Robert P. Meech

d-Methionine provides excellent protection from cisplatin ototoxicity in the rat

Cisplatin (CDDP) is a widely used chemotherapeutic agent. Unfortunately, CDDP is highly ototoxic. We tested D-methionine (D-Met), a sulfur containing compound, as an otoprotectant in male Wistar rats. Complete data sets were obtained for five groups of five animals each, including a treated control group (16 mg/kg CDDP), an untreated control group (administered an equivalent volume of saline) and three groups that received either 75, 150, or 300 mg/kg D-Met 30 min prior to the 16 mg/kg CDDP dosing. Auditory brainstem response (ABR) thresholds were obtained in response to clicks, and 1 kHz, 4 kHz, 8 kHz, and 14 kHz toneburst stimuli, before and 3 days after drug administration. Scanning electron microscopy (SEM) was used to examine the outer hair cells of the apical, middle and basal turns of the cochlea. Animal weight was measured on the first and final day. D-Met provided excellent otoprotection even at the lowest level with complete otoprotection obtained for the 300 mg/kg dosing as measured by both ABR and SEM. D-Met also markedly reduced weight loss and mortality. All animals receiving D-Met (15/15) survived to the end of the study period as opposed to only 5/10 of the treated controls.

Prevention of noise- and drug-induced hearing loss with d-methionine ☆

A number of otoprotective agents are currently being investigated. Various types of agents have been found in animal studies to protect against hearing loss induced by cisplatin, carboplatin, aminoglycosides, or noise exposure. For over a decade we have been investigating D-methionine (D-met) as an otoprotective agent. Studies in our laboratory and others around the world have documented D-mets otoprotective action, in a variety of species, against a variety of ototoxic insults including cisplatin-, carboplatin-, aminoglycoside- and noise-induced auditory threshold elevations and cochlear hair cell loss. For cisplatin-induced ototoxicity, protection of the stria vascularis has also been documented. Further D-met has an excellent safety profile. D-met may act as both a direct and indirect antioxidant. In this report, we provide the results of three experiments, expanding findings in D-met protection in three of our translational research areas: protection from platinum based chemotherapy-, aminoglycoside- and noise-induced hearing loss. These experiments demonstrate oral D-met protection against cisplatin-induced ototoxicity, D-met protection against amikacin-induced ototoxicity, and D-met rescue from permanent noise-induced hearing loss when D-met is initiated 1h after noise exposure. These studies demonstrate some of the animal experiments needed as steps to translate a protective agent from bench to bedside.

D-Methionine protects against cisplatin damage to the stria vascularis.

D-Methionine (D-met) protects against cisplatin (CDDP)-induced hearing loss and outer hair cell loss (Campbell et al., 1996). However, D-mets protective effects on the stria vascularis has not been previously investigated. The purpose of this study was to examine, using semi-quantitative analysis, whether D-met also protects the stria vascularis. We removed a basal turn section of the stria vascularis from five groups of five male Wistar rats each: (1) a CDDP-treated control group receiving a 30 min i.p. infusion of 16 mg/kg CDDP, (2) a saline-injected control group receiving an equivalent volume of saline, and (3) three groups injected with either 75, 150, or 300 mg/kg D-methionine (D-met) i.p. 30 min prior to receiving the 16 mg/kg CDDP dosing. Using transmission electron microscopy and light microscopy, we analyzed strial volume (i.e. edema), marginal cell damage classification (bulging and/or compression), and relative optical density (ROD) ratios (i.e. depletion of marginal cell cytoplasmic organelles). All three levels of D-met provided complete protection against marginal cell bulging and/or compression but only partial protection against strial edema. At 300 mg/kg, D-met significantly reduced ROD ratio degradation in the spiral prominence and middle stria vascularis regions. In Reissners membrane region, values from the D-met pretreated group were not significantly different from either the treated or untreated control groups suggesting only partial protection for that area. Protection of marginal cell cytoplasmic organelles was also noted. In summary, D-met partially or fully protects the stria vascularis from several types of CDDP-induced damage.

A semiquantitative analysis of the effects of cisplatin on the rat stria vascularis

Cisplatin (CDDP) is a very effective chemotherapeutic agent but is highly ototoxic. Most studies have focused on the effects of CDDP on the outer hair cells. The purpose of this study was to examine changes in the stria vascularis in cisplatin treated male Wistar rats and to provide semiquantitative analysis of the results. We removed a section of the stria vascularis from the basal turn of five control and five CDDP (16 mg/kg) treated rats. Using transmission electron microscopy (TEM) we analyzed: (1) changes to the strial tissue as a whole; and (2) intracellular changes in the marginal cells. We also subjected the samples to semiquantitative analysis using the MCID, focusing on three aspects of strial profile abnormalities; the number of abnormal marginal cells in CDDP treated tissue, intracellular strial edema and densitometry. Controls appeared normal, but many pathologic changes were apparent in the experimental group. Results from the semiquantitative analysis indicate cisplatin has a deleterious effect on the stria vascularis including strial edema; bulging, rupture and/or compression of the marginal cells and depletion of the cytoplasmic organelles.

D-methionine pre-loading reduces both noise-induced permanent threshold shift and outer hair cell loss in the chinchilla.

Abstract Objective: This study tested multiple dosing epochs of pre-loaded D-methionine (D-met) for otoprotection from noise-induced hearing loss (NIHL). Design: Auditory brainstem response (ABR) thresholds were measured at baseline, 1 day, and 21 days following a 6-hour 105 dB sound pressure level (SPL) octave band noise (OBN) exposure. Outer hair cell (OHC) counts were measured after day 21 sacrifice. Study sample: Three groups of five Chinchillas laniger each were given a 2-day regimen comprising five doses of D-met (200 mg/kg/dose) intraperitoneally (IP) starting 2, 2.5, or 3 days prior to noise exposure. A control group (n = 5) received five doses of equivalent volume saline IP starting 2.5 days prior to noise exposure. Results: ABR threshold shifts from baseline to day-21 post-noise exposure were reduced in all D-met groups versus controls, reaching significance (p < 0.05) in the 3-day group. D-met groups showed reduced OHC loss relative to controls at day-21 post-noise exposure, reaching significance (p < 0.05) at all frequency regions in the 3-day group and at the 2, 4, and 8 kHz frequency regions in the 2.5-day group. Conclusions: D-met administration in advance of noise-exposure, without further administration, significantly protects from noise-induced ABR threshold shift and OHC loss.

D-methionine (D-met) significantly reduces kanamycin-induced ototoxicity in pigmented guinea pigs.

Abstract Objective: Test D-methionine (D-met) as an otoprotectant from kanamycin-induced ototoxicity and determine the lowest maximally protective D-met dose. Design: Auditory brainstem responses (ABR) were measured at 4, 8, 14, and 20 kHz at baseline and two, four, and six weeks after kanamycin and D-met administration initiation. ABR threshold shifts assessed auditory function. Following six-week ABR testing, animals were decapitated and cochleae collected for outer hair cell (OHC) quantification. Study sample: Eight groups of 10 male pigmented guinea pigs were administered a subcutaneous kanamycin (250 mg/kg/dose) injection once per day and an intraperitoneal D-met injection (0 (saline), 120, 180, 240, 300, 360, 420, or 480 mg/kg/day) twice per day for 23 days. Results: Significant ABR threshold shift reductions and increased OHC counts (p ≤0.01) were measured at multiple D-met-dosed groups starting at two-week ABR assessments. A 300 mg/kg/day optimal otoprotective D-met dose provided 34–41 dB ABR threshold shift reductions and OHC protection. Lesser, but significant, D-met otoprotection was measured at lower and higher D-met doses. Conclusions: D-met significantly reduced ABR threshold shifts and increased OHC percentages compared to kanamycin-treated controls. Results may be clinically significant particularly for multidrug-resistant tuberculosis patients who frequently suffer from kanamycin-induced hearing loss in developing countries.

d-Methionine reduces tobramycin-induced ototoxicity without antimicrobial interference in animal models

BACKGROUND Tobramycin is a critical cystic fibrosis treatment however it causes ototoxicity. This study tested d-methionine protection from tobramycin-induced ototoxicity and potential antimicrobial interference. METHODS Auditory brainstem responses (ABRs) and outer hair cell (OHC) quantifications measured protection in guinea pigs treated with tobramycin and a range of d-methionine doses. In vitro antimicrobial interference studies tested inhibition and post antibiotic effect assays. In vivo antimicrobial interference studies tested normal and neutropenic Escherichia coli murine survival and intraperitoneal lavage bacterial counts. RESULTS d-Methionine conferred significant ABR threshold shift reductions. OHC protection was less robust but significant at 20kHz in the 420mg/kg/day group. In vitro studies did not detect d-methionine-induced antimicrobial interference. In vivo studies did not detect d-methionine-induced interference in normal or neutropenic mice. CONCLUSIONS d-Methionine protects from tobramycin-induced ototoxicity without antimicrobial interference. The study results suggest d-met as a potential otoprotectant from clinical tobramycin use in cystic fibrosis patients.