Effects of extracellular lactate on production of reactive oxygen species by equine polymorphonuclear leukocytes in vitro.

This research investigates how lactate, a substance produced by the body during high-intensity exercise, influences the behavior of a specific type of white blood cell in horses. The study notes changes in cell size, metabolism, and their ability to produce reactive oxygen species (ROS), which are involved in immune function and inflammation.

Research Methodology

• The study began by isolating polymorphonuclear leukocytes (PMNs), a particular type of white blood cell, from equine blood samples.
• These PMNs were then exposed to varying concentrations of lactate, ranging from 0 to 300mM, for thirty minutes.
• The researchers assessed cell viability (whether they were alive or not) using trypan blue exclusion, a dye that only colors dead cells.
• The team utilized flow cytometry and light microscopy to evaluate changes in the size and density of the PMNs.
• The researchers also measured the relative amounts of certain types of enzymes and transporters involved in lactate metabolism – monocarboxylic acid transporter and lactate dehydrogenase (LDH), using a real-time PCR assay.
• The effects of varying pH levels on the production of reactive oxygen species (ROS) — molecules involved in cellular metabolism and immune response — in the presence of specific chemical triggers were also assessed.

Key Results

• The study found that lactate exposure did not impact the viability of the PMNs — that is, it did not cause cell death.
• However, lactate did alter the size and density of these cells.
• The levels of certain enzymes (LDH-A) and transporters (MCT 4) involved in lactate metabolism were significantly decreased following lactate exposure, whilst levels of LDH-B and MCT 1 remained consistent.
• Lactate exposure also led to a notable decrease in luminol-dependent chemiluminescence, which suggests reduced ROS production in the cells.
• The researchers noted different sensitivities to chemical stimulants following lactate exposure, hinting at changes in cell metabolic activity.
• The study also discovered that exposure to (up to) 50mM lactate can “prime” PMNs, leading to a significant increase in ROS production.
• They also found a synergistic effect on ROS production when cells were exposed to lactate along with acidic pH.

Conclusions and Implications

• This research suggests that extracellular lactate may have a direct impact on the ability of equine PMNs to produce ROS.
• This change could have implications for the horses’ immune response and inflammation, especially following high-intensity exercise.
• The study implies a complex interplay between exercise, lactate production, immune cell behavior, and potentially, the overall health and performance of the horse.