Fig. 4

Increased oxidative stress and neuroinflammation in the cochlea after styrene exposure. A, B Representative dot blots showing high protein tyrosine nitration (3-NT, n = 3 rats for each group; Student’s t test, p = 0.013) and lipid peroxidation (4-HNE, n = 4 animals for each group; Student’s t test, p = 0.006) in the cochlea of styrene-treated animals compared to control samples. Ponceau S staining confirmed equal protein loading. C Western blot images showing elevated levels of iNOS, indicating oxidative damage in the cochlea of styrene-treated animals compared to controls (n = 3 animals for each group; Student’s t test, p = 0.029). D, E Representative images of cochlear longitudinal sections showing high magnifications of the lateral wall (LW) with stria vascularis (SV; d1, e1), the organ of Corti (oC; d2, e2) and spiral ganglion neurons (SGNs; d3, e3) stained with COX-2, as a marker of oxidative-inflammatory damage (green fluorescence) and DAPI (blue fluorescence) to label cell nuclei. A marked increase of fluorescence signal was observed in Styrene (E) compared to Control (Ctrl) group (D). Data are representative of three independent experiments from three animals/group. Scale bar: 100 μm in d1; 30 μm in d2 and 50 μm in d3. F, G Western blot bands showing high levels of COX-2 (F) and CXCR1 (G) in Styrene group compared to Ctrl group. Histograms (means ± SEM) show data from densitometric analyses on all samples (COX-2 n = 3 animals for each group; Student’s t test, p = 0.001; CXCR1 n = 3 animals for each group; Student’s t test, p = 0.0002) normalized to GAPDH. Asterisks indicate significant differences between groups (*p < 0.05; **p < 0.01; ***p < 0.001)