This study was aimed to evaluate the expression patterns of mitochondrial complex I and III in retinoblastoma by immunohistochemical staining, and the association between their expression and histopathological features.

Four-micrometer formalin-fixed paraffin-embedded tissue sections were for immunohistochistry, and then the sections were dewaxed, rehydrated, and then deparaffinized. After antigen retrieval by using citrate buffer (pH 6.0), at 100 °C and cooling, the incubation of sections was performed with 3 % hydrogen peroxide at room temperature to inactive endogenous peroxidase activity. After rinsing, the slides were incubated with OXPHOS complex I (Subunit NDUFS3 monoclonal antibody) and OXPHOS complex III (Subunit Core 1 monoclonal antibody), at room temperature (1 h). The slides were incubated with 1:30 dilution biotin-labeled secondary antibodies and streptavidin-peroxidase for 20 min. Visualization was conducted using 3,3′diaminobenzidine tetrahydrochloride (Sigma) in PBS with 0.05 % H2O2. Sections were lightly counterstained with hematoxylin.

Mitochondrial complex I immunoreactivity was seen in 34.78 % of patients, while mitochondrial complex III expression was observed in 69.56%. Our result showed that mitochondrial complex I expression was decreased in retinoblastoma tumor. Furthermore, decreased expression of complex I was significantly associated with well differentiated retinoblastoma tumors (P = 0.001), tumor staging (P=0.015), and invasion of tumor (P=0.013). But no correlation was found between expression levels of mitochondrial complex I and other clinicopathological characteristics. Moreover, High expression of mitochondrial complex III was significantly correlated with mitochondrial complex III, tumor staging (P=0.001), poor tumor differentiation (P= 0.002) and tumor invasion (P= 0.017), but no correlation was determined between expression levels of mitochondrial complex III and other clinicopathological factors.

In current study, the clinical significance of mitochondrial complexes I, and III expressions were evaluated in retinoblastoma tumor tissues. Our result showed that mitochondrial complex I was decreased in patients with retinoblastoma, and may be as a prognostic factor in patients with retinoblastoma.