Nanoplastics internalization impairs mitochondrial activity in equine sperm.

Overview

• This study investigated how nanoplastics (NP) enter horse sperm cells and the negative effects this internalization has on sperm function, particularly focusing on mitochondrial activity, viability, and oxidative stress.

Background

• Nanoplastics (NP) are tiny plastic particles resulting from the breakdown of larger plastic waste.
• NP contamination is widespread in the environment and is known to accumulate in biological tissues.
• Previous research has shown NP can cause fertility problems through inflammation and oxidative stress in tissues.
• However, the direct impact of NP on gametes (sperm and eggs) is not well understood.

Research Objective

• To determine whether nanoplastics are internalized by mature equine sperm cells.
• To assess how NP exposure affects sperm viability, mitochondrial function, intracellular reactive oxygen species (ROS), and motility.

Methods

• Frozen-thawed ejaculates from five stallions were used as samples.
• Sperm samples were divided into a control group (no NP) and groups exposed to varying concentrations of 30 nm polystyrene NP (10, 50, 100, 200 μg/mL).
• Sperm were incubated at 38°C and assessed at baseline (T0), after 1 hour (T1), and after 3 hours (T3).
• Sperm viability, mitochondrial activity, and intracellular ROS levels were measured using flow cytometry techniques.
• Sperm motility was analyzed using a Computer Assisted Sperm Analysis (CASA) system.
• Internalization of fluorescently labeled NP was confirmed by confocal microscopy and flow cytometry.

Findings

• Nanoplastics were found inside live sperm cells, accumulating mainly in the post-acrosomal region (near the sperm head) and/or the midpiece (region with mitochondria).
• Exposure to higher NP concentrations led to a significant decrease in sperm viability:
  • At 1 hour, control viability was about 50.7%, whereas 200 μg/mL NP treatment dropped viability to 36.6%.
• There was a marked reduction in mitochondrial activity with NP exposure:
  • At 1 hour, mitochondrial activity decreased from 35.4% in controls to 16.3% at the highest NP dose.
• Intracellular reactive oxygen species (ROS), specifically oxygen radicals, increased in live sperm exposed to NP:
  • At 1 hour, control samples showed 39% of live sperm with high ROS, increasing to 47.3% in the 200 μg/mL NP group.
• These changes indicate oxidative stress and mitochondrial impairment due to NP internalization.

Conclusions and Implications

• The study demonstrates that nanoplastics can enter horse sperm and accumulate in regions critical for sperm function.
• This internalization negatively impacts sperm quality by reducing viability and mitochondrial activity and increasing oxidative stress.
• Because mitochondria are essential for sperm energy production and motility, NP exposure may impair fertility.
• This research provides foundational data to further explore how environmental exposure to nanoplastics could threaten reproductive health in animals and potentially in humans.