Melatonin and Caffeine Supplementation Used, Respectively, as Protective and Stimulating Agents in the Cryopreservation of Human Sperm Improves Survival, Viability, and Motility after Thawing compared to Traditional TEST-Yolk Buffer

Figure 1

Sperm structure and energy production mechanisms in the sperm cytoplasm and mitochondria. Energy production is initiated by the glycolytic pathway generating two ATPs and one pyruvate molecule. Pyruvate is essential for the initiation of the acid citric cycle and the oxidative phosphorylation steps of the mitochondrial pathway to produce ATP. Caffeine binds to the adenosine receptor to stimulate the adenylyl cyclase, an enzyme present in mitochondria, leading to the conversion of ATP into cAMP. Protein kinase A (PKA) is activated by cAMP which increases cytochrome c oxidase (COX) activity and oxidative phosphorylation. Caffeine also acts as an inhibitor of phosphodiesterase enzyme activity, inhibiting the degradation of cAMP and promoting an increase in its intracellular concentration.