsulfide (DAS) or trans-1,2-dichloroethylene (TDCE). Both in female 129S1/SvImJ (129S1) mice co-treated with DAS and cis-crotononitrile and in male RjOrl:Swiss/CD-1 (Swiss) mice co-treated with TDCE and allylnitrile, the nitrile caused a dose-dependent loss of vestibular function, as assessed by a specific behavioral test battery, and of hair cells, as assessed by hair bundle counts using scanning electron microscopy. In the experiments, the CYP2E1 inhibitors provided significant protection against the lethal effects of the nitriles and did not diminish the vestibular toxicity as assessed by behavioral effects in comparison to animals receiving no inhibitor. Additional experiments using a single dose of allylnitrile demonstrated that TDCE does not cause hair cell loss on its own and does not modify the vestibular toxicity of the nitrile in either male or female 129S1 mice. In all the experiments, high vestibular dysfunction scores in the behavioral test battery predicted extensive to complete loss of hair cells in the utricles. This provides a means of selecting animals for subsequent studies of vestibular hair cell regeneration or replacement.

Calyx junction dismantlement and synaptic uncoupling precede hair cell extrusion in the vestibular sensory epithelium during sub-chronic 3,3′-iminodipropionitrile ototoxicity in the mouse

“…In most control specimens ( Fig. 2A), the appearance and density of the stereociliary bundles matched the literature descriptions for epithelia from healthy adult rats and mice (Dechesne et al, 1986;Soler-Martín et al, 2007;Saldaña-Ruíz et al, 2013), and were given a pathology score of 0. Nevertheless, some control samples attained SEM Pathology Scores of 1 or 2, as they displayed blebs or stererociliary fusion in a small number of HCs, respectively.…”

“…Except for cis-2-pentenenitrile (Saldaña-Ruíz et al, 2012a), human exposure is unlikely or very low (Tanii et al, 2004). Nevertheless, their use to study ototoxicity phenomena is supported by the many identified similarities between nitrile and aminoglycoside ototoxicity, and their greater dependency of use in rodent models (Soler-Martín et al, 2007;Saldaña-Ruíz et al, 2013;Sedó-Cabezón et al, 2015).…”

Relationship between vestibular hair cell loss and deficits in two anti-gravity reflexes in the rat

“…In view of the known combinations of common features and species-specific differences in vestibular histology and physiology (Boyle et al, 1992;Curthoys et al, 2017;Desai et al, 2005a,b;Eatock, 2018;Goldberg, 2000), it would be premature to assume that a similar relationship between tail-lift angles and HC loss will occur in the mouse as in the rat. Although ventral curling during tail-lift has been reported in many vestibular-deficient mice, our observations after vestibular toxicity in rats (Llorens et al, 1993;Llorens and Rodríguez-Farré., 1997;Martins-Lopes et al, 2019; this study) and mice (Soler-Martin et al, 2007;Saldaña-Ruíz et al, 2013;Boadas-Vaello et al, 2017;Greguske et al, 2019) suggest that the abnormal tail-lift response develops more easily and robustly in the former than the latter species.…”

Allyl nitrile: Toxicity and health effects

“…Rats receiving 1.5, 1.75, and 2.0 mmol / kg of cis-2-pentenenitrile displayed reduced rearing activity in the open field and increased rating scores on the vestibular dysfunction test battery as well as hair cell loss (1-3, 1-4, and 3-4 vestibular ratings as compared with control (0-1) 12) . Dose-response studies on allyl showed the match between behavioral effects and hair cell loss in mice 21) . In addition, it is reported that behavioral effects, observed in animals administered 3,3 'iminodipropionitrile (400, 600, and 1000 mg/kg) or crotononitrile (250 mg/kg), are identical to those observed in mutant mice lacking vestibular function and in rodents with bilateral labyrinthectomy 13,14 ) .…”