Background: The study about chronic tinnitus was seldom reported. We aimed to investigate the effects of Spirulina on the mRNA expressions of N-methyl D-aspartate receptor (NR)-2B, matrix metalloproteinase (MMP)-7, tumor necrosis factor (TNF)-α, and cyclooxygenase type 2 (COX-2) genes in chronic tinnitus.
Methods: Three-month-old male C57BL/6 mice were trained for an active avoidance task. Then, 17 conditioned mice with tinnitus, confirmed 2 weeks after a noise exposure to the left ear, were randomly divided into two groups on the start day: control group (9 mice, normal diet) and Spirulina group (8 mice, normal diet with S. platensis water extract, 200 mg/kg body weight). All mice were fed a different diet for 80 days; then, their tinnitus scores were tested, and they were sacrificed for mRNA studies.
Results: The Spirulina group (–6.3 ± 16.5) had a significantly lower mean difference in tinnitus scores, which were calculated on the 80th day and the start day for each mouse, than the control group (9.6 ± 13.3). NR2B mRNA expressions were not significantly different between the two groups in the cochlea, brainstem, inferior colliculus (IC), or temporal lobes. Compared with the control group, MMP-7 mRNA expressions in the Spirulina group were significantly increased in the cochlea (1.15 ± 0.28 for the control group vs 1.82 ± 0.30 for the Spirulina group) and temporal lobes (1.18 ± 0.26 vs 1.80 ± 0.20, respectively). TNT-α mRNA expressions in the Spirulina group had decreased significantly in the cochlea (2.91 ± 0.53 for the control group vs 2.12 ± 0.56 for the Spirulina group), brainstem (1.72 ± 0.35 vs 1.37 ± 0.27, respectively), and IC (2.77 ± 0.56 vs 2.13 ± 0.25, respectively). COX-2 mRNA expressions in the Spirulina group were significantly decreased in the brainstem (1.49 ± 0.73 for the control group vs 0.66 ± 0.37 for the Spirulina group).
Conclusions: Spirulina could reduce chronic tinnitus possibly by increasing MMP-7 gene expression but by decreasing TNF-α and COX-2 gene expressions in the cochlea and/or some tinnitus-related brain regions.