Background: Type 2 diabetes mellitus causes impaired spermatogenesis by increasing inflammation and apoptosis and decreasing testosterone synthesis in testicular tissue. Myo-inositol is a six-carbon sugar alcohol and a natural antioxidant. The concentration of free myo-inositol in the testes is 30-40 times higher than its concentration in the blood. Given that myo-inositol synthesis is reduced by 50% in the testes of diabetic individuals and is also excreted in the urine. Objective: The present study aim to investigate the effect of myo-inositol on spermatogenesis in diabetic rats by evaluating inflammatory factors, oxidative stress, expression of apoptosis-regulating genes, and terminal deoxynucleotidyl transferase dUTP nick end labeling test. Materials and Methods: Eighteen adult male Wistar rats were divided into 3 groups: control, diabetic (streptozotocin [65 mg/kg] + nicotinamide [110 mg/kg]) and diabetic + myo-inositol (300 mg/kg). The treatment period with myo-inositol was 56 days (by gavage). After the treatment period and dissection of the rats, each pair of testes was removed for histological, molecular, and biochemical examination. Testicular supernatant was used to evaluate the expression of Bax, Bcl2, and Nrf2 genes (using real-time polymerase chain reaction), inflammatory factors and testosterone levels (using enzyme-linked immunosorbent assay kits), and oxidative stress factors including superoxide dismutase (SOD), total antioxidant capacity (TAC), and malondialdehyde (MDA) (using spectrophotometer). Also, tissue sections prepared from the testis were used for histopathological examination of the testis (counting the number of spermatogenic, Leydig, and Sertoli cells) using the stereological method as well as the terminal deoxynucleotidyl transferase dUTP nick end labeling test. Results: In the diabetic group, there was a notable elevation in the average levels of IL-6, TNF-α, Bax, and MDA (p ≤ 0.001 for all). Additionally, the number of apoptotic cells increased significantly (p ≤ 0.001), while the mean concentrations of TAC, SOD, Nrf2, Bcl2, testicular testosterone (p ≤ 0.001 for all), as well as the numbers of spermatogonia, spermatocytes, spermatids, Sertoli cells, and Leydig cells all decreased markedly (p = 0.000 for each comparison), when compared to the control group. Conversely, in the diabetic + myo- inositol group, there was a significant reduction in the levels of IL-6 (p = 0.021), TNF-α (p ≤ 0.001), Bax (p = 0.019), MDA (p ≤ 0.001), and the number of apoptotic cells (p ≤ 0.001). At the same time, this group showed a substantial rise in antioxidant levels such as TAC (p = 0.024), SOD (p = 0.013), Nrf2 (p ≤ 0.001), and Bcl2 (p = 0.044), along with increased testicular testosterone and a higher count of spermatogonia, spermatocytes, spermatids, Sertoli cells, and Leydig cells (p ≤ 0.001 for all), compared to the diabetic group. Conclusion: The results of our study showed that myo- inositol supplementation reduces apoptosis in the testis by reducing oxidative stress and inflammation caused by type 2 diabetes, leading to an increase in the number of spermatogenic and somatic testicular cells and reducing the destructive effects of type 2 diabetes on the process of spermatogenesis.
