Sperm viability, apoptosis, and intracellular reactive oxygen species levels in human spermatozoa before and after induction of oxidative stress

Abstract

Objective: To investigate sperm viability, incidence of apoptosis, and intracellular basal and induced reactive oxygen species (ROS) in sperm fractions.

Design: Prospective controlled study.

Setting: Center for Reproductive Medicine at a tertiary care hospital.

Method(s): Liquefied seminal ejaculates (n = 12) prepared by density gradient centrifugation were reconstituted to 2 mL with phosphate-buffered saline. Oxidative stress was induced by hydrogen peroxide (H(2)O(2), 100 muM). Sperm viability, intracellular ROS, and incidence of apoptosis/necrosis in neat, immature, and mature sperm fractions were assessed.

Result(s): Before H(2)O(2) exposure, mature spermatozoa fractions showed a significantly lower incidence of apoptotic sperm and intracellular O(2)(-*) levels but higher amounts of intracellular H(2)O(2) compared with neat semen. Higher levels of intracellular H(2)O(2) were demonstrated in immature sperm fractions compared with neat or mature fractions. In all sperm fractions, intracellular H(2)O(2) levels correlated with the intracellular concentration of O(2)(-*). After H(2)O(2) exposure, neat semen showed a significantly higher percentage of apoptosis compared with the prepared mature spermatozoa. However, no differences were observed in the incidence of apoptosis between immature and mature sperm fractions.

Conclusion(s): There is a differential shift of both intracellular H(2)O(2) and O(2)(-*) in each sperm fraction that may affect sperm quality. Sperm apoptosis is related to intracellular H(2)O(2) levels, which in turn are affected by intracellular O(-*) levels. Oxidative stress was not associated with an increased incidence of apoptosis in immature or mature sperm fractions.