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Effects of cyclophosphamide on the pathogenesis of cytomegalovirus-induced labyrinthitis
G L Darmstadt1, E M Keithley, J P Harris
1Department of Surgery, University of California Medical Center, San Diego.
Abstract:
Cyclophosphamide was used in this study to define the contribution of the inflammatory response relative to direct cytopathic effects of guinea pig cytomegalovirus (GPCMV) in inducing sensorineural hearing loss in the guinea pig. The eighth nerve compound action potential (CAP) threshold on day 7 after inoculation of GPCMV into the scala tympani was an average of 35 dB greater for control animals than for those that were immunosuppressed with daily intraperitoneal injections of cyclophosphamide (20 mg/kg body weight). The amount of GPCMV antigen in the cochlea, detected immunohistochemically did not correlate with the CAP threshold. However, the greater the inflammatory response to GPCMV in the cochlea, the higher the CAP threshold and thus the greater the hearing loss. This study demonstrates that the inflammatory response to GPCMV may be more important than direct cytopathic effects of the virus in producing sensorineural hearing loss in GPCMV-induced labyrinthitis.
Insights
Inflammation, not direct viral damage, drives hearing loss in guinea pigs infected with guinea pig cytomegalovirus (GPCMV). This finding is crucial for understanding GPCMV-induced labyrinthitis and sensorineural hearing loss.
Area of Science:
- Virology
- Immunology
- Otolaryngology
Background:
- Guinea pig cytomegalovirus (GPCMV) can cause sensorineural hearing loss.
- The mechanisms underlying GPCMV-induced hearing loss, whether direct viral cytopathic effects or inflammatory responses, require clarification.
Purpose of the Study:
- To differentiate the roles of inflammatory response versus direct cytopathic effects of GPCMV in inducing sensorineural hearing loss.
- To investigate the relationship between cochlear inflammation, viral load, and auditory function.
Main Methods:
- Guinea pigs were inoculated with GPCMV.
- Cyclophosphamide was administered to induce immunosuppression, modulating the inflammatory response.
- Auditory function was assessed by measuring the eighth nerve compound action potential (CAP) threshold.
- Cochlear GPCMV antigen levels and inflammatory responses were evaluated using immunohistochemistry.
Main Results:
- Animals treated with cyclophosphamide showed significantly better CAP thresholds compared to control animals, indicating less hearing loss.
- Cochlear GPCMV antigen levels did not correlate with CAP thresholds.
- A stronger inflammatory response in the cochlea correlated positively with higher CAP thresholds and greater hearing loss.
Conclusions:
- The inflammatory response to GPCMV, rather than direct viral cytopathic effects, is the primary driver of sensorineural hearing loss in this model.
- These findings highlight the critical role of inflammation in GPCMV-induced labyrinthitis and subsequent hearing impairment.