Zinc Combined with Metformin Corrects Zinc Homeostasis and Improves Steroid Synthesis and Semen Quality in Male Type 2 Diabetic Mice by Activating PI3K/AKT/mTOR Pathway

Male infertility is a common complication of diabetes. Diabetes leads to the decrease of zinc (Zn) content, which is a necessary trace element to maintain the normal structure and function of reproductive organs and spermatogenesis. The purpose of this study was to investigate the effect of metformin combined with zinc on testis and sperm in diabetic mice. 10 of 50 male mice were randomly divided into control group (group C), and the remaining 40 mice were randomly divided into untreated diabetes group (group D), diabetes + zinc group (group Z, 10 mg/(kg • d)), diabetes + metformin group (group M, 200 mg/(kg • d)), and diabetes + zinc + metformin group (group ZM, Z 10 mg/(kg • d) + M 200 mg/(kg • d)), with 10 mice in each group. Mice fasted overnight were killed, and testes and sperm were collected for further experiments. In group D, the structure of testis was disordered, and the structure of sperm tail was destroyed and the deformity rate increased. In group D, total zinc, free zinc ions, metallothionein (MT), and metal transcription factor (MTF1) in testis were significantly decreased, while the expressions of zinc transporters ZNT7, ZIP13, and ZIP14 were significantly increased. In group D, the fluorescence intensity of free zinc in sperm tail, the expression of MT2, and MTF1 mRNA decreased significantly, while the expression of ZNT7, ZIP13, and ZIP14 mRNA increased significantly. Estrogen (E2) levels, steroid synthesis-related proteins (including CYP19A1, 3β-HSD, LHR, and STAR), and PI3K/AKT/mTOR pathway-related proteins (PI3K, p-AKT/AKT, p-mTOR/mTOR) expression were significantly decreased in group D. In addition, zinc combined with metformin activates PI3K/AKT/mTOR pathway, corrects zinc homeostasis imbalance in testis and sperm, and improves testosterone synthesis and semen quality in male type 2 diabetic mice.