Combined effects of pre-freeze cholesterol-loaded cyclodextrin and post-thaw pentoxifylline on the functional longevity of cryopreserved stallion sperm.

Overview

• This study investigated the effects of adding cholesterol-loaded cyclodextrin (CLC) before freezing and pentoxifylline (PTX) after thawing on the quality and functionality of frozen stallion sperm.
• The goal was to determine if this combined treatment improves sperm survival, motility, mitochondrial activity, oxidative stress, and preliminary fertility following cryopreservation.

Introduction and Background

• Cryopreservation of stallion sperm often causes damage at both the structural and metabolic levels, leading to reduced sperm function after thawing.
• Cholesterol-loaded cyclodextrin (CLC) is known to stabilize sperm membranes by delivering cholesterol, which may protect sperm during freezing.
• Pentoxifylline (PTX) is utilized post-thaw for its potential to stimulate sperm motility and reduce oxidative stress by acting as a phosphodiesterase inhibitor and free radical scavenger.
• The researchers aimed to assess the separate and combined effects of these two compounds on sperm functional longevity post-thaw.

Methods

• Semen was collected from twelve healthy stallions and divided into four treatment groups based on CLC concentration: 0 mg (control), 1 mg, 1.5 mg, and 2 mg per sample.
• Semen samples were then frozen and thawed according to standard protocols.
• After thawing, each sample was split into subgroups with or without the addition of 7.18 mM PTX.
• Sperm kinetic parameters (e.g., velocity, linearity) were measured over 120 minutes of incubation in a thermoresistance test to assess motility and durability.
• Flow cytometry was employed to analyze mitochondrial membrane potential (via JC-1 aggregate/monomer ratio), membrane destabilization, and intracellular hydrogen peroxide (a marker of oxidative stress).
• Preliminary fertility trials involved inseminating mares with semen from the control, 1.5 mg CLC, and 1.5 mg CLC + PTX groups to observe pregnancy outcomes.

Results

• CLC supplementation improved structural preservation of sperm membranes and enhanced immediate post-thaw kinetic performance at certain concentrations.
• In contrast, PTX treatment led to reductions in sperm velocity, linearity, and motility parameters consistently during the incubation period.
• PTX also increased intracellular hydrogen peroxide levels, indicating elevated oxidative stress.
• In groups with lower CLC concentrations, PTX negatively affected mitochondrial membrane potential as shown by a decreased JC-1 aggregate/monomer ratio.
• At higher CLC concentrations, mitochondrial potential was better preserved despite PTX exposure, suggesting some protective effect of CLC against PTX-mediated mitochondrial impairment.
• Pregnancy rates were similar across control, CLC-treated, and CLC + PTX groups; however, limited sample size prevented meaningful statistical conclusions regarding fertility.

Discussion

• CLC appears beneficial in maintaining sperm structural integrity and helps sustain some motility parameters immediately after thawing.
• Contrarily, PTX supplementation during the post-thaw incubation period seemed to impair motility and mitochondrial function and increase oxidative stress, contrary to some expectations.
• The combination treatment did not demonstrate a clear synergistic benefit and the effects were dependent on the CLC concentration.
• PTX dosing may need refinement as the concentration used could have adverse effects on stallion sperm despite its use in other species or contexts.
• Limitations include a small sample size, particularly in the fertility assessment, limiting the ability to confirm benefits for actual reproductive success.

Conclusions and Future Directions

• The study concludes that while pre-freeze cholesterol loading can improve some aspects of stallion sperm cryopreservation outcomes, post-thaw PTX administration does not clearly enhance and may even impair sperm function under the tested conditions.
• No definitive synergistic improvements were observed from combining CLC and PTX at the tested doses.
• Further research is recommended to optimize PTX dosing or to explore alternative antioxidants and motility enhancers in post-thaw stallion sperm treatments.
• Expanded fertility trials with larger mare populations are necessary to determine if these biochemical improvements translate to better reproductive success.