Abstract: Background: Systemic inflammatory response syndrome (SIRS) is associated with many equine diseases. Therapeutic strategies for equine SIRS are limited and an urgent research need. Insulin dysregulation is observed in SIRS and contributes to case morbidity and mortality. Oxidative damage and reactive oxygen species (ROS) produced by neutrophils influence immune and insulin dysregulation in SIRS. The insulin-sensitizing drug metformin has demonstrated beneficial metabolic and immunomodulatory effects in rodent SIRS/sepsis models and human patients with concurrent insulin dysregulation and sepsis. Currently, metformin is only used in chronic insulin resistance for horses, and effects on equine leukocyte function are unknown.
Hypothesis/Objectives: Insulin and metformin treatment will modulate ROS production in activated equine neutrophils.
Animals: Six healthy adult horses.
Methods: Neutrophils were isolated from peripheral blood via density-gradient centrifugation. Ex vivo ROS production was stimulated with phorbol myristate acetate, killed whole-cell Staphylococcus aureus, and lipopolysaccharide in the presence and absence of insulin (25, 50, 100, 200 µIU/mL) and metformin (0.075, 0.75, 7.5 mM) alone and in combination. A previously validated fluorometric assay was used to measure ROS production.
Results: Insulin and metformin both significantly reduced stimulant-induced ROS production by 26-42% (P=0.001-0.036) and 3-20% (P=0.001-0.022) respectively. In combination, metformin enhanced insulin’s reduction of neutrophil ROS production by 5.5 to 33% following activation (P range: 0.001-0.020).
Conclusions and clinical importance: These data support our hypothesis that insulin and insulin-sensitizing drug metformin have direct immunomodulatory effects on equine neutrophils. Further ex vivo and in vivo studies should investigate whether metformin modulates other aspects of equine immune function.
