Reactive oxygen-induced reactive oxygen formation during human sperm capacitation

Area of Science:

• Reproductive Biology
• Cellular Physiology
• Biochemistry

Background:

• Reactive oxygen species (ROS), such as nitric oxide (NO*) and superoxide anion (O(2)(*)(-)), play significant roles in various physiological processes.
• Sperm capacitation, a prerequisite for fertilization, involves complex cellular transformations influenced by ROS.
• The precise roles and interactions of NO* and O(2)(*)(-), and their generating enzymes, during human sperm capacitation remain incompletely understood.

Purpose of the Study:

• To investigate the intricate interactions between NO* and O(2)(*)(-), and their respective generators (NO* synthase and an oxidase), during human sperm capacitation.
• To elucidate the necessity of continuous NO* generation versus transient O(2)(*)(-)* generation for successful capacitation.
• To explore the potential involvement of peroxynitrite (ONOO(-)) formation in ROS-mediated capacitation.

Main Methods:

• Human spermatozoa were subjected to capacitation conditions using stimuli like albumin, fetal cord serum ultrafiltrate, and L-arginine.
• The generation of NO* and O(2)(*)(-)* was measured using specific probes.
• Inhibitors of superoxide dismutase (SOD) and NO* synthase (NOS) were employed to assess the roles of these enzymes.
• Protein tyrosine nitration was analyzed to detect the formation of peroxynitrite (ONOO(-)).

Main Results:

• Capacitation was triggered by specific stimuli and accompanied by increased generation of NO* and O(2)(*)(-)*.
• Inhibitors of SOD and NOS, as well as exogenous NO* or O(2)(*)(-)*, demonstrated a complex interplay, with inhibitors blocking exogenous ROS-induced capacitation.
• Continuous NO* generation was essential for several hours, whereas O(2)(*)(-)* was required for a shorter duration (30 min).
• Capacitation led to increased protein tyrosine nitration, indicating peroxynitrite (ONOO(-)) formation, which was abrogated by SOD and NOS inhibition.
• Exogenous NO* or O(2)(*)(-)* induced a dose-dependent production of the other ROS, providing evidence for ROS-induced ROS generation.

Conclusions:

• NO* and O(2)(*)(-)*, along with their generators, exhibit a critical and interactive role in human sperm capacitation.
• The findings reveal a novel mechanism of two-sided ROS-induced ROS generation in human spermatozoa.
• These ROS interactions and the subsequent formation of peroxynitrite (ONOO(-)) are integral to the acquisition of sperm fertility.