Actions of various sweeteners on rat sperm.

抄録

Purpose: Sweeteners other than sugar are often used in foods aimed at reducing calories. However, it has been reported that some of these sweeteners exhibit reproductive toxicity such as sperm count reduction and decreased sperm motility caused by the involvement of reactive oxygen species (ROS). In this study, we evaluated the actions of sucrose (Suc), sucralose (SCL), aspartame (APM), or neotame (NTM), which are food additive sweeteners frequently consumed on a daily basis, on rat sperm in vitro. In addition, rats were given APM and NTM to examine their actions on sperm. Methods: The animals used were Wistar male rats aged 12 to 15 weeks. Spermatozoa were removed from the epididymis and subjected to experiments. In the in vitro experiment, a stock solution of TYH medium containing sperm was prepared, and various concentrations of additives were added; after 5 min, the sperm motility was measured by a sperm motility analysis system (SMAS). Also, sperm stock solution containing sperm was diluted 5-fold, and L-012 (100 µM) was added as a fluorescent probe of ROS, followed by measuring the luminescence intensity by the chemiluminescence method. In in vivo studies, APM (250 mg/kg/day) or NTM (40 or 100 mg/kg/day) below the NOAEL (no observable adverse effect level) was administered as a mixed diet; after 2, 4, and 8 weeks, blood and epididymis were collected. As in the in vitro study, sperm motility and ROS production were measured, and the organs were analyzed for oxidative stress-related proteins. Results: In In vitro tests, ROS production had little effect on the addition of Suc (≦500 µM), SCL (≦1 µM) or APM (≦10 µM), while there was a tendency for NTM (1 µM) to decrease compared to the control group. Impacts were negligible on sperm motility by the addition of Suc (≦5 mM), SCL (≦10 µM), or APM (≦100 µM), however, sperm motility was significantly reduced by the addition of NTM (≧0.1 µM ). In in vivo tests, APM administration did not change the sperm count, but ROS production was significantly increased at 2 weeks compared to the control group; at 8 weeks, the total sperm motility showed a declining trend. NTM significantly increased ROS production after 4 weeks of administration, and decreased sperm linear velocity, curve velocity, head amplitude, and head frequency at 8 weeks; the sperm count and total sperm motility were not affected; in parallel with the increase in ROS production, NTM increased the amount of lipid peroxidation-modified protein with positive 4-hydroxy-2-nonenal (4-HNE) in the cauda epididymis. Conclusion: Some sweeteners affected sperm where the administration of APM and NTM increased ROS production prior to sperm dysfunction. This mechanism could be caused by abnormalities in the electron transport system of mitochondria and oxidative stress due to decreased antioxidant capacity.